@article {pmid40630703, year = {2025}, author = {Li, D and Xing, J and Zhang, Z and Wang, H}, title = {Numerical investigation on the dynamic behavior of bubbles under forced flow in a microchannel.}, journal = {RSC advances}, volume = {15}, number = {29}, pages = {23414-23426}, pmid = {40630703}, issn = {2046-2069}, abstract = {Understanding the process of bubble detachment and motion along microchannel walls, driven by liquid flow, is crucial for elucidating bubble dynamics and realizing diverse applications within the realm of microfluidics. This paper uses the phase-field method to perform a comprehensive numerical study on the conversion of surface gas bubbles into bulk bubbles at the lower wall of a microfluidic channel. The study identifies several key factors that have a coupled impact on the 'surface-bulk' conversion, including wall wettability, Reynolds number, and the initial contact angle/volume of the surface bubbles (with contact angle and volume positively correlated at a fixed base radius). Specifically, higher Reynolds numbers, smaller initial bubble contact angles, and more hydrophilic channel walls facilitate the detachment of surface bubbles from the channel wall. However, at high Reynolds numbers, bubbles on superhydrophilic surfaces may be split, causing fluctuations or longer conversion time. Conversely, as wall hydrophobicity increases, surface bubbles remain attached.}, }
@article {pmid40623989, year = {2025}, author = {Yazdanpanah Moghadam, E and Sonenberg, N and Packirisamy, M}, title = {Alzheimer model chip with microglia BV2 cells.}, journal = {Microsystems & nanoengineering}, volume = {11}, number = {1}, pages = {135}, doi = {10.1038/s41378-024-00862-7}, pmid = {40623989}, issn = {2055-7434}, abstract = {Amyloid beta oligomers (AβO) are pivotal in Alzheimer's Disease (AD), cleared by microglia cells, as immune cells in the brain. Microglia cells exposed to AβO are involved with migration, apoptosis, phagocytosis, and activated microglial receptors through AβO, impacting cellular mechanobiological characteristics such as microglial adhesion strength to the underlying substrate. Herein, a label-free microfluidic device was used to detect advancing AD conditions with increasing AβO concentrations on microglia BV2 cells by quantitatively comparing the cell-substrate adhesion. The microfluidic device, acting as an AD model, comprises a single channel, which functions as a cell adhesion assay. To assess cell-substrate adhesion under different AβO concentrations of 1 µM, 2.5 µM, and 5 µM, the number of the cells attached to the substrate was counted by real-time microscopy when the cells were under the flow shear stress of 3 Pa and 7.5 Pa corresponding to Reynolds number (Re) of 10 and 25, respectively. The data showed that quantifying the cell-substrate adhesion using the microfluidic device could successfully identify conditions of advancing AβO concentrations. Our findings indicated that the increased incubation time with AβO caused reduced cell-substrate adhesion strength. Additionally, increased AβO concentration was another factor that weakened microglial interaction with the substrate. The quantification of cell-substrate adhesion using 3 Pa compared to 7.5 Pa clearly demonstrated advancing AβO in AD. This study using the chip provides an AD model for a deeper understanding mechanobiological behaviors of microglia exposed to AβO corresponding to diagnosed AD conditions under an in vitro microenvironment.}, }
@article {pmid40619480, year = {2025}, author = {Donga, RK and Kumar, S and Velidi, G}, title = {Heat transfer enhancement in a parabolic trough collector using finned tubular absorber.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {24142}, pmid = {40619480}, issn = {2045-2322}, abstract = {This study presents an investigation into enhancing heat transfer in parabolic trough collectors (PTCs). The research focuses on improving convective heat transfer by incorporating longitudinal fins within the tubular absorber of a PTC. The study examines a PTC (parabolic trough collector) system with the following specifications: a 1.84 m focal length, a 5 m aperture width, and an absorber measuring 70 mm in outer diameter. The variable solar flux on the absorber is determined using SolTrace software. The receiver was simulated using the finite volume method. The heat flux derived from SolTrace simulations serves as a boundary condition. A comparative analysis is conducted between the findings from a parametric investigation on a standard receiver and those equipped with finned tubular absorbers. This comparison spans Reynolds numbers from 0.25 × 10[5] to 2.82 × 10[5]. Studies have demonstrated that absorbers with fins substantially improve heat transfer. The tubular absorber equipped with fins shows a significant rise of 40.1% in the Nusselt number. Its performance evaluation criteria reach a peak of 1.28 when the Reynolds number is 2.82 × 10[5].}, }
@article {pmid40609600, year = {2025}, author = {Adak, R and Mandal, A and Saha, S}, title = {Direct Numerical Simulations of Dragonfly-Inspired Corrugated Tandem Airfoils at Low Reynolds Number.}, journal = {Bioinspiration & biomimetics}, volume = {}, number = {}, pages = {}, doi = {10.1088/1748-3190/adebcf}, pmid = {40609600}, issn = {1748-3190}, abstract = {A corrugated wing is known to significantly enhance aerodynamic efficiency in the low Reynolds number regime. Although the result may be relatable directly to two-winged insects, larger insects flying at similar Reynolds numbers, like dragonflies, have four wings, and the role of the gap between the fore and hindwing in flight has rarely been analyzed. In particular, we perform direct numerical simulations of the flow past a tandem corrugated airfoil configuration at a chord Reynolds number of 10[4]that is of relevance to the micro-aerial vehicle (MAV) community. We assessed the tandem wing configuration for different horizontal and vertical offsets. In general, the aerodynamic efficiency for tandem configurations is quite high (~10). Furthermore, we find that vertical offsets have a greater impact on aerodynamic forces than horizontal offsets. Positioning the hindwing below the forewing improves aerodynamic efficiency compared to placing the hindwing above because of the generation of a favorable pressure gradient on the forewing. The vortex shedding and correlations evaluate the hindwing/forewing interaction and the fluctuation of the forces. The horizontal offset results demonstrate improved aerodynamic efficiency and reduced flow unsteadiness as the gap between the two wings is minimized, primarily because the interaction between the forewing's wake and the hindwing is suppressed. A study with NACA 0008 is done to corroborate the range of optimal configurations and assess performance benefits of corrugated profile. The comparative study reveals that the tandem wing configuration maintains efficiency comparable to that of a single wing while allowing us to utilize its advantages for MAV applications.}, }
@article {pmid40608667, year = {2025}, author = {Polanco, JI and Roche, PE and Danaila, L and Lévêque, E}, title = {Disentangling temperature and Reynolds number effects in quantum turbulence.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {122}, number = {27}, pages = {e2426598122}, doi = {10.1073/pnas.2426598122}, pmid = {40608667}, issn = {1091-6490}, support = {ANR-18-CE46-0013 QUTE-HPC//Agence Nationale de la Recherche (ANR)/ ; }, abstract = {The interplay between viscous and frictional dissipation is key to understanding quantum turbulence dynamics in superfluid [4]He. Based on a coarse-grained two-fluid description, an original scale-by-scale energy budget that identifies each scale's contribution to energy dissipation is derived. Using the Hall-Vinen-Bekharevich-Khalatnikov (HVBK) model to further characterize mutual friction, direct numerical simulations at temperatures 1.44 K ≲ T ≲ 2.16 K indicate that mutual friction promotes intense momentum exchanges between the two fluids to maintain a joint energy cascade despite their viscosity mismatch. However, the resulting overall frictional dissipation remains small (compared to the viscous dissipation) and confined to far-dissipative scales. This remarkable feature allows us to define an effective Reynolds number for the turbulence intensity in a two-fluid system, helping to disentangle the effects of Reynolds number and temperature in quantum turbulence. Thereby, simple physical arguments predict that the distance ℓ between quantized vortices (normalized by the turbulence integral scale L0) should behave as [Formula: see text] with the Reynolds number based on the quantum of circulation κ. This law is well supported by a large set of experimental and numerical data within the temperature range of the HVBK model. Finally, this approach offers the possibility of revisiting the ongoing controversy on intermittency in quantum turbulence. It is shown that observed changes in intermittency arise from Reynolds number effects rather than from temperature variations, as proposed in recent studies.}, }
@article {pmid40603935, year = {2025}, author = {Kazemi, M and Mani, M}, title = {Owl airfoil aerodynamic noise sources and performance compared to hawk and NACA0012 airfoils for low Reynolds applications.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {23261}, pmid = {40603935}, issn = {2045-2322}, abstract = {The investigation of low Reynolds number flows is crucial, particularly for applications such as wind turbines and small-scale UAVs. This study compares the owl airfoil with the NACA0012 and hawk airfoils through wind tunnel testing, utilizing pressure sensors and force balance to examine the aerodynamic noise sources and aerodynamic performance of the airfoils. A total of six airfoils were investigated at various Reynolds numbers from 44 × 10[3] to 160 × 10[3], considering the glide flight envelop for various owl species. Wind tunnel test results showed higher Cl and L/D ratio for the owl airfoil, outperforming the NACA0012 and hawk airfoils by up to 6.7% and 44.1%, respectively. This is attributed to the optimal camber of the owl airfoil compared to the two other airfoils, and its lower relative thickness too. This helps flight with this airfoil at lower AOA, which reduces noise. In addition, the stall angle for owl airfoil was ranging from 8° to 15° higher than NACA0012 airfoil, which stalled at 10°-11°, and higher than 6° to 12° hawk stall angle. This feature allowed owls to perform efficient flights in glide phase at lower AOA that minimized the main aerodynamic noise sources such as the separations and pressure fluctuations. Pressure measurements represented the initiation of LSB for the owl airfoil at around AOA = 6° to 10° at different Reynolds numbers, while the hawk airfoil shown the presence of LSB starting from AOA = 0°. A detailed analysis of the pressure fluctuations showed that the owl airfoil had fewer sources of aerodynamic noise, such as LSB, stall phenomena, and separated shear layers, on both its upper and lower surfaces, compared to other types of airfoils. Additionally, an analysis in the frequency domain showed that the amplitude of FFT for NACA0012 and hawk airfoil is generally higher compared with the owl airfoil. These findings shed light on the aerodynamic characteristics and noise generation mechanisms of owl airfoil for future research and design considerations.}, }
@article {pmid40572435, year = {2025}, author = {Qiu, Y and Zhang, X and Hao, M and Yin, X and Zhou, M and Ma, S and Zhang, Y and Jiang, N and Xie, L and Yuan, X and Chang, H}, title = {Investigation of Efficient Mixing Enhancement in a Droplet Micromixer with Short Mixing Length at Low Reynolds Number.}, journal = {Micromachines}, volume = {16}, number = {6}, pages = {}, pmid = {40572435}, issn = {2072-666X}, support = {52205601//National Natural Science Foundation of China/ ; Hefei 230026//Deep Space Exploration Laboratory/ ; }, abstract = {Rapid mixing is widely prevalent in the field of microfluidics, encompassing applications such as biomedical diagnostics, drug delivery, chemical synthesis, and enzyme reactions. Mixing efficiency profoundly impacts the overall performance of these devices. However, at the micro-scale, the flow typically presents as laminar flow due to low Reynolds numbers, rendering rapid mixing challenging. Leveraging the vortices within a droplet of the Taylor flow and inducing chaotic convection within the droplet through serpentine channels can significantly enhance mixing efficiency. Based on this premise, we have developed a droplet micromixer that integrates the T-shaped channels required for generating Taylor flow and the serpentine channels required for inducing chaotic convection within the droplet. We determined the range of inlet liquid flow rate and gas pressure required to generate Taylor flow and conducted experimental investigations to examine the influence of the inlet conditions on droplet length, total flow rate, and mixing efficiency. Under conditions where channel dimensions and liquid flow rates are identical, Taylor flow achieves a nine-fold improvement in mixing efficiency compared to single-phase flow. At low Reynolds number (0.57 ≤ Re ≤ 1.05), the chip can achieve a 95% mixing efficiency within a 2 cm distance in just 0.5-0.8 s. The mixer proposed in this study offers the advantages of simplicity in manufacturing and ease of integration. It can be readily integrated into Lab-on-a-Chip devices to perform critical functions, including microfluidic switches, formation of nanocomposites, synthesis of oxides and adducts, velocity measurement, and supercritical fluid fractionation.}, }
@article {pmid40549011, year = {2025}, author = {Harrison, A and Strychalski, W and Hamlet, C and Miller, L}, title = {Fluid Dynamics of Multiple Fast-Firing Extrusomes : Fast extrusomes.}, journal = {Bulletin of mathematical biology}, volume = {87}, number = {7}, pages = {100}, pmid = {40549011}, issn = {1522-9602}, support = {DMS-1937229//National Science Foundation/ ; IOS-2227068//National Science Foundation/ ; GM132008//Foundation for the National Institutes of Health/ ; }, mesh = {Animals ; Mathematical Concepts ; *Models, Biological ; Hydrodynamics ; *Organelles/physiology ; Dinoflagellida/physiology ; Computer Simulation ; Predatory Behavior/physiology ; Viscosity ; }, abstract = {The contact and puncturing of cells and organisms in fluid at microscales are difficult due to viscous-dominated effects and the interactions of boundary layers. This challenge can be overcome in part through the ultra-fast firing of organelles such as the nematocysts of jellyfish. Such super-fast extrusive organelles found in cnidarians, protists, and dinoflagellates are known as extrusomes. It has previously been shown that a single barb at the cellular microscale must be fired fast enough to reach the inertial regime to contact prey. The fluid physics of multiple-fired extrusomes has not been carefully studied, however. The simultaneous firing of extrusomes can be seen in nature, with one example being the dinoflagellate Nematodunium, where each nematocyst consists of a ring of parallel sub-capsules similar to a Gatling gun. In this paper, the immersed boundary method was used to numerically simulate the dynamics of one, two, and three barb-like structures that are accelerated and released towards a passive elastic prey in two dimensions. We considered the simultaneous release of all three barbs as well as a sequential release of the barbs. We also vary the Reynolds number of the simulation for several orders of magnitude to consider the biologically relevant range of extrusome firing, given that different organelles are fired at different speeds and that some extrusomes are fired in viscous mucus. For multiple barbs, we found that there is a nonmonotonic relationship between the distance between the top of the center barb and the prey and the Reynolds number when fired simultaneously. This is because the prey is not pushed out of the way by boundary effects at higher Reynolds numbers, while barbs at lower Reynolds numbers entrain more fluid and are carried farther. Furthermore, the center barbs at the highest Reynolds numbers always hit the prey and are robust to firing order and the spacing between barbs. Overall, our simple model shows that the extreme nonlinearity of the fluid at this scale results in nonmonotonic relationships between the distance to the prey and various parameters.}, }
@article {pmid40534053, year = {2025}, author = {Ramirez, FR and Diamond, PH}, title = {Layered patterns of active scalar fields in a two-dimensional magnetohydrodynamic system.}, journal = {Physical review. E}, volume = {111}, number = {5-2}, pages = {055107}, doi = {10.1103/PhysRevE.111.055107}, pmid = {40534053}, issn = {2470-0053}, abstract = {We observe the formation of staircase patterns in the magnetic potential (A) in a weakly magnetized two-dimensional magnetohydrodynamic system driven by a forced, fluctuating vortex array. Layering occurs due to inhomogeneous mixing of A by vortex cells. Magnetic Reynolds number (R_{m})-dependent quenching of the turbulent diffusion of A by weak magnetic fields increases the disparity between the (short) cell circulation time and the (long) time for intercell transport of magnetic potential. Thus, magnetic fields strengthen transport barriers between cells and reinforce the staircase, relative to its passive scalar counterpart. The analysis reveals a feedback mechanism, which promotes staircase formation. Magnetic staircases persist in both the flux expulsion (R_{m}v_{A}^{2}/U_{0}^{2}<1) and vortex disruption (R_{m}v_{A}^{2}/U_{0}^{2}≥1) limits. In the latter case, residual vortex cells homogenize A. Global layering morphology is shown to be well characterized by staircase curvature. Stochastic forcing of magnetic potential can support magnetic staircases against resistive decay.}, }
@article {pmid40533935, year = {2025}, author = {Baños, R and Méndez, F and Bautista, O and Arcos, J}, title = {Spreading of a diffusive soluble surfactant in a deep layer with inertial effects.}, journal = {Physical review. E}, volume = {111}, number = {5-2}, pages = {055501}, doi = {10.1103/PhysRevE.111.055501}, pmid = {40533935}, issn = {2470-0053}, abstract = {In this study, we conduct a numerical analysis of the spreading dynamics of a soluble and diffusive surfactant in a deep layer of Newtonian fluid. We investigate three different initial conditions for the surfactant distributions: a Gaussian pulse, a Cauchy hole, and a periodic distribution. We solved the momentum equations in the Stokes limit (Re→0) and also considering inertial effects (Re≫1), where Re denotes the Reynolds number. Furthermore, we include the convective-diffusion equation for both nondiffusive (Pe_{s} and Pe→∞) and diffusive (finite Pe_{s} and Pe) surfactants, with Pe_{s} and Pe representing surface and bulk Péclet numbers, respectively. The governing equations are coupled through a tangential stress balance at the interface, where a nonlinear Langmuir equation of state relates interfacial surface tension to surfactant concentration. The temporal evolution of the initial surfactant distribution is primarily influenced by several dimensionless parameters: the bulk and surface Péclet numbers, the Biot number (Bi), the solubility parameter (β), and the dimensionless surfactant depletion depth (α). Our findings indicate that the initial surfactant concentration is diminished due to diffusivity, and its decay toward a homogeneous state is significantly affected by solubility. The adsorption and desorption processes operate as an equilibrium mechanism that tends to homogenize the surface surfactant concentration.}, }
@article {pmid40521143, year = {2025}, author = {Može, M and Jereb, S and Lovšin, R and Berce, J and Zupančič, M and Golobič, I}, title = {Dataset on droplet spreading and rebound behavior of water and viscous water-glycerol mixtures on superhydrophobic surfaces with laser-made channels.}, journal = {Data in brief}, volume = {61}, number = {}, pages = {111697}, pmid = {40521143}, issn = {2352-3409}, abstract = {Droplet impact, spreading and rebound was investigated experimentally on superhydrophobic laser-textured surfaces, yielding a dataset of 1498 datapoints. Data was collected on twelve types of surfaces with square grids of laser-made channels of various spacings (from 50 µm to 800 µm), with two groups of six surfaces possessing either deep or shallow laser-made channels. Droplet impact tests were performed with water and viscous water-glycerol mixtures with viscosity values up to 160 mPa·s and droplet impact behavior was images with a high-speed camera at 5000 fps. Maximum spreading factor, contact time, droplet rebound efficiency, and maximum lamella velocity were extracted from the videos using software image processing. Moreover, information on droplet diameter, velocity, density, surface tension, dynamic viscosity, Weber number, and Reynolds number are provided. A supplementary dataset includes the same quantitative information for droplet impacts on a smooth, hydrophobic surface, resembling the surface between the laser-made channels on other superhydrophobic surfaces (125 additional datapoints). Furthermore, scanning electron microscopy images of the surfaces are provided alongside the measurements of static and dynamic contact angles with water and water-glycerol mixtures. The data may be useful for fields like wettability studies, surface engineering, and anti-icing research. It can help validate theoretical and numerical models of droplet spreading, retracting, and rebounding from poorly wettable surfaces, optimize superhydrophobic surfaces for applications such as self-cleaning and drag reduction, and contribute to machine learning models predicting droplet behavior. The data is particularly relevant for designing anti-icing surfaces by minimizing contact time and maximizing the restitution coefficient. Additionally, it supports applications in 3D printing, coating technologies, and inkjet printing by providing data on viscous liquid impacts on poorly wettable surfaces.}, }
@article {pmid40518711, year = {2025}, author = {Mikhil, S and Biswas, K and Bakshi, S}, title = {Measurement of Lamella Thickness Evolution during Droplet Spreading on a Dry Surface and Insights into Energy Distribution during the Process.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {}, number = {}, pages = {}, doi = {10.1021/acs.langmuir.5c01182}, pmid = {40518711}, issn = {1520-5827}, abstract = {The present study deals with the evolution of a liquid film formed by droplet impact onto a dry flat surface at high Weber and Reynolds numbers. A Chromatic Confocal Sensor is employed to measure the temporal evolution of the lamella thickness of the impacting droplet, and droplet spread factors are measured using shadow imaging. These measurements were then used to identify appropriate theoretical representations for different phases of the evolving droplet height/lamella thickness. The evolution of the lamella thickness is a critical input for estimating the energy dissipation in the boundary layer during lamella spread. Existing energy budgeting approaches consider a constant boundary layer thickness to estimate the boundary layer dissipation and predict the maximum spread of the droplet. The present study instead proposes the use of a transient boundary layer thickness along with a suitable velocity scale. Furthermore, the significance of considering early-stage energy dissipation in energy budgeting is demonstrated, and an approach for integrating both early-stage and wall boundary layer dissipations into an energy-based model is presented. A differential form of the energy balance equation is proposed for high Weber and Reynolds number impacts and is used to capture the time variation of the spreading diameter. The temporal evolution of the droplet spread factors obtained using this model is in good agreement with our measurements.}, }
@article {pmid40504656, year = {2025}, author = {Juyal, M and Adhikari, S and Gautam, R and Bhaskar, T and Bhattacharya, S and Ghosh, D}, title = {β-Carotene Production by Oleaginous Yeasts in a Pilot Plant Fermenter: Yield Standardization and Process Scale-Up.}, journal = {Journal of agricultural and food chemistry}, volume = {}, number = {}, pages = {}, doi = {10.1021/acs.jafc.5c02321}, pmid = {40504656}, issn = {1520-5118}, abstract = {This study reports selective β-carotene pigment production by an oleaginous yeast, Rhodotorula mucilaginosa IIPL32 (MTCC 25056), in a 500 L fermenter working scale with a practically feasible approach for microbial pigment production scale-up from small (500 mL) to pilot scale (500 L) submerged fermenters using medium rheology and fermenter hydrodynamics. The pigment production was initially standardized by optimizing the carbon and nitrogen load of the fermentation medium. The pigment was purified using a solvent extraction process followed by thin-layer chromatography and analyzed by UV-visible spectrophotometry, high-pressure liquid chromatography, and Fourier-transform infrared spectroscopy, suggesting the dominant presence of β-carotene. Using 20 g/L glucose as a carbon feed, a 500 L fermenter yielded 3.3 kg yeast cell biomass and 5.1 g β-carotene. It was concluded that the process is scalable at an industrial level and could be integrated with any existing lipid biorefinery without any additional modification in Capex, thus substantially lowering the microbial lipid production cost.}, }
@article {pmid40504298, year = {2025}, author = {Maeda, S and Otani, T and Yamada, S and Watanabe, Y and Wada, S}, title = {Subject-specific variability in cerebrospinal fluid flow characteristics through cerebral aqueducts in a healthy population: a magnetic resonance imaging and computational investigation.}, journal = {Medical &amp; biological engineering &amp; computing}, volume = {}, number = {}, pages = {}, pmid = {40504298}, issn = {1741-0444}, support = {23KJ1471//Japan Society for the Promotion of Science/ ; 23K11830//Japan Society for the Promotion of Science/ ; 24K02557//Japan Society for the Promotion of Science/ ; JPMXP1020230118//Ministry of Education, Culture, Sports, Science and Technology/ ; }, abstract = {Ventricular cerebrospinal fluid (CSF) flow has bi-directional flow profiles synchronized with cardiac pulsation. The increase in CSF stroke volume through the aqueduct (flow pathway between the third and fourth ventricle) is believed to be a biomarker of idiopathic normal pressure hydrocephalus (iNPH). However, several studies have reported that CSF stroke volume varies considerably even in healthy populations. To explore these variations from a fluid mechanics perspective, this study analyzed CSF flow characteristics in healthy individuals using magnetic resonance imaging (MRI)-based computational simulations. MRI data from 47 healthy subjects were acquired, and the maximum Reynolds number of the CSF flow through the aqueduct and the degree of CSF mixing were evaluated. Results showed that the Reynolds number of the CSF flow through the aqueduct was 28.6 ± 13.3, and the limited variation suggested fluid mechanical similarities of CSF flow characteristics in the healthy population. A positive correlation between CSF flow mixing and the Reynolds number was observed in both healthy populations and iNPH patients. These findings demonstrate that CSF flow through the aqueduct, especially in healthy populations, can be well characterized by examining fluid mechanical similarities.}, }
@article {pmid40493811, year = {2025}, author = {Silva, A and Efrati, E}, title = {Path integral approach for predicting the diffusive statistics of geometric phases in chaotic Hamiltonian systems.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {35}, number = {6}, pages = {}, doi = {10.1063/5.0271479}, pmid = {40493811}, issn = {1089-7682}, abstract = {From the integer quantum Hall effect to swimming at a low Reynolds number, geometric phases arise in the description of many different physical systems. In many of these systems, the temporal evolution prescribed by the geometric phase can be directly measured by an external observer. By definition, geometric phases rely on the history of the system's internal dynamics, and so their measurement is directly related to the temporal correlations in the system. They, thus, provide a sensitive tool for studying chaotic Hamiltonian systems. In this work, we present a toy model consisting of an autonomous, low-dimensional, chaotic Hamiltonian system designed to have a simple planar internal state space and a single geometric phase. The diffusive phase dynamics in the highly chaotic regime is, thus, governed by the loop statistics of planar random walks. We show that the naïve loop statistics result in ballistic behavior of the phase and recover the diffusive behavior by considering a bounded shape space or a quadratic confining potential.}, }
@article {pmid40468799, year = {2025}, author = {Zhang, M and Shen, J and Liu, R and Cui, P and Wu, H and Liu, Z}, title = {A numerical study of circulating tumor cell behavior in constricted microvessels based on the immersed boundary-lattice Boltzmann method.}, journal = {Soft matter}, volume = {}, number = {}, pages = {}, doi = {10.1039/d5sm00363f}, pmid = {40468799}, issn = {1744-6848}, abstract = {In this study, the lattice Boltzmann method (LBM) and the immersed boundary (IB) method are employed to quantitatively investigate the dynamics of circulating tumor cells (CTCs) at the cellular scale, and their interactions with red blood cells, platelets and microvascular wall are analyzed based on the obtained data. This reveals that CTC adhesion most likely occurs in the constricted vessels as the Reynolds number is around 0.01. An increase in hematocrit leads to enhanced adhesion, and cell stiffness influences the probability of adhesion. Furthermore, the activated platelets adhering to the CTCs exacerbate the metastatic spread, so the role of platelets in the deformation, adhesion and survival of tumor cells actively arrested by the endothelial cells is crucial. The findings in this work provide important quantitative insights into the underlying mechanisms of cancer metastasis.}, }
@article {pmid40460863, year = {2025}, author = {Ford, MP and Santhanakrishnan, A}, title = {Metachronal rowing provides robust propulsive performance across four orders of magnitude variation in Reynolds number.}, journal = {Journal of the Royal Society, Interface}, volume = {22}, number = {227}, pages = {20240822}, doi = {10.1098/rsif.2024.0822}, pmid = {40460863}, issn = {1742-5662}, support = {//Division of Chemical, Bioengineering, Environmental, and Transport Systems/ ; }, mesh = {Animals ; *Swimming/physiology ; *Models, Biological ; Hydrodynamics ; Viscosity ; *Crustacea/physiology ; Biomechanical Phenomena ; }, abstract = {Metachronal rowing of multiple appendages is a swimming strategy used by numerous organisms across various taxa, with body sizes ranging of the orders of [Formula: see text] to [Formula: see text] m. This corresponds to a huge variation in fluid flow regimes, characterized by paddle-scale Reynolds numbers ([Formula: see text]) ranging from the orders of [Formula: see text] (viscosity dominated) to [Formula: see text] (inertially dominated). Though the rhythmic stroking of the paddles is conserved across species and developmental stages, the hydrodynamic scalability of metachronal rowing has not been examined across this broad [Formula: see text] range. Using a self-propelled metachronal paddling robot, we examine swimming performance changes across four orders of magnitude variation in [Formula: see text] most relevant to crustaceans ([Formula: see text] to [Formula: see text]). We found that wake Strouhal number ([Formula: see text]), which characterizes momentum transfer from paddles to the wake, was unchanged for [Formula: see text] ([Formula: see text]). This is within the reported range of Strouhal numbers of various flying and swimming animals. Peak dimensionless circulation of paddle tip vortices increased linearly with stroke kinematics but was mostly unaffected by fluid viscosity. These findings show that the swimming performance of metachronal rowing is conserved across widely varying flow regimes, with dimensionless swimming speed scaling linearly with [Formula: see text] across the entire tested range.}, }
@article {pmid40460369, year = {2025}, author = {Sharma, KV and Naik, MT and Kanti, PK and Prasad, DMR and Paramasivam, P and Ayanie, AG}, title = {Flow and heat transfer of Poly Dispersed SiO2 Nanoparticles in Aqueous Glycerol in a Horizontal pipe: Application of ensemble and evolutionary machine learning for model-prediction.}, journal = {PloS one}, volume = {20}, number = {6}, pages = {e0323347}, doi = {10.1371/journal.pone.0323347}, pmid = {40460369}, issn = {1932-6203}, mesh = {*Silicon Dioxide/chemistry ; *Glycerol/chemistry ; *Nanoparticles/chemistry ; *Machine Learning ; Hot Temperature ; Water/chemistry ; Models, Theoretical ; }, abstract = {Stable nanofluid dispersion with SiO2 particles of 15, 50, and 100 nm is generated in a base liquid composed of water and glycerol in a 7:3 ratio and tested for physical characteristics in the temperature range of 20-100oC. The nanofluid showed excellent stability for over a month. Experiments are undertaken for the flow of nanofluid in a copper pipe and measured for their heat transfer coefficient and flow behavior. The convection heat transfer coefficient increases with the flow Reynolds number in the transition-turbulent flow regime. The experimental results further reveal that the friction factor enhancement with 0.5% concentration has increased by 6% as compared to the base liquid. It was employed for prognostic model development using XGBoost and multi-gene genetic programming (MGGP) to model and predict the complex and nonlinear data acquired during experiments. Both techniques provided robust predictions, as witnessed by the statistical evaluation. The R2 statistics of the XGBoost-based model was 0.9899 throughout the model test, while it was lowered to 0.9455 for the MGGP-based model. However, the change was insignificant. The mean squared value was 8.37 for XGBoost, while it increased in the MGGP model to 45.12. Similarly, the mean absolute error (MAE) value was higher (6.623) in the case of MGGP than in XGBoost at 2.733. The statistical evaluation, Taylor diagrams, and violin plots helped determine that XGBoost was superior to MGGP in the present work.}, }
@article {pmid40455197, year = {2025}, author = {Sudarsanan, S and Pavithran, I and Sujith, RI}, title = {On the nature of nonequilibrium phase transition in a complex system.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {35}, number = {6}, pages = {}, doi = {10.1063/5.0265336}, pmid = {40455197}, issn = {1089-7682}, abstract = {The transition from a chaotic to a periodic oscillatory state can be smooth or abrupt in real-world complex systems. We study smooth and abrupt transitions in a turbulent reactive flow system. The turbulent reactive flow system consists of the flame, the acoustic field, and the hydrodynamic field interacting nonlinearly. Generally, as the Reynolds number is increased, a laminar flow becomes turbulent, and the range of time scales associated with the flow broadens. Yet, as the Reynolds number is increased in a turbulent reactive flow system, a single dominant time scale emerges in the acoustic pressure oscillations. By varying the Reynolds number at different rates, we observe smooth and abrupt transitions from chaos to order. For such smooth and abrupt transitions, we study the evolution of correlated (conformists and contrarians) and uncorrelated (disordered) dynamics between the acoustic pressure and the heat release rate oscillations in the spatiotemporal domain of the turbulent reactive flow system. We discover that the spatial extent of the disordered dynamics plays a critical role in deciding the abruptness of the transition. During the smooth transition, we observe a significant presence of disordered dynamics in the spatial domain. In contrast, abrupt transitions are accompanied by the abrupt disappearance of disordered dynamics from the spatial domain.}, }
@article {pmid40450040, year = {2025}, author = {Tuo, D and Zeng, G and Zhang, Y and Liao, M}, title = {Effects of Reynolds number and scale ratio on VIV tests for railway blunt box girders.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {19146}, pmid = {40450040}, issn = {2045-2322}, abstract = {Blunt steel box girder as a form of main girder used in large-span railway bridges, the vortex-induced vibrations (VIVs) phenomenon is significant. In order to investigate the effect of model scale on the test results of section model VIV tests of railway bridge blunt box girders, 1:90, 1:50 and 1:25 section model wind tunnel tests were carried out. The test results show that the VIV experimental results are greatly affected by the scale of the model, in which the amplitudes obtained from the 1:50 model test is the most significant, and the VIV characteristics of the two scale models of 1:50 and 1:25 coincide with each other roughly; However, the 1:90 small-scale model is not able to effectively respond to the VIV characteristics of the real bridge. The CFD numerical simulation results also confirm the phenomenon that the 1:90 small-scale model test cannot effectively respond to the real VIVs characteristics. Although VIVs, obtained in a small-scale model test, are not possible to determine the vibration response of the actual railway bridge, it can be used to compare the VIV performance of the cross-section and to assist in the study of aerodynamic optimization measures at the early design stage.}, }
@article {pmid40440770, year = {2025}, author = {Rathore, S and Africa, PC and Ballarin, F and Pichi, F and Girfoglio, M and Rozza, G}, title = {Projection-based reduced order modelling for unsteady parametrized optimal control problems in 3D cardiovascular flows.}, journal = {Computer methods and programs in biomedicine}, volume = {269}, number = {}, pages = {108813}, doi = {10.1016/j.cmpb.2025.108813}, pmid = {40440770}, issn = {1872-7565}, abstract = {BACKGROUND AND OBJECTIVE: Accurately defining outflow boundary conditions in patient-specific models poses significant challenges due to complex vascular morphologies, physiological conditions, and high computational demands. These challenges hinder the computation of realistic and reliable cardiovascular (CV) haemodynamics by incorporating clinical data such as 4D magnetic resonance imaging. The objective is to control the outflow boundary conditions to optimize CV haemodynamics and minimize the discrepancy between target and computed flow velocity profiles. This paper presents a projection-based reduced order modelling (ROM) framework for unsteady parametrized optimal control problems (OCP(μ)s) arising from CV applications.<br><br>METHODS: Numerical solutions of OCP(&#x3bc;)s require substantial computational resources, highlighting the need for robust and efficient ROMs to perform real-time and many-query simulations. We investigate the performance of a projection-based reduction technique that relies on the offline-online paradigm, enabling significant computational cost savings. In this study, the fluid flow is governed by unsteady Navier-Stokes equations with physical parametric dependence, i.e. the Reynolds number. The Galerkin finite element method is used to compute the high-fidelity solutions in the offline phase. We implemented a nested-proper orthogonal decomposition (nested-POD) for fast simulation of OCP(&#x3bc;)s that encompasses two stages: temporal compression for reducing dimensionality in time, followed by parametric-space compression on the precomputed POD modes.<br><br>RESULTS: We tested the efficacy of the proposed methodology on vascular models, namely an idealized bifurcation geometry and a patient-specific coronary artery bypass graft, incorporating stress control at the outflow boundary and observing consistent speed-up with respect to high-fidelity strategies. We observed the inter-dependency between the state, adjoint, and control solutions and presented detailed flow field characteristics, providing valuable insights into factors such as atherosclerosis risk.<br><br>CONCLUSION: The projection-based ROM framework provides an efficient and accurate approach for simulating parametrized CV flows. By enabling real-time, patient-specific modelling, this advancement supports personalized medical interventions and improves the predictions of disease progression in vascular regions.}, }
@article {pmid40436033, year = {2025}, author = {Fardi, A and Farooq, H and Akhtar, I and Hemmati, A and Khalid, MSU}, title = {Characterizing the Role of Hind Flippers in Hydrodynamics of A Harbor Seal.}, journal = {Bioinspiration &amp; biomimetics}, volume = {}, number = {}, pages = {}, doi = {10.1088/1748-3190/adde07}, pmid = {40436033}, issn = {1748-3190}, abstract = {In this paper, we investigate the hydrodynamic characteristics of harbor seal locomotion, focusing on the role of hind flippers in thrust generation and wake dynamics. Through three-dimensional numerical simulations using an immersed boundary method at Reynolds number of 3000, we analyze the impact of varying Strouhal number (St = 0.2-0.35) and propulsive wavelength (λ∗ = 1.0-1.2) on swimming performance. Our findings reveal two distinct wake patterns: a single-row structure at lower Strouhal numbers (St ≤ 0.25) and a double-row configuration at higher St (St ≥ 0.3). Increasing wavelength generally enhances thrust production by reducing both pressure and friction of drag components. Additionally, we identify critical vortex interactions between the front and hind flippers, with destructive interference occurring at lower St and constructive patterns emerging at higher St. Circulation analysis confirms stronger vortex formation at higher St and λ∗, particularly during the left stroke phase. These results provide novel insights into the hydrodynamic mechanisms underlying seal locomotion and contribute to our understanding of efficient aquatic propulsion systems.}, }
@article {pmid40430862, year = {2025}, author = {Mattusch, AM and Schaldach, G and Bartsch, J and Thommes, M}, title = {Intrinsic Dissolution Modeling: Interdependence Between Dissolution Rate, Solubility, and Boundary Layer Thickness.}, journal = {Pharmaceutics}, volume = {17}, number = {5}, pages = {}, doi = {10.3390/pharmaceutics17050570}, pmid = {40430862}, issn = {1999-4923}, abstract = {Background/Objectives: In the past, many drug release models have been presented which attempt to describe the interaction of drugs and excipients in a formulation. Nevertheless, modeling the intrinsic dissolution behavior is essential for understanding the fundamental dissolution mechanisms of drugs and for enhancing the quality of computational approaches in the long term. Methods: In this study, the intrinsic dissolution of various pharmaceutical model substances (benzocaine, carbamazepine, griseofulvin, ibuprofen, naproxen, phenytoin, theophylline monohydrate, and trimethoprim) was investigated in dissolution experiments, taking into account the flow conditions in a dissolution channel apparatus. A practicable and generally valid representation was identified to describe the diffusion properties of the drugs in terms of the boundary layer thickness without considering the particle size distribution, physical state, or viscoelastic properties. This representation was supported by numerical simulations using a high-resolution mesh. The influence of the topography on the modeling was also examined. Results: Besides the prediction of the influence of a surface reaction limitation or the solubility of a diffusion controlled drug, the boundary layer thickness at the tablet surface is modellable in terms of a freely selectable length and as a function of the diffusion coefficient, drug solubility, and the flow velocity of the dissolution medium. Conclusions: Using different methods and a large dataset, this study presents a modeling approach that can contribute to a deeper understanding of intrinsic dissolution behavior.}, }
@article {pmid40428718, year = {2025}, author = {Juraeva, M and Kang, DJ}, title = {Design and Analysis of a Passive Micromixer Based on Multiple Passages.}, journal = {Micromachines}, volume = {16}, number = {5}, pages = {}, doi = {10.3390/mi16050592}, pmid = {40428718}, issn = {2072-666X}, abstract = {We propose a novel passive micromixer based on multiple passages and analyze its mixing performance comprehensively. The multiple passages are constructed with straight channels, making them easier to manufacture, compared to conventional SAR micromixers and other micromixers based on curved channels. Its mixing performance has been demonstrated to be superior to that of the previous micromixers across a broad range of Reynolds numbers. Five distinct designs incorporating converging passages were explored to study the significance of the number of passages on the mixing performance. Across a broad range of Reynolds number ranges (0.1 to 80), the two-passage design significantly improved mixing performance, with a degree of mixing (DOM) consistently exceeding 0.84. Particularly, the mixing enhancement is prominent within the low and intermediate range of Reynolds numbers (Re≤20). This enhancement in the regime of molecular diffusion dominance stems from the elongated interface between the two fluids. The mixing enhancement in the transition regime is due to a secondary flow being generated on the cross-section normal to the main stream direction. The intensity of this secondary flow is significantly influenced by the number of multiple passages. The optimal number for the present micromixer design is two. The DOM remains almost constant for the submergence of multiple passages in the range of 40 to 70 (μm).}, }
@article {pmid40428712, year = {2025}, author = {Moscato, S and Cutuli, E and Camarda, M and Bucolo, M}, title = {Experimental and Numerical Study of Slug-Flow Velocity Inside Microchannels Through In Situ Optical Monitoring.}, journal = {Micromachines}, volume = {16}, number = {5}, pages = {}, doi = {10.3390/mi16050586}, pmid = {40428712}, issn = {2072-666X}, support = {CUP: E63C220009000022//MUR-PNRR project SAMOTHRACE/ ; }, abstract = {Miniaturization and reliable, real-time, non-invasive monitoring are essential for investigating microfluidic processes in Lab-on-a-Chip (LoC) systems. Progress in this field is driven by three complementary approaches: analytical modeling, computational fluid dynamics (CFD) simulations, and experimental validation techniques. In this study, we present an on-chip experimental method for estimating the slug-flow velocity in microchannels through in situ optical monitoring. Slug flow involving two immiscible fluids was investigated under both liquid-liquid and gas-liquid conditions via an extensive experimental campaign. The measured velocities were used to determine the slug length and key dimensionless parameters, including the Reynolds number and Capillary number. A comparison with analytical models and CFD simulations revealed significant discrepancies, particularly in gas-liquid flows. These differences are mainly attributed to factors such as gas compressibility, pressure fluctuations, the presence of a liquid film, and leakage flows, all of which substantially affect flow dynamics. Notably, the percentage error in liquid-liquid flows was lower than that in gas-liquid flows, largely due to the incompressibility assumption inherent in the model. The high-frequency monitoring capability of the proposed method enables in situ mapping of evolving multiphase structures, offering valuable insights into slug-flow dynamics and transient phenomena that are often difficult to capture using conventional measurement techniques.}, }
@article {pmid40428670, year = {2025}, author = {Li, Y and Yonemoto, Y and Yamahata, Y and Kawahara, A}, title = {Rheological Property Changes in Polyacrylamide Aqueous Solution Flowed Through Microchannel Under Low Reynolds Number and High Shear Rate Conditions.}, journal = {Micromachines}, volume = {16}, number = {5}, pages = {}, doi = {10.3390/mi16050545}, pmid = {40428670}, issn = {2072-666X}, support = {22K03907 and 21K03860//JSPS KAKENHI/ ; }, abstract = {As an important structure of microfluidic devices, microchannels have the advantages of precise flow control and high reaction efficiency. This study investigates experimentally changing the rheological properties of a polyacrylamide (PAM) aqueous solution after flowing through a square microchannel with a hydraulic diameter of 0.5 mm under low Reynolds number and high shear rate conditions. To know the effect of the channel length on the change in viscosity and relaxation time, the length is changed to 100 mm and 200 mm. From the experiment, it is found that both the viscosity and relaxation time of the solution decrease with increasing the shear rate and the microchannel length. Based on the present experimental data, an empirical model is proposed to predict the change ratio of the relaxation time before and after passing through the microchannel, and the calculation with the model has an agreement with the experiment with root-mean-square absolute error of 0.007.}, }
@article {pmid40428660, year = {2025}, author = {Lu, X and Wang, L and Wang, L and Hu, Y}, title = {Heat Transfer Enhancement of Diamond Rib Mounted in Periodic Merging Chambers of Micro Channel Heat Sink.}, journal = {Micromachines}, volume = {16}, number = {5}, pages = {}, doi = {10.3390/mi16050533}, pmid = {40428660}, issn = {2072-666X}, support = {52476076//National Natural Science Foundation of China/ ; 21ZD4GA027//Major Special Projects of Gansu Province, China/ ; 25JRRA963,23JRRA1704//Science and Technology Program Basic research program natural science Foundation of Gansu Province China/ ; }, abstract = {The heat transfer enhancement of diamond-shaped ribs mounted in the periodic merging chambers of microchannel (MC) heat sinks is investigated using a numerical method for Reynolds number in the region of 300-700. Compared to triangular, rectangular, and cylindrical ribs, diamond-shaped ribs achieve 3.59%, 13.24%, and 6.34% higher enhancement effects, respectively, under the same mass flow rate. Further analysis of geometric parameters (length, width, and height) and rib positioning reveals that a rib height of h/Hch = 0.8 provides optimal heat dissipation performance. For Re < 500, the optimal configuration is a rib length of l/Lmerg = 0.55 and a width of b/Wch = 0.8, while for 500 < Re < 700, it shifts to l/Lmerg = 0.36 and b/Wch = 1.6. For s/Lmerg, the smaller it is, the shorter the main flow separation time, thereby improving heat transfer efficiency.}, }
@article {pmid40423248, year = {2025}, author = {Wirth, M and Hagedorn, J and Weigand, B and Kabelac, S}, title = {Design of a test rig for the investigation of falling film flows with counter-current gas flows.}, journal = {The Review of scientific instruments}, volume = {96}, number = {5}, pages = {}, doi = {10.1063/5.0263158}, pmid = {40423248}, issn = {1089-7623}, abstract = {Geothermal phase change probes employ falling film evaporation to efficiently harness geothermal heat for space heating applications. Despite successful applications in research, commercial use remains limited due to the lack of validated models capable of accurately representing the complex flow phenomena within these probes. To address this issue, a test rig was developed, replicating the flow phenomena within these probes and facilitating the validation of future models. This paper presents the results of the first measurement campaign conducted with water and humid air as working fluids. For the gas phase, velocity profiles were measured with a hot-wire anemometer, and for the liquid phase, high temporal resolution film thickness measurements were conducted with a confocal chromatic imaging sensor. The results of both measurement systems were qualitatively consistent with existing literature. The time-averaged film thickness h̄film in the flow direction, without gas flow, revealed an increase of h̄film along the flow direction for Reliq = 500. In contrast, for Reliq ≥ 980, an opposing trend was observed. In addition, the influence of the gas flow on h̄film was investigated in the flow direction. The results show no noticeable influence below a threshold gas Reynolds number near the liquid film inlet (x = 0.1 m), while an increase appeared beyond this Reliq-dependent value. Observations further downstream (x = 0.6 m) indicated an h̄film increase toward the threshold and a decrease beyond it. The latter observation aligns with findings in the literature, suggesting the onset of flooding. This observation was further strengthened by a film flow transition captured through high-speed camera imaging, indicating the test rig's capability of investigating flooding conditions.}, }
@article {pmid40422158, year = {2025}, author = {Li, K and Xu, N and Zhong, L and Mou, X}, title = {Corrugation at the Trailing Edge Enhances the Aerodynamic Performance of a Three-Dimensional Wing During Gliding Flight.}, journal = {Biomimetics (Basel, Switzerland)}, volume = {10}, number = {5}, pages = {}, doi = {10.3390/biomimetics10050329}, pmid = {40422158}, issn = {2313-7673}, support = {11802262//National Natural Science Foundation of China/ ; 11502228//National Natural Science Foundation of China/ ; }, abstract = {Dragonflies exhibit remarkable flight capabilities, and their wings feature corrugated structures that are distinct from conventional airfoils. This study investigates the aerodynamic effects of three corrugation parameters on gliding performance at a Reynolds number of 1350 and angles of attack ranging from 0° to 20°: (1) chordwise corrugation position, (2) linear variation in corrugation amplitude toward the trailing edge, and (3) the number of trailing-edge corrugations. The results show that when corrugation structures are positioned closer to the trailing edge, they generate localized vortices in the mid-forward region of the upper surface, thereby enhancing aerodynamic performance. Further studies show that a linear increase in corrugation amplitude toward the trailing edge significantly delays the shedding of the leading-edge vortex (LEV), produces a more coherent LEV, and reduces the number of vortices within the corrugation grooves on the lower surface. Consequently, the lift coefficient is maximized with an enhancement of 28.99%. Additionally, reducing the number of trailing-edge corrugations makes the localized vortices on the upper surface approach the trailing edge and merge into larger, more continuous LEVs. The vortices on the lower surface grooves also decrease in number, and the lift coefficient is maximally increased by 20.09%.}, }
@article {pmid40422087, year = {2025}, author = {Shanmugam, AR and Sohn, CH and Park, KS}, title = {Numerical Investigation on the Aerodynamic Benefits of Corrugated Wing in Dragonfly-like Hovering Flapping Wing.}, journal = {Biomimetics (Basel, Switzerland)}, volume = {10}, number = {5}, pages = {}, doi = {10.3390/biomimetics10050256}, pmid = {40422087}, issn = {2313-7673}, support = {G00004258//United Arab Emirates University/ ; G00004882//United Arab Emirates University/ ; }, abstract = {The effect of corrugated wings on the aerodynamic characteristics of a dragonfly-like hovering flapping wing is investigated using two-dimensional numerical simulations. Two types of pitch motion profiles, namely 'sinusoidal' and 'trapezoidal', are employed. The results obtained from the corrugated wings at Reynolds number Re = 2150 are then compared with the flat plate geometries to analyze the aerodynamic benefits of wing corrugation. The aerodynamic characteristics of corrugated wings are investigated quantitatively using cycle-averaged vertical force coefficient. For the qualitative investigation, time histories of vertical force coefficient, vorticity, and surface pressure distribution are used. The results reveal that the corrugated wings perform better than the flat plates in all three flapping configurations for both sinusoidal and trapezoidal pitch profiles. For a tandem wing with a sinusoidal pitch profile, the corrugated wings yield a vertical force generation nearly 14%, 22%, and 12%, higher than the flat plate geometries for ψ = 0°, 90°, and 180°, respectively. The corrugated wing sheds a relatively stronger detached counter clockwise vortex (CCWV) on the lower surface as compared to the flat plate, and hence, the vertical force is much higher for the corrugated wing. For a tandem wing with a trapezoidal pitch profile, the corrugated wings yield a vertical force generation nearly 27%, 22%, and 57%, higher than the flat plate geometries for ψ = 0°, 90°, and 180°, respectively. In corrugated wing geometry, the delayed stall mechanism is slightly postponed due to the corrugation shape's ability to trap the vortex structures, leading to a positive effect on vertical force production.}, }
@article {pmid40415832, year = {2025}, author = {Zou, S and Xiao, J and Chen, XD}, title = {A Comprehensive Comparison of Different Reynolds-Averaged Navier-Stokes Turbulence Models in Modeling Turbulent Plane Jets.}, journal = {ACS omega}, volume = {10}, number = {19}, pages = {19873-19886}, pmid = {40415832}, issn = {2470-1343}, abstract = {Turbulent plane jets are of great interest in a broad range of engineering applications such as combustion, mixing, and ventilation. Accurate prediction of the velocity field of jets is essential for accurate calculation of the mass and energy transfer in it. However, to date, no modeling works has comprehensively evaluated the computational accuracy and advantages of various Reynolds-averaged Navier-Stokes (RANS) turbulence models for calculating plane jets. Here, the plane jet of air was investigated under various Reynolds numbers using a suite of RANS models, including standard k - ε (SKE), realizable k - ε (RKE), renormalization group k - ε (RNGKE), standard k - ω (SKO), and shear-stress transport k - ω (SSTKO). The velocity fields were comprehensively compared to the experimental results. It was found that the SKO model exhibits a significant mesh dependency and poor convergence. No model can accurately predict the effect of the Reynolds number on velocity fields with an accuracy of R [2] ≥ 0.97. Moreover, (1) the SKE model has the best prediction under low or moderate Reynolds numbers (Re ≤ 10000); (2) the RKE model is more applicable under high Reynolds numbers (Re ≥ 10000); (3) the RNGKE model has the worst prediction; (4) the SSTKO model is more applicable under moderate Reynolds numbers (3000 ≤ Re ≤ 10000). It is hoped that these results can guide the selection of RANS models and stimulate greater efforts in creating an appropriate turbulence model that can accurately model such a "simple" case of flow.}, }
@article {pmid40415070, year = {2025}, author = {Javed, SF and Khan, ME and Yahya, Z and Idrisi, MJ and Tenna, W}, title = {Performance analysis of three-dimensional passive micromixers using k-means priority clustering with AHP-based sustainable design optimization.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {18140}, pmid = {40415070}, issn = {2045-2322}, abstract = {This novel study presents an in-depth mathematical analysis, investigation, and comparative peculiar assessment of mixing behaviors across different microchannel configurations: the Simple T-shape, Spiral T-shape, and Three-Dimensional Serpentine Passive Micromixer (TDSPM). Considering the pivotal role of micromixing in various applications, the research thoroughly employs the Navier-Stokes equations to analyze flow dynamics and measure the mixing performance of water and water-dye mixtures. The TDSPM, with its distinctive rectangular inlet duct and U-shaped repeating structures, optimizes fluid interaction by constricting flow pathways. The study highlights the superior performance of the TDSPM and thoroughly evaluates the mixing indices for all three micromixer types at Reynolds numbers ranging from 5 to 250. From the priority analysis, Reynolds number (38.49%) and velocity (38.69%) are the most influential factors in micromixer performance, followed by mixing path length (15.35%) and channel width (6.87%). Test 18 (Re = 200, Mixing Path = 25 mm, Velocity = 4.2 m/s, Channel Width = 5 mm) achieves 98% mixing efficiency with a 500 Pa pressure drop, optimizing performance with lower energy costs. Finally, this design leads to remarkable improvements in mixing efficiency over a broad spectrum of Reynolds numbers.}, }
@article {pmid40414908, year = {2025}, author = {Ma, H and Sun, X and Li, Y}, title = {Design of structural parameters and study on the energy dissipation characteristics of vertical jet-type energy dissipators.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {18204}, pmid = {40414908}, issn = {2045-2322}, support = {202303021211141//Natural Science Foundation for Young Scientists of Shanxi Province/ ; 202303021211141//Natural Science Foundation for Young Scientists of Shanxi Province/ ; 202303021211141//Natural Science Foundation for Young Scientists of Shanxi Province/ ; 51179116//the National Natural Science Foundation of China/ ; 51179116//the National Natural Science Foundation of China/ ; 51179116//the National Natural Science Foundation of China/ ; }, abstract = {In order to isolate energy dissipators from hydraulic engineering projects and address the issues of vibration damage caused by the discharge structures. This study develops a novel vertical jet-type energy dissipator by placing fragmentation needles at the vertical jet pipe nozzle, which mainly uses the fragmentation needles to fragment the high-energy jet into multiple smaller jets. Along with the mixing of air into the water flow, the mechanical energy of the flow is converted into internal energy and dissipated in the air. The structural parameters of the vertical jet-type energy dissipator include the size, shape, and number of fragmentation needles. The study employs numerical simulations primarily, with physical model experiments for validation, to investigate the nappe characteristics, energy dissipation rate, and energy dissipation mechanisms of the vertical jet energy dissipator under various structural parameters. The results show that within the scope of this study, the energy dissipation rate of the vertical jet increases with the Reynolds number, the number of fragmentation needles, and the size of the fragmentation needles. Compared to the case without fragmentation needles, the energy dissipation rate increases by 1.04-4.89 times. Under the same Reynolds number, the total height of the jet and the height of the potential core decrease as the number and size of the fragmentation needles increase. The height and diameter of the nappe crown increase, and the diameter and thickness of the vortex ring decrease as the number and size of the fragmentation needles increase. The jet under the influence of rectangular fragmentation needles is more dispersed compared to the jet under the influence of cylindrical fragmentation needles. The total height and potential core height of the jet are smaller with rectangular fragmentation needles, while the height and diameter of the nappe crown are larger. The air concentration in the nappe under rectangular fragmentation needles is higher than that under cylindrical fragmentation needles, and the energy dissipation rate of the vertical jet is also higher under rectangular fragmentation needles than under cylindrical fragmentation needles. The vertical jet-type energy dissipator proposed in this study addresses key engineering challenges, such as terrain constraints and the need for flexible design solutions. Its ability to efficiently dissipate energy while maintaining adaptability makes it a valuable tool for hydraulic engineers designing energy dissipation systems. The conclusions of this study provide a reference for the application of vertical jet-type energy dissipators.}, }
@article {pmid40411012, year = {2025}, author = {Jiang, H and Pfister, JL and Huang, DZ and Cao, S}, title = {Koopman reduced-order modeling and analysis of flag flapping in the wake of a cylinder.}, journal = {Physical review. E}, volume = {111}, number = {4-2}, pages = {045101}, doi = {10.1103/PhysRevE.111.045101}, pmid = {40411012}, issn = {2470-0053}, abstract = {We develop a Koopman reduced-order model (ROM) to analyze the instability mechanism and predict the hydrodynamic behavior for the flag flapping in the wake of a cylinder. The Koopman ROM is constructed using a kernel dynamic mode decomposition method and enhanced through a residual dynamical mode decomposition algorithm, which improves accuracy by identifying and eliminating spurious modes. Our analysis reveals a flow transition from the "2S" mode in the periodic phase to the "2P" mode in the quasiperiodic phase, with the main Koopman mode M_{1} providing insights into the instability mechanism. In the case of chaotic flapping at a Reynolds number of Re=1200, the Koopman ROM demonstrates high accuracy in predicting the chaotic fluid-structure interaction flow when comparing the fractal dimension d_{c} and the maximum Lyapunov exponent λ_{max} of the true and reconstructed flow. Additionally, we observe similar flag flapping and vortex shedding characteristics in the near-structure region throughout the investigated Reynolds number range Re∈[500,1200], leading to similar vorticity patterns for M_{1}. The flag flapping has a local minimum displacement at position x_{0}≈3.0 in the flag's displacement envelope. Notably, this position closely matches the critical position x_{c} obtained from global linear instability analysis at low Reynolds numbers. This conclusion aligns with the performance of the Koopman ROM using sparse measurement probes attached to the flag. The position of the probes influences the accuracy of the ROM, where higher accuracy corresponds to a larger displacement of the eigenfunction.}, }
@article {pmid40406451, year = {2025}, author = {Suárez, P and Alcántara-Ávila, F and Miró, A and Rabault, J and Font, B and Lehmkuhl, O and Vinuesa, R}, title = {Active Flow Control for Drag Reduction Through Multi-agent Reinforcement Learning on a Turbulent Cylinder at R e D = 3900.}, journal = {Flow, turbulence and combustion}, volume = {115}, number = {1}, pages = {3-27}, pmid = {40406451}, issn = {1573-1987}, abstract = {This study presents novel drag reduction active-flow-control (AFC) strategies for a three-dimensional cylinder immersed in a flow at a Reynolds number based on freestream velocity and cylinder diameter of R e D = 3900 . The cylinder in this subcritical flow regime has been extensively studied in the literature and is considered a classic case of turbulent flow arising from a bluff body. The strategies presented are explored through the use of deep reinforcement learning. The cylinder is equipped with 10 independent zero-net-mass-flux jet pairs, distributed on the top and bottom surfaces, which define the AFC setup. The method is based on the coupling between a computational-fluid-dynamics solver and a multi-agent reinforcement-learning (MARL) framework using the proximal-policy-optimization algorithm. This work introduces a multi-stage training approach to expand the exploration space and enhance drag reduction stabilization. By accelerating training through the exploitation of local invariants with MARL, a drag reduction of approximately 9 % is achieved. The cooperative closed-loop strategy developed by the agents is sophisticated, as it utilizes a wide bandwidth of mass-flow-rate frequencies, which classical control methods are unable to match. Notably, the mass cost efficiency is demonstrated to be two orders of magnitude lower than that of classical control methods reported in the literature. These developments represent a significant advancement in active flow control in turbulent regimes, critical for industrial applications.}, }
@article {pmid40374935, year = {2025}, author = {Xu, L and Miao, Y and Wu, X and Li, P and Qin, H}, title = {Experimental investigation on loads of nets with different types under current.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {16891}, pmid = {40374935}, issn = {2045-2322}, support = {BK20220221//Jiangsu Province Science Foundation for Youths/ ; }, abstract = {The drag of the net is the main component of the total hydrodynamic loads on the cage. It is crucial to the operational safety and structural integrity of the net cage. Despite this, there is a paucity of research examining the impact of various parameters, including materials, mesh types, solidity ratios, and angles of attack, on the hydrodynamic loads of nets. In this paper, a series of flume tests are used to investigate the drag on the nets and the relationships between the drag coefficient and the net material, net solidity ratio, mesh shape, current velocity, and current direction. The drag of six nets with different types under varying current velocities and current directions are calculated, and the curves between the drag coefficient and the current velocity or Reynolds number are further obtained. The test results show that the drag and drag coefficients of the net are not only related to the current velocity and the windward area but also to the mesh shape, net solidity ratio, material properties, etc. On this basis, the drag coefficients of these nets obtained from the prediction models and the tests are compared and analyzed, and the applicable conditions of different prediction models are further clarified. This paper can provide data support for the drag calculation of the cage.}, }
@article {pmid40372907, year = {2025}, author = {Xiao, X and Lin, D and Wu, Y and Bai, K and Liu, X}, title = {Simulating Two-phase Fluid-rigid Interactions with an Overset-Grid Kinetic Solver.}, journal = {IEEE transactions on visualization and computer graphics}, volume = {PP}, number = {}, pages = {}, doi = {10.1109/TVCG.2025.3570570}, pmid = {40372907}, issn = {1941-0506}, abstract = {Simulating the coupled dynamics between rigid bodies and two-phase fluids, especially those with a large density ratio and a high Reynolds number, is computationally demanding but visually compelling with a broad range of applications. Traditional approaches that directly solve the Navier-Stokes equations often struggle to reproduce these flow phenomena due to stronger numerical diffusion, resulting in lower accuracy. While recent advancements in kinetic lattice Boltzmann methods for two-phase flows have notably enhanced efficiency and accuracy, challenges remain in correctly managing fluid-rigid boundaries, resulting in physically inconsistent results. In this paper, we propose a novel kinetic framework for fluid-rigid interaction involving two fluid phases. Our approach leverages the idea of an overset grid, and proposes a novel formulation in the two-phase flow context with multiple improvements to handle complex scenarios and support moving multi-resolution domains with boundary layer control. These new contributions successfully resolve many issues inherent in previous methods and enable physically more consistent simulations of two-phase flow phenomena. We have conducted both quantitative and qualitative evaluations, compared our method to previous techniques, and validated its physical consistency through real-world experiments. Additionally, we demonstrate the versatility of our method across various scenarios.}, }
@article {pmid40372072, year = {2025}, author = {Kumar, S and Bhumkar, YG}, title = {Beat of sound generated from NACA0012 airfoil on application of suction-blowing excitation.}, journal = {The Journal of the Acoustical Society of America}, volume = {157}, number = {5}, pages = {3730-3741}, doi = {10.1121/10.0036698}, pmid = {40372072}, issn = {1520-8524}, abstract = {The present numerical study explores the effect of periodic suction-blowing excitation (SBE) on sound generation in the flow over a NACA0012 airfoil, with a focus on inducing beats in the resulting sound signals. Simulations are conducted at a Reynolds number (Re) of 5000 and an angle of attack of 5° using direct numerical simulation (DNS) approach where compressible Navier-Stokes equations are solved to compute both flow and sound fields directly. At low Re, vortex-shedding generates tonal noise at the Strouhal frequency (St). The introduction of periodic SBE adds sound sources at the excitation frequency (ff), with the resultant sound field arising from the interaction between vortex-shedding and excitation-induced sound sources. This study investigates the effects of excitation forcing frequency (ff) and amplitude (Ae), identifying conditions that lead to beat formation. Beats are observed when ff is close to St and the sound intensities of both sources are comparable. Distinct wave propagation patterns emerge during beat formation, significantly differing from non-beat scenarios. A key contribution of this work is to offer a guideline on the relationship between excitation amplitude and the formation of sound beats, either in the axial direction of flow or normal to it.}, }
@article {pmid40343671, year = {2025}, author = {Li, Z and He, L and Pan, T and Yin, Y and Li, S and Yuan, W and Meng, B}, title = {Influence of the stability of boundary vortex on drag reduction induced by transverse V-grooves.}, journal = {The European physical journal. E, Soft matter}, volume = {48}, number = {4-5}, pages = {24}, pmid = {40343671}, issn = {1292-895X}, support = {52176032//National Natural Science Foundation of China/ ; 52322603//National Natural Science Foundation of China/ ; 52006002//National Natural Science Foundation of China/ ; }, abstract = {Previous studies revealed the skin-friction drag reduction properties induced by transverse grooves. However, the effects of unsteady characteristics of vortices within the grooves on the drag reduction properties have not been investigated. A hypothesis that the unsteady motion of vortices may reduce the friction drag-reduction rate induced by transverse V-grooves is proposed in this paper. To verify this hypothesis, we use the LES (large eddy simulation) method to investigate the flow field in the range of Reynolds number 0.5E5 to 7.5E5 over the different profiles of symmetric V-grooves, whose depths are 0.2 mm and AR's are 0.5, 1, 2, 5, and 8. The results show that the AR (aspect ratio of a transverse groove) affects the stability of boundary vortices, thus driving the variation of total viscous drag and pressure drag. With the increase of AR, the boundary vortices tend to be stable at first and then gradually become unstable. When AR is 2, the boundary vortices are stable within the grooves, corresponding to optimal drag reduction. In this case, the slip velocities induced by boundary vortices are the largest, and the Reynolds shear stress is the least, suggesting that the grooves have the strongest abilities to reduce the total viscous drag. When the stability of the boundary vortices is broken, a larger area containing high pressure and low pressure is formed in the groove, and the difference also becomes greater between the high pressure and low pressure. The results provide improved understandings of the drag reduction mechanism of transverse grooves.}, }
@article {pmid40341596, year = {2025}, author = {Kanti, PK and Wanatasanappan, VV and Said, NM and Saini, S and Mishra, V and Paramasivam, P and Yusuf, M}, title = {Thermal performance, entropy generation, and machine learning insights of Al2O3-TiO2 hybrid nanofluids in turbulent flow.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {16035}, pmid = {40341596}, issn = {2045-2322}, abstract = {This study investigates the heat transfer performance of water-based Al2O3-TiO2 (50:50) hybrid nanofluids under turbulent flow conditions. Al2O3 and TiO2 nanoparticles (13 and 21 nm, respectively) were dispersed in water to prepare the nanofluids in the concentrations range of 0 to 1 vol%. Thermal conductivity and viscosity are measured in the temperature range of 30 to 60[o]C for the prepared nanofluids. Experimental and numerical analyses explored the effect of concentration and Reynolds number on Nusselt number, entropy generation, and friction factor. The results demonstrate that maximum viscosity enhancement of 15.77 and 14.76% is observed for 1 vol% of hybrid nanofluid and Al2O3 nanofluid compared to base fluid at 30 [o]C, respectively. The maximum Nusselt number enchantment is 70.4% for 1 vol% of hybrid nanofluid compared to the water. Similarly, hybrid nanofluids achieved a remarkable reduction in total entropy generation of 46% in contrast to the base fluid. New correlations are proposed to predict both the Nusselt number and friction factor for hybrid nanofluids. Furthermore, employing machine learning techniques, highly accurate models are developed. These findings highlight the promising role of hybrid nanofluids in achieving efficient thermal management in various applications.}, }
@article {pmid40331166, year = {2018}, author = {Baek, S and Bradley, PE and Radebaugh, R}, title = {Heat transfer coefficient measurement of LN2 and GN2 in a microchannel at low Reynolds flow.}, journal = {International journal of heat and mass transfer}, volume = {127}, number = {}, pages = {}, doi = {10.1016/j.ijheatmasstransfer.2018.07.145}, pmid = {40331166}, issn = {0017-9310}, abstract = {The heat transfer coefficients of single-phase fluids in the laminar flow regime have been studied for decades. However, inconsistent results are found in the literature. The common finding is that the Nusselt number is dependent on the Reynolds number in the laminar flow regime, which is contrary to laminar flow heat transfer theory. Recently, researchers indicated that axial conduction in the wall of the microchannel can affect the measurement. However, there have not been thorough studies that demonstrate consistency or lack thereof between experiment and theory. This study provides an experimental investigation on heat transfer performance of gaseous and liquid nitrogen flow through microchannels with hydraulic diameters of 110 μm and 180 μm. A model has been developed to investigate heat transfer in a microchannel from which analysis shows that the temperature profile of the fluid and wall change non-linearly along the length of the microchannel when the flow rate is low (e.g., R e < 1000). The nonlinear temperature profile conflicts with the assumption of a linear temperature profile commensurate with the traditional Nusselt number estimation method, which leads to dependency on the Reynolds number. Comparison between the experiment and numerical model of the present work validates the conclusion that the heat transfer coefficient is uniform within the laminar flow regime (R e < 2000) for microchannels.}, }
@article {pmid40322754, year = {2025}, author = {Rosi, G and Barnes, M and Kaiser, F and Rival, D}, title = {Exploring separation and reattachment in shear-thinning suspensions through pipe-wall ultrasound measurements.}, journal = {Experiments in fluids}, volume = {66}, number = {5}, pages = {99}, pmid = {40322754}, issn = {0723-4864}, abstract = {To better understand how turbulent flow structures develop within shear-thinning suspensions (STSs), we investigate the behavior of a shear layer forming within an STS downstream of a sudden expansion with an expansion ratio of 0.5. Specifically, the shear-layer reattachment behavior downstream of an axisymmetric expansion is characterized through ultrasound imaging velocimetry (UIV) and through pressure measurements, and the observed behavior is used to surmise how the shear layer is modified within the STS. Four fluids are investigated, which include pure water, as well as three 1750 ppm xanthan-gum-in-water solutions mixed with non-reactive mineral microspheres at volume fractions of 0%, 15%, and 30%. Wall-pressure measurements were collected through pressure taps located at 0h to 25.8h downstream of the expansion with subsequent UIV measurements collected from 1h to 9h downstream of the expansion, where h is the step height and equals the difference between the pipe and throat radii. For single-phase cases, pressure-recovery profiles and UIV flow fields indicate a predictably large reattachment length at low Reynolds numbers, which shortens as the Reynolds number increases from O (10 2) to O (10 4) and finally stabilizes at roughly 8h. In contrast, the STSs exhibit pressure-recovery and pipe-wall velocity profiles indicating a reattachment length that is consistently short (8h) and independent of Reynolds number. The results indicate that the suspended phase within the STSs causes the shear layer to diffuse far more rapidly, thereby promoting momentum transfer toward the wall, which results in a consistently short reattachment length.}, }
@article {pmid40316668, year = {2025}, author = {Madhwesh, N and Karanth, KV and Kumar, S}, title = {Heat transfer enhancement of a solar air heater using capsule-shaped turbulators: a numerical analysis.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {15391}, pmid = {40316668}, issn = {2045-2322}, abstract = {The development of a laminar sublayer inside the channel of the solar collector results in a poor heat transfer coefficient. Adding artificial roughness to the absorber plate in the form of turbulators is an effective and promising method of increasing heat transmission by interrupting the laminar sublayer. In this study, a capsule-shaped turbulator is used to enhance the thermal performance of the solar air heater. With flow Re (Reynolds number) fluctuating from 3000 to 21,000, the flow and heat transfer-related parameters of an air heater fitted with turbulators were numerically examined. The orientation angle of the capsule turbulator corresponding to the flow direction is modified from 0° to 90° in steps of 15°. The outcomes indicated that the overall thermal performance of the solar collector was optimized for the orientation angle of 45° at all the Reynolds numbers chosen for the study. Beyond this angle, the turbulators block the flow, increasing the pumping power. The number of rows of turbulator, pitch and height ratios of the optimized turbulator design is varied in the range of 1-3, 0.025-0.25 and 0.004-0.008, respectively, to determine their optimum values for better performance. It is observed that the turbulator having two rows with a pitch ratio of 0.05 and height ratio of 0.006 produces a relatively higher overall thermal enhancement by about 15.76% when compared with the base model without turbulators. The same configuration yields about 52.64% improvement in the exergy efficiency with respect to the base model.}, }
@article {pmid40304526, year = {2025}, author = {Lopez, M and Kone, TC and Benchikh Le Hocine, AE and Dupont, T and Panneton, R}, title = {Mass-spring model for a perforated periodic metamaterial in nonlinear regimea).}, journal = {The Journal of the Acoustical Society of America}, volume = {157}, number = {4}, pages = {3192-3203}, doi = {10.1121/10.0036369}, pmid = {40304526}, issn = {1520-8524}, abstract = {This study is interested in the nonlinear acoustic response of a metamaterial composed of a periodic array of single-perforation plates spaced by thin air cavities. An equivalent mass-spring model is adapted to predict the metamaterial acoustic response under high sound pressure levels. The increase in losses induced by the high level is considered by a quadratic law for the airflow resistivity in an effective fluid model. The airflow resistivity coefficients are determined from predictions by the computational fluid dynamics method at different flow velocities. The model is validated with impedance tube measurements for samples with different numbers of periodic unit cells and perforation sizes. The results show that the acoustic resistance of the metamaterial increases with increasing sound pressure levels, while the reactance is almost unchanged. The absorption peaks at low frequencies are more impacted by high sound pressure levels. A criterion based on the viscous characteristic frequency is proposed to determine the limit of the beginnings of the nonlinear material response. This limit is given by an acoustic Reynolds number, which depends on the frequency and perforation size. Experimentally, an absorption peak is observed, shifting to lower frequencies with increasing sound levels. A preliminary explanation of underlying mechanisms is provided.}, }
@article {pmid40302383, year = {2025}, author = {Shen, Z and Fu, D and Lintuvuori, JS}, title = {Inertia-driven propulsion of asymmetric spinner-dimers at moderate Reynolds numbers.}, journal = {Soft matter}, volume = {}, number = {}, pages = {}, doi = {10.1039/d5sm00108k}, pmid = {40302383}, issn = {1744-6848}, abstract = {We investigate the translational motion of rotating colloidal systems at moderate Reynolds numbers (Re), focusing on particle dimers in snowman-like configurations in three scenarios: (i) two co-rotating spheres driven by an external field, (ii) two counter-rotating spheres driven by an internal torque as a swimmer, and (iii) a single rotating spinner with a passive sphere for cargo delivery, using hydrodynamic simulations. In all three cases, the particles are bound together hydrodynamically, and the purely rotational motion of the spinners produces a net propulsion of the dimers along the axis of rotation due to symmetry breaking. We demonstrate tunable dynamics, where the propulsion direction of the co-rotating dimer can be reversed by tuning the aspect ratio and Reynolds number, as well as cargo transport where a dimer consisting of a single spinner and a passive cargo particle can have a sustained locomotion due to broken head-to-tail symmetry of the overall flow fields. These findings highlight the critical role of inertia in creating locomotion from rotational motion and offer new avenues for controlling and optimizing translational motion in colloidal assemblies through rotational degrees of freedom.}, }
@article {pmid40290984, year = {2025}, author = {Li, F and Shao, D and Wang, Y and Wang, S and Zhang, C and Yu, M and Su, W and Rao, Y}, title = {Numerical Simulation Study on the Solid-Carrying Capacity of Hydrate-Sediment Slurry in a Vertical Pipe.}, journal = {ACS omega}, volume = {10}, number = {15}, pages = {15432-15452}, pmid = {40290984}, issn = {2470-1343}, abstract = {Solid fluidization is a green mining developed method for seabed nondiagenetic gas hydrate reservoirs, which can safely and controllably transport hydrate to land through seabed mining, closed fluidization, and gas-liquid-solid multiphase lift. However, there are many technical problems, such as hydrate and sediment fluidization and improvement of pipeline transportation capacity in the process of multiphase lift. Based on forced spiral flow in a vertical pipe, the numerical simulation of hydrate and sediment slurry in a vertical pipe with a twisted tape is carried out to explore the solid-carrying capacity of spiral flow and expand the safe boundary of multiphase flow. The effects of hydrate volume fraction, Reynolds number, hydrate particle size, and sediment particle size on turbulent kinetic energy, turbulent dissipation, solid volume fraction, and pressure of hydrate-sediment slurry have been studied. The results show that turbulent kinetic energy and turbulent dissipation decrease with the increase of hydrate volume fraction. The turbulent kinetic energy and turbulent dissipation increase with the increase of the Reynolds number. The concentration gradient of hydrate and sediment at the outlet section is larger than that of the horizontal spiral pipe. The hydrate particle volume fraction at the hydrate axis increases with the increase of hydrate volume fraction, Reynolds number, and hydrate particle size. Sediment particles are mainly distributed near the pipe wall, and hydrate particles are mainly distributed on the inner side of the sediment and form a high-concentration ring. The pressure change in the vertical pipe is similar to that in the horizontal pipe. When Re = 30,000, the critical volume fraction of hydrate blockage in the vertical pipe is 47%, while the critical volume fraction is 22% in the vertical smooth pipe. The transport capacity of hydrate particles is increased by 1.14 times. Under the same conditions, the pressure drop of the whole pipe exceeds that of the ordinary smooth pipe by about 15%.}, }
@article {pmid40287521, year = {2025}, author = {Kunal,  and Dhiman, SK}, title = {An experimental study on effect of curvatures of upstream tube on thermal performance of downstream tube in cross-flow of air.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {14669}, pmid = {40287521}, issn = {2045-2322}, abstract = {Heat transfer on a straight tube in the wake of a tube of same diameter with different curvatures was investigated in cross-flow of air at Reynolds number of 35,000. The straight tube was given constant heat flux condition and placed at different spacing ratios of 2.0, 2.25, 2.5, 3.0, 3.5, and 4.0, from the curved tubes at blockage ratio of 0.1. Four different curvatures ratios 0.5, 1.0, 1.5 and 2.0, on curved tubes were given which were aligned with the mainstream as concave and convex profiles forming different combinations of curvature ratios and spacing ratios to analyse their thermal performance. The study shows a paramount advantage of enhanced thermal performance using curved tube combinations over straight tube combinations and identifies a Reynolds number-based inflection point describing "Heat Promoter" as upstream segment of the tube. The results illustrate that concave curved combination with curvature ratio 1.0 at spacing ratio 2.5 exhibited highest thermal performance with 2.36 times enhanced heat transfer.}, }
@article {pmid40283266, year = {2025}, author = {Hou, Y and Hu, M and Sun, D and Sun, Y}, title = {Numerical Simulation in Microvessels for the Design of Drug Carriers with the Immersed Boundary-Lattice Boltzmann Method.}, journal = {Micromachines}, volume = {16}, number = {4}, pages = {}, doi = {10.3390/mi16040389}, pmid = {40283266}, issn = {2072-666X}, support = {52301035//National Natural Science Foundation of China/ ; BK20230844//Natural Science Foundation of Jiangsu Province/ ; }, abstract = {This study employs numerical techniques to investigate the motion characteristics of red blood cells (RBCs) and drug carriers (DCs) within microvessels. A coupled model of the lattice Boltzmann method (LBM) and immersed boundary method (IBM) is proposed to investigate the migration of particles in blood flow. The lattice Bhatnagar-Gross-Krook (LBGK) model is utilized to simulate the flow dynamics of blood. While the IBM is employed to simulate the motion of particles, using a membrane model based on the finite element method. The present model was validated and demonstrated good agreements with previous theoretical and numerical results. Our study mainly examines the impact of the Reynolds number, DC size, and stiffness. Results suggest that these factors would influence particles' equilibrium regions, motion stability and interactions between RBCs and DCs. Within a certain range, under a higher Reynolds number, the motion of DCs remains stable and DCs can swiftly attain their equilibrium states. DCs with smaller sizes and softer stiffness demonstrate a relatively stable motion state and their interactions with RBCs are weakened. The findings would offer novel perspectives on drug transport mechanisms and the impact of drug release, providing valuable guidance for the design of DCs.}, }
@article {pmid40281346, year = {2025}, author = {Ali, N and Sajid, M}, title = {Inertial swimming in an Oldroyd-B fluid.}, journal = {The European physical journal. E, Soft matter}, volume = {48}, number = {4-5}, pages = {19}, pmid = {40281346}, issn = {1292-895X}, abstract = {The effects of fluid inertia on a self-propelling inextensible waving sheet in an Oldroyd-B fluid are examined. The swimming velocity of the sheet is calculated in the limit in which the amplitude of the waves propagating along the sheet is small relative to the wavelength of the waves. The rate of work done by the sheet is also calculated. It is found that the swimming speed decreases monotonically approaching a limiting value with increasing Reynolds number (R) for a Newtonian fluid. For an Oldroyd-B fluid, the swimming speed increases to a maximum and then decreases asymptotically to a limiting value with increasing R. In contrast, it increases monotonically to a limiting value with increasing R for a Maxwell fluid. The limiting value is highest for the Maxwell fluid and lowest for the Oldroyd-B fluid. The corresponding value for the Newtonian fluid lies in between. The rate of work done by the sheet increases with increasing Reynolds number for all Deborah numbers. However, the energy consumed at a fixed swimming speed is lesser for an Oldroyd-B fluid than that of a Newtonian fluid. These results suggest that contrary to the Newtonian case, the fluid inertia supports the swimming sheet motion in a complex fluid. At a particular Deborah number, the oscillation frequency of the sheet could be adjusted to achieve the maximum speed. Similarly, at a particular frequency of oscillation, the Deborah numbers could be adjusted to achieve the maximum speed. These observations are in sharp contrast with the previous results reported for Newtonian and second-order fluids.}, }
@article {pmid40276589, year = {2025}, author = {Suzuki, K and Nakane, D and Mizutani, M and Nishizaka, T}, title = {Gliding direction of Mycoplasma mobile correlates with the curved configuration of its cell shape.}, journal = {Biophysics and physicobiology}, volume = {22}, number = {1}, pages = {e220006}, pmid = {40276589}, issn = {2189-4779}, abstract = {The gliding motility of bacteria is not linear but somehow exhibits a curved trajectory. This general observation is explained by the helical structure of protein tracks (Nakane et al., 2013) or the asymmetric array of gliding machineries (Morio et al., 2016), but these interpretations have not been directly examined. Here, we introduced a simple assumption: the gliding trajectory of M. mobile is guided by the cell shape. To test this idea, the intensity profile of a bacterium, Mycoplasma mobile, was analyzed and reconstructed at the single-cell level from images captured under a highly stable dark-field microscope, which minimized the mechanical drift and noise during sequential image recording. The raw image with the size of ~1 μm, which is about four times larger than the diffraction limit of visible light, was successfully fitted by double Gaussians to quantitatively determine the curved configuration of its shape. By comparing the shape and curvature of a gliding motility, we found that the protruded portion of M. mobile correlated with, or possibly guided, its gliding direction. Considering the balance between decomposed gliding force and torque as a drag, a simple and general model that explains the curved trajectory of biomolecules under a low Reynolds number is proposed.}, }
@article {pmid40274926, year = {2025}, author = {Dey, R and Patni, HK and Anand, S}, title = {Improved aerosol deposition predictions in human upper respiratory tract using coupled mesh phantom-based computational model.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {14260}, pmid = {40274926}, issn = {2045-2322}, abstract = {Aerosol deposition in the human respiratory tract significantly impacts drug delivery, pollutant exposure, and radiological protection. While existing models, such as the Multiple-Path Particle Dosimetry (MPPD) and the Human Respiratory Tract Model (HRTM) from International Commission on Radiological Protection (ICRP) provide valuable insights, their reliance on simplified geometries and flow dynamics, limits their ability to accurately predict particle deposition within realistic anatomies. This study integrates Mesh-type Reference Computational Phantoms (MRCPs) with computational fluid-particle dynamics (CFPD) to address these limitations. Our simulations reveal the influence of complex anatomical features, including nasal cavity, trachea, and bronchial regions, on aerosol deposition patterns. For ambient aerosol particles in the diffusion-dominated regime (< 0.5 μm), CFPD results reveal enhanced nasal deposition fractions than ICRP predictions, while, above this size, the ICRP semi-empirical model shows overestimations. In the extrathoracic (ET) airways, deposition distribution varied significantly between ET1 and ET2, with ET2 receiving 65-75% of deposits (near the junction of ET1 and ET2) under certain flow conditions. In the bronchial bifurcation (BB1), deposition efficiency varies with Stokes number and Reynolds number, revealing localized preferential deposition. These findings enhance our understanding of aerosol behaviour and paves the way for more accurate therapeutic and safety models in radiological protection.}, }
@article {pmid40274905, year = {2025}, author = {Boudet, JF and Bergmann, M and Iollo, A and Kellay, H}, title = {Effects of boundaries for high Reynolds number artificial swimmers.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {14264}, pmid = {40274905}, issn = {2045-2322}, support = {ANR-22-CE06-0007-02.//Agence Nationale de la Recherche/ ; ANR-22-CE06-0007-02.//Agence Nationale de la Recherche/ ; }, abstract = {The spatial organization of active particles or swimmers may depend strongly on the nature of the interaction between the particles and the boundary. Here we use robotic fish of several centimeters dimensions that swim at high enough velocities to reach Reynolds numbers Re of order [Formula: see text] or [Formula: see text]. Under confinement in circular arenas filled with a shallow layer of water, these robots swim mostly near the walls and undergo a gradual transition from swirling motion near the boundaries to large cluster formation as the number of particles in the assembly is increased. This transition is highly dependent on the nature of the walls: for solid impermeable walls this transition occurs for small numbers of fish robots. For porous walls this transition is delayed and occurs at larger numbers. The main reason why the two boundaries affect the swimming differently is the alignment of the fish robots at the wall: for the impermeable boundary the fish robots align with a smaller angle to the wall while for the porous case, the fish robots align with a larger angle at the wall allowing the formation of linear clusters. We carry out numerical simulations of model fish in three dimensions to examine how such experimental results can be understood. The interest of these simulations is that they provide a direct and quantitative view of the properties of the flow engendered by the fish like objects. The interaction of this flow with other fish or with the boundaries is the crucial aspect behind the self organization. These simulations reproduce the main features of the behavior of the swimmers such as their swimming near the walls or their angle with respect to the boundary. By using flexible and free to move arenas in experiments and simulations, we show that the assembly of fish robots is capable of creating large deformations as well as induce mobility of the arenas through the self-organization of the robotic fish opening the possibility of making sub-aquatic flexible robots of robots.}, }
@article {pmid40273102, year = {2025}, author = {Chen, X and Sreenivasan, KR}, title = {Bounded dissipation law and profiles of turbulent velocity moments in wall flows.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {122}, number = {17}, pages = {e2502265122}, doi = {10.1073/pnas.2502265122}, pmid = {40273102}, issn = {1091-6490}, support = {92252201 12072012//National Science Foundation of China/ ; None//NYU | Tandon School of Engineering, New York University (Tandon)/ ; }, abstract = {Understanding the effects of solid boundaries on turbulent fluctuations remains a long-standing challenge. Available data on mean-square fluctuations in these flows show apparent contradiction with classical scaling. We had earlier proposed an alternative model based on the principle of bounded dissipation. Despite its putative success, a conclusive outcome requires much higher Reynolds numbers than are available at present, or can be expected to be available in the near future. However, the model can be validated satisfactorily even within the Reynolds number range already available by considering high-order moments and their distributions in the wall-normal direction. Expressions for high-order moments of streamwise velocity fluctuation [Formula: see text] are derived in the form [Formula: see text], where the superscript [Formula: see text] indicates the wall unit normalization, and brackets stand for averages over time and the homogeneous plane normal to the wall, [Formula: see text] is an integer, [Formula: see text] and [Formula: see text] are constants independent of the friction Reynolds number [Formula: see text], and [Formula: see text] is the distance away from the wall, normalized by the flow thickness [Formula: see text]. In particular, [Formula: see text] according to the "linear q-norm Gaussian" process, where [Formula: see text] and [Formula: see text] are flow-independent constants. Excellent agreement is found between this formula and the available data in boundary layers, pipes, and channels for [Formula: see text]. For fixed [Formula: see text], the present formulation leads to the bounded state [Formula: see text] as [Formula: see text]. This work demonstrates the success of the present model in describing the behavior of fluctuations in wall flows.}, }
@article {pmid40269237, year = {2025}, author = {Bhattacharyya, S and Vishwakarma, DK}, title = {Mixed and forced convection heat transfer and pressure drop in inclined tube with twisted tape in transition flow.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {14018}, pmid = {40269237}, issn = {2045-2322}, abstract = {Understanding the influence of angular orientation on mixed convection heat transfer and pressure drop in circular tubes with swirl generators is crucial for optimizing thermal performance in various engineering applications, including heat exchangers and energy systems. This study aims to investigate the impact of angular orientation on heat transfer enhancement and pressure drop characteristics in a uniformly heated circular tube equipped with a twisted-tape longitudinal swirl generator. An experimental approach was employed, varying key parameters such as Reynolds number (435-10,130), heat flux (2, 3, and 4 kW/m[2]), twist ratio (P/D = 3, 4, and 5), and angular orientation (15° and 30°). The setup was validated against established correlations for Nusselt number and friction factor, demonstrating strong agreement. The results reveal that angular orientation significantly affects heat transfer and pressure drop at Reynolds numbers up to ~ 1000, where mixed convection plays a dominant role. Beyond this, forced convection prevails. In a plain channel, the transition from laminar to transitional flow occurs at Reynolds numbers of 2924-4088 for a 15° angle of inclination (AoI) and 3001-4274 for a 30° AoI, with the transition occurring slightly earlier at the lower angle. The Richardson number varied from 2.5 in the low laminar regime to 0.0087 in the turbulent regime, with additional variations observed when turbulators were introduced.}, }
@article {pmid40269048, year = {2025}, author = {Kaziz, S and Echouchene, F and Gazzah, MH}, title = {Optimizing microfluidic chip for rapid SARS-CoV-2 detection using Taguchi method and artificial neural network PSO.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {14052}, pmid = {40269048}, issn = {2045-2322}, mesh = {*Neural Networks, Computer ; *SARS-CoV-2/isolation &amp; purification ; *COVID-19/diagnosis/virology ; Humans ; *Biosensing Techniques/methods/instrumentation ; *Lab-On-A-Chip Devices ; }, abstract = {Microfluidic biosensors offer a promising solution for real-time analysis of coronaviruses with minimal sample volumes. This study optimizes a biochip for the rapid detection of SARS-CoV-2 using the Taguchi orthogonal table L9(3[4]), which comprises nine groups of experiments varying four key parameters: Reynolds number (Re), Damköhler number (Da), Schmidt number (Sc), and the dimensionless position of the reaction surface (X). Signal-to-noise (S/N) ratios and analysis of variance (ANOVA) are employed to determine optimal parameters and assess their impact on binding kinetics and response time of the detection device. These obtained optimal parameters correspond to Re = 4.10[-2], Da = 1000, Sc = 10[5], and X = 1. Additionally, results highlight Da as the most influential factor, accounting for 91%, while X has a minimal effect of 0.3%. Furthermore, an artificial neural network optimization technique, specifically particle swarm optimization (PSO), was utilized to predict biosensor performance. Derived from the Full L81(3[4]) design experiment, the PSO model demonstrates its effectiveness compared to the conventional multi-layer perception (MLP) model, thus underlining its potential in this innovative optimization context.}, }
@article {pmid40262639, year = {2025}, author = {Yaqoob, B and Porfiri, M and Pugno, NM}, title = {Optimizing energetics of lateral undulatory locomotion: unveiling morphological adaptations in different environments.}, journal = {Journal of the Royal Society, Interface}, volume = {22}, number = {225}, pages = {20240440}, doi = {10.1098/rsif.2024.0440}, pmid = {40262639}, issn = {1742-5662}, support = {//Italian Ministry of Education, University and Research (MIUR)/ ; //National Science Foundation/ ; }, abstract = {Ongoing efforts seek to unravel theories that can make simple, quantitative and reasonably accurate predictions of the morphological adaptive changes that arise with the size variation. Yet, relatively scant attention has been directed towards lateral undulatory locomotion. In the current study, we explore: (i) the constraints imposed by the variation of length and mass in viscous and dry friction environments on the cost of transport (COT) of lateral undulatory locomotion and (ii) the role of the body, environment and input oscillations in such an intricate interplay. In a dry friction environment, minimum COT correlates with stiffer and longer bodies, higher frictional anisotropy and angular amplitudes greater than approximately 10[o]. Conversely, a viscous environment favours flexible long bodies, higher frictional anisotropy and angular amplitudes lower than approximately 30[o]. In both environments, optimizing mass and maintaining low angular frequencies minimizes COT. Our conclusions are applicable only in the low-Reynolds-number regime, and it is essential to consider the interdependence of parameters when applying the generalized results. Our findings highlight musculoskeletal and biomechanical adaptations that animals may use to mitigate the consequences of size variation and to meet the energetic demands of lateral undulatory locomotion. These insights enhance foundational biomechanics knowledge while offering practical applications in robotics and ecology.}, }
@article {pmid40256679, year = {2025}, author = {Shankaran, A and Hearst, RJ}, title = {Simultaneous measurements of velocity, oxygen concentration, and deformed interface position in an air-water channel using PIV and LIF.}, journal = {Experiments in fluids}, volume = {66}, number = {5}, pages = {95}, pmid = {40256679}, issn = {0723-4864}, abstract = {Oxygen transfer across a deforming air-water interface is studied using a synergy of particle image velocimetry and laser-induced fluorescence (LIF). Such approaches have previously been limited to flat interfaces. We develop simultaneous measurements of velocity fields, dissolved oxygen (DO) concentration fields, and interface positions for spatial and temporal tracking. The imaging process begins after the DO in the water has been chemically depleted and continues until the water is saturated with DO. The oxygen LIF intensity field is calibrated using measurements from an optical oxygen probe to ensure accurate conversion into physical unit (mg/L). A canonical air turbulent channel flow, with a centerline velocity of 6.6 m/s (Reynolds number based on channel height of 21,700), develops for more than 100 heights before the bottom boundary condition is changed from a solid wall to a water surface. This induces transient and wavy structures on the air-water interface and generates velocity fluctuations and vorticity on the water side, which drives DO transport. The spatial evolution of DO concentration reveals steep gradients near the interface that diminish with depth, while the temporal evolution shows a reduction in concentration differences between the bulk and interface from about 35% to less than 5% as the water saturates. Concentration fluctuations are lower near the interface compared to the bulk and diminish in time as the system approaches saturation. Turbulent scalar transport analysis shows high vertical flux near the interface, and this too changes as the bulk DO concentration evolves, emphasizing that the observed phenomena are transient and should be treated as such.}, }
@article {pmid40250393, year = {2025}, author = {Wang, Y and Ebrahimi, F and Lu, H and Goodman, J and Gilson, EP and Ji, H}, title = {Observation of Nonaxisymmetric Standard Magnetorotational Instability Induced by a Free-Shear Layer.}, journal = {Physical review letters}, volume = {134}, number = {13}, pages = {135101}, doi = {10.1103/PhysRevLett.134.135101}, pmid = {40250393}, issn = {1079-7114}, abstract = {The standard magnetorotational instability (SMRI) with a magnetic field component parallel to the rotation axis is widely believed to be responsible for the fast accretion in astronomical disks. In conventional base flows with a Keplerian profile or an ideal Couette profile, most studies focus on axisymmetric SMRI, since excitation of nonaxisymmetric SMRI in such flows requires a magnetic Reynolds number (Rm) more than an order of magnitude larger. Here, we report that, in a magnetized Taylor-Couette flow, nonaxisymmetric SMRI with an azimuthal mode number m=1 can be triggered by a free-shear layer in the base flow at Rm≳1, the same threshold as for axisymmetric SMRI. Global linear analysis reveals that the free-shear layer reduces the required Rm, possibly by introducing an extremum in the vorticity of the base flow. Nonlinear simulations validate the results from linear analysis and confirm that a novel instability recently discovered experimentally [Wang et al., Nat. Commun. 13, 4679 (2022)NCAOBW2041-172310.1038/s41467-022-32278-0] is the nonaxisymmetric m=1 SMRI. Our finding has astronomical implications as free-shear layers are ubiquitous in celestial systems, such as the disk-star boundary layer, the solar tachocline, and the edge of planet-opened gaps in protoplanetary disks.}, }
@article {pmid40225806, year = {2025}, author = {Kavitha, R and Ladu, NSD and Ravi, S}, title = {Soret Effect and Chemical Process on MHD Oscillatory Flow in a Physiological Fluid.}, journal = {Applied bionics and biomechanics}, volume = {2025}, number = {}, pages = {8818822}, pmid = {40225806}, issn = {1176-2322}, abstract = {This paper investigates the impact of chemical and Soret reactions on magnetohydrodynamic (MHD) oscillatory flow in a porous arteriole. Using appropriate mathematical techniques, a model of a mathematical equation is developed and solved. The flow governing equations are formulated based on certain assumptions. Exact solutions are attained for the profiles of velocity, temperature, and concentration. To highlight the key features, the numerical computations of the physical parameters, Grashof number, Reynolds number, Magnetic number, and Soret number were presented graphically. The present study reveals the viscoelasticity of blood significantly reduces flow velocity. And also illustrates blood flow (BF) in the artery is affected by the Lorentz force, which causes the velocity of the BF to increase as the magnetic field parameter values increase. The obtained outcome may be very useful in controlling BF during the surgical procedure.}, }
@article {pmid40224519, year = {2025}, author = {Jayatilake, S and Lowenberg, M and Woods, BKS and Titurus, B}, title = {Nonlinear aeroelastic modelling and analysis of a geometrically nonlinear wing with combined unsteady sectional and lifting line aerodynamics.}, journal = {Nonlinear dynamics}, volume = {113}, number = {12}, pages = {14657-14693}, pmid = {40224519}, issn = {0924-090X}, abstract = {This research develops a novel geometrically nonlinear aeroelastic model of a cantilevered flexible wing capable of capturing unsteady aerodynamics with finite span effects. The structural model is developed using a Chebyshev-Ritz approach with the ONERA unsteady aerodynamic formulation coupled to a three-dimensional wing analysis based on the lifting line approach. The resulting system describing the evolution of the generalised structural coordinates and the aerodynamic states is formulated as a continuous state space model. The model is validated against experimental results from the wind tunnel testing of a highly flexible wing demonstrator at the University of Bristol. The numerical results are computed by applying a numerical continuation procedure, exercising the benefits of the state space formulation. The extensive numerical-experimental comparative analysis includes the bifurcation characteristics of the system and the behaviour of the aeroelastic modes. The developed model reflected the experimentally identified bifurcation behaviour. The predicted variations of the flutter onset speed with the wing root pitch angles were found to be within 5% of the experimental values. The model also correctly captured the post-flutter Limit Cycle Oscillation (LCO). This work further showed that the predicted flutter speeds are sensitive to the semi-empirical coefficients present in the ONERA unsteady aerodynamics formulation. Consequently, further calibration of the model was based on the analysis of the experimental flutter speeds and airspeed-driven eigenvalue variations. This approach was necessitated by the influence of application-specific conditions (e.g., the Reynolds number) on the unsteady aerodynamic characteristics. Despite this limitation, the tuned model agreed with the experimental observations across a wide range of test conditions. The approaches presented in this work can benefit multiple applications during research on geometrically nonlinear wings, such as the analysis of root causes influencing critical aeroelastic phenomena or design of aeroelastic control laws.}, }
@article {pmid40209649, year = {2025}, author = {Zhu, F and Hu, X and Wu, X and Xu, D and Li, Q and Chen, X and Pang, W and Duan, X and Wang, Y and He, M}, title = {Synergistic effect of acoustic streaming and nanozymes on enhanced intracellular dopamine detection.}, journal = {Biosensors &amp; bioelectronics}, volume = {280}, number = {}, pages = {117431}, doi = {10.1016/j.bios.2025.117431}, pmid = {40209649}, issn = {1873-4235}, abstract = {Microfluidic electrochemical biosensing has been widely recognized, but it suffers the slow mass transfer caused by low Reynolds number in the microenvironment. This work proposes a multifunctional portable microfluidic electrochemical platform integrated with a gigahertz acoustic resonator, achieving improved electrochemical response, in situ nanozymes modification, cellular pre-treatment and portable detection on one chip. It was observed that the acoustic streaming (AS) generated by the resonator could reduce the thickness of the double electric diffusion layer and improve the mass transfer in bulk solution, leading to an enhancement in microfluidic electrochemical current response. In addition, in situ electrodeposition of polypyrrole (Ppy) and Ni3(HHTP)2 nano-composite nanozymes (Ppy-Ni3(HHTP)2) was achieved to increase the electrocatalytic activity of dopamine (DA). The results further revealed that AS and Ppy-Ni3(HHTP)2 collectively enhance the electrochemical detection of DA. Moreover, cell pre-treatment and intracellular DA detection was achieved to distinguish the passage of dopaminergic cells by the microfluidic electrochemical platform. Finally, portable detection of intracellular dopamine was realized by integrating the platform with the portable electrochemical sensing system. This study presented a novel approach to collectively enhance electrochemical biosensing using AS and nanozymes.}, }
@article {pmid40206413, year = {2018}, author = {Brindise, MC and Vlachos, PP}, title = {Pulsatile pipe flow transition: Flow waveform effects.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {30}, number = {1}, pages = {}, pmid = {40206413}, issn = {1070-6631}, abstract = {Although transition is known to exist in various hemodynamic environments, the mechanisms that govern this flow regime and their subsequent effects on biological parameters are not well understood. Previous studies have investigated transition in pulsatile pipe flow using non-physiological sinusoidal waveforms at various Womersley numbers but have produced conflicting results, and multiple input waveform shapes have yet to be explored. In this work, we investigate the effect of the input pulsatile waveform shape on the mechanisms that drive the onset and development of transition using particle image velocimetry, three pulsatile waveforms, and six mean Reynolds numbers. The turbulent kinetic energy budget including dissipation rate, production, and pressure diffusion was computed. The results show that the waveform with a longer deceleration phase duration induced the earliest onset of transition, while the waveform with a longer acceleration period delayed the onset of transition. In accord with the findings of prior studies, for all test cases, turbulence was observed to be produced at the wall and either dissipated or redistributed into the core flow by pressure waves, depending on the mean Reynolds number. Turbulent production increased with increasing temporal velocity gradients until an asymptotic limit was reached. The turbulence dissipation rate was shown to be independent of mean Reynolds number, but a relationship between the temporal gradients of the input velocity waveform and the rate of turbulence dissipation was found. In general, these results demonstrated that the shape of the input pulsatile waveform directly affected the onset and development of transition.}, }
@article {pmid40199959, year = {2025}, author = {Khan, SH and Danish, M and Ayaz, M and Husain, A and Saeed, S and Abdulla, S and Shaheen, S and Saeed, A and Thaher, A}, title = {Aerodynamic analysis and ANN-based optimization of NACA airfoils for enhanced UAV performance.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {11998}, pmid = {40199959}, issn = {2045-2322}, support = {G00004417//Research Office at UAE University/ ; G00004417//Research Office at UAE University/ ; G00004417//Research Office at UAE University/ ; G00004501//College of Graduate Studies, United Arab Emirates University/ ; }, abstract = {The performance of unmanned aerial vehicles (UAVs) is strongly dependent on the design of their airfoils, particularly in applications necessitating high maneuverability, stability, and efficiency. This study analyzed three National Advisory Committee for Aeronautics (NACA) airfoil profiles: NACA 2412, NACA 4415, and NACA 0012, using a combination of computational fluid dynamics (CFD), XFOIL simulations, and a hybrid artificial neural network-genetic algorithm (ANN-GA) model. This study aimed to evaluate and optimize the aerodynamic performance of these airfoils under various flight conditions. Through CFD simulations and XFOIL analysis, we explored the lift, drag, and stall characteristics of each airfoil at different angles of attack and Reynolds numbers. The NACA 4415 airfoil consistently outperformed the others, achieving the highest lift-to-drag ratio ([Formula: see text]) and exhibiting favorable stall behavior. Thus, it is particularly well-suited for UAVs operating in challenging environments. Further, streamline and velocity profile analyses confirmed that NACA 4415 exhibited a smooth airflow and delayed flow separation, thereby contributing to its superior aerodynamic efficiency. Using the hybrid ANN-GA model, we optimized key parameters, such as the angle of attack and Reynolds number with optimal values of [Formula: see text] and 770,801, respectively, for maximum efficiency. Additionally, the ANN model demonstrated a high accuracy in predicting the aerodynamic performance, closely matching the results of the CFD simulations. Overall, this study highlighted the potential of combining computational techniques and machine- learning models to optimize UAV airfoil designs. These findings offer valuable insights for improving the efficiency and agility of UAVs, particularly in industries such as precision agriculture, infrastructure inspection, and environmental monitoring.}, }
@article {pmid40199935, year = {2025}, author = {Dong, L and Zhang, R}, title = {Numerical study on falling film flow outside the refrigerant tube.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {11952}, doi = {10.1038/s41598-025-96057-9}, pmid = {40199935}, issn = {2045-2322}, support = {2023ZR04//Natural Science Foundation of Dongying/ ; 2024ZDJH75//Dongying City Science and Technology Innovation Major Project (Science and Technology Development Guidance Scheme)/ ; DJ2023004//Science Development Funding Program of Dongying of China/ ; }, abstract = {The liquefied natural gas (LNG) floating production storage and offloading (FPSO) unit is a new type of floating production device developed for the exploitation, pretreatment, liquefaction, and storage of offshore natural gas. In this study, the shell side structure of the spiral-wound heat exchanger is analyzed, and the effects of varying the Reynolds number (Re), tube outer diameter, and number of distributors on the thickness of the shell-side liquid film are investigated. The results show that as the fluid flows down from the distributor, it hits the upper wall of the pipeline and diffuses evenly to both sides, before converging in between the two distributors. In the axial direction, the thickness of the liquid film increases first, reaches the highest at the peak, then decreases, reaches the lowest at the trough, and then increases again, forming a secondary peak at the drop. The thickness of the liquid film changes periodically, and the period is the distance between the two distributors. The thickness of the circumferential liquid film is negatively correlated with the circumferential angle, α. Moreover, the liquid film is thinnest at α = 120°, and is positively correlated with both the liquid mass flow rate and the outer diameter of the tube. The most uniform liquid film thickness is obtained when Re = 1500, the tube outer diameter is 12 mm, and the number of distributors is 6. The results from this study can guide the design of spiral-wound heat exchangers and facilitate their safe and efficient operation in natural gas liquefaction processes.}, }
@article {pmid40183380, year = {2025}, author = {Qin, L and Liu, X and Fei, F}, title = {CFD-Based Optimization of a Dielectrophoretic Device to Isolate CTCs.}, journal = {Electrophoresis}, volume = {}, number = {}, pages = {}, doi = {10.1002/elps.8129}, pmid = {40183380}, issn = {1522-2683}, support = {2024B05//Open Project of Key Laboratory of Education/ ; }, abstract = {Cancer cells that have separated from the main tumor and entered the bloodstream are known as circulating tumor cells (CTCs). Once there, they may spread to other parts of the body and cause metastases. This work proposes a novel inertial-based dielectrophoresis (DEP) device designed for the separation of CTCs from red blood cells (RBCs). The microchannel features a rectangular zigzag segment combined with a circular curved section, optimized to improve separation efficiency by integrating inertial and DEP forces. Numerical simulations are conducted to evaluate the effects of microchannel depth, applied voltage and frequency, and Reynolds number (Re) on the separation efficiency and trajectory of cells. The simulations identify four optimal scenarios that achieve 100% separation efficiency. Early cancer diagnosis and treatment may benefit from the use of the proposed device for CTC detection.}, }
@article {pmid40177117, year = {2025}, author = {Clemens, AL and Jung, K and Ferrucci, M and Ellis, ME and Davis, JT and Chandrasekaran, S and Qi, Z and Orme, CA and Worsley, MA and Akolkar, R and Ivanovskaya, A and Dudukovic, NA}, title = {Understanding the Current Distribution and Mass Transport Properties in 3D-Printed Architected Flow-Through Electrodes.}, journal = {ACS applied engineering materials}, volume = {3}, number = {3}, pages = {600-612}, doi = {10.1021/acsaenm.4c00561}, pmid = {40177117}, issn = {2771-9545}, abstract = {Architected materials offer promising advancements in energy storage by enabling highly customizable, high-surface-area, ordered, and low-defect porous structures. This study investigates the current distribution and mass transport within complex 3D-printed lattice electrodes under flow-through conditions. Conductive lattices were fabricated using microstereolithography followed by pyrolytic carbonization. Lattice geometry effects were analyzed by varying the unit cell type [simple cubic (SC), body- and face-centered cubic (BCC/FCC), IsoTruss, and Octet], porosity, and current density. Current distribution uniformity was investigated using a model high-efficiency copper deposition reaction. Local film thickness distributions were predicted using a numerical model and validated experimentally using micro-X-ray computed tomography. Scaling relationships for informing electrochemical reaction conditions and current uniformity are formulated as a modified lattice-based Wagner number (Wa Lattice) and a corresponding inverse Damkohler number (Da Lattice [-1]). Validated models reveal that mass-transfer coefficients scale as Octet > IsoTruss > FCC ∼ BCC > SC. Inertial effects become significant at Reynolds number Re > 3 and are particularly pronounced in Octet structures due to an abundance of struts oriented away from the fluid flow direction. The study underscores the importance of electrode engineering and process conditions necessary to tailor mass transport and current uniformities to various device applications.}, }
@article {pmid40167398, year = {2025}, author = {Zhang, P and Wang, Y and Wang, Y}, title = {Development of pulse-type skin friction balance use in shock tunnel.}, journal = {The Review of scientific instruments}, volume = {96}, number = {4}, pages = {}, doi = {10.1063/5.0246911}, pmid = {40167398}, issn = {1089-7623}, abstract = {The wall shear stress significantly affects the aerodynamic characteristics and flight safety of hypersonic aircraft. More accurate and reliable diagnostic instruments are required to fully understand and optimize the distribution of wall shear stress in hypersonic high-enthalpy flow. Two types of assembled and integrated skin friction balances for high-enthalpy impulse facilities were developed. The integrated balance was processed using additive manufacturing, also known as 3D printing. The static calibration uncertainty of the two types of skin friction balances is lower than 0.2% FS at 95% confidence. The first-order vibration frequency is about 50 Hz. The applicability and reliability of the developed skin friction balance were verified in the JF-12 shock tunnel built by the Institute of Mechanics, Chinese Academy of Sciences. A series of wall shear measurement tests for flat-plate boundary layers were carried out, in a freestream with a nominal Mach number of 7 and a unit Reynolds number of about 106. The wall shear results were in good agreement with the numerical simulation and empirical formula results. The minimum deviation can reach 3.67% of the measured value, which verifies the applicability and reliability of the two types of skin friction balances for accurate wall shear stress in high-enthalpy pulse flow, especially providing experimental support for the feasibility of the additive-manufactured balance.}, }
@article {pmid40160717, year = {2025}, author = {Turkevich, LA and Chen, H and Jog, MA}, title = {Dust resuspension from the splash of a falling powder: A numerical aerodynamic simulation of a pellet falling onto a powder monolayer.}, journal = {Aerosol science and technology : the journal of the American Association for Aerosol Research}, volume = {59}, number = {1}, pages = {49-65}, doi = {10.1080/02786826.2024.2417976}, pmid = {40160717}, issn = {0278-6826}, abstract = {A falling powder can generate a dust cloud from its interaction with the ambient air and from its splash onto a substrate. This article reports the results of a numerical simulation study, which attempts to model this second process. We argue that the dust cloud arises from the aerodynamic resuspension of previously deposited small particles. The agglomerated falling powder is modeled as a falling pellet disk impacting a surface covered with a monolayer of previously deposited particles. The Reynolds number of the air flow in the vicinity of the impacting pellet is Re ~ 1860, so the air flow is modeled as laminar and incompressible. The dust particles are incorporated via a Lagrangian multiphase treatment. The sudden deceleration of the disk sheds an aerodynamic vortex, which suspends particles from the monolayer. Characteristics of the dust cloud (average and maximum height and radius) are tracked; these are conveniently summarized by following the trajectory of the dust cloud centroid. The probability of aerosolization decreases with distance from the impacted pellet. The centroid trajectory is studied as a function of dust particle size. The model is relatively insensitive to disk radius and thickness. More realistic modeling of dust clouds generated by the splash of falling powders will require a statistical analysis of aggregate size and location, as well as the inclusion of interparticle and particle-surface interactions.}, }
@article {pmid40153508, year = {2025}, author = {Sui, F and Yue, W and Behrouzi, K and Gao, Y and Mueller, M and Lin, L}, title = {Untethered subcentimeter flying robots.}, journal = {Science advances}, volume = {11}, number = {13}, pages = {eads6858}, doi = {10.1126/sciadv.ads6858}, pmid = {40153508}, issn = {2375-2548}, abstract = {The miniaturization of insect-scale flying robots with untethered flights is extremely challenging as the tradeoff between mass and power becomes problematic. Here, a subcentimeter rotating-wing robot of 21 mg in weight and 9.4 mm in wingspan driven by a single-axis alternating magnetic field has accomplished navigable flights. This artificial flying robot is the lightest and smallest to realize untethered and controllable aerial travels including hovering, collision recovery, and route adjustments. Experimentally, it has achieved a high aerodynamic efficacy with a measured lift-to-drag ratio of 0.7 and lift-to-flying power ratio of 7.2 × 10[-2] N/W at a Reynolds number of ~2500. The wireless driving mechanism, system operation principle, and flight characteristics can be further optimized for the advancement and miniaturization of subcentimeter scale flying robots.}, }
@article {pmid40152021, year = {2025}, author = {Kuddushi, M and Kanike, C and Xu, BB and Zhang, X}, title = {Recent advances in nanoprecipitation: from mechanistic insights to applications in nanomaterial synthesis.}, journal = {Soft matter}, volume = {}, number = {}, pages = {}, doi = {10.1039/d5sm00006h}, pmid = {40152021}, issn = {1744-6848}, abstract = {Nanoprecipitation is a versatile, low-energy technique for synthesizing nanomaterials through controlled precipitation, enabling precise tuning of material properties. This review offers a comprehensive and up-to-date perspective on nanoprecipitation, focusing on its role in nanoparticle synthesis and its adaptability in designing diverse nanostructures. The review begins with the foundational principles of nanoprecipitation, emphasizing the impact of key parameters such as flow rate, mixing approach, injection rate, and Reynolds number on nanomaterial characteristics. It also discusses the influence of physicochemical factors, including solvent choice, polymer type, and drug properties. Various nanoprecipitation configurations-batch, flash, and microfluidic are examined for their specific advantages in controlling particle size, morphology, and internal structure. The review further explores the potential of nanoprecipitation to create complex nanostructures, such as core-shell particles, Janus nanoparticles, and porous and semiconducting polymer nanoparticles. Applications in biomedicine and other fields highlight nanoprecipitation's promise as a sustainable and tunable method for fabricating advanced nanomaterials. Finally, the review identifies future directions, including scaling microfluidic techniques, expanding compatibility with hydrophilic compounds, and integrating machine learning to further enhance the development of nanoprecipitation.}, }
@article {pmid40138794, year = {2025}, author = {Zhang, L and Wang, K and Zhang, X and Liu, S and Jing, Z and Lu, J and Cui, X and Liu, Z}, title = {Research on the aerodynamic performance and bionic application of dragonfly wing corrugation.}, journal = {Bioinspiration &amp; biomimetics}, volume = {}, number = {}, pages = {}, doi = {10.1088/1748-3190/adc5bc}, pmid = {40138794}, issn = {1748-3190}, abstract = {To investigate the aerodynamic performance of dragonfly wing corrugations under gliding conditions, a new method of corrugation deformation is proposed. Firstly, the coordinate transformation functions that describe the amplitude and camber deformation of the corrugation and numerical simulation model are established. Then the effects of the corrugation structural parameters on airfoil performance are investigated by orthogonal experiment. Subsequently, the optimal structural parameters are selected sequentially, and the mechanism of the corrugation producing a high lift-to-drag ratio is analyzed. The results show that the optimized corrugation parameters are: corrugation profile as profile 5, amplitude coefficient λ = 0.8, vertex x-coordinate a = 0.9c, vertex y-coordinate b = 0.04c. The optimal airfoil achieves the highest lift-to-drag ratio of 5.090, which is increased by 42.82% compared with the flat airfoil. The pressure surface corrugation can increase the pressure difference between the upper and lower surfaces, which is the main reason for the high lift-to-drag ratio. Finally, the bionic airfoils are built by arranging the corrugation on the FFA-W3-211 airfoil, which prove that the dragonfly corrugation with a low Reynolds number is also applicable to the wind turbine airfoil with a high Reynolds number, thereby increasing the lift-to-drag ratio of the prototype airfoil by 1.22%. .}, }
@article {pmid40121369, year = {2025}, author = {Xia, T and Wei, N and Shi, L}, title = {Large eddy simulation on the wake characteristics of linearly stratified flow past a sphere.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {9970}, doi = {10.1038/s41598-025-94870-w}, pmid = {40121369}, issn = {2045-2322}, support = {12172227//National Natural Science Foundation of China/ ; }, abstract = {In this study, Large Eddy Simulation (LES) has been employed to examine the influence of the Froude number (Fr) on the linearly stratified wake and internal waves behind a sphere at a subcritical Reynolds number of Re = 3700. Six distinct sets of models with varying Fr (Fr = 0.05, 0.25, 0.5, 1, 2, ∞) have been chosen to establish density linear stratification through the use of a User Defined Function (UDF). The analysis focuses on the impact of stratification on wake characteristics, velocity distribution, and the structure of internal waves within stratified flow. It is evident that density stratification plays a pivotal role in shaping wake structure. Notably, in stratified flows, wakes exhibit unique characteristics including the generation of internal waves, suppression of vertical velocity, and the emergence of oscillating wake patterns. The study reveals that a decrease in the Froude number leads to heightened vertical suppression of the wake and increased anisotropy of the velocity distribution. Furthermore, as the Froude number ascends from 0.05 to 2, the wake undergoes a transition from quasi-two-dimensional vortex shedding to three-dimensional turbulence.}, }
@article {pmid40117956, year = {2025}, author = {Zhu, K and Huang, Y and Yang, L and Xuan, M and Zhou, T and He, Q}, title = {Motion control of chemically powered colloidal motors.}, journal = {Advances in colloid and interface science}, volume = {341}, number = {}, pages = {103475}, doi = {10.1016/j.cis.2025.103475}, pmid = {40117956}, issn = {1873-3727}, abstract = {Chemically powered colloidal motors can convert chemical energy into directional mechanical movement, making them promising for applications such as targeted drug delivery, environmental decontamination, and precision disease treatment. However, their self-propulsion is constantly disrupted by random Brownian motion, making precise control under low Reynolds number conditions highly challenging. This review provides a brief overview of the three main propulsion mechanisms of chemically powered colloidal motors. It also summarizes recent advances in motion control, including speed regulation and trajectory navigation. Finally, we discuss future directions for achieving more precise motion control. We hope this review will inspire further research on developing more effective and practical control strategies for colloidal motors.}, }
@article {pmid40117304, year = {2025}, author = {Ogawa, T and Koyama, S and Omori, T and Kikuchi, K and de Maleprade, H and Goldstein, RE and Ishikawa, T}, title = {The architecture of sponge choanocyte chambers is well adapted to mechanical pumping functions.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {122}, number = {12}, pages = {e2421296122}, doi = {10.1073/pnas.2421296122}, pmid = {40117304}, issn = {1091-6490}, support = {JPMJSP2114//MEXT | Japan Science and Technology Agency (JST)/ ; JP24KJ0400//MEXT | Japan Society for the Promotion of Science (JSPS)/ ; JPMJPR2142//MEXT | JST | Precursory Research for Embryonic Science and Technology (PRESTO)/ ; 21H05303//MEXT | Japan Society for the Promotion of Science (JSPS)/ ; 21H05306//MEXT | Japan Society for the Promotion of Science (JSPS)/ ; 22H01394//MEXT | Japan Society for the Promotion of Science (JSPS)/ ; 21H04999//MEXT | Japan Society for the Promotion of Science (JSPS)/ ; 21H05308//MEXT | Japan Society for the Promotion of Science (JSPS)/ ; }, mesh = {Animals ; *Porifera/physiology ; *Flagella/physiology ; Models, Biological ; }, abstract = {Sponges, the basalmost members of the animal kingdom, exhibit a range of complex architectures in which microfluidic channels connect multitudes of spherical chambers lined with choanocytes, flagellated filter-feeding cells. Choanocyte chambers can possess scores or even hundreds of such cells, which drive complex flows entering through porous walls and exiting into the sponge channels. One of the mysteries of the choanocyte chamber is its spherical shape, as it seems inappropriate for inducing directional transport since many choanocyte flagella beat in opposition to such a flow. Here, we combine direct imaging of choanocyte chambers in living sponges with computational studies of many-flagella models to understand the connection between chamber architecture and directional flow. We find that those flagella that beat against the flow play a key role in raising the pressure inside the choanocyte chamber, with the result that the flow rate and mechanical pumping efficiency reach a maximum at a small outlet opening angle. Comparison between experimental observations and the results of numerical simulations reveal that the chamber diameter, flagellar wave number, and the outlet opening angle of the freshwater sponge Ephydatia muelleri, as well as several other species, are related in a manner that maximizes the mechanical pumping functions. These results indicate the subtle balances at play during morphogenesis of choanocyte chambers, and give insights into the physiology and body design of sponges.}, }
@article {pmid40108425, year = {2025}, author = {Fu, J and Du, M and Jing, J and Liu, H and Sun, J and Chen, W and Chen, Y}, title = {Prediction of pressure drop in heavy oil water ring based on modified two fluid model.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {9557}, pmid = {40108425}, issn = {2045-2322}, support = {52106208//National Natural Science Foundation of China/ ; 2023NSFSC0924//Natural Science Foundation of Sichuan Province/ ; }, abstract = {Accurate prediction of pressure drop of the heavy oil-water ring flow in pipeline is of great significance for establishing an optimal drag reduction model and ensuring safe production. The effects of different factors on the flow pattern and pressure drop of heavy oil-water annular two-phase flow were systematically analyzed, and a standard two-fluid pressure drop prediction model for annular flow was established. By modifying the shear stress equation of oil-water interface and introducing the wave-flow theory to modify the shear stress equation of water wall, a pressure drop prediction model for the generalized concentric water ring was obtained to calculate the periodic fluctuations of oil phase. Furthermore, by introducing the comprehensive Reynolds number expression of eccentric water ring, the pressure drop prediction model for the generalized eccentric water ring was obtained to calculate the periodic fluctuations of oil phase. The results show that the pressure drop prediction accuracy of the concentric water ring for ultra-heavy oil is improved by 80% by using the modified pressure drop prediction model. The comprehensive Reynolds number expression of eccentric water ring can effectively reflect the influence of eccentric effect on shear stress of water wall and the calculation error is less than 20% by predicting the pressure drop of the generalized eccentric water ring with different density differences.}, }
@article {pmid40102431, year = {2025}, author = {Gomaa, A and Mhrous, Y and Abdelmagied, MM}, title = {Investigation of the hydraulic and thermal characteristics of a double concentric tubes with an inner twisted spiral tube.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {9301}, pmid = {40102431}, issn = {2045-2322}, abstract = {The characteristics of heat transfer and fluid flow of twisted spiral tubes with different pitches and depths have been investigated experimentally with respect to a conventional tube (smooth tube) as a particular reference. The effects of the twisted spiral pitch ratios, S/Dhy, depth ratios, H/Dhy, Reynolds number and flow arrangement on the thermal performance of a twisted spiral tube heat exchanger are investigated. Three twisted spiral tubes with different pitches, S, of 3.9, 5.2 and 8.2 mm corresponding to twisted spiral pitch ratios, S/Dhy, of 0.278, 0.372 and 0.586; besides three twisted spiral tubes at different depths, H, of 0.6, 0.95, and 1.15 mm corresponding to twisted spiral height ratio, H/Dhy, of 0.043, 0.068 and 0.082 are experimentally examined in this study. The Reynolds number, Re, ranges in both inner tube side and annular side are 5000-50,000 and 1400-10,400, respectively. The results revealed that the twisted spiral pitch ratios S/Dhy of the 0.278achieved an enhancement of Nu by 38% compare to the smooth tube with a corresponding increase of 33.2% in the f. Also, the twisted spiral depths ratios, H/Dhy, of 0.082 achieved higher Nu by 44.9%, compared to the smooth tube with a corresponding increase of 36.4% in the f. The thermal performance criteria reached 1.93 and 2.03 at S/Dhy of 0.278 and H/Dhy of 0.082, respectively. New correlations to expect Nuc and fc were predicted.}, }
@article {pmid40085914, year = {2025}, author = {Kiran, KV and Kumar, K and Gupta, A and Pandit, R and Ray, SS}, title = {Onset of Intermittency and Multiscaling in Active Turbulence.}, journal = {Physical review letters}, volume = {134}, number = {8}, pages = {088302}, doi = {10.1103/PhysRevLett.134.088302}, pmid = {40085914}, issn = {1079-7114}, abstract = {Recent results suggest that highly active, chaotic, nonequilibrium states of living fluids might share much in common with high Reynolds number, inertial turbulence. We now show, by using a hydrodynamical model, the onset of intermittency and the consequent multiscaling of Eulerian and Lagrangian structure functions as a function of the bacterial activity. Our results bridge the worlds of low and high Reynolds number flows as well as open up intriguing possibilities of what makes flows intermittent.}, }
@article {pmid40077274, year = {2025}, author = {Weng, C and Wang, Z and Luo, X and Li, H}, title = {Numerical Analysis of Steady-State Multi-Field Coupling in Electro-Fused Magnesia Furnace.}, journal = {Materials (Basel, Switzerland)}, volume = {18}, number = {5}, pages = {}, doi = {10.3390/ma18051049}, pmid = {40077274}, issn = {1996-1944}, support = {No. 2023-GX-102//Special Project for Transformation of Scientific and Technological Achievements of Qinghai Province/ ; 2018YFC1903805//the National Key Research and Development Program of China/ ; 2022YFC2904305//the National Key Research and Development Program of China/ ; 51604059//National Natural Science Foundation of China/ ; }, abstract = {The internal conditions of the high-temperature molten pool in an electro-fused magnesia furnace (EFMF) are difficult to measure, and the temperature distribution-energy conservation relationship in the EFMF cannot be effectively evaluated. Assuming that the feeding speed is constant, the heat absorbed by the newly added raw materials is equal to the rated power minus the heating power required to maintain thermal balance. Therefore, the EFMF can be approximately described by a steady-state model. In order to analyze the state of the molten pool of EFMF at different smelting stages, this study first constructed a three-dimensional steady-state multi-physics field numerical simulation model. The calculations show that the equivalent resistance of the molten pool varies approximately between 1 mΩ and 0.4 mΩ. Furthermore, the equivalent reactance produced by the whole conductive circuit is almost of the same order as the resistance. The Reynolds number of the convection inside the molten pool exceeds 105, which means that the flow inside the molten pool is forced convection dominated by the Lorentz force. Moreover, the turbulence makes the temperature uniformity of the molten pool (the temperature gradient near the solid-liquid interface is approximately within 300 K/m) far greater than that of the unmelted raw materials with very low thermal conductivity (the average temperature gradient reaches over 1000 K/m); the respective proportions of arc power and Joule heating power can be predicted by the model. When the molten pool size is small, the proportion of Joule heating power is high, reaching about 20% of the rated power (3700 kVA); as the molten pool size increases, the convection effect is relatively weakened, and the proportion of Joule heating power also decreases accordingly, only 5% to 10%; the model prediction and experimental estimation results are in good agreement, which makes it feasible to conduct a quantitative analysis of the power distribution in different smelting stages.}, }
@article {pmid40051847, year = {2025}, author = {Fardin, MM and Hossain, MS and Hasan, MN}, title = {CFD based neural network model framework for mixed convection in a lid-driven cavity with conductive cylinder.}, journal = {Heliyon}, volume = {11}, number = {4}, pages = {e42637}, pmid = {40051847}, issn = {2405-8440}, abstract = {The current study investigates the application of an Artificial Neural Network (ANN) model to analyze and predict mixed convection heat transfer within a 2-dimensional square cavity with a conductive cylinder at the centre. The top lid of the cavity is maintained at a constant cold temperature and slides with a constant linear velocity, while the bottom wall is heated to maintain a constant temperature. The governing equations are discretized using Galerkin Weighted Residual Method and numerically solved using Gauss Quadrature procedure. The ANN model is trained using the data derived from CFD simulations and used to predict the heat transfer performance quantitatively and qualitatively. The setup is investigated for a wide range of Richardson numbers (0.1≤ Ri ≤ 10.0), Reynolds numbers (50 ≤ Re ≤ 250) and cylinder diameters (0.1≤ D/L ≤ 0.8). Heat transfer performance is evaluated from the average Nusselt number along the heated bottom wall. Correlations are established showing dependency of Nusselt number on Ri, Re and D/L. Velocity and thermal fields are expressed by streamlines and isothermal contours. The study shows that higher Richardson and Reynolds numbers lead to an enhancement in the overall heat transfer. But for larger cylinder diameters, heat transfer is mostly dependent on Reynolds number. It is also revealed that substantial improvements in computational efficiency are achieved by the ANN model as it has reduced 82 % of computation time and 83 % of storage requirements to predict the results by maintaining mean absolute error below 0.1 %. The study provides an insight that ANN modelling could open a new dimension to the heat transfer research field and significantly reduce the requirement of time and resources to solve complex problems.}, }
@article {pmid40046270, year = {2025}, author = {Muhamad Pauzi, A and Iacovides, H and Cioncolini, A and Li, H and Nabawy, MRA}, title = {Application of URANS Simulation and Experimental Validation of Axial Flow-Induced Vibrations on a Blunt-End Cantilever Rod for Nuclear Applications.}, journal = {Arabian journal for science and engineering}, volume = {50}, number = {5}, pages = {3435-3455}, pmid = {40046270}, issn = {2193-567X}, abstract = {Fretting wear caused by flow-induced vibration (FIV) is a leading cause of fuel failure in light water nuclear reactors. This study describes a numerical methodology, validated with dedicated experiments, for predicting flow-induced vibrations in cantilever rods exposed to axial water flow, a paradigmatic configuration informative for fuel rods in water-cooled nuclear reactor cores. Utilising strong two-way fluid-structure interaction (FSI) simulations with an efficient computational approach, the study focuses on two key aspects of self-excited FIV: the dominant vibration frequency and the amplitude of the vibration. Correctly reproducing the former depends on optimising the solid domain and FSI coupling, while the latter hinges on the fluid solver's ability to accurately replicate unsteady flow behaviour, especially in areas of flow separation. Two unsteady Reynolds averaged Navier-Stokes turbulence models, both being high-Reynolds number versions, and several discretisation schemes for the convection transport are evaluated for their capacity to reproduce the correct unsteady flow behaviour. When the axial flow is directed from the free end to the fixed end of the rod, both the Eddy viscosity model k- ω SST and the Reynolds stress model by Launder, Reece, and Rodi reliably predicted the frequency and amplitude of vibrations for a Reynolds number range between 16.4k and 61.7k. When the flow direction is reversed, while vibration frequencies were accurately modelled, replicating precise unsteady flow behaviour proved more challenging. The study underscores the importance of properly resolving the flow in areas of flow separation to achieve accurate simulation of unsteady flow behaviour.}, }
@article {pmid40034269, year = {2025}, author = {Jahin, AS and Samin, JH and Chhoa, MF and Faisal, F and Nokib, MHI and Rabby, MII}, title = {Computational study of thermofluidic characteristics of Al2O3-Cu hybrid nanofluids in backward facing step channel with varying step angles.}, journal = {Heliyon}, volume = {11}, number = {4}, pages = {e42638}, pmid = {40034269}, issn = {2405-8440}, abstract = {Backward-Facing Step (BFS) channels are frequently utilized in technical implementation due to their ability to model intricate fluid flow patterns, such as recirculation zones, which have significant impacts on thermal exchange rates. This research investigates the thermal and heating efficiency of Al2O3-Cu hybrid nanofluids in a BFS channel, focusing on the effects of varying step angles and Reynolds numbers (Re) on thermal efficiency. ANSYS Fluent (2021 R2) was used to analyze Al2O3-Cu nanofluids across Reynolds numbers (500-800), step angles (70°, 75°, 80°, and 85°), and particle volumes (1%-4%) applying the finite volume method. The results demonstrate that as the Reynolds number increases, the Nusselt number rises by an average of 18.505 %. In contrast, varying the step angle results in an average increase of 4.94 %. It is also observed that an increase in volume fraction of nanoparticles enhances the Nusselt number due to the superior thermal conductivity of the Al2O3-Cu nanofluid. Additionally, a positive correlation between step angle, skin friction coefficient, and pressure drop was observed.}, }
@article {pmid40019202, year = {2025}, author = {Lopez, M and Benchikh Le Hocine, AE and Kone, TC and Dupont, T and Panneton, R}, title = {Inertial effects on single-perforation plates resistivity at high flow rates: Computational fluid dynamics and experimental studies.}, journal = {The Journal of the Acoustical Society of America}, volume = {157}, number = {2}, pages = {1512-1522}, doi = {10.1121/10.0035642}, pmid = {40019202}, issn = {1520-8524}, abstract = {This article is focused on the viscous and inertial effects on airflow resistivity of periodic arrays of single-perforation plates spaced by thin air cavities. Analyzing this effect would provide better insight into losses within the material, including additional losses due to increasing sound excitation levels. In this way, the material pressure drop is predicted by computational fluid dynamics function (CFD) of the flow rate for corresponding pore Reynolds numbers between 0.3 and 1500. The static airflow resistivity coefficient is determined by the linear part of the pressure drop (viscous effect) and the Forchheimer coefficient from the nonlinear part of the pressure drop (inertial effect). Both coefficients are determined on the entirety of the material (globally) and at the plate levels (locally). Good agreement is observed between CFD predictions and experimental measurements on the whole range of studied Reynolds numbers. By locally investigating the pressure drops, the observations show that the viscous effects are constant through the material. With increasing pore Reynolds number, inertial effects of the first plate dominate over those of the other plates. The consideration of the local inertial effect will be a key component in the acoustic modeling of this type of material under high sound excitation levels.}, }
@article {pmid40011611, year = {2025}, author = {Gomaa, A and Gamal, Y and Abdelmagied, MM}, title = {Enhancement of thermofluid characteristics via a triple-helical tube heat exchanger.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {6978}, pmid = {40011611}, issn = {2045-2322}, abstract = {An investigation of the thermal and hydraulic performance of a novel triple-helical tube heat exchanger, the THTHE, is presented. The novel design is a modified design of a DHTHE created by adding a third tube to a DHTHE tube. The third passage is expected to enhance the thermal performance of the DHTHE as a result of an increase in the temperature gradient between the hot and cold fluids. The effects of the coil radius, inner annulus spacing, water inlet temperature, direction of flow arrangement, and Dean number were explored. Five test samples with different coil radii of 150 mm, 125 mm, and 90 mm and different inner annulus spacings of 6.2 mm, 9 mm, and 12 mm were examined. The test samples were designed, fabricated, and tested to demonstrate the influence of design parameters on the thermal and hydraulic performance of the triple-helical tube heat exchanger. The experimental runs were conducted on the hot water side with the water inlet temperature Th,i ranging from 50:80 °C. Moreover, at Dean number 400 ≤ Deh ≤ 5500, corresponding to Reynolds number 2700 ≤ Reh ≤ 31,000. Compared with the double-helical tube heat exchanger, the THTHE resulted in a higher Nusselt number by 146.1% and 109.3% for both the counterflow and parallel-flow arrangements, respectively. Furthermore, lowering the hot water source temperature from 80 to 50 °C results in a 60.6% increase in the Nusselt number of 60.6%, with no increase in the pumping power. Additionally, with a decreasing coil radius from 150 to 90 mm and inner annulus spacing from 12 to 6.2 mm, a significant increase in Nu occurs by 58.2% and 130.4%, respectively. A general correlation was presented for predicting Nu, f, and ε.}, }
@article {pmid40009542, year = {2025}, author = {Zhang, Y and Wang, X and Han, J and Xiao, J and Yong, Y and Yu, C and Yue, N and Sun, J and He, K and Hao, W and Zhang, T and Wang, B and Wang, D and Yang, X}, title = {Dynamic simulations of feeding and respiration of the early Cambrian periderm-bearing cnidarian polyps.}, journal = {eLife}, volume = {12}, number = {}, pages = {}, doi = {10.7554/eLife.90211}, pmid = {40009542}, issn = {2050-084X}, support = {42372012//Natural Science Foundation of China/ ; XDB26000000//Chinese Academy of Sciences/ ; D17013//Ministry of Education of China/ ; BJ11060//Northwest University/ ; 2023YFF0803601//National Key Research and Development Program of China/ ; Z6122059//Linyi University/ ; 41720104002//Natural Science Foundation of China/ ; 41911530236//Natural Science Foundation of China/ ; }, mesh = {Animals ; *Feeding Behavior/physiology ; *Fossils ; *Respiration ; *Cnidaria/physiology/anatomy &amp; histology ; China ; Computer Simulation ; Hydrodynamics ; }, abstract = {Although fossil evidence suggests the existence of an early muscular system in the ancient cnidarian jellyfish from the early Cambrian Kuanchuanpu biota (ca. 535 Ma), south China, the mechanisms underlying the feeding and respiration of the early jellyfish are conjectural. Recently, the polyp inside the periderm of olivooids was demonstrated to be a calyx-like structure, most likely bearing short tentacles and bundles of coronal muscles at the edge of the calyx, thus presumably contributing to feeding and respiration. Here, we simulate the contraction and expansion of the microscopic periderm-bearing olivooid Quadrapyrgites via the fluid-structure interaction computational fluid dynamics (CFD) method to investigate their feeding and respiratory activities. The simulations show that the rate of water inhalation by the polyp subumbrella is positively correlated with the rate of contraction and expansion of the coronal muscles, consistent with the previous feeding and respiration hypothesis. The dynamic simulations also show that the frequent inhalation/exhalation of water through the periderm polyp expansion/contraction conducted by the muscular system of Quadrapyrgites most likely represents the ancestral feeding and respiration patterns of Cambrian sedentary medusozoans that predated the rhythmic jet-propelled swimming of the modern jellyfish. Most importantly for these Cambrian microscopic sedentary medusozoans, the increase of body size and stronger capacity of muscle contraction may have been indispensable in the stepwise evolution of active feeding and subsequent swimming in a higher flow (or higher Reynolds number) environment.}, }
@article {pmid40007569, year = {2025}, author = {Mohan, A and Ramanan, SR}, title = {Surface imprinted microhelical magnetic polymer nanocomposite fibers for targeted lysozyme separation.}, journal = {Nanoscale advances}, volume = {}, number = {}, pages = {}, pmid = {40007569}, issn = {2516-0230}, abstract = {Magnetic microhelical structures have recently drawn attention as microswimmers capable of mimicking bacterial propulsion in the low Reynolds number regime. Such structures can be used in microfluidic bioseparation or targeted delivery and their interaction with proteins is extremely important. In this study we fabricated silica coated magnetic microhelices resembling artificial bacterial flagella like structures via electrospinning magnetite nanoparticle incorporated polystyrene nanocomposite solution followed by silica sol coating. Two model proteins, Lysozyme (Lyz) and Bovine Serum Albumin (BSA), were used for protein imprinting along with a polydopamine layer on the magnetic microhelical substrates. The adsorption mechanism of lysozyme on the molecularly imprinted support system was analyzed using adsorption model fitting (Langmuir, Freundlich and Temkin). Adsorption capacity, selective binding and imprinting factor values were calculated for both imprinted (Lyz and BSA) and non-imprinted samples. A significantly higher adsorption capacity was obtained compared to previously reported studies.}, }
@article {pmid40001473, year = {2025}, author = {Zhuang, XY and Lo, CJ}, title = {Decoding Bacterial Motility: From Swimming States to Patterns and Chemotactic Strategies.}, journal = {Biomolecules}, volume = {15}, number = {2}, pages = {}, doi = {10.3390/biom15020170}, pmid = {40001473}, issn = {2218-273X}, support = {NSTC-109-2628-M-008-01-MY4//NSTC/ ; NSTC 113-2112-M-001-059-MY3.//NSTC/ ; }, mesh = {*Chemotaxis ; *Flagella/physiology ; *Bacteria/metabolism ; Bacterial Physiological Phenomena ; Movement ; }, abstract = {The bacterial flagellum serves as a crucial propulsion apparatus for motility and chemotaxis. Bacteria employ complex swimming patterns to perform essential biological tasks. These patterns involve transitions between distinct swimming states, driven by flagellar motor rotation, filament polymorphism, and variations in flagellar arrangement and configuration. Over the past two decades, advancements in fluorescence staining technology applied to bacterial flagella have led to the discovery of diverse bacterial movement states and intricate swimming patterns. This review provides a comprehensive overview of nano-filament observation methodologies, swimming states, swimming patterns, and the physical mechanisms underlying chemotaxis. These novel insights and ongoing research have the potential to inspire the design of innovative active devices tailored for operation in low-Reynolds-number environments.}, }
@article {pmid39972743, year = {2025}, author = {Verma, S and Seshasayanan, K}, title = {Effects of radial conductivity variation on the Ponomarenko dynamo.}, journal = {Physical review. E}, volume = {111}, number = {1-2}, pages = {015207}, doi = {10.1103/PhysRevE.111.015207}, pmid = {39972743}, issn = {2470-0053}, abstract = {We study the effects of conductivity variation on the Ponomarenko dynamo. Taking monotonically increasing, decreasing and sinusoidally varying radial profiles, we study the kinematic dynamo problem. The threshold of the dynamo, given by the critical magnetic Reynolds number Rm_{c}, is found to strongly depend on the form of conductivity variation near the discontinuity of the velocity field where the shear is dominant. For monotonically varying profiles in the limit of sharp variation, this threshold maps to the problem of the dynamo with a jump in conductivity, while for the sinusoidal profile with large variations or wave numbers, the threshold increases due to effective diffusivity arising from the rapid changes in conductivity. Far from the threshold, it is found that the growth rate depends only on the local gradient of the conductivity near the discontinuity, with the opposite sign of shear and conductivity gradient leading to a larger growth rate, thereby aiding the dynamo instability in regenerating B_{ϕ} from B_{r}. We calculate the expression for the growth rate in the limit of large Rm(≫1) and find that the conductivity variation leads to a modification proportional to the local gradient of conductivity times Rm^{-1/2}. This correction is found to depend only on the local gradient of the conductivity at the discontinuity. Similar dependencies are found for realistic, smooth velocity profiles and for different magnetic boundary conditions.}, }
@article {pmid39958364, year = {2025}, author = {Bose, C and Bruce, C and Viola, IM}, title = {Porous plates at incidence.}, journal = {Theoretical and computational fluid dynamics}, volume = {39}, number = {2}, pages = {19}, pmid = {39958364}, issn = {0935-4964}, abstract = {This paper investigates the effect of permeability on two-dimensional rectangular plates at incidences. The flow topology is investigated for Reynolds number (Re) values between 30 and 90, and the forces on the plate are discussed for R e = 30 , where the wake is found to be steady for any value of the Darcy number (Da) and the flow incidence (α). At R e = 30 , for a plate normal to the stream and vanishing Da, the wake shows a vortex dipole with a stagnation point on the plate surface. With increasing Da, the separation between the vortex dipole and the plate increases; the vortex dipole shortens and is eventually annihilated at a critical Da. For any value of Da below the critical one, the vortex dipole disappears with decreasing α . However, at low Da, the two saddle-node pairs merge at the same α , annihilating the dipole; while at high Da, they merge at different α , resulting in a single recirculating region for intermediate incidences. The magnitudes of lift, drag, and torque decrease with Da. Nevertheless, there exists a range of Da and α , where the magnitude of the plate-wise force component increases with Da, driven by the shear on the plate's pressure side. Finally, the analysis of the fluid impulse suggests that the lift and drag reduction with Da are associated with the weakening of the leading and trailing edge shear layer, respectively. The present findings will be directly beneficial in understanding the role of permeability on small permeable bodies.}, }
@article {pmid39953100, year = {2025}, author = {Zhang, T and Li, F and Fan, J}, title = {Impact of corner optimization measures on the interference effects between two square section buildings.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {5558}, pmid = {39953100}, issn = {2045-2322}, support = {//National Natural Science Foundation of China/ ; }, abstract = {Wind-induced interference effects occur between high-rise twin buildings. To elucidate the impact of aerodynamic optimization measures on the interference effects between high-rise buildings, large eddy simulations (LES) were conducted to analyze the wind load characteristics of buildings with varying spacing. The simulation results were compared with experimental data and previous studies to validate the method's accuracy. To investigate the influence of various aerodynamic corner optimizations on interference effects between high-rise buildings, LES was employed to simulate wind load characteristics. Simulation results were compared with experimental data and previous studies to ensure the method's accuracy. Three corner treatments-chamfered, rounded, and recessed-were applied to the model, with a corner modification rate of 10%. Under wind field conditions corresponding to a Reynolds number (Re) of 22,000, 10 simulated schemes with spacing ratios (B/L) ranging from 1.2 to 8 were considered, where B represents the center-to-center distance between two square cylinders, and L denotes the side length of each square cylinder. The aerodynamic coefficients, flow field mechanisms, and vorticity of the two side-by-side square cylinders under three corner treatments were compared. Additionally, peak factors were calculated based on predefined measurement points to further assess differences in interference factors. Using the Lorentz function, the peak fitting curve of the wind pressure probability density was compared with the Gaussian fitting curve. The analysis indicates that the wind pressure shielding effect is most pronounced for the rounded corner square cylinder, while the amplification effect is strongest for the chamfered corner square cylinder. At critical spacing, the adjacent facades of the recessed corner square cylinders exhibited a bimodal distribution in wind pressure probability density.}, }
@article {pmid39946945, year = {2025}, author = {Lu, Y and Chu, K and Hua, Z and Gao, C and Liu, Y}, title = {The response of PFAA mobility in highly contaminated sediment to sluice operation: Coupled effects of scour behavior and physicochemical properties.}, journal = {Water research}, volume = {276}, number = {}, pages = {123260}, doi = {10.1016/j.watres.2025.123260}, pmid = {39946945}, issn = {1879-2448}, abstract = {Despite their widespread occurrence and significant environmental implications, the influence of sluice operations on the mobility of perfluoroalkyl acid (PFAA) in riverine sediments remains largely unexplored. To address this gap, a series of flume experiments were conducted to simulate the sedimentary migration of PFAA under the turbulent conditions generated by opening a sluice. Our study provides novel insights into the mechanisms by which plunging turbulence modulates the transfer of sedimentary PFAAs across the sediment‒water interface. Significant transient release effects were observed in the dissolved and suspended particulate matter (SPM) phases of PFAA, with total concentrations maintaining relative stability over extended periods following disturbance. The fluviraption of plunging turbulence increased PFAA concentrations in the surface sedimentary and porewater phases but weakened the adsorption performance of resuspended particles for the chemicals in the lower reach of the sluice. The instantaneous release of PFAA from sediment, fueled by turbulence, was identified as the primary driver of total mass transfer across the interface, increasing exponentially with the Reynolds number (Rex, R[2]=0.99, p < 0.01). Notably, the peak PFAA release flux in the SPM phase lagged behind that in the dissolved phase, underscoring the dynamic interplay between phases. A structural equation model (SEM) revealed that plunging turbulence indirectly governs the cross-interface transfer of sedimentary PFAA by altering environmental physicochemical parameters and enhancing porewater diffusion. This finding underscores the complex, coupled effects of scour behavior and physicochemical properties on PFAA fate. Our study offers a unique perspective on the dynamic mechanisms underlying PFAA multimedia migration under sluice operation, contributing valuable insights for managing and regulating these emerging contaminants in aquatic environments.}, }
@article {pmid39944342, year = {2025}, author = {Biswas, S and Harish, R}, title = {Effect of unsteady cavitation on hydrodynamic performance of NACA 4412 Hydrofoil with novel triangular slot.}, journal = {Heliyon}, volume = {11}, number = {3}, pages = {e42266}, pmid = {39944342}, issn = {2405-8440}, abstract = {This study demonstrates the hydrodynamic performance of a modified NACA 4412 hydrofoil and compares it with the base NACA 4412 hydrofoil in the presence of cavitation. A triangular slot has been introduced at the mid-section of the suction side of the hydrofoil to modify the flow characteristics and assess its effects on the performance at different operational cavitation numbers spanning from 0.8 to 2.5, and at different angles of attack ranging from 4° to 16°. The performance metrics considered include the coefficient of lift, coefficient of drag, and the lift-to-drag ratio. The Reynolds number considered in this study is approximately 1.5 million. The SST k-ω turbulence model, homogeneous mixture multiphase model, and Schnerr&amp; Sauer cavitation model have been employed in this study. At lower cavitation numbers, the modified hydrofoil is better able to control cavitation phenomena compared to the base hydrofoil. However, at higher cavitation numbers, the base hydrofoil exhibits slightly better performance than the modified hydrofoil in terms of lift-to-drag ratio, despite having a lower lift coefficient. Furthermore, the modified hydrofoil demonstrates improved performance at 4°, 8°, and 16° angles of attack, while the base hydrofoil performs better at a 12° angle of attack. It was also observed that stalling occurs at a 16° angle of attack for the base hydrofoil, whereas the modified hydrofoil successfully avoids stalling.}, }
@article {pmid39941600, year = {2025}, author = {Nuche, J and Ponz, I and Sánchez Sánchez, V and Bóbeda, J and Gaitán, &#xc1; and López-Linares, K and García-Cosío, MD and Sarnago Cebada, F and González, JS and Arribas Ynsaurriaga, F and Ruíz-Cabello, J and Ibáñez, B and Delgado, JF}, title = {Four-Dimensional Magnetic Resonance Pulmonary Flow Imaging for Assessing Pulmonary Vasculopathy in Patients with Postcapillary Pulmonary Hypertension.}, journal = {Journal of clinical medicine}, volume = {14}, number = {3}, pages = {}, doi = {10.3390/jcm14030929}, pmid = {39941600}, issn = {2077-0383}, support = {PI17/01569//Instituto de Salud Carlos III/ ; }, abstract = {Background: Noninvasive techniques for diagnosing combined postcapillary pulmonary hypertension (CpcPH) are unavailable. Objective: To assess the diagnostic performance of cardiac magnetic resonance (CMR)-based four-dimensional (4D)-flow analysis in identifying CpcPH. Methods: Prospective observational study of heart failure (HF) patients with suspected pulmonary hypertension (PH) who underwent simultaneous CMR and right heart catheterization. The 4D-flow biomarkers were calculated using an automatic pipeline. A predictive model including 4D-flow biomarkers associated with CpcPH with a p-value < 0.20 was built to determine the diagnostic performance of 4D-flow analysis to identify CpcPH. Results: A total of 46 HF patients (55.4 ± 14 years, 63% male) with confirmed PH (19 [41%] isolated postcapillary PH [IpcPH], 27 [59%] CpcPH) were included. No differences were found in baseline characteristics, echocardiography, or CMR anatomical and functional parameters, except for a higher Doppler-estimated systolic pulmonary pressure and larger pulmonary artery in CpcPH patients. The 4D-flow CMR analysis was performed in 31 patients (67%). The maximal peak velocity (67.1 [62.2-77.5] cm/s-IpcPH vs. 58.2 [45.8-66.0] cm/s-CpcPH; p = 0.021) and maximal helicity (339.9 [290.0-391.8]) cm/s[2]-IpcPH vs. 226.0 (173.5-343.7) cm/s[2]-CpcPH; p = 0.026) were significantly lower in patients with CpcPH. A maximal multivariable model including sex, maximal average, and peak velocities, Reynolds number, flow rate, and helicity showed fair diagnostic performance (area under the curve: 0.768 [95%-CI: 0.572-0.963]; sensitivity: 100%; specificity: 55%). Conclusions: In HF patients with PH, 4D-flow-derived maximal peak velocity and maximal helicity were significantly lower in CpcPH patients. A multiparametric model including maximal 4D-flow-derived biomarkers showed good diagnostic performance for identifying CpcPH.}, }
@article {pmid39938336, year = {2025}, author = {Rüttgers, M and Waldmann, M and Ito, S and Wüstenhagen, C and Grundmann, S and Brede, M and Lintermann, A}, title = {Patient-specific lattice-Boltzmann simulations with inflow conditions from magnetic resonance velocimetry measurements for analyzing cerebral aneurysms.}, journal = {Computers in biology and medicine}, volume = {187}, number = {}, pages = {109794}, doi = {10.1016/j.compbiomed.2025.109794}, pmid = {39938336}, issn = {1879-0534}, abstract = {Magnetic resonance velocimetry (MRV) measurements were used as inflow conditions for lattice-Boltzmann (LB) simulations to analyze cerebral aneurysms. Unlike previous studies on larger vascular structures, aneurysm analysis involves smaller scales and higher pressure differences, making near-wall velocity measurements challenging with standard 3 Tesla scanners. To address this, the aneurysm geometry was scaled 5-fold for sufficient magnetic resonance velocimetry (MRV) resolution, with inflow measurements interpolated onto the simulation grid while ensuring dimensionless equivalence via the Reynolds number. Zero-velocity points were included near walls to enforce the no-slip condition if measurement points exceed the simulation domain. The proposed interpolation-based inflow method was compared to a nearest-neighbor approach and a parabolic velocity profile. It achieved the best agreement with MRV centerline velocity measurements (mean error: 3.12%), followed by the nearest-neighbor method (3.18%) and the parabolic profile (9.85%). The parabolic inflow led to centerline velocity overpredictions and total pressure underpredictions, while the nearest-neighbor approach underestimated the wall shear stress (WSS) and exhibited inconsistencies in wall normal stress (e.g., maximum WSS was 18.3% lower than with interpolation). Using the interpolated inflow method, Newtonian and non-Newtonian flows based on the Carreau-Yasuda model were compared. The non-Newtonian model showed lower centerline velocities and total pressure but higher WSS than the Newtonian case. These findings highlight the importance of accurate, patient-specific inflow conditions and the necessity of non-Newtonian modeling for reliable WSS predictions. Combining MRV measurements with non-Newtonian LB simulations provides a robust framework for personalized cerebral aneurysm hemodynamic evaluation.}, }
@article {pmid39937070, year = {2025}, author = {Beckedorff, L and Caridi, GCA and Soldati, A}, title = {Jet-stirred homogeneous isotropic turbulent water tank for bubble and droplet fragmentation.}, journal = {The Review of scientific instruments}, volume = {96}, number = {2}, pages = {}, doi = {10.1063/5.0218326}, pmid = {39937070}, issn = {1089-7623}, abstract = {We present a new jet-stirred turbulent water tank designed to produce homogeneous isotropic turbulence, focusing on multiphase flow phenomena. In particular, the facility features a high Taylor-microscale Reynolds number of O(103) that can ensure a large inertial range and is suitable for studying the breakage of droplets and bubbles in line with the Kolmogorov-Hinze theory. The turbulence is created in an octagonal horizontal water tank by two opposing jet arrays, where each jet can release continuous flow with adjustable velocity. The acrylic section design allows optical access for six high-speed cameras to apply time-resolved visualization techniques. Using 3D Lagrangian particle tracking, we provide a complete statistical characterization of the turbulence field: our measurements reveal a maximum turbulence anisotropy of 10% in the center of the water tank with an energy dissipation rate up to ɛ = 0.3 m2 s-3. This high energy dissipation rate is sufficient to trigger the breakage of bubbles and droplets of O(1-10 mm), which falls in the turbulence inertial range. Furthermore, we demonstrate the capability of our imaging system and reconstruction methods for multiphase flow studies with examples of full 3D topology reconstruction coupled with surrounding flow measurements.}, }
@article {pmid39924563, year = {2025}, author = {Rezapour, M and Esmaiili, M and Mahmoudian, M and Sarand, AB}, title = {Design and modeling of a nanocomposite system for demineralization of sweet whey.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {4824}, pmid = {39924563}, issn = {2045-2322}, mesh = {*Nanocomposites/chemistry ; *Whey/chemistry/metabolism ; *Whey Proteins/chemistry/metabolism ; *Graphite/chemistry ; Hydrogen-Ion Concentration ; Neural Networks, Computer ; Filtration/methods ; Membranes, Artificial ; Temperature ; }, abstract = {This research investigates the design of a nanofiltration (NF) system based on a nanocomposite membrane containing graphene oxide (GO) for the demineralization of sweet whey and the modeling the NF process. The effects of various process variables, including, transmembrane pressure (TMP), Reynolds number, feed pH, and temperature, on the rejection of the minerals were surveyed. Consequently, the recovery of whey proteins from industrial whey using fabricated membranes in a cross-flow membrane module was also investigated. Among the input variables, the pH of the whey solution has the greatest effect on membrane flux and salt rejection performance. In the dead-end filtration system, the highest flux was achieved for the GO-modified membrane under laboratory conditions with a pressure of 10 bar and a pH of 6. The dynamic flux behavior of whey output and salt rejection from whey was modeled using convolutional neural network (CNN) machine learning tools. Linear and non-linear correlations demonstrated that the CNN model correlates well with experimental data on dynamic flux (R[2]-1.00). Overall, this study on dynamic flux and rejection of minerals from whey using CNN modeling can improve optimal conditions for whey demineralization and reduce laboratory testing costs by predicting the results of untested experimental variables.}, }
@article {pmid39905159, year = {2025}, author = {Aziz, MA and Khalifa, MA and Abdelrahman, MA and Elshimy, H and Elsayed, AM}, title = {Multi-slotted airfoil design for enhanced aerodynamic performance and economic efficiency.}, journal = {Scientific reports}, volume = {15}, number = {1}, pages = {4290}, pmid = {39905159}, issn = {2045-2322}, abstract = {Recently, slotted airfoils have been introduced as a passive flow control approach. The slotted airfoil method resulted in stall delay and enhanced the lift coefficient. The single-slot airfoil is unable to delay stall if the flow is injected downstream of the separation point at the stall angle of attack. A multi-slot airfoil ensures air is injected along the airfoil suction side, delaying stalls over a large range of AOA. The current study focuses on enhancing wind turbine blades' efficiency by utilizing a novel multi-slot NACA23012C airfoil design as a passive control approach. A numerical study of the optimal grid number was carried out, followed by validating the numerical model with previous experimental results in the literature. The numerical study is followed by a study of the effect of the number of airfoil slots: one, two, three, four, five, and six. The characteristics of the flow field were analyzed to explain the benefit of applying multi-slotted on the aerodynamic performance of an airfoil with a high AOA at Reynolds number 2.74 × 10[5]. The findings showed a significant improvement in the lift coefficient values and the delayed stall AOA for multi-slot airfoils compared to the clean and single-slot airfoils. Increasing the slots number is effective up to four slots. The four-slot airfoil improved lift by 15.8%, and the two slots achieved a 22.31% CL/CD increase. Future work could optimize slot geometry, validate findings experimentally, and study dynamic and 3D effects.}, }
@article {pmid39879652, year = {2025}, author = {Winter, A and Schoombie, J and Smith, L}, title = {A numerical approach to model and analyse geometric characteristics of a grey-headed albatross aerofoil in flight.}, journal = {Bioinspiration &amp; biomimetics}, volume = {}, number = {}, pages = {}, doi = {10.1088/1748-3190/adaff4}, pmid = {39879652}, issn = {1748-3190}, abstract = {Limited research exists on the 3D geometric models and aerodynamic characteristics of the Grey-headed Albatross (GHA). Despite existing methods for extracting bird wing cross-sections, few studies consider deflections due to aerodynamic pressure. With the GHA known for its exceptional flight speed and purported wing-lock mechanism, it offers a valuable subject for studying fixed-wing aerodynamicsin nature. This study aims to develop and validate a numerical approach to estimate the GHA's wing cross-section in flight. The PARSEC method is combined with a scanned 3D point cloud of a dried GHA wing to create a 3D model and analyze an averaged aerofoil section. Using a pseudo-2D computational fluid dynamics model, the study explores passive morphing of bird wings due to aerodynamic pressure. Results show that the aerofoil morphs to achieve maximum potential aerodynamic efficiency at a Reynolds number of 2 × 105, decreasing in camber. The maximum lift-to-drag ratio ((/)max) increases from 3 to 44, primarily due to pressure drag reduction. However, the lack of comparison to true bird geometry in flight remains a limitation. Future research should compare the predicted morphing with actual bird specimens in flight. .}, }
@article {pmid39876791, year = {2025}, author = {Ishimoto, K and Moreau, C and Herault, J}, title = {Robust undulatory locomotion through neuromechanical adjustments in a dissipative medium.}, journal = {Journal of the Royal Society, Interface}, volume = {22}, number = {222}, pages = {20240688}, pmid = {39876791}, issn = {1742-5662}, support = {//Fusion Oriented REsearch for disruptive Science and Technology/ ; //Japan Society for the Promotion of Science/ ; //Agence Nationale de la Recherche/ ; }, mesh = {Animals ; *Locomotion/physiology ; *Caenorhabditis elegans/physiology ; Models, Biological ; Swimming/physiology ; Models, Neurological ; Biomechanical Phenomena ; }, abstract = {Dissipative environments are ubiquitous in nature, from microscopic swimmers in low-Reynolds-number fluids to macroscopic animals in frictional media. In this study, we consider a mathematical model of a slender elastic locomotor with an internal rhythmic neural pattern generator to examine various undulatory locomotion such as Caenorhabditis elegans swimming and crawling behaviours. By using local mechanical load as mechanosensory feedback, we have found that undulatory locomotion robustly emerges in different rheological media. This progressive behaviour is then characterized as a global attractor through dynamical systems analysis with a Poincaré section. Furthermore, by controlling the mechanosensation, we were able to design the dynamical systems to manoeuvre with progressive, reverse and turning motions as well as apparently random, complex behaviours, reminiscent of those experimentally observed in C. elegans. The mechanisms found in this study, together with our dynamical systems methodology, are useful for deciphering complex animal adaptive behaviours and designing robots capable of locomotion in a wide range of dissipative environments.}, }
@article {pmid39865967, year = {2025}, author = {Weihs, D and Farsani, A and Gurka, R}, title = {Towards a standard application of the Reynolds number in studies of aquatic animal locomotion.}, journal = {The Journal of experimental biology}, volume = {}, number = {}, pages = {}, doi = {10.1242/jeb.249896}, pmid = {39865967}, issn = {1477-9145}, abstract = {Nondimensional groups of measured quantities enable comparison between measurements of animals under different conditions and comparison between species. One of the most used such group is the Reynolds number, which compares inertial and viscous contributions to forces on swimming animals. This group includes two quantities that are chosen by the researcher: a typical length and speed. Choosing these parameters will affect the numerical value of the Reynolds number, defining the state of the fluid flow. For example: by choosing fish body length as opposed to propulsive fin chord, results may vary by an order of magnitude with consequences for analysis and hydrodynamic regimes. Here we suggest a standardized sets of lengths and speeds to be used for aquatic animal locomotion to enable confident utilization of data from different sources. This framework aims to improve comparative studies within the field.}, }
@article {pmid39860147, year = {2025}, author = {Lim, HS and Choi, WI and Lim, JM}, title = {Continuous Production of Docetaxel-Loaded Nanostructured Lipid Carriers Using a Coaxial Turbulent Jet Mixer with Heating System.}, journal = {Molecules (Basel, Switzerland)}, volume = {30}, number = {2}, pages = {}, pmid = {39860147}, issn = {1420-3049}, support = {2023 Sabbatical Year//Soonchunhyang University/ ; NRF-2022R1C1C1007442//National Research Foundation of Korea/ ; 5199991614564//Ministry of Education/ ; 23C0113L1//Ministry of Science and ICT/ ; }, mesh = {*Drug Carriers/chemistry ; *Lipids/chemistry ; *Docetaxel/chemistry ; *Nanostructures/chemistry ; Nanoparticles/chemistry ; Particle Size ; Heating ; Antineoplastic Agents/chemistry/administration &amp; dosage ; }, abstract = {The continuous synthesis of nanoparticles (NPs) has been actively studied due to its great potential to produce NPs with reproducible and controllable physicochemical properties. Here, we achieved the high throughput production of nanostructured lipid carriers (NLCs) using a coaxial turbulent jet mixer with an added heating system. This device, designed for the crossflow of precursor solution and non-solvent, combined with the heating system, efficiently dissolves solid lipids and surfactants. We reported the flow regime according to the Reynolds number (Re). Also, we confirmed the size controllability of NLCs as dependent on both Re and lipid concentration. The optimized synthesis yields NLCs around 80 nm, ideal for targeted drug delivery by enhanced permeability and retention (EPR) effect. The coaxial turbulent jet mixer enables effective mixing, producing uniform size distribution of NLCs. The NLCs prepared using the coaxial turbulent jet mixer were smaller, more uniform, and had higher drug loading compared to the NLCs synthesized by a bulk nanoprecipitation method, showcasing its potential for advancing nanomedicine.}, }
@article {pmid39858737, year = {2025}, author = {Waqas, M and Palevicius, A and Jurenas, V and Pilkauskas, K and Janusas, G}, title = {Design and Investigation of a Passive-Type Microfluidics Micromixer Integrated with an Archimedes Screw for Enhanced Mixing Performance.}, journal = {Micromachines}, volume = {16}, number = {1}, pages = {}, pmid = {39858737}, issn = {2072-666X}, abstract = {In recent years, microfluidics has emerged as an interdisciplinary field, receiving significant attention across various biomedical applications. Achieving a noticeable mixing of biofluids and biochemicals at laminar flow conditions is essential in numerous microfluidics systems. In this research work, a new kind of micromixer design integrated with an Archimedes screw is designed and investigated using numerical simulation and experimental approaches. First, the geometrical parameters such as screw length (l), screw pitch (p) and gap (s) are optimized using the Design of Expert (DoE) approach and the Central Composite Design (CCD) method. The experimental designs generated by DoE are then numerically simulated aiming to determine Mixing Index (MI) and Performance Index (PI). For this purpose, COMSOL Multiphysics with two physics modules-laminar and transport diluted species-is used. The results revealed a significant influence of screw length, screw pitch and gap on mixing performance. The optimal design achieved is then scaled up and fabricated using a 3D additive manufacturing technique. In addition, the optimal micromixer design is numerically and experimentally investigated at diverse Reynolds numbers, ranging from 2 to 16. The findings revealed the optimal geometrical parameters that produce the best result compared to other designs are a screw length of 0.5 mm, screw pitch of 0.23409 mm and a 0.004 mm gap. The obtained values of the mixing index and the performance index are 98.47% and 20.15 Pa[-1], respectively. In addition, a higher mixing performance is achieved at the lower Reynolds number of 2, while a lower mixing performance is observed at the higher Reynolds number of 16. This study can be very beneficial for understanding the impact of geometrical parameters and their interaction with mixing performance.}, }
@article {pmid39858707, year = {2024}, author = {Demircali, AA and Yilmaz, A and Uvet, H}, title = {Enhanced Fluid Mixing in Microchannels Using Levitated Magnetic Microrobots: A Numerical Study.}, journal = {Micromachines}, volume = {16}, number = {1}, pages = {}, pmid = {39858707}, issn = {2072-666X}, support = {FBA-2022-5328//Council of Higher Education (YOK) of Turkey/ ; }, abstract = {The efficient mixing of fluids at microscale dimensions presents challenges due to the dominant laminar flow regime which restricts convective mixing. This study introduces a numerical analysis of a novel microrobotic mixing system with a levitated propeller robot, driven by magnetic fields, within a Y-shaped microchannel with a square cross-section (500 × 500 μm). Our research investigates the fluid mixing effectiveness facilitated by the microrobot through various levitation heights and orientations to enhance the mixing index (MI). This index is tested under different conditions by leveraging the dynamics of the propeller robot, characterized by adjustable roll and pitch angles and varying levitation heights. The numerical simulations, conducted using COMSOL[®] (Finite Element Method, FEM) software, integrate Maxwell's equations for magnetic field interaction with momentum and transport-diffusion equations to analyze fluid dynamics within the microchannel. Results indicate that the propeller robot can achieve an MI of up to 98.94% at a 150 μm levitation height and 1500 rpm propeller speed within 3 s. Additionally, the study examines the impact of propeller speed, Reynolds number, and robot length on mixing performance, providing comprehensive guidance for optimizing microscale fluid mixing in lab-on-a-chip applications.}, }
@article {pmid39848283, year = {2025}, author = {Pal, TK and Das, S}, title = {Dynamics search of highly magnetized blood laden with copper-gold-titania nanoparticles in a ciliary artery with catheterization and entropy.}, journal = {Electromagnetic biology and medicine}, volume = {44}, number = {1}, pages = {26-64}, doi = {10.1080/15368378.2024.2443835}, pmid = {39848283}, issn = {1536-8386}, mesh = {*Copper/chemistry/pharmacology ; *Gold/chemistry/pharmacology ; *Entropy ; *Titanium/chemistry ; Hydrodynamics ; Metal Nanoparticles/chemistry ; Catheters ; Arteries/physiology ; Nanoparticles/chemistry ; }, abstract = {Biomagnetic fluid dynamics (BFD) is an emerging and promising field within fluid mechanics, focusing on the dynamics of bio-fluids like blood in the presence of magnetic fields. This research is crucial in the medical arena for applications such as medication delivery, diagnostic and therapeutic procedures, prevention of excessive bleeding, and treatment of malignant tumors using magnetic particles. This study delves into the intricacies of blood flow induced by cilia, carrying trihybrid nanoparticles (gold, copper, and titania), within a catheterized arterial annulus under a robust magnetic field. The model incorporates factors like Hall and ion-slip currents (electromagnetic effects on charged particles), metachronal propulsion (movement of cilia for propulsion), viscous dissipation, and entropy. The physical equations in the model are transformed from the laboratory frame to a wave frame and then simplified using conditions like low Reynolds number and long wavelength. Optimal series solutions are obtained through the homotopy perturbation method (HPM). The research explores how various physical parameters shape the bloodstream's features, presenting and analyzing these visually. A notable finding is that an intensification in Hall and ion-slip parameters results in higher blood velocity within the catheterized annulus. Blood cooling is observed with a higher loading of suspended nanoparticles. Entropy generation increases with growing values of Hall and ion-slip parameters, while the reverse trend is noted for the Bejan number. The wall shearing stress (WSS) reduces by 2.84% for 1% increase in Hall parameter. The study also provides a brief overview of how blood boluses (or clumps of blood) are structured under the influence of operating parameters. The modified hybrid nano-blood (MHNB) forms smaller and fewer boluses compared to pure blood (PB). Additionally, longer cilia length results in enhanced trapping of boluses due to stronger recovery motions of the cilia. This research holds potential benefits for practitioners and researchers in diagnosing and assessing conditions such as coronary artery disease, valvular heart disease, and congenital heart abnormalities, as well as for understanding traumatic brain injury and neurological surgeries.}, }
@article {pmid39834443, year = {2025}, author = {Zohora, FT and Haque, MR and Chowdhury, NM and Fahad, MK and Ifraj, NF}, title = {Optimization of hydrothermal performance in industrial heat sinks with innovative perforated pin fin designs: A numerical approach.}, journal = {Heliyon}, volume = {11}, number = {1}, pages = {e41496}, pmid = {39834443}, issn = {2405-8440}, abstract = {This study emphasizes the importance of optimizing pin-finned heat sinks as a means of addressing thermal engineering issues. It aims to investigate the use of perforations and unique fin designs in relation to staggered pin arrays in order to fill a gap in existing research. Three-dimensional incompressible flow simulation is performed with the Fluent software. Modeling turbulence is accomplished by employing the realizable κ-ε models, while the numerical solution of all equations pertaining to fluid flow is carried out with the proper boundary conditions. In order to make a comparison of geometry, the hydrothermal performance factor (HTPF) is utilized for Reynolds number (Re) values ranging from 8500 to 44,502. Using a Re of 44502, the Nusselt number (Nu) was found to be raised by 66.2 % for spherical cube pin fins with hexagonal perforation and 70.2 % for elliptical perforation, respectively. A reduction of about 17.6 % in the pressure drop was seen when compared with an elliptical perforated infinity loop design, which resulted in a higher hydrothermal performance factor (HTPF) that was 70 % higher than that of the cylindrical case. Furthermore, the copper-diamond composite, which was placed on an infinity loop-shaped pin fin and had elliptical perforations, yielded a 144 % increase in HTPF when the Re is 44502. Taking into account this fact, it can be concluded that the designs that have been offered are ideal for a wide variety of industrial applications that aim to significantly enhance thermal potential.}, }
@article {pmid39816520, year = {2025}, author = {Dinesh Kumar, M and Díaz Palencia, JL and Dharmaiah, G and Wakif, A and Noeiaghdam, S and Fernandez-Gamiz, U and Dinarvand, S}, title = {ANFIS-PSO analysis on axisymmetric tetra hybrid nanofluid flow of Cu-CNT-Graphene-Tio2 with WEG-Blood under linear thermal radiation and inclined magnetic field: A bio-medicine application.}, journal = {Heliyon}, volume = {11}, number = {1}, pages = {e41429}, pmid = {39816520}, issn = {2405-8440}, abstract = {BACKGROUND: The development of heat transfer devices used for heat conversion and recovery in several industrial and residential applications has long focused on improving heat transfer between two parallel plates. Numerous articles have examined the relevance of enhancing thermal performance for the system's performance and economics. Heat transport is improved by increasing the Reynolds number as the turbulent effects grow.<br><br>APPLICATIONS: Regarding heat transfer, hybrid nanofluids are superior to mono nanofluids. The hybrid fluid of Cu-CNT&#xa0;+&#xa0;Graphene&#xa0;+&#xa0;TiO2/WEG-Blood, which is subject to heat transfer in a channel between two parallel plates with an angled magnetic field and linear thermal radiation, has numerous applications in engineering, industry, and biomedical research, such as electronic cooling, drug delivery, cancer treatment, optics, missiles, satellites, transformer-electronic cooling, and military solar-equipment.<br><br>OBJECTIVE: Examining the qualities of mass, flow, and heat transmission is the aim of the study of a hybrid Cu-CNT- Graphene-TiO2/WEG-Blood nanofluid as it moves via a tube of porous material that is exposed to linear thermal radiation, inclined magnetic, Forchheimer, and buoyancy influences. ANFIS-PSO model is assumed.<br><br>METHOD: Applying the ODE45 integration technique to the given numerical solutions yields non-linear, non-dimensionalized, and highly partial differential equations that control the momentum, energy, and concentration. Consequently, the numerical simulation shows the concentration, velocity, and temperature profiles of the hybrid Cu-CNT- Graphene-TiO2/WEG-Blood nanofluid. A strong concordance is noted between recent and past results.<br><br>Radiation regulates the microchannel temperature distribution, which significantly contributes to cooling the flow transport system, and the thermal radiation parameter shows that radiation has a retarding influence on the temperature profile.}, }
@article {pmid39787163, year = {2025}, author = {Mal, B and Dolui, S and Bhaumik, B and De, S}, title = {Impacts of variable magnetic field on ternary Casson nanofluid flow through ciliated arterial walls incorporating interfacial nanolayer.}, journal = {Electromagnetic biology and medicine}, volume = {44}, number = {1}, pages = {79-106}, doi = {10.1080/15368378.2024.2446506}, pmid = {39787163}, issn = {1536-8386}, mesh = {*Magnetic Fields ; *Hydrodynamics ; *Arteries/physiology ; Cilia/physiology ; Humans ; Rheology ; Nanoparticles/chemistry ; Nanotechnology ; }, abstract = {The current investigation explores tri-hybrid mediated blood flow through a ciliary annular model, designed to emulate an endoscopic environment. The human circulatory system, driven by the metachronal ciliary waves, is examined in this study to understand how ternary nanoparticles influence wave-like flow dynamics in the presence of interfacial nanolayers. We also analyze the effect of an induced magnetic field on Ag-Cu-Al2O3/blood flow within the annulus, focusing on thermal radiation, heat sources, buoyancy forces and ciliary motion. The Casson fluid model characterizes the non-Newtonian viscous properties of the biofluid. To describe the steady fluid flow mathematically, we use coupled partial differential equations and apply the homotopy perturbation method to derive rapidly convergent series solutions for the non-linear flow equations. The obtained hemodynamic consequences are graphically represented with the variations of emerging parameters. These are significantly influenced by the rheological factors of the nanofluid flow, improving flow velocity with changes in shear viscosity, while a decrease in flow is observed for intensified Lorentz forces. Ciliary motion accelerates the expansion of the induced magnetic field on nanolayers, while a higher Magnetic Reynolds number decreases the current density distribution. Increased radiative heat generation lowers the temperature, indicating that thermal radiation enhances heat transfer and improves cooling efficiency. In contrast, an increased ciliary length along the wall raises the temperature due to wave-like motion, which strengthens the thermal boundary layer in the fluid flow. Additionally, a higher nanoparticle concentration increases wall shear stress due to frictional forces, while enhanced magnetic forces decrease the shear stress along the ciliary wall. Furthermore, a higher Strommer's number may regulate the formation of blood boluses in the wavy flow. The key findings play an important role in the development of analytical benchmarks to validate computational methods, ensuring accuracy in clinical research tools and supporting reliable medical applications.}, }
@article {pmid39786510, year = {2025}, author = {Deymi, P and Karimi, H and Sharififard, H and Salehi, F}, title = {Simulation of solar photocatalytic reactor with immobilized photocatalyst for degradation of pharmaceutical pollutants.}, journal = {Environmental science and pollution research international}, volume = {}, number = {}, pages = {}, pmid = {39786510}, issn = {1614-7499}, abstract = {This study focuses on the simulation of a solar photocatalytic reactor with linear parabolic reflectors and continuous fluid flow. The simulation approach was initially validated against experimental data reported by Miranda-Garcia et al. Catal Today 151:107-113 (2010), yielding a high degree of accuracy of approximately 0.99%. In this article, the effect of light intensity, Reynolds number, and fluid residence time on the performance of a photoreactor system using titanium dioxide catalyst and ibuprofen pollutant has been investigated. The results show that the intensity of light intensity has an effect of up to 29% on the decomposition of pollutant. With the increase of radiation intensity, the removal of pollutants reached from 85.5% to 99.46%. It has been demonstrated that higher flow turbulence significantly impacts removal efficiency, achieving rates of up to 71%. Moreover, enhancing the fluid's residence time through implementing a recirculating flow within the photoreactor has resulted in a 13% enhancement in removal efficiency. These results can be an important guide for optimizing the design of photocatalytic reactors. By adjusting the examined parameters, it is possible to obtain a higher efficiency in the removal of pollutants, which will be very effective in the scaling and industrial design of solar reactors.}, }
@article {pmid39769641, year = {2024}, author = {Dutkowski, K and Kruzel, M and Kochanowska, M}, title = {Transition Boundary from Laminar to Turbulent Flow of Microencapsulated Phase Change Material Slurry-Experimental Results.}, journal = {Materials (Basel, Switzerland)}, volume = {17}, number = {24}, pages = {}, pmid = {39769641}, issn = {1996-1944}, abstract = {An ice slurry or an emulsion of a phase change material (PCM) is a multiphase working fluid from the so-called Latent Functional Thermal Fluid (LFTF) group. LFTF is a fluid that uses, in addition to specific heat, the specific enthalpy of the phase change of its components to transfer heat. Another fluid type has joined the LFTF group: a slurry of encapsulated phase change material (PCM). Technological progress has made it possible for the phase change material to be enclosed in a capsule of the size of the order of micrometers (microencapsulated PCM-mPCM) or nanometers (nanoencapsulated PCM-nPCM). This paper describes a method for determining the Reynolds number (Re) at which the nature of the flow of the mPCM slurry inside a straight pipe changes. In addition, the study results of the effect of the concentration of mPCM in the slurry and the state of the PCM inside the microcapsule on the value of the critical Reynolds number (Recr) are presented. The aqueous slurry of mPCM with a concentration from 4.30% to 17.20% wt. flowed through a channel with an internal diameter of d = 4 mm with a flow rate of up to 110 kg/h (Re = 11,250). The main peak melting temperature of the microencapsulated paraffin wax used in the experiments was around 24 °C. The slurry temperature during the tests was maintained at a constant level. It was 7 °C, 24 °C and 44 °C (the PCM in the microcapsule was, respectively, a solid, underwent a phase change and was a liquid). The experimental studies clearly show that the concentration of microcapsules in the slurry and the state of the PCM in the microcapsule affect the critical Reynolds number. The higher the concentration of microcapsules in the slurry, the more difficult it was to maintain laminar fluid flow inside the channel. Furthermore, the laminar flow of the slurry terminated at a lower critical Reynolds number when the PCM in the microcapsule was solid. Caution is advised when choosing the relationship to calculate the flow resistance or heat transfer coefficients, because assuming that the flow motion changes at Re = 2300, as in the case of pure liquids, may be an incorrect assumption.}, }
@article {pmid39766673, year = {2024}, author = {Heinz, S}, title = {Physically Consistent Resolving Simulations of Turbulent Flows.}, journal = {Entropy (Basel, Switzerland)}, volume = {26}, number = {12}, pages = {}, pmid = {39766673}, issn = {1099-4300}, abstract = {Usually applied simulation methods for turbulent flows as large eddy simulation (LES), wall-modeled LES (WMLES), and detached eddy simulation (DES) face significant challenges: they are characterized by improper resolution variations and essential practical simulation problems given by huge computational cost, imbalanced resolution transitions, and resolution mismatch. Alternative simulation methods are described here. By using an extremal entropy analysis, it is shown how minimal error simulation methods can be designed. It is shown that these methods can overcome the typical shortcomings of usually applied simulation methods. A crucial ingredient of this analysis is the identification of a mathematically implied general hybridization mechanism, which is missing in existing methods. Applications to several complex high Reynolds number flow simulations reveal essential performance, functionality, and computational cost advantages of minimal error simulation methods.}, }
@article {pmid39756050, year = {2025}, author = {Hernández-Melchor, DJ and López-Pérez, PA and Ferrera-Cerrato, R and Alarcón, A}, title = {Study of the hydrodynamic parameters in an internal flat-plate airlift reactor for the increased degradation of newspaper by Trichoderma reesei.}, journal = {Environmental technology}, volume = {}, number = {}, pages = {1-16}, doi = {10.1080/09593330.2024.2447959}, pmid = {39756050}, issn = {1479-487X}, abstract = {The aim of our study was to characterize the hydrodynamics and mass transfer in a novel internal flat-plate airlift cylindrical reactor to increase the biodegradation of newspaper. We evaluated the degradation kinetics of newspaper in a batch culture with Trichoderma reesei. Gas holdup, mixing time, the Reynolds number, and volumetric mass transfer coefficient (kLa) properties were characterized in biphasic and triphasic systems in order to optimize their operational conditions. An analysis of two effective factors in three levels including kLa, and Reynolds number (Re) were optimized by a full factorial design. Furthermore, a follow-up analysis of the ANOVA results p ≤ 0.05 was performed using Tukey's rank test method for p-value corrections. The overall kLa (triphasic system) was calculated to be between 2.34 and 14.76 h[-1] with an optimal value of 8.0 h[-1] (Flow: 3 L min[-1]) and a Re of 1757. In addition, to show the optimal conditions, kinetic experiments were developed for 20 days using newspaper as carbon source for quantified the enzyme activities, biomass, residual cellulose, and reducing sugars 1421 IU L[-1] CMCase, 8.02, 2.19, and 0.07 g L[-1], respectively. The degradation rate of newspaper was over 80%, which was significantly higher than that of the nominal value. Finally, the theoretical correlation proposed for kLa was compared and estimated with respect to the experimental values with an error of ±20%. The kLa and the Re are important criteria in assessing an optimal degradation of newspaper in an industrial process scale-up.}, }
@article {pmid39738111, year = {2024}, author = {Rao, Y and Wang, Y and Wang, S and Gong, Z and Zhang, C}, title = {Numerical simulation study on the influence of bend diameter rate on the flow characteristics of nature gas hydrate particles.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {31604}, pmid = {39738111}, issn = {2045-2322}, support = {BE2022001-5//Project of Emission Peak and Carbon Neutrality of Jiangsu Province/ ; BE2022001-5//Project of Emission Peak and Carbon Neutrality of Jiangsu Province/ ; 2022N045//Quanzhou Science and Technology Planning Project/ ; 2022N045//Quanzhou Science and Technology Planning Project/ ; KYCX24_3245 and SJCX24_1682//Jiangsu Provincial Graduate Research and Innovation Program Project/ ; KYCX24_3245 and SJCX24_1682//Jiangsu Provincial Graduate Research and Innovation Program Project/ ; }, abstract = {Bend pipe is a common part of long distance pipeline. There is very important to study the flow law of hydrate particles in the bend pipe, and pipeline design will be optimized. In addition, the efficiency and safety of pipeline gas transmission will be improved. With the flow of hydrate particles in a curved pipe as the object of study, the effects of Bend diameter rate and Reynolds number on the velocity distribution, turbulent kinetic energy change, wall shear force, particle motion and pressure drop distribution of the spiral flow carrying hydrate particles were investigated by numerical simulation method. The results show that bend diameter rate is the smaller, and the high speed zone is easier to appear inside the bend. Moreover, the uniformity of the velocity distribution of the fluid flowing through the bend is slower with the smaller the rate of the bend to the diameter. When Re = 20,000, the curve fluctuates more, and the peak speed reaches 4 times that of Re = 10,000. Increasing the Reynolds number of the initial transport can maintain the helical flow strength of the fluid after passing through the bend pipe, so that the flow can obtain higher tangential force. Because the fluid flows into the pipe by spiral flow, the shear force inside the pipe is higher under the combined action of its tangential velocity at the pipe wall and the high speed zone inside the pipe wall. The presence of the twisted tape leads to greater flow resistance, which makes the pressure drop increase at the position of the twisted tape different. At the same position, the Reynolds number is larger, and the pressure drop increases larger, and the Bend diameter rate is larger, and the fluid speed recovers faster, and the velocity is smaller, and the unit pressure drop is smaller, and Unit pressure drop is down 72.9%. The increase of Reynolds number can reduce the resistance coefficient of the Bend part, but the increase of the Bend diameter rate makes the resistance coefficient decrease first and then increase.}, }
@article {pmid39732920, year = {2024}, author = {Žáček, J and Strecker, Z and Jeniš, F and Macháček, O and Goldasz, J and Sapinski, B and Vrbka, M and Kubík, M}, title = {Impact of magnetorheological fluid composition on their behaviour in gradient pinch mode.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {31320}, pmid = {39732920}, issn = {2045-2322}, support = {GACR 21-45236L//Grantov&#xe1; Agentura &#x10c;esk&#xe9; republiky-GACR/ ; GACR 21-45236L//Grantov&#xe1; Agentura &#x10c;esk&#xe9; republiky-GACR/ ; GACR 21-45236L//Grantov&#xe1; Agentura &#x10c;esk&#xe9; republiky-GACR/ ; GACR 21-45236L//Grantov&#xe1; Agentura &#x10c;esk&#xe9; republiky-GACR/ ; GACR 21-45236L//Grantov&#xe1; Agentura &#x10c;esk&#xe9; republiky-GACR/ ; GACR 21-45236L//Grantov&#xe1; Agentura &#x10c;esk&#xe9; republiky-GACR/ ; 2020/39/I/ST8/02916//Narodowe Centrum Nauki-NCN/ ; 2020/39/I/ST8/02916//Narodowe Centrum Nauki-NCN/ ; }, abstract = {Magnetorheological (MR) fluids can be utilized in one of the fundamental operating modes of which the gradient pinch mode has been the least explored. In this unique mode non-uniform magnetic field distributions are taken advantage of to develop a so-called Venturi-like contraction in MR fluids. By adequately directing magnetic flux the material can be made solidified in the regions near the flow channel wall, thus creating a passage in the middle of the channel for the fluid to pass through. This leads to unique variations of the slope in the pressure-flow rate characteristics. It can be stated that the effect of the MR fluid composition on the behaviour of the MR fluid in gradient pinch mode has not been thoroughly investigated yet. In this study, the behaviour of MR fluids was assessed with a dedicated pinch mode MR valve that provided a valuable insight into the contraction mechanism using fluorescence microscopy. Briefly, seven MR fluid samples were prepared with different particle concentrations (10%, 22% and 32 vol%) and mean particle sizes (2, 4.5 and 8.2 μm). It was found that the MR fluid sample with the larger particle size exhibits a significantly larger slope change observed in the pressure-flow rate characteristics. Increasing the particle size from 2 μm (base) to 8 μm resulted in the slope increase by a factor of 2.6 compared to the base sample. Increasing the particle concentration has a negligible effect on the pinch mode effect. Finally, these results were analysed using the modified Wuest equation, which is commonly used for characterizing sharp-edged orifices in low Reynolds number flow regimes. The simple equation was determined to describe the behaviour of MR fluids in gradient pinch mode with adequate accuracy.}, }
@article {pmid39730787, year = {2024}, author = {Wei, T and Wang, C and Zhao, Y and Shen, M and Chen, Z}, title = {Numerical study on the evolution characteristics of contact and fluid flow in shear-induced rough joint.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {30971}, doi = {10.1038/s41598-024-82008-3}, pmid = {39730787}, issn = {2045-2322}, support = {52364004//National Natural Science Foundation of China/ ; }, abstract = {In order to investigate the influence of shear on contact characteristics and fluid flow evolution of rough rock fractures, a series of shear-flow tests were carried out by numerical experiments. Firstly, a sandstone specimen with a rough fracture was made in the laboratory, and the numerical model of the fracture was reconstructed in FLAC3D software. Experiments were conducted to investigate the depth of penetration of the fracture under different normal stress (1, 3, and 5 MPa) and shear displacement (2, 4, 6, 8, and 10 mm). By establishing the relationship between the shear direction and the apparent inclination of the fracture asperity, the effects on the asperity contact characteristics and seepage properties are explored. The results of the study indicated that the larger the normal stress the larger the surface contact section and the smaller the aperture, showing the opposite trend with increasing shear displacement. Positive apparent inclination distribution can effectively predict the location of shear damage during the shear process. Negative apparent dip implies that those regions increase permeability after shear, and decrease with increasing crack opening. Fracture seepage shows obvious nonlinear characteristics, where the nonlinear coefficients are 5-6 orders of magnitude larger than the linear coefficients. The critical Reynolds number Rec is used to distinguish the linear and nonlinear categories of fluid flow, and the calculated results show that the range of Rec is between 0.0081 and 0.11.3, and the Rec increases with shear displacement and decreases with normal stress.}, }
@article {pmid39722445, year = {2025}, author = {Zhang, M and Tu, C and Guo, L and Hou, L and Li, Y and Du, P and Chen, J and Lin, J and Bao, F}, title = {Spontaneous Cargo Transport via Sliding Bubbles on a Superhydrophobic Wire.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {41}, number = {1}, pages = {1175-1181}, doi = {10.1021/acs.langmuir.4c04539}, pmid = {39722445}, issn = {1520-5827}, abstract = {The transportation and carrying behavior of underwater bubbles have been widely used for an underwater microactuator, cargo displacement assembly, and drug delivery. This study explores a method for underwater cargo transportation using sliding bubbles as a vehicle with directionally guided superhydrophobic wires. By exploitation of the adhesion between superhydrophobic surfaces and bubble interfaces, a bubble is able to transport a superhydrophobic O-ring along a superhydrophobic wire, effectively delivering the O-ring to the water surface. The capability of the bubble-driven O-ring to rise along superhydrophobic wires was systematically evaluated and analyzed, focusing on the two configurations formed by the bubbles and O-rings. Additionally, we identified the conditions necessary for the successful rising of bubbles and O-rings of varying sizes as well as their trajectories and rising velocities. Through an analysis of the relationship between the Ohnesorge number and Reynolds number, the kinetic characteristics of the bubble-carrying O-ring are elucidated. Furthermore, the applications of bubble transportation in cyclic actuation and underwater data collection are substantiated. This strategy offers a highly reliable method for underwater information transmission and patrol as well as potential applications in bubble transportation.}, }
@article {pmid39708495, year = {2025}, author = {Aghaee, A and Khan, MO}, title = {Pinning down the accuracy of physics-informed neural networks under laminar and turbulent-like aortic blood flow conditions.}, journal = {Computers in biology and medicine}, volume = {185}, number = {}, pages = {109528}, doi = {10.1016/j.compbiomed.2024.109528}, pmid = {39708495}, issn = {1879-0534}, mesh = {Humans ; *Neural Networks, Computer ; *Models, Cardiovascular ; Blood Flow Velocity/physiology ; Aorta/physiopathology ; Aortic Coarctation/physiopathology/diagnostic imaging ; Computer Simulation ; }, abstract = {BACKGROUND: Physics-informed neural networks (PINNs) are increasingly being used to model cardiovascular blood flow. The accuracy of PINNs is dependent on flow complexity and could deteriorate in the presence of highly-dynamical blood flow conditions, but the extent of this relationship is currently unknown. Therefore, we investigated the accuracy and performance of PINNs under a range of blood flow conditions, from laminar to turbulent-like flows.<br><br>METHODS: A stenosis was virtually induced in the thoracic segment of a patient's aorta to represent aortic coarctation. Stenosis severity was varied from 0% to 70% in increments of 5% (NCFD=15 cases), corresponding to stenotic Reynolds number that ranged from 1000 to 3333. CFD simulations at high spatial and temporal resolutions (6.9 million mesh, 10,000 time-steps) were performed for all NCFD=15 cases to obtain ground-truth velocity data. Fourier-based activation function in feed-forward PINNs with dynamic loss coefficients were trained to reconstruct CFD velocity field. Losses included those from physical equations, boundary conditions and sensor data sampled evenly from CFD simulations. Number of sensor points were increased from 200-1600 in increments of 200. This resulted in a total of 8 sensor point variations for each stenotic model (Nsens=8). Hence, a total of 120 (NCFDxNsens) cases were trained in this study. The PINNs architecture and data have been made open-sourced.<br><br>RESULTS: PINNs errors increased substantially for stenosis severity >50% (stenotic Reynolds numer > 2000) due to the presence of complex turbulent-like flow features. When using 400 sensor points, PINNs velocity magnitude errors ranged from 30% for no-stenosis model to 57% for the model with 70% stenosis, and dropped to 10% and 20%, respectively when the number of sensor points were increased to 1600. PINNs velocity magnitude errors increased monotonically with turbulent intensity, particularly beyond stenosis severity of 50%.<br><br>CONCLUSIONS: Our findings indicate that the accuracy of PINNs is dependent on the complexity of blood flow conditions. Using conventional PINNs architecture, the errors in trained velocity can increase substantially in the presence of turbulent-like blood flows that are typically found in various vascular pathologies.}, }
@article {pmid39703560, year = {2024}, author = {Chen, J and Hu, W and Dong, X and Lin, J and Gao, Z and Qiu, B}, title = {Experimental investigation on modes of spray formation, droplet size and size distribution in a spinning disc atomizer.}, journal = {Frontiers in plant science}, volume = {15}, number = {}, pages = {1470745}, pmid = {39703560}, issn = {1664-462X}, abstract = {The spinning disc atomizer is extensively utilized in agricultural spraying, with optimized operating conditions significantly enhancing atomization performance. In this paper, the atomization characteristics of a spinning disc were studied using photographs taken by a high-speed camera. Ethanol-water solutions were used at various flow rates and the disc speed was varied in a wide range. The influence of disc speed, flow rate, and surface tension on modes of spray formation, droplet size, and size distribution were investigated. The correlations for Reynolds number (Re), Stability number (St), and dimensionless droplet size (d[*]) were proposed in a wide range of operational conditions. The Rosin-Rammler (RR) and modified Rosin-Rammler (MRR) distributions appropriately represented the droplet size distribution. It was found that the increase in flow rate resulted in modes of spray formation translation under the same disc speed and ethanol-water solution. The predicted droplet sizes showed good agreement with the experiment values. Most of the predicted droplet sizes were within the band of ±15% of the experiment values. The droplet size decreased with increasing Re or St, but was hardly affected by q. Besides, the droplet size decreased with increasing disc speed and decreasing surface tension. The RR and MRR distribution matched with the calculated cumulative volume fraction from the experimental data reasonably well for the entire range. It was recommended to appropriately elevate Re during the spinning disc atomization process to narrow the range of droplet sizes and enhance uniformity.}, }
@article {pmid39687179, year = {2024}, author = {Harahap, MG and Abfertiawan, MS and Syafila, M and Handajani, M and Gultom, TH}, title = {Electrocoagulation for nickel, chromium, and iron removal from mine water using aluminum electrodes.}, journal = {Heliyon}, volume = {10}, number = {23}, pages = {e40784}, pmid = {39687179}, issn = {2405-8440}, abstract = {High global demand for nickel metal has contributed significantly to the growth of the nickel mining industry in Indonesia. This growth has a positive multiplier effect on the economy, with the potential to affect aquatic life and humans owing to the high levels of chromium, nickel, and iron in mine water. Therefore, this study aims to develop an electrocoagulation (EC) reactor to remove nickel, chromium, and iron from mine water. This study used a continuous reactor and aluminum electrodes with variations in current density (3.378, 6.757, and 10.135 mA/cm[2]) and inflow (0.3, 0.5, and 1 L/min). The results showed that the operating scenario with a current strength of 6 A and an inflow of 0.3 L/min had a removal efficiency of 86.89 % nickel, 99.51 % chromium, and 80.61 % iron with a charge loading value of 11,194 F/ma[3] and Reynolds number of 39. These results are expected to provide valuable information for the development of an effective EC technology, thereby demonstrating its potential for the removal of metals from nickel mine water.}, }
@article {pmid39679780, year = {2024}, author = {Song, Y and Ming, P and Xun, B}, title = {Research on similarity law of the flow-induced noise of the submarine.}, journal = {The Journal of the Acoustical Society of America}, volume = {156}, number = {6}, pages = {4010-4023}, doi = {10.1121/10.0034606}, pmid = {39679780}, issn = {1520-8524}, abstract = {Flow-induced noise is a complex source that significantly impacts submarines' stealth performance. While previous studies have provided valuable insights into the acoustic radiation of scaled-down submarine models, addressing the flow noise of full-scale prototypes has remained a daunting challenge. To bridge this gap, the research team undertook an extensive investigation to unveil the elusive similarity law of flow noise in both small and large-scale submarine models. By leveraging computational algorithms and turbulence models, the flow field of the submarine model was simulated, and the Kirchhoff and Ffowcs Williams-Hawkings model was employed to calculate the submarine's flow noise. This comprehensive study meticulously considered various influential factors, including Mach number, Reynolds number, etc., ultimately formulating a similarity correlation formula for submarine flow noise. The findings of this study revealed several key insights, including the minimal impact of accessories on submarine flow noise similarity, the adherence of the frequency of submarine flow noise to the Helmholtz number, and the intricate relationship between sound pressure level similarity law with Mach and Reynolds number. Ultimately, this study introduces and summarizes the submarine flow noise similarity law. This law enables the estimation of real-scale model flow noise by using small-scale model flow noise as a reference.}, }
@article {pmid39677972, year = {2024}, author = {Rosafio, N and Salvadori, S and Misul, DA}, title = {Implementation of a high-order spatial discretization into a finite volume solver: Applications to turbomachinery test cases using an eddy-viscosity turbulence closure.}, journal = {Heliyon}, volume = {10}, number = {16}, pages = {e36478}, pmid = {39677972}, issn = {2405-8440}, abstract = {In this study, the implementation of a high-order spatial discretization method into a Finite Volume solver is presented. Specific emphasis is put on the analysis of the performance over selected turbomachinery test cases. High-order numerical discretization is achieved by adopting the cell-centered Least-Square reconstruction, which is implemented in the in-house solver HybFlow. The validation of the adopted methodology is performed by assessing the solution of a turbulent flat plate with zero pressure gradient, using a eddy-viscosity transitional model. The test case also evidences the effect of the discretization of gradient-based source terms when a high-order reconstruction methodology is used. In the second part of the paper, the solver is used for the solution of relevant two-dimensional turbomachinery test cases, assessing the impact of 2 n d and 3 r d order reconstruction on the prediction of the aerodynamics and the heat transfer for respectively a low-pressure blade and a high-pressure turbine vane. It is shown how a high-order reconstruction allows for obtaining a better prediction of turbomachinery aerodynamics, with lower number of elements. The benefits over heat transfer predictions in high Reynolds number conditions are instead limited to the reduction of heat transfer coefficient spikes in under-resolved regions of the blade. Eventually, the methodology is validated for a three-dimensional low-pressure turbine cascade with realistic boundary layer inflow conditions.}, }
@article {pmid39657794, year = {2024}, author = {Yoshizawa, K and Motani, R}, title = {Waveform geometry dictating optimal cruising in animals.}, journal = {Journal of the Royal Society, Interface}, volume = {21}, number = {221}, pages = {20240442}, pmid = {39657794}, issn = {1742-5662}, support = {//Japan Society for the Promotion of Science/ ; }, mesh = {Animals ; *Swimming/physiology ; *Models, Biological ; *Fishes/physiology ; Biomechanical Phenomena ; }, abstract = {For sustained swimming and flights, vertebrates and insects oscillate their propulsors periodically within a narrow range of Strouhal number (St), a dimensionless quantity describing the rate and density of the motion, suggesting a close relationship between the range and cruising optimality. The persistence of this range across size and fluids has puzzled biologists and engineers, resulting in multiple interpretations of its cause. Here, we propose that the optimal St range is largely constrained by power output efficiency of the trailing edge of the caudal fin. A mathematical model of the periodic wake of the trailing edge, which defines the proportion of power lost without contributing to propulsion, predicts that such energy loss is minimal in the observed range of St preferred by fish. The constraints apply across a range of Reynolds number in cruising fish. The same constraints dictate the optimal speed across a wide range of swimmers, in combination with morphological characteristics. Other factors such as drag properties also affect the optimal swimming speed, but probably to a smaller extent. The result that the geometry of periodic waveforms is key to cruising optimality provides an additional angle to study animal locomotion in fluids and related bioinspired robotics.}, }
@article {pmid39636852, year = {2024}, author = {Chen, MA and Lee, SH and Kang, PK}, title = {Inertia-induced mixing and reaction maximization in laminar porous media flows.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {121}, number = {50}, pages = {e2407145121}, pmid = {39636852}, issn = {1091-6490}, support = {DE-SC0023429//U.S. Department of Energy (DOE)/ ; EAR-1952686//NSF (NSF)/ ; EAR-2046015//NSF (NSF)/ ; }, abstract = {Solute transport and biogeochemical reactions in porous and fractured media flows are controlled by mixing, as are subsurface engineering operations such as contaminant remediation, geothermal energy production, and carbon sequestration. Porous media flows are generally regarded as slow, so the effects of fluid inertia on mixing and reaction are typically ignored. Here, we demonstrate through microfluidic experiments and numerical simulations of mixing-induced reaction that inertial recirculating flows readily emerge in laminar porous media flows and dramatically alter mixing and reaction dynamics. An optimal Reynolds number that maximizes the reaction rate is observed for individual pore throats of different sizes. This reaction maximization is attributed to the effects of recirculation flows on reactant availability, mixing, and reaction completion, which depend on the topology of recirculation relative to the boundary of the reactants or mixing interface. Recirculation enhances mixing and reactant availability, but a further increase in flow velocity reduces the residence time in recirculation, leading to a decrease in reaction rate. The reaction maximization is also confirmed in a flow channel with grain inclusions and randomized porous media. Interestingly, the domain-wide reaction rate shows a dramatic increase with increasing Re in the randomized porous media case. This is because fluid inertia induces complex three-dimensional flows in randomized porous media, which significantly increases transverse spreading and mixing. This study shows how inertial flows control reaction dynamics at the pore scale and beyond, thus having major implications for a wide range of environmental systems.}, }
@article {pmid39632088, year = {2024}, author = {Zhu, W and Shen, Y and Jia, Y and Dai, X and Liu, S and Lin, Y and Xu, Y}, title = {Gradient Nonwettability Controls Water-Film Flowing Features.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {40}, number = {50}, pages = {26487-26499}, doi = {10.1021/acs.langmuir.4c03243}, pmid = {39632088}, issn = {1520-5827}, abstract = {The flow of the water film on solid surface depended on the film Reynolds number and wind speed. Moreover, environmental factors had an impact on the flow process. This study explored how surface wettability impacts the stability and detachment of water film under varying conditions. Superhydrophobic surface played a critical role in speeding up the detachment of water film, especially under conditions of strong wind and specific flow dynamics, such as a wind speed of 19 m/s and a Reynolds number of 83. The efficiency in water removal was due to a combination of forces: capillary action, which pulls the water into smaller areas, reduced surface tension, and decreased adhesion between the liquid and surface. These factors worked together to shrink the area of contact, allowing the film to break and detach more easily. The findings suggested that enhancing nonwettability can improve water removal efficiency, with potential applications in fields like aerospace. Furthermore, additional trials across varying wind speeds and Reynolds numbers consistently supported the superior performance of superhydrophobic surface in driving rapid water-film detachment. To advance this effect, a gradient nonwetting surface was introduced, specifically engineered within the superhydrophobic regime, to amplify the velocity of film separation. This design innovation leveraged variations in surface energy across the gradient, which fostered directional water-film movement and accelerated detachment. A comprehensive analysis of the underlying physical mechanisms further elucidated its potential in enhancing water-shedding applications across a range of environmental conditions.}, }
@article {pmid39626617, year = {2024}, author = {Ahnn, S and Kim, H and Choi, H}, title = {Aerodynamic performance enhancement of a vertical-axis wind turbine by a biomimetic flap.}, journal = {Bioinspiration &amp; biomimetics}, volume = {20}, number = {1}, pages = {}, doi = {10.1088/1748-3190/ad9a45}, pmid = {39626617}, issn = {1748-3190}, mesh = {Animals ; *Flight, Animal/physiology ; *Wings, Animal/physiology ; *Wind ; *Equipment Design ; *Biomimetic Materials/chemistry ; Computer Simulation ; Models, Biological ; Equipment Failure Analysis ; Biomimetics/instrumentation/methods ; Energy Transfer ; Birds/physiology ; Feathers/physiology ; Computer-Aided Design ; }, abstract = {We improve the aerodynamic performance of a simplified vertical-axis wind turbine (VAWT) using a biomimetic flap, inspired by the movement of secondary feathers of a bird's wing at landing (Liebe 1979Aerokurier1254). The VAWT considered has three NACA0018 straight blades at the Reynolds number of80000based on the turbine diameter and free-stream velocity. The biomimetic flap is made of a rigid rectangular curved plate, and its streamwise length is 0.2cand axial (spanwise) length is the same as that of blade, wherecis the blade chord length. This device is installed on the inner surface of each blade. Its one side is attached near the blade leading edge (pivot point), and the other side automatically rotates around the pivot point (without external power input) in response to the surrounding flow field during blade rotation. The flap increases the time-averaged power coefficient by 88% at the tip-speed ratio of 0.8, when its pivot point is at 0.1cdownstream from the blade leading edge. While the torque on the blade itself does not change even in the presence of the flap, the flap itself generates additional torque, thus increasing the overall power coefficient. The phase analysis indicates that the power coefficient of VAWT significantly increases during flap opening to full deployment through the interaction with vortices separated from the blade leading edge. When the pivot point of flap is farther downstream from the leading edge or the flap operates at a high tip-speed ratio, the performance of the flap diminishes due to its weaker interaction with the separating vortices.}, }
@article {pmid39621288, year = {2024}, author = {Palahnuk, H and Su, B and Harbaugh, T and Gesenberg, C and Zhou, S and Rizk, E and Bernstein, J and Hazard, SW and Manning, KB}, title = {Fluid Dynamic and in Vitro Blood Study to Understand Catheter-Related Thrombosis.}, journal = {Cardiovascular engineering and technology}, volume = {}, number = {}, pages = {}, pmid = {39621288}, issn = {1869-4098}, support = {UL1 TR002014/TR/NCATS NIH HHS/United States ; }, abstract = {PURPOSE: Central venous catheters (CVCs) provide a direct route to the venous circulation but are prone to catheter-related thrombosis (CRT). A known CRT risk factor is a high catheter-to-vein ratio (CVR), or a large catheter diameter with respect to the indwelling vein size. In this study, the CVR's effect on CVC hemodynamics and its impact on CRT is investigated with in vitro and in silico experiments.<br><br>METHODS: An in vitro flow loop is used to characterize the hemodynamics around CVCs using particle image velocimetry. In addition, CRT is investigated using an in vitro flow loop with human blood and clinical catheters. The wall shear rate of flow around the CVC is computed numerically. CVRs of 0.20, 0.33, and 0.49 and Reynolds numbers of 200, 800, and 1300 are evaluated. No flow is used through CVC lumens to model chronic indwelling catheters.<br><br>RESULTS: Results show CVR &#x2265; 0.33 promotes platelet-rich clot growth at the device tip and at an increased rate compared to lower CVR cases. A high wall shear rate gradient on the CVC tip and an extended wake distal to the tip exists for higher CVR cases, promoting the aggregation of platelets and subsequent stagnation for clot formation. Further, the combination of the CVR and Reynolds number are crucial to CRT potential, not the CVR alone. Specifically, thrombosis risk is increased with low (stasis driven) and/or high (platelet activation driven) flow conditions, with the CVR and CVC's geometry playing an additional role in promoting fluid mechanic driven thrombus development. A high CVR (&#x2265; 0.33) and high flow condition (&#x2265; 1300) results in the highest risk for clot growth at the tip of the device; other locations of the device are at risk for thrombus development in lower flow conditions, regardless of the CVR. The importance of the device geometry and flow in promoting thrombus and fibrin sheath formation is also shown for the device investigated.<br><br>CONCLUSIONS: This work demonstrates that the CVR, flow, and device geometry affect CRT. For clinical cases with CVR &#x2265; 0.33 and/or Re &#x2265; 1300, the device tip may be monitored more consistently for clot formation. Thrombosis risks remain on the entire catheter, regardless of the flow condition, for a CVR = 0.49. Device placement should be chosen carefully with respect to the combination of the Reynolds number and CVR. Further study is needed on the effect of catheterization to confirm these findings.}, }
@article {pmid39619498, year = {2024}, author = {Harte, NC and Obrist, D and Versluis, M and Jebbink, EG and Caversaccio, M and Wimmer, W and Lajoinie, G}, title = {Second order and transverse flow visualization through three-dimensional particle image velocimetry in millimetric ducts.}, journal = {Experimental thermal and fluid science}, volume = {159}, number = {}, pages = {None}, pmid = {39619498}, issn = {1879-2286}, abstract = {Despite recent advances in 3D particle image velocimetry (PIV), challenges remain in measuring small-scale 3D flows, in particular flows with large dynamic range. This study presents a scanning 3D-PIV system tailored for oscillatory flows, capable of resolving transverse flows less than a percent of the axial flow amplitude. The system was applied to visualize transverse flows in millimetric straight, toroidal, and twisted ducts. Two PIV analysis techniques, stroboscopic and semi-Lagrangian PIV, enable the quantification of net motion as well as time-resolved axial and transverse velocities. The experimental results closely align with computational fluid dynamics (CFD) simulations performed in a digitized representation of the experimental model. The proposed method allows the examination of periodic flows in systems down to microscopic scale and is particularly well-suited for applications that cannot be scaled up due to their complex, multi-physics nature.}, }
@article {pmid39613755, year = {2024}, author = {Du, P and Parikh, MH and Fan, X and Liu, XY and Wang, JX}, title = {Conditional neural field latent diffusion model for generating spatiotemporal turbulence.}, journal = {Nature communications}, volume = {15}, number = {1}, pages = {10416}, pmid = {39613755}, issn = {2041-1723}, support = {N00014-23-1-2071//United States Department of Defense | United States Navy | ONR | Office of Naval Research Global (ONR Global)/ ; OAC-2047127//National Science Foundation (NSF)/ ; }, abstract = {Eddy-resolving turbulence simulations are essential for understanding and controlling complex unsteady fluid dynamics, with significant implications for engineering and scientific applications. Traditional numerical methods, such as direct numerical simulations (DNS) and large eddy simulations (LES), provide high accuracy but face severe computational limitations, restricting their use in high-Reynolds number or real-time scenarios. Recent advances in deep learning-based surrogate models offer a promising alternative by providing efficient, data-driven approximations. However, these models often rely on deterministic frameworks, which struggle to capture the chaotic and stochastic nature of turbulence, especially under varying physical conditions and complex, irregular geometries. Here, we introduce the Conditional Neural Field Latent Diffusion (CoNFiLD) model, a generative learning framework for efficient high-fidelity stochastic generation of spatiotemporal turbulent flows in complex, three-dimensional domains. CoNFiLD synergistically integrates conditional neural field encoding with latent diffusion processes, enabling memory-efficient and robust generation of turbulence under diverse conditions. Leveraging Bayesian conditional sampling, CoNFiLD flexibly adapts to various turbulence generation scenarios without retraining. This capability supports applications such as zero-shot full-field flow reconstruction from sparse sensor data, super-resolution generation, and spatiotemporal data restoration. Extensive numerical experiments demonstrate CoNFiLD's capability to accurately generate inhomogeneous, anisotropic turbulent flows within complex domains. These findings underscore CoNFiLD's potential as a versatile, computationally efficient tool for real-time unsteady turbulence simulation, paving the way for advancements in digital twin technology for fluid dynamics. By enabling rapid, adaptive high-fidelity simulations, CoNFiLD can bridge the gap between physical and virtual systems, allowing real-time monitoring, predictive analysis, and optimization of complex fluid processes.}, }
@article {pmid39609494, year = {2024}, author = {Abderrahmane, A and Younis, O and Ahmed, SE and Mourad, A and Raizha, Z and Ahmed, A}, title = {Magnetic mixed convection within wavy trapezoidal thermal energy storage systems using nano enhanced phase change material.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {29565}, pmid = {39609494}, issn = {2045-2322}, support = {RGP2/47/45//the Deanship of Research and Graduate Studies at King Khalid University/ ; }, abstract = {The three-dimensional (3D) MHD mixed convection mode confined 3D wavy trapezoidal enclosure is examined. The bottom plane of the trapezoidal system is irregular, particularly a wavy plane with various undulation numbers [Formula: see text]. The forced convection phenomenon arises due to the displacement of the top region plane, whereas the porosity-enthalpy methodology characterizes the progression of charging. The heat transfer is enhanced using the nanoencapsulation phase change material (NePCM), consisting of Polyurethane as a shell and Nonadecane as a core, with water as the primary liquid base. The (GFEM) is used to treat the governing system, and a comparison between the HT (heat transmission) irreversibility and FF (fluid friction) irreversibility is performed using the function of the BeAvg. The significant findings revealed that parabolic behaviors for the melting ribbon curve are given at lower values of Re and higher values of Ha. Also, reducing the undulation number is better for obtaining a higher heat transmission rate. The average Nusselt number was lowered by 60% and 19%, respectively, at the highest Reynolds number when the Hartmann number increased from 0 to 100 and N from 2 to 8. Also, the values of [Formula: see text] between 1 and 100 improve the heat transfer rates up to 51%.}, }
@article {pmid39597362, year = {2024}, author = {Sawka, A}, title = {Nanocrystalline Lanthanum Oxide Layers on Tubes Synthesized Using the Metalorganic Chemical Vapor Deposition Technique.}, journal = {Materials (Basel, Switzerland)}, volume = {17}, number = {22}, pages = {}, pmid = {39597362}, issn = {1996-1944}, abstract = {Lanthanum oxide (La2O3) layers are widely used in electronics, optics, and optoelectronics due to their properties. Lanthanum oxide is also used as a dopant, modifying and improving the properties of other materials in the form of layers, as well as having a large volume. In this work, lanthanum oxide layers were obtained using MOCVD (Metalorganic Chemical Vapor Deposition) on the inner walls of tubular substrates at 600-750 °C. The basic reactant was La(tmhd)3 (tris(2,2,6,6-tetramethyl-3,5-heptanedionato)lanthanum(III)). The evaporation temperature of La(tmhd)3 amounted to 170-200 °C. Pure argon (99.9999%) and air were used as the carrier gases. The air was also intended to remove the carbon from the synthesized layers. Tubes of quartz glass were used as the substrates. La2O3 layers were found to be growing on their inner surfaces. The value of the extended Grx/Rex[2] criterion, where Gr-Grashof's number, Re-Reynolds' number, x-the distance from the gas inflow point, was below 0.01. The microstructure of the deposited layers of lanthanum oxide was investigated using an electron scanning microscope (SEM). Their chemical composition was analyzed via energy-dispersive X-ray (EDS) analysis. Their phase composition was tested via X-ray diffraction. The transmittance of the layers of lanthanum oxide was determined with the use of UV-Vis spectroscopy. The obtained layers of lanthanum oxide were characterized by a nanocrystalline microstructure and stable cubic structure. They also exhibited good transparency in both ultraviolet (UV) and visible (Vis) light.}, }
@article {pmid39597124, year = {2024}, author = {Blaschke, O and Kluitmann, J and Elsner, J and Xie, X and Drese, KS}, title = {Consistent Evaluation Methods for Microfluidic Mixers.}, journal = {Micromachines}, volume = {15}, number = {11}, pages = {}, pmid = {39597124}, issn = {2072-666X}, support = {031B1124A//Federal Ministry of Education and Research/ ; }, abstract = {The study presents a unifying methodology for characterizing micromixers, integrating both experimental and simulation techniques. Focusing on Dean mixer designs, it employs an optical evaluation for experiments and a modified Sobolev norm for simulations, yielding a unified dimensionless characteristic parameter for the whole mixer at a given Reynolds number. The results demonstrate consistent mixing performance trends across both methods for various operation points. This paper also proposes enhancements in the evaluation process to improve accuracy and reduce noise impact. This approach provides a valuable framework for optimizing micromixer designs, essential in advancing microfluidic technologies.}, }
@article {pmid39590232, year = {2024}, author = {Reynolds, A}, title = {Swarming Insects May Have Finely Tuned Characteristic Reynolds Numbers.}, journal = {Biomimetics (Basel, Switzerland)}, volume = {9}, number = {11}, pages = {}, pmid = {39590232}, issn = {2313-7673}, support = {BBS/OS/CP/000001//Biotechnology and Biological Sciences Research Council's Industrial Strategy Challenge Fund./ ; }, abstract = {Over the last few years, there has been much effort put into the development and validation of stochastic models of the trajectories of swarming insects. These models typically assume that the positions and velocities of swarming insects can be represented by continuous jointly Markovian processes. These models are first-order autoregressive processes. In more sophisticated models, second-order autoregressive processes, the positions, velocities, and accelerations of swarming insects are collectively Markovian. Although it is mathematically conceivable that this hierarchy of stochastic models could be extended to higher orders, here I show that such a procedure would not be well-based biologically because some terms in these models represent processes that have the potential to destabilize insect flight dynamics. This prediction is supported by an analysis of pre-existing data for laboratory swarms of the non-biting midge Chironomus riparius. I suggest that the Reynolds number is a finely tuned property of swarming, as swarms may disintegrate at both sufficiently low and sufficiently high Reynolds numbers.}, }
@article {pmid39562910, year = {2024}, author = {McMullen, RM and Gallis, MA}, title = {Hydrodynamic fluctuations near a Hopf bifurcation: Stochastic onset of vortex shedding behind a circular cylinder.}, journal = {Physical review. E}, volume = {110}, number = {4-2}, pages = {045104}, doi = {10.1103/PhysRevE.110.045104}, pmid = {39562910}, issn = {2470-0053}, abstract = {We investigate hydrodynamic fluctuations in the flow past a circular cylinder near the critical Reynolds number Re_{c} for the onset of vortex shedding. Starting from the fluctuating Navier-Stokes equations, we perform a perturbation expansion around Re_{c} to derive analytical expressions for the statistics of the fluctuating lift force. Molecular-level simulations using the direct simulation Monte Carlo method support the theoretical predictions of the lift power spectrum and amplitude distribution. Notably, we have been able to collect sufficient statistics at distances Re/Re_{c}-1=O(10^{-3}) from the instability that confirm the appearance of non-Gaussian fluctuations, and we observe that they are associated with intermittent vortex shedding. These results emphasize how unavoidable thermal-noise-induced fluctuations become dramatically amplified in the vicinity of oscillatory flow instabilities and that their onset is fundamentally stochastic.}, }
@article {pmid39562882, year = {2024}, author = {Śnieżek, D and Naqvi, SB and Matyka, M}, title = {Inertia onset in disordered porous media flow.}, journal = {Physical review. E}, volume = {110}, number = {4-2}, pages = {045103}, doi = {10.1103/PhysRevE.110.045103}, pmid = {39562882}, issn = {2470-0053}, abstract = {We investigate the onset of the inertial regime in the fluid flow at the pore level in three-dimensional, disordered, highly porous media. We analyze the flow structure in a wide range of Reynolds numbers starting from 0.01 up to 100. We focus on qualitative and quantitative changes that appear with increasing Reynolds number. To do that, we investigate the weakening of the channeling effect, defined as the existence of preferred flow paths in a system. We compute tortuosity, spatial kinetic energy localization, and the pore-space volume fraction containing negative streamwise velocity to assess accompanying changes quantitatively. Our results of tortuosity and participation number derivatives show that the onset of inertia is apparent for Reynolds number Re∼0.1, an order of magnitude lower than indicated by analyzing relations of friction factor with the Reynolds number. Moreover, we show that the vortex structures appear at Reynolds number two orders of magnitude higher than the onset of inertia.}, }
@article {pmid39561136, year = {2024}, author = {Depoilly, F and Millet, S and Ben Hadid, H and Dagois-Bohy, S and Rousset, F}, title = {Unifying the roll waves.}, journal = {PloS one}, volume = {19}, number = {11}, pages = {e0310805}, pmid = {39561136}, issn = {1932-6203}, mesh = {*Rheology ; Viscosity ; *Models, Theoretical ; }, abstract = {Free surface flows down a slope occur in various real-life scenarios, such as civil engineering, industry, and natural hazards. Unstable waves can develop at the free surface when inertia is sufficiently strong, indicated by the Reynolds number exceeding a critical value. Although this instability has been investigated for specific fluids with different rheologies, a common framework is still lacking to facilitate comparison among the various models. In this study, we investigate the linear stability of a generalized Newtonian fluid, where the viscosity [Formula: see text] remains unspecified. We meticulously construct new dimensionless quantities to minimize dependence on the rheology, and subsequently derive the Orr-Sommerfeld equation of stability for any generalized Newtonian fluid, which has never been done before. We conduct a long-wave expansion and generate a novel analytical expression for the wave celerity, along with the critical Reynolds number. The originality in this study is that the analytical expressions obtained are valid for any rheology, and are easy to compute from a rheological measurement or from a base flow profile measurement. These results are subsequently scrutinized using various shear-thinning, shear-thickening, and viscoplastic rheology models. They exhibit excellent agreement with experimental or numerical data as well as theoretical findings from existing literature. Furthermore, the novel analytical expressions enable a much more comprehensive investigation into the impact of rheology on stability. While our approach does not encompass singular or non-monotonous rheology, the analytical expressions derived from the long-wave expansion exhibit remarkable resilience and they continue to accurately predict both the wave speed and the instability threshold in such cases.}, }
@article {pmid39553381, year = {2024}, author = {Kadivar, M and Tormey, D and McGranaghan, G}, title = {CFD of roughness effects on laminar heat transfer applied to additive manufactured minichannels.}, journal = {Heat and mass transfer = Warme- und Stoffubertragung}, volume = {60}, number = {12}, pages = {1915-1929}, pmid = {39553381}, issn = {0947-7411}, abstract = {Additive manufacturing has received significant interest in the fabrication of functional channels for heat transfer; however, the inherent rough surface finish of the additively manufactured channels can influence thermal performance. This study investigates the impact of roughness on the thermo-fluid characteristics of laminar forced convection in rough minichannels. A numerical model was developed to create 3D Gaussian roughness with specified root-mean-square height. The finite volume method was used to solve the conjugate heat transfer of developed laminar flow in square minichannels. For Reynolds numbers ranging from 200 to 1600, the simulation results indicated enhanced heat transfer and increased flow resistance as Reynolds number increases, compared to a smooth minichannel, where effects on heat transfer and flow friction were negligible. For channels with relative roughness (root-mean-square height to channel hydraulic diameter) of 0.0068, 0.0113, and 0.0167, increasing the Reynolds number led to increased friction factor by 1.56, 1.71, and 2.91%, while the Nusselt number was enhanced up to 0.03%, 32.74%, and 46.05%, respectively. Heat transfer reduced in roughness valleys due to the presence of local low-velocity fluid in these regions; however, recirculation regions can occur in deep valleys of high roughness, increasing heat transfer and flow friction. Heat transfer was enhanced over roughness peaks due to flow impingement on the windward face of roughness as well as intensified energy transfer to the channel wall from roughness. Moreover, surfaces with higher roughness have a greater number of high peaks providing a thermal-flow path of a larger area and a thermal conductivity greater than that of the fluid.}, }
@article {pmid39551763, year = {2024}, author = {Yi, S and Ding, H and Luo, S and Sun, X and Xia, Z}, title = {Research progress on aero-optical effects of hypersonic optical window with film cooling.}, journal = {Light, science &amp; applications}, volume = {13}, number = {1}, pages = {310}, pmid = {39551763}, issn = {2047-7538}, support = {12102463//National Natural Science Foundation of China (National Science Foundation of China)/ ; 92271203//National Natural Science Foundation of China (National Science Foundation of China)/ ; }, abstract = {In recent years, the demand for optical imaging and detection in hypersonic aircraft has been on the rise. The high-temperature and high-pressure compressed flow field near airborne optoelectronic devices creates significant interference with light transmission, known as hypersonic aero-optical effects. This effect has emerged as a key technological challenge, limiting hypersonic optical imaging and detection capabilities. This article focuses on introducing the thermal effects and optical transmission effects of hypersonic aero-optical effects, as along with corresponding suppression techniques. In addition, this article critically reviews and succinctly summarizes the advancements made in hypersonic aero-optical effects testing technology, while also delineating avenues for future research needs in this field. In conclusion, there is an urgent call for further exploration into the study of aero-optical effects under conditions characterized by high Mach, high enthalpy, and high Reynolds number in the future.}, }
@article {pmid39524866, year = {2024}, author = {Monokrousos, N and Könözsy, L and Pachidis, V and Sozio, E and Rossi, F}, title = {A numerical approach to overcome the very-low Reynolds number limitation of the artificial compressibility for incompressible flows.}, journal = {Heliyon}, volume = {10}, number = {21}, pages = {e39587}, pmid = {39524866}, issn = {2405-8440}, abstract = {We propose a numerical approach to solve a long-standing challenge which is the applicability of the artificial compressibility (AC) formulation for solving the incompressible Navier-Stokes equations at very-low Reynolds numbers. A wide range of engineering applications involves very-low Reynolds number flows in Micro-ElectroMechanical Systems (MEMS) and in the fields of chemical-, agricultural- and biomedical engineering. It is known that the already existing numerical methods using the AC approach fail to provide physically correct results at very-low Reynolds numbers (Re ≤ 1). To overcome the limitation of the AC method for these engineering applications, we propose a higher-order Neumann-type pressure outflow boundary condition treatment along with their up to fourth-order numerical approximations. We found that the numerical treatment of the pressure at the outlet boundary plays the main role in overcoming the limitation of the AC method at very-low Reynolds numbers (Re << 1). Therefore, we provide numerical evidence on the accuracy of the AC method beyond its previously reported limitations, e.g., the low Reynolds number Oseen flow (Re << 1) is first presented in this work. A third-order explicit total-variation diminishing (TVD) Runge-Kutta scheme has been employed with standard finite difference spatial discretisation schemes for improving the accuracy of the numerical solution. For modelling strongly viscous flows, the Reynolds number ranges from 10 - 1 to 10 - 4 . Overall, we found that the accuracy limitation of the AC method below Re < 1 can be overcome with an accurate numerical treatment of the outlet pressure boundary condition instead of using high-order schemes in the governing equations. For the investigated Reynolds number range (10 - 1 ≤ Re ≤ 10 - 4), the obtained results show that the relative errors were smaller than 1% for the numerical simulations performed on the configurations of both the two- and three-dimensional, straight microfluidic channels. The imposition of high-order derivative Neumann-type pressure outflow boundary conditions reduced the maximum relative errors of the numerical solutions from 85% and 95% to below than 1% at the outlet section of the two- and three-dimensional, straight microfluidic channel flows, respectively. Taking the advantage of the numerical approach proposed here, two- and three-dimensional benchmark problems employed in the current investigation in comparison with analytical solutions available in the literature, clearly demonstrate that the artificial compressibility can be used beyond its previously known constraints for very-low Reynolds number incompressible flows.}, }
@article {pmid39532903, year = {2024}, author = {Vishwakarma, DK and Bhattacharyya, S and Soni, MK}, title = {Thermal and flow dynamics of an inclined air heat exchanger equipped with spring turbulators in the transition flow regime.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {27640}, pmid = {39532903}, issn = {2045-2322}, abstract = {The research involves an experimental investigation into the performance of a flow assisting air heat exchanger under varying angular orientation and uniform external heat fluxes without and with spring turbulators. The investigation was performed for Reynolds numbers ranging from 511 to 9676 and inclination angle 15° and 30°. Three heat fluxes (2, 3, and 4 kW/m[2]) were applied to the test section to investigate the effect of external surface heating on the range of transition flow regime and thermohydraulic performance. Transition from laminar to turbulent flow for plain channel at different heat fluxes and inclinations occurs within specific Reynolds number ranges: 2436-4446 for 15° inclination at 4 kW/m[2], 2574-4289 at 3 kW/m[2], and 2850-4152 at 2 kW/m[2]; for 30° inclination, the ranges are 2518-4151, 2712-4361, and 2992-4346 at the respective heat fluxes. When it comes to the effect of inclination on Nusselt number, the transition occurs sooner at lower angles, but is delayed as the angle increases. Additionally, the Nusselt number decreases as the angle of inclination increases. When comparing the Nusselt numbers of plain tubes to those with spring turbulators, the latter shows a significantly greater enhancement. In laminar flow, a maximum 100% deviation exists between highest and lowest friction factors, decreasing to 75% with increasing Reynolds number; all insert configurations exhibit highest friction factor at 15° due to stronger buoyancy forces.}, }
@article {pmid39530646, year = {2024}, author = {Thouvenot, E and Charnay, L and Burshtein, N and Guigner, JM and Dec, L and Loew, D and Silva, AKA and Lindner, A and Wilhelm, C}, title = {High-Yield Bioproduction of Extracellular Vesicles from Stem Cell Spheroids via Millifluidic Vortex Transport.}, journal = {Advanced materials (Deerfield Beach, Fla.)}, volume = {}, number = {}, pages = {e2412498}, doi = {10.1002/adma.202412498}, pmid = {39530646}, issn = {1521-4095}, support = {682367//ERC Consolidator Grant PaDyFlow/ ; N&#xb0;EX061034//la R&#xe9;gion &#xce;le-de-France/ ; //ITMO Cancer of Aviesan/ ; 21CQ016-00//Inserm/ ; ERC-2019-CoG project NanoBioMade 865629//HORIZON EUROPE European Research Council/ ; }, abstract = {Extracellular vesicles (EVs) are emerging as novel therapeutics, particularly in cancer and degenerative diseases. Nevertheless, from both market and clinical viewpoints, high-yield production methods using minimal cell materials are still needed. Herein, a millifluidic cross-slot chip is proposed to induce high-yield release of biologically active EVs from less than three million cells. Depending on the flow rate, a single vortex forms in the outlet channels, exposing transported cellular material to high viscous stresses. Importantly, the chip accommodates producer cells within their physiological environment, such as human mesenchymal stem cells (hMSCs) spheroids, while facilitating their visualization and individual tracking within the vortex. This precise control of viscous stresses at the spheroid level allows for the release of up to 30000 EVs per cell at a Reynolds number of ≈400, without compromising cellular integrity. Additionally, it reveals a threshold initiating EV production, providing evidence for a stress-dependent mechanism governing vesicle secretion. EVs mass-produced at high Reynolds displayed pro-angiogenic and wound healing capabilities, as confirmed by proteomic and cytometric analysis of their cargo. These distinct molecular signatures of these EVs, compared to those derived from monolayers, underscore the critical roles of the production method and the 3D cellular environment in EV generation.}, }
@article {pmid39528766, year = {2024}, author = {Hassaan, AM}, title = {An experimental investigation examining the usage of a hybrid nanofluid in an automobile radiator.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {27597}, pmid = {39528766}, issn = {2045-2322}, abstract = {Several modifications have been made to the radiator's dimensions and materials as part of the evolution of the automotive cooling cycle. Coolant is an important factor that greatly affects the efficiency of the cooling cycle. In applications involving heat transmission, nanofluids have become a viable possibility coolant. Two distinct types of nanoparticles floating in the base fluid make up the hybrid nanofluid, a newly invented class of nanofluids. Tests of hybrid nanofluids as a working fluid substitute for conventional fluids have been assisted by the current study. In the radiator of a 2005 Honda, the MWCNT-Al2O3/water nanofluid was tested at various volumetric concentrations (Φ) using a 50:50 mixing ratio. The outcomes of the experiments were compared with those obtained by using pure water. The radiator's performance was evaluated by adjusting the fluid flow rate and operating the fluid at two distinct temperatures (60, 80 °C). The outcomes demonstrated that the convection heat transfer coefficient increased with a ratio reached 28.5% over the distilled water at the same temperature and flow rate. Both effectiveness and the Nusselt number had improved, coming in at 22.54% and 23.74%, respectively. Depending on the fluid concentration there is an increase in the pressure drop up to 24% than ordinary fluid. It discovered considerable agreement between the research outcomes by comparing them with earlier publications. An experimental correlation was inferred from the results to estimate the Nusselt number as a function of the Reynolds number and (Φ).}, }
@article {pmid39520057, year = {2025}, author = {Noreen, S and Aslam, F}, title = {Electro-Osmotic Mechanism of Ellis Fluid With Joule Heating, Viscous Dissipation, and Magnetic Field Effects in a Pumping Microtube.}, journal = {Journal of biomechanical engineering}, volume = {147}, number = {1}, pages = {}, doi = {10.1115/1.4067083}, pmid = {39520057}, issn = {1528-8951}, mesh = {Viscosity ; *Magnetic Fields ; Hot Temperature ; Osmosis ; Hydrodynamics ; Rheology ; }, abstract = {The dynamics of electro-osmotically generated flow of biological viscoelastic fluid in a cylindrical geometry are investigated in this paper. This flux is the result of walls contracting and relaxing sinusoidally in a magnetic environment. The blood's viscoelasticity and shear-thinning viscosity are the primary causes of its non-Newtonian characteristics. Hence, the rheology of the fluid (blood) is accurately captured with the Ellis fluid model. Both Joule heating and viscous dissipation are accounted for during thermal analysis. The electric potential induced in the electric double layer (EDL) is obtained by applying the Debye-Huckel linearization to the nonlinear Poisson-Boltzmann equation. Mathematical modelling is incorporated in cylindrical coordinates in wave frame of reference. Assuming a long wavelength and creeping flow characterized by a low Reynolds number, the Ellis fluid model's governing equations are simplified. The resulting differential equations are evaluated numerically via the built-in tool NDSolve of the Mathematica. Graphical representations are utilized to visually and comprehensively assess the thermal characteristics, flow features, heat transfer coefficient, and skin friction coefficient. Various factors are taken into consideration, including the impact of Ellis fluid parameters, electric double layer, magnetic field, Brinkman number, and Ohmic dissipation. Ellis fluid's axial velocity boosts with a rise of the electro-osmotic parameter and power-law index while decreasing with an increase in the Hartmann number and material fluid parameter. The fluid temperature is directly proportional to EDL parameter and parameters of Ohmic and viscous dissipation. The presence of both electric and magnetic fields may aid in the management and control of Ellis fluid (blood) mobility at different temperatures, which is helpful in controlling bleeding during surgeries. The current model may be used in clinical scenarios involving the gastrointestinal system and capillaries, electrohydrodynamic therapy, delivery of drugs in pharmacological, and biomedical devices. This research creates a theoretical model that can predict the effects of different parameters on the characteristics of fluid flows that are like blood.}, }
@article {pmid39512462, year = {2024}, author = {Kananipour, M and Mohseni, MM and Jahanmardi, R and Khonakdar, HA}, title = {Heat and mass transfer analysis of s-PTT nanofluid in microchannels under combined electroosmotic and pressure-driven flows with wall slip using the homotopy perturbation method.}, journal = {Heliyon}, volume = {10}, number = {21}, pages = {e39526}, pmid = {39512462}, issn = {2405-8440}, abstract = {The heat and mass transfer of the electroosmotic flow in microchannel transporting viscoelastic nanofluid is investigated considering Brownian motion of nanoparticles and slip boundary conditions. The simplified Phan-Thien-Tanner model is employed to describe the rheological behavior of fluid and the nonlinear Navier model with non-zero slip critical shear stress is considered at walls. The governing nonlinear momentum, mass, and heat transfer equations are solved using the Homotopy Perturbation Method. The study reveals that increasing the fluid elasticity, nanoparticle concentration, and size significantly enhances the flow rate, heat and mass transfer. Additionally, elasticity and Reynolds number decrease the friction factor. Reducing the double-layer thickness and increasing the Reynolds number lead to higher flow rates and fluid velocities. Notably, the findings emphasize the critical role of the slip conditions on the Sherwood and Nusselt numbers.}, }
@article {pmid39507597, year = {2024}, author = {Karyawan,  and Suwasono, B and Supartono,  and Syamsuar, S and Muharam, A and Widyawasta,  and Pane, IZ and Haryanto, I and Tauviqirrahman, M and Yohana, E}, title = {Dataset of the twin floater of amphibian aircraft in wind tunnel test.}, journal = {Data in brief}, volume = {57}, number = {}, pages = {111008}, pmid = {39507597}, issn = {2352-3409}, abstract = {It is well known that seaplanes have twin floaters. Therefore, it is necessary to conduct a wind tunnel test that aims to determine the performance of twin floaters paired on a mock aircraft model. The twin floaters use the same scale as the mock aircraft, which is 1:6.3 with a length of 1555 mm and a distance between floaters of 668.8 mm or S/L of 0.43. The test plan uses a speed of 65 m s[-1] and a Reynolds number 1.5 times the model configuration with flap angle variations of 0°, 10°, 18°, 30°, and 40°. The final test results showed that tabulations and graphs of lift coefficient (CL), drag coefficient (CD), and pitching moment coefficient (CM) with angle of attack (α) variations of -10° to 16°.}, }
@article {pmid39501069, year = {2024}, author = {Venkateswaran, VK and Fernandez-Gamiz, U and Portal-Porras, K and Blanco, JM}, title = {Numerical study on aerodynamics of small scale horizontal axis wind turbine with Weibull analysis.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {26790}, pmid = {39501069}, issn = {2045-2322}, support = {Energ&#xb4;&#x131;a eo&#xb4;lica offshore 348 para el ensayo y el desarrollo energe&#xb4;tico de energ&#xb4;&#x131;as renovables e hidro&#xb4;geno verde//Centro de Investigaciones Energ&#xe9;ticas, Medioambientales y Tecnol&#xf3;gicas/ ; Energ&#xb4;&#x131;a eo&#xb4;lica offshore 348 para el ensayo y el desarrollo energe&#xb4;tico de energ&#xb4;&#x131;as renovables e hidro&#xb4;geno verde//Centro de Investigaciones Energ&#xe9;ticas, Medioambientales y Tecnol&#xf3;gicas/ ; IT1514-22//Ekonomiaren Garapen eta Lehiakortasun Saila, Eusko Jaurlaritza/ ; IT1514-22//Ekonomiaren Garapen eta Lehiakortasun Saila, Eusko Jaurlaritza/ ; }, abstract = {This paper presents a computational fluid dynamics (CFD) analysis and blade element momentum (BEM) analysis of horizontal small-scale wind turbines under various parameters. Random airfoils such as the NACA 0012, NACA 0018, NACA 4412, S1016, S1210, S1223, and SC20402 are chosen, and the glide ratio is analysed. A Reynolds number of 100,000 is considered because of the small wind turbine design. The foil with the highest glide ratio is selected. Various notations are used to represent the chord and the twist angle of the blade, and the blade with the best chord and twist angle is chosen. The lift, drag, and power coefficients and power curves are analysed via the BEM. The power curves are evaluated for different air densities, and a higher value of power is obtained. Finally, via CFD, the SST K - ω model for turbulence is analysed for various angles of attack via Ansys Fluent for different air densities. The results are satisfactory compared with those of the CFD and BEM analyses. The Weibull distribution is analysed to understand the required frequencies for various wind speeds so that the installation of wind turbines can be made convenient in preferred areas with suitable wind properties.}, }
@article {pmid39467183, year = {2024}, author = {Roy, A and Dhar, P}, title = {Capillary Orientation and Morphology Dictated Oscillatory Electro-magneto-imbibition of Viscoelastic Electrolytes.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {40}, number = {45}, pages = {23788-23805}, doi = {10.1021/acs.langmuir.4c02762}, pmid = {39467183}, issn = {1520-5827}, abstract = {We explore the intricate dynamics of imbibition by a viscoelastic electrolyte within an arbitrarily oriented, nonuniform microcapillary, while under the stimulus of external electromagnetic fields and internal electroviscous forces stemming from streaming potential. The microcapillary walls are envisaged to be tapered relative to each other, with the entire system inclined with respect to the horizontal plane. The rheological behavior of the electrolyte is characterized using the Phan-Thien-Tanner (PTT) model. To manipulate the imbibition dynamics, external transverse magnetic and electric fields are imposed. Incorporating all contributing forces, we obtain semianalytical formulations for the velocity and shear stress distributions. We identify distinct stages during the imbibition process: (i) initial, (ii) filling, (iii) oscillatory, and (iv) stagnation stages. Moreover, we scrutinize the impact of four pivotal parameters, namely, the Weissenberg number (Wi), the Hartmann number (Ha), the transverse electric to viscous force (EVF) number (S), and the electric Reynolds number (Ree), on the imbibition dynamics across different inclinations and taper angles. We also delineate the parameter space for these four parameters, identifying where the onset of oscillations occurs. Finally, through scaling analysis, we establish the existence of four distinct regimes corresponding to the aforementioned stages: (i) the linear regime, (ii) the Washburn regime, (iii) the oscillatory regime, and (iv) the equilibrium regime. Our findings are anticipated to enhance the understanding of capillary imbibition under such complex flow conditions and contribute significantly to the advancement of capillarity-driven microfluidic devices.}, }
@article {pmid39451841, year = {2024}, author = {Feraru, MD and Măriuța, D and Stoia-Djeska, M and Grigorie, LT}, title = {Numerical Investigation of an NACA 13112 Morphing Airfoil.}, journal = {Biomimetics (Basel, Switzerland)}, volume = {9}, number = {10}, pages = {}, pmid = {39451841}, issn = {2313-7673}, abstract = {This article presents a numerical study on the 2D aerodynamic characteristics of an airfoil with a morphed camber. The operational regime of the main rotor blade of the IAR 330 PUMA helicopter was encompassed in CFD simulations, performed over an angle of attack range of α=[-3°; 18°], and a Mach number of M=0.38. Various degrees of camber adjustment were smoothly implemented to the trailing-edge section of the NACA13112 airfoil, with a corresponding chord length of c=600 mm at the Reynolds number, Re=5.138×106, and the resulting changes in static lift and drag were calculated. The study examines the critical parameters that affect the configuration of the morphing airfoil, particularly the length of the trailing edge morphing. This analysis demonstrates that increasing the morphed camber near the trailing edge enhances lift capability and indicates that the maximum lift of the airfoil depends on the morphed chord length. The suggested approach demonstrates potential and can be implemented across various categories of aerodynamic structures, such as propeller blade sections, tails, or wings.}, }
@article {pmid39442395, year = {2024}, author = {Moulia, V and Heran, M and Lesage, G and Hamelin, J and Pinta, J and Gazon, A and Penlae, M and Bru-Adan, V and Wéry, N and Ait-Mouheb, N}, title = {Biofilm growth dynamics in a micro-irrigation with reclaimed wastewater in the field scale.}, journal = {Journal of environmental management}, volume = {370}, number = {}, pages = {122976}, doi = {10.1016/j.jenvman.2024.122976}, pmid = {39442395}, issn = {1095-8630}, mesh = {*Biofilms ; *Wastewater ; Biofouling ; Agricultural Irrigation ; Waste Disposal, Fluid/methods ; }, abstract = {The dripper clogging due to the development of biofilm can reduce the benefits of micro-irrigation technology implementation using reclaimed wastewater. The narrow cross-section and labyrinth geometry of the dripper channel enhance the fouling mechanisms. The aim of this study was to evaluate the water distribution and biofouling of drip irrigation systems at the field scale during irrigation with treated wastewater. Six 100 m lines of commercial pipes with two pressure-compensating dripper types (flow rate, Q, of 0.65 L h[-1] and 1.5 L h[-1], respectively) were monitored for four months. Different zones along the pipes were selected to evaluate the influence of hydrodynamical conditions (Reynolds number = 5400 to 0) on biofouling. Destructive methods involving the biofilm extraction by mechanical means, showed little biofilm development without significant differences in dry and organic matter content in function of the sampling location along the pipe or dripper flow rate (Q0.65 and Q1.5). These results were confirmed by non-destructive methods, such as optical coherence tomography, that nevertheless showed that biofouling concerned 15-20% of the total dripper labyrinth volume. Total organic carbon monitoring and its composition (by three-dimensional excitation and emission matrix fluorescence microscopy) showed that the biofilm did not significantly influence the organic matter nature. Our results indicated that the biological activity and biofilm development in irrigation systems were more affected by the environmental conditions, particularly water temperature, rather than flow conditions. This confirmed that treated wastewater with low organic content can be used in micro-irrigation systems without significant loss of efficiency, even in conditions requiring intensive irrigation, such as the Mediterranean climate.}, }
@article {pmid39441889, year = {2024}, author = {Rudyi, S and Shcherbinin, D and Ivanov, A}, title = {Butterflies and bifurcations in surface radio-frequency traps: The diversity of routes to chaos.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {34}, number = {10}, pages = {}, doi = {10.1063/5.0223552}, pmid = {39441889}, issn = {1089-7682}, abstract = {In the present article, we investigate the charged micro-particle dynamics in the surface radio-frequency trap (SRFT). We have developed a new configuration of the SRFT that consists of three curved electrodes on a glass substrate for massive micro-particles trapping. We provide the results of numerical simulations for the dynamical regimes of charged silica micro-particles in the SRFT. Here, we introduce a term of a "main route" to chaos, i.e., the sequence of dynamical regimes for the given particles with the increase of the strength of an electric field. Using the Lyapunov exponent formalism, typical Reynolds number map, Poincaré sections, bifurcation diagrams, and attractor basin boundaries, we have classified three typical main routes to chaos depending on the particle size. Interestingly, in the system described here, all main scenarios of a transition to chaos are implemented, including the Feigenbaum scenario, the Landau-Ruelle-Takens-Newhouse scenario as well as intermittency.}, }
@article {pmid39438574, year = {2024}, author = {Rajenderan, E and Prasad, VR}, title = {Numerical study of magneto convective ag (silver) graphene oxide (GO) hybrid nanofluid in a square enclosure with hot and cold slits and internal heat generation/absorption.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {24868}, pmid = {39438574}, issn = {2045-2322}, abstract = {Energy transmission is widely used in various engineering industries. In recent times, the utilization of hybrid nanofluids has become one of the most popular choices in various industrial fields to increase thermal performance and enhance power generation, entropy reduction, solar collectors, and solar systems. Motivated by this wide range of applications, the present article explores the mixed convection flow and heat transfer of magnetohydrodynamic [Formula: see text] (Silver) and [Formula: see text] (Graphene) nanofluids hybrid nanofluids in a square enclosure with heat generation/absorption by using the MAC method. The vertical walls of the enclosure are assumed to be adiabatic. The horizontal walls are also assumed adiabatic except for the center portion of the top and bottom walls of the cavity. The center portion of the horizontal upper wall is maintained as a cold is [Formula: see text]and the lower wall is maintained as hot [Formula: see text]. The dimension equations are transformed into dimensionless form and then discretized and solved with the finite difference Marker and cell (MAC) method. Numerical modelling is implemented, by changing Richardson number [Formula: see text], The results are located graphically using MATLAB software. The Nusselt number graph was displayed for the Reynolds number (Re), Richardson number[Formula: see text], and Hartmann number [Formula: see text]. The findings show that enhancing the values of the Richardson number and Reynolds number enhances the Nusselt number values except for the Hartmann number. The findings indicate that the combination of the new model is very good at predicting thermal conductivity and correlates experimental results well. The augmenting strength of magnetic force diminishes fluid flow. Developing the coefficients for the heat source and sink improves energy transmission and heat transfer enhancement. Hybrid nanofluids like [Formula: see text] enhance heat transfer and efficiency. They improve cooling in heat exchangers, radiators, and electronics, boost solar energy systems, aid in cancer treatment and drug delivery, enhance geothermal and wind turbine efficiency, and improve manufacturing processes. Overall, they optimize thermal management in various applications.}, }
@article {pmid39436732, year = {2024}, author = {Zheng, K and Liu, Z and Pang, Y and Wang, X and Zhao, S and Zheng, N and Cai, F and Zhang, C}, title = {Predictive Model for Cell Positioning during Periodic Lateral Migration in Spiral Microchannels.}, journal = {Analytical chemistry}, volume = {96}, number = {45}, pages = {18230-18238}, doi = {10.1021/acs.analchem.4c04456}, pmid = {39436732}, issn = {1520-6882}, abstract = {The periodic lateral migration of submicrometer cells is the primary factor leading to low precision in a spiral microchannel during cell isolation. In this study, a mathematical predictive model (PM) is derived for the lateral position of cells during the periodic lateral migration process. We analyze the relationship of migration period, migration width, and starting point of lateral migration with microchannel structure and flow conditions and determine the empirical coefficients in PM. Results indicate that the aspect ratio of the microchannel and the Reynolds number (Re) are key factors that influence the periodicity of the cell lateral migration. The lateral migration width is jointly affected by Re, the cell blockage ratio, and the microchannel curvature radius. The inlet structure of the microchannel and the ratio of the cell sample to the sheath flow rate are critical parameters for regulating the initial position. Moreover, the structure of the pressure field at the inlet constrains the distribution range of the starting point of the lateral migration. Regardless of whether the particles/cells undergo 0.5, 1, or multiple lateral migration cycles, the lateral positions predicted by PM align well with the experimental observations, thus verifying the accuracy of PM. This research helps to elucidate the characteristics of periodic lateral migration of cells in spiral microchannels and can provide practical guidance for the development and optimization of miniature spiral microchannel chips for precise cell isolation.}, }
@article {pmid39436364, year = {2024}, author = {Chen, M and Liu, L and Chen, Y and Wimsatt, J}, title = {Aeroacoustic and aerodynamic measurements at the rotor plane in the interaction of a small rotor with wings.}, journal = {The Journal of the Acoustical Society of America}, volume = {156}, number = {4}, pages = {2816-2826}, doi = {10.1121/10.0032471}, pmid = {39436364}, issn = {1520-8524}, abstract = {Current research on tiltrotor noise predominantly concentrates on configurations with high disk loading and Reynolds numbers, leaving smaller aircraft setups underexplored. This study investigates aeroacoustic and aerodynamic trends resulting from rotor-wing interaction at low disk loading (<100 N/m2) and Reynolds number (Re < 100 000). The experimental setup comprises an anechoic chamber housing a two-blade rotor, flat and National Advisory Committee for Aeronautics 0012 airfoil wings, an ATI mini 40 load cell for aerodynamic data acquisition, and microphones positioned at the rotor height and installed on a rotation stage for acoustic data capture and directivity check. Investigated factors encompass rotor height, rotation direction, revolutions per minute (RPM), and wing curvature. Contrary to expectation, wing curvature does not visibly impact rotor performance. However, the deflected rotor wake in rotor-wing interaction markedly amplifies low-frequency broadband noise and the overall sound pressure level for the tested scenarios. The presence and strength of the deflected rotor wake tend to obscure the primary tonal noise and mitigate the effect of rotor RPM at smaller rotor spacings. This study provides valuable insights into mitigating noise resulting from rotor wake impingement on the wing in smaller aircraft configurations, contributing to the ongoing evolution of urban air mobility design considerations.}, }
@article {pmid39431684, year = {2024}, author = {Schwaar, N and Benke, D and Retsch, M and Goedel, WA}, title = {Float-Cast Microsieves with Elliptical Pores.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {40}, number = {43}, pages = {22516-22525}, pmid = {39431684}, issn = {1520-5827}, abstract = {Polymeric microsieves bearing elliptical pores were successfully prepared via float-casting: a dispersion comprising nonvolatile acrylate monomers and ellipsoidal polystyrene particles was spread onto a water surface. The resulting self-organized monolayer was laterally compressed, and the monomer was photopolymerized, giving rise to a membrane comprising ellipsoidal particles laterally embedded in a 0.5 μm thin polymer membrane. The particles were dissolved, leaving behind elliptical pores. These pores had an average length of the major axis of 0.87 ± 0.1 μm and of the minor axis of 0.42 ± 0.07 μm and an aspect ratio of approximately 2. The microsieve bearing these submicrometric elliptical pores was transferred to a hierarchical structure made out of microsieves bearing circular pores of 6 μm diameter on top of a microsieve with 70 μm diameter pores. The resulting hierarchically structured microsieve had a porosity of 0.13. At a pressure difference of typically 10[3] Pa (Reynolds number aprox. 0.002), the volumetric permeance for water was Pe = V˙/A/Δp = 0.5·10[-6] m/s/Pa, the product viscosity·permeance is η·V˙/A/Δp = 0.5·10[-9] m. This value is lower than the corresponding values of microsieves with circular pores of similar diameter produced by the same technique. The beneficial effects of higher permeance per pore caused by the elliptical shape are countered by lower porosity caused by less efficient packing of the ellipsoidal particles.}, }
@article {pmid39426070, year = {2024}, author = {Xiao, H and Liu, Y and Sun, B and Guo, Y and Wang, M}, title = {Multi-scale modeling of aerosol transport in a mouth-to-truncated bronchial tree system.}, journal = {Computers in biology and medicine}, volume = {183}, number = {}, pages = {109292}, doi = {10.1016/j.compbiomed.2024.109292}, pmid = {39426070}, issn = {1879-0534}, mesh = {*Aerosols ; Humans ; *Models, Biological ; *Bronchi/metabolism ; Computer Simulation ; Mouth ; Hydrodynamics ; }, abstract = {Computational fluid particle dynamics (CFPD) is widely employed to predict aerosol transport in a truncated bronchial tree model on account of its capacity to reveal details of flow field and particle movement. However, setting a physiologically consistent boundary condition in the CFPD for the idealized or image-based truncated bronchial tree model is still a challenge. This paper proposes a multi-scale modeling method, which contains an Extend-Bronchial tree-Network (EBN) boundary condition for a mouth-to-truncated bronchi system. The comparison between EBN boundary condition and a commonly used uniform pressure (UP) boundary condition is conducted. Subsequently, EBN method is used to study the nano-micron (100 nm-10 μm) particles transport in the mouth-to-truncated bronchi model at different inhalation volume rates (15, 60, 90 L/min). Results show that EBN method is more physiologically rational and two methods differ in flow distribution in lobes, vortex structure, and particle transport. The maximum difference in flow rate distribution in lobes between two methods is about 20 %, while the maximum relative disparity of particle penetration fraction from lobes and deposition fraction in the TLB is about 93 % and 30 %, respectively. Meanwhile, this paper reveals the variation of deposition fraction and penetration fraction with the changes in particle diameter and inhalation volume. Deposition efficiency, deposition hotspots and deposition mechanism are also analyzed with inlet Stokes number (Stk) and Reynolds number (Re). This research establishes a foundation for the simulation of aerosol transport in a whole respiratory tract and provides references for inhalation drug delivery and air pollutant management.}, }
@article {pmid39418306, year = {2024}, author = {Coquinot, B and Bocquet, L and Kavokine, N}, title = {Hydroelectric energy conversion of waste flows through hydroelectronic drag.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {121}, number = {43}, pages = {e2411613121}, pmid = {39418306}, issn = {1091-6490}, support = {101071937//EC | ERC | HORIZON EUROPE European Research Council (ERC)/ ; }, abstract = {Hydraulic energy is a key component of the global energy mix, yet there exists no practical way of harvesting it at small scales, from flows with low Reynolds number. This has triggered a search for alternative hydroelectric conversion methodologies, leading to unconventional proposals based on droplet triboelectricity, water evaporation, osmotic energy, or flow-induced ionic Coulomb drag. Yet, these approaches systematically rely on ions as intermediate charge carriers, limiting the achievable power density. Here, we predict that the kinetic energy of small-scale "waste" flows can be directly and efficiently converted into electricity thanks to the hydroelectronic drag effect, by which an ion-free liquid induces an electronic current in the solid wall along which it flows. This effect originates in the fluctuation-induced coupling between fluid motion and electron transport. We develop a nonequilibrium thermodynamic formalism to assess the efficiency of such hydroelectric energy conversion, dubbed hydronic energy. We find that hydronic energy conversion is analogous to thermoelectricity, with the efficiency being controlled by a dimensionless figure of merit. However, in contrast to its thermoelectric analogue, this figure of merit combines independently tunable parameters of the solid and the liquid, and can thus significantly exceed unity. Our findings suggest strategies for blue energy harvesting without electrochemistry, and for waste flow mitigation in membrane-based filtration processes.}, }
@article {pmid39418303, year = {2024}, author = {Ding, L and Sabidussi, LF and Holloway, BC and Hultmark, M and Smits, AJ}, title = {Acceleration is the key to drag reduction in turbulent flow.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {121}, number = {43}, pages = {e2403968121}, pmid = {39418303}, issn = {1091-6490}, abstract = {A turbulent pipe flow experiment was conducted where the surface of the pipe was oscillated azimuthally over a wide range of frequencies, amplitudes, and Reynolds numbers. The drag was reduced by as much as 35%. Past work has suggested that the drag reduction scales with the velocity amplitude of the motion, its period, and/or the Reynolds number. Here, we find that the key parameter is the acceleration, which greatly simplifies the complexity of the phenomenon. This result is shown to apply to channel flows with spanwise surface oscillation as well. This insight opens potential avenues for reducing fuel consumption by large vehicles and for reducing energy costs in large piping systems.}, }
@article {pmid39406736, year = {2024}, author = {Gao, H and Kaltenbach, S and Koumoutsakos, P}, title = {Generative learning for forecasting the dynamics of high-dimensional complex systems.}, journal = {Nature communications}, volume = {15}, number = {1}, pages = {8904}, pmid = {39406736}, issn = {2041-1723}, abstract = {We introduce generative models for accelerating simulations of high-dimensional systems through learning and evolving their effective dynamics. In the proposed Generative Learning of Effective Dynamics (G-LED), instances of high dimensional data are down sampled to a lower dimensional manifold that is evolved through an auto-regressive attention mechanism. In turn, Bayesian diffusion models, that map this low-dimensional manifold onto its corresponding high-dimensional space, operate on batches of physics correlated, time sequences of data and capture the statistics of the system dynamics. We demonstrate the capabilities and drawbacks of G-LED in simulations of several benchmark systems, including the Kuramoto-Sivashinsky (KS) equation, two-dimensional high Reynolds number flow over a backward-facing step, and simulations of three-dimensional turbulent channel flow. The results demonstrate that generative learning offers new frontiers for the accurate forecasting of the statistical properties of high-dimensional systems at a reduced computational cost.}, }
@article {pmid39398115, year = {2024}, author = {Kumar, KR and Shaik, AH}, title = {Novel 2D Layered MXene Nanofluids for Enhancing the Convective Heat Transfer Performance of Double-Pipe Heat Exchangers.}, journal = {ACS omega}, volume = {9}, number = {40}, pages = {41758-41775}, pmid = {39398115}, issn = {2470-1343}, abstract = {This paper proposes a new class of novel 2D layered structured materials, such as MXene (MX), for the synthesis of innovative nanofluids as coolants to evaluate the convective heat transfer performance of a double-pipe heat exchanger (DPHE). Convective heat transfer experiments were successfully conducted in lab-scale fabricated DPHE using low-concentration MXene nanofluids by varying the volume concentration of MXene nanoparticles (0.01-0.05 vol %) in different base fluids. The influence of the MXene nanofluids on various convective heat transfer parameters, such as LMTD, Nusselt number, heat transfer coefficient, and heat transfer rate without using any inserts in the DPHE was experimentally investigated. The results of the experiments revealed that the heat transfer coefficient and Nusselt number increase with increasing Reynolds number (Re) and concentration of MXene nanoparticles in the base fluids. Maximum enhancement in heat transfer coefficient (126%) was achieved for methanol-based MXene nanofluids at 0.05 vol %. Moreover, the Nusselt number exhibits a maximum enhancement of ∼50% for methanol- and water-based MXene nanofluids. In contrast, the thermal performance factor was also estimated, and it was observed that water- and methanol- based MXene nanofluids showed higher values than castor oil- and silicone oil-based MXene nanofluids. Finally, the LMTD and heat transfer coefficients were successfully validated using Aspen HYSYS 12.1 software.}, }
@article {pmid39387629, year = {2024}, author = {Küchler, C and Ibanez Landeta, A and Moláček, J and Bodenschatz, E}, title = {Lagrangian particle tracking at large Reynolds numbers.}, journal = {The Review of scientific instruments}, volume = {95}, number = {10}, pages = {}, doi = {10.1063/5.0211508}, pmid = {39387629}, issn = {1089-7623}, abstract = {In the study of fluid turbulence, the Lagrangian frame of reference represents the most appropriate methodology for investigating transport and mixing. This necessitates the tracking of particles advected by the flow over space and time at high resolution. In the past, the purely spatial counterpart, the Eulerian frame of reference, has been the subject of extensive investigation utilizing hot wire anemometry that employs Taylor's frozen flow hypotheses. Measurements were reported for Taylor scale Reynolds number Rλ > 104 in atmospheric flows, which represent the highest strength of turbulence observed on Earth. The inherent difficulties in accurately tracking particles in turbulent flows have thus far constrained Lagrangian measurements to Taylor scale Reynolds numbers up to approximately Rλ = 103. This study presents the Lagrangian particle tracking setup in the Max Planck Variable Density Turbulence Tunnel (VDTT), where Taylor scale Reynolds numbers between 100 and 6000 can be reached. It provides a comprehensive account of the imaging setup within the pressurized facility, the laser illumination, the particles used, and the particle seeding mechanism employed, as well as a detailed description of the experimental procedure. The suitability of KOBO Cellulobeads D-10 particles as tracers within the VDTT is illustrated. The results demonstrate that there is no significant charge exhibited by the particles and that the impact of their inertia on the results is negligible across a wide range of experimental conditions. Typical data are presented, and the challenges and constraints of the experimental approach are discussed in detail.}, }
@article {pmid39386854, year = {2024}, author = {Das, P and Mamun, MAH}, title = {Predicting MHD mixed convection in a semicircular cavity with hybrid nanofluids using AI.}, journal = {Heliyon}, volume = {10}, number = {19}, pages = {e38303}, pmid = {39386854}, issn = {2405-8440}, abstract = {This study presents a numerical analysis of magnetohydrodynamic (MHD) mixed convection in a semicircular enclosure containing a rotating inner cylinder and filled with nanofluids and hybrid nanofluids. The investigation explores the effects of Al2O3-TiO2-SWCNT-water hybrid nanofluids with varying nanoparticle compositions, as well as Al2O3-water, TiO2-water, and SWCNT-water nanofluids. The analysis includes the development of an artificial neural network (ANN) model to predict outcomes, achieving 97.34 % accuracy in training and 97.41 % in testing for the average Nusselt number. The study examines the impact of Reynolds number (Re), Richardson number (Ri), Hartmann number (Ha), cylinder rotation speed (Ω), cylinder size, and nanoparticle volume fraction (φ) on heat transfer and fluid flow. Key findings include a 6.98 % increase in heat transfer for SWCNT-water nanofluid from Ri = 1 to Ri = 10, a reduction in heat transfer with higher Hartmann numbers, and a significant 21.12 % enhancement when cylinder speed increases to Ω = 10 compared to a stationary cylinder. Larger cylinder sizes also improve convective heat transfer, with a 66.14 % increase for SWCNT-water nanofluid. Additionally, higher concentrations of SWCNT and Al2O3 in hybrid nanofluids enhance heat transfer performance.}, }
@article {pmid39386260, year = {2024}, author = {Wessies, SS and Yang, JC}, title = {On the Nusselt number correlations of tandem surrogate firebrands on a flat surface.}, journal = {Fire safety journal}, volume = {148}, number = {}, pages = {}, pmid = {39386260}, issn = {0379-7112}, support = {9999-NIST/ImNIST/Intramural NIST DOC/United States ; }, abstract = {Through the heat-mass transfer analogy, naphthalene sublimation experiments were conducted in a heated-air wind tunnel to study the effects of aspect ratio and dimensionless separation distance on the convective heat transfer coefficients of three tandem naphthalene cylinders. Nusselt number correlations were presented for the individual naphthalene cylinders and the full configuration of three cylinders. In all the cases studied, the Reynolds number had the strongest effect on the Nusselt number followed by the aspect ratio and the dimensionless separation distance. Nusselt numbers were higher for the smaller aspect ratios. For a given Reynolds number and aspect ratio, the Nusselt number increases with the dimensionless separation distance.}, }
@article {pmid39341974, year = {2024}, author = {Huang, N and Han, S and Zhang, X and Wang, G and Jiang, Y}, title = {Effects of surface roughness and Reynolds number on the solute transport through three-dimensional rough-walled rock fractures under different flow regimes.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {22452}, pmid = {39341974}, issn = {2045-2322}, support = {No. tsqnz20221142//Research Fund for Young Expert of Taishan Scholars Project in Shandong Province/ ; No. 52109132//National Natural Science Foundation of China/ ; No. ZR2019ZD14//Major basic research projects of Natural Science Foundation of Shandong Province/ ; }, abstract = {In this study, the effects of surface roughness and Reynolds number (Re) on fluid flow and solute transport are investigated based on a double rough-walled fracture model that precisely represents the natural geometries of rock fractures. The double rough-walled fracture model is composed of two three-dimensional(3D) self-affine fracture surfaces generated using the improved successive random additions (SRA). Simulation of fluid flow and solute transport through the models were conducted by directly solving the Navier-Stokes equation and advection-diffusion equation (ADE), respectively. The results indicate that as the Re increases from 0.1 to 200, the flow regime changes from linear flow to nonlinear flow accompanied with the tortuous streamlines and significant eddies. Those eddies lead to the temporary stagnant zones that delay the solute migration. The increment of Re enhances the transport heterogeneity with the transport mode changing from the diffusion-dominated to the advection-dominated behavior, which is more significant in the fracture with a larger joint roughness coefficient (JRC). All breakthrough curves (BTCs) of rough-walled fractures exhibited typical non-Fickian transport characteristics with "early arrival" and "long tailing" of BTCs. Increasing the JRC and/or Re will enhances the non-Fickian transport characteristics. The ADE model is able to accurately fit the numerical BTCs and residence time distributions (RTDs) at a low Re, but fails to capture the non-Fickian transport characteristics at a large Re. In contrast, the continuous time random walk (CTRW) model provides a better fit to the numerical simulation results over the whole range of Re. Whereas, the fitting error gradually increases with increasing Re.}, }
@article {pmid39329783, year = {2024}, author = {Li, T and Yang, C and Shao, Z and Chen, Y and Zheng, J and Yang, J and Hu, N}, title = {Fabrication of Patterned Magnetic Particles in Microchannels and Their Application in Micromixers.}, journal = {Biosensors}, volume = {14}, number = {9}, pages = {}, pmid = {39329783}, issn = {2079-6374}, support = {32071408 and 21827812//National Natural Science Foundation of China/ ; }, mesh = {*Lab-On-A-Chip Devices ; Microfluidic Analytical Techniques ; Microfluidics ; Dimethylpolysiloxanes/chemistry ; Magnetics ; }, abstract = {Due to the extremely low Reynolds number, the mixing of substances in laminar flow within microfluidic channels primarily relies on slow intermolecular diffusion, whereas various rapid reaction and detection requirements in lab-on-a-chip applications often necessitate the efficient mixing of fluids within short distances. This paper presents a magnetic pillar-shaped particle fabrication device capable of producing particles with planar shapes, which are then utilized to achieve the rapid mixing of multiple fluids within microchannels. During the particle fabrication process, a degassed PDMS chip provides self-priming capabilities, drawing in a UV-curable adhesive-containing magnetic powder and distributing it into distinct microwell structures. Subsequently, an external magnetic field is applied, and the chip is exposed to UV light, enabling the mass production of particles with specific magnetic properties through photo-curing. Without the need for external pumping, this chip-based device can fabricate hundreds of magnetic particles in less than 10 min. In contrast to most particle fabrication methods, the degassed PDMS approach enables self-priming and precise dispensing, allowing for precise control over particle shape and size. The fabricated dual-layer magnetic particles, featuring fan-shaped blades and disk-like structures, are placed within micromixing channels. By manipulating the magnetic field, the particles are driven into motion, altering the flow patterns to achieve fluid mixing. Under conditions where the Reynolds number in the chip ranges from 0.1 to 0.9, the mixing index for substances in aqueous solutions exceeds 0.9. In addition, experimental analyses of mixing efficiency for fluids with different viscosities, including 25 wt% and 50 wt% glycerol, reveal mixing indices exceeding 0.85, demonstrating the broad applicability of micromixers based on the rapid rotation of magnetic particles.}, }
@article {pmid39329575, year = {2024}, author = {Moscato, G and Romano, GP}, title = {Biomimetic Wings for Micro Air Vehicles.}, journal = {Biomimetics (Basel, Switzerland)}, volume = {9}, number = {9}, pages = {}, pmid = {39329575}, issn = {2313-7673}, abstract = {In this work, micro air vehicles (MAVs) equipped with bio-inspired wings are investigated experimentally in wind tunnel. The starting point is that insects such as dragonflies, butterflies and locusts have wings with rigid tubular elements (corrugation) connected by flexible parts (profiling). So far, it is important to understand the specific aerodynamic effects of corrugation and profiling as applied to conventional wings for the optimization of low-Reynolds-number aerodynamics. The present study, in comparison to previous investigations on the topic, considers whole MAVs rather than isolated wings. A planform with a low aperture-to-chord ratio is employed in order to investigate the interaction between large tip vortices and the flow over the wing surface at large angles of incidence. Comparisons are made by measuring global aerodynamic loads using force balance, specifically drag and lift, and detailed local velocity fields over wing surfaces, by means of particle image velocimetry (PIV). This type of combined global-local investigation allows describing and relating overall MAV performance to detailed high-resolution flow fields. The results indicate that the combination of wing corrugation and profiling gives effective enhancements in performance, around 50%, in comparison to the classical flat-plate configuration. These results are particularly relevant in the framework of low-aspect-ratio MAVs, undergoing beneficial interactions between tip vortices and large-scale separation.}, }
@article {pmid39323288, year = {2024}, author = {Carrazco-Escalante, M and Hernández-Calderón, &#xd3; and Ríos-Iribe, E and Alarid-García, C and Iribe-Salazar, R and Vázquez-López, Y and Caro-Hernández, O and Pacheco-Plata, F and Caro-Corrales, J}, title = {Heat transfer and friction factor analysis for tomato puree flowing in a concentric-tube heat exchanger.}, journal = {Journal of food science}, volume = {89}, number = {11}, pages = {7729-7746}, doi = {10.1111/1750-3841.17396}, pmid = {39323288}, issn = {1750-3841}, mesh = {*Solanum lycopersicum/chemistry ; *Hot Temperature ; *Rheology ; *Friction ; Food Handling/methods ; Hydrodynamics ; }, abstract = {The heat and momentum transfer of tomato puree through a concentric-tube heat exchanger over a range of generalized Reynolds number (0.05 < Re < 66.5) was experimentally and numerically analyzed. Thermophysical and rheological properties of tomato puree (12°Brix) were measured from 20 to 60°C. The velocity, pressure, and temperature were calculated using the computational fluid dynamics (CFD) software FLUENT[TM] with temperature-dependent transport properties. The thermal operation of the concentric-tube exchanger was satisfactorily predicted using CFD, indicating accurate measurement of tomato puree properties with temperature variations. A concordance was found between the calculated Fanning friction factor and generalized Reynolds with the experimental correlation. A modified Sieder-Tate correlation was established, which allows properly expressing the Nusselt number as a function of the Peclet number. Simple correlations for the mechanical work and the heat transfer rate as a function of the volumetric flow rate were derived. The thermal efficiency was high at low puree flow rates but decreased with higher rates. However, at high flow rates, ceased its decline, instead showing a slight improvement. The analysis confirmed higher heat transfer rates in the concentric-tube heat exchanger compared to a plain tube at low puree flow rates. The results offer valuable insights for assessing diverse operational conditions in dairy, beverage, sauce, and concentrated food industries. Additionally, they also enhance the analysis and design of concentric-tube heat exchangers. PRACTICAL APPLICATION: The knowledge of the rheological and hydrodynamical behavior of fluids in concentric-tube heat exchangers allows to explore a set of different operating conditions to improve the yield and effectiveness on the system heating/cooling design.}, }
@article {pmid39319149, year = {2024}, author = {Ali, MY and Islam, S and Alim, MA and Biplob, RA and Islam, MZ}, title = {Numerical investigation of MHD mixed convection in an octagonal heat exchanger containing hybrid nanofluid.}, journal = {Heliyon}, volume = {10}, number = {17}, pages = {e37162}, pmid = {39319149}, issn = {2405-8440}, abstract = {Nowadays, the advancement of heat transmission for the heat exchanger device is an important field of research for many researchers. In this work, a numerical study has been conducted to investigate the thermal performance of a mixed convective flow through the octagonal heat exchanger covered by hybrid nanofluid (Cu-TiO2-H2O). A magnetic field has been introduced inside the cavity to investigate the mixed convective hydrodynamics heat flow characteristics. The nanofluid cores absorb/release energy to manage heat transmission by increasing or decreasing inside the cavity domain as the host fluid and dispersed hybrid nanofluid circulate within the cavity. After transforming the governing equations into a generalized, non-dimensional formulation, the finite element approach is utilized to solve the associated equations. Additionally, response surface methodology is also applied to test the responses of the associated factors. Heat transport was examined in relation to the effects of nanofluids fusion temperature, boundary wall properties, Reynolds number, Hartmann number and nanoparticle volume fractions. The outcomes of this study are analysed by measuring streamline profiles, isotherms, average Nusselt number, velocity profile, and 2D and 3D response surfaces of the computational domain. The underlying flow controlling parameters for instance Reynolds number (10 ≤ Re ≤ 200), Hartmann number (0 ≤ Ha ≤100), and nanoparticle volume fractions (0 ≤ ϕ ≤ 0.1), the influences have been considered. The findings also reveal that the thermal performance is being boosted due to augmentation of Re and ϕ, but reverse behavior is noticed for Ha. Furthermore, the response surfaces obtained from response surfaces methodology express that the Re and ϕ have shown positive influence, and Ha has shown negative influence on Nuav. Utilizing a hybrid nanofluid of Cu-TiO2-H2O increases the heat transfer capacity of water to 25.75 %. Moreover, the findings could guide to design of a mixed convective heat exchanger for industrial purposes.}, }
@article {pmid39314537, year = {2024}, author = {Takyi, J and Beem, HR}, title = {Design &amp; automation of a small-scale towing tank for flow visualization.}, journal = {HardwareX}, volume = {20}, number = {}, pages = {e00585}, pmid = {39314537}, issn = {2468-0672}, abstract = {Although the towing tank is a standard piece of equipment used to investigate fluid phenomena, it primarily exists as custom-built hardware that takes up a significant footprint. The size, cost, and custom-built nature have heretofore inhibited the production of this equipment in the authors' context, an African university. This paper presents a small-scale (1000 mm x 200 mm x 200 mm), low-cost (<$1,000) towing tank made using readily available components and basic digital fabrication tools. Other universities on the continent and beyond can hence create this foundational platform for fluid mechanics-related teaching and research. Leveraging an Arduino microcontroller loaded with the GRBL firmware, G-code is sent from the computer to stepper motors to execute movements in two axes. This allows for automation capabilities, controlled towing speeds, and consistent experimental conditions. Validation tests revealed motion accuracy within 1 %. A glitter-based flow visualization approach to measuring surface phenomena is demonstrated here. Experiments conducted successfully visualized relevant flow characteristics generated by bluff bodies being towed in the tank. As the Reynolds number increased within the operating range, wider wakes and larger, more distinct vortices were generated, as expected. This platform can be replicated widely in institutions that may otherwise forego experimentation in fluid mechanics.}, }
@article {pmid39302246, year = {2024}, author = {Gomez, M and Montalvo, S and Sanchez, A and Conde, D and Ibarra-Mejia, G and Peñailillo, LE and Gurovich, AN}, title = {Effects of Different Eccentric Cycling Intensities on Brachial Artery Endothelial Shear Stress and Blood Flow Patterns.}, journal = {Research quarterly for exercise and sport}, volume = {}, number = {}, pages = {1-11}, doi = {10.1080/02701367.2024.2404139}, pmid = {39302246}, issn = {2168-3824}, abstract = {Eccentric exercise has gained attention as a novel exercise modality that increases muscle performance at a lower metabolic demand. However, vascular responses to eccentric cycling (ECC) are unknown, thus gaining knowledge regarding endothelial shear stress (ESS) during ECC may be crucial for its application in patients. The purpose of this study was to explore ECC-induced blood flow patterns and ESS across three different intensities in ECC. Eighteen young, apparently healthy subjects were recruited for two laboratory visits. Maximum oxygen consumption, power output, and blood lactate (BLa) threshold were measured to determine workload intensities. Blood flow patterns in the brachial artery were measured via ultrasound imaging and Doppler on an eccentric ergometer during a 5 min workload steady exercise test at low (BLa of 0-2 mmol/L), moderate (BLa 2-4 mmol/L), and high intensity (BLa levels > 4 mmol/L). There was a significant increase in the antegrade ESS in an intensity-dependent manner (baseline: 44.2 ± 8.97; low: 55.6 ± 15.2; moderate: 56.0 ± 10.5; high: 70.7 ± 14.9, all dynes/cm2, all p values < 0.0002) with the exception between low and moderate and Re (AU) showed turbulent flow at all intensities. Regarding retrograde flow, ESS also increased in an intensity-dependent manner (baseline 9.72 ± 4.38; low: 12.5 ± 3.93; moderate: 15.8 ± 5.45; high: 15.7 ± 6.55, all dynes/cm2, all p values < 0.015) with the exception between high and moderate and Re (AU) showed laminar flow in all intensities. ECC produced exercise-induced blood flow patterns that are intensity-dependent. This suggests that ECC could be beneficial as a modulator of endothelial homeostasis.}, }
@article {pmid39294953, year = {2024}, author = {Sznajder, P and Zdybel, P and Liu, L and Ekiel-Jeżewska, ML}, title = {Scaling law for a buckled elastic filament in a shear flow.}, journal = {Physical review. E}, volume = {110}, number = {2-2}, pages = {025104}, doi = {10.1103/PhysRevE.110.025104}, pmid = {39294953}, issn = {2470-0053}, abstract = {We analyze the three-dimensional (3D) buckling of an elastic filament in a shear flow of a viscous fluid at low Reynolds number and high Péclet number. We apply the Euler-Bernoulli beam (elastica) theoretical model. We show the universal character of the full 3D spectral problem for a small perturbation of a thin filament from a straight position of arbitrary orientation. We use the eigenvalues and eigenfunctions for the linearized elastica equation in the shear plane, found earlier by Liu et al. [Phys. Rev. Fluids 9, 014101 (2024)2469-990X10.1103/PhysRevFluids.9.014101] with the Chebyshev spectral collocation method, to solve the full 3D eigenproblem. We provide a simple analytic approximation of the eigenfunctions, represented as Gaussian wave packets. As the main result of the paper, we derive the square-root dependence of the eigenfunction wave number on the parameter χ[over ̃]=-ηsin2ϕsin^{2}θ, where η is the elastoviscous number and the filament orientation is determined by the zenith angle θ with respect to the vorticity direction and the azimuthal angle ϕ relative to the flow direction. We also compare the eigenfunctions with shapes of slightly buckled elastic filaments with a non-negligible thickness with the same Young's modulus, using the bead model and performing numerical simulations with the precise hydromultipole numerical codes.}, }
@article {pmid39277710, year = {2024}, author = {Ueki, N and Wakabayashi, KI}, title = {Multicellularity and increasing Reynolds number impact on the evolutionary shift in flash-induced ciliary response in Volvocales.}, journal = {BMC ecology and evolution}, volume = {24}, number = {1}, pages = {119}, pmid = {39277710}, issn = {2730-7182}, mesh = {*Cilia/physiology ; *Biological Evolution ; Chlorophyta/physiology/genetics ; Volvox/genetics/physiology ; Light ; }, abstract = {BACKGROUND: Volvocales in green algae have evolved by multicellularity of Chlamydomonas-like unicellular ancestor. Those with various cell numbers exist, such as unicellular Chlamydomonas, four-celled Tetrabaena, and Volvox species with different cell numbers (~1,000, ~5,000, and ~10,000). Each cell of these organisms shares two cilia and an eyespot, which are used for swimming and photosensing. They are all freshwater microalgae but inhabit different fluid environments: unicellular species live in low Reynolds-number (Re) environments where viscous forces dominate, whereas multicellular species live in relatively higher Re where inertial forces become non-negligible. Despite significant changes in the physical environment, during the evolution of multicellularity, they maintained photobehaviors (i.e., photoshock and phototactic responses), which allows them to survive under changing light conditions.<br><br>RESULTS: In this study, we utilized high-speed imaging to observe flash-induced changes in the ciliary beating manner of 27 Volvocales strains. We classified flash-induced ciliary responses in Volvocales into four patterns: "1: temporal waveform conversion", "2: no obvious response", "3: pause in ciliary beating", and "4: temporal changes in ciliary beating directions". We found that which species exhibit which pattern depends on Re, which is associated with the individual size of each species rather than phylogenetic relationships.<br><br>CONCLUSIONS: These results suggest that only organisms that acquired different patterns of ciliary responses survived the evolutionary transition to multicellularity with a greater number of cells while maintaining photobehaviors. This study highlights the significance of the Re as a selection pressure in evolution and offers insights for designing propulsion systems in biomimetic micromachines.}, }
@article {pmid39270724, year = {2024}, author = {Herrera-Amaya, A and Byron, ML}, title = {Propulsive efficiency of spatiotemporally asymmetric oscillating appendages at intermediate Reynolds numbers.}, journal = {Bioinspiration &amp; biomimetics}, volume = {}, number = {}, pages = {}, doi = {10.1088/1748-3190/ad7abf}, pmid = {39270724}, issn = {1748-3190}, abstract = {Many organisms use flexible appendages for locomotion, feeding, and other functional behaviors. The efficacy of these behaviors is determined in large part by the fluid dynamics of the appendage interacting with its environment. For oscillating appendages at low Reynolds numbers, viscosity dominates over inertia, and appendage motion must be spatially asymmetric to generate net flow. At high Reynolds numbers, viscous forces are negligible and appendage motion is often also temporally asymmetric, with a fast power stroke and a slow recovery stroke; such temporal asymmetry does not affect the produced flow at low Reynolds numbers. At intermediate Reynolds numbers, both viscous and inertial forces play non-trivial roles---correspondingly, both spatial and temporal asymmetry can strongly affect overall propulsion. Here we perform experiments on three robotic paddles with different material flexibilities and geometries, allowing us to explore the effects of motion asymmetry (both spatial and temporal) on force production. We show how a flexible paddle's time-varying shape throughout the beat cycle can reorient the direction of the produced force, generating both thrust and lift. We also evaluate the propulsive performance of the paddle by introducing a new quantity, which we term "integrated efficiency". This new definition of propulsive efficiency can be used to directly evaluate an appendage's performance independently from full-body swimming dynamics. Use of the integrated efficiency allows for accurate performance assessment, generalization, and comparison of oscillating appendages in both robotic devices and behaving organisms. Finally, we show that a curved flexible paddle generates thrust more efficiently than a straight paddle, and produces spatially asymmetric motion---thereby improving performance---without the need for complex actuation and controls, opening new avenues for bioinspired technology development.}, }
@article {pmid39269970, year = {2024}, author = {Hudha, MN and Hasan, MJ and Bairagi, T and Azad, AK and Rahman, MM}, title = {Artificial Neural Network analysis on the effect of mixed convection in triangular-shaped geometry using water-based Al2O3 nanofluid.}, journal = {PloS one}, volume = {19}, number = {9}, pages = {e0304826}, pmid = {39269970}, issn = {1932-6203}, mesh = {*Neural Networks, Computer ; *Aluminum Oxide/chemistry ; *Water/chemistry ; *Convection ; Hydrodynamics ; Finite Element Analysis ; }, abstract = {The objective of the study is to investigate the fluid flow and heat transfer characteristics applying Artificial Neural Networks (ANN) analysis in triangular-shaped cavities for the analysis of magnetohydrodynamics (MHD) mixed convection with varying fluid velocity of water/Al2O3 nanofluid. No study has yet been conducted on this geometric configuration incorporating ANN analysis. Therefore, this study analyzes and predicts the complex interactions among fluid flow, heat transfer, and various influencing factors using ANN analysis. The process of finite element analysis was conducted, and the obtained results have been verified by previous literature. The Levenberg-Marquardt backpropagation technique was selected for ANN. Various values of the Richardson number (0.01 ≤ Ri ≤ 5), Hartmann number (0 ≤ Ha ≤ 100), Reynolds number (50 ≤ Re ≤ 200), and solid volume fraction of the nanofluid (ϕ = 1%, 3% and 4%) have been selected. The ANN model incorporates the Gauss-Newton method and the method of damped least squares, making it suitable for tackling complex problems with a high degree of non-linearity and uncertainty. The findings have been shown through the use of streamlines, isotherm plots, Nusselt numbers, and the estimated Nusselt number obtained by ANN. Increasing the solid volume fraction improves the rate of heat transmission for all situations with varying values of Ri, Re, and Ha. The Nusselt number is greater with larger values of the Ri and Re parameters, but it lessens for higher value of Ha. Furthermore, ANN demonstrates exceptional precision, as evidenced by the Mean Squared Error and R values of 1.05200e-6 and 0.999988, respectively.}, }
@article {pmid39261548, year = {2024}, author = {Guo, Y and Zou, H and Wei, F and Li, Q and Guo, D and Pirov, J}, title = {Analysis of pedestrian second crossing behavior based on physics-informed neural networks.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {21278}, pmid = {39261548}, issn = {2045-2322}, support = {Z2023178//Undergraduate Education Reform in Shandong Province/ ; M2022179//Undergraduate Education Reform in Shandong Province/ ; 52272343//Foundation for Innovative Research Groups of the National Natural Science Foundation of China/ ; }, abstract = {Pedestrian two-stage crossings are common at large, busy signalized intersections with long crosswalks and high traffic volumes. This design aims to address pedestrian operation and safety by allowing navigation in two stages, negotiating each traffic direction separately. Understanding crosswalk behavior, especially during bidirectional interactions, is essential. This paper presents a two-stage pedestrian crossing model based on Physics-Informed Neural Networks (PINNs), incorporating fluid dynamics equations to determine characteristics such as speed, density, acceleration, and Reynolds number during crossings. The study shows that PINNs outperform traditional deep learning methods in calculating and predicting pedestrian fluid properties, achieving a mean squared error as low as 10[-8]. The model effectively captures dynamic pedestrian flow characteristics and provides insights into pedestrian behavior impacts. The results are significant for designing pedestrian facilities to ensure comfort and optimizing signal timing to enhance mobility and safety. Additionally, these findings can aid autonomous vehicles in better understanding pedestrian intentions in intelligent transportation systems.}, }
@article {pmid39247324, year = {2024}, author = {Tavakoli, MR and Akbari, OA and Mohammadian, A and Pourfattah, F}, title = {Investigation of the effect of rectangular winglet angles on turbulent flow and heat transfer of water/Cu nanofluid in a three-dimensional channel.}, journal = {Heliyon}, volume = {10}, number = {16}, pages = {e36482}, pmid = {39247324}, issn = {2405-8440}, abstract = {This numerical simulation studies a homogenous and single-phase nanofluid's turbulent flow and heat transfer behavior in a three-dimensional rectangular microchannel. This study's main purpose is to investigate the use of rectangular winglet angles on flow path and its effect on turbulent flow regime and heat transfer parameters. In the current study, the Reynolds number, winglet attack angle (θ), and twisted angle range (α) (or Pitch angle) from 3000 to 12000, 30°≤ θ ≤ 60°, and 15°≤α ≤ 45°, respectively. Also, Cu nanoparticles with volume fractions of 0-4% are used in water as the base fluid. Results of this study show that heat transfer and flow physics of cooling fluid are affected by the variations of attack angle and winglet twist, and the creation of secondary flows leads to the mixture and deviation of flow. A decrease in the attack angle of the winglet causes the creation of strong vortexes and an increase in Nusselt number and heat transfer. In all investigated situations, with the angle of attack constant, increasing the twist angle can improve the Nusselt number between 11 and 18 percent. Also, increasing the angle of attack of the winglet from 30 to 60° can reduce the Nusselt number by 4-8 percent. The results indicate that changing the winglet angle increases the friction coefficient, and at higher Reynolds numbers, this parameter decreases. Also, by increasing Reynolds number, the ratio of friction coefficient to Nusselt number reduces, leading to the decrease of performance evaluation criterion (PEC).}, }
@article {pmid39239773, year = {2024}, author = {Grigor, E and Carver, J and Bulan, E and Scott, S and Chew, YJ and Perera, S}, title = {A New Generation of Activated Carbon Adsorbent Microstructures.}, journal = {Advanced science (Weinheim, Baden-Wurttemberg, Germany)}, volume = {11}, number = {42}, pages = {e2406551}, pmid = {39239773}, issn = {2198-3844}, support = {//Avon Protection - Melksham, UK, SN12 6NB/ ; //Defence Science and Technology Laboratory - Salisbury, UK, SP4 0JQ/ ; //University of Bath - Bath, UK, BA2 7AY/ ; }, abstract = {This work presents the successful manufacture and characterization of bespoke carbon adsorbent microstructures such as tessellated (TES) or serpentine spiral grooved (SSG) by using 3D direct light printing. This is the first time stereolithographic printing has been used to exert precise control over specific micromixer designs to quantify the impact of channel structure on the removal of n-butane. Activated microstructures achieved nitrogen Brunauer Emmett Teller (BET) surface areas up to 1600 m[2] g[-1] while maintaining uniform channel geometries. When tested with 1000 ppm n-butane at 1 L min[-1], the microstructures exceeded the equilibrium loading of commercial carbon-packed beds by over 40%. Dynamic adsorption breakthrough testing using a constant Reynolds number (Re 80) shows that complex micromixer designs surpassed simpler geometries, with the SSG geometry achieving a 41% longer breakthrough time. Shorter mass transfer zones were observed in all the complex geometries, suggesting superior kinetics and carbon structure utilization as a result of the micromixer-based etched grooves and interlinked channels. Furthermore, pressure drop testing demonstrates that all microstructures had half the pressure drop of commercial carbon-packed beds. This study shows the power of leveraging 3D printing to produce optimized microstructures, providing a glimpse into the future of high-performance gas separation.}, }
@article {pmid39236358, year = {2024}, author = {Gritti, F and Chen, EY and Datta, SS}, title = {Harnessing an elastic flow instability to improve the kinetic performance of chromatographic columns.}, journal = {Journal of chromatography. A}, volume = {1735}, number = {}, pages = {465326}, doi = {10.1016/j.chroma.2024.465326}, pmid = {39236358}, issn = {1873-3778}, mesh = {Chromatography, High Pressure Liquid/methods ; Kinetics ; *Acrylic Resins/chemistry ; Elasticity ; }, abstract = {Despite decades of research and development, the optimal efficiency of slurry-packed HPLC columns is still hindered by inherent long-range flow heterogeneity from the wall to the central bulk region of these columns. Here, we show an example of how this issue can be addressed through the straightforward addition of a semidilute amount (500 ppm) of a large, flexible, synthetic polymer (18 MDa partially hydrolyzed polyacrylamide, HPAM) to the mobile phase (1% NaCl aqueous solution, hereafter referred to as "brine") during operation of a 4.6 mm × 300 mm column packed with 10μm BEH[TM] 125 Å particles. Addition of the polymer imparts elasticity to the mobile phase, causing the flow in the interparticle pore space to become unstable above a threshold flow rate. We verify the development of this elastic flow instability using pressure drop measurements of the friction factor versus Reynolds number. In prior work, we showed that this flow instability is characterized by large spatiotemporal fluctuations in the pore-scale flow velocities that may promote analyte dispersion across the column. Axial dispersion measurements of the quasi non-retained tracer thiourea confirm this possibility: they reveal that operating above the onset of the instability improves column efficiency by greater than 100%. These experiments thereby suggest that elastic flow instabilities can be harnessed to mitigate the negative impact of trans-column flow heterogeneities on the efficiency of slurry-packed HPLC columns. While this approach has its own inherent limitations and constraints, our results lay the groundwork for future targeted development of polymers that can impart elasticity when dissolved in commonly used liquid chromatography mobile phases, and can thereby generate elastic flow instabilities to help improve the resolution of HPLC columns.}, }
@article {pmid39220585, year = {2024}, author = {Harte, NC and Obrist, D and Caversaccio, M and Lajoinie, GPR and Wimmer, W}, title = {Transverse flow under oscillating stimulation in helical square ducts with cochlea-like geometrical curvature and torsion.}, journal = {European journal of mechanics. B, Fluids}, volume = {107}, number = {}, pages = {165-174}, pmid = {39220585}, issn = {0997-7546}, abstract = {The cochlea, situated within the inner ear, is a spiral-shaped, liquid-filled organ responsible for hearing. The physiological significance of its shape remains uncertain. Previous research has scarcely addressed the occurrence of transverse flow within the cochlea, particularly in relation to its unique shape. This study aims to investigate the impact of the geometric features of the cochlea on fluid dynamics by characterizing transverse flow induced by harmonically oscillating axial flow in square ducts with curvature and torsion resembling human cochlear anatomy. We examined four geometries to investigate curvature and torsion effects on axial and transverse flow components. Twelve frequencies from 0.125 Hz to 256 Hz were studied, covering infrasound and low-frequency hearing, with mean inlet velocity amplitudes representing levels expected for normal conversation or louder situations. Our simulations show that torsion contributes significantly to transverse flow in unsteady conditions, and that its contribution increases with increasing oscillation frequency. Curvature alone has a small effect on transverse flow strength, which decreases rapidly with increasing frequency. Strikingly, the combined effect of curvature and torsion on transverse flow is greater than expected from a simple superposition of the two effects, especially when the relative contribution of curvature alone becomes negligible. These findings may be relevant to understanding physiological processes in the cochlea, including metabolite transport and wall shear stress. Further studies are needed to investigate possible implications for cochlear mechanics.}, }
@article {pmid39181970, year = {2024}, author = {Zaman, SU and Hussain, A and Ashraf, K and Sarwar, L and Hussain, F and Altalbe, A and Bekir, A and Muhammad, T}, title = {Mathematical analysis of isothermal study of reverse roll coating using Micropolar fluid.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {19709}, pmid = {39181970}, issn = {2045-2322}, support = {(PSAU/2024/01/921063)//Ali Altalbe/ ; }, abstract = {This article demonstrates a mathematical model and theoretical analysis of the Micropolar fluid in the reverse roll coating process. It is important because micropolar fluids account for the microstructure and microrotation of particles within the fluid. These characteristics are significant for accurately describing the behavior of complex fluids such as polymer solutions, biological fluids, and colloidal suspensions. First, we modeled the flow equations using basic laws of fluid dynamics. The flow equations are made modified using low Reynolds number theory. The simplified equations are solved analytically. The exact expression for velocity and pressure gradient are obtained, while pressure is calculated numerically using Simpson Rule. Graphical depictions are carried out to comprehend the impact of the newly emerged physical constraints. The influence of micropolar and microrotation parameters on the velocity, pressure and pressure gradient are elaborated with the help of different graphs.}, }
@article {pmid39180481, year = {2024}, author = {Lyons, BM and Maynes, D and Crockett, J and Iverson, BD}, title = {Drop Retention and Departure in Adiabatic Shear Flow on Structured Superhydrophobic Surfaces.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {40}, number = {36}, pages = {18882-18895}, doi = {10.1021/acs.langmuir.4c00777}, pmid = {39180481}, issn = {1520-5827}, abstract = {Drops are retained or held on surfaces due to a retention force exerted on the drop by the surface. This retention force is a function of the surface tension of the liquid, drop geometry, and the contact angle between the drop and the surface. When external or body forces exceed the retention force, the drop begins to move. This work explores the conditions for which drop departure occurs on structured superhydrophobic surfaces in the presence of an applied shear flow. Drop departure is explored for five microstructured superhydrophobic surfaces, one nanostructured carbon nanotube surface and one smooth hydrophobic surface. Surface solid fractions range from 0.05 to 1.00, and measured static contact angles range from 121° to 161°. Droplet volumes of 5, 10, 20, 30, 40, and 50 μL are tested on each surface. For each experiment, increasing air velocity is applied to a droplet placed on a surface until the droplet departs. High-speed imaging is used to track droplet base length, height, cross-section area (as viewed from the side) and advancing/receding contact angles. Measurements of drop advancing and receding contact angles are reported at the point of departure, with increasing contact angle hysteresis observed prior to departure. Contact angle hysteresis is observed to be a good indicator of droplet mobility. Measurements of the average air velocity over the height of the droplet are determined at the point of departure for all conditions. The measured air velocity shows strong dependence on the surface solid fraction, and the required shear flow velocity decreases as the surface solid fraction decreases. This is most pronounced at very low solid fractions. A coefficient of drag for the departing drops in shear flow is calculated and is shown to decrease with increasing Reynolds number.}, }
@article {pmid39175794, year = {2024}, author = {Gerolymos, GA and Vallet, I}, title = {Compressible turbulent plane channel DNS datasets.}, journal = {Data in brief}, volume = {55}, number = {}, pages = {110737}, pmid = {39175794}, issn = {2352-3409}, abstract = {The database contains detailed statistics of compressible turbulent plane channel (TPC) flow, obtained from direct numerical simulation (DNS), with a very-high-order massively parallel solver of the compressible Navier-Stokes equations. It contains datasets for 25 different flow conditions determined by the corresponding HCB friction Reynolds number and centerline Mach number, covering the ranges 100 ⪅ R e τ ★ ⪅ 1000 and 0.3 ⪅ M ¯ CL x ⪅ 2.5 . All calculations are for strictly isothermal wall conditions at temperature T w = 298 K in a medium-size (MB) computational box (8 π δ × 2 δ × 4 π δ where 2 δ is the channel-height). Statistics (moments and pdfs) were collected after the elimination of the transient, and post-processed to create the dataset, which contains only plain text (.txt) space-separated multicolumn files for ease of use. The dataset for each flow-condition is tagged by the values of (R e τ ★ , M ¯ CL x) and is organized in 4 directories: (0) global data files, (1) profiles and budgets (meanflow profiles, velocity-moments up to 6-order, budgets of Reynolds-stresses transport, turbulent fluxes appearing in transport equations for velocity-moments and thermodynamic quantities, correlation coefficients between thermodynamic variables, and skewness and flatness profiles) as a function of the wall-distance, (2) single-variable probability density functions (pdfs) for numerous flow quantities at selected wall-normal distances, and (3) two-variable joint pdfs for numerous couples of flow-quantities at the same selected wall-normal distances.}, }
@article {pmid39170061, year = {2024}, author = {Morley, EJ and Brockett, CL and Verbruggen, SW}, title = {Analytical and computational studies predict negligible risk of cell death from eddy generation off flat surfaces in cell culture flow systems.}, journal = {Frontiers in bioengineering and biotechnology}, volume = {12}, number = {}, pages = {1340653}, pmid = {39170061}, issn = {2296-4185}, abstract = {Cell-based therapies represent the current frontier of biomedical innovations, with the technologies required underpinning treatments as broad as CAR-T cell therapies, stem cell treatments, genetic therapies and mRNA manufacture. A key bottleneck in the manufacturing process for each of these lies in the expansion of cells within a bioreactor vessel, requiring by far the greatest share of time for what are often time-critical therapies. While various designs, culture feeding and mixing methods are employed in these bioreactors, a common concern among manufacturers and researchers lies in whether shear stresses generated by culture media flow will damage cells and inhibit expansion. This study develops an analytical tool to link macro-scale measures of flow to risk of cell death using relationships with eddy size and dissipation rates, from eddies generated off flat surfaces. This analytical tool was then employed using computational fluid dynamics (CFD) to replicate a range of generic bioreactor geometries and flow conditions. We found that no combination of flow condition or design parameter was predicted by the tool to cause cell death within eddies, indicating negligible risk of cell death due to eddy formation within cell culture systems. While this requires experimental validation, and does not apply when cells are expanded using microcarriers, this tool nonetheless provides reassurance and accessible prediction of bioreactor design parameters that could result in cell death. Finally, our findings show that bioreactor design can be tailored such that the shear stress stimulation of cells can be selectively altered through small changes in flow rate.}, }
@article {pmid39166020, year = {2024}, author = {Ahmadi Azar, A and Jalili, P and Poolaei Moziraji, Z and Jalili, B and Domiri Ganji, D}, title = {Analytical solution for MHD nanofluid flow over a porous wedge with melting heat transfer.}, journal = {Heliyon}, volume = {10}, number = {15}, pages = {e34888}, pmid = {39166020}, issn = {2405-8440}, abstract = {This study employs the Hybrid Analytical-Numerical (HAN) method to investigate steady two-dimensional magnetohydrodynamic (MHD) nanofluid flow over a permeable wedge. Analyzing hyperbolic tangent nanofluid flow, the governing time-independent partial differential equations (PDEs) for continuity, momentum, energy, and concentration transform into a set of nonlinear third-order coupled ordinary differential equations (ODEs) through similarity transformations. These ODEs encompass critical parameters such as Lewis and Prandtl numbers, Brownian diffusion, Weissenberg number, thermophoresis, Dufour and Soret numbers, magnetic field strength, thermal radiation, power law index, and medium permeability. The study explores how variations in these parameters impact the velocity field, skin friction coefficient, Nusselt, and Sherwood numbers. Noteworthy findings include the sensitivity of fluid velocity to parameters like Weissenberg number, power law index, wedge angle, magnetic field strength, permeability, and melting heat transfer. The skin friction coefficient experiences a significant increase with specific parameter changes, while Nusselt and Sherwood numbers remain relatively constant. The local Reynolds number significantly affects Nusselt and Sherwood numbers, with a less pronounced impact on the skin friction coefficient. The study's uniqueness lies in employing the analytical HAN method and extracting recent insights from the results.}, }
@article {pmid39165174, year = {2024}, author = {Liu, Y and Zhang, J and Peng, X and Yan, S}, title = {Deciphering the Evolution of Inertial Migration in Serpentine Channels.}, journal = {Analytical chemistry}, volume = {96}, number = {35}, pages = {14306-14314}, pmid = {39165174}, issn = {1520-6882}, abstract = {Serpentine channels coupling inertial and secondary flows enable effective particle focusing and separation, showing great potential in clinical diagnostics and drug screening. However, the nonsteady secondary flows in the serpentine channel make the evolution of inertial migration unclear, hindering the development and application of the serpentine channel. Herein, to refine the inertial migration mechanism, we established a model with varying curvature ratios to study the effect of secondary flow on particle migration in the serpentine channel. This method used direct numerical simulation (DNS) to calculate inertial lift, mapped the inertial lift to cross sections of the serpentine channel, and deciphered the inertial migration by using the Lagrangian particle tracking (LPT) method. The inertial migration of microparticles is experimentally investigated to validate the established numerical model. The results indicate that particle migration in serpentine channels follows a two-stage migration. An increase in secondary flow accelerates the second stage of the migration process while slowing the first stage process. Subsequently, we investigated the effects of different parameters, including Reynolds number, aspect ratio, and blockage ratio, on the equilibrium positions of particles, providing guidelines for the high-resolution separation of particles. Taking flow resistance into account, the dimensionless study makes the separation of arbitrary-sized particles possible. This work reveals the migration mechanism in serpentine channels, paving the way for the inertial separation of the particles.}, }
@article {pmid39160957, year = {2024}, author = {Zigelman, A and Ben Zvi, G and Or, Y}, title = {Dynamics of Purcell-type microswimmers with active-elastic joints.}, journal = {Physical review. E}, volume = {110}, number = {1-1}, pages = {014207}, doi = {10.1103/PhysRevE.110.014207}, pmid = {39160957}, issn = {2470-0053}, abstract = {Purcell's planar three-link microswimmer is a classic model of swimming in low-Reynolds-number fluid, inspired by motion of flagellated microorganisms. Many works analyzed this model, assuming that the two joint angles are directly prescribed in phase-shifted periodic inputs. In this work, we study a more realistic scenario by considering an extension of this model which accounts for joints' elasticity and mechanical actuation of periodic torques so that the joint angles are dynamically evolving. Numerical analysis of the swimmer's dynamics reveals multiplicity of periodic solutions, depending on parameters of the inputs-frequency and amplitude of excitation, joints' stiffness ratio, as well as joint's activation. We numerically study swimming direction reversal, as well as bifurcations, stability transitions, and symmetry breaking of the periodic solutions, which represent the effect of buckling instability observed in swimming microorganisms. The results demonstrate that this variant of Purcell's simple model displays rich nonlinear dynamic behavior with actuated-elastic joints. Similar results are also obtained when studying an extended model of a six-link microswimmer.}, }
@article {pmid39160917, year = {2024}, author = {Puggioni, L and Musacchio, S}, title = {Orientational order and topological defects in a dilute solutions of rodlike polymers at low Reynolds number.}, journal = {Physical review. E}, volume = {110}, number = {1-2}, pages = {015104}, doi = {10.1103/PhysRevE.110.015104}, pmid = {39160917}, issn = {2470-0053}, abstract = {The relationship between the polymer orientation and the chaotic flow, in a dilute solution of rigid rodlike polymers at low Reynolds number, is investigated by means of direct numerical simulations. It is found that the rods tend to align with the velocity field in order to minimize the friction with the solvent fluid, while regions of rotational disorder are related to strong vorticity gradients, and therefore to the chaotic flow. The "turbulent-like" behavior of the system is therefore associated with the emergence and interaction of topological defects of the mean director field, similarly to active nematic turbulence. The analysis has been carried out in both two and three spatial dimensions.}, }
@article {pmid39140230, year = {2024}, author = {Mohammadali, R and Bayareh, M and Nadooshan, AA}, title = {Performance optimization of a DLD microfluidic device for separating deformable CTCs.}, journal = {Electrophoresis}, volume = {45}, number = {19-20}, pages = {1775-1784}, doi = {10.1002/elps.202400136}, pmid = {39140230}, issn = {1522-2683}, mesh = {*Neoplastic Cells, Circulating/pathology ; Humans ; *Microfluidic Analytical Techniques/instrumentation/methods ; *Cell Separation/instrumentation/methods ; Equipment Design ; Computer Simulation ; Elastic Modulus ; Cell Line, Tumor ; }, abstract = {Deterministic lateral displacement (DLD) microfluidic devices work based on the streamlines created by an array of micro-posts. The configuration of pillars alters the isolation efficiency of these devices. The present paper optimizes the performance of a DLD device for isolating deformable circulating tumor cells. The input variables include cell diameter (d), Young's modulus (E s ${E}_s$), Reynolds number (Re), and tan θ, where θ is the tilted angle of micro-posts. The output, which is the response of the system, is DLD. The numerical simulation results are employed to optimize the device using the response surface method, leading to the proposition of a correlation to estimate DLD as a function of input variables. It is demonstrated that the maximum and minimum impacts on cell lateral displacement correspond to E s ${E}_s$ and Re, respectively.}, }
@article {pmid39138284, year = {2024}, author = {Nagalingam, N and Korede, V and Irimia, D and Westerweel, J and Padding, JT and Hartkamp, R and Eral, HB}, title = {Unified framework for laser-induced transient bubble dynamics within microchannels.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {18763}, pmid = {39138284}, issn = {2045-2322}, support = {16714//Nederlandse Organisatie voor Wetenschappelijk Onderzoek/ ; }, abstract = {Oscillatory flow in confined spaces is central to understanding physiological flows and rational design of synthetic periodic-actuation based micromachines. Using theory and experiments on oscillating flows generated through a laser-induced cavitation bubble, we associate the dynamic bubble size (fluid velocity) and bubble lifetime to the laser energy supplied-a control parameter in experiments. Employing different channel cross-section shapes, sizes and lengths, we demonstrate the characteristic scales for velocity, time and energy to depend solely on the channel geometry. Contrary to the generally assumed absence of instability in low Reynolds number flows (< 1000), we report a momentary flow distortion that originates due to the boundary layer separation near channel walls during flow deceleration. The emergence of distorted laminar states is characterized using two stages. First the conditions for the onset of instabilities is analyzed using the Reynolds number and Womersley number for oscillating flows. Second the growth and the ability of an instability to prevail is analyzed using the convective time scale of the flow. Our findings inform rational design of microsystems leveraging pulsatile flows via cavitation-powered microactuation.}, }
@article {pmid39130567, year = {2024}, author = {Miah, MAK and Ahasan, K and Kingston, TA and Olsen, MG and Juárez, JJ}, title = {Microscopic Particle Image Velocimetry Analysis of Multiphase Flow in a Porous Media Micromodel.}, journal = {ACS omega}, volume = {9}, number = {31}, pages = {34070-34080}, pmid = {39130567}, issn = {2470-1343}, abstract = {Pore-scale oil displacement behavior was investigated in a porous media micromodel using microscopic particle image velocimetry (μPIV). Porous media micromodels consisting of an ordered square array of cylindrical pillars with 50 and 70% porosities were fabricated with photolithography. The oil displacement was performed with the injection of water at flow rates of 37.5, 75, and 150 μL/h. These flow rates correspond to Reynolds number of 1.1 × 10[-2], 2.2 × 10[-2], and 4.4 × 10[-2], respectively in the 50% porous channel, and 1.84 × 10[-3], 3.69 × 10[-3], and 7.38 × 10[-3], respectively in the 70% porous channel. The capillary numbers for these flow rates are 2.18 × 10[-5], 4.36 × 10[-5], and 8.72 × 10[-5], respectively in the 50% porous channel, and 1.56 × 10[-5], 3.12 × 10[-5], and 6.23 × 10[-5], respectively in the 70% porous channel. The micromodel is initially saturated with oil, with the invading water phase following the path of least resistance as it displaces the oil. The μPIV data were used to construct probability density functions (PDFs) which show an initial, nonzero, peak in transverse velocity as the water enters the micromodel. The PDFs broaden with time, indicating that the water is spreading, before retracting to a peak velocity of 0 mm/s, indicating that the water displacement has achieved equilibrium. We developed a model based on conservation of mass to describe the efficiency of the displacement process. All flow conditions demonstrate peak displacement efficiency when the amount of oil phase displacement is ∼9 pore volumes in 50% porous channel and ∼4 pore volumes in 70% porous channel.}, }
@article {pmid39130463, year = {2024}, author = {Akhter, R and Ali, MM and Alim, MA}, title = {Data analysis of thermal performance and irreversibility of convective flow in porous-wavy channel having triangular obstacle under magnetic field effect.}, journal = {Heliyon}, volume = {10}, number = {14}, pages = {e34580}, pmid = {39130463}, issn = {2405-8440}, abstract = {Mixed convective nanofluid flow has substantial importance in improvement of thermal performance, and thermal engineering to meet the global energy crisis. In this study, mixed convective nanofluid flow in a porous-wavy channel with an inner heated triangular obstacle under magnetic field effect is numerically examined. Nanofluid within the channel is heated and cooled from its bottom and top wavy-surfaces. A heated triangular cylinder is located at the centerline of the wavy-channel. Finite element method is utilized to solve the non-dimensional governing equations. The code is validated comparing present results with published numerical and experimental results. The response surface method is also implemented to analyze the obtained results and its sensitivity. The numerical results indicate that strength of flow velocity is accelerated with rising Reynolds number, Darcy numbers and inlet-outlet ports length but declined for Hartmann number and volume fraction. Heat transferring rate and heat transfer irreversibility are substantially increased for higher values of Reynolds number, inlet-outlet ports length, Darcy number and nanoparticle volume fraction but a reverse trend is occurred for magnetic field effect. The thermal performance is found significantly improved with simultaneous increment in Re, ϕ, Da and decrement in Ha. Positive sensitivity is achieved for input factors Re, ϕ, Da in computing N u a v while negative sensitivity to Ha. Heat transfer rate is found more sensitive to the impact of Re and ϕ compared to Da and Ha. 45.59 % more heat transmission potentiality is developed for using Al2O3-H2O nanofluid (vol.5 %) instead of using base fluid water. Heat transfer enhancement rate is decreased by 36.22 % due to impact of magnetic field strength. In addition, 84.12 % more heat transferring rate is recorded in presence of triangular obstacle. Moreover, irreversibility components are influenced significantly for the presence of heated triangular obstacle. Bejan number is also found declined for increasing physical parameters. The findings of this investigation may offer a guideline for finding experimental results to design high-performance convective heat exchangers.}, }
@article {pmid39124977, year = {2024}, author = {Chou, YF and Keh, HJ}, title = {Axisymmetric Slow Rotation of Coaxial Soft/Porous Spheres.}, journal = {Molecules (Basel, Switzerland)}, volume = {29}, number = {15}, pages = {}, pmid = {39124977}, issn = {1420-3049}, support = {MOST 110-2221-E-002-017-MY3//National Science and Technology Council Taiwan/ ; }, abstract = {The steady low-Reynolds-number rotation of a chain of coaxial soft spheres (each with an impermeable hard core covered by a permeable porous layer) about the axis in a viscous fluid is analyzed. The particles may be unequally spaced, and may differ in the permeability and inner and outer radii of the porous surface layer as well as angular velocity. By using a method of boundary collocation, the Stokes and Brinkman equations for the external fluid flow and flow within the surface layers, respectively, are solved semi-analytically. The particle interaction effect increases as the relative gap thickness between adjacent particles or their permeability decreases, which can be significant as the gap thickness approaches zero. A particle's hydrodynamic torque is reduced (its rotation is enhanced) when other particles rotate in the same direction at equivalent or greater angular velocities, but increases (its rotation is hindered) when other particles rotate in the opposite direction at arbitrary angular velocities. For particles with different radii or permeabilities, the particle interaction has a greater effect on smaller or more permeable particles than on larger or less permeable particles. For the rotation of three particles, the presence of the third particle can significantly affect the hydrodynamic torques acting on the other two particles. For the rotation of numerous particles, shielding effects between particles can be substantial. When the permeability of porous layers is low, relative fluid motion is barely felt by the hard cores of the soft particles. The insights gained from this analysis on the effects of interactions among rotating soft particles may be of great importance in many physicochemical applications of colloidal suspensions.}, }
@article {pmid39110849, year = {2024}, author = {Zhang, L and Wan, X and Zhou, X and Cao, Y and Duan, H and Yan, J and Li, H and Lv, P}, title = {Pyramid-Shaped Superhydrophobic Surfaces for Underwater Drag Reduction.}, journal = {ACS applied materials &amp; interfaces}, volume = {16}, number = {33}, pages = {44319-44327}, doi = {10.1021/acsami.4c09631}, pmid = {39110849}, issn = {1944-8252}, abstract = {Superhydrophobic surfaces hold immense potential in underwater drag reduction. However, as the Reynolds number increases, the drag reduction rate decreases, and it may even lead to a drag increase. The reason lies in the collapse of the air mattress. To address this issue, this paper develops a pyramid-shaped robust superhydrophobic surface with wedged microgrooves, which exhibits a high gas fraction when immersed underwater and good ability to achieve complete spreading and recovery of the air mattress through air replenishment in the case of collapse of the air mattress. Pressure drop tests in a water tunnel confirm that with continuous air injection, the drag reduction reaches 64.8% in laminar flow conditions, substantially greater than 38.4% in the case without air injection, and can achieve 50.8% drag reduction in turbulent flow. This result highlights the potential applications of superhydrophobic surfaces with air mattress recovery for drag reduction.}, }
@article {pmid39103401, year = {2024}, author = {Refaie Ali, A and Abbasi, WS and Bibi, B and Rahman, H and Ul Islam, S and Hussain Majeed, A and Ahmad, I}, title = {Spacing effects on flows around two square cylinders in staggered arrangement via LBM.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {18049}, pmid = {39103401}, issn = {2045-2322}, abstract = {This study presents a computational analysis of fluid flow characteristics around two staggered arranged square cylinders using the Lattice Boltzmann Method (LBM). With Reynolds number (Re) fixed at 200, numerical simulations explore the influence of varying gap ratios (G) ranging from 0 to 10 times the cylinder size. Emphasis is placed on understanding the impact of cylinders spacing on flow structure mechanisms and induced forces. Investigation of fluid flow parameters includes vorticity behavior, pressure streamlines, and variations in drag and lift coefficients alongside the Strouhal number under different values of G. From the results, four distinct flow patterns emerge: single bluff body flow, flip flopping flow, modulated synchronized flow, and synchronized flow, each exhibiting unique characteristics. This study reveals the strong dependence of fluid forces on G, with low spacing values leading to complex vortex structures and fluctuating forces influenced by jet flow effects. At higher spacing values, proximity effects between cylinders diminish, resulting in a smoother periodic flow. The Strouhal number, average drag force and the rms values of drag and lift force coefficients vary abruptly at narrow gaps and become smooth at higher gap ratios. Unlike the tandem and side-by-side arrangements the staggered cylinders arrangement is found to have significant impact on the pressure variations around both cylinders. Overall, this research could contribute to a comprehensive understanding of staggered cylinder arrangements and their implications for engineering applications.}, }
@article {pmid39102543, year = {2024}, author = {Saito, M and Arai, F and Yamanishi, Y and Sakuma, S}, title = {Spatiotemporally controlled microvortices provide advanced microfluidic components.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {121}, number = {33}, pages = {e2306182121}, pmid = {39102543}, issn = {1091-6490}, support = {22J23814//MEXT | Japan Society for the Promotion of Science (JSPS)/ ; JPMJFR2157//MEXT | JST | Fusion Oriented REsearch for disruptive Science and Technology (FOREST)/ ; }, abstract = {Microvortices are emerging components that impart functionality to microchannels by exploiting inertia effects such as high shear stress, effective fluid diffusion, and large pressure loss. Exploring the dynamic generation of vortices further expands the scope of microfluidic applications, including cell stimulation, fluid mixing, and transport. Despite the crucial role of vortices' development within sub-millisecond timescales, previous studies in microfluidics did not explore the modulation of the Reynolds number (Re) in the range of several hundred. In this study, we modulated high-speed flows (54 < [Formula: see text] < 456) within sub-millisecond timescales using a piezo-driven on-chip membrane pump. By applying this method to microchannels with asymmetric geometries, we successfully controlled the spatiotemporal development of vortices, adjusting their behavior in response to oscillatory flow directions. These different vortices induced different pressure losses, imparting the microchannels with direction-dependent flow resistance, mimicking a diode-like behavior. Through precise control of vortex development, we managed to regulate this direction-dependent resistance, enabling the rectification of oscillatory flow resembling a diode and the ability to switch its rectification direction. This component facilitated bidirectional flow control without the need for mechanical valves. Moreover, we demonstrated its application in microfluidic cell pipetting, enabling the isolation of single cells. Consequently, based on modulating high-speed flow, our approach offers precise control over the spatiotemporal development of vortices in microstructures, thereby introducing innovative microfluidic functionalities.}, }
@article {pmid39093039, year = {2024}, author = {Van Blitterswyk, J and Rocha, J}, title = {Erratum: An experimental study of the wall-pressure fluctuations beneath low Reynolds number turbulent boundary layers [J. Acoust. Soc. Am. 141, 1257-1268 (2017)].}, journal = {The Journal of the Acoustical Society of America}, volume = {156}, number = {2}, pages = {725}, doi = {10.1121/10.0028125}, pmid = {39093039}, issn = {1520-8524}, }
@article {pmid39082012, year = {2024}, author = {Fahad, MK and Hasan, MJ and Ifraj, NF and Chandra Dey, D}, title = {Numerical investigation on the impact of different design arrangements of helical heat exchangers with varying cross-sections utilizing ternary hybrid nanofluids.}, journal = {Heliyon}, volume = {10}, number = {14}, pages = {e34481}, pmid = {39082012}, issn = {2405-8440}, abstract = {Helical tube heat exchangers (HTHE) are commonly used as thermal devices in various thermal engineering applications. A comparative investigation was undertaken to examine several helical tube designs in relation to their potential uses with water and nanofluids. Additionally, employing the ternary hybrid nanofluid (THNF) flow in helical-type heat exchangers to assess the heat transfer and frictional loss is a unique concept, as there is currently no research on this specific application. This study involves analyzing three different design configurations, each of which has three different inlet profiles: round, square, and oval shapes. Hence, a numerical analysis has been conducted on nine cases, each including the same pipe length, helix diameter, and pitch distance. The specified range for the Reynolds number under the water and THNF flow condition is 5000-25000. The results are acquired for both fluids, considering the Nusselt number (Nu), friction factor (f), outlet temperature (T out), and entropy production (S g). Multi-Criteria Decision Making (MCDM) is employed to provide a thorough assessment of the overall performance of the proposed designs. The results have been shown as graphical representations, streamlines and contours where Nusselt number, friction factor and entropy generation have been evaluated. The Nusselt number has a higher value for the oval cross-section, while it reaches its lowest value for the square cross-section. The highest heat transfer rate is got for Design 1 with the oval-shaped case. The friction factor for a circular cross-section HHTE is 48 % higher than the friction factor for a square cross-section profile. In addition, the square shape at a Reynolds number (Re) of 25000 exhibits 5 % less entropy formation compared to the oval shape geometry at a Reynolds number of 5000. The results of MCDM analysis indicate that Design 1, which features a square section, exhibits superior performance. Conversely, Design 2, which incorporates a circular cross-section, demonstrates poor performance. Among the six ternary hybrid nanofluids, the Al2O3+CNT+Graphene nanofluid with a water basis exhibits the greatest Nusselt number.}, }
@article {pmid39064393, year = {2024}, author = {Qing, Y and Wang, J and Li, F}, title = {Electro-Osmotic Flow and Mass Transfer through a Rough Microchannel with a Modulated Charged Surface.}, journal = {Micromachines}, volume = {15}, number = {7}, pages = {}, pmid = {39064393}, issn = {2072-666X}, support = {11902164//The National Natural Science Foundation of China/ ; }, abstract = {In this paper, we investigate the electro-osmotic flow (EOF) and mass transfer of a Newtonian fluid propelled by a pressure gradient and alternating current (AC) electric field in a parallel microchannel with sinusoidal roughness and modulated charged surfaces. The two-wall roughness is described by in-phase or out-of-phase sine functions with a small amplitude δ. By employing the method of perturbation expansion, the semi-analytical solutions of the Poisson-Boltzmann (P-B) equation based on the Debye-Hückel approximation and the modified Navier-Stokes (N-S) equation are obtained. The numerical solution of the concentration equation is obtained by the finite difference method. The effects of sinusoidal roughness, modulated charged surface, and the AC electric field on the potential field, velocity field, and concentration field are discussed. Under the influence of the modulated charged surface and sinusoidal roughness, vortices are generated. The velocity oscillates due to the effect of the AC electric field. The results indicate that solute diffusion becomes enhanced when the oscillation Reynolds number is below a specific critical value, and it slows down when the oscillation Reynolds number exceeds this critical value.}, }
@article {pmid39056856, year = {2024}, author = {Chen, D and Zhang, B and Zhang, H and Shangguan, Z and Sun, C and Cui, X and Liu, X and Zhao, Z and Liu, G and Chen, H}, title = {Laser Ablating Biomimetic Periodic Array Fish Scale Surface for Drag Reduction.}, journal = {Biomimetics (Basel, Switzerland)}, volume = {9}, number = {7}, pages = {}, pmid = {39056856}, issn = {2313-7673}, support = {52305311, 52205297, 51935001, 51725501, and T2121003//National Natural Science Foundation of China/ ; ZR2023QE018//Shandong Provincial Natural Science Foundation/ ; }, abstract = {Reducing resistance to surface friction is challenging in the field of engineering. Natural biological systems have evolved unique functional surfaces or special physiological functions to adapt to their complex environments over centuries. Among these biological wonders, fish, one of the oldest in the vertebrate group, have garnered attention due to their exceptional fluid dynamics capabilities. Fish skin has inspired innovation in reducing surface friction due to its unique structures and material properties. Herein, drawing inspiration from the unique properties of fish scales, a periodic array of fish scales was fabricated by laser ablation on a polished aluminum template. The morphology of the biomimetic fish scale surface was characterized using scanning electron microscopy and a white-light interfering profilometer. Drag reduction performance was measured in a closed circulating water tunnel. The maximum drag reduction was 10.26% at a Reynolds number of 39,532, and the drag reduction performance gradually decreased with an increase in the distance between fish scales. The mechanism of the biomimetic drag reduction surface was analyzed using computational fluid dynamics. Streamwise vortices were generated at the valley of the biomimetic fish scale, replacing sliding friction with rolling friction. These results are expected to provide a foundation for in-depth analysis of the hydrodynamic performance of fish and serve as new inspiration for drag reduction and antifouling.}, }
@article {pmid39036949, year = {2024}, author = {Raihan, MK and Kim, N and Song, Y and Xuan, X}, title = {Elasto-inertial instabilities in the merging flow of viscoelastic fluids.}, journal = {Soft matter}, volume = {20}, number = {30}, pages = {6059-6067}, doi = {10.1039/d4sm00743c}, pmid = {39036949}, issn = {1744-6848}, abstract = {Many engineering and natural phenomena involve the merging of two fluid streams through a T-junction. Previous studies of such merging flows have been focused primarily upon Newtonian fluids. We observed in our recent experiment with five different polymer solutions a direct change from an undisturbed to either a steady vortical or unsteady three-dimensional flow at the T-junction with increasing inertia. The transition state(s) in between these two types of merging flow patterns is, however, yet to be known. We present here a systematic experimental study of the merging flow of polyethylene oxide (PEO) solutions with varying polymer concentrations and molecular weights. Two new paths of flow development are identified with the increase of Reynolds number: one is the transition in very weakly viscoelastic fluids first to steady vortical flow and then to a juxtaposition state with an unsteady elastic eddy zone in the middle and a steady inertial vortex on each side, and the other is the transition in weakly viscoelastic fluids first to a steady vortical and/or a juxtaposition state and then to a fully unsteady flow. Interestingly, the threshold Reynolds number for the onset of elastic instabilities in the merging flow is not a monotonic function of the elasticity number, but instead follows a power-law dependence on the polymer concentration relative to its overlap value. Such a dependence turns out qualitatively consistent with the prediction of the McKinley-Pakdel criterion.}, }
@article {pmid39027729, year = {2024}, author = {Arshi, S and Madane, K and Shortall, K and Hailo, G and Alvarez-Malmagro, J and Xiao, X and Szymanńska, K and Belochapkine, S and Ranade, VV and Magner, E}, title = {Controlled Delivery of H2O2: A Three-Enzyme Cascade Flow Reactor for Peroxidase-Catalyzed Reactions.}, journal = {ACS sustainable chemistry &amp; engineering}, volume = {12}, number = {28}, pages = {10555-10566}, pmid = {39027729}, issn = {2168-0485}, abstract = {Peroxidases are promising catalysts for oxidation reactions, yet their practical utility has been hindered by the fact that they require hydrogen peroxide (H2O2), which at high concentrations can cause deactivation of enzymes. Practical processes involving the use of peroxidases require the frequent addition of low concentrations of H2O2. In situ generation of H2O2 can be achieved using oxidase-type enzymes. In this study, a three-enzyme cascade system comprised of a H2O2 generator (glucose oxidase (GOx)), H2O2-dependent enzymes (chloroperoxidase (CPO) or horseradish peroxidase (HRP)), and a H2O2 scavenger (catalase (CAT)) was deployed in a flow reactor. Immobilization of the enzymes on a graphite rod was achieved through electrochemically driven physical adsorption, followed by cross-linking with glutaraldehyde. Modeling studies indicated that the flow in the reactor was laminar (Reynolds number, R e < 2000) and was nearly fully developed at the midplane of the annular reactor. Immobilized CAT and GOx displayed good stability, retaining 79% and 84% of their initial activity, respectively, after three cycles of operation. Conversely, immobilized CPO exhibited a considerable reduction in activity after one use, retaining only 30% of its initial activity. The GOx-CAT-GRE system enabled controlled delivery of H2O2 in a more stable manner with a 4-fold enhancement in the oxidation of indole compared to the direct addition of H2O2. Using CPO in solution coupled with GOx-CAT-GRE yields of 90% for the oxidation of indole to 2-oxyindole and of 93% and 91% for the chlorination of thymol and carvacrol, respectively.}, }
@article {pmid39025780, year = {2024}, author = {Ashikhmin, A and Piskunov, M and Kochkin, D and Ronshin, F and Chen, L}, title = {Droplet Microfluidic Method for Estimating the Dynamic Interfacial Tension of Ion-Crosslinked Sodium Alginate Microspheres.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {}, number = {}, pages = {}, doi = {10.1021/acs.langmuir.4c01940}, pmid = {39025780}, issn = {1520-5827}, abstract = {The research focuses on optimizing the production of hydrogel microspheres using droplet microfluidics for pharmaceutical and bioengineering applications. A semiempirical method has been developed to predict the dynamic interfacial tension at the interface of ion-cross-linked sodium alginate microsphere-sunflower oil modified with glacial acetic acid and Tween 80 surfactant. These microspheres are produced in a small-scale coaxial device that is manufactured using affordable DLP/LCD 3D printing technology with a transparent photopolymer. The method was tested to design the minireactor in the device, which allows for the production of fully cross-linked microspheres that are ready for use at the output of the reactor without additional cross-linking steps in the microsphere collector. The mathematical expression for estimating the interfacial tension at the moment of formation of a hydrogel microsphere includes the Reynolds number for a two-phase liquid, the Ohnesorge number, and the surface tension at the liquid-air interface for continuous medium flow (modified oil). The reliability of the prediction is confirmed for continuous medium and dispersed phase flow rates of 0.8-3.2 and 0.01-0.08 mL/min, respectively. The evolution of the interfacial tension from the moment the microspheres formed and the estimated ultimate interfacial tension in a cross-linked hydrogel-modified oil system contributed to the reliable determination of the linear size of a minireactor. The ultimate interfacial tension of 76.5 ± 0.3 mN/m was determined using the Young-Laplace equation, which is based on measuring the surface free energy of the hydrogel as soft matter using the Owens-Wendt method. Additionally, the equilibrium static contact angle of the fully cross-linked hydrogel surface wetted with oil is measured using the sessile drop method. From a practical perspective, a method for optimizing and streamlining the high-tech manufacturing of cross-linked polymer microspheres and mini- and microchannel devices for use in bioengineering and pharmaceutical applications is suggested.}, }
@article {pmid39020933, year = {2024}, author = {Sudarsanan, S and Roy, A and Pavithran, I and Tandon, S and Sujith, RI}, title = {Emergence of order from chaos through a continuous phase transition in a turbulent reactive flow system.}, journal = {Physical review. E}, volume = {109}, number = {6-1}, pages = {064214}, doi = {10.1103/PhysRevE.109.064214}, pmid = {39020933}, issn = {2470-0053}, abstract = {As the Reynolds number is increased, a laminar fluid flow becomes turbulent, and the range of time and length scales associated with the flow increases. Yet, in a turbulent reactive flow system, as we increase the Reynolds number, we observe the emergence of a single dominant timescale in the acoustic pressure fluctuations, as indicated by its loss of multifractality. Such emergence of order from chaos is intriguing. We perform experiments in a turbulent reactive flow system consisting of flame, acoustic, and hydrodynamic subsystems interacting nonlinearly. We study the evolution of short-time correlated dynamics between the acoustic field and the flame in the spatiotemporal domain of the system. The order parameter, defined as the fraction of the correlated dynamics, increases gradually from zero to one. We find that the susceptibility of the order parameter, correlation length, and correlation time diverge at a critical point between chaos and order. Our results show that the observed emergence of order from chaos is a continuous phase transition. Moreover, we provide experimental evidence that the critical exponents characterizing this transition fall in the universality class of directed percolation. Our paper demonstrates how a real-world complex, nonequilibrium turbulent reactive flow system exhibits universal behavior near a critical point.}, }
@article {pmid39020875, year = {2024}, author = {Samanta, A}, title = {Insights on phase speed and the critical Reynolds number of falling films.}, journal = {Physical review. E}, volume = {109}, number = {6-2}, pages = {065103}, doi = {10.1103/PhysRevE.109.065103}, pmid = {39020875}, issn = {2470-0053}, abstract = {We revisit the studies of gravity-driven viscous falling films with and without imposed shear stress to provide new perspectives on phase speed and the critical Reynolds number for surface instability. We use the traditional long-wave expansion technique implemented for investigating the linear stability analysis [C. S. Yih, Phys. Fluids 6, 321 (1963)0031-917110.1063/1.1706737]. The principal purpose is to create a unified relationship between the leading-order phase speed and the critical Reynolds number that will hold for falling films on impermeable substrates with or without shear stress acting at the liquid film surface. The analytical result demonstrates that the critical Reynolds number for the onset of surface instability is [5/(2c_{0})]cotθ, where c_{0} is the leading-order phase speed of the surface mode and θ is the angle of inclination with the horizontal. Clearly, the critical Reynolds number of the surface mode is explicitly dependent on the leading-order phase speed. Furthermore, we reveal that the basic parallel flow with or without imposed shear stress is linearly unstable to infinitesimal disturbances if the modified Reynolds number, Re_{M}=(Rec_{0}/cotθ)[ReistheReynoldsnumber,andθ≠π/2], is greater than its critical value of 5/2, which is independent of the shear stress applied at the film surface. In addition, it is demonstrated that Re_{M} controls the surface instability in the long-wave regime for both shear-imposed and non-shear-imposed film flows.}, }
@article {pmid39009602, year = {2024}, author = {Kheirkhah Barzoki, A}, title = {Optimization of passive micromixers: effects of pillar configuration and gaps on mixing efficiency.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {16245}, pmid = {39009602}, issn = {2045-2322}, abstract = {Chemical bioreactions play a significant role in many of the microfluidic devices, and their applications in biomedical science have seen substantial growth. Given that effective mixing is vital for initiating biochemical reactions in many applications, micromixers have become increasingly prevalent for high-throughput assays. In this research, a numerical study using the finite element method was conducted to examine the fluid flow and mass transfer characteristics in novel micromixers featuring an array of pillars. The study utilized two-dimensional geometries. The impact of pillar configuration on mixing performance was evaluated using concentration distribution and mixing index as key metrics. The study explores the effects of pillar array design on mixing performance and pressure drop, drawing from principles such as contraction-expansion and split-recombine. Two configurations of pillar arrays, slanted and arrowhead, are introduced, each undergoing investigation regarding parameters such as pillar diameter, gap size between pillar groups, distance between pillars, and vertical shift in pillar groups. Subsequently, optimal micromixers are identified, exhibiting mixing efficiency exceeding 99.7% at moderate Reynolds number (Re = 1), a level typically challenging for micromixers to attain high mixing efficiency. Notably, the pressure drop remains low at 1102 Pa. Furthermore, the variations in mixing index over time and across different positions along the channel are examined. Both configurations demonstrate short mixing lengths and times. At a distance of 4300 μm from the inlet, the slanted and arrowhead configurations yielded mixing indices of 97.2% and 98.9%, respectively. The micromixers could provide a mixing index of 99.5% at the channel's end within 8 s. Additionally, both configurations exceeded 90% mixing indices by the 3 s. The combination of rapid mixing, low pressure drop, and short mixing length positions the novel micromixers as highly promising for microfluidic applications.}, }
@article {pmid38994047, year = {2024}, author = {Aziz, MA and Gaheen, OA and Benini, E and Elsayed, AM}, title = {Experimental investigation of multi-step airfoils in low Reynolds numbers applications.}, journal = {Heliyon}, volume = {10}, number = {12}, pages = {e32919}, pmid = {38994047}, issn = {2405-8440}, abstract = {This study provides a detailed analysis of the aerodynamic performance of various airfoil configurations, focusing on lift coefficient, stall characteristics, and maximum lift-to-drag ratio. The investigation includes the NACA23012C profile and configurations with different step geometries, ranging from one-step to five-step designs. Experimental measurements were conducted using a well-equipped aerodynamic laboratory, Institute of Aviation Engineering and Technology (IAET), Giza, Egypt. The lab features a wind tunnel, propeller test rig, and data acquisition system. The experiments were conducted meticulously to ensure accuracy and reproducibility, with a standardized method employed for uncertainty analysis. The results reveal distinct aerodynamic behaviors among the different configurations, highlighting the significant impact of design variations on aerodynamic performance. Notably, the three-step configuration consistently exhibited high performance, with a competitive or superior lift coefficient across a range of Reynolds numbers, showing an improvement of up to 35.1 %. Similarly, the four-step configuration demonstrated substantial increases in lift-to-drag ratios, reaching up to 53.2 %, while the five-step configuration exhibited varying trends with a minimum drag coefficient. The study also investigated stall characteristics and sensitivity to Reynolds numbers, revealing the complex trade-offs inherent in airfoil design. The findings provide valuable insights into optimizing airfoil performance under different operational conditions. Additionally, the adoption of two and three stepped airfoils resulted in significant reductions in blade material and associated costs for turbine blades.}, }
@article {pmid38991421, year = {2024}, author = {Luciano, RD and da Silva, BL and Chen, XB and Bergstrom, DJ}, title = {Turbulent blood flow in a cerebral artery with an aneurysm.}, journal = {Journal of biomechanics}, volume = {172}, number = {}, pages = {112214}, doi = {10.1016/j.jbiomech.2024.112214}, pmid = {38991421}, issn = {1873-2380}, mesh = {Humans ; *Intracranial Aneurysm/physiopathology ; *Models, Cardiovascular ; *Computer Simulation ; *Cerebral Arteries/physiopathology ; Blood Flow Velocity/physiology ; Cerebrovascular Circulation/physiology ; Hydrodynamics ; Pulsatile Flow/physiology ; Stress, Mechanical ; }, abstract = {Unruptured intracranial aneurysms are common in the general population, and many uncertainties remain when predicting rupture risks and treatment outcomes. One of the cutting-edge tools used to investigate this condition is computational fluid dynamics (CFD). However, CFD is not yet mature enough to guide the clinical management of this disease. In addition, recent studies have reported significant flow instabilities when refined numerical methods are used. Questions remain as to how to properly simulate and evaluate this flow, and whether these instabilities are really turbulence. The purpose of the present study is to evaluate the impact of the simulation setup on the results and investigate the occurrence of turbulence in a cerebral artery with an aneurysm. For this purpose, direct numerical simulations were performed with up to 200 cardiac cycles and with data sampling rates of up to 100,000 times per cardiac cycle. Through phase-averaging or triple decomposition, the contributions of turbulence and of laminar pulsatile waves to the velocity, pressure and wall shear stress fluctuations were distinguished. For example, the commonly used oscillatory shear index was found to be closely related to the laminar waves introduced at the inlet, rather than turbulence. The turbulence energy cascade was evaluated through energy spectrum estimates, revealing that, despite the low flow rates and Reynolds number, the flow is turbulent near the aneurysm. Phase-averaging was shown to be an approach that can help researchers better understand this flow, although the results are highly dependent on simulation setup and post-processing choices.}, }
@article {pmid38987632, year = {2024}, author = {Oz, F and Kara, K}, title = {Controlling hypersonic boundary layer transition with localized cooling and metasurface treatments.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {15928}, pmid = {38987632}, issn = {2045-2322}, support = {OAC-1531128//National Science Foundation/ ; }, abstract = {This study investigates a novel method to control hypersonic boundary layer transition using a combined local cooling and local metasurface treatment. The method's effectiveness was investigated on a 5-degree half-angle blunt wedge with a nose radius of 0.0254 mm at a freestream Mach number of 6.0 using direct numerical simulations and linear stability theory. We explored four cases: (i) adiabatic baseline case, (ii) locally cooled case, (iii) local metasurface case, and (iv) combined local cooling-local metasurface case. Results showed that the combined local cooling-local metasurface treatment significantly reduced both wall pressure disturbance amplitude and the density perturbation amplitude around the sonic line, indicating a potential for controlling hypersonic boundary layer transition. In the local cooling-local metasurface case, the disturbance amplitude at the end of the computational domain was 270 times lower than the baseline case. The study also examined the impact of Reynolds numbers, ranging from 25.59 million per meter to 32.80 million per meter. Unsteady simulations revealed that the Reynolds number had a negligible effect on the local cooling-local metasurface performance, indicating that the proposed method applies to a wide range of flight conditions.}, }
@article {pmid38986513, year = {2024}, author = {Maire, Y and Schmitt, FG and Kormas, K and Vasileiadis, S and Caruana, A and Skouroliakou, DI and Bampouris, V and Courcot, L and Hervé, F and Crouvoisier, M and Christaki, U}, title = {Effects of turbulence on diatoms of the genus Pseudo-nitzschia spp. and associated bacteria.}, journal = {FEMS microbiology ecology}, volume = {100}, number = {8}, pages = {}, pmid = {38986513}, issn = {1574-6941}, support = {ANR-21-EXES-0011//IFSEA/ ; CPER MARCO 2015-2021//ERASMUS+/ ; }, mesh = {*Diatoms/genetics/growth &amp; development ; *Bacteria/genetics/classification/isolation &amp; purification/metabolism ; Kainic Acid/analogs &amp; derivatives/metabolism ; Phytoplankton/genetics ; Chlorophyll A/metabolism ; Photosynthesis ; Transcriptome ; }, abstract = {Turbulence is one of the least investigated environmental factors impacting the ecophysiology of phytoplankton, both at the community and individual species level. Here, we investigated, for the first time, the effect of a turbulence gradient (Reynolds number, from Reλ = 0 to Reλ = 360) on two species of the marine diatom Pseudo-nitzschia and their associated bacterial communities under laboratory conditions. Cell abundance, domoic acid (DA) production, chain formation, and Chl a content of P. fraudulenta and P. multiseries were higher for intermediate turbulence (Reλ = 160 or 240). DA was detectable only in P. multiseries samples. These observations were supported by transcriptomic analyses results, which suggested the turbulence related induction of the expression of the DA production locus, with a linkage to an increased photosynthetic activity of the total metatranscriptome. This study also highlighted a higher richness of the bacterial community associated with the nontoxic strain of P. fraudulenta in comparison to the toxic strain of P. multiseries. Bacillus was an important genus in P. multiseries cultures (relative abundance 15.5%) and its highest abundances coincided with the highest DA levels. However, associated bacterial communities of both Pseudo-nitzschia species did not show clear patterns relative to turbulence intensity.}, }
@article {pmid38975123, year = {2024}, author = {Nilpueng, K and Kaseethong, P and Wongwises, S}, title = {Heat transfer and flow characteristics of a plate-fin heat sink equipped with copper foam and twisted tapes.}, journal = {Heliyon}, volume = {10}, number = {12}, pages = {e32307}, doi = {10.1016/j.heliyon.2024.e32307}, pmid = {38975123}, issn = {2405-8440}, abstract = {The objective of this paper is to present new heat transfer enhancement approaches in plate-fin heat sinks (PFHS) using copper foam and twisted tapes. The motivation behind these concepts is to reduce pressure drop while enhancing heat transfer compared to PFHSs fully inserted with copper foam. The impact of twisted tape type, twist ratio, and Reynolds number (Re) on the heat and flow behaviors inside the PFHS equipped with copper foam (PFHSCF) is investigated. Copper foam has a porosity of 0.932 and a pore density of 40 pores per inch. Stationary and rotating twisted tapes with twist ratios between 2.7 and 4 are tested at Re between 3000 and 6000. The experimental results indicated that the pressure drop of the airflow inside a PFHS equipped with copper foam and a stationary twisted tape (PFHSCF_STT) as well as a PFHS equipped with copper foam and rotating twisted tapes (PFHSCF_RTT) decreased by an average of 34.8 % and 37.9 %, respectively, compared to a PFHSCF. When the twist ratio is decreased from 4 to 2.7, the thermal resistances of PFHSCF_STT and PFHSCF_RTT are reduced by 14.2 and 14.8 %, respectively. Based on assessment, the thermal-hydraulic performance of a PFHSCF_RTT with twist ratios of 2.7 and 3.3 is higher than that of a PFHSCF. To facilitate practical applications, correlations are proposed to predict the Nusselt number and friction factor. Additionally, considering the outcomes of the current study, conducting numerical investigations on the thermal performance of PFHS under different pore densities of copper foam and wider twist ratios of twisted tapes is recommended to determine optimal working conditions for future research.}, }
@article {pmid38971061, year = {2024}, author = {Li, Z and Wang, B and Wang, F and Sun, B and Li, L}, title = {Flow dynamics and turbulent coherent structures around sediment reduction plates of a sewer system.}, journal = {Journal of environmental management}, volume = {366}, number = {}, pages = {121594}, doi = {10.1016/j.jenvman.2024.121594}, pmid = {38971061}, issn = {1095-8630}, mesh = {*Hydrodynamics ; *Sewage ; Geologic Sediments ; Drainage, Sanitary ; Models, Theoretical ; Waste Disposal, Fluid/methods ; Water Movements ; }, abstract = {In the management of urban drainage networks, great interest has been generated in the removal of sediments from sewer systems. The unsteady three-dimensional (3D) flow and turbulent coherent structures surrounding sediment reduction plates in a sewer system are investigated by means of the detached-eddy simulation (DES). Particular emphasis is given to detailing the instantaneous velocity and vorticity fields within the grooves, along with an examination of the three-dimensional, long-term, average flow structure at a Reynolds number of approximately 10[5]. Velocity vectors demonstrate continuous flapping of the flow on the groove wall, periodically interacting with ejections of positive and negative vorticity originating from the grooves. The interaction between the three-dimensional groove flow and the shear flow leads to the downstream transport of patches of positive and negative vorticity, which significantly influence sediment transport. The high-velocity shear flows and strong vortices generated in undulating topography, as identified by the Q-criteria, are the key factors contributing to the efficient sediment reduction capabilities of the sediment reduction plates. The sediment reduction plates with partially enclosed structures exhibit low sedimentation rates in grooves on the plate, a broader acceleration region, and a lesser impact on the flow capacity. The results improve the understanding of the hydrodynamics and turbulent coherent structures surrounding the sediment reduction plates while elucidating the driving factors behind the enhancement of sediment scouring and suspension capacities. These results indicate that the redesign of the plates as partially enclosed structures contributes to further improving their sediment reduction performance.}, }
@article {pmid38968103, year = {2024}, author = {Yang, W and Chen, MA and Lee, SH and Kang, PK}, title = {Fluid inertia controls mineral precipitation and clogging in pore to network-scale flows.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {121}, number = {28}, pages = {e2401318121}, pmid = {38968103}, issn = {1091-6490}, support = {DE-SC0023429//U.S. Department of Energy (DOE)/ ; ECCS-2025124//National Science Foundation (NSF)/ ; }, abstract = {Mineral precipitation caused by fluid mixing presents complex control and predictability challenges in a variety of natural and engineering processes, including carbon mineralization, geothermal energy, and microfluidics. Precipitation dynamics, particularly under the influence of fluid flow, remain poorly understood. Combining microfluidic experiments and three-dimensional reactive transport simulations, we demonstrate that fluid inertia controls mineral precipitation and clogging at flow intersections, even in laminar flows. We observe distinct precipitation regimes as a function of Reynolds number (Re). At low Reynolds numbers (Re < 10), precipitates form a thin, dense layer along the mixing interface, which shuts precipitation off, while at high Reynolds numbers (Re > 50), strong three-dimensional flows significantly enhance precipitation over the entire intersection, resulting in rapid clogging. When injection rates from two inlets are uneven, flow symmetry-breaking leads to unexpected flow bifurcation phenomena, which result in enhanced concurrent precipitation in both downstream channels. Finally, we extend our findings to rough channel networks and demonstrate that the identified inertial effects on precipitation at the intersection scale are also present and even more dramatic at the network scale. This study sheds light on the fundamental mechanisms underlying mixing-induced mineral precipitation and provides a framework for designing and optimizing processes involving mineral precipitation.}, }
@article {pmid38958090, year = {2024}, author = {Wang, H and Xiong, J and Cai, Y and Fu, W and Zhong, Y and Jiang, T and Cheang, UK}, title = {Stabilization of CsPbBr3 Nanowires Through SU-8 Encapsulation for the Fabrication of Bilayer Microswimmers with Magnetic and Fluorescence Properties.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {20}, number = {42}, pages = {e2400346}, doi = {10.1002/smll.202400346}, pmid = {38958090}, issn = {1613-6829}, support = {52375569//National Natural Science Foundation of China/ ; RCYX20210609103644015//Science and Technology Innovation Committee Foundation of Shenzhen/ ; 2021ZDZX2037//Department of Education of Guangdong/ ; 2021A1515110212//Guangdong Basic and Applied Basic Research Foundation/ ; 2023A1515012229//Guangdong Basic and Applied Basic Research Foundation/ ; }, abstract = {All-inorganic cesium lead halide (CsPbX3, X = Cl, Br, I) perovskite nanocrystals have drawn great interest because of their excellent photophysical properties and potential applications. However, their poor stability in water greatly limited their use in applications that require stable structures. In this work, a facile approach to stabilize CsPbBr3 nanowires is developed by using SU-8 as a protection medium; thereby creating stable CsPbBr3/SU-8 microstructures. Through photolithography and layer-by-layer deposition, CsPbBr3/SU-8 is used to fabricate bilayer achiral microswimmers (BAMs), which consist of a top CsPbBr3/SU-8 layer and a bottom Fe3O4 magnetic layer. Compared to pure CsPbBr3 nanowires, the CsPbBr3/SU-8 shows long-term structural and fluorescence stability in water against ultrasonication treatment. Due to the magnetic layer, the motion of the microswimmers can be controlled precisely under a rotating magnetic field, allowing them to swim at low Reynolds number and tumble or roll on surfaces. Furthermore, CsPbBr3/SU-8 can be used to fabricate various types of planar microstructures with high throughput, high consistency, and fluorescence properties. This work provides a method for the stabilization of CsPbBr3 and demonstrates the potential to mass fabricate planar microstructures with various shapes, which can be used in different applications such as microrobotics.}, }
@article {pmid38950632, year = {2024}, author = {Stachurska, B and Sulisz, W}, title = {Laboratory investigations of wave-induced transport of plastic debris over a rippled bottom.}, journal = {The Science of the total environment}, volume = {946}, number = {}, pages = {174380}, doi = {10.1016/j.scitotenv.2024.174380}, pmid = {38950632}, issn = {1879-1026}, abstract = {Laboratory experiments are conducted in a wave flume to investigate the effect of water waves on the transport of plastic pellets over a rippled bottom. The horizontal velocities of plastic debris are analyzed over the rippled bottom for different wave conditions and plastic elements with different properties. Laboratory investigations determined the characteristic transport patterns of wave-induced plastic debris with a density of ∼2.0g/cm3 moving along the rippled bottom. In the first, swing-type motion, the grains move only in the ripple trough with velocities lower than 0.10 m/s. For sliding-type movement, the grains move along the entire rippled surface with velocities in the range of 0.10-0.13 m/s. For higher velocities in the range of 0.15-0.20 m/s, a saltation-type motion becomes dominant. The results show that plastic grains may move up to 2-3 cm above the ripple crest depending on hydrodynamic conditions. The analysis shows that for velocity-skewed flows, sliding-type motion and onshore transport dominate. For acceleration-skewed flows, saltation-type motion and offshore transport dominate, which is attributed to higher boundary layer thickness and phase lag effects. The analysis of the relationship between the particle Reynolds number and the thickness of the turbulent boundary layer reveals that for values of Rep≥1000 and a boundary layer thickness mm saltation-type motion becomes dominant. The direction of transport is affected not only by the density of the sediment and the wave skewness coefficients but also by the dimensions of the bottom ripples. The laboratory investigations also provide insight into the hydrodynamic conditions affecting the transport of plastic debris along the bottom covered with ripples in oscillating nonlinear water flows.}, }
@article {pmid38947461, year = {2024}, author = {Amsie, AB and Ayalew, AT and Mada, ZM and Finsa, MM}, title = {Acclimatize experimental approach to adjudicate hydraulic coefficients under different bed material configurations and slopes with and without weir.}, journal = {Heliyon}, volume = {10}, number = {11}, pages = {e32162}, pmid = {38947461}, issn = {2405-8440}, abstract = {The primary purpose of this study was to evaluate the hydraulic coefficient of coarse aggregate grain size beds and hydraulic parameters under random and perpendicular bed configurations, as well as to explore the discharge coefficient for rectangular weirs. The research objectives were to compare flow resistance coefficients, evaluate the discharge coefficient for rectangular weirs, investigate the relationship between roughness coefficient and hydraulic parameters, and validate the theoretical hydraulic equation for the rectangular weir. This was achieved by analysing different bed configurations, bed slopes, and 20 and 30-mm bed materials. Sieve analysis was conducted on bed materials using American-standard sieves to determine their particle size distribution. The experiment was performed in a rectangular flume measuring 12 m in length, 0.31 m in width, and 0.45 m in depth. In a laboratory experiment, water was pumped into a flume using centrifugal pumps, and a rectangular weir was attached downstream for discharge measurement. The experiment investigated factors such as Manning roughness coefficient, bed material geometry, bed slope, and weir shapes. Approximately 1680 tests were conducted to analysed the impact of these factors on discharge and the coefficient of discharge. The average Manning's roughness coefficients for a grain size of 20 mm were 0.019 (with weir) and 0.019 (without weir) in a random bed configuration, and 0.028 (with weir) and 0.027 (without weir) in a perpendicular flow bed configuration. For a grain size of 30 mm, the coefficients were 0.023 (with weir) and 0.022 (without weir) in a random bed configuration, and 0.033 (with weir) and 0.026 (without weir) in a perpendicular flow bed configuration. The presence of a weir has affected Manning's roughness coefficients and discharge coefficients. With a weir, the roughness coefficients have generally been higher compared to without a weir, indicating increased roughness in the channel. The discharge coefficient for a rectangular weir with a grain size of 20 mm ranged from 0.39 to 0.84 (random bed) and 0.27 to 0.68 (perpendicular flow bed), while for a grain size of 30 mm it ranged from 0.31 to 0.81 (random bed) and 0.23 to 0.48 (perpendicular flow bed). The discharge coefficients have varied depending on the grain size and bed configuration, reflecting different flow efficiencies over the weir. Rough particles influenced flow and Manning's roughness coefficient value, then reduced discharge and velocity values. Under two bed configurations and slopes, beds with a grain size of 30 mm have higher roughness coefficients compared to those with a grain size of 20 mm. The models have shown that the roughness coefficient is inversely proportional to the discharge and directly proportional to the tailgate water levels. The coefficient of roughness and discharge coefficient are mainly influenced by the channel slopes, bed roughness, bed grain size, and bed configuration. A randomly configured bed with a 20 mm grain size gravel bed is preferred over a perpendicular bed configuration to handle high discharges. Using a 20 mm grain-size gravel bed in open-channel flow is more suitable than a 30 mm grain-size bed. Relying on the constant friction factor, Manning's n, is not recommended as it may result in design errors. These findings have the potential to improve hydraulic engineering design practices, enhancing the accuracy and efficiency of open-channel flow systems.}, }
@article {pmid38947451, year = {2024}, author = {Mahammedi, A and Tayeb, NT and Kim, JH and Hossain, S}, title = {Entropy generation analysis and thermal synergy efficiency in the T-shaped micro-kenics.}, journal = {Heliyon}, volume = {10}, number = {11}, pages = {e32233}, pmid = {38947451}, issn = {2405-8440}, abstract = {In this work, three different twist angles of a micro helical insert in a T-shaped are studied numerically in order to evaluate the laminar steady flow behavior of Newtonian fluid in chaotic geometry. In the geometries under consideration, thermal mixing behavior is carried out using fluids having two distinct input temperatures. Under the influence of chaotic advection and low rates of Reynolds number, the second law of thermodynamics is controlled in terms of the entropy generation caused by hydrodynamic and thermal processes. The governing equations are numerically solved using the CFD Fluent code. Thus, the micromixer's configuration demonstrated a very significant improvement in mixing degree while minimizing friction and thermal irreversibilities. The synergy coefficient, which depicts the link between velocity and heat transfer in angle form, is analyzed and the results are provided.}, }
@article {pmid38937518, year = {2024}, author = {Akilu, S and Sharma, KV and Baheta, AT and Kanti, PK and Paramasivam, P}, title = {Machine learning analysis of thermophysical and thermohydraulic properties in ethylene glycol- and glycerol-based SiO2 nanofluids.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {14829}, pmid = {38937518}, issn = {2045-2322}, abstract = {The study investigates the heat transfer and friction factor properties of ethylene glycol and glycerol-based silicon dioxide nanofluids flowing in a circular tube under continuous heat flux circumstances. This study tackles the important requirement for effective thermal management in areas such as electronics cooling, the automobile industry, and renewable energy systems. Previous research has encountered difficulties in enhancing thermal performance while handling the increased friction factor associated with nanofluids. This study conducted experiments in the Reynolds number range of 1300 to 21,000 with particle volume concentrations of up to 1.0%. Nanofluids exhibited superior heat transfer coefficients and friction factor values than the base liquid values. The highest enhancement in heat transfer was 5.4% and 8.3% for glycerol and ethylene glycol -based silicon dioxide Nanofluid with a relative friction factor penalty of ∼30% and 75%, respectively. To model and predict the complicated, nonlinear experimental data, five machine learning approaches were used: linear regression, random forest, extreme gradient boosting, adaptive boosting, and decision tree. Among them, the decision tree-based model performed well with few errors, while the random forest and extreme gradient boosting models were also highly accurate. The findings indicate that these advanced machine learning models can accurately anticipate the thermal performance of nanofluids, providing a dependable tool for improving their use in a variety of thermal systems. This study's findings help to design more effective cooling solutions and improve the sustainability of energy systems.}, }
@article {pmid38930772, year = {2024}, author = {Kottmeier, J and Wullenweber, MS and Kampen, I and Kwade, A and Dietzel, A}, title = {A High-Aspect-Ratio Deterministic Lateral Displacement Array for High-Throughput Fractionation.}, journal = {Micromachines}, volume = {15}, number = {6}, pages = {}, pmid = {38930772}, issn = {2072-666X}, support = {SPP 2045//Deutsche Forschungsgemeinschaft/ ; }, abstract = {Future industrial applications of microparticle fractionation with deterministic lateral displacement (DLD) devices are hindered by exceedingly low throughput rates. To enable the necessary high-volume flows, high flow velocities as well as high aspect ratios in DLD devices have to be investigated. However, no experimental studies have yet been conducted on the fractionation of bi-disperse suspensions containing particles below 10 µm with DLD at a Reynolds number (Re) above 60. Furthermore, devices with an aspect ratio of more than 4:1, which require advanced microfabrication, are not known in the DLD literature. Therefore, we developed a suitable process with deep reactive ion etching of silicon and anodic bonding of a glass lid to create pressure-resistant arrays. With a depth of 120 µm and a gap of 23 µm between posts, a high aspect ratio of 6:1 was realized, and devices were investigated using simulations and fractionation experiments. With the two-segmented array of 3° and 7° row shifts, critical diameters of 8 µm and 12 µm were calculated for low Re conditions, but it was already known that vortices behind the posts can shift these values to lower critical diameters. Suspensions with polystyrene particles in different combinations were injected with an overall flow rate of up to 15 mL/min, corresponding to Re values of up to 90. Suspensions containing particle combinations of 2 µm with 10 µm as well as 5 µm with 10 µm were successfully fractionated, even at the highest flow rate. Under these conditions, a slight widening of the displacement position was observed, but there was no further reduction in the critical size as it was for Re = 60. With an unprecedented fractionation throughput of nearly 1 L per hour, entirely new applications are being developed for chemical, pharmaceutical, and recycling technologies.}, }
@article {pmid38930743, year = {2024}, author = {Juraeva, M and Kang, DJ}, title = {Mixing Performance of a Passive Micromixer Based on Split-to-Circulate (STC) Flow Characteristics.}, journal = {Micromachines}, volume = {15}, number = {6}, pages = {}, pmid = {38930743}, issn = {2072-666X}, abstract = {We propose a novel passive micromixer leveraging STC (split-to-circulate) flow characteristics and analyze its mixing performance comprehensively. Three distinct designs incorporating submerged circular walls were explored to achieve STC flow characteristics, facilitating flow along a convex surface and flow impingement on a concave surface. Across a broad Reynolds number range (0.1 to 80), the present micromixer substantially enhances mixing, with a degree of mixing (DOM) consistently exceeding 0.84. Particularly, the mixing enhancement is prominent within the low and intermediate range of Reynolds numbers (0.1<Re<20). This enhancement stems from key flow characteristics of STC: the formation of saddle points around convex walls and flow impingement on concave walls. Compared to other passive micromixers, the DOM of the present micromixer stands out as notably high over a broad range of Reynolds numbers (0.1≤Re≤80).}, }
@article {pmid38930665, year = {2024}, author = {Huang, H and Liu, J and Yu, J and Pan, W and Yan, Z and Pan, Z}, title = {Behind the Non-Uniform Breakup of Bubble Slug in Y-Shaped Microchannel: Dynamics and Mechanisms.}, journal = {Micromachines}, volume = {15}, number = {6}, pages = {}, pmid = {38930665}, issn = {2072-666X}, abstract = {Bubble flow in confined geometries is a problem of fundamental and technological significance. Among all the forms, bubble breakup in bifurcated microchannels is one of the most commonly encountered scenarios, where an in-depth understanding is necessary for better leveraging the process. This study numerically investigates the non-uniform breakup of a bubble slug in Y-shaped microchannels under different flow ratios, Reynolds numbers, and initial bubble volumes. Overall, the bubble can either breakup or non-breakup when passing through the bifurcation and shows different forms depending on flow regimes. The flow ratio-Reynolds number phase diagrams indicate a power-law transition line of breakup and non-breakup. The bubble takes longer to break up with rising flow ratios yet breaks earlier with higher Reynolds numbers and volumes. Non-breakup takes less time than the breakup patterns. Flow ratio is the origin of non-uniform breakup. Both the Reynolds number and initial volume influence the bubble states when reaching the bifurcation and thus affect subsequent processes. Bubble neck dynamics are analyzed to describe the breakup further. The volume distribution after breaking up is found to have a quadratic relation with the flow ratio. Our study is hoped to provide insights for practical applications related to non-uniform bubble breakups.}, }
@article {pmid38930661, year = {2024}, author = {Ganguli, A and Bhatt, V and Yagodnitsyna, A and Pinjari, D and Pandit, A}, title = {A Review of Pressure Drop and Mixing Characteristics in Passive Mixers Involving Miscible Liquids.}, journal = {Micromachines}, volume = {15}, number = {6}, pages = {}, pmid = {38930661}, issn = {2072-666X}, abstract = {The present review focuses on the recent studies carried out in passive micromixers for understanding the hydrodynamics and transport phenomena of miscible liquid-liquid (LL) systems in terms of pressure drop and mixing indices. First, the passive micromixers have been categorized based on the type of complexity in shape, size, and configuration. It is observed that the use of different aspect ratios of the microchannel width, presence of obstructions, flow and operating conditions, and fluid properties majorly affect the mixing characteristics and pressure drop in passive micromixers. A regime map for the micromixer selection based on optimization of mixing index (MI) and pressure drop has been identified based on the literature data for the Reynolds number (Re) range (1 ≤ Re ≤ 100). The map comprehensively summarizes the favorable, moderately favorable, or non-operable regimes of a micromixer. Further, regions for special applications of complex micromixer shapes and micromixers operating at low Re have been identified. Similarly, the operable limits for a micromixer based on pressure drop for Re range 0.1 < Re < 100,000 have been identified. A comparison of measured pressure drop with fundamentally derived analytical expressions show that Category 3 and 4 micromixers mostly have higher pressure drops, except for a few efficient ones. An MI regime map comprising diffusion, chaotic advection, and mixed advection-dominated zones has also been devised. An empirical correlation for pressure drop as a function of Reynolds number has been developed and a corresponding friction factor has been obtained. Predictions on heat and mass transfer based on analogies in micromixers have also been proposed.}, }
@article {pmid38920538, year = {2024}, author = {Gerolymos, GA and Vallet, I}, title = {Entropy Fluctuations and Correlations in Compressible Turbulent Plane Channel Flow.}, journal = {Entropy (Basel, Switzerland)}, volume = {26}, number = {6}, pages = {}, pmid = {38920538}, issn = {1099-4300}, support = {2023-022139, 2022-022139, 2021-022139, 2020-022139, 2019-022139, 2018-022139 TGCC-CINES-IDRIS//Grand &#xc9;quipement National de Calcul Intensif (France)/ ; 2021-240083 JUWELS//Partnership for Advanced Computing in Europe/ ; ANR-15-CE06-0009 NumERICCS//Agence Nationale de la Recherche/ ; }, abstract = {The thermodynamic turbulence structure of compressible aerodynamic flows is often characterised by the correlation coefficient of entropy with pressure or temperature. We study entropy fluctuations s' and their correlations with the fluctuations of the other thermodynamic variables in compressible turbulent plane channel flow using dns data. We investigate the influence of the hcb (Huang-Coleman-Bradshaw) friction Reynolds number (100⪅Reτ★⪅1000) and of the centreline Mach number (0.3⪅M¯CLx⪅2.5) on the magnitude and location of the peak of the root-mean-square srms'. The complete series expansions of s' with respect to the fluctuations of the basic thermodynamic variables (pressure p, density ρ and temperature T) are calculated for the general case of variable heat-capacity cp(T) thermodynamics. The correlation coefficients of s' with the fluctuations of the basic thermodynamic quantities (cs'p', cs'ρ', cs'T'), for varying (Reτ★,M¯CLx), are studied. Insight on these correlations is provided by considering the probability density function (pdf) of s' and its joint pdfs with the other thermodynamic variables.}, }
@article {pmid38919163, year = {2024}, author = {Tanriverdi, S and Cruz, J and Habibi, S and Amini, K and Costa, M and Lundell, F and Mårtensson, G and Brandt, L and Tammisola, O and Russom, A}, title = {Elasto-inertial focusing and particle migration in high aspect ratio microchannels for high-throughput separation.}, journal = {Microsystems &amp; nanoengineering}, volume = {10}, number = {}, pages = {87}, pmid = {38919163}, issn = {2055-7434}, abstract = {The combination of flow elasticity and inertia has emerged as a viable tool for focusing and manipulating particles using microfluidics. Although there is considerable interest in the field of elasto-inertial microfluidics owing to its potential applications, research on particle focusing has been mostly limited to low Reynolds numbers (Re<1), and particle migration toward equilibrium positions has not been extensively examined. In this work, we thoroughly studied particle focusing on the dynamic range of flow rates and particle migration using straight microchannels with a single inlet high aspect ratio. We initially explored several parameters that had an impact on particle focusing, such as the particle size, channel dimensions, concentration of viscoelastic fluid, and flow rate. Our experimental work covered a wide range of dimensionless numbers (0.05 < Reynolds number < 85, 1.5 < Weissenberg number < 3800, 5 < Elasticity number < 470) using 3, 5, 7, and 10 µm particles. Our results showed that the particle size played a dominant role, and by tuning the parameters, particle focusing could be achieved at Reynolds numbers ranging from 0.2 (1 µL/min) to 85 (250 µL/min). Furthermore, we numerically and experimentally studied particle migration and reported differential particle migration for high-resolution separations of 5 µm, 7 µm and 10 µm particles in a sheathless flow at a throughput of 150 µL/min. Our work elucidates the complex particle transport in elasto-inertial flows and has great potential for the development of high-throughput and high-resolution particle separation for biomedical and environmental applications.}, }
@article {pmid38907454, year = {2024}, author = {Zero, EN and Crespi, VH}, title = {Emergence of inertia in the low-Reynolds regime of self-diffusiophoretic motion.}, journal = {Physical review. E}, volume = {109}, number = {5-1}, pages = {054602}, doi = {10.1103/PhysRevE.109.054602}, pmid = {38907454}, issn = {2470-0053}, abstract = {For isotropic swimming particles driven by self-diffusiophoresis at zero Reynolds number (where particle velocity responds instantaneously to applied force), the diffusive timescale of emitted solute can produce an emergent quasi-inertial behavior. These particles can orbit in a central potential and reorient under second-order dynamics, not the first-order dynamics of classical zero-Reynolds motion. They are described by a simple effective model that embeds their history-dependent behavior as an effective inertia, this being the most primitive expression of memory. The system can be parameterized with dynamic quantities such as particle size and swimming speed, without detailed knowledge of the diffusiophoretic mechanism.}, }
@article {pmid38905672, year = {2024}, author = {Matsuda, K and Yoshimatsu, K and Schneider, K}, title = {Heavy Particle Clustering in Inertial Subrange of High-Reynolds Number Turbulence.}, journal = {Physical review letters}, volume = {132}, number = {23}, pages = {234001}, doi = {10.1103/PhysRevLett.132.234001}, pmid = {38905672}, issn = {1079-7114}, abstract = {Direct numerical simulation of homogeneous isotropic turbulence shows pronounced clustering of inertial particles in the inertial subrange at high Reynolds number, in addition to the clustering typically observed in the near dissipation range. The clustering in the inertial subrange is characterized by the bump in the particle number density spectra and is due to modulation of preferential concentration. The number density spectrum can be modeled by a rational function of the scale-dependent Stokes number.}, }
@article {pmid38900310, year = {2024}, author = {Li, Z and Ye, H and Lin, J and Ouyang, Z}, title = {Analysis of the number of topological defects in active nematic fluids under applied shear flow.}, journal = {The European physical journal. E, Soft matter}, volume = {47}, number = {6}, pages = {43}, pmid = {38900310}, issn = {1292-895X}, support = {12132015//Key Programme/ ; 12332015//Key Programme/ ; }, abstract = {The number of topological defects in the shear flow of active nematic fluids is numerically investigated in this study. The evolution of the flow state of extensile active nematic fluids is explored by increasing the activity of active nematic fluids. Evidently, medium-activity active nematic fluids exhibit a highly ordered vortex lattice fluid state. However, high-activity active nematic fluids exhibit a meso-scale turbulent flow accompanied by topological defects. The number of topological defects (Ndef) increases with increasing shear Reynolds number (Res). Fluid viscosity strongly influences Ndef, while the influence of fluid density is relatively weak. Ndef decreases with increasing activity length scale (lζ) value. A small Res value strongly influences Ndef, whereas a large lζ value only weakly influences Ndef. As the activity increases, Ndef in contractile active nematic fluids becomes larger than that of extensile active nematic fluids.}, }
@article {pmid38893741, year = {2024}, author = {Hanzlik, J and Vanek, J and Pata, V and Senkerik, V and Polaskova, M and Kruzelak, J and Bednarik, M}, title = {The Impact of Surface Roughness on Conformal Cooling Channels for Injection Molding.}, journal = {Materials (Basel, Switzerland)}, volume = {17}, number = {11}, pages = {}, pmid = {38893741}, issn = {1996-1944}, support = {IGA/FT/2024/003//Internal Grant Agency of Tomas Bata University in Zlin/ ; }, abstract = {Injection molding technology is widely utilized across various industries for its ability to fabricate complex-shaped components with exceptional dimensional accuracy. However, challenges related to injection quality often arise, necessitating innovative approaches for improvement. This study investigates the influence of surface roughness on the efficiency of conformal cooling channels produced using additive manufacturing technologies, specifically Direct Metal Laser Sintering (DMLS) and Atomic Diffusion Additive Manufacturing (ADAM). Through a combination of experimental measurements, including surface roughness analysis, scanning electron microscopy, and cooling system flow analysis, this study elucidates the impact of surface roughness on coolant flow dynamics and pressure distribution within the cooling channels. The results reveal significant differences in surface roughness between DMLS and ADAM technologies, with corresponding effects on coolant flow behavior. Following that fact, this study shows that when cooling channels' surface roughness is lowered up to 90%, the reduction in coolant media pressure is lowered by 0.033 MPa. Regression models are developed to quantitatively describe the relationship between surface roughness and key parameters, such as coolant pressure, Reynolds number, and flow velocity. Practical implications for the optimization of injection molding cooling systems are discussed, highlighting the importance of informed decision making in technology selection and post-processing techniques. Overall, this research contributes to a deeper understanding of the role of surface roughness in injection molding processes and provides valuable insights for enhancing cooling system efficiency and product quality.}, }
@article {pmid38882326, year = {2024}, author = {Ali, I and Hussain, T and Unar, IN and Kumar, L and Ahad, IU}, title = {Turbulence model study for aerodynamic analysis of the leading edge tubercle wing for low Reynolds number flows.}, journal = {Heliyon}, volume = {10}, number = {11}, pages = {e32148}, pmid = {38882326}, issn = {2405-8440}, abstract = {A turbulence model study was performed to analyze the flow around the Tubercle Leading Edge (TLE) wing. Five turbulence models were selected to evaluate aerodynamic force coefficients and flow mechanism by comparing with existing literature results. The selected models are realizable k-ε, k-ω Shear Stress Transport (SST), (γ - R e θ) SST model, Transition k-k l -ω model and Stress- ω Reynolds Stress Model (RSM). For that purpose, the TLE wing model was developed by using the NACA0021 airfoil profile. The wing model is designed with tubercle wavelength of 0.11c and amplitude of 0.03c. Numerical simulation was performed at chord-based Reynolds number of Rec = 120,000. The Computational Fluid Dynamic (CFD) simulation reveals that among the selected turbulence models, Stress- ω RSM estimated aerodynamic forces (i.e. lift and drag) coefficients closest to that of the experimental values followed by realizable k-ε, (γ - R e θ) SST model, k-ω SST model and k-k l -ω model. However, at a higher angle of attacks i.e. at 16° &amp; 20° k-ω SST model predicted closest drag and lift coefficient to that of the experimental values. Additionally, the critical observation of pressure contour confirmed that at the lower angle of attack Stress- ω RSM predicted strong Leading Edge (LE) suction followed by realizable k-ε, (γ - R e θ)SST model, k-ω SST model and k-k l -ω model. Thus, the superiority of Stress- ω RSM in predicting the aerodynamic force coefficients is shown by the flow behavior. In addition to this pressure contours also confirmed that k-k l -ω model failed to predict tubercled wing aerodynamic performance. At higher angles of attacks k-ω SST model estimated aerodynamic force coefficients closest to that of the experimental values, thus k-ω SST model is used at 16° &amp; 20° AoAs. The observed streamline behavior for different turbulence models showed that the Stress- ω RSM model and k-k l -ω model failed to model flow behavior at higher AoAs, whereas k-ω SST model is a better approach to model separated flows that experience strong flow recirculation zone.}, }
@article {pmid38858424, year = {2024}, author = {Khashan, S and Odhah, AA and Taha, M and Alazzam, A and Al-Fandi, M}, title = {Enhanced microfluidic multi-target separation by positive and negative magnetophoresis.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {13293}, pmid = {38858424}, issn = {2045-2322}, support = {ENG/1/13/2018//Scientific Research and Innovation Support Fund (SRSF)/ ; }, mesh = {Humans ; *Microfluidic Analytical Techniques/instrumentation/methods ; Cell Separation/methods/instrumentation ; Erythrocytes ; Microfluidics/methods/instrumentation ; Leukocytes ; Hydrodynamics ; Cell Line, Tumor ; }, abstract = {We introduce magnetophoresis-based microfluidics for sorting biological targets using positive Magnetophoresis (pM) for magnetically labeled particles and negative Magnetophoresis (nM) for label-free particles. A single, externally magnetized ferromagnetic wire induces repulsive forces and is positioned across the focused sample flow near the main channel's closed end. We analyze magnetic attributes and separation performance under two transverse dual-mode magnetic configurations, examining magnetic fields, hydrodynamics, and forces on microparticles of varying sizes and properties. In pM, the dual-magnet arrangement (DMA) for sorting three distinct particles shows higher magnetic gradient generation and throughput than the single-magnet arrangement (SMA). In nM, the numerical results for SMA sorting of red blood cells (RBCs), white blood cells (WBCs), and prostate cancer cells (PC3-9) demonstrate superior magnetic properties and throughput compared to DMA. Magnetized wire linear movement is a key design parameter, allowing device customization. An automated device for handling more targets can be created by manipulating magnetophoretic repulsion forces. The transverse wire and magnet arrangement accommodate increased channel depth without sacrificing efficiency, yielding higher throughput than other devices. Experimental validation using soft lithography and 3D printing confirms successful sorting and separation, aligning well with numerical results. This demonstrates the successful sorting and separating of injected particles within a hydrodynamically focused sample in all systems. Both numerical and experimental findings indicate a separation accuracy of 100% across various Reynolds numbers. The primary channel dimensions measure 100 µm in height and 200 µm in width. N52 permanent magnets were employed in both numerical simulations and experiments. For numerical simulations, a remanent flux density of 1.48 T was utilized. In the experimental setup, magnets measuring 0.5 × 0.5 × 0.125 inches and 0.5 × 0.5 × 1 inch were employed. The experimental data confirm the device's capability to achieve 100% separation accuracy at a Reynolds number of 3. However, this study did not explore the potential impact of increased flow rates on separation accuracy.}, }
@article {pmid38857262, year = {2024}, author = {Islam, M and Ali, U and Mone, S}, title = {Harnessing flow-induced vibrations for energy harvesting: Experimental and numerical insights using piezoelectric transducer.}, journal = {PloS one}, volume = {19}, number = {6}, pages = {e0304489}, pmid = {38857262}, issn = {1932-6203}, mesh = {*Vibration ; *Transducers ; Models, Theoretical ; Renewable Energy ; Micro-Electrical-Mechanical Systems/instrumentation ; Computer Simulation ; }, abstract = {Flow-induced vibrations (FIV) were considered as unwanted vibrations analogous to noise. However, in a recent trend, the energy of these vibrations can be harvested and converted to electrical power. In this study, the potential of FIV as a source of renewable energy is highlighted through experimental and numerical analyses. The experimental study was conducted on an elastically mounted circular cylinder using helical and leaf springs in the wind tunnel. The Reynolds number (Re) varied between 2300-16000. The motion of the cylinder was restricted in all directions except the transverse direction. The micro-electromechanical system (MEMS) was mounted on the leaf spring to harvest the mechanical energy. Numerical simulations were also performed with SST k-ω turbulence model to supplement the experiments and were found to be in good agreement with the experimental results. The flow separation and vortex shedding induce aerodynamic forces in the cylinder causing it to vibrate. 2S vortex shedding pattern was observed in all of the cases in this study. The maximum dimensionless amplitude of vibration (A/D) obtained was 0.084 and 0.068 experimentally and numerically, respectively. The results showed that the region of interest is the lock-in region where maximum amplitude of vibration is observed and, therefore, the maximum power output. The piezoelectric voltage and power output were recorded for different reduced velocities (Ur = 1-10) at different resistance values in the circuit. It was observed that as the amplitude of oscillation of the cylinder increases, the voltage and power output of the MEMS increases due to high strain in piezoelectric transducer. The maximum output voltage of 0.6V was observed at Ur = 4.95 for an open circuit, i.e., for a circuit with the resistance value of infinity. As the resistance value reduced, a drop in voltage output was observed. Maximum power of 10.5μW was recorded at Ur = 4.95 for a circuit resistance of 100Ω.}, }
@article {pmid38844512, year = {2024}, author = {Mizuno, Y and Misaka, T and Furukawa, Y}, title = {Fluid-particle-structure interaction in single shot peening.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {13029}, pmid = {38844512}, issn = {2045-2322}, abstract = {Shot peening is a widely used cold-working process. Physical phenomena of shot peening are analyzed using the developed fluid-particle-structure coupled solver. The influences of the flow field and shot peening parameters such as the shot impact velocity and shot size are investigated in the case of the falling, impacting, and rebounding single particle. The weakly coupled solver applies the immersed boundary method which enables direct evaluation of the interactions between the unsteady flow field and moving/deforming objects. The elastoplastic object of AISI4340 during the collision of rigid steel shot is analyzed dynamically using the finite element method. Consequently, it is clarified that the flow field of the post-collision between the shot and structure can be characterized by the relative Reynolds number, which is based on the shot diameter and relative velocity between the uniform flow and rebounding shot velocities. As the relative Reynolds number increases, the complex flow field and vortex structures are generated at the collision location. These fluid structures affect the collision phenomena resulting in the random behavior of the shot and the asymmetric indentation in the structure.}, }
@article {pmid38833948, year = {2024}, author = {Lou, S and Zou, Y and Wang, H and Zhou, F and Liu, S and Tu, J and Fedorova, IV}, title = {Influence of vegetation on heavy metal Cr release process from bottom sediment under unidirectional flows and regular waves.}, journal = {Marine pollution bulletin}, volume = {204}, number = {}, pages = {116535}, doi = {10.1016/j.marpolbul.2024.116535}, pmid = {38833948}, issn = {1879-3363}, mesh = {*Geologic Sediments/chemistry ; *Water Pollutants, Chemical/analysis ; *Chromium/analysis ; *Metals, Heavy/analysis ; Environmental Monitoring ; Plants ; Wetlands ; Water Movements ; }, abstract = {As human activities become more intensive, a substantial number of heavy metals are discharged into estuarine or wetland environments. Due to the poor degradability, heavy metals are prone to adsorption and deposition on suspended particles in bottom sediments. Subsequently, under the influence of disturbances, there is a potential for their re-release, causing secondary pollution. To investigate the release process of the heavy metal Cr from sediment, laboratory experiments were conducted under both unidirectional flow and regular wave conditions. At the initial stage, the temporal trends of particulate (CrP) and dissolved (CrD) Chromium concentrations were both characterized by initial increments followed by stabilization and continuous escalation. Vertically, the stable concentrations of CrP and CrD increased with the presence of vegetation and the enhancement of hydrodynamics. The Elovich equation, pseudo-second-order kinetic equation, Double constant equation (Freundlich model), and parabolic diffusion equation were employed to predict the release process of CrD from bottom sediment. The Elovich equation proved most suitable for describing the release process of CrD, with an R[2] exceeding 0.9. In order to assess the influence of vegetation on the Cr release process, the Stem-Reynolds were introduced to modify the Elovich equation. The final maximum error was 12 % (excluding the initial stage), which was much lower than that using the original Elovich equation (maximum error of 32 %). The study findings provide practical support for estuarine and wetland managers to formulate effective heavy metal management measures, which contribute to the conservation and sustainable management of aquatic ecosystems.}, }
@article {pmid38809093, year = {2024}, author = {Li, D and Dong, J and Li, H}, title = {Electromagnetohydrodynamic (EMHD) flow of Jeffrey fluid through a rough circular microchannel with surface charge-dependent slip.}, journal = {Electrophoresis}, volume = {45}, number = {19-20}, pages = {1727-1747}, doi = {10.1002/elps.202300297}, pmid = {38809093}, issn = {1522-2683}, support = {11962021//National Natural Science Foundation of China/ ; 2021MS05020//Natural Science Foundation of Inner Mongolia Autonomous Region/ ; JY20220138//Basic Science Research Fund in the Universities Directly under the Inner Mongolia Autonomous Region/ ; JY20220331//Basic Science Research Fund in the Universities Directly under the Inner Mongolia Autonomous Region/ ; }, mesh = {*Hydrodynamics ; *Surface Properties ; Models, Theoretical ; Microfluidic Analytical Techniques/instrumentation ; Computer Simulation ; }, abstract = {This research examines the electromagnetohydrodynamic (EMHD) flow of Jeffrey fluid in a rough circular microchannel while considering the effect of surface charge on slip. The channel wall corrugations are described as periodic sinusoidal waves with small amplitudes. The perturbation method is employed to derive solutions for velocity and volumetric flow rate, and a combination of three-dimensional (3D) and two-dimensional (2D) graphical representations is utilized to effectively illustrate the impacts of relevant parameters on them. The significance of the Reynolds number R e $Re$ in investigations of EMHD flow is particularly emphasized. Furthermore, the effect of wall roughness ε $\varepsilon $ and wave number k $k$ on velocity and the influence of wall roughness ε $\varepsilon $ and surface charge density σ s ${\sigma }_s$ on volumetric flow rate are primarily focused on, respectively, at various Reynolds numbers. The results suggest that increasing the wall roughness leads to a reduction in velocity at low Reynolds numbers (R e = 1 $Re = 1$) and an increment at high Reynolds numbers (R e = 10 $Re = 10$). For any Reynolds number, a roughness with an odd multiple of wave number (k = 6 , 10 $k = 6,10$) will result in a more stable velocity profile compared to one with an even multiple of wave number (k = 4 , 8 $k = 4,8$). Decreasing the relaxation time λ ¯ 1 ${\bar{\lambda }}_1$ while increasing the retardation time λ ¯ 2 ${\bar{\lambda }}_2$ and Hartmann number H a $Ha$ can diminish the impact of wall roughness ε $\varepsilon $ and surface charge density σ s ${\sigma }_s$ on volumetric flow rate, independent of the Reynolds number. Interestingly, in the existence of wall roughness, further consideration of the effect of surface charge on slip leads to a 15% drop in volumetric flow rate at R e = 1 $Re = 1$ and a 32% slippage at R e = 10 $Re = 10$ . However, in the condition where the effect of surface charge on slip is considered, further examination of the presence of wall roughness only results in a 1.4% decline in volumetric flow rate at R e = 1 $Re = 1$ and a 1.6% rise at R e = 10 $Re = 10$ . These findings are crucial for optimizing the EMHD flow models in microchannels.}, }
@article {pmid38794969, year = {2024}, author = {Shi, X and He, Q and Tan, W and Lu, Y and Zhu, G}, title = {Experiment study on focusing pattern prediction of particles in asymmetric contraction-expansion array channel.}, journal = {Electrophoresis}, volume = {45}, number = {23-24}, pages = {2169-2181}, doi = {10.1002/elps.202400042}, pmid = {38794969}, issn = {1522-2683}, support = {22078236//National Natural Science Foundation of China/ ; 21JCZDJC00420//Science and Technology Plan Project of Tianjin/ ; }, mesh = {*Microfluidic Analytical Techniques/instrumentation/methods ; Equipment Design ; Models, Theoretical ; Computer Simulation ; Particle Size ; }, abstract = {Contraction-expansion array (CEA) microchannel is a typical structure applied on particle/cell manipulation. The prediction of the particle focusing pattern in CEA microchannel is worthwhile to be investigate deeply. Here, we demonstrated a virtual boundary method by flow field analysis and theoretical derivation. The calculating method of the virtual boundary location, related to the Reynolds number (Re) and the structure parameter RW, was proposed. Combining the approximate Poiseuille flow pattern based on the virtual boundary method with the simulation results of Dean flow, the main line pattern and the main/lateral lines pattern were predicted and validated in experiments. The transformation from the main line pattern to the main/lateral lines pattern can be facilitated by increasing Re, decreasing RW , and decreasing α. An empirical formula was derived to characterize the critical condition of the transformation. The virtual boundary method can provide a guidance for asymmetric CEA channel design and contribute to the widespread application of microfluidic particle focusing.}, }
@article {pmid38786503, year = {2024}, author = {Zhang, H and Zhu, B and Chen, W}, title = {Enhancing Energy Harvesting Efficiency of Flapping Wings with Leading-Edge Magnus Effect Cylinder.}, journal = {Biomimetics (Basel, Switzerland)}, volume = {9}, number = {5}, pages = {}, pmid = {38786503}, issn = {2313-7673}, support = {51576131//National Natural Science Foundation of China/ ; 91852117//National Natural Science Foundation of China/ ; 23PJD070//Shanghai Pujiang Programme/ ; LAB-2023-07-WD//National Key Laboratory of Marine Engine Science and Technology/ ; }, abstract = {According to the Magnus principle, a rotating cylinder experiences a lateral force perpendicular to the incoming flow direction. This phenomenon can be harnessed to boost the lift of an airfoil by positioning a rotating cylinder at the leading edge. In this study, we simulate flapping-wing motion using the sliding mesh technique in a heaving coordinate system to investigate the energy harvesting capabilities of Magnus effect flapping wings (MEFWs) featuring a leading-edge rotating cylinder. Through analysis of the flow field vortex structure and pressure distribution, we explore how control parameters such as gap width, rotational speed ratio, and phase difference of the leading-edge rotating cylinder impact the energy harvesting characteristics of the flapping wing. The results demonstrate that MEFWs effectively mitigate the formation of leading-edge vortices during wing motion. Consequently, this enhances both lift generation and energy harvesting capability. MEFWs with smaller gap widths are less prone to induce the detachment of leading-edge vortices during motion, ensuring a higher peak lift force and an increase in the energy harvesting efficiency. Moreover, higher rotational speed ratios and phase differences, synchronized with wing motion, can prevent leading-edge vortex generation during wing motion. All three control parameters contribute to enhancing the energy harvesting capability of MEFWs within a certain range. At the examined Reynolds number, the optimal parameter values are determined to be a∗ = 0.0005, R = 3, and ϕ0 = 0°.}, }
@article {pmid38758518, year = {2024}, author = {Rezazadeh, MR and Dastan, A and Sadrizadeh, S and Abouali, O}, title = {A quasi-realistic computational model development and flow field study of the human upper and central airways.}, journal = {Medical &amp; biological engineering &amp; computing}, volume = {62}, number = {10}, pages = {3025-3041}, pmid = {38758518}, issn = {1741-0444}, mesh = {Humans ; *Computer Simulation ; *Hydrodynamics ; *Models, Biological ; Tomography, X-Ray Computed ; Respiratory System/diagnostic imaging/anatomy &amp; histology ; Algorithms ; Lung/physiology/diagnostic imaging ; Trachea/physiology/diagnostic imaging ; }, abstract = {The impact of drug delivery and particulate matter exposure on the human respiratory tract is influenced by various anatomical and physiological factors, particularly the structure of the respiratory tract and its fluid dynamics. This study employs computational fluid dynamics (CFD) to investigate airflow in two 3D models of the human air conducting zone. The first model uses a combination of CT-scan images and geometrical data from human cadaver to extract the upper and central airways down to the ninth generation, while the second model develops the lung airways from the first Carina to the end of the ninth generation using Kitaoka's deterministic algorithm. The study examines the differences in geometrical characteristics, airflow rates, velocity, Reynolds number, and pressure drops of both models in the inhalation and exhalation phases for different lobes and generations of the airways. From trachea to the ninth generation, the average air flowrates and Reynolds numbers exponentially decay in both models during inhalation and exhalation. The steady drop is the case for the average air velocity in Kitaoka's model, while that experiences a maximum in the 3rd or 4th generation in the quasi-realistic model. Besides, it is shown that the flow field remains laminar in the upper and central airways up to the total flow rate of 15 l/min. The results of this work can contribute to the understanding of flow behavior in upper respiratory tract.}, }
@article {pmid38755908, year = {2024}, author = {Vasconcelos, GL and Ribeiro, LRC and Macêdo, AMS and González, IRR and Ospina, R and Brum, AA}, title = {Turbulence hierarchy in foreign exchange markets.}, journal = {Physical review. E}, volume = {109}, number = {4-1}, pages = {044313}, doi = {10.1103/PhysRevE.109.044313}, pmid = {38755908}, issn = {2470-0053}, abstract = {We present a multiscale stochastic analysis of foreign exchange rates using the H-theory formalism, which provides a hierarchical intermittency model for the information cascade in the currency market. We examine the distributions of returns and volatilities for the three most traded currency pairs: euro-U.S. dollar, U.S. dollar-Japanese yen, and British pound-U.S. dollar. We find that these markets have a hierarchy of timescales, with larger markets exhibiting more hierarchy levels. We provide a theoretical framework for understanding why the number of levels in the information cascade increases with market size, in analogy with similar behavior for the energy cascade in turbulence as a function of Reynolds number. We briefly argue that using turbulence-like models for financial markets can also provide valuable insights for developing efficient algorithmic trading strategies.}, }
@article {pmid38755871, year = {2024}, author = {Doranehgard, MH and Karimi, N and Borazjani, I and Li, LKB}, title = {Breaking the symmetry of a wavy channel alters the route to chaotic flow.}, journal = {Physical review. E}, volume = {109}, number = {4-2}, pages = {045103}, doi = {10.1103/PhysRevE.109.045103}, pmid = {38755871}, issn = {2470-0053}, abstract = {We numerically explore the two-dimensional, incompressible, isothermal flow through a wavy channel, with a focus on how the channel geometry affects the routes to chaos at Reynolds numbers between 150 and 1000. We find that (i) the period-doubling route arises in a symmetric channel, (ii) the Ruelle-Takens-Newhouse route arises in an asymmetric channel, and (iii) the type-II intermittency route arises in both asymmetric and semiwavy channels. We also find that the flow through the semiwavy channel evolves from a quasiperiodic torus to an unstable invariant set (chaotic saddle), before eventually settling on a period-1 limit-cycle attractor. This study reveals that laminar channel flow at elevated Reynolds numbers can exhibit a variety of nonlinear dynamics. Specifically, it highlights how breaking the symmetry of a wavy channel can not only influence the critical Reynolds number at which chaos emerges, but also diversify the types of bifurcation encountered en route to chaos itself.}, }
@article {pmid38744984, year = {2024}, author = {Refaie Ali, A and Mahmood, R and Asghar, A and Majeed, AH and Behiry, MH}, title = {AI-based predictive approach via FFB propagation in a driven-cavity of Ostwald de-Waele fluid using CFD-ANN and Levenberg-Marquardt.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {11024}, pmid = {38744984}, issn = {2045-2322}, abstract = {The integration of Artificial Intelligence (AI) and Machine Learning (ML) techniques into computational science has ushered in a new era of innovation and efficiency in various fields, with particular significance in computational fluid dynamics (CFD). Several methods based on AI and Machine Learning (ML) have been standardized in many fields of computational science, including computational fluid dynamics (CFD). This study aims to couple CFD with artificial neural networks (ANNs) to predict the fluid forces that arise when a flowing fluid interacts with obstacles installed in the flow domain. The momentum equation elucidating the flow has been simulated by adopting the finite element method (FEM) for a range of rheological and kinematic conditions. Hydrodynamic forces, including pressure drop between the back and front of the obstacle, surface drag, and lift variations, are measured on the outer surface of the cylinder via CFD simulations. This data has subsequently been fed into a Feed-Forward Back (FFB) propagation neural network for the prediction of such forces with completely unknown data. For all cases, higher predictivity is achieved for the drag coefficient (CD) and lift coefficient (CL) since the mean square error (MSE) is within ± 2% and the coefficient of determination (R) is approximately 99% for all the cases. The influence of pertinent parameters like the power law index (n) and Reynolds number (Re) on velocity, pressure, and drag and lift coefficients is also presented for limited cases. Moreover, a significant reduction in computing time has been noticed while applying hybrid CFD-ANN approach as compared with CFD simulations only.}, }
@article {pmid38725533, year = {2024}, author = {Si, X and Fang, L}, title = {Biologically generated turbulent energy flux in shear flow depends on tensor geometry.}, journal = {PNAS nexus}, volume = {3}, number = {2}, pages = {pgae056}, pmid = {38725533}, issn = {2752-6542}, abstract = {It has been proposed that biologically generated turbulence plays an important role in material transport and ocean mixing. Both experimental and numerical studies have reported evidence of the nonnegligible mixing by moderate Reynolds number swimmers, such as zooplankton, in quiescent water, especially at aggregation scales. However, the interaction between biologically generated agitation and the background flow, as a key factor in biologically generated turbulence that could reshape our previous knowledge of biologically generated turbulence, has long been ignored. Here, we show that the geometry between the biologically generated agitation and the background hydrodynamic shear can determine both the intensity and direction of biologically generated turbulent energy flux. Measuring the migration of a centimeter-scale swimmer-as represented by the brine shrimp Artemia salina-in a shear flow and verifying through an analog experiment with an artificial jet revealed that different geometries between the biologically generated agitation and the background shear can result in spectral energy transferring toward larger or smaller scales, which consequently intensifies or attenuates the large-scale hydrodynamic shear. Our results suggest that the long ignored geometry between the biologically generated agitation and the background flow field is an important factor that should be taken into consideration in future studies of biologically generated turbulence.}, }
@article {pmid38707334, year = {2024}, author = {Mohadjer, A and Nobakhti, MH and Nezamabadi, A and Mousavi Ajarostaghi, SS}, title = {Thermohydraulic analysis of nanofluid flow in tubular heat exchangers with multi-blade turbulators: The adverse effects.}, journal = {Heliyon}, volume = {10}, number = {9}, pages = {e30333}, pmid = {38707334}, issn = {2405-8440}, abstract = {Based on the significance of heat transfer in tubular flows, various methods of heat transfer enhancement have been developed by scholars. The use of turbulator inserts like twisted tapes is widely discussed and suggested by researchers, and many studies have concentrated on the positive influence of these devices. However, the question is whether these devices always positively impact heat transfer and fluid flow. In this study, efforts were made to find possible adverse impacts of using twisted tapes on the average Nusselt number (Nu), friction factor (f), flow behavior, and performance evaluation criterion (PEC) of water-titania nanofluid. Three-dimensional (3D) numerical methods were used to assess a combination of three different configurations of 156 cases with/without turbulators with different numbers of blades and pitch ratios (PR). Results suggest that at Reynolds number (Re) = 4000, 6000, and 8000, only 25 %, 25 %, and 22.9 % of the examined cases led to PEC values over 1. Based on the results, while twisted tapes raised the Nu by up to 65.1 %, the f can be increased by up to more than six times. Furthermore, streamlines and velocity magnitude contours were employed to discuss the fluid flow behavior in the presence of the turbulators. According to the findings, while with the best turbulator, the PEC value was increased by only 6.3 %, some of the turbulators reduced this parameter by up to 11.8 %, which is more severe. The worst performance was observed with the Case C (three-bladed) turbulator at a PR value of 11, which reduced the PEC by 11.8 %.}, }
@article {pmid38702376, year = {2024}, author = {Bahrami, HR and Ghaedi, M}, title = {Enhancement of thermal energy transfer behind a double consecutive expansion utilizing a variable magnetic field.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {10236}, pmid = {38702376}, issn = {2045-2322}, abstract = {This research focuses on utilizing non-uniform magnetic fields, induced by dipoles, to control and enhance thermal energy transfer in a two-dimensional cooling conduit including a double backward-facing step. The presence of electronic equipment along the straight channel path creates such arrangements, and cooling is often ineffective in the corners of the formed steps. The use of a non-constant magnetic field is a passive technique to improve the cooling rate in these sections without changing the internal geometry, thereby increasing the heat transfer rate. A commercial software based on the finite volume technique is employed to solve the governing equations of fluid flow and heat transfer. Multiple parameters are examined in this study, including the flow Reynolds number (12.5-50), dipole location and strength (0.1-5 A-m), and the number of dipoles (single or double). The results indicate that all of these parameters have a significant impact on the thermal energy transfer. The results of the study show that a single dipole increase the average heat transfer by about 22%, two magnetic fields by 40%, the strength of the magnetic source by 24% with respect to the non-magnetic field in the present study.}, }
@article {pmid38691288, year = {2024}, author = {Liu, ZL and Rao, QH and Yi, W and Huang, W}, title = {A modified drag coefficient model for calculating the terminal settling velocity and horizontal diffusion distance of irregular plume particles in deep-sea mining.}, journal = {Environmental science and pollution research international}, volume = {31}, number = {23}, pages = {33848-33866}, pmid = {38691288}, issn = {1614-7499}, support = {2021JC0010//Major project of Hunan Natural Science Foundation/ ; 2022zzts0036//Fundamental Research Funds for Central Universities of the Central South University/ ; }, mesh = {*Mining ; *Models, Theoretical ; Oceans and Seas ; Diffusion ; }, abstract = {Deep-sea mining inevitably produces plumes, which will pose a serious threat to the marine environment with the continuous movement and diffusion of plumes along with ocean currents. The terminal settling velocity (wt) of irregular particles is one of the crucial factors for determining the plumes' diffusion range. It is generally calculated by drag coefficient (CD), while most existing CD models only consider single shape characteristic parameter or have a smaller range of Reynolds number (Re). In this study, a new shape factor (γ) of irregular particles is proposed by considering the thickness (one-dimension), the projected area (two-dimension), and the surface area (three-dimension) of irregular particles as well as their coupling effect to establish a modified CD model for calculating the wt. A modified Gaussian plume model is proposed to predict the horizontal diffusion distance of the plume particles by considering the settling velocity and diffusion effect of irregular particles. Research results show that the wt increases nearly linearly, with a gradually decreased slope and slightly then greatly with the increasing of γ, dp (diameter) and ρp (density), respectively. The modified CD model is verified to be more valid with a wider application range (Re < 3×10[5]) than five existing CD models by the test results. The larger the ρp or dp, the larger the wt and thus the smaller the Sh. This study could provide a theoretical basis for calculating the plume diffusion range to further study the impact of deep-sea mining on the ocean environment.}, }
@article {pmid38667261, year = {2024}, author = {Yoshida, M and Fukui, T}, title = {Numerical Simulation of the Advantages of the Figure-Eight Flapping Motion of an Insect on Aerodynamics under Low Reynolds Number Conditions.}, journal = {Biomimetics (Basel, Switzerland)}, volume = {9}, number = {4}, pages = {}, pmid = {38667261}, issn = {2313-7673}, abstract = {In proceeding with the advanced development of small unmanned aerial vehicles (UAVs), which are small flying machines, understanding the flight of insects is important because UAVs that use flight are attracting attention. The figure-eight trajectory of the wing tips is often observed in the flight of insects. In this study, we investigated the more efficient figure-eight motion patterns in generating lift during the hovering motion and the relationship between figure-eight motion and Reynolds number. For this purpose, we compared the ratios of the cycle-averaged lift coefficient to the power coefficient generated from each motion by varying the elevation motion angle, which is the rotational motion that represents the figure-eight motion, and the Reynolds number. The result showed that the motion with a smaller initial phase of the elevation motion angle (φe0≤90°) could generate lift more efficiently at all Reynolds numbers. In addition, the figure-eight motion was more effective when the Reynolds number was low.}, }
@article {pmid38655341, year = {2024}, author = {Dong, H and Huang, L and Zhao, L}, title = {Influence of the internal structure of straight microchannels on inertial transport behavior of particles.}, journal = {Heliyon}, volume = {10}, number = {8}, pages = {e29577}, pmid = {38655341}, issn = {2405-8440}, abstract = {The rapid advancement of Micro-Electro-Mechanical Systems (MEMS) technology has established microfluidics as a pivotal field. This technology marks the onset of a new era in various applications, including drug testing, cell culture, and disease monitoring, underscoring its extensive practicality and potential for future exploration. This research delves into the intricate behavior of particle inertial migration within microchannels, particularly focusing on the impact of different channel structures and Reynolds numbers (Re). Our studies reveal that particles in microchannels with one-sided sharp-cornered microstructures migrate towards the sharp corner at a relative position of 0.4 under low flow rates, and towards the straight wall side at a relative position of 0.8 under high flow rates. The migration pattern of equilibrium positions varies with different arrangements of sharp-corner structures, achieving stability at the channel's center only when the sharp corners are symmetrically arranged on both sides. Our investigation into the shape of microstructures indicates that sharp-cornered structures generate a more stable secondary flow compared to rectangular and semi-circular structures, preventing particle aggregation at the outlet. To address the challenges associated with handling variable cross-section geometries and solid-wall boundaries in dissipative particle dynamics methods effectively, we have developed a dissipative particle dynamics model specifically for analyzing such microchannels. Building upon our previous research, this model introduces a conservative force coefficient for particles within the microstructured region and an interaction zone that only involves repulsive forces, aligning well with experimental outcomes. Through the study of microstructures' geometric shapes, this paper offers guidance for designing microchannels for particle enrichment. Furthermore, the dissipative particle dynamics model established for the particle flow and solid structure interaction within microstructured channels provides insights into the mesoscale dynamics of liquid-solid two-phase flow and particle motion. In conclusion, this paper aims to enhance particle motion sample preparation techniques, thereby broadening the scope of microfluidic applications in the biomedical field.}, }
@article {pmid38654100, year = {2024}, author = {Lee, D and Ruf, M and Karadimitriou, N and Steeb, H and Manousidaki, M and Varouchakis, EA and Tzortzakis, S and Yiotis, A}, title = {Development of stochastically reconstructed 3D porous media micromodels using additive manufacturing: numerical and experimental validation.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {9375}, pmid = {38654100}, issn = {2045-2322}, support = {SFB1313-327154368//Deutsche Forschungsgemeinschaft/ ; 3DmicroPores//Hellenic Foundation for Research and Innovation/ ; }, abstract = {We propose an integrated methodology for the design and fabrication of 3D micromodels that are suitable for the pore-scale study of transport processes in macroporous materials. The micromodels, that bear the pore-scale characteristics of sandstone, such as porosity, mean pore size, etc, are designed following a stochastic reconstruction algorithm that allows for fine-tuning the porosity and the correlation length of the spatial distribution of the solid material. We then construct a series of 3D micromodels at very fine resolution (i.e. 16 μ m) using a state-of-the-art 3D printing infrastructure, specifically a ProJet MJP3600 3D printer, that utilizes the Material Jetting technology. Within the technical constraints of the 3D printer resolution, the fabricated micromodels represent scaled-up replicas of natural sandstones, that are suitable for the study of the scaling between the permeability, the porosity and the mean pore size. The REV- and pore-scale characteristics of the resulting physical micromodels are recovered using a combination of X-ray micro-CT and microfluidic studies. The experimental results are then compared with single-phase flow simulations at pore-scale and geostatistic models in order to determine the effects of the design parameters on the intrinsic permeability and the spatial correlation of the velocity profile. Our numerical and experimental measurements reveal an excellent match between the properties of the designed and fabricated 3D domains, thus demonstrating the robustness of the proposed methodology for the construction of 3D micromodels with fine-tuned and well-controlled pore-scale characteristics. Furthermore, a pore-scale numerical study over a wider range of 3D digital domain realizations reveals a very good match of the measured permeabilities with the predictions of the Kozeny-Carman formulation based on a single control parameter, k 0 , that is found to have a practically constant value for porosities ϕ ≥ 0.2 . This, in turn, enables us to customize the sample size to meet REV constraints, including enlarging pore morphology while considering the Reynolds number. It is also found that at lower porosities there is a significant increase in the fraction of the non-percolating pores, thus leading to different k 0 , as the porosity approaches a numerically determined critical porosity value, ϕ c , where the domain is no longer percolating.}, }
@article {pmid38649298, year = {2024}, author = {Smeltz, AM and Patel, DS and Williams, JH}, title = {The influence of needleless connectors and inserted catheters on flow rates through vascular introducer sheaths.}, journal = {Anaesthesia and intensive care}, volume = {52}, number = {3}, pages = {180-183}, doi = {10.1177/0310057X241226715}, pmid = {38649298}, issn = {0310-057X}, mesh = {*Equipment Design ; Humans ; Vascular Access Devices ; Catheters ; }, abstract = {SummaryA vascular introducer sheath is often used for rapid volume replacement. However, common manipulations such as the addition of needleless connectors to infusion ports and the insertion of catheters or other devices through the introducer sheath may impede flow. In this study we utilised a rapid infuser to deliver room-temperature normal saline through two introducer sheath configurations with and without the addition of needleless connectors and the placement of catheters through the introducer sheaths. The maximal flow rate delivered by the rapid infuser was 1000 mL/min, which was observed with both introducer sheath sizes tested without additional resistive elements. However, with the addition of a needleless connector, flow rates through the introducer sheaths were substantially lower (64 (standard deviation (SD) 6) mL/min and 61 (SD 7) mL/min for the 8.5 Fr and 9 Fr introducers, respectively). Flow rates were also reduced when catheters were placed within the sheaths (298 (SD 9) mL/min with the 7 Fr catheter and 74 (SD 9) mL/min with the 8 Fr catheter placed in an 8.5 Fr sheath; 649 (SD 6) mL/min with the 7 Fr catheter and 356 (SD 14) mL/min with the 8 Fr catheter placed in the 9 Fr sheath). These findings indicated that both needleless connectors and the placement of catheters through vascular introducer sheaths substantially reduced potential flow rates. Even 'large' vascular introducer sheaths capable of delivering high flow rates could be rendered minimally effective for rapid fluid administration when used in this way. Clinicians should consider these impediments to flow when rapid fluid administration is required, and obtain alternative vascular access if necessary.}, }
@article {pmid38633639, year = {2024}, author = {Azad, AK and Parvin, S and Hossain, T}, title = {Performance evaluation of nanofluid-based photovoltaic thermal (PVT) system with regression analysis.}, journal = {Heliyon}, volume = {10}, number = {7}, pages = {e29252}, pmid = {38633639}, issn = {2405-8440}, abstract = {The recent global energy crisis has shocked Bangladesh's power sectors, and experts recommend using alternative energy sources to conserve natural gas, fossil fuels, and electricity. Numerous investigations on the photovoltaic thermal (PVT) system have been carried out to get the source efficiently. As a result, a parametric evaluation of the PVT system's efficiency in Dhaka, Bangladesh, is investigated numerically using CNT nanofluid as a coolant. The numerical simulation is performed using the Galerkin weighted residual based finite element method. For accurate computations, the meteorological data for Dhaka, Bangladesh, is taken from open sources of Renewables.ninja. The effect of regulating parameters Reynolds number (200 ≤ Re ≤ 1000), solar irradiation (200 W/m[2] ≤ G ≤ 1000 W/m[2]), and the monthly influence on performance such as cell temperature, fluid domain exit temperature, efficiencies, and energy are discussed. In addition, regression analyses of electrical efficiency and thermal efficiency are discussed for the input variables Reynolds number and solar irradiation. After postprocessing, empirical results are compiled and presented as 3D surface graphs, tables, and line diagrams. As the Reynolds number increased, the cell temperature and discharge temperature decreased, resulting in increased efficiency. However, the opposite situation is found for solar irradiation. Month-to-month variation also has a considerable impact on photovoltaic thermal performance. This research will help to improve the efficacy of PVTs in Dhaka, Bangladesh, by identifying useful alternative renewable energy sources.}, }
@article {pmid38625980, year = {2024}, author = {Deissler, RJ and Al Helo, R and Brown, R}, title = {From an obliquely falling rod in a viscous fluid to the motion of suspended magnetic bead chains that are driven by a gradient magnetic field and that make an arbitrary angle with the magnetic force vector: A Stokes flow study.}, journal = {PloS one}, volume = {19}, number = {4}, pages = {e0301852}, pmid = {38625980}, issn = {1932-6203}, mesh = {Magnetic Fields ; *Magnetics ; Motion ; Physical Phenomena ; }, abstract = {In view of the growing role of magnetic particles under magnetic field influence in medical and other applications, and perforce the bead chaining, it is important to understand more generally the chain dynamics. As is well known, in the presence of a magnetic field, magnetic beads tend to form chains that are aligned with the magnetic field vector. In addition, if there is a magnetic field gradient, there will be a magnetic force acting on this chain. The main goal of the present research is to study the motion of a magnetic bead chain that makes an arbitrary angle with the magnetic force vector in the Stokes flow limit, that is, in the limit of zero Reynolds number. We used the public-domain computer program HYDRO++ to calculate the mobility matrix, which relates the magnetic force acting on the chain to the velocity of the chain, for a chain of N beads making an arbitrary angle with the magnetic force vector. Because of the presence of off-diagonal elements of the mobility matrix, as the chain is drawn in the direction of the magnetic force, it is also deflected to the side. We derived analytic solutions for this motion. Also, for bead chains moving in directions both parallel and perpendicular to their lengths, we fit three-parameter functions to solutions from HYDRO++. We found the fits to be excellent. Combining these results with the analytic solutions, we obtained expressions for the velocity components for the bead chains that provide excellent fits to HYDRO++ solutions for arbitrary angles. Finally, we apply the methodology used for the bead chain studies to the study of an obliquely falling rod in a viscous fluid and derive analytic solutions for the velocity components of the obliquely falling rod.}, }
@article {pmid38617919, year = {2024}, author = {Ahamed, R and Salehin, M and Ehsan, MM}, title = {Thermal-hydraulic performance and flow phenomenon evaluation of a curved trapezoidal corrugated channel with E-shaped baffles implementing hybrid nanofluid.}, journal = {Heliyon}, volume = {10}, number = {7}, pages = {e28698}, pmid = {38617919}, issn = {2405-8440}, abstract = {A numerical investigation of a curved trapezoidal-corrugated channel with E-shaped baffles is conducted for thermal-hydraulic performance and flow behavior involving the use of single and hybrid nanofluids. This investigation introduces a unique integrated methodology for enhancing heat transfer efficiency by simultaneously combining geometric modifications and optimizing coolant utilization. To simulate turbulent, single-phase flow in three-dimensional corrugated channels, a computational model has been developed. The model considers a Reynolds number (Re) range of 5 × 10[3]≤Re ≤ 35 × 10[3] and implies a uniform heat flux of 1000 W/m[2]. A commercial software, Ansys fluent was used in order to simulate the fluid flow by setting the inlet temperature at 300 K and velocity according to the Reynolds number. The continuity equation, momentum equation, and energy equations are discretized using a second-order upwind method. The equation's residual has been assigned a value of 1 × 10[6] for absolute criteria. The study evaluates the thermal-hydraulic performance of single nanofluids (Al2O3/water, CuO/water, SiO2/water) and hybrid nanofluids (Al2O3-Cu/water, TiO2-SiO2/EG-water) at varying volume fractions (1%≤φ ≤ 5%). Additionally, the investigation examines the effects of corrugations, baffles, and geometric parameter: blockage ratio (BR = 0.10, 0.15, 0.25). The findings demonstrate that the effects of baffles and corrugations can lead to the creation of vortex flow and greater turbulence, which can promote heat transfer enhancement. Various nanofluids demonstrated a significant rise in the Nusselt number, ranging from 35% to 60%, when compared to water in a curved corrugated channel. Additionally, a lower BR resulted in a smaller but still notable gain of 15%-19%. An effective heat exchanger that results in a significant energy dissipation is measured by the energy ratio (ER). The use of corrugated channels with narrow baffles has been found to consistently outperform smooth channels in terms of thermo-hydraulic parameters, leading to enhanced heat transfer. Using BR = 0.10 over 0.25 resulted in an increase in ΔP, HTC, and ER of 48.44%, 18.71%, and 45.86%, respectively. The implementation of a hybrid nanofluid consisting of 1% (20% TiO2-80% SiO2)/(60% Water-40% EG) volume fraction in a curved corrugated channel with baffles resulted in a significant improvement of 36.49% in thermal performance. This finding suggests that the aforementioned nanofluid composition and design parameter, characterized by a blockage ratio of 0.10, are the most effective in enhancing thermal performance.}, }
@article {pmid38617679, year = {2024}, author = {Srinivasarao, M and Lee, BJ and Reddy, VM}, title = {Modified Reacting Solver: A Simplified Approach for Capturing the Molecular and Flow Diffusivities for the Nonpremixed MILD Flames.}, journal = {ACS omega}, volume = {9}, number = {14}, pages = {15804-15817}, pmid = {38617679}, issn = {2470-1343}, abstract = {The present study investigates the applicability of the inlet boundary species Lewis number (combined effect of molecular and flow diffusion) for the nonpremixed moderate and intense low oxygen dilution (MILD) flames. A modified reactive solver named modifiedReactingFoam is developed by including the enthalpy flux in the energy equation and using modified model constants in OpenFOAM. The present solver is tested on the delft-jet-in-hot-coflow burner operating under a moderate and intense low oxygen dilution combustion environment. Along with the flame with Reynolds number 4100, eight other jet-in-hot-coflow flames are simulated to test the capability of the present proposed solver. The main aim of the current work is to investigate the efficacy of the proposed solver in predicting the velocity field, temperatures, and flame lift-off height for the considered flames with a significant reduction in computational time. The predictions with the modified eddy dissipation concept model are improved. However, a significant deviation is still observed in the downstream direction of the burner. The numerical simulations are performed with methane Lewis numbers of 0.9-1.14 by keeping the respective constant Lewis numbers for the inlet boundary species. The modifiedReactingFoam predictions at a methane Lewis number of 1.12 are in very close agreement with the experimental results. The maximum deviation in lift-off heights is within ±3% of the experimental results. The present modified solver outperformed the other combustion models in the literature and reduced the computational time up to 10 times with a combination of DLBFoam compared to the inbuilt solver.}, }
@article {pmid38610530, year = {2024}, author = {Magos-Rivera, M and Avilés-Cruz, C and Ramírez-Muñoz, J}, title = {A Novel Experimental Apparatus for Characterizing Flow Regime in Mechanically Stirred Tanks through Force Sensors.}, journal = {Sensors (Basel, Switzerland)}, volume = {24}, number = {7}, pages = {}, pmid = {38610530}, issn = {1424-8220}, abstract = {Pressure fluctuations in a mixing tank can provide valuable information about the existing flow regime within the tank, which in turn influences the degree of mixing that can be achieved. In the present work, we propose a prototype for identifying the flow regime in mechanically stirred tanks equipped with four vertical baffles through the characterization of pressure fluctuations. Our innovative proposal is based on force sensors strategically placed in the baffles of the mixing tank. The signals coming from the sensors are transmitted to an electronic module based on an Arduino UNO development board. In the electronic module, the pressure signals are conditioned, amplified and sent via Bluetooth to a computer. In the computer, the signals can be plotted or stored in an Excel file. In addition, the proposed system includes a moving average filtering and a hierarchical bottom-up clustering analysis that can determine the real-time flow regime (i.e., the Reynolds number, Re) in which the tank was operated during the mixing process. Finally, to demonstrate the versatility of the proposed prototype, experiments were conducted to identify the Reynolds number for different flow regimes (static, laminar, transition and turbulent), i.e., 0≤Re≤ 42,955. Obtained results were in agreement with the prevailing consensus on the onset and developed from different flow regimes in mechanically stirred tanks.}, }
@article {pmid38589633, year = {2024}, author = {Muñóz, AJ and Reca, J and Martínez, J}, title = {Application of a hydrophobic coating to a pressurized pipe and its effect on energy losses and fluid flow profile.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {8236}, pmid = {38589633}, issn = {2045-2322}, support = {PID2020-118492RB-C21//Ministerio de Ciencia e Innovaci&#xf3;n/ ; }, abstract = {The use of additives, generally called DRAs (Drag Reducing Additives), has been proposed to re-duce the energy consumption in pressurized pipes. Although many research works have been conducted to analyze the effect of these additives, less attention have been devoted to the application of coatings to the pipe wall. This paper demonstrates that the application of a hydrophobic coating to the pipe can lead to a head loss reduction for a transition flow regime with moderate Reynolds number values (Re). For this purpose, an experiment was conducted to compare the performance of both coated and uncoated pipes by measuring the head losses and assessing the Drag Reduction Percentage (%DR) and the pipe friction factor (f). This was done for two Polyvinylchloride (PVC) pipes with different nominal diameters (PVC90 and PVC63). In addition, the flow velocity distribution was also measured in all these tests. The %DR decreased as the Re values increased, with the reduction being notably less pronounced for higher Re values. This could be explained by the fact that a partial slip condition is induced by the hydrophobic product. Its effect is significant for a transition regime where the effect of viscosity is important, but it becomes negligible for increasing levels of turbulence. No significant differences were observed in the flow distribution between coated and uncoated pipes, which seems to indicate that the velocity change could be limited to the near-wall viscous sublayer. The results of this work open an important research line aimed at reducing energy costs and the carbon footprint in pipe fluid distribution systems.}, }
@article {pmid38588326, year = {2024}, author = {Seder, I and Zheng, T and Zhang, J and Rojas, CC and Helalat, SH and Téllez, RC and Sun, Y}, title = {A Scalable Microfluidic Platform for Nanoparticle Formulation: For Exploratory- and Industrial-Level Scales.}, journal = {Nano letters}, volume = {24}, number = {17}, pages = {5132-5138}, doi = {10.1021/acs.nanolett.3c05057}, pmid = {38588326}, issn = {1530-6992}, mesh = {*Nanoparticles/chemistry ; Humans ; Microfluidic Analytical Techniques ; Microfluidics/methods ; T-Lymphocytes/cytology ; Polymers/chemistry ; DNA/chemistry ; }, abstract = {Nanoparticle synthesis on microfluidic platforms provides excellent reproducibility and control over bulk synthesis. While there have been plenty of platforms for producing nanoparticles (NPs) with controlled physicochemical properties, such platforms often operate in a narrow range of predefined flow rates. The flow rate limitation restricts either up-scalability for industrial production or down-scalability for exploratory research use. Here, we present a universal flow rate platform that operates over a wide range of flow rates (0.1-75 mL/min) for small-scale exploratory research and industrial-level synthesis of NPs without compromising the mixing capabilities. The wide range of flow rate is obtained by using a coaxial flow with a triangular microstructure to create a vortex regardless of the flow regime (Reynolds number). The chip synthesizes several types of NPs for gene and protein delivery, including polyplex, lipid NPs, and solid polymer NPs via self-assembly and precipitation, and successfully expresses GFP plasmid DNA in human T cells.}, }
@article {pmid38577258, year = {2024}, author = {Cordes, J and Schadschneider, A and Nicolas, A}, title = {Dimensionless numbers reveal distinct regimes in the structure and dynamics of pedestrian crowds.}, journal = {PNAS nexus}, volume = {3}, number = {4}, pages = {pgae120}, pmid = {38577258}, issn = {2752-6542}, abstract = {In fluid mechanics, dimensionless numbers like the Reynolds number help classify flows. We argue that such a classification is also relevant for crowd flows by putting forward the dimensionless Intrusion and Avoidance numbers, which quantify the intrusions into the pedestrians' personal spaces and the imminency of the collisions that they face, respectively. Using an extensive dataset, we show that these numbers delineate regimes where distinct variables characterize the crowd's arrangement, namely, Euclidean distances at low Avoidance number and times-to-collision at low Intrusion number. On the basis of these findings, a perturbative expansion of the individual pedestrian dynamics is carried out around the noninteracting state, in quite general terms. Simulations confirm that this expansion performs well in its expected regime of applicability.}, }
@article {pmid38560223, year = {2024}, author = {Tripty, TA and Nasrin, R}, title = {Efficiency upgrading of solar PVT finned hybrid system in Bangladesh: Flow rate and temperature influences.}, journal = {Heliyon}, volume = {10}, number = {7}, pages = {e28323}, pmid = {38560223}, issn = {2405-8440}, abstract = {This research aims to determine the impact of mass flow rate and inflow temperature on the utility and effectiveness of solar thermal systems using fins with air in various applications in Bangladesh. This study examines a three-dimensional (3D) photovoltaic thermal (PVT) system where we analyze the behavior of a hybrid system with six aluminum sheets (1 mm thick fin as a heat exchange material) inside the heat exchanger where the air takes the direction to pass in waveform through the channels (made of aluminum) using fins. The top side of the fins is bent and affixed to the bottom of the floor of the PV panel to allow heat transfer utilizing the conduction-based method. This study selects inlet fluid mass flow rate and inflow temperature between (0.015-0.535 kg/s), and (10-40 °C) respectively, while comparing the result with experimental/numerical published data based on Bangladesh's weather conditions and applies the finite element method (FEM) to solve heat transfer equations. A brief analysis of the association among Reynolds number with pressure drop and fanning friction factor is included in this paper. Our model can be mounted on building rooftops or open fields where air velocity will be controlled mechanically; thus, it has many applications. This model can be implemented within an agricultural photovoltaic (APV) system, domestic functions, dry agricultural products, and provide heat for greenhouses. The result indicates that 302-514 W thermal energy has been produced for 0.015-0.535 kg/s. For growing inflow temperature, despite the reduction in electrical efficiency, the value of adding electrical and thermal efficiency (overall efficiency) comes with elevation. A 5 °C increase in inflow temperature leads to an overall efficiency increase of 0.33%. This study's findings can help researchers better comprehend air's properties as a heat exchanger in a developed design, and they can be applied to government and commercial projects.}, }
@article {pmid38534866, year = {2024}, author = {Gan, W and Zuo, Z and Zhuang, J and Bie, D and Xiang, J}, title = {Aerodynamic/Hydrodynamic Investigation of Water Cross-Over for a Bionic Unmanned Aquatic-Aerial Amphibious Vehicle.}, journal = {Biomimetics (Basel, Switzerland)}, volume = {9}, number = {3}, pages = {}, pmid = {38534866}, issn = {2313-7673}, support = {U2141249, 11902018, and U2141252//National Natural Science Foundation of China/ ; }, abstract = {An aerodynamic/hydrodynamic investigation of water cross-over is performed for a bionic unmanned aquatic-aerial amphibious vehicle (bionic UAAV). According to flying fish features and UAAV flight requirements of water cross-over, the bionic conceptual design of crossing over water is described and planned in multiple stages and modes of motion. A solution procedure for the numerical simulation method, based on a modified SST turbulence model and the VOF model, is expressed, and a verification study is presented using a typical case. Longitudinal-lateral numerical simulation analysis investigates the cruise performance underwater and in the air. The numerical simulation and principal experiment verification are conducted for crossing over water and water surface acceleration. The results indicate that the bionic UAAV has an excellent aerodynamic/hydrodynamic performance and variant configuration to adapt to water cross-over. The bionic UAAV has good water and air navigation stability, and the cruise flying lift-drag ratio is greater than 15 at a low Reynolds number. Its pitching moment has the phenomenon of a "water mound" forming and breaking at the water cross-over process. The present method and the bionic variant configuration provide a feasible water cross-over design and analysis strategy for bionic UAAVs.}, }
@article {pmid38518328, year = {2024}, author = {Zapata, F and Angriman, S and Ferran, A and Cobelli, P and Obligado, M and Mininni, PD}, title = {Turbulence Unsteadiness Drives Extreme Clustering.}, journal = {Physical review letters}, volume = {132}, number = {10}, pages = {104005}, doi = {10.1103/PhysRevLett.132.104005}, pmid = {38518328}, issn = {1079-7114}, abstract = {We show that the unsteadiness of turbulence has a drastic effect on turbulence parameters and in particle cluster formation. To this end we use direct numerical simulations of particle laden flows with a steady forcing that generates an unsteady large-scale flow. Particle clustering correlates with the instantaneous Taylor-based flow Reynolds number, and anticorrelates with its instantaneous turbulent energy dissipation constant. A dimensional argument for these correlations is presented. In natural flows, unsteadiness can result in extreme particle clustering, which is stronger than the clustering expected from averaged inertial turbulence effects.}, }
@article {pmid38518311, year = {2024}, author = {Bandak, D and Mailybaev, AA and Eyink, GL and Goldenfeld, N}, title = {Spontaneous Stochasticity Amplifies Even Thermal Noise to the Largest Scales of Turbulence in a Few Eddy Turnover Times.}, journal = {Physical review letters}, volume = {132}, number = {10}, pages = {104002}, doi = {10.1103/PhysRevLett.132.104002}, pmid = {38518311}, issn = {1079-7114}, abstract = {How predictable are turbulent flows? Here, we use theoretical estimates and shell model simulations to argue that Eulerian spontaneous stochasticity, a manifestation of the nonuniqueness of the solutions to the Euler equation that is conjectured to occur in Navier-Stokes turbulence at high Reynolds numbers, leads to universal statistics at finite times, not just at infinite time as for standard chaos. These universal statistics are predictable, even though individual flow realizations are not. Any small-scale noise vanishing slowly enough with increasing Reynolds number can trigger spontaneous stochasticity, and here we show that thermal noise alone, in the absence of any larger disturbances, would suffice. If confirmed for Navier-Stokes turbulence, our findings would imply that intrinsic stochasticity of turbulent fluid motions at all scales can be triggered even by unavoidable molecular noise, with implications for modeling in engineering, climate, astrophysics, and cosmology.}, }
@article {pmid38516562, year = {2023}, author = {Marschik, C and Roland, W}, title = {Correction factors for the drag and pressure flows of power-law fluids through rectangular ducts.}, journal = {Polymer engineering and science}, volume = {63}, number = {7}, pages = {2043-2058}, pmid = {38516562}, issn = {1548-2634}, abstract = {There are many industrial examples of low Reynolds number non-Newtonian flows through rectangular ducts in polymer processing. They occur in all types of manufacturing processes in which raw polymeric materials are converted into products, ranging from screw extrusion to shaping operations in dies and molds. In addition, they are found in numerous rheological measurement systems. The literature provides various mathematical formulations for non-Newtonian flows through rectangular ducts, but-if not simplified further-their solution usually requires use of numerical techniques. Removing the need for these time-consuming techniques, we present novel analytical correction factors for the drag and pressure flows of power-law fluids in rectangular flow channels. We approximated numerical results for a fully developed flow under isothermal conditions using symbolic regression based on genetic programming. The correction factors can be applied to the analytical theory that describes the flow of power-law fluids between parallel plates to include effects of the side walls in the prediction of flow rate and viscous dissipation.}, }
@article {pmid38509923, year = {2024}, author = {Iqra, T and Nadeem, S and Ghazwani, HA and Duraihem, FZ and Alzabut, J}, title = {Instability analysis for MHD boundary layer flow of nanofluid over a rotating disk with anisotropic and isotropic roughness.}, journal = {Heliyon}, volume = {10}, number = {6}, pages = {e26779}, pmid = {38509923}, issn = {2405-8440}, abstract = {The study focuses on the instability of local linear convective flow in an incompressible boundary layer caused by a rough rotating disk in a steady MHD flow of viscous nanofluid. Miklavčič and Wang's (Miklavčič and Wang, 2004) [9] MW roughness model are utilized in the presence of MHD of Cu-water nanofluid with enforcement of axial flows. This study will investigate the instability characteristics with the MHD boundary layer flow of nanofluid over a rotating disk and incorporate the effects of axial flow with anisotropic and isotropic surface roughness. The resulting ordinary differential equations (ODEs) are obtained by using von Kàrmàn (Kármán, 1921) [3] similarity transformation on partial differential equations (PDEs). Subsequently, numerical solutions are obtained using the shooting method, specifically the Runge-Kutta technique. Steady-flow profiles for MHD and volume fractions of nanoparticles are analyzed by the partial-slip conditions with surface roughness. Convective instability for stationary modes and neutral stability curves are also obtained and investigated by the formulation of linear stability equations with the MHD of nanofluid. Linear convective growth rates are utilized to analyze the stability of magnetic fields and nanoparticles and to confirm the outcomes of this analysis. Stationary disturbances are also considered in the energy analysis. The investigation indicates the correlation between instability modes Type I and Type II, in the presence of MHD, nanoparticles, and the growth rates of the critical Reynolds number. An integral energy equation enhances comprehension of the fundamental physical mechanisms. The factors contributing to convective instability in the system are clarified using this approach.}, }
@article {pmid38509193, year = {2024}, author = {Rehman, N and Mahmood, R and Majeed, AH and Khan, I and Mohamed, A}, title = {Multigrid simulations of non-Newtonian fluid flow and heat transfer in a ventilated square cavity with mixed convection and baffles.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {6694}, pmid = {38509193}, issn = {2045-2322}, abstract = {The impact of baffles on a convective heat transfer of a non-Newtonian fluid is experimentally studied within a square cavity. The non-Newtonian fluid is pumped into the cavity through the inlet and subsequently departs from the cavity via the outlet. Given the inherent non-linearity of the model, a numerical technique has been selected as the method for obtaining the outcomes. Primarily, the governing equations within the two-dimensional domain have been discretized using the finite element method. For approximating velocity and pressure, we have employed the reliable P 2 - P 1 finite element pair, while for temperature, we have opted for the quadratic basis. To enhance convergence speed and accuracy, we employ the powerful multigrid approach. This study investigates how key parameters like Richardson number (Ri), Reynolds number (Re), and baffle gap b g influence heat transfer within a cavity comprising a non-Newtonian fluid. The baffle gap (b g) has been systematically altered within the range of 0.2-0.6, and for this research, three distinct power law indices have been selected namely: 0.5, 1.0, and 1.5. The primary outcomes of the investigation are illustrated through velocity profiles, streamlines, and isotherm visualizations. Furthermore, the study includes the computation of the Nu avg (average Nusselt number) across a range of parameter values. As the Richardson number (Ri) increases, Nu avg also rises, indicating that an increase in Ri results in augmented average heat transfer. Making the space between the baffles wider makes heat flow more intense. This, in turn, heats up more fluid within the cavity.}, }
@article {pmid38502909, year = {2024}, author = {Cao, Y and Liu, X and Zhang, L and Wu, Y and You, C and Li, H and Duan, H and Huang, J and Lv, P}, title = {Water Impalement Resistance and Drag Reduction of the Superhydrophobic Surface with Hydrophilic Strips.}, journal = {ACS applied materials &amp; interfaces}, volume = {16}, number = {13}, pages = {16973-16982}, doi = {10.1021/acsami.3c18905}, pmid = {38502909}, issn = {1944-8252}, abstract = {Superhydrophobic surfaces (SHS) offer versatile applications by trapping an air layer within microstructures, while water jet impact can destabilize this air layer and deactivate the functions of the SHS. The current work presents for the first time that introducing parallel hydrophilic strips to SHS (SHS-s) can simultaneously improve both water impalement resistance and drag reduction (DR). Compared with SHS, SHS-s demonstrates a 125% increase in the enduring time against the impact of water jet with velocity of 11.9 m/s and a 97% improvement in DR at a Reynolds number of 1.4 × 10[4]. The key mechanism lies in the enhanced stability of the air layer due to air confinement by the adjacent three-phase contact lines. These lines not only impede air drainage through the surface microstructures during water jet impact, entrapping the air layer to resist water impalement, but also prevent air floating up due to buoyancy in Taylor-Couette flow, ensuring an even spread of the air layer all over the rotor, boosting DR. Moreover, failure modes of SHS under water jet impact are revealed to be related to air layer decay and surface structure destruction. This mass-producible structured surface holds the potential for widespread use in DR for hulls, autonomous underwater vehicles, and submarines.}, }
@article {pmid38501605, year = {2024}, author = {Mattusch, AM and Schaldach, G and Bartsch, J and Thommes, M}, title = {Intrinsic dissolution rate modeling for the pharmacopoeia apparatus rotating disk compared to flow channel method.}, journal = {Pharmaceutical development and technology}, volume = {29}, number = {4}, pages = {281-290}, doi = {10.1080/10837450.2024.2329115}, pmid = {38501605}, issn = {1097-9867}, mesh = {*Solubility ; *Hydrodynamics ; Tablets/chemistry ; Drug Liberation ; Pharmacopoeias as Topic ; Computer Simulation ; Chemistry, Pharmaceutical/methods ; Temperature ; }, abstract = {For a solid understanding of drug characteristics, in vitro measurement of the intrinsic dissolution rate is important. Hydrodynamics are often emphasized as the decisive parameter influencing the dissolution. In this study, experiments and computational fluid dynamic (CFD) simulations showed that the mixing behavior in the rotating disc apparatus causes an inhomogeneous flow field and a systematic error in the calculation of the intrinsic dissolution rate. This error is affected by both the experimental time and the velocity. Due to the rotational movement around the tablet center, commonly utilized in pharmacopeia methods, a broad variance is present with regard to the impact of fluid velocity on individual particles of the specimen surface. As this is significantly reduced in the case of uniform overflow, the flow channel is recommended for investigating the dissolution behavior. It is shown that rotating disc measurements can be compared with flow channel measurements after adjusting the measured data for the rotating disc based on a proposed, representative Reynolds number and a suggested apparatus-dependent correction factor. Additionally, modeling the apparatus-independent intrinsic dissolution rate for different temperatures in the rotating disc apparatus is possible using the adapted Levich's equation.}, }
@article {pmid38493264, year = {2024}, author = {Mwapinga, A}, title = {Mathematical formulation and computation of the dynamics of blood flow, heat and mass transfer during MRI scanning.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {6364}, pmid = {38493264}, issn = {2045-2322}, mesh = {*Models, Theoretical ; *Hot Temperature ; Computer Simulation ; Software ; Magnetic Resonance Imaging ; }, abstract = {Computational modeling of arterial blood flow, heat and mass transfer during MRI scanning is studied. The flow is assumed to be unsteady, in-compressible, and asymmetric. Mathematical formulation considers the presence of stenosis, joule heating viscous dissipation and chemical reaction. The explicit finite difference scheme is used to numerically solve the model equations. The MATLAB software was used to plot the graphical results. The study reveals that, during MRI scanning, both radial and axial velocities diminish with increase in the strength of magnetic fields. Besides, the study found that, Eckert number and Hartman number enhance the blood's temperature and the same, diminishes with increase in Prandtl and Reynolds numbers. Concentration profile is observed to decline with increase in chemical reaction parameter, Schmidt number and Reynolds number. Soret number on the other hand, is observed to positively influence the concentration.}, }
@article {pmid38467620, year = {2024}, author = {Labonte, D and Bishop, PJ and Dick, TJM and Clemente, CJ}, title = {Dynamic similarity and the peculiar allometry of maximum running speed.}, journal = {Nature communications}, volume = {15}, number = {1}, pages = {2181}, pmid = {38467620}, issn = {2041-1723}, support = {851705//EC | EU Framework Programme for Research and Innovation H2020 | H2020 Priority Excellent Science | H2020 European Research Council (H2020 Excellent Science - European Research Council)/ ; RGY0073/2020//Human Frontier Science Program (HFSP)/ ; }, mesh = {Animals ; *Running/physiology ; Muscles ; Biomechanical Phenomena ; }, abstract = {Animal performance fundamentally influences behaviour, ecology, and evolution. It typically varies monotonously with size. A notable exception is maximum running speed; the fastest animals are of intermediate size. Here we show that this peculiar allometry results from the competition between two musculoskeletal constraints: the kinetic energy capacity, which dominates in small animals, and the work capacity, which reigns supreme in large animals. The ratio of both capacities defines the physiological similarity index Γ, a dimensionless number akin to the Reynolds number in fluid mechanics. The scaling of Γ indicates a transition from a dominance of muscle forces to a dominance of inertial forces as animals grow in size; its magnitude defines conditions of "dynamic similarity" that enable comparison and estimates of locomotor performance across extant and extinct animals; and the physical parameters that define it highlight opportunities for adaptations in musculoskeletal "design" that depart from the eternal null hypothesis of geometric similarity. The physiological similarity index challenges the Froude number as prevailing dynamic similarity condition, reveals that the differential growth of muscle and weight forces central to classic scaling theory is of secondary importance for the majority of terrestrial animals, and suggests avenues for comparative analyses of locomotor systems.}, }
@article {pmid38464493, year = {2024}, author = {Golmirzaee, N and Wood, DH}, title = {Some effects of domain size and boundary conditions on the accuracy of airfoil simulations.}, journal = {Advances in aerodynamics}, volume = {6}, number = {1}, pages = {7}, pmid = {38464493}, issn = {2524-6992}, abstract = {This paper investigates a specific case of one of the most popular fluid dynamic simulations, the incompressible flow around an airfoil (NACA 0012 here) at a high Reynolds number (6×106). OpenFOAM software was used to study the effect of domain size and four common choices of boundary conditions on airfoil lift, drag, surface friction, and pressure. We also examine the relation between boundary conditions and the velocity, pressure, and vorticity distributions throughout the domain. In addition to the common boundary conditions, we implement the "point vortex" boundary condition that was introduced many years ago but is now rarely used. We also applied the point vortex condition for the outlet pressure instead of using the traditional Neumann condition. With the airfoil generating significant lift at incidence angles of 5∘,10∘, and 14∘, we confirm a previous finding that the boundary conditions combine with domain size to produce an induced (pressure) drag. The change in the pressure drag with domain size is significant for the commonly-used boundary conditions but is much smaller for the point vortex alternative. The point vortex boundary condition increases the execution time, but this is more than offset by the reduction in domain size needed to achieve a specified accuracy in the lift and drag. This study also estimates the error in total drag and lift due to domain size and shows it can be almost eliminated using the point vortex boundary condition. We also used the impulse form of the momentum equations to study the relation between drag and lift and spurious vorticity, which is generated as a result of using non-exact boundary conditions. These equations reveal that the spurious vorticity throughout the domain is associated with cancelling circulation around the domain boundaries.}, }
@article {pmid38463765, year = {2024}, author = {Uddin, MN and Hoque, KE and Billah, MM}, title = {The impact of multiple stenosis and aneurysms on arterial diseases: A cardiovascular study.}, journal = {Heliyon}, volume = {10}, number = {5}, pages = {e26889}, pmid = {38463765}, issn = {2405-8440}, abstract = {The comparative effect of serial stenosis and aneurysms arteries on blood flow is examined to identify atherosclerotic diseases. The finite element approach has been used to solve the continuity, momentum, and Oldroyd-B partial differential equations to analyze the blood flow. Newtonian and non-Newtonian both cases are taken for the viscoelastic response of blood. In this study, the impact of multiple stenotic and aneurysmal arteries on blood flow have been studied to determine the severity of atherosclerosis diseases through the analysis of blood behavior. The novel aspect of the study is its assessment of the severity of atherosclerotic disorders for the occurrence of serial stenosis and aneurysm simultaneously in the blood vessel wall in each of the four cases. The maximum abnormal arterial blood flow effect is found for the presence of serial stenoses compared to aneurysms which refers to the severity of atherosclerosis. At the hub of stenosis, the blood velocity magnitude and wall shear stress (WSS) are higher, whereas the arterial wall normal gradient values are lower. For all cases, the contrary results are observed at the hub of the aneurysmal model. The blood flow has been affected significantly by the increases in Reynolds number for both models. The influence of stenotic and aneurysmal arteries on blood flow is graphically illustrated in terms of the velocity profile, pressure distribution, and WSS. Medical experts may use this study's findings to assess the severity of cardiovascular diseases.}, }
@article {pmid38457940, year = {2024}, author = {Wang, Z and Xu, P and Ren, Z and Yu, L and Zuo, Z and Liu, S}, title = {Dynamics of cavitation bubbles in viscous liquids in a tube during a transient process.}, journal = {Ultrasonics sonochemistry}, volume = {104}, number = {}, pages = {106840}, pmid = {38457940}, issn = {1873-2828}, abstract = {We experimentally, numerically, and theoretically investigate the dynamics of cavitation bubbles in viscous liquids in a tube during a transient process. In experiments, cavitation bubbles are generated by a modified tube-arrest setup, and the bubble evolution is captured with high-speed imaging. Numerical simulations using OpenFOAM are employed to validate our quasi-one-dimensional theoretical model, which effectively characterizes the bubble dynamics. We find that cavitation onset is minimally affected by the liquid viscosity. However, once cavitation occurs, various aspects of bubble dynamics, such as the maximum bubble length, bubble lifetime, collapse time, and collapse speed, are closely related to the liquid viscosity. We further establish that normalized bubble dynamics are solely determined by the combination of the Reynolds number and the Euler number. Moreover, we also propose a new dimensionless number, Ca2, to predict the maximum bubble length, a critical factor in determining the occurrence of liquid column separation.}, }
@article {pmid38445957, year = {2024}, author = {Hu, X and Chen, W and Lin, J and Nie, D and Zhu, Z and Lin, P}, title = {The motion of micro-swimmers over a cavity in a micro-channel.}, journal = {Soft matter}, volume = {20}, number = {12}, pages = {2789-2803}, doi = {10.1039/d3sm01589k}, pmid = {38445957}, issn = {1744-6848}, abstract = {This article combines the lattice Boltzmann method (LBM) with the squirmer model to investigate the motion of micro-swimmers in a channel-cavity system. The study analyses various influential factors, including the value of the squirmer-type factor (β), the swimming Reynolds number (Rep), the size of the cavity, initial position and particle size on the movement of micro-swimmers within the channel-cavity system. We simultaneously studied three types of squirmer models, Puller (β > 0), Pusher (β < 0), and Neutral (β = 0) swimmers. The findings reveal that the motion of micro-swimmers is determined by the value of β and Rep, which can be classified into six distinct motion modes. For Puller and Pusher, when the β value is constant, an increase in Rep will lead to transition in the motion mode. Moreover, the appropriate depth of cavity within the channel-cavity system plays a crucial role in capturing and separating Neutral swimmers. This study, for the first time, explores the effect of complex channel-cavity systems on the behaviour of micro-swimmers and highlights their separation and capture ability. These findings offer novel insights for the design and enhancement of micro-channel structures in achieving efficient separation and capture of micro-swimmers.}, }
@article {pmid38434303, year = {2024}, author = {Wannapop, R and Jearsiripongkul, T and Jiamjiroch, K}, title = {Adaptive urban drinking water supply model using the effect of node elevation and head loss formula: A case study.}, journal = {Heliyon}, volume = {10}, number = {5}, pages = {e26181}, pmid = {38434303}, issn = {2405-8440}, abstract = {Along with population growth and health improvement, water demand due to urbanization is increasing and creating a need to develop a strategy for handling water supply networks (WSNs). In the last decade, software modeling of WSNs has been developed to evaluate the state of networks in terms of pressure control, leakage analysis, and overall demand determination. In the case of very complex and extremely large networks, it is very difficult to manage the water supply. Metropolitan Waterworks Authority (MWA) in Thailand has to supply drinking water to the three densely populated cities; Bangkok, Nonthaburi, and Samut Prakan, that cover an area of 2944.05 km[2]. Hence, MWA has developed a main pipe model using EPANET software as a managing tool. This tool can offer a good solution for the water supply, but there is approximately a 14 percent error, mainly due to not having the elevation data of the pipe network. The current research is based on demand and pressure modeling analysis with utilizing two important parameters, node elevations, and head loss. The first trial model was an initial revision of the node elevation based on a road surface map. It was found that the model with elevation data could offer a better solution and was 3.95% more accurate than the existing model. The result was significantly improved, but another error, which may have been caused by using an inappropriate head loss model, was found. As the introduced model is based on the Hazen-William model, it cannot offer an accurate solution for all Reynolds number ranges. Even though Darcy-Weisbach is more complex to use, it could provide a better solution. The results indicate the Darcy-Weisbach model produces results that are 8.65% more accurate than the Hazen-William model.}, }
@article {pmid38430250, year = {2024}, author = {Pandey, SK and Prajapati, A}, title = {An analytical and comparative study of swallowing in a tumor-infected oesophagus: a mathematical model.}, journal = {Journal of mathematical biology}, volume = {88}, number = {3}, pages = {37}, pmid = {38430250}, issn = {1432-1416}, mesh = {Humans ; *Deglutition ; Models, Theoretical ; Esophagus ; Peristalsis ; *Neoplasms ; }, abstract = {This study discusses non-steady effects encountered in peristaltic flows in oesophagus. The purpose of this communication is to evolve a mechanism to diagnose tumor in an oesophagus mathematically. The tumor is modelled by generic bump function of certain height and width. The method of solution follows long wavelength and low-Reynolds number approximations for unsteady flow, while integrations have been performed numerically in order to plot graphs, which reveal various characteristics of the flow. The goal is to assess how pressure varies across the tumor's width. The spatial, as well as temporal, dependence of pressure has been studied in the laboratory frame of reference. The pressure distribution for tumor-infected oesophagus is compared with that of normal oesophagus. An intensified pressure is obtained in the presence of tumor. The interruption while swallowing through benign oesophageal tumor is confirmed by an abrupt pressure rise across the tumor's width. Tumor position also plays a significant role whether it is at contraction or relaxation of walls. Additionally, wall-shear-stress, volumetric flow rate and streamlines have also been described and compared with that without tumor growth. The expressions corresponding to all the physical quantities are computed numerically. Further, this model may also be implemented to the two-dimensional channel flow for an industrial application.}, }
@article {pmid38427109, year = {2024}, author = {Zidi, K and Texier, BD and Gauthier, G and Seguin, A}, title = {Viscosimetric squeeze flow of suspensions.}, journal = {The European physical journal. E, Soft matter}, volume = {47}, number = {3}, pages = {17}, pmid = {38427109}, issn = {1292-895X}, support = {ANR-10-LABX-0039-PALM//Laboratoire d'excellence Physique Atomes Lumi&#xe8;re Mati&#xe8;re/ ; }, abstract = {The rheology of particle suspensions has been extensively explored in the case of a simple shear flow, but less in other flow configurations which are also important in practice. Here we investigate the behavior of a suspension in a squeeze flow, which we revisit using local pressure measurements to deduce the effective viscosity. The flow is generated by approaching a moving disk to a fixed wall at constant velocity in the low Reynolds number limit. We measure the evolution of the pressure field at the wall and deduce the effective viscosity from the radial pressure drop. After validation of our device using a Newtonian fluid, we measure the effective viscosity of a suspension for different squeezing speeds and volume fractions of particles. We find results in agreement with the Maron-Pierce law, an empirical expression for the viscosity of suspensions that was established for simple shear flows. We prove that this method to determine viscosity remains valid in the limit of large gap width. This makes it possible to study the rheology of suspensions within this limit and therefore suspensions composed of large particles, in contrast to Couette flow cells which require small gaps.}, }
@article {pmid38413619, year = {2024}, author = {Elmhedy, Y and Abd-Alla, AM and Abo-Dahab, SM and Alharbi, FM and Abdelhafez, MA}, title = {Influence of inclined magnetic field and heat transfer on the peristaltic flow of Rabinowitsch fluid model in an inclined channel.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {4735}, pmid = {38413619}, issn = {2045-2322}, abstract = {The recent study is focused on discussion of heat transfer and magnetic field results of peristaltic flow of Rabinowitsch fluid model in an Inclined Channel. In this piece of research, peristalsis's fundamental problem with heat transfer in the presence of a magnetic field is checked. An incompressible Rabinowitsch fluid is present in an inclined channel, which is considered as the reference for this research. The solutions are devised with the assumptions of long wavelength and low Reynolds number approximations. The resulting equations are then solved exactly by implementing various command of MATHEMATICA subject to relevant boundary conditions. Results are discussed for various flow quantities like temperature, velocity, tangential stress, pressure gradient and rise, and friction force. Computational simulations are performed to determine the flow quantities. This investigation goes beyond mere calculations and examines particle motion to gain deeper insights into flow quantities. Furthermore, this investigates how magnetic field and heat transfer parameters influence these peristaltic flow phenomena. The outcomes of important parameters were plotted and scrutinized. There is amultitude of medical implementations derived from the current consideration, such as the depiction of the gastric juice motion in the small intestine when an endoscope is inserted through it.}, }
@article {pmid38407396, year = {2024}, author = {Chand, K and Rosenberger, H and Sanderse, B}, title = {A pressure-free long-time stable reduced-order model for two-dimensional Rayleigh-Bénard convection.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {34}, number = {2}, pages = {}, doi = {10.1063/5.0168857}, pmid = {38407396}, issn = {1089-7682}, abstract = {The present work presents a stable proper orthogonal decomposition (POD)-Galerkin based reduced-order model (ROM) for two-dimensional Rayleigh-Bénard convection in a square geometry for three Rayleigh numbers: 104 (steady state), 3×105 (periodic), and 6×106 (chaotic). Stability is obtained through a particular (staggered-grid) full-order model (FOM) discretization that leads to a ROM that is pressure-free and has skew-symmetric (energy-conserving) convective terms. This yields long-time stable solutions without requiring stabilizing mechanisms, even outside the training data range. The ROM's stability is validated for the different test cases by investigating the Nusselt and Reynolds number time series and the mean and variance of the vertical temperature profile. In general, these quantities converge to the FOM when increasing the number of modes, and turn out to be a good measure of accuracy. However, for the chaotic case, convergence with increasing numbers of modes is relatively difficult and a high number of modes is required to resolve the low-energy structures that are important for the global dynamics.}, }
@article {pmid38381133, year = {2024}, author = {Chang, R and Davydov, A and Jaroenlak, P and Budaitis, B and Ekiert, DC and Bhabha, G and Prakash, M}, title = {Energetics of the microsporidian polar tube invasion machinery.}, journal = {eLife}, volume = {12}, number = {}, pages = {}, pmid = {38381133}, issn = {2050-084X}, support = {P30 CA016087/CA/NCI NIH HHS/United States ; HHMI Faculty fellowship/HHMI/Howard Hughes Medical Institute/United States ; R35 GM128777/GM/NIGMS NIH HHS/United States ; R35GM128777/GM/NIGMS NIH HHS/United States ; S10 OD019974/OD/NIH HHS/United States ; R01 AI147131/AI/NIAID NIH HHS/United States ; }, mesh = {*Anatomy, Regional ; Biophysics ; *Cell Nucleus ; }, abstract = {Microsporidia are eukaryotic, obligate intracellular parasites that infect a wide range of hosts, leading to health and economic burdens worldwide. Microsporidia use an unusual invasion organelle called the polar tube (PT), which is ejected from a dormant spore at ultra-fast speeds, to infect host cells. The mechanics of PT ejection are impressive. Anncaliia algerae microsporidia spores (3-4 μm in size) shoot out a 100-nm-wide PT at a speed of 300 μm/s, creating a shear rate of 3000 s[-1]. The infectious cargo, which contains two nuclei, is shot through this narrow tube for a distance of ∼60-140 μm (Jaroenlak et al, 2020) and into the host cell. Considering the large hydraulic resistance in an extremely thin tube and the low-Reynolds-number nature of the process, it is not known how microsporidia can achieve this ultrafast event. In this study, we use Serial Block-Face Scanning Electron Microscopy to capture 3-dimensional snapshots of A. algerae spores in different states of the PT ejection process. Grounded in these data, we propose a theoretical framework starting with a systematic exploration of possible topological connectivity amongst organelles, and assess the energy requirements of the resulting models. We perform PT firing experiments in media of varying viscosity, and use the results to rank our proposed hypotheses based on their predicted energy requirement. We also present a possible mechanism for cargo translocation, and quantitatively compare our predictions to experimental observations. Our study provides a comprehensive biophysical analysis of the energy dissipation of microsporidian infection process and demonstrates the extreme limits of cellular hydraulics.}, }
@article {pmid38378438, year = {2024}, author = {Qiao, S and Cai, C and Pan, C and Liu, Y and Zhang, Q}, title = {Study on the Performance of a Surface with Coupled Wettability Difference and Convex-Stripe Array for Improved Air Layer Stability.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {40}, number = {9}, pages = {4940-4952}, doi = {10.1021/acs.langmuir.3c03929}, pmid = {38378438}, issn = {1520-5827}, abstract = {The existence of an air layer reduces friction drag on superhydrophobic surfaces. Therefore, improving the air layer stability of superhydrophobic surfaces holds immense significance in reducing both energy consumption and environmental pollution caused by friction drag. Based on the properties of mathematical discretization and the contact angle hysteresis generated by the wettability difference, a surface coupled with a wettability difference treatment and a convex-stripe array is developed by laser engraving and fluorine modification, and its performance in improving the air layer stability is experimentally studied in a von Kármán swirling flow field. The results show that the destabilization of the air layer is mainly caused by the Kelvin-Helmholtz instability, which is triggered by the density difference between gas and liquid, as well as the tangential velocity difference between gas and liquid. When the air layer is relatively thin, tangential wave destabilization occurs, whereas for larger thicknesses, the destabilization mode is coupled wave destabilization. The maximum Reynolds number that keeps the air layer fully covering the surface of the rotating disk (with drag reduction performance) during the disk rotation process is defined as the critical Reynolds number (Rec), which is 1.62 × 10[5] for the uniform superhydrophobic surface and 3.24 × 10[5] for the superhydrophobic surface with a convex stripe on the outermost ring (SCSSP). Individual treatments of wettability difference and a convex-stripe array on the SCSSP further improve the air layer stability, but Rec remains at 3.24 × 10[5]. Finally, the coupling of the wettability difference treatment with a convex-stripe array significantly improves the air layer stability, resulting in an increase of Rec to 4.05 × 10[5], and the drag reduction rate stably maintained around 30%.}, }
@article {pmid38377615, year = {2024}, author = {Dunt, TK and Heck, KS and Lyons, K and Murphy, CT and Bayoán Cal, R and Franck, JA}, title = {Wavelength-induced shedding frequency modulation of seal whisker inspired cylinders.}, journal = {Bioinspiration &amp; biomimetics}, volume = {19}, number = {3}, pages = {}, doi = {10.1088/1748-3190/ad2b04}, pmid = {38377615}, issn = {1748-3190}, mesh = {Animals ; *Vibrissae ; *Seals, Earless ; Vibration ; }, abstract = {The spanwise undulated cylinder geometry inspired by seal whiskers has been shown to alter shedding frequency and reduce fluid forces significantly compared to smooth cylindrical geometry. Prior research has parameterized the whisker-inspired geometry and demonstrated the relevance of geometric variations on force reduction properties. Among the geometric parameters, undulation wavelength was identified as a significant contributor to forcing changes. To analyze the effect of undulation wavelength, a thorough investigation isolating changes in wavelength is performed to expand upon previous research that parameterized whisker-inspired geometry and the relevance of geometric variations on the force reduction properties. A set of five whisker-inspired models of varying wavelength are computationally simulated at a Reynolds number of 250 and compared with an equivalent aspect ratio smooth elliptical cylinder. Above a critical non-dimensional value, the undulation wavelength reduces the amplitude and frequency of vortex shedding accompanied by a reduction in oscillating lift force. Frequency shedding is tied to the creation of wavelength-dependent vortex structures which vary across the whisker span. These vortices produce distinct shedding modes in which the frequency and phase of downstream structures interact to decrease the oscillating lift forces on the whisker model with particular effectiveness around the wavelength values typically found in nature. The culmination of these location-based modes produces a complex and spanwise-dependent lift frequency spectra at those wavelengths exhibiting maximum force reduction. Understanding the mechanisms of unsteady force reduction and the relationship between undulation wavelength and frequency spectra is critical for the application of this geometry to vibration tuning and passive flow control for vortex-induced vibration (VIV) reduction.}, }
@article {pmid38366478, year = {2024}, author = {Zhou, H and Blackman, EG}, title = {Helical dynamo growth and saturation at modest versus extreme magnetic Reynolds numbers.}, journal = {Physical review. E}, volume = {109}, number = {1-2}, pages = {015206}, doi = {10.1103/PhysRevE.109.015206}, pmid = {38366478}, issn = {2470-0053}, abstract = {Understanding magnetic field growth in astrophysical objects is a persistent challenge. In stars and galaxies, turbulent flows with net kinetic helicity are believed to be responsible for driving large-scale magnetic fields. However, numerical simulations have demonstrated that such helical dynamos in closed volumes saturate at lower magnetic field strengths when increasing the magnetic Reynolds number Rm. This would imply that helical large-scale dynamos cannot be efficient in astrophysical bodies without the help of helicity outflows such as stellar winds. But do these implications actually apply for very large Rm? Here we tackle the long-standing question of how much helical large-scale dynamo growth occurs independent of Rm in a closed volume. We analyze data from numerical simulations with a new method that tracks resistive versus nonresistive drivers of helical field growth. We identify a presaturation regime when the large-scale field grows at a rate independent of Rm, but to an Rm-dependent magnitude. The latter Rm dependence is due to a dominant resistive contribution, but whose fractional contribution to the large-scale magnetic energy decreases with increasing Rm. We argue that the resistive contribution would become negligible at large Rm and an Rm-independent dynamical contribution would dominate if the current helicity spectrum in the inertial range is steeper than k^{0}. As such helicity spectra are plausible, this renews optimism for the relevance of closed dynamos. Our work pinpoints how modest Rm simulations can cause misapprehension of the Rm→∞ behavior.}, }
@article {pmid38361591, year = {2024}, author = {Chen, Y and Chong, KL and Liu, H and Verzicco, R and Lohse, D}, title = {Buoyancy-driven attraction of active droplets.}, journal = {Journal of fluid mechanics}, volume = {980}, number = {}, pages = {}, pmid = {38361591}, issn = {0022-1120}, support = {740479/ERC_/European Research Council/International ; }, abstract = {For dissolving active oil droplets in an ambient liquid, it is generally assumed that the Marangoni effect results in repulsive interactions, while the buoyancy effects caused by the density difference between the droplets, diffusing product and the ambient fluid are usually neglected. However, it has been observed in recent experiments that active droplets can form clusters due to buoyancy-driven convection (Krüger et al. Eur. Phys. J. E, vol. 39, 2016, pp. 1-9). In this study, we numerically analyze the buoyancy effect, in addition to the propulsion caused by Marangoni flow (with its strength characterized by Péclet number Pe). The buoyancy effects have their origin in (i) the density difference between the droplet and the ambient liquid, which is characterized by Galileo number Ga, and (ii) the density difference between the diffusing product (i.e. filled micelles) and the ambient liquid, which can be quantified by a solutal Rayleigh number Ra. We analyze how the attracting and repulsing behaviour of neighbouring droplets depends on the control parameters Pe, Ga, and Ra. We find that while the Marangoni effect leads to the well-known repulsion between the interacting droplets, the buoyancy effect of the reaction product leads to buoyancy-driven attraction. At sufficiently large Ra, even collisions between the droplets can take place. Our study on the effect of Ga further shows that with increasing Ga, the collision becomes delayed. Moreover, we derive that the attracting velocity of the droplets, which is characterized by a Reynolds number Red, is proportional to Ra[1/4]/(ℓ/R), where ℓ/R is the distance between the neighbouring droplets normalized by the droplet radius. Finally, we numerically obtain the repulsive velocity of the droplets, characterized by a Reynolds number Rerep, which is proportional to PeRa[-0.38]. The balance of attractive and repulsive effect leads to Pe ~ Ra[0.63], which agrees well with the transition curve between the regimes with and without collision.}, }
@article {pmid38359059, year = {2024}, author = {Xi, Y and Meng, F}, title = {Numerical study on flow and heat transfer characteristics of rectangular mini-channel of interpolated double S turbulators.}, journal = {PloS one}, volume = {19}, number = {2}, pages = {e0297678}, pmid = {38359059}, issn = {1932-6203}, mesh = {*Hot Temperature ; Temperature ; *Body Temperature Regulation ; Commerce ; Computer Simulation ; }, abstract = {In this study, we propose a new type of small-channel plug-in, the double S turbulators, for passive heat transfer enhancement to improve the flow and heat transfer performance of the fluid in the channel. In the range of Reynolds number 254.51~2545.09, under constant wall temperature heating conditions, the effects of interpolated double S turbulators with different long axial radii (1mm, 1.5mm, 2mm) on the average Nusselt number, pressure drop, total thermal resistance and field synergy number in the rectangular mini-channel were studied. The simulation results show that compared with the smooth rectangular mini-channel, after interpolating double S turbulators with different long axial radii (1mm, 1.5mm, 2mm), the average Nusselt number increased by 81.74%~101.74%, 71.29%~94.06%, 67.16%~88.48%, the total thermal resistance decreased by 45.1%~50.72%, 41.72%~48.74%, 40.28%~47.2%, and the number of field synergies increased by 85.58%~111.65%, 74.1%~102.6%, 69.64%~96.12%. At present, there are few studies on the boundary condition of constant wall temperature, and this paper supplements the research on this aspect. At the same time, the heat transfer performance of the rectangular mini-channel of the interpolated double S turbulators is stronger than that of the ordinary smooth rectangular mini-channel, which not only provides a new idea for the manufacture of micro heat dissipation equipment, but also improves the heat transfer performance of micro heat dissipation equipment and improves its work efficiency. According to the simulation data, the prediction formula of average Nusselt number and pressure drop was established by nonlinear regression method, which can be used to predict the flow and heat transfer characteristics of the rectangular mini-channel of the interpolated double S turbulators.}, }
@article {pmid38352662, year = {2024}, author = {Gnanasekaran, M and Satheesh, A}, title = {Numerical analysis of turbulent flow characteristics with the influence of speed ratio in a double-sided cavity.}, journal = {MethodsX}, volume = {12}, number = {}, pages = {102594}, pmid = {38352662}, issn = {2215-0161}, abstract = {The present study numerically investigates the two-dimensional steady incompressible turbulent flow characteristics in an enclosed cavity. The finite volume method (FVM) is used to discretize the governing equations, and k-ε turbulence models are adopted to predict the flow characteristics. The turbulent flow behavior is studied by varying the speed ratio (0.05 ≤ S ≤ 1.0), aspect ratio (0.5 ≤ K ≤ 2.0), and Reynolds number (1 × 10[4] ≤ Re ≤ 2 × 10[5]). The flow characteristics are analyzed using stream function (ψ), Reynolds stresses (u'v'), and turbulent quantities. Results show the Reynolds number and speed ratio significantly influence the formation of vortices over the selected range of operating parameters. With the speed ratio, the turbulent kinetic energy reduces considerably by increasing the Reynolds number and aspect ratio. Similarly, for S = 0.05 and K = 0.5, the turbulent kinetic energy and dissipation rate are decreased by 89.16% and 42.28%, respectively. When Re is increased from 1 × 10[4] to 2 × 10[5], the turbulent viscosity increases by 92.10%. By comparing the results, average turbulent quantities are decreased by increasing the flow parameters.•Turbulent flow behavior is investigated by using the FVM near-wall treatment approach.One of the unique parameters called speed ratio is emphasized.•Contours of turbulence kinetic energy, dissipation, and viscosity are examined.•The average intensity of turbulent quantities is decreased by increasing the speed ratio.}, }
@article {pmid38336842, year = {2024}, author = {Kim, SJ and Kos, &#x17d; and Um, E and Jeong, J}, title = {Symmetrically pulsating bubbles swim in an anisotropic fluid by nematodynamics.}, journal = {Nature communications}, volume = {15}, number = {1}, pages = {1220}, pmid = {38336842}, issn = {2041-1723}, abstract = {Swimming in low-Reynolds-number fluids requires the breaking of time-reversal symmetry and centrosymmetry. Microswimmers, often with asymmetric shapes, exhibit nonreciprocal motions or exploit nonequilibrium processes to propel. The role of the surrounding fluid has also attracted attention because viscoelastic, non-Newtonian, and anisotropic properties of fluids matter in propulsion efficiency and navigation. Here, we experimentally demonstrate that anisotropic fluids, nematic liquid crystals (NLC), can make a pulsating spherical bubble swim despite its centrosymmetric shape and time-symmetric motion. The NLC breaks the centrosymmetry by a deformed nematic director field with a topological defect accompanying the bubble. The nematodynamics renders the nonreciprocity in the pulsation-induced fluid flow. We also report speed enhancement by confinement and the propulsion of another symmetry-broken bubble dressed by a bent disclination. Our experiments and theory propose another possible mechanism of moving bodies in complex fluids by spatiotemporal symmetry breaking.}, }
@article {pmid38335533, year = {2024}, author = {Wang, Z and Liu, X and Guo, Y and Tong, B and Zhang, G and Liu, K and Jiao, Y}, title = {Armored Superhydrophobic Surfaces with Excellent Drag Reduction in Complex Environmental Conditions.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {}, number = {}, pages = {}, doi = {10.1021/acs.langmuir.3c03544}, pmid = {38335533}, issn = {1520-5827}, abstract = {Superhydrophobic surfaces (SHSs) have possibilities for achieving significantly reduced solid-liquid frictional drag in the marine sector due to their excellent water-repelling properties. Although the stability of SHSs plays a key role in drag reduction, little consideration was given to the effect of extreme environments on the ability of SHSs to achieve drag reduction underwater, particularly when subjected to acidic conditions. Here, we propose interconnected microstructures to protect superhydrophobic coatings with the aim of enhancing the stability of SHSs in extreme environments. The stability of armored SHSs (ASHSs) was demonstrated by the contact angle and bounce time of droplets on superhydrophobic surfaces treated by various methods, resulting in an ASHS surface with excellent stability under extreme environmental conditions. Additionally, inspired by microstructures protecting superhydrophobic nanomaterials from frictional wear, the armored superhydrophobic spheres (ASSPs) were designed to explain from theoretical and experimental perspectives why ASSPs can achieve sustainable drag reduction and demonstrate that the ASSPs can achieve drag reduction of over 90.4% at a Reynolds number of 6.25 × 10[4] by conducting water entry experiments on spheres treated in various solutions. These studies promote a fundamental understanding of what drives the application of SHSs under extreme environmental conditions and provide practical strategies to maximize frictional drag reduction.}, }
@article {pmid38335336, year = {2024}, author = {Wang, K and Sprinkle, B and Zuo, M and Ristroph, L}, title = {Centrifugal Flows Drive Reverse Rotation of Feynman's Sprinkler.}, journal = {Physical review letters}, volume = {132}, number = {4}, pages = {044003}, doi = {10.1103/PhysRevLett.132.044003}, pmid = {38335336}, issn = {1079-7114}, abstract = {The issue of reversibility in hydromechanical sprinklers that auto-rotate while ejecting fluid from S-shaped tubes raises fundamental questions that remain unresolved. Here, we report on precision experiments that reveal robust and persistent reverse rotation under suction and a model that accounts for the observed motions. We implement an ultralow friction bearing in an apparatus that allows for free rotation under ejection and suction for a range of flow rates and arbitrarily long times. Flow measurements reveal a rocketlike mechanism shared by the reverse and forward modes that involves angular momentum flux, whose subtle manifestation in the reverse case stems from centrifugal effects for flows in curved conduits. These findings answer Feynman's long-standing question by providing quantitatively accurate explanations of both modes, and they suggest further inquiries into flux-based force generation and the roles of geometry and Reynolds number.}, }
@article {pmid38322951, year = {2024}, author = {Mishra, NK and Sharma, P and Sharma, BK and Almohsen, B and Pérez, LM}, title = {Electroosmotic MHD ternary hybrid Jeffery nanofluid flow through a ciliated vertical channel with gyrotactic microorganisms: Entropy generation optimization.}, journal = {Heliyon}, volume = {10}, number = {3}, pages = {e25102}, pmid = {38322951}, issn = {2405-8440}, abstract = {In this study, the computational analysis of entropy generation optimization for synthetic cilia regulated ternary hybrid Jeffery nanofluid (Ag-Au-TiO2/PVA) flow through a peristaltic vertical channel with swimming motile Gyrotactic microorganisms is investigated. Understanding the intricate interaction of multiple physical phenomena in biomedical applications is essential for optimizing entropy generation and advancing microfluidic systems. The characteristics of nanofluid are explored for the electroosmotic MHD fluid flow in the presence of thermophoresis and Brownian motion, viscous dissipation, Ohmic heating and chemical reaction. Using the appropriate transformations, a set of ordinary differential equations are created from the governing partial differential equations. The resulting ODEs are numerically solved using the shooting technique using BVP5C in MATLAB after applying the long-wavelength and low Reynolds number approximation. The velocity, temperature, concentration, electroosmosis, and microorganism density profiles are analyzed graphically for different emerging parameters. Graphical investigation of engineering interest quantities like heat transfer rate, mass transfer rate, skin friction coefficient, and entropy generation optimization are also presented. It is observed that the rate of mass transfer increases for increasing thermophoretic parameter, while reverse effect is noted for Brownian motion parameter, Schmidt number, and chemical reaction number. The outcomes of present study can be pertinent in studying Cilia properties of respiratory tract, reproductive system, and brain ventricles.}, }
@article {pmid38322945, year = {2024}, author = {Selimefendigil, F and Ghachem, K and Albalawi, H and AlShammari, BM and Labidi, T and Kolsi, L}, title = {Magneto-convection of nanofluid flow over multiple rotating cylinders in a confined space with elastic walls and ventilated ports.}, journal = {Heliyon}, volume = {10}, number = {3}, pages = {e25101}, doi = {10.1016/j.heliyon.2024.e25101}, pmid = {38322945}, issn = {2405-8440}, abstract = {In this study, convective heat transfer for nanofluid flow over multiple rotating cylinder in a confined space is analyzed under magnetic field while enclosure has one inlet and one outlet port. Three identical circular cylinder are used and the two walls of the cavity are considered to be elastic. The coupled fluid-structure interaction and magneto-convection problem is solved by finite element method. Impacts of rotational Reynolds number (Rew between -100 and 100), Hartmann number (Ha between 0 and 50), cylinder size (R between 0.001H and 0.11H) and Cauchy number (Ca between 10-8 and 10-3) on the flow and thermal performance features are explored. The flow field and recirculation inside the cavity are significantly affected by the activation of rotation and magnetic field. The vortices are suppressed by increasing the strength of magnetic field and thermal performance is improved. Thermal performance of 56.6% is achieved by activation of magnetic field at the highest strength with rotations of the circular cylinders. When rotations are active, heat transfer rate is reduced while up to 40% reduction is obtained without magnetic field. Cylinder size has the highest impact on the overall thermal performance improvement while up to 132% enhancements are achieved. The contribution of elastic walls on the thermal performance is slight while less than 5% improvements in the average heat transfer is obtained. An optimization study leads to 12.7% higher thermal performance improvements as compared to best case of parametric computational fluid dynamics simulation results while the optimum values of (Rew, Ha, R) is obtained as (-80.66, 50, 0.11H).}, }
@article {pmid38321050, year = {2024}, author = {Massaro, D and Karp, M and Jansson, N and Markidis, S and Schlatter, P}, title = {Direct numerical simulation of the turbulent flow around a Flettner rotor.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {3004}, pmid = {38321050}, issn = {2045-2322}, abstract = {The three-dimensional turbulent flow around a Flettner rotor, i.e. an engine-driven rotating cylinder in an atmospheric boundary layer, is studied via direct numerical simulations (DNS) for three different rotation speeds ([Formula: see text]). This technology offers a sustainable alternative mainly for marine propulsion, underscoring the critical importance of comprehending the characteristics of such flow. In this study, we evaluate the aerodynamic loads produced by the rotor of height h, with a specific focus on the changes in lift and drag force along the vertical axis of the cylinder. Correspondingly, we observe that vortex shedding is inhibited at the highest [Formula: see text] values investigated. However, in the case of intermediate [Formula: see text], vortices continue to be shed in the upper section of the cylinder ([Formula: see text]). As the cylinder begins to rotate, a large-scale motion becomes apparent on the high-pressure side, close to the bottom wall. We offer both a qualitative and quantitative description of this motion, outlining its impact on the wake deflection. This finding is significant as it influences the rotor wake to an extent of approximately one hundred diameters downstream. In practical applications, this phenomenon could influence the performance of subsequent boats and have an impact on the cylinder drag, affecting its fuel consumption. This fundamental study, which investigates a limited yet significant (for DNS) Reynolds number and explores various spinning ratios, provides valuable insights into the complex flow around a Flettner rotor. The simulations were performed using a modern GPU-based spectral element method, leveraging the power of modern supercomputers towards fundamental engineering problems.}, }
@article {pmid38305052, year = {2024}, author = {Mandujano, F and Vázquez-Luis, E}, title = {Chaotic vortex-induced rotation of an elliptical cylinder.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {34}, number = {2}, pages = {}, doi = {10.1063/5.0170987}, pmid = {38305052}, issn = {1089-7682}, abstract = {Non-linear oscillations of an elliptical cylinder, which can rotate about an axis that passes through its symmetry axle due to a torsional spring and hydrodynamic torque produced by the flow of a Newtonian fluid, were analyzed in terms of a single parameter that compares vortex shedding frequency with the torsional spring's natural frequency. The governing equations for the flow coupled with a rigid body with one degree of freedom were solved numerically using the lattice-Boltzmann method. The Reynolds number used was Re=200, which, in the absence of torsional spring, produces chaotic oscillations of the elliptical cylinder. When the torsional spring is included, we identified three branches separated by transition regions when stiffness of the restorative torque changes, as in the case of vortex-induced vibrations. However, in this case, several regions presenting chaotic dynamics were identified. Two regions with stable limit cycles were found when both torques synchronized and when stiffness of the torsional spring is big enough so that the ellipse's oscillation is small.}, }
@article {pmid38302543, year = {2024}, author = {Ashkani, A and Jafari, A and Ghomsheh, MJ and Dumas, N and Funfschilling, D}, title = {Enhancing particle focusing: a comparative experimental study of modified square wave and square wave microchannels in lift and Dean vortex regimes.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {2679}, pmid = {38302543}, issn = {2045-2322}, abstract = {Serpentine microchannels are known for their effective particle focusing through Dean flow-induced rotational effects, which are used in compact designs for size-dependent focusing in medical diagnostics. This study explores square serpentine microchannels, a geometry that has recently gained prominence in inertial microfluidics, and presents a modification of square wave microchannels for improved particle separation and focusing. The proposed modification incorporates an additional U-shaped unit to convert the square wave microchannel into a non-axisymmetric structure, which enhances the Dean flow and consequently increases the Dean drag force. Extensive experiments were conducted covering a wide range of Reynolds numbers and particle sizes (2.45 µm to 12 µm). The particle concentration capability and streak position dynamics of the two structures were compared in detail. The results indicate that the modified square-wave microchannel exhibits efficient particle separation in the lower part of the Dean vortex-dominated regime. With increasing Reynolds number, the particles are successively focused into two streaks in the lift force-dominated regime and into a single streak in the Dean vortex-dominated regime, in this modified square wave geometry. These streaks have a low standard deviation around a mean value. In the Dean vortex-dominated regime, the location of the particle stream is highly dependent on the particle size, which allows good particle separation. Particle focusing occurs at lower Reynolds numbers in both the lift-dominated and lift/Dean drag-dominated regions than in the square wave microchannel. The innovative serpentine channel is particularly useful for the Dean drag-dominated regime and introduces a unique asymmetry that affects the particle focusing dynamics. The proposed device offers significant advantages in terms of efficiency, parallelization, footprint, and throughput over existing geometries.}, }
@article {pmid38298735, year = {2024}, author = {Xia, Y and Lyu, S}, title = {Direct numerical simulation of contaminant removal in presence of underfloor air distribution system.}, journal = {Heliyon}, volume = {10}, number = {2}, pages = {e24331}, pmid = {38298735}, issn = {2405-8440}, abstract = {Indoor contaminant removal over 0.5 ≤ FrT ≤ 5.0, 0.5 ≤ N ≤ 5.0, and 50 ≤ Re ≤ 500 was investigated numerically, wherein FrT refers to the Froude number, N refers to the buoyancy ratio, and Re refers to the Reynolds number. As demonstrated, the ventilation effectiveness increased with increasing contaminant source intensity and air supply intensity at a constant air temperature, indicating that increase the fresh air can effectively eliminate contaminants in this case. At high air supply temperatures, the heat retention time and contaminant transport was extremely short, and the fresh air induced by strong natural convection floating lift was rapidly discharged. Additioanlly, the air supply intensity had significant effects on contaminant removal. Quantification of the ventilation effectiveness under the combined effects of air supply intensity, air supply temperature and contaminant source intensity was determined based on the results of direct numerical simulations.}, }
@article {pmid38298636, year = {2024}, author = {Almutairi, DK}, title = {Mathematical modelling and heat transfer observations for Jeffrey nanofluid with applications of extended Fourier theory and temperature dependent thermal conductivity.}, journal = {Heliyon}, volume = {10}, number = {2}, pages = {e24353}, pmid = {38298636}, issn = {2405-8440}, abstract = {The suspension of non-Newtonian materials with nanoparticles is important to enhance the thermal phenomenon in various engineering and industrial processes. The versatile research in nanomaterials provide different applications in thermal processes, heat exchangers, thermoelectric devices, HVAC systems, energy processes etc. Following to such novel motivations in mind, current research endorsed the enhancement in heat transfer due to suspension of Jeffrey nanofluid comprising the variable thermal conductivity. The cause of flow is associated to two disks attaining fixed distance. The modified developed relations for Fourier's hypothesis are utilized to model the problem. The flow problem is modeled with appliance of fundamental novel laws. By applying suitable transformations, corresponding differential equations are renovated into dimensionless forms which are solved with applications of analytic homotopic algorithm. The behavior of temperature and velocity due to various parameters is discussed. The numerical calculations have been done for wall shear force and Nusselt number. The results show that the velocity profile boosted due to variation of stretching ratio constant. The enhancement in heat transfer is observed due to Reynolds number. Moreover, the increasing observations for wall shear force in upper and lower disk surfaces are obtained against larger material parameter. The simulated results may find applications in improving heat transfer phenomenon, manufacturing systems, recovery processes, cooling systems, chemical phenomenon, fuel cells etc.}, }
@article {pmid38298373, year = {2024}, author = {Gande, VV and Podupu, PKR and Berry, B and Nere, NK and Pushpavanam, S and Singh, MR}, title = {Engineering advancements in microfluidic systems for enhanced mixing at low Reynolds numbers.}, journal = {Biomicrofluidics}, volume = {18}, number = {1}, pages = {011502}, pmid = {38298373}, issn = {1932-1058}, abstract = {Mixing within micro- and millichannels is a pivotal element across various applications, ranging from chemical synthesis to biomedical diagnostics and environmental monitoring. The inherent low Reynolds number flow in these channels often results in a parabolic velocity profile, leading to a broad residence time distribution. Achieving efficient mixing at such small scales presents unique challenges and opportunities. This review encompasses various techniques and strategies to evaluate and enhance mixing efficiency in these confined environments. It explores the significance of mixing in micro- and millichannels, highlighting its relevance for enhanced reaction kinetics, homogeneity in mixed fluids, and analytical accuracy. We discuss various mixing methodologies that have been employed to get a narrower residence time distribution. The role of channel geometry, flow conditions, and mixing mechanisms in influencing the mixing performance are also discussed. Various emerging technologies and advancements in microfluidic devices and tools specifically designed to enhance mixing efficiency are highlighted. We emphasize the potential applications of micro- and millichannels in fields of nanoparticle synthesis, which can be utilized for biological applications. Additionally, the prospects of machine learning and artificial intelligence are offered toward incorporating better mixing to achieve precise control over nanoparticle synthesis, ultimately enhancing the potential for applications in these miniature fluidic systems.}, }
@article {pmid38295375, year = {2024}, author = {Shi, Q and Wu, J and Chen, H and Xu, X and Yang, YB and Ding, M}, title = {Inertial migration of polymer micelles in a square microchannel.}, journal = {Soft matter}, volume = {20}, number = {8}, pages = {1760-1766}, doi = {10.1039/d3sm01304a}, pmid = {38295375}, issn = {1744-6848}, abstract = {Using a hybrid simulation approach that combines a lattice-Boltzmann method for fluid flow and a molecular dynamics model for polymers, we investigate the inertial migration of star-like and crew-cut polymer micelles in a square microchannel. It is found that they exhibit two types of equilibrium positions, which shift further away from the center of the microchannel when the Reynolds number (Re) increases, as can be observed for soft particles. What differs from the behaviors of soft particles is that here, the blockage ratio is no longer the decisive factor. When the sizes are the same, the star-like micelles are always relatively closer to the microchannel wall as they gradually transition from spherical to disc-like with the increase of Re. In comparison, the crew-cut micelles are only transformed into an ellipsoid. Conversely, when the hydrophobic core sizes are the same, the equilibrium position of the star-like micelles becomes closer to that of the crew-cut micelles. Our results demonstrate that for polymer micelles with a core-shell structure, the equilibrium position is no longer solely determined by their overall dimensions but depends on the core and shell's specific dimensions, especially the hydrophobic core size. This finding opens up a new approach for achieving the separation of micelles in inertial migration.}, }
@article {pmid38284759, year = {2024}, author = {Maar, K and Shavit, U and Andersen, A and Kiørboe, T}, title = {The fluid dynamics of barnacle feeding.}, journal = {The Journal of experimental biology}, volume = {227}, number = {5}, pages = {}, doi = {10.1242/jeb.246541}, pmid = {38284759}, issn = {1477-9145}, support = {//EuroTech Universities Alliance/ ; //Uddannelses- og Forskningsministeriet/ ; //Carlsbergfondet/ ; //Villum Fonden/ ; }, mesh = {Animals ; *Thoracica ; Hydrodynamics ; *Copepoda ; Rheology ; Water ; }, abstract = {Sessile barnacles feed by sweeping their basket-like cirral fan through the water, intercepting suspended prey. A primary component of the diet of adult barnacles is copepods that are sensitive to fluid disturbances and capable of escaping. How do barnacles manage to capture copepods despite the fluid disturbances they generate? We examined this question by describing the feeding current architecture of 1 cm sized Balanus crenatus using particle image velocimetry, and by studying the trajectories of captured copepods and the escapes of evading copepods. We found that barnacles produce a feeding current that arrives both from behind and the sides of the barnacle. The flow from the sides represents quiescent corridors of low fluid deformation and uninterrupted by the beating cirral fan. Potential prey arriving from behind are likely to encounter the cirral fan and, hence, capture here is highly unlikely. Accordingly, most captured copepods arrived through the quiet corridors, while most copepods arriving from behind managed to escape. Thus, it is the unique feeding flow architecture that allows feeding on evasive prey. We used the Landau-Squire jet as a simple model of the feeding current. For the Reynolds number of our experiments, the model reproduces the main features of the feeding current, including the lateral feeding corridors. Furthermore, the model suggests that smaller barnacle specimens, operating at lower Reynolds numbers, will produce a fore-aft symmetric feeding current without the lateral corridors. This suggests an ontogenetic diet shift from non-evasive prey to inclusion of evasive prey as the barnacle grows.}, }
@article {pmid38282920, year = {2023}, author = {Abbas, N and Mustafa, Z and Abodayeh, K and Shatnawi, TAM and Shatanawi, W}, title = {Darcy resistant of Soret and Dufour impact of radiative induced magnetic field sutterby fluid flow over stretching cylinder.}, journal = {Heliyon}, volume = {9}, number = {12}, pages = {e22503}, pmid = {38282920}, issn = {2405-8440}, abstract = {The incompressible two-dimensional steady flow of Sutterby fluid over a stretching cylinder is taken into account. The magnetic Reynolds number is not deliberated low in the present analysis. Radiation and variable thermal conductivity are considered to debate the impact on the cylindrical surface. The Dufour and Soret impacts are considered on the cylinder. The mathematical model is settled by employing boundary layer approximations in the form of differential equations. The system of differential equations becomes dimensionless using suitable transformations. The dimensionless nonlinear differential equations are solved through a numerical scheme(bvp4c technique). The flow parameters of physical effects on the velocity, temperature, heat transfer rate, and friction between surface and liquid are presented in tabular as well as graphical form. The velocity function declined by improving the values of the Sponginess parameter. The fluid temperature is reduced by increment in curvature parameter.}, }
@article {pmid38276832, year = {2023}, author = {Chang, L and Zhao, G and Buren, M and Sun, Y and Jian, Y}, title = {Alternating Current Electroosmotic Flow of Maxwell Fluid in a Parallel Plate Microchannel with Sinusoidal Roughness.}, journal = {Micromachines}, volume = {15}, number = {1}, pages = {}, pmid = {38276832}, issn = {2072-666X}, support = {Nos. 12162003, 11862018, 12262026//the National Natural Science Foundation of China/ ; Grant Nos. 2022LHMS01001, 2021MS01007//the Natural Science Foundation of the Inner Mongolia Autonomous Region of China/ ; No. NMGIRT2323//Innovative Research Team in the Universities of Inner Mongolia Autonomous Region/ ; No. NCYWT23035//Basic Research funds for Universities Directly under the Autonomous Region/ ; Grant No. NJZY23054//the Research Program of Science and Technology in the Universities of Inner Mongolia Autonomous Region/ ; }, abstract = {The EOF of a viscoelastic Maxwell fluid driven by an alternating pressure gradient and electric field in a parallel plate microchannel with sinusoidal roughness has been investigated within the Debye-Hückel approximation based on boundary perturbation expansion and separation of variables. Perturbation solutions were obtained for the potential distribution, the velocity and the mean velocity, and the relation between the mean velocity and the roughness. There are significant differences in the velocity amplitudes of the Newtonian and Maxwell fluids. It is shown here that the velocity distribution of the viscoelastic fluid is significantly affected by the roughness of the walls, which leads to the appearance of fluctuations in the fluid. Also, the velocity is strongly dependent on the phase difference θ of the roughness of the upper and lower plates. As the oscillation Reynolds number ReΩ increases, the velocity profile and the average velocity um(t) of AC EOF oscillate rapidly but the velocity amplitude decreases. The Deborah number De plays a similar role to ReΩ, which makes the AC EOF velocity profile more likely to oscillate. Meanwhile, phase lag χ (representing the phase difference between the electric field and the mean velocity) decreases when G and θ are increased. However, for larger λ (e.g., λ > 3), it almost has no phase lag χ.}, }
@article {pmid38267645, year = {2024}, author = {Salman, M and Liu, J and Chauhan, R and Souby, MM and Kim, SC}, title = {A MATLAB simulation-based analytical study of energy, exergy, and cost benefits in jet-impinged protrusion-roughened double pass solar air collector.}, journal = {Environmental science and pollution research international}, volume = {}, number = {}, pages = {}, pmid = {38267645}, issn = {1614-7499}, support = {2019R1A5A8080290//National Research Foundation of Korea/ ; }, abstract = {This study analyzes the performance and cost-effectiveness of a protrusion-roughened jet-impinged double-pass solar air collector (PRJDPSAC) within a Reynolds number (Re) range of 2500 to 22,500. Examining jet slot parameters, i.e., the jet height ratio (Hjp/Dhd = 0.11-0.44), stream-wise pitch ratio (Xjp/Dhd = 0.44-1.32), and span-wise pitch ratio (Yjp/Dhd = 0.44-1.32), the model demonstrates enhanced energy conversion, minimizes losses, improves efficiency, and brings positive economic impact, making it a promising solution for diverse applications including drying processes, livestock facilities, remote accommodations, and HVAC system pre-heating. The examination incorporates advanced MATLAB simulations to assess energy-exergy performance and cost viability. At lower Re values, both energy ([Formula: see text]) and exergy ([Formula: see text]) efficiencies increase uniformly; however, stabilization and decline occur at higher Re values. The maximum [Formula: see text] for the PRJDPSAC is 4.38% under a temperature rise parameter of 60 × 10[-3] Km[2]/W for obtaining optimum values of Xjp/Dhd = 1.32, Hjp/Dhd = 0.22, and Yjp/Dhd = 1.32, which is 31% higher than that of the smooth double-pass solar air collector (DPSAC). Economic benefits are significant for PRJDPSAC within mair (0.01-0.07 kg/s), but above 0.07 kg/s, the DPSAC becomes more cost-effective. Integrating simulation and experimental data, the study highlights MATLAB's effectiveness for solar energy system analysis and optimization, reinforcing the practicality of the proposed collector design.}, }
@article {pmid38265427, year = {2024}, author = {Wu, Y and Wang, F and Zheng, S and Nestler, B}, title = {Evolution dynamics of thin liquid structures investigated using a phase-field model.}, journal = {Soft matter}, volume = {20}, number = {7}, pages = {1523-1542}, doi = {10.1039/d3sm01553j}, pmid = {38265427}, issn = {1744-6848}, abstract = {Liquid structures of thin-films and torus droplets are omnipresent in daily lives. The morphological evolution of liquid structures suspending in another immiscible fluid and sitting on a solid substrate is investigated by using three-dimensional (3D) phase-field (PF) simulations. Here, we address the evolution dynamics by scrutinizing the interplay of surface energy, kinetic energy, and viscous dissipation, which is characterized by Reynolds number Re and Weber number We. We observe special droplet breakup phenomena by varying Re and We. In addition, we gain the essential physical insights into controlling the droplet formation resulting from the morphological evolution of the liquid structures by characterizing the top and side profiles under different circumstances. We find that the shape evolution of the liquid structures is intimately related to the initial shape, Re, We as well as the intrinsic wettability of the substrate. Furthermore, it is revealed that the evolution dynamics are determined by the competition between the coalescence phenomenology and the hydrodynamic instability of the liquid structures. For the coalescence phenomenology, the liquid structure merges onto itself, while the hydrodynamic instability leads to the breakup of the liquid structure. Last but not least, we investigate the influence of wall relaxation on the breakup outcome of torus droplets on substrates with different contact angles. We shed light on how the key parameters including the initial shape, Re, We, wettability, and wall relaxation influence the droplet dynamics and droplet formation. These findings are anticipated to contribute insights into droplet-based systems, potentially impacting areas like ink-jet printing, drug delivery systems, and microfluidic devices, where the interplay of surface energy, kinetic energy, and viscous dissipation plays a crucial role.}, }
@article {pmid38264707, year = {2024}, author = {Jeon, H and Lee, SH and Shin, J and Song, K and Ahn, N and Park, J}, title = {Elasto-inertial microfluidic separation of microspheres with submicron resolution at high-throughput.}, journal = {Microsystems &amp; nanoengineering}, volume = {10}, number = {}, pages = {15}, pmid = {38264707}, issn = {2055-7434}, abstract = {Elasto-inertial microfluidic separation offers many advantages including high throughput and separation resolution. Even though the separation efficiency highly depends on precise control of the flow conditions, no concrete guidelines have been reported yet in elasto-inertial microfluidics. Here, we propose a dimensionless analysis for precise estimation of the microsphere behaviors across the interface of Newtonian and viscoelastic fluids. Reynolds number, modified Weissenberg number, and modified elastic number are used to investigate the balance between inertial and elastic lift forces. Based on the findings, we introduce a new dimensionless number defined as the width of the Newtonian fluid stream divided by microsphere diameter. The proposed dimensionless analysis allows us to predict whether the microspheres migrate across the co-flow interface. The theoretical estimation is found to be in good agreement with the experimental results using 2.1- and 3.2-μm-diameter polystyrene microspheres in a co-flow of water and polyethylene oxide solution. Based on the theoretical estimation, we also realize submicron separation of the microspheres with 2.1 and 2.5 μm in diameter at high throughput, high purity (>95%), and high recovery rate (>97%). The applicability of the proposed method was validated by separation of platelets from similar-sized Escherichia coli (E.coli).}, }
@article {pmid38248619, year = {2024}, author = {Macías, MM and García-Ortiz, JH and Oliveira, TF and Brasil Junior, ACP}, title = {Numerical Investigation of Dimensionless Parameters in Carangiform Fish Swimming Hydrodynamics.}, journal = {Biomimetics (Basel, Switzerland)}, volume = {9}, number = {1}, pages = {}, pmid = {38248619}, issn = {2313-7673}, abstract = {Research into how fish and other aquatic organisms propel themselves offers valuable natural references for enhancing technology related to underwater devices like vehicles, propellers, and biomimetic robotics. Additionally, such research provides insights into fish evolution and ecological dynamics. This work carried out a numerical investigation of the most relevant dimensionless parameters in a fish swimming environment (Reynolds Re, Strouhal St, and Slip numbers) to provide valuable knowledge in terms of biomechanics behavior. Thus, a three-dimensional numerical study of the fish-like lambari, a BCF swimmer with carangiform kinematics, was conducted using the URANS approach with the k-ω-SST transition turbulence closure model in the OpenFOAM software. In this study, we initially reported the equilibrium Strouhal number, which is represented by St∗, and its dependence on the Reynolds number, denoted as Re. This was performed following a power-law relationship of St∝Re(-α). We also conducted a comprehensive analysis of the hydrodynamic forces and the effect of body undulation in fish on the production of swimming drag and thrust. Additionally, we computed propulsive and quasi-propulsive efficiencies, as well as examined the influence of the Reynolds number and Slip number on fish performance. Finally, we performed a vortex dynamics analysis, in which different wake configurations were revealed under variations of the dimensionless parameters St, Re, and Slip. Furthermore, we explored the relationship between the generation of a leading-edge vortex via the caudal fin and the peak thrust production within the motion cycle.}, }
@article {pmid38243509, year = {2023}, author = {Xiong, J and Liu, X and Feng, H and Huang, H}, title = {Inertial migration of spherical and oblate particles in a triangular microchannel.}, journal = {Physical review. E}, volume = {108}, number = {6-2}, pages = {065105}, doi = {10.1103/PhysRevE.108.065105}, pmid = {38243509}, issn = {2470-0053}, abstract = {The. inertial migration of both spherical and oblate particles within an equilateral triangular channel is studied numerically. Our study primarily focuses on the effects of fluid inertia, quantified by the Reynolds number (Re) and particle size (β). Our observations reveal two distinct equilibrium positions: the corner equilibrium position (CEP) is situated along the angle bisector near the corner, while the face equilibrium position (FEP) is located on a segment of the line perpendicular from the triangle's center to one of its sides. Spherical particles with varying initial positions predominantly reach the FEP. For oblate particles initially positioned along the angle bisector with a specific orientation, meaning the particle's evolution axis is inside the plane bisecting the angle, they will migrate along the angle bisector to reach the CEP while rotating in the tumbling mode. Conversely, for particles with different initial orientations and positions, they will employ the log-rolling mode to reach the FEP. Notably, we identify a dual-stage particle migration process to the FEP, with trajectories converging to an equilibrium manifold, which bears a resemblance to the cross section of the channel. To further illustrate the transition between FEP and CEP under general initial conditions, except for those along the angle bisector, we construct a phase diagram in the (Re, β) parameter space. This transition is often triggered by the size of larger particles (as the FEP cannot accommodate them) or the influence of inertia for smaller particles. For the FEP, especially for medium- or small-size particles, we notice an initial outward movement of the FEP from the center of the cross section as Re increases, followed by a return towards the center. This behavior results from the interplay of three forces acting on the particle. This research holds potential implications for the design of microfluidic devices, offering insights into the behavior of particles within equilateral triangular channels.}, }
@article {pmid38243467, year = {2023}, author = {Wang, S and Wang, J and Deng, J}, title = {Effect of layer thickness for the bounce of a particle settling through a density transition layer.}, journal = {Physical review. E}, volume = {108}, number = {6-2}, pages = {065108}, doi = {10.1103/PhysRevE.108.065108}, pmid = {38243467}, issn = {2470-0053}, abstract = {We study numerically a spherical particle settling through a density transition layer at moderate Reynolds numbers Re_{u}=69∼259 for the upper fluid. We investigate how the transition layer thickness affects the particle's bouncing behavior as it crosses the interface. The previous intuitive understanding was that the bounce occurs when the relative thickness of the transition layer, L/D, which is characterized by the ratio of the layer thickness L to the particle diameter D, is small. Indeed, we report no bounce phenomenon for very thick interfaces, i.e., L/D>10 in the current parametric range. However, we argue that the bounce can also be inhibited when L/D is too small. Upon a fixed upper layer Reynolds number Re_{u}=207 with varying L/D, we examine the flow evolution of these cases. We propose that this inhibition is attributed to two mechanisms. First, as the interface thickness decreases, the detachment of the attached lighter fluid from the upper layer occurs more rapidly, resulting in a faster decrease in buoyancy. Second, in the case of a very thin interface (L/D=0.5-3.0), the residual light fluid accumulates and undergoes a secondary detachment, separating from the particle at an angle relative to the central axis. This secondary detachment reduces the drag force and effectively prevents the particle from experiencing a rebound motion.}, }
@article {pmid38237184, year = {2024}, author = {Liu, T and Deng, H and He, F and Wu, Y and Wu, Z and Wan, F and Chen, T and Xu, W and Song, Y and Guo, X}, title = {Synthesizing high performance LNMO cathode materials with porous structure by manipulating reynolds number in a microreactor.}, journal = {Nanotechnology}, volume = {35}, number = {19}, pages = {}, doi = {10.1088/1361-6528/ad2017}, pmid = {38237184}, issn = {1361-6528}, abstract = {The demand for Lithium-ion batteries (LIBs) has significantly grown in the last decade due to their extensive use electric vehicles. To further advance the commercialization of LIBs for various applications, there is a pressing need to develop electrode materials with enhanced performance. The porous microsphere morphology LiNixMn2-xO4(LNMO) is considered to be an effective material with both high energy density and excellent rate performance. Nevertheless, LNMO synthesis technology still has problem such as long reaction time, high energy consumption and environmental pollution. Herein, LNMO microsphere was successfully synthesized with short precursors reaction time (18 s) at 40 °C without using chelating agent by microreaction technology combined solid-state lithiation. The optimized LNMO cathode shows microsphere (∼8μm) morphology stacked by nano primary particles, with abundant mesoporous and fully exposed low-energy plane. The electrochemical analysis indicates that the optimized LNMO cathode demonstrates 97.33% capacity retention even after 200 cycles at 1C. Additionally, the material shows a highly satisfactory discharge capacity of 92.3 mAh·g[-1]at 10C. Overall, microreaction technology is anticipated to offer a novel approach in the synthesis of LNMO cathode materials with excellent performance.}, }
@article {pmid38233489, year = {2024}, author = {Ashraf, H and Siddique, I and Siddiqa, A and Tawfiq, FMO and Tchier, F and Zulqarnain, RM and Rehman, HU and Bhatti, S and Rehman, A}, title = {Analysis of two layered peristaltic-ciliary transport of Jeffrey fluid and in vitro preimplantation embryo development.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {1469}, pmid = {38233489}, issn = {2045-2322}, mesh = {Pregnancy ; Female ; Humans ; *Prolactin ; *Luteinizing Hormone ; Follicle Stimulating Hormone ; Estradiol ; Progesterone ; Embryonic Development ; Thyrotropin ; }, abstract = {The analysis of peristaltic-ciliary transport in the human female fallopian tube, specifically in relation to the growing embryo, is a matter of considerable physiological importance. This paper proposes a biomechanical model that incorporates a finite permeable tube consisting of two layers, where the Jeffrey fluid model characterizes the viscoelastic properties of the growing embryo and continuously secreting fluid. Jeffrey fluid entering with some negative pressure gradient forms the core fluid layer while continuously secreting Jeffrey fluid forms the peripheral fluid layer. The resulting partial differential equations are solved for closed-form solutions after employing the assumption of long wavelength. The analysis delineated that increasing the constant secretion velocity, Darcy number, and Reynolds number leads to a decrease in the appropriate residue time of the core fluid layer and a reduction in the size of the secreting fluid bolus in the peripheral fluid layer. Eventually, the boluses completely disappear when the constant secretion velocity exceeds 3.0 Progesterone ([Formula: see text]) and estradiol ([Formula: see text]) directly regulate the transportation of the growing embryo, while luteinizing hormone (LH) and follicle-stimulating hormone (FSH), prolactin, anti-mullerian hormone (AMH), and thyroid-stimulating hormone (TSH) have an indirect effects. Based on the number and size of blastomeres, the percentage of fragmentation, and the presence of multinucleated blastomeres two groups were formed in an in vitro experiment. Out of 50 patients, 26 (76.5%) were pregnant in a group of the good quality embryos, and only 8 (23.5%) were in a group of the bad quality embryos. The transport of growing embryo in the human fallopian tube and preimplantation development of human embryos in in vitro are constraint by baseline hormones FSH, LH, prolactin, [Formula: see text], AMH, and TSH.}, }
@article {pmid38233420, year = {2024}, author = {Akbar, NS and Rafiq, M and Muhammad, T and Alghamdi, M}, title = {Microbic flow analysis of nano fluid with chemical reaction in microchannel with flexural walls under the effects of thermophoretic diffusion.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {1474}, pmid = {38233420}, issn = {2045-2322}, abstract = {The current investigation examines the peristaltic flow, in curved conduit, having complaint boundaries for nanofluid. The effects of curvature are taken into account when developing the governing equations for the nano fluid model for curved channels. Nonlinear &amp; coupled differential equations are then simplified by incorporating the long wavelength assumption along with smaller Reynolds number. The homotopy perturbation approach is used to analytically solve the reduced coupled differential equations. The entropy generation can be estimated through examining the contributions of heat and fluid viscosities. The results of velocity, temperature, concentration, entropy number, and stream functions have been plotted graphically in order to discuss the physical attributes of the essential quantities. Increase in fluid velocity within the curved conduit is noticed for higher values of thermophoresis parameter and Brownian motion parameter further entropy generation number is boosted by increasing values of Grashof number.}, }
@article {pmid38226962, year = {2024}, author = {Armitage, JP}, title = {Microbial Primer: The bacterial flagellum - how bacteria swim.}, journal = {Microbiology (Reading, England)}, volume = {170}, number = {1}, pages = {}, pmid = {38226962}, issn = {1465-2080}, mesh = {*Cytoskeleton ; *Flagella ; }, abstract = {Bacteria swim using membrane-spanning, electrochemical gradient-powered motors that rotate semi-rigid helical filaments. This primer provides a brief overview of the basic synthesis, structure and operation of these nanomachines. Details and variations on the basic system can be found in suggested further reading.}, }
@article {pmid38213601, year = {2023}, author = {Allehiany, FM and Riaz, A and Shoukat, S and Alhamzi, G and Mahmoud, EE}, title = {Three dimensional study for entropy optimization in nanofluid flow through a compliant curved duct: A drug delivery and therapy application.}, journal = {Heliyon}, volume = {9}, number = {12}, pages = {e22255}, pmid = {38213601}, issn = {2405-8440}, abstract = {This research explores the three-dimensional characteristics of nanofluid dynamics within curved ducts, in contrast to earlier studies that mainly focus on two-dimensional flow. By using this ground-breaking method, we can capture a more accurate depiction of fluid behavior that complies with the intricate duct design. In this study, we investigate the three dimensional flow and entropic analysis of peristaltic nanofluid flows in a flexible curved duct, comparing the effects of silver and copper nanoparticles. To obtain accurate results, we assume physical constraints such as long wavelength and low Reynolds number and used a perturbation technique through NDSolve commands for finding exact solutions of the obtained differential equations. A comprehensive error analysis is provided through residual error table and figures to estimate a suitable range of the physical factors. Our findings indicate that the velocity of the nanofluid is directly proportional to the elasticity of the walls, while the mass per unit volume inversely affects velocity. We show that reducing the aspect ratio of the duct rectangular section can decrease entropy generation by raising magnitudes of damping force exerted by to the flexible walls of the enclosure. Additionally, using a larger height of the channel than the breadth can reduce stream boluses. The practical implications of this study extend beyond turbines and endoscopy to biomedical processes such as drug delivery and microfluidic systems.}, }
@article {pmid38212397, year = {2024}, author = {Uttieri, M and Svetlichny, L}, title = {Escape performance in the cyclopoid copepod Oithona davisae.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {1078}, pmid = {38212397}, issn = {2045-2322}, support = {CN00000033//Ministero dell'Universit&#xe0; e della Ricerca/ ; }, mesh = {Animals ; Female ; Male ; *Copepoda/physiology ; *Escape Reaction ; }, abstract = {Escaping a predator is one of the keys to success for any living creature. The performance of adults (males, females, and ovigerous females) of the cyclopoid copepod Oithona davisae exposed to an electrical stimulus is analysed as a function of temperature by measuring characteristic parameters associated with the escape movement (distance covered, duration of the appendage movement, mean and maximum escape speeds, Reynolds number). In addition, as a proxy for the efficiency of the motion, the Strouhal number was calculated. The escape performance showed temperature-dependent relationships within each adult state, as well as differences between sexes; additionally, changes owing to the presence of the egg sac were recorded in females. In a broader perspective, the results collected reveal the occurrence of different behavioural adaptations in males and females, adding to the comprehension of the mechanisms by which O. davisae interacts with its environment and shedding new light on the in situ population dynamics of this species.}, }
@article {pmid38198675, year = {2024}, author = {Banerjee, A and Pavithran, I and Sujith, RI}, title = {Early warnings of tipping in a non-autonomous turbulent reactive flow system: Efficacy, reliability, and warning times.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {34}, number = {1}, pages = {}, doi = {10.1063/5.0160918}, pmid = {38198675}, issn = {1089-7682}, abstract = {Real-world complex systems such as the earth's climate, ecosystems, stock markets, and combustion engines are prone to dynamical transitions from one state to another, with catastrophic consequences. State variables of such systems often exhibit aperiodic fluctuations, either chaotic or stochastic in nature. Often, the parameters describing a system vary with time, showing time dependency. Constrained by these effects, it becomes difficult to be warned of an impending critical transition, as such effects contaminate the precursory signals of the transition. Therefore, a need for efficient and reliable early-warning signals (EWSs) in such complex systems is in pressing demand. Motivated by this fact, in the present work, we analyze various EWSs in the context of a non-autonomous turbulent thermoacoustic system. In particular, we investigate the efficacy of different EWS in forecasting the onset of thermoacoustic instability (TAI) and their reliability with respect to the rate of change of the control parameter. This is the first experimental study of tipping points in a non-autonomous turbulent thermoacoustic system. We consider the Reynolds number (Re) as the control parameter, which is varied linearly with time at finite rates. The considered EWSs are derived from critical slowing down, spectral properties, and fractal characteristics of the system variables. The state of TAI is associated with large amplitude acoustic pressure oscillations that could lead thermoacoustic systems to break down. We consider acoustic pressure fluctuations as a potential system variable to perform the analysis. Our analysis shows that irrespective of the rate of variation of the control parameter, the Hurst exponent and variance of autocorrelation coefficients warn of an impending transition well in advance and are more reliable than other EWS measures. Additionally, we show the variation in the warning time to an impending TAI with rates of change of the control parameter. We also investigate the variation in amplitudes of the most significant modes of acoustic pressure oscillations with the Hurst exponent. Such variations lead to scaling laws that could be significant in prediction and devising control actions to mitigate TAI.}, }
@article {pmid38191806, year = {2024}, author = {Faisal, S and Barbour, M and Seibel, EJ and Aliseda, A}, title = {Hemodynamics of Saline Flushing in Endoscopic Imaging of Partially Occluded Coronary Arteries.}, journal = {Cardiovascular engineering and technology}, volume = {15}, number = {2}, pages = {211-223}, pmid = {38191806}, issn = {1869-4098}, support = {1R43HL139323-01/GF/NIH HHS/United States ; GCR 2120774//National Science Foundation/ ; }, mesh = {*Saline Solution/administration &amp; dosage ; *Coronary Vessels/physiopathology/diagnostic imaging ; Humans ; *Models, Cardiovascular ; *Hemodynamics ; Computer Simulation ; Coronary Circulation ; Plaque, Atherosclerotic ; Coronary Artery Disease/diagnostic imaging/physiopathology/therapy ; Equipment Design ; Cardiac Catheters ; Endoscopy/instrumentation ; Coronary Occlusion/diagnostic imaging/physiopathology/therapy ; Time Factors ; }, abstract = {PURPOSE: Intravascular endoscopy can aid in the diagnosis of coronary atherosclerosis by providing direct color images of coronary plaques. The procedure requires a blood-free optical path between the catheter and plaque, and achieving clearance safely remains an engineering challenge. In this study, we investigate the hemodynamics of saline flushing in partially occluded coronary arteries to advance the development of intravascular forward-imaging catheters that do not require balloon occlusion.<br><br>METHODS: In-vitro experiments and CFD simulations are used to quantify the influence of plaque size, catheter stand-off distance, saline injection flowrate, and injection orientation on the time required to achieve blood clearance.<br><br>RESULTS: Experiments and simulation of saline injection from a dual-lumen catheter demonstrated that flushing times increase both as injection flow rate (Reynolds number) decreases and as the catheter moves distally away from the plaque. CFD simulations demonstrated that successful flushing was achieved regardless of lumen axial orientation in a 95% occluded artery. Flushing time was also found to increase as plaque size decreases for a set injection flowrate, and a lower limit for injection flowrate was found to exist for each plaques size, below which clearance was not achieved. For the three occlusion sizes investigated (90, 95, 97% by area), successful occlusion was achieved in less than 1.2&#xa0;s. Investigation of the pressure fields developed during injection, highlight that rapid clearance can be achieved while keeping the arterial overpressure to&#x2009;<&#x2009;1&#xa0;mmHg.<br><br>CONCLUSIONS: A dual lumen saline injection catheter was shown to produce clearance safely and effectively in models of partially occluded coronary arteries. Clearance was achieved across a range of engineering and clinical parameters without the use of a balloon occlusion, providing development guideposts for a fluid injection system in forward-imaging coronary endoscopes.}, }
@article {pmid38181350, year = {2023}, author = {Inubushi, M and Saiki, Y and Kobayashi, MU and Goto, S}, title = {Characterizing Small-Scale Dynamics of Navier-Stokes Turbulence with Transverse Lyapunov Exponents: A Data Assimilation Approach.}, journal = {Physical review letters}, volume = {131}, number = {25}, pages = {254001}, doi = {10.1103/PhysRevLett.131.254001}, pmid = {38181350}, issn = {1079-7114}, abstract = {Data assimilation (DA) of turbulence, which involves reconstructing small-scale turbulent structures based on observational data from large-scale ones, is crucial not only for practical forecasting but also for gaining a deeper understanding of turbulent dynamics. We propose a theoretical framework for DA of turbulence based on the transverse Lyapunov exponents (TLEs) in synchronization theory. Through stability analysis using TLEs, we identify a critical length scale as a key condition for DA; turbulent dynamics smaller than this scale are synchronized with larger-scale turbulent dynamics. Furthermore, considering recent findings for the maximal Lyapunov exponent and its relation with the TLEs, we clarify the Reynolds number dependence of the critical length scale.}, }
@article {pmid38177658, year = {2024}, author = {Akbar, NS and Rafiq, M and Muhammad, T and Alghamdi, M}, title = {Electro osmotically interactive biological study of thermally stratified micropolar nanofluid flow for Copper and Silver nanoparticles in a microchannel.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {518}, pmid = {38177658}, issn = {2045-2322}, abstract = {A novel mathematical analysis is established that summits the key features of peristaltic propulsion for a non-Newtonian micropolar fluid with the electroosmosis and heat transfer enhancement using nanoparticles. In such physiological models, the channel have a symmetric configuration in accordance with the biological problem. Being mindful of this fact, we have disclosed an integrated analysis on symmetric channel that incorporates major physiological applications. The creeping flow inference is reviewed to model this realistic problem. Flow equations are model using cartesian coordinates and simplified using long wave length and low Reynolds number approximation. Nonlinear linear couple equations are solving numerically. We have studied the variation in the properties of nanofluid developed by two different types of nanoparticles (i.e. Cu and Ag nanoparticles). Graphical illustrations are unveiled to highlight the physical aspects of nanoparticles and flow parameters. The exploration demonstrates that the micro-rotation of the nano-liquid elements enhances the thermal conductivity of the fluid movement. The effect of micropolar fluid parameters on mean flow and pressure variables is also presented.}, }
@article {pmid38177235, year = {2024}, author = {Chinnasamy, P and Sivajothi, R and Sathish, S and Abbas, M and Jeyakrishnan, V and Goel, R and Alqahtani, MS and Loganathan, K}, title = {Peristaltic transport of Sutterby nanofluid flow in an inclined tapered channel with an artificial neural network model and biomedical engineering application.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {555}, pmid = {38177235}, issn = {2045-2322}, support = {R.G.P.2/453/44//Deanship of Scientific Research, King Khalid University/ ; R.G.P.2/453/44//Deanship of Scientific Research, King Khalid University/ ; }, mesh = {Humans ; *Biomedical Engineering ; *Neural Networks, Computer ; Temperature ; Hot Temperature ; Motion ; }, abstract = {Modern energy systems are finding new applications for magnetohydrodynamic rheological bio-inspired pumping systems. The incorporation of the electrically conductive qualities of flowing liquids into the biological geometries, rheological behavior, and propulsion processes of these systems was a significant effort. Additional enhancements to transport properties are possible with the use of nanofluids. Due to their several applications in physiology and industry, including urine dynamics, chyme migration in the gastrointestinal system, and the hemodynamics of tiny blood arteries. Peristaltic processes also move spermatozoa in the human reproductive system and embryos in the uterus. The present research examines heat transport in a two-dimensional deformable channel containing magnetic viscoelastic nanofluids by considering all of these factors concurrently, which is vulnerable to peristaltic waves and hall current under ion slip and other situations. Nanofluid rheology makes use of the Sutterby fluid model, while nanoscale effects are modeled using the Buongiorno model. The current study introduces an innovative numerical computing solver utilizing a Multilayer Perceptron feed-forward back-propagation artificial neural network (ANN) with the Levenberg-Marquardt algorithm. Data were collected for testing, certifying, and training the ANN model. In order to make the dimensional PDEs dimensionless, the non-similar variables are employed and calculated by the Homotopy perturbation technique. The effects of developing parameters such as Sutterby fluid parameter, Froude number, thermophoresis, ion-slip parameter, Brownian motion, radiation, Eckert number, and Hall parameter on velocity, temperature, and concentration are demonstrated. The machine learning model chooses data, builds and trains a network, and subsequently assesses its performance using the mean square error metric. Current results declare that the improving Reynolds number tends to increase the pressure rise. Improving the Hall parameter is shown to result in a decrease in velocity. When raising a fluid's parameter, the temperature profile rises.}, }
@article {pmid38167620, year = {2024}, author = {Heronimczak, M and Mrowiec, A and Rząsa, M and Koszela, K}, title = {Measurements of the flow of a liquid-solid mixture/suspension through a segmented orifice.}, journal = {Scientific reports}, volume = {14}, number = {1}, pages = {269}, pmid = {38167620}, issn = {2045-2322}, abstract = {The paper attempts to solve the metrological problem that occurs when measuring the intensity of a flowing fluid with suspended solids with densities greater and less than the density of the fluid. The issue of the possibility of self-cleaning of a prototype variant of a segmented orifice from floating solid particles forming mixture/suspensions is discussed. For spherical particles of solids calculations have been made to allow for determining a borderline between their floating and entrainment by the flow, based on dimensionless numbers: Archimedes number and Reynolds number. Experimental tests and CFD simulations were conducted with a variable flow determined by Reynolds number for comparable segmental orifices with orifice module m = 0.102. Flow characteristics were plotted. Based on the results obtained from numerical simulations, positive influence of the inclination of skew segmental orifice downflow plane was presented. The results obtained from the study are a guideline for planning further studies to expand the knowledge of segmented orifices with inclined inflow plane.}, }
@article {pmid38164243, year = {2024}, author = {Jubaer, H and Thomas, M and Farkas, D and Kolanjiyil, AV and Momin, MAM and Hindle, M and Longest, W}, title = {Development of an effective two-equation turbulence modeling approach for simulating aerosol deposition across a range of turbulence levels.}, journal = {Journal of aerosol science}, volume = {175}, number = {}, pages = {106262}, pmid = {38164243}, issn = {0021-8502}, abstract = {Pharmaceutical aerosol systems present a significant challenge to computational fluid dynamics (CFD) modeling based on the need to capture multiple levels of turbulence, frequent transition between laminar and turbulent flows, anisotropic turbulent particle dispersion, and near-wall particle transport phenomena often within geometrically complex systems over multiple time scales. Two-equation turbulence models, such as the k-ω family of approximations, offer a computationally efficient solution approach, but are known to require the use of near-wall (NW) corrections and eddy interaction model (EIM) modifications for accurate predictions of aerosol deposition. The objective of this study was to develop an efficient and effective two-equation turbulence modeling approach that enables accurate predictions of pharmaceutical aerosol deposition across a range of turbulence levels. Key systems considered were the traditional aerosol deposition benchmark cases of a 90-degree bend (Re=6,000) and a vertical straight section of pipe (Re=10,000), as well as a highly complex case of direct-to-infant (D2I) nose-to-lung pharmaceutical aerosol delivery from an air-jet dry powder inhaler (DPI) including a patient interface and infant nasal geometry through mid-trachea (500<Re<7,000). Of the k-ω family of models, the low Reynolds number (LRN) shear stress transport (SST) approach was determined to provide the best agreement with experimental aerosol deposition data in the D2I system, based on an improved simulation of turbulent jet flow that frequently occurs in DPIs. Considering NW corrections, a new correlation was developed to quantitatively predict best regional values of the y+limit, within which anisotropic NW turbulence is approximated. Considering EIM modifications, a previously described drift correction approach was implemented in pharmaceutical aerosol simulations for the first time. Considering all model corrections and modifications applied to the D2I system, regional relative errors in deposition fractions between CFD predictions and new experimental data were improved from 19-207% (no modifications) to 2-15% (all modifications) with a notable decrease in computational time (up to ∼15%). In conclusion, the highly efficient two-equation k-ω models with physically realistic corrections and modifications provided a viable, efficient and accurate approach to simulate the transport and deposition of pharmaceutical aerosols in complex airway systems that include laminar, turbulent and transitional flows.}, }
@article {pmid38153415, year = {2024}, author = {Xu, Z and Chen, Z and Yang, S and Chen, S and Guo, T and Chen, H}, title = {Passive Focusing of Single Cells Using Microwell Arrays for High-Accuracy Image-Activated Sorting.}, journal = {Analytical chemistry}, volume = {96}, number = {1}, pages = {347-354}, doi = {10.1021/acs.analchem.3c04195}, pmid = {38153415}, issn = {1520-6882}, mesh = {Humans ; *Particle Size ; Microspheres ; K562 Cells ; Computer Simulation ; }, abstract = {Sorting single cells from a population was of critical importance in areas such as cell line development and cell therapy. Image-based sorting is becoming a promising technique for the nonlabeling isolation of cells due to the capability of providing the details of cell morphology. This study reported the focusing of cells using microwell arrays and the following automatic size sorting based on the real-time recognition of cells. The simulation first demonstrated the converged streamlines to the symmetrical plane contributed to the focusing effect. Then, the influence of connecting microchannel, flowing length, particle size, and the sample flow rate on the focusing effect was experimentally analyzed. Both microspheres and cells could be aligned in a straight line at the Reynolds number (Re) of 0.027-0.187 and 0.027-0.08, respectively. The connecting channel was proved to drastically improve the focusing performance. Afterward, a tapered microwell array was utilized to focus sphere/cell spreading in a wide channel to a straight line. Finally, a custom algorithm was employed to identify and sort the size of microspheres/K562 cells with a throughput of 1 event/s and an accuracy of 97.8/97.1%. The proposed technique aligned cells to a straight line at low Reynolds numbers and greatly facilitated the image-activated sorting without the need for a high-speed camera or flow control components with high frequency. Therefore, it is of enormous application potential in the field of nonlabeled separation of single cells.}, }
@article {pmid38150446, year = {2023}, author = {Shams, M and Sarwar, S}, title = {Channelized water driven flow of MHD carbon-nanotube nanofluid influenced by rotation, heat source and thermal radiation.}, journal = {PloS one}, volume = {18}, number = {12}, pages = {e0295406}, pmid = {38150446}, issn = {1932-6203}, abstract = {The efficiency enhancements of thermal energy systems are made with advancements made in the effective use of thermal solar collectors, operating fluid and the introduction of curved and transparent solar panels. In this paper, we present a prototype theoretical/mathematical model for the carbon nanotube-based curved solar panels combined with the solar thermal collector and the porous rotating channel. The analysis is carried out to study the effect of transversely applied magnetic, rotation of the porous channel, linear thermal radiation and the uniformly distributed heat source on the heat transfer characteristics of the single-walled (SWCNT) and multi-walled carbon nanotubes (MWCNT). Due to the nonlinearity of the governing momentum and the heat transport equations and the limitation of the exact methods, numerical similarity solutions are obtained for the boundary value problem using the MATLAB function bvp4c. Influences of different parameters are observed through graphs on the nanofluid flow and temperature profiles. The velocity profile exhibits dual behavior for rising the nanoparticles' volume fraction, the magnetic parameter, rotation, and the Reynolds number. The temperature profile increases with increasing nanoparticles and heat source parameters and decreases for increasing suction, rotation, Reynolds number, and thermal radiation. In some cases, flow profiles for SWCNT exceed those of MWCNT.}, }
@article {pmid38148634, year = {2024}, author = {Jahangiri, AR and Ziarati, N and Dadkhah, E and Bucak, MN and Rahimizadeh, P and Shahverdi, A and Sadighi Gilani, MA and Topraggaleh, TR}, title = {Microfluidics: The future of sperm selection in assisted reproduction.}, journal = {Andrology}, volume = {12}, number = {6}, pages = {1236-1252}, doi = {10.1111/andr.13578}, pmid = {38148634}, issn = {2047-2927}, support = {//NanoLund Organization/ ; }, mesh = {Male ; Humans ; *Spermatozoa/physiology ; *Reproductive Techniques, Assisted ; *Microfluidics/methods ; Infertility, Male/therapy ; Sperm Motility/physiology ; }, abstract = {BACKGROUND: Obtaining functional sperm cells is the first step to treat infertility. With the ever-increasing trend in male infertility, clinicians require access to effective solutions that are able to single out the most viable spermatozoa, which would max out the chance for a successful pregnancy. The new generation techniques for sperm selection involve microfluidics, which offers laminar flow and low Reynolds number within the platforms can provide unprecedented opportunities for sperm selection. Previous studies showed that microfluidic platforms can provide a novel approach to this challenge and since then researchers across the globe have attacked this problem from multiple angles.<br><br>OBJECTIVE: In this review, we seek to provide a much-needed bridge between the technical and medical aspects of microfluidic sperm selection. Here, we provide an up-to-date list on microfluidic sperm selection procedures and its application in assisted reproductive technology laboratories.<br><br>SEARCH METHOD: A literature search was performed in Web of Science, PubMed, and Scopus to select papers reporting microfluidic sperm selection using the keywords: microfluidic sperm selection, self-motility, non-motile sperm selection, boundary following, rheotaxis, chemotaxis, and thermotaxis. Papers published before March 31, 2023 were selected.<br><br>OUTCOMES: Our results show that most studies have used motility-based properties for sperm selection. However, microfluidic platforms are ripe for making use of other properties such as chemotaxis and especially rheotaxis. We have identified that low throughput is one of the major hurdles to current microfluidic sperm selection chips, which can be solved via parallelization.<br><br>CONCLUSION: Future work needs to be performed on numerical simulation of the microfluidics chip prior to fabrication as well as relevant clinical assessment after the selection procedure. This would require a close collaboration and understanding among engineers, biologists, and medical professionals. It is interesting that in spite of two decades of microfluidics sperm selection, numerical simulation and clinical studies are lagging behind. It is expected that microfluidic sperm selection platforms will play a major role in the development of fully integrated start-to-finish assisted reproductive technology systems.}, }
@article {pmid38144068, year = {2023}, author = {Liu, L and Meng, Z and Zhang, Y and Sun, Y}, title = {Simulation of High-Viscosity Generalized Newtonian Fluid Flows in the Mixing Section of a Screw Extruder Using the Lattice Boltzmann Model.}, journal = {ACS omega}, volume = {8}, number = {50}, pages = {47991-48018}, pmid = {38144068}, issn = {2470-1343}, abstract = {The mixing quality of polymer melts in the mixing section of a single-screw extruder and an injection molding machine has considerable effects on the properties of the molded products. Therefore, the study of the flow field of polymer melts in the mixing section is of great importance. The lattice Boltzmann method (LBM) exhibits unique advantages in simulating non-Newtonian fluids. Many researchers have used LBM to study the flow of medium- and low-viscosity fluids. In their studies, the Reynolds number of fluid flows is generally moderate. However, polymer melts are typical high-viscosity fluids, and their flow Reynolds number is generally very small. The single-relaxation-time lattice Boltzmann method (SRT-LBM) has been used previously to study the flow field of power law fluids in the mixing section. Herein, the flow field of high-viscosity generalized Newtonian fluids in the mixing section of a single-screw extruder is studied using SRT-LBM, the two-relaxation-time lattice Boltzmann method (TRT-LBM), and the multiple-relaxation-time lattice Boltzmann method (MRT-LBM). Through comparison, TRT-LBM has been found to exhibit obvious advantages regarding stability, calculation accuracy, calculation efficiency, and selection of simulation parameters. The TRT-LBM is more suitable for studying high-viscosity generalized Newtonian fluids than SRT-LBM and MRT-LBM. SRT-LBM has low computational efficiency when simulating high-viscosity generalized Newtonian fluids, and instability is easily caused when the fluid has a yield stress. For MRT-LBM, only by studying the relaxation parameters can its advantages be fully utilized. However, optimizing the accuracy and stability of the MRT-LBM via parameter research and linear stability analysis is difficult. For non-Newtonian fluids, it is difficult to optimize the relaxation parameters to make the MRT-LBM more stable and accurate than the TRT-LBM. It is difficult for the MRT-LBM to realize its potential when simulating high-viscosity generalized Newtonian fluids. In addition, we studied the flow pattern in the cross section of the screw channel and compared it to the results reported in previous studies.}, }
@article {pmid38132896, year = {2023}, author = {Qiao, Z and Pan, Y and Tang, Y and Cao, Y and Si, F}, title = {Numerical Simulation of Membrane Separation Characteristics of Supercritical Carbon Dioxide and Water.}, journal = {Membranes}, volume = {13}, number = {12}, pages = {}, pmid = {38132896}, issn = {2077-0375}, abstract = {To solve the problem of water carryover in the supercritical CO2 separation and mining process in the CO2 plume geothermal system, a three-dimensional shell-tube hollow fiber membrane absorption separator is designed in this study. A coupled species transport model, a porous medium model, and an absorption mathematical model are established, and the flow field and separation characteristics in the circular and flat tubes are analyzed using numerical simulation. The results show that the membrane separation efficiency increases with an increase in the flatness and membrane tube length. When the inlet velocity of the mixture is 0.1 m/s, the separation efficiency can reach 75.92%. Selecting a smaller flow Reynolds number and a more significant membrane tube flatness will reduce the water mass fraction at the outlet. When adding baffles of different shapes to the membrane tube, the mixture fluid in the membrane tube meanders forward and flows in the shape of "Z" under the blocking effect of the arcuate baffles. With an increase in the number of arcuate baffles in the membrane tube, the membrane separation efficiency of the separator increases continuously. The mixture fluid flows in the membrane tube with the built-in torsional baffles in a spiral manner, and the separation efficiency of the membrane separator increases with a torsion ratio reduction in the membrane tube.}, }
@article {pmid38118145, year = {2024}, author = {L'Estimé, M and Schindler, M and Shahidzadeh, N and Bonn, D}, title = {Droplet Size Distribution in Emulsions.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {40}, number = {1}, pages = {275-281}, pmid = {38118145}, issn = {1520-5827}, abstract = {The droplet size in emulsions is known to affect the rheological properties and plays a crucial role in many applications of emulsions. Despite its importance, the underlying mechanisms governing droplet size in emulsification remain poorly understood. We investigate the average drop size and size distribution upon emulsification with a high-shear mixer for model oil-in-water emulsions stabilized by a surfactant. The size distribution is found to be a log-normal distribution resulting from the repetitive random breakup of drops. High-shear emulsification, the usual way of making emulsions, is therefore found to be very different from turbulent emulsification given by the Kolmogorov-Hinze theory, for which power-law distributions of the drop size are expected. In agreement with this, the mean droplet size does not follow a scaling with the Reynolds number of the emulsification flow but rather a capillary number scaling based on the viscosity of the continuous phase.}, }
@article {pmid38117193, year = {2023}, author = {Tang, Y and Li, G and Wu, J and Wang, G and He, Y and Wei, J}, title = {Charging characteristics of long distance accumulator for underwater electro-hydraulic control system.}, journal = {The Review of scientific instruments}, volume = {94}, number = {12}, pages = {}, doi = {10.1063/5.0168419}, pmid = {38117193}, issn = {1089-7623}, abstract = {Long distance accumulators are widely used in underwater electro-hydraulic control systems. However, as the working depth increases, the underwater umbilical cable becomes longer. The actual physical properties of the gas in the accumulator change. These factors affect the charging characteristics of the accumulator. To address the above issues, a simulation model of the charging of the long distance accumulator under real operating conditions is developed. Among them, the real properties of the gas inside the accumulator were calculated using the Redlich-Kwong-Soave method. The coefficient of friction within the umbilical cable is based on the Reynolds number and relative roughness. The simulation data were compared with the experimental results in the South China Sea to verify the accuracy of the simulation model. The effects of key factors on the charging characteristics of the long distance accumulators were also analyzed. The results show that the simulation results are in good agreement with the experimental results. The law of accumulator charging was analyzed: the greater the pressure of the gas source, the smaller the accumulator charging time; the greater the working water depth, the shorter the accumulator charging time. The research provides guidance for the design of long distance accumulators.}, }
@article {pmid38089999, year = {2023}, author = {Shuvo, MS and Mahmud, MJ and Saha, S}, title = {Multi-scaling analysis of turbulent boundary layers over an isothermally heated flat plate with zero pressure gradient.}, journal = {Heliyon}, volume = {9}, number = {12}, pages = {e22721}, pmid = {38089999}, issn = {2405-8440}, abstract = {A meticulous investigation into turbulent boundary layers over an isothermally heated flat plate with zero pressure gradient has been conducted. Eight distinct turbulence models, including algebraic yPlus, standard k-ω, standard k-ε, length-velocity, Spalart-Allmaras, low Reynolds number k-ε, shear stress transport, and v[2]-f turbulence models, are carefully chosen for numerical simulation alongside thermal energy and Reynolds-Averaged Navier-Stokes equations. A comparative analysis has determined that the Spalart-Allmaras model exhibits remarkable agreement with the results from direct numerical simulation, making it a reliable tool for predicting turbulent heat transfer and fluid flow, particularly at higher Prandtl and Reynolds numbers. Subsequently, a multi-scale investigation employs a comprehensive four-layer structure scheme and encompasses various momentum thickness Reynolds numbers of 1432, 2522, and 4000, and Prandtl numbers of 0.71, 2, and 5. The subsequent investigation reveals the governing non-dimensional numbers' substantial impact on the distribution and magnitude of mean thermal and flow characteristics. Notably, the scaling of mean thermal and momentum fields discloses the existence of a meso or intermediate layer characterized by a logarithmic nature unique to itself. The multi-scaling analysis of the flow field demonstrates greater conformity with the selected scaling variables primarily relying on the Reynolds number. Furthermore, the scaling of the energy field yields compelling outcomes within the inner and intermediate layers. However, according to the four-layer theory, minor discrepancies are observed in the outer layer when using the current scaling.}, }
@article {pmid38083455, year = {2023}, author = {Akram, MM and Nazila Hosseini, S and Levesque, J and Shi, W and Gosselin, B}, title = {A fully-flexible and thermally adjustable implantable neural probe with a U-turn polyester microchannel.}, journal = {Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference}, volume = {2023}, number = {}, pages = {1-4}, doi = {10.1109/EMBC40787.2023.10340838}, pmid = {38083455}, issn = {2694-0604}, mesh = {*Polyesters ; *Microfluidics/methods ; Dimethylpolysiloxanes ; Computer Simulation ; }, abstract = {This work presents a fully flexible implantable neural probe fabricated with Polydimethylsiloxane (PDMS) and including a thermally-tunable stiffness microchannel filled with Polyester. The probe includes an optimized microfluidics mixer for drug delivery. Polyester, which is solid at room temperature and has a low melting point close to body temperature, is used to decrease the stiffness of the probe after insertion, after getting in contact with tissues. We designed a U-turn microchannel inside the PDMS neural probe and filled it up with melted polyester. The microchannel has a cross-section of 30 μm × 5 μm and a length of 14.7 mm. The following probe dimensions were chosen after extensive simulation: thickness = 20 μm, width = 300 μm, and length = 7 mm. These values yield a buckling force above 1 mN, which is sufficient for proper insertion into the brain tissues. Simulation results show that the microfluidics mixer with a cross-section of 90 μm × 5 μm and a length of 7 mm has optimum performance for the desired flow rate and quantity of drug to deliver. The pressure drop inside the microfluidic channel is less than 0.43 kPa, which is appropriate for PDMS-PDMS bonding, whereas the Reynolds number is near 1.91k in the laminar regime. No leakage or bubble occurred during the experimental validation, which suggests an appropriate pressure and a laminar flow in the channel.}, }
@article {pmid38076113, year = {2023}, author = {Srivathsan, B and G, T and Ram, KV and R, H}, title = {Multiphase simulation of sustainable nanoenhanced ionic liquid coolants for improved thermal performance in Ti-6Al-4V alloy drilling.}, journal = {Heliyon}, volume = {9}, number = {12}, pages = {e23020}, pmid = {38076113}, issn = {2405-8440}, abstract = {Extensive research has been conducted by the manufacturing industry to enhance the efficiency of drilling processes by focusing on the utilization of nanoenhanced cutting fluids that possess excellent heat conductivity. Due to their eco-friendliness and adaptability of physical and chemical properties, ionic fluids offer enormous potential for application as cutting fluids. This study investigates the computational fluid dynamics analysis of the heat transfer performance of various ionanofluid pairs dispersed with nanoparticles as cutting fluids in the drilling process using Ansys Fluent software. For this purpose, 1-Hexyl-3-methyl-imidazolium-tetrafluoroborate is considered the ionic fluid, and its thermal behavior is examined by dispersing it with nanoparticles of copper, silver, and multiwalled carbon nanotubes (MWCNT) at different particle volume fractions and Reynolds numbers. The workpiece is composed of an alloy of titanium Ti-6Al-4V, while the drill bit is made of tungsten carbide-cobalt. It is observed that the ionic nanocoolant mist emanates from the spray tip and moves towards the drill bit-workpiece interface. Initially, the coolant's velocity is greatest close to the orifice, and as time passes, it approaches the drilling space. The data indicates that the spraying velocity of the coolant augments over time and that it disperses heat at the tool-chip interface. The results help us validate the flow and interaction of ionanocoolant with the drilling zone. With a rise in the volume fraction of added nanoparticles and Reynolds number, the results indicated a significant decrease in the drilling temperature. With a higher particle volume fraction, the MWCNT-ionic coolant combination decreases the drilling temperature of pure ionic liquid by 25.64 %. The copper, silver, and MWCNT ionanofluids enhance the average heat transfer coefficient of pure ionic coolant by 35.14 %, 47.42 %, and 62.75 %, respectively. In addition, MWCNT nanocoolants demonstrated improved thermal performance and heat removal rate in comparison to copper and silver ionanocoolants.}, }
@article {pmid38071256, year = {2023}, author = {Ahmadi Azar, A and Jalili, B and Jalili, P and Domiri Ganji, D}, title = {Investigating the effect of structural changes of two stretching disks on the dynamics of the MHD model.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {21833}, pmid = {38071256}, issn = {2045-2322}, abstract = {The purpose of this theoretical study is to explore the behavior of an electrically conducting micropolar fluid when subjected to a uniform magnetic field along the vertical axis between two stretching disks as the structure of the problem changes. In this context, structural changes refer to alterations in the distance between the two discs or the stretching rate of the two discs. The governing equations of this problem are a set of nonlinear coupled partial differential equations, which are transformed into a nonlinear coupled ordinary differential equation set by a similarity transformation. The transformation results in four dimensionless quantities and their derivatives that appear in the equations. Nine dimensionless parameters are derived via similarity variables, including stretching Reynolds number, magnetic parameter, radiation parameter, Prandtl number, Eckert number, Schmidt number, and three micropolar parameters. Previous similarity solutions focused on analyzing the effect of changes in each parameter on the four dimensionless quantities. However, this type of analysis is mainly mathematical and does not provide practical results. This study's primary novelty is to redefine the magnetic parameter, Eckert number, stretching Reynolds number, and two micropolar parameters to analyze physical parameters that depend on the stretching rate of the two discs or the distance between them. The semi-analytical hybrid analytical and numerical method (HAN-method) is used to solve the equations. The results demonstrate that structural changes affect all five quantities of radial velocity, axial velocity, microrotation, temperature, and concentration. The study's most significant finding is that an increase in the stretching rate of the two disks causes a sharp increase in temperature and Nusselt number. Conversely, increasing the distance between the two disks causes a sharp decrease in micro-rotation and wall couple stress. They were compared to a previous study in a specific case to validate the results' accuracy.}, }
@article {pmid38059033, year = {2023}, author = {Alqarni, MM and Memon, AA and Memon, MA and Mahmoud, EE and Fenta, A}, title = {Numerical investigation of heat transfer and fluid flow characteristics of ternary nanofluids through convergent and divergent channels.}, journal = {Nanoscale advances}, volume = {5}, number = {24}, pages = {6897-6912}, pmid = {38059033}, issn = {2516-0230}, abstract = {The characteristics of nanomaterials have garnered significant attention in recent research on natural and forced convection. This study focuses on the forced convection characteristics of ternary nanofluids within convergent and divergent channels. The ternary nanofluid comprises titanium oxide (TiO2), zinc oxide (ZnO), and silver suspended in water, which serves as the base fluid. Using COMSOL Multiphysics 6.0, a reliable software for finite element analysis, numerical simulations were conducted for steady and incompressible two-dimensional flow. Reynolds numbers varying from 100 to 800 were employed to investigate forced convection. Additionally, we explored aspect ratios (channel height divided by the height of the convergent or divergent section) of -0.4, -0.2, 0, 0.2, and 0.4. Our findings revealed that only at aspect ratio a = 0.4 did the average outlet temperature increase as the Reynolds number rose, while other aspect ratios exhibited decreasing average temperatures with declining Reynolds numbers. Moreover, as the Reynolds number increased from 100 to 800 and the total volume fraction of the ternary nanofluids ranged from 0.003 to 0.15, there was a significant 100% enhancement in the average Nusselt number. For clarity, this article briefly presents essential information, such as the study's numerical nature, fluid properties (constant-property fluid), and the methodology (COMSOL Multiphysics 6.0, finite element analysis). Key conclusions are highlighted to enable readers to grasp the main outcomes at a glance. These details are also adequately covered in the manuscript to facilitate a comprehensive understanding of the research. The utilization of this emerging phenomenon holds immense potential in various applications, ranging from the development of highly efficient heat exchangers to the optimization of thermal energy systems. This phenomenon can be harnessed in scenarios in which effective cost management in thermal production is a critical consideration.}, }
@article {pmid38046301, year = {2023}, author = {Wang, Q and Pang, Z and Tian, C and Chen, J}, title = {New Design Method of a Supersonic Steam Injection Nozzle and Its Numerical Simulation Verification.}, journal = {ACS omega}, volume = {8}, number = {47}, pages = {44485-44496}, pmid = {38046301}, issn = {2470-1343}, abstract = {Steam huff-n-puff in horizontal wells often had limitations, such as uneven steam injection and low reservoir utilization. To improve steam injection efficiency, a new method for designing a supersonic nozzle was proposed based on the principles of aerodynamics and thermodynamics. The nozzle featured a tapering section, a throat, and a diverging section. The best geometric shape of the tapering section was the Witoszynski curve. A set of nozzle size designs were established, and the size parameters were optimized. The results showed that the nozzle could inject steam into the formation at supersonic speed and it had the characteristics of constant flow rate and uniform development of the steam chamber. According to the steam Reynolds number and the good aggregation distribution characteristics of the size design model, three sequential nozzles of 3.0, 5.0, and 6.5 mm were formed based on the throat. When the throat diameter was 5.0 mm, the tapering length was 4.3 mm, the diverging length was 5.5 mm, the throat length was 3.0 mm, the inlet diameter was 9.8 mm, and the outlet diameter was 6.2 mm. Numerical simulations indicated that the pressure drop loss during steam huff-n-puff injection in horizontal wells was within 10%. It was of great significance to establish the nozzle size design model of the steam injection effect of horizontal wells.}, }
@article {pmid38042993, year = {2024}, author = {Liu, X and Zhao, Z and Xu, S and Zhang, J and Zhou, Y and He, Y and Yamaguchi, T and Ouyang, H and Tanaka, T and Chen, MK and Shi, S and Qi, F and Tsai, DP}, title = {Meta-Lens Particle Image Velocimetry.}, journal = {Advanced materials (Deerfield Beach, Fla.)}, volume = {36}, number = {17}, pages = {e2310134}, doi = {10.1002/adma.202310134}, pmid = {38042993}, issn = {1521-4095}, support = {AoE/P-502/20//University Grants Committee / Research Grants Council of the Hong Kong Special Administrative Region/ ; C1015-21E//University Grants Committee / Research Grants Council of the Hong Kong Special Administrative Region/ ; C5031-22G//University Grants Committee / Research Grants Council of the Hong Kong Special Administrative Region/ ; CityU15303521//University Grants Committee / Research Grants Council of the Hong Kong Special Administrative Region/ ; CityU11305223//University Grants Committee / Research Grants Council of the Hong Kong Special Administrative Region/ ; CityU11310522//University Grants Committee / Research Grants Council of the Hong Kong Special Administrative Region/ ; CityU11300123//University Grants Committee / Research Grants Council of the Hong Kong Special Administrative Region/ ; 9380131//City University of Hong Kong/ ; 9610628//City University of Hong Kong/ ; 7005867//City University of Hong Kong/ ; 12172222//National Natural Science Foundation of China/ ; 12302368//National Natural Science Foundation of China/ ; //Fundamental Research Funds for the Central Universities/ ; JPMJCR1904//Japan Science and Technology Corporation/ ; 2020B1515120073//Guangdong Provincial Department of Science and Technology/ ; 2023M742231//China Postdoctoral Science Foundation/ ; }, abstract = {Fluid flow behavior is visualized through particle image velocimetry (PIV) for understanding and studying experimental fluid dynamics. However, traditional PIV methods require multiple cameras and conventional lens systems for image acquisition to resolve multi-dimensional velocity fields. In turn, it introduces complexity to the entire system. Meta-lenses are advanced flat optical devices composed of artificial nanoantenna arrays. It can manipulate the wavefront of light with the advantages of ultrathin, compact, and no spherical aberration. Meta-lenses offer novel functionalities and promise to replace traditional optical imaging systems. Here, a binocular meta-lens PIV technique is proposed, where a pair of GaN meta-lenses are fabricated on one substrate and integrated with a imaging sensor to form a compact binocular PIV system. The meta-lens weigh only 116 mg, much lighter than commercial lenses. The 3D velocity field can be obtained by the binocular disparity and particle image displacement information of fluid flow. The measurement error of vortex-ring diameter is ≈1.25% experimentally validates via a Reynolds-number (Re) 2000 vortex-ring. This work demonstrates a new development trend for the PIV technique for rejuvenating traditional flow diagnostic tools toward a more compact, easy-to-deploy technique. It enables further miniaturization and low-power systems for portable, field-use, and space-constrained PIV applications.}, }
@article {pmid38039459, year = {2023}, author = {Buaria, D and Sreenivasan, KR}, title = {Saturation and Multifractality of Lagrangian and Eulerian Scaling Exponents in Three-Dimensional Turbulence.}, journal = {Physical review letters}, volume = {131}, number = {20}, pages = {204001}, doi = {10.1103/PhysRevLett.131.204001}, pmid = {38039459}, issn = {1079-7114}, abstract = {Inertial-range scaling exponents for both Lagrangian and Eulerian structure functions are obtained from direct numerical simulations of isotropic turbulence in triply periodic domains at Taylor-scale Reynolds number up to 1300. We reaffirm that transverse Eulerian scaling exponents saturate at ≈2.1 for moment orders p≥10, significantly differing from the longitudinal exponents (which are predicted to saturate at ≈7.3 for p≥30 from a recent theory). The Lagrangian scaling exponents likewise saturate at ≈2 for p≥8. The saturation of Lagrangian exponents and transverse Eulerian exponents is related by the same multifractal spectrum by utilizing the well-known frozen hypothesis to relate spatial and temporal scales. Furthermore, this spectrum is different from the known spectra for Eulerian longitudinal exponents, suggesting that Lagrangian intermittency is characterized solely by transverse Eulerian intermittency. We discuss possible implications of this outlook when extending multifractal predictions to the dissipation range, especially for Lagrangian acceleration.}, }
@article {pmid38036626, year = {2023}, author = {Abd-Alla, AM and Abo-Dahab, SM and Salah, DM and Bayones, FS and Abdelhafez, MA}, title = {Magneto-hydrodynamic peristaltic flow of a Jeffery fluid in the presence of heat transfer through a porous medium in an asymmetric channel.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {21088}, pmid = {38036626}, issn = {2045-2322}, abstract = {In the present paper, the effects of magnetic field and heat transfer on the peristaltic flow of a Jeffery fluid through a porous medium in an asymmetric channel have been studied. The governing non-linear partial differential equations representing the flow model are transmuted into linear ones by employing the appropriate non-dimensional parameters under the assumption of long wavelength and low Reynolds number. Exact solutions are presented for the stream function, pressure gradient, and temperature. The frictional force and pressure rise are both computed using numerical integration. Using MATLAB R2023a software, a parametric analysis is performed, and the resulting data is represented graphically. For all physical quantities considered, numerical calculations were made and represented graphically. Trapping phenomena are discussed graphically. The obtained results can be applied to enhance pumping systems in engineering and gastrointestinal functions. This analysis permits body fluids such as blood and lymph to easily move inside the arteries and veins, allowing oxygen supply, waste elimination, and other necessary elements.}, }
@article {pmid38036570, year = {2023}, author = {Ahmad, S and Ali, K and Castellanos, HG and Aryanfar, Y and Rashid, FL and Hendy, AS and Deifalla, A and Ragab, AE and Khan, M and Gomaa, HG}, title = {Complex dynamics of induced vortex formation and thermal-fluid coupling in tri-hybrid nanofluid under localized magnetic field: a novel study.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {21140}, pmid = {38036570}, issn = {2045-2322}, support = {RSPD2023R711//King Saud University/ ; }, abstract = {Hybrid nanofluids offer higher stability, synergistic effects, and better heat transfer compared to simple nanofluids. Their higher thermal conductivity, lower viscosity, and interaction with magnetic fields make them ideal for various applications, including materials science, transportation, medical technology, energy, and fundamental physics. The governing partial differential equations are numerically solved by employing a finite volume approach, and the effects of various parameters on the nanofluid flow and thermal characteristics are systematically examined from the simulations based on a self-developed MATLAB code. The parameters included magnetic field strength, the Reynolds number, the nanoparticle volume fraction, and the number and position of the strips in which the magnetic field is localized. It has been noted that the magnetized field induces the spinning of the tri-hybrid nanoparticles, which generates the intricate structure of vortices in the flow. The local skin friction (CfRe) and the Nusselt number (Nu) increase significantly when the magnetic field is intensified. Moreover, adding more nanoparticles in the flow enhances both Nu and CfRe, but with different effects for different nanoparticles. Silver (Ag) shows the highest increase in both Nu (52%) and CfRe (110%), indicating strong thermal-fluid coupling. Alumina (Al2O3) and Titanium Dioxide (TiO2) show lower increases in both Nu (43% and 34%) and CfRe (14% and 10%), indicating weaker coupling in the flow. Finally, compared with the localized one, the uniform magnetic field has a minor effect on the flow and temperature distributions.}, }
@article {pmid38034878, year = {2023}, author = {Han, J and Lee, H}, title = {Control Volume Analysis of the Infusion Rate in Cephalic and Median Cubital Veins Based on Infusion Bag Height and Peripheral Venous Catheter Inner Diameter: Application of Bernoulli's Equation and Consideration of Frictional Forces.}, journal = {Journal of multidisciplinary healthcare}, volume = {16}, number = {}, pages = {3609-3618}, pmid = {38034878}, issn = {1178-2390}, abstract = {PURPOSE: This pilot study aimed to provide basic data on intravenous infusion nursing by analyzing the infusion rate in the cephalic and median cubital veins depending on the height of the infusion bag and inner diameter of the peripheral venous catheter (PVC).<br><br>METHODS: While infusing 0.9% normal saline at 22 &#xb0;C (room temperature) into elbow cephalic and median cubital veins, the infusion rate may be controlled by adjusting the fluid height and PVC diameter. To assess the validity of the laminar flow assumption, the study estimated the Reynolds number (Re) using the velocity obtained by applying Bernoulli's equation considering the friction coefficient.<br><br>RESULTS: At a constant fluid height, the infusion rate increased with increasing PVC diameter. At a constant PVC diameter, the infusion rate increased with increasing fluid height. In a comparison between the cephalic and median cubital veins at constant fluid height and PVC diameter, the solution was infused at a higher rate into the cephalic vein, which was under lower venous pressure.<br><br>CONCLUSION: The analysis of the infusion rate according to fluid height and PVC diameter provided basic data on intravenous infusion nursing. The results are expected to provide evidence for the standardization of intravenous infusion nursing.}, }
@article {pmid38027788, year = {2023}, author = {Jamil, DF and Uddin, S and Kazi, M and Roslan, R and Gorji, MR and Kamalrulzaman Md Akhir, M}, title = {MHD blood flow effects of Casson fluid with Caputo-Fabrizio fractional derivatives through an inclined blood vessels with thermal radiation.}, journal = {Heliyon}, volume = {9}, number = {11}, pages = {e21780}, pmid = {38027788}, issn = {2405-8440}, abstract = {This study investigates a fractional-order time derivative model of non-Newtonian magnetic blood flow in the presence of thermal radiation and body acceleration through an inclined artery. The blood flow is formulated using the Casson fluid model under the control of a uniformly distributed magnetic field and an oscillating pressure gradient. Caputo-Fabrizio's fractional derivative mathematical model was used, along with Laplace transform and the finite Hankel transform technique. Analytical expressions were obtained for the velocity of blood flow, magnetic particle distribution, and temperature profile. These distributions are presented graphically using Mathcad software. The results show that the velocity increases with the time, Reynolds number and Casson fluid parameters, and diminishes when Hartmann number increases. Moreover, fractional parameters, radiation values, and metabolic heat source play an essential role in controlling the blood temperature. More precisely, these results are beneficial for the diagnosis and treatment of certain medical issues.}, }
@article {pmid38027752, year = {2023}, author = {Alklaibi, AM and Chandra Mouli, KVV and Syam Sundar, L}, title = {Experimental and support vector machine predictions of entropy generations and exergy efficiency of Fe3O4-SiO2/Water hybrid nanofluid in a plate heat exchanger.}, journal = {Heliyon}, volume = {9}, number = {11}, pages = {e21730}, pmid = {38027752}, issn = {2405-8440}, abstract = {Several experiments of Fe3O4-SiO2/water hybrid nanofluids with volumetric concentrations ranging from 0.2 % to 1.0 % circulating in the cold-side of a plate heat exchanger at flow rates ranging from 0.05 kg/s to 0.1166 kg/s are performed. Under these ranges of flow rates and volumetric concentrations, the flow of Fe3O4-SiO2/water hybrid nanofluids remains laminar. The results of these experiments are predicted with support vector machine (SVM) algorithm to determine hybrid nanofluid entropy generation thermal, entropy generation frictional, and efficiency of exergy. Fe3O4-SiO2 nanomaterials was synthesized with reduction of chemicals and insitu development techniques, with XRD, FTIR and VSM instruments, characterizations were done. The SVM model gives large precision predictions of the measured data with correlations coefficients of 0.9944, 0.99798, and 0.99428 for frictional entropy generation, thermal entropy generation and exergy efficiency. At a flow rate of 0.1166 kg/s in the cold-side of PHE, the exergy efficiency is found to be 77.96 % for water (Reynolds number of 935.4) and with 1.0 vol% of Fe3O4-SiO2/water hybrid nanofluid in the cold-side of PHE, the efficiency is increased to 82.97 %, respectively. Under similar conditions of 0.1166 kg/s of flow circulation and 1.0 % vol. concentration of hybrid nanofluid, the thermal entropy generation is dropped off to 18.37 %, but the frictional entropy generation is increased by 20.97 %, compared to water, with the results that the total entropy generation drops off by 15.91 %, compared to water data. Preliminary curve-fitting correlations have been developed for the frictional entropy generation, thermal entropy generation, and exergy efficiency.}, }
@article {pmid38011727, year = {2023}, author = {Bao, H and Song, B and Ma, D and Xue, D}, title = {Aerodynamic performance of flapping wing with alula under different kinematics of complex flapping motion.}, journal = {Bioinspiration &amp; biomimetics}, volume = {19}, number = {1}, pages = {}, doi = {10.1088/1748-3190/ad0ffd}, pmid = {38011727}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; *Models, Biological ; *Flight, Animal ; Wings, Animal ; Motion ; Birds ; }, abstract = {The flight of birds is a remarkable feat, and their remarkable ability to fly derives from complex multi-degree-of-freedom flapping motions and small-scale feather structures that have evolved over millions of years. One of these feather structures is the alula, which can enhance the birds' flight performance at low speeds and large angles of attack. Previous studies on the alula have focused on the steady state. This undoubtedly ignores the unsteady effect caused by complex flapping motion, which is also the most important characteristic of avian flight. Therefore, this paper carries out a study on the effect of different motion modes and motion parameters on the aerodynamic mechanism of the alula. Previous studies found the dominate effect in the lift enhancement is influenced by Reynolds number, stall condition and geometric parameters. After coupling complex flapping motion, aerodynamic characteristics of the flapping wing are greatly influenced by different motion patterns and parameters. For pure plunge motion, both the slot effect and the vortex generator effect of the alula dominate the lift enhancement; while for plunge-twist and plunge-sweep motion, the vortex generator dominates more. At a low plunge amplitude, a low twist amplitude and a low sweep amplitude, the deflection of the alula has a good lift enhancement compared with the baseline wing. Increasing these amplitudes attenuates both the slot effect and the vortex generator effect. The alula can enhance the lift by 10.4% at the plunge amplitude of 25 deg (for pure plunge motion), by 7.9% at the plunge amplitude of 25 deg and twist amplitude of 10 deg (for plunge-twist motion), by 3.3% at the plunge amplitude of 25 deg and sweep amplitude of 15 deg (for plunge-sweep motion). Meanwhile, at a large sweep phase angle, the alula has a better lift enhancement. Increasing the phase angle enhances the vortex generator effect of the alula, and it has an optimal lift enhancement effect of 11% at the phase angle of 180 deg.}, }
@article {pmid38005406, year = {2023}, author = {Krauter, N and Stefani, F}, title = {Simultaneous Measurement of Flow Velocity and Electrical Conductivity of a Liquid Metal Using an Eddy Current Flow Meter in Combination with a Look-Up-Table Method.}, journal = {Sensors (Basel, Switzerland)}, volume = {23}, number = {22}, pages = {}, pmid = {38005406}, issn = {1424-8220}, support = {787544/ERC_/European Research Council/International ; }, abstract = {The Eddy Current Flow Meter (ECFM) is a commonly employed inductive sensor for assessing the local flow rate or flow velocity of liquid metals with temperatures up to 700 ∘C. One limitation of the ECFM lies in its dependency on the magnetic Reynolds number for measured voltage signals. These signals are influenced not only by the flow velocity but also by the electrical conductivity of the liquid metal. In scenarios where temperature fluctuations are significant, leading to corresponding variations in electrical conductivity, it becomes imperative to calibrate the ECFM while concurrently monitoring temperature to discern the respective impacts of flow velocity and electrical conductivity on the acquired signals. This paper introduces a novel approach that enables the concurrent measurement of electrical conductivity and flow velocity, even in the absence of precise knowledge of the liquid metal's conductivity or temperature. This method employs a Look-Up-Table methodology. The feasibility of this measurement technique is substantiated through numerical simulations and further validated through experiments conducted on the liquid metal alloy GaInSn at room temperature.}, }
@article {pmid38004897, year = {2023}, author = {Borbas, SW and Shen, K and Ji, C and Viallat, A and Helfer, E and Peng, Z}, title = {Transit Time Theory for a Droplet Passing through a Slit in Pressure-Driven Low Reynolds Number Flows.}, journal = {Micromachines}, volume = {14}, number = {11}, pages = {}, pmid = {38004897}, issn = {2072-666X}, support = {DMS 1951526//National Science Foundation/ ; 1948347//National Science Foundation/ ; IIP-1841473//National Science Foundation/ ; PHY2210366//National Science Foundation/ ; }, abstract = {Soft objects squeezing through small apertures are crucial for many in vivo and in vitro processes. Red blood cell transit time through splenic inter-endothelial slits (IESs) plays a crucial role in blood filtration and disease progression, while droplet velocity through constrictions in microfluidic devices is important for effective manipulation and separation processes. As these transit phenomena are not well understood, we sought to establish analytical and numerical solutions of viscous droplet transit through a rectangular slit. This study extends from our former theory of a circular pore because a rectangular slit is more realistic in many physiological and engineering applications. Here, we derived the ordinary differential equations (ODEs) of a droplet passing through a slit by combining planar Poiseuille flow, the Young-Laplace equations, and modifying them to consider the lubrication layer between the droplet and the slit wall. Compared to the pore case, we used the Roscoe solution instead of the Sampson one to account for the flow entering and exiting a rectangular slit. When the surface tension and lubrication layer were negligible, we derived the closed-form solutions of transit time. When the surface tension and lubrication layer were finite, the ODEs were solved numerically to study the impact of various parameters on the transit time. With our solutions, we identified the impact of prescribed pressure drop, slit dimensions, and droplet parameters such as surface tension, viscosity, and volume on transit time. In addition, we also considered the effect of pressure drop and surface tension near critical values. For this study, critical surface tension for a given pressure drop describes the threshold droplet surface tension that prevents transit, and critical pressure for a given surface tension describes the threshold pressure drop that prevents transit. Our solutions demonstrate that there is a linear relationship between pressure and the reciprocal of the transit time (referred to as inverse transit time), as well as a linear relationship between viscosity and transit time. Additionally, when the droplet size increases with respect to the slit dimensions, there is a corresponding increase in transit time. Most notably, we emphasize the initial antagonistic effect of surface tension which resists droplet passage but at the same time decreases the lubrication layer, thus facilitating passage. Our results provide quantitative calculations for understanding cells passing through slit-like constrictions and designing droplet microfluidic experiments.}, }
@article {pmid37964837, year = {2023}, author = {Rahman, MT and Habib, K and Quader, MN and Aslfattahi, N and Kadirgama, K and Das, L}, title = {Effect of porous density of twisted tape inserts on heat transfer performance inside a closed conduit.}, journal = {Heliyon}, volume = {9}, number = {11}, pages = {e21206}, doi = {10.1016/j.heliyon.2023.e21206}, pmid = {37964837}, issn = {2405-8440}, abstract = {This study examines the impact of varying the porosity density of twisted tape inserts (TTI) on the temperature distribution, fluid velocities, heat transfer coefficients (HTC), Nusselt numbers (Nu), turbulent kinetic energy (TKE), and performance from 5000 to 12500 Reynolds numbers (Re). The entire process involved the design of TTIs and double pipe heat exchangers using SolidWorks. Subsequently, a three-dimensional fluid flow model was employed to solve equations related to energy mass, energy, and momentum within the ANSYS Fluent interfaces. The findings highlight the noteworthy impact of high porosity TTIs, which consistently reduce temperature spans, increase fluid velocities, and greatly HTC and Nu when compared to low porosity TTI, typical TTI, and plain tubes. Furthermore, high porosity TTI significantly increases TKE, indicating increased fluid turbulence and higher heat transfer efficiency, especially at Re = 12500. The assessment of PEC emphasizes the superiority of high porosity TTI, demonstrating their significant performance increase potential of over 6.44 % over low porosity TTI and a staggering 62.5 % above typical TTI. In conclusion, high porosity TTI emerges as a potential solution for improving heat transfer efficiency and overall system performance in a variety of industrial applications, promising enhanced energy efficiency and superior performance.}, }
@article {pmid37963561, year = {2023}, author = {Htet, PH and Lauga, E}, title = {Cortex-driven cytoplasmic flows in elongated cells: fluid mechanics and application to nuclear transport in Drosophila embryos.}, journal = {Journal of the Royal Society, Interface}, volume = {20}, number = {208}, pages = {20230428}, pmid = {37963561}, issn = {1742-5662}, mesh = {Animals ; *Drosophila/metabolism ; Drosophila melanogaster/metabolism ; Active Transport, Cell Nucleus ; Cytoplasm/metabolism ; *Drosophila Proteins/metabolism ; }, abstract = {The Drosophila melanogaster embryo, an elongated multi-nucleated cell, is a classical model system for eukaryotic development and morphogenesis. Recent work has shown that bulk cytoplasmic flows, driven by cortical contractions along the walls of the embryo, enable the uniform spreading of nuclei along the anterior-posterior axis necessary for proper embryonic development. Here, we propose two mathematical models to characterize cytoplasmic flows driven by tangential cortical contractions in elongated cells. Assuming Newtonian fluid flow at low Reynolds number in a spheroidal cell, we first compute the flow field exactly, thereby bypassing the need for numerical computations. We then apply our results to recent experiments on nuclear transport in cell cycles 4-6 of Drosophila embryo development. By fitting the cortical contractions in our model to measurements, we reveal that experimental cortical flows enable near-optimal axial spreading of nuclei. A second mathematical approach, applicable to general elongated cell geometries, exploits a long-wavelength approximation to produce an even simpler solution, with errors below [Formula: see text] compared with the full model. An application of this long-wavelength result to transport leads to fully analytical solutions for the nuclear concentration that capture the essential physics of the system, including optimal axial spreading of nuclei.}, }
@article {pmid37957450, year = {2023}, author = {Bureau, L and Coupier, G and Salez, T}, title = {Lift at low Reynolds number.}, journal = {The European physical journal. E, Soft matter}, volume = {46}, number = {11}, pages = {111}, doi = {10.1140/epje/s10189-023-00369-5}, pmid = {37957450}, issn = {1292-895X}, support = {101039103/ERC_/European Research Council/International ; }, abstract = {Lift forces are widespread in hydrodynamics. These are typically observed for big and fast objects and are often associated with a combination of fluid inertia (i.e. large Reynolds numbers) and specific symmetry-breaking mechanisms. In contrast, the properties of viscosity-dominated (i.e. low Reynolds numbers) flows make it more difficult for such lift forces to emerge. However, the inclusion of boundary effects qualitatively changes this picture. Indeed, in the context of soft and biological matter, recent studies have revealed the emergence of novel lift forces generated by boundary softness, flow gradients and/or surface charges. The aim of the present review is to gather and analyse this corpus of literature, in order to identify and unify the questioning within the associated communities, and pave the way towards future research.}, }
@article {pmid37952804, year = {2024}, author = {Lordifard, P and Shariatpanahi, SP and Khajeh, K and Saboury, AA and Goliaei, B}, title = {Frequency dependence of ultrasonic effects on the kinetics of hen egg white lysozyme fibrillation.}, journal = {International journal of biological macromolecules}, volume = {254}, number = {Pt 3}, pages = {127871}, doi = {10.1016/j.ijbiomac.2023.127871}, pmid = {37952804}, issn = {1879-0003}, mesh = {Animals ; *Muramidase/chemistry ; *Egg White/chemistry ; Ultrasonics ; Protein Structure, Secondary ; Spectrometry, Fluorescence ; Amyloid/chemistry ; Chickens/metabolism ; Kinetics ; }, abstract = {Our study aimed to investigate the effects of ultrasound on the fibrillation kinetics of HEWL (hen egg white lysozyme) and its physicochemical properties. Ultrasound, a mechanical wave, can induce conformational changes in proteins. To achieve this, we developed an ultrasound exposure system and used various biophysical techniques, including ThT fluorescence spectroscopy, ATR-FTIR, Far-UV CD spectrophotometry, Fluorescence microscopy, UV-spectroscopy, and seeding experiments. Our results revealed that higher frequencies significantly accelerated the fibrillation of lysozyme by unfolding the native protein and promoting the fibrillation process, thereby reducing the lag time. We observed a change in the secondary structure of the sonicated protein change to the β-structure, but there was no difference in the Tm of native and sonicated proteins. Furthermore, we found that higher ultrasound frequencies had a greater seeding effect. We propose that the effect of frequency can be explained by the impact of the Reynolds number, and for the Megahertz frequency range, we are almost at the transition regime of turbulence. Our results suggest that laminar flows may not induce any significant change in the fibrillation kinetics, while turbulent flows may affect the process.}, }
@article {pmid37942161, year = {2023}, author = {Abdalkarem, AAM and Ansaf, R and Muzammil, WK and Ibrahim, A and Harun, Z and Fazlizan, A}, title = {Preliminary assessment of the NACA0021 trailing edge wedge for wind turbine application.}, journal = {Heliyon}, volume = {9}, number = {11}, pages = {e21193}, pmid = {37942161}, issn = {2405-8440}, abstract = {The airfoil blade is the primary component of a wind turbine, and its aerodynamic properties play a crucial role in determining the energy conversion efficiency of these blades. Many researchers have proposed different airfoil modifications intending to enhance the aerodynamic characteristics and limit the unsteady interaction with the atmospheric boundary layer. This study evaluates the benefits of mounting wedge tails (WTs) on the trailing edge of an airfoil. The aerodynamic characteristics of a 2-D, steady-state NACA 0021 airfoil featuring the wedge tails (WT) and fish wedge tails (FWT) were studied computationally by employing the shear stress transport (SST) k-ω turbulence model. Different WT and FWT configurations were studied at various wedge length (L) to wedge height (H) ratios, L/H, at the airfoil's trailing edge. The effects of different L/H ratios, including L/H > 1, L/H = 1, and L/H < 1, were considered in the present study to determine the optimal configuration to achieve the maximum glide ratio, CL/CD at the Reynolds number of 180,000. The findings indicate that the performance of the NACA 0021 airfoil was notably affected by the height of the tail; however, the length had only a minor impact when L/H was less than 1. The mounted FWT resulted in significant enhancements to both the lift and glide ratio of the airfoil. Specifically, the lift ratio experienced an increase of over 41 % compared to the clean airfoil, while the glide ratio increased by more than 31 %. These improvements were observed at an ideal height and length of 2.5 % and 1 % of the airfoil, respectively. Moreover, the mounted FWT performed better than the Gurney flap using the same configurations.}, }
@article {pmid37939394, year = {2023}, author = {Ferčák, O and Lyons, KM and Murphy, CT and Kamensky, KM and Cal, RB and Franck, JA}, title = {Multicolor dye-based flow structure visualization for seal-whisker geometry characterized by computer vision.}, journal = {Bioinspiration &amp; biomimetics}, volume = {19}, number = {1}, pages = {}, doi = {10.1088/1748-3190/ad0aa8}, pmid = {37939394}, issn = {1748-3190}, mesh = {Animals ; Vibrissae ; *Caniformia ; *Seals, Earless ; Vibration ; Computer Simulation ; }, abstract = {Pinniped vibrissae possess a unique and complex three-dimensional topography, which has beneficial fluid flow characteristics such as substantial reductions in drag, lift, and vortex induced vibration. To understand and leverage these effects, the downstream vortex dynamics must be studied. Dye visualization is a traditional qualitative method of capturing these downstream effects, specifically in comparative biological investigations where complex equipment can be prohibitive. High-fidelity numerical simulations or experimental particle image velocimetry are commonplace for quantitative high-resolution flow measurements, but are computationally expensive, require costly equipment, and can have limited measurement windows. This study establishes a method for extracting quantitative data from standard dye visualization experiments on seal whisker geometries by leveraging novel but intuitive computer vision techniques, which maintain simplicity and an advantageous large experimental viewing window while automating the extraction of vortex frequency, position, and advection. Results are compared to direct numerical simulation (DNS) data for comparable geometries. Power spectra and Strouhal numbers show consistent behavior between methods for a Reynolds number of 500, with minima at the canonical geometry wavelength of 3.43 and a peak frequency of 0.2 for a Reynolds number of 250. The vortex tracking reveals a clear increase in velocity from roll-up to 3.5 whisker diameters downstream, with a strong overlap with the DNS data but shows steady results beyond the limited DNS window. This investigation provides insight into a valuable bio-inspired engineering model while advancing an analytical methodology that can readily be applied to a broad range of comparative biological studies.}, }
@article {pmid37927848, year = {2023}, author = {Gjerde, IG and Rognes, ME and Sánchez, AL}, title = {The directional flow generated by peristalsis in perivascular networks-Theoretical and numerical reduced-order descriptions.}, journal = {Journal of applied physics}, volume = {134}, number = {17}, pages = {174701}, pmid = {37927848}, issn = {0021-8979}, support = {R01 NS120343/NS/NINDS NIH HHS/United States ; }, abstract = {Directional fluid flow in perivascular spaces surrounding cerebral arteries is hypothesized to play a key role in brain solute transport and clearance. While various drivers for a pulsatile flow, such as cardiac or respiratory pulsations, are well quantified, the question remains as to which mechanisms could induce a directional flow within physiological regimes. To address this question, we develop theoretical and numerical reduced-order models to quantify the directional (net) flow induceable by peristaltic pumping in periarterial networks. Each periarterial element is modeled as a slender annular space bounded internally by a circular tube supporting a periodic traveling (peristaltic) wave. Under reasonable assumptions of a small Reynolds number flow, small radii, and small-amplitude peristaltic waves, we use lubrication theory and regular perturbation methods to derive theoretical expressions for the directional net flow and pressure distribution in the perivascular network. The reduced model is used to derive closed-form analytical expressions for the net flow for simple network configurations of interest, including single elements, two elements in tandem, and a three element bifurcation, with results compared with numerical predictions. In particular, we provide a computable theoretical estimate of the net flow induced by peristaltic motion in perivascular networks as a function of physiological parameters, notably, wave length, frequency, amplitude, and perivascular dimensions. Quantifying the maximal net flow for specific physiological regimes, we find that vasomotion may induce net pial periarterial flow velocities on the order of a few to tens of μm/s and that sleep-related changes in vasomotion pulsatility may drive a threefold flow increase.}, }
@article {pmid37920481, year = {2023}, author = {Vakilabadi, KA and Ghafari, HR and Ghassemi, H}, title = {Experimental and numerical investigation on a trimaran airwake, geometry modification.}, journal = {Heliyon}, volume = {9}, number = {11}, pages = {e21144}, doi = {10.1016/j.heliyon.2023.e21144}, pmid = {37920481}, issn = {2405-8440}, abstract = {The aerodynamic interaction between a helicopter and a trimaran ship's flight deck can be complex and have an impact on handling quality and performance, especially in turbulent conditions. This article presents research on the flight deck geometry of a trimaran vessel without the presence of a helicopter. Both Particle Image Velocimetry (PIV) and computational fluid dynamics (CFD) were used to analyze the effect of wind velocity on air pressure in the flight deck region. The study proposed and evaluated different geometries of the top structure at several air velocities to minimize pressure differences. The results of the numerical simulation were validated by experimental measurements using PIV, which showed that the effect of the Reynolds number on the non-dimensional pressure near the top structure is negligible except for the biggest Reynolds number (Re = 50e6), while at x/L = 0.5 the significant difference can be seen, however, the same result found for Re = 38e6 and 50e6. At the farthest distance (x/L = 1), the pressure difference for different Reynolds numbers case studies is negligible. Among the various geometries assessed, the maximum non-dimensional pressure differences along the lines show the highest value occurs for the base geometry (A) while geometries C and F show lower values, which have chamfering along the middle and side horizontal edges at a 45-degree angle and chamfering along all vertical and horizontal edges at a 30-degree angle.}, }
@article {pmid37918090, year = {2023}, author = {Zhou, ZL and Zhu, LF and Li, TX and Wu, LH and Guan, M and Ma, ZK and Liu, YH and Qin, J and Gao, BL}, title = {Sub-satisfactory stenting recanalization of severe vascular stenosis of the posterior circulation can significantly improve cerebral hemodynamic perfusion.}, journal = {European journal of radiology}, volume = {169}, number = {}, pages = {111135}, doi = {10.1016/j.ejrad.2023.111135}, pmid = {37918090}, issn = {1872-7727}, mesh = {Humans ; Constriction, Pathologic/surgery ; Retrospective Studies ; *Hemodynamics ; Cerebrovascular Circulation ; Perfusion ; Stents ; *Carotid Stenosis ; }, abstract = {PURPOSE: To investigate the effect of sub-satisfactory stenting recanalization of severe vascular stenosis of the posterior circulation on cerebral hemodynamic perfusion.<br><br>MATERIALS AND METHODS: Patients with severe vascular stenosis of the posterior circulation who had undergone three-dimensional cerebral angiography before and after stenting were retrospectively enrolled. Computational fluid dynamic (CFD) analysis of hemodynamic parameters at the stenosis, perforating branch, and normal arterial segments proximal and distal to the stenosis were performed.<br><br>RESULTS: Sixty-two patients with basilar artery stenosis aged 60.9&#x202f;&#xb1;&#x202f;9.6&#x202f;years were enrolled, and stent angioplasty resulted in the reduction of stenosis degree from 85.3&#x202f;&#xb1;&#x202f;7.2% before to 18.6&#x202f;&#xb1;&#x202f;6.4% after stenting. After stenting, at the proximal normal artery, the total pressures had significantly (P&#x202f;<&#x202f;0.05) decreased, whereas all the other parameters (WSS, cell Reynolds number, velocity, vorticity, turbulence intensity, turbulence kinetic energy and dissipation rate) had significantly (P&#x202f;<&#x202f;0.05) increased. At the stenosis, all hemodynamic parameters had significantly decreased. At the stenosis perforating branch, the WSS, cell Reynolds number, velocity, and vorticity were all significantly decreased, and the total pressure, turbulence intensity, kinetic energy, and dissipation rate were all significantly increased. At the distal normal artery, the total flow pressure (perfusion pressure) and velocity were both significantly (P&#x202f;<&#x202f;0.05) increased, and the total pressure, WSS, cell Reynolds number, vorticity, turbulence intensity, kinetic energy, and dissipation rate were all significantly (P&#x202f;<&#x202f;0.05) decreased. The hemodynamic parameters after stenting were closer to those after virtual stenosis repair at all measurements.<br><br>CONCLUSION: Sub-satisfactory recanalization has significantly restored the stenosis and improved the hemodynamic parameters near the stenosis and at the root of the perforating branch, thus significantly improving the cerebral perfusion, similar to the changes of hemodynamic status and cerebral perfusion after virtual removal of the vascular stenosis. This may indicate the good effect of sub-satisfactory stenting recanalization of the vascular stenosis at the posterior circulation.}, }
@article {pmid37914697, year = {2023}, author = {Javaherchian, J and Moosavi, A and Tabatabaei, SA}, title = {Numerical analysis of pressure drop reduction of bubbly flows through hydrophobic microgrooved channels.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {18861}, pmid = {37914697}, issn = {2045-2322}, abstract = {Due to the high performance of hydrophobic surfaces in pressure drop reduction, they have been proposed for various applications. However, despite the extensive uses of two-phase flows in many industries, the effect of hydrophobic surfaces on the pressure drop reduction of two-phase flows has not been well understood yet. Thus, in the present study, by implementing the phase-field and finite element methods, the bubbly flows as an example of two-phase flows are considered for examining the effect of hydrophobic microgrooved microchannels on the pressure drop reduction of these regimes in the laminar state. We found out that hydrophobic microgrooved surfaces not only can be efficient in the bubbly flow but also can even cause a maximum pressure drop reduction of up to 70%, which is almost 3.5 times higher than in single-phase flow. We also studied the influence of each parameter, such as bubbles volume or length, Reynolds number, capillary number, and their combination on this phenomenon. The pressure drop reduction grows by increasing the volume of the bubbles but decreases by increasing the flow velocity or the surface tension coefficient. The combination of these parameters demonstrated different results in some circumstances.}, }
@article {pmid37909299, year = {2023}, author = {Zhao, W and Shang, X and Zhang, B and Yuan, D and Nguyen, BTT and Wu, W and Zhang, JB and Peng, N and Liu, AQ and Duan, F and Chin, LK}, title = {Squeezed state in the hydrodynamic focusing regime for Escherichia coli bacteria detection.}, journal = {Lab on a chip}, volume = {23}, number = {23}, pages = {5039-5046}, doi = {10.1039/d3lc00434a}, pmid = {37909299}, issn = {1473-0189}, mesh = {*Hydrodynamics ; Escherichia coli ; Microfluidics/methods ; *Microfluidic Analytical Techniques/methods ; Flow Cytometry ; }, abstract = {Flow cytometry is an essential technique in single particle analysis and cell sorting for further downstream diagnosis, exhibiting high-throughput and multiplexing capabilities for many biological and biomedical applications. Although many hydrodynamic focusing-based microfluidic cytometers have been demonstrated with reduced size and cost to adapt to point-of-care settings, the operating conditions are not characterized systematically. This study presents the flow transition process in the hydrodynamic focusing mechanism when the flow rate or the Reynolds number increases. The characteristics of flow fields and mass transport were studied under various operating conditions, including flow rates and microchannel heights. A transition from the squeezed focusing state to the over-squeezed anti-focusing state in the hydrodynamic focusing regime was observed when the Reynolds number increased above 30. Parametric studies illustrated that the focusing width increased with the Reynolds number but decreased with the microchannel height in the over-squeezed state. The microfluidic cytometric analyses using microbeads and E. coli show that the recovery rate was maintained by limiting the Reynolds number to 30. The detailed analysis of the flow transition will provide new insight into microfluidic cytometric analyses with a broad range of applications in food safety, water monitoring and healthcare sectors.}, }
@article {pmid37906645, year = {2023}, author = {Zöttl, A and Tesser, F and Matsunaga, D and Laurent, J and du Roure, O and Lindner, A}, title = {Asymmetric bistability of chiral particle orientation in viscous shear flows.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {120}, number = {45}, pages = {e2310939120}, pmid = {37906645}, issn = {1091-6490}, support = {682367//European Commission (EC)/ ; M 2458-N36//Austrian Science Fund (FWF)/ ; ANR-10- EQPX-34//Agence Nationale de la Recherche (ANR)/ ; 21H05879//MEXT | Japan Society for the Promotion of Science (JSPS)/ ; JPMJPR21OA//MEXT | JST | Precursory Research for Embryonic Science and Technology (PRESTO)/ ; }, abstract = {The migration of helical particles in viscous shear flows plays a crucial role in chiral particle sorting. Attaching a nonchiral head to a helical particle leads to a rheotactic torque inducing particle reorientation. This phenomenon is responsible for bacterial rheotaxis observed for flagellated bacteria as Escherichia coli in shear flows. Here, we use a high-resolution microprinting technique to fabricate microparticles with controlled and tunable chiral shape consisting of a spherical head and helical tails of various pitch and handedness. By observing the fully time-resolved dynamics of these microparticles in microfluidic channel flow, we gain valuable insights into chirality-induced orientation dynamics. Our experimental model system allows us to examine the effects of particle elongation, chirality, and head heaviness for different flow rates on the orientation dynamics, while minimizing the influence of Brownian noise. Through our model experiments, we demonstrate the existence of asymmetric bistability of the particle orientation perpendicular to the flow direction. We quantitatively explain the particle equilibrium orientations as a function of particle properties, initial conditions and flow rates, as well as the time-dependence of the reorientation dynamics through a theoretical model. The model parameters are determined using boundary element simulations, and excellent agreement with experiments is obtained without any adjustable parameters. Our findings lead to a better understanding of chiral particle transport and bacterial rheotaxis and might allow the development of targeted delivery applications.}, }
@article {pmid37898603, year = {2023}, author = {Jalili, B and Shateri, A and Akgül, A and Bariq, A and Asadi, Z and Jalili, P and Ganji, DD}, title = {An investigation into a semi-porous channel's forced convection of nano fluid in the presence of a magnetic field as a result of heat radiation.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {18505}, pmid = {37898603}, issn = {2045-2322}, abstract = {This study investigates the impact of heat radiation on magnetically-induced forced convection of nanofluid in a semi-porous channel. The research employs Akbari-Ganji's and Homotopy perturbation methods to analyze the effects of multiple parameters, including Hartmann number, Reynolds number, Eckert number, radiation parameter, and suction parameter, on the flow and heat transfer characteristics. The results demonstrate that increasing Reynolds number, suction, and radiation parameters increases temperature gradient, providing valuable insights into improving heat transfer in semi-porous channels. The study validates the proposed methods by comparing the results with those obtained from other established methods in the literature. The main focus of this work is to understand the behavior of nanofluids in semi-porous channels under the influence of magnetic fields and heat radiation, which is essential for various industrial and engineering applications. The future direction of this research includes exploring the effects of different nanoparticle shapes and materials on heat transfer performance and investigating the influence of other parameters, such as buoyancy forces and variable properties, on the flow and heat transfer characteristics. The findings of this study are expected to contribute to the development of more efficient thermal management systems in the future.}, }
@article {pmid37893255, year = {2023}, author = {Zhao, H and Ma, H and Yan, X and Yu, H and Xiao, Y and Xiao, X and Liu, H}, title = {Investigation of Hydrothermal Performance in Micro-Channel Heat Sink with Periodic Rectangular Fins.}, journal = {Micromachines}, volume = {14}, number = {10}, pages = {}, pmid = {37893255}, issn = {2072-666X}, abstract = {The micro-channel heat sink (MCHS) is an excellent choice due to its exceptional cooling capabilities, surpassing those of its competitors. In this research paper, a computational fluid dynamics analysis was performed to investigate the laminar flow and heat transfer characteristics of five different configurations of a variable geometry rectangular fin. The study utilized a water-cooled smooth MCHS as the basis. The results indicate that the micro-channel heat sink with a variable geometry rectangular fin has better heat dissipation capacity than a straight-type micro-channel heat sink, but at the same time, it has larger pressure loss. Based on the analysis of various rectangular fin shapes and Reynolds numbers in this study, the micro-channel heat sink with rectangular fins exhibits Nusselt numbers and friction factors that are 1.40-2.02 and 2.64-4.33 times higher, respectively, compared to the smooth heat sink. This significant improvement in performance results in performance evaluation criteria ranging from 1.23-1.95. Further, it is found that at a relatively small Reynolds number, the micro-channel heat sink with a variable geometry rectangular fin has obvious advantages in terms of overall cooling performance. Meanwhile, this advantage will decrease when the Reynolds number is relatively large.}, }
@article {pmid37886753, year = {2023}, author = {Vaferi, K and Vajdi, M and Nekahi, S and Heydari, A and Sadegh Moghanlou, F and Nami, H and Jafarzadeh, H}, title = {Thermo-hydraulic performance optimization of a disk-shaped microchannel heat sink applying computational fluid dynamics, artificial neural network, and response surface methodology.}, journal = {Heliyon}, volume = {9}, number = {10}, pages = {e21031}, pmid = {37886753}, issn = {2405-8440}, abstract = {The current research focuses on optimizing the Nusselt number (Nu) and pressure drop (ΔP) in a bionic fractal heat sink. The artificial neural network (ANN) and response surface methodology (RSM) were used to model the thermos-hydraulic behavior of the MCHS. The aspect ratios of t/b (cavities' upper side to bottom side ratio) and h/b (cavities' height to bottom side ratio), as well as the Reynolds number, were set as the independent variables in both ANN and RSM models. After finding the optimum state for the copper-made MCHS (containing the optimum design of the cavities along with the best applied velocity), different materials were tested and compared with the base case (heat sink made of copper). The obtained results indicated that both ANN and RSM models (with determination coefficient of 99.9 %) could exactly anticipate heat transfer and ΔP to a large extent. To achieve the optimal design of the microchannel heat sink (MCHS) with the objective of maximizing Nu and minimizing ΔP, the efficiency index of the device was evaluated. The analysis revealed that the highest efficiency index (1.070 by RSM and 1.067 by ANN methods) was attained when the aspect ratios were t/b = 0.2, h/b = 0.2, and the Reynolds number was 1000. Next, the effect of the different materials on heat sink performance was investigated, and it was observed that by reducing the thermal conductivity, the thermal resistance of the heat sink increased and its overall performance decreased.}, }
@article {pmid37849125, year = {2023}, author = {Paludan, MV and Biviano, MD and Jensen, KH}, title = {Elastohydrodynamic autoregulation in soft overlapping channels.}, journal = {Physical review. E}, volume = {108}, number = {3-2}, pages = {035106}, doi = {10.1103/PhysRevE.108.035106}, pmid = {37849125}, issn = {2470-0053}, mesh = {Humans ; Animals ; *Blood Pressure ; Pressure ; Homeostasis/physiology ; }, abstract = {Controlling fluid flow from an unsteady source is a challenging problem that is relevant in both living and man-made systems. Animals have evolved various autoregulatory mechanisms to maintain homeostasis in vital organs. This keeps the influx of nutrients essentially constant and independent of the perfusion pressure. Up to this point, the autoregulation processes have primarily been ascribed to active mechanisms that regulate vessel size, thereby adjusting the hydraulic conductance in response to, e.g., sensing of wall shear stress. We propose an alternative elastohydrodynamic mechanism based on contacting soft vessels. Inspired by Starling's resistor, we combine experiments and theory to study the flow of a viscous liquid through a self-intersecting soft conduit. In the overlapping region, the pressure difference between the two channel segments can cause one pipe segment to dilate while the other is compressed. If the tissue is sufficiently soft, this mode of fluid-structure interactions can lead to flow autoregulation. Our experimental observations compare well to a predictive model based on low-Reynolds-number fluid flow and linear elasticity. Implications for conduit arrangement and passive autoregulation in organs and limbs are discussed.}, }
@article {pmid37848600, year = {2023}, author = {Maruai, NM and Ali, MSM and Zaki, SA and Ardila-Rey, JA and Ishak, IA}, title = {The influence of different downstream plate length towards the flow-induced vibration on a square cylinder.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {17681}, pmid = {37848600}, issn = {2045-2322}, support = {PY/2021/00886//Universiti Teknologi Malaysia/ ; PY/2021/00886//Universiti Teknologi Malaysia/ ; PY/2021/00886//Universiti Teknologi Malaysia/ ; Agencia Nacional de Investigaci&#xf3;n y Desarrollo (ANID)//FONDECYT Regular 1230135/ ; }, abstract = {The investigations of flow-induced vibration have been around for decades to solve many engineering problems related to structural element. In a hindsight of advancing technology of microelectronics devices, the implementation of flow-induced vibration for energy harvesting is intrigued. The influence of downstream flat plate to flow-induced vibration experienced by a square cylinder is discussed in this study to surpass the limitation of wind energy due to geographical constraints and climate change. The mechanism of flow-induced vibration experienced by a square cylinder with downstream flat plate is numerically simulated based on the unsteady Reynolds Navier-Stokes (URANS) flow field. The Reynolds number, Re assigned in this study is ranging between [Formula: see text]-[Formula: see text] and the mass damping ratio designated for the square cylinder is [Formula: see text] = 2.48. The influence of three different flat plate lengths [Formula: see text], 1 and 3 is examined. Each case of different flat plate is explored for gap separation between the square cylinder and the plate in the range [Formula: see text]. Based on the numerical findings, the configuration of cylinder-flat plate with length [Formula: see text] has shown the highest potential to harvest high energy at comparatively low reduced velocity.}, }
@article {pmid37822907, year = {2023}, author = {Akram, M and Memon, AA and Memon, MA and Obalalu, AM and Khan, U}, title = {Investigation of a two-dimensional photovoltaic thermal system using hybrid nanofluids and a rotating cylinder.}, journal = {Nanoscale advances}, volume = {5}, number = {20}, pages = {5529-5542}, pmid = {37822907}, issn = {2516-0230}, abstract = {This article focuses on a numerical investigation aimed at enhancing the electrical performance of a two-dimensional photovoltaic thermal system (PV/T) through the application of cooling using hybrid nanofluids. The hybrid nanofluids consist of titanium oxide and silver nanoparticles suspended in water, while the PV/T system is based on polycrystalline silicon, copper, and a flow channel with a rotating cylinder. PV/T devices generate electricity from sunlight, but their performance degrades over time due to the heat generated by solar radiation. Therefore, nanofluids can be circulated through the bottom flow channel to cool the device. This study utilizes 2D incompressible Navier-Stokes equations to control fluid flow and energy equations to manage energy distribution. The COMSOL 6.0 finite element software is employed for comprehensive modeling and simulation. To enhance the performance of the PV/T system, a parametric study is conducted by varying the Reynolds number (ranging from 100 to 1000), cylinder rotational speed (varying from 0.01 to 0.2 m s[-1]), and silver volume fraction (ranging from 0.01 to 0.2). The results show that increasing the Reynolds number and the volume fraction of silver leads to a reduction in the maximum temperature of the cell. The maximum temperature of the cell also decreases with the rotational speed of the cylinder but only for high Reynolds numbers. By applying the present model, the cell's efficiency is improved by 5.93%.}, }
@article {pmid37822766, year = {2023}, author = {Sutton, GP and Szczecinski, NS and Quinn, RD and Chiel, HJ}, title = {Phase shift between joint rotation and actuation reflects dominant forces and predicts muscle activation patterns.}, journal = {PNAS nexus}, volume = {2}, number = {10}, pages = {pgad298}, pmid = {37822766}, issn = {2752-6542}, support = {MR/T046619/1/MRC_/Medical Research Council/United Kingdom ; }, abstract = {During behavior, the work done by actuators on the body can be resisted by the body's inertia, elastic forces, gravity, or viscosity. The dominant forces that resist actuation have major consequences on the control of that behavior. In the literature, features and actuation of locomotion, for example, have been successfully predicted by nondimensional numbers (e.g. Froude number and Reynolds number) that generally express the ratio between two of these forces (gravitational, inertial, elastic, and viscous). However, animals of different sizes or motions at different speeds may not share the same dominant forces within a behavior, making ratios of just two of these forces less useful. Thus, for a broad comparison of behavior across many orders of magnitude of limb length and cycle period, a dimensionless number that includes gravitational, inertial, elastic, and viscous forces is needed. This study proposes a nondimensional number that relates these four forces: the phase shift (ϕ) between the displacement of the limb and the actuator force that moves it. Using allometric scaling laws, ϕ for terrestrial walking is expressed as a function of the limb length and the cycle period at which the limb steps. Scale-dependent values of ϕ are used to explain and predict the electromyographic (EMG) patterns employed by different animals as they walk.}, }
@article {pmid37821662, year = {2023}, author = {Saparbayeva, N and Balakin, BV}, title = {CFD-DEM model of plugging in flow with cohesive particles.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {17188}, pmid = {37821662}, issn = {2045-2322}, support = {300286//Norges Forskningsr&#xe5;d/ ; }, abstract = {Plugging in flows with cohesive particles is crucial in many industrial and real-life applications such as hemodynamics, water distribution, and petroleum flow assurance. Although probabilistic models for plugging risk estimation are presented in the literature, multiple details of the process remain unclear. In this paper, we present a CFD-DEM model of plugging validated against several experimental benchmarks. Using the simulations, we consider the process of plugging in a slurry of ice in decane, focusing on inter-particle collisions and plugging dynamics. We conduct a parametric study altering the Reynolds number (3000...9000), particle concentration (1.6...7.3%), and surface energy (21...541 mJ/m[Formula: see text]). We note the process possesses complex non-linear behaviour for the cases where particle-wall adhesion reduces by more than 20% relative to inter-particle cohesion. Finally, we demonstrate how the simulation results match the flow maps based on the third-party experiments.}, }
@article {pmid37810730, year = {2023}, author = {Sun, T and Liu, H and Yan, T and Zhang, Y}, title = {Numerical Study on Enhanced Heat Transfer of Downhole Slotted-Type Heaters for In Situ Oil Shale Exploitation.}, journal = {ACS omega}, volume = {8}, number = {39}, pages = {36043-36052}, pmid = {37810730}, issn = {2470-1343}, abstract = {In order to improve the flow state of the heater shell side and enhance the performance evaluation of the heater, this paper proposes a perforated plate-type heater model. Based on Fluent, numerical studies are conducted on the heat transfer performance and shell-side fluid flow characteristics of a perforated plate-type heater. The variations of the heat transfer factor Nu, friction factor f, and evaluation parameter Nu/f[1/3] are analyzed for different helix angles β and ratios of the long and short semiaxes of the circular holes on the heating plate under different Reynolds numbers Re. The results reveal that under the same shell-side Reynolds number Re, the heat transfer factor Nu shows an increasing trend with the increase in the proportion of the helix angle β. The heat transfer factor Nu for the heating plate with the hole shape ratio a/b = 1 does not exhibit significant improvement compared to hole shape ratios a/b = 0.8 and a/b = 0.6, but it increases by 4.87 to 7.07% compared to the hole shape ratio a/b = 0.4 in the perforated plate-type heater. On the other hand, the friction factor f decreases as the helix angle β and the ratio of hole shapes on the heating plate increase. The lowest friction factor f is observed for the helix angle β of 25° and the hole shape ratio a/b = 1 in the perforated plate-type heater. When the helix angle β is 25° and the hole shape ratio is a/b = 1, the evaluation parameter Nu/f[1/3] reaches its highest value, indicating the optimal overall performance of the perforated plate-type heater.}, }
@article {pmid37809404, year = {2023}, author = {Hosseinzadeh, K and Roshani, M and Attar, MA and Ganji, DD and Shafii, MB}, title = {Heat transfer study and optimization of nanofluid triangular cavity with a pentagonal barrier by finite element approach and RSM.}, journal = {Heliyon}, volume = {9}, number = {9}, pages = {e20193}, pmid = {37809404}, issn = {2405-8440}, abstract = {Nowadays, several engineering applications and academic investigations have demonstrated the significance of heat transfers in general and mixed convection heat transfer (MCHT) in particular in cavities containing obstacles. This study's main goal is to analyze the MCHT of a nanofluid in a triangular cavity with a pentagonal barrier using magneto hydrodynamics (MHD). The cavity's-oriented walls are continuous cold temperature, whereas the bottom wall of the triangle and all pentagonal obstacle walls are kept at a constant high temperature. For solving governing equations, we utilized the Galerkin's finite element approach. Four dimensionless factors, Richardson number (0.01 ≤ Ri ≤ 5), Reynolds number (10 ≤ Re ≤ 50), Buoyancy ratio (0.01 ≤ Br ≤ 10) and Hartmann number (0 ≤ Ha ≤20) are examined for their effects on streamlines, isotherms, concentration, velocity, and the Nusselt number. Also, with the help of Taguchi method and Response Surface Method (RSM) the optimization of the studied dimensionless parameters has been done. The optimum values of Ri, Re, Ha and Br are obtained 4.95, 30.49,18.35 and 0.05 respectively. Ultimately, a correlation has been extracted for obtaining the optimum average Nusselt number (Nu) in mentioned cavity.}, }
@article {pmid37809384, year = {2023}, author = {Rasul, MG and Ahmed, S and Sattar, MA and Jahirul, MI}, title = {Hydrodynamic performance assessment of photocatalytic reactor with baffles and roughness in the flow path: A modelling approach with experimental validation.}, journal = {Heliyon}, volume = {9}, number = {9}, pages = {e19623}, pmid = {37809384}, issn = {2405-8440}, abstract = {Purification of wastewater is essential for human being as well as for the flora and fauna, and sustainable environment. Photocatalytic reactor with TiO2 coated layer can be used to degrade the pollutants but without proper pollutant mass transfer in the reactive surface, photocatalytic reactor decreases its effectiveness. The baffles and rough surface in the flow path can improve the fluid mixing to enhance pollutant mass transfer to improve the reactor's performance. In this study, a computational fluid dynamics (CFD) model has been developed to investigate the effect of four top baffles and three rough surfaces (semi-circular, triangle, and rectangle) on pressure drops, mass transfer and the hydrodynamic performance of the reactor. The experimental investigation was carried out using Formic Acid (FA) as pollutant in feed water for model validation. The simulated result varies only within 5% with the experimental data of FA concentration versus feed flow rate and fluid velocity. The model was run at fluid velocity of 0.15 m/s and 0.5 m/s (Reynolds number of 2150 (laminar flow) and 7500 (turbulent flow), respectively. The simulation result shows that the addition of baffles and roughness on the reactive surfaces increases the turbulent kinetic energy (minimum increase 8%) and consequently increases the mass transfer (maximum increase 37%) of the pollutant. The highest wall shear was observed to be 40 Pa when both square and triangular elements were used as roughness elements at turbulent flow condition. The results also shows that the highest pressure-drop of 8 kPa was found when the square roughness element was used at turbulent flow condition. Overall, the photocatalytic reactor performance is significantly enhanced by the application of combined baffles and roughness elements in the reactive surface.}, }
@article {pmid37807009, year = {2023}, author = {Allehiany, FM and Memon, AA and Memon, MA and Fenta, A}, title = {Maximizing electrical output and reducing heat-related losses in photovoltaic thermal systems with a thorough examination of flow channel integration and nanofluid cooling.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {16961}, pmid = {37807009}, issn = {2045-2322}, abstract = {In recent years, global energy demand has surged, emphasizing the need for nations to enhance energy resources. The photovoltaic thermal (PV/T) system, capable of generating electrical energy from sunlight, is a promising renewable energy solution. However, it faces the challenge of overheating, which reduces efficiency. To address this, we introduce a flow channel within the PV/T system, allowing coolant circulation to improve electrical efficiency. Within this study, we explore into the workings of a PV/T system configuration, featuring a polycrystalline silicon panel atop a copper absorber panel. This innovative setup incorporates a rectangular flow channel, enhanced with a centrally positioned rotating circular cylinder, designed to augment flow velocity. This arrangement presents a forced convection scenario, where heat transfer primarily occurs through conduction in the uppermost two layers, while the flow channel beneath experiences forced convection. To capture this complex phenomenon, we accurately address the two-dimensional Navier-Stokes and energy equations, employing simulations conducted via COMSOL 6.0 software, renowned for its utilization of the finite element method. To optimize heat dissipation and efficiency, we introduce a hybrid nanofluid comprised of titanium oxide and silver nanoparticles dispersed in water, circulating through the flow channel. Various critical parameters come under scrutiny, including the Reynolds number, explored across the range of 100-1000, the volume fractions of both nanoparticle types, systematically tested within the range of 0.001-0.05, and the controlled speed of the circular cylinder, maintained within the range of 0.1-0.25 m/s. It was found that incorporating silver nanoparticles as a suspended component is more effective in enhancing PV/T efficiency than the addition of titanium oxide. Additionally, maintaining the volume fraction of titanium oxide between 4 and 5% yields improved efficiency, provided that the cylinder rotates at a higher speed. It was observed that cell efficiency can be regulated by adjusting four parameters, such as the Reynolds number, cylinder rotation speed, and the volume fraction of both nanoparticles.}, }
@article {pmid37798525, year = {2023}, author = {Zhang, B and Liu, G and Li, Y and Lin, Z}, title = {Experimental study on the seepage mutation of natural karst collapse pillar (KCP) fillings over mass outflow.}, journal = {Environmental science and pollution research international}, volume = {30}, number = {51}, pages = {110995-111007}, pmid = {37798525}, issn = {1614-7499}, support = {41807209//Natural Science Foundation of China/ ; }, mesh = {*Mining ; *Water ; China ; Coal/analysis ; Permeability ; }, abstract = {Conduction between the unique geological formation karst collapse pillar (KCP) and the fractures caused by mining in the coal seam floor can lead to catastrophic water inrush disasters in many coalmines in Northern China. It is widely recognized that seepage mutation induced by the migration/loss of KCP fillings (highly broken rocks filling the fractured rocks) happens during occurrence of the KCP-related water inrush. However, roles of fluid path (mining-induced fracture) scale and KCP filling porosity in seepage mutation evolution remain unclear. Here, we conducted seepage tests on natural KCP fillings containing rock particles of different sizes. The filling specimens were deformed to different porosities from 14 to 26% through axial compression, and small to large fluid paths were simulated by seepage plates with distinct pore sizes from 2.5 to 12.5 mm. We found that seepage mutation occurs with significant permeability enhancement by 2 orders of magnitude under a pore diameter of 12.5 mm and a specimen porosity of 26%. There is a strong linear relationship between specimen permeability and Reynolds number (Re) over seepage mutation. The mutation is caused by the sudden collapse of the specimen skeleton and subsequent quick outflow of the particles. Therefore, it is inferred that the KCP-related water inrush is more likely to happen when highly porous KCP fillings are present and mining-induced fractures are well developed.}, }
@article {pmid37787128, year = {2023}, author = {Duraes, ADS and Gezelter, JD}, title = {A theory of pitch for the hydrodynamic properties of molecules, helices, and achiral swimmers at low Reynolds number.}, journal = {The Journal of chemical physics}, volume = {159}, number = {13}, pages = {}, doi = {10.1063/5.0152546}, pmid = {37787128}, issn = {1089-7690}, abstract = {We present a theory for pitch, a matrix property that is linked to the coupling of rotational and translational motion of rigid bodies at low Reynolds numbers. The pitch matrix is a geometric property of objects in contact with a surrounding fluid, and it can be decomposed into three principal axes of pitch and their associated moments of pitch. The moments of pitch predict the translational motion in a direction parallel to each pitch axis when the object is rotated around that axis and can be used to explain translational drift, particularly for rotating helices. We also provide a symmetrized boundary element model for blocks of the resistance tensor, allowing calculation of the pitch matrix for arbitrary rigid bodies. We analyze a range of chiral objects, including chiral molecules and helices. Chiral objects with a Cn symmetry axis with n > 2 show additional symmetries in their pitch matrices. We also show that some achiral objects have non-vanishing pitch matrices, and we use this result to explain recent observations of achiral microswimmers. We also discuss the small but non-zero pitch of Lord Kelvin's isotropic helicoid.}, }
@article {pmid37774714, year = {2023}, author = {Zhu, Q}, title = {Locomotion performance of an axisymmetric 'flapping fin'.}, journal = {Bioinspiration &amp; biomimetics}, volume = {18}, number = {6}, pages = {}, doi = {10.1088/1748-3190/acfeb9}, pmid = {37774714}, issn = {1748-3190}, mesh = {Biomechanical Phenomena ; *Locomotion ; *Swimming ; Hydrodynamics ; }, abstract = {Inspired by the jet-propulsion mechanism of aquatic creatures such as sea salps, a novel locomotion system based on an axisymmetric body design is proposed. This system consists of an empty tube with two ends open. When the diameters of the front and back openings are changed periodically, the forward-backward symmetry is broken so that the system starts swimming. Viewed within a cross section, this system resembles a two-dimensional flapping fin with its leading edge located at the front opening and the trailing edge at the back opening. The feasibility of this system has been proven via numerical simulations using a fluid-structure interaction model based on the immersed-boundary framework. According to the results, at relatively low Reynolds number (O(10[2])), this simple locomotion method can easily achieve a mean swimming speed of 2 to 3 body lengths per deformation period. Further simulations illustrate the following characteristics: (1) within the chamber, the hydrodynamic interactions among different parts of the body leads to a performance-enhancing mechanism similar to the ground effect; (2) reducing the diameter of the body can strengthen this effect so that both the swimming speed and the energy efficiency are improved; (3) for better performance the amplitude of diameter oscillation at the trailing edge should be larger or at least equal to the one at the leading edge.}, }
@article {pmid37763958, year = {2023}, author = {Juraeva, M and Kang, DJ}, title = {Design and Mixing Analysis of a Passive Micromixer Based on Curly Baffles.}, journal = {Micromachines}, volume = {14}, number = {9}, pages = {}, pmid = {37763958}, issn = {2072-666X}, support = {Daedong2023//Daedong Heavy Industry/ ; }, abstract = {A novel passive micromixer based on curly baffles is proposed and optimized through the signal-to-noise analysis of various design parameters. The mixing performance of the proposed design was evaluated across a wide Reynolds number range, from 0.1 to 80. Through the analysis, the most influential parameter was identified, and its value was found to be constant regardless of the mixing mechanism. The optimized design, refined using the signal-to-noise analysis, demonstrated a significant enhancement of mixing performance, particularly in the low Reynolds number range (Re< 10). The design set obtained at the diffusion dominance range shows the highest degree of mixing (DOM) in the low Reynolds number range of Re< 10, while the design set optimized for the convection dominance range exhibited the least pressure drop across the entire Reynolds number spectrum (Re< 80). The present design approach proved to be a practical tool for identifying the most influential design parameter and achieving excellent mixing and pressure drop characteristics. The enhancement is mainly due to the curvature of the most influential design parameter.}, }
@article {pmid37757685, year = {2023}, author = {Jafari, E and Malayeri, MR and Brückner, H and Weimer, T and Krebs, P}, title = {Innovative spiral electrode configuration for enhancement of electrocoagulation-flotation.}, journal = {Journal of environmental management}, volume = {347}, number = {}, pages = {119085}, doi = {10.1016/j.jenvman.2023.119085}, pmid = {37757685}, issn = {1095-8630}, mesh = {*Electrocoagulation/methods ; *Metals, Heavy ; Wastewater ; Electrodes ; Waste Disposal, Fluid/methods ; }, abstract = {The performance of electrocoagulation-flotation (ECF) process can profoundly be affected by the reactor design and electrode configuration. These may, in turn, influence the removal efficiency, flow hydrodynamic, floc formation, and flotation/settling characteristics. The present work aimed at developing a new spiral electrode configuration to enhance the ECF process. To do so, the impacts of parameters such as energy consumption, removal efficiency of the contaminants from industrial wastewater with a composition of turbidity, emulsified oil, and heavy metals (Si, Zn, Pb, Ni, Cu, Cr, and Cd), as well as stirring speed and foaming have been investigated. Comparison was also made between the experimental results of the new electrode configuration with the conventional rectangular cell with plate electrode configuration with the same volume and electrode surface area. The findings revealed that energy consumption of the spiral electrode configuration within the operating times of 10, 20, 30, 32, 48, and 70 min, was approximately 20% lower compared to that of the conventional ECF. Moreover, the maximum and minimum removal efficiency of 97% and 60% were obtained for turbidity and TOC for the stirring speed of 500 rpm and Reynolds number of 10,035, respectively. Finally, the formed gas bubbles tilted toward the center due to the enhanced flow hydrodynamic which resulted in substantial reduction of foam formation.}, }
@article {pmid37756554, year = {2023}, author = {Rajendran, S and Jog, MA and Manglik, RM}, title = {Predicting the Splash of a Drop Impacting a Thin Liquid Film.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {39}, number = {41}, pages = {14764-14773}, doi = {10.1021/acs.langmuir.3c02185}, pmid = {37756554}, issn = {1520-5827}, abstract = {An experimental study is carried out to investigate droplet-film interactions when a drop impinges on a thin stagnant film of the same liquid. The impacting drop causes either liquid deposition or splash, consisting of prompt generation of secondary drops or a delayed process. By varying the drop diameter and impact velocity, measurements are made to characterize the phenomena using five different liquids that are chosen to cover a wide range of liquid properties (viscosity and surface tension). The drop impact dynamics are captured with a high-speed digital camera with real-time, high-resolution image processing. The drop-splash threshold is found to scale with inertial and viscous forces, or Reynolds number (Re), as well as capillary forces, as described by the balance of gravitational and interfacial tension forces, or Bond number (Bo); fluid properties are described by their Morton number (Mo). A correlation, functionally expressed as Re = ϕ(Bo,Mo), is devised to determine the splash/no-splash (or deposition) boundary, and the predictions for the splash/no-splash outcomes agree well with the experimental outcomes as well as those readily available in the literature.}, }
@article {pmid37756336, year = {2023}, author = {Hickey, DJ and Golestanian, R and Vilfan, A}, title = {Nonreciprocal interactions give rise to fast cilium synchronization in finite systems.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {120}, number = {40}, pages = {e2307279120}, pmid = {37756336}, issn = {1091-6490}, support = {//Max Planck Society/ ; P1-0099//Javna Agencija za Raziskovalno Dejavnost RS (ARRS)/ ; }, abstract = {Motile cilia beat in an asymmetric fashion in order to propel the surrounding fluid. When many cilia are located on a surface, their beating can synchronize such that their phases form metachronal waves. Here, we computationally study a model where each cilium is represented as a spherical particle, moving along a tilted trajectory with a position-dependent active driving force and a position-dependent internal drag coefficient. The model thus takes into account all the essential broken symmetries of the ciliary beat. We show that taking into account the near-field hydrodynamic interactions, the effective coupling between cilia even over an entire beating cycle can become nonreciprocal: The phase of a cilium is more strongly affected by an adjacent cilium on one side than by a cilium at the same distance in the opposite direction. As a result, synchronization starts from a seed at the edge of a group of cilia and propagates rapidly across the system, leading to a synchronization time that scales proportionally to the linear dimension of the system. We show that a ciliary carpet is characterized by three different velocities: the velocity of fluid transport, the phase velocity of metachronal waves, and the group velocity of order propagation. Unlike in systems with reciprocal coupling, boundary effects are not detrimental for synchronization, but rather enable the formation of the initial seed.}, }
@article {pmid37749273, year = {2023}, author = {Younis, O and Abderrahmane, A and Hatami, M and Mourad, A and Guedri, K}, title = {Nanoencapsulated phase change material in a trapezoidal prism wall under the magnetic field effect for energy storage purposes.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {16060}, pmid = {37749273}, issn = {2045-2322}, abstract = {Recently, Nano-encapsulated phase change materials (NEPCM) have attracted the attention of researchers due to their promising application in thermal management. This research investigates magnetohydrodynamic mixed convection of NEPCM contained within a lid-driven trapezoidal prism enclosure containing a hot-centered elliptical obstacle. The upper cavity wall is moving at a constant velocity; both inclined walls are cold, while the rest of the walls are insulated. The Galerkin Finite Element Method was used to solve the system's governing equations. The influence of Reynolds number (Re 1-500), Hartmann number (Ha = 0-100), NEPCM volumetric fraction φ (0-8%), and elliptical obstacle orientation α (0-3π/4) on thermal fields and flow patterns are introduced and analyzed. The results indicated that the maximum heat transfer rate is observed when the hot elliptic obstacle is oriented at 90°; an increment of 6% in the Nu number is obtained in this orientation compared to other orientations. Reducing Ha from 100 to 0 increased Nu by 14%. The Maximum value of the Bejan number was observed for the case of Ha = 0, α = 90° and φ = 0.08.}, }
@article {pmid37749138, year = {2023}, author = {Abd-Alla, AM and Abo-Dahab, SM and Abdelhafez, MA and Elmhedy, Y}, title = {Effect of heat and mass transfer on the nanofluid of peristaltic flow in a ciliated tube.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {16008}, pmid = {37749138}, issn = {2045-2322}, abstract = {The current work focuses attention on discussing the peristaltic flow of Rabinowitsch nanofluid through ciliated tube. This technical study analyzes heat and mass transfer effects on the flow of a peristaltic flow, incompressible, nanofluid via a ciliated tube. The governing non-linear partial differential equations representing the flow model are transmuted into linear ones by employing the appropriate non-dimensional parameters under the assumption of long wavelength and low Reynolds number. The flow is examined in wave frame of reference moving with the velocity [Formula: see text]. The governing equations have been solved to determine velocity, temperature, concentration, the pressure gradient, pressure rise and the friction force. Using MATLAB R2023a software, a parametric analysis is performed, and the resulting data is represented graphically. The results indicate that the various emerging parameters of interest significantly affect the nanofluid properties within the tube. The present study enhances the comprehension of nanofluid dynamics in tube and offers valuable insights into the influence of heat and mass transfer in such setups. Convective heat transfer is found to be greater at the boundaries resulting in decreased temperature there.}, }
@article {pmid37749119, year = {2023}, author = {Abbas, N and Shatanawi, W and Hasan, F and Mustafa, Z}, title = {Thermodynamic flow of radiative induced magneto modified Maxwell Sutterby fluid model at stretching sheet/cylinder.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {16002}, pmid = {37749119}, issn = {2045-2322}, abstract = {A steady flow of Maxwell Sutterby fluid is considered over a stretchable cylinder. The magnetic Reynolds number is considered very high and induced magnetic and electric fields are applied on the fluid flow. Joule heating and radiation impacts are studied under the temperature-dependent properties of the liquid. Having the above assumptions, the mathematical model has been evolving via differential equations. The differential equations are renovated in the dimensionless form of ordinary differential equations using the appropriate transformations. The numerical results have been developed employing numerical techniques on the ordinary differential equations. The impact of involving physical factors on velocity, induced magneto hydrodynamic, and temperature function is debated in graphical and tabular form. The velocity profile is boosted by thicker momentum boundary layers, which are caused by higher values of the magnetic field factor. So, the fluid flow becomes higher velocity due to enlarging values of the magnetic field factor. Heat transfer factor and friction at surface factor boosted up for increment of [Formula: see text] (Magnetic field factor). The [Formula: see text](Magnetic field factor) is larger which better-quality of heat transfer at surface and also offered the results of friction factor boosting up in both cases of stretching sheet/cylinder. The [Formula: see text](Magnetic Prandtl number) increased which provided better-quality of heat transfer at surface.}, }
@article {pmid37741030, year = {2023}, author = {Wang, Z and Sedighi, M}, title = {Dispersion properties of nanoplastic spheres in granular media at low Reynolds numbers.}, journal = {Journal of contaminant hydrology}, volume = {259}, number = {}, pages = {104244}, doi = {10.1016/j.jconhyd.2023.104244}, pmid = {37741030}, issn = {1873-6009}, mesh = {*Microplastics ; *Plastics ; Soil ; Rivers ; Water ; }, abstract = {Nanoplastic particles (<1 μm) are among the contaminants of emerging concern, and compared to microplastic (<5 mm), our understanding of the transport and fate of nanoplastic in water, sediments and soil is very limited. This paper focuses on developing fundamental insight into the dispersion behaviour (sum of hydrodynamic dispersion and diffusion) of nanoplastic spheres, which are likely the most mobile shape of nanoplastic. We measured the dispersion coefficient and dispersivity of nanoplastic spheres (100 nm, 300 nm and 1000 nm diameter) in granular media with a range of pore sizes. We investigated the mechanisms that control the behaviour at low Reynolds number (smaller than 2), relevant to the dispersion of nanoplastic across the riparian area at water velocities of the common river and shallow groundwater. The measured dispersion coefficients were compared with the predictions by two commonly used models. The results show that there are significant differences between measurements and predictions for the case of colloidal size nanoplastics (MAPE>100%). The retarded dispersion caused by the size-exclusion effect was observed to be important in the case of 1.7 mm and 0.4 mm granular media for 300 nm and 1000 nm nanoplastics, reducing the dispersivity and sensitivity to Reynolds number. The methodology in this paper can be adopted in studies on other sizes and shapes of nanoplastic, assisting with predicting the transport and fate of nanoplastic granular media.}, }
@article {pmid37723692, year = {2023}, author = {Mamori, H and Nabae, Y and Fukuda, S and Gotoda, H}, title = {Dynamic state of low-Reynolds-number turbulent channel flow.}, journal = {Physical review. E}, volume = {108}, number = {2-2}, pages = {025105}, doi = {10.1103/PhysRevE.108.025105}, pmid = {37723692}, issn = {2470-0053}, abstract = {We numerically study the dynamic state of a low-Reynolds-number turbulent channel flow from the viewpoints of symbolic dynamics and nonlinear forecasting. A low-dimensionally (high-dimensionally) chaotic state of the streamwise velocity fluctuations emerges at a viscous sublayer (logarithmic layer). The possible presence of the chaotic states is clearly identified by orbital instability-based nonlinear forecasting and ordinal partition transition network entropy in combination with the surrogate data method.}, }
@article {pmid37690262, year = {2023}, author = {Dong, B and Guo, Y and Yang, J and Yang, X and Wang, L and Huang, D}, title = {Turbulence induced shear controllable synthesis of nano FePO4 irregularly-shaped particles in a counter impinging jet flow T-junction reactor assisted by ultrasound irradiation.}, journal = {Ultrasonics sonochemistry}, volume = {99}, number = {}, pages = {106590}, pmid = {37690262}, issn = {1873-2828}, abstract = {FePO4 (FP) particles with a mesoporous structure amalgamated by nanoscale primary crystals were controllably prepared using an ultrasound-intensified turbulence T-junction microreactor (UTISR). The use of this type of reaction system can effectively enhance the micro-mixing and remarkably improve the mass transfer and chemical reaction rates. Consequently, the synergistic effects of the impinging streams and ultrasonic irradiation on the formation of mesoporous structure of FP nanoparticles have been systematically investigated through experimental validation and CFD simulation. The results revealed that the FP particles with a mesoporous structure can be well synthesised by precisely controlling the operation parameters by applying ultrasound irradiation with the input power in the range of 0-900 W and the impinging stream volumetric flow rate in the range of 17.15-257.22 mL·min[-1]. The findings obtained from the experimental observation and CFD modelling has clearly indicated that there exists a strong correlation between the particle size, morphology, and the local turbulence shear. The application of ultrasonic irradiation can effectively intensify the local turbulence shear in the reactor even at low Reynolds number based on the impinging stream diameter (Re < 2000), leading to an effective reduction in the particle size (from 273.48 to 56.1 nm) and an increase in the specific surface area (from 21.97 to 114.97 m[2]·g[-1]) of FP samples. The FPirregularly-shaped particles prepared by UTISR exhibited a mesoporous structure with a particle size of 56.10 nm, a specific surface area of 114.97 m[2]·g[-1]and a total pore adsorption volume of 0.570 cm[3]·g[-1] when the volumetric flow rate and ultrasound power are 85.74 mL·min[-1]and 600 W, respectively.}, }
@article {pmid37689862, year = {2023}, author = {Fuciños, C and Rodríguez-Sanz, A and García-Caamaño, E and Gerbino, E and Torrado, A and Gómez-Zavaglia, A and Rúa, ML}, title = {Microfluidics potential for developing food-grade microstructures through emulsification processes and their application.}, journal = {Food research international (Ottawa, Ont.)}, volume = {172}, number = {}, pages = {113086}, doi = {10.1016/j.foodres.2023.113086}, pmid = {37689862}, issn = {1873-7145}, mesh = {*Microfluidics ; *Biological Assay ; Biological Availability ; Food ; Gastrointestinal Tract ; Liposomes ; }, abstract = {The food sector continues to face challenges in developing techniques to increase the bioavailability of bioactive chemicals. Utilising microstructures capable of encapsulating diverse compounds has been proposed as a technological solution for their transport both in food and into the gastrointestinal tract. The present review discusses the primary elements that influence the emulsification process in microfluidic systems to form different microstructures for food applications. In microfluidic systems, reactions occur within small reaction channels (1-1000 μm), using small amounts of samples and reactants, ca. 102-103 times less than conventional assays. This geometry provides several advantages for emulsion and encapsulating structure production, like less waste generation, lower cost and gentle assays. Also, from a food application perspective, it allows the decrease in particle dispersion, resulting in a highly repeatable and efficient synthesis method that also improves the palatability of the food products into which the encapsulates are incorporated. However, it also entails some particular requirements. It is important to obtain a low Reynolds number (Re < approx. 250) for greater precision in droplet formation. Also, microfluidics requires fluid viscosity typically between 0.3 and 1400 mPa s at 20 °C. So, it is a challenge to find food-grade fluids that can operate at the micro-scale of these systems. Microfluidic systems can be used to synthesise different food-grade microstructures: microemulsions, solid lipid microparticles, microgels, or self-assembled structures like liposomes, niosomes, or polymersomes. Besides, microfluidics is particularly useful for accurately encapsulating bacterial cells to control their delivery and release on the action site. However, despite the significant advancement in these systems' development over the past several years, developing and implementing these systems on an industrial scale remains challenging for the food industry.}, }
@article {pmid37676785, year = {2023}, author = {Giurgiu, V and Caridi, GCA and Alipour, M and De Paoli, M and Soldati, A}, title = {The TU Wien Turbulent Water Channel: Flow control loop and three-dimensional reconstruction of anisotropic particle dynamics.}, journal = {The Review of scientific instruments}, volume = {94}, number = {9}, pages = {}, doi = {10.1063/5.0157490}, pmid = {37676785}, issn = {1089-7623}, abstract = {A horizontal water channel facility was built to study particle dynamics in a turbulent flow. The channel is sufficiently long to produce fully developed turbulence at the test section, and the width-to-height ratio is sufficiently large to avoid the sidewall effect for a large proportion of the cross-section. The system was designed to study the dynamics of complex-shaped particles in wall-bounded turbulence, the characteristics of which can be finely controlled. A maximum bulk velocity of up to 0.8 m s-1 can be achieved, corresponding to a bulk Reynolds number of up to 7 × 104 (shear Reynolds number ≈1580), and flow parameters can be controlled within ±0.1%. The transparent channel design and aluminum structures allow easy optical access, which enables multiple laser and camera arrangements. With the current optical setup, a measurement volume of up to 54 × 14 × 54 mm3 can be imaged and reconstructed with six cameras from the top, bottom, and sides of the channel. Finally, the in-house developed reconstruction and tracking procedure allows us to measure the full motion of complex objects (i.e., shape reconstruction, translational, and rotational motions), and in this instance, it is applied to the case of microscopic, non-isotropic polyamide fibers.}, }
@article {pmid37663493, year = {2023}, author = {Zheng, Y and Min, F and Zhu, H}, title = {Study on the Classification Performance of a Novel Wide-Neck Classifier.}, journal = {ACS omega}, volume = {8}, number = {34}, pages = {31237-31245}, pmid = {37663493}, issn = {2470-1343}, abstract = {A novelty-designed wide-neck classifier (WNC) was proposed to enhance the passing ability and classification efficiency of fine particles. Using computational fluid dynamics (CFD), we studied the flow field and velocity distribution in the newly designed WNC. The velocity of the fluid gradually decreased from the wall to the center and from the cylinder to the cone, which facilitates particle classification and thickening. The Reynolds number (Re) and turbulent intensity (I) inside the WNC were discussed. The turbulent intensity increased with increasing feed velocity and overflow outlet diameter and decreased with increasing feed concentration and spigot diameter. The classification of coal slurry was performed to analyze the performance of WNC. The classification efficiency increased with increasing feed velocity but decreased as the feed concentration, spigot diameter, and overflow outlet diameter increased. The predictive models for classification efficiency influenced by the operational and structural parameters were constructed at high correlation coefficients, and the average error of these models was analyzed at 0.28%. Our results can provide valuable insights into the development of mineral classification.}, }
@article {pmid37660186, year = {2023}, author = {Mishra, NK and Sharma, BK and Sharma, P and Muhammad, T and Pérez, LM}, title = {Entropy generation optimization of cilia regulated MHD ternary hybrid Jeffery nanofluid with Arrhenius activation energy and induced magnetic field.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {14483}, pmid = {37660186}, issn = {2045-2322}, support = {SA77210040//Convocatoria Nacional Subvenci&#xf3;n a Instalaci&#xf3;n en la Academia Convocatoria A&#xf1;o 2021/ ; }, abstract = {This study deals with the entropy generation analysis of synthetic cilia using a ternary hybrid nanofluid (Al-Cu-Fe2O3/Blood) flow through an inclined channel. The objective of the current study is to investigate the effects of entropy generation optimization, heat, and mass transfer on ternary hybrid nanofluid passing through an inclined channel in the proximity of the induced magnetic field. The novelty of the current study is present in studying the combined effect of viscous dissipation, thermophoresis, Brownian motion, exponential heat sink/source, porous medium, endothermic-exothermic chemical reactions, and activation energy in the proximity of induced magnetic field is examined. The governing partial differential equations (PDEs) are transformed into the ordinary differential equations (ODEs) using appropriate transformations. Applying the low Reynolds number and the long-wavelength approximation, resultant ODEs are numerically solved using shooting technique via BVP5C in MATLAB. The velocity, temperature, concentration, and induced magnetism profiles are visually discussed and graphically analyzed for various fluid flow parameters. Graphical analysis of physical interest quantities like mass transfer rate, heat transfer rate, entropy generation optimization, and skin friction coefficient are also graphically discussed. The entropy generation improves for enhancing values of Reynolds number, solutal Grashof number, heat sink/source parameter, Brinkman number, magnetic Prandtl number, and endothermic-exothermic reaction parameter while the reverse effect is noticed for chemical reaction and induced magnetic field parameter. The findings of this study can be applied to enhance heat transfer efficiency in biomedical devices, optimizing cooling systems, designing efficient energy conversion processes, and spanning from renewable energy technologies to aerospace propulsion systems.}, }
@article {pmid37659126, year = {2023}, author = {Adeyemi, I and Meribout, M and Khezzar, L and Kharoua, N and AlHammadi, K and Tiwari, V}, title = {Experimental and numerical analysis of the emulsification of oil droplets in water with high frequency focused ultrasound.}, journal = {Ultrasonics sonochemistry}, volume = {99}, number = {}, pages = {106566}, pmid = {37659126}, issn = {1873-2828}, abstract = {Focused high frequency ultrasound emulsification provides significant benefits such as enhanced stability, finer droplets, elevated focal pressure, lowered power usage, minimal surfactant usage and improved dispersion. Hence, in this study, the high frequency focused ultrasound emulsification of oil droplets in water was investigated through experiments and numerical modeling. The effect of transducer power (74-400 W), frequency (1.1 and 3.3 MHz), oil viscosity (10.6-512 mPas), interfacial tension (25-250 mN/m) and initial droplet radius (10-750 µm) on the emulsification process was assessed. In addition, the mechanism of droplet break-up was examined. The experiments showed that the acoustic pressure increased from 9.01 MPa to 26.24 MPa as the power was raised from 74 W to 400 W. At 74 W, the Weber number (We) at the surface and focal zone are 0.5 and 939.8, respectively. However, at 400 W, the We at the transducer surface and focal region reached 2.7 and 6451.8, respectively. Thus, bulb-like and weak catastrophic break up dominates the emulsification at 74 W. The catastrophic break up at 400 W is more vigorous because the ultrasound disruptive stress and We are higher. The time for the catastrophic dispersion of a single droplet at We = 939.8 and We = 6451.8 are 1.01 ms and 0.45 ms, respectively. The numerical model gives reasonable prediction of the trend and magnitude of the experimental acoustic pressure data. The surface and focal pressure amplitudes were estimated with errors of ∼ 6.5% and ∼ 10%, respectively. The predicted Reynolds number (Re) between 74 and 400 W were 8442 and 21364, respectively. The acoustic pressure at the focal region were ∼ 26 MPa and ∼ 69 MPa at frequencies of 1.1 MHz and 3.3 MHz, respectively. Moreover, the acoustic velocities were ∼ 16 m/s and ∼ 42 m/s at 1.1 MHz and 3.3 MHz, respectively. Hence, smaller droplets could be attained at higher frequency excitation under intense catastrophic modes. The Ohnesorge number (Oh) increased from 0.062 to 3.12 with the viscosity between 10.6 mPas and 530 mPas. However, the We remained constant at 856.14 for the studied range. Generally, higher critical We is required for the different breakup stages as the viscosity ratio is elevated. Moreover, the We increased from 25.68 to 1284.22 as the droplet radius was elevated from 15 to 750 µm. Larger droplets allow for higher possibility and intensity of breakup due to diminished viscous and interfacial resistance.}, }
@article {pmid37655637, year = {2023}, author = {Gladman, NW and Askew, GN}, title = {The hydrodynamics of jet propulsion swimming in hatchling and juvenile European common cuttlefish, Sepia officinalis.}, journal = {The Journal of experimental biology}, volume = {226}, number = {18}, pages = {}, pmid = {37655637}, issn = {1477-9145}, mesh = {Animals ; *Decapodiformes ; Swimming ; *Sepia ; Hydrodynamics ; Biomechanical Phenomena ; }, abstract = {Cuttlefish swim using jet propulsion, taking a small volume of fluid into the mantle cavity before it is expelled through the siphon to generate thrust. Jet propulsion swimming has been shown to be more metabolically expensive than undulatory swimming, which has been suggested to be due to the lower efficiency of jet propulsion. The whole-cycle propulsive efficiency of cephalopod molluscs ranges from 38 to 76%, indicating that in some instances jet propulsion can be relatively efficient. Here, we determined the hydrodynamics of hatchling and juvenile cuttlefish during jet propulsion swimming to understand the characteristics of their jets, and whether their whole-cycle propulsive efficiency changes during development. Cuttlefish were found to utilise two jet types: isolated jet vortices (termed jet mode I) and elongated jets (leading edge vortex ring followed by a trailing jet; termed jet mode II). The use of these jet modes differed between the age classes, with newly hatched animals nearly exclusively utilising mode I jets, while juveniles showed no strong preferences. Whole-cycle propulsive efficiency was found to be high, ranging from 72 to 80%, and did not differ between age classes. During development, Strouhal number decreased as Reynolds number increased, which is consistent with animals adjusting their jetting behaviour in order to maximise whole-cycle propulsive efficiency and locomotor performance. Although jet propulsion swimming can have a relatively high energetic cost, in cuttlefish and nautilus, both neutrally buoyant species, the whole-cycle propulsive efficiency is actually relatively high.}, }
@article {pmid37651341, year = {2023}, author = {Sun, B and Zheng, W and Tong, A and Di, D and Li, Z}, title = {Prediction of the roughness coefficient for drainage pipelines with sediments using GA-BPNN.}, journal = {Water science and technology : a journal of the International Association on Water Pollution Research}, volume = {88}, number = {4}, pages = {1111-1130}, doi = {10.2166/wst.2023.249}, pmid = {37651341}, issn = {0273-1223}, mesh = {*Neural Networks, Computer ; *Drainage, Sanitary ; }, abstract = {Accurate prediction of the roughness coefficient of sediment-containing drainage pipes can help engineers optimize urban drainage systems. In this paper, the variation of the roughness coefficient of circular drainage pipes containing different thicknesses of sediments under different flows and slopes was studied by experimental measurements. Back Propagation Neural Network (BPNN) and Genetic Algorithm-Back Propagation Neural Network (GA-BPNN) were used to predict the roughness coefficient. To explore the potential of artificial neural networks to predict the roughness coefficient, a formula based on drag segmentation was established to calculate the roughness coefficient. The results show that the variation trend of the roughness coefficient with flow, hydraulic radius, and Reynolds number is consistent. With the increase of the three parameters, the roughness coefficient decreases overall. Compared to the traditional empirical formula, the BPNN model and the GA-BPNN model increased the determination factors in the testing stage by 3.47 and 3.99%, respectively, and reduced the mean absolute errors by 41.18 and 47.06%, respectively. The study provides an intelligent method for accurate prediction of sediment-containing drainage pipes roughness coefficient.}, }
@article {pmid37646074, year = {2023}, author = {Pandian, SK and Broom, M and Balzan, M and Willmott, GR}, title = {Influence of rheology and micropatterns on spreading, retraction and fingering of an impacting drop.}, journal = {Soft matter}, volume = {19}, number = {35}, pages = {6784-6796}, doi = {10.1039/d3sm00944k}, pmid = {37646074}, issn = {1744-6848}, abstract = {Rheology and surface microstructure affect many drop impact processes, including in emerging printing and patterning applications. This study reports on experiments systematically addressing the influence of these parameters on drop impacts. The experiments involved drop impacts of water, glycerol, and shear-thinning carbopol solutions on ten different microstructured surfaces, captured using high-speed photography. The impact Weber number (We) was varied from 70 to 350, and the microstructures consisted of 20 μm wide pillars with circular and square cross sections arranged in square arrays. The data focus on maximum spreading, retraction rates, threshold conditions for asymmetric (non-circular) spreading, and fingers protruding from the spreading rim. The extent of spreading was reduced by the presence of micropillars, and was well-explained using a hybrid scaling model. The drop retraction rate ((?)) showed moderate agreement with the inertial regime scaling (?) ∝ We[-0.50], but did decrease with effective viscosity. Retraction was slower when the contact line was pinned on surfaces that were flat or had relatively tall or closely-spaced pillars, and was disrupted by drop break-up at We ≳ 250 for low-viscosity fluids. Impact velocities at the onset of asymmetric spreading had weak dependence on viscosity. Fingers were more numerous for greater We, lower effective viscosity, lower pillar height, and for pillars with square cross-sections. Fingers were favoured in directions parallel to the rows of the pillar array, especially near the onset of finger formation. Consistent comparisons between Newtonian and non-Newtonian fluids were enabled by calculating an effective Reynolds number.}, }
@article {pmid37631640, year = {2023}, author = {Gao, S and Rui, X and Zeng, X and Zhou, J}, title = {EWOD Chip with Micro-Barrier Electrode for Simultaneous Enhanced Mixing during Transportation.}, journal = {Sensors (Basel, Switzerland)}, volume = {23}, number = {16}, pages = {}, pmid = {37631640}, issn = {1424-8220}, support = {62274039//The National Natural Science Foundation of China/ ; }, abstract = {Digital microfluidic platforms have been extensively studied in biology. However, achieving efficient mixing of macromolecules in microscale, low Reynolds number fluids remains a major challenge. To address this challenge, this study presents a novel design solution based on dielectric electro-wetting (EWOD) by optimizing the geometry of the transport electrode. The new design integrates micro-barriers on the electrodes to generate vortex currents that promote mixing during droplet transport. This design solution requires only two activation signals, minimizing the number of pins required. The mixing performance of the new design was evaluated by analyzing the degree of mixing inside the droplet and quantifying the motion of the internal particles. In addition, the rapid mixing capability of the new platform was demonstrated by successfully mixing the sorbitol solution with the detection solution and detecting the resulting reaction products. The experimental results show that the transfer electrode with a micro-barrier enables rapid mixing of liquids with a six-fold increase in mixing efficiency, making it ideal for the development of EWOD devices.}, }
@article {pmid37630135, year = {2023}, author = {Fu, Q and Liu, Z and Cao, S and Wang, Z and Liu, G}, title = {Topology-Optimized Micromixer Design with Enhanced Reverse Flow to Increase Mixing Efficiency.}, journal = {Micromachines}, volume = {14}, number = {8}, pages = {}, pmid = {37630135}, issn = {2072-666X}, abstract = {In this work, a serpentine mixing unit model based on topology optimization is proposed to enhance the reverse flow in both horizontal and vertical directions. The increase in reverse flow in both directions can enhance the chaotic advection phenomenon, leading to a rapid increase in the mixing index. The proposed mixing unit model is applied in a T-shaped micromixer to create a new micromixer design, named TOD. Numerical simulations of TOD are performed using Comsol Multiphysics software to analyze the characteristics of the liquid flow, mixing surface, and pressure drop. The simulation results confirm that TOD has an outstanding mixing performance. By widening the surface area of contact and enhancing the chaotic advection phenomenon, TOD shows an excellent mixing performance at both a high and low Reynolds number, making it a promising micromixer design. For Re > 5, the mixing indexes of TOD are all beyond 90%.}, }
@article {pmid37630030, year = {2023}, author = {Knüppel, F and Sun, A and Wurm, FH and Hussong, J and Torner, B}, title = {Effect of Particle Migration on the Stress Field in Microfluidic Flows of Blood Analog Fluids at High Reynolds Numbers.}, journal = {Micromachines}, volume = {14}, number = {8}, pages = {}, pmid = {37630030}, issn = {2072-666X}, support = {469384587//Deutsche Forschungsgemeinschaft/ ; }, abstract = {In the present paper, we investigate how the reductions in shear stresses and pressure losses in microfluidic gaps are directly linked to the local characteristics of cell-free layers (CFLs) at channel Reynolds numbers relevant to ventricular assist device (VAD) applications. For this, detailed studies of local particle distributions of a particulate blood analog fluid are combined with wall shear stress and pressure loss measurements in two complementary set-ups with identical flow geometry, bulk Reynolds numbers and particle Reynolds numbers. For all investigated particle volume fractions of up to 5%, reductions in the stress and pressure loss were measured in comparison to a flow of an equivalent homogeneous fluid (without particles). We could explain this due to the formation of a CFL ranging from 10 to 20 μm. Variations in the channel Reynolds number between Re = 50 and 150 did not lead to measurable changes in CFL heights or stress reductions for all investigated particle volume fractions. These measurements were used to describe the complete chain of how CFL formation leads to a stress reduction, which reduces the apparent viscosity of the suspension and results in the Fåhræus-Lindqvist effect. This chain of causes was investigated for the first time for flows with high Reynolds numbers (Re∼100), representing a flow regime which can be found in the narrow gaps of a VAD.}, }
@article {pmid37622989, year = {2023}, author = {Gojon, R and Parisot-Dupuis, H and Mellot, B and Jardin, T}, title = {Aeroacoustic radiation of low Reynolds number rotors in interaction with beams.}, journal = {The Journal of the Acoustical Society of America}, volume = {154}, number = {2}, pages = {1248-1260}, doi = {10.1121/10.0020672}, pmid = {37622989}, issn = {1520-8524}, abstract = {The radiation characteristics of rotor-beam interaction noise are studied experimentally for low Reynolds number small-scale rotors in interaction with beams of different shapes, sizes, and downstream positions. The number of blades ranges from two to four. For the two-bladed rotor, the presence of the beam has no effect on the mean aerodynamic performance. Moreover, the blade passing frequency (BPF) and the high frequency broadband noise (BBN) appear not to be affected by the presence of the beam. On the contrary, the magnitude of the 2×BPF-25×BPF harmonics increases up to 30 dB compared to the case without beam, with an envelope consisting of two humps: one centered around 5×BPF and another around 20×BPF-25×BPF. For the first hump, a dipole-like pattern with minimal amplitude aligned with the beam can be observed, whereas another dipole-like pattern is observed for the higher frequency hump, but with a minimal amplitude over all the rotor disk plane. Compared to the two-bladed rotor, the presence of the beam has an effect on the mean aerodynamic performance of the three- and four-bladed rotors, increasing both the torque and the thrust at iso-rotational speed. This change leads to a change in the directivity of the BPF tone that decreases at a latitude angle of θ=0° and increases at a latitude angle of θ=40°. Moreover, the same two competing humps are observed on the BPF harmonics envelope. Interestingly, the frequency range over which an amplification of the harmonic magnitude is observed seems not to be influenced by the number of blades. Finally, the magnitude of the low frequency hump increases with the beam diameter, the rotational speed, and the number of blades but decreases with the rotor-beam distance. That of the high frequency hump increases also with the rotational speed and the number of blades, but not anymore with the beam diameter, and reaches a maximum value when the rotor-beam distance is at an intermediate distance of L = 25 mm. This hump is also influenced, to a lesser extent, by the shape of the beam. The two different evolutions permit us to conclude that the noise generation mechanisms leading to the two humps must be different. Scaling laws of the acoustical energy are derived for all those parameters. As already done for previous experiments without beam, all of the results are made available as an open database, at https://dataverse.isae-supaero.fr/.}, }
@article {pmid37611057, year = {2023}, author = {Cui, Z and Wang, Y and Zhang, S and Wang, T and den Toonder, JMJ}, title = {Miniaturized metachronal magnetic artificial cilia.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {120}, number = {35}, pages = {e2304519120}, pmid = {37611057}, issn = {1091-6490}, mesh = {*Cilia ; Physical Phenomena ; Motion ; Cell Membrane ; *Magnetic Fields ; }, abstract = {Biological cilia, hairlike organelles on cell surfaces, often exhibit collective wavelike motion known as metachrony, which helps generating fluid flow. Inspired by nature, researchers have developed artificial cilia as microfluidic actuators, exploring several methods to mimic the metachrony. However, reported methods are difficult to miniaturize because they require either control of individual cilia properties or the generation of a complex external magnetic field. We introduce a concept that generates metachronal motion of magnetic artificial cilia (MAC), even though the MAC are all identical, and the applied external magnetic field is uniform. This is achieved by integrating a paramagnetic substructure in the substrate underneath the MAC. Uniquely, we can create both symplectic and antiplectic metachrony by changing the relative positions of MAC and substructure. We demonstrate the flow generation of the two metachronal motions in both high and low Reynolds number conditions. Our research marks a significant milestone by breaking the size limitation barrier in metachronal artificial cilia. This achievement not only showcases the potential of nature-inspired engineering but also opens up a host of exciting opportunities for designing and optimizing microsystems with enhanced fluid manipulation capabilities.}, }
@article {pmid37607926, year = {2023}, author = {Barbhuiya, NH and Yodh, AG and Mishra, CK}, title = {Direction-dependent dynamics of colloidal particle pairs and the Stokes-Einstein relation in quasi-two-dimensional fluids.}, journal = {Nature communications}, volume = {14}, number = {1}, pages = {5109}, pmid = {37607926}, issn = {2041-1723}, abstract = {Hydrodynamic interactions are important for diverse fluids, especially those with low Reynolds number such as microbial and particle-laden suspensions, and proteins diffusing in membranes. Unfortunately, while far-field (asymptotic) hydrodynamic interactions are fully understood in two- and three-dimensions, near-field interactions are not, and thus our understanding of motions in dense fluid suspensions is still lacking. In this contribution, we experimentally explore the hydrodynamic correlations between particles in quasi-two-dimensional colloidal fluids in the near-field. Surprisingly, the measured displacement and relaxation of particle pairs in the body frame exhibit direction-dependent dynamics that can be connected quantitatively to the measured near-field hydrodynamic interactions. These findings, in turn, suggest a mechanism for how and when hydrodynamics can lead to a breakdown of the ubiquitous Stokes-Einstein relation (SER). We observe this breakdown, and we show that the direction-dependent breakdown of the SER is ameliorated along directions where hydrodynamic correlations are smallest. In total, the work uncovers significant ramifications of near-field hydrodynamics on transport and dynamic restructuring of fluids in two-dimensions.}, }
@article {pmid37595246, year = {2023}, author = {Bätge, T and Fouxon, I and Wilczek, M}, title = {Quantitative Prediction of Sling Events in Turbulence at High Reynolds Numbers.}, journal = {Physical review letters}, volume = {131}, number = {5}, pages = {054001}, doi = {10.1103/PhysRevLett.131.054001}, pmid = {37595246}, issn = {1079-7114}, abstract = {Collisional growth of droplets, such as occurring in warm clouds, is known to be significantly enhanced by turbulence. Whether particles collide depends on their flow history, in particular on their encounters with highly intermittent small-scale turbulent structures, which despite their rarity can dominate the overall collision rate. Here, we develop a quantitative criterion for sling events based on the velocity gradient history along particle paths. We show by a combination of theory and simulations that the problem reduces to a one-dimensional localization problem as encountered in condensed matter physics. The reduction demonstrates that the creation of slings is controlled by the minimal real eigenvalue of the velocity gradient tensor. We use fully resolved turbulence simulations to confirm our predictions and study their Stokes and Reynolds number dependence. We also discuss extrapolations to the parameter range relevant for typical cloud droplets, showing that sling events at high Reynolds numbers are enhanced by an order of magnitude for small Stokes numbers. Thus, intermittency could be a significant ingredient in the collisional growth of rain droplets.}, }
@article {pmid37585463, year = {2023}, author = {Tian, Y and Woodward, M and Stepanov, M and Fryer, C and Hyett, C and Livescu, D and Chertkov, M}, title = {Lagrangian large eddy simulations via physics-informed machine learning.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {120}, number = {34}, pages = {e2213638120}, pmid = {37585463}, issn = {1091-6490}, support = {20180059DR//DOE | NNSA | LDRD | Los Alamos National Laboratory (LANL)/ ; }, abstract = {High-Reynolds number homogeneous isotropic turbulence (HIT) is fully described within the Navier-Stokes (NS) equations, which are notoriously difficult to solve numerically. Engineers, interested primarily in describing turbulence at a reduced range of resolved scales, have designed heuristics, known as large eddy simulation (LES). LES is described in terms of the temporally evolving Eulerian velocity field defined over a spatial grid with the mean-spacing correspondent to the resolved scale. This classic Eulerian LES depends on assumptions about effects of subgrid scales on the resolved scales. Here, we take an alternative approach and design LES heuristics stated in terms of Lagrangian particles moving with the flow. Our Lagrangian LES, thus L-LES, is described by equations generalizing the weakly compressible smoothed particle hydrodynamics formulation with extended parametric and functional freedom, which is then resolved via Machine Learning training on Lagrangian data from direct numerical simulations of the NS equations. The L-LES model includes physics-informed parameterization and functional form, by combining physics-based parameters and physics-inspired Neural Networks to describe the evolution of turbulence within the resolved range of scales. The subgrid-scale contributions are modeled separately with physical constraints to account for the effects from unresolved scales. We build the resulting model under the differentiable programming framework to facilitate efficient training. We experiment with loss functions of different types, including physics-informed ones accounting for statistics of Lagrangian particles. We show that our L-LES model is capable of reproducing Eulerian and unique Lagrangian turbulence structures and statistics over a range of turbulent Mach numbers.}, }
@article {pmid37583155, year = {2023}, author = {Keirsbulck, L and Cadot, O and Basley, J and Lippert, M}, title = {Base suction, entrainment flux, and wake modes in the vortex formation region at the rear of a three-dimensional blunt bluff body.}, journal = {Physical review. E}, volume = {108}, number = {1-2}, pages = {015101}, doi = {10.1103/PhysRevE.108.015101}, pmid = {37583155}, issn = {2470-0053}, abstract = {A slitted base cavity of constant depth with a varying filling ratio 0≤R_{f}≤100% is experimentally investigated to reduce the form drag of a three-dimensional blunt body (the so-called squareback Ahmed body) at a Reynolds number Re=2.89×10^{5}. The drag reduction is achieved by a decrease of base suction (or, equivalently, the increase of pressure at the base). The plain cavity (R_{f}=100%) reduces the base suction by 22% compared to the case with no cavity (R_{f}=0). All intermediate filling ratio are obtained by the enlargement of the slits, initially having a zero width for the plain cavity case. It is shown that the gradual base suction change can be related to the level of the entrainment flux of the free shear layers developing from the rear separation and to the suppression of the transverse steady asymmetric instability of the wake. The model of the vortex formation region length of Gerrard [J. Fluid Mech. 25, 401 (1966)0022-112010.1017/S0022112066001721] is shown to provide an insightful interpretation of the drag reduction mechanism using ventilated base cavities.}, }
@article {pmid37583143, year = {2023}, author = {Maji, M and Eswaran, KS and Ghosh, S and Seshasayanan, K and Shukla, V}, title = {Equivalence of nonequilibrium ensembles: Two-dimensional turbulence with a dual cascade.}, journal = {Physical review. E}, volume = {108}, number = {1-2}, pages = {015102}, doi = {10.1103/PhysRevE.108.015102}, pmid = {37583143}, issn = {2470-0053}, abstract = {We examine the conjecture of equivalence of nonequilibrium ensembles for turbulent flows in two dimensions in a dual-cascade setup. We construct a formally time-reversible Navier-Stokes equation in two dimensions by imposing global constraints of energy and enstrophy conservation. A comparative study of the statistical properties of its solutions with those obtained from the standard Navier-Stokes equations clearly shows that a formally time-reversible system is able to reproduce the features of a two-dimensional turbulent flow. Statistical quantities based on one- and two-point measurements show an excellent agreement between the two systems for the inverse- and direct-cascade regions. Moreover, we find that the conjecture holds very well for two-dimensional turbulent flows with both conserved energy and enstrophy at finite Reynolds number.}, }
@article {pmid37576259, year = {2023}, author = {Uwadoka, O and Adelaja, AO and Olakoyejo, OT and Fadipe, OL and Efe, S}, title = {Numerical study of heat transfer, pressure drop and entropy production characteristics in inclined heat exchangers with uniform heat flux using mango bark/CO2 nanofluid.}, journal = {Heliyon}, volume = {9}, number = {8}, pages = {e18694}, pmid = {37576259}, issn = {2405-8440}, abstract = {For sustainable low-carbon cities, using sustainable urban energy system solutions is imperative. CO2-based bionanofluid is one proposed energy system solution that is sustainable and environmentally friendly. This paper examines the thermal-hydraulic and entropy production properties of mango bark/CO2 nanofluid for industrial-inclined gas cooling applications. The influence of gravitational force (in terms of tube inclination angle), volume fraction, and Reynolds number on the heat transfer, pressure drop, and entropy production of CO2-based mango bark nanofluids in laminar flow through a circular aluminum tube are numerically studied. The bionanofluid flows through a tube with an inner radius of 2.25 mm, a length of 970.0 mm, and an initial temperature of 320.0 K. A constant heat flux of -10.0 W/m[2] is applied to the flow at its walls. The laminar flow regime with Reynolds numbers of 100, 400, 700, and 1000 are subjected to flow inclinations of ±90°, ±60°, ±45°, ±30°, and 0° and bionanofluid volume fractions of 0.5%, 1.0%, and 2.0%. Results show that ±45° tube inclination angle offers the optimal heat transfer coefficient, maximum pressure drop, and minimum total entropy production rates for Re > 100; however, for Re = 100, these occur at the inclination angle of -30° and +60°. The pressure drop shows less sensitivity to the inclination angle; however, it offers peak values at the same inclination angles as the heat transfer coefficient for the respective Reynolds number values. The maximum thermal enhancements due to gravitational effect are 42%, 93.98%, 121.28%, and 150% for Reynolds numbers of 100, 400, 700, and 1000, respectively, while that due to nanofluid volume fraction are less than 16%.}, }
@article {pmid37567889, year = {2023}, author = {Mohamed, RA and Abo-Dahab, SM and Abd-Alla, AM and Soliman, MS}, title = {Magnetohydrodynamic double-diffusive peristaltic flow of radiating fourth-grade nanofluid through a porous medium with viscous dissipation and heat generation/absorption.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {13096}, pmid = {37567889}, issn = {2045-2322}, abstract = {This article focuses on determining how to double diffusion affects the non-Newtonian fourth-grade nanofluids peristaltic motion within a symmetrical vertical elastic channel supported by a suitable porous medium as well as, concentrating on the impact of a few significant actual peculiarities on the development of the peristaltic liquid, such as rotation, initial pressure, non-linear thermal radiation, heat generation/absorption in the presence of viscous dissipation and joule heating with noting that the fluid inside the channel is subject to an externally induced magnetic field, giving it electromagnetic properties. Moreover, the constraints of the long-wavelength approximation and neglecting the wave number along with the low Reynolds number have been used to transform the nonlinear partial differential equations in two dimensions into a system of nonlinear ordinary differential equations in one dimension, which serve as the basic governing equations for fluid motion. The suitable numerical method for solving the new system of ordinary differential equations is the Runge-Kutta fourth-order numerical method with the shooting technique using the code MATLAB program. Using this code, a 2D and 3D graphical analysis was done to show how each physical parameter affected the distributions of axial velocity, temperature, nanoparticle volume fraction, solutal concentration, pressure gradients, induced magnetic field, magnetic forces, and finally the trapping phenomenon. Under the influence of rotation [Formula: see text], heat Grashof number [Formula: see text], solutal Grashof number [Formula: see text], and initial stress [Formula: see text], the axial velocity distribution [Formula: see text] changes from increasing to decreasing, according to some of the study's findings. On the other hand, increasing values of nonlinear thermal radiation [Formula: see text] and temperature ratio [Formula: see text] have a negative impact on the temperature distribution [Formula: see text] but a positive impact on the distributions of nanoparticle volume fraction [Formula: see text] and solutal concentration [Formula: see text]. Darcy number [Formula: see text] and mean fluid rate [Formula: see text] also had a positive effect on the distribution of pressure gradients, making it an increasing function.}, }
@article {pmid37535112, year = {2023}, author = {Mounkaila Noma, D and Dagois-Bohy, S and Millet, S and Ben Hadid, H and Botton, V and Henry, D}, title = {Nonlinear evolution of viscoplastic film flows down an inclined plane.}, journal = {The European physical journal. E, Soft matter}, volume = {46}, number = {8}, pages = {68}, pmid = {37535112}, issn = {1292-895X}, abstract = {In this article, we experimentally investigate the nonlinear behaviour of a viscoplastic film flow down an inclined plane. We focus on the nonlinear instabilities that appear as roll waves. Roll waves are generated by perturbing a permanent flow of Herschel-Bulkley fluid (Carbopol 980) at low frequencies. To determine the local thickness of the film, we used a laser sensor and a camera to globally capture the transverse shape of the waves. For a regular forcing, the results show the existence of different regimes. First, we observe primary instabilities below the cut-off frequency at the entrance of the channel. After the exponential growth of the wave in the linear regime, we recognise the nonlinear dynamics with the existence of finite amplitude waves. This finite amplitude depends on the frequency, the Reynolds number and the inclination angle. The results show that this instability is supercritical. At moderate Reynolds numbers, the finite 2-D waves become sensitive to transverse perturbations, due to a secondary instability, and become 3-D waves. The experimental results illustrate a phenomenology of viscoplastic film flows similar to Newtonian fluids, except for the capillary waves.}, }
@article {pmid37519826, year = {2023}, author = {Kechagidis, K and Owen, B and Guillou, L and Tse, H and Di Carlo, D and Krüger, T}, title = {Numerical investigation of the dynamics of a rigid spherical particle in a vortical cross-slot flow at moderate inertia.}, journal = {Microsystems &amp; nanoengineering}, volume = {9}, number = {}, pages = {100}, pmid = {37519826}, issn = {2055-7434}, abstract = {The study of flow and particle dynamics in microfluidic cross-slot channels is of high relevance for lab-on-a-chip applications. In this work, we investigate the dynamics of a rigid spherical particle in a cross-slot junction for a channel height-to-width ratio of 0.6 and at a Reynolds number of 120 for which a steady vortex exists in the junction area. Using an in-house immersed-boundary-lattice-Boltzmann code, we analyse the effect of the entry position of the particle in the junction and the particle size on the dynamics and trajectory shape of the particle. We find that the dynamics of the particle depend strongly on its lateral entry position in the junction and weakly on its vertical entry position; particles that enter close to the centre show trajectory oscillations. Larger particles have longer residence times in the junction and tend to oscillate less due to their confinement. Our work contributes to the understanding of particle dynamics in intersecting flows and enables the design of optimised geometries for cytometry and particle manipulation.}, }
@article {pmid37518499, year = {2023}, author = {Yokoo, H and Yamamoto, M and Matsumoto, T and Yamada, T and Kanda, T}, title = {Study of the reverse transition in pipe flow.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {12333}, pmid = {37518499}, issn = {2045-2322}, abstract = {In the reverse transition in pipe flow, turbulent flow changes to less disturbed laminar flow. The entropy of the flow appears to decrease. This study examined the reverse transition experimentally and theoretically using entropy change and momentum balance models, not in terms of disturbance in the flow. The reverse transition was accomplished by decreasing the Reynolds number. The transitions approximately correlated with local Reynolds numbers. The initial Reynolds number of the transition became larger, and the pressure at low Reynolds numbers was greater than in ordinary pipe flow. These behaviours were caused by turbulent flow in the pipe undergoing a reverse transition. We showed that the entropy did not decrease in the reverse transition by including the entropy due to friction in the development region.}, }
@article {pmid37512786, year = {2023}, author = {Tahir, MT and Anwar, S and Ahmad, N and Sattar, M and Qazi, UW and Ghafoor, U and Bhutta, MR}, title = {Thermal Management of Microelectronic Devices Using Nanofluid with Metal foam Heat Sink.}, journal = {Micromachines}, volume = {14}, number = {7}, pages = {}, pmid = {37512786}, issn = {2072-666X}, support = {2020R1G1A1012741//National Research Foundation of Korea/ ; }, abstract = {Microelectronic components are used in a variety of applications that range from processing units to smart devices. These components are prone to malfunctions at high temperatures exceeding 373 K in the form of heat dissipation. To resolve this issue, in microelectronic components, a cooling system is required. This issue can be better dealt with by using a combination of metal foam, heat sinks, and nanofluids. This study investigates the effect of using a rectangular-finned heat sink integrated with metal foam between the fins, and different water-based nanofluids as the working fluid for cooling purposes. A 3D numerical model of the metal foam with a BCC-unit cell structure is used. Various parameters are analyzed: temperature, pressure drop, overall heat transfer coefficient, Nusselt number, and flow rate. Fluid flows through the metal foam in a turbulent flow with a Reynold's number ranging from 2100 to 6500. The optimum fin height, thickness, spacing, and base thickness for the heat sink are analyzed, and for the metal foam, the material, porosity, and pore density are investigated. In addition, the volume fraction, nanoparticle material, and flow rate for the nanofluid is obtained. The results showed that the use of metal foam enhanced the thermal performance of the heat sink, and nanofluids provided better thermal management than pure water. For both cases, a higher Nusselt number, overall heat transfer coefficient, and better temperature reduction is achieved. CuO nanofluid and high-porosity low-pore-density metal foam provided the optimum results, namely a base temperature of 314 K, compared to 341 K, with a pressure drop of 130 Pa. A trade-off was achieved between the temperature reduction and pumping power, as higher concentrations of nanofluid provided better thermal management and resulted in a large pressure drop.}, }
@article {pmid37512778, year = {2023}, author = {Mihai, I and Suciu, C and Picus, CM}, title = {Assessment of Vapor Formation Rate and Phase Shift between Pressure Gradient and Liquid Velocity in Flat Mini Heat Pipes as a Function of Internal Structure.}, journal = {Micromachines}, volume = {14}, number = {7}, pages = {}, pmid = {37512778}, issn = {2072-666X}, abstract = {Flat mini heat pipes (FMHPs) are often used in cooling systems for various power electronic components, as they rapidly dissipate high heat flux densities. The main objective of the present work is to experimentally investigate whether differences in the rate of vapor formation occur on an internal structure containing trapezoidal microchannels and porous sintered copper powder material. Several parameters, such as hydraulic diameter and fluid velocity through the material, as a function of the internal structure porosity, were determined by calculation for a steady state regime. Reynolds number was determined as a function of porosity, according to Darcy's law, and the Nusselt number was calculated. Since the flow is Darcy-type through the porous medium inside the FMHP, the Darcy friction factor was calculated using five methods: Colebrook, Darcy-Weisbach, Swamee-Jain, Blasius, and Haaland. After experimental tests, it was found that when the porous and trapezoidal microchannel layers are wetted at the same time, the vaporization progresses at a faster rate in the porous material, and the duration of the process is shorter. This recommends the use of such an internal structure in FMHPs since the manufacturing technology is simpler, the materials are cheaper, and the heat flux transport capacity is higher.}, }
@article {pmid37512729, year = {2023}, author = {Ray, DR and Das, DK}, title = {Simulations of Flows via CFD in Microchannels for Characterizing Entrance Region and Developing New Correlations for Hydrodynamic Entrance Length.}, journal = {Micromachines}, volume = {14}, number = {7}, pages = {}, pmid = {37512729}, issn = {2072-666X}, abstract = {Devices with microchannels are relatively new, and many correlations are not yet developed to design them efficiently. In microchannels, the flow regime is primarily laminar, where entrance length may occupy a significant section of the flow channel. Therefore, several computational fluid dynamic simulations were performed in this research to characterize the developing flow regime. The new correlations of entrance length were developed from a vast number of numerical results obtained from these simulations. A three-dimensional laminar flow for 37 Reynolds numbers (0.1, 0.2, …, 1, 2, …, 10, 20, …, 100, 200, …, 1000), primarily in low regime with water flow through six rectangular microchannels (aspect ratio: 1, 0.75, 0.5, 0.25, 0.2, 0.125), has been modeled, conducting 222 simulations to characterize flow developments and ascertain progressive velocity profile shapes. Examination of the fully developed flow condition was considered using traditional criteria such as velocity and incremental pressure drop number. Additionally, a new criterion was presented based on fRe. Numerical results from the present simulations were validated by comparing the fully developed velocity profile, friction factor, and hydrodynamic entrance length for Re > 100 in rectangular channels, for which accurate data are available in the literature. There is a need for hydrodynamic entrance length correlations in a low Reynolds number regime (Re < 100). So, the model was run numerous times to generate a vast amount of numerical data that yielded two new correlations based on the velocity and fRe criteria.}, }
@article {pmid37507561, year = {2023}, author = {Singh, S and Suman, S and Mitra, S and Kumar, M}, title = {Optimization of a novel trapezoidal staggered ribs configuration for enhancement of a solar air heater performance using CFD.}, journal = {Environmental science and pollution research international}, volume = {30}, number = {41}, pages = {93582-93601}, pmid = {37507561}, issn = {1614-7499}, mesh = {*Sunlight ; Hot Temperature ; Ribs ; *Household Articles ; }, abstract = {A novel transverse trapezoidal staggered ribs configuration as artificial roughness is investigated using CFD to understand the fluid flow and heat transfer behaviors for improving the performance of a solar air heater. In addition, experimental validation of Nusselt numbers for smooth duct against CFD results is established. The staggered ribs arrangement outperforms the continuous ribs and insights obtained from the thermal-fluid flow behaviors are further applied to optimize the staggered arrangements of the rib. Reynolds number Re is varied from 5000 to 24,000, and rib parameters are optimized with a special focus on understanding the effects of discontinuous rib width (w) and gap width (g). Two widely studied shapes of rib, namely, cylindrical and rectangular, are also investigated for the transverse staggered arrangement with the same optimized parameters for the comparison of thermo-hydraulic performances. Trapezoidal ribs having discontinuous rib width of 50 mm and gap width of 10 mm give the maximum thermo-hydraulic performance of 1.57 at Reynolds number of 5000. The optimized staggered trapezoidal ribs outperform the staggered cylindrical and rectangular ribs. However, staggered rectangular ribs give the highest increase in the Nusselt number and these may be preferred for application when pressure drop is not of concern.}, }
@article {pmid37506216, year = {2023}, author = {Shinder, II and Johnson, AN and Filla, BJ and Khromchenko, VB and Moldover, MR and Boyd, J and Wright, JD and Stoup, J}, title = {Non-nulling protocols for fast, accurate, 3-D velocity measurements in stacks.}, journal = {Journal of the Air &amp; Waste Management Association (1995)}, volume = {73}, number = {8}, pages = {600-617}, pmid = {37506216}, issn = {2162-2906}, support = {9999-NIST/ImNIST/Intramural NIST DOC/United States ; }, mesh = {*Coal ; Calibration ; *Power Plants ; Environmental Monitoring/methods ; }, abstract = {The authors present protocols for making fast, accurate, 3D velocity measurements in the stacks of coal-fired power plants. The measurements are traceable to internationally-recognized standards; therefore, they provide a rigorous basis for measuring and/or regulating the emissions from stacks. The authors used novel, five-hole, hemispherical, differential-pressure probes optimized for non-nulling (no-probe rotation) measurements. The probes resist plugging from ash and water droplets. Integrating the differential pressures for only 5 seconds determined the axial velocity Va with an expanded relative uncertainty Ur(Va) ≤ 2% of the axial velocity at the probe's location, the flow's pitch (α) and yaw (β) angles with expanded uncertainties U(α) = U(β) = 1 °, and the static pressure ps with Ur(ps) = 0.1% of the static pressure. This accuracy was achieved 1) by calibrating each probe in a wind tunnel at 130, strategically-chosen values of (Va, α, β) spanning the conditions found in the majority of stacks (|α| ≤ 20 °; |β| ≤ 40 °; 4.5 m/s ≤ Va ≤27 m/s), and 2) by using a long-forgotten definition of the pseudo-dynamic pressure that scales with the dynamic pressure. The resulting calibration functions span the probe-diameter Reynolds number range from 7,600 to 45,000.Implications: The continuous emissions monitoring systems (CEMS) that measure the flue gas flow rate in coal-fired power plant smokestacks are calibrated (at least) annually by a velocity profiling method. The stack axial velocity profile is measured by traversing S-type pitot probes (or one of the other EPA-sanctioned pitot probes) across two orthogonal, diametric chords in the stack cross-section. The average area-weighted axial velocity calculated from the pitot traverse quantifies the accuracy of the CEMS flow monitor. Therefore, the flow measurement accuracy of coal-fired power plants greenhouse gas (GHG) emissions depends on the accuracy of pitot probe velocity measurements. Coal-fired power plants overwhelmingly calibrate CEMS flow monitors using S-type pitot probes. Almost always, stack testers measure the velocity without rotating or nulling the probe (i.e., the non-nulling method). These 1D non-nulling velocity measurements take significantly less time than the corresponding 2D nulling measurements (or 3D nulling measurements for other probe types). However, the accuracy of the 1D non-nulling velocity measurements made using S-type probes depends on the pitch and yaw angles of the flow. Measured axial velocities are accurate at pitch and yaw angles near zero, but the accuracy degrades at larger pitch and yaw angles.The authors developed a 5-hole hemispherical pitot probe that accurately measures the velocity vector in coal-fired smokestacks without needing to rotate or null the probe. This non-nulling, 3D probe is designed with large diameter pressure ports to prevent water droplets (or particulates) from obstructing its pressure ports when applied in stack flow measurement applications. This manuscript presents a wind tunnel calibration procedure to determine the non-nulling calibration curves for 1) dynamic pressure; 2) pitch angle; 3) yaw angle; and 4) static pressure. These calibration curves are used to determine axial velocities from 6 m/s to 27 m/s, yaw angles between ±40°, and pitch angles between ±20°. The uncertainties at the 95% confidence limit for axial velocity, yaw angle, and pitch angle are 2% (or less), 1°, and 1°, respectively. Therefore, in contrast to existing EPA-sanctioned probes, the non-nulling hemispherical probe provides fast, low uncertainty velocity measurements independent of the pitch and yaw angles of the stack flow.}, }
@article {pmid37505953, year = {2023}, author = {Küchler, C and Bewley, GP and Bodenschatz, E}, title = {Universal Velocity Statistics in Decaying Turbulence.}, journal = {Physical review letters}, volume = {131}, number = {2}, pages = {024001}, doi = {10.1103/PhysRevLett.131.024001}, pmid = {37505953}, issn = {1079-7114}, abstract = {In turbulent flows, kinetic energy is transferred from large spatial scales to small ones, where it is converted to heat by viscosity. For strong turbulence, i.e., high Reynolds numbers, Kolmogorov conjectured in 1941 that this energy transfer is dominated by inertial forces at intermediate spatial scales. Since Kolmogorov's conjecture, the velocity difference statistics in this so-called inertial range have been expected to follow universal power laws for which theoretical predictions have been refined over the years. Here we present experimental results over an unprecedented range of Reynolds numbers in a well-controlled wind tunnel flow produced in the Max Planck Variable Density Turbulence Tunnel. We find that the measured second-order velocity difference statistics become independent of the Reynolds number, suggesting a universal behavior of decaying turbulence. However, we do not observe power laws even at the highest Reynolds number, i.e., at turbulence levels otherwise only attainable in atmospheric flows. Our results point to a Reynolds number-independent logarithmic correction to the classical power law for decaying turbulence that calls for theoretical understanding.}, }
@article {pmid37501997, year = {2023}, author = {Aich, W and Javid, K and Tag-ElDin, ESM and Ghachem, K and Ullah, I and Iqbal, MA and Khan, SU and Kolsi, L}, title = {Thermal and physical impact of viscoplastic nanoparticles in a complex divergent channel due to peristalsis phenomenon: Heat generation and multiple slip effects.}, journal = {Heliyon}, volume = {9}, number = {7}, pages = {e17644}, pmid = {37501997}, issn = {2405-8440}, abstract = {In the advance studies, researchers have performed productive research contributions in the field of nanofluid mechanics under various biological assumptions. These contributions are fruitful to understand the applications of nanofluids in the various fields such as hybrid-powered engine, heart-diagnose, to prevent numerous diseases, heat exchanger, pharmaceutical processes, etc. The current analysis explores the combined effects of heat generation and chemical reaction on the peristaltic flow of viscoplastic nanofluid through a non-uniform (divergent) channel. The physical effects of second-order velocity slip, thermal slip and mass slip parameters on the rheological characteristics are also considered. To describe non-Newtonian effects, the Casson fluid is deployed. The greater wavelength assumption and low Reynolds number theory are used to attain the rheological equations. Numerical solutions of these governing equations associated with suitable boundary conditions are obtained via Mathematica symbolic software. The velocity magnitude of Casson fluid is higher than associated with Newtonian fluid. Radiation parameter has a vigorous impact in the reduction (enhancement) of temperature (mass concentration) profile. The porous parameter has a remarkable impact in reduction of temperature and velocity profile. Thermal enhancement is perceived by intensifying the chemical reaction parameter, and opposite inclination is noticed in mass concentration. Temperature has been demonstrated to be increased by increasing the Darcy number. The magnitudes of both axial velocity and temperature distribution are smaller in the presence of second-order velocity slip parameters effect as compared with no-slip condition. The magnitudes of axial velocity and mass (or, nanoparticle) concentration are augmented by accumulating the Prandtl number. A rise in Brownian parameter is noticed to depress the mass concentration. The present study has been used in bio-mechanical processes, nanomaterial devices, heat transfer enhancement, radiators, and electronics cooling systems.}, }
@article {pmid37467268, year = {2023}, author = {Buaria, D and Sreenivasan, KR}, title = {Forecasting small-scale dynamics of fluid turbulence using deep neural networks.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {120}, number = {30}, pages = {e2305765120}, pmid = {37467268}, issn = {1091-6490}, abstract = {Turbulence in fluid flows is characterized by a wide range of interacting scales. Since the scale range increases as some power of the flow Reynolds number, a faithful simulation of the entire scale range is prohibitively expensive at high Reynolds numbers. The most expensive aspect concerns the small-scale motions; thus, major emphasis is placed on understanding and modeling them, taking advantage of their putative universality. In this work, using physics-informed deep learning methods, we present a modeling framework to capture and predict the small-scale dynamics of turbulence, via the velocity gradient tensor. The model is based on obtaining functional closures for the pressure Hessian and viscous Laplacian contributions as functions of velocity gradient tensor. This task is accomplished using deep neural networks that are consistent with physical constraints and explicitly incorporate Reynolds number dependence to account for small-scale intermittency. We then utilize a massive direct numerical simulation database, spanning two orders of magnitude in the large-scale Reynolds number, for training and validation. The model learns from low to moderate Reynolds numbers and successfully predicts velocity gradient statistics at both seen and higher (unseen) Reynolds numbers. The success of our present approach demonstrates the viability of deep learning over traditional modeling approaches in capturing and predicting small-scale features of turbulence.}, }
@article {pmid37464695, year = {2023}, author = {Zheng, JL and Liu, YL}, title = {Experimental study on the flow structures and dynamics of turbulent Rayleigh-Bénard convection in an annular cell.}, journal = {Physical review. E}, volume = {107}, number = {6-2}, pages = {065112}, doi = {10.1103/PhysRevE.107.065112}, pmid = {37464695}, issn = {2470-0053}, abstract = {We conduct an experimental study on the flow structures and dynamics of turbulent Rayleigh-Bénard convection in an annular cell with radius ratio η≃0.5 and aspect ratio Γ≃4. The working fluid is water with a Prandtl number of Pr≃5.4, and the Rayleigh number (Ra) ranges from 5.05×10^{7} to 5.05×10^{8}. The multithermal-probe method and the particle image velocimetry technique are employed to measure the temperature profiles and the velocity fields, respectively. Two distinct states with multiroll standing waves are observed, which are the quadrupole state (QS) characterized by a four-roll structure and the sextupole state (SS) by a six-roll structure. The scaling exponents of Reynolds number Re with Ra are different for the two states, which are 0.56 for QS and 0.41 for SS. In addition, the standing waves become unstable upon tilting the cell by 1^{∘} in relation to the horizontal plane, and they evolve into traveling waves. At relatively high Ra, for instance, Ra⩾2.55×10^{8}, it is observed that the traveling wave state SS undergoes a transition to the traveling wave state QS. However, the opposite transition from QS to SS is not observed in our experiments. Our findings provide insights into the flow structures and dynamics in the convection flow with rotation symmetry.}, }
@article {pmid37455389, year = {2023}, author = {Zhang, T and Inglis, DW and Ngo, L and Wang, Y and Hosokawa, Y and Yalikun, Y and Li, M}, title = {Inertial Separation of Particles Assisted by Symmetrical Sheath Flows in a Straight Microchannel.}, journal = {Analytical chemistry}, volume = {95}, number = {29}, pages = {11132-11140}, doi = {10.1021/acs.analchem.3c02089}, pmid = {37455389}, issn = {1520-6882}, abstract = {Over the past two decades, inertial microfluidics, which works at an intermediate range of Reynolds number (∼1 < Re < ∼100), has been widely used for particle separation due to its high-throughput and label-free features. This work proposes a novel method for continuous separation of particles by size using inertial microfluidics, with the assistance of symmetrical sheath flows in a straight microchannel. Here, larger particles (>3 μm) are arranged close to the channel sidewalls, while smaller particles (<2 μm) remain flowing along the channel centerline. This conclusion is supported by experimental data with particles of different sizes ranging from 0.79 to 10.5 μm. Symmetrical Newtonian sheath flows are injected on both sides of particle mixtures into a straight rectangular microchannel with an aspect ratio (AR = height/width) of 2.5. Results show that the separation performance of the developed microfluidic device is affected by three main factors: channel length, total flow rate, and flow rate ratio of sheath to sample. Besides, separation of platelets from whole blood is demonstrated. The developed microfluidic platform owns the advantages of low fabrication cost, simple experiment setup, versatile selections of particle candidates, and stable operations. This systematic study provides a new perspective for particle separation, which is expected to find applications across various fields spanning physics, biology, biomedicine, and industry.}, }
@article {pmid37449188, year = {2023}, author = {Ahmad, S and Ali, K and Katbar, NM and Akhtar, Y and Cai, J and Jamshed, W and El Din, SM and Abd-Elmonem, A and Elmki Abdalla, NS}, title = {Vortex generation due to multiple localized magnetic fields in the hybrid nanofluid flow - A numerical investigation.}, journal = {Heliyon}, volume = {9}, number = {7}, pages = {e17756}, pmid = {37449188}, issn = {2405-8440}, abstract = {Vortices capture the attention of every scientist (as soon as they come into existence) while studying any flow problem because of their significance in comprehending fluid mixing and mass transport processes. A vortex is indeed a physical phenomenon that happens when a liquid or a gas flow in a circular motion. They are generated due to the velocity difference and may be seen in hurricanes, air moving across the plane wing, tornadoes, etc. The study of vortices is important for understanding various natural phenomena in different settings. This work explores the complex dynamics of the Lorentz force that drives the rotation of nanostructures and the emergence of intricate vortex patterns in a hybrid fluid with Fe3O4-Cu nanoparticles. The hybrid nanofluid is modeled as a single-phase fluid, and the partial differential equations (PDEs) that govern its behavior are solved numerically. This work also introduces a novel analysis that enables us to visualize the flow lines and isotherms around the magnetic strips in the flow domain. The Lorentz force confined to the strips causes the spinning of hybrid nanoparticles, resulting in complex vortex structures in the flow domain. The results indicate that the magnetic field lowers the Nusselt number by 34% while raising the skin friction by 9%. The Reynolds number amplifies the influence of the localized magnetic field on the flow dynamics. Lastly, the nano-scaled structures in the flow enhance the Nusselt number significantly while having a minor effect on the skin friction factor.}, }
@article {pmid37449115, year = {2023}, author = {Li, S and Khan, MI and Alruqi, AB and Khan, SU and Abdullaev, SS and Fadhl, BM and Makhdoum, BM}, title = {Entropy optimized flow of Sutterby nanomaterial subject to porous medium: Buongiorno nanofluid model.}, journal = {Heliyon}, volume = {9}, number = {7}, pages = {e17784}, pmid = {37449115}, issn = {2405-8440}, abstract = {Owing to enhanced thermal impact of nanomaterials, different applications are suggested in engineering and industrial systems like heat transfer devices, energy generation, extrusion processes, engine cooling, thermal systems, heat exchanger, chemical processes, manufacturing systems, hybrid-powered plants etc. The current communication concerns the optimized flow of Sutterby nanofluid due to stretched surface in view of different thermal sources. The investigation is supported with the applications of external heat source, magnetic force and radiative phenomenon. The irreversibility investigation is deliberated with implementation of thermodynamics second law. The thermophoresis and random movement characteristics are also studied. Additionally, first order binary reaction is also examined. The nonlinear system of the governing problem is obtained which are numerically computed by s method. The physical aspects of prominent flow parameters are attributed graphically. Further, the analysis for entropy generation and Bejan number is focused. It is observed that the velocity profile increases due to Reynolds number and Deborah number. Larger Schmidt number reduces the concentration distribution. Further, the entropy generation is improved against Reynolds number and Brinkman parameter.}, }
@article {pmid37437157, year = {2023}, author = {Saxena, A and Kroll-Rabotin, JS and Sanders, RS}, title = {Role of Flow Inertia in Aggregate Restructuring and Breakage at Finite Reynolds Numbers.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {39}, number = {29}, pages = {10066-10078}, doi = {10.1021/acs.langmuir.3c01012}, pmid = {37437157}, issn = {1520-5827}, abstract = {Forces acting on aggregates depend on their properties, such as size and structure. Breakage rate, stable size, and structure of fractal aggregates in multiphase flows are strongly related to the imposed hydrodynamic forces. While these forces are prevalently viscous for finite Reynolds number conditions, flow inertia cannot be ignored, thereby requiring one to fully resolve the Navier-Stokes equations. To highlight the effect of flow inertia on aggregate evolution, numerical investigation of aggregate evolution in simple shear flow at the finite Reynolds number is conducted. The evolution of aggregates exposed to shear flow is tracked over time. Particle coupling with the flow is resolved with an immersed boundary method, and flow dynamics are solved using a lattice Boltzmann method. Particle dynamics are tracked by a discrete element method, accounting for interactions between primary particles composing the aggregates. Over the range of aggregate-scale Reynolds numbers tested, the breakage rate appears to be governed by the combined effect of momentum diffusion and the ratio of particle interaction forces to the hydrodynamic forces. For higher shear stresses, even when no stable size exists, breakage is not instantaneous because of momentum diffusion kinetics. Simulations with particle interaction forces scaled with the viscous drag, to isolate the effect of finite Reynolds hydrodynamics on aggregate evolution, show that flow inertia at such moderate aggregate Reynolds numbers has no impact on the morphology of nonbreaking aggregates but significantly favors breakage probability. This is a first-of-its-kind study that establishes the role of flow inertia in aggregate evolution. The findings present a novel perspective into breakage kinetics for systems in low but finite Reynolds number conditions.}, }
@article {pmid37425484, year = {2023}, author = {Birtek, MT and Alseed, MM and Sarabi, MR and Ahmadpour, A and Yetisen, AK and Tasoglu, S}, title = {Machine learning-augmented fluid dynamics simulations for micromixer educational module.}, journal = {Biomicrofluidics}, volume = {17}, number = {4}, pages = {044101}, pmid = {37425484}, issn = {1932-1058}, abstract = {Micromixers play an imperative role in chemical and biomedical systems. Designing compact micromixers for laminar flows owning a low Reynolds number is more challenging than flows with higher turbulence. Machine learning models can enable the optimization of the designs and capabilities of microfluidic systems by receiving input from a training library and producing algorithms that can predict the outcomes prior to the fabrication process to minimize development cost and time. Here, an educational interactive microfluidic module is developed to enable the design of compact and efficient micromixers at low Reynolds regimes for Newtonian and non-Newtonian fluids. The optimization of Newtonian fluids designs was based on a machine learning model, which was trained by simulating and calculating the mixing index of 1890 different micromixer designs. This approach utilized a combination of six design parameters and the results as an input data set to a two-layer deep neural network with 100 nodes in each hidden layer. A trained model was achieved with R[2] = 0.9543 that can be used to predict the mixing index and find the optimal parameters needed to design micromixers. Non-Newtonian fluid cases were also optimized using 56700 simulated designs with eight varying input parameters, reduced to 1890 designs, and then trained using the same deep neural network used for Newtonian fluids to obtain R[2] = 0.9063. The framework was subsequently used as an interactive educational module, demonstrating a well-structured integration of technology-based modules such as using artificial intelligence in the engineering curriculum, which can highly contribute to engineering education.}, }
@article {pmid37420830, year = {2023}, author = {Scheuer, KG and DeCorby, RG}, title = {All-Optical, Air-Coupled Ultrasonic Detection of Low-Pressure Gas Leaks and Observation of Jet Tones in the MHz Range.}, journal = {Sensors (Basel, Switzerland)}, volume = {23}, number = {12}, pages = {}, pmid = {37420830}, issn = {1424-8220}, support = {Innovation Catalyst Grant//Government of Alberta/ ; AI//Alberta Innovates/ ; CREATE 495446-17//Natural Sciences and Engineering Research Council/ ; Quantum Technologies//Alberta EDT Major Innovation Fund/ ; }, mesh = {*Ultrasonics ; *Syringes ; Ultrasonography ; }, abstract = {We used an ultrasensitive, broadband optomechanical ultrasound sensor to study the acoustic signals produced by pressurized nitrogen escaping from a variety of small syringes. Harmonically related jet tones extending into the MHz region were observed for a certain range of flow (i.e., Reynolds number), which is in qualitative agreement with historical studies on gas jets emitted from pipes and orifices of much larger dimensions. For higher turbulent flow rates, we observed broadband ultrasonic emission in the ~0-5 MHz range, which was likely limited on the upper end due to attenuation in air. These observations are made possible by the broadband, ultrasensitive response (for air-coupled ultrasound) of our optomechanical devices. Aside from being of theoretical interest, our results could have practical implications for the non-contact monitoring and detection of early-stage leaks in pressured fluid systems.}, }
@article {pmid37420356, year = {2022}, author = {Li, X and Su, H}, title = {A Modular Grad-Div Stabilization Method for Time-Dependent Thermally Coupled MHD Equations.}, journal = {Entropy (Basel, Switzerland)}, volume = {24}, number = {10}, pages = {}, pmid = {37420356}, issn = {1099-4300}, abstract = {In this paper, we consider a fully discrete modular grad-div stabilization algorithm for time-dependent thermally coupled magnetohydrodynamic (MHD) equations. The main idea of the proposed algorithm is to add an extra minimally intrusive module to penalize the divergence errors of velocity and improve the computational efficiency for increasing values of the Reynolds number and grad-div stabilization parameters. In addition, we provide the unconditional stability and optimal convergence analysis of this algorithm. Finally, several numerical experiments are performed and further indicated these advantages over the algorithm without grad-div stabilization.}, }
@article {pmid37418738, year = {2023}, author = {Gotoh, T and Watanabe, T and Saito, I}, title = {Kinematic Effects on Probability Density Functions of Energy Dissipation Rate and Enstrophy in Turbulence.}, journal = {Physical review letters}, volume = {130}, number = {25}, pages = {254001}, doi = {10.1103/PhysRevLett.130.254001}, pmid = {37418738}, issn = {1079-7114}, mesh = {*Biomechanical Phenomena ; Probability ; }, abstract = {Direct numerical simulation and theoretical analyses showed that the probability density functions (PDFs) of the energy dissipation rate and enstrophy in turbulence are asymptotically stretched gamma distributions with the same stretching exponent, and both the left and right tails of the enstrophy PDF are longer than those of the energy dissipation rate regardless of the Reynolds number. The differences in PDF tails arise due to the kinematics, with differences in the number of terms contributing to the dissipation rate and enstrophy. Meanwhile, the stretching exponent is determined by the dynamics and likeliness of singularities.}, }
@article {pmid37414852, year = {2023}, author = {Kim, M and Schanz, D and Novara, M and Godbersen, P and Yeom, E and Schröder, A}, title = {Experimental study on flow and turbulence characteristics of jet impinging on cylinder using three-dimensional Lagrangian particle tracking velocimetry.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {10929}, pmid = {37414852}, issn = {2045-2322}, support = {2021R1C1C2009287//National Research Foundation of Korea/ ; 2021R1I1A3047664//National Research Foundation of Korea/ ; DFG SPP 1881//Deutsche Forschungsgemeinschaft/ ; }, mesh = {*Rheology/methods ; Stress, Mechanical ; }, abstract = {When a round jet impinges on a convex cylindrical surface, complex three-dimensional (3D) flow structures occur, accompanied by the Coanda effect. To characterize the flow and turbulence properties of the general system, ensemble averages of 3D Lagrangian particle tracking velocimetry measurements were taken. The radial bin-averaging method was used in post-processing the tracked particles and corresponding instantaneous velocity vectors to generate appropriate ensemble-averaged statistics. Two impinging angles were selected, and at a fixed Reynolds number, the ensemble-averaged volumetric velocity field and turbulent stress tensor components were measured. The flow and turbulence characteristics of the impinging jet on the cylinder were notably different based on the impinging angle, especially in the downstream region. Surprisingly, the attached wall jet with a half-elliptic shape was abruptly thickened in the wall-normal direction, similar to the axis switching phenomenon observed in elliptic jets in the case of oblique impingement. In the jet-impinging region, the flow spread in all directions with high mean vorticity values. With the development of a 3D curved wall jet, both the Coanda effect and centrifugal force played a significant role in the flow behavior. A notable feature of the self-preserving region was the similarity of mean velocity profiles with scaling by the maximum velocity and the jet half-width for both impinging angle cases. Local isotropy of turbulent normal stresses was observed in this region, supporting the existence of self-preservation in the 3D curved wall jet. The volumetric ensemble-averaged Reynolds stress tensor revealed strong inhomogeneous turbulence in the boundary layer region and the curvature effect on the Reynolds shear stress in the free shear layer.}, }
@article {pmid37407860, year = {2023}, author = {Dutt, N and Hedau, AJ and Kumar, A and Awasthi, MK and Singh, VP and Dwivedi, G}, title = {Thermo-hydraulic performance of solar air heater having discrete D-shaped ribs as artificial roughness.}, journal = {Environmental science and pollution research international}, volume = {}, number = {}, pages = {}, pmid = {37407860}, issn = {1614-7499}, abstract = {In this paper, the thermo-hydraulic performance of a solar air heater (SAH) duct roughened with discrete D-shaped ribs is numerically investigated using ANSYS Fluent 2020 R2. The numerical investigation is carried out at rib radius to transverse pitch ratio (r/Pt) from 0.1 to 0.35 and longitudinal pitch to rib radius ratio (Pl /r) from 4 to 10 under various operating conditions with Reynolds number (Re) varied from 10,200 to 20,200. The numerical results are validated with previous experimental results for the Nusselt number (Nu) values, and good agreement is found with mean absolute percentage error (MAPE) of 3.6%. Based on the results of the numerical investigation, it was found that the value of Nu and the friction factor (f) decreases with the increase of the value of Pl/r, while the ratio r/Pt is kept constant. From the overall analysis, it is concluded that the optimum results are obtained for r/Pt of 0.25 and Pl/r = 4, and the maximum thermo-hydraulic performance parameter is 1.12. Further correlations are developed for the value of Nu and f for the whole range of r/Pt as 0.10-0.35 and Pl/r as 4-10. According to the developed correlations, the values of Nu are within ± 2% of the results of CFD, while the values of f are within ± 2.7% of the results of CFD.}, }
@article {pmid37391140, year = {2023}, author = {Firatoglu, ZA}, title = {The effect of natural ventilation on airborne transmission of the COVID-19 virus spread by sneezing in the classroom.}, journal = {The Science of the total environment}, volume = {896}, number = {}, pages = {165113}, doi = {10.1016/j.scitotenv.2023.165113}, pmid = {37391140}, issn = {1879-1026}, mesh = {Humans ; *SARS-CoV-2 ; Sneezing ; *COVID-19 ; Respiratory Aerosols and Droplets ; Computer Simulation ; Ventilation ; }, abstract = {Since school classrooms are of vital importance due to their impact on public health in COVID-19 and similar epidemics, it is imperative to develop new ventilation strategies to reduce the risk of transmission of the virus in the classroom. To be able to develop new ventilation strategies, the effect of local flow behaviors in the classroom on the airborne transmission of the virus under the most dramatic conditions must first be determined. In this study, the effect of natural ventilation on the airborne transmission of COVID-19-like viruses in the classroom in the case of sneezing by two infected students in a reference secondary school classroom was investigated in five scenarios. Firstly, experimental measurements were carried out in the reference class to validate the computational fluid dynamics (CFD) simulation results and determine the boundary conditions. Next, the effects of local flow behaviors on the airborne transmission of the virus were evaluated for five scenarios using the Eulerian-Lagrange method, a discrete phase model, and a temporary three-dimensional CFD model. In all scenarios, immediately after sneezing, between 57 and 60.2 % of the droplets containing the virus, mostly large and medium-sized (150 μm < d < 1000 μm) settled on the infected student's desk, while small droplets continued to move in the flow field. In addition, it was determined that the effect of natural ventilation in the classroom on the travel of virus droplets in the case of Redh < 8.04 × 10[4] (Reynolds number, Redh=Udh/νu, dh and are fluid velocity, hydraulic diameters of the door and window sections of the class and kinematic viscosity, respectively) was negligible.}, }
@article {pmid37388310, year = {2023}, author = {Théry, A and Maaß, CC and Lauga, E}, title = {Hydrodynamic interactions between squirmers near walls: far-field dynamics and near-field cluster stability.}, journal = {Royal Society open science}, volume = {10}, number = {6}, pages = {230223}, pmid = {37388310}, issn = {2054-5703}, abstract = {Confinement increases contacts between microswimmers in dilute suspensions and affects their interactions. In particular, boundaries have been shown experimentally to lead to the formation of clusters that would not occur in bulk fluids. To what extent does hydrodynamics govern these boundary-driven encounters between microswimmers? We consider theoretically the symmetric boundary-mediated encounters of model microswimmers under gravity through far-field interaction of a pair of weak squirmers, as well as the lubrication interactions occurring after contact between two or more squirmers. In the far field, the orientation of microswimmers is controlled by the wall and the squirming parameter. The presence of a second swimmer influences the orientation of the original squirmer, but for weak squirmers, most of the interaction occurs after contact. We thus analyse next the near-field reorientation of circular groups of squirmers. We show that a large number of swimmers and the presence of gravity can stabilize clusters of pullers, while the opposite is true for pushers; to be stable, clusters of pushers thus need to be governed by other interactions (e.g. phoretic). This simplified approach to the phenomenon of active clustering enables us to highlight the hydrodynamic contribution, which can be hard to isolate in experimental realizations.}, }
@article {pmid37366832, year = {2023}, author = {Saeed, A and Farooq, H and Akhtar, I and Tariq, MA and Khalid, MSU}, title = {Deep-Learning-Based Reduced-Order Model for Power Generation Capacity of Flapping Foils.}, journal = {Biomimetics (Basel, Switzerland)}, volume = {8}, number = {2}, pages = {}, pmid = {37366832}, issn = {2313-7673}, support = {Digital Pakistan Lab, National Center for Big Data and Cloud Computing//Higher Education Commission/ ; }, abstract = {Inspired by nature, oscillating foils offer viable options as alternate energy resources to harness energy from wind and water. Here, we propose a proper orthogonal decomposition (POD)-based reduced-order model (ROM) of power generation by flapping airfoils in conjunction with deep neural networks. Numerical simulations are performed for incompressible flow past a flapping NACA-0012 airfoil at a Reynolds number of 1100 using the Arbitrary Lagrangian-Eulerian approach. The snapshots of the pressure field around the flapping foil are then utilized to construct the pressure POD modes of each case, which serve as the reduced basis to span the solution space. The novelty of the current research relates to the identification, development, and employment of long-short-term neural network (LSTM) models to predict temporal coefficients of the pressure modes. These coefficients, in turn, are used to reconstruct hydrodynamic forces and moment, leading to computations of power. The proposed model takes the known temporal coefficients as inputs and predicts the future temporal coefficients followed by previously estimated temporal coefficients, very similar to traditional ROM. Through the new trained model, we can predict the temporal coefficients for a long time duration that can be far beyond the training time intervals more accurately. It may not be attained by traditional ROMs that lead to erroneous results. Consequently, the flow physics including the forces and moment exerted by fluids can be reconstructed accurately using POD modes as the basis set.}, }
@article {pmid37361718, year = {2023}, author = {Ben Mariem, I and Kaziz, S and Belkhiria, M and Echouchene, F and Belmabrouk, H}, title = {Numerical optimization of microfluidic biosensor detection time for the SARS-CoV-2 using the Taguchi method.}, journal = {Indian journal of physics and proceedings of the Indian Association for the Cultivation of Science (2004)}, volume = {}, number = {}, pages = {1-8}, pmid = {37361718}, issn = {0973-1458}, abstract = {The performance of microfluidic biosensor of the SARS-Cov-2 was numerically analyzed through finite element method. The calculation results have been validated with comparison with experimental data reported in the literature. The novelty of this study is the use of the Taguchi method in the optimization analysis, and an L8(2[5]) orthogonal table of five critical parameters-Reynolds number (Re), Damköhler number (Da), relative adsorption capacity (σ), equilibrium dissociation constant (KD), and Schmidt number (Sc), with two levels was designed. ANOVA methods are used to obtain the significance of key parameters. The optimal combination of the key parameters is Re = 10[-2], Da = 1000, σ = 0.2, KD = 5, and Sc 10[4] to achieve the minimum response time (0.15). Among the selected key parameters, the relative adsorption capacity (σ) has the highest contribution (42.17%) to the reduction of the response time, while the Schmidt number (Sc) has the lowest contribution (5.19%). The presented simulation results are useful in designing microfluidic biosensors in order to reduce their response time.}, }
@article {pmid37360015, year = {2023}, author = {Ahmed, A and Ul Islam, S and Khan, AQ and Wahid, A}, title = {Reduction of fluid forces for flow past side-by-side cylinders using downstream attached splitter plates.}, journal = {Computational particle mechanics}, volume = {}, number = {}, pages = {1-19}, pmid = {37360015}, issn = {2196-4378}, abstract = {A two-dimensional numerical simulation is performed to investigate the drag reduction and vortex shedding suppression behind three square cylinders with attached splitter plates in the downstream region at a low Reynolds number (Re = 150). Numerical calculations are carried out using the lattice Boltzmann method. The study is carried out for various values of gap spacing between the cylinders and different splitter plate lengths. The vortices are completely chaotic at very small spacing, as observed. The splitter plates are critical in suppressing shedding and reducing drag on the objects. The splitter plates with lengths greater than two fully control the jet interaction at low spacing values. There is maximum percentage reduction in CDmean for small spacing and the selected largest splitter plate length. Furthermore, systematic investigation reveals that splitter plates significantly suppress the fluctuating lift in addition to drastically reducing the drag.}, }
@article {pmid37344457, year = {2023}, author = {Baldygin, A and Ahmed, A and Baily, R and Ismail, MF and Khan, M and Rodrigues, N and Salehi, AR and Ramesh, M and Bhattacharya, S and Willers, T and Gowanlock, D and Waghmare, PR}, title = {Effect of gravity on the spreading of a droplet deposited by liquid needle deposition technique.}, journal = {NPJ microgravity}, volume = {9}, number = {1}, pages = {49}, pmid = {37344457}, issn = {2373-8065}, support = {19FAALBB36 - FAST 2019//Gouvernement du Canada | Canadian Space Agency (Agence Spatiale Canadienne)/ ; }, abstract = {This study represents an experimental investigation, complemented with a mathematical model, to decipher the effect of gravity on the spreading dynamics of a water droplet. For the theoretical discussion, an overall energy balance approach is adopted to explain the droplet spreading under both microgravity (μg) and terrestrial gravity condition. Besides explaining the mechanism of the droplet spreading under microgravity condition achieved during the parabolic flight, a technique with a detailed experimental set-up has also been developed for the successful deposition of droplet. A rational understanding is formulated through experimental investigation and theoretical analysis, which allows us to distinguish the transient variation of the spreading of a droplet, between microgravity and terrestrial gravity condition. The spreading of the droplet is predicted by the non-linear overall energy balance equation, which accounts for the operating parameters in the form of non-dimensional groups like Reynolds number ([Formula: see text]), Weber number (We) and Bond number (Bo). To distinctly identify the difference in the drop spreading at terrestrial and microgravity conditions, the Bo with transient gravitational field obtained through the on-board accelerometer is considered. The obtained theoretical results are further corroborated by experimental results which are obtained from the parabolic flight.}, }
@article {pmid37338259, year = {2023}, author = {Qiao, S and Ouyang, H and Zheng, X and Qi, C and Ma, L}, title = {Magnetically actuated hydrogel-based capsule microrobots for intravascular targeted drug delivery.}, journal = {Journal of materials chemistry. B}, volume = {11}, number = {26}, pages = {6095-6105}, doi = {10.1039/d3tb00852e}, pmid = {37338259}, issn = {2050-7518}, mesh = {*Hydrogels ; Drug Delivery Systems/methods ; Magnetics ; Computer Simulation ; *Robotics/methods ; }, abstract = {Microrobots for targeted drug delivery in blood vessels have attracted increasing interest from researchers. In this work, hydrogel-based capsule microrobots are used to wrap drugs and deliver drugs in blood vessels. In order to prepare capsule microrobots of different sizes, a triaxial microfluidic chip is designed and built, and the formation mechanism of three flow phases including the plug flow phase, bullet flow phase and droplet phase during the preparation of capsule microrobots is studied. The analysis and simulation results show that the size of the capsule microrobots can be controlled by the flow rate ratio of two phases in the microfluidic chip, and when the flow rate of the outer phase is 20 times that of the inner phase in the microfluidic chip, irregular multicore capsule microrobots can be prepared. On this basis, a three degree of freedom magnetic drive system is developed to drive the capsule microrobots to reach the destination along the predetermined trajectory in the low Reynolds number environment, and the magnetic field performance of the magnetic drive system is simulated and analyzed. Finally, in order to verify the feasibility of targeted drug delivery of the capsule microrobots in the blood vessel, the motion process of the capsule microrobots in the vascular microchannel is simulated, and the relationship between the motion performance of the capsule microrobots and the magnetic field is studied. The experimental results show that the capsule microrobots can reach a speed of 800 μm s[-1] at a low frequency of 0.4 Hz. At the same time, the capsule microrobots can reach a peak speed of 3077 μm s[-1] and can continuously climb over a 1000 μm high obstacle under a rotating magnetic field of 2.4 Hz and 14.4 mT. Experiments show that the capsule microrobots have excellent drug delivery potential in similar vascular curved channels driven by this system.}, }
@article {pmid37330555, year = {2023}, author = {Algehyne, EA and Ahammad, NA and Elnair, ME and Zidan, M and Alhusayni, YY and El-Bashir, BO and Saeed, A and Alshomrani, AS and Alzahrani, F}, title = {Entropy optimization and response surface methodology of blood hybrid nanofluid flow through composite stenosis artery with magnetized nanoparticles (Au-Ta) for drug delivery application.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {9856}, pmid = {37330555}, issn = {2045-2322}, mesh = {Humans ; Entropy ; Constriction, Pathologic ; *Tantalum ; *Nanoparticles ; Arteries ; }, abstract = {Entropy creation by a blood-hybrid nanofluid flow with gold-tantalum nanoparticles in a tilted cylindrical artery with composite stenosis under the influence of Joule heating, body acceleration, and thermal radiation is the focus of this research. Using the Sisko fluid model, the non-Newtonian behaviour of blood is investigated. The finite difference (FD) approach is used to solve the equations of motion and entropy for a system subject to certain constraints. The optimal heat transfer rate with respect to radiation, Hartmann number, and nanoparticle volume fraction is calculated using a response surface technique and sensitivity analysis. The impacts of significant parameters such as Hartmann number, angle parameter, nanoparticle volume fraction, body acceleration amplitude, radiation, and Reynolds number on the velocity, temperature, entropy generation, flow rate, shear stress of wall, and heat transfer rate are exhibited via the graphs and tables. Present results disclose that the flow rate profile increase by improving the Womersley number and the opposite nature is noticed in nanoparticle volume fraction. The total entropy generation reduces by improving radiation. The Hartmann number expose a positive sensitivity for all level of nanoparticle volume fraction. The sensitivity analysis revealed that the radiation and nanoparticle volume fraction showed a negative sensitivity for all magnetic field levels. It is seen that the presence of hybrid nanoparticles in the bloodstream leads to a more substantial reduction in the axial velocity of blood compared to Sisko blood. An increase in the volume fraction results in a noticeable decrease in the volumetric flow rate in the axial direction, while higher values of infinite shear rate viscosity lead to a significant reduction in the magnitude of the blood flow pattern. The blood temperature exhibits a linear increase with respect to the volume fraction of hybrid nanoparticles. Specifically, utilizing a hybrid nanofluid with a volume fraction of 3% leads to a 2.01316% higher temperature compared to the base fluid (blood). Similarly, a 5% volume fraction corresponds to a temperature increase of 3.45093%.}, }
@article {pmid37329080, year = {2023}, author = {Kim, M and Borhan, A}, title = {Critical conditions for development of a second pair of Dean vortices in curved microfluidic channels.}, journal = {Physical review. E}, volume = {107}, number = {5-2}, pages = {055103}, doi = {10.1103/PhysRevE.107.055103}, pmid = {37329080}, issn = {2470-0053}, mesh = {*Microfluidics ; Computer Simulation ; *Hydrodynamics ; }, abstract = {The centrifugal force in flow through a curved channel initiates a hydrodynamic instability that results in the development of Dean vortices, a pair of counter-rotating roll cells across the channel that deflect the high velocity fluid in the center toward the outer (concave) wall. When this secondary flow toward the concave (outer) wall is too strong to be dissipated by viscous effects, an additional pair of vortices emerges near the outer wall. Combining numerical simulation and dimensional analysis, we find that the critical condition for the onset of the second vortex pair depends on γ^{1/2}Dn (γ: channel aspect ratio; Dn: Dean number). We also investigate the development length for the additional vortex pair in channels with different aspect ratios and curvatures. The larger centrifugal force at higher Dean numbers produces the additional vortices further upstream, with the required development length being inversely proportional to the Reynolds number and increasing linearly with the radius of curvature of the channel.}, }
@article {pmid37329043, year = {2023}, author = {Mizerski, KA}, title = {Helical correction to turbulent magnetic diffusivity.}, journal = {Physical review. E}, volume = {107}, number = {5-2}, pages = {055205}, doi = {10.1103/PhysRevE.107.055205}, pmid = {37329043}, issn = {2470-0053}, mesh = {Physical Phenomena ; Diffusion ; *Magnetic Phenomena ; }, abstract = {The effect of helicity in magnetohydrodynamic turbulence on the effective turbulent magnetic diffusion is considered here. The helical correction to turbulent diffusivity is analytically calculated with the use of the renormalization group approach. In agreement with previous numerical findings, this correction is shown to be negative and proportional to the second power of the magnetic Reynolds number, when the latter is small. In addition, the helical correction to turbulent diffusivity is found to obey a power-law-type dependence on the wave number of the most energetic turbulent eddies, k_{ℓ}, of the form k_{ℓ}^{-10/3}.}, }
@article {pmid37329025, year = {2023}, author = {Parfenyev, V and Mogilevskiy, E and Falkovich, G}, title = {Sum-of-squares bounds on correlation functions in a minimal model of turbulence.}, journal = {Physical review. E}, volume = {107}, number = {5-1}, pages = {054114}, doi = {10.1103/PhysRevE.107.054114}, pmid = {37329025}, issn = {2470-0053}, abstract = {We suggest a new computer-assisted approach to the development of turbulence theory. It allows one to impose lower and upper bounds on correlation functions using sum-of-squares polynomials. We demonstrate it on the minimal cascade model of two resonantly interacting modes when one is pumped and the other dissipates. We show how to present correlation functions of interest as part of a sum-of-squares polynomial using the stationarity of the statistics. That allows us to find how the moments of the mode amplitudes depend on the degree of nonequilibrium (analog of the Reynolds number), which reveals some properties of marginal statistical distributions. By combining scaling dependence with the results of direct numerical simulations, we obtain the probability densities of both modes in a highly intermittent inverse cascade. As the Reynolds number tends to infinity, we show that the relative phase between modes tends to π/2 and -π/2 in the direct and inverse cascades, respectively, and derive bounds on the phase variance. Our approach combines computer-aided analytical proofs with a numerical algorithm applied to high-degree polynomials.}, }
@article {pmid37324036, year = {2023}, author = {Jiang, J and Wang, F and Huang, W and Sun, J and Ye, Y and Ou, J and Liu, M and Gao, J and Wang, S and Fu, D and Chen, B and Liu, L and Peng, F and Tu, Y}, title = {Mobile mechanical signal generator for macrophage polarization.}, journal = {Exploration (Beijing, China)}, volume = {3}, number = {2}, pages = {20220147}, pmid = {37324036}, issn = {2766-2098}, abstract = {The importance of mechanical signals in regulating the fate of macrophages is gaining increased attention recently. However, the recently used mechanical signals normally rely on the physical characteristics of matrix with non-specificity and instability or mechanical loading devices with uncontrollability and complexity. Herein, we demonstrate the successful fabrication of self-assembled microrobots (SMRs) based on magnetic nanoparticles as local mechanical signal generators for precise macrophage polarization. Under a rotating magnetic field (RMF), the propulsion of SMRs occurs due to the elastic deformation via magnetic force and hydrodynamics. SMRs perform wireless navigation toward the targeted macrophage in a controllable manner and subsequently rotate around the cell for mechanical signal generation. Macrophages are eventually polarized from M0 to anti-inflammatory related M2 phenotypes by blocking the Piezo1-activating protein-1 (AP-1）-CCL2 signaling pathway. The as-developed microrobot system provides a new platform of mechanical signal loading for macrophage polarization, which holds great potential for precise regulation of cell fate.}, }
@article {pmid37323615, year = {2023}, author = {Madonia, M and Guzmán, AJA and Clercx, HJH and Kunnen, RPJ}, title = {Reynolds number scaling and energy spectra in geostrophic convection.}, journal = {Journal of fluid mechanics}, volume = {962}, number = {}, pages = {A36}, pmid = {37323615}, issn = {0022-1120}, abstract = {We report flow measurements in rotating Rayleigh-Bénard convection in the rotationally-constrained geostrophic regime. We apply stereoscopic particle image velocimetry to measure the three components of velocity in a horizontal cross-section of a water-filled cylindrical convection vessel. At a constant, small Ekman number Ek = 5 × 10[-8] we vary the Rayleigh number Ra between 10[11] and 4 × 10[12] to cover various subregimes observed in geostrophic convection. We also include one nonrotating experiment. The scaling of the velocity fluctuations (expressed as the Reynolds number Re) is compared to theoretical relations expressing balances of viscous-Archimedean-Coriolis (VAC) and Coriolis-inertial-Archimedean (CIA) forces. Based on our results we cannot decide which balance is most applicable here; both scaling relations match equally well. A comparison of the current data with several other literature datasets indicates a convergence towards diffusion-free scaling of velocity as Ek decreases. However, the use of confined domains leads at lower Ra to prominent convection in the wall mode near the sidewall. Kinetic energy spectra point at an overall flow organisation into a quadrupolar vortex filling the cross-section. This quadrupolar vortex is a quasi-two-dimensional feature; it only manifests in energy spectra based on the horizontal velocity components. At larger Ra the spectra reveal the development of a scaling range with exponent close to -5/3, the classical exponent for inertial-range scaling in three-dimensional turbulence. The steeper Re(Ra) scaling at low Ek and development of a scaling range in the energy spectra are distinct indicators that a fully developed, diffusion-free turbulent bulk flow state is approached, sketching clear perspectives for further investigation.}, }
@article {pmid37308628, year = {2024}, author = {Sharma, M and Jilte, R}, title = {Heat transfer and hydraulics for a novel receiver pipe of solar parabolic trough: a computational approach.}, journal = {Environmental science and pollution research international}, volume = {31}, number = {53}, pages = {62442-62463}, pmid = {37308628}, issn = {1614-7499}, mesh = {*Hot Temperature ; Models, Theoretical ; }, abstract = {The effect of symmetrical convex-concave corrugations on receiver pipe of a parabolic trough solar collector is numerically investigated. Twelve distinct geometrically configured receiver pipes with corrugations have been examined for this purpose. The computational study is conducted for varying corrugation pitch (4 mm to 10 mm) and height (1.5 mm to 2.5 mm). Heat transfer enhancement, flow behavior, and overall thermal performance of fluid moving through a pipe under non-uniform heat flux condition are all determined in this work. The Reynolds number ranges from 5000 to 50,000. The findings reveal that presence of corrugations leads to axial whirling and vortices in the receiver pipe, thus enhancing the heat transfer. The receiver pipe having corrugations of 8 mm pitch and 2 mm height gave the best results. The maximum enhancement in average Nusselt number over smooth pipe has been observed as 28.51%. In addition, relationships of Nusselt number and friction factor against selected design parameters and operating conditions are also displayed as correlations.}, }
@article {pmid37303552, year = {2023}, author = {Alizadeh, A and Shahabi Takami, SF and Iranmanesh, R and Pasha, P}, title = {Evaluation of AGM and FEM method for thermal radiation on nanofluid flow between two tubes in nearness of magnetism field.}, journal = {Heliyon}, volume = {9}, number = {6}, pages = {e16788}, doi = {10.1016/j.heliyon.2023.e16788}, pmid = {37303552}, issn = {2405-8440}, abstract = {The nanofluid flow through two orbicular cylinders is explored utilizing the overall Koo-Kleinstreuer-Li (KKL) model within the nearness of a magnetic field. The impact of thermal radiation is considered in the energy equation. The novelty of this study is examining convective heat transfer for nanofluid flow between two flat tubes with the Akbari-Ganji method and Finite Element Techniques to examine the heat flux field by implies of 2D forms of temperature and velocity at unprecedented Reynolds numbers. The approaches for solving ODEs are AGM and FEM. Semi-analytical methods are assessed for specific parameters of aspect ratio, Hartmann number, Eckert number, and Reynolds quantity with various values. Adding Ha, Ec, and G causes the temperature gradient to grow, while adding the Reynolds number causes it to decrease. As the Lorentz forces increase, the velocity decreases; nevertheless, as the Reynolds number rises, the velocity decreases. With the reduction of the fluid's dynamic viscosity, the temperature will decrease, which will decrease the thermal trend along the vertical length of the pipes.}, }
@article {pmid37297077, year = {2023}, author = {Tang, TL and Salleh, H and Sadiq, MI and Mohd Sabri, MA and Ahmad, MIM and Ghopa, WAW}, title = {Experimental and Numerical Investigation of Flow Structure and Heat Transfer Behavior of Multiple Jet Impingement Using MgO-Water Nanofluids.}, journal = {Materials (Basel, Switzerland)}, volume = {16}, number = {11}, pages = {}, pmid = {37297077}, issn = {1996-1944}, support = {FRGS/1/2021/TK0/UKM/03/2//National University of Malaysia/ ; FRGS/1/2020/TK02/UKM/03/1//National University of Malaysia/ ; }, abstract = {Nanofluids have attracted significant attention from researchers due to their ability to significantly enhance heat transfer, especially in jet impingement flows, which can improve their cooling performance. However, there is a lack of research on the use of nanofluids in multiple jet impingements, both in terms of experimental and numerical studies. Therefore, further investigation is necessary to fully understand the potential benefits and limitations of using nanofluids in this type of cooling system. Thus, an experimental and numerical investigation was performed to study the flow structure and heat transfer behavior of multiple jet impingement using MgO-water nanofluids with a 3 × 3 inline jet array at a nozzle-to-plate distance of 3 mm. The jet spacing was set to 3, 4.5, and 6 mm; the Reynolds number varies from 1000 to 10,000; and the particle volume fraction ranges from 0% to 0.15%. A 3D numerical analysis using ANSYS Fluent with SST k-ω turbulent model was presented. The single-phase model is adopted to predict the thermal physical nanofluid. The flow field and temperature distribution were investigated. Experimental results show that a nanofluid can provide a heat transfer enhancement at a small jet-to-jet spacing using a high particle volume fraction under a low Reynolds number; otherwise, an adverse effect on heat transfer may occur. The numerical results show that the single-phase model can predict the heat transfer trend of multiple jet impingement using nanofluids correctly but with significant deviation from experimental results because it cannot capture the effect of nanoparticles.}, }
@article {pmid37296306, year = {2023}, author = {Liu, Y and Zou, Z and Pak, OS and Tsang, ACH}, title = {Learning to cooperate for low-Reynolds-number swimming: a model problem for gait coordination.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {9397}, pmid = {37296306}, issn = {2045-2322}, mesh = {*Swimming ; *Artificial Intelligence ; Locomotion ; Gait ; Motion ; }, abstract = {Biological microswimmers can coordinate their motions to exploit their fluid environment-and each other-to achieve global advantages in their locomotory performance. These cooperative locomotion require delicate adjustments of both individual swimming gaits and spatial arrangements of the swimmers. Here we probe the emergence of such cooperative behaviors among artificial microswimmers endowed with artificial intelligence. We present the first use of a deep reinforcement learning approach to empower the cooperative locomotion of a pair of reconfigurable microswimmers. The AI-advised cooperative policy comprises two stages: an approach stage where the swimmers get in close proximity to fully exploit hydrodynamic interactions, followed a synchronization stage where the swimmers synchronize their locomotory gaits to maximize their overall net propulsion. The synchronized motions allow the swimmer pair to move together coherently with an enhanced locomotion performance unattainable by a single swimmer alone. Our work constitutes a first step toward uncovering intriguing cooperative behaviors of smart artificial microswimmers, demonstrating the vast potential of reinforcement learning towards intelligent autonomous manipulations of multiple microswimmers for their future biomedical and environmental applications.}, }
@article {pmid37296249, year = {2024}, author = {Kumar, D and Layek, A and Kumar, A}, title = {Enhancement of thermal efficiency and development of Nusselt number correlation for the solar air heater collector roughened with artificial ribs for thermal applications.}, journal = {Environmental science and pollution research international}, volume = {31}, number = {53}, pages = {62427-62441}, pmid = {37296249}, issn = {1614-7499}, support = {EEQ/2018/001012//DST- SERB/ ; }, mesh = {*Solar Energy ; }, abstract = {The thermal efficiency of conventional solar air heater is very low. This research article concentrates on incorporating V-shaped staggered twisted ribs over absorber surface of solar air heater. Various roughness parameters were tested to determine their effect on the Nusselt number, friction factor, thermo-hydraulic performance index, and thermal efficiency. During experiment, the Reynolds number is varied from 3000 to 21,000; while relative roughness length varied for 4.39 to 10.26 and relative staggered distance for 2 to 6. However, relative roughness pitch, twist length, and angle of attack were kept constant. The Nusselt number and friction factor of the roughened collector enhances to 3.41 and 2.56 times that of the smooth collector, respectively. The thermal efficiency of the roughened solar air heater increases to 73.64% of the roughened plate as it was noticed 42.63% for smooth surface due to breakage of the laminar sublayer. The correlations for Nusselt number and friction factor as function of Reynolds number and roughness parameters are also developed. The maximum thermohydraulic performance gained at the optimum parameters of d/e of 4 and S/e of 6.15 is 2.69. The percentage deviation between the developed correlations and the experimental findings shows very satisfactory outcomes. Therefore, it can be concluded that inclusion of twisted V staggered ribs enhances the thermal performance of solar air heater with the lowest frictional penalty.}, }
@article {pmid37295437, year = {2023}, author = {Liu, F and Li, S and Dong, X and Wang, Z and Xiang, J and Li, D and Tu, Z}, title = {Design, modelling, and experimental validation of a self-rotating flapping wing rotorcraft with motor-spring resonance actuation system.}, journal = {Bioinspiration &amp; biomimetics}, volume = {18}, number = {4}, pages = {}, doi = {10.1088/1748-3190/acdd3d}, pmid = {37295437}, issn = {1748-3190}, mesh = {Animals ; *Models, Biological ; *Flight, Animal ; Biomimetics ; Insecta ; Vibration ; Wings, Animal ; Biomechanical Phenomena ; }, abstract = {Compared with traditional flapping motion, the flapping wing rotor (FWR) allows rotating freedom by installing the two wings asymmetrically, which introduces rotary motion characteristics and enables the FWR to have higher lift and aerodynamic efficiency at low Reynolds number. However, most of the proposed FWRs contain linkage mechanical transmission structures, the fixed degrees of freedom of which prohibit the wings from achieving variable flapping trajectories, limiting further optimization and controller design of FWRs. In order to fundamentally address the above challenges of FWRs, this paper presents a new type of FWR with two mechanically decoupled wings, which are directly driven by two independent motor-spring resonance actuation systems. The proposed FWR has 12.4 g of system weight and 165-205 mm wingspan. In addition, a theoretical electromechanical model based on the DC motor model and quasi-steady aerodynamic forces is established, and a series of experiments are conducted in order to determine the ideal working point of the proposed FWR. It is notable that both our theoretical model and experiments exhibit uneven rotation of the FWR during flight, i.e. rotation speed dropping in the downstroke and increasing in the upstroke, which further tests the proposed theoretical model and uncovers the relationship between flapping and passive rotation in the FWR. To further validate the performance of the design, free flight tests are conducted, and the proposed FWR demonstrates stable liftoff at the designed working point.}, }
@article {pmid37295099, year = {2023}, author = {Zhu, HY and Xie, JH and Xia, KQ}, title = {Circulation in Quasi-2D Turbulence: Experimental Observation of the Area Rule and Bifractality.}, journal = {Physical review letters}, volume = {130}, number = {21}, pages = {214001}, doi = {10.1103/PhysRevLett.130.214001}, pmid = {37295099}, issn = {1079-7114}, abstract = {We present an experimental study of the velocity circulation in a quasi-two-dimensional turbulent flow. We show that the area rule of circulation around simple loops holds in both the forward cascade enstrophy inertial range (ΩIR) and the inverse cascade energy inertial range (EIR): When the side lengths of a loop are all within the same inertial range, the circulation statistics depend on the loop area alone. It is also found that, for circulation around figure-eight loops, the area rule still holds in EIR but is not applicable in ΩIR. In ΩIR, the circulation is nonintermittent; whereas in EIR, the circulation is bifractal: space filling for moments of the order of 3 and below and a monofractal with a dimension of 1.42 for higher orders. Our results demonstrate, as in a numerical study of 3D turbulence [K. P. Iyer et al., Circulation in High Reynolds Number Isotropic Turbulence is a Bifractal, Phys. Rev. X 9, 041006 (2019).PRXHAE2160-330810.1103/PhysRevX.9.041006], that, in terms of circulation, turbulent flows exhibit a simpler behavior than velocity increments, as the latter are multifractals.}, }
@article {pmid37292291, year = {2023}, author = {Das, A and Mahmood, FT and Smriti, RB and Saha, S and Hasan, MN}, title = {CFD analysis of heat transfer enhancement by wall mounted flexible flow modulators in a channel with pulsatile flow.}, journal = {Heliyon}, volume = {9}, number = {6}, pages = {e16741}, pmid = {37292291}, issn = {2405-8440}, abstract = {The aim of the present study is to explore heat transfer and pressure drop characteristics in a pulsating channel flow due to wall-mounted flexible flow modulators (FFM). Cold air in pulsating fashion is forced to enter through the channel having isothermally heated top and bottom walls with one/multiple FFMs mounted on them. The dynamic conditions of pulsating inflow are characterized by Reynolds number, non-dimensional pulsation frequency and amplitude. Applying the Galerkin finite element method in an Arbitrary Lagrangian-Eulerian (ALE) framework, the present unsteady problem has been solved. Flexibility (10[-4] ≤ Ca ≤ 10[-7]), orientation angle (60° ≤ θ ≤ 120°), and location of FFM(s) have been considered in this study to find out the best-case scenario for heat transfer enhancement. The system characteristics have been analyzed by vorticity contours and isotherms. Heat transfer performance has been evaluated in terms of Nusselt number variations and pressure drop across the channel. Besides, power spectrum analysis of thermal field oscillation along with that of the FFM's motion induced by pulsating inflow has been performed. The present study reveals that single FFM having flexibility of Ca = 10[-5] and an orientation angle of θ = 90° offers the best-case scenario for heat transfer enhancement.}, }
@article {pmid37285818, year = {2023}, author = {Derikvand, M and Salehi, AA and Solari, MS and Najafi, F}, title = {Investigation into the effects of hydrophobicity on thermohydraulic characteristics and entropy generation of hybrid nanofluid with the magnetic property in a micro-heat sink under a magnetic field.}, journal = {Nanotechnology}, volume = {34}, number = {36}, pages = {}, doi = {10.1088/1361-6528/acdc2f}, pmid = {37285818}, issn = {1361-6528}, mesh = {Entropy ; *Hot Temperature ; *Nanotubes, Carbon ; Magnetic Fields ; Hydrophobic and Hydrophilic Interactions ; }, abstract = {The cooling of devices is a big challenge in the electronics industry, and most process units (graphical are central process units) experience defects under harsh temperature conditions, so dissipating generated heat under various working conditions should be studied seriously. This study investigates the magnetohydrodynamics of hybrid ferro-nanofluids in the presence of hydrophobic surfaces in a micro-heat sink. To scrutinize this study, a finite volume method (FVM) is applied. The ferro-nanofluid includes water as a base fluid and multiwall carbon nanotubes (MWCNTs) and Fe3O4as nanoadditives, which are used in three concentrations (0, 1, and 3%). Other parameters such as the Reynolds number (5-120), Hartmann number (magnitude of the magnetic field from 0 to 6), and hydrophobicity of surfaces are scrutinized for their impacts on heat transfer and hydraulic variables as well as entropy generation variables. The outcomes indicate that increasing the level of hydrophobicity in surfaces leads simultaneously to improved heat exchange and reduced pressure drop. Likewise, it decreases the frictional and thermal types of entropy generation. Intensifying the magnitude of the magnetic field enhances the heat exchange as much as the pressure drop. It can also decrease the thermal term in entropy generation equations for the fluid, but increase the frictional entropy generation and adds a new term, magnetic entropy generation. Incrementing the Reynolds number improves the convection heat transfer parameters, although it intensifies the pressure drop in the length of the channel. Also, the thermal entropy generation and frictional entropy generation decrease and increase with an increasing flow rate (Reynolds number).}, }
@article {pmid37280357, year = {2023}, author = {Ibrahim, MG and Abou-Zeid, MY}, title = {Computational simulation for MHD peristaltic transport of Jeffrey fluid with density-dependent parameters.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {9191}, pmid = {37280357}, issn = {2045-2322}, abstract = {This study aimed to give a new theoretical recommendation for non-dimensional parameters depending on the fluid temperature and concentration. This suggestion came from the fact of fluid density may change with the fluid temperature ([Formula: see text]) and concentration ([Formula: see text]). So, a newly released mathematical form of Jeffrey fluid with peristalsis through the inclined channel is constructed. The problem model defines a mathematical fluid model which converts using non-dimensional values. A sequentially used technique called the Adaptive shooting method for finding the problem solutions. Axial velocity behavior has become a novel concern to Reynolds number. In contradiction to different values of parameters, the temperature and concentration profiles are designated/sketched. The results show that the high value of the Reynolds number acts as a fluid temperature damper, while it boosts the concentration of the fluid particle. The non-constant fluid density recommendation makes the Darcy number controls with a fluid velocity which is virtually significant in drug carries applications or blood circulation systems. To verify the obtained results, a numerical comparison for obtained results has been made with a trustful algorithm with aid of AST using wolfram Mathematica version 13.1.1.}, }
@article {pmid37278331, year = {2023}, author = {Shashank, HJ and Melikhov, Y and Ekiel-Jeżewska, ML}, title = {Dynamics of ball chains and highly elastic fibres settling under gravity in a viscous fluid.}, journal = {Soft matter}, volume = {19}, number = {26}, pages = {4829-4846}, doi = {10.1039/d3sm00255a}, pmid = {37278331}, issn = {1744-6848}, abstract = {We study experimentally the dynamics of one and two ball chains settling under gravity in a highly viscous silicon oil at a Reynolds number much smaller than unity. We record the motion and shape deformation using two cameras. We demonstrate that single ball chains in most cases do not tend to be planar and often rotate, not keeping the ends at the same horizontal level. Shorter ball chains usually form shapes resembling distorted U. Longer ones in the early stage of the evolution form a shape resembling distorted W, and later deform non-symmetrically and significantly out of a plane. The typical evolution of shapes observed in our experiments with single ball chains is reproduced in our numerical simulations of a single elastic filament. In the computations, the filament is modelled as a chain of beads. Consecutive beads are connected by springs. Additional springs link consecutive pairs of beads. Elastic forces are assumed to be much smaller than gravity. As a result, the fibre is very flexible. We assume that the fluid sticks to the surfaces of the beads. We perform multipole expansion of the Stokes equations, with a lubrication correction. This method is implemented in the precise HYDROMULTIPOLE numerical codes. In our experiments, two ball chains, initially one above the other, later move away or approach each other, for a larger or smaller initial distance, respectively.}, }
@article {pmid37276558, year = {2023}, author = {Lustro, JRT and Shimizu, Y and Kawahara, G}, title = {Homoclinic bifurcation and switching of edge state in plane Couette flow.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {33}, number = {6}, pages = {}, doi = {10.1063/5.0133492}, pmid = {37276558}, issn = {1089-7682}, abstract = {We identify the presence of three homoclinic bifurcations that are associated with edge states in a system that is governed by the full Navier-Stokes equation. In plane Couette flow with a streamwise period slightly longer than the minimal unit, we describe a rich bifurcation scenario that is related to new time-periodic solutions and the Nagata steady solution [M. Nagata, J. Fluid Mech. 217, 519-527 (1990)]. In this computational domain, the vigorous time-periodic solution (PO3) with comparable fluctuation amplitude to turbulence and the lower branch of the Nagata steady solution are considered as edge states at different ranges of Reynolds number. These edge states can help in understanding the mechanism of subcritical transition to turbulence in wall-bounded shear flows. At the Reynolds numbers at which the homoclinic bifurcations occur, we find the creation (or destruction) of the time-periodic solutions. At a higher Reynolds number, we observe the edge state switching from the lower-branch Nagata steady solution to PO3 at the creation of this vigorous cycle due to the homoclinic bifurcation. Consequently, the formation of the boundary separating the basins of attraction of the laminar attractor and the time-periodic/chaotic attractor also switches to the respective stable manifolds of the edge states, providing a change in the behavior of a typical amplitude of perturbation toward triggering the transition to turbulence.}, }
@article {pmid37274523, year = {2023}, author = {Ijaz, S and Abdullah, M and Sadaf, H and Nadeem, S}, title = {Generalized complex cilia tip modeled flow through an electroosmotic region.}, journal = {Journal of Central South University}, volume = {30}, number = {4}, pages = {1217-1230}, pmid = {37274523}, issn = {2227-5223}, abstract = {In this analysis, we explore a nanofluid model that represents the role of ciliary carpets in the transport of magnetohydrodynamic fluid in an electroosmotic channel. Hybrid nanofluid features are also taken into interpretation. The equations leading the flow analysis are converted into non-dimensional form by supposing long wavelength and low Reynolds number approximations. Analytical solutions for velocity distribution, pressure gradient and stream function are acquired and solved by a mathematic solver. The effects of the relevant physical parameters are graphically noted. The consequence of the present model has remarkable applications, which can be used in various areas of biological transport processes, artificial cilia design and in the operation of other mechanical devices.}, }
@article {pmid37263239, year = {2023}, author = {Ronco, C and Bellomo, R}, title = {The Process of Adsorption and Cartridge Design.}, journal = {Contributions to nephrology}, volume = {200}, number = {}, pages = {74-81}, doi = {10.1159/000529295}, pmid = {37263239}, issn = {1662-2782}, mesh = {Humans ; *Adsorption ; }, abstract = {The mechanism of adsorption is regulated by various factors including the nature of the sorbent and the molecules involved in the adsorption process. The design of a device for adsorption therapies must fulfil specific requirements. The device should allow the use of the minimum amount of sorbent material sufficient to achieve safe and effective blood purification therapy. Each component of the device must respond to criteria of safety and function in order to maximize the efficiency of the cartridge. The design should be optimized to enable utilization of all the sorbent surface available for adsorption. The structure and packing of the sorbent particles should allow the even distribution of flow inside the cartridge and the avoidance of channeling phenomena and excessive resistance to flow. All these factors depend on specific governing laws such as the Kozeny-Carman equation and Darcy's law. The system must also consider blood viscosity and possible turbulent flows (Reynolds number). The final manufacturing process of a sorbent unit must also consider the dimensions and the cost, and the final performance after sterilization and storage.}, }
@article {pmid37259126, year = {2023}, author = {Bocanegra Evans, H and Segnini, JM and Doosttalab, A and Cordero, J and Castillo, L}, title = {Effect of cartilaginous rings in tracheal flow with stenosis.}, journal = {BMC biomedical engineering}, volume = {5}, number = {1}, pages = {5}, pmid = {37259126}, issn = {2524-4426}, abstract = {BACKGROUND: In respiratory fluid dynamics research, it is typically assumed that the wall of the trachea is smooth. However, the trachea is structurally supported by a series of cartilaginous rings that create undulations on the wall surface, which introduce perturbations into the flow. Even though many studies use realistic Computer Tomography (CT) scan data to capture the complex geometry of the respiratory system, its limited spatial resolution does not resolve small features, including those introduced by the cartilaginous rings.<br><br>RESULTS: Here we present an experimental comparison of two simplified trachea models with Grade II stenosis (70% blockage), one with smooth walls and second with cartilaginous rings. The use a unique refractive index-matching method provides unprecedented optical access and allowed us to perform non-intrusive velocity field measurements close to the wall (e.g., Particle Image Velocimetry (PIV)). Measurements were performed in a flow regime comparable to a resting breathing state (Reynolds number ReD&#x2009;=&#x2009;3350). The cartilaginous rings induce velocity fluctuations in the downstream flow, enhancing the near-wall transport of momentum flux and thus reducing flow separation in the downstream flow. The maximum upstream velocity in the recirculation region is reduced by 38%, resulting in a much weaker recirculation zone- a direct consequence of the cartilaginous rings.<br><br>CONCLUSIONS: These results highlight the importance of the cartilaginous rings in respiratory flow studies and the mechanism to reduce flow separation in trachea stenosis.}, }
@article {pmid37255166, year = {2023}, author = {Silva, MLFD and Gonçalves, SF and Haniel, J and Lucas, TC and Huebner, R}, title = {Comparative study between 1-way and 2-way coupled fluid-structure interaction in numerical simulation of aortic arch aneurysms.}, journal = {Anais da Academia Brasileira de Ciencias}, volume = {95}, number = {suppl 1}, pages = {e20210859}, doi = {10.1590/0001-3765202320210859}, pmid = {37255166}, issn = {1678-2690}, mesh = {Humans ; *Aneurysm, Aortic Arch ; Models, Cardiovascular ; *Aortic Aneurysm ; Computer Simulation ; }, abstract = {Hemodynamic forces are related to pathological variations of the cardiovascular system, and numerical simulations for fluid-structure interaction have been systematically used to analyze the behavior of blood flow and the arterial wall in aortic aneurysms. This paper proposes a comparative analysis of 1-way and 2-way coupled fluid-structure interaction for aortic arch aneurysm. The coupling models of fluid-structure interaction were conducted using 3D geometry of the thoracic aorta from computed tomography. Hyperelastic anisotropic properties were estimated for the Holzapfel arterial wall model. The rheological behavior of the blood was modeled by the Carreau-Yasuda model. The results showed that the 1-way approach tends to underestimate von Mises stress, displacement, and strain over the entire cardiac cycle, compared to the 2-way approach. In contrast, the behavior of the variables of flow field, velocity, wall shear stress, and Reynolds number when coupled by the 1-way model was overestimated at the systolic moment and tends to be equal at the diastolic moment. The quantitative differences found, especially during the systole, suggest the use of 2-way coupling in numerical simulations of aortic arch aneurysms due to the hyperelastic nature of the arterial wall, which leads to a strong iteration between the fluid and the arterial wall.}, }
@article {pmid37249683, year = {2023}, author = {Deng, X and Sheng, P}, title = {Evolution of channel flow and Darcy's law beyond the critical Reynolds number.}, journal = {The European physical journal. E, Soft matter}, volume = {46}, number = {6}, pages = {37}, pmid = {37249683}, issn = {1292-895X}, support = {16303918//Research Grants Council of Hong Kong/ ; }, abstract = {For incompressible channel flow, there is a critical state, characterized by a critical Reynolds number Rec and a critical wavevector mc along the channel direction, beyond which the channel flow becomes unstable in the linear regime. In this work, we investigate the channel flow beyond the critical state and find the existence of a new fluctuating, quasi-stationary flow that comprises the laminar Poiseuille flow superposed with a counter-flow component, accompanied by vortices and anti-vortices. The net flow rate is reduced by ~ 15% from the linear, laminar regime. Our study is facilitated by the analytical solution of the linearized, incompressible, three-dimensional (3D) Navier-Stokes (NS) equation in the channel geometry, with the Navier boundary condition, alternatively denoted as the hydrodynamic modes (HMs). By using the HMs as the complete mathematical basis for expanding the velocity in the NS equation, the Rec is evaluated to 5-digit accuracy when compared to the well-known Orszag result, without invoking the standard Orr-Sommerfeld equation. Beyond Rec, the analytical solution is indispensable in offering physical insight to those features of the counter-flow component that differs from any of the pressure-driven channel flows. In particular, the counter flow is found to comprise multiple HMs, some with opposite flow direction, that can lead to a net boundary reaction force along the counter-flow direction. The latter is analyzed to be necessary for satisfying Newton's law. Experimental verification of the predictions is discussed.}, }
@article {pmid37241559, year = {2023}, author = {Che, H and Xu, Q and Xu, G and Fu, X and Wang, X and He, N and Zhu, Z}, title = {Numerical Study on Characteristics of Convection and Temperature Evolution in Microchannel of Thermal Flowmeter.}, journal = {Micromachines}, volume = {14}, number = {5}, pages = {}, pmid = {37241559}, issn = {2072-666X}, support = {No. U1738119//National Natural Science Foundation of China/ ; TZYY08001//China Manned Space Engineering Application Program/ ; MT1401S//China Manned Space Engineering Application Program-Two-Phase system research Rack/ ; }, abstract = {During practical usage, thermal flowmeters have a limited range of applications. The present work investigates the factors influencing thermal flowmeter measurements and observes the effects of buoyancy convection and forced convection on the flow rate measurement sensitivity. The results show that the gravity level, inclination angle, channel height, mass flow rate, and heating power affect the flow rate measurements by influencing the flow pattern and the temperature distribution. Gravity determines the generation of convective cells, while the inclination angle affects the location of the convective cells. Channel height affects the flow pattern and temperature distribution. Higher sensitivity can be achieved with smaller mass flow rates or higher heating power. According to the combined influence of the aforementioned parameters, the present work investigates the flow transition based on the Reynolds number and the Grashof number. When the Reynolds number is below the critical value corresponding to the Grashof number, convective cells emerge and affect the accuracy of flowmeter measurements. The research on influencing factors and flow transition presented in this paper has potential implications for the design and manufacture of thermal flowmeters under different working conditions.}, }
@article {pmid37231052, year = {2023}, author = {Li, S and Mao, L and Alizadeh, A and Zhang, X and Mousavi, SV}, title = {The application of non-uniform magnetic field for thermal enhancement of the nanofluid flow inside the U-turn pipe at solar collectors.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {8471}, pmid = {37231052}, issn = {2045-2322}, abstract = {The improvement of heat transfer inside the solar heat exchangers is important for the development of solar energy in an urban area. In this study, the usage of a non-uniform magnetic field on the thermal efficiency of the nanofluid (Fe3O4) streaming inside the U-turn pipe of solar heat exchangers is examined. Computational fluid dynamic is applied to visualize the nanofluid flow inside the solar heat exchanger. The role of magnetic intensity and Reynolds number on thermal efficiency are fully investigated. The effect of single and triple sources of the magnetic field is also studied in our research. Obtained results indicate that the usage of the magnetic field results in the production of vortex in the base fluid and heat transfer improves inside the domain. Our finding indicates that the usage of the magnetic field with Mn = 25 K would improve the average heat transfer by about 21% along the U-turn pipe of solar heat exchangers.}, }
@article {pmid37230014, year = {2023}, author = {Yeom, J and Park, J and Park, JY}, title = {Fluid dynamic simulation for cellular damage due to lymphatic flow within the anatomical arrangement of the outer hair cells in the cochlea.}, journal = {Computers in biology and medicine}, volume = {161}, number = {}, pages = {106986}, doi = {10.1016/j.compbiomed.2023.106986}, pmid = {37230014}, issn = {1879-0534}, mesh = {Humans ; *Hair Cells, Auditory, Outer/physiology ; *Hydrodynamics ; Cochlea/physiology ; Hair Cells, Auditory, Inner/physiology ; }, abstract = {Damage to the sensory hair cells in the cochlea is a major cause of hearing loss since human sensory hair cells do not regenerate naturally after damage. As these sensory hair cells are exposed to a vibrating lymphatic environment, they may be affected by physical flow. It is known that the outer hair cells (OHCs) are physically more damaged by sound than the inner hair cells (IHCs). In this study, the lymphatic flow is compared using computational fluid dynamics (CFD) based on the arrangement of the OHCs, and the effects of such flow on the OHCs is analyzed. In addition, flow visualization is used to validate the Stokes flow. The Stokes flow behavior is attributed to the low Reynolds number, and the same behavior is observed even when the flow direction is reversed. When the distance between the rows of the OHCs is large, each row is independent, but when this distance is short, the flow change in each row influences the other rows. The stimulation caused by flow changes on the OHCs is confirmed through surface pressure and shear stress. The OHCs located at the base with a short distance between the rows receive excess hydrodynamic stimulation, and the tip of the V-shaped pattern receives an excess mechanical force. This study attempts to understand the contributions of lymphatic flow to OHC damage by quantitatively suggesting stimulation of the OHCs and is expected to contribute to the development of OHC regeneration technologies in the future.}, }
@article {pmid37220708, year = {2023}, author = {Tisdell, CC}, title = {Improved perturbation solution for two-dimensional viscous flow between expanding or contracting permeable walls.}, journal = {Journal of biomechanics}, volume = {155}, number = {}, pages = {111642}, doi = {10.1016/j.jbiomech.2023.111642}, pmid = {37220708}, issn = {1873-2380}, mesh = {Viscosity ; *Physical Examination ; }, abstract = {Despite the continuing interest in the transport of biological fluid within contracting or expanding vessels, our knowledge is yet to be fully developed, even in the two-dimensional case. For example, explicit solutions and close approximations to these models remain unknown, and the physical problem has been restricted to the "slow" expansion or contraction of the walls. Thus, the purpose of this short communication is to partially address such challenges and gaps by generating explicit solutions and improving approximations to the flow problem without the "slowness" restriction being imposed. We show that when the Reynolds number is zero (i.e., the inviscid case), the corresponding homogeneous differential equation under consideration may be completely solved. We then illustrate how this exact solution may be leveraged to form more precise approximations to the flow via perturbation techniques when the Reynolds number is small. Our perturbation approach is only in one parameter (the Reynolds number) instead of the usual two parameters (the Reynolds number and wall dilation rate), and thus we make no restriction regarding the "slowness" of wall expansion or contraction for our general perturbation scheme. Our act of "shining new light through old windows" improves and extends the results of Majdalani, Zhou and Dawson and, moreover, our method has significant potential to be applied by researchers to form more precise one-parameter perturbation approximations to flow problems in contrast to the limitations of the traditional two-parameter perturbation approaches that have dominated the literature.}, }
@article {pmid37215871, year = {2023}, author = {Zhao, L and Wang, Y and Qi, Z}, title = {Investigation of periodic characteristics of perturbed flow over a slender body.}, journal = {Heliyon}, volume = {9}, number = {5}, pages = {e16194}, pmid = {37215871}, issn = {2405-8440}, abstract = {The asymmetric flow over a slender body was particularly sensitive to the nose at a high angle of attack (AoA). Two patterns of separation occurred on the noses of the pointed-nosed slender body and blunt-nosed slender body as open- and close-type separation, respectively. The effects of the bluntness were investigated at high AoA (α = 50°) to clarify the evolution of the separated pattern from open-to close-type separation by the nose and by the periodic characteristics of perturbed flow. Wind tunnel experimental tests were conducted to investigate the periodic characteristics of asymmetric flow at a Reynolds number ReD = 1.54 × 10[5], based on incoming free-stream velocity (U∞) and the diameter (D) of the model. A particle was attached to the tip of the nose to induce the perturbed flow and attain a definite and predictable asymmetric flow in experimental tests. The pressure scanning and surface oil-flow visualization techniques were used to capture the pressure distributions and flow separations. The major findings were that axial flow increases with the increase of bluntness, resulting in open-type separation turning into close-type separation, and the perturbation moved from downstream to upstream of starting points of the separation line. The critical bluntness of separation pattern switching from open-type to close-type located between 1.5 and 3. Thus, the management of perturbation on asymmetric flow pattern switched from directly participating in separation to influencing separation through micro-flow. Therefore, the locations of perturbation and starting points of the separation line were closely related to asymmetric flow management by perturbation, then affecting the periodic characteristics of perturbed flow.}, }
@article {pmid37198775, year = {2023}, author = {Yoo, H and Wissocq, G and Jacob, J and Favier, J and Sagaut, P}, title = {Compressible lattice Boltzmann method with rotating overset grids.}, journal = {Physical review. E}, volume = {107}, number = {4-2}, pages = {045306}, doi = {10.1103/PhysRevE.107.045306}, pmid = {37198775}, issn = {2470-0053}, abstract = {The numerical instability of the lattice Boltzmann method (LBM) at high Mach or high Reynolds number flow is well identified, and it remains a major barrier to its application in more complex configurations such as moving geometries. This work combines the compressible lattice Boltzmann model with rotating overset grids (the so-called Chimera method, sliding mesh, or moving reference frame) for high Mach flows. This paper proposes to use the compressible hybrid recursive regularized collision model with fictitious forces (or inertial forces) in a noninertial rotating reference frame. Also, polynomial interpolations are investigated, which allow fixed inertial and rotating noninertial grids to communicate with each other. We suggest a way to effectively couple the LBM with the MUSCL-Hancock scheme in the rotating grid, which is needed to account for thermal effect of compressible flow. As a result, this approach is demonstrated to have an extended Mach stability limit for the rotating grid. It also demonstrates that this complex LBM scheme can maintain the second-order accuracy of the classic LBM by appropriately using numerical methods like polynomial interpolations and the MUSCL-Hancock scheme. Furthermore, the method shows a very good agreement on aerodynamic coefficients compared to experiments and the conventional finite-volume scheme. This work presents a thorough academic validation and error analysis of the LBM for simulating moving geometries in high Mach compressible flows.}, }
@article {pmid37190405, year = {2023}, author = {Niven, RK}, title = {Dimensionless Groups by Entropic Similarity: I - Diffusion, Chemical Reaction and Dispersion Processes.}, journal = {Entropy (Basel, Switzerland)}, volume = {25}, number = {4}, pages = {}, pmid = {37190405}, issn = {1099-4300}, abstract = {Since the time of Buckingham in 1914, dimensional analysis and similarity arguments based on dimensionless groups have served as powerful tools for the analysis of systems in all branches of science and engineering. Dimensionless groups are generally classified into those arising from geometric similarity, based on ratios of length scales; kinematic similarity, based on ratios of velocities or accelerations; and dynamic similarity, based on ratios of forces. We propose an additional category of dimensionless groups based on entropic similarity, defined by ratios of (i) entropy production terms; (ii) entropy flow rates or fluxes; or (iii) information flow rates or fluxes. Since all processes involving work against friction, dissipation, diffusion, dispersion, mixing, separation, chemical reaction, gain of information or other irreversible changes are driven by (or must overcome) the second law of thermodynamics, it is appropriate to analyze them directly in terms of competing entropy-producing and transporting phenomena and the dominant entropic regime, rather than indirectly in terms of forces. In this study, entropic groups are derived for a wide variety of diffusion, chemical reaction and dispersion processes relevant to fluid mechanics, chemical engineering and environmental engineering. It is shown that many dimensionless groups traditionally derived by kinematic or dynamic similarity (including the Reynolds number) can also be recovered by entropic similarity-with a different entropic interpretation-while many new dimensionless groups can also be identified. The analyses significantly expand the scope of dimensional analysis and similarity arguments for the resolution of new and existing problems in science and engineering.}, }
@article {pmid37186956, year = {2023}, author = {Guo, Q and Zhang, J and Li, D and Yu, H}, title = {Effect of Wettability on the Collision Behavior of Acoustically Excited Droplets.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {39}, number = {21}, pages = {7408-7417}, doi = {10.1021/acs.langmuir.3c00571}, pmid = {37186956}, issn = {1520-5827}, abstract = {Acoustic droplet ejection (ADE) is a noncontact technique for micro-liquid handling (usually nanoliters or picoliters) that is not restricted by nozzles and enables high-throughput liquid dispensing without sacrificing precision. It is widely regarded as the most advanced solution for liquid handling in large-scale drug screening. Stable coalescence of the acoustically excited droplets on the target substrate is a fundamental requirement during the application of the ADE system. However, it is challenging to investigate the collision behavior of nanoliter droplets flying upward during the ADE. In particular, the dependence of the droplet's collision behavior on substrate wettability and droplet velocity has yet to be thoroughly analyzed. In this paper, the kinetic processes of binary droplet collisions were investigated experimentally for different wettability substrate surfaces. Four states occur as the droplet collision velocity increases: coalescence after minor deformation, complete rebound, coalescence during rebound, and direct coalescence. For the hydrophilic substrate, there are wider ranges of Weber number (We) and Reynolds number (Re) in the complete rebound state. And with the decrease of the substrate wettability, the critical Weber and Reynolds numbers for the coalescence during rebound and the direct coalescence decrease. It is further revealed that the hydrophilic substrate is susceptible to droplet rebound because the sessile droplet has a larger radius of curvature and the viscous energy dissipation is greater. Besides, the prediction model of the maximum spreading diameter was established by modifying the droplet morphology in the complete rebound state. It is found that, under the same Weber and Reynolds numbers, droplet collisions on the hydrophilic substrate achieve a smaller maximum spreading coefficient and greater viscous energy dissipation, so the hydrophilic substrate is prone to droplet bounce.}, }
@article {pmid37123410, year = {2023}, author = {Ishimoto, K and Gaffney, EA and Smith, DJ}, title = {Squirmer hydrodynamics near a periodic surface topography.}, journal = {Frontiers in cell and developmental biology}, volume = {11}, number = {}, pages = {1123446}, pmid = {37123410}, issn = {2296-634X}, abstract = {The behaviour of microscopic swimmers has previously been explored near large-scale confining geometries and in the presence of very small-scale surface roughness. Here, we consider an intermediate case of how a simple microswimmer, the tangential spherical squirmer, behaves adjacent to singly and doubly periodic sinusoidal surface topographies that spatially oscillate with an amplitude that is an order of magnitude less than the swimmer size and wavelengths that are also within an order of magnitude of this scale. The nearest neighbour regularised Stokeslet method is used for numerical explorations after validating its accuracy for a spherical tangential squirmer that swims stably near a flat surface. The same squirmer is then introduced to different surface topographies. The key governing factor in the resulting swimming behaviour is the size of the squirmer relative to the surface topography wavelength. For instance, directional guidance is not observed when the squirmer is much larger, or much smaller, than the surface topography wavelength. In contrast, once the squirmer size is on the scale of the topography wavelength, limited guidance is possible, often with local capture in the topography troughs. However, complex dynamics can also emerge, especially when the initial configuration is not close to alignment along topography troughs or above topography crests. In contrast to sensitivity in alignment and topography wavelength, reductions in the amplitude of the surface topography or variations in the shape of the periodic surface topography do not have extensive impacts on the squirmer behaviour. Our findings more generally highlight that the numerical framework provides an essential basis to elucidate how swimmers may be guided by surface topography.}, }
@article {pmid37115869, year = {2023}, author = {Ambruş, VE and Schlichting, S and Werthmann, C}, title = {Establishing the Range of Applicability of Hydrodynamics in High-Energy Collisions.}, journal = {Physical review letters}, volume = {130}, number = {15}, pages = {152301}, doi = {10.1103/PhysRevLett.130.152301}, pmid = {37115869}, issn = {1079-7114}, abstract = {We simulate the space-time dynamics of high-energy collisions based on a microscopic kinetic description in the conformal relaxation time approximation, in order to determine the range of applicability of an effective description in relativistic viscous hydrodynamics. We find that hydrodynamics provides a quantitatively accurate description of collective flow when the average inverse Reynolds number Re^{-1} is sufficiently small and the early preequilibrium stage is properly accounted for. We further discuss the implications of our findings for the (in)applicability of hydrodynamics in proton-proton, proton-nucleus, and light nucleus collisions.}, }
@article {pmid37112102, year = {2023}, author = {Lin, W and Li, Z and Zhang, S and Lin, J}, title = {Numerical Study on the Distribution of Rodlike Particles in Laminar Flows of Power Law Fluids Past a Cylinder.}, journal = {Polymers}, volume = {15}, number = {8}, pages = {}, pmid = {37112102}, issn = {2073-4360}, support = {12132015//National Natural Science Foundation of China/ ; }, abstract = {The contraction/expansion laminar flow containing rodlike particles in power-law fluid is studied numerically when the particles are in a dilute phase. The fluid velocity vector and streamline of flow are given at the finite Reynolds number (Re) region. The effects of Re, power index n and particle aspect ratio β on the spatial and orientation distributions of particles are analyzed. The results showed that for the shear-thickening fluid, particles are dispersed in the whole area in the contraction flow, while more particles are gathered near the two walls in the expansion flow. The spatial distribution of particles with small β is more regular. Β has a significant, n has a moderate, but Re has a small impact on the spatial distribution of particles in the contraction and expansion flow. In the case of large Re, most particles are oriented in the flow direction. The particles near the wall show obvious orientation along the flow direction. In shear-thickening fluid, when the flow changes from contraction to expansion, the orientation distribution of particles becomes more dispersed; while in shear-thinning fluid, the opposite is true. More particles orient to the flow direction in expansion flow than that in contraction flow. The particles with a large β tend to align with the flow direction more obviously. Re, n and β have great influence on the orientation distribution of particles in the contraction and expansion flow. Whether the particles initially located at the inlet can bypass the cylinder depends on the transverse position and initial orientation of the particles at the inlet. The number of particles with θ0 = 90° bypassing the cylinder is the largest, followed by θ0 = 45° and θ0 = 0°. The conclusions obtained in this paper have reference value for practical engineering applications.}, }
@article {pmid37100809, year = {2023}, author = {Pilloton, C and Lugni, C and Graziani, G and Fedele, F}, title = {Wave dispersion in moderate channel turbulence.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {6801}, pmid = {37100809}, issn = {2045-2322}, abstract = {We study channel turbulence by interpreting its vorticity as a random sea of ocean wave packet analogues. In particular, we investigate the ocean-like properties of vortical packets applying stochastic methods developed for oceanic fields. Taylor's hypothesis of frozen eddies does not hold when turbulence is not weak, and vortical packets change shape as they are advected by the mean flow, altering their own speed. This is the physical manifestation of a hidden wave dispersion of turbulence. Our analysis at the bulk Reynolds number Reb = 5600 suggests that turbulent fluctuations behave dispersively as gravity-capillary waves, with capillarity being dominant near the wall region.}, }
@article {pmid37097943, year = {2023}, author = {Prasad, V and Sharma, A and Kulkarni, SS}, title = {Chaotic advection in a recirculating flow: Effect of a fluid multiple-flexible-solid interaction.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {33}, number = {4}, pages = {}, doi = {10.1063/5.0132986}, pmid = {37097943}, issn = {1089-7682}, abstract = {This paper deals with chaotic advection due to a two-way interaction between flexible elliptical-solids and a laminar lid-driven cavity flow in two dimensions. The present Fluid multiple-flexible-Solid Interaction study involves various number N(= 1-120) of equal-sized neutrally buoyant elliptical-solids (aspect ratio β = 0.5) such that they result in the total volume fraction Φ = 10 % as in our recent study on single solid, done for non-dimensional shear modulus G ∗ = 0.2 and Reynolds number R e = 100. Results are presented first for flow-induced motion and deformation of the solids and later for chaotic advection of the fluid. After the initial transients, the fluid as well as solid motion (and deformation) attain periodicity for smaller N ≤ 10 while they attain aperiodic states for larger N > 10. Adaptive material tracking (AMT) and Finite-Time Lyapunov Exponent (FTLE)-based Lagrangian dynamical analysis revealed that the chaotic advection increases up to N = 6 and decreases at larger N(= 6-10) for the periodic state. Similar analysis for the transient state revealed an asymptotic increase in the chaotic advection with increasing N ≤ 120. These findings are demonstrated with the help of two types of chaos signatures: exponential growth of material blob's interface and Lagrangian coherent structures, revealed by the AMT and FTLE, respectively. Our work, which is relevant to several applications, presents a novel technique based on the motion of multiple deformable-solids for enhancement of chaotic advection.}, }
@article {pmid37092929, year = {2023}, author = {Yang, C and Arcondoulis, EJG and Yang, Y and Guo, J and Maryami, R and Bi, C and Liu, Y}, title = {Active control of airfoil turbulent boundary layer noise with trailing-edge blowing.}, journal = {The Journal of the Acoustical Society of America}, volume = {153}, number = {4}, pages = {2115}, doi = {10.1121/10.0017787}, pmid = {37092929}, issn = {1520-8524}, abstract = {Large Eddy Simulation (LES) and Ffowcs Williams-Hawkings acoustic analogy are performed to study the effect of trailing-edge blowing on airfoil self-noise. Simulations were conducted using a National Advisory Committee for Aeronautics 0012 airfoil at zero angle of attack and a chord-based Reynolds number of 4 × 10 5. The aerodynamic and aeroacoustic characteristics of the baseline airfoil were thoroughly verified by comparison with previous numerical and experimental data. The noise reduction effects of continuous and local blowing with different blowing ratios and blowing momentum coefficients were compared. A maximum noise reduction of 20 dB was achieved via trailing-edge blowing and the noise reduction mechanisms of the two blowing methods were discussed. The LES results show a pair of recirculation bubbles in the airfoil wake which are suppressed by trailing-edge blowing. As the blowing vortices convect into the wake, they stretch and stabilize the shear flows from airfoil surfaces. Instantaneous vorticity and root mean square velocity fluctuations are also weakened. There is a decrease in the spanwise coherence and an increase in the phase difference, which contribute to noise reduction. It is concluded that the suppression of turbulence fluctuations in the near wake is the main mechanism of noise reduction for airfoil trailing-edge blowing.}, }
@article {pmid37073470, year = {2023}, author = {Roggeveen, JV and Stone, HA and Kurzthaler, C}, title = {Transport of a passive scalar in wide channels with surface topography: An asymptotic theory.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {35}, number = {27}, pages = {}, doi = {10.1088/1361-648X/acc8ad}, pmid = {37073470}, issn = {1361-648X}, abstract = {We generalize classical dispersion theory for a passive scalar to derive an asymptotic long-time convection-diffusion equation for a solute suspended in a wide, structured channel and subject to a steady low-Reynolds-number shear flow. Our asymptotic theory relies on a domain perturbation approach for small roughness amplitudes of the channel and holds for general surface shapes expandable as a Fourier series. We determine an anisotropic dispersion tensor, which depends on the characteristic wavelengths and amplitude of the surface structure. For surfaces whose corrugations are tilted with respect to the applied flow direction, we find that dispersion along the principal direction (i.e. the principal eigenvector of the dispersion tensor) is at an angle to the main flow direction and becomes enhanced relative to classical Taylor dispersion. In contrast, dispersion perpendicular to it can decrease compared to the short-time diffusivity of the particles. Furthermore, for an arbitrary surface shape represented in terms of a Fourier decomposition, we find that each Fourier mode contributes at leading order a linearly-independent correction to the classical Taylor dispersion diffusion tensor.}, }
@article {pmid37069324, year = {2023}, author = {Nyatchouba Nsangue, BT and Tang, H and Liu, W and Xu, L and Hu, F}, title = {Turbulent flow interacting with flexible trawl net structure including simulation catch in flume tank.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {6249}, pmid = {37069324}, issn = {2045-2322}, support = {Grant No. 31902426//National Natural Science Foundation of China/ ; 19YF1419800//Shanghai Sailing Program/ ; D-8002-18-0097//Special Project for the Exploitation and Utilization of Antarctic Biological Resources of the Ministry of Agriculture and Rural Affairs/ ; }, abstract = {The interaction between fluid and the midwater trawl with stocked catches is extremely complex, but essential to improve the understanding of the drag force acting on the trawl, the behavior of the fishing structure during a trawling process, and to predict its selectivity process. The present study assesses the turbulent characteristics inside and around the midwater trawls with catch and without catch linked to its fluttering motion. The analysis is based on three-dimensional electromagnetic current velocity meter measurements performed in the multiple points inside and outside different parts of a 1/35 scaled midwater trawl model with the aim of access the main turbulent flow structure inside and around the gear. Time-averaged normalized flow velocity fields and turbulent flow parameters were analyzed from the measured flow data. Furthermore, Fourier analysis was conducted by watching the time-frequency Power spectrum content of instantaneous flow velocities fields, the fluttering trawl motions, turbulent kinetic energy, and momentum flux. Based on successive analyzes of mean flow characteristics and turbulent flow parameters, it has been demonstrated that the presence of catch inside the trawl net impacts the evolution of unsteady turbulent flow by creating large trawl fluttering motions that strongly affect the flow passage. The results showed that the time-averaged normalized streamwise and transverse flow velocities inside and around the trawl net with catch were 12.41% lower compared with that obtained inside and around the trawl without catch. The turbulent length scale and turbulent Reynolds number obtained in the different part of the trawl net with catch were about 33.05% greater than those obtained on the trawl net without catch, confirming that the unsteady turbulent flow developing inside and around the midwater trawl is influence by the catch and liner. It is observed that the motions of both the trawl without catch and the trawl with catch are mainly of a low-frequency activity and another component related to unsteady turbulent flow street. A complex fluid-structure interaction is then demonstrated where the fluttering motions of the trawl net affect the fluid flow inside and around trawl net, the fluid force, turbulent pattern, and simultaneously, the periodic unsteady turbulent flow influence the trawl motions.}, }
@article {pmid37064396, year = {2023}, author = {Ding, Y and Liu, Z and Wang, X and Xin, R and Shan, D and He, B and Jing, J and Gao, Q and Yang, J and Chen, Y}, title = {Validation of hemodynamic stress calculation in coronary computed tomography angiography versus intravascular ultrasound.}, journal = {Quantitative imaging in medicine and surgery}, volume = {13}, number = {4}, pages = {2339-2351}, pmid = {37064396}, issn = {2223-4292}, abstract = {BACKGROUND: Development in computational fluid dynamics and 3D construction could facilitate the calculation of hemodynamic stresses in coronary computed tomography angiography (CCTA). However, the agreement between CCTA derived stresses and intravascular ultrasound/intravascular coronary angiography (IVUS/ICA)-derived stresses remains undetermined. Thus, the purpose of this study is to investigate if CCTA can serve as alternative to IVUS/ICA for hemodynamic evaluation.<br><br>METHODS: In this retrospective study, 13 patients (14 arteries) with unstable angina who underwent both CCTA and IVUS/ICA at an interval of less than 7 days were consecutively included at the Chinese PLA General Hospital within the year of 2021. Slice-level minimal lumen area (MLA), percent area stenosis, velocity, pressure, Reynolds number, wall shear stress (WSS) and axial plaque stress (APS) were determined by both modalities. The agreement between CCTA and IVUS/ICA was assessed using the intraclass correlation coefficient (ICC), Pearson's correlation coefficient and Bland-Altman analysis.<br><br>RESULTS: CCTA overestimated the degree of area stenosis (50.22%&#xb1;16.15% vs. 36.41%&#xb1;19.37%, P=0.004) with the MLA showing no significant difference (5.81&#xb1;2.24 vs. 6.72&#xb1;2.04 mm[2], P=0.126). No statistical difference was observed in WSS (6.57&#xb1;6.26 vs. 5.98&#xb1;5.55 Pa, P=0.420) and APS (16.03&#xb1;1,159.45 vs. -1.27&#xb1;890.39 Pa, P=0.691) between CCTA and IVUS. Good correlation was found in velocity (ICC: 0.796, 95% CI: 0.752-0.833), Reynolds number (ICC: 0.810, 95% CI: 0.768-0.844) and WSS (ICC: 0.769, 95% CI: 0.718-0.810), while the ICC of APS was (ICC: 0.341, 95% CI: 0.197-0.458), indicating a relatively poor correlation.<br><br>CONCLUSIONS: CCTA can serve as a satisfactory alternative to the reference standard, IVUS/ICA in morphology simulation and hemodynamic stress calculation, especially in the calculation of WSS.}, }
@article {pmid37039923, year = {2023}, author = {Guastoni, L and Rabault, J and Schlatter, P and Azizpour, H and Vinuesa, R}, title = {Deep reinforcement learning for turbulent drag reduction in channel flows.}, journal = {The European physical journal. E, Soft matter}, volume = {46}, number = {4}, pages = {27}, pmid = {37039923}, issn = {1292-895X}, support = {2021-CoG-101043998/ERC_/European Research Council/International ; }, abstract = {We introduce a reinforcement learning (RL) environment to design and benchmark control strategies aimed at reducing drag in turbulent fluid flows enclosed in a channel. The environment provides a framework for computationally efficient, parallelized, high-fidelity fluid simulations, ready to interface with established RL agent programming interfaces. This allows for both testing existing deep reinforcement learning (DRL) algorithms against a challenging task, and advancing our knowledge of a complex, turbulent physical system that has been a major topic of research for over two centuries, and remains, even today, the subject of many unanswered questions. The control is applied in the form of blowing and suction at the wall, while the observable state is configurable, allowing to choose different variables such as velocity and pressure, in different locations of the domain. Given the complex nonlinear nature of turbulent flows, the control strategies proposed so far in the literature are physically grounded, but too simple. DRL, by contrast, enables leveraging the high-dimensional data that can be sampled from flow simulations to design advanced control strategies. In an effort to establish a benchmark for testing data-driven control strategies, we compare opposition control, a state-of-the-art turbulence-control strategy from the literature, and a commonly used DRL algorithm, deep deterministic policy gradient. Our results show that DRL leads to 43% and 30% drag reduction in a minimal and a larger channel (at a friction Reynolds number of 180), respectively, outperforming the classical opposition control by around 20 and 10 percentage points, respectively.}, }
@article {pmid37037634, year = {2023}, author = {Wang, YH and Lin, XY and Cheng, Y and Wang, H and Liu, W and Zhuge, XK and Huo, XL and Bao, N}, title = {Vibration for enhancement of electrochemical analysis of biomolecules in a droplet on the rough surface of a disposable working electrode.}, journal = {Analytica chimica acta}, volume = {1256}, number = {}, pages = {341158}, doi = {10.1016/j.aca.2023.341158}, pmid = {37037634}, issn = {1873-4324}, mesh = {*Vibration ; *Electrochemical Techniques/methods ; Electrodes ; }, abstract = {Although electrochemical detection of microliters-level solutions is attractive for analysis of low-amount biological samples, its performance could be weakened by limited mass transfer due to low Reynolds number and laminar flow. Herein we designed a 3D-printed electroanalytical device to apply vibration for improvement of mass transfer during electrochemical detection. In our approach, the droplet-size sample solution containing Indole-3-acetic acid (IAA, as a model) was directly applied on the effective surface of a disposable working electrode. We demonstrated that vibration could enhance electrochemical responses of IAA more on the rough surface than on the smooth surface of the working electrodes. After optimization, the sensitivity for electrochemical detection of a 20-μL droplet under vibration with the voltage of 7 V increased more than 100% compared with the static condition. The enhanced electrochemical responses brought by vibration could be achieved reproducibly, which could be ascribed to improved mass transfer. Our strategy could be practically applied for differentiation of IAA in different tissues of Marchantia polymorpha with enhanced responses. This study suggested that vibration might become a simple and effective method to improve mass transfer in analysis of microliter-volume solutions, which might be extended for more biochemical assays.}, }
@article {pmid37034318, year = {2023}, author = {Dyverfeldt, P and Trenti, C and Ziegler, M and Bjarnegård, N and Lindenberger, M}, title = {Helical flow in tortuous aortas and its relationship to turbulence: A whole-aorta 4D flow MRI study.}, journal = {Frontiers in cardiovascular medicine}, volume = {10}, number = {}, pages = {1124604}, pmid = {37034318}, issn = {2297-055X}, abstract = {BACKGROUND: Increased vascular tortuosity is a hallmark of ageing of the vascular system, including the aorta. However, the impact of tortuosity on aortic blood flow is unknown. We hypothesized that increased tortuosity would be associated with increased blood flow helicity and with decreased degree of blood flow turbulence as measured by the turbulent kinetic energy (TKE).<br><br>METHODS: 4D Flow MR images covering the entire aorta from the aortic valve to the iliac bifurcation were acquired in 23 normal volunteers aged 18-30 years ("Young") and 23 normal volunteers aged 66-76 years ("Old") without aortic disease. The aorta was segmented and divided into four regions: the ascending, descending, suprarenal abdominal and infrarenal abdominal aorta. Tortuosity, helicity, TKE, flow velocity, and Reynolds number were computed for the whole aorta and for each section.<br><br>RESULTS: Tortuosity and helicity were higher whereas TKE, velocity, and Reynolds number were lower in Old than in Young, for all aortic regions (p&#x2009;<&#x2009;0.05) except for helicity in the descending aorta. Tortuosity correlated positively with helicity and negatively with TKE for all aortic regions (Spearman rho=&#xb1;0.45-&#xb1;0.72, p&#x2009;<&#x2009;=0.002) except for TKE in the ascending aorta. Further, helicity correlated with TKE in the descending, suprarenal abdominal and infrarenal abdominal aorta (Spearman rho=-0.56--0.77).<br><br>CONCLUSION: Tortuosity increases with age and blood flow in tortuous aortas is more helical. Increasing helicity, in turn, is associated with decreasing TKE.}, }
@article {pmid37033871, year = {2023}, author = {Meng, M and Yang, Q}, title = {Investigation of the Microscopic Process of the Media Coalescence Treatment of Water-in-Oil Emulsion.}, journal = {ACS omega}, volume = {8}, number = {13}, pages = {11908-11915}, pmid = {37033871}, issn = {2470-1343}, abstract = {Medium coalescence technology is a research hotspot for the separation of oil-in-water emulsions. However, the coalescence mechanism is still unclear, making it challenging to effectively improve the separation performance. Herein, the microscopic mechanism of medium coalescence was revealed. We found that the effective collision positions under the action of the flow field include the exposed granule surface, adherent droplet surface, and three-phase contact line. Furthermore, a numerical model of the microscopic process of water-in-oil emulsion permeation through a granular bed was established. The effects of different parameters (including the number of medium layers, Reynolds number, and inlet concentration) on the microscopic process of capturing dispersed-phase droplets in the bed and the pressure drop in the coalescence area were studied. The numerical results show that the droplets form the bridging structure between the granules. On the one hand, the bridging structure promotes the capture of the droplets by the bed; on the other hand, it causes pressure-drop fluctuations in the coalescence area and asymmetric distribution of the velocity field.}, }
@article {pmid37029144, year = {2023}, author = {Abdelhafez, MA and Abd-Alla, AM and Abo-Dahab, SM and Elmhedy, Y}, title = {Influence of an inclined magnetic field and heat and mass transfer on the peristaltic flow of blood in an asymmetric channel.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {5749}, pmid = {37029144}, issn = {2045-2322}, mesh = {*Hot Temperature ; Rheology/methods ; *Models, Theoretical ; Temperature ; Peristalsis ; }, abstract = {This article presents a theoretical study on heat and mass transfer analysis of the peristaltic flow of blood conveying through an asymmetric channel in the presence of inclined to the magnetic field. The effects of ratio of relaxation to retardation times, non-uniform parameter, the non-dimensional amplitude, Hartman number and phase difference have been taken into account. The governing coupled non-linear partial differential equations representing the flow model are transmuted into linear ones by assuming that the wave is very long with a small Reynolds number. The converted mathematical formulations are solved analytically via the Mathematica software. Analytical expressions for the dimensionless velocity profiles of fluid, temperature, concentration, pressure gradient, increase in pressure, heat transfer coefficient and shear stress of the blood are derived. The velocity, temperature, concentration, pressure gradient, increase in pressure, heat transfer coefficient and shear stress were calculated numerically for different values of the parameters, which were represented graphically and find their physical meaning.}, }
@article {pmid37025873, year = {2023}, author = {Nishu, IZ and Samad, MF}, title = {Modeling and simulation of a split and recombination-based passive micromixer with vortex-generating mixing units.}, journal = {Heliyon}, volume = {9}, number = {4}, pages = {e14745}, pmid = {37025873}, issn = {2405-8440}, abstract = {As a state-of-the-art technology, micromixers are being used in various chemical and biological processes, including polymerization, extraction, crystallization, organic synthesis, biological screening, drug development, drug delivery, etc. The ability of a micromixer to perform efficient mixing while consuming little power is one of its basic needs. In this paper, a passive micromixer having vortex-generating mixing units is proposed which shows effective mixing with a small pressure drop. The micromixer works on the split and recombination (SAR) flow principle. In this study, four micromixers are designed with different arrangements of mixing units, and the effect of the placement of connecting channels is evaluated in terms of mixing index, pressure drop, and mixing performance. The channel width of 200 μm, height of 300 μm, and size of mixing units are maintained constant for all the micromixers throughout the evaluation process. The numerical simulation is performed for the Reynolds number (Re) range of 0.1-100 using Comsol Multiphysics software. By categorizing the flow patterns into three regimes based on the range of Re, the fluid flow throughout the length of the micromixer is visualized. The micromixer with dislocated connecting channels provides a satisfactory result with the mixing index of 0.96 and 0.94, and the pressure drop of 2.5 Pa and 7.8 kPa at Re = 0.1 and Re = 100 respectively. It also outperformed the other models in terms of the mixing performance. The proposed micromixer might very well be used in microfluidic devices for a variety of analytical procedures due to its straightforward construction and outstanding performance.}, }
@article {pmid37018723, year = {2023}, author = {Van Impe, M and Caboor, L and Deleeuw, V and Olbinado, M and De Backer, J and Sips, P and Segers, P}, title = {Fluid-Structure Interaction Modeling of the Aortic Hemodynamics in Adult Zebrafish: A Pilot Study Based on Synchrotron X-Ray Tomography.}, journal = {IEEE transactions on bio-medical engineering}, volume = {70}, number = {7}, pages = {2101-2110}, doi = {10.1109/TBME.2023.3236488}, pmid = {37018723}, issn = {1558-2531}, mesh = {Adult ; Humans ; Animals ; Mice ; *Zebrafish ; Pilot Projects ; *Cardiovascular Diseases ; Synchrotrons ; Aorta/diagnostic imaging ; Hemodynamics ; Tomography, X-Ray Computed ; Models, Cardiovascular ; Stress, Mechanical ; }, abstract = {OBJECTIVE: The zebrafish is increasingly used as a small animal model for cardiovascular disease, including vascular disorders. Nevertheless, a comprehensive biomechanical understanding of the zebrafish cardiovascular circulation is still lacking and possibilities for phenotyping the zebrafish heart and vasculature at adult - no longer optically transparent - stages are limited. To improve these aspects, we developed imaging-based 3D models of the cardiovascular system of wild-type adult zebrafish.<br><br>METHODS: In vivo high-frequency echocardiography and ex vivo synchrotron X-ray tomography were combined to build fluid-structure interaction finite element models of the fluid dynamics and biomechanics inside the ventral aorta.<br><br>RESULTS: We successfully generated a reference model of the circulation in adult zebrafish. The dorsal side of the most proximal branching region was found as the location of highest first principal wall stress and was also a location of low wall shear stress. Reynolds number and oscillatory shear were very low compared to mice and humans.<br><br>SIGNIFICANCE: The presented wild-type results provide a first extensive biomechanical reference for adult zebrafish. This framework can be used for advanced cardiovascular phenotyping of adult genetically engineered zebrafish models of cardiovascular disease, showing disruptions of the normal mechano-biology and homeostasis. By providing reference values for key biomechanical stimuli (including wall shear stress and first principal stress) in wild-type animals, and a pipeline for image-based animal-specific computational biomechanical models, this study contributes to a more comprehensive understanding of the role of altered biomechanics and hemodynamics in heritable cardiovascular pathologies.}, }
@article {pmid37012373, year = {2023}, author = {Lee, S and Bui-Vinh, D and Baek, M and Kwak, DB and Lee, H}, title = {Modeling pressure drop values across ultra-thin nanofiber filters with various ranges of filtration parameters under an aerodynamic slip effect.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {5449}, pmid = {37012373}, issn = {2045-2322}, abstract = {Computational fluid dynamics simulations of fibrous filters with 56 combinations of different fiber sizes, packing densities, face velocities, and thicknesses were conducted for developing models that predict pressure drops across nanofiber filters. The accuracy of the simulation method was confirmed by comparing the numerical pressure drops to the experimental data obtained for polyacrylonitrile electrospun nanofiber filters. In the simulations, an aerodynamic slip effect around the surface of the small nanofibers was considered. The results showed that, unlike in the case of conventional filtration theory, pressure drops across the thin layers of electrospun nanofiber filters are not proportional to the thickness. This might be a critical factor for obtaining precise pressure drops across the electrospun nanofiber filters with extremely thin layers. Finally, we derived the product of drag coefficient and Reynolds number as a function of packing density, Knudsen number, and ratio of thickness to fiber diameter to get the correlation equation for pressure drop prediction. The obtained equation predicted the pressure drops across the nanofiber filters with the maximum relative difference of less than 15%.}, }
@article {pmid37009788, year = {2023}, author = {Connor, AA and Webster, DR}, title = {Hydrodynamics of the fast-start caridoid escape response in Antarctic krill, Euphausia superba.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {5376}, pmid = {37009788}, issn = {2045-2322}, mesh = {Animals ; *Euphausiacea/physiology ; Hydrodynamics ; Swimming/physiology ; Biomechanical Phenomena ; Antarctic Regions ; }, abstract = {Krill are shrimp-like crustaceans with a high degree of mobility and variety of documented swimming behaviors. The caridoid escape response, a fast-start mechanism unique to crustaceans, occurs when the animal performs a series of rapid abdominal flexions and tail flipping that results in powerful backward strokes. The current results quantify the animal kinematics and three-dimensional flow field around a free-swimming Euphausia superba as it performs the caridoid escape maneuver. The specimen performs a single abdominal flexion-tail flip combination that leads to an acceleration over a 42 ms interval allowing it to reach a maximum speed of 57.0 cm/s (17.3 body lengths/s). The krill's tail flipping during the abdominal closure is a significant contributor to the thrust generation during the maneuver. The krill sheds a complex chain of vortex rings in its wake due to the viscous flow effects while the organism accelerates. The vortex ring structure reveals a strong suction flow in the wake, which suggests that the pressure distribution and form drag play a role in the force balance for this maneuver. Antarctic krill typically swim in a low to intermediate Reynolds number (Re) regime where viscous forces are significant, but as shown by this analysis, its high maneuverability allows it to quickly change its body angle and swimming speed.}, }
@article {pmid37004257, year = {2023}, author = {Ozawa, K and Nakamura, H and Shimamura, K and Dietze, GF and Yoshikawa, HN and Zoueshtiagh, F and Kurose, K and Mu, L and Ueno, I}, title = {Capillary-driven horseshoe vortex forming around a micro-pillar.}, journal = {Journal of colloid and interface science}, volume = {642}, number = {}, pages = {227-234}, doi = {10.1016/j.jcis.2023.03.039}, pmid = {37004257}, issn = {1095-7103}, abstract = {HYPOTHESIS: Horseshoe vortices are known to emerge around large-scale obstacles, such as bridge pillars, due to an inertia-driven adverse pressure gradient forming on the upstream-side of the obstacle. We contend that a similar flow structure can arise in thin-film Stokes flow around micro-obstacles, such as used in textured surfaces to improve wettability. This could be exploited to enhance mixing in microfluidic devices, typically limited to creeping-flow regimes.<br><br>EXPERIMENTS: Numerical simulations based on the Navier-Stokes equations are carried out to elucidate the flow structure associated with the wetting dynamics of a liquid film spreading around a 50&#xa0;&#x3bc;m diameter micro-pillar. The employed multiphase solver, which is based on the volume of fluid method, accurately reproduces the wetting dynamics observed in current and previous (Mu et al., Langmuir, 2019) experiments.<br><br>FINDINGS: The flow structure within the liquid meniscus forming at the foot of the micro-pillar evinces a horseshoe vortex wrapping around the obstacle, notwithstanding that the Reynolds number in our system is extremely low. Here, the adverse pressure gradient driving flow reversal near the bounding wall is caused by capillarity instead of inertia. The horseshoe vortex is entangled with other vortical structures, leading to an intricate flow system with high-potential mixing capabilities.}, }
@article {pmid36997565, year = {2023}, author = {Monti, A and Olivieri, S and Rosti, ME}, title = {Collective dynamics of dense hairy surfaces in turbulent flow.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {5184}, pmid = {36997565}, issn = {2045-2322}, abstract = {Flexible filamentous beds interacting with a turbulent flow represent a fundamental setting for many environmental phenomena, e.g., aquatic canopies in marine current. Exploiting direct numerical simulations at high Reynolds number where the canopy stems are modelled individually, we provide evidence on the essential features of the honami/monami collective motion experienced by hairy surfaces over a range of different flexibilities, i.e., Cauchy number. Our findings clearly confirm that the collective motion is essentially driven by fluid flow turbulence, with the canopy having in this respect a fully-passive behavior. Instead, some features pertaining to the structural response turn out to manifest in the motion of the individual canopy elements when focusing, in particular, on the spanwise oscillation and/or on sufficiently small Cauchy numbers.}, }
@article {pmid36984947, year = {2023}, author = {Lei, Y and Wang, J and Li, Y and Gao, Q}, title = {In-Hover Aerodynamic Analysis of a Small Rotor with a Thin Circular-Arc Airfoil and a Convex Structure at Low Reynolds Number.}, journal = {Micromachines}, volume = {14}, number = {3}, pages = {}, pmid = {36984947}, issn = {2072-666X}, support = {52275095//National Natural Science Foundation of China/ ; 20200201294JC//Science and Technology Development Plan Project of Jilin Province/ ; }, abstract = {This study focused on the in-hover aerodynamics of a small rotor with a thin circular-arc airfoil and a convex structure at a low Reynolds number. The method combined computational fluid dynamics (CFD) with the blade element momentum theory (BEMT). The former was used for studying the two-dimensional parametric aerodynamics of the airfoil at a low Reynolds number and the latter was used for the prediction of the rotor's hover performance. A novel thin circular-arc airfoil with a convex structure with a high aerodynamic performance, high structural strength, light weight and easy manufacturing process is presented in this paper. A convex curve on the upper surface was adopted to increase the thickness of the airfoil at partial chord, and a stiffener in the airfoil was installed to improve the structural strength of rotor span-wise. The aerodynamic performance of the airfoil was numerically simulated by the two-dimensional steady and incompressible Navier-Stokes equations. The in-hover performance of the rotor for small-scale vehicles was predicted by an improved version of the blade element momentum theory (BEMT). Finally, a carbon-fiber rotor with the presented airfoil was manufactured that had a diameter of 40 cm and a pitch of 6.2 inches. The analysis results were verified by experiments. It was shown that the maximum calculation errors were below 6%. The improved BEMT can be used in the analysis of in-hover micro-rotor aerodynamics at low Reynolds numbers.}, }
@article {pmid36984677, year = {2023}, author = {Park, JE and Kang, TG and Moon, H}, title = {The Effect of the Rotating Disk Geometry on the Flow and Flux Enhancement in a Dynamic Filtration System.}, journal = {Membranes}, volume = {13}, number = {3}, pages = {}, pmid = {36984677}, issn = {2077-0375}, support = {2022R1A2C1007886//National Research Foundation of Korea/ ; 2019 Faculty Research grant//Korea Aerospace University/ ; }, abstract = {A numerical study was conducted to investigate the effect of rotating patterned disks on the flow and permeate flux in a dynamic filtration (DF) system. The DF system consists of a rotating patterned disk and a stationary housing with a circular flat membrane. The feed flow is driven by the rotating disk with the angular velocity ranging from 200 to 1000 rpm and the applied pressure difference between inlet and outlet ports. Wheel-shaped patterns are engraved on the disk surfaces to add perturbation to the flow field and improve the permeate flux in the filtration system. Five disks with varying numbers of patterns were used in numerical simulations to examine the effects of the number of patterns and the angular velocity of the disk on the flow and permeate flux in the DF system. The flow characteristics are studied using the velocity profiles, the cross-sectional velocity vectors, the vortex structures, and the shear stress distribution. The wheel-shaped patterns shift the central core layer in the circumferential velocity profile towards the membrane, leading to higher shear stresses at the membrane and higher flux compared to a plain disk. When the number of patterns on the disk exceeded eight at a fixed Reynolds number, there were significant increases in wall shear stress and permeate flux compared to a plain disk filtration system with no pattern.}, }
@article {pmid36967929, year = {2023}, author = {Sakib, MN and Shuvo, MS and Rahman, R and Saha, S}, title = {Particle deposition and fluid flow characteristics in turbulent corrugated pipe flow using Eulerian-Lagrangian approach.}, journal = {Heliyon}, volume = {9}, number = {3}, pages = {e14603}, pmid = {36967929}, issn = {2405-8440}, abstract = {A numerical simulation of aerosol particle deposition in a horizontal circular pipe with a corrugated wall under turbulent flow has been carried out in this research. This paper uses the RNG k-ε turbulence model with Enhanced Wall Treatment to simulate fluid flow. Furthermore, the Lagrangian particle tracking model simulates particle deposition in the corrugated pipe. Air-particle interaction is influenced by Stokes number, surface roughness, flow velocity, particle diameter, and pipe diameter. For the parametric simulation, particle diameter varies from 1 to 30 μm, whereas the Reynolds number ranges from 5000 to 10,000. The effect of corrugation height and pipe diameter on deposition efficiency is also investigated. This study shows that corrugation height significantly increases particle deposition compared to the smooth wall pipe. As the pipe diameter decreases, keeping the corrugation ratio constant, deposition efficiency also increases. Moreover, high flow velocity enhances deposition efficiency for particle diameters lower than 5 μm.}, }
@article {pmid36966222, year = {2023}, author = {Memon, AA and Memon, MA and Fenta, A}, title = {A laminar forced convection via transport of water-copper-aluminum hybrid nanofluid through heated deep and shallow cavity with Corcione model.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {4915}, pmid = {36966222}, issn = {2045-2322}, abstract = {The article explores how fluid flows and heat transfers in both deep and shallow cavities when using a nanofluid made of water, copper, and aluminum oxide. The study applies the Corcione model to hybrid nanofluids, which considers viscosity, conductivity, and the size of the nanoparticle, temperature, and Reynolds number. The cavity is connected to a rectangular channel, with the cavity's length being half the total length of the enclosure, and the aspect ratio (cavity height divided by height of the channel) is tested from 1 to 3. The study uses the Navier-Stokes equation and energy equation in two dimensions, along with finite element-based software, COMSOL 5.6, to simulate the combination of fluid flow and heat transmission. The results show a circular distribution of temperature in the cavity, and the average temperature drops as the volume fraction of copper upsurges. However, both the Reynolds number and volume fraction of copper improve the average Nusselt number, which shows how well the fluid transfers heat, along the cavity's middle line. The percentage change in the average Nusselt number decreases as the aspect ratio increases, indicating improved conduction.}, }
@article {pmid36959904, year = {2023}, author = {Xiong, J and Zhang, J and Zhong, Y and Song, X and Wang, H and Cheang, UK}, title = {Magnetically-actuated hydrogel-based achiral planar microswimmers for SERS detection: In situ coprecipitation for continuous loading of iron oxide nanoparticles.}, journal = {Frontiers in bioengineering and biotechnology}, volume = {11}, number = {}, pages = {1086106}, pmid = {36959904}, issn = {2296-4185}, abstract = {Ultraviolet lithography is a very promising technology used for the batch fabrication of biomedical microswimmers. However, creating microswimmers that can swim at low Reynolds number using biocompatible materials while retaining strong magnetic properties and excellent biomedical functionality is a great challenge. Most of the previously reported biomedical microswimmers possess either strong magnetic properties by using non-biocompatible nickel coating or good biocompatibility by using iron oxide particle-embedded hydrogel with weak magnetism, but not both. Alternatively, iron oxide nanoparticles can be coated on the surface of microswimmers to improve magnetic properties; however, this method limited the usability of the microswimmers' surfaces. To address these shortcomings, this work utilized an in situ synthesis technique to generate high magnetic content inside hydrogel-based achiral planar microswimmers while leaving their surfaces free to be functionalized for SERS detection. The hydrogel matrices of the magnetically actuated hydrogel-based microswimmers were first prepared by ultraviolet lithography. Then, the high concentration of iron oxide was achieved through multiple continuous in situ coprecipitation cycles. Finally, the SERS detection capability of magnetically actuated hydrogel-based microswimmers was enabled by uniformly growing silver nanoparticles on the surface of the microswimmers. In the motion control tests, the microswimmers showed a high swimming efficiency, high step-out frequency, and consistent synchronized motion. Furthermore, the magnetically actuated hydrogel-based microswimmers were able to improve the detection efficiency of analytes under magnetic guidance.}, }
@article {pmid36951265, year = {2023}, author = {Liu, D and Chen, S and Luo, X}, title = {Influence factors of channel geometry for separation of circulating tumor cells by four-ring inertial focusing microchannel.}, journal = {Cell biochemistry and function}, volume = {41}, number = {3}, pages = {375-388}, doi = {10.1002/cbf.3791}, pmid = {36951265}, issn = {1099-0844}, support = {52165046//National Natural Science Foundation of China/ ; }, mesh = {Humans ; *Microfluidic Analytical Techniques/methods ; *Neoplastic Cells, Circulating ; Microfluidics/methods ; MCF-7 Cells ; Cell Line, Tumor ; Cell Separation/methods ; }, abstract = {Inertial microfluidics is a high-throughput and high-efficiency cell separation approach to which attention has been progressively paid in recent years. However, research on the influencing factors that compromise the efficiency of cell separation is still lacking. Therefore, the aim of this study was to evaluate the cell separation efficiency by changing the influencing factors. A four-ring inertial focusing spiral microchannel was designed to separate two kinds of circulating tumor cells (CTCs) from blood. Human breast cancer (MCF-7) cells and human epithelial cervical cancer (HeLa) cells enter the four-ring inertial focusing spiral microchannel together with blood cells, and cancer cells and blood cells were separated from each other at the outlet of the channel by inertial force. The cell separation efficiency at the inlet flow rate in the Reynolds number range of 40-52 was studied by changing the influencing factors such as the cross-sectional shape of the microchannel, the average thickness of the cross-section, and the trapezoidal inclination angle. The results showed that the reduction of the channel thickness and the increase of a certain trapezoidal inclination enhanced the cell separation efficiency to a certain extent, the study showed that when the channel inclination was 6 ° and the average channel thickness was 160 μm. The two kinds of CTC cells could be completely separated from the blood and the efficiency could reached 100%.}, }
@article {pmid36938115, year = {2023}, author = {Kitzinger, E and Leclercq, T and Marquet, O and Piot, E and Sipp, D}, title = {Attachment-line, crossflow and Tollmien-Schlichting instabilities on swept ONERA-D and Joukowski airfoils.}, journal = {Journal of fluid mechanics}, volume = {957}, number = {}, pages = {}, doi = {10.1017/jfm.2023.38}, pmid = {36938115}, issn = {0022-1120}, abstract = {Linear stability analyses are performed to investigate the boundary layer instabilities developing in an incompressible flow around the whole leading-edge of swept ONERA-D and Joukowski airfoils of infinite span. The stability analyses conducted in our study are global in the chordwise direction and local in the spanwise direction. A neutral curve is drawn at a given leading-edge Reynolds number ReR and several overlapping regions, called "lobes", are identified on a physical basis. A detailed study of the marginal modes reveals the presence of attachment-line and crossflow instabilities, as well as modes whose features do not fall within the standards of a specific type. Connected crossflow/Tollmien-Schlichting modes, that show a dominant spatial structure reminiscent of Tollmien-Schlichting waves but whose destabilization is linked to a crossflow mechanism, have been identified. The comparison of several neutral curves at different ReR values reveals the greater stabilizing effect of the increase of ReR on the crossflow instability compared to the attachment-line instability. The influence of the airfoil shape is also studied by comparing the neutral curves of the ONERA-D with the neutral curves of the Joukowski airfoil. These curves reveal similar characteristics with the presence of distinct lobes and their comparison at constant sweep angle shows that, under the conditions studied, the ONERA-D airfoil is more stable than the Joukowski airfoil, even for crossflow instabilities. The absolutely or convectively unstable nature of the flow in the spanwise direction is also tackled and our results suggest that the flow is only convectively unstable.}, }
@article {pmid36936325, year = {2023}, author = {Rehman, S and Hashim,  and Hassine, SBH and Tag Eldin, E and Shah, SO}, title = {Investigation of Entropy Production with Thermal Analysis under Soret and Dufour Effects in MHD Flow between Convergent and Divergent Channels.}, journal = {ACS omega}, volume = {8}, number = {10}, pages = {9121-9136}, pmid = {36936325}, issn = {2470-1343}, abstract = {Hydromagnetic flow and heat transport have sustainable importance in conventional system design along with high-performance thermal equipment and geothermal energy structures. The current computational study investigates the energy transport and entropy production due to the pressure-driven flow of non-Newtonian fluid filled inside the wedge-shaped channel. The nonlinear radiation flux and uniform magnetic field are incorporated into the flow analysis. To be more precise, non-Newtonian fluid initiates from an inlet with the bound of the parabolic profile and leaves at outlet of a convergent/divergent channel. We assume that the channel flow is adiabatic and influenced by the wall friction. The leading flow equations are modeled via the Carreau fluid model using fundamental conservation laws. The thermodynamical aspect of the system is visualized using a two-phase model and analyses of the entropy equation due to fluid friction, ohmic heating, and diffusion of heat and mass fluxes. The modeled system of equations is normalized using a dimensionless variable mechanism. The system was elevated for the significant variation of controlling parameters. The outcomes obtained from the computational investigation are validated with the theoretical results that are available in the literature. An increasing semivertex angle and Reynolds number increase the converging channel flow. In the core flow zone, an increase in the divergent semiangle causes the flow to decelerate, while near and at the channel wall it causes a slight acceleration. Outcomes designate that the main contribution to the irreversibility is due to ohmic loss, frictional loss, and heat loss. The thermal performance and entropy production is dominant for a diverging flow. The outcomes of this research will assist in comprehending the process of entropy minimization in conjunction with the flow of nanomaterials in a nonuniform channel, which is essential in engineering processes such as the creation of micro machines, supersonic Jets, nozzles, and clean energy.}, }
@article {pmid36932601, year = {2023}, author = {Fan, Y and Cadot, O}, title = {Reynolds number effect on the bistable dynamic of a blunt-base bluff body.}, journal = {Physical review. E}, volume = {107}, number = {2-2}, pages = {025103}, doi = {10.1103/PhysRevE.107.025103}, pmid = {36932601}, issn = {2470-0053}, abstract = {A three-dimensional blunt-base bluff body in a uniform flow is subjected to long-time stochastic dynamics of switching between two opposite wake states. This dynamic is investigated experimentally within the Reynolds number range Re ≃10^{4}-10^{5}. Long-time statistics coupled to a sensitivity analysis to the body attitude (defined as the pitch angle of the body with respect to the incoming flow) show that the wake switching rate decreases as Re increases. Equipping the body with passive roughness elements (turbulators) modifies the boundary layers before separation, seen as the inlet condition for the wake dynamic. Depending on their location and Re, the viscous sublayer length scale and the turbulent layer thickness can be modified independently. This sensitivity analysis to the inlet condition shows that a decrease of the viscous sublayer length scale at a given turbulent layer thickness leads to a decrease in the switching rate, whereas the modification of the turbulent layer thickness has almost no effect on the switching rate.}, }
@article {pmid36932550, year = {2023}, author = {Ginzburg, I and Silva, G and Marson, F and Chopard, B and Latt, J}, title = {Unified directional parabolic-accurate lattice Boltzmann boundary schemes for grid-rotated narrow gaps and curved walls in creeping and inertial fluid flows.}, journal = {Physical review. E}, volume = {107}, number = {2-2}, pages = {025303}, doi = {10.1103/PhysRevE.107.025303}, pmid = {36932550}, issn = {2470-0053}, abstract = {The goal of this work is to advance the characteristics of existing lattice Boltzmann Dirichlet velocity boundary schemes in terms of the accuracy, locality, stability, and mass conservation for arbitrarily grid-inclined straight walls, curved surfaces, and narrow fluid gaps, for both creeping and inertial flow regimes. We reach this objective with two infinite-member boundary classes: (1) the single-node "Linear Plus" (LI^{+}) and (2) the two-node "Extended Multireflection" (EMR). The LI^{+} unifies all directional rules relying on the linear combinations of up to three pre- or postcollision populations, including their "ghost-node" interpolations and adjustable nonequilibrium approximations. On this basis, we propose three groups of LI^{+} nonequilibrium local corrections: (1) the LI_{1}^{+} is parametrized, meaning that its steady-state solution is physically consistent: the momentum accuracy is viscosity-independent in Stokes flow, and it is fixed by the Reynolds number (Re) in inertial flow; (2) the LI_{3}^{+} is parametrized, exact for arbitrary grid-rotated Poiseuille force-driven Stokes flow and thus most accurate in porous flow; and (3) the LI_{4}^{+} is parametrized, exact for pressure and inertial term gradients, and hence advantageous in very narrow porous gaps and at higher Reynolds range. The directional, two-relaxation-time collision operator plays a crucial role for all these features, but also for efficiency and robustness of the boundary schemes due to a proposed nonequilibrium linear stability criterion which reliably delineates their suitable coefficients and relaxation space. Our methodology allows one to improve any directional rule for Stokes or Navier-Stokes accuracy, but their parametrization is not guaranteed. In this context, the parametrized two-node EMR class enlarges the single-node schemes to match exactness in a grid-rotated linear Couette flow modeled with an equilibrium distribution designed for the Navier-Stokes equation (NSE). However, exactness of a grid-rotated Poiseuille NSE flow requires us to perform (1) the modification of the standard NSE term for exact bulk solvability and (2) the EMR extension towards the third neighbor node. A unique relaxation and equilibrium exact configuration for grid-rotated Poiseuille NSE flow allows us to classify the Galilean invariance characteristics of the boundary schemes without any bulk interference; in turn, its truncated solution suggests how, when increasing the Reynolds number, to avoid a deterioration of the mass-leakage rate and momentum accuracy due to a specific Reynolds scaling of the kinetic relaxation collision rate. The optimal schemes and strategies for creeping and inertial regimes are then singled out through a series of numerical tests, such as grid-rotated channels and rotated Couette flow with wall-normal injection, cylindrical porous array, and Couette flow between concentric cylinders, also comparing them against circular-shape fitted FEM solutions.}, }
@article {pmid36930713, year = {2023}, author = {Hu, T and Wang, H and Gomez, H}, title = {Direct van der Waals simulation (DVS) of phase-transforming fluids.}, journal = {Science advances}, volume = {9}, number = {11}, pages = {eadg3007}, pmid = {36930713}, issn = {2375-2548}, abstract = {We present the method of direct van der Waals simulation (DVS) to study computationally flows with liquid-vapor phase transformations. Our approach is based on a discretization of the Navier-Stokes-Korteweg equations, which couple flow dynamics with van der Waals' nonequilibrium thermodynamic theory of phase transformations, and opens an opportunity for first-principles simulation of a wide range of boiling and cavitating flows. The proposed algorithm enables unprecedented simulations of the Navier-Stokes-Korteweg equations involving cavitating flows at strongly under-critical conditions and 𝒪(10[5]) Reynolds number. The proposed technique provides a pathway for a fundamental understanding of phase-transforming flows with multiple applications in science, engineering, and medicine.}, }
@article {pmid36929245, year = {2023}, author = {Sheikhshoaei, A and Rajabi, M}, title = {Utilizing passive elements to break time reversibility at low Reynolds number: a swimmer with one activated element.}, journal = {The European physical journal. E, Soft matter}, volume = {46}, number = {3}, pages = {15}, pmid = {36929245}, issn = {1292-895X}, abstract = {In the realm of low Reynolds number, the shape-changing biological and artificial matters need to break time reversibility in the course of their strokes to achieve motility. This necessity is well described in the so-called scallop theorem. In this work, considering low Reynolds number, a novel and versatile swimmer is proposed as an example of a new scheme to break time reversibility kinematically and, in turn, produce net motion. The swimmer consists of one sphere as a cargo or carried body, joined by one activated link with time-varying length, to another perpendicular rigid link, as the support of two passively flapping disks, at its end. The disks are free to rotate between their fixed minimum and maximum angles. The system's motion in two dimensions is simulated, and the maneuverability of the swimmer is discussed. The minimal operating parameters for steering of the swimmer are studied, and the limits of the swimmer are identified. The introduced swimming mechanism can be employed as a simple model system for biological living matters as well as artificial microswimmers.}, }
@article {pmid36920868, year = {2023}, author = {Spatafora-Salazar, A and Kuei, S and Cunha, LHP and Biswal, SL}, title = {Coiling of semiflexible paramagnetic colloidal chains.}, journal = {Soft matter}, volume = {19}, number = {13}, pages = {2385-2396}, doi = {10.1039/d3sm00066d}, pmid = {36920868}, issn = {1744-6848}, abstract = {Semiflexible filaments deform into a variety of configurations that dictate different phenomena manifesting at low Reynolds number. Harnessing the elasticity of these filaments to perform transport-related processes at the microfluidic scale requires structures that can be directly manipulated to attain controllable geometric features during their deformation. The configuration of semiflexible chains assembled from paramagnetic colloids can be readily controlled upon the application of external time-varying magnetic fields. In circularly rotating magnetic fields, these chains undergo coiling dynamics in which their ends close into loops that wrap inward, analogous to the curling of long nylon filaments under shear. The coiling is promising for the precise loading and targeted transport of small materials, however effective implementation requires an understanding of the role that field parameters and chain properties play on the coiling features. Here, we investigate the formation of coils in semiflexible paramagnetic chains using numerical simulations. We demonstrate that the size and shape of the initial coils are governed by the Mason and elastoviscous numbers, related to the field parameters and the chain bending stiffness. The size of the initial coil follows a nonmonotonic behavior with Mason number from which two regions are identified: (1) an elasticity-dependent nonlinear regime in which the coil size decreases with increasing field strength and for which loop shape tends to be circular, and (2) an elasticity-independent linear regime where the size increases with field strength and the shape become more elliptical. From the time scales associated to these regimes, we identify distinct coiling mechanisms for each case that relate the coiling dynamics to two other configurational dynamics of paramagnetic chains: wagging and folding behaviors.}, }
@article {pmid36916641, year = {2023}, author = {Lim, S and Yadunandan, A and Khalid Jawed, M}, title = {Bacteria-inspired robotic propulsion from bundling of soft helical filaments at low Reynolds number.}, journal = {Soft matter}, volume = {19}, number = {12}, pages = {2254-2264}, doi = {10.1039/d2sm01398c}, pmid = {36916641}, issn = {1744-6848}, abstract = {The bundling of flagella is known to create a "run" phase, where the bacteria moves in a nearly straight line rather than making changes in direction. Historically, mechanical explanations for the bundling phenomenon intrigued many researchers, and significant advances were made in physical models and experimental methods. Contributing to the field of research, we present a bacteria-inspired centimeter-scale soft robotic hardware platform and a computational framework for a physically plausible simulation model of the multi-flagellated robot under low Reynolds number (∼10[-1]). The fluid-structure interaction simulation couples the discrete elastic rods algorithm with the method of regularized Stokeslet segments. Contact between two flagella is handled by a penalty-based method. We present a comparison between our experimental and simulation results and verify that the simulation tool can capture the essential physics of this problem. Preliminary findings on robustness to buckling provided by the bundling phenomenon and the efficiency of a multi-flagellated soft robot are compared with the single-flagellated counterparts. Observations were made on the coupling between geometry and elasticity, which manifests itself in the propulsion of the robot by nonlinear dependency on the rotational speed of the flagella.}, }
@article {pmid36907215, year = {2023}, author = {Kang, C and Mirbod, P}, title = {Transitions in Taylor-Couette flow of concentrated non-colloidal suspensions.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {381}, number = {2246}, pages = {20220126}, doi = {10.1098/rsta.2022.0126}, pmid = {36907215}, issn = {1471-2962}, abstract = {Taylor-Couette flow of concentrated non-colloidal suspensions with a rotating inner cylinder and a stationary outer one is numerically investigated. We consider suspensions of the bulk particle volume fraction ϕb = 0.2, 0.3 with the ratio of annular gap to the particle radius ε = 60 confined in a cylindrical annulus of the radius ratio (i.e. ratio of inner and outer radii) η = 0.877. Numerical simulations are performed by applying suspension-balance model and rheological constitutive laws. To observe flow patterns caused by suspended particles, the Reynolds number of the suspension, based on the bulk particle volume fraction and the rotating velocity of the inner cylinder, is varied up to 180. At high Reynolds number, modulated patterns undiscovered in the flow of a semi-dilute suspension emerge beyond a wavy vortex flow. Thus, a transition occurs from the circular Couette flow via ribbons, spiral vortex flow, wavy spiral vortex flow, wavy vortex flow and modulated wavy vortex flow for the concentrated suspensions. Moreover, friction and torque coefficients for suspensions are estimated. It turns out that suspended particles significantly enhance the torque on the inner cylinder while reducing friction coefficient and the pseudo-Nusselt number. In particular, the coefficients are reduced in the flow of more dense suspensions. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (Part 2)'.}, }
@article {pmid36907213, year = {2023}, author = {Nagata, M}, title = {Taylor-Couette flow in the narrow-gap limit.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {381}, number = {2246}, pages = {20220134}, doi = {10.1098/rsta.2022.0134}, pmid = {36907213}, issn = {1471-2962}, abstract = {A Cartesian representation of the Taylor-Couette system in the vanishing limit of the gap between coaxial cylinders is presented, where the ratio, [Formula: see text], of the angular velocities, [Formula: see text] and [Formula: see text], of the inner and the outer cylinders, respectively, affects its axisymmetric flow structures. Our numerical stability study finds remarkable agreement with previous studies for the critical Taylor number, [Formula: see text], for the onset of axisymmetric instability. The Taylor number [Formula: see text] can be expressed as [Formula: see text], where [Formula: see text] (the rotation number) and [Formula: see text] (the Reynolds number) in the Cartesian system are related to the average and the difference of [Formula: see text] and [Formula: see text]. The instability sets in the region [Formula: see text], while the product of [Formula: see text] and [Formula: see text] is kept finite. Furthermore, we developed a numerical code to calculate nonlinear axisymmetric flows. It is found that the mean flow distortion of the axisymmetric flow is antisymmetric across the gap when [Formula: see text], while a symmetric part of the mean flow distortion appears additionally when [Formula: see text]. Our analysis also shows that for a finite [Formula: see text] all flows with [Formula: see text] approach the [Formula: see text] axis, so that the plane Couette flow system is recovered in the vanishing gap limit. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (Part 2)'.}, }
@article {pmid36907211, year = {2023}, author = {Moazzen, M and Lacassagne, T and Thomy, V and Bahrani, SA}, title = {Friction dynamics of elasto-inertial turbulence in Taylor-Couette flow of viscoelastic fluids.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {381}, number = {2246}, pages = {20220300}, doi = {10.1098/rsta.2022.0300}, pmid = {36907211}, issn = {1471-2962}, abstract = {Dynamic properties of elasto-inertial turbulence (EIT) are studied in a Taylor-Couette geometry. EIT is a chaotic flow state that develops upon both non-negligible inertia and viscoelasticity. A combination of direct flow visualization and torque measurement allows to verify the earlier onset of EIT compared with purely inertial instabilities (and inertial turbulence). The scaling of the pseudo-Nusselt number with inertia and elasticity is discussed here for the first time. Variations in the friction coefficient, temporal frequency spectra and spatial power density spectra highlight that EIT undergoes an intermediate behaviour before transitioning to its fully developed chaotic state that requires both high inertia and elasticity. During this transition, the contribution of secondary flows to the overall friction dynamics is limited. This is expected to be of great interest in the aim of achieving efficiency mixing at low drag and low but finite Reynolds number. This article is part of the theme issue "Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical transactions paper (Part 2)".}, }
@article {pmid36907210, year = {2023}, author = {Krivonosova, O and Gritsevich, M and Zhilenko, D and Read, P}, title = {Noise induced effects in the axisymmetric spherical Couette flow.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {381}, number = {2246}, pages = {20220124}, doi = {10.1098/rsta.2022.0124}, pmid = {36907210}, issn = {1471-2962}, abstract = {We study the axisymmetric, wide gap, spherical Couette flow in the presence of noise in numerical simulations and experiments. Such studies are important because most of the flows in nature are subjected to random fluctuations. Noise is introduced into the flow by adding fluctuations to the inner sphere rotation which are random in time with zero mean. Flows of a viscous incompressible fluid are induced either by rotation of the inner sphere only or by the co-rotation of the spheres. Mean flow generation was found to occur under the action of additive noise. A higher relative amplification of meridional kinetic energy compared to the azimuthal component was also observed under certain conditions. Calculated flow velocities were validated by laser Doppler anemometer measurements. A model is proposed to elucidate the rapid growth of meridional kinetic energy for flows induced by varying the co-rotation of the spheres. Our linear stability analysis for flows induced by the rotation of the inner sphere revealed a decrease in the critical Reynolds number, corresponding to the onset of the first instability. Also, in this case, a local minimum of the mean flow generation on approaching the critical Reynolds number was observed, which is consistent with the available theoretical predictions. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (Part 2)'.}, }
@article {pmid36903819, year = {2023}, author = {Akram, S and Athar, M and Saeed, K and Razia, A and Muhammad, T and Alghamdi, HA}, title = {Mechanism of Double-Diffusive Convection on Peristaltic Transport of Thermally Radiative Williamson Nanomaterials with Slip Boundaries and Induced Magnetic Field: A Bio-Nanoengineering Model.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {13}, number = {5}, pages = {}, pmid = {36903819}, issn = {2079-4991}, abstract = {The present work has mathematically modeled the peristaltic flow in nanofluid by using thermal radiation, induced a magnetic field, double-diffusive convection, and slip boundary conditions in an asymmetric channel. Peristalsis propagates the flow in an asymmetric channel. Using the linear mathematical link, the rheological equations are translated from fixed to wave frames. Next, the rheological equations are converted to nondimensional forms with the help of dimensionless variables. Further, the flow evaluation is determined under two scientific assumptions: a finite Reynolds number and a long wavelength. Mathematica software is used to solve the numerical value of rheological equations. Lastly, the impact of prominent hydromechanical parameters on trapping, velocity, concentration, magnetic force function, nanoparticle volume fraction, temperature, pressure gradient, and pressure rise are evaluated graphically.}, }
@article {pmid36902954, year = {2023}, author = {Liu, C and Wang, W and Hu, X and Liu, F}, title = {Drag Reduction Technology of Water Flow on Microstructured Surfaces: A Novel Perspective from Vortex Distributions and Densities.}, journal = {Materials (Basel, Switzerland)}, volume = {16}, number = {5}, pages = {}, pmid = {36902954}, issn = {1996-1944}, support = {52079113//National Natural Science Foundation of China/ ; U2243235//Key project of National Natural Science Foundation of China/ ; }, abstract = {Revealing the turbulent drag reduction mechanism of water flow on microstructured surfaces is beneficial to controlling and using this technology to reduce turbulence losses and save energy during water transportation. Two microstructured samples, including a superhydrophobic and a riblet surface, were fabricated near which the water flow velocity, and the Reynolds shear stress and vortex distribution were investigated using a particle image velocimetry. The dimensionless velocity was introduced to simplify the Ω vortex method. The definition of vortex density in water flow was proposed to quantify the distribution of different strength vortices. Results showed that the velocity of the superhydrophobic surface (SHS) was higher compared with the riblet surface (RS), while the Reynolds shear stress was small. The vortices on microstructured surfaces were weakened within 0.2 times that of water depth when identified by the improved ΩM method. Meanwhile, the vortex density of weak vortices on microstructured surfaces increased, while the vortex density of strong vortices decreased, proving that the reduction mechanism of turbulence resistance on microstructured surfaces was to suppress the development of vortices. When the Reynolds number ranged from 85,900 to 137,440, the drag reduction impact of the superhydrophobic surface was the best, and the drag reduction rate was 9.48%. The reduction mechanism of turbulence resistance on microstructured surfaces was revealed from a novel perspective of vortex distributions and densities. Research on the structure of water flow near the microstructured surface can promote the drag reduction application in the water field.}, }
@article {pmid36899067, year = {2023}, author = {Suresh Kumar, Y and Hussain, S and Raghunath, K and Ali, F and Guedri, K and Eldin, SM and Khan, MI}, title = {Numerical analysis of magnetohydrodynamics Casson nanofluid flow with activation energy, Hall current and thermal radiation.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {4021}, pmid = {36899067}, issn = {2045-2322}, abstract = {In this study we analyzed the flow, heat and mass transfer behavior of Casson nanofluid past an exponentially stretching surface under the impact of activation energy, Hall current, thermal radiation, heat source/sink, Brownian motion and thermophoresis. Transverse magnetic field with the assumption of small Reynolds number is implemented vertically. The governing partial nonlinear differential equations of the flow, heat and mass transfer are transformed into ordinary differential equations by using similarity transformation and solved numerically by using Matlab bvp4c package. The impact of each of the Hall current parameter, thermal radiation parameter, heat source/sink parameter, Brownian motion parameter, Prandtl number, thermophoresis parameter and magnetic parameter on velocity, concentration and temperature, is discussed through graphs. The skin friction coefficient along the x-and z-directions, the local Nusselt number and the Sherwood number are calculated numerically to look into the inside behavior of the emerging parameters. It is witnessed that the flow velocity is a diminishing function of the thermal radiation parameter and the behavior has observed in the case of Hall parameter. Moreover, mounting values of Brownian motion parameter reduce the nanoparticle concentration profile.}, }
@article {pmid36897856, year = {2023}, author = {Bae, AJ and Ahmad, R and Bodenschatz, E and Pumir, A and Gholami, A}, title = {Flagellum-driven cargoes: Influence of cargo size and the flagellum-cargo attachment geometry.}, journal = {PloS one}, volume = {18}, number = {3}, pages = {e0279940}, pmid = {36897856}, issn = {1932-6203}, mesh = {*Flagella ; Cilia ; *Chlamydomonas reinhardtii ; Mechanical Phenomena ; Calcium, Dietary ; }, abstract = {The beating of cilia and flagella, which relies on an efficient conversion of energy from ATP-hydrolysis into mechanical work, offers a promising way to propel synthetic cargoes. Recent experimental realizations of such micro-swimmers, in which micron-sized beads are propelled by isolated and demembranated flagella from the green algae Chlamydomonas reinhardtii (C. reinhardtii), revealed a variety of propulsion modes, depending in particular on the calcium concentration. Here, we investigate theoretically and numerically the propulsion of a bead as a function of the flagellar waveform and the attachment geometries between the bead and the flagellum. To this end, we take advantage of the low Reynolds number of the fluid flows generated by the micro-swimmer, which allows us to neglect fluid inertia. By describing the flagellar waveform as a superposition of a static component and a propagating wave, and using resistive-force theory, we show that the asymmetric sideways attachment of the flagellum to the bead makes a contribution to the rotational velocity of the micro-swimmer that is comparable to the contribution caused by the static component of the flagellar waveform. Remarkably, our analysis reveals the existence of a counter-intuitive propulsion regime in which an increase in the size of the cargo, and hence its drag, leads to an increase in some components of the velocity of the bead. Finally, we discuss the relevance of the uncovered mechanisms for the fabrication of synthetic, bio-actuated medical micro-robots for targeted drug delivery.}, }
@article {pmid36895389, year = {2023}, author = {Lei, Y and Wang, X and Zhou, D and Qiu, T and Jin, W and Qin, C and Zhou, D}, title = {Experimental investigation on high-pressure methane jet characteristic single-hole injector.}, journal = {Heliyon}, volume = {9}, number = {3}, pages = {e13645}, doi = {10.1016/j.heliyon.2023.e13645}, pmid = {36895389}, issn = {2405-8440}, abstract = {High-pressure gas direct injection (DI) technology benefits engines with high efficiency and clean emissions, and the gas jet process causes crucial effects especially inside an mm-size space. This study presents an investigation on the high-pressure methane jet characteristics from a single-hole injector by analysing jet performance parameters including jet impact force, gas jet impulse, and jet mass flow rate. The results show that the methane jet exhibited a two-zone behaviour along the jet direction in the spatial dimension induced by high-speed jet flow from the nozzle: zone 1 near the nozzle-the jet impact force and jet impulse increased consistently except for a fluctuation due to shock wave effects induced by the sonic jet and no entrainment occurs, and zone II farther away from the nozzle-the jet impact force and jet impulse became stable when the shock wave effects became weak and the jet impulse was conserved with a linear conservation boundary. The Mach disk height was exactly the turning point of two zones. Moreover, the methane jet parameters, such as the methane jet mass flow rate, jet initial jet impact force, jet impulse, and Reynolds number had a monotonous and linearly increasing correlation with injection pressure.}, }
@article {pmid36890189, year = {2023}, author = {Vieira, GS and Allshouse, MR and Mahadevan, A}, title = {Seagrass deformation affects fluid instability and tracer exchange in canopy flow.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {3910}, pmid = {36890189}, issn = {2045-2322}, abstract = {Monami is the synchronous waving of a submerged seagrass bed in response to unidirectional fluid flow. Here we develop a multiphase model for the dynamical instabilities and flow-driven collective motions of buoyant, deformable seagrass. We show that the impedance to flow due to the seagrass results in an unstable velocity shear layer at the canopy interface, leading to a periodic array of vortices that propagate downstream. Our simplified model, configured for unidirectional flow in a channel, provides a better understanding of the interaction between these vortices and the seagrass bed. Each passing vortex locally weakens the along-stream velocity at the canopy top, reducing the drag and allowing the deformed grass to straighten up just beneath it. This causes the grass to oscillate periodically even in the absence of water waves. Crucially, the maximal grass deflection is out of phase with the vortices. A phase diagram for the onset of instability shows its dependence on the fluid Reynolds number and an effective buoyancy parameter. Less buoyant grass is more easily deformed by the flow and forms a weaker shear layer, with smaller vortices and less material exchange across the canopy top. While higher Reynolds number leads to stronger vortices and larger waving amplitudes of the seagrass, waving amplitude is maximized at intermediate grass buoyancy. All together, our theory and computations develop an updated schematic of the instability mechanism consistent with experimental observations.}, }
@article {pmid36889000, year = {2023}, author = {Zhu, Q}, title = {Wall effect on the start maneuver of a jet swimmer.}, journal = {Bioinspiration &amp; biomimetics}, volume = {18}, number = {3}, pages = {}, doi = {10.1088/1748-3190/acc293}, pmid = {36889000}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; *Locomotion ; *Swimming ; Motion ; Decapodiformes ; }, abstract = {Inspired by aquatic creatures such as squid, the novel propulsion method based on pulsed jetting is a promising way to achieve high speed and high maneuverability. To study the potential application of this locomotion method in confined space with complicated boundary conditions, it is critical to understand their dynamics in the vicinity of solid boundaries. In this study we numerically examine the start maneuver of an idealized jet swimmer near a wall. Our simulations illustrate three important mechanisms: (1) due to the blocking effect of the wall the pressure inside the body is affected so that the forward acceleration is increased during deflation and decreased during inflation; (2) the wall affects the internal flow so that the momentum flux at the nozzle and subsequently the thrust generation during the jetting phase are slightly increased; (3) the wall affects the wake so that the refilling phase is influenced, leading to a scenario in which part of the energy expended during jetting is recovered during refilling to increase forward acceleration and reduce power expenditure. In general, the second mechanism is weaker than the other two. The exact effects of these mechanisms depend on physical parameters such as the initial phase of the body deformation, the distance between the swimming body and the wall, and the Reynolds number.}, }
@article {pmid36888616, year = {2023}, author = {Gao, P and Wang, Q and Liu, T}, title = {Numerical method investigation on the aggregation characteristics of non-spherical particles.}, journal = {PloS one}, volume = {18}, number = {3}, pages = {e0282804}, pmid = {36888616}, issn = {1932-6203}, mesh = {*Microfluidics/methods ; Motion ; *Particulate Matter ; }, abstract = {Under the background of the mechanical mechanism research of microfluidic technology for separating and screening pipeline particulate matter, this paper proposes an improved relative motion model by combining the multiple reference frame method and the relative motion model. Worked with a quasi-fixed constant method, this model can numerically calculate the aggregation features of non-spherical particles in the low Reynolds number channels. The results demonstrate that when Re = 40~80, ellipsoids exhibit an aggregation trend similar to circular particles with the same diameter as its largest circumscribed sphere. The aggregation position is affected by the ratio of long and short axes of particles, and the distribution trend is determined by the relative size of these particles. When the channel's Reynolds number is less than the critical Reynolds number, the aggregation position of elliptical particles will be closer to the pipe center with the increase in the Reynolds number, which is contrary to the aggregation tendency of circular particles more proximate to the pipe wall with the increase in the Reynolds number. This finding provides a novel idea and method for further exploring the aggregation rules of non-spherical particles and offers substantial guidance for separating and monitoring pipeline particulate matter via microfluidic technology and other related industrial applications.}, }
@article {pmid36871543, year = {2023}, author = {Ram, D and Bhandari, DS and Sharma, K and Tripathi, D}, title = {Progression of blood-borne viruses through bloodstream: A comparative mathematical study.}, journal = {Computer methods and programs in biomedicine}, volume = {232}, number = {}, pages = {107425}, doi = {10.1016/j.cmpb.2023.107425}, pmid = {36871543}, issn = {1872-7565}, mesh = {Humans ; *Hepatitis B ; Blood Viscosity ; Viscosity ; Computer Simulation ; *Viruses ; *HIV Infections ; }, abstract = {BACKGROUND AND OBJECTIVES: Blood-borne pathogens are contagious microorganisms that can cause life-threatening illnesses, and are found in human blood. It is crucial to examine how these viruses spread through blood flow in the blood vessel. Keeping that in view, this study aims to determine how blood viscosity, and diameter of the viruses can affect the virus transmission through the blood flow in the blood vessel. A comparative study of bloodborne viruses (BBVs) such as HIV, Hepatitis B, and C, has been addressed in the present model. A couple stress fluid model is used to represent blood as a carrying medium for virus transmission. The Basset-Boussinesq-Oseen equation is taken into account for the simulation of virus transmission.<br><br>METHODS: An analytical approach to derive the exact solutions under the assumption of long wavelength and low Reynolds number approximations is employed. For the computation of the results, a segment (wavelength) of blood vessels about 120&#x2005;mm with wave velocities in the range of 49&#xa0;-&#xa0;190&#x2005;mm/sec&#x2005;are considered, where the diameter of BBVs ranges from 40-120&#xa0;nm. The viscosity of the blood varies from 3.5-5.5&#xa0;&#xd7;&#xa0;10[-3]Ns/m[2] which affect the virion motion having a density range 1.03&#xa0;-&#xa0;1.&#x2005;25&#x2005;g/m[3].<br><br>RESULTS: It shows that the Hepatitis B virus is more harmful than other blood-borne viruses considered in the analysis. Patients with high blood pressure are highly susceptible for transmission of BBVs.<br><br>CONCLUSIONS: The present fluid dynamics approach for virus spread through blood flow can be helpful in understanding the dynamics of virus propagation inside the human circulatory system.}, }
@article {pmid36869078, year = {2023}, author = {Ashin, K and Girishkumar, MS and D'Asaro, E and Jofia, J and Sherin, VR and Sureshkumar, N and Rao, EPR}, title = {Observational evidence of salt finger in the diurnal thermocline.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {3627}, pmid = {36869078}, issn = {2045-2322}, abstract = {Due to strong turbulent mixing, the ocean surface boundary layer region is generally not conducive to double diffusion. However, vertical microstructure profiles observations in the northeastern Arabian Sea during May 2019 imply the formation of salt fingers in the diurnal thermocline (DT) region during the daytime. In the DT layer, conditions are favorable for salt fingering: Turner angle values are between 50 and 55° with both temperature and salinity decreasing with depth; shear-driven mixing is weak with a turbulent Reynolds number of about 30. The presence of salt fingering in the DT is confirmed by the presence of staircase-like structures with step sizes larger than the Ozmidov length and by the dissipation ratio that is larger than the mixing coefficient. The unusual daytime salinity maximum in the mixed layer that supports salt fingering is primarily due to a daytime reduction in vertical entrainment of fresh water along with minor contributions from evaporation and horizontal advection and a significant contribution from detrainment processes.}, }
@article {pmid36858981, year = {2023}, author = {Arif, I and Leung, RCK and Naseer, MR}, title = {A computational study of trailing edge noise suppression with embedded structural compliance.}, journal = {JASA express letters}, volume = {3}, number = {2}, pages = {023602}, doi = {10.1121/10.0017321}, pmid = {36858981}, issn = {2691-1191}, abstract = {A unique concept for suppression of trailing edge noise scattering from a splitter plate in a low Reynolds number flow is proposed. The key idea of the concept is the adoption of a structural compliance system embedded with a finite number of elastic panels. Specific compliance system designs are devised for promotion of panel structural resonance that effectively absorbs broadband flow/acoustic fluctuation energy responsible for noise scattering. The concept is examined using high-fidelity direct aeroacoustic simulation together with spatiotemporal aeroacoustic-structural interaction analysis. The concept is confirmed feasible and outperforms many similar trailing edge noise reduction approaches reported in the literature.}, }
@article {pmid39569021, year = {2023}, author = {Veigel, D and Rishi, K and Okoli, U and Beaucage, G and Galloway, JA and Campanelli, H and Ilavsky, J and Kuzmenko, I and Fickenscher, M}, title = {Comparison of nanocomposite dispersion and distribution for several melt mixers.}, journal = {Polymer}, volume = {269}, number = {}, pages = {}, pmid = {39569021}, issn = {0032-3861}, support = {CC999999/ImCDC/Intramural CDC HHS/United States ; }, abstract = {Breakup (dispersion) and distribution of nanoparticles are the chief hurdles towards taking advantage of nanoparticles in polymer nanocomposites for reinforcement, flame retardancy, conductivity, chromaticity, and other properties. Microscopy is often used to quantify mixing, but it has a limited field of view, does not average over bulk samples, and fails to address nano-particle hierarchical structures. Ultra-small-angle X-ray scattering (USAXS) can provide a macroscopic statistical average of nanoscale dispersion (breakup) and emergent hierar-chical structure, as well as the distribution on the nanoscale. This work compares several common mixer geometries for carbon black-polystyrene nanocomposites. Two twin-screw extruder geometries, typical for industrial processing of melt blends, are compared with a laboratory-scale single screw extruder and a Banbury mixer. It is found that for a given mixer, nanoscale distribution increases following a van der Waals function using accumulated strain as an analogue for temperature while macroscopic distribution/dispersion, using microscopy, does not follow this dependency. Breakup and aggregation in dispersive mixing follow expected behavior on the nanoscale. Across these drastically different mixing geometries an unexpected dependency is observed for nanoscale distributive mixing (both nano and macroscopic) as a function of accumulated strain that may reflect a transition from distributive turbulent to dispersive laminar mixing as the mixing gap is reduced.}, }
@article {pmid36853773, year = {2023}, author = {Stricker, M and Littfinski, T and Pecher, KH and Lübken, M and Wichern, M}, title = {Hydraulic modeling of a compact stormwater treatment device applying concepts of dynamic similitude.}, journal = {Water science and technology : a journal of the International Association on Water Pollution Research}, volume = {87}, number = {4}, pages = {954-968}, doi = {10.2166/wst.2023.025}, pmid = {36853773}, issn = {0273-1223}, mesh = {*Rain ; *Water Purification ; Water Supply ; Filtration ; Particle Size ; }, abstract = {The development of compact treatment devices (CTDs) with high removal efficiencies and low space requirements is a key objective of urban stormwater treatment. Thus, many devices utilize a combination of sedimentation and upward-flow filtration in a single system. Here, sedimentation is used before filtration, which makes it difficult to evaluate the individual treatment stages separately. This study determines the removal efficiency by sedimentation and the expected filter load in a specific compact treatment device designed for a catchment area of up to 10,000 m[2]. In contrast to a full-scale investigation, small-scale physical hydraulic modeling is applied as a new cost-saving alternative. To validate upscaling laws, tracer signals and particle-size-specific removal efficiencies are determined for two geometrically similar models at different length scales. Thereby, Reynolds number similarity produces similar flow patterns, while the similarity of Hazen numbers allows to upscale removal efficiencies. Upscaling to the full-scale reveals that the filter in the device is only partly loaded by particulate matter that consists mostly of particles ≤63 μm. Thus, sedimentation upstream of a filter is of relevant importance in CTDs. The proposed dimensionless relationship may be used for particles from different catchments and helps to size the device accordingly.}, }
@article {pmid36842977, year = {2023}, author = {Lyubimova, TP and Fomicheva, AA and Ivantsov, AO}, title = {Dynamics of a bubble in oscillating viscous liquid.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {381}, number = {2245}, pages = {20220085}, doi = {10.1098/rsta.2022.0085}, pmid = {36842977}, issn = {1471-2962}, abstract = {This article is devoted to the investigation of gaseous bubble dynamics in oscillating viscous liquids of different density values. The study is conducted numerically using the level-set method with a non-stationary approach. The bubble is initially located near the upper wall of the container. The effects of the inclusion and host liquid viscosities on interaction of the bubble with the wall are analysed. The calculations show that in the absence of gravity, for low-viscosity fluids the bubble is attracted to the nearest wall, which is consistent with previous analytical and experimental results. With increasing viscosity, the vibrational attraction to the wall becomes weaker and is then replaced by repulsion, which can be explained by the decelerative effect of viscosity in the boundary layer near the rigid surface, where the average flow becomes less intensive. The dependencies of the repulsion force on the parameter values are obtained by using the balance method (investigation of the gravity level needed to attain the quasi-equilibrium state at a certain distance between the bubble and the wall). The calculations show that the repulsion force grows with decreasing Reynolds number (increase of the viscosity). This article is part of the theme issue 'New trends in pattern formation and nonlinear dynamics of extended systems'.}, }
@article {pmid36842115, year = {2023}, author = {Abe, K and Takabe, K and Nakamura, S}, title = {Force Measurement of Bacterial Swimming Using Optical Tweezers.}, journal = {Methods in molecular biology (Clifton, N.J.)}, volume = {2646}, number = {}, pages = {169-179}, pmid = {36842115}, issn = {1940-6029}, mesh = {*Swimming ; *Optical Tweezers ; Biomechanical Phenomena ; Mechanical Phenomena ; Bacteria ; }, abstract = {Velocity is a physical parameter most commonly used to quantify bacterial swimming. In the steady-state motion at a low Reynolds number, the swimming force can be estimated from the swimming velocity and the drag coefficient based on the assumption that the swimming force balances with the drag force exerted on the bacterium. Though the velocity-force relation provides a significant clue to understand the swimming mechanism, the odd configuration of bacteria could develop problems with the accuracy of the force estimation. This chapter describes the force measurement using optical tweezers. The method uses parameters obtained from the shape and movement of a microsphere attached to the bacteria, improving the quantitativeness of force measurement.}, }
@article {pmid36828913, year = {2023}, author = {Omrani, V and Targhi, MZ and Rahbarizadeh, F and Nosrati, R}, title = {High-throughput isolation of cancer cells in spiral microchannel by changing the direction, magnitude and location of the maximum velocity.}, journal = {Scientific reports}, volume = {13}, number = {1}, pages = {3213}, pmid = {36828913}, issn = {2045-2322}, mesh = {Humans ; Cell Line, Tumor ; Cell Separation/methods ; *Microfluidic Analytical Techniques ; *Neoplastic Cells, Circulating/pathology ; Microfluidics ; }, abstract = {Circulating tumor cells (CTCs) are scarce cancer cells that rarely spread from primary or metastatic tumors inside the patient's bloodstream. Determining the genetic characteristics of these paranormal cells provides significant data to guide cancer staging and treatment. Cell focusing using microfluidic chips has been implemented as an effective method for enriching CTCs. The distinct equilibrium positions of particles with different diameters across the microchannel width in the simulation showed that it was possible to isolate and concentrate breast cancer cells (BCCs) from WBCs at a moderate Reynolds number. Therefore we demonstrate high throughput isolation of BCCs using a passive, size-based, label-free microfluidic method based on hydrodynamic forces by an unconventional (combination of long loops and U-turn) spiral microfluidic device for isolating both CTCs and WBCs with high efficiency and purity (more than 90%) at a flow rate about 1.7 mL/min, which has a high throughput compared to similar ones. At this golden flow rate, up to 92% of CTCs were separated from the cell suspension. Its rapid processing time, simplicity, and potential ability to collect CTCs from large volumes of patient blood allow the practical use of this method in many applications.}, }
@article {pmid36827557, year = {2023}, author = {Moore, CP and Husson, J and Boudaoud, A and Amselem, G and Baroud, CN}, title = {Clogging of a Rectangular Slit by a Spherical Soft Particle.}, journal = {Physical review letters}, volume = {130}, number = {6}, pages = {064001}, doi = {10.1103/PhysRevLett.130.064001}, pmid = {36827557}, issn = {1079-7114}, abstract = {The capture of a soft spherical particle in a rectangular slit leads to a nonmonotonic pressure-flow rate relation at low Reynolds number. Simulations reveal that the flow induced deformations of the trapped particle focus the streamlines and pressure drop to a small region. This increases the resistance to flow by several orders of magnitude as the driving pressure is increased. As a result, two regimes are observed in experiments and simulations: a flow-dominated regime for small particle deformations, where flow rate increases with pressure, and an elastic-dominated regime in which solid deformations block the flow.}, }
@article {pmid36820228, year = {2023}, author = {Baba, YD and Chiacchia, M and Patwardhan, SV}, title = {A Novel Method for Understanding the Mixing Mechanisms to Enable Sustainable Manufacturing of Bioinspired Silica.}, journal = {ACS engineering Au}, volume = {3}, number = {1}, pages = {17-27}, pmid = {36820228}, issn = {2694-2488}, abstract = {Bioinspired silica (BIS) has received unmatched attention in recent times owing to its green synthesis, which offers a scalable, sustainable, and economical method to produce high-value silica for a wide range of applications, including catalysis, environmental remediation, biomedical, and energy storage. To scale-up BIS synthesis, it is critically important to understand how mixing affects the reaction at different scales. In particular, successful scale-up can be achieved if mixing time is measured, modeled, and kept constant across different production scales. To this end, a new image analysis technique was developed using pH, as one of the key parameters, to monitor the reaction and the mixing. Specifically, the technique involved image analysis of color (pH) change using a custom-written algorithm to produce a detailed pH map. The degree of mixing and mixing time were determined from this analysis for different impeller speeds and feed injection locations. Cross validation of the mean pH of selected frames with measurements using a pH calibration demonstrated the reliability of the image processing technique. The results suggest that the bioinspired silica formation is controlled by meso- and, to a lesser extent, micromixing. Based on the new data from this investigation, a mixing time correlation is developed as a function of Reynolds number-the first of a kind for green nanomaterials. Further, we correlated the effects of mixing conditions on the reaction and the product. These results provide valuable insights into the scale-up to enable sustainable manufacturing of BIS and other nanomaterials.}, }
@article {pmid36813941, year = {2023}, author = {Han, F and Zhao, Y and Liu, M and Hu, F and Peng, Y and Ma, L}, title = {Wetting behavior during impacting bituminous coal surface for dust suppression droplets of fatty alcohol polyoxyethylene ether.}, journal = {Environmental science and pollution research international}, volume = {30}, number = {18}, pages = {51816-51829}, pmid = {36813941}, issn = {1614-7499}, support = {LJ2020JCL008//Scientific research project of Education Department of Liaoning Province/ ; JSK202104//Research Grant of Key Laboratory of Mine Thermodynamic Disasters and Control, Ministry of Education, Liaoning Technical University/ ; 51604143//National Natural Science Foundation of China/ ; }, mesh = {*Coal ; *Dust ; Fatty Alcohols ; Polyethylene Glycols ; Water ; Ethers ; }, abstract = {The wetting behavior of droplets during impacting coal surface widely exists in the dust control process. Understanding the effect of surfactants on the diffusion of water droplets on coal surface is critical. To study the effect of fatty alcohol polyoxyethylene ether (AEO) on the dynamic wetting behavior of droplets on bituminous coal surface, a high-speed camera is used to record the impact process of ultrapure water droplets and three different molecular weight AEO solution droplets. A dynamic evaluation index, dimensionless spreading coefficient ([Formula: see text]), is used to evaluate the dynamic wetting process. The research results show that maximum dimensionless spreading coefficient ([Formula: see text]) of AEO-3, AEO-6, and AEO-9 droplets is greater than that of ultrapure water droplets. With the increase of impact velocity, the [Formula: see text] increases, but the required time decreases. Moderately increasing the impact velocity is conducive to promoting the spreading of droplets on the coal surface. Below the critical micelle concentration (CMC), the concentration of AEO droplets is positively correlated with the [Formula: see text] and the required time. When the polymerization degree increases, the Reynolds number ([Formula: see text]) and Weber number ([Formula: see text]) of droplets decrease, and the [Formula: see text] decreases. AEO can effectively enhance the spreading of droplets on the coal surface, but the increase in polymerization degree can inhibit this process. Viscous force hinders droplet spreading during droplet interaction with the coal surface, and surface tension promotes droplet retraction. Under the experimental conditions of this paper ([Formula: see text], [Formula: see text]), there is a power exponential relationship between [Formula: see text] and [Formula: see text].}, }
@article {pmid36813725, year = {2023}, author = {Rahimi, A and Shahsavari, A and Pakzad, H and Moosavi, A and Nouri-Borujerdi, A}, title = {Laminar drag reduction ability of liquid-infused microchannels by considering different infused lubricants.}, journal = {The Journal of chemical physics}, volume = {158}, number = {7}, pages = {074702}, doi = {10.1063/5.0137100}, pmid = {36813725}, issn = {1089-7690}, abstract = {We numerically investigate the pressure drop reduction (PDR) performance of microchannels equipped with liquid-infused surfaces, along with determining the shape of the interface between the working fluid and lubricant within the microgrooves. The effects of different parameters, such as the Reynolds number of working fluid, density and viscosity ratios between the lubricant and working fluid, the ratio of the thickness of the lubricant layer over the ridges to the depth of the groove, and the Ohnesorge number as a representative of the interfacial tension, on the PDR and interfacial meniscus within the microgrooves are comprehensively studied. The results reveal that the density ratio and Ohnesorge number do not significantly affect the PDR. On the other hand, the viscosity ratio considerably affects the PDR, and a maximum PDR of 62% compared to a smooth non-lubricated microchannel is achieved for a viscosity ratio of 0.01. Interestingly, the higher the Reynolds number of the working fluid, the higher the PDR. The meniscus shape within the microgrooves is strongly affected by the Reynolds number of the working fluid. Despite the insignificant effect of interfacial tension on the PDR, the interface shape within the microgrooves is appreciably influenced by this parameter.}, }
@article {pmid36810678, year = {2023}, author = {O'Callaghan, F and Lehmann, FO}, title = {Flow development and leading edge vorticity in bristled insect wings.}, journal = {Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology}, volume = {209}, number = {2}, pages = {219-229}, pmid = {36810678}, issn = {1432-1351}, mesh = {Animals ; *Models, Biological ; *Wings, Animal/physiology ; Flight, Animal/physiology ; Insecta/physiology ; Biomechanical Phenomena/physiology ; }, abstract = {Small flying insects such as the tiny thrip Gynaikothrips ficorum have wings with bristles attached to a solid shaft instead of solid membranes. Air passing through the bristle fringe, however, makes bristled insect wings less effective for aerodynamic force production. In this study, we quantified the ability of bristled wings to generate a leading edge vortex (LEV) for lift support during wing flapping, scored its circulation during wing translation, and investigated its behaviour at the stroke reversals. The data were measured in robotic model wings flapping with a generic kinematic pattern at Reynolds number of ~ 3.4, while applying two-dimensional particle image velocimetry. We found that aerodynamic performance due to LEV circulation linearly decreases with increasing bristle spacing. The wings of Gynaikothrips ficorum might thus produce approximately 9% less aerodynamic force for flight than a solid membranous wing. At the stroke reversals, leading and trailing edge vortices dissipate quickly within no more than ~ 2% of the stroke cycle duration. This elevated dissipation makes vortex shedding obsolete during the reversals and allows a quick build-up of counter-vorticity when the wing reverses flapping direction. In sum, our findings highlight the flow conditions associated with bristled wing design in insects and are thus significant for assessing biological fitness and dispersal of insects flying in a viscosity-dominated fluid regime.}, }
@article {pmid36789875, year = {2023}, author = {Hamlet, CL and Strickland, WC and Battista, N and Miller, LA}, title = {Multiscale flow between the branches and polyps of gorgonians.}, journal = {The Journal of experimental biology}, volume = {226}, number = {5}, pages = {}, pmid = {36789875}, issn = {1477-9145}, mesh = {Animals ; *Anthozoa ; Hydrodynamics ; }, abstract = {Gorgonians, including sea fans, are soft corals well known for their elaborate branching structure and how they sway in the ocean. This branching structure can modify environmental flows to be beneficial for feeding in a particular range of velocities and, presumably, for a particular size of prey. As water moves through the elaborate branches, it is slowed, and recirculation zones can form downstream of the colony. At the smaller scale, individual polyps that emerge from the branches expand their tentacles, further slowing the flow. At the smallest scale, the tentacles are covered in tiny pinnules where exchange occurs. In this paper, we quantified the gap to diameter ratios for various gorgonians at the scale of the branches, the polyp tentacles and the pinnules. We then used computational fluid dynamics to determine the flow patterns at all three levels of branching. We quantified the leakiness between the branches, tentacles and pinnules over the biologically relevant range of Reynolds numbers and gap-to-diameter ratios, and found that the branches and tentacles can act as either leaky rakes or solid plates depending upon these dimensionless parameters. The pinnules, in contrast, mostly impede the flow. Using an agent-based modeling framework, we quantified plankton capture as a function of the gap-to-diameter ratio of the branches and the Reynolds number. We found that the capture rate depends critically on both morphology and Reynolds number. The results of the study have implications for how gorgonians modify ambient flows for efficient feeding and exchange.}, }
@article {pmid36785427, year = {2023}, author = {Liu, W and Yu, Z and Duan, F and Hu, H and Fu, X and Bao, R}, title = {Robust five-degree-of-freedom measurement system with self-compensation and air turbulence protection.}, journal = {Optics express}, volume = {31}, number = {3}, pages = {4652-4666}, doi = {10.1364/OE.480772}, pmid = {36785427}, issn = {1094-4087}, abstract = {A robust five-degree-of-freedom (5-DOF) measurement system is proposed in this paper. The compact optical configuration with high resolution is designed based on lens combination and multiple reflections. Beam drift and dual-beam parallelism are monitored and compensated by autocollimator units and a polarizer unit respectively. In addition, a protection method is proposed to reduce the intensity of air turbulence by reducing the Reynolds number of the beam path. The performance of the system is verified by experiments. The experimental results show that the self-compensation methods and air turbulence protection can effectively improve the accuracy and stability of the system under the long-term interference of external environments. The proposed system has high precision, desirable robustness, and convenient pre-calibration, which can be used for error measurement of precision machines.}, }
@article {pmid36779398, year = {2023}, author = {Millett, PC}, title = {Rheology and structure of elastic capsule suspensions within rectangular channels.}, journal = {Soft matter}, volume = {19}, number = {9}, pages = {1759-1771}, doi = {10.1039/d3sm00055a}, pmid = {36779398}, issn = {1744-6848}, abstract = {Three-dimensional simulations of the pressure-driven flow dynamics of elastic capsule suspensions within both slit and rectangular cross-section channels are presented. The simulations utilize the Immersed Boundary Method and the Lattice-Boltzmann Method models. The capsule volume fraction is fixed at 0.1 (i.e., a semi-dilute suspension), while the channel Reynolds number (Re), the capillary number (Ca), and the cross-sectional channel dimensions are systematically varied. Comparing results for slit and rectangular channels, it is found that multi-directional confinement hinders inertial focusing due to the capsule-free layers that develop in the two transverse directions. Furthermore, the thicknesses of the capsule-free layers in the two transverse directions differ when the height and width of the channel are not equal. Both the size and aspect ratio of the channel impact the apparent viscosity. It is found that square channels exhibit maximal viscosity and that holding one dimension fixed while increasing or decreasing the other results in a decrease in viscosity. The results therefore represent an expansion of the Fahraeus-Lindqvist effect from 1D cylindrical channels to 2D rectangular channels.}, }
@article {pmid36736259, year = {2023}, author = {Yang, G and Yu, Z and Baki, ABM and Yao, W and Ross, M and Chi, W and Zhang, W}, title = {Settling behaviors of microplastic disks in water.}, journal = {Marine pollution bulletin}, volume = {188}, number = {}, pages = {114657}, doi = {10.1016/j.marpolbul.2023.114657}, pmid = {36736259}, issn = {1879-3363}, mesh = {*Microplastics ; Water ; Plastics ; *Water Pollutants, Chemical/analysis ; }, abstract = {Microplastic (MP) disks have not been studied for settling behaviors in aquatic environments, which affects the transport and fate of MPs. Therefore, settling experiments were conducted on MP disks of three shapes and four common-seen materials. Lighter MP disks (with density ρs = 1.038 g/cm[3] and length l ≤ 5 mm) followed rectilinear vertical trajectories, while heavier MP disks (ρs = 1.161-1.343 g/cm[3] and l = 5 mm) followed zigzag trajectories with oscillations and rotations. The mean terminal settling velocities of MP disks were 19.6-48.8 mm/s. Instantaneous settling velocities of heavier MP disks fluctuated. Existing formulas could not accurately predict the settling velocity of MP disks; thus, a new model was proposed with an error of 15.5 %. Finally, the Red - I* diagram (Red is the disk Reynolds number and I* is the dimensionless moment of inertia) was extended for MP disks to predict settling trajectories.}, }
@article {pmid36733611, year = {2022}, author = {Fahim, T and Laouedj, S and Abderrahmane, A and Driss, Z and Tag-ElDin, ESM and Guedri, K and Younis, O}, title = {Numerical study of perforated obstacles effects on the performance of solar parabolic trough collector.}, journal = {Frontiers in chemistry}, volume = {10}, number = {}, pages = {1089080}, pmid = {36733611}, issn = {2296-2646}, abstract = {The current work presents and discusses a numerical analysis of improving heat transmission in the receiver of a parabolic trough solar collector by introducing perforated barriers. While the proposed approach to enhance the collector's performance is promising, the use of obstacles results in increased pressure loss. The Computational Fluid Dynamics (CFD) model analysis is conducted based on the renormalization-group (RNG) k-ɛ turbulent model associated with standard wall function using thermal oil D12 as working fluid The thermo-hydraulic analysis of the receiver tube with perforated obstacles is taken for various configurations and Reynolds number ranging from 18,860 to 81,728. The results are compared with that of the receiver without perforated obstacles. The receiver tube with three holes (PO3) showed better heat transfer characteristics. In addition, the Nusselt number (Nu) increases about 115% with the increase of friction factor 5-6.5 times and the performance evaluation criteria (PEC) changes from 1.22 to 1.24. The temperature of thermal oil fluid attains its maximum value at the exit, and higher temperatures (462.1 K) are found in the absorber tube with perforated obstacles with three holes (PO3). Accordingly, using perforated obstacles receiver for parabolic trough concentrator is highly recommended where significant enhancement of system's performance is achieved.}, }
@article {pmid36725545, year = {2023}, author = {Chen, X and Sun, S and Tian, X and Liu, L and Yang, J}, title = {A quasi-two-dimensional fluid experimental apparatus based on tank-in-tank configuration.}, journal = {The Review of scientific instruments}, volume = {94}, number = {1}, pages = {015115}, doi = {10.1063/5.0125679}, pmid = {36725545}, issn = {1089-7623}, abstract = {The fluid tank is an essential facility for experimental research on fluid mechanics. However, owing to the hydrostatic fluid pressure, a fine uniformity of the narrow channel is difficult to be maintained in a tall narrow-channel tank. To address this issue, we proposed a quasi-two-dimensional fluid experimental apparatus based on a "tank-in-tank" configuration and built with an outer tank and an inner tank. The outer tank was cuboid-shaped and used to load the fluid medium, while the inner tank, consisting of two parallel glass plates, was embedded into the outer tank and served as the experimental channel. The hydrostatic pressure acting on the channel was balanced so that a high level of uniformity was maintained over the whole channel. The available height and width of the channel were 2800 and 1500 mm, respectively, while its gap distance could be adaptive from 0 to 120 mm. Experimental research on motion characteristics of circular disks falling in the quasi-2D channel was implemented to investigate the effects of the falling environment and disk geometry. Four distinct falling types were observed, and the wake flow fields of the falling disks were visualized. The Reynolds numbers of falling disks ranged from 400 to 63 000 presently. Chaotic motion and regular motion were demarcated at Re ≈ 30 000. An analytical model was established to predict the final average falling velocity and Reynolds number. Finally, potential directions for future research and improvements to the apparatus were suggested.}, }
@article {pmid36714791, year = {2023}, author = {Misiulia, D and Lidén, G and Antonyuk, S}, title = {Secondary Lip Flow in a Cyclone Separator.}, journal = {Flow, turbulence and combustion}, volume = {110}, number = {3}, pages = {581-600}, pmid = {36714791}, issn = {1573-1987}, abstract = {Three secondary flows, namely the inward radial flow along the cyclone lid, the downward axial flow along the external surface of the vortex finder, and the radial inward flow below the vortex finder (lip flow) have been studied at a wide range of flow rate 0.22-7.54 LPM using the LES simulations. To evaluate these flows the corresponding methods were originally proposed. The highly significant effect of the Reynolds number on these secondary flows has been described by equations. The main finding is that the magnitude of all secondary flows decrease with increasing Reynolds number. The secondary inward radial flow along the cyclone lid is not constant and reaches its maximum value at the central radial position between the vortex finder external wall and the cyclone wall. The secondary downward axial flow along the external surface of the vortex finder significantly increases at the lowest part of the vortex finder and it is much larger than the secondary flow along the cyclone lid. The lip flow is much larger than the secondary inward radial flow along the cyclone lid, which was assumed in cyclone models to be equal to the lip flow, and the ratio of these two secondary flows is practically independent of the Reynolds number.}, }
@article {pmid36711805, year = {2023}, author = {Chang, R and Davydov, A and Jaroenlak, P and Budaitis, B and Ekiert, DC and Bhabha, G and Prakash, M}, title = {Energetics of the Microsporidian Polar Tube Invasion Machinery.}, journal = {bioRxiv : the preprint server for biology}, volume = {}, number = {}, pages = {}, pmid = {36711805}, issn = {2692-8205}, support = {P30 CA016087/CA/NCI NIH HHS/United States ; R01 AI147131/AI/NIAID NIH HHS/United States ; R35 GM128777/GM/NIGMS NIH HHS/United States ; S10 OD019974/OD/NIH HHS/United States ; }, abstract = {Microsporidia are eukaryotic, obligate intracellular parasites that infect a wide range of hosts, leading to health and economic burdens worldwide. Microsporidia use an unusual invasion organelle called the polar tube (PT), which is ejected from a dormant spore at ultra-fast speeds, to infect host cells. The mechanics of PT ejection are impressive. Anncaliia algerae microsporidia spores (3-4 μm in size) shoot out a 100-nm-wide PT at a speed of 300 μm/sec, creating a shear rate of 3000 sec[-1]. The infectious cargo, which contains two nuclei, is shot through this narrow tube for a distance of ~60-140 μm (Jaroenlak et al., 2020) and into the host cell. Considering the large hydraulic resistance in an extremely thin tube and the low-Reynolds-number nature of the process, it is not known how microsporidia can achieve this ultrafast event. In this study, we use Serial Block-Face Scanning Electron Microscopy to capture 3-dimensional snapshots of A. algerae spores in different states of the PT ejection process. Grounded in these data, we propose a theoretical framework starting with a systematic exploration of possible topological connectivity amongst organelles, and assess the energy requirements of the resulting models. We perform PT firing experiments in media of varying viscosity, and use the results to rank our proposed hypotheses based on their predicted energy requirement. We also present a possible mechanism for cargo translocation, and quantitatively compare our predictions to experimental observations. Our study provides a comprehensive biophysical analysis of the energy dissipation of microsporidian infection process and demonstrates the extreme limits of cellular hydraulics.}, }
@article {pmid36709783, year = {2023}, author = {Jeganathan, V and Alba, K and Ostilla-Mónico, R}, title = {Exploring the origin of turbulent Taylor rolls.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {381}, number = {2243}, pages = {20220130}, doi = {10.1098/rsta.2022.0130}, pmid = {36709783}, issn = {1471-2962}, abstract = {Since Taylor's seminal paper, the existence of large-scale quasi-axisymmetric structures has been a matter of interest when studying Taylor-Couette flow. In this article, we probe their formation in the highly turbulent regime by conducting a series of numerical simulations at a fixed Reynolds number [Formula: see text] while varying the Coriolis parameter to analyse the flow characteristics as the structures arise and dissipate. We show how the Coriolis force induces a one-way coupling between the radial and azimuthal velocity fields inside the boundary layer, but in the bulk, there is a two-way coupling that causes competing effects. We discuss how this complicates the analogy of narrow-gap Taylor-Couette to other convective flows. We then compare these statistics with a similar shear flow without no-slip boundary layers, showing how this double coupling causes very different effects. We finish by reflecting on the possible origins of turbulent Taylor rolls. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (part 1)'.}, }
@article {pmid36709780, year = {2023}, author = {Baroudi, L and Majji, MV and Peluso, S and Morris, JF}, title = {Taylor-Couette flow of hard-sphere suspensions: overview of current understanding.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {381}, number = {2243}, pages = {20220125}, doi = {10.1098/rsta.2022.0125}, pmid = {36709780}, issn = {1471-2962}, abstract = {Although inertial particle-laden flows occur in a wide range of industrial and natural processes, there is both a lack of fundamental understanding of these flows and continuum-level governing equations needed to predict transport and particle distribution. Towards this effort, the Taylor-Couette flow (TCF) system has been used recently to study the flow behaviour of particle-laden fluids under inertia. This article provides an overview of experimental, theoretical and computational work related to the TCF of neutrally buoyant non-Brownian suspensions, with an emphasis on the effect of finite-sized particles on the series of flow transitions and flow structures. Particles, depending on their size and concentration, cause several significant deviations from Newtonian fluid behaviour, including shifting the Reynolds number corresponding to transitions in flow structure and changing the possible structures present in the flow. Furthermore, particles may also migrate depending on the flow structure, leading to hysteretic effects that further complicate the flow behaviour. The current state of theoretical and computational modelling efforts to describe the experimental observations is discussed, and suggestions for potential future directions to improve the fundamental understanding of inertial particle-laden flows are provided. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (part 1)'.}, }
@article {pmid36688050, year = {2022}, author = {Hasan, HA and Sherza, JS and Abed, AM and Togun, H and Ben Khedher, N and Sopian, K and Mahdi, JM and Talebizadehsardari, P}, title = {Thermal and flow performance analysis of a concentrated linear Fresnel solar collector with transverse ribs.}, journal = {Frontiers in chemistry}, volume = {10}, number = {}, pages = {1074581}, pmid = {36688050}, issn = {2296-2646}, abstract = {This article deals with the impact of including transverse ribs within the absorber tube of the concentrated linear Fresnel collector (CLFRC) system with a secondary compound parabolic collector (CPC) on thermal and flow performance coefficients. The enhancement rates of heat transfer due to varying governing parameters were compared and analyzed parametrically at Reynolds numbers in the range 5,000-13,000, employing water as the heat transfer fluid. Simulations were performed to solve the governing equations using the finite volume method (FVM) under various boundary conditions. For all Reynolds numbers, the average Nusselt number in the circular tube in the CLFRC system with ribs was found to be larger than that of the plain absorber tube. Also, the inclusion of transverse ribs inside the absorber tube increases the average Nusselt number by approximately 115% at Re = 5,000 and 175% at Re = 13,000. For all Reynolds numbers, the skin friction coefficient of the circular tube with ribs in the CLFRC system is larger than that of the plain absorber tube. The coefficient of surface friction reduces as the Reynolds number increases. The performance assessment criterion was found to vary between 1.8 and 1.9 as the Reynolds number increases.}, }
@article {pmid36673306, year = {2023}, author = {Fuchs, M and Lubos, N and Kabelac, S}, title = {Numerical Calculation of the Irreversible Entropy Production of Additively Manufacturable Off-Set Strip Fin Heat-Transferring Structures.}, journal = {Entropy (Basel, Switzerland)}, volume = {25}, number = {1}, pages = {}, pmid = {36673306}, issn = {1099-4300}, support = {KK5174901SN0//Federal Ministry for Economic Affairs and Energy/ ; KK5174901SN0//German Federation of Industrial Research Associations/ ; }, abstract = {In this manuscript, off-set strip fin structures are presented which are adapted to the possibilities of additive manufacturing. For this purpose, the geometric parameters, including fin height, fin spacing, fin length, and fin longitudinal displacement, are varied, and the Colburn j-factor and the Fanning friction factor are numerically calculated in the Reynolds number range of 80-920. The structures are classified with respect to their entropy production number according to Bejan. This method is compared with the results from partial differential equations for the calculation of the irreversible entropy production rate due to shear stresses and heat conduction. This study reveals that the chosen temperature difference leads to deviation in terms of entropy production due to heat conduction, whereas the dissipation by shear stresses shows only small deviations of less than 2%. It is further shown that the variation in fin height and fin spacing has only a small influence on heat transfer and pressure drop, while a variation in fin length and fin longitudinal displacement shows a larger influence. With respect to the entropy production number, short and long fins, as well as large fin spacing and fin longitudinal displacement, are shown to be beneficial. A detailed examination of a single structure shows that the entropy production rate due to heat conduction is dominated by the entropy production rate in the wall, while the fluid has only a minor influence.}, }
@article {pmid36673217, year = {2022}, author = {Rajupillai, K and Alessa, N and Eswaramoorthi, S and Loganathan, K}, title = {Thermal Behavior of the Time-Dependent Radiative Flow of Water-Based CNTs/Au Nanoparticles Past a Riga Plate with Entropy Optimization and Multiple Slip Conditions.}, journal = {Entropy (Basel, Switzerland)}, volume = {25}, number = {1}, pages = {}, pmid = {36673217}, issn = {1099-4300}, support = {Researchers Supporting Project number (PNURSP2023R59)//Princess Nourah Bint Abdulrahman University/ ; }, abstract = {This communication deliberates the time-reliant and Darcy-Forchheimer flow of water-based CNTs/gold nanoparticles past a Riga plate. In addition, nonlinear radiation, heat consumption and multiple slip conditions are considered. Entropy generation is computed through various flow parameters. A suitable transformation with symmetry variables is invoked to remodel the governing mathematical flow models into the ODE equations. The homotopy analysis scheme and MATLAB bvp4c method are imposed to solve the reduced ODE equations analytically and numerically. The impact of sundry flow variables on nanofluid velocity, nanofluid temperature, skin friction coefficient, local Nusselt number, entropy profile and Bejan number are computed and analyzed through graphs and tables. It is found that the nanofluid velocity is reduced by greater porosity and slip factors. The thickness of the thermal boundary layer increases with increasing radiation, temperature ratio, and heat consumption/generation parameters. The surface drag force is reduced when there is a higher Forchheimer number, unsteadiness parameter and porosity parameter. The amount of entropy created is proportional to the radiation parameter, porosity parameter and Reynolds number. The Bejan number profile increases with radiation parameter, heat consumption/generation parameter and the Forchheimer number.}, }
@article {pmid36658185, year = {2023}, author = {Méry, F and Sebbane, D}, title = {Aerodynamic characterisation of porous fairings: pressure drop and Laser Doppler Velocimetry measurements.}, journal = {Scientific data}, volume = {10}, number = {1}, pages = {39}, pmid = {36658185}, issn = {2052-4463}, support = {8605383//EC | EU Framework Programme for Research and Innovation H2020 | H2020 Euratom (H2020 Euratom Research and Training Programme 2014-2018)/ ; }, abstract = {Wind tunnel measurements of pressure drop and steady and unsteady velocity field of a flow through fairing samples are described. 10 samples have been tested in pressure drop among which the velocity fields of 3 samples have been characterized by means of laser Doppler velocimetry. The samples are perforated plates, wiremesh plates or complex 3D geometries resulting from additive manufacturing methods. The Reynolds number of the experiments ranges from 55 000 to 117 000.}, }
@article {pmid36649407, year = {2023}, author = {Li, Y and Pahlavan, AA and Chen, Y and Liu, S and Li, Y and Stone, HA and Granick, S}, title = {Oil-on-water droplets faceted and stabilized by vortex halos in the subphase.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {120}, number = {4}, pages = {e2214657120}, pmid = {36649407}, issn = {1091-6490}, mesh = {*Water ; Surface Tension ; Thermodynamics ; *Convection ; }, abstract = {For almost 200 y, the dominant approach to understand oil-on-water droplet shape and stability has been the thermodynamic expectation of minimized energy, yet parallel literature shows the prominence of Marangoni flow, an adaptive gradient of interfacial tension that produces convection rolls in the water. Our experiments, scaling arguments, and linear stability analysis show that the resulting Marangoni-driven high-Reynolds-number flow in shallow water overcomes radial symmetry of droplet shape otherwise enforced by the Laplace pressure. As a consequence, oil-on-water droplets are sheared to become polygons with distinct edges and corners. Moreover, subphase flows beneath individual droplets can inhibit the coalescence of adjacent droplets, leading to rich many-body dynamics that makes them look alive. The phenomenon of a "vortex halo" in the liquid subphase emerges as a hidden variable.}, }
@article {pmid36648820, year = {2023}, author = {Jo, BW and Majid, T}, title = {Enhanced Range and Endurance Evaluation of a Camber Morphing Wing Aircraft.}, journal = {Biomimetics (Basel, Switzerland)}, volume = {8}, number = {1}, pages = {}, pmid = {36648820}, issn = {2313-7673}, support = {2021K2A9A2A06049018//National Research Foundation of Korea/ ; 20210901//InnoScience Co. Ltd/ ; }, abstract = {Flight range, endurance, maneuverability, and agility are the key elements that determine an aircraft's performance. Both conventional and morphing wing aircraft have been well studied and estimated in all aspects of performance. When considering the performance of morphing aircraft, most works address aspects of the aerodynamical performance such as L and D as well as flight envelopes for flight dynamics and control perspectives. However, the actual benefits of adopting morphing technologies in practical aspects such as aircraft operation, mission planning, and sustainability have not been addressed so far. Thus, this paper addresses the practical aspect of the benefits when adopting a camber morphing wing aircraft. Identical geometrical and computational conditions were applied to an already-existing aircraft: the RQ-7a Shadow. The wing structure was switched between a fixed wing and a camber morphing wing to generate conventional and morphing wing geometries. The fixed-wing cases had varying flap deflection angles, and the camber morphing wing cases had varying camber rates from 4% to 8%. Once the CL values of the fixed and morphing wing cases were matched up to two significant figures, the CD and CL/CD were analyzed for these matching cases to calculate the flight endurance, range, and improvement. When NACA 6410 is adopted, a 17% improvement in flight range and endurance average was expected. In the case of NACA 8410, an average 60% improvement was expected.}, }
@article {pmid36648720, year = {2023}, author = {Jain, PK and Lanjewar, A and Chaurasiya, PK and Tiwari, D and Sharma, VK}, title = {Experimental testing of solar-based air heater roughed with discrete V-down rib and staggered element.}, journal = {Environmental science and pollution research international}, volume = {30}, number = {15}, pages = {43137-43151}, pmid = {36648720}, issn = {1614-7499}, mesh = {*Sunlight ; *Air ; Hot Temperature ; Ribs ; }, abstract = {A rough rectangular channel of solar-based air heater (SBAH) is made and tested. The work consists of an effort to perceive the proportion of heat discharge and frictional behavior of air passing over a roughened rectangular channel. The absorber surface of SBAH is roughed with discrete V-down rib and staggered element roughness having different values of relative rib pitch (P/e) that ranged from 6 to 14. Fixed parameters such as relative gap size (g/e), relative staggered element pitch (P'/P), numeral of gaps (Ng), relative staggered element size (r/g), and relative rib height (e/D) are considered 4, 0.4, 3,1, and 0.0433, respectively, all throughout the study. The flow Reynolds number (Re) changes from 4000 to 14,000; consequently the Nusselt number (Nu) and friction factor (f) reach up to 2.16 and 2.73 times, respectively, with respect to plane surface. The optimum rise in terms of thermal-hydraulic performance (THP) is gained analogous to a P/e of 10. The correlation for heat transfer function, R(e[+]), and roughness function, G(e[+]), is given to anticipate the performance of roughness.}, }
@article {pmid36643326, year = {2022}, author = {Voskoboinick, V and Onyshchenko, A and Voskoboinyk, O and Makarenkova, A and Voskobiinyk, A}, title = {Junction flow inside and around three-row cylindrical group on rigid flat surface.}, journal = {Heliyon}, volume = {8}, number = {12}, pages = {e12595}, doi = {10.1016/j.heliyon.2022.e12595}, pmid = {36643326}, issn = {2405-8440}, abstract = {Groups of bluff bodies are widespread in nature and technology. These are the supports of bridge crossings, high-rise buildings in cities, offshore drilling and wind platforms, algae and vegetation in the seas and rivers, forests and other objects. The flow of air or water around such structures has a complex vortex and jet character and requires significant efforts in the process of scientific research to improve the environmental situation and reduce material and technical costs in the process of operating such structures. The purpose of the research is study the features of the generation and evolution of vortex and jet flows near and inside the three-row group of cylinders, which are installed on the rigid flat surface. The results of experimental studies showed that the flow around the group of cylinders had a complex unsteady nature, which is due to the interaction of vortex and jet flows typical flow elements with the three-row cylindrical group, which was located installed on the rigid flat surface. The three-row cylindrical group (31 piles with a diameter of 0.027 m) is a model of a bridge support, which was streamlined at a velocity of 0.06 m/s to 0.5 m/s (Reynolds number Red=(1600-6700) and Froude number Fr=(0.04-0.18)). Visual investigations and measurements of the velocity field were carried out inside and around the three-row structure. The features of the formation and evolution of vortex and jet flows inside and near the cylindrical group were established. Integral, spectral and correlation characteristics of the velocity fluctuation field were obtained. Mean, root-mean-square values of velocity and probability density functions of velocity fluctuations integrally displayed the changes in the velocity field in the spatial and temporal domain in the junction area of grillage and plate. The power spectral densities of velocity fluctuations and mutual correlation functions made it possible to study the features of the generation of the velocity fluctuation field in the frequency domain and its interrelationships in space. It was revealed that the velocity field inside the horseshoe vortex structures was multimodal. The spectral levels of velocity fluctuations at the periphery of the quasistable horseshoe vortex structures were higher than in the cores of these structures. The highest levels of the velocity fluctuation spectra were observed in front of the second lateral cylinder where the interaction of the vortex and jet flows took place. Discrete peaks in the spectral levels of velocity fluctuations are found at the frequencies of formation of large-scale wake vortices and the frequencies of formation of small-scale vortex structures of the shear layer, which are due to the Kelvin-Helmholtz instability. It has been established that the frequency of formation of shear layer vortices is (10-40) times higher than the frequency of formation of wake vortices.}, }
@article {pmid36622597, year = {2024}, author = {Munusamy, A and Barik, D and Sharma, P and Medhi, BJ and Bora, BJ}, title = {Performance analysis of parabolic type solar water heater by using copper-dimpled tube with aluminum coating.}, journal = {Environmental science and pollution research international}, volume = {31}, number = {53}, pages = {62376-62391}, pmid = {36622597}, issn = {1614-7499}, mesh = {*Aluminum/chemistry ; *Copper/chemistry ; *Solar Energy ; Water/chemistry ; }, abstract = {A solar water heater has been developed to convert solar radiation into heat for use in residential and commercial settings. The collector makes up the bulk of a solar water heating system. The solar energy is captured by the collector and transferred to the tube that delivers the working fluid, water. In addition to the collector's tube, which carries the working fluid, researchers have focused on the design of the collector's tube. This paper examines the performance of a parabolic plate solar water heater that uses a copper dimpled tube with aluminum-coated tube channels. During the test, the flow rate of base fluid was in the range of 1.0 to 3.0 kg/min in steps of 0.5. The performance of the solar water heater was also evaluated and verified using CFD. The test data such as friction factor, Reynolds number, uncertainty analysis, Nusselt number, solar collector efficiency, coefficient of convective heat transfer, linear dimpled tube velocity analysis, achieving maximum energy efficiency and thermal efficiency have been used to generate parametric values for parabolic plate solar water heaters. The results suggest that the best outcomes can be achieved with a mass flow rate of 2.5 kg/min and the overall thermal efficiency was raised to 31.85%, which is 11% greater than that of the plain tube with base fluid. At mass flow rates of 2.5 kg/min, the pressure drop was found to be 6.24% higher than that of 3.0 kg/min. The experimental results were analyzed and compared with the CFD results, and the overall deviation was ± 3.24% which is in the acceptable range.}, }
@article {pmid36597964, year = {2023}, author = {Kanies, OS and Kremer, KR and Mason, BM and Dudley, MG and Hlavay, JM and Miller, CT and Spero, RC and Fisher, JK}, title = {A modular microfluidic device that uses magnetically actuatable microposts for enhanced magnetic bead-based workflows.}, journal = {Lab on a chip}, volume = {23}, number = {2}, pages = {330-340}, pmid = {36597964}, issn = {1473-0189}, support = {R41 GM136084/GM/NIGMS NIH HHS/United States ; R42 GM136084/GM/NIGMS NIH HHS/United States ; R44 AI150263/AI/NIAID NIH HHS/United States ; }, mesh = {*Microfluidic Analytical Techniques ; Workflow ; Microfluidics/methods ; Immunomagnetic Separation ; Magnetic Phenomena ; }, abstract = {Magnetic beads have been widely and successfully used for target enrichment in life science assays. There exists a large variety of commercially available magnetic beads functionalized for specific target capture, as well as options that enable simple surface modifications for custom applications. While magnetic beads are ideal for use in the macrofluidic context of typical laboratory workflows, their performance drops in microfluidic contexts, such as consumables for point-of-care diagnostics. A primary cause is the diffusion-limited analyte transport in these low Reynolds number environments. A new method, BeadPak, uses magnetically actuatable microposts to enhance analyte transport, improving yield of the desired targets. Critical parameters were defined for the operation of this technology and its performance characterized in canonical life-science assays. BeadPak achieved up to 1000× faster capture than a microfluidic chamber relying on diffusion alone, enabled a significant specimen concentration via volume reduction, and demonstrated compatibility with a range of biological specimens. The results shown in this work can be extended to other systems that utilize magnetic beads for target capture, concentration, and/or purification.}, }
@article {pmid36597923, year = {2023}, author = {Tingting, Q and Jianzhong, L and Zhenyu, O and Jue, Z}, title = {Settling mode of a bottom-heavy squirmer in a narrow vessel.}, journal = {Soft matter}, volume = {19}, number = {4}, pages = {652-669}, doi = {10.1039/d2sm01442d}, pmid = {36597923}, issn = {1744-6848}, abstract = {The lattice Boltzmann-immersed boundary (IB-LB) method is used to numerically simulate the sedimentation motion of a single two-dimensional, bottom-heavy squirmer in a narrow vessel. The effects of the swimming Reynolds number Res = 0.1-3, eccentricity distance l = 0.15d-0.75d, and density ratio of squirmer to fluid γ = 1.1-2.0 on the settlement motion characteristics are investigated and analyzed. The results showed that four settling modes exist: vertical motion, unilateral oscillation, oscillation, and tilt. The bottom-heavy neutral squirmer and puller settle in the vessel during vertical motion when Res is 0.1-1.5. By increasing Res and swimming strength |β|, the bottom-heavy squirmer becomes more self-driven, shifting its settling mode from vertical motion to unilateral oscillation or oscillation. Increasing l or |β| does not affect the bottom-heavy neutral squirmer and puller's vertical settling mode but shifts the bottom-heavy pusher's settling mode from unilateral oscillation to oscillation or oscillation to unilateral oscillation. Similarly, altering γ or |β| has no impact on the eccentric neutral squirmer and puller's settling mode; however, pushers will switch from oscillation mode to attraction mode or from oscillation mode to tilt mode. Additionally, it was found that after the squirmer collided with the bottom wall, the bottom-heavy squirmer settled at the bottom of the vessel in a different state of motion.}, }
@article {pmid36583152, year = {2022}, author = {Abed, AM and Mouziraji, HR and Bakhshi, J and Dulaimi, A and Mohammed, HI and Ibrahem, RK and Ben Khedher, N and Yaïci, W and Mahdi, JM}, title = {Numerical analysis of the energy-storage performance of a PCM-based triplex-tube containment system equipped with arc-shaped fins.}, journal = {Frontiers in chemistry}, volume = {10}, number = {}, pages = {1057196}, pmid = {36583152}, issn = {2296-2646}, abstract = {This study numerically intends to evaluate the effects of arc-shaped fins on the melting capability of a triplex-tube confinement system filled with phase-change materials (PCMs). In contrast to situations with no fins, where PCM exhibits relatively poor heat response, in this study, the thermal performance is modified using novel arc-shaped fins with various circular angles and orientations compared with traditional rectangular fins. Several inline and staggered layouts are also assessed to maximize the fin's efficacy. The effect of the nearby natural convection is further investigated by adding a fin to the bottom of the heat-storage domain. Additionally, the Reynolds number and temperature of the heat-transfer fluid (HTF) are evaluated. The outcomes showed that the arc-shaped fins could greatly enhance the PCMs' melting rate and the associated heat-storage properties. The melting rate is 17% and 93.1% greater for the case fitted with an inline distribution of the fins with a circular angle of 90° and an upward direction, respectively, than the cases with uniform rectangular fins and no fins, which corresponded to the shorter melting time of 14.5% and 50.4%. For the case with arc-shaped fins with a 90° circular angle, the melting rate increases by 9% using a staggered distribution. Compared to the staggered fin distribution, adding an extra fin to the bottom of the domain indicates adverse effects. The charging time reduces by 5.8% and 9.2% when the Reynolds number (Re) rises from 500 to 1000 and 1500, respectively, while the heat-storage rate increases by 6.3% and 10.3%. When the fluid inlet temperature is 55°C or 50°C, compared with 45°C, the overall charging time increases by 98% and 47%, respectively.}, }
@article {pmid36579881, year = {2022}, author = {Issa, M and Haupt, D and Muddemann, T and Kunz, U and Sievers, M}, title = {Investigation of an electrolysis system with boron-doped diamond anode and gas diffusion cathode to remove water micropollutants.}, journal = {Water science and technology : a journal of the International Association on Water Pollution Research}, volume = {86}, number = {12}, pages = {3236-3247}, doi = {10.2166/wst.2022.390}, pmid = {36579881}, issn = {0273-1223}, mesh = {*Diamond ; Boron ; Water ; Wastewater ; Electrolysis/methods ; Oxidation-Reduction ; Electrodes ; *Water Pollutants, Chemical/analysis ; }, abstract = {Using electrolysis systems to degrade organics in wastewater encourages this technique to remove micropollutants (MPs) in different types of water. In this work, a cell consisting of an anode as a boron-doped diamond (BDD) electrode combined with a gas diffusion (GDE) cathode without a separator showed that MPs degradation can be effectively achieved. Investigating different operating parameters, it was stated that applying a low current density (2 mA/cm[2]) and setting the Reynolds number of the electrolyte flow through the cell at the laminar range raised the treatment time by 3-fold at the same energy demand. This arrangement increased the MPs removal. Some substances like diclofenac were removed up to 84% at a longer treatment time of 180 min coupled with an increase in energy demand. The results at the mentioned parameters indicated an adequate generation rate of radicals needed to remove MPs and the oxidation reactions were promoted. The results show high potential to the investigated electrolysis system in removing MPs in wastewater under considering the need for further reduction of the energy demand.}, }
@article {pmid36574794, year = {2023}, author = {Al-Amshawee, SKA and Yunus, MYBM}, title = {Electrodialysis desalination: The impact of solution flowrate (or Reynolds number) on fluid dynamics throughout membrane spacers.}, journal = {Environmental research}, volume = {219}, number = {}, pages = {115115}, doi = {10.1016/j.envres.2022.115115}, pmid = {36574794}, issn = {1096-0953}, mesh = {Hydrodynamics ; *Membranes, Artificial ; *Water Purification/instrumentation/methods ; Salinity ; *Dialysis/instrumentation/methods ; Electrochemistry/instrumentation/methods ; }, abstract = {The incorporation of a spacer among membranes has a major influence on fluid dynamics and performance metrics. Spacers create feed channels and operate as turbulence promoters to increase mixing and reduce concentration/temperature polarization effects. However, spacer geometry remains unoptimized, and studies continue to investigate a wide range of commercial and custom-made spacer designs. The in-depth discussion of the present systematic review seeks to discover the influence of Reynolds number or solution flowrate on flow hydrodynamics throughout a spacer-filled channel. A fast-flowing solution sweeping one membrane's surface first, then the neighboring membrane's surface produces good mixing action, which does not happen commonly at laminar solution flowrates. A sufficient flowrate can suppress the polarization layer, which may normally require the utilization of a simple feed channel rather than complex spacer configurations. When a recirculation eddy occurs, it disrupts the continuous flow and effectively curves the linear fluid courses. The higher the flowrate, the better the membrane performance, the higher the critical flux (or recovery rate), and the lower the inherent limitations of spacer design, spacer shadow effect, poor channel hydrodynamics, and high concentration polarization. In fact, critical flow achieves an acceptable balance between improving flow dynamics and reducing the related trade-offs, such as pressure losses and the occurrence of concentration polarization throughout the cell. If the necessary technical flowrate is not used, the real concentration potential for transport is relatively limited at low velocities than would be predicted based on bulk concentrations. Electrodialysis stack therefore may suffer from the dissociation of water molecules. Next studies should consider that applying a higher flowrate results in greater process efficiency, increased mass transfer potential at the membrane interface, and reduced stack thermal and electrical resistance, where pressure drop should always be indicated as a consequence of the spacer and circumstances used, rather than a problem.}, }
@article {pmid36562423, year = {2023}, author = {de Timary, G and Rousseau, CJ and Van Melderen, L and Scheid, B}, title = {Shear-enhanced sorting of ovoid and filamentous bacterial cells using pinch flow fractionation.}, journal = {Lab on a chip}, volume = {23}, number = {4}, pages = {659-670}, doi = {10.1039/d2lc00969b}, pmid = {36562423}, issn = {1473-0189}, mesh = {*Escherichia coli ; Rotation ; Cell Movement ; }, abstract = {In this paper, we experimentally investigate the influence of the flow rate on the trajectory of ovoid and filamentous bacterial cells of E. coli in a low aspect ratio pinch flow fractionation device. To that aim, we vary the Reynolds number over two orders of magnitude, while monitoring the dynamics of the cells across our device. At low flow rates, filamentous cells adopt several rotational motions in the pinched segment, which are induced both by the shear rate and by their close interactions with the nearest wall. As a result, the geometrical centre of the filamentous cells deviates towards the centre of the channel, which increases their effective sorting diameter depending on the length of their major axis as well as on the rotational mode they adopt in the pinch. As the flow rate increases, particles are forced to align vertically in the pinch, in the direction of the main shear gradient, which reduces the amplitude of the lateral deviation generated by their rotation. The trajectory of the particles in the expansion is directly determined by their position at the pinch outlet. As a consequence, the position of the filamentous cells at the outlet of the device strongly depends on the flow rate as well as on the length of their major axis. Based on these observations we optimized the flow conditions to successfully extract an ultra high purity sample of filamentous cells from a solution containing mainly ovoid cells.}, }
@article {pmid36562333, year = {2023}, author = {Marnoto, S and Hashmi, SM}, title = {Application of droplet migration scaling behavior to microchannel flow measurements.}, journal = {Soft matter}, volume = {19}, number = {3}, pages = {565-573}, doi = {10.1039/d2sm00980c}, pmid = {36562333}, issn = {1744-6848}, abstract = {In confined channels in low Reynolds number flow, droplets drift perpendicular to the flow, moving across streamlines. The phenomenon has proven useful for understanding microfluidic droplet separation, drug delivery vehicle optimization, and single-cell genomic amplification. Particles or droplets undergo several migration mechanisms including wall migration, hydrodynamic diffusion, and migration down gradients of shear. In simple shear flow only wall migration and hydrodynamic diffusion are present. In parabolic flow, droplets also move down gradients of shear. The resulting separation depends on parameters including particle size and stiffness, concentration, and flow rate. Computational methods can incorporate these effects in an exact manner to predict margination phenomena for specific systems, but do not generate a descriptive parametric dependence. In this paper, we present a scaling model that elucidates the parametric dependence of margination on emulsion droplet size, volume fraction, shear rate and suspending fluid viscosity. We experimentally measure the droplet depletion layer of silicone oil droplets and compare the results to theoretical scaling behavior that includes hydrodynamic diffusion and wall migration with and without an added shear-gradient migration. Results demonstrate the viability and limitations of applying a simple scaling behavior to experimental systems to describe parametric dependence. Our conclusions open the possibility for parametric descriptions of migration with broad applicability to particle and droplet systems.}, }
@article {pmid36559702, year = {2022}, author = {Ayas, M and Skočilas, J and Štípek, J and Gutiérrez, CA and Žitný, R and Jirout, T}, title = {An Approximate Method for Predicting the Friction Factor of Viscoplastic Shear-Thinning Fluids in Non-Circular Channels of Regular Cross-Sections.}, journal = {Polymers}, volume = {14}, number = {24}, pages = {}, pmid = {36559702}, issn = {2073-4360}, abstract = {The objective of this study is to provide a straightforward generalized simple and quick method for the prediction of the friction factor for fully developed laminar flow of viscoplastic shear-thinning fluids in non-circular channels of regular cross-sections. The most frequently represented substances processed under these conditions are polymers in the processing and plastics industry. A generalized approximate method was proposed to express the relationship between the friction factor and the Reynolds number for the Herschel-Bulkley rheological model. This method uses the generalized Reynolds number for power-law fluids. Moreover, an additional simplified method for rapid engineering calculations was obtained as well. The suggested method was verified by comparing experimental data for concentric annulus found in the literature and results from simulations for concentric annulus, rectangular, square duct with a central cylindrical core and elliptical cross-sections. The results showed that the suggested methods enable us to estimate the friction factor with high accuracy for the investigated geometries.}, }
@article {pmid36559442, year = {2022}, author = {Moriconi, L and Pereira, RM}, title = {Statistics of extreme turbulent circulation events from multifractality breaking.}, journal = {Physical review. E}, volume = {106}, number = {5-1}, pages = {054121}, doi = {10.1103/PhysRevE.106.054121}, pmid = {36559442}, issn = {2470-0053}, abstract = {Recent numerical explorations of extremely intense circulation fluctuations at high Reynolds number flows have brought to light novel aspects of turbulent intermittency. Vortex gas modeling ideas, which are related to a picture of turbulence as a dilute system of vortex tube structures, have been introduced alongside such developments, leading to accurate descriptions of the core and the intermediate tails of circulation probability distribution functions (cPDFs), as well as the scaling exponents associated to statistical moments of circulation. We extend the predictive reach of the vortex gas picture of turbulence by emphasizing that multifractality breaking, one of its salient phenomenological ingredients, is the key concept to disclose the asymptotic form of cPDF tails. A remarkable analytical agreement is found with previous results derived within the framework of the instanton approach to circulation intermittency, a functional formalism devised to single out the statistically dominant velocity configurations associated to extreme circulation events.}, }
@article {pmid36559415, year = {2022}, author = {Maity, R and Burada, PS}, title = {Near- and far-field hydrodynamic interaction of two chiral squirmers.}, journal = {Physical review. E}, volume = {106}, number = {5-1}, pages = {054613}, doi = {10.1103/PhysRevE.106.054613}, pmid = {36559415}, issn = {2470-0053}, abstract = {Hydrodynamic interaction strongly influences the collective behavior of microswimmers. With this work, we study the behavior of two hydrodynamically interacting self-propelled chiral swimmers in the low Reynolds number regime, considering both the near- and far-field interactions. We use the chiral squirmer model [see Burada et al., Phys. Rev. E 105, 024603 (2022)2470-004510.1103/PhysRevE.105.024603], a spherically shaped body with nonaxisymmetric surface slip velocity, which generalizes the well-known squirmer model. The previous work was restricted only to the case, while the far-field hydrodynamic interaction was influential among the swimmers. It did not approach the scenario while both the swimmers are very close and lubrication effects become dominant. We calculate the lubrication force between the swimmers when they are very close. By varying the slip coefficients and the initial configuration of the swimmers, we investigate their hydrodynamic behavior. In the presence of lubrication force, the swimmers either repel each other or exhibit bounded motion where the distance between the swimmers alters periodically. We identify the possible behaviors exhibited by the chiral squirmers, such as monotonic divergence, divergence, and bounded, as was found in the previous study. However, in the current study, we observe that both the monotonic convergence and the convergence states are converted into divergence states due to the arising lubrication effects. The lubrication force favors the bounded motion in some parameter regimes. This study helps to understand the collective behavior of dense suspension of ciliated microorganisms and artificial swimmers.}, }
@article {pmid36559353, year = {2022}, author = {Lutz, T and Richter, SK and Menzel, AM}, title = {Effect of boundaries on displacements and motion in two-dimensional fluid or elastic films and membranes.}, journal = {Physical review. E}, volume = {106}, number = {5-1}, pages = {054609}, doi = {10.1103/PhysRevE.106.054609}, pmid = {36559353}, issn = {2470-0053}, abstract = {Thin fluid or elastic films and membranes are found in nature and technology, for instance, as confinements of living cells or in loudspeakers. When applying a net force, the resulting flows in an unbounded two-dimensional incompressible low-Reynolds-number fluid or displacements in a two-dimensional linearly elastic solid seem to diverge logarithmically with the distance from the force center, which has led to some debate. Recently, we have demonstrated that such divergences cancel when the total (net) force vanishes. Here, we illustrate that if a net force is present, the boundaries play a prominent role. Already a single no-slip boundary regulates the flow and displacement fields and leads to their decay to leading order inversely in distance from a force center and the boundary. In other words, it is the boundary that stabilizes the system in this situation, unlike the three-dimensional case, where an unbounded medium by itself is able to absorb a net force. We quantify the mobility and displaceability of an inclusion as a function of the distance from the boundary, as well as interactions between different inclusions. In the case of free-slip boundary conditions, a kinked boundary is necessary to achieve stabilization.}, }
@article {pmid36557435, year = {2022}, author = {Guan, X and Xie, Z and Nan, G and Xi, K and Lu, Z and Ge, Y}, title = {Thermal-Hydrodynamic Behavior and Design of a Microchannel Pin-Fin Hybrid Heat Sink.}, journal = {Micromachines}, volume = {13}, number = {12}, pages = {}, pmid = {36557435}, issn = {2072-666X}, support = {51979278 and 51579244//National Natural Science Foundation of China/ ; }, abstract = {A three-dimensional convective heat transfer model of a microchannel pin-fin hybrid heat sink was established. Considering the non-uniform heat generation of 3D stacked chips, the splitting distance of pin-fins was optimized by minimizing the maximum heat sink temperature under different heat fluxes in the hotspot, the Reynolds numbers at the entrance of the microchannel, and the proportions of the pin-fin volume. The average pressure drop and the performance evaluation criteria were considered to be the performance indexes to analyze the influence of each parameter on the flow performance and comprehensive performance, respectively. The results showed that the maximum temperature of the hybrid heat sink attained a minimum value with an increase in the splitting distance. The average pressure drop in the center passage of the microchannel first increased and then decreased. Furthermore, the optimal value could not be simultaneously obtained with the maximum temperature. Therefore, it should be comprehensively considered in the optimization design. The heat flux in the hotspot was positively correlated with the maximum heat sink temperature. However, it had no effect on the flow pressure drop. When the Reynolds number and the pin-fin diameter increased, the maximum heat sink temperature decreased and the average pressure drop of the microchannel increased. The comprehensive performance of the hybrid heat sink was not good at small Reynolds numbers, but it significantly improved as the Reynolds number gradually increased. Choosing a bigger pin-fin diameter and the corresponding optimal value of the splitting distance in a given Reynolds number would further improve the comprehensive performance of a hybrid heat sink.}, }
@article {pmid36547837, year = {2023}, author = {Salman, M and Chauhan, R and Singh, T and Prabakaran, R and Kim, SC}, title = {Experimental investigation and optimization of dimple-roughened impinging jet solar air collector using a novel AHP-MABAC approach.}, journal = {Environmental science and pollution research international}, volume = {30}, number = {13}, pages = {36259-36275}, pmid = {36547837}, issn = {1614-7499}, mesh = {Reproducibility of Results ; *Sunlight ; }, abstract = {The effect of the flow and geometric parameters of a dimple-roughened absorber plate on the enactment of solar air collectors (SACs) with air-impinged jets was investigated in this study. The performance-defining criteria (PDCs) of a jet-impinged dimple-roughened SAC (JIDRSAC)-forced convection airflow system are significantly affected by variations in the system's control factors (CFs), such as the arc angle (αaa) ranging from 30° to 75°, dimple pitch ratio (pd/Dh) ranging from 0.269 to 1.08, and dimple height ratio (ed/Dh) ranging from 0.016 to 0.0324. The constant parameters of the jet slot are a stream-wise pitch ratio (Xi/Dhd) is 1.079, a span-wise pitch ratio (Yi/Dhd) is 1.619, and a jet diameter(Di/Dhd) is 0.081. Based on the combined approach of the analytic hierarchy process and multi-attributive border approximation area comparison (AHP-MABAC), the Reynolds number (Re) = 15,000, αaa = 60°, pd/Dh = 0.27, and ed/Dh = 0.027 depicted the best alternative (A-9) set among 16 alternatives to deliver the optimal performance of the JIDRSAC. The jet impingement pass compared to the smooth pass, the Nusselt number increased by 2.16-2.81, and friction factor increased by 3.35-5.95, and JIDRSAC was compared to the jet impingement pass, exhibiting an enhancement in Nusselt number and friction factor in the range of 0.55-0.80 and 0.05-0.15, respectively. In addition, sensitivity analysis is used to examine the ranking's stability and reliability in relation to the PDC weights.}, }
@article {pmid36547831, year = {2024}, author = {Raju, LB and Sastry, GR and Gugulothu, SK and Kumar, R and Balakrishnan, D}, title = {Computational analysis on solar air heater with combination of alternate dimple protrusions and intrusions on absorber plate with one rounded corner triangular duct.}, journal = {Environmental science and pollution research international}, volume = {31}, number = {53}, pages = {62360-62375}, pmid = {36547831}, issn = {1614-7499}, mesh = {*Models, Theoretical ; Hot Temperature ; Solar Energy ; }, abstract = {This study focuses on improving heat transfer by converting one of the corners of the duct to a rounded structure. To study the effect of dimpled shaped protrusions and intrusions on the rounded corner triangular duct with a constant radius of curvature by varying relative streamwise distance (z/e) with a constant transverse distance x'/e = 10,14 and 18. Steady-state, turbulent flow heat transfer under thermal boundary conditions is to be analyzed by varying different Reynolds numbers (5600 to 21000). The duct with dimple-shaped protrusions and intrusions is compared with a simple triangular duct. Optimization of relative horizontal distance (z'/e) by keeping constant protrusion to protrusion distance as z/e = 28 and relative transverse distance as x/e = 10, 14, and 18. It was noted that there was a significant loss in friction and a rise in heat transfer. The relationship between friction factor and Nusselt number was formulated using operating and roughness parameters, using the data collected from the numerical investigation. The friction factor increases significantly with roughness elements, and it is maximum for x'/e = 20 at a low Reynolds number. Nusselt number increases with roughness elements, and it is maximum for x'/e = 14 for all Reynolds numbers and all the models. Enhancement of Nusselt number is due to increase of local heat transfer because of local vortex neat heat transfer zone. The maximum outlet temperature is obtained at a low Reynolds number. The maximum temperature of the heated surface is obtained for Rc = 0.67 h and the minimum for Rc = 0.33 h.}, }
@article {pmid36533860, year = {2022}, author = {Lim, S and Du, Y and Lee, Y and Panda, SK and Tong, D and Khalid Jawed, M}, title = {Fabrication, control, and modeling of robots inspired by flagella and cilia.}, journal = {Bioinspiration &amp; biomimetics}, volume = {18}, number = {1}, pages = {}, doi = {10.1088/1748-3190/aca63d}, pmid = {36533860}, issn = {1748-3190}, mesh = {*Cilia ; *Flagella ; Locomotion ; }, abstract = {Flagella and cilia are slender structures that serve important functionalities in the microscopic world through their locomotion induced by fluid and structure interaction. With recent developments in microscopy, fabrication, biology, and modeling capability, robots inspired by the locomotion of these organelles in low Reynolds number flow have been manufactured and tested on the micro-and macro-scale, ranging from medicalin vivomicrobots, microfluidics to macro prototypes. We present a collection of modeling theories, control principles, and fabrication methods for flagellated and ciliary robots.}, }
@article {pmid36517549, year = {2022}, author = {Hafez, NM and Alsemiry, RD and Alharbi, SA and Abd-Alla, AM}, title = {Peristaltic transport characteristics of a second-grade dusty fluid flown with heat transfer through a tube revisited.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {21605}, pmid = {36517549}, issn = {2045-2322}, abstract = {This paper provides a rudimentary insight into the influence of heat transfer on the transport characteristics of a second-grade dusty fluid flown in a flexible tube with walls subjected to the peristaltic motion. Both dust particles and fluid movements were modeled using the coupled differential equations. The effects of different types of parameters such as Reynolds number, Prandtl number, Grashof number, wave number, wave amplitude ratio, second grade parameter as well as nature of the heat source and sink are studies on the dust particles velocity, fluid velocity, temperature, pressure profiles of the fluid and streamline patterns of the fluid. The derived equations were solved analytically via the standard perturbation method to determine the fluid temperature, streamline pattern and velocity of the dust particles as well as fluid. The values in the increase of pressure and frictional forces were calculated numerically using DSolve of the Mathematica 11 software (https://www.wolfram.com/mathematica/new-in-11/). In addition, the trapping mechanisms were ascertained by computing the streamlines and various physical parameters. The obtained results were validated with the state-of-the-art literature reports. It was claimed that our systematic approach may constitute a basis for accurately examining the impact of heat transfer on the peristaltic transport of a complex fluid through narrow tubes, useful for diverse medical applications such as the gastric fluid flow through the small intestine during endoscopy. Numerical results are computed and discussed numerically and presented through graphs. The impacts of pertinent parameters on the aforementioned quantities are examined by plotting graphs on the basis of computational results. The results indicate that the effect of parameters is very pronounced. A suitable comparison has been made with the prior results in the literature as a limiting case of the considered problem.}, }
@article {pmid36513785, year = {2022}, author = {Abd-Alla, AM and Abo-Dahab, SM and Thabet, EN and Abdelhafez, MA}, title = {Heat and mass transfer for MHD peristaltic flow in a micropolar nanofluid: mathematical model with thermophysical features.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {21540}, pmid = {36513785}, issn = {2045-2322}, abstract = {According to a survey of the literature, nanofluids are superior to traditional fluids at transferring heat. A detailed analysis of the models mentioned above is crucial since there are large gaps in the illumination of current solutions for improving heat transfer in nanomaterials. The ongoing investigation's purpose is to ascertain the tiny size gold particles drift in free with the heat and mass transfer, buoyancy forces, thermophoresis, and Brownian motion of a micropolar nanofluid being transported through a porous medium in an asymmetric channel with a uniform magnetic field using a long-wavelength and low Reynolds number approximation. The resulting dimensionless nonlinear governing equations have been numerically solved using a MATLAB software and the Runge-Kutta-Fehlberg integration scheme. Two comparisons with previously investigated problems are also made to confirm our findings, and an excellent concurrence is discovered. As a result, trustworthy results are being given. Numerical solutions are used to describe the effects of different thermal-fluidic parameters on velocity profiles, temperature, concentration, micropolar rotation, pressure gradient, shear stress, heat flux, and nanoparticle volume flux, etc. Tables, graphs, and bar charts are used to present and discuss numerical results that have been produced. A comparison of the resulting numerical solution to earlier literature also reveals a satisfactory level of agreement. Insight into real-world applications such nanofluidic, energy conservation, friction reduction, and power generation are provided by this work. Furthermore, the Brownian and thermophoresis parameters behave significantly differently in a concentration field. On the other hand, the study puts forward an important note that for peristaltic flow of a micropolar fluid with nanoparticles can be controlled by suitably adjusting the micropolar parameter, thermophoresis parameter, nanoparticle Grashof number, and Brownian motion parameter.}, }
@article {pmid36506398, year = {2022}, author = {Shuvo, MS and Hasib, MH and Saha, S}, title = {Entropy generation and characteristics of mixed convection in lid-driven trapezoidal tilted enclosure filled with nanofluid.}, journal = {Heliyon}, volume = {8}, number = {12}, pages = {e12079}, pmid = {36506398}, issn = {2405-8440}, abstract = {The investigation of steady, incompressible, laminar mixed convective fluid flow within two different types of tilted lid-driven trapezoidal enclosures filled with nanofluid composed of water and Al2O3 nanoparticles has been carried out in this paper. The upper wall of the enclosure is an isothermal cold surface that travels at a constant speed, while the bottom surface of the cavity maintains a constant high temperature. Non-dimensional governing equations along with the appropriate boundary conditions are solved using Galerkin finite element technique. Parametric simulation has been conducted by varying tilt angle of the base wall from 0° to 45°, Reynolds number from 0.1 to 10[3], Grashof number from 10[-2] to 10[6], and Richardson number between 0.1 and 10 for three different cases. The streamlines and the isotherms are used to describe the fluid flow and heat transfer characteristics within the enclosure. Besides, the quantitative evaluations of thermal enhancement in terms of the average Nusselt number, average fluid temperature, and Bejan number of the enclosure are presented. Effects of base wall tilt angle and the presence of nanofluid on convection heat transmission characteristics as well as Bejan number are also explored.}, }
@article {pmid36506374, year = {2022}, author = {Hamza, NFA and Aljabair, S}, title = {Evaluation of thermal performance factor by hybrid nanofluid and twisted tape inserts in heat exchanger.}, journal = {Heliyon}, volume = {8}, number = {12}, pages = {e11950}, pmid = {36506374}, issn = {2405-8440}, abstract = {The thermal performance parameters of an improved heat exchanger tube fitted with various vortex generator inserts were investigated using numerical and experimental methods. The governing equations have been solved numerically by a Finite Volume approach employing the turbulence model (κ - ε). Two twisted tape types, which being inserted across a circular pipe (plain twisted tape) and (Double V-cut twisted tape), have been achieved. The hybrid nanofluid is prepared by using metal oxide [Al2O3+CuO] with distilled water at volume fraction range (0.6%, 1.2% and 1.8%), Reynolds number range (3560-8320) at twisted ratio (9.25). The experimental data for a plain tube, plain twisted tapes and double v-cut twisted tape are validated using the standard correlations available in the literature. The effect of such variables upon the average Nusselt number, friction factor, and thermal performance factor have been investigated and compared with a plain tube at the same conditions. As compared to plain twisted tape, the tube equipped with a double V-cut twisted tape with hybrid nanofluid displayed increased thermal performance. The greater vortex flow induced by the V-cuts results in more active thermal boundary layer disturbance, resulting in a greater heat transfer rate. The results show that thermal performance factor for hybrid nanofluid in plain circular tube at (∅ = 1.8 %) and Reynolds number (8320) is about (1.068), when the plain twisted tape and double v-cut twisted tape inserted with hybrid nanofluid the thermal performance factor increased to (1.33) and (1.37), respectively. The results show a similar trend for both numerical and experimental cases. The comparison between the experimental and numerical results have maximum error was (9.7)%.}, }
@article {pmid36500800, year = {2022}, author = {Arshad, M and Hassan, A and Haider, Q and Alharbi, FM and Alsubaie, N and Alhushaybari, A and Burduhos-Nergis, DP and Galal, AM}, title = {Rotating Hybrid Nanofluid Flow with Chemical Reaction and Thermal Radiation between Parallel Plates.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {23}, pages = {}, pmid = {36500800}, issn = {2079-4991}, abstract = {This research investigates the two different hybrid nanofluid flows between two parallel plates placed at two different heights, y0 and yh, respectively. Water-based hybrid nanofluids are obtained by using Al2O3, TiO2 and Cu as nanoparticles, respectively. The upper-level plate is fixed, while the lower-level plate is stretchable. The fluid rotates along the y-axis. The governing equations of momentum, energy and concentration are transformed into partial differential equations by using similarity transformations. These transformed equations are grasped numerically at MATLAB by using the boundary value problem technique. The influence of different parameters are presented through graphs. The numerical outcomes for rotation, Nusselt, Prandtl, and Schmidt numbers are obtained in the form of tables. The heat transfer rate increases by augmentation in the thermophoresis parameter, while it decays by increasing the Reynolds number. Oxide nanoparticles hybrid nanofluid proved more efficient as compared to mixed nanoparticles hybrid nanofluid. This research suggests using oxide nanoparticles for good heat transfer.}, }
@article {pmid36475799, year = {2022}, author = {Dong, C and Wang, L and Huang, YM and Comisso, L and Sandstrom, TA and Bhattacharjee, A}, title = {Reconnection-driven energy cascade in magnetohydrodynamic turbulence.}, journal = {Science advances}, volume = {8}, number = {49}, pages = {eabn7627}, pmid = {36475799}, issn = {2375-2548}, abstract = {Magnetohydrodynamic turbulence regulates the transfer of energy from large to small scales in many astrophysical systems, including the solar atmosphere. We perform three-dimensional magnetohydrodynamic simulations with unprecedentedly large magnetic Reynolds number to reveal how rapid reconnection of magnetic field lines changes the classical paradigm of the turbulent energy cascade. By breaking elongated current sheets into chains of small magnetic flux ropes (or plasmoids), magnetic reconnection leads to a previously undiscovered range of energy cascade, where the rate of energy transfer is controlled by the growth rate of the plasmoids. As a consequence, the turbulent energy spectra steepen and attain a spectral index of -2.2 that is accompanied by changes in the anisotropy of turbulence eddies. The omnipresence of plasmoids and their consequences on, for example, solar coronal heating, can be further explored with current and future spacecraft and telescopes.}, }
@article {pmid36464577, year = {2023}, author = {Song, F and Yan, Y and Sun, J}, title = {Review of insect-inspired wing micro air vehicle.}, journal = {Arthropod structure &amp; development}, volume = {72}, number = {}, pages = {101225}, doi = {10.1016/j.asd.2022.101225}, pmid = {36464577}, issn = {1873-5495}, mesh = {Animals ; *Aircraft ; Biomechanical Phenomena ; *Equipment Design ; Flight, Animal ; Insecta ; *Models, Biological ; Wings, Animal ; }, abstract = {Micro air vehicles (MAVs) have wide application prospects in environmental monitoring, disaster rescue and other civil fields because of their flexibility and maneuverability. Compared with fixed wing and rotary wing aircraft, flapping wing micro air vehicles (FWMAVs) have higher energy utilization efficiency and lower cost and have attracted extensive attention from scientists. Insects have become excellent bionic objects for the study of FWMAVs due to their characteristics of low Reynolds number, low noise, hoverability, small size and light weight. By mimicking flying insects, it may be possible to create highly efficient biomimetic FWMAVs. In this paper, insect flight aerodynamics are reviewed, and the mechanism designs of insect-inspired FWMAVs and their aerodynamics are summarized, including the wing type effect, vibration characteristics and aerodynamic characteristics of the flapping wing.}, }
@article {pmid36463256, year = {2022}, author = {Zhu, F and Cheng, J}, title = {Comparison of the effects of litter decomposition process on soil erosion under simulated rainfall.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {20929}, pmid = {36463256}, issn = {2045-2322}, mesh = {*Soil Erosion ; Soil ; Forests ; *Pinus ; Plant Leaves ; }, abstract = {Overland flow parameters play a pivotal role in soil erosion, which are affected by litter cover in forests. In this study, the litter layer of Pinus massoniana (Masson pine) was divided into non-decomposed and semi-decomposed layers. Seven litter coverage mass gradients, two slopes (5° and 10°), and two rainfall intensities (60 and 120 mm·h[-1]) were used for a systematic study of the effects of litter layer changes on overland flow dynamic characteristics. The objectives of this study were to explore the soil erosion process in litter different decomposition stages; to explore various relationships between hydraulic variables and litter characteristics. In the process of litter decomposition, overland flow patterns changed from transitional flow to laminar flow and from rapid flow to slow flow. The semi-decomposed layer's Reynold's number (Re), resistance coefficient (f), and soil separation rate ([Formula: see text]) were lower than that of the non-decomposed layer under the same conditions. Litter coverage, runoff and the diameter of the litter were major parameters that affected the Re, f, Fr, and Dr. Shrubs with wide leaves should be selected for understory vegetation replanting. The results of this study are helpful to understand the mechanisms of litter influencing erosion processes in different decomposition stages.}, }
@article {pmid36462002, year = {2022}, author = {Jiang, H and Wang, D and Liu, S and Sun, C}, title = {Experimental Evidence for the Existence of the Ultimate Regime in Rapidly Rotating Turbulent Thermal Convection.}, journal = {Physical review letters}, volume = {129}, number = {20}, pages = {204502}, doi = {10.1103/PhysRevLett.129.204502}, pmid = {36462002}, issn = {1079-7114}, abstract = {What is the final state of turbulence when the driving parameter approaches infinity? For the traditional Rayleigh-Bénard convection, a possible ultimate scaling dependence of the heat transport (quantified by the Nusselt number Nu) on the Rayleigh number (Ra), which can be extrapolated to arbitrarily high Ra, is predicted by theories. The existence of the ultimate scaling has been intensively debated in the past decades. In this Letter, we adopt a novel supergravitational thermal convection experimental setup to study the possible transition to the ultimate regime. This system is characterized by the combined effects of radial-dependent centrifugal force, the Earth's gravity, and the Coriolis force. With an effective gravity up to 100 times the Earth's gravity, both Ra and shear Reynolds number can be boosted due to the increase of the buoyancy driving and the additional Coriolis forces. With over a decade of Ra range, we demonstrate the existence of ultimate regime with four direct evidences: the ultimate scaling dependence of Nu versus Ra; the appearance of the turbulent velocity boundary layer profile; the enhanced strength of the shear Reynolds number; and the new statistical properties of local temperature fluctuations. The present findings will greatly improve the understanding of the flow dynamics in geophysical and astrophysical flows.}, }
@article {pmid36461968, year = {2022}, author = {Rorai, C and Toschi, F and Pagonabarraga, I}, title = {Coexistence of Active and Hydrodynamic Turbulence in Two-Dimensional Active Nematics.}, journal = {Physical review letters}, volume = {129}, number = {21}, pages = {218001}, doi = {10.1103/PhysRevLett.129.218001}, pmid = {36461968}, issn = {1079-7114}, abstract = {In active nematic liquid crystals, activity is able to drive chaotic spatiotemporal flows referred to as active turbulence. Active turbulence has been characterized through theoretical and experimental work as a low Reynolds number phenomenon. We show that, in two dimensions, the active forcing alone is able to trigger hydrodynamic turbulence leading to the coexistence of active and inertial turbulence. This type of flow develops for sufficiently active and extensile flow-aligning nematics. We observe that the combined effect of an extensile nematic and large values of the flow-aligning parameter leads to a broadening of the elastic energy spectrum that promotes a growth of kinetic energy able to trigger an inverse energy cascade.}, }
@article {pmid36437305, year = {2022}, author = {Robles, V and Gonzalez-Parra, JC and Cuando-Espitia, N and Aguilar, G}, title = {The effect of scalable PDMS gas-entrapping microstructures on the dynamics of a single cavitation bubble.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {20379}, pmid = {36437305}, issn = {2045-2322}, support = {825115//Consejo Nacional de Ciencia y Tecnolog&#xed;a/ ; }, abstract = {The effect of gas-entrapping polydimethylsiloxane (PDMS) microstructures on the dynamics of cavitation bubbles laser-induced next to the PDMS surface is investigated and compared against the cavitation dynamics next to a flat smooth boundary. Local pressure gradients produced by a cavitation bubble cause the air pockets entrapped in the PDMS microstructures to expand and oscillate, leading to a repulsion of the cavitation bubble. The microstructures were fabricated as boxed crevices via a simple and scalable laser ablation technique on cast acrylic, allowing for testing of variable structure sizes and reusable molds. The bubble dynamics were observed using high speed photography and the surrounding flows were visualized and quantified using particle tracking velocimetry. Smaller entrapped air pockets showed an enhanced ability to withstand deactivation at three stand-off distances and over 50 subsequent cavitation events. This investigation provides insight into the potential to direct the collapse of a cavitation bubble away from a surface to mitigate erosion or to enhance microfluidic mixing in low Reynolds number flows.}, }
@article {pmid36429949, year = {2022}, author = {Luo, J and Ma, X and Wang, L and Zhang, B and Yang, X and Yue, T}, title = {The Influence of Short-Term Heavy Rainfall on Hydraulic Characteristics and Rill Formation in the Yuanmou Dry-Hot Valley.}, journal = {International journal of environmental research and public health}, volume = {19}, number = {22}, pages = {}, pmid = {36429949}, issn = {1660-4601}, mesh = {*Water Movements ; *Rain ; Geologic Sediments ; Soil ; Rivers ; }, abstract = {Rill erosion is one of the major environmental problems in the world; it is an important factor with regard to land degradation and has a serious impact on production and daily life in the region. The widely distributed Yuanmou group stratum promotes the development of rill erosion, whereby the strong time-concentrated rainfall and the alternating arid-humid climate prepare the ground for the development of rills in soils. Therefore, a study of the processes of slope rill erosion was carried out, and a gravel-soil slope in the Yuanmou dry-hot valley was chosen to simulate short-term heavy rainfall (25 mm/h) (No. 1 plot) and moderate rainfall (15 mm/h) (No. 2 plot), to study the erosion processes of soil and the dynamic characteristics of runoff involved in erosion. The study results showed that the width of runoff was significantly different between the two plots, while the depth of runoff was not significantly different. During the rill formation process, the width of the two plots first decreased and then increased with increasing washout duration, while its depth did not change significantly. Flow was the key factor in determining the hydraulic characteristics of runoff, and it had a significant or extremely significant positive correlation with hydraulic characteristics parameters, except in the case of Fr (Froude number) (r = 0.039). The total sediment content (CS) of plot No. 1 (0.158 g/cm[3]) was significantly different from that of plot No. 2 (0.153 g/cm[3]), and both CSs in the two plots decreased with increasing washout duration. The CS had an extremely significant negative correlation with τ (runoff shear force) (r = -0.863 **) and DW-f (Darcy-Weisbach drag coefficient) (r = -0.863 **) and a significant negative correlation with Re (Reynolds number) (r = -0.735 *) in the short-term heavy rainfall experiment, while the CS had a significant positive correlation with V (velocity) (r = 0.814 *), R (hydraulic radius) (r = 0.811 *) and P (unit stream power) (r = 0.811 *) in the moderate rainfall experiment. The results of this study will help guide further examination of the processes involved in the dynamic mechanisms of rill erosion on slopes under short-term heavy rainfall conditions.}, }
@article {pmid36422415, year = {2022}, author = {Kumari, N and Alam, T and Ali, MA and Yadav, AS and Gupta, NK and Siddiqui, MIH and Dobrotă, D and Rotaru, IM and Sharma, A}, title = {A Numerical Investigation on Hydrothermal Performance of Micro Channel Heat Sink with Periodic Spatial Modification on Sidewalls.}, journal = {Micromachines}, volume = {13}, number = {11}, pages = {}, pmid = {36422415}, issn = {2072-666X}, abstract = {Electronic gadgets have been designed to incorporating very small components such as microcontrollers, electronic chips, transistors, microprocessors, etc. These components are exceptionally heat sensitive and can be wrecked if heat is not released. As a result, the thermal control of such components is critical to their optimum performance and extended life. The use of a microchannel heat sink (MCHS) has shown promising solutions to remove the excess heat. In this paper, we have proposed a novel design of MCHS and investigated it numerically. Four different surface modifications on the sidewall of the passage, namely, extended triangular surface (ETS), extended circular surface (ECS), triangular groove surface (TGS), and the circular groove surface (CGS) in the passage of the microchannel have been exploited in the Reynolds number of 100-900. In the presence of geometrical modification, the cooling capacities have been enhanced. The results show that the Nusselt numbers of ETS-MCHS, ECS-MCHS, TGS-MCHS, and CGS-MCHS are increased by 4.30, 3.61, 1.62, and 1.41 times in comparison to the Nusselt number of MCHS with smooth passage, while the friction factor values are increased by 7.33, 6.03, 2.74, and 1.68 times, respectively. In addition, the thermohydraulic performance parameter (THPP) has been evaluated and discussed. The fact that MCHS have THPP values greater than unity demonstrates that the passage's geometries are a practical means of achieving effective thermal management.}, }
@article {pmid36411532, year = {2023}, author = {Toyama, K and Togi, F and Harada, S}, title = {Mass Transfer from Mobile to Immobile Regions in Irregularly Shaped Micro-Channels at Low Reynolds Number.}, journal = {Ground water}, volume = {61}, number = {5}, pages = {639-647}, doi = {10.1111/gwat.13276}, pmid = {36411532}, issn = {1745-6584}, abstract = {Transient mass transfer in rough-walled micro-channels was investigated experimentally. We conducted experiments using rough-walled channels with various irregularities at small Reynolds number conditions. Mass transfer in the mainstream (mobile region) and dead water region (immobile region) were quantified using an image analysis technique based on absorption photometry. The experimental results showed that the solute dispersion in the mobile region was influenced by the irregular shape of the channel wall complicatedly. In contrast, mass transfer in the immobile region occurred by molecular diffusion independently on the wall roughness in our experimental conditions. The irregular shape of channel wall may enhance the mass transfer in mobile region by distorting the velocity distribution (Togi et al., 2020), while the solute redistribution to immobile region may suppress it in streamwise direction, just on a longer time scale. We developed a mass transfer model analogous to Mobile-Immobile model (MIM model) proposed by previous studies. The concept of the model is the same as the previous study (Zhou et al., 2019) and the coefficients of the model describing mass transfer in each region were quantified from the experimental results as functions of geometric characteristics of the rough-walled channel. In addition, mass transfer coefficient from mobile to immobile regions were derived mathematically based on the experimental results. The MIM model with the coefficients derived in this study well describes solute dispersion in variously shaped irregular channels quantitatively.}, }
@article {pmid36405040, year = {2022}, author = {Kaziz, S and Ben Mariem, I and Echouchene, F and Belkhiria, M and Belmabrouk, H}, title = {Taguchi optimization of integrated flow microfluidic biosensor for COVID-19 detection.}, journal = {European physical journal plus}, volume = {137}, number = {11}, pages = {1235}, pmid = {36405040}, issn = {2190-5444}, abstract = {In this research, Taguchi's method was employed to optimize the performance of a microfluidic biosensor with an integrated flow confinement for rapid detection of the SARS-CoV-2. The finite element method was used to solve the physical model which has been first validated by comparison with experimental results. The novelty of this study is the use of the Taguchi approach in the optimization analysis. An L 8 2 7 orthogonal array of seven critical parameters-Reynolds number (Re), Damköhler number (Da), relative adsorption capacity (σ), equilibrium dissociation constant (KD), Schmidt number (Sc), confinement coefficient (α) and dimensionless confinement position (X), with two levels was designed. Analysis of variance (ANOVA) methods are also used to calculate the contribution of each parameter. The optimal combination of these key parameters was Re = 10[-2], Da = 1000, σ = 0.5, K D = 5, Sc = 10[5], α = 2 and X = 2 to achieve the lowest dimensionless response time (0.11). Among the all-optimization factors, the relative adsorption capacity (σ) has the highest contribution (37%) to the reduction of the response time, while the Schmidt number (Sc) has the lowest contribution (7%).}, }
@article {pmid36399789, year = {2023}, author = {Jhun, CS and Xu, L and Siedlecki, C and Bartoli, CR and Yeager, E and Lukic, B and Scheib, CM and Newswanger, R and Cysyk, JP and Shen, C and Bohnenberger, K and Weiss, WJ and Rosenberg, G}, title = {Kinetic and Dynamic Effects on Degradation of von Willebrand Factor.}, journal = {ASAIO journal (American Society for Artificial Internal Organs : 1992)}, volume = {69}, number = {5}, pages = {467-474}, pmid = {36399789}, issn = {1538-943X}, support = {R01 HL136369/HL/NHLBI NIH HHS/United States ; }, mesh = {Humans ; von Willebrand Factor/metabolism ; *von Willebrand Diseases ; *Heart-Assist Devices ; Kinetics ; Molecular Weight ; }, abstract = {The loss of high molecular weight multimers (HMWM) of von Willebrand factor (vWF) in aortic stenosis (AS) and continuous-flow left ventricular assist devices (cf-LVADs) is believed to be associated with high turbulent blood shear. The objective of this study is to understand the degradation mechanism of HMWM in terms of exposure time (kinetic) and flow regime (dynamics) within clinically relevant pathophysiologic conditions. A custom high-shear rotary device capable of creating fully controlled exposure times and flows was used. The system was set so that human platelet-poor plasma flowed through at 1.75 ml/sec, 0.76 ml/sec, or 0.38 ml/sec resulting in the exposure time (texp) of 22, 50, or 100 ms, respectively. The flow was characterized by the Reynolds number (Re). The device was run under laminar (Re = 1,500), transitional (Re = 3,000; Re = 3,500), and turbulent (Re = 4,500) conditions at a given texp followed by multimer analysis. No degradation was observed at laminar flow at all given texp . Degradation of HMWM at a given texp increases with the Re. Re (p < 0.0001) and texp (p = 0.0034) are significant factors in the degradation of HMWM. Interaction between Re and texp , however, is not always significant (p = 0.73).}, }
@article {pmid36399753, year = {2022}, author = {Bermudez, G and Alexakis, A}, title = {Saturation of Turbulent Helical Dynamos.}, journal = {Physical review letters}, volume = {129}, number = {19}, pages = {195101}, doi = {10.1103/PhysRevLett.129.195101}, pmid = {36399753}, issn = {1079-7114}, abstract = {The presence of large scale magnetic fields in nature is often attributed to the inverse cascade of magnetic helicity driven by turbulent helical dynamos. In this Letter, we show that in turbulent helical dynamos, the inverse flux of magnetic helicity toward the large scales Π_{H} is bounded by |Π_{H}|≤cεk_{η}^{-1}, where ε is the energy injection rate, k_{η} is the Kolmogorov magnetic dissipation wave number, and c an order one constant. Assuming the classical isotropic turbulence scaling, the inverse flux of magnetic helicity Π_{H} decreases at least as a -3/4 power law with the magnetic Reynolds number Rm: |Π_{H}|≤cεℓ_{f}Rm^{-3/4}max[Pm,1]^{1/4}, where Pm is the magnetic Prandtl number and ℓ_{f} the forcing length scale. We demonstrate this scaling with Rm using direct numerical simulations of turbulent dynamos forced at intermediate scales. The results further indicate that nonlinear saturation is achieved by a balance between the inverse cascade and dissipation at domain size scales L for which the saturation value of the magnetic energy is bounded by E_{m}≤cL(εℓ_{f})^{2/3}Rm^{1/4}max[1,Pm]^{1/4}. Numerical simulations also demonstrate this bound. These results are independent of the dynamo mechanism considered. In our setup, they imply that inviscid mechanisms cannot explain large scale magnetic fields and have critical implications for the modeling of astrophysical dynamos.}, }
@article {pmid36397500, year = {2022}, author = {Budanur, NB and Kantz, H}, title = {Scale-dependent error growth in Navier-Stokes simulations.}, journal = {Physical review. E}, volume = {106}, number = {4-2}, pages = {045102}, doi = {10.1103/PhysRevE.106.045102}, pmid = {36397500}, issn = {2470-0053}, abstract = {We estimate the maximal Lyapunov exponent at different resolutions and Reynolds numbers in large eddy simulations (LES) and direct numerical simulations of sinusoidally driven Navier-Stokes equations in three dimensions. Independent of the Reynolds number when nondimensionalized by Kolmogorov units, the LES Lyapunov exponent diverges as an inverse power of the effective grid spacing showing that the fine scale structures exhibit much faster error growth rates than the larger ones. Effectively, i.e., ignoring the cutoff of this phenomenon at the Kolmogorov scale, this behavior introduces an upper bound to the prediction horizon that can be achieved by improving the precision of initial conditions through refining of the measurement grid.}, }
@article {pmid36388976, year = {2022}, author = {Yao, N and Wang, H and Wang, B and Wang, X and Huang, J}, title = {Convective thermal cloaks with homogeneous and isotropic parameters and drag-free characteristics for viscous potential flows.}, journal = {iScience}, volume = {25}, number = {11}, pages = {105461}, pmid = {36388976}, issn = {2589-0042}, abstract = {Although convective thermal cloaking has been advanced significantly, the majority of related researches have concentrated on creeping viscous potential flows. Here, we consider convective thermal cloaking works in non-creeping viscous potential flows, and propose a combination of the separation of variables method and the equivalent-medium integral method to analytically deduce the parameters of convective thermal cloaks with isotropic-homogeneous dynamic viscosity and thermal conductivity. Through numerical simulation, we demonstrate the cloaks can hide the object from thermo-hydrodynamic fields. Besides, by comparing the drag force cloaks bear in cloak case and the objects bear in object-existent case, we find convective thermal cloaks can considerably reduce the drag force, which appears drag-free characteristics. Finally, it is our hope that these developed methods can reduce the difficulties of metadevices fabrications, promote the development of drag reduction technology under higher Reynolds number, and shed light on the control of other multi-physics systems.}, }
@article {pmid36384832, year = {2022}, author = {Cao, BZ and Wang, J and Zhao, YJ and Liu, C}, title = {[Hydrodynamic characteristics of grass swale runoff in Guanzhong area of Loess Plateau, Northwest China.].}, journal = {Ying yong sheng tai xue bao = The journal of applied ecology}, volume = {33}, number = {11}, pages = {2979-2986}, doi = {10.13287/j.1001-9332.202211.023}, pmid = {36384832}, issn = {1001-9332}, mesh = {*Poaceae ; *Water Movements ; Hydrodynamics ; Rain ; Soil ; China ; }, abstract = {Grass swale has been widely used in sponge city construction, which can effectively improve the urban ecological environment. To explore the regulation mechanism of runoff in grass swale, runoff scouring experiment was carried out to study the hydrodynamic characteristics of runoff and the distribution of cross-section velocity under the combined conditions of five slopes (1%, 2%, 3%, 4%, 5%) and five scour flows (20, 30, 40, 50, 60 L·min[-1]). With the increases of flow rate and slope, flow velocity, Reynolds number and Froude number all increased gradually, while the Manning roughness coefficient and Darcy-Weisbach friction coefficient decreased gradually. The velocity (V) could be expressed as a power function V=0.3387Q[0.555]S[0.6601] of flow rate (Q) and slope (S). The variation ranges of Reynolds number and Froude number were 1160.95-6596.82 and 0.17-1.21, respectively. The runoff flow patterns were all turbulent. The flow pattern was greatly affected by the slope. When flow rate and slope were small, they had great influence on friction coefficient. Under the experimental conditions, the Darcy-Weisbach friction coefficient was negatively correlated with Reynolds number. The velocity distribution of cross-section showed symmetrical distribution on both sides of the center. The maximum velocity point was located at the center of water surface. With the increases of flow rate and slope, the velocity contours of cross section gradually became dense and the gradient of the velocity change increased. Our results provide a theoretical basis for the design, application and hydraulic calculation of grass swale in the construction of sponge cities in loess areas, and reveal the runoff regulation mechanism by analyzing the hydraulic characteristics of grass swale runoff.}, }
@article {pmid36383261, year = {2022}, author = {Karami, A and Ranjbar, B and Rahimi, M and Mohammadi, F}, title = {Novel hybrid neuro-fuzzy model to anticipate the heat transfer in a heat exchanger equipped with a new type of self-rotating tube insert.}, journal = {The European physical journal. E, Soft matter}, volume = {45}, number = {11}, pages = {92}, pmid = {36383261}, issn = {1292-895X}, mesh = {*Hot Temperature ; *Algorithms ; Friction ; }, abstract = {In this investigation, a combination of the wingsuit flying search (WFS) and teaching-learning-based optimization (TLBO) algorithms is developed as a new combinatorial optimization algorithm. The proposed combinatorial algorithm is tested over some well-known benchmark functions and then integrated with the artificial neural network (ANN) to construct a novel hybrid model. After that, the obtained hybrid model is employed to anticipate the experimentally obtained values of the average Nusselt number (Nu), average friction coefficient (f) as well as thermal-hydraulic performance ratio (η), in a heat exchanger equipped with a new type of self-rotating tube insert, against governing parameters. The insert is placed in the tube side of the water heater to heat natural gas. The proposed insert consists of various numbers of self-rotating modules. Indeed, the rotating insert is introduced to create effective secondary sweeping flow on the inner side of the tube. Since this type of tube insert simultaneously provides heat transfer enhancement and undesired pressure drop, a thermal-hydraulic performance ratio is defined to consider both of them. The governing parameters are the number of inserts (0 ≤ N ≤ 30), reservoir's temperature (40 °C ≤ TR ≤ 50 °C) as well as Reynolds number (6 × 10[3] ≤ Re ≤ 18 × 10[3]). It was found that the WFS-TLBO enhances the effectiveness of the main ANN in anticipating the Nusselt number (Nu), average friction coefficient (f) as well as performance ratio (η). Moreover, introducing the WFS-TLBO algorithm into the neural network provides an enhancement in the effectiveness of the hybrid models based on the single WFS and TLBO algorithms in anticipating the same parameters.}, }
@article {pmid36378533, year = {2022}, author = {Wei, SX and Yang, H and Au, CT and Xie, TL and Yin, SF}, title = {Mixing Characteristic and High-Throughput Synthesis of Cadmium Sulfide Nanoparticles with Cubic Hexagonal Phase Junctions in a Chaotic Millireactor.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {38}, number = {47}, pages = {14439-14450}, doi = {10.1021/acs.langmuir.2c02087}, pmid = {36378533}, issn = {1520-5827}, abstract = {A four-stage oscillating feedback millireactor with splitters (S-OFM) was designed to improve the mixing performance based on chaotic advection. Three-dimensional CFD simulations were used to investigate its flow characteristics and mixing performance, and the generation mechanisms of secondary flows were examined. The results show that the mixing index (MIcup) increased with the increase in the Reynolds number (Re), and MIcup could reach 99.8% at Re = 663. Poincaré mapping and Kolmogorov entropy were adopted to characterize the chaotic advection intensity, which indicates that there is a intensity increase with the increase in Re. In addition, the results of Villermaux-Dushman experiments demonstrate that S-OFM performs excellently, and the mixing time could reach 1.04 ms at Re = 2764. Finally, S-OFM was successfully used to synthesize CdS nanoparticles with cubic hexagonal phase junctions. At a flow rate of 180 mL/min, the average particle size was 10.5 nm and the particle size distribution was narrow (with a coefficient of variation of 0.14).}, }
@article {pmid36374705, year = {2022}, author = {Antunes, GC and Malgaretti, P and Harting, J and Dietrich, S}, title = {Pumping and Mixing in Active Pores.}, journal = {Physical review letters}, volume = {129}, number = {18}, pages = {188003}, doi = {10.1103/PhysRevLett.129.188003}, pmid = {36374705}, issn = {1079-7114}, abstract = {We show both numerically and analytically that a chemically patterned active pore can act as a micro- or nanopump for fluids, even if it is fore-aft symmetric. This is possible due to a spontaneous symmetry breaking which occurs when advection rather than diffusion is the dominant mechanism of solute transport. We further demonstrate that, for pumping and tuning the flow rate, a combination of geometrical and chemical inhomogeneities is required. For certain parameter values, the flow is unsteady, and persistent oscillations with a tunable frequency appear. Finally, we find that the flow exhibits convection rolls and hence promotes mixing in the low Reynolds number regime.}, }
@article {pmid36374283, year = {2022}, author = {Hopkins, CC and Shen, AQ and Haward, SJ}, title = {Effect of blockage ratio on flow of a viscoelastic wormlike micellar solution past a cylinder in a microchannel.}, journal = {Soft matter}, volume = {18}, number = {46}, pages = {8856-8866}, pmid = {36374283}, issn = {1744-6848}, abstract = {We present experiments on the flow of a viscoelastic wormlike micellar solution around cylinders (radius R) confined in straight microchannels (width W). Thirteen flow geometries are tested where the blockage ratio is varied over a wide range 0.055 ≤ BR = 2R/W ≤ 0.63. Experiments are performed at negligible Reynolds number, and for Weissenberg numbers Wi = λU/R up to 1000, where U is the average flow speed and λ is the relaxation time of the fluid. Micro-particle image velocimetry is used to characterise the flow state at each BR and Wi. In all of the geometries, a first critical Weissenberg number marks a transition from symmetric flow to an asymmetric but time-steady flow state, while a second higher critical Weissenberg number marks the onset of time-dependent flows. However, we report a clear shift in behaviour over a narrow intermediate range of 0.33 ≲ BR ≲ 0.41. Channels with BR ≤ 0.33 fall in a 'low' BR regime, with instabilities that originate from the downstream stagnation point, while those with BR ≥ 0.44 fall in a 'high' BR regime, with instabilities developing at the upstream stagnation point. Behaviour within the newly-identified intermediate BR regime is complex due to the competing influence of the two stagnation points. We summarise all our results in a flow state diagram covering Wi-BR parameter space, clearly defining the different regimes of blockage ratio for the first time. Our results contribute to the understanding of the complexities of viscoelastic flow in this benchmark geometry.}, }
@article {pmid36369608, year = {2023}, author = {Chen, Y and Feng, X and Shi, X and Cai, W and Li, B and Zhao, Y}, title = {Evaluation of computational fluid dynamics models for predicting pediatric upper airway airflow characteristics.}, journal = {Medical &amp; biological engineering &amp; computing}, volume = {61}, number = {1}, pages = {259-270}, pmid = {36369608}, issn = {1741-0444}, support = {IR2021211//harbin institute of technology/ ; }, mesh = {Humans ; Child ; *Hydrodynamics ; Computer Simulation ; *Larynx ; Trachea ; Respiration ; }, abstract = {Computational fluid dynamics (CFD) has the potential for use as a clinical tool to predict the aerodynamics and respiratory function in the upper airway (UA) of children; however, careful selection of validated computational models is necessary. This study constructed a 3D model of the pediatric UA based on cone beam computed tomography (CBCT) imaging. The pediatric UA was 3D printed for pressure and velocity experiments, which were used as reference standards to validate the CFD simulation models. Static wall pressure and velocity distribution inside of the UA under inhale airflow rates from 0 to 266.67 mL/s were studied by CFD simulations based on the large eddy simulation (LES) model and four Reynolds-averaged Navier-Stokes (RANS) models. Our results showed that the LES performed best for pressure prediction; however, it was much more time-consuming than the four RANS models. Among the RANS models, the Low Reynolds number (LRN) SST k-ω model had the best overall performance at a series of airflow rates. Central flow velocity determined by particle image velocimetry was 3.617 m/s, while velocities predicted by the LES, LRN SST k-ω, and k-ω models were 3.681, 3.532, and 3.439 m/s, respectively. All models predicted jet flow in the oropharynx. These results suggest that the above CFD models have acceptable accuracy for predicting pediatric UA aerodynamics and that the LRN SST k-ω model has the most potential for clinical application in pediatric respiratory studies.}, }
@article {pmid36365668, year = {2022}, author = {de Araujo, MT and Furlan, L and Brandi, A and Souza, L}, title = {A Semi-Analytical Method for Channel and Pipe Flows for the Linear Phan-Thien-Tanner Fluid Model with a Solvent Contribution.}, journal = {Polymers}, volume = {14}, number = {21}, pages = {}, pmid = {36365668}, issn = {2073-4360}, support = {2013/07375-0//S&#xe3;o Paulo Research Foundation/ ; 001//Coordena&#xe7;&#xe3;o de Aperfeicoamento de Pessoal de N&#xed;vel Superior/ ; }, abstract = {This work presents a semi-analytical method for laminar steady-state channel and pipe flows of viscoelastic fluids using the Linear Phan-Thien-Tanner (LPTT) constitutive equation, with solvent viscosity contribution. For the semi-analytical method validation, it compares its results and two analytical solutions: the Oldroyd-B model and the simplified LPTT model (without solvent viscosity contribution). The results adopted different values of the dimensionless parameters, showing their influence on the viscoelastic fluid flow. The results include the distribution of the streamwise velocity component and the extra-stress tensor components in the wall-normal direction. In order to investigate the proposed semi-analytical method, different solutions were obtained, both for channel and pipe flows, considering different values of Reynolds number, solvent viscosity contribution in the homogeneous mixture, elongational parameter, shear parameter, and Weissenberg number. The results show that the proposed semi-analytical method can find a laminar solution using the non-Newtonian LPTT model with solvent viscosity contribution and verify the effect of the parameters in the resulting flow field.}, }
@article {pmid36364597, year = {2022}, author = {Baig, MF and Chen, GM and Tso, CP}, title = {The Thermal Performance Analysis of an Al2O3-Water Nanofluid Flow in a Composite Microchannel.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {21}, pages = {}, pmid = {36364597}, issn = {2079-4991}, support = {FRGS/1/2019/TK03/MMU/02/1.//Ministry of Higher Education Malaysia/ ; }, abstract = {Partial filling of porous medium insert in a channel alleviates the tremendous pressure drop associated with a porous medium saturated channel, and enhances heat transfer at an optimum fraction of porous medium filling. This study pioneered an investigation into the viscous dissipative forced convective heat transfer in a parallel-plate channel, partially occupied with a porous medium at the core, under local thermal non-equilibrium condition. Solving the thermal energy equation along the Darcy-Brinkman equation, new exact temperature fields and Nusselt number are presented under symmetrical isoflux thermal boundary condition. Noteworthy is the heat flux bifurcation at the interface between the clear fluid and porous medium driven by viscous dissipation, in cases where the combined hydrodynamic resistance to fluid flow and thermal resistance to fluid conduction is considerable in low Darcy number porous medium insert. However, viscous dissipation does not affect the qualitative variation of the Nusselt number with the fraction of porous medium filling. By using Al2O3-Water nanofluid as the working fluid in a uniformly heated microchannel, partially filled with an optimum volume fraction of porous medium, the heat transfer coefficient improves as compared to utilizing water. The accompanied viscous dissipation however has a more adverse impact on the heat transfer coefficient of nanofluids with an increasing Reynolds number.}, }
@article {pmid36363954, year = {2022}, author = {Chen, Z and Wang, Y and Zhou, S}, title = {Numerical Analysis of Mixing Performance in an Electroosmotic Micromixer with Cosine Channel Walls.}, journal = {Micromachines}, volume = {13}, number = {11}, pages = {}, pmid = {36363954}, issn = {2072-666X}, support = {51705184//National Natural Science Foundation of China/ ; GDZB-062//Program for Distinguished Talents of Six Domains in Jiangsu Province of China/ ; SJCX22_1671//Jiangsu Province Graduate Research and Practice Innovation Program Project/ ; }, abstract = {Micromixers have significant potential in the field of chemical synthesis and biological pharmaceuticals, etc. In this study, the design and numerical simulations of a passive micromixer and a novel active electroosmotic micromixer by assembling electrode pairs were both presented with a cosine channel wall. The finite element method (FEM) coupled with Multiphysics modeling was used. To propose an efficient micromixer structure, firstly, different geometrical parameters such as amplitude-to-wavelength ratio (a/c) and mixing units (N) in the steady state without an electric field were investigated. This paper aims to seek a high-quality mixing solution. Therefore, based on the optimization of the above parameters of the passive micromixer, a new type of electroosmotic micromixer with an AC electric field was proposed. The results show that the vortices generated by electroosmosis can effectively induce fluid mixing. The effects of key parameters such as the Reynolds number, the number of electrode pairs, phase shift, voltage, and electrode frequency on the mixing performance were specifically discussed through numerical analysis. The mixing efficiency of the electroosmotic micromixer is quantitatively analyzed, which can be achieved at 96%. The proposed micromixer has a simple structure that can obtain a fast response and high mixing index.}, }
@article {pmid36363898, year = {2022}, author = {Dai, Y and Cha, H and Nguyen, NK and Ouyang, L and Galogahi, F and Yadav, AS and An, H and Zhang, J and Ooi, CH and Nguyen, NT}, title = {Dynamic Behaviours of Monodisperse Double Emulsion Formation in a Tri-Axial Capillary Device.}, journal = {Micromachines}, volume = {13}, number = {11}, pages = {}, pmid = {36363898}, issn = {2072-666X}, support = {DP220100261//Australian Research Council/ ; }, abstract = {We investigated experimentally, analytically, and numerically the formation process of double emulsion formations under a dripping regime in a tri-axial co-flow capillary device. The results show that mismatches of core and shell droplets under a given flow condition can be captured both experimentally and numerically. We propose a semi-analytical model using the match ratio between the pinch-off length of the shell droplet and the product of the core growth rate and its pinch-off time. The mismatch issue can be avoided if the match ratio is lower than unity. We considered a model with the wall effect to predict the size of the matched double emulsion. The model shows slight deviations with experimental data if the Reynolds number of the continuous phase is lower than 0.06 but asymptotically approaches good agreement if the Reynolds number increases from 0.06 to 0.14. The numerical simulation generally agrees with the experiments under various flow conditions.}, }
@article {pmid36363842, year = {2022}, author = {Cao, M and Cao, S and Zhao, J and Zhu, J}, title = {Numerical Study of Thermal Enhancement in a Single- and Double-Layer Microchannel Heat Sink with Different Ribs.}, journal = {Micromachines}, volume = {13}, number = {11}, pages = {}, pmid = {36363842}, issn = {2072-666X}, abstract = {In this paper, a microchannel heat sink model was proposed to realize single- and double- layer flow through built-in ribs. The finite element volume method was used to analyze the influence of the length, thickness and angle of the inner rib on the flow and heat transfer characteristics of the microchannel heat sink. The pressure drop, temperature field, flow field, and thermal characteristics are given. The numerical simulation results show that the rectangular rib plate makes the fluid in the microchannel heat sink flow alternately in the upper and lower layers, which can effectively enhance heat transfer. However, with the increase in rib length, the comprehensive evaluation factor decreases. The change of the angle of the rectangular rib plate has little influence on the Nusselt number. The change rate of the comprehensive evaluation factor of the thickness of the rectangular rib plate is the largest. When the Reynolds number is 1724, the comprehensive evaluation factor of Case 9 is 4.7% higher than that of Case 2. According to the parameter study of the built-in rib plate, the optimal parameter combination is given, in which the angle is 0°, the length is 7.5 mm, and the thickness is 0.2-0.3 mm.}, }
@article {pmid36363584, year = {2022}, author = {Cancilla, N and Tamburini, A and Tarantino, A and Visconti, S and Ciofalo, M}, title = {Friction and Heat Transfer in Membrane Distillation Channels: An Experimental Study on Conventional and Novel Spacers.}, journal = {Membranes}, volume = {12}, number = {11}, pages = {}, pmid = {36363584}, issn = {2077-0375}, abstract = {The results of an experimental investigation on pressure drop and heat transfer in spacer-filled plane channels, which are representative of Membrane Distillation units, are presented and discussed. Local and mean heat transfer coefficients were obtained by using Thermochromic Liquid Crystals and Digital Image Processing. The performances of a novel spacer geometry, consisting of spheres that are connected by cylindrical rods, and are hereafter named spheres spacers, were compared with those of more conventional woven and overlapped spacers at equal values of the Reynolds number Re (in the range ~150 to ~2500), the pitch-to-channel height ratio, the flow attack angle and the thermal boundary conditions (two-side heat transfer). For any flow rate, the novel spacer geometry provided the least friction coefficient and a mean Nusselt number intermediate between those of the overlapped and the woven spacers. For any pressure drop and for any pumping power, the novel spacer provided the highest mean Nusselt number over the whole Reynolds number range that was investigated. The influence of buoyancy was also assessed for the case of the horizontal channels. Under the experimental conditions (channel height H ≈ 1 cm, ΔT ≈ 10 °C), it was found to be large in empty (spacer-less) channels that were up to Re ≈ 1200 (corresponding to a Richardson number Ri of ~0.1), but it was much smaller and limited to the range Re < ~500 (Ri < ~0.5) in the spacer-filled channels.}, }
@article {pmid36359756, year = {2022}, author = {Soulsbury, CD and Humphries, S}, title = {Biophysical Determinants and Constraints on Sperm Swimming Velocity.}, journal = {Cells}, volume = {11}, number = {21}, pages = {}, pmid = {36359756}, issn = {2073-4409}, mesh = {Animals ; Male ; *Sperm Motility ; *Semen ; Spermatozoa ; Biological Evolution ; Flagella ; }, abstract = {Over the last 50 years, sperm competition has become increasingly recognised as a potent evolutionary force shaping male ejaculate traits. One such trait is sperm swimming speed, with faster sperm associated with increased fertilisation success in some species. Consequently, sperm are often thought to have evolved to be longer in order to facilitate faster movement. However, despite the intrinsic appeal of this argument, sperm operate in a different biophysical environment than we are used to, and instead increasing length may not necessarily be associated with higher velocity. Here, we test four predictive models (ConstantPower Density, Constant Speed, Constant Power Transfer, Constant Force) of the relationship between sperm length and speed. We collated published data on sperm morphology and velocity from 141 animal species, tested for structural clustering of sperm morphology and then compared the model predictions across all morphologically similar sperm clusters. Within four of five morphological clusters of sperm, we did not find a significant positive relationship between total sperm length and velocity. Instead, in four morphological sperm clusters we found evidence for the Constant Speed model, which predicts that power output is determined by the flagellum and so is proportional to flagellum length. Our results show the relationship between sperm morphology (size, width) and swimming speed is complex and that traditional models do not capture the biophysical interactions involved. Future work therefore needs to incorporate not only a better understanding of how sperm operate in the microfluid environment, but also the importance of fertilising environment, i.e., internal and external fertilisers. The microenvironment in which sperm operate is of critical importance in shaping the relationship between sperm length and form and sperm swimming speed.}, }
@article {pmid36351992, year = {2022}, author = {Abdizadeh, GR and Farokhinejad, M and Ghasemloo, S}, title = {Numerical investigation on the aerodynamic efficiency of bio-inspired corrugated and cambered airfoils in ground effect.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {19117}, pmid = {36351992}, issn = {2045-2322}, mesh = {Animals ; *Flight, Animal ; *Wings, Animal ; Models, Biological ; Computer Simulation ; }, abstract = {This research numerically investigates the flapping motion effect on the flow around two subsonic airfoils near a ground wall. Thus far, the aerodynamic efficiency of the dragonfly-inspired flapping airfoil has not been challenged by an asymmetric cambered airfoil considering the ground effect phenomenon, especially in the MAV flight range. The analysis is carried out on the basis of an unsteady Reynolds-averaged Navier-stokes (URANS) simulation, whereby the Transition SST turbulence model simulates the flow characteristics. Dragonfly-inspired and NACA4412 airfoils are selected in this research to assess the geometry effect on aerodynamic efficiency. Moreover, the impacts of Reynolds number (Re), Strouhal number (St), and average ground clearance of the flapping airfoil are investigated. The results indicate a direct relationship between the airfoil's aerodynamic performance ([Formula: see text]/[Formula: see text]) and the ground effect. The [Formula: see text]/[Formula: see text] increases by reducing the airfoil and ground distance, especially at [Formula: see text]. At [Formula: see text], by increasing the St from 0.2 to 0.6, the values of [Formula: see text]/[Formula: see text] decrease from 10.34 to 2.1 and 3.22 to 1.8 for NACA4412 and dragonfly airfoils, respectively. As a result, the [Formula: see text]/[Formula: see text] of the NACA4412 airfoil is better than that of the dragonfly airfoil, especially at low oscillation frequency. The efficiency difference between the two airfoils at St=0.6 is approximately 14%, indicating that the [Formula: see text]/[Formula: see text] difference decreases substantially with increasing frequency. For [Formula: see text], the results show the dragonfly airfoil to have better [Formula: see text]/[Formula: see text] in all frequencies than the NACA4412 airfoil.}, }
@article {pmid36340085, year = {2022}, author = {Dang, J and Duan, X and Tian, S}, title = {Wall Effects for Spheroidal Particle in Confined Bingham Plastic Fluids.}, journal = {ACS omega}, volume = {7}, number = {43}, pages = {38717-38727}, pmid = {36340085}, issn = {2470-1343}, abstract = {The wall effects on the sedimentation motion of a single spheroidal particle in cylindrical tubes filled with Bingham plastic fluid are investigated with the fixed computational domain using the Computational Fluid Dynamic (CFD) model in steady-state mode. The CFD model is validated with literature in both bounded and unbounded mediums. The rheological model of the Bingham plastic fluid is regularized with a smoothly varying viscosity. The retardation effects of the tube wall are presented in functions of Reynolds number Re, radius ratio λ (the radius of the tube to the semiaxis of the particle normal to the flow λ = R/r), aspect ratio E (the ratio of the semiaxis of the particle along the flow to r, E = b/r), and Bingham number Bn. The simulation results demonstrate that the drag coefficient C D declines with the rise in Reynolds number. The relative contribution to drag coefficient from the pressure force increases with larger Bingham number comparing with that from the friction force. The formation and size of the recirculation wake is suppressed by the yield stress. While Bn is approaching infinity, the limiting behavior is observed in the location of yield surface and the value of yield-gravity parameter. The values of critical yield-gravity parameter are explicitly given at different values of E, showing independence with Re and λ. For the flow with Bn ≥ 100, the influence of wall can be even ignored while λ is larger than 5.}, }
@article {pmid36337262, year = {2022}, author = {Rutledge, KM}, title = {Sniffing out Stingray Noses: The Functional Morphology of Batoid Olfaction.}, journal = {Integrative organismal biology (Oxford, England)}, volume = {4}, number = {1}, pages = {obac043}, pmid = {36337262}, issn = {2517-4843}, abstract = {Batoid fishes (rays, skates, sawfishes, and guitarfishes) are macrosmatic, meaning they rely on their sense of smell as one of the primary senses for survival and reproduction. Olfaction is important for long-distance tracking and navigation, predator and prey recognition, and conspecific signaling. However, the mechanisms by which batoids harness odorants is unknown. Without a direct pump-like system, it is hypothesized that batoids irrigate their nostrils via one or a combination of the following: the motion pump, buccopharyngeal pump, pressure (ex. pitot-like mechanism), or a shearing force (ex. viscous entrainment). These mechanisms rely on the size, shape, and position of the nostrils with respect to the head and to each other. Batoids are united as a group by their dorsoventrally compressed body plans, with nostrils on the ventral side of their body. This position presents several challenges for odor capture and likely limits the effectivity of the motion pump. Batoid fishes display an expansive nasal morphology, with inlet nostrils ranging from thin, vertical slits to wide, horizontal ovals to protruding, tube-like funnels, and more. In this paper, a morphometric model is developed to quantify the vast diversity in batoid nose shapes, sizes, and positions on the head in an ecological and functional framework. Specifically, swimming mode, lifestyle, habitat, and diet are examined for correlations with observed nasal morphotypes. Morphometric measurements were taken on all 4 orders present in Batoidea to broadly encompass batoid nasal diversity (Rhinopristiformes 4/5 families; Rajiformes 2/4 families; Torpediniformes 4/4 families; Myliobatiformes 8/11 families). All batoid external nasal diversity was found to be categorized into 5 major morphological groups and were termed: flush nare [circle, comma, intermediate], open nare, and protruding nare. Several morphometric traits remained significant when accounting for shared ancestry, including the position and angle of the nostril on the head, the width of the inlet hole, and the spacing of the nostrils from each other. These measurements were found to be closely correlated and statistically significant with the swimming mode of the animal. This study provides the first crucial step in understanding batoid olfaction, by understanding the diversity of the morphology of the system. Because odor capture is a strictly hydrodynamic process, it may be that factors relating more directly to the fluid dynamics (i.e., swimming mode, velocity, Reynolds number) may be more important in shaping the evolution of the diversity of batoid noses than other ecological factors like habitat and diet.}, }
@article {pmid36332888, year = {2023}, author = {Saleem, T and Powell, T and Walker, W and Raju, S}, title = {Assessment of flow mechanics in the lower extremity venous system.}, journal = {Journal of vascular surgery. Venous and lymphatic disorders}, volume = {11}, number = {2}, pages = {365-372.e3}, doi = {10.1016/j.jvsv.2022.10.009}, pmid = {36332888}, issn = {2213-3348}, mesh = {Humans ; Female ; Young Adult ; Adult ; Middle Aged ; Male ; *Femoral Vein/diagnostic imaging ; *Vena Cava, Inferior/diagnostic imaging ; Iliac Vein/diagnostic imaging ; Leg/blood supply ; Ultrasonography ; }, abstract = {BACKGROUND: The Reynolds number (Re) is a dimensionless parameter that describes fluid flow mechanics. Veins are compliant and collapsible vascular conduits that can accommodate large volume changes in response to small pressure changes. However, only sparse information is available about flow parameters such as the Re in the venous system.<br><br>METHODS: Bilateral duplex ultrasound examination of 15 healthy volunteers (30 limbs) was performed before and after exercise (four flights of stairs) of the veins of the lower extremity (left and right sides) and inferior vena cava. These volunteers had been confirmed to not have any signs or symptoms of lower extremity venous disease via focused history and physical examination findings.<br><br>RESULTS: Most of the volunteers were women (73%). Their mean age was 37&#xa0;&#xb1; 12.8&#xa0;years. The Re was highest in the inferior vena cava among all the veins examined (470&#xa0;&#xb1; 144 before exercise and 589&#xa0;&#xb1; 205 after exercise; P&#xa0;= .04). The association between the change in Re before and after exercise and the specific vein examined was also significant for the right and left external iliac veins, right and left common femoral veins, right and left profunda femoris veins, right and left femoral veins, and right common iliac vein. Resistance and velocity maps for the lower extremity venous system were also created. The velocity increased and the resistance decreased as one moved up the venous tree toward the right atrium.<br><br>CONCLUSIONS: The Re increased for most of the lower extremity veins after exercise in our healthy volunteers. However, the critical value for turbulent flow was not reached despite the exercise.}, }
@article {pmid36329077, year = {2022}, author = {Roósz, A and Rónaföldi, A and Svéda, M and Veres, Z}, title = {Effect of crucible wall roughness on the laminar/turbulent flow transition of the Ga75In25 alloy stirred by a rotating magnetic field.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {18592}, pmid = {36329077}, issn = {2045-2322}, support = {ANN 130946//Hungarian National Research, Development, and Innovation Office/ ; ANN 130946//Hungarian National Research, Development, and Innovation Office/ ; ANN 130946//Hungarian National Research, Development, and Innovation Office/ ; ANN 130946//Hungarian National Research, Development, and Innovation Office/ ; }, abstract = {The critical magnetic induction (Bcr) values of a melt flow produced by a rotating magnetic field (RMF), remaining laminar or turbulent, are essential in different solidification processes. In an earlier paper (Metall Res Technol 100: 1043-1061, 2003), we showed that Bcr depends on the crucible radius (R) and frequency of the magnetic field (f). The effect of wall roughness (WR) on Bcr was investigated in this study. Using ten different wall materials, we determined the angular frequency (ω) and Reynolds number (Re) as a function of the magnetic induction (B) and f using two different measuring methods (pressure compensation method, PCM; height measuring method, HMM). The experiments were performed at room temperature; therefore, the Ga75wt%In25wt% alloy was chosen for the experiments. Based on the measured and calculated results, a simple relationship was determined between Bcr and Re*, f, R, and WR, where the constants K1, K2, K3, and K4 depended on the physical properties of the melt and wall material:[Formula: see text].}, }
@article {pmid36319372, year = {2022}, author = {Datta, R and Russell, DR and Tang, I and Clayson, T and Suttle, LG and Chittenden, JP and Lebedev, SV and Hare, JD}, title = {Time-resolved velocity and ion sound speed measurements from simultaneous bow shock imaging and inductive probe measurements.}, journal = {The Review of scientific instruments}, volume = {93}, number = {10}, pages = {103530}, doi = {10.1063/5.0098823}, pmid = {36319372}, issn = {1089-7623}, abstract = {We present a technique to measure the time-resolved velocity and ion sound speed in magnetized, supersonic high-energy-density plasmas. We place an inductive ("b-dot") probe in a supersonic pulsed-power-driven plasma flow and measure the magnetic field advected by the plasma. As the magnetic Reynolds number is large (RM > 10), the plasma flow advects a magnetic field proportional to the current at the load. This enables us to estimate the flow velocity as a function of time from the delay between the current at the load and the signal at the probe. The supersonic flow also generates a hydrodynamic bow shock around the probe, the structure of which depends on the upstream sonic Mach number. By imaging the shock around the probe with a Mach-Zehnder interferometer, we determine the upstream Mach number from the shock Mach angle, which we then use to determine the ion sound speed from the known upstream velocity. We use the sound speed to infer the value of Z̄Te, where Z̄ is the average ionization and Te is the electron temperature. We use this diagnostic to measure the time-resolved velocity and sound speed of a supersonic (MS ∼ 8), super-Alfvénic (MA ∼ 2) aluminum plasma generated during the ablation stage of an exploding wire array on the Magpie generator (1.4 MA, 250 ns). The velocity and Z̄Te measurements agree well with the optical Thompson scattering measurements reported in the literature and with 3D resistive magnetohydrodynamic simulations in GORGON.}, }
@article {pmid36313190, year = {2022}, author = {Qiao, Y and Ma, Z and Onyango, C and Cheng, X and Dorfman, KD}, title = {DNA fragmentation in a steady shear flow.}, journal = {Biomicrofluidics}, volume = {16}, number = {5}, pages = {054109}, pmid = {36313190}, issn = {1932-1058}, support = {R21 HG011251/HG/NHGRI NIH HHS/United States ; }, abstract = {We have determined the susceptibility of T4 DNA (166 kilobase pairs, kbp) to fragmentation under steady shear in a cone-and-plate rheometer. After shearing for at least 30 min at a shear rate of 6000 s - 1 , corresponding to a Reynolds number of O (10 3) and a Weissenberg number of O (10 3) , 97.9 ± 1.3 % of the sample is broken into a polydisperse mixture with a number-averaged molecular weight of 62.6 ± 3.2 kbp and a polydispersity index of 1.29 ± 0.03 , as measured by pulsed-field gel electrophoresis (with a 95% confidence interval). The molecular weight distributions observed here from a shear flow are similar to those produced by a (dominantly extensional) sink flow of DNA and are qualitatively different than the midpoint scission observed in simple extensional flow. Given the inability of shear flow to produce a sharp coil-stretch transition, the data presented here support a model where polymers can be fragmented in flow without complete extension. These results further indicate that DNA fragmentation by shear is unlikely to be a significant issue in microfluidic devices, and anomalous molecular weight observations in experiments are due to DNA processing prior to observation in the device.}, }
@article {pmid36301473, year = {2023}, author = {Bryan, MT}, title = {Assessing the Challenges of Nanotechnology-Driven Targeted Therapies: Development of Magnetically Directed Vectors for Targeted Cancer Therapies and Beyond.}, journal = {Methods in molecular biology (Clifton, N.J.)}, volume = {2575}, number = {}, pages = {105-123}, pmid = {36301473}, issn = {1940-6029}, mesh = {Humans ; *Neoplasms/genetics/therapy ; Nanotechnology ; Magnetics ; Drug Delivery Systems/methods ; Motion ; }, abstract = {Targeted delivery, in which therapeutic agents are preferentially concentrated at the diseased site, has the potential to improve therapeutic outcomes by minimizing off-target interactions in healthy tissue. Both passive and active methods of targeting delivery have been proposed, often with particular emphasis on cancer treatment. Passive methods rely on the overexpression of a biomarker in diseased tissue that can then be used to target the therapy. Active techniques involve physically guiding therapeutic agents toward the target region. Since the motion of magnetic particles can be remotely controlled by external magnetic fields, magnetic technologies have the potential to drive and hold drugs or other cargo at the required therapeutic site, increasing the localized dose while minimizing overall exposure. Directed motion may be generated either by simple magnetic attraction or by causing the particles to perform swimming strokes to produce propulsion. This chapter will compare the different strategies using magnetic nanotechnology to produce directed motion compatible with that required for targeted cargo delivery and magnetically assisted therapies and assess their potential to meet the challenges of operating within the human body.}, }
@article {pmid36296816, year = {2022}, author = {Beck, J and Palmer, M and Inman, K and Wohld, J and Cummings, M and Fulmer, R and Scherer, B and Vafaei, S}, title = {Heat Transfer Enhancement in the Microscale: Optimization of Fluid Flow.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {20}, pages = {}, pmid = {36296816}, issn = {2079-4991}, abstract = {The focus of this paper is to investigate the effects of the addition of a connector between two serial microchannels. The idea of adding connector at the inlet of microchannels to enhance the random motion of molecules or nanoparticles in low Reynolds numbers was developed in our research group for the first time. It was experimentally determined that the shape of a connector between two microchannels has a significant impact on the enhancement of the random motion of molecules or nanoparticles. Consequently, the heat transfer coefficient is improved inside the second microchannel. The connector is large enough to refresh the memory of the fluid before entering the second channel, causing a higher maximum heat transfer coefficient in the second channel. It was also observed that the heat transfer coefficient can be increased at the end of the channel when the outlet temperature is relatively high. This may be explained by the fact that as temperature increases, the fluid viscosity tends to decrease, which generally drives an increase in the local random motion of base fluid molecules and nanoparticles. This causes an increase in the microchannel heat transfer coefficient. It was found that the addition of nanoparticles significantly modified the impact of the connector on the microchannel heat transfer coefficient. In addition, the effects of changing the Reynolds number and the shape of the connector were investigated through use of computational fluid dynamics (CFD) calculations. It was found that both factors have an important impact on the variation of velocity and enhancement of random motion of molecules and consequently significantly affect the heat transfer coefficient.}, }
@article {pmid36296785, year = {2022}, author = {Chang, Q and Fu, Z and Zhang, S and Wang, M and Pan, X}, title = {Experimental Investigation of Reynolds Number and Spring Stiffness Effects on Vortex-Induced Vibration Driven Wind Energy Harvesting Triboelectric Nanogenerator.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {20}, pages = {}, pmid = {36296785}, issn = {2079-4991}, support = {51979045//National Natural Science Foundation of China/ ; }, abstract = {Vortex-induced vibration (VIV) is a process that wind energy converts to the mechanical energy of the bluff body. Enhancing VIV to harvest wind energy is a promising method to power wireless sensor nodes in the Internet of Things. In this work, a VIV-driven square cylinder triboelectric nanogenerator (SC-TENG) is proposed to harvest broadband wind energy. The vibration characteristic and output performance are studied experimentally to investigate the effect of the natural frequency by using five different springs in a wide range of stiffnesses (27 N/m<K<90 N/m). The square cylinder is limited to transverse oscillation and experiments were conducted in the Reynolds regime (3.93×103−3.25×104). The results demonstrate the strong dependency of VIV on natural frequency and lock-in observed in a broad range of spring stiffness. Moreover, the amplitude ratio and range of lock-in region increase by decreasing spring stiffness. On the other hand, the SC-TENG with higher spring stiffness can result in higher output under high wind velocities. These observations suggest employing an adjustable natural frequency system to have optimum energy harvesting in VIV-based SC-TENG in an expanded range of operations.}, }
@article {pmid36290555, year = {2022}, author = {Khan, MI and Lashin, MMA and Khedher, NB and Ahmed, B and Khan, SU and Oreijah, M and Guedri, K and Tag-ElDin, ESM and Galal, AM}, title = {Peristaltic Phenomenon in an Asymmetric Channel Subject to Inclined Magnetic Force and Porous Space.}, journal = {Bioengineering (Basel, Switzerland)}, volume = {9}, number = {10}, pages = {}, pmid = {36290555}, issn = {2306-5354}, abstract = {This research is engaged to explore biological peristaltic transport under the action of an externally applied magnetic field passing through an asymmetric channel which is saturated with porous media. The set of governing partial differential equations for the present peristaltic flow are solved in the absence of a low Reynolds number and long wavelength assumptions. The governing equations are to be solved completely, so that inertial effects can be studied. The numerical simulations and results are obtained by the help of a finite element method based on quadratic six-noded triangular elements equipped with a Galerkin residual procedure. The inertial effects and effects of other pertinent parameters are discussed by plotting graphs based on a finite element (FEM) solution. Trapped bolus is discussed using the graphs of streamlines. The obtained results are also compared with the results given in the literature which are highly convergent. It is concluded that velocity and the number of boluses is enhanced by an increase in Hartmann number and porosity parameter K Increasing inertial forces increase the velocity of flow but increasing values of the porosity parameter lead to a decrease in the pressure gradient. The study elaborates that magnetic field and porosity are useful tools to control the velocity, pressure, and boluses in the peristaltic flow pattern.}, }
@article {pmid36284940, year = {2022}, author = {Ebrahimi, S and Tahmasebipour, M}, title = {Numerical Study of a Centrifugal Platform for the Inertial Separation of Circulating Tumor Cells Using Contraction-Expansion Array Microchannels.}, journal = {Archives of Razi Institute}, volume = {77}, number = {2}, pages = {647-660}, pmid = {36284940}, issn = {2008-9872}, mesh = {Cell Separation/instrumentation/methods ; Erythrocytes ; Microfluidic Analytical Techniques/methods ; *Neoplastic Cells, Circulating/pathology ; Humans ; }, abstract = {Label-free inertial separation of the circulating tumor cells (CTCs) has attracted significant attention recently. The present study proposed a centrifugal platform for the inertial separation of the CTCs from the white blood cells. Particle trajectories of the contraction-expansion array (CEA) microchannels were analyzed by the finite element method. Four expansion geometries (i.e., circular, rectangular, trapezoidal, and triangular) were compared to explore their differences in separation possibilities. Different operational and geometrical parameters were investigated to achieve maximum separation efficiency. Results indicated that the trapezoidal CEA microchannel with ten expansions and a 100 µm channel depth had the best separation performance at an angular velocity of 100 rad/s. Reynolds number of 47 was set as the optimum value to apply minimum shear stress on the CTCs leading to 100% efficiency and 95% purity. Furthermore, the proposed system was simulated for whole blood by considering the red blood cells.}, }
@article {pmid36283263, year = {2023}, author = {Treegosol, P and Priyadumkol, J and Kamutavanich, W and Katchasuwanmanee, K and Chaiworapuek, W}, title = {Experimental investigation of the heat transfer and friction loss of turbulent flow in circular pipe under low-frequency ultrasound propagation along the mainstream flow.}, journal = {Ultrasonics}, volume = {128}, number = {}, pages = {106866}, doi = {10.1016/j.ultras.2022.106866}, pmid = {36283263}, issn = {1874-9968}, abstract = {The characteristics of the heat transfer and friction loss of turbulent water flow in a circular pipe were investigated experimentally at a constant surface temperature of 45 ℃ for 28 kHz ultrasound propagation along the mainstream flow. Transducers were installed in five rows and three columns in the upstream section of the test pipe, and the number of active transducers was varied (1, 3, and 15) for a Reynolds number range of 10,000-25,000. The results indicated that the ultrasonic effects yielded positive results for both the heat transfer and pressure loss of the pipe flow. Under the influence of 15 ultrasonic transducers, the maximum Nusselt number ratio was 1.57 and the greatest reduction in the friction factor was 21.6 % for a Reynolds number of 10,000. The corresponding maximum thermal performance factor was approximately 1.7. However, the thermal efficiency tended to decrease with an increase in the number of transducers. The maximum thermal efficiency values under ultrasonic waves with 1, 3, and 15 transducers were 5.43, 3.37, and 1.95, respectively. When the change in the friction factor per ultrasonic input power was considered, the most suitable number of ultrasonic transducers was three. Finally, predictive formulas were proposed for the Nusselt number ratio and friction factor ratio under low-frequency ultrasound, with deviations from -5.5 % to 5.4 % and -7.4 % to 7.4 %, respectively.}, }
@article {pmid36282393, year = {2022}, author = {Sharma, A and Gunreddy, N and Mulamalla, AR and Duraisamy, S and Sivan, S and Poongavanam, GK and Kumar, B}, title = {Conductive and convective heat transfer augmentation in flat plate solar collector from energy, economic and environmental perspectives - a comprehensive review.}, journal = {Environmental science and pollution research international}, volume = {29}, number = {58}, pages = {87019-87067}, pmid = {36282393}, issn = {1614-7499}, mesh = {*Hot Temperature ; Silicon Dioxide ; Sunlight ; Models, Theoretical ; Water ; *Solar Energy ; }, abstract = {The primary objective of the paper is to identify the effective way to enhance the conductive and convective heat transfer of the FPSC. The performance enhancements of different FPSC components such as absorber plate, absorber tube, and heat transfer fluid are reviewed in detail. The influence of absorber plate configurations, material properties, a center-to-center distance of the absorber tube, plate thickness, coatings, and tube geometry have been assessed to increase the conduction heat transfer. Also, the augmentations of convective heat transfer using different nanofluids in FPSC such as Al2O3/water, CuO/water, CNT/water, TiO2/water, SiO2/water, graphene oxide/water, MgO/water, CeO2/water, WO3/water, ZnO/water, and hybrid nanofluids are evaluated in detail. The performance improvements using both conductive and convective (combined) passive technique have been elaborated. The table representation has been used to describe the activities performed in each paper which include FPSC type, passive technique detail, properties of heat transfer fluid, Reynolds number, heat transfer aspects, pumping power, energy, exergy, environmental aspects, and inference. These data will help the researcher to identify existing activities and the potential gap. This review paper also deals with the suggestions for the research work which can be carried out in the direction of heat transfer from solar flat plate collectors.}, }
@article {pmid36278718, year = {2022}, author = {Molteno, TCA}, title = {Nature's Wind Turbines: The Measured Aerodynamic Efficiency of Spinning Seeds Approaches Theoretical Limits.}, journal = {Biomimetics (Basel, Switzerland)}, volume = {7}, number = {4}, pages = {}, pmid = {36278718}, issn = {2313-7673}, abstract = {This paper describe a procedure to measure experimentally the power coefficient, Cp, of winged seeds, and apply this technique to seeds from the Norway maple (Acer platanoides). We measure Cp=56.9±2% at a tip speed ratio of 3.21±0.06. Our results are in agreement with previously published CFD simulations that indicate that these seeds-operating in low-Reynolds number conditions-approach the Betz limit (Cp=59.3%) the maximum possible efficiency for a wind turbine. In addition, this result is not consistent with the recent theoretical work of Okulov &amp; Sørensen, which suggests that a single-bladed turbine with a tip-speed ratio of 3.2 can achieve a power efficiency of no more than 30%.}, }
@article {pmid36271129, year = {2022}, author = {Tao, H and Alawi, OA and Hussein, OA and Ahmed, W and Abdelrazek, AH and Homod, RZ and Eltaweel, M and Falah, MW and Al-Ansari, N and Yaseen, ZM}, title = {Thermohydraulic analysis of covalent and noncovalent functionalized graphene nanoplatelets in circular tube fitted with turbulators.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {17710}, pmid = {36271129}, issn = {2045-2322}, abstract = {Covalent and non-covalent nanofluids were tested inside a circular tube fitted with twisted tape inserts with 45° and 90° helix angles. Reynolds number was 7000 ≤ Re ≤ 17,000, and thermophysical properties were assessed at 308 K. The physical model was solved numerically via a two-equation eddy-viscosity model (SST k-omega turbulence). GNPs-SDBS@DW and GNPs-COOH@DW nanofluids with concentrations (0.025 wt.%, 0.05 wt.% and 0.1 wt.%) were considered in this study. The twisted pipes' walls were heated under a constant temperature of 330 K. The current study considered six parameters: outlet temperature, heat transfer coefficient, average Nusselt number, friction factor, pressure loss, and performance evaluation criterion. In both cases (45° and 90° helix angles), GNPs-SDBS@DW nanofluids presented higher thermohydraulic performance than GNPs-COOH@DW and increased by increasing the mass fractions such as 1.17 for 0.025 wt.%, 1.19 for 0.05 wt.% and 1.26 for 0.1 wt.%. Meanwhile, in both cases (45° and 90° helix angles), the value of thermohydraulic performance using GNPs-COOH@DW was 1.02 for 0.025 wt.%, 1.05 for 0.05 wt.% and 1.02 for 0.1 wt.%.}, }
@article {pmid36270503, year = {2022}, author = {Ibanez, R and Kelley, DH}, title = {A bioinspired apparatus for modeling peristaltic pumping in biophysical flows.}, journal = {Bioinspiration &amp; biomimetics}, volume = {17}, number = {6}, pages = {}, doi = {10.1088/1748-3190/ac9c7e}, pmid = {36270503}, issn = {1748-3190}, mesh = {*Models, Biological ; *Peristalsis ; Biophysics ; Biomimetics ; }, abstract = {In this study, we present a novel, bioinspired experimental apparatus, its construction, data acquisition methodology, and validation for the study of peristaltic flows. The apparatus consists of a series of stepper motor actuators, which deflect a deformable membrane to produce peristaltic flows. We show that this apparatus design has significant advantages over previous designs that have been used to study peristaltic flows by offering a much wider range of modeling capabilities. Comparisons between the capabilities of our apparatus and previous ones show our apparatus spanning a larger range of wavelengthλ, wave speedc, amplitudeA, and waveform (i.e. the apparatus is not constrained to nondispersive waves or to a sinusoidal shape). This large parameter range makes the apparatus a useful tool for biomimetic experimental modeling, particularly for systems that have complex waveforms, such as peristaltic flows in perivascular vessels, arteries, the cochlea, and the urethra. We provide details on the experimental design and construction for ease of reconstruction to the reader. The apparatus capabilities are validated for a large parameter range by comparing experimental measurements to analytic results from (Ibanezet al2021Phys. Rev. Fluids6103101) for high Reynolds number (Re > 1) and (Jaffrin and Shapiro 1971Annu. Rev. Fluid Mech.33-37) for low Reynolds number (Re < 1) applications. We show that the apparatus is useful for biophysical peristaltic studies and has potential applications in other types of studies.}, }
@article {pmid36266390, year = {2022}, author = {Benhanifia, K and Redouane, F and Lakhdar, R and Brahim, M and Al-Farhany, K and Jamshed, W and Eid, MR and El Din, SM and Raizah, Z}, title = {Investigation of mixing viscoplastic fluid with a modified anchor impeller inside a cylindrical stirred vessel using Casson-Papanastasiou model.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {17534}, pmid = {36266390}, issn = {2045-2322}, mesh = {*Bioreactors ; *Hydrodynamics ; }, abstract = {In process engineering as chemical and biotechnological industry, agitated vessels are commonly used for various applications; mechanical agitation and mixing are performed to enhance heat transfer and improve specific Physico-chemical characteristics inside a heated tank. The research subject of this work is a numerical investigation of the thermo-hydrodynamic behavior of viscoplastic fluid (Casson-Papanastasiou model) in a stirred tank, with introducing a new anchor impeller design by conducting some modifications to the standard anchor impeller shape. Four geometry cases have been presented for achieving the mixing process inside the stirred vessel, CAI; classical anchor impeller, AI1; anchor impeller with added horizontal arm blade, AI2 and AI3 anchor impeller with two and three added arm blades, respectively. The investigation is focused on the effect of inertia and plasticity on the thermo-hydrodynamic behavior (flow pattern, power consumption, and heat transfer) by varying the Reynolds number (Re = 1, 10, 100, 200), Bingham number (Bn = 1, 10, 50), in addition to the effect of geometry design in the overall stirred system parameters. The findings revealed an excellent enhancement of flow pattern and heat transfer in the stirred system relatively to the increase of inertia values. Also, an energy reduction has been remarked and the effect of anchor impeller shape. AI3 geometry design significantly improves the flow pattern and enhances heat transfer by an increased rate of 10.46% over the other cases.}, }
@article {pmid36261993, year = {2022}, author = {Ji, Y and Cao, R and Wang, C and Xu, X and Zhu, L}, title = {Effect of flow regime on mass transfer diffusion and stability of aerobic granular sludge (AGS) in view of interfacial thermodynamic.}, journal = {Journal of environmental management}, volume = {323}, number = {}, pages = {116293}, doi = {10.1016/j.jenvman.2022.116293}, pmid = {36261993}, issn = {1095-8630}, mesh = {Humans ; *Sewage/chemistry ; *Waste Disposal, Fluid/methods ; Wastewater ; Bioreactors ; Aerobiosis ; Thermodynamics ; Proteins ; Oxygen ; Water ; }, abstract = {Aerobic granular sludge (AGS) technology has been widely studied as "The Next Generation Wastewater Treatment technology". The effect of hydraulic conditions on the structural stability of AGS has been widely studied. However, the function of flow regime on the AGS stability, especially dissolved oxygen (DO) mass transfer, is still unknown. In this study, we used the Reynolds number (Re) to quantify the flow regime and selected different stages of AGS as experimental subjects. Results showed that the relatively suitable Re (Re = 150) could create lower DO mass transfer limitation (Lc = 27.4 μm) and increase protein (PN) contents and the abundance of hydrophobic functional groups in AGS. At this condition (Re = 150), the interfacial Gibbs free energy of sludge-water (ΔGLS[a]) was at a lower state (-129.75 ± 2.15 mJ·m[-2]), which favored the stability of AGS. Principal component analysis (PCA) and correlation analysis indicated that the response of ΔGLS[a] was affected by Lc, PN, and hydrophobic groups. In addition, results obtained for unstable AGS further verified that suitable Re regulates the structural stability of AGS. This study deepens the understanding of Re as an important hydraulic parameter for structural stability of AGS, which is also of great significance for energy saving of sequential batch reactors (SBRs) with agitation in practical engineering.}, }
@article {pmid36261048, year = {2022}, author = {Ben-Gida, H and Gurka, R}, title = {The leading-edge vortex over a swift-like high-aspect-ratio wing with nonlinear swept-back geometry.}, journal = {Bioinspiration &amp; biomimetics}, volume = {17}, number = {6}, pages = {}, doi = {10.1088/1748-3190/ac9bb5}, pmid = {36261048}, issn = {1748-3190}, mesh = {Humans ; Animals ; *Flight, Animal ; *Wings, Animal ; Birds ; Rheology/methods ; Biomechanical Phenomena ; Models, Biological ; }, abstract = {The leading-edge vortex (LEV) is a common flow structure that forms over wings at high angles of attack. Over the years, LEVs were exploited for augmenting the lift of man-made slender delta wings aircraft. However, recent observations suggested that natural flyers with high-aspect-ratio (high-AR) wings, such as the common swift (Apus apus), can also generate LEVs while gliding. We hypothesize that the planform shape and nonlinear sweep (increasing towards the wingtip) enable the formation and control of such LEVs. In this paper, we investigate whether a stationary LEV can form over a nonlinear swept-back high-AR wing inspired by the swift's wing shape and evaluate its characteristics and potential aerodynamic benefit. Particle image velocimetry (PIV) measurements were performed in a water flume on a high-AR swept-back wing inspired by the swift wing. Experiments were performed at four spanwise sections and a range of angles of attack for a chord-based Reynolds number of20000. Stationary LEV structures were identified across the wingspan by utilizing the proper orthogonal decomposition (POD) method for angles of attack of 5[∘]-15[∘]. The size and circulation of the stationary LEV were found to grow towards the wingtip in a nonlinear manner due to shear layer feeding and spanwise transport of mass and vorticity within the LEV, thus confirming that nonlinear high-AR swept-back wings can generate stationary LEVs. Our results suggest that the common swift can generate stationary LEVs over its swept-back wings to glide slower and at a higher rate of descent, with the LEVs potentially supporting up to 60% of its weight.}, }
@article {pmid36234399, year = {2022}, author = {Abderrahmane, A and Younis, O and Al-Khaleel, M and Laidoudi, H and Akkurt, N and Guedri, K and Marzouki, R}, title = {2D MHD Mixed Convection in a Zigzag Trapezoidal Thermal Energy Storage System Using NEPCM.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {19}, pages = {}, pmid = {36234399}, issn = {2079-4991}, support = {xxxx//Khalifa University of Science and Technology/ ; }, abstract = {In a magnetic field, two-dimensional (2D) mixed convection is investigated within a zigzagged trapezoidal chamber. The lower side of the trapezoidal chamber is irregular, in particular, a zigzagged wall with different zigzag numbers N. The fluid particles move in the room due to the motion of the upper wall, while the porosity-enthalpy approach represents the melting process. The thermal parameters of the fluid are enhanced by what is called a nano-encapsulated phase change material (NEPCM) consisting of polyurethane as the shell and a nonadecane as the core, while water is used as the base fluid. In order to treat the governing equations, the well-known Galerkin finite element method (GFEM) is applied. In addition, the heat transfer (HT) irreversibility and the fluid friction (FF) irreversibility are compared in terms of the average Bejan number. The main results show that the melt band curve behaves parabolically at smaller values of Reynolds number (Re) and larger values of Hartmann number (Ha). Moreover, minimizing the wave number is better in order to obtain a higher heat transfer rate.}, }
@article {pmid36229498, year = {2022}, author = {Khan, A and Khan, MS and Pasha, AA and Marzouki, R and Rahman, MM and Mahmoud, O and Galal, AM and Najati, SA}, title = {Hydrodynamic analysis of the magnetic field dependent viscous fluid flow and thermosolutal convection between rotating channels.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {17170}, pmid = {36229498}, issn = {2045-2322}, mesh = {Colloids ; *Convection ; Humans ; *Hydrodynamics ; Magnetic Fields ; Models, Theoretical ; Reproducibility of Results ; Viscosity ; }, abstract = {According to research, exposing a person to a magnetic field enhances blood flow and minimizes their risk of suffering a heart attack. Ferrohydrodynamics is the study of fluid motion mechanics that is affected by strong magnetic polarisation forces (FHD). Ferrofluids may transmit heat in a variety of ways by using magnetic fluids. This behaviour is demonstrated by liquid-cooled speakers, which utilise less ferrofluid to prevent heat from reaching the speaker coil. This modification boosts the coil's ability to expand, which enables the loudspeaker to create high-fidelity sound. It is investigated how the fluid dynamics of spinning, squeezing plates are affected by thermosolutal convection and a magnetic field dependent (MFD) viscosity. Standard differential equations are used to represent the equations of the modified form of Navier Stokes, Maxwell's, and thermosolutal convection. The magnetic field, modified velocity field equations, and thermosolutal convection equations all yield suitable answers. Additionally computed and thoroughly detailed are the MHD torque and fluid pressure that are imparted to the top plate. To create a technique with quick and certain convergence, the resulting equations for uniform plates are solved using the Homotopy Analysis Method (HAM) with appropriate starting estimates and auxiliary parameters. The validity and reliability of the HAM outcomes are shown by comparing the HAM solutions with the BVP4c numerical solver programme. It has been found that a magnetic Reynolds number lowers the temperature of the fluid as well as the tangential and axial components of the velocity field. Additionally, when the fluid's MFD viscosity rises, the axial and azimuthal components of the magnetic field behave in opposition to one another. This study has applications in the development of new aircraft take-off gear, magnetorheological airbags for automobiles, heating and cooling systems, bio-prosthetics, and biosensor systems.}, }
@article {pmid36219300, year = {2023}, author = {Tang, P and Chen, L and Zhang, W and Zhou, Y}, title = {Bioclogging alleviation for constructed wetland based on the interaction among biofilm growth and hydrodynamics.}, journal = {Environmental science and pollution research international}, volume = {30}, number = {7}, pages = {18755-18763}, pmid = {36219300}, issn = {1614-7499}, support = {51878597//National Natural Science Foundation of China/ ; }, mesh = {*Wetlands ; *Hydrodynamics ; Models, Theoretical ; Biofilms ; Porosity ; Waste Disposal, Fluid/methods ; }, abstract = {Bioclogging is the most crucial operation problem of the constructed wetlands, which reduce its removal efficiency and life span. A strategy through properly increasing hydraulic loading is proposed in this study to alleviate the bioclogging for CWs. The two-dimensional porous media flow cell (2D PMFC) test indicated that a quadratic correlation was found between local biofilms growth rate and the near-wall Reynolds number (r > 0.765, p < 0.05). The biofilm growth rate declined with the flowrate when Re exceeded about 6.0. It was also found that the higher flowrate (6 mL/min) lead to the homogeneous biofilm and velocity distribution in the PMFC. The column test indicated that the highest hydraulic loading (9.2 cm/h) produced the smallest decrease in hydraulic conductivity, which was 80 times more than that of low hydraulic load (3.0 cm/h) at the end (40 days) of experiment. Moreover, the relatively homogenized distribution of biofilm was found along the column with the highest hydraulic loading, which confirmed that the proper increase in hydraulic loading can alleviate bioclogging.}, }
@article {pmid36215970, year = {2022}, author = {Li, H and Nabawy, MRA}, title = {Capturing wake capture: a 2D numerical investigation into wing-wake interaction aerodynamics.}, journal = {Bioinspiration &amp; biomimetics}, volume = {17}, number = {6}, pages = {}, doi = {10.1088/1748-3190/ac98e5}, pmid = {36215970}, issn = {1748-3190}, mesh = {Animals ; *Flight, Animal ; Models, Biological ; Wings, Animal ; Biomechanical Phenomena ; Insecta ; *Stroke ; }, abstract = {A wing generating lift leaves behind a region of disturbed air in the form of a wake. For a hovering insect, the wings must return through the wake produced by the previous half-stroke and this can have significant effects on the aerodynamic performance. This paper numerically investigates 2D wings interacting with their own wake at Reynolds numbers of 10[2]and 10[3], enabling an improved understanding of the underlying physics of the 'wake capture' aerodynamic mechanism of insect flight. We adopt a simple kinematic motion pattern comprised of a translational stroke motion followed by a complete stop to expose wake interaction effects. Representative stroke distance to chord ratios between 1.5 and 6.0 are considered, enabling different leading-edge vortex (LEV) attachment states. We also allow pitching rotation towards the end of stroke, leading to wake intercepting angles of 135°, 90°, and 45°, analogous to delayed, symmetric, and advanced pitching rotations of insect wings. It is shown that both vortex suction and jet flow impingement mechanisms can lead to either positive or negative effects depending on the LEV attachment state, and that stroke distances resulting in a detached/attached LEV lead to beneficial/detrimental wake interaction lift. Pitching rotation at the end of the stroke motion is found to induce a strong rotational trailing-edge vortex (RTEV). For advanced pitching, this RTEV serves to enable either a stronger flow impingement effect leading to positive wake interaction lift if the LEV is detached, or a less favourable vortex suction effect leading to negative wake interaction lift if the LEV is closely attached. The higher Reynolds number led to faster development of the wake vortices, but the primary wake interaction mechanisms remained the same for both Reynolds numbers.}, }
@article {pmid36202970, year = {2022}, author = {Usman,  and Memon, AA and Alghamdi, M and Muhammad, T}, title = {A forced convection of water aluminum oxide nanofluid flow and heat transfer study for a three dimensional annular with inner rotated cylinder.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {16735}, pmid = {36202970}, issn = {2045-2322}, abstract = {The article examines a water alumina nanofluid and heat transfer through the three-dimensional annular. The annular is constructed by the two concentric cylinders in which the inner cylinder can rotate along the tangential direction at a constant speed. A slip boundary condition will be imposed to vanish the viscous effect in the vicinity of the outer cylinder wall. Moreover, the rotating cylinder is kept at a hot temperature, and the outer one is at a cold temperature. A three-dimensional incompressible Navier Stokes and energy equations were carried in cylindrical coordinates. The simulation was observed using the emerging computational tool of COMSOL Multiphysics 5.6, which implements Least Square Galerkin's scheme of finite element method. The parametric study will be done by altering the speed of rotation of the inner cylinder from 1 to 4, volume fraction from 0.001 to 0.9, and the aspect ratio from 0.4 to 0.6 for a fixed Reynolds number of 35,000. The results will be displayed with graphs and tables for average values of the Nusselt number, the percentage change in the temperature, and the skin friction at the middle plan. It was found that the average Nusselt number at the middle of the annular increases before the volume fraction of 0.2 and then decreases for all values of the volume fraction for a fixed rotation of the inner cylinder. The average percentage change relative to the inner cylinder's hot temperature decreases with the volume fraction increase for the fixed rotation. Also, it was found that the quantity of nanoparticles in the domain is improving the average skin friction in the middle of the channel, and it can be reduced by improving the rotation of the inner cylinder by about 10-23% strictly depending upon the aspect ratio for a particular case.}, }
@article {pmid36198707, year = {2022}, author = {Shoukat, G and Idrees, H and Sajid, M and Ali, S and Ayaz, Y and Nawaz, R and Ansari, AR}, title = {Numerical analysis of permeate flux in reverse osmosis by varying strand geometry.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {16636}, pmid = {36198707}, issn = {2045-2322}, mesh = {*Biofouling ; *Drinking Water ; Membranes, Artificial ; Osmosis ; *Water Purification/methods ; }, abstract = {In regions with limited potable water availability, membrane desalination is being employed to filter water using a pressure-driven approach. Because of the high energy consumption required to produce the pressure differential needed for this method, researchers have been trying different geometric designs of spacer filaments to enhance the amount of permeate flux in terms of energy utilization. The purpose of spacer filaments is to support membranes structurally and induce turbulent mixing in spiral wound membrane desalination. In this paper, the improvement of mass transfer in desalination driven by reverse osmosis has been studied using Computational Fluid Dynamics (CFD) with the introduction of spiral wound membranes that are lined with spacer filaments in a zig-zag formation having alternating diameters for strands. The fluid flow characteristics for a 2-dimensional geometric model were resolved using the open-source program OpenFOAM by changing the Reynolds number to just before the inception of instabilities. Ratios of alternate strand diameters were also varied between one and two. Based on a detailed analysis of velocity contours, pressure distribution, wall shear stresses, and steady-state vortex systems, the research findings offer guidance for employing alternating strand design in zig-zag formation for optimum mass transfer and minimal pressure drop when accounting for concentration polarization.}, }
@article {pmid36193889, year = {2023}, author = {Pinto Costa, R and Nwotchouang, BST and Yao, J and Biswas, D and Casey, D and McKenzie, R and Sebastian, F and Amini, R and Steinman, DA and Loth, F}, title = {Impact of Blood Rheology on Transition to Turbulence and Wall Vibration Downstream of a Stenosis.}, journal = {Journal of biomechanical engineering}, volume = {145}, number = {4}, pages = {}, doi = {10.1115/1.4055856}, pmid = {36193889}, issn = {1528-8951}, mesh = {Humans ; Constriction, Pathologic ; Stress, Mechanical ; *Vibration ; Rheology ; Blood Flow Velocity ; *Models, Cardiovascular ; }, abstract = {Previous experimental flow studies have demonstrated a delay (∼20%) in transition to turbulence for whole blood compared to a Newtonian analog fluid in both a straight pipe and eccentric stenosis model with ridged walls. The impact of wall compliance on the transition to turbulence of blood compared to Newtonian analog and on wall vibration is unknown. The present study employed flexible walls downstream of an eccentric stenosis model and examined the wall vibration during the transition to turbulence with whole blood and a Newtonian analog. Measurements of tube wall vibration velocity (WVV) were used as an indicator of the turbulence level within the flexible tube. WVV was measured at 5, 10, and 15 diameters downstream of the stenosis using a laser Doppler vibrometer at Reynolds numbers 0, 200, 300, 350, 400, 450, 500, 550, 600, 650, 700, and 750. The root mean squares (RMS) of the measured WVV were utilized as an indirect measure of fluid velocity fluctuations present at that location, and hence, an indicator of transition to turbulence. WVV RMS was near-constant until approximately Reynolds number 400. It increased monotonically with Reynolds number for both whole blood and the Newtonian fluid. No differences in the transition to turbulence were observed between whole blood and the Newtonian fluid, as the WVV RMS curves were remarkably similar in shape. This result suggests that rheology had minimal impact on the WVV downstream of a stenosis for transition to turbulence since the fluids had a similar level of vibration.}, }
@article {pmid36182967, year = {2022}, author = {Moon, J and Kang, G and Im, B and Kim, J and Cho, DH and Byun, D}, title = {Flapping and powering characteristics of a flexible piezoelectric nanogenerator at Reynolds number range simulating ocean current.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {16465}, pmid = {36182967}, issn = {2045-2322}, support = {2018R1C1B3008634//National Research Foundation of Korea/ ; 2017R1E1A1A01075353//National Research Foundation of Korea/ ; 20009618//Ministry of Trade, Industry and Energy/ ; }, abstract = {For effective ocean energy harvesting, it is necessary to understand the coupled motion of the piezoelectric nanogenerator (PENG) and ocean currents. Herein, we experimentally investigate power performance of the PENG in the perspective of the fluid-structure interaction considering ocean conditions with the Reynolds number (Re) values ranging from 1 to 141,489. A piezoelectric polyvinylidene fluoride micromesh was constructed via electrohydrodynamic (EHD) jet printing technique to produce the β-phase dominantly that is desirable for powering performance. Water channel was set to generate water flow to vibrate the flexible PENG. By plotting the Re values as a function of nondimensional bending rigidity (KB) and the structure-to-fluid mass ratio (M*), we could find neutral curves dividing the stable and flapping regimes. Analyzing the flow velocities between the vortex and surroundings via a particle image velocimetry, the larger displacement of the PENG in the chaotic flapping regime than that in the flapping regime was attributed to the sharp pressure gradient. By correlating M*, Re, KB, and the PENG performance, we conclude that there is critical KB that generate chaotic flapping motion for effective powering. We believe this study contributes to the establishment of a design methodology for the flexible PENG harvesting of ocean currents.}, }
@article {pmid36171438, year = {2022}, author = {Ismael, AM and Eldabe, NT and Abou Zeid, MY and El Shabouri, SM}, title = {Thermal micropolar and couple stresses effects on peristaltic flow of biviscosity nanofluid through a porous medium.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {16180}, pmid = {36171438}, issn = {2045-2322}, mesh = {*Gold ; *Metal Nanoparticles ; Peristalsis ; Porosity ; Viscosity ; }, abstract = {The main aim of the current study is to analyze couple stresses effects on MHD peristaltic transport of a micropolar non-Newtonian nanofluid. The fluid flows through a porous media between two horizontal co-axial tubes. The effects of radiation, chemical reaction, viscous and ohmic dissipation are considered. The inner tube is solid and uniform, while the outer tube has a sinusoidal wave traveling down its wall. The governing equations have been simplified using low-Reynolds number and long wave-length approximations, thus a semi-analytical solutions have been obtained using the homotopy perturbation method. Numerical results for the behaviors of the axial velocity, microrotation velocity, temperature and nanoparticles concentration with the physical parameters are depicted graphically through a set of graphs. Furthermore, the values of the skin friction coefficient, Nusselt and nano Sherwood numbers are computed and presented graphically through some draws. Moreover, the trapping phenomenon is discussed throughout a set of figures. The present study is very important in many medical applications, as the gastric juice motion in the small intestine when an endoscope is inserted through it. Further, gold nanoparticles are utilized in the remedy of cancer tumor.}, }
@article {pmid36154406, year = {2022}, author = {Wang, Y and Gilson, EP and Ebrahimi, F and Goodman, J and Ji, H}, title = {Observation of Axisymmetric Standard Magnetorotational Instability in the Laboratory.}, journal = {Physical review letters}, volume = {129}, number = {11}, pages = {115001}, doi = {10.1103/PhysRevLett.129.115001}, pmid = {36154406}, issn = {1079-7114}, abstract = {We report the first direct evidence for the axisymmetric standard magnetorotational instability (SMRI) from a combined experimental and numerical study of a magnetized liquid-metal shear flow in a Taylor-Couette cell with independently rotating and electrically conducting end caps. When a uniform vertical magnetic field B_{i} is applied along the rotation axis, the measured radial magnetic field B_{r} on the inner cylinder increases linearly with a small magnetic Reynolds number Rm due to the magnetization of the residue Ekman circulation. Onset of the axisymmetric SMRI is identified from the nonlinear increase of B_{r} beyond a critical Rm in both experiments and nonlinear numerical simulations. The axisymmetric SMRI exists only at sufficiently large Rm and intermediate B_{i}, a feature consistent with theoretical predictions. Our simulations further show that the axisymmetric SMRI causes the velocity and magnetic fields to contribute an outward flux of axial angular momentum in the bulk region, just as it should in accretion disks.}, }
@article {pmid36153578, year = {2023}, author = {}, title = {Correction to: Trends in Stroke Kinematics, Reynolds Number, and Swimming Mode in Shrimp-Like Organisms.}, journal = {Integrative and comparative biology}, volume = {63}, number = {3}, pages = {860}, doi = {10.1093/icb/icac142}, pmid = {36153578}, issn = {1557-7023}, }
@article {pmid36145671, year = {2022}, author = {Bernad, SI and Socoliuc, V and Susan-Resiga, D and Crăciunescu, I and Turcu, R and Tombácz, E and Vékás, L and Ioncica, MC and Bernad, ES}, title = {Magnetoresponsive Functionalized Nanocomposite Aggregation Kinetics and Chain Formation at the Targeted Site during Magnetic Targeting.}, journal = {Pharmaceutics}, volume = {14}, number = {9}, pages = {}, pmid = {36145671}, issn = {1999-4923}, abstract = {Drug therapy for vascular disease has been promoted to inhibit angiogenesis in atherosclerotic plaques and prevent restenosis following surgical intervention. This paper investigates the arterial depositions and distribution of PEG-functionalized magnetic nanocomposite clusters (PEG_MNCs) following local delivery in a stented artery model in a uniform magnetic field produced by a regionally positioned external permanent magnet; also, the PEG_MNCs aggregation or chain formation in and around the implanted stent. The central concept is to employ one external permanent magnet system, which produces enough magnetic field to magnetize and guide the magnetic nanoclusters in the stented artery region. At room temperature (25 °C), optical microscopy of the suspension model's aggregation process was carried out in the external magnetic field. According to the optical microscopy pictures, the PEG_MNC particles form long linear aggregates due to dipolar magnetic interactions when there is an external magnetic field. During magnetic particle targeting, 20 mL of the model suspensions are injected (at a constant flow rate of 39.6 mL/min for the period of 30 s) by the syringe pump in the mean flow (flow velocity is Um = 0.25 m/s, corresponding to the Reynolds number of Re = 232) into the stented artery model. The PEG_MNC clusters are attracted by the magnetic forces (generated by the permanent external magnet) and captured around the stent struts and the bottom artery wall before and inside the implanted stent. The colloidal interaction among the MNC clusters was investigated by calculating the electrostatic repulsion, van der Waals and magnetic dipole-dipole energies. The current work offers essential details about PEG_MNCs aggregation and chain structure development in the presence of an external magnetic field and the process underlying this structure formation.}, }
@article {pmid36144168, year = {2022}, author = {Mostefa, T and Eddine, AD and Tayeb, NT and Hossain, S and Rahman, A and Mohamed, B and Kim, KY}, title = {Kinematic Properties of a Twisted Double Planetary Chaotic Mixer: A Three-Dimensional Numerical Investigation.}, journal = {Micromachines}, volume = {13}, number = {9}, pages = {}, pmid = {36144168}, issn = {2072-666X}, abstract = {In this study, a numerical investigation based on the CFD method is carried out to study the unsteady laminar flow of Newtonian fluid with a high viscosity in a three-dimensional simulation of a twisted double planetary mixer, which is composed of two agitating rods inside a moving tank. The considered stirring protocol is a "Continuous sine squared motion" by using the dynamic mesh model and user-defined functions (UDFs)to define the velocity profiles. The chaotic advection is obtained in our active mixers by the temporal modulation of rotational velocities of the moving walls in order to enhance the mixing of the fluid for a low Reynolds number and a high Peclet number. For this goal, we applied the Poincaré section and Lyapunov exponent as reliable mathematic tools for checking mixing quality by tracking a number of massless particles inside the fluid domain. Additionally, we investigated the development of fluid kinematics proprieties, such as vorticity, helicity, strain rate and elongation rate, at various time periods in order to view the impact of temporal modulation on the flow properties. The results of the mentioned simulation showed that it is possible to obtain a chaotic advection after a relatively short time, which can deeply enhance mixing fluid efficiency.}, }
@article {pmid36144120, year = {2022}, author = {Ahmed, MF and Zaib, A and Ali, F and Bafakeeh, OT and Khan, NB and Mohamed Tag-ElDin, ES and Oreijah, M and Guedri, K and Galal, AM}, title = {Cattaneo-Christov Double Diffusion (CCDD) on Sutterby Nanofluid with Irreversibility Analysis and Motile Microbes Due to a RIGA Plate.}, journal = {Micromachines}, volume = {13}, number = {9}, pages = {}, pmid = {36144120}, issn = {2072-666X}, abstract = {In this article, a Riga plate is exhibited with an electric magnetization actuator consisting of permanent magnets and electrodes assembled alternatively. This Riga plate creates an electric and magnetic field, where a transverse Lorentz force is generated that contributes to the flow along the plate. A new study field has been created by Sutterby nanofluid flows down the Riga plate, which is crucial to the creation of several industrial advancements, including thermal nuclear reactors, flow metres, and nuclear reactor design. This article addresses the second law analysis of MHD Sutter by nanofluid over a stretching sheet with the Riga plate. The Cattaneo-Christov Double Diffusion heat and mass flux have been created to examine the behaviour of relaxation time. The bioconvection of motile microorganisms and chemical reactions are taken into consideration. Similarity transformations are used to make the governing equations non-dimensional ordinary differential equations (ODE's) that are subsequently solved through an efficient and powerful analytic technique, the homotopy analysis method (HAM). The effect of pertained variables on velocity, temperature, concentration, and motile microorganism distributions are elaborated through the plot in detail. Further, the velocity distribution enhances and reduces for greater value Deborah number and Reynold number for the two cases of pseudoplastic and dilatant flow. Microorganism distribution decreases with the augmented magnitude of Peclet number (Pe), Bioconvection Lewis number (Lb), and microorganism concentration difference number (ϖ). The entropy production distribution is increased for the greater estimations of the Reynolds number (ReL) and Brinkman parameter (Br). Two sets of graphical outputs are presented for the Sutterby fluid parameter. Finally, for the justification of these outcomes, tables of comparison are made with various variables.}, }
@article {pmid36143998, year = {2022}, author = {Juraeva, M and Kang, DJ}, title = {Mixing Performance of the Modified Tesla Micromixer with Tip Clearance.}, journal = {Micromachines}, volume = {13}, number = {9}, pages = {}, pmid = {36143998}, issn = {2072-666X}, support = {Bokuk2022//Bokuk/ ; }, abstract = {A passive micromixer based on the modified Tesla mixing unit was designed by embedding tip clearance above the wedge-shape divider, and its mixing performance was simulated over a wider range of the Reynolds numbers from 0.1 to 80. The mixing performance was evaluated in terms of the degree of mixing (DOM) at the outlet and the required pressure load between inlet and outlet. The height of tip clearance was varied from 40 μm to 80 μm, corresponding to 25% to 33% of the micromixer depth. The numerical results show that the mixing enhancement by the tip clearance is noticeable over a wide range of the Reynolds numbers Re < 50. The height of tip clearance is optimized in terms of the DOM, and the optimum value is roughly h = 60 μm. It corresponds to 33% of the present micromixer depth. The mixing enhancement in the molecular diffusion regime of mixing, Re ≤ 1, is obtained by drag and connection of the interface in the two sub-streams of each Tesla mixing unit. It appears as a wider interface in the tip clearance zone. In the intermediate range of the Reynolds number, 1 < Re ≤ 50, the mixing enhancement is attributed to the interaction of the flow through the tip clearance and the secondary flow in the vortex zone of each Tesla mixing unit. When the Reynolds number is larger than about 50, vortices are formed at various locations and drive the mixing in the modified Tesla micromixer. For the Reynolds number of Re = 80, a pair of vortices is formed around the inlet and outlet of each Tesla mixing unit, and it plays a role as a governing mechanism in the convection-dominant regime of mixing. This vortex pattern is little affected as long as the tip clearance remains smaller than about h = 70 μm. The DOM at the outlet is little enhanced by the presence of tip clearance for the Reynolds numbers Re ≥ 50. The tip clearance contributes to reducing the required pressure load for the same value of the DOM.}, }
@article {pmid36135913, year = {2022}, author = {Yokoyama, F and Nakajima, M and Ichikawa, S}, title = {Analysis of Calcium Sulfate Scaling Phenomena on Reverse Osmosis Membranes by Scaling-Based Flux Model.}, journal = {Membranes}, volume = {12}, number = {9}, pages = {}, pmid = {36135913}, issn = {2077-0375}, abstract = {In this study, the behavior of permeate flux decline due to scale precipitation of calcium sulfate on reverse osmosis membranes was investigated. The proposed scaling-based flux model is able to explain that permeate fluxes attributed to three mechanisms of scale precipitation-cake formation, surface blockage, and mixed crystallization-converge to the same newly defined scaling-based critical flux. In addition, a scaling index is defined, which determines whether scale precipitates on the membrane. The experimental results were analyzed based on this index. The mass-transfer coefficients of flat membrane cells used in the experiments were measured and, although the coefficients differed, they could be summarized in the same form as the Leveque equation. Considering the results of the scale precipitation experiments, where the operating conditions of pressure, solute concentration, temperature, and Reynolds number were varied, the convergent values of the permeate fluxes are explained by the scaling-based critical fluxes and the scale precipitation zones by the scaling indexes.}, }
@article {pmid36120040, year = {2022}, author = {Shakeel, MR and Mokheimer, EMA}, title = {Numerical Study of Stratified Flames Using Reynolds Averaged Navier Stokes Modeling.}, journal = {ACS omega}, volume = {7}, number = {36}, pages = {31822-31833}, pmid = {36120040}, issn = {2470-1343}, abstract = {Reynolds averaged Navier Stokes technique was used to develop a validated numerical model for stratified flames. The validation was carried out with the experimental data of the non-swirl flames of the Cambridge dual annulus swirl burner. The RNG k-ε turbulence model along with the SG-35 skeletal chemical mechanism was found to give a good prediction of scalar and vector quantities while resulting in the reduction of computational time by 99.75% in comparison with that required for large eddy simulation techniques used in the literature. The effect of stratification at a constant input power, global equivalence ratio, and Reynolds number was examined. At stratification ratios (SRs = ϕin/ϕout) 1 and 2, intense burning, marked by the higher OH concentration, was observed close to the bluff body. Beyond SR = 2, the region of intense burning shifts downstream away from the bluff body. This is a result of the high equivalence ratio in the inner annulus, which is beyond the rich flammability limit of methane-air flames, and as a result, the primary flame region is shifted downstream after the mixtures from inner and outer annulus have mixed properly to produce a mixture with the equivalence ratio in the flammability limit. The maximum temperature was found to increase by 24.1% when the SR is increased from 1 to 2 and the combustion efficiency was found to significantly improve by 267%. The highest maximum temperature of 2249 K is observed for the mildly stratified flame at SR = 2. Beyond SR = 2, the maximum temperature decreases, while the combustion efficiency increases slightly.}, }
@article {pmid36119891, year = {2022}, author = {Kotnurkar, AS and Talawar, VT}, title = {Influence of thermal jump and inclined magnetic field on peristaltic transport of Jeffrey fluid with silver nanoparticle in the eccentric annulus.}, journal = {Heliyon}, volume = {8}, number = {9}, pages = {e10543}, pmid = {36119891}, issn = {2405-8440}, abstract = {This study investigates the impacts of thermal jump and inclined magnetic field on the peristaltic transport of Jeffrey fluid containing silver nanoparticles in the eccentric annuls under the long wavelength and low Reynolds number assumption. In medical studies, the impact of thermal jumps and slanted magnetic fields on public health is of interest. Peristaltic motion's ability to transmit heat and create a magnetic field has several uses in biomedical and bioengineering. The non-Newtonian Jeffrey fluid with silver nanoparticles is considered in the space between two cylindrical tubes that are eccentrically aligned. The homotopic perturbation method is semi-analytical for modeling and nonlinear partial differential equations (HPM). Analytical solutions for velocity, pressure gradient, and pressure rise were found. To show how physical parameters affect temperature, velocity, concentration, frictional force, and pressure rise of inner and outer tubes were plotted. A comparison of the present method with the exact solution for temperature and nanoparticle concentration profile is shown graphically. The present analysis of analytical solution approaches to the exact solution. The most significant thing in the current investigation is that the Hartmann number and thermophoresis number make the velocity profile decline. Jeffrey fluid parameter and magnetic field angle make the velocity rise. The nanofluid's temperature rises as a result of the thermal jump. In addition, the Jeffrey nanofluid has a higher momentum and temperature than the Jeffrey fluid. This analysis can better evaluate the syringe's injection speed and fluid flow features during cancer treatment, artery blockage removal, and reduced bleeding throughout the surgery.}, }
@article {pmid36115732, year = {2023}, author = {Akram, J and Akbar, NS and Tripathi, D}, title = {Blood-based graphene oxide nanofluid flow through capillary in the presence of electromagnetic fields: A Sutterby fluid model.}, journal = {Microvascular research}, volume = {145}, number = {}, pages = {104435}, doi = {10.1016/j.mvr.2022.104435}, pmid = {36115732}, issn = {1095-9319}, abstract = {Pumping devices with the electrokinetics phenomena are important in many microscale transport phenomena in physiology. This study presents a theoretical and numerical investigation on the peristaltic pumping of non-Newtonian Sutterby nanofluid through capillary in presence of electromagnetohydrodynamics. Here blood (Sutterby fluid) is taken as a base fluid and nanofluid is prepared by the suspension of graphene oxide nanoparticles in blood. Graphene oxide is extremely useful in the medical domain for drug delivery and cancer treatment. The modified Buongiorno model for nanofluids and Poisson-Boltzmann ionic distribution is adopted for the formulation of the present problem. Constitutive flow equations are linearized by the implementation of approximations of low Reynolds number, large wavelength, and the Debye-Hückel linearization. The numerical solution of reduced coupled and nonlinear set of equations is computed through Mathematica and graphical illustration is presented. Further, the impacts of buoyancy forces, thermal radiation, and mixed convection are also studied. It is revealed in this investigation that the inclusion of a large number of nanoparticles alters the flow characteristics significantly and boosts the heat transfer mechanism. Moreover, the pumping power of the peristaltic pump can be enhanced by the reduction in the width of the electric double layer which can be done by altering the electrolyte concentration.}, }
@article {pmid36112448, year = {2022}, author = {Serafini, F and Battista, F and Gualtieri, P and Casciola, CM}, title = {Drag Reduction in Turbulent Wall-Bounded Flows of Realistic Polymer Solutions.}, journal = {Physical review letters}, volume = {129}, number = {10}, pages = {104502}, doi = {10.1103/PhysRevLett.129.104502}, pmid = {36112448}, issn = {1079-7114}, mesh = {*DNA ; Friction ; *Polymers ; Viscosity ; }, abstract = {Suspensions of DNA macromolecules (0.8 wppm, 60 kbp), modeled as finitely extensible nonlinear elastic dumbbells coupled to the Newtonian fluid, show drag reduction up to 27% at friction Reynolds number 180, saturating at the previously unachieved Weissenberg number ≃10^{4}. At a large Weissenberg number, the drag reduction is entirely induced by the fully stretched polymers, as confirmed by the extensional viscosity field. The polymer extension is strongly non-Gaussian, in contrast to the assumptions of classical viscoelastic models.}, }
@article {pmid36109998, year = {2022}, author = {Parfenyev, V}, title = {Profile of a two-dimensional vortex condensate beyond the universal limit.}, journal = {Physical review. E}, volume = {106}, number = {2-2}, pages = {025102}, doi = {10.1103/PhysRevE.106.025102}, pmid = {36109998}, issn = {2470-0053}, abstract = {It is well known that an inverse turbulent cascade in a finite (2π×2π) two-dimensional periodic domain leads to the emergence of a system-sized coherent vortex dipole. We report a numerical hyperviscous study of the spatial vorticity profile inside one of the vortices. The exciting force was shortly correlated in time, random in space, and had a correlation length l_{f}=2π/k_{f} with k_{f} ranging from 100 to 12.5. Previously, it was found that in the asymptotic limit of small-scale forcing, the vorticity exhibits the power-law behavior Ω(r)=(3ε/α)^{1/2}r^{-1}, where r is the distance to the vortex center, α is the bottom friction coefficient, and ε is the inverse energy flux. Now we show that for a spatially homogeneous forcing with finite k_{f} the vorticity profile becomes steeper, with the difference increasing with the pumping scale but decreasing with the Reynolds number at the forcing scale. Qualitatively, this behavior is related to a decrease in the effective pumping of the coherent vortex with distance from its center. To support this statement, we perform an additional simulation with spatially localized forcing, in which the effective pumping of the coherent vortex, on the contrary, increases with r, and show that in this case the vorticity profile can be flatter than the asymptotic limit.}, }
@article {pmid36109911, year = {2022}, author = {Koyano, Y and Kitahata, H}, title = {Anomalous diffusion and transport by a reciprocal convective flow.}, journal = {Physical review. E}, volume = {106}, number = {2-1}, pages = {024102}, doi = {10.1103/PhysRevE.106.024102}, pmid = {36109911}, issn = {2470-0053}, abstract = {Under low-Reynolds-number conditions, dynamics of convection and diffusion are usually considered separately because their dominant spatial and temporal scales are different, but cooperative effects of convection and diffusion can cause diffusion enhancement [Koyano et al., Phys. Rev. E 102, 033109 (2020)2470-004510.1103/PhysRevE.102.033109]. In this paper, such cooperative effects are investigated in detail. Numerical simulations based on the convection-diffusion equation revealed that anisotropic diffusion and net shift as well as diffusion enhancement occur under a reciprocal flow. Such anomalous diffusion and transport are theoretically derived by the analyses of the Langevin dynamics.}, }
@article {pmid36109885, year = {2022}, author = {Agrawal, V and Mitra, D}, title = {Chaos and irreversibility of a flexible filament in periodically driven Stokes flow.}, journal = {Physical review. E}, volume = {106}, number = {2-2}, pages = {025103}, doi = {10.1103/PhysRevE.106.025103}, pmid = {36109885}, issn = {2470-0053}, abstract = {The flow of Newtonian fluid at low Reynolds number is, in general, regular and time-reversible due to absence of nonlinear effects. For example, if the fluid is sheared by its boundary motion that is subsequently reversed, then all the fluid elements return to their initial positions. Consequently, mixing in microchannels happens solely due to molecular diffusion and is very slow. Here, we show, numerically, that the introduction of a single, freely floating, flexible filament in a time-periodic linear shear flow can break reversibility and give rise to chaos due to elastic nonlinearities, if the bending rigidity of the filament is within a carefully chosen range. Within this range, not only the shape of the filament is spatiotemporally chaotic, but also the flow is an efficient mixer. Overall, we find five dynamical phases: the shape of a stiff filament is time-invariant-either straight or buckled; it undergoes a period-two bifurcation as the filament is made softer; becomes spatiotemporally chaotic for even softer filaments but, surprisingly, the chaos is suppressed if bending rigidity is decreased further.}, }
@article {pmid36089943, year = {2022}, author = {Bohm, S and Phi, HB and Moriyama, A and Runge, E and Strehle, S and König, J and Cierpka, C and Dittrich, L}, title = {Highly efficient passive Tesla valves for microfluidic applications.}, journal = {Microsystems &amp; nanoengineering}, volume = {8}, number = {}, pages = {97}, pmid = {36089943}, issn = {2055-7434}, abstract = {A multistage optimization method is developed yielding Tesla valves that are efficient even at low flow rates, characteristic, e.g., for almost all microfluidic systems, where passive valves have intrinsic advantages over active ones. We report on optimized structures that show a diodicity of up to 1.8 already at flow rates of 20 μl s[-] [1] corresponding to a Reynolds number of 36. Centerpiece of the design is a topological optimization based on the finite element method. It is set-up to yield easy-to-fabricate valve structures with a small footprint that can be directly used in microfluidic systems. Our numerical two-dimensional optimization takes into account the finite height of the channel approximately by means of a so-called shallow-channel approximation. Based on the three-dimensionally extruded optimized designs, various test structures were fabricated using standard, widely available microsystem manufacturing techniques. The manufacturing process is described in detail since it can be used for the production of similar cost-effective microfluidic systems. For the experimentally fabricated chips, the efficiency of the different valve designs, i.e., the diodicity defined as the ratio of the measured pressure drops in backward and forward flow directions, respectively, is measured and compared to theoretical predictions obtained from full 3D calculations of the Tesla valves. Good agreement is found. In addition to the direct measurement of the diodicities, the flow profiles in the fabricated test structures are determined using a two-dimensional microscopic particle image velocimetry (μPIV) method. Again, a reasonable good agreement of the measured flow profiles with simulated predictions is observed.}, }
@article {pmid36080113, year = {2022}, author = {Xiao, X and Li, G and Liu, T and Gu, M}, title = {Experimental Study of the Jetting Behavior of High-Viscosity Nanosilver Inks in Inkjet-Based 3D Printing.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {17}, pages = {}, pmid = {36080113}, issn = {2079-4991}, support = {52005263//National Natural Science Foundation of China/ ; BK20190466//Natural Science Foundation of Jiangsu Province/ ; }, abstract = {Inkjet printing of high-viscosity (up to 10[5] mPa·s) nanosilver inks is an interesting emerging technology to achieve the 3D fully printed fabrication of electronic products. The highly viscous force of the ink makes it impossible to achieve droplet ejection with the traditional piezoelectric-driven drop-on-demand inkjet method. In this study, a pneumatic needle jetting valve is adopted to provide sufficient driving force. A large number of high-viscosity inkjet printing tests are carried out, and the jetting behavior is recorded with a high-speed camera. Different jetting states are determined according to the recorded images, and the causes of their formation are revealed. Additionally, the effects of the operating pressure, preload angle, and fluid pressure on jetting states are elucidated. Furthermore, the jetting phase diagram is obtained with the characterization of the Reynolds number and the printable region is clarified. This provides a better understanding of high-viscosity inkjet printing and will promote the application of high-viscosity inkjet printing in 3D fully printed electronic products.}, }
@article {pmid36067311, year = {2022}, author = {Zhao, D and Bittner, B and Clifton, G and Gravish, N and Revzen, S}, title = {Walking is like slithering: A unifying, data-driven view of locomotion.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {119}, number = {37}, pages = {e2113222119}, pmid = {36067311}, issn = {1091-6490}, mesh = {Animals ; Biomechanical Phenomena ; Foot ; Friction ; Gait ; *Locomotion ; *Models, Biological ; *Walking ; }, abstract = {Legged movement is ubiquitous in nature and of increasing interest for robotics. Most legged animals routinely encounter foot slipping, yet detailed modeling of multiple contacts with slipping exceeds current simulation capacity. Here we present a principle that unifies multilegged walking (including that involving slipping) with slithering and Stokesian (low Reynolds number) swimming. We generated data-driven principally kinematic models of locomotion for walking in low-slip animals (Argentine ant, 4.7% slip ratio of slipping to total motion) and for high-slip robotic systems (BigANT hexapod, slip ratio 12 to 22%; Multipod robots ranging from 6 to 12 legs, slip ratio 40 to 100%). We found that principally kinematic models could explain much of the variability in body velocity and turning rate using body shape and could predict walking behaviors outside the training data. Most remarkably, walking was principally kinematic irrespective of leg number, foot slipping, and turning rate. We find that grounded walking, with or without slipping, is governed by principally kinematic equations of motion, functionally similar to frictional swimming and slithering. Geometric mechanics thus leads to a unified model for swimming, slithering, and walking. Such commonality may shed light on the evolutionary origins of animal locomotion control and offer new approaches for robotic locomotion and motion planning.}, }
@article {pmid36056085, year = {2022}, author = {Hasegawa, M and Chen, YC and Sakaue, H}, title = {Drag reduction study of a microfiber-coated cylinder.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {15022}, pmid = {36056085}, issn = {2045-2322}, abstract = {Drag reduction for a bluff body is imperative in a time of increasing awareness of the environmental impact and sustainability of air travel. Microfiber coating has demonstrated its ability to reduce drag on a bluff body. This was done by applying strips of the coating to a cylinder. To widen the application range of the microfiber coating, a fully microfiber-coated cylinder is studied as it has no directionality relative to incoming flow. It is hypothesized that a large coating coverage will cause a reduction in drag dependent on the Reynolds number Re. The fully microfiber-coated cylinder is studied in a wind tunnel and the drag coefficient is determined at a range of Re in the subcritical-flow regime. It is found that the drag coefficient of the microfiber-coated cylinder is a function of Re, and the critical Reynolds number, where the maximum drag reduction occurs, is lower for a microfiber-coated cylinder compared to that of a conventional smooth-surface cylinder.}, }
@article {pmid36050069, year = {2022}, author = {Bearden, KP and Padilla, VE and Taubert, L and Craig, SA}, title = {Calibration and performance characterization of a Mach 5 Ludwieg tube.}, journal = {The Review of scientific instruments}, volume = {93}, number = {8}, pages = {085104}, doi = {10.1063/5.0093052}, pmid = {36050069}, issn = {1089-7623}, abstract = {Calibration, commissioning, and design features of a new Mach 5 Ludwieg Tube wind tunnel at the University of Arizona are discussed. Mach number uniformity and free-stream noise levels are measured using a Pitot rake at a range of unit Reynolds numbers and at multiple spanwise and streamwise positions. The wind tunnel is shown to have a free-stream Mach number of 4.82 with maximum variance less than 0.8% (and less than 0.5% at most streamwise positions). The average free-stream acoustic noise level in the core (based on Pitot pressure) is shown to be less than 1.2% at an intermediate Reynolds number with some regions dropping locally below 1.0%. The core flow region is measured to be 282.4 mm (11.1 in.) in diameter at the nozzle exit.}, }
@article {pmid36044879, year = {2022}, author = {Luo, Y and Xiao, Q and Zhu, Q and Pan, G}, title = {Thrust and torque production of a squid-inspired swimmer with a bent nozzle for thrust vectoring.}, journal = {Bioinspiration &amp; biomimetics}, volume = {17}, number = {6}, pages = {}, doi = {10.1088/1748-3190/ac8e3f}, pmid = {36044879}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; *Decapodiformes ; *Swimming ; Torque ; Viscosity ; }, abstract = {A three-dimensional pulsed-jet propulsion model consisting of a flexible body and a steerable bent nozzle in tethered mode is presented and studied numerically. By prescribing the body deformation and nozzle angle, we examine the flow evolution and propulsive/turning performance via thrust vectoring. Our results show that the vortex ring is no longer axis-symmetric when the jet is ejected at an angle with the incoming flow. A torque peak is observed during jetting, which is mainly sourced from the suction force (negative pressure) at the lower part of the internal nozzle surface when the flow is directed downward through an acute angle. After this crest, the torque is dominated by the positive pressure at the upper part of the internal nozzle surface, especially at a relatively low jet-based Reynolds number (O(10[2])). The torque production increases with a larger nozzle bent angle as expected. Meanwhile, the thrust production remains almost unchanged, showing little trade-off between thrust and torque production which demonstrates the advantage of thrust vectoring via a bent nozzle. By decoupling the thrust at the internal and outer surfaces considering special characteristics of force generation by pulsed-jet propulsion, we find that variations in Reynolds number mostly affect the viscous friction at the outer surfaces. The influence of the maximum stroke ratio is also studied. Results show that both the time-averaged thrust and the torque decrease at a larger stroke ratio.}, }
@article {pmid36043842, year = {2022}, author = {Werwinski, S and Wharton, JA and Nie, M and Stokes, KR}, title = {Monitoring Aerobic Marine Bacterial Biofilms on Gold Electrode Surfaces and the Influence of Nitric Oxide Attachment Control.}, journal = {Analytical chemistry}, volume = {94}, number = {36}, pages = {12323-12332}, pmid = {36043842}, issn = {1520-6882}, mesh = {Biofilms ; Electrodes ; *Gold/pharmacology ; *Nitric Oxide/metabolism ; Nitric Oxide Donors/pharmacology ; }, abstract = {Detection of aerobic marine bacterial biofilms using electrochemical impedance spectroscopy has been done to monitor the interfacial response of Pseudoalteromonas sp. NCIMB 2021 attachment and growth in order to identify characteristic events on a 0.2 mm diameter gold electrode surface. Uniquely, the applicability of surface charge density has been proven to be valuable in determining biofilm attachment and cell enumeration over a 72 h duration on a gold surface within a modified continuous culture flow cell (a controlled low laminar flow regime with Reynolds number ≈ 1). In addition, biofilm dispersal has been evaluated using 500 nM sodium nitroprusside, a nitric oxide donor (nitric oxide is important for the regulation of several diverse biological processes). Ex situ confocal microscopy studies have been performed to confirm biofilm coverage and morphology, plus the determination and quantification of the nitric oxide biofilm dispersal effects. Overall, the capability of the sensor to electrochemically detect the presence of initial bacterial biofilm formation and extent has been established and shown to have potential for real-time biofilm monitoring.}, }
@article {pmid36036196, year = {2022}, author = {Khan, M and Sarfraz, M and Mehmood, S and Ullah, MZ}, title = {Irreversibility process analysis for SiO2-MoS2/water-based flow over a rotating and stretching cylinder.}, journal = {Journal of applied biomaterials &amp; functional materials}, volume = {20}, number = {}, pages = {22808000221120329}, doi = {10.1177/22808000221120329}, pmid = {36036196}, issn = {2280-8000}, mesh = {Entropy ; *Hydrodynamics ; *Nanostructures ; Nanotechnology ; Water ; }, abstract = {Entropy is the measure of the amount of energy in any physical system that is not accessible for the useful work, which causes a decrease in a system's thermodynamic efficiency. The idea of entropy generation analysis plays a vital role in characterizing the evolution of thermal processes and minimizing the impending loss of available mechanical power in thermo-fluid systems from an analytical perspective. It has a wide range of applications in biological, information, and engineering systems, such as transportation, telecommunication, and rate processes. The analysis of the entropy generation of axisymmetric magnetohydrodynamic hybrid nanofluid (SiO2-MoS2)/water flow induced by rotating and stretching cylinder in the presence of heat radiation, ohmic heating, and the magnetic field is focus of this study. Thermal energy transport of hybrid nanofluids is performed by applying the Maxwell model. Heat transport is carried out by using convective boundary condition. The dimensionless ordinary differential equations are acquired by similarity transformations. The numerical solution for these differential equations is obtained by the bvp4c program in MATLAB. A comparison between nanofluid and hybrid nanofluid is made for flow field, temperature, and entropy generation. Comparison of nanofluid flow with hybrid nanofluid flow exhibits a higher rate of heat transmission, while entropy generation exhibits the opposite behavior. It is observed that the flow and heat distribution increase as the solid volume fraction's value grows. An increase in entropy is indicated by augmentation in the Brinkman number and temperature ratio parameter, but the Bejan number shows a declining trend. Furthermore, outcomes of the Nusselt number for hybrid nanofluid and nanofluid are calculated for various parameters. It is noticed that the Nusselt number is reduced for enlarging the magnetic field and Eckert number. The axial and azimuthal wall stress parameters are declined by augmenting the Reynolds number.}, }
@article {pmid36031990, year = {2022}, author = {Saeed, A and Shah, RA and Khan, MS and Fernandez-Gamiz, U and Bani-Fwaz, MZ and Noeiaghdam, S and Galal, AM}, title = {Theoretical analysis of unsteady squeezing nanofluid flow with physical properties.}, journal = {Mathematical biosciences and engineering : MBE}, volume = {19}, number = {10}, pages = {10176-10191}, doi = {10.3934/mbe.2022477}, pmid = {36031990}, issn = {1551-0018}, abstract = {Theoretical analysis of physical characteristics of unsteady, squeezing nanofluid flow is studied. The flow of nanofluid between two plates that placed parallel in a rotating system by keeping the variable physical properties: viscosity and thermal conductivity. It is analyzed by using Navier Stokes Equation, Energy Equation and Concentration equation. The prominent equations are transformed by virtue of suitable similarity transformation. Nanofluid model includes the important effects of Thermophoresis and Brownian motion. For analysis graphical results are drawn for verity parameters of our interest i.e., Injection parameter, Squeezing number, Prandtle number and Schmidt number are investigated for the Velocity field, Temperature variation and Concentration profile numerically. The findings underline that the parameter of skin friction increases when the Squeezing Reynolds number, Injection parameter and Prandtle number increases. However, it shows inverse relationship with Schmidt number and Rotation parameter. Furthermore, direct relationship of Nusselt number with injection parameter and Reynolds number is observed while its relation with Schmidt number, Rotation parameter, Brownian parameter and Thermophoretic parameter shows an opposite trend. The results are thus obtained through Parametric Continuation Method (PCM) which is further validated through BVP4c. Moreover, the results are tabulated and set forth for comparison of findings through PCM and BVP4c which shows that the obtained results correspond to each other.}, }
@article {pmid36030369, year = {2023}, author = {Marfoglio, S and Kovarovic, B and Fiorella, DJ and Sadasivan, C}, title = {A novel angiographic method to estimate arterial blood flow rates using contrast reflux: Effect of injection parameters.}, journal = {Medical physics}, volume = {50}, number = {1}, pages = {259-273}, doi = {10.1002/mp.15948}, pmid = {36030369}, issn = {2473-4209}, mesh = {Reproducibility of Results ; *Arteries/physiology ; *Contrast Media ; Angiography ; Injections ; }, abstract = {BACKGROUND: Contrast reflux, which is the retrograde movement of contrast against flow direction, is commonly observed during angiography. Despite a vast body of literature on angiography, the hemodynamic factors affecting contrast reflux have not been studied. Numerous methods have been developed to extract flow from angiography, but the reliability of these methods is not yet sufficient to be of routine clinical use.<br><br>PURPOSE: To evaluate the effect of baseline blood flow rates and injection conditions on the extent of contrast reflux. To estimate arterial flow rates based on measurement of contrast reflux length.<br><br>MATERIALS AND METHODS: Iodinated contrast was injected into an idealized tube as well as a physiologically accurate model of the cervico-cerebral vasculature. A total of 194 high-speed angiograms were acquired under varying "blood" flow rates and injection conditions (catheter size, injection rate, and injection time). The length of contrast reflux was compared to the input variables and to dimensionless fluid dynamics parameters at the catheter-tip. Arterial blood flow rates were estimated using contrast reflux length as well as a traditional transit-time method and compared to measured flow rates.<br><br>RESULTS: Contrast reflux lengths were significantly affected by contrast injection rate (p < 0.0001), baseline blood flow rate (p&#xa0;= 0.0004), and catheter size (p&#xa0;= 0.04), but not by contrast injection time (p&#xa0;= 0.4). Reflux lengths were found to be correlated to dimensionless fluid dynamics parameters by an exponential function (R[2] &#xa0;= 0.6-0.99). When considering the entire dataset in unison, flow estimation errors with the reflux-length method (39% &#xb1; 33%) were significantly higher (p&#xa0;= 0.003) than the transit-time method (33% &#xb1; 36%). However, when subgrouped by catheter, the error with the reflux-length method was substantially reduced and was significantly lower (14% &#xb1; 14%, p < 0.0001) than the transit-time method.<br><br>CONCLUSION: Results show correlations between contrast reflux length and baseline hemodynamic parameters that have not been reported previously. Clinically relevant blood flow rate estimation is feasible by simple measurement of reflux length. In vivo and clinical studies are required to confirm these correlations and to refine the methodology of estimating blood flow by reflux.}, }
@article {pmid36014668, year = {2022}, author = {Shi, R and Lin, J and Yang, H}, title = {Particle Distribution and Heat Transfer of SiO2/Water Nanofluid in the Turbulent Tube Flow.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {16}, pages = {}, pmid = {36014668}, issn = {2079-4991}, support = {12132015//National Natural Science Foundation of China/ ; }, abstract = {In order to clarify the effect of particle coagulation on the heat transfer properties, the governing equations of nanofluid together with the equation for nanoparticles in the SiO2/water nanofluid flowing through a turbulent tube are solved numerically in the range of Reynolds number 3000 ≤ Re ≤ 16,000 and particle volume fraction 0.005 ≤ φ ≤ 0.04. Some results are validated by comparing with the experimental results. The effect of particle convection, diffusion, and coagulation on the pressure drop ∆P, particle distribution, and heat transfer of nanofluid are analyzed. The main innovation is that it gives the effect of particle coagulation on the pressure drop, particle distribution, and heat transfer. The results showed that ∆P increases with the increase in Re and φ. When inlet velocity is small, the increase in ∆P caused by adding particles is relatively large, and ∆P increases most obviously compared with the case of pure water when the inlet velocity is 0.589 m/s and φ is 0.004. Particle number concentration M0 decreases along the flow direction, and M0 near the wall is decreased to the original 2% and decreased by about 90% in the central area. M0 increases with increasing Re but with decreasing φ, and basically presents a uniform distribution in the core area of the tube. The geometric mean diameter of particle GMD increases with increasing φ, but with decreasing Re. GMD is the minimum in the inlet area, and gradually increases along the flow direction. The geometric standard deviation of particle diameter GSD increases sharply at the inlet and decreases in the inlet area, remains almost unchanged in the whole tube, and finally decreases rapidly again at the outlet. The effects of Re and φ on the variation in GSD along the flow direction are insignificant. The values of convective heat transfer coefficient h and Nusselt number Nu are larger for nanofluids than that for pure water. h and Nu increase with the increase in Re and φ. Interestingly, the variation in φ from 0.005 to 0.04 has little effect on h and Nu.}, }
@article {pmid36014601, year = {2022}, author = {Akram, S and Athar, M and Saeed, K and Razia, A and Alghamdi, M and Muhammad, T}, title = {Impact of Partial Slip on Double Diffusion Convection of Sisko Nanofluids in Asymmetric Channel with Peristaltic Propulsion and Inclined Magnetic Field.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {16}, pages = {}, pmid = {36014601}, issn = {2079-4991}, abstract = {The current article discusses the outcomes of the double diffusion convection of peristaltic transport in Sisko nanofluids along an asymmetric channel having an inclined magnetic field. Consideration is given to the Sisko fluid model, which can forecast both Newtonian and non-Newtonian fluid properties. Lubricating greases are the best examples of Sisko fluids. Experimental research shows that most realistic fluids, including human blood, paint, dirt, and other substances, correspond to Sisko's proposed definition of viscosity. Mathematical modelling is considered to explain the flow behavior. The simpler non-linear PEDs are deduced by using an elongated wavelength and a minimal Reynolds number. The expression is also numerically calculated. The impacts of the physical variables on the quantities of flow are plotted graphically as well as numerically. The results reveal that there is a remarkable increase in the concentration, temperature, and nanoparticle fraction with the rise in the Dufour and thermophoresis variables.}, }
@article {pmid36001259, year = {2023}, author = {Canli, E and Kucuksariyildiz, H and Carman, K}, title = {Impact assessment of new generation high-speed agricultural tractor aerodynamics on transportation fuel consumption and related phenomena.}, journal = {Environmental science and pollution research international}, volume = {30}, number = {3}, pages = {6658-6680}, pmid = {36001259}, issn = {1614-7499}, mesh = {*Accidents, Occupational ; *Transportation ; Agriculture ; Carbon ; Gravitation ; }, abstract = {New generation agricultural tractors contribute to transportation by increased travel speeds. There is not any available aerodynamic data on the authentic agricultural tractor form. On-road transportation by tractors is between 8 and 30% of their operational time. In this work, two agricultural tractors are modelled via computational fluid dynamics for nine different speeds to determine aerodynamic resistances. Constant speed travel scenarios are analyzed. Corresponding speeds are 5 and 10 to 80 km/h with 10 km/h increments. Reynolds number changes between 1.6 × 10[5] and 2.98 × 10[6]. The characteristic lengths are taken as the square root of the streamwise projected area of the tractor geometries. Aerodynamic forces exerted on the tractors change between 3 and 746 N. The calculated drag coefficients are found as independent from Reynolds number and are 0.6 and 0.78 for the two different types of driver compartments. The approximated aerodynamic related fuel consumptions for 1-h changes between 0.002 and 8.28 lt/s which correspond to 0.001 to 5.76 kg/s carbon emission. A potential improvement in decreasing aerodynamic resistance about 20% is discussed by spatial data. Since the conducted work is being regarded as the first instance in the literature, it is estimated that several consecutive reports will be triggered.}, }
@article {pmid35999194, year = {2022}, author = {Nan, K and Shi, Y and Zhao, T and Tang, X and Zhu, Y and Wang, K and Bai, J and Zhao, W}, title = {Mixing and Flow Transition in an Optimized Electrokinetic Turbulent Micromixer.}, journal = {Analytical chemistry}, volume = {94}, number = {35}, pages = {12231-12239}, doi = {10.1021/acs.analchem.2c02960}, pmid = {35999194}, issn = {1520-6882}, abstract = {Micromixer is a key element in a lab on a chip for broad applications in the analysis and measurement of chemistry and engineering. Previous investigations reported that electrokinetic (EK) turbulence could be realized in a "Y" type micromixer with a cross-sectional dimension of 100 μm order. Although the ultrafast turbulent mixing can be generated at a bulk flow Reynolds number on the order of unity, the micromixer has not been optimized. In this investigation, we systematically investigated the influence of electric field intensity, AC frequency, electric conductivity ratio, and channel width at the entrance on the mixing effect and transition electric Rayleigh number in the "Y" type electrokinetic turbulent micromixer. It is found that the optimal mixing is realized in a 350 μm wide micromixer, under 100 kHz and 1.14 × 10[5] V/m AC electric field, with an electric conductivity ratio of 1:3000. Under these conditions, a degree of mixedness of 0.93 can be achieved at 84 μm from the entrance and 100 ms. A further investigation of the critical electric field and the critical electric Rayleigh number indicates that the most unstable condition of EK flow instability is inconsistent with that of the optimal mixing in EK turbulence. To predict the evolution of EK flow under high Raσ and guide the design of EK turbulent micromixers, it is necessary to apply a computational turbulence model instead of linear instability analysis.}, }
@article {pmid35990482, year = {2022}, author = {Mondal, T and Hnaien, N and Ajmi, M and Ghachem, K and Kolsi, L}, title = {CFD Investigation of Thermal Characteristics for a Dual Jet with a Parallel Co-flow.}, journal = {ACS omega}, volume = {7}, number = {32}, pages = {27864-27875}, pmid = {35990482}, issn = {2470-1343}, abstract = {A combined turbulent wall jet and offset jet (also known as the dual jet) with and without the presence of a parallel co-flow stream is studied. The standard k-ω turbulence model is used to predict the turbulent flow. The study focuses on the effects of the co-flow velocity (CFV) on the heat-transfer characteristics of the dual jet flow with the bottom wall maintained at a constant wall temperature. The CFV is varied up to 40% of the jet inlet velocity, and the height of the offset jet is varied from 5 to 11 times the jet width with the inlet Reynolds number taken as 15,000. The heat-transfer results reveal that the local Nusselt number (Nu x) along the bottom wall exhibits a peak at the immediate downstream of the nozzle exit, followed by a continuous decay in the rest of the converging region before showing a small rise for a short streamwise distance in the merging region. Further downstream, in the combined region, Nu x gradually decreases with the downstream distance. Except the merging region, no influence of co-flow is observed in the other two flow zones (converging and combined regions). In the merging region, for a given offset ratio (OR), Nu x remains nearly constant for a certain axial distance, and it decreases as the CFV increases. As a result of the increase in the CFV, the average Nusselt number decreases, indicating a reduction in overall convective heat transfer for higher values of the CFV. A regression analysis among the average Nusselt number (), CFV, and OR results in a correlation function in the form of within the range OR = 5-11 and CFV = 0-40%.}, }
@article {pmid35965667, year = {2022}, author = {Wüthrich, D and Shi, R and Chanson, H}, title = {Hydraulic jumps with low inflow Froude numbers: air-water surface patterns and transverse distributions of two-phase flow properties.}, journal = {Environmental fluid mechanics (Dordrecht, Netherlands : 2001)}, volume = {22}, number = {4}, pages = {789-818}, pmid = {35965667}, issn = {1567-7419}, abstract = {ABSTRACT: Hydraulic jumps are commonly employed as energy dissipators to guarantee long-term operation of hydraulic structures. A comprehensive and in-depth understanding of their main features is therefore fundamental. In this context, the current study focused on hydraulic jumps with low Froude numbers, i.e. Fr1 = 2.1 and 2.4, at relatively high Reynolds number: Re ~2 × 10[5]. Experimental tests employed a combination of dual-tip phase-detection probes and ultra-high-speed video camera to provide a comprehensive characterisation of the main air-water flow properties of the hydraulic jump, including surface flow features, void fraction, bubble count rate and interfacial velocities. The current research also focused on the transverse distributions of air-water flow properties, i.e. across the channel width, with the results revealing lower values of void fraction and bubble count rate next to the sidewalls compared to the channel centreline data. Such a spatial variability in the transverse direction questions whether data near the side walls may be truly representative of the behaviour in the bulk of the flow, raising the issue of sidewall effects in image-based techniques. Overall, these findings provide new information to both researchers and practitioners for a better understanding of the physical processes inside the hydraulic jump with low Froude numbers, leading to an optimised design of hydraulic structures.<br><br>ARTICLE HIGHLIGHTS: Experimental investigation of air-water flow properties in hydraulic jumps with low Froude numbersDetailed description of the main air-water surface features on the breaking rollerTransversal distribution of the air-water flow properties across the channel width and comparison between centreline and sidewall.}, }
@article {pmid35958096, year = {2022}, author = {Mohanty, RK and Setia, N and Khurana, G and Manchanda, G}, title = {High precision compact numerical approximation in exponential form for the system of 2D quasilinear elliptic BVPs on a discrete irrational region.}, journal = {MethodsX}, volume = {9}, number = {}, pages = {101790}, pmid = {35958096}, issn = {2215-0161}, abstract = {This article presents a new approximation of order four in exponential form for two-dimensional (2D) quasilinear partial differential equation (PDE) of elliptic form with solution domain being irrational. It is further extended for application to a system of quasilinear elliptic PDEs with Dirichlet boundary conditions (DBCs). The main highlights of the method framed in this article are as under:•It uses a 9-point stencil with unequal mesh to approach the solution. The error analysis is discussed to authenticate the order of convergence of the proposed numerical approximation.•Various validating problems, for instance the Burgers' equation, Poisson equation in cylindrical coordinates, Navier-Stokes (NS) equations in rectangular and cylindrical coordinates are solved using the proposed techniques to depict their stability. The proposed approximation produces solution free of oscillations for large values of Reynolds Number in the vicinity of a singularity.•The results of the proposed method are superior in comparison to the existing methods of [49] and [56].}, }
@article {pmid35957150, year = {2022}, author = {Togun, H and Homod, RZ and Yaseen, ZM and Abed, AM and Dhabab, JM and Ibrahem, RK and Dhahbi, S and Rashidi, MM and Ahmadi, G and Yaïci, W and Mahdi, JM}, title = {Efficient Heat Transfer Augmentation in Channels with Semicircle Ribs and Hybrid Al2O3-Cu/Water Nanofluids.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {15}, pages = {}, pmid = {35957150}, issn = {2079-4991}, abstract = {Global technological advancements drive daily energy consumption, generating additional carbon-induced climate challenges. Modifying process parameters, optimizing design, and employing high-performance working fluids are among the techniques offered by researchers for improving the thermal efficiency of heating and cooling systems. This study investigates the heat transfer enhancement of hybrid "Al2O3-Cu/water" nanofluids flowing in a two-dimensional channel with semicircle ribs. The novelty of this research is in employing semicircle ribs combined with hybrid nanofluids in turbulent flow regimes. A computer modeling approach using a finite volume approach with k-ω shear stress transport turbulence model was used in these simulations. Six cases with varying rib step heights and pitch gaps, with Re numbers ranging from 10,000 to 25,000, were explored for various volume concentrations of hybrid nanofluids Al2O3-Cu/water (0.33%, 0.75%, 1%, and 2%). The simulation results showed that the presence of ribs enhanced the heat transfer in the passage. The Nusselt number increased when the solid volume fraction of "Al2O3-Cu/water" hybrid nanofluids and the Re number increased. The Nu number reached its maximum value at a 2 percent solid volume fraction for a Reynolds number of 25,000. The local pressure coefficient also improved as the Re number and volume concentration of "Al2O3-Cu/water" hybrid nanofluids increased. The creation of recirculation zones after and before each rib was observed in the velocity and temperature contours. A higher number of ribs was also shown to result in a larger number of recirculation zones, increasing the thermal performance.}, }
@article {pmid35926485, year = {2022}, author = {Bhattacharjee, A and Jabbarzadeh, M and Kararsiz, G and Fu, HC and Kim, MJ}, title = {Bacteria-inspired magnetically actuated rod-like soft robot in viscous fluids.}, journal = {Bioinspiration &amp; biomimetics}, volume = {17}, number = {6}, pages = {}, doi = {10.1088/1748-3190/ac870f}, pmid = {35926485}, issn = {1748-3190}, mesh = {Magnets ; Models, Biological ; *Robotics ; Swimming ; Viscosity ; }, abstract = {This paper seeks to design, develop, and explore the locomotive dynamics and morphological adaptability of a bacteria-inspired rod-like soft robot propelled in highly viscous Newtonian fluids. The soft robots were fabricated as tapered, hollow rod-like soft scaffolds by applying a robust and economic molding technique to a polyacrylamide-based hydrogel polymer. Cylindrical micro-magnets were embedded in both ends of the soft scaffolds, which allowed bending (deformation) and actuation under a uniform rotating magnetic field. We demonstrated that the tapered rod-like soft robot in viscous Newtonian fluids could perform two types of propulsion; boundary rolling was displayed when the soft robot was located near a boundary, and swimming was displayed far away from the boundary. In addition, we performed numerical simulations to understand the swimming propulsion along the rotating axis and the way in which this propulsion is affected by the soft robot's design, rotation frequency, and fluid viscosity. Our results suggest that a simple geometrical asymmetry enables the rod-like soft robot to perform propulsion in the low Reynolds number (Re≪ 1) regime; these promising results provide essential insights into the improvements that must be made to integrate the soft robots into minimally invasivein vivoapplications.}, }
@article {pmid35918493, year = {2022}, author = {Xiao, L and Liu, Q and Huang, W}, title = {Experimental research and analysis on the resistance characteristics of simulated ore bin in water.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {13211}, pmid = {35918493}, issn = {2045-2322}, support = {51774193//National Natural Science Foundation of China/ ; ZR2017MEE025//Shandong Provincial Natural Science Foundation/ ; }, abstract = {In order to research the variation law of the longitudinal resistance coefficient of the ore bin in the marine mining system under different length-diameter ratio, external shape, additional weight and Reynolds number, a set of experimental system for testing the resistance coefficient was designed and built independently. By analyzing the experimental results, it can be seen that under the same conditions, the resistance coefficient decreases gradually with the increase of Reynolds number and finally fluctuates around a certain value. Increasing the excitation displacement will reduce the overall resistance coefficient of the ore bin. The smaller the length-diameter ratio is, the larger the corresponding force value when the vibration acceleration of the ore bin is 0, and the larger the overall resistance coefficient is. The resistance coefficient of the cylindrical section is greater than that of the rectangular shape. In order to reduce the longitudinal vibration and the transverse towing offset, the shape of the ore bin should be cylindrical in actual design and production. At low Reynolds number, the increase of added weight will increase the resistance coefficient, while at high Reynolds number, the change of added weight will not cause the change of resistance coefficient.}, }
@article {pmid35912042, year = {2022}, author = {Ram, D and Bhandari, DS and Tripathi, D and Sharma, K}, title = {Propagation of H1N1 virus through saliva movement in oesophagus: a mathematical model.}, journal = {European physical journal plus}, volume = {137}, number = {7}, pages = {866}, pmid = {35912042}, issn = {2190-5444}, abstract = {H1N1 (Swine flu) is caused by the influenza A virus which belongs to the Orthomyxoviridae family. Influenza A is very harmful to the elderly, and people with chronic respiratory disease and cardiovascular disease. Therefore, it is essential to analyse the behaviour of virus transmission through the saliva movement in oesophagus. A mathematical paradigm is developed to study the saliva movement under the applications of transverse magnetic field. Jeffrey fluid model is considered for saliva to show the viscoelastic nature. The flow nature is considered creeping and assumptions of long wavelength and low Reynolds number are adopted for analytical solutions. The Basset-Boussinesq-Oseen equation is employed to understand the propagation of H1N1 virus through saliva under the effect of applicable forces such as gravity, virtual mass, basset force, and drag forces. The suitable data for saliva, oesophagus and H1N1 virus are taken from the existing literature for simulation of the results using MATLAB software. From the graphical results, it is observed that the susceptibility to viral infections is less because the magnetic field reduces the motion of the virus particle. Further, the chances of infections in males are more as compared to females and children due to variation in viscosity of saliva. Such findings provide an understanding of the mechanics of the virus floating through the saliva (viscoelastic fluids) in the oesophagus.}, }
@article {pmid35912036, year = {2022}, author = {Strazzullo, M and Girfoglio, M and Ballarin, F and Iliescu, T and Rozza, G}, title = {Consistency of the full and reduced order models for evolve-filter-relax regularization of convection-dominated, marginally-resolved flows.}, journal = {International journal for numerical methods in engineering}, volume = {123}, number = {14}, pages = {3148-3178}, pmid = {35912036}, issn = {0029-5981}, abstract = {Numerical stabilization is often used to eliminate (alleviate) the spurious oscillations generally produced by full order models (FOMs) in under-resolved or marginally-resolved simulations of convection-dominated flows. In this article, we investigate the role of numerical stabilization in reduced order models (ROMs) of marginally-resolved, convection-dominated incompressible flows. Specifically, we investigate the FOM-ROM consistency, that is, whether the numerical stabilization is beneficial both at the FOM and the ROM level. As a numerical stabilization strategy, we focus on the evolve-filter-relax (EFR) regularization algorithm, which centers around spatial filtering. To investigate the FOM-ROM consistency, we consider two ROM strategies: (i) the EFR-noEFR, in which the EFR stabilization is used at the FOM level, but not at the ROM level; and (ii) the EFR-EFR, in which the EFR stabilization is used both at the FOM and at the ROM level. We compare the EFR-noEFR with the EFR-EFR in the numerical simulation of a 2D incompressible flow past a circular cylinder in the convection-dominated, marginally-resolved regime. We also perform model reduction with respect to both time and Reynolds number. Our numerical investigation shows that the EFR-EFR is more accurate than the EFR-noEFR, which suggests that FOM-ROM consistency is beneficial in convection-dominated, marginally-resolved flows.}, }
@article {pmid35905362, year = {2022}, author = {Wang, X and Shih, HY and Goldenfeld, N}, title = {Stochastic Model for Quasi-One-Dimensional Transitional Turbulence with Streamwise Shear Interactions.}, journal = {Physical review letters}, volume = {129}, number = {3}, pages = {034501}, doi = {10.1103/PhysRevLett.129.034501}, pmid = {35905362}, issn = {1079-7114}, abstract = {The transition to turbulence in wall-bounded shear flows is typically subcritical, with a poorly understood interplay between spatial fluctuations, pattern formation, and stochasticity near the critical Reynolds number. Here, we present a spatially extended stochastic minimal model for the energy budget in transitional pipe flow, which successfully recapitulates the way localized patches of turbulence (puffs) decay, split, and grow, respectively, as the Reynolds number increases through the laminar-turbulent transition. Our approach takes into account the flow geometry, as we demonstrate by extending the model to quasi-one-dimensional Taylor-Couette flow, reproducing the observed directed percolation pattern of turbulent patches in space and time.}, }
@article {pmid35899947, year = {2022}, author = {Godeau, AL and Leoni, M and Comelles, J and Guyomar, T and Lieb, M and Delanoë-Ayari, H and Ott, A and Harlepp, S and Sens, P and Riveline, D}, title = {3D single cell migration driven by temporal correlation between oscillating force dipoles.}, journal = {eLife}, volume = {11}, number = {}, pages = {}, pmid = {35899947}, issn = {2050-084X}, mesh = {*Actins/metabolism ; Cell Movement/physiology ; Cell Nucleus/metabolism ; *Cell Polarity/physiology ; Myosins/metabolism ; }, abstract = {Directional cell locomotion requires symmetry breaking between the front and rear of the cell. In some cells, symmetry breaking manifests itself in a directional flow of actin from the front to the rear of the cell. Many cells, especially in physiological 3D matrices, do not show such coherent actin dynamics and present seemingly competing protrusion/retraction dynamics at their front and back. How symmetry breaking manifests itself for such cells is therefore elusive. We take inspiration from the scallop theorem proposed by Purcell for micro-swimmers in Newtonian fluids: self-propelled objects undergoing persistent motion at low Reynolds number must follow a cycle of shape changes that breaks temporal symmetry. We report similar observations for cells crawling in 3D. We quantified cell motion using a combination of 3D live cell imaging, visualization of the matrix displacement, and a minimal model with multipolar expansion. We show that our cells embedded in a 3D matrix form myosin-driven force dipoles at both sides of the nucleus, that locally and periodically pinch the matrix. The existence of a phase shift between the two dipoles is required for directed cell motion which manifests itself as cycles with finite area in the dipole-quadrupole diagram, a formal equivalence to the Purcell cycle. We confirm this mechanism by triggering local dipolar contractions with a laser. This leads to directed motion. Our study reveals that these cells control their motility by synchronizing dipolar forces distributed at front and back. This result opens new strategies to externally control cell motion as well as for the design of micro-crawlers.}, }
@article {pmid35896094, year = {2022}, author = {Zhang, JD and Sung, HJ and Huang, WX}, title = {Hydrodynamic interaction of dorsal fin and caudal fin in swimming tuna.}, journal = {Bioinspiration &amp; biomimetics}, volume = {17}, number = {6}, pages = {}, doi = {10.1088/1748-3190/ac84b8}, pmid = {35896094}, issn = {1748-3190}, mesh = {*Animal Fins ; Animals ; Biomechanical Phenomena ; Hydrodynamics ; *Swimming ; Tuna ; }, abstract = {Tuna, which are known for high-performance swimming, possess a large crescent dorsal fin (DF) and a caudal fin (CF) that differ from those of other fishes. The hydrodynamic interaction between the DF and CF in tuna, which are represented by two tandem 3D flapping plates, is numerically explored in the present study. Hydrodynamic properties and wake structures of the models with and without a DF are compared to investigate the effects of the DF. The thrust on the CF is substantially enhanced by the DF, whereas the force on the DF is not affected by the CF. The constructive interaction between the leading-edge vortex (LEV) on the CF and the vortices shed from the dorsal fin (DFVs) is identified from 3D wake topology and 2D vorticity distributions. The circulation of spanwise vorticity quantitatively reveals that the LEV on the CF is strengthened by the same-signed DFV. The effect of the flapping phase of the CF is examined. The DF-CF interaction is sensitive to the flapping phase at a short spacing, whereas a long spacing between the two fins enables a robust constructive interaction in tuna swimming. A systematic study is carried out to explore the effects of the Strouhal number (St) and the Reynolds number (Re) on the interaction of the fins. The enhancement of thrust due to the DF is diminished at St = 0.63, whereas the Re does not substantially influence the constructive DF-CF interaction.}, }
@article {pmid35892036, year = {2022}, author = {Mane, NS and Puri, DB and Mane, S and Hemadri, V and Banerjee, A and Tripathi, S}, title = {Separation of motile human sperms in a T-shaped sealed microchannel.}, journal = {Biomedical engineering letters}, volume = {12}, number = {3}, pages = {331-342}, pmid = {35892036}, issn = {2093-985X}, abstract = {UNLABELLED: Microfluidic methods act as an effective motile sperm separation technique used in infertility treatments. This work presents a standalone microfluidic device to separate motile sperm cells from non-motile sperm cells and debris. The separation mechanism is based on the centrifugal force acting on sperms and the ability of progressive motile sperms to swim upstream. The separation of motile sperm is carried out using a simple T-shaped microchannel which constitutes three reservoirs: one inlet and two outlets. Herein, one of the outlets is kept sealed. The sealed channel leads to a high-velocity gradient and a rheotaxis zone at the T junction resulting in the separation of motile sperms. Separated sperms are isolated in a sealed channel with a low Reynolds number flow so that sperms cannot have a net displacement, which ensures that the sperms do not re-enter the fluid flow. CFD simulation is conducted to study the flow fields inside the channel and experimental investigation is carried to observe the separation behaviour of sperms. The reported device provides 100% sperm separation efficiency and ensures the entrapment of sperm cells for a longer period. A modified colorimetric nitroblue tetrazolium test conducted on separated sperm cells shows that there is only a marginal increase in superoxide (O2 [-]) production, proving normal sperm integrity. This device offers an effective and safe alternative to conventional sperm sorting methods.<br><br>SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13534-022-00229-9.}, }
@article {pmid35889690, year = {2022}, author = {Ghachem, K and Selimefendigil, F and Alshammari, BM and Maatki, C and Kolsi, L}, title = {Coupled Effects of Using Magnetic Field, Rotation and Wavy Porous Layer on the Forced Convection of Hybrid Nanoliquid Flow over 3D-Backward Facing Step.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {14}, pages = {}, pmid = {35889690}, issn = {2079-4991}, support = {PNURSP2022R41//Princess Nourah bint Abdulrahman University/ ; }, abstract = {In the present study, the effects of using a corrugated porous layer on the forced convection of a hybrid nanofluid flow over a 3D backward facing step are analyzed under the coupled effects of magnetic field and surface rotation. The thermal analysis is conducted for different values of the Reynolds number (Re between 100 and 500), the rotational Reynolds number (Rew between 0 and 2000), the Hartmann number (Ha between 0 and 15), the permeability of the porous layer (the Darcy number, Da between 10-5 and 10-2) and the amplitude (ax between 0.01 ap and 0.7 ap) and wave number (N between 1 and 16) of the porous layer corrugation. When rotations are activated, the average Nusselt number (Nu) and pressure coefficient values rise, while the increment of the latter is less. The increment in the average Nu is higher for the case with a higher permeability of the layer. When the corrugation amplitude and wave number are increased, favorable impacts of the average Nu are observed, but at the same time pressure coefficients are increased. Successful thermal performance estimations are made by using a neural-based modeling approach with a four input-two output system.}, }
@article {pmid35889569, year = {2022}, author = {Minea, AA and El-Maghlany, WM and Massoud, EZ}, title = {Heat Transfer Analysis of Nanocolloids Based on Zinc Oxide Nanoparticles Dispersed in PEG 400.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {14}, pages = {}, pmid = {35889569}, issn = {2079-4991}, abstract = {Cooling and heating are extremely important in many industrial applications, while the thermal performance of these processes generally depends on many factors, such as fluid flow rate, inlet temperature, and many more. Hence, tremendous efforts are dedicated to the investigation of several parameters to reach an efficient cooling or heating process. The interest in adding nanoparticles in regular heat transfer fluids delivered new fluids to the market, the nanofluids. In this paper, a new nanoparticle-enhanced fluid based on polyethylene glycol with ZnO nanoparticles is considered and its hydrothermal performance is investigated for HVAC applications. The thermophysical properties of PEG 400-ZnO and their variation with temperature at different nanoparticle loading are previously determined on experimental bases and here implemented in a numerical application. The numerical results are completed at Reynolds number from 200 to 2000, while the nanoparticle concentration varies from 0.5 to 5%. Results are discussed in terms of Nusselt number, friction factor, and dimensionless pressure drop ratio at different temperatures and ZnO loading in the PEG 400 base fluid. Additionally, the evaluation performance criteria (EC) are calculated and discussed. Concluding, the newly developed fluid enhances the heat transfer up to 16% with a 13% pressure drop penalty, while the performance evaluation criteria are enhanced. Plus, several correlations are developed for both Nusselt number and friction factor as a function of relevant operating conditions.}, }
@article {pmid35888927, year = {2022}, author = {Wang, Y and Yin, Z and Bao, F and Shen, J}, title = {CFD-DEM Coupling Model for Deposition Process Analysis of Ultrafine Particles in a Micro Impinging Flow Field.}, journal = {Micromachines}, volume = {13}, number = {7}, pages = {}, pmid = {35888927}, issn = {2072-666X}, abstract = {Gas with ultrafine particle impaction on a solid surface is a unique case of curvilinear motion that can be widely used for the devices of surface coatings or instruments for particle size measurement. In this work, the Eulerian-Lagrangian method was applied to calculate the motion of microparticles in a micro impinging flow field with consideration of the interactions between particle to particle, particle to wall, and particle to fluid. The coupling computational fluid dynamics (CFD) with the discrete element method (DEM) was employed to investigate the different deposition patterns of microparticles. The vortex structure and two types of particle deposits ("halo" and "ring") have been discussed. The particle deposition characteristics are affected both by the flow Reynolds number (Re) and Stokes number (stk). Moreover, two particle deposition patterns have been categorized in terms of Re and stk. Finally, the characteristics and mechanism of particle deposits have been analyzed using the particle inertia, the process of impinging (particle rebound or no rebound), vortical structures, and the kinetic energy conversion in two-phase flow, etc.}, }
@article {pmid35888885, year = {2022}, author = {Zhou, Y and Dai, L and Jiao, N}, title = {Review of Bubble Applications in Microrobotics: Propulsion, Manipulation, and Assembly.}, journal = {Micromachines}, volume = {13}, number = {7}, pages = {}, pmid = {35888885}, issn = {2072-666X}, support = {Nos. 62127811, 91748212, 61821005//National Natural Science Foundation of China/ ; }, abstract = {In recent years, microbubbles have been widely used in the field of microrobots due to their unique properties. Microbubbles can be easily produced and used as power sources or tools of microrobots, and the bubbles can even serve as microrobots themselves. As a power source, bubbles can propel microrobots to swim in liquid under low-Reynolds-number conditions. As a manipulation tool, microbubbles can act as the micromanipulators of microrobots, allowing them to operate upon particles, cells, and organisms. As a microrobot, microbubbles can operate and assemble complex microparts in two- or three-dimensional spaces. This review provides a comprehensive overview of bubble applications in microrobotics including propulsion, micromanipulation, and microassembly. First, we introduce the diverse bubble generation and control methods. Then, we review and discuss how bubbles can play a role in microrobotics via three functions: propulsion, manipulation, and assembly. Finally, by highlighting the advantages and current challenges of this progress, we discuss the prospects of microbubbles in microrobotics.}, }
@article {pmid35888870, year = {2022}, author = {Juraeva, M and Kang, DJ}, title = {Mixing Enhancement of a Passive Micromixer with Submerged Structures.}, journal = {Micromachines}, volume = {13}, number = {7}, pages = {}, pmid = {35888870}, issn = {2072-666X}, support = {BOKUK2022//BOKUK/ ; }, abstract = {A passive micromixer combined with two different mixing units was designed by submerging planar structures, and its mixing performance was simulated over a wider range of the Reynolds numbers from 0.1 to 80. The two submerged structures are a Norman window and rectangular baffles. The mixing performance was evaluated in terms of the degree of mixing (DOM) at the outlet and the required pressure load between inlet and outlet. The amount of submergence was varied from 30 μm to 70 μm, corresponding to 25% to 58% of the micromixer depth. The enhancement of mixing performance is noticeable over a wide range of the Reynolds numbers. When the Reynolds number is 10, the DOM is improved by 182% from that of no submergence case, and the required pressure load is reduced by 44%. The amount of submergence is shown to be optimized in terms of the DOM, and the optimum value is about 40 μm. This corresponds to a third of the micromixer depth. The effects of the submerged structure are most significant in the mixing regime of convection dominance from Re = 5 to 80. In a circular passage along the Norman window, one of the two Dean vortices burst into the submerged space, promoting mixing in the cross-flow direction. The submerged baffles in the semi-circular mixing units generate a vortex behind the baffles that contributes to the mixing enhancement as well as reducing the required pressure load.}, }
@article {pmid35888205, year = {2022}, author = {Vatsa, A and Alam, T and Siddiqui, MIH and Ali, MA and Dobrotă, D}, title = {Performance of Microchannel Heat Sink Made of Silicon Material with the Two-Sided Wedge.}, journal = {Materials (Basel, Switzerland)}, volume = {15}, number = {14}, pages = {}, pmid = {35888205}, issn = {1996-1944}, abstract = {New designs of the microchannel with a two-sided wedge shape at the base were studied numerically. Five different wedge angles ranging from 3° to 15° were incorporated into the microchannel design. Simulation of this novel microchannel was carried out using Computational Fluid Dynamics (CFD). Three-dimensional models of the microchannel heat sink were created, discretized, and based on Navier-Stokes and energy equations; laminar numerical solutions were obtained for heat transfer and pressure drop. Flow characteristics of water as coolant in a microchannel were studied. It was observed that numerical results are in good agreement with experimental results. It was found that the Nusselt number and friction factor are significantly varied with the increase in Reynolds number. The Nusselt number varies in the following ranges of 5.963-8.521, 5.986-8.550, 6.009-8.568, 6.040-8.609, and 6.078-8.644 at 3°, 6°, 9°, 12°, and 15°, respectively. The microchannel with a wedge angle of 15° was found to be better in terms of Nusselt number and thermo-hydraulic performance. The enhancement in the Nusselt number is found as 1.017-1.036 for a wedge angle of 15°; however, friction factors do not show the perceptible values at distinct values of wedge angle. Moreover, the thermo-hydraulic performance parameters (THPP) were evaluated and found to be maximum in the range of 1.027-1.045 for a wedge angle of 15°. However, minimum THPP was found in the range of 1.005-1.0185 for a wedge angle of 3°.}, }
@article {pmid35885078, year = {2022}, author = {Qi, T and Lin, J and Ouyang, Z}, title = {Hydrodynamic Behavior of Self-Propelled Particles in a Simple Shear Flow.}, journal = {Entropy (Basel, Switzerland)}, volume = {24}, number = {7}, pages = {}, pmid = {35885078}, issn = {1099-4300}, support = {12132015//National Natural Science Foundation of China/ ; }, abstract = {The hydrodynamic properties of a squirmer type of self-propelled particle in a simple shear flow are investigated using the immersed boundary-lattice Boltzmann method in the range of swimming Reynolds number 0.05 ≤ Res ≤ 2.0, flow Reynolds number 40 ≤ Rep ≤ 160, blocking rate 0.2 ≤ κ ≤ 0.5. Some results are validated by comparing with available other results. The effects of Res, Rep and κ on the hydrodynamic properties of squirmer are discussed. The results show that there exist four distinct motion modes for the squirmer, i.e., horizontal mode, attractive oscillation mode, oscillation mode, and chaotic mode. Increasing Res causes the motion mode of the squirmer to change from a constant tumbling near the centerline to a stable horizontal mode, even an oscillatory or appealing oscillatory mode near the wall. Increasing the swimming intensity of squirmer under the definite Res will induce the squirmer to make periodic and stable motion at a specific distance from the wall. Increasing Rep will cause the squirmer to change from a stable swimming state to a spiral motion or continuous rotation. Increasing κ will strengthen the wall's attraction to the squirmer. Increasing swimming intensity of squirmer will modify the strength and direction of the wall's attraction to the squirmer if κ remains constant.}, }
@article {pmid35879876, year = {2022}, author = {Punyaratabandhu, N and Dechadilok, P and Triampo, W and Katavetin, P}, title = {Hydrodynamic model for renal microvascular filtration: Effects of physiological and hemodynamic changes on glomerular size-selectivity.}, journal = {Microcirculation (New York, N.Y. : 1994)}, volume = {29}, number = {8}, pages = {e12779}, doi = {10.1111/micc.12779}, pmid = {35879876}, issn = {1549-8719}, mesh = {Humans ; Hydrodynamics ; *Diabetic Nephropathies ; Models, Biological ; Hemodynamics/physiology ; *Hypertension ; Glomerular Filtration Rate/physiology ; }, abstract = {OBJECTIVE: The first step in renal urine formation is ultrafiltration across the glomerular barrier. The change in its nanostructure has been associated with nephrotic syndromes. Effects of physiological and hemodynamic factor alterations associated with diabetic nephropathy (DN) on glomerular permselectivity are examined through a mathematical model employing low-Reynolds-number hydrodynamics and hindered transport theory.<br><br>METHODS: Glomerular capillaries are represented as networks of cylindrical tubes with multilayered walls. Glomerular basement membrane (GBM) is a fibrous medium with bimodal fiber sizes. Epithelial slit fiber spacing follows a lognormal distribution based on reported electron micrographs with the highest resolution. Endothelial fenestrae are filled with fibers the size of glycosaminoglycans (GAGs). Effects of fiber-macromolecule steric and hydrodynamic interactions are included. Focusing on diabetic nephropathy, the physiological and hemodynamic factors employed in the computation are those reported for healthy humans and patients with early-but-overt diabetic nephropathy. The macromolecule concentration is obtained as a finite element solution of the convection-diffusion equation.<br><br>RESULTS: Computed sieving coefficients averaged along the capillary length agree well with ficoll sieving coefficients from studies in humans for most solute radii. GBM thickening and the loss of the slit diaphragm hardly affect glomerular permselectivity. GAG volume fraction reduction in the endothelial fenestrae, however, significantly increases macromolecule filtration. Increased renal plasma flow rate (RPF), glomerular hypertension, and reduction of lumen osmotic pressure cause a slight sieving coefficient decrease. These effects are amplified by an increased macromolecule size.<br><br>CONCLUSION: Our results indicate that glomerular hypertension and the reduction in the oncotic pressure decreases glomerular macromolecule filtration. Reduction of RPF and changes in the glomerular barrier structure associated with DN, however, increase the solute sieving. Damage to GAGs caused by hyperglycemia is likely to be the most prominent factor affecting glomerular size-selectivity.}, }
@article {pmid35879342, year = {2022}, author = {Skotnicka-Siepsiak, A}, title = {Pressure distribution on a flat plate in the context of the phenomenon of the Coanda effect hysteresis.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {12687}, pmid = {35879342}, issn = {2045-2322}, abstract = {As a result of the Coanda effect, a symmetrical free jet will flow as an asymmetrical wall jet. At the same time, at the obstacle along which the flow is observed, the wall jet generates pressure distribution. In this study, the obstacle located at the diffuser outlet is a flat plate with a variable inclination angle. The article presents results of the study on pressure distributions on a flat plate with a variable angle of inclination. In the experiment, the Reynolds number ranged from 16,192 to 42,240. A fixed geometry diffuser (Witoszyński nozzle) with a height of 0.60 m, width of 0.02 m and outlet velocity of 11.33-29.57 m/s was used. A plate with a length of 1.00 m and a variable inclination angle was installed at the diffuser outlet. What is new, however, is that the presented results of the experimental research include the influence of the Coanda effect hysteresis on the pressure distribution on the plate. The article shows how pressure distributions change on the plate depending on whether the initial angle of inclination was 0° and was increased gradually in the course of the experiment until a detachment of the jet flowing from the plate was observed, or the initial angle of inclination was close to 90° in the primal state and as the angle of the plate inclination was decreased, the jet flowing towards the plate reached the state of attachment to the plate surface. The study demonstrated that for a turbulent jet, pressure distribution on a flat plate is determined not only by the plate's inclination angle, but also by the direction of its rotation.}, }
@article {pmid35863190, year = {2022}, author = {Hatte, S and Pitchumani, R}, title = {Novel nonwetting solid-infused surfaces for superior fouling mitigation.}, journal = {Journal of colloid and interface science}, volume = {627}, number = {}, pages = {308-319}, doi = {10.1016/j.jcis.2022.06.155}, pmid = {35863190}, issn = {1095-7103}, mesh = {*Calcium Sulfate ; *Copper ; Lubricants ; }, abstract = {Fouling is a ubiquitous issue in several environmental and energy applications. Here we introduce novel nonwetting solid-infused surfaces (SIS) with superior anti-fouling characteristics that are durable than conventional nonwetting surfaces in a dynamic flow environment. A systematic study is presented to elucidate the fouling mitigation performance of SIS in comparison to lubricant-infused surface (LIS) and conventional smooth surface. Copper tubes with SIS, LIS or smooth inner walls are fabricated and subjected to accelerated calcium sulfate fouling in a flow fouling experimental setup. Fouling on the various surface types is quantified in terms of asymptotic fouling resistance, and the fundamental morphological differences in the interactions of the foulant and the various surface types are analyzed. Based on a systematic sweep of the parameter combinations using design of experiments and Taguchi analysis, an analytical dependence of asymptotic fouling resistance on the governing parameters namely, Reynolds number, foulant concentration and temperature is derived. The analytical model is shown to predict the asymptotic fouling resistance to within 20% accuracy with a 95% confidence. In addition, for the first time, the effects of shear durability on the fouling mitigation performance of LIS vis-à-vis SIS are studied. It is shown that the novel nonwetting SIS offers a robust option for superior fouling mitigation over LIS in the long run.}, }
@article {pmid35859200, year = {2022}, author = {Pumm, AK and Engelen, W and Kopperger, E and Isensee, J and Vogt, M and Kozina, V and Kube, M and Honemann, MN and Bertosin, E and Langecker, M and Golestanian, R and Simmel, FC and Dietz, H}, title = {A DNA origami rotary ratchet motor.}, journal = {Nature}, volume = {607}, number = {7919}, pages = {492-498}, pmid = {35859200}, issn = {1476-4687}, support = {724261/ERC_/European Research Council/International ; }, mesh = {*DNA/chemistry ; *Facilitated Diffusion ; Hydrogen-Ion Concentration ; *Molecular Motor Proteins/chemistry/metabolism ; Motion ; Movement ; Osmolar Concentration ; Proton-Translocating ATPases/chemistry/metabolism ; Stochastic Processes ; Temperature ; Thermodynamics ; }, abstract = {To impart directionality to the motions of a molecular mechanism, one must overcome the random thermal forces that are ubiquitous on such small scales and in liquid solution at ambient temperature. In equilibrium without energy supply, directional motion cannot be sustained without violating the laws of thermodynamics. Under conditions away from thermodynamic equilibrium, directional motion may be achieved within the framework of Brownian ratchets, which are diffusive mechanisms that have broken inversion symmetry[1-5]. Ratcheting is thought to underpin the function of many natural biological motors, such as the F1F0-ATPase[6-8], and it has been demonstrated experimentally in synthetic microscale systems (for example, to our knowledge, first in ref. [3]) and also in artificial molecular motors created by organic chemical synthesis[9-12]. DNA nanotechnology[13] has yielded a variety of nanoscale mechanisms, including pivots, hinges, crank sliders and rotary systems[14-17], which can adopt different configurations, for example, triggered by strand-displacement reactions[18,19] or by changing environmental parameters such as pH, ionic strength, temperature, external fields and by coupling their motions to those of natural motor proteins[20-26]. This previous work and considering low-Reynolds-number dynamics and inherent stochasticity[27,28] led us to develop a nanoscale rotary motor built from DNA origami that is driven by ratcheting and whose mechanical capabilities approach those of biological motors such as F1F0-ATPase.}, }
@article {pmid35854607, year = {2022}, author = {Bandak, D and Goldenfeld, N and Mailybaev, AA and Eyink, G}, title = {Dissipation-range fluid turbulence and thermal noise.}, journal = {Physical review. E}, volume = {105}, number = {6-2}, pages = {065113}, doi = {10.1103/PhysRevE.105.065113}, pmid = {35854607}, issn = {2470-0053}, abstract = {We revisit the issue of whether thermal fluctuations are relevant for incompressible fluid turbulence and estimate the scale at which they become important. As anticipated by Betchov in a prescient series of works more than six decades ago, this scale is about equal to the Kolmogorov length, even though that is several orders of magnitude above the mean free path. This result implies that the deterministic version of the incompressible Navier-Stokes equation is inadequate to describe the dissipation range of turbulence in molecular fluids. Within this range, the fluctuating hydrodynamics equation of Landau and Lifschitz is more appropriate. In particular, our analysis implies that both the exponentially decaying energy spectrum and the far-dissipation-range intermittency predicted by Kraichnan for deterministic Navier-Stokes will be generally replaced by Gaussian thermal equipartition at scales just below the Kolmogorov length. Stochastic shell model simulations at high Reynolds numbers verify our theoretical predictions and reveal furthermore that inertial-range intermittency can propagate deep into the dissipation range, leading to large fluctuations in the equipartition length scale. We explain the failure of previous scaling arguments for the validity of deterministic Navier-Stokes equations at any Reynolds number and we provide a mathematical interpretation and physical justification of the fluctuating Navier-Stokes equation as an "effective field theory" valid below some high-wave-number cutoff Λ, rather than as a continuum stochastic partial differential equation. At Reynolds number around a million, comparable to that in Earth's atmospheric boundary layer, the strongest turbulent excitations observed in our simulation penetrate down to a length scale of about eight microns, still two orders of magnitude greater than the mean free path of air. However, for longer observation times or for higher Reynolds numbers, more extreme turbulent events could lead to a local breakdown of fluctuating hydrodynamics.}, }
@article {pmid35854520, year = {2022}, author = {Margazoglou, G and Biferale, L and Cencini, M and Gallavotti, G and Lucarini, V}, title = {Nonequilibrium ensembles for the three-dimensional Navier-Stokes equations.}, journal = {Physical review. E}, volume = {105}, number = {6-2}, pages = {065110}, doi = {10.1103/PhysRevE.105.065110}, pmid = {35854520}, issn = {2470-0053}, abstract = {At the molecular level fluid motions are, by first principles, described by time reversible laws. On the other hand, the coarse grained macroscopic evolution is suitably described by the Navier-Stokes equations, which are inherently irreversible, due to the dissipation term. Here, a reversible version of three-dimensional Navier-Stokes is studied, by introducing a fluctuating viscosity constructed in such a way that enstrophy is conserved, along the lines of the paradigm of microcanonical versus canonical treatment in equilibrium statistical mechanics. Through systematic simulations we attack two important questions: (a) What are the conditions that must be satisfied in order to have a statistical equivalence between the two nonequilibrium ensembles? (b) What is the empirical distribution of the fluctuating viscosity observed by changing the Reynolds number and the number of modes used in the discretization of the evolution equation? The latter point is important also to establish regularity conditions for the reversible equations. We find that the probability to observe negative values of the fluctuating viscosity becomes very quickly extremely small when increasing the effective Reynolds number of the flow in the fully resolved hydrodynamical regime, at difference from what was observed previously.}, }
@article {pmid35854514, year = {2022}, author = {Choudhury, A and Samanta, A}, title = {Linear stability of a falling film over a heated slippery plane.}, journal = {Physical review. E}, volume = {105}, number = {6-2}, pages = {065112}, doi = {10.1103/PhysRevE.105.065112}, pmid = {35854514}, issn = {2470-0053}, abstract = {A detailed parametric study on the linear stability analysis of a three-dimensional thin liquid film flowing down a uniformly heated slippery inclined plane is carried out for disturbances of arbitrary wavenumbers, where the liquid film satisfies Newton's law of cooling at the film surface. A coupled system of boundary value problems is formulated in terms of the amplitudes of perturbation normal velocity and perturbation temperature, respectively. Analytical solution of the boundary value problems demonstrates the existence of three dominant modes, the so-called H mode, S mode, and P mode, where the S mode and P mode emerge due to the thermocapillary effect. It is found that the onset of instabilities for the H mode, S mode, and P mode reduces in the presence of wall slip and leads to a destabilizing influence. Numerical solution based on the Chebyshev spectral collocation method unveils that the finite wavenumber H-mode instability can be stabilized, but the S-mode instability and the finite wavenumber P-mode instability can be destabilized by increasing the value of the Marangoni number. On the other hand, the Biot number shows a dual role in the H-mode and S-mode instabilities. But the P-mode instability can be made stable with the increasing value of the Biot number and the decreasing values of the Marangoni number and the Prandtl number. Furthermore, the H-mode and S-mode instabilities become weaker, but the P-mode instability becomes stronger, with the increasing value of the spanwise wavenumber. In addition, the shear mode emerges in the numerical simulation when the Reynolds number is large, which can be destabilized slightly with the increasing value of the Marangoni number; however, it can be stabilized with the increasing value of the slip length and introducing the spanwise wavenumber to the infinitesimal perturbation.}, }
@article {pmid35854482, year = {2022}, author = {Ishimoto, K and Moreau, C and Yasuda, K}, title = {Self-organized swimming with odd elasticity.}, journal = {Physical review. E}, volume = {105}, number = {6-1}, pages = {064603}, doi = {10.1103/PhysRevE.105.064603}, pmid = {35854482}, issn = {2470-0053}, abstract = {We theoretically investigate self-oscillating waves of an active material, which were recently introduced as a nonsymmetric part of the elastic moduli, termed odd elasticity. Using Purcell's three-link swimmer model, we reveal that an odd-elastic filament at low Reynolds number can swim in a self-organized manner and that the time-periodic dynamics are characterized by a stable limit cycle generated by elastohydrodynamic interactions. Also, we consider a noisy shape gait and derive a swimming formula for a general elastic material in the Stokes regime with its elasticity modulus being represented by a nonsymmetric matrix, demonstrating that the odd elasticity produces biased net locomotion from random noise.}, }
@article {pmid35853555, year = {2022}, author = {Kumar, M and Panneerselvam, E and Prabhu, K and Ganesh, SK and Vb, KKR}, title = {Prospective cohort study on short-term evaluation of septoplasty as early management of naso-septal fractures - A correlation of clinical outcomes with computational fluid dynamic parameters.}, journal = {Journal of stomatology, oral and maxillofacial surgery}, volume = {123}, number = {6}, pages = {639-644}, doi = {10.1016/j.jormas.2022.07.010}, pmid = {35853555}, issn = {2468-7855}, mesh = {Humans ; *Nasal Obstruction/diagnosis/etiology/surgery ; Nasal Septum/surgery ; Prospective Studies ; Hydrodynamics ; Pain ; }, abstract = {PURPOSE: Post-traumatic deviated nasal septum (PTDNS) leads to impaired breathing and poor esthetics. The aim of this study was to assess treatment outcomes of early septoplasty for correction of PTDNS and correlate it with computational fluid dynamic (CFD) parameters.<br><br>METHODS: This prospective cohort study included patients who underwent early septoplasty for PTDNS. Outcome variables were clinical (pain, nasal symmetry, and nasal obstruction) and computational (velocity, pressure, wall shear stress and Reynold's number). The cohort consisted of two groups: patients with history of closed reduction for nasal fractures (CR) and patients without (NCR). The primary outcome measure was response to treatment. Correlation between clinical and computational parameters, and influence of closed reduction on septoplasty outcomes were the secondary and tertiary outcomes, respectively. Descriptive and inferential statistics were performed to analyze data. Level of significance was fixed at 5% (&#x3b1;&#xa0;=&#xa0;0.05).<br><br>RESULTS: The sample included 12 patients, of which 5 underwent CFD analysis. Pain score reduced from a pre-operative mean of 7.3 to 0.5 post-operatively (p<0.001). All patients demonstrated reduction of nasal obstruction (p<0.001) and deviation (p<0.001) post-operatively. CFD analysis revealed post-operative reduction of velocity (p&#xa0;=&#xa0;0.005) and Reynold's number (p&#xa0;=&#xa0;0.007), with positive correlation between nasal obstruction and CFD parameters. Though patients in the CR group demonstrated reduced nasal deviation and obstruction before septoplasty, as compared to the NCR group, their outcomes were comparable following septoplasty.<br><br>CONCLUSION: Early septoplasty improves functional and esthetic outcomes in patients with PTDNS. CFD simulation is a predictable method to objectively evaluate nasal function.}, }
@article {pmid35851297, year = {2022}, author = {Shahzad, H and Wang, X and Ghaffari, A and Iqbal, K and Hafeez, MB and Krawczuk, M and Wojnicz, W}, title = {Fluid structure interaction study of non-Newtonian Casson fluid in a bifurcated channel having stenosis with elastic walls.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {12219}, pmid = {35851297}, issn = {2045-2322}, mesh = {Arteries ; Blood Flow Velocity ; Computer Simulation ; Constriction, Pathologic ; *Hemodynamics ; Humans ; *Models, Cardiovascular ; Stress, Mechanical ; }, abstract = {Fluid-structure interaction (FSI) gained a huge attention of scientists and researchers due to its applications in biomedical and mechanical engineering. One of the most important applications of FSI is to study the elastic wall behavior of stenotic arteries. Blood is the suspension of various cells characterized by shear thinning, yield stress, and viscoelastic qualities that can be assessed by using non-Newtonian models. In this study we explored non-Newtonian, incompressible Casson fluid flow in a bifurcated artery with a stenosis. The two-dimensional Casson model is used to study the hemodynamics of the flow. The walls of the artery are supposed to be elastic and the stenosis region is constructed in both walls. Suitable scales are used to transform the nonlinear differential equations into a dimensionless form. The problem is formulated and discretized using Arbitrary Lagrangian-Eulerian (ALE) approach. The finite element method (FEM) technique is used to solve the system of equations, together with appropriate boundary conditions. The analysis is carried out for the Bingham number, Hartmann number, and Reynolds number. The graphical results of pressure field, velocity profile, and load on the walls are assessed and used to study the influence of hemodynamic effects on stenotic arteries, bifurcation region, and elastic walls. This study shows that there is an increase in wall shear stresses (WSS) with increasing values of Bingham number and Hartmann number. Also, for different values of the Bingham number, the load on the upper wall is computed against the Hartmann number. The result indicate that load at the walls increases as the values of Bingham number and Hartmann number increase.}, }
@article {pmid39659981, year = {2024}, author = {Lin, A and Liu, G and Chang, R and Chen, Y and Feng, Q}, title = {Comprehensive evaluations of heat transfer performance with conjugate heat dissipation effect in high-speed rotating free-disk modeling of aero-engines.}, journal = {Fundamental research}, volume = {4}, number = {3}, pages = {611-623}, pmid = {39659981}, issn = {2667-3258}, abstract = {Thermal boundary conditions of the turbine disk cavity system are of great importance in the design of secondary air systems in aero-engines. This study aims to investigate the complex heat transfer mechanisms of a rotating turbine disk under high-speed conditions. A high-speed rotating free-disk model with Dorfman empirical solutions is developed to evaluate the heat transfer performance considering various factors. Specifically, the influence of compressibility, variable properties, and heat dissipation is determined using theoretical and numerical analyses. In particular, a novel combined solution method is proposed to simplify the complex heat transfer problem. The results indicate that the heat transfer performance of a free disk is primarily influenced by the rotating Mach number, rotating Reynolds number, Rossby number, and wall temperature ratio. The heat transfer temperature and Nusselt number of the free disk are strongly correlated with the rotating Mach number and rotating Reynolds number. Analysis reveals that heat dissipation is a critical factor affecting the accurate evaluation of the heat transfer performance of the turbine disk. Thus, the combined solution method can serve as a reference for future investigations of flow and heat transfer in high-speed rotating turbine disk cavity systems in aero-engines.}, }
@article {pmid35820476, year = {2022}, author = {Zhao, X and Zuo, H and Jia, G}, title = {Effects of the continuous pulsation regeneration on the soot combustion in diesel particulate filter for heavy-duty truck.}, journal = {Chemosphere}, volume = {306}, number = {}, pages = {135651}, doi = {10.1016/j.chemosphere.2022.135651}, pmid = {35820476}, issn = {1879-1298}, mesh = {Dust ; Motor Vehicles ; *Soot/analysis ; Temperature ; *Vehicle Emissions/analysis ; }, abstract = {Continuous pulsation regeneration combustion of soot is employed for sine and cosine simulation study. Data showed that pressure uniformity of sine condition is better than that of cosine condition with the maximum pressure difference of 4353.5 Pa under the same simulation boundary conditions. The maximum regeneration temperature under cosine pressure is 46.12 K which is higher than that in sine form. Regeneration combustion reaction zone tends to be more stable laminar flow and Reynolds number of sine condition is 435.23 less than that of under cosine condition. The maximum Stanton number of cosine pressure condition is 3.67 and that of sine pressure condition is 5.15, which investigates heat transfer capacity of the sine pressure condition is better than that of the pressure of cosine form. The regeneration efficiency of inlet gradually increased from the minimum regeneration efficiency 74.18%-88.45% of sine and cosine. The soot under both pressure forms has achieved complete regeneration and the regeneration efficiency has exceeded 88% of porous medium filter body section. The soot regeneration combustion efficiency of the porous media filter section and outlet section is more sufficient under sine condition and the heat carried by the fluid can maintain the soot regeneration.}, }
@article {pmid35811899, year = {2022}, author = {Sun, R and Chen, P and Li, L and Liu, Y and Zhai, X}, title = {Experimental Investigation of the Combustion Behavior of Transformer Oil Jet Flame.}, journal = {ACS omega}, volume = {7}, number = {26}, pages = {22969-22976}, pmid = {35811899}, issn = {2470-1343}, abstract = {Transformer oil jet fire is one of the most dangerous types of fires in substations. The combustion behavior of transformer oil jet fire produces uncontrollable hazards to personnel and equipment and even triggers a domino effect. However, the jet fire combustion behavior of such materials as transformer oil has not been revealed before. Investigation of the combustion behavior of transformer oil jet fire has positive implications for the prevention and control of substation fires. In this paper, KI25X transformer oil was used as fuel. A series of transformer oil jet fire experiments were conducted with variable orifice diameters (5, 10, and 15 mm) with heat release rates ranging from 200 to 659.2 kW. The results showed that the entrainment coefficient of transformer oil jet fire was greater than that of pure gas phase jet fire. The entrainment coefficient of transformer oil jet fire was 0.029. Using dimensionless theory, it was proposed that the imaginary point source was proportional to the 0.317 power of Froude number. Based on the point source model, a dimensional analysis model with Reynolds number was developed. The radiation fraction of transformer oil jet fire was proportional to the -0.133 power of Reynolds number. This study played an important role in improving the jet combustion behavior of transformer oil.}, }
@article {pmid35787191, year = {2022}, author = {Jamshed, W and Safdar, R and Rehman, Z and Lashin, MMA and Ehab, M and Moussa, M and Rehman, A}, title = {Computational technique of thermal comparative examination of Cu and Au nanoparticles suspended in sodium alginate as Sutterby nanofluid via extending PTSC surface.}, journal = {Journal of applied biomaterials &amp; functional materials}, volume = {20}, number = {}, pages = {22808000221104004}, doi = {10.1177/22808000221104004}, pmid = {35787191}, issn = {2280-8000}, mesh = {*Alginates ; Copper ; Gold ; Hot Temperature ; *Metal Nanoparticles ; }, abstract = {Current research underscores entropy investigation in an infiltrating mode of Sutterby nanofluid (SNF) stream past a dramatically expanding flat plate that highlights Parabolic Trough Solar Collector (PTSC). Satisfactory likeness factors are utilized to change halfway differential conditions (PDEs) to nonlinear conventional differential conditions (ODEs) along with relating limit requirements. A productive Keller-box system is locked in to achieve approximated arrangement of decreased conventional differential conditions. In the review, two sorts of nanofluids including Copper-sodium alginate (Cu-SA) and Gold-sodium alginate (Au-SA) are dissected. Results are graphically plotted as well as talked about in actual viewpoints. As indicated by key discoveries, an improvement in Brinkmann, as well as Reynolds number, brings about expanding the general framework entropy. Sutterby nanofluid boundary improves heat rate in PTSC. Additionally, Copper-sodium alginate nanofluid is detected as a superior thermal conductor than Gold-sodium alginate nanofluid. Further to that, the reported breakthroughs are beneficial to updating extremely bright lighting bulbs, heating and cooling machinery, fiber required to generate light, power production, numerous boilers, and other similar technologies.}, }
@article {pmid37663238, year = {2022}, author = {Beaver, LE and Wu, B and Das, S and Malikopoulos, AA}, title = {A First-Order Approach to Model Simultaneous Control of Multiple Microrobots.}, journal = {... International Conference on Manipulation Automation and Robotics at Small Scales (MARSS). International Conference on Manipulation Automation and Robotics at Small Scales}, volume = {2022}, number = {}, pages = {}, pmid = {37663238}, support = {P20 GM103446/GM/NIGMS NIH HHS/United States ; }, abstract = {The control of swarm systems is relatively well understood for simple robotic platforms at the macro scale. However, there are still several unanswered questions about how similar results can be achieved for microrobots. In this paper, we propose a modeling framework based on a dynamic model of magnetized self-propelling Janus microrobots under a global magnetic field. We verify our model experimentally and provide methods that can aim at accurately describing the behavior of microrobots while modeling their simultaneous control. The model can be generalized to other microrobotic platforms in low Reynolds number environments.}, }
@article {pmid35771996, year = {2022}, author = {Saro-Cortes, V and Cui, Y and Dufficy, T and Boctor, A and Flammang, BE and Wissa, AW}, title = {An Adaptable Flying Fish Robotic Model for Aero- and Hydrodynamic Experimentation.}, journal = {Integrative and comparative biology}, volume = {}, number = {}, pages = {}, doi = {10.1093/icb/icac101}, pmid = {35771996}, issn = {1557-7023}, abstract = {Flying fishes (family Exocoetidae) are known for achieving multi-modal locomotion through air and water. Previous work on understanding this animal's aerodynamic and hydrodynamic nature has been based on observations, numerical simulations, or experiments on preserved dead fish, and has focused primarily on flying pectoral fins. The first half of this paper details the design and validation of a modular flying fish inspired robotic model organism (RMO). The second half delves into a parametric aerodynamic study of flying fish pelvic fins, which to date have not been studied in-depth. Using wind tunnel experiments at a Reynolds number of 30,000, we investigated the effect of the pelvic fin geometric parameters on aerodynamic efficiency and longitudinal stability. The pelvic fin parameters investigated in this study include the pelvic fin pitch angle and its location along the body. Results show that the aerodynamic efficiency is maximized for pelvic fins located directly behind the pectoral fins and is higher for more positive pitch angles. In contrast, pitching stability is neither achievable for positive pitching angles nor pelvic fins located directly below the pectoral fin. Thus, there is a clear a trade-off between stability and lift generation, and an optimal pelvic fin configuration depends on the flying fish locomotion stage, be it gliding, taxiing, or taking off. The results garnered from the RMO experiments are insightful for understanding the physics principles governing flying fish locomotion and designing flying fish inspired aerial-aquatic vehicles.}, }
@article {pmid35764779, year = {2022}, author = {Wu, YK and Liu, YP and Sun, M}, title = {Aerodynamics of two parallel bristled wings in low Reynolds number flow.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {10928}, pmid = {35764779}, issn = {2045-2322}, mesh = {Animals ; Biomechanical Phenomena ; *Flight, Animal/physiology ; Insecta/physiology ; Models, Biological ; *Wings, Animal/physiology ; }, abstract = {Most of the smallest flying insects use bristled wings. It was observed that during the second half of their upstroke, the left and right wings become parallel and close to each other at the back, and move upward at zero angle of attack. In this period, the wings may produce drag (negative vertical force) and side forces which tend to push two wings apart. Here we study the aerodynamic forces and flows of two simplified bristled wings experiencing such a motion, compared with the case of membrane wings (flat-plate wings), to see if there is any advantage in using the bristled wings. The method of computational fluid dynamics is used in the study. The results are as follows. In the motion of two bristled wings, the drag acting on each wing is 40% smaller than the case of a single bristled wing conducting the same motion, and only a very small side force is produced. But in the case of the flat-plate wings, although there is similar drag reduction, the side force on each wing is larger than that of the bristled wing by an order of magnitude (the underlying physical reason is discussed in the paper). Thus, if the smallest insects use membrane wings, their flight muscles need to overcome large side forces in order to maintain the intended motion for less negative lift, whereas using bristled wings do not have this problem. Therefore, the adoption of bristled wings can be beneficial during upward movement of the wings near the end of the upstroke, which may be one reason why most of the smallest insects adopt them.}, }
@article {pmid35755331, year = {2022}, author = {Huang, X and Wang, Y and Wang, L and Yu, G and Wang, F}, title = {Effect of Structural Optimization of Scrubbing Cooling Rings on Vertical Falling Film Flow Characteristics.}, journal = {ACS omega}, volume = {7}, number = {24}, pages = {21291-21305}, pmid = {35755331}, issn = {2470-1343}, abstract = {In order to study the influence of the structural optimization of the scrubbing cooling ring in the scrubbing cooling chamber on the flow characteristics of the vertical falling film, the flow characteristics of the turbulent falling film in the rising section of the development region at different internal platform heights of the scrubbing cooling ring and a high Reynolds number were studied by FLUENT software. First, the correctness of the model was verified by the maximum error of simulation and experimental results of no more than 9.836%. Then, the distribution of liquid film thickness (δ), velocity (V), and turbulence intensity (I z) at 0° of the tube in the axial direction x = 0-500 mm were calculated and obtained when the platform height (H) was 0-30 mm and the liquid film Reynolds number (Re l) = 1.1541 × 10[4]-3.4623 × 10[4]. The results showed that δ in the entrance region increased sharply due to the "jet" effect with solid wall constraints formed by the structure of the water inlet pipe and the scrubbing cooling ring. On the contrary, the liquid film in the fully developed region showed a stable fluctuation trend due to the weakening of the "jet" effect. When H = 30 mm, the change of δ was relatively stable and the change of I z was small, indicating that this platform height is conducive to the stable and uniform distribution of the liquid film. In addition, when Re l < 1.1541 × 10[4], the liquid film was unstable due to the low flow rate and insufficient cohesion of the liquid film, but V increased slightly. In addition, with the increase of Re l, δ did not change significantly along the axial direction, that is, the Plateau-Rayleigh hindered the growth of δ. Finally, the empirical formula for δ applicable to Re l = 1.1541 × 10[4]-3.4623 × 10[4] at the axial fixed position was fitted for the first time.}, }
@article {pmid35751170, year = {2022}, author = {Ducos, S and Pugliese, S and Demolliens, M and Beraud, L and Boussard, A and Delmas, A and Agostini, S and Garcia, J and Aiello, A and Durieux, EDH}, title = {Ontogeny of swimming performance of hatchery-reared post-larvae and juvenile fish: a case of two threatened Mediterranean species.}, journal = {Journal of fish biology}, volume = {101}, number = {4}, pages = {846-856}, pmid = {35751170}, issn = {1095-8649}, support = {//European Regional Fund FEDER 2017-2020/ ; //National funding CPER 2020-2022/ ; //Territorial collectivity of Corsica (CdC)/ ; }, mesh = {Animals ; *Endangered Species ; Fishes/physiology ; Larva/physiology ; *Perciformes/physiology ; *Swimming/physiology ; }, abstract = {Swimming performance is a well-established key physiological parameter of fish that is highly linked to their fitness in the wild. In the context of fish restocking purposes, it therefore appears crucial to study this specific behaviour. Here, the authors investigated intra and interspecies differences in the swimming performance of hatchery-reared post-larvae and juveniles belonging to two Mediterranean candidate threatened species, the common dentex, Dentex dentex (Sparidae), and the brown meagre, Sciaena umbra (Sciaenidae), with body sizes ranging from 8 to 37 mm total length (TL, from 24 to 58 days post-hatch). The swimming abilities were estimated through the calculation of their critical swimming speed (Ucrit), their relative Ucrit and their Reynolds number (Re). Two different patterns were observed between D. dentex and S. umbra, showing a different effect of ontogeny on the performance of both species. The relative Ucrit of S. umbra decreased linearly through ontogeny, whereas the relative Ucrit and Ucrit of D. dentex increased linearly through the range of sizes tested. The ontogenetic change in Ucrit of S. umbra occurred in two stages: a first stage of sharp improvement and a second stage of a slow decrease in performance. Both stages were separated by a breakpoint that coincided with the appearance of a refusal to swim behaviour that occurred shortly after the end of metamorphosis and can potentially be associated with the establishment of this species sedentary behaviour. The swimming performance of both species showed ontogenetic differences. Sciaena umbra had the highest relative performance when its body sizes were the smallest, whereas D. dentex showed the highest relative performance when its body sizes were the largest. These results will be linked to future research on both of these species concerning their escape, exploratory and predatory behaviours, and for restocking purposes to draw a more realistic overview of hatchery-reared juvenile performance. Knowledge of both species' behavioural and swimming performance through ontogeny is important to consider when using hatchery-reared fish juveniles for restocking, as size-at-release can have a large impact on fish survival and thus on restocking success.}, }
@article {pmid35750772, year = {2022}, author = {Zhang, S and Ahmad, F and Khan, A and Ali, N and Badran, M}, title = {Performance improvement and thermodynamic assessment of microchannel heat sink with different types of ribs and cones.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {10802}, pmid = {35750772}, issn = {2045-2322}, abstract = {The present study aims to investigate the performance of microchannel heat sink via numerical simulations, based on the first and second law of thermodynamics. The heat transfer and flow characteristics of rectangular microchannel heat sinks have been improved by adding six different types of surface enhancers. The cross-sections include rectangular, triangular, and hexagonal-shaped ribs and cones. The cones have been created from the same cross-sections of ribs by drafting them at an angle of 45° orthogonal to the base, which is expected to decrease the pressure drop, dramatically. The performance of ribs and cones has been evaluated using different parameters such as friction factor, wall shear stress, entropy generation rate, augmentation entropy generation number, thermal resistance, and transport efficiency of thermal energy. The results of the present study revealed that the novel effect of coning at an angle of 45° reduces frictional losses (Maximum pressure drop reduced is 85%), however; a compromise on thermal behavior has been shown (Maximum Nusselt number reduced is 25%). Similarly, the application of coning has caused a significant reduction in wall shear stress and friction factor which can lead to reducing the pumping power requirements. Moreover, triangular ribs have more ability to transfer thermal energy than rectangular and hexagonal ribs. Furthermore, it has been examined in the present study that the trend of total entropy generation rate for triangular ribs decreases up to Re = 400 and then increases onwards which means that thermal losses are more significant than frictional losses at lower Reynolds number. However, frictional losses dominate over thermal losses at higher Reynolds numbers, where vortex generation takes place, especially in triangular ribs.}, }
@article {pmid35749192, year = {2022}, author = {Buaria, D and Sreenivasan, KR}, title = {Scaling of Acceleration Statistics in High Reynolds Number Turbulence.}, journal = {Physical review letters}, volume = {128}, number = {23}, pages = {234502}, doi = {10.1103/PhysRevLett.128.234502}, pmid = {35749192}, issn = {1079-7114}, abstract = {The scaling of acceleration statistics in turbulence is examined by combining data from the literature with new data from well-resolved direct numerical simulations of isotropic turbulence, significantly extending the Reynolds number range. The acceleration variance at higher Reynolds numbers departs from previous predictions based on multifractal models, which characterize Lagrangian intermittency as an extension of Eulerian intermittency. The disagreement is even more prominent for higher-order moments of the acceleration. Instead, starting from a known exact relation, we relate the scaling of acceleration variance to that of Eulerian fourth-order velocity gradient and velocity increment statistics. This prediction is in excellent agreement with the variance data. Our Letter highlights the need for models that consider Lagrangian intermittency independent of the Eulerian counterpart.}, }
@article {pmid35745944, year = {2022}, author = {Chen, D and Lin, J}, title = {Steady State of Motion of Two Particles in Poiseuille Flow of Power-Law Fluid.}, journal = {Polymers}, volume = {14}, number = {12}, pages = {}, pmid = {35745944}, issn = {2073-4360}, support = {12132015//National Natural Science Foundation of China/ ; }, abstract = {The steady state of motion of two particles in Poiseuille flow of power-law fluid is numerically studied using the lattice Boltzmann method in the range of Reynolds number 20 ≤ Re ≤ 60, diameter ratio of two particles 0.125 ≤ β ≤ 2.4, and power-law index of the fluid 0.4 ≤ n ≤ 1.2. Some results are validated by comparing with other available results. The effects of Re, β, and n on the steady state of motion of two particles are discussed. The results show that, for two particles of the same diameter, the particle spacing l in the steady state is independent of n. In shear-thinning fluid, l increases rapidly at first and then slowly, finally approaching a constant for different Re. In shear-thickening fluid, although l tends to be stable in the end, the values of l after stabilization are different. For two particles of different sizes, l does not always reach a stable state, and whether it reaches a stable state depends on n. When the small particle is downstream, l increases rapidly at first and then slowly in shear-thickening fluid, but increases rapidly at first and then decreases slowly, finally approaching a constant in a shear-thinning fluid. In shear-thinning fluid, the larger n is, the smaller l is. In shear-thickening fluid, β has no effect on l in steady-state. When the large particle is downstream, l increases rapidly at first and then slowly in shear-thinning fluid but increases rapidly at first and then decreases in a shear-thickening fluid. The effect of n on l in the steady state is obvious. In shear-thinning fluid, l increases rapidly at first and then slowly, the larger Re is, the smaller l is. In shear- thickening fluid, l will reach a stable state.}, }
@article {pmid35745906, year = {2022}, author = {Bui, CM and Ho, AT and Nguyen, XB}, title = {Flow Behaviors of Polymer Solution in a Lid-Driven Cavity.}, journal = {Polymers}, volume = {14}, number = {12}, pages = {}, pmid = {35745906}, issn = {2073-4360}, support = {T2021-06-03//University of Technology and Education - The University of Danang/ ; }, abstract = {In this work, a numerical study of polymer flow behaviors in a lid-driven cavity, which is inspired by the coating process, at a broad range of Oldroyd numbers (0≤Od≤50), is carried out. The Reynolds number is height-based and kept at Re=0.001. The fluid investigated is of Carbopol gel possessing yield stress and shear-thinning properties. To express rheological characteristics, the Herschel-Bulkley model cooperated with Papanastasiou's regularization scheme is utilized. Results show that the polymer flow characteristics, i.e., velocity, viscosity, and vortex distributions, are considerably influenced by viscoplastic behaviors. Additionally, there exist solid-like regions which can be of either moving rigid or static dead types in the flow patterns; they become greater and tend to merge together to construct larger ones when Od increases. Furthermore, various polymer flow aspects in different cavity configurations are discussed and analyzed; the cavity width/aspect ratio and skewed angle are found to have significant impacts on the vortex structures and the formation of solid-like regions. Moreover, results for the critical aspect ratio at which the static dead zone is broken into two parts and the characteristic height of this zone are also reported in detail.}, }
@article {pmid35744569, year = {2022}, author = {Saghir, MZ and Rahman, MM}, title = {Thermo-Hydraulic Performance of Pin-Fins in Wavy and Straight Configurations.}, journal = {Micromachines}, volume = {13}, number = {6}, pages = {}, pmid = {35744569}, issn = {2072-666X}, abstract = {Pin-fins configurations have been investigated recently for different engineering applications and, in particular, for a cooling turbine. In the present study, we investigated the performance of three different pin-fins configurations: pin-fins forming a wavy mini-channel, pin-fins forming a straight mini-channel, and a mini-channel without pin-fins considering water as the working fluid. The full Navier-Stokes equations and the energy equation are solved numerically using the finite element technique. Different flow rates are studied, represented by the Reynolds number in the laminar flow regime. The thermo-hydraulic performance of the three configurations is determined by examining the Nusselt number, the pressure drop, and the performance evaluation criterion. Results revealed that pin-fins forming a wavy mini-channel exhibited the highest Nusselt number, the lowest pressure drop, and the highest performance evaluation criterion. This finding is valid for any Reynolds number under investigation.}, }
@article {pmid35744548, year = {2022}, author = {Tayeb, NT and Hossain, S and Khan, AH and Mostefa, T and Kim, KY}, title = {Evaluation of Hydrodynamic and Thermal Behaviour of Non-Newtonian-Nanofluid Mixing in a Chaotic Micromixer.}, journal = {Micromachines}, volume = {13}, number = {6}, pages = {}, pmid = {35744548}, issn = {2072-666X}, abstract = {Three-dimensional numerical investigations of a novel passive micromixer were carried out to analyze the hydrodynamic and thermal behaviors of Nano-Non-Newtonian fluids. Mass and heat transfer characteristics of two heated fluids have been investigated to understand the quantitative and qualitative fluid faction distributions with temperature homogenization. The effect of fluid behavior and different Al2O3 nanoparticles concentrations on the pressure drop and thermal mixing performances were studied for different Reynolds number (from 0.1 to 25). The performance improvement simulation was conducted in intervals of various Nanoparticles concentrations (φ = 0 to 5%) with Power-law index (n) using CFD. The proposed micromixer displayed a mixing energy cost of 50-60 comparable to that achieved for a recent micromixer (2021y) in terms of fluid homogenization. The analysis exhibited that for high nanofluid concentrations, having a strong chaotic flow enhances significantly the hydrodynamic and thermal performances for all Reynolds numbers. The visualization of vortex core region of mass fraction and path lines presents that the proposed design exhibits a rapid thermal mixing rate that tends to 0.99%, and a mass fraction mixing rate of more than 0.93% with very low pressure losses, thus the proposed micromixer can be utilized to enhance homogenization in different Nano-Non-Newtonian mechanism with minimum energy.}, }
@article {pmid35739213, year = {2022}, author = {Abd-Alla, AM and Abo-Dahab, SM and Thabet, EN and Abdelhafez, MA}, title = {Peristaltic pump with heat and mass transfer of a fractional second grade fluid through porous medium inside a tube.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {10608}, pmid = {35739213}, issn = {2045-2322}, mesh = {Friction ; *Hot Temperature ; Magnetic Fields ; *Peristalsis ; Porosity ; }, abstract = {In magnetic resonance imaging (MRI), this MRI is used for the diagnosis of the brain. The dynamic of these particles occurs under the action of the peristaltic waves generated on the flexible walls of the brain. Studying such fluid flow of a Fractional Second-Grade under this action is therefore useful in treating tissues of cancer. This paper deals with a theoretical investigation of the interaction of heat and mass transfer in the peristaltic flow of a magnetic field fractional second-grade fluid through a tube, under the assumption of low Reynolds number and long-wavelength. The analytical solution to a problem is obtained by using Caputo's definition. The effect of different physical parameters, the material constant, magnetic field, and fractional parameter on the temperature, concentration, axial velocity, pressure gradient, pressure rise, friction forces, and coefficient of heat and mass transfer are discussed with particular emphasis. The computed results are presented in graphical form. It is because the nature of heat and mass transfer coefficient is oscillatory which is following the physical expectation due to the oscillatory nature of the tube wall. It is perceived that with an increase in Hartmann number, the velocity decreases. A suitable comparison has been made with the prior results in the literature as a limiting case of the considered problem.}, }
@article {pmid35736684, year = {2022}, author = {Zubairova, US and Kravtsova, AY and Romashchenko, AV and Pushkareva, AA and Doroshkov, AV}, title = {Particle-Based Imaging Tools Revealing Water Flows in Maize Nodal Vascular Plexus.}, journal = {Plants (Basel, Switzerland)}, volume = {11}, number = {12}, pages = {}, pmid = {35736684}, issn = {2223-7747}, support = {19-74-10037//Russian Science Foundation/ ; 19-79-10217//Russian Science Foundation/ ; }, abstract = {In plants, water flows are the major driving force behind growth and play a crucial role in the life cycle. To study hydrodynamics, methods based on tracking small particles inside water flows attend a special place. Thanks to these tools, it is possible to obtain information about the dynamics of the spatial distribution of the flux characteristics. In this paper, using contrast-enhanced magnetic resonance imaging (MRI), we show that gadolinium chelate, used as an MRI contrast agent, marks the structural characteristics of the xylem bundles of maize stem nodes and internodes. Supplementing MRI data, the high-precision visualization of xylem vessels by laser scanning microscopy was used to reveal the structural and dimensional characteristics of the stem vascular system. In addition, we propose the concept of using prototype "Y-type xylem vascular connection" as a model of the elementary connection of vessels within the vascular system. A Reynolds number could match the microchannel model with the real xylem vessels.}, }
@article {pmid35699409, year = {2022}, author = {Martin, AR and Finlay, WH}, title = {Empirical Deposition Correlations.}, journal = {Journal of aerosol medicine and pulmonary drug delivery}, volume = {35}, number = {3}, pages = {109-120}, doi = {10.1089/jamp.2022.29062.arm}, pmid = {35699409}, issn = {1941-2703}, mesh = {Administration, Inhalation ; Aerosols ; *Lung/diagnostic imaging ; Particle Size ; *Pharynx ; }, abstract = {Traditionally, empirical correlations for predicting respiratory tract deposition of inhaled aerosols have been developed using limited available in vivo data. More recently, advances in medical image segmentation and additive manufacturing processes have allowed researchers to conduct extensive in vitro deposition experiments in realistic replicas of the upper and central branching airways. This work has led to a collection of empirical equations for predicting regional aerosol deposition, especially in the upper, nasal and oral airways. The present section reviews empirical correlations based on both in vivo and in vitro data, which may be used to predict total and regional deposition. Equations are presented for predicting total respiratory deposition fraction, mouth-throat fraction, nasal, and nose-throat fractions for a large variety of aerosol sizes, subject age groups, and breathing maneuvers. Use of these correlations to estimate total lung deposition is also described.}, }
@article {pmid35683052, year = {2022}, author = {George, GR and Bockelmann, M and Schmalhorst, L and Beton, D and Gerstle, A and Lindermeir, A and Wehinger, GD}, title = {Influence of Foam Morphology on Flow and Heat Transport in a Random Packed Bed with Metallic Foam Pellets-An Investigation Using CFD.}, journal = {Materials (Basel, Switzerland)}, volume = {15}, number = {11}, pages = {}, pmid = {35683052}, issn = {1996-1944}, support = {ZF 4640501VS8//Federal Ministry for Economic Affairs and Energy/ ; }, abstract = {Open-cell metallic foams used as catalyst supports exhibit excellent transport properties. In this work, a unique application of metallic foam, as pelletized catalyst in a packed bed reactor, is examined. By using a wall-segment Computational Fluid Dynamics (CFD) setup, parametric analyses are carried out to investigate the influence of foam morphologies (cell size ϕ=0.45−3 mm and porosity ε=0.55−0.95) and intrinsic conductivity on flow and heat transport characteristics in a slender packed bed (N=D/dp=6.78) made of cylindrical metallic foam pellets. The transport processes have been modeled using an extended version of conventional particle-resolved CFD, i.e., flow and energy in inter-particle spaces are fully resolved, whereas the porous-media model is used for the effective transport processes inside highly-porous foam pellets. Simulation inputs include the processing parameters relevant to Steam Methane Reforming (SMR), analyzed for low (Rep~100) and high (Rep~5000) flow regimes. The effect of foam morphologies on packed beds has shown that the desired requirements contradict each other, i.e., an increase in cell size and porosity favors the reduction in pressure drop, but, it reduces the heat transfer efficiency. A design study is also conducted to find the optimum foam morphology of a cylindrical foam pellet at a higher Rep~5000, which yields ϕ = 0.45, ε = 0.8. Suitable correlations to predict the friction factor and the overall heat transfer coefficient in a foam-packed bed have been presented, which consider the effect of different foam morphologies over a range of particle Reynolds number, 100≤Rep≤5000.}, }
@article {pmid35676272, year = {2022}, author = {Castro, JM and Feisel, Y}, title = {Eruption of ultralow-viscosity basanite magma at Cumbre Vieja, La Palma, Canary Islands.}, journal = {Nature communications}, volume = {13}, number = {1}, pages = {3174}, pmid = {35676272}, issn = {2041-1723}, abstract = {The viscosity of magma exerts control on all aspects of its migration through the crust to eruption. This was particularly true for the 2021 eruption of Cumbre Vieja (La Palma), which produced exceptionally fast and fluid lava at high discharge rates. We have performed concentric cylinder experiments to determine the effective viscosities of the Cumbre Vieja magma, while accounting for its chemistry, crystallinity, and temperature. Here we show that this event produced a nepheline-normative basanite with the lowest viscosity of historical basaltic eruptions, exhibiting values of less than 10 to about 160 Pa s within eruption temperatures of ~1200 to ~1150 °C. The magma's low viscosity was responsible for many eruptive phenomena that lead to particularly impactful events, including high-Reynolds number turbulent flow and supercritical states. Increases in viscosity due to crystallization-induced melt differentiation were subdued in this eruption, due in part to subtle degrees of silica enrichment in alkaline magma.}, }
@article {pmid35672348, year = {2022}, author = {Saadoon, ZH and Ali, FH and Hamzah, HK and Abed, AM and Hatami, M}, title = {Improving the performance of mini-channel heat sink by using wavy channel and different types of nanofluids.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {9402}, pmid = {35672348}, issn = {2045-2322}, abstract = {The combination of nano fluid and changing cross-section mini-channel heat sink effects have become a remarkable choice for the use of thermal devices such as miniature electronic devices to be effectively cooled. In this paper, the comparison of three dimensional straight and wavy channel configuration with using different types nano fluids are numerically investigated. The effects of wave amplitude and A particular type of volume fraction of (Copper Oxide CuO, Dimond Al2O3, Iron Oxide Fe3O4, Titanium Oxide TiO2 and Silver Ag-nano fluids are offered. Three amplitudes of waves (0.15 mm, 0.2 mm and 0.25 mm) and Reynold's number from 200 to 1000 and concentration volume varieties from 0 to 0.075 are used. The effect on thermal resistance, pressures drop, factor of friction of the mini channel is displayed. It is observed that the mini-channel sink's heat transfer efficiency is greatly enhanced compared to the straight channel in an event of adding distilled water as accoolant. The results indicate that nano fluid and wavy mini-channel can boost the heat sink's hydrothermal efficiency and Ag- water nano fluid in term of heat transfer, it outperforms other nanofluids an enhancement in the Nusselt number reached to 54% at concentration volume 0.075.}, }
@article {pmid35662323, year = {2022}, author = {Ruszczyk, M and Webster, DR and Yen, J}, title = {Trends in Stroke Kinematics, Reynolds Number, and Swimming Mode in Shrimp-Like Organisms.}, journal = {Integrative and comparative biology}, volume = {}, number = {}, pages = {}, doi = {10.1093/icb/icac067}, pmid = {35662323}, issn = {1557-7023}, abstract = {Metachronal propulsion is commonly seen in organisms with the caridoid facies body plan, i.e. shrimp-like organisms, as they beat their pleopods in an adlocomotory sequence. These organisms exist across length scales ranging several orders of Reynolds number magnitude, from 10 to 104, during locomotion. Further, by altering their stroke kinematics, these organisms achieve three distinct swimming modes. To better understand the relationship between Reynolds number, stroke kinematics, and resulting swimming mode, Euphausia pacifica stroke kinematics were quantified using high-speed digital recordings and compared to the results for the larger E. superba. Euphausia pacifica consistently operate with a greater beat frequency and smaller stroke amplitude than E. superba for each swimming mode, suggesting that length scale may affect the kinematics needed to achieve similar swimming modes. To expand on this observation, these euphausiid data are used in combination with previously-published stroke kinematics from mysids and stomatopods to identify broad trends across swimming mode and length scale in metachrony. Principal component analysis (PCA) reveals trends in stroke kinematics and Reynolds number as well as the variation among taxonomic order. Overall, larger beat frequencies, stroke amplitudes, between-cycle phase lags, and Reynolds numbers are more representative of the fast forward swimming mode compared to the slower hovering mode. Additionally, each species has a unique combination of kinematics that result in metachrony, indicating that there are other factors, perhaps morphological, which affect the overall metachronal characteristics of an organism. Finally, uniform phase lag, in which the timing between power strokes of all pleopods is equal, in 5-paddle systems is achieved at different Reynolds numbers for different swimming modes, highlighting the importance of taking into consideration stroke kinematics, length scale, and the resulting swimming mode.}, }
@article {pmid35642428, year = {2022}, author = {Broadley, P and Nabawy, MRA and Quinn, MK and Crowther, WJ}, title = {Dynamic experimental rigs for investigation of insect wing aerodynamics.}, journal = {Journal of the Royal Society, Interface}, volume = {19}, number = {191}, pages = {20210909}, pmid = {35642428}, issn = {1742-5662}, mesh = {Animals ; Biomechanical Phenomena ; *Flight, Animal ; Insecta ; *Models, Biological ; Wings, Animal ; }, abstract = {This paper provides a systematic and critical review of dynamic experimental rigs used for insect wing aerodynamics research. The goal is to facilitate meaningful comparison of data from existing rigs and provide insights for designers of new rigs. The scope extends from simple one degree of freedom rotary rigs to multi degrees of freedom rigs allowing various rotation and translation motions. Experimental methods are characterized using a consistent set of parameters that allows objective comparison of different approaches. A comprehensive catalogue is presented for the tested flow conditions (assessed through Reynolds number, Rossby number and advance ratio), wing morphologies (assessed through aspect ratio, planform shape and thickness to mean chord ratio) and kinematics (assessed through motion degrees of freedom). Links are made between the type of aerodynamic characteristics being studied and the type of experimental set-up used. Rig mechanical design considerations are assessed, and the aerodynamic measurements obtained from these rigs are discussed.}, }
@article {pmid35637889, year = {2022}, author = {Semenov, AP and Mendgaziev, RI and Stoporev, AS and Istomin, VA and Sergeeva, DV and Tulegenov, TB and Vinokurov, VA}, title = {Dataset for the dimethyl sulfoxide as a novel thermodynamic inhibitor of carbon dioxide hydrate formation.}, journal = {Data in brief}, volume = {42}, number = {}, pages = {108289}, pmid = {35637889}, issn = {2352-3409}, abstract = {The temperatures and pressures of the three-phase equilibrium V-Lw-H (gas - aqueous solution - gas hydrate) were measured in the CO2 - H2O - dimethyl sulfoxide (DMSO) system at concentrations of organic solute in the aqueous phase up to 50 mass%. Measurements of CO2 hydrate equilibrium conditions were carried out using a constant volume autoclave by continuous heating at a rate of 0.1 K/h with simultaneous stirring of fluids by a four-blade agitator at 600 rpm. The equilibrium temperature and pressure of CO2 hydrate were determined for the endpoint of the hydrate dissociation in each experiment. The CO2 gas fugacity was calculated by the equation of state for carbon dioxide for the measured points. The flow regime in the autoclave during the operation of the stirring system was characterized by calculating the Reynolds number using literature data on the viscosity and density of water and DMSO aqueous solutions. We employed regression analysis to approximate the dependences of equilibrium pressure (CO2 gas fugacity) on temperature by two- and three-parameter equations. For each measured point, the value of CO2 hydrate equilibrium temperature suppression ΔTh was computed. The dependences of this quantity on CO2 gas fugacity are considered for all DMSO concentrations. The coefficients of empirical correlation describing ΔTh as a function of the DMSO mass fraction in solution and the equilibrium gas pressure are determined. This article is a co-submission with a paper [1].}, }
@article {pmid35635664, year = {2022}, author = {Eldesoukey, A and Hassan, H}, title = {Study of the performance of thermoelectric generator for waste heat recovery from chimney: impact of nanofluid-microchannel cooling system.}, journal = {Environmental science and pollution research international}, volume = {29}, number = {49}, pages = {74242-74263}, pmid = {35635664}, issn = {1614-7499}, abstract = {A huge number of chimneys all over the world utilized in many industrial applications and applications like restaurants, homes, etc. contribute badly on the global warming and climate change due to their waste heat. So, in this paper, the performance of thermoelectric generator (TEG) cooled by microchannel heat spreader having nanofluid and used for waste heat recovery from vertical chimney is investigated. Using heat spreader with microchannel cooling system increases the output TEG power compared to natural convection cooling system. In this paper, the impact of microchannel sizes, using nanofluid and heat spreader with different sizes on the TEG performance and cooling, is considered. Three-dimensional mathematical models including TEG, microchannel, nanofluid, and heat spreader are presented and solved by Ansys Fluent software utilizing user-defined memory, user-defined function, and user-defined scalar. All TEG effects (Joule, Seebeck, and Thomson) are considered in TEG model. Results indicate that TEG power rises with increasing the heat spreader and microchannel sizes together. Increasing microchannel and heat spreader sizes four times of TEG size raises the TEG output power by 10%. This also achieves the maximum cooling system efficiency of 88.9% and the maximum net output power. Microchannel heat spreader cooling system raises the system (TEG power-pumping power) net power by 125.2% compared to the normal channel and decreases the required cooling fluid flow rate. Utilizing copper-water and Al2O3-water nanofluids rises maximally the TEG output power by 14% and 4%, respectively; however, it increases the pumping power. Moreover, using nanofluids increases the net output power at low Reynolds number and decreases it at higher Reynolds number.}, }
@article {pmid35630837, year = {2022}, author = {Souayeh, B and Ramesh, K and Hdhiri, N and Yasin, E and Alam, MW and Alfares, K and Yasin, A}, title = {Heat Transfer Attributes of Gold-Silver-Blood Hybrid Nanomaterial Flow in an EMHD Peristaltic Channel with Activation Energy.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {10}, pages = {}, pmid = {35630837}, issn = {2079-4991}, support = {AN00052//Deanship of Scientific Research at King Faisal University/ ; }, abstract = {The heat enhancement in hybrid nanofluid flow through the peristaltic mechanism has received great attention due to its occurrence in many engineering and biomedical systems, such as flow through canals, the cavity flow model and biomedicine. Therefore, the aim of the current study was to discuss the hybrid nanofluid flow in a symmetric peristaltic channel with diverse effects, such as electromagnetohydrodynamics (EMHD), activation energy, gyrotactic microorganisms and solar radiation. The equations governing this motion were simplified under the approximations of a low Reynolds number (LRN), a long wavelength (LWL) and Debye-Hückel linearization (DHL). The numerical solutions for the non-dimensional system of equations were tackled using the computational software Mathematica. The influences of diverse physical parameters on the flow and thermal characteristics were computed through pictorial interpretations. It was concluded from the results that the thermophoresis parameter and Grashof number increased the hybrid nanofluid velocity near the right wall. The nanoparticle temperature decreased with the radiation parameter and Schmidt number. The activation energy and radiation enhanced the nanoparticle volume fraction, and motile microorganisms decreased with an increase in the Peclet number and Schmidt number. The applications of the current investigation include chyme flow in the gastrointestinal tract, the control of blood flow during surgery by altering the magnetic field and novel drug delivery systems in pharmacological engineering.}, }
@article {pmid35630375, year = {2022}, author = {Soares, A and Gomes, LC and Monteiro, GA and Mergulhão, FJ}, title = {Hydrodynamic Effects on Biofilm Development and Recombinant Protein Expression.}, journal = {Microorganisms}, volume = {10}, number = {5}, pages = {}, pmid = {35630375}, issn = {2076-2607}, support = {LA/P/0045/2020 (ALiCE), UIDB/00511/2020 and UIDP/00511/2020 (LEPABE)//FCT/MCTES (PIDDAC)/ ; PTDC/BII-BIO/29589/2017 - POCI-01-0145-FEDER-029589//FEDER funds through COMPETE2020 - Programa Operacional Competitividade e Internacionaliza&#xe7;&#xe3;o (POCI) and by national funds (PIDDAC) through FCT/MCTES/ ; SFRH/BD/141614/2018; CEECIND/01700/2017//FCT/ ; }, abstract = {Hydrodynamics play an important role in the rate of cell attachment and nutrient and oxygen transfer, which can affect biofilm development and the level of recombinant protein production. In the present study, the effects of different flow conditions on the development of Escherichia coli biofilms and the expression of a model recombinant protein (enhanced green fluorescent protein, eGFP) were examined. Planktonic and biofilm cells were grown at two different flow rates in a recirculating flow cell system for 7 days: 255 and 128 L h[-1] (corresponding to a Reynolds number of 4600 and 2300, respectively). The fluorometric analysis showed that the specific eGFP production was higher in biofilms than in planktonic cells under both hydrodynamic conditions (3-fold higher for 255 L h[-1] and 2-fold higher for 128 L h[-1]). In the biofilm cells, the percentage of eGFP-expressing cells was on average 52% higher at a flow rate of 255 L h[-1]. Furthermore, a higher plasmid copy number (PCN) was obtained for the highest flow rate for both planktonic (244 PCN/cell versus 118 PCN/cell) and biofilm cells (43 PCN/cell versus 29 PCN/cell). The results suggested that higher flow velocities promoted eGFP expression in E. coli biofilms.}, }
@article {pmid35626546, year = {2022}, author = {Alenezi, A and Almutairi, A and Alhajeri, H and Almekmesh, SF and Alzuwayer, BB}, title = {Impact of Surface Roughness on Flow Physics and Entropy Generation in Jet Impingement Applications.}, journal = {Entropy (Basel, Switzerland)}, volume = {24}, number = {5}, pages = {}, pmid = {35626546}, issn = {1099-4300}, abstract = {In this paper, a numerical investigation was performed of an air jet incident that normally occurs on a horizontal heated plane. Analysis of flow physics and entropy generation due to heat and friction is included using a simple easy-to-manufacture, surface roughening element: a circular rib concentric with the air jet. This study shows how varying the locations and dimensions of the rib can deliver a favorable trade-off between entropy generation and flow parameters, such as vortex generation and heat transfer. The performance of the roughness element was tested at three different radii; R/D = 1, 1.5 and 2, where D was the jet hydraulic diameter and R was the radial distance from the geometric center. At each location, the normalized rib height (e/D) was increased from 0.019 to 0.074 based on an increment of (e/D) = 0.019. The jet-to-target distance was H/D = 6 and the jet Reynolds number (Re) ranged from 10,000 to 50,000 Re, which was obtained from the jet hydraulic diameter (D), and the jet exit velocity (U). All results are presented in the form of entropy generation due to friction and heat exchange, as well as the total entropy generated. A detailed comparison of flow physics is presented for all ribs and compared with the baseline case of a smooth surface. The results show that at higher Reynolds numbers, adding a rib of a suitable height reduced the total entropy (St) by 31% compared to the no rib case. In addition, with ribs of heights 0.019, 0.037 and 0.054, respectively, the entropy generated by friction (Sf) was greater than that due to heat exchange (Sh) by about 42%, 26% and 4%, respectively. The rib of height e/D = 0.074 produced the minimum St at R/D = 1. As for varying R/D, varying rib location and Re values had a noticeable impact on Sh, Sf and (St). Placing the rib at R/D = 1 gave the highest total entropy generation (St) followed by R/D = 1.5 for all Re. Finally, the Bejan number increased as both rib height and rib location increased.}, }
@article {pmid35626500, year = {2022}, author = {Dressler, L and Nicolai, H and Agrebi, S and Ries, F and Sadiki, A}, title = {Computation of Entropy Production in Stratified Flames Based on Chemistry Tabulation and an Eulerian Transported Probability Density Function Approach.}, journal = {Entropy (Basel, Switzerland)}, volume = {24}, number = {5}, pages = {}, pmid = {35626500}, issn = {1099-4300}, support = {SA 836/15-1//Deutsche Forschungsgemeinschaft/ ; }, abstract = {This contribution presents a straightforward strategy to investigate the entropy production in stratified premixed flames. The modeling approach is grounded on a chemistry tabulation strategy, large eddy simulation, and the Eulerian stochastic field method. This enables a combination of a detailed representation of the chemistry with an advanced model for the turbulence chemistry interaction, which is crucial to compute the various sources of exergy losses in combustion systems. First, using detailed reaction kinetic reference simulations in a simplified laminar stratified premixed flame, it is demonstrated that the tabulated chemistry is a suitable approach to compute the various sources of irreversibilities. Thereafter, the effects of the operating conditions on the entropy production are investigated. For this purpose, two operating conditions of the Darmstadt stratified burner with varying levels of shear have been considered. The investigations reveal that the contribution to the entropy production through mixing emerging from the chemical reaction is much larger than the one caused by the stratification. Moreover, it is shown that a stronger shear, realized through a larger Reynolds number, yields higher entropy production through heat, mixing and viscous dissipation and reduces the share by chemical reaction to the total entropy generated.}, }
@article {pmid35621794, year = {2022}, author = {Li, H and Nabawy, MRA}, title = {Wing Planform Effect on the Aerodynamics of Insect Wings.}, journal = {Insects}, volume = {13}, number = {5}, pages = {}, pmid = {35621794}, issn = {2075-4450}, support = {RPG-2019-366//Leverhulme Trust/ ; }, abstract = {This study investigates the effect of wing planform shape on the aerodynamic performance of insect wings by numerically solving the incompressible Navier-Stokes equations. We define the wing planforms using a beta-function distribution and employ kinematics representative of normal hovering flight. In particular, we use three primary parameters to describe the planform geometry: aspect ratio, radial centroid location, and wing root offset. The force coefficients, flow structures, and aerodynamic efficiency for different wing planforms at a Reynolds number of 100 are evaluated. It is found that the wing with the lowest aspect ratio of 1.5 results in the highest peaks of lift and drag coefficients during stroke reversals, whereas the higher aspect ratio wings produce higher lift and drag coefficients during mid half-stroke translation. For the wings considered, the leading-edge vortex detachment is found to be approximately at a location that is 3.5-5 mean chord lengths from the wing center of rotation for all aspect ratios and root offsets investigated. Consequently, the detachment area increases with the increase of aspect ratio and root offset, resulting in reduced aerodynamic coefficients. The radial centroid location is found to influence the local flow evolution time, and this results in earlier formation/detachment of the leading-edge vortex for wings with a smaller radial centroid location. Overall, the best performance, when considering both average lift coefficient and efficiency, is found at the intermediate aspect ratios of 4.5-6; increasing the centroid location mainly increases efficiency; and increasing the root offset leads to a decreased average lift coefficient whilst leading to relatively small variations in aerodynamic efficiency for most aspect ratios.}, }
@article {pmid35620608, year = {2022}, author = {Montalvo, S and Gomez, M and Lozano, A and Arias, S and Rodriguez, L and Morales-Acuna, F and Gurovich, AN}, title = {Differences in Blood Flow Patterns and Endothelial Shear Stress at the Carotid Artery Using Different Exercise Modalities and Intensities.}, journal = {Frontiers in physiology}, volume = {13}, number = {}, pages = {857816}, pmid = {35620608}, issn = {1664-042X}, support = {SC2 GM140952/GM/NIGMS NIH HHS/United States ; }, abstract = {Endothelial dysfunction is the first pathophysiological step of atherosclerosis, which is responsible for 90% of strokes. Exercise programs aim to reduce the risk of developing stroke; however, the majority of the beneficial factors of exercise are still unknown. Endothelial shear stress (ESS) is associated with endothelial homeostasis. Unfortunately, ESS has not been characterized during different exercise modalities and intensities in the carotid artery. Therefore, the purpose of this study was to determine exercise-induced blood flow patterns in the carotid artery. Fourteen apparently healthy young adults (males = 7, females = 7) were recruited for this repeated measures study design. Participants completed maximal oxygen consumption (VO2max) tests on a Treadmill, Cycle-ergometer, and Arm-ergometer, and 1-repetition maximum (1RM) tests of the Squat, Bench Press (Bench), and Biceps Curl (Biceps) on separate days. Thereafter, participants performed each exercise at 3 different exercise intensities (low, moderate, high) while a real-time ultrasound image and blood flow of the carotid artery was obtained. Blood flow patterns were assessed by estimating ESS via Womersley's estimation and turbulence via Reynold's number (Re). Data were analyzed using a linear mixed-effects model. Pairwise comparisons with Holm-Bonferroni correction were conducted with Hedge's g effect size to determine the magnitude of the difference. There was a main effect of intensity, exercise modality, and intensity * exercise modality interaction on both ESS (p < 0.001). Treadmill at a high intensity yielded the greatest ESS when compared to the other exercise modalities and intensities, while Bench Press and Biceps curls yielded the least ESS. All exercise intensities across all modalities resulted in turbulent blood flow. Clinicians must take into consideration how different exercise modalities and intensities affect ESS and Re of the carotid artery.}, }
@article {pmid35617810, year = {2022}, author = {Huang, F and Noël, R and Berg, P and Hosseini, SA}, title = {Simulation of the FDA nozzle benchmark: A lattice Boltzmann study.}, journal = {Computer methods and programs in biomedicine}, volume = {221}, number = {}, pages = {106863}, doi = {10.1016/j.cmpb.2022.106863}, pmid = {35617810}, issn = {1872-7565}, mesh = {*Benchmarking ; Computer Simulation ; *Hemodynamics ; Rheology ; }, abstract = {BACKGROUND AND OBJECTIVE: Contrary to flows in small intracranial vessels, many blood flow configurations such as those found in aortic vessels and aneurysms involve larger Reynolds numbers and, therefore, transitional or turbulent conditions. Dealing with such systems require both robust and efficient numerical methods.<br><br>METHODS: We assess here the performance of a lattice Boltzmann solver with full Hermite expansion of the equilibrium and central Hermite moments collision operator at higher Reynolds numbers, especially for under-resolved simulations. To that end the food and drug administration's benchmark nozzle is considered at three different Reynolds numbers covering all regimes: (1) laminar at a Reynolds number of 500, (2) transitional at a Reynolds number of 3500, and (3) low-level turbulence at a Reynolds number of 6500.<br><br>RESULTS: The lattice Boltzmann results are compared with previously published inter-laboratory experimental data obtained by particle image velocimetry. Our results show good agreement with the experimental measurements throughout the nozzle, demonstrating the good performance of the solver even in under-resolved simulations.<br><br>CONCLUSION: In this manner, fast but sufficiently accurate numerical predictions can be achieved for flow configurations of practical interest regarding medical applications.}, }
@article {pmid35598483, year = {2022}, author = {Sharma, S and Jain, S and Saha, A and Basu, S}, title = {Evaporation dynamics of a surrogate respiratory droplet in a vortical environment.}, journal = {Journal of colloid and interface science}, volume = {623}, number = {}, pages = {541-551}, doi = {10.1016/j.jcis.2022.05.061}, pmid = {35598483}, issn = {1095-7103}, mesh = {Crystallization ; Gases ; *Respiratory Aerosols and Droplets ; *Sodium Chloride/chemistry ; Water/chemistry ; }, abstract = {HYPOTHESIS: Vortex droplet interaction is crucial for understanding the route of disease transmission through expiratory jet where several such embedded droplets continuously interact with vortical structures of different strengths and sizes.<br><br>EXPERIMENTS: A train of vortex rings with different vortex strength, quantified with vortex Reynolds number (Re[']=0,53,221,297) are made to interact with an isolated levitated droplet, and the evolution dynamics is captured using shadowgraphy, particle image velocimetry (PIV), and backlight imaging technique. NaCl-DI water solution of 0, 1, 10 and 20 wt% concentrations are used as test fluids for the droplet.<br><br>FINDINGS: The results show the dependence of evaporation characteristics on vortex strength, while the crystallization dynamics was found to be independent of it. A reduction of 12.23% and 14.6% in evaporation time was seen in case of de-ionized (DI) water and 1% wt NaCl solution respectively in presence of vortex ring train at Re[']=221. In contrast to this, a minimal reduction in evaporation time (0.6% and 0.9% for DI water and 1% wt NaCl solution, respectively) is observed when Re['] is increased from 221 to 297. The mechanisms for evaporation time reduction due to enhancement of convective heat and mass transfer from the droplet and shearing away of vapor layer by vortex ring interaction are discussed in this work.}, }
@article {pmid35591423, year = {2022}, author = {Karmveer,  and Kumar Gupta, N and Siddiqui, MIH and Dobrotă, D and Alam, T and Ali, MA and Orfi, J}, title = {The Effect of Roughness in Absorbing Materials on Solar Air Heater Performance.}, journal = {Materials (Basel, Switzerland)}, volume = {15}, number = {9}, pages = {}, pmid = {35591423}, issn = {1996-1944}, abstract = {Artificial roughness on the absorber of the solar air heater (SAH) is considered to be the best passive technology for performance improvement. The roughened SAHs perform better in comparison to conventional SAHs under the same operational conditions, with some penalty of higher pumping power requirements. Thermo-hydraulic performance, based on effective efficiency, is much more appropriate to design roughened SAH, as it considers both the requirement of pumping power and useful heat gain. The shape, size, and arrangement of artificial roughness are the most important factors for the performance optimization of SAHs. The parameters of artificial roughness and operating parameters, such as the Reynolds number (Re), temperature rise parameter (ΔT/I) and insolation (I) show a combined effect on the performance of SAH. In this case study, various performance parameters of SAH have been evaluated to show the effect of distinct artificial roughness, investigated previously. Therefore, thermal efficiency, thermal efficiency improvement factor (TEIF) and the effective efficiency of various roughened absorbers of SAH have been predicted. As a result, thermal and effective efficiencies strongly depend on the roughness parameter, Re and ΔT/I. Staggered, broken arc hybrid-rib roughness shows a higher value of TEIF, thermal and effective efficiencies consistently among all other distinct roughness geometries for the ascending values of ΔT/I. This roughness shows the maximum value of effective efficiency equals 74.63% at a ΔT/I = 0.01 K·m[2]/W. The unique combination of parameters p/e = 10, e/Dh = 0.043 and α = 60° are observed for best performance at a ΔT/I higher than 0.00789 K·m[2]/W.}, }
@article {pmid35591154, year = {2022}, author = {Salem, S and Fraňa, K}, title = {A Wind Tunnel Study of the Flow-Induced Vibrations of a Cylindrical Piezoelectric Transducer.}, journal = {Sensors (Basel, Switzerland)}, volume = {22}, number = {9}, pages = {}, pmid = {35591154}, issn = {1424-8220}, support = {SGS-2022-5040//Technical University of Liberec - SGS/ ; CZ.02.1.01/0.0/0.0/16_019/0000843//European Union and the Czech Government/ ; }, abstract = {Piezoelectric transducers are used as a sensing device to study the fluids' motion. Moreover, they are used as a harvester of energy of Flow-Induced Vibration (FIV). The current FIV harvesters in the literature rely on piezoelectric cantilevers coupled with a bluff body that creates flow instabilities. This paper studies the use of piezoelectric cylinders as a novel transducer in the field of fluid mechanics, where the transducer makes use of its bluff geometry to create instability. The study was based on wind tunnel measurements performed on four piezoelectric cylinders of different sizes over a speed range of 1-7 m/s. The paper looks at the variation of the generated voltage across the Reynolds number. It also compares the spectra of the generated open-circuit voltage to the turbulence spectra features known from the literature.}, }
@article {pmid35590864, year = {2022}, author = {Funatani, S and Tsukamoto, Y and Toriyama, K}, title = {Temperature Measurement of Hot Airflow Using Ultra-Fine Thermo-Sensitive Fluorescent Wires.}, journal = {Sensors (Basel, Switzerland)}, volume = {22}, number = {9}, pages = {}, pmid = {35590864}, issn = {1424-8220}, abstract = {In this paper, we propose a temperature measurement method that uses ultrafine fluorescent wires to reduce the wire diameter to a much lesser extent than a thermocouple. This is possible because its structure is simple and any material can be used for the wire. Hence, ultrafine wires with a Reynolds number of less than 1.0 can be selected. Ultra-fine wires less than 50 µm in diameter were set in the test volume. The wire surfaces were coated with fluorescent paint. The test volume was illuminated using an ultraviolet light-emitting diode. The paint emits very tiny, orange-colored fluorescent light with an intensity that changes with the temperature of the atmosphere. The experimental results showed that the heating/cooling layers were well visualized and the temperature field was well analyzed.}, }
@article {pmid35590633, year = {2022}, author = {Wang, G and Fei, L and Luo, KH}, title = {Unified lattice Boltzmann method with improved schemes for multiphase flow simulation: Application to droplet dynamics under realistic conditions.}, journal = {Physical review. E}, volume = {105}, number = {4-2}, pages = {045314}, doi = {10.1103/PhysRevE.105.045314}, pmid = {35590633}, issn = {2470-0053}, abstract = {As a powerful mesoscale approach, the lattice Boltzmann method (LBM) has been widely used for the numerical study of complex multiphase flows. Recently, Luo et al. [Philos. Trans. R. Soc. A: Math. Phys. Eng. Sci. 379, 20200397 (2021)10.1098/rsta.2020.0397] proposed a unified lattice Boltzmann method (ULBM) to integrate the widely used lattice Boltzmann collision operators into a unified framework. In this study, we incorporate additional features into this ULBM in order to simulate multiphase flow under realistic conditions. A nonorthogonal moment set [Fei et al., Phys. Rev. E 97, 053309 (2018)10.1103/PhysRevE.97.053309] and the entropic-multi-relaxation-time (KBC) lattice Boltzmann model are used to construct the collision operator. An extended combined pseudopotential model is proposed to realize multiphase flow simulation at high-density ratio with tunable surface tension over a wide range. The numerical results indicate that the improved ULBM can significantly decrease the spurious velocities and adjust the surface tension without appreciably changing the density ratio. The ULBM is validated through reproducing various droplet dynamics experiments, such as binary droplet collision and droplet impingement on superhydrophobic surfaces. Finally, the extended ULBM is applied to complex droplet dynamics, including droplet pancake bouncing and droplet splashing. The maximum Weber number and Reynolds number in the simulation reach 800 and 7200, respectively, at a density ratio of 1000. The study demonstrates the generality and versatility of ULBM for incorporating schemes to tackle challenging multiphase problems.}, }
@article {pmid35590627, year = {2022}, author = {Verma, S and Hemmati, A}, title = {Route to transition in propulsive performance of oscillating foil.}, journal = {Physical review. E}, volume = {105}, number = {4-2}, pages = {045102}, doi = {10.1103/PhysRevE.105.045102}, pmid = {35590627}, issn = {2470-0053}, abstract = {Transition in the propulsive performance and vortex synchronization of an oscillating foil in a combined heaving and pitching motion is numerically investigated at a range of reduced frequencies (0.16 ≤f^{*}≤ 0.64), phase offsets (0^{∘} ≤ϕ≤ 315^{∘}), and Reynolds number (1000≤Re≤16000). Focusing on the common case of Re=1000, the drag to thrust transition is identified on a ϕ-f^{*} phase map. Here, the range of 90^{∘} ≤ϕ≤ 225^{∘} depicted a drag-dominated regime for increasing reduced frequency. However, thrust-dominated regimes were observed for ϕ< 90^{∘} and ϕ> 225^{∘}, where increasing the reduced frequency led to an increased thrust production. The isoline-depicting drag-thrust boundary was further observed to coincide with transitions in the characteristic near-wake modes with increasing reduced frequency, which ranged from 2P+2S to 2P and reverse von Kármán modes. However, evaluation of the wake with changing phase offsets at individual reduced frequencies only depicted effects on the spatial configuration of the vortex structures, while the number of vortices shed in one oscillation period was unchanged. The existence of similar wake modes with significantly different propulsive performance clearly suggests that transitions of the wake topology may not always be a reliable tool for understanding propulsive mechanisms of fish swimming or development of underwater propulsion systems. We further assessed a possible route to drag production via investigation into the mean velocity fields at increasing phase offset and at intermediate reduced frequencies ranging from 0.24 to 0.40. This revealed bifurcation of a velocity jet behind the foil on account of the wake topology and dynamics of shed vortex structures. The changes posed by increasing ϕ on wake structure interactions further hints at potential mechanisms that limit the achievement of optimum efficiency in underwater locomotion.}, }
@article {pmid35580542, year = {2022}, author = {Ge, M and Sun, C and Zhang, G and Coutier-Delgosha, O and Fan, D}, title = {Combined suppression effects on hydrodynamic cavitation performance in Venturi-type reactor for process intensification.}, journal = {Ultrasonics sonochemistry}, volume = {86}, number = {}, pages = {106035}, pmid = {35580542}, issn = {1873-2828}, abstract = {Hydrodynamic cavitation is an emerging intensification technology in water treatment or chemical processing, and Venturi-type cavitation reactors exhibit advantages for industrial-scale production. The effects of temperature on hydrodynamic cavitating flows are investigated to find the optimum reaction conditions enhancing cavitating treatment intensity. Results show that the cavitation performance, including the cavitation intensity and cavitation unsteady behavior, is influenced by (1) cavitation number σ (the pressure difference affecting the vaporization process), (2) Reynolds number Re (the inertial/viscous ratio affecting the bubble size and liquid-vapor interface area), and (3) thermodynamic parameter Σ (the thermal effect affecting the temperature drop). With increasing temperature, the cavitation length first increases and then decreases, with a cavitation intensity peak at the transition temperature of 58 °C. With the growth of cavitation extent, the cavity-shedding regimes tend to transition from the attached sheet cavity to the periodic cloud cavity, and the vapor volume fluctuating frequency decreases accordingly. A combined suppression parameter (CSP) is provided to predict that, with increasing CSP value, the cavitation intensity can be decreased. Recommendations are given that working under the low-CSP range (55-60 °C) could enhance the intensification of the cavitation process.}, }
@article {pmid35567865, year = {2022}, author = {Cherkaoui, I and Bettaibi, S and Barkaoui, A and Kuznik, F}, title = {Magnetohydrodynamic blood flow study in stenotic coronary artery using lattice Boltzmann method.}, journal = {Computer methods and programs in biomedicine}, volume = {221}, number = {}, pages = {106850}, doi = {10.1016/j.cmpb.2022.106850}, pmid = {35567865}, issn = {1872-7565}, mesh = {*Atherosclerosis ; Blood Flow Velocity/physiology ; Computer Simulation ; Constriction, Pathologic ; *Coronary Vessels ; Hemodynamics/physiology ; Humans ; Hydrodynamics ; Models, Cardiovascular ; }, abstract = {BACKGROUND AND OBJECTIVE: Cardiovascular diseases such as atherosclerosis are the first engender of death in the world. The malfunctioning of cardiovascular system is attributed mainly to hemodynamics. However, blood magnetic properties are of major haemodynamic interest, with significant clinical applications. The aim of this work is to study numerically the effect of high magnetic field on blood flow in stenotic artery.<br><br>METHODS: In this paper, a double population D2Q9 lattice Boltzmann model is proposed. Velocity and magnetic field are both solved using Lattice Boltzmann method with single relaxation time. Blood is considered homogeneous and Newtonian bio-magnetic fluid. The results of the proposed model are compared and validated by recent numerical and experimental studies in the literature and show good agreement. In this study, simulations are carried out for both hydrodynamics and magneto-hydrodynamics. For the magneto-hydrodynamic case, five values of Hartmann number of 10, 30, 50, 75 and 100 at Reynolds number of 400, 600 and 800 are investigated Results: The results show that velocity and recirculation zone increase with the increase of the degree of stenosis and Reynolds number. In addition, a considerable decrease in velocity, recirculation zones and pressure drop across the stenotic artery is noticed with the increase of Hartmann number.<br><br>CONCLUSION: The suggested model is found to be effective and accurate in the treatment of magneto-hydrodynamic blood flow in stenotic artery. The found results can be used by clinicians in the treatment of certain cardiovascular disorders and in regulating blood flow movement, especially during surgical procedures.}, }
@article {pmid35551230, year = {2022}, author = {Chew, SH and Hoi, SM and Tran, MV and Foo, JJ}, title = {Partially-covered fractal induced turbulence on fins thermal dissipation.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {7861}, pmid = {35551230}, issn = {2045-2322}, support = {FRGS/1/2018/TK07/MUSM/02/1//Ministry of Higher Education, Malaysia/ ; FRGS/1/2018/TK07/MUSM/02/1//Ministry of Higher Education, Malaysia/ ; MUM25929267//Monash University Malaysia/ ; }, abstract = {The impacts of partially-covered fractal grids induced turbulence on the forced convective heat transfer across plate-fin heat sink at Reynolds number ReDh = 22.0 × 10[3] were numerically and experimentally investigated. Results showed that partially covered grids rendered a higher thermal dissipation performance, with partially-covered square fractal grid (PCSFG) registering an outstanding increase of 43% in Nusselt number relative to the no grid configuration. The analyzation via an in-house developed single particle tracking velocimetry (SPTV) system displayed the findings of unique "Turbulence Annulus" formation, which provided a small degree of predictivity in the periodic annulus oscillations. Further assessments on PCSFG revealed the preferred inter-fin flow dynamics of (i) high flow velocity, (ii) strong turbulence intensity, (iii) vigorous flow fluctuations, (iv) small turbulence length scale, and (v) heightened decelerated flow events. These features stemmed from the coupling effects of multilength-scale fractal bar thicknesses in generating a veracity of eddy sizes, and a vertical segmentation producing heightened mass flow rate while inducing favourable wake-flow structures to penetrate inter-fin regions. Teeming effects of such energetic eddies within plate-fin array unveiled a powerful vortex shedding effect, with PCSFG achieving fluctuation frequency f = 18.5 Hz close to an optimal magnitude. The coaction of such traits limits the growth of fin boundary layers, providing superior thermal transfer capabilities which benefits the community in developing for higher efficiency heat transfer systems.}, }
@article {pmid35547578, year = {2022}, author = {Qiao, Y and Luo, K and Fan, J}, title = {Computational Prediction of Thrombosis in Food and Drug Administration's Benchmark Nozzle.}, journal = {Frontiers in physiology}, volume = {13}, number = {}, pages = {867613}, pmid = {35547578}, issn = {1664-042X}, abstract = {Thrombosis seriously threatens human cardiovascular health and the safe operation of medical devices. The Food and Drug Administration's (FDA) benchmark nozzle model was designed to include the typical structure of medical devices. However, the thrombosis in the FDA nozzle has yet not been investigated. The objective of this study is to predict the thrombus formation process in the idealized medical device by coupling computational fluid dynamics and a macroscopic hemodynamic-based thrombus model. We developed the hemodynamic-based thrombus model by considering the effect of platelet consumption. The thrombus model was quantitatively validated by referring to the latest thrombosis experiment, which was performed in a backward-facing step with human blood flow. The same setup was applied in the FDA nozzle to simulate the thrombus formation process. The thrombus shaped like a ring was firstly observed in the FDA benchmark nozzle. Subsequently, the accuracy of the shear-stress transport turbulence model was confirmed in different turbulent flow conditions. Five scenarios with different Reynolds numbers were carried out. We found that turbulence could change the shape of centrosymmetric thrombus to axisymmetric and high Reynolds number blood flow would delay or even prevent thrombosis. Overall, the present study reports the thrombosis process in the FDA benchmark nozzle using the numerical simulation method, and the primary findings may shed light on the effect of turbulence on thrombosis.}, }
@article {pmid35546646, year = {2022}, author = {Gil, A and Navarro, R and Quintero, P and Mares, A and Pérez, M and Montero, JA}, title = {CFD analysis of the HVAD's hemodynamic performance and blood damage with insight into gap clearance.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {21}, number = {4}, pages = {1201-1215}, pmid = {35546646}, issn = {1617-7940}, support = {MODELVAD//Fundaci&#xf3;n para la Investigaci&#xf3;n del Hospital Universitari La Fe/ ; }, mesh = {Equipment Design ; *Heart Failure ; *Heart-Assist Devices ; Hemodynamics ; Hemolysis ; Humans ; }, abstract = {Mechanical circulatory support using ventricular assist devices has become commonplace in the treatment of patients suffering from advanced stages of heart failure. While blood damage generated by these devices has been evaluated in depth, their hemodynamic performance has been investigated much less. This work presents the analysis of the complete operating map of a left ventricular assist device, in terms of pressure head, power and efficiency. Further investigation into its hemocompatibility is included as well. To achieve these objectives, computational fluid dynamics simulations of a centrifugal blood pump with a wide-blade impeller were performed. Several conditions were considered by varying the rotational speed and volumetric flow rate. Regarding the device's hemocompatibility, blood damage was evaluated by means of the hemolysis index. By relating the hemocompatibility of the device to its hemodynamic performance, the results have demonstrated that the highest hemolysis occurs at low flow rates, corresponding to operating conditions of low efficiency. Both performance and hemocompatibility are affected by the gap clearance. An innovative investigation into the influence of this design parameter has yielded decreased efficiencies and increased hemolysis as the gap clearance is reduced. As a further novelty, pump operating maps were non-dimensionalized to highlight the influence of Reynolds number, which allows their application to any working condition. The pump's operating range places it in the transitional regime between laminar and turbulent, leading to enhanced efficiency for the highest Reynolds number.}, }
@article {pmid35544978, year = {2022}, author = {Sander, A and Petračić, A and Zokić, I and Vrsaljko, D}, title = {Scaling up extractive deacidification of waste cooking oil.}, journal = {Journal of environmental management}, volume = {316}, number = {}, pages = {115222}, doi = {10.1016/j.jenvman.2022.115222}, pmid = {35544978}, issn = {1095-8630}, mesh = {*Biofuels/analysis ; Cooking ; *Fatty Acids, Nonesterified ; Plant Oils ; Solvents ; }, abstract = {Biodiesel produced from waste feedstocks can play a significant role in fighting climate change, improperly disposed waste and growing energy demand. Waste feedstocks such as used cooking oil have a great potential for energy production. However, they often have to be purified from free fatty acids prior to biodiesel production. Extractive deacidification with deep eutectic solvents is a promising alternative to conventional purification methods. To evaluate the process of extractive deacidification of waste cooking oil, a full set of physical, hydrodynamic and kinetic data were experimentally determined on a laboratory scale. Hydrodynamic and kinetic experiments were performed in three geometrically similar jacketed agitated vessels. Vessels were equipped with axial flow impeller (four pitched blade impeller). Physical properties (density, viscosity and surface tension) were experimentally determined. Preliminary hydrodynamic experiments involved several model systems without mass transfer. As a result, correlation between power number and Reynolds number as well as scale-up criterion was developed. Obtained dependencies were correlated with the physical properties. Mixing intensity for achieving complete dispersion was determined. Second stage of investigation involved two sets of experiments, hydrodynamic and kinetic, with interphase mass transfer (the extraction of free fatty acids from waste cooking oil with deep eutectic solvent, potassium carbonate:ethylene glycol, 1:10). Obtained results enabled understanding interphase mass transfer and prediction of mass transfer coefficient from the derived dimensionless correlations. The values of volumetric mass transfer coefficients were smaller for the dispersed phase, indicating that the prevailing mass transfer resistance was within the droplets. The working hypothesis was that the same process result should be achieved at the same dispersion rate, and that hypothesis was confirmed - at all scales extraction efficiency was 97.9 ± 0.1%.}, }
@article {pmid35544559, year = {2022}, author = {Callaham, JL and Rigas, G and Loiseau, JC and Brunton, SL}, title = {An empirical mean-field model of symmetry-breaking in a turbulent wake.}, journal = {Science advances}, volume = {8}, number = {19}, pages = {eabm4786}, pmid = {35544559}, issn = {2375-2548}, abstract = {Improved turbulence modeling remains a major open problem in mathematical physics. Turbulence is notoriously challenging, in part due to its multiscale nature and the fact that large-scale coherent structures cannot be disentangled from small-scale fluctuations. This closure problem is emblematic of a greater challenge in complex systems, where coarse-graining and statistical mechanics descriptions break down. This work demonstrates an alternative data-driven modeling approach to learn nonlinear models of the coherent structures, approximating turbulent fluctuations as state-dependent stochastic forcing. We demonstrate this approach on a high-Reynolds number turbulent wake experiment, showing that our model reproduces empirical power spectra and probability distributions. The model is interpretable, providing insights into the physical mechanisms underlying the symmetry-breaking behavior in the wake. This work suggests a path toward low-dimensional models of globally unstable turbulent flows from experimental measurements, with broad implications for other multiscale systems.}, }
@article {pmid35535750, year = {2022}, author = {Zhang, R and Toonder, JD and Onck, PR}, title = {Metachronal patterns by magnetically-programmable artificial cilia surfaces for low Reynolds number fluid transport and mixing.}, journal = {Soft matter}, volume = {18}, number = {20}, pages = {3902-3909}, doi = {10.1039/d1sm01680f}, pmid = {35535750}, issn = {1744-6848}, mesh = {Biological Transport ; *Cilia/metabolism ; *Magnetics ; Models, Biological ; Motion ; }, abstract = {Motile cilia can produce net fluid flows at low Reynolds number because of their asymmetric motion and metachrony of collective beating. Mimicking this with artificial cilia can find application in microfluidic devices for fluid transport and mixing. Here, we study the metachronal beating of nonidentical, magnetically-programmed artificial cilia whose individual non-reciprocal motion and collective metachronal beating pattern can be independently controlled. We use a finite element method that accounts for magnetic forces, cilia deformation and fluid flow in a fully coupled manner. Mimicking biological cilia, we study magnetic cilia subject to a full range of metachronal driving patterns, including antiplectic, symplectic, laeoplectic and diaplectic waves. We analyse the induced primary flow, secondary flow and mixing rate as a function of the phase lag between cilia and explore the underlying physical mechanism. Our results show that shielding effects between neighboring cilia lead to a primary flow that is larger for antiplectic than for symplectic metachronal waves. The secondary flow can be fully explained by the propagation direction of the metachronal wave. Finally, we show that the mixing rate can be strongly enhanced by laeoplectic and diaplectic metachrony resulting in large velocity gradients and vortex-like flow patterns.}, }
@article {pmid35527637, year = {2022}, author = {Gomé, S and Tuckerman, LS and Barkley, D}, title = {Extreme events in transitional turbulence.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {380}, number = {2226}, pages = {20210036}, doi = {10.1098/rsta.2021.0036}, pmid = {35527637}, issn = {1471-2962}, abstract = {Transitional localized turbulence in shear flows is known to either decay to an absorbing laminar state or to proliferate via splitting. The average passage times from one state to the other depend super-exponentially on the Reynolds number and lead to a crossing Reynolds number above which proliferation is more likely than decay. In this paper, we apply a rare-event algorithm, Adaptative Multilevel Splitting, to the deterministic Navier-Stokes equations to study transition paths and estimate large passage times in channel flow more efficiently than direct simulations. We establish a connection with extreme value distributions and show that transition between states is mediated by a regime that is self-similar with the Reynolds number. The super-exponential variation of the passage times is linked to the Reynolds number dependence of the parameters of the extreme value distribution. Finally, motivated by instantons from Large Deviation theory, we show that decay or splitting events approach a most-probable pathway. This article is part of the theme issue 'Mathematical problems in physical fluid dynamics (part 2)'.}, }
@article {pmid35527633, year = {2022}, author = {Drivas, TD}, title = {Self-regularization in turbulence from the Kolmogorov 4/5-law and alignment.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {380}, number = {2226}, pages = {20210033}, doi = {10.1098/rsta.2021.0033}, pmid = {35527633}, issn = {1471-2962}, abstract = {A defining feature of three-dimensional hydrodynamic turbulence is that the rate of energy dissipation is bounded away from zero as viscosity is decreased (Reynolds number increased). This phenomenon-anomalous dissipation-is sometimes called the 'zeroth law of turbulence' as it underpins many celebrated theoretical predictions. Another robust feature observed in turbulence is that velocity structure functions [Formula: see text] exhibit persistent power-law scaling in the inertial range, namely [Formula: see text] for exponents [Formula: see text] over an ever increasing (with Reynolds) range of scales. This behaviour indicates that the velocity field retains some fractional differentiability uniformly in the Reynolds number. The Kolmogorov 1941 theory of turbulence predicts that [Formula: see text] for all [Formula: see text] and Onsager's 1949 theory establishes the requirement that [Formula: see text] for [Formula: see text] for consistency with the zeroth law. Empirically, [Formula: see text] and [Formula: see text], suggesting that turbulent Navier-Stokes solutions approximate dissipative weak solutions of the Euler equations possessing (nearly) the minimal degree of singularity required to sustain anomalous dissipation. In this note, we adopt an experimentally supported hypothesis on the anti-alignment of velocity increments with their separation vectors and demonstrate that the inertial dissipation provides a regularization mechanism via the Kolmogorov 4/5-law. This article is part of the theme issue 'Mathematical problems in physical fluid dynamics (part 2)'.}, }
@article {pmid35527631, year = {2022}, author = {Parente, E and Farano, M and Robinet, JC and De Palma, P and Cherubini, S}, title = {Continuing invariant solutions towards the turbulent flow.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {380}, number = {2226}, pages = {20210031}, doi = {10.1098/rsta.2021.0031}, pmid = {35527631}, issn = {1471-2962}, abstract = {A new mathematical framework is proposed for characterizing the coherent motion of fluctuations around a mean turbulent channel flow. We search for statistically invariant coherent solutions of the unsteady Reynolds-averaged Navier-Stokes equations written in a perturbative form with respect to the turbulent mean flow, using a suitable approximation of the Reynolds stress tensor. This is achieved by setting up a continuation procedure of known solutions of the perturbative Navier-Stokes equations, based on the continuous increase of the turbulent eddy viscosity towards its turbulent value. The recovered solutions, being sustained only in the presence of the Reynolds stress tensor, are representative of the statistically coherent motion of turbulent flows. For small friction Reynolds number and/or domain size, the statistically invariant motion is almost identical to the corresponding invariant solution of the Navier-Stokes equations. Whereas, for sufficiently large friction number and/or domain size, it considerably departs from the starting invariant solution of the Navier-Stokes equations, presenting spatial structures, main wavelengths and scaling very close to those characterizing both large- and small-scale motion of turbulent channel flows. This article is part of the theme issue 'Mathematical problems in physical fluid dynamics (part 2)'.}, }
@article {pmid35523801, year = {2022}, author = {Tretola, G and Vogiatzaki, K}, title = {Unveiling the dynamics of ultra high velocity droplet impact on solid surfaces.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {7416}, pmid = {35523801}, issn = {2045-2322}, support = {EP/S001824/1//Engineering and Physical Sciences Research Council/ ; EP/S001824/1//Engineering and Physical Sciences Research Council/ ; }, abstract = {The impact of a liquid droplet onto a solid surface is a phenomenon present in a wide range of natural processes and technological applications. In this study, we focus on impact conditions characterised by ultra high velocities (up to 500 m/s), to investigate-for the first time-how the impact dynamics change when the compressibility of the liquid in the droplet is no longer negligible. A water droplet impacting a dry substrate at four different velocities, from 50 to 500 m/s, is simulated. Such conditions are particularly relevant to aviation as well as industrial gas turbine engine risk management. Thus, numerical investigations as the one we present here provide a powerful tool to analyse the process. We find that increasing the impact velocity changes the flow field within and outside the droplet the moment that the compressibility can no longer be neglected, with the rise of pressure fronts in both regions. Increasing the impact velocity, the compressibility affects also the lamella formed and changes its ejection velocity observed over time (and thus the wetting behaviour) when the region shift from incompressible to compressible. Moreover, it is found that the maximum pressure observed at the wall during the impact is located at the corner of the impact, where the lamella is ejected, not in the centre, and it is influenced by the initial velocity. To predict the maximum pressure experienced by the surface during the high velocity impact, we propose a correlation based on the initial Weber and Reynolds number of the droplet. The complexity and the scales of the dynamics involved in the ultra-high velocity impact is limiting the experimental and analytical studies. To the best of our knowledge there are no experimental data currently available at such conditions. In this study, through numerical simulations, new insights about the impact dynamics at such conditions are provided.}, }
@article {pmid35523157, year = {2022}, author = {D'Adamo, J and Collaud, M and Sosa, R and Godoy-Diana, R}, title = {Wake and aeroelasticity of a flexible pitching foil.}, journal = {Bioinspiration &amp; biomimetics}, volume = {17}, number = {4}, pages = {}, doi = {10.1088/1748-3190/ac6d96}, pmid = {35523157}, issn = {1748-3190}, abstract = {A flexible foil undergoing pitching oscillations is studied experimentally in a wind tunnel with different imposed free stream velocities. The chord-based Reynolds number is in the range 1600-4000, such that the dynamics of the system is governed by inertial forces and the wake behind the foil exhibits the reverse Bénard-von Kármán vortex street characteristic of flapping-based propulsion. Particle image velocimetry (PIV) measurements are performed to examine the flow around the foil, whilst the deformation of the foil is also tracked. The first natural frequency of vibration of the foil is within the range of flapping frequencies explored, determining a strongly-coupled dynamics between the elastic foil deformation and the vortex shedding. Cluster-based reduced order modelling is applied on the PIV data in order to identify the coherent flow structures. Analysing the foil kinematics and using a control-volume calculation of the average drag forces from the corresponding velocity fields, we determine the optimal flapping configurations for thrust generation. We show that propulsive force peaks occur at dimensionless frequencies shifted with respect to the elastic resonances that are marked by maximum trailing edge oscillation amplitudes. The thrust peaks are better explained by a wake resonance, which we examine using the tools of classic hydrodynamic stability on the mean propulsive jet profiles.}, }
@article {pmid35522515, year = {2022}, author = {Schindler, F and Eckert, S and Zürner, T and Schumacher, J and Vogt, T}, title = {Collapse of Coherent Large Scale Flow in Strongly Turbulent Liquid Metal Convection.}, journal = {Physical review letters}, volume = {128}, number = {16}, pages = {164501}, doi = {10.1103/PhysRevLett.128.164501}, pmid = {35522515}, issn = {1079-7114}, abstract = {The large-scale flow structure and the turbulent transfer of heat and momentum are directly measured in highly turbulent liquid metal convection experiments for Rayleigh numbers varied between 4×10^{5} and ≤5×10^{9} and Prandtl numbers of 0.025≤Pr≤0.033. Our measurements are performed in two cylindrical samples of aspect ratios Γ=diameter/height=0.5 and 1 filled with the eutectic alloy GaInSn. The reconstruction of the three-dimensional flow pattern by 17 ultrasound Doppler velocimetry sensors detecting the velocity profiles along their beam lines in different planes reveals a clear breakdown of coherence of the large-scale circulation for Γ=0.5. As a consequence, the scaling laws for heat and momentum transfer inherit a dependence on the aspect ratio. We show that this breakdown of coherence is accompanied with a reduction of the Reynolds number Re. The scaling exponent β of the power law Nu∝Ra^{β} crosses eventually over from β=0.221 to 0.124 when the liquid metal flow at Γ=0.5 reaches Ra≳2×10^{8} and the coherent large-scale flow is completely collapsed.}, }
@article {pmid35512019, year = {2022}, author = {Fei, L and Qin, F and Zhao, J and Derome, D and Carmeliet, J}, title = {Pore-Scale Study on Convective Drying of Porous Media.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {38}, number = {19}, pages = {6023-6035}, doi = {10.1021/acs.langmuir.2c00267}, pmid = {35512019}, issn = {1520-5827}, abstract = {In this work, a numerical model for isothermal liquid-vapor phase change (evaporation) of the two-component air-water system is proposed based on the pseudopotential lattice Boltzmann method. Through the Chapman-Enskog multiscale analysis, we show that the model can correctly recover the macroscopic governing equations of the multicomponent multiphase system with a built-in binary diffusion mechanism. The model is verified based on the two-component Stefan problem where the measured binary diffusivity is consistent with theoretical analysis. The model is then applied to convective drying of a dual-porosity porous medium at the pore scale. The simulation captures a classical transition in the drying process of porous media, from the constant rate period (CRP, first phase) showing significant capillary pumping from large to small pores, to the falling rate period (FRP, second phase) with the liquid front receding in small pores. It is found that, in the CRP, the evaporation rate increases with the inflow Reynolds number (Re), while in the FRP, the evaporation curves almost collapse at different Res. The underlying mechanism is elucidated by introducing an effective Péclet number (Pe). It is shown that convection is dominant in the CRP and diffusion in the FRP, as evidenced by Pe > 1 and Pe < 1, respectively. We also find a log-law dependence of the average evaporation rate on the inflow Re in the CRP regime. The present work provides new insights into the drying physics of porous media and its direct modeling at the pore scale.}, }
@article {pmid35493567, year = {2021}, author = {Salari, A and Appak-Baskoy, S and Coe, IR and Tsai, SSH and Kolios, MC}, title = {An ultrafast enzyme-free acoustic technique for detaching adhered cells in microchannels.}, journal = {RSC advances}, volume = {11}, number = {52}, pages = {32824-32829}, pmid = {35493567}, issn = {2046-2069}, abstract = {Adherent cultured cells are widely used biological tools for a variety of biochemical and biotechnology applications, including drug screening and gene expression analysis. One critical step in culturing adherent cells is the dissociation of cell monolayers into single-cell suspensions. Different enzymatic and non-enzymatic methods have been proposed for this purpose. Trypsinization, the most common enzymatic method for dislodging adhered cells, can be detrimental to cells, as it can damage cell membranes and ultimately cause cell death. Additionally, all available techniques require a prolonged treatment duration, typically on the order of minutes (5-10 min). Dissociation of cells becomes even more challenging in microfluidic devices, where, due to the nature of low Reynolds number flow and reduced mixing efficiency, multiple washing steps and prolonged trypsinization may be necessary to treat all cells. Here, we report a novel acoustofluidic method for the detachment of cells adhered onto a microchannel surface without exposing the cells to any enzymatic or non-enzymatic chemicals. This method enables a rapid (i.e., on the order of seconds), cost-effective, and easy-to-operate cell detachment strategy, yielding a detachment efficiency of ∼99% and cellular viability similar to that of the conventional trypsinization method. Also, as opposed to biochemical-based techniques (e.g., enzymatic), in our approach, cells are exposed to the dissociating agent (i.e., substrate-mediated acoustic excitation and microstreaming flow) only for as long as they remain attached to the substrate. After dissociation, the effect of acoustic excitation is reduced to microstreaming flow, therefore, minimizing unwanted effects of the dissociating agent on the cell phenotype. Additionally, our results suggest that cell excitation at acoustic powers lower than that required for complete cell detachment can potentially be employed for probing the adhesion strength of cell-substrate attachment. This novel approach can, therefore, be used for a wide range of lab-on-a-chip applications.}, }
@article {pmid35489898, year = {2022}, author = {Das, A and Styslinger, M and Harris, DM and Zenit, R}, title = {Force and torque-free helical tail robot to study low Reynolds number micro-organism swimming.}, journal = {The Review of scientific instruments}, volume = {93}, number = {4}, pages = {044103}, doi = {10.1063/5.0079815}, pmid = {35489898}, issn = {1089-7623}, mesh = {Models, Biological ; *Robotics ; *Swimming/physiology ; Torque ; Viscosity ; }, abstract = {Helical propulsion is used by many micro-organisms to swim in viscous-dominated environments. Their swimming dynamics are relatively well understood, but a detailed study of the flow fields is still needed to understand wall effects and hydrodynamic interactions among swimmers. In this letter, we describe the development of an autonomous swimming robot with a helical tail that operates in the Stokes regime. The device uses a battery-based power system with a miniature motor that imposes a rotational speed on a helical tail. The speed, direction, and activation are controlled electronically using an infrared remote control. Since the robot is about 5 cm long, we use highly viscous fluids to match the Reynolds number, Re, to be less than 0.1. Measurements of swimming speeds are conducted for a range of helical wavelengths, λ, head geometries, and rotation rates, ω. We provide comparisons of the experimental measurements with analytical predictions derived from resistive force theory. This force and torque-free neutrally buoyant swimmer mimics the swimming strategy of bacteria more closely than previously used designs and offers a lot of potential for future applications.}, }
@article {pmid35489862, year = {2022}, author = {Prasad, V and Kulkarni, SS and Sharma, A}, title = {Chaotic advection in a recirculating flow: Effect of a fluid-flexible-solid interaction.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {32}, number = {4}, pages = {043122}, doi = {10.1063/5.0079141}, pmid = {35489862}, issn = {1089-7682}, abstract = {The present work is on laminar recirculating flow-induced deformation as well as motion of a neutrally buoyant flexible elliptical solid, resulting in Lagrangian chaos in a two-dimensional lid-driven cavity flow. Using a fully Eulerian and monolithic approach-based single-solver for the fluid flow and flexible-solid deformation, a chaotic advection study is presented for various aspect ratios β (=0.5-1.0) and a constant volume fraction Φ=10% of an elliptical solid at a constant Ericksen number Er=0.05 and Reynolds number Re=100. Our initial analysis reveals maximum chaotic advection at β=0.5 for which a comprehensive nonlinear dynamical analysis is presented. The Poincaré map revealed elliptic islands and chaotic sea in the fluid flow. Three large elliptic islands, apart from certain smaller islands, were identified near the solid. Periodic point analysis revealed the lowest order hyperbolic/elliptic periodic points to be three. Adaptive material tracking gave a physical picture of a deforming material blob revealing its exponential stretch along with steep folds and demonstrated unstable/stable manifolds corresponding to lowest order hyperbolic points. Furthermore, adaptive material tracking demonstrates heteroclinic connections and tangles in the system that confirm the existence of chaos. For the transient as compared to the periodic flow, adaptive material tracking demonstrates a larger exponential increase of the blob's interfacial area. The finite-time Lyapunov exponent field revealed attracting/repelling Lagrangian coherent structures and entrapped fluid zones. Our work demonstrates an immersed deformable solid-based onset of chaotic advection, for the first time in the literature, which is relevant to a wide range of applications.}, }
@article {pmid35487201, year = {2022}, author = {Akanyeti, O and Di Santo, V and Goerig, E and Wainwright, DK and Liao, JC and Castro-Santos, T and Lauder, GV}, title = {Fish-inspired segment models for undulatory steady swimming.}, journal = {Bioinspiration &amp; biomimetics}, volume = {17}, number = {4}, pages = {}, doi = {10.1088/1748-3190/ac6bd6}, pmid = {35487201}, issn = {1748-3190}, support = {R01 DC010809/DC/NIDCD NIH HHS/United States ; }, mesh = {Animals ; Biological Evolution ; Biomechanical Phenomena/physiology ; *Fishes/physiology ; Hydrodynamics ; *Swimming/physiology ; }, abstract = {Many aquatic animals swim by undulatory body movements and understanding the diversity of these movements could unlock the potential for designing better underwater robots. Here, we analyzed the steady swimming kinematics of a diverse group of fish species to investigate whether their undulatory movements can be represented using a series of interconnected multi-segment models, and if so, to identify the key factors driving the segment configuration of the models. Our results show that the steady swimming kinematics of fishes can be described successfully using parsimonious models, 83% of which had fewer than five segments. In these models, the anterior segments were significantly longer than the posterior segments, and there was a direct link between segment configuration and swimming kinematics, body shape, and Reynolds number. The models representing eel-like fishes with elongated bodies and fishes swimming at high Reynolds numbers had more segments and less segment length variability along the body than the models representing other fishes. These fishes recruited their anterior bodies to a greater extent, initiating the undulatory wave more anteriorly. Two shape parameters, related to axial and overall body thickness, predicted segment configuration with moderate to high success rate. We found that head morphology was a good predictor of its segment length. While there was a large variation in head segments, the length of tail segments was similar across all models. Given that fishes exhibited variable caudal fin shapes, the consistency of tail segments could be a result of an evolutionary constraint tuned for high propulsive efficiency. The bio-inspired multi-segment models presented in this study highlight the key bending points along the body and can be used to decide on the placement of actuators in fish-inspired robots, to model hydrodynamic forces in theoretical and computational studies, or for predicting muscle activation patterns during swimming.}, }
@article {pmid35481832, year = {2022}, author = {Hu, S and Zhang, J and Shelley, MJ}, title = {Enhanced clamshell swimming with asymmetric beating at low Reynolds number.}, journal = {Soft matter}, volume = {18}, number = {18}, pages = {3605-3612}, doi = {10.1039/d2sm00292b}, pmid = {35481832}, issn = {1744-6848}, abstract = {A single flexible filament can be actuated to escape from the scallop theorem and generate net propulsion at low Reynolds number. In this work, we study the dynamics of a simple boundary-driven multi-filament swimmer, a two-arm clamshell actuated at the hinged point, using a nonlocal slender body approximation with hydrodynamic interactions. We first consider an elastic clamshell consisted of flexible filaments with intrinsic curvature, and then build segmental models consisted of rigid segments connected by different mechanical joints with different forms of response torques. The simplicity of the system allows us to fully explore the effect of various parameters on the swimming performance. Optimal included angles and elastoviscous numbers are identified. The segmental models capture the characteristic dynamics of the elastic clamshell. We further demonstrate how the swimming performance can be significantly enhanced by the asymmetric beating patterns induced by biased torques.}, }
@article {pmid35478056, year = {2022}, author = {Kotnurkar, A and Kallolikar, N}, title = {Effect of Joule heating and entropy generation on multi-slip condition of peristaltic flow of Casson nanofluid in an asymmetric channel.}, journal = {Journal of biological physics}, volume = {48}, number = {3}, pages = {273-293}, pmid = {35478056}, issn = {1573-0689}, mesh = {Entropy ; *Heating ; Hot Temperature ; *Nanoparticles ; Peristalsis/physiology ; }, abstract = {In the present investigation, the effect of multi-slip condition on peristaltic flow through asymmetric channel with Joule heating effect is considered. We also considered the incompressible non-Newtonian Casson nanofluid model for blood, which is electrically conducting. Second law of thermodynamics is used to examine the entropy generation. Multi-slip condition is used at the boundary of the wall and the analysis is also restricted under the low Reynolds number and long wavelength assumption. The governing equations were transformed into a non-dimensional form by using suitable terms. The reduced non-dimensional highly nonlinear partial differential equations are solved by using the Homotopy Perturbation Sumudu transformation method (HPSTM). The influence of different physical parameters on dimensionless velocity, pressure gradient, temperature, concentration and nanoparticle is graphically presented. From the results, one can understand that the Joule heating effect controls the heat transfer in the system and as the magnetic parameter is increased, there will be decay in the velocity of fluid. The outcomes of the present investigation can be applicable in examining the chyme motion in the gastrointestinal tract and controlling the blood flow during surgery. Present study shows an excellent agreement with the previously available studies in the limiting case.}, }
@article {pmid35460986, year = {2022}, author = {Liu, J and Yang, Z and Li, M and Lu, K and Li, D}, title = {Evaluating the concrete grade-control structures built by modified fish-nest bricks in the river restoration: A lab-based case study.}, journal = {Journal of environmental management}, volume = {314}, number = {}, pages = {115056}, doi = {10.1016/j.jenvman.2022.115056}, pmid = {35460986}, issn = {1095-8630}, mesh = {Animals ; Ecosystem ; *Fishes ; *Rivers ; Water ; }, abstract = {Concrete grade-control structures (CGCSs) have broad application prospects in the restoration of large rivers. But there is a lack of indicators to evaluate CGCSs at laboratory study. In this study, we proposed two evaluation indicators from the perspective of the impact of CGCSs on geomorphology change and fish habitat, namely the spatial-averaged occurrence probability of sweep events near the bed and flow diversity. To verify the reasonableness of these indicators, flume experiments were conducted with CGCSs built by modified fish-nest bricks in different Reynolds number and layout condition. Data of the flow field around structures in streamwise, transverse and vertical direction was obtained and analyzed. Results of mean flow field show that large recirculation zones are found in the cavity and behind the element. The mechanism of suspended sediment deposition around CGCSs in the flow can be further clarified by combining sweep and ejection according to quadrant analysis. In the vertical direction, the ratio of sweep to total events near bed after spatial-averaged processing is found to be higher for the staggered array. According to the Shannon's entropy, water flow diversity was calculated to quantify the fish habitat. The water flow diversity index around the CGCSs is higher for the staggered. It can be concluded that the elements of CGCSs in staggered manners have a better protection for riverbed and can provide a more stable fish habitat suitability. The results anticipated by the spatial-averaged occurrence probability of sweep events near bed and flow diversity in the experiment are consistent with the result of previous research on landform change and fish habitat. The research could provide a theoretical basis for the application of CGCSs for river restoration.}, }
@article {pmid35457904, year = {2022}, author = {Martin, E and Valeije, A and Sastre, F and Velazquez, A}, title = {Impact of Channels Aspect Ratio on the Heat Transfer in Finned Heat Sinks with Tip Clearance.}, journal = {Micromachines}, volume = {13}, number = {4}, pages = {}, pmid = {35457904}, issn = {2072-666X}, abstract = {A 3D numerical study is used to analyze the flow topology and performance, in terms of heat transfer efficiency and required pumping power, of heat sink devices with different channel aspect-ratio in the presence of tip-clearance. Seven different channel aspect ratios AR, from 0.25 to 1.75, were analyzed. The flow Reynolds numbers Re, based on the average velocity evaluated in the device channels region, were in the range of 200 to 1000. Two different behaviors of the global Nusselt were obtained depending on the flow Reynolds number: for Re<600, the heat transfer increased with the channels aspect ratio, e.g., for Re=400, the global Nusselt number increased by 14% for configuration AR=1.75 when compared to configuration AR=0.25. For Re>600, the maximum Nusselt is obtained for the squared-channel configuration, and, for some configurations, flow destabilization to a unsteady regime appeared. For Re=700, Nusselt number reduced when compared with the squared-channel device, 11% and 2% for configurations with AR=0.25 and 1.75, respectively. Dimensionless pressure drop decreased with the aspect ratio for all cases. In the context of micro-devices, where the Reynolds number is small, these results indicate that the use of channels with high aspect-ratios is more beneficial, both in terms of thermal and dynamic efficiency.}, }
@article {pmid35454454, year = {2022}, author = {Ayub, R and Ahmad, S and Ahmad, S and Akhtar, Y and Alam, MM and Mahmoud, O}, title = {Numerical Assessment of Dipole Interaction with the Single-Phase Nanofluid Flow in an Enclosure: A Pseudo-Transient Approach.}, journal = {Materials (Basel, Switzerland)}, volume = {15}, number = {8}, pages = {}, pmid = {35454454}, issn = {1996-1944}, abstract = {Nanofluids substantially enhance the physical and thermal characteristics of the base or conducting fluids specifically when interacting with the magnetic field. Several engineering processes like geothermal energy extraction, metal casting, nuclear reactor coolers, nuclear fusion, magnetohydrodynamics flow meters, petrochemicals, and pumps incorporate magnetic field interaction with the nanofluids. On the other hand, an enhancement in heat transfer due to nanofluids is essentially required in various thermal systems. The goal of this study is to figure out that how much a magnetic field affects nanofluid flow in an enclosure because of a dipole. The nanofluid is characterized using a single-phase model, and the governing partial differential equations are computed numerically. A Pseudo time based numerical algorithm is developed to numerically solve the problem. It can be deduced that the Reynolds number and the magnetic parameter have a low effect on the Nusselt number and skin friction. The Nusselt number rises near the dipole location because of an increase in the magnetic parameter Mn and the Reynolds number Re. The imposed magnetic field alters the region of high temperature nearby the dipole, while newly generated vortices rotate in alternate directions. Furthermore, nanoparticle volume fraction causes a slight change in the skin friction while it marginally reduces the Nusselt number.}, }
@article {pmid35448318, year = {2022}, author = {Chandrasekaran, AS and Fix, AJ and Warsinger, DM}, title = {Combined Membrane Dehumidification with Heat Exchangers Optimized Using CFD for High Efficiency HVAC Systems.}, journal = {Membranes}, volume = {12}, number = {4}, pages = {}, pmid = {35448318}, issn = {2077-0375}, support = {CHPB-50-2020//Purdue Center for High Performance Buildings/ ; }, abstract = {Traditional air conditioning systems use a significant amount of energy on dehumidification by condensing water vapor out from the air. Membrane-based air conditioning systems help overcome this problem by avoiding condensation and treating the sensible and latent loads separately, using membranes that allow water vapor transport, but not air (nitrogen and oxygen). In this work, a computational fluid dynamics (CFD) model has been developed to predict the heat and mass transfer and concentration polarization performance of a novel active membrane-based energy exchanger (AMX). The novel design is the first of its kind to integrate both vapor removal via membranes and air cooling into one device. The heat transfer results from the CFD simulations are compared with common empirical correlations for similar geometries. The performance of the AMX is studied over a broad range of operating conditions using the compared CFD model. The results show that strong tradeoffs result in optimal values for the channel length (0.6-0.8 m) and the ratio of coil diameter to channel height (~0.5). Water vapor transport is best if the flow is just past the turbulence transition around 3000-5000 Reynolds number. These trends hold over a range of conditions and dimensions.}, }
@article {pmid35446443, year = {2022}, author = {Torres-Saucedo, OL and Morales-Cruzado, B and Pérez-Gutiérrez, FG}, title = {Experimental determination of shear stresses on an artificial transcoelomic metastasis model using optical tweezers: A comparison with numerical simulation.}, journal = {Lasers in surgery and medicine}, volume = {54}, number = {7}, pages = {1027-1037}, doi = {10.1002/lsm.23554}, pmid = {35446443}, issn = {1096-9101}, mesh = {Blood Flow Velocity ; Computer Simulation ; Humans ; *Neoplasms ; *Optical Tweezers ; Stress, Mechanical ; }, abstract = {BACKGROUND: One of the reported pathways of cancer spread is the transcoelomic pathway, which is understood as the spread of cancer cells in the abdominal and thoracic cavities through interstitial fluid. It has been proven that the shear stresses caused by microfluidic currents on cancer tumors in the abdominal and thoracic cavities cause the detachment of cancer cells triggering transcoelomic metastasis; however, the magnitude of shear stresses has not yet been measured experimentally.<br><br>OBJECTIVES: The objective of this study is to develop an experimental methodology using optical tweezers to approximate the shear stresses suffered by a nonporous, rigid artificial cancerous nodule model.<br><br>METHODS: Artificial cancerous nodule model was made by the agglomeration of 2&#x2009;&#x3bc;m diameter polystyrene particles in a microfluidic platform. Optical tweezers were used as a velocimetry tool and shear stresses on the surface of the nodule model were approximated with the viscous shear stress equation. The results were verified with a numerical simulation performed in Ansys Fluent.<br><br>RESULTS: Shear stress originated by microflow over artificial cancerous nodule model were quantified both experimentally and numerically, showing good agreement between both methods. Such stress on the nodules' surface was much greater than that suffered by the wall on which the nodule model was located and dependent of the nodule model geometry. Although the experiment and simulation of this study were performed using a rigid and nonporous nodule model, the conclusion obtained about the increase of shear stresses applies to permeable, porous, and soft nodules as well, because the shear stresses are associated to the acceleration of the fluid originated by the reduction of the cross-sectional area.<br><br>CONCLUSIONS: Shear stress over artificial nodule model were successfully quantified using optical tweezer-based velocimetry technique and verified through numerical calculation. Advantages of experimental technique are: (1) it allows to control the position in a three-dimensional plane, allowing measurements in the vicinity of the analyzed surfaces, and (2) it is applicable for very low Reynolds number (Re &#x2009;&#xab;&#x2009;1). On the other hand, as disadvantages: (1) it tends to be complicated to perform velocity measurements over obstacles and (2) it is limited in trapping distance.}, }
@article {pmid35436159, year = {2023}, author = {Ibrahim, MG}, title = {Numerical simulation to the activation energy study on blood flow of seminal nanofluid with mixed convection effects.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {26}, number = {3}, pages = {315-325}, doi = {10.1080/10255842.2022.2063018}, pmid = {35436159}, issn = {1476-8259}, mesh = {*Convection ; Computer Simulation ; Viscosity ; Motion ; *Body Fluids ; }, abstract = {This study sheds light on the influences of Arrhenius activation energy and variable velocity slip on MHD blood motion of Seminal nanofluid in a vertical symmetric channel. In addition, mixed convection, hall current and thermal jump are taken into consideration. The governing system of differential equations with highly nonlinear terms is simplified with facts of long wavelength and low Reynolds number. Pade' approximant and differential transform techniques are combined mathematically to obtain the semi-numerical solutions for the governing system of PDEs. The results are computed and verified graphically with aid of Mathematica 12.3. Physical parameters considered are studied in detail sketchily for the proposed model. Verification/signification of results is approved semi-numerically by comparing the prior results by the newest existing published results by Ahmad et al 2021. Results show that, Velocity of seminal fluid is diminishes with a rise in viscosity-dependent parameter that is a significant feature which can be utilized in controlling the transport of spermatozoa into the cervical canal.}, }
@article {pmid35428793, year = {2022}, author = {Koo, D and So, H}, title = {Facile microfabrication of three dimensional-patterned micromixers using additive manufacturing technology.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {6346}, pmid = {35428793}, issn = {2045-2322}, mesh = {Computer Simulation ; Equipment Design ; *Lab-On-A-Chip Devices ; *Microtechnology ; Printing, Three-Dimensional ; }, abstract = {This study investigates the manufacturing method of oblique patterns in microchannels and the effect of these patterns on mixing performance in microchannels. To fabricate three-dimensional (3D) and oblique patterns in microchannels, 3D printing and replica methods were utilized to mold patterns and microchannels, respectively. The angle and size of the patterns were controlled by the printing angle and resolution, respectively. The mixing efficiency was experimentally characterized, and the mixing principle was analyzed using computational fluid dynamics simulation. The analysis showed that the mixing channel cast from the mold printed with a printing angle of 30° and resolution of 300 μm exhibited the best mixing efficiency with a segregation index of approximately 0.05 at a Reynolds number of 5.4. This was because, as the patterns inside the microchannel were more oblique, "split" and "recombine" behaviors between two fluids were enhanced owing to the geometrical effect. This study supports the use of the 3D printing method to create unique patterns inside microchannels and improve the mixing performance of two laminar flows for various applications such as point-of-care diagnostics, lab-on-a-chip, and chemical synthesis.}, }
@article {pmid35428381, year = {2022}, author = {Ilg, P}, title = {Multiparticle collision dynamics for ferrofluids.}, journal = {The Journal of chemical physics}, volume = {156}, number = {14}, pages = {144905}, doi = {10.1063/5.0087981}, pmid = {35428381}, issn = {1089-7690}, abstract = {Detailed studies of the intriguing field-dependent dynamics and transport properties of confined flowing ferrofluids require efficient mesoscopic simulation methods that account for fluctuating ferrohydrodynamics. Here, we propose such a new mesoscopic model for the dynamics and flow of ferrofluids, where we couple the multi-particle collision dynamics method as a solver for the fluctuating hydrodynamics equations to the stochastic magnetization dynamics of suspended magnetic nanoparticles. This hybrid model is validated by reproducing the magnetoviscous effect in Poiseuille flow, obtaining the rotational viscosity in quantitative agreement with theoretical predictions. We also illustrate the new method for the benchmark problem of flow around a square cylinder. Interestingly, we observe that the length of the recirculation region is increased, whereas the drag coefficient is decreased in ferrofluids when an external magnetic field is applied compared with the field-free case at the same effective Reynolds number. The presence of thermal fluctuations and the flexibility of this particle-based mesoscopic method provide a promising tool to investigate a broad range of flow phenomena of magnetic fluids, and the method could also serve as an efficient way to simulate solvent effects when colloidal particles are immersed in ferrofluids.}, }
@article {pmid35428147, year = {2022}, author = {Nagy, PT}, title = {Enstrophy change of the Reynolds-Orr solution in channel flow.}, journal = {Physical review. E}, volume = {105}, number = {3-2}, pages = {035108}, doi = {10.1103/PhysRevE.105.035108}, pmid = {35428147}, issn = {2470-0053}, abstract = {The plane Poiseuille flow is one of the elementary flow configurations. Although its laminar-turbulent transition mechanism has been investigated intensively in the last century, the significant difference in the critical Reynolds number between the experiments and the theory lacks a clear explanation. In this paper, an attempt is made to reduce this gap by analyzing the solution of the Reynolds-Orr equation. Recent published results have shown that the usage of enstrophy (the volume integral of the squared vorticity) instead of the kinetic energy as the norm of perturbations predicts higher Reynolds numbers in the two-dimensional case. In addition, other research show has shown an improvement of the original Reynolds-Orr energy equation using the weighted norm in a tilted coordinate system. In this paper the enstrophy is used in three dimensions combined with the tilted coordinate system approach. The zero-enstrophy-growth constraint is applied to the classical Reynolds-Orr equation, and then the solution is further refined in the tilted coordinate system. The results are compared to direct numerical simulations published previously.}, }
@article {pmid35428113, year = {2022}, author = {Steiros, K}, title = {Balanced nonstationary turbulence.}, journal = {Physical review. E}, volume = {105}, number = {3-2}, pages = {035109}, doi = {10.1103/PhysRevE.105.035109}, pmid = {35428113}, issn = {2470-0053}, abstract = {Kolmogorov's 1941 (K41) framework remains central to the understanding of turbulent flows. However, in unsteady turbulence, K41's critical equilibrium assumption is expected to hold in an asymptotic manner, as the Reynolds number and wave numbers tend to infinity, rendering K41 not strictly valid at finite wave numbers. This work proposes a generalization of K41 for out-of-equilibrium effects and cascades far from initial conditions. The main result is a correction to the -5/3 law for out-of-equilibrium eddies, unrelated to intermittency effects. Experimental and numerical evidence is provided in support of the theoretical results.}, }
@article {pmid35428103, year = {2022}, author = {Rana, N and Perlekar, P}, title = {Phase ordering, topological defects, and turbulence in the three-dimensional incompressible Toner-Tu equation.}, journal = {Physical review. E}, volume = {105}, number = {3}, pages = {L032603}, doi = {10.1103/PhysRevE.105.L032603}, pmid = {35428103}, issn = {2470-0053}, abstract = {We investigate the phase-ordering dynamics of the incompressible Toner-Tu equation in three dimensions. We show that the phase ordering proceeds via defect merger events and the dynamics is controlled by the Reynolds number Re. At low Re, the dynamics is similar to that of the Ginzburg-Landau equation. At high Re, turbulence controls phase ordering. In particular, we observe a forward energy cascade from the coarsening length scale to the dissipation scale, clustering of defects, and multiscaling in velocity correlations.}, }
@article {pmid35420623, year = {2022}, author = {Thurgood, P and Chheang, C and Needham, S and Pirogova, E and Peter, K and Baratchi, S and Khoshmanesh, K}, title = {Generation of dynamic vortices in a microfluidic system incorporating stenosis barrier by tube oscillation.}, journal = {Lab on a chip}, volume = {22}, number = {10}, pages = {1917-1928}, doi = {10.1039/d2lc00135g}, pmid = {35420623}, issn = {1473-0189}, mesh = {Constriction, Pathologic ; Humans ; *Microfluidics/methods ; }, abstract = {Microfluidic systems incorporating sudden expansions are widely used for generation of vortex flow patterns. However, the formation of vortices requires high flow rates to induce inertial effects. Here, we introduce a new method for generating dynamic vortices in microfluidics at low static flow rates. Human blood is driven through a microfluidic channel incorporating a semi-circular stenosis barrier. The inlet tube of the channel is axially oscillated using a computer-controlled audio-speaker. The tube oscillation induces high transient flow rates in the channel, which generates dynamic vortices across the stenosis barrier. The size of the vortices can be modulated by varying the frequency and amplitude of tube oscillation. Various vortex flow patterns can be generated by varying the flow rate. The formation and size of the vortices can be predicted using the Reynolds number of the oscillating tube. We demonstrate the potential application of the system for investigating the adhesion and phagocytosis of circulating immune cells under pathologically high shear rates induced at the stenosis. This approach facilitates the development of versatile and controllable inertial microfluidic systems for performing various cellular assays while operating at low static flow rates and low sample volumes.}, }
@article {pmid35407874, year = {2022}, author = {Behura, AK and Mohanty, CP and Singh, MR and Kumar, A and Linul, E and Rajak, DK}, title = {Performance Analysis of Three Side Roughened Solar Air Heater: A Preliminary Investigation.}, journal = {Materials (Basel, Switzerland)}, volume = {15}, number = {7}, pages = {}, pmid = {35407874}, issn = {1996-1944}, abstract = {In recent years, sunlight has been used in several fields such as photovoltaic cells, flat plate collectors, solar cookers, green buildings, and agricultural applications. Improved thermal performance has been seen which comes of three sides absorber plate with glass cover compared to the traditional one. This paper presents the Nusselt (Nu) number, collector efficiency factor (CEF), and collector heat removal factor (CHRF) for the optimal solution of three sides artificially roughened solar air heater. Five input variables such as Reynolds (Re) number, relative roughness pitch, relative roughness height, mass flow rate, and air temperature of the duct are taken into account for improved efficiency optimization of collector, collector heat removal factor, and Nu number. Technique for order of preference by similarity to ideal solution (TOPSIS) technique is used to identify the best alternative amongst a number of performance measures by converting them into an equivalent single variable. Moreover, the results revealed the high accuracy of the CEF, CHRF, and Nu number of 75-80%, 74-78%, and 63-71%, respectively. Meanwhile, it has been also observed that roughness Re number varies between 12,500 and 13,500, and height of relative roughness is 0.0245, including pitch of relative roughness 10 along with the rate of mass flow is 0.041 kg/s.}, }
@article {pmid35407169, year = {2022}, author = {Bhatti, MM and Bég, OA and Abdelsalam, SI}, title = {Computational Framework of Magnetized MgO-Ni/Water-Based Stagnation Nanoflow Past an Elastic Stretching Surface: Application in Solar Energy Coatings.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {7}, pages = {}, pmid = {35407169}, issn = {2079-4991}, abstract = {In this article, motivated by novel nanofluid solar energy coating systems, a mathematical model of hybrid magnesium oxide (MgO) and nickel (Ni) nanofluid magnetohydrodynamic (MHD) stagnation point flow impinging on a porous elastic stretching surface in a porous medium is developed. The hybrid nanofluid is electrically conducted, and a magnetic Reynolds number is sufficiently large enough to invoke an induced magnetic field. A Darcy model is adopted for the isotropic, homogenous porous medium. The boundary conditions account for the impacts of the velocity slip and thermal slip. Heat generation (source)/absorption (sink) and also viscous dissipation effects are included. The mathematical formulation has been performed with the help of similarity variables, and the resulting coupled nonlinear dimensionless ordinary differential equations have been solved numerically with the help of the shooting method. In order to test the validity of the current results and the convergence of the solutions, a numerical comparison with previously published results is included. Numerical results are plotted for the effect of emerging parameters on velocity, temperature, magnetic induction, skin friction, and Nusselt number. With an increment in nanoparticle volume fraction of both MgO and Ni nanoparticles, the temperature and thermal boundary layer thickness of the nanofluid are elevated. An increase in the porous medium parameter (Darcy number), velocity slip, and thermal Grashof number all enhance the induced magnetic field. Initial increments in the nanoparticle volume fraction for both MgO and Ni suppress the magnetic induction near the wall, although, subsequently, when further from the wall, this effect is reversed. Temperature is enhanced with heat generation, whereas it is depleted with heat absorption and thermal slip effects. Overall, excellent thermal enhancement is achieved by the hybrid nanofluid.}, }
@article {pmid35401713, year = {2022}, author = {Fang, L and Li, H and Li, B}, title = {Dynamic Analysis of Deep Water Highway Tunnel under Ocean Current.}, journal = {Computational intelligence and neuroscience}, volume = {2022}, number = {}, pages = {9551792}, pmid = {35401713}, issn = {1687-5273}, abstract = {Comprehensively comparing the merits and demerits of the existing means of transportation across the water, a new underwater transportation structure for crossing the wide water area, named as "deep water highway tunnel" (hereinafter called "DWHT"), is proposed. The characteristics of flow field around the typical section of DWHT at different flow velocities are investigated, which can provide reference for the values of hydrodynamic coefficient at high Reynolds number. The vibration modes and natural by the sound-solid coupling method. In addition, considering the factors of fluid-structure coupling, the dynamic response of displacement and internal force is analyzed based on CFD for the weak parts of the structure. The results show that the deepening of water and the increase of flow will significantly increase the flow field pressure and structure stress, and when the span (or width-span ratio) of the tunnel body extends beyond a certain range, the dynamic characteristics and dynamic response rules of the structure will change.}, }
@article {pmid35393485, year = {2022}, author = {Ghorbani, N and Targhi, MZ and Heyhat, MM and Alihosseini, Y}, title = {Investigation of wavy microchannel ability on electronic devices cooling with the case study of choosing the most efficient microchannel pattern.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {5882}, pmid = {35393485}, issn = {2045-2322}, abstract = {A numerical study was conducted to investigate the ability of wavy microchannels to damp the temperature fluctuations generates in electronic devices. Five wavy patterns are considered with the amplitude and wavelength in the ranges of 62.5 to 250 μm and 1250 to 5000 μm, respectively to study the effect of governing phenomena of flow within wavy patterns on thermal-hydraulic performance. The flow regime is laminar and the Reynolds number is in the range of 300 to 900, and a relatively high heat flux of 80 W/cm[2] is applied to the microchannels substrate. Also, variable flux condition is studied for heat fluxes of 80, 120, 160, 200, and 240 W/cm[2] and for the most efficient wavy and straight microchannels. Results showed that the geometries with larger amplitude to wavelength ratio have a lower radius of curvature and larger Dean number, and as a result of transverse flow (secondary flow) amplification, they have enhanced heat transfer. Also, by comparing the ratio of the transverse velocity components to the axial component, it was found that by decreasing the radius of curvature and increasing the Dean number, transverse velocity increases, which intensifies the heat transfer between the wall and the fluid. The appraisement of the performance evaluation criterion (PEC) illustrates that the wavy case with an amplitude of 250 μm and wavelength of 2500 μm is the best geometry from the thermal-hydraulic point of view in the studied range. Finally, with variable flux condition, the wavy microchannel has responded well to the temperature increase and has created a much more uniform surface temperature compared to straight pattern. The proposed wavy pattern ensures that there are no hotspots which could damage the electronic chip. Presented wavy patterns can be used in heat sinks heat transfer enhancement to allow the chip to run in higher heat fluxes.}, }
@article {pmid35390073, year = {2022}, author = {Almerol, JLO and Liponhay, MP}, title = {Clustering of fast gyrotactic particles in low-Reynolds-number flow.}, journal = {PloS one}, volume = {17}, number = {4}, pages = {e0266611}, pmid = {35390073}, issn = {1932-6203}, mesh = {Cluster Analysis ; Computer Simulation ; *Hydrodynamics ; Physical Phenomena ; *Swimming ; }, abstract = {Systems of particles in turbulent flows exhibit clustering where particles form patches in certain regions of space. Previous studies have shown that motile particles accumulate inside the vortices and in downwelling regions, while light and heavy non-motile particles accumulate inside and outside the vortices, respectively. While strong clustering is generated in regions of high vorticity, clustering of motile particles is still observed in fluid flows where vortices are short-lived. In this study, we investigate the clustering of fast swimming particles in a low-Reynolds-number turbulent flow and characterize the probability distributions of particle speed and acceleration and their influence on particle clustering. We simulate gyrotactic swimming particles in a cubic system with homogeneous and isotropic turbulent flow. Here, the swimming velocity explored is relatively faster than what has been explored in other reports. The fluid flow is produced by conducting a direct numerical simulation of the Navier-Stokes equation. In contrast with the previous results, our results show that swimming particles can accumulate outside the vortices, and clustering is dictated by the swimming number and is invariant with the stability number. We have also found that highly clustered particles are sufficiently characterized by their acceleration, where the increase in the acceleration frequency distribution of the most clustered particles suggests a direct influence of acceleration on clustering. Furthermore, the acceleration of the most clustered particles resides in acceleration values where a cross-over in the acceleration PDFs are observed, an indicator that particle acceleration generates clustering. Our findings on motile particles clustering can be applied to understanding the behavior of faster natural or artificial swimmers.}, }
@article {pmid35389496, year = {2022}, author = {Letendre, F and Cameron, CB}, title = {The capture of crude oil droplets by filter feeders at high and low Reynolds numbers.}, journal = {The Journal of experimental biology}, volume = {225}, number = {8}, pages = {}, doi = {10.1242/jeb.243819}, pmid = {35389496}, issn = {1477-9145}, support = {RGPIN/05058-2017//Natural Sciences and Engineering Research Council of Canada/ ; //Natural Sciences and Engineering Research Council of Canada/ ; }, mesh = {Animals ; Daphnia ; Food Chain ; *Petroleum ; *Petroleum Pollution ; *Thoracica ; }, abstract = {Crustacean filter feeders capture oil droplets with the use of their ramified appendages. These appendages behave as paddles or sieves, based on the system's Reynolds number. Here, we used high-speed videography, scanning electron microscopy and fluid mechanics to study the capturing mechanisms of crude oil droplets and the filtering appendage's wettability by two species of barnacles (Balanus glandula and Balanus crenatus) and of the freshwater cladoceran Daphnia magna. Our results show that barnacle appendages behave as paddles and capture droplets in their boundary layers at low Reynolds number. At high Reynolds number, droplets are most likely to be captured via direct interception. There is an intermediate range of Reynolds number where droplets can be captured by both mechanisms at the same time. Daphnia magna captures droplets in the boundary layers of the third and fourth pair of thoracic legs with a metachronal motion of the appendages. All studied surfaces were revealed to be highly lipophobic, demonstrating captured oil droplets with high contact angles. We also discuss implications of such capture mechanisms and wettability on potential ingestion of crude oil by filter feeders. These results further our understanding of the capture of crude oil by filter feeders, shedding light on the main entry point of oil in marine food webs.}, }
@article {pmid35385160, year = {2022}, author = {Wang, J and Dong, Y and Ma, P and Wang, Y and Zhang, F and Cai, B and Chen, P and Liu, BF}, title = {Intelligent Micro-/Nanorobots for Cancer Theragnostic.}, journal = {Advanced materials (Deerfield Beach, Fla.)}, volume = {34}, number = {52}, pages = {e2201051}, doi = {10.1002/adma.202201051}, pmid = {35385160}, issn = {1521-4095}, support = {2021YFA1101500//National Key R&amp;D Program of China/ ; 22074047//National Natural Science Foundation of China/ ; 21775049//National Natural Science Foundation of China/ ; }, mesh = {Humans ; *Neoplasms/diagnostic imaging/therapy ; Drug Delivery Systems/methods ; *Nanoparticles/therapeutic use ; }, abstract = {Cancer is one of the most intractable diseases owing to its high mortality rate and lack of effective diagnostic and treatment tools. Advancements in micro-/nanorobot (MNR)-assisted sensing, imaging, and therapeutics offer unprecedented opportunities to develop MNR-based cancer theragnostic platforms. Unlike ordinary nanoparticles, which exhibit Brownian motion in biofluids, MNRs overcome viscous resistance in an ultralow Reynolds number (Re << 1) environment by effective self-propulsion. This unique locomotion property has motivated the advanced design and functionalization of MNRs as a basis for next-generation cancer-therapy platforms, which offer the potential for precise distribution and improved permeation of therapeutic agents. Enhanced barrier penetration, imaging-guided operation, and biosensing are additionally studied to enable the promising cancer-related applications of MNRs. Herein, the recent advances in MNR-based cancer therapy are comprehensively addresses, including actuation engines, diagnostics, medical imaging, and targeted drug delivery; promising research opportunities that can have a profound impact on cancer therapy over the next decade is highlighted.}, }
@article {pmid35379035, year = {2022}, author = {Saeed Khan, MW and Ali, N and Bég, OA}, title = {Thermal entrance problem for blood flow inside an axisymmetric tube: The classical Graetz problem extended for Quemada's bio-rheological fluid with axial conduction.}, journal = {Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine}, volume = {236}, number = {6}, pages = {848-859}, doi = {10.1177/09544119221086479}, pmid = {35379035}, issn = {2041-3033}, mesh = {*Algorithms ; *Hemodynamics ; Hot Temperature ; Humans ; Rheology ; Viscosity ; }, abstract = {The heat-conducting nature of blood is critical in the human circulatory system and features also in important thermal regulation and blood processing systems in biomedicine. Motivated by these applications, in the present investigation, the classical Graetz problem in heat transfer is extended to the case of a bio-rheological fluid model. The Quemada bio-rheological fluid model is selected since it has been shown to be accurate in mimicking physiological flows (blood) at different shear rates and hematocrits. The steady two-dimensional energy equation without viscous dissipation in stationary regime is tackled via a separation of variables approach for the isothermal wall temperature case. Following the introduction of transformation variables, the ensuing dimensionless boundary value problem is solved numerically via MATLAB based algorithm known as bvp5c (a finite difference code that implements the four-stage Lobatto IIIa collocation formula). Numerical validation is also presented against two analytical approaches namely, series solutions and Kummer function techniques. Axial conduction in terms of Péclet number is also considered. Typical values of Reynolds number and Prandtl number are used to categorize the vascular regions. The graphical representation of mean temperature, temperature gradient, and Nusselt numbers along with detail discussions are presented for the effects of Quemada non-Newtonian parameters and Péclet number. The current analysis may also have potential applications for the development of microfluidic and biofluidic devices particularly which are used in the diagnosis of diseases in addition to blood oxygenation technologies.}, }
@article {pmid35363001, year = {2022}, author = {Tan, S and Ni, R}, title = {Universality and Intermittency of Pair Dispersion in Turbulence.}, journal = {Physical review letters}, volume = {128}, number = {11}, pages = {114502}, doi = {10.1103/PhysRevLett.128.114502}, pmid = {35363001}, issn = {1079-7114}, abstract = {Turbulence can disperse a concentrated parcel of pollutants at a rate over nine orders of magnitude higher than its purely diffusive counterpart. One intriguing signature of turbulent dispersion is its superdiffusive scaling. However, the universality of this scaling law is still in question. By leveraging a new laboratory facility, particle pairs with small initial separations can be tracked over four decades of separation in time and five decades of separation in squared displacement, thereby observing the full range of dispersion scaling laws. The results show that the classical Richardson cubic scaling will be reached not for an initial separation asymptotically close to zero but at a critical value, and this value does not appear to depend on the Reynolds number, providing an effective way to study universal dispersion dynamics. Additionally, the results agree well with the prediction based on the multifractal model and may help reconcile different reported scaling laws from laboratory experiments and field studies.}, }
@article {pmid35355005, year = {2022}, author = {Kamdar, S and Shin, S and Leishangthem, P and Francis, LF and Xu, X and Cheng, X}, title = {The colloidal nature of complex fluids enhances bacterial motility.}, journal = {Nature}, volume = {603}, number = {7903}, pages = {819-823}, pmid = {35355005}, issn = {1476-4687}, mesh = {Bacteria ; *Colloids ; *Ecosystem ; Humans ; Hydrodynamics ; Polymers ; }, abstract = {The natural habitats of microorganisms in the human microbiome, ocean and soil ecosystems are full of colloids and macromolecules. Such environments exhibit non-Newtonian flow properties, drastically affecting the locomotion of microorganisms[1-5]. Although the low-Reynolds-number hydrodynamics of swimming flagellated bacteria in simple Newtonian fluids has been well developed[6-9], our understanding of bacterial motility in complex non-Newtonian fluids is less mature[10,11]. Even after six decades of research, fundamental questions about the nature and origin of bacterial motility enhancement in polymer solutions are still under debate[12-23]. Here we show that flagellated bacteria in dilute colloidal suspensions display quantitatively similar motile behaviours to those in dilute polymer solutions, in particular a universal particle-size-dependent motility enhancement up to 80% accompanied by a strong suppression of bacterial wobbling[18,24]. By virtue of the hard-sphere nature of colloids, whose size and volume fraction we vary across experiments, our results shed light on the long-standing controversy over bacterial motility enhancement in complex fluids and suggest that polymer dynamics may not be essential for capturing the phenomenon[12-23]. A physical model that incorporates the colloidal nature of complex fluids quantitatively explains bacterial wobbling dynamics and mobility enhancement in both colloidal and polymeric fluids. Our findings contribute to the understanding of motile behaviours of bacteria in complex fluids, which are relevant for a wide range of microbiological processes[25] and for engineering bacterial swimming in complex environments[26,27].}, }
@article {pmid35343677, year = {2022}, author = {Chen, H and Li, Y and Wang, Y and Ning, P and Shen, Y and Wei, X and Feng, Q and Liu, Y and Li, Z and Xu, C and Huang, S and Deng, C and Wang, P and Cheng, Y}, title = {An Engineered Bacteria-Hybrid Microrobot with the Magnetothermal Bioswitch for Remotely Collective Perception and Imaging-Guided Cancer Treatment.}, journal = {ACS nano}, volume = {16}, number = {4}, pages = {6118-6133}, doi = {10.1021/acsnano.1c11601}, pmid = {35343677}, issn = {1936-086X}, mesh = {Humans ; Bacteria ; Hypoxia ; *Neoplasms/diagnostic imaging/drug therapy ; Perception ; }, abstract = {Microrobots driven by multiple propelling forces hold great potential for noninvasively targeted delivery in the physiologic environment. However, the remotely collective perception and precise propelling in a low Reynold's number bioenvironment remain the major challenges of microrobots to achieve desired therapeutic effects in vivo. Here, we reported a biohybrid microrobot that integrated with magnetic, thermal, and hypoxia sensitivities and an internal fluorescent protein as the dual reporter of thermal and positioning signals for targeted cancer treatment. There were three key elements in the microrobotic system, including the magnetic nanoparticle (MNP)-loaded probiotic Escherichia coli Nissle1917 (EcN@MNP) for spatially magnetic and hypoxia perception, a thermal-logic circuit engineered into the bacteria to control the biosynthesis of mCherry as the temperature and positioning reporter, and NDH-2 enzyme encoded in the EcN for enhanced anticancer therapy. According to the fluorescent-protein-based imaging feedback, the microrobot showed good thermal sensitivity and active targeting ability to the tumor area in a collective manner under the magnetic field. The cancer cell apoptosis was efficiently triggered in vitro and in vivo by the hybrid microrobot coupled with the effects of magnetothermal ablation and NDH-2-induced reactive oxygen species (ROS) damage. Our study demonstrates that the biohybrid EcN microrobot is an ideal platform to integrate the physical, biological, and chemical properties for collective perception and propelling in targeted cancer treatment.}, }
@article {pmid35338884, year = {2022}, author = {Mezali, F and Benmamar, S and Naima, K and Ameur, H and Rafik, O}, title = {Evaluation of stent effect and thrombosis generation with different blood rheology on an intracranial aneurysm by the Lattice Boltzmann method.}, journal = {Computer methods and programs in biomedicine}, volume = {219}, number = {}, pages = {106757}, doi = {10.1016/j.cmpb.2022.106757}, pmid = {35338884}, issn = {1872-7565}, mesh = {Blood Flow Velocity ; Hemodynamics/physiology ; Humans ; *Intracranial Aneurysm/surgery ; Rheology ; Stents ; *Thrombosis/prevention &amp; control ; }, abstract = {BACKGROUND AND OBJECTIVE: Treatment of intracranial aneurysms with flow-diverting stents prevents rupture by reducing blood flow and creating thrombosis within the aneurysm. This paper aims to assess the hemodynamic effect of placing stents with different struts (0, 3, 5, 7 struts) on intracranial aneurysms and to propose a simple prediction model of thrombosis zone without any further computational cost.<br><br>METHOD: Lattice Boltzmann method with different rheological models (Newtonian, Carreau-Yasuda, KL) of blood are used to study the hemodynamic effect of flow-diverting stents in the aneurysm. Pulsatile flow boundary conditions were applied in the inlet of the artery. The average Reynolds number was resulting Re&#xa0;=&#xa0;111. The Lagrangian tracking of the particle was developed to assess the intra-aneurysmal blood stagnation. To predict the probable thrombose zone induced by flow-diverting stents, the shear rate threshold is utilized to determine the nodes of fluid to clot.<br><br>RESULTS: The results show that the flow patterns into the aneurysmal sac develop a vortex, decreasing after stent placement until disappearance for the stent with seven struts (porosity 71.4%). Velocity, shear rate, shear stress, trajectory, path length, and occlusion rate are compared before and after stent placement. These parameters decrease inversely with the porosity of the stent. The three models yield a closes result of the (velocity, shear rate, occlusion rate). Tracking the fluid-particle trajectory shows that the length of the particle paths decreases with the number of struts causing fluid to slow down and increase, consequently, the residence time into the sac.<br><br>CONCLUSION: The flow-diverting stents placement cause the reduction of dynamic flow within aneurysm. The reduction effect is almost the same below five struts (80% of porosity). The results show that, if our objective is restricted to estimating the hemodynamic effect, measured by (velocity, shear rate, occlusion rate), the differences between rheological behavior models are, practically, not significant, and the models can be used indifferently.}, }
@article {pmid35334666, year = {2022}, author = {Nuwairan, MA and Souayeh, B}, title = {Simulation of Gold Nanoparticle Transport during MHD Electroosmotic Flow in a Peristaltic Micro-Channel for Biomedical Treatment.}, journal = {Micromachines}, volume = {13}, number = {3}, pages = {}, pmid = {35334666}, issn = {2072-666X}, support = {Grant No.207021//Deanship of Scientific Research at King Faisal University/ ; }, abstract = {The study of gold nanoparticles (AuNPs) in the blood flow has emerged as an area of interest for numerous researchers, due to its many biomedical applications, such as cancer radiotherapy, DNA and antigens, drug and gene delivery, in vitro evaluation, optical bioimaging, radio sensitization and laser phototherapy of cancer cells and tumors. Gold nanoparticles can be amalgamated in various shapes and sizes. Due to this reason, gold nanoparticles can be diffused efficiently, target the diseased cells and destroy them. The current work studies the effect of gold nanoparticles of different shapes on the electro-magneto-hydrodynamic (EMHD) peristaltic propulsion of blood in a micro-channel under various effects, such as activation energy, bioconvection, radiation and gyrotactic microorganisms. Four kinds of nanoparticle shapes, namely bricks, cylinders and platelets, are considered. The governing equations are simplified under the approximations of low Reynolds number (LRN), long wavelength (LWL) and Debye-Hückel linearization (DHL). The numerical solutions for the non-dimensional equations are solved using the computational software MATLAB with the help of the bvp4c function. The influences of different physical parameters on the flow and thermal characteristics are computed through pictorial interpretations.}, }
@article {pmid35329572, year = {2022}, author = {Sawka, A}, title = {Chemical Vapour Deposition of Scandia-Stabilised Zirconia Layers on Tubular Substrates at Low Temperatures.}, journal = {Materials (Basel, Switzerland)}, volume = {15}, number = {6}, pages = {}, pmid = {35329572}, issn = {1996-1944}, support = {16.16.160.557//Subvention of the Polish State Ministry of Education and Science for AGH University of Science and Technology, Faculty of Materials Science and Ceramics/ ; }, abstract = {The paper presents results of investigation on synthesis of non-porous ZrO2-Sc2O2 layers on tubular substrates by MOCVD (metalorganic chemical vapor deposition) method using Sc(tmhd)3 (Tris(2,2,6,6-tetramethyl-3,5-heptanedionato)scandium(III), 99%) and Zr(tmhd)4 (Tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)zirconium)(IV), 99.9+%) as basic reactants. The molar content of Sc(tmhd)3 in the gas mixture was as follows: 14, 28%. The synthesis temperature was in the range of 600-700 °C. The value of extended Grx/Rex[2] expression (Gr-Grashof number, Re-Reynolds number and x-the distance from the gas inflow point) was less than 0.01. The layers were deposited under reduced pressure or close to atmospheric pressure. The layers obtained were tested using scanning electron microscope (SEM) with an energy dispersive X-ray spectroscope (EDS) microanalyzer, X-ray diffractometer and UV-Vis spectrophotometer. The layers deposited were non-porous, amorphous or nanocrystalline with controlled chemical composition. The layers synthesized at 700 °C were nanocrystalline. ZrO2-Sc2O3 layers with 14 mol.% Sc2O3 content had a rhombohedral structure.}, }
@article {pmid35327926, year = {2022}, author = {Lin, W and Shi, R and Lin, J}, title = {Heat Transfer and Pressure Drop of Nanofluid with Rod-like Particles in Turbulent Flows through a Curved Pipe.}, journal = {Entropy (Basel, Switzerland)}, volume = {24}, number = {3}, pages = {}, pmid = {35327926}, issn = {1099-4300}, support = {12132015//National Natural Science Foundation of China/ ; }, abstract = {Pressure drop, heat transfer, and energy performance of ZnO/water nanofluid with rodlike particles flowing through a curved pipe are studied in the range of Reynolds number 5000 ≤ Re ≤ 30,000, particle volume concentration 0.1% ≤ Φ ≤ 5%, Schmidt number 10[4] ≤ Sc ≤ 3 × 10[5], particle aspect ratio 2 ≤ λ ≤ 14, and Dean number 5 × 10[3] ≤ De ≤ 1.5 × 10[4]. The momentum and energy equations of nanofluid, together with the equation of particle number density for particles, are solved numerically. Some results are validated by comparing with the experimental results. The effect of Re, Φ, Sc, λ, and De on the friction factor f and Nusselt number Nu is analyzed. The results showed that the values of f are increased with increases in Φ, Sc, and De, and with decreases in Re and λ. The heat transfer performance is enhanced with increases in Re, Φ, λ, and De, and with decreases in Sc. The ratio of energy PEC for nanofluid to base fluid is increased with increases in Re, Φ, λ, and De, and with decreases in Sc. Finally, the formula of ratio of energy PEC for nanofluid to base fluid as a function of Re, Φ, Sc, λ, and De is derived based on the numerical data.}, }
@article {pmid35327850, year = {2022}, author = {Dou, HS}, title = {No Existence and Smoothness of Solution of the Navier-Stokes Equation.}, journal = {Entropy (Basel, Switzerland)}, volume = {24}, number = {3}, pages = {}, pmid = {35327850}, issn = {1099-4300}, abstract = {The Navier-Stokes equation can be written in a form of Poisson equation. For laminar flow in a channel (plane Poiseuille flow), the Navier-Stokes equation has a non-zero source term (∇[2]u(x, y, z) = Fx (x, y, z, t) and a non-zero solution within the domain. For transitional flow, the velocity profile is distorted, and an inflection point or kink appears on the velocity profile, at a sufficiently high Reynolds number and large disturbance. In the vicinity of the inflection point or kink on the distorted velocity profile, we can always find a point where ∇[2]u(x, y, z) = 0. At this point, the Poisson equation is singular, due to the zero source term, and has no solution at this point due to singularity. It is concluded that there exists no smooth orphysically reasonable solutions of the Navier-Stokes equation for transitional flow and turbulence in the global domain due to singularity.}, }
@article {pmid35299996, year = {2022}, author = {Marchello, R and Morandotti, M and Shum, H and Zoppello, M}, title = {The N -Link Swimmer in Three Dimensions: Controllability and Optimality Results.}, journal = {Acta applicandae mathematicae}, volume = {178}, number = {1}, pages = {6}, pmid = {35299996}, issn = {0167-8019}, abstract = {The controllability of a fully three-dimensional N -link swimmer is studied. After deriving the equations of motion in a low Reynolds number fluid by means of Resistive Force Theory, the controllability of the minimal 2-link swimmer is tackled using techniques from Geometric Control Theory. The shape of the 2-link swimmer is described by two angle parameters. It is shown that the associated vector fields that govern the dynamics generate, via taking their Lie brackets, all eight linearly independent directions in the combined configuration and shape space, leading to controllability; the swimmer can move from any starting configuration and shape to any target configuration and shape by operating on the two shape variables. The result is subsequently extended to the N -link swimmer. Finally, the minimal time optimal control problem and the minimization of the power expended are addressed and a qualitative description of the optimal strategies is provided.}, }
@article {pmid35297830, year = {2022}, author = {Wang, Y and Zhao, W and Wang, B and Wang, Y}, title = {Prediction model of combustion characteristics of methane-air using hyperspectral imaging.}, journal = {Applied optics}, volume = {61}, number = {7}, pages = {D75-D84}, doi = {10.1364/AO.444118}, pmid = {35297830}, issn = {1539-4522}, abstract = {Hyperspectral imaging can obtain considerable flame information, which can improve the prediction accuracy of combustion characteristics. This paper studies the hyperspectral characteristics of methane flames and proposes several prediction models. The experimental results show that the radiation intensity and radiation types of free radicals are related to the equivalent ratio, and the radiation region of free radicals becomes larger with the increase of the Reynolds number. The polynomial regression prediction models include the linear model and quadratic model. It takes C2∗/CH[∗] as input parameters, and results can be available immediately. The three-dimensional convolutional neural network (3D-CNN) prediction model takes all spectral and spatial information in the flame hyperspectral image as input parameters. By improving the structural parameters of the convolution network, the final prediction errors of the equivalent ratio and Reynolds number are 2.84% and 3.11%, respectively. The method of combining the 3D-CNN model with hyperspectral imaging significantly improves the prediction accuracy, and it can be used to predict other combustion characteristics such as pollutant emissions and combustion efficiency.}, }
@article {pmid35291149, year = {2022}, author = {Ma, X and Gong, X and Tang, Z and Jiang, N}, title = {Control of leading-edge separation on bioinspired airfoil with fluttering coverts.}, journal = {Physical review. E}, volume = {105}, number = {2-2}, pages = {025107}, doi = {10.1103/PhysRevE.105.025107}, pmid = {35291149}, issn = {2470-0053}, abstract = {In this work, the aerodynamic role of the artificial covert feathers (i.e., coverts) on an airfoil is experimentally studied in a wind tunnel to investigate the flow control effect on the leading-edge separation. We apply flexible featherlike devices on a high-angle-of-attack airfoil. We use a hot-wire anemometer to measure the velocity profiles and turbulent fluctuations in the downstream wake flow. As a baseline of flow separation, a two-dimensional NACA 0018 airfoil model is set at the angle of attack of 15 ° at the chord-based Reynolds number of 1.0×10^{5}, causing strong leading-edge and trailing-edge shear layers and a low-speed wake flow area in between as large as 0.35 chord length. When deployed on the upper wing surface, the flexible coverts adaptively flutter under the influence of the local unsteady airflow. Hot-wire measurement results show that the leading-edge coverts effectively suppress the flow separation and reduce the size of the wake flow area. The change of power spectral density shows that the predominant peaks as the fundamental and harmonic frequencies are both attenuated due to the suppression of unsteady motions of the shear layers. On the other hand, the fluttering coverts at the trailing edge modify the trailing-edge shear layer by redistributing the turbulent kinetic energy to the high-frequency components. By simultaneous double-point measurement, we find that the leading-edge and trailing-edge shear layers are drawn closer to each other, and the two shear layers show an increased peak in the coherence spectrum. Further multiscale wavelet analysis shows that the perturbations at the 60% chord length increase the large-scale amplitude modulation of small-scale turbulence and therefore they stabilize the leading-edge and trailing-edge shear layers. Meanwhile, the flow intermittency outside of the wake flow area is attenuated as well. The effective flow control effects in the present work are in good agreement with the previous direct observations of bird flight in literature that the coverts on the upper wing surface play an important role in flow separation control during high-angle-of-attack flight. These findings advance the understanding of aerodynamic contribution of the covers on bird wings and reveal the engineering potential of bioinspired coverts for flow separation control of aircrafts and unmanned air vehicles.}, }
@article {pmid35270649, year = {2022}, author = {Ovando-Chacon, GE and Rodríguez-León, A and Ovando-Chacon, SL and Hernández-Ordoñez, M and Díaz-González, M and Pozos-Texon, FJ}, title = {Computational Study of Thermal Comfort and Reduction of CO2 Levels inside a Classroom.}, journal = {International journal of environmental research and public health}, volume = {19}, number = {5}, pages = {}, pmid = {35270649}, issn = {1660-4601}, mesh = {*Air Pollution, Indoor/analysis/prevention &amp; control ; *COVID-19/epidemiology ; Carbon Dioxide/analysis ; Humans ; Pandemics ; SARS-CoV-2 ; }, abstract = {Due to the current COVID-19 pandemic, guaranteeing thermal comfort and low CO2 levels in classrooms through efficient ventilation has become vitally important. This study presents three-dimensional simulations based on computational fluid dynamics of airflow inside an air-conditioned classroom located in Veracruz, Mexico. The analysis included various positions of an air extractor, Reynolds numbers up to 3.5 × 10[4], four different concentrations of pollutant sources, and three different times of the day. The simulations produced velocity, air temperature, and CO2 concentrations fields, and we calculated average air temperatures, average CO2 concentrations, and overall ventilation effectiveness. Our results revealed an optimal extractor position and Reynolds number conducive to thermal comfort and low CO2 levels due to an adequate ventilation configuration. At high pollutant concentrations, it is necessary to reduce the number of students in the classroom to achieve safe CO2 levels.}, }
@article {pmid35264611, year = {2022}, author = {Memon, AA and Memon, MA and Bhatti, K and Khan, I and Alshammari, N and Al-Johani, AS and Hamadneh, NN and Andualem, M}, title = {Thermal decomposition of propylene oxide with different activation energy and Reynolds number in a multicomponent tubular reactor containing a cooling jacket.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {4169}, pmid = {35264611}, issn = {2045-2322}, abstract = {In this article, we are focusing on heat and mass transfer through a Multicomponent tubular reactor containing a cooling jacket by thermal decomposition of propylene oxide in water. The chemical reaction is an irreversible, 1st order reaction and an exothermic reaction that yields propylene glycol with enthalpy = -84,666 J/mol. The constant rate of the reaction is followed by the Arrhenius equation in which the activation energy is taken on a trial basis in the range from 75,000 to 80,000 J/mol with a fixed frequency factor. For the fluid to flow, the Reynolds number is kept in the range from 100 to 1000. The three partial differential equations of mass, momentum, and energy are coupled to study heat and mass transfer in a tubular reactor by using the chemistry interface in COMSOL Multiphysics 5.4. The initial concentration of propylene oxide is tested in the range from 2 to 3% and the thermal conductivity of the mixture is tested in the range 0.599-0.799. It was found that the amount deactivated of the compound decreases with an increase in Reynolds number. Propylene oxide is decomposed at about 99.8% at Re = 100 at lower activation energy and gives the total maximum enthalpy change in the tubular reactor. Observing the relationship between Sherwood numbers to Nusselt numbers, it was deducted that the convective heat transfer is opposite to convective mass transfer for high Reynolds numbers.}, }
@article {pmid35236870, year = {2022}, author = {Khan, Z and Ul Haq, S and Ali, F and Andualem, M}, title = {Free convection flow of second grade dusty fluid between two parallel plates using Fick's and Fourier's laws: a fractional model.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {3448}, pmid = {35236870}, issn = {2045-2322}, abstract = {The paper aims to investigate the channel flow of second grade visco-elastic fluid generated due to an oscillating wall. The effect of heat and mass transfer has been taken into account. The phenomenon has been modelled in terms of PDEs. The constitutive equations are fractionalized by using the definition of the Caputo fractional operator with Fick's and Fourier's Laws. The system of fractional PDEs is non-dimensionalized by using appropriate dimensionless variables. The closed-form solutions of thermal and concentration boundary layers are obtained by using the Laplace and finite Fourier-Sine transforms, while the momentum equation is solved by a numerical approach by Zakian using [Formula: see text]. Furthermore, the parametric influence of various embedded physical parameters on momentum, temperature, and concentration distributions is depicted through various graphs. It is observed that the fractional approach is more convenient and realistic as compared to the classical approach. It is worth noting that the increasing values of [Formula: see text], [Formula: see text] and [Formula: see text] retard the boundary layer profile. For instance, this behaviour of [Formula: see text] is significant where boundary control is necessary. That is, in the case of resonance, the physical solution may be obtained by adding the effect of MHD. The Reynolds number is useful in characterising the transport properties of a fluid or a particle travelling through a fluid. The Reynolds number is one of the main controlling parameters in all viscous flow. It determines whether the fluid flow is laminar or turbulent. The evolution of the rate of heat, mass transfer, and skin friction on the left plate with various physical parameters are presented in tables. These quantities are of high interest for engineers. Keeping in mind the effect of various parameters on these engineering quantities, they make their feasibility reports.}, }
@article {pmid35233704, year = {2022}, author = {Cai, C and Wen, C and Guan, L and Huang, Y and Jiang, Q}, title = {Influence of sodium hypochlorite concentration on cavitation effect and fluid dynamics induced by photon-induced photoacoustic streaming (PIPS): A visualization study.}, journal = {Lasers in medical science}, volume = {37}, number = {5}, pages = {2537-2544}, pmid = {35233704}, issn = {1435-604X}, support = {[2017]-210//Guangzhou Medical University/ ; [2017-160]//Guangzhou Medical University/ ; }, mesh = {Dental Pulp Cavity ; Hydrodynamics ; Photons/therapeutic use ; *Root Canal Irrigants/pharmacology ; Root Canal Preparation ; *Sodium Hypochlorite/pharmacology ; }, abstract = {PURPOSE: The aim of the present study was to visualize and compare the cavitation effect and fluid dynamics induced by photon-induced photoacoustic streaming (PIPS) using sodium hypochlorite (NaOCl) with different concentrations as irrigant.<br><br>METHODS: Forty artificial root canals were prepared using MTWO Niti file up to size #25/.06. The canals were randomly divided into four groups (n&#x2009;=&#x2009;10/group). High-speed camera was used to visualize and compare the cavitation effect induced by PIPS in the artificial root canals containing saline or NaOCl. Fluid velocity and Reynolds number of saline, 1%-, 2.5%-&#xa0;and 5.25% NaOCl irrigants induced by PIPS in the apical region were calculated using TEMA 2D software while the fluid motions were recorded.<br><br>RESULTS: Visualization profile revealed that NaOCl presented a stronger cavitation effect and fluid dynamics than saline during PIPS activation. In the apical region, 1% NaOCl group presented the highest average velocity of 3.868&#xa0;m/s, followed by 2.5% NaOCl group (3.685&#xa0;m/s), 5.25% NaOCl group (2.353&#xa0;m/s) and saline group (1.268&#xa0;m/s), corresponding to Reynolds number of 1653.173, 1572.196, 995.503 and 477.692. Statistically higher fluid velocity was calculated in 1% and 2.5% NaOCl groups compared to saline group, respectively (p&#x2009;<&#x2009;0.05).<br><br>CONCLUSIONS: The application of NaOCl and its concentration significantly influence the cavitation effect and fluid dynamics during PIPS activation. 1% and 2.5% NaOCl groups presented a more violent fluid motion in the apical region when activated by PIPS.}, }
@article {pmid35232981, year = {2022}, author = {Abd-Alla, AM and Thabet, EN and Bayones, FS}, title = {Numerical solution for MHD peristaltic transport in an inclined nanofluid symmetric channel with porous medium.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {3348}, pmid = {35232981}, issn = {2045-2322}, abstract = {The significance of the study is to determine of transferred heat and mass impact on the magneto-hydrodynamic peristalsis of Jeffery nanofluid through porous media with inclined symmetric channels whose walls are induced by peristaltic motion within porous media. The aim of this investagtion is to study the influence of various types of parameters such as Brownian motion, thermophoresis, buoyancy forces, and magnetic fields are studies on concentration, temperature, and axial velocity. The numerical solution has been achieved according to the long-wavelength and low Reynolds number approximation utilizing the MATLAB bvp4c function. The resultant dimensions of nonlinear governing equations were approached numerically through the Runge-Kutta- Fehlberg integration scheme, a MATLAB program. The influence of different factors such as the ratio of relaxation to retardation times, nanoparticle Grashof number, and magnetic field was discussed on concentration, temperature, and velocity profiles. tables and graphs were used to demonstrate the numerically computed numerical results. Plotting graphs were utilized for evaluating the pertinent parameters impacts on the aforementioned quantities based on computational results. According to the findings, the effect of the parameters are significant.}, }
@article {pmid35214965, year = {2022}, author = {Khan, NA and Sulaiman, M and Tavera Romero, CA and Alshammari, FS}, title = {Analysis of Nanofluid Particles in a Duct with Thermal Radiation by Using an Efficient Metaheuristic-Driven Approach.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {4}, pages = {}, pmid = {35214965}, issn = {2079-4991}, abstract = {This study investigated the steady two-phase flow of a nanofluid in a permeable duct with thermal radiation, a magnetic field, and external forces. The basic continuity and momentum equations were considered along with the Buongiorno model to formulate the governing mathematical model of the problem. Furthermore, the intelligent computational strength of artificial neural networks (ANNs) was utilized to construct the approximate solution for the problem. The unsupervised objective functions of the governing equations in terms of mean square error were optimized by hybridizing the global search ability of an arithmetic optimization algorithm (AOA) with the local search capability of an interior point algorithm (IPA). The proposed ANN-AOA-IPA technique was implemented to study the effect of variations in the thermophoretic parameter (Nt), Hartmann number (Ha), Brownian (Nb) and radiation (Rd) motion parameters, Eckert number (Ec), Reynolds number (Re) and Schmidt number (Sc) on the velocity profile, thermal profile, Nusselt number and skin friction coefficient of the nanofluid. The results obtained by the designed metaheuristic algorithm were compared with the numerical solutions obtained by the Runge-Kutta method of order 4 (RK-4) and machine learning algorithms based on a nonlinear autoregressive network with exogenous inputs (NARX) and backpropagated Levenberg-Marquardt algorithm. The mean percentage errors in approximate solutions obtained by ANN-AOA-IPA are around 10-6 to 10-7. The graphical analysis illustrates that the velocity, temperature, and concentration profiles of the nanofluid increase with an increase in the suction parameter, Eckert number and Schmidt number, respectively. Solutions and the results of performance indicators such as mean absolute deviation, Theil's inequality coefficient and error in Nash-Sutcliffe efficiency further validate the proposed algorithm's utility and efficiency.}, }
@article {pmid35214944, year = {2022}, author = {Apmann, K and Fulmer, R and Scherer, B and Good, S and Wohld, J and Vafaei, S}, title = {Nanofluid Heat Transfer: Enhancement of the Heat Transfer Coefficient inside Microchannels.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {4}, pages = {}, pmid = {35214944}, issn = {2079-4991}, abstract = {The purpose of this paper is to investigate the effects of a connector between two microchannels, for the first time. A brief literature review is provided to offer a better understanding on the impacts of concentration and the characteristics of nanoparticles on thermal conductivity, viscosity, and, consequently, the heat transfer coefficient inside the microchannels. The given literature review aims to help engineer nanofluids to enhance the heat transfer coefficient inside the microchannels. In this research, Fe3O4 nanoparticles were introduced into the base liquid to enhance the heat transfer coefficient inside the microchannels and to provide a better understanding of the impact of the connector between two microchannels. It was observed that the connector has a significant impact on enhancing the heat transfer coefficient inside the second microchannel, by increasing the level of randomness of molecules and particles prior to entering the second channel. The connector would act to refresh the memory of the fluid before entering the second channel, and as a result, the heat transfer coefficient in the second channel would start at a maximum value. Therefore, the overall heat transfer coefficient in both microchannels would increase for given conditions. The impacts of the Reynolds number and introducing nanoparticles in the base liquid on effects induced by the connector were investigated, suggesting that both factors play a significant role on the connector's impact on the heat transfer coefficient.}, }
@article {pmid35209192, year = {2022}, author = {Kim, GB and Park, KH and Kim, SJ}, title = {Hemodynamics and Wall Shear Stress of Blood Vessels in Aortic Coarctation with Computational Fluid Dynamics Simulation.}, journal = {Molecules (Basel, Switzerland)}, volume = {27}, number = {4}, pages = {}, pmid = {35209192}, issn = {1420-3049}, support = {2021R1A2C1091322//National Research Foundation of Korea/ ; }, mesh = {Algorithms ; Aorta/abnormalities/diagnostic imaging/physiopathology ; Aortic Coarctation/*diagnosis/*physiopathology ; Blood Flow Velocity ; *Hemodynamics ; Humans ; *Models, Cardiovascular ; *Stress, Mechanical ; }, abstract = {The purpose of this study was to identify the characteristics of blood flow in aortic coarctation based on stenotic shape structure, stenosis rate, and the distribution of the wall load delivered into the blood vessels and to predict the impact on aneurysm formation and rupture of blood vessels by using a computational fluid dynamics modeling method. It was applied on the blood flow in abdominal aortic blood vessels in which stenosis occurred by using the commercial finite element software ADINA on fluid-solid interactions. The results of modeling, with an increasing stenosis rate and Reynolds number, showed the pressure drop was increased and the velocity was greatly changed. When the stenosis rate was the same, the pressure drop and the velocity change were larger in the stenosis with a symmetric structure than in the stenosis with an asymmetric one. Maximal changes in wall shear stress were observed in the area before stenosis and minimal changes were shown in stenosis areas. The minimal shear stress occurred at different locations depending on the stenosis shape models. With an increasing stenosis rate and Reynolds number, the maximal wall shear stress was increased and the minimal wall shear stress was decreased. Through such studies, it is thought that the characteristics of blood flow in the abdominal aorta where a stenosis is formed will be helpful in understanding the mechanism of growth of atherosclerosis and the occurrence and rupture of the abdominal aortic flow.}, }
@article {pmid35208284, year = {2022}, author = {Antognoli, M and Tomasi Masoni, S and Mariotti, A and Mauri, R and Salvetti, MV and Brunazzi, E and Galletti, C}, title = {Mixing Improvement in a T-Shaped Micro-Junction through Small Rectangular Cavities.}, journal = {Micromachines}, volume = {13}, number = {2}, pages = {}, pmid = {35208284}, issn = {2072-666X}, abstract = {The T-shaped micro-junction is among the most used geometry in microfluidic applications, and many design modifications of the channel walls have been proposed to enhance mixing. In this work, we investigate through numerical simulations the introduction of one pair of small rectangular cavities in the lateral walls of the mixing channel just downstream of the confluence region. The aim is to preserve the simple geometry that has contributed to spread the practical use of the T-shaped micro-junction while suggesting a modification that should, in principle, work jointly with the vortical structures present in the mixing channel, further enhancing their efficiency in mixing without significant additional pressure drops. The performance is analyzed in the different flow regimes occurring by increasing the Reynolds number. The cavities are effective in the two highly-mixed flow regimes, viz., the steady engulfment and the periodic asymmetric regimes. This presence does not interfere with the formation of the vortical structures that promote mixing by convection in these two regimes, but it further enhances the mixing of the inlet streams in the near-wall region of the mixing channel without any additional cost, leading to better performance than the classical configuration.}, }
@article {pmid35207114, year = {2022}, author = {Nichka, V and Mareev, S and Pismenskaya, N and Nikonenko, V and Bazinet, L}, title = {Mathematical Modeling of the Effect of Pulsed Electric Field Mode and Solution Flow Rate on Protein Fouling during Bipolar Membrane Electroacidificaiton of Caseinate Solution.}, journal = {Membranes}, volume = {12}, number = {2}, pages = {}, pmid = {35207114}, issn = {2077-0375}, support = {21-19-00087//Russian Science Foundation/ ; 210829409//Natural Sciences and Engineering Research Council/ ; }, abstract = {A one-dimensional non-stationary model was developed for a better understanding of the protein fouling formation mechanism during electroacidification of caseinate solution using electrodialysis with bipolar membranes (EDBM) in pulsed electric field (PEF) mode. Four different PEF modes were investigated with pulse-pause durations of 10-10 s, 10-20 s, 10-33 s, 10-50 s. For each current mode 3 different flow rates were considered, corresponding to Reynolds numbers, Re, equal to 187, 374 and 560. The processes are considered in the diffusion boundary layer between the surface of the cation-exchange layer of bipolar membrane and bulk solution of the desalination compartment. The Nernst-Planck and material balance equation systems describe the ion transport. The electroneutrality condition and equilibrium chemical reactions are taken into account. The calculation results using the developed model are in qualitative agreement with the experimental data obtained during the previous experimental part of the study. It is confirmed that both the electrical PEF mode and the flow rate have a significant effect on the thickness (and mass) of the protein fouling during EDBM. Moreover, the choice of the electric current mode has the main impact on the fouling formation rate; an increase in the PEF pause duration leads to a decrease in the amount of fouling. It was shown that an increase in the PEF pause duration from 10 s to 50 s, in combination with an increase in Reynolds number (the flow rate) from 187 to 560, makes it possible to reduce synergistically the mass of protein deposits from 6 to 1.3 mg/cm[2], which corresponds to a 78% decrease.}, }
@article {pmid35205589, year = {2022}, author = {Yang, X and Yang, L}, title = {Numerical Study of Entropy Generation in Fully Developed Turbulent Circular Tube Flow Using an Elliptic Blending Turbulence Model.}, journal = {Entropy (Basel, Switzerland)}, volume = {24}, number = {2}, pages = {}, pmid = {35205589}, issn = {1099-4300}, abstract = {As computational fluid dynamics (CFD) advances, entropy generation minimization based on CFD becomes attractive for optimizing complex heat-transfer systems. This optimization depends on the accuracy of CFD results, such that accurate turbulence models, such as elliptic relaxation or elliptic blending turbulence models, become important. The performance of a previously developed elliptic blending turbulence model (the SST&amp;nbsp;k-ω-φ-α model) to predict the rate of entropy generation in the fully developed turbulent circular tube flow with constant heat flux was studied to provide some guidelines for using this class of turbulence model to calculate entropy generation in complex systems. The flow and temperature fields were simulated by using a CFD package, and then the rate of entropy generation was calculated in post-processing. The analytical correlations and results of two popular turbulence models (the realizable k-ε and the shear stress transport (SST) k-ω models) were used as references to demonstrate the accuracy of the SST&amp;nbsp;k-ω-φ-α model. The findings indicate that the turbulent Prandtl number (Prt) influences the entropy generation rate due to heat-transfer irreversibility. Prt = 0.85 produces the best results for the SST&amp;nbsp;k-ω-φ-α model. For the realizable k-ε and SST k-ω models, Prt = 0.85 and Prt = 0.92 produce the best results, respectively. For the realizable k-ε and the SST k-ω models, the two methods used to predict the rate of entropy generation due to friction irreversibility produce the same results. However, for the SST&amp;nbsp;k-ω-φ-α model, the rates of entropy generation due to friction irreversibility predicted by the two methods are different. The difference at a Reynolds number of 100,000 is about 14%. The method that incorporates the effective turbulent viscosity should be used to predict the rate of entropy generation due to friction irreversibility for the SST&amp;nbsp;k-ω-φ-α model. Furthermore, when the temperature in the flow field changes dramatically, the temperature-dependent fluid properties must be considered.}, }
@article {pmid35196405, year = {2022}, author = {Xia, N and Jin, B and Jin, D and Yang, Z and Pan, C and Wang, Q and Ji, F and Iacovacci, V and Majidi, C and Ding, Y and Zhang, L}, title = {Decoupling and Reprogramming the Wiggling Motion of Midge Larvae Using a Soft Robotic Platform.}, journal = {Advanced materials (Deerfield Beach, Fla.)}, volume = {34}, number = {17}, pages = {e2109126}, doi = {10.1002/adma.202109126}, pmid = {35196405}, issn = {1521-4095}, support = {JLFS/E-402/18//Hong Kong Research Grants Council/ ; MRP/036/18X//ITF/ ; //HKSAR Innovation and Technology Commission/ ; CAS20403//Croucher Foundation Grant/ ; U1930402//National Science Foundation of China/ ; }, mesh = {Animals ; Biomimetics ; Larva ; Locomotion ; *Robotics ; Swimming ; }, abstract = {The efficient motility of invertebrates helps them survive under evolutionary pressures. Reconstructing the locomotion of invertebrates and decoupling the influence of individual basic motion are crucial for understanding their underlying mechanisms, which, however, generally remain a challenge due to the complexity of locomotion gaits. Herein, a magnetic soft robot to reproduce midge larva's key natural swimming gaits is developed, and the coupling effect between body curling and rotation on motility is investigated. Through the authors' systematically decoupling studies using programmed magnetic field inputs, the soft robot (named LarvaBot) experiences various coupled gaits, including biomimetic side-to-side flexures, and unveils that the optimal rotation amplitude and the synchronization of curling and rotation greatly enhance its motility. The LarvaBot achieves fast locomotion and upstream capability at the moderate Reynolds number regime. The soft robotics-based platform provides new insight to decouple complex biological locomotion, and design programmed swimming gaits for the fast locomotion of soft-bodied swimmers.}, }
@article {pmid35193246, year = {2022}, author = {Czelusniak, LE and Mapelli, VP and Wagner, AJ and Cabezas-Gómez, L}, title = {Shaping the equation of state to improve numerical accuracy and stability of the pseudopotential lattice Boltzmann method.}, journal = {Physical review. E}, volume = {105}, number = {1-2}, pages = {015303}, doi = {10.1103/PhysRevE.105.015303}, pmid = {35193246}, issn = {2470-0053}, abstract = {It has recently been shown that altering the shape of the metastable and unstable branches of an equation of state (EOS) can substantially improve the numerical accuracy of liquid and vapor densities in the pseudopotential lattice Boltzmann method [Peng et al., Phys. Rev. E 101, 063309 (2020)2470-004510.1103/PhysRevE.101.063309]. We found that this approach reduces stability of the method in nonequilibrium conditions and is unstable for bubbles at low reduced temperatures. Here we present an improved method for altering the shape of the metastable and unstable branches of the EOS which remains stable for both equilibrium and nonequilibrium situations and has no issues with bubbles. We also performed a detailed study of the stability of the methods for a droplet impact on a liquid film for reduced temperatures down to 0.35 with Reynolds number of 300. Our approach remained stable for a density ratio of up to 3.38×10^{4}.}, }
@article {pmid35193206, year = {2022}, author = {Richter, SK and Menzel, AM}, title = {Mediated interactions between rigid inclusions in two-dimensional elastic or fluid films.}, journal = {Physical review. E}, volume = {105}, number = {1-1}, pages = {014609}, doi = {10.1103/PhysRevE.105.014609}, pmid = {35193206}, issn = {2470-0053}, abstract = {Interactions between rigid inclusions in continuous three-dimensional linearly elastic solids and low-Reynolds-number viscous fluids have largely been quantified in the past. Prime example systems are given by functionalized elastic composite materials or fluid colloidal suspensions. Here, we address the significantly less frequently studied situation of rigid inclusions in two-dimensional elastic or low-Reynolds-number fluid films. We concentrate on the situation in which disklike inclusions remain well separated from each other and do not get into contact. Specifically, we demonstrate and explain that the logarithmic divergence of the associated Green's function is removed in the absence of net external forces on the inclusions, in line with physical intuition. For instance, this situation applies when only pairwise mutual interactions between the inclusions prevail. Our results will support, for example, investigations on membranes functionalized by appropriate inclusions, both of technical or biological origin, or the dynamics of active microswimmers in appropriately prepared thin films.}, }
@article {pmid35190663, year = {2022}, author = {Hamzah, HK and Ali, FH and Hatami, M}, title = {MHD mixed convection and entropy generation of CNT-water nanofluid in a wavy lid-driven porous enclosure at different boundary conditions.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {2881}, pmid = {35190663}, issn = {2045-2322}, abstract = {In this study, Galerkin Finite Element Method or GFEM is used for the modeling of mixed convection with the entropy generation in wavy lid-driven porous enclosure filled by the CNT-water nanofluid under the magnetic field. Two different cases of boundary conditions for hot and cold walls are considered to study the fluid flow (streamlines) and heat transfer (local and average Nusselt numbers) as well as the entropy generation parameters. Richardson (Ri), Darcy (Da), Hartmann angle (γ), Amplitude (A), Number of peaks (N), Volume fraction (φ), Heat generation factor (λ), Hartmann number (Ha) and Reynolds number (Re) are studied parameters in this study which results indicated that at low Richardson numbers (< 1) increasing the inclined angle of magnetic field, decreases the Nu numbers, but at larger Richardson numbers (> 1) it improves the Nu numbers.}, }
@article {pmid35184017, year = {2022}, author = {Bakos, V and Gyarmati, B and Csizmadia, P and Till, S and Vachoud, L and Nagy Göde, P and Tardy, GM and Szilágyi, A and Jobbágy, A and Wisniewski, C}, title = {Viscous and filamentous bulking in activated sludge: Rheological and hydrodynamic modelling based on experimental data.}, journal = {Water research}, volume = {214}, number = {}, pages = {118155}, doi = {10.1016/j.watres.2022.118155}, pmid = {35184017}, issn = {1879-2448}, abstract = {Although achieving good activated sludge settleability is a key requirement for meeting effluent quality criteria, wastewater treatment plants often face undesired floc structure changes. Filamentous bulking has widely been studied, however, viscous sludge formation much less investigated so far. Our main goal was to find relationship between sludge floc structure and related rheological properties, moreover, to estimate pressure loss in pipe networks through hydrodynamic modelling of the non-Newtonian flows in case of well settling (ideal-like), viscous and filamentous sludge. Severe viscous and filamentous kinds of bulking were generated separately in continuous-flow lab-scale systems initially seeded with the same reference (ideal-like) biomass and the entire evolution of viscous and filamentous bulking was monitored. The results suggested correlation between the rheological properties and the floc structure transformations, and showed the most appropriate fit for the Herschel-Bulkley model (vs. Power-law and Bingham). Validated computational fluid dynamics studies estimated the pipe pressure loss in a wide Reynolds number range for the initial well settling (reference) and the final viscous and filamentous sludge as well. A practical standard modelling protocol was developed for improving energy efficiency of sludge pumping in different floc structure scenarios.}, }
@article {pmid35183949, year = {2022}, author = {Yu, Z and Yang, G and Zhang, W}, title = {A new model for the terminal settling velocity of microplastics.}, journal = {Marine pollution bulletin}, volume = {176}, number = {}, pages = {113449}, doi = {10.1016/j.marpolbul.2022.113449}, pmid = {35183949}, issn = {1879-3363}, mesh = {Environmental Monitoring ; *Microplastics ; Plastics ; *Water Pollutants, Chemical/analysis ; }, abstract = {Microplastic (MP) settling process is important for the transport of microplastic particles (MPs, <5 mm) in water bodies. However, for the control parameter of the drag coefficient (Cd), no generalized formula has been proposed for MPs of different shapes and materials. In this study, a total of 1343 MP settling data were collected from the literature. It was found that the drag law for perfect spheres cannot reasonably predict Cd for MPs with particle Reynolds number of 1-10[3]. A new formula for Cd was developed by introducing the dimensionless particle diameter (d⁎) and two shape descriptors. The absolute error of the new formula is 15.2%, smaller than those (42.5-72.8%) of other existing formulas. Moreover, an explicit model was developed for MP settling velocity by correlating Cd, d⁎, and shape descriptors, with lower absolute error (8.8%) than those (15.4-77.2%) of existing models.}, }
@article {pmid35160419, year = {2022}, author = {Faroughi, SA and Roriz, AI and Fernandes, C}, title = {A Meta-Model to Predict the Drag Coefficient of a Particle Translating in Viscoelastic Fluids: A Machine Learning Approach.}, journal = {Polymers}, volume = {14}, number = {3}, pages = {}, pmid = {35160419}, issn = {2073-4360}, support = {UID-B/05256/2020, UID-P/05256/2020, MIT-EXPL/TDI/0038/2019//FEDER funds through the COMPETE 2020 Programme and National Funds through FCT (Portuguese Foundation for Science and Technology)/ ; NORTE-07-0162-FEDER-000086//University of Minho cluster/ ; CPCA A2 6052 2020//Minho Advanced Computing Center/ ; HPC-EUROPA3 (INFRAIA-2016-1-730897)//Consorzio Interuniversitario dell'Italia Nord Est per il Calcolo Automatico (CINECA)/ ; icei-prace-2020-0009//PRACE - Partnership for Advanced Computing in Europe/ ; }, abstract = {This study presents a framework based on Machine Learning (ML) models to predict the drag coefficient of a spherical particle translating in viscoelastic fluids. For the purpose of training and testing the ML models, two datasets were generated using direct numerical simulations (DNSs) for the viscoelastic unbounded flow of Oldroyd-B (OB-set containing 12,120 data points) and Giesekus (GI-set containing 4950 data points) fluids past a spherical particle. The kinematic input features were selected to be Reynolds number, 0<Re≤50, Weissenberg number, 0≤Wi≤10, polymeric retardation ratio, 0<ζ<1, and shear thinning mobility parameter, 0<α<1. The ML models, specifically Random Forest (RF), Deep Neural Network (DNN) and Extreme Gradient Boosting (XGBoost), were all trained, validated, and tested, and their best architecture was obtained using a 10-Fold cross-validation method. All the ML models presented remarkable accuracy on these datasets; however the XGBoost model resulted in the highest R2 and the lowest root mean square error (RMSE) and mean absolute percentage error (MAPE) measures. Additionally, a blind dataset was generated using DNSs, where the input feature coverage was outside the scope of the training set or interpolated within the training sets. The ML models were tested against this blind dataset, to further assess their generalization capability. The DNN model achieved the highest R2 and the lowest RMSE and MAPE measures when inferred on this blind dataset. Finally, we developed a meta-model using stacking technique to ensemble RF, XGBoost and DNN models and output a prediction based on the individual learner's predictions and a DNN meta-regressor. The meta-model consistently outperformed the individual models on all datasets.}, }
@article {pmid35159644, year = {2022}, author = {Ba, TL and Gróf, G and Odhiambo, VO and Wongwises, S and Szilágyi, IM}, title = {A CFD Study on Heat Transfer Performance of SiO2-TiO2 Nanofluids under Turbulent Flow.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {12}, number = {3}, pages = {}, pmid = {35159644}, issn = {2079-4991}, support = {VEKOP-2.3.2-16-2017-00013//European Union/ ; }, abstract = {A CFD model was performed with commercial software through the adoption of the finite volume method and a SIMPLE algorithm. SiO2-P25 particles were added to water/ethylene glycol as a base fluid. The result is considered a new hybrid nanofluid (HN) for investigating heat transfer (HT). The volume concentrations were 0.5, 1.0, and 1.5%. The Reynolds number was in the range of 5000-17,000. The heat flux (HF) was 7955 W/m[2], and the wall temperature was 340.15 K. The numerical experiments were performed strictly following the rules that one should follow in HT experiments. This is important because many studies related to nanofluid HT overlook these details. The empirical correlations that contain the friction factor perform better with higher Reynolds numbers than the correlations based only on Reynolds and Prandtl numbers. When temperature differences are moderate, researchers may consider using constant properties to lower computational costs, as they may give results that are similar to temperature-dependent ones. Compared with previous research, our simulation results are in agreement with the experiments in real time.}, }
@article {pmid35153576, year = {2021}, author = {Ali, SZ and Dey, S and Mahato, RK}, title = {Mega riverbed-patterns: linear and weakly nonlinear perspectives.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {477}, number = {2252}, pages = {20210331}, pmid = {35153576}, issn = {1364-5021}, abstract = {In this paper, we explore the mega riverbed-patterns, whose longitudinal and vertical length dimensions scale with a few channel widths and the flow depth, respectively. We perform the stability analyses from both linear and weakly nonlinear perspectives by considering a steady-uniform flow in an erodible straight channel comprising a uniform sediment size. The mathematical framework stands on the dynamic coupling between the depth-averaged flow model and the particle transport model including both bedload and suspended load via the Exner equation, which drives the pattern formation. From the linear perspective, we employ the standard linearization technique by superimposing the periodic perturbations on the undisturbed system to find the dispersion relationship. From the weakly nonlinear perspective, we apply the centre-manifold-projection technique, where the fast dynamics of stable modes is projected on the slow dynamics of weakly unstable modes to obtain the Stuart-Landau equation for the amplitude dynamics. We examine the marginal stability, growth rate and amplitude of patterns for a given quintet formed by the channel aspect ratio, wavenumber of patterns, shear Reynolds number, Shields number and relative roughness number. This study highlights the sensitivity of pattern formation to the key parameters and shows how the classical results can be reconstructed on the parameter space.}, }
@article {pmid35153464, year = {2022}, author = {Kingora, K and Burks, WL and Sadat, H}, title = {Flow and mass transfer characteristics for interacting side-by-side cylinders.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {34}, number = {2}, pages = {023602}, pmid = {35153464}, issn = {1070-6631}, support = {R15 HL156127/HL/NHLBI NIH HHS/United States ; }, abstract = {This study investigates the local and global flow structures and mass transfer characteristics for a group of interacting side-by-side cylinders in unbounded flow. Configurations with 2, 3, 4, and 5 members are considered for a range of pitch-ratios (1.05 ≤ S / D ≤ 4) at the Reynolds number Re = 90. The focus is laid on the time-averaged and instantaneous local flow features including wake field, jet flow, vortical structures, λ 2, pressure coefficient, and mass transfer coefficient as well as integral variables including hydrodynamic forces. Four flow regimes are identified based on the vortical structures and average stream-wise velocity field. At low pitch-ratio, the whole structure behaves like a single bluff body, while each member in the configuration behaves like an independent isolated bluff body when the pitch-ratio is large. Between these two regimes, asymmetrically and symmetrically deflected wake regimes are observed. Flow regimes dictate hydrodynamic and mass transfer characteristics such that a jump in the hydrodynamic forces and mass transfer coefficient is observed as the flow regime evolves from a single body to a deflected wake. The configuration's size and the position of member cylinders in the structure have more profound effects on hydrodynamic forces and mass transfer characteristics at small pitch-ratio. For all configurations, drag increases as one progresses deeper into the structure, while lift forces are always repulsive between any two neighboring cylinders. Member cylinders have comparable mass transfer coefficients at intermediate and high pitch-ratios, while exterior cylinders exhibit a higher mass transfer coefficient at low pitch-ratio. Overall, the structure's size has a more profound effect on the values of scalars at low pitch-ratios.}, }
@article {pmid35145137, year = {2022}, author = {Yang, L and Baghaei, S and Suksatan, W and Barnoon, P and Sharma, S and Davidyants, A and El-Shafay, AS}, title = {Numerical assessment of the influence of helical baffle on the hydrothermal aspects of nanofluid turbulent forced convection inside a heat exchanger.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {2245}, pmid = {35145137}, issn = {2045-2322}, abstract = {This study is devoted to the numerical assessment of the influence of helical baffle on the hydrothermal aspects and irreversibility behavior of the turbulent forced convection flow of water-CuO nanofluid (NF) inside a hairpin heat exchanger with 100 mm length, 10 mm inner tube internal diameter, and 15 mm outer diameter internal diameter. The variations of the first-law and second-law performance metrics are investigated in terms of Reynolds number (Re = 5000-10,000), volume concentration of NF ([Formula: see text]) and baffle pitch (B = 25-100 mm). The results show that the NF Nusselt number grows with the rise of both the Re and [Formula: see text] whereas it declines with the rise of B. In addition, the outcomes depicted that the rise of both Re and [Formula: see text] results in the rise of pressure drop, while it declines with the increase of B. Moreover, it was found that the best thermal performance of NF is equal to 1.067, which belongs to the case B = 33.3 mm, [Formula: see text]=2%, and Re = 10,000. Furthermore, it was shown that irreversibilities due to fluid friction and heat transfer augment with the rise of Re while the rise of B results in the decrease of frictional irreversibilities. Finally, the outcomes revealed that with the rise of B, the heat transfer irreversibilities first intensify and then diminish.}, }
@article {pmid35141369, year = {2022}, author = {Masroor, E and Yang, W and Stremler, MA}, title = {Flow visualization data from experiments with an oscillating circular cylinder in a gravity-driven soap film.}, journal = {Data in brief}, volume = {41}, number = {}, pages = {107819}, pmid = {35141369}, issn = {2352-3409}, abstract = {This article contains flow visualization data from experiments conducted in an inclined gravity-driven soap film intersected by a circular cylinder undergoing controlled transverse oscillations at a Reynolds number of Re ≈ 235 . The dimensionless frequency and amplitude of cylinder oscillation were varied systematically over the ranges 0.2 < f * < 1.8 and 0.1 < A * < 1.3 . A high-speed camera was used to capture the interference fringe patterns reflected from the soap film. These videos show the structure of the wake behind the cylinder, including the initial formation of vortices and the extended 'vortex street'. Several wake patterns were identified, including the classic 2S, P+S, 2P, and 2T patterns, which are discussed in detail in the accompanying research article titled "The wake of a transversely oscillating circular cylinder in a flowing soap film at low Reynolds number" [1]. The videos presented in this article can be accessed through the Virginia Tech University Libraries' Repository at https://doi.org/10.7294/14448027.v5[2].}, }
@article {pmid35136141, year = {2022}, author = {Gallo-Méndez, I and Moya, PS}, title = {Langevin based turbulence model and its relationship with Kappa distributions.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {2136}, pmid = {35136141}, issn = {2045-2322}, support = {21182002//Comisi&#xf3;n Nacional de Investigaci&#xf3;n Cient&#xed;fica y Tecnol&#xf3;gica/ ; 1191351//Fondo Nacional de Desarrollo Cient&#xed;fico y Tecnol&#xf3;gico/ ; }, abstract = {Kappa distributions (or [Formula: see text]-like distributions) represent a robust framework to characterize and understand complex phenomena with high degrees of freedom, as turbulent systems, using non-extensive statistical mechanics. Here we consider a coupled map lattice Langevin based model to analyze the relation of a turbulent flow, with its spatial scale dynamic, and [Formula: see text]-like distributions. We generate the steady-state velocity distribution of the fluid at each scale, and show that the generated distributions are well fitted by [Formula: see text]-like distributions. We observe a robust relation between the [Formula: see text] parameter, the scale, and the Reynolds number of the system, Re. In particular, our results show that there is a closed scaling relation between the level of turbulence and the [Formula: see text] parameter; namely [Formula: see text]. We expect these results to be useful to characterize turbulence in different contexts, and our numerical predictions to be tested by observations and experimental setups.}, }
@article {pmid35105911, year = {2022}, author = {Zhang, X and Gomez-Paz, J and Chen, X and McDonough, JM and Islam, MM and Andreopoulos, Y and Zhu, L and Yu, H}, title = {Volumetric lattice Boltzmann method for wall stresses of image-based pulsatile flows.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {1697}, pmid = {35105911}, issn = {2045-2322}, abstract = {Image-based computational fluid dynamics (CFD) has become a new capability for determining wall stresses of pulsatile flows. However, a computational platform that directly connects image information to pulsatile wall stresses is lacking. Prevailing methods rely on manual crafting of a hodgepodge of multidisciplinary software packages, which is usually laborious and error-prone. We present a new computational platform, to compute wall stresses in image-based pulsatile flows using the volumetric lattice Boltzmann method (VLBM). The novelty includes: (1) a unique image processing to extract flow domain and local wall normality, (2) a seamless connection between image extraction and VLBM, (3) an en-route calculation of strain-rate tensor, and (4) GPU acceleration (not included here). We first generalize the streaming operation in the VLBM and then conduct application studies to demonstrate its reliability and applicability. A benchmark study is for laminar and turbulent pulsatile flows in an image-based pipe (Reynolds number: 10 to 5000). The computed pulsatile velocity and shear stress are in good agreements with Womersley's analytical solutions for laminar pulsatile flows and concurrent laboratory measurements for turbulent pulsatile flows. An application study is to quantify the pulsatile hemodynamics in image-based human vertebral and carotid arteries including velocity vector, pressure, and wall-shear stress. The computed velocity vector fields are in reasonably well agreement with MRA (magnetic resonance angiography) measured ones. This computational platform is good for image-based CFD with medical applications and pore-scale porous media flows in various natural and engineering systems.}, }
@article {pmid35099851, year = {2023}, author = {Ranftl, S and Müller, TS and Windberger, U and Brenn, G and von der Linden, W}, title = {A Bayesian approach to blood rheological uncertainties in aortic hemodynamics.}, journal = {International journal for numerical methods in biomedical engineering}, volume = {39}, number = {4}, pages = {e3576}, doi = {10.1002/cnm.3576}, pmid = {35099851}, issn = {2040-7947}, mesh = {Humans ; Bayes Theorem ; Uncertainty ; *Hemodynamics ; *Aorta ; Rheology ; Stress, Mechanical ; Models, Cardiovascular ; Blood Flow Velocity ; Computer Simulation ; }, abstract = {Computational hemodynamics has received increasing attention recently. Patient-specific simulations require questionable model assumptions, for example, for geometry, boundary conditions, and material parameters. Consequently, the credibility of these simulations is much doubted, and rightly so. Yet, the matter may be addressed by a rigorous uncertainty quantification. In this contribution, we investigated the impact of blood rheological models on wall shear stress uncertainties in aortic hemodynamics obtained in numerical simulations. Based on shear-rheometric experiments, we compare the non-Newtonian Carreau model to a simple Newtonian model and a Reynolds number-equivalent Newtonian model. Bayesian Probability Theory treats uncertainties consistently and allows to include elusive assumptions such as the comparability of flow regimes. We overcome the prohibitively high computational cost for the simulation with a surrogate model, and account for the uncertainties of the surrogate model itself, too. We have two main findings: (1) The Newtonian models mostly underestimate the uncertainties as compared to the non-Newtonian model. (2) The wall shear stresses of specific persons cannot be distinguished due to largely overlapping uncertainty bands, implying that a more precise determination of person-specific blood rheological properties is necessary for person-specific simulations. While we refrain from a general recommendation for one rheological model, we have quantified the error of the uncertainty quantification associated with these modeling choices.}, }
@article {pmid35094560, year = {2022}, author = {Cartes, C and Tirapegui, E and Pandit, R and Brachet, M}, title = {The Galerkin-truncated Burgers equation: crossover from inviscid-thermalized to Kardar-Parisi-Zhang scaling.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {380}, number = {2219}, pages = {20210090}, doi = {10.1098/rsta.2021.0090}, pmid = {35094560}, issn = {1471-2962}, abstract = {The one-dimensional Galerkin-truncated Burgers equation, with both dissipation and noise terms included, is studied using spectral methods. When the truncation-scale Reynolds number [Formula: see text] is varied, from very small values to order 1 values, the scale-dependent correlation time [Formula: see text] is shown to follow the expected crossover from the short-distance [Formula: see text] Edwards-Wilkinson scaling to the universal long-distance Kardar-Parisi-Zhang scaling [Formula: see text]. In the inviscid limit, [Formula: see text], we show that the system displays another crossover to the Galerkin-truncated inviscid-Burgers regime that admits thermalized solutions with [Formula: see text]. The scaling forms of the time-correlation functions are shown to follow the known analytical laws and the skewness and excess kurtosis of the interface increments distributions are characterized. This article is part of the theme issue 'Scaling the turbulence edifice (part 2)'.}, }
@article {pmid35094557, year = {2022}, author = {Alexakis, A and Biferale, L}, title = {λ-Navier-Stokes turbulence.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {380}, number = {2219}, pages = {20210243}, doi = {10.1098/rsta.2021.0243}, pmid = {35094557}, issn = {1471-2962}, abstract = {We investigate numerically the model proposed in Sahoo et al. (2017 Phys. Rev. Lett. 118, 164501) where a parameter λ is introduced in the Navier-Stokes equations such that the weight of homochiral to heterochiral interactions is varied while preserving all original scaling symmetries and inviscid invariants. Decreasing the value of λ leads to a change in the direction of the energy cascade at a critical value [Formula: see text]. In this work, we perform numerical simulations at varying λ in the forward energy cascade range and at changing the Reynolds number [Formula: see text]. We show that for a fixed injection rate, as [Formula: see text], the kinetic energy diverges with a scaling law [Formula: see text]. The energy spectrum is shown to display a larger bottleneck as λ is decreased. The forward heterochiral flux and the inverse homochiral flux both increase in amplitude as [Formula: see text] is approached while keeping their difference fixed and equal to the injection rate. As a result, very close to [Formula: see text] a stationary state is reached where the two opposite fluxes are of much higher amplitude than the mean flux and large fluctuations are observed. Furthermore, we show that intermittency as [Formula: see text] is approached is reduced. The possibility of obtaining a statistical description of regular Navier-Stokes turbulence as an expansion around this newly found critical point is discussed. This article is part of the theme issue 'Scaling the turbulence edifice (part 2)'.}, }
@article {pmid35089772, year = {2022}, author = {Wagner, CG and Norton, MM and Park, JS and Grover, P}, title = {Exact Coherent Structures and Phase Space Geometry of Preturbulent 2D Active Nematic Channel Flow.}, journal = {Physical review letters}, volume = {128}, number = {2}, pages = {028003}, doi = {10.1103/PhysRevLett.128.028003}, pmid = {35089772}, issn = {1079-7114}, abstract = {Confined active nematics exhibit rich dynamical behavior, including spontaneous flows, periodic defect dynamics, and chaotic "active turbulence." Here, we study these phenomena using the framework of exact coherent structures, which has been successful in characterizing the routes to high Reynolds number turbulence of passive fluids. Exact coherent structures are stationary, periodic, quasiperiodic, or traveling wave solutions of the hydrodynamic equations that, together with their invariant manifolds, serve as an organizing template of the dynamics. We compute the dominant exact coherent structures and connecting orbits in a preturbulent active nematic channel flow, which enables a fully nonlinear but highly reduced-order description in terms of a directed graph. Using this reduced representation, we compute instantaneous perturbations that switch the system between disparate spatiotemporal states occupying distant regions of the infinite-dimensional phase space. Our results lay the groundwork for a systematic means of understanding and controlling active nematic flows in the moderate- to high-activity regime.}, }
@article {pmid35089743, year = {2022}, author = {Oberlack, M and Hoyas, S and Kraheberger, SV and Alcántara-Ávila, F and Laux, J}, title = {Turbulence Statistics of Arbitrary Moments of Wall-Bounded Shear Flows: A Symmetry Approach.}, journal = {Physical review letters}, volume = {128}, number = {2}, pages = {024502}, doi = {10.1103/PhysRevLett.128.024502}, pmid = {35089743}, issn = {1079-7114}, abstract = {The calculation of turbulence statistics is considered the key unsolved problem of fluid mechanics, i.e., precisely the computation of arbitrary statistical velocity moments from first principles alone. Using symmetry theory, we derive turbulent scaling laws for moments of arbitrary order in two regions of a turbulent channel flow. Besides the classical scaling symmetries of space and time, the key symmetries for the present work reflect the two well-known characteristics of turbulent flows: non-Gaussianity and intermittency. To validate the new scaling laws we made a new simulation at an unprecedented friction Reynolds number of 10 000, large enough to test the new scaling laws. Two key results appear as an application of symmetry theory, which allowed us to generate symmetry invariant solutions for arbitrary orders of moments for the underlying infinite set of moment equations. First, we show that in the sense of the generalization of the deficit law all moments of the streamwise velocity in the channel center follow a power-law scaling, with exponents depending on the first and second moments alone. Second, we show that the logarithmic law of the mean streamwise velocity in wall-bounded flows is indeed a valid solution of the moment equations, and further, all higher moments in this region follow a power law, where the scaling exponent of the second moment determines all higher moments. With this we give a first complete mathematical framework for all moments in the log region, which was first discovered about 100 years ago.}, }
@article {pmid35079064, year = {2022}, author = {Fujimori, T and Yamashita, D and Kishibe, Y and Sakai, M and Inoue, H and Onoki, T and Otsuka, J and Tanioka, D and Hikata, T and Okubo, S and Akada, K and Fujita, JI}, title = {One step fabrication of aligned carbon nanotubes using gas rectifier.}, journal = {Scientific reports}, volume = {12}, number = {1}, pages = {1285}, pmid = {35079064}, issn = {2045-2322}, support = {JPJ004596//ATLA/ ; }, abstract = {We report the one-step fabrication of aligned and high-quality carbon nanotubes (CNTs) using floating-catalyst chemical vapor deposition (FCCVD) with controlled fluidic properties assisted by a gas rectifier. The gas rectifier consists of one-dimensional straight channels for regulating the Reynolds number of the reaction gas. Our computational fluid dynamics simulation reveals that the narrow channels of the gas rectifier provide steady and accelerated laminar flow of the reaction gas. In addition, strong shear stress is induced near the side wall of the channels, resulting in the spontaneous formation of macroscopic CNT bundles aligned along the direction of the gas flow. After a wet-process using chlorosulfonic acid, the inter-tube voids inherently observed in as-grown CNT bundles are reduced from 16 to 0.3%. The resulting CNT fiber exhibits a tensile strength of 2.1 ± 0.1 N tex[-1] with a Young's modulus of 39 ± 4 N tex[-1] and an elongation of 6.3 ± 0.6%. FCCVD coupled with the strong shear stress of the reaction gas is an important pre-processing route for the fabrication of high-performance CNT fibers.}, }
@article {pmid35078340, year = {2022}, author = {Hamann, L and Blanke, A}, title = {Suspension feeders: diversity, principles of particle separation and biomimetic potential.}, journal = {Journal of the Royal Society, Interface}, volume = {19}, number = {186}, pages = {20210741}, pmid = {35078340}, issn = {1742-5662}, mesh = {Animals ; *Biomimetics ; Feeding Behavior ; Plankton ; *Sharks ; Suspensions ; }, abstract = {Suspension feeders (SFs) evolved a high diversity of mechanisms, sometimes with remarkably convergent morphologies, to retain plankton, detritus and man-made particles with particle sizes ranging from less than 1 µm to several centimetres. Based on an extensive literature review, also including the physical and technical principles of solid-liquid separation, we developed a set of 18 ecological and technical parameters to review 35 taxa of suspension-feeding Metazoa covering the diversity of morphological and functional principles. This includes passive SFs, such as gorgonians or crinoids that use the ambient flow to encounter particles, and sponges, bivalves or baleen whales, which actively create a feeding current. Separation media can be flat or funnel-shaped, built externally such as the filter houses in larvaceans, or internally, like the pleated gills in bivalves. Most SFs feed in the intermediate flow region of Reynolds number 1-50 and have cleaning mechanisms that allow for continuous feeding. Comparison of structure-function patterns in SFs to current filtration technologies highlights potential solutions to common technical design challenges, such as mucus nets which increase particle adhesion in ascidians, vanes which reduce pressure losses in whale sharks and changing mesh sizes in the flamingo beak which allow quick adaptation to particle sizes.}, }
@article {pmid35072796, year = {2022}, author = {Liu, S and Dong, F and Zhang, D and Zhang, J and Wang, X}, title = {Effect of microfluidic channel geometry on Bacillus subtilis biofilm formation.}, journal = {Biomedical microdevices}, volume = {24}, number = {1}, pages = {11}, pmid = {35072796}, issn = {1572-8781}, mesh = {*Bacillus subtilis ; Biofilms ; Extracellular Matrix ; *Microfluidics ; Stress, Mechanical ; }, abstract = {Biofilms are microbial colonies encased in an extracellular polymer matrix self-secreted through bacterial proliferation and differentiation. Biofilms exist almost everywhere such as sewers, rivers and oceans. In the fluid environment, the formation of biofilms is closely related to the relevant parameters of the flow field, such as the shear stress, the secondary flow, and the Reynolds number. In this paper, we use microfluidic channels made of polydimethylsiloxane to study the channel-geometry effect on Bacillus subtilis biofilms formation, such as the biofilm adhesion and structure. Our study shows that both the shear stress and the secondary flow play roles in the biofilm adhesion at the initial stage, the shear stress decides whether the biofilm adheres, if yes, then the secondary flow determines the adhesion rate. Our study further shows that after the biofilm forms, its structure evolves from loose to dense, with a concomitant 20-times rise in adhesion. Our study provides new insights into the adhesion of biofilms in natural and industrial fluid environments and helps understand the growth of biofilms.}, }
@article {pmid35072747, year = {2022}, author = {Pajic-Lijakovic, I and Milivojevic, M}, title = {Mechanical waves caused by collective cell migration: generation.}, journal = {European biophysics journal : EBJ}, volume = {51}, number = {1}, pages = {1-13}, pmid = {35072747}, issn = {1432-1017}, support = {Contract No. 451-03-9/2021-14/200135//Ministarstvo Prosvete, Nauke i Tehnolo&#x161;kog Razvoja/ ; }, mesh = {Cell Movement ; *Mechanical Phenomena ; *Models, Biological ; Viscosity ; }, abstract = {Long-timescale viscoelasticity caused by collective cell migration (CCM) significantly influences cell rearrangement and induces generation of mechanical waves. The phenomenon represents a product of the active turbulence occurring at low Reynolds number. The generation of mechanical waves has been a subject of intensive research primarily in 2D multicellular systems, while 3D systems have not been considered in this context. The aim of this contribution is to discuss the generation of mechanical waves during 3D CCM in two model systems: (1) the fusion of two-cell aggregates and (2) cell aggregate rounding after uni-axial compression, pointing out that mechanical waves represent a characteristic of CCM in general. Such perturbations are also involved in various biological processes, such as embryogenesis, wound healing and cancer invasion. The inter-relation between the viscoelasticity and the appearance of active turbulence remains poorly understood even in 2D. The phenomenon represents a consequence of the competition between the viscoelastic force and the surface tension force which induces successive stiffening and softening of parts of multicellular systems. The viscoelastic force is a product of the residual cell stress accumulation and its inhomogeneous distribution caused by CCM. This modeling consideration represents a powerful tool to address the generation of mechanical waves in CCM towards an understanding of this important but still controversial topic.}, }
@article {pmid35052037, year = {2021}, author = {Lee, TW and Park, JE}, title = {Entropy and Turbulence Structure.}, journal = {Entropy (Basel, Switzerland)}, volume = {24}, number = {1}, pages = {}, pmid = {35052037}, issn = {1099-4300}, abstract = {Some new perspectives are offered on the spectral and spatial structure of turbulent flows, in the context of conservation principles and entropy. In recent works, we have shown that the turbulence energy spectra are derivable from the maximum entropy principle, with good agreement with experimental data across the entire wavenumber range. Dissipation can also be attributed to the Reynolds number effect in wall-bounded turbulent flows. Within the global energy and dissipation constraints, the gradients (d/dy+ or d[2]/dy+[2]) of the Reynolds stress components neatly fold onto respective curves, so that function prescriptions (dissipation structure functions) can serve as a template to expand to other Reynolds numbers. The Reynolds stresses are fairly well prescribed by the current scaling and dynamical formalism so that the origins of the turbulence structure can be understood and quantified from the entropy perspective.}, }
@article {pmid35034493, year = {2022}, author = {Eyink, GL and Kumar, S and Quan, H}, title = {The Onsager theory of wall-bounded turbulence and Taylor's momentum anomaly.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {380}, number = {2218}, pages = {20210079}, pmid = {35034493}, issn = {1471-2962}, abstract = {We discuss the Onsager theory of wall-bounded turbulence, analysing the momentum dissipation anomaly hypothesized by Taylor. Turbulent drag laws observed with both smooth and rough walls imply ultraviolet divergences of velocity gradients. These are eliminated by a coarse-graining operation, filtering out small-scale eddies and windowing out near-wall eddies, thus introducing two arbitrary regularization length-scales. The regularized equations for resolved eddies correspond to the weak formulation of the Navier-Stokes equation and contain, in addition to the usual turbulent stress, also an inertial drag force modelling momentum exchange with unresolved near-wall eddies. Using an Onsager-type argument based on the principle of renormalization group invariance, we derive an upper bound on wall friction by a function of Reynolds number determined by the modulus of continuity of the velocity at the wall. Our main result is a deterministic version of Prandtl's relation between the Blasius [Formula: see text] drag law and the 1/7 power-law profile of the mean streamwise velocity. At higher Reynolds, the von Kármán-Prandtl drag law requires instead a slow logarithmic approach of velocity to zero at the wall. We discuss briefly also the large-eddy simulation of wall-bounded flows and use of iterative renormalization group methods to establish universal statistics in the inertial sublayer. This article is part of the theme issue 'Scaling the turbulence edifice (part 1)'.}, }
@article {pmid35034489, year = {2022}, author = {Buaria, D and Pumir, A and Bodenschatz, E}, title = {Generation of intense dissipation in high Reynolds number turbulence.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {380}, number = {2218}, pages = {20210088}, pmid = {35034489}, issn = {1471-2962}, abstract = {Intense fluctuations of energy dissipation rate in turbulent flows result from the self-amplification of strain rate via a quadratic nonlinearity, with contributions from vorticity (via the vortex stretching mechanism) and pressure-Hessian-which are analysed here using direct numerical simulations of isotropic turbulence on up to [Formula: see text] grid points, and Taylor-scale Reynolds numbers in the range 140-1300. We extract the statistics involved in amplification of strain and condition them on the magnitude of strain. We find that strain is self-amplified by the quadratic nonlinearity, and depleted via vortex stretching, whereas pressure-Hessian acts to redistribute strain fluctuations towards the mean-field and hence depletes intense strain. Analysing the intense fluctuations of strain in terms of its eigenvalues reveals that the net amplification is solely produced by the third eigenvalue, resulting in strong compressive action. By contrast, the self-amplification acts to deplete the other two eigenvalues, whereas vortex stretching acts to amplify them, with both effects cancelling each other almost perfectly. The effect of the pressure-Hessian for each eigenvalue is qualitatively similar to that of vortex stretching, but significantly weaker in magnitude. Our results conform with the familiar notion that intense strain is organized in sheet-like structures, which are in the vicinity of, but never overlap with tube-like regions of intense vorticity due to fundamental differences in their amplifying mechanisms. This article is part of the theme issue 'Scaling the turbulence edifice (part 1)'.}, }
@article {pmid35033287, year = {2022}, author = {Chakraborty, R and Maiti, A and Sharma, N and Dey, KK}, title = {Active matter dynamics in confined microfluidic environments.}, journal = {Progress in molecular biology and translational science}, volume = {186}, number = {1}, pages = {245-265}, doi = {10.1016/bs.pmbts.2021.07.014}, pmid = {35033287}, issn = {1878-0814}, mesh = {Humans ; *Microfluidics ; *Technology ; }, abstract = {The field of active matter is a nascent area of research in soft condensed matter physics, which is drawing on the expertise of researchers from diverse disciplines. Small scale active particles-both inorganic and biological-display non-trivial emergent dynamics and interactions that could help us understand complex biological processes and phenomena. Recently, using microfluidic technologies, several research groups have performed important experimental and theoretical studies to understand the behavior of self-propelled particles and molecular active matter within confined environments-to glean a fundamental understanding of the cellular processes occurring under ultra-low Reynolds number conditions. In this chapter, we would like to review applications of microfluidics in active matter research, highlighting a few important theoretical and experimental investigations. We will conclude the discussion with a note on the future of this field mentioning a few open questions that are at the forefront of our minds.}, }
@article {pmid35029495, year = {2021}, author = {Koch, CM and Wilczek, M}, title = {Role of Advective Inertia in Active Nematic Turbulence.}, journal = {Physical review letters}, volume = {127}, number = {26}, pages = {268005}, doi = {10.1103/PhysRevLett.127.268005}, pmid = {35029495}, issn = {1079-7114}, abstract = {Suspensions of active agents with nematic interactions exhibit complex spatiotemporal dynamics such as mesoscale turbulence. Since the Reynolds number of microscopic flows is very small on the scale of individual agents, inertial effects are typically excluded in continuum theories of active nematic turbulence. Whether active stresses can collectively excite inertial flows is currently unclear. To address this question, we investigate a two-dimensional continuum theory for active nematic turbulence. In particular, we compare mesoscale turbulence with and without the effects of advective inertia. We find that inertial effects can influence the flow already close to the onset of the turbulent state and, moreover, give rise to large-scale fluid motion for strong active driving. A detailed analysis of the kinetic energy budget reveals an energy transfer to large scales mediated by inertial advection. While this transfer is small in comparison to energy injection and dissipation, its effects accumulate over time. The inclusion of friction, which is typically present in experiments, can compensate for this effect. The findings suggest that the inclusion of inertia and friction may be necessary for dynamically consistent theories of active nematic turbulence.}, }
@article {pmid35016537, year = {2022}, author = {Olsson, KH and Gurka, R and Holzman, R}, title = {Trophic guilds of suction-feeding fishes are distinguished by their characteristic hydrodynamics of swimming and feeding.}, journal = {Proceedings. Biological sciences}, volume = {289}, number = {1966}, pages = {20211968}, pmid = {35016537}, issn = {1471-2954}, mesh = {Animals ; Biomechanical Phenomena ; Feeding Behavior ; Fishes ; *Hydrodynamics ; Male ; Phylogeny ; Predatory Behavior ; Suction ; *Swimming ; }, abstract = {Suction-feeding in fishes is a ubiquitous form of prey capture whose outcome depends both on the movements of the predator and the prey, and on the dynamics of the surrounding fluid, which exerts forces on the two organisms. The inherent complexity of suction-feeding has challenged previous efforts to understand how the feeding strikes are modified when species evolve to feed on different prey types. Here, we use the concept of dynamic similarity, commonly applied to understanding the mechanisms of swimming, flying, walking and aquatic feeding. We characterize the hydrodynamic regimes pertaining to (i) the forward movement of the fish (ram), and (ii) the suction flows for feeding strikes of 71 species of acanthomorph fishes. A discriminant function analysis revealed that feeding strikes of zooplanktivores, generalists and piscivores could be distinguished based on their hydrodynamic regimes. Furthermore, a phylogenetic comparative analysis revealed that there are distinctive hydrodynamic adaptive peaks associated with zooplanktivores, generalists and piscivores. The scaling of dynamic similarity across species, body sizes and feeding guilds in fishes indicates that elementary hydrodynamic principles govern the trophic evolution of suction-feeding in fishes.}, }
@article {pmid35009552, year = {2021}, author = {Węgrzyn, D and Wrzeciono, P and Wieczorkowska, A}, title = {The Dependence of Flue Pipe Airflow Parameters on the Proximity of an Obstacle to the Pipe's Mouth.}, journal = {Sensors (Basel, Switzerland)}, volume = {22}, number = {1}, pages = {}, pmid = {35009552}, issn = {1424-8220}, mesh = {*Mouth ; *Sound ; }, abstract = {This paper describes the influence of the presence of an obstacle near the flue pipe's mouth on the air jet, which directly affects the parameters of the sound generated by the flue pipe. Labial pipes of the most common types of mouth were tested. The method of interval calculus was used instead of invasive measuring instruments. The obtained results prove that the proximity of an obstacle affects the sound's fundamental frequency, as the airflow speed coming out of the flue pipe's mouth changes. The relationship between the airflow speed, the value of the Reynolds number, and the Strouhal number was also established. The thesis of the influence of the proximity of an obstacle on the fundamental frequency of the sound of a flue pipe was generalized, and formulas for calculating the untuning of the sound of the pipe were presented for various types of mouth.}, }
@article {pmid34996050, year = {2022}, author = {Xu, WH and Xu, GD and Shan, L}, title = {Real-time parametric estimation of periodic wake-foil interactions using bioinspired pressure sensing and machine learning.}, journal = {Bioinspiration &amp; biomimetics}, volume = {17}, number = {2}, pages = {}, doi = {10.1088/1748-3190/ac4953}, pmid = {34996050}, issn = {1748-3190}, mesh = {Biomechanical Phenomena ; Biomimetics ; Machine Learning ; *Models, Biological ; *Swimming ; }, abstract = {Periodic wake-foil interactions occur in the collective swimming of bio-inspired robots. Wake interaction pattern estimation (and control) is crucial to thrust enhancement and propulsive efficiency optimization. In this paper, we study the wake interaction pattern estimation of two flapping foils in tandem configurations. The experiments are conducted at a Reynolds number of 1.41 × 10[4]in a water channel. A modified wake-foil phase parameter Φ, which unifies the influences of inter-foil distanceLx, motion phase difference Δφand wake convection velocityUv, is introduced to describe the wake interaction patterns parametrically. We use a differential pressure sensor on the downstream foil to capture wake interaction characteristics. Data sets at different tandem configurations are collected. The wake-foil phase Φ is used to label the pressure signals. A one-dimensional convolutional neural networks (1D-CNN) model is used to learn an end-to-end mapping between the raw pressure measurements and the wake-foil phase Φ. The trained 1D-CNN model shows accurate estimations (average error 3.5%) on random wake interaction patterns and is fast enough (within 40 ms). Then the trained 1D-CNN model is applied to online thrust enhancement control of a downstream foil swimming in a periodic wake. Synchronous force monitoring and flow visualization demonstrate the effectiveness of the 1D-CNN model. The limitations of the model are discussed. The proposed approach can be applied to the online estimation and control of wake interactions in the collective swimming and flying of biomimetic robots.}, }
@article {pmid34993288, year = {2022}, author = {Khojasteh, AR and Laizet, S and Heitz, D and Yang, Y}, title = {Lagrangian and Eulerian dataset of the wake downstream of a smooth cylinder at a Reynolds number equal to 3900.}, journal = {Data in brief}, volume = {40}, number = {}, pages = {107725}, pmid = {34993288}, issn = {2352-3409}, abstract = {The dataset contains Eulerian velocity and pressure fields, and Lagrangian particle trajectories of the wake flow downstream of a smooth cylinder at a Reynolds number equal to 3900. An open source Direct Numerical Simulation (DNS) flow solver named Incompact3d was used to calculate the Eulerian field around the cylinder. The synthetic Lagrangian tracer particles were transported using a fourth-order Runge-Kutta scheme in time and trilinear interpolations in space. Trajectories of roughly 200,000 particles for two 3D sub-domains are available to the public. This dataset can be used as a test case for tracking algorithm assessment, exploring the Lagrangian physics, statistic analyses, machine learning, and data assimilation interests.}, }
@article {pmid34982565, year = {2022}, author = {Dev, AA and Dunne, P and Hermans, TM and Doudin, B}, title = {Fluid Drag Reduction by Magnetic Confinement.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {38}, number = {2}, pages = {719-726}, doi = {10.1021/acs.langmuir.1c02617}, pmid = {34982565}, issn = {1520-5827}, mesh = {Friction ; Lubrication ; *Magnetic Phenomena ; *Microfluidics ; Viscosity ; }, abstract = {The frictional forces of a viscous liquid flow are a major energy loss issue and severely limit microfluidics practical use. Reducing this drag by more than a few tens of percent remain elusive. Here, we show how cylindrical liquid-in-liquid flow leads to drag reduction of 60-99% for sub-mm and mm-sized channels, regardless of whether the viscosity of the transported liquid is larger or smaller than that of the confining one. In contrast to lubrication or sheath flow, we do not require a continuous flow of the confining lubricant, here made of a ferrofluid held in place by magnetic forces. In a laminar flow model with appropriate boundary conditions, we introduce a modified Reynolds number with a scaling that depends on geometrical factors and viscosity ratio of the two liquids. It explains our whole range of data and reveals the key design parameters for optimizing the drag reduction values. Our approach promises a new route for microfluidics designs with pressure gradient reduced by orders of magnitude.}, }
@article {pmid34972296, year = {2021}, author = {Daru, V and Weisman, C and Baltean-Carlès, D and Bailliet, H}, title = {A numerical study of the coupling between Rayleigh streaming and heat transfer at high acoustic level.}, journal = {The Journal of the Acoustical Society of America}, volume = {150}, number = {6}, pages = {4501}, doi = {10.1121/10.0009026}, pmid = {34972296}, issn = {1520-8524}, abstract = {Complex coupling between thermal effects and Rayleigh streaming in a standing wave guide at high acoustic levels is analyzed numerically. The approach is guided by the recent analytical study, showing that reverse streaming cells can form if the nonlinear Reynolds number exceeds a value depending on the wave frequency and thermophysical properties of the fluid and solid wall. A numerical configuration is introduced to investigate the evolution of the streaming flow structure and the average temperature field at high acoustic levels. Special attention is given to inhibit the development of shock waves. The heat conduction is accounted for in the wall. As the acoustic level is increased, the average temperature field becomes stratified transversely. The simulations show the relevance of the criterion for characterizing the appearance of additional contrarotating streaming cells near the acoustic velocity antinodes. For higher acoustic levels, these additional cells evolve into increasingly large stagnant zones, where the streaming flow is of very small amplitude and the contours of temperature are stratified longitudinally. The overall outer streaming flow decreases. These results are consistent with previous experimental observations, showing that the intrinsic coupling between the thermal effects and acoustic streaming at high levels is very well described.}, }
@article {pmid34964615, year = {2022}, author = {Sznitman, J}, title = {Revisiting Airflow and Aerosol Transport Phenomena in the Deep Lungs with Microfluidics.}, journal = {Chemical reviews}, volume = {122}, number = {7}, pages = {7182-7204}, doi = {10.1021/acs.chemrev.1c00621}, pmid = {34964615}, issn = {1520-6890}, mesh = {Aerosols ; Computer Simulation ; Lung ; *Microfluidics ; Models, Biological ; Particle Size ; *Pulmonary Alveoli ; }, abstract = {The dynamics of respiratory airflows and the associated transport mechanisms of inhaled aerosols characteristic of the deep regions of the lungs are of broad interest in assessing both respiratory health risks and inhalation therapy outcomes. In the present review, we present a comprehensive discussion of our current understanding of airflow and aerosol transport phenomena that take place within the unique and complex anatomical environment of the deep lungs, characterized by submillimeter 3D alveolated airspaces and nominally slow resident airflows, known as low-Reynolds-number flows. We exemplify the advances brought forward by experimental efforts, in conjunction with numerical simulations, to revisit past mechanistic theories of respiratory airflow and particle transport in the distal acinar regions. Most significantly, we highlight how microfluidic-based platforms spanning the past decade have accelerated opportunities to deliver anatomically inspired in vitro solutions that capture with sufficient realism and accuracy the leading mechanisms governing both respiratory airflow and aerosol transport at true scale. Despite ongoing challenges and limitations with microfabrication techniques, the efforts witnessed in recent years have provided previously unattainable in vitro quantifications on the local transport properties in the deep pulmonary acinar airways. These may ultimately provide new opportunities to explore improved strategies of inhaled drug delivery to the deep acinar regions by investigating further the mechanistic interactions between airborne particulate carriers and respiratory airflows at the pulmonary microscales.}, }
@article {pmid34947623, year = {2021}, author = {Strizhenov, EM and Chugaev, SS and Men'shchikov, IE and Shkolin, AV and Zherdev, AA}, title = {Heat and Mass Transfer in an Adsorbed Natural Gas Storage System Filled with Monolithic Carbon Adsorbent during Circulating Gas Charging.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {11}, number = {12}, pages = {}, pmid = {34947623}, issn = {2079-4991}, support = {20-19-00421//Russian Science Foundation/ ; }, abstract = {Adsorbed natural gas (ANG) technology is a promising alternative to traditional compressed (CNG) and liquefied (LNG) natural gas systems. Nevertheless, the energy efficiency and storage capacity of an ANG system strongly depends on the thermal management of its inner volume because of significant heat effects occurring during adsorption/desorption processes. In the present work, a prototype of a circulating charging system for an ANG storage tank filled with a monolithic nanoporous carbon adsorbent was studied experimentally under isobaric conditions (0.5-3.5 MPa) at a constant volumetric flow rate (8-18 m[3]/h) or flow mode (Reynolds number at the adsorber inlet from 100,000 to 220,000). The study of the thermal state of the monolithic adsorbent layer and internal heat exchange processes during the circulating charging of an adsorbed natural gas storage system was carried out. The correlation between the gas flow mode, the dynamic gas flow temperature, and the heat transfer coefficient between the gas and adsorbent was determined. A one-dimensional mathematical model of the circulating low-temperature charging process was developed, the results of which correspond to the experimental measurements.}, }
@article {pmid34947165, year = {2021}, author = {Sawka, A}, title = {Deposition of Gadolinia-Doped Zirconia Layers Using Metalorganic Compounds at Low Temperatures.}, journal = {Materials (Basel, Switzerland)}, volume = {14}, number = {24}, pages = {}, pmid = {34947165}, issn = {1996-1944}, support = {project no. 16.16.160.557//The Polish State Ministry of Education and Science for AGH University of Science and Technology, Faculty of Materials Science and Ceramics/ ; }, abstract = {This paper shows the results of an investigation on the synthesis of non-porous and nanocrystalline ZrO2-Gd2O3 layers by metalorganic chemical vapor deposition (MOCVD) with the use of Zr(tmhd)4 (tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)zirconium(IV)) and Gd(tmhd)3 (tris(2,2,6,6-tetramethyl-3,5-heptanedionato)gadolinium(III)). Argon and air were used as carrier gases. The molar content of Gd(tmhd)3 in the gas reaction mixture was as follows: 10% and 20%. The layers were synthesized on tubular substrates made of quartz glass at the temperatures of 550-700 °C. Synthesis conditions were established using the Grx/Rex[2] expression (Gr is the Grashof number; Re is the Reynolds number; x is the distance from the gas inflow point). The value of this criterion was below 0.01. ZrO2-Gd2O3 layers synthesized at 600-700 °C were crystalline. When the molar content of Gd(tmhd)3 in the gas reaction mixture was 10 mol.%, a relationship between the chemical composition of the gas reaction mixture and that of the deposited layer could be observed. The synthesized layers underwent scanning electron microscopy, as well as X-ray analysis. The transparency of coated and uncoated glass was tested using UV-Vis spectroscopy. Their chemical composition was examined with the use of an EDS analyzer.}, }
@article {pmid34945681, year = {2021}, author = {Kumbár, V and Ondrušíková, S and Trost, D and Polcar, A and Nedomová, &#x160;}, title = {Rheological and Flow Behaviour of Yolk, Albumen and Liquid Whole Egg from Eggs of Six Different Poultry Species.}, journal = {Foods (Basel, Switzerland)}, volume = {10}, number = {12}, pages = {}, pmid = {34945681}, issn = {2304-8158}, support = {AF-IGA-2020-TP006//Mendel University in Brno/ ; }, abstract = {Liquid egg products are one of the basic raw materials for the food industry. Knowledge of their rheological and flow behaviour in real technical elements is absolutely necessary for the selection of suitable technological equipment for their processing. In this article, the rheological properties of liquid egg products were determined. Eggs from six different species of poultry are used: domestic hen (Gallus gallus domesticus) hybrid Hisex Brown; Japanese quail (Coturnix japonica); German carrier goose (Anser anser f. domestica); domestic ducks (Anas platyrhynchos f. domestica); domestic guinea fowl (Numida meleagris f. domestica); and domestic turkeys (Meleagris gallopavo f. domestica). Liquid egg products showed pseudoplastic behaviour in range of shear strain rates from 0.2 up to 200 s[-1] and at the temperature of 18 °C. Thus, the flow curves were constructed using the Ostwald-de Waele rheological model, with respect to the pseudoplastic behaviour of liquid egg products. According to the values of the coefficients of determination (R[2]), the sum of squared estimate of errors (SSE) and the root mean square error (RMSE), this model was appropriately chosen. Using the consistency coefficient K, the flow index n and the adjusted equations for the flow rate of technical and biological fluids in standard pipelines, the 3D velocity profiles of liquid egg products were successfully modelled. The values of the Reynolds number of the individual liquid egg products were calculated, and the type of flow was also determined. A turbulent flow has been detected for some liquid egg products.}, }
@article {pmid34945430, year = {2021}, author = {Fukuda, T and Harada, MR}, title = {Analysis of Aspect Ratio in a Miniature Rectangle Channel for Low Frictional Resistance.}, journal = {Micromachines}, volume = {12}, number = {12}, pages = {}, pmid = {34945430}, issn = {2072-666X}, support = {KAKENHI Grant Number 15K18263//Japan Society for the Promotion of Science/ ; }, abstract = {We conducted a theoretical investigation of the cross-sectional aspect ratio of a rectangular channel to have sufficiently low frictional resistance under less than 150 of the Reynolds number. From the theoretical consideration, it was clarified that 3.40 or more is recommended as a criterion for determining the aspect ratio. This addresses the problem of determining the interval of rectangle channels, installed in a plate reactor. There is a concern that the real system does not follow the analytical solution, assuming laminar flow, since the higher aspect ratio leads to disturbances of the flow such as the emergence of vortices. However, in the channel's volume range of (W × H × L) = (7.0 mm × 0.38 mm × 0.26 m), such a turbulence was not observed in the detailed numerical calculation by CFD, where both calculation results were in agreement to within 3% accuracy. Moreover, even in an experimental system with a surface roughness of ca. 7%, friction resistance took agreement within an accuracy of ±30%.}, }
@article {pmid34945380, year = {2021}, author = {Juraeva, M and Kang, DJ}, title = {Mixing Performance of a Passive Micro-Mixer with Mixing Units Stacked in Cross Flow Direction.}, journal = {Micromachines}, volume = {12}, number = {12}, pages = {}, pmid = {34945380}, issn = {2072-666X}, support = {2021//bokuk(c)/ ; 2021//bokuk(c)/ ; }, abstract = {A new passive micro-mixer with mixing units stacked in the cross flow direction was proposed, and its performance was evaluated numerically. The present micro-mixer consisted of eight mixing units. Each mixing unit had four baffles, and they were arranged alternatively in the cross flow and transverse direction. The mixing units were stacked in four different ways: one step, two step, four step, and eight step stacking. A numerical study was carried out for the Reynolds numbers from 0.5 to 50. The corresponding volume flow rate ranged from 6.33 μL/min to 633 μL/min. The mixing performance was analyzed in terms of the degree of mixing (DOM) and relative mixing energy cost (MEC). The numerical results showed a noticeable enhancement of the mixing performance compared with other micromixers. The mixing enhancement was achieved by two flow characteristics: baffle wall impingement by a stream of high concentration and swirl motion within the mixing unit. The baffle wall impingement by a stream of high concentration was observed throughout all Reynolds numbers. The swirl motion inside the mixing unit was observed in the cross flow direction, and became significant as the Reynolds number increased to larger than about five. The eight step stacking showed the best performance for Reynolds numbers larger than about two, while the two step stacking was better for Reynolds numbers less than about two.}, }
@article {pmid34945343, year = {2021}, author = {Mahammedi, A and Tayeb, NT and Kim, KY and Hossain, S}, title = {Mixing Enhancement of Non-Newtonian Shear-Thinning Fluid for a Kenics Micromixer.}, journal = {Micromachines}, volume = {12}, number = {12}, pages = {}, pmid = {34945343}, issn = {2072-666X}, abstract = {In this work, a numerical investigation was analyzed to exhibit the mixing behaviors of non-Newtonian shear-thinning fluids in Kenics micromixers. The numerical analysis was performed using the computational fluid dynamic (CFD) tool to solve 3D Navier-Stokes equations with the species transport equations. The efficiency of mixing is estimated by the calculation of the mixing index for different cases of Reynolds number. The geometry of micro Kenics collected with a series of six helical elements twisted 180° and arranged alternately to achieve the higher level of chaotic mixing, inside a pipe with a Y-inlet. Under a wide range of Reynolds numbers between 0.1 to 500 and the carboxymethyl cellulose (CMC) solutions with power-law indices among 1 to 0.49, the micro-Kenics proves high mixing Performances at low and high Reynolds number. Moreover the pressure losses of the shear-thinning fluids for different Reynolds numbers was validated and represented.}, }
@article {pmid34942753, year = {2021}, author = {Gizynski, K and Makuch, K and Paczesny, J and Zhang, Y and Maciołek, A and Holyst, R}, title = {Internal energy in compressible Poiseuille flow.}, journal = {Physical review. E}, volume = {104}, number = {5-2}, pages = {055107}, doi = {10.1103/PhysRevE.104.055107}, pmid = {34942753}, issn = {2470-0053}, abstract = {We analyze a compressible Poiseuille flow of ideal gas in a plane channel. We provide the form of internal energy U for a nonequilibrium stationary state that includes viscous dissipation and pressure work. We demonstrate that U depends strongly on the ratio Δp/p_{0}, where Δp is the pressure difference between inlet and outlet and p_{0} is the outlet's pressure. In addition, U depends on two other variables: the channel aspect ratio and the parameter equivalent to Reynolds number. The stored internal energy, ΔU=U-U_{0}, is small compared to the internal energy U_{0} of the equilibrium state for a moderate range of values of Δp/p_{0}. However, ΔU can become large for big Δp or close to vacuum conditions at the outlet (p_{0}≈0Pa).}, }
@article {pmid34928851, year = {2021}, author = {Nejatipour, P and Khorsandi, B}, title = {Effect of nozzle geometry on the dynamics and mixing of self-similar turbulent jets.}, journal = {Water science and technology : a journal of the International Association on Water Pollution Research}, volume = {84}, number = {12}, pages = {3907-3915}, doi = {10.2166/wst.2021.483}, pmid = {34928851}, issn = {0273-1223}, abstract = {The effect of nozzle geometry on the dynamics and mixing of turbulent jets is experimentally investigated. The jets with a Reynolds number of 13,000 were issued from four different pipes with circular, elliptical, square and triangular cross sections. The velocity field was measured in the self-similar region of the jets using an acoustic Doppler velocimeter. Statistical parameters, such as the mean velocities, velocity variances, spreading rates, mass flow rates, and entrainment rates are presented. The results show that despite having approximately similar decay rates for the mean centerline velocities, the radial profiles of the axial mean velocity varied in jets with different nozzle cross sections and were widest for elliptical jets and narrowest for the triangular ones. On the other hand, velocity variances were greatest for the triangular jet when compared to the jets released from cross sections of other geometries. Furthermore, the spreading rate, mass flow rate, and entrainment rate were highest for the elliptical jet, and lowest for the triangular jet. From this it can be inferred that the elliptical jet has the highest mixing and dilution. The results of this study could help to improve the initial mixing of pollutants by optimizing the initial conditions.}, }
@article {pmid34903853, year = {2021}, author = {Shahzad, H and Wang, X and Sarris, I and Iqbal, K and Hafeez, MB and Krawczuk, M}, title = {Study of Non-Newtonian biomagnetic blood flow in a stenosed bifurcated artery having elastic walls.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {23835}, pmid = {34903853}, issn = {2045-2322}, mesh = {Animals ; Arteries/*physiology ; *Blood Circulation ; Constriction, Pathologic/*physiopathology ; Elasticity ; Finite Element Analysis ; Hemodynamics ; Humans ; Hydrodynamics ; *Magnetic Fields ; *Models, Cardiovascular ; }, abstract = {Fluid structure interaction (FSI) gained attention of researchers and scientist due to its applications in science fields like biomedical engineering, mechanical engineering etc. One of the major application in FSI is to study elastic wall behavior of stenotic arteries. In this paper we discussed an incompressible Non-Newtonian blood flow analysis in an elastic bifurcated artery. A magnetic field is applied along [Formula: see text] direction. For coupling of the problem an Arbitrary Lagrangian-Eulerian formulation is used by two-way fluid structure interaction. To discretize the problem, we employed [Formula: see text] finite element technique to approximate the velocity, displacement and pressure and then linearized system of equations is solved using Newton iteration method. Analysis is carried out for power law index, Reynolds number and Hartmann number. Hemodynamic effects on elastic walls, stenotic artery and bifurcated region are evaluated by using velocity profile, pressure and loads on the walls. Study shows there is significant increase in wall shear stresses with an increase in Power law index and Hartmann number. While as expected increase in Reynolds number decreases the wall shear stresses. Also load on the upper wall is calculated against Hartmann number for different values of power law index. Results show load increases as the Hartmann number and power law index increases. From hemodynamic point of view, the load on the walls is minimum for shear thinning case but when power law index increased i.e. for shear thickening case load on the walls increased.}, }
@article {pmid34877378, year = {2021}, author = {Pichler, M and Haddadi, B and Jordan, C and Norouzi, H and Harasek, M}, title = {Dataset for the simulated biomass pyrolysis in rotary kilns with varying particle residence time distributions.}, journal = {Data in brief}, volume = {39}, number = {}, pages = {107603}, pmid = {34877378}, issn = {2352-3409}, abstract = {Slow pyrolysis of biomass is commonly performed in rotary kilns. The effect of the particle residence time distribution on biomass conversion is often neglected when numerically modeling such systems. But this effect might be significant under certain conditions. The data presented here are results of numerical simulation of the biomass pyrolysis in rotary kilns under numerous operating conditions and levels of axial dispersion of biomass particles. The varied operating conditions are the kiln diameter (D = 0.1 -1 m), the ratio of particle to kiln diameter (d / D = 5 × 10 - 3 - 40 × 10 - 3), the ratio of kiln length to kiln diameter (L / D = 1 -10), the kiln's inclination angle (β = 0.1 -8 ∘), the Froude number (Fr = 10 - 3 - 10 - 2), the rotational Reynolds number (Re = 10 2 - 16 × 10 3), and the Péclet number (Pe = 5 -100). Data of 13,851 single case simulations are provided with this article. This includes the mean particle residence time, gas, bed and kiln wall temperatures, solid and gaseous species mass flows, heat fluxes, and the solid bed height over the kiln length. These comprehensive data have the potential to help in modeling, design, analysis, and optimization of rotary kilns used for the pyrolysis of biomass. The main characterization and interpretation is presented in the related main research paper by Pichler et al. (2021)[1].}, }
@article {pmid34853364, year = {2021}, author = {Casas-Arozamena, C and Otero-Cacho, A and Carnero, B and Almenglo, C and Aymerich, M and Alonso-Alconada, L and Ferreiros, A and Abalo, A and Bao-Varela, C and Flores-Arias, MT and Alvarez, E and Munuzuri, AP and Abal, M}, title = {Haemodynamic-dependent arrest of circulating tumour cells at large blood vessel bifurcations as new model for metastasis.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {23231}, pmid = {34853364}, issn = {2045-2322}, mesh = {Animals ; *Blood Flow Velocity ; Cell Adhesion ; Cell Line, Tumor ; *Hemodynamics ; Human Umbilical Vein Endothelial Cells ; Humans ; Leukocytes, Mononuclear ; Mice ; Models, Cardiovascular ; Models, Theoretical ; *Neoplastic Cells, Circulating ; }, abstract = {Homing of circulating tumour cells (CTC) at distant sites represents a critical event in metastasis dissemination. In addition to physical entrapment, probably responsible of the majority of the homing events, the vascular system provides with geometrical factors that govern the flow biomechanics and impact on the fate of the CTC. Here we mathematically explored the distribution of velocities and the corresponding streamlines at the bifurcations of large blood vessel and characterized an area of low-velocity at the carina of bifurcation that favours the residence of CTC. In addition to this fluid physics effect, the adhesive capabilities of the CTC provide with a biological competitive advantage resulting in a marginal but systematic arrest as evidenced by dynamic in vitro recirculation in Y-microchannels and by perfusion in in vivo mice models. Our results also demonstrate that viscosity, as a main determinant of the Reynolds number that define flow biomechanics, may be modulated to limit or impair CTC accumulation at the bifurcation of blood vessels, in agreement with the apparent positive effect observed in the clinical setting by anticoagulants in advanced oncology disease.}, }
@article {pmid34851844, year = {2023}, author = {Behera, S and Dogra, DP and Bandyopadhyay, MK and Roy, PP}, title = {Crowd Characterization in Surveillance Videos Using Deep-Graph Convolutional Neural Network.}, journal = {IEEE transactions on cybernetics}, volume = {53}, number = {6}, pages = {3428-3439}, doi = {10.1109/TCYB.2021.3126434}, pmid = {34851844}, issn = {2168-2275}, abstract = {Crowd behavior is a natural phenomenon that can provide valuable insight into the crowd characterization process. Modeling the visual appearance of a large crowd gathering can reveal meaningful information about its dynamics. Parametric modeling can be used to develop efficient and robust crowd monitoring systems. A crowd can be structured or unstructured based on the organization. In this article, crowd characterization has been mapped to a graph classification problem to classify movements based on order parameter (ϕ), active force components, and steadiness (Reynolds number). The graphs are constructed from the motion groups obtained using an active Langevin framework. These graphs are processed using a deep graph convolutional neural network for crowd characterization. For experimentation, we have prepared a dataset comprising of videos from popular publicly available datasets and our own recorded videos. The proposed framework has been compared with the latest deep learning-based frameworks in terms of accuracy and area under the curve (AUC). We have obtained a 4%-5% improvement in accuracy and AUC values over the existing frameworks. The insights obtained from the proposed framework can be used for better crowd monitoring and management.}, }
@article {pmid34848078, year = {2022}, author = {Corda, JV and Shenoy, BS and Ahmad, KA and Lewis, L and K, P and Khader, SMA and Zuber, M}, title = {Nasal airflow comparison in neonates, infant and adult nasal cavities using computational fluid dynamics.}, journal = {Computer methods and programs in biomedicine}, volume = {214}, number = {}, pages = {106538}, doi = {10.1016/j.cmpb.2021.106538}, pmid = {34848078}, issn = {1872-7565}, mesh = {Computer Simulation ; Humans ; *Hydrodynamics ; Infant, Newborn ; *Nasal Cavity/diagnostic imaging ; Stress, Mechanical ; Tomography, X-Ray Computed ; }, abstract = {BACKGROUND AND OBJECTIVE: Neonates are preferential nasal breathers up to 3 months of age. The nasal anatomy in neonates and infants is at developing stages whereas the adult nasal cavities are fully grown which implies that the study of airflow dynamics in the neonates and infants are significant. In the present study, the nasal airways of the neonate, infant and adult are anatomically compared and their airflow patterns are investigated.<br><br>METHODS: Computational Fluid Dynamics (CFD) approach is used to simulate the airflow in a neonate, an infant and an adult in sedentary breathing conditions. The healthy CT scans are segmented using MIMICS 21.0 (Materialise, Ann arbor, MI). The patient-specific 3D airway models are analyzed for low Reynolds number flow using ANSYS FLUENT 2020 R2. The applicability of the Grid Convergence Index (GCI) for polyhedral mesh adopted in this work is also verified.<br><br>RESULTS: This study shows that the inferior meatus of neonates accounted for only 15% of the total airflow. This was in contrast to the infants and adults who experienced 49 and 31% of airflow at the inferior meatus region. Superior meatus experienced 25% of total flow which is more than normal for the neonate. The highest velocity of 1.8, 2.6 and 3.7&#xa0;m/s was observed at the nasal valve region for neonates, infants and adults, respectively. The anterior portion of the nasal cavity experienced maximum wall shear stress with average values of 0.48, 0.25 and 0.58&#xa0;Pa for the neonates, infants and adults.<br><br>CONCLUSIONS: The neonates have an underdeveloped nasal cavity which significantly affects their airway distribution. The absence of inferior meatus in the neonates has limited the flow through the inferior regions and resulted in uneven flow distribution.}, }
@article {pmid34846896, year = {2021}, author = {Kim, AR and Mitra, SK and Zhao, B}, title = {Reduced Pressure Drop in Viscoelastic Polydimethylsiloxane Wall Channels.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {37}, number = {49}, pages = {14292-14301}, doi = {10.1021/acs.langmuir.1c02087}, pmid = {34846896}, issn = {1520-5827}, mesh = {Biological Transport ; *Dimethylpolysiloxanes ; *Lab-On-A-Chip Devices ; Viscosity ; }, abstract = {Polydimethylsiloxane (PDMS) is an important viscoelastic material that finds applications in a large number of engineering systems, particularly lab-on-chip microfluidic devices built with a flexible substrate. Channels made of PDMS, used for transporting analytes, are integral to these applications. The PDMS viscoelastic nature can induce additional hydrodynamic contributions at the soft wall/fluid interface compared to rigid walls. In this research, we investigated the pressure drop within PDMS channels bounded by rigid tubes (cellulose tubes). The bulging effect of the PDMS was limited by the rigid tubes under flowing fluids. The PDMS viscoelasticity was modulated by changing the ratio of the base to the cross-linker from 10:1 to 35:1. We observed that the pressure drop of the flowing fluids within the channel decreased with the increased loss tangent of the PDMS in the examined laminar regime [Reynolds number (Re) ∼ 23-58.6 for water and Re ∼ 0.69-8.69 for glycerol solution]. The elastic PDMS 10:1 wall channels followed the classical Hagen Poiseuille's equation, but the PDMS walls with lower cross-linker concentrations and thicker walls decreased pressure drops. The friction factor (f) for the PDMS channels with the two working fluids could be approximated as f = 47/Re. We provide a correlation between the pressure drop and PDMS viscoelasticity based on experimental findings. In the correlation, the loss tangent predominates; the larger the loss tangent, the smaller is the pressure drop. The research findings appear to be unexpected if only considering the energy dissipation of viscoelastic PDMS walls. We attributed the reduction in the pressure drop to a lubricating effect of the viscoelastic PDMS walls in the presence of the working fluids. Our results reveal the importance of the subtle diffusion of the residual oligomers and water from the bulk to the soft wall/fluid interface for the observed pressure drop in soft wall channels.}, }
@article {pmid34846030, year = {2021}, author = {Chen, X and Zhan, Y and Fu, YI and Lin, J and Ji, Y and Zhao, C and Fang, Y and Wu, J}, title = {The effect of stenosis rate and Reynolds number on local flow characteristics and plaque formation around the atherosclerotic stenosis.}, journal = {Acta of bioengineering and biomechanics}, volume = {23}, number = {1}, pages = {135-147}, pmid = {34846030}, issn = {2450-6303}, mesh = {*Atherosclerosis ; Constriction, Pathologic ; Hemodynamics ; Humans ; *Models, Cardiovascular ; Stress, Mechanical ; }, abstract = {PURPOSE: Atherosclerosis causes plaque to build-up in arteries. Effect of the specific local hemodynamic environment around an atherosclerotic plaque on the thrombosis formation does not remain quite clear but is believed to be crucial. The aim of this study is to uncover the flow effects on plaques formation.<br><br>METHODS: To study the mechanically regulated plaque formation, the flow fields in artery blood vessels with different stenosis rates at various Reynolds numbers were simulated numerically with the two-dimensional axisymmetric models, and the hemodynamic characteristics around the plaque were scaled with stenosis rate and Reynolds number.<br><br>RESULTS: The results showed that increases of both Reynolds number and stenosis rate facilitated the occurrence of flow separation phenomenon, extended recirculation zone, and upregulated the maximum normalized wall shear stress near the plaque throat section while downregulated the minimal normalized wall shear stress at the front shoulder of plaque, as it should be; in the atherosclerotic plaque leeside of the recirculation zone, an obvious catch bond region of wall shear stress might exist especially under low Reynolds number with stenosis rate smaller than 30%. This catch bond region in the plaque leeside might be responsible for the LBF (low blood flow)-enhanced formation of the atherosclerotic plaque.<br><br>CONCLUSIONS: This work may provide a novel insight into understanding the biomechanical effects behind the formation and damage of atherosclerotic plaques and propose a new strategy for preventing atherosclerotic diseases.}, }
@article {pmid34845537, year = {2021}, author = {Patel, K and Stark, H}, title = {Instability of a liquid sheet with viscosity contrast in inertial microfluidics.}, journal = {The European physical journal. E, Soft matter}, volume = {44}, number = {11}, pages = {144}, pmid = {34845537}, issn = {1292-895X}, abstract = {Flows at moderate Reynolds numbers in inertial microfluidics enable high throughput and inertial focusing of particles and cells with relevance in biomedical applications. In the present work, we consider a viscosity-stratified three-layer flow in the inertial regime. We investigate the interfacial instability of a liquid sheet surrounded by a density-matched but more viscous fluid in a channel flow. We use linear stability analysis based on the Orr-Sommerfeld equation and direct numerical simulations with the lattice Boltzmann method (LBM) to perform an extensive parameter study. Our aim is to contribute to a controlled droplet production in inertial microfluidics. In the first part, on the linear stability analysis we show that the growth rate of the fastest growing mode [Formula: see text] increases with the Reynolds number [Formula: see text] and that its wavelength [Formula: see text] is always smaller than the channel width w for sufficiently small interfacial tension [Formula: see text]. For thin sheets we find the scaling relation [Formula: see text], where m is viscosity ratio and [Formula: see text] the sheet thickness. In contrast, for thicker sheets [Formula: see text] decreases with increasing [Formula: see text] or m due to the nearby channel walls. Examining the eigenvalue spectra, we identify Yih modes at the interface. In the second part on the LBM simulations, the thin liquid sheet develops two distinct dynamic states: waves traveling along the interface and breakup into droplets with bullet shape. For smaller flow rates and larger sheet thicknesses, we also observe ligament formation and the sheet eventually evolves irregularly. Our work gives some indication how droplet formation can be controlled with a suitable parameter set [Formula: see text].}, }
@article {pmid34845318, year = {2021}, author = {Pang, M and Zhang, T and Meng, Y and Ling, Z}, title = {Experimental study on the permeability of crushed coal medium based on the Ergun equation.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {23030}, pmid = {34845318}, issn = {2045-2322}, support = {51774234//the National Natural Science Foundations of China/ ; }, abstract = {Accurate determination of the permeability of crushed coal medium is the basis for the study of their permeability characteristics. To investigate the permeability characteristics of this special porous medium composed of crushed coal particles, the permeability parameters of crushed coal specimens of different initial porosities were measured by designing a lateral-limit compression seepage test system. Parameters were determined separately for specimens of different initial porosities. (1) the Reynolds number distribution region characterising the seepage state was determined and obtained. Specimens with initial porosity distribution between 0.02 and 0.08, and seepage Reynolds number distribution in the low-permeability zone, under Darcy flow; (2) the intrinsic permeability of the crushed coal medium was obtained by using the Ergun equation. The complex inverse proportional relationship between the drag coefficient and Reynolds number was derived; (3) Through the determination of the permeability of the crushed coal medium, the mean value of βK value was obtained to be about 45.7, and the analysis of the permeability of porous medium can determine its critical permeability. The relationship between the Forchheimer number Fo and critical Reynolds number was measured. The results indicate that it conforms to a linear distribution. In-depth analysis of these two parameters can be used to explore the flow transition process between laminar, transition, and turbulent flow. This study provides insight into the permeability characteristics of the media in fractured coal bodies.}, }
@article {pmid37101581, year = {2022}, author = {Sun, R and Yu, P and Zuo, P and Alvarez, PJJ}, title = {Bacterial Concentrations and Water Turbulence Influence the Importance of Conjugation Versus Phage-Mediated Antibiotic Resistance Gene Transfer in Suspended Growth Systems.}, journal = {ACS environmental Au}, volume = {2}, number = {2}, pages = {156-165}, pmid = {37101581}, issn = {2694-2518}, abstract = {Despite the abundance of phage-borne antibiotic resistance genes (ARGs) in the environment, the frequency of ARG propagation via phage-mediated transduction (relative to via conjugation) is poorly understood. We investigated the influence of bacterial concentration and water turbulence level [quantified as Reynold's number (Re)] in suspended growth systems on the frequency of ARG transfer by two mechanisms: delivery by a lysogenic phage (phage λ carrying gentamycin-resistance gene, genR) and conjugation mediated by the self-transmissible plasmid RP4. Using Escherichia coli (E. coli) as the recipient, phage delivery had a comparable frequency (1.2 ± 0.9 × 10[-6]) to that of conjugation (1.1 ± 0.9 × 10[-6]) in suspensions with low cell concentration (10[4] CFU/mL) and moderate turbulence (Re = 5 × 10[4]). Turbulence affected cell (or phage)-to-cell contact rates and detachment (due to shear force), and thus, it affected the relative importance of conjugation versus phage delivery. At 10[7] CFU/mL, no significant difference was observed between the frequencies of ARG transfer by the two mechanisms under quiescent water conditions (2.8 ± 0.3 × 10[-5] for conjugation vs 2.2 ± 0.5 × 10[-5] for phage delivery, p = 0.19) or when Re reached 5 × 10[5] (3.4 ± 1.5 × 10[-5] for conjugation vs 2.9 ± 1.0 × 10[-5] for phage delivery, p = 0.52). Transcriptomic analysis of genes related to conjugation and phage delivery and simulation of cell (or phage)-to-cell collisions at different Re values corroborate that the importance of phage delivery relative to conjugation increases under either quiescent or turbulent conditions. This finding challenges the prevailing view that conjugation is the dominant ARG transfer mechanism and underscores the need to consider and mitigate potential ARG dissemination via transduction.}, }
@article {pmid34840965, year = {2021}, author = {Krane, M}, title = {Vortex Formation Times in the Glottal Jet, Measured in a Scaled-Up Model.}, journal = {Fluids (Basel, Switzerland)}, volume = {6}, number = {11}, pages = {}, pmid = {34840965}, issn = {2311-5521}, support = {R01 DC005642/DC/NIDCD NIH HHS/United States ; }, abstract = {In this paper, the timing of vortex formation on the glottal jet is studied using previously published velocity measurements of flow through a scaled-up model of the human vocal folds. The relative timing of the pulsatile glottal jet and the instability vortices are acoustically important since they determine the harmonic and broadband content of the voice signal. Glottis exit jet velocity time series were extracted from time-resolved planar DPIV measurements. These measurements were acquired at four glottal flow speeds (u SS = 16.1-38 cm/s) and four glottis open times (T o = 5.67-23.7 s), providing a Reynolds number range Re = 4100-9700 and reduced vibration frequency f* = 0.01-0.06. Exit velocity waveforms showed temporal behavior on two time scales, one that correlates to the period of vibration and another characterized by short, sharp velocity peaks (which correlate to the passage of instability vortices through the glottis exit plane). The vortex formation time, estimated by computing the time difference between subsequent peaks, was shown to be not well-correlated from one vibration cycle to the next. The principal finding is that vortex formation time depends not only on cycle phase, but varies strongly with reduced frequency of vibration. In all cases, a strong high-frequency burst of vortex motion occurs near the end of the cycle, consistent with perceptual studies using synthesized speech.}, }
@article {pmid34832781, year = {2021}, author = {Jbeili, M and Zhang, J}, title = {Effects of Microscopic Properties on Macroscopic Thermal Conductivity for Convective Heat Transfer in Porous Materials.}, journal = {Micromachines}, volume = {12}, number = {11}, pages = {}, pmid = {34832781}, issn = {2072-666X}, support = {Discovery Grant - Individual//Natural Sciences and Engineering Research Council/ ; }, abstract = {Porous materials are widely used in many heat transfer applications. Modeling porous materials at the microscopic level can accurately incorporate the detailed structure and substance parameters and thus provides valuable information for the complex heat transfer processes in such media. In this study, we use the generalized periodic boundary condition for pore-scale simulations of thermal flows in porous materials. A two-dimensional porous model consisting of circular solid domains is considered, and comprehensive simulations are performed to study the influences on macroscopic thermal conductivity from several microscopic system parameters, including the porosity, Reynolds number, and periodic unit aspect ratio and the thermal conductance at the solid-fluid interface. Our results show that, even at the same porosity and Reynolds number, the aspect ratio of the periodic unit and the interfacial thermal conductance can significantly affect the macroscopic thermal behaviors of porous materials. Qualitative analysis is also provided to relate the apparent thermal conductivity to the complex flow and temperature distributions in the microscopic porous structure. The method, findings and discussions presented in this paper could be useful for fundamental studies, material development, and engineering applications of porous thermal flow systems.}, }
@article {pmid34828226, year = {2021}, author = {Li, W and Xie, Z and Xi, K and Xia, S and Ge, Y}, title = {Constructal Optimization of Rectangular Microchannel Heat Sink with Porous Medium for Entropy Generation Minimization.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {11}, pages = {}, pmid = {34828226}, issn = {1099-4300}, support = {51979278//National Natural Science Foundation of China/ ; 51579244//National Natural Science Foundation of China/ ; }, abstract = {A model of rectangular microchannel heat sink (MCHS) with porous medium (PM) is developed. Aspect ratio of heat sink (HS) cell and length-width ratio of HS are optimized by numerical simulation method for entropy generation minimization (EGM) according to constructal theory. The effects of inlet Reynolds number (Re) of coolant, heat flux on bottom, porosity and volume proportion of PM on dimensionless entropy generation rate (DEGR) are analyzed. From the results, there are optimal aspect ratios to minimize DEGR. Given the initial condition, DEGR is 33.10% lower than its initial value after the aspect ratio is optimized. With the increase of Re, the optimal aspect ratio declines, and the minimum DEGR drops as well. DEGR gets larger and the optimal aspect ratio remains constant with the increasing of heat flux on bottom. For the different volume proportion of PM, the optimal aspect ratios are diverse, but the minimum DEGR almost stays unchanged. The twice minimized DEGR, which results from aspect ratio and length-width ratio optimized simultaneously, is 10.70% lower than the once minimized DEGR. For a rectangular bottom, a lower DEGR can be reached by choosing the proper direction of fluid flow.}, }
@article {pmid34828211, year = {2021}, author = {Khan, MF and Sulaiman, M and Tavera Romero, CA and Alkhathlan, A}, title = {A Hybrid Metaheuristic Based on Neurocomputing for Analysis of Unipolar Electrohydrodynamic Pump Flow.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {11}, pages = {}, pmid = {34828211}, issn = {1099-4300}, abstract = {A unipolar electrohydrodynamic (UP-EHD) pump flow is studied with known electric potential at the emitter and zero electric potential at the collector. The model is designed for electric potential, charge density, and electric field. The dimensionless parameters, namely the electrical source number (Es), the electrical Reynolds number (ReE), and electrical slip number (Esl), are considered with wide ranges of variation to analyze the UP-EHD pump flow. To interpret the pump flow of the UP-EHD model, a hybrid metaheuristic solver is designed, consisting of the recently developed technique sine-cosine algorithm (SCA) and sequential quadratic programming (SQP) under the influence of an artificial neural network. The method is abbreviated as ANN-SCA-SQP. The superiority of the technique is shown by comparing the solution with reference solutions. For a large data set, the technique is executed for one hundred independent experiments. The performance is evaluated through performance operators and convergence plots.}, }
@article {pmid34828180, year = {2021}, author = {Jia, Y and Huang, J and Wang, J and Li, H}, title = {Heat Transfer and Fluid Flow Characteristics of Microchannel with Oval-Shaped Micro Pin Fins.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {11}, pages = {}, pmid = {34828180}, issn = {1099-4300}, support = {5210060458//National Natural Science Foundation of China/ ; JJKH20210112KJ//The Scientific research project of Jilin Provincial Department of Education/ ; }, abstract = {A novel microchannel heat sink with oval-shaped micro pin fins (MOPF) is proposed and the characteristics of fluid flow and heat transfer are studied numerically for Reynolds number (Re) ranging from 157 to 668. In order to study the influence of geometry on flow and heat transfer characteristics, three non-dimensional variables are defined, such as the fin axial length ratio (α), width ratio (β), and height ratio (γ). The thermal enhancement factor (η) is adopted as an evaluation criterion to evaluate the best comprehensive thermal-hydraulic performance of MOPF. Results indicate that the oval-shaped pin fins in the microchannel can effectively prevent the rise of heat surface temperature along the flow direction, which improves the temperature distribution uniformity. In addition, results show that for the studied Reynolds number range and microchannel geometries in this paper, the thermal enhancement factor η increases firstly and then decreases with the increase of α and β. In addition, except for Re = 157, η decreases first and then increases with the increase of the fin height ratio γ. The thermal enhancement factor for MOPF with α = 4, β = 0.3, and γ = 0.5 achieves 1.56 at Re = 668. The results can provide a theoretical basis for the design of a microchannel heat exchanger.}, }
@article {pmid34818642, year = {2021}, author = {Hernández Meza, JM and Vélez-Cordero, JR and Ramírez Saito, A and Aranda-Espinoza, S and Arauz-Lara, JL and Yáñez Soto, B}, title = {Particle/wall electroviscous effects at the micron scale: comparison between experiments, analytical and numerical models.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {34}, number = {9}, pages = {}, doi = {10.1088/1361-648X/ac3cef}, pmid = {34818642}, issn = {1361-648X}, abstract = {We report a experimental study of the motion of 1 μm single particles interacting with functionalized walls at low and moderate ionic strengths conditions. The 3D particle's trajectories were obtained by analyzing the diffracted particle images (point spread function). The studied particle/wall systems include negatively charged particles interacting with bare glass, glass covered with polyelectrolytes and glass covered with a lipid monolayer. In the low salt regime (pure water) we observed a retardation effect of the short-time diffusion coefficients when the particle interacts with a negatively charged wall; this effect is more severe in the perpendicular than in the lateral component. The decrease of the diffusion as a function of the particle-wall distancehwas similar regardless the origin of the negative charge at the wall. When surface charge was screened or salt was added to the medium (10 mM), the diffusivity curves recover the classical hydrodynamic behavior. Electroviscous theory based on the thin electrical double layer (EDL) approximation reproduces the experimental data except for smallh. On the other hand, 2D numerical solutions of the electrokinetic equations showed good qualitative agreement with experiments. The numerical model also showed that the hydrodynamic and Maxwellian part of the electroviscous total drag tend to zero ash→ 0 and how this is linked with the merging of both EDL's at close proximity.}, }
@article {pmid34816334, year = {2021}, author = {Díaz, MV}, title = {On the long-time persistence of hydrodynamic memory.}, journal = {The European physical journal. E, Soft matter}, volume = {44}, number = {11}, pages = {141}, pmid = {34816334}, issn = {1292-895X}, abstract = {The Basset-Boussinesq-Oseen (BBO) equation correctly describes the nonuniform motion of a spherical particle at a low Reynolds number. It contains an integral term with a singular kernel which accounts for the diffusion of vorticity around the particle throughout its entire history. However, if there are any departures in either rigidity or shape from a solid sphere, besides the integral force with a singular kernel, the Basset history force, we should add a second history force with a non-singular kernel, related to the shape or composition of the particle. In this work, we introduce a fractional generalized Basset-Boussinesq-Oseen equation which includes both history terms as fractional derivatives. Using the Laplace transform, an integral representation of the solution is obtained. For a driven single particle, the solution shows that memory effects persist indefinitely under rather general driving conditions.}, }
@article {pmid34805706, year = {2021}, author = {Yin, B and Yue, W and Sohan, ASMMF and Zhou, T and Qian, C and Wan, X}, title = {Micromixer with Fine-Tuned Mathematical Spiral Structures.}, journal = {ACS omega}, volume = {6}, number = {45}, pages = {30779-30789}, pmid = {34805706}, issn = {2470-1343}, abstract = {Micromixers with the microchannel structure can enable rapid and efficient mixing of multiple types of fluids on a microfluidic chip. Herein, we report the mixing performance of three passive micromixers based on the different mathematical spiral structures. We study the fluid flow characteristics of Archimedes spiral, Fermat spiral, and hyperbolic spiral structures with various channel widths and Reynolds number (Re) ranging from 0 to 10 via numerical simulation and visualization experiments. In addition, we analyze the mechanism of streamlines and Dean vortices at different cross sections during fluid flows. As the fluid flows in the Fermat spiral channel, the centrifugal force induces the Dean vortex to form a chaotic advection, enhancing the fluid mixing performance. By integrating the Fermat spiral channel into a microfluidic chip, we successfully detect acute myocardial infarction (AMI) marker with the double-antibody sandwich method and reduce the detection time to 10 min. This method has a low reagent consumption and a high reaction efficiency and demonstrates great potential in point-of-care testing (POCT).}, }
@article {pmid34797128, year = {2021}, author = {Jaccod, A and Chibbaro, S}, title = {Constrained Reversible System for Navier-Stokes Turbulence.}, journal = {Physical review letters}, volume = {127}, number = {19}, pages = {194501}, doi = {10.1103/PhysRevLett.127.194501}, pmid = {34797128}, issn = {1079-7114}, abstract = {Following a Gallavotti's conjecture, stationary states of Navier-Stokes fluids are proposed to be described equivalently by alternative equations besides the Navier-Stokes equation itself. We discuss a model system symmetric under time reversal based on the Navier-Stokes equations constrained to keep the enstrophy constant. It is demonstrated through highly resolved numerical experiments that the reversible model evolves to a stationary state which reproduces quite accurately all statistical observables relevant for the physics of turbulence extracted by direct numerical simulations (DNS) at different Reynolds numbers. The possibility of using reversible models to mimic turbulence dynamics is of practical importance for the coarse-grained version of Navier-Stokes equations, as used in large-eddy simulations. Furthermore, the reversible model appears mathematically simpler, since enstrophy is bounded to be constant for every Reynolds number. Finally, the theoretical interest in the context of statistical mechanics is briefly discussed.}, }
@article {pmid34781498, year = {2021}, author = {An, X and Dong, B and Wang, Y and Zhang, Y and Zhou, X and Li, W}, title = {Coupled lattice Boltzmann-large eddy simulation model for three-dimensional multiphase flows at large density ratio and high Reynolds number.}, journal = {Physical review. E}, volume = {104}, number = {4-2}, pages = {045305}, doi = {10.1103/PhysRevE.104.045305}, pmid = {34781498}, issn = {2470-0053}, abstract = {A coupled lattice Boltzmann-large eddy simulation model is developed for modeling three-dimensional multiphase flows at large density ratios and high Reynolds numbers. In the framework of the lattice Boltzmann method, the model is proposed based on the standard Smagorinsky subgrid-scale approach, and a reconstructed multiple-relaxation-time collision operator is adopted. The conservative Allen-Cahn equation and Navier-Stokes equations are solved through the lattice Boltzmann discretization scheme for the interface tracking and velocity field evolution, respectively. Relevant benchmark cases are carried out to validate the performance of this model in simulating multiphase flows at a large density ratio and a high Reynolds number, including a stationary droplet, the process of spinodal decomposition, the Rayleigh-Taylor instability, the phenomenon of a droplet splashing on a thin liquid film, and the liquid jet breakup process. The maximum values of density ratio and Re number are 1000 and 10 240, respectively. The capability and reliability of the proposed model have been demonstrated by the good agreement between simulation results and the analytical solutions or the previously available results.}, }
@article {pmid34776531, year = {2021}, author = {Braun, S and Scheichl, S and Kuzdas, D}, title = {The triple-deck stage of marginal separation.}, journal = {Journal of engineering mathematics}, volume = {128}, number = {1}, pages = {16}, pmid = {34776531}, issn = {0022-0833}, support = {P 31873/FWF_/Austrian Science Fund FWF/Austria ; }, abstract = {UNLABELLED: The method of matched asymptotic expansions is applied to the investigation of transitional separation bubbles. The problem-specific Reynolds number is assumed to be large and acts as the primary perturbation parameter. Four subsequent stages can be identified as playing key roles in the characterization of the incipient laminar-turbulent transition process: due to the action of an adverse pressure gradient, a classical laminar boundary layer is forced to separate marginally (I). Taking into account viscous-inviscid interaction then enables the description of localized, predominantly steady, reverse flow regions (II). However, certain conditions (e.g. imposed perturbations) may lead to a finite-time breakdown of the underlying reduced set of equations. The ensuing consideration of even shorter spatio-temporal scales results in the flow being governed by another triple-deck interaction. This model is capable of both resolving the finite-time singularity and reproducing the spike formation (III) that, as known from experimental observations and direct numerical simulations, sets in prior to vortex shedding at the rear of the bubble. Usually, the triple-deck stage again terminates in the form of a finite-time blow-up. The study of this event gives rise to a noninteracting Euler-Prandtl stage (IV) associated with unsteady separation, where the vortex wind-up and shedding process takes place. The focus of the present paper lies on the triple-deck stage III and is twofold: firstly, a comprehensive numerical investigation based on a Chebyshev collocation method is presented. Secondly, a composite asymptotic model for the regularization of the ill-posed Cauchy problem is developed.<br><br>SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10665-021-10125-3.}, }
@article {pmid34766181, year = {2022}, author = {Yu, P and Durgesh, V}, title = {Application of Dynamic Mode Decomposition to Study Temporal Flow Behavior in a Saccular Aneurysm.}, journal = {Journal of biomechanical engineering}, volume = {144}, number = {5}, pages = {}, doi = {10.1115/1.4052999}, pmid = {34766181}, issn = {1528-8951}, mesh = {Blood Flow Velocity ; Hemodynamics ; Humans ; *Intracranial Aneurysm ; Models, Cardiovascular ; Rheology ; }, abstract = {Aneurysms are abnormal expansion of weakened blood vessels which can cause mortality or long-term disability upon rupture. Several studies have shown that inflow conditions spatially and temporally influence aneurysm flow behavior. The objective of this investigation is to identify impact of inflow conditions on spatio-temporal flow behavior in an aneurysm using dynamic mode decomposition (DMD). For this purpose, low-frame rate velocity field measurements are performed in an idealized aneurysm model using particle image velocimetry (PIV). The inflow conditions are precisely controlled using a ViVitro SuperPump system where nondimensional fluid parameters such as peak Reynolds number (Rep) and Womersely number (α) are varied from 50-270 and 2-5, respectively. The results show the ability of DMD to identify the spatial flow structures and their frequency content. Furthermore, DMD captured the impact of inflow conditions, and change in mode shapes, amplitudes, frequency, and growth rate information is observed. The DMD low-order flow reconstruction also showed the complex interplay of flow features for each inflow scenario. Furthermore, the low-order reconstruction results provided a mathematical description of the flow behavior in the aneurysm which captured the vortex formation, evolution, and convection in detail. These results indicated that the vortical structure behavior varied with the change in α while its strength and presence of secondary structures are influenced by the change in Rep.}, }
@article {pmid34756978, year = {2022}, author = {Hu, F and Zhang, S and Wang, X and Wang, C and Wu, J and Poncin, S and Xu, L and Xu, G and Hu, Y and Li, HZ}, title = {Quantitative hydrodynamic characterization of high solid anaerobic digestion: Correlation of "mixing-fluidity-energy" and scale-up effect.}, journal = {Bioresource technology}, volume = {344}, number = {Pt B}, pages = {126237}, doi = {10.1016/j.biortech.2021.126237}, pmid = {34756978}, issn = {1873-2976}, mesh = {Anaerobiosis ; *Bioreactors ; *Hydrodynamics ; Rheology ; }, abstract = {High solid anaerobic digestion (HSAD)'s complex rheological behavior exhibits short-circuiting and dead zone. Mixing optimization is potential to enhance HSAD hydrodynamics. Besides, scale-up effect is quite essential for HSAD's applications, but remains rarely studied yet. Effect of impeller with different width on the correlation of "mixing-fluidity-energy" at different rotating speeds was first investigated at pilot-scale in present work. Then, scale-up effect based on rotating speed and a generalized Reynolds number was revealed from the aspects of fluidity and energy consumption. Results show that impeller width of 100 mm (10 rpm), 200 mm and 300 mm (5 and 10 rpm) are preferred for hydrodynamics and energy economics. Furthermore, Re similarity has better referential significance for the scale-up. In this study, new insight is gained into the correlation of "mixing-fluidity-energy" within a pilot-scale digester. Scale-up effect based Re similarity could potentially offer guidance for HSAD's application in the practical engineering.}, }
@article {pmid34746583, year = {2021}, author = {Lian, SJ and Hu, ZX and Lan, Z and Wen, RF and Ma, XH}, title = {Optimal Operation of an Oscillatory Flow Crystallizer: Coupling Disturbance and Stability.}, journal = {ACS omega}, volume = {6}, number = {43}, pages = {28912-28922}, pmid = {34746583}, issn = {2470-1343}, abstract = {In the process of industrial crystallization, it is always difficult to balance the secondary nucleation rate and metastable zone width (MSZW). Herein, we report an experimental and numerical study for the cooling crystallization of paracetamol in an oscillatory flow crystallizer (OFC), finding the optimal operating conditions for balancing the secondary nucleation rate and MSZW. The results show that the MSZW decreases with the increase of oscillation Reynolds number (Re o). Compared to the traditional stirring system, the OFC has an MSZW three times larger than that of the stirring system under a similar power density of consumption. With the numerical simulation, the OFC can produce a stable space environment and instantaneous strong disturbance, which is conducive to the crystallization process. Above all, a high Re o is favorable to produce a sufficient nucleation rate, which may inevitably constrict the MSZW to a certain degree. Then, the optimization strategy of the operating parameter (Re o) in the OFC is proposed.}, }
@article {pmid34739321, year = {2021}, author = {Browne, CA and Datta, SS}, title = {Elastic turbulence generates anomalous flow resistance in porous media.}, journal = {Science advances}, volume = {7}, number = {45}, pages = {eabj2619}, pmid = {34739321}, issn = {2375-2548}, abstract = {Many energy, environmental, industrial, and microfluidic processes rely on the flow of polymer solutions through porous media. Unexpectedly, the macroscopic flow resistance often increases above a threshold flow rate in a porous medium, but not in bulk solution. The reason why has been a puzzle for over half a century. Here, by directly visualizing flow in a transparent 3D porous medium, we demonstrate that this anomalous increase is due to the onset of an elastic instability in which the flow exhibits strong spatiotemporal fluctuations reminiscent of inertial turbulence, despite the small Reynolds number. Our measurements enable us to quantitatively establish that the energy dissipated by pore-scale fluctuations generates the anomalous increase in the overall flow resistance. Because the macroscopic resistance is one of the most fundamental descriptors of fluid flow, our results both help deepen understanding of complex fluid flows and provide guidelines to inform a broad range of applications.}, }
@article {pmid34739267, year = {2021}, author = {Bott, AFA and Chen, L and Boutoux, G and Caillaud, T and Duval, A and Koenig, M and Khiar, B and Lantuéjoul, I and Le-Deroff, L and Reville, B and Rosch, R and Ryu, D and Spindloe, C and Vauzour, B and Villette, B and Schekochihin, AA and Lamb, DQ and Tzeferacos, P and Gregori, G and Casner, A}, title = {Inefficient Magnetic-Field Amplification in Supersonic Laser-Plasma Turbulence.}, journal = {Physical review letters}, volume = {127}, number = {17}, pages = {175002}, doi = {10.1103/PhysRevLett.127.175002}, pmid = {34739267}, issn = {1079-7114}, abstract = {We report a laser-plasma experiment that was carried out at the LMJ-PETAL facility and realized the first magnetized, turbulent, supersonic (Ma_{turb}≈2.5) plasma with a large magnetic Reynolds number (Rm≈45) in the laboratory. Initial seed magnetic fields were amplified, but only moderately so, and did not become dynamically significant. A notable absence of magnetic energy at scales smaller than the outer scale of the turbulent cascade was also observed. Our results support the notion that moderately supersonic, low-magnetic-Prandtl-number plasma turbulence is inefficient at amplifying magnetic fields compared to its subsonic, incompressible counterpart.}, }
@article {pmid34737529, year = {2021}, author = {Behera, S and Bhardwaj, R and Agrawal, A}, title = {Effect of co-flow on fluid dynamics of a cough jet with implications in spread of COVID-19.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {33}, number = {10}, pages = {101701}, pmid = {34737529}, issn = {1070-6631}, abstract = {We discuss the temporal evolution of a cough jet of an infected subject in the context of the spread of COVID-19. Computations were carried out using large eddy simulation, and, in particular, the effect of the co-flow (5% and 10% of maximum cough velocity) on the evolution of the jet was quantified. The Reynolds number (Re) of the cough jet, based on the mouth opening diameter (D) and the average cough velocity, is 13 002. The time-varying inlet velocity profile of the cough jet is represented as a combination of gamma-probability-distribution functions. Simulations reveal the detailed structure of cough jet with and without a co-flow for the first time, to the best of our knowledge. The cough jet temporal evolution is similar to that of a continuous free-jet and follows the same routes of instability, as documented for a free-jet. The convection velocity of the cough jet decays with time and distance, following a power-law variation. The cough jet is observed to travel a distance of approximately 1.1 m in half a second. However, in the presence of 10% co-flow, the cough jet travels faster and covers the similar distance in just 0.33 s. Therefore, in the presence of a co-flow, the probability of transmission of COVID-19 by airborne droplets and droplet nuclei increases, since they can travel a larger distance. The cough jet without the co-flow corresponds to a larger volume content compared to that with the co-flow and spreads more within the same range of distance. These simulations are significant as they help to reveal the intricate structure of the cough jet and show that the presence of a co-flow can significantly augment the risk of infection of COVID-19.}, }
@article {pmid34732570, year = {2021}, author = {Choueiri, GH and Lopez, JM and Varshney, A and Sankar, S and Hof, B}, title = {Experimental observation of the origin and structure of elastoinertial turbulence.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {118}, number = {45}, pages = {}, pmid = {34732570}, issn = {1091-6490}, abstract = {Turbulence generally arises in shear flows if velocities and hence, inertial forces are sufficiently large. In striking contrast, viscoelastic fluids can exhibit disordered motion even at vanishing inertia. Intermediate between these cases, a state of chaotic motion, "elastoinertial turbulence" (EIT), has been observed in a narrow Reynolds number interval. We here determine the origin of EIT in experiments and show that characteristic EIT structures can be detected across an unexpectedly wide range of parameters. Close to onset, a pattern of chevron-shaped streaks emerges in qualitative agreement with linear and weakly nonlinear theory. However, in experiments, the dynamics remain weakly chaotic, and the instability can be traced to far lower Reynolds numbers than permitted by theory. For increasing inertia, the flow undergoes a transformation to a wall mode composed of inclined near-wall streaks and shear layers. This mode persists to what is known as the "maximum drag reduction limit," and overall EIT is found to dominate viscoelastic flows across more than three orders of magnitude in Reynolds number.}, }
@article {pmid34732141, year = {2021}, author = {Zhou, Y and Wang, DM and Liu, L and Huang, P}, title = {The morphometric of lycopsid sporophylls and the evaluation of their dispersal potential: an example from the Upper Devonian of Zhejiang Province, China.}, journal = {BMC ecology and evolution}, volume = {21}, number = {1}, pages = {198}, pmid = {34732141}, issn = {2730-7182}, mesh = {China ; *Fossils ; }, abstract = {BACKGROUND: Previous studies have discussed the special structural adaptations of Late Palaeozoic lycopsids, for example, the dispersal potential of reproductive organs. Based on materials from the Upper Devonian Wutong Formation in Changxing County, Zhejiang Province, China, we now analyze the morphometric and perform some calculation to evaluate the dispersal of sporophyll units of lycopsids.<br><br>RESULTS: The fossil sporophyll units are divided into two types in view of obvious difference in shape and we name two new (form) species for them. We also analyze the falling process and give the calculation method of dispersal distance.<br><br>CONCLUSIONS: The fossil sporophyll units show relatively poor potential of wind dispersal compared with modern samaras, and show potential adaptation to the turbulent environment.}, }
@article {pmid34731319, year = {2021}, author = {Miles, JG and Battista, NA}, title = {Exploring the sensitivity in jellyfish locomotion under variations in scale, frequency, and duty cycle.}, journal = {Journal of mathematical biology}, volume = {83}, number = {5}, pages = {56}, pmid = {34731319}, issn = {1432-1416}, mesh = {Animals ; Biomechanical Phenomena ; Locomotion ; *Models, Biological ; *Scyphozoa ; Swimming ; }, abstract = {Jellyfish have been called one of the most energy-efficient animals in the world due to the ease in which they move through their fluid environment, by product of their bell kinematics coupled with their morphological, muscular, material properties. We investigated jellyfish locomotion by conducting in silico comparative studies and explored swimming performance across different fluid scales (i.e., Reynolds Number), bell contraction frequencies, and contraction phase kinematics (duty cycle) for a jellyfish with a fineness ratio of 1 (ratio of bell height to bell diameter). To study these relationships, an open source implementation of the immersed boundary method was used (IB2d) to solve the fully coupled fluid-structure interaction problem of a flexible jellyfish bell in a viscous fluid. Thorough 2D parameter subspace explorations illustrated optimal parameter combinations in which give rise to enhanced swimming performance. All performance metrics indicated a higher sensitivity to bell actuation frequency than fluid scale or duty cycle, via Sobol sensitivity analysis, on a higher performance parameter subspace. Moreover, Pareto-like fronts were identified in the overall performance space involving the cost of transport and forward swimming speed. Patterns emerged within these performance spaces when highlighting different parameter regions, which complemented the global sensitivity results. Lastly, an open source computational model for jellyfish locomotion is offered to the science community that can be used as a starting place for future numerical experimentation.}, }
@article {pmid34693101, year = {2021}, author = {Grande Gutiérrez, N and Shankar, KN and Sinno, T and Diamond, SL}, title = {Thrombosis and Hemodynamics: external and intrathrombus gradients.}, journal = {Current opinion in biomedical engineering}, volume = {19}, number = {}, pages = {}, pmid = {34693101}, issn = {2468-4511}, support = {R01 HL103419/HL/NHLBI NIH HHS/United States ; U01 HL131053/HL/NHLBI NIH HHS/United States ; }, abstract = {Distinct from dilute, isotropic, and homogeneous reaction systems typically used in laboratory kinetic assays, blood is concentrated, two-phase, flowing, and highly anisotropic when clotting on a surface. This review focuses on spatial gradients that are generated and can dictate thrombus structure and function. Novel experimental and computational tools have recently emerged to explore reaction-transport coupling during clotting. Multiscale simulations help bridge tissue length scales (the coronary arteries) to millimeter scales of a growing clot to the microscopic scale of single-cell signaling and adhesion. Microfluidic devices help create and control pathological velocity profiles, albeit at a low Reynolds number. Since rate processes and force loading are often coupled, this review highlights prevailing convective-diffusive transport physics that modulate cellular and molecular processes during thrombus formation.}, }
@article {pmid34685088, year = {2021}, author = {Sun, X and Mohammed, HI and Tiji, ME and Mahdi, JM and Majdi, HS and Wang, Z and Talebizadehsardari, P and Yaïci, W}, title = {Investigation of Heat Transfer Enhancement in a Triple Tube Latent Heat Storage System Using Circular Fins with Inline and Staggered Arrangements.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {11}, number = {10}, pages = {}, pmid = {34685088}, issn = {2079-4991}, abstract = {Inherent fluctuations in the availability of energy from renewables, particularly solar, remain a substantial impediment to their widespread deployment worldwide. Employing phase-change materials (PCMs) as media, saving energy for later consumption, offers a promising solution for overcoming the problem. However, the heat conductivities of most PCMs are limited, which severely limits the energy storage potential of these materials. This study suggests employing circular fins with staggered distribution to achieve improved thermal response rates of PCM in a vertical triple-tube heat exchanger involving two opposite flow streams of the heat-transfer fluid (HTF). Since heat diffusion is not the same at various portions of the PCM unit, different fin configurations, fin dimensions and HTF flow boundary conditions were explored using computational studies of melting in the PCM triple-tube system. Staggered configuration of fin distribution resulted in significant increases in the rates of PCM melting. The results indicate that the melting rate and heat charging rate could be increased by 37.2 and 59.1%, respectively, in the case of staggered distribution. Furthermore, the use of lengthy fins with smaller thickness in the vertical direction of the storage unit resulted in a better positive role of natural convection; thus, faster melting rates were achieved. With fin dimensions of 0.666 mm × 15 mm, the melting rate was found to be increased by 23.6%, when compared to the base case of 2 mm × 5 mm. Finally, it was confirmed that the values of the Reynolds number and inlet temperatures of the HTF had a significant impact on melting time savings when circular fins of staggered distribution were included.}, }
@article {pmid34683293, year = {2021}, author = {Yamashita, H and Akinaga, T and Sugihara-Seki, M}, title = {Pattern Transition on Inertial Focusing of Neutrally Buoyant Particles Suspended in Rectangular Duct Flows.}, journal = {Micromachines}, volume = {12}, number = {10}, pages = {}, pmid = {34683293}, issn = {2072-666X}, support = {JP20H02072//JSPS KAKENHI/ ; }, abstract = {The continuous separation and filtration of particles immersed in fluid flows are important interests in various applications. Although the inertial focusing of particles suspended in a duct flow is promising in microfluidics, predicting the focusing positions depending on the parameters, such as the shape of the duct cross-section and the Reynolds number (Re) has not been achieved owing to the diversity of the inertial-focusing phenomena. In this study, we aimed to elucidate the variation of the inertial focusing depending on Re in rectangular duct flows. We performed a numerical simulation of the lift force exerted on a spherical particle flowing in a rectangular duct and determined the lift-force map within the duct cross-section over a wide range of Re. We estimated the particle trajectories based on the lift map and Stokes drag, and identified the particle-focusing points appeared in the cross-section. For an aspect ratio of the duct cross-section of 2, we found that the blockage ratio changes transition structure of particle focusing. For blockage ratios smaller than 0.3, particles focus near the centres of the long sides of the cross-section at low Re and near the centres of both the long and short sides at relatively higher Re. This transition is expressed as a subcritical pitchfork bifurcation. For blockage ratio larger than 0.3, another focusing pattern appears between these two focusing regimes, where particles are focused on the centres of the long sides and at intermediate positions near the corners. Thus, there are three regimes; the transition between adjacent regimes at lower Re is found to be expressed as a saddle-node bifurcation and the other transition as a supercritical pitchfork bifurcation.}, }
@article {pmid34678790, year = {2021}, author = {Christov, IC}, title = {Soft hydraulics: from Newtonian to complex fluid flows through compliant conduits.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {34}, number = {6}, pages = {}, doi = {10.1088/1361-648X/ac327d}, pmid = {34678790}, issn = {1361-648X}, mesh = {Cross-Sectional Studies ; *Hydrodynamics ; Lab-On-A-Chip Devices ; *Microfluidics/methods ; Viscosity ; }, abstract = {Microfluidic devices manufactured from soft polymeric materials have emerged as a paradigm for cheap, disposable and easy-to-prototype fluidic platforms for integrating chemical and biological assays and analyses. The interplay between the flow forces and the inherently compliant conduits of such microfluidic devices requires careful consideration. While mechanical compliance was initially a side-effect of the manufacturing process and materials used, compliance has now become a paradigm, enabling new approaches to microrheological measurements, new modalities of micromixing, and improved sieving of micro- and nano-particles, to name a few applications. This topical review provides an introduction to the physics of these systems. Specifically, the goal of this review is to summarize the recent progress towards a mechanistic understanding of the interaction between non-Newtonian (complex) fluid flows and their deformable confining boundaries. In this context, key experimental results and relevant applications are also explored, hand-in-hand with the fundamental principles for their physics-based modeling. The key topics covered include shear-dependent viscosity of non-Newtonian fluids, hydrodynamic pressure gradients during flow, the elastic response (deformation and bulging) of soft conduits due to flow within, the effect of cross-sectional conduit geometry on the resulting fluid-structure interaction, and key dimensionless groups describing the coupled physics. Open problems and future directions in this nascent field of soft hydraulics, at the intersection of non-Newtonian fluid mechanics, soft matter physics, and microfluidics, are noted.}, }
@article {pmid34677517, year = {2021}, author = {Park, NS and Yoon, S and Jeong, W and Jeong, YW}, title = {A Study on the Evaluation of Flow Distribution Evenness in Parallel-Arrayed-Type Low-Pressure Membrane Module Piping.}, journal = {Membranes}, volume = {11}, number = {10}, pages = {}, pmid = {34677517}, issn = {2077-0375}, support = {No. 2020R1A2C1006495//National Research Foundation of Korea (NRF)/ ; }, abstract = {The objectives of this study were to measure the flow rate distribution from a header pipe to each module installed in parallel for a water treatment membrane filtration process in operation and to investigate the reason for an uneven distribution of the flow rate via the CFD technique. In addition, this study attempted to propose the ratio of the branch pipe to the header pipe required to equalize the flow distribution for the same membrane filtration process. Finally, the relationship between the Reynolds number in the header pipe and the degree of the manifold flow distribution evenness was investigated. Mobile ultrasonic flow meter was used to measure the flow rate flowing from the membrane module pipe to each module, and the CFD technique was used to verify this. From the results of the actual measurement using ultrasonic flow meter and CFD simulation, it was confirmed that the outflow flow rate from the branch pipe located at the end of the header pipe was three times higher than that of the branch pipe near the inlet. The reason was that the differential pressure generated between each membrane module was higher toward the end of the header pipe. When the ratio of the sum of the cross-sectional area of the branch pipe and the cross-sectional area of the header pipe was reduced by about 30 times, it was confirmed that the flow rate flowing from each branch pipe to the membrane module was almost equal. Also, if the flow in the header pipe is transitional or laminar (Reynolds No. is approximately 4000 or less), the flow rate flowing from each branch pipe to the membrane module can be more even.}, }
@article {pmid34677490, year = {2021}, author = {Kim, KT and Park, JE and Jung, SY and Kang, TG}, title = {Fouling Mitigation via Chaotic Advection in a Flat Membrane Module with a Patterned Surface.}, journal = {Membranes}, volume = {11}, number = {10}, pages = {}, pmid = {34677490}, issn = {2077-0375}, support = {2019R1F1A1058001//National Research Foundation of Korea/ ; }, abstract = {Fouling mitigation using chaotic advection caused by herringbone-shaped grooves in a flat membrane module is numerically investigated. The feed flow is laminar with the Reynolds number (Re) ranging from 50 to 500. In addition, we assume a constant permeate flux on the membrane surface. Typical flow characteristics include two counter-rotating flows and downwelling flows, which are highly influenced by the groove depth at each Re. Poincaré sections are plotted to represent the dynamical systems of the flows and to analyze mixing. The flow systems become globally chaotic as the groove depth increases above a threshold value. Fouling mitigation via chaotic advection is demonstrated using the dimensionless average concentration (c¯w*) on the membrane and its growth rate. When the flow system is chaotic, the growth rate of c¯w* drops significantly compared to that predicted from the film theory, demonstrating that chaotic advection is an attractive hydrodynamic technique that mitigates membrane fouling. At each Re, there exists an optimal groove depth minimizing c¯w* and the growth rate of c¯w*. Under the optimum groove geometry, foulants near the membrane are transported back to the bulk flow via the downwelling flows, distributed uniformly in the entire channel via chaotic advection.}, }
@article {pmid34663851, year = {2021}, author = {Khan, WU and Imran, A and Raja, MAZ and Shoaib, M and Awan, SE and Kausar, K and He, Y}, title = {A novel mathematical modeling with solution for movement of fluid through ciliary caused metachronal waves in a channel.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {20601}, pmid = {34663851}, issn = {2045-2322}, abstract = {In the present research, a novel mathematical model for the motion of cilia using non-linear rheological fluid in a symmetric channel is developed. The strength of analytical perturbation technique is employed for the solution of proposed physical process using mectachoronal rhythm based on Cilia induced flow for pseudo plastic nano fluid model by considering the low Reynolds number and long wave length approximation phenomena. The role of ciliary motion for the fluid transport in various animals is explained. Analytical expressions are gathered for stream function, concentration, temperature profiles, axial velocity, and pressure gradient. Whereas, transverse velocity, pressure rise per wave length, and frictional force on the wall of the tubule are investigated with aid of numerical computations and their outcomes are demonstrated graphically. A comprehensive analysis for comparison of Perturb and numerical solution is done. This analysis validates the analytical solution.}, }
@article {pmid34659649, year = {2022}, author = {Cui, PY and Chen, WQ and Wang, JQ and Zhang, JH and Huang, YD and Tao, WQ}, title = {Numerical studies on issues of Re-independence for indoor airflow and pollutant dispersion within an isolated building.}, journal = {Building simulation}, volume = {15}, number = {7}, pages = {1259-1276}, pmid = {34659649}, issn = {1996-3599}, abstract = {This study conducted the numerical models validated by wind-tunnel experiments to investigate the issues of Re-independence of indoor airflow and pollutant dispersion within an isolated building. The window Reynolds number (Re w) was specified to characterize the indoor flow and dispersion. The indicators of RRC (ratio of relative change) or DR (K_DR) (difference ratio of dimensionless concentration) ≤ 5% were applied to quantitatively determine the critical Re w for indoor flow and turbulent diffusion. The results show that the critical Re (Re crit) value is position-dependent, and Re crit at the most unfavorable position should be suggested as the optimal value within the whole areas of interest. Thus Re H,crit = 27,000 is recommended for the outdoor flows; while Re w,crit = 15,000 is determined for the indoor flows due to the lower part below the window showing the most unfavorable. The suggested Re w,crit (=15,000) for indoor airflow and cross ventilation is independence of the window size. Moreover, taking K_DR ≤ 5% as the indicator, the suggested Re w,crit for ensuring indoor pollutant diffusion enter the Re-independence regime should also be 15,000, indicating that indoor passive diffusion is completely determined by the flow structures. The contours of dimensionless velocity (U/U 0) and concentration (K) against the increasing Re w further confirmed this critical value. This study further reveals the Re-independence issues for indoor flow and dispersion to ensure the reliability of the data obtained by reduced-scale numerical or wind-tunnel models.}, }
@article {pmid34656560, year = {2022}, author = {Moitoi, AJ and Shaw, S}, title = {Magnetic drug targeting during Caputo-Fabrizio fractionalized blood flow through a permeable vessel.}, journal = {Microvascular research}, volume = {139}, number = {}, pages = {104262}, doi = {10.1016/j.mvr.2021.104262}, pmid = {34656560}, issn = {1095-9319}, mesh = {Antineoplastic Agents/*blood/chemistry/therapeutic use ; Blood Vessels/*metabolism ; Computer Simulation ; *Drug Carriers ; Drug Compounding ; *Magnetic Fields ; *Metal Nanoparticles ; *Models, Cardiovascular ; Nanotechnology ; Neoplasms/*blood supply/drug therapy/metabolism ; Numerical Analysis, Computer-Assisted ; Permeability ; Regional Blood Flow ; }, abstract = {Nanoparticle-based drug targeting is an important platform for the treatment of cardiovascular disorders. Magnetic drug targeting is more significant as it is a noninvasive procedure and biocompatible. The present problem aims to understand magnetic drug delivery to a specific location in a permeable blood vessel under the vibration and magnetic environment. Caputo-Fabrizio fractional-order time derivatives are used in the governing equations. The momentum equations are solved analytically and presented in the form of Lorenzo-Hartley and Robotonov-Hartley functions and convolution of the Laplace transform. Convolution integrations are solved by using the numerical integration technique. The Fourth order Runge-Kutta method (RK4) is used to solve the force balance equation. The influence of pertinent parameters such as Reynolds number, pulsatile frequency, magnetic field strength, Darcy number and fractional-order parameters are presented through graphs. It is observed that increasing Reynolds number results in decreasing the tendency of the drug to capture near the tumor site, whereas the pulsatile frequency presents an opposite phenomenon. Increasing the magnetic field strength and Darcy number boosts the capture efficiency of drug particles near the tumor site. The short memory effect efficiently captures the magnetic drug carriers to a specific location under the action of suitable magnetic field strength.}, }
@article {pmid34654198, year = {2021}, author = {Calderer, MC and Golovaty, D and Yao, L and Zhao, L}, title = {Shear flow of active matter in thin channels.}, journal = {Physical review. E}, volume = {104}, number = {3-1}, pages = {034607}, doi = {10.1103/PhysRevE.104.034607}, pmid = {34654198}, issn = {2470-0053}, abstract = {We study the shear flow of active filaments confined in a thin channel for extensile and contractile fibers. We apply the Ericksen-Leslie equations of liquid crystal flow with an activity source term. The dimensionless form of this system includes the Ericksen, activity, and Reynolds numbers, together with the aspect ratio of the channel, as the main driving parameters. We perform a normal mode stability analysis of the base shear flow. For both types of fibers, we arrive at a comprehensive description of the stability properties and their dependence on the parameters of the system. The transition to unstable frequencies in extensile fibers occurs at a positive threshold value of the activity parameter, whereas for contractile ones a complex behavior is found at low absolute value of the activity number. The latter might be an indication of the biologically relevant plasticity and phase transition issues. In contrast with extensile fibers, flows of contractile ones are also found to be highly sensitive to the Reynolds number. The work on extensile fibers is guided by experiments on active filaments in confined channels and aims at quantifying their findings in the prechaotic regime.}, }
@article {pmid34651149, year = {2021}, author = {Gallen, AF and Castro, M and Hernandez-Machado, A}, title = {Red blood cells in low Reynolds number flow: A vorticity-based characterization of shapes in two dimensions.}, journal = {Soft matter}, volume = {17}, number = {42}, pages = {9587-9594}, doi = {10.1039/d1sm00559f}, pmid = {34651149}, issn = {1744-6848}, mesh = {Cell Movement ; Cell Shape ; *Erythrocytes ; *Hydrodynamics ; Physical Phenomena ; }, abstract = {Studies on the mechanical properties of red blood cells improve the diagnosis of some blood-related diseases. Some existing numerical methods have successfully simulated the coupling between a fluid and red blood cells. This paper introduces an alternative phase-field model formulation of two-dimensional cells that solves the vorticity and stream function that simplifies the numerical implementation. We integrate red blood cell dynamics immersed in a Poiseuille flow and reproduce previously reported morphologies (slippers or parachutes). In the case of flow in a very wide channel, we discover a new metastable shape referred to as 'anti-parachute' that evolves into a horizontal slipper centered on the channel. This sort of metastable morphology may contribute to the dynamical response of the blood.}, }
@article {pmid34644682, year = {2022}, author = {Truong, H and Engels, T and Wehmann, H and Kolomenskiy, D and Lehmann, FO and Schneider, K}, title = {An experimental data-driven mass-spring model of flexibleCalliphorawings.}, journal = {Bioinspiration &amp; biomimetics}, volume = {17}, number = {2}, pages = {}, doi = {10.1088/1748-3190/ac2f56}, pmid = {34644682}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Elasticity ; *Flight, Animal ; Humans ; Insecta ; Models, Biological ; *Wings, Animal ; }, abstract = {Insect wings can undergo significant deformation during flapping motion owing to inertial, elastic and aerodynamic forces. Changes in shape then alter aerodynamic forces, resulting in a fully coupled fluid-structure interaction (FSI) problem. Here, we present detailed three-dimensional FSI simulations of deformable blowfly (Calliphora vomitoria) wings in flapping flight. A wing model is proposed using a multi-parameter mass-spring approach, chosen for its implementation simplicity and computational efficiency. We train the model to reproduce static elasticity measurements by optimizing its parameters using a genetic algorithm with covariance matrix adaptation (CMA-ES). Wing models trained with experimental data are then coupled to a high-performance flow solver run on massively parallel supercomputers. Different features of the modeling approach and the intra-species variability of elastic properties are discussed. We found that individuals with different wing stiffness exhibit similar aerodynamic properties characterized by dimensionless forces and power at the same Reynolds number. We further study the influence of wing flexibility by comparing between the flexible wings and their rigid counterparts. Under equal prescribed kinematic conditions for rigid and flexible wings, wing flexibility improves lift-to-drag ratio as well as lift-to-power ratio and reduces peak force observed during wing rotation.}, }
@article {pmid34642447, year = {2021}, author = {Ali, A and Kanwal, T and Awais, M and Shah, Z and Kumam, P and Thounthong, P}, title = {Impact of thermal radiation and non-uniform heat flux on MHD hybrid nanofluid along a stretching cylinder.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {20262}, pmid = {34642447}, issn = {2045-2322}, abstract = {The current research investigates the thermal radiations and non-uniform heat flux impacts on magnetohydrodynamic hybrid nanofluid (CuO-Fe2O3/H2O) flow along a stretching cylinder, which is the main aim of this study. The velocity slip conditions have been invoked to investigate the slippage phenomenon on the flow. The impact of induced magnetic field with the assumption of low Reynolds number is imperceptible. Through the use of appropriate non-dimensional parameters and similarity transformations, the ruling PDE's (partial differential equations) are reduced to set of ODE's (ordinary differential equations), which are then numerically solved using Adams-Bashforth Predictor-Corrector method. Velocity and temperature fields with distinct physical parameters are investigated and explored graphically. The main observations about the hybrid nanofluid and non-uniform heat flux are analyzed graphically. A decrease in the velocity of the fluid is noted with addition of Hybrid nanofluid particles while temperature of the fluid increases by adding the CuO-Fe2O3 particles to the base fluid. Also, velocity of the fluid decreases when we incorporate the effects of magnetic field and slip. Raise in curvature parameter γ caused enhancement of velocity and temperature fields at a distance from the cylinder but displays opposite behavior nearby the surface of cylinder. The existence of heat generation and absorption for both mass dependent and time dependent parameters increases the temperature of the fluid.}, }
@article {pmid34636830, year = {2021}, author = {Ho, TM and Yang, J and Tsai, PA}, title = {Microfluidic mass transfer of CO2 at elevated pressures: implications for carbon storage in deep saline aquifers.}, journal = {Lab on a chip}, volume = {21}, number = {20}, pages = {3942-3951}, doi = {10.1039/d1lc00106j}, pmid = {34636830}, issn = {1473-0189}, mesh = {*Carbon Dioxide ; *Groundwater ; Microfluidics ; Water ; }, abstract = {Carbon capture and sequestration (CCS) in a deep saline aquifer is one of the most promising technologies to mitigate anthropologically emitted carbon dioxide. Accurately quantifying the mass transport of CO2 at pore-scales is crucial but challenging for successful CCS deployment. Here, we conduct high-pressure microfluidic experiments, mimicking reservoir conditions up to 9.5 MPa and 35 °C, to elucidate the microfluidic mass transfer process of CO2 at three different states (i.e., gas, liquid, and supercritical phase) into water. We measure the size change of CO2 micro-bubbles/droplets generated using a microfluidic T-junction to estimate the volumetric mass transfer coefficient (kLa), quantifying the rate change of CO2 concentration under the driving force of concentration gradient. The results show that bubbles/droplets under high-pressure conditions reach a steady state faster than low pressure. The measured volumetric mass transfer coefficient increases with the Reynolds number (based on the liquid slug) and is nearly independent of the injection pressure for both the gas and liquid phases. In addition, kLa significantly enlarges with increasing high pressure at the supercritical state. Compared with various chemical engineering applications using millimeter-sized capillaries (with typical kLa measured ranging from ≈0.005 to 0.8 s[-1]), the microfluidic results show a significant increase in the volumetric mass transfer of CO2 into water by two to three orders of magnitude, O (10[2]-10[3]), with decreasing hydrodynamic diameter (of ≈50 μm).}, }
@article {pmid34635693, year = {2021}, author = {Liao, Y and Mechulam, Y and Lassalle-Kaiser, B}, title = {A millisecond passive micromixer with low flow rate, low sample consumption and easy fabrication.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {20119}, pmid = {34635693}, issn = {2045-2322}, mesh = {Complex Mixtures/*analysis ; *Computer Simulation ; Equipment Design ; Humans ; Lab-On-A-Chip Devices/*standards ; Microfluidic Analytical Techniques/*instrumentation/*methods ; }, abstract = {Fast mixing of small volumes of solutions in microfluidic devices is essential for an accurate control and observation of the dynamics of a reaction in biological or chemical studies. It is often, however, a challenging task, as the Reynolds number (Re) in microscopic devices is typically < 100. In this report, we detail a novel mixer based on the "staggered herring bone" (SHB) pattern and "split-recombination" strategies with an optimized geometry, the periodic rotation of the flow structure can be controlled and recombined in a way that the vortices and phase shifts of the flow induce intertwined lamellar structures, thus increasing the contact surface and enhancing mixing. The optimization improves the mixing while using a low flow rate, hence a small volume for mixing and moderate pressure drops. The performances of the patterns were first simulated using COMSOL Multiphysics under different operating conditions. The simulation indicates that at very low flow rate (1-12 µL·min[-1]) and Re (3.3-40), as well as a very small working volume (~ 3 nL), a very good mixing (~ 98%) can be achieved in the ms time range (4.5-78 ms). The most promising design was then visualized experimentally, showing results that are consistent with the outcomes of the simulations. Importantly, the devices were fabricated using a classical soft-lithography method, as opposed to additive manufacturing often used to generate complex mixing structures. This new device minimizes the sample consumption and could therefore be applied for studies using precious samples.}, }
@article {pmid34625588, year = {2021}, author = {Hussain, A and Hassan, A and Mdallal, QA and Ahmad, H and Sherif, EM and Rehman, A and Arshad, M}, title = {Comsolic solution of an elliptic cylindrical compressible fluid flow.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {20030}, pmid = {34625588}, issn = {2045-2322}, abstract = {In this article, the primary focus is to investigate the heat transfer effects with viscous compressible laminar flow in the permeable elliptic cylinder. The Reynolds number is kept 100 for flow to be laminar. The physics of heat transfer is selected to be coupled with the laminar flow. The results for particular step-size time for Velocity distribution, pressure profile, temperature profile, isothermal temperature contours, and drag coefficient have been analyzed. Mesh has been generated through COMSOL, mesh entities have been elaborated statistically. The maximum and minimum velocity profile is observed at the elliptical cylinder's walls and upper, lower boundary respectively. The maximum velocity observed is 2.22 m/s. Pressure profile around elliptic corners is found maximum, distinct patterns are observed even under the influence of applied heat. Temperature is observed maximum at walls but it gradually increases as moving from the upper boundary towards the lower boundary. The isothermal contour patterns are observed maximum near the walls, drag coefficient of gradual decrease is observed. COMSOL multi-physics is utilized for mathematical modeling of problems and the Backward-Differentiation-Formula has been exploited to handle problems numerically. The results will help greatly to understand the characterizations of viscous fluids and in industries like air furnaces and automobile cooling systems.}, }
@article {pmid34623848, year = {2021}, author = {Khalid, M and Shankar, V and Subramanian, G}, title = {Continuous Pathway between the Elasto-Inertial and Elastic Turbulent States in Viscoelastic Channel Flow.}, journal = {Physical review letters}, volume = {127}, number = {13}, pages = {134502}, doi = {10.1103/PhysRevLett.127.134502}, pmid = {34623848}, issn = {1079-7114}, abstract = {Viscoelastic plane Poiseuille flow is shown to become linearly unstable in the absence of inertia, in the limit of high elasticities, for ultradilute polymer solutions. While inertialess elastic instabilities have been predicted for curvilinear shear flows, this is the first ever report of a purely elastic linear instability in a rectilinear shear flow. The novel instability continues up to a Reynolds number (Re) of O(1000), corresponding to the recently identified elasto-inertial turbulent state believed to underlie the maximum-drag-reduced regime. Thus, for highly elastic ultradilute polymer solutions, a single linearly unstable modal branch may underlie transition to elastic turbulence at zero Re and to elasto-inertial turbulence at moderate Re, implying the existence of continuous pathways connecting the turbulent states to each other and to the laminar base state.}, }
@article {pmid34608161, year = {2021}, author = {Marusic, I and Chandran, D and Rouhi, A and Fu, MK and Wine, D and Holloway, B and Chung, D and Smits, AJ}, title = {An energy-efficient pathway to turbulent drag reduction.}, journal = {Nature communications}, volume = {12}, number = {1}, pages = {5805}, pmid = {34608161}, issn = {2041-1723}, abstract = {Simulations and experiments at low Reynolds numbers have suggested that skin-friction drag generated by turbulent fluid flow over a surface can be decreased by oscillatory motion in the surface, with the amount of drag reduction predicted to decline with increasing Reynolds number. Here, we report direct measurements of substantial drag reduction achieved by using spanwise surface oscillations at high friction Reynolds numbers ([Formula: see text]) up to 12,800. The drag reduction occurs via two distinct physical pathways. The first pathway, as studied previously, involves actuating the surface at frequencies comparable to those of the small-scale eddies that dominate turbulence near the surface. We show that this strategy leads to drag reduction levels up to 25% at [Formula: see text] = 6,000, but with a power cost that exceeds any drag-reduction savings. The second pathway is new, and it involves actuation at frequencies comparable to those of the large-scale eddies farther from the surface. This alternate pathway produces drag reduction of 13% at [Formula: see text] = 12,800. It requires significantly less power and the drag reduction grows with Reynolds number, thereby opening up potential new avenues for reducing fuel consumption by transport vehicles and increasing power generation by wind turbines.}, }
@article {pmid34607142, year = {2022}, author = {Yogarathinam, LT and Velswamy, K and Gangasalam, A and Ismail, AF and Goh, PS and Narayanan, A and Abdullah, MS}, title = {Performance evaluation of whey flux in dead-end and cross-flow modes via convolutional neural networks.}, journal = {Journal of environmental management}, volume = {301}, number = {}, pages = {113872}, doi = {10.1016/j.jenvman.2021.113872}, pmid = {34607142}, issn = {1095-8630}, mesh = {*Cheese/analysis ; Filtration ; Membranes, Artificial ; Neural Networks, Computer ; *Whey ; Whey Proteins ; }, abstract = {Effluent originating from cheese production puts pressure onto environment due to its high organic load. Therefore, the main objective of this work was to compare the influence of different process variables (transmembrane pressure (TMP), Reynolds number and feed pH) on whey protein recovery from synthetic and industrial cheese whey using polyethersulfone (PES 30 kDa) membrane in dead-end and cross-flow modes. Analysis on the fouling mechanistic model indicates that cake layer formation is dominant as compared to other pore blocking phenomena evaluated. Among the input variables, pH of whey protein solution has the biggest influence towards membrane flux and protein rejection performances. At pH 4, electrostatic attraction experienced by whey protein molecules prompted a decline in flux. Cross-flow filtration system exhibited a whey rejection value of 0.97 with an average flux of 69.40 L/m[2]h and at an experimental condition of 250 kPa and 8 for TMP and pH, respectively. The dynamic behavior of whey effluent flux was modeled using machine learning (ML) tool convolutional neural networks (CNN) and recursive one-step prediction scheme was utilized. Linear and non-linear correlation indicated that CNN model (R[2] - 0.99) correlated well with the dynamic flux experimental data. PES 30 kDa membrane displayed a total protein rejection coefficient of 0.96 with 55% of water recovery for the industrial cheese whey effluent. Overall, these filtration studies revealed that this dynamic whey flux data studies using the CNN modeling also has a wider scope as it can be applied in sensor tuning to monitor flux online by means of enhancing whey recovery efficiency.}, }
@article {pmid34599248, year = {2021}, author = {Almalki, MM and Alaidarous, ES and Maturi, DA and Raja, MAZ and Shoaib, M}, title = {Intelligent computing technique based supervised learning for squeezing flow model.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {19597}, pmid = {34599248}, issn = {2045-2322}, abstract = {In this study, the unsteady squeezing flow between circular parallel plates (USF-CPP) is investigated through the intelligent computing paradigm of Levenberg-Marquard backpropagation neural networks (LMBNN). Similarity transformation introduces the fluidic system of the governing partial differential equations into nonlinear ordinary differential equations. A dataset is generated based on squeezing fluid flow system USF-CPP for the LMBNN through the Runge-Kutta method by the suitable variations of Reynolds number and volume flow rate. To attain approximation solutions for USF-CPP to different scenarios and cases of LMBNN, the operations of training, testing, and validation are prepared and then the outcomes are compared with the reference data set to ensure the suggested model's accuracy. The output of LMBNN is discussed by the mean square error, dynamics of state transition, analysis of error histograms, and regression illustrations.}, }
@article {pmid39650054, year = {2021}, author = {Cartwright, A and Du, J}, title = {Low Reynolds Number Swimming Near Interfaces in Multi-Fluid Media.}, journal = {Applied sciences (Basel, Switzerland)}, volume = {11}, number = {19}, pages = {}, pmid = {39650054}, issn = {2076-3417}, support = {R01 GM131408/GM/NIGMS NIH HHS/United States ; }, abstract = {Microorganisms often swim within heterogeneous fluid media composed of multiple materials with very different properties. The swimming speed is greatly affected by the composition and rheology of the fluidic environment. In addition, biological locomotions are also strongly influenced by the presence of phase boundaries and free interfaces, across which physical properties of the fluid media may vary significantly. Using a two-fluid immersed boundary method, we investigate the classical Taylor's swimming sheet problem near interfaces within multi-fluid media. The accuracy of the methodology is illustrated through comparisons with analytical solutions. Our simulation results indicate that the interface dynamics and phase separation in the multi-fluid mixture are closely coupled with the movement of the swimmer. Depending on the interface location, the frictional coefficient, and the multi-fluid composition, the swimmer can move faster or slower than that in a single phase fluid.}, }
@article {pmid34588473, year = {2021}, author = {Ramzan, M and Khan, NS and Kumam, P}, title = {Mechanical analysis of non-Newtonian nanofluid past a thin needle with dipole effect and entropic characteristics.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {19378}, pmid = {34588473}, issn = {2045-2322}, abstract = {The study concerns with the mechanical characteristics of heat and mass transfer flow of a second grade nanofluid as well as gyrotatic microorganism motion past a thin needle with dipole effect, entropy generation, thermal radiation, Arrhenius activation energy and binar chemical reaction. The governing equations and boundary conditions are simplified by the use of suitable similarity transformations. Homotopy analysis method is implemented to obtain the series solution of non-linear ordinary differential equations. Physical behaviors of heat and mass transfer flow with gyrotatic microorganisms and entropy generation are investigated through the embedded parameters. The nanofluid velocity is enhanced for higher values of the ferromagnetic parameter, local Grashof number, bioconvection Rayleigh number and radiation parameter. The Reynolds number, radiation parameter and Eckert number decrease the nanofluid temperature. The entropy generation is increased with the enhancement of radiation parameter, Eckert number, Lewis number, temperature difference parameter, dimensionless constant parameter, Curie temperature, Prandtl number and concentration difference parameter.}, }
@article {pmid34586089, year = {2021}, author = {Treiser, MD and Miles, MR and Albino, FP and Giladi, AM and Katz, RD and Higgins, JP}, title = {Long-Term Patency and Fluid Dynamics of Recipient Artery after End-to-Side Anastomosis for Free Tissue Transfer.}, journal = {Plastic and reconstructive surgery}, volume = {148}, number = {5}, pages = {800e-803e}, doi = {10.1097/PRS.0000000000008439}, pmid = {34586089}, issn = {1529-4242}, mesh = {Adolescent ; Adult ; Anastomosis, Surgical/methods ; Arteries/diagnostic imaging/physiology/*surgery ; Blood Flow Velocity ; Collateral Circulation ; Extremities/blood supply/*injuries/surgery ; Follow-Up Studies ; Free Tissue Flaps/blood supply/*transplantation ; Humans ; Middle Aged ; Plastic Surgery Procedures/*methods ; Treatment Outcome ; Ultrasonography, Doppler, Duplex ; *Vascular Patency ; Young Adult ; }, abstract = {BACKGROUND: End-to-end microvascular anastomoses sacrifice downstream inline perfusion of the recipient vessels. End-to-side anastomoses, in theory, maintain distal inline flow of the recipient vessel. The proposed benefit of the end-to-side technique depends on patency of the distal vessels and subsequent flow parameters, but maintenance of distal perfusion has not been conclusively demonstrated.<br><br>METHODS: Fifteen patients who underwent a successful extremity free flap procedure via end-to-side anastomoses to a noncritical vessel between 2003 and 2017 were enrolled. Recipient artery patency distal to the anastomosis was assessed using pulse volume recordings and duplex ultrasound imaging. Resistance indices, flow velocities, vessel diameters, volumetric flow, and turbulent flow dimensionless number (Reynolds number) were measured. Comparisons were made to the ipsilateral collateral vessel as well as to the vessels on the nonoperative contralateral limb using paired t tests.<br><br>RESULTS: Downstream flow was identified in 14 of 15 patients (93 percent patency). There was no statistical difference in resistive indices comparing the anastomotic vessel (0.859 &#xb1; 0.300) and the collateral vessel (0.853 &#xb1; 0.179) of the ipsilateral extremity. Ultrasound flows were similar; the anastomotic vessel demonstrated downstream volumetric flows of 139 &#xb1; 92.0 cm3/min versus 137 &#xb1; 41.6 cm3/min within the same vessel of the nonoperative contralateral limb. The anastomotic vessel had Reynolds numbers well below the turbulent threshold (448 &#xb1; 202 and 493 &#xb1; 127 for the anastomotic and nonoperative contralateral limb, respectively).<br><br>CONCLUSION: End-to-side anastomosis to noncritical vessels resulted in a 93 percent long-term recipient vessel patency rate, with no statistically significant changes in volumetric flows, resistive indices, or fluid dynamics in the vessels that remained patent.}, }
@article {pmid34577719, year = {2021}, author = {Huang, L and Du, J and Zhu, Z}, title = {Neutrally Buoyant Particle Migration in Poiseuille Flow Driven by Pulsatile Velocity.}, journal = {Micromachines}, volume = {12}, number = {9}, pages = {}, pmid = {34577719}, issn = {2072-666X}, support = {11572107//National Natural Science Foundation of China/ ; GK199900299012-026//the Fundamental Research Funds for the Provincial Universities of Zhejiang/ ; }, abstract = {A neutrally buoyant circular particle migration in two-dimensional (2D) Poiseuille channel flow driven by pulsatile velocity is numerical studied by using immersed boundary-lattice Boltzmann method (IB-LBM). The effects of Reynolds number (25≤Re≤200) and blockage ratio (0.15≤k≤0.40) on particle migration driven by pulsatile and non-pulsatile velocity are all numerically investigated for comparison. The results show that, different from non-pulsatile cases, the particle will migrate back to channel centerline with underdamped oscillation during the time period with zero-velocity in pulsatile cases. The maximum lateral travel distance of the particle in one cycle of periodic motion will increase with increasing Re, while k has little impact. The quasi frequency of such oscillation has almost no business with Re and k. Moreover, Re plays an essential role in the damping ratio. Pulsatile flow field is ubiquitous in aorta and other arteries. This article is conducive to understanding nanoparticle migration in those arteries.}, }
@article {pmid34577699, year = {2021}, author = {Farahinia, A and Jamaati, J and Niazmand, H and Zhang, W}, title = {Numerical Analysis of the Heterogeneity Effect on Electroosmotic Micromixers Based on the Standard Deviation of Concentration and Mixing Entropy Index.}, journal = {Micromachines}, volume = {12}, number = {9}, pages = {}, pmid = {34577699}, issn = {2072-666X}, abstract = {One approach to achieve a homogeneous mixture in microfluidic systems in the quickest time and shortest possible length is to employ electroosmotic flow characteristics with heterogeneous surface properties. Mixing using electroosmotic flow inside microchannels with homogeneous walls is done primarily under the influence of molecular diffusion, which is not strong enough to mix the fluids thoroughly. However, surface chemistry technology can help create desired patterns on microchannel walls to generate significant rotational currents and improve mixing efficiency remarkably. This study analyzes the function of a heterogeneous zeta-potential patch located on a microchannel wall in creating mixing inside a microchannel affected by electroosmotic flow and determines the optimal length to achieve the desired mixing rate. The approximate Helmholtz-Smoluchowski model is suggested to reduce computational costs and simplify the solving process. The results show that the heterogeneity length and location of the zeta-potential patch affect the final mixing proficiency. It was also observed that the slip coefficient on the wall has a more significant effect than the Reynolds number change on improving the mixing efficiency of electroosmotic micromixers, benefiting the heterogeneous distribution of zeta-potential. In addition, using a channel with a heterogeneous zeta-potential patch covered by a slip surface did not lead to an adequate mixing in low Reynolds numbers. Therefore, a homogeneous channel without any heterogeneity would be a priority in such a range of Reynolds numbers. However, increasing the Reynolds number and the presence of a slip coefficient on the heterogeneous channel wall enhances the mixing efficiency relative to the homogeneous one. It should be noted, though, that increasing the slip coefficient will make the mixing efficiency decrease sharply in any situation, especially in high Reynolds numbers.}, }
@article {pmid34575038, year = {2021}, author = {Gimsa, J and Gimsa, U}, title = {Contributions to a Discussion of Spinosaurus aegyptiacus as a Capable Swimmer and Deep-Water Predator.}, journal = {Life (Basel, Switzerland)}, volume = {11}, number = {9}, pages = {}, pmid = {34575038}, issn = {2075-1729}, abstract = {The new findings on Spinosaurus' swim tail strongly suggest that Spinosaurus was a specialized deep-water predator. However, the tail must be seen in the context of the propelled body. The comparison of the flow characteristics of Spinosaurus with geometrically similar animals and their swimming abilities under water must take their Reynolds numbers into account and provide a common context for the properties of Spinosaurus' tail and dorsal sail. Head shape adaptations such as the head crest reduced hydrodynamic disturbance and facilitated stealthy advance, especially when hunting without visual contact, when Spinosaurus could have used its rostral integumentary mechanoreceptors for prey detection. The muscular neck permitted 'pivot' feeding, where the prey's escape abilities were overcome by rapid dorsoventral head movement, facilitated by crest-mediated lower friction.}, }
@article {pmid34549120, year = {2021}, author = {Wu, R and Xie, F and Wei, J and Song, X and Yang, H and Lv, P and Yu, G}, title = {Study on Soot Emission Characteristics of Methane/Oxygen Inverse Diffusion Flame.}, journal = {ACS omega}, volume = {6}, number = {36}, pages = {23191-23202}, pmid = {34549120}, issn = {2470-1343}, abstract = {Inverse diffusion flame (IDF) is an effective and widely used reaction form in the process of noncatalytic partial oxidation (NC-POX) of gaseous hydrocarbons (such as natural gas and coke oven gas). However, soot is generated in the combustion chamber in the case of unreasonable feeding conditions, and thus causes serious damage to the wall and nozzle. In this study, the effects of the equivalence ratio ([O/C]e), the oxygen flow rate, and the Reynolds number on the soot and CH* emission characteristics of CH4/O2 inverse diffusion flame were comprehensively analyzed based on a hyperspectral imaging system. In addition, the relationship between CH* and soot is explored using Ansys Fluent simulation. The experimental results show that the soot radiation core generation area is located in the outer ring of the flame, and the radial distribution of the radiation intensity is bimodal. With the increase in [O/C]e, the initial position for soot radiation and the overall radiation intensity of soot decrease. In addition, the CH* radiation intensity decreases as [O/C]e increases, and CH* exists in the whole flame. The simulation results clearly show that the existence of CH* is conducive to soot production. The emission intensity and the core area of soot formation increase with the increase in the oxygen velocity. Additionally, the soot emission region increases and the flame tip changes from a round blunt to symmetrical tip with the increase in the Reynolds number.}, }
@article {pmid34547732, year = {2021}, author = {Haider, N and Shahzad, A and Qadri, MNM and Shams, TA}, title = {Aerodynamic analysis of hummingbird-like hovering flight.}, journal = {Bioinspiration &amp; biomimetics}, volume = {16}, number = {6}, pages = {}, doi = {10.1088/1748-3190/ac28eb}, pmid = {34547732}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Birds ; Computer Simulation ; *Flight, Animal ; Insecta ; Models, Biological ; *Wings, Animal ; }, abstract = {Flapping wing micro aerial vehicles are studied as the substitute for fixed and rotary wing micro aerial vehicles because of the advantages such as agility, maneuverability, and employability in confined environments. Hummingbird's sustainable hovering capability inspires many researchers to develop micro aerial vehicles with similar dynamics. In this research, a wing of a ruby-throated hummingbird is modeled as an insect wing using membrane and stiffeners. The effect of flexibility on the aerodynamic performance of a wing in hovering flight has been studied numerically by using a fluid-structure interaction scheme at a Reynolds number of 3000. Different wings have been developed by using different positions and thicknesses of the stiffeners. The chordwise and spanwise flexural stiffnesses of all the wings modeled in this work are comparable to insects of similar span and chord length. When the position of the stiffener is varied, the best-performing wing has an average lift coefficient of 0.51. Subsequently, the average lift coefficient is increased to 0.56 when the appropriate thickness of the stiffeners is chosen. The best flexible wing outperforms its rigid counterpart and produces lift and power economy comparable to a real hummingbird's wing. That is, the average lift coefficient and power economy of 0.56 and 0.88 for the best flexible wing as compared to 0.61 and 1.07 for the hummingbird's wing. It can be concluded that a simple manufacturable flexible wing design based on appropriate positioning and thickness of stiffeners can serve as a potential candidate for bio-inspired flapping-wing micro aerial vehicles.}, }
@article {pmid34528156, year = {2021}, author = {Javid, K and Hassan, M and Tripathi, D and Khan, S and Bobescu, E and Bhatti, MM}, title = {Double-diffusion convective biomimetic flow of nanofluid in a complex divergent porous wavy medium under magnetic effects.}, journal = {Journal of biological physics}, volume = {47}, number = {4}, pages = {477-498}, pmid = {34528156}, issn = {1573-0689}, mesh = {*Biomimetics ; Diffusion ; *Magnetic Fields ; *Nanotechnology ; Porosity ; }, abstract = {We explore the physical influence of magnetic field on double-diffusive convection in complex biomimetic (peristaltic) propulsion of nanofluid through a two-dimensional divergent channel. Additionally, porosity effects along with rheological properties of the fluid are also retained in the analysis. The mathematical model is developed by equations of continuity, momentum, energy, and mass concentration. First, scaling analysis is introduced to simplify the rheological equations in the wave frame of reference and then get the final form of equations after applying the low Reynolds number and lubrication approach. The obtained equations are solved analytically by using integration method. Physical interpretation of velocity, pressure gradient, pumping phenomena, trapping phenomena, heat, and mass transfer mechanisms are discussed in detail under magnetic and porous environment. The magnitude of velocity profile is reduced by increasing Grashof parameter. The bolus circulations disappeared from trapping phenomena for larger strength of magnetic and porosity medium. The magnitude of temperature profile and mass concentration are increasing by enhancing the Brownian motion parameter. This study can be productive in manufacturing non-uniform and divergent shapes of micro-lab-chip devices for thermal engineering, industrial, and medical technologies.}, }
@article {pmid34505131, year = {2022}, author = {Costa, RP and Simplice Talla Nwotchouang, B and Yao, J and Biswas, D and Casey, D and McKenzie, R and Steinman, DA and Loth, F}, title = {Transition to Turbulence Downstream of a Stenosis for Whole Blood and a Newtonian Analog Under Steady Flow Conditions.}, journal = {Journal of biomechanical engineering}, volume = {144}, number = {3}, pages = {}, doi = {10.1115/1.4052370}, pmid = {34505131}, issn = {1528-8951}, mesh = {Animals ; Blood Flow Velocity ; Constriction, Pathologic ; *Glycerol ; *Models, Cardiovascular ; Rheology ; Stress, Mechanical ; Swine ; Water ; }, abstract = {Blood, a multiphase fluid comprised of plasma, blood cells, and platelets, is known to exhibit a shear-thinning behavior at low shear rates and near-Newtonian behavior at higher shear rates. However, less is known about the impact of its multiphase nature on the transition to turbulence. In this study, we experimentally determined the critical Reynolds number at which the flow began to transition to turbulence downstream of eccentric stenosis for whole porcine blood and a Newtonian blood analog (water-glycerin mixture). Velocity profiles for both fluids were measured under steady-state flow conditions using an ultrasound Doppler probe placed 12 diameters downstream of eccentric stenosis. Velocity was recorded at 21 locations along the diameter at 11 different flow rates. Normalized turbulent kinetic energy was used to determine the critical Reynolds number for each fluid. Blood rheology was measured before and after each experiment. Tests were conducted on five samples of each fluid inside a temperature-controlled in vitro flow system. The viscosity at a shear rate of 1000 s-1 was used to define the Reynolds number for each fluid. The mean critical Reynolds numbers for blood and water-glycerin were 470 ± 27.5 and 395 ± 10, respectively, indicating a ∼19% delay in transition to turbulence for whole blood compared to the Newtonian fluid. This finding is consistent with a previous report for steady flow in a straight pipe, suggesting some aspect of blood rheology may serve to suppress, or at least delay, the onset of turbulence in vivo.}, }
@article {pmid34497885, year = {2021}, author = {Bu, X and Zhou, S and Sun, M and Alheshibri, M and Khan, MS and Xie, G and Chelgani, SC}, title = {Exploring the Relationships between Gas Dispersion Parameters and Differential Pressure Fluctuations in a Column Flotation.}, journal = {ACS omega}, volume = {6}, number = {34}, pages = {21900-21908}, pmid = {34497885}, issn = {2470-1343}, abstract = {Flotation separation, which is the most important mineral beneficiation technique, is dependent on gas dispersion (hydrodynamic conditions). Thus, many investigations have focused on the precise determination of hydrodynamic conditions such as Reynolds number of the bubbles, bubble velocity, and bubble diameter. However, few studies have examined their relationships with pressure fluctuations in a column flotation. This study introduced the differential pressure fluctuations as an actual variable that could be considered to determine the collection zone's hydrodynamic conditions in a cyclonic microbubble flotation column. In general, the outcomes indicated that superficial gas velocity had the most substantial relationship with the differential pressure fluctuations among other flotation factors (such as pump speed, superficial gas velocity, superficial water velocity, and frother dosage). Furthermore, a high coefficient of determination (R [2] > 0.77) for the equation generated to assess the relationships demonstrated that differential pressure fluctuations could be used as a promising tool to determine the hydrodynamic parameters' characteristics in the flotation columns.}, }
@article {pmid34497293, year = {2021}, author = {Aghamiri, H and Niknejadi, M and Toghraie, D}, title = {Analysis of the forced convection of two-phase Ferro-nanofluid flow in a completely porous microchannel containing rotating cylinders.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {17811}, pmid = {34497293}, issn = {2045-2322}, abstract = {In the present work, the forced convection of nanofluid flow in a microchannel containing rotating cylinders is investigated in different geometries. The heat flux applied to the microchannel wall is 10,000 W m[-2]. The effects of Reynolds number, the volume fraction of nanoparticles, and the porosity percentage of the porous medium are investigated on the flow fields, temperature, and heat transfer rate. Reynolds number values vary from Re = 250-1000, non-dimensional rotational velocities 1 and 2, respectively, and volume fraction of nanoparticles 0-2%. The results show that increasing the velocity of rotating cylinders increases the heat transfer; also, increasing the Reynolds number and volume fraction of nanoparticles increases the heat transfer, pressure drop, and Cf,ave. By comparing the porosity percentages with each other, it is concluded that due to the greater contact of the nanofluid with the porous medium and the creation of higher velocity gradients, the porosity percentage is 45% and the values of are 90% higher than the porosity percentage. Comparing porosity percentages with each other, at porosity percentage 90% is greater than at porosity percentage 45%. On the other hand, increasing the Reynolds number reduces the entropy generation due to heat transfer and increases the entropy generation due to friction. Increasing the volume fraction of nanoparticles increases the entropy generations due to heat transfer and friction.}, }
@article {pmid34482836, year = {2021}, author = {Mandell, JG and Loke, YH and Mass, PN and Cleveland, V and Delaney, M and Opfermann, J and Aslan, S and Krieger, A and Hibino, N and Olivieri, LJ}, title = {Altered hemodynamics by 4D flow cardiovascular magnetic resonance predict exercise intolerance in repaired coarctation of the aorta: an in vitro study.}, journal = {Journal of cardiovascular magnetic resonance : official journal of the Society for Cardiovascular Magnetic Resonance}, volume = {23}, number = {1}, pages = {99}, pmid = {34482836}, issn = {1532-429X}, support = {R38 HL167247/HL/NHLBI NIH HHS/United States ; R38AI140298/AI/NIAID NIH HHS/United States ; R38 AI140298/AI/NIAID NIH HHS/United States ; R01HL143468-0/HL/NHLBI NIH HHS/United States ; R01 HL143468/HL/NHLBI NIH HHS/United States ; }, mesh = {Aorta ; Aorta, Thoracic/diagnostic imaging/surgery ; *Aortic Coarctation/diagnostic imaging/surgery ; Blood Flow Velocity ; Hemodynamics ; Humans ; Magnetic Resonance Spectroscopy ; Predictive Value of Tests ; Retrospective Studies ; }, abstract = {BACKGROUND: Coarctation of the aorta (CoA) is associated with decreased exercise capacity despite successful repair. Altered flow patterns have been identified due to abnormal aortic arch geometry. Our previous work demonstrated aorta size mismatch to be associated with exercise intolerance in this population. In this study, we studied aortic flow patterns during simulations of exercise in repaired CoA using 4D flow cardiovascular magnetic resonance (CMR) using aortic replicas connected to an in vitro flow pump and correlated findings with exercise stress test results to identify biomarkers of exercise intolerance.<br><br>METHODS: Patients with CoA repair were retrospectively analyzed after CMR and exercise stress test. Each aorta was manually segmented and 3D printed. Pressure gradient measurements from ascending aorta (AAo) to descending aorta (DAo) and 4D flow CMR were performed during simulations of rest and exercise using a mock circulatory flow loop. Changes in wall shear stress (WSS) and secondary flow formation (vorticity and helicity) from rest to exercise were quantified, as well as estimated DAo Reynolds number. Parameters were correlated with percent predicted peak oxygen consumption (VO2max) and aorta size mismatch (DAAo/DDAo).<br><br>RESULTS: Fifteen patients were identified (VO2max 47 to 126% predicted). Pressure gradient did not correlate with VO2max at rest or exercise. VO2max correlated positively with the change in peak vorticity (R&#x2009;=&#x2009;0.55, p&#x2009;=&#x2009;0.03), peak helicity (R&#x2009;=&#x2009;0.54, p&#x2009;=&#x2009;0.04), peak WSS in the AAo (R&#x2009;=&#x2009;0.68, p&#x2009;=&#x2009;0.005) and negatively with peak WSS in the DAo (R&#x2009;=&#x2009;-&#xa0;0.57, p&#x2009;=&#x2009;0.03) from rest to exercise. DAAo/DDAo correlated strongly with change in vorticity (R&#x2009;=&#x2009;-&#xa0;0.38, p&#x2009;=&#x2009;0.01), helicity (R&#x2009;=&#x2009;-&#xa0;0.66, p&#x2009;=&#x2009;0.007), and WSS in the AAo (R&#x2009;=&#x2009;-&#xa0;0.73, p&#x2009;=&#x2009;0.002) and DAo (R&#x2009;=&#x2009;0.58, p&#x2009;=&#x2009;0.02). Estimated DAo Reynolds number negatively correlated with VO2max for exercise (R&#x2009;=&#x2009;-&#xa0;0.59, p&#x2009;=&#x2009;0.02), but not rest (R&#x2009;=&#x2009;-&#xa0;0.28, p&#x2009;=&#x2009;0.31). Visualization of streamline patterns demonstrated more secondary flow formation in aortic arches with better exercise capacity, larger DAo, and lower Reynolds number.<br><br>CONCLUSIONS: There are important associations between secondary flow characteristics and exercise capacity in repaired CoA that are not captured by traditional pressure gradient, likely due to increased turbulence and inefficient flow. These 4D flow CMR parameters are a target of investigation to identify optimal aortic arch geometry and improve long term clinical outcomes after CoA repair.}, }
@article {pmid34455847, year = {2021}, author = {Simonis, S and Haussmann, M and Kronberg, L and Dörfler, W and Krause, MJ}, title = {Linear and brute force stability of orthogonal moment multiple-relaxation-time lattice Boltzmann methods applied to homogeneous isotropic turbulence.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {379}, number = {2208}, pages = {20200405}, doi = {10.1098/rsta.2020.0405}, pmid = {34455847}, issn = {1471-2962}, abstract = {Multiple-relaxation-time (MRT) lattice Boltzmann methods (LBM) based on orthogonal moments exhibit lattice Mach number dependent instabilities in diffusive scaling. The present work renders an explicit formulation of stability sets for orthogonal moment MRT LBM. The stability sets are defined via the spectral radius of linearized amplification matrices of the MRT collision operator with variable relaxation frequencies. Numerical investigations are carried out for the three-dimensional Taylor-Green vortex benchmark at Reynolds number 1600. Extensive brute force computations of specific relaxation frequency ranges for the full test case are opposed to the von Neumann stability set prediction. Based on that, we prove numerically that a scan over the full wave space, including scaled mean flow variations, is required to draw conclusions on the overall stability of LBM in turbulent flow simulations. Furthermore, the von Neumann results show that a grid dependence is hardly possible to include in the notion of linear stability for LBM. Lastly, via brute force stability investigations based on empirical data from a total number of 22 696 simulations, the existence of a deterministic influence of the grid resolution is deduced. This article is part of the theme issue 'Progress in mesoscale methods for fluid dynamics simulation'.}, }
@article {pmid34455509, year = {2021}, author = {Ali, A and Jana, RN and Das, S}, title = {Significance of entropy generation and heat source: the case of peristaltic blood flow through a ciliated tube conveying Cu-Ag nanoparticles using Phan-Thien-Tanner model.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {20}, number = {6}, pages = {2393-2412}, pmid = {34455509}, issn = {1617-7940}, mesh = {Copper/*chemistry ; *Entropy ; *Hot Temperature ; Metal Nanoparticles/*chemistry ; *Models, Biological ; Peristalsis/*physiology ; Pressure ; Reproducibility of Results ; Silver/*chemistry ; }, abstract = {The present speculative investigation is concentrated to analyze the entropy generation and heat transfer phenomena in ciliary induced peristalsis of blood with the suspension of hybrid nanoparticles in a tube with heat source impact. The blood is assumed to contain copper (Cu) and silver (Ag) nanoparticles (NPs). The ciliary inner wall of the tube has been considered with small hair-like structures. The Phan-Thien-Tanner (PTT) fluid model is employed to describe the non-Newtonian rheological characteristics of blood. The conservative equations are normalized and simplified by utilizing scaling analysis with the assumption of low Reynolds number and large wavelength approximations. The analytical inspection exposes that the total entropy generation gets a decrement for mounting values of cilia length, while reversed impact is detected for an increment in heat source parameter. Hybrid nano-blood exhibits a greater total entropy number than mono nano-blood. This research study may be beneficial to medical experts and researchers in the field of embryology. Cysts in the ciliated fallopian tube, where embryos develop, are removed by using nanoparticles (nano-drug delivery).}, }
@article {pmid34442509, year = {2021}, author = {Parveen, N and Awais, M and Awan, SE and Khan, WU and He, Y and Malik, MY}, title = {Entropy Generation Analysis and Radiated Heat Transfer in MHD (Al2O3-Cu/Water) Hybrid Nanofluid Flow.}, journal = {Micromachines}, volume = {12}, number = {8}, pages = {}, pmid = {34442509}, issn = {2072-666X}, abstract = {This research concerns the heat transfer and entropy generation analysis in the MHD axisymmetric flow of Al2O3-Cu/H2O hybrid nanofluid. The magnetic induction effect is considered for large magnetic Reynolds number. The influences of thermal radiations, viscous dissipation and convective temperature conditions over flow are studied. The problem is modeled using boundary layer theory, Maxwell's equations and Fourier's conduction law along with defined physical factors. Similarity transformations are utilized for model simplification which is analytically solved with the homotopy analysis method. The h-curves up to 20th order for solutions establishes the stability and convergence of the adopted computational method. Rheological impacts of involved parameters on flow variables and entropy generation number are demonstrated via graphs and tables. The study reveals that entropy in system of hybrid nanofluid affected by magnetic induction declines for β while it enhances for Bi, R and λ. Moreover, heat transfer rate elevates for large Bi with convective conditions at surface.}, }
@article {pmid34441209, year = {2021}, author = {Ahammad, NA and Badruddin, IA and Kamangar, S and Khaleed, HMT and Saleel, CA and Mahlia, TMI}, title = {Heat Transfer and Entropy in a Vertical Porous Plate Subjected to Suction Velocity and MHD.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {8}, pages = {}, pmid = {34441209}, issn = {1099-4300}, support = {RGP.1/327/42//Deanship of Scientific Research at King Khalid University/ ; }, abstract = {This article presents an investigation of heat transfer in a porous medium adjacent to a vertical plate. The porous medium is subjected to a magnetohydrodynamic effect and suction velocity. The governing equations are nondepersonalized and converted into ordinary differential equations. The resulting equations are solved with the help of the finite difference method. The impact of various parameters, such as the Prandtl number, Grashof number, permeability parameter, radiation parameter, Eckert number, viscous dissipation parameter, and magnetic parameter, on fluid flow characteristics inside the porous medium is discussed. Entropy generation in the medium is analyzed with respect to various parameters, including the Brinkman number and Reynolds number. It is noted that the velocity profile decreases in magnitude with respect to the Prandtl number, but increases with the radiation parameter. The Eckert number has a marginal effect on the velocity profile. An increased radiation effect leads to a reduced thermal gradient at the hot surface.}, }
@article {pmid34432464, year = {2021}, author = {Gu, R and Lehn, JM}, title = {Constitutional Dynamic Selection at Low Reynolds Number in a Triple Dynamic System: Covalent Dynamic Adaptation Driven by Double Supramolecular Self-Assembly.}, journal = {Journal of the American Chemical Society}, volume = {143}, number = {35}, pages = {14136-14146}, doi = {10.1021/jacs.1c04446}, pmid = {34432464}, issn = {1520-5126}, abstract = {A triple dynamic complex system has been designed, implementing a dynamic covalent process coupled to two supramolecular self-assembly steps. To this end, two dynamic covalent libraries (DCLs), DCL-1 and DCL-2, have been established on the basis of dynamic covalent C═C/C═N organo-metathesis between two Knoevenagel derivatives and two imines. Each DCL contains a barbituric acid-based Knoevenagel constituent that may undergo a sequential double self-organization process involving first the formation of hydrogen-bonded hexameric supramolecular macrocycles that subsequently undergo stacking to generate a supramolecular polymer SP yielding a viscous gel state. Both DCLs display selective self-organization-driven amplification of the constituent that leads to the SP. Dissociation of the SP on heating causes reversible randomization of the constituent distributions of the DCLs as a function of temperature. Furthermore, diverse distribution patterns of DCL-2 were induced by modulation of temperature and solvent composition. The present dynamic systems display remarkable self-organization-driven constitutional adaption and tunable composition by coupling between dynamic covalent component selection and two-stage supramolecular organization. In more general terms, they reveal dynamic adaptation by component selection in low Reynolds number conditions of living systems where frictional effects dominate inertial behavior.}, }
@article {pmid34410363, year = {2021}, author = {Herrera-Amaya, A and Seber, EK and Murphy, DW and Patry, WL and Knowles, TS and Bubel, MM and Maas, AE and Byron, ML}, title = {Spatiotemporal Asymmetry in Metachronal Rowing at Intermediate Reynolds Numbers.}, journal = {Integrative and comparative biology}, volume = {61}, number = {5}, pages = {1579-1593}, doi = {10.1093/icb/icab179}, pmid = {34410363}, issn = {1557-7023}, mesh = {Animals ; Biomechanical Phenomena ; Body Size ; *Extremities ; Models, Theoretical ; *Swimming ; }, abstract = {In drag-based swimming, individual propulsors operating at low Reynolds numbers (where viscous forces dominate over inertial forces) must execute a spatially asymmetric stroke to produce net fluid displacement. Temporal asymmetry (that is, differing duration between the power vs. recovery stroke) does not affect the overall generated thrust in this time-reversible regime. Metachronal rowing, in which multiple appendages beat sequentially, is used by a wide variety of organisms from low to intermediate Reynolds numbers. At the upper end of this range, inertia becomes important, and increasing temporal asymmetry can be an effective way to increase thrust. However, the combined effects of spatial and temporal asymmetry are not fully understood in the context of metachronal rowing. To explore the role of spatiotemporal asymmetry in metachronal rowing, we combine laboratory experiments and reduced-order analytical modeling. We measure beat kinematics and generated flows in two species of lobate ctenophores across a range of body sizes, from 7 to 40 mm in length. We observe characteristically different flows in ctenophores of differing body size and Reynolds number, and a general decrease in spatial asymmetry and increase in temporal asymmetry with increasing Reynolds number. We also construct a one-dimensional mathematical model consisting of a row of oscillating flat plates whose flow-normal areas change with time, and use it to explore the propulsive forces generated across a range of Reynolds numbers and kinematic parameters. The model results show that while both types of asymmetry increase force production, they have different effects in different regions of the parameter space. These results may have strong biological implications, as temporal asymmetry can be actively controlled while spatial asymmetry is likely to be partially or entirely driven by passive fluid-structure interaction.}, }
@article {pmid34391375, year = {2022}, author = {Pattnaik, PK and Abbas, MA and Mishra, S and Khan, SU and Bhatti, MM}, title = {Free Convective Flow of Hamilton-Crosser Model Gold-water Nanofluid Through a Channel with Permeable Moving Walls.}, journal = {Combinatorial chemistry &amp; high throughput screening}, volume = {25}, number = {7}, pages = {1103-1114}, doi = {10.2174/1386207324666210813112323}, pmid = {34391375}, issn = {1875-5402}, mesh = {Computer Simulation ; Gold ; Hot Temperature ; *Metal Nanoparticles ; *Water ; }, abstract = {BACKGROUND: The present manuscript analyzes the influence of buoyant forces of a conducting time-dependent nanofluid flow through porous moving walls. The medium is also filled with porous materials. In addition to that, uniform heat source and absorption parameters are considered that affect the nanofluid model.<br><br>INTRODUCTION: The model is based on the thermophysical properties of Hamilton-Crosser's nanofluid model, in which a gold nanoparticle is submerged into the base fluid water. Before simulation is obtained by a numerical method, suitable transformation is used to convert nonlinear coupled PDEs to ODEs.<br><br>METHOD: Runge-Kutta's fourth-order scheme is applied successfully for the first-order ODEs in conjunction with the shooting technique.<br><br>RESULT: Computations for the coefficients of rate constants are presented through graphs, along with the behavior of several physical parameters augmented by the flow phenomena.<br><br>CONCLUSION: The present investigation may be compatible with the applications of biotechnology. It is seen that the inclusion of volume concentration and the fluid velocity enhances near the middle layer of the channel and retards near the permeable walls. Also, augmented values of the Reynolds number and both cooling and heating of the wall increase the rate of shear stress.}, }
@article {pmid34384065, year = {2021}, author = {Luo, Y and Wright, M and Xiao, Q and Yue, H and Pan, G}, title = {Fluid-structure interaction analysis on motion control of a self-propelled flexible plate near a rigid body utilizing PD control.}, journal = {Bioinspiration &amp; biomimetics}, volume = {16}, number = {6}, pages = {}, doi = {10.1088/1748-3190/ac1cee}, pmid = {34384065}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Fishes ; *Models, Biological ; Motion ; *Swimming ; }, abstract = {Inspired by a previous experimental study of fish swimming near a cylinder, we numerically investigate the swimming and station-holding behavior of a flexible plate ahead of a circular cylinder whose motion is controlled by a proportional-derivative (PD) controller. Specifically, the deformation of this two-dimensional plate is actuated by a periodically varying external force applied on the body surface, which mimics the fish muscle force to produce propulsive thrust. The actuation force amplitude is dynamically adjusted by a feedback controller to instruct the plate to swim the desired distance from an initial position to a target location and then hold the station there. Instead of directly using the instantaneous position signal, an average speed measured over one force actuation period is proposed with the inclusion of instantaneous position information to form the tracking error for the PD control. Our results show that the motion control of swimming and station holding has been achieved by this simple but effective feedback control without large overshoot when approaching the target at different flow conditions and actuation force formulas. Although the swimming distance remains the same, a plate whose initial position is closer to the cylinder requires less energy expenditure to swim to the target location and hold the station there. This is because the low-pressure zone near the trailing edge of the plate is reduced in size, which provides drag reduction, contributing to reduced swimming energy. A higher Reynolds number also leads to energy savings. Under the same control strategy, the swimming performance is more affected by the force-frequency while the phase shift of the actuation force has a less significant impact.}, }
@article {pmid34381068, year = {2021}, author = {Lin, P and Liu, X and Xiong, N and Wang, X and Shang, M and Liu, G and Tao, Y}, title = {Numerical study on the influence of wall temperature gradient on aerodynamic characteristics of low aspect ratio flying wing configuration.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {16295}, pmid = {34381068}, issn = {2045-2322}, abstract = {With the aim for a low-aspect-ratio flying wing configuration, this study explores the influence of wall temperature gradient on the laminar and turbulent boundary layers of aircraft surface and determines the effect on the transition Reynolds number and wall friction drag. A four-equation turbulence model with transition mode is used to numerically simulate the flow around the model. The variation of wall friction coefficient, transition Reynolds number, and turbulent boundary layer flow with wall temperature are emphatically investigated. Results show that when the wall temperature increases from 288 to 500 K, the boundary layer transition Reynolds number for the wing section increased by approximately 28% and the surface friction drags decreases by approximately 10.7%. The hot wall enhances the viscous effects of the laminar temperature boundary layer, reduces the Reynolds shear stress and turbulent kinetic energy, and increases the flow stability. However, the velocity gradient and shear stress in the bottom of the turbulent boundary layer decreases, which leads to reduced friction shear stress on the wall surface. Therefore, for the low-aspect-ratio flying wing model, the hot wall can delay the boundary layer transition and reduce the friction drag coefficient in the turbulent region.}, }
@article {pmid34373556, year = {2021}, author = {Xia, WF and Hafeez, MU and Khan, MI and Shah, NA and Chung, JD}, title = {Entropy optimized dissipative flow of hybrid nanofluid in the presence of non-linear thermal radiation and Joule heating.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {16067}, pmid = {34373556}, issn = {2045-2322}, abstract = {Present article reads three dimensional flow analysis of incompressible viscous hybrid nanofluid in a rotating frame. Ethylene glycol is used as a base liquid while nanoparticles are of copper and silver. Fluid is bounded between two parallel surfaces in which the lower surface stretches linearly. Fluid is conducting hence uniform magnetic field is applied. Effects of non-linear thermal radiation, Joule heating and viscous dissipation are entertained. Interesting quantities namely surface drag force and Nusselt number are discussed. Rate of entropy generation is examined. Bvp4c numerical scheme is used for the solution of transformed O.D.Es. Results regarding various flow parameters are obtained via bvp4c technique in MATLAB Software version 2019, and displayed through different plots. Our obtained results presents that velocity field decreases with respect to higher values of magnetic parameter, Reynolds number and rotation parameter. It is also observed that the temperature field boots subject to radiation parameter. Results are compared with Ishak et al. (Nonlinear Anal R World Appl 10:2909-2913, 2009) and found very good agreement with them. This agreement shows that the results are 99.99% match with each other.}, }
@article {pmid34373493, year = {2021}, author = {Alihosseini, Y and Azaddel, MR and Moslemi, S and Mohammadi, M and Pormohammad, A and Targhi, MZ and Heyhat, MM}, title = {Effect of liquid cooling on PCR performance with the parametric study of cross-section shapes of microchannels.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {16072}, pmid = {34373493}, issn = {2045-2322}, abstract = {In recent years, PCR-based methods as a rapid and high accurate technique in the industry and medical fields have been expanded rapidly. Where we are faced with the COVID-19 pandemic, the necessity of a rapid diagnosis has felt more than ever. In the current interdisciplinary study, we have proposed, developed, and characterized a state-of-the-art liquid cooling design to accelerate the PCR procedure. A numerical simulation approach is utilized to evaluate 15 different cross-sections of the microchannel heat sink and select the best shape to achieve this goal. Also, crucial heat sink parameters are characterized, e.g., heat transfer coefficient, pressure drop, performance evaluation criteria, and fluid flow. The achieved result showed that the circular cross-section is the most efficient shape for the microchannel heat sink, which has a maximum heat transfer enhancement of 25% compared to the square shape at the Reynolds number of 1150. In the next phase of the study, the circular cross-section microchannel is located below the PCR device to evaluate the cooling rate of the PCR. Also, the results demonstrate that it takes 16.5 s to cool saliva samples in the PCR well, which saves up to 157.5 s for the whole amplification procedure compared to the conventional air fans. Another advantage of using the microchannel heat sink is that it takes up a little space compared to other common cooling methods.}, }
@article {pmid34372345, year = {2021}, author = {Costantini, M and Henne, U and Klein, C and Miozzi, M}, title = {Skin-Friction-Based Identification of the Critical Lines in a Transonic, High Reynolds Number Flow via Temperature-Sensitive Paint.}, journal = {Sensors (Basel, Switzerland)}, volume = {21}, number = {15}, pages = {}, pmid = {34372345}, issn = {1424-8220}, abstract = {In this contribution, three methodologies based on temperature-sensitive paint (TSP) data were further developed and applied for the optical determination of the critical locations of flow separation and reattachment in compressible, high Reynolds number flows. The methodologies rely on skin-friction extraction approaches developed for low-speed flows, which were adapted in this work to study flow separation and reattachment in the presence of shock-wave/boundary-layer interaction. In a first approach, skin-friction topological maps were obtained from time-averaged surface temperature distributions, thus enabling the identification of the critical lines as converging and diverging skin-friction lines. In the other two approaches, the critical lines were identified from the maps of the propagation celerity of temperature perturbations, which were determined from time-resolved TSP data. The experiments were conducted at a freestream Mach number of 0.72 and a chord Reynolds number of 9.7 million in the Transonic Wind Tunnel Göttingen on a VA-2 supercritical airfoil model, which was equipped with two exchangeable TSP modules specifically designed for transonic, high Reynolds number tests. The separation and reattachment lines identified via the three different TSP-based approaches were shown to be in mutual agreement, and were also found to be in agreement with reference experimental and numerical data.}, }
@article {pmid34359055, year = {2021}, author = {Diaz, K and Robinson, TL and Aydin, YO and Aydin, E and Goldman, DI and Wan, KY}, title = {A minimal robophysical model of quadriflagellate self-propulsion.}, journal = {Bioinspiration &amp; biomimetics}, volume = {16}, number = {6}, pages = {}, doi = {10.1088/1748-3190/ac1b6e}, pmid = {34359055}, issn = {1748-3190}, mesh = {Flagella ; Gait ; Locomotion ; *Robotics ; *Swimming ; }, abstract = {Locomotion at the microscale is remarkably sophisticated. Microorganisms have evolved diverse strategies to move within highly viscous environments, using deformable, propulsion-generating appendages such as cilia and flagella to drive helical or undulatory motion. In single-celled algae, these appendages can be arranged in different ways around an approximately 10 μm long cell body, and coordinated in distinct temporal patterns. Inspired by the observation that some quadriflagellates (bearing four flagella) have an outwardly similar morphology and flagellar beat pattern, yet swim at different speeds, this study seeks to determine whether variations in swimming performance could arise solely from differences in swimming gait. Robotics approaches are particularly suited to such investigations, where the phase relationships between appendages can be readily manipulated. Here, we developed autonomous, algae-inspired robophysical models that can self-propel in a viscous fluid. These macroscopic robots (length and width = 8.5 cm, height = 2 cm) have four independently actuated 'flagella' (length = 13 cm) that oscillate under low-Reynolds number conditions (Re∼O(10-1)). We tested the swimming performance of these robot models with appendages arranged two distinct configurations, and coordinated in three distinct gaits. The gaits, namely the pronk, the trot, and the gallop, correspond to gaits adopted by distinct microalgal species. When the appendages are inserted perpendicularly around a central 'body', the robot achieved a net performance of 0.15-0.63 body lengths per cycle, with the trot gait being the fastest. Robotic swimming performance was found to be comparable to that of the algal microswimmers across all gaits. By creating a minimal robot that can successfully reproduce cilia-inspired drag-based swimming, our work paves the way for the design of next-generation devices that have the capacity to autonomously navigate aqueous environments.}, }
@article {pmid34357216, year = {2021}, author = {Li, L and Chen, Q and Sui, G and Qian, J and Tsai, CT and Cheng, X and Jing, W}, title = {A Three-Dimensional Micromixer Using Oblique Embedded Ridges.}, journal = {Micromachines}, volume = {12}, number = {7}, pages = {}, pmid = {34357216}, issn = {2072-666X}, abstract = {A micromixer is one of the most significant components in a microfluidic system. A three-dimensional micromixer was developed with advantages of high efficiency, simple fabrication, easy integration, and ease of mass production. The designed principle is based on the concepts of splitting-recombination and chaotic advection. A numerical model of this micromixer was established to characterize the mixing performance for different parameters. A critical Reynolds number (Re) was obtained from the simulation results. When the Re number is smaller than the critical value, the fluid mixing is mainly dependent on the mechanism of splitting-recombination, therefore, the length of the channel capable of complete mixing (complete mixing length) increases as the Re number increases. When the Re number is larger than the critical value, the fluid mixing is dominated by chaotic advection, and the complete mixing length decreases as the Re number increases. For normal fluids, a complete mixing length of 500 µm can be achieved at a very small Re number of 0.007 and increases to 2400 µm as the Re number increases to the critical value of 4.7. As the Re number keep increasing and passes the critical Re number, the complete mixing length continues to descend to 650 µm at the Re number of 66.7. For hard-to-mix fluids (generally referring to fluids with high viscosity and low diffusion coefficient, which are difficult to mix), even though no evidence of strong chaotic advection is presented in the simulation, the micromixer can still achieve a complete mixing length of 2550 µm. The mixing performance of the micromixer was also verified by experiments. The experimental results showed a consistent trend with the numerical simulation results, which both climb upward when the Re number is around 0.007 (flow rate of 0.03 μm/min) to around 10 (flow rate of 50 μm/min), then descend when the Re number is around 13.3 (flow rate of 60 µm/min).}, }
@article {pmid34357184, year = {2021}, author = {Nichka, VS and Nikonenko, VV and Bazinet, L}, title = {Fouling Mitigation by Optimizing Flow Rate and Pulsed Electric Field during Bipolar Membrane Electroacidification of Caseinate Solution.}, journal = {Membranes}, volume = {11}, number = {7}, pages = {}, pmid = {34357184}, issn = {2077-0375}, support = {19-38-90256//Russian Foundation for Basic Research/ ; 210829409//Natural Sciences and Engineering Research Council of Canada/ ; }, abstract = {The efficiency of separation processes using ion exchange membranes (IEMs), especially in the food industry, is significantly limited by the fouling phenomenon, which is the process of the attachment and growth of certain species on the surface and inside the membrane. Pulsed electric field (PEF) mode, which consists in the application of constant current density pulses during a fixed time (Ton) alternated with pause lapses (Toff), has a positive antifouling impact. The aim of this study was to investigate the combined effect of three different relatively high flow rates of feed solution (corresponding to Reynolds numbers of 187, 374 and 560) and various pulse-pause ratios of PEF current regime on protein fouling kinetics during electrodialysis with bipolar membranes (EDBM) of a model caseinate solution. Four different pulse/pause regimes (with Ton/Toff ratios equal to 10 s/10 s, 10 s/20 s, 10 s/33 s and 10 s/50 s) during electrodialysis (ED) treatment were evaluated at a current density of 5 mA/cm[2]. It was found that increasing the pause duration and caseinate solution flow rate had a positive impact on the minimization of protein fouling occurring on the cationic surface of the bipolar membrane (BPM) during the EDBM. Both a long pause and high flow rate contribute to a more effective decrease in the concentration of protons and caseinate anions at the BPM surface: a very good membrane performance was achieved with 50 s of pause duration of PEF and a flow rate corresponding to Re = 374. A further increase in PEF pause duration (above 50 s) or flow rate (above Re = 374) did not lead to a significant decrease in the amount of fouling.}, }
@article {pmid34349343, year = {2021}, author = {Ferroni, C and Bracconi, M and Ambrosetti, M and Maestri, M and Groppi, G and Tronconi, E}, title = {A Fundamental Investigation of Gas/Solid Heat and Mass Transfer in Structured Catalysts Based on Periodic Open Cellular Structures (POCS).}, journal = {Industrial &amp; engineering chemistry research}, volume = {60}, number = {29}, pages = {10522-10538}, pmid = {34349343}, issn = {0888-5885}, abstract = {In this work, we investigate the gas-solid heat and mass transfer in catalytically activated periodic open cellular structures, which are considered a promising solution for intensification of catalytic processes limited by external transport, aiming at the derivation of suitable correlations. Computational fluid dynamics is employed to investigate the Tetrakaidekahedral and Diamond lattice structures. The influence of the morphological features and flow conditions on the external transport properties is assessed. The strut diameter is an adequate characteristic length for the formulation of heat and mass transfer correlations; accordingly, a power-law dependence of the Sherwood number to the Reynolds number between 0.33 and 0.67 was found according to the flow regimes in the range 1-128 of the Reynolds number. An additional -1.5-order dependence on the porosity is found. The formulated correlations are in good agreement with the simulation results and allow for the accurate evaluation of the external transfer coefficients for POCS.}, }
@article {pmid34335006, year = {2021}, author = {Liu, K and Allahyari, M and Salinas, J and Zgheib, N and Balachandar, S}, title = {Investigation of theoretical scaling laws using large eddy simulations for airborne spreading of viral contagion from sneezing and coughing.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {33}, number = {6}, pages = {063318}, pmid = {34335006}, issn = {1070-6631}, abstract = {Using a set of large eddy point-particle simulations, we explore the fluid dynamics of an ejected puff resulting from a cough/sneeze. The ejection contains over 61 000 potentially virus-laden droplets at an injection Reynolds number of about 46 000, comparable to an actual cough/sneeze. We observe that global puff properties, such as centroid, puff volume, momentum, and buoyancy vary little across realizations. Other properties, such as maximum extent, shape, and edge velocity of the puff, may exhibit substantial variation. In many realizations, a portion of the puff splits off and advances along a random direction, while keeping airborne droplet nuclei afloat. This peeled-off portion provides a mechanism for virus-laden droplets to travel over large distances in a short amount of time. We also observe that the vast majority of droplets remain suspended within the puff after all liquid has evaporated. The main objectives of the study are to (i) evaluate assumptions of Balachandar's et al. theory [Int. J. Multiphase Flow 132, 103439 (2020)], which include buoyancy effects, shape of the puff, and droplet evaporation rate, (ii) obtain values of closure parameters, which include location and time of the virtual origin, and puff entrainment and drag coefficients, and (iii) evaluate the accuracy of the theory in predicting the shape, size, and location of the puff, as well as droplet number density long after ejection. The theory adequately predicts global puff properties including size, velocity, and distance traveled, the largest size of droplets that exit the puff due to settling, and the droplet size distribution within the puff long after ejection.}, }
@article {pmid34319753, year = {2021}, author = {Singh, RK and Mahato, LK and Mandal, DK}, title = {Airflow-Assisted Impact of Drops of Various Viscosities: The Role of Viscous Dissipation, Normal Imposed Pressure, and Shear Flow of Air.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {37}, number = {31}, pages = {9504-9517}, doi = {10.1021/acs.langmuir.1c01367}, pmid = {34319753}, issn = {1520-5827}, abstract = {The role of liquid viscosity on the spreading for an airflow-assisted impact of drops on a surface is investigated. The spreading diameter is found to increase with the Reynolds number of the airflow (Reair) for a given viscosity and impact Weber number (We) compared to the still air. The increment is higher at a low We for viscous drops, whereas the effect of Reair dominates at the intermediate We as the viscosity decreases. Two extra forces, the normal imposed pressure and shear force of air, act on the drop and influence the spreading along with the viscous dissipation. The drop's curvature decreases depending on the viscosity and impact velocity while spreading. Large-scale eddies near the drop-surface region are observed due to the separation of the incident airflow. The formation of eddies signifies low-pressure zones, which extract the trapped air, causing the spreading diameter of the viscous drop to increase at a low We. With the increase in the We, the lamella thickness of low-viscosity drops decreases and is pushed out by the air shear causing the spreading factor to increase. The boundary layer thickness is estimated using the energy balance method to predict the maximum spreading factor. The prediction compares well with the experimental one for higher viscosities. The accuracy improves when the effect of low pressure is incorporated. To confirm, the experimental spreading is compared with that obtained from three existing models, and one, which considers the influence, is observed to provide a better prediction.}, }
@article {pmid34297252, year = {2021}, author = {Sharifi, A and Gendernalik, A and Garrity, D and Bark, D}, title = {Valveless pumping behavior of the simulated embryonic heart tube as a function of contractile patterns and myocardial stiffness.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {20}, number = {5}, pages = {2001-2012}, pmid = {34297252}, issn = {1617-7940}, mesh = {Animals ; Biomechanical Phenomena ; Cardiac Output ; Computer Simulation ; Electric Impedance ; Heart/*embryology/*physiology ; Heart Rate ; *Hemodynamics ; Models, Cardiovascular ; Models, Theoretical ; *Myocardial Contraction ; Myocardium/*pathology ; Peristalsis ; Pressure ; Stress, Mechanical ; Zebrafish/*embryology ; }, abstract = {During development, the heart begins pumping as a valveless multilayered tube capable of driving blood flow throughout the embryonic vasculature. The mechanical properties and how they interface with pumping function are not well-defined at this stage. Here, we evaluate pumping patterns using a fluid-structure interaction computational model, combined with experimental data and an energetic analysis to investigate myocardial mechanical properties. Through this work, we propose that a myocardium modeled as a Neo-Hookean material with a material constant on the order of 10 kPa is necessary for the heart tube to function with an optimal pressure and cardiac output.}, }
@article {pmid34293964, year = {2021}, author = {Akram, S and Athar, M and Saeed, K and Razia, A}, title = {Crossbreed impact of double-diffusivity convection on peristaltic pumping of magneto Sisko nanofluids in non-uniform inclined channel: A bio-nanoengineering model.}, journal = {Science progress}, volume = {104}, number = {3}, pages = {368504211033677}, pmid = {34293964}, issn = {2047-7163}, abstract = {The consequences of double-diffusivity convection on the peristaltic transport of Sisko nanofluids in the non-uniform inclined channel and induced magnetic field are discussed in this article. The mathematical modeling of Sisko nanofluids with induced magnetic field and double-diffusivity convection is given. To simplify PDEs that are highly nonlinear in nature, the low but finite Reynolds number, and long wavelength estimation are used. The Numerical solution is calculated for the non-linear PDEs. The exact solution of concentration, temperature and nanoparticle are obtained. The effect of various physical parameters of flow quantities is shown in numerical and graphical data. The outcomes show that as the thermophoresis and Dufour parameters are raised, the profiles of temperature, concentration, and nanoparticle fraction all significantly increase.}, }
@article {pmid34286832, year = {2021}, author = {Kasoju, VT and Moen, DS and Ford, MP and Ngo, TT and Santhanakrishnan, A}, title = {Interspecific variation in bristle number on forewings of tiny insects does not influence clap-and-fling aerodynamics.}, journal = {The Journal of experimental biology}, volume = {224}, number = {18}, pages = {}, doi = {10.1242/jeb.239798}, pmid = {34286832}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; *Flight, Animal ; Insecta ; Models, Biological ; Phylogeny ; *Wings, Animal ; }, abstract = {Miniature insects must overcome significant viscous resistance in order to fly. They typically possess wings with long bristles on the fringes and use a clap-and-fling mechanism to augment lift. These unique solutions to the extreme conditions of flight at tiny sizes (<2 mm body length) suggest that natural selection has optimized wing design for better aerodynamic performance. However, species vary in wingspan, number of bristles (n) and bristle gap (G) to diameter (D) ratio (G/D). How this variation relates to body length (BL) and its effects on aerodynamics remain unknown. We measured forewing images of 38 species of thrips and 21 species of fairyflies. Our phylogenetic comparative analyses showed that n and wingspan scaled positively and similarly with BL across both groups, whereas G/D decreased with BL, with a sharper decline in thrips. We next measured aerodynamic forces and visualized flow on physical models of bristled wings performing clap-and-fling kinematics at a chord-based Reynolds number of 10 using a dynamically scaled robotic platform. We examined the effects of dimensional (G, D, wingspan) and non-dimensional (n, G/D) geometric variables on dimensionless lift and drag. We found that: (1) increasing G reduced drag more than decreasing D; (2) changing n had minimal impact on lift generation; and (3) varying G/D minimally affected aerodynamic forces. These aerodynamic results suggest little pressure to functionally optimize n and G/D. Combined with the scaling relationships between wing variables and BL, much wing variation in tiny flying insects might be best explained by underlying shared growth factors.}, }
@article {pmid34283850, year = {2021}, author = {Dvoriashyna, M and Lauga, E}, title = {Hydrodynamics and direction change of tumbling bacteria.}, journal = {PloS one}, volume = {16}, number = {7}, pages = {e0254551}, pmid = {34283850}, issn = {1932-6203}, mesh = {Biomechanical Phenomena ; Escherichia coli/chemistry/*physiology ; Flagella/*physiology ; *Hydrodynamics ; Models, Biological ; Movement/*physiology ; Rotation ; Swimming/physiology ; }, abstract = {The bacterium Escherichia coli (E. coli) swims in viscous fluids by rotating several helical flagellar filaments, which are gathered in a bundle behind the cell during 'runs' wherein the cell moves steadily forward. In between runs, the cell undergoes quick 'tumble' events, during which at least one flagellum reverses its rotation direction and separates from the bundle, resulting in erratic motion in place and a random reorientation of the cell. Alternating between runs and tumbles allows cells to sample space by stochastically changing their propulsion direction after each tumble. The change of direction during a tumble is not uniformly distributed but is skewed towards smaller angles with an average of about 62°-68°, as first measured by Berg and Brown (1972). Here we develop a theoretical approach to model the angular distribution of swimming E. coli cells during tumbles. We first use past experimental imaging results to construct a kinematic description of the dynamics of the flagellar filaments during a tumble. We then employ low-Reynolds number hydrodynamics to compute the consequences of the kinematic model on the force and torque balance of the cell and to deduce the overall change in orientation. The results of our model are in good agreement with experimental observations. We find that the main change of direction occurs during the 'bundling' part of the process wherein, at the end of a tumble, the dispersed flagellar filaments are brought back together in the helical bundle, which we confirm using a simplified forced-sphere model.}, }
@article {pmid34282226, year = {2021}, author = {Ishak, MS and Alsabery, AI and Hashim, I and Chamkha, AJ}, title = {Entropy production and mixed convection within trapezoidal cavity having nanofluids and localised solid cylinder.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {14700}, pmid = {34282226}, issn = {2045-2322}, support = {FRGS/1/2019/STG06/UKM/01/2//Malaysian Ministry of Education/ ; FRGS/1/2019/STG06/UKM/01/2//Malaysian Ministry of Education/ ; }, abstract = {The entropy production and mixed convection within a trapezoidal nanofluid-filled cavity having a localised solid cylinder is numerically examined using the finite element technique. The top horizontal surface moving at a uniform velocity is kept at a cold temperature, while the bottom horizontal surface is thermally activated. The remaining surfaces are maintained adiabatic. Water-based nanofluids ([Formula: see text] nanoparticles) are used in this study, and the Boussinesq approximation applies. The influence of the Reynolds number, Richardson number, nanoparticles volume fraction, dimensionless radius and location of the solid cylinder on the streamlines, isotherms and isentropic are examined. The results show that the solid cylinder's size and location are significant control parameters for optimising the heat transfer and the Bejan number inside the trapezoidal cavity. Furthermore, the maximum average Nusselt numbers are obtained for high R values, where the average Nusselt number is increased by 30% when R is raised from 0 to 0.25.}, }
@article {pmid34275183, year = {2021}, author = {Gurovich, AN and Rodriguez, L and Morales-Acuna, F}, title = {There are no differences in brachial artery endothelial shear stress and blood flow patterns between males and females during exercise.}, journal = {Clinical physiology and functional imaging}, volume = {41}, number = {6}, pages = {471-479}, doi = {10.1111/cpf.12722}, pmid = {34275183}, issn = {1475-097X}, mesh = {*Brachial Artery/diagnostic imaging ; Cross-Sectional Studies ; *Endothelium, Vascular ; Exercise ; Female ; Hemodynamics ; Humans ; Male ; Regional Blood Flow ; Vasodilation ; }, abstract = {Premenopausal females have a lower cardiovascular risk than males. Sex differences on exercise-induced endothelial shear stress (ESS) and blood flow patterns may explain part of this risk reduction. The purpose of this cross-sectional study was to determine the differences in brachial artery exercise-induced ESS and blood flow patterns between males and females. Thirty subjects (13 females) were recruited to perform a three-workload steady-state exercise test based on blood lactate levels (i.e. <2.0, 2.0-4.0, >4.0 mmol/l). ESS and blood flow patterns were estimated at rest and during each workload using Womersley's approximation and Reynolds number, respectively. Both males and females showed an exercise intensity-dependent increase in antegrade and retrograde ESS. There was no significant sex effect or interaction for antegrade ESS (F(1, 30) = 0.715, p = 0.405 and F(1·672, 60) = 1.511, p = 0.232, respectively) or retrograde ESS (F(1, 30) = 0.794, p = 0.380 and F(1·810, 60) = 1.022, p = 0.361, respectively). Additionally, antegrade blood flow was turbulent during all bouts of exercise while retrograde blood flow became disturbed at moderate and high exercise intensities in both groups. There are no differences in exercise-induced ESS and blood flow patterns between males and females when the exercise load is equivalent. This suggests that the vascular benefits of exercise training are similar in both sexes from a haemodynamic standpoint.}, }
@article {pmid34272432, year = {2021}, author = {Gul, H and Ramzan, M and Chung, JD and Chu, YM and Kadry, S}, title = {Multiple slips impact in the MHD hybrid nanofluid flow with Cattaneo-Christov heat flux and autocatalytic chemical reaction.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {14625}, pmid = {34272432}, issn = {2045-2322}, support = {20202020900060//Korea Institute of Energy Technology Evaluation and Planning/ ; }, abstract = {The present study deliberates the nanofluid flow containing multi and single-walled carbon nanotubes submerged into Ethylene glycol in a Darcy-Forchheimer permeable media over a stretching cylinder with multiple slips. The innovation of the envisaged mathematical model is enriched by considering the impacts of non-uniform source/sink and modified Fourier law in the energy equation and autocatalytic chemical reaction in the concentration equation. Entropy optimization analysis of the mathematical model is also performed in the present problem. Pertinent transformations procedure is implemented for the conversion of the non-linear system to the ordinary differential equations. The succor of the Shooting technique combined with the bvp4c MATLAB software is utilized for the solution of a highly nonlinear system of equations. The impacts of the leading parameters versus engaged fields are inspected through graphical sketches. The outcomes show that a strong magnetic field strengthens the temperature profile and decays the velocity profile. Also, the fluid velocity is lessened for growing estimates of the parameter of slip. Additionally, it is detected that entropy number augmented for higher thermal relaxation parameter and Reynolds number. To substantiate the existing mathematical model, a comparison table is also added. An excellent correlation is achieved here.}, }
@article {pmid34272408, year = {2021}, author = {Wang, H and Enders, A and Preuss, JA and Bahnemann, J and Heisterkamp, A and Torres-Mapa, ML}, title = {3D printed microfluidic lab-on-a-chip device for fiber-based dual beam optical manipulation.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {14584}, pmid = {34272408}, issn = {2045-2322}, abstract = {3D printing of microfluidic lab-on-a-chip devices enables rapid prototyping of robust and complex structures. In this work, we designed and fabricated a 3D printed lab-on-a-chip device for fiber-based dual beam optical manipulation. The final 3D printed chip offers three key features, such as (1) an optimized fiber channel design for precise alignment of optical fibers, (2) an optically clear window to visualize the trapping region, and (3) a sample channel which facilitates hydrodynamic focusing of samples. A square zig-zag structure incorporated in the sample channel increases the number of particles at the trapping site and focuses the cells and particles during experiments when operating the chip at low Reynolds number. To evaluate the performance of the device for optical manipulation, we implemented on-chip, fiber-based optical trapping of different-sized microscopic particles and performed trap stiffness measurements. In addition, optical stretching of MCF-7 cells was successfully accomplished for the purpose of studying the effects of a cytochalasin metabolite, pyrichalasin H, on cell elasticity. We observed distinct changes in the deformability of single cells treated with pyrichalasin H compared to untreated cells. These results demonstrate that 3D printed microfluidic lab-on-a-chip devices offer a cost-effective and customizable platform for applications in optical manipulation.}, }
@article {pmid34271062, year = {2021}, author = {Dubey, A and B, V and Bég, OA and Gorla, RSR}, title = {Finite element computation of magneto-hemodynamic flow and heat transfer in a bifurcated artery with saccular aneurysm using the Carreau-Yasuda biorheological model.}, journal = {Microvascular research}, volume = {138}, number = {}, pages = {104221}, doi = {10.1016/j.mvr.2021.104221}, pmid = {34271062}, issn = {1095-9319}, mesh = {Aorta/*physiopathology ; Aortic Aneurysm/*physiopathology ; Blood Flow Velocity ; Computer Simulation ; Electric Conductivity ; Energy Transfer ; Finite Element Analysis ; *Hemorheology ; Hot Temperature ; Humans ; *Magnetic Fields ; *Models, Cardiovascular ; Pulsatile Flow ; Regional Blood Flow ; Stress, Mechanical ; Time Factors ; }, abstract = {"Existing computational fluid dynamics studies of blood flows have demonstrated that the lower wall stress and higher oscillatory shear index might be the cause of acceleration in atherogenesis of vascular walls in hemodynamics. To prevent the chances of aneurysm wall rupture in the saccular aneurysm at distal aortic bifurcation, clinical biomagnetic studies have shown that extra-corporeal magnetic fields can be deployed to regulate the blood flow. Motivated by these developments, in the current study a finite element computational fluid dynamics simulation has been conducted of unsteady two-dimensional non-Newtonian magneto-hemodynamic heat transfer in electrically conducting blood flow in a bifurcated artery featuring a saccular aneurysm. The fluid flow is assumed to be pulsatile, non-Newtonian and incompressible. The Carreau-Yasuda model is adopted for blood to mimic non-Newtonian characteristics. The transformed equations with appropriate boundary conditions are solved numerically by employing the finite element method with the variational approach in the FreeFEM++ code. Hydrodynamic and thermal characteristics are elucidated in detail for the effects of key non-dimensional parameters i.e. Reynolds number (Re = 14, 21, 100, 200), Prandtl number (Pr = 14, 21) and magnetic body force parameter (Hartmann number) (M = 0.6, 1.2, 1.5) at the aneurysm and throughout the arterial domain. The influence of vessel geometry on blood flow characteristics i.e. velocity, pressure and temperature fields are also visualized through instantaneous contour patterns. It is found that an increase in the magnetic parameter reduces the pressure but increases the skin-friction coefficient in the domain. The temperature decreases at the parent artery (inlet) and both the distant and prior artery with the increment in the Prandtl number. A higher Reynolds number also causes a reduction in velocity as well as in pressure. The blood flow shows different characteristic contours with time variation at the aneurysm as well as in the arterial segment. The novelty of the current research is therefore to present a combined approach amalgamating the Carreau-Yasuda model, heat transfer and magnetohydrodynamics with complex geometric features in realistic arterial hemodynamics with extensive visualization and interpretation, in order to generalize and extend previous studies. In previous studies these features have been considered separately and not simultaneously as in the current study. The present simulations reveal some novel features of biomagnetic hemodynamics in bifurcated arterial transport featuring a saccular aneurysm which are envisaged to be of relevance in furnishing improved characterization of the rheological biomagnetic hemodynamics of realistic aneurysmic bifurcations in clinical assessment, diagnosis and magnetic-assisted treatment of cardiovascular disease."}, }
@article {pmid34266946, year = {2021}, author = {Han, E and Zhu, L and Shaevitz, JW and Stone, HA}, title = {Low-Reynolds-number, biflagellated Quincke swimmers with multiple forms of motion.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {118}, number = {29}, pages = {}, pmid = {34266946}, issn = {1091-6490}, mesh = {Hydrodynamics ; Locomotion/*physiology ; *Models, Biological ; Motion ; Rheology ; Rotation ; }, abstract = {In the limit of zero Reynolds number (Re), swimmers propel themselves exploiting a series of nonreciprocal body motions. For an artificial swimmer, a proper selection of the power source is required to drive its motion, in cooperation with its geometric and mechanical properties. Although various external fields (magnetic, acoustic, optical, etc.) have been introduced, electric fields are rarely utilized to actuate such swimmers experimentally in unbounded space. Here we use uniform and static electric fields to demonstrate locomotion of a biflagellated sphere at low Re via Quincke rotation. These Quincke swimmers exhibit three different forms of motion, including a self-oscillatory state due to elastohydrodynamic-electrohydrodynamic interactions. Each form of motion follows a distinct trajectory in space. Our experiments and numerical results demonstrate a method to generate, and potentially control, the locomotion of artificial flagellated swimmers.}, }
@article {pmid34260387, year = {2021}, author = {Zhang, B and Leishangthem, P and Ding, Y and Xu, X}, title = {An effective and efficient model of the near-field hydrodynamic interactions for active suspensions of bacteria.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {118}, number = {28}, pages = {}, pmid = {34260387}, issn = {1091-6490}, mesh = {Computer Simulation ; Escherichia coli/*physiology ; *Hydrodynamics ; *Models, Biological ; Suspensions ; }, abstract = {Near-field hydrodynamic interactions in active fluids are essential to determine many important emergent behaviors observed, but have not been successfully modeled so far. In this work, we propose an effective model capturing the essence of the near-field hydrodynamic interactions through a tensorial coefficient of resistance, validated numerically by a pedagogic model system consisting of an Escherichia coli bacterium and a passive sphere. In a critical test case that studies the scattering angle of the bacterium-sphere pair dynamics, we prove that the near-field hydrodynamics can make a qualitative difference even for this simple two-body system: Calculations based on the proposed model reveal a region in parameter space where the bacterium is trapped by the passive sphere, a phenomenon that is regularly observed in experiments but cannot be explained by any existing model. In the end, we demonstrate that our model also leads to efficient simulation of active fluids with tens of thousands of bacteria, sufficiently large for investigations of many emergent behaviors.}, }
@article {pmid34251258, year = {2021}, author = {Charakopoulos, A and Karakasidis, T and Sarris, I}, title = {Analysis of magnetohydrodynamic channel flow through complex network analysis.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {31}, number = {4}, pages = {043123}, doi = {10.1063/5.0043817}, pmid = {34251258}, issn = {1089-7682}, abstract = {Velocity time series of hydrodynamic and magnetohydrodynamic (MHD) turbulent flow are analyzed by means of complex network analysis in order to understand the mechanism of fluid patterns modification due to the external magnetic field. Direct numerical simulations of two cases are used, one for the plane hydrodynamic turbulent channel flow at the low Reynolds number of 180, based on the friction velocity, and the corresponding MHD flow with an external streamwise magnetic field with a magnetic interaction number of 0.1. By applying the visibility graph algorithm, we first transformed the time series into networks and then we evaluated the network topological properties. Results show that the proposed network analysis is not only able to identify and detect dynamical transitions in the system's behavior that identifies three distinct fluid areas in accordance with turbulent flow theory but also can quantify the effect of the magnetic field on the time series transitions. Moreover, we find that the topological measures of networks without a magnetic field and as compared to the one with a magnetic field are statistically different within a 95% confidence interval. These results provide a way to discriminate and characterize the influence of the magnetic field on the turbulent flows.}, }
@article {pmid34247118, year = {2021}, author = {Tang, TQ and Hsu, SY and Dahiya, A and Soh, CH and Lin, KC}, title = {Numerical modeling of pulsatile blood flow through a mini-oxygenator in artificial lungs.}, journal = {Computer methods and programs in biomedicine}, volume = {208}, number = {}, pages = {106241}, doi = {10.1016/j.cmpb.2021.106241}, pmid = {34247118}, issn = {1872-7565}, mesh = {Equipment Design ; Humans ; Hydrodynamics ; Lung ; *Oxygen ; *Oxygenators, Membrane ; Pulsatile Flow ; }, abstract = {While previous in vitro studies showed divergent results concerning the influence of pulsatile blood flow on oxygen advection in oxygenators, no study was done to investigate the uncertainty affected by blood flow dynamics. The aim of this study is to utilize a computational fluid dynamics model to clarify the debate concerning the influence of pulsatile blood flow on the oxygen transport. The computer model is based on a validated 2D finite volume approach that predicts oxygen transfer in pulsatile blood flow passing through a 300-micron hollow-fiber membrane bundle with a length of 254 mm, a building block for an artificial lung device. In this study, the flow parameters include the steady Reynolds number (Re = 2, 5, 10 and 20), Womersley parameter (Wo = 0.29, 0.38 and 0.53) and sinusoidal amplitude (A = 0.25, 0.5 and 0.75). Specifically, the computer model is extended to verify, for the first time, the previously measured O2 transport that was observed to be hindered by pulsating flow in the Biolung, developed by Michigan Critical Care Consultants. A comprehensive analysis is carried out on computed profiles and fields of oxygen partial pressure (PO2) and oxygen saturation (SO2) as a function of Re, Wo and A. Based on the present results, we observe the positive and negative effects of pulsatile flow on PO2 at different blood flow rates. Besides, the SO2 variation is not much influenced by the pulsatile flow conditions investigated. While being consistent with a recent experimental study, the computed O2 volume flow rate is found to be increased at high blood flow rates operated with low frequency and high amplitude. Furthermore, the present study qualitatively explains that divergent outcomes reported in previous in vitro experimental studies could be owing to the different blood flow rates adopted. Finally, the contour analysis reveals how the spatial distributions of PO2 and SO2 vary over time.}, }
@article {pmid34243174, year = {2021}, author = {Meng, X and Ghaffar, A and Zhang, Y and Deng, C}, title = {Very low Reynolds number causes a monotonic force enhancement trend for a three-dimensional hovering wing in ground effect.}, journal = {Bioinspiration &amp; biomimetics}, volume = {16}, number = {5}, pages = {}, doi = {10.1088/1748-3190/ac1308}, pmid = {34243174}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; *Flight, Animal ; Insecta ; Models, Biological ; *Wings, Animal ; }, abstract = {This research reports the numerical results of the ground effect trend for a three-dimensional flapping insect wing at a very low Reynolds number (Re = 10). It demonstrates that the ground effect trend at this Re has a 'single force regime,' i.e. the forces only enhance as the ground distance decreases. This phenomenon is unlike the widely expected non-monotonic trend publicized in previous studies for higher Reynolds numbers, that shows 'three force regimes,' i.e. the forces reduce, recover, and also enhance as the ground distance decreases. The force trend in the ground effect correlates to a similar trend in wing-wake interaction or the downwash strength on the wing's head. At very low Re (10), the very large viscosity causes diffused vortices and less advected vortex wake, while at relatively high Re, the vortices are easily separated from the wing and then advected downwards. This different development of the vortex wake caused different force trends for the flapping wing in the ground effect. Furthermore, by examining only the first stroke when there is no vortex wake, we found that the 'ramming effect' enhances the forces on the wing. This effect increases the pressure of the lower wing surface due to the squeezed air between the wing and the ground. The 'ramming effect', combined with the reduced downwash (or wing-wake interaction) effect, causes the force enhancement of the wing near the ground's vicinity. It is further comprehended that the trend is dependent on Re. As the Re is increased, the trend becomes non-monotonic. The effect of varying angles of attack, flapping amplitude and wing planform at very low Re does not change this trend. This ground effect might help insects by enhancing their lift while they hover above the surface. This finding might prove beneficial for developing micro air vehicles.}, }
@article {pmid34241532, year = {2021}, author = {Iyer, KP and Bewley, GP and Biferale, L and Sreenivasan, KR and Yeung, PK}, title = {Oscillations Modulating Power Law Exponents in Isotropic Turbulence: Comparison of Experiments with Simulations.}, journal = {Physical review letters}, volume = {126}, number = {25}, pages = {254501}, doi = {10.1103/PhysRevLett.126.254501}, pmid = {34241532}, issn = {1079-7114}, abstract = {Inertial-range features of turbulence are investigated using data from experimental measurements of grid turbulence and direct numerical simulations of isotropic turbulence simulated in a periodic box, both at the Taylor-scale Reynolds number R_{λ}∼1000. In particular, oscillations modulating the power-law scaling in the inertial range are examined for structure functions up to sixth-order moments. The oscillations in exponent ratios decrease with increasing sample size in simulations, although in experiments they survive at a low value of 4 parts in 1000 even after massive averaging. The two datasets are consistent in their intermittent character but differ in small but observable respects. Neither the scaling exponents themselves nor all the viscous effects are consistently reproduced by existing models of intermittency.}, }
@article {pmid34241478, year = {2021}, author = {Gojon, R and Jardin, T and Parisot-Dupuis, H}, title = {Experimental investigation of low Reynolds number rotor noise.}, journal = {The Journal of the Acoustical Society of America}, volume = {149}, number = {6}, pages = {3813}, doi = {10.1121/10.0005068}, pmid = {34241478}, issn = {1520-8524}, abstract = {In this paper, an experimental characterisation of low Reynolds number rotors is performed in an anechoic room. Two commercially available two-bladed rotors as well as four three-dimensional (3D)-printed rotors with different numbers of blades (from two to five) are tested. The latter have canonical geometry, with an NACA0012 blade section profile, extruded in the radial direction with constant chord and constant 10° pitch. The experimental setup and the 3D printing strategy are first validated using results from the literature for the commercially available rotors. For all the tested rotors, four noise characteristics are analysed: the overall sound pressure level (OASPL), the amplitude of the blade passing frequency (BPF), and the amplitude of its first harmonic and the high-frequency broadband noise. For all the rotors, an increase in all noise characteristics is observed with the rotational speed (rpm) for all directivity angles. Moreover, an interesting change of pattern is observed for the amplitudes of the BPF and of its first harmonic, with, in the vicinity of the rotor plane, a minimum value for low rpm and/or high number of blades, and a maximum value for high rpm and/or low number of blades. This change in directivity leads to a similar change of directivity of the OASPL. For the broadband noise, a dipole-like pattern is obtained with a minimum value at θ=-10°, i.e., aligned with the trailing edge and thus indicating the generation of trailing edge noise. Finally, scaling laws that characterise the amplitude of the different noise components with respect to the rpm are proposed.}, }
@article {pmid34234957, year = {2021}, author = {Mazharmanesh, S and Stallard, J and Medina, A and Fisher, A and Ando, N and Tian, FB and Young, J and Ravi, S}, title = {Effects of uniform vertical inflow perturbations on the performance of flapping wings.}, journal = {Royal Society open science}, volume = {8}, number = {6}, pages = {210471}, pmid = {34234957}, issn = {2054-5703}, abstract = {Flapping wings have attracted significant interest for use in miniature unmanned flying vehicles. Although numerous studies have investigated the performance of flapping wings under quiescent conditions, effects of freestream disturbances on their performance remain under-explored. In this study, we experimentally investigated the effects of uniform vertical inflows on flapping wings using a Reynolds-scaled apparatus operating in water at Reynolds number ≈ 3600. The overall lift and drag produced by a flapping wing were measured by varying the magnitude of inflow perturbation from J Vert = -1 (downward inflow) to J Vert = 1 (upward inflow), where J Vert is the ratio of the inflow velocity to the wing's velocity. The interaction between flapping wing and downward-oriented inflows resulted in a steady linear reduction in mean lift and drag coefficients, C ¯ L and C ¯ D , with increasing inflow magnitude. While a steady linear increase in C ¯ L and C ¯ D was noted for upward-oriented inflows between 0 < J Vert < 0.3 and J Vert > 0.7, a significant unsteady wing-wake interaction occurred when 0.3 ≤ J Vert < 0.7, which caused large variations in instantaneous forces over the wing and led to a reduction in mean performance. These findings highlight asymmetrical effects of vertically oriented perturbations on the performance of flapping wings and pave the way for development of suitable control strategies.}, }
@article {pmid34234155, year = {2021}, author = {Connolly, S and Newport, D and McGourty, K}, title = {Cell specific variation in viability in suspension in in vitro Poiseuille flow conditions.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {13997}, pmid = {34234155}, issn = {2045-2322}, mesh = {Algorithms ; Cell Line, Tumor ; *Cell Survival ; Fibroblasts ; Humans ; *Lab-On-A-Chip Devices ; *Microfluidic Analytical Techniques ; *Models, Theoretical ; Neoplastic Cells, Circulating ; Suspensions ; T-Lymphocytes ; }, abstract = {The influence of Poiseuille flow on cell viability has applications in the areas of cancer metastasis, lab-on-a-chip devices and flow cytometry. Indeed, retaining cell viability is important in the emerging field of adoptive cell therapy, as cells need to be returned to patients' bodies, while the viability of other cells, which are perhaps less accustomed to suspension in a fluidic environment, is important to retain in flow cytometers and other such devices. Despite this, it is unclear how Poiseuille flow affects cell viability. Following on from previous studies which investigated the viability and inertial positions of circulating breast cancer cells in identical flow conditions, this study investigated the influence that varying flow rate, and the corresponding Reynolds number has on the viability of a range of different circulating cells in laminar pipe flow including primary T-cells, primary fibroblasts and neuroblastoma cells. It was found that Reynolds numbers as high as 9.13 had no effect on T-cells while the viabilities of neuroblastoma cells and intestinal fibroblasts were significantly reduced in comparison. This indicates that in vitro flow devices need to be tailored to cell-specific flow regimes.}, }
@article {pmid34208685, year = {2021}, author = {Shanbrom, C and Balisacan, J and Wilkens, G and Chyba, M}, title = {Geometric Methods for Efficient Planar Swimming of Copepod Nauplii.}, journal = {Micromachines}, volume = {12}, number = {6}, pages = {}, pmid = {34208685}, issn = {2072-666X}, support = {359510//Simons Foundation/ ; }, abstract = {Copepod nauplii are larval crustaceans with important ecological functions. Due to their small size, they experience an environment of low Reynolds number within their aquatic habitat. Here we provide a mathematical model of a swimming copepod nauplius with two legs moving in a plane. This model allows for both rotation and two-dimensional displacement by the periodic deformation of the swimmer's body. The system is studied from the framework of optimal control theory, with a simple cost function designed to approximate the mechanical energy expended by the copepod. We find that this model is sufficiently realistic to recreate behavior similar to those of observed copepod nauplii, yet much of the mathematical analysis is tractable. In particular, we show that the system is controllable, but there exist singular configurations where the degree of non-holonomy is non-generic. We also partially characterize the abnormal extremals and provide explicit examples of families of abnormal curves. Finally, we numerically simulate normal extremals and observe some interesting and surprising phenomena.}, }
@article {pmid34204328, year = {2021}, author = {Ali, A and Bukhari, Z and Umar, M and Ismail, MA and Abbas, Z}, title = {Cu and Cu-SWCNT Nanoparticles' Suspension in Pulsatile Casson Fluid Flow via Darcy-Forchheimer Porous Channel with Compliant Walls: A Prospective Model for Blood Flow in Stenosed Arteries.}, journal = {International journal of molecular sciences}, volume = {22}, number = {12}, pages = {}, pmid = {34204328}, issn = {1422-0067}, mesh = {Algorithms ; Arteries/pathology/physiopathology ; Blood Circulation ; Constriction, Pathologic ; *Copper/chemistry ; *Hemodynamics ; Humans ; *Hydrodynamics ; *Metal Nanoparticles/chemistry ; *Models, Cardiovascular ; Porosity ; *Pulsatile Flow ; Suspensions ; }, abstract = {The use of experimental relations to approximate the efficient thermophysical properties of a nanofluid (NF) with Cu nanoparticles (NPs) and hybrid nanofluid (HNF) with Cu-SWCNT NPs and subsequently model the two-dimensional pulsatile Casson fluid flow under the impact of the magnetic field and thermal radiation is a novelty of the current study. Heat and mass transfer analysis of the pulsatile flow of non-Newtonian Casson HNF via a Darcy-Forchheimer porous channel with compliant walls is presented. Such a problem offers a prospective model to study the blood flow via stenosed arteries. A finite-difference flow solver is used to numerically solve the system obtained using the vorticity stream function formulation on the time-dependent governing equations. The behavior of Cu-based NF and Cu-SWCNT-based HNF on the wall shear stress (WSS), velocity, temperature, and concentration profiles are analyzed graphically. The influence of the Casson parameter, radiation parameter, Hartmann number, Darcy number, Soret number, Reynolds number, Strouhal number, and Peclet number on the flow profiles are analyzed. Furthermore, the influence of the flow parameters on the non-dimensional numbers such as the skin friction coefficient, Nusselt number, and Sherwood number is also discussed. These quantities escalate as the Reynolds number is enhanced and reduce by escalating the porosity parameter. The Peclet number shows a high impact on the microorganism's density in a blood NF. The HNF has been shown to have superior thermal properties to the traditional one. These results could help in devising hydraulic treatments for blood flow in highly stenosed arteries, biomechanical system design, and industrial plants in which flow pulsation is essential.}, }
@article {pmid34203635, year = {2021}, author = {Ju, Y and Zhu, T and Mashayekhi, R and Mohammed, HI and Khan, A and Talebizadehsardari, P and Yaïci, W}, title = {Evaluation of Multiple Semi-Twisted Tape Inserts in a Heat Exchanger Pipe Using Al2O3 Nanofluid.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {11}, number = {6}, pages = {}, pmid = {34203635}, issn = {2079-4991}, abstract = {The hydrothermal performance of multiple semi-twisted tape inserts inside a heat exchanger pipe is numerically examined in three-dimensions. This study aims to find the optimum case for having the highest heat transfer enhancement with the lowest friction factor using nanofluid (Al2O3/water). A performance evaluation criterion (PEC) is defined to characterize the performance based on both friction factor and heat transfer. It was found that increasing the number of semi-twisted tapes increases the number of swirl flow streams and leads to an enhancement in the local Nusselt number as well as the friction factor. The average Nusselt number increases from 15.13 to 28.42 and the average friction factor enhances from 0.022 to 0.052 by increasing the number of the semi-twisted tapes from 0 to 4 for the Reynolds number of 1000 for the base fluid. By using four semi-twisted tapes, the average Nusselt number increases from 12.5 to 28.5, while the friction factor reduces from 0.155 to 0.052 when the Reynolds number increases from 250 to 1000 for the base fluid. For the Reynolds number of 1000, the increase in nanofluid concentration from 0 to 3% improves the average Nusselt number and friction factor by 6.41% and 2.29%, respectively. The highest PEC is equal to 1.66 and belongs to the Reynolds number of 750 using four semi-twisted tape inserts with 3% nanoparticles. This work offers instructions to model an advanced design of twisted tape integrated with tubes using multiple semi-twisted tapes, which helps to provide a higher amount of energy demand for solar applications.}, }
@article {pmid34199619, year = {2021}, author = {Elsafy, KM and Saghir, MZ}, title = {Forced Convection in Wavy Microchannels Porous Media Using TiO2 and Al2O3-Cu Nanoparticles in Water Base Fluids: Numerical Results.}, journal = {Micromachines}, volume = {12}, number = {6}, pages = {}, pmid = {34199619}, issn = {2072-666X}, abstract = {In the present work, an attempt is made to investigate the performance of three fluids with forced convection in a wavy channel. The fluids are water, a nanofluid of 1% TiO2 in a water solution and a hybrid fluid which consists of 1% Al2O3-Cu nanoparticles in a water solution. The wavy channel has a porous insert with a permeability of 10 PPI, 20 PPI and 40 PPI, respectively. Since Reynolds number is less than 1000, the flow is assumed laminar, Newtonian and steady state. Results revealed that wavy channel provides a better heat enhancement than a straight channel of the same dimension. Porous material increases heat extraction at the expenses of the pressure drop. The nanofluid of 1% TiO2 in water provided the highest performance evaluation criteria.}, }
@article {pmid34185996, year = {2021}, author = {Ahmed, S and Perez-Mercader, J}, title = {Autonomous Low-Reynolds-Number Soft Robots with Structurally Encoded Motion and Their Thermodynamic Efficiency.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {37}, number = {27}, pages = {8148-8156}, doi = {10.1021/acs.langmuir.1c00765}, pmid = {34185996}, issn = {1520-5827}, support = {1541959//National Science Foundation/ ; }, mesh = {Biocompatible Materials ; Motion ; *Robotics ; Thermodynamics ; }, abstract = {Soft low-Reynolds-number robotics hold the potential to significantly impact numerous fields including drug delivery, sensing, and diagnostics. Realizing this potential is predicated upon the ability to design soft robots tailored to their intended function. In this work, we identify the effect of different geometric and symmetry parameters on the motion of soft, autonomous robots that operate in the low-Reynolds-number regime and use organic fuel. The ability to power low-Reynolds-number soft robots using an organic fuel would provide a new avenue for their potential use in biomedical applications, as is the use of a polymeric biocompatible material as is done here. We introduce a simple and cost-effective 3D-printer-assisted method to fabricate robots of different shapes that is scalable and widely applicable for a variety of materials. The efficiency of chemical energy to mechanical energy conversion is measured in soft low-Reynolds-number robots for the first time, and their mechanism of motion is assessed. Motion is a result of a periodic and oscillatory change in the charge state of the gel. This work lays the groundwork for the structure-function design of soft, chemically operated, and autonomous low-Reynolds-number robots.}, }
@article {pmid34184223, year = {2021}, author = {Yang, F and Zeng, YH and Huai, WX}, title = {A new model for settling velocity of non-spherical particles.}, journal = {Environmental science and pollution research international}, volume = {28}, number = {43}, pages = {61636-61646}, pmid = {34184223}, issn = {1614-7499}, support = {51879197//National Natural Science Foundation of China/ ; 51622905//National Natural Science Foundation of China/ ; 2016YFA0600901//National key research and development of China/ ; }, mesh = {*Ecosystem ; Particle Size ; }, abstract = {The settlement of non-spherical particles, such as propagules of plants and natural sediments, is commonly observed in riverine ecosystems. The settling process is influenced by both particle properties (size, density, and shape) and fluid properties (density and viscosity). Therefore, the drag law of non-spherical particles is a function of both particle Reynolds number and particle shape. Herein, a total of 828 settling data are collected from the literatures, which cover a wide range of particle Reynolds number (0.008-10000). To characterize the influence of particle shapes, sphericity is adopted as the general shape factor, which varies from 0.421 to 1.0. By comparing the measured drag with the standard drag curve of spheres, we modify the spherical drag law with three shape-dependent functions to develop a new drag law for non-spherical particles. Combined with an iterative procedure, a new model is thus obtained to predict the settling velocity of non-spherical particles of various shapes and materials. Further applications in hydrochorous propagule dispersal and sediment transport are projected based on deeper understanding of the settling process.}, }
@article {pmid34143104, year = {2021}, author = {Hill, JL and Hsu, PS and Jiang, N and Grib, SW and Roy, S and Borg, M and Thomas, L and Reeder, M and Schumaker, SA}, title = {Hypersonic N2 boundary layer flow velocity profile measurements using FLEET.}, journal = {Applied optics}, volume = {60}, number = {15}, pages = {C38-C46}, doi = {10.1364/AO.417470}, pmid = {34143104}, issn = {1539-4522}, abstract = {Femtosecond laser electronic excitation tagging (FLEET) velocimetry was used in the boundary layer of an ogive-cylinder model in a Mach-6 Ludwieg tube. One-dimensional velocity profiles were extracted from the FLEET signal in laminar boundary layers from pure N2 flows at unit Reynolds numbers ranging from 3.4×10[6]/m to3.9×10[6]/m. The effects of model tip bluntness and the unit Reynolds number on the velocity profiles were investigated. The challenges and strategies of applying FLEET for direct boundary layer velocity measurement are discussed. The potential of utilizing FLEET velocimetry for understanding the dynamics of laminar and turbulent boundary layers in hypersonic flows is demonstrated.}, }
@article {pmid34139680, year = {2021}, author = {Mazharmanesh, S and Stallard, J and Medina, A and Fisher, A and Ando, N and Tian, FB and Young, J and Ravi, S}, title = {Performance of passively pitching flapping wings in the presence of vertical inflows.}, journal = {Bioinspiration &amp; biomimetics}, volume = {16}, number = {5}, pages = {}, doi = {10.1088/1748-3190/ac0c60}, pmid = {34139680}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; *Flight, Animal ; *Models, Biological ; Wings, Animal ; }, abstract = {The successful implementation of passively pitching flapping wings strongly depends on their ability to operate efficiently in wind disturbances. In this study, we experimentally investigated the interaction between a uniform vertical inflow perturbation and a passive-pitching flapping wing using a Reynolds-scaled apparatus operating in water at Reynolds number ≈3600. A parametric study was performed by systematically varying the Cauchy number (Ch) of the wings from 0.09 to 11.52. The overall lift and drag, and pitch angle of the wing were measured by varying the magnitude of perturbation fromJVert= -0.6 (downward inflow) toJVert= 0.6 (upward inflow) at eachCh, whereJVertis the ratio of the inflow velocity to the wing's velocity. We found that the lift and drag had remarkably different characteristics in response to bothChandJVert. Across allCh, while mean lift tended to increase as the inflow perturbation varied from -0.6 to 0.6, drag was significantly less sensitive to the perturbation. However effect of the vertical inflow on drag was dependent onCh, where it tended to vary from an increasing to a decreasing trend asChwas changed from 0.09 to 11.52. The differences in the lift and drag with perturbation magnitude could be attributed to the reorientation of the net force over the wing as a result of the interaction with the perturbation. These results highlight the complex interactions between passively pitching flapping wings and freestream perturbations and will guide the design of miniature flying crafts with such architectures.}, }
@article {pmid34134196, year = {2021}, author = {Li, H and Tian, B and He, Z and Zhang, Y}, title = {Growth mechanism of interfacial fluid-mixing width induced by successive nonlinear wave interactions.}, journal = {Physical review. E}, volume = {103}, number = {5-1}, pages = {053109}, doi = {10.1103/PhysRevE.103.053109}, pmid = {34134196}, issn = {2470-0053}, abstract = {Interfacial fluid mixing induced by successive waves, such as shock, rarefaction, and compression waves, plays a fundamental role in engineering applications, e.g., inertial confinement fusion, and in natural phenomena, e.g., supernova explosion. These waves bring nonuniform, unsteady external forces into the mixing zone, which leads to a complex mixing process. The growth rate of the mixing width is analyzed by decomposing the turbulent flow field into the averaged field and the fluctuating counterpart. The growth rate is thus divided into three parts: (i) the stretching or compression (S(C)) effect induced by the averaged-velocity difference between two ends of the mixing zone, (ii) the penetration effect induced by the fluctuations which represent the penetration of the two species into each other, and (iii) the diffusive effect, which is induced by the molecular diffusion and is negligible in high-Reynolds-number flows at Schmidt number of order unity. The penetration effect is further divided into the Richtmyer-Meshkov (RM) effect, which is induced by fluctuations that were deposited by earlier wave interactions, and the Rayleigh-Taylor (RT) effect, which is caused by the fluctuations that arise in an overall acceleration of the mixing zone. During the passage of the rarefaction waves, the mixing zone is stretched, while during the passage of the compression waves or shock waves, the mixing zone is compressed. To illustrate these effects, a physical model of RM mixing with reshock is used. By combining the S(C), RM, and RT effects, the entire evolution of mixing width is restructured, which agrees well with numerical simulations for problems with a wide range of density ratios.}, }
@article {pmid34129919, year = {2021}, author = {Ahookhosh, K and Saidi, M and Mohammadpourfard, M and Aminfar, H and Hamishehkar, H and Farnoud, A and Schmid, O}, title = {Flow Structure and Particle Deposition Analyses for Optimization of a Pressurized Metered Dose Inhaler (pMDI) in a Model of Tracheobronchial Airway.}, journal = {European journal of pharmaceutical sciences : official journal of the European Federation for Pharmaceutical Sciences}, volume = {164}, number = {}, pages = {105911}, doi = {10.1016/j.ejps.2021.105911}, pmid = {34129919}, issn = {1879-0720}, mesh = {Administration, Inhalation ; Adult ; Aerosols ; Equipment Design ; Female ; Humans ; Lung ; *Metered Dose Inhalers ; *Nebulizers and Vaporizers ; Particle Size ; }, abstract = {Inhalation therapy plays an important role in management or treatment of respiratory diseases such asthma and chronic obstructive pulmonary diseases (COPDs). For decades, pressurized metered dose inhalers (pMDIs) have been the most popular and prescribed drug delivery devices for inhalation therapy. The main objectives of the present computational work are to study flow structure inside a pMDI, as well as transport and deposition of micron-sized particles in a model of human tracheobronchial airways and their dependence on inhalation air flow rate and characteristic pMDI parameters. The upper airway geometry, which includes the extrathoracic region, trachea, and bronchial airways up to the fourth generation in some branches, was constructed based on computed tomography (CT) images of an adult healthy female. Computational fluid dynamics (CFD) simulation was employed using the k-ω model with low-Reynolds number (LRN) corrections to accomplish the objectives. The deposition results of the present study were verified with the in vitro deposition data of our previous investigation on pulmonary drug delivery using a hollow replica of the same airway geometry as used for CFD modeling. It was found that the flow structure inside the pMDI and extrathoracic region strongly depends on inhalation flow rate and geometry of the inhaler. In addition, regional aerosol deposition patterns were investigated at four inhalation flow rates between 30 and 120 L/min and for 60 L/min yielding highest deposition fractions of 24.4% and 3.1% for the extrathoracic region (EX) and the trachea, respectively. It was also revealed that particle deposition was larger in the right branches of the bronchial airways (right lung) than the left branches (left lung) for all of the considered cases. Also, optimization of spray characteristics showed that the optimum values for initial spray velocity, spray cone angle and spray duration were 100 m/s, 10° and 0.1 sec, respectively. Moreover, spray cone angle, more than any other of the investigated pMDI parameters can change the deposition pattern of inhaled particles in the airway model. In conclusion, the present investigation provides a validated CFD model for particle deposition and new insights into the relevance of flow structure for deposition of pMDI-emitted pharmaceutical aerosols in the upper respiratory tract.}, }
@article {pmid34127716, year = {2021}, author = {Shah, Z and Jafaryar, M and Sheikholeslami, M and Ikramullah,  and Kumam, P}, title = {Heat transfer intensification of nanomaterial with involve of swirl flow device concerning entropy generation.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {12504}, pmid = {34127716}, issn = {2045-2322}, abstract = {The thermal features of hybrid nano-powder turbulent motion through a pipe employing helical turbulator is numerically simulated via Finite Volume Method (FVM). The hybrid nanofluid (MWCNTs + Fe3O4 + H2O) is obtained by uniformly dispersing MWCNTs + Fe3O4 nanomaterials in H2O. The characteristics features of thermal energy transfer of hybrid nanofluid are investigated by varying the pitch ratio (P) of the helical turbulator and Reynolds number (Re) of the fluid. The outputs of the study are depicted in terms of contour plots of temperature, velocity, frictional irreversibility Sgen,f, and thermal irreversibility Sgen,th. The variation of Sgen,f, and Sgen,th with changing P and Re are also displayed by 3D plots. It is found that making the fluid more turbulent by increasing Re, the temperature of the fluid drops whereas the fluid velocity augments. The frictional irreversibility enhances, whereas the thermal irreversibility drops with the increasing turbulent motion. The decreasing P causes to drop the temperature of the higher turbulent fluid flow, while opposite effect is observed for smaller Re. The decreasing P causes to enhance the fluid mixing and thus augments the fluid velocity. Sgen,f and Sgen,th both augment with decreasing P. The comparison of current outputs with the older article shows an acceptable accuracy. The results of the present investigation will be useful in modelling of efficient thermal energy transfer systems.}, }
@article {pmid34124445, year = {2021}, author = {Tian, G and Zhu, Y and Feng, X and Zhou, H and Zhang, Y}, title = {Investigation of the Turbulent Boundary Layer Structure over a Sparsely Spaced Biomimetic Spine-Covered Protrusion Surface.}, journal = {ACS omega}, volume = {6}, number = {22}, pages = {14220-14229}, pmid = {34124445}, issn = {2470-1343}, abstract = {Multiperspective particle image velocimetry was used to investigate the turbulent boundary layer structure over biomimetic spine-covered protrusion (BSCP) samples inspired by dorsal skin of pufferfish. The comparison of BSCP samples of two sparse "k-type" arrangements (aligned and staggered) with roughness height k [+] = 5-7 (nearly hydraulically smooth) and smooth case were manufactured in bulk Reynolds number Re b = 37,091, 44,510. The negative value of the roughness function ΔU [+] shows a downward shift of the mean velocity profile of BSCP samples, which shows a drag reduction effect. The results of turbulent statistics present strong fluctuation over the aligned case in the streamwise direction, while little influence is observed in the wall-normal and spanwise direction, which promotes turbulence stability. The same phenomenon was found based on the probability density function of fluctuation velocity that the suppression of turbulent flow is better over the staggered case. It is obvious that the shear stress induced is governed by the streamwise fluctuations. Furthermore, the Q-criterion and the λci-criterion improved with vorticity ω were introduced for vortex identification, which indicates less prograde vortex population and weaker swirling strength over BSCP samples than over the smooth one. Finally, the spatial coherent structure appeared similar and more orderly over the staggered case in the streamwise and wall-normal direction based on the analysis of two-point correlations R uu. These results provide further guidance to reveal the mechanism of drag reduction on the BSCP surface.}, }
@article {pmid34111118, year = {2021}, author = {Velho Rodrigues, MF and Lisicki, M and Lauga, E}, title = {The bank of swimming organisms at the micron scale (BOSO-Micro).}, journal = {PloS one}, volume = {16}, number = {6}, pages = {e0252291}, pmid = {34111118}, issn = {1932-6203}, mesh = {Animals ; Male ; *Swimming/physiology ; Bacteria ; Models, Biological ; Ciliophora/physiology ; Spermatozoa/physiology ; Archaea/physiology ; Flagella/physiology ; Biomechanical Phenomena ; }, abstract = {Unicellular microscopic organisms living in aqueous environments outnumber all other creatures on Earth. A large proportion of them are able to self-propel in fluids with a vast diversity of swimming gaits and motility patterns. In this paper we present a biophysical survey of the available experimental data produced to date on the characteristics of motile behaviour in unicellular microswimmers. We assemble from the available literature empirical data on the motility of four broad categories of organisms: bacteria (and archaea), flagellated eukaryotes, spermatozoa and ciliates. Whenever possible, we gather the following biological, morphological, kinematic and dynamical parameters: species, geometry and size of the organisms, swimming speeds, actuation frequencies, actuation amplitudes, number of flagella and properties of the surrounding fluid. We then organise the data using the established fluid mechanics principles for propulsion at low Reynolds number. Specifically, we use theoretical biophysical models for the locomotion of cells within the same taxonomic groups of organisms as a means of rationalising the raw material we have assembled, while demonstrating the variability for organisms of different species within the same group. The material gathered in our work is an attempt to summarise the available experimental data in the field, providing a convenient and practical reference point for future studies.}, }
@article {pmid34091219, year = {2021}, author = {Amani, M and Amani, P and Bahiraei, M and Ghalambaz, M and Ahmadi, G and Wang, LP and Wongwises, S and Mahian, O}, title = {Latest developments in nanofluid flow and heat transfer between parallel surfaces: A critical review.}, journal = {Advances in colloid and interface science}, volume = {294}, number = {}, pages = {102450}, doi = {10.1016/j.cis.2021.102450}, pmid = {34091219}, issn = {1873-3727}, abstract = {The enhancement of heat transfer between parallel surfaces, including parallel plates, parallel disks, and two concentric pipes, is vital because of their wide applications ranging from lubrication systems to water purification processes. Various techniques can be utilized to enhance heat transfer in such systems. Adding nanoparticles to the conventional working fluids is an effective solution that could remarkably enhance the heat transfer rate. No published review article focuses on the recent advances in nanofluid flow between parallel surfaces; therefore, the present paper aims to review the latest experimental and numerical studies on the flow and heat transfer of nanofluids (mixtures of nanoparticles and conventional working fluids) in such configurations. For the performance analysis of thermal systems composed of parallel surfaces and operating with nanofluids, it is necessary to know the physical phenomena and parameters that influence the flow and heat transfer characteristics in these systems. Significant results obtained from this review indicate that, in most cases, the heat transfer rate between parallel surfaces is enhanced with an increase in the Rayleigh number, the Reynolds number, the magnetic number, and Brownian motion. On the other hand, an increase in thermophoresis parameter, as well as flow parameters, including the Eckert number, buoyancy ratio, Hartmann number, and Lewis number, leads to heat transfer rate reduction.}, }
@article {pmid34081994, year = {2021}, author = {Das, S and Pal, TK and Jana, RN and Giri, B}, title = {Significance of Hall currents on hybrid nano-blood flow through an inclined artery having mild stenosis: Homotopy perturbation approach.}, journal = {Microvascular research}, volume = {137}, number = {}, pages = {104192}, doi = {10.1016/j.mvr.2021.104192}, pmid = {34081994}, issn = {1095-9319}, mesh = {Animals ; Arterial Occlusive Diseases/*physiopathology ; Arteries/*physiopathology ; Constriction, Pathologic ; Copper/*chemistry ; *Hemodynamics ; Humans ; *Metal Nanoparticles ; *Models, Cardiovascular ; *Nanotechnology ; Porosity ; Regional Blood Flow ; Stress, Mechanical ; }, abstract = {The rheological perspective of blood flow with the suspension of metallic or non-metallic nanoparticles through arteries having cardiovascular diseases is getting more attention due to momentous applications in obstructed hemodynamics, nano-hemodynamics, nano-pharmacology, blood purification system, treatment of hemodynamic ailments, etc. Motivated by the novel significance and research in this direction, a mathematical hemodynamics model is developed to mimic the hemodynamic features of blood flow under the concentration of hybrid nanoparticles through an inclined artery with mild stenosis in the existence of dominating electromagnetic field force, Hall currents, heat source, and porous substance. Copper (Cu) and copper oxide (CuO) nanoparticles are submerged into the blood to form hybrid nano-blood suspension (Cu-CuO/blood). The attribute of the medium porosity on the blood flow is featured by Darcy's law. The mathematical equations describing the flow are formulated and simplified under mild stenosis and small Reynolds number assumptions. To determine the analytical solution of the resulting nonlinear momentum equation, the homotopy perturbation method (HPM) is employed. Several figures are graphed to assess the hemodynamical contributions of various intricate physical parameters on blood flow phenomena through the inclined stenosed artery. Significant outcomes from graphical elucidation envisage that the hemodynamic resistance to the blood flow is reduced due to the dispersion of more hybrid nanoparticles in the blood. The hemodynamic resistance (impedance) increases approximately two times by dispersing 0.11% hybrid nanoparticles in the blood flow. The temperature of Cu-CuO/blood is found to be lower in comparison to Cu-blood and pure blood. Intensification of Hall parameter attenuates the wall shear stress at the arterial wall. The trapping phenomena are also outlined via streamline plots which exemplify the blood flow pattern in the stenosed artery under the variation of the emerging parameters. As anticipated, the addition of a large number of hybrid nanoparticles significantly modulates the blood flow pattern in the stenotic region. The novel feature of this model is the impressive impact of Hall currents on hybrid nanoparticle doped blood flow through the stenosed artery. There is another piece of significance is that HPM is the most suitable method to handle the nonlinear momentum equation under the aforementioned flow constraints. Outcomes of this simulation may be valuable for advanced study and research in biomedical engineering, bio-nanofluid mechanics, nano-pharmacodynamics.}, }
@article {pmid34078976, year = {2021}, author = {Usman, AH and Khan, NS and Humphries, UW and Ullah, Z and Shah, Q and Kumam, P and Thounthong, P and Khan, W and Kaewkhao, A and Bhaumik, A}, title = {Computational optimization for the deposition of bioconvection thin Oldroyd-B nanofluid with entropy generation.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {11641}, pmid = {34078976}, issn = {2045-2322}, abstract = {The behavior of an Oldroyd-B nanoliquid film sprayed on a stretching cylinder is investigated. The system also contains gyrotactic microorganisms with heat and mass transfer flow. Similarity transformations are used to make the governing equations non-dimensional ordinary differential equations and subsequently are solved through an efficient and powerful analytic technique namely homotopy analysis method (HAM). The roles of all dimensionless profiles and spray rate have been investigated. Velocity decreases with the magnetic field strength and Oldroyd-B nanofluid parameter. Temperature is increased with increasing the Brownian motion parameter while it is decreased with the increasing values of Prandtl and Reynolds numbers. Nanoparticle's concentration is enhanced with the higher values of Reynolds number and activation energy parameter. Gyrotactic microorganism density increases with bioconvection Rayleigh number while it decreases with Peclet number. The film size naturally increases with the spray rate in a nonlinear way. A close agreement is achieved by comparing the present results with the published results.}, }
@article {pmid34076781, year = {2021}, author = {Kadiri, VM and Günther, JP and Kottapalli, SN and Goyal, R and Peter, F and Alarcón-Correa, M and Son, K and Barad, HN and Börsch, M and Fischer, P}, title = {Light- and magnetically actuated FePt microswimmers.}, journal = {The European physical journal. E, Soft matter}, volume = {44}, number = {6}, pages = {74}, pmid = {34076781}, issn = {1292-895X}, support = {253407113//Deutsche Forschungsgemeinschaft/ ; }, abstract = {Externally controlled microswimmers offer prospects for transport in biological research and medical applications. This requires biocompatibility of the swimmers and the possibility to tailor their propulsion mechanisms to the respective low Reynolds number environment. Here, we incorporate low amounts of the biocompatible alloy of iron and platinum (FePt) in its [Formula: see text] phase in microstructures by a versatile one-step physical vapor deposition process. We show that the hard magnetic properties of [Formula: see text] FePt are beneficial for the propulsion of helical micropropellers with rotating magnetic fields. Finally, we find that the FePt coatings are catalytically active and also make for Janus microswimmers that can be light-actuated and magnetically guided.}, }
@article {pmid34069236, year = {2021}, author = {Choe, YW and Sim, SB and Choo, YM}, title = {New Equation for Predicting Pipe Friction Coefficients Using the Statistical Based Entropy Concepts.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {5}, pages = {}, pmid = {34069236}, issn = {1099-4300}, abstract = {In general, this new equation is significant for designing and operating a pipeline to predict flow discharge. In order to predict the flow discharge, accurate determination of the flow loss due to pipe friction is very important. However, existing pipe friction coefficient equations have difficulties in obtaining key variables or those only applicable to pipes with specific conditions. Thus, this study develops a new equation for predicting pipe friction coefficients using statistically based entropy concepts, which are currently being used in various fields. The parameters in the proposed equation can be easily obtained and are easy to estimate. Existing formulas for calculating pipe friction coefficient requires the friction head loss and Reynolds number. Unlike existing formulas, the proposed equation only requires pipe specifications, entropy value and average velocity. The developed equation can predict the friction coefficient by using the well-known entropy, the mean velocity and the pipe specifications. The comparison results with the Nikuradse's experimental data show that the R2 and RMSE values were 0.998 and 0.000366 in smooth pipe, and 0.979 to 0.994 or 0.000399 to 0.000436 in rough pipe, and the discrepancy ratio analysis results show that the accuracy of both results in smooth and rough pipes is very close to zero. The proposed equation will enable the easier estimation of flow rates.}, }
@article {pmid34064079, year = {2021}, author = {Zhou, T and Chen, B and Liu, H}, title = {Study of the Performance of a Novel Radiator with Three Inlets and One Outlet Based on Topology Optimization.}, journal = {Micromachines}, volume = {12}, number = {6}, pages = {}, pmid = {34064079}, issn = {2072-666X}, abstract = {In recent years, in order to obtain a radiator with strong heat exchange capacity, researchers have proposed a lot of heat exchangers to improve heat exchange capacity significantly. However, the cooling abilities of heat exchangers designed by traditional design methods is limited even if the geometric parameters are optimized at the same time. However, using topology optimization to design heat exchangers can overcome this design limitation. Furthermore, researchers have used topology optimization theory to designed one-to-one and many-to-many inlet and outlet heat exchangers because it can effectively increase the heat dissipation rate. In particular, it can further decrease the hot-spot temperature for many-to-many inlet and outlet heat exchangers. Therefore, this article proposes novel heat exchangers with three inlets and one outlet designed by topology optimization to decrease the fluid temperature at the outlet. Subsequently, the effect of the channel depth on the heat exchanger design is also studied. The results show that the type of exchanger varies with the channel depth, and there exists a critical depth value for obtaining the minimum substrate temperature difference. Then, the flow and heat transfer performance of the heat exchangers are numerically investigated. The numerical results show that the heat exchanger derived by topology optimization with the minimum temperature difference as the goal (Model-2) is the best design for flow and heat transfer performance compared to other heat sink designs, including the heat exchanger derived by topology optimization having the average temperature as the goal (Model-1) and conventional straight channels (Model-3). The temperature difference of Model-1 can be reduced by 37.5%, and that of Model-2 can be decreased by 62.5% compared to Model-3. Compared with Model-3, the thermal resistance of Model-1 can be reduced by 21.86%, while that of Model-2 can be decreased by 47.99%. At room temperature, we carried out the forced convention experimental test for Model-2 to measure its physical parameters (temperature, pressure drop) to verify the numerical results. The error of the average wall temperature between experimental results and simulation results is within 2.6 K, while that of the fluid temperature between the experimental and simulation results is within 1.4 K, and the maximum deviation of the measured Nu and simulated Nu was less than 5%. This indicated that the numerical results agreed well with the experimental results.}, }
@article {pmid34062924, year = {2021}, author = {Gu, B and Adjiman, CS and Xu, XY}, title = {Correlations for Concentration Polarization and Pressure Drop in Spacer-Filled RO Membrane Modules Based on CFD Simulations.}, journal = {Membranes}, volume = {11}, number = {5}, pages = {}, pmid = {34062924}, issn = {2077-0375}, support = {na//BP International Centre for Advanced Materials (BP-ICAM)/ ; }, abstract = {Empirical correlations for mass transfer coefficient and friction factor are often used in process models for reverse osmosis (RO) membrane systems. These usually involve four dimensionless groups, namely Reynolds number (Re), Sherwood number (Sh), friction factor (f), and Schmidt number (Sc), with the associated coefficients and exponents being obtained by fitting to experimental data. However, the range of geometric and operating conditions covered by the experiments is often limited. In this study, new dimensionless correlations for concentration polarization (CP) modulus and friction factor are presented, which are obtained by dimensional analysis and using simulation data from computational fluid dynamics (CFD). Two-dimensional CFD simulations are performed on three configurations of spacer-filled channels with 76 combinations of operating and geometric conditions for each configuration, covering a broad range of conditions encountered in RO membrane systems. Results obtained with the new correlations are compared with those from existing correlations in the literature. There is good consistency in the predicted CP with mean discrepancies less than 6%, but larger discrepancies for pressure gradient are found among the various friction factor correlations. Furthermore, the new correlations are implemented in a process model with six spiral wound modules in series and the predicted recovery, pressure drop, and specific energy consumption are compared with a reference case obtained by ROSA (Reverse Osmosis System Analysis, The Dow Chemical Company). Differences in predicted recovery and pressure drop are up to 5% and 83%, respectively, highlighting the need for careful selection of correlations when using predictive models in process design. Compared to existing mass transfer correlations, a distinct advantage of our correlations for CP modulus is that they can be directly used to estimate the impact of permeate flux on CP at a membrane surface without having to resort to the film theory.}, }
@article {pmid34059714, year = {2021}, author = {Pang, M and Zhang, T and Guo, Y and Zhang, L}, title = {Re-crushing process and non-Darcian seepage characteristics of broken coal medium in coal mine water inrush.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {11380}, pmid = {34059714}, issn = {2045-2322}, support = {51774234//Study on the Mechanism of Water-Gas Coupling Fracture Expansion and Ultrasonic Characteristics of Coal Rock Mass in Drilling Holes/ ; 2021JM-390//Fracture Evolution and Water-Gas Coupled Permeability Mechanism of Coal Body Around Extraction Borehole/ ; }, abstract = {The initiation process of the mine water inrush accident, the essence of this process is the sudden change of the seepage state of the broken coal medium under pressure and the instability of the skeleton. In order to study the re-crushing mechanism and seepage characteristics of the broken coal medium under load, a set of three-axis seepage system was designed independently. Using the steady-state infiltration method, multiple flow factors under different particle size combinations and different stress conditions of the broken coal medium were obtained. The results of the study indicate: in one hand, the reduction of the porosity of the broken coal medium will cause the flow channel to be rebuilt, and the sudden change of flow rate will directly lead to the non-Darcian flow behavior. The early stage of compaction mainly affects the permeability k value, and the later stage of compaction mainly affects the non-Darcian β value; On the other hand, the seepage throat in the broken coal medium may have a sharp increase in its flow rate, leading to a sudden change in the flow pattern. The critical Reynolds number is also used to determine whether non-Darcian flow is formed, and its value in the water inrush system is about 40-133; at the same time, the non-Darcian flow in the broken coal medium conforms to the Forchheimer-type flow law. By analyzing the dependence relationship between factors, a seepage factor representation algebraic relationship suitable for Forchheimer type non-Darcian flow of broken coal medium is given, which can be used as a calculation basis in the prevention and treatment of mine water inrush accidents.}, }
@article {pmid34056212, year = {2021}, author = {Agarwal, JR and Torres, CF and Shah, S}, title = {Development of Dimensionless Parameters and Groups of Heat and Mass Transfer to Predict Wax Deposition in Crude Oil Pipelines.}, journal = {ACS omega}, volume = {6}, number = {16}, pages = {10578-10591}, pmid = {34056212}, issn = {2470-1343}, abstract = {A new methodology has been developed for analyzing heat and mass transfer to predict wax deposition in crude oil pipelines using the law of the wall dimensionless parameters. A set of physically meaningful dimensionless groups and parameters has laid a strong foundation behind the proposed methodology. The paper presents a discussion regarding the development of scale-up correlations from laboratory scale to field scale, considering the combination of both analytical groups and empirical correlations. Data from previous literature studies were employed for determining realistic values for the developed parameters and scale-up correlations. The utilization of new dimensionless scale-up parameters indicated that the wax deposition in crude oil pipelines is independent of the Reynolds number and the inner diameter of the pipeline. It further indicates that wax deposition in crude oil pipelines is mainly dependent on the heat transfer process and not on the shear reduction process. The dimensionless technique developed here can be utilized for determining the optimum pipe size and pigging frequencies to reduce and mitigate the effect of the wax deposition process.}, }
@article {pmid34050744, year = {2021}, author = {Ford, MP and Santhanakrishnan, A}, title = {Closer Appendage Spacing Augments Metachronal Swimming Speed by Promoting Tip Vortex Interactions.}, journal = {Integrative and comparative biology}, volume = {61}, number = {5}, pages = {1608-1618}, doi = {10.1093/icb/icab112}, pmid = {34050744}, issn = {1557-7023}, mesh = {Animals ; Biomechanical Phenomena ; *Extremities ; Hydrodynamics ; Invertebrates ; *Swimming ; }, abstract = {Numerous species of aquatic invertebrates, including crustaceans, swim by oscillating multiple closely spaced appendages. The coordinated, out-of-phase motion of these appendages, known as "metachronal paddling," has been well-established to improve swimming performance relative to synchronous paddling. Invertebrates employing this propulsion strategy cover a wide range of body sizes and shapes, but the ratio of appendage spacing (G) to the appendage length (L) has been reported to lie in a comparatively narrow range of 0.2 < G/L ≤ 0.65. The functional role of G/L on metachronal swimming performance is unknown. We hypothesized that for a given Reynolds number and stroke amplitude, hydrodynamic interactions promoted by metachronal stroke kinematics with small G/L can increase forward swimming speed. We used a dynamically scaled self-propelling robot to comparatively examine swimming performance and wake development of metachronal and synchronous paddling under varying G/L, phase lag, and stroke amplitude. G/L was varied from 0.4 to 1.5, with the expectation that when G/L is large, there should be no performance difference between metachronal and synchronous paddling due to a lack of interaction between vortices that form on the appendages. Metachronal stroking at nonzero phase lag with G/L in the biological range produced faster swimming speeds than synchronous stroking. As G/L increased and as stroke amplitude decreased, the influence of phase lag on the swimming speed of the robot was reduced. For smaller G/L, vortex interactions between adjacent appendages generated a horizontally oriented wake and increased momentum fluxes relative to larger G/L, which contributed to increasing swimming speed. We find that while metachronal motion augments swimming performance for closely spaced appendages (G/L <1), moderately spaced appendages (1.0 ≤ G/L ≤ 1.5) can benefit from the metachronal motion only when the stroke amplitude is large.}, }
@article {pmid34035439, year = {2021}, author = {Shankar, BM and Shivakumara, IS}, title = {Benchmark solution for the stability of plane Couette flow with net throughflow.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {10901}, pmid = {34035439}, issn = {2045-2322}, abstract = {This paper investigates the stability of an incompressible viscous fluid flow between relatively moving horizontal parallel plates in the presence of a uniform vertical throughflow. A linear stability analysis has been performed by employing the method of normal modes and the resulting stability equation is solved numerically using the Chebyshev collocation method. Contrary to the stability of plane Couette flow (PCF) to small disturbances for all values of the Reynolds number in the absence of vertical throughflow, it is found that PCF becomes unstable owing to the change in the sign of growth rate depending on the magnitude of throughflow. The critical Reynolds number triggering the instability is computed for different values of throughflow dependent Reynolds number and it is shown that throughflow instills both stabilizing and destabilizing effect on the base flow. It is seen that the direction of throughflow has no influence on the stability of fluid flow. A comparative study between plane Poiseuille flow and PCF has also been carried out and the similarities and differences are highlighted.}, }
@article {pmid34034247, year = {2021}, author = {Kasoju, VT and Santhanakrishnan, A}, title = {Pausing after clap reduces power required to fling wings apart at low Reynolds number.}, journal = {Bioinspiration &amp; biomimetics}, volume = {16}, number = {5}, pages = {}, doi = {10.1088/1748-3190/ac050a}, pmid = {34034247}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; *Flight, Animal ; Insecta ; Models, Biological ; *Thysanoptera ; Wings, Animal ; }, abstract = {The smallest flying insects, such as thrips (body length < 2 mm), are challenged with needing to move in air at a chord-based Reynolds number (Rec) of the order of 10. Pronounced viscous dissipation at such a low Recrequires considerable energetic expenditure for tiny insects to stay aloft. Thrips flap their densely bristled wings at large stroke amplitudes, bringing both wings in close proximity to each other at the end of upstroke ('clap') and moving their wings apart at the start of downstroke ('fling'). From high-speed videos of free take-off flights of thrips, we observed that their forewings remain clapped for approximately 10% of the wingbeat cycle before the start of downstroke (fling stroke). We sought to examine if there are aerodynamic advantages associated with pausing wing motion after upstroke (clap stroke) and before downstroke (fling stroke) at Rec= 10. A dynamically scaled robotic clap and fling platform was used to measure lift and drag forces generated by physical models of solid (non-bristled) and bristled wings in single wing and wing pair configurations, for pause times ranging between 0% to 41% of the cycle. For solid and bristled wing pairs, pausing before the start of downstroke (fling stroke) dissipated vorticity generated at the end of upstroke (clap stroke). This resulted in a decrease in the drag coefficient averaged across downstroke (fling stroke) and in turn reduced power requirements. Also, increasing the pause time resulted in a larger decrease in the dimensionless power coefficient for the wing-pair configurations compared to the single-wing configurations. Our findings show that wing-wing interaction observed in the clap and fling motion of tiny insect wings is necessary to realize the aerodynamic benefits of pausing before fling, by reducing the power required to clap and fling for a small compromise in lift.}, }
@article {pmid34030500, year = {2021}, author = {Wanzheng, A and Pengfei, Z}, title = {Correction and laboratory investigation for energy loss coefficient of square-edged orifice plate.}, journal = {Science progress}, volume = {104}, number = {2}, pages = {368504211018571}, doi = {10.1177/00368504211018571}, pmid = {34030500}, issn = {2047-7163}, abstract = {A lot of studies have shown that the hydraulic characteristics of orifice plate are mainly controlled by its contraction ratio, but the thickness of square-edged orifice plate also has many impacts on energy loss characteristics. The primary objective of this study was to investigated the effects of square-edged orifice plate thickness on energy loss characteristics. In this paper, the effects of square-edged orifice plate thickness on energy loss characteristics are investigated by numerical simulation using CFD. Orifice plate discharge tunnel is axial symmetric, two dimensional numerical simulations of orifice plate discharge tunnel flow was used. The equation (9) for calculating energy loss coefficient of square-edged orifice plate energy dissipater considering the influence of thickness is proposed. The results of the present research demonstrate that energy loss coefficient decreases with increase of the orifice plate thickness. The results of model experiment are consistence with the results calculated by using rectified equation in present paper. The CFD simulations and Model experiment for the flow through an orifice plate are carried out. For square-edged orifice plate energy dissipater, the relative orifice plate thickness T/D has remarkable impacts on its energy loss coefficient ξ. The Traditional equation (8) is corrected by numerical results. The equation (9) for calculating energy loss coefficient of square-edged orifice plate energy dissipater considering the influence of thickness is proposed and this equation is available in the condition of d/D = 0.4-0.8, T/D = 0.05-0.25, and Re > 105(Re is Reynolds number). Comparing with the physical model experimental data, the relative errors of equation (9) is smaller than 15%.}, }
@article {pmid34026737, year = {2021}, author = {Murayama, Y and Nakata, T and Liu, H}, title = {Flexible Flaps Inspired by Avian Feathers Can Enhance Aerodynamic Robustness in low Reynolds Number Airfoils.}, journal = {Frontiers in bioengineering and biotechnology}, volume = {9}, number = {}, pages = {612182}, pmid = {34026737}, issn = {2296-4185}, abstract = {Unlike rigid rotors of drones, bird wings are composed of flexible feathers that can passively deform while achieving remarkable aerodynamic robustness in response to wind gusts. In this study, we conduct an experimental study on the effects of the flexible flaps inspired by the covert of bird wings on aerodynamic characteristics of fixed-wings in disturbances. Through force measurements and flow visualization in a low-speed wind tunnel, it is found that the flexible flaps can suppress the large-scale vortex shedding and hence reduce the fluctuations of aerodynamic forces in a disturbed flow behind an oscillating plate. Our results demonstrate that the stiffness of the flaps strongly affects the aerodynamic performance, and the force fluctuations are observed to be reduced when the deformation synchronizes with the strong vortex generation. The results point out that the simple attachment of the flexible flaps on the upper surface of the wing is an effective method, providing a novel biomimetic design to improve the aerodynamic robustness of small-scale drones with fixed-wings operating in unpredictable aerial environments.}, }
@article {pmid34024939, year = {2021}, author = {Chassagne, F and Barbour, MC and Chivukula, VK and Machicoane, N and Kim, LJ and Levitt, MR and Aliseda, A}, title = {The effect of Dean, Reynolds, and Womersley number on the flow in a spherical cavity on a curved round pipe. Part 1. Fluid mechanics in the cavity as a canonical flow representing intracranial aneurysms.}, journal = {Journal of fluid mechanics}, volume = {915}, number = {}, pages = {}, pmid = {34024939}, issn = {0022-1120}, support = {18CDA34110295/AHA/American Heart Association-American Stroke Association/United States ; R01 NS088072/NS/NINDS NIH HHS/United States ; R01 NS105692/NS/NINDS NIH HHS/United States ; R03 NS078539/NS/NINDS NIH HHS/United States ; }, abstract = {Flow in side-wall cerebral aneurysms can be ideally modelled as the combination of flow over a spherical cavity and flow in a curved circular pipe, two canonical flows. Flow in a curved pipe is known to depend on the Dean number De, combining the effects of Reynolds number, Re, and of the curvature along the pipe centreline, κ. Pulsatility in the flow introduces a dependency on the Womersley number Wo. Using stereo PIV measurements, this study investigated the effect of these three key non-dimensional parameters, by modifying pipe curvature (De), flow-rate (Re), and pulsatility frequency (Wo), on the flow patterns in a spherical cavity. A single counter-rotating vortex was observed in the cavity for all values of pipe curvature κ and Re, for both steady and pulsatile inflow conditions. Increasing the pipe curvature impacted both the flow patterns in the pipe and the cavity, by shifting the velocity profile towards the cavity opening and increasing the flow rate into the cavity. The circulation in the cavity was found to collapse well with only the Dean number, for both steady and pulsatile inflows. For pulsatile inflow, the counter-rotating vortex was unstable and the location of its centre over time was impacted by the curvature of the pipe, as well as the Re and the Wo in the freestream. The circulation in the cavity was higher for steady inflow than for the equivalent average Reynolds and Dean number pulsatile inflow, with very limited impact of the Womersley in the range studied.}, }
@article {pmid34007926, year = {2021}, author = {Aljabair, S and Ekaid, AL and Ibrahim, SH and Alesbe, I}, title = {Mixed convection in sinusoidal lid driven cavity with non-uniform temperature distribution on the wall utilizing nanofluid.}, journal = {Heliyon}, volume = {7}, number = {5}, pages = {e06907}, pmid = {34007926}, issn = {2405-8440}, abstract = {Mixed convection heat transfer of Cu-water nanofluid in an arc cavity with non-uniform heating has been numerically studied. The top flat moving wall is isothermally cooled at Tc and moved with a constant velocity. While the heated arc stationary wall of the cavity is maintained at a hot temperature Th. FORTRAN code is used to solve the mass, momentum, and energy equations in dimensionless form with suitable boundary conditions. In this study, the Reynolds number changed from 1 to 2000, and the Rayleigh number changed from 0 to 10[7]. Also, the range of nanoparticles volume fraction extends from ϕ = 0 to 0.07. Stream vorticity method selected for the discretization of flow and energy equations. The present results are compared with the previous results for the validation part, where the results found a good agreement with the others works. The isotherms are regulated near the arc-shape wall causing a steep temperature gradient at these regions and the local and average heat transfer rate increases with increased volume fraction or Reynolds number or Rayleigh number. Finally, Correlation equations of the average Nusselt number from numerical results are presented.}, }
@article {pmid34006011, year = {2021}, author = {Fouxon, I and Feinberg, J and Mond, M}, title = {Linear and nonlinear hydromagnetic stability in laminar and turbulent flows.}, journal = {Physical review. E}, volume = {103}, number = {4-1}, pages = {043104}, doi = {10.1103/PhysRevE.103.043104}, pmid = {34006011}, issn = {2470-0053}, abstract = {We consider the evolution of arbitrarily large perturbations of a prescribed pure hydrodynamical flow of an electrically conducting fluid. We study whether the flow perturbations as well as the generated magnetic fields decay or grow with time and constitute a dynamo process. For that purpose we derive a generalized Reynolds-Orr equation for the sum of the kinetic energy of the hydrodynamic perturbation and the magnetic energy. The flow is confined in a finite volume so the normal component of the velocity at the boundary is zero. The tangential component is left arbitrary in contrast with previous works. For the magnetic field we mostly employ the classical boundary conditions where the field extends in the whole space. We establish critical values of hydrodynamic and magnetic Reynolds numbers below which arbitrarily large initial perturbations of the hydrodynamic flow decay. This involves generalization of the Rayleigh-Faber-Krahn inequality for the smallest eigenvalue of an elliptic operator. For high Reynolds number turbulence we provide an estimate of critical magnetic Reynolds number below which arbitrarily large fluctuations of the magnetic field decay.}, }
@article {pmid34005982, year = {2021}, author = {Gissinger, JR and Zinchenko, AZ and Davis, RH}, title = {Internal circulation and mixing within tight-squeezing deformable droplets.}, journal = {Physical review. E}, volume = {103}, number = {4-1}, pages = {043106}, doi = {10.1103/PhysRevE.103.043106}, pmid = {34005982}, issn = {2470-0053}, abstract = {The internal flow and mixing properties inside deformable droplets, after reaching the steady state within two types of passive droplet traps, are visualized and analyzed as dynamical systems. The first droplet trap (constriction) is formed by three spheres arranged in an equilateral triangle, while the second consists of two parallel spherocylinders (capsules). The systems are assumed to be embedded in a uniform far-field flow at low Reynolds number, and the steady shapes and interfacial velocities on the drops are generated using the boundary-integral method. The internal velocity field is recovered by solving the internal Dirichlet problem, also via a desingularized boundary-integral method. Calculation of 2D streamlines within planes of symmetry reveals the internal equilibria of the flow. The type of each equilibrium is classified in 3D and their interactions probed using passive tracers and their Poincaré maps. For the two-capsule droplet, saddle points located on orthogonal symmetry planes influence the regular flow within the drop. For the three-sphere droplet, large regions of chaos are observed, embedded with simple periodic orbits. Flow is visualized via passive dyes, using material lines and surfaces. In 2D, solely the interface between two passive interior fluids is advected using an adaptive number of linked tracer particles. The reduction in dimension decreases the number of required tracer points, and also resolves arbitrarily thin filaments, in contrast to backward cell-mapping methods. In 3D, the advection of a material surface, bounded by the droplet interface, is enabled using an adaptive mesh scheme. Off-lattice 3D contour advection allows for highly resolved visualizations of the internal flow and quantification of the associated degree of mixing. Analysis of the time-dependent growth of material surfaces and 3D mixing numbers suggests the three-sphere droplet exhibits superior mixing properties compared to the two-capsule droplet.}, }
@article {pmid34005876, year = {2021}, author = {Brahmachary, S and Natarajan, G and Kulkarni, V and Sahoo, N and Ashok, V and Kumar, V}, title = {Role of solution reconstruction in hypersonic viscous computations using a sharp interface immersed boundary method.}, journal = {Physical review. E}, volume = {103}, number = {4-1}, pages = {043302}, doi = {10.1103/PhysRevE.103.043302}, pmid = {34005876}, issn = {2470-0053}, abstract = {This work discusses the development of a sharp interface immersed boundary (IB) method for viscous compressible flows and its assessment for accurate computations of wall shear and heat fluxes in hypersonic flows. The IB method is implemented in an unstructured Cartesian finite-volume (FV) framework and resolves the geometric interface sharply on the nonconformal mesh through direct imposition of boundary conditions employing a local reconstruction approach. The efficacy of the IB-FV solver is investigated for canonical high-speed viscous flows over a range of Mach numbers. The numerical results indicate that the surface pressure and shear stress distributions are computed with reasonable accuracy, whereas surface heat fluxes for aerodynamically blunt configurations are underpredicted. Employing a set of carefully designed experiments and simple diagnostic tools, we probe the possible causes for the underprediction in heat flux. We show that there exist two sources of error-one due to grid resolution and the other due to solution reconstruction, with the latter being more prominent and responsible for the observed underprediction in heat fluxes. Studies reveal that the heat flux estimates are sensitive to the choice of temperature reconstruction and linear interpolations could lead to poor estimates of heat flux. Our investigations conclusively point out the fact that existing polynomial-based reconstruction approaches for sharp interface IB techniques are not necessarily adequate for heat transfer predictions in high Reynolds number hypersonic flows.}, }
@article {pmid34001882, year = {2021}, author = {Nguyen, QM and Abouezzi, J and Ristroph, L}, title = {Early turbulence and pulsatile flows enhance diodicity of Tesla's macrofluidic valve.}, journal = {Nature communications}, volume = {12}, number = {1}, pages = {2884}, pmid = {34001882}, issn = {2041-1723}, abstract = {Microfluidics has enabled a revolution in the manipulation of small volumes of fluids. Controlling flows at larger scales and faster rates, or macrofluidics, has broad applications but involves the unique complexities of inertial flow physics. We show how such effects are exploited in a device proposed by Nikola Tesla that acts as a diode or valve whose asymmetric internal geometry leads to direction-dependent fluidic resistance. Systematic tests for steady forcing conditions reveal that diodicity turns on abruptly at Reynolds number [Formula: see text] and is accompanied by nonlinear pressure-flux scaling and flow instabilities, suggesting a laminar-to-turbulent transition that is triggered at unusually low [Formula: see text]. To assess performance for unsteady forcing, we devise a circuit that functions as an AC-to-DC converter, rectifier, or pump in which diodes transform imposed oscillations into directed flow. Our results confirm Tesla's conjecture that diodic performance is boosted for pulsatile flows. The connections between diodicity, early turbulence and pulsatility uncovered here can inform applications in fluidic mixing and pumping.}, }
@article {pmid33998932, year = {2021}, author = {Chen, X and Zhang, Y and Wang, J}, title = {Simulation analysis of mixing in passive microchannel with fractal obstacles based on Murray's law.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {24}, number = {15}, pages = {1670-1678}, doi = {10.1080/10255842.2021.1906867}, pmid = {33998932}, issn = {1476-8259}, mesh = {Computer Simulation ; Diffusion ; *Fractals ; }, abstract = {In this paper, we designed fractal obstacles according to Murray's law and set them in a microchannel. We study the influence of the numbers of fractal obstacles, channel widths, branch widths, and the distance between fractal obstacles on mixing efficiency. The optimized micromixer has a high mixing efficiency of more than 90% at all velocities. This paper focuses on the analysis of the variation of mixing efficiency and pressure drop in the range of Reynolds number (Re) 0.1-150. The simulation results show that when the fluid velocity is low, the mixing efficiency of the fluids is mainly improved by molecular diffusion, when the fluid velocity is high, the microchannel with fractal obstacles can promote chaotic convection of the fluids and improve the mixing efficiency. The fractal structure based on Murray's law can be widely used in the design of passive micromixer.}, }
@article {pmid33998624, year = {2021}, author = {Su, J and Chen, X and Zhu, Y and Hu, G}, title = {Machine learning assisted fast prediction of inertial lift in microchannels.}, journal = {Lab on a chip}, volume = {21}, number = {13}, pages = {2544-2556}, doi = {10.1039/d1lc00225b}, pmid = {33998624}, issn = {1473-0189}, mesh = {Cross-Sectional Studies ; Lab-On-A-Chip Devices ; Machine Learning ; *Microfluidic Analytical Techniques ; Microfluidics ; }, abstract = {Inertial effect has been extensively used in manipulating both engineered particles and biocolloids in microfluidic platforms. The design of inertial microfluidic devices largely relies on precise prediction of particle migration that is determined by the inertial lift acting on the particle. In spite of being the only means to accurately obtain the lift forces, direct numerical simulation (DNS) often consumes high computational cost and even becomes impractical when applied to microchannels with complex geometries. Herein, we proposed a fast numerical algorithm in conjunction with machine learning techniques for the analysis and design of inertial microfluidic devices. A database of inertial lift forces was first generated by conducting DNS over a wide range of operating parameters in straight microchannels with three types of cross-sectional shapes, including rectangular, triangular and semicircular shapes. A machine learning assisted model was then developed to gain the inertial lift distribution, by simply specifying the cross-sectional shape, Reynolds number and particle blockage ratio. The resultant inertial lift was integrated into the Lagrangian tracking method to quickly predict the particle trajectories in two types of microchannels in practical devices and yield good agreement with experimental observations. Our database and the associated codes allow researchers to expedite the development of the inertial microfluidic devices for particle manipulation.}, }
@article {pmid33997904, year = {2021}, author = {Garayev, K and Murphy, DW}, title = {Metachronal Swimming of Mantis Shrimp: Kinematics and Interpleopod Vortex Interactions.}, journal = {Integrative and comparative biology}, volume = {61}, number = {5}, pages = {1631-1643}, doi = {10.1093/icb/icab052}, pmid = {33997904}, issn = {1557-7023}, mesh = {Animals ; Biomechanical Phenomena ; *Copepoda ; *Decapoda ; Extremities ; Models, Biological ; Swimming ; }, abstract = {Mantis shrimp swim via metachronal rowing, a pattern in which the pleopods (swimming limbs) stroke sequentially, starting with the last pair and followed by anterior neighbors. A similar swimming pattern is used at various sizes, Reynolds numbers, and advance ratios by diverse organisms including ciliates, ctenophores, copepods, krill, and lobsters. Understanding this type of locomotion is important because it is widespread and may inspire the design of underwater vehicles where efficiency, robustness, and maneuverability are desired. However, detailed measurements of the flow around free-swimming, metachronally rowing organisms are scarce, especially for organisms swimming in a high Reynolds number regime (Re ≥ 104). In this study, we present time-resolved, planar PIV measurements of a swimming peacock mantis shrimp (Odontodactylus scyllarus). Simultaneous kinematics measurements of the animal, which had body and pleopod lengths of 114 and 20 mm, respectively, reveal mean swimming speeds of 0.2-1.9 m s-1 and pleopod beat frequencies of 3.6-13 Hz, corresponding to advance ratios of 0.75-1.84 and body-based Reynolds numbers of 23,000-217,000. Further, the animal's stroke is not purely metachronal, with a long phase lag between initiation of the first and fifth pleopod power strokes. Flow measurements in the sagittal plane show that each stroking pleopod pair creates a posteriorly moving tip vortex which evades destruction by the recovery strokes of other pleopod pairs. The vortex created by the anteriormost pleopod pair is the strongest and, owing to the animal's high advance ratio, is intercepted by the power stroke of the posteriormost pleopod pair. The vortex strength increases as a result of this interaction, which may increase swimming speed or efficiency. A relationship for vortex interception by the posterior pleopod is proposed that relates the phase lag between the interacting pleopods to the beat frequency, distance between those pleopods, and speed of the vortex relative to the animal. We describe this interaction with a novel parameter called the interpleopod vortex phase matching Strouhal number StIVPM which is equal to the phase lag between interacting pleopods. This new nondimensional parameter may be useful in predicting the conditions where a constructive interaction may occur in other species or in physical models. Finally, we relate the advance ratio to the Reynolds number ratio, the ratio between the body-based Reynolds number and the pleopod-based Reynolds number. The importance of these parameters in promoting the interpleopod vortex interactions identified here, in dynamically scaled experiments, and in wake signatures behind schooling metachronal swimmers is discussed.}, }
@article {pmid33986400, year = {2021}, author = {Mehboudi, A and Yeom, J}, title = {A passive Stokes flow rectifier for Newtonian fluids.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {10182}, pmid = {33986400}, issn = {2045-2322}, abstract = {Non-linear effects of the Navier-Stokes equations disappear under the Stokes regime of Newtonian fluid flows disallowing a flow rectification behavior. Here we show that passive flow rectification of Newtonian fluids is obtainable under the Stokes regime of both compressible and incompressible flows by introducing nonlinearity into the otherwise linear Stokes equations. Asymmetric flow resistances arise in shallow nozzle/diffuser microchannels with deformable ceiling, in which the fluid flow is governed by a non-linear coupled fluid-solid mechanics equation. The proposed model captures the unequal deflection profile of the deformable ceiling depending on the flow direction under the identical applied pressure, permitting a larger flow rate in the nozzle configuration. Ultra-low aspect ratio microchannels sealed by a flexible membrane have been fabricated to demonstrate passive flow rectification for low-Reynolds-number flows (0.001 < Re < 10) of common Newtonian fluids such as water, methanol, and isopropyl alcohol. The proposed rectification mechanism is also extended to compressible flows, leading to the first demonstration of rectifying equilibrium gas flows under the Stokes flow regime. While the maximum rectification ratio experimentally obtained in this work is limited to 1.41, a higher value up to 1.76 can be achieved by optimizing the width profile of the asymmetric microchannels.}, }
@article {pmid33976300, year = {2021}, author = {Kazemi, A and Castillo, L and Curet, OM}, title = {Mangrove roots model suggest an optimal porosity to prevent erosion.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {9969}, pmid = {33976300}, issn = {2045-2322}, abstract = {Mangrove swamps are extremely productive ecosystems providing many ecological services in coastal regions. The hydrodynamic interactions of mangrove roots and water flow have been proposed as a key element to mitigate erosion. Several studies reveal that precise prediction of the morphological evolution of coastal areas, in the face of global warming and the consequent sea-level rise, requires an understanding of interactions between root porosity (the fraction of the volume of void space over the total volume), water flows, and sediment transport. Water flows around the mangrove prop roots create a complex energetic process that mixes up sediments and generates a depositional region posterior to the roots. In this work, we investigated the boundary layer behind permeable arrays of cylinders (patch) that represent the mangrove roots to explore the impact of patch porosity on the onset of sediment transport. The flow measurements were performed in a vertical plane along the water depth downstream of the mangrove root models. A high-resolution Particle Image Velocimetry (PIV) was used in a flume to observe the impact of porosity on the mean flow, velocity derivatives, skin friction coefficient, and production of turbulent kinetic energy for Reynolds number of 2500 (based on patch diameter length-scale). Here, we proposed a predictive model for critical velocity for incipient motion that takes into account the mangrove roots porosity and the near-bed turbulence effect. It is found that the patch with the [Formula: see text] porosity, has the maximum critical velocity over which the sediment transport initiates. We found the optimum porosity has the minimum sediment erosion and creates negative vorticity sources near the bed that increases the critical velocity. This signifies an optimum porosity for the onset of sediment transport consistent with the porosity of mangroves in nature. The phenomenological model is elucidated based on an analysis of the vorticity evolution equation for viscous incompressible flows. For the optimum porous patch, a sink of vorticity was formed which yielded to lower the near-bed turbulence and vorticity. The minimum velocity fluctuations were sufficient to initiate the boundary layer transition, however, the viscous dissipation dominated the turbulence production to obstruct the sediment transport. This work identified the pivotal role of mangrove root porosity in sediment transport in terms of velocity and its derivatives in wall-bounded flows. Our work also provides insight into the sediment transport and erosion processes that govern the evolution of the shapes of shorelines.}, }
@article {pmid33956314, year = {2021}, author = {Vasilopoulos, K and Lekakis, I and Sarris, IE and Tsoutsanis, P}, title = {Large eddy simulation of dispersion of hazardous materials released from a fire accident around a cubical building.}, journal = {Environmental science and pollution research international}, volume = {28}, number = {36}, pages = {50363-50377}, pmid = {33956314}, issn = {1614-7499}, mesh = {Accidents ; *Air Pollutants/analysis ; *Hazardous Substances ; Models, Theoretical ; Wind ; }, abstract = {The turbulent smoke dispersion from a pool fire around a cubical building is studied using large eddy simulation at a high Reynolds number, corresponding to existing experimental measurements both in laboratory and field test scales. Emphasis of this work is on the smoke dispersion due to two different fuel pool fire accident scenarios, initiated behind the building. For the setup of fire in the first case, crude oil was used with a heat release rate of 7.8 MW, and in the second, diesel oil with a heat release rate of 13.5 MW. It is found that in both fire scenarios, the downstream extent of the toxic zone is approximately the same. This is explained in terms of the fact that the smoke concentration and dispersion are influenced mainly by the convective buoyant forces and the strong turbulence mixing processes within the wake zone of the building. It is suggested that wind is the dominating factor in these accident scenarios, which represent the conditions resulting in the highest toxicity levels.}, }
@article {pmid33953255, year = {2021}, author = {Asai, T and Hong, S}, title = {Aerodynamics of the newly approved football for the English Premier League 2020-21 season.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {9578}, pmid = {33953255}, issn = {2045-2322}, abstract = {Footballs are typically constructed with 32 panels. Recently, the number of panels has been successively reduced to 14, 8, and 6 panels, and official balls have been adopted with complex panel shapes and aerodynamics that differ from those of 32-panel balls. The official ball for the 2020-21 season of the English Premier League comprises just four panels with a complex panel shape and surface groove design; however, its aerodynamics have not yet been clarified. This study aims to clarify the aerodynamic characteristics (drag, side force, lift force, their deviations, and critical Reynolds number) of the new 4-panel ball (Flight 2020, Nike) in comparison to a 6-panel ball (Tsubasa 2020, Adidas) and conventional 32-panel ball (Pelada 2020, Molten) using a wind tunnel test, surface design measurement, and a simple 2D flight simulation. The results showed that Flight 2020 has greater surface roughness and smaller critical Reynolds number than Pelada 2020 and Tsubasa 2020, resulting to its marginally greater drag force in the supercritical region, and slightly smaller fluctuations of the side and lift forces. Furthermore, Flight with a symmetrical orientation exhibits a significantly higher drag coefficient in the supercritical region, suggesting its greater air resistance during flight under this condition.}, }
@article {pmid33949106, year = {2021}, author = {Sharan, P and Nsamela, A and Lesher-Pérez, SC and Simmchen, J}, title = {Microfluidics for Microswimmers: Engineering Novel Swimmers and Constructing Swimming Lanes on the Microscale, a Tutorial Review.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {17}, number = {26}, pages = {e2007403}, doi = {10.1002/smll.202007403}, pmid = {33949106}, issn = {1613-6829}, mesh = {Engineering ; *Microfluidics ; *Swimming ; }, abstract = {This paper provides an updated review of recent advances in microfluidics applied to artificial and biohybrid microswimmers. Sharing the common regime of low Reynolds number, the two fields have been brought together to take advantage of the fluid characteristics at the microscale, benefitting microswimmer research multifold. First, microfluidics offer simple and relatively low-cost devices for high-fidelity production of microswimmers made of organic and inorganic materials in a variety of shapes and sizes. Microscale confinement and the corresponding fluid properties have demonstrated differential microswimmer behaviors in microchannels or in the presence of various types of physical or chemical stimuli. Custom environments to study these behaviors have been designed in large part with the help of microfluidics. Evaluating microswimmers in increasingly complex lab environments such as microfluidic systems can ensure more effective implementation for in-field applications. The benefits of microfluidics for the fabrication and evaluation of microswimmers are balanced by the potential use of microswimmers for sample manipulation and processing in microfluidic systems, a large obstacle in diagnostic and other testing platforms. In this review various ways in which these two complementary technology fields will enhance microswimmer development and implementation in various fields are introduced.}, }
@article {pmid33947812, year = {2021}, author = {Hartl, B and Hübl, M and Kahl, G and Zöttl, A}, title = {Microswimmers learning chemotaxis with genetic algorithms.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {118}, number = {19}, pages = {}, pmid = {33947812}, issn = {1091-6490}, mesh = {Algorithms ; Animals ; Caenorhabditis elegans/physiology ; Chemotaxis/*genetics/*physiology ; Computer Simulation ; Flagella/physiology ; Learning/*physiology ; Machine Learning ; Models, Biological ; Motion ; Neural Networks, Computer ; Swimming/*physiology ; }, abstract = {Various microorganisms and some mammalian cells are able to swim in viscous fluids by performing nonreciprocal body deformations, such as rotating attached flagella or by distorting their entire body. In order to perform chemotaxis (i.e., to move toward and to stay at high concentrations of nutrients), they adapt their swimming gaits in a nontrivial manner. Here, we propose a computational model, which features autonomous shape adaptation of microswimmers moving in one dimension toward high field concentrations. As an internal decision-making machinery, we use artificial neural networks, which control the motion of the microswimmer. We present two methods to measure chemical gradients, spatial and temporal sensing, as known for swimming mammalian cells and bacteria, respectively. Using the genetic algorithm NeuroEvolution of Augmenting Topologies, surprisingly simple neural networks evolve. These networks control the shape deformations of the microswimmers and allow them to navigate in static and complex time-dependent chemical environments. By introducing noisy signal transmission in the neural network, the well-known biased run-and-tumble motion emerges. Our work demonstrates that the evolution of a simple and interpretable internal decision-making machinery coupled to the environment allows navigation in diverse chemical landscapes. These findings are of relevance for intracellular biochemical sensing mechanisms of single cells or for the simple nervous system of small multicellular organisms such as Caenorhabditis elegans.}, }
@article {pmid33938005, year = {2021}, author = {Wang, S and Liu, Z and Wu, S and Sun, H and Zeng, W and Wei, J and Fan, Z and Sui, Z and Liu, L and Pan, X}, title = {Microalgae separation by inertia-enhanced pinched flow fractionation.}, journal = {Electrophoresis}, volume = {42}, number = {21-22}, pages = {2223-2229}, doi = {10.1002/elps.202000325}, pmid = {33938005}, issn = {1522-2683}, mesh = {Chemical Fractionation ; Chlorella ; *Microalgae ; Ships ; Water ; }, abstract = {To improve the accuracy and efficiency of ships' ballast water detection, the separation of microalgae according to size is significant. In this article, a method to separate microalgae based on inertia-enhanced pinched flow fractionation (iPFF) was reported. The method utilized the inertial lift force induced by flow to separate microalgae according to size continuously. The experimental results show that, as the Reynolds number increases, the separation effect becomes better at first, but then stays unchanged. The best separation effect can be obtained when the Reynolds number is 12.3. In addition, with the increase of the flow rate ratio between sheath fluid and microalgae mixture, the separation effect becomes better and the best separation effect can be obtained when the flow rate ratio reaches 10. In this case, the recovery rate of Tetraselmis sp. is about 90%, and the purity is about 86%; the recovery rate of Chlorella sp. is as high as 99%, and the purity is about 99%. After that, the separation effect keeps getting better but very slowly. In general, this study provides a simple method for the separation of microalgae with different sizes, and lays a foundation for the accurate detection of microalgae in the ballast water.}, }
@article {pmid33924044, year = {2021}, author = {Rao, Y and Li, L and Wang, S and Zhao, S and Zhou, S}, title = {Numerical Simulation Study on Flow Laws and Heat Transfer of Gas Hydrate in the Spiral Flow Pipeline with Long Twisted Band.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {4}, pages = {}, pmid = {33924044}, issn = {1099-4300}, support = {51574045//National Nature Science Foundation of China/ ; 51974037//National Nature Science Foundation of China/ ; 2020D-5007-0211//CNPC Innovation Foundation/ ; CJ20200085//Changzhou Applied Basic Research Project/ ; }, abstract = {The natural gas hydrate plugging problems in the mixed pipeline are becoming more and more serious. The hydrate plugging has gradually become an important problem to ensure the safety of pipeline operation. The deposition and heat transfer characteristics of natural gas hydrate particles in the spiral flow pipeline have been studied. The DPM model (discrete phase model) was used to simulate the motion of solid particles, which was used to simulate the complex spiral flow characteristics of hydrate in the pipeline with a long twisted band. The deposition and heat transfer characteristics of gas hydrate particles in the spiral flow pipeline were studied. The velocity distribution, pressure drop distribution, heat transfer characteristics, and particle settling characteristics in the pipeline were investigated. The numerical results showed that compared with the straight flow without a long twisted band, two obvious eddies are formed in the flow field with a long twisted band, and the velocities are maximum at the center of the vortices. Along the direction of the pipeline, the two vortices move toward the pipe wall from near the twisted band, which can effectively carry the hydrate particles deposited on the wall. With the same Reynolds number, the twisted rate was greater, the spiral strength was weaker, the tangential velocity was smaller, and the pressure drop was smaller. Therefore, the pressure loss can be reduced as much as possible with effect of the spiral flow. In a straight light flow, the Nusselt number is in a parabolic shape with the opening downwards. At the center of the pipe, the Nusselt number gradually decreased toward the pipe wall at the maximum, and at the near wall, the attenuation gradient of the Nu number was large. For spiral flow, the curve presented by the Nusselt number was a trough at the center of the pipe and a peak at 1/2 of the pipe diameter. With the reduction of twist rate, the Nusselt number becomes larger. Therefore, the spiral flow can make the temperature distribution more even and prevent the large temperature difference, resulting in the mass formation of hydrate particles in the pipeline wall. Spiral flow has a good carrying effect. Under the same condition, the spiral flow carried hydrate particles at a distance about 3-4 times farther than that of the straight flow.}, }
@article {pmid33923993, year = {2021}, author = {Yuan, S and Jiang, B and Peng, T and Li, Q and Zhou, M}, title = {An Investigation of Flow Patterns and Mixing Characteristics in a Cross-Shaped Micromixer within the Laminar Regime.}, journal = {Micromachines}, volume = {12}, number = {4}, pages = {}, pmid = {33923993}, issn = {2072-666X}, support = {51920105008//National Natural Science Foundation of China/ ; 2019SK2221//Key Research and Development Program of Hunan Province of China/ ; }, abstract = {A fast mixing is critical for subsequent practical development of microfluidic devices, which are often used for assays in the detection of reagents and samples. The present work sets up computational fluid dynamics simulations to explore the flow characteristic and mixing mechanism of fluids in cross-shaped mixers within the laminar regime. First, the effects of increasing an operating parameter on local mixing quality along the microchannels are investigated. It is found that sufficient diffusion cannot occur even though the concentration gradient is large at a high Reynolds number. Meanwhile, a method for calculating local mixing efficiency is also characterized. The mixing efficiency varies exponentially with the flow distance. Second, in order to optimize the cross-shaped mixer, the effects of design parameters, namely aspect ratio, mixing angle and blockage, on mixing quality are captured and the visualization of velocity and concentration distribution are demonstrated. The results show that the aspect ratio and the blockage play an important role in accelerating the mixing process. They can improve the mixing efficiency by increasing the mass transfer area and enhancing the chaotic advection, respectively. In contrast, the inflow angle that affects dispersion length is not an effective parameter. Besides, the surface roughness, which makes the disturbance of fluid flow by roughness more obvious, is considered. Three types of rough elements bring benefits for enhancing mixing quality due to the convection induced by the lateral velocity.}, }
@article {pmid33922337, year = {2021}, author = {Ansari, A and Kavousi, S and Helfer, F and Millar, G and Thiel, DV}, title = {An Improved Modelling Approach for the Comprehensive Study of Direct Contact Membrane Distillation.}, journal = {Membranes}, volume = {11}, number = {5}, pages = {}, pmid = {33922337}, issn = {2077-0375}, abstract = {Direct Contact Membrane Distillation (DCMD) is a promising and feasible technology for water desalination. Most of the models used to simulate DCMD are one-dimensional and/or use a linear function of vapour pressure which relies on experimentally determined parameters. In this study, the model of DCMD using Nusselt correlations was improved by coupling the continuity, momentum, and energy equations to better capture the downstream alteration of flow field properties. A logarithmic function of vapour pressure, which is independent from experiments, was used. This allowed us to analyse DCMD with different membrane properties. The results of our developed model were in good agreement with the DCMD experimental results, with less than 7% deviation. System performance metrics, including water flux, temperature, and concentration polarisation coefficient and thermal efficiency, were analysed by varying inlet feed and permeate temperature, inlet velocity, inlet feed concentration, channel length. In addition, twenty-two commercial membranes were analysed to obtain a real vision on the influence of membrane characteristics on system performance metrics. The results showed that the feed temperature had the most significant effect on water flux and thermal efficiency. The increased feed temperature enhanced the water flux and thermal efficiency; however, it caused more concentration and temperature polarisation. On the other hand, the increased inlet velocity was found to provide increased water flux and reduced temperature and concertation polarisation as well. It was also found that the membrane properties, especially thickness and porosity, can affect the DCMD performance significantly. A two-fold increase of feed temperature increased the water flux and thermal efficiency, 10-fold and 27%, respectively; however, it caused an increase in temperature and concertation polarisation, at 48% and 34%, respectively. By increasing Reynolds number from 80 to 1600, the water flux, CPC, and TPC enhanced by 2.3-fold, 2%, and 21%, respectively. The increased feed concentration from 0 to 250 [g/L] caused a 26% reduction in water flux. To capture the downstream alteration of flow properties, it was shown that the ratio of inlet value to outlet value of system performance metrics decreased significantly throughout the module. Therefore, improvement over the conventional model is undeniable, as the new model can assist in achieving optimal operation conditions.}, }
@article {pmid33922099, year = {2021}, author = {Yuan, C and Zhang, H and Li, X and Oishi, M and Oshima, M and Yao, Q and Li, F}, title = {Numerical Investigation of T-Shaped Microfluidic Oscillator with Viscoelastic Fluid.}, journal = {Micromachines}, volume = {12}, number = {5}, pages = {}, pmid = {33922099}, issn = {2072-666X}, support = {51776057, 51606054, 51911540073 and 11972384//National Natural Science Foundation of China/ ; }, abstract = {Oscillatory flow has many applications in micro-scaled devices. The methods of realizing microfluidic oscillators reported so far are typically based on the impinging-jet and Coanda effect, which usually require the flow Reynolds number to be at least at the order of unity. Another approach is to introduce elastomeric membrane into the microfluidic units; however, the manufacturing process is relatively complex, and the membrane will become soft after long-time operation, which leads to deviation from the design condition. From the perspective of the core requirement of a microfluidic circuit, i.e., nonlinearity, the oscillatory microfluidic flow can be realized via the nonlinear characteristics of viscoelastic fluid flow. In this paper, the flow characteristics of viscoelastic fluid (Boger-type) in a T-shaped channel and its modified structures are studied by two-dimensional direct numerical simulation (DNS). The main results obtained from the DNS study are as follows: (1) Both Weissenberg (Wi) number and viscosity ratio need to be within a certain range to achieve a periodic oscillating performance; (2) With the presence of the dynamic evolution of the pair of vortices in the upstream near the intersection, the oscillation intensity increases as the elasticity-dominated area in the junction enlarges; (3) Considering the simplicity of the T-type channel as a potential oscillator, the improved structure should have a groove carved toward the entrance near the upper wall. The maximum oscillation intensity measured by the standard deviation of flow rate at outlet is increased by 129% compared with that of the original standard T-shaped channel under the same condition. To sum up, with Wi number and viscosity ratio within a certain range, the regular periodic oscillation characteristics of Oldroyd-B type viscoelastic fluid flow in standard T-shaped and its modified channels can be obtained. This structure can serve as a passive microfluidic oscillator with great potential value at an extremely low Reynolds number, which has the advantages of simplicity, no moving parts and fan-out of two.}, }
@article {pmid33920267, year = {2021}, author = {Abbasnezhad, N and Kebdani, M and Shirinbayan, M and Champmartin, S and Tcharkhtchi, A and Kouidri, S and Bakir, F}, title = {Development of a Model Based on Physical Mechanisms for the Explanation of Drug Release: Application to Diclofenac Release from Polyurethane Films.}, journal = {Polymers}, volume = {13}, number = {8}, pages = {}, pmid = {33920267}, issn = {2073-4360}, support = {9 bis, Avenue I&#xe9;na 75783 PARIS Cedex 16 France//Foundation Arts et M&#xe9;tiers/ ; }, abstract = {In this study, we present a method for prediction of the drug-release profile based on the physical mechanisms that can intervene in drug release from a drug-carrier. The application presented here incorporates the effects of drug concentration and Reynolds number defining the circulating flow in the testing vein. The experimental data used relate to the release of diclofenac from samples of non-degradable polyurethane subjected to static and continuous flow. This case includes simultaneously three mechanisms: burst-release, diffusion and osmotic pressure, identified beforehand here as being able to contribute to the drug liberation. For this purpose, authors coded the Sequential Quadratic Programming Algorithm to solve the problem of non-linear optimization. The experimental data used to develop the mathematical model obtained from release studies carried out in water solution at 37 °C, for three concentrations of diclofenac and two water flow rates. We discuss the contribution of mechanisms and kinetics by considering two aforementioned parameters and, following that, we obtain the specific-model and compare the calculated results with the experimental results for the reserved cases. The results showed that drug percentage mostly affect the burst release, however flow rate has affected the osmotic release. In addition, release kinetics of all the mechanisms have increased by increasing the values of two considered parameters.}, }
@article {pmid33917762, year = {2021}, author = {Wang, R and Duan, R and Jia, H}, title = {Experimental Validation of Falling Liquid Film Models: Velocity Assumption and Velocity Field Comparison.}, journal = {Polymers}, volume = {13}, number = {8}, pages = {}, pmid = {33917762}, issn = {2073-4360}, support = {Grant No. 51779126//National Natural Science Foundation of China/ ; }, abstract = {This publication focuses on the experimental validation of film models by comparing constructed and experimental velocity fields based on model and elementary experimental data. The film experiment covers Kapitza numbers Ka = 278.8 and Ka = 4538.6, a Reynolds number range of 1.6-52, and disturbance frequencies of 0, 2, 5, and 7 Hz. Compared to previous publications, the applied methodology has boundary identification procedures that are more refined and provide additional adaptive particle image velocimetry (PIV) method access to synthetic particle images. The experimental method was validated with a comparison with experimental particle image velocimetry and planar laser induced fluorescence (PIV/PLIF) results, Nusselt's theoretical prediction, and experimental particle tracking velocimetry (PTV) results of flat steady cases, and a good continuity equation reproduction of transient cases proves the method's fidelity. The velocity fields are reconstructed based on different film flow model velocity profile assumptions such as experimental film thickness, flow rates, and their derivatives, providing a validation method of film model by comparison between reconstructed velocity experimental data and experimental velocity data. The comparison results show that the first-order weighted residual model (WRM) and regularized model (RM) are very similar, although they may fail to predict the velocity field in rapidly changing zones such as the front of the main hump and the first capillary wave troughs.}, }
@article {pmid33915686, year = {2021}, author = {Rasool, G and Shafiq, A and Alqarni, MS and Wakif, A and Khan, I and Bhutta, MS}, title = {Numerical Scrutinization of Darcy-Forchheimer Relation in Convective Magnetohydrodynamic Nanofluid Flow Bounded by Nonlinear Stretching Surface in the Perspective of Heat and Mass Transfer.}, journal = {Micromachines}, volume = {12}, number = {4}, pages = {}, pmid = {33915686}, issn = {2072-666X}, abstract = {The aim of this research is mainly concerned with the numerical examination of Darcy-Forchheimer relation in convective magnetohydrodynamic nanofluid flow bounded by non-linear stretching sheet. A visco-elastic and strictly incompressible liquid saturates the designated porous medium under the direct influence of the Darcy-Forchheimer model and convective boundary. The magnetic effect is taken uniformly normal to the flow direction. However, the model is bounded to a tiny magnetic Reynolds number for practical applications. Boundary layer formulations are taken into consideration. The so-formulated leading problems are converted into highly nonlinear ordinary problems using effectively modified transformations. The numerical scheme is applied to solve the governing problems. The outcomes stipulate that thermal layer receives significant modification in the incremental direction for augmented values of thermal radiation parameter Rd. Elevation in thermal Biot number γ1 apparently results a significant rise in thermal layer and associated boundary layer thickness. The solute Biot number is found to be an enhancing factor the concentration profile. Besides the three main profiles, the contour and density graphs are sketched for both the linear and non-linear cases. Furthermore, skin friction jumps for larger porosity and larger Forchheimer number. Both the heat and mass flux numbers receive a reduction for augmented values of the Forchheimer number. Heat flux enhances, while mass flux reduces, the strong effect of thermal Biot number. The considered problem could be helpful in any several industrial and engineering procedures, such as rolling, polymeric extrusion, continuously stretching done in plastic thin films, crystal growth, fiber production, and metallic extrusion, etc.}, }
@article {pmid33907644, year = {2021}, author = {Kesserwani, H}, title = {Space Flight-Associated Neuroocular Syndrome, Idiopathic Intracranial Hypertension, and Pseudotumor Cerebri: Phenotypic Descriptions, Pathogenesis, and Hydrodynamics.}, journal = {Cureus}, volume = {13}, number = {3}, pages = {e14103}, pmid = {33907644}, issn = {2168-8184}, abstract = {Recent data from astronauts who have returned to Earth from a long-duration space flight have unequivocally distinguished spaceflight-associated neuro-ocular syndrome (SANS) from idiopathic intracranial hypertension (IIH) and pseudotumor cerebri (PTC). We review the semiology and pathogenesis of these three entities, noting that optic disc edema is what unites them, and this where the similarities between SANS and IIH/PTC end. We distinguish between PTC and IIH and between SANS and IIH/PTC and review the medical and surgical therapy of IIH/PTC. The key to understanding the phenomenon of optic disc edema is the geometry of the optic nerve sheath, which is a simulacrum of an inverted Venturi tube. This allows us to theoretically study the hydrodynamics of the optic nerve sheath by applying simple physical laws, including the Venturi effect, Poiseuille's law, and Reynold's number, and we speculate on nature's design and the correlation of form and function in understanding how cerebrospinal fluid (CSF) circulates in the optic nerve sheath as it approaches the optic nerve head. Recent spectacular data on the histology of the blood nerve-barrier of the optic nerve disc and the glymphatic system of the optic nerve sheath will also help us understand the development of optic disc edema due to the microgravity-induced cephalad shift of CSF in SANS. We will explore the role of the sodium/potassium adenosine triphosphatase (ATPase) pump on choroid plexus epithelial cells and the aquaporin-4 water receptors located on astrocyte end-feet and their complex interactions with the tetracyclines, mineralocorticoids, and therapeutic agents with carbonic anhydrase activity. We also adumbrate the complex interactions between obesity, vitamin A, and 11-beta-hydroxysteroid dehydrogenase and how the aquaporin-4 receptor relates to these interactions.}, }
@article {pmid33905256, year = {2021}, author = {Sasaki, K and Okue, T and Nakai, T and Uchida, Y and Nishiyama, N}, title = {Lateral Growth of Uniformly Thin Gold Nanosheets Facilitated by Two-Dimensional Precursor Supply.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {37}, number = {19}, pages = {5872-5877}, doi = {10.1021/acs.langmuir.1c00344}, pmid = {33905256}, issn = {1520-5827}, abstract = {The nanosheets of highly symmetric materials with a face-centered cubic lattice such as gold have been synthesized by adsorbing the precursors on a flat surface, whose chemical specificity induces the anisotropy of growth rates. We have succeeded in the fabrication of gold nanosheets in a hydrophilic space inside highly separated bilayers, which work as two-dimensional hydrophilic reactors, in a hyperswollen lamellar liquid crystalline phase of an amphiphile solution. One of the physical properties, amphiphilicity, confines the ingredients therein. The nanosheets can only grow in the in-plane direction due to the inhibition of the out-of-plane growth rather than the anisotropy of growth rates probably. Thus, the synthesis can be accelerated; the particles can be completed within 15 min. As not relying on chemical specificity, silver nanosheets could also be synthesized in the same way. The suspension of gold and silver nanosheets without any amphiphiles could be obtained, and the solvent is replaceable. We found that the width of the obtained gold nanosheets is proportional to the Reynolds number of the solution because the area of the bilayer in the hyperswollen lamellar phase depends on shear stress. This implies that the areas of gold nanosheets depend on the areas of the bilayers, and it can be controlled by changing the Reynolds number. This method could be widely used to continuously obtain large-area nanosheets of various materials in a roll-to-roll manufacturing process.}, }
@article {pmid33902681, year = {2021}, author = {Heyland, A and Roszell, J and Chau, J and Chai, K and Eaton, A and Nolan, K and Madden, K and Ahmed, WH}, title = {Mass transfer and flow characterization of novel algae-based nutrient removal system.}, journal = {Biotechnology for biofuels}, volume = {14}, number = {1}, pages = {104}, pmid = {33902681}, issn = {1754-6834}, support = {Seeding Food Innovation Grant//George Weston Foundation/ ; }, abstract = {BACKGROUND: Recirculating aquaculture systems (RAS) are an essential component of sustainable inland seafood production. Still, nutrient removal from these systems can result in substantial environmental problems, or present a major cost factor with few added value options. In this study, an innovative and energy-efficient algae based nutrient removal system (NRS) was developed that has the potential to generate revenue through algal commercialization. We optimized mass transfer in our NRS design using novel aeration and mixing technology, using air lift pumps and developed an original membrane cartridge for the continuous operation of nutrient removal and algae production. Specifically, we designed, manufactured and tested a 60-L NRS prototype. Based on specific airlift mixing conditions as well as concentration gradients, we assessed NRS nutrient removal capacity. We then examined the effects of different internal bioreactor geometries and radial orientations on the mixing efficiency.<br><br>RESULTS: Using the start-up dynamic method, the overall mass transfer coefficient was found to be in the range of 0.00164-0.0074&#xa0;[Formula: see text], depending on flow parameters and we confirmed a scaling relationship of mass transfer across concentration gradients. We found the optimal Reynolds number to be 500 for optimal mass transfer, as higher Reynolds numbers resulted in a relatively reduced increase of mass transfer. This relationship between mass transfer and Reynolds number is critical to assess scalability of our system. Our results demonstrate an even distribution of dissolved oxygen levels across the reactor core, demonstrating adequate mixing by the airlift pump, a critical consideration for optimal algal growth. Distribution of dissolved gases in the reactor was further assessed using flow visualization in order to relate the bubble distribution to the mass transfer capabilities of the reactor. We run a successful proof of principle trial using the green alga Dunaliella tertiolecta to assess mass transfer of nutrients across the membrane and biomass production.<br><br>CONCLUSIONS: Manipulation of the concentration gradient across the membrane demonstrates a more prominent role of airlift mixing at higher concentration gradients. Specifically, the mass transfer rate increased threefold when the concentration gradient was increased 2.5-fold. We found that we can grow algae in the reactor chamber at rates comparable to those of other production systems and that the membrane scaffolds effectively remove nutrients form the wastewater. Our findings provide support for scalability of the design and support the use of this novel NRS for nutrient removal in aquaculture and potentially other applications.}, }
@article {pmid33895456, year = {2021}, author = {Song, Z and Tong, J and Pfleging, W and Sun, J}, title = {A review: Learning from the flight of beetles.}, journal = {Computers in biology and medicine}, volume = {133}, number = {}, pages = {104397}, doi = {10.1016/j.compbiomed.2021.104397}, pmid = {33895456}, issn = {1879-0534}, mesh = {Animals ; Biomechanical Phenomena ; *Coleoptera ; Mechanical Phenomena ; Miniaturization ; Wings, Animal ; }, abstract = {Some Coleoptera (popularly referred to as beetles) can fly at a low Reynolds number with their deployable hind wings, which directly enables a low body weight-a good bioinspiration strategy for miniaturization of micro-air vehicles (MAVs). The hind wing is a significant part of the body and has a folding/unfolding mechanism whose unique function benefits from different structures and materials. This review summarizes the actions, factors, and mechanisms of beetle flight and bioinspired MAVs with deployable wings. The elytron controlled by muscles is the protected part for the folded hind wing and influences flight performance. The resilin, the storage material for elasticity, is located in the folding parts. The hind wings' folding/unfolding mechanism and flight performance can be influenced by vein structures of hollow, solid and wrinkled veins, the hemolymph that flows in hollow veins and its hydraulic mechanism, and various mechanical properties of veins. The action of beetle flight includes flapping flight, hovering, gliding, and landing. The hind wing is passively deformed through force and hemolymph, and the attack angle of the hind wing and the nanomechanics of the veins, muscles and mass body determine the flight performance. Based these factors, bioinspired MAVs with a new deployable wing structure and new materials will be designed to be much more effective and miniaturized. The new fuels and energy supply are significant aspects of MAVs.}, }
@article {pmid33889684, year = {2021}, author = {Sadeq, AM and Ahmed, SF and Sleiti, AK}, title = {Dataset for transient 3D simulations of turbulent premixed flames of Gas-to-Liquid (GTL) fuel.}, journal = {Data in brief}, volume = {36}, number = {}, pages = {106956}, pmid = {33889684}, issn = {2352-3409}, abstract = {A fan-stirred combustion vessel is used to study the premixed turbulent combustion of diesel, Gas to Liquids (GTL) and 50/50 diesel-GTL and to generate these datasets. A numerical simulation approach is implemented for modelling the premixed combustion of the three fuels under different thermodynamics and turbulence initial conditions, using Zimont Turbulent Flame Speed Closure (Zimont TFC) model. Different parameters are obtained from these simulation runs such as turbulent eddy viscosity (µ), turbulent kinetic energy (k), Damkohler number (Da), Reynolds number (ReT) and turbulent flame speed (St). The raw, filtered and pre-processed data are imported from ANSYS Fluent and then listed on filtered tables for the ease of accessibility. These datasets can be then used to perform research in different related areas such as chemical kinetic mechanisms, ignition delay time, flame ignition mechanisms and flame extinction and diffusion. Also, they can be employed to further understand trends, patterns, and anomalies in data. In addition, they can be compared with other numerical models to establish a robust knowledge about the modelling of premixed turbulent combustion. For more information and discussion of the dataset creation, the reader is directed to the full-length article, "Abdellatif M. Sadeq, Samer F. Ahmed, Ahmad K. Sleiti, Transient 3D simulations of turbulent premixed flames of gas-to-liquid (GTL) fuel in a fan-stirred combustion vessel, Fuel, Volume 291, 2021, 120,184, ISSN 0016 2361, https://doi.org/10.1016/j.fuel.2021.120184" [1].}, }
@article {pmid33871634, year = {2021}, author = {Lamont, EI and Emlet, RB}, title = {Swimming Kinematics of Cyprids of the Barnacle Balanus glandula.}, journal = {Integrative and comparative biology}, volume = {61}, number = {5}, pages = {1567-1578}, doi = {10.1093/icb/icab028}, pmid = {33871634}, issn = {1557-7023}, mesh = {Animals ; Biomechanical Phenomena ; *Copepoda ; Larva ; Swimming ; *Thoracica ; }, abstract = {Larvae of barnacles typically pass through naupliar and cyprid planktonic stages before settlement and metamorphosis. As the final larval stage, cyprids swim much faster than nauplii and in turbulent fluid environments with high shears as they seek habitat. Cyprids swim with six pairs of reciprocating thoracic appendages and use two anterior antennules during settlement. Our understanding of how thoracic appendages generate movement is limited due to short stroke intervals (∼5 ms) that impede observations of the shape and trajectory of appendages. Here, we used high-speed videography to observe both free-swimming and tethered cyprids of the intertidal acorn barnacle Balanus glandula to produce a comprehensive description of thoracic appendage swimming kinematics. Cyprids used a drag-based method of swimming: their six pairs of thoracic appendages moved through metachronal power strokes and synchronous recovery strokes similar to the thoracopod motions in calanoid copepods during escape swimming. During the power stroke, plumose setae on each appendage pair spread laterally into a high surface area and high drag paddle composed of a meshwork of fused setules. This interconnected setal array collapsed into a low surface area and low drag shape during the recovery stroke. These effective swimming appendages allowed cyprids to move upward at an average speed of 1.4 cm/s (∼25 body lengths/s) with an average beat frequency of 16 beats/s, and reach an instantaneous velocity of up to 6 cm/s. Beat frequency of the thoracic appendages was significantly associated with speed, with higher beat frequencies indicating faster swimming speed. At their average speed, cyprids moved at the intermediate Reynolds number of ∼10, in which both viscous and inertial forces affected movement. Cyprids could alter swimming direction by sweeping the posterior-most appendage pair to one side and beating the remaining thoracic appendages synchronously through the power stroke with greater motion on the outside of their turn. These results greatly enhance our understanding both of cyprid motility and how small planktonic organisms can use swimming appendages with fused setule arrays to reach high swimming speeds and affect directional changes.}, }
@article {pmid33870835, year = {2021}, author = {Si, XA and Talaat, M and Su, WC and Xi, J}, title = {Inhalation dosimetry of nasally inhaled respiratory aerosols in the human respiratory tract with locally remodeled conducting lungs.}, journal = {Inhalation toxicology}, volume = {33}, number = {4}, pages = {143-159}, doi = {10.1080/08958378.2021.1912860}, pmid = {33870835}, issn = {1091-7691}, mesh = {*Administration, Inhalation ; Aerosols/*administration &amp; dosage ; *Airway Remodeling ; Dose-Response Relationship, Drug ; Humans ; Lung/anatomy &amp; histology/pathology ; Models, Biological ; Nanoparticles/*administration &amp; dosage ; Nose/anatomy &amp; histology ; }, abstract = {Objective: Respiratory diseases are often accompanied by alterations to airway morphology. However, inhalation dosimetry data in remodeled airways are scarce due to the challenges in reconstructing diseased respiratory morphologies. This study aims to study the airway remodeling effects on the inhalation dosimetry of nasally inhaled nanoparticles in a nose-lung geometry that extends to G9 (ninth generation).Materials and methods: Statistical shape modeling was used to develop four diseased lung models with varying levels of bronchiolar dilation/constriction in the left-lower (LL) lobe (i.e. M1-M4). Respiratory airflow and particle deposition were simulated using a low Reynolds number k-ω turbulence model and a Lagrangian tracking approach.Results: Significant discrepancies were observed in the flow partitions between the left and right lungs, as well as between the lower and upper lobes of the left lung, which changed by 10-fold between the most dilated and constricted models.Much lower doses were predicted on the surface of the constricted LL bronchioles G4-G9, as well as into the peripheral airways beyond G9 of the LL lung. However, the LL lobar remodeling had little effect on the dosimetry in the nasopharynx, as well as on the total dosimetry in the nose-lung geometry (up to G9).Conclusion: It is suggested that airway remodeling may pose a higher viral infection risk to the host by redistributing the inhaled viruses to healthy lung lobes. Airway remodeling effects should also be considered in the treatment planning of inhalation therapies, not only because of the dosimetry variation from altered lung morphology but also its evolution as the disease progresses.}, }
@article {pmid33863724, year = {2021}, author = {Trkulja, CL and Jungholm, O and Davidson, M and Jardemark, K and Marcus, MM and Hägglund, J and Karlsson, A and Karlsson, R and Bruton, J and Ivarsson, N and Srinivasa, SP and Cavallin, A and Svensson, P and Jeffries, GDM and Christakopoulou, MN and Reymer, A and Ashok, A and Willman, G and Papadia, D and Johnsson, E and Orwar, O}, title = {Rational antibody design for undruggable targets using kinetically controlled biomolecular probes.}, journal = {Science advances}, volume = {7}, number = {16}, pages = {}, pmid = {33863724}, issn = {2375-2548}, mesh = {*Antibodies, Monoclonal/chemistry ; *Antigens ; Binding Sites, Antibody ; Epitopes ; Humans ; }, abstract = {Several important drug targets, e.g., ion channels and G protein-coupled receptors, are extremely difficult to approach with current antibody technologies. To address these targets classes, we explored kinetically controlled proteases as structural dynamics-sensitive druggability probes in native-state and disease-relevant proteins. By using low-Reynolds number flows, such that a single or a few protease incisions are made, we could identify antibody binding sites (epitopes) that were translated into short-sequence antigens for antibody production. We obtained molecular-level information of the epitope-paratope region and could produce high-affinity antibodies with programmed pharmacological function against difficult-to-drug targets. We demonstrate the first stimulus-selective monoclonal antibodies targeting the transient receptor potential vanilloid 1 (TRPV1) channel, a clinically validated pain target widely considered undruggable with antibodies, and apoptosis-inducing antibodies selectively mediating cytotoxicity in KRAS-mutated cells. It is our hope that this platform will widen the scope of antibody therapeutics for the benefit of patients.}, }
@article {pmid33862704, year = {2021}, author = {Fouxon, I and Feinberg, J and Käpylä, P and Mond, M}, title = {Reynolds number dependence of Lyapunov exponents of turbulence and fluid particles.}, journal = {Physical review. E}, volume = {103}, number = {3-1}, pages = {033110}, doi = {10.1103/PhysRevE.103.033110}, pmid = {33862704}, issn = {2470-0053}, abstract = {The Navier-Stokes equations generate an infinite set of generalized Lyapunov exponents defined by different ways of measuring the distance between exponentially diverging perturbed and unperturbed solutions. This set is demonstrated to be similar, yet different, from the generalized Lyapunov exponent that provides moments of distance between two fluid particles below the Kolmogorov scale. We derive rigorous upper bounds on dimensionless Lyapunov exponent of the fluid particles that demonstrate the exponent's decay with Reynolds number Re in accord with previous studies. In contrast, terms of cumulant series for exponents of the moments have power-law growth with Re. We demonstrate as an application that the growth of small fluctuations of magnetic field in ideal conducting turbulence is hyperintermittent, being exponential in both time and Reynolds number. We resolve the existing contradiction between the theory, that predicts slow decrease of dimensionless Lyapunov exponent of turbulence with Re, and observations exhibiting quite fast growth. We demonstrate that it is highly plausible that a pointwise limit for the growth of small perturbations of the Navier-Stokes equations exists.}, }
@article {pmid33854256, year = {2021}, author = {Waringer, J and Vitecek, S and Martini, J and Zittra, C and Handschuh, S and Vieira, A and Kuhlmann, HC}, title = {Hydraulic niche utilization by larvae of the three Drusinae clades (Insecta: Trichoptera).}, journal = {Biologia}, volume = {76}, number = {5}, pages = {1465-1473}, pmid = {33854256}, issn = {0006-3088}, support = {P 31258/FWF_/Austrian Science Fund FWF/Austria ; }, abstract = {Hydraulic niche descriptors of final instar larvae of nine Drusus species (Trichoptera) were studied in small, spring-fed, first-order headwaters located in the Mühlviertel (Upper Austria), Koralpe (Carinthia, Austria), and in the Austrian and Italian Alps. The species investigated covered all three clades of Drusinae: the shredder clade (Drusus franzi, D. alpinus), the grazer clade (D. biguttatus, D. chauvinianus, D. dudor, D. monticola), and the filtering carnivore clade (D. chrysotus, D. katagelastos, D. muelleri). Flow velocity was measured at front center of 68 larvae, head upstream, on the top of mineral substrate particles at water depths of 10-30 mm, using a tripod-stabilized Micro propeller meter (propeller diameter = 10 mm). Each data series consisted of a sampled measurement lasting 30 s (measuring interval = 1 s). In total, 2040 single velocity measurements were taken. Instantaneous flow velocities and drag at the sites of the 68 larvae varied from 0 to 0.93 m s[-1] and 0 to 8346 *10[-6] N, respectively. Flow velocities and drag between the three clades were highly significantly different (p < 0.001); mean velocity (± 95% confidence limits) for the three clades were 0.09 ± 0.00 m s[-1] for the shredder, 0.25 ± 0.00 m s[-1] for the grazer, and 0.31 ± 0.01ms[-1] for the filtering carnivore clade; the corresponding data for drag were (85 ± 18)*10[-6] N, (422 ± 61)*10[-6] N and (1125 ± 83)*10[-6] N, respectively. Adhesive friction ranged from (41.07 ± 53.03)*10[-6] N in D. franzi to (255.24 ± 216.87)*10[-6] N in D. chrysotus. Except in D. franzi and D. dudor adhesive friction was always well below drag force, indicating that submerged weight alone was not sufficient to stabilize the larvae in their hydraulic environment. Reynolds numbers varied between 0 in D. franzi and D. alpinus, and 12,634 in D. katagelastos, with 7% of the total in the laminar (R < 500), 30%in the transitional (R = 500-2000), and 61%in the fully turbulent stage (R > 2000). Froude numbers (Fr) varied from 0 to 2.97. The two Drusus species of the shredder clade and three out of four species of the grazer clade were exposed to subcritical Fr < 1, one species of the grazer clade and two out of three species of the filtering clade to supercritical Froude numbers >1.}, }
@article {pmid33853049, year = {2021}, author = {Wang, Q and Wu, H}, title = {Mathematical modeling of chemotaxis guided amoeboid cell swimming.}, journal = {Physical biology}, volume = {18}, number = {4}, pages = {}, doi = {10.1088/1478-3975/abf7d8}, pmid = {33853049}, issn = {1478-3975}, support = {S10 OD016290/OD/NIH HHS/United States ; }, mesh = {*Chemotaxis ; Computational Biology ; Dictyostelium/*physiology ; Models, Biological ; Swimming/physiology ; }, abstract = {Cells and microorganisms adopt various strategies to migrate in response to different environmental stimuli. To date, many modeling research has focused on the crawling-basedDictyostelium discoideum(Dd) cells migration induced by chemotaxis, yet recent experimental results reveal that even without adhesion or contact to a substrate, Dd cells can still swim to follow chemoattractant signals. In this paper, we develop a modeling framework to investigate the chemotaxis induced amoeboid cell swimming dynamics. A minimal swimming system consists of one deformable Dd amoeboid cell and a dilute suspension of bacteria, and the bacteria produce chemoattractant signals that attract the Dd cell. We use themathematical amoeba modelto generate Dd cell deformation and solve the resulting low Reynolds number flows, and use a moving mesh based finite volume method to solve the reaction-diffusion-convection equation. Using the computational model, we show that chemotaxis guides a swimming Dd cell to follow and catch bacteria, while on the other hand, bacterial rheotaxis may help the bacteria to escape from the predator Dd cell.}, }
@article {pmid33834308, year = {2021}, author = {Solovev, A and Friedrich, BM}, title = {Lagrangian mechanics of active systems.}, journal = {The European physical journal. E, Soft matter}, volume = {44}, number = {4}, pages = {49}, pmid = {33834308}, issn = {1292-895X}, abstract = {We present a multi-scale modeling and simulation framework for low-Reynolds number hydrodynamics of shape-changing immersed objects, e.g., biological microswimmers and active surfaces. The key idea is to consider principal shape changes as generalized coordinates and define conjugate generalized hydrodynamic friction forces. Conveniently, the corresponding generalized friction coefficients can be pre-computed and subsequently reused to solve dynamic equations of motion fast. This framework extends Lagrangian mechanics of dissipative systems to active surfaces and active microswimmers, whose shape dynamics is driven by internal forces. As an application case, we predict in-phase and anti-phase synchronization in pairs of cilia for an experimentally measured cilia beat pattern.}, }
@article {pmid33833251, year = {2021}, author = {Abdal, S and Hussain, S and Siddique, I and Ahmadian, A and Ferrara, M}, title = {On solution existence of MHD Casson nanofluid transportation across an extending cylinder through porous media and evaluation of priori bounds.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {7799}, pmid = {33833251}, issn = {2045-2322}, abstract = {It is a theoretical exportation for mass transpiration and thermal transportation of Casson nanofluid over an extending cylindrical surface. The Stagnation point flow through porous matrix is influenced by magnetic field of uniform strength. Appropriate similarity functions are availed to yield the transmuted system of leading differential equations. Existence for the solution of momentum equation is proved for various values of Casson parameter [Formula: see text], magnetic parameter M, porosity parameter [Formula: see text] and Reynolds number Re in two situations of mass transpiration (suction/injuction). The core interest for this study aroused to address some analytical aspects. Therefore, existence of solution is proved and uniqueness of this results is discussed with evaluation of bounds for existence of solution. Results for skin friction factor are established to attain accuracy for large injection values. Thermal and concentration profiles are delineated numerically by applying Runge-Kutta method and shooting technique. The flow speed retards against M, [Formula: see text] and [Formula: see text] for both situations of mass injection and suction. The thermal boundary layer improves with Brownian and thermopherotic diffusions.}, }
@article {pmid33809995, year = {2021}, author = {Abramowicz-Gerigk, T and Burciu, Z and Jachowski, J and Kreft, O and Majewski, D and Stachurska, B and Sulisz, W and Szmytkiewicz, P}, title = {Experimental Method for the Measurements and Numerical Investigations of Force Generated on the Rotating Cylinder under Water Flow.}, journal = {Sensors (Basel, Switzerland)}, volume = {21}, number = {6}, pages = {}, pmid = {33809995}, issn = {1424-8220}, support = {WN/2020/PZ/01 and WN/2020/PZ/03//Gdynia Maritime University/ ; }, abstract = {The paper presents the experimental test setup and measurement method of hydrodynamic force generated on the rotating cylinder (rotor) under uniform flow including the free surface effect. The experimental test setup was a unique construction installed in the flume tank equipped with advanced flow generating and measuring systems. The test setup consisted of a bearing mounted platform with rotor drive and sensors measuring the hydrodynamic force. The low length to diameter ratio cylinders were selected as models of bow rotor rudders of a shallow draft river barge. The rotor dynamics was tested for the rotational speeds up to 550 rpm and water current velocity up to 0.85 m/s. The low aspect ratio of the cylinder and free surface effect had significant impacts on the phenomena influencing the generated hydrodynamic force. The effects of the rotor length to diameter ratio, rotational velocity to flow velocity ratio, and the Reynolds number on the lift force were analyzed. The validation of the computational model against experimental results is presented. The results show a similar trend of results for the simulation and experiment.}, }
@article {pmid33808487, year = {2021}, author = {Okuducu, MB and Aral, MM}, title = {Toward the Next Generation of Passive Micromixers: A Novel 3-D Design Approach.}, journal = {Micromachines}, volume = {12}, number = {4}, pages = {}, pmid = {33808487}, issn = {2072-666X}, abstract = {Passive micromixers are miniaturized instruments that are used to mix fluids in microfluidic systems. In microchannels, combination of laminar flows and small diffusion constants of mixing liquids produce a difficult mixing environment. In particular, in very low Reynolds number flows, e.g., Re < 10, diffusive mixing cannot be promoted unless a large interfacial area is formed between the fluids to be mixed. Therefore, the mixing distance increases substantially due to a slow diffusion process that governs fluid mixing. In this article, a novel 3-D passive micromixer design is developed to improve fluid mixing over a short distance. Computational Fluid Dynamics (CFD) simulations are used to investigate the performance of the micromixer numerically. The circular-shaped fluid overlapping (CSFO) micromixer design proposed is examined in several fluid flow, diffusivity, and injection conditions. The outcomes show that the CSFO geometry develops a large interfacial area between the fluid bodies. Thus, fluid mixing is accelerated in vertical and/or horizontal directions depending on the injection type applied. For the smallest molecular diffusion constant tested, the CSFO micromixer design provides more than 90% mixing efficiency in a distance between 260 and 470 µm. The maximum pressure drop in the micromixer is found to be less than 1.4 kPa in the highest flow conditioned examined.}, }
@article {pmid33807063, year = {2021}, author = {Rudl, J and Hanzelmann, C and Feja, S and Meyer, A and Potthoff, A and Buschmann, MH}, title = {Laminar Pipe Flow with Mixed Convection under the Influence of Magnetic Field.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {11}, number = {3}, pages = {}, pmid = {33807063}, issn = {2079-4991}, support = {49VF180041//Bundesministerium f&#xfc;r Wirtschaft und Energie/ ; }, abstract = {Magnetic influence on ferronanofluid flow is gaining increasing interest from not only the scientific community but also industry. The aim of this study is the examination of the potentials of magnetic forces to control heat transfer. Experiments are conducted to investigate the interaction between four different configurations of permanent magnets and laminar pipe flow with mixed convection. For that purpose a pipe flow test rig is operated with a water-magnetite ferronanofluid. The Reynolds number is varied over one order of magnitude (120-1200). To characterise this suspension, density, solid content, viscosity, thermal conductivity, and specific heat capacity are measured. It is found that, depending on the positioning of the magnet(s) and the Reynolds number, heat transfer is either increased or decreased. The experiments indicate that this is a local effect. After relaxation lengths ranging between 2 and 3.5 lengths of a magnet, all changes disappeared. The conclusion from these findings is that magnetic forces are rather a tool to control heat transfer locally than to enhance the overall heat transfer of heat exchangers or the like. Magnetically caused disturbances decay due to viscous dissipation and the flow approaches the basic state again.}, }
@article {pmid33800534, year = {2021}, author = {Naas, TT and Hossain, S and Aslam, M and Rahman, A and Hoque, ASM and Kim, KY and Islam, SMR}, title = {Kinematic Measurements of Novel Chaotic Micromixers to Enhance Mixing Performances at Low Reynolds Numbers: Comparative Study.}, journal = {Micromachines}, volume = {12}, number = {4}, pages = {}, pmid = {33800534}, issn = {2072-666X}, abstract = {In this work, a comparative investigation of chaotic flow behavior inside multi-layer crossing channels was numerically carried out to select suitable micromixers. New micromixers were proposed and compared with an efficient passive mixer called a Two-Layer Crossing Channel Micromixer (TLCCM), which was investigated recently. The computational evaluation was a concern to the mixing enhancement and kinematic measurements, such as vorticity, deformation, stretching, and folding rates for various low Reynolds number regimes. The 3D continuity, momentum, and species transport equations were solved by a Fluent ANSYS CFD code. For various cases of fluid regimes (0.1 to 25 values of Reynolds number), the new configuration displayed a mixing enhancement of 40%-60% relative to that obtained in the older TLCCM in terms of kinematic measurement, which was studied recently. The results revealed that all proposed micromixers have a strong secondary flow, which significantly enhances the fluid kinematic performances at low Reynolds numbers. The visualization of mass fraction and path-lines presents that the TLCCM configuration is inefficient at low Reynolds numbers, while the new designs exhibit rapid mixing with lower pressure losses. Thus, it can be used to enhance the homogenization in several microfluidic systems.}, }
@article {pmid33800140, year = {2021}, author = {De Bartolo, S and Vittorio, M and Francone, A and Guido, F and Leone, E and Mastronardi, VM and Notaro, A and Tomasicchio, GR}, title = {Direct Scaling of Measure on Vortex Shedding through a Flapping Flag Device in the Open Channel around a Cylinder at Re∼10[3]: Taylor's Law Approach.}, journal = {Sensors (Basel, Switzerland)}, volume = {21}, number = {5}, pages = {}, pmid = {33800140}, issn = {1424-8220}, abstract = {The problem of vortex shedding, which occurs when an obstacle is placed in a regular flow, is governed by Reynolds and Strouhal numbers, known by dimensional analysis. The present work aims to propose a thin films-based device, consisting of an elastic piezoelectric flapping flag clamped at one end, in order to determine the frequency of vortex shedding downstream an obstacle for a flow field at Reynolds number Re∼103 in the open channel. For these values, Strouhal number obtained in such way is in accordance with the results known in literature. Moreover, the development of the voltage over time, generated by the flapping flag under the load due to flow field, shows a highly fluctuating behavior and satisfies Taylor's law, observed in several complex systems. This provided useful information about the flow field through the constitutive law of the device.}, }
@article {pmid33794172, year = {2021}, author = {Chen, WH and Mutuku, JK and Yang, ZW and Hwang, CJ and Lee, WJ and Ashokkumar, V}, title = {An investigation for airflow and deposition of PM2.5 contaminated with SAR-CoV-2 virus in healthy and diseased human airway.}, journal = {Environmental research}, volume = {197}, number = {}, pages = {111096}, doi = {10.1016/j.envres.2021.111096}, pmid = {33794172}, issn = {1096-0953}, mesh = {*Asthma ; Computer Simulation ; Humans ; Italy ; *Lung ; Mexico ; Models, Biological ; Particulate Matter/toxicity ; }, abstract = {This study is motivated by the amplified transmission rates of the SAR-CoV-2 virus in areas with high concentrations of fine particulates (PM2.5) as reported in northern Italy and Mexico. To develop a deeper understanding of the contribution of PM2.5 in the propagation of the SAR-CoV-2 virus in the population, the deposition patterns and efficiencies (DEs) of PM2.5 laced with the virus in healthy and asthmatic airways are studied. Physiologically correct 3-D models for generations 10-12 of the human airways are applied to carry out a numerical analysis of two-phase flow for full breathing cycles. Two concentrations of PM2.5 are applied for the simulation, i.e., 30 μg⋅m[-3] and 80 μg⋅m[-3] for three breathing statuses, i.e., rest, light exercise, and moderate activity. All the PM2.5 injected into the control volume is assumed to be 100% contaminated with the SAR-CoV-2 virus. Skewed air-flow phenomena at the bifurcations are proportional to the Reynolds number at the inlet, and their intensity in the asthmatic airway exceeded that of the healthy one. Upon exhalation, two peak air-flow vectors from daughter branches combine to form one big vector in the parent generation. Asthmatic airway models has higher deposition efficiencies (DEs) for contaminated PM2.5 as compared to the healthy one. Higher DEs arise in the asthmatic airway model due to complex secondary flows which increase the impaction of contaminated PM2.5 on airways' walls.}, }
@article {pmid38620251, year = {2021}, author = {Qian, S and Jiang, M and Liu, Z}, title = {Inertial migration of aerosol particles in three-dimensional microfluidic channels.}, journal = {Particuology}, volume = {55}, number = {}, pages = {23-34}, pmid = {38620251}, issn = {2210-4291}, abstract = {In recent years, manipulation of particles by inertial microfluidics has attracted significant attention. However, most studies focused on inertial focusing of particles suspended within liquid phase, in which the ratio of the density of the particle to that of the medium is O(1). The investigation on manipulation of aerosol particles in an inertial microfluidics is very limited. In this study, we numerically investigate the aerosol particle's motion in a 3D straight microchannel with rectangular cross section by fully resolved simulation of the particle-air flow. The air flow is modeled by the Navier-Stokes equations. The particle's motions, including translation and rotation, are governed, respectively, by the Newton's second law and the Euler equations without using any approximation models for the lift and drag forces. The coupled mathematical model is numerically solved by combining immersed boundary with lattice Boltzmann method (IB-LBM). We find that the Reynolds number (Re), the particle's initial position, particle's density and diameter are the influential parameters in this process. The equilibrium positions and their stabilities of aerosols are different from those suspended in liquid.}, }
@article {pmid33768184, year = {2021}, author = {Edomwonyi-Otu, LC and Dosumu, AI and Yusuf, N}, title = {Effect of oil on the performance of biopolymers as drag reducers in fresh water flow.}, journal = {Heliyon}, volume = {7}, number = {3}, pages = {e06535}, doi = {10.1016/j.heliyon.2021.e06535}, pmid = {33768184}, issn = {2405-8440}, abstract = {This study looks at the effectiveness of natural polymers (biopolymers) as drag reducers in flows of oil-water mixtures. The technique of using drag reducers to minimize the frictional drag in pipeline transportation of fluids is getting more challenging and there is need to be more environmentally friendly by using natural polymers. In this report, two natural polymers: xanthan gum (XG) and guar gum (GG), were used as drag reducers in a 12-mm ID straight conduit with water. The concentration of the gums was varied from 50 to 250 pm while 25, 0.50 and 0.75 fractions of oil were mixed with freshwater. The molecular weight of the gums was also determined to gain insight into their influence on the rheology of the fluids. The result showed that the gums (natural polymers) performed better as drag reducer in freshwater than in mixture with oil. Specifically, the drag reduction (DR) of 200 pm GG and XG solutions at Reynolds number of 59000 in freshwater was 39% and 44% respectively, while with the addition of 50% oil fraction, it was reduced to 19% and 32% respectively. DR reduced with oil fraction. It was concluded that XG performs better in the presence of oil than GG.}, }
@article {pmid33767256, year = {2021}, author = {Wang, L and Ni, P and Xi, G}, title = {The effect of off-center placement of twisted tape on flow and heat transfer characteristics in a circular tube.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {6844}, pmid = {33767256}, issn = {2045-2322}, abstract = {This study is conducted to investigate the effect of off-center placement of twisted tape on flow distribution and heat transfer in a circular tube. The effect of tape width of 20, 18, 16, 14 and 12 mm on the heat transfer performance is discussed under the same twist ratio of 2.0. The numerical analysis of the flow field, average Nusselt number, friction factor and thermo-hydraulic performance parameter of the tube are discussed with Reynolds number ranged from 2600 to 8760. The results indicate that the Nusselt number of the tube fitted with center-placed twisted tapes at various width is 7-51% higher than the plain tube, and performance in low Reynolds region was found more effective than that in high Reynolds region. The heat transfer for circular tube with twisted tape attached to the wall shows better performance than that for the tube with center-placed twisted tape. With a smaller tape width, a higher increasing ratio of Nu-wall/Nu-center is obtained. The increasing ratio for Nusselt number ranged from 3 to 18%. However, the use of twisted tape inserts is not beneficial for energy saving. The thermo-hydraulic performance parameters for convective heat transfer of helium gas flowing in a circular tube are below unity for the calculated Reynolds region.}, }
@article {pmid33766315, year = {2021}, author = {Wang, X and Liu, Z and Cai, Y and Wang, B and Luo, X}, title = {A cost-effective serpentine micromixer utilizing ellipse curve.}, journal = {Analytica chimica acta}, volume = {1155}, number = {}, pages = {338355}, doi = {10.1016/j.aca.2021.338355}, pmid = {33766315}, issn = {1873-4324}, abstract = {Due to high mixing performance and simple geometry structure, serpentine micromixer is one typical passive micromixer that has been widely investigated. Traditional zigzag and square-wave serpentine micromixers can achieve sufficient mixing, but tend to induce significant pressure drop. The excessive pressure drop means more energy consumption, which leads to low cost-performance of mixing. To mitigate excessive pressure drop, a novel serpentine micromixer utilizing ellipse curve is proposed. While fluids flowing through ellipse curve microchannels, the flow directions keep continuous changing. Therefore, the Dean vortices are induced throughout the whole flow path. Numerical simulation and visualization experiments are conducted at Reynolds number (Re) ranging from 0.1 to 100. Dean vortices varies with the changing curvature in different ellipse curves, and local Dean numbers are calculated for quantitative evaluation. The results suggest that the ellipse with a larger eccentricity induces stronger Dean vortices, thus better mixing performance can be obtained. A parameter, named mixing performance cost (Mec), is proposed to evaluate the cost-performance of micromixers. Compared with the zigzag, square-wave and other improved serpentine micromixers, the ellipse curve micromixer produces lower pressure drop while have the capability to maintain excellent mixing performance. The ellipse curve micromixer is proved to be more cost-effective for rapid mixing in complex microfluidic systems.}, }
@article {pmid33765646, year = {2021}, author = {Ghosh, UU and Ali, H and Ghosh, R and Kumar, A}, title = {Bacterial streamers as colloidal systems: Five grand challenges.}, journal = {Journal of colloid and interface science}, volume = {594}, number = {}, pages = {265-278}, doi = {10.1016/j.jcis.2021.02.102}, pmid = {33765646}, issn = {1095-7103}, mesh = {*Bacteria ; *Biofilms ; Hydrodynamics ; Rivers ; }, abstract = {Bacteria can thrive in biofilms, which are intricately organized communities with cells encased in a self-secreted matrix of extracellular polymeric substances (EPS). Imposed hydrodynamic stresses can transform this active colloidal dispersion of bacteria and EPS into slender thread-like entities called streamers. In this perspective article, the reader is introduced to the world of such deformable 'bacteria-EPS' composites that are a subclass of the generic flow-induced colloidal structures. While bacterial streamers have been shown to form in a variety of hydrodynamic conditions (turbulent and creeping flows), its abiotic analogues have only been demonstrated in low Reynolds number (Re < 1) particle-laden polymeric flows. Streamers are relevant to a variety of situations ranging from natural formations in caves and river beds to clogging of biomedical devices and filtration membranes. A critical review of the relevant biophysical aspects of streamer formation phenomena and unique attributes of its material behavior are distilled to unveil five grand scientific challenges. The coupling between colloidal hydrodynamics, device geometry and streamer formation are highlighted.}, }
@article {pmid33759003, year = {2021}, author = {Mohammadinejad, S and Faivre, D and Klumpp, S}, title = {Stokesian dynamics simulations of a magnetotactic bacterium.}, journal = {The European physical journal. E, Soft matter}, volume = {44}, number = {3}, pages = {40}, pmid = {33759003}, issn = {1292-895X}, mesh = {*Flagella/physiology ; *Magnetic Fields ; *Models, Biological ; Hydrodynamics ; Movement ; Torque ; Magnetospirillum/physiology ; }, abstract = {The swimming of bacteria provides insight into propulsion and steering under the conditions of low-Reynolds number hydrodynamics. Here we address the magnetically steered swimming of magnetotactic bacteria. We use Stokesian dynamics simulations to study the swimming of single-flagellated magnetotactic bacteria (MTB) in an external magnetic field. Our model MTB consists of a spherical cell body equipped with a magnetic dipole moment and a helical flagellum rotated by a rotary motor. The elasticity of the flagellum as well as magnetic and hydrodynamic interactions is taken into account in this model. We characterized how the swimming velocity is dependent on parameters of the model. We then studied the U-turn motion after a field reversal and found two regimes for weak and strong fields and, correspondingly, two characteristic time scales. In the two regimes, the U-turn time is dominated by the turning of the cell body and its magnetic moment or the turning of the flagellum, respectively. In the regime for weak fields, where turning is dominated by the magnetic relaxation, the U-turn time is approximately in agreement with a theoretical model based on torque balance. In the strong-field regime, strong deformations of the flagellum are observed. We further simulated the swimming of a bacterium with a magnetic moment that is inclined relative to the flagellar axis. This scenario leads to intriguing double helical trajectories that we characterize as functions of the magnetic moment inclination and the magnetic field. For small inclination angles ([Formula: see text]) and typical field strengths, the inclination of the magnetic moment has only a minor effect on the swimming of MTB in an external magnetic field. Large inclination angles result in a strong reduction in the velocity in direction of the magnetic field, consistent with recent observations that bacteria with large inclination angles use a different propulsion mechanism.}, }
@article {pmid33756187, year = {2021}, author = {Jamil, DF and Saleem, S and Roslan, R and Al-Mubaddel, FS and Rahimi-Gorji, M and Issakhov, A and Din, SU}, title = {Analysis of non-Newtonian magnetic Casson blood flow in an inclined stenosed artery using Caputo-Fabrizio fractional derivatives.}, journal = {Computer methods and programs in biomedicine}, volume = {203}, number = {}, pages = {106044}, doi = {10.1016/j.cmpb.2021.106044}, pmid = {33756187}, issn = {1872-7565}, mesh = {Arteries ; *Atherosclerosis ; Blood Flow Velocity ; Constriction, Pathologic ; Hemodynamics ; Humans ; *Models, Cardiovascular ; }, abstract = {BACKGROUND AND OBJECTIVE: Arterial diseases would lead to several serious disorders in the cardiovascular system such as atherosclerosis. These disorders are mainly caused by the presence of fatty deposits, cholesterol and lipoproteins inside blood vessel. This paper deals with the analysis of non-Newtonian magnetic blood flow in an inclined stenosed artery.<br><br>METHODS: The Casson fluid was used to model the blood that flows under the influences of uniformly distributed magnetic field and oscillating pressure gradient. The governing fractional differential equations were expressed using the Caputo Fabrizio fractional derivative without singular kernel.<br><br>RESULTS: The analytical solutions of velocities for non-Newtonian model were then calculated by means of Laplace and finite Hankel transforms. These velocities were then presented graphically. The result shows that the velocity increases with respect to Reynolds number and Casson parameter, while decreases when Hartmann number increases.<br><br>CONCLUSIONS: Casson blood was treated as the non-Newtonian fluid. The MHD blood flow was accelerated by pressure gradient. These findings are beneficial for studying atherosclerosis therapy, the diagnosis and therapeutic treatment of some medical problems.}, }
@article {pmid33754747, year = {2021}, author = {Mouzourides, P and Kyprianou, A and Neophytou, MK}, title = {Exploring the multi-fractal nature of the air flow and pollutant dispersion in a turbulent urban atmosphere and its implications for long range pollutant transport.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {31}, number = {1}, pages = {013110}, doi = {10.1063/1.5123918}, pmid = {33754747}, issn = {1089-7682}, abstract = {This work investigates the multi-fractal nature of a turbulent urban atmosphere using high-resolution atmospheric data. Meteorological and concentration measurements of passive and reactive pollutants collected over a 3-year period in a sub-urban high-Reynolds number atmospheric field were analyzed. Scaling laws characterizing the self-similarity and thereby depicting the multi-fractal nature are determined by calculating the singularity spectra, where a range of Hölder exponents, h, are estimated. In doing so, the complexity of the urban atmosphere entailing different stability regimes was addressed. Using the Monin-Obukhov length (LMO) as a marker of atmospheric stability and thereby an indication of the magnitude of anisotropy, we find where and how self-similarity is manifested relative to the different regimes and we estimate corresponding appropriate scaling laws. We find that the wind speed obeys the -5/3 law suggested by Kolmogorov only when the atmosphere lies within the stable regime as defined by Monin-Obukhov theory. Specifically, when the ratio of the atmospheric boundary layer height (Hb.l) over LMO is greater than 15, and at the same time, the ratio of the height above ground of the wind measurements (z0) over LMO is higher than 3 (i.e., in stable regime), then the singularity spectra of wind speed time series indicate that the dominant Hölder exponent, hmax, coincides with Kolmogorov's second hypothesis. On the contrary under unstable regimes in the atmosphere where the anisotropy is approached, different scaling laws are estimated. In detail, when z0/LMO<0, the dominant Hölder exponent, hmax, of the singularity spectra of the wind speed time series is either negative or close to zero, which is an indication of an impulse-like singularity, that is associated with rapid changes. For the ambient temperature and air quality measurements such as of carbon monoxide and particulate matter concentrations, it was found that they obey different laws, which are related with the long-term correlation of their data fluctuation.}, }
@article {pmid33754568, year = {2021}, author = {Ji, JY and Zhao, YG and Yang, K and Zhang, WT and Gao, LQ and Ming, J and Wang, SS}, title = {Effects of the distribution of biological soil crust on the hydrodynamic characteristics of surface runoff.}, journal = {Ying yong sheng tai xue bao = The journal of applied ecology}, volume = {32}, number = {3}, pages = {1015-1022}, doi = {10.13287/j.1001-9332.202103.017}, pmid = {33754568}, issn = {1001-9332}, mesh = {Geologic Sediments ; Hydrodynamics ; *Rain ; *Soil ; }, abstract = {The distribution pattern of biological soil crusts (biocrusts) is one of the main factors affecting runoff and sediment yield. The relationship between runoff and sediment yield and biocrusts' distribution pattern is not clear, which hinders understanding the mechanism underlying the effects of biocrusts on runoff and sediment from slopes. To fill the knowledge gap, we investigated the relationship between the landscape indices of three biocrusts' distribution patterns, i.e. zonation, chessboard and random, and the hydraulic parameters, using of simulated rainfall experiments and landscape ecology methods. The results showed that biocrust significantly affected the erosion force of slopes and that its distribution pattern could affect slope erosion dynamics. Compared to bare soil, the presence of biocrusts significantly reduced the runoff velocity (54.6%) and Froude number (67.0%), increased the runoff depth (86.2%) and Darcy-Weisbach resistance coefficient (10.68 times), but did not affect the Reynolds number and runoff power. Expect for the runoff depth, there were significant differences in the hydraulic parameters of the three biocrusts' distribution patterns, with the random pattern having the strongest impacts on the dynamics of slope erosion. Based on factor analysis and cluster analysis, five indices of percentage of patch to landscape area, patch density, landscape shape index, patch cohesion and splitting could be used as the indicators for the distribution characteristics of biocrust patches. The patch cohesion and splitting of biocrust patches were the main distribution pattern indices of the hydrodynamics of surface runoff. As the patches patch cohesion decreased, the splitting increased, which caused the surface runoff velocity increase, the resistance decrease, and the slope erosion became more severe.}, }
@article {pmid33752093, year = {2021}, author = {Pejcic, S and Najjari, MR and Bisleri, G and Rival, DE}, title = {Characterization of the dynamic viscoelastic response of the ascending aorta imposed via pulsatile flow.}, journal = {Journal of the mechanical behavior of biomedical materials}, volume = {118}, number = {}, pages = {104395}, doi = {10.1016/j.jmbbm.2021.104395}, pmid = {33752093}, issn = {1878-0180}, mesh = {Animals ; *Aorta ; Elastic Modulus ; Elasticity ; Pulsatile Flow ; Stress, Mechanical ; Swine ; }, abstract = {This study characterizes the material properties of a viscoelastic, ex vivo porcine ascending aorta under dynamic-loading conditions via pulsatile flow. The deformation of the opaque vessel wall and the pulsatile flow field inside the vessel were recorded using ultrasound imaging. The internal pressure was extracted from the pulsatile flow results and, when coupled with the vessel-wall expansion, was used to calculate the instantaneous elastic modulus from a novel, time-resolved two-dimensional (i.e. axial and circumferential) stress model. The circumferential instantaneous elasticity obtained from the two-dimensional stress model was found to match the uniaxial tensile test for strains below 50%. The agreement in elasticity between the two stress states reveals that the two-dimensional stress model accurately resolves the circumferential stress of the viscoelastic aorta at physiological strains (8%-30%). At higher strains, results from pulsatile flow generated a more compliant response than the uniaxial measurements. Viscoelastic properties (storage modulus and loss factor) were also calculated using the two-dimensional stress model and compared to those obtained from uniaxial tests. While instantaneous elasticity matched between the cylindrical and uniaxial loading, the viscoelastic behaviour significantly diverged between stress states. The storage modulus obtained from the pulsatile flow data was dependent on mean Reynolds number, while the uniaxial storage modulus results exhibited a strong inverse dependency on the frequency. The loss factor for the pulsatile flow data increased alongside the frequency, while the uniaxial data indicated a constant loss factor over the entire frequency range. The results of the current study show that the two-dimensional stress model can accurately extract the material properties of the ex vivo porcine aorta.}, }
@article {pmid33748634, year = {2021}, author = {Lu, H and Chen, L and Wang, J and Zhang, X and Li, G and Wang, J and Chen, W and Yan, B}, title = {Using a Modified Turian-Yuan Model to Enhance Heterogeneous Resistance in Municipal Sludge Transportation Pipeline.}, journal = {ACS omega}, volume = {6}, number = {10}, pages = {7199-7211}, pmid = {33748634}, issn = {2470-1343}, abstract = {Based on the Turian-Yuan heterogeneous resistance model, the simulation results of three urban sludge pipelines with a volumetric concentration of 2.38, 3.94, and 5.39% were analyzed. The reasons for the large deviation of the simulation results under high Reynolds number conditions were also analyzed. The results showed that the deviation of the simulation was mainly caused by the difference between the sludge volumetric concentration (C V), the settlement resistance coefficient (C D), and the values of the two parameters in the Turian-Yuan heterogeneous resistance model. Consequently, it was necessary to optimize the index m 1 of C V and the index m 2 of C D. Taking mean square deviation as the objective function, using Matlab programming, the abovementioned two indexes were optimized by the simulated annealing algorithm. The optimized index m 1 of C V was 0.887, and the index m 2 of C D was -0.162. Hence, a modified Turian-Yuan heterogeneous resistance model was obtained. The model verified that the minimum value of the regression coefficient, R [2], of the simulated value reached 0.9701, proving that, the model can be used to simulate the heterogeneous resistance of urban sludge pipeline transportation.}, }
@article {pmid33736076, year = {2021}, author = {Tajfirooz, S and Meijer, JG and Kuerten, JGM and Hausmann, M and Fröhlich, J and Zeegers, JCH}, title = {Statistical-learning method for predicting hydrodynamic drag, lift, and pitching torque on spheroidal particles.}, journal = {Physical review. E}, volume = {103}, number = {2-1}, pages = {023304}, doi = {10.1103/PhysRevE.103.023304}, pmid = {33736076}, issn = {2470-0053}, abstract = {A statistical learning approach is presented to predict the dependency of steady hydrodynamic interactions of thin oblate spheroidal particles on particle orientation and Reynolds number. The conventional empirical correlations that approximate such dependencies are replaced by a neural-network-based correlation which can provide accurate predictions for high-dimensional input spaces occurring in flows with nonspherical particles. By performing resolved simulations of steady uniform flow at 1≤Re≤120 around a 1:10 spheroidal body, a database consisting of Reynolds number- and orientation-dependent drag, lift, and pitching torque acting on the particle is collected. A multilayer perceptron is trained and validated with the generated database. The performance of the neural network is tested in a point-particle simulation of the buoyancy-driven motion of a 1:10 disk. Our statistical approach outperforms existing empirical correlations in terms of accuracy. The agreement between the numerical results and the experimental observations prove the potential of the method.}, }
@article {pmid33731341, year = {2021}, author = {Corbetta, A and Menkovski, V and Benzi, R and Toschi, F}, title = {Deep learning velocity signals allow quantifying turbulence intensity.}, journal = {Science advances}, volume = {7}, number = {12}, pages = {}, pmid = {33731341}, issn = {2375-2548}, abstract = {Turbulence, the ubiquitous and chaotic state of fluid motions, is characterized by strong and statistically nontrivial fluctuations of the velocity field, and it can be quantitatively described only in terms of statistical averages. Strong nonstationarities impede statistical convergence, precluding quantifying turbulence, for example, in terms of turbulence intensity or Reynolds number. Here, we show that by using deep neural networks, we can accurately estimate the Reynolds number within 15% accuracy, from a statistical sample as small as two large-scale eddy turnover times. In contrast, physics-based statistical estimators are limited by the convergence rate of the central limit theorem and provide, for the same statistical sample, at least a hundredfold larger error. Our findings open up previously unexplored perspectives and the possibility to quantitatively define and, therefore, study highly nonstationary turbulent flows as ordinarily found in nature and in industrial processes.}, }
@article {pmid33730564, year = {2021}, author = {Wiputra, H and Lim, M and Yap, CH}, title = {A transition point for the blood flow wall shear stress environment in the human fetal left ventricle during early gestation.}, journal = {Journal of biomechanics}, volume = {120}, number = {}, pages = {110353}, doi = {10.1016/j.jbiomech.2021.110353}, pmid = {33730564}, issn = {1873-2380}, mesh = {Computer Simulation ; Female ; *Heart Ventricles/diagnostic imaging ; *Hemodynamics ; Humans ; Hydrodynamics ; Models, Cardiovascular ; Pregnancy ; Stress, Mechanical ; }, abstract = {Development of the fetal heart is a fascinating process that involves a tremendous amount of growth. Here, we performed image-based flow simulations of 3 human fetal left ventricles (LV), and investigated the hypothetical scenario where the sizes of the hearts are scaled down, leading to reduced Reynolds number, to emulate earlier fetal stages. The shape and motion of the LV were retained over the scaling to isolate and understand the effects of length scaling on its fluid dynamics. We observed an interesting cut-off point in Reynolds number (Re), across which the dependency of LV wall shear stress (WSS) on Re changed. This was in line with classical fluid mechanic theory where skin friction coefficient exhibited first a decreasing trend and then a plateauing trend with increasing Re. Below this cut-off point, viscous effects dominated, stifling the formation of LV diastolic vorticity structures, and WSS was roughly independent of Reynolds number. However, above this cut-off, inertial effects dominated to cause diastolic vortex ring formation and detachment, and to cause WSS to scale linearly with Reynolds number. Results suggested that this transition point is found at approximately 11 weeks of gestation. Since WSS is thought to be a biomechanical stimuli for growth, this may have implications on normal fetal heart growth and malformation diseases like Hypoplastic Left Heart Syndrome.}, }
@article {pmid33728053, year = {2021}, author = {Kumar, VRS and Choudhary, SK and Radhakrishnan, PK and Bharath, RS and Chandrasekaran, N and Sankar, V and Sukumaran, A and Oommen, C}, title = {Lopsided Blood-Thinning Drug Increases the Risk of Internal Flow Choking Leading to Shock Wave Generation Causing Asymptomatic Cardiovascular Disease.}, journal = {Global challenges (Hoboken, NJ)}, volume = {5}, number = {3}, pages = {2000076}, pmid = {33728053}, issn = {2056-6646}, abstract = {The discovery of Sanal flow choking in the cardiovascular-system calls for multidisciplinary and global action to develop innovative treatments and to develop new drugs to negate the risk of asymptomatic-cardiovascular-diseases. Herein, it is shown that when blood-pressure-ratio (BPR) reaches the lower-critical-hemorrhage-index (LCHI) internal-flow-choking and shock wave generation can occur in the cardiovascular-system, with sudden expansion/divergence/vasospasm or bifurcation regions, without prejudice to the percutaneous-coronary-intervention (PCI). Analytical findings reveal that the relatively high and the low blood-viscosity are cardiovascular-risk factors. In vitro studies have shown that nitrogen, oxygen, and carbon dioxide gases are dominant in fresh blood samples of humans/guinea pigs at a temperature range of 98.6-104 F. An in silico study demonstrated the Sanal flow choking phenomenon leading to shock-wave generation and pressure-overshoot in the cardiovascular-system. It has been established that disproportionate blood-thinning treatment increases the risk of the internal-flow-choking due to the enhanced boundary-layer-blockage-factor, resulting from an increase in flow-turbulence level in the cardiovascular-system, caused by an increase in Reynolds number as a consequence of low blood-viscosity. The cardiovascular-risk can be diminished by concurrently lessening the viscosity of biofluid/blood and flow-turbulence by raising the thermal-tolerance-level in terms of blood-heat-capacity-ratio (BHCR) and/or by decreasing the systolic-to-diastolic blood-pressure-ratio.}, }
@article {pmid33723624, year = {2021}, author = {Challita, EJ and Alexander, SLM and Han, SI and Blackledge, TA and Coddington, JA and Jung, S and Bhamla, MS}, title = {Slingshot spiders build tensed, underdamped webs for ultrafast launches and speedy halts.}, journal = {Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology}, volume = {207}, number = {2}, pages = {205-217}, pmid = {33723624}, issn = {1432-1351}, mesh = {Animals ; Biomechanical Phenomena/*physiology ; *Models, Theoretical ; Predatory Behavior/physiology ; Silk/*physiology ; Spiders/*physiology ; Time Factors ; Video Recording/methods ; Walking Speed/*physiology ; }, abstract = {We develop a mathematical model to capture the web dynamics of slingshot spiders (Araneae: Theridiosomatidae), which utilize a tension line to deform their orb webs into conical springs to hunt flying insects. Slingshot spiders are characterized by their ultrafast launch speeds and accelerations (exceeding 1300 [Formula: see text]), however a theoretical approach to characterize the underlying spatiotemporal web dynamics remains missing. To address this knowledge gap, we develop a 2D-coupled damped oscillator model of the web. Our model reveals three key insights into the dynamics of slingshot motion. First, the tension line plays a dual role: enabling the spider to load elastic energy into the web for a quick launch (in milliseconds) to displacements of 10-15 body lengths, but also enabling the spider to halt quickly, attenuating inertial oscillations. Second, the dominant energy dissipation mechanism is viscous drag by the silk lines - acting as a low Reynolds number parachute. Third, the web exhibits underdamped oscillatory dynamics through a finely-tuned balance between the radial line forces, the tension line force and viscous drag dissipation. Together, our work suggests that the conical geometry and tension-line enables the slingshot web to act as both an elastic spring and a shock absorber, for the multi-functional roles of risky predation and self-preservation.}, }
@article {pmid33721123, year = {2021}, author = {Basha, HT and Sivaraj, R}, title = {Exploring the heat transfer and entropy generation of Ag/Fe[Formula: see text]O[Formula: see text]-blood nanofluid flow in a porous tube: a collocation solution.}, journal = {The European physical journal. E, Soft matter}, volume = {44}, number = {3}, pages = {31}, pmid = {33721123}, issn = {1292-895X}, mesh = {*Silver/chemistry ; *Entropy ; Porosity ; Hot Temperature ; Iron/chemistry ; Metal Nanoparticles/chemistry ; Humans ; }, abstract = {Evaluating the entropy generation is essential in thermal systems to avoid the unnecessarily wasted thermal energy during the thermal processes. Nowadays, researchers are greatly fascinated to scrutinize the entropy generation in a human system because it is utilized as a thermodynamic approach to understand the heat transfer characteristics of cancer systems or wounded tissue and their accessibility status. Further, numerous nanoparticles have been employed as an agent to control the heat transfer of blood and wounded tissue. As a result, the present model manifests the entropy generation, flow characteristics and heat transport of Ag/Fe[Formula: see text]O[Formula: see text]-blood flow of a nanofluid in a permeable circular tube with the influence of variable electrical conductivity and linear radiation. Nonlinear transport equations are converted into ordinary differential equations by suitable similarity variables which are solved with weighted residual method. Significant parameters like Reynolds number, dimensionless permeability parameter, extending/contracting parameter, Eckert number and Hartmann number on the radial pressure, axial velocity, radial velocity and temperature are explored through graphs. The obtained results show that temperature distribution of Fe[Formula: see text]O[Formula: see text] nanoparticles is higher than Ag nanoparticle, in case of suction. The dimensionless permeability parameter has an opposite nature on the radial pressure for the suction and injection cases. Growing values of Hartmann number enhance the total entropy generation for the cases of suction and injection.}, }
@article {pmid33719755, year = {2021}, author = {Liu, Z and Zhang, H and Lai, H}, title = {Fluid flow effects on the degradation kinetics of bioresorbable polymers.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {24}, number = {10}, pages = {1073-1084}, doi = {10.1080/10255842.2020.1867115}, pmid = {33719755}, issn = {1476-8259}, mesh = {*Absorbable Implants ; Biocompatible Materials ; Kinetics ; *Polymers ; Tissue Scaffolds ; }, abstract = {Implants, tissue engineering scaffolds made of biodegradable polymers are widely used in biomedical engineering. The degradation of polymers plays a critical role in the effectiveness of these applications. In this paper, the mechanism of the hydrolytic degradation affected by the flow medium is studied. The results indicate that both high porosity and dynamic conditions may significantly slow down degradation speed. A critical value of the Reynolds number is found to exist. When the Reynolds number is higher than the critical value, the autocatalysis was suppressed. The models reported in this article might serve as a guide to design 3D biodegradable implants.}, }
@article {pmid33713991, year = {2021}, author = {Al-Mubarak, HFI and Vallatos, A and Holmes, WM}, title = {Impact of turbulence-induced asymmetric propagators on the accuracy of phase-contrast velocimetry.}, journal = {Journal of magnetic resonance (San Diego, Calif. : 1997)}, volume = {325}, number = {}, pages = {106929}, doi = {10.1016/j.jmr.2021.106929}, pmid = {33713991}, issn = {1096-0856}, abstract = {Phase-contrast magnetic resonance velocimetry (PC-MRI) has been widely used to investigate flow properties in numerous systems. In a horizontal cylindrical pipe (3 mm diameter), we investigated the accuracy of PC-MRI as the flow transitioned from laminar to turbulent flow (Reynolds number 352-2708). We focus primarily on velocimetry errors introduced by skewed intra-voxel displacement distributions, a consequence of PC-MRI theory assuming symmetric distributions. We demonstrated how rapid fluctuations in the velocity field, can produce broad asymmetric intravoxel displacement distributions near the wall. Depending on the shape of the distribution, this resulted in PC-MRI measurements under-estimating (positive skewness) or over-estimating (negative skewness) the true mean intravoxel velocity, which could have particular importance to clinical wall shear stress measurements. The magnitude of these velocity errors was shown to increase with the variance and decrease with the kurtosis of the intravoxel displacement distribution. These experimental results confirm our previous theoretical analysis, which gives a relationship for PC-MRI velocimetry errors, as a function of the higher moments of the intravoxel displacement distribution (skewness, variance, and kurtosis) and the experimental parameters q and Δ. This suggests that PC-MRI errors in such unsteady/turbulent flow conditions can potentially be reduced by employing lower q values or shorter observation times Δ.}, }
@article {pmid33712884, year = {2021}, author = {Cho, M}, title = {Aerodynamics and the role of the earth's electric field in the spiders' ballooning flight.}, journal = {Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology}, volume = {207}, number = {2}, pages = {219-236}, pmid = {33712884}, issn = {1432-1351}, mesh = {Animals ; *Earth, Planet ; Electrophysiological Phenomena/*physiology ; Flight, Animal/*physiology ; Silk/*physiology ; Spiders/*physiology ; Static Electricity ; }, abstract = {Some spiders aerially disperse relying on their fine fibres. This behaviour has been known as 'ballooning'. Observations on the ballooning behaviour of spiders have a long history and have more recently received special attention, yet its underlying physics is still poorly understood. It was traditionally believed that spiders rely on the airflows by atmospheric thermal convection to do ballooning. However, a recent experiment showed that exposure to an electric field alone can induce spiders' pre-ballooning behaviours (tiptoe and dropping/dangling) and even pulls them upwards in the air. The controversy between explanations of ballooning by aerodynamic flow or the earth's electric field has long existed. The major obstacle in studying the physics of ballooning is the fact that airflow and electric field are both invisible and our naked eyes can hardly recognise the ballooning silk fibres of spiders. This review explores the theory and evidence for the physical mechanisms of spiders' ballooning connects them to the behavioural physiology of spiders for ballooning. Knowledge gaps that need to be addressed in future studies are identified.}, }
@article {pmid33683671, year = {2021}, author = {Riley, JM and Price, NS and Saaid, HM and Good, BC and Aycock, KI and Craven, BA and Manning, KB}, title = {In Vitro Clot Trapping Efficiency of the FDA Generic Inferior Vena Cava Filter in an Anatomical Model: An Experimental Fluid-Structure Interaction Benchmark.}, journal = {Cardiovascular engineering and technology}, volume = {12}, number = {3}, pages = {339-352}, doi = {10.1007/s13239-021-00524-z}, pmid = {33683671}, issn = {1869-4098}, mesh = {Animals ; Cattle ; Models, Cardiovascular ; Rheology ; *Thrombosis ; *Vena Cava Filters ; }, abstract = {PURPOSE: Robust experimental data for performing validation of fluid-structure interaction (FSI) simulations of the transport of deformable solid bodies in internal flow are currently lacking. This in vitro experimental study characterizes the clot trapping efficiency of a new generic conical-type inferior vena cava (IVC) filter in a rigid anatomical model of the IVC with carefully characterized test conditions, fluid rheological properties, and clot mechanical properties.<br><br>METHODS: Various sizes of spherical and cylindrical clots made of synthetic materials (nylon and polyacrylamide gel) and bovine blood are serially injected into the anatomical IVC model under worst-case exercise flow conditions. Clot trapping efficiencies and their uncertainties are then quantified for each combination of clot shape, size, and material.<br><br>RESULTS: Experiments reveal the clot trapping efficiency increases with increasing clot diameter and length, with trapping efficiencies ranging from as low as approximately 42% for small 3.2&#xa0;mm diameter spherical clots up to 100% for larger clot sizes. Because of the asymmetry of the anatomical IVC model, the data also reveal the iliac vein of clot origin influences the clot trapping efficiency, with the trapping efficiency for clots injected into the left iliac vein up to a factor of 7.5 times greater than that for clots injected into the right iliac (trapping efficiencies of approximately 10% versus 75%, respectively).<br><br>CONCLUSION: Overall, this data set provides a benchmark for validating simulations predicting IVC filter clot trapping efficiency and, more generally, low-Reynolds number FSI modeling.}, }
@article {pmid33673667, year = {2021}, author = {Mariotti, A and Antognoli, M and Galletti, C and Mauri, R and Salvetti, MV and Brunazzi, E}, title = {A Study on the Effect of Flow Unsteadiness on the Yield of a Chemical Reaction in a T Micro-Reactor.}, journal = {Micromachines}, volume = {12}, number = {3}, pages = {}, pmid = {33673667}, issn = {2072-666X}, abstract = {Despite the very simple geometry and the laminar flow, T-shaped microreactors have been found to be characterized by different and complex steady and unsteady flow regimes, depending on the Reynolds number. In particular, flow unsteadiness modifies strongly the mixing process; however, little is known on how this change may affect the yield of a chemical reaction. In the present work, experiments and 3-dimensional numerical simulations are carried out jointly to analyze mixing and reaction in a T-shaped microreactor with the ultimate goal to investigate how flow unsteadiness affects the reaction yield. The onset of the unsteady asymmetric regime enhances the reaction yield by more than 30%; however, a strong decrease of the yield back to values typical of the vortex regime is observed when the flow undergoes a transition to the unsteady symmetric regime.}, }
@article {pmid33672972, year = {2021}, author = {Gao, Y and Magaud, P and Baldas, L and Wang, Y}, title = {Inertial Migration of Neutrally Buoyant Spherical Particles in Square Channels at Moderate and High Reynolds Numbers.}, journal = {Micromachines}, volume = {12}, number = {2}, pages = {}, pmid = {33672972}, issn = {2072-666X}, support = {BK20200336//Natural Science Foundation of Jiangsu Province/ ; }, abstract = {The inertial migration of particles in microchannel flows has been deeply investigated in the last two decades. In spite of numerous reports on the inertial focusing patterns in a square channel, the particle inertial focusing and longitudinal ordering processes remain unclear at high Reynolds numbers (>200) in square microchannels smaller than 100 µm in width. Thus, in this work, in situ visualization of particles flowing in square micro-channels at Reynolds numbers Re ranging from 5 to 280 has been conducted and their migration behaviors have been analyzed. The obtained results confirm that new equilibrium positions appear above a critical Re depending on the particle to channel size ratio and the particle volume fraction. It is also shown that, for a given channel length, an optimal Reynolds number can be identified, for which the ratio of particles located on equilibrium positions is maximal. Moreover, the longitudinal ordering process, i.e., the formation of trains of particles on equilibrium positions and the characterization of their length, has also been analyzed for the different flow conditions investigated in this study.}, }
@article {pmid33670962, year = {2021}, author = {Xie, GF and Zhao, L and Dong, YY and Li, YG and Zhang, SL and Yang, C}, title = {Hydraulic and Thermal Performance of Microchannel Heat Sink Inserted with Pin Fins.}, journal = {Micromachines}, volume = {12}, number = {3}, pages = {}, pmid = {33670962}, issn = {2072-666X}, abstract = {With the development of micromachining technologies, a wider use of microchannel heat sink (MCHS) is achieved in many fields, especially for cooling electronic chips. A microchannel with a width of 500 μm and a height of 500 μm is investigated through the numerical simulation method. Pin fins are arranged at an inclined angle of 0°, 30°, 45°, and 60°, when arrangement method includes in-lined pattern and staggered pattern. The effects of inclined angle and arrangement method on flow field and temperature field of MCHSs are studied when Reynolds number ranges from 10 to 300. In addition to this, quantitative analyses of hydraulic and thermal performance are also discussed in this work. With the increase of inclined angle, the variation of friction factor and Nusselt number do not follow certain rules. The best thermal performance is achieved in MCHS with in-lined fines at an inclined angle of 30° accompanied with the largest friction factor. Arrangement method of pin fins plays a less significant role compared with inclined angle from a general view, particularly in the Reynolds number range of 100~300.}, }
@article {pmid33670569, year = {2021}, author = {Malviya, R and Jha, S and Fuloria, NK and Subramaniyan, V and Chakravarthi, S and Sathasivam, K and Kumari, U and Meenakshi, DU and Porwal, O and Sharma, A and Kumar, DH and Fuloria, S}, title = {Determination of Temperature-Dependent Coefficients of Viscosity and Surface Tension of Tamarind Seeds (Tamarindus indica L.) Polymer.}, journal = {Polymers}, volume = {13}, number = {4}, pages = {}, pmid = {33670569}, issn = {2073-4360}, abstract = {The rheological properties of tamarind seed polymer are characterized for its possible commercialization in the food and pharmaceutical industry. Seed polymer was extracted using water as a solvent and ethyl alcohol as a precipitating agent. The temperature's effect on the rheological behavior of the polymeric solution was studied. In addition to this, the temperature coefficient, viscosity, surface tension, activation energy, Gibbs free energy, Reynolds number, and entropy of fusion were calculated by using the Arrhenius, Gibbs-Helmholtz, Frenkel-Eyring, and Eotvos equations, respectively. The activation energy of the gum was found to be 20.46 ± 1.06 kJ/mol. Changes in entropy and enthalpy were found to be 23.66 ± 0.97 and -0.10 ± 0.01 kJ/mol, respectively. The calculated amount of entropy of fusion was found to be 0.88 kJ/mol. A considerable decrease in apparent viscosity and surface tension was produced when the temperature was raised. The present study concludes that the tamarind seed polymer solution is less sensitive to temperature change in comparison to Albzia lebbac gum, Ficus glumosa gum and A. marcocarpa gum. This study also concludes that the attainment of the transition state of viscous flow for tamarind seed gum is accompanied by bond breaking. The excellent physicochemical properties of tamarind seed polymers make them promising excipients for future drug formulation and make their application in the food and cosmetics industry possible.}, }
@article {pmid33669613, year = {2021}, author = {Hossain, S and Tayeb, NT and Islam, F and Kaseem, M and Bui, PDH and Bhuiya, MMK and Aslam, M and Kim, KY}, title = {Enhancement of Mixing Performance of Two-Layer Crossing Micromixer through Surrogate-Based Optimization.}, journal = {Micromachines}, volume = {12}, number = {2}, pages = {}, pmid = {33669613}, issn = {2072-666X}, abstract = {Optimum configuration of a micromixer with two-layer crossing microstructure was performed using mixing analysis, surrogate modeling, along with an optimization algorithm. Mixing performance was used to determine the optimum designs at Reynolds number 40. A surrogate modeling method based on a radial basis neural network (RBNN) was used to approximate the value of the objective function. The optimization study was carried out with three design variables; viz., the ratio of the main channel thickness to the pitch length (H/PI), the ratio of the thickness of the diagonal channel to the pitch length (W/PI), and the ratio of the depth of the channel to the pitch length (d/PI). Through a primary parametric study, the design space was constrained. The design points surrounded by the design constraints were chosen using a well-known technique called Latin hypercube sampling (LHS). The optimal design confirmed a 32.0% enhancement of the mixing index as compared to the reference design.}, }
@article {pmid33667105, year = {2021}, author = {Brik, M and Harmand, S and Zaaroura, I and Saboni, A}, title = {Experimental and Numerical Study for the Coalescence Dynamics of Vertically Aligned Water Drops in Oil.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {37}, number = {10}, pages = {3139-3147}, doi = {10.1021/acs.langmuir.0c03624}, pmid = {33667105}, issn = {1520-5827}, abstract = {In this paper, we propose an experimental and numerical investigation for the impact of the surface tension and the continuous phase viscosity on the dynamics of the liquid bridge during the coalescence process in liquid-liquid systems. A specific configuration of a sessile drop in direct contact with another drop placed over it has been studied. Calculating the redefined Reynolds number Re, it is found that for all studied cases, the coalescence process is dominated by the inertial force. The first step of the work was the validation of the numerical model that has been performed in an axisymmetric coordinate system. This has been done by the comparison between numerical and experimental results obtained in the framework of experimental series realized in parallel for two different liquid-liquid (LL) systems: water drops in silicone oil (SilOil M40.165) and water drops in sunflower oil. A good agreement was found between different results for numerous parameters used for comparisons. It is found that for the first stages of the coalescence (at the start of the drops merging), for a given drop's viscosity, the dynamics of the dimensionless liquid bridge is conducted by the viscosity of the continuous phase where it is illustrated that the more the surrounded viscosity is large, the lower the rate of the liquid bridge growth, the lower the earlier radial velocity of the bridge, and the higher the external capillary pressure generated around the bridge. Moreover, it is depicted that the impact of the surface tension starts appearing after the complete development of the liquid bridge where it is observed that for the same surrounding phase viscosity, the propagation of the capillary wave is faster for a LL system with higher surface tensions than those of lower surface tensions.}, }
@article {pmid33666462, year = {2021}, author = {Buaria, D and Clay, MP and Sreenivasan, KR and Yeung, PK}, title = {Turbulence is an Ineffective Mixer when Schmidt Numbers Are Large.}, journal = {Physical review letters}, volume = {126}, number = {7}, pages = {074501}, doi = {10.1103/PhysRevLett.126.074501}, pmid = {33666462}, issn = {1079-7114}, abstract = {We solve the advection-diffusion equation for a stochastically stationary passive scalar θ, in conjunction with forced 3D Navier-Stokes equations, using direct numerical simulations in periodic domains of various sizes, the largest being 8192^{3}. The Taylor-scale Reynolds number varies in the range 140-650 and the Schmidt number Sc≡ν/D in the range 1-512, where ν is the kinematic viscosity of the fluid and D is the molecular diffusivity of θ. Our results show that turbulence becomes an ineffective mixer when Sc is large. First, the mean scalar dissipation rate ⟨χ⟩=2D⟨|∇θ|^{2}⟩, when suitably nondimensionalized, decreases as 1/logSc. Second, 1D cuts through the scalar field indicate increasing density of sharp fronts on larger scales, oscillating with large excursions leading to reduced mixing, and additionally suggesting weakening of scalar variance flux across the scales. The scaling exponents of the scalar structure functions in the inertial-convective range appear to saturate with respect to the moment order and the saturation exponent approaches unity as Sc increases, qualitatively consistent with 1D cuts of the scalar.}, }
@article {pmid33665269, year = {2021}, author = {Sleiti, AK}, title = {Dataset for measured viscosity of Polyalpha-Olefin- boron nitride nanofluids.}, journal = {Data in brief}, volume = {35}, number = {}, pages = {106881}, pmid = {33665269}, issn = {2352-3409}, abstract = {Datasets of measured viscosity of Polyalpha-Olefin- boron nitride (PAO/hBN) nanofluids are reported. An AR-G2 rheometer (from TA Instruments) experimental setup is used for measuring the rheological property of PAO/hBN nanofluids, which is a combined motor and transducer (CMT) instrument. The test fluid sample size is approximately 1.5 ml and the tests were conducted over a temperature range of the tested fluids from - 20 °C to 70 °C by a water circulator chamber. The dataset includes measured viscosities as a function of the BN volumetric concentration (ϕ) of 0, 0.6 and 1%. Two sets of viscosity measurements are conducted insuring the thermal equilibrium conditions are reached for all experiments. In set (1), the viscosity is measured at intervals of 10 °C by fixing the temperature at each interval (at -20, -10, 0, 10, 20, 30, 40, 50, 60 and 70 °C), while the shear stress and shear rate are varied. In set (2), the temperature is varied from -20 °C to 70 °C at intervals of 0.5 °C, while the shear stress is fixed and the shear rate is varied accordingly. Set (1) is designed to verify whether the fluids are Newtonian or not and set (2) is designed to derive correlations for the viscosity as a function of temperature. Several characteristics data are recorded including rotational speed of the spindle (RPM), torque, viscosity (Pa- s), shear stress (Pa), shear strain rate (1/s) and temperature (°C). The reuse potential of the dataset includes calculating Reynolds number for further flow studies; heat transfer performance studies of nanofluids; lubrication and lubricants' development studies and characteristics of Newtonian and non-Newtonian fluids. The dataset reported here were used (but not published) in the article published by the author in [1] (https://doi.org/10.1016/j.csite.2020.100776).}, }
@article {pmid33652896, year = {2021}, author = {Charlton, AJ and Blandin, G and Leslie, G and Le-Clech, P}, title = {Impact of Forward Osmosis Operating Pressure on Deformation, Efficiency and Concentration Polarisation with Novel Links to CFD.}, journal = {Membranes}, volume = {11}, number = {3}, pages = {}, pmid = {33652896}, issn = {2077-0375}, abstract = {Forward osmosis (FO) modules currently suffer from performance efficiency limitations due to concentration polarisation (CP), as well as pressure drops during operation. There are incentives to further reduce CP effects, as well as optimise spacer design for pressure drop improvements and mechanical support. In this study, the effects of applying transmembrane pressure (TMP) on FO membrane deformation and the subsequent impact on module performance was investigated by comparing experimental data to 3D computational fluid dynamics (CFD) simulations for three commercial FO modules. At a TMP of 1.5 bar the occlusion of the draw-channel induced by longitudinal pressure hydraulic drop was comparable for the Toray (16%) and HTI modules (12%); however, the hydraulic perimeter of the Profiera module was reduced by 46%. CFD simulation of the occluded channels indicated that a change in hydraulic perimeter due to a 62% increase in shear strain resulted in a 31% increase in the Reynolds number. This reduction in channel dimensions enhanced osmotic efficiency by reducing CP via improved draw-channel hydrodynamics, which significantly disrupted the external concentration polarization (ECP) layer. Furthermore, simulations indicated that the Reynolds number experienced only modest increases with applied TMP and that shear strain at the membrane surface was found to be the most important factor when predicting flux performance enhancement, which varied between the different modules. This work suggests that a numerical approach to assess the effects of draw-spacers on pressure drop and CP can optimize and reduce investment in the design and validation of FO module designs.}, }
@article {pmid33639789, year = {2021}, author = {Ramadan, IA and Bailliet, H and Valière, JC}, title = {Experimental investigation of oscillating flow characteristics at the exit of a stacked mesh grid regenerator.}, journal = {The Journal of the Acoustical Society of America}, volume = {149}, number = {2}, pages = {807}, doi = {10.1121/10.0003375}, pmid = {33639789}, issn = {1520-8524}, abstract = {The aim of this study is to investigate the oscillating flow velocity field at the exit of different stacked mesh grid regenerators using Particle Image Velocimetry measurements. Twelve different experimental cases are discussed, yielding oscillating flow fields at the exit of four kinds of regenerators for different acoustic levels. The regenerators are classified according to the mesh wire size to viscous penetration depth ratio and according to the method of stacking the mesh grids. Based on the analysis of the vorticity fields at the exit of the regenerator, three groups of flow patterns are identified. This classification is correctly verified by using the Reynolds number (based on the acoustic amplitude and wire diameter) and the Strouhal number (based on the acoustic displacement amplitude and wire diameter). The characteristics of the fluctuating velocity components are investigated for these various flow patterns. The critical Reynolds number, past which the flow is highly dissipative, is determined. The dissipation timescale is investigated and the quasi-steady approximation is found to be valid for the analysis of the oscillating flow at the exit of the regenerator mesh.}, }
@article {pmid33635696, year = {2021}, author = {Bakhuis, D and Ezeta, R and Bullee, PA and Marin, A and Lohse, D and Sun, C and Huisman, SG}, title = {Catastrophic Phase Inversion in High-Reynolds-Number Turbulent Taylor-Couette Flow.}, journal = {Physical review letters}, volume = {126}, number = {6}, pages = {064501}, doi = {10.1103/PhysRevLett.126.064501}, pmid = {33635696}, issn = {1079-7114}, abstract = {Emulsions are omnipresent in the food industry, health care, and chemical synthesis. In this Letter the dynamics of metastable oil-water emulsions in highly turbulent (10^{11}≤Ta≤3×10^{13}) Taylor-Couette flow, far from equilibrium, is investigated. By varying the oil-in-water void fraction, catastrophic phase inversion between oil-in-water and water-in-oil emulsions can be triggered, changing the morphology, including droplet sizes, and rheological properties of the mixture, dramatically. The manifestation of these different states is exemplified by combining global torque measurements and local in situ laser induced fluorescence microscopy imaging. Despite the turbulent state of the flow and the dynamic equilibrium of the oil-water mixture, the global torque response of the system is found to be as if the fluid were Newtonian, and the effective viscosity of the mixture was found to be several times bigger or smaller than either of its constituents.}, }
@article {pmid33635462, year = {2021}, author = {Jain, PK and Lanjewar, A and Jain, R and Rana, KB}, title = {Performance analysis of multi-gap V-roughness with staggered elements of solar air heater based on artificial neural network and experimental investigations.}, journal = {Environmental science and pollution research international}, volume = {}, number = {}, pages = {}, pmid = {33635462}, issn = {1614-7499}, abstract = {Among all renewable energy sources, solar power is one of the major sources which contributes for pollution control and protection of environment. For a number of decades, technologies for utilizing the solar power have been the area of research and development. In the current research, thermal performance parameters of multi-gap V-roughness with staggered elements of a solar air heater (SAH) are experimentally investigated. The artificial neural network (ANN) is also utilized for predicting the thermal performance parameters of SAH. Experiments were executed in a rectangular channel with one roughened side at the top exposed to a uniform heat flux. A significant rise in thermal efficiency performance was reported under a predefined range of Reynolds number (Re) from 3000 to 14000 with an optimized value of relative roughness pitch ratio (P/e) and relative staggered rib length (w/g) as 12 and 1, respectively. The maximum thermal efficiency was attained in the range from 42.15 to 87.02% under considered Reynolds numbers for optimum value of P/e as 12 and w/g as 1. A multilayered perceptron (MLP) feed-forward ANN trained by the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm was utilized to predict the thermal efficiency (ηth), friction (f), and Nusselt number (Nu). The thermal performance parameters such as P/e, w/g, Re, and temperature at the inlet, outlet, and plate were the critical input parameters/signals used in the ANN method. The optimum ANN arrangement/structure to predict the Nu, f, and ηth demonstrate higher accurateness in assessing the performance characteristics of SAH by attaining the root mean squared error (RMSE) in prediction and the Pearson coefficient of association (R[2]) of 1.591 and 0.994; 0.0012 and 0.851; and 0.025 and 0.981, respectively. The prediction profile plots of the ANN demonstrate the influence of various input parameters on the thermal performance parameters.}, }
@article {pmid33633249, year = {2021}, author = {Altmeyer, S}, title = {On the ridge of instability in ferrofluidic Couette flow via alternating magnetic field.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {4705}, pmid = {33633249}, issn = {2045-2322}, abstract = {There is a huge number of natural and industrial flows, which are subjected to time-dependent boundary conditions. The flow of a magnetic fluid under the influence of temporal modulations is such an example. Here, we perform numerical simulations of ferrofluidic Couette flow subject to time-periodic modulation (with frequency [Formula: see text]) in a spatially homogeneous magnetic field and report how such a modulation can lead to a significant Reynolds number Re enhancement. Consider a modified Niklas approximation we explain the relation between modulation amplitude, driving frequency and stabilization effect. From this, we describe the system response around the primary instability to be sensitive/critical by an alternating field. We detected that such an alternating field provides an easy and in particular accurate controllable key parameter to trigger the system to change from subcritical to supercritical and vice versa. Our findings provide a framework to study other types of magnetic flows driven by time-dependent forcing.}, }
@article {pmid33625506, year = {2021}, author = {Sera, T and Kamiya, N and Fukushima, T and Tanaka, G}, title = {Visualizing the Flow Patterns in an Expanding and Contracting Pulmonary Alveolated Duct Based on Microcomputed Tomography Images.}, journal = {Journal of biomechanical engineering}, volume = {143}, number = {7}, pages = {}, doi = {10.1115/1.4050285}, pmid = {33625506}, issn = {1528-8951}, mesh = {*Pulmonary Alveoli/physiology/diagnostic imaging ; *X-Ray Microtomography ; Animals ; Models, Biological ; Rheology ; Mechanical Phenomena ; }, abstract = {We visualized the flow patterns in an alveolated duct model with breathing-like expanding and contracting wall motions using particle image velocimetry, and then, we investigated the effect of acinar deformation on the flow patterns. We reconstructed a compliant, scaled-up model of an alveolated duct from synchrotron microcomputed tomography images of a mammalian lung. The alveolated duct did not include any bifurcation, and its entire surface was covered with alveoli. We embedded the alveolated duct in a sealed container that was filled with fluid. We oscillated the fluid in the duct and container simultaneously and independently to control the flow and duct volume. We examined the flow patterns in alveoli, with the Reynolds number (Re) at 0.03 or 0.22 and the acinar volume change at 0%, 20%, or 80%. At the same Re, the heterogeneous deformation induced different inspiration and expiration flow patterns, and the recirculating regions in alveoli changed during respiratory cycle. During a larger acinar deformation at Re = 0.03, the flow patterns tended to change from recirculating flow to radial flow during inspiration and vice versa during expiration. Additionally, the alveolar geometric characteristics, particularly the angle between the alveolar duct and mouth, affected these differences in flow patterns. At Re = 0.22, recirculating flow patterns tended to form during inspiration and expiration, regardless of the magnitude of the acinar deformation. Our in vitro experiments suggest that the alveolated flows with nonself-similar and heterogeneous wall motions may promote particle mixing and deposition.}, }
@article {pmid33622143, year = {2021}, author = {Pepper, RE and Riley, EE and Baron, M and Hurot, T and Nielsen, LT and Koehl, MAR and Kiørboe, T and Andersen, A}, title = {The effect of external flow on the feeding currents of sessile microorganisms.}, journal = {Journal of the Royal Society, Interface}, volume = {18}, number = {175}, pages = {20200953}, pmid = {33622143}, issn = {1742-5662}, mesh = {*Ecosystem ; *Feeding Behavior ; Suspensions ; }, abstract = {Microscopic sessile suspension feeders live attached to surfaces and, by consuming bacteria-sized prey and by being consumed, they form an important part of aquatic ecosystems. Their environmental impact is mediated by their feeding rate, which depends on a self-generated feeding current. The feeding rate has been hypothesized to be limited by recirculating eddies that cause the organisms to feed from water that is depleted of food particles. However, those results considered organisms in still water, while ambient flow is often present in their natural habitats. We show, using a point-force model, that even very slow ambient flow, with speed several orders of magnitude less than that of the self-generated feeding current, is sufficient to disrupt the eddies around perpendicular suspension feeders, providing a constant supply of food-rich water. However, the feeding rate decreases in external flow at a range of non-perpendicular orientations due to the formation of recirculation structures not seen in still water. We quantify the feeding flow and observe such recirculation experimentally for the suspension feeder Vorticella convallaria in external flows typical of streams and rivers.}, }
@article {pmid33622097, year = {2021}, author = {Ge-JiLe, H and Javid, K and Khan, SU and Raza, M and Khan, MI and Qayyum, S}, title = {Double diffusive convection and Hall effect in creeping flow of viscous nanofluid through a convergent microchannel: a biotechnological applications.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {24}, number = {12}, pages = {1326-1343}, doi = {10.1080/10255842.2021.1888373}, pmid = {33622097}, issn = {1476-8259}, mesh = {*Convection ; Diffusion ; *Peristalsis ; Rheology ; Viscosity ; }, abstract = {Current analysis presents the mathematical modeling for peristaltic transport of nanofluid with applications of double-diffusive convection and Hall features. The flow has been induced by a convergent channel due to peristaltic propulsion. These rheological equations are transformed from fixed to wave frames by using a linear mathematical relation between these two frames. The dimensionless variables are used to transform these rheological equations into nondimensional forms. The flow analysis is carried out under two distinct scientific biological assumptions, one is known as long wavelength and the second one is low Reynolds number. The analytical solutions of these rheological equations are obtained with the help of a rigorous analytical method known as integration in the term of stream function. The physical effects of magnetic and Hall devices, respectively, on the flow features are also considered in the present analysis. The physical influences of dominant hydro-mechanical parameters on the axial velocity, pressure gradient, trapping, volumetric fraction of nanofluid, heat and mass transfer phenomena are studied. The complex scenario of biomimetic propulsions are considered in boundary walls to boost the proficiency of peristaltic micropumps.}, }
@article {pmid33601572, year = {2021}, author = {Bao, G and Jian, Y}, title = {Odd-viscosity-induced instability of a falling thin film with an external electric field.}, journal = {Physical review. E}, volume = {103}, number = {1-1}, pages = {013104}, doi = {10.1103/PhysRevE.103.013104}, pmid = {33601572}, issn = {2470-0053}, abstract = {The influence of odd viscosity of Newtonian fluid on the instability of thin film flowing along an inclined plane under a normal electric field is studied. By odd viscosity, we mean apart from the well-known coefficient of shear viscosity, a classical liquid with broken time-reversal symmetry is endowed with a second viscosity coefficient in biological, colloidal, and granular systems. Under the long wave approximation, a nonlinear evolution equation of the free surface is derived by the method of systematic asymptotic expansion. The effects of the odd viscosity and external electric field are considered in this evolution equation and an analytical expression of critical Reynolds number is obtained. It is interesting to find that, by linear stability analysis, the critical Reynolds number increases with odd viscosity and decreases with external strength of electric field. In other words, odd viscosity has a stable effect and electric field has a destabilized effect on flowing of thin film. In addition, through nonlinear analysis, we obtain a Ginsburg-Landau equation and find that the film has not only the supercritical stability zone and the subcritical instability zone but also the unconditional stability zone and the explosive zone. The variations of each zone with related parameters, such as the strength of electric field, odd viscosity, and Reynolds number, etc., are investigated. The results are conducive to the further development of related experiments.}, }
@article {pmid33601565, year = {2021}, author = {Pereira, FS and Grinstein, FF and Israel, DM and Rauenzahn, R}, title = {Molecular viscosity and diffusivity effects in transitional and shock-driven mixing flows.}, journal = {Physical review. E}, volume = {103}, number = {1-1}, pages = {013106}, doi = {10.1103/PhysRevE.103.013106}, pmid = {33601565}, issn = {2470-0053}, abstract = {This paper investigates the importance of molecular viscosity and diffusivity for the prediction of transitional and shock-driven mixing flows featuring high and low Reynolds and Mach number regions. Two representative problems are computed with implicit large-eddy simulations using the inviscid Euler equations (EE) and viscous Navier-Stokes equations (NSE): the Taylor-Green vortex at Reynolds number Re=3000 and initial Mach number Ma=0.28, and an air-SF_{6}-air gas curtain subjected to two shock waves at Ma=1.2. The primary focus is on differences between NSE and EE predictions due to viscous effects. The outcome of the paper illustrates the advantages of utilizing NSE. In contrast to the EE, where the effective viscosity decreases upon grid refinement, NSE predictions can be assessed for simulations of flows with transition to turbulence at prescribed constant Re. The NSE can achieve better agreement between solutions and reference data, and the results converge upon grid refinement. On the other hand, the EE predictions do not converge with grid refinement, and can only exhibit similarities with the NSE results at coarse grid resolutions. We also investigate the effect of viscous effects on the dynamics of the coherent and turbulent fields, as well as on the mechanisms contributing to the production and diffusion of vorticity. The results show that nominally inviscid calculations can exhibit significantly varying flow dynamics driven by changing effective resolution-dependent Reynolds number, and highlight the role of viscous processes affecting the vorticity field. These tendencies become more pronounced upon grid refinement. The discussion of the results concludes with the assessment of the computational cost of inviscid and viscous computations.}, }
@article {pmid33601495, year = {2021}, author = {Livi, C and Di Staso, G and Clercx, HJH and Toschi, F}, title = {Influence of numerical resolution on the dynamics of finite-size particles with the lattice Boltzmann method.}, journal = {Physical review. E}, volume = {103}, number = {1-1}, pages = {013303}, doi = {10.1103/PhysRevE.103.013303}, pmid = {33601495}, issn = {2470-0053}, abstract = {We investigate and compare the accuracy and efficiency of different numerical approaches to model the dynamics of finite-size particles using the lattice Boltzmann method (LBM). This includes the standard bounce-back (BB) and the equilibrium interpolation (EI) schemes. To accurately compare the different implementations, we first introduce a boundary condition to approximate the flow properties of an unbounded fluid in a finite simulation domain, taking into account the perturbation induced by a moving particle. We show that this boundary treatment is efficient in suppressing detrimental effects on the dynamics of spherical and ellipsoidal particles arising from the finite size of the simulation domain. We then investigate the performances of the BB and EI schemes in modeling the dynamics of a spherical particle settling under Stokes conditions, which can now be reproduced with great accuracy thanks to the treatment of the exterior boundary. We find that the EI scheme outperforms the BB scheme in providing a better accuracy scaling with respect to the resolution of the settling particle, while suppressing finite-size effects due to the particle discretization on the lattice grid. Additionally, in order to further increase the capability of the algorithm in modeling particles of sizes comparable to the lattice spacing, we propose an improvement to the EI scheme, the complete equilibrium interpolation (CEI). This approach allows us to accurately capture the boundaries of the particle also when located between two fluid nodes. We evaluate the CEI performance in solving the dynamics of an under-resolved particle under analogous Stokes conditions and also for the case of a rotating ellipsoid in a shear flow. Finally, we show that EI and CEI are able to recover the correct flow solutions also at small, but finite, Reynolds number. Adopting the CEI scheme it is not only possible to detect particles with zero lattice occupation, but also to increase up to one order of magnitude the accuracy of the dynamics of particles with a size comparable to the lattice spacing with respect to the BB and the EI schemes.}, }
@article {pmid33590890, year = {2021}, author = {Pskowski, A and Bagchi, P and Zahn, JD}, title = {Investigation of red blood cell partitioning in an in vitro microvascular bifurcation.}, journal = {Artificial organs}, volume = {45}, number = {9}, pages = {1083-1096}, doi = {10.1111/aor.13941}, pmid = {33590890}, issn = {1525-1594}, support = {CBET 1604308//National Science Foundation/ ; }, mesh = {Blood Flow Velocity ; Equipment Design ; Erythrocytes/*physiology ; *Hematocrit ; Hemorheology/*physiology ; Humans ; In Vitro Techniques ; Microcirculation ; Models, Cardiovascular ; }, abstract = {There is a long history of research examining red blood cell (RBC) partitioning in microvasculature bifurcations. These studies commonly report results describing partitioning that exists as either regular partitioning, which occurs when the RBC flux ratio is greater than the bulk fluid flowrate ratio, or reverse partitioning when the RBC flux ratio is less than or equal to that of the bulk fluid flowrate. This paper presents a study of RBC partitioning in a single bifurcating microchannel with dimensions of 6 to 16 μm, investigating the effects of hematocrit, channel width, daughter channel flowrate ratio, and bifurcation angle. The erythrocyte flux ratio, N*, manifests itself as either regular or reverse partitioning, and time-dependent partitioning is much more dynamic, occurring as both regular and reverse partitioning. We report a significant reduction in the well-known sigmoidal variation of the erythrocyte flux ratio (N*) versus the volumetric flowrate ratio (Q*), partitioning behavior with increasing hematocrit in microchannels when the channel dimensions are comparable with cell size. RBCs "lingering" or jamming at the bifurcation were also observed and quantified in vitro. Results from trajectory analyses suggest that the RBC position in the feeder channel strongly affects both partitioning and lingering frequency of RBCs, with both being significantly reduced when RBCs flow on streamlines near the edge of the channel as opposed to the center of the channel. Furthermore, our experiments suggest that even at low Reynolds number, partitioning is affected by the bifurcation angle by increasing cell-cell interactions. The presented results provide further insight into RBC partitioning as well as perfusion throughout the microvasculature.}, }
@article {pmid33580288, year = {2021}, author = {Ender, H and Kierfeld, J}, title = {From diffusive mass transfer in Stokes flow to low Reynolds number Marangoni boats.}, journal = {The European physical journal. E, Soft matter}, volume = {44}, number = {1}, pages = {4}, pmid = {33580288}, issn = {1292-895X}, abstract = {We present a theory for the self-propulsion of symmetric, half-spherical Marangoni boats (soap or camphor boats) at low Reynolds numbers. Propulsion is generated by release (diffusive emission or dissolution) of water-soluble surfactant molecules, which modulate the air-water interfacial tension. Propulsion either requires asymmetric release or spontaneous symmetry breaking by coupling to advection for a perfectly symmetrical swimmer. We study the diffusion-advection problem for a sphere in Stokes flow analytically and numerically both for constant concentration and constant flux boundary conditions. We derive novel results for concentration profiles under constant flux boundary conditions and for the Nusselt number (the dimensionless ratio of total emitted flux and diffusive flux). Based on these results, we analyze the Marangoni boat for small Marangoni propulsion (low Peclet number) and show that two swimming regimes exist, a diffusive regime at low velocities and an advection-dominated regime at high swimmer velocities. We describe both the limit of large Marangoni propulsion (high Peclet number) and the effects from evaporation by approximative analytical theories. The swimming velocity is determined by force balance, and we obtain a general expression for the Marangoni forces, which comprises both direct Marangoni forces from the surface tension gradient along the air-water-swimmer contact line and Marangoni flow forces. We unravel whether the Marangoni flow contribution is exerting a forward or backward force during propulsion. Our main result is the relation between Peclet number and swimming velocity. Spontaneous symmetry breaking and, thus, swimming occur for a perfectly symmetrical swimmer above a critical Peclet number, which becomes small for large system sizes. We find a supercritical swimming bifurcation for a symmetric swimmer and an avoided bifurcation in the presence of an asymmetry.}, }
@article {pmid33573067, year = {2021}, author = {Hosseini, SA and Safari, H and Thevenin, D}, title = {Lattice Boltzmann Solver for Multiphase Flows: Application to High Weber and Reynolds Numbers.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {2}, pages = {}, pmid = {33573067}, issn = {1099-4300}, support = {TRR287-422037413//Deutsche Forschungsgemeinschaft/ ; }, abstract = {The lattice Boltzmann method, now widely used for a variety of applications, has also been extended to model multiphase flows through different formulations. While already applied to many different configurations in low Weber and Reynolds number regimes, applications to higher Weber/Reynolds numbers or larger density/viscosity ratios are still the topic of active research. In this study, through a combination of a decoupled phase-field formulation-the conservative Allen-Cahn equation-and a cumulant-based collision operator for a low-Mach pressure-based flow solver, we present an algorithm that can be used for higher Reynolds/Weber numbers. The algorithm was validated through a variety of test cases, starting with the Rayleigh-Taylor instability in both 2D and 3D, followed by the impact of a droplet on a liquid sheet. In all simulations, the solver correctly captured the flow dynamics andmatched reference results very well. As the final test case, the solver was used to model droplet splashing on a thin liquid sheet in 3D with a density ratio of 1000 and kinematic viscosity ratio of 15, matching the water/air system at We = 8000 and Re = 1000. Results showed that the solver correctly captured the fingering instabilities at the crown rim and their subsequent breakup, in agreement with experimental and numerical observations reported in the literature.}, }
@article {pmid33571986, year = {2021}, author = {Gungor, A and Hemmati, A}, title = {Implications of changing synchronization in propulsive performance of side-by-side pitching foils.}, journal = {Bioinspiration &amp; biomimetics}, volume = {16}, number = {3}, pages = {}, doi = {10.1088/1748-3190/abe54b}, pmid = {33571986}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Fishes ; Hydrodynamics ; *Models, Biological ; *Swimming ; }, abstract = {The unsteady hydrodynamics of side-by-side pitching foils are studied numerically at Reynolds number of 4000 with altering phase differences in the middle of an oscillation cycle. This represents a change in synchronization of oscillating foils, inspired by experimental observations on group swimming of red nose tetra fish. The hybrid oscillation cases are based on an initially out-of-phase pitching that switch to in-phase at the 20th cycle of oscillation. Various sequential combinations of out-of-phase and in-phase pitching are also examined in terms of foil propulsive performance. It is observed that out-of-phase pitching foils initially produce zero total side-force. However, they start producing negative total side-force after 13 oscillation cycles. Contrarily for the in-phase oscillation cases, the initially positive total side-force reverted to zero over time. In hybrid oscillation cases, the negative total side-force produced during the initial out-of-phase oscillations abruptly adjusted to zero following a change of synchronization that led to in-phase oscillations, which is inspired from a particular swimming behavior in fish. Based on three hybrid modes, defined on the onset of mid-cycle switch to in-phase oscillations, it was apparent that the benefit of synchronization, or there lack of, greatly depended on the timing of the change in synchronization. Thus, mid-swimming change of synchronization in side-by-side systems inspired by fish schools compensates for their non-zero total side-force production to maintain their lateral position. Such changes do not translate to significant gains in neither thrust generation nor efficiency.}, }
@article {pmid33561405, year = {2021}, author = {Longo, SJ and Ray, W and Farley, GM and Harrison, J and Jorge, J and Kaji, T and Palmer, AR and Patek, SN}, title = {Snaps of a tiny amphipod push the boundary of ultrafast, repeatable movement.}, journal = {Current biology : CB}, volume = {31}, number = {3}, pages = {R116-R117}, doi = {10.1016/j.cub.2020.12.025}, pmid = {33561405}, issn = {1879-0445}, mesh = {*Amphipoda ; Animals ; Biomechanical Phenomena ; Humans ; Male ; *Movement ; Water ; }, abstract = {Surprisingly, the fastest motions are not produced by large animals or robots. Rather, small organisms or structures, including cnidarian stinging cells, fungal shooting spores, and mandible strikes of ants, termites, and spiders, hold the world acceleration records.[1-5] These diverse systems share common features: they rapidly convert potential energy - stored in deformed material or fluid - into kinetic energy when a latch is released.[4-6] However, the fastest of these are not repeatable, because mechanical components are broken or ejected.[5,6] Furthermore, some of these systems must overcome the added challenge of moving in water, where high density and viscosity constrain acceleration at small sizes. Here we report the kinematics of repeatable, ultrafast snaps by tiny marine amphipods (Dulichiella cf. appendiculata). Males use their enlarged major claw, which can exceed 30% of body mass, to snap a 1 mm-long dactyl with a diameter equivalent to a human hair (184 μm). The claw snaps closed extremely rapidly, averaging 93 μs, 17 m s[-1], and 2.4 x 10[5] m s[-2]. These snaps are among the smallest and fastest of any documented repeatable movement, and are sufficiently fast to operate in the inertial hydrodynamic regime (Reynolds number (Re) >10,000). They generate audible pops and rapid water jets, which occasionally yield cavitation, and may be used for defense. These amphipod snaps push the boundaries of acceleration and size for repeatable movements, particularly in water, and exemplify how new biomechanical insights can arise from unassuming animals. VIDEO ABSTRACT.}, }
@article {pmid33544100, year = {2021}, author = {Yang, F}, title = {Homogeneous nucleation in a Poiseuille flow.}, journal = {Physical chemistry chemical physics : PCCP}, volume = {23}, number = {6}, pages = {3974-3982}, doi = {10.1039/d0cp06132h}, pmid = {33544100}, issn = {1463-9084}, abstract = {Nucleation in a dynamical environment plays an important role in the synthesis and manufacturing of quantum dots and nanocrystals. In this work, we investigate the effects of fluid flow (low Reynolds number flow) on the homogeneous nucleation in a circular microchannel in the framework of the classical nucleation theory. The contributions of the configuration entropy from the momentum-phase space and the kinetic energy and strain energy of a microcluster are incorporated in the calculation of the change of the Gibbs free energy from a flow state without a microcluster to a flow state with a microcluster. An analytical equation is derived for the determination of the critical nucleus size. Using this analytical equation, an analytical solution of the critical nucleus size for the formation of a critical liquid nucleus is found. For the formation of a critical solid nucleus, the contributions from both the kinetic energy and the strain energy are generally negligible. We perform numerical analysis of the homogeneous nucleation of a sucrose microcluster in a representative volume element of an aqueous solution, which flows through a circular microchannel. The numerical results reveal the decrease of the critical nucleus size and the corresponding work of formation of a critical nucleus with the increase of the distance to axisymmetric axis for the same numbers of solvent atoms and solute atoms/particles.}, }
@article {pmid33543985, year = {2021}, author = {Buaria, D and Clay, MP and Sreenivasan, KR and Yeung, PK}, title = {Small-Scale Isotropy and Ramp-Cliff Structures in Scalar Turbulence.}, journal = {Physical review letters}, volume = {126}, number = {3}, pages = {034504}, doi = {10.1103/PhysRevLett.126.034504}, pmid = {33543985}, issn = {1079-7114}, abstract = {Passive scalars advected by three-dimensional Navier-Stokes turbulence exhibit a fundamental anomaly in odd-order moments because of the characteristic ramp-cliff structures, violating small-scale isotropy. We use data from direct numerical simulations with grid resolution of up to 8192^{3} at high Péclet numbers to understand this anomaly as the scalar diffusivity, D, diminishes, or as the Schmidt number, Sc=ν/D, increases; here ν is the kinematic viscosity of the fluid. The microscale Reynolds number varies from 140 to 650 and Sc varies from 1 to 512. A simple model for the ramp-cliff structures is developed and shown to characterize the scalar derivative statistics very well. It accurately captures how the small-scale isotropy is restored in the large-Sc limit, and additionally suggests a possible correction to the Batchelor length scale as the relevant smallest scale in the scalar field.}, }
@article {pmid33543965, year = {2021}, author = {Nasouri, B and Vilfan, A and Golestanian, R}, title = {Minimum Dissipation Theorem for Microswimmers.}, journal = {Physical review letters}, volume = {126}, number = {3}, pages = {034503}, doi = {10.1103/PhysRevLett.126.034503}, pmid = {33543965}, issn = {1079-7114}, abstract = {We derive a theorem for the lower bound on the energy dissipation rate by a rigid surface-driven active microswimmer of arbitrary shape in a fluid at a low Reynolds number. We show that, for any swimmer, the minimum dissipation at a given velocity can be expressed in terms of the resistance tensors of two passive bodies of the same shape with a no-slip and perfect-slip boundary. To achieve the absolute minimum dissipation, the optimal swimmer needs a surface velocity profile that corresponds to the flow around the perfect-slip body, and a propulsive force density that corresponds to the no-slip body. Using this theorem, we propose an alternative definition of the energetic efficiency of microswimmers that, unlike the commonly used Lighthill efficiency, can never exceed unity. We validate the theory by calculating the efficiency limits of spheroidal swimmers.}, }
@article {pmid33537715, year = {2021}, author = {Yu, P and Durgesh, V and Xing, T and Budwig, R}, title = {Application of Proper Orthogonal Decomposition to Study Coherent Flow Structures in a Saccular Aneurysm.}, journal = {Journal of biomechanical engineering}, volume = {143}, number = {6}, pages = {}, doi = {10.1115/1.4050032}, pmid = {33537715}, issn = {1528-8951}, mesh = {*Aneurysm/physiopathology ; Models, Cardiovascular ; Rheology ; Hemodynamics ; Humans ; Blood Flow Velocity ; }, abstract = {Aneurysms are localized expansions of weakened blood vessels that can be debilitating or fatal upon rupture. Previous studies have shown that flow in an aneurysm exhibits complex flow structures that are correlated with its inflow conditions. Therefore, the objective of this study was to demonstrate the application of proper orthogonal decomposition (POD) to study the impact of different inflow conditions on energetic flow structures and their temporal behavior in an aneurysm. To achieve this objective, experiments were performed on an idealized rigid sidewall aneurysm model. A piston pump system was used for precise inflow control, i.e., peak Reynolds number (Rep) and Womersley number (α) were varied from 50 to 270 and 2 to 5, respectively. The velocity flow field measurements at the midplane location of the idealized aneurysm model were performed using particle image velocimetry (PIV). The results demonstrate the efficacy of POD in decomposing complex data, and POD was able to capture the energetic flow structures unique to each studied inflow condition. Furthermore, the time-varying coefficient results highlighted the interplay between the coefficients and their corresponding POD modes, which in turn helped explain how POD modes impact certain flow features. The low-order reconstruction results were able to capture the flow evolution and provide information on complex flow in an aneurysm. The POD and low-order reconstruction results also indicated that vortex formation, evolution, and convection varied with an increase in α, while vortex strength and formation of secondary structures were correlated with an increase in Rep.}, }
@article {pmid33530578, year = {2021}, author = {Selimefendigil, F and Öztop, HF}, title = {Thermal Management and Modeling of Forced Convection and Entropy Generation in a Vented Cavity by Simultaneous Use of a Curved Porous Layer and Magnetic Field.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {2}, pages = {}, pmid = {33530578}, issn = {1099-4300}, abstract = {The effects of using a partly curved porous layer on the thermal management and entropy generation features are studied in a ventilated cavity filled with hybrid nanofluid under the effects of inclined magnetic field by using finite volume method. This study is performed for the range of pertinent parameters of Reynolds number (100≤Re≤1000), magnetic field strength (0≤Ha≤80), permeability of porous region (10-4≤Da≤5×10-2), porous layer height (0.15H≤tp≤0.45H), porous layer position (0.25H≤yp≤0.45H), and curvature size (0≤b≤0.3H). The magnetic field reduces the vortex size, while the average Nusselt number of hot walls increases for Ha number above 20 and highest enhancement is 47% for left vertical wall. The variation in the average Nu with permeability of the layer is about 12.5% and 21% for left and right vertical walls, respectively, while these amounts are 12.5% and 32.5% when the location of the porous layer changes. The entropy generation increases with Hartmann number above 20, while there is 22% increase in the entropy generation for the case at the highest magnetic field. The porous layer height reduced the entropy generation for domain above it and it give the highest contribution to the overall entropy generation. When location of the curved porous layer is varied, the highest variation of entropy generation is attained for the domain below it while the lowest value is obtained at yp=0.3H. When the size of elliptic curvature is varied, the overall entropy generation decreases from b=0 to b=0.2H by about 10% and then increases by 5% from b=0.2H to b=0.3H.}, }
@article {pmid33510410, year = {2021}, author = {Sato, N and Kawashima, D and Takei, M}, title = {Concentration profiles of ions and particles under hydrodynamic focusing in Y-shaped square microchannel.}, journal = {Scientific reports}, volume = {11}, number = {1}, pages = {2585}, pmid = {33510410}, issn = {2045-2322}, abstract = {Three-dimensional ion and particle concentrations under hydrodynamic focusing in a Y-shaped square microchannel are numerically simulated to clarify the decrease of the ion concentration along the flow direction within the focused particle stream. The simulation model is theoretically governed by the laminar flow and advection-diffusion equations. The governing equations are solved by the finite volume method. The ion and particle concentration distributions at five cross sections after the confluence of the branch channels are analyzed in 30 cases in which the sheath to sample flow rate ratio Qsh/Qsam and the Reynolds number Re are varied as parameters. The results show that the decrease of the cross-sectional average ion concentration along the flow direction within the particle stream [Formula: see text] is described by the diffusion length during the residence time with a characteristic velocity scale. In addition, the deformation of the particle stream due to inertial effects is described by a scaled Reynolds number that is a function of the flow rate ratio. The simulated particle stream thicknesses are validated by theory and a simple experiment. This paper reveals the relationship between the ion and particle concentrations and the dimensionless parameters for hydrodynamic focusing in the Y-shaped square microchannel under typical conditions.}, }
@article {pmid33509927, year = {2021}, author = {Andreotti, B and Claudin, P and Iversen, JJ and Merrison, JP and Rasmussen, KR}, title = {A lower-than-expected saltation threshold at Martian pressure and below.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {118}, number = {5}, pages = {}, pmid = {33509927}, issn = {1091-6490}, abstract = {Aeolian sediment transport is observed to occur on Mars as well as other extraterrestrial environments, generating ripples and dunes as on Earth. The search for terrestrial analogs of planetary bedforms, as well as environmental simulation experiments able to reproduce their formation in planetary conditions, are powerful ways to question our understanding of geomorphological processes toward unusual environmental conditions. Here, we perform sediment transport laboratory experiments in a closed-circuit wind tunnel placed in a vacuum chamber and operated at extremely low pressures to show that Martian conditions belong to a previously unexplored saltation regime. The threshold wind speed required to initiate saltation is only quantitatively predicted by state-of-the art models up to a density ratio between grain and air of [Formula: see text] but unexpectedly falls to much lower values for higher density ratios. In contrast, impact ripples, whose emergence is continuously observed on the granular bed over the whole pressure range investigated, display a characteristic wavelength and propagation velocity essentially independent of pressure. A comparison of these findings with existing models suggests that sediment transport at low Reynolds number but high grain-to-fluid density ratio may be dominated by collective effects associated with grain inertia in the granular collisional layer.}, }
@article {pmid33503087, year = {2021}, author = {Hoeger, K and Ursell, T}, title = {Steric scattering of rod-like swimmers in low Reynolds number environments.}, journal = {Soft matter}, volume = {17}, number = {9}, pages = {2479-2489}, doi = {10.1039/d0sm01551b}, pmid = {33503087}, issn = {1744-6848}, mesh = {*Ecosystem ; Hydrodynamics ; *Models, Biological ; Movement ; Swimming ; }, abstract = {Microbes form integral components of all natural ecosystems. In most cases, the surrounding micro-environment has physical variations that affect the movements of micro-swimmers, including solid objects of varying size, shape and density. As swimmers move through viscous environments, a combination of hydrodynamic and steric forces are known to significantly alter their trajectories in a way that depends on surface curvature. In this work, our goal was to clarify the role of steric forces when rod-like swimmers interact with solid objects comparable to cell size. We imaged hundreds-of-thousands of scattering interactions between swimming bacteria and micro-fabricated pillars with radii from ∼1 to ∼10 cell lengths. Scattering interactions were parameterized by the angle of the cell upon contact with the pillar, and primarily produced forward-scattering events that fell into distinct chiral distributions for scattering angle - no hydrodynamic trapping was observed. The chirality of a scattering event was a stochastic variable whose probability smoothly and symmetrically depended on the contact angle. Neglecting hydrodynamics, we developed a model that only considers contact forces and torques for a rear-pushed thin-rod scattering from a cylinder - the model predictions were in good agreement with measured data. Our results suggest that alteration of bacterial trajectories is subject to distinct mechanisms when interacting with objects of different size; primarily steric for objects below ∼10 cell lengths and requiring incorporation of hydrodynamics at larger scales. These results contribute to a mechanistic framework in which to examine (and potentially engineer) microbial movements through natural and synthetic environments that present complex steric structure.}, }
@article {pmid33494348, year = {2021}, author = {Ambreen, T and Saleem, A and Park, CW}, title = {Homogeneous and Multiphase Analysis of Nanofluids Containing Nonspherical MWCNT and GNP Nanoparticles Considering the Influence of Interfacial Layering.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {11}, number = {2}, pages = {}, pmid = {33494348}, issn = {2079-4991}, abstract = {The practical implication of nanofluids is essentially dependent on their accurate modelling, particularly in comparison with the high cost of experimental investigations, yet the accuracy of different computational approaches to simulate nanofluids remains controversial to this day. Therefore, the present study is aimed at analysing the homogenous, multiphase Eulerian-Eulerian (volume of fluid, mixture, Eulerian) and Lagrangian-Eulerian approximation of nanofluids containing nonspherical nanoparticles. The heat transfer and pressure drop characteristics of the multiwalled carbon nanotubes (MWCNT)-based and multiwalled carbon nanotubes/graphene nanoplatelets (MWCNT/GNP)-based nanofluids are computed by incorporating the influence of several physical mechanisms, including interfacial nanolayering. The accuracy of tested computational approaches is evaluated by considering particle concentration and Reynolds number ranges of 0.075-0.25 wt% and 200-470, respectively. The results demonstrate that for all nanofluid combinations and operational conditions, the Lagrangian-Eulerian approximation provides the most accurate convective heat transfer coefficient values with a maximum deviation of 5.34% for 0.25 wt% of MWCNT-water nanofluid at the largest Reynolds number, while single-phase and Eulerian-Eulerian multiphase models accurately estimate the thermal fields of the diluted nanofluids at low Reynolds numbers, but overestimate the results for denser nanofluids at high Reynolds numbers.}, }
@article {pmid33493237, year = {2021}, author = {Mahrous, SA and Sidik, NAC and Saqr, KM}, title = {Numerical study on the energy cascade of pulsatile Newtonian and power-law flow models in an ICA bifurcation.}, journal = {PloS one}, volume = {16}, number = {1}, pages = {e0245775}, pmid = {33493237}, issn = {1932-6203}, mesh = {Humans ; Intracranial Aneurysm/pathology/*physiopathology ; Kinetics ; *Models, Biological ; *Pulsatile Flow ; }, abstract = {The complex physics and biology underlying intracranial hemodynamics are yet to be fully revealed. A fully resolved direct numerical simulation (DNS) study has been performed to identify the intrinsic flow dynamics in an idealized carotid bifurcation model. To shed the light on the significance of considering blood shear-thinning properties, the power-law model is compared to the commonly used Newtonian viscosity hypothesis. We scrutinize the kinetic energy cascade (KEC) rates in the Fourier domain and the vortex structure of both fluid models and examine the impact of the power-law viscosity model. The flow intrinsically contains coherent structures which has frequencies corresponding to the boundary frequency, which could be associated with the regulation of endothelial cells. From the proposed comparative study, it is found that KEC rates and the vortex-identification are significantly influenced by the shear-thinning blood properties. Conclusively, from the obtained results, it is found that neglecting the non-Newtonian behavior could lead to underestimation of the hemodynamic parameters at low Reynolds number and overestimation of the hemodynamic parameters by increasing the Reynolds number. In addition, we provide physical insight and discussion onto the hemodynamics associated with endothelial dysfunction which plays significant role in the pathogenesis of intracranial aneurysms.}, }
@article {pmid33490686, year = {2021}, author = {Ibrahim, W and Hirpho, M}, title = {Finite element analysis of mixed convection flow in a trapezoidal cavity with non-uniform temperature.}, journal = {Heliyon}, volume = {7}, number = {1}, pages = {e05933}, doi = {10.1016/j.heliyon.2021.e05933}, pmid = {33490686}, issn = {2405-8440}, abstract = {A two dimensional flow analysis in a cavity shaped isosceles trapezium is carried out. Non-parallel sides of a trapezium are adiabatic. A varying sinusoidal temperature is applied to the lower wall while the upper wall is at constant temperature. Upper wall of the cavity moves with a velocity η 0 in the positive x-direction. Also, B 0 is constant magnetic field of strength aligned in the same x-direction and Newtonian fluid is considered. The values of magnetic field parameter used are H a = 0 , 50 , the Richardson number is R i = 0.1 , 1 , 10 , R e = 100 is Reynolds number used for the analysis, the amplitude of sinusoidal temperature is m = 0.25 , 0.5 , 1 . The impacts of different leading parameters are analyzed by plotting streamlines for flow fields and isotherm contours for temperature of the flow dynamics. The graphs that signify the variation of average Nusselt number and local Nusselt number are sketched for both lower and upper walls of the cavity. Result indicated that with constant temperature the top wall of the boundary layer thickness decreases as Richardson number Ri increases and for bottom wall with variable temperature. The Nusselt number gets higher with an increment in the amplitude of the oscillation of temperature function. Furthermore, the study revealed that the average Nusselt number gets reduced as the intensity of magnetic field is enhanced. The variation in transit of heat at the bottom wall is similar but the maximum value of heat transfer at the bottom wall shows a variation from 3.8 to 20 when H a = 0 and from 3 to 18 when H a = 50 . The accuracy of the present numerical algorithms is also established.}, }
@article {pmid33477950, year = {2021}, author = {Kim, GY and Son, J and Han, JI and Park, JK}, title = {Inertial Microfluidics-Based Separation of Microalgae Using a Contraction-Expansion Array Microchannel.}, journal = {Micromachines}, volume = {12}, number = {1}, pages = {}, pmid = {33477950}, issn = {2072-666X}, support = {NRF-2011-0031348//National Research Foundation of Korea/ ; NRF-2019R1A2B5B03070494//National Research Foundation of Korea/ ; }, abstract = {Microalgae separation technology is essential for both executing laboratory-based fundamental studies and ensuring the quality of the final algal products. However, the conventional microalgae separation technology of micropipetting requires highly skilled operators and several months of repeated separation to obtain a microalgal single strain. This study therefore aimed at utilizing microfluidic cell sorting technology for the simple and effective separation of microalgae. Microalgae are characterized by their various morphologies with a wide range of sizes. In this study, a contraction-expansion array microchannel, which utilizes these unique properties of microalgae, was specifically employed for the size-based separation of microalgae. At Reynolds number of 9, two model algal cells, Chlorella vulgaris (C. vulgaris) and Haematococcus pluvialis (H. pluvialis), were successfully separated without showing any sign of cell damage, yielding a purity of 97.9% for C. vulgaris and 94.9% for H. pluvialis. The result supported that the inertia-based separation technology could be a powerful alternative to the labor-intensive and time-consuming conventional microalgae separation technologies.}, }
@article {pmid33465973, year = {2020}, author = {Liu, C and Gayme, DF}, title = {Input-output inspired method for permissible perturbation amplitude of transitional wall-bounded shear flows.}, journal = {Physical review. E}, volume = {102}, number = {6-1}, pages = {063108}, doi = {10.1103/PhysRevE.102.063108}, pmid = {33465973}, issn = {2470-0053}, abstract = {The precise set of parameters governing transition to turbulence in wall-bounded shear flows remains an open question; many theoretical bounds have been obtained, but there is not yet a consensus between these bounds and experimental or simulation results. In this work, we focus on a method to provide a provable Reynolds-number-dependent bound on the amplitude of perturbations a flow can sustain while maintaining the laminar state. Our analysis relies on an input-output approach that partitions the dynamics into a feedback interconnection of the linear and nonlinear dynamics (i.e., a Luré system that represents the nonlinearity as static feedback). We then construct quadratic constraints of the nonlinear term that is restricted by system physics to be energy-conserving (lossless) and to have bounded input-output energy. Computing the region of attraction of the laminar state (set of safe perturbations) and permissible perturbation amplitude are then reformulated as linear matrix inequalities, which allows more computationally efficient solutions than prevailing nonlinear approaches based on the sum of squares programming. The proposed framework can also be used for energy method computations and linear stability analysis. We apply our approach to low-dimensional nonlinear shear flow models for a range of Reynolds numbers. The results from our analytically derived bounds are consistent with the bounds identified through exhaustive simulations. However, they have the added benefit of being achieved at a much lower computational cost and providing a provable guarantee that a certain level of perturbation is permissible.}, }
@article {pmid33462593, year = {2021}, author = {Shaheen, S and Anwar Bég, O and Gul, F and Maqbool, K}, title = {Electro-Osmotic Propulsion of Jeffrey Fluid in a Ciliated Channel Under the Effect of Nonlinear Radiation and Heat Source/Sink.}, journal = {Journal of biomechanical engineering}, volume = {143}, number = {5}, pages = {}, doi = {10.1115/1.4049810}, pmid = {33462593}, issn = {1528-8951}, mesh = {*Hot Temperature ; *Nonlinear Dynamics ; *Cilia/physiology ; Electroosmosis ; Hydrodynamics ; Osmosis ; Rheology ; Microfluidics ; }, abstract = {Mathematical modeling of mechanical system in microfluidics is an emerging area of interest in microscale engineering. Since microfluidic devices use the hair-like structure of artificial cilia for pumping, mixing, and sensing in different fields, electro-osmotic cilia-driven flow helps to generate the fluid velocity for the Newtonian and viscoelastic fluid. Due to the deployment of artificial ciliated walls, the present research reports the combined effect of an electro-osmotic flow and convective heat transfer on Jeffrey viscoelastic electrolytic fluid flow in a two-dimensional ciliated vertical channel. Heat generation/absorption and nonlinear radiation effects are included in the present mathematical model. After applying Debye-Huckel approximation and small Reynolds number approximation to momentum and energy equation, the system of nonlinear partial differential equation is reduced into nonhomogenous boundary value problem. The problem determines the velocity, pressure, and temperature profiles by the application of semi-analytical technique known as homotopy perturbation method (HPM) with the help of software Mathematica. The graphical results of the study suggest that HPM is a reliable methodology for thermo physical electro-osmotic rheological transport in microchannels.}, }
@article {pmid33450503, year = {2021}, author = {Javid, K and Riaz, M and Chu, YM and Ijaz Khan, M and Ullah Khan, S and Kadry, S}, title = {Peristaltic activity for electro-kinetic complex driven cilia transportation through a non-uniform channel.}, journal = {Computer methods and programs in biomedicine}, volume = {200}, number = {}, pages = {105926}, doi = {10.1016/j.cmpb.2020.105926}, pmid = {33450503}, issn = {1872-7565}, mesh = {*Body Fluids ; *Cilia ; Kinetics ; Peristalsis ; Viscosity ; }, abstract = {MOTIVATIONS: Now-a-days in medical science, the transport study of biological fluids through non-uniform vessels are going to increase due to their close relation to the reality. Motivated through such type of complex transportation, the current study is presented of cilia hydro-dynamics of an aqueous electrolytic viscous fluid through a non-uniform channel under an applied axial electric field. Mathematical Formulations: Because of the complexity shape and nature of flow channel, we have used curvilinear coordinates in the derivation of continuity and momentum equationsin a fixed frame of reference. A linear transformation is used to renovate the flow system of equations from fixed (laboratory) to moving (wave) frame. For further simplification, the dimensionless variables are introduced to make the flow system of equations into the dimensionless form and at last convert these equations in term of stream function by using the mathematical terminologies of streamlines. The whole analysis is performed under (low Reynolds number) creeping phenomena and long wavelength approximation, respectively. Additionally, small ionic Peclet number and Debye-Huckel linearization are used to simplify the Nernst-Planck and Poisson-Boltzmann equations. The BVP4C technique is used to obtain the numerical solution for velocity distribution, pressure gradient, pressure rise and stream function through MATLAB.<br><br>MAIN OUTCOMES: The amplitude of velocity distribution is increased (decreased) at larger values of non-uniform parameter (cilia length). The non-uniform parameter played a vital role not only in the enhancement of circulation at the upper half of the channel but also the length of bolus increased. Results of straight channel are gained for larger value of the dimensionless radius of curvature parameter as well as cilia length.}, }
@article {pmid33449773, year = {2020}, author = {Pan, Z and Nunes, JK and Stone, HA}, title = {Regime Map and Triple Point in Selective Withdrawal.}, journal = {Physical review letters}, volume = {125}, number = {26}, pages = {264502}, doi = {10.1103/PhysRevLett.125.264502}, pmid = {33449773}, issn = {1079-7114}, abstract = {Entrainment in selective withdrawal occurs when both the top and bottom phases are withdrawn through a capillary tube oriented perpendicular to a flat gravitationally separated liquid-liquid interface. The tube introduces two distinct features to the conditions for fluid entrainment. First, the ratio of the two phases being withdrawn is affected by the region of influence of the flow upstream of the tube's orifice. Second, a minimum withdrawal flow rate must be reached for entrainment regardless of the distance between the interface and the tube. We show that these phenomena can be understood based on the Reynolds number that governs the external flow field around the capillary tube and the capillary number that regulates the effect of the viscosity and capillarity.}, }
@article {pmid33438620, year = {2020}, author = {Shit, GC and Bera, A}, title = {Mathematical model to verify the role of magnetic field on blood flow and its impact on thermal behavior of biological tissue for tumor treatment.}, journal = {Biomedical physics &amp; engineering express}, volume = {6}, number = {1}, pages = {015032}, doi = {10.1088/2057-1976/ab6e22}, pmid = {33438620}, issn = {2057-1976}, mesh = {Blood Flow Velocity ; Computer Simulation ; Hemodynamics ; Humans ; Hyperthermia, Induced/*methods ; *Magnetic Fields ; Microvessels/*pathology ; Models, Biological ; *Models, Theoretical ; Neoplasms/blood supply/*pathology/therapy ; }, abstract = {The numerical computation has been performed to study the effects of static magnetic field on thermal behavior of tumor surrounded by living biological tissues and blood vessels. A small rectangular shaped tumor enclosing the blood vessel surrounded by healthy tissue is considered. The model consists of two-layer composite system in which the microvessel for blood flow is considered as a fluid layer and the living biological tissue including tumor as a solid layer. The wave bioheat transfer equation in the tissue layer together with energy transport equation for blood flow layer has been used in the cylindrical polar coordinates. The analytical expression for blood velocity in the presence of magnetic field has been used from Gold's solution. The computational work has been performed by employing the Crank-Nicolson finite difference method. A comparison has been made to validate our numerical results with the previous solution by setting some parameters. The temperature profiles have been plotted at different locations of the axial tissue length for various values of the Hartmann number, Prandtl number, Womersley number and Reynolds number. It is observed that the application of magnetic field increases heat transfer rate within tumor tissues which in turn attribute to an enhancement of temperature about 316 K or above for hyperthermic treatment in cancer therapy.}, }
@article {pmid33430317, year = {2021}, author = {Gnapowski, E and Pytka, J and Józwik, J and Laskowski, J and Michałowska, J}, title = {Wind Tunnel Testing of Plasma Actuator with Two Mesh Electrodes to Boundary Layer Control at High Angle of Attack.}, journal = {Sensors (Basel, Switzerland)}, volume = {21}, number = {2}, pages = {}, pmid = {33430317}, issn = {1424-8220}, abstract = {The manuscript presents experimental research carried out on the wing model with the SD 7003 profile. A plasma actuator with DBD (Dielectric Barrier Discharge) discharges was placed on the wing surface to control boundary layer. The experimental tests were carried out in the AeroLab wind tunnel where the forces acting on the wing during the tests were measured. The conducted experimental research concerns the analysis of the phenomena that take place on the surface of the wing with the DBD plasma actuator turned off and on. The plasma actuator used during the experimental tests has a different structure compared to the classic plasma actuator. The commonly tested plasma actuator uses solid/impermeable electrodes, while in the research, the plasma actuator uses a new type of electrodes, two mesh electrodes separated by an impermeable Kapton dielectric. The experimental research was carried out for the angle of attack α = 15° and several air velocities V = 5-15 m/s with a step of 5 m/s for the Reynolds number Re = 87,500-262,500. The critical angle of attack at which the SD 7003 profile has the maximum lift coefficient is about 11°; during the experimental research, the angle was 15°. Despite the high angle of attack, it was possible to increase the lift coefficient. The use of a plasma actuator with two mesh electrodes allowed to increase the lift by 5%, even at a high angle of attack. During experimental research used high voltage power supply for powering the DBD plasma actuator in the voltage range from 7.5 to 15 kV.}, }
@article {pmid33416336, year = {2020}, author = {Monsalve, E and Brunet, M and Gallet, B and Cortet, PP}, title = {Quantitative Experimental Observation of Weak Inertial-Wave Turbulence.}, journal = {Physical review letters}, volume = {125}, number = {25}, pages = {254502}, doi = {10.1103/PhysRevLett.125.254502}, pmid = {33416336}, issn = {1079-7114}, abstract = {We report the quantitative experimental observation of the weak inertial-wave turbulence regime of rotating turbulence. We produce a statistically steady homogeneous turbulent flow that consists of nonlinearly interacting inertial waves, using rough top and bottom boundaries to prevent the emergence of a geostrophic flow. As the forcing amplitude increases, the temporal spectrum evolves from a discrete set of peaks to a continuous spectrum. Maps of the bicoherence of the velocity field confirm such a gradual transition between discrete wave interactions at weak forcing amplitude and the regime described by weak turbulence theory (WTT) for stronger forcing. In the former regime, the bicoherence maps display a near-zero background level, together with sharp localized peaks associated with discrete resonances. By contrast, in the latter regime, the bicoherence is a smooth function that takes values of the order of the Rossby number in line with the infinite-domain and random-phase assumptions of WTT. The spatial spectra then display a power-law behavior, both the spectral exponent and the spectral level being accurately predicted by WTT at high Reynolds number and low Rossby number.}, }
@article {pmid33404675, year = {2022}, author = {Klein, AK and Dietzel, A}, title = {A Primer on Microfluidics: From Basic Principles to Microfabrication.}, journal = {Advances in biochemical engineering/biotechnology}, volume = {179}, number = {}, pages = {17-35}, pmid = {33404675}, issn = {0724-6145}, mesh = {*Microfluidics/methods ; *Microtechnology/methods ; }, abstract = {Microfluidic systems enable manipulating fluids in different functional units which are integrated on a microchip. This chapter describes the basics of microfluidics, where physical effects have a different impact compared to macroscopic systems. Furthermore, an overwiew is given on the microfabrication of these systems. The focus lies on clean-room fabrication methods based on photolithography and soft lithography. Finally, an outlook on advanced maskless micro- and nanofabrication methods is given. Special attention is paid to laser structuring processes.}, }
@article {pmid33398321, year = {2021}, author = {Chen, W and Wen, Y and Fan, X and Sun, M and Tian, C and Yang, M and Xie, H}, title = {Magnetically actuated intelligent hydrogel-based child-parent microrobots for targeted drug delivery.}, journal = {Journal of materials chemistry. B}, volume = {9}, number = {4}, pages = {1030-1039}, doi = {10.1039/d0tb02384a}, pmid = {33398321}, issn = {2050-7518}, mesh = {Cells, Cultured ; Child ; Doxorubicin/*chemistry ; *Drug Delivery Systems ; Humans ; Hydrogels/*chemistry ; Lab-On-A-Chip Devices ; Magnetic Phenomena ; Magnetite Nanoparticles/*chemistry ; Particle Size ; *Robotics/instrumentation ; Surface Properties ; }, abstract = {Small intestine-targeted drug delivery by oral administration has aroused the growing interest of researchers. In this work, the child-parent microrobot (CPM) as a vehicle protects the child microrobots (CMs) under a gastric acid environment and releases them in the small intestinal environment. The intelligent hydrogel-based CPMs with sphere, mushroom, red blood cell, and teardrop shapes are fabricated by an extrusion-dripping method. The CPMs package uniform CMs, which are fabricated by designed microfluidic (MF) devices. The fabrication mechanism and tunability of CMs and CPMs with different sizes and shapes are analyzed, modeled, and simulated. The shape of CPM can affect its drug release efficiency and kinetic characteristics. A vision-feedback magnetic driving system (VMDS) actuates and navigates CPM along the predefined path to the destination and continuously releases drug in the simulated intestinal fluid (SIF, a low Reynolds number (Re) regime) using a new motion control method with the tracking-learning-detection (TLD) algorithm. The newly designed CPM combines the advantages of powerful propulsion, good biocompatibility, and remarkable drug loading and release capacity at the intestinal level, which is expected to be competent for oral administration of small intestine-targeted therapy in the future.}, }
@article {pmid33396499, year = {2020}, author = {Avila, K and Hof, B}, title = {Second-Order Phase Transition in Counter-Rotating Taylor-Couette Flow Experiment.}, journal = {Entropy (Basel, Switzerland)}, volume = {23}, number = {1}, pages = {}, pmid = {33396499}, issn = {1099-4300}, support = {ZF04B /2019/FB04 Avila_Kerstin//Central Reserach Development Fund of the University of Bremen/ ; }, abstract = {In many basic shear flows, such as pipe, Couette, and channel flow, turbulence does not arise from an instability of the laminar state, and both dynamical states co-exist. With decreasing flow speed (i.e., decreasing Reynolds number) the fraction of fluid in laminar motion increases while turbulence recedes and eventually the entire flow relaminarizes. The first step towards understanding the nature of this transition is to determine if the phase change is of either first or second order. In the former case, the turbulent fraction would drop discontinuously to zero as the Reynolds number decreases while in the latter the process would be continuous. For Couette flow, the flow between two parallel plates, earlier studies suggest a discontinuous scenario. In the present study we realize a Couette flow between two concentric cylinders which allows studies to be carried out in large aspect ratios and for extensive observation times. The presented measurements show that the transition in this circular Couette geometry is continuous suggesting that former studies were limited by finite size effects. A further characterization of this transition, in particular its relation to the directed percolation universality class, requires even larger system sizes than presently available.}, }
@article {pmid37850032, year = {2021}, author = {Xing, Y and Burdsall, AC and Owens, A and Magnuson, M and Harper, WF}, title = {The effect of mixing and free-floating carrier media on bioaerosol release from wastewater: a multiscale investigation with Bacillus globigii.}, journal = {Environmental science : water research &amp; technology}, volume = {7}, number = {}, pages = {}, pmid = {37850032}, issn = {2053-1400}, support = {EPA999999/ImEPA/Intramural EPA/United States ; }, abstract = {Aeration tanks in wastewater treatment plants (WWTPs) are significant sources of bioaerosols, which contain microbial contaminants and can travel miles from the site of origin, risking the health of operators and the general public. One potential mitigation strategy is to apply free-floating carrier media (FFCM) to suppress bioaerosol emission. This article presents a multiscale study on the effects of mixing and FFCM on bioaerosol release using Bacillus globigii spores in well-defined liquid media. Bioaerosol release, defined as percentage of spores aerosolized during a 30 minute sampling period, ranged from 6.09 × 10[-7]% to 0.057%, depending upon the mixing mode and intensity. Bioaerosol release increased with the intensity of aeration (rotating speed in mechanical agitation and aeration rate in diffused aeration). A surface layer of polystyrene beads reduced bioaerosol released by >92% in the bench-scale studies and >74% in the pilot-scale study. This study discovered strong correlations (R[2] > 0.82) between bioaerosol release and superficial gas velocity, Froude number, and volumetric gas flow per unit liquid volume per minute. The Reynolds number was found to be poorly correlated with bioaerosol release (R[2] < 0.5). This study is a significant step toward the development of predictive models for full scale systems.}, }
@article {pmid33362423, year = {2020}, author = {Elsinga, GE and Ishihara, T and Hunt, JCR}, title = {Extreme dissipation and intermittency in turbulence at very high Reynolds numbers.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {476}, number = {2243}, pages = {20200591}, pmid = {33362423}, issn = {1364-5021}, abstract = {Extreme dissipation events in turbulent flows are rare, but they can be orders of magnitude stronger than the mean dissipation rate. Despite its importance in many small-scale physical processes, there is presently no accurate theory or model for predicting the extrema as a function of the Reynolds number. Here, we introduce a new model for the dissipation probability density function (PDF) based on the concept of significant shear layers, which are thin regions of elevated local mean dissipation. At very high Reynolds numbers, these significant shear layers develop layered substructures. The flow domain is divided into the different layer regions and a background region, each with their own PDF of dissipation. The volume-weighted regional PDFs are combined to obtain the overall PDF, which is subsequently used to determine the dissipation variance and maximum. The model yields Reynolds number scalings for the dissipation maximum and variance, which are in agreement with the available data. Moreover, the power law scaling exponent is found to increase gradually with the Reynolds numbers, which is also consistent with the data. The increasing exponent is shown to have profound implications for turbulence at atmospheric and astrophysical Reynolds numbers. The present results strongly suggest that intermittent significant shear layer structures are key to understanding and quantifying the dissipation extremes, and, more generally, extreme velocity gradients.}, }
@article {pmid33362112, year = {2021}, author = {Foo, CT and Unterberger, A and Menser, J and Mohri, K}, title = {Tomographic imaging using multi-simultaneous measurements (TIMes) for flame emission reconstructions.}, journal = {Optics express}, volume = {29}, number = {1}, pages = {244-255}, doi = {10.1364/OE.412048}, pmid = {33362112}, issn = {1094-4087}, abstract = {The method of tomographic imaging using multi-simultaneous measurements (TIMes) for flame emission reconstructions is presented. Measurements of the peak natural CH* chemiluminescence in the flame and luminescence from different vaporised alkali metal salts that were seeded in a multi-annulus burner were used. An array of 29 CCD cameras around the Cambridge-Sandia burner was deployed, with 3 sets of cameras each measuring a different colour channel using bandpass optical filters. The three-dimensional instantaneous and time-averaged fields of the individual measured channels were reconstructed and superimposed for two new operating conditions, with differing cold flow Reynolds numbers. The contour of the reconstructed flame front followed the interface between the burnt side of the flame, where the alkali salt luminescence appears, and the cold gas region. The increased mixing between different reconstructed channels in the downstream direction that is promoted by the higher levels of turbulence in the larger Reynolds number case was clearly demonstrated. The TIMes method enabled combustion zones originating from different streams and the flame front to be distinguished and their overlap regions to be identified, in the entire volume.}, }
@article {pmid33361564, year = {2021}, author = {Brum, J and Bernal, M and Barrere, N and Negreira, C and Cabeza, C}, title = {Vortex dynamics and transport phenomena in stenotic aortic models using Echo-PIV.}, journal = {Physics in medicine and biology}, volume = {66}, number = {5}, pages = {}, doi = {10.1088/1361-6560/abd670}, pmid = {33361564}, issn = {1361-6560}, mesh = {Aortic Valve Stenosis/*diagnostic imaging/physiopathology ; Hemodynamics ; Humans ; *Models, Cardiovascular ; Pulsatile Flow ; *Rheology ; Ultrasonography ; }, abstract = {Atherosclerosis is the most fatal cardiovascular disease. As disease progresses, stenoses grow inside the arteries blocking their lumen and altering blood flow. Analysing flow dynamics can provide a deeper insight on the stenosis evolution. In this work we combined Eulerian and Lagrangian descriptors to analyze blood flow dynamics and fluid transport in stenotic aortic models with morphology, mechanical and optical properties close to those of real arteries. To this end, vorticity, particle residence time (PRT), particle's final position (FP) and finite time Lyapunov's exponents (FTLE) were computed from the experimental fluid velocity fields acquired using ultrasonic particle imaging velocimetry (Echo-PIV). For the experiments, CT-images were used to create morphological realistic models of the descending aorta with 0%, 35% and 50% occlusion degree with same mechanical properties as real arteries. Each model was connected to a circuit with a pulsatile programmable pump which mimics physiological flow and pressure conditions. The pulsatile frequency was set to ≈0.9 Hz (55 bpm) and the upstream peak Reynolds number (Re) was changed from 1100 to 2000. Flow in the post-stenotic region was composed of two main structures: a high velocity jet over the stenosis throat and a recirculation region behind the stenosis where vortex form and shed. We characterized vortex kinematics showing that vortex propagation velocity increases withRe. Moreover, from the FTLE field we identified Lagrangian coherent structures (i.e. material barriers) that dictate transport behind the stenosis. The size and strength of those barriers increased withReand the occlusion degree. Finally, from the PRT and FP maps, we showed that independently ofRe, the same amount of fluid remains on the stenosis over more than a pulsatile period.}, }
@article {pmid33352968, year = {2020}, author = {Wu, CY and Lai, BH}, title = {Numerical Study of T-Shaped Micromixers with Vortex-Inducing Obstacles in the Inlet Channels.}, journal = {Micromachines}, volume = {11}, number = {12}, pages = {}, pmid = {33352968}, issn = {2072-666X}, support = {NSC 101 - 2221 - E - 006 - 108 - MY3//Ministry of Science and Technology of the Republic of China on Taiwan/ ; }, abstract = {To enhance fluid mixing, a new approach for inlet flow modification by adding vortex-inducing obstacles (VIOs) in the inlet channels of a T-shaped micromixer is proposed and investigated in this work. We use a commercial computational fluid dynamics code to calculate the pressure and the velocity vectors and, to reduce the numerical diffusion in high-Peclet-number flows, we employ the particle-tracking simulation with an approximation diffusion model to calculate the concentration distribution in the micromixers. The effects of geometric parameters, including the distance between the obstacles and the angle of attack of the obstacles, on the mixing performance of micromixers are studied. From the results, we can observe the following trends: (i) the stretched contact surface between different fluids caused by antisymmetric VIOs happens for the cases with the Reynolds number (Re) greater than or equal to 27 and the enhancement of mixing increases with the increase of Reynolds number gradually, and (ii) the onset of the engulfment flow happens at Re≈125 in the T-shaped mixer with symmetric VIOs or at Re≈140 in the standard planar T-shaped mixer and results in a sudden increase of the degree of mixing. The results indicate that the early initiation of transversal convection by either symmetric or antisymmetric VIOs can enhance fluid mixing at a relatively lower Re.}, }
@article {pmid33333847, year = {2020}, author = {Li, YH and Chen, SC}, title = {Propulsion Mechanism of Flexible Microbead Swimmers in the Low Reynolds Number Regime.}, journal = {Micromachines}, volume = {11}, number = {12}, pages = {}, pmid = {33333847}, issn = {2072-666X}, support = {MOST 107-2218-E-606-003-MY2 and MOST 109-2221-E-606-003//Ministry of Science and Technology, Taiwan/ ; }, abstract = {A propulsion mechanism for a flexible microswimmer constructed from superparamagnetic microbeads with different diameters and subjected to an oscillating field was studied experimentally and theoretically herein. Various types of artificial swimmers with different bending patterns were fabricated to determine the flexibility and an effective waveform for a planar beating flagellum. Waveform evolutions for various swimmer configurations were studied to determine the flexible mechanism of the swimmers. A one-armed microswimmer can propel itself only if the friction of its wavelike body is anisotropic. A swimmer with a larger head and a stronger magnetic dipole moment with a flexible tail allows the bending wave to propagate from the head toward the tail to generate forward thrust. The oscillating head and tail do not simultaneously generate positive thrust all the time within a period of oscillation. To increase the propulsion for a bending swimmer, this study proposes a novel configuration for a microbead swimmer that ensures better swimming efficiency. The ratio of the oscillation amplitude of the head to the length of the swimmer (from 0.26 to 0.28) produces a faster swimmer. On the other hand, the swimmer is propelled more effectively if the ratio of the oscillation amplitude of the tail to the length of the swimmer is from 0.29 to 0.33. This study determined the optimal configuration for a flexible microbead swimmer that generates the greatest propulsion in a low Reynolds number environment.}, }
@article {pmid33331388, year = {2021}, author = {Dou, Y and Tzelios, PM and Livitz, D and Bishop, KJM}, title = {Programmable topotaxis of magnetic rollers in time-varying fields.}, journal = {Soft matter}, volume = {17}, number = {6}, pages = {1538-1547}, doi = {10.1039/d0sm01443e}, pmid = {33331388}, issn = {1744-6848}, abstract = {We describe how spatially uniform, time-periodic magnetic fields can be designed to power and direct the migration of ferromagnetic spheres up (or down) local gradients in the topography of a solid substrate. Our results are based on a dynamical model that considers the time-varying magnetic torques on the particle and its motion through the fluid at low Reynolds number. We use both analytical theory and numerical simulation to design magnetic fields that maximize the migration velocity up (or down) an inclined plane. We show how "topotaxis" of spherical particles relies on differences in the hydrodynamic resistance to rotation about axes parallel and perpendicular to the plane. Importantly, the designed fields can drive multiple independent particles to move simultaneously in different directions as determined by gradients in their respective environments. Experiments on ferromagnetic spheres provide evidence for topotactic motions up inclined substrates. The ability to program the autonomous navigation of driven particles within anisotropic environments is relevant to the design of colloidal robots.}, }
@article {pmid33327115, year = {2020}, author = {Slanina, F}, title = {Colloid particles in microfluidic inertial hydrodynamic ratchet at moderate Reynolds number.}, journal = {Physical review. E}, volume = {102}, number = {5-1}, pages = {052601}, doi = {10.1103/PhysRevE.102.052601}, pmid = {33327115}, issn = {2470-0053}, abstract = {The movement of spherical Brownian particle carried by an alternating fluid flow in a tube of periodically variable diameter is investigated. On the basis of our previous results [Phys. Rev. E 99, 012604 (2019)10.1103/PhysRevE.99.012604] on the hydrodynamics of the problem, we look at the competition of hydrodynamics and diffusion. We use the method of Fick-Jacobs mapping on an effective one-dimensional problem. We calculate the ratchet current and show that is is strictly related to finite size of the particles. The ratchet current grows quadratically with particle radius. We also show that the dominant contribution to the ratchet current is due to inertial hydrodynamic effects. This means that Reynolds number must be at least of order one. We discuss the possible use for separation of particles by size and perspectives of optimization of the tube shape.}, }
@article {pmid33325030, year = {2021}, author = {Turon, V and Ollivier, S and Cwicklinski, G and Willison, JC and Anxionnaz-Minvielle, Z}, title = {H2 production by photofermentation in an innovative plate-type photobioreactor with meandering channels.}, journal = {Biotechnology and bioengineering}, volume = {118}, number = {3}, pages = {1342-1354}, doi = {10.1002/bit.27656}, pmid = {33325030}, issn = {1097-0290}, mesh = {Hydrogen/*metabolism ; *Photobioreactors ; Rhodobacter capsulatus/*growth &amp; development ; }, abstract = {Hydrogen production by Rhodobacter capsulatus is an anaerobic, photobiological process requiring specific mixing conditions. In this study, an innovative design of a photobioreactor is proposed. The design is based on a plate-type photobioreactor with an interconnected meandering channel to allow culture mixing and H2 degassing. The culture flow was characterized as a quasi-plug-flow with radial mixing caused by a turbulent-like regime achieved at a low Reynolds number. The dissipated volumetric power was decreased 10-fold while maintaining PBR performances (production and yields) when compared with a magnetically stirred tank reactor. To increase hydrogen production flow rate, several bacterial concentrations were tested by increasing the glutamate concentration using fed-batch cultures. The maximum hydrogen production flow rate (157.7 ± 9.3 ml H2 /L/h) achieved is one of the highest values so far reported for H2 production by R. capsulatus. These first results are encouraging for future scale-up of the plate-type reactor.}, }
@article {pmid33322374, year = {2020}, author = {Liu, J and Xiao, Y and Li, M and Tao, J and Xu, S}, title = {Intermittency, Moments, and Friction Coefficient during the Subcritical Transition of Channel Flow.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {12}, pages = {}, pmid = {33322374}, issn = {1099-4300}, support = {91752203, 11772173, 11490553//National Natural Science Foundation of China/ ; }, abstract = {The intermittent distribution of localized turbulent structures is a key feature of the subcritical transitions in channel flows, which are studied in this paper with a wind channel and theoretical modeling. Entrance disturbances are introduced by small beads, and localized turbulent patches can be triggered at low Reynolds numbers (Re). High turbulence intensity represents strong ability of perturbation spread, and a maximum turbulence intensity is found for every test case as Re ≥ 950, where the turbulence fraction increases abruptly with Re. Skewness can reflect the velocity defects of localized turbulent patches and is revealed to become negative when Re is as low as about 660. It is shown that the third-order moments of the midplane streamwise velocities have minima, while the corresponding forth-order moments have maxima during the transition. These kinematic extremes and different variation scenarios of the friction coefficient during the transition are explained with an intermittent structure model, where the robust localized turbulent structure is simplified as a turbulence unit, a structure whose statistical properties are only weak functions of the Reynolds number.}, }
@article {pmid33289747, year = {2021}, author = {Yang, PJ and Lee, AB and Chan, M and Kowalski, M and Qiu, K and Waid, C and Cervantes, G and Magondu, B and Biagioni, M and Vogelnest, L and Martin, A and Edwards, A and Carver, S and Hu, DL}, title = {Intestines of non-uniform stiffness mold the corners of wombat feces.}, journal = {Soft matter}, volume = {17}, number = {3}, pages = {475-488}, doi = {10.1039/d0sm01230k}, pmid = {33289747}, issn = {1744-6848}, mesh = {Animals ; Australia ; Feces ; Fungi ; Intestines ; *Marsupialia ; }, abstract = {The bare-nosed wombat (Vombatus ursinus) is a fossorial, herbivorous, Australian marsupial, renowned for its cubic feces. However, the ability of the wombat's soft intestine to sculpt flat faces and sharp corners in feces is poorly understood. In this combined experimental and numerical study, we show one mechanism for the formation of corners in a highly damped environment. Wombat dissections show that cubes are formed within the last 17 percent of the intestine. Using histology and tensile testing, we discover that the cross-section of the intestine exhibits regions with a two-fold increase in thickness and a four-fold increase in stiffness, which we hypothesize facilitates the formation of corners by contractions of the intestine. Using a mathematical model, we simulate a series of azimuthal contractions of a damped elastic ring composed of alternating stiff and soft regions. Increased stiffness ratio and higher Reynolds number yield shapes that are more square. The corners arise from faster contraction in the stiff regions and relatively slower movement in the center of the soft regions. These results may have applications in manufacturing, clinical pathology, and digestive health.}, }
@article {pmid33286895, year = {2020}, author = {Agrawal, R and Ng, HC and Davis, EA and Park, JS and Graham, MD and Dennis, DJC and Poole, RJ}, title = {Low- and High-Drag Intermittencies in Turbulent Channel Flows.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {10}, pages = {}, pmid = {33286895}, issn = {1099-4300}, support = {FA9550-16-1-0076//Air Force Office of Scientific Research/ ; FA9550-18-1-0174//Air Force Office of Scientific Research/ ; OIA-1832976//National Science Foundation/ ; }, abstract = {Recent direct numerical simulations (DNS) and experiments in turbulent channel flow have found intermittent low- and high-drag events in Newtonian fluid flows, at Reτ=uτh/ν between 70 and 100, where uτ, h and ν are the friction velocity, channel half-height and kinematic viscosity, respectively. These intervals of low-drag and high-drag have been termed "hibernating" and "hyperactive", respectively, and in this paper, a further investigation of these intermittent events is conducted using experimental and numerical techniques. For experiments, simultaneous measurements of wall shear stress and velocity are carried out in a channel flow facility using hot-film anemometry (HFA) and laser Doppler velocimetry (LDV), respectively, for Reτ between 70 and 250. For numerical simulations, DNS of a channel flow is performed in an extended domain at Reτ = 70 and 85. These intermittent events are selected by carrying out conditional sampling of the wall shear stress data based on a combined threshold magnitude and time-duration criteria. The use of three different scalings (so-called outer, inner and mixed) for the time-duration criterion for the conditional events is explored. It is found that if the time-duration criterion is kept constant in inner units, the frequency of occurrence of these conditional events remain insensitive to Reynolds number. There exists an exponential distribution of frequency of occurrence of the conditional events with respect to their duration, implying a potentially memoryless process. An explanation for the presence of a spike (or dip) in the ensemble-averaged wall shear stress data before and after the low-drag (or high-drag) events is investigated. During the low-drag events, the conditionally-averaged streamwise velocities get closer to Virk's maximum drag reduction (MDR) asymptote, near the wall, for all Reynolds numbers studied. Reynolds shear stress (RSS) characteristics during these conditional events are investigated for Reτ = 70 and 85. Except very close to the wall, the conditionally-averaged RSS is higher than the time-averaged value during the low-drag events.}, }
@article {pmid33286770, year = {2020}, author = {Kashyap, PV and Duguet, Y and Dauchot, O}, title = {Flow Statistics in the Transitional Regime of Plane Channel Flow.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {9}, pages = {}, pmid = {33286770}, issn = {1099-4300}, abstract = {The transitional regime of plane channel flow is investigated above the transitional point below which turbulence is not sustained, using direct numerical simulation in large domains. Statistics of laminar-turbulent spatio-temporal intermittency are reported. The geometry of the pattern is first characterized, including statistics for the angles of the laminar-turbulent stripes observed in this regime, with a comparison to experiments. High-order statistics of the local and instantaneous bulk velocity, wall shear stress and turbulent kinetic energy are then provided. The distributions of the two former quantities have non-trivial shapes, characterized by a large kurtosis and/or skewness. Interestingly, we observe a strong linear correlation between their kurtosis and their skewness squared, which is usually reported at much higher Reynolds number in the fully turbulent regime.}, }
@article {pmid33286441, year = {2020}, author = {Lee, T}, title = {Lognormality in Turbulence Energy Spectra.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {6}, pages = {}, pmid = {33286441}, issn = {1099-4300}, abstract = {The maximum entropy principle states that the energy distribution will tend toward a state of maximum entropy under the physical constraints, such as the zero energy at the boundaries and a fixed total energy content. For the turbulence energy spectra, a distribution function that maximizes entropy with these physical constraints is a lognormal function due to its asymmetrical descent to zero energy at the boundary lengths scales. This distribution function agrees quite well with the experimental data over a wide range of energy and length scales. For turbulent flows, this approach is effective since the energy and length scales are determined primarily by the Reynolds number. The total turbulence kinetic energy will set the height of the distribution, while the ratio of length scales will determine the width. This makes it possible to reconstruct the power spectra using the Reynolds number as a parameter.}, }
@article {pmid33286423, year = {2020}, author = {Wang, R and Xie, Z and Yin, Y and Chen, L}, title = {Constructal Design of Elliptical Cylinders with Heat Generating for Entropy Generation Minimization.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {6}, pages = {}, pmid = {33286423}, issn = {1099-4300}, support = {51579244//National Natural Science Foundation of China/ ; }, abstract = {A heat dissipation model of discrete elliptical cylinders with heat generation on a thermal conduction pedestal cooled by forced convection is established. Constructal design is conducted numerically by taking the distributions of thermal conductivity and heat generating intensity as design variables, the dimensionless entropy generation rate (DEGR) as performance indicator. The optimal designs for discrete elliptical cylinders with heat generating are obtained respectively, i.e., there are optimal distributions of heat generating intensity with its fixed total amount of heat sources, and there are optimal distributions of thermal conductivity with its fixed total amount of heat sources. These optimums for minimum DEGRs are different at different Reynolds numbers of airflow. The heat generating intensity can be decreased one by one appropriately in the fluid flow direction to achieve the best effect. When the Reynolds number of airflow is smaller, the thermal conductivity of heat source can be increased one by one appropriately in the fluid flow direction to achieve the best effect; when the Reynolds number of airflow is larger, the thermal conductivity of each heat source should be equalized to achieve the best effect. The results can give thermal design guidelines for the practical heat generating devices with different materials and heat generating intensities.}, }
@article {pmid33285959, year = {2020}, author = {Yu, S and Tang, T and Li, J and Yu, P}, title = {Effect of Prandtl Number on Mixed Convective Heat Transfer from a Porous Cylinder in the Steady Flow Regime.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {2}, pages = {}, pmid = {33285959}, issn = {1099-4300}, support = {11672124//the National Natural Science Foundation of China/ ; ZDSYS201802081843517//Shenzhen Key Laboratory of Complex Aerospace Flows/ ; KQTD2016022620054656//the Shenzhen Peacock Plan/ ; }, abstract = {The effect of the Prandtl number (Pr) on the flow and heat transfer from a porous circular cylinder with internal heat generation in the mixed convection regime is numerically investigated. The steady flow regime is considered over the ranges of the Reynolds number (Re), Darcy number (Da), and Richardson number (Ri), varying from 5 to 40, 10[-6] to 10[-2], and 0 to 2, respectively. The wake structure, the temperature distribution, and the heat transfer rate are discussed. Besides precipitating the growth of the recirculating wake, the Prandtl number is found to have a significant impact on the thermal characteristics. The concave isotherms, resembling a saddle-shaped structure, occur behind the cylinder at larger Pr, resulting in swells of the isotherms pairing off at the lateral sides. These swells are found to have a negative effect on heat transfer owing to a relatively smaller temperature gradient there. Then, the heat transfer rate in terms of the local Nusselt number (Nu) and enhancement ratio (Er) is calculated, which is closely related to Pr, Re, Da, and Ri. The local minimum heat transfer rate along the cylinder surface is found at the position where the swells of the isotherms form.}, }
@article {pmid33285875, year = {2020}, author = {Deriszadeh, A and de Monte, F}, title = {On Heat Transfer Performance of Cooling Systems Using Nanofluid for Electric Motor Applications.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {1}, pages = {}, pmid = {33285875}, issn = {1099-4300}, abstract = {This paper studies the fluid flow and heat transfer characteristics of nanofluids as advance coolants for the cooling system of electric motors. Investigations are carried out using numerical analysis for a cooling system with spiral channels. To solve the governing equations, computational fluid dynamics and 3D fluid motion analysis are used. The base fluid is water with a laminar flow. The fluid Reynolds number and turn-number of spiral channels are evaluation parameters. The effect of nanoparticles volume fraction in the base fluid on the heat transfer performance of the cooling system is studied. Increasing the volume fraction of nanoparticles leads to improving the heat transfer performance of the cooling system. On the other hand, a high-volume fraction of the nanofluid increases the pressure drop of the coolant fluid and increases the required pumping power. This paper aims at finding a trade-off between effective parameters by studying both fluid flow and heat transfer characteristics of the nanofluid.}, }
@article {pmid33285793, year = {2019}, author = {Rasool, G and Zhang, T and Chamkha, AJ and Shafiq, A and Tlili, I and Shahzadi, G}, title = {Entropy Generation and Consequences of Binary Chemical Reaction on MHD Darcy-Forchheimer Williamson Nanofluid Flow Over Non-Linearly Stretching Surface.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {1}, pages = {}, pmid = {33285793}, issn = {1099-4300}, support = {11771389 and 11621101//The National Science Foundation of China/ ; }, abstract = {The current article aims to present a numerical analysis of MHD Williamson nanofluid flow maintained to flow through porous medium bounded by a non-linearly stretching flat surface. The second law of thermodynamics was applied to analyze the fluid flow, heat and mass transport as well as the aspects of entropy generation using Buongiorno model. Thermophoresis and Brownian diffusion is considered which appears due to the concentration and random motion of nanoparticles in base fluid, respectively. Uniform magnetic effect is induced but the assumption of tiny magnetic Reynolds number results in zero magnetic induction. The governing equations (PDEs) are transformed into ordinary differential equations (ODEs) using appropriately adjusted transformations. The numerical method is used for solving the so-formulated highly nonlinear problem. The graphical presentation of results highlights that the heat flux receives enhancement for augmented Brownian diffusion. The Bejan number is found to be increasing with a larger Weissenberg number. The tabulated results for skin-friction, Nusselt number and Sherwood number are given. A decent agreement is noted in the results when compared with previously published literature on Williamson nanofluids.}, }
@article {pmid33285790, year = {2019}, author = {Xu, L and Xiong, Y and Xi, L and Gao, J and Li, Y and Zhao, Z}, title = {Numerical Simulation of Swirling Impinging Jet Issuing from a Threaded Hole under Inclined Condition.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {1}, pages = {}, pmid = {33285790}, issn = {1099-4300}, support = {51876157//National Natural Science Foundation of China/ ; 2018A030313183//Guangdong Natural Science Foundation/ ; xjj2018044//special fund for basic scientific research business expenses of Central Universities/ ; }, abstract = {There are some inclined jet holes in the cooling structure of the leading edge region of gas turbine blades. In order to improve the cooling effect of traditional round holes, this paper proposes to replace the round holes with threaded holes, and studies the complex flow and heat transfer performance of the swirling impinging jet (SIJ) issuing from the 45° threaded holes in the inclined condition by numerical simulation. The influencing factors include jet inclination angle α (45°-90°), jet-to-plate distance (H/d = 2, 4, 6), and Reynolds number (6000-24,000). The results show that the inclination angle and jet-to-plate distance have a great influence on the size, shape, and position of vortices in the jet space, while the Reynolds number has little effect on the vortices. In the inclined state, the impinging cooling effect of the swirling impinging jet is better than that of the circular impinging jet (CIJ), both heat transfer coefficients will degrade significantly when the inclination angle is 45°. When the inclination angle is greater than 45°, compared with the round hole, the enhanced heat transfer region for the swirling jet is in the region of r/d < 3, while both of the Nusselt numbers in the wall jet region are weak, with a value of just 20. At the same time, with the increasing of the inclination angle (α > 45°), the average Nusselt number on target surface holds a constant value. Under the inclined conditions, the heat transfer coefficient on the target surface for the swirling jet is increased totally with the increasing of the Re, but when the Re is larger than 18,000, the rate of enhanced heat transfer gradually weakens.}, }
@article {pmid33285453, year = {2021}, author = {Maurer, L and Villette, C and Reiminger, N and Jurado, X and Laurent, J and Nuel, M and Mosé, R and Wanko, A and Heintz, D}, title = {Distribution and degradation trend of micropollutants in a surface flow treatment wetland revealed by 3D numerical modelling combined with LC-MS/MS.}, journal = {Water research}, volume = {190}, number = {}, pages = {116672}, doi = {10.1016/j.watres.2020.116672}, pmid = {33285453}, issn = {1879-2448}, mesh = {Chromatography, Liquid ; Tandem Mass Spectrometry ; Waste Disposal, Fluid ; Wastewater/analysis ; *Water Pollutants, Chemical/analysis ; *Wetlands ; }, abstract = {Conventional wastewater treatment plants are not designed to treat micropollutants; thus, for 20 years, several complementary treatment systems, such as surface flow wetlands have been used to address this issue. Previous studies demonstrate that higher residence time and low global velocities promote nutrient removal rates or micropollutant photodegradation. Nevertheless, these studies were restricted to the system limits (inlet/outlet). Therefore, detailed knowledge of water flow is crucial for identifying areas that promote degradation and optimise surface flow wetlands. The present study combines 3D water flow numerical modelling and liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS/MS). Using this numerical model, validated by tracer experimental data, several velocity areas were distinguished in the wetland. Four areas were selected to investigate the waterflow influence and led to the following results: on the one hand, the number and concentration of micropollutants are independent of the waterflow, which could be due to several assumptions, such as the chronic exposure associated with a low Reynolds number; on the other hand, the potential degradation products (metabolites) were also assessed in the sludge to investigate the micropollutant biodegradation processes occurring in the wetland; micropollutant metabolites or degradation products were detected in higher proportions (both number and concentration) in lower flow rate areas. The relation to higher levels of plant and microorganism metabolites suggests higher biological activity that promotes degradation.}, }
@article {pmid33268359, year = {2020}, author = {Milana, E and Zhang, R and Vetrano, MR and Peerlinck, S and De Volder, M and Onck, PR and Reynaerts, D and Gorissen, B}, title = {Metachronal patterns in artificial cilia for low Reynolds number fluid propulsion.}, journal = {Science advances}, volume = {6}, number = {49}, pages = {}, pmid = {33268359}, issn = {2375-2548}, abstract = {Cilia are hair-like organelles, present in arrays that collectively beat to generate flow. Given their small size and consequent low Reynolds numbers, asymmetric motions are necessary to create a net flow. Here, we developed an array of six soft robotic cilia, which are individually addressable, to both mimic nature's symmetry-breaking mechanisms and control asymmetries to study their influence on fluid propulsion. Our experimental tests are corroborated with fluid dynamics simulations, where we find a good agreement between both and show how the kymographs of the flow are related to the phase shift of the metachronal waves. Compared to synchronous beating, we report a 50% increase of net flow speed when cilia move in an antiplectic wave with phase shift of -π/3 and a decrease for symplectic waves. Furthermore, we observe the formation of traveling vortices in the direction of the wave when metachrony is applied.}, }
@article {pmid33266252, year = {2020}, author = {Morimatsu, H and Tsukahara, T}, title = {Laminar-Turbulent Intermittency in Annular Couette-Poiseuille Flow: Whether a Puff Splits or Not.}, journal = {Entropy (Basel, Switzerland)}, volume = {22}, number = {12}, pages = {}, pmid = {33266252}, issn = {1099-4300}, support = {16H06066, 19H02071//Japan Society for the Promotion of Science/ ; }, abstract = {Direct numerical simulations were carried out with an emphasis on the intermittency and localized turbulence structure occurring within the subcritical transitional regime of a concentric annular Couette-Poiseuille flow. In the annular system, the ratio of the inner to outer cylinder radius is an important geometrical parameter affecting the large-scale nature of the intermittency. We chose a low radius ratio of 0.1 and imposed a constant pressure gradient providing practically zero shear on the inner cylinder such that the base flow was approximated to that of a circular pipe flow. Localized turbulent puffs, that is, axial uni-directional intermittencies similar to those observed in the transitional circular pipe flow, were observed in the annular Couette-Poiseuille flow. Puff splitting events were clearly observed rather far from the global critical Reynolds number, near which given puffs survived without a splitting event throughout the observation period, which was as long as 104 outer time units. The characterization as a directed-percolation universal class was also discussed.}, }
@article {pmid33252039, year = {2020}, author = {Asadzadeh, SS and Kiørboe, T and Larsen, PS and Leys, SP and Yahel, G and Walther, JH}, title = {Hydrodynamics of sponge pumps and evolution of the sponge body plan.}, journal = {eLife}, volume = {9}, number = {}, pages = {}, pmid = {33252039}, issn = {2050-084X}, support = {7014-00033B//Danish council for Independent Research/International ; 9278//Villum Fonden/International ; 2016-05446//NSERC/International ; }, mesh = {Animals ; *Biological Evolution ; Hydrodynamics ; Porifera/*anatomy &amp; histology/*physiology ; }, abstract = {Sponges are suspension feeders that filter vast amounts of water. Pumping is carried out by flagellated chambers that are connected to an inhalant and exhalant canal system. In 'leucon' sponges with relatively high-pressure resistance due to a complex and narrow canal system, pumping and filtering are only possible owing to the presence of a gasket-like structure (forming a canopy above the collar filters). Here, we combine numerical and experimental work and demonstrate how sponges that lack such sealing elements are able to efficiently pump and force the flagella-driven flow through their collar filter, thanks to the formation of a 'hydrodynamic gasket' above the collar. Our findings link the architecture of flagellated chambers to that of the canal system, and lend support to the current view that the sponge aquiferous system evolved from an open-type filtration system, and that the first metazoans were filter feeders.}, }
@article {pmid33244217, year = {2020}, author = {Arumuru, V and Pasa, J and Samantaray, SS}, title = {Experimental visualization of sneezing and efficacy of face masks and shields.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {32}, number = {11}, pages = {115129}, pmid = {33244217}, issn = {1070-6631}, abstract = {In the present work, we propose and demonstrate a simple experimental visualization to simulate sneezing by maintaining dynamic similarity to actual sneezing. A pulsed jet with Reynolds number Re = 30 000 is created using compressed air and a solenoid valve. Tracer particles are introduced in the flow to capture the emulated turbulent jet formed due to a sneeze. The visualization is accomplished using a camera and laser illumination. It is observed that a typical sneeze can travel up to 25 ft in ∼22 s in a quiescent environment. This highlights that the present widely accepted safe distance of 6 ft is highly underestimated, especially under the act of a sneeze. Our study demonstrates that a three-layer homemade mask is just adequate to impede the penetration of fine-sized particles, which may cause the spreading of the infectious pathogen responsible for COVID-19. However, a surgical mask cannot block the sneeze, and the sneeze particle can travel up to 2.5 ft. We strongly recommend using at least a three-layer homemade mask with a social distancing of 6 ft to combat the transmission of COVID-19 virus. In offices, we recommend the use of face masks and shields to prevent the spreading of droplets carrying the infectious pathogen. Interestingly, an N-95 mask blocks the sneeze in the forward direction; however, the leakage from the sides and top spreads the sneeze in the backward direction up to 2 ft. We strongly recommend using the elbow or hands to prevent droplet leakage even after wearing a mask during sneezing and coughing.}, }
@article {pmid33244213, year = {2020}, author = {Mallik, AK and Mukherjee, S and Panchagnula, MV}, title = {An experimental study of respiratory aerosol transport in phantom lung bronchioles.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {32}, number = {11}, pages = {111903}, pmid = {33244213}, issn = {1070-6631}, abstract = {The transport and deposition of micrometer-sized particles in the lung is the primary mechanism for the spread of aerosol borne diseases such as corona virus disease-19 (COVID-19). Considering the current situation, modeling the transport and deposition of drops in human lung bronchioles is of utmost importance to determine their consequences on human health. The current study reports experimental observations on deposition in micro-capillaries, representing distal lung bronchioles, over a wide range of Re that imitates the particle dynamics in the entire lung. The experiment investigated deposition in tubes of diameter ranging from 0.3 mm to 2 mm and over a wide range of Reynolds number (10[-2] ⩽ Re ⩽ 10[3]). The range of the tube diameter and Re used in this study is motivated by the dimensions of lung airways and typical breathing flow rates. The aerosol fluid was loaded with boron doped carbon quantum dots as fluorophores. An aerosol plume was generated from this mixture fluid using an ultrasonic nebulizer, producing droplets with 6.5 µm as a mean diameter and over a narrow distribution of sizes. The amount of aerosol deposited on the tube walls was measured using a spectrofluorometer. The experimental results show that dimensionless deposition (δ) varies inversely with the bronchiole aspect ratio (L ¯), with the effect of the Reynolds number (Re) being significant only at low L ¯ . δ also increased with increasing dimensionless bronchiole diameter (D ¯), but it is invariant with the particle size based Reynolds number. We show that δ L ¯ ∼ R e - 2 for 10[-2] ⩽ Re ⩽ 1, which is typical of a diffusion dominated regime. For Re ⩾ 1, in the impaction dominated regime, δ L ¯ is shown to be independent of Re. We also show a crossover regime where sedimentation becomes important. The experimental results conclude that lower breathing frequency and higher breath hold time could significantly increase the chances of getting infected with COVID-19 in crowded places.}, }
@article {pmid34095645, year = {2020}, author = {Zhang, X and Graham, MD}, title = {Multiplicity of stable orbits for deformable prolate capsules in shear flow.}, journal = {Physical review fluids}, volume = {5}, number = {2}, pages = {}, pmid = {34095645}, issn = {2469-990X}, support = {R21 MD011590/MD/NIMHD NIH HHS/United States ; R35 HL145000/HL/NHLBI NIH HHS/United States ; }, abstract = {This work investigates the orbital dynamics of a fluid-filled deformable prolate capsule in unbounded simple shear flow at zero Reynolds number using direct simulations. The motion of the capsule is simulated using a model that incorporates shear elasticity, area dilatation, and bending resistance. Here the deformability of the capsule is characterized by the nondimensional capillary number Ca, which represents the ratio of viscous stresses to elastic restoring stresses on the capsule. For a capsule with small bending stiffness, at a given Ca, the orientation converges over time towards a unique stable orbit independent of the initial orientation. With increasing Ca, four dynamical modes are found for the stable orbit, namely, rolling, wobbling, oscillating-swinging, and swinging. On the other hand, for a capsule with large bending stiffness, multiplicity in the orbit dynamics is observed. When the viscosity ratio λ ≲ 1, the long-axis of the capsule always tends towards a stable orbit in the flow-gradient plane, either tumbling or swinging, depending on Ca. When λ ≳ 1, the stable orbit of the capsule is a tumbling motion at low Ca, irrespective of the initial orientation. Upon increasing Ca, there is a symmetry-breaking bifurcation away from the tumbling orbit, and the capsule is observed to adopt multiple stable orbital modes including nonsymmetric precessing and rolling, depending on the initial orientation. As Ca further increases, the nonsymmetric stable orbit loses existence at a saddle-node bifurcation, and rolling becomes the only attractor at high Ca, whereas the rolling state coexists with the nonsymmetric state at intermediate values of Ca. A symmetry-breaking bifurcation away from the rolling orbit is also found upon decreasing Ca. The regime with multiple attractors becomes broader as the aspect ratio of the capsule increases, while narrowing as viscosity ratio increases. We also report the particle contribution to the stress, which also displays multiplicity.}, }
@article {pmid34045778, year = {2020}, author = {Sherman, E and Lambert, L and White, B and Krane, MH and Wei, T}, title = {Cycle-to-cycle flow variations in a square duct with a symmetrically oscillating constriction.}, journal = {Fluid dynamics research}, volume = {52}, number = {1}, pages = {}, pmid = {34045778}, issn = {0169-5983}, support = {R01 DC005642/DC/NIDCD NIH HHS/United States ; }, abstract = {Spatially and temporally resolved Digital Particle Image Velocimetry (DPIV) measurements are presented of flow complexities in a nominally two-dimensional, symmetric, duct with an oscillating constriction. The motivation for this research lies in advancing the state-of-the-art in applying integral control volume analysis to modeling unsteady internal flows. The specific target is acoustic modeling of human phonation. The integral mass and momentum equations are directly coupled to the acoustic equations and provide quantitative insight into acoustic source strengths in addition to the dynamics of the fluid-structure interactions in the glottis. In this study, a square cross-section duct was constructed with symmetric, computer controlled, oscillating constrictions that incorporate both rocking as well as oscillatory open/close motions. Experiments were run in a free-surface water tunnel over a Strouhal number range, based on maximum jet speed and model length, of 0.012 - 0.048, for a fixed Reynolds number, based on maximum gap opening and maximum jet speed, of 8000. In this study, the constriction motions were continuous with one open-close cycle immediately following another. While the model and its motions were nominally two-dimensional and symmetric, flow asymmetries and oscillation frequency dependent cycle-to-cycle variations were observed. These are examined in the context of terms in the integral conservation equations.}, }
@article {pmid35072172, year = {2020}, author = {McCain, JL and Pohly, JA and Sridhar, MK and Kang, CK and Landrum, DB and Aono, H}, title = {Experimental Force and Deformation Measurements of Bioinspired Flapping Wings in Ultra-Low Martian Density Environment.}, journal = {Applied aerodynamics : papers presented at the AIAA SciTech Forum and Exposition 2020 : Orlando, Florida, USA, 6-10 January 2020. AIAA SciTech Forum and Exposition (2020 : Orlando, Fla.)}, volume = {2020}, number = {}, pages = {}, pmid = {35072172}, support = {80NSSC18K0870/ImNASA/Intramural NASA/United States ; }, abstract = {A Mars flight vehicle could provide a third-dimension for ground-based rovers and supplement orbital observation stations, providing a much more detailed aerial view of the landscape as well as unprecedented survey of the atmosphere of Mars. However, flight on Mars is a difficult proposition due to the very low atmospheric density, which is approximately 1.3% of sea level density on Earth. While traditional aircraft efficiency suffers in the low Reynolds number environment, insect inspired flapping wing flyers on Mars might be able to take advantage of the same lift enhancing effects as insects on Earth. The present work investigates the feasibility of using a bioinspired, flapping wing flight vehicle to produce lift in an ultra-low-density Martian atmosphere. A four-wing prototype, inspired by a prior computational study, was placed in an atmospheric chamber to simulate Martian density. Lift and wing deformation were simultaneously recorded. In Earth density conditions, the passive pitch wing deflection increased monotonically with flapping frequency. On the other hand, in the Martian density environment, the passive pitch deflection angles were very erratic. The measured lift peaked at around 8 grams at 16 Hz. These measurements suggest that sufficient aerodynamic forces for hover on Mars can be generated for a 6-gram flapping wing vehicle. Also, the performance can potentially be improved by better understanding the fluid-structure interaction in ultra-low Mars density condition.}, }
@article {pmid35527935, year = {2019}, author = {Krainer, S and Smit, C and Hirn, U}, title = {The effect of viscosity and surface tension on inkjet printed picoliter dots.}, journal = {RSC advances}, volume = {9}, number = {54}, pages = {31708-31719}, pmid = {35527935}, issn = {2046-2069}, abstract = {In this study, we investigated the effect of liquid viscosity and surface tension for inkjet printing on porous cellulose sheets. We used five model liquids, representing the operational field of an industrial high speed inkjet printer, as specified by Ohnesorge- and Reynolds number. Drops with 30 pl and 120 pl drop size were jetted with a commercial HSI printhead. We printed on four uncoated papers representing the most relevant grades on the market in terms of hydrophobisation and surface treatment. We are presenting a quantitative analysis of viscosity and surface tension on the print outcome, evaluating dot size, liquid penetration (print through) and surface coverage of the printed dots. The most important finding is that for liquids within the jetting window the variation of the liquid viscosity typically has a 2-3 times higher impact on the print outcome than variation of the liquid surface tension. Increased viscosity in all cases reduces dot area, liquid penetration and liquid surface coverage. Surface tension plays a smaller role for liquid spreading and penetration, except for hydrophobised substrates, where both are reduced for higher surface tension. Interestingly, higher surface tension consistently increases liquid surface coverage for all papers and drop sizes. A detailed analysis on the competing effect of dot spreading and liquid penetration is presented, in terms of viscosity, surface tension and surface coverage of the liquid.}, }
@article {pmid33267453, year = {2019}, author = {Ma, H and Duan, Z and Su, L and Ning, X and Bai, J and Lv, X}, title = {Fluid Flow and Entropy Generation Analysis of Al2O3-Water Nanofluid in Microchannel Plate Fin Heat Sinks.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {8}, pages = {}, pmid = {33267453}, issn = {1099-4300}, support = {2019YJS155//Fundamental Research Funds for the Central Universities/ ; }, abstract = {The flow in channels of microdevices is usually in the developing regime. Three-dimensional laminar flow characteristics of a nanofluid in microchannel plate fin heat sinks are investigated numerically in this paper. Deionized water and Al2O3-water nanofluid are employed as the cooling fluid in our work. The effects of the Reynolds number (100 < Re < 1000), channel aspect ratio (0 < ε < 1), and nanoparticle volume fraction (0.5% < Φ < 5%) on pressure drop and entropy generation in microchannel plate fin heat sinks are examined in detail. Herein, the general expression of the entropy generation rate considering entrance effects is developed. The results revealed that the frictional entropy generation and pressure drop increase as nanoparticle volume fraction and Reynolds number increase, while decrease as the channel aspect ratio increases. When the nanoparticle volume fraction increases from 0 to 3% at Re = 500, the pressure drop of microchannel plate fin heat sinks with ε = 0.5 increases by 9%. It is demonstrated that the effect of the entrance region is crucial for evaluating the performance of microchannel plate fin heat sinks. The study may shed some light on the design and optimization of microchannel heat sinks.}, }
@article {pmid35519474, year = {2019}, author = {Peng, Y and Alsagri, AS and Afrand, M and Moradi, R}, title = {A numerical simulation for magnetohydrodynamic nanofluid flow and heat transfer in rotating horizontal annulus with thermal radiation.}, journal = {RSC advances}, volume = {9}, number = {39}, pages = {22185-22197}, pmid = {35519474}, issn = {2046-2069}, abstract = {The impact of an axial magnetic field on the heat transfer and nanofluid flow among two horizontal coaxial tubes in the presence of thermal radiation was considered in this study. The impact of viscous dissipation was also considered. The well-known KKL (Koo-Kleinsteuer-Li) model was applied to approximate the viscosity of the nanofluid and the effective thermal conductivity. Furthermore, proper transformations for the velocity and temperature were applied in this study to obtain a set of ODEs (ordinary differential equations) for basic equations governing the flow, heat and mass transfer. In addition, the 4th order Runge-Kutta (RK) numerical scheme was applied to solve the differential equations along with the associated boundary conditions. The impacts of different parameters, including Hartmann number, Reynolds number, radiation parameter and aspect ratio, on the heat transfer and flow features were studied. According to the results, the value of the Nusselt number increases with an increase in the radiation parameter, Hartmann number and aspect ratio and a decrease in the Reynolds number and Eckert number.}, }
@article {pmid33267389, year = {2019}, author = {Lee, TW}, title = {Maximum Entropy Method for Solving the Turbulent Channel Flow Problem.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {7}, pages = {}, pmid = {33267389}, issn = {1099-4300}, abstract = {There are two components in this work that allow for solutions of the turbulent channel flow problem: One is the Galilean-transformed Navier-Stokes equation which gives a theoretical expression for the Reynolds stress (u'v'); and the second the maximum entropy principle which provides the spatial distribution of turbulent kinetic energy. The first concept transforms the momentum balance for a control volume moving at the local mean velocity, breaking the momentum exchange down to its basic components, u'v', u'[2], pressure and viscous forces. The Reynolds stress gradient budget confirms this alternative interpretation of the turbulence momentum balance, as validated with DNS data. The second concept of maximum entropy principle states that turbulent kinetic energy in fully-developed flows will distribute itself until the maximum entropy is attained while conforming to the physical constraints. By equating the maximum entropy state with maximum allowable (viscous) dissipation at a given Reynolds number, along with other constraints, we arrive at function forms (inner and outer) for the turbulent kinetic energy. This allows us to compute the Reynolds stress, then integrate it to obtain the velocity profiles in channel flows. The results agree well with direct numerical simulation (DNS) data at Reτ = 400 and 1000.}, }
@article {pmid35136273, year = {2019}, author = {Kempski, P and Quataert, E and Squire, J and Kunz, MW}, title = {Shearing-box simulations of MRI-driven turbulence in weakly collisional accretion discs.}, journal = {Monthly notices of the Royal Astronomical Society}, volume = {486}, number = {3}, pages = {4013-4029}, pmid = {35136273}, issn = {0035-8711}, support = {NNX17AK63G/NASA/NASA/United States ; }, abstract = {We present a systematic shearing-box investigation of MRI-driven turbulence in a weakly collisional plasma by including the effects of an anisotropic pressure stress, i.e. anisotropic (Braginskii) viscosity. We constrain the pressure anisotropy (Δp) to lie within the stability bounds that would be otherwise imposed by kinetic microinstabilities. We explore a broad region of parameter space by considering different Reynolds numbers and magnetic-field configurations, including net vertical flux, net toroidal-vertical flux and zero net flux. Remarkably, we find that the level of turbulence and angular-momentum transport are not greatly affected by large anisotropic viscosities: the Maxwell and Reynolds stresses do not differ much from the MHD result. Angular-momentum transport in Braginskii MHD still depends strongly on isotropic dissipation, e.g., the isotropic magnetic Prandtl number, even when the anisotropic viscosity is orders of magnitude larger than the isotropic diffusivities. Braginskii viscosity nevertheless changes the flow structure, rearranging the turbulence to largely counter the parallel rate of strain from the background shear. We also show that the volume-averaged pressure anisotropy and anisotropic viscous transport decrease with increasing isotropic Reynolds number (Re); e.g., in simulations with net vertical field, the ratio of anisotropic to Maxwell stress (α A/α M) decreases from ~ 0.5 to ~ 0.1 as we move from Re ~ 10[3] to Re ~ 10[4], while 〈4πΔp/B [2]〉 → 0. Anisotropic transport may thus become negligible at high Re. Anisotropic viscosity nevertheless becomes the dominant source of heating at large Re, accounting for ≳50% of the plasma heating. We conclude by briefly discussing the implications of our results for RIAFs onto black holes.}, }
@article {pmid33267306, year = {2019}, author = {Abd El-Aziz, M and Afify, AA}, title = {MHD Casson Fluid Flow over a Stretching Sheet with Entropy Generation Analysis and Hall Influence.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {6}, pages = {}, pmid = {33267306}, issn = {1099-4300}, abstract = {The impacts of entropy generation and Hall current on MHD Casson fluid over a stretching surface with velocity slip factor have been numerically analyzed. Numerical work for the governing equations is established by using a shooting method with a fourth-order Runge-Kutta integration scheme. The outcomes show that the entropy generation is enhanced with a magnetic parameter, Reynolds number and group parameter. Further, the reverse behavior is observed with the Hall parameter, Eckert number, Casson parameter and slip factor. Also, it is viewed that Bejan number reduces with a group parameter.}, }
@article {pmid33267233, year = {2019}, author = {de Divitiis, N}, title = {Statistical Lyapunov Theory Based on Bifurcation Analysis of Energy Cascade in Isotropic Homogeneous Turbulence: A Physical-Mathematical Review.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {5}, pages = {}, pmid = {33267233}, issn = {1099-4300}, abstract = {This work presents a review of previous articles dealing with an original turbulence theory proposed by the author and provides new theoretical insights into some related issues. The new theoretical procedures and methodological approaches confirm and corroborate the previous results. These articles study the regime of homogeneous isotropic turbulence for incompressible fluids and propose theoretical approaches based on a specific Lyapunov theory for determining the closures of the von Kármán-Howarth and Corrsin equations and the statistics of velocity and temperature difference. While numerous works are present in the literature which concern the closures of the autocorrelation equations in the Fourier domain (i.e., Lin equation closure), few articles deal with the closures of the autocorrelation equations in the physical space. These latter, being based on the eddy-viscosity concept, describe diffusive closure models. On the other hand, the proposed Lyapunov theory leads to nondiffusive closures based on the property that, in turbulence, contiguous fluid particles trajectories continuously diverge. Therefore, the main motivation of this review is to present a theoretical formulation which does not adopt the eddy-viscosity paradigm and summarizes the results of the previous works. Next, this analysis assumes that the current fluid placements, together with velocity and temperature fields, are fluid state variables. This leads to the closures of the autocorrelation equations and helps to interpret the mechanism of energy cascade as due to the continuous divergence of the contiguous trajectories. Furthermore, novel theoretical issues are here presented among which we can mention the following ones. The bifurcation rate of the velocity gradient, calculated along fluid particles trajectories, is shown to be much larger than the corresponding maximal Lyapunov exponent. On that basis, an interpretation of the energy cascade phenomenon is given and the statistics of finite time Lyapunov exponent of the velocity gradient is shown to be represented by normal distribution functions. Next, the self-similarity produced by the proposed closures is analyzed and a proper bifurcation analysis of the closed von Kármán-Howarth equation is performed. This latter investigates the route from developed turbulence toward the non-chaotic regimes, leading to an estimate of the critical Taylor scale Reynolds number. A proper statistical decomposition based on extended distribution functions and on the Navier-Stokes equations is presented, which leads to the statistics of velocity and temperature difference.}, }
@article {pmid33793688, year = {2019}, author = {Kenaley, CP and Stote, A and Ludt, WB and Chakrabarty, P}, title = {Comparative Functional and Phylogenomic Analyses of Host Association in the Remoras (Echeneidae), a Family of Hitchhiking Fishes.}, journal = {Integrative organismal biology (Oxford, England)}, volume = {1}, number = {1}, pages = {obz007}, pmid = {33793688}, issn = {2517-4843}, abstract = {The family Echeneidae consists of eight species of marine fishes that hitchhike by adhering to a wide variety of vertebrate hosts via a sucking disc. While several studies have focused on the interrelationships of the echeneids and the adhesion performance of a single species, no clear phylogenetic hypothesis has emerged and the morphological basis of adhesion remains largely unknown. We first set out to resolve the interrelationships of the Echeneidae by taking a phylogenomic approach using ultraconserved elements. Then, within this framework, we characterized disc morphology through µ-CT analysis, evaluated host specificity through an analysis of host phylogenetic distance, and determined which axes of disc morphological variation are associated with host diversity, skin surface properties, mean pairwise phylogenetic distance (MPD obs.), and swimming regime. We recovered an extremely well-supported topology, found that the specificity of host choice is more variable in a pelagic group and less variable in a reef-generalist group than previously proposed, and that axes of disc morphospace are best explained by models that include host skin surface roughness, host MPD obs., and maximum host Reynolds number. This suggests that ecomorphological diversification was driven by the selection pressures of host skin surface roughness, host specialization, and hydrodynamic regime.}, }
@article {pmid33267198, year = {2019}, author = {Abd El-Aziz, M and Saleem, S}, title = {Numerical Simulation of Entropy Generation for Power-Law Liquid Flow over a Permeable Exponential Stretched Surface with Variable Heat Source and Heat Flux.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {5}, pages = {}, pmid = {33267198}, issn = {1099-4300}, support = {G.R.P-2/16/40//King Khalid University/ ; }, abstract = {This novel work explored the second law analysis and heat transfer in a magneto non-Newtonian power-law fluid model with the presence of an internal non-uniform heat source/sink. In this investigation, the motion of the studied fluid was induced by an exponentially stretching surface. The rheological behavior of the fluid model, including the shear thinning and shear thickening properties, are also considered as special case studies. The physical problem developed meaningfully with the imposed heat flux and the porosity of the stretched surface. Extensive numerical simulations were carried out for the present boundary layer flow, in order to study the influence of each control parameter on the boundary layer flow and heat transfer characteristics via various tabular and graphical illustrations. By employing the Shooting Runge-Kutta-Fehlberg Method (SRKFM), the resulting nonlinear ordinary differential equations were solved accurately. Based on this numerical procedure, the velocity and temperature fields are displayed graphically. By applying the second law of thermodynamics, and characterizing the entropy generation and Bejan number, the present physical problem was examined and discussed thoroughly in different situations. The attained results showed that the entropy generation can be improved significantly by raising the magnetic field strength and the group parameter. From an energetic point of view, it was found that the Reynolds number boosts the entropy generation of the fluidic medium and reduces the Bejan number. Also, it was observed that an amplification of the power-law index diminished the entropy generation near the stretched surface. As main results, it was proven that the heat transfer rate can be reduced with both the internal heat source intensity and the magnetic field strength.}, }
@article {pmid33267194, year = {2019}, author = {Hussien, AA and Abdullah, MZ and Yusop, NM and Al-Kouz, W and Mahmoudi, E and Mehrali, M}, title = {Heat Transfer and Entropy Generation Abilities of MWCNTs/GNPs Hybrid Nanofluids in Microtubes.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {5}, pages = {}, pmid = {33267194}, issn = {1099-4300}, abstract = {Massive improvements in the thermophysical properties of nanofluids over conventional fluids have led to the rapid evolution of using multiwalled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) in the field of heat transfer. In this study, the heat transfer and entropy generation abilities of MWCNTs/GNPs hybrid nanofluids were explored. Experiments on forced convective flow through a brass microtube with 300 µm inner diameter and 0.27 m in length were performed under uniform heat flux. MWCNTs/GNPs hybrid nanofluids were developed by adding 0.035 wt.% GNPs to MWCNTs water-based nanofluids with mass fractions of 0.075-0.125 wt.%. The range of the Reynolds number in this experiment was maintained at Re = 200-500. Results showed that the conventional approach for predicting the heat transfer coefficient was applicable for microtubes. The heat transfer coefficient increased markedly with the use of MWCNTs and MWCNTs/GNPs nanofluids, with increased pressure dropping by 12.4%. Results further showed a reduction by 37.5% in the total entropy generation rate in microtubes for hybrid nanofluids. Overall, MWCNTs/GNPs hybrid nanofluids can be used as alternative fluids in cooling systems for thermal applications.}, }
@article {pmid33267040, year = {2019}, author = {Geneste, D and Faller, H and Nguyen, F and Shukla, V and Laval, JP and Daviaud, F and Saw, EW and Dubrulle, B}, title = {About Universality and Thermodynamics of Turbulence.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {3}, pages = {}, pmid = {33267040}, issn = {1099-4300}, support = {ANR-16-CE06-0006-01//Agence Nationale de la Recherche/ ; 2A30096//Grand &#xc9;quipement National De Calcul Intensif/ ; CFR//Commissariat &#xe0; l'&#xc9;nergie Atomique et aux &#xc9;nergies Alternatives/ ; }, abstract = {This paper investigates the universality of the Eulerian velocity structure functions using velocity fields obtained from the stereoscopic particle image velocimetry (SPIV) technique in experiments and direct numerical simulations (DNS) of the Navier-Stokes equations. It shows that the numerical and experimental velocity structure functions up to order 9 follow a log-universality (Castaing et al. Phys. D Nonlinear Phenom. 1993); this leads to a collapse on a universal curve, when units including a logarithmic dependence on the Reynolds number are used. This paper then investigates the meaning and consequences of such log-universality, and shows that it is connected with the properties of a "multifractal free energy", based on an analogy between multifractal and thermodynamics. It shows that in such a framework, the existence of a fluctuating dissipation scale is associated with a phase transition describing the relaminarisation of rough velocity fields with different Hölder exponents. Such a phase transition has been already observed using the Lagrangian velocity structure functions, but was so far believed to be out of reach for the Eulerian data.}, }
@article {pmid33479548, year = {2019}, author = {Hein, S and Theiss, A and Di Giovanni, A and Stemmer, C and Schilden, T and Schröder, W and Paredes, P and Choudhari, MM and Li, F and Reshotko, E}, title = {Numerical Investigation of Roughness Effects on Transition on Spherical Capsules.}, journal = {Journal of spacecraft and rockets}, volume = {56}, number = {2}, pages = {388-404}, pmid = {33479548}, issn = {0022-4650}, support = {/ARMD/Aeronautics NASA/United States ; }, abstract = {To address the hitherto unknown mechanism of boundary-layer transition on blunt reentry capsules, the role of roughness-induced disturbance growth on a spherical-section forebody is assessed via optimal transient growth theory and direct numerical simulations (DNS). Optimal transient-growth studies have been performed for the blunt capsule experiments at Mach 5.9 in the Hypersonic Ludwieg tube Braunschweig (HLB) of the Technische Universität Braunschweig, which included measurements behind a patch of controlled, distributed micron-sized surface roughness. Transient-growth results for the HLB capsule indicate similar trends as the corresponding numerical data for a Mach 6 experiment in the Actively Controlled Expansion (ACE) facility of the Texas A&amp;M University (TAMU) at a lower Reynolds number. Both configurations indicate a similar dependence on surface temperature ratio, and more important, rather low values of maximum energy gain. DNS are performed for the conditions of the HLB experiment to understand the generation of stationary disturbances by the roughness patch and the accompanying evolution of unsteady perturbations. However, no evidence of either modal or nonmodal disturbance growth in the wake of the roughness patch is found in the DNS data; thus, the physical mechanism underlying the observed onset of transition still remains unknown.}, }
@article {pmid33266906, year = {2019}, author = {Kurnia, JC and Lim, DC and Chen, L and Jiang, L and Sasmito, AP}, title = {Entropy Generation and Heat Transfer Performance in Microchannel Cooling.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {2}, pages = {}, pmid = {33266906}, issn = {1099-4300}, support = {015LCO-026//Yayasan Universiti Teknologi PETRONAS/ ; }, abstract = {Owing to its relatively high heat transfer performance and simple configurations, liquid cooling remains the preferred choice for electronic cooling and other applications. In this cooling approach, channel design plays an important role in dictating the cooling performance of the heat sink. Most cooling channel studies evaluate the performance in view of the first thermodynamics aspect. This study is conducted to investigate flow behaviour and heat transfer performance of an incompressible fluid in a cooling channel with oblique fins with regards to first law and second law of thermodynamics. The effect of oblique fin angle and inlet Reynolds number are investigated. In addition, the performance of the cooling channels for different heat fluxes is evaluated. The results indicate that the oblique fin channel with 20° angle yields the highest figure of merit, especially at higher Re (250-1000). The entropy generation is found to be lowest for an oblique fin channel with 90° angle, which is about twice than that of a conventional parallel channel. Increasing Re decreases the entropy generation, while increasing heat flux increases the entropy generation.}, }
@article {pmid33266845, year = {2019}, author = {Ries, F and Li, Y and Nishad, K and Janicka, J and Sadiki, A}, title = {Entropy Generation Analysis and Thermodynamic Optimization of Jet Impingement Cooling Using Large Eddy Simulation.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {2}, pages = {}, pmid = {33266845}, issn = {1099-4300}, support = {SFB/TRR150//Deutsche Forschungsgemeinschaft/ ; }, abstract = {In this work, entropy generation analysis is applied to characterize and optimize a turbulent impinging jet on a heated solid surface. In particular, the influence of plate inclinations and Reynolds numbers on the turbulent heat and fluid flow properties and its impact on the thermodynamic performance of such flow arrangements are numerically investigated. For this purpose, novel model equations are derived in the frame of Large Eddy Simulation (LES) that allows calculation of local entropy generation rates in a post-processing phase including the effect of unresolved subgrid-scale irreversibilities. From this LES-based study, distinctive features of heat and flow dynamics of the impinging fluid are detected and optimal operating designs for jet impingement cooling are identified. It turned out that (1) the location of the stagnation point and that of the maximal Nusselt number differ in the case of plate inclination; (2) predominantly the impinged wall acts as a strong source of irreversibility; and (3) a flow arrangement with a jet impinging normally on the heated surface allows the most efficient use of energy which is associated with lowest exergy lost. Furthermore, it is found that increasing the Reynolds number intensifies the heat transfer and upgrades the second law efficiency of such thermal systems. Thereby, the thermal efficiency enhancement can overwhelm the frictional exergy loss.}, }
@article {pmid33266771, year = {2019}, author = {Zhu, Z and Wang, H and Peng, D and Dou, J}, title = {Modelling the Hindered Settling Velocity of a Falling Particle in a Particle-Fluid Mixture by the Tsallis Entropy Theory.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {1}, pages = {}, pmid = {33266771}, issn = {1099-4300}, support = {51509004//National Natural Science Foundation of China/ ; 2018KJ01//the Open Research Foundation of the Key Laboratory of the Pearl River Estuarine Dynamics and Associated Process Regulation, Ministry of Water Resources, China/ ; }, abstract = {The settling velocity of a sediment particle is an important parameter needed for modelling the vertical flux in rivers, estuaries, deltas and the marine environment. It has been observed that a particle settles more slowly in the presence of other particles in the fluid than in a clear fluid, and this phenomenon has been termed 'hindered settling'. The Richardson and Zaki equation has been a widely used expression for relating the hindered settling velocity of a particle with that in a clear fluid in terms of a concentration function and the power of the concentration function, and the power index is known as the exponent of reduction of the settling velocity. This study attempts to formulate the model for the exponent of reduction of the settling velocity by using the probability method based on the Tsallis entropy theory. The derived expression is a function of the volumetric concentration of the suspended particle, the relative mass density of the particle and the particle's Reynolds number. This model is tested against experimental data collected from the literature and against five existing deterministic models, and this model shows good agreement with the experimental data and gives better prediction accuracy than the other deterministic models. The derived Tsallis entropy-based model is also compared with the existing Shannon entropy-based model for experimental data, and the Tsallis entropy-based model is comparable to the Shannon entropy-based model for predicting the hindered settling velocity of a falling particle in a particle-fluid mixture. This study shows the potential of using the Tsallis entropy together with the principle of maximum entropy to predict the hindered settling velocity of a falling particle in a particle-fluid mixture.}, }
@article {pmid33867572, year = {2019}, author = {Paredes, P and Choudhari, MM and Li, F}, title = {Instability wave-streak interactions in a hypersonic boundary layer at flight conditions.}, journal = {Journal of fluid mechanics}, volume = {858}, number = {}, pages = {474-499}, pmid = {33867572}, issn = {0022-1120}, support = {/ARMD/Aeronautics NASA/United States ; }, abstract = {The interaction of stationary streaks undergoing nonmodal growth with modally unstable instability waves in a hypersonic boundary-layer flow is studied using numerical computations. The geometry and flow conditions are selected to match a relevant trajectory location from the ascent phase of the HIFiRE-1 flight experiment; namely, a 7 degree half-angle, circular cone with 2.5 mm nose radius, freestream Mach number equal to 5.30, unit Reynolds number equal to 13.42 m[-1], and wall-to-adiabatic temperature ratio of approximately 0.35 over most of the vehicle. This paper investigates the nonlinear evolution of initially linear optimal disturbances that evolve into finite-amplitude streaks, followed by an analysis of the modal instability characteristics of the perturbed, streaky boundary-layer flow. The investigation is performed with stationary direct numerical simulations (DNS) and plane-marching parabolized stability equations (PSE), in conjunction with partial-differential-equation-based planar eigenvalue analysis. The overall effect of streaks is to reduce the peak amplification factors of instability waves, indicating a possible downstream shift in the onset of laminar-turbulent transition. The present study confirms previous findings that the mean flow distorsion of the nonlinear streak perturbation reduces the amplification rates of the Mack-mode instability. More importantly, however, the present results demonstrate that the spanwise varying component of the streak can produce a larger effect on the Mack-mode amplification. The study with selected azimuthal wavenumbers for the stationary streaks reveals that a wavenumber of approximately 1.4 times larger than the optimal wavenumber is more effective in stabilizing the planar Mack-mode instabilities. In the absence of unstable first-mode waves for the present cold-wall condition, transition onset is expected to be delayed until the peak streak amplitude increases to nearly 35 percent of the freestream velocity, when intrinsic instabilities of the boundary-layer streaks begin to dominate the transition process. For streak amplitudes below that limit a significant net stabilization is achieved, yielding a potential transition delay that can exceed 100 percent of the length of the laminar region in the uncontrolled case.}, }
@article {pmid33266740, year = {2018}, author = {Wang, W and Pan, C and Wang, J}, title = {Wall-Normal Variation of Spanwise Streak Spacing in Turbulent Boundary Layer With Low-to-Moderate Reynolds Number.}, journal = {Entropy (Basel, Switzerland)}, volume = {21}, number = {1}, pages = {}, pmid = {33266740}, issn = {1099-4300}, support = {11672020,11490552//National Natural Science Foundation of China/ ; }, abstract = {Low-speed streaks in wall-bounded turbulence are the dominant structures in the near-wall turbulent self-sustaining cycle. Existing studies have well characterized their spanwise spacing in the buffer layer and below. Recent studies suggested the existence of these small-scale structures in the higher layer where large-scale structures usually receive more attention. The present study is thus devoted to extending the understanding of the streak spacing to the log layer. An analysis is taken on two-dimensional (2D) wall-parallel velocity fields in a smooth-wall turbulent boundary layer with R e τ = 440∼2400, obtained via either 2D Particle Image Velocimetry (PIV) measurement taken here or public Direct Numerical Simulation (DNS). Morphological-based streak identification analysis yields a R e -independent log-normal distribution of the streak spacing till the upper bound of the log layer, based on which an empirical model is proposed to account for its wall-normal growth. The small-scale part of the spanwise spectra of the streamwise fluctuating velocity below y + = 100 is reasonably restored by a synthetic simulation that distributes elementary streak units based on the proposed empirical streak spacing model, which highlights the physical significance of streaks in shaping the small-scale part of the velocity spectra beyond the buffer layer.}, }
@article {pmid33266619, year = {2018}, author = {Abdollahzadeh Jamalabadi, MY}, title = {Optimal Design of Nanoparticle Enhanced Phan-Thien-Tanner Flow of a Viscoelastic Fluid in a Microchannel.}, journal = {Entropy (Basel, Switzerland)}, volume = {20}, number = {12}, pages = {}, pmid = {33266619}, issn = {1099-4300}, abstract = {The excellent thermal characteristics of nanoparticles have increased their application in the field of heat transfer. In this paper, a thermophysical and geometrical parameter study is performed to minimize the total entropy generation of the viscoelastic flow of nanofluid. Entropy generation with respect to volume fraction (<0.04), the Reynolds number (20,000-100,000), and the diameter of the microchannel (20-20,000 μm) with the circular cross-section under constant flux are calculated. As is shown, most of the entropy generation owes to heat transfer and by increasing the diameter of the channel, the Bejan number increases. The contribution of heat entropy generation in the microchannel is very poor and the major influence of entropy generation is attributable to friction. The maximum quantity of in-channel entropy generation happens in nanofluids with TiO2, CuO, Cu, and Ag nanoparticles, in turn, despite the fact in the microchannel this behavior is inverted, the minimum entropy generation occurs in nanofluids with CuO, Cu, Ag, and TiO2 nanoparticles, in turn. In the channel and microchannel for all nanofluids except water-TiO2, increasing the volume fraction of nanoparticles decreases entropy generation. In the channel and microchannel the total entropy generation increases by augmentation the Reynolds number.}, }
@article {pmid33265887, year = {2018}, author = {Qiang, Y and Wei, L and Luo, X and Jian, H and Wang, W and Li, F}, title = {Heat Transfer and Flow Structures of Laminar Confined Slot Impingement Jet with Power-Law Non-Newtonian Fluid.}, journal = {Entropy (Basel, Switzerland)}, volume = {20}, number = {10}, pages = {}, pmid = {33265887}, issn = {1099-4300}, support = {51765033//National Natural Science Foundation of China/ ; }, abstract = {Heat transfer performances and flow structures of laminar impinging slot jets with power-law non-Newtonian fluids and corresponding typical industrial fluids (Carboxyl Methyl Cellulose (CMC) solutions and Xanthangum (XG) solutions) have been studied in this work. Investigations are performed for Reynolds number Re less than 200, power-law index n ranging from 0.5 to 1.5 and consistency index K varying from 0.001 to 0.5 to explore heat transfer and flow structure of shear-thinning fluid and shear-thickening fluid. Results indicate that with the increase of n, K for a given Re, wall Nusselt number increases mainly attributing to the increase of inlet velocity U. For a given inlet velocity, wall Nusselt number decreases with the increase of n and K, which mainly attributes to the increase of apparent viscosity and the reduction of momentum diffusion. For the same Re, U and Pr, wall Nusselt number decreases with the increase of n. Among the study of industrial power-law shear-thinning fluid, CMC solution with 100 ppm shows the best heat transfer performance at a given velocity. Moreover, new correlation of Nusselt number about industrial fluid is proposed. In general, for the heat transfer of laminar confined impinging jet, it is best to use the working fluid with low viscosity.}, }
@article {pmid33265465, year = {2018}, author = {Mathur, A and Seddighi, M and He, S}, title = {Transition of Transient Channel Flow with High Reynolds Number Ratios.}, journal = {Entropy (Basel, Switzerland)}, volume = {20}, number = {5}, pages = {}, pmid = {33265465}, issn = {1099-4300}, abstract = {Large-eddy simulations of turbulent channel flow subjected to a step-like acceleration have been performed to investigate the effect of high Reynolds number ratios on the transient behaviour of turbulence. It is shown that the response of the flow exhibits the same fundamental characteristics described in He &amp; Seddighi (J. Fluid Mech., vol. 715, 2013, pp. 60-102 and vol. 764, 2015, pp. 395-427)-a three-stage response resembling that of the bypass transition of boundary layer flows. The features of transition are seen to become more striking as the Re-ratio increases-the elongated streaks become stronger and longer, and the initial turbulent spot sites at the onset of transition become increasingly sparse. The critical Reynolds number of transition and the transition period Reynolds number for those cases are shown to deviate from the trends of He &amp; Seddighi (2015). The high Re-ratio cases show double peaks in the transient response of streamwise fluctuation profiles shortly after the onset of transition. Conditionally-averaged turbulent statistics based on a λ_2-criterion are used to show that the two peaks in the fluctuation profiles are due to separate contributions of the active and inactive regions of turbulence generation. The peak closer to the wall is attributed to the generation of "new" turbulence in the active region, whereas the peak farther away from the wall is attributed to the elongated streaks in the inactive region. In the low Re-ratio cases, the peaks of these two regions are close to each other during the entire transient, resulting in a single peak in the domain-averaged profile.}, }
@article {pmid36718068, year = {2017}, author = {Niu, Z and Wang, R and Jiao, K and Du, Q and Yin, Y}, title = {Direct numerical simulation of low Reynolds number turbulent air-water transport in fuel cell flow channel.}, journal = {Science bulletin}, volume = {62}, number = {1}, pages = {31-39}, doi = {10.1016/j.scib.2016.11.010}, pmid = {36718068}, issn = {2095-9281}, abstract = {With performance improvement of low-temperature fuel cell (FC), high reactant supply and water generation rates may induce air-water turbulence in the FC flow channel. In this research, an air-water turbulent direct numerical simulation (DNS) model is developed to simulate different droplet sizes, locations and interactions in the air-water transport processes comprehensively. It is found that a larger droplet breaks up more easily in turbulence, and a smaller droplet tends to keep lumped. The droplet at corner does not break up because it is away from channel center. The droplet interaction simulations show that the small droplets merge to form slugs, but still keep lumped in turbulence. It is suggested that two conditions need to be satisfied for droplet break up in FC flow channel, one is turbulent flow, and another is that the droplet needs to be large enough and occupy the center region of flow channel to suffer sufficient turbulence fluctuations. The DNS results illustrate some unique phenomena in turbulent flow, and show that the turbulence has significant effect on the air-water flow behavior in FC flow channel.}, }
@article {pmid33440477, year = {2016}, author = {LeBlanc, KJ and Niemi, SR and Bennett, AI and Harris, KL and Schulze, KD and Sawyer, WG and Taylor, C and Angelini, TE}, title = {Stability of High Speed 3D Printing in Liquid-Like Solids.}, journal = {ACS biomaterials science &amp; engineering}, volume = {2}, number = {10}, pages = {1796-1799}, doi = {10.1021/acsbiomaterials.6b00184}, pmid = {33440477}, issn = {2373-9878}, abstract = {Fluid instabilities limit the ability of features to hold their shape in many types of 3D printing as liquid inks solidify into written structures. By 3D printing directly into a continuum of jammed granular microgels, these instabilities are circumvented by eliminating surface tension and body forces. However, this type of 3D printing process is potentially limited by inertial instabilities if performed at high speeds where turbulence may destroy features as they are written. Here, we design and test a high-speed 3D printing experimental system to identify the instabilities that arise when an injection nozzle translates at 1 m/s. We find that the viscosity of the injected material can control the Reynold's instability, and we discover an additional, unanticipated instability near the top surface of the granular microgel medium.}, }
@article {pmid35607219, year = {2016}, author = {Mao, C and Kong, M and Yang, Q and Li, G and Huang, Y}, title = {Vorticity Deformation in Polymeric Emulsions Induced by Anisotropic Ellipsoids.}, journal = {ACS macro letters}, volume = {5}, number = {8}, pages = {900-903}, doi = {10.1021/acsmacrolett.6b00456}, pmid = {35607219}, issn = {2161-1653}, abstract = {We study the influence of particle shape on shear-induced droplet deformation in polymeric emulsions. During shearing, droplets become elongated and rotate periodically about their major axes while aligning along the vorticity direction in ellipsoid-filled emulsions, while similar behavior is not observed in the pristine, microsphere-filled or ellipsoid-filled inverse systems. Based on the Jeffery orbit theory, the formation of anisotropic droplets with extremely small Reynolds number due to arrested coalescence in Newtonian matrix and strong confinement effect are suggested to be responsible for the vorticity alignment of droplets during slow shearing.}, }
@article {pmid34434625, year = {2016}, author = {Kedzierski, MA}, title = {Diesel Adsorption to Polyvinyl Chloride and Iron During Contaminated Water Flow and Flushing Tests.}, journal = {Journal of research of the National Institute of Standards and Technology}, volume = {121}, number = {}, pages = {314-341}, pmid = {34434625}, issn = {1044-677X}, abstract = {This paper presents an experimental and theoretical study of aqueous diesel contamination and decontamination of a polyvinyl chloride (PVC) surface and an iron (Fe) surface. A test apparatus designed for the purpose of studying adsorption of diesel from a flowing dilute diesel/water mixture was used to measure the mass of diesel adsorbed per unit surface area (the excess surface density) and the bulk concentration of the diesel in the flow using a fluorescence based measurement technique. Both bulk composition and the excess surface density measurements were achieved via a traverse of the fluorescent measurement probe perpendicular to the test surface. The diesel adsorption to each test surface was examined for three different Reynolds numbers between zero and 7000. Measurements for a given condition were made over a period of approximately 200 h for a diesel mass fraction of approximately 0.15 % in tap water. For a Reynolds number of approximately 7000, the largest excess layer thickness was approximately 4.4 μm, which was measured on a PVC surface. Averaging over all contaminating flow rates and exposure times, the excess layer thickness on the PVC surface was approximately 2.0 μm. Reynolds number had little or no effect on the accumulation of diesel on an iron surface, which was approximately 0.71 μm. The adsorbed diesel on the PVC and iron surfaces was removed by flushing with tap water. Models to predict excess layer thickness during flushing and contamination were developed. The models predict flushing times to within 7 h and predict the influence of pipe surface on contamination level.}, }
@article {pmid37064764, year = {2011}, author = {Fan, DL and Zhu, FQ and Cammarata, RC and Chien, CL}, title = {Electric Tweezers.}, journal = {Nano today}, volume = {6}, number = {4}, pages = {339-354}, pmid = {37064764}, issn = {1748-0132}, support = {R41 EB012885/EB/NIBIB NIH HHS/United States ; }, abstract = {Electric tweezers utilize DC and AC electric fields through voltages applied on patterned electrodes to manipulate nanoentities suspended in a liquid. Nanowires with a large aspect ratio are particularly suitable for use in electric tweezers for patterning, assembling, and manipulation. Despite operating in the regime of extremely small particle Reynolds number (of order 10[-5]), electric tweezers can manipulate nanowires with high precision to follow any prescribed trajectory, to rotate nanowires with controlled chirality, angular velocity and rotation angle, and to assemble nanowires to fabricate nanoelectromechanical system (NEMS) devices such as nanomotors and nano-oscillators. Electric tweezers have also been used to transport in a highly controlled manner drug-carrying functionalized nanowires for cell-specific drug delivery.}, }
@article {pmid33327683, year = {1981}, author = {Wegener, WA}, title = {Diffusion coefficients for rigid macromolecules with irregular shapes that allow rotational-translational coupling.}, journal = {Biopolymers}, volume = {20}, number = {2}, pages = {303-326}, doi = {10.1002/bip.1981.360200205}, pmid = {33327683}, issn = {1097-0282}, abstract = {We consider six-dimensional diffusion and frictional tensors for a rigid macromolecule immersed in a viscous fluid at low Reynolds number. Our treatment allows for screwlike properties which couple rotational and translational movements. We show that the center of diffusion of a screwlike body can be distinct from its hydrodynamic center of reaction. Symmetry conditions which ensure coincidence are examined. The center of diffusion is found to be the point of a body with the slowest diffusive movements, while rotations about the center of reaction encounter the least average resistance. The macroscopic translational diffusion coefficient is evaluated from a perturbation analysis of the six-dimensional diffusion equation. We show that methodologies which ignore translational-rotational coupling will necessarily underestimate the diffusion rate of screwlike particles. A procedural framework is presented to calculate diffusion coefficients of complicated bodies. As an example we treat a long bent rod.}, }
@article {pmid33220061, year = {2020}, author = {Battista, NA}, title = {Diving into a Simple Anguilliform Swimmer's Sensitivity.}, journal = {Integrative and comparative biology}, volume = {60}, number = {5}, pages = {1236-1250}, doi = {10.1093/icb/icaa131}, pmid = {33220061}, issn = {1557-7023}, mesh = {Animals ; Biomechanical Phenomena ; Caenorhabditis elegans ; *Locomotion ; *Models, Biological ; Motion ; *Swimming ; }, abstract = {Computational models of aquatic locomotion range from modest individual simple swimmers in 2D to sophisticated 3D multi-swimmer models that attempt to parse collective behavioral dynamics. Each of these models contain a multitude of model input parameters to which its outputs are inherently dependent, that is, various performance metrics. In this work, the swimming performance's sensitivity to parameters is investigated for an idealized, simple anguilliform swimming model in 2D. The swimmer considered here propagates forward by dynamically varying its body curvature, similar to motion of a Caenorhabditis elegans. The parameter sensitivities were explored with respect to the fluid scale (Reynolds number), stroke (undulation) frequency, as well as a kinematic parameter controlling the velocity and acceleration of each upstroke and downstroke. The input Reynolds number and stroke frequencies sampled were from [450, 2200] and [1, 3] Hz, respectively. In total, 5000 fluid-structure interaction simulations were performed, each with a unique parameter combination selected via a Sobol sequence, in order to conduct global sensitivity analysis. Results indicate that the swimmer's performance is most sensitive to variations in its stroke frequency. Trends in swimming performance were discovered by projecting the performance data onto particular 2D subspaces. Pareto-like optimal fronts were identified. This work is a natural extension of the parameter explorations of the same model from Battista in 2020.}, }
@article {pmid33212661, year = {2020}, author = {Gungor, A and Hemmati, A}, title = {Wake symmetry impacts the performance of tandem hydrofoils during in-phase and out-of-phase oscillations differently.}, journal = {Physical review. E}, volume = {102}, number = {4-1}, pages = {043104}, doi = {10.1103/PhysRevE.102.043104}, pmid = {33212661}, issn = {2470-0053}, abstract = {The hydrodynamics of two oscillating foils in side-by-side configuration is numerically investigated for in-phase and out-of-phase pitching at Reynolds number of 4000 and Strouhal numbers of St=0.25-0.5. The effects of phase difference (in-phase and out-of-phase) and Strouhal number on symmetric attributes of the wake and unsteady propulsive performance of the foils are studied in detail. At lower Strouhal numbers, there is a quasisteady performance in both thrust generation and power consumption, which coincides with persistence of the wake symmetry. As Strouhal number increases, however, in-phase and out-of-phase pitching display unsteady cycle-averaged behavior with very different wake characteristics. The asymmetric wake of in-phase pitching foils at high Strouhal numbers transitions to a quasisymmetric wake, when an extensive interaction between the two vortex streets is observed in the wake. This coincides with an improvement on the propulsive performance of the foils. In contrast, the symmetric wake of the out-of-phase pitching foils at a high Strouhal number transitions to an asymmetric wake. The adverse effect of this transition is only observed on the propulsive performance of one foil while the other exploits the wake towards a better performance. The collective performance of the the out-of-phase pitching system, however, remains unchanged. There is also a strong correlation between the wake symmetric characteristics and total nonzero side-force production.}, }
@article {pmid33212599, year = {2020}, author = {Inubushi, M and Goto, S}, title = {Transfer learning for nonlinear dynamics and its application to fluid turbulence.}, journal = {Physical review. E}, volume = {102}, number = {4-1}, pages = {043301}, doi = {10.1103/PhysRevE.102.043301}, pmid = {33212599}, issn = {2470-0053}, abstract = {We introduce transfer learning for nonlinear dynamics, which enables efficient predictions of chaotic dynamics by utilizing a small amount of data. For the Lorenz chaos, by optimizing the transfer rate, we accomplish more accurate inference than the conventional method by an order of magnitude. Moreover, a surprisingly small amount of learning is enough to infer the energy dissipation rate of the Navier-Stokes turbulence because we can, thanks to the small-scale universality of turbulence, transfer a large amount of the knowledge learned from turbulence data at lower Reynolds number.}, }
@article {pmid33211148, year = {2021}, author = {Ikoma, T and Suwa, K and Sano, M and Ushio, T and Saotome, M and Ogawa, N and Satoh, H and Maekawa, Y}, title = {Early changes of pulmonary arterial hemodynamics in patients with systemic sclerosis: flow pattern, WSS, and OSI analysis with 4D flow MRI.}, journal = {European radiology}, volume = {31}, number = {6}, pages = {4253-4263}, pmid = {33211148}, issn = {1432-1084}, support = {26461065//Ministry of Education, Culture, Sports, Science and Technology/ ; }, mesh = {Blood Flow Velocity ; Hemodynamics ; Humans ; *Hypertension, Pulmonary/diagnostic imaging ; Magnetic Resonance Imaging ; Pulmonary Artery/diagnostic imaging ; *Scleroderma, Systemic/complications/diagnostic imaging ; Stress, Mechanical ; }, abstract = {OBJECTIVES: To study the pulmonary artery (PA) hemodynamics in patients with systemic sclerosis (SSc) using 4D flow MRI (4D-flow).<br><br>METHODS: Twenty-three patients with SSc (M/F: 2/21, 57&#x2009;&#xb1;&#x2009;15&#xa0;years, 3 manifest PA hypertension (PAH) by right heart catheterization) and 10 control subjects (M/F: 1/9, 55&#x2009;&#xb1;&#x2009;17&#xa0;years) underwent 4D-flow for the in vivo measurement of 3D blood flow velocities in the PA. Data analysis included area-averaged flow quantification at the main PA, 3D wall shear stress (WSS), oscillatory shear index (OSI) calculation along the PA surface, and Reynolds number. The composite outcome of all-cause death and major adverse cardiac events was also investigated.<br><br>RESULTS: The maximum PA flow at the systole did not differ, but the minimum flow at the diastole was significantly greater in patients with SSc compared with that in control subjects (7.7&#x2009;&#xb1;&#x2009;16.0&#xa0;ml/s vs. &#x2011;&#xa0;13.0&#x2009;&#xb1;&#x2009;17.3&#xa0;ml/s, p&#x2009;<&#x2009;0.01). The maximum WSS at the peak systole was significantly lower and OSI was significantly greater in patients with SSc compared with those in control subjects (maximum WSS: 1.04&#x2009;&#xb1;&#x2009;0.20&#xa0;Pa vs. 1.33&#x2009;&#xb1;&#x2009;0.34&#xa0;Pa, p&#x2009;<&#x2009;0.01, OSI: 0.139&#x2009;&#xb1;&#x2009;0.031 vs. 0.101&#x2009;&#xb1;&#x2009;0.037, p&#x2009;<&#x2009;0.01). The cumulative event-free rate for the composite event was significantly lower in patients with minimum flow in main PA &#x2264;&#x2009;9.22&#xa0;ml/s (p&#x2009;=&#x2009;0.012) and in patients with Reynolds number &#x2264;&#x2009;2560 (p&#x2009;<&#x2009;0.001).<br><br>CONCLUSIONS: 4D-flow has the potential to detect changes of PA hemodynamics noninvasively and predict the outcome in patients with SSc at the stage before manifest PAH.<br><br>KEY POINTS: &#x2022; The WSS at the peak systolic phase was significantly lower (p&#x2009;<&#x2009;0.05), whereas OSI was greater (p&#x2009;<&#x2009;0.01) in patients with SSc without manifest PAH than in controls. &#x2022; The hemodynamic change detected by 4D-flow may help patient management even at the stage before manifest PAH in SSc. &#x2022; The minimum PA flow and Reynolds number by 4D-flow will serve as a predictive marker for SSc.}, }
@article {pmid33201951, year = {2021}, author = {Lochab, V and Prakash, S}, title = {Combined electrokinetic and shear flows control colloidal particle distribution across microchannel cross-sections.}, journal = {Soft matter}, volume = {17}, number = {3}, pages = {611-620}, pmid = {33201951}, issn = {1744-6848}, support = {P30 CA016058/CA/NCI NIH HHS/United States ; R01 HL141941/HL/NHLBI NIH HHS/United States ; }, abstract = {Recent experimental observations on combined electrokinetic and shear flows of colloidal suspensions in rectangular cross-section microfluidic channels have shown unusual cross-stream colloidal particle migration and dynamic assembly. Although a new electrophoresis-induced lift force has been postulated to cause the lateral migration of colloidal particles, little is known about how fluid properties and flow conditions impact this force and therefore subsequent colloidal particle migration. Furthermore, no experimental quantification of this electrophoresis-induced lift force is available. We report several key advances by demonstrating that the kinematic viscosity of the fluid can be used to modulate the spatial distribution of particles over the entire microchannel cross-section, with suppression of the colloidal particle migration observed with increase in fluid kinematic viscosity. Colloidal particle migration of ∼10 μm from not only the top and bottom microchannel walls but also from the side walls is shown with the corresponding electrophoresis-induced lift force of up to ∼30 fN. The breadth of flow conditions tested capture the channel Reynolds number in the 0.1-1.1 range, with inertial migration of colloidal particles shown in flow regimes where the migration was previously thought to be ineffective, if not for the electrophoresis-induced lift force. The ability of the electrophoresis-induced lift force to migrate colloidal particles across the entire microchannel cross-section establishes a new paradigm for three-dimensional control of colloidal particles within confined microchannels.}, }
@article {pmid33199601, year = {2020}, author = {Omori, T and Ito, H and Ishikawa, T}, title = {Swimming microorganisms acquire optimal efficiency with multiple cilia.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {117}, number = {48}, pages = {30201-30207}, pmid = {33199601}, issn = {1091-6490}, mesh = {Bacteria/*metabolism ; Cilia/*physiology ; Hydrodynamics ; Movement ; Rheology ; }, abstract = {Planktonic microorganisms are ubiquitous in water, and their population dynamics are essential for forecasting the behavior of global aquatic ecosystems. Their population dynamics are strongly affected by these organisms' motility, which is generated by their hair-like organelles, called cilia or flagella. However, because of the complexity of ciliary dynamics, the precise role of ciliary flow in microbial life remains unclear. Here, we have used ciliary hydrodynamics to show that ciliates acquire the optimal propulsion efficiency. We found that ciliary flow highly resists an organism's propulsion and that the swimming velocity rapidly decreases with body size, proportional to the power of minus two. Accordingly, the propulsion efficiency decreases as the cube of body length. By increasing the number of cilia, however, efficiency can be significantly improved, up to 100-fold. We found that there exists an optimal number density of cilia, which provides the maximum propulsion efficiency for all ciliates. The propulsion efficiency in this case decreases inversely proportionally to body length. Our estimated optimal density of cilia corresponds to those of actual microorganisms, including species of ciliates and microalgae, which suggests that now-existing motile ciliates and microalgae have survived by acquiring the optimal propulsion efficiency. These conclusions are helpful for better understanding the ecology of microorganisms, such as the energetic costs and benefits of multicellularity in Volvocaceae, as well as for the optimal design of artificial microswimmers.}, }
@article {pmid33199599, year = {2020}, author = {Andersen, A and Kiørboe, T}, title = {The effect of tethering on the clearance rate of suspension-feeding plankton.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {117}, number = {48}, pages = {30101-30103}, pmid = {33199599}, issn = {1091-6490}, mesh = {Feeding Behavior/*physiology ; Models, Biological ; Plankton/*physiology ; Rheology ; Suspensions ; Swimming ; }, abstract = {Many planktonic suspension feeders are attached to particles or tethered by gravity when feeding. It is commonly accepted that the feeding flows of tethered suspension feeders are stronger than those of their freely swimming counterparts. However, recent flow simulations indicate the opposite, and the cause of the opposing conclusions is not clear. To explore the effect of tethering on suspension feeding, we use a low-Reynolds-number flow model. We find that it is favorable to be freely swimming instead of tethered since the resulting feeding flow past the cell body is stronger, leading to a higher clearance rate. Our result underscores the significance of the near-field flow in shaping planktonic feeding modes, and it suggests that organisms tether for reasons that are not directly fluid dynamical (e.g., to stay near surfaces where the concentration of bacterial prey is high).}, }
@article {pmid33197195, year = {2020}, author = {Hatte, S and Pitchumani, R}, title = {Fractal Model for Drag Reduction on Multiscale Nonwetting Rough Surfaces.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {36}, number = {47}, pages = {14386-14402}, doi = {10.1021/acs.langmuir.0c02790}, pmid = {33197195}, issn = {1520-5827}, abstract = {Rough surfaces in contact with a flow of fluid exhibit alternating no-slip and free shear boundary conditions at the solid-liquid and air-liquid interfaces, respectively, thereby potentially offering drag reduction benefits. The balance between the dynamic pressure in the flow and the restoring capillary pressure in the interasperity spaces determines the stability of the Cassie state of wettability and is a function of the relative extent of no-slip and free shear regions per unit surface area. In the present study, using a fractal representation of rough surface topography, an analytical model is developed to quantify the stability of the Cassie state of wettability as well as drag reduction and the friction factor for laminar flow in a rectangular channel between nonwetting multiscale rough surfaces. A systematic study is conducted to quantify the effects of fractal parameters of the surfaces and the flow Reynolds number on drag reduction and the friction factor. The studies are used to develop friction factor curves extending the classical Moody diagram to hydrophobic and superhydrophobic surfaces. On the basis of the studies, regime maps are derived for estimating the extent of drag reduction offered by hydrophobic and superhydrophobic surfaces, revealing that superhydrophobic surfaces do not always offer the best drag reduction performance. The application of the fractal model to practical topographies of nonwetting surfaces of copper, aluminum, and zinc oxide fabricated via electrodeposition and etching is also discussed.}, }
@article {pmid33184652, year = {2020}, author = {Rader, JA and Hedrick, TL and He, Y and Waldrop, LD}, title = {Functional Morphology of Gliding Flight II. Morphology Follows Predictions of Gliding Performance.}, journal = {Integrative and comparative biology}, volume = {60}, number = {5}, pages = {1297-1308}, doi = {10.1093/icb/icaa126}, pmid = {33184652}, issn = {1557-7023}, mesh = {Animals ; Biomechanical Phenomena ; *Birds ; *Flight, Animal ; Models, Biological ; *Wings, Animal ; }, abstract = {The evolution of wing morphology among birds, and its functional consequences, remains an open question, despite much attention. This is in part because the connection between form and function is difficult to test directly. To address this deficit, in prior work, we used computational modeling and sensitivity analysis to interrogate the impact of altering wing aspect ratio (AR), camber, and Reynolds number on aerodynamic performance, revealing the performance landscapes that avian evolution has explored. In the present work, we used a dataset of three-dimensionally scanned bird wings coupled with the performance landscapes to test two hypotheses regarding the evolutionary diversification of wing morphology associated with gliding flight behavior: (1) gliding birds would exhibit higher wing AR and greater chordwise camber than their non-gliding counterparts; and (2) that two strategies for gliding flight exist, with divergent morphological conformations. In support of our first hypothesis, we found evidence of morphological divergence in both wing AR and camber between gliders and non-gliders, suggesting that wing morphology of birds that utilize gliding flight is under different selective pressures than the wings of non-gliding taxa. Furthermore, we found that these morphological differences also yielded differences in coefficient of lift measured both at the maximum lift to drag ratio and at minimum sinking speed, with gliding taxa exhibiting higher coefficient of lift in both cases. Minimum sinking speed was also lower in gliders than non-gliders. However, contrary to our hypothesis, we found that the maximum ratio of the coefficient of lift to the coefficient of drag differed between gliders and non-gliders. This may point to the need for gliders to maintain high lift capability for takeoff and landing independent of gliding performance or could be due to the divergence in flight styles among gliders, as not all gliders are predicted to optimize either quantity. However, direct evidence for the existence of two morphologically defined gliding flight strategies was equivocal, with only slightly stronger support for an evolutionary model positing separate morphological optima for these strategies than an alternative model positing a single peak. The absence of a clear result may be an artifact of low statistical power owing to a relatively small sample size of gliding flyers expected to follow the "aerial search" strategy.}, }
@article {pmid33184554, year = {2020}, author = {Lee, JY and Kottke, PA and Fedorov, AG}, title = {Hydrodynamics of Vortical Gas Jets Coupled to Point-Like Suction.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {32}, number = {10}, pages = {}, pmid = {33184554}, issn = {1070-6631}, support = {R01 GM112662/GM/NIGMS NIH HHS/United States ; }, abstract = {Vortical jet flows in the Reynolds number (Re) range from 1000 to 3425 and swirl number (S) below 0.5, alone and in combination with suction through a small aperture, are experimentally investigated using optical visualization. Schlieren photography is employed to assess the vortical flow structure and establish the fundamental understanding of the source-to-sink gas-dynamic coupling, including the role played by flow rate, jet diameter, and the separation distance between the gas jet source and the suction sink. Compared to vortex-free jets, vortical jets for Re>2700 with swirl number S>0.27 experience earlier laminar-to-turbulent transition, with resulting rapid growth of the jet boundary. The ability to control growth of the jet expansion and mass and momentum dissipation into the surrounding is demonstrated via use of a coaxially aligned flow suction placed in the path of a jet. When a swirling jet is completely coupled with a flow suction, jet expansion is significantly suppressed. The suction/sink flow rate imposes a limit on the maximum input/source flow rate of gas jet to achieve complete coupling. Furthermore, there is a maximum distance over which effective coupling can occur, and for all Reynolds numbers considered this distance is shorter than the distance at which the jet structure breaks up into turbulent eddies in the absence of a sink.}, }
@article {pmid33172214, year = {2020}, author = {Astudillo-Castro, C and Cordova, A and Oyanedel-Craver, V and Soto-Maldonado, C and Valencia, P and Henriquez, P and Jimenez-Flores, R}, title = {Prediction of the Limiting Flux and Its Correlation with the Reynolds Number during the Microfiltration of Skim Milk Using an Improved Model.}, journal = {Foods (Basel, Switzerland)}, volume = {9}, number = {11}, pages = {}, pmid = {33172214}, issn = {2304-8158}, support = {11110402//Fondo Nacional de Desarrollo Cient&#xed;fico y Tecnol&#xf3;gico/ ; }, abstract = {Limiting flux (JL) determination is a critical issue for membrane processing. This work presents a modified exponential model for JL calculation, based on a previously published version. Our research focused on skim milk microfiltrations. The processing variables studied were the crossflow velocity (CFV), membrane hydraulic diameter (dh), temperature, and concentration factor, totaling 62 experimental runs. Results showed that, by adding a new parameter called minimum transmembrane pressure, the modified model not only improved the fit of the experimental data compared to the former version (R[2] > 97.00%), but also revealed the existence of a minimum transmembrane pressure required to obtain flux (J). This result is observed as a small shift to the right on J versus transmembrane pressure curves, and this shift increases with the flow velocity. This fact was reported in other investigations, but so far has gone uninvestigated. The JL predicted values were correlated with the Reynolds number (Re) for each dh tested. Results showed that for a same Re; JL increased as dh decreased; in a wide range of Re within the turbulent regime. Finally, from dimensionless correlations; a unique expression JL = f (Re, dh) was obtained; predicting satisfactorily JL (R[2] = 84.11%) for the whole set of experiments.}, }
@article {pmid33171451, year = {2021}, author = {Ford, MP and Santhanakrishnan, A}, title = {On the role of phase lag in multi-appendage metachronal swimming of euphausiids.}, journal = {Bioinspiration &amp; biomimetics}, volume = {16}, number = {6}, pages = {}, doi = {10.1088/1748-3190/abc930}, pmid = {33171451}, issn = {1748-3190}, mesh = {Biomechanical Phenomena ; *Extremities ; Gait ; *Swimming ; }, abstract = {Metachronal paddling is a common method of drag-based aquatic propulsion, in which a series of swimming appendages are oscillated, with the motion of each appendage phase-shifted relative to the neighboring appendages. Ecologically and economically important euphausiid species such as Antarctic krill (Euphausia superba) swim constantly by stroking their paddling appendages (pleopods), with locomotion accounting for the bulk of their metabolic expenditure. They tailor their swimming gaits for behavioral and energetic needs by changing pleopod kinematics. The functional importance of inter-pleopod phase lag (ϕ) to metachronal swimming performance and wake structure is unknown. To examine this relation, we developed a geometrically and dynamically scaled robot ('krillbot') capable of self-propulsion. Krillbot pleopods were prescribed to mimic published kinematics of fast-forward swimming (FFW) and hovering (HOV) gaits ofE. superba, and the Reynolds number and Strouhal number of the krillbot matched well with those calculated for freely-swimmingE. superba. In addition to examining published kinematics with unevenϕbetween pleopod pairs, we modifiedE. superbakinematics to uniformly varyϕfrom 0% to 50% of the cycle. Swimming speed and thrust were largest for FFW withϕbetween 15%-25%, coincident withϕrange observed in FFW gait ofE. superba. In contrast to synchronous rowing (ϕ= 0%) where distances between hinged joints of adjacent pleopods were nearly constant throughout the cycle, metachronal rowing (ϕ> 0%) brought adjacent pleopods closer together and moved them farther apart. This factor minimized body position fluctuation and augmented metachronal swimming speed. Though swimming speed was lowest for HOV, a ventrally angled downward jet was generated that can assist with weight support during feeding. In summary, our findings show that inter-appendage phase lag can drastically alter both metachronal swimming speed and the large-scale wake structure.}, }
@article {pmid33159347, year = {2020}, author = {Ichikawa, C and Ishikawa, D and Yang, JM and Fujii, T}, title = {Phenomenological analysis on whipping behavior of rice flour batter.}, journal = {Journal of food science}, volume = {85}, number = {12}, pages = {4327-4334}, pmid = {33159347}, issn = {1750-3841}, mesh = {Edible Grain/*chemistry ; *Food ; Food Handling ; Oryza/*chemistry ; Particle Size ; Powders ; Surface Tension ; Viscosity ; Wettability ; }, abstract = {In this study, the bubbles in rice flour batter were investigated under a constant temperature, because the bubble size distribution is important for the control of food texture. We obtained experimental data using a hand mixer and compared the properties of doughs prepared using six rice flours; each flour was prepared through a different milling process. We also added the size effect of the rice flour particles as the Bond number. Furthermore, we performed a dynamic wettability test to estimate the wettability of the rice flour surface. The results of this test were described well by the Washburn equation, and dc cosθ/dp was calculated as a wettability parameter (where, dc = effective diameter of a capillary in a powder bed, cosθ = the contact angle, dp = mean particle diameter of rice flour). If bubble sizes depend mainly on the inertial force, viscous force, surface tension, and gravity, then the normalized mean bubble diameter should be a function of the Reynolds number, Weber number, and Froude number. The mean bubble diameter (dbm) generated by whipping was expected to be affected by the thickness (d) of the rod of the mixer, its movement speed, and physical properties of the material. Therefore, dimensionless mean diameter (dbm /d) was expressed based on a dimensionless equation. In the three-phase dispersion, different empirical equations were obtained depending on the amount of rice flour added, and the bubble diameter could be predicted using dimensionless parameters. In addition, the equations were generally applicable to the various materials selected for this study. PRACTICAL APPLICATION: The powder properties of rice flour were investigated, and dimensionless parameters were analyzed to construct an appropriate process control system for rice flour-based food products. Although the process method optimized for flour products is also used for rice flour products in practical situations, the comprehensive evaluation based on dimensionless parameters leads to optimization of the process for rice-flour based products. Moreover, this optimization might strongly support the creation of a new texture, and thus, the potential for market expansion of rice-flour based products is considerable.}, }
@article {pmid33158219, year = {2020}, author = {Sana, S and Zivkovic, V and Boodhoo, K}, title = {Empirical Modelling of Hydrodynamic Effects on Starch Nanoparticles Precipitation in a Spinning Disc Reactor.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {10}, number = {11}, pages = {}, pmid = {33158219}, issn = {2079-4991}, abstract = {Empirical correlations have been developed to relate experimentally determined starch nanoparticle size obtained in a solvent-antisolvent precipitation process with key hydrodynamic parameters of a spinning disc reactor (SDR). Three different combinations of dimensionless groups including a conventional Reynolds number (Re), rotational Reynolds number (Reω) and Rossby number (Ro) have been applied in individual models for two disc surfaces (smooth and grooved) to represent operating variables affecting film flow such as liquid flowrate and disc rotational speed, whilst initial supersaturation (S) has been included to represent varying antisolvent concentrations. Model 1 featuring a combination of Re, Reω and S shows good agreement with the experimental data for both the grooved and smooth discs. For the grooved disc, Re has a greater impact on particle size, whereas Reω is more influential on the smooth disc surface, the difference likely being due to the passive mixing induced by the grooves irrespective of the magnitude of the disc speed. Supersaturation has little impact on particle size within the limited initial supersaturation range studied. Model 2 which characterises both flow rate and disc rotational speed through Ro alone and combined with Re was less accurate in predicting particle size due to several inherent limitations.}, }
@article {pmid33157545, year = {2021}, author = {Harvey, C and Inman, DJ}, title = {Aerodynamic efficiency of gliding birds vs comparable UAVs: a review.}, journal = {Bioinspiration &amp; biomimetics}, volume = {16}, number = {3}, pages = {}, doi = {10.1088/1748-3190/abc86a}, pmid = {33157545}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Birds ; *Flight, Animal ; *Wings, Animal ; }, abstract = {Here, we reviewed published aerodynamic efficiencies of gliding birds and similar sized unmanned aerial vehicles (UAVs) motivated by a fundamental question: are gliding birds more efficient than comparable UAVs? Despite a multitude of studies that have quantified the aerodynamic efficiency of gliding birds, there is no comprehensive summary of these results. This lack of consolidated information inhibits a true comparison between birds and UAVs. Such a comparison is complicated by variable uncertainty levels between the different techniques used to predict avian efficiency. To support our comparative approach, we began by surveying theoretical and experimental estimates of avian aerodynamic efficiency and investigating the uncertainty associated with each estimation method. We found that the methodology used by a study affects the estimated efficiency and can lead to incongruent conclusions on gliding bird aerodynamic efficiency. Our survey showed that studies on live birds gliding in wind tunnels provide a reliable minimum estimate of a birds' aerodynamic efficiency while simultaneously quantifying the wing configurations used in flight. Next, we surveyed the aeronautical literature to collect the published aerodynamic efficiencies of similar-sized, non-copter UAVs. The compiled information allowed a direct comparison of UAVs and gliding birds. Contrary to our expectation, we found that there is no definitive evidence that any gliding bird species is either more or less efficient than a comparable UAV. This non-result highlights a critical need for new technology and analytical advances that can reduce the uncertainty associated with estimating a gliding bird's aerodynamic efficiency. Nevertheless, our survey indicated that species flying within subcritical Reynolds number regimes may inspire UAV designs that can extend their operational range to efficiently operate in subcritical regimes. The survey results provided here point the way forward for research into avian gliding flight and enable informed UAV designs.}, }
@article {pmid33156686, year = {2020}, author = {Friedrich, J and Gallon, S and Pumir, A and Grauer, R}, title = {Stochastic Interpolation of Sparsely Sampled Time Series via Multipoint Fractional Brownian Bridges.}, journal = {Physical review letters}, volume = {125}, number = {17}, pages = {170602}, doi = {10.1103/PhysRevLett.125.170602}, pmid = {33156686}, issn = {1079-7114}, abstract = {We propose and test a method to interpolate sparsely sampled signals by a stochastic process with a broad range of spatial and/or temporal scales. To this end, we extend the notion of a fractional Brownian bridge, defined as fractional Brownian motion with a given scaling (Hurst) exponent H and with prescribed start and end points, to a bridge process with an arbitrary number of intermediate and nonequidistant points. Determining the optimal value of the Hurst exponent H_{opt}, appropriate to interpolate the sparse signal, is a very important step of our method. We demonstrate the validity of our method on a signal from fluid turbulence in a high Reynolds number flow and discuss the implications of the non-self-similar character of the signal. The method introduced here could be instrumental in several physical problems, including astrophysics, particle tracking, and specific tailoring of surrogate data, as well as in domains of natural and social sciences.}, }
@article {pmid33153075, year = {2020}, author = {Coclite, A and Coclite, GM and De Tommasi, D}, title = {Capsules Rheology in Carreau-Yasuda Fluids.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {10}, number = {11}, pages = {}, pmid = {33153075}, issn = {2079-4991}, support = {Prin 2017, 267 project code 2017J4EAYB//Ministero dell'Istruzione, dell'Universit&#xe0; e della Ricerca/ ; CUP - D94I18000260001//Ministero dell'Istruzione, dell'Universit&#xe0; e della Ricerca/ ; }, abstract = {In this paper, a Multi Relaxation Time Lattice Boltzmann scheme is used to describe the evolution of a non-Newtonian fluid. Such method is coupled with an Immersed-Boundary technique for the transport of arbitrarily shaped objects navigating the flow. The no-slip boundary conditions on immersed bodies are imposed through a convenient forcing term accounting for the hydrodynamic force generated by the presence of immersed geometries added to momentum equation. Moreover, such forcing term accounts also for the force induced by the shear-dependent viscosity model characterizing the non-Newtonian behavior of the considered fluid. Firstly, the present model is validated against well-known benchmarks, namely the parabolic velocity profile obtained for the flow within two infinite laminae for five values of the viscosity model exponent, n = 0.25, 0.50, 0.75, 1.0, and 1.5. Then, the flow within a squared lid-driven cavity for Re = 1000 and 5000 (being Re the Reynolds number) is computed as a function of n for a shear-thinning (n < 1) fluid. Indeed, the local decrements in the viscosity field achieved in high-shear zones implies the increment in the local Reynolds number, thus moving the position of near-walls minima towards lateral walls. Moreover, the revolution under shear of neutrally buoyant plain elliptical capsules with different Aspect Ratio (AR = 2 and 3) is analyzed for shear-thinning (n < 1), Newtonian (n = 1), and shear-thickening (n > 1) surrounding fluids. Interestingly, the power law by Huang et al. describing the revolution period of such capsules as a function of the Reynolds number and the existence of a critical value, Rec, after which the tumbling is inhibited in confirmed also for non-Newtonian fluids. Analogously, the equilibrium lateral position yeq of such neutrally buoyant capsules when transported in a plane-Couette flow is studied detailing the variation of yeq as a function of the Reynolds number as well as of the exponent n.}, }
@article {pmid33152635, year = {2020}, author = {Kim, J and Jin, D and Choi, H and Kweon, J and Yang, DH and Kim, YH}, title = {A zero-dimensional predictive model for the pressure drop in the stenotic coronary artery based on its geometric characteristics.}, journal = {Journal of biomechanics}, volume = {113}, number = {}, pages = {110076}, doi = {10.1016/j.jbiomech.2020.110076}, pmid = {33152635}, issn = {1873-2380}, mesh = {Blood Flow Velocity ; Constriction, Pathologic ; Coronary Angiography ; *Coronary Stenosis/diagnostic imaging ; *Coronary Vessels/diagnostic imaging ; Humans ; Models, Cardiovascular ; Models, Statistical ; }, abstract = {The diameter- or area-reduction ratio measured from coronary angiography, commonly used in clinical practice, is not accurate enough to represent the functional significance of the stenosis, i.e., the pressure drop across the stenosis. We propose a new zero-dimensional model for the pressure drop across the stenosis considering its geometric characteristics and flow rate. To identify the geometric parameters affecting the pressure drop, we perform three-dimensional numerical simulations for thirty-three patient-specific coronary stenoses. From these numerical simulations, we show that the pressure drop is mostly determined by the curvature as well as the area-reduction ratio of the stenosis before the minimal luminal area (MLA), but heavily depends on the area-expansion ratio after the MLA due to flow separation. Based on this result, we divide the stenosis into the converging and diverging parts in the present zero-dimensional model. The converging part is segmented into a series of straight and curved pipes with curvatures, and the loss of each pipe is estimated by an empirical relation between the total pressure drop, flow rate, and pipe geometric parameters (length, diameter, and curvature). The loss in the diverging part is predicted by a relation among the total pressure drop, Reynolds number, and area expansion ratio with the coefficients determined by a machine learning method. The pressure drops across the stenoses predicted by the present zero-dimensional model agree very well with those obtained from three-dimensional numerical simulations.}, }
@article {pmid33147949, year = {2020}, author = {Wang, Y and Zhou, G and Yan, Y and Shao, B and Hou, J}, title = {Construction of Natural Loofah/Poly(vinylidene fluoride) Core-Shell Electrospun Nanofibers via a Controllable Janus Nozzle for Switchable Oil-Water Separation.}, journal = {ACS applied materials &amp; interfaces}, volume = {12}, number = {46}, pages = {51917-51926}, doi = {10.1021/acsami.0c12912}, pmid = {33147949}, issn = {1944-8252}, abstract = {Developing microstructure and multifunctional membranes toward switchable oil-water separation has been highly desired in oily wastewater treatment. Herein, a controllable Janus nozzle was employed to innovatively electrospin natural loofah/poly(vinylidene fluoride) (PVDF) nanofibers with a core-shell structure for gravity-driven water purification. By adjusting flow rates of the PVDF component, a core-shell structure of the composite fibers was obtained caused by the lower viscosity and surface tension of PVDF. In addition, a steady laminar motion of fluids was constructed based on the Reynolds number of flow fields being less than 2300. In order to investigate the formation mechanism of the microstructure, a series of Janus nozzles with different lengths were controlled to study the blending of the two immiscible components. The gravity difference between the two components might cause disturbance of the jet motion, and the PVDF component unidirectionally encapsulated the loofah to form the shell layer. Most importantly, the dry loofah/PVDF membranes could separate oil from an oil-water mixture, while the water-wetted membrane exhibited switchable separation that could separate water from the mixtures because of the hydroxyl groups of the hydrophilic loofah hydrogen-bonding with water molecules and forming a hydration layer. The composite fibers can be applied in water remediation in practice, and the method to produce core-shell structures seems attractive for technological applications involving macroscopic core-shell nano- or microfibers.}, }
@article {pmid33136360, year = {2020}, author = {Jeon, W and Ahn, J and Kim, T and Kim, SM and Baik, S}, title = {Intertube Aggregation-Dependent Convective Heat Transfer in Vertically Aligned Carbon Nanotube Channels.}, journal = {ACS applied materials &amp; interfaces}, volume = {12}, number = {45}, pages = {50355-50364}, doi = {10.1021/acsami.0c13361}, pmid = {33136360}, issn = {1944-8252}, abstract = {The heat transfer of carbon nanotube fin geometry has received considerable attention. However, the flow typically occurred over or around the pillars of nanotubes due to the greater flow resistance between the tubes. Here, we investigated the forced convective heat transfer of water through the interstitial space of vertically aligned multiwalled carbon nanotubes (VAMWNTs, intertube distance = 69 nm). The water flow provided significantly a greater Reynolds number (Re) and Nusselt number (Nu) than air flow due to the greater density, heat capacity, and thermal conductivity. However, it resulted in surface tension-induced nanotube aggregation after the flow and drying process, generating random voids in the nanotube channel. This increased permeability (1.27 × 10[-11] m[2]) and Re (2.83 × 10[-1]) but decreased the heat transfer coefficient (h, 9900 W m[-2] K[-1]) and Nu (53.77), demonstrating a trade-off relationship. The h (25,927 W m[-2] K[-1]) and Nu (153.49) could be further increased, at an equivalent permeability or Re, by increasing nanotube areal density from 2.08 × 10[10] to 1.04 × 10[11] cm[-2]. The area-normalized thermal resistance of the densified and aggregated VAMWNTs was smaller than those of the Ni foam, Si microchannel, and carbon nanotube fin array, demonstrating excellent heat transfer characteristics.}, }
@article {pmid33119653, year = {2020}, author = {Lyons, K and Murphy, CT and Franck, JA}, title = {Flow over seal whiskers: Importance of geometric features for force and frequency response.}, journal = {PloS one}, volume = {15}, number = {10}, pages = {e0241142}, pmid = {33119653}, issn = {1932-6203}, mesh = {Animals ; Computer Simulation ; *Hydrodynamics ; Phoca/*anatomy &amp; histology ; *Vibration ; Vibrissae/*anatomy &amp; histology ; }, abstract = {The complex undulated geometry of seal whiskers has been shown to substantially modify the turbulent structures directly downstream, resulting in a reduction of hydrodynamic forces as well as modified vortex-induced-vibration response when compared with smooth whiskers. Although the unique hydrodynamic response has been well documented, an understanding of the fluid flow effects from each geometric feature remains incomplete. In this computational investigation, nondimensional geometric parameters of the seal whisker morphology are defined in terms of their hydrodynamic relevance, such that wavelength, aspect ratio, undulation amplitudes, symmetry and undulation off-set can be varied independently of one another. A two-factor fractional factorial design of experiments procedure is used to create 16 unique geometries, each of which dramatically amplifies or attenuates the geometric parameters compared with the baseline model. The flow over each unique topography is computed with a large-eddy simulation at a Reynolds number of 500 with respect to the mean whisker thickness and the effects on force and frequency are recorded. The results determine the specific fluid flow impact of each geometric feature which will inform both biologists and engineers who seek to understand the impact of whisker morphology or lay out a framework for biomimetic design of undulated structures.}, }
@article {pmid33095615, year = {2020}, author = {Neuhaus, L and Hölling, M and Bos, WJT and Peinke, J}, title = {Generation of Atmospheric Turbulence with Unprecedentedly Large Reynolds Number in a Wind Tunnel.}, journal = {Physical review letters}, volume = {125}, number = {15}, pages = {154503}, doi = {10.1103/PhysRevLett.125.154503}, pmid = {33095615}, issn = {1079-7114}, abstract = {Generating laboratory flows resembling atmospheric turbulence is of prime importance to study the effect of wind fluctuations on objects such as buildings, vehicles, or wind turbines. A novel driving of an active grid following a stochastic process is used to generate velocity fluctuations with correlation lengths, and, thus, integral scales, much larger than the transverse dimension of the wind tunnel. The combined action of the active grid and a modulation of the fan speed allows one to generate a flow characterized by a four-decade inertial range and an integral scale Reynolds number of 2×10^{7}.}, }
@article {pmid33092016, year = {2020}, author = {Domínguez-Pumar, M and Kowalski, L and Jiménez, V and Rodríguez, I and Soria, M and Bermejo, S and Pons-Nin, J}, title = {Analyzing the Performance of a Miniature 3D Wind Sensor for Mars.}, journal = {Sensors (Basel, Switzerland)}, volume = {20}, number = {20}, pages = {}, pmid = {33092016}, issn = {1424-8220}, support = {RTI2018-098728-B-C33//Ministerio de Econom&#xed;a y Competitividad/ ; }, abstract = {This paper analyzes the behavior of a miniature 3D wind sensor designed for Mars atmosphere. The sensor is a spherical structure of 10 mm diameter divided in four sectors. By setting all the sectors to constant temperature, above that of the air, the 3D wind velocity vector can be measured. Two sets of experiments have been performed. First, an experimental campaign made under typical Mars conditions at the Aarhus Wind Tunnel Simulator is presented. The results demonstrate that both wind speed and angle can be efficiently measured, using a simple inverse algorithm. The effect of sudden wind changes is also analyzed and fast response times in the range of 0.7 s are obtained. The second set of experiments is focused on analyzing the performance of the sensor under extreme Martian wind conditions, reaching and going beyond the Dust Devil scale. To this purpose, both high-fidelity numerical simulations of fluid dynamics and heat transfer and experiments with the sensor have been performed. The results of the experiments, made for winds in the Reynolds number 1000-2000 range, which represent 65-130 m/s of wind speed under typical Mars conditions, further confirm the simulation predictions and show that it will be possible to successfully measure wind speed and direction even under these extreme regimes.}, }
@article {pmid33076024, year = {2020}, author = {Czelusniak, LE and Mapelli, VP and Guzella, MS and Cabezas-Gómez, L and Wagner, AJ}, title = {Force approach for the pseudopotential lattice Boltzmann method.}, journal = {Physical review. E}, volume = {102}, number = {3-1}, pages = {033307}, doi = {10.1103/PhysRevE.102.033307}, pmid = {33076024}, issn = {2470-0053}, abstract = {One attractive feature of the original pseudopotential method consists on its simplicity of adding a force dependent on a nearest-neighbor potential function. In order to improve the method, regarding thermodynamic consistency and control of surface tension, different approaches were developed in the literature, such as multirange interactions potential and modified forcing schemes. In this work, a strategy to combine these enhancements with an appropriate interaction force field using only nearest-neighbor interactions is devised, starting from the desired pressure tensor. The final step of our procedure is implementing this external force by using the classical Guo forcing scheme. Numerical tests regarding static and dynamic flow conditions were performed. Static tests showed that current procedure is suitable to control the surface tension and phase densities. Based on thermodynamic principles, it is devised a solution for phase densities in a droplet, which states explicitly dependence on the surface tension and interface curvature. A comparison with numerical results suggest a physical inconsistency in the pseudopotential method. This fact is not commonly discussed in the literature, since most of studies are limited to the Maxwell equal area rule. However, this inconsistency is shown to be dependent on the equation of state (EOS), and its effects can be mitigated by an appropriate choice of Carnahan-Starling EOS parameters. Also, a droplet oscillation test was performed, and the most divergent solution under certain flow conditions deviated 7.5% from the expected analytical result. At the end, a droplet impact test against a solid wall was performed to verify the method stability, and it was possible to reach stable simulation results with density ratio of almost 2400 and Reynolds number of Re=373. The observed results corroborate that the proposed method is able to replicate the desired macroscopic multiphase behavior.}, }
@article {pmid33076003, year = {2020}, author = {Rana, N and Perlekar, P}, title = {Coarsening in the two-dimensional incompressible Toner-Tu equation: Signatures of turbulence.}, journal = {Physical review. E}, volume = {102}, number = {3-1}, pages = {032617}, doi = {10.1103/PhysRevE.102.032617}, pmid = {33076003}, issn = {2470-0053}, abstract = {We investigate coarsening dynamics in the two-dimensional, incompressible Toner-Tu equation. We show that coarsening proceeds via vortex merger events, and the dynamics crucially depend on the Reynolds number Re. For low Re, the coarsening process has similarities to Ginzburg-Landau dynamics. On the other hand, for high Re, coarsening shows signatures of turbulence. In particular, we show the presence of an enstrophy cascade from the intervortex separation scale to the dissipation scale.}, }
@article {pmid33075904, year = {2020}, author = {Bos, WJT and Laadhari, F and Agoua, W}, title = {Linearly forced isotropic turbulence at low Reynolds numbers.}, journal = {Physical review. E}, volume = {102}, number = {3-1}, pages = {033105}, doi = {10.1103/PhysRevE.102.033105}, pmid = {33075904}, issn = {2470-0053}, abstract = {We investigate the forcing strength needed to sustain a flow using linear forcing. A critical Reynolds number R_{c} is determined, based on the longest wavelength allowed by the system, the forcing strength and the viscosity. A simple model is proposed for the dissipation rate, leading to a closed expression for the kinetic energy of the flow as a function of the Reynolds number. The dissipation model and the prediction for the kinetic energy are assessed using direct numerical simulations and two-point closure integrations. An analysis of the dissipation-rate equation and the triadic structure of the nonlinear transfer allows to refine the model in order to reproduce the low-Reynolds-number asymptotic behavior, where the kinetic energy is proportional to R-R_{c}.}, }
@article {pmid33075884, year = {2020}, author = {Rinoshika, H and Rinoshika, A and Wang, JJ}, title = {Three-dimensional multiscale flow structures behind a wall-mounted short cylinder based on tomographic particle image velocimetry and three-dimensional orthogonal wavelet transform.}, journal = {Physical review. E}, volume = {102}, number = {3-1}, pages = {033101}, doi = {10.1103/PhysRevE.102.033101}, pmid = {33075884}, issn = {2470-0053}, abstract = {Three-dimensional (3D) flow structures around a wall-mounted short cylinder of height-to-diameter ratio 1 were instantaneously measured by a high-resolution tomographic particle image velocimetry (Tomo-PIV) at Reynolds number of 10 720 in a water tunnel. 3D velocity fields, 3D vorticity, the Q criterion, the rear separation region, and the characteristic of arch type vortex and tip vortices were first discussed. We found a strong 3D W-type arch vortex behind the short cylinder, which was originated by the interaction between upwash and downwash flows. This W-type arch vortex was reshaped to the M-shaped arch vortex downstream. It indicated that the head shape of the arch vortex structure depended on the aspect ratio of the cylinder. The large-scale streamwise vortices were originated by the downwash and upwash flows near the center location of W-type arch vortex. Then the 3D orthogonal wavelet multiresolution technique was developed to analyze instantaneous 3D velocity fields of Tomo-PIV in order to clarify 3D multiscale wake flow structures. The W-type shape arch vortex was extracted in the time-averaged intermediate-scale structure, while an M-shaped arch vortex was identified in the time-averaged large-scale structure. The tip vortices distributed in the time-averaged large- and intermediate-scale structures. The instantaneous intermediate-scale upwash vortices played an essential role in producing W-type head of arch structure. It was also observed that strong small-scale vortices appeared in the shear layer or near the bottom plate and most of them were contained in the intermediate-scale structures.}, }
@article {pmid33057044, year = {2020}, author = {Riasat, S and Ramzan, M and Kadry, S and Chu, YM}, title = {Significance of magnetic Reynolds number in a three-dimensional squeezing Darcy-Forchheimer hydromagnetic nanofluid thin-film flow between two rotating disks.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {17208}, pmid = {33057044}, issn = {2045-2322}, support = {11971142//National Natural Science Foundation of China/ ; 11871202//National Natural Science Foundation of China/ ; 61673169//National Natural Science Foundation of China/ ; 11701176//National Natural Science Foundation of China/ ; 11626101//National Natural Science Foundation of China/ ; 11601485//National Natural Science Foundation of China/ ; }, abstract = {The remarkable aspects of carbon nanotubes like featherweight, durability, exceptional electrical and thermal conduction capabilities, and physicochemical stability make them desirous materials for electrochemical devices. Having such astonishing characteristics of nanotubes in mind our aspiration is to examine the squeezing three dimensional Darcy-Forchheimer hydromagnetic nanofluid thin-film flow amid two rotating disks with suspended multiwalled carbon nanotubes (MWCNTs) submerged into the base fluid water. The analysis is done by invoking partial slip effect at the boundary in attendance of autocatalytic reactions. The mathematical model consists of axial and azimuthal momentum and magnetic fields respectively. The tangential and axial velocity profiles and components of the magnetic field are examined numerically by employing the bvp4c method for varying magnetic, rotational, and squeezing Reynolds number. The torque effect near the upper and lower disks are studied critically using their graphical depiction. The values of the torque at the upper and lower disks are obtained for rotational and squeezed Reynolds numbers and are found in an excellent concurrence when compared with the existing literature. Numerically it is computed that the torque at the lower disk is higher in comparison to the upper disk for mounting estimates of the squeezed Reynolds number and the dimensionless parameter for magnetic force in an axial direction. From the graphical illustrations, it is learned that thermal profile declines for increasing values of the squeezed Reynolds number.}, }
@article {pmid33049170, year = {2020}, author = {Wong, JY and Chan, BKK and Chan, KYK}, title = {Swimming kinematics and hydrodynamics of barnacle larvae throughout development.}, journal = {Proceedings. Biological sciences}, volume = {287}, number = {1936}, pages = {20201360}, pmid = {33049170}, issn = {1471-2954}, mesh = {Animals ; Biomechanical Phenomena ; Extremities ; Hydrodynamics ; Larva/physiology ; Rheology ; Swimming/*physiology ; Thoracica/*physiology ; Zooplankton ; }, abstract = {Changes in size strongly influence organisms' ecological performances. For aquatic organisms, they can transition from viscosity- to inertia-dominated fluid regimes as they grow. Such transitions are often associated with changes in morphology, swimming speed and kinematics. Barnacles do not fit into this norm as they have two morphologically distinct planktonic larval phases that swim differently but are of comparable sizes and operate in the same fluid regime (Reynolds number 10[0]-10[1]). We quantified the hydrodynamics of the rocky intertidal stalked barnacle Capitulum mitella from the nauplius II to cyprid stage and examined how kinematics and size increases affect its swimming performance. Cyprids beat their appendages in a metachronal wave to swim faster, more smoothly, and with less backwards slip per beat cycle than did all naupliar stages. Micro-particle image velocimetry showed that cyprids generated trailing viscous vortex rings that pushed water backwards for propulsion, contrary to the nauplii's forward suction current for particle capture. Our observations highlight that zooplankton swimming performance can shift via morphological and kinematic modifications without a significant size increase. The divergence in ecological functions through ontogeny in barnacles and the removal of feeding requirement likely contributed to the evolution of the specialized, taxonomically unique cyprid phase.}, }
@article {pmid33026993, year = {2021}, author = {Jakob, J and Gross, M and Gunther, T}, title = {A Fluid Flow Data Set for Machine Learning and its Application to Neural Flow Map Interpolation.}, journal = {IEEE transactions on visualization and computer graphics}, volume = {27}, number = {2}, pages = {1279-1289}, doi = {10.1109/TVCG.2020.3028947}, pmid = {33026993}, issn = {1941-0506}, mesh = {Computer Graphics ; *Deep Learning ; Machine Learning ; Neural Networks, Computer ; }, abstract = {In recent years, deep learning has opened countless research opportunities across many different disciplines. At present, visualization is mainly applied to explore and explain neural networks. Its counterpart-the application of deep learning to visualization problems-requires us to share data more openly in order to enable more scientists to engage in data-driven research. In this paper, we construct a large fluid flow data set and apply it to a deep learning problem in scientific visualization. Parameterized by the Reynolds number, the data set contains a wide spectrum of laminar and turbulent fluid flow regimes. The full data set was simulated on a high-performance compute cluster and contains 8000 time-dependent 2D vector fields, accumulating to more than 16 TB in size. Using our public fluid data set, we trained deep convolutional neural networks in order to set a benchmark for an improved post-hoc Lagrangian fluid flow analysis. In in-situ settings, flow maps are exported and interpolated in order to assess the transport characteristics of time-dependent fluids. Using deep learning, we improve the accuracy of flow map interpolations, allowing a more precise flow analysis at a reduced memory IO footprint.}, }
@article {pmid33022594, year = {2020}, author = {Di Luca, M and Mintchev, S and Su, Y and Shaw, E and Breuer, K}, title = {A bioinspired Separated Flow wing provides turbulence resilience and aerodynamic efficiency for miniature drones.}, journal = {Science robotics}, volume = {5}, number = {38}, pages = {}, doi = {10.1126/scirobotics.aay8533}, pmid = {33022594}, issn = {2470-9476}, abstract = {Small-scale drones have enough sensing and computing power to find use across a growing number of applications. However, flying in the low-Reynolds number regime remains challenging. High sensitivity to atmospheric turbulence compromises vehicle stability and control, and low aerodynamic efficiency limits flight duration. Conventional wing designs have thus far failed to address these two deficiencies simultaneously. Here, we draw inspiration from nature's small flyers to design a wing with lift generation robust to gusts and freestream turbulence without sacrificing aerodynamic efficiency. This performance is achieved by forcing flow separation at the airfoil leading edge. Water and wind tunnel measurements are used to demonstrate the working principle and aerodynamic performance of the wing, showing a substantial reduction in the sensitivity of lift force production to freestream turbulence, as compared with the performance of an Eppler E423 low-Reynolds number wing. The minimum cruise power of a custom-built 104-gram fixed-wing drone equipped with the Separated Flow wing was measured in the wind tunnel indicating an upper limit for the flight time of 170 minutes, which is about four times higher than comparable existing fixed-wing drones. In addition, we present scaling guidelines and outline future design and manufacturing challenges.}, }
@article {pmid33020499, year = {2020}, author = {Phelps, PR and Lee, CA and Morton, DM}, title = {Episodes of fast crystal growth in pegmatites.}, journal = {Nature communications}, volume = {11}, number = {1}, pages = {4986}, pmid = {33020499}, issn = {2041-1723}, abstract = {Pegmatites are shallow, coarse-grained magmatic intrusions with crystals occasionally approaching meters in length. Compared to their plutonic hosts, pegmatites are thought to have cooled rapidly, suggesting that these large crystals must have grown fast. Growth rates and conditions, however, remain poorly constrained. Here we investigate quartz crystals and their trace element compositions from miarolitic cavities in the Stewart pegmatite in southern California, USA, to quantify crystal growth rates. Trace element concentrations deviate considerably from equilibrium and are best explained by kinetic effects associated with rapid crystal growth. Kinetic crystal growth theory is used to show that crystals accelerated from an initial growth rate of 10[-6]-10[-7] m s[-1] to 10[-5]-10[-4] m s[-1] (10-100 mm day[-1] to 1-10 m day[-1]), indicating meter sized crystals could have formed within days, if these rates are sustained throughout pegmatite formation. The rapid growth rates require that quartz crystals grew from thin (micron scale) chemical boundary layers at the fluid-crystal interfaces. A strong advective component is required to sustain such thin boundary layers. Turbulent conditions (high Reynolds number) in these miarolitic cavities are shown to exist during crystallization, suggesting that volatile exsolution, crystallization, and cavity generation occur together.}, }
@article {pmid32992553, year = {2020}, author = {Qiu, Y and Hu, W and Wu, C and Chen, W}, title = {An Experimental Study of Microchannel and Micro-Pin-Fin Based On-Chip Cooling Systems with Silicon-to-Silicon Direct Bonding.}, journal = {Sensors (Basel, Switzerland)}, volume = {20}, number = {19}, pages = {}, pmid = {32992553}, issn = {1424-8220}, support = {51575487//National Natural Science Foundation of China/ ; 6162790014//National Natural Science Foundation of China/ ; }, abstract = {This paper describes an experimental study of the cooling capabilities of microchannel and micro-pin-fin based on-chip cooling systems. The on-chip cooling systems integrated with a micro heat sink, simulated power IC (integrated circuit) and temperature sensors are fabricated by micromachining and silicon-to-silicon direct bonding. Three micro heat sink structures: a microchannel heat sink (MCHS), an inline micro-pin-fin heat sink (I-MPFHS) and a staggered micro-pin-fin heat sink (S-MPFHS) are tested in the Reynolds number range of 79.2 to 882.3. The results show that S-MPFHS is preferred if the water pump can provide enough pressure drop. However, S-MPFHS has the worst performance when the rated pressure drop of the pump is lower than 1.5 kPa because the endwall effect under a low Reynolds number suppresses the disturbance generated by the staggered micro pin fins but S-MPFHS is still preferred when the rated pressure drop of the pump is in the range of 1.5 to 20 kPa. When the rated pressure drop of the pump is higher than 20 kPa, I-MPFHS will be the best choice because of high heat transfer enhancement and low pressure drop price brought by the unsteady vortex street.}, }
@article {pmid32992113, year = {2021}, author = {Chen, Y and Chen, Y and Hu, S and Ni, Z}, title = {Continuous ultrasonic flow measurement for aerospace small pipelines.}, journal = {Ultrasonics}, volume = {109}, number = {}, pages = {106260}, doi = {10.1016/j.ultras.2020.106260}, pmid = {32992113}, issn = {1874-9968}, abstract = {Aerospace explorations stimulate extensive research on innovative propellant flow measurement technologies in microgravity conditions. Ultrasonic-based measurements have advantages of non-invasive and non-moving-component constructions as well as fast responses to bi-directional flow detection, its applications in aerospace explorations have already been reported. To avoid the shortages of pulse ultrasonic measurement configurations, flow measurement of continuous ultrasonic wave propagation is presented to match the requirements of large measurement range and high precision. Fabrication process and laboratory validations using water flow are presented. Ground experiments show that the linearity of the proposed ultrasonic flow meter is obtained in the measurement range [0, 80 ml/s] which is typical requirement in aerospace applications. Meanwhile, the fitted linear feature from the experimental data matches well the theoretical prediction except the flow prediction of stationary fluid. Under specific configurations, the absolute measurement error is significantly affected by the corresponding Reynolds number. Furthermore, the absolute measurement error is smaller when excitation signals with higher frequency are used if the phase tracking performance for different frequencies is identical.}, }
@article {pmid32984706, year = {2020}, author = {Ye, Y and Luo, X and Dong, C and Xu, Y and Zhang, Z}, title = {Numerical and Experimental Investigation of Soot Suppression by Acoustic Oscillated Combustion.}, journal = {ACS omega}, volume = {5}, number = {37}, pages = {23866-23875}, pmid = {32984706}, issn = {2470-1343}, abstract = {The soot suppression by acoustic oscillations for acetylene diffusion flames was investigated combining numerical and experimental studies. The combustion and soot formation were predicted by the finite-rate detailed chemistry model and modified Moss-Brookes model, respectively, while the turbulence was predicted by the detached eddy simulation (DES) with a low Reynolds number correction. Experimental results showed that the soot rate almost decreased linearly with the amplitude of acoustic oscillation, and the pinch-off of the flame occurred at a large acoustic oscillation. Numerical results showed that the flame structure was well predicted, while the soot rate was over-predicted at large acoustic oscillations; the consumption of O2 increased obviously with the acoustic oscillation. The soot suppression was mainly caused by the decrease of the surface growth rate when the air was pushed toward the flame.}, }
@article {pmid32982135, year = {2020}, author = {Dbouk, T and Drikakis, D}, title = {Weather impact on airborne coronavirus survival.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {32}, number = {9}, pages = {093312}, pmid = {32982135}, issn = {1070-6631}, abstract = {The contribution of this paper toward understanding of airborne coronavirus survival is twofold: We develop new theoretical correlations for the unsteady evaporation of coronavirus (CoV) contaminated saliva droplets. Furthermore, we implement the new correlations in a three-dimensional multiphase Eulerian-Lagrangian computational fluid dynamics solver to study the effects of weather conditions on airborne virus transmission. The new theory introduces a thermal history kernel and provides transient Nusselt (Nu) and Sherwood (Sh) numbers as a function of the Reynolds (Re), Prandtl (Pr), and Schmidt numbers (Sc). For the first time, these new correlations take into account the mixture properties due to the concentration of CoV particles in a saliva droplet. We show that the steady-state relationships induce significant errors and must not be applied in unsteady saliva droplet evaporation. The classical theory introduces substantial deviations in Nu and Sh values when increasing the Reynolds number defined at the droplet scale. The effects of relative humidity, temperature, and wind speed on the transport and viability of CoV in a cloud of airborne saliva droplets are also examined. The results reveal that a significant reduction of virus viability occurs when both high temperature and low relative humidity occur. The droplet cloud's traveled distance and concentration remain significant at any temperature if the relative humidity is high, which is in contradiction with what was previously believed by many epidemiologists. The above could explain the increase in CoV cases in many crowded cities around the middle of July (e.g., Delhi), where both high temperature and high relative humidity values were recorded one month earlier (during June). Moreover, it creates a crucial alert for the possibility of a second wave of the pandemic in the coming autumn and winter seasons when low temperatures and high wind speeds will increase airborne virus survival and transmission.}, }
@article {pmid32973078, year = {2020}, author = {York, CA and Bartol, IK and Krueger, PS and Thompson, JT}, title = {Squids use multiple escape jet patterns throughout ontogeny.}, journal = {Biology open}, volume = {9}, number = {11}, pages = {}, pmid = {32973078}, issn = {2046-6390}, mesh = {Age Factors ; Animals ; Biomechanical Phenomena ; Decapodiformes/*anatomy &amp; histology/*physiology ; Escape Reaction ; Models, Theoretical ; *Predatory Behavior ; Rheology ; Swimming ; }, abstract = {Throughout their lives, squids are both predators and prey for a multitude of animals, many of which are at the top of ocean food webs, making them an integral component of the trophic structure of marine ecosystems. The escape jet, which is produced by the rapid expulsion of water from the mantle cavity through a funnel, is central to a cephalopod's ability to avoid predation throughout its life. Although squid undergo morphological and behavioral changes and experience remarkably different Reynolds number regimes throughout their development, little is known about the dynamics and propulsive efficiency of escape jets throughout ontogeny. We examine the hydrodynamics and kinematics of escape jets in squid throughout ontogeny using 2D/3D velocimetry and high-speed videography. All life stages of squid produced two escape jet patterns: (1) 'escape jet I' characterized by short rapid pulses resulting in vortex ring formation and (2) 'escape jet II' characterized by long high-volume jets, often with a leading-edge vortex ring. Paralarvae exhibited higher propulsive efficiency than adult squid during escape jet ejection, and propulsive efficiency was higher for escape jet I than escape jet II in juveniles and adults. These results indicate that although squid undergo major ecological transitions and morphology changes from paralarvae to adults, all life stages demonstrate flexibility in escape jet responses and produce escape jets of surprisingly high propulsive efficiency.This article has an associated First Person interview with the first author of the paper.}, }
@article {pmid32968087, year = {2020}, author = {Saqr, KM and Tupin, S and Rashad, S and Endo, T and Niizuma, K and Tominaga, T and Ohta, M}, title = {Physiologic blood flow is turbulent.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {15492}, pmid = {32968087}, issn = {2045-2322}, mesh = {Blood Circulation/*physiology ; Blood Vessels/physiology ; Hemodynamics ; Humans ; Hydrodynamics ; Models, Biological ; Nonlinear Dynamics ; Pulsatile Flow/physiology ; }, abstract = {Contemporary paradigm of peripheral and intracranial vascular hemodynamics considers physiologic blood flow to be laminar. Transition to turbulence is considered as a driving factor for numerous diseases such as atherosclerosis, stenosis and aneurysm. Recently, turbulent flow patterns were detected in intracranial aneurysm at Reynolds number below 400 both in vitro and in silico. Blood flow is multiharmonic with considerable frequency spectra and its transition to turbulence cannot be characterized by the current transition theory of monoharmonic pulsatile flow. Thus, we decided to explore the origins of such long-standing assumption of physiologic blood flow laminarity. Here, we hypothesize that the inherited dynamics of blood flow in main arteries dictate the existence of turbulence in physiologic conditions. To illustrate our hypothesis, we have used methods and tools from chaos theory, hydrodynamic stability theory and fluid dynamics to explore the existence of turbulence in physiologic blood flow. Our investigation shows that blood flow, both as described by the Navier-Stokes equation and in vivo, exhibits three major characteristics of turbulence. Womersley's exact solution of the Navier-Stokes equation has been used with the flow waveforms from HaeMod database, to offer reproducible evidence for our findings, as well as evidence from Doppler ultrasound measurements from healthy volunteers who are some of the authors. We evidently show that physiologic blood flow is: (1) sensitive to initial conditions, (2) in global hydrodynamic instability and (3) undergoes kinetic energy cascade of non-Kolmogorov type. We propose a novel modification of the theory of vascular hemodynamics that calls for rethinking the hemodynamic-biologic links that govern physiologic and pathologic processes.}, }
@article {pmid32959981, year = {2021}, author = {Gibson, BM and Furbish, DJ and Rahman, IA and Schmeeckle, MW and Laflamme, M and Darroch, SAF}, title = {Ancient life and moving fluids.}, journal = {Biological reviews of the Cambridge Philosophical Society}, volume = {96}, number = {1}, pages = {129-152}, pmid = {32959981}, issn = {1469-185X}, support = {9968-16//National Geographic Society/ ; EAR-1735992//National Science Foundation/ ; Arthur Boucot Award//Paleontological Society/ ; Alberstadt-Reesman-Stearns Research Grant//Vanderbilt University/ ; }, mesh = {Animals ; *Biological Evolution ; Biota ; Computer Simulation ; *Ecosystem ; Fossils ; }, abstract = {Over 3.7 billion years of Earth history, life has evolved complex adaptations to help navigate and interact with the fluid environment. Consequently, fluid dynamics has become a powerful tool for studying ancient fossils, providing insights into the palaeobiology and palaeoecology of extinct organisms from across the tree of life. In recent years, this approach has been extended to the Ediacara biota, an enigmatic assemblage of Neoproterozoic soft-bodied organisms that represent the first major radiation of macroscopic eukaryotes. Reconstructing the ways in which Ediacaran organisms interacted with the fluids provides new insights into how these organisms fed, moved, and interacted within communities. Here, we provide an in-depth review of fluid physics aimed at palaeobiologists, in which we dispel misconceptions related to the Reynolds number and associated flow conditions, and specify the governing equations of fluid dynamics. We then review recent advances in Ediacaran palaeobiology resulting from the application of computational fluid dynamics (CFD). We provide a worked example and account of best practice in CFD analyses of fossils, including the first large eddy simulation (LES) experiment performed on extinct organisms. Lastly, we identify key questions, barriers, and emerging techniques in fluid dynamics, which will not only allow us to understand the earliest animal ecosystems better, but will also help to develop new palaeobiological tools for studying ancient life.}, }
@article {pmid32959135, year = {2021}, author = {Sonnenberg, AH and Taylor, E and Mondoñedo, JR and Jawde, SB and Amin, SD and Song, J and Grinstaff, MW and Suki, B}, title = {Breath Hold Facilitates Targeted Deposition of Aerosolized Droplets in a 3D Printed Bifurcating Airway Tree.}, journal = {Annals of biomedical engineering}, volume = {49}, number = {2}, pages = {812-821}, pmid = {32959135}, issn = {1573-9686}, support = {U01 HL139466/HL/NHLBI NIH HHS/United States ; U01 HL-139466/HL/NHLBI NIH HHS/United States ; HU0001810012//Defense Health Agency/ ; }, mesh = {Aerosols ; *Breath Holding ; Computer Simulation ; Humans ; Lung/*metabolism ; *Models, Anatomic ; *Models, Biological ; Particle Size ; Printing, Three-Dimensional ; }, abstract = {The lungs have long been considered a desired route for drug delivery but, there is still a lack of strategies to rationally target delivery sites especially in the presence of heterogeneous airway disease. Furthermore, no standardized system has been proposed to rapidly test different ventilation strategies and how they alter the overall and regional deposition pattern in the airways. In this study, a 3D printed symmetric bifurcating tree model mimicking part of the human airway tree was developed that can be used to quantify the regional deposition patterns of different delivery methodologies. The model is constructed in a novel way that allows for repeated measurements of regional deposition using reusable parts. During ventilation, nebulized ~3-micron-sized fluid droplets were delivered into the model. Regional delivery, quantified by precision weighing individual airways, was highly reproducible. A successful strategy to control regional deposition was achieved by combining an inspiratory wave form with a "breath hold" pause after each inspiration. Specifically, the second generation of the tree was successfully targeted, and deposition was increased by up to four times in generation 2 when compared to a ventilation without the breath hold (p < 0.0001). Breath hold was also demonstrated to facilitate deposition into blocked regions of the model, which mimic airway closure during an asthma that receive no flow during inhalation. Additionally, visualization experiments demonstrated that in the absence of fluid flow, the deposition of 3-micron water droplets is dominated by gravity, which, to our knowledge, has not been confirmed under standard laboratory conditions.}, }
@article {pmid32952737, year = {2020}, author = {Bortot, M and Sharifi, A and Ashworth, K and Walker, F and Cox, A and Ruegg, K and Clendenen, N and Neeves, KB and Bark, D and Di Paola, J}, title = {Pathologic Shear and Elongation Rates Do Not Cause Cleavage of Von Willebrand Factor by ADAMTS13 in a Purified System.}, journal = {Cellular and molecular bioengineering}, volume = {13}, number = {4}, pages = {379-390}, pmid = {32952737}, issn = {1865-5025}, support = {R01 HL120728/HL/NHLBI NIH HHS/United States ; R33 HL141794/HL/NHLBI NIH HHS/United States ; R61 HL141794/HL/NHLBI NIH HHS/United States ; }, abstract = {INTRODUCTION: Pathological flows in patients with severe aortic stenosis are associated with acquired von Willebrand syndrome. This syndrome is characterized by excessive cleavage of von Willebrand factor by its main protease, A Disintegrin and Metalloproteinase with a Thrombospondin Type 1 Motif, Member 13 (ADAMTS13) leading to decreased VWF function and mucocutaneous bleeding. Aortic valve replacement and correction of the flow behavior to physiological levels reverses the syndrome, supporting the association between pathological flow and acquired von Willebrand syndrome. We investigated the effects of shear and elongational rates on von Willebrand factor cleavage in the presence of ADAMTS13.<br><br>METHODS: We identified acquired von Willebrand syndrome in five patients with severe aortic stenosis. Doppler echography values from these patients were used to develop three computational fluid dynamic (CFD) aortic valve models (normal, mild and severe stenosis). Shear, elongational rates and exposure times identified in the CFD simulations were used as parameters for the design of microfluidic devices to test the effects of pathologic shear and elongational rates on the structure and function of von Willebrand factor.<br><br>RESULTS: The shear rates (0-10,000s[-1]), elongational rates (0-1000 s[-1]) and exposure times (1-180 ms) tested in our microfluidic designs mimicked the flow features identified in patients with aortic stenosis. The shear and elongational rates tested in vitro did not lead to excessive cleavage or decreased function of von Willebrand factor in the presence of the protease.<br><br>CONCLUSIONS: High shear and elongational rates in the presence of ADAMTS13 are not sufficient for excessive cleavage of von Willebrand Factor.}, }
@article {pmid32946425, year = {2020}, author = {Gao, D and Bai, M and Hu, C and Lv, J and Wang, C and Zhang, X}, title = {Investigating control of convective heat transfer and flow resistance of Fe3O4/deionized water nanofluid in magnetic field in laminar flow.}, journal = {Nanotechnology}, volume = {31}, number = {49}, pages = {495402}, doi = {10.1088/1361-6528/abb15c}, pmid = {32946425}, issn = {1361-6528}, abstract = {This paper studies the convective heat transfer and flow resistance of Fe3O4/deionized water nanofluids in laminar flow under the control of an external magnetic field. The basic thermophysical parameters including viscosity, specific heat capacity and thermal conductivity are investigated to describe the fundamental performance of heat transfer and flow resistance. In the absence of the magnetic field, the heat transfer coefficients and flow friction could not change significantly at nanoparticle volume concentration of 0.05%. In the presence of the magnetic field, it can enhance heat transfer and flow resistance by 6% and 3.5% when the magnets interlace on both sides of the tube. The dynamic magnetic experiments discussed the heat transfer increase process in detail. The heat transfer and the flow resistance increase by 11.7% and 5.4% when magnetic field strength is 600 Gs, nanoparticle volume concentration is 2% and Reynolds number is 2000. The radial shuttle movement of magnetic nanoparticles in the cross-section, micro convection in base fluid and the slip velocity between the nanoparticles and the base fluid are considered the main reasons for heat transfer enhancement.}, }
@article {pmid32942486, year = {2020}, author = {Mukhopadhyay, S and Mukhopadhyay, A}, title = {Waves and instabilities of viscoelastic fluid film flowing down an inclined wavy bottom.}, journal = {Physical review. E}, volume = {102}, number = {2-1}, pages = {023117}, doi = {10.1103/PhysRevE.102.023117}, pmid = {32942486}, issn = {2470-0053}, abstract = {Evolution of waves and hydrodynamic instabilities of a thin viscoelastic fluid film flowing down an inclined wavy bottom of moderate steepness have been analyzed analytically and numerically. The classical long-wave expansion method has been used to formulate a nonlinear evolution equation for the development of the free surface. A normal-mode approach has been adopted to discuss the linear stability analysis from the viewpoint of the spatial and temporal study. The method of multiple scales is used to derive a Ginzburg-Landau-type nonlinear equation for studying the weakly nonlinear stability solutions. Two significant wave families, viz., γ_{1} and γ_{2}, are found and discussed in detail along with the traveling wave solution of the evolution system. A time-dependent numerical study is performed with Scikit-FDif. The entire investigation is conducted primarily for a general periodic bottom, and the detailed results of a particular case study of sinusoidal topography are then discussed. The case study reveals that the bottom steepness ζ plays a dual role in the linear regime. Increasing ζ has a stabilizing effect in the uphill region, and the opposite occurs in the downhill region. While the viscoelastic parameter Γ has a destabilizing effect throughout the domain in both the linear and the nonlinear regime. Both supercritical and subcritical solutions are possible through a weakly nonlinear analysis. It is interesting to note that the unconditional zone decreases and the explosive zone increases in the downhill region rather than the uphill region for a fixed Γ and ζ. The same phenomena occur in a particular region if we increase Γ and keep ζ fixed. The traveling wave solution reveals the fact that to get the γ_{1} family of waves we need to increase the Reynolds number a bit more than the value at which the γ_{2} family of waves is found. The spatiotemporal evolution of the nonlinear surface equation indicates that different kinds of finite-amplitude permanent waves exist.}, }
@article {pmid32942407, year = {2020}, author = {Hassan, MR and Wang, C}, title = {Lateral migration of a ferrofluid droplet in a plane Poiseuille flow under uniform magnetic fields.}, journal = {Physical review. E}, volume = {102}, number = {2-1}, pages = {022611}, doi = {10.1103/PhysRevE.102.022611}, pmid = {32942407}, issn = {2470-0053}, abstract = {The lateral migration of a two-dimensional (2D) viscous ferrofluid droplet in a plane Poiseuille flow under a uniform magnetic field is studied numerically by using the level set method. Focusing on low droplet Reynolds number flows (Re_{d}≤0.05), several numerical simulations are carried out to analyze the effects of magnetic field direction and strength, droplet size, and viscosity ratio on the lateral migration behavior of the droplet. The results indicate that the magnetic field direction plays a pivotal role in the trajectory of lateral migration of the droplet and the final equilibrium position in the channel. When the magnetic field is parallel to the channel, i.e., α=0^{∘} (the direction of magnetic field), the droplet is found to settle closer to the wall with an increase in magnetic Bond number Bo_{m}, while at α=45^{∘}, the droplet settles closer to the channel center. Varying the initial droplet sizes at a fixed magnetic Bond number Bo_{m} and viscosity ratio λ results in different final equilibrium positions within the channel. Additionally, the effect of different viscosity ratios on the migration behavior of the droplet is examined at variable magnetic Bond numbers Bo_{m}. At α=45^{∘}, a critical steady state of deformation is found for λ=0.5 and 1 where the droplet changes its migration direction and shifts toward the center of the channel, while at λ=0.05, the droplet crosses the center. At α=90^{∘}, the droplet is found to settle exactly at the center of the flow domain irrespective of different magnetic Bond numbers, droplet sizes, and viscosity ratios.}, }
@article {pmid32926106, year = {2020}, author = {Beratlis, N and Capuano, F and Krishnan, K and Gurka, R and Squires, K and Balaras, E}, title = {Direct Numerical Simulations of a Great Horn Owl in Flapping Flight.}, journal = {Integrative and comparative biology}, volume = {60}, number = {5}, pages = {1091-1108}, doi = {10.1093/icb/icaa127}, pmid = {32926106}, issn = {1557-7023}, mesh = {Animals ; Biomimetics ; *Flight, Animal ; *Models, Biological ; *Strigiformes ; Wings, Animal ; }, abstract = {The fluid dynamics of owls in flapping flight is studied by coordinated experiments and computations. The great horned owl was selected, which is nocturnal, stealthy, and relatively large sized raptor. On the experimental side, perch-to-perch flight was considered in an open wind tunnel. The owl kinematics was captured with multiple cameras from different view angles. The kinematic extraction was central in driving the computations, which were designed to resolve all significant spatio-temporal scales in the flow with an unprecedented level of resolution. The wing geometry was extracted from the planform image of the owl wing and a three-dimensional model, the reference configuration, was reconstructed. This configuration was then deformed in time to best match the kinematics recorded during flights utilizing an image-registration technique based on the large deformation diffeomorphic metric mapping framework. All simulations were conducted using an eddy-resolving, high-fidelity, solver, where the large displacements/deformations of the flapping owl model were introduced with an immersed boundary formulation. We report detailed information on the spatio-temporal flow dynamics in the near wake including variables that are challenging to measure with sufficient accuracy, such as aerodynamic forces. At the same time, our results indicate that high-fidelity computations over smooth wings may have limitations in capturing the full range of flow phenomena in owl flight. The growth and subsequent separation of the laminar boundary layers developing over the wings in this Reynolds number regime is sensitive to the surface micro-features that are unique to each species.}, }
@article {pmid32920676, year = {2020}, author = {Sprenger, AR and Shaik, VA and Ardekani, AM and Lisicki, M and Mathijssen, AJTM and Guzmán-Lastra, F and Löwen, H and Menzel, AM and Daddi-Moussa-Ider, A}, title = {Towards an analytical description of active microswimmers in clean and in surfactant-covered drops.}, journal = {The European physical journal. E, Soft matter}, volume = {43}, number = {9}, pages = {58}, doi = {10.1140/epje/i2020-11980-9}, pmid = {32920676}, issn = {1292-895X}, mesh = {Computer Simulation ; *Hydrodynamics ; *Models, Theoretical ; Rheology ; Stress, Mechanical ; *Surface-Active Agents ; Suspensions ; Swimming ; Viscosity ; }, abstract = {Geometric confinements are frequently encountered in the biological world and strongly affect the stability, topology, and transport properties of active suspensions in viscous flow. Based on a far-field analytical model, the low-Reynolds-number locomotion of a self-propelled microswimmer moving inside a clean viscous drop or a drop covered with a homogeneously distributed surfactant, is theoretically examined. The interfacial viscous stresses induced by the surfactant are described by the well-established Boussinesq-Scriven constitutive rheological model. Moreover, the active agent is represented by a force dipole and the resulting fluid-mediated hydrodynamic couplings between the swimmer and the confining drop are investigated. We find that the presence of the surfactant significantly alters the dynamics of the encapsulated swimmer by enhancing its reorientation. Exact solutions for the velocity images for the Stokeslet and dipolar flow singularities inside the drop are introduced and expressed in terms of infinite series of harmonic components. Our results offer useful insights into guiding principles for the control of confined active matter systems and support the objective of utilizing synthetic microswimmers to drive drops for targeted drug delivery applications.}, }
@article {pmid32916991, year = {2020}, author = {Khan, MZU and Uddin, E and Akbar, B and Akram, N and Naqvi, AA and Sajid, M and Ali, Z and Younis, MY and García Márquez, FP}, title = {Investigation of Heat Transfer and Pressure Drop in Microchannel Heat Sink Using Al2O3 and ZrO2 Nanofluids.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {10}, number = {9}, pages = {}, pmid = {32916991}, issn = {2079-4991}, support = {01110G0137//Universidad de Castilla-La Mancha/ ; }, abstract = {A new micro heat exchanger was analyzed using numerical formulation of conjugate heat transfer for single-phase fluid flow across copper microchannels. The flow across bent channels harnesses asymmetric laminar flow and dean vortices phenomena for heat transfer enhancement. The single-channel analysis was performed to select the bent channel aspect ratio by varying width and height between 35-300 μm for Reynolds number and base temperature magnitude range of 100-1000 and 320-370 K, respectively. The bent channel results demonstrate dean vortices phenomenon at the bend for Reynolds number of 500 and above. Thermal performance factor analysis shows an increase of 18% in comparison to straight channels of 200 μm width and height. Alumina nanoparticles at 1% and 3% concentration enhance the Nusselt number by an average of 10.4% and 23.7%, respectively, whereas zirconia enhances Nusselt number by 16% and 33.9% for same concentrations. On the other hand, thermal performance factor analysis shows a significant increase in pressure drop at high Reynolds number with 3% particle concentration. Using zirconia for nanofluid, Nusselt number of the bent multi-channel model is improved by an average of 18% for a 3% particle concentration as compared to bent channel with deionized water.}, }
@article {pmid32910129, year = {2020}, author = {Tang, W and Zhu, S and Jiang, D and Zhu, L and Yang, J and Xiang, N}, title = {Channel innovations for inertial microfluidics.}, journal = {Lab on a chip}, volume = {20}, number = {19}, pages = {3485-3502}, doi = {10.1039/d0lc00714e}, pmid = {32910129}, issn = {1473-0189}, abstract = {Inertial microfluidics has gained significant attention since first being proposed in 2007 owing to the advantages of simplicity, high throughput, precise manipulation, and freedom from an external field. Superior performance in particle focusing, filtering, concentrating, and separating has been demonstrated. As a passive technology, inertial microfluidics technology relies on the unconventional use of fluid inertia in an intermediate Reynolds number range to induce inertial migration and secondary flow, which depend directly on the channel structure, leading to particle migration to the lateral equilibrium position or trapping in a specific cavity. With the advances in micromachining technology, many channel structures have been designed and fabricated in the past decade to explore the fundamentals and applications of inertial microfluidics. However, the channel innovations for inertial microfluidics have not been discussed comprehensively. In this review, the inertial particle manipulations and underlying physics in conventional channels, including straight, spiral, sinusoidal, and expansion-contraction channels, are briefly described. Then, recent innovations in channel structure for inertial microfluidics, especially channel pattern modification and unconventional cross-sectional shape, are reviewed. Finally, the prospects for future channel innovations in inertial microfluidic chips are also discussed. The purpose of this review is to provide guidance for the continued study of innovative channel designs to improve further the accuracy and throughput of inertial microfluidics.}, }
@article {pmid32901617, year = {2021}, author = {Oâ Neill, G and Tolley, NS}, title = {Modelling nasal airflow coefficients: an insight into the nature of airflow.}, journal = {Rhinology}, volume = {59}, number = {1}, pages = {66-74}, doi = {10.4193/Rhin19.440}, pmid = {32901617}, issn = {0300-0729}, mesh = {Computer Simulation ; Humans ; Hydrodynamics ; *Nose ; *Pulmonary Ventilation ; }, abstract = {BACKGROUND: There has been considerable discussion and conflicting views regarding the presence of laminar or turbulent flow within the nose. The aim of this study was to investigate how the modelling of variable flow coefficients can assist in the evalua- tion of the characteristics of flow in the resistive segments of the nose.<br><br>METHODOLOGY: A comparison was made between the flow coefficient for the nasal valve, obtained from a mathematical model, and resistive flow components such as a Venturi meter and orifice tube. Also, a variable loss coefficient was formulated for the whole (unilateral) nose which, by utilising the intersection of the laminar and turbulent asymptotes, provided an estimation for the critical Reynolds number (Rcrit).<br><br>RESULTS: The results show that the flow resistance of the nasal valve is considerably greater than that for both a Venturi meter and an orifice tube implying turbulent or turbulent-like flow for much of nasal inspiration. Regarding the loss coefficient for the whole (unilateral) nose, normal respiration flowrates are displaced well away from the laminar asymptote. The critical Reynolds number was estimated to be 450.<br><br>CONCLUSIONS: A novel method of determining the flow characteristics of the nose, particularly the critical Reynolds number, is presented. The analysis indicates a higher degree of turbulence than is assumed from a simple traditional calculation using a hy- draulic diameter and flow through straight tubes. There are implications for computational fluid dynamics (CFD) modelling where either the entire nasal airflow is assumed to be laminar or a low turbulence model implemented.}, }
@article {pmid32895674, year = {2020}, author = {Tegze, G and Podmaniczky, F and Somfai, E and Börzsönyi, T and Gránásy, L}, title = {Orientational order in dense suspensions of elliptical particles in the non-Stokesian regime.}, journal = {Soft matter}, volume = {16}, number = {38}, pages = {8925-8932}, doi = {10.1039/d0sm00370k}, pmid = {32895674}, issn = {1744-6848}, abstract = {Suspensions of neutrally buoyant elliptic particles are modeled in 2D using fully resolved simulations that provide two-way interaction between the particle and the fluid medium. Forces due to particle collisions are represented by a diffuse interface approach that allows the investigation of dense suspensions (up to 47% packing fraction). We focus on the role inertial forces play at low and high particle Reynolds numbers termed low Reynolds number and inertial regimes, respectively. The suspensions are characterized by the orientation distribution function (ODF) that reflects shear induced rotation of the particles at low Reynolds numbers, and nearly stationary (swaying) particles at high Reynolds numbers. In both cases, orientational ordering differs qualitatively from the behavior observed in the Stokesian-regime. The ODF becomes flatter with increasing packing fraction, as opposed to the sharpening previous work predicted in the Stokesian regime. The ODF at low particle concentrations differs significantly for the low Reynolds number and inertial regimes, whereas with increasing packing fraction convergence is observed. For dense suspensions, the particle-particle interactions dominate the particle motion.}, }
@article {pmid32881533, year = {2020}, author = {Cui, G and Jacobi, I}, title = {Magnetic Control of Ferrofluid Droplet Adhesion in Shear Flow and on Inclined Surfaces.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {36}, number = {36}, pages = {10885-10891}, doi = {10.1021/acs.langmuir.0c02369}, pmid = {32881533}, issn = {1520-5827}, abstract = {The manipulation of ferrofluidic droplets by magnetic fields is a popular technique for controlling fluid transport in open microfluidic systems. We examine the effect of gravity and shear flow external forces on the adhesion properties of sessile ferrofluidic droplets in the presence of a uniform magnetic field. The magnetic field was found to enhance the critical Bond number at which sliding begins on a tilting substrate but suppress the critical Weber number at which sliding begins in a moderate Reynolds number channel flow. The divergent adhesion trends are explained in terms of the shape deformation induced in the ferrofluidic droplet, the substrate wettability, and the apparent contact angle variation induced by the droplet deformation.}, }
@article {pmid32879533, year = {2019}, author = {Battista, F and Mollicone, JP and Gualtieri, P and Messina, R and Casciola, CM}, title = {Exact regularized point particle (ERPP) method for particle-laden wall-bounded flows in the two-way coupling regime.}, journal = {Journal of fluid mechanics}, volume = {878}, number = {}, pages = {420-444}, pmid = {32879533}, issn = {0022-1120}, support = {339446/ERC_/European Research Council/International ; }, abstract = {The Exact Regularized Point Particle (ERPP) method is extended to treat the interphase momentum coupling between particles and fluid in the presence of walls by accounting for the vorticity generation due to the particles close to solid boundaries. The ERPP method overcomes the limitations of other methods by allowing the simulation of an extensive parameter space (Stokes number, mass loading, particle-to-fluid density ratio and Reynolds number) and of particle spatial distributions that are uneven (few particles per computational cell). The enhanced ERPP method is explained in detail and validated by considering the global impulse balance. In conditions when particles are located close to the wall, a common scenario in wall-bounded turbulent flows, the main contribution to the total impulse arises from the particle-induced vorticity at the solid boundary. The method is applied to direct numerical simulations of particle-laden turbulent pipe flow in the two-way coupling regime to address the turbulence modulation. The effects of the mass loading, the Stokes number and the particle-to-fluid density ratio are investigated. The drag is either unaltered or increased by the particles with respect to the uncoupled case. No drag reduction is found in the parameter space considered. The momentum stress budget, which includes an extra stress contribution by the particles, provides the rationale behind the drag behaviour. The extra stress produces a momentum flux towards the wall that strongly modifies the viscous stress, the culprit of drag at solid boundaries.}, }
@article {pmid32876861, year = {2020}, author = {Mottaghi, S and Nazari, M and Fattahi, SM and Nazari, M and Babamohammadi, S}, title = {Droplet size prediction in a microfluidic flow focusing device using an adaptive network based fuzzy inference system.}, journal = {Biomedical microdevices}, volume = {22}, number = {3}, pages = {61}, doi = {10.1007/s10544-020-00513-4}, pmid = {32876861}, issn = {1572-8781}, mesh = {*Fuzzy Logic ; *Neural Networks, Computer ; Lab-On-A-Chip Devices ; Particle Size ; Microfluidic Analytical Techniques/instrumentation ; }, abstract = {Microfluidics has wide applications in different technologies such as biomedical engineering, chemistry engineering, and medicine. Generating droplets with desired size for special applications needs costly and time-consuming iterations due to the nonlinear behavior of multiphase flow in a microfluidic device and the effect of several parameters on it. Hence, designing a flexible way to predict the droplet size is necessary. In this paper, we use the Adaptive Neural Fuzzy Inference System (ANFIS), by mixing the artificial neural network (ANN) and fuzzy inference system (FIS), to study the parameters which have effects on droplet size. The four main dimensionless parameters, i.e. the Capillary number, the Reynolds number, the flow ratio and the viscosity ratio are regarded as the inputs and the droplet diameter as the output of the ANFIS. Using dimensionless groups cause to extract more comprehensive results and avoiding more experimental tests. With the ANFIS, droplet sizes could be predicted with the coefficient of determination of 0.92.}, }
@article {pmid32873833, year = {2020}, author = {McGurk, KA and Owen, B and Watson, WD and Nethononda, RM and Cordell, HJ and Farrall, M and Rider, OJ and Watkins, H and Revell, A and Keavney, BD}, title = {Heritability of haemodynamics in the ascending aorta.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {14356}, pmid = {32873833}, issn = {2045-2322}, support = {RG/12/16/29939/BHF_/British Heart Foundation/United Kingdom ; RG/07/012/24110/BHF_/British Heart Foundation/United Kingdom ; MR/K501311/1/MRC_/Medical Research Council/United Kingdom ; RG/15/12/31616/BHF_/British Heart Foundation/United Kingdom ; CH/13/2/30154/BHF_/British Heart Foundation/United Kingdom ; }, mesh = {Adult ; Aged ; Aorta/*diagnostic imaging/*physiopathology ; Blood Flow Velocity ; Cardiovascular Abnormalities/*genetics ; Cohort Studies ; Female ; Genetic Predisposition to Disease/*genetics ; Genotyping Techniques ; Hemodynamics/*genetics ; Humans ; Magnetic Resonance Imaging/methods ; Male ; Middle Aged ; *Pedigree ; Phenotype ; *Polymorphism, Single Nucleotide ; Young Adult ; }, abstract = {Blood flow in the vasculature can be characterised by dimensionless numbers commonly used to define the level of instabilities in the flow, for example the Reynolds number, Re. Haemodynamics play a key role in cardiovascular disease (CVD) progression. Genetic studies have identified mechanosensitive genes with causal roles in CVD. Given that CVD is highly heritable and abnormal blood flow may increase risk, we investigated the heritability of fluid metrics in the ascending aorta calculated using patient-specific data from cardiac magnetic resonance (CMR) imaging. 341 participants from 108 British Caucasian families were phenotyped by CMR and genotyped for 557,124 SNPs. Flow metrics were derived from the CMR images to provide some local information about blood flow in the ascending aorta, based on maximum values at systole at a single location, denoted max, and a 'peak mean' value averaged over the area of the cross section, denoted pm. Heritability was estimated using pedigree-based (QTDT) and SNP-based (GCTA-GREML) methods. Estimates of Reynolds number based on spatially averaged local flow during systole showed substantial heritability ([Formula: see text], [Formula: see text]), while the estimated heritability for Reynolds number calculated using the absolute local maximum velocity was not statistically significant (12-13%; [Formula: see text]). Heritability estimates of the geometric quantities alone; e.g. aortic diameter ([Formula: see text], [Formula: see text]), were also substantially heritable, as described previously. These findings indicate the potential for the discovery of genetic factors influencing haemodynamic traits in large-scale genotyped and phenotyped cohorts where local spatial averaging is used, rather than instantaneous values. Future Mendelian randomisation studies of aortic haemodynamic estimates, which are swift to derive in a clinical setting, will allow for the investigation of causality of abnormal blood flow in CVD.}, }
@article {pmid32859015, year = {2020}, author = {Nichka, VS and Geoffroy, TR and Nikonenko, V and Bazinet, L}, title = {Impacts of Flow Rate and Pulsed Electric Field Current Mode on Protein Fouling Formation during Bipolar Membrane Electroacidification of Skim Milk.}, journal = {Membranes}, volume = {10}, number = {9}, pages = {}, pmid = {32859015}, issn = {2077-0375}, support = {SD-210829409//Natural Sciences and Engineering Research Council of Canada/ ; 19-38-90256//Russian Foundation for Basic Research/ ; }, abstract = {Fouling is one of the major problems in electrodialysis. The aim of the present work was to investigate the effect of five different solution flow rates (corresponding to Reynolds numbers of 162, 242, 323, 404 and 485) combined with the use of pulsed electric field (PEF) current mode on protein fouling of bipolar membrane (BPM) during electrodialysis with bipolar membranes (EDBM) of skim milk. The application of PEF prevented the fouling formation by proteins on the cationic interface of the BPM almost completely, regardless of the flow rate or Reynolds number. Indeed, under PEF mode of current the weight of protein fouling was negligible in comparison with CC current mode (0.07 ± 0.08 mg/cm[2] versus 5.56 ± 2.40 mg/cm[2]). When a continuous current (CC) mode was applied, Reynolds number equals or higher than 323 corresponded to a minimal value of protein fouling of BPM. This positive effect of both increasing the flow rate and using PEF is due to the facts that during pauses, the solution flow flushes the accumulated protein from the membrane while in the same time there is a decrease in concentration polarization (CP) and consequently decrease in H[+] generation at the cationic interface of the BPM, minimizing fouling formation and accumulation.}, }
@article {pmid32858042, year = {2020}, author = {Tripathi, D and Prakash, J and Tiwari, AK and Ellahi, R}, title = {Thermal, microrotation, electromagnetic field and nanoparticle shape effects on Cu-CuO/blood flow in microvascular vessels.}, journal = {Microvascular research}, volume = {132}, number = {}, pages = {104065}, doi = {10.1016/j.mvr.2020.104065}, pmid = {32858042}, issn = {1095-9319}, mesh = {Animals ; Blood Flow Velocity ; Copper/*chemistry ; *Electromagnetic Fields ; Humans ; Hydrodynamics ; *Microcirculation ; *Microfluidic Analytical Techniques ; Microvessels/*physiology ; *Models, Cardiovascular ; *Nanoparticles ; Pulsatile Flow ; Regional Blood Flow ; Rotation ; *Temperature ; Time Factors ; }, abstract = {A thermal analysis of Cu-CuO/ blood nanofluids flow in asymmetric microchannel propagating with wave velocity is presented in this study. For the blood, a micropolar fluid model is considered to investigate the microrotation effects of blood flow. Thermal radiation effects and the influence of nanoparticle shape, electric double layer thickness, and electromagnetic fields on the flow are studied. Three types of nanoparticles shapes namely cylinder, bricks and platelets are taken into account. Governing equations are solved under the approximations of long wavelength, low Reynolds number, and Debye-Hückel linearization. Numerical computations are performed for the axial pressure gradient, axial velocity, spin velocity and temperature distribution. The effects of various physical parameters on flow and thermal characteristics are computed and their physical interpretation is also discussed. The outcomes indicate that the axial velocity of Cu-CuO/blood nanoparticles strongly depends on applied electromagnetic field and microrotation. The model's finding will be applicable in designing the smart electromagnetic micro pumps for the hemodialysis and lungs-on-chip devices for the pumping of the blood.}, }
@article {pmid32850285, year = {2020}, author = {Zhu, L and Xu, B and Wu, X and Lei, J and Hacker, DL and Liang, X and Wurm, FM}, title = {Analysis of volumetric mass transfer coefficient (k L a) in small- (250 mL) to large-scale (2500 L) orbitally shaken bioreactors.}, journal = {3 Biotech}, volume = {10}, number = {9}, pages = {397}, pmid = {32850285}, issn = {2190-572X}, abstract = {In this study, the combination of dimensional analysis (DA) and analysis of variance (ANOVA) was used to predict the volumetric mass transfer coefficient (k L a) values under different operating conditions for orbitally shaken bioreactors (OSRs) with different filling volumes. It was found that Reynolds number and the interaction between Froude number and geometric number have the largest impact on k L a with impact indexes of 7.41 and 7.50, respectively. Moreover, the volume number has the largest negative impact on k L a, with an impact index of - 5.34. Thus, an effective way to increase the oxygen supply is by increasing the shaking speed and shaking diameter or decreasing the vessel diameter. However, cell cultivation with a higher filling volume will have an increased risk of oxygen scarcity. Therefore, with the help of the k L a prediction model, a suitable operating condition can be determined effectively and easily.}, }
@article {pmid32846914, year = {2020}, author = {Ghalambaz, M and Arasteh, H and Mashayekhi, R and Keshmiri, A and Talebizadehsardari, P and Yaïci, W}, title = {Investigation of Overlapped Twisted Tapes Inserted in a Double-Pipe Heat Exchanger Using Two-Phase Nanofluid.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {10}, number = {9}, pages = {}, pmid = {32846914}, issn = {2079-4991}, abstract = {This study investigated the laminar convective heat transfer and fluid flow of Al2O3 nanofluid in a counter flow double-pipe heat exchanger equipped with overlapped twisted tape inserts in both inner and outer tubes. Two models of the same (co-swirling twisted tapes) and opposite (counter-swirling twisted tapes) angular directions for the stationary twisted tapes were considered. The computational fluid dynamic simulations were conducted through varying the design parameters, including the angular direction of twisted tape inserts, nanofluid volume concentration, and Reynolds number. It was found that inserting the overlapped twisted tapes in the heat exchanger significantly increases the thermal performance as well as the friction factor compared with the plain heat exchanger. The results indicate that models of co-swirling twisted tapes and counter-swirling twisted tapes increase the average Nusselt number by almost 35.2-66.2% and 42.1-68.7% over the Reynolds number ranging 250-1000, respectively. To assess the interplay between heat transfer enhancement and pressure loss penalty, the dimensionless number of performance evaluation criterion was calculated for all the captured configurations. Ultimately, the highest value of performance evaluation criterion is equal to 1.40 and 1.26 at inner and outer tubes at the Reynolds number of 1000 and the volume fraction of 3% in the case of counter-swirling twisted tapes model.}, }
@article {pmid32845950, year = {2020}, author = {Zhang, S and Cui, Z and Wang, Y and den Toonder, JMJ}, title = {Metachronal actuation of microscopic magnetic artificial cilia generates strong microfluidic pumping.}, journal = {Lab on a chip}, volume = {20}, number = {19}, pages = {3569-3581}, doi = {10.1039/d0lc00610f}, pmid = {32845950}, issn = {1473-0189}, mesh = {*Cilia ; Magnetic Fields ; Magnetics ; *Microfluidics ; Motion ; }, abstract = {Biological cilia that generate fluid flow or propulsion are often found to exhibit a collective wavelike metachronal motion, i.e. neighboring cilia beat slightly out-of-phase rather than synchronously. Inspired by this observation, this article experimentally demonstrates that microscopic magnetic artificial cilia (μMAC) performing a metachronal motion can generate strong microfluidic flows, though, interestingly, the mechanism is different from that in biological cilia, as is found through a systematic experimental study. The μMAC are actuated by a facile magnetic setup, consisting of an array of rod-shaped magnets. This arrangement imposes a time-dependent non-uniform magnetic field on the μMAC array, resulting in a phase difference between the beatings of adjacent μMAC, while each cilium exhibits a two-dimensional whip-like motion. By performing the metachronal 2D motion, the μMAC are able to generate a strong flow in a microfluidic chip, with velocities of up to 3000 μm s[-1] in water, which, different from biological cilia, is found to be a result of combined metachronal and inertial effects, in addition to the effect of asymmetric beating. The pumping performance of the metachronal μMAC outperforms all previously reported microscopic artificial cilia, and is competitive with that of most of the existing microfluidic pumping methods, while the proposed platform requires no physical connection to peripheral equipment, reduces the usage of reagents by minimizing "dead volumes", avoids undesirable electrical effects, and accommodates a wide range of different fluids. The 2D metachronal motion can also generate a flow with velocities up to 60 μm s[-1] in pure glycerol, where Reynolds number is less than 0.05 and the flow is primarily caused by the metachronal motion of the μMAC. These findings offer a novel solution to not only create on-chip integrated micropumps, but also design swimming and walking microrobots, as well as self-cleaning and antifouling surfaces.}, }
@article {pmid32833583, year = {2020}, author = {Latt, J and Coreixas, C and Beny, J and Parmigiani, A}, title = {Efficient supersonic flow simulations using lattice Boltzmann methods based on numerical equilibria.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {378}, number = {2175}, pages = {20190559}, pmid = {32833583}, issn = {1471-2962}, abstract = {A double-distribution-function based lattice Boltzmann method (DDF-LBM) is proposed for the simulation of polyatomic gases in the supersonic regime. The model relies on a numerical equilibrium that has been extensively used by discrete velocity methods since the late 1990s. Here, it is extended to reproduce an arbitrary number of moments of the Maxwell-Boltzmann distribution. These extensions to the standard 5-constraint (mass, momentum and energy) approach lead to the correct simulation of thermal, compressible flows with only 39 discrete velocities in 3D. The stability of this BGK-LBM is reinforced by relying on Knudsen-number-dependent relaxation times that are computed analytically. Hence, high Reynolds-number, supersonic flows can be simulated in an efficient and elegant manner. While the 1D Riemann problem shows the ability of the proposed approach to handle discontinuities in the zero-viscosity limit, the simulation of the supersonic flow past a NACA0012 aerofoil confirms the excellent behaviour of this model in a low-viscosity and supersonic regime. The flow past a sphere is further simulated to investigate the 3D behaviour of our model in the low-viscosity supersonic regime. The proposed model is shown to be substantially more efficient than the previous 5-moment D3Q343 DDF-LBM for both CPU and GPU architectures. It then opens up a whole new world of compressible flow applications that can be realistically tackled with a purely LB approach. This article is part of the theme issue 'Fluid dynamics, soft matter and complex systems: recent results and new methods'.}, }
@article {pmid32828761, year = {2020}, author = {Akram, J and Akbar, NS and Tripathi, D}, title = {Blood-based graphene oxide nanofluid flow through capillary in the presence of electromagnetic fields: A Sutterby fluid model.}, journal = {Microvascular research}, volume = {132}, number = {}, pages = {104062}, doi = {10.1016/j.mvr.2020.104062}, pmid = {32828761}, issn = {1095-9319}, mesh = {Animals ; Blood Flow Velocity ; Capillaries/*physiology ; Computer Simulation ; *Electromagnetic Fields ; Graphite/*chemistry ; Humans ; *Microcirculation ; *Models, Cardiovascular ; *Nanoparticles ; Numerical Analysis, Computer-Assisted ; *Pulsatile Flow ; Time Factors ; }, abstract = {Pumping devices with the electrokinetics phenomena are important in many microscale transport phenomena in physiology. This study presents a theoretical and numerical investigation on the peristaltic pumping of non-Newtonian Sutterby nanofluid through capillary in presence of electromagnetohydrodynamics. Here blood (Sutterby fluid) is taken as a base fluid and nanofluid is prepared by the suspension of graphene oxide nanoparticle in blood. Graphene oxide is extremely useful in the medical domain for drug delivery and cancer treatment. The modified Buongiorno model for nanofluids and Poisson-Boltzmann ionic distribution is adopted for the formulation of the present problem. Constitutive flow equations are linearized by the implementation of approximations low Reynolds number, large wavelength, and the Debye-Hückel linearization. The numerical solution of reduced coupled and nonlinear set of equations is computed through Mathematica and graphical illustration is presented. Further, the impacts of buoyancy forces, thermal radiation, and mixed convection are also studied. It is revealed in this investigation that the inclusion of a large number of nanoparticles alters the flow characteristics significantly and boosts the heat transfer mechanism. Moreover, the pumping power of the peristaltic pump can be enhanced by the reduction in the width of the electric double layer which can be done by altering the electrolyte concentration.}, }
@article {pmid32810744, year = {2020}, author = {Moruzzi, RB and Campos, LC and Sharifi, S and da Silva, PG and Gregory, J}, title = {Nonintrusive investigation of large Al-kaolin fractal aggregates with slow settling velocities.}, journal = {Water research}, volume = {185}, number = {}, pages = {116287}, doi = {10.1016/j.watres.2020.116287}, pmid = {32810744}, issn = {1879-2448}, mesh = {Flocculation ; *Fractals ; *Kaolin ; Particle Size ; Rheology ; }, abstract = {Although a combination of aggregate characteristics dictate particle settling, it is commonly assumed that large particles have higher terminal velocities. This simplifying assumption often leads to overprediction of large aggregate settling velocities which in turn negatively impacts on estimates of sedimentation clarification efficiency. Despite its importance, little attention has been given to large aggregates with slow-settling velocities. This paper addresses this gap by investigating slow-settling velocities of large, heterodisperse and multi-shape Al-kaolin aggregates using non-intrusive methods. A particle image velocimetry technique (PIV) was applied to track aggregate velocity and a non-intrusive image technique was used to determine aggregate characteristics, including size (df), three-dimensional fractal dimension (Df), density (ρf), aggregate velocity (Vexp) and Reynolds number (Re). Results showed no strict dependence of settling velocity on large aggregate size, shape and density, as Al-kaolin aggregates with the same size exhibited different settling velocities. A comparison of the results with the well-known Stokes' law for velocity modified by a shape factor showed that the settling velocities measured here can vary from 2 to 14 fold lower than the predicted values for perfect sphere-shape aggregates with the same density and size. Furthermore, results have also shown large Al-kaolin aggregate's drag coefficient (Cd) to be around 56/Re, for average fractal aggregate sphericity of around 0.58.}, }
@article {pmid32809129, year = {2021}, author = {Cui, J and Liu, Y and Xiao, L and Chen, S and Fu, BM}, title = {Numerical study on the adhesion of a circulating tumor cell in a curved microvessel.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {20}, number = {1}, pages = {243-254}, pmid = {32809129}, issn = {1617-7940}, support = {G-UAHL//Hong Kong Polytechnic University/ ; G-UACM//Hong Kong Polytechnic University/ ; 19YF1417400//Science and Technology Commission of Shanghai Municipality/ ; 11902188//National Natural Science Foundation of China/ ; }, mesh = {Cell Adhesion ; Computer Simulation ; Humans ; Membranes ; Microvessels/*pathology ; Neoplastic Cells, Circulating/*pathology ; *Numerical Analysis, Computer-Assisted ; Probability ; Time Factors ; }, abstract = {The adhesion of a circulating tumor cell (CTC) in a three-dimensional curved microvessel was numerically investigated. Simulations were first performed to characterize the differences in the dynamics and adhesion of a CTC in the straight and curved vessels. After that, a parametric study was performed to investigate the effects of the applied driven force density f (or the flow Reynolds number Re) and the CTC membrane bending modulus Kb on the CTC adhesion. Our simulation results show that the CTC prefers to adhere to the curved vessel as more bonds are formed around the transition region of the curved part due to the increased cell-wall contact by the centrifugal force. The parametric study also indicates that when the flow driven force f (or Re) increases or when the CTC becomes softer (Kb decreases), the bond formation probability increases and the bonds will be formed at more sites of a curved vessel. The increased f (or Re) brings a larger centrifugal force, while the decreased Kb generates more contact areas at the cell-wall interface, both of which are beneficial to the bond formation. In the curved vessel, it is found that the site where bonds are formed the most (hotspot) varies with the applied f and the Kb. For our vessel geometry, when f is small, the hotspot tends to be within the first bend of the vessel, while as f increases or Kb decreases, the hotspot may shift to the second bend of the vessel.}, }
@article {pmid32805051, year = {2020}, author = {Rao, C and Liu, H}, title = {Effects of Reynolds Number and Distribution on Passive Flow Control in Owl-Inspired Leading-Edge Serrations.}, journal = {Integrative and comparative biology}, volume = {60}, number = {5}, pages = {1135-1146}, doi = {10.1093/icb/icaa119}, pmid = {32805051}, issn = {1557-7023}, mesh = {Animals ; Biomechanical Phenomena ; Computer Simulation ; Feathers ; *Flight, Animal ; *Models, Biological ; Wings, Animal ; }, abstract = {As a sophisticated micro device for noise reduction, the owl-inspired leading-edge (LE) serrations have been confirmed capable of achieving passive control of laminar-turbulent transition while normally paying a cost of lowering the aerodynamic performance in low Reynolds number (Re∼O[103]) regime. In order to explore potential applications of the owl-inspired serrated airfoils or blades in developing low noise wind turbines or multi-copters normally operating at higher Res, we conducted a large-eddy simulation (LES)-based study of Re effects on the aerodynamic performance of 2D clean and serrated models. Our results show that the LE serrations keep working effectively in mitigating turbulent fluctuations over a broad range of Re (O[103] ∼ O[105]), capable of achieving marked improvement in lift-to-drag ratio with increasing Res. As the aeroacoustic fields are in close association with the propagation of the turbulence sources, it is observed that the tradeoff between passive mitigation of turbulent fluctuations (hence aeroacoustic noise suppression) and aerodynamic performance can be noticeably mitigated at large angles of attack (AoAs) and at high Res. This indicates that the LE serrations present an alternative passive flow control mechanism at high Res through a straightforward local excitation of the flow transition while capable of mitigating the turbulent intensity passively. We further developed a 3D LES model of clean and partially serrated rectangular wings to investigate the effects of the LE serrations' distribution on aerodynamic features, on the basis of the observation that longer serrations are often distributed intensively in the mid-span of real owl's feathers. We find that the mid-span distributed LE serrations can facilitate the break-up of LE vortices and the turbulent transition passively and effectively while achieving a low level of turbulence kinetic energy over the upper suction surface of the wing.}, }
@article {pmid32801384, year = {2020}, author = {Ardeshiri, H and Cassiani, M and Park, SY and Stohl, A and Pisso, I and Dinger, AS}, title = {On the Convergence and Capability of the Large-Eddy Simulation of Concentration Fluctuations in Passive Plumes for a Neutral Boundary Layer at Infinite Reynolds Number.}, journal = {Boundary-layer meteorology}, volume = {176}, number = {3}, pages = {291-327}, pmid = {32801384}, issn = {0006-8314}, abstract = {Large-eddy simulation (LES) experiments have been performed using the Parallelized LES Model (PALM). A methodology for validating and understanding LES results for plume dispersion and concentration fluctuations in an atmospheric-like flow is presented. A wide range of grid resolutions is shown to be necessary for investigating the convergence of statistical characteristics of velocity and scalar fields. For the scalar, the statistical moments up to the fourth order and the shape of the concentration probability density function (p.d.f.) are examined. The mean concentration is influenced by grid resolution, with the highest resolution simulation showing a lower mean concentration, linked to larger turbulent structures. However, a clear tendency to convergence of the concentration variance is observed at the two higher resolutions. This behaviour is explained by showing that the mechanisms driving the mean and the variance are differently influenced by the grid resolution. The analysis of skewness and kurtosis allows also the obtaining of general results on plume concentration fluctuations. Irrespective of grid resolution, a family of Gamma p.d.f.s well represents the shape of the concentration p.d.f. but only beyond the peak of the concentration fluctuation intensity. In the early plume dispersion phases, the moments of the p.d.f. are in good agreement with those generated by a fluctuating plume model. To the best of our knowledge, our study demonstrates for the first time that, if resolution and averaging time are adequate, atmospheric LES provides a trustworthy representation of the high order moments of the concentration field, up to the fourth order, for a dispersing plume.}, }
@article {pmid32796948, year = {2020}, author = {Ryan, DP and Chen, Y and Nguyen, P and Goodwin, PM and Carey, JW and Kang, Q and Werner, JH and Viswanathan, HS}, title = {3D particle transport in multichannel microfluidic networks with rough surfaces.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {13848}, pmid = {32796948}, issn = {2045-2322}, support = {20180151ER//Laboratory Directed Research and Development,United States/ ; ACI-1548562//National Science Foundation/ ; FWP LANLE3W1//Basic Energy Sciences/ ; }, abstract = {The transport of particles and fluids through multichannel microfluidic networks is influenced by details of the channels. Because channels have micro-scale textures and macro-scale geometries, this transport can differ from the case of ideally smooth channels. Surfaces of real channels have irregular boundary conditions to which streamlines adapt and with which particle interact. In low-Reynolds number flows, particles may experience inertial forces that result in trans-streamline movement and the reorganization of particle distributions. Such transport is intrinsically 3D and an accurate measurement must capture movement in all directions. To measure the effects of non-ideal surface textures on particle transport through complex networks, we developed an extended field-of-view 3D macroscope for high-resolution tracking across large volumes ([Formula: see text]) and investigated a model multichannel microfluidic network. A topographical profile of the microfluidic surfaces provided lattice Boltzmann simulations with a detailed feature map to precisely reconstruct the experimental environment. Particle distributions from simulations closely reproduced those observed experimentally and both measurements were sensitive to the effects of surface roughness. Under the conditions studied, inertial focusing organized large particles into an annular distribution that limited their transport throughout the network while small particles were transported uniformly to all regions.}, }
@article {pmid32783851, year = {2020}, author = {Deng, D and Pan, Y and Liu, G and Liu, W and Ma, L}, title = {Seeking the hotspots of nitrogen removal: A comparison of sediment denitrification rate and denitrifier abundance among wetland types with different hydrological conditions.}, journal = {The Science of the total environment}, volume = {737}, number = {}, pages = {140253}, doi = {10.1016/j.scitotenv.2020.140253}, pmid = {32783851}, issn = {1879-1026}, mesh = {China ; Denitrification ; Hydrology ; *Nitrogen ; *Wetlands ; }, abstract = {Wetlands play a vital role in removing nitrogen (N) from aquatic environments via the denitrification process, which is regulated by multiple environmental and biological factors. Until now, the mechanisms by which environmental factors and microbial abundance regulate denitrification rates in wetlands under different hydrological conditions remain poorly understood. Here, we investigated sediment potential denitrification rate (PDR) and unamended denitrification rate (UDR), and quantified denitrifier abundance (nirS, nirK, and nosZ genes) in 36 stream, river, pond, and ditch wetland sites along the Dan River, a nitrogen-rich river in central China. The result indicated that ditches had the highest denitrification rates and denitrifier abundance. Both PDR and UDR showed strong seasonality, and were observed to be negatively correlated with water velocity in streams and rivers. Moreover, denitrification rates were significantly related to denitrifier abundance and many water quality parameters and sediment properties. Interestingly, PDR and UDR were generally positively associated with N and carbon (C) availability in streams and rivers, but such correlations were not found in ponds and ditches. Using a scaling analysis, we found that environmental parameters, including Reynolds number, sediment total C ratio, and interstitial space, coupled with relative nirS gene abundance could predict the hotspots of denitrification rates in wetlands with varying hydrologic regimes. Our findings highlight that hydrological conditions, especially water velocity and hydrologic pulsing, play a nonnegligible role in determining N biogeochemical processes in wetlands.}, }
@article {pmid32770358, year = {2020}, author = {Patterson, LHC and Walker, JL and Naivar, MA and Rodriguez-Mesa, E and Hoonejani, MR and Shields, K and Foster, JS and Doyle, AM and Valentine, MT and Foster, KL}, title = {Inertial flow focusing: a case study in optimizing cellular trajectory through a microfluidic MEMS device for timing-critical applications.}, journal = {Biomedical microdevices}, volume = {22}, number = {3}, pages = {52}, doi = {10.1007/s10544-020-00508-1}, pmid = {32770358}, issn = {1572-8781}, support = {1631656//Division of Chemical, Bioengineering, Environmental, and Transport Systems/International ; 1254893//Division of Civil, Mechanical and Manufacturing Innovation/International ; }, mesh = {Buffers ; Equipment Design ; *Lab-On-A-Chip Devices ; Micro-Electrical-Mechanical Systems/*instrumentation ; Microspheres ; Particle Size ; Polystyrenes/chemistry ; Temperature ; Viscosity ; }, abstract = {Although microfluidic micro-electromechanical systems (MEMS) are well suited to investigate the effects of mechanical force on large populations of cells, their high-throughput capabilities cannot be fully leveraged without optimizing the experimental conditions of the fluid and particles flowing through them. Parameters such as flow velocity and particle size are known to affect the trajectories of particles in microfluidic systems and have been studied extensively, but the effects of temperature and buffer viscosity are not as well understood. In this paper, we explored the effects of these parameters on the timing of our own cell-impact device, the μHammer, by first tracking the velocity of polystyrene beads through the device and then visualizing the impact of these beads. Through these assays, we find that the timing of our device is sensitive to changes in the ratio of inertial forces to viscous forces that particles experience while traveling through the device. This sensitivity provides a set of parameters that can serve as a robust framework for optimizing device performance under various experimental conditions, without requiring extensive geometric redesigns. Using these tools, we were able to achieve an effective throughput over 360 beads/s with our device, demonstrating the potential of this framework to improve the consistency of microfluidic systems that rely on precise particle trajectories and timing.}, }
@article {pmid32766844, year = {2020}, author = {Waldrop, LD and He, Y and Hedrick, TL and Rader, JA}, title = {Functional Morphology of Gliding Flight I: Modeling Reveals Distinct Performance Landscapes Based on Soaring Strategies.}, journal = {Integrative and comparative biology}, volume = {60}, number = {5}, pages = {1283-1296}, doi = {10.1093/icb/icaa114}, pmid = {32766844}, issn = {1557-7023}, mesh = {Animals ; Biomechanical Phenomena ; *Birds ; *Flight, Animal ; *Wings, Animal ; }, abstract = {The physics of flight influences the morphology of bird wings through natural selection on flight performance. The connection between wing morphology and performance is unclear due to the complex relationships between various parameters of flight. In order to better understand this connection, we present a holistic analysis of gliding flight that preserves complex relationships between parameters. We use a computational model of gliding flight, along with analysis by uncertainty quantification, to (1) create performance landscapes of gliding based on output metrics (maximum lift-to-drag ratio, minimum gliding angle, minimum sinking speed, and lift coefficient at minimum sinking speed) and (2) predict what parameters of flight (chordwise camber, wing aspect ratio [AR], and Reynolds number) would differ between gliding and nongliding species of birds. We also examine performance based on the soaring strategy for possible differences in morphology within gliding birds. Gliding birds likely have greater ARs than non-gliding birds, due to the high sensitivity of AR on most metrics of gliding performance. Furthermore, gliding birds can use two distinct soaring strategies based on performance landscapes. First, maximizing distance traveled (maximizing lift-to-drag ratio and minimizing gliding angle) should result in wings with high ARs and middling-to-low wing chordwise camber. Second, maximizing lift extracted from updrafts should result in wings with middling ARs and high wing chordwise camber. Following studies can test these hypotheses using morphological measurements.}, }
@article {pmid32762434, year = {2020}, author = {Arrieta, J and Cartwright, JHE and Gouillart, E and Piro, N and Piro, O and Tuval, I}, title = {Geometric mixing.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {378}, number = {2179}, pages = {20200168}, pmid = {32762434}, issn = {1471-2962}, abstract = {Mixing fluids often involves a periodic action, like stirring one's tea. But reciprocating motions in fluids at low Reynolds number, in Stokes flows where inertia is negligible, lead to periodic cycles of mixing and unmixing, because the physics, molecular diffusion excepted, is time reversible. So how can fluid be mixed in such circumstances? The answer involves a geometric phase. Geometric phases are found everywhere in physics as anholonomies, where after a closed circuit in the parameters, some system variables do not return to their original values. We discuss the geometric phase in fluid mixing: geometric mixing. This article is part of the theme issue 'Stokes at 200 (part 2)'.}, }
@article {pmid32752686, year = {2020}, author = {Seyler, SL and Pressé, S}, title = {Surmounting potential barriers: Hydrodynamic memory hedges against thermal fluctuations in particle transport.}, journal = {The Journal of chemical physics}, volume = {153}, number = {4}, pages = {041102}, doi = {10.1063/5.0013722}, pmid = {32752686}, issn = {1089-7690}, abstract = {Recently, trapped-particle experiments have probed the instantaneous velocity of Brownian motion revealing that, at early times, hydrodynamic history forces dominate Stokes damping. In these experiments, nonuniform particle motion is well described by the Basset-Boussinesq-Oseen (BBO) equation, which captures the unsteady Basset history force at a low Reynolds number. Building off of these results, earlier we showed that, at low temperature, BBO particles could exploit fluid inertia in order to overcome potential barriers (generically modeled as a tilted washboard), while its Langevin counter-part could not. Here, we explore the behavior of neutrally buoyant BBO particles at finite temperature for moderate Stokes damping. Remarkably, we find that the transport of particles injected into a bumpy potential with sufficiently high barriers can be completely quenched at intermediate temperatures, whereas itinerancy may be possible above and below that temperature window. This effect is present for both Langevin and BBO dynamics, though these occur over drastically different temperature ranges. Furthermore, hydrodynamic memory mitigates these effects by sustaining initial particle momentum, even in the difficult intermediate temperature regime.}, }
@article {pmid32752632, year = {2020}, author = {Romanò, F and Türkbay, T and Kuhlmann, HC}, title = {Lagrangian chaos in steady three-dimensional lid-driven cavity flow.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {30}, number = {7}, pages = {073121}, doi = {10.1063/5.0005792}, pmid = {32752632}, issn = {1089-7682}, abstract = {Steady three-dimensional flows in lid-driven cavities are investigated numerically using a high-order spectral-element solver for the incompressible Navier-Stokes equations. The focus is placed on critical points in the flow field, critical limit cycles, their heteroclinic connections, and on the existence, shape, and dependence on the Reynolds number of Kolmogorov-Arnold-Moser (KAM) tori. In finite-length cuboidal cavities at small Reynolds numbers, a thin layer of chaotic streamlines covers all walls. As the Reynolds number is increased, the chaotic layer widens and the complementary KAM tori shrink, eventually undergoing resonances, until they vanish. Accurate data for the location of closed streamlines and of KAM tori are provided, both of which reach very close to the moving lid. For steady periodic Taylor-Görtler vortices in spanwise infinitely extended cavities with a square cross section, chaotic streamlines occupy a large part of the flow domain immediately after the onset of Taylor-Görtler vortices. As the Reynolds number increases, the remaining KAM tori vanish from the Taylor-Görtler vortices, while KAM tori grow in the central region further away from the solid walls.}, }
@article {pmid32752610, year = {2020}, author = {Chatterjee, S and Verma, MK}, title = {Kolmogorov flow: Linear stability and energy transfers in a minimal low-dimensional model.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {30}, number = {7}, pages = {073110}, doi = {10.1063/5.0002751}, pmid = {32752610}, issn = {1089-7682}, abstract = {In this paper, we derive a four-mode model for the Kolmogorov flow by employing Galerkin truncation and the Craya-Herring basis for the decomposition of velocity field. After this, we perform a bifurcation analysis of the model. Though our low-dimensional model has fewer modes than past models, it captures the essential features of the primary bifurcation of the Kolmogorov flow. For example, it reproduces the critical Reynolds number for the supercritical pitchfork bifurcation and the flow structures of past works. We also demonstrate energy transfers from intermediate scales to large scales. We perform direct numerical simulations of the Kolmogorov flow and show that our model predictions match the numerical simulations very well.}, }
@article {pmid32752609, year = {2020}, author = {Josserand, C and Le Berre, M and Pomeau, Y}, title = {Scaling laws in turbulence.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {30}, number = {7}, pages = {073137}, doi = {10.1063/1.5144147}, pmid = {32752609}, issn = {1089-7682}, abstract = {Following the idea that dissipation in turbulence at high Reynolds number is dominated by singular events in space-time and described by solutions of the inviscid Euler equations, we draw the conclusion that in such flows, scaling laws should depend only on quantities appearing in the Euler equations. This excludes viscosity or a turbulent length as scaling parameters and constrains drastically possible analytical pictures of this limit. We focus on the drag law deduced by Newton for a projectile moving quickly in a fluid at rest. Inspired by this Newton's drag force law (proportional to the square of the speed of the moving object in the limit of large Reynolds numbers), which is well verified in experiments when the location of the detachment of the boundary layer is defined, we propose an explicit relationship between the Reynolds stress in the turbulent wake and quantities depending on the velocity field (averaged in time but depending on space). This model takes the form of an integrodifferential equation for the velocity which is eventually solved for a Poiseuille flow in a circular pipe.}, }
@article {pmid32751881, year = {2020}, author = {Voglhuber-Brunnmaier, T and Jakoby, B}, title = {Higher-Order Models for Resonant Viscosity and Mass-Density Sensors.}, journal = {Sensors (Basel, Switzerland)}, volume = {20}, number = {15}, pages = {}, pmid = {32751881}, issn = {1424-8220}, support = {LCM (COMET-K2)//&#xd6;sterreichische Forschungsf&#xf6;rderungsgesellschaft/ ; }, abstract = {Advanced fluid models relating viscosity and density to resonance frequency and quality factor of vibrating structures immersed in fluids are presented. The numerous established models which are ultimately all based on the same approximation are refined, such that the measurement range for viscosity can be extended. Based on the simple case of a vibrating cylinder and dimensional analysis, general models for arbitrary order of approximation are derived. Furthermore, methods for model parameter calibration and the inversion of the models to determine viscosity and/or density from measured resonance parameters are shown. One of the two presented fluid models is a viscosity-only model, where the parameters of it can be calibrated without knowledge of the fluid density. The models are demonstrated for a tuning fork-based commercial instrument, where maximum deviations between measured and reference viscosities of approximately ±0.5% in the viscosity range from 1.3 to 243 mPas could be achieved. It is demonstrated that these results show a clear improvement over the existing models.}, }
@article {pmid32738822, year = {2020}, author = {Manchester, EL and Xu, XY}, title = {The effect of turbulence on transitional flow in the FDA's benchmark nozzle model using large-eddy simulation.}, journal = {International journal for numerical methods in biomedical engineering}, volume = {36}, number = {10}, pages = {e3389}, doi = {10.1002/cnm.3389}, pmid = {32738822}, issn = {2040-7947}, mesh = {*Benchmarking ; *Computer Simulation ; *Models, Cardiovascular ; Stress, Mechanical ; United States ; *United States Food and Drug Administration ; }, abstract = {The Food and Drug Administration's (FDA) benchmark nozzle model has been studied extensively both experimentally and computationally. Although considerable efforts have been made on validations of a variety of numerical models against available experimental data, the transitional flow cases are still not fully resolved, especially with regards to detailed comparison of predicted turbulence quantities with experimental measurements. This study aims to fill this gap by conducting large-eddy simulations (LES) of flow through the FDA's benchmark model, at a transitional Reynolds number of 2000. Numerical results are compared to previous interlaboratory experimental results, with an emphasis on turbulence characteristics. Our results show that the LES methodology can accurately capture laminar quantities throughout the model. In the pre-jet breakdown region, predicted turbulence quantities are generally larger than high resolution experimental data acquired with laser Doppler velocimetry. In the jet breakdown regions, where maximum Reynolds stresses occur, Reynolds shear stresses show excellent agreement. Differences of up to 4% and 20% are observed near the jet core in the axial and radial normal Reynolds stresses, respectively. Comparisons between viscous and Reynolds shear stresses show that peak viscous shear stresses occur in the nozzle throat reaching a value of 18 Pa in the boundary layer, whilst peak Reynolds shear stresses occur in the jet breakdown region reaching a maximum value of 87 Pa. Our results highlight the importance in considering both laminar and turbulent contributions towards shear stresses and that neglecting the turbulence effect can significantly underestimate the total shear force exerted on the fluid.}, }
@article {pmid32731122, year = {2020}, author = {Ahmed, R and Ali, N and Al-Khaled, K and Khan, SU and Tlili, I}, title = {Finite difference simulations for non-isothermal hydromagnetic peristaltic flow of a bio-fluid in a curved channel: Applications to physiological systems.}, journal = {Computer methods and programs in biomedicine}, volume = {195}, number = {}, pages = {105672}, doi = {10.1016/j.cmpb.2020.105672}, pmid = {32731122}, issn = {1872-7565}, mesh = {*Body Fluids ; Equipment Design ; *Peristalsis ; Rheology ; Temperature ; }, abstract = {Owing to the fundamental significances of peristalsis phenomenon in various biological systems like circulation of blood in vessels, lungs devices, pumping of blood in heart and movement of chyme in the gastrointestinal tract, variety of research by scientist on this topic has been presented in recently years. The peristaltic pumping plays a novel role in various industrial processes like transfer of sanitary materials, the pumping equipment design of roller pumps and many more. The present article investigates numerically the theoretical aspects of heat and mass transportation in peristaltic pattern of Carreau fluid through a curved channel. The computations for axial velocity, pressure rise, temperature field, mass concentration, and stream function are carried out under low Reynolds number and long wavelength approximation in the wave frame of reference by utilizing appropriate numerical implicit finite difference technique (FDM). The implementation of numerical procedure and graphical representation of the computations are accomplished using MATLAB language. The impacts of rheological parameters of Carreau fluid, Brinkmann number, curvature parameter and Hartmann number are shown and discussed briefly. The study shows that for shear thinning of bio-materials, the velocity exhibits the boundary layer character near the boundary walls for greater Hartmann number. The interesting observations based on numerical simulations are graphically elaborated. The results show that the curvature of channel with larger value allows more heat transportation within the flow domain. On the contrary, inside the channel wall, the solutal mass concentration follows an increasing trend with decreasing the channel curvature. The temperature profile enhanced with increment of power-law index and curvature parameter. Moreover, the concentration profile increases with Brinkmann number and Hartmann number.}, }
@article {pmid32728231, year = {2020}, author = {Boukharfane, R and Parsani, M and Bodart, J}, title = {Characterization of pressure fluctuations within a controlled-diffusion blade boundary layer using the equilibrium wall-modelled LES.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {12735}, pmid = {32728231}, issn = {2045-2322}, abstract = {In this study, the generation of airfoil trailing edge broadband noise that arises from the interaction of turbulent boundary layer with the airfoil trailing edge is investigated. The primary objectives of this work are: (i) to apply a wall-modelled large-eddy simulation (WMLES) approach to predict the flow of air passing a controlled-diffusion blade, and (ii) to study the blade broadband noise that is generated from the interaction of a turbulent boundary layer with a lifting surface trailing edge. This study is carried out for two values of the Mach number, [Formula: see text] and 0.5, two values of the chord Reynolds number, [Formula: see text] and [Formula: see text], and two angles of attack, AoA [Formula: see text] and [Formula: see text]. To examine the influence of the grid resolution on aerodynamic and aeroacoustic quantities, we compare our results with experimental data available in the literature. We also compare our results with two in-house numerical solutions generated from two wall-resolved LES (WRLES) calculations, one of which has a DNS-like resolution. We show that WMLES accurately predicts the mean pressure coefficient distribution, velocity statistics (including the mean velocity), and the traces of Reynolds tensor components. Furthermore, we observe that the instantaneous flow structures computed by the WMLES resemble those found in the reference WMLES database, except near the leading edge region. Some of the differences observed in these structures are associated with tripping and the transition to a turbulence mechanism near the leading edge, which are significantly affected by the grid resolution. The aeroacoustic noise calculations indicate that the power spectral density profiles obtained using the WMLES compare well with the experimental data.}, }
@article {pmid32709009, year = {2020}, author = {Wang, Y and Zhang, Y and Qiao, Z and Wang, W}, title = {A 3D Printed Jet Mixer for Centrifugal Microfluidic Platforms.}, journal = {Micromachines}, volume = {11}, number = {7}, pages = {}, pmid = {32709009}, issn = {2072-666X}, support = {G-231823//The Gulf of Mexico Research Initiative/ ; }, abstract = {Homogeneous mixing of microscopic volume fluids at low Reynolds number is of great significance for a wide range of chemical, biological, and medical applications. An efficient jet mixer with arrays of micronozzles was designed and fabricated using additive manufacturing (three-dimensional (3D) printing) technology for applications in centrifugal microfluidic platforms. The contact surface of miscible liquids was enhanced significantly by impinging plumes from two opposite arrays of micronozzles to improve mixing performance. The mixing efficiency was evaluated and compared with the commonly used Y-shaped micromixer. Effective mixing in the jet mixer was achieved within a very short timescale (3s). This 3D printed jet mixer has great potential to be implemented in applications by being incorporated into multifarious 3D printing devices in microfluidic platforms.}, }
@article {pmid32702453, year = {2020}, author = {Emami, MS and Haghshenasfard, M and Zarghami, R and Sadeghi, R and Esfahany, MN}, title = {Experimental study on the reduction of loratadine particle size through confined liquid impinging jets.}, journal = {International journal of pharmaceutics}, volume = {587}, number = {}, pages = {119668}, doi = {10.1016/j.ijpharm.2020.119668}, pmid = {32702453}, issn = {1873-3476}, mesh = {*Loratadine ; *Nanoparticles ; Particle Size ; Solubility ; Solvents ; }, abstract = {The confined liquid impinging jets (CLIJ) technique was applied as a simple and effective approach to reducing the particle size of loratadine to enhance its solubility. The effect of anti-solvent (AS) to solution (S) flow rate ratio, organic phase concentration, Reynolds number (Re), and stabilizer concentration was investigated in this reduction process. After the synthesis, the chemical and physical properties of loratadine nanoparticles were determined through different characterization and analytical techniques. The results indicated that the particle size of loratadine decreases from 320 nm to 80 nm by increasing the AS/S ratio from 1 to 25. It was found that the particle size of loratadine was unchanged at the higher AS/S ratios. The loratadine nanoparticle size was optimized by changing the solution concentration, Re, and Tween 80 as a stabilizer. The finest loratadine nanoparticle size of about 53 nm was obtained with a narrow size distribution, which corresponds to solution concentration of 35 mg/mL, Re of 5687, and 0.1% (w/v) stabilizer concentration. It was revealed that the optimized loratadine nanoparticles completely dissolved after 11 min, indicating the loratadine nanoparticle dissolution rate 50 times faster than raw loratadine.}, }
@article {pmid32688541, year = {2020}, author = {Fouxon, I and Lee, C}, title = {Large deviations, singularity, and lognormality of energy dissipation in turbulence.}, journal = {Physical review. E}, volume = {101}, number = {6-1}, pages = {061101}, doi = {10.1103/PhysRevE.101.061101}, pmid = {32688541}, issn = {2470-0053}, abstract = {We study implications of the assumption of power-law dependence of moments of energy dissipation in turbulence on the Reynolds number Re, holding due to intermittency. We demonstrate that at Re→∞ the dissipation's logarithm divided by lnRe converges with probability one to a negative constant. This implies that the dissipation is singular in the limit, as is known phenomenologically. The proof uses a large deviations function, whose existence is implied by the power-law assumption, and which provides the general asymptotic form of the dissipation's distribution. A similar function exists for vorticity and for velocity differences where it proves the moments representation of the multifractal model (MF). Then we observe that derivative of the scaling exponents of the dissipation, considered as a function of the order of the moment, is small at the origin. Thus the variation with the order is slow and can be described by a quadratic function. Indeed, the quadratic function, which corresponds to log-normal statistics, fits the data. Moreover, combining the lognormal scaling with the MF we derive a formula for the anomalous scaling exponents of turbulence which also fits the data. Thus lognormality, not to be confused with the Kolmogorov (1962) assumption of lognormal dissipation in the inertial range, when used in conjunction with the MF provides a concise way to get all scaling exponents of turbulence available at present.}, }
@article {pmid32688510, year = {2020}, author = {Morita, T and Omori, T and Nakayama, Y and Toyabe, S and Ishikawa, T}, title = {Harnessing random low Reynolds number flow for net migration.}, journal = {Physical review. E}, volume = {101}, number = {6-1}, pages = {063101}, doi = {10.1103/PhysRevE.101.063101}, pmid = {32688510}, issn = {2470-0053}, abstract = {Random noise in low Reynolds number flow has rarely been used to obtain net migration of microscale objects. In this study, we numerically show that net migration of a microscale object can be extracted from random directional fluid forces in Stokes flow, by introducing deformability and inhomogeneous density into the object. We also developed a mathematical framework to describe the deformation-induced migration caused by noise. These results provide a basis for understanding the noise-induced migration of a microswimmer and are useful for harnessing energy from low Reynolds number flow.}, }
@article {pmid32685735, year = {2020}, author = {Askar, AH and Kadham, SA and Mshehid, SH}, title = {The surfactants effect on the heat transfer enhancement and stability of nanofluid at constant wall temperature.}, journal = {Heliyon}, volume = {6}, number = {7}, pages = {e04419}, doi = {10.1016/j.heliyon.2020.e04419}, pmid = {32685735}, issn = {2405-8440}, abstract = {Surfactants role in the enhancement of the heat transfer and stability of alumina oxide - distilled water nanofluid was introduced in this research, where there are limited studies that conjugate between the stability improvement and its effect on the heat transfer coefficients. Four weight concentrations for the experiment were used (0.1, 0.3, 0.6, and 0.9%) with 20 nm particle size under a constant wall temperature. The selection of appropriate surfactants weight was tested too by implementing three weight concentrations (0.5, 1, 1.5, and 2 %) related to each nanofluid concentration via measuring their effect on the zeta potential value. The heat transfer augmentation was tested through a double horizontal pipe under a constant wall temperature at entrance region with Reynolds number range (4000-11800). The results manifested the use of nanofluid worked on enhancement the heat transfer performance better than water, and the stable nanofluid elucidated better results.}, }
@article {pmid32680965, year = {2020}, author = {Yang, T and Sprinkle, B and Guo, Y and Qian, J and Hua, D and Donev, A and Marr, DWM and Wu, N}, title = {Reconfigurable microbots folded from simple colloidal chains.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {117}, number = {31}, pages = {18186-18193}, pmid = {32680965}, issn = {1091-6490}, support = {R01 NS102465/NS/NINDS NIH HHS/United States ; R21 AI138214/AI/NIAID NIH HHS/United States ; }, mesh = {*Chemical Engineering ; Colloids/*chemistry ; Magnetics ; *Robotics ; }, abstract = {To overcome the reversible nature of low-Reynolds-number flow, a variety of biomimetic microrobotic propulsion schemes and devices capable of rapid transport have been developed. However, these approaches have been typically optimized for a specific function or environment and do not have the flexibility that many real organisms exhibit to thrive in complex microenvironments. Here, inspired by adaptable microbes and using a combination of experiment and simulation, we demonstrate that one-dimensional colloidal chains can fold into geometrically complex morphologies, including helices, plectonemes, lassos, and coils, and translate via multiple mechanisms that can be varied with applied magnetic field. With chains of multiblock asymmetry, the propulsion mode can be switched from bulk to surface-enabled, mimicking the swimming of microorganisms such as flagella-rotating bacteria and tail-whipping sperm and the surface-enabled motion of arching and stretching inchworms and sidewinding snakes. We also demonstrate that reconfigurability enables navigation through three-dimensional and narrow channels simulating capillary blood vessels. Our results show that flexible microdevices based on simple chains can transform both shape and motility under varying magnetic fields, a capability we expect will be particularly beneficial in complex in vivo microenvironments.}, }
@article {pmid32680443, year = {2020}, author = {Ma, Y and Zhang, M and Luo, H}, title = {Numerical and experimental studies of gas-liquid flow and pressure drop in multiphase pump valves.}, journal = {Science progress}, volume = {103}, number = {3}, pages = {36850420940885}, doi = {10.1177/0036850420940885}, pmid = {32680443}, issn = {2047-7163}, abstract = {A numerical and experimental study was carried out to investigate the two-phase flow fields of the typical three valves used in the multiphase pumps. Under the gas volume fraction conditions in the range of 0%-100%, the three-dimensional steady and dynamic two-phase flow characteristics, pressure drops, and their multipliers of the ball valve, cone valve, and disk valve were studied, respectively, using Eulerian-Eulerian approach and dynamic grid technique in ANSYS FLUENT. In addition, a valve test system was built to verify the simulated results by the particle image velocimetry and pressure test. The flow coefficient CQ (about 0.989) of the disk valve is greater than those of the other valves (about 0.864) under the steady flow with a high Reynolds number. The two-phase pressure drops of the three valves fluctuate in different forms with the vibration of the cores during the dynamic opening. The two-phase multipliers of the fully opened ball valve are consistent with the predicted values of the Morris model, while those of the cone valve and disk valve had the smallest differences with the predicted values of the Chisholm model. Through the comprehensive analysis of the flow performance, pressure drop, and dynamic stability of the three pump valves, the disk valve is found to be more suitable for the multiphase pumps due to its smaller axial space, resistance loss, and better flow capacity.}, }
@article {pmid32679732, year = {2020}, author = {Juraeva, M and Kang, DJ}, title = {Mixing Performance of a Cross-Channel Split-and-Recombine Micro-Mixer Combined with Mixing Cell.}, journal = {Micromachines}, volume = {11}, number = {7}, pages = {}, pmid = {32679732}, issn = {2072-666X}, abstract = {A new cross-channel split-and-recombine (CC-SAR) micro-mixer was proposed, and its performance was demonstrated numerically. A numerical study was carried out over a wide range of volume flow rates from 3.1 μL/min to 826.8 μL/min. The corresponding Reynolds number ranges from 0.3 to 80. The present micro-mixer consists of four mixing units. Each mixing unit is constructed by combining one split-and-recombine (SAR) unit with a mixing cell. The mixing performance was analyzed in terms of the degree of mixing and relative mixing cost. All numerical results show that the present micro-mixer performs better than other micro-mixers based on SARs over a wide range of volume flow rate. The mixing enhancement is realized by a particular motion of vortex flow: the Dean vortex in the circular sub-channel and another vortex inside the mixing cell. The two vortex flows are generated on the different planes perpendicular to each other. They cause the two fluids to change their relative position as the fluids flow into the circular sub-channel of the SAR, eventually promoting violent mixing. High vorticity in the mixing cell elongates the flow interface between two fluids, and promotes mixing in the flow regime of molecular diffusion dominance.}, }
@article {pmid32675836, year = {2020}, author = {Liu, J and Yang, W and Dong, M and Marsden, AL}, title = {The nested block preconditioning technique for the incompressible Navier-Stokes equations with emphasis on hemodynamic simulations.}, journal = {Computer methods in applied mechanics and engineering}, volume = {367}, number = {}, pages = {}, pmid = {32675836}, issn = {0045-7825}, support = {R01 EB018302/EB/NIBIB NIH HHS/United States ; R01 HL121754/HL/NHLBI NIH HHS/United States ; R01 HL123689/HL/NHLBI NIH HHS/United States ; R01 HL139796/HL/NHLBI NIH HHS/United States ; }, abstract = {We develop a novel iterative solution method for the incompressible Navier-Stokes equations with boundary conditions coupled with reduced models. The iterative algorithm is designed based on the variational multiscale formulation and the generalized-α scheme. The spatiotemporal discretization leads to a block structure of the resulting consistent tangent matrix in the Newton-Raphson procedure. As a generalization of the conventional block preconditioners, a three-level nested block preconditioner is introduced to attain a better representation of the Schur complement, which plays a key role in the overall algorithm robustness and efficiency. This approach provides a flexible, algorithmic way to handle the Schur complement for problems involving multiscale and multiphysics coupling. The solution method is implemented and benchmarked against experimental data from the nozzle challenge problem issued by the US Food and Drug Administration. The robustness, efficiency, and parallel scalability of the proposed technique are then examined in several settings, including moderately high Reynolds number flows and physiological flows with strong resistance effect due to coupled downstream vasculature models. Two patient-specific hemodynamic simulations, covering systemic and pulmonary flows, are performed to further corroborate the efficacy of the proposed methodology.}, }
@article {pmid32666327, year = {2020}, author = {Xue, Y and Hellmuth, R and Shin, DH}, title = {Formation of Vortices in Idealised Branching Vessels: A CFD Benchmark Study.}, journal = {Cardiovascular engineering and technology}, volume = {11}, number = {5}, pages = {544-559}, doi = {10.1007/s13239-020-00477-9}, pmid = {32666327}, issn = {1869-4098}, mesh = {Arteries/pathology/*physiopathology ; Atherosclerosis/pathology/*physiopathology ; Blood Flow Velocity ; Computer Simulation ; *Hemodynamics ; Humans ; Hydrodynamics ; *Models, Cardiovascular ; Numerical Analysis, Computer-Assisted ; Plaque, Atherosclerotic ; Stress, Mechanical ; }, abstract = {PURPOSE: Atherosclerosis preferentially occurs near the junction of branching vessels, where blood recirculation tends to occur (Malek et al. in J Am Med Assoc 282(21):2035-2042, 1999, https://doi.org/10.1001/jama.282.21.2035). For decades, CFD has been used to predict flow patterns such as separation and recirculation zones in hemodynamic models, but those predictions have rarely been validated with experimental data. In the context of verification and validation (V&amp;V), we first conduct a CFD benchmark calculation that reproduces the vortex detection experiments of Karino and Goldsmith (1980) with idealised branching blood vessels (Karino and Goldsmith in Trans. Am. Soc. Artif. Internal Organs 26:500-506, 1980). The critical conditions for the formation of recirculation vortices, the so-called critical Reynolds numbers, are the main parameters for comparison with the experimental data to demonstrate the credibility of the CFD workflow. We then characterise the wall shear stresses and develop a surrogate model for the size of formed vortices.<br><br>METHODS: An automated parametric study generating more than 12,000 CFD simulations was performed, sweeping the geometries and flow conditions found in the experiments by Karino and Goldsmith. The flow conditions were restricted to steady-state laminar flow, with a range of inflow Reynolds numbers up to 350, with various flow ratios between the main branch outlet and side branch outlet. The side branch diameter was scaled relative to the main branch diameter, ranging from 1.05/3 to 3/3; and the branching angles ranged in size from [Formula: see text] to [Formula: see text]. Recirculation vortices were detected by the inversion of the velocity vector at certain locations, as well as by the inversion of the wall shear stress (WSS) vector.<br><br>RESULTS: The CFD simulations demonstrated good agreement with the experimental data on the critical Reynolds numbers. The spatial distributions of WSS on each branch were analysed to identify potential regions of disease. Once a vortex is formed, the size of the vortex increases by the square root of the Reynolds number. The CFD data was fitted to a surrogate model that accurately predicts the vortex size without the need to run computationally more expensive CFD simulations.<br><br>CONCLUSIONS: This benchmark study validates the CFD simulation of vortex detection in idealised branching vessels under comprehensive flow conditions. This work also proposes a surrogate model for the size of the vortex, which could reduce the computational requirements in the studies related to branching vessels and complex vascular systems.}, }
@article {pmid32664605, year = {2020}, author = {Forte, P and Morais, JE and P Neiva, H and Barbosa, TM and Marinho, DA}, title = {The Drag Crisis Phenomenon on an Elite Road Cyclist-A Preliminary Numerical Simulations Analysis in the Aero Position at Different Speeds.}, journal = {International journal of environmental research and public health}, volume = {17}, number = {14}, pages = {}, pmid = {32664605}, issn = {1660-4601}, mesh = {Arm ; *Bicycling ; Head Protective Devices ; Humans ; *Hydrodynamics ; Male ; *Sports ; }, abstract = {The drag crisis phenomenon is the drop of drag coefficient (Cd) with increasing Reynolds number (Re) or speed. The aim of this study was to assess the hypothetical drag crisis phenomenon in a sports setting, assessing it in a bicycle-cyclist system. A male elite-level cyclist was recruited for this research and his competition bicycle, helmet, suit, and shoes were used. A three-dimensional (3D) geometry was obtained with a 3D scan with the subject in a static aero position. A domain with 7 m of length, 2.5 m of width and 2.5 m of height was created around the cyclist. The domain was meshed with 42 million elements. Numerical simulations by computer fluid dynamics (CFD) fluent numerical code were conducted at speeds between 1 m/s and 22 m/s, with increments of 1 m/s. The drag coefficient ranged between 0.60 and 0.95 across different speeds and Re. The highest value was observed at 2 m/s (Cd = 0.95) and Re of 3.21 × 10[5], whereas the lower Cd was noted at 9 m/s (Cd = 0.60) and 9.63 × 10[5]. A drag crisis was noted between 3 m/s and 9 m/s. Pressure Cd ranged from 0.35 to 0.52 and the lowest value was observed at 3 m/s and the highest at 2 m/s. The viscous drag coefficient ranged between 0.15 and 0.43 and presented a trend decreasing from 4 m/s to 22 m/s. Coaches, cyclists, researchers, and support staff must consider that Cd varies with speed and Re, and the bicycle-cyclist dimensions, shape, or form may affect drag and performance estimations. As a conclusion, this preliminary work noted a drag crisis between 3 m/s and 9 m/s in a cyclist in the aero position.}, }
@article {pmid32660001, year = {2020}, author = {Granados-Ortiz, FJ and Ortega-Casanova, J}, title = {Mechanical Characterisation and Analysis of a Passive Micro Heat Exchanger.}, journal = {Micromachines}, volume = {11}, number = {7}, pages = {}, pmid = {32660001}, issn = {2072-666X}, support = {UMA18-FEDERJA-184//UMA/Junta de Andalucia/European Union/ ; }, abstract = {Heat exchangers are widely used in many mechanical, electronic, and bioengineering applications at macro and microscale. Among these, the use of heat exchangers consisting of a single fluid passing through a set of geometries at different temperatures and two flows in T-shape channels have been extensively studied. However, the application of heat exchangers for thermal mixing over a geometry leading to vortex shedding has not been investigated. This numerical work aims to analyse and characterise a heat exchanger for microscale application, which consists of two laminar fluids at different temperature that impinge orthogonally onto a rectangular structure and generate vortex shedding mechanics that enhance thermal mixing. This work is novel in various aspects. This is the first work of its kind on heat transfer between two fluids (same fluid, different temperature) enhanced by vortex shedding mechanics. Additionally, this research fully characterise the underlying vortex mechanics by accounting all geometry and flow regime parameters (longitudinal aspect ratio, blockage ratio and Reynolds number), opposite to the existing works in the literature, which usually vary and analyse blockage ratio or longitudinal aspect ratio only. A relevant advantage of this heat exchanger is that represents a low-Reynolds passive device, not requiring additional energy nor moving elements to enhance thermal mixing. This allows its use especially at microscale, for instance in biomedical/biomechanical and microelectronic applications.}, }
@article {pmid32656413, year = {2020}, author = {Dai, X and Liu, C and Zhao, J and Li, L and Yin, S and Liu, H}, title = {Optimization of Application Conditions of Drag Reduction Agent in Product Oil Pipelines.}, journal = {ACS omega}, volume = {5}, number = {26}, pages = {15931-15935}, pmid = {32656413}, issn = {2470-1343}, abstract = {Drag reduction performance was studied with a rotating disk instrument in the laboratory, and experiments show that there is an initial rapid growth stage and stability stage for drag reduction ratio change. The higher the rotational speed, the larger the initial drag reduction ratio is; the larger the concentration, the shorter the drag reduction stabilization time is. Under high concentration and high speed, the drag reduction onset time is short. Because of the shear degradation, the Reynolds number should be taken into account during use. Through a comparison of diesel properties after adding agents with national standard, it is confirmed that drag reduction agents could be used in this pipeline.}, }
@article {pmid32639756, year = {2020}, author = {Pusztai, I and Juno, J and Brandenburg, A and TenBarge, JM and Hakim, A and Francisquez, M and Sundström, A}, title = {Dynamo in Weakly Collisional Nonmagnetized Plasmas Impeded by Landau Damping of Magnetic Fields.}, journal = {Physical review letters}, volume = {124}, number = {25}, pages = {255102}, doi = {10.1103/PhysRevLett.124.255102}, pmid = {32639756}, issn = {1079-7114}, abstract = {We perform fully kinetic simulations of flows known to produce dynamo in magnetohydrodynamics (MHD), considering scenarios with low Reynolds number and high magnetic Prandtl number, relevant for galaxy cluster scale fluctuation dynamos. We find that Landau damping on the electrons leads to a rapid decay of magnetic perturbations, impeding the dynamo. This collisionless damping process operates on spatial scales where electrons are nonmagnetized, reducing the range of scales where the magnetic field grows in high magnetic Prandtl number fluctuation dynamos. When electrons are not magnetized down to the resistive scale, the magnetic energy spectrum is expected to be limited by the scale corresponding to magnetic Landau damping or, if smaller, the electron gyroradius scale, instead of the resistive scale. In simulations we thus observe decaying magnetic fields where resistive MHD would predict a dynamo.}, }
@article {pmid32620000, year = {2020}, author = {Silverberg, O and Demir, E and Mishler, G and Hosoume, B and Trivedi, N and Tisch, C and Plascencia, D and Pak, OS and Araci, IE}, title = {Realization of a push-me-pull-you swimmer at low Reynolds numbers.}, journal = {Bioinspiration &amp; biomimetics}, volume = {15}, number = {6}, pages = {}, doi = {10.1088/1748-3190/aba2b9}, pmid = {32620000}, issn = {1748-3190}, mesh = {Locomotion ; Models, Biological ; *Robotics ; *Swimming ; Viscosity ; }, abstract = {Locomotion at low Reynolds numbers encounters stringent physical constraints due to the dominance of viscous over inertial forces. A variety of swimming microorganisms have demonstrated diverse strategies to generate self-propulsion in the absence of inertia. In particular, ameboid and euglenoid movements exploit shape deformations of the cell body for locomotion. Inspired by these biological organisms, the 'push-me-pull-you' (PMPY) swimmer (Avron J Eet al2005New J. Phys.7234) represents an elegant artificial swimmer that can escape from the constraints of the scallop theorem and generate self-propulsion in highly viscous fluid environments. In this work, we present the first experimental realization of the PMPY swimmer, which consists of a pair of expandable spheres connected by an extensible link. We designed and constructed robotic PMPY swimmers and characterized their propulsion performance in highly viscous silicone oil in dynamically similar, macroscopic experiments. The proof-of-concept demonstrates the feasibility and robustness of the PMPY mechanism as a viable locomotion strategy at low Reynolds numbers.}, }
@article {pmid32618067, year = {2021}, author = {Kashima, Y and Ninomiya, S}, title = {Hemodialysis efficiency management from the viewpoint of blood removal pressure.}, journal = {Therapeutic apheresis and dialysis : official peer-reviewed journal of the International Society for Apheresis, the Japanese Society for Apheresis, the Japanese Society for Dialysis Therapy}, volume = {25}, number = {2}, pages = {152-159}, doi = {10.1111/1744-9987.13557}, pmid = {32618067}, issn = {1744-9987}, mesh = {Blood Flow Velocity/*physiology ; Blood Pressure ; Blood Viscosity/*physiology ; Equipment Design ; Hematocrit ; Humans ; *Needles ; Regression Analysis ; Renal Dialysis/instrumentation/*methods ; Reproducibility of Results ; }, abstract = {Degradation of dialysis efficiency during hemodialysis, caused by incompatible indwelling needle size or increase in hematocrit, is a serious problem that can threaten a patient's life. This study aims to derive a quantitative index for determining the indwelling needle diameter that can maintain an appropriate blood flow rate, and presents an effective method to prevent a decrease in the actual blood flow rate. The relationships between the set flow rate and various parameters such as indwelling needle diameter, blood viscosity, and arterial line pressure are analyzed. A simple and reliable method for estimating the actual blood flow rate is derived from these relationships. A correlation between viscosity and actual blood flow rate is estimated adequately by regression analysis using a least-squares method. The relationship between Reynolds number and the flow rate reduction ratio is also evaluated. A new parameter (simple estimation method for actual blood flow) is derived by measuring the blood removal pressure. A pump control approach that uses blood removal pressure is suggested, which can be a future research direction in the field of hemodialysis.}, }
@article {pmid32611152, year = {2020}, author = {Zhou, T and Zhang, X and Zhong, S}, title = {An experimental study of trailing edge noise from a heaving airfoil.}, journal = {The Journal of the Acoustical Society of America}, volume = {147}, number = {6}, pages = {4020}, doi = {10.1121/10.0001419}, pmid = {32611152}, issn = {1520-8524}, abstract = {In this study, the far-field noise and near-field flow properties from a heaving NACA 0012 airfoil at the Reynolds number of 6.6×10[4] were investigated experimentally in a 0.4 m[2] anechoic wind tunnel. The airfoil had an incident angle of 0° and followed a sinusoidal heaving motion. The Strouhal number, controlled by changing the heaving frequency and amplitude, varied from 0.0024 to 0.008. The acoustic properties were measured by a free-field microphone placed at a distance of 1.2 m away from the tunnel central line, and the flow structures near the trailing edge were acquired using the particle image velocimetry. It was found that the heaving motion could reduce the sound pressure level (SPL) of the primary peak in the time-averaged spectra. The spectrograms obtained by the short-time Fourier transform revealed that the discrete tones were produced when the airfoil passed through the maximum heaving position. During the corresponding period, a sequence of large-scaled vortices convected on the airfoil surface was observed, and then was shed from the trailing edge to the wake region at the same frequency as the primary tone of the induced sound. With the increase of Strouhal number, the sound signals tended to be broadband, and the overall SPL was increased in the far field.}, }
@article {pmid32609698, year = {2020}, author = {Xu, W and Luo, W and Wang, Y and You, Y}, title = {Data-driven three-dimensional super-resolution imaging of a turbulent jet flame using a generative adversarial network.}, journal = {Applied optics}, volume = {59}, number = {19}, pages = {5729-5736}, doi = {10.1364/AO.392803}, pmid = {32609698}, issn = {1539-4522}, abstract = {Three-dimensional (3D) computed tomography (CT) is becoming a well-established tool for turbulent combustion diagnostics. However, the 3D CT technique suffers from contradictory demands of spatial resolution and domain size. This work therefore reports a data-driven 3D super-resolution approach to enhance the spatial resolution by two times along each spatial direction. The approach, named 3D super-resolution generative adversarial network (3D-SR-GAN), builds a generator and a discriminator network to learn the topographic information and infer high-resolution 3D turbulent flame structure with a given low-resolution counterpart. This work uses numerically simulated 3D turbulent jet flame structures as training data to update model parameters of the GAN network. Extensive performance evaluations are then conducted to show the superiority of the proposed 3D-SR-GAN network, compared with other direct interpolation methods. The results show that a convincing super-resolution (SR) operation with the overall error of ∼4% and the peak signal-to-noise ratio of 37 dB can be reached with an upscaling factor of 2, representing an eight times enhancement of the total voxel number. Moreover, the trained network can predict the SR structure of the jet flame with a different Reynolds number without retraining the network parameters.}, }
@article {pmid32600217, year = {2021}, author = {Moum, JN}, title = {Variations in Ocean Mixing from Seconds to Years.}, journal = {Annual review of marine science}, volume = {13}, number = {}, pages = {201-226}, doi = {10.1146/annurev-marine-031920-122846}, pmid = {32600217}, issn = {1941-0611}, mesh = {El Nino-Southern Oscillation ; *Hydrodynamics ; *Models, Theoretical ; Oceans and Seas ; Rheology ; Seasons ; Seawater/*chemistry ; Temperature ; Tidal Waves ; Time Factors ; }, abstract = {Over the past several decades, there has developed a community-wide appreciation for the importance of mixing at the smallest scales to geophysical fluid dynamics on all scales. This appreciation has spawned greater participation in the investigation of ocean mixing and new ways to measure it. These are welcome developments given the tremendous separation in scales between the basins, [Formula: see text]) m, and the turbulence, [Formula: see text]) m, and the fact that turbulence that leads to thermodynamically irreversible mixing in high-Reynolds-number geophysical flows varies by at least eight orders of magnitude in both space and time. In many cases, it is difficult to separate the dependencies because measurements are sparse, also in both space and time. Comprehensive shipboard turbulence profiling experiments supplemented by Doppler sonar current measurements provide detailed observations of the evolution of the vertical structure of upper-ocean turbulence on timescales of minutes to weeks. Recent technical developments now permit measurements of turbulence in the ocean, at least at a few locations, for extended periods. This review summarizes recent and classic results in the context of our expanding knowledge of the temporal variability of ocean mixing, beginning with a discussion of the timescales of the turbulence itself (seconds to minutes) and how turbulence-enhanced mixing varies over hours, days, tidal cycles, monsoons, seasons, and El Niño-Southern Oscillation timescales (years).}, }
@article {pmid32581842, year = {2020}, author = {Campinho, P and Vilfan, A and Vermot, J}, title = {Blood Flow Forces in Shaping the Vascular System: A Focus on Endothelial Cell Behavior.}, journal = {Frontiers in physiology}, volume = {11}, number = {}, pages = {552}, pmid = {32581842}, issn = {1664-042X}, abstract = {The endothelium is the cell monolayer that lines the interior of the blood vessels separating the vessel lumen where blood circulates, from the surrounding tissues. During embryonic development, endothelial cells (ECs) must ensure that a tight barrier function is maintained whilst dynamically adapting to the growing vascular tree that is being formed and remodeled. Blood circulation generates mechanical forces, such as shear stress and circumferential stretch that are directly acting on the endothelium. ECs actively respond to flow-derived mechanical cues by becoming polarized, migrating and changing neighbors, undergoing shape changes, proliferating or even leaving the tissue and changing identity. It is now accepted that coordinated changes at the single cell level drive fundamental processes governing vascular network morphogenesis such as angiogenic sprouting, network pruning, lumen formation, regulation of vessel caliber and stability or cell fate transitions. Here we summarize the cell biology and mechanics of ECs in response to flow-derived forces, discuss the latest advances made at the single cell level with particular emphasis on in vivo studies and highlight potential implications for vascular pathologies.}, }
@article {pmid32575895, year = {2020}, author = {Nichols, A and Rubinato, M and Cho, YH and Wu, J}, title = {Optimal Use of Titanium Dioxide Colourant to Enable Water Surfaces to Be Measured by Kinect Sensors.}, journal = {Sensors (Basel, Switzerland)}, volume = {20}, number = {12}, pages = {}, pmid = {32575895}, issn = {1424-8220}, support = {EP/L015412/1//Engineering and Physical Sciences Research Council/ ; Singapore attachment scheme//A*STAR UK-IHPC/ ; Early Career Researcher Scheme//The University of Sheffield/ ; }, abstract = {Recent studies have sought to use Microsoft Kinect sensors to measure water surface shape in steady flows or transient flow processes. They have typically employed a white colourant, usually titanium dioxide (TiO2), in order to make the surface opaque and visible to the infrared-based sensors. However, the ability of Kinect Version 1 (KV1) and Kinect Version 2 (KV2) sensors to measure the deformation of ostensibly smooth reflective surfaces has never been compared, with most previous studies using a V1 sensor with no justification. Furthermore, the TiO2 has so far been used liberally and indeterminately, with no consideration as to the type of TiO2 to use, the optimal proportion to use or the effect it may have on the very fluid properties being measured. This paper examines the use of anatase TiO2 with two generations of the Microsoft Kinect sensor. Assessing their performance for an ideal flat surface, it is shown that surface data obtained using the V2 sensor is substantially more reliable. Further, the minimum quantity of colourant to enable reliable surface recognition is discovered (0.01% by mass). A stability test shows that the colourant has a strong tendency to settle over time, meaning the fluid must remain well mixed, having serious implications for studies with low Reynolds number or transient processes such as dam breaks. Furthermore, the effect of TiO2 concentration on fluid properties is examined. It is shown that previous studies using concentrations in excess of 1% may have significantly affected the viscosity and surface tension, and thus the surface behaviour being measured. It is therefore recommended that future studies employ the V2 sensor with an anatase TiO2 concentration of 0.01%, and that the effects of TiO2 on the fluid properties are properly quantified before any TiO2-Kinect-derived dataset can be of practical use, for example, in validation of numerical models or in physical models of hydrodynamic processes.}, }
@article {pmid32574537, year = {2020}, author = {Rhodeland, B and Hoeger, K and Ursell, T}, title = {Bacterial surface motility is modulated by colony-scale flow and granular jamming.}, journal = {Journal of the Royal Society, Interface}, volume = {17}, number = {167}, pages = {20200147}, pmid = {32574537}, issn = {1742-5662}, mesh = {*Bacillus subtilis ; Biophysical Phenomena ; Cell Movement ; *Surface-Active Agents ; Water ; }, abstract = {Microbes routinely face the challenge of acquiring territory and resources on wet surfaces. Cells move in large groups inside thin, surface-bound water layers, often achieving speeds of 30 µm s[-1] within this environment, where viscous forces dominate over inertial forces (low Reynolds number). The canonical Gram-positive bacterium Bacillus subtilis is a model organism for the study of collective migration over surfaces with groups exhibiting motility on length-scales three orders of magnitude larger than themselves within a few doubling times. Genetic and chemical studies clearly show that the secretion of endogenous surfactants and availability of free surface water are required for this fast group motility. Here, we show that: (i) water availability is a sensitive control parameter modulating an abiotic jamming-like transition that determines whether the group remains fluidized and therefore collectively motile, (ii) groups self-organize into discrete layers as they travel, (iii) group motility does not require proliferation, rather groups are pulled from the front, and (iv) flow within expanding groups is capable of moving material from the parent colony into the expanding tip of a cellular dendrite with implications for expansion into regions of varying nutrient content. Together, these findings illuminate the physical structure of surface-motile groups and demonstrate that physical properties, like cellular packing fraction and flow, regulate motion from the scale of individual cells up to length scales of centimetres.}, }
@article {pmid32564722, year = {2020}, author = {Coreixas, C and Wissocq, G and Chopard, B and Latt, J}, title = {Impact of collision models on the physical properties and the stability of lattice Boltzmann methods.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {378}, number = {2175}, pages = {20190397}, doi = {10.1098/rsta.2019.0397}, pmid = {32564722}, issn = {1471-2962}, abstract = {The lattice Boltzmann method (LBM) is known to suffer from stability issues when the collision model relies on the BGK approximation, especially in the zero viscosity limit and for non-vanishing Mach numbers. To tackle this problem, two kinds of solutions were proposed in the literature. They consist in changing either the numerical discretization (finite-volume, finite-difference, spectral-element, etc.) of the discrete velocity Boltzmann equation (DVBE), or the collision model. In this work, the latter solution is investigated in detail. More precisely, we propose a comprehensive comparison of (static relaxation time based) collision models, in terms of stability, and with preliminary results on their accuracy, for the simulation of isothermal high-Reynolds number flows in the (weakly) compressible regime. It starts by investigating the possible impact of collision models on the macroscopic behaviour of stream-and-collide based D2Q9-LBMs, which clarifies the exact physical properties of collision models on LBMs. It is followed by extensive linear and numerical stability analyses, supplemented with an accuracy study based on the transport of vortical structures over long distances. In order to draw conclusions as generally as possible, the most common moment spaces (raw, central, Hermite, central Hermite and cumulant), as well as regularized approaches, are considered for the comparative studies. LBMs based on dynamic collision mechanisms (entropic collision, subgrid-scale models, explicit filtering, etc.) are also briefly discussed. This article is part of the theme issue 'Fluid dynamics, soft matter and complex systems: recent results and new methods'.}, }
@article {pmid32563162, year = {2020}, author = {Sonwani, RK and Giri, BS and Jaiswal, RP and Singh, RS and Rai, BN}, title = {Performance evaluation of a continuous packed bed bioreactor: Bio-kinetics and external mass transfer study.}, journal = {Ecotoxicology and environmental safety}, volume = {201}, number = {}, pages = {110860}, doi = {10.1016/j.ecoenv.2020.110860}, pmid = {32563162}, issn = {1090-2414}, mesh = {Bacillales/growth &amp; development/metabolism ; Biodegradation, Environmental ; Bioreactors/*microbiology ; Cells, Immobilized/microbiology ; Kinetics ; Naphthalenes/*analysis ; Polyethylene/chemistry ; Water Pollutants, Chemical/*analysis ; Water Purification/*methods ; }, abstract = {The biodegradation of naphthalene using low-density polyethylene (LDPE) immobilized Exiguobacterium sp. RKS3 (MG696729) in a packed bed bioreactor (PBBR) was studied. The performance of a continuous PBBR was evaluated at different inlet flow rates (IFRs) (20-100 mL/h) under 64 days of operation. The maximum naphthalene removal efficiency (RE) was found at low IFR, and it further decreased with increasing IFRs. In a continuous PBBR, the external mass transfer (EMT) aspect was analysed at various IFRs, and experimental data were interrelated between Colburn factor (JD) and Reynolds number (NRe) as [Formula: see text] . A new correlation [Formula: see text] was obtained to predict the EMT aspect of naphthalene biodegradation. Andrew-Haldane model was used to evaluate the bio-kinetic parameters of naphthalene degradation, and kinetic constant νmax, Js, and Ji were found as 0.386 per day, 13.6 mg/L, and 20.54 mg/L, respectively.}, }
@article {pmid32557795, year = {2020}, author = {Dial, TR and Lauder, GV}, title = {Longer development provides first-feeding fish time to escape hydrodynamic constraints.}, journal = {Journal of morphology}, volume = {281}, number = {8}, pages = {956-969}, doi = {10.1002/jmor.21224}, pmid = {32557795}, issn = {1097-4687}, mesh = {Animals ; Biomechanical Phenomena ; Bone and Bones/anatomy &amp; histology ; Feeding Behavior/*physiology ; Female ; *Hydrodynamics ; Larva/growth &amp; development ; Male ; Models, Biological ; Predatory Behavior ; Time Factors ; Viscosity ; Zebrafish/*growth &amp; development ; }, abstract = {What is the functional effect of prolonged development? By controlling for size, we quantify first-feeding performance and hydrodynamics of zebrafish and guppy offspring (5 ± 0.5 mm in length), which differ fivefold in developmental time and twofold in ontogenetic state. By manipulating water viscosity, we control the hydrodynamic regime, measured as Reynolds number. We predicted that if feeding performance were strictly the result of hydrodynamics, and not development, feeding performance would scale with Reynolds number. We find that guppy offspring successfully feed at much greater distances to prey (1.0 vs. 0.2 mm) and with higher capture success (90 vs. 20%) compared with zebrafish larvae, and that feeding performance was not a result of Reynolds number alone. Flow visualization shows that zebrafish larvae produce a bow wave ~0.2 mm in length, and that the flow field produced during suction does not extend beyond this bow wave. Due to well-developed oral jaw protrusion, the similar-sized suction field generated by guppy offspring extends beyond the horizon of their bow wave, leading to successful prey capture from greater distances. These findings suggest that prolonged development and increased ontogenetic state provides first-feeding fish time to escape the pervasive hydrodynamic constraints (bow wave) of being small.}, }
@article {pmid32555272, year = {2020}, author = {Gangfu, L and Haiwang, L and Ruquan, Y and Huijie, W and Zhi, T and Shuangzhi, X}, title = {Experimental Investigation on Velocity and Temperature Field in a Rotating Non-isothermal Turbulent Boundary Layer using Hot-wire.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {9892}, pmid = {32555272}, issn = {2045-2322}, support = {51906008//National Natural Science Foundation of China (National Science Foundation of China)/ ; 51822602//National Natural Science Foundation of China (National Science Foundation of China)/ ; 51906008//National Natural Science Foundation of China (National Science Foundation of China)/ ; }, abstract = {This experiment measured the instantaneous temperature and velocity field synchronously in non-isothermal turbulent boundary layer in a rotating straight channel with a parallel-array hot-wire probe. The Reynolds number based on the bulk mean velocity (U) and hydraulic diameter (D) is 19000, and the rotation numbers are 0, 0.07, 0.14, 0.21 and 0.28. The mean velocity u and mean temperature T as well as their fluctuating quantity u' and T' were measured at three streamwise locations (x/D = 4.06, 5.31, 6.56). A method for temperature-changing calibration with constant temperature hot-wire anemometers was proposed. It achieved the calibration in operational temperature range (15.5 °C-50 °C) of the hot-wire via a home-made heating section. The measurement system can obtain the velocity and temperature in a non-isothermal turbulent boundary layer at rotating conditions. The result analysis mainly contains the dimensionless mean temperature, temperature fluctuation as well as its skewness and flatness and streamwise turbulent heat flux. For the trailing side, the rotation effect is more obvious, and makes the dimensionless temperature profiles lower than that under static conditions. The dimensionless streamwise heat flux shows a linear decrease trend in the boundary layer. It is hoped that this research can improve our understanding of the flow and heat transfer mechanism in the internal cooling passages of turbine rotor blades.}, }
@article {pmid32555239, year = {2020}, author = {Gepner, SW and Floryan, JM}, title = {Use of Surface Corrugations for Energy-Efficient Chaotic Stirring in Low Reynolds Number Flows.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {9865}, pmid = {32555239}, issn = {2045-2322}, abstract = {We demonstrate that an intensive stirring can be achieved in laminar channel flows in a passive manner by utilizing the recently discovered instability waves which lead to chaotic particle movements. The stirring is suitable for mixtures made of delicate constituents prone to mechanical damage, such as bacteria and DNA samples, as collisions between the stream and both the bounding walls as well as mechanical mixing devices are avoided. Debris accumulation is prevented as no stagnant fluid zones are formed. Groove symmetries can be used to limit stirring to selected parts of the flow domain. The energy cost of flows with such stirring is either smaller or marginally larger than the energy cost of flows through smooth channels.}, }
@article {pmid32543084, year = {2020}, author = {Xu, K and Wang, M and Tang, W and Ding, Y and Hu, A}, title = {Flash nanoprecipitation with Gd(III)-based metallosurfactants to fabricate polylactic acid nanoparticles as highly efficient contrast agents for magnetic resonance imaging.}, journal = {Chemistry, an Asian journal}, volume = {15}, number = {16}, pages = {2475-2479}, doi = {10.1002/asia.202000624}, pmid = {32543084}, issn = {1861-471X}, support = {21274042//National Natural Science Foundation of China/ ; 21503078//National Natural Science Foundation of China/ ; 22221818014//Fundamental Research Funds for the Central Universities/ ; B502//Shanghai Leading Academic Discipline Project/ ; //Eastern Scholar Professorship/ ; //Shanghai local government/ ; }, mesh = {Biocompatible Materials/chemistry ; Contrast Media/*chemistry ; Gadolinium/*chemistry ; Hydrophobic and Hydrophilic Interactions ; Magnetic Resonance Imaging/*methods ; Nanoparticles/*chemistry ; Particle Size ; Polyesters/*chemistry ; Polyethylene Glycols/chemistry ; Surface-Active Agents/chemistry ; }, abstract = {Polylactic acid (PLA) nanoparticles coated with Gd(III)-based metallosurfactants (MS) are prepared using a simple and rapid one-step method, flash nanoprecipitation (FNP), for magnetic resonance imaging (MRI) applications. By co-assembling the Gd(III)-based MS and an amphiphilic polymer, methoxy poly(ethylene glycol)-b-poly(ϵ-caprolactone) (mPEG-b-PCL), PLA cores were rapidly encapsulated to form biocompatible T1 contrast agents with tunable particle size and narrow size distribution. The hydrophobic property of Gd(III)-based MS were finely tuned to achieve their high loading efficiency. The size of the nanoparticles was easily controlled by tuning the stream velocity, Reynolds number and the amount of the amphiphilic block copolymer during the FNP process. Under the optimized condition, the relaxivity of the nanoparticles was achieved up to 35.39 mM[-1] s[-1] (at 1.5 T), which is over 8 times of clinically used MRI contrast agents, demonstrating the potential application for MR imaging.}, }
@article {pmid32537967, year = {2020}, author = {Zhao, M and Yang, XN and Chen, PY and Sun, WY and Mu, XM and Gao, P and Zhao, GJ}, title = {[Effects of shrub patch pattern on runoff and sediment yield].}, journal = {Ying yong sheng tai xue bao = The journal of applied ecology}, volume = {31}, number = {3}, pages = {735-743}, doi = {10.13287/j.1001-9332.202003.017}, pmid = {32537967}, issn = {1001-9332}, mesh = {*Environmental Monitoring ; *Geologic Sediments ; Rivers ; Soil ; }, abstract = {Understanding the changes of runoff, sediment transport, and hydrodynamic parameters of slopes under the influence of landscape patch coverage and connectivity is of great significance for revealing the hydrodynamic mechanism and hydrological connectivity of slope soil erosion process. In this study, the changes of runoff, sediment transport and hydrodynamic parameters of downhill surface in different coverage levels (0%, 20%, 40%, 60%, 90%) and different connectivity modes (vertical path, horizonal path, S-shaped path, random patches) of shrublands were analyzed by field artificial simulated rainfall test. The results showed that, with the increases of shrub cove-rage, runoff yield and sediment yield decreased exponentially. When the coverage increased to more than 60%, the capacity of shrubs to reduce runoff and sediment became stable. With the increases of shrub coverage, flow velocity, flow depth, Reynolds number, Froude number, stream power, and flow shear resistance significantly decreased, while Manning's roughness coefficient and Darcy-Weisbach resistance coefficient increased significantly. When shrub coverage increased to more than 60%, there was no significant difference in the eigenvalues of hydraulic parameters. The runoff rate under the four connectivity modes followed the order of vertical path > S-shaped path > horizonal path > random patches. The sediment rate was the largest in the vertical path, followed by the S-shaped path, and the horizonal path was not significantly different from the random patches. The path with poor connectivity (horizonal path, random patches) exhibited stronger resistance of hydraulic transmission and poor hydraulic sedimentation capacity than the well-connected path (vertical path, S-shaped path). Our results could provide important theoretical basis for soil erosion control on the Loess Plateau and high-quality development of the Yellow River basin.}, }
@article {pmid32531594, year = {2020}, author = {Lequette, K and Ait-Mouheb, N and Wéry, N}, title = {Hydrodynamic effect on biofouling of milli-labyrinth channel and bacterial communities in drip irrigation systems fed with reclaimed wastewater.}, journal = {The Science of the total environment}, volume = {738}, number = {}, pages = {139778}, doi = {10.1016/j.scitotenv.2020.139778}, pmid = {32531594}, issn = {1879-1026}, mesh = {Bacteria ; Biofilms ; *Biofouling ; Hydrodynamics ; Membranes, Artificial ; Wastewater ; *Water Purification ; }, abstract = {The clogging of drippers due to the development of biofilms reduces the benefits and is an obstacle to the implementation of drip irrigation technology in a reclaimed water context. The narrow section and labyrinth geometry of the dripper channel results the development of a heterogeneous flow behaviours with the vortex zones which it enhance the fouling mechanisms. The objective of this study was to analyse the influence of the three dripper types, defined by their geometric and hydraulic parameters, fed with reclaimed wastewater, on the biofouling kinetics and the bacterial communities. Using optical coherence tomography, we demonstrated that the inlet of the drippers (mainly the first baffle) and vortex zones are the most sensitive area for biofouling. Drippers with the lowest Reynolds number and average cross-section velocity v (1 l·h[-1]) were the most sensible to biofouling, even if detachment events seemed more frequent in this dripper type. Therefore, dripper flow path with larger v should be consider to improve the anti-clogging performance. In addition, the dripper type and the geometry of the flow path influenced the structure of the bacterial communities from dripper biofilms. Relative abundancy of filamentous bacteria belonging to Chloroflexi phylum was higher in 1 l·h[-1] drippers, which presented a higher level of biofouling. However, further research on the role of this phylum in dripper biofouling is required.}, }
@article {pmid32521517, year = {2020}, author = {Gamble, LL and Harvey, C and Inman, DJ}, title = {Load alleviation of feather-inspired compliant airfoils for instantaneous flow control.}, journal = {Bioinspiration &amp; biomimetics}, volume = {15}, number = {5}, pages = {}, doi = {10.1088/1748-3190/ab9b6f}, pmid = {32521517}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Birds/physiology ; *Feathers/physiology ; *Flight, Animal/physiology ; Models, Biological ; Wings, Animal/physiology ; }, abstract = {Birds morph their wing shape to adjust to changing environments through muscle-activated morphing of the skeletal structure and passive morphing of the flexible skin and feathers. The role of feather morphing has not been well studied and its impact on aerodynamics is largely unknown. Here we investigate the aero-structural response of a flexible airfoil, designed with biologically accurate structural and material data from feathers, and compared the results to an equivalent rigid airfoil. Two coupled aero-structural models are developed and validated to simulate the response of a bioinspired flexible airfoil across a range of aerodynamic flight conditions. We found that the bioinspired flexible airfoil maintained lift at Reynolds numbers below 1.5 × 10[5], within the avian flight regime, performing similarly to its rigid counterpart. At greater Reynolds numbers, the flexible airfoil alleviated the lift force and experienced trailing edge tip displacement. Principal component analysis identified that the Reynolds number dominated this passive shape change which induced a decambering effect, although the angle of attack was found to effect the location of maximum camber. These results imply that birds or aircraft that have tailored chordwise flexible wings will respond like rigid wings while operating at low speeds, but will passively unload large lift forces while operating at high speeds.}, }
@article {pmid32519077, year = {2020}, author = {Wierzchowski, K and Grabowska, I and Pilarek, M}, title = {Efficient propagation of suspended HL-60 cells in a disposable bioreactor supporting wave-induced agitation at various Reynolds number.}, journal = {Bioprocess and biosystems engineering}, volume = {43}, number = {11}, pages = {1973-1985}, pmid = {32519077}, issn = {1615-7605}, support = {DEC-2015/17/B/ST8/00631//Narodowe Centrum Nauki/ ; }, mesh = {Biomass ; *Bioreactors ; *Cell Culture Techniques ; Culture Media ; Equipment Design ; Glucose/chemistry ; HL-60 Cells/*cytology ; Humans ; Hydrodynamics ; Models, Theoretical ; Oscillometry ; Oxygen ; }, abstract = {Growth of human nonadherent HL-60 cell cultures performed in disposable bioreactor under various hydrodynamic conditions of 2-D wave-assisted agitation has been compared and discussed. Influence of Reynolds number for liquid (ReL) and the kLa coefficient, as key parameters characterized the bioprocessing of HL-60 cells in ReadyToProcess WAVE[TM] 25 system, on reached values of the apparent maximal specific growth rate (μmax) and the specific yield of biomass (Y[*]X/S) has been identified. The values of ReL (i.e., 510-10,208), as well as kLa coefficient (i.e., 2.83-13.55 h[-1]), have been estimated for the cultures subjected to wave-induced mixing, based on simplified dimensionless correlation for various presents of WAVE 25 system. The highest values of apparent μmax = 0.038 h[-1] and Y[*]X/S = 25.64 × 10[8] cells gglc[-1] have been noted for cultures independently performed at wave-induced agitation characterized by ReL equaled to 5104 and 510, respectively. The presented results have high applicability potential in scale-up of bioprocesses focused on nonadherent animal cells, or in the case of any application of disposable bioreactors presenting similitude.}, }
@article {pmid32518305, year = {2020}, author = {Waini, I and Ishak, A and Pop, I}, title = {Hybrid nanofluid flow towards a stagnation point on a stretching/shrinking cylinder.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {9296}, pmid = {32518305}, issn = {2045-2322}, abstract = {This paper examines the stagnation point flow towards a stretching/shrinking cylinder in a hybrid nanofluid. Here, copper (Cu) and alumina (Al2O3) are considered as the hybrid nanoparticles while water as the base fluid. The governing equations are reduced to the similarity equations using a similarity transformation. The resulting equations are solved numerically using the boundary value problem solver, bvp4c, available in the Matlab software. It is found that the heat transfer rate is greater for the hybrid nanofluid compared to the regular nanofluid as well as the regular fluid. Besides, the non-uniqueness of the solutions is observed for certain physical parameters. It is also noticed that the bifurcation of the solutions occurs in the shrinking regions. In addition, the heat transfer rate and the skin friction coefficients increase in the presence of nanoparticles and for larger Reynolds number. It is found that between the two solutions, only one of them is stable as time evolves.}, }
@article {pmid32516363, year = {2020}, author = {Cho, M and Koref, IS}, title = {The Importance of a Filament-like Structure in Aerial Dispersal and the Rarefaction Effect of Air Molecules on a Nanoscale Fiber: Detailed Physics in Spiders' Ballooning.}, journal = {Integrative and comparative biology}, volume = {60}, number = {4}, pages = {864-875}, doi = {10.1093/icb/icaa063}, pmid = {32516363}, issn = {1557-7023}, mesh = {Animals ; Physics ; *Silk ; *Spiders ; }, abstract = {Many flying insects utilize a membranous structure for flight, which is known as a "wing." However, some spiders use silk fibers for their aerial dispersal. It is well known that spiders can disperse over hundreds of kilometers and rise several kilometers above the ground in this way. However, little is known about the ballooning mechanisms of spiders, owing to the lack of quantitative data. Recently, Cho et al. discovered previously unknown information on the types and physical properties of spiders' ballooning silks. According to the data, a crab spider weighing 20 mg spins 50-60 ballooning silks simultaneously, which are about 200 nm thick and 3.22 m long for their flight. Based on these physical dimensions of ballooning silks, the significance of these filament-like structures is explained by a theoretical analysis reviewing the fluid-dynamics of an anisotropic particle (like a filament or a high-slender body). (1) The filament-like structure is materially efficient geometry to produce (or harvest, in the case of passive flight) fluid-dynamic force in a low Reynolds number flow regime. (2) Multiple nanoscale fibers are the result of the physical characteristics of a thin fiber, the drag of which is proportional to its length but not to its diameter. Because of this nonlinear characteristic of a fiber, spinning multiple thin ballooning fibers is, for spiders, a better way to produce drag forces than spinning a single thick spider silk, because spiders can maximize their drag on the ballooning fibers using the same amount of silk dope. (3) The mean thickness of fibers, 200 nm, is constrained by the mechanical strength of the ballooning fibers and the rarefaction effect of air molecules on a nanoscale fiber, because the slip condition on a fiber could predominate if the thickness of the fiber becomes thinner than 100 nm.}, }
@article {pmid32508348, year = {2020}, author = {van Hooft, JA}, title = {A Note on Scalar-Gradient Sharpening in the Stable Atmospheric Boundary Layer.}, journal = {Boundary-layer meteorology}, volume = {176}, number = {1}, pages = {149-156}, pmid = {32508348}, issn = {0006-8314}, abstract = {The scalar front generated by the horizontal self advection of a dipolar vortex through a modest scalar gradient is investigated. This physical scenario is an idealization of the emergence of strong temperature ramps in the stable atmospheric boundary layer. The proposed mechanism is discussed and a two-dimensional analogy is studied in depth using direct numerical simulation. More specifically, the scalar-gradient sharpening is investigated as a function of the Reynolds number. It appears that the process of gradient sharpening at large-eddy scales may be challenging for turbulence-resolving methods applied to the stable-boundary-layer regime.}, }
@article {pmid32507933, year = {2020}, author = {Jain, K}, title = {Efficacy of the FDA nozzle benchmark and the lattice Boltzmann method for the analysis of biomedical flows in transitional regime.}, journal = {Medical &amp; biological engineering &amp; computing}, volume = {58}, number = {8}, pages = {1817-1830}, pmid = {32507933}, issn = {1741-0444}, mesh = {Benchmarking/*methods ; Computer Simulation ; Equipment and Supplies ; United States ; United States Food and Drug Administration ; }, abstract = {Flows through medical devices as well as in anatomical vessels despite being at moderate Reynolds number may exhibit transitional or even turbulent character. In order to validate numerical methods and codes used for biomedical flow computations, the US Food and Drug Administration (FDA) established an experimental benchmark, which was a pipe with gradual contraction and sudden expansion representing a nozzle. The experimental results for various Reynolds numbers ranging from 500 to 6500 were publicly released. Previous and recent computational investigations of flow in the FDA nozzle found limitations in various CFD approaches and some even questioned the adequacy of the benchmark itself. This communication reports the results of a lattice Boltzmann method (LBM) - based direct numerical simulation (DNS) approach applied to the FDA nozzle benchmark for transitional cases of Reynolds numbers 2000 and 3500. The goal is to evaluate if a simple off the shelf LBM would predict the experimental results without the use of complex models or synthetic turbulence at the inflow. LBM computations with various spatial and temporal resolutions are performed-in the extremities of 45 million to 2.88 billion lattice cells-executed respectively on 32 CPU cores of a desktop to more than 300,000 cores of a modern supercomputer to explore and characterize miniscule flow details and quantify Kolmogorov scales. The LBM simulations transition to turbulence at a Reynolds number 2000 like the FDA's experiments and acceptable agreement in jet breakdown locations, average velocity, shear stress, and pressure is found for both the Reynolds numbers. Graphical Abstract A bisecting plane showing the FDA nozzle and vorticity magnitude at t = 10 s for throat Reynolds numbers of 2000 and 3500.}, }
@article {pmid32505518, year = {2020}, author = {Cui, X and Wu, W and Ge, H}, title = {Investigation of airflow field in the upper airway under unsteady respiration pattern using large eddy simulation method.}, journal = {Respiratory physiology &amp; neurobiology}, volume = {279}, number = {}, pages = {103468}, doi = {10.1016/j.resp.2020.103468}, pmid = {32505518}, issn = {1878-1519}, mesh = {*Computer Simulation ; Humans ; Larynx ; Models, Biological ; Mouth ; Nose ; Pharynx ; *Respiratory Mechanics ; *Respiratory Physiological Phenomena ; Trachea ; }, abstract = {In this paper, the airflow field in the upper airway under unsteady respiration process is predicted using large eddy simulation. The geometrical model is created by combining a popular cast-based mouth-throat model with tracheo-bronchial airways modeled with a trumpet-shaped conduit. The respiration process is simulated by sinusoidal displacing the bottom surface of the geometrical model. Large eddy simulation with dynamic sub-grid scale model is adopted for modeling the turbulent flow via a commercial CFD software, Converge. This study has found that (1) the secondary vortices in the mouth cavity are much more complex considering the lung expansion than setting the quasi-steady inspiration flow at the mouth-inlet; (2) the properties of secondary vortices in the trachea are not evidently different at the same Reynolds number at the accelerating and decelerating inspiration phases; (3) the reversed pharynx jet as well as recirculation zone is much unsteadier at the accelerating expiration phase than decelerating expiration phase for the same Reynolds number. We conclude that the properties of airflow structures are highly impacted by the respiration pattern and more investigations should be conducted, particularly, on the airflow structures during expiration phase for further understanding the properties of flow field.}, }
@article {pmid32505137, year = {2020}, author = {Howard, MP and Statt, A and Stone, HA and Truskett, TM}, title = {Stability of force-driven shear flows in nonequilibrium molecular simulations with periodic boundaries.}, journal = {The Journal of chemical physics}, volume = {152}, number = {21}, pages = {214113}, doi = {10.1063/5.0010697}, pmid = {32505137}, issn = {1089-7690}, abstract = {We analyze the hydrodynamic stability of force-driven parallel shear flows in nonequilibrium molecular simulations with three-dimensional periodic boundary conditions. We show that flows simulated in this way can be linearly unstable, and we derive an expression for the critical Reynolds number as a function of the geometric aspect ratio of the simulation domain. Approximate periodic extensions of Couette and Poiseuille flows are unstable at Reynolds numbers two orders of magnitude smaller than their aperiodic equivalents because the periodic boundaries impose fundamentally different constraints on the flow. This instability has important implications for simulating shear rheology and for designing nonequilibrium simulation methods that are compatible with periodic boundary conditions.}, }
@article {pmid32499595, year = {2020}, author = {Meloni, S and Di Marco, A and Mancinelli, M and Camussi, R}, title = {Experimental investigation of jet-induced wall pressure fluctuations over a tangential flat plate at two Reynolds numbers.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {9140}, pmid = {32499595}, issn = {2045-2322}, abstract = {The wall pressure fluctuations induced by a subsonic circular jet on a rigid flat plate have been investigated considering two jets with different exit section diameters at the same Mach number. The analysis is aimed at completing the series of papers presented by the authors on the interaction between a subsonic jet and infinite tangential flat plate where the exit Mach number was the only parameter of the jet flow that was varied. In order to analyse other effects out of the Mach number, two configurations with different nozzle exhaust diameters were explored with the objective of isolating the Reynolds number effect keeping fixed the exit Mach number. The nozzle exhaust diameters are 12 mm and 25.4 mm and the instrumented flat plate, installed parallel to the jet flow, is moved at different radial distances from the jet axis. The pressure footprint on the plate has been measured in the stream-wise direction by means of a pair of flush-mounted pressure transducers, providing point-wise pressure signals. Wall pressure fluctuations have been characterised in terms of spectral and statistical quantities. The effect of Reynolds is evidenced and possible scaling relationships that account for the Reynolds dependence are proposed. Implications for modeling the spectral coherence have been considered by the application of the Corcos' model and the effect of the jet Reynolds number on the model coefficients is analyzed.}, }
@article {pmid32498258, year = {2020}, author = {Benedict, F and Kumar, A and Kadirgama, K and Mohammed, HA and Ramasamy, D and Samykano, M and Saidur, R}, title = {Thermal Performance of Hybrid-Inspired Coolant for Radiator Application.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {10}, number = {6}, pages = {}, pmid = {32498258}, issn = {2079-4991}, support = {RDU190323 and RDU1803136//Universiti Malaysia Pahang/ ; FRGS/1/2017/TK03/UMP/02/25//Malaysia higher education ministry/ ; }, abstract = {Due to the increasing demand in industrial application, nanofluids have attracted the considerable attention of researchers in recent decades. The addition of nanocellulose (CNC) with water (W) and ethylene glycol (EG) to a coolant for a radiator application exhibits beneficial properties to improve the efficiency of the radiator. The focus of the present work was to investigate the performance of mono or hybrid metal oxide such as Al2O3 and TiO2 with or without plant base-extracted CNC with varying concentrations as a better heat transfer nanofluid in comparison to distilled water as a radiator coolant. The CNC is dispersed in the base fluid of EG and W with a 60:40 ratio. The highest absorption peak was noticed at 0.9% volume concentration of TiO2, Al2O3, CNC, Al2O3/TiO2, and Al2O3/CNC nanofluids which indicates a better stability of the nanofluids' suspension. Better thermal conductivity improvement was observed for the Al2O3 nanofluids in all mono nanofluids followed by the CNC and TiO2 nanofluids, respectively. The thermal conductivity of the Al2O3/CNC hybrid nanofluids with 0.9% volume concentration was found to be superior than that of the Al2O3/TiO2 hybrid nanofluids. Al2O3/CNC hybrid nanofluid dominates over other mono and hybrid nanofluids in terms of viscosity at all volume concentrations. CNC nanofluids (all volume concentrations) exhibited the highest specific heat capacity than other mono nanofluids. Additionally, in both hybrid nanofluids, Al2O3/CNC showed the lowest specific heat capacity. The optimized volume concentration from the statistical analytical tool was found to be 0.5%. The experimental results show that the heat transfer coefficient, convective heat transfer, Reynolds number and the Nusselt number have a proportional relationship with the volumetric flow rate. Hybrid nanofluids exhibit better thermal conductivity than mono nanofluids. For instance, a better thermal conductivity improvement was shown by the mono Al2O3 nanofluids than the CNC and TiO2 nanofluids. On the other hand, superior thermal conductivity was observed for the Al2O3/CNC hybrid nanofluids compared to the other mono and hybrid ones (Al2O3/TiO2).}, }
@article {pmid32495156, year = {2020}, author = {Ahasan, K and Landry, CM and Chen, X and Kim, JH}, title = {Effect of angle-of-attacks on deterministic lateral displacement (DLD) with symmetric airfoil pillars.}, journal = {Biomedical microdevices}, volume = {22}, number = {2}, pages = {42}, doi = {10.1007/s10544-020-00496-2}, pmid = {32495156}, issn = {1572-8781}, support = {1707056//Division of Chemical, Bioengineering, Environmental, and Transport Systems/International ; 1917299//Division of Electrical, Communications and Cyber Systems/International ; }, mesh = {Microfluidic Analytical Techniques/*methods ; Particle Size ; Pressure ; }, abstract = {Deterministic lateral displacement (DLD) is a microfluidic technique for size fractionation of particles/cells in continuous flow with a great potential for biological and clinical applications. Growing interest of DLD devices in enabling high-throughput operation for practical applications, such as circulating tumor cell (CTC) separation, necessitates employing higher flow rates, leading to operation at moderate to high Reynolds number (Re) regimes. Recently, it has been shown that symmetric airfoil shaped pillars with neutral angle-of-attack (AoA) can be used for high-throughput design of DLD devices due to their mitigation of vortex effects and preservation of flow symmetry under high Re conditions. While high-Re operation with symmetric airfoil shaped pillars has been established, the effect of AoAs on the DLD performance has not been investigated. In this paper, we have characterized the airfoil DLD device with various AoAs. The transport behavior of microparticles has been observed and analyzed with various AoAs in realistic high-Re. Furthermore, we have modeled the flow fields and anisotropy in a representative airfoil pillar array, for both positive and negative AoA configurations. Unlike the conventional DLD device, lateral displacement has been suppressed with +5° and + 15° AoA configurations regardless of particle sizes. On the other hand, stronger lateral displacement has been seen with -5° and - 15° AoAs. This can be attributed to growing flow anisotropy as Re climbs, and significant expansion or compression of streamlines between airfoils with AoAs. The findings in this study can be utilized for the design and optimization of airfoil DLD microfluidic devices with various AoAs.}, }
@article {pmid32488023, year = {2020}, author = {Li, X and Gao, J and Guo, Z and Yin, Y and Zhang, X and Sun, P and Gao, Z}, title = {A Study of Rainfall-Runoff Movement Process on High and Steep Slopes Affected by Double Turbulence Sources.}, journal = {Scientific reports}, volume = {10}, number = {1}, pages = {9001}, pmid = {32488023}, issn = {2045-2322}, support = {41371276//National Natural Science Foundation of China (National Science Foundation of China)/ ; }, abstract = {To increase the available land area, a large-scale land remediation campaign was carried out in the loess hilly and gully area. A large number of high and steep slopes have been produced in the construction of road engineering and water conservancy engineering, and these slopes will cause serious soil erosion under rainfall conditions. Because rainfall runoff is simultaneously affected by slope, bed surface and rainfall, the runoff movement characteristics are complex. It is difficult to consider all influencing factors in the existing models, especially for steep slopes. In this study, artificial rainfall experiments were conducted to study the rainfall-runoff hydraulic processes under different rainfall intensities and slope gradients, and a modified method was proposed to model the key hydraulic parameters (i.e., equilibrium time, water surface line, and runoff processes) on steep slopes. The results showed that (1) For steep slopes (a 70° slope compared to a 5° slope), the runoff generation time, confluence time and equilibrium time of the slope decreased significantly. At the same time, the single width runoff of the steep slope had a power function relationship with the rainfall intensity and gradient. (2) The runoff patterns of steep slopes were different from those on gentle slopes and runoff patterns were more likely to change. The Reynolds number and Froude number for slope flow changed slowly when the slope was less than the critical gradient and increased significantly when the slope exceeded the critical gradient. (3) Based on the analysis of the "double turbulent model theory of thin-layer flow on a high-steep slope", combined with the dispersed motion wave model, a modified method for calculating the hydrodynamic factors of rainfall runoff was proposed. Then, this method was verified with indoor and outdoor experiments. The research results not only have theoretical significance, but also provide a more accurate calculation method for the design of high and steep slopes involved in land treatment engineering, road engineering and water conservancy engineering.}, }
@article {pmid32481597, year = {2020}, author = {Robles-Romero, JM and Romero-Martín, M and Conde-Guillén, G and Cruces-Romero, D and Gómez-Salgado, J and Ponce-Blandón, JA}, title = {The Physics of Fluid Dynamics Applied to Vascular Ulcers and Its Impact on Nursing Care.}, journal = {Healthcare (Basel, Switzerland)}, volume = {8}, number = {2}, pages = {}, pmid = {32481597}, issn = {2227-9032}, abstract = {The high incidence of vascular ulcers and the difficulties encountered in their healing process require the understanding of their multiple etiologies to develop effective strategies focused on providing different treatment options. This work provides a description of the principles of the physics of fluid dynamics related to vascular ulcers. The morphological characteristics of the cardiovascular system promote blood flow. The contraction force of the left ventricle is enhanced by its ability to reduce its radius of curvature and by increasing the thickness of the ventricular wall (Laplace's Law). Arterial flow must overcome vascular resistance (Ohm's equation). The elastic nature of the artery and the ability to reduce its diameter as flow rate progresses facilitate blood conduction at high speed up to arteriolar level, and this can be determined by the second equation of continuity. As it is a viscous fluid, we must discuss laminar flow, calculated by the Reynolds number, which favors proper conduction while aiming at the correct net filtration pressure. Any endothelial harmful process that affects the muscle wall of the vessel increases the flow speed, causing a decrease in capillary hydrostatic pressure, thus reducing the exchange of nutrients at the interstitial level. With regard to the return system, the flow direction is anti-gravity and requires endogenous aid to establish the Starling's equilibrium. Knowledge on the physics of vascular fluid dynamics makes it easier to understand the processes of formation of these ulcers so as to choosing the optimal healing and prevention techniques for these chronic wounds.}, }
@article {pmid32466224, year = {2020}, author = {Charlton, AJ and Lian, B and Blandin, G and Leslie, G and Le-Clech, P}, title = {Impact of FO Operating Pressure and Membrane Tensile Strength on Draw-Channel Geometry and Resulting Hydrodynamics.}, journal = {Membranes}, volume = {10}, number = {5}, pages = {}, pmid = {32466224}, issn = {2077-0375}, abstract = {In an effort to improve performances of forward osmosis (FO) systems, several innovative draw spacers have been proposed. However, the small pressure generally applied on the feed side of the process is expected to result in the membrane bending towards the draw side, and in the gradual occlusion of the channel. This phenomenon potentially presents detrimental effects on process performance, including pressure drop and external concentration polarization (ECP) in the draw channel. A flat sheet FO system with a dot-spacer draw channel geometry was characterized to determine the degree of draw channel occlusion resulting from feed pressurization, and the resulting implications on flow performance. First, tensile testing was performed on the FO membrane to derive a Young's modulus, used to assess the membrane stretching, and the resulting draw channel characteristics under a range of moderate feed pressures. Membrane apex reached up to 67% of the membrane channel height when transmembrane pressure (TMP) of 1.4 bar was applied. The new FO channels considerations were then processed by computational fluid dynamics model (computational fluid dynamics (CFD) by ANSYS Fluent v19.1) and validated against previously obtained experimental data. Further simulations were conducted to better assess velocity profiles, Reynolds number and shear rate. Reynolds number on the membrane surface (draw side) increased by 20% and shear rate increased by 90% when occlusion changed from 0 to 70%, impacting concentration polarisation (CP) on the membrane surface and therefore FO performance. This paper shows that FO draw channel occlusion is expected to have a significant impact on fluid hydrodynamics when the membrane is not appropriately supported in the draw side.}, }
@article {pmid32462438, year = {2020}, author = {Asghar, Z and Ali, N and Waqas, M and Nazeer, M and Khan, WA}, title = {Locomotion of an efficient biomechanical sperm through viscoelastic medium.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {19}, number = {6}, pages = {2271-2284}, pmid = {32462438}, issn = {1617-7940}, mesh = {Algorithms ; Animals ; Biomechanical Phenomena ; *Computer Simulation ; Elasticity ; Fourier Analysis ; Humans ; Locomotion ; *Magnetic Fields ; *Magnetics ; Male ; Models, Theoretical ; *Movement ; *Rheology ; Spermatozoa/*physiology ; Viscosity ; }, abstract = {Every group of microorganism utilizes a diverse mechanical strategy to propel through complex environments. These swimming problems deal with the fluid-organism interaction at micro-scales in which Reynolds number is of the order of 10[-3]. By adopting the same propulsion mechanism of so-called Taylor's sheet, here we address the biomechanical principle of swimming via different wavy surfaces. The passage (containing micro-swimmers) is considered to be passive two-dimensional channel filled with viscoelastic liquid, i.e., Oldroyd-4 constant fluid. For some initial value of unknowns, i.e., cell speed and flow rate of surrounding liquid, the resulting boundary value problem is solved by robust finite difference scheme. This convergent solution is further employed in the equilibrium conditions which will obviously not be satisfied for such crude values of unknowns. These unknowns are further refined (to satisfy the equilibrium conditions) by modified Newton-Raphson algorithm. These computed pairs are also utilized to compute the energy losses. The speed of swimming sheet its power delivered and flow rate of Oldroyd-4 constant fluid are compared for different kinds of wavy sheets. These results are also useful in the manufacturing of artificial (soft) microbots and the optimization of locomotion strategies.}, }
@article {pmid32438546, year = {2020}, author = {Cassineri, S and Cioncolini, A and Smith, L and Curioni, M and Scenini, F}, title = {Experiments on Liquid Flow through Non-Circular Micro-Orifices.}, journal = {Micromachines}, volume = {11}, number = {5}, pages = {}, pmid = {32438546}, issn = {2072-666X}, support = {EP/L01680X/1//Engineering and Physical Sciences Research Council/ ; }, abstract = {Microfluidics is an active research area in modern fluid mechanics, with several applications in science and engineering. Despite their importance in microfluidic systems, micro-orifices with non-circular cross-sections have not been extensively investigated. In this study, micro-orifice discharge with single-phase liquid flow was experimentally investigated for seven square and rectangular cross-section micro-orifices with a hydraulic diameter in the range of 326-510 µm. The discharge measurements were carried out in pressurized water (12 MPa) at ambient temperature (298 K) and high temperature (503 K). During the tests, the Reynolds number varied between 5883 and 212,030, significantly extending the range in which data are currently available in the literature on non-circular micro-orifices. The results indicate that the cross-sectional shape of the micro-orifice has little, if any, effect on the hydrodynamic behavior. Thus, existing methods for the prediction of turbulent flow behavior in circular micro-orifices can be used to predict the flow behavior in non-circular micro-orifices, provided that the flow geometry of the non-circular micro-orifice is described using a hydraulic diameter.}, }
@article {pmid32422718, year = {2020}, author = {Moriconi, L}, title = {Magnetic dissipation of near-wall turbulent coherent structures in magnetohydrodynamic pipe flows.}, journal = {Physical review. E}, volume = {101}, number = {4-1}, pages = {043111}, doi = {10.1103/PhysRevE.101.043111}, pmid = {32422718}, issn = {2470-0053}, abstract = {Relaminarization of wall-bounded turbulent flows by means of external static magnetic fields is a long-known phenomenon in the physics of electrically conducting fluids at low magnetic Reynolds numbers. Despite the large literature on the subject, it is not yet completely clear what combination of the Hartmann (M) and the Reynolds number has to be used to predict the laminar-turbulent transition in channel or pipe flows fed by upstream turbulent flows free of magnetic perturbations. Relying upon standard phenomenological approaches related to mixing length and structural concepts, we put forward that M/R_{τ}, where R_{τ} is the friction Reynolds number, is the appropriate controlling parameter for relaminarization, a proposal which finds good support from available experimental data.}, }
@article {pmid32422715, year = {2020}, author = {Ekanem, EM and Berg, S and De, S and Fadili, A and Bultreys, T and Rücker, M and Southwick, J and Crawshaw, J and Luckham, PF}, title = {Signature of elastic turbulence of viscoelastic fluid flow in a single pore throat.}, journal = {Physical review. E}, volume = {101}, number = {4-1}, pages = {042605}, doi = {10.1103/PhysRevE.101.042605}, pmid = {32422715}, issn = {2470-0053}, abstract = {When a viscoelastic fluid, such as an aqueous polymer solution, flows through a porous medium, the fluid undergoes a repetitive expansion and contraction as it passes from one pore to the next. Above a critical flow rate, the interaction between the viscoelastic nature of the polymer and the pore configuration results in spatial and temporal flow instabilities reminiscent of turbulentlike behavior, even though the Reynolds number Re≪1. To investigate whether this is caused by many repeated pore body-pore throat sequences, or simply a consequence of the converging (diverging) nature present in a single pore throat, we performed experiments using anionic hydrolyzed polyacrylamide (HPAM) in a microfluidic flow geometry representing a single pore throat. This allows the viscoelastic fluid to be characterized at increasing flow rates using microparticle image velocimetry in combination with pressure drop measurements. The key finding is that the effect, popularly known as "elastic turbulence," occurs already in a single pore throat geometry. The critical Deborah number at which the transition in rheological flow behavior from pseudoplastic (shear thinning) to dilatant (shear thickening) strongly depends on the ionic strength, the type of cation in the anionic HPAM solution, and the nature of pore configuration. The transition towards the elastic turbulence regime was found to directly correlate with an increase in normal stresses. The topology parameter, Q_{f}, computed from the velocity distribution, suggests that the "shear thickening" regime, where much of the elastic turbulence occurs in a single pore throat, is a consequence of viscoelastic normal stresses that cause a complex flow field. This flow field consists of extensional, shear, and rotational features around the constriction, as well as upstream and downstream of the constriction. Furthermore, this elastic turbulence regime, has high-pressure fluctuations, with a power-law decay exponent of up to |-2.1| which is higher than the Kolmogorov value for turbulence of |-5/3|.}, }
@article {pmid32388985, year = {2020}, author = {Jain, SK and Banerjee, U and Sen, AK}, title = {Trapping and Coalescence of Diamagnetic Aqueous Droplets Using Negative Magnetophoresis.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {36}, number = {21}, pages = {5960-5966}, doi = {10.1021/acs.langmuir.0c00846}, pmid = {32388985}, issn = {1520-5827}, abstract = {The manipulation of aqueous droplets has a profound significance in biochemical assays. Magnetic field-driven droplet manipulation, offering unique advantages, is consequently gaining attention. However, the phenomenon relating to diamagnetic droplets is not well understood. Here, we report the understanding of trapping and coalescence of flowing diamagnetic aqueous droplets in a paramagnetic (oil-based ferrofluid) medium using negative magnetophoresis. Our study revealed that the trapping phenomenon is underpinned by the interplay of magnetic energy (Em) and frictional (viscous) energy (Ef), in terms of magnetophoretic stability number, Sm = (Em/Ef). The trapping and nontrapping regimes are characterized based on the peak value of magnetophoretic stability number, Smp, and droplet size, D*. The study of coalescence of a trapped droplet with a follower droplet (and a train of droplets) revealed that the film-drainage Reynolds number (Refd) representing the coalescence time depends on the magnetic Bond number, Bom. The coalesced droplet continues to remain trapped or gets self-released obeying the Smp and D* criterion. Our study offers an understanding of the magnetic manipulation of diamagnetic aqueous droplets that can potentially be used for biochemical assays in microfluidics.}, }
@article {pmid32357661, year = {2020}, author = {Garcia, F and Seilmayer, M and Giesecke, A and Stefani, F}, title = {Chaotic wave dynamics in weakly magnetized spherical Couette flows.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {30}, number = {4}, pages = {043116}, doi = {10.1063/1.5140577}, pmid = {32357661}, issn = {1089-7682}, abstract = {Direct numerical simulations of a liquid metal filling the gap between two concentric spheres are presented. The flow is governed by the interplay between the rotation of the inner sphere (measured by the Reynolds number Re) and a weak externally applied axial magnetic field (measured by the Hartmann number Ha). By varying the latter, a rich variety of flow features, both in terms of spatial symmetry and temporal dependence, is obtained. Flows with two or three independent frequencies describing their time evolution are found as a result of Hopf bifurcations. They are stable on a sufficiently large interval of Hartmann numbers where regions of multistability of two, three, and even four types of these different flows are detected. The temporal character of the solutions is analyzed by means of an accurate frequency analysis and Poincaré sections. An unstable branch of flows undergoing a period doubling cascade and frequency locking of three-frequency solutions is described as well.}, }
@article {pmid32357025, year = {2020}, author = {Kang, S and Kwak, R}, title = {Pattern Formation of Three-Dimensional Electroconvection on a Charge Selective Surface.}, journal = {Physical review letters}, volume = {124}, number = {15}, pages = {154502}, doi = {10.1103/PhysRevLett.124.154502}, pmid = {32357025}, issn = {1079-7114}, abstract = {When a charge selective surface consumes or transports only cations or anions in the electrolyte, biased ion rejection initiates hydrodynamic instability, resulting in vortical fluid motions called electroconvection. In this Letter, we describe the first laboratory observation of three-dimensional electroconvection on a charge selective surface. Combining experiment and scaling analysis, we successfully categorized three distinct patterns of 3D electroconvection according to [(Ra_{E})/(Re^{2}Sc)] [electric Rayleigh number (Ra_{E}), Reynolds number (Re), Schmidt number (Sc)] as (i) polygonal, (ii) transverse, or (iii) longitudinal rolls. If Re increases or Ra_{E} decreases, pure longitudinal rolls are presented. On the other hand, transverse rolls are formed between longitudinal rolls, and two rolls are transformed as polygonal one at higher Ra_{E} or lower Re. In this pattern selection scenario, Sc determines the critical electric Rayleigh number (Ra_{E}^{*}) for the onset of each roll, resulting in Ra_{E}^{*}∼Re^{2}Sc. We also verify that convective ion flux by electroconvection (represented by an electric Nusselt number Nu_{E}) is fitted to a power law, Nu_{E}∼[(Ra_{E}-Ra_{E}^{*})/(Re^{2}Sc)]^{α_{1}}Re^{α_{2}}Pe^{α_{3}} [Péclet number (Pe)], where each term represents the characteristics of electroconvection, shear flow, and ion transport.}, }
@article {pmid32349452, year = {2020}, author = {Raza, W and Hossain, S and Kim, KY}, title = {A Review of Passive Micromixers with a Comparative Analysis.}, journal = {Micromachines}, volume = {11}, number = {5}, pages = {}, pmid = {32349452}, issn = {2072-666X}, support = {2019R1A2C1007657//National Research Foundation of Korea/ ; }, abstract = {A wide range of existing passive micromixers are reviewed, and quantitative analyses of ten typical passive micromixers were performed to compare their mixing indices, pressure drops, and mixing costs under the same axial length and flow conditions across a wide Reynolds number range of 0.01-120. The tested micromixers were selected from five types of micromixer designs. The analyses of flow and mixing were performed using continuity, Navier-Stokes and convection-diffusion equations. The results of the comparative analysis were presented for three different Reynolds number ranges: low-Re (Re ≤ 1), intermediate-Re (1 < Re ≤ 40), and high-Re (Re > 40) ranges, where the mixing mechanisms are different. The results show a two-dimensional micromixer of Tesla structure is recommended in the intermediate- and high-Re ranges, while two three-dimensional micromixers with two layers are recommended in the low-Re range due to their excellent mixing performance.}, }
@article {pmid32342660, year = {2020}, author = {Storm, TJ and Nolan, KE and Roberts, EM and Sanderson, SL}, title = {Oropharyngeal morphology related to filtration mechanisms in suspension-feeding American shad (Clupeidae).}, journal = {Journal of experimental zoology. Part A, Ecological and integrative physiology}, volume = {333}, number = {7}, pages = {493-510}, doi = {10.1002/jez.2363}, pmid = {32342660}, issn = {2471-5646}, support = {/HHMI/Howard Hughes Medical Institute/United States ; }, mesh = {Animals ; *Feeding Behavior ; Fishes/*anatomy &amp; histology/physiology ; Gills ; Oropharynx/*anatomy &amp; histology ; }, abstract = {To assess potential filtration mechanisms, scanning electron microscopy was used in a comprehensive quantification and analysis of the morphology and surface ultrastructure for all five branchial arches in the ram suspension-feeding fish, American shad (Alosa sapidissima, Clupeidae). The orientation of the branchial arches and the location of mucus cells on the gill rakers were more consistent with mechanisms of crossflow filtration and cross-step filtration rather than conventional dead-end sieving. The long, thin gill rakers could lead to a large area for the exit of water from the oropharyngeal cavity during suspension feeding (high fluid exit ratio). The substantial elongation of gill rakers along the dorsal-ventral axis formed d-type ribs with a groove aspect ratio of 0.5 and a Reynolds number of approximately 500, consistent with the potential operation of cross-step filtration. Mucus cell abundance differed significantly along the length of the raker and the height of the raker. The mucus cell abundance data and the observed sloughing of denticles along the gill raker margins closest to the interior of the oropharyngeal cavity suggest that gill raker growth may occur primarily at the raker tips, the denticle bases, and the internal raker margins along the length of the raker. These findings will be applied in ongoing experiments with 3D-printed physical models of fish oral cavities in flow tanks, and in future ecological studies on the diet and nutrition of suspension-feeding fishes.}, }
@article {pmid32340402, year = {2020}, author = {Singh, AV and Ansari, MHD and Mahajan, M and Srivastava, S and Kashyap, S and Dwivedi, P and Pandit, V and Katha, U}, title = {Sperm Cell Driven Microrobots-Emerging Opportunities and Challenges for Biologically Inspired Robotic Design.}, journal = {Micromachines}, volume = {11}, number = {4}, pages = {}, pmid = {32340402}, issn = {2072-666X}, abstract = {With the advent of small-scale robotics, several exciting new applications like Targeted Drug Delivery, single cell manipulation and so forth, are being discussed. However, some challenges remain to be overcome before any such technology becomes medically usable; among which propulsion and biocompatibility are the main challenges. Propulsion at micro-scale where the Reynolds number is very low is difficult. To overcome this, nature has developed flagella which have evolved over millions of years to work as a micromotor. Among the microscopic cells that exhibit this mode of propulsion, sperm cells are considered to be fast paced. Here, we give a brief review of the state-of-the-art of Spermbots - a new class of microrobots created by coupling sperm cells to mechanical loads. Spermbots utilize the flagellar movement of the sperm cells for propulsion and as such do not require any toxic fuel in their environment. They are also naturally biocompatible and show considerable speed of motion thereby giving us an option to overcome the two challenges of propulsion and biocompatibility. The coupling mechanisms of physical load to the sperm cells are discussed along with the advantages and challenges associated with the spermbot. A few most promising applications of spermbots are also discussed in detail. A brief discussion of the future outlook of this extremely promising category of microrobots is given at the end.}, }
@article {pmid32325022, year = {2020}, author = {Zhou, Q and Fidalgo, J and Calvi, L and Bernabeu, MO and Hoskins, PR and Oliveira, MSN and Krüger, T}, title = {Spatiotemporal Dynamics of Dilute Red Blood Cell Suspensions in Low-Inertia Microchannel Flow.}, journal = {Biophysical journal}, volume = {118}, number = {10}, pages = {2561-2573}, pmid = {32325022}, issn = {1542-0086}, mesh = {Computer Simulation ; *Erythrocytes ; *Hydrodynamics ; Reproducibility of Results ; Suspensions ; }, abstract = {Microfluidic technologies are commonly used for the manipulation of red blood cell (RBC) suspensions and analyses of flow-mediated biomechanics. To enhance the performance of microfluidic devices, understanding the dynamics of the suspensions processed within is crucial. We report novel, to our knowledge, aspects of the spatiotemporal dynamics of RBC suspensions flowing through a typical microchannel at low Reynolds number. Through experiments with dilute RBC suspensions, we find an off-center two-peak (OCTP) profile of cells contrary to the centralized distribution commonly reported for low-inertia flows. This is reminiscent of the well-known "tubular pinch effect," which arises from inertial effects. However, given the conditions of negligible inertia in our experiments, an alternative explanation is needed for this OCTP profile. Our massively parallel simulations of RBC flow in real-size microfluidic dimensions using the immersed-boundary-lattice-Boltzmann method confirm the experimental findings and elucidate the underlying mechanism for the counterintuitive RBC pattern. By analyzing the RBC migration and cell-free layer development within a high-aspect-ratio channel, we show that such a distribution is co-determined by the spatial decay of hydrodynamic lift and the global deficiency of cell dispersion in dilute suspensions. We find a cell-free layer development length greater than 46 and 28 hydraulic diameters in the experiment and simulation, respectively, exceeding typical lengths of microfluidic designs. Our work highlights the key role of transient cell distribution in dilute suspensions, which may negatively affect the reliability of experimental results if not taken into account.}, }
@article {pmid32317809, year = {2020}, author = {Navah, F and de la Llave Plata, M and Couaillier, V}, title = {A High-Order Multiscale Approach to Turbulence for Compact Nodal Schemes.}, journal = {Computer methods in applied mechanics and engineering}, volume = {363}, number = {}, pages = {}, pmid = {32317809}, issn = {0045-7825}, support = {R01 DC005788/DC/NIDCD NIH HHS/United States ; R01 DC018577/DC/NIDCD NIH HHS/United States ; }, abstract = {This article presents a formulation that extends the multiscale modelling for compressible large-eddy simulation to a vast family of compact nodal numerical methods represented by the high-order flux reconstruction scheme. The theoretical aspects of the proposed formulation are laid down via mathematical derivations which clearly expose the underlying assumptions and approximations and provide sufficient details for accurate reproduction of the methodology. The final form is assessed on a Taylor-Green vortex benchmark with Reynolds number of 5000 and compared to filtered direct numerical simulation data. These numerical experiments exhibit the important role of sufficient de-aliasing, appropriate amount of upwinding from Roe's numerical flux and large/small scale partition, in achieving better agreement with reference data, especially on coarse grids, when compared to the baseline implicit large-eddy simulation.}, }
@article {pmid32315915, year = {2020}, author = {Banerjee, A and Sharma, T and Nautiyal, AK and Dasgupta, D and Hazra, S and Bhaskar, T and Ghosh, D}, title = {Scale-up strategy for yeast single cell oil production for Rhodotorula mucilagenosa IIPL32 from corn cob derived pentosan.}, journal = {Bioresource technology}, volume = {309}, number = {}, pages = {123329}, doi = {10.1016/j.biortech.2020.123329}, pmid = {32315915}, issn = {1873-2976}, mesh = {Fermentation ; *Rhodotorula ; Xylose ; Yeasts ; *Zea mays ; }, abstract = {This work was aimed to strategically scale-up the yeast lipid production process using Reynolds number as a standard rheological parameter from 50 mL to 50 L scale. Oleaginous yeast Rhodotorula mucilaginosa IIPL32 was cultivated in xylose rich corncob hydrolysate. The fermentation process for growth and maturation was operated in fed-batch with two different C/N ratios of 40 and 60. The hydrodynamic parameters were used to standardize and represent the effect of rheology on the fermentation process. The growth pattern of the yeast was found similar in both shake flask and fermenter with the maximum growth observed at 48 h. The lipid yield increased from 0.4 g/L and 0.5 g/L to 1.3 g/L and 1.83 g/L for 50 mL to 50 L for C/N ratio 40 and 60 respectively. The increase in productivity during the growth phase and lipid accumulation during the maturation phase showed that the scale-up strategy was successful.}, }
@article {pmid32295138, year = {2020}, author = {Erdem, K and Ahmadi, VE and Kosar, A and Kuddusi, L}, title = {Differential Sorting of Microparticles Using Spiral Microchannels with Elliptic Configurations.}, journal = {Micromachines}, volume = {11}, number = {4}, pages = {}, pmid = {32295138}, issn = {2072-666X}, support = {Project Number: MDK-2017-40845//Istanbul Teknik &#xdc;niversitesi/ ; }, abstract = {Label-free, size-dependent cell-sorting applications based on inertial focusing phenomena have attracted much interest during the last decade. The separation capability heavily depends on the precision of microparticle focusing. In this study, five-loop spiral microchannels with a height of 90 µm and a width of 500 µm are introduced. Unlike their original spiral counterparts, these channels have elliptic configurations of varying initial aspect ratios, namely major axis to minor axis ratios of 3:2, 11:9, 9:11, and 2:3. Accordingly, the curvature of these configurations increases in a curvilinear manner through the channel. The effects of the alternating curvature and channel Reynolds number on the focusing of fluorescent microparticles with sizes of 10 and 20 µm in the prepared suspensions were investigated. At volumetric flow rates between 0.5 and 3.5 mL/min (allowing separation), each channel was tested to collect samples at the designated outlets. Then, these samples were analyzed by counting the particles. These curved channels were capable of separating 20 and 10 µm particles with total yields up to approximately 95% and 90%, respectively. The results exhibited that the level of enrichment and the focusing behavior of the proposed configurations are promising compared to the existing microfluidic channel configurations.}, }
@article {pmid32294955, year = {2020}, author = {Sun, HCM and Liao, P and Wei, T and Zhang, L and Sun, D}, title = {Magnetically Powered Biodegradable Microswimmers.}, journal = {Micromachines}, volume = {11}, number = {4}, pages = {}, pmid = {32294955}, issn = {2072-666X}, abstract = {The propulsive efficiency and biodegradability of wireless microrobots play a significant role in facilitating promising biomedical applications. Mimicking biological matters is a promising way to improve the performance of microrobots. Among diverse locomotion strategies, undulatory propulsion shows remarkable efficiency and agility. This work proposes a novel magnetically powered and hydrogel-based biodegradable microswimmer. The microswimmer is fabricated integrally by 3D laser lithography based on two-photon polymerization from a biodegradable material and has a total length of 200 μm and a diameter of 8 μm. The designed microswimmer incorporates a novel design utilizing four rigid segments, each of which is connected to the succeeding segment by spring to achieve undulation, improving structural integrity as well as simplifying the fabrication process. Under an external oscillating magnetic field, the microswimmer with multiple rigid segments connected by flexible spring can achieve undulatory locomotion and move forward along with the directions guided by the external magnetic field in the low Reynolds number (Re) regime. In addition, experiments demonstrated that the microswimmer can be degraded successfully, which allows it to be safely applied in real-time in vivo environments. This design has great potential in future in vivo applications such as precision medicine, drug delivery, and diagnosis.}, }
@article {pmid32290599, year = {2020}, author = {Huang, B and Li, H and Xu, T}, title = {Experimental Investigation of the Flow and Heat Transfer Characteristics in Microchannel Heat Exchangers with Reentrant Cavities.}, journal = {Micromachines}, volume = {11}, number = {4}, pages = {}, pmid = {32290599}, issn = {2072-666X}, support = {No.51906008, No.51822602//National Natural Science Foundation of China/ ; No. YWF-19-BJ-J-293//Fundamental Research Funds for the Central Universities/ ; 2017-&#x2162;-0003-0027//National Major Science and Technology Projects of China/ ; }, abstract = {The application of microchannel heat exchangers is of great significance in industrial fields due to their advantages of miniaturized scale, large surface-area-to-volume ratio, and high heat transfer rate. In this study, microchannel heat exchangers with and without fan-shaped reentrant cavities were designed and manufactured, and experiments were conducted to investigate the flow and heat-transfer characteristics. The impact rising from the radius of reentrant cavities, as well as the Reynolds number on the heat transfer and the pressure drop, is also analyzed. The results indicate that, compared with straight microchannels, microchannels with reentrant cavities could enhance the heat transfer and, more importantly, reduce the pressure drop at the same time. For the ranges of parameters studied, increasing the radius of reentrant cavities could augment the effect of pressure-drop reduction, while the corresponding variation of heat transfer is complicated. It is considered that adding reentrant cavities in microchannel heat exchangers is an ideal approach to improve performance.}, }
@article {pmid32290016, year = {2020}, author = {Alboussière, T and Drif, K and Plunian, F}, title = {Dynamo action in sliding plates of anisotropic electrical conductivity.}, journal = {Physical review. E}, volume = {101}, number = {3-1}, pages = {033107}, doi = {10.1103/PhysRevE.101.033107}, pmid = {32290016}, issn = {2470-0053}, abstract = {With materials of anisotropic electrical conductivity, it is possible to generate a dynamo with a simple velocity field, of the type precluded by Cowling's theorems with isotropic materials. Following a previous study by Ruderman and Ruzmaikin [M. S. Ruderman and A. A. Ruzmaikin, Magnetic field generation in an anisotropically conducting fluid, Geophys. Astrophys. Fluid Dyn. 28, 77 (1984)GAFDD30309-192910.1080/03091928408210135], who considered the dynamo effect induced by a uniform shear flow, we determine the conditions for the dynamo threshold when a solid plate is sliding over another one, both with anisotropic electrical conductivity. We obtain numerical solutions for a general class of anisotropy and obtain the conditions for the lowest magnetic Reynolds number, using a collocation Chebyshev method. In a particular geometry of anisotropy and wave number, we also derive an analytical solution, where the eigenvectors are just combinations of four exponential functions. An explicit analytical expression is obtained for the critical magnetic Reynolds number. Above the critical magnetic Reynolds number, we have also derived an analytical expression for the growth rate showing that this is a "very fast" dynamo, extrapolating on the "slow" and "fast" terminology introduced by Vainshtein and Zeldovich [S. I. Vainshtein and Y. B. Zeldovich, Reviews of topical problems: Origin of magnetic fields in astrophysics (turbulent "dynamo" mechanisms), Sov. Phys. Usp. 15, 159 (1972)SOPUAP0038-567010.1070/PU1972v015n02ABEH004960].}, }
@article {pmid32289979, year = {2020}, author = {Reyes, F and Torrejón, V and Falcón, C}, title = {Wave damping of a sloshing wave by an interacting turbulent vortex flow.}, journal = {Physical review. E}, volume = {101}, number = {3-1}, pages = {033106}, doi = {10.1103/PhysRevE.101.033106}, pmid = {32289979}, issn = {2470-0053}, abstract = {We report on the enhancement of the hydrodynamic damping of gravity waves at the surface of a fluid layer as they interact with a turbulent vortex flow in a sloshing experiment. Gravity surface waves are excited by oscillating horizontally a square container holding our working fluid (water). At the bottom of the container, four impellers in a quadrupole configuration generate a vortex array at moderate to high Reynolds number, which interact with the wave. We measure the surface fluctuations using different optical nonintrusive methods and the local velocity of the flow. In our experimental range, we show that as we increase the angular velocity of the impellers, the gravity wave amplitude decreases without changing the oscillation frequency or generating transverse modes. This wave dissipation enhancement is contrasted with the increase of the turbulent velocity fluctuations from particle image velocimetry measurements via a turbulent viscosity. To rationalize the damping enhancement a periodically forced shallow water model including viscous terms is presented, which is used to calculate the sloshing wave resonance curve. The enhanced viscous dissipation coefficient is found to scale linearly with the measured turbulent viscosity. Hence, the proposed scheme is a good candidate as an active surface gravity wave dampener via vortex flow reconfiguration.}, }
@article {pmid32284987, year = {2020}, author = {Spandan, V and Putt, D and Ostilla-Mónico, R and Lee, AA}, title = {Fluctuation-induced force in homogeneous isotropic turbulence.}, journal = {Science advances}, volume = {6}, number = {14}, pages = {eaba0461}, pmid = {32284987}, issn = {2375-2548}, abstract = {Understanding force generation in nonequilibrium systems is a notable challenge in statistical physics. We uncover a fluctuation-induced force between two plates immersed in homogeneous isotropic turbulence using direct numerical simulations. The force is a nonmonotonic function of plate separation. The mechanism of force generation reveals an intriguing analogy with fluctuation-induced forces: In a fluid, energy and vorticity are localized in regions of defined length scales. When varying the distance between the plates, we exclude energy structures modifying the overall pressure on the plates. At intermediate plate distances, the intense vorticity structures (worms) are forced to interact in close vicinity between the plates. This interaction affects the pressure in the slit and the force between the plates. The combination of these two effects causes a nonmonotonic attractive force with a complex Reynolds number dependence. Our study sheds light on how length scale-dependent distributions of energy and high-intensity vortex structures determine Casimir forces.}, }
@article {pmid32260002, year = {2020}, author = {Asakawa, J and Nishii, K and Nakagawa, Y and Koizumi, H and Komurasaki, K}, title = {Direct measurement of 1-mN-class thrust and 100-s-class specific impulse for a CubeSat propulsion system.}, journal = {The Review of scientific instruments}, volume = {91}, number = {3}, pages = {035116}, doi = {10.1063/1.5121411}, pmid = {32260002}, issn = {1089-7623}, abstract = {This paper presents the development of a thrust stand to enable direct measurement of thrust and specific impulse for a CubeSat propulsion system during firing. The thrust stand is an inverted pendulum and incorporates a mass balance for direct in situ mass measurement. The proposed calibration procedure allows precise performance characterization and achieves a resolution of 80 μN thrust and 0.01 g mass loss, by taking into account the drift of the thrust-stand zero caused by propellant consumption. The performance of a water micro-resistojet propulsion system for CubeSats was directly characterized as a proof of concept of the thrust stand. Continuous profiles of thrust, specific impulse, and mass consumption were acquired under various conditions in a single firing test. A thrust from 1 mN to 10 mN and a specific impulse from 45 s to 100 s with a maximum measurement uncertainty of ±15.3% were measured for the throat Reynolds number in the range 100-400.}, }
@article {pmid32244961, year = {2020}, author = {Joseph, J and Rehman, D and Delanaye, M and Morini, GL and Nacereddine, R and Korvink, JG and Brandner, JJ}, title = {Numerical and Experimental Study of Microchannel Performance on Flow Maldistribution.}, journal = {Micromachines}, volume = {11}, number = {3}, pages = {}, pmid = {32244961}, issn = {2072-666X}, support = {Grant Agreement No. 643095//European Community H2020 Framework/ ; }, abstract = {Miniaturized heat exchangers are well known for their superior heat transfer capabilities in comparison to macro-scale devices. While in standard microchannel systems the improved performance is provided by miniaturized distances and very small hydraulic diameters, another approach can also be followed, namely, the generation of local turbulences. Localized turbulence enhances the heat exchanger performance in any channel or tube, but also includes an increased pressure loss. Shifting the critical Reynolds number to a lower value by introducing perturbators controls pressure losses and improves thermal efficiency to a considerable extent. The objective of this paper is to investigate in detail collector performance based on reduced-order modelling and validate the numerical model based on experimental observations of flow maldistribution and pressure losses. Two different types of perturbators, Wire-net and S-shape, were analyzed. For the former, a metallic wire mesh was inserted in the flow passages (hot and cold gas flow) to ensure stiffness and enhance microchannel efficiency. The wire-net perturbators were replaced using an S-shaped perturbator model for a comparative study in the second case mentioned above. An optimum mass flow rate could be found when the thermal efficiency reaches a maximum. Investigation of collectors with different microchannel configurations (s-shaped, wire-net and plane channels) showed that mass flow rate deviation decreases with an increase in microchannel resistance. The recirculation zones in the cylindrical collectors also changed the maldistribution pattern. From experiments, it could be observed that microchannels with S-shaped perturbators shifted the onset of turbulent transition to lower Reynolds number values. Experimental studies on pressure losses showed that the pressure losses obtained from numerical studies were in good agreement with the experiments (<4%).}, }
@article {pmid32168670, year = {2020}, author = {Thirani, S and Gupta, P and Scalo, C}, title = {Knudsen number effects on the nonlinear acoustic spectral energy cascade.}, journal = {Physical review. E}, volume = {101}, number = {2-1}, pages = {023101}, doi = {10.1103/PhysRevE.101.023101}, pmid = {32168670}, issn = {2470-0053}, abstract = {We present a numerical investigation of the effects of gas rarefaction on the energy dynamics of resonating planar nonlinear acoustic waves. The problem setup is a gas-filled, adiabatic tube, excited from one end by a piston oscillating at the fundamental resonant frequency of the tube and closed at the other end; nonlinear wave steepening occurs until a limit cycle is reached, resulting in shock formation for sufficiently high densities. The Knudsen number, defined here as the ratio of the characteristic molecular collision timescale to the resonance period, is varied in the range Kn=10^{-1}-10^{-5}, from rarefied to dense regime, by changing the base density of the gas. The working fluid is Argon. A numerical solution of the Boltzmann equation, closed with the Bhatnagar-Gross-Krook model, is used to simulate cases for Kn≥0.01. The fully compressible one-dimensional Navier-Stokes equations are used for Kn<0.01 with adaptive mesh refinement to resolve the resonating weak shocks, reaching wave Mach numbers up to 1.01. Nonlinear wave steepening and shock formation are associated with spectral broadening of the acoustic energy in the wavenumber-frequency domain; the latter is defined based on the exact energy corollary for second-order nonlinear acoustics derived by Gupta and Scalo [Phys. Rev. E 98, 033117 (2018)2470-004510.1103/PhysRevE.98.033117], representing the Lyapunov function of the system. At the limit cycle, the acoustic energy spectra exhibit an equilibrium energy cascade with a -2 slope in the inertial range, also observed in freely decaying nonlinear acoustic waves by the same authors. In the present system, energy is introduced externally via a piston at low wavenumbers or frequencies and balanced by thermoviscous dissipation at high wavenumbers or frequencies, responsible for the base temperature increase in the system. The thermoviscous dissipation rate is shown to scale as Kn^{2} for fixed Reynolds number based on the maximum velocity amplitude, i.e., increasing with the degree of flow rarefaction; consistently, the smallest length scale of the steepened waves at the limit cycle, corresponding to the thickness of the shock (when present) also increases with Kn. For a given fixed piston velocity amplitude, the bandwidth of the inertial range of the spectral energy cascade decreases with increasing Knudsen numbers, resulting in a reduced resonant response of the system. By exploiting dimensionless scaling laws borrowed by Kolmogorov's theory of hydrodynamic turbulence, it is shown that an inertial range for spectral energy transfer can be expected for acoustic Reynolds numbers Re_{U_{max}}>100, based on the maximum acoustic velocity amplitude in the domain.}, }
@article {pmid32151621, year = {2020}, author = {Krieg, M and Mohseni, K}, title = {Transient pressure modeling in jetting animals.}, journal = {Journal of theoretical biology}, volume = {494}, number = {}, pages = {110237}, doi = {10.1016/j.jtbi.2020.110237}, pmid = {32151621}, issn = {1095-8541}, mesh = {Animals ; *Aquatic Organisms ; Biomechanical Phenomena ; *Decapodiformes/physiology ; Larva/anatomy &amp; histology/physiology ; *Models, Biological ; Odonata/physiology ; Pressure ; *Scyphozoa/physiology ; *Swimming ; }, abstract = {There are many marine animals that employ a form of jet propulsion to move through the water, often creating the jets by expanding and collapsing internal fluid cavities. Due to the unsteady nature of this form of locomotion and complex body/nozzle geometries, standard modeling techniques prove insufficient at capturing internal pressure dynamics, and hence swimming forces. This issue has been resolved with a novel technique for predicting the pressure inside deformable jet producing cavities (M. Krieg and K. Mohseni, J. Fluid Mech., 769, 2015), which is derived from evolution of the surrounding fluid circulation. However, this model was only validated for an engineered jet thruster with simple geometry and relatively high Reynolds number (Re) jets. The purpose of this manuscript is twofold: (i) to demonstrate how the circulation based pressure model can be used to analyze different animal body motions as they relate to propulsive output, for multiple species of jetting animals, (ii) and to quantitatively validate the pressure modeling for biological jetting organisms (typically characterized by complicated cavity geometry and low/intermediate Re flows). Using jellyfish (Sarsia tubulosa) as an example, we show that the pressure model is insensitive to complex cavity geometry, and can be applied to lower Re swimming. By breaking down the swimming behavior of the jellyfish, as well as that of squid and dragonfly larvae, according to circulation generating mechanisms, we demonstrate that the body motions of Sarsia tubulosa are optimized for acceleration at the beginning of pulsation as a survival response. Whereas towards the end of jetting, the velar morphology is adjusted to decrease the energetic cost. Similarly, we show that mantle collapse rates in squid maximize propulsive efficiency. Finally, we observe that the hindgut geometry of dragonfly larvae minimizes the work required to refill the cavity. Date Received: 10-18-2019, Date Accepted: 99-99-9999 *kriegmw@hawaii.edu, UHM Ocean and Res Eng, 2540 Dole St, Honolulu, HI 96822.}, }
@article {pmid32125866, year = {2020}, author = {Fang, WZ and Ham, S and Qiao, R and Tao, WQ}, title = {Magnetic Actuation of Surface Walkers: The Effects of Confinement and Inertia.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {36}, number = {25}, pages = {7046-7055}, doi = {10.1021/acs.langmuir.9b03487}, pmid = {32125866}, issn = {1520-5827}, abstract = {Driven by a magnetic field, the rotation of a particle near a wall can be rectified into a net translation. The particles thus actuated, or surface walkers, are a kind of active colloid that finds application in biology and microfluidics. Here, we investigate the motion of spherical surface walkers confined between two walls using simulations based on the immersed-boundary lattice Boltzmann method. The degree of confinement and the nature of the confining walls (slip vs no-slip) significantly affect a particle's translational speed and can even reverse its translational direction. When the rotational Reynolds number Reω is larger than 1, inertia effects reduce the critical frequency of the magnetic field, beyond which the sphere can no longer follow the external rotating field. The reduction of the critical frequency is especially pronounced when the sphere is confined near a no-slip wall. As Reω increases beyond 1, even when the sphere can still rotate in the synchronous regime, its translational Reynolds number ReT no longer increases linearly with Reω and even decreases when Reω exceeds ∼10.}, }
@article {pmid32098945, year = {2020}, author = {Stixrude, L and Scipioni, R and Desjarlais, MP}, title = {A silicate dynamo in the early Earth.}, journal = {Nature communications}, volume = {11}, number = {1}, pages = {935}, pmid = {32098945}, issn = {2041-1723}, support = {291432//EC | EC Seventh Framework Programm | FP7 Ideas: European Research Council (FP7-IDEAS-ERC - Specific Programme: "Ideas" Implementing the Seventh Framework Programme of the European Community for Research, Technological Development and Demonstration Activities (2007 to 2013))/ ; EAR-1853388//National Science Foundation (NSF)/ ; }, abstract = {The Earth's magnetic field has operated for at least 3.4 billion years, yet how the ancient field was produced is still unknown. The core in the early Earth was surrounded by a molten silicate layer, a basal magma ocean that may have survived for more than one billion years. Here we use density functional theory-based molecular dynamics simulations to predict the electrical conductivity of silicate liquid at the conditions of the basal magma ocean: 100-140 GPa, and 4000-6000 K. We find that the electrical conductivity exceeds 10,000 S/m, more than 100 times that measured in silicate liquids at low pressure and temperature. The magnetic Reynolds number computed from our results exceeds the threshold for dynamo activity and the magnetic field strength is similar to that observed in the Archean paleomagnetic record. We therefore conclude that the Archean field was produced by the basal magma ocean.}, }
@article {pmid32093331, year = {2020}, author = {Rehman, D and Joseph, J and Morini, GL and Delanaye, M and Brandner, J}, title = {A Hybrid Numerical Methodology Based on CFD and Porous Medium for Thermal Performance Evaluation of Gas to Gas Micro Heat Exchanger.}, journal = {Micromachines}, volume = {11}, number = {2}, pages = {}, pmid = {32093331}, issn = {2072-666X}, support = {643095//Horizon 2020 Framework Programme/ ; }, abstract = {In micro heat exchangers, due to the presence of distributing and collecting manifolds as well as hundreds of parallel microchannels, a complete conjugate heat transfer analysis requires a large amount of computational power. Therefore in this study, a novel methodology is developed to model the microchannels as a porous medium where a compressible gas is used as a working fluid. With the help of such a reduced model, a detailed flow analysis through individual microchannels can be avoided by studying the device as a whole at a considerably less computational cost. A micro heat exchanger with 133 parallel microchannels (average hydraulic diameter of 200 μ m) in both cocurrent and counterflow configurations is investigated in the current study. Hot and cold streams are separated by a stainless-steel partition foil having a thickness of 100 μ m. Microchannels have a rectangular cross section of 200 μ m × 200 μ m with a wall thickness of 100 μ m in between. As a first step, a numerical study for conjugate heat transfer analysis of microchannels only, without distributing and collecting manifolds is performed. Mass flow inside hot and cold fluid domains is increased such that inlet Reynolds number for both domains remains within the laminar regime. Inertial and viscous coefficients extracted from this study are then utilized to model pressure and temperature trends within the porous medium model. To cater for the density dependence of inertial and viscous coefficients due to the compressible nature of gas flow in microchannels, a modified formulation of Darcy-Forschheimer law is adopted. A complete model of a double layer micro heat exchanger with collecting and distributing manifolds where microchannels are modeled as the porous medium is finally developed and used to estimate the overall heat exchanger effectiveness of the investigated micro heat exchanger. A comparison of computational results using proposed hybrid methodology with previously published experimental results of the same micro heat exchanger showed that adopted methodology can predict the heat exchanger effectiveness within the experimental uncertainty for both cocurrent and counterflow configurations.}, }
@article {pmid32082068, year = {2020}, author = {Luo, J and Chen, L and Li, K and Jackson, A}, title = {Optimal kinematic dynamos in a sphere.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {476}, number = {2233}, pages = {20190675}, pmid = {32082068}, issn = {1364-5021}, abstract = {A variational optimization approach is used to optimize kinematic dynamos in a unit sphere and locate the enstrophy-based critical magnetic Reynolds number for dynamo action. The magnetic boundary condition is chosen to be either pseudo-vacuum or perfectly conducting. Spectra of the optimal flows corresponding to these two magnetic boundary conditions are identical since theory shows that they are relatable by reversing the flow field (Favier &amp; Proctor 2013 Phys. Rev. E 88, 031001 (doi:10.1103/physreve.88.031001)). A no-slip boundary for the flow field gives a critical magnetic Reynolds number of 62.06, while a free-slip boundary reduces this number to 57.07. Optimal solutions are found to possess certain rotation symmetries (or anti-symmetries) and optimal flows share certain common features. The flows localize in a small region near the sphere's centre and spiral upwards with very large velocity and vorticity, so that they are locally nearly Beltrami. We also derive a new lower bound on the magnetic Reynolds number for dynamo action, which, for the case of enstrophy normalization, is five times larger than the previous best bound.}, }
@article {pmid32082060, year = {2020}, author = {Jose, S and Govindarajan, R}, title = {Non-normal origin of modal instabilities in rotating plane shear flows.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {476}, number = {2233}, pages = {20190550}, pmid = {32082060}, issn = {1364-5021}, abstract = {Small variations introduced in shear flows are known to affect stability dramatically. Rotation of the flow system is one example, where the critical Reynolds number for exponential instabilities falls steeply with a small increase in rotation rate. We ask whether there is a fundamental reason for this sensitivity to rotation. We answer in the affirmative, showing that it is the non-normality of the stability operator in the absence of rotation which triggers this sensitivity. We treat the flow in the presence of rotation as a perturbation on the non-rotating case, and show that the rotating case is a special element of the pseudospectrum of the non-rotating case. Thus, while the non-rotating flow is always modally stable to streamwise-independent perturbations, rotating flows with the smallest rotation are unstable at zero streamwise wavenumber, with the spanwise wavenumbers close to that of disturbances with the highest transient growth in the non-rotating case. The instability critical rotation number scales inversely as the square of the Reynolds number, which we demonstrate is the same as the scaling obeyed by the minimum perturbation amplitude in non-rotating shear flow needed for the pseudospectrum to cross the neutral line. Plane Poiseuille flow and plane Couette flow are shown to behave similarly in this context.}, }
@article {pmid32067001, year = {2020}, author = {Razavi Bazaz, S and Mashhadian, A and Ehsani, A and Saha, SC and Krüger, T and Ebrahimi Warkiani, M}, title = {Computational inertial microfluidics: a review.}, journal = {Lab on a chip}, volume = {20}, number = {6}, pages = {1023-1048}, doi = {10.1039/c9lc01022j}, pmid = {32067001}, issn = {1473-0189}, abstract = {Since the discovery of inertial focusing in 1961, numerous theories have been put forward to explain the migration of particles in inertial flows, but a complete understanding is still lacking. Recently, computational approaches have been utilized to obtain better insights into the underlying physics. In particular, fundamental aspects of particle focusing inside straight and curved microchannels have been explored in detail to determine the dependence of focusing behavior on particle size, channel shape, and flow Reynolds number. In this review, we differentiate between the models developed for inertial particle motion on the basis of whether they are semi-analytical, Navier-Stokes-based, or built on the lattice Boltzmann method. This review provides a blueprint for the consideration of numerical solutions for modeling of inertial particle motion, whether deformable or rigid, spherical or non-spherical, and whether suspended in Newtonian or non-Newtonian fluids. In each section, we provide the general equations used to solve particle motion, followed by a tutorial appendix and specified sections to engage the reader with details of the numerical studies. Finally, we address the challenges ahead in the modeling of inertial particle microfluidics for future investigators.}, }
@article {pmid32066045, year = {2020}, author = {Tanveer, A and Salahuddin, T and Khan, M and Malik, MY and Alqarni, MS}, title = {Theoretical analysis of non-Newtonian blood flow in a microchannel.}, journal = {Computer methods and programs in biomedicine}, volume = {191}, number = {}, pages = {105280}, doi = {10.1016/j.cmpb.2019.105280}, pmid = {32066045}, issn = {1872-7565}, mesh = {*Electroosmosis ; Hemodynamics ; Hydrodynamics ; *Models, Biological ; Models, Statistical ; Nanotechnology ; Rheology ; Viscosity ; }, abstract = {BACKGROUND: In this work the theoretical analysis is presented for a electroosmotic flow of Bingham nanofluid induced by applied electrostatic potential. The linearized Poisson-Boltzmann equation is considered in the presence of Electric double layer (EDL). A Bingham fluid model is employed to describe the rheological behavior of the non-Newtonian fluid. Mathematical formulation is presented under the assumption of long wavelength and small Reynolds number. Flow characteristics are investigated by employing Debye-Huckel linearization principle. Such preferences have not been reported previously for non-Newtonian Bingham nanofluid to the best of author's knowledge.<br><br>METHOD: The transformed equations for electroosmotic flow are solved to seek values for the nanofluid velocity, concentration and temperature along the channel length.<br><br>RESULTS: The effects of key parameters like Brinkmann number, Prandtl number, Debey Huckel parameter, thermophoresis parameter, Brownian motion parameter are plotted on velocity, temperature and concentration profiles. Graphical results for the flow phenomenon are discussed briefly.<br><br>CONCLUSIONS: Non-uniformity in channel as well as yield stress &#x3c4;0 cause velocity declaration for both positive and negative values of U. Nanofluid temperature is found an increasing function of electro osmotic parameter &#x3ba; if U is positive while it is a decreasing function if U is negative. A completely reverse response is seen in case of concentration profile. The thermophoresis parameter Nt, the Brow nian motion parameter Nb and Brinkman number Br cause an enhancement in temperature. The results are new in case of U.}, }
@article {pmid32062487, year = {2020}, author = {Yan, SR and Sedeh, S and Toghraie, D and Afrand, M and Foong, LK}, title = {Analysis and manegement of laminar blood flow inside a cerebral blood vessel using a finite volume software program for biomedical engineering.}, journal = {Computer methods and programs in biomedicine}, volume = {190}, number = {}, pages = {105384}, doi = {10.1016/j.cmpb.2020.105384}, pmid = {32062487}, issn = {1872-7565}, mesh = {Adult ; Algorithms ; *Biomedical Engineering ; *Blood Flow Velocity ; *Cerebral Veins/physiology ; Female ; *Hemodynamics ; Humans ; Image Processing, Computer-Assisted ; Shear Strength ; *Software ; }, abstract = {BACKGROUND AND OBJECTIVE: Hemodynamic blood flow analysis in the cerebrovascular is has become one of the important research topics in the bio-mechanic in recent decades. The primary duty of the cerebral blood vessel is supplying Glucose and oxygen for the brain.<br><br>METHODS: In this investigation, the non-Newtonian blood flow in the cerebral blood vessels studied. For modeling the geometry of this problem, we used Magnetic Resonance Image (MRI) approach to take Digital Imaging and Communications in Medicine (DICOM) images and using an open-source software package to construct the geometry, which is a complicated one. The power-law indexes, heat flux, and Reynolds number range in the investigation are 0.6 &#x2264; n &#x2264; 0.8, 5 &#x2264; q &#x2264; 15Wm[-2] and 160&#x2264;Re&#x2264;310. Effects of Reynolds number, power-law indexes and heat fluxes are investigated.<br><br>RESULTS: We found that the pressure drop increase with increasing the Reynolds number and power-law index. The maximum Nusselt number in the cerebral blood vessels accrued in the running position of the body in n&#xa0;=&#xa0;0.8. Also, the highest average wall shear stress occurs in maximum power-law indexes and Reynolds number.<br><br>CONCLUSION: By increasing the power-law index and Reynolds number, the wall shear stress increases.}, }
@article {pmid32052248, year = {2020}, author = {Waheed, S and Noreen, S and Tripathi, D and Lu, DC}, title = {Electrothermal transport of third-order fluids regulated by peristaltic pumping.}, journal = {Journal of biological physics}, volume = {46}, number = {1}, pages = {45-65}, pmid = {32052248}, issn = {1573-0689}, mesh = {Electroosmosis/*instrumentation ; *Hot Temperature ; Hydrodynamics ; Models, Theoretical ; }, abstract = {The study of heat and electroosmotic characteristics in the flow of a third-order fluid regulated by peristaltic pumping is examined by using governing equations, i.e., the continuity equation, momentum equation, energy equation, and concentration equation. The wavelength is considered long compared to its height and a low Reynolds number is assumed. The velocity slip condition is employed. Analytical solutions are performed through the perturbation technique. The expressions for the dimensionless velocity components, temperature, concentration, and heat transfer rate are obtained. Pumping features were computed numerically for discussion of results. Trapping and heat transfer coefficient distributions were also studied graphically. The findings of the present study can be applied to design biomicrofluidic devices like tumor-on-a-chip and organ-on-a-chip.}, }
@article {pmid32042893, year = {2020}, author = {Cerbus, RT and Liu, CC and Gioia, G and Chakraborty, P}, title = {Small-scale universality in the spectral structure of transitional pipe flows.}, journal = {Science advances}, volume = {6}, number = {4}, pages = {eaaw6256}, pmid = {32042893}, issn = {2375-2548}, abstract = {Turbulent flows are not only everywhere, but every turbulent flow is the same at small scales. The extraordinary simplification engendered by this "small-scale universality" is a hallmark of turbulence theory. However, on the basis of the restrictive assumptions invoked by A. N. Kolmogorov to demonstrate this universality, it is widely thought that only idealized turbulent flows conform to this framework. Using experiments and simulations that span a wide range of Reynolds number, we show that small-scale universality governs the spectral structure of a class of flows with no apparent ties to the idealized flows: transitional pipe flows. Our results not only extend the universality of Kolmogorov's framework beyond expectation but also establish an unexpected link between transitional pipe flows and Kolmogorovian turbulence.}, }
@article {pmid32041775, year = {2020}, author = {Usherwood, JR and Cheney, JA and Song, J and Windsor, SP and Stevenson, JPJ and Dierksheide, U and Nila, A and Bomphrey, RJ}, title = {High aerodynamic lift from the tail reduces drag in gliding raptors.}, journal = {The Journal of experimental biology}, volume = {223}, number = {Pt 3}, pages = {}, pmid = {32041775}, issn = {1477-9145}, support = {/WT_/Wellcome Trust/United Kingdom ; 202854/Z/16/Z/WT_/Wellcome Trust/United Kingdom ; BB/G021627/1/BB_/Biotechnology and Biological Sciences Research Council/United Kingdom ; 202854/Z/16/Z/WT_/Wellcome Trust/United Kingdom ; }, mesh = {Animals ; Biomechanical Phenomena ; Flight, Animal/*physiology ; Hawks/*physiology ; Species Specificity ; Strigiformes/*physiology ; Tail/*physiology ; }, abstract = {Many functions have been postulated for the aerodynamic role of the avian tail during steady-state flight. By analogy with conventional aircraft, the tail might provide passive pitch stability if it produced very low or negative lift. Alternatively, aeronautical principles might suggest strategies that allow the tail to reduce inviscid, induced drag: if the wings and tail act in different horizontal planes, they might benefit from biplane-like aerodynamics; if they act in the same plane, lift from the tail might compensate for lift lost over the fuselage (body), reducing induced drag with a more even downwash profile. However, textbook aeronautical principles should be applied with caution because birds have highly capable sensing and active control, presumably reducing the demand for passive aerodynamic stability, and, because of their small size and low flight speeds, operate at Reynolds numbers two orders of magnitude below those of light aircraft. Here, by tracking up to 20,000, 0.3 mm neutrally buoyant soap bubbles behind a gliding barn owl, tawny owl and goshawk, we found that downwash velocity due to the body/tail consistently exceeds that due to the wings. The downwash measured behind the centreline is quantitatively consistent with an alternative hypothesis: that of constant lift production per planform area, a requirement for minimizing viscous, profile drag. Gliding raptors use lift distributions that compromise both inviscid induced drag minimization and static pitch stability, instead adopting a strategy that reduces the viscous drag, which is of proportionately greater importance to lower Reynolds number fliers.}, }
@article {pmid32024757, year = {2020}, author = {Wu, Z and Zaki, TA and Meneveau, C}, title = {High-Reynolds-number fractal signature of nascent turbulence during transition.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {117}, number = {7}, pages = {3461-3468}, pmid = {32024757}, issn = {1091-6490}, abstract = {Transition from laminar to turbulent flow occurring over a smooth surface is a particularly important route to chaos in fluid dynamics. It often occurs via sporadic inception of spatially localized patches (spots) of turbulence that grow and merge downstream to become the fully turbulent boundary layer. A long-standing question has been whether these incipient spots already contain properties of high-Reynolds-number, developed turbulence. In this study, the question is posed for geometric scaling properties of the interface separating turbulence within the spots from the outer flow. For high-Reynolds-number turbulence, such interfaces are known to display fractal scaling laws with a dimension [Formula: see text], where the 1/3 excess exponent above 2 (smooth surfaces) follows from Kolmogorov scaling of velocity fluctuations. The data used in this study are from a direct numerical simulation, and the spot boundaries (interfaces) are determined by using an unsupervised machine-learning method that can identify such interfaces without setting arbitrary thresholds. Wide separation between small and large scales during transition is provided by the large range of spot volumes, enabling accurate measurements of the volume-area fractal scaling exponent. Measurements show a dimension of [Formula: see text] over almost 5 decades of spot volume, i.e., trends fully consistent with high-Reynolds-number turbulence. Additional observations pertaining to the dependence on height above the surface are also presented. Results provide evidence that turbulent spots exhibit high-Reynolds-number fractal-scaling properties already during early transitional and nonisotropic stages of the flow evolution.}, }
@article {pmid32024433, year = {2020}, author = {Xu, Z and Qin, H and Li, P and Liu, R}, title = {Computational fluid dynamics approaches to drag and wake of a long-line mussel dropper under tidal current.}, journal = {Science progress}, volume = {103}, number = {1}, pages = {36850419901235}, pmid = {32024433}, issn = {2047-7163}, mesh = {Animals ; *Bivalvia ; *Hydrodynamics ; Porosity ; Tidal Waves ; }, abstract = {Hydrodynamic effects of mussel farms have attracted increased research attentions in recent years. The understanding of the hydrodynamic impacts is essential for predicting the sustainability of mussel farms. A large mussel farm includes thousands of mussel droppers, and the combined drag on the mussel droppers is sufficient to possibly affect the longevity of the entire long-lines. This article intends to study the drag and wake of an individual long-line mussel dropper using computational fluid dynamics approaches. Two equivalent rough cylinders, namely, Curved-Model and Sharp-Model, have been utilized to simulate the mussel dropper, and each rough cylinder is assigned with surface roughness. The porosity is not considered in this article due to its complexity from inhalant and exhalant of mussels. Two-dimensional laminar simulations are conducted at Reynolds number from 10 to 200, and three-dimensional large eddy simulations are conducted at subcritical Reynolds number ranging from 3900 to 105. The results show that larger drag coefficients and Strouhal numbers are attributed to surface roughness and sharp crowns on the rough cylinder. The obtained drag coefficient ranges from 1.1 to 1.2 with respect to the diameter of the mussel dropper and the peak value of the tidal velocities. Wakes behind rough cylinders fluctuate more actively compared to those of smooth cylinders. This research work provides new insight for further investigations on hydrodynamic interactions between fluid and mussel droppers.}, }
@article {pmid32007018, year = {2020}, author = {Ganta, N and Mahato, B and Bhumkar, YG}, title = {Prediction of the aerodynamic sound generated due to flow over a cylinder performing combined steady rotation and rotary oscillations.}, journal = {The Journal of the Acoustical Society of America}, volume = {147}, number = {1}, pages = {325}, doi = {10.1121/10.0000585}, pmid = {32007018}, issn = {1520-8524}, abstract = {Analysis of sound generated due to a laminar flow past a circular cylinder subjected to the mean rotation along with the rotary oscillating motion has been performed for the Reynolds number Re = 150 and the Mach number M = 0.2. The direct numerical simulation approach has been used to study modifications in the generated sound field over a range of forcing parameters using disturbance pressure field information. Flow and sound fields are accurately resolved over a nondimensional radial distance r≤100 from the center of the cylinder. Frequencies, as well as wavelengths of generated sound waves, have been effectively altered by varying the forcing frequency-ratio, whereas the directivity nature of the radiated sound field has been modified by varying the forcing amplitude-ratio. Doak's decomposition technique has been used to understand the reasons behind changes in the radiated sound fields as the forcing parameters are varied.}, }
@article {pmid32006194, year = {2020}, author = {Alouges, F and Di Fratta, G}, title = {Parking 3-sphere swimmer: II. The long-arm asymptotic regime.}, journal = {The European physical journal. E, Soft matter}, volume = {43}, number = {2}, pages = {6}, pmid = {32006194}, issn = {1292-895X}, abstract = {The paper carries on our previous investigations on the complementary version of Purcell's rotator (sPr3): a low-Reynolds-number swimmer composed of three balls of equal radii. In the asymptotic regime of very long arms, the Stokes-induced governing dynamics is derived, and then experimented in the context of energy-minimizing self-propulsion characterized in the first part of the paper.}, }
@article {pmid31999751, year = {2020}, author = {Liu, P and Liu, H and Yang, Y and Wang, M and Sun, Y}, title = {Comparison of design methods for negative pressure gradient rotary bodies: A CFD study.}, journal = {PloS one}, volume = {15}, number = {1}, pages = {e0228186}, pmid = {31999751}, issn = {1932-6203}, mesh = {Animals ; Computer Simulation ; *Hydrodynamics ; Models, Theoretical ; *Pressure ; Ships ; Stress, Mechanical ; Surface Properties ; }, abstract = {Computational fluid dynamics (CFD) simulation is used to test two body design methods which use negative pressure gradient to suppress laminar flow separation and drag reduction. The steady-state model of the Transition SST model is used to calculate the pressure distribution, wall shear stress, and drag coefficient under zero angle of attack at different velocities. Four bodies designed by two different methods are considered. Our results show the first method is superior to the body of Hansen in drag reduction and the body designed by the first method is more likely to obtain the characteristics of suppressing or eliminating separation, which can effectively improve laminar flow coverage to achieve drag reduction under higher Reynolds number conditions. The results show that the negative pressure gradient method can suppress separation and drag reduction better than the second method. This successful design method is expected to open a promising prospect for its application in the design of small drag, small noise subsonic hydrodynamic hull and underwater weapons.}, }
@article {pmid31991147, year = {2020}, author = {Nguyen, KH and Gemmell, BJ and Rohr, JR}, title = {Effects of temperature and viscosity on miracidial and cercarial movement of Schistosoma mansoni: ramifications for disease transmission.}, journal = {International journal for parasitology}, volume = {50}, number = {2}, pages = {153-159}, pmid = {31991147}, issn = {1879-0135}, support = {HHSN272201000005C/AI/NIAID NIH HHS/United States ; HHSN272201000005I/AI/NIAID NIH HHS/United States ; R01 TW010286/TW/FIC NIH HHS/United States ; }, mesh = {Animals ; Biomphalaria/parasitology ; Cercaria/*physiology ; Climate Change ; Host-Parasite Interactions ; Humans ; Larva/physiology ; Life Cycle Stages ; Movement/*physiology ; Schistosoma mansoni/*physiology ; Schistosomiasis mansoni/*transmission ; Temperature ; Viscosity ; }, abstract = {Parasites with complex life cycles can be susceptible to temperature shifts associated with seasonal changes, especially as free-living larvae that depend on a fixed energy reserve to survive outside the host. The life cycle of Schistosoma, a trematode genus containing some species that cause human schistosomiasis, has free-living, aquatic miracidial and cercarial larval stages that swim using cilia or a forked tail, respectively. The small size of these swimmers (150-350 µm) dictates that their propulsion is dominated by viscous forces. Given that viscosity inhibits the swimming ability of small organisms and is inversely correlated with temperature, changes in temperature should affect the ability of free-living larval stages to swim and locate a host. By recording miracidial and cercarial movement of Schistosoma mansoni using a high-speed camera and manipulating temperature and viscosity independently, we assessed the role each factor plays in the swimming mechanics of the parasite. We found a positive effect of temperature and a negative effect of viscosity on miracidial and cercarial speed. Reynolds numbers, which describe the ratio of inertial to viscous forces exerted on an aquatic organism, were <1 across treatments. Q10 values were <2 when comparing viscosity treatments at 20 °C and 30 °C, further supporting the influence of viscosity on miracidial and cercarial speed. Given that both larval stages have limited energy reserves and infection takes considerable energy, successful transmission depends on both speed and lifespan. We coupled our speed data with mortality measurements across temperatures and discovered that the theoretical maximum distance travelled increased with temperature and decreased with viscosity for both larval stages. Thus, our results suggest that S. mansoni transmission is high during warm times of the year, partly due to improved swimming performance of the free-living larval stages, and that increases in temperature variation associated with climate change might further increase transmission.}, }
@article {pmid31989130, year = {2020}, author = {Fauzi, FB and Ismail, E and Syed Abu Bakar, SN and Ismail, AF and Mohamed, MA and Md Din, MF and Illias, S and Ani, MH}, title = {The role of gas-phase dynamics in interfacial phenomena during few-layer graphene growth through atmospheric pressure chemical vapour deposition.}, journal = {Physical chemistry chemical physics : PCCP}, volume = {22}, number = {6}, pages = {3481-3489}, doi = {10.1039/c9cp05346h}, pmid = {31989130}, issn = {1463-9084}, abstract = {The complicated chemical vapour deposition (CVD) is currently the most viable method of producing graphene. Most studies have extensively focused on chemical aspects either through experiments or computational studies. However, gas-phase dynamics in CVD reportedly plays an important role in improving graphene quality. Given that mass transport is the rate-limiting step for graphene deposition in atmospheric-pressure CVD (APCVD), the interfacial phenomena at the gas-solid interface (i.e., the boundary layer) are a crucial controlling factor. Accordingly, only by understanding and controlling the boundary-layer thickness can uniform full-coverage graphene deposition be achieved. In this study, a simplified computational fluid dynamics analysis of APCVD was performed to investigate gas-phase dynamics during deposition. Boundary-layer thickness was also estimated through the development of a customised homogeneous gas model. Interfacial phenomena, particularly the boundary layer and mass transport within it, were studied. The effects of Reynolds number on these factors were explored and compared with experimentally obtained results of the characterised graphene deposit. We then discussed and elucidated the important relation of fluid dynamics to graphene growth through APCVD.}, }
@article {pmid31982669, year = {2020}, author = {Asghar, Z and Ali, N and Javid, K and Waqas, M and Dogonchi, AS and Khan, WA}, title = {Bio-inspired propulsion of micro-swimmers within a passive cervix filled with couple stress mucus.}, journal = {Computer methods and programs in biomedicine}, volume = {189}, number = {}, pages = {105313}, doi = {10.1016/j.cmpb.2020.105313}, pmid = {31982669}, issn = {1872-7565}, mesh = {Algorithms ; Cervix Uteri/*physiology ; Female ; Humans ; Male ; Models, Biological ; Mucus/*physiology ; Rheology ; Spermatozoa ; Stress, Psychological/metabolism ; }, abstract = {BACKGROUND AND OBJECTIVE: The swimming mechanism of self-propelling organisms has been imitated by biomedical engineers to design the mechanical micro bots. The interaction of these swimmers with surrounding environment is another important aspect. The present swimming problem integrates Taylor sheet model with couple stress fluid model. The thin passage containing micro-swimmers and mucus is approximated as a rigid (passive) two-dimensional channel. The spermatozoa forms a pack quite similar as a complex wavy sheet.<br><br>METHODS: Swimming problem with couple stress cervical liquid (at low Reynolds number) leads to a linear sixth order differential equation. The boundary value problem (BVP) is solved analytically with two unknowns i.e. speed of complex wavy sheet and flow rate of couple stress mucus. After utilizing this solution into equilibrium conditions these unknowns can be computed via Newton-Raphson algorithm. Furthermore, the pairs of numerically calculated organism speed and flow rate are utilized in the expression of power dissipation.<br><br>RESULTS: This work describes that the speed of micro-swimmers can be enhanced by suitable rheology of the surrounding liquid. The usage of couple stress fluid as compared to Newtonian fluid enhances the energy dissipation and reduces the flow rate. On the other hand complex wavy surface also aids the organisms to swim faster.}, }
@article {pmid31978919, year = {2020}, author = {Zhu, Y and Yang, G and Zhuang, C and Li, C and Hu, D}, title = {Oral cavity flow distribution and pressure drop in balaenid whales feeding: a theoretical analysis.}, journal = {Bioinspiration &amp; biomimetics}, volume = {15}, number = {3}, pages = {036004}, doi = {10.1088/1748-3190/ab6fb8}, pmid = {31978919}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Bionics ; Feeding Behavior/*physiology ; Models, Theoretical ; Mouth/*physiology ; Whales/*physiology ; }, abstract = {Balaenid whales, as continuous ram filter feeders, can efficiently separate prey from water by baleen. The feeding process of balaenid whales is extremely complex, in which the flow distribution and pressure drop in the oral cavity play a significant role. In this paper, a theoretical model coupled with oral cavity velocity and pressure in balaenid whales is established based on mass conservation, momentum conservation and pressure drop equations, considering both the inertial and the friction terms. A discrete method with section-by-section calculation is adopted to solve the theoretical model. The effects of four crucial parameters, i.e. the ratio of filtration area to inlet area (S), the Reynolds number of entrance (Re in), the ratio of thickness to permeability of the porous media formed by the fringe layer (ϕ) and the width ratio of the anteroposterior canal within the mouth along the tongue (APT channel) to that along the lip (APL channel) (H) are discussed. The results show that, for a given case, the flow distribution and the pressure drop both show increasing trends with the flow direction. For different cases, when S is small, Re in is small and ϕ is large, a good flow pattern emerges with a smoother flow speed near the oropharynx, better drainage, better shunting and filtration, and higher energy efficiency. However, for smaller values of H, some energy efficiency is sacrificed to achieve additional average transverse flow in order to produce better shunting and filtration. The research in this paper provides a reference for the design of high-efficiency bionic filters.}, }
@article {pmid31978870, year = {2020}, author = {Afrouzi, HH and Ahmadian, M and Hosseini, M and Arasteh, H and Toghraie, D and Rostami, S}, title = {Simulation of blood flow in arteries with aneurysm: Lattice Boltzmann Approach (LBM).}, journal = {Computer methods and programs in biomedicine}, volume = {187}, number = {}, pages = {105312}, doi = {10.1016/j.cmpb.2019.105312}, pmid = {31978870}, issn = {1872-7565}, mesh = {Algorithms ; Aneurysm/*diagnostic imaging ; Arteries/diagnostic imaging ; *Blood Flow Velocity ; Cardiovascular Diseases/*diagnostic imaging ; Computer Simulation ; Hemodynamics ; Humans ; Hydrodynamics ; Models, Cardiovascular ; Rheology ; Shear Strength ; Stress, Mechanical ; Stroke/*diagnostic imaging ; Viscosity ; }, abstract = {BACKGROUND AND OBJECTIVE: In most countries, the higher death rates are due to cardiovascular disease and stroke. These problems often derive from irregular blood flow and the circulatory system disorder.<br><br>METHODS: In this paper, the blood flow is simulated in a created aneurysm in the artery upon using Lattice Boltzmann Method (LBM). Blood is selected as a non-Newtonian fluid which was simulated with power-law model. The lattice Boltzmann results for non-Newtonian fluid flow with power-law model and the curved boundary are compared and validated with previous studies which show a good agreement. In this study, simulations are carried out for two types of aneurysms. For the first aneurysm, three power-law exponents of 0.6, 0.8 and 1.0 at Reynolds number of 100 for three different cases are investigated.<br><br>RESULTS: The results show that the wall shear stress increases with increasing the power-law exponent. In addition, in the main duct of artery where the velocity is larger, shear stress is lower due to the smaller velocity gradient. For the second Aneurysm, the simulations are done for three Reynolds numbers of 100, 150 and 200, and three Womersley numbers of 4, 12 and 20. The blood flow is pulsating at the inlet such as the real pulsating wave in the blood. Results show that with increasing the Womersley number, the velocity profiles in the middle of the aneurysm are closer at a constant Reynolds number.<br><br>CONCLUSIONS: With increasing the Reynolds number, the range of vortices and values of velocity and tension grow in the aneurysm.}, }
@article {pmid31975701, year = {2020}, author = {Porté-Agel, F and Bastankhah, M and Shamsoddin, S}, title = {Wind-Turbine and Wind-Farm Flows: A Review.}, journal = {Boundary-layer meteorology}, volume = {174}, number = {1}, pages = {1-59}, pmid = {31975701}, issn = {0006-8314}, abstract = {Wind energy, together with other renewable energy sources, are expected to grow substantially in the coming decades and play a key role in mitigating climate change and achieving energy sustainability. One of the main challenges in optimizing the design, operation, control, and grid integration of wind farms is the prediction of their performance, owing to the complex multiscale two-way interactions between wind farms and the turbulent atmospheric boundary layer (ABL). From a fluid mechanical perspective, these interactions are complicated by the high Reynolds number of the ABL flow, its inherent unsteadiness due to the diurnal cycle and synoptic-forcing variability, the ubiquitous nature of thermal effects, and the heterogeneity of the terrain. Particularly important is the effect of ABL turbulence on wind-turbine wake flows and their superposition, as they are responsible for considerable turbine power losses and fatigue loads in wind farms. These flow interactions affect, in turn, the structure of the ABL and the turbulent fluxes of momentum and scalars. This review summarizes recent experimental, computational, and theoretical research efforts that have contributed to improving our understanding and ability to predict the interactions of ABL flow with wind turbines and wind farms.}, }
@article {pmid31962497, year = {2019}, author = {Kaminsky, J and Klewicki, J and Birnir, B}, title = {Application of the stochastic closure theory to the Townsend-Perry constants.}, journal = {Physical review. E}, volume = {100}, number = {6-1}, pages = {061101}, doi = {10.1103/PhysRevE.100.061101}, pmid = {31962497}, issn = {2470-0053}, abstract = {We compare the stochastic closure theory (SCT) to the Townsend-Perry constants as estimated from measurements in the Flow Physic Facility (FPF) at the University of New Hampshire. First, we explain the derivation of the Townsend-Perry constants, which were originally formulated by Meneveau and Marusic, in analogy with a Gaussian distribution. However, this was not supported by the data. Instead, the data show a sub-Gaussian relation that was explained by Birnir and Chen. We show herein how the SCT can be used to compute the constants, which explains their sub-Gaussian relations. We then compare the SCT theory predictions, including Reynolds-number-dependent corrections, with the data, showing good agreement.}, }
@article {pmid31962492, year = {2019}, author = {Jin, Y and Cheng, S and Chamorro, LP}, title = {Active pitching of short splitters past a cylinder: Drag increase and wake.}, journal = {Physical review. E}, volume = {100}, number = {6-1}, pages = {063106}, doi = {10.1103/PhysRevE.100.063106}, pmid = {31962492}, issn = {2470-0053}, abstract = {The flow and drag induced by active pitching of plates in the wake of a cylinder of diameter d were experimentally studied for various plate lengths L as well as pitching frequencies f_{p} and amplitudes A_{0} at Reynolds number Re=1.6×10^{4}. Planar particle image velocimetry and a load cell were used to characterize the flow statistics and mean drag of a variety of cylinder-splitter assemblies. Results show the distinctive effect of active pitching on these quantities. In particular, flow recovery was significantly modulated by L, f_{p}, or A_{0}. Specific pitching settings resulted in a wake with dominant meandering patterns and faster flow recovery. We defined a modified version of the amplitude-based Strouhal number of the system St_{A} to account for the effect of the cylinder in active pitching. It characterizes the drag coefficient C_{d} across all the cases studied, and reveals two regions intersecting at a critical value of St_{A}≈0.035. Below this value, the C_{d} remained nearly constant; however, it exhibited a linear increase with increasing St_{A} past this critical point. Inspection of the integral momentum equation showed the dominant role of velocity fluctuations in modulating C_{d} past the critical St_{A}.}, }
@article {pmid31955110, year = {2020}, author = {Rajwa-Kuligiewicz, A and Radecki-Pawlik, A and Skalski, T and Plesiński, K and Rowiński, PM and Manson, JR}, title = {Hydromorphologically-driven variability of thermal and oxygen conditions at the block ramp hydraulic structure: The Porębianka River, Polish Carpathians.}, journal = {The Science of the total environment}, volume = {713}, number = {}, pages = {136661}, doi = {10.1016/j.scitotenv.2020.136661}, pmid = {31955110}, issn = {1879-1026}, abstract = {Growing anthropopressure in mountain streams aimed at limiting erosion and flood protection often caused adverse effects on the natural environment. In recent years, great attention has been paid to the restoration and conservation of natural habitats in mountain streams using environmentally friendly solutions such as the Block Ramp (BR) Hydraulic Structures. In this study we investigated the factors responsible for spatial variability in thermal and oxygen conditions at the single BR structure in the growing season, and the relation between water temperature and dissolved oxygen (DO) concentration. This has been done by measurements of hydraulic characteristics along with physicochemical properties of water, such as water temperature and DO concentration, at two different discharges. The redundancy analysis has been applied in order to describe the relationships among hydraulic parameters and physicochemical variables, and extract potential sources of water temperature and DO variability within the BR hydraulic structure. Results have shown that DO and water temperature distributions within the BR hydraulic structure depend on discharge conditions and are associated with the submergence of the block ramp. The highest heterogeneity in hydraulic, DO and water temperature conditions occurs at low flow and is associated with the presence of crevices between protruding cobbles at the block ramp. The lowest variability, in turn, occurs at high discharge, when the block ramp is completely submerged. The results indicated that thermal and oxygen conditions within the BR hydraulic structure are independent of hydraulic parameters at low flow. Moreover, the relation between DO concentration and water temperature is positive at low flow indicating potential impact of biological processes. On the contrary, at high discharge both, the DO concentrations and water temperature within the BR structure, depend on bed shear velocity and maximum Reynolds number.}, }
@article {pmid31948589, year = {2020}, author = {Haghighinia, A and Movahedirad, S}, title = {Mass transfer in a novel passive micro-mixer: Flow tortuosity effects.}, journal = {Analytica chimica acta}, volume = {1098}, number = {}, pages = {75-85}, doi = {10.1016/j.aca.2019.11.028}, pmid = {31948589}, issn = {1873-4324}, abstract = {Hydroynamic fluid tortuosity is a parameter to describe the fluid streamlines average elongation. The motivation of the present study is introducing a new concept for theoretical predictions of dynamic tortuosity effects on mass transfer in a novel three-dimensional passive T-shape micro-mixer both experimentally and by numerical simulation. In the numerical analysis, continuity, motion, and diffusion-convection equations were solved, and the amount of mass transfer and the fluid tortuosity was calculated for different rectangular winglet angles. The Reynolds number is considered in the range of 0.1-93. The results show that when the angle of winglet tends to 22.5°, the fluid tortuosity, lateral velocity, and fluid mass transfer tend to maximum values. Furthermore, the effect of fluid tortuosity on the fluid stretching as a theory of chaotic mixing is investigated.}, }
@article {pmid31947897, year = {2020}, author = {Rhoades, T and Kothapalli, CR and Fodor, PS}, title = {Mixing Optimization in Grooved Serpentine Microchannels.}, journal = {Micromachines}, volume = {11}, number = {1}, pages = {}, pmid = {31947897}, issn = {2072-666X}, support = {Undergraduate Summer Research Award 2019 and Graduate Faculty Research Award 2019//Cleveland State University/ ; }, abstract = {Computational fluid dynamics modeling at Reynolds numbers ranging from 10 to 100 was used to characterize the performance of a new type of micromixer employing a serpentine channel with a grooved surface. The new topology exploits the overlap between the typical Dean flows present in curved channels due to the centrifugal forces experienced by the fluids, and the helical flows induced by slanted groove-ridge patterns with respect to the direction of the flow. The resulting flows are complex, with multiple vortices and saddle points, leading to enhanced mixing across the section of the channel. The optimization of the mixers with respect to the inner radius of curvature (Rin) of the serpentine channel identifies the designs in which the mixing index quality is both high (M > 0.95) and independent of the Reynolds number across all the values investigated.}, }
@article {pmid31947174, year = {2019}, author = {Oktamuliani, S and Hasegawa, K and Saijo, Y}, title = {Left Ventricular Vortices in Myocardial Infarction Observed with Echodynamography.}, journal = {Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference}, volume = {2019}, number = {}, pages = {5816-5819}, doi = {10.1109/EMBC.2019.8856394}, pmid = {31947174}, issn = {2694-0604}, mesh = {Blood Flow Velocity ; Case-Control Studies ; Echocardiography, Doppler, Color ; Heart Ventricles ; Hemodynamics ; Humans ; Myocardial Infarction/*diagnostic imaging ; *Ventricular Function, Left ; }, abstract = {Echodynamography (EDG) is a computational method to deduce two-dimensional (2D) blood flow vector from conventional color Doppler ultrasound image by considering that the blood flow is divided into vortex and base flow components. Left ventricular (LV) vortices indicate cardiac flow status influenced by LV wall motion. Thus, quantitative assessment of LV vortices may become new and sensitive parameters for cardiac function. In the present study, quantitative parameters of LV vortices such as vortex index, vortex size, and Reynolds number were calculated and relation between each parameter was assessed. Six healthy volunteers and three patients with myocardial infarction (MI) who underwent color Doppler echocardiography (CDE) were involved in the study. Serial CDE images in apical three-chamber view were recorded and 2D blood flow vector was superimposed on the CDE image. Vortex index, vortex size, and Reynolds number were compared between the normal volunteers and the MI patients. The results showed that vortex index (3.09±2.06 vs. 3.34±2.33, p<; 0.05), vortex size (1.76 0.69 vs. 2.01 ±0.68, p<; 0.05), Reynolds number (1020±603 vs.±1312 1046, p<; ±0.05) were significantly greater in the MI patients than in the healthy volunteers. Vortex equivalent diameter in LV showed significant positive correlation with Reynolds number (R[2] = 0.799, y = 0.001x + 0.7098, p <; 0.05) in healthy volunteers and (R[2] = 0.6404, y = 0.0005x+1.3185, p<; 0.05) in MI patients. Vortex index showed positive correlation with Reynolds number (R[2] = 0.9351, y = 0.002x+0.1397, p<; 0.05) in healthy volunteers and (R[2] = 0.758, y = 0.0019x+0.7957, p<; 0.05) in MI patients. In conclusion, EDG provides information on LV hemodynamics by quantitative LV vortices parameters both in healthy volunteers and MI patients.}, }
@article {pmid31946085, year = {2019}, author = {Hamad, EM and Sawalmeh, B and Mhawsh, AA and Mansour, M and Awad, M and Al-Halhouli, AT and Al-Gharabli, SI}, title = {Investigation of Bifurcation Effect on Various Microfluidic Designs for Blood Separation.}, journal = {Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference}, volume = {2019}, number = {}, pages = {1097-1100}, doi = {10.1109/EMBC.2019.8856380}, pmid = {31946085}, issn = {2694-0604}, mesh = {Equipment Design ; *Lab-On-A-Chip Devices ; *Microfluidic Analytical Techniques ; *Microfluidics ; Plasma ; Software ; }, abstract = {In this project, a microfluidic device for blood separation will be designed and tested in order to separate plasma from whole blood for diagnostic purposes. The design will be based on previously implemented designs that will be further discussed in the next sections. When designing microfluidic devices, it is essential to consider the different physical phenomena that arise from switching from the macro scale to the micro scale. Parameters such as the Reynolds number and the forces affecting the fluid must be studied in order to produce a suitable and effective design. Finite element methods have been implemented prior to the production of the microfluidic devices. Various geometries/designs have been tested using Fluent ANSYS software. Later on, the successful design was fabricated using micromachining on an acrylic substrate and was tested using simulated blood through of a syringe pump.}, }
@article {pmid31942792, year = {2020}, author = {Martínez-Merino, P and Midgley, SD and Martín, EI and Estellé, P and Alcántara, R and Sánchez-Coronilla, A and Grau-Crespo, R and Navas, J}, title = {Novel WS2-Based Nanofluids for Concentrating Solar Power: Performance Characterization and Molecular-Level Insights.}, journal = {ACS applied materials &amp; interfaces}, volume = {12}, number = {5}, pages = {5793-5804}, doi = {10.1021/acsami.9b18868}, pmid = {31942792}, issn = {1944-8252}, abstract = {Nano-colloidal suspensions of nanomaterials in a fluid, nanofluids, are appealing because of their interesting properties related to heat transfer processes. While nanomaterials based on transition metal chalcogenides (TMCs) have been widely studied in catalysis, sensing, and energy storage applications, there are few studies of nanofluids based on TMCs for heat transfer applications. In this study, the preparation and analysis of nanofluids based on 2D-WS2 in a typical heat transfer fluid (HTF) used in concentrating solar power (CSP) plants are reported. Nanofluids prepared using an exfoliation process exhibited well-defined nanosheets and were highly stable. The nanofluids were characterized in terms of properties related to their application in CSP. The presence of WS2 nanosheets did not modify significantly the surface tension, the viscosity, or the isobaric specific heat, but the thermal conductivity was improved by up to 30%. The Ur factor, which characterizes the thermal efficiency of the fluid in the solar collector, shows an enhancement of up to 22% in the nanofluid, demonstrating great promise for CSP applications. The Reynolds number and friction factor of the fluid were not significantly modified by the addition of the nanomaterial to the HTF, which is also positive for practical applications in CSP plants. Ab initio molecular dynamics simulations of the nanoparticle/fluid interface showed an irreversible dissociative adsorption of diphenyl oxide molecules on the WS2 edge, with very low kinetic barrier. The resulting "decoration" of the WS2 edge dramatically affects the nature of the interface interactions and is therefore expected to affect significantly the rheological and transport properties of the nanofluids.}, }
@article {pmid31938721, year = {2020}, author = {Zhang, T and Moreau, D and Geyer, T and Fischer, J and Doolan, C}, title = {Dataset on tip vortex formation noise produced by wall-mounted finite airfoils with flat and rounded tip geometries.}, journal = {Data in brief}, volume = {28}, number = {}, pages = {105058}, pmid = {31938721}, issn = {2352-3409}, abstract = {The vortex generated at the tip of an airfoil such as an aircraft wing, wind turbine blade, submarine fin or propeller blade can dominate its wake and be a significant source of unwanted noise. The data collection presented in this paper consists of measurements of tip vortex formation noise produced by finite length airfoils with flat and rounded tips. These data were obtained using the specialist aeroacoustic test facilities at the Brandenburg University of Technology (BTU) in Cottbus, Germany and a 47-channel planar microphone array. Over 1200 unique test cases with variations in airfoil profile shape, tip geometry, angle of attack and Reynolds number were measured during the experimental campaign. The dataset contains one-third-octave band tip noise spectra that have been processed using Acoular, a Python module for acoustic beamforming.}, }
@article {pmid31935152, year = {2020}, author = {Salazar-Magallón, JA and Huerta de la Peña, A}, title = {Production of antifungal saponins in an airlift bioreactor with a cell line transformed from Solanum chrysotrichum and its activity against strawberry phytopathogens.}, journal = {Preparative biochemistry &amp; biotechnology}, volume = {50}, number = {2}, pages = {204-214}, doi = {10.1080/10826068.2019.1676781}, pmid = {31935152}, issn = {1532-2297}, mesh = {Antifungal Agents/*chemical synthesis/pharmacology ; *Bioreactors ; Cell Line, Transformed ; Fragaria/*microbiology ; Saponins/*chemical synthesis/*pharmacology ; Solanum/*chemistry ; }, abstract = {Biotechnology through plant cell cultures in bioreactors is a tool that allows increasing the production of secondary metabolites of commercial interest. The hydrodynamic characterization, in addition to the transfer (OTR) and uptake (OUR) of oxygen through the dynamic method with different aeration rate, were used to see their influence on the production of biomass and saponins. The culture poisoning technique was used to determine the antifungal activity of the SC-2 and SC-3 saponins in vitro. Likewise, the shear or hydrodynamic stress of 273.6 mN/m[2] were calculated based on the Reynolds Number. The oxygen supply (OTR) was always greater than the demand (OUR) for all the aeration rate evaluated. Dry weight values of 8.6 gDW/L and a concentration of 2.7 mg/L and 187.3 mg/L of the saponins SC-2 and SC-3 respectively were obtained with an air flow of 0.1 vvm. In addition, it was possible to inhibit the growth of phytopathogenic fungi in vitro by up to 93%, while in vivo it was possible to reduce the infections of strawberry seeds inoculated with phytopathogens, obtaining up to 94% of germinated seeds. This information will facilitate the rational operation of the bioreactor culture system that produces secondary metabolites.}, }
@article {pmid31933715, year = {2020}, author = {Hu, X and Lin, J and Chen, D and Ku, X}, title = {Influence of non-Newtonian power law rheology on inertial migration of particles in channel flow.}, journal = {Biomicrofluidics}, volume = {14}, number = {1}, pages = {014105}, pmid = {31933715}, issn = {1932-1058}, abstract = {In this paper, the inertial migration of particles in the channel flow of power-law fluid is numerically investigated. The effects of the power-law index (n), Reynolds number (Re), blockage ratio (k), and channel aspect ratio (AR) on the inertial migration of particles and equilibrium position are explored. The results show that there exist two stages of particle migration and four stable equilibrium positions for particles in the cross section of a square channel. The particle equilibrium positions in a rectangular channel are much different from those in a square channel. In shear-thinning fluids, the long channel face equilibrium position and two kinds of particle trajectories are found at low Re. With increasing Re, the short channel face equilibrium position turns to be stable, multiequilibrium positions, and three kinds of particle trajectories along the long wall start to form. Only two stable equilibrium positions exist in shear-thickening fluids. The equilibrium positions are getting closer to the channel centerline with increasing n and k and with decreasing Re. The inertial focusing length L 2 in the second stage of particle migration is much longer than inertial focusing length L 1 in the first stage. In the square channel, L 2 is decreased with increasing Re and k and with decreasing n. In the rectangular channel, L 2 is the shortest in the shear-thinning fluid.}, }
@article {pmid31931378, year = {2020}, author = {Feng, Y and Wang, Q and Duan, JL and Li, XY and Ma, JY and Wu, L and Han, Y and Liu, XY and Zhang, YB and Yuan, XZ}, title = {Attachment and adhesion force between biogas bubbles and anaerobic granular sludge in the up-flow anaerobic sludge blanket.}, journal = {Water research}, volume = {171}, number = {}, pages = {115458}, doi = {10.1016/j.watres.2019.115458}, pmid = {31931378}, issn = {1879-2448}, mesh = {Anaerobiosis ; *Biofuels ; Bioreactors ; *Sewage ; Waste Disposal, Fluid ; }, abstract = {The performance of the up-flow anaerobic sludge blanket (UASB) is significantly governed by the hydrodynamics of the reactor. Though the influence of hydrodynamics on mass transfer, granular size distribution, and biogas production was well studied, the interaction between biogas bubbles and anaerobic granular sludge (AGS) is poorly understood. This study used the impinging-jet technique and bubble probe atomic force microscope (AFM) to investigate the attachment and adhesion force between biogas bubbles (CH4 and CO2) and AGS. The fluxes of normalized CH4 or CO2 bubble-attachment on two kinds of AGS were directly affected by gas velocity and decreased with an increase in the Reynolds number ranged from 40 to 140. The bubble-attachment had a positive linear relationship with the contact angles, ratio of exopolymeric protein and polysaccharide, and hydrophilic functional groups of AGS. A bubble probe AFM was used to explore the adhesion force between a single bubble and AGS. The results indicated that the adhesion force between the bubbles and the two kinds of AGS also decreased with increasing approach velocity. Overall, these results contribute to a new insight into the understanding of interaction between biogas bubbles and AGS in UASB reactors.}, }
@article {pmid31923819, year = {2020}, author = {Muhammad, R and Khan, MI and Jameel, M and Khan, NB}, title = {Fully developed Darcy-Forchheimer mixed convective flow over a curved surface with activation energy and entropy generation.}, journal = {Computer methods and programs in biomedicine}, volume = {188}, number = {}, pages = {105298}, doi = {10.1016/j.cmpb.2019.105298}, pmid = {31923819}, issn = {1872-7565}, mesh = {Algorithms ; Computer Simulation ; Convection ; Diffusion ; Elasticity ; Entropy ; *Hot Temperature ; Hydrodynamics ; *Models, Theoretical ; Nanotechnology/methods ; *Rheology ; Software ; Viscosity ; }, abstract = {BACKGROUND: Mixed convection (forced+natural convection) is frequently observed in exceptionally high output devices where the forced convection isn't sufficient to dissipate all of the heat essential. At this point, consolidating natural convection with forced convection will frequently convey the ideal outcomes. Nuclear reactor technology and a few features of electronic cooling are the examples of these processes. Mixed convection problems are categorized by Richardson number (Ri), which is the ratio of Grashof number (for natural convection) and Reynolds number (for forced convection). For buoyancy or mixed convection the relative effect can be addressed by Richardson number. Typically, the natural convection is negligible when Richardson number is less than 0.1 (Ri < 0.1), forced convection is negligible when Richardson number is greater than 10 (Ri > 10) and neither is negligible when (0.1 < Ri < 10). It might be noticed that generally the forced convection is large comparative with natural convection except in case of remarkably low forced flow velocities. The current work gives significant insights regarding dissipative mixed convective Darcy-Forchheimer flow with entropy generation over a stretched curved surface. The energy equation is developed with respect to nonlinear radiation, dissipation and Ohmic heating (Joule heating). Binary reaction via activation energy is accounted.<br><br>METHOD: Curvilinear transformations are utilized to change the nonlinear PDE's into ordinary ones. Computational outcomes are obtained via NDSolve MATHEMATICA. The results are computed and discussed graphically.<br><br>RESULTS: Velocity decays for Forchheimer number. Entropy generation enhances for diffusion parameter and chemical reaction parameter. Concentration profile reduces chemical reaction parameter and enhances for activation parameter.}, }
@article {pmid31923536, year = {2020}, author = {Rane, YS and Marston, JO}, title = {Computational study of fluid flow in tapered orifices for needle-free injectors.}, journal = {Journal of controlled release : official journal of the Controlled Release Society}, volume = {319}, number = {}, pages = {382-396}, doi = {10.1016/j.jconrel.2020.01.013}, pmid = {31923536}, issn = {1873-4995}, mesh = {Injections, Jet ; *Rheology ; Viscosity ; }, abstract = {Transdermal drug delivery using spring-powered jet injection has been studied for several decades and continues to be highly sought after due to the advent of targeted needle-free techniques, especially for viscous and complex fluids. As such, this paper reports results from numerical simulations to study the role of fluid rheology and cartridge geometry on characteristics such as jet exit velocity, total pressure drop and boundary layer thickness, since these all factor in to jet stability and collimation. The numerical approach involves incompressible steady flow with turbulence modelling based on the system Reynolds number at the orifice (Re = ρdovj/μ). The results are experimentally validated for a given geometry over a wide range of Reynolds numbers (10[1] < Re < 10[4]), and our results indicate a sharp decrease in dimensionless pressure drop (Eu = 2∆P/ρvj[2]) for Re < 10[2)] and gradually approaching the inviscid limit at Re ≥ 10[4]. By extending the study to non-Newtonian fluids, whose rheological profile is approximated by the Carreau model, we also elucidated the effect of different rheological parameters. Lastly by studying a range of nozzle geometries such as conical, sigmoid taper and multi-tier tapers, we observe that fluid acceleration suppresses the boundary layer growth, which indicates there may be optimal geometries for creating jets to target specific tissue depths.}, }
@article {pmid31907556, year = {2020}, author = {Pan, X and Tang, L and Feng, J and Liang, R and Pu, X and Li, R and Li, K}, title = {Experimental Research on the Degradation Coefficient of Ammonia Nitrogen Under Different Hydrodynamic Conditions.}, journal = {Bulletin of environmental contamination and toxicology}, volume = {104}, number = {2}, pages = {288-292}, doi = {10.1007/s00128-019-02781-0}, pmid = {31907556}, issn = {1432-0800}, support = {2019YFS0505//Major Project for Specialized Science and Technology Fund of Sichuan Province/ ; 2018SZDZX0027//Major Project of Specialized Science and Technology Fund of Sichuan Province/ ; }, mesh = {Ammonia/*analysis/chemistry ; Environmental Monitoring ; Hydrodynamics ; Kinetics ; Nitrogen/*analysis/chemistry ; Rivers/chemistry ; Water Pollutants, Chemical/*analysis/chemistry ; }, abstract = {Degradation coefficients for pollutants in water are important parameters that are significantly influenced by environmental conditions. In controlled experiments, the processes and trends of ammonia nitrogen (NH3-N) degradation in raw waters were studied under different flow conditions using a laboratory annular flume. Analysis of the observed change in NH3-N concentration with time under various flow conditions allowed calculation of a degradation efficiency (concentration change amount/initial concentration) which for NH3-N increased as the flow velocity increased. According to a first-order kinetic equation to fit the experimental data, the range of variation of the degradation coefficient of NH3-N at different flowrates was between 0.047 per day (0.01 m/s) and 0.203 per day (0.30 m/s). Dimensional analysis was used to analyze the relationship between the degradation coefficient and flow velocity (v), water depth (H), Froude number (Fr), and Reynolds number (Re), which was verified through field data collected in the Chishui River.}, }
@article {pmid31905597, year = {2019}, author = {Sobecki, C and Zhang, J and Wang, C}, title = {Numerical Study of Paramagnetic Elliptical Microparticles in Curved Channels and Uniform Magnetic Fields.}, journal = {Micromachines}, volume = {11}, number = {1}, pages = {}, pmid = {31905597}, issn = {2072-666X}, abstract = {We numerically investigated the dynamics of a paramagnetic elliptical particle immersed in a low Reynolds number Poiseuille flow in a curved channel and under a uniform magnetic field by direct numerical simulation. A finite element method, based on an arbitrary Lagrangian-Eulerian approach, analyzed how the channel geometry, the strength and direction of the magnetic field, and the particle shape affected the rotation and radial migration of the particle. The net radial migration of the particle was analyzed after executing a π rotation and at the exit of the curved channel with and without a magnetic field. In the absence of a magnetic field, the rotation is symmetric, but the particle-wall distance remains the same. When a magnetic field is applied, the rotation of symmetry is broken, and the particle-wall distance increases as the magnetic field strength increases. The causation of the radial migration is due to the magnetic angular velocity caused by the magnetic torque that constantly changes directions during particle transportation. This research provides a method of magnetically manipulating non-spherical particles on lab-on-a-chip devices for industrial and biological applications.}, }
@article {pmid31893769, year = {2019}, author = {Bahrami, A and Hoseinzadeh, S and Heyns, PS and Mirhosseini, SM}, title = {Experimental investigation of co-flow jet's airfoil flow control by hot wire anemometer.}, journal = {The Review of scientific instruments}, volume = {90}, number = {12}, pages = {125107}, doi = {10.1063/1.5113592}, pmid = {31893769}, issn = {1089-7623}, abstract = {An experimental flow control technique is given in this paper to study the jet effect on the coflow jet's airfoil with injection and suction and compared with the jet-off condition. The airfoil is CFJ0025-065-196, and the Reynolds number based on the airfoil's chord length is 10[5]. To measure the turbulence components of flow, a hot wire anemometry apparatus in a wind tunnel has been used. In this paper, the effect of the average velocity and boundary layer thickness on the coflow jet's airfoil is analyzed. The test is done for two different coflow velocities and for different angles of attack. It is also shown that, by increasing the velocity difference between the jet and the main flow, separation is delayed, and this delay can be preserved by raising coflow velocity at higher angles of attack. So, this flow control method has a good efficiency, and it is possible to reach higher numbers of lift and lower numbers of drag coefficients.}, }
@article {pmid31890822, year = {2020}, author = {Pendse, V and Mazumdar, B and Kumar, H}, title = {Formulation of experimental data based model for solid-liquid mass transfer enhancement in three phase fluidized bed using nanofluid.}, journal = {Data in brief}, volume = {28}, number = {}, pages = {104990}, pmid = {31890822}, issn = {2352-3409}, abstract = {This experimental data based model in three phase fluidized bed was designed to enhance the solid-liquid mass transfer. This data focuses on mass transfer enhancement using nanomaterial. In present investigation benzoic acid-water-air system was used as three phases ie solid, liquid and gas respectively with Arachitol nano as nanomaterial in different volume percent in three phase fluidized bed. Data from experiment were collected by varying gas velocity, bed height, nanomaterial percentage and time. After a convenient selection various correlation have been derived. The data presented here is the full set of experimental value and coefficients and exponents in correlation were estimated from nonlinear optimization technique in MATLAB.}, }
@article {pmid31882681, year = {2019}, author = {Krishnan, SR and Bal, J and Putnam, SA}, title = {A simple analytic model for predicting the wicking velocity in micropillar arrays.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {20074}, pmid = {31882681}, issn = {2045-2322}, support = {N00014-15-1-2481//United States Department of Defense | United States Navy | Office of Naval Research (ONR)/ ; 1653396//National Science Foundation (NSF)/ ; }, abstract = {Hemiwicking is the phenomena where a liquid wets a textured surface beyond its intrinsic wetting length due to capillary action and imbibition. In this work, we derive a simple analytical model for hemiwicking in micropillar arrays. The model is based on the combined effects of capillary action dictated by interfacial and intermolecular pressures gradients within the curved liquid meniscus and fluid drag from the pillars at ultra-low Reynolds numbers [Formula: see text]. Fluid drag is conceptualized via a critical Reynolds number: [Formula: see text], where v0 corresponds to the maximum wetting speed on a flat, dry surface and x0 is the extension length of the liquid meniscus that drives the bulk fluid toward the adsorbed thin-film region. The model is validated with wicking experiments on different hemiwicking surfaces in conjunction with v0 and x0 measurements using Water [Formula: see text], viscous FC-70 [Formula: see text] and lower viscosity Ethanol [Formula: see text].}, }
@article {pmid31881751, year = {2019}, author = {Li, H and Li, Y and Huang, B and Xu, T}, title = {Flow Characteristics of the Entrance Region with Roughness Effect within Rectangular Microchannels.}, journal = {Micromachines}, volume = {11}, number = {1}, pages = {}, pmid = {31881751}, issn = {2072-666X}, abstract = {We conducted systematic numerical investigations of the flow characteristics within the entrance region of rectangular microchannels. The effects of the geometrical aspect ratio and roughness on entrance lengths were analyzed. The incompressible laminar Navier-Stokes equations were solved using finite volume method (FVM). In the simulation, hydraulic diameters (Dh) ranging from 50 to 200 µm were studied, and aspect ratios of 1, 1.25, 1.5, 1.75, and 2 were considered as well. The working fluid was set as water, and the Reynolds number ranged from 0.5 to 100. The results showed a good agreement with the conducted experiment. Correlations are proposed to predict the entrance lengths of microchannels with respect to different aspect ratios. Compared with other correlations, these new correlations are more reliable because a more practical inlet condition was considered in our investigations. Instead of considering the influence of the width and height of the microchannels, in our investigation we proved that the critical role is played by the aspect ratio, representing the combination of the aforementioned parameters. Furthermore, the existence of rough elements obviously shortens the entrance region, and this effect became more pronounced with increasing relative roughness and Reynolds number. A similar effect could be seen by shortening the roughness spacing. An asymmetric distribution of rough elements decreased the entrance length compared with a symmetric distribution, which can be extrapolated to other irregularly distributed forms.}, }
@article {pmid31878263, year = {2019}, author = {Kang, DJ}, title = {Effects of Channel Wall Twisting on the Mixing in a T-Shaped Micro-Channel.}, journal = {Micromachines}, volume = {11}, number = {1}, pages = {}, pmid = {31878263}, issn = {2072-666X}, support = {2018//Yeungnam University/ ; }, abstract = {A new design scheme is proposed for twisting the walls of a microchannel, and its performance is demonstrated numerically. The numerical study was carried out for a T-shaped microchannel with twist angles in the range of 0 to 34π. The Reynolds number range was 0.15 to 6. The T-shaped microchannel consists of two inlet branches and an outlet branch. The mixing performance was analyzed in terms of the degree of mixing and relative mixing cost. All numerical results show that the twisting scheme is an effective way to enhance the mixing in a T-shaped microchannel. The mixing enhancement is realized by the swirling of two fluids in the cross section and is more prominent as the Reynolds number decreases. The twist angle was optimized to maximize the degree of mixing (DOM), which increases with the length of the outlet branch. The twist angle was also optimized in terms of the relative mixing cost (MC). The two optimum twisting angles are generally not coincident. The optimum twist angle shows a dependence on the length of the outlet branch but it is not affected much by the Reynolds number.}, }
@article {pmid31875772, year = {2020}, author = {Zhang, L and Zhou, J and Zhang, B and Gong, W}, title = {Numerical investigation on the solid particle erosion in elbow with water-hydrate-solid flow.}, journal = {Science progress}, volume = {103}, number = {1}, pages = {36850419897245}, doi = {10.1177/0036850419897245}, pmid = {31875772}, issn = {2047-7163}, abstract = {Erosion in pipeline caused by solid particles, which may lead to premature failure of the pipe system, is regarded as one of the most important concerns in the field of oil and gas. Therefore, the Euler-Lagrange, erosion model, and discrete phase model are applied for the purpose of simulating the erosion of water-hydrate-solid flow in submarine hydrate transportation pipeline. In this article, the flow and erosion characteristics are well verified on the basis of experiments. Moreover, analysis is conducted to have a good understanding of the effects of hydrate volume, mean curvature radius/pipe diameter (R/D) rate, flow velocity, and particle diameter on elbow erosion. It is finally obtained that the hydrate volume directly affects the Reynolds number through viscosity and the trend of the Reynolds number is consistent with the trend of erosion rate. Taking into account different R/D rates, the same Stokes number reflects different dynamic transforms of the maximum erosion zone. However, the outmost wall (zone D) will be the final erosion zone when the value of the Stokes number increases to a certain degree. In addition, the erosion rate increases sharply along with the increase of flow velocity and particle diameter. The effect of flow velocity on the erosion zone can be ignored in comparison with the particle diameter. Moreover, it is observed that flow velocity is deemed as the most sensitive factor on erosion rate among these factors employed in the orthogonal experiment.}, }
@article {pmid31874992, year = {2019}, author = {Liu, X and Fan, D and Yu, X and Liu, Z and Sun, J}, title = {Effects of Simulated Gravel on Hydraulic Characteristics of Overland Flow Under Varying Flow Discharges, Slope Gradients and Gravel Coverage Degrees.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {19781}, pmid = {31874992}, issn = {2045-2322}, abstract = {To quantify the hydraulic characteristics of overland flow on gravel-covered slopes, eight flow discharges (Q) (8.44-122 L/min), five slope gradients (J) (2°-10°) and four gravel coverage degrees (Cr) (0-30%) were examined via a laboratory flume. The results showed that (1) gravel changed flow regime. Gravel increased the Reynolds number (Re) by 2.94-33.03%. Re were less affected by J and positively correlated with Cr and Q. Gravel decreased the Froude number (Fr) by 6.83-77.31%. Fr was positively correlated with Q and J and negatively correlated with Cr. (2) Gravel delayed the flow velocity (u) and increased the flow depth (h) and flow resistance (f). Gravel reduced u by 1.20-58.95%. u was positively correlated with Q and J and negatively correlated with Cr. Gravel increased h by 0.12-2.41 times. h was positively correlated with Q and Cr and negatively correlated with J. Gravel increased f by 0.15-18.42 times. f were less affected by J, positively correlated with Cr and negatively correlated with Q. (3) The relationships between hydraulic parameters and Q, J and Cr identified good power functions. Hydraulic parameters were mainly affected by Cr. These results can guide the ecological construction of soil and water conservation.}, }
@article {pmid31868425, year = {2019}, author = {Panickacheril John, J and Donzis, DA and Sreenivasan, KR}, title = {Solenoidal Scaling Laws for Compressible Mixing.}, journal = {Physical review letters}, volume = {123}, number = {22}, pages = {224501}, doi = {10.1103/PhysRevLett.123.224501}, pmid = {31868425}, issn = {1079-7114}, abstract = {Mixing of passive scalars in compressible turbulence does not obey the same classical Reynolds number scaling as its incompressible counterpart. We first show from a large database of direct numerical simulations that even the solenoidal part of the velocity field fails to follow the classical incompressible scaling when the forcing includes a substantial dilatational component. Though the dilatational effects on the flow remain significant, our main results are that both the solenoidal energy spectrum and the passive scalar spectrum assume incompressible forms, and that the scalar gradient essentially aligns with the most compressive eigenvalue of the solenoidal part, provided that only the solenoidal components are consistently used for scaling. A slight refinement of this statement is also pointed out.}, }
@article {pmid31862924, year = {2019}, author = {Nath, R and Krishnan, M}, title = {Optimization of double diffusive mixed convection in a BFS channel filled with Alumina nanoparticle using Taguchi method and utility concept.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {19536}, pmid = {31862924}, issn = {2045-2322}, abstract = {This research work focuses on the implementation of Taguchi method and utility concept for optimization of flow, geometrical and thermo-physical parameters for mixed convective heat and mass transfer in a backward facing step (BFS) channel filled with Alumina nanoparticle doped in water-ethylene glycol mixture. Mass, momentum, energy and solutal conservation equations for the flow field are cast in velocity-vorticity form of Navier-Stokes equations, which are solved using Galerkin's weighted residual finite element method through isoparametric formulation. The following six parameters, expansion ratio of the BFS channel (H/h), Reynolds number (Re), buoyancy ratio (N), nanoparticle volume fraction (χ), shape of nanoparticles and thermal Grashof number (GrT) at three levels are considered as controlling parameters for optimization using Taguchi method. An L27 orthogonal array has been chosen to get the levels of the six parameters for the 27 trial runs. Simulation results were obtained for 27 trial runs from which three different sets of optimum levels of the control parameters were obtained for maximum Nu and Sh and minimum wall shear stress during double diffusive mixed convection in the channel. Then, in order to obtain a single set of optimum levels of the control parameters to achieve maximum heat and mass transfer and minimum wall shear stress concurrently, utility concept has been implemented. Taguchi results indicate that expansion ratio and volume fraction of nanoparticles are the significant contributing parameters to achieve maximum heat and mass transfer and minimum wall shear stress. Utility concept predicts the average Nusselt number less by 2% and Sherwood number less by 3% compared to the Taguchi method with equal weightage of 40% assumed for Nusselt and Sherwood numbers and 20% for wall shear stress.}, }
@article {pmid31861736, year = {2019}, author = {Maklad, O and Eliasy, A and Chen, KJ and Theofilis, V and Elsheikh, A}, title = {Simulation of Air Puff Tonometry Test Using Arbitrary Lagrangian-Eulerian (ALE) Deforming Mesh for Corneal Material Characterisation.}, journal = {International journal of environmental research and public health}, volume = {17}, number = {1}, pages = {}, pmid = {31861736}, issn = {1660-4601}, mesh = {Cornea/*diagnostic imaging ; Corneal Injuries/*diagnosis ; Humans ; Intraocular Pressure/*physiology ; Manometry/*methods ; *Surgical Mesh ; Tonometry, Ocular/*methods ; }, abstract = {UNLABELLED: : Purpose: To improve numerical simulation of the non-contact tonometry test by using arbitrary Lagrangian-Eulerian deforming mesh in the coupling between computational fluid dynamics model of an air jet and finite element model of the human eye.<br><br>METHODS: Computational fluid dynamics model simulated impingement of the air puff and employed Spallart-Allmaras model to capture turbulence of the air jet. The time span of the jet was 30 ms and maximum Reynolds number was Re=2.3&#xd7;104, with jet orifice diameter 2.4 mm and impinging distance 11 mm. The model of the human eye was analysed using finite element method with regional hyperelastic material variation and corneal patient-specific topography starting from stress-free configuration. The cornea was free to deform as a response to the air puff using an adaptive deforming mesh at every time step of the solution. Aqueous and vitreous humours were simulated as a fluid cavity filled with incompressible fluid with a density of 1000 kg/m[3].<br><br>RESULTS: Using the adaptive deforming mesh in numerical simulation of the air puff test improved the traditional understanding of how pressure distribution on cornea changes with time of the test. There was a mean decrease in maximum pressure (at corneal apex) of 6.29 &#xb1; 2.2% and a development of negative pressure on a peripheral corneal region 2-4 mm away from cornea centre.<br><br>CONCLUSIONS: The study presented an improvement of numerical simulation of the air puff test, which will lead to more accurate intraocular pressure (IOP) and corneal material behaviour estimation. The parametric study showed that pressure of the air puff is different from one model to another, value-wise and distribution-wise, based on cornea biomechanical parameters.}, }
@article {pmid31847758, year = {2019}, author = {Sum Wu, K and Nowak, J and Breuer, KS}, title = {Scaling of the performance of insect-inspired passive-pitching flapping wings.}, journal = {Journal of the Royal Society, Interface}, volume = {16}, number = {161}, pages = {20190609}, pmid = {31847758}, issn = {1742-5662}, mesh = {Animals ; Biomechanical Phenomena ; Biomimetics/*methods ; *Computer Simulation ; Flight, Animal/*physiology ; Insecta/*physiology ; Models, Biological ; *Robotics ; Wings, Animal/*physiology ; }, abstract = {Flapping flight using passive pitch regulation is a commonly used mode of thrust and lift generation in insects and has been widely emulated in flying vehicles because it allows for simple implementation of the complex kinematics associated with flapping wing systems. Although robotic flight employing passive pitching to regulate angle of attack has been previously demonstrated, there does not exist a comprehensive understanding of the effectiveness of this mode of aerodynamic force generation, nor a method to accurately predict its performance over a range of relevant scales. Here, we present such scaling laws, incorporating aerodynamic, inertial and structural elements of the flapping-wing system, validating the theoretical considerations using a mechanical model which is tested for a linear elastic hinge and near-sinusoidal stroke kinematics over a range of scales, hinge stiffnesses and flapping frequencies. We find that suitably defined dimensionless parameters, including the Reynolds number, Re, the Cauchy number, Ch, and a newly defined 'inertial-elastic' number, IE, can reliably predict the kinematic and aerodynamic performance of the system. Our results also reveal a consistent dependency of pitching kinematics on these dimensionless parameters, providing a connection between lift coefficient and kinematic features such as angle of attack and wing rotation.}, }
@article {pmid31835453, year = {2019}, author = {Tan, L and Ali, J and Cheang, UK and Shi, X and Kim, D and Kim, MJ}, title = {µ-PIV Measurements of Flows Generated by Photolithography-Fabricated Achiral Microswimmers.}, journal = {Micromachines}, volume = {10}, number = {12}, pages = {}, pmid = {31835453}, issn = {2072-666X}, support = {JCYJ20180302174151692//Science, Technology and Innovation Commission of Shenzhen Municipality/ ; 51850410516//National Natural Science Foundation of China/ ; 20181119590C//Shenzhen Peacock Plan/ ; 2017KTSCX167//Department of Education of Guangdong Province/ ; 1735968//National Science Foundation/ ; }, abstract = {Robotic micro/nanoswimmers can potentially be used as tools for medical applications, such as drug delivery and noninvasive surgery. Recently, achiral microswimmers have gained significant attention because of their simple structures, which enables high-throughput fabrication and size scalability. Here, microparticle image velocimetry (µ-PIV) was used to study the hydrodynamics of achiral microswimmers near a boundary. The structures of these microswimmers resemble the letter L and were fabricated using photolithography and thin-film deposition. Through µ-PIV measurements, the velocity flow fields of the microswimmers rotating at different frequencies were observed. The results herein yield an understanding of the hydrodynamics of the L-shaped microswimmers, which will be useful in applications such as fluidic manipulation.}, }
@article {pmid31824735, year = {2019}, author = {Ford, MP and Lai, HK and Samaee, M and Santhanakrishnan, A}, title = {Hydrodynamics of metachronal paddling: effects of varying Reynolds number and phase lag.}, journal = {Royal Society open science}, volume = {6}, number = {10}, pages = {191387}, pmid = {31824735}, issn = {2054-5703}, abstract = {Negatively buoyant freely swimming crustaceans such as krill must generate downward momentum in order to maintain their position in the water column. These animals use a drag-based propulsion strategy, where pairs of closely spaced swimming limbs are oscillated rhythmically from the tail to head. Each pair is oscillated with a phase delay relative to the neighbouring pair, resulting in a metachronal wave travelling in the direction of animal motion. It remains unclear how oscillations of limbs in the horizontal plane can generate vertical momentum. Using particle image velocimetry measurements on a robotic model, we observed that metachronal paddling with non-zero phase lag created geometries of adjacent paddles that promote the formation of counter-rotating vortices. The interaction of these vortices resulted in generating large-scale angled downward jets. Increasing phase lag resulted in more vertical orientation of the jet, and phase lags in the range used by Antarctic krill produced the most total momentum. Synchronous paddling produced lower total momentum when compared with metachronal paddling. Lowering Reynolds number by an order of magnitude below the range of adult krill (250-1000) showed diminished downward propagation of the jet and lower vertical momentum. Our findings show that metachronal paddling is capable of producing flows that can generate both lift (vertical) and thrust (horizontal) forces needed for fast forward swimming and hovering.}, }
@article {pmid31824223, year = {2019}, author = {Wang, X and Christov, IC}, title = {Theory of the flow-induced deformation of shallow compliant microchannels with thick walls.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {475}, number = {2231}, pages = {20190513}, pmid = {31824223}, issn = {1364-5021}, abstract = {Long, shallow microchannels embedded in thick, soft materials are widely used in microfluidic devices for lab-on-a-chip applications. However, the bulging effect caused by fluid-structure interactions between the internal viscous flow and the soft walls has not been completely understood. Previous models either contain a fitting parameter or are specialized to channels with plate-like walls. This work is a theoretical study of the steady-state response of a compliant microchannel with a thick wall. Using lubrication theory for low-Reynolds-number flows and the theory for linearly elastic isotropic solids, we obtain perturbative solutions for the flow and deformation. Specifically, only the channel's top wall deformation is considered, and the ratio between its thickness t and width w is assumed to be (t/w)[2]≫1. We show that the deformation at each stream-wise cross section can be considered independently, and that the top wall can be regarded as a simply supported rectangle subject to uniform pressure at its bottom. The stress and displacement fields are found using Fourier series, based on which the channel shape and the hydrodynamic resistance are calculated, yielding a new flow rate-pressure drop relation without fitting parameters. Our results agree favourably with, and thus rationalize, previous experiments.}, }
@article {pmid31816973, year = {2019}, author = {Raza, W and Kim, KY}, title = {Asymmetrical Split-and-Recombine Micromixer with Baffles.}, journal = {Micromachines}, volume = {10}, number = {12}, pages = {}, pmid = {31816973}, issn = {2072-666X}, support = {2019R1A2C1007657//National Research Foundation of Korea/ ; }, abstract = {The present work proposes a planar micromixer design comprising hybrid mixing modules of split-and-recombine units and curved channels with radial baffles. The mixing performance was evaluated numerically by solving the continuity and momentum equations along with the advection-diffusion equation in a Reynolds number range of 0.1-80. The variance of the concentration of the mixed species was considered to quantify the mixing index. The micromixer showed far better mixing performance over whole Reynolds number range than an earlier split-and-recombine micromixer. The mixer achieved mixing indices greater than 90% at Re ≥ 20 and a mixing index of 99.8% at Re = 80. The response of the mixing quality to the change of three geometrical parameters was also studied. A mixing index over 80% was achieved within 63% of the full length at Re = 20.}, }
@article {pmid31808773, year = {2020}, author = {Abay, A and Recktenwald, SM and John, T and Kaestner, L and Wagner, C}, title = {Cross-sectional focusing of red blood cells in a constricted microfluidic channel.}, journal = {Soft matter}, volume = {16}, number = {2}, pages = {534-543}, doi = {10.1039/c9sm01740b}, pmid = {31808773}, issn = {1744-6848}, mesh = {Erythrocytes/*chemistry ; Humans ; Microfluidics/instrumentation ; Rheology ; }, abstract = {Constrictions in blood vessels and microfluidic devices can dramatically change the spatial distribution of passing cells or particles and are commonly used in biomedical cell sorting applications. However, the three-dimensional nature of cell focusing in the channel cross-section remains poorly investigated. Here, we explore the cross-sectional distribution of living and rigid red blood cells passing a constricted microfluidic channel by tracking individual cells in multiple layers across the channel depth and across the channel width. While cells are homogeneously distributed in the channel cross-section pre-contraction, we observe a strong geometry-induced focusing towards the four channel faces post-contraction. The magnitude of this cross-sectional focusing effect increases with increasing Reynolds number for both living and rigid red blood cells. We discuss how this non-uniform cell distribution downstream of the contraction results in an apparent double-peaked velocity profile in particle image velocimetry analysis and show that trapping of red blood cells in the recirculation zones of the abrupt construction depends on cell deformability.}, }
@article {pmid31805484, year = {2020}, author = {Shah, Z and Khan, A and Khan, W and Kamran Alam, M and Islam, S and Kumam, P and Thounthong, P}, title = {Micropolar gold blood nanofluid flow and radiative heat transfer between permeable channels.}, journal = {Computer methods and programs in biomedicine}, volume = {186}, number = {}, pages = {105197}, doi = {10.1016/j.cmpb.2019.105197}, pmid = {31805484}, issn = {1872-7565}, mesh = {Gold/*chemistry ; *Hot Temperature ; *Hydrodynamics ; Nanotechnology/*methods ; Permeability ; }, abstract = {This article characterizes flow and heat transmission of blood that carries the micropolar nanofluid of gold in a permeable channel. The thermal radiations are also present in the channel while its walls are either moving or stationary. The base-fluid is considered as blood while micro polar nanofluid is taken as gold. By using similarity transformations along with dimensionless quantities the modeled equations of the problem are transmuted into a system of non-linear ODEs with a set of appropriate boundary conditions. The semi-analytical method, HAM is then applied to determine the solution of a set of resultant equations. The results obtained by HAM have also compared with numerical solutions. The influence of non-dimensional parameters like fractional parameter suction/injection β, Reynolds Number Re, Darcys Number Da, micropolar parameter K, Prandtl number Pr and Radiation parameter Rd etc., which provides physical interpretations of temperature, microrotation n and velocity fields are discussed in detail with the help of graphical representations. Nusselt number is calculated and presented through table. This study determined that the temperature of micropolar nanofluid augmented along with augmentation in the volume fraction. Radiation Rd augmented the heat transfer rate at the upper wall and reduce it at the lower wall. The suction/injection parameter 'β' reduces the heat transfer rate in case of β < 0 at the upper wall, where it is augmented at lower wall.}, }
@article {pmid31805457, year = {2020}, author = {Pandey, R and Kumar, M and Majdoubi, J and Rahimi-Gorji, M and Srivastav, VK}, title = {A review study on blood in human coronary artery: Numerical approach.}, journal = {Computer methods and programs in biomedicine}, volume = {187}, number = {}, pages = {105243}, doi = {10.1016/j.cmpb.2019.105243}, pmid = {31805457}, issn = {1872-7565}, mesh = {Aneurysm/diagnostic imaging/physiopathology ; Biomedical Engineering ; Coronary Artery Bypass ; Coronary Artery Disease/diagnostic imaging/physiopathology ; Coronary Vessels/*anatomy &amp; histology/diagnostic imaging/*physiology ; Hemodynamics ; Humans ; Hydrodynamics ; Image Processing, Computer-Assisted ; Imaging, Three-Dimensional ; Models, Cardiovascular ; Tomography, Optical Coherence ; Viscosity ; }, abstract = {Computational fluid dynamics (CFD) study of blood flow in human coronary artery is one of the emerging fields of Biomed- ical engineering. In present review paper, Finite Volume Method with governing equations and boundary conditions are briefly discussed for different coronary models. Many researchers have come up with astonishing results related to the various factors (blood viscosity, rate of blood flow, shear stress on the arterial wall, Reynolds number, etc.) affecting the hemodynamic of blood in the right/left coronary artery. The aim of this paper is to present an overview of all those work done by the researchers to justify their work related to factors which hampers proper functioning of heart and lead to Coronary Artery Disease (CAD). Governing equations like Navier-stokes equations, continuity equations etc. are widely used and are solved using CFD solver to get a clearer view of coronary artery blockage. Different boundary conditions and blood properties published in the last ten years are summarized in the tabulated form. This table will help new researchers to work on this area.}, }
@article {pmid31801127, year = {2020}, author = {Pöhnl, R and Popescu, MN and Uspal, WE}, title = {Axisymmetric spheroidal squirmers and self-diffusiophoretic particles.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {32}, number = {16}, pages = {164001}, doi = {10.1088/1361-648X/ab5edd}, pmid = {31801127}, issn = {1361-648X}, abstract = {We study, by means of an exact analytical solution, the motion of a spheroidal, axisymmetric squirmer in an unbounded fluid, as well as the low Reynolds number hydrodynamic flow associated to it. In contrast to the case of a spherical squirmer-for which, e.g. the velocity of the squirmer and the magnitude of the stresslet associated with the flow induced by the squirmer are respectively determined by the amplitudes of the first two slip ('squirming') modes-for the spheroidal squirmer each squirming mode either contributes to the velocity, or contributes to the stresslet. The results are straightforwardly extended to the self-phoresis of axisymmetric, spheroidal, chemically active particles in the case when the phoretic slip approximation holds.}, }
@article {pmid31797965, year = {2019}, author = {Rajappan, A and McKinley, GH}, title = {Epidermal biopolysaccharides from plant seeds enable biodegradable turbulent drag reduction.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {18263}, pmid = {31797965}, issn = {2045-2322}, mesh = {Engineering ; Flax/*chemistry ; Friction ; Lubrication ; Plant Mucilage/*chemistry ; Polyethylene Glycols/*chemistry ; *Rheology ; Seeds/*chemistry ; Viscosity ; Water ; }, abstract = {The high cost of synthetic polymers has been a key impediment limiting the widespread adoption of polymer drag reduction techniques in large-scale engineering applications, such as marine drag reduction. To address consumable cost constraints, we investigate the use of high molar mass biopolysaccharides, present in the mucilaginous epidermis of plant seeds, as inexpensive drag reducers in large Reynolds number turbulent flows. Specifically, we study the aqueous mucilage extracted from flax seeds (Linum usitatissimum) and compare its drag reduction efficacy to that of poly(ethylene oxide) or PEO, a common synthetic polymer widely used as a drag reducing agent in aqueous flows. Macromolecular and rheological characterisation confirm the presence of high molar mass (≥2 MDa) polysaccharides in the extracted mucilage, with an acidic fraction comprising negatively charged chains. Frictional drag measurements, performed inside a bespoke Taylor-Couette apparatus, show that the as-extracted mucilage has comparable drag reduction performance under turbulent flow conditions as aqueous PEO solutions, while concurrently offering advantages in terms of raw material cost, availability, and bio-compatibility. Our results indicate that plant-sourced mucilage can potentially serve as a cost-effective and eco-friendly substitute for synthetic drag reducing polymers in large scale turbulent flow applications.}, }
@article {pmid31786449, year = {2020}, author = {Ibrahim, M and Ijaz Khan, M}, title = {Mathematical modeling and analysis of SWCNT-Water and MWCNT-Water flow over a stretchable sheet.}, journal = {Computer methods and programs in biomedicine}, volume = {187}, number = {}, pages = {105222}, doi = {10.1016/j.cmpb.2019.105222}, pmid = {31786449}, issn = {1872-7565}, mesh = {Algorithms ; Biomechanical Phenomena ; Carbon/*chemistry ; Computer Simulation ; Convection ; Hot Temperature ; Hydrodynamics ; Models, Theoretical ; Nanotechnology/*methods ; Nanotubes, Carbon/*chemistry ; Porosity ; Temperature ; Viscosity ; Water/*chemistry ; }, abstract = {In this article we focused on the mixed convection flow of SWCNT-Water and MWCNT-Water over a stretchable permeable sheet. The nanofluid occupied porous medium. Darcy's law is used to characterize porous medium. The impact of viscous dissipation is considered. Transformation procedure is adopted to transform the governing PDE's system into dimensionless form. In order to solve the dimensionless PDE's system we used numerical method known as Finite difference method. Effects of flow variables i.e porosity parameter, suction parameter, Grashof number and Reynolds number on velocity, skin friction, temperature and Nusselt number are described graphically. The obtained results shows that velocity is dominant in SWCNT-Water over MWCNT-Water. Temperature is dominant in MWCNT-Water over SWCNT-Water.}, }
@article {pmid31785535, year = {2020}, author = {Turkyilmazoglu, M}, title = {Single phase nanofluids in fluid mechanics and their hydrodynamic linear stability analysis.}, journal = {Computer methods and programs in biomedicine}, volume = {187}, number = {}, pages = {105171}, doi = {10.1016/j.cmpb.2019.105171}, pmid = {31785535}, issn = {1872-7565}, mesh = {Algorithms ; Colloids/chemistry ; Hot Temperature ; *Hydrodynamics ; Linear Models ; *Nanoparticles ; Nanotechnology/*methods ; *Rheology ; Software ; Viscosity ; }, abstract = {BACKGROUND AND OBJECTIVE: The hydrodynamic stability of nanofluids of one phase is investigated in this paper based on linear stability theory. The overall thrust here is that the linear stability features of nanofluids can be estimated from their corresponding working fluid, at least in special circumstances.<br><br>METHODS: The approach uses the adjusting parameter to make assertions about stability. This is possible by certain correlations between the resulting eigenvalues.<br><br>RESULTS: It is shown that as the nanoparticles are added, the mean flow of nanofluids is slightly modified and the resulting eigen space of nano disturbances is built on the corresponding pure flow eigen space of perturbations. Several fluid dynamics problems are revisited to verify the usefulness of the obtained correlations.<br><br>CONCLUSION: The presented approach in this work serves us to understand the stabilizing/destabilizing effects of nanofluids as compared to the standard base fluids in terms of stability of viscous/inviscid and temporal/spatial senses. To illustrate, the critical Reynolds number in a traditional boundary layer flow is shown to be pushed to higher values with the dispersed nanoparticles in a working fluid, clearly implying the delay in transition from laminar to turbulent state.}, }
@article {pmid31784839, year = {2019}, author = {Chen, J and He, Y and Wang, J and Huang, M and Guo, C}, title = {Dynamics of nitrogen transformation and bacterial community with different aeration depths in malodorous river.}, journal = {World journal of microbiology &amp; biotechnology}, volume = {35}, number = {12}, pages = {196}, pmid = {31784839}, issn = {1573-0972}, support = {41877477//National Natural Science Foundation of China/ ; 16ZR1408800//Natural Science Foundation of Shanghai/ ; 16PJD023//Shanghai Pujiang Talent Program/ ; 18DZ1203806//Shanghai Science and Technology Development Foundation/ ; 1701K005//Research Funds of The Guangxi Key Laboratory of Theory and Technology for Environmental Pollution Control/ ; }, mesh = {Bacteria/classification/genetics/*metabolism ; China ; Geologic Sediments/microbiology ; Microbiota/*physiology ; Nitrogen/*metabolism ; Oxygen/metabolism ; Phylogeny ; RNA, Ribosomal, 16S ; Rivers/*chemistry/*microbiology ; Sulfur/metabolism ; }, abstract = {In this research, the dynamics of nitrogen transformation and bacterial community in malodorous river were investigated with different aeration depths. Computational flow dynamics (CFD) and Reynolds number (Re) were specially used to characterize the hydrodynamics condition under different aeration depths. The results indicated that aeration depth had vital impact on nitrogen transformation and bacterial community structure. It was found that a range of aeration depth (0.20-0.45 m above sediment-water interface) facilitated the removal of NH4[+]-N and TN with Re ranging between 6211 and 8930. Proteobacteria took over Firmicutes to become the predominant phylum (36-78%) under aeration, and the main subdivisions of γ-, β- and δ-Proteobacteria also varied greatly with different aeration depths. Interestingly, there was a marked shift of the inferentially identified dominant functional role within Proteobacteria from organic-matter degradation to nitrogen metabolism and then to sulfur metabolism as well as the coupling of nitrogen and sulfur with the increase of disturbance. The redundancy analysis (RDA) further confirmed the importance of aeration disturbance in shaping bacterial community. These findings help to gain improved understanding of endogenous N-behavior and aquatic microbial ecology, and underline the need for integrating the hydrodynamics factors with microbial community.}, }
@article {pmid31779425, year = {2019}, author = {Singh, H and Bonnesoeur, A and Besnard, H and Houssin, C and Prigent, A and Crumeyrolle, O and Mutabazi, I}, title = {A large thermal turbulent Taylor-Couette (THETACO) facility for investigation of turbulence induced by simultaneous action of rotation and radial temperature gradient.}, journal = {The Review of scientific instruments}, volume = {90}, number = {11}, pages = {115112}, doi = {10.1063/1.5119811}, pmid = {31779425}, issn = {1089-7623}, abstract = {A thermal turbulent Taylor-Couette facility has been designed to investigate turbulent flows generated by differential rotation and radial temperature gradient. It consists of a cylindrical annulus with a rotating inner cylinder and a fixed outer cylinder. The electric heating system is installed inside the inner cylinder, and the annulus is immersed in a large cylindrical container filled with cooling fluid. Temperature regulators independently control the temperature of the inner surface of the inner cylinder and that of the cooling fluid. The facility allows us to reach values of the Reynolds number (Re ∼ 5 × 10[5]) and of the Rayleigh number (Ra ∼ 3 × 10[6]) for water as the working fluid. The facility provides torque measurements, a full optical access at the side and from the bottom for velocity measurements using particle image velocimetry (2D, stereoscopic, and tomographic). Temperature measurements in the flow can be performed by thermochromic liquid crystals or laser induced fluorescence.}, }
@article {pmid31777765, year = {2019}, author = {Zhang, X and Lam, WA and Graham, MD}, title = {Dynamics of deformable straight and curved prolate capsules in simple shear flow.}, journal = {Physical review fluids}, volume = {4}, number = {4}, pages = {}, pmid = {31777765}, issn = {2469-990X}, support = {R21 MD011590/MD/NIMHD NIH HHS/United States ; }, abstract = {This work investigates the motion of neutrally-buoyant, slightly deformable straight and curved prolate fluid-filled capsules in unbounded simple shear flow at zero Reynolds number using direct simulations. The curved capsules serve as a model for the typical crescent-shaped sickle red blood cells in sickle cell disease (SCD). The effects of deformability and curvature on the dynamics are revealed. We show that with low deformability, straight prolate spheroidal capsules exhibit tumbling in the shear plane as their unique asymptotically stable orbit. This result contrasts with that for rigid spheroids, where infinitely many neutrally stable Jeffery orbits exist. The dynamics of curved prolate capsules are more complicated due to a combined effect of deformability and curvature. At short times, depending on the initial orientation, slightly deformable curved prolate capsules exhibit either a Jeffery-like motion such as tumbling or kayaking, or a non-Jeffery-like behavior in which the director (end-to-end vector) of the capsule crosses the shear-gradient plane back and forth. At long times, however, a Jeffery-like quasiperiodic orbit is taken regardless of the initial orientation. We further show that the average of the long-time trajectory can be well approximated using the analytical solution for Jeffery orbits with an effective orbit constant C eff and aspect ratio ℓ eff. These parameters are useful for characterizing the dynamics of curved capsules as a function of given deformability and curvature. As the capsule becomes more deformable or curved, C eff decreases, indicating a shift of the orbit towards log-rolling motion, while ℓ eff increases weakly as the degree of curvature increases but shows negligible dependency on deformability. These features are not changed substantially as the viscosity ratio between the inner and outer fluids is changed from 1 to 5. As cell deformability, cell shape, and cell-cell interactions are all pathologically altered in blood disorders such as SCD, these results will have clear implications on improving our understanding of the pathophysiology of hematologic disease.}, }
@article {pmid31771023, year = {2019}, author = {Shan, X}, title = {Central-moment-based Galilean-invariant multiple-relaxation-time collision model.}, journal = {Physical review. E}, volume = {100}, number = {4-1}, pages = {043308}, doi = {10.1103/PhysRevE.100.043308}, pmid = {31771023}, issn = {2470-0053}, abstract = {Aiming at systematically correcting the non-Galilean-invariant thermal diffusivity in the previous multiple-relaxation-time Boltzmann equation collision model [Shan and Chen, Int. J. Mod. Phys. C 18, 635 (2007)IJMPEO0129-183110.1142/S0129183107010887], we show that by separately relaxing the central moments of the distribution function, Chapman-Enskog calculation leads to the correct hydrodynamic equations with mutually independent and Galilean invariant viscosity and thermal diffusivity, provided the velocity-space discretization preserves moments up to the fourth order. By transforming the central moments back to the absolute reference frame and evaluating using fixed discrete velocities, the efficient and accurate streaming-collision time-stepping algorithm is preserved. The lattice Boltzmann model is found to have excellent numerical stability in high-Reynolds-number simulations.}, }
@article {pmid31771016, year = {2019}, author = {Berera, A and Clark, D}, title = {Information production in homogeneous isotropic turbulence.}, journal = {Physical review. E}, volume = {100}, number = {4-1}, pages = {041101}, doi = {10.1103/PhysRevE.100.041101}, pmid = {31771016}, issn = {2470-0053}, abstract = {We study the Reynolds number scaling of the Kolmogorov-Sinai entropy and attractor dimension for three-dimensional homogeneous isotropic turbulence through the use of direct numerical simulation. To do so, we obtain Lyapunov spectra for a range of different Reynolds numbers by following the divergence of a large number of orthogonal fluid trajectories. We find that the attractor dimension grows with the Reynolds number as Re^{2.35} with this exponent being larger than predicted by either dimensional arguments or intermittency models. The distribution of Lyapunov exponents is found to be finite around λ≈0 contrary to a possible divergence suggested by Ruelle. The relevance of the Kolmogorov-Sinai entropy and Lyapunov spectra in comparing complex physical systems is discussed.}, }
@article {pmid31770976, year = {2019}, author = {Chitsaz, M and Fathali, M}, title = {Impact of an initial random magnetic field on the evolution of two-dimensional shearless mixing layers.}, journal = {Physical review. E}, volume = {100}, number = {4-1}, pages = {043106}, doi = {10.1103/PhysRevE.100.043106}, pmid = {31770976}, issn = {2470-0053}, abstract = {The impact of an initial random magnetic field on the temporal evolution of a two-dimensional incompressible turbulent shearless mixing layer is investigated using direct numerical simulation. Different intensities of the initial random magnetic field are imposed with uniform probability distribution on an identical flow field. The initial flow field condition is the turbulent shearless mixing layer with different kinetic energy ratio (E_{H}/E_{L}=6.7) and identical integral length scale. Simulations are carried out in a moderate magnetic Reynolds number, which causes a two-way interaction between the velocity and magnetic fields. In order to analyze the effect of the initial random magnetic field on the mixing characteristics, the intermittency inside the mixing layer and the mixing evolution parameters are investigated. It is found that with small initial magnetic field intensity, the intermittency in both large and small scales are larger than those values in hydrodynamic flow. However, increasing the intensity of the initial magnetic field reduces the intermittency in the mixing region to lower values compared to the hydrodynamic flow. The mixing layer growth rate and the mixing efficiency both show reduction by increasing the initial magnetic field intensity, which is attributed to the reduction of the averaged Reynolds number of both homogenous isotropic turbulent regions due to the suppressing effect of the Lorentz force on the velocity fields of these regions.}, }
@article {pmid31759716, year = {2020}, author = {Ćmiel, AM and Strużyński, A and Wyrębek, M and Lipińska, AM and Zając, K and Zając, T}, title = {Response of freshwater mussel recruitment to hydrological changes in a eutrophic floodplain lake.}, journal = {The Science of the total environment}, volume = {703}, number = {}, pages = {135467}, doi = {10.1016/j.scitotenv.2019.135467}, pmid = {31759716}, issn = {1879-1026}, mesh = {Animals ; Ecosystem ; Endangered Species ; Eutrophication ; Hydrology ; *Lakes ; *Unionidae ; }, abstract = {Although eutrophication of freshwaters is a natural process, the human impact often leads to inland waters becoming overloaded with nutrients, impoverishing many valuable and vanishing habitats, such as floodplain lakes. These changes need to be reversed if the occurrence of endangered aquatic species is to be restored. In this paper we analyse the impact of a change in the water regime of a naturally eutrophic floodplain lake, which harbours a large diversity of Unionidae (large freshwater mussels), a globally threatened taxonomic group that provides important ecosystem functions and services. We found that a slight increase in the discharge from this waterbody, following the construction of an additional outflow pipe, positively influenced recruitment in three of the five mussel species inhabiting the lake. We also found that, after the construction of this additional outflow, the niches of juveniles of Anodonta cygnea and Unio spp. changed, revealing differences in their hydrological requirements. Our results suggest that, as in lotic habitats, complex hydraulic parameters are highly significant to unionid mussels in lentic conditions.}, }
@article {pmid31744080, year = {2019}, author = {Taheri, RA and Goodarzi, V and Allahverdi, A}, title = {Mixing Performance of a Cost-effective Split-and-Recombine 3D Micromixer Fabricated by Xurographic Method.}, journal = {Micromachines}, volume = {10}, number = {11}, pages = {}, pmid = {31744080}, issn = {2072-666X}, abstract = {This paper presents experimental and numerical investigations of a novel passive micromixer based on the lamination of fluid layers. Lamination-based mixers benefit from increasing the contact surface between two fluid phases by enhancing molecular diffusion to achieve a faster mixing. Novel three-dimensional split and recombine (SAR) structures are proposed to generate fluid laminations. Numerical simulations were conducted to model the mixer performance. Furthermore, experiments were conducted using dyes to observe fluid laminations and evaluate the proposed mixer's characteristics. Mixing quality was experimentally obtained by means of image-based mixing index (MI) measurement. The multi-layer device was fabricated utilizing the Xurography method, which is a simple and low-cost method to fabricate 3D microfluidic devices. Mixing indexes of 96% and 90% were obtained at Reynolds numbers of 0.1 and 1, respectively. Moreover, the device had an MI value of 67% at a Reynolds number of 10 (flow rate of 116 µL/min for each inlet). The proposed micromixer, with its novel design and fabrication method, is expected to benefit a wide range of lab-on-a-chip applications, due to its high efficiency, low cost, high throughput and ease of fabrication.}, }
@article {pmid31737769, year = {2019}, author = {Shaikh, MM and Massan, SU and Wagan, AI}, title = {A sixteen decimal places' accurate Darcy friction factor database using non-linear Colebrook's equation with a million nodes: A way forward to the soft computing techniques.}, journal = {Data in brief}, volume = {27}, number = {}, pages = {104733}, doi = {10.1016/j.dib.2019.104733}, pmid = {31737769}, issn = {2352-3409}, abstract = {The Colebrook's equation is considered as an empirical model to accurately compute the Darcy friction factor in pipes under fully-developed turbulent flow. Due to non-linearity and implicitness of the Colebrook's equation, one needs to use numerical methods to acquire reasonably good approximation to the true friction factor values. However, such idea is not preferred by practitioners as it demands use of computers - also more computational time and effort. To overcome this, explicit equations that can describe Darcy friction factor directly in terms of the Reynolds number and relative roughness are essential. Using Fixed point iteration method in the MATLAB software, we have developed a 16 decimal places' accurate friction factor database for the Darcy friction factor for a 1000 by 1000 mesh of Reynolds number and relative roughness values. The accurate dataset described in this work will serve to be basis for the construction of new and more reliable explicit equations using regression modeling, artificial intelligence techniques and other soft computing methods.}, }
@article {pmid31736648, year = {2019}, author = {Papageorgiou, DT and Tanveer, S}, title = {Analysis and computations of a non-local thin-film model for two-fluid shear driven flows.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {475}, number = {2230}, pages = {20190367}, pmid = {31736648}, issn = {1364-5021}, abstract = {This paper is concerned with analysis and computations of a non-local thin-film model developed in Kalogirou &amp; Papageorgiou (J. Fluid Mech. 802, 5-36, 2016) for a perturbed two-layer Couette flow when the thickness of the more viscous fluid layer next to the stationary wall is small compared to the thickness of the less viscous fluid. Travelling wave solutions and their stability are determined numerically, and secondary bifurcation points are identified in the process. We also determine regions in parameter space where bistability is observed with two branches being linearly stable at the same time. The travelling wave solutions are mathematically justified through a quasi-solution analysis in a neighbourhood of an empirically constructed approximate solution. This relies in part on precise asymptotics of integrals of Airy functions for large wave numbers. The primary bifurcation about the trivial state is shown rigorously to be supercritical, and the dependence of bifurcation points, as a function of Reynolds number R and the primary wavelength 2πν [-1/2] of the disturbance, is determined analytically.}, }
@article {pmid31734470, year = {2020}, author = {Farooq, S and Hayat, T and Khan, MI and Alsaedi, A}, title = {Entropy generation minimization (EGM) in magneto peristalsis with variable properties.}, journal = {Computer methods and programs in biomedicine}, volume = {186}, number = {}, pages = {105045}, doi = {10.1016/j.cmpb.2019.105045}, pmid = {31734470}, issn = {1872-7565}, mesh = {*Entropy ; *Magnetics ; Thermal Conductivity ; *Viscosity ; }, abstract = {OBJECTIVE AND BACKGROUND: This article featuring the peristaltic transport of viscous material with variable properties (i.e. temperature dependent viscosity and thermal conductivity) through curved configuration. Fluid saturating through porous channel walls of uniform space. Entropy generation consideration here is to analyze irreversibility aspects. Channel boundaries retain the velocity and thermal slip conditions.<br><br>METHOD: Wave frame of reference is attained with the utilization of long wavelength and small Reynolds number approach. Solution of the simplified coupled system of dimensionless constraints is obtained numerically. Detailed analysis of important quantities of interest has been presented in discussion portion.<br><br>RESULTS: Entropy generation variation near center is very small whereas in the vicinity of the channel wall is larger. Bejan number has reverse variation as observed for entropy generation.<br><br>CONCLUSION: Variable characteristics of viscosity has opposite impact on velocity and temperature is observed. It is also noticed small irreversibility effects are obtained for higher varying viscosity and thermal conductivity near the vicinity of the channel walls.}, }
@article {pmid31719582, year = {2019}, author = {Ying, Y and Lin, Y}, title = {Inertial Focusing and Separation of Particles in Similar Curved Channels.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {16575}, pmid = {31719582}, issn = {2045-2322}, abstract = {Inertial particle focusing in curved channels has enormous potential for lab-on-a-chip applications. This paper compares a zigzag channel, which has not been used previously for inertial focusing studies, with a serpentine channel and a square wave channel to explore their differences in terms of focusing performance and separation possibilities. The particle trajectories and fluid fields in the curved channels are studied by a numerical simulation. The effects of different conditions (structure, Reynolds number, and particle size) on the competition between forces and the focusing performance are studied. The results indicate that the zigzag channel has the best focusing effect at a high Reynolds number and that the serpentine channel is second in terms of performance. Regarding the particle separation potential, the zigzag channel has a good performance in separating 5 μm and 10 μm particles at ReC = 62.5. In addition, the pressure drop of the channel is also considered to evaluate the channel performance, which has not been taken into account in the literature on inertial microfluidics. This result is expected to be instructive for the selection and optimization of inertial microchannel structures.}, }
@article {pmid31718189, year = {2019}, author = {Zhang, Z and Zhang, P}, title = {Numerical Interpretation to the Roles of Liquid Viscosity in Droplet Spreading at Small Weber Numbers.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {35}, number = {49}, pages = {16164-16171}, doi = {10.1021/acs.langmuir.9b02736}, pmid = {31718189}, issn = {1520-5827}, abstract = {Droplet impacting a free-slip plane at small Weber numbers (We < 30) was numerically investigated by a front tracking method, with particular emphasis on clarifying the roles of the liquid viscosity and the "left-over" internal kinetic energy in droplet spreading. The most interesting discovery is that there exists a certain range of We in which the maximum diameter rate, D̃m, shows a nonmonotonic variation with the Reynolds number, Re. This non-monotonic variation is owing to the dual role of liquid viscosity in influencing droplet spreading. Specifically, when the initial surface energy is comparable to the initial kinetic energy (the corresponding We is around 10-30), the high strain rates of the droplet internal flow dominate its viscous dissipation at a relatively large Re, while the liquid viscosity dominates the viscous dissipation at a relatively small Re. Furthermore, to unravel the influence of droplet attachment and detachment on droplet spreading, we considered two limiting situations such as full attachment (with no gas film throughout droplet spreading) and full detachment (with a gas film throughout droplet spreading). The results show that the droplet with a gas film tends to generate a stronger vortical motion in its rim, results in a larger left-over kinetic energy, and hence causes a smaller spreading.}, }
@article {pmid31718021, year = {2019}, author = {Kottmeier, J and Wullenweber, M and Blahout, S and Hussong, J and Kampen, I and Kwade, A and Dietzel, A}, title = {Accelerated Particle Separation in a DLD Device at Re &gt; 1 Investigated by Means of µPIV.}, journal = {Micromachines}, volume = {10}, number = {11}, pages = {}, pmid = {31718021}, issn = {2072-666X}, abstract = {A pressure resistant and optically accessible deterministic lateral displacement (DLD) device was designed and microfabricated from silicon and glass for high-throughput fractionation of particles between 3.0 and 7.0 µm comprising array segments of varying tilt angles with a post size of 5 µm. The design was supported by computational fluid dynamic (CFD) simulations using OpenFOAM software. Simulations indicated a change in the critical particle diameter for fractionation at higher Reynolds numbers. This was experimentally confirmed by microparticle image velocimetry (µPIV) in the DLD device with tracer particles of 0.86 µm. At Reynolds numbers above 8 an asymmetric flow field pattern between posts could be observed. Furthermore, the new DLD device allowed successful fractionation of 2 µm and 5 µm fluorescent polystyrene particles at Re = 0.5-25.}, }
@article {pmid31715344, year = {2019}, author = {Di, D and Qu, X and Liu, C and Fang, L and Quan, P}, title = {Continuous production of celecoxib nanoparticles using a three-dimensional-coaxial-flow microfluidic platform.}, journal = {International journal of pharmaceutics}, volume = {572}, number = {}, pages = {118831}, doi = {10.1016/j.ijpharm.2019.118831}, pmid = {31715344}, issn = {1873-3476}, mesh = {Animals ; Biological Availability ; Celecoxib/*administration &amp; dosage/chemistry/pharmacokinetics ; Glass ; High-Throughput Screening Assays ; Male ; *Microfluidic Analytical Techniques ; *Nanoparticles ; Particle Size ; Rats ; Rats, Wistar ; Solubility ; Water/chemistry ; }, abstract = {Increasing the dissolution rate of water insoluble drugs by decreasing the particle size of the drugs into nano-size is a well-known strategy. However, continuous production of drug nanoparticles with uniform particle size is critical for clinical application of the strategy. Here we report a simple microfluidic mixing method that can achieve continuous production of celecoxib nanoparticles with uniform particle size and high dissolution rate. A three-dimensional (3D) coaxial-flow microfluidic device was fabricated by assembling two coaxial aligned borosilicate glass capillaries on a glass slide, and a tapered glass capillary was inserted into another bigger cylindrical one with coaxial alignment. Celecoxib nanoparticles were prepared by the microfluidic device under the turbulent jet regime. The 3D-coaxial-flow pattern and high Reynolds number ensured the extremely short mixing time, consequently, resulted in the high throughput production of drug nanoparticles with uniform particle size. The obtained nanoparticles were spherical in shape, and showed superior dissolution rate compared with the coarse powder both in sink and non-sink conditions. The bioavailability of the water insoluble drug was also significantly improved by the reduction of particle size into nano-size.}, }
@article {pmid31700559, year = {2019}, author = {Herrmann, N and Neubauer, P and Birkholz, M}, title = {Spiral microfluidic devices for cell separation and sorting in bioprocesses.}, journal = {Biomicrofluidics}, volume = {13}, number = {6}, pages = {061501}, pmid = {31700559}, issn = {1932-1058}, abstract = {Inertial microfluidic systems have been arousing interest in medical applications due to their simple and cost-efficient use. However, comparably small sample volumes in the microliter and milliliter ranges have so far prevented efficient applications in continuous bioprocesses. Nevertheless, recent studies suggest that these systems are well suited for cell separation in bioprocesses because of their facile adaptability to various reactor sizes and cell types. This review will discuss potential applications of inertial microfluidic cell separation systems in downstream bioprocesses and depict recent advances in inertial microfluidics for bioprocess intensification. This review thereby focusses on spiral microchannels that separate particles at a moderate Reynolds number in a laminar flow (Re < 2300) according to their size by applying lateral hydrodynamic forces. Spiral microchannels have already been shown to be capable of replacing microfilters, extracting dead cells and debris in perfusion processes, and removing contaminant microalgae species. Recent advances in parallelization made it possible to process media on a liter-scale, which might pave the way toward industrial applications.}, }
@article {pmid31674812, year = {2019}, author = {Sharzehee, M and Chang, Y and Song, JP and Han, HC}, title = {Hemodynamic effects of myocardial bridging in patients with hypertrophic cardiomyopathy.}, journal = {American journal of physiology. Heart and circulatory physiology}, volume = {317}, number = {6}, pages = {H1282-H1291}, doi = {10.1152/ajpheart.00466.2019}, pmid = {31674812}, issn = {1522-1539}, mesh = {Adolescent ; Adult ; Aged ; Cardiomyopathy, Hypertrophic/complications/pathology/*physiopathology ; Coronary Circulation ; Female ; *Hemodynamics ; Humans ; Male ; Middle Aged ; *Models, Cardiovascular ; Myocardial Bridging/complications/pathology/*physiopathology ; *Patient-Specific Modeling ; }, abstract = {Myocardial bridging (MB) is linked to angina and myocardial ischemia and may lead to sudden cardiac death in patients with hypertrophic cardiomyopathy (HCM). However, it remains unclear how MB affect the coronary blood flow in HCM patients. The aim of this study was to assess the effects of MB on coronary hemodynamics in HCM patients. Fifteen patients with MB (7 HCM and 8 non-HCM controls) in their left anterior descending (LAD) coronary artery were chosen. Transient computational fluid dynamics (CFD) simulations were conducted in anatomically realistic models of diseased (with MB) and virtually healthy (without MB) LAD from these patients, reconstructed from biplane angiograms. Our CFD simulation results demonstrated that dynamic compression of MB led to diastolic flow disturbances and could significantly reduce the coronary flow in HCM patients as compared with non-HCM group (P < 0.01). The pressure drop coefficient was remarkably higher (P < 0.05) in HCM patients. The flow rate change is strongly correlated with both upstream Reynolds number and MB compression ratio, while the MB length has less impact on coronary flow. The hemodynamic results and clinical outcomes revealed that HCM patients with an MB compression ratio higher than 65% required a surgical intervention. In conclusion, the transient MB compression can significantly alter the diastolic flow pattern and wall shear stress distribution in HCM patients. HCM patients with severe MB may need a surgical intervention.NEW &amp; NOTEWORTHY In this study, the hemodynamic significance of myocardial bridging (MB) in patients with hypertrophic cardiomyopathy (HCM) was investigated to provide valuable information for surgical decision-making. Our results illustrated that the transient MB compression led to complex flow patterns, which can significantly alter the diastolic flow and wall shear stress distribution. The hemodynamic results and clinical outcomes demonstrated that patients with HCM and an MB compression ratio higher than 65% required a surgical intervention.}, }
@article {pmid31673592, year = {2019}, author = {Desmond, CJ and Thiebaut, F and Murphy, J}, title = {Drag force as a function of cross section and angle of attack. A hydraulic laboratory dataset for numerical validation.}, journal = {Data in brief}, volume = {27}, number = {}, pages = {104596}, doi = {10.1016/j.dib.2019.104596}, pmid = {31673592}, issn = {2352-3409}, abstract = {This data relates to a set of hydraulic laboratory experiments in which the flow around four cross-sections was investigated. Each cross section was examined at four angles of attack (0, 5, 10, 90°), seven velocities (0-0.7 m/s in 0.1 m/s steps) and two flow directions. The data is primarily from an array of load cell which monitored the loading on the cross-sections during testing in six degrees of freedom during testing. Video and photographs are also included.}, }
@article {pmid31671753, year = {2019}, author = {Shanko, ES and van de Burgt, Y and Anderson, PD and den Toonder, JMJ}, title = {Microfluidic Magnetic Mixing at Low Reynolds Numbers and in Stagnant Fluids.}, journal = {Micromachines}, volume = {10}, number = {11}, pages = {}, pmid = {31671753}, issn = {2072-666X}, abstract = {Microfluidic mixing becomes a necessity when thorough sample homogenization is required in small volumes of fluid, such as in lab-on-a-chip devices. For example, efficient mixing is extraordinarily challenging in capillary-filling microfluidic devices and in microchambers with stagnant fluids. To address this issue, specifically designed geometrical features can enhance the effect of diffusion and provide efficient mixing by inducing chaotic fluid flow. This scheme is known as "passive" mixing. In addition, when rapid and global mixing is essential, "active" mixing can be applied by exploiting an external source. In particular, magnetic mixing (where a magnetic field acts to stimulate mixing) shows great potential for high mixing efficiency. This method generally involves magnetic beads and external (or integrated) magnets for the creation of chaotic motion in the device. However, there is still plenty of room for exploiting the potential of magnetic beads for mixing applications. Therefore, this review article focuses on the advantages of magnetic bead mixing along with recommendations on improving mixing in low Reynolds number flows (Re ≤ 1) and in stagnant fluids.}, }
@article {pmid31671339, year = {2020}, author = {Ijaz Khan, M and Ali, A and Hayat, T and Alsaedi, A}, title = {Entropy optimized dissipative CNTs based flow with probable error and statistical declaration.}, journal = {Computer methods and programs in biomedicine}, volume = {185}, number = {}, pages = {105137}, doi = {10.1016/j.cmpb.2019.105137}, pmid = {31671339}, issn = {1872-7565}, mesh = {*Entropy ; Nanotubes, Carbon/*chemistry ; Probability ; Thermodynamics ; }, abstract = {BACKGROUND: CNTs are categorized subject to their structures i.e., SWCNTs (single wall nanotubes), DWCNTs (double wall nanotubes) and MWCNTs (multi-wall nanotubes). The various structures have distinct characteristics that make the nanotubes suitable for various physical applications. It is due their unique electrical, mechanical and thermal attributes CNTs present thrilling opportunities for mechanical engineering, industrial, scientific research and commercial applications. There is fruitful potential for carbon nanotubes in the composites business and industry. Today, CNTs find utilization in frequent various products, and analyst continue to explore new applications. Currently applications comprise wind turbines, bicycle components, scanning probe microscopes, flat panel displays, marine paints, sensing devices, electronics, batteries with longer lifetime and electrical circuitry etc. Such applications in mind, entropy optimized dissipative CNTs based flow of nanomaterial by a stretched surface. Flow is caused due to stretching phenomenon and studied in 3D coordinates. Both types of CNTs are studied i.e., SWCNTs and MWCNTs. CNTs are considered for nanoparticles and water for continuous phase fluid. Special consideration is given to the analysis of statistical declaration and probable error for skin friction and Nusselt number. Furthermore, entropy rate is calculated. Entropy rate is discussed in the presence of four main irreversibilities i.e., heat transfer, Joule heating, porosity and dissipation.<br><br>METHOD: Homotopy technique is utilized to develop the convergence series solutions.<br><br>RESULTS: Impacts of sundry variables subject to both SWCNTs (single) and MWCNTs (multi) are graphically discussed. Statistical analysis and probable error for surface drag force and Nusselt number are numerically calculated subject to various flow variables. Numerical results for such engineering quantities are displayed through tables. In addition, comparative analysis for SWCNTs and MWCNTs are presented for the velocity, concentration and thermal fields.<br><br>CONCLUSIONS: Results for entropy rate is calculated in the presence of various sundry variable through implementation of second law of thermodynamics. It is examined from the results that velocity decreases for both CNTs via higher magnetic, inertia coefficient and porosity parameters. Secondary velocity i.e., velocity in g-direction boosts up versus rotation parameter while it declines for larger slip parameter for both CNTs. thermal field intensifies for both CNTs via larger heat generation/absorption parameter. Concentration which shows the mass transfer of species increases subject to higher homogeneous parameter and Schmidt number in case of both CNTs. Entropy rate in more for larger magnetic, Reynolds number and slip parameter. Bejan number boosts up for higher Reynold number and slip parameter while it declines for magnetic parameter.}, }
@article {pmid31657131, year = {2020}, author = {Dincau, B and Dressaire, E and Sauret, A}, title = {Pulsatile Flow in Microfluidic Systems.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {16}, number = {9}, pages = {e1904032}, doi = {10.1002/smll.201904032}, pmid = {31657131}, issn = {1613-6829}, mesh = {Cell Culture Techniques ; Hydrodynamics ; *Microfluidics/trends ; *Pulsatile Flow ; }, abstract = {This review describes the current knowledge and applications of pulsatile flow in microfluidic systems. Elements of fluid dynamics at low Reynolds number are first described in the context of pulsatile flow. Then the practical applications in microfluidic processes are presented: the methods to generate a pulsatile flow, the generation of emulsion droplets through harmonic flow rate perturbation, the applications in mixing and particle separation, and the benefits of pulsatile flow for clog mitigation. The second part of the review is devoted to pulsatile flow in biological applications. Pulsatile flows can be used for mimicking physiological systems, to alter or enhance cell cultures, and for bioassay automation. Pulsatile flows offer unique advantages over a steady flow, especially in microfluidic systems, but also require some new physical insights and more rigorous investigation to fully benefit future applications.}, }
@article {pmid31656395, year = {2019}, author = {Folkersma, M and Schmehl, R and Viré, A}, title = {Boundary layer transition modeling on leading edge inflatable kite airfoils.}, journal = {Wind energy (Chichester, England)}, volume = {22}, number = {7}, pages = {908-921}, pmid = {31656395}, issn = {1099-1824}, abstract = {We present a computational fluid dynamic analysis of boundary layer transition on leading edge inflatable kite airfoils used for airborne wind energy generation. Because of the operation in pumping cycles, the airfoil is generally subject to a wide range of Reynolds numbers. The analysis is based on the combination of the shear stress transport turbulence model with the γ - R ˜ e θ t transition model, which can handle the laminar boundary layer and its transition to turbulence. The implementation of both models in OpenFOAM is described. We show a validation of the method for a sailwing (ie, a wing with a membrane) airfoil and an application to a leading edge inflatable kite airfoil. For the sailwing airfoil, the results computed with transition model agree well with the existing low Reynolds number experiment over the whole range of angles of attack. For the leading edge inflatable kite airfoil, the transition modeling has both favorable and unfavorable effects on the aerodynamics. On the one hand, the aerodynamics suffer from the laminar separation. But, on the other hand, the laminar boundary layer thickens slower than the turbulent counterpart, which, in combination with transition, delays the separation. The results also indicate that the aerodynamics of the kite airfoil could be improved by delaying the boundary layer transition during the traction phase and tripping the transition in the retraction phase.}, }
@article {pmid31648622, year = {2020}, author = {Ozden, K and Sert, C and Yazicioglu, Y}, title = {Numerical investigation of wall pressure fluctuations downstream of concentric and eccentric blunt stenosis models.}, journal = {Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine}, volume = {234}, number = {1}, pages = {48-60}, doi = {10.1177/0954411919884167}, pmid = {31648622}, issn = {2041-3033}, mesh = {Acoustics ; Blood Vessels/*physiopathology ; *Constriction, Pathologic ; *Models, Biological ; *Pressure ; }, abstract = {Pressure fluctuations that cause acoustic radiation from vessel models with concentric and eccentric blunt stenoses are investigated. Large eddy simulations of non-pulsatile flow condition are performed using OpenFOAM. Calculated amplitude and spatial-spectral distribution of acoustic pressures at the post-stenotic region are compared with previous experimental and theoretical results. It is found that increasing the Reynolds number does not change the location of the maximum root mean square wall pressure, but causes a general increase in the spectrum level, although the change in the shape of the spectrum is not significant. On the contrary, compared to the concentric model at the same Reynolds number, eccentricity leads to an increase both at the distance of the location of the maximum root mean square wall pressure from the stenosis exit and the spectrum level. This effect becomes more distinct when radial eccentricity of the stenosis increases. Both the flow rate and the eccentricity of the stenosis shape are evaluated to be clinically important parameters in diagnosing stenosis.}, }
@article {pmid31640254, year = {2019}, author = {Su, L and Duan, Z and He, B and Ma, H and Xu, Z}, title = {Thermally Developing Flow and Heat Transfer in Elliptical Minichannels with Constant Wall Temperature.}, journal = {Micromachines}, volume = {10}, number = {10}, pages = {}, pmid = {31640254}, issn = {2072-666X}, support = {2019YJS158//Fundamental Research Funds for the Central Universities/ ; }, abstract = {Laminar convective heat transfer of elliptical minichannels is investigated for hydrodynamically fully developed but thermal developing flow with no-slip condition. A three-dimensional numerical model is developed in different elliptical geometries with the aspect ratio varying from 0.2 to 1. The effect of Reynolds number (25 ≤ Re ≤ 2000) on the local Nusselt number is examined in detail. The results indicate that the local Nusselt number is a decreasing function of Reynolds number and it is sensitive to Reynolds number especially for Re less than 250. The effect of aspect ratio on local Nusselt number is small when compared with the effect of Reynolds number on local Nusselt number. The local Nusselt number is independent of cross-section geometry at the inlet. The maximum effect of aspect ratio on local Nusselt number arises at the transition section rather than the fully developed region. However, the non-dimensional thermal entrance length is a monotonic decreasing concave function of aspect ratio but a weak function of Reynolds number. Correlations for the local Nusselt number and the thermal developing length for elliptical channels are developed with good accuracy, which may provide guidance for design and optimization of elliptical minichannel heat sinks.}, }
@article {pmid31640175, year = {2019}, author = {Raza, W and Ma, SB and Kim, KY}, title = {Single and Multi-Objective Optimization of a Three-Dimensional Unbalanced Split-and-Recombine Micromixer.}, journal = {Micromachines}, volume = {10}, number = {10}, pages = {}, pmid = {31640175}, issn = {2072-666X}, support = {No. 2019R1A2C1007657//National Research Foundation of Korea/ ; }, abstract = {The three-dimensional geometry of a micromixer with an asymmetrical split-and-recombine mechanism was optimized to enhance the fluid-mixing capability at a Reynolds number of 20. Single and multi-objective optimizations were carried out by using particle swarm optimization and a genetic algorithm on a modeled surrogate surface. Surrogate modeling was performed using the computational results for the mixing. Mixing and flow analyses were carried out by solving the convection-diffusion equation in combination with the three-dimensional continuity and momentum equations. The optimization was carried out with two design variables related to dimensionless geometric parameters. The mixing effectiveness was chosen as the objective function for the single-objective optimization, and the pressure drop and mixing index at the outlet were chosen for the multi-objective optimization. The sampling points in the design space were determined using a design of experiment technique called Latin hypercube sampling. The surrogates for the objective functions were developed using a Kriging model. The single-objective optimization resulted in 58.9% enhancement of the mixing effectiveness compared to the reference design. The multi-objective optimization provided Pareto-optimal solutions that showed a maximum increase of 48.5% in the mixing index and a maximum decrease of 55.0% in the pressure drop in comparison to the reference design.}, }
@article {pmid31639948, year = {2019}, author = {Basu, A and Bhattacharjee, JK}, title = {Kolmogorov or Bolgiano-Obukhov scaling: Universal energy spectra in stably stratified turbulent fluids.}, journal = {Physical review. E}, volume = {100}, number = {3-1}, pages = {033117}, doi = {10.1103/PhysRevE.100.033117}, pmid = {31639948}, issn = {2470-0053}, abstract = {We set up the scaling theory for stably stratified turbulent fluids. For a system having infinite extent in the horizontal directions, but with a finite width in the vertical direction, this theory predicts that the inertial range can display three possible scaling behavior, which are essentially parametrized by the buoyancy frequency N, or dimensionless horizontal Froude number F_{h}, and the vertical length scale l_{v} that sets the scale of variation of the velocity field in the vertical direction for a fixed Reynolds number. For very low N or very high Re_{b} or F_{h}, and with l_{v}≫l_{h}, the typical horizontal length scale, buoyancy forces are irrelevant and hence, unsurprisingly, the kinetic energy spectra show the well-known K41 scaling in the inertial range. In this regime, the local temperature behaves as a passively advected scalar, without any effect on the flow fields. For intermediate ranges of values of N,F_{h}∼O(1), corresponding to moderate stratification, buoyancy forces are important enough to affect the scaling. This leads to the Bolgiano-Obukhov scaling which is isotropic, when l_{v}∼l_{h}. Finally, for very large N, corresponding to strong stratification, together with a very small l_{v}, the inertial-range flow fields effectively two-dimensionalize. The kinetic energy spectra are predicted to be anisotropic with only the horizontal part of the kinetic energy spectra following the K41 scaling. This suggests an intriguing re-entrant K41 scaling, as a function of stratification, for the horizontal components of the velocity field in this regime. The scaling theory further predicts the scaling of the thermal energy in each of these three scaling regimes. Our theory can be tested in large-scale simulations and appropriate laboratory-based experiments.}, }
@article {pmid31631905, year = {2019}, author = {Bae, HJ and Lozano-Durán, A and Bose, ST and Moin, P}, title = {Dynamic slip wall model for large-eddy simulation.}, journal = {Journal of fluid mechanics}, volume = {859}, number = {}, pages = {400-432}, pmid = {31631905}, issn = {0022-1120}, support = {NNX15AU93A//NASA/United States ; }, abstract = {Wall modelling in large-eddy simulation (LES) is necessary to overcome the prohibitive near-wall resolution requirements in high-Reynolds-number turbulent flows. Most existing wall models rely on assumptions about the state of the boundary layer and require a priori prescription of tunable coefficients. They also impose the predicted wall stress by replacing the no-slip boundary condition at the wall with a Neumann boundary condition in the wall-parallel directions while maintaining the no-transpiration condition in the wall-normal direction. In the present study, we first motivate and analyse the Robin (slip) boundary condition with transpiration (non-zero wall-normal velocity) in the context of wall-modelled LES. The effect of the slip boundary condition on the one-point statistics of the flow is investigated in LES of turbulent channel flow and a flat-plate turbulent boundary layer. It is shown that the slip condition provides a framework to compensate for the deficit or excess of mean momentum at the wall. Moreover, the resulting non-zero stress at the wall alleviates the well-known problem of the wall-stress under-estimation by current subgrid-scale (SGS) models (Jiménez &amp; Moser, AIAA J., vol. 38 (4), 2000, pp. 605-612). Second, we discuss the requirements for the slip condition to be used in conjunction with wall models and derive the equation that connects the slip boundary condition with the stress at the wall. Finally, a dynamic procedure for the slip coefficients is formulated, providing a dynamic slip wall model free of a priori specified coefficients. The performance of the proposed dynamic wall model is tested in a series of LES of turbulent channel flow at varying Reynolds numbers, non-equilibrium three-dimensional transient channel flow and a zero-pressure-gradient flat-plate turbulent boundary layer. The results show that the dynamic wall model is able to accurately predict one-point turbulence statistics for various flow configurations, Reynolds numbers and grid resolutions.}, }
@article {pmid31631902, year = {2019}, author = {Lozano-Durán, A and Bae, HJ}, title = {Error scaling of large-eddy simulation in the outer region of wall-bounded turbulence.}, journal = {Journal of computational physics}, volume = {392}, number = {}, pages = {532-555}, pmid = {31631902}, issn = {0021-9991}, support = {NNX15AU93A//NASA/United States ; }, abstract = {We study the error scaling properties of large-eddy simulation (LES) in the outer region of wall-bounded turbulence at moderately high Reynolds numbers. In order to avoid the additional complexity of wall-modeling, we perform LES of turbulent channel flows in which the no-slip condition at the wall is replaced by a Neumann condition supplying the exact mean wall-stress. The statistics investigated are the mean velocity profile, turbulence intensities, and kinetic energy spectra. The errors follow (Δ / L) α R e τ γ , where Δ is the characteristic grid resolution, Re τ is the friction Reynolds number, and L is the meaningful length-scale to normalize Δ in order to collapse the errors across the wall-normal distance. We show that Δ can be expressed as the L 2-norm of the grid vector and that L is well represented by the ratio of the friction velocity and mean shear. The exponent α is estimated from theoretical arguments for each statistical quantity of interest and shown to roughly match the values computed by numerical simulations. For the mean profile and kinetic energy spectra, α ≈ 1, whereas the turbulence intensities converge at a slower rate α < 1. The exponent γ is approximately 0, i.e. the LES solution is independent of the Reynolds number. The expected behavior of the turbulence intensities at high Reynolds numbers is also derived and shown to agree with the classic log-layer profiles for grid resolutions lying within the inertial range. Further examination of the LES turbulence intensities and spectra reveals that both quantities resemble their filtered counterparts from direct numerical simulation (DNS) data, but that the mechanism responsible for this similarity is related to the balance between the input power and dissipation rather than to filtering.}, }
@article {pmid31627151, year = {2020}, author = {Hayat, T and Waqar Ahmad, M and Ijaz Khan, M and Alsaedi, A}, title = {Entropy optimization in CNTs based nanomaterial flow induced by rotating disks: A study on the accuracy of statistical declaration and probable error.}, journal = {Computer methods and programs in biomedicine}, volume = {184}, number = {}, pages = {105105}, doi = {10.1016/j.cmpb.2019.105105}, pmid = {31627151}, issn = {1872-7565}, mesh = {*Entropy ; Models, Theoretical ; Nanostructures/*chemistry ; Nanotubes, Carbon/*chemistry ; Probability ; Reproducibility of Results ; }, abstract = {BACKGROUND: CNTs (Carbon nanotubes) being allotropes of carbon, made of graphene and diameters of single and multi-walls carbon nanotubes are typically 0.8 to 2 nm and 5 to 20 mn, although diameter of MWCNTs can exceed 100 nm. Carbon nanotubes lengths range from less than 100 nm to 0.5 m. Their impressive structural, electronic and mechanical attributes subject to their small size and mass, their high electrical and thermal conductivities, and their strong mechanical potency. CNTs based materials are successfully applied in medicine and pharmacy subject to their huge surface area that is proficient of conjugating or adsorbing with a wide variety of genes, drugs, antibodies, vaccines and biosensors etc. Therefore, we have presented a theoretical study about mathematical modeling of CNTs based viscous material flow between two rotating disks. Both types of nanotubes i.e., SWCNTs and MWCNTs are considered. Xue model is used for the mathematical modeling. Fluid flow is due to rotating disks. Main focus here is given to probable error and statistical declaration. Entropy is calculated for both single and multi-walls nanotubes.<br><br>METHOD: Nonlinear PDEs are first converted into ODEs and then computed for homotopy convergent solutions.<br><br>RESULTS AND CONCLUSION: Statistical declaration and probable error for skin friction and Nusselt number are numerically computed and discussed through Tables. From obtained outcomes it is concluded that magnitude of skin friction increases at both disks surface for higher values of Reynolds number, lower stretching parameter and porosity parameter while it decays for both of disks versus larger rotation parameter. Nusselt number or heat transfer rate also enhances at both disks in the presence of radiation and Reynolds number while it decays against Eckert number.}, }
@article {pmid31620754, year = {2019}, author = {Bukowicki, M and Ekiel-Jeżewska, ML}, title = {Sedimenting pairs of elastic microfilaments.}, journal = {Soft matter}, volume = {15}, number = {46}, pages = {9405-9417}, doi = {10.1039/c9sm01373c}, pmid = {31620754}, issn = {1744-6848}, abstract = {The dynamics of two identical elastic filaments settling under gravity in a viscous fluid in the low Reynolds number regime is investigated numerically. A large family of initial configurations symmetric with respect to a vertical plane is considered, as well as their non-symmetric perturbations. The behaviour of the filaments is primarily governed by the elasto-gravitational number, which depends on the filament's length and flexibility, and the strength of the external force. Flexible filaments usually converge toward horizontal and parallel orientation. We explain this phenomenon and show that it occurs also for curved rigid particles of similar shapes. Once aligned, the two fibres either converge toward a stationary, flexibility-dependent distance, or tend to collide or continuously repel each other. Rigid and straight rods perform periodic motions while settling down. Apart from very stiff particles, the dynamics is robust to non-symmetric perturbations.}, }
@article {pmid31611726, year = {2019}, author = {Holdenried-Chernoff, D and Chen, L and Jackson, A}, title = {A trio of simple optimized axisymmetric kinematic dynamos in a sphere.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {475}, number = {2229}, pages = {20190308}, pmid = {31611726}, issn = {1364-5021}, abstract = {Planetary magnetic fields are generated by the motion of conductive fluid in the planet's interior. Complex flows are not required for dynamo action; simple flows have been shown to act as efficient kinematic dynamos, whose physical characteristics are more straightforward to study. Recently, Chen et al. (2018, J. Fluid Mech. 839, 1-32. (doi:10.1017/jfm.2017.924)) found the optimal, unconstrained kinematic dynamo in a sphere, which, despite being of theoretical importance, is of limited practical use. We extend their work by restricting the optimization to three simple two-mode axisymmetric flows based on the kinematic dynamos of Dudley &amp; James (1989, Proc. R. Soc. Lond. A 425, 407-429. (doi:10.1098/rspa.1989.0112)). Using a Lagrangian optimization, we find the smallest critical magnetic Reynolds number for each flow type, measured using an enstrophy-based norm. A Galerkin method is used, in which the spectral coefficients of the fluid flow and magnetic field are updated in order to maximize the final magnetic energy. We consider the t [0] 1 s [0] 1, t [0] 1 s [0] 2 and t [0] 2 s [0] 2 flows and find enstrophy-based critical magnetic Reynolds numbers of 107.7, 142.4 and 125.5 (13.7, 19.6 and 16.4, respectively, with the energy-based definition). These are up to four times smaller than the original flows. These simple and efficient flows may be used as benchmarks in future studies.}, }
@article {pmid31602809, year = {2020}, author = {Browne, CA and Shih, A and Datta, SS}, title = {Pore-Scale Flow Characterization of Polymer Solutions in Microfluidic Porous Media.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {16}, number = {9}, pages = {e1903944}, doi = {10.1002/smll.201903944}, pmid = {31602809}, issn = {1613-6829}, abstract = {Polymer solutions are frequently used in enhanced oil recovery and groundwater remediation to improve the recovery of trapped nonaqueous fluids. However, applications are limited by an incomplete understanding of the flow in porous media. The tortuous pore structure imposes both shear and extension, which elongates polymers; moreover, the flow is often at large Weissenberg numbers, Wi, at which polymer elasticity in turn strongly alters the flow. This dynamic elongation can even produce flow instabilities with strong spatial and temporal fluctuations despite the low Reynolds number, Re. Unfortunately, macroscopic approaches are limited in their ability to characterize the pore-scale flow. Thus, understanding how polymer conformations, flow dynamics, and pore geometry together determine these nontrivial flow patterns and impact macroscopic transport remains an outstanding challenge. This review describes how microfluidic tools can shed light on the physics underlying the flow of polymer solutions in porous media at high Wi and low Re. Specifically, microfluidic studies elucidate how steady and unsteady flow behavior depends on pore geometry and solution properties, and how polymer-induced effects impact nonaqueous fluid recovery. This work thus provides new insights for polymer dynamics, non-Newtonian fluid mechanics, and applications such as enhanced oil recovery and groundwater remediation.}, }
@article {pmid31594959, year = {2019}, author = {Houba, T and Dasgupta, A and Gopalakrishnan, S and Gosse, R and Roy, S}, title = {Supersonic turbulent flow simulation using a scalable parallel modal discontinuous Galerkin numerical method.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {14442}, doi = {10.1038/s41598-019-50546-w}, pmid = {31594959}, issn = {2045-2322}, support = {GS04T09DBC0017//Science Applications International Corporation (SAIC)/ ; GS04T09DBC0017//Science Applications International Corporation (SAIC)/ ; GS04T09DBC0017//Science Applications International Corporation (SAIC)/ ; GS04T09DBC0017//Science Applications International Corporation (SAIC)/ ; ACI-1548562//National Science Foundation (NSF)/ ; ACI-1548562//National Science Foundation (NSF)/ ; ACI-1548562//National Science Foundation (NSF)/ ; ACI-1548562//National Science Foundation (NSF)/ ; ACI-1548562//NSF | National Science Board (NSB)/ ; }, abstract = {The scalability and efficiency of numerical methods on parallel computer architectures is of prime importance as we march towards exascale computing. Classical methods like finite difference schemes and finite volume methods have inherent roadblocks in their mathematical construction to achieve good scalability. These methods are popularly used to solve the Navier-Stokes equations for fluid flow simulations. The discontinuous Galerkin family of methods for solving continuum partial differential equations has shown promise in realizing parallel efficiency and scalability when approaching petascale computations. In this paper an explicit modal discontinuous Galerkin (DG) method utilizing Implicit Large Eddy Simulation (ILES) is proposed for unsteady turbulent flow simulations involving the three-dimensional Navier-Stokes equations. A study of the method was performed for the Taylor-Green vortex case at a Reynolds number ranging from 100 to 1600. The polynomial order P = 2 (third order accurate) was found to closely match the Direct Navier-Stokes (DNS) results for all Reynolds numbers tested outside of Re = 1600, which had a normalized RMS error of 3.43 × 10[-4] in the dissipation rate for a 60[3] element mesh. The scalability and performance study of the method was then conducted for a Reynolds number of 1600 for polynomials orders from P = 2 to P = 6. The highest order polynomial that was tested (P = 6) was found to have the most efficient scalability using both the MPI and OpenMP implementations.}, }
@article {pmid31590559, year = {2019}, author = {Porteous, R and Moreau, DJ and Doolan, CJ}, title = {The effect of the incoming boundary layer thickness on the aeroacoustics of finite wall-mounted square cylinders.}, journal = {The Journal of the Acoustical Society of America}, volume = {146}, number = {3}, pages = {1808}, doi = {10.1121/1.5126693}, pmid = {31590559}, issn = {1520-8524}, abstract = {This paper is concerned with the influence of the incoming wall boundary layer thickness on the noise produced by a square finite wall-mounted cylinder in cross-flow. Acoustic and near wake velocity measurements have been taken in an anechoic wind tunnel for a cylinder in two different near-zero-pressure gradient turbulent boundary layers with thicknesses of 130% and 370% of the cylinder width, W. The cylinders have an aspect ratio of 0.29≤L/W≤22.9 (where L is the cylinder span) and were examined at a Reynolds number, based on width, of ReW = 1.4 × 10[4]. The results presented in this paper demonstrate that increasing the height of the boundary layer delays the production of acoustic tones to higher aspect ratios. The height of the boundary layer changes the balance between upwash and downwash across the cylinder span, resulting in a delayed onset of the shedding regimes and correspondingly, the production of acoustic tones.}, }
@article {pmid31590317, year = {2019}, author = {Kawaguchi, M and Fukui, T and Funamoto, K and Tanaka, M and Tanaka, M and Murata, S and Miyauchi, S and Hayase, T}, title = {Viscosity Estimation of a Suspension with Rigid Spheres in Circular Microchannels Using Particle Tracking Velocimetry.}, journal = {Micromachines}, volume = {10}, number = {10}, pages = {}, pmid = {31590317}, issn = {2072-666X}, abstract = {Suspension flows are ubiquitous in industry and nature. Therefore, it is important to understand the rheological properties of a suspension. The key to understanding the mechanism of suspension rheology is considering changes in its microstructure. It is difficult to evaluate the influence of change in the microstructure on the rheological properties affected by the macroscopic flow field for non-colloidal particles. In this study, we propose a new method to evaluate the changes in both the microstructure and rheological properties of a suspension using particle tracking velocimetry (PTV) and a power-law fluid model. Dilute suspension (0.38%) flows with fluorescent particles in a microchannel with a circular cross section were measured under low Reynolds number conditions (Re ≈ 10[-4]). Furthermore, the distribution of suspended particles in the radial direction was obtained from the measured images. Based on the power-law index and dependence of relative viscosity on the shear rate, we observed that the non-Newtonian properties of the suspension showed shear-thinning. This method will be useful in revealing the relationship between microstructural changes in a suspension and its rheology.}, }
@article {pmid31574775, year = {2019}, author = {Singh, G and Lakkaraju, R}, title = {Wall-mounted flexible plates in a two-dimensional channel trigger early flow instabilities.}, journal = {Physical review. E}, volume = {100}, number = {2-1}, pages = {023109}, doi = {10.1103/PhysRevE.100.023109}, pmid = {31574775}, issn = {2470-0053}, abstract = {A high level of mixing by passive means is a desirable feature in microchannels for various applications, and use of flexible obstacles (or plates) is one of the prime choices in that regard. To gain further insight, we carry out two-dimensional numerical simulations for flow past one or two flexible plates anchored to a channel's opposite walls using a fluid-structure interaction framework. For the inlet flow Reynolds number vs the Strouhal number plane, we observe a sudden flow change from a laminar to a time-periodic vortex shedding state when flexible plates are present in the channel. We found the critical Reynolds number to be Re_{cr}≈370 when a single plate is anchored on the channel wall and Re_{cr}≈290 or even lower when two plates are anchored. With an increase in the inlet flow Reynolds number (up to 3200), we found that vortices detach regularly at the plates' tips, which causes the flow to meander in the channel. In a two-plate anchored configuration, primary vortices generated at the first plate are constrained by the second plate and result in an energetic secondary vortex generation in the downstream side. The overall flow features and the energy dissipation in the channel are mainly controlled by the separation gap between the plates. At high-inlet-flow Reynolds numbers (≥1600), the probability density function (F) of the kinetic energy dissipation in a flexible plate configuration shows a stretched exponential shape in the form F(Z)∼1/sqrt[Z]e^{-pZ^{q}}, where Z is the normalized kinetic energy dissipation and the constants p=0.89 and q=0.86. The observed increase in energy dissipation comes at the cost of an increase in pressure loss in the channel, and we found that the loss is inversely related to the plates' separation gap. From our simulations, we found that if high mixing levels are desired, then two flexible plates anchored to the channel walls is a better choice than a channel flow without obstacles or flow past a single plate. The two-plate configuration with zero separation gap between the plates is best suited to achieve a high mixing level.}, }
@article {pmid31574747, year = {2019}, author = {Feng, Y and Boivin, P and Jacob, J and Sagaut, P}, title = {Hybrid recursive regularized lattice Boltzmann simulation of humid air with application to meteorological flows.}, journal = {Physical review. E}, volume = {100}, number = {2-1}, pages = {023304}, doi = {10.1103/PhysRevE.100.023304}, pmid = {31574747}, issn = {2470-0053}, abstract = {An extended version of the hybrid recursive regularized lattice-Boltzmann model which incorporates external force is developed to simulate humid air flows with phase change mechanisms under the Boussinesq approximation. Mass and momentum conservation equations are solved by a regularized lattice Boltzmann approach well suited for high Reynolds number flows, whereas the energy and humidity related equations are solved by a finite volume approach. Two options are investigated to account for cloud formation in atmospheric flow simulations. The first option considers a single conservation equation for total water and an appropriate invariant variable of temperature. In the other approach, liquid and vapor are considered via two separated equations, and phase transition is accounted for via a relaxation procedure. The obtained models are then systematically validated on four well-established benchmark problems including a double diffusive Rayleigh Bénard convection of humid air, two- and three-dimensional thermal moist rising bubble under convective atmospheric environment, as well as a shallow cumulus convection in the framework of large-eddy simulation.}, }
@article {pmid31574698, year = {2019}, author = {Topayev, S and Nouar, C and Bernardin, D and Neveu, A and Bahrani, SA}, title = {Taylor-vortex flow in shear-thinning fluids.}, journal = {Physical review. E}, volume = {100}, number = {2-1}, pages = {023117}, doi = {10.1103/PhysRevE.100.023117}, pmid = {31574698}, issn = {2470-0053}, abstract = {This paper deals with the Taylor-Couette flow of shear-thinning fluids. It focuses on the first principles understanding of the influence of the viscosity stratification and the nonlinear variation of the effective viscosity μ with the shear rate γ[over ̇] on the flow structure in the Taylor-vortex flow regime. A wide gap configuration (η=0.4) is mainly considered. A weakly nonlinear analysis, using the amplitude expansion method at high order, is adopted as a first approach to study nonlinear effects. For the numerical computation, the shear-thinning behavior is described by the Carreau model. The rheological parameters are varied in a wide range. The results indicate that the flow field undergoes a significant change as shear-thinning effects increase. First, vortices are squeezed against the inner wall and the center of the patterns is shifted axially toward the radial outflow boundaries (z=0,z/λ_{z}=1). This axial shift leads to increasing concentration of vorticity at these positions. The outflow becomes stronger than the inflow and the extent of the inflow zone where the vorticity is low increases acoordingly. Nevertheless, the strength of the vortices relative to the velocity of the inner cylinder is weaker. Second, the pseudo-Nusselt number, ratio of the torque to that obtained in the laminar flow, decreases. Third, higher harmonics become more relevant and grow faster with Reynolds number. Finally, the modification of the viscosity field is described.}, }
@article {pmid31574640, year = {2019}, author = {Krämer, A and Wilde, D and Küllmer, K and Reith, D and Foysi, H}, title = {Pseudoentropic derivation of the regularized lattice Boltzmann method.}, journal = {Physical review. E}, volume = {100}, number = {2-1}, pages = {023302}, doi = {10.1103/PhysRevE.100.023302}, pmid = {31574640}, issn = {2470-0053}, abstract = {The lattice Boltzmann method (LBM) facilitates efficient simulations of fluid turbulence based on advection and collision of local particle distribution functions. To ensure stable simulations on underresolved grids, the collision operator must prevent drastic deviations from local equilibrium. This can be achieved by various methods, such as the multirelaxation time, entropic, quasiequilibrium, regularized, and cumulant schemes. Complementing a part of a unified theoretical framework of these schemes, the present work presents a derivation of the regularized lattice Boltzmann method (RLBM), which follows a recently introduced entropic multirelaxation time LBM by Karlin, Bösch, and Chikatamarla (KBC). It is shown that both methods can be derived by locally maximizing a quadratic Taylor expansion of the entropy function. While KBC expands around the local equilibrium distribution, the RLBM is recovered by expanding entropy around a global equilibrium. Numerical tests were performed to elucidate the role of pseudoentropy maximization in these models. Simulations of a two-dimensional shear layer show that the RLBM successfully reproduces the largest eddies even on a 16×16 grid, while the conventional LBM becomes unstable for grid resolutions of 128×128 and lower. The RLBM suppresses spurious vortices more effectively than KBC. In contrast, simulations of the three-dimensional Taylor-Green and Kida vortices show that KBC performs better in resolving small scale vortices, outperforming the RLBM by a factor of 1.8 in terms of the effective Reynolds number.}, }
@article {pmid31574614, year = {2019}, author = {Morris, RG and Rao, M}, title = {Active morphogenesis of epithelial monolayers.}, journal = {Physical review. E}, volume = {100}, number = {2-1}, pages = {022413}, doi = {10.1103/PhysRevE.100.022413}, pmid = {31574614}, issn = {2470-0053}, mesh = {Epithelium/*growth &amp; development/metabolism ; Hydrodynamics ; *Models, Biological ; *Morphogenesis ; Thermodynamics ; }, abstract = {During typical early-stage embryo development, single-cell-thick tissues of tightly bound epithelial cells autonomously generate profound changes in their shape, forming the basis of organism anatomy. We report on a (covariant) active-hydrodynamic theory of such monolayer morphogenesis that is closed under its shape-changing dynamics-i.e., the degrees of freedom that encode monolayer geometry appear properly as broken-symmetry variables. In our theory, the salient physics of tissue-scale deformations emerges from a balance between the displacement and/or shear of a low-Reynolds-number embedding fluid (the "yolk") and cell-autonomous stresses, themselves a result of combining apical contractile stresses with an elastic-like mechanical response under the constraint of constant cell volume. The leading-order hydrodynamic instabilities include both passive constrained-buckling and active deformation, which can be further categorized by cell shape changes that are either "squamous to columnar" or "regular-prism to truncated-pyramid." The deformations resulting from the latter qualitatively reproduce in vivo observations of the onset of both mesoderm and posterior midgut invaginations, which take place during gastrulation in the model organism Drosophila melanogaster.}, }
@article {pmid31546025, year = {2020}, author = {Phuong, NL and Quang, TV and Khoa, ND and Kim, JW and Ito, K}, title = {CFD analysis of the flow structure in a monkey upper airway validated by PIV experiments.}, journal = {Respiratory physiology &amp; neurobiology}, volume = {271}, number = {}, pages = {103304}, doi = {10.1016/j.resp.2019.103304}, pmid = {31546025}, issn = {1878-1519}, mesh = {Animals ; *Computer Simulation ; Haplorhini ; *Hydrodynamics ; Inhalation Exposure ; Macaca fascicularis ; Male ; Mouth/diagnostic imaging/physiology ; Nasal Cavity/diagnostic imaging/*physiology ; *Particle Size ; Respiratory Mechanics/*physiology ; Rheology/*methods ; }, abstract = {Inhalation exposure to airborne contaminants has adverse effects on humans; however, related research is typically conducted using in vivo/in vitro tests on animals. Extrapolating the test results is complicated by anatomical and physiological differences between animals and humans and a lack of understanding of the transport mechanism inside their respective respiratory tracts. This study determined the detailed air-flow structure in the upper airway of a monkey. A steady computational fluid dynamics simulation, which was validated by previous particle image velocimetry measurements, was adopted for flow rates of 4 L/min and 10 L/min to analyze the flow structure from the nasal/oral cavities to the trachea region in a monkey airway model. The low Reynolds number type k-ε model provided a reasonably accurate prediction of the airflow in a monkey upper airway. Furthermore, it was confirmed that large velocity gradients were generated in the nasal vestibule and larynx regions, as well as increased turbulent air kinetic energy and wall sheer stress.}, }
@article {pmid31542476, year = {2020}, author = {Shi, L and Wu, J and Krenn, HW and Yang, Y and Yan, S}, title = {Temporal model of fluid-feeding mechanisms in a long proboscid orchid bee compared to the short proboscid honey bee.}, journal = {Journal of theoretical biology}, volume = {484}, number = {}, pages = {110017}, doi = {10.1016/j.jtbi.2019.110017}, pmid = {31542476}, issn = {1095-8541}, mesh = {Animals ; *Bees/anatomy &amp; histology/physiology ; *Feeding Behavior/physiology ; Flowers ; *Models, Biological ; Plant Nectar ; Time ; Tongue/anatomy &amp; histology ; }, abstract = {Bees (Apidae) are flower-visiting insects that possess highly efficient mouthparts for the ingestion of nectar and other sucrose fluids. Their mouthparts are composed of mandibles and a tube-like proboscis. The proboscis forms a food canal, which encompasses a protrusible and hairy tongue to load and imbibe nectar, representing a fluid-feeding technique with a low Reynolds number. The western honey bee, Apis mellifera ligustica, can rhythmically erect the tongue microtrichia to regulate the glossal shape, achieving a tradeoff between nectar intake rate and viscous drag. Neotropical orchid bees (Euglossa imperialis) possess a proboscis longer than the body and combines this lapping-sucking mode of fluid-feeding with suction feeding. This additional technique of nectar uptake may have different biophysics. In order to reveal the effect of special structures of mouthparts in terms of feeding efficiency, we build a temporal model for orchid bees considering fluid transport in multi-states including active suction, tongue protraction and viscous dipping. Our model indicates that the dipping technique employed by honey bees can contribute to more than seven times the volumetric and energetic intake rate at a certain nectar concentration compared with the combined mode used by orchid bees. The high capability of the honey bee's proboscis to ingest nectar may inspire micropumps for transporting viscous liquid with higher efficiency.}, }
@article {pmid31538112, year = {2019}, author = {Onyiriuka, EJ and Ighodaro, OO and Adelaja, AO and Ewim, DRE and Bhattacharyya, S}, title = {A numerical investigation of the heat transfer characteristics of water-based mango bark nanofluid flowing in a double-pipe heat exchanger.}, journal = {Heliyon}, volume = {5}, number = {9}, pages = {e02416}, pmid = {31538112}, issn = {2405-8440}, abstract = {In this study, the heat transfer characteristics of a new class of nanofluids made from mango bark was numerically simulated and studied during turbulent flow through a double pipe heat exchanger. A range of volume fractions was considered for a particle size of 100 nm. A two-phase flow was considered using the mixture model. The mixture model governing equations of continuity, momentum, energy and volume fraction were solved using the finite-volume method. The results showed an increase of the Nusselt number by 68% for a Reynolds number of 5,000 and 45% for a Reynolds number of 13 000, and the heat transfer coefficient of the nanofluid was about twice that of the base fluid. In addition, the Nusselt number decreased by an average value of 0.76 with an increase of volume fraction by 1%. It was also found that there was a range of Reynolds numbers in which the trend of the average heat transfer coefficient of the nanofluid was completely reversed, and several plots showing zones of higher heat transfer which if taken advantage of in design will lead to higher heat transfer while avoiding other zones that have low heat transfer. It is hoped that these results will influence the thermal design of new heat exchangers.}, }
@article {pmid31534269, year = {2019}, author = {Blumenthal, BT and Elmiligui, AA and Geiselhart, KA and Campbell, RL and Maughmer, MD and Schmitz, S}, title = {Computational Investigation of a Boundary-Layer Ingesting Propulsion System for the Common Research Model.}, journal = {Journal of aircraft}, volume = {55}, number = {3}, pages = {1141-1153}, pmid = {31534269}, issn = {0021-8669}, support = {//Langley Research Center NASA/United States ; N-999999//Intramural NASA/United States ; }, abstract = {The present paper examines potential propulsive and aerodynamic benefits of integrating a Boundary-Layer Ingestion (BLI) propulsion system into the Common Research Model (CRM) geometry and the NASA Tetrahedral Unstructured Software System (TetrUSS). The Numerical Propulsion System Simulation (NPSS) environment is used to generate engine conditions for Computational Fluid Dynamics (CFD) analyses. Improvements to the BLI geometry are made using the Constrained Direct Iterative Surface Curvature (CDISC) design method. Potential benefits of the BLI system relating to cruise propulsive power are quantified using a power balance method, and a comparison to the baseline case is made. Iterations of the BLI geometric design are shown, and improvements between subsequent BLI designs are presented. Simulations are conducted for a cruise flight condition of Mach 0.85 at an altitude of 38,500 feet, with Reynolds number of 40 million based on mean aerodynamic chord and an angle of attack of 2° for all geometries. Results indicate an 8% reduction in engine power requirements at cruise for the BLI configuration compared to the baseline geometry. Small geometric alterations of the aft portion of the fuselage using CDISC has been shown to marginally increase the benefit from boundary-layer ingestion further, resulting in an 8.7% reduction in power requirements for cruise, as well as a drag reduction of approximately twelve counts over the baseline geometry.}, }
@article {pmid31533305, year = {2019}, author = {Wang, R and Wang, J and Yuan, W}, title = {Analysis and Optimization of a Microchannel Heat Sink with V-Ribs Using Nanofluids for Micro Solar Cells.}, journal = {Micromachines}, volume = {10}, number = {9}, pages = {}, pmid = {31533305}, issn = {2072-666X}, support = {11572107, 51376055//National Natural Science Foundation of China/ ; }, abstract = {It is crucial to control the temperature of solar cells for enhancing efficiency with the increasing power intensity of multiple photovoltaic systems. In order to improve the heat transfer efficiency, a microchannel heat sink (MCHS) with V-ribs using a water-based nanofluid as a coolant for micro solar cells was designed. Numerical simulations were carried out to investigate the flows and heat transfers in the MCHS when the Reynolds number ranges from 200 to 1000. The numerical results showed that the periodically arranged V-ribs can interrupt the thermal boundary, induce chaotic convection, increase heat transfer area, and subsequently improve the heat transfer performance of a MCHS. In addition, the preferential values of the geometric parameters of V-ribs and the physical parameters of the nanofluid were obtained on the basis of the Nusselt numbers at identical pump power. For MCHS with V-ribs on both the top and bottom wall, preferential values of V-rib are rib width d / W = 1 , flare angle α = 75 ° , rib height h r / H = 0.3 , and ratio of two slant sides b / a = 0.75 , respectively. This can provide sound foundations for the design of a MCHS in micro solar cells.}, }
@article {pmid31533232, year = {2019}, author = {Tang, L and Pan, X and Feng, J and Pu, X and Liang, R and Li, R and Li, K}, title = {Experimental Investigation on the Relationship Between COD Degradation and Hydrodynamic Conditions in Urban Rivers.}, journal = {International journal of environmental research and public health}, volume = {16}, number = {18}, pages = {}, pmid = {31533232}, issn = {1660-4601}, mesh = {*Biological Oxygen Demand Analysis ; China ; Cities ; Hydrodynamics ; Rivers/*chemistry ; Water Pollution, Chemical/*analysis ; *Water Quality ; }, abstract = {Due to extensive pollution and the relatively weak flow replacement in urban rivers, determining how to fully utilize the self-purification abilities of water bodies for water quality protection has been a complex and popular topic of research and social concern. Organic pollution is an important type of urban river pollution, and COD (chemical oxygen demand) is one of the key pollution factors. Currently, there is a lack of research on the relationship between COD degradation and the flow characteristics of urban rivers. In this paper, COD degradation experiments were conducted in an annular flume with Jinjiang River water at controlled flow velocities and the COD degradation coefficients under different hydraulic conditions were analyzed. A good correlation was observed between the degradation coefficient and hydraulic conditions. According to dimensional analysis, the relationship between the COD degradation coefficient and hydraulic conditions such as the flow velocity, water depth, Reynolds number (Re), and Froude number (Fr) was established as K COD = 86400 u h F r 0.8415 R e - 1.2719 + 0.258 . The COD degradation coefficients of the Chishui River in Guizhou Province ranged from 0.175-0.373 1/d based on this formula, and the field-measured values varied from 0.234-0.463 1/d. The error in the formula ranged from 5.4-25.3%. This study provides a scientific basis for the prediction of the COD degradation coefficients of urban rivers.}, }
@article {pmid31533091, year = {2019}, author = {Wang, C and Ren, F and Tang, H}, title = {Enhancing propulsion performance of a flexible heaving foil through dynamically adjusting its flexibility.}, journal = {Bioinspiration &amp; biomimetics}, volume = {14}, number = {6}, pages = {064002}, doi = {10.1088/1748-3190/ab45d9}, pmid = {31533091}, issn = {1748-3190}, mesh = {Algorithms ; Animals ; Biomechanical Phenomena ; Biomimetics/instrumentation/*methods ; Fishes/*physiology ; Hydrodynamics ; Models, Biological ; Robotics/instrumentation/methods ; }, abstract = {This study investigates how dynamically adjusting the bending stiffness of a heaving foil affects its propulsion performance in a flow of Reynolds number 200. The foil is forced to oscillate sinusoidally at the leading edge, and its bending stiffness is tuned in a square-wave manner. Such a fluid-structure interaction (FSI) problem is explored using an immersed boundary lattice Boltzmann method (IBLBM) based numerical framework. The results reveal that when the lower and upper bounds of the foil's time-dependent bending stiffness are moderate, the net thrust can be evidently enhanced compared to those in the corresponding constant-bending-stiffness cases, while the propulsion efficiency is not apparently ameliorated. The most significant enhancement is observed when the bending stiffness has lower and upper bounds of the same duration (i.e. a duty cycle of 1/2) and also it remains at the lower bound during stroke reversals (corresponding to an actuation phase angle of [Formula: see text]). When the two bounds simultaneously increase or decrease, however, dynamically adjusting the bending stiffness fails to improve the net thrust. Through this study, competitions among various forces/moments, including the inertial force, tension force, bending moment and fluid loading, acting on the foil and their influences on the foil's dynamics are also unveiled.}, }
@article {pmid31511924, year = {2019}, author = {Acosta-Avalos, D and Rodrigues, E}, title = {On the motion of magnetotactic bacteria: theoretical predictions and experimental observations.}, journal = {European biophysics journal : EBJ}, volume = {48}, number = {8}, pages = {691-700}, pmid = {31511924}, issn = {1432-1017}, mesh = {*Bacteria ; *Bacterial Physiological Phenomena ; Biomechanical Phenomena ; *Magnetic Fields ; *Models, Biological ; *Movement ; }, abstract = {The movement of magnetotactic bacteria is done in a viscous media in the low Reynolds number regime. In the present research, the simple model for magnetotactic bacteria motion, proposed by Nogueira and Lins de Barros (Eur Biophys J 24:13-21, 1995), was used to numerically simulate their trajectory. The model was done considering a spherical bacterium with a single flagellum and a magnetic moment positioned in the sphere center and parallel to the flagella. The numerical solution shows that the trajectory is a cylindrical helix and that the body Euler angles have linear dependencies on time. Using that information, analytical expressions were obtained for the first time for the center-of-mass coordinates, showing that the trajectories are helixes oriented to the magnetic field direction. They also show that the magnetic moment does not align to the magnetic field, but it precesses around it, being fully oriented only for very high magnetic fields. The analytical solution obtained permits to relate for the first time the flagellar force to the axial velocity and helical radius. Trajectories of uncultivated magnetotactic bacteria were registered in video and the coordinates were obtained for several bacteria in different magnetic fields. The trajectories showed to be a complex mixture of two oscillating functions: one with frequency lower than 5 Hz and the other one with frequency higher than 10 Hz. The simple model of Nogueira and Lins de Barros shows to be incomplete, because is unable to explain the trajectories composed of two oscillating functions observed in uncultivated magnetotactic bacteria.}, }
@article {pmid31499817, year = {2019}, author = {Falsaperla, P and Giacobbe, A and Mulone, G}, title = {Nonlinear stability results for plane Couette and Poiseuille flows.}, journal = {Physical review. E}, volume = {100}, number = {1-1}, pages = {013113}, doi = {10.1103/PhysRevE.100.013113}, pmid = {31499817}, issn = {2470-0053}, abstract = {We prove that the plane Couette and Poiseuille flows are nonlinearly stable if the Reynolds number is less than Re_{Orr}(2π/(λsinθ))/sinθ when a perturbation is a tilted perturbation in the direction x^{'} which forms an angle θ∈(0,π/2] with the direction i of the basic motion and does not depend on x^{'}. Re_{Orr} is the critical Orr-Reynolds number for spanwise perturbations which is computed for wave number 2π/(λsinθ), with λ being any positive wavelength. By taking the minimum with respect to λ, we obtain the critical energy Reynolds number for a fixed inclination angle and any wavelength: for plane Couette flow, it is Re_{Orr}=44.3/sinθ, and for plane Poiseuille flow, it is Re_{Orr}=87.6/sinθ (in particular, for θ=π/2 we have the classical values Re_{Orr}=44.3 for plane Couette flow and Re_{Orr}=87.6 for plane Poiseuille flow). Here the nondimensional interval between the planes bounding the channel is [-1,1]. In particular, these results improve those obtained by Joseph, who found for streamwise perturbations a critical nonlinear value of 20.65 in the plane Couette case, and those obtained by Joseph and Carmi who found the value 49.55 for plane Poiseuille flow for streamwise perturbations. If we fix some wavelengths from the experimental data and the numerical simulations, the critical Reynolds numbers that we obtain are in a very good agreement both with the the experiments and the numerical simulation. These results partially solve the Couette-Sommerfeld paradox.}, }
@article {pmid31499421, year = {2019}, author = {Shah, F and Khan, MI and Hayat, T and Khan, MI and Alsaedi, A and Khan, WA}, title = {Theoretical and mathematical analysis of entropy generation in fluid flow subject to aluminum and ethylene glycol nanoparticles.}, journal = {Computer methods and programs in biomedicine}, volume = {182}, number = {}, pages = {105057}, doi = {10.1016/j.cmpb.2019.105057}, pmid = {31499421}, issn = {1872-7565}, mesh = {Aluminum/*chemistry ; *Entropy ; Ethylene Glycol/*chemistry ; *Hydrodynamics ; *Models, Theoretical ; Nanoparticles/*chemistry ; }, abstract = {BACKGROUND: Here we have conducted a magnetohydrodynamic (MHD) flow of viscous material with alumina water and ethylene glycol over a stretched surface. The flow is discussed with and without effective Prandtl number. MHD liquid is considered. Electric field is absent. Effect of uniform magnetic field is taken in the vertical direction to the surface. Influence of thermal radiation as well as Joule heating are taken into account for both aluminum oxide-water and aluminum oxide-Ethylene glycol nanofluids. Velocity slip and melting heat effects are considered.<br><br>METHODS: The nonlinear flow expressions are numerically solved via ND-solve technique (built-in-Shooting).<br><br>RESULTS: The physical impacts of flow variables like mixed convection parameter, magnetic parameter, Reynold number, Eckert number, melting parameter and heat source/sink parameter are graphically discussed. Moreover, entropy generation (irreversibility) and Bejan number are discussed graphically through various flow variables. Physical quantities like skin friction coefficient and Sherwood and Nusselt numbers are numerically calculated and discussed through Tables.<br><br>CONCLUSIONS: Impact of magnetic and slip parameters on the velocity field show decreasing behavior for both effective and without effective Prandtl number. Temperature field increases for both effective and without effective Prandtl number for higher values of magnetic and radiative parameters. Entropy number is an increasing function of Reynolds number while Bejan number shows opposite impact against Reynolds number. Moreover, heat transfer rate upsurges versus larger melting and radiative parameter.}, }
@article {pmid31481279, year = {2021}, author = {DeJonckere, P and Lebacq, J}, title = {Intraglottal Aerodynamics at Vocal Fold Vibration Onset.}, journal = {Journal of voice : official journal of the Voice Foundation}, volume = {35}, number = {1}, pages = {156.e23-156.e32}, doi = {10.1016/j.jvoice.2019.08.002}, pmid = {31481279}, issn = {1873-4588}, mesh = {Glottis ; Humans ; Models, Biological ; Phonation ; Pressure ; *Vibration ; *Vocal Cords ; }, abstract = {The most frequently observed type of voice onset in spontaneous speech in normal subjects is the soft onset, and it may be considered as the "physiological" onset. It starts from an immobile narrow glottal slit crossed by a continuous airflow, and then a few oscillations (even a single one in some cases) precede the first glottal closure. It is a transient event, during which the acting forces, lung pressure, intraglottal pressure, myoelastic tension of the vocal fold (VF) oscillator and inertance of the supraglottal vocal tract, interact to progressively reach the steady state of a sustained oscillation. Combined measurements of flow, area, and pressure provide a detailed qualitative and quantitative analysis of the intraglottal mechanical events at the precise moment of starting oscillation in a physiological (soft or soft/breathy) onset. Our in vivo measurements of airflow and glottal area show that the very first oscillation occurs exactly at the time when turbulence appears at the level of the glottal narrowing, ie, when the Reynolds number reaches its critical value. The turbulence may be assumed to trigger an oscillator consisting in the ensemble of the VFs and the air of the vocal tract, which is known to be weakly damped. Turbulence can act here as an aspecific flick, triggering the oscillator, the frequency of oscillation being determined by its mechanical properties. Furthermore, the first noticeable glottal oscillations are sinusoidal: the VFs are neither steeply sucked together by a negative Bernoulli pressure, nor burst apart by the lung pressure. Our measurements show that, at the critical time, the rising positive lung pressure is balanced by the rising negative Bernoulli pressure generated by the transglottal flow.}, }
@article {pmid31480452, year = {2019}, author = {Tsai, CD and Lin, XY}, title = {Experimental Study on Microfluidic Mixing with Different Zigzag Angles.}, journal = {Micromachines}, volume = {10}, number = {9}, pages = {}, pmid = {31480452}, issn = {2072-666X}, support = {108-2321-B-009-004-//Ministry of Science and Technology, Taiwan/ ; 108-2221-E-009-107-//Ministry of Science and Technology, Taiwan/ ; 108-2218-E-009-013-//Ministry of Science and Technology, Taiwan/ ; }, abstract = {This paper presents experimental investigations of passive mixing in a microfluidic channel with different zigzag angles. Zigzag channel is commonly used for microfluidic mixing because it does not need an additional control unit and can be easily implemented in a lab-on-a-chip system. In this work, microfluidic channels with six different zigzag angles, from θ = 0° to θ = 75°, are tested under ten different flow rates corresponding to Reynolds number from 0.309 to 309. Two colored liquids are mixed with the zigzag channels and mixing performance is evaluated based on the color of the pixels on the region of interest from captured images. According to the results, we found that the mixing performance is almost independent of the zigzag angle in the low-speed regime where its Reynolds number is less than 4. The mixing became very much depending on the zigzag angle in the high-speed regime where its Reynolds number is greater than 100. Microfluidic mixing is needed for Lab-on-a-chip applications in both low flow speed, such as medium perfusion for cell culture, and high flow speed, such as high-speed sensing on a point-of-care device. This work is aimed to provide practical information on zigzag mixing for chip design and applications.}, }
@article {pmid31473843, year = {2020}, author = {Waheed, W and Alazzam, A and Al-Khateeb, AN and Abu-Nada, E}, title = {Dissipative particle dynamics for modeling micro-objects in microfluidics: application to dielectrophoresis.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {19}, number = {1}, pages = {389-400}, doi = {10.1007/s10237-019-01216-3}, pmid = {31473843}, issn = {1617-7940}, mesh = {*Algorithms ; Animals ; *Electrophoresis ; Erythrocytes/physiology ; Humans ; *Microfluidics ; *Models, Theoretical ; }, abstract = {The dissipative particle dynamics (DPD) technique is employed to model the trajectories of micro-objects in a practical microfluidic device. The simulation approach is first developed using an in-house Fortran code to model Stokes flow at Reynolds number of 0.01. The extremely low Reynolds number is achieved by adjusting the DPD parameters, such as force coefficients, thermal energies of the particles, and time steps. After matching the numerical flow profile with the analytical results, the technique is developed further to simulate the deflection of micro-objects under the effect of a deflecting external force in a rectangular microchannel. A mapping algorithm is introduced to establish the scaling relationship for the deflecting force between the physical device and the DPD domain. Dielectrophoresis is studied as a case study for the deflecting force, and the trajectory of a single red blood cell under the influence of the dielectrophoretic force is simulated. The device is fabricated using standard microfabrication techniques, and the experiments involving a dilute sample of red blood cells are performed at two different cases of the actuation voltage. Good agreement between the numerical and experimental results is achieved.}, }
@article {pmid31473190, year = {2019}, author = {Chaput, R and Majoris, JE and Buston, PM and Paris, CB}, title = {Hydrodynamic and biological constraints on group cohesion in plankton.}, journal = {Journal of theoretical biology}, volume = {482}, number = {}, pages = {109987}, doi = {10.1016/j.jtbi.2019.08.018}, pmid = {31473190}, issn = {1095-8541}, mesh = {Animals ; Behavior, Animal/*physiology ; Coral Reefs ; *Ecosystem ; Environment ; Fishes/growth &amp; development/*physiology ; *Hydrodynamics ; Larva ; *Mass Behavior ; Plankton/*physiology ; Social Behavior ; Swimming/physiology ; Viscosity ; }, abstract = {The dynamics of plankton in the ocean are determined by biophysical interactions. Although physics and biotic behaviors are known to influence the observed patchiness of planktonic populations, it is still unclear how much, and if, group behavior contributes to this biophysical interaction. Here, we demonstrate how simple rules of behavior can enhance or inhibit active group cohesion in plankton in a turbulent environment. In this study, we used coral-reef fish larvae as a model to investigate the interaction between microscale turbulence and planktonic organisms. We synthesized available information on the swimming speeds and sizes of reef fish larvae, and developed a set of equations to investigate the effects of viscosity and turbulence on larvae dispersion. We then calculated the critical dispersion rates for three different swimming strategies - cruise, random-walk, and pause-travel - to determine which strategies could facilitate group cohesion during dispersal. Our results indicate that swimming strategies and migration to low-turbulence regions are the key to maintaining group cohesion, suggesting that many reef fish species have the potential to remain together, from hatching to settlement. In addition, larvae might change their swimming strategies to maintain group cohesion, depending on environmental conditions and/or their ontogenic stage. This study provides a better understanding of the hydrodynamic and biological constraints on group formation and cohesion in planktonic organisms, and reveals a wide range of conditions under which group formation may occur.}, }
@article {pmid31472558, year = {2019}, author = {Zhang, C and Sanjose, M and Moreau, S}, title = {Aeolian noise of a cylinder in the critical regime.}, journal = {The Journal of the Acoustical Society of America}, volume = {146}, number = {2}, pages = {1404}, doi = {10.1121/1.5122185}, pmid = {31472558}, issn = {1520-8524}, abstract = {The noise from the flow around a circular cylinder in the critical regime is investigated by combining a compressible wall-resolved large eddy simulation and a Ffowcs Williams and Hawkings analogy on solid and porous surfaces. This simulation is validated by comparing several flow parameters with previous experimental and numerical data in the same flow regime. Significantly reduced drag and increased vortex shedding Strouhal number (0.33) are observed. Two slightly asymmetric laminar separation bubbles (LSBs) on the cylinder surface at about 100° are shown to trigger turbulence through Kelvin-Helmholtz (KH) shear-layer instability. The latter contributes to a narrowband hump in the wall-pressure fluctuations with a tone at a Strouhal number of 27, which can be as intense as the dominant vortex shedding tone. The ratio of the corresponding Strouhal numbers is consistent with the proposed variation with the Reynolds number by Prasad and Williamson [(1997). J. Fluid Mech. 333, 375-402]. The dominant far-field noise source is still the vortex shedding dipolar tone radiating mostly at 90°. Yet, two additional broadband noise sources are evidenced in the wake, one at low frequencies caused by the wake oscillation and another one at high frequencies caused by the KH instability mostly directly toward the LSB locations.}, }
@article {pmid31462974, year = {2019}, author = {Gholampour, S and Bahmani, M and Shariati, A}, title = {Comparing the Efficiency of Two Treatment Methods of Hydrocephalus: Shunt Implantation and Endoscopic Third Ventriculostomy.}, journal = {Basic and clinical neuroscience}, volume = {10}, number = {3}, pages = {185-198}, pmid = {31462974}, issn = {2008-126X}, abstract = {INTRODUCTION: Hydrocephalus is one of the most common diseases in children, and its treatment requires brain operation. However, the pathophysiology of the disease is very complicated and still unknown.<br><br>METHODS: Endoscopic Third Ventriculostomy (ETV) and Ventriculoperitoneal Shunt (VPS) implantation are among the common treatments of hydrocephalus. In this study, Cerebrospinal Fluid (CSF) hydrodynamic parameters and efficiency of the treatment methods were compared with numerical simulation and clinical follow-up of the treated patients.<br><br>RESULTS: Studies have shown that in patients under 19 years of age suffering from hydrocephalus related to a Posterior Fossa Brain Tumor (PFBT), the cumulative failure rate was 21% and 29% in ETV and VPS operation, respectively. At first, the ETV survival curve shows a sharp decrease and after two months it gets fixed while VPS curve makes a gradual decrease and reaches to a level lower than ETV curve after 5.7 months. Post-operative complications in ETV and VPS methods are 17% and 31%, respectively. In infants younger than 12 months with hydrocephalus due to congenital Aqueduct Stenosis (AS), and also in the elderly patients suffering from Normal Pressure Hydrocephalus (NPH), ETV is a better treatment option. Computer simulations show that the maximum CSF pressure is the most reliable hydrodynamic index for the evaluation of the treatment efficacy in these patients. After treatment by ETV and shunt methods, CSF pressure decreases about 9 and 5.3 times, respectively and 2.5 years after shunt implantation, this number returns to normal range.<br><br>CONCLUSION: In infants with hydrocephalus, initial treatment by ETV was more reasonable than implanting the shunt. In adult with hydrocephalus, the initial failure in ETV occurred sooner compared to shunt therapy; however, ETV was more efficient.}, }
@article {pmid31446522, year = {2020}, author = {Foo, YY and Pant, S and Tay, HS and Imangali, N and Chen, N and Winkler, C and Yap, CH}, title = {4D modelling of fluid mechanics in the zebrafish embryonic heart.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {19}, number = {1}, pages = {221-232}, doi = {10.1007/s10237-019-01205-6}, pmid = {31446522}, issn = {1617-7940}, mesh = {Algorithms ; Animals ; Blood Flow Velocity ; Computer Simulation ; Embryo, Nonmammalian/*physiology ; Heart/diagnostic imaging/*embryology/*physiology ; *Hydrodynamics ; *Models, Cardiovascular ; Myocardial Contraction ; Ventricular Function ; Zebrafish/*embryology ; }, abstract = {Abnormal blood flow mechanics can result in pathological heart malformation, underlining the importance of understanding embryonic cardiac fluid mechanics. In the current study, we performed image-based computational fluid dynamics simulation of the zebrafish embryonic heart ventricles and characterized flow mechanics, organ dynamics, and energy dynamics in detail. 4D scans of 5 days post-fertilization embryonic hearts with GFP-labelled myocardium were acquired using line-scan focal modulation microscopy. This revealed that the zebrafish hearts exhibited a wave-like contractile/relaxation motion from the inlet to the outlet during both systole and diastole, which we showed to be an energy efficient configuration. No impedance pumping effects of pressure and velocity waves were observed. Due to its tube-like configuration, inflow velocities were higher near the inlet and smaller at the outlet and vice versa for outflow velocities. This resulted in an interesting spatial wall shear stress (WSS) pattern where WSS waveforms near the inlet and those near the outlet were out of phase. There was large spatial variability in WSS magnitudes. Peak WSS was in the range of 47.5-130 dyne/cm[2] at the inflow and outflow tracts, but were much smaller, in the range of 4-11 dyne/cm[2], in the mid-ventricular segment. Due to very low Reynolds number and the highly viscous environment, intraventricular pressure gradients were high, suggesting substantial energy losses of flow through the heart.}, }
@article {pmid31431815, year = {2019}, author = {Rackus, DG and Riedel-Kruse, IH and Pamme, N}, title = {"Learning on a chip:" Microfluidics for formal and informal science education.}, journal = {Biomicrofluidics}, volume = {13}, number = {4}, pages = {041501}, pmid = {31431815}, issn = {1932-1058}, abstract = {Microfluidics is a technique for the handling of small volumes of liquids on the order of picoliters to nanoliters and has impact for miniaturized biomedical science and fundamental research. Because of its multi- and interdisciplinary nature (i.e., combining the fields of biology, chemistry, physics, and engineering), microfluidics offers much potential for educational applications, both at the university level as well as primary and secondary education. Microfluidics is also an ideal "tool" to enthuse and educate members of the general public about the interdisciplinary aspects of modern sciences, including concepts of science, technology, engineering, and mathematics subjects such as (bio)engineering, chemistry, and biomedical sciences. Here, we provide an overview of approaches that have been taken to make microfluidics accessible for formal and informal learning. We also point out future avenues and desired developments. At the extreme ends, we can distinguish between projects that teach how to build microfluidic devices vs projects that make various microscopic phenomena (e.g., low Reynolds number hydrodynamics, microbiology) accessible to learners and the general public. Microfluidics also enables educators to make experiments low-cost and scalable, and thereby widely accessible. Our goal for this review is to assist academic researchers working in the field of microfluidics and lab-on-a-chip technologies as well as educators with translating research from the laboratory into the lecture hall, teaching laboratory, or public sphere.}, }
@article {pmid31421603, year = {2019}, author = {Hayat, T and Aslam, N and Ijaz Khan, M and Imran Khan, M and Alsaedi, A}, title = {MHD peristaltic motion of Johnson-Segalman fluid in an inclined channel subject to radiative flux and convective boundary conditions.}, journal = {Computer methods and programs in biomedicine}, volume = {180}, number = {}, pages = {104999}, doi = {10.1016/j.cmpb.2019.104999}, pmid = {31421603}, issn = {1872-7565}, mesh = {Algorithms ; Body Fluids/physiology ; Elasticity ; Humans ; *Hydrodynamics ; *Models, Biological ; Peristalsis/*physiology ; Rheology ; }, abstract = {BACKGROUND: In abundant of a digestive tract like smooth muscle tissue, human gastrointestinal tract contracts in sequence to generate a peristaltic wave, which pushes a food along the tract. The peristaltic motion contains circular relaxation smooth muscles, then their shrinkage (contraction) behind the chewed material to keep it from moving backward, then longitudinal contraction to shove it ahead. Therefore, we have conducted a theoretical investigation on peristaltic transport in flow of Johnson-Segalman liquid subject to inclined magnetic field. The energy equation is developed with extra heat transport assumptions like thermal radiative flux and dissipation. The channel walls are heated convectively.<br><br>METHODS: Dimensionless problems subject to small Reynolds number and long wavelength are tackled. Perturbation technique is implemented for small Weissenberg number.<br><br>RESULTS: The physical importance of involved parameters that directly affect the heat transfer rate temperature and velocity. The pertinent variables are amplitude ratio, wave number, Reynolds number, Hartman number, Prandtl number, Weissenberg number, thermal radiative heat flux, Biot number, elasticity variables and Froude number are graphically discussed. The obtained outcome shows that the velocity field increases against higher values of elasticity variables but velocity the material decays through higher fluid parameter. Temperature field declines through higher Hartman number. Furthermore, it is also examined that the heat transfer rate decays against rising Hartman number.<br><br>CONCLUSIONS: The impact of complaint walls on radiative peristaltic transport of Johnson-Segalman liquid in symmetric channel subject to inclined angle. The influence of Johnson-Segalman variable on the velocity field shows decreasing behavior. Velocity also declines against larger Hartman number. Temperature and heat transfer rate boosts through rising values of E1 E2 while decays versus larger E3. Furthermore, reduction in heat transfer coefficient is observed when the values of &#x3b1; and Br are increased.}, }
@article {pmid31421600, year = {2019}, author = {Tanveer, A and Khan, M and Salahuddin, T and Malik, MY}, title = {Numerical simulation of electroosmosis regulated peristaltic transport of Bingham nanofluid.}, journal = {Computer methods and programs in biomedicine}, volume = {180}, number = {}, pages = {105005}, doi = {10.1016/j.cmpb.2019.105005}, pmid = {31421600}, issn = {1872-7565}, mesh = {*Electroosmosis ; Hydrodynamics ; Models, Statistical ; *Nanoparticles ; Peristalsis/*physiology ; Rheology ; Solutions/chemistry ; Thermal Conductivity ; }, abstract = {The effects of slip condition and Joule heating on the peristaltic flow of Bingham nanofluid are investigated. The flow is taken in a porous channel with elastic walls. Mathematical formulation is presented under the assumption of long wavelength and small Reynolds number. The transformed equations for the flow are solved to seek values for the nanoparticles velocity, concentration and temperature along the channel length. Graphs are plotted to evaluate the behavior of various physical parameters on flow quantities in both slip and no-slip cases. The main features of the physical parameters are highlighted on the inclined non uniform channel. The results show an increment in velocity with rise in inclination and porosity while it reduces with magnetic field. Moreover, nanofluid favors the heat transfer and decline the concentration.}, }
@article {pmid31417749, year = {2019}, author = {Lambert, WB and Stanek, MJ and Gurka, R and Hackett, EE}, title = {Leading-edge vortices over swept-back wings with varying sweep geometries.}, journal = {Royal Society open science}, volume = {6}, number = {7}, pages = {190514}, pmid = {31417749}, issn = {2054-5703}, abstract = {Micro air vehicles are used in a myriad of applications, such as transportation and surveying. Their performance can be improved through the study of wing designs and lift generation techniques including leading-edge vortices (LEVs). Observation of natural fliers, e.g. birds and bats, has shown that LEVs are a major contributor to lift during flapping flight, and the common swift (Apus apus) has been observed to generate LEVs during gliding flight. We hypothesize that nonlinear swept-back wings generate a vortex in the leading-edge region, which can augment the lift in a similar manner to linear swept-back wings (i.e. delta wing) during gliding flight. Particle image velocimetry experiments were performed in a water flume to compare flow over two wing geometries: one with a nonlinear sweep (swift-like wing) and one with a linear sweep (delta wing). Experiments were performed at three spanwise planes and three angles of attack at a chord-based Reynolds number of 26 000. Streamlines, vorticity, swirling strength, and Q-criterion were used to identify LEVs. The results show similar LEV characteristics for delta and swift-like wing geometries. These similarities suggest that sweep geometries other than a linear sweep (i.e. delta wing) are capable of creating LEVs during gliding flight.}, }
@article {pmid31411455, year = {2020}, author = {Brown, AI and Sivak, DA}, title = {Theory of Nonequilibrium Free Energy Transduction by Molecular Machines.}, journal = {Chemical reviews}, volume = {120}, number = {1}, pages = {434-459}, doi = {10.1021/acs.chemrev.9b00254}, pmid = {31411455}, issn = {1520-6890}, abstract = {Biomolecular machines are protein complexes that convert between different forms of free energy. They are utilized in nature to accomplish many cellular tasks. As isothermal nonequilibrium stochastic objects at low Reynolds number, they face a distinct set of challenges compared with more familiar human-engineered macroscopic machines. Here we review central questions in their performance as free energy transducers, outline theoretical and modeling approaches to understand these questions, identify both physical limits on their operational characteristics and design principles for improving performance, and discuss emerging areas of research.}, }
@article {pmid31406979, year = {2019}, author = {Berg, O and Singh, K and Hall, MR and Schwaner, MJ and Müller, UK}, title = {Thermodynamics of the Bladderwort Feeding Strike-Suction Power from Elastic Energy Storage.}, journal = {Integrative and comparative biology}, volume = {59}, number = {6}, pages = {1597-1608}, doi = {10.1093/icb/icz144}, pmid = {31406979}, issn = {1557-7023}, mesh = {Biomechanical Phenomena ; Energy Transfer/*physiology ; *Food Chain ; Lamiales/*physiology ; Thermodynamics ; }, abstract = {The carnivorous plant bladderwort exemplifies the use of accumulated elastic energy to power motion: respiration-driven pumps slowly load the walls of its suction traps with elastic energy (∼1 h). During a feeding strike, this energy is released suddenly to accelerate water (∼1 ms). However, due to the traps' small size and concomitant low Reynolds number, a significant fraction of the stored energy may be dissipated as viscous friction. Such losses and the mechanical reversibility of Stokes flow are thought to degrade the feeding success of other suction feeders in this size range, such as larval fish. In contrast, triggered bladderwort traps are generally successful. By mapping the energy budget of a bladderwort feeding strike, we illustrate how this smallest of suction feeders can perform like an adult fish.}, }
@article {pmid31394810, year = {2019}, author = {Alazzam, A and Al-Khaleel, M and Riahi, MK and Mathew, B and Gawanmeh, A and Nerguizian, V}, title = {Dielectrophoresis Multipath Focusing of Microparticles through Perforated Electrodes in Microfluidic Channels.}, journal = {Biosensors}, volume = {9}, number = {3}, pages = {}, pmid = {31394810}, issn = {2079-6374}, support = {CIRA-2019-014//Khalifa University of Science, Technology and Research/ ; }, mesh = {Biosensing Techniques ; Electrodes ; Electrophoresis/methods ; Microfluidics/instrumentation/*methods ; *Models, Theoretical ; Particle Size ; Polystyrenes/analysis ; Silicon Dioxide/analysis ; }, abstract = {This paper presents focusing of microparticles in multiple paths within the direction of the flow using dielectrophoresis. The focusing of microparticles is realized through partially perforated electrodes within the microchannel. A continuous electrode on the top surface of the microchannel is considered, while the bottom side is made of a circular meshed perforated electrode. For the mathematical model of this microfluidic channel, inertia, buoyancy, drag and dielectrophoretic forces are brought up in the motion equation of the microparticles. The dielectrophoretic force is accounted for through a finite element discretization taking into account the perforated 3D geometry within the microchannel. An ordinary differential equation is solved to track the trajectories of the microparticles. For the case of continuous electrodes using the same mathematical model, the numerical simulation shows a very good agreement with the experiments, and this confirms the validation of focusing of microparticles within the proposed perforated electrode microchannel. Microparticles of silicon dioxide and polystyrene are used for this analysis. Their initial positions and radius, the Reynolds number, and the radius of the pore in perforated electrodes mainly conduct microparticles trajectories. Moreover, the radius of the pore of perforated electrode is the dominant factor in the steady state levitation height.}, }
@article {pmid31386484, year = {2019}, author = {Samanta, T and Tian, H and Nakariakov, VM}, title = {Evidence for Vortex Shedding in the Sun's Hot Corona.}, journal = {Physical review letters}, volume = {123}, number = {3}, pages = {035102}, doi = {10.1103/PhysRevLett.123.035102}, pmid = {31386484}, issn = {1079-7114}, abstract = {Vortex shedding is an oscillating flow that is commonly observed in fluids due to the presence of a blunt body in a flowing medium. Numerical simulations have shown that the phenomenon of vortex shedding could also develop in the magnetohydrodynamic (MHD) domain. The dimensionless Strouhal number, the ratio of the blunt body diameter to the product of the period of vortex shedding and the speed of a flowing medium, is a robust indicator for vortex shedding, and, generally of the order of 0.2 for a wide range of Reynolds number. Using an observation from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we report a wavelike or oscillating plasma flow propagating upward against the Sun's gravitational force. A newly formed shrinking loop in the postflare region possibly generates the oscillation of the upflow in the wake of the hot and dense loop through vortex shedding. The computed Strouhal number is consistent with the prediction from previous MHD simulations. Our observation suggests the possibility of vortex shedding in the solar corona.}, }
@article {pmid31382385, year = {2019}, author = {Yu, X and Li, Y and Liu, Y and Yang, Y and Wu, Y}, title = {Flow Patterns of Viscoelastic Fracture Fluids in Porous Media: Influence of Pore-Throat Structures.}, journal = {Polymers}, volume = {11}, number = {8}, pages = {}, pmid = {31382385}, issn = {2073-4360}, support = {U1663206, 51704313, 51425406, 21706284//National Natural Science Foundation of China/ ; 18CX02028A, 24720182146A//Fundamental Research Funds for the Central Universities/ ; }, abstract = {Viscoelastic surfactant (VES) fluid and hydrolyzed polyacryamide (HPAM) solution are two of the most common fracturing fluids used in the hydraulic fracturing development of unconventional reservoirs. The filtration of fracturing fluids in porous media is mainly determined by the flow patterns in pore-throat structures. In this paper, three different microdevices analogue of porous media allow access to a large range of Deborah number (De) and concomitantly low Reynolds number (Re). Continuous pore-throat structures were applied to study the feedback effect of downstream structure on upstream flow of VES fluid and HPAM solution with Deborah (De) number from 1.11 to 146.4. In the infinite straight channel, flow patterns between VES fluids and HPAM solution were similar. However, as pore length shortened to 800 μm, flow field of VES fluid exhibited the triangle shape with double-peaks velocity patterns. The flow field of HPAM solution presented stable and centralized streamlines when Re was larger than 4.29 × 10[-2]. Additionally, when the pore length was further shortened to 400 μm, double-peaks velocity patterns were vanished for VES fluid and the stable convergent flow characteristic of HPAM solution was observed with all flow rates.}, }
@article {pmid31380864, year = {2019}, author = {Feng, X and Ren, Y and Hou, L and Tao, Y and Jiang, T and Li, W and Jiang, H}, title = {Tri-fluid mixing in a microchannel for nanoparticle synthesis.}, journal = {Lab on a chip}, volume = {19}, number = {17}, pages = {2936-2946}, doi = {10.1039/c9lc00425d}, pmid = {31380864}, issn = {1473-0189}, abstract = {It is becoming more difficult to use bulk mixing and bi-fluid micromixing in multi-step continuous-flow reactions, multicomponent reactions, and nanoparticle synthesis because they typically involve multiple reactants. To date, most micromixing studies, both passive and active, have focused on how to efficiently mix two fluids, while micromixing of three or more fluids together (multi-fluid mixing) has been rarely explored. This study is the first on tri-fluid mixing in microchannels. We investigated tri-fluid mixing in three microchannel models: a straight channel, a classical staggered herringbone mixing (SHM) channel, and a three-dimensional (3D) X-crossing microchannel. Numerical simulations and experiments were jointly conducted. A two-step experimental process was performed to determine the tri-fluid mixing efficiencies of these microchannels. We found that the SHM cannot significantly enhance mixing of three streams especially for a Reynolds number (Re) higher than 10. However, the 3D X-crossing channel based on splitting-and-recombination (SAR) showed effective tri-mixing performance over a wide Re range up to 275 (with a corresponding flow rate of 1972.5 μL min[-1]), thereby enabling high microchannel throughput. Furthermore, this tri-fluid micromixing process was used to synthesize a kind of Si-based nanoparticle. This achieved a narrower particle size distribution than traditional bulk mixing. Therefore, SAR-based tri-fluid mixing is an alternative for chemical and biochemical reactions where three reactants need to be mixed.}, }
@article {pmid31374925, year = {2019}, author = {Henein, C and Awwad, S and Ibeanu, N and Vlatakis, S and Brocchini, S and Tee Khaw, P and Bouremel, Y}, title = {Hydrodynamics of Intravitreal Injections into Liquid Vitreous Substitutes.}, journal = {Pharmaceutics}, volume = {11}, number = {8}, pages = {}, pmid = {31374925}, issn = {1999-4923}, support = {513211//NIHR Biomedical Research Centre/ ; }, abstract = {Intravitreal injections have become the cornerstone of retinal care and one of the most commonly performed procedures across all medical specialties. The impact of hydrodynamic forces of intravitreal solutions when injected into vitreous or vitreous substitutes has not been well described. While computational models do exist, they tend to underestimate the starting surface area of an injected bolus of a drug. Here, we report the dispersion profile of a dye bolus (50 µL) injected into different vitreous substitutes of varying viscosities, surface tensions, and volumetric densities. A novel 3D printed in vitro model of the vitreous cavity of the eye was designed to visualize the dispersion profile of solutions when injected into the following vitreous substitutes-balanced salt solution (BSS), sodium hyaluronate (HA), and silicone oils (SO)-using a 30G needle with a Reynolds number (Re) for injection ranging from approximately 189 to 677. Larger bolus surface areas were associated with faster injection speeds, lower viscosity of vitreous substitutes, and smaller difference in interfacial surface tensions. Boluses exhibited buoyancy when injected into standard S1000. The hydrodynamic properties of liquid vitreous substitutes influence the initial injected bolus dispersion profile and should be taken into account when simulating drug dispersion following intravitreal injection at a preclinical stage of development, to better inform formulations and performance.}, }
@article {pmid31370481, year = {2019}, author = {Gvozdić, B and Dung, OY and van Gils, DPM and Bruggert, GH and Alméras, E and Sun, C and Lohse, D and Huisman, SG}, title = {Twente mass and heat transfer water tunnel: Temperature controlled turbulent multiphase channel flow with heat and mass transfer.}, journal = {The Review of scientific instruments}, volume = {90}, number = {7}, pages = {075117}, doi = {10.1063/1.5092967}, pmid = {31370481}, issn = {1089-7623}, abstract = {A new vertical water tunnel with global temperature control and the possibility for bubble and local heat and mass injection has been designed and constructed. The new facility offers the possibility to accurately study heat and mass transfer in turbulent multiphase flow (gas volume fraction up to 8%) with a Reynolds-number range from 1.5 × 10[4] to 3 × 10[5] in the case of water at room temperature. The tunnel is made of high-grade stainless steel permitting the use of salt solutions in excess of 15% mass fraction. The tunnel has a volume of 300 l. The tunnel has three interchangeable measurement sections of 1 m height but with different cross sections (0.3 × 0.04 m[2], 0.3 × 0.06 m[2], and 0.3 × 0.08 m[2]). The glass vertical measurement sections allow for optical access to the flow, enabling techniques such as laser Doppler anemometry, particle image velocimetry, particle tracking velocimetry, and laser-induced fluorescent imaging. Local sensors can be introduced from the top and can be traversed using a built-in traverse system, allowing, for example, local temperature, hot-wire, or local phase measurements. Combined with simultaneous velocity measurements, the local heat flux in single phase and two phase turbulent flows can thus be studied quantitatively and precisely.}, }
@article {pmid31369336, year = {2019}, author = {O'Neill, G and Tolley, NS}, title = {The complexities of nasal airflow: theory and practice.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {127}, number = {5}, pages = {1215-1223}, doi = {10.1152/japplphysiol.01118.2018}, pmid = {31369336}, issn = {1522-1601}, mesh = {Humans ; *Inhalation ; *Models, Biological ; Turbinates/*physiology ; }, abstract = {The objective of this study was to investigate the effects of nasal valve area, valve stiffness, and turbinate region cross-sectional area on airflow rate, nasal resistance, flow limitation, and inspiratory "hysteresis" by the use of a mathematical model of nasal airflow. The model of O'Neill and Tolley (Clin Otolaryngol Allied Sci 13: 273-277, 1988) describing the effects of valve area and stiffness on the nasal pressure-flow relationship was improved by the incorporation of additional terms involving 1) airflow through the turbinate region, 2) the dependence of the flow coefficients for the valve and turbinate region on the Reynolds number, and 3) effects of unsteady flow. The model was found to provide a good fit for normal values for nasal resistance and for pressure-flow curves reported in the literature for both congested and decongested states. Also, by showing the relative contribution of the nasal valve and turbinate region to nasal resistance, the model sheds light in explaining the generally poor correlation between nasal resistance measurements and the results from acoustic rhinometry. Furthermore, by proposing different flow conditions for the acceleration and deceleration phases of inspiration, the model produces an inspiratory loop (commonly referred to as hysteresis) consistent with those reported in the literature. With simulation of nasal flaring, the magnitude of the loop, the nasal resistance, and flow limitation all show change similar to that observed in the experimental results.NEW &amp; NOTEWORTHY The present model provides considerable insight into some difficult conundrums in both clinical and technical aspects of nasal airflow. Also, the description of nasal airflow mechanics based on the Hagen-Poiseuille equation and Reynolds laminar-turbulent transition in long straight tubes, which has figured prominently in medical textbooks and journal articles for many years, is shown to be seriously in error at a fundamental level.}, }
@article {pmid31363000, year = {2019}, author = {R Ferreira, R and Fukui, H and Chow, R and Vilfan, A and Vermot, J}, title = {The cilium as a force sensor-myth versus reality.}, journal = {Journal of cell science}, volume = {132}, number = {14}, pages = {}, doi = {10.1242/jcs.213496}, pmid = {31363000}, issn = {1477-9137}, mesh = {Animals ; Biomechanical Phenomena ; Cilia/*physiology ; Humans ; Mechanotransduction, Cellular ; Organ Specificity ; Rheology ; }, abstract = {Cells need to sense their mechanical environment during the growth of developing tissues and maintenance of adult tissues. The concept of force-sensing mechanisms that act through cell-cell and cell-matrix adhesions is now well established and accepted. Additionally, it is widely believed that force sensing can be mediated through cilia. Yet, this hypothesis is still debated. By using primary cilia sensing as a paradigm, we describe the physical requirements for cilium-mediated mechanical sensing and discuss the different hypotheses of how this could work. We review the different mechanosensitive channels within the cilium, their potential mode of action and their biological implications. In addition, we describe the biological contexts in which cilia are acting - in particular, the left-right organizer - and discuss the challenges to discriminate between cilium-mediated chemosensitivity and mechanosensitivity. Throughout, we provide perspectives on how quantitative analysis and physics-based arguments might help to better understand the biological mechanisms by which cells use cilia to probe their mechanical environment.}, }
@article {pmid31359287, year = {2020}, author = {Jain, K}, title = {Transition to turbulence in an oscillatory flow through stenosis.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {19}, number = {1}, pages = {113-131}, doi = {10.1007/s10237-019-01199-1}, pmid = {31359287}, issn = {1617-7940}, mesh = {Blood Flow Velocity ; Computer Simulation ; Constriction, Pathologic ; Numerical Analysis, Computer-Assisted ; Pressure ; *Rheology ; }, abstract = {Onset of flow transition in a sinusoidally oscillating flow through a rigid, constant area circular pipe with a smooth sinusoidal obstruction in the center of the pipe is studied by performing direct numerical simulations, with resolutions close to the Kolmogorov microscales. The studied pipe is stenosed in the center with a 75% reduction in area in two distinct configurations-one that is symmetric to the axis of the parent pipe and the other that is offset by 0.05 diameters to introduce an eccentricity, which disturbs the flow thereby triggering the onset of flow transition. The critical Reynolds number at which the flow transitions to turbulence for a zero-mean oscillatory flow through a stenosis is shown to be nearly tripled in comparison with studies of pulsating unidirectional flow through the same stenosis. The onset of transition is further explored with three different flow pulsation frequencies resulting in a total of 90 simulations conducted on a supercomputer. It is found that the critical Reynolds number at which the oscillatory flow transitions is not affected by the pulsation frequencies. The locations of flow breakdown and re-stabilization post-stenosis are, however, respectively shifted closer to the stenosis throat with increasing pulsation frequencies. The results show that oscillatory physiological flows, while more stable, exhibit fluctuations due to geometric complexity and have implications in studies of dispersion and solute transport in the cerebrospinal fluid flow and understanding of pathological conditions.}, }
@article {pmid31345119, year = {2020}, author = {Krishnam, U and Sharma, V and Jha, PK}, title = {The Reynolds number modulated low frequency dynamical modes of aqueous medium embedded spherical virus and implications to detecting and killing viruses.}, journal = {Journal of biomolecular structure &amp; dynamics}, volume = {38}, number = {10}, pages = {3123-3129}, doi = {10.1080/07391102.2019.1648320}, pmid = {31345119}, issn = {1538-0254}, mesh = {*Viruses ; Water ; }, }
@article {pmid31342935, year = {2019}, author = {Liu, G and Xue, Q and Zheng, X}, title = {Phase-difference on seal whisker surface induces hairpin vortices in the wake to suppress force oscillation.}, journal = {Bioinspiration &amp; biomimetics}, volume = {14}, number = {6}, pages = {066001}, doi = {10.1088/1748-3190/ab34fe}, pmid = {31342935}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Biomimetics/*instrumentation ; Hydrodynamics ; Models, Biological ; Phoca/*physiology ; Vibrissae/*physiology ; }, abstract = {Seals are able to use their uniquely shaped whiskers to track hydrodynamic trails generated 30 s ago and detect hydrodynamic velocities as low as 245 [Formula: see text]m s[-1]. The high sensibility has long thought to be related to the wavy shape of the whiskers. This work revisited the hydrodynamics of a seal whisker model in a uniform flow, and discovered a new mechanism of seal whiskers in reducing self-induced noises, which is different from the long thought-of effect of the wavy shape. It was reported that the major and minor axes of the elliptical cross-sections of seal whisker are out of phase by approximately 180 degrees. Three-dimensional numerical simulations of laminar flow (Reynolds number range: 150-500) around seal-whisker-like cylinders were performed to examine the effect of the phase-difference on hydrodynamic forces and wake structures. It was found that the phase-difference induced hairpin vortices in the wake over a wide range of geometric and flow parameters (wavelength, wavy amplitude and Reynolds number), therefore substantially reducing lift-oscillations and self-induced noises. The formation mechanism of the hairpin vortices was analyzed and is discussed in details. The results provide valuable insights into an innovative vibration reduction and hydrodynamic sensing mechanism.}, }
@article {pmid31330717, year = {2019}, author = {Jian, X and Zhang, W and Deng, Q and Huang, Y}, title = {Turbulent lithosphere deformation in the Tibetan Plateau.}, journal = {Physical review. E}, volume = {99}, number = {6-1}, pages = {062122}, doi = {10.1103/PhysRevE.99.062122}, pmid = {31330717}, issn = {2470-0053}, abstract = {In this work, we show that the Tibetan Plateau deformation demonstrates turbulence-like statistics, e.g., spatial invariance across continuous scales. A dual-power-law behavior is evident to show the existence of two possible conservation laws for the enstrophy-like cascade in the range 500≲r≲2000km and kinetic-energy-like cascade in the range 50≲r≲500km. The measured second-order structure-function scaling exponents ζ(2) are similar to their counterparts in the Fourier scaling exponents observed in the atmosphere, where in the latter case the earth's rotation is relevant. The turbulent statistics observed here for nearly zero-Reynolds-number flow can be interpreted by the geostrophic turbulence theory. Moreover, the intermittency correction is recognized with an intensity close to that of the hydrodynamic turbulence of high-Reynolds-number turbulent flows, implying a universal scaling feature of very different turbulent flows. Our results not only shed new light on the debate regarding the mechanism of the Tibetan Plateau deformation but also lead to new challenges for the geodynamic modeling using Newton or non-Newtonian models because the observed turbulence-like features have to be taken into account.}, }
@article {pmid31318280, year = {2019}, author = {Dölger, J and Kiørboe, T and Andersen, A}, title = {Dense Dwarfs versus Gelatinous Giants: The Trade-Offs and Physiological Limits Determining the Body Plan of Planktonic Filter Feeders.}, journal = {The American naturalist}, volume = {194}, number = {2}, pages = {E30-E40}, doi = {10.1086/703656}, pmid = {31318280}, issn = {1537-5323}, mesh = {Animals ; Body Composition/*physiology ; Body Size ; Energy Metabolism ; Feeding Behavior/*physiology ; Models, Theoretical ; Predatory Behavior ; Zooplankton/*physiology ; }, abstract = {Most marine plankton have a high energy (carbon) density, but some are gelatinous with approximately 100 times more watery bodies. How do those distinctly different body plans emerge, and what are the trade-offs? We address this question by modeling the energy budget of planktonic filter feeders across life-forms, from micron-sized unicellular microbes such as choanoflagellates to centimeter-sized gelatinous tunicates such as salps. We find two equally successful strategies, one being small with high energy density (dense dwarf) and the other being large with low energy density (gelatinous giant). The constraint that forces large-but not small-filter feeders to be gelatinous is identified as a lower limit to the size-specific filter area, below which the energy costs lead to starvation. A further limit is found from the maximum size-specific motor force that restricts the access to optimum strategies. The quantified constraints are discussed in the context of other resource-acquisition strategies. We argue that interception feeding strategies can be accessed by large organisms only if they are gelatinous. On the other hand, organisms that use remote prey sensing do not need to be gelatinous, even if they are large.}, }
@article {pmid31315935, year = {2019}, author = {Samson, JE and Miller, LA and Ray, D and Holzman, R and Shavit, U and Khatri, S}, title = {A novel mechanism of mixing by pulsing corals.}, journal = {The Journal of experimental biology}, volume = {222}, number = {Pt 15}, pages = {}, doi = {10.1242/jeb.192518}, pmid = {31315935}, issn = {1477-9145}, mesh = {Animals ; Anthozoa/*physiology ; *Hydrodynamics ; Models, Theoretical ; Rheology ; Video Recording ; Water Movements ; }, abstract = {The dynamic pulsation of xeniid corals is one of the most fascinating phenomena observed in coral reefs. We quantify for the first time the flow near the tentacles of these soft corals, the active pulsations of which are thought to enhance their symbionts' photosynthetic rates by up to an order of magnitude. These polyps are approximately 1 cm in diameter and pulse at frequencies between approximately 0.5 and 1 Hz. As a result, the frequency-based Reynolds number calculated using the tentacle length and pulse frequency is on the order of 10 and rapidly decays as with distance from the polyp. This introduces the question of how these corals minimize the reversibility of the flow and bring in new volumes of fluid during each pulse. We estimate the Péclet number of the bulk flow generated by the coral as being on the order of 100-1000 whereas the flow between the bristles of the tentacles is on the order of 10. This illustrates the importance of advective transport in removing oxygen waste. Flow measurements using particle image velocimetry reveal that the individual polyps generate a jet of water with positive vertical velocities that do not go below 0.1 cm s[-1] and with average volumetric flow rates of approximately 0.71 cm[3] s[-1] Our results show that there is nearly continual flow in the radial direction towards the polyp with only approximately 3.3% back flow. 3D numerical simulations uncover a region of slow mixing between the tentacles during expansion. We estimate that the average flow that moves through the bristles of the tentacles is approximately 0.03 cm s[-1] The combination of nearly continual flow towards the polyp, slow mixing between the bristles, and the subsequent ejection of this fluid volume into an upward jet ensures the polyp continually samples new water with sufficient time for exchange to occur.}, }
@article {pmid31314164, year = {2019}, author = {Liao, P and Xing, L and Zhang, S and Sun, D}, title = {Magnetically Driven Undulatory Microswimmers Integrating Multiple Rigid Segments.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {15}, number = {36}, pages = {e1901197}, doi = {10.1002/smll.201901197}, pmid = {31314164}, issn = {1613-6829}, mesh = {Biosensing Techniques/methods ; Holography/methods ; Lasers ; Locomotion ; Microtechnology/*methods ; *Robotics ; }, abstract = {Mimicking biological locomotion strategies offers important possibilities and motivations for robot design and control methods. Among bioinspired microrobots, flexible microrobots exhibit remarkable efficiency and agility. These microrobots traditionally rely on soft material components to achieve undulatory propulsion, which may encounter challenges in design and manufacture including the complex fabrication processes and the interfacing of rigid and soft components. Herein, a bioinspired magnetically driven microswimmer that mimics the undulatory propulsive mechanism is proposed. The designed microswimmer consists of four rigid segments, and each segment is connected to the succeeding segment by joints. The microswimmer is fabricated integrally by 3D laser lithography without further assembly, thereby simplifying microrobot fabrication while enhancing structural integrity. Experimental results show that the microswimmer can successfully swim forward along guided directions via undulatory locomotion in the low Reynolds number (Re) regime. This work demonstrates for the first time that the flexible characteristic of microswimmers can be emulated by 3D structures with multiple rigid segments, which broadens possibilities in microrobot design. The proposed magnetically driven microswimmer can potentially be used in biomedical applications, such as medical diagnosis and treatment in precision medicine.}, }
@article {pmid31300927, year = {2019}, author = {Hoell, C and Löwen, H and Menzel, AM and Daddi-Moussa-Ider, A}, title = {Creeping motion of a solid particle inside a spherical elastic cavity: II. Asymmetric motion.}, journal = {The European physical journal. E, Soft matter}, volume = {42}, number = {7}, pages = {89}, pmid = {31300927}, issn = {1292-895X}, abstract = {An analytical method is proposed for computing the low-Reynolds-number hydrodynamic mobility function of a small colloidal particle asymmetrically moving inside a large spherical elastic cavity, the membrane of which is endowed with resistance toward shear and bending. In conjunction with the results obtained in the first part (A. Daddi-Moussa-Ider, H. Löwen, S. Gekle, Eur. Phys. J. E 41, 104 (2018)), in which the axisymmetric motion normal to the surface of an elastic cavity is investigated, the general motion for an arbitrary force direction can now be addressed. The elastohydrodynamic problem is formulated and solved using the classic method of images through expressing the hydrodynamic flow fields as a multipole expansion involving higher-order derivatives of the free-space Green's function. In the quasi-steady limit, we demonstrate that the particle self-mobility function of a particle moving tangent to the surface of the cavity is larger than that predicted inside a rigid stationary cavity of equal size. This difference is justified by the fact that a stationary rigid cavity introduces additional hindrance to the translational motion of the encapsulated particle, resulting in a reduction of its hydrodynamic mobility. Furthermore, the motion of the cavity is investigated, revealing that the translational pair (composite) mobility, which linearly couples the velocity of the elastic cavity to the force exerted on the solid particle, is solely determined by membrane shear properties. Our analytical predictions are favorably compared with fully-resolved computer simulations based on a completed-double-layer boundary integral method.}, }
@article {pmid31299253, year = {2019}, author = {Novelli, GL and Ferrari, LA and Vargas, GG and Loureiro, BV}, title = {A synergistic analysis of drag reduction on binary polymer mixtures containing guar gum.}, journal = {International journal of biological macromolecules}, volume = {137}, number = {}, pages = {1121-1129}, doi = {10.1016/j.ijbiomac.2019.07.042}, pmid = {31299253}, issn = {1879-0003}, mesh = {Acrylic Resins/*chemistry ; Feasibility Studies ; Galactans/*chemistry ; Mannans/*chemistry ; Molecular Weight ; *Motion ; Plant Gums/*chemistry ; Polyethylene Glycols/*chemistry ; Polysaccharides, Bacterial/chemistry ; Rheology ; Rotation ; Shear Strength ; }, abstract = {Drag reduction by the addition of polymer additives has been widely studied. However, there are only a few studies on binary polymer mixtures, here named blends. In this work, xanthan gum, polyacrylamide and poly(ethylene oxide) were associated with guar gum and drag reduction was used as a parameter to determine the synergistic interaction between polymers. The aim was to verify the relation of the synergy with the rigidity of the polymeric chains, the molecular weights and the magnitude of the molecular interactions between the studied polymers. To that end, several ratios of mixtures were tested at different Reynolds numbers in a rotational rheometer with double-gap concentric cylinders geometry. Finally, experiments were done to verify the behaviour of the blends over time at a fixed Reynolds number. From all these tests, it was documented that blends containing rigid chain polymers show positive synergism in the interaction in at least one of the ratios and that this interaction is more pronounced when the molecular weights are closer and intermolecular forces are stronger. It was also noted that, in general, blends are great substitutes for solutions containing only one type of polymer.}, }
@article {pmid31294955, year = {2019}, author = {Mazinani, S and Al-Shimmery, A and Chew, YMJ and Mattia, D}, title = {3D Printed Fouling-Resistant Composite Membranes.}, journal = {ACS applied materials &amp; interfaces}, volume = {11}, number = {29}, pages = {26373-26383}, doi = {10.1021/acsami.9b07764}, pmid = {31294955}, issn = {1944-8252}, abstract = {Fouling remains a long-standing unsolved problem that hinders the widespread use of membrane applications in industry. This article reports the use of numerical simulations coupled with extensive material synthesis and characterization to fabricate fouling-resistant 3D printed composite membranes. The membranes consist of a thin polyethersulfone selective layer deposited onto a 3D printed flat and double sinusoidal (wavy) support. Fouling and cleaning of the composite membranes were tested by using bovine serum albumin solution in a cross-flow ultrafiltration setup. The transmembrane pressure was regulated at 1 bar and the cross-flow Reynolds number (Re) varied between 400 and 1000. In comparison to the flat membrane, the wavy membrane showed superior performance in terms of pure water permeance (PWP) (10% higher) and permeance recovery ratio (87% vs 53%) after the first filtration cycle at Re = 1000. Prolong testing showed that the wavy membrane could retain approximately 87% of its initial PWP after 10 complete filtration cycles. This impressive fouling-resistant behavior is attributed to the localized fluid turbulence induced by the 3D printed wavy structure. These results show that not only the lifetime of membrane operations could be favorably extended but also the operational costs and environmental damage of membrane-based processes could also be significantly reduced.}, }
@article {pmid31283274, year = {2019}, author = {Chajwa, R and Menon, N and Ramaswamy, S}, title = {Kepler Orbits in Pairs of Disks Settling in a Viscous Fluid.}, journal = {Physical review letters}, volume = {122}, number = {22}, pages = {224501}, doi = {10.1103/PhysRevLett.122.224501}, pmid = {31283274}, issn = {1079-7114}, abstract = {We show experimentally that a pair of disks settling at negligible Reynolds number (∼10^{-4}) displays two classes of bound periodic orbits, each with transitions to scattering states. We account for these dynamics, at leading far-field order, through an effective Hamiltonian in which gravitational driving endows orientation with the properties of momentum. This treatment is successfully compared against the measured properties of orbits and critical parameters of transitions between types of orbits. We demonstrate a precise correspondence with the Kepler problem of planetary motion for a wide range of initial conditions, find and account for a family of orbits with no Keplerian analog, and highlight the role of orientation as momentum in the many-disk problem.}, }
@article {pmid31266939, year = {2019}, author = {Ren, Z and Hu, W and Dong, X and Sitti, M}, title = {Multi-functional soft-bodied jellyfish-like swimming.}, journal = {Nature communications}, volume = {10}, number = {1}, pages = {2703}, pmid = {31266939}, issn = {2041-1723}, mesh = {Animals ; Biomechanical Phenomena ; Elastomers/chemistry ; *Equipment Design ; Locomotion ; Magnetics/instrumentation ; Robotics/*instrumentation ; Scyphozoa/*physiology ; Swimming ; }, abstract = {The functionalities of the untethered miniature swimming robots significantly decrease as the robot size becomes smaller, due to limitations of feasible miniaturized on-board components. Here we propose an untethered jellyfish-inspired soft millirobot that could realize multiple functionalities in moderate Reynolds number by producing diverse controlled fluidic flows around its body using its magnetic composite elastomer lappets, which are actuated by an external oscillating magnetic field. We particularly investigate the interaction between the robot's soft body and incurred fluidic flows due to the robot's body motion, and utilize such physical interaction to achieve different predation-inspired object manipulation tasks. The proposed lappet kinematics can inspire other existing jellyfish-like robots to achieve similar functionalities at the same length and time scale. Moreover, the robotic platform could be used to study the impacts of the morphology and kinematics changing in ephyra jellyfish.}, }
@article {pmid31236828, year = {2019}, author = {Klusak, E and Quinlan, NJ}, title = {High-Resolution Measurements of Leakage Flow Inside the Hinge of a Large-scale Bileaflet Mechanical Heart Valve Hinge Model.}, journal = {Cardiovascular engineering and technology}, volume = {10}, number = {3}, pages = {469-481}, pmid = {31236828}, issn = {1869-4098}, mesh = {Blood Flow Velocity ; *Heart Valve Prosthesis ; Heart Valve Prosthesis Implantation/adverse effects/*instrumentation ; *Hemodynamics ; Humans ; Materials Testing ; Prosthesis Design ; Stress, Mechanical ; Thrombosis/etiology/physiopathology ; }, abstract = {PURPOSE: It is believed that non-physiological leakage flow through hinge gaps during diastole contributes to thrombus formation in Bileaflet Mechanical Heart Valves (BMHVs). Because of the small scale and difficulty of experimental access, fluid dynamics inside the hinge cavity has not yet been characterised in detail. The objective is to investigate small-scale structure inside the hinge experimentally, and gain insight into its role in stimulating cellular responses.<br><br>METHODS: An optically accessible scaled-up model of a BMHV hinge was designed and built, preserving dynamic similarity to a clinical BMHV. Particle Image Velocimetry (PIV) was used to visualize and quantify the flow fields inside the hinge at physiological Reynolds number and dimensionless pressure drop. The flow was measured at in-plane and out-of-plane spatial resolution of 32 and 86&#xa0;&#x3bc;m, respectively, and temporal resolution of [Formula: see text] RESULTS: Likely flow separation on the ventricular surface of the cavity has been observed for the first time, and is a source of unsteadiness and perhaps turbulence. The shear stress found in all planes exceeds the threshold of platelet activation, ranging up to 168 Pa.<br><br>CONCLUSIONS: The scale-up approach provided new insight into the nature of the hinge flow and enhanced understanding of its complexity. This study revealed flow features that may induce blood element damage.}, }
@article {pmid31236057, year = {2019}, author = {Cafiero, G and Vassilicos, JC}, title = {Non-equilibrium turbulence scalings and self-similarity in turbulent planar jets.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {475}, number = {2225}, pages = {20190038}, pmid = {31236057}, issn = {1364-5021}, abstract = {We study the self-similarity and dissipation scalings of a turbulent planar jet and the theoretically implied mean flow scalings. Unlike turbulent wakes where such studies have already been carried out (Dairay et al. 2015 J. Fluid Mech. 781, 166-198. (doi:10.1017/jfm.2015.493); Obligado et al. 2016 Phys. Rev. Fluids 1, 044409. (doi:10.1103/PhysRevFluids.1.044409)), this is a boundary-free turbulent shear flow where the local Reynolds number increases with distance from inlet. The Townsend-George theory revised by (Dairay et al. 2015 J. Fluid Mech. 781, 166-198. (doi:10.1017/jfm.2015.493)) is applied to turbulent planar jets. Only a few profiles need to be self-similar in this theory. The self-similarity of mean flow, turbulence dissipation, turbulent kinetic energy and Reynolds stress profiles is supported by our experimental results from 18 to at least 54 nozzle sizes, the furthermost location investigated in this work. Furthermore, the non-equilibrium dissipation scaling found in turbulent wakes, decaying grid-generated turbulence, various instances of periodic turbulence and turbulent boundary layers (Dairay et al. 2015 J. Fluid Mech. 781, 166-198. (doi:10.1017/jfm.2015.493); Vassilicos 2015 Annu. Rev. Fluid Mech. 95, 114. (doi:10.1146/annurev-fluid-010814-014637); Goto &amp; Vassilicos 2015 Phys. Lett. A 3790, 1144-1148. (doi:10.1016/j.physleta.2015.02.025); Nedic et al. 2017 Phys. Rev. Fluids 2, 032601. (doi:10.1103/PhysRevFluids.2.032601)) is also observed in the present turbulent planar jet and in the turbulent planar jet of (Antonia et al. 1980 Phys. Fluids 23, 863055. (doi:10.1063/1.863055)). Given these observations, the theory implies new mean flow and jet width scalings which are found to be consistent with our data and the data of (Antonia et al. 1980 Phys. Fluids 23, 863055. (doi:10.1063/1.863055)). In particular, it implies a hitherto unknown entrainment behaviour: the ratio of characteristic cross-stream to centreline streamwise mean flow velocities decays as the -1/3 power of streamwise distance in the region, where the non-equilibrium dissipation scaling holds.}, }
@article {pmid31229600, year = {2019}, author = {Garwood, RJ and Behnsen, J and Haysom, HK and Hunt, JN and Dalby, LJ and Quilter, SK and Maclaine, JS and Cox, JPL}, title = {Olfactory flow in the sturgeon is externally driven.}, journal = {Comparative biochemistry and physiology. Part A, Molecular &amp; integrative physiology}, volume = {235}, number = {}, pages = {211-225}, doi = {10.1016/j.cbpa.2019.06.013}, pmid = {31229600}, issn = {1531-4332}, mesh = {Animals ; Computer Simulation ; Fishes/*physiology ; Models, Anatomic ; Nasal Cavity/physiology ; Nose/*physiology ; *Odorants ; Smell/*physiology ; Swimming/physiology ; }, abstract = {Fluid dynamics plays an important part in olfaction. Using the complementary techniques of dye visualisation and computational fluid dynamics (CFD), we investigated the hydrodynamics of the nasal region of the sturgeon Huso dauricus. H. dauricus offers several experimental advantages, including a well-developed, well-supported, radial array (rosette) of visible-by-eye olfactory sensory channels. We represented these features in an anatomically accurate rigid model derived from an X-ray scan of the head of a preserved museum specimen. We validated the results from the CFD simulation by comparing them with data from the dye visualisation experiments. We found that flow through both the nasal chamber and, crucially, the sensory channels could be induced by an external flow (caused by swimming in vivo) at a physiologically relevant Reynolds number. Flow through the nasal chamber arises from the anatomical arrangement of the incurrent and excurrent nostrils, and is assisted by the broad, cartilage-supported, inner wall of the incurrent nostril. Flow through the sensory channels arises when relatively high speed flow passing through the incurrent nostril encounters the circular central support of the olfactory rosette, decelerates, and is dispersed amongst the sensory channels. Vortices within the olfactory flow may assist odorant transport to the sensory surfaces. We conclude that swimming alone is sufficient to drive olfactory flow in H. dauricus, and consider the implications of our results for the three other extant genera of sturgeons (Acipenser, Pseudoscaphirhynchus and Scaphirhynchus), and for other fishes with olfactory rosettes.}, }
@article {pmid31215548, year = {2019}, author = {Man, Y and Kanso, E}, title = {Morphological transitions of axially-driven microfilaments.}, journal = {Soft matter}, volume = {15}, number = {25}, pages = {5163-5173}, doi = {10.1039/c8sm02397b}, pmid = {31215548}, issn = {1744-6848}, mesh = {Actin Cytoskeleton/*metabolism ; Biomechanical Phenomena ; Elasticity ; *Models, Molecular ; }, abstract = {The interactions of microtubules with motor proteins are ubiquitous in cellular and sub-cellular processes that involve motility and cargo transport. In vitro motility assays have demonstrated that motor-driven microtubules exhibit rich dynamical behaviors from straight to curved configurations. Here, we theoretically investigate the dynamic instabilities of elastic filaments, with free-ends, driven by single follower forces that emulate the action of molecular motors. Using the resistive force theory at low Reynolds number, and a combination of numerical techniques with linear stability analysis, we show the existence of four distinct regimes of filament behavior, including a novel buckled state with locked curvature. These successive instabilities recapitulate the full range of experimentally-observed microtubule behavior, implying that neither structural nor actuation asymmetry are needed to elicit this rich repertoire of motion.}, }
@article {pmid31212518, year = {2019}, author = {He, G and Wang, J and Rinoshika, A}, title = {Orthogonal wavelet multiresolution analysis of the turbulent boundary layer measured with two-dimensional time-resolved particle image velocimetry.}, journal = {Physical review. E}, volume = {99}, number = {5-1}, pages = {053105}, doi = {10.1103/PhysRevE.99.053105}, pmid = {31212518}, issn = {2470-0053}, abstract = {The turbulent boundary layer flow measured by two-dimensional time-resolved particle image velocimetry is analyzed using the discrete orthogonal wavelet method. The Reynolds number of the turbulent boundary layer based on the friction velocity is Re_{τ}=235. The flow field is decomposed into a number of wavelet levels which have different characteristic scales. The velocity statistics and coherent structures at different wavelet levels are investigated. It is found that the fluctuation intensities and their peak locations differ for varying scales. The proper orthogonal decomposition (POD) of different wavelet components reveals a cascade of scales of coherent structures, especially the small-scale ones that are usually difficult to be identified in POD modes of the undecomposed flow field. The interactions among the scales are investigated in terms of large-scale amplitude modulations of the small-scale structures. In previous studies the velocity fluctuations are separated into two parts, the large scale and the small scale, divided usually by the boundary layer thickness. In the present study, however, the scales smaller than the boundary layer thickness are further separated. Therefore, the modulation analysis is a refined investigation that differentiates the modulation effects on separated small scales. The results reveal that the modulation effects vary among the small scales.}, }
@article {pmid31212497, year = {2019}, author = {Puljiz, M and Menzel, AM}, title = {Displacement field around a rigid sphere in a compressible elastic environment, corresponding higher-order Faxén relations, as well as higher-order displaceability and rotateability matrices.}, journal = {Physical review. E}, volume = {99}, number = {5-1}, pages = {053002}, doi = {10.1103/PhysRevE.99.053002}, pmid = {31212497}, issn = {2470-0053}, abstract = {An efficient route to the displacement field around a rigid spherical inclusion in an infinitely extended homogeneous elastic medium is presented in a slightly alternative way when compared to some common textbook methods. Moreover, two Faxén relations of next-higher order beyond the stresslet are calculated explicitly for compressible media. They quantify higher-order moments involving the force distribution on a rigid spherical particle in a deformed elastic medium. As a consequence, additional contributions to the distortions of the deformed elastic medium are identified that are absent to lower order. Furthermore, the displaceability and rotateability matrices for an ensemble of rigid spheres are calculated up to (including) sixth order in inverse particle separation distance. These matrices describe the interactions mediated between the rigid embedded particles by the elastic environment. In this way, additional coupling effects are identified that are absent to lower order, particularly when rotations and torques are involved. All methods and results can formally be transferred to the corresponding case of incompressible hydrodynamic low-Reynolds-number Stokes flow by considering the limit of an incompressible environment. The roles of compressibility of the embedding medium and of the here additionally derived higher-order contributions are highlighted by some selected example configurations.}, }
@article {pmid31212461, year = {2019}, author = {Nie, D and Lin, J}, title = {Discontinuity in the sedimentation system with two particles having different densities in a vertical channel.}, journal = {Physical review. E}, volume = {99}, number = {5-1}, pages = {053112}, doi = {10.1103/PhysRevE.99.053112}, pmid = {31212461}, issn = {2470-0053}, abstract = {The two-dimensional lattice Boltzmann method was used to numerically study a sedimentation system with two particles having different densities in a vertical channel for Galileo numbers in the range of 5≤Ga≤15 (resulting in a Reynolds number, based on the settling velocity, approximately ranging between 0.6 and 7). Two types of periodic motion, differing from each other in terms of the size of the limit cycle, the magnitude of the time period, and their changes upon increasing the density difference between particles, are identified depending on whether there is a wake effect. The most prominent features of this system are discontinuous changes in the settling velocity (6.7≤Ga<9.7) and time period of oscillation (10.5≤Ga≤15) at a critical value of the density difference between particles. The first discontinuity results in an abrupt increase in the Reynolds number, associated with a Hopf bifurcation without the presence of vortex shedding. The second discontinuity is accompanied by the disappearance of "abnormal rotation" (referring to the situation in which a particle appears to roll up a wall when settling) of the heavy particle, which directly results from a sharp increase in the amplitude of oscillation induced by the enhanced wake effect at another critical density difference between particles. The wall effects on these discontinuous changes were also examined.}, }
@article {pmid31212451, year = {2019}, author = {Wang, L and Tian, FB}, title = {Numerical simulation of flow over a parallel cantilevered flag in the vicinity of a rigid wall.}, journal = {Physical review. E}, volume = {99}, number = {5-1}, pages = {053111}, doi = {10.1103/PhysRevE.99.053111}, pmid = {31212451}, issn = {2470-0053}, abstract = {Flow over a parallel cantilevered flag in the vicinity of a rigid wall is numerically studied using an immersed boundary-lattice Boltzmann method (IB-LBM) in two-dimensional domain, where the dynamics of the fluid and structure are, respectively, solved by the LBM and a finite-element method (FEM), with a penalty IB to handle the fluid-structure interaction (FSI). Specifically, a benchmark case considering a plate attached to the downstream of a stationary cylinder is first conducted to validate the current solver. Then, the wall effects on the flag are systemically studied, considering the effects of off-wall distance, structure-to-fluid mass ratio, bending rigidity, and Reynolds number. Three flapping modes, including symmetrical flapping, asymmetrical flapping, and chaotic flapping, along with a steady state are observed in the simulations. It is found that the flag is vibrating or stable with a mean angle inclined in the fluid when it is mounted in the vicinity of a rigid wall. The mean inclined angle first increases in the steady state and then decreases in the unsteady state with the off-wall distance. In the unsteady regime, the dependency of the inclined angle on the off-wall distance is similar to that of the gradient of the fluid velocity. In addition, the rigid wall near the flag decreases the lift and drag generation and further stabilizes the flag-fluid system. Contrarily, the flag inertia destabilizes the flag, and large flag inertia induces chaotic vibrating modes.}, }
@article {pmid31207995, year = {2019}, author = {Zhang, H and Li, X and Chuai, R and Zhang, Y}, title = {Chaotic Micromixer Based on 3D Horseshoe Transformation.}, journal = {Micromachines}, volume = {10}, number = {6}, pages = {}, pmid = {31207995}, issn = {2072-666X}, support = {20180550950//Natural Science Foundation of Liaoning/ ; }, abstract = {To improve the efficiency of mixing under laminar flow with a low Reynolds number (Re), a novel three-dimensional Horseshoe Transformation (3D HT) was proposed as the basis for the design of a micromixer. Compared with the classical HT, the Lyapunov exponent of the 3D HT, which was calculated based on a symbolic dynamic system, proved the chaotic enhancement. Based on the 3D HT, a micromixer with a mixing length of 12 mm containing six mixing units was obtained by sequentially applying "squeeze", "stretch", "twice fold", "inverse transformation", and "intersection" operations. Numerical simulation and Peclet Number (Pe) calculations indicated that when the squeeze amplitude 0 < α < 1/2, 0 < β < 1/2, the stretch amplitude γ > 4, and Re ≥ 1, the mass transfer in the mixer was dominated by convective diffusion induced by chaotic flow. When Re = 10, at the outlet of the mixing chamber, the simulated mixing index was 96.4%, which was far less than the value at Re = 0.1 (σ = 0.041). Microscope images of the mixing chamber and the curve trend of pH buffer solutions obtained from a mixing experiment were both consistent with the results of the simulation. When Re = 10, the average mixing index of the pH buffer solutions was 91.75%, which proved the excellent mixing efficiency of the mixer based on the 3D HT.}, }
@article {pmid31206776, year = {2019}, author = {Belut, E and Sánchez Jiménez, A and Meyer-Plath, A and Koivisto, AJ and Koponen, IK and Jensen, AC&#xd8; and MacCalman, L and Tuinman, I and Fransman, W and Domat, M and Bivolarova, M and van Tongeren, M}, title = {Indoor dispersion of airborne nano and fine particles: Main factors affecting spatial and temporal distribution in the frame of exposure modeling.}, journal = {Indoor air}, volume = {29}, number = {5}, pages = {803-816}, doi = {10.1111/ina.12579}, pmid = {31206776}, issn = {1600-0668}, mesh = {Aerosols/*analysis ; Air Pollutants/*analysis ; Air Pollution, Indoor/*analysis ; Environmental Monitoring ; Humans ; Models, Theoretical ; Nanoparticles ; Particle Size ; Spatio-Temporal Analysis ; Ventilation ; }, abstract = {A particle exposure experiment inside a large climate-controlled chamber was conducted. Data on spatial and temporal distribution of nanoscale and fine aerosols in the range of mobility diameters 8-600 nm were collected with high resolution, for sodium chloride, fluorescein sodium, and silica particles. Exposure scenarios studied included constant and intermittent source emissions, different aggregation conditions, high (10 h[-1]) and low (3.5 h[-1]) air exchange rates (AERs) corresponding to chamber Reynolds number, respectively, equal to 1 × 10[5] and 3 × 10[4] . Results are presented and analyzed to highlight the main determinants of exposure and to determine whether the assumptions underlying two-box models hold under various scenarios. The main determinants of exposure found were the source generation rate and the ventilation rate. The effect of particles nature was indiscernible, and the decrease of airborne total number concentrations attributable to surface deposition was estimated lower than 2% when the source was active. A near-field/far-field structure of aerosol concentration was always observed for the AER = 10 h[-1] but for AER = 3.5 h[-1] , a single-field structure was found. The particle size distribution was always homogeneous in space but a general shift of particle diameter (-8% to +16%) was observed between scenarios in correlation with the AER and with the source position, presumably largely attributable to aggregation.}, }
@article {pmid31186821, year = {2019}, author = {Aghilinejad, A and Aghaamoo, M and Chen, X}, title = {On the transport of particles/cells in high-throughput deterministic lateral displacement devices: Implications for circulating tumor cell separation.}, journal = {Biomicrofluidics}, volume = {13}, number = {3}, pages = {034112}, pmid = {31186821}, issn = {1932-1058}, abstract = {Deterministic lateral displacement (DLD), which takes advantage of the asymmetric bifurcation of laminar flow around the embedded microposts, has shown promising capabilities in separating cells and particles of different sizes. Growing interest in utilizing high-throughput DLD devices for practical applications, such as circulating tumor cell separation, necessitates employing higher flow rates in these devices, leading to operating in moderate to high Reynolds number (Re) regimes. Despite extensive research on DLD devices in the creeping regime, limited research has focused on the physics of flow, critical size of the device, and deformable cell behavior in DLD devices at moderate to high Re. In this study, the transport behavior of particles/cells is investigated in realistic high-throughput DLD devices with hundreds of microposts by utilizing multiphysics modeling. A practical formula is proposed for the prediction of the device critical size, which could serve as a design guideline for high-throughput DLD devices. Then, the complex hydrodynamic interactions between a deformable cell and DLD post arrays are investigated. A dimensionless index is utilized for comparing different post designs to quantify the cell-post interaction. It is shown that the separation performances in high-throughput devices are highly affected by Re as well as the micropost shapes. These findings can be utilized for the design and optimization of high-throughput DLD microfluidic devices.}, }
@article {pmid31185351, year = {2019}, author = {Tshumah-Mutingwende, RRMS and Takahashi, F}, title = {Physio-chemical effects of freshwaters on the dissolution of elementary mercury.}, journal = {Environmental pollution (Barking, Essex : 1987)}, volume = {252}, number = {Pt A}, pages = {627-636}, doi = {10.1016/j.envpol.2019.05.130}, pmid = {31185351}, issn = {1873-6424}, mesh = {Ecosystem ; Environmental Monitoring/methods ; Fresh Water/*chemistry ; Gold/analysis ; Humans ; Mercury/*analysis/chemistry ; Methylmercury Compounds/analysis ; Solubility ; Water Pollutants, Chemical/*analysis/chemistry ; }, abstract = {Elemental mercury (Hg[0]) is widely used by Artisanal and small-scale gold miners (ASGMs) to extract gold from ore. Due to the unavailability of appropriate waste disposal facilities, Hg[0]-rich amalgamation tailings are often discharged into nearby aquatic systems where the Hg[0] droplets settle in bottom sediment and sediment-water interfaces. Hg[0] dissolution and following biogeochemical transformations to methylmercury (MeHg) have been concerned owing to its potential risk to human health and the ecosystem. For reliable estimates of Hg exposure to human bodies using pollutant environmental fate and transport models, knowledge of the Hg[0] dissolution rate is important. However, only limited literature is available. Therefore, it was investigated in this study. Dissolution tests in a 'dark chamber' revealed that an increase in medium pH resulted in a decrease in the dissolution rate, whereas, a large Hg[0] droplet surface area (SA) and high Reynolds number (Re) resulted in a faster dissolution. A multivariate first order dissolution model of the form:kˆ=-7.9×10[-5][pH]+7.0×10[-4][logRe]+7.9×10[-4][SA]-2.5×10[-3] was proposed (adjusted R[2] = 0.99). The Breusch-Pagan and White heteroscedasticity tests revealed that the model residuals are homoscedastic (p-value = 0.05) at the 5% significance level. Parameter sensitivity analysis suggests that slow mercury dissolution from the Hg[0] droplets to aquatic systems might mask emerging environmental risk of mercury. Even after mercury usage in ASGM is banned, mercury dissolution and following contamination will continue for about 40 years or longer owing to previously discharged Hg[0] droplets.}, }
@article {pmid31176976, year = {2019}, author = {Almohammadi, H and Amirfazli, A}, title = {Droplet impact: Viscosity and wettability effects on splashing.}, journal = {Journal of colloid and interface science}, volume = {553}, number = {}, pages = {22-30}, doi = {10.1016/j.jcis.2019.05.101}, pmid = {31176976}, issn = {1095-7103}, abstract = {HYPOTHESES: The wettability of a surface affects the splashing behavior of a droplet upon impact onto a surface only when surface exhibits either a very high or a very low contact angle. Viscosity affects the splashing threshold in a non-monotony way.<br><br>EXPERIMENTS: To examine the roles of drop viscosity and surface wettability on splashing, a wide range of liquid viscosities (1-100 cSt), surface wettabilities (from hydrophilic to hydrophobic), drop velocities (0.5-3.3&#x202f;m/s), and liquid surface tensions (&#x223c;20 and 70 mN/m) were examined. High speed imaging was used.<br><br>FINDINGS: Wettability affects the splashing threshold at very extreme limits of the wettability i.e. at very high or very low contact angle values; however, the wettability effect is less prominent on spreading-splashing regime map. For drops of any surface tension impacting surfaces with any wettability, an increase in viscosity (up to &#x223c;5 cSt or Reynolds number of 2000) promotes splashing; whereas using liquids with viscosities larger than 5 cSt, suppress splashing. We explained such behaviors using evolution of the lamella rim, dynamic contact angle, and velocity of the expanding lamella. Finally, to predict the splashing, we developed a general empirical relationship which explains all of ours, and previously reported data.}, }
@article {pmid31167483, year = {2019}, author = {Siddiqui, AA and Turkyilmazoglu, M}, title = {A New Theoretical Approach of Wall Transpiration in the Cavity Flow of the Ferrofluids.}, journal = {Micromachines}, volume = {10}, number = {6}, pages = {}, pmid = {31167483}, issn = {2072-666X}, abstract = {An idea of permeable (suction/injection) chamber is proposed in the current work to control the secondary vortices appearing in the well-known lid-driven cavity flow by means of the water based ferrofluids. The Rosensweig model is conveniently adopted for the mathematical analysis of the physical problem. The governing equation of model is first transformed into the vorticity transport equation. A special finite difference method in association with the successive over-relaxation method (SOR) is then employed to numerically simulate the flow behavior. The effects of intensity of magnetic source (controlled by the Stuart number), aspect ratio of the cavity, rate of permeability (i.e., α p = V 0 U), ratio of speed of suction/injection V 0 to the sliding-speed U of the upper wall of a cavity, and Reynolds number on the ferrofluid in the cavity are fully examined. It is found that the secondary vortices residing on the lower wall of the cavity are dissolved by the implementation of the suction/injection chamber. Their character is dependent on the rate of permeability. The intensity of magnetic source affects the system in such a way to alter the flow and to transport the fluid away from the magnetic source location. It also reduces the loading effects on the walls of the cavity. If the depth of cavity (or the aspect ratio) is increased, the secondary vortices join together to form a single secondary vortex. The number of secondary vortices is shown to increase if the Reynolds number is increased for both the clear fluid as well as the ferrofluids. The suction and injection create resistance in settlement of solid ferroparticles on the bottom. The results obtained are validated with the existing data in the literature and satisfactory agreement is observed. The presented problem may find applications in biomedical, pharmaceutical, and engineering industries.}, }
@article {pmid31165744, year = {2019}, author = {Arumuru, V and Dash, JN and Dora, D and Jha, R}, title = {Vortex Shedding Optical Flowmeter based on Photonic Crystal Fiber.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {8313}, pmid = {31165744}, issn = {2045-2322}, abstract = {In the present work we propose a PCF (photonic crystal fiber) based Modal interferometer detector for sensing low flow velocity by detecting the frequency of vortices shed from a bluff body. The proposed novel design encapsulates the interferometric arm inside a metal casing to protect the sensor from harsh process fluids. The characterization of the developed probe is conducted under no flow conditions using a piezo actuator to evaluate the sensor response over wide frequency range (0-500 Hz). The developed sensors shows a reasonably flat response in the tested frequency range. Experiments are conducted by employing the developed sensor behind a bluff body of a vortex flowmeter to measure the frequency of the shed vortices and hence, the fluid flow rate. The low flow rate sensitivity of the vortex flowmeter is improved many folds by using the present sensor and the minimum Reynolds number detected is Re = 5000. A linear trend is observed between the frequency of the vortices and the flow velocity which is desirable for fluid flow measurement. The PCF based interferometric sensor with metal encapsulation makes the vortex flowmeter, sensitive at low flow rates, robust and economical to be used in industrial application.}, }
@article {pmid31153354, year = {2019}, author = {Farouk, B and Antao, DS and Hasan, N}, title = {Acoustically driven oscillatory flow fields in a cylindrical resonator at resonance.}, journal = {The Journal of the Acoustical Society of America}, volume = {145}, number = {5}, pages = {2932}, doi = {10.1121/1.5097594}, pmid = {31153354}, issn = {1520-8524}, abstract = {Generation and development of acoustic waves in an air-filled cylindrical resonator driven by a conical electro-mechanical speaker are studied experimentally and simulated numerically. The driving frequencies of the speaker are chosen such that a standing wave field is produced at each chosen frequency in the resonator. The amplitude of the generated acoustic (pressure) waves is measured along the axis of the resonator by a fast response piezo-resistive pressure transducer, while the radial distribution of the oscillatory axial velocities is measured at the corresponding velocity anti-node locations by a constant temperature hot-film anemometer. For the cases studied, the acoustic Reynolds number ranged between 20.0 and 60.0 and the flow fields were always found to be in the laminar regime. The flow field in the resonator is also simulated by a high-fidelity numerical scheme with low numerical diffusion. Formation of the standing wave and quasi-steady acoustic streaming are numerically simulated by solving the fully compressible form of the Navier-Stokes equations. The effects of the sound field intensity (i.e., input power to the speaker) and driving frequency on the standing wave field and the resultant formation process of the streaming structures are also investigated.}, }
@article {pmid31144946, year = {2019}, author = {Kaneda, Y and Yamamoto, Y and Tsuji, Y}, title = {Linear Response Theory for One-Point Statistics in the Inertial Sublayer of Wall-Bounded Turbulence.}, journal = {Physical review letters}, volume = {122}, number = {19}, pages = {194502}, doi = {10.1103/PhysRevLett.122.194502}, pmid = {31144946}, issn = {1079-7114}, abstract = {The idea of linear response theory well known in the statistical mechanics for thermal equilibrium systems is applied to one-point statistics in the inertial sublayer of wall-bounded turbulence (WBT). A close analogy between the energy transfer from large to small scales in isotropic turbulence and the momentum transfer in the wall normal direction in WBT plays a key role in the application. The application gives estimates of the influence of the finite Reynolds number on the statistics. The estimates are consistent with data by high-resolution direct numerical simulations of turbulent channel flow.}, }
@article {pmid31140495, year = {2019}, author = {Fadel, M and Daurelle, JV and Fourmond, V and Vicente, J}, title = {A new electrochemical cell with a uniformly accessible electrode to study fast catalytic reactions.}, journal = {Physical chemistry chemical physics : PCCP}, volume = {21}, number = {23}, pages = {12360-12371}, doi = {10.1039/c9cp01487j}, pmid = {31140495}, issn = {1463-9084}, abstract = {The electrochemical study of fast catalytic reactions is limited by mass transport when using the conventional electrochemical cell with a rotating disk electrode (RDE). To overcome this issue, it is important to find a new device with improved transport properties that respects electrochemical constraints. We used numerical simulations of computational fluid dynamics to design a new electrochemical cell based on the so-called "jet flow" design for the kinetic studies of catalytic chemical reactions at the surface of an electrode. The new cell is characterized by a high, reliable and uniform mass transport over the electroactive part of its surface. We investigated the effects of the nozzle and the electrode diameters, the nozzle-electrode distance and the Reynolds number on the performance of the jet-electrode in the flow system. Through the optimization of the geometry of this jet electrode cell, we achieved a factor of 3 enhancement in transport compared to the rotating disk electrode. We succeeded in constructing the designed electrode, characterized it with electrochemical techniques, and found an excellent agreement between the transport properties deduced from the numerical simulations and those from the measurements.}, }
@article {pmid31137243, year = {2019}, author = {Maqbool, K and Shaheen, S and Siddiqui, AM}, title = {Effect of nano-particles on MHD flow of tangent hyperbolic fluid in a ciliated tube: an application to fallopian tube.}, journal = {Mathematical biosciences and engineering : MBE}, volume = {16}, number = {4}, pages = {2927-2941}, doi = {10.3934/mbe.2019144}, pmid = {31137243}, issn = {1551-0018}, mesh = {Cilia/*physiology ; Copper ; Electromagnetic Phenomena ; Fallopian Tube Diseases/therapy ; Fallopian Tubes/blood supply/*physiology ; Female ; Hemodynamics ; Hot Temperature/therapeutic use ; Humans ; *Hydrodynamics ; Magnetic Field Therapy/methods ; Mathematical Concepts ; Metal Nanoparticles ; Models, Biological ; Thrombosis/therapy ; }, abstract = {This study shows the effects of magnetic field and copper nanoparticles on the flow of tangent hyperbolic fluid (blood) through a ciliated tube (fallopian tube). The present study will be very helpful for those patients who are facing blood clotting in fallopian tube that may cause for infertility or cancer. The nanoparticles and magnetic field are very helpful to break the clots in blood flowing in fallopian tube. Since blood flows in fallopian tube due to ciliary movement, therefore medicines containing copper nanoparticles and magnetic field with radiation therapy help to improve the patient. Ciliary movement has a particular pattern of motion i.e., metachronal wavy motion which helps to fluid flow. For the forced convective MHD flow of tangent hyperbolic nano-fluid, momentum and energy equations are solved by the small Reynolds' number approximation and Adomian decomposition method by constructing the recursive relation of ADM and solved by software "MATHEMATICA". The effects of parameters such as nanoparticle volume fraction, Hartmann number, entropy generation and Bejan's number have been discussed through graphs plotted in software "MATHEMATICA". It is found that blood flow is accelerated and heat transfer enhancement is maximum in the presence of nano particles, also magnetic effects accelerates the blood flow and help to enhance the heat transfer whereas the presence of porous medium increases the fluid's velocity and reduce the transfer of heat through fluid flow.}, }
@article {pmid31123743, year = {2019}, author = {Wang, P and Zhang, Q and Wang, M and Yin, B and Hou, D and Zhang, Y}, title = {Atomistic insights into cesium chloride solution transport through the ultra-confined calcium-silicate-hydrate channel.}, journal = {Physical chemistry chemical physics : PCCP}, volume = {21}, number = {22}, pages = {11892-11902}, doi = {10.1039/c8cp07676f}, pmid = {31123743}, issn = {1463-9084}, abstract = {The transport of water and ions in the gel pores of calcium silicate hydrate (C-S-H) determines the durability of cement material. In this study, molecular dynamics was employed to investigate the capillary imbibition process of CsCl solution in the C-S-H channel. The advanced frontier of CsCl solution flow inside the C-S-H capillary shows a concave meniscus shape, which reflects the hydrophilic properties of the C-S-H substrate. Reynolds number calculations show that the transport process is laminar flow and dominated by viscous forces. The invading depth of the CsCl solution deviates from the theoretical prediction of the classic Lucas-Washburn (L-W) equation, but the modified theoretical equation, by incorporating the effect of slip length, dynamic contact angle, and effective viscosity into the L-W equation, can describe the penetration curve of the solution very well. The validity of our developed theoretical equation was confirmed by additional systems with different ion concentrations. In addition, the local structure of ions was analyzed to elucidate the effect of ion concentration on the transport process. The adsorption and accumulation of ions retard the transport process of water. With an increase in the ionic concentration, the effects of immobilization and cluster accumulation became more pronounced, further reducing the transport rate of water. This study provides fundamental insight into the transport behavior of liquid in the gel pores of cement-based material.}, }
@article {pmid31120757, year = {2019}, author = {Zhang, J and Liu, H and Ba, Y}, title = {Numerical Study of Droplet Dynamics on a Solid Surface with Insoluble Surfactants.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {35}, number = {24}, pages = {7858-7870}, doi = {10.1021/acs.langmuir.9b00495}, pmid = {31120757}, issn = {1520-5827}, abstract = {Surfactants are widely used in many industrial processes, where the presence of surfactants not only reduces the interfacial tension between fluids but also alters the wetting properties of solid surfaces. To understand how the surfactants influence the droplet motion on a solid surface, a hybrid method for interfacial flows with insoluble surfactants and contact-line dynamics is developed. This method solves immiscible two-phase flows through a lattice Boltzmann color-gradient model and simultaneously solves the convection-diffusion equation for surfactant concentration through a finite difference method. In addition, a dynamic contact angle formulation that describes the dependence of the local contact angle on the surfactant concentration is derived, and the resulting contact angle is enforced by a geometrical wetting condition. Our method is first used to simulate static contact angles for a droplet resting on a solid surface, and the results show that the presence of surfactants can significantly modify surface wettability, especially when the surface is more hydrophilic or more hydrophobic. This is then applied to simulate a surfactant-laden droplet moving on a substrate subject to a linear shear flow for varying effective capillary number (Cae), Reynolds number (Re), and surface wettability, where the results are often compared with those of a clean droplet. For varying Cae, the simulations are conducted by considering a neutral surface. At low values of Cae, the droplet eventually reaches a steady deformation and moves at a constant velocity. In either a clean or surfactant-laden case, the moving velocity of the droplet linearly increases with the moving wall velocity, but the slope is always higher (i.e., the droplet moves faster) in the surfactant-laden case where the droplet exhibits a bigger deformation. When Cae is increased beyond a critical value (Cae,c), the droplet breakup would happen. The presence of surfactants is found to decrease the value of Cae,c, but it shows a non-monotonic effect on the droplet breakup. An increase in Re is able to increase not only droplet deformation but also surfactant dilution. The role of surfactants in the droplet behavior is found to greatly depend upon the surface wettability. For a hydrophilic surface, the presence of surfactants can decrease the wetting length and enables the droplet to reach a steady state faster; while for a hydrophobic surface, it increases the wetting length and delays the departure of the droplet from the solid surface.}, }
@article {pmid31083953, year = {2019}, author = {Tian, C and Wang, X and Liu, Y and Yang, W and Hu, H and Pei, X and Zhou, F}, title = {In Situ Grafting Hydrophilic Polymeric Layer for Stable Drag Reduction.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {35}, number = {22}, pages = {7205-7211}, doi = {10.1021/acs.langmuir.9b00321}, pmid = {31083953}, issn = {1520-5827}, abstract = {Developing drag reduction techniques has attracted great attention because of their need in practical applications. However, many of the proposed strategies exhibit some inevitable limitations, especially for long period of adhibition. In this work, the dynamic but stable drag reduction effect of superhydrophilic hydrogel-coated iron sphere falling freely in a cylindrical water tank was investigated. The absolute instantaneous velocities and displacements of either the hydrogel-encapsulated or unmodified iron sphere falling freely in water were monitored via a high-speed video. It was revealed that, in the range of Reynolds number from 10[4] to 10[6], the optimized hydrogel-coated iron sphere with uniform stability could reduce the resistance by up to 40%, which was mainly due to the boundary slip of water and the delayed boundary separation that resulted from the coated hydrogel. Besides, the deliberate experiments and analysis further indicated that the superhydrophilic hydrogel layer accompanied by the emergence of the drag crisis has largely effected the distribution of flow field at the boundary around the sphere. More importantly, the drag reduction behavior based on the proposed method was thermodynamically stable and resistant to external stimulus, including fluidic oscillator and hydrodynamic pressure. The effective long-term drag reduction performance of the hydrophilic substrate can be expected, correspondingly, and also provides a novel preliminary protocol and avenues for the development of durable drag reduction technologies.}, }
@article {pmid31083496, year = {2019}, author = {Li, H and Huang, B and Wu, M}, title = {Experimental and Numerical Investigations on the Flow Characteristics within Hydrodynamic Entrance Regions in Microchannels.}, journal = {Micromachines}, volume = {10}, number = {5}, pages = {}, pmid = {31083496}, issn = {2072-666X}, abstract = {Flow characteristics within entrance regions in microchannels are important due to their effect on heat and mass transfer. However, relevant research is limited and some conclusions are controversial. In order to reveal flow characteristics within entrance regions and to provide empiric correlation estimating hydrodynamic entrance length, experimental and numerical investigations were conducted in microchannels with square cross-sections. The inlet configuration was elaborately designed in a more common pattern for microdevices to diminish errors caused by separation flow near the inlet and fabrication faults so that conclusions which were more applicable to microchannels could be drawn. Three different microchannels with hydraulic diameters of 100 μm, 150 μm, and 200 μm were investigated with Reynolds (Re) number ranging from 0.5 to 50. For the experiment, deionized water was chosen as the working fluid and microscopic particle image velocimetry (micro-PIV) was adopted to record and analyze velocity profiles. For numerical simulation, the test-sections were modeled and incompressible laminar Navier-Stokes equations were solved with commercial software. Strong agreement was achieved between the experimental data and the simulated data. According to the results of both the experiments and the simulations, new correlations were proposed to estimate entrance length. Re numbers ranging from 12.5 to 15 was considered as the transition region where the relationship between entrance length and Re number converted. For the microchannels and the Reynolds number range investigated compared with correlations for conventional channels, noticeable deviation was observed for lower Re numbers (Re < 12.5) and strong agreement was found for higher Re numbers (Re > 15).}, }
@article {pmid31074118, year = {2019}, author = {Xin, C and Yang, L and Li, J and Hu, Y and Qian, D and Fan, S and Hu, K and Cai, Z and Wu, H and Wang, D and Wu, D and Chu, J}, title = {Conical Hollow Microhelices with Superior Swimming Capabilities for Targeted Cargo Delivery.}, journal = {Advanced materials (Deerfield Beach, Fla.)}, volume = {31}, number = {25}, pages = {e1808226}, doi = {10.1002/adma.201808226}, pmid = {31074118}, issn = {1521-4095}, support = {51875544//National Science Foundation of China/ ; 51675503//National Science Foundation of China/ ; 61805230//National Science Foundation of China/ ; 51805508//National Science Foundation of China/ ; 51805509//National Science Foundation of China/ ; WK2090000011//Fundamental Research Funds for the Central Universities/ ; WK2090090012//Fundamental Research Funds for the Central Universities/ ; WK2090000013//Fundamental Research Funds for the Central Universities/ ; WK2480000002//Fundamental Research Funds for the Central Universities/ ; WK2090090021//Fundamental Research Funds for the Central Universities/ ; 2017495//Youth Innovation Promotion Association CAS/ ; YZ201566//Chinese Academy of Sciences Instrument/ ; 2017YFB1104303//National Key R&amp;D Program of China/ ; 2018YFB1105400//National Key R&amp;D Program of China/ ; }, abstract = {Inspired by flagellate microorganisms in nature, the microhelix is considered as an ideal model for transportation in fluid environment with low Reynolds number. However, how to promote the swimming and loading capabilities of microhelices with controllable geometries remains challenging. In this study, a novel kind of conical hollow microhelices is proposed and a method is developed to rapidly fabricate these microhelices with controllable parameters by femtosecond vortex beams generated from spatial light modulation along helical scanning. Conical hollow microhelices with designable heights (H = 45-75 µm), diameters (D = 6-18 µm), pitch numbers (Pi = 2-4), taper angles (T = 0.1-0.6 rad), and pitch periods (ΔP = 10-30 µm) are efficiently fabricated. In addition, compared with straight microhelices, the forward swimming capability of conical microhelices increases by 50% and the lateral drift of the conical hollow microhelices is reduced by 70%. Finally, the capabilities of these conical hollow microhelices for nanocargo loading and release by the inner hollow core, as well as transportation of neural stem cells by the outer surface are demonstrated. This work provides new insights into faster and simultaneous transportation of multicargoes for hybrid drug delivery, targeted therapy, and noninvasive surgery in vivo.}, }
@article {pmid31067939, year = {2019}, author = {Feng, Y and Gao, Y and Tang, K and Jin, T}, title = {Numerical investigation on turbulent oscillatory flow through a jet pump.}, journal = {The Journal of the Acoustical Society of America}, volume = {145}, number = {3}, pages = {1417}, doi = {10.1121/1.5094346}, pmid = {31067939}, issn = {1520-8524}, abstract = {A jet pump with an asymmetrical channel can induce a time-averaged pressure drop in oscillatory flow, which can effectively suppress Gedeon streaming in looped thermoacoustic engines. In this work, the flow characteristics and time-averaged pressure drop caused by a jet pump in turbulent oscillatory flow are investigated through numerical simulation. Through the analysis of the dimensionless governing equations, the emphasis is put on the effects of Womersley number and maximum acoustic Reynolds number on the performance of the jet pump. Meanwhile, the steady flow resistance coefficients are also measured numerically. The results indicate that the oscillatory flow resistance coefficients are relatively insensitive to Womersley number when it is less than 46. Moreover, the oscillatory flow resistance coefficients agree well with the steady state flow results, which validate the quasi-static assumption in turbulent oscillatory flow. However, further increasing Womersley number will lead to a reduction in the time-averaged pressure drop. The simulation method and results, as well as the hydrodynamic mechanism beneath the results, are presented and discussed in detail.}, }
@article {pmid31067919, year = {2019}, author = {Ramadan, AB and Abd El-Rahman, AI and Sabry, AS}, title = {Assessment of the transition k-k-ω model application to transitional oscillatory pipe flows.}, journal = {The Journal of the Acoustical Society of America}, volume = {145}, number = {3}, pages = {1195}, doi = {10.1121/1.5092605}, pmid = {31067919}, issn = {1520-8524}, abstract = {The flow transition from laminar to turbulent inside of typical thermoacoustic devices influences the heat-exchange capacities of these devices and dramatically impacts overall performances as well. A few measurements [Eckmann and Grotberg (1991), J. Fluid Mech. 222, 329-350; Hino, Sawamoto, and Takasu (1976). J. Fluid Mech. 75, 193-207] and direct simulations [Feldmann and Wagner (2012). J. Turbul. 13(32), 1-28; Feldmann and Wagner (2016a). New Results in Numerical and Experimental Fluid Mechanics X, pp. 113-122] were reported that describe the transitional oscillatory flows; however, almost no turbulence model has been developed that enables accurate detection and characterization of the reported intermittent turbulent fluctuations. The present work aims to assess the applicability of the k-kL-ω transition model to transitional oscillatory pipe flows. A sinusoidal pressure gradient is introduced into ANSYS finite-volume solver for flow field simulation at different acoustic frequencies, while a friction Reynolds number of 1440 is retained. The stationary turbulent and the laminar oscillatory pipe flows are first considered for validation and model calibration against published LDA measurements [Durst, Kikura, Lekakis, Jovanovic, and Ye (1996). Exp. Fluids 20, 417-428] and DNS results [Feldmann and Wagner (2012). J. Turbul. 13(32), 1-28] in addition to the Sexl's laminar-flow theory [Sexl (1930). Zeitschrift Phys. 61(5), 349-362]. Investigation of the total fluctuation kinetic energy of transitional oscillations reveals the appearance of intermittent fluctuations within the near-wall region at Wo = 13 during deceleration, while fully turbulent oscillations are predicted in the entire pipe domain at Wo = 5. Although the present results are qualitatively in good agreement with reported experimental [Eckmann and Grotberg (1991). J. Fluid Mech. 222, 329-350] and DNS findings [Feldmann and Wagner (2012). J. Turbul. 13(32), 1-28], the velocity profiles show poor agreement with corresponding DNS data during flow acceleration at Wo = 5.}, }
@article {pmid31046340, year = {2019}, author = {Zhou, T and Sun, Y and Fattah, R and Zhang, X and Huang, X}, title = {An experimental study of trailing edge noise from a pitching airfoil.}, journal = {The Journal of the Acoustical Society of America}, volume = {145}, number = {4}, pages = {2009}, doi = {10.1121/1.5094898}, pmid = {31046340}, issn = {1520-8524}, abstract = {In this study, the far-field noise from a pitching NACA 0012 airfoil was measured at a Reynolds number of 6.6 × 10[4]. The pitching motion was in sinusoidal functions with a mean incident angle of 0°. Cases with the pitching amplitude varying from 7.5° to 15° and frequency from 3 to 8 Hz were tested, corresponding to the reduced frequency from 0.094 to 0.25. A microphone was placed in the far-field and the particle image velocimetry technique was utilized to study the flow structures near the trailing edge. The short-time Fourier transformation results of the noise signals revealed that a high-level narrow-band noise hump occurred at a specific angle of attack in a pitching cycle. At the corresponding moment, a coherent vortex street convecting on the airfoil surface was observed, and the vortex shedding frequency was in good agreement with the central frequency of the noise hump. The occurrence of the noise humps was attributed to the laminar boundary layer separation. In one pitching period, the moment when the narrow-band noise hump occurs is independent from the pitching amplitude and it is delayed as the pitching frequency increases. Larger pitching frequency or amplitude results in lower peak level of the noise humps.}, }
@article {pmid31045081, year = {2019}, author = {Gao, Y and Yang, X and Fu, C and Yang, Y and Li, Z and Zhang, H and Qi, F}, title = {10 kHz simultaneous PIV/PLIF study of the diffusion flame response to periodic acoustic forcing.}, journal = {Applied optics}, volume = {58}, number = {10}, pages = {C112-C120}, doi = {10.1364/AO.58.00C112}, pmid = {31045081}, issn = {1539-4522}, abstract = {Response of a laminar diffusion dimethyl-ether flame forced by an acoustic field is provided. A forcing frequency of 100 Hz, which is chosen based on the typical thermo-acoustic instability frequency in a practical combustor, is applied to the flame at a Reynolds number of 250. The development of the forced vortical structures present in this flame has been investigated utilizing a burst mode laser with a repetition rate of 10 kHz. Flame/vortex interaction is visualized by planar laser-induced fluorescence (PLIF) of formaldehyde, which is used to identify the early-stage fuel decomposition in the flame. The flame structure is also correlated with the velocity field, which is obtained utilizing particle imaging velocimetry (PIV). The resulting phase-resolved and time-averaged velocity and vortex images indicate that the amplitude of excitation has pronounced effects on the flame via modifying the local heat release.}, }
@article {pmid31045033, year = {2019}, author = {Wang, S and Liu, X and Wang, G and Xu, L and Li, L and Liu, Y and Huang, Z and Qi, F}, title = {High-repetition-rate burst-mode-laser diagnostics of an unconfined lean premixed swirling flame under external acoustic excitation.}, journal = {Applied optics}, volume = {58}, number = {10}, pages = {C68-C78}, doi = {10.1364/AO.58.000C68}, pmid = {31045033}, issn = {1539-4522}, abstract = {Lean premixed swirling flames are important in practical combustors, but a commonly encountered problem of practical swirl combustors is thermo-acoustic instability, which may cause internal structure damage to combustors. In this research, a high-repetition-rate burst-mode laser is used for simultaneous particle image velocimetry and planar laser-induced fluorescence measurement in an unconfined acoustically excited swirl burner. The time-resolved flow field and transient flame response to the acoustic perturbation are visualized at 20 kHz, offering insight into the heat release rate oscillation. The premixed mixture flow rate and acoustic modulation are varied to study the effects of Reynolds number, Strouhal number, and acoustic modulation amplitude on the swirling flame. The results suggest that the Strouhal number has a notable effect on the periodic movements of the inner recirculation zone and swirling flame configuration.}, }
@article {pmid31039316, year = {2019}, author = {Mozhi Devan Padmanathan, A and Sneha Ravi, A and Choudhary, H and Varanakkottu, SN and Dalvi, SV}, title = {Predictive Framework for the Spreading of Liquid Drops and the Formation of Liquid Marbles on Hydrophobic Particle Bed.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {35}, number = {20}, pages = {6657-6668}, doi = {10.1021/acs.langmuir.9b00698}, pmid = {31039316}, issn = {1520-5827}, abstract = {In this work, we have developed a model to describe the behavior of liquid drops upon impaction on hydrophobic particle bed and verified it experimentally. Poly(tetrafluoroethylene) (PTFE) particles were used to coat drops of water, aqueous solutions of glycerol (20, 40, and 60% v/v), and ethanol (5 and 12% v/v). The experiments were conducted for Weber number (We) ranging from 8 to 130 and Reynolds number (Re) ranging from 370 to 4460. The bed porosity was varied from 0.8 to 0.6. The experimental values of βmax (ratio of the diameter at the maximum spreading condition to the initial drop diameter) were estimated from the time-lapsed images captured using a high-speed camera. The theoretical βmax was estimated by making energy balances on the liquid drop. The proposed model accounts for the energy losses due to viscous dissipation and crater formation along with a change in kinetic energy and surface energy. A good agreement was obtained between the experimental βmax and the estimated theoretical βmax. The proposed model yielded a least % absolute average relative deviation (% AARD) of 5.5 ± 4.3 compared to other models available in the literature. Further, it was found that the liquid drops impacting on particle bed are completely coated with PTFE particles with βmax values greater than 2.}, }
@article {pmid31037445, year = {2019}, author = {Hatoum, H and Mo, XM and Crestanello, JA and Dasi, LP}, title = {Modeling of the Instantaneous Transvalvular Pressure Gradient in Aortic Stenosis.}, journal = {Annals of biomedical engineering}, volume = {47}, number = {8}, pages = {1748-1763}, pmid = {31037445}, issn = {1573-9686}, support = {R01HL119824//National Institutes of Health/ ; R01 HL119824/HL/NHLBI NIH HHS/United States ; 19POST34380804//American Heart Association/ ; R01 HL135505/HL/NHLBI NIH HHS/United States ; R03 EB014255/EB/NIBIB NIH HHS/United States ; }, mesh = {Aortic Valve/*physiopathology ; Aortic Valve Stenosis/*physiopathology ; Cardiac Output ; Hemodynamics ; Humans ; *Models, Cardiovascular ; Pressure ; }, abstract = {The simplified and modified Bernoulli equations break down in estimating the true pressure gradient across the stenotic aortic valve due to their over simplifying assumptions of steady and inviscid conditions as well as the fundamental nature in which aortic valves are different than idealized orifices. Nevertheless, despite having newer models based on time-dependent momentum balance across an orifice, the simplified and modified Bernoulli continue to be the clinical standard because to date, they remain the only models clinically implementable. The objective of this study is to (1) illustrate the fundamental considerations necessary to accurately model the time-dependent instantaneous pressure gradient across a fixed orifice and (2) propose empirical corrections when applying orifice based models to severely stenotic aortic valves. We introduce a general model to predict the time-dependent instantaneous pressure gradient across an orifice that explicitly model the Reynolds number dependence of both the steady and unsteady terms. The accuracy of this general model is assessed with respect to previous models through pulse duplicator experiments on a round orifice model as well as an explanted stenotic surgical aortic valve both with geometric areas of 0.6 cm[2] (less than 1 cm[2] which is the threshold for stenosis determination) over cardiac outputs of 3 and 5 L/min and heart rates of 60, 90 and 120 bpm. The model and the raw experimental data corresponding to the orifice showed good agreement over a wide range of cardiac outputs and heart rates (R[2] exceeding 0.91). The derived average and peak transvalvular pressure gradients also demonstrated good agreement with no significant differences between the respective peaks (p > 0.09). The new model proposed holds promise with its physical and closed form representation of pressure drop, however accurate modeling of the time-variability of the valve area is necessary for the model to be applied on stenotic valves.}, }
@article {pmid31028849, year = {2019}, author = {Heidarinejad, G and Roozbahani, MH and Heidarinejad, M}, title = {Studying airflow structures in periodic cylindrical hills of human tracheal cartilaginous rings.}, journal = {Respiratory physiology &amp; neurobiology}, volume = {266}, number = {}, pages = {103-114}, doi = {10.1016/j.resp.2019.04.012}, pmid = {31028849}, issn = {1878-1519}, mesh = {Cartilage/*anatomy &amp; histology ; Computer Simulation ; Humans ; *Models, Anatomic ; *Models, Biological ; *Respiratory Physiological Phenomena ; Trachea/*anatomy &amp; histology ; }, abstract = {The objective of this study is to assess tracheobronchial flow features with the cartilaginous rings during a light exercising. Tracheobronchial is part of human's body airway system that carries oxygen-rich air to human's lungs as well as takes carbon dioxide out of the human's lungs. Consequently, evaluation of the flow structures in tracheobronchial is important to support diagnosis of tracheal disorders. Computational Fluid Dynamics (CFD) allows evaluating effectiveness of tracheal cartilage rings in human body under different configurations. This study utilizes Large Eddy Simulation (LES) to model an anatomically-based human large conducting airway model with and without cartilaginous rings at the breathing conditions at Reynolds number of 5,176 in trachea region. It is observed that small recirculating areas shaped between rings cavities. While these recirculating areas are decaying, similar to periodic 2D-hills, the cartilaginous rings contribute to the construction of a vortical flow structure in the main flow. The separated vortically-shaped zone creates a wake in the flow and passes inside of the next ring cavity and disturb its boundary layer. At last, the small recirculation flow impinges onto tracheal wall. The outcome of this impinge flow is a latitudinal rotating flow perpendicular to the main flow in a cavity between the two cartilaginous rings crest which appear and disappear within a hundredth of a second. Kelvin-Helmholtz instability is observed in trachea caused by shear flow created behind of interaction between these flow structures near to tracheal wavy wall and main flow. A comparison of the results between a smooth wall model named simplified model and a rough wall model named modified model shows that these structures do not exist in simplified model, which is common in modeling tracheobronchial flow. This study proposes to consider macro surface roughness to account for the separating and rotating instantaneous flow structures. Finally, solving trachea airflow with its cartilages can become one of major issues in measuring the validity and capability of solving flow in developing types of sub-grid scale models as a turbulence studies benchmark.}, }
@article {pmid31008408, year = {2019}, author = {Vasilopoulos, K and Sarris, IE and Tsoutsanis, P}, title = {Assessment of air flow distribution and hazardous release dispersion around a single obstacle using Reynolds-averaged Navier-Stokes equations.}, journal = {Heliyon}, volume = {5}, number = {4}, pages = {e01482}, pmid = {31008408}, issn = {2405-8440}, abstract = {The flow around a cubical building, with a pollution source at the central point of the top of the cube, is studied. The Reynolds-averaged Navier-Stokes and species concentration equations are solved for Reynolds number, Re = 40,000, is based on the height of the cube. The predictions obtained with the standard, the Kato-Launder, and the low-Reynolds number k-epsilon models are examined with various wall functions for the near wall treatment of the flow. Results are compared against Martinuzzi and Tropea measurements (J. of Fluids Eng., 115, 85-92, 1993) for the flow field and against Li and Meroney (J. of Wind Eng. and Industrial Aerodynamics, 81, 333-345, 1983) experiments and Gaussian models for the concentration distribution. It is found that the present unstructured mesh model performs similarly to the structured mesh models. Results from the Kato-Launder model are closer to the experimental data for the flow patterns and contaminant distribution on the cube's roof. However, the Kato-Launder model has an over-prediction for the recirculation zone and the contaminant distribution windward of the cube. The standard k-epsilon and the low-Reynolds number k-epsilon models predict similar flow patterns and are closer to the experimental data of the cube's windward and side face.}, }
@article {pmid31007546, year = {2019}, author = {Martins Afonso, M and Mitra, D and Vincenzi, D}, title = {Kazantsev dynamo in turbulent compressible flows.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {475}, number = {2223}, pages = {20180591}, pmid = {31007546}, issn = {1364-5021}, abstract = {We consider the kinematic fluctuation dynamo problem in a flow that is random, white-in-time, with both solenoidal and potential components. This model is a generalization of the well-studied Kazantsev model. If both the solenoidal and potential parts have the same scaling exponent, then, as the compressibility of the flow increases, the growth rate decreases but remains positive. If the scaling exponents for the solenoidal and potential parts differ, in particular if they correspond to typical Kolmogorov and Burgers values, we again find that an increase in compressibility slows down the growth rate but does not turn it off. The slow down is, however, weaker and the critical magnetic Reynolds number is lower than when both the solenoidal and potential components display the Kolmogorov scaling. Intriguingly, we find that there exist cases, when the potential part is smoother than the solenoidal part, for which an increase in compressibility increases the growth rate. We also find that the critical value of the scaling exponent above which a dynamo is seen is unity irrespective of the compressibility. Finally, we realize that the dimension d = 3 is special, as for all other values of d the critical exponent is higher and depends on the compressibility.}, }
@article {pmid31003548, year = {2019}, author = {Zhang, M and Zhang, W and Wu, Z and Shen, Y and Chen, Y and Lan, C and Li, F and Cai, W}, title = {Comparison of Micro-Mixing in Time Pulsed Newtonian Fluid and Viscoelastic Fluid.}, journal = {Micromachines}, volume = {10}, number = {4}, pages = {}, pmid = {31003548}, issn = {2072-666X}, abstract = {Fluid mixing plays an essential role in many microfluidic applications. Here, we compare the mixing in time pulsing flows for both a Newtonian fluid and a viscoelastic fluid at different pulsing frequencies. In general, the mixing degree in the viscoelastic fluid is higher than that in the Newtonian fluid. Particularly, the mixing in Newtonian fluid with time pulsing is decreased when the Reynolds number Re is between 0.002 and 0.01, while it is enhanced when Re is between 0.1 and 0.2 compared with that at a constant flow rate. In the viscoelastic fluid, on the other hand, the time pulsing does not change the mixing degree when the Weissenberg number Wi ≤ 20, while a larger mixing degree is realized at a higher pulsing frequency when Wi = 50.}, }
@article {pmid30999540, year = {2019}, author = {Duran-Matute, M and van Gorp, MD and van Heijst, GJF}, title = {Wavelength selection of vortex ripples in an oscillating cylinder: The effect of curvature and background rotation.}, journal = {Physical review. E}, volume = {99}, number = {3-1}, pages = {033105}, doi = {10.1103/PhysRevE.99.033105}, pmid = {30999540}, issn = {2470-0053}, abstract = {We present results of laboratory experiments on the formation, evolution, and wavelength selection of vortex ripples. These ripples formed on a sediment bed at the bottom of a water-filled oscillating cylindrical tank mounted on top of a rotating table. The table is made to oscillate sinusoidally in time, while a constant background rotation was added for some experiments. The changes in bed thickness are measured using a light attenuation technique. It was found that the wavelength normalized with the excursion length depends on both a Reynolds number and the Strouhal number. This differs from straight or annular geometries where the wavelength is proportional to the excursion length. The flow in an oscillating cylinder has the peculiarity that it develops a secondary flow in the radial direction that depends on the excursion length. The effect of this secondary circulation is evident in the radial transport for small values of the Strouhal number or in the orientation of the ripples for strong enough background rotation. Additionally, ripples in an oscillating cylinder present a rich dynamic behavior where the number of ripples can oscillate even with constant forcing parameters.}, }
@article {pmid30999463, year = {2019}, author = {Dutta, AK and Ramachandran, G and Chaudhuri, S}, title = {Investigating thermoacoustic instability mitigation dynamics with a Kuramoto model for flamelet oscillators.}, journal = {Physical review. E}, volume = {99}, number = {3-1}, pages = {032215}, doi = {10.1103/PhysRevE.99.032215}, pmid = {30999463}, issn = {2470-0053}, abstract = {In this paper, we present experimental observations and phenomenological modeling of the intermittent dynamics that emerge while mitigating thermoacoustic instability by rotating the otherwise static swirler in a lean premixed, laboratory-scale combustor. Starting with a self-excited thermoacoustically unstable combustor, here we find that a progressive increase in swirler rotation rate does not uniformly decrease amplitudes of coherent, sinusoidal pressure or heat-release-rate oscillations. Instead, these oscillations emerge as high-amplitude bursts separated by low-amplitude noise in the signal. At increased rotational speeds, the high-amplitude coherent oscillations become scarce and their duration in the signal reduces. The velocity field from high-speed particle image velocimetry and simultaneous pressure and chemiluminescence data support these observations. Such an intermittent route to instability mitigation is reminiscent of the opposite transition implemented by changing the Reynolds number from a fully chaotic state to a fully unstable state. To model such dynamics phenomenologically, we discretize the swirling turbulent premixed flame into an ensemble of flamelet oscillators arranged circumferentially around the center body of the swirler. The Kuramoto model is proposed for these flamelet oscillators which is subsequently used to analyze their synchronization dynamics. The order parameter r, which is a measure of the synchronization between the oscillator phases, provides critical insights on the transition from the thermoacoustically unstable to stable states via intermittency. Finally, it is shown that the Kuramoto model for flamelet oscillator can qualitatively reproduce the time-averaged and intermittent dynamics while transitioning from the state of thermoacoustic instability to a state of incoherent noisy oscillations.}, }
@article {pmid30999454, year = {2019}, author = {Shaik, VA and Ardekani, AM}, title = {Swimming sheet near a plane surfactant-laden interface.}, journal = {Physical review. E}, volume = {99}, number = {3-1}, pages = {033101}, doi = {10.1103/PhysRevE.99.033101}, pmid = {30999454}, issn = {2470-0053}, abstract = {In this work we analyze the velocity of a swimming sheet near a plane surfactant-laden interface by assuming the Reynolds number and the sheet's deformation to be small. We observe a nonmonotonic dependence of the sheet's velocity on the Marangoni number (Ma) and the surface Péclet number (Pe_{s}). For a sheet passing only transverse waves, the swimming velocity increases with an increase in Ma for any fixed Pe_{s}. When Pe_{s} is increasing, on the other hand, the swimming velocity of the same sheet either increases (at large Ma) or it initially increases and then decreases (at small Ma). This dependence of the swimming velocity on Ma and Pe_{s} is altered if the sheet is passing longitudinal waves in addition to the transverse waves along its surface.}, }
@article {pmid30993773, year = {2019}, author = {Cheng, JL and Au, JS and MacDonald, MJ}, title = {Peripheral artery endothelial function responses to altered shear stress patterns in humans.}, journal = {Experimental physiology}, volume = {104}, number = {7}, pages = {1126-1135}, doi = {10.1113/EP087597}, pmid = {30993773}, issn = {1469-445X}, support = {DG #238819-13//Natural Sciences and Engineering Research Council/International ; }, mesh = {Adult ; Blood Flow Velocity/*physiology ; Brachial Artery/*physiology ; Electrocardiography/methods ; Endothelium, Vascular/*physiology ; Hand Strength/physiology ; Hot Temperature ; Humans ; Male ; Regional Blood Flow/*physiology ; Shear Strength/*physiology ; *Stress, Mechanical ; Vasodilation/physiology ; Young Adult ; }, abstract = {NEW FINDINGS: What is the central question of this study? What is the effect of altered shear stress pattern, with or without concurrent neurohumoral and metabolic activation, on the acute endothelial function response assessed via brachial artery flow-mediated dilatation? What is the main finding and its importance? Despite generating distinctive shear stress patterns (i.e. increases in anterograde only, anterograde only with neurohumoral and metabolic activation, and both anterograde and retrograde), similar acute improvements were observed in the brachial artery flow-mediated dilatation response in all conditions, indicating that anterograde and/or turbulent shear stress might be the essential element to induce acute increases in endothelial function.<br><br>ABSTRACT: Endothelial function is influenced by both the direction and the magnitude of shear stress. Acute improvements in endothelial function have mostly been attributed to increased anterograde shear, whereas results from many interventional models in humans suggest that enhancing shear stress in an oscillatory manner (anterograde and retrograde) might be optimal. Here, we determined the acute brachial artery shear stress (SS) and flow-mediated dilatation (FMD) responses to three shear-altering interventions [passive heat stress (HEAT), mechanical forearm compression (CUFF) and handgrip exercise (HGEX)] and examined the relationship between changes in oscillatory shear index (OSI) and changes in FMD. During separate visits, 10 young healthy men (22&#xa0;&#xb1;&#xa0;3&#xa0;years old) underwent 10&#xa0;min of HEAT, CUFF or HGEX in their left forearm. Anterograde and retrograde SS, Reynolds number, OSI and FMD were assessed at rest and during/after each intervention. Anterograde SS increased during all interventions in a stepwise manner (P&#xa0;<&#xa0;0.05 between interventions), with the change in HGEX (&#x2206;37.7&#xa0;&#xb1;&#xa0;12.2&#xa0;dyn&#xa0;cm[-2] , P&#xa0;<&#xa0;0.05)&#xa0;>&#xa0;CUFF (&#x2206;25.1&#xa0;&#xb1;&#xa0;11.9&#xa0;dyn&#xa0;cm[-2] , P&#xa0;<&#xa0;0.05)&#xa0;>&#xa0;HEAT (&#x2206;14.5&#xa0;&#xb1;&#xa0;7.9&#xa0;dyn&#xa0;cm[-2] , P&#xa0;<&#xa0;0.05). Retrograde SS increased during CUFF (&#x2206;-19.6&#xa0;&#xb1;&#xa0;4.3&#xa0;dyn&#xa0;cm[-2] , P&#xa0;<&#xa0;0.05). Anterograde blood flow was turbulent (i.e. Reynolds number&#xa0;&#x2265;&#xa0;|2000|) during all interventions (P&#xa0;<&#xa0;0.05). The relative FMD improved after all interventions (P&#xa0;=&#xa0;0.01), and there was no relationship between &#x2206;OSI and &#x2206;FMD. We elicited changes in SS profiles including increased anterograde SS (HEAT and HGEX) and both increased anterograde and retrograde SS (CUFF); regardless of the SS pattern, FMD improved to the same extent. These findings suggest that the presence of anterograde and/or turbulent SS might be the key to optimizing endothelial function in acute assessment protocols.}, }
@article {pmid30985778, year = {2019}, author = {Occhicone, A and Sinibaldi, A and Sonntag, F and Munzert, P and Danz, N and Michelotti, F}, title = {Study of fluid dynamics at the boundary wall of a microchannel by Bloch surface waves.}, journal = {Optics letters}, volume = {44}, number = {8}, pages = {1932-1935}, doi = {10.1364/OL.44.001932}, pmid = {30985778}, issn = {1539-4794}, abstract = {Understanding how a fluid flows at the boundaries when it is confined at the microscale/nanoscale is crucial for a broad range of engineering and biology applications. We propose an experimental technique based on Bloch surface waves sustained by a one-dimensional photonic crystal to evaluate the speed of the contact line, i.e., the triple junction separating three phases, in the low Reynold's number regime, and with a nanometric resolution. Here, we report on the experimental characterization of the translatory motion of the contact line that separates two water solutions with a relatively high refractive index mismatch (7.35×10[-3]) and its slipping over a solid surface. The advantages are the relative simplicity and economy of the experimental configuration.}, }
@article {pmid30978086, year = {2019}, author = {Wei, D and Dehnavi, PG and Aubin-Tam, ME and Tam, D}, title = {Is the Zero Reynolds Number Approximation Valid for Ciliary Flows?.}, journal = {Physical review letters}, volume = {122}, number = {12}, pages = {124502}, doi = {10.1103/PhysRevLett.122.124502}, pmid = {30978086}, issn = {1079-7114}, abstract = {Stokes equations are commonly used to model the hydrodynamic flow around cilia on the micron scale. The validity of the zero Reynolds number approximation is investigated experimentally with a flow velocimetry approach based on optical tweezers, which allows the measurement of periodic flows with high spatial and temporal resolution. We find that beating cilia generate a flow, which fundamentally differs from the stokeslet field predicted by Stokes equations. In particular, the flow velocity spatially decays at a faster rate and is gradually phase delayed at increasing distances from the cilia. This indicates that the quasisteady approximation and use of Stokes equations for unsteady ciliary flow are not always justified and the finite timescale for vorticity diffusion cannot be neglected. Our results have significant implications in studies of synchronization and collective dynamics of microswimmers.}, }
@article {pmid30978052, year = {2019}, author = {Shekar, A and McMullen, RM and Wang, SN and McKeon, BJ and Graham, MD}, title = {Critical-Layer Structures and Mechanisms in Elastoinertial Turbulence.}, journal = {Physical review letters}, volume = {122}, number = {12}, pages = {124503}, doi = {10.1103/PhysRevLett.122.124503}, pmid = {30978052}, issn = {1079-7114}, abstract = {Simulations of elastoinertial turbulence (EIT) of a polymer solution at low Reynolds number are shown to display localized polymer stretch fluctuations. These are very similar to structures arising from linear stability (Tollmien-Schlichting modes) and resolvent analyses, i.e., critical-layer structures localized where the mean fluid velocity equals the wave speed. Computations of self-sustained nonlinear Tollmien-Schlichting waves reveal that the critical layer exhibits stagnation points that generate sheets of large polymer stretch. These kinematics may be the genesis of similar structures in EIT.}, }
@article {pmid30976530, year = {2019}, author = {M, AA and V, M}, title = {Demand factor definition-A dimensionless parameter for Vertical Axis Wind Turbines.}, journal = {MethodsX}, volume = {6}, number = {}, pages = {567-581}, pmid = {30976530}, issn = {2215-0161}, abstract = {The use of dimensionless numbers like Reynolds Number, Froude Number and Webber Number has historically simplified the process of comparison of phenomena irrespective of their scales and in their classification into different categories. This paper deals with the derivational aspects of a dimensionless parameter named "Demand Factor" for optimization of Vertical Axis Wind Turbine (VAWT). •The input parameters considered in this derivation are power, wind velocity, the aspect ratio of the turbine, density of air and viscosity of air and the output parameters are length of the blade, number of blades, chord length, aerofoil shape, radius of the turbine and angular velocity at rated speed.•Four rounds of variable definition trials are carried out through the arrangement of the input parameters on the numerator and denominator positions. With the filtering out of unsuitable combinations at different stages of elimination, out of 32 combinations the expression that holds the potential to represent demand factor was identified. The process of carrying out single point optimization based on Demand factor expression is discussed along with the steps involved in numerically calculating output parameters.•The expression of Demand factor developed provides a different perspective on the process of design and optimization of VAWTs.}, }
@article {pmid30960580, year = {2019}, author = {Wang, Y and Wang, Y and Cheng, Z}, title = {Direct Numerical Simulation of Gas-Liquid Drag-Reducing Cavity Flow by the VOSET Method.}, journal = {Polymers}, volume = {11}, number = {4}, pages = {}, pmid = {30960580}, issn = {2073-4360}, support = {No.51576210//National Natural Science Foundation of China (NSFC)/ ; }, abstract = {Drag reduction by polymer is an important energy-saving technology, which can reduce pumping pressure or promote the flow rate of the pipelines transporting fluid. It has been widely applied to single-phase pipelines, such as oil pipelining, district heating systems, and firefighting. However, the engineering application of the drag reduction technology in two-phase flow systems has not been reported. The reason is an unrevealed complex mechanism of two-phase drag reduction and lack of numerical tools for mechanism study. Therefore, we aim to propose governing equations and numerical methods of direct numerical simulation (DNS) for two-phase gas-liquid drag-reducing flow and try to explain the reason for the two-phase drag reduction. Efficient interface tracking method-coupled volume-of-fluid and level set (VOSET) and typical polymer constitutive model Giesekus are combined in the momentum equation of the two-phase turbulent flow. Interface smoothing for conformation tensor induced by polymer is used to ensure numerical stability of the DNS. Special features and corresponding explanations of the two-phase gas-liquid drag-reducing flow are found based on DNS results. High shear in a high Reynolds number flow depresses the efficiency of the gas-liquid drag reduction, while a high concentration of polymer promotes the efficiency. To guarantee efficient drag reduction, it is better to use a high concentration of polymer drag-reducing agents (DRAs) for high shear flow.}, }
@article {pmid30958231, year = {2018}, author = {Stocking, JB and Laforsch, C and Sigl, R and Reidenbach, MA}, title = {The role of turbulent hydrodynamics and surface morphology on heat and mass transfer in corals.}, journal = {Journal of the Royal Society, Interface}, volume = {15}, number = {149}, pages = {20180448}, pmid = {30958231}, issn = {1742-5662}, mesh = {Animals ; Anthozoa/*physiology ; *Coral Reefs ; *Hot Temperature ; *Hydrodynamics ; *Models, Biological ; }, abstract = {Corals require efficient heat and mass transfer with the overlying water column to support key biological processes, such as nutrient uptake and mitigation of thermal stress. Transfer rates are primarily determined by flow conditions, coral morphology and the physics of the resulting fluid-structure interaction, yet the relationship among these parameters is poorly understood especially for wave-dominated coral habitats. To investigate the interactive effects of these factors on fluxes of heat and mass, we measure hydrodynamic characteristics in situ over three distinct surface morphologies of massive stony corals in a Panamanian reef. Additionally, we implement a numerical model of flow and thermal transport for both current and wave conditions past a natural coral surface, as well as past three simplified coral morphologies with varying ratios of surface roughness spacing-to-height. We find oscillatory flow enhances rates of heat and mass transfer by 1.2-2.0× compared with unidirectional flow. Additionally, increases in Reynolds number and in surface roughness ratio produce up to a 3.3× and a 2.0× enhancement, respectively. However, as waves begin to dominate the flow regime relative to unidirectional currents, the underlying physical mechanisms mediating transfer rates shift from predominantly turbulence-driven to greater control by inertial accelerations, resulting in larger heat and mass transfer for small surface roughness ratios. We show that for rough corals in wave-dominated flows, novel trade-off dynamics for heat and mass transfer exist between broadly spaced roughness that enhances turbulence production versus narrowly spaced roughness that produces greater surface area. These findings have important implications for differential survivorship during heat-induced coral bleaching, particularly as thermal stress events become increasingly common with global climate change.}, }
@article {pmid30958200, year = {2019}, author = {Tuttle, LJ and Robinson, HE and Takagi, D and Strickler, JR and Lenz, PH and Hartline, DK}, title = {Going with the flow: hydrodynamic cues trigger directed escapes from a stalking predator.}, journal = {Journal of the Royal Society, Interface}, volume = {16}, number = {151}, pages = {20180776}, pmid = {30958200}, issn = {1742-5662}, mesh = {Animals ; *Biobehavioral Sciences ; Copepoda/*physiology ; Escape Reaction/*physiology ; Fishes/*physiology ; Food Chain ; Predatory Behavior/*physiology ; Zooplankton/*physiology ; }, abstract = {In the coevolution of predator and prey, different and less well-understood rules for threat assessment apply to freely suspended organisms than to substrate-dwelling ones. Particularly vulnerable are small prey carried with the bulk movement of a surrounding fluid and thus deprived of sensory information within the bow waves of approaching predators. Some planktonic prey have solved this apparent problem, however. We quantified cues generated by the slow approach of larval clownfish (Amphiprion ocellaris) that triggered a calanoid copepod (Bestiolina similis) to escape before the fish could strike. To estimate water deformation around the copepod immediately preceding its jump, we represented the body of the fish as a rigid sphere in a hydrodynamic model that we parametrized with measurements of fish size, approach speed and distance to the copepod. Copepods of various developmental stages (CII-CVI) were sensitive to the water flow caused by the live predator, at deformation rates as low as 0.04 s[-1]. This rate is far lower than that predicted from experiments that used artificial predator-mimics. Additionally, copepods localized the source, with 87% of escapes directed away (greater than or equal to 90°) from the predator. Thus, copepods' survival in life-threatening situations relied on their detection of small nonlinear signals within an environment of locally linear deformation.}, }
@article {pmid30958167, year = {2019}, author = {Nguyen, H and Koehl, MAR and Oakes, C and Bustamante, G and Fauci, L}, title = {Effects of cell morphology and attachment to a surface on the hydrodynamic performance of unicellular choanoflagellates.}, journal = {Journal of the Royal Society, Interface}, volume = {16}, number = {150}, pages = {20180736}, pmid = {30958167}, issn = {1742-5662}, mesh = {Cell Adhesion/*physiology ; Choanoflagellata/cytology/*physiology ; *Hydrodynamics ; *Models, Biological ; Surface Properties ; Swimming/*physiology ; }, abstract = {Choanoflagellates, eukaryotes that are important predators on bacteria in aquatic ecosystems, are closely related to animals and are used as a model system to study the evolution of animals from protozoan ancestors. The choanoflagellate Salpingoeca rosetta has a complex life cycle with different morphotypes, some unicellular and some multicellular. Here we use computational fluid dynamics to study the hydrodynamics of swimming and feeding by different unicellular stages of S. rosetta: a swimming cell with a collar of prey-capturing microvilli surrounding a single flagellum, a thecate cell attached to a surface and a dispersal-stage cell with a slender body, long flagellum and short collar. We show that a longer flagellum increases swimming speed, longer microvilli reduce speed and cell shape only affects speed when the collar is very short. The flux of prey-carrying water into the collar capture zone is greater for swimming than sessile cells, but this advantage decreases with collar size. Stalk length has little effect on flux for sessile cells. We show that ignoring the collar, as earlier models have done, overestimates flux and greatly overestimates the benefit to feeding performance of swimming versus being attached, and of a longer stalk for attached cells.}, }
@article {pmid30958164, year = {2019}, author = {Asadzadeh, SS and Nielsen, LT and Andersen, A and Dölger, J and Kiørboe, T and Larsen, PS and Walther, JH}, title = {Hydrodynamic functionality of the lorica in choanoflagellates.}, journal = {Journal of the Royal Society, Interface}, volume = {16}, number = {150}, pages = {20180478}, pmid = {30958164}, issn = {1742-5662}, mesh = {*Choanoflagellata/physiology/ultrastructure ; *Hydrodynamics ; *Models, Biological ; Movement/*physiology ; }, abstract = {Choanoflagellates are unicellular eukaryotes that are ubiquitous in aquatic habitats. They have a single flagellum that creates a flow toward a collar filter composed of filter strands that extend from the cell. In one common group, the loricate choanoflagellates, the cell is suspended in an elaborate basket-like structure, the lorica, the function of which remains unknown. Here, we use Computational Fluid Dynamics to explore the possible hydrodynamic function of the lorica. We use the choanoflagellate Diaphaoneca grandis as a model organism. It has been hypothesized that the function of the lorica is to prevent refiltration (flow recirculation) and to increase the drag and, hence, increase the feeding rate and reduce the swimming speed. We find no support for these hypotheses. On the contrary, motile prey are encountered at a much lower rate by the loricate organism. The presence of the lorica does not affect the average swimming speed, but it suppresses the lateral motion and rotation of the cell. Without the lorica, the cell jiggles from side to side while swimming. The unsteady flow generated by the beating flagellum causes reversed flow through the collar filter that may wash away captured prey while it is being transported to the cell body for engulfment. The lorica substantially decreases such flow, hence it potentially increases the capture efficiency. This may be the main adaptive value of the lorica.}, }
@article {pmid30958143, year = {2019}, author = {Asadzadeh, SS and Larsen, PS and Riisgård, HU and Walther, JH}, title = {Hydrodynamics of the leucon sponge pump.}, journal = {Journal of the Royal Society, Interface}, volume = {16}, number = {150}, pages = {20180630}, pmid = {30958143}, issn = {1742-5662}, mesh = {Animals ; Flagella/*physiology ; *Hydrodynamics ; *Models, Biological ; Porifera/*anatomy &amp; histology/*physiology ; }, abstract = {Leuconoid sponges are filter-feeders with a complex system of branching inhalant and exhalant canals leading to and from the close-packed choanocyte chambers. Each of these choanocyte chambers holds many choanocytes that act as pumping units delivering the relatively high pressure rise needed to overcome the system pressure losses in canals and constrictions. Here, we test the hypothesis that, in order to deliver the high pressures observed, each choanocyte operates as a leaky, positive displacement-type pump owing to the interaction between its beating flagellar vane and the collar, open at the base for inflow but sealed above. The leaking backflow is caused by small gaps between the vaned flagellum and the collar. The choanocyte pumps act in parallel, each delivering the same high pressure, because low-pressure and high-pressure zones in the choanocyte chamber are separated by a seal (secondary reticulum). A simple analytical model is derived for the pump characteristic, and by imposing an estimated system characteristic we obtain the back-pressure characteristic that shows good agreement with available experimental data. Computational fluid dynamics is used to verify a simple model for the dependence of leak flow through gaps in a conceptual collar-vane-flagellum system and then applied to models of a choanocyte tailored to the parameters of the freshwater demosponge Spongilla lacustris to study its flows in detail. It is found that both the impermeable glycocalyx mesh covering the upper part of the collar and the secondary reticulum are indispensable features for the choanocyte pump to deliver the observed high pressures. Finally, the mechanical pump power expended by the beating flagellum is compared with the useful (reversible) pumping power received by the water flow to arrive at a typical mechanical pump efficiency of about 70%.}, }
@article {pmid30940542, year = {2019}, author = {Janke, T and Koullapis, P and Kassinos, SC and Bauer, K}, title = {PIV measurements of the SimInhale benchmark case.}, journal = {European journal of pharmaceutical sciences : official journal of the European Federation for Pharmaceutical Sciences}, volume = {133}, number = {}, pages = {183-189}, doi = {10.1016/j.ejps.2019.03.025}, pmid = {30940542}, issn = {1879-0720}, mesh = {Acrylic Resins ; Benchmarking ; Butadienes ; Computer Simulation ; Humans ; Lung/*metabolism ; *Models, Biological ; Polystyrenes ; Printing, Three-Dimensional ; *Rheology ; }, abstract = {Particle Image Velocimetry (PIV) measurements with the aim of providing experimental data for the SimInhale benchmark case are presented within this work. We, therefore, present a refractive index matched, transparent model of the benchmark geometry, in which the velocity and turbulent kinetic energy fields are examined at flow rates comparable to 15, 30 and 60 L/min (Re ≈ 1000-4500) in air. Furthermore, these results are compared with Large Eddy Simulations (LES). The results reveal a Reynolds number independence of the qualitative velocity field in the range covered within this work. Good agreement is found between the PIV and LES data, with a slight over-prediction of turbulent kinetic energies by the simulations. The obtained experimental data will be part of a common, publicly accessible ERCOFTAC database along with additional results published recently.}, }
@article {pmid30937853, year = {2019}, author = {Mancini, V and Bergersen, AW and Vierendeels, J and Segers, P and Valen-Sendstad, K}, title = {High-Frequency Fluctuations in Post-stenotic Patient Specific Carotid Stenosis Fluid Dynamics: A Computational Fluid Dynamics Strategy Study.}, journal = {Cardiovascular engineering and technology}, volume = {10}, number = {2}, pages = {277-298}, pmid = {30937853}, issn = {1869-4098}, mesh = {Aged ; Asymptomatic Diseases ; Blood Flow Velocity ; Carotid Artery, Common/*physiopathology ; Carotid Stenosis/*diagnosis/physiopathology ; Computed Tomography Angiography ; Finite Element Analysis ; *Hemodynamics ; Humans ; Hydrodynamics ; Male ; *Models, Cardiovascular ; Numerical Analysis, Computer-Assisted ; *Patient-Specific Modeling ; Predictive Value of Tests ; Proof of Concept Study ; Pulsatile Flow ; Regional Blood Flow ; Time Factors ; Vibration ; }, abstract = {PURPOSE: Screening of asymptomatic carotid stenoses is performed by auscultation of the carotid bruit, but the sensitivity is poor. Instead, it has been suggested to detect carotid bruit as neck's skin vibrations. We here take a first step towards a computational fluid dynamics proof-of-concept study, and investigate the robustness of our numerical approach for capturing high-frequent fluctuations in the post-stenotic flow. The aim was to find an ideal solution strategy from a pragmatic point of view, balancing accuracy with computational cost comparing an under-resolved direct numerical simulation (DNS) approach vs. three common large eddy simulation (LES) models (static/dynamic Smagorinsky and Sigma).<br><br>METHOD: We found a reference solution by performing a spatial and temporal refinement study of a stenosed carotid bifurcation with constant flow rate. The reference solution [Formula: see text] was compared against LES for both a constant and pulsatile flow.<br><br>RESULTS: Only the Sigma and Dynamic Smagorinsky models were able to replicate the flow field of the reference solution for a pulsatile simulation, however the computational cost of the Sigma model was lower. However, none of the sub-grid scale models were able to replicate the high-frequent flow in the peak-systolic constant flow rate simulations, which had a higher mean Reynolds number.<br><br>CONCLUSIONS: The Sigma model was the best combination between accuracy and cost for simulating the pulsatile post-stenotic flow field, whereas for the constant flow rate, the under-resolved DNS approach was better. These results can be used as a reference for future studies investigating high-frequent flow features.}, }
@article {pmid30934360, year = {2019}, author = {Ma, J and Xu, L and Tian, FB and Young, J and Lai, JCS}, title = {Dynamic characteristics of a deformable capsule in a simple shear flow.}, journal = {Physical review. E}, volume = {99}, number = {2-1}, pages = {023101}, doi = {10.1103/PhysRevE.99.023101}, pmid = {30934360}, issn = {2470-0053}, abstract = {The dynamic characteristics of a two-dimensional deformable capsule in a simple shear flow are studied with an immersed boundary-lattice Boltzmann method. Simulations are conducted by varying the Reynolds number (Re) from 0.0125 to 2000 and the dimensionless shear rate (G) from 0.001 to 0.5. The G-Re plane can be divided into four regions according to the deformation dependence on the parameters considered: viscous dominant, inertia dominant, transitional, and anomalous regions. There are four typical dynamic behaviors over the G-Re plane: steady deformation, prerupture state, quasisteady deformation, and continuous elongation. Analysis indicates that the pressure distribution and its variations due to the interplay of the fluid inertia force, the viscous shear stress, and the membrane elastic force determines the complex behaviors of the capsule. The effects of the bending rigidity and the internal-to-external viscosity ratio on the dynamics of the capsule are further studied. It is found that the capsule experiences smaller deformation when the higher bending rigidity is included, and the low bending rigidity does not have a remarkable influence on the capsule deformation. The capsule normally experiences smaller deformation due to the increase of the internal-to-external viscosity ratio.}, }
@article {pmid30934349, year = {2019}, author = {Pereira, M and Gissinger, C and Fauve, S}, title = {1/f noise and long-term memory of coherent structures in a turbulent shear flow.}, journal = {Physical review. E}, volume = {99}, number = {2-1}, pages = {023106}, doi = {10.1103/PhysRevE.99.023106}, pmid = {30934349}, issn = {2470-0053}, abstract = {A shear flow of liquid metal (Galinstan) is driven in an annular channel by counter-rotating traveling magnetic fields imposed at the end caps. When the traveling velocities are large, the flow is turbulent and its azimuthal component displays random reversals. Power spectra of the velocity field exhibit a 1/f^{α} power law on several decades and are related to power-law probability distributions P(τ)∼τ^{-β} of the waiting times between successive reversals. This 1/f type spectrum is observed only when the Reynolds number is large enough. In addition, the exponents α and β are controlled by the symmetry of the system; a continuous transition between two different types of Flicker noise is observed as the equatorial symmetry of the flow is broken, in agreement with theoretical predictions.}, }
@article {pmid30899783, year = {2019}, author = {Tang, X and Staack, D}, title = {Bioinspired mechanical device generates plasma in water via cavitation.}, journal = {Science advances}, volume = {5}, number = {3}, pages = {eaau7765}, pmid = {30899783}, issn = {2375-2548}, abstract = {Nature can generate plasma in liquids more efficiently than human-designed devices using electricity, acoustics, or light. In the animal world, snapping shrimp can induce cavitation that collapses to produce high pressures and temperatures, leading to efficient plasma formation with photon and shock wave emission via energy focusing. Here, we report a bioinspired mechanical device that mimics the plasma generation technique of the snapping shrimp. This device was manufactured using additive manufacturing based on micro-x-ray computed tomography of a snapping shrimp claw molt. A spring fixture was designed to reliably actuate the claw with appropriate force and velocity to produce a high-speed water jet that matches the cavitation number and Reynolds number of the shrimp. Light emission and shocks were imaged, which indicate that our device reproduces the shrimp's plasma generation technique and is more efficient than other plasma generation methods.}, }
@article {pmid30891517, year = {2019}, author = {Nagaraju, G and Garvandha, M}, title = {Magnetohydrodynamic viscous fluid flow and heat transfer in a circular pipe under an externally applied constant suction.}, journal = {Heliyon}, volume = {5}, number = {2}, pages = {e01281}, pmid = {30891517}, issn = {2405-8440}, abstract = {An analytical investigation of two-dimensional heat transfer behavior of an axisymmetric incompressible dissipative viscous fluid flow in a circular pipe is considered. The flow is subjected to an externally applied uniform suction over the pipe wall in the transverse direction and a constant magnetic field opposite to the wall. The reduced Navier-Stokes equations in the cylindrical system are applied for the velocity and temperature fields. Constant wall temperature is considered as the thermal boundary condition. The velocity components are expressed into stream function and its solution is acquired by the Homotopy analysis method (HAM). The effects of magnetic body force parameter(M), suction Reynolds number (Re), Prandtl number (Pr)and Eckert number (Ec) on velocity and temperature are examined and are presented in a graphical frame. Streamlines, isotherms and pressure contours are likewise pictured. It is observed that with increasing suction Reynold number decelerates axial flow, whereas it enhances the radial flow. The temperature distribution increases with an increase in Prandtl number, whereas it decreases with an increase in Eckert number (viscous dissipation effect).}, }
@article {pmid30879156, year = {2019}, author = {El-Sapa, S}, title = {Settling slip velocity of a spherical particle in an unbounded micropolar fluid.}, journal = {The European physical journal. E, Soft matter}, volume = {42}, number = {3}, pages = {32}, pmid = {30879156}, issn = {1292-895X}, abstract = {The gravitational settling of small spherical particles in an unbounded micropolar fluid with slip surfaces is considered. The motion is studied under the assumption of low Reynolds number. The slip boundary conditions on velocity and microrotation at the surface of the spherical particle is used. The solution for the stream function of the fluid flow is obtained analytically. The settling velocity is obtained and is plotted against the Knudsen number for various values of the micropolarity parameter and constants depending on the material of the solid surface. The problem of rotational motion of a particle with slip surface is also solved and the torque coefficient acting on the spherical particle is obtained and is plotted against Knudsen number for different values of micropolarity parameter, spin parameter, and the material constants. The correction to the Basset equation for settling velocity under gravity for slip particle in micropolar fluids is discussed with the range of Knudsen number which has been proven with known results available in the literature.}, }
@article {pmid30875616, year = {2019}, author = {Sun, J and Liu, C and Bhushan, B}, title = {A review of beetle hindwings: Structure, mechanical properties, mechanism and bioinspiration.}, journal = {Journal of the mechanical behavior of biomedical materials}, volume = {94}, number = {}, pages = {63-73}, doi = {10.1016/j.jmbbm.2019.02.031}, pmid = {30875616}, issn = {1878-0180}, mesh = {Animals ; Biomechanical Phenomena ; *Biomimetics ; Coleoptera/*anatomy &amp; histology/physiology ; *Mechanical Phenomena ; Movement ; Wings, Animal/*anatomy &amp; histology/physiology ; }, abstract = {Insects have a small mass and size and a low flying Reynolds number. Consequently, they serve as an excellent bionic representation of a micro air vehicle (MAV). Coleoptera (popularly referred to as beetles) have different characteristics from other flying insects. Not only can they fly at a low Reynolds number, but they also have deployable hindwings, which directly leads to a reduction in the size of their bodies. In narrow working spaces or unfavorable environments, a beetle's hindwings can fold automatically under the hard elytron. When the environment becomes conducive to flight, the hindwings can extend and help the beetle take off. This characteristic provides inspiration for the design of a bionic deployable wing system. In this paper, the structures and mechanical properties of hindwings and the mechanism of hindwing movement are reviewed, in addition to research on bioinspired deployable wings.}, }
@article {pmid30873209, year = {2019}, author = {Sepehr, H and Nikrityuk, P and Breakey, D and Sanders, RS}, title = {Numerical study of crude oil batch mixing in a long channel.}, journal = {Petroleum science}, volume = {16}, number = {1}, pages = {187-198}, pmid = {30873209}, issn = {1672-5107}, abstract = {The main objective of this work is to predict the mixing of two different miscible oils in a very long channel. The background to this problem relates to the mixing of heavy and light oil in a pipeline. As a first step, a 2D channel with an aspect ratio of 250 is considered. The batch-mixing of two miscible crude oils with different viscosities and densities is modeled using an unsteady laminar model and unsteady RANS model available in the commercial CFD solver ANSYS-Fluent. For a comparison, a LES model was used for a 3D version of the 2D channel. The distinguishing feature of this work is the Lagrangian coordinate system utilized to set no-slip wall boundary conditions. The global CFD model has been validated against classical analytical solutions. Excellent agreement has been achieved. Simulations were carried out for a Reynolds number of 6300 (calculated using light oil properties) and a Schmidt number of 10 4 . The results show that, in contrast to the unsteady RANS model, the LES and unsteady laminar models produce comparable mixing dynamics for two oils in the channel. Analysis of simulations also shows that, for a channel length of 100 m and a height of 0.4 m, the complete mixing of two oils across the channel has not been achieved. We showed that the mixing zone consists of the three different mixing sub-zones, which have been identified using the averaged mass fraction of the heavy oil along the flow direction. The first sub-zone corresponds to the main front propagation area with a length of several heights of the channel. The second and third sub-zones are characterized by so-called shear-flow-driven mixing due to the Kelvin-Helmholtz vortices occurring between oils in the axial direction. It was observed that the third sub-zone has a steeper mass fraction gradient of the heavy oil in the axial direction in comparison with the second sub-zone, which corresponds to the flow-averaged mass fraction of 0.5 for the heavy oil.}, }
@article {pmid30867881, year = {2019}, author = {Kawale, D and Jayaraman, J and Boukany, PE}, title = {Microfluidic rectifier for polymer solutions flowing through porous media.}, journal = {Biomicrofluidics}, volume = {13}, number = {1}, pages = {014111}, pmid = {30867881}, issn = {1932-1058}, abstract = {Fluidic rectification refers to anisotropic flow resistance upon changing the flow direction. Polymeric solutions, in contrast to Newtonian fluids, can exhibit an anisotropic flow resistance in microfluidic devices by tuning the channel shape at low Reynolds number. Such a concept has not been investigated in an anisotropic porous medium. We have developed a fluidic rectifier based on an anisotropic porous medium consisting of a periodic array of triangular pillars that can operate at a low Reynolds number. Rectification is achieved, when the type of high Weissenberg number elastic instabilities changes with the flow direction. The flow resistance differs across the two directions of the anisotropic porous medium geometry. We have identified the type of elastic instabilities that appear in both forward and backward directions. Particularly, we found a qualitative relation between the dead-zone instability and the onset of fluidic rectification.}, }
@article {pmid30866409, year = {2019}, author = {Faris Abdullah, M and Zulkifli, R and Harun, Z and Abdullah, S and Wan Ghopa, WA and Soheil Najm, A and Humam Sulaiman, N}, title = {Impact of the TiO2 Nanosolution Concentration on Heat Transfer Enhancement of the Twin Impingement Jet of a Heated Aluminum Plate.}, journal = {Micromachines}, volume = {10}, number = {3}, pages = {}, pmid = {30866409}, issn = {2072-666X}, abstract = {Here, the researchers carried out an experimental analysis of the effect of the TiO2 nanosolution concentration on the heat transfer of the twin jet impingement on an aluminum plate surface. We used three different heat transfer enhancement processes. We considered the TiO2 nanosolution coat, aluminum plate heat sink, and a twin jet impingement system. We also analyzed several other parameters like the nozzle spacing, nanosolution concentration, and the nozzle-to-plate distance and noted if these parameters could increase the heat transfer rate of the twin jet impingement system on a hot aluminum surface. The researchers prepared different nanosolutions, which consisted of varying concentrations, and coated them on the metal surface. Thereafter, we carried out an X-ray diffraction (XRD) and a Field Emission Scanning Electron Microscopy (FESEM) analysis for determining the structure and the homogeneous surface coating of the nanosolutions. This article also studied the different positions of the twin jets for determining the maximal Nusselt number (Nu). The researchers analyzed all the results and noted that the flow structure of the twin impingement jets at the interference zone was the major issue affecting the increase in the heat transfer rate. The combined influence of the spacing and nanoparticle concentration affected the flow structure, and therefore the heat transfer properties, wherein the Reynolds number (1% by volume concentration) maximally affected the Nusselt number. This improved the performance of various industrial and engineering applications. Hypothesis: Nusselt number was affected by the ratio of the nanoparticle size to the surface roughness. Heat transfer characteristics could be improved if the researchers selected an appropriate impingement system and selected the optimal levels of other factors. The surface coating with the TiO2 nanosolution also positively affected the heat transfer rate.}, }
@article {pmid30863983, year = {2019}, author = {Hamid, AH and Javed, T and Ali, N}, title = {Numerical study of hydromagnetic axisymmetric peristaltic flow at high Reynolds number and wave number.}, journal = {Biophysical reviews}, volume = {11}, number = {2}, pages = {139-147}, pmid = {30863983}, issn = {1867-2450}, abstract = {The computational study of MHD peristaltic motion is investigated for axisymmetric flow problem. The developed model is present in the form of partial differential equations. Then obtained partial differential equations are transferred into stream-vorticity (ψ - ω) form. Then Galerkin Finite element method is used to find the computational results of governing problem. The current study is compared with the existing well-known results at low Reynolds number and wave number. It is revealed that the present results are in well agreement with existing results in the literature. So, it is effective for higher values of Reynolds number and wave number. The variations of streamline are present graphically against high Reynolds number. It concludes that high Reynolds number and Hartmann number increase pressure rise per unit wavelength in positive pumping region sharply.}, }
@article {pmid30861480, year = {2019}, author = {Luo, X and Yin, H and Ren, J and Yan, H and Huang, X and Yang, D and He, L}, title = {Enhanced mixing of binary droplets induced by capillary pressure.}, journal = {Journal of colloid and interface science}, volume = {545}, number = {}, pages = {35-42}, doi = {10.1016/j.jcis.2019.03.016}, pmid = {30861480}, issn = {1095-7103}, abstract = {The mixing of binary droplets is of paramount importance in microfluidic systems. In order to reveal the mixing mechanism of two free droplets suspended in the immiscible phase, we have developed a novel experimental setup to study the internal mixing in coalescing droplets with varying interfacial tension differences and droplet sizes. It is confirmed that the interfacial energy of droplets supports the jet flow and liquid bridge expansion during the coalescence of droplets. The increase of interfacial tension difference can increase the intensity of jet flow accompanied with slower liquid bridge expansion, which enhances the mixing of droplets. The decrease of droplet size can increase the initial velocity of jet flow. However, the intensity of jet flow decreases due to the rapid expansion of the liquid bridge, which results in weaker internal mixing. On this basis, a Reynolds number incorporating the jet velocity and droplet size is proposed to characterize the vortex size, which represents the degree of droplet mixing. This study presents an effective approach for enhancing the mixing of droplets.}, }
@article {pmid30845732, year = {2019}, author = {Ye, C and Liu, J and Wu, X and Wang, B and Zhang, L and Zheng, Y and Xu, T}, title = {Hydrophobicity Influence on Swimming Performance of Magnetically Driven Miniature Helical Swimmers.}, journal = {Micromachines}, volume = {10}, number = {3}, pages = {}, pmid = {30845732}, issn = {2072-666X}, support = {61703392//National Natural Science Foundation of China(NSFC) for Young Scholar with 223 the Project/ ; U1713201//the joint Research Fund between the NSFC and Shenzhen/ ; JCYJ20170413152640731//Fundamental Research and 224 Discipline Layout project/ ; 2018YFC0115200//National Key R&amp;D Program of China/ ; }, abstract = {Helical microswimmers have been involved in a wide variety of applications, ranging from in vivo tasks such as targeted drug delivery to in vitro tasks such as transporting micro objects. Over the past decades, a number of studies have been established on the swimming performance of helical microswimmers and geometrical factors influencing their swimming performance. However, limited studies have focused on the influence of the hydrophobicity of swimmers' surface on their swimming performance. In this paper, we first demonstrated through theoretical analysis that the hydrophobicity of swimmer's surface material of the swimmer does affect its swimming performance: the swimmer with more hydrophobic surface is exerted less friction drag torque, and should therefore exhibit a higher step-out frequency, indicating that the swimmer with more hydrophobic surface should have better swimming performance. Then a series of experiments were conducted to verify the theoretical analysis. As a result, the main contribution of this paper is to demonstrate that one potential approach to improve the helical microswimmers' swimming performance could be making its surface more hydrophobic.}, }
@article {pmid30845671, year = {2019}, author = {Xia, Z and Xiao, Y and Yang, Z and Li, L and Wang, S and Liu, X and Tian, Y}, title = {Droplet Impact on the Super-Hydrophobic Surface with Micro-Pillar Arrays Fabricated by Hybrid Laser Ablation and Silanization Process.}, journal = {Materials (Basel, Switzerland)}, volume = {12}, number = {5}, pages = {}, pmid = {30845671}, issn = {1996-1944}, support = {51675371//National Natural Science Foundation of China/ ; }, abstract = {A super-hydrophobic aluminum alloy surface with decorated pillar arrays was obtained by hybrid laser ablation and further silanization process. The as-prepared surface showed a high apparent contact angle of 158.2 ± 2.0° and low sliding angle of 3 ± 1°. Surface morphologies and surface chemistry were explored to obtain insights into the generation process of super-hydrophobicity. The main objective of this current work is to investigate the maximum spreading factor of water droplets impacting on the pillar-patterned super-hydrophobic surface based on the energy conservation concept. Although many previous studies have investigated the droplet impacting behavior on flat solid surfaces, the empirical models were proposed based on a few parameters including the Reynolds number (Re), Weber number (We), as well as the Ohnesorge number (Oh). This resulted in limitations for the super-hydrophobic surfaces due to the ignorance of the geometrical parameters of the pillars and viscous energy dissipation for liquid flow within the pillar arrays. In this paper, the maximum spreading factor was deduced from the perspective of energy balance, and the predicted results were in good agreement with our experimental results with a mean error of 4.99% and standard deviation of 0.10.}, }
@article {pmid30842437, year = {2019}, author = {Yang, G and Hou, C and Zhao, M and Mao, W}, title = {Comparison of convective heat transfer for Kagome and tetrahedral truss-cored lattice sandwich panels.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {3731}, pmid = {30842437}, issn = {2045-2322}, support = {20160953008//Aeronautical Science Foundation of China (Aeronautic Science Foundation of China)/ ; }, abstract = {The aim of this paper is to make a thorough comparison between Kagome and tetrahedral truss-cored lattices both experimentally and numerically. Two titanium sandwich panels -one cored with the Kagome lattice and the other with the tetrahedral lattice -are manufactured by 3D printing technology. Comparisons of the thermal insulation, the inner flow pattern and the heat transfer between the two sandwich panels are completed subsequently according to the results from forced convective experiments and numerical simulation. Within the Reynolds number range of interest for this study, the Kagome lattice exhibits excellent heat dissipation compared with the tetrahedral lattice. In particular, when the cooling air flows in the direction OB of the two sandwich panels, the Kagome lattice provides an 8~37% higher overall Nusselt number for the sandwich panel compared to the tetrahedral lattice. The superiority of the Kagome lattice comes from a unique configuration in which the centre vertex acting as the vortex generator not only disturbs the primary flow but also induces more serious flow stagnation and separation. The complex fluid flow behaviours enhance heat transfer on both the endwalls and the trusses while causing a pressure drop that is almost two times higher than that of the tetrahedral lattice in the flow direction OB.}, }
@article {pmid30830969, year = {2019}, author = {Khair, AS and Balu, B}, title = {The lift force on a charged sphere that translates and rotates in an electrolyte.}, journal = {Electrophoresis}, volume = {40}, number = {18-19}, pages = {2407-2414}, doi = {10.1002/elps.201900029}, pmid = {30830969}, issn = {1522-2683}, support = {CBET-135064//National Science Foundation/International ; }, mesh = {Colloids/*chemistry ; Diffusion ; Electrolytes/*chemistry ; Electrophoresis/*methods ; Ions/*chemistry ; Kinetics ; Rotation ; }, abstract = {The distortion of the charge cloud around a uniformly charged, dielectric, rigid sphere that translates and rotates in an unbounded binary, symmetric electrolyte at zero Reynolds number is examined. The zeta potential of the particle ζ is assumed small relative to the thermal voltage scale. It is assumed that the equilibrium structure of the cloud is slightly distorted, which requires that the Péclet numbers characterizing distortion due to particle translation, Pet=Ua/D , and rotation, Per=Ωa2/D , are small compared to unity. Here, a is radius of the particle; D is the ionic diffusion coefficient; U=|U| and Ω=|Ω| , where U and Ω are the rectilinear and angular velocities of the particle, respectively. Perturbation expansions for small Pet and Per are employed to calculate the nonequilibrium structure of the cloud, whence the force and torque on the particle are determined. In particular, we predict that the sphere experiences a force orthogonal to its directions of translation and rotation. This "lift" force arises from the nonlinear distortion of the cloud under the combined actions of particle translation and rotation. The lift force is given by Flift=L(κa)(εa3ζ2/D2)U×Ω[1+O(Pet,Per)] . Here, ε is the permittivity of the electrolyte; κ-1 is the Debye length; and L(κa) is a negative function that decreases in magnitude with increasing κa . The lift force implies that an unconstrained particle would follow a curved path; an electrokinetic analog of the inertial Magnus effect. Finally, the implication of the lift force on cross-streamline migration of an electrophoretic particle in shear flow is discussed.}, }
@article {pmid30823482, year = {2019}, author = {Rehman, D and Morini, GL and Hong, C}, title = {A Comparison of Data Reduction Methods for Average Friction Factor Calculation of Adiabatic Gas Flows in Microchannels.}, journal = {Micromachines}, volume = {10}, number = {2}, pages = {}, pmid = {30823482}, issn = {2072-666X}, support = {643095//Horizon 2020 Framework Programme/ ; }, abstract = {In this paper, a combined numerical and experimental approach for the estimation of the average friction factor along adiabatic microchannels with compressible gas flows is presented. Pressure-drop experiments are performed for a rectangular microchannel with a hydraulic diameter of 295 μ m by varying Reynolds number up to 17,000. In parallel, the calculation of friction factor has been repeated numerically and results are compared with the experimental work. The validated numerical model was also used to gain an insight of flow physics by varying the aspect ratio and hydraulic diameter of rectangular microchannels with respect to the channel tested experimentally. This was done with an aim of verifying the role of minor loss coefficients for the estimation of the average friction factor. To have laminar, transitional, and turbulent regimes captured, numerical analysis has been performed by varying Reynolds number from 200 to 20,000. Comparison of numerically and experimentally calculated gas flow characteristics has shown that adiabatic wall treatment (Fanno flow) results in better agreement of average friction factor values with conventional theory than the isothermal treatment of gas along the microchannel. The use of a constant value for minor loss coefficients available in the literature is not recommended for microflows as they change from one assembly to the other and their accurate estimation for compressible flows requires a coupling of numerical analysis with experimental data reduction. Results presented in this work demonstrate how an adiabatic wall treatment along the length of the channel coupled with the assumption of an isentropic flow from manifold to microchannel inlet results in a self-sustained experimental data reduction method for the accurate estimation of friction factor values even in presence of significant compressibility effects. Results also demonstrate that both the assumption of perfect expansion and consequently wrong estimation of average temperature between inlet and outlet of a microchannel can be responsible for an apparent increase in experimental average friction factor in choked flow regime.}, }
@article {pmid30818010, year = {2019}, author = {Xia, Y and Yuan, M and Chen, M and Li, J and Ci, T and Ke, X}, title = {Liquid jet breakup: A new method for the preparation of poly lactic-co-glycolic acid microspheres.}, journal = {European journal of pharmaceutics and biopharmaceutics : official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V}, volume = {137}, number = {}, pages = {140-147}, doi = {10.1016/j.ejpb.2019.02.021}, pmid = {30818010}, issn = {1873-3441}, mesh = {Chemistry, Pharmaceutical/methods ; Delayed-Action Preparations ; Drug Carriers/*chemistry ; Drug Compounding/methods ; Drug Liberation ; Microspheres ; Particle Size ; Polylactic Acid-Polyglycolic Acid Copolymer/*chemistry ; Risperidone/*administration &amp; dosage/chemistry ; Surface Tension ; Technology, Pharmaceutical/*methods ; Viscosity ; }, abstract = {The purpose of this study was to apply the phenomenon of liquid jet breakup to the preparation of sustained-release microspheres. The mechanisms of liquid jet breakup in different jet states were investigated and the single factor method was used to study the effect of each process parameter on the particle size and size distribution of microspheres. Meantime, the prepared microspheres were characterized by morphology, drug loading, encapsulation efficiency and in vitro release. The results indicated that the process of liquid jet breakup could have 5 different states. The laminar flow state dominated when the Reynolds number (Re) was low, and the prepared microspheres had larger particle sizes. When the Re was high, the turbulent state was dominant and the microspheres had smaller particle sizes. And during the transition state from the laminar flow to the turbulence, the microspheres had a wide particle size distribution. Different process parameters could affect the particle size and distribution of microspheres by changing the Re, surface tension coefficient and viscosity. The microspheres prepared by liquid jet breakup were smooth and round with the drug loading of 35% and the encapsulation efficiency of 88%. In addition, when the polymeric carrier materials were different, the microspheres could have various drug release models such as sustained release with a lag phase, sustained release with no lag phase, pulsed release and so on, which could be applied widespread in the future.}, }
@article {pmid30813604, year = {2019}, author = {Kim, J and Davidson, S and Mani, A}, title = {Characterization of Chaotic Electroconvection near Flat Inert Electrodes under Oscillatory Voltages.}, journal = {Micromachines}, volume = {10}, number = {3}, pages = {}, pmid = {30813604}, issn = {2072-666X}, abstract = {The onset of electroconvective instability in an aqueous binary electrolyte under external oscillatory electric fields at a single constant frequency is investigated in a 2D parallel flat electrode setup. Direct numerical simulations (DNS) of the Poisson[-]Nernst[-]Planck equations coupled with the Navier[-]Stokes equations at a low Reynolds number are carried out. Previous studies show that direct current (DC) electric field can create electroconvection near ion-selecting membranes in microfluidic devices. In this study, we show that electroconvection can be generated near flat inert electrodes when the applied electric field is oscillatory in time. A range of applied voltage, the oscillation frequency and the ratio of ionic diffusivities is examined to characterize the regime in which electroconvection takes place. Similar to electroconvection under DC voltages, AC electroconvection occurs at sufficiently high applied voltages in units of thermal volts and is characterized by transverse instabilities, physically manifested by an array of counter-rotating vortices near the electrode surfaces. The oscillating external electric field periodically generate and destroy such unsteady vortical structures. As the oscillation frequency is reduced to O (10 - 1) of the intrinsic resistor[-]capacitor (RC) frequency of electrolyte, electroconvective instability is considerably amplified. This is accompanied by severe depletion of ionic species outside the thin electric double layer and by vigorous convective transport involving a wide range of scales including those comparable to the distance L between the parallel electrodes. The underlying mechanisms are distinctly nonlinear and multi-dimensional. However, at higher frequencies of order of the RC frequency, the electrolyte response becomes linear, and the present DNS prediction closely resembles those explained by 1D asymptotic studies. Electroconvective instability supports increased electric current across the system. Increasing anion diffusivity results in stronger amplification of electroconvection over all oscillation frequencies examined in this study. Such asymmetry in ionic diffusivity, however, does not yield consistent changes in statistics and energy spectrum at all wall-normal locations and frequencies, implying more complex dynamics and different scaling for electrolytes with unequal diffusivities. Electric current is substantially amplified beyond the ohmic current at high oscillation frequencies. Also, it is found that anion diffusivity higher than cation has stronger impact on smaller-scale motions (≲ 0.1 L).}, }
@article {pmid30811449, year = {2019}, author = {Khani, M and Lawrence, BJ and Sass, LR and Gibbs, CP and Pluid, JJ and Oshinski, JN and Stewart, GR and Zeller, JR and Martin, BA}, title = {Characterization of intrathecal cerebrospinal fluid geometry and dynamics in cynomolgus monkeys (macaca fascicularis) by magnetic resonance imaging.}, journal = {PloS one}, volume = {14}, number = {2}, pages = {e0212239}, pmid = {30811449}, issn = {1932-6203}, support = {P20 GM103408/GM/NIGMS NIH HHS/United States ; U54 GM104944/GM/NIGMS NIH HHS/United States ; }, mesh = {Animals ; Central Nervous System Diseases/*diagnostic imaging ; Cerebrospinal Fluid/*diagnostic imaging ; Female ; Hydrodynamics ; Macaca fascicularis ; *Magnetic Resonance Imaging ; Male ; Spine/*diagnostic imaging ; }, abstract = {Recent advancements have been made toward understanding the diagnostic and therapeutic potential of cerebrospinal fluid (CSF) and related hydrodynamics. Increased understanding of CSF dynamics may lead to improved detection of central nervous system (CNS) diseases and optimized delivery of CSF based CNS therapeutics, with many proposed therapeutics hoping to successfully treat or cure debilitating neurological conditions. Before significant strides can be made toward the research and development of interventions designed for human use, additional research must be carried out with representative subjects such as non-human primates (NHP). This study presents a geometric and hydrodynamic characterization of CSF in eight cynomolgus monkeys (Macaca fascicularis) at baseline and two-week follow-up. Results showed that CSF flow along the entire spine was laminar with a Reynolds number ranging up to 80 and average Womersley number ranging from 4.1-7.7. Maximum CSF flow rate occurred ~25 mm caudal to the foramen magnum. Peak CSF flow rate ranged from 0.3-0.6 ml/s at the C3-C4 level. Geometric analysis indicated that average intrathecal CSF volume below the foramen magnum was 7.4 ml. The average surface area of the spinal cord and dura was 44.7 and 66.7 cm2 respectively. Subarachnoid space cross-sectional area and hydraulic diameter ranged from 7-75 mm2 and 2-3.7 mm, respectively. Stroke volume had the greatest value of 0.14 ml at an axial location corresponding to C3-C4.}, }
@article {pmid30808870, year = {2019}, author = {Mayzel, J and Steinberg, V and Varshney, A}, title = {Stokes flow analogous to viscous electron current in graphene.}, journal = {Nature communications}, volume = {10}, number = {1}, pages = {937}, pmid = {30808870}, issn = {2041-1723}, abstract = {Electron transport in two-dimensional conducting materials such as graphene, with dominant electron-electron interaction, exhibits unusual vortex flow that leads to a nonlocal current-field relation (negative resistance), distinct from the classical Ohm's law. The transport behavior of these materials is best described by low Reynolds number hydrodynamics, where the constitutive pressure-speed relation is Stoke's law. Here we report evidence of such vortices observed in a viscous flow of Newtonian fluid in a microfluidic device consisting of a rectangular cavity-analogous to the electronic system. We extend our experimental observations to elliptic cavities of different eccentricities, and validate them by numerically solving bi-harmonic equation obtained for the viscous flow with no-slip boundary conditions. We verify the existence of a predicted threshold at which vortices appear. Strikingly, we find that a two-dimensional theoretical model captures the essential features of three-dimensional Stokes flow in experiments.}, }
@article {pmid30802483, year = {2019}, author = {Tassew, FA and Bergland, WH and Dinamarca, C and Bakke, R}, title = {Settling velocity and size distribution measurement of anaerobic granular sludge using microscopic image analysis.}, journal = {Journal of microbiological methods}, volume = {159}, number = {}, pages = {81-90}, doi = {10.1016/j.mimet.2019.02.013}, pmid = {30802483}, issn = {1872-8359}, mesh = {Anaerobiosis ; Bioreactors/microbiology ; Microscopy/*methods ; Particle Size ; Sewage/*chemistry/microbiology ; }, abstract = {Settling velocity and size distribution of anaerobic granular sludge samples were studied using microscopic image analysis and settling column experiments. Five granule samples were considered in this study. Three samples were collected at the Top, Middle and Bottom sections of a lab scale upflow anaerobic sludge bed reactor (UASB). Two other granule samples were obtained from industries. This paper aims to establish a method that uses microscopic image analysis and shape factor as a tool to determine the size distribution and settling velocity of anaerobic granules. Image analysis technique was used to calculate the shape factor and equivalent diameter of granules. The equivalent diameter was then used to calculate the theoretical settling velocities based on Allen's formula and estimate size distributions. The results showed that there was a good agreement between the theoretical and experimental mean settling velocity values. Both measured and calculated settling velocities increased with increasing Reynolds number (Re). However, the agreement between measured and calculated values was found to be weaker at higher Re values. Size distribution analyses of the granules have revealed that there was significant difference in the size distribution of granule samples collected at different heights of the lab scale reactor. Overall, granules from the bottom section of the reactor had larger diameter, settling velocity and shape factor than those at the middle and top section granules. Whereas granules collected from the top section exhibited the smallest granular diameter, settling velocity and shape factor.}, }
@article {pmid30800393, year = {2019}, author = {Marner, F and Scholle, M and Herrmann, D and Gaskell, PH}, title = {Competing Lagrangians for incompressible and compressible viscous flow.}, journal = {Royal Society open science}, volume = {6}, number = {1}, pages = {181595}, pmid = {30800393}, issn = {2054-5703}, abstract = {A recently proposed variational principle with a discontinuous Lagrangian for viscous flow is reinterpreted against the background of stochastic variational descriptions of dissipative systems, underpinning its physical basis from a different viewpoint. It is shown that additional non-classical contributions to the friction force occurring in the momentum balance vanish by time averaging. Accordingly, the discontinuous Lagrangian can alternatively be understood from the standpoint of an analogous deterministic model for irreversible processes of stochastic character. A comparison is made with established stochastic variational descriptions and an alternative deterministic approach based on a first integral of Navier-Stokes equations is undertaken. The applicability of the discontinuous Lagrangian approach for different Reynolds number regimes is discussed considering the Kolmogorov time scale. A generalization for compressible flow is elaborated and its use demonstrated for damped sound waves.}, }
@article {pmid30795856, year = {2019}, author = {Medici, G and West, LJ and Banwart, SA}, title = {Groundwater flow velocities in a fractured carbonate aquifer-type: Implications for contaminant transport.}, journal = {Journal of contaminant hydrology}, volume = {222}, number = {}, pages = {1-16}, doi = {10.1016/j.jconhyd.2019.02.001}, pmid = {30795856}, issn = {1873-6009}, mesh = {Carbonates ; England ; *Groundwater ; *Water Movements ; Water Wells ; }, abstract = {Contaminants that are highly soluble in groundwater are rapidly transported via fractures in mechanically resistant sedimentary rock aquifers. Hence, a rigorous methodology is needed to estimate groundwater flow velocities in such fractured aquifers. Here, we propose an approach using borehole hydraulic testing to compute flow velocities in an un-faulted area of a fractured carbonate aquifer by applying the cubic law to a parallel plate model. The Cadeby Formation (Yorkshire, NE England) - a Permian dolostone aquifer present beneath the University of Leeds Farm - is the fractured aquifer selected for this hydraulic experiment. The bedding plane fractures of this dolostone aquifer, which are sub-horizontal, sub-parallel and laterally persistent, largely dominate the flow at shallow (<~40 mBGL) depths. These flowing bedding plane discontinuities are separated by a rock matrix which is relatively impermeable (Kwell-test/Kcore-plug~10[4]) as is common in fractured carbonate aquifers. In the workflow reported here, the number of flowing fractures - mainly bedding plane fractures - intersecting three open monitoring wells are found from temperature/fluid conductivity and acoustic/optical televiewer logging. Following well installation, average fracture hydraulic apertures for screened intervals are found from analysis of slug tests. For the case study aquifer, this workflow predicts hydraulic apertures ranging from 0.10 up to 0.54 mm. However, groundwater flow velocities range within two order of magnitude from 13 up to 242 m/day. Notably, fracture apertures and flow velocities rapidly reduce with increasing depth below the water table; the upper ~10 m shows relatively high values of hydraulic conductivity (0.30-2.85 m/day) and corresponding flow velocity (33-242 m/day). Permeability development around the water table in carbonate aquifer-types is common, and arises where high pCO2 recharge water from the soil zone causes calcite/dolomite dissolution. Hence, agricultural contaminants entering the aquifer with recharge water are laterally transported rapidly within this upper part. Computation of groundwater flow velocities allows determination of the Reynolds number. Values of up ~1, indicating the lower limit of the transition from laminar to turbulent flow, are found at the studied site, which is situated away from major fault traces. Hence, turbulent flow is likely to arise in proximity to tectonic structures, such as normal faults, which localize flow and enhance karstification. The occurrence of turbulent flow in correspondence of such tectonic structures should be represented in regional groundwater flow simulations.}, }
@article {pmid30790045, year = {2019}, author = {Hyeon, J and So, H}, title = {Microfabricaton of microfluidic check valves using comb-shaped moving plug for suppression of backflow in microchannel.}, journal = {Biomedical microdevices}, volume = {21}, number = {1}, pages = {19}, doi = {10.1007/s10544-019-0365-1}, pmid = {30790045}, issn = {1572-8781}, mesh = {Equipment Design ; Humans ; *Lab-On-A-Chip Devices ; *Microfluidic Analytical Techniques/instrumentation/methods ; *Microfluidics/instrumentation/methods ; }, abstract = {This study reports on an efficient microscale one-way valve system that combines the physical properties of photopolymerized microstructures and viscoelastic microchannels to rectify flows with low Reynolds numbers. The comb-shaped moving plug in the microchannel prevented backflow in the closed state to ensure that the microchannel remained completely blocked in the closed state, but allowed forward flow in the open state. This microfluidic check valve was microfabricated using the combination of the soft lithography and the releasing methods with the use of a double photoresist layer to create microchannels and free-moving comb-shaped microstructures, respectively. As a result, the microfluidic check valves elicited average high-pressure differences as much as 10.75 kPa between the backward and forward flows at low Reynolds numbers of the order of 0.253, thus demonstrating efficient rectification of microfluids. This study supports the use of rectification systems for the development of biomedical devices, such as drug delivery, micropumps, and lab-on-a-chip, by allowing unidirectional flow.}, }
@article {pmid30785756, year = {2019}, author = {Wang, P and Cilliers, JJ and Neethling, SJ and Brito-Parada, PR}, title = {Effect of Particle Size on the Rising Behavior of Particle-Laden Bubbles.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {35}, number = {10}, pages = {3680-3687}, doi = {10.1021/acs.langmuir.8b04112}, pmid = {30785756}, issn = {1520-5827}, abstract = {The rising behavior of bubbles, initially half and fully coated with glass beads of various sizes, was investigated. The bubble velocity, aspect ratio, and oscillation periods were determined using high-speed photography and image analysis. In addition, the acting forces, drag modification factor, and modified drag coefficient were calculated and interpreted. Results show that the aspect ratio oscillation of the rising bubbles is similar, irrespective of the attached particle size. As the particle size is increased, the rising bubbles have a lower velocity and aspect ratio amplitude, with the time from release to each aspect ratio peak increasing. Higher particle coverage is shown to decrease the bubble velocity and dampen the oscillations, reducing the number of aspect ratio peaks observed. The highest rise velocities correspond to the lowest aspect ratios and vice versa, whereas a constant aspect ratio yields a constant rise velocity, independent of the particle size. Force analysis shows that the particle drag modification factor increases with the increased particle size and is greatest for fully laden bubbles. The modified drag coefficient of particle-laden bubbles increases with the increased particle size, although it decreases with the increased Reynolds number independent of the particle size. The drag force exerted by the particles plays a more dominant role in decreasing bubble velocities as the particle size increases. The results and interpretation produced a quantitative description of the behavior of rising particle-laden bubbles and the development of correlations will enhance the modeling of industrial applications.}, }
@article {pmid30781378, year = {2019}, author = {Álvarez-Regueiro, E and Vallejo, JP and Fernández-Seara, J and Fernández, J and Lugo, L}, title = {Experimental Convection Heat Transfer Analysis of a Nano-Enhanced Industrial Coolant.}, journal = {Nanomaterials (Basel, Switzerland)}, volume = {9}, number = {2}, pages = {}, pmid = {30781378}, issn = {2079-4991}, support = {ENE2014-55489-C2-1/2-R; ENE2017-86425-C2-1/2-R//Ministerio de Econom&#xed;a, Industria y Competitividad, Gobierno de Espa&#xf1;a/ ; }, abstract = {Convection heat transfer coefficients and pressure drops of four functionalized graphene nanoplatelet nanofluids based on the commercial coolant Havoline[®] XLC Pre-mixed 50/50 were experimentally determined to assess its thermal performance. The potential heat transfer enhancement produced by nanofluids could play an important role in increasing the efficiency of cooling systems. Particularly in wind power, the increasing size of the wind turbines, up to 10 MW nowadays, requires sophisticated liquid cooling systems to keep the nominal temperature conditions and protect the components from temperature degradation and hazardous environment in off-shore wind parks. The effect of nanoadditive loading, temperature and Reynolds number in convection heat transfer coefficients and pressure drops is discussed. A dimensionless analysis of the results is carried out and empirical correlations for the Nusselt number and Darcy friction factor are proposed. A maximum enhancement in the convection heat transfer coefficient of 7% was found for the nanofluid with nanoadditive loading of 0.25 wt %. Contrarily, no enhancement was found for the nanofluids of higher functionalized graphene nanoplatelet mass fraction.}, }
@article {pmid30780337, year = {2019}, author = {Lyu, YZ and Zhu, HJ and Sun, M}, title = {Flapping-mode changes and aerodynamic mechanisms in miniature insects.}, journal = {Physical review. E}, volume = {99}, number = {1-1}, pages = {012419}, doi = {10.1103/PhysRevE.99.012419}, pmid = {30780337}, issn = {2470-0053}, mesh = {*Air ; Animals ; Biomechanical Phenomena ; *Flight, Animal ; Insecta/*physiology ; }, abstract = {Miniature insects fly at very low Reynolds number (Re); low Re means large viscous effect. If flapping as larger insects, sufficient vertical force cannot be produced. We measure the wing kinematics for miniature-insect species of different sizes and compute the aerodynamic forces. The planar upstroke commonly used by larger insects changes to a U-shaped upstroke, which becomes deeper as size or Re decreases. For relatively large miniature insects, the U-shaped upstroke produces a larger vertical force than a planar upstroke by having a larger wing velocity and, for very small ones, the deep U-shaped upstroke produces a large transient drag directed upwards, providing the required vertical force.}, }
@article {pmid30780316, year = {2019}, author = {Jiang, L and Sun, C and Calzavarini, E}, title = {Robustness of heat transfer in confined inclined convection at high Prandtl number.}, journal = {Physical review. E}, volume = {99}, number = {1-1}, pages = {013108}, doi = {10.1103/PhysRevE.99.013108}, pmid = {30780316}, issn = {2470-0053}, abstract = {We investigate the dependency of the magnitude of heat transfer in a convection cell as a function of its inclination by means of experiments and simulations. The study is performed with a working fluid of large Prandtl number, Pr≃480, and at Rayleigh numbers Ra≃10^{8} and Ra≃5×10^{8} in a quasi-two-dimensional rectangular cell with unit aspect ratio. By changing the inclination angle (β) of the convection cell, the character of the flow can be changed from moderately turbulent, for β=0^{∘}, to laminar and steady at β=90^{∘}. The global heat transfer is found to be insensitive to the drastic reduction of turbulent intensity, with maximal relative variations of the order of 20% at Ra≃10^{8} and 10% at Ra≃5×10^{8}, while the Reynolds number, based on the global root-mean-square velocity, is strongly affected with a decay of more than 85% occurring in the laminar regime. We show that the intensity of the heat flux in the turbulent regime can be only weakly enhanced by establishing a large-scale circulation flow by means of small inclinations. However, in the laminar regime the heat is transported solely by a slow large-scale circulation flow which exhibits large correlations between the velocity and temperature fields. For inclination angles close to the transition regime in-between the turbulentlike and laminar state, a quasiperiodic heat-flow bursting phenomenon is observed.}, }
@article {pmid30780239, year = {2019}, author = {Suman, VK and Viknesh S, S and Tekriwal, MK and Bhaumik, S and Sengupta, TK}, title = {Grid sensitivity and role of error in computing a lid-driven cavity problem.}, journal = {Physical review. E}, volume = {99}, number = {1-1}, pages = {013305}, doi = {10.1103/PhysRevE.99.013305}, pmid = {30780239}, issn = {2470-0053}, abstract = {The investigation on grid sensitivity for the bifurcation problem of the canonical lid-driven cavity (LDC) flow results is reported here with very fine grids. This is motivated by different researchers presenting different first bifurcation critical Reynolds number (Re_{cr1}), which appears to depend on the formulation, numerical method, and choice of grid. By using a very-high-accuracy parallel algorithm, and the same method with which sequential results were presented by Lestandi et al. [Comput. Fluids 166, 86 (2018)CPFLBI0045-793010.1016/j.compfluid.2018.01.038] [for (257 × 257) and (513 × 513) uniformly spaced grid], we present results using (1025×1025) and (2049×2049) grid points. Detailed results presented using these grids help us understand the computational physics of the numerical receptivity of the LDC flow, with and without explicit excitation. The mathematical physics of the investigated problem will become apparent when we identify the roles of numerical errors with the ambient omnipresent disturbances in real physical flows as interchangeable. In physical or in numerical setups, presence of disturbances cannot be ignored. In this context, the need for explicit excitation for the used compact scheme arises for a definitive threshold amplitude, below which the flow relaxes back to quiescent state after the excitation is removed in computations. We also implement the present parallel method to show the physical aspects of primary and secondary instabilities to be maintained for other numerical schemes, and we show the results to reflect the complex physics during multiple subcritical Hopf bifurcation. Also, we relate the various sources of errors during computations that is typical of such shear-driven flow. These results, with near spectral accuracy, constitute universal benchmark results for the solution of Navier-Stokes equation for LDC.}, }
@article {pmid30780221, year = {2019}, author = {Takamure, K and Ozono, S}, title = {Relative importance of initial conditions on outflows from multiple fans.}, journal = {Physical review. E}, volume = {99}, number = {1-1}, pages = {013112}, doi = {10.1103/PhysRevE.99.013112}, pmid = {30780221}, issn = {2470-0053}, abstract = {Generation of homogeneous isotropic turbulence was attempted using an innovative "multifan wind tunnel" with 99 fans installed. The driving method used is based on a principle that the shear layers generated between outflows from the adjacent ducts lead to turbulent flow downstream. First, a signal composed of two frequency components is set, and then it is fed to all the fans for three kinds of arrangements of phases. Here, parameter N is introduced as the number of phases used for the 99 fans, which represents a variety of emanated shear layers. Furthermore, S is introduced as a measure of shear magnitude at the inlet of the test section. Relative importance of the initial conditions (N and S) in the development of turbulence was investigated. To estimate the contribution from naturally induced turbulence, we numerically decomposed the resulting velocity fluctuations into the periodic and nonperiodic component. Energy spectra for three values of N were calculated using nonperiodic data. The inertial subrange of a gradient of -5/3 widens with increasing N. The value S is the largest for N=2, but the turbulence intensity of the nonperiodic component is the largest for N=99. Hence, it might be suggested that the shear magnitude at the inlet of the test section is not as important as the variety of shear layers for effective generation of high-Reynolds-number turbulence.}, }
@article {pmid30771128, year = {2019}, author = {Li, R and Xu, D and Yin, Q}, title = {Effects of channel morphology on nitrate retention in a headwater agricultural stream in Lake Chaohu Basin, China.}, journal = {Environmental science and pollution research international}, volume = {26}, number = {11}, pages = {10651-10661}, pmid = {30771128}, issn = {1614-7499}, support = {Grant No. 51579061//National Natural Science Foundation of China/ ; }, mesh = {Agriculture ; China ; Environmental Monitoring/methods ; Lakes/*chemistry ; Nitrates/*analysis ; Rivers/chemistry ; Water Resources ; }, abstract = {Five field tracer experiments and relevant detailed investigations of physical characterizations were conducted to investigate the effects of channel geomorphic settings on nitrate uptake efficiency on a 310-m long geomorphically distinct stream reach in a headwater agricultural stream in Hefei District, Lake Chaohu Basin. The model-fitted parameters from the one-dimensional transport with inflow and storage model were used to estimate the transient storage metric ([Formula: see text]) and determine the total nitrate uptake coefficient (k) for the study reach. And then, a nutrient spiraling approach was applied to reach-scale nitrate uptake estimates (Sw, Vf, and U). The results showed that the main channel was the major contributor to nitrate uptake retention, and the higher geomorphic complexity might result in better nitrate uptake efficiency. The partial least squares regression (PLSR) analysis showed strong correlations between the independent variables as geomorphic settings, Reynolds number and transient storage, and the dependent variables as nitrate uptake metrics, which further underscored the importance of stream physical characteristics on measurement of stream nitrate uptake.}, }
@article {pmid30770644, year = {2019}, author = {Morales-Acuna, F and Ochoa, L and Valencia, C and Gurovich, AN}, title = {Characterization of blood flow patterns and endothelial shear stress during flow-mediated dilation.}, journal = {Clinical physiology and functional imaging}, volume = {39}, number = {4}, pages = {240-245}, doi = {10.1111/cpf.12564}, pmid = {30770644}, issn = {1475-097X}, mesh = {Adolescent ; Adult ; Blood Flow Velocity ; Brachial Artery/diagnostic imaging/*physiology ; Endothelium, Vascular/diagnostic imaging/*physiology ; Female ; Healthy Volunteers ; Humans ; Male ; Models, Cardiovascular ; *Pulsatile Flow ; Regional Blood Flow ; Time Factors ; *Vasodilation ; Young Adult ; }, abstract = {INTRODUCTION: Endothelial dysfunction is considered the first step in the development of atherosclerosis. Flow-mediated dilation (FMD) has been the most common assessment of endothelial function in research but it has failed in obtaining a widespread use in clinical settings due to a lack of standardization and a large inter-subject variability. Normalization of FMD to endothelial shear stress (ESS) has been proposed to solve its technical limitations. However, studies have not considered the characteristic of the blood flow during FMD under pulsatile conditions in their ESS estimations.<br><br>METHODS: A total of 26 young healthy subjects (15 females and 11 males) underwent FMD testing. Microhematocrit measurement was used to determine blood viscosity (&#x3bc;). ESS was calculated by Womersley's approximation, ESS&#xa0;= &#x3bc;*2K*Velocity/Diameter, where K is a function of Womersley's parameter (&#x3b1;). Blood flow patterns were determined by critical Reynolds number. Statistical analysis included repeated measures ANOVA to detect ESS differences during FMD until peak dilation. Significance was established at P&#x2264;0.05.<br><br>RESULTS: The mean (SD) FMD% and time to peak dilation were 7&#xb7;4 (3&#xb7;1) % and 35 (9&#xb7;3) seconds, respectively. ESS was significantly reduced during FMD until peak dilation (P<0&#xb7;001). Turbulent blood flow was the only pattern observed until peak dilation in 96&#xb7;15% of the sample.<br><br>CONCLUSION: Peak FMD dilation in a young healthy population is triggered mostly by high-ESS under turbulent flow conditions. Due to the pulsatile nature of blood flow and the appearance of a turbulent pattern during FMD, ESS should be estimated by Womersley's approximation rather than Poiseuille's law.}, }
@article {pmid30761361, year = {2018}, author = {Shah, RA and Khan, A and Shuaib, M}, title = {On the study of flow between unsteady squeezing rotating discs with cross diffusion effects under the influence of variable magnetic field.}, journal = {Heliyon}, volume = {4}, number = {11}, pages = {e00925}, pmid = {30761361}, issn = {2405-8440}, abstract = {The aim of this article is to provide an analytical and numerical investigation to the viscous fluid flow, heat and mass transfer under the influence of a variable magnetic field. The governing system of partial differential equations are transformed by means of similarity transformations to a system of ordinary differential equations which are solved by Homotopy Analysis Method (HAM) and BVP4c. The effects of involved physical parameters are illustrated for the velocity components, magnetic field components, heat and mass transfers. Authentification of HAM results for various involved physical parameters are supported by comparison with numerical results obtained by BVP4c. It is observed that increasing distance between discs increase pressure on lower disc and torque on upper disc. It is also observed that increase in axial component of magnetic field increase fluid's axial velocity and increase in magnetic Reynold's number decrease magnetic flux it lower disc. Heat flux from lower to upper disc is increased by increase in Dufour number.}, }
@article {pmid30760794, year = {2019}, author = {Tang, H and Hu, F and Xu, L and Dong, S and Zhou, C and Wang, X}, title = {Variations in hydrodynamic characteristics of netting panels with various twine materials, knot types, and weave patterns at small attack angles.}, journal = {Scientific reports}, volume = {9}, number = {1}, pages = {1923}, pmid = {30760794}, issn = {2045-2322}, abstract = {It is essential to conduct hydrodynamic experiments for fishing gear at small attack angles along the flow direction to better understand the hydrodynamic characteristics of netting and application of gear. The hydrodynamic characteristics of netting panels made of different materials at small attack angles were investigated by a self-designed setup; this is essential for the effective use of netting on different types of gears. As confirmed by experiments, the measured drag of designed frame without netting accounted for less than 20% of the total setup drag including experimental netting and remained in a steady state under various current speeds and small attack angles, indicating that the self-designed frame setup is suitable for such trials. The drag coefficient was determined by varying the attack angle, solidity ratio, Reynolds number, knot types, weave pattern, and twine materials at small attack angles. The results indicate that the drag coefficient increased as the attack angle increased, but decreased as the solidity ratio and Reynolds number increased. The drag generated by knot accounted for 21% of the total drag of nylon (PA) netting. For braided knotless netting, the drag coefficient of PA netting was about 8.4% lower than that of polythene netting (PE) and 7% lower than that of polyester netting (PES). Compared with twined netting, the braided netting exhibited a higher resistance to flow, corresponding to higher values of drag coefficient.}, }
@article {pmid30759039, year = {2019}, author = {Sera, T and Kuninaga, H and Fukasaku, K and Yokota, H and Tanaka, M}, title = {The Effectiveness of An Averaged Airway Model in Predicting the Airflow and Particle Transport Through the Airway.}, journal = {Journal of aerosol medicine and pulmonary drug delivery}, volume = {32}, number = {5}, pages = {278-292}, doi = {10.1089/jamp.2018.1500}, pmid = {30759039}, issn = {1941-2703}, mesh = {Administration, Inhalation ; Adult ; Aerosols/*administration &amp; dosage/pharmacokinetics ; Algorithms ; Biological Transport ; Computer Simulation ; Humans ; *Hydrodynamics ; Male ; Middle Aged ; *Models, Anatomic ; Respiratory System/*anatomy &amp; histology ; Tissue Distribution ; }, abstract = {Background: In this study, we proposed an averaged airway model design based on four healthy subjects and numerically evaluated its effectiveness for predicting the airflow and particle transport through an airway. Methods: Direct-averaged models of the conducting airways of four subjects were restored by averaging the three-dimensional (3D) skeletons of four healthy airways, which were calculated using an inverse 3D thinning algorithm. We simulated the airflow and particle transport in the individual and the averaged airway models using computational fluid dynamics. Results: The bifurcation geometry differs even among healthy subjects, but the averaged model retains the typical geometrical characteristics of the airways. The Reynolds number of the averaged model varied within the range found in the individual subject models, and the averaged model had similar inspiratory flow characteristics as the individual subject models. The deposition fractions at almost all individual lobes ranged within the variation observed in the subjects, however, the deposition fraction was higher in only one lobe. The deposition distribution at the main bifurcation point differed among the healthy subjects, but the characteristics of the averaged model fell within the variation observed in the individual subject models. On the contrary, the deposition fraction of the averaged model was higher than that of the average of the individual subject models and deviated from the range observed in the subject models. Conclusion: These results indicate that the direct-averaged model may be useful for predicting the individual airflow and particle transport on a macroscopic scale.}, }
@article {pmid30758910, year = {2019}, author = {Amer, M and Feng, Y and Ramsey, JD}, title = {Using CFD simulations and statistical analysis to correlate oxygen mass transfer coefficient to both geometrical parameters and operating conditions in a stirred-tank bioreactor.}, journal = {Biotechnology progress}, volume = {35}, number = {3}, pages = {e2785}, doi = {10.1002/btpr.2785}, pmid = {30758910}, issn = {1520-6033}, mesh = {Bioreactors ; Cell Culture Techniques/*instrumentation ; Gases/chemistry ; Hydrodynamics ; Kinetics ; Mathematical Computing ; Oxygen/*chemistry ; }, abstract = {Optimization of a bioreactor design can be an especially challenging process. For instance, testing different bioreactor vessel geometries and different impeller and sparger types, locations, and dimensions can lead to an exceedingly large number of configurations and necessary experiments. Computational fluid dynamics (CFD), therefore, has been widely used to model multiphase flow in stirred-tank bioreactors to minimize the number of optimization experiments. In this study, a multiphase CFD model with population balance equations are used to model gas-liquid mixing, as well as gas bubble distribution, in a 50 L single-use bioreactor vessel. The vessel is the larger chamber in an early prototype of a multichamber bioreactor for mammalian cell culture. The model results are validated with oxygen mass transfer coefficient (kL a) measurements within the prototype. The validated model is projected to predict the effect of using ring or pipe spargers of different sizes and the effect of varying the impeller diameter on kL a. The simulations show that ring spargers result in a superior kL a compared to pipe spargers, with an optimum sparger-to-impeller diameter ratio of 0.8. In addition, larger impellers are shown to improve kL a. A correlation of kL a is presented as a function of both the reactor geometry (i.e., sparger-to-impeller diameter ratio and impeller-to-vessel diameter ratio) and operating conditions (i.e., Reynolds number and gas flow rate). The resulting correlation can be used to predict kL a in a bioreactor and to optimize its design, geometry, and operating conditions.}, }
@article {pmid30746446, year = {2019}, author = {Huang, HW and Uslu, FE and Katsamba, P and Lauga, E and Sakar, MS and Nelson, BJ}, title = {Adaptive locomotion of artificial microswimmers.}, journal = {Science advances}, volume = {5}, number = {1}, pages = {eaau1532}, pmid = {30746446}, issn = {2375-2548}, support = {743217/ERC_/European Research Council/International ; }, abstract = {Bacteria can exploit mechanics to display remarkable plasticity in response to locally changing physical and chemical conditions. Compliant structures play a notable role in their taxis behavior, specifically for navigation inside complex and structured environments. Bioinspired mechanisms with rationally designed architectures capable of large, nonlinear deformation present opportunities for introducing autonomy into engineered small-scale devices. This work analyzes the effect of hydrodynamic forces and rheology of local surroundings on swimming at low Reynolds number, identifies the challenges and benefits of using elastohydrodynamic coupling in locomotion, and further develops a suite of machinery for building untethered microrobots with self-regulated mobility. We demonstrate that coupling the structural and magnetic properties of artificial microswimmers with the dynamic properties of the fluid leads to adaptive locomotion in the absence of on-board sensors.}, }
@article {pmid30736676, year = {2019}, author = {Waheed, W and Alazzam, A and Al-Khateeb, AN and Sung, HJ and Abu-Nada, E}, title = {Investigation of DPD transport properties in modeling bioparticle motion under the effect of external forces: Low Reynolds number and high Schmidt scenarios.}, journal = {The Journal of chemical physics}, volume = {150}, number = {5}, pages = {054901}, doi = {10.1063/1.5079835}, pmid = {30736676}, issn = {1089-7690}, abstract = {We have used a dissipative particle dynamics (DPD) model to study the movement of microparticles in a microfluidic device at extremely low Reynolds number (Re). The particles, immersed in a medium, are transported in the microchannel by a flow force and deflected transversely by an external force along the way. An in-house Fortran code is developed to simulate a two-dimensional fluid flow using DPD at Re ≥ 0.0005, which is two orders of magnitude less than the minimum Re value previously reported in the DPD literature. The DPD flow profile is verified by comparing it with the exact solution of Hagen-Poiseuille flow. A bioparticle based on a rigid spring-bead model is introduced in the DPD fluid, and the employed model is verified via comparing the velocity profile past a stationary infinite cylinder against the profile obtained via the finite element method. Moreover, the drag force and drag coefficient on the stationary cylinder are also computed and compared with the reported literature results. Dielectrophoresis (DEP) is investigated as a case study for the proposed DPD model to compute the trajectories of red blood cells in a microfluidic device. A mapping mechanism to scale the external deflecting force from the physical to DPD domain is performed. We designed and built our own experimental setup with the aim to compare the experimental trajectories of cells in a microfluidic device to validate our DPD model. These experimental results are used to investigate the dependence of the trajectory results on the Reynolds number and the Schmidt number. The numerical results agree well with the experiment results, and it is found that the Schmidt number is not a significant parameter for the current application; Reynolds numbers combined with the DEP-to-drag force ratio are the only important parameters influencing the behavior of particles inside the microchannel.}, }
@article {pmid30736476, year = {2019}, author = {Tai, J and Lam, YC}, title = {Elastic Turbulence of Aqueous Polymer Solution in Multi-Stream Micro-Channel Flow.}, journal = {Micromachines}, volume = {10}, number = {2}, pages = {}, pmid = {30736476}, issn = {2072-666X}, abstract = {Viscous liquid flow in micro-channels is typically laminar because of the low Reynolds number constraint. However, by introducing elasticity into the fluids, the flow behavior could change drastically to become turbulent; this elasticity can be realized by dissolving small quantities of polymer molecules into an aqueous solvent. Our recent investigation has directly visualized the extension and relaxation of these polymer molecules in an aqueous solution. This elastic-driven phenomenon is known as 'elastic turbulence'. Hitherto, existing studies on elastic flow instability are mostly limited to single-stream flows, and a comprehensive statistical analysis of a multi-stream elastic turbulent micro-channel flow is needed to provide additional physical understanding. Here, we investigate the flow field characteristics of elastic turbulence in a 3-stream contraction-expansion micro-channel flow. By applying statistical analyses and flow visualization tools, we show that the flow field bares many similarities to that of inertia-driven turbulence. More interestingly, we observed regions with two different types of power-law dependence in the velocity power spectra at high frequencies. This is a typical characteristic of two-dimensional turbulence and has hitherto not been reported for elastic turbulent micro-channel flows.}, }
@article {pmid30715051, year = {2018}, author = {Mehrdel, P and Karimi, S and Farré-Lladós, J and Casals-Terré, J}, title = {Novel Variable Radius Spiral[-]Shaped Micromixer: From Numerical Analysis to Experimental Validation.}, journal = {Micromachines}, volume = {9}, number = {11}, pages = {}, pmid = {30715051}, issn = {2072-666X}, abstract = {A novel type of spiral micromixer with expansion and contraction parts is presented in order to enhance the mixing quality in the low Reynolds number regimes for point-of-care tests (POCT). Three classes of micromixers with different numbers of loops and modified geometries were studied. Numerical simulation was performed to study the flow behavior and mixing performance solving the steady-state Navier[-]Stokes and the convection-diffusion equations in the Reynolds range of 0.1[-]10.0. Comparisons between the mixers with and without expansion parts were made to illustrate the effect of disturbing the streamlines on the mixing performance. Image analysis of the mixing results from fabricated micromixers was used to verify the results of the simulations. Since the proposed mixer provides up to 92% of homogeneity at Re 1.0, generating 442 Pa of pressure drop, this mixer makes a suitable candidate for research in the POCT field.}, }
@article {pmid30714602, year = {2019}, author = {Schaaf, C and Rühle, F and Stark, H}, title = {A flowing pair of particles in inertial microfluidics.}, journal = {Soft matter}, volume = {15}, number = {9}, pages = {1988-1998}, doi = {10.1039/c8sm02476f}, pmid = {30714602}, issn = {1744-6848}, abstract = {A flowing pair of particles in inertial microfluidics gives important insights into understanding and controlling the collective dynamics of particles like cells or droplets in microfluidic devices. They are applied in medical cell analysis and engineering. We study the dynamics of a pair of solid particles flowing through a rectangular microchannel using lattice Boltzmann simulations. We determine the inertial lift force profiles as a function of the two particle positions, their axial distance, and the Reynolds number. Generally, the profiles strongly differ between particles leading and lagging in flow and the lift forces are enhanced due to the presence of a second particle. At small axial distances, they are determined by viscous forces, while inertial forces dominate at large separations. We identify cross-streamline pairs as stable fixed points in the lift force profiles and argue that same-streamline configurations are only one-sided stable. Depending on the initial conditions, the two-particle lift forces in combination with the Poiseuille flow give rise to three types of unbound particle trajectories, called moving-apart, passing, and swapping, and one type of bound trajectory, where the particles perform damped oscillations towards the cross-stream line configuration. The damping rate scales with Reynolds number squared, since inertial forces are responsible for driving the particles to their steady-state positions.}, }
@article {pmid30712849, year = {2019}, author = {Lippert, T and Bandelin, J and Schlederer, F and Drewes, JE and Koch, K}, title = {Impact of ultrasound-induced cavitation on the fluid dynamics of water and sewage sludge in ultrasonic flatbed reactors.}, journal = {Ultrasonics sonochemistry}, volume = {55}, number = {}, pages = {217-222}, doi = {10.1016/j.ultsonch.2019.01.024}, pmid = {30712849}, issn = {1873-2828}, abstract = {The fluid dynamics of water, thickened waste activated sludge (WAS, total solids concentration 4.4%) and digested sludge (DS, total solids concentration 2.5%) within a lab-scale ultrasonic flatbed reactor were experimentally investigated. For a visual observation of the opaque sludge flow, sewage sludges were approximated by transparent xanthan solutions with identical flow behavior. The visualization of the flow was realized by use of an ultrasonic reactor with a transparent panel and dye streams injected into the flow. Without ultrasonic treatment, xanthan solutions showed distinct laminar flow behavior (generalized Reynolds numbers < 1), at a flow rate of 100 L/h. In water, dye streams remained coherent as well, but with slightly unsteady features (Reynolds number ∼ 350). Activation of the ultrasound reactor caused strong fluid dynamic disturbance in the water flow and dye streams were dissolved instantly, thus indicating turbulent mixing. For the xanthan solutions, however, mixing was considerably less pronounced. The dye streams in the DS substitute (0.5% xanthan solution) remained overall in laminar shape, but exhibited an eruption-like branching and an increase in diameter with advancing treatment duration. For the solution resembling WAS (2.0% xanthan solution), only weak dye stream disruption was observed, thus indicating that WAS flow in flatbed reactors is nearly laminar during ultrasonic treatment.}, }
@article {pmid30712603, year = {2019}, author = {Ibrahim, MG and Hasona, WM and ElShekhipy, AA}, title = {Concentration-dependent viscosity and thermal radiation effects on MHD peristaltic motion of Synovial Nanofluid: Applications to rheumatoid arthritis treatment.}, journal = {Computer methods and programs in biomedicine}, volume = {170}, number = {}, pages = {39-52}, doi = {10.1016/j.cmpb.2019.01.001}, pmid = {30712603}, issn = {1872-7565}, mesh = {Algorithms ; Arthritis, Rheumatoid/*physiopathology/*radiotherapy ; Humans ; Models, Statistical ; *Nanoparticles ; Peristalsis/*radiation effects ; Synovial Fluid/*radiation effects ; Viscosity/*radiation effects ; }, abstract = {BACKGROUND AND OBJECTIVE: The biomedical fluid which fills the Synovial joint cavity is called Synovial fluid which behaves as in the fluid classifications to Non-Newtonian fluids. Also it's described as a several micrometers thick layer among the interstitial cartilages with very low friction coefficient. Consequently, the present paper opts to investigate the influence of the concentration-dependent viscosity on Magnetohydrodynamic peristaltic flow of Synovial Nanofluid in an asymmetric channel in presence of thermal radiation effect.<br><br>METHOD: Our problem is solved for two models, in the first model which referred as Model-(I), viscosity is considered exponentially dependent on the concentration. Model-(2), Shear thinning index is considered as a function of concentration. Those models are introduced for the first time in peristaltic or Nanofluid flows literature. The governing problem is reformulated under the assumption of low Reynolds number and long wavelength. The resulting system of equations is solved numerically with the aid of Parametric ND Solve.<br><br>RESULTS: Detailed comparisons have been made between Model-(I) and Model-(2) and found unrealistic results between them. Results for velocity, temperature and nanoparticle concentration distributions as well as pressure gradient and pressure rise are offered graphically for different values of various physical parameters.<br><br>CONCLUSIONS: Such models are applicable to rheumatoid arthritis (RA) treatment. Rheumatoid arthritis patients can be treated by applying the magnetic field on an electrically conducting fluid, due to the movement of the ions within the cell which accelerates the metabolism of fluids.}, }
@article {pmid30671967, year = {2019}, author = {Tandler, T and Gellman, E and De La Cruz, D and Ellerby, DJ}, title = {Drag coefficient estimates from coasting bluegill sunfish Lepomis macrochirus.}, journal = {Journal of fish biology}, volume = {94}, number = {3}, pages = {532-534}, doi = {10.1111/jfb.13906}, pmid = {30671967}, issn = {1095-8649}, support = {IOS1354274//NSF/ ; IOS1754650//NSF/ ; 1354274//Division of Integrative Organismal Systems/ ; 1754650//Division of Integrative Organismal Systems/ ; }, mesh = {Animals ; Biomechanical Phenomena ; Perciformes/*physiology ; *Swimming ; }, abstract = {The drag coefficient bluegill sunfish Lepomis macrochirus was estimated from coasting deceleration as (mean ± SD) 0.0154 ± 0.0070 at a Reynolds number of 41,000 ± 14,000. This was within the coasting range in other species and lower than values obtained from dead drag measurements in this species and others. Low momentum losses during coasting may allow its use during intermittent propulsion to modulate power output or maximize energy economy.}, }
@article {pmid30657156, year = {2019}, author = {Haward, SJ and Kitajima, N and Toda-Peters, K and Takahashi, T and Shen, AQ}, title = {Flow of wormlike micellar solutions around microfluidic cylinders with high aspect ratio and low blockage ratio.}, journal = {Soft matter}, volume = {15}, number = {9}, pages = {1927-1941}, doi = {10.1039/c8sm02099j}, pmid = {30657156}, issn = {1744-6848}, abstract = {We employ time-resolved flow velocimetry and birefringence imaging methods to study the flow of a well-characterized shear-banding wormlike micellar solution around a novel glass-fabricated microfluidic circular cylinder. In contrast with typical microfluidic cylinders, our geometry is characterized by a high aspect ratio α = H/W = 5 and a low blockage ratio β = 2r/W = 0.1, where H and W are the channel height and width, and the cylinder radius r = 20 μm. The small cylinder radius allows access up to very high Weissenberg numbers 1.9 ≤ Wi = λMU/r ≤ 3750 (where λM is the Maxwell relaxation time) while inertial effects remain entirely negligible (Reynolds number, Re < 10-4). At low Wi values, the flow remains steady and symmetric and a birefringent region (indicating micellar alignment and tensile stress) develops downstream of the cylinder. Above a critical value Wic ≈ 60 the flow transitions to a steady asymmetric state, characterized as a supercritical pitchfork bifurcation, in which the fluid takes a preferential path around one side of the cylinder. At a second critical value Wic2 ≈ 130, the flow becomes time-dependent, with a characteristic frequency f0 ≈ 1/λM. This initial transition to time dependence has characteristics of a subcritical Hopf bifurcation. Power spectra of the measured fluctuations become complex as Wi is increased further, showing a gradual slowing down of the dynamics and emergence of harmonics. A final transition at very high Wic3 corresponds to the re-emergence of a single peak in the power spectrum but at much higher frequency. We discuss this in terms of possible flow-induced breakage of micelles into shorter species with a faster relaxation time.}, }
@article {pmid30650659, year = {2019}, author = {Luo, L and He, Y}, title = {Magnetically Induced Flow Focusing of Non-Magnetic Microparticles in Ferrofluids under Inclined Magnetic Fields.}, journal = {Micromachines}, volume = {10}, number = {1}, pages = {}, pmid = {30650659}, issn = {2072-666X}, support = {11502102//National Natural Science Foundation of China/ ; }, abstract = {The ability to focus biological particles into a designated position of a microchannel is vital for various biological applications. This paper reports particle focusing under vertical and inclined magnetic fields. We analyzed the effect of the angle of rotation (θ) of the permanent magnets and the critical Reynolds number (Rec) on the particle focusing in depth. We found that a rotation angle of 10° is preferred; a particle loop has formed when Re < Rec and Rec of the inclined magnetic field is larger than that of the vertical magnetic field. We also conducted experiments with polystyrene particles (10.4 μm in diameter) to prove the calculations. Experimental results show that the focusing effectiveness improved with increasing applied magnetic field strength or decreasing inlet flow rate.}, }
@article {pmid30636127, year = {2018}, author = {Iyer, KP and Schumacher, J and Sreenivasan, KR and Yeung, PK}, title = {Steep Cliffs and Saturated Exponents in Three-Dimensional Scalar Turbulence.}, journal = {Physical review letters}, volume = {121}, number = {26}, pages = {264501}, doi = {10.1103/PhysRevLett.121.264501}, pmid = {30636127}, issn = {1079-7114}, abstract = {The intermittency of a passive scalar advected by three-dimensional Navier-Stokes turbulence at a Taylor-scale Reynolds number of 650 is studied using direct numerical simulations on a 4096^{3} grid; the Schmidt number is unity. By measuring scalar increment moments of high orders, while ensuring statistical convergence, we provide unambiguous evidence that the scaling exponents saturate to 1.2 for moment orders beyond about 12, indicating that scalar intermittency is dominated by the most singular shocklike cliffs in the scalar field. We show that the fractal dimension of the spatial support of steep cliffs is about 1.8, whose sum with the saturation exponent value of 1.2 adds up to the space dimension of 3, thus demonstrating a deep connection between the geometry and statistics in turbulent scalar mixing. The anomaly for the fourth and sixth order moments is comparable to that in the Kraichnan model for the roughness exponent of 4/3.}, }
@article {pmid30624119, year = {2018}, author = {Caracappa, JC and Munroe, DM}, title = {Morphological Variability Among Broods of First-Stage Blue Crab (Callinectes sapidus) Zoeae.}, journal = {The Biological bulletin}, volume = {235}, number = {3}, pages = {123-133}, doi = {10.1086/699922}, pmid = {30624119}, issn = {1939-8697}, mesh = {Animals ; Biological Variation, Population ; Brachyura/*anatomy &amp; histology ; Female ; Larva/anatomy &amp; histology ; Models, Biological ; Swimming ; }, abstract = {External morphology has been shown to influence predation and locomotion of decapod larvae and is, therefore, directly related to their ability to survive and disperse. The first goal of this study was to characterize first-stage blue crab zoeal morphology and its variability across larval broods to test whether inter-brood differences in morphology exist. The second was to identify possible correlations between maternal characteristics and zoeal morphology. The offspring of 21 individuals were hatched in the laboratory, photographed, and measured. Zoeae exhibited substantial variability, with all metrics showing significant inter-brood differences. The greatest variability was seen in the zoeal abdomen, rostrum, and dorsal spine length. A principal component analysis showed no distinct clustering of broods, with variation generally driven by larger zoeae. Using observed morphology, models of drag induced by swimming and sinking also showed significant inter-brood differences, with a maximum twofold difference across broods. In contrast to trends in other decapod taxa, maternal characteristics (female carapace width and mass and egg sponge volume and mass) are not significant predictors of zoeal morphology. These results suggest that brood effects are present across a wide range of morphological characteristics and that future experiments involving Callinectes sapidus morphology or its functionality should explicitly account for inter-brood variation. Additionally, inter-brood morphological differences may result in differential predation mortality and locomotory abilities among broods.}, }
@article {pmid30624117, year = {2018}, author = {Lamont, EI and Emlet, RB}, title = {Permanently Fused Setules Create Unusual Folding Fans Used for Swimming in Cyprid Larvae of Barnacles.}, journal = {The Biological bulletin}, volume = {235}, number = {3}, pages = {185-194}, doi = {10.1086/700084}, pmid = {30624117}, issn = {1939-8697}, mesh = {Animals ; Larva/anatomy &amp; histology/ultrastructure ; *Swimming ; Thoracica/*anatomy &amp; histology/ultrastructure ; }, abstract = {Many crustacean swimming appendages carry arrays of plumose setae-exoskeletal, feather-like structures of long bristles (setae) with short branches (setules) distributed along two sides. Although closely spaced, setae are not physically interconnected. Setal arrays function during swimming as drag-based leaky paddles that push the organism through water. Barnacle cyprids, the final, non-feeding larval stage, swim with six pairs of legs (thoracopods) that open and close setal arrays in alternating high-drag power strokes and low-drag recovery strokes. While studying cyprid swimming, we found that their thoracopods contained setae permanently cross-linked by fused setules. These cuticular connections would seem highly unlikely because setae are individually produced exoskeletal secretions, and the connections imply unknown processes for the production or modification of crustacean setae. We describe the morphology and function of plumose setae on cyprids of Balanus glandula and other species across the clade Cirripedia. Setules from adjacent plumose setae are seamlessly joined at their tips and occur in three distinct linkage patterns. Thoracopods lack muscles to open and close the array; interconnected setae are instead pulled apart, producing a paddle-like fan with high drag when appendages spread laterally during power strokes. Setules are spring-like, passively closing setae into tight bundles with low drag during recovery strokes. The linked setules occur in the three main clades of the Cirripedia. This cuticular arrangement is effective in swimming, may eliminate the need for muscles to close the setal array, and may represent a unique swimming structure within the Crustacea.}, }
@article {pmid30606096, year = {2019}, author = {Kunze, E}, title = {Biologically Generated Mixing in the Ocean.}, journal = {Annual review of marine science}, volume = {11}, number = {}, pages = {215-226}, doi = {10.1146/annurev-marine-010318-095047}, pmid = {30606096}, issn = {1941-0611}, mesh = {Aquatic Organisms/*physiology ; Diffusion ; Gravitation ; Swimming ; Temperature ; *Water Movements ; Wind ; }, abstract = {This article assesses the contribution to ocean mixing by the marine biosphere at both high and low Reynolds numbers Re= uℓ/ ν. While back-of-the-envelope estimates have suggested that swimming marine organisms might generate as much high-Reynolds-number turbulence as deep-ocean tide- and wind-generated internal waves, and that turbulent dissipation rates of O(10[-5] W kg[-1]) (Re ∼ 10[5]) could be produced by aggregations of organisms ranging from O(0.01 m) krill to O(10 m) cetaceans, comparable to strong wind and buoyancy forcing near the surface, microstructure measurements do not find consistently elevated dissipation associated with diel vertically migrating krill. Elevated dissipation rates are associated with schools of O(0.1- 1 m) fish but with low mixing coefficients (γ ∼ 0.002-0.02, as compared with γ ∼ 0.2 for geophysical turbulence). Likewise, viscously induced drift at low Reynolds numbers produces little mixing of temperature, solutes, dissolved nutrients, and gases when realistic swimmers and molecular scalar diffusion are taken into account. The conclusion is that, while the marine biosphere can generate turbulence, it contributes little ocean mixing compared with breaking internal gravity waves.}, }
@article {pmid30605404, year = {2019}, author = {Itzhak, N and Greenblatt, D}, title = {Aerodynamic factors affecting rebreathing in infants.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {126}, number = {4}, pages = {952-964}, doi = {10.1152/japplphysiol.00784.2018}, pmid = {30605404}, issn = {1522-1601}, mesh = {Carbon Dioxide/metabolism ; Humans ; Infant, Newborn ; Oxygen/metabolism ; Prone Position/*physiology ; Respiration ; Risk Factors ; Sleep/*physiology ; Sudden Infant Death/*prevention &amp; control ; Temperature ; Tidal Volume/physiology ; }, abstract = {The rebreathing of expire air, with high carbon dioxide and low oxygen concentrations, has long been implicated in unexplained Sudden Infant Death Syndrome (SIDS) when infants are placed to sleep in a prone (facedown) position. This study elucidates the effect of the aerodynamic parameters Reynolds number, Strouhal number, and Froude number on the percentage of expired air that is reinspired (rebreathed). A nasal module was designed that served as a simplified geometric representation of infant nostrils and placed above a hard, flat surface. Quantitative and flow visualization experiments were performed to measure rebreathing, using water as the working medium, under conditions of dynamic similarity. Different anatomic (e.g., tidal volume, nostril diameter), physiological (e.g., breathing frequency), and environmental (e.g., temperature, distance from the surface) factors were considered. Increases in Strouhal number (simultaneously faster and shallower breathing) always produced higher rebreathed percentages, because rolled-up vortices in the vicinity of the nostrils had less time to move away by self-induction. Positively and negatively buoyant flows resulted in significant rebreathing. In the latter case, consistent with a warm environment and a high percentage of rebreathed CO2, denser gas pooled in the vicinity of the nostrils. Reynolds numbers below 200 also dramatically increased rebreathing because the expired gas pooled much closer to the nostrils. These results clearly elucidated how the prone position dramatically increases rebreathing by a number of different mechanisms. Furthermore, the results offer plausible explanations of why a high-temperature environment and low birthweight are SIDS risk factors. NEW &amp; NOTEWORTHY A fundamentally new aerodynamics-based approach to the study of rebreathing of expired air in infants is presented. Rebreathing is implicated in unexplained Sudden Infant Death Syndrome (SIDS) when infants sleep in a prone position. This is the first time that aerodynamic parameters are systematically varied and their effects on rebreathing quantified. The study provides us with a deeper understanding of the effects of breathing frequency, tidal volume (birthweight) and environmental conditions.}, }
@article {pmid30604300, year = {2019}, author = {Wu, P and Gao, Q and Hsu, PL}, title = {On the representation of effective stress for computing hemolysis.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {18}, number = {3}, pages = {665-679}, doi = {10.1007/s10237-018-01108-y}, pmid = {30604300}, issn = {1617-7940}, support = {51406127//National Natural Science Foundation of China/ ; BK20140344//Natural Science Foundation of Jiangsu Province/ ; }, mesh = {Animals ; Capillaries/physiopathology ; Heart-Assist Devices ; *Hemolysis ; Humans ; Hydrodynamics ; *Models, Cardiovascular ; Pressure ; *Stress, Mechanical ; United States ; United States Food and Drug Administration ; }, abstract = {Hemolysis is a major concern in blood-circulating devices, which arises due to hydrodynamic loading on red blood cells from ambient flow environment. Hemolysis estimation models have often been used to aid hemocompatibility design. The preponderance of hemolysis models was formulated on the basis of laminar flows. However, flows in blood-circulating devices are rather complex and can be laminar, transitional or turbulent. It is an extrapolation to apply these models to turbulent flows. For the commonly used power-law models, effective stress has often been represented using Reynolds stresses for estimating hemolysis in turbulent flows. This practice tends to overpredict hemolysis. This study focused on the representation of effective stress in power-law models. Through arithmetic manipulations from Navier-Stokes equation, we showed that effective stress can be represented in terms of energy dissipation, which can be readily obtained from CFD simulations. Three cases were tested, including a capillary tube, the FDA benchmark cases of nozzle model and blood pump. The results showed that the representation of effective stress in terms of energy dissipation greatly improved the prediction of hemolysis for a wide range of flow conditions. The improvement increases as Reynolds number increases; the overprediction of hemolysis was reduced by up to two orders of magnitude.}, }
@article {pmid30603681, year = {2018}, author = {Szaszák, N and Roloff, C and Bordás, R and Bencs, P and Szabó, S and Thévenin, D}, title = {A novel type of semi-active jet turbulence grid.}, journal = {Heliyon}, volume = {4}, number = {12}, pages = {e01026}, pmid = {30603681}, issn = {2405-8440}, abstract = {This article describes a novel approach to generate increased turbulence levels in an incoming flow. It relies on a cost-effective and robust semi-active jet grid, equipped with flexible tubes as moving elements attached onto tube connections placed at the intersections of a fixed, regular grid. For the present study, these flexible tubes are oriented in counter-flow direction in a wind tunnel. Tube motion is governed by multiple interactions between the main flow and the jets exiting the tubes, resulting in chaotic velocity fluctuations and high turbulence intensities in the test section. After describing the structure of the turbulence generator, the turbulent properties of the airflow downstream of the grid in both passive and active modes are measured by hot-wire anemometry and compared with one another. When activating the turbulence generator, turbulence intensity, turbulent kinetic energy, and the Taylor Reynolds number are noticeably increased in comparison with the passive mode (corresponding to simple grid turbulence). Furthermore, the inertial subrange of the turbulent energy spectrum becomes wider and closely follows Kolmogorov's -5/3 law. These results show that the semi-active grid, in contrast to passive systems, is capable of producing high turbulence levels, even at low incoming flow velocity. Compared to alternatives based on actuators driven by servo-motors, the production and operation costs of the semi-active grid are very moderate and its robustness is much higher.}, }
@article {pmid30602925, year = {2018}, author = {Garcia, F and Stefani, F}, title = {Continuation and stability of rotating waves in the magnetized spherical Couette system: secondary transitions and multistability.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {474}, number = {2220}, pages = {20180281}, pmid = {30602925}, issn = {1364-5021}, abstract = {Rotating waves (RW) bifurcating from the axisymmetric basic magnetized spherical Couette (MSC) flow are computed by means of Newton-Krylov continuation techniques for periodic orbits. In addition, their stability is analysed in the framework of Floquet theory. The inner sphere rotates while the outer is kept at rest and the fluid is subjected to an axial magnetic field. For a moderate Reynolds number Re = 10[3] (measuring inner rotation), the effect of increasing the magnetic field strength (measured by the Hartmann number Ha) is addressed in the range Ha∈(0, 80) corresponding to the working conditions of the HEDGEHOG experiment at Helmholtz-Zentrum Dresden-Rossendorf. The study reveals several regions of multistability of waves with azimuthal wavenumber m = 2, 3, 4, and several transitions to quasi-periodic flows, i.e modulated rotating waves. These nonlinear flows can be classified as the three different instabilities of the radial jet, the return flow and the shear layer, as found in the previous studies. These two flows are continuously linked, and part of the same branch, as the magnetic forcing is increased. Midway between the two instabilities, at a certain critical Ha, the non-axisymmetric component of the flow is maximum.}, }
@article {pmid30602310, year = {2018}, author = {Murphy, EAK and Barros, JM and Schultz, MP and Flack, KA and Steppe, CN and Reidenbach, MA}, title = {Roughness effects of diatomaceous slime fouling on turbulent boundary layer hydrodynamics.}, journal = {Biofouling}, volume = {34}, number = {9}, pages = {976-988}, doi = {10.1080/08927014.2018.1517867}, pmid = {30602310}, issn = {1029-2454}, mesh = {Biofilms/*growth &amp; development ; Biofouling/*prevention &amp; control ; Friction ; *Hydrodynamics ; Rheology ; *Ships ; Stress, Mechanical ; Surface Properties ; }, abstract = {Biofilm fouling significantly impacts ship performance. Here, the impact of biofilm on boundary layer structure at a ship-relevant, low Reynolds number was investigated. Boundary layer measurements were performed over slime-fouled plates using high resolution particle image velocimetry (PIV). The velocity profile over the biofilm showed a downward shift in the log-law region (ΔU[+]), resulting in an effective roughness height (ks) of 8.8 mm, significantly larger than the physical thickness of the biofilm (1.7 ± 0.5 mm) and generating more than three times as much frictional drag as the smooth-wall. The skin-friction coefficient, Cf, of the biofilm was 9.0 × 10[-3] compared with 2.9 × 10[-3] for the smooth wall. The biofilm also enhances turbulent kinetic energy (tke) and Reynolds shear stress, which are more heterogeneous in the streamwise direction than smooth-wall flows. This suggests that biofilms increase drag due to high levels of momentum transport, likely resulting from protruding streamers and surface compliance.}, }
@article {pmid32625002, year = {2019}, author = {Pérez-Hernández, J and Nicasio-Torres, MDP and Sarmiento-López, LG and Rodríguez-Monroy, M}, title = {Production of anti-inflammatory compounds in Sphaeralcea angustifolia cell suspension cultivated in stirred tank bioreactor.}, journal = {Engineering in life sciences}, volume = {19}, number = {3}, pages = {196-205}, pmid = {32625002}, issn = {1618-0240}, abstract = {Sphaeralcea angustifolia is a plant used for the treatment of inflammatory processes. Scopoletin, tomentin, and sphaeralcic acid were identified as the compounds with anti-inflammatory and immunomodulatory effects. Successful establishment of the cell culture in Erlenmeyer flasks has been reported previously. The aim of this study was to evaluate the ability of cells in suspension from S. angustifolia grown in a stirred tank bioreactor and demonstrate their capacity to produce bioactive compounds. Cells in suspension grown at 200 rpm reached a maximal cell biomass in dry weight at 19.11 g/L and produced 3.47 mg/g of sphaeralcic acid. The mixture of scopoletin and tomentin was only detected at the beginning of the culture (12.13 μg/g). Considering that the profile of dissolved oxygen during the cultures was lesser than 15%, it is possible that the low growth at 100 rpm could be due to oxygen limitations or to cell sedimentation. At 400 rpm, a negative effect on cell viability could be caused by the increase in the hydrodynamic stress, including the impeller tip, average shear rate, and Reynolds number. The sphaeralcic acid content in the cell suspension of S. angustifolia obtained in the bioreactor was two orders of magnitude greater than that reported for the culture grown in Erlenmeyer flasks.}, }
@article {pmid32116345, year = {2019}, author = {Mensch, AE and Cleary, TG}, title = {Measurements and predictions of thermophoretic soot deposition.}, journal = {International journal of heat and mass transfer}, volume = {143}, number = {}, pages = {}, pmid = {32116345}, issn = {0017-9310}, support = {9999-NIST/ImNIST/Intramural NIST DOC/United States ; }, abstract = {A thin laminar flow channel with a transverse temperature gradient was used to examine thermophoretic deposition of soot aerosol particles in experiments and modeled in Fire Dynamics Simulator (FDS) simulations. Conditions investigated included three flowrates, with nominal Reynolds number based on the hydraulic diameter of 55, 115 and 230, and two applied temperature gradients, nominally 10 °C/mm and 20 °C/mm, with repeats. Soot was generated from a propene diffusion flame. The burner exhaust was mixed with dilution air, and most large agglomerates greater than 1 μm aerodynamic diameter were removed prior to the channel inlet. The expected thermophoretic velocity of the aerosol was calculated from the applied temperature gradient. A calculated deposition velocity was determined from the mass of deposition, the channel inlet soot concentration, and the exposure time. Uniform soot deposition allowed targets to be used to measure the mass of deposition on the cold side of the channel. The mass of deposition was also determined by subtracting the mass of soot exiting the channel from the mass of soot entering the channel during the exposure time. The deposition velocities from these two methods generally agreed with the thermophoretic velocity and with each other. The deposition mass predicted by the FDS model also compared well with the experiments in most cases. The disagreements for the lowest flow rate cases are attributed to buoyant flow effects adding uncertainty to the actual temperature gradients present in the channel. (The opinions, findings, and conclusions expressed in this paper are the authors' and do not represent the views or policies of NIST or the United States Government.).}, }
@article {pmid30584714, year = {2018}, author = {Wang, WX and Wang, WL and Kang, HL and Guo, MM and Yang, B and Chen, ZX and Zhao, M}, title = {Effect of naturally restored grassland on the ephemeral gully erosion in the loess hilly and gully region.}, journal = {Ying yong sheng tai xue bao = The journal of applied ecology}, volume = {29}, number = {12}, pages = {3891-3899}, doi = {10.13287/j.1001-9332.201812.016}, pmid = {30584714}, issn = {1001-9332}, mesh = {Agriculture ; China ; *Conservation of Natural Resources ; Environmental Monitoring ; *Grassland ; *Soil ; }, abstract = {Ephemeral gully erosion is an important erosion type in hilly and gully regions of Loess Plateau. While previous studies mainly focused on ephemeral gullies in agricultural land, little is known about the effects of naturally restored grassland on ephemeral gully erosion. In this study, taking the bare ephemeral gullies as the baseline, we conducted in-situ flushing tests to explore runoff and sediment yield characteristics and erosion mechanism of grassland ephemeral gullies under the runoff conditions of 5, 10, 15, 20 and 25 L·min[-1]. Compared to the bare ephemeral gully, average flow velocity, stable runoff rate, Reynolds number and Froude number of grassland ephe-meral gullies was reduced by 25.4%-67.3%, 8.4%-26.6%, 54.9%-80.5%, 18.6%-65.1%, respectively, whereas resistance coefficient was increased by 0.09-7.18 folds. Compared to the bare ephemeral gully, the maximum sediment yield rate, stable sediment yield rate, average sediment yield rate of grassland ephemeral gullies was decreased by 55.1%-90.9%, 61.8%-95.4%, and 64.8%-92.4%, respectively. The sediment yield reduction benefit of the naturally restored grassland under the discharge flow rate of 5-25 L·min[-1] could reach 65.9%-88.8%, which decreased with increasing discharge flow rate. Compared to the bare ephemeral gully, average stream power and average shear stress of grassland ephemeral gullies was reduced by 54.9%-80.5% and 12.4%-51.1%, respectively, whereas the critical stream power and critical shear stress was increased by 1.43 folds and 33.7%, respectively. The average sediment yield of grassland and bare ephemeral gullies was signifi-cantly linearly related to average stream power and shear stress. Naturally restored grassland significantly increased the erosion resistance and reduced runoff erosion potential of ephemeral gullies.}, }
@article {pmid30576199, year = {2018}, author = {Gabbana, A and Polini, M and Succi, S and Tripiccione, R and Pellegrino, FMD}, title = {Prospects for the Detection of Electronic Preturbulence in Graphene.}, journal = {Physical review letters}, volume = {121}, number = {23}, pages = {236602}, doi = {10.1103/PhysRevLett.121.236602}, pmid = {30576199}, issn = {1079-7114}, abstract = {Based on extensive numerical simulations, accounting for electrostatic interactions and dissipative electron-phonon scattering, we propose experimentally realizable geometries capable of sustaining electronic preturbulence in graphene samples. In particular, preturbulence is predicted to occur at experimentally attainable values of the Reynolds number between 10 and 50, over a broad spectrum of frequencies between 10 and 100 GHz.}, }
@article {pmid30556777, year = {2019}, author = {Bass, K and Boc, S and Hindle, M and Dodson, K and Longest, W}, title = {High-Efficiency Nose-to-Lung Aerosol Delivery in an Infant: Development of a Validated Computational Fluid Dynamics Method.}, journal = {Journal of aerosol medicine and pulmonary drug delivery}, volume = {32}, number = {3}, pages = {132-148}, pmid = {30556777}, issn = {1941-2703}, support = {R01 HD087339/HD/NICHD NIH HHS/United States ; R01 HL139673/HL/NHLBI NIH HHS/United States ; }, mesh = {Administration, Inhalation ; Administration, Intranasal ; Aerosols/*administration &amp; dosage/pharmacokinetics ; Computer Simulation ; *Drug Delivery Systems ; Equipment Design ; Humans ; *Hydrodynamics ; Infant ; Lung/metabolism ; *Models, Biological ; Particle Size ; }, abstract = {Background: Computational fluid dynamics (CFD) provides a powerful tool for developing new high-efficiency aerosol delivery strategies, such as nose-to-lung (N2L) aerosol administration to infants and children using correctly sized aerosols. The objective of this study was to establish numerically efficient CFD solution methods and guidelines for simulating N2L aerosol administration to an infant based on comparisons with concurrent in vitro experiments. Materials and Methods: N2L administration of a micrometer-sized aerosol (mass median aerodynamic diameter [MMAD] = 1.4 μm) was evaluated using concurrent CFD simulations and in vitro experiments. Aerosol transport and deposition was assessed in a new nasal airway geometry of a 6-month-old infant with a streamlined nasal cannula interface, which was constructed as a CFD mesh and three-dimensionally printed to form an identical physical prototype. CFD meshes explored were a conventional tetrahedral approach with near-wall (NW) prism elements and a new polyhedral mesh style with an equally refined NW layer. The presence of turbulence in the model was evaluated using a highly efficient low-Reynolds number (LRN) k-ω turbulence model, with previously established NW corrections that accounted for anisotropic wall-normal turbulence as well as improved NW velocity interpolations and hydrodynamic particle damping. Results: Use of the new polyhedral mesh was found to improve numerical efficiency by providing more rapid convergence and requiring fewer control volumes. Turbulent flow was found in the nasal geometry, generated by the inlet jets from the nasal cannula interface. However, due to the small particle size, turbulent dispersion was shown to have little effect on deposition. Good agreement was established between the CFD predictions using the numerically efficient LRN k-ω model with appropriate NW corrections and in vitro deposition data. Aerosol transmission efficiencies through the delivery tube, nasal cannula, and infant nasal model, based on experimental and CFD predictions, were 93.0% and 91.5%, respectively. Conclusions: A numerically efficient CFD approach was established to develop transnasal aerosol administration to infants and children. Small particle aerosols with aerodynamic diameters of ∼1.5 μm were confirmed to have low inertial depositional loss, and have low deposition from turbulent dispersion, making them ideal for high-efficiency lung delivery through an infant nasal cannula interface.}, }
@article {pmid30548194, year = {2019}, author = {Enders, A and Siller, IG and Urmann, K and Hoffmann, MR and Bahnemann, J}, title = {3D Printed Microfluidic Mixers-A Comparative Study on Mixing Unit Performances.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {15}, number = {2}, pages = {e1804326}, doi = {10.1002/smll.201804326}, pmid = {30548194}, issn = {1613-6829}, abstract = {One of the basic operations in microfluidic systems for biological and chemical applications is the rapid mixing of different fluids. However, flow profiles in microfluidic systems are laminar, which means molecular diffusion is the only mixing effect. Therefore, mixing structures are crucial to enable more efficient mixing in shorter times. Since traditional microfabrication methods remain laborious and expensive, 3D printing has emerged as a potential alternative for the fabrication of microfluidic devices. In this work, five different passive micromixers known from literature are redesigned in comparable dimensions and manufactured using high-definition MultiJet 3D printing. Their mixing performance is evaluated experimentally, using sodium hydroxide and phenolphthalein solutions, and numerically via computational fluid dynamics. Both experimental and numerical analysis results show that HC and Tesla-like mixers achieve complete mixing after 0.99 s and 0.78 s, respectively, at the highest flow rate (Reynolds number (Re) = 37.04). In comparison, Caterpillar mixers exhibit a lower mixing rate with complete mixing after 1.46 s and 1.9 s. Furthermore, the HC mixer achieves very good mixing performances over all flow rates (Re = 3.7 to 37.04), while other mixers show improved mixing only at higher flow rates.}, }
@article {pmid30545916, year = {2019}, author = {Sreenivasan, KR}, title = {Turbulent mixing: A perspective.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {116}, number = {37}, pages = {18175-18183}, pmid = {30545916}, issn = {1091-6490}, abstract = {Mixing of initially distinct substances plays an important role in our daily lives as well as in ecological and technological worlds. From the continuum point of view, which we adopt here, mixing is complete when the substances come together across smallest flow scales determined in part by molecular mechanisms, but important stages of the process occur via the advection of substances by an underlying flow. We know how smooth flows enable mixing but less well the manner in which a turbulent flow influences it; but the latter is the more common occurrence on Earth and in the universe. We focus here on turbulent mixing, with more attention paid to the postmixing state than to the transient process of initiation. In particular, we examine turbulent mixing when the substance is a scalar (i.e., characterized only by the scalar property of its concentration), and the mixing process does not influence the flow itself (i.e., the scalar is "passive"). This is the simplest paradigm of turbulent mixing. Within this paradigm, we discuss how a turbulently mixed state depends on the flow Reynolds number and the Schmidt number of the scalar (the ratio of fluid viscosity to the scalar diffusivity), point out some fundamental aspects of turbulent mixing that render it difficult to be addressed quantitatively, and summarize a set of ideas that help us appreciate its physics in diverse circumstances. We consider the so-called universal and anomalous features and summarize a few model studies that help us understand them both.}, }
@article {pmid30523914, year = {2018}, author = {Bodling, A and Sharma, A}, title = {Numerical investigation of low-noise airfoils inspired by the down coat of owls.}, journal = {Bioinspiration &amp; biomimetics}, volume = {14}, number = {1}, pages = {016013}, doi = {10.1088/1748-3190/aaf19c}, pmid = {30523914}, issn = {1748-3190}, mesh = {Animals ; Computer Simulation ; Flight, Animal/*physiology ; Models, Biological ; Noise ; Pressure ; Rotation ; Strigiformes/*physiology ; Wings, Animal/physiology ; }, abstract = {Numerical analysis of airfoil geometries inspired by the down coat of the night owl is presented. The bioinspired geometry consists of an array of 'finlet fences', which is placed near the trailing edge of the baseline (NACA 0012) airfoil. Two fences with maximum nondimensional heights, [Formula: see text] and [Formula: see text] are investigated, where [Formula: see text] is the displacement thickness at 2.9% chord upstream of the airfoil trailing edge. Wall-resolved large eddy simulations are performed at chord-based Reynolds number, [Formula: see text], flow Mach number, [Formula: see text], and angle of attack, [Formula: see text]. The simulation results show significant reductions in unsteady surface pressure and farfield radiated noise with the fences, in agreement with the measurements available in the literature. Analysis of the results reveals that the fences increase the distance between the boundary layer turbulence (source) and the airfoil trailing (scattering) edge, which is identified to be the mechanism behind high-frequency noise reduction. These reductions are larger for the taller fence as the source-scattering edge separation is greater. Two-point correlations show that the fences reduce the spanwise coherence at low frequencies for separation distances greater than a fence pitch (distance between two adjacent fences) and increase the coherence for smaller distances, the increase being higher for the taller fence. This increase in coherence and the reduced obliqueness of the leading edge of the fence are hypothesized to be responsible for the small increase in farfield noise at low frequencies observed in the simulations with the taller fence.}, }
@article {pmid30522876, year = {2019}, author = {Paxman, T and Noga, M and Finlay, WH and Martin, AR}, title = {Experimental evaluation of pressure drop for flows of air and heliox through upper and central conducting airway replicas of 4- to 8-year-old children.}, journal = {Journal of biomechanics}, volume = {82}, number = {}, pages = {134-141}, doi = {10.1016/j.jbiomech.2018.10.028}, pmid = {30522876}, issn = {1873-2380}, mesh = {*Air ; *Airway Resistance ; Child ; Child, Preschool ; Female ; *Helium ; Humans ; Inhalation ; Male ; Models, Biological ; *Oxygen ; *Pressure ; *Respiratory Physiological Phenomena ; }, abstract = {Airway resistance describes the ratio between pressure drop and flow rate through the conducting respiratory airways. Analytical models of airway resistance for tracheobronchial airways have previously been developed and assessed without upper airways positioned upstream of the trachea. This work investigated pressure drop as a function of flow rate and gas properties for upper and central airway replicas of 10 child subjects, ages 4-8. Replica geometries were built based on computed tomography scan data and included airways from the nose through 3-5 distal branching airway generations. Pressure drop through the replicas was measured for constant inspiratory flows of air and heliox. For both the nose-throat and branching airways, the relationship between non-dimensional coefficient of friction, CF, with Reynolds number, Re, was found to resemble the turbulent Blasius equation for pipe flow, where CF∝Re[-0.25]. Additionally, pressure drop ratios between heliox and air were consistent with analytical predictions for turbulent flow. The presence of turbulence in the branching airways likely resulted from convection of turbulence produced upstream in the nose and throat. An airway resistance model based on the Blasius pipe friction correlation for turbulent flow was proposed for prediction of pressure drop through the branching bronchial airways downstream from the upper airway.}, }
@article {pmid30522286, year = {2018}, author = {Acconcia, CN and Wright, A and Goertz, DE}, title = {Translational dynamics of individual microbubbles with millisecond scale ultrasound pulses.}, journal = {The Journal of the Acoustical Society of America}, volume = {144}, number = {5}, pages = {2859}, doi = {10.1121/1.5063353}, pmid = {30522286}, issn = {1520-8524}, abstract = {It is established that radiation forces can be used to transport ultrasound contrast agents, particularly for molecular imaging applications. However, the ability to model and control this process in the context of therapeutic ultrasound is limited by a paucity of data on the translational dynamics of encapsulated microbubbles under the influence of longer pulses. In this work, the translation of individual microbubbles, isolated with optical tweezers, was experimentally investigated over a range of diameters (1.8-8.8 μm, n = 187) and pressures (25, 50, 100, 150, and 200 kPa) with millisecond pulses. Data were compared with theoretical predictions of the translational dynamics, assessing the role of shell and history force effects. A pronounced feature of the displacement curves was an effective threshold size, below which there was only minimal translation. At higher pressures (≥150 kPa) a noticeable structure emerged where multiple local maxima occurred as a function of bubble size. The ability to accurately capture these salient features depended on the encapsulation model employed. In low Reynolds number conditions (i.e., low pressures, or high pressures, off-resonance) the inclusion of history force more accurately fit the data. After pulse cessation, bubbles exhibited substantial displacements consistent with the influence of history effects.}, }
@article {pmid30511712, year = {2018}, author = {Jeon, W and Kim, T and Kim, SM and Baik, S}, title = {Fast mass transport-assisted convective heat transfer through a multi-walled carbon nanotube array.}, journal = {Nanoscale}, volume = {10}, number = {48}, pages = {23103-23112}, doi = {10.1039/c8nr07529h}, pmid = {30511712}, issn = {2040-3372}, abstract = {The recently reported fast mass transport through nanochannels provides a unique opportunity to explore nanoscale energy transport. Here we experimentally investigated the convective heat transport of air through vertically aligned multi-walled carbon nanotubes (VAMWNTs). The flow through the unit cell, defined as an interstitial space among four adjacent nanotubes (hydraulic diameter = 84.9 nm), was in the transition (0.62 ≤ Knudsen number ≤ 0.78) and creeping flow (3.83 × 10-5 ≤ Reynolds number (Re) ≤ 1.55 × 10-4) regime. The constant heat flux (0.102 or 0.286 W m-2) was supplied by a single-mode microwave (2.45 GHz) instantly heating the VAMWNTs. The volume flow rate was two orders of magnitude greater than the Hagen-Poiseuille theory value. The experimentally determined convective heat transfer coefficient (h, 3.70 × 10-4-4.01 × 10-3 W m-2 K-1) and Nusselt number (Nu, 1.17 × 10-9-1.26 × 10-8) were small partly due to the small Re. A further increase in Re (2.12 × 10-3) with the support of a polytetrafluoroethylene mesh significantly increased h (5.48 × 10-2 W m-2 K-1) and Nu (2.37 × 10-7). A large number of nanochannels in a given cross-section of heat sinks may enhance the heat dissipation significantly.}, }
@article {pmid30511653, year = {2018}, author = {Wang, C and Tang, H}, title = {Influence of complex driving motion on propulsion performance of a heaving flexible foil.}, journal = {Bioinspiration &amp; biomimetics}, volume = {14}, number = {1}, pages = {016011}, doi = {10.1088/1748-3190/aaf17a}, pmid = {30511653}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena/physiology ; Biomimetics/*methods ; Fishes/physiology ; Models, Biological ; Motion ; Movement/*physiology ; Swimming/physiology ; }, abstract = {This study explores the effects of complex driving motion on the propulsion performance of a flexible foil heaving in the flight regimes of natural flyers. Such a fluid-structure interaction problem is numerically studied using an immersed boundary lattice Boltzmann method (IBLBM) based numerical framework. It is found that, at the Reynolds number 200 and when the foil's bending stiffness and mass ratio are moderate, adding an extra driving motion of doubled frequency to a purely harmonic motion on the foil's leading edge can enhance the thrust and propulsive efficiency by about 860% and 70%, respectively. The improvement in thrust increases with the extra-driving-motion amplitude. When the extra-driving-motion amplitude is fixed, there exists an optimal extra-driving-motion phase angle. As the foil becomes much stiffer or lighter, the improvement in the propulsion performance turns less. On the other hand, as the foil becomes much more flexible or heavier, drag instead of thrust is generated, and extra driving motion brings no improvement. Although the extra driving motion can improve the foil's propulsion performance in flows of different Reynolds numbers, the increasing rate of the thrust reduces with the Reynolds number. Through this study, details about the competitions among various forces exerted on the foil and their roles in the foil's dynamics are also revealed.}, }
@article {pmid30487240, year = {2018}, author = {Kamal, A and Keaveny, EE}, title = {Enhanced locomotion, effective diffusion and trapping of undulatory micro-swimmers in heterogeneous environments.}, journal = {Journal of the Royal Society, Interface}, volume = {15}, number = {148}, pages = {}, pmid = {30487240}, issn = {1742-5662}, mesh = {Helicobacter/*physiology ; Locomotion/*physiology ; *Models, Biological ; Plasmodium/*physiology ; }, abstract = {Swimming cells and microorganisms must often move through complex fluids that contain an immersed microstructure such as polymer molecules or filaments. In many important biological processes, such as mammalian reproduction and bacterial infection, the size of the immersed microstructure is comparable to that of the swimming cells. This leads to discrete swimmer-microstructure interactions that alter the swimmer's path and speed. In this paper, we use a combination of detailed simulation and data-driven stochastic models to examine the motion of a planar undulatory swimmer in an environment of spherical obstacles tethered via linear springs to random points in the plane of locomotion. We find that, depending on environmental parameters, the interactions with the obstacles can enhance swimming speeds or prevent the swimmer from moving at all. We also show how the discrete interactions produce translational and angular velocity fluctuations that over time lead to diffusive behaviour primarily due to the coupling of swimming and rotational diffusion. Our results demonstrate that direct swimmer-microstructure interactions can produce changes in swimmer motion that may have important implications for the spreading of cell populations in or the trapping of harmful pathogens by complex fluids.}, }
@article {pmid30467607, year = {2018}, author = {Grosjean, G and Hubert, M and Collard, Y and Pillitteri, S and Vandewalle, N}, title = {Surface swimmers, harnessing the interface to self-propel.}, journal = {The European physical journal. E, Soft matter}, volume = {41}, number = {11}, pages = {137}, pmid = {30467607}, issn = {1292-895X}, abstract = {In the study of microscopic flows, self-propulsion has been particularly topical in recent years, with the rise of miniature artificial swimmers as a new tool for flow control, low Reynolds number mixing, micromanipulation or even drug delivery. It is possible to take advantage of interfacial physics to propel these microrobots, as demonstrated by recent experiments using the proximity of an interface, or the interface itself, to generate propulsion at low Reynolds number. This paper discusses how a nearby interface can provide the symmetry breaking necessary for propulsion. An overview of recent experiments illustrates how forces at the interface can be used to generate locomotion. Surface swimmers ranging from the microscopic scale to typically the capillary length are covered. Two systems are then discussed in greater detail. The first is composed of floating ferromagnetic spheres that assemble through capillarity into swimming structures. Two previously studied configurations, triangular and collinear, are discussed and contrasted. A new interpretation for the triangular swimmer is presented. Then, the non-monotonic influence of surface tension and viscosity is evidenced in the collinear case. Finally, a new system is introduced. It is a magnetically powered, centimeter-sized piece that swims similarly to water striders.}, }
@article {pmid30465777, year = {2019}, author = {Walker, BJ and Wheeler, RJ and Ishimoto, K and Gaffney, EA}, title = {Boundary behaviours of Leishmania mexicana: A hydrodynamic simulation study.}, journal = {Journal of theoretical biology}, volume = {462}, number = {}, pages = {311-320}, pmid = {30465777}, issn = {1095-8541}, mesh = {Animals ; Biophysical Phenomena ; *Hydrodynamics ; Insect Vectors/parasitology ; Leishmania mexicana/*physiology ; Life Cycle Stages ; Psychodidae/*parasitology ; Swimming ; }, abstract = {It is well established that the parasites of the genus Leishmania exhibit complex surface interactions with the sandfly vector midgut epithelium, but no prior study has considered the details of their hydrodynamics. Here, the boundary behaviours of motile Leishmania mexicana promastigotes are explored in a computational study using the boundary element method, with a model flagellar beating pattern that has been identified from digital videomicroscopy. In particular a simple flagellar kinematics is observed and quantified using image processing and mode identification techniques, suggesting a simple mechanical driver for the Leishmania beat. Phase plane analysis and long-time simulation of a range of Leishmania swimming scenarios demonstrate an absence of stable boundary motility for an idealised model promastigote, with behaviours ranging from boundary capture to deflection into the bulk both with and without surface forces between the swimmer and the boundary. Indeed, the inclusion of a short-range repulsive surface force results in the deflection of all surface-bound promastigotes, suggesting that the documented surface detachment of infective metacyclic promastigotes may be the result of their particular morphology and simple hydrodynamics. Further, simulation elucidates a remarkable morphology-dependent hydrodynamic mechanism of boundary approach, hypothesised to be the cause of the well-established phenomenon of tip-first epithelial attachment of Leishmania promastigotes to the sandfly vector midgut.}, }
@article {pmid30464056, year = {2018}, author = {Digumarti, KM and Conn, AT and Rossiter, J}, title = {EuMoBot: replicating euglenoid movement in a soft robot.}, journal = {Journal of the Royal Society, Interface}, volume = {15}, number = {148}, pages = {}, pmid = {30464056}, issn = {1742-5662}, mesh = {Euglenida/*physiology ; *Locomotion ; *Robotics ; }, abstract = {Swimming is employed as a form of locomotion by many organisms in nature across a wide range of scales. Varied strategies of shape change are employed to achieve fluidic propulsion at different scales due to changes in hydrodynamics. In the case of microorganisms, the small mass, low Reynolds number and dominance of viscous forces in the medium, requires a change in shape that is non-invariant under time reversal to achieve movement. The Euglena family of unicellular flagellates evolved a characteristic type of locomotion called euglenoid movement to overcome this challenge, wherein the body undergoes a giant change in shape. It is believed that these large deformations enable the organism to move through viscous fluids and tiny spaces. The ability to drastically change the shape of the body is particularly attractive in robots designed to move through constrained spaces and cluttered environments such as through the human body for invasive medical procedures or through collapsed rubble in search of survivors. Inspired by the euglenoids, we present the design of EuMoBot, a multi-segment soft robot that replicates large body deformations to achieve locomotion. Two robots have been fabricated at different sizes operating with a constant internal volume, which exploit hyperelasticity of fluid-filled elastomeric chambers to replicate the motion of euglenoids. The smaller robot moves at a speed of [Formula: see text] body lengths per cycle (20 mm min[-1] or 2.2 cycles min[-1]) while the larger one attains a speed of [Formula: see text] body lengths per cycle (4.5 mm min[-1] or 0.4 cycles min[-1]). We show the potential for biomimetic soft robots employing shape change to both replicate biological motion and act as a tool for studying it. In addition, we present a quantitative method based on elliptic Fourier descriptors to characterize and compare the shape of the robot with that of its biological counterpart. Our results show a similarity in shape of 85% and indicate that this method can be applied to understand the evolution of shape in other nonlinear, dynamic soft robots where a model for the shape does not exist.}, }
@article {pmid30457929, year = {2019}, author = {Huang, HW and Tibbitt, MW and Huang, TY and Nelson, BJ}, title = {Matryoshka-Inspired Micro-Origami Capsules to Enhance Loading, Encapsulation, and Transport of Drugs.}, journal = {Soft robotics}, volume = {6}, number = {1}, pages = {150-159}, doi = {10.1089/soro.2018.0028}, pmid = {30457929}, issn = {2169-5180}, support = {/ERC_/European Research Council/International ; }, mesh = {Capsules/*chemistry ; Drug Delivery Systems/*methods ; Hydrogel, Polyethylene Glycol Dimethacrylate/chemistry ; Hydrogels/chemistry ; Russia ; Technology, Pharmaceutical/*methods ; Temperature ; }, abstract = {Stimuli-responsive hydrogels are promising candidates for use in the targeted delivery of drugs using microrobotics. These devices enable the delivery and sustained release of quantities of drugs several times greater than their dry weight and are responsive to external stimuli. However, existing systems have two major drawbacks: (1) severe drug leakage before reaching the targeted areas within the body and (2) impeded locomotion through liquids due to the inherent hydrophilicity of hydrogels. This article outlines an approach to the assembly of hydrogel-based microcapsules in which one device is assembled within another to prevent drug leakage during transport. Inspired by the famous Russian stacking dolls (Matryoshka), the proposed scheme not only improves drug-loading efficiency but also facilitates the movement of hydrogel-based microcapsules driven by an external magnetic field. At room temperature, drug leakage from the hydrogel matrix is 90%. However, at body temperature the device folds up and assembles to encapsulate the drug, thereby reducing leakage to a mere 6%. The Matryoshka-inspired micro-origami capsule (MIMC) can disassemble autonomously when it arrives at a targeted site, where the temperature is slightly above body temperature. Up to 30% of the encapsulated drug was shown to diffuse from the hydrogel matrix within 1 h when it unfolds and disassembles. The MIMC is also shown to enhance the movement of magnetically driven microcapsules while navigating through media with a low Reynolds number. The translational velocity of the proposed MIMC (four hydrogel-based microcapsules) driven by magnetic gradients is more than three times greater than that of a conventional (single) hydrogel-based microcapsule.}, }
@article {pmid30425950, year = {2018}, author = {Rigatelli, G and Zuin, M and Dell'Avvocata, F and Nanjundappa, A and Daggubati, R and Nguyen, T}, title = {Non-invasive Evaluation of Fluid Dynamic of Aortoiliac Atherosclerotic Disease: Impact of Bifurcation Angle and Different Stent Configurations.}, journal = {Journal of translational internal medicine}, volume = {6}, number = {3}, pages = {138-145}, pmid = {30425950}, issn = {2450-131X}, abstract = {OBJECTIVES: To non-invasively evaluate by computational fluid dynamic (CFD) analysis the physiology and rheology of aortoiliac bifurcation disease at different angles and different stent configurations.<br><br>MATERIAL AND METHODS: For the analysis, we considered a physiologic model of abdominal aorta with an iliac bifurcation set at 30&#xb0;, 45&#xb0; and 70&#xb0; without stenosis. Subsequently, a bilateral ostial common iliac stenosis of 80% was considered for each type of bifurcation. For the stent simulation, we reconstructed Zilver vascular self-expanding (Zilver; Cook, Bloomington, MN) and Palmaz Genesis Peripheral (Cordis, Miami, FL) stents.<br><br>RESULTS: The physiologic model, across the different angles, static pressure, Reynolds number and stream function, were lower for the 30&#xb0; bifurcation angle with a gradient from 70&#xb0; to 30&#xb0; angles, whereas all the other parameters were inversely higher. After stenting, all the fluid parameters decreased homogenously independent of the stent type, maintaining a gradient in favour of 30&#xb0; compared to 45&#xb0; and 70&#xb0; angles. The absolute greater deviation from physiology was observed for low kissing when self-expandable stents were used across all angles; in particular, the wall shear stress was high at at 45&#xb0; angle.<br><br>CONCLUSION: Bifurcation angle deeply impacts the physiology of aortoiliac bifurcations, which are used to predict the fluid dynamic profile after stenting. CFD, having the potential to be derived both from computed tomography scan or invasive angiography, appears to be an ideal tool to predict fluid dynamic profile before and after stenting in aortoiliac bifurcation.}, }
@article {pmid30424640, year = {2018}, author = {Sadri, M and Hejranfar, K and Ebrahimi, M}, title = {Prediction of fluid flow and acoustic field of a supersonic jet using vorticity confinement.}, journal = {The Journal of the Acoustical Society of America}, volume = {144}, number = {3}, pages = {1521}, doi = {10.1121/1.5055215}, pmid = {30424640}, issn = {1520-8524}, abstract = {In this study, the numerical simulation of the fluid flow and acoustic field of a supersonic jet is performed by using high-order discretization and the vorticity confinement (VC) method on coarse grids. The three-dimensional Navier-Stokes equations are considered in the generalized curvilinear coordinate system and the high-order compact finite-difference scheme is applied for the space discretization, and the time integration is performed by the fourth-order Runge-Kutta scheme. A low-pass high-order filter is applied to stabilize the numerical solution. The non-reflecting boundary conditions are adopted for all the free boundaries, and the Kirchhoff surface integration is utilized to obtain the far-field sound pressure levels in a number of observer locations. Comparisons of the jet mean flow and jet aeroacoustics results with the other numerical and experimental data at similar flow conditions are made and show a reasonable agreement. The study shows that the proposed solution methodology based on the high-order compact finite-difference scheme in conjunction with the VC method can reasonably predict the near-field flow and the far-field noise of high Reynolds number jets with a fairly coarser grid than that used in the large eddy simulations and, thus, the computational cost can be significantly decreased.}, }
@article {pmid30424188, year = {2018}, author = {Jung, BJ and Kim, J and Kim, JA and Jang, H and Seo, S and Lee, W}, title = {PDMS-Parylene Hybrid, Flexible Microfluidics for Real-Time Modulation of 3D Helical Inertial Microfluidics.}, journal = {Micromachines}, volume = {9}, number = {6}, pages = {}, pmid = {30424188}, issn = {2072-666X}, support = {NRF-2015M2A2A4A02044826//National Research Foundation of Korea/ ; 10054488//Ministry of Trade, Industry &amp; Energy (MOTIE, Korea)/ ; }, abstract = {Inertial microfluidics has drawn much attention for its applications for circulating tumor cell separations from blood. The fluid flows and the inertial particle focusing in inertial microfluidic systems are highly dependent on the channel geometry and structure. Flexible microfluidic systems can have adjustable 3D channel geometries by curving planar 2D channels into 3D structures, which will enable tunable inertial separation. We present a poly(dimethylsiloxane) (PDMS)-parylene hybrid thin-film microfluidic system that can provide high flexibility for 3D channel shaping while maintaining the channel cross-sectional shape. The PDMS-parylene hybrid microfluidic channels were fabricated by a molding and bonding technique using initiated chemical vapor deposition (iCVD) bonding. We constructed 3D helical inertial microfluidic channels by coiling a straight 2D channel and studied the inertial focusing while varying radius of curvature and Reynolds number. This thin film structure allows for high channel curvature and high Dean numbers which leads to faster inertial particle focusing and shorter channel lengths than 2D spiral channels. Most importantly, the focusing positions of particles and cells in the microchannel can be tuned in real time by simply modulating the channel curvature. The simple mechanical modulation of these 3D structure microfluidic systems is expected to provide unique advantages of convenient tuning of cell separation thresholds with a single device.}, }
@article {pmid30424137, year = {2018}, author = {Ansari, MA and Kim, KY and Kim, SM}, title = {Numerical and Experimental Study on Mixing Performances of Simple and Vortex Micro T-Mixers.}, journal = {Micromachines}, volume = {9}, number = {5}, pages = {}, pmid = {30424137}, issn = {2072-666X}, support = {NRF- 2016R1A2B4006987//National Research Foundation of Korea/ ; //Inha University/ ; }, abstract = {Vortex flow increases the interface area of fluid streams by stretching along with providing continuous stirring action to the fluids in micromixers. In this study, experimental and numerical analyses on a design of micromixer that creates vortex flow were carried out, and the mixing performance was compared with a simple micro T-mixer. In the vortex micro T-mixer, the height of the inlet channels is half of the height of the main mixing channel. The inlet channel connects to the main mixing channel (micromixer) at the one end at an offset position in a fashion that creates vortex flow. In the simple micro T-mixer, the height of the inlet channels is equal to the height of the channel after connection (main mixing channel). Mixing of fluids and flow field have been analyzed for Reynolds numbers in a range from 1[-]80. The study has been further extended to planar serpentine microchannels, which were combined with a simple and a vortex T-junction, to evaluate and verify their mixing performances. The mixing performance of the vortex T-mixer is higher than the simple T-mixer and significantly increases with the Reynolds number. The design is promising for efficiently increasing mixing simply at the T-junction and can be applied to all micromixers.}, }
@article {pmid30424044, year = {2018}, author = {Raza, W and Ma, SB and Kim, KY}, title = {Multi-Objective Optimizations of a Serpentine Micromixer with Crossing Channels at Low and High Reynolds Numbers.}, journal = {Micromachines}, volume = {9}, number = {3}, pages = {}, pmid = {30424044}, issn = {2072-666X}, abstract = {In order to maximize the mixing performance of a micromixer with an integrated three-dimensional serpentine and split-and-recombination configuration, multi-objective optimizations were performed at two different Reynolds numbers, 1 and 120, based on numerical simulation. Numerical analyses of fluid flow and mixing in the micromixer were performed using three-dimensional Navier-Stokes equations and convection-diffusion equation. Three dimensionless design variables that were related to the geometry of the micromixer were selected as design variables for optimization. Mixing index at the exit and pressure drop through the micromixer were employed as two objective functions. A parametric study was carried out to explore the effects of the design variables on the objective functions. Latin hypercube sampling method as a design-of-experiment technique has been used to select design points in the design space. Surrogate modeling of the objective functions was performed by using radial basis neural network. Concave Pareto-optimal curves comprising of Pareto-optimal solutions that represents the trade-off between the objective functions were obtained using a multi-objective genetic algorithm at Re = 1 and 120. Through the optimizations, maximum enhancements of 18.8% and 6.0% in mixing index were achieved at Re = 1 and 120, respectively.}, }
@article {pmid30411937, year = {2018}, author = {Galitski, V and Kargarian, M and Syzranov, S}, title = {Dynamo Effect and Turbulence in Hydrodynamic Weyl Metals.}, journal = {Physical review letters}, volume = {121}, number = {17}, pages = {176603}, doi = {10.1103/PhysRevLett.121.176603}, pmid = {30411937}, issn = {1079-7114}, abstract = {The dynamo effect is a class of macroscopic phenomena responsible for generating and maintaining magnetic fields in astrophysical bodies. It hinges on the hydrodynamic three-dimensional motion of conducting gases and plasmas that achieve high hydrodynamic and/or magnetic Reynolds numbers due to the large length scales involved. The existing laboratory experiments modeling dynamos are challenging and involve large apparatuses containing conducting fluids subject to fast helical flows. Here we propose that electronic solid-state materials-in particular, hydrodynamic metals-may serve as an alternative platform to observe some aspects of the dynamo effect. Motivated by recent experimental developments, this Letter focuses on hydrodynamic Weyl semimetals, where the dominant scattering mechanism is due to interactions. We derive Navier-Stokes equations along with equations of magnetohydrodynamics that describe the transport of a Weyl electron-hole plasma appropriate in this regime. We estimate the hydrodynamic and magnetic Reynolds numbers for this system. The latter is a key figure of merit of the dynamo mechanism. We show that it can be relatively large to enable observation of the dynamo-induced magnetic field bootstrap in an experiment. Finally, we generalize the simplest dynamo instability model-the Ponomarenko dynamo-to the case of a hydrodynamic Weyl semimetal and show that the chiral anomaly term reduces the threshold magnetic Reynolds number for the dynamo instability.}, }
@article {pmid30400531, year = {2017}, author = {Guo, X and Qi, H}, title = {Analytical Solution of Electro-Osmotic Peristalsis of Fractional Jeffreys Fluid in a Micro-Channel.}, journal = {Micromachines}, volume = {8}, number = {12}, pages = {}, pmid = {30400531}, issn = {2072-666X}, support = {11402108//National Natural Science Foundation of China/ ; 11672163//National Natural Science Foundation of China/ ; 11571157//National Natural Science Foundation of China/ ; }, abstract = {The electro-osmotic peristaltic flow of a viscoelastic fluid through a cylindrical micro-channel is studied in this paper. The fractional Jeffreys constitutive model, including the relaxation time and retardation time, is utilized to describe the viscoelasticity of the fluid. Under the assumptions of long wavelength, low Reynolds number, and Debye-Hückel linearization, the analytical solutions of pressure gradient, stream function and axial velocity are explored in terms of Mittag-Leffler function by Laplace transform method. The corresponding solutions of fractional Maxwell fluid and generalized second grade fluid are also obtained as special cases. The numerical analysis of the results are depicted graphically, and the effects of electro-osmotic parameter, external electric field, fractional parameters and viscoelastic parameters on the peristaltic flow are discussed.}, }
@article {pmid30397239, year = {2018}, author = {Nourazar, SS and Nazari-Golshan, A and Soleymanpour, F}, title = {On the expedient solution of the magneto-hydrodynamic Jeffery-Hamel flow of Casson fluid.}, journal = {Scientific reports}, volume = {8}, number = {1}, pages = {16358}, pmid = {30397239}, issn = {2045-2322}, abstract = {The equation of magneto-hydrodynamic Jeffery-Hamel flow of non-Newtonian Casson fluid in a stretching/shrinking convergent/divergent channel is derived and solved using a new modified Adomian decomposition method (ADM). So far in all problems where semi-analytical methods are used the boundary conditions are not satisfied completely. In the present research, a hybrid of the Fourier transform and the Adomian decomposition method (FTADM), is presented in order to incorporate all boundary conditions into our solution of magneto-hydrodynamic Jeffery-Hamel flow of non-Newtonian Casson fluid in a stretching/shrinking convergent/divergent channel flow. The effects of various emerging parameters such as channel angle, stretching/shrinking parameter, Casson fluid parameter, Reynolds number and Hartmann number on velocity profile are considered. The results using the FTADM are compared with the results of ADM and numerical Range-Kutta fourth-order method. The comparison reveals that, for the same number of components of the recursive sequences over a wide range of spatial domain, the relative errors associated with the new method, FTADM, are much less than the ADM. The results of the new method show that the method is an accurate and expedient approximate analytic method in solving the third-order nonlinear equation of Jeffery-Hamel flow of non-Newtonian Casson fluid.}, }
@article {pmid30393471, year = {2018}, author = {Shahzad, K and Aeken, WV and Mottaghi, M and Kamyab, VK and Kuhn, S}, title = {Aggregation and clogging phenomena of rigid microparticles in microfluidics: Comparison of a discrete element method (DEM) and CFD-DEM coupling method.}, journal = {Microfluidics and nanofluidics}, volume = {22}, number = {9}, pages = {104}, pmid = {30393471}, issn = {1613-4982}, abstract = {We developed a numerical tool to investigate the phenomena of aggregation and clogging of rigid microparticles suspended in a Newtonian fluid transported through a straight microchannel. In a first step, we implement a time-dependent one-way coupling Discrete Element Method (DEM) technique to simulate the movement and effect of adhesion on rigid microparticles in two- and three-dimensional computational domains. The Johnson-Kendall-Roberts (JKR) theory of adhesion is applied to investigate the contact mechanics of particle-particle and particle-wall interactions. Using the one-way coupled solver, the agglomeration, aggregation and deposition behavior of the microparticles is studied by varying the Reynolds number and the particle adhesion. In a second step, we apply a two-way coupling CFD-DEM approach, which solves the equation of motion for each particle, and transfers the force field corresponding to particle-fluid interactions to the CFD toolbox OpenFOAM. Results for the one-way (DEM) and two-way (CFD-DEM) coupling techniques are compared in terms of aggregate size, aggregate percentages, spatial and temporal evaluation of aggregates in 2D and 3D. We conclude that two-way coupling is the more realistic approach, which can accurately capture the particle-fluid dynamics in microfluidic applications.}, }
@article {pmid30393363, year = {2018}, author = {Ma, N and Duan, Z and Ma, H and Su, L and Liang, P and Ning, X and He, B and Zhang, X}, title = {Lattice Boltzmann Simulation of the Hydrodynamic Entrance Region of Rectangular Microchannels in the Slip Regime.}, journal = {Micromachines}, volume = {9}, number = {2}, pages = {}, pmid = {30393363}, issn = {2072-666X}, abstract = {Developing a three-dimensional laminar flow in the entrance region of rectangular microchannels has been investigated in this paper. When the hydrodynamic development length is the same magnitude as the microchannel length, entrance effects have to be taken into account, especially in relatively short ducts. Simultaneously, there are a variety of non-continuum or rarefaction effects, such as velocity slip and temperature jump. The available data in the literature appearing on this issue is quite limited, the available study is the semi-theoretical approximate model to predict pressure drop of developing slip flow in rectangular microchannels with different aspect ratios. In this paper, we apply the lattice Boltzmann equation method (LBE) to investigate the developing slip flow through a rectangular microchannel. The effects of the Reynolds number (1 < Re < 1000), channel aspect ratio (0 < ε < 1), and Knudsen number (0.001 < Kn < 0.1) on the dimensionless hydrodynamic entrance length, and the apparent friction factor, and Reynolds number product, are examined in detail. The numerical solution of LBM can recover excellent agreement with the available data in the literature, which proves its accuracy in capturing fundamental fluid characteristics in the slip-flow regime.}, }
@article {pmid30393335, year = {2018}, author = {Afzal, MJ and Ashraf, MW and Tayyaba, S and Hossain, MK and Afzulpurkar, N}, title = {Sinusoidal Microchannel with Descending Curves for Varicose Veins Implantation.}, journal = {Micromachines}, volume = {9}, number = {2}, pages = {}, pmid = {30393335}, issn = {2072-666X}, abstract = {Approximately 26% of adult people, mostly females, are affected by varicose veins in old age. It is a common reason for distress, loss of efficiency, and worsening living conditions. Several traditional treatment techniques (sclerotherapy and foam sclerotherapy of large veins, laser surgeries and radiofrequency ablation, vein ligation and stripping, ambulatory phlebectomy, and endoscopic vein surgery) have failed to handle this disease effectively. Herein, authors have presented an alternative varicose vein implant method-the descending sinusoidal microchannel (DSMC). DSMC was simulated by Fuzzy logic MATLAB (The MathWorks, Natick, MA, USA) and ANSYS (ANSYS 18.2, perpetual license purchased by Ibadat Education Trust, The University of Lahore, Pakistan) with real and actual conditions. After simulations of DSMC, fabrication and testing were performed. The silver DSMC was manufactured by utilizing a micromachining procedure. The length, width, and depth of the silver substrate were 51 mm, 25 mm, and 1.1 mm, respectively. The measurements of the DSMC channel in the silver wafer substrate were 0.9 mm in width and 0.9 mm in depth. The three descending curves of the DSMC were 7 mm, 6 mm, and 5 mm in height. For pressure, actual conditions were carefully taken as 1.0 kPa to 1.5 kPa for varicose veins. For velocity, actual conditions were carefully taken as 0.02 m/s to 0.07 m/s for these veins. These are real and standard values used in simulations and experiments. At Reynolds number 323, the flow rate and velocity were determined as 1001.0 (0.1 nL/s), 11.4 cm/s and 1015.3 (0.1 nL/s), 12.19 cm/s by MATLAB (The MathWorks, Natick, MA, USA) and ANSYS simulations, respectively. The flow rate and velocity were determined to be 995.3 (0.1 nL/s) and 12.2 cm/s, respectively, at the same Reynolds number (323) in the experiment. Moreover, the Dean number was also calculated to observe Dean vortices. All simulated and experimental results were in close agreement. Consequently, DSMC can be implanted in varicose veins as a new treatment to preserve excellent blood flow in human legs from the original place to avoid tissue damage and other problems.}, }
@article {pmid30389406, year = {2019}, author = {Amiri Delouei, A and Sajjadi, H and Mohebbi, R and Izadi, M}, title = {Experimental study on inlet turbulent flow under ultrasonic vibration: Pressure drop and heat transfer enhancement.}, journal = {Ultrasonics sonochemistry}, volume = {51}, number = {}, pages = {151-159}, doi = {10.1016/j.ultsonch.2018.10.032}, pmid = {30389406}, issn = {1873-2828}, abstract = {This experimental study examines the impact of ultrasonic vibration on pressure drop and heat transfer enhancement of inlet turbulent flows. A stainless steel tube connected to an ultrasonic transducer and immersed in a constant temperature two-phase fluid was considered as the test section. Regarding the designed configuration, the ultrasonic transducer utilized had an acoustic frequency of 28 kHz and two different power levels of 75 W and 100 W. The experiments were conducted for different ultrasonic power levels, inlet temperatures, and flow rates. The accuracy of measurements was successfully validated via the existing empirical correlations. The results indicate that the effect of ultrasonic vibration on pressure drop and heat transfer enhancement diminishes with the growth of both Reynolds number and inlet temperature. Based on previously reported results on inlet flows with a laminar flow regime, the effect of ultrasonic vibration is very trivial in current turbulent inlet flows (up to 7.28% for heat convection enhancement). The results of the present study will be beneficial for future investigations on designing vibrating heat exchangers.}, }
@article {pmid30387646, year = {2018}, author = {Falkovich, G and Vladimirova, N}, title = {Turbulence Appearance and Nonappearance in Thin Fluid Layers.}, journal = {Physical review letters}, volume = {121}, number = {16}, pages = {164501}, doi = {10.1103/PhysRevLett.121.164501}, pmid = {30387646}, issn = {1079-7114}, abstract = {Flows in fluid layers are ubiquitous in industry, geophysics, and astrophysics. Large-scale flows in thin layers can be considered two dimensional with bottom friction added. Here we find that the properties of such flows depend dramatically on the way they are driven. We argue that a wall-driven (Couette) flow cannot sustain turbulence, no matter how small the viscosity and friction. Direct numerical simulations (DNSs) up to the Reynolds number Re=10^{6} confirm that all perturbations die in a plane Couette flow. On the contrary, for sufficiently small viscosity and friction, perturbations destroy the pressure-driven laminar (Poiseuille) flow. What appears instead is a traveling wave in the form of a jet slithering between wall vortices. For 5×10^{3}<Re<3×10^{4}, the mean flow in most cases has remarkably simple structure: the jet is sinusoidal with a parabolic velocity profile, and vorticity is constant inside vortices, while the fluctuations are small. At higher Re, strong fluctuations appear, yet the mean traveling wave survives. Considering the momentum flux barrier in such a flow, we derive a new scaling law for the Re dependence of the friction factor and confirm it by DNS.}, }
@article {pmid30387627, year = {2018}, author = {Dong, C and Wang, L and Huang, YM and Comisso, L and Bhattacharjee, A}, title = {Role of the Plasmoid Instability in Magnetohydrodynamic Turbulence.}, journal = {Physical review letters}, volume = {121}, number = {16}, pages = {165101}, doi = {10.1103/PhysRevLett.121.165101}, pmid = {30387627}, issn = {1079-7114}, abstract = {The plasmoid instability in evolving current sheets has been widely studied due to its effects on the disruption of current sheets, the formation of plasmoids, and the resultant fast magnetic reconnection. In this Letter, we study the role of the plasmoid instability in two-dimensional magnetohydrodynamic (MHD) turbulence by means of high-resolution direct numerical simulations. At a sufficiently large magnetic Reynolds number (R_{m}=10^{6}), the combined effects of dynamic alignment and turbulent intermittency lead to a copious formation of plasmoids in a multitude of intense current sheets. The disruption of current sheet structures facilitates the energy cascade towards small scales, leading to the breaking and steepening of the energy spectrum. In the plasmoid-mediated regime, the energy spectrum displays a scaling that is close to the spectral index -2.2 as proposed by recent analytic theories. We also demonstrate that the scale-dependent dynamic alignment exists in 2D MHD turbulence and the corresponding slope of the alignment angle is close to 0.25.}, }
@article {pmid30374981, year = {2019}, author = {Jhun, CS and Siedlecki, C and Xu, L and Lukic, B and Newswanger, R and Yeager, E and Reibson, J and Cysyk, J and Weiss, W and Rosenberg, G}, title = {Stress and Exposure Time on von Willebrand Factor Degradation.}, journal = {Artificial organs}, volume = {43}, number = {2}, pages = {199-206}, doi = {10.1111/aor.13323}, pmid = {30374981}, issn = {1525-1594}, mesh = {Heart-Assist Devices/*adverse effects ; Hemodynamics/physiology ; Humans ; Materials Testing ; von Willebrand Diseases/blood/*etiology ; von Willebrand Factor/*metabolism ; }, abstract = {Despite the prevailing use of the continuous flow left ventricular assist devices (cf-LVAD), acquired von Willebrand syndrome (AvWS) associated with cf-LVAD still remains a major complication. As AvWS is known to be dependent on shear stress (τ) and exposure time (texp), this study examined the degradation of high molecular weight multimers (HMWM) of von Willebrand factor (vWF) in terms of τ and texp . Two custom apparatus, i.e., capillary-tubing-type degrader (CTD) and Taylor-Couette-type degrader (TCD) were developed for short-term (0.033 sec ≤ texp ≤ 1.05 s) and long-term (10 s ≤ texp ≤ 10 min) shear exposures of vWF, respectively. Flow conditions indexed by Reynolds number (Re) for CTD were 14 ≤ Re ≤ 288 with corresponding laminar stress level of 52 ≤ τ CTD ≤ 1042 dyne/cm[2] . Flow conditions for TCD were 100 ≤ Re ≤ 2500 with corresponding rotor speed of 180 ≤ o ≤ 4000 RPM and laminar stress level of 50 ≤ τ TCD ≤ 1114 dyne/cm[2] . Due to transitional and turbulent flows in TCD at Re > 1117, total stress (i.e., τ total = laminar + turbulent) was also calculated using a computational fluid dynamics (CFD) solver, Converge CFD (Converge Science Inc., Madison, WI, USA). Inhibition of ADAMTS13 with different concentration of EDTA (5 mM and 10 mM) was also performed to investigate the mechanism of cleavage in terms of mechanical and enzymatic aspects. Degradation of HMWM with CTD was negligible at all given testing conditions. Although no degradation of HMWM was observed with TCD at Re < 1117 (τ total = 1012 dyne/cm[2]), increase in degradation of HMWM was observed beyond Re of 1117 for all given exposure times. At Re ~ 2500 (τ total = 3070 dyne/cm[2]) with texp = 60 s, a severe degradation of HMWM (90.7 ± 3.8%, abnormal) was observed, and almost complete degradation of HMWM (96.1 ± 1.9%, abnormal) was observed with texp = 600 s. The inhibition studies with 5 mM EDTA at Re ~ 2500 showed that loss of HMWM was negligible (<10%, normal) for all given exposure times except for texp = 10 min (39.5 ± 22.3%, borderline-abnormal). With 10 mM EDTA, no degradation of HMWM was observed (11.1 ± 4.4%, normal) even for texp = 10 min. This study investigated the effect of shear stress and exposure time on the HMWM of vWF in laminar and turbulent flows. The inhibition study by EDTA confirms that degradation of HMWM is initiated by shear-induced unfolding followed by enzymatic cleavage at given conditions. Determination of magnitude of each mechanism needs further investigation. It is also important to note that the degradation of vWF is highly dependent on turbulence regardless of the time exposed within our testing conditions.}, }
@article {pmid30362460, year = {2018}, author = {Kim, H and Kim, J and Choi, H}, title = {Flow structure modifications by leading-edge tubercles on a 3D wing.}, journal = {Bioinspiration &amp; biomimetics}, volume = {13}, number = {6}, pages = {066011}, doi = {10.1088/1748-3190/aae6fc}, pmid = {30362460}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena/physiology ; Flight, Animal/physiology ; Humpback Whale/*physiology ; Hydrodynamics ; Models, Biological ; Rheology/methods ; Wings, Animal/*physiology ; }, abstract = {Leading-edge tubercles on a humpback whale flipper are known to enhance its hydrodynamic performance at post-stall angles of attack (Miklosovic et al 2004 Phys. Fluids 16 39-42). We investigate vortical structures above a three-dimensional wing with tubercles using surface-oil-flow visualization and particle image velocimetry measurement. Two wing models with and without tubercles, previously studied by Miklosovic et al (2004 Phys. Fluids 16 39-42), are considered at the Reynolds number of 180 000 based on the free-stream velocity and mean chord length. At this Reynolds number, tubercles delay the stall angle by 7° and increase the maximum lift coefficient by about 22%. At a low angle of attack, flow separation first occurs near the tip region for both wing models. While flow separation rapidly progresses inboard (toward the wing root) for the model without tubercles with increasing angle of attack, tubercles produce two types of vortical motions and block the inboard progression of flow separation, resulting in delayed stall from α = 8° to 15°. One of these two vortical structures is pairs of counter-rotating streamwise vortices evolving from hemi-spherical separation bubbles near the leading-edge troughs at pre-, near-, and post-stall angles of attack, and the other is asymmetric pairs of streamwise vortices evolving from separated flow regions after the mid-chord region at near-stall angle of attack. At a post-stall angle of attack (α = 16°), strong clockwise and counter-clockwise streamwise vortices are generated from foci at the root and tip near the trailing edge, respectively, and delay flow separation in the mid-span, resulting in a higher lift coefficient than that without tubercles.}, }
@article {pmid30349146, year = {2018}, author = {Bass, K and Longest, PW}, title = {Recommendations for Simulating Microparticle Deposition at Conditions Similar to the Upper Airways with Two-Equation Turbulence Models.}, journal = {Journal of aerosol science}, volume = {119}, number = {}, pages = {31-50}, pmid = {30349146}, issn = {0021-8502}, support = {R01 HD087339/HD/NICHD NIH HHS/United States ; R01 HL107333/HL/NHLBI NIH HHS/United States ; }, abstract = {The development of a CFD model, from initial geometry to experimentally validated result with engineering insight, can be a time-consuming process that often requires several iterations of meshing and solver set-up. Applying a set of guidelines in the early stages can help to streamline the process and improve consistency between different models. The objective of this study was to determine both mesh and CFD solution parameters that enable the accurate simulation of microparticle deposition under flow conditions consistent with the upper respiratory airways including turbulent flow. A 90° bend geometry was used as a characteristic model that occurs throughout the airways and for which high-quality experimental aerosol deposition data is available in the transitional and turbulent flow regimes. Four meshes with varying degrees of near-wall resolution were compared, and key solver settings were applied to determine the parameters that minimize sensitivity to the near-wall (NW) mesh. The Low Reynolds number (LRN) k-ω model was used to resolve the turbulence field, which is a numerically efficient two-equation turbulence model, but has recently been considered overly simplistic. Some recent studies have used more complex turbulence models, such as Large Eddy Simulation (LES), to overcome the perceived weaknesses of two-equation models. Therefore, the secondary objective was to determine whether the more computationally efficient LRN k-ω model was capable of providing deposition results that were comparable to LES. Results show how NW mesh sensitivity is reduced through application of the Green-Gauss Node-based gradient discretization scheme and physically realistic near-wall corrections. Using the newly recommended meshing parameters and solution guidelines gives an excellent match to experimental data. Furthermore, deposition data from the LRN k-ω model compares favorably with LES results for the same characteristic geometry. In summary, this study provides a set of meshing and solution guidelines for simulating aerosol deposition in transitional and turbulent flows found in the upper respiratory airways using the numerically efficient LRN k-ω approach.}, }
@article {pmid30348646, year = {2018}, author = {Karakas, F and D'Oliveira, D and Maas, AE and Murphy, DW}, title = {Using a shell as a wing: pairing of dissimilar appendages in atlantiid heteropod swimming.}, journal = {The Journal of experimental biology}, volume = {221}, number = {Pt 23}, pages = {}, doi = {10.1242/jeb.192062}, pmid = {30348646}, issn = {1477-9145}, mesh = {Animal Fins/*physiology ; *Animal Shells ; Animals ; Biomechanical Phenomena ; Gastropoda/*physiology ; Swimming/*physiology ; Video Recording/methods ; Zooplankton ; }, abstract = {Atlantiid heteropods are zooplanktonic marine snails which have a calcium carbonate shell and single swimming fin. They actively swim to hunt prey and vertically migrate. Previous accounts of atlantiid heteropod swimming described these animals sculling with the swimming fin while the shell passively hung beneath the body. Here, we show, via high-speed stereophotogrammetric measurements of body, fin and shell kinematics, that the atlantiid heteropod Atlanta selvagensis actively flaps both the swimming fin and shell in a highly coordinated wing-like manner in order to swim in the intermediate Reynolds number regime (Re=10-100). The fin and shell kinematics indicate that atlantiid heteropods use unsteady hydrodynamic mechanisms such as clap-and-fling and delayed stall. Unique features of atlantiid heteropod swimming include the coordinated pairing of dissimilar appendages, use of the clap and fling mechanism twice during each stroke cycle, and the fin's extremely large stroke amplitude, which exceeds 180 deg.}, }
@article {pmid30346731, year = {2018}, author = {Astumian, RD}, title = {Trajectory and Cycle-Based Thermodynamics and Kinetics of Molecular Machines: The Importance of Microscopic Reversibility.}, journal = {Accounts of chemical research}, volume = {51}, number = {11}, pages = {2653-2661}, doi = {10.1021/acs.accounts.8b00253}, pmid = {30346731}, issn = {1520-4898}, abstract = {A molecular machine is a nanoscale device that provides a mechanism for coupling energy from two (or more) processes that in the absence of the machine would be independent of one another. Examples include walking of a protein in one direction along a polymeric track (process 1, driving "force" X1 = - F⃗· l⃗) and hydrolyzing ATP (process 2, driving "force" X2 = ΔμATP); or synthesis of ATP (process 1, X1 = -ΔμATP) and transport of protons from the periplasm to the cytoplasm across a membrane (process 2, X2 = ΔμH[+]); or rotation of a flagellum (process 1, X1 = -torque) and transport of protons across a membrane (process 2, X2 = ΔμH[+]). In some ways, the function of a molecular machine is similar to that of a macroscopic machine such as a car that couples combustion of gasoline to translational motion. However, the low Reynolds number regime in which molecular machines operate is very different from that relevant for macroscopic machines. Inertia is negligible in comparison to viscous drag, and omnipresent thermal noise causes the machine to undergo continual transition among many states even at thermodynamic equilibrium. Cyclic trajectories among the states of the machine that result in a change in the environment can be broken into two classes: those in which process 1 in either the forward or backward direction ([Formula: see text]) occurs and which thereby exchange work [Formula: see text] with the environment; and those in which process 2 in either the forward or backward direction ([Formula: see text]) occurs and which thereby exchange work [Formula: see text] with the evironment. These two types of trajectories, [Formula: see text] and [Formula: see text], overlap, i.e., there are some trajectories in which both process 1 and process 2 occur, and for which the work exchanged is [Formula: see text]. The four subclasses of overlap trajectories [(+1,+2), (+1,-2), (-1,+2), (-1,-2)] are the coupled processes. The net probabilities for process 1 and process 2 are designated π+2 - π-2 and π+1 - π-1, respectively. The probabilities [Formula: see text] for any single trajectory [Formula: see text] and [Formula: see text] for its microscopic reverse [Formula: see text] are related by microscopic reversibility (MR), [Formula: see text], an equality that holds arbitrarily far from thermodynamic equilibrium, i.e., irrespective of the magnitudes of X1 and X2, and where [Formula: see text]. Using this formalism, we arrive at a remarkably simple and general expression for the rates of the processes, [Formula: see text], i = 1, 2, where the angle brackets indicate an average over the ensemble of all microscopic reverse trajectories. Stochastic description of coupling is doubtless less familiar than typical mechanical depictions of chemical coupling in terms of ATP induced violent kicks, judo throws, force generation and power-strokes. While the mechanical description of molecular machines is comforting in its familiarity, conclusions based on such a phenomenological perspective are often wrong. Specifically, a "power-stroke" model (i.e., a model based on energy driven "promotion" of a molecular machine to a high energy state followed by directional relaxation to a lower energy state) that has been the focus of mechanistic discussions of biomolecular machines for over a half century is, for catalysis driven molecular machines, incorrect. Instead, the key principle by which catalysis driven motors work is kinetic gating by a mechanism known as an information ratchet. Amazingly, this same principle is that by which catalytic molecular systems undergo adaptation to new steady states while facilitating an exergonic chemical reaction.}, }
@article {pmid30327167, year = {2019}, author = {Zhang, H and Liu, C and Ou, Y and Chen, T and Yang, L and Hu, Z}, title = {Development of a helical coagulation reactor for harvesting microalgae.}, journal = {Journal of bioscience and bioengineering}, volume = {127}, number = {4}, pages = {447-450}, doi = {10.1016/j.jbiosc.2018.09.012}, pmid = {30327167}, issn = {1347-4421}, mesh = {Biomass ; *Bioreactors ; Cell Culture Techniques/instrumentation/methods ; Chemical Precipitation ; Flocculation ; Hydrodynamics ; Mechanical Phenomena ; Microalgae/*chemistry/*cytology/metabolism ; *Scenedesmus/cytology/metabolism ; Specimen Handling/instrumentation/methods ; }, abstract = {In this study, an innovative helical coagulation reactor (HCR) was developed for harvesting microalgae by sedimentation with polyaluminium chloride (PAC). The effects of construction and hydrodynamic characteristics on harvesting performance were investigated. Results showed that a higher harvesting efficiency, 96.37%, was achieved for the large and compact flocs generated by the HCR, and the settling rate of flocs was substantially influenced by the velocity gradient (G) and the Reynolds number (Re). When the Reynolds number closed to the transition between laminar and turbulent flow (4000), the flocs settled faster (20.51 m h[-1]), although settling slowed as the Reynolds number increased further because of ruptured flocs. The settling rate of flocs could be further improved to 23.27 m h[-1] by a pulse flow field, mainly due to larger and more compact flocs forming in the plug pipe flow. Furthermore, a comparative investigation of a mechanically agitated vessel and the HCR with the same Camp number (Gt) showed that the HCR achieved higher settling rates and a shorter residence time than those with a mechanical agitator. The HCR provided a uniform dissipation of energy and high velocity gradient while avoiding electrical and mechanical energy consumption, suggesting this reactor is an efficient and economic option for microalgae harvesting.}, }
@article {pmid30327024, year = {2019}, author = {Hong, W and Shi, H and Huang, Z and Long, M and Xu, H and Liu, Z}, title = {Design and Simulation of a Passive Micromixer with Gourd-Shaped Channel.}, journal = {Journal of nanoscience and nanotechnology}, volume = {19}, number = {1}, pages = {206-212}, doi = {10.1166/jnn.2019.16431}, pmid = {30327024}, issn = {1533-4880}, abstract = {A gourd-shaped contraction-expansion design is proposed for a passive planar micromixer in this study. The mixing performance of the micromixer is analyzed numerically and compared with a T-shaped planar micromixer. The gourd-shaped contraction-expansion structure can enhance the vortex-formation and mixing abilities of the micromixer. The numerical simulation reveals that the gourd-shaped structure can improved vortex generation and mixing efficiency within a high Reynolds number range. The micromixer with an optimized waist width of 50 μm reaches a mixing efficiency of approximately 83.25% and maintains a moderate pressure drop of 4860 Pa at Re = 100. This study can shed light on the design of new 2D micromixers from the point view of bionics.}, }
@article {pmid30326635, year = {2018}, author = {Sun, B and Wang, P and Luo, J and Deng, J and Guo, S and Ma, B}, title = {A Flexible Hot-Film Sensor Array for Underwater Shear Stress and Transition Measurement.}, journal = {Sensors (Basel, Switzerland)}, volume = {18}, number = {10}, pages = {}, pmid = {30326635}, issn = {1424-8220}, support = {2013YQ040911//National Instrumentation Program of China/ ; 51775446//National Natural Science Foundation of China/ ; }, abstract = {A flexible hot-film sensor array for wall shear stress, flow separation, and transition measurement has been fabricated and implemented in experiments. Parylene C waterproof layer is vapor phase deposited to encapsulate the sensor. Experimental studies of shear stress and flow transition on a flat plate have been undertaken in a water tunnel with the sensor array. Compared with the shear stress derived from velocity profile and empirical formulas, the measuring errors of the hot-film sensors are less than 5%. In addition, boundary layer transition of the flat plate has also been detected successfully. Ensemble-averaged mean, normalized root mean square, and power spectra of the sensor output voltage indicate that the Reynolds number when transition begins at where the sensor array located is 1.82 × 10[5], 50% intermittency transition is 2.52 × 10[5], and transition finishes is 3.96 × 10[5]. These results have a good agreement with the transition Reynolds numbers, as measured by the Laser Doppler Velocimetry (LDV) system.}, }
@article {pmid30302623, year = {2019}, author = {Tiwari, A and Chauhan, SS}, title = {Effect of Varying Viscosity on Two-Fluid Model of Blood Flow through Constricted Blood Vessels: A Comparative Study.}, journal = {Cardiovascular engineering and technology}, volume = {10}, number = {1}, pages = {155-172}, doi = {10.1007/s13239-018-00379-x}, pmid = {30302623}, issn = {1869-4098}, mesh = {Arterial Occlusive Diseases/*blood/physiopathology ; Arteries/*physiopathology ; Blood Flow Velocity ; *Blood Viscosity ; *Computer Simulation ; *Erythrocytes ; Humans ; *Models, Cardiovascular ; *Pulsatile Flow ; Regional Blood Flow ; }, abstract = {PURPOSE: Most of the previously studied non-Newtonian blood flow models considered blood viscosity to be constant but for correct measurement of flow rate and flow resistance, the hematocrit dependent viscosity will be better as various literature suggested the variable nature of blood viscosity. Present work concerns the steady and pulsatile nature of blood flow through constricted blood vessels. Two-fluid model for blood is considered with the suspension of all the RBCs (erythrocytes) in the core region as a non-Newtonian (Herschel-Bulkley) fluid and the plasma in the cell free region near wall as a Newtonian fluid. No slip condition on the wall and radially varying viscosity has been taken.<br><br>METHODS: For steady flow the analytical approach has been taken to obtain the exact solution. Regular perturbation expansion method has been used to solve the governing equations for pulsatile flow up to first order of approximation by assuming the pulsatile Reynolds number to be very small (much less than unity).<br><br>RESULTS: Flow rate, wall shear stress and velocity profile have been graphically analyzed and compared with constant viscosity model. A noteworthy observation of the present study is that rise in viscosity index leads to decay in velocity, velocity of plug flow region, flow rate while flow resistance increases with rising viscosity index (m). The results for Power-law fluid (PL), Bingham-plastic fluid (BP), Newtonian fluid (NF) are found as special cases from this model. Like the constant viscosity model, it has been also observed that the velocity, flow rate and plug core velocity of two-fluid model are higher than the single-fluid model for variable viscosity.<br><br>CONCLUSIONS: The two-phase fluid model is more significant than the single-fluid model. Effect of viscosity parameter on various hemodynamical quantities has been obtained. It is also concluded that a rising viscosity parameter (varying nature of viscosity) significantly distinguishes the single and two-fluid models in terms of changes in blood flow resistance. The outcome of present study may leave a significant impact on analyzing blood flow through small blood vessels with constriction, where correct measurement of flow rate and flow resistance for medical treatment is very important.}, }
@article {pmid30297857, year = {2018}, author = {Karathanassis, IK and Trickett, K and Koukouvinis, P and Wang, J and Barbour, R and Gavaises, M}, title = {Illustrating the effect of viscoelastic additives on cavitation and turbulence with X-ray imaging.}, journal = {Scientific reports}, volume = {8}, number = {1}, pages = {14968}, pmid = {30297857}, issn = {2045-2322}, abstract = {The effect of viscoelastic additives on the topology and dynamics of the two-phase flow arising within an axisymmetric orifice with a flow path constriction along its main axis has been investigated employing high-flux synchrotron radiation. X-ray Phase Contrast Imaging (XPCI) has been conducted to visualise the cavitating flow of different types of diesel fuel within the orifice. An additised blend containing Quaternary Ammonium Salt (QAS) additives with a concentration of 500 ppm has been comparatively examined against a pure (base) diesel compound. A high-flux, 12 keV X-ray beam has been utilised to obtain time resolved radiographs depicting the vapour extent within the orifice from two views (side and top) with reference to its main axis. Different test cases have been examined for both fuel types and for a range of flow conditions characterised by Reynolds number of 35500 and cavitation numbers (CN) lying in the range 3.0-7.7. It has been established that the behaviour of viscoelastic micelles in the regions of shear flow is not consistent depending on the cavitation regimes encountered. Namely, viscoelastic effects enhance vortical (string) cavitation, whereas hinder cloud cavitation. Furthermore, the use of additised fuel has been demonstrated to suppress the level of turbulence within the orifice.}, }
@article {pmid30280982, year = {2020}, author = {de Matos, DB and Barbosa, MPR and Leite, OM and Steter, JR and Lima, NS and Torres, NH and Marques, MN and de Alsina, OLS and Cavalcanti, EB}, title = {Characterization of a tubular electrochemical reactor for the degradation of the commercial diuron herbicide.}, journal = {Environmental technology}, volume = {41}, number = {10}, pages = {1307-1321}, doi = {10.1080/09593330.2018.1531941}, pmid = {30280982}, issn = {1479-487X}, mesh = {Diuron ; Electrodes ; *Herbicides ; Hydrogen Peroxide ; Oxidation-Reduction ; *Water Pollutants, Chemical ; }, abstract = {After designing and constructing an electrochemical reactor with concentric electrodes and tangential feed (RECT), it is necessary to characterize it and to study its performance. The experimental study of the residence time distribution (RTD) was conducted for flow rates of 2.78 × 10[-6] m[3] s[-1], 8.33 × 10[-6] m[3] s[-1] and 13.9 × 10[-6] m[3] s[-1]. According to the values obtained from the Pe number (0.67-1.52), the RECT fits as tubular with great dispersion. The determined empirical correlation (Sh = 18.16 Re[0.50] Sc[0.33]) showed a laminar flow behavior in the range of Reynolds number (Re) between 23 and 117. In order to use RECT in effluent treatment, an electrochemical oxidation study of the Diuron model molecule (Nortox[®]) was performed to analyze reactor performance in a closed system with total reflux. A decay kinetics of pseudo-first order was associated with the decay of the concentration of diuron and 30% mineralization in 180 min of process were obtained, having a total volume of 4 × 10[-3] m[3] and an initial concentration of commercial Diuron in 215.83 mg dm[-3]. Eleven by-products were identified by HPLC-MS analysis and, from this, it was possible to propose a route of degradation of the diuron. From these observations, it can be inferred that the studied electrochemical reactor had applicability in the degradation of recalcitrant compounds, as is the case of commercial diuron. Make some changes in the electrochemical reactor studied and other advanced oxidative processes, such as electro-Fenton, can be associated with the studied system to achieve a better conversion efficiency.}, }
@article {pmid30242545, year = {2018}, author = {Waldrop, LD and He, Y and Khatri, S}, title = {What Can Computational Modeling Tell Us about the Diversity of Odor-Capture Structures in the Pancrustacea?.}, journal = {Journal of chemical ecology}, volume = {44}, number = {12}, pages = {1084-1100}, pmid = {30242545}, issn = {1573-1561}, support = {1505061//Division of Physics/ ; TG-CDA160015//Extreme Science and Engineering Discovery Environment/ ; TG-BIO170090//Extreme Science and Engineering Discovery Environment/ ; }, mesh = {Air ; Animals ; Arthropod Antennae/metabolism ; Biological Evolution ; *Models, Theoretical ; *Odorants/analysis ; Water/chemistry ; }, abstract = {A major transition in the history of the Pancrustacea was the invasion of several lineages of these animals onto land. We investigated the functional performance of odor-capture organs, antennae with olfactory sensilla arrays, through the use of a computational model of advection and diffusion of odorants to olfactory sensilla while varying three parameters thought to be important to odor capture (Reynolds number, gap-width-to-sensillum-diameter ratio, and angle of the sensilla array with respect to oncoming flow). We also performed a sensitivity analysis on these parameters using uncertainty quantification to analyze their relative contributions to odor-capture performance. The results of this analysis indicate that odor capture in water and in air are fundamentally different. Odor capture in water and leakiness of the array are highly sensitive to Reynolds number and moderately sensitive to angle, whereas odor capture in air is highly sensitive to gap widths between sensilla and moderately sensitive to angle. Leakiness is not a good predictor of odor capture in air, likely due to the relative importance of diffusion to odor transport in air compared to water. We also used the sensitivity analysis to make predictions about morphological and kinematic diversity in extant groups of aquatic and terrestrial crustaceans. Aquatic crustaceans will likely exhibit denser arrays and induce flow within the arrays, whereas terrestrial crustaceans will rely on more sparse arrays with wider gaps and little-to-no animal-induced currents.}, }
@article {pmid30212772, year = {2018}, author = {Fu, Q and Chen, H and Liao, Q and Huang, Y and Xia, A and Zhu, X and Xiao, C and Reungsang, A and Liu, Z}, title = {Drag reduction and shear-induced cells migration behavior of microalgae slurry in tube flow.}, journal = {Bioresource technology}, volume = {270}, number = {}, pages = {38-45}, doi = {10.1016/j.biortech.2018.08.133}, pmid = {30212772}, issn = {1873-2976}, mesh = {*Chlorella ; Physical Phenomena ; }, abstract = {To optimize the designing of microalgae slurry pumping system and enhance the efficiency of microalgae products production, the flow characteristics of microalgae slurries (Chlorella pyrenoidosa) in tube flow were for the first time investigated combining experiments and numerical simulation. The drag reduction behavior of microalgae slurry in the fully developed laminar flow regime was studied. In addition, the transition Reynolds number of microalgae slurries from laminar flow to turbulent flow was about 1000-1300, which was similar to the expression of two-phase flow. To provide a further understanding of flow feature of microalgae slurries in tube, a two-phase mixture model was proposed by considering the heterogeneity of concentration due to the shear-induced microalgae cells migration behavior. Simulation results revealed that the heterogeneous distribution of concentration was affected by average velocity and volume fraction of microalgae slurries, significantly affecting the flow resistance and flow stability of microalgae slurry in the tube flow.}, }
@article {pmid30211982, year = {2019}, author = {Bergersen, AW and Mortensen, M and Valen-Sendstad, K}, title = {The FDA nozzle benchmark: "In theory there is no difference between theory and practice, but in practice there is".}, journal = {International journal for numerical methods in biomedical engineering}, volume = {35}, number = {1}, pages = {e3150}, doi = {10.1002/cnm.3150}, pmid = {30211982}, issn = {2040-7947}, mesh = {*Benchmarking ; Computer Simulation ; *Hydrodynamics ; United States ; United States Food and Drug Administration ; }, abstract = {The utility of flow simulations relies on the robustness of computational fluid dynamics (CFD) solvers and reproducibility of results. The aim of this study was to validate the Oasis CFD solver against in vitro experimental measurements of jet breakdown location from the FDA nozzle benchmark at Reynolds number 3500, which is in the particularly challenging transitional regime. Simulations were performed on meshes consisting of 5, 10, 17, and 28 million (M) tetrahedra, with Δt = 10[-5] seconds. The 5M and 10M simulation jets broke down in reasonable agreement with the experiments. However, the 17M and 28M simulation jets broke down further downstream. But which of our simulations are "correct"? From a theoretical point of view, they are all wrong because the jet should not break down in the absence of disturbances. The geometry is axisymmetric with no geometrical features that can generate angular velocities. A stable flow was supported by linear stability analysis. From a physical point of view, a finite amount of "noise" will always be present in experiments, which lowers transition point. To replicate noise numerically, we prescribed minor random angular velocities (approximately 0.31%), much smaller than the reported flow asymmetry (approximately 3%) and model accuracy (approximately 1%), at the inlet of the 17M simulation, which shifted the jet breakdown location closer to the measurements. Hence, the high-resolution simulations and "noise" experiment can potentially explain discrepancies in transition between sometimes "sterile" CFD and inherently noisy "ground truth" experiments. Thus, we have shown that numerical simulations can agree with experiments, but for the wrong reasons.}, }
@article {pmid30200611, year = {2018}, author = {Wan, G and Jin, C and Trase, I and Zhao, S and Chen, Z}, title = {Helical Structures Mimicking Chiral Seedpod Opening and Tendril Coiling.}, journal = {Sensors (Basel, Switzerland)}, volume = {18}, number = {9}, pages = {}, pmid = {30200611}, issn = {1424-8220}, support = {Dartmouth College//Startup fund from Thayer School of Engineering at Dartmouth College/ ; Branco Weiss-Society in Science fellowship//Branco Weiss-Society in Science fellowship (administered by ETH Z&#xfc;rich)/ ; }, mesh = {Biomimetic Materials/*chemistry ; *Biomimetics ; Elastomers/chemistry ; Hydrogels/chemistry ; Liquid Crystals/chemistry ; *Plant Physiological Phenomena ; Plants/*anatomy &amp; histology ; Polymers/chemistry ; }, abstract = {Helical structures are ubiquitous in natural and engineered systems across multiple length scales. Examples include DNA molecules, plants' tendrils, sea snails' shells, and spiral nanoribbons. Although this symmetry-breaking shape has shown excellent performance in elastic springs or propulsion generation in a low-Reynolds-number environment, a general principle to produce a helical structure with programmable geometry regardless of length scales is still in demand. In recent years, inspired by the chiral opening of Bauhinia variegata's seedpod and the coiling of plant's tendril, researchers have made significant breakthroughs in synthesizing state-of-the-art 3D helical structures through creating intrinsic curvatures in 2D rod-like or ribbon-like precursors. The intrinsic curvature results from the differential response to a variety of external stimuli of functional materials, such as hydrogels, liquid crystal elastomers, and shape memory polymers. In this review, we give a brief overview of the shape transformation mechanisms of these two plant's structures and then review recent progress in the fabrication of biomimetic helical structures that are categorized by the stimuli-responsive materials involved. By providing this survey on important recent advances along with our perspectives, we hope to solicit new inspirations and insights on the development and fabrication of helical structures, as well as the future development of interdisciplinary research at the interface of physics, engineering, and biology.}, }
@article {pmid30194679, year = {2018}, author = {Daddi-Moussa-Ider, A and Löwen, H and Gekle, S}, title = {Creeping motion of a solid particle inside a spherical elastic cavity[⋆].}, journal = {The European physical journal. E, Soft matter}, volume = {41}, number = {9}, pages = {104}, pmid = {30194679}, issn = {1292-895X}, abstract = {On the basis of the linear hydrodynamic equations, we present an analytical theory for the low-Reynolds-number motion of a solid particle moving inside a larger spherical elastic cavity which can be seen as a model system for a fluid vesicle. In the particular situation where the particle is concentric with the cavity, we use the stream function technique to find exact analytical solutions of the fluid motion equations on both sides of the elastic cavity. In this particular situation, we find that the solution of the hydrodynamic equations is solely determined by membrane shear properties and that bending does not play a role. For an arbitrary position of the solid particle within the spherical cavity, we employ the image solution technique to compute the axisymmetric flow field induced by a point force (Stokeslet). We then obtain analytical expressions of the leading-order mobility function describing the fluid-mediated hydrodynamic interactions between the particle and the confining elastic cavity. In the quasi-steady limit of vanishing frequency, we find that the particle self-mobility function is higher than that predicted inside a rigid no-slip cavity. Considering the cavity motion, we find that the pair-mobility function is determined only by membrane shear properties. Our analytical predictions are supplemented and validated by fully resolved boundary integral simulations where a very good agreement is obtained over the whole range of applied forcing frequencies.}, }
@article {pmid30140921, year = {2019}, author = {Molony, DS and Park, J and Zhou, L and Fleischer, CC and Sun, HY and Hu, XP and Oshinski, JN and Samady, H and Giddens, DP and Rezvan, A}, title = {Bulk Flow and Near Wall Hemodynamics of the Rabbit Aortic Arch and Descending Thoracic Aorta: A 4D PC-MRI Derived Computational Fluid Dynamics Study.}, journal = {Journal of biomechanical engineering}, volume = {141}, number = {1}, pages = {0110031-01100311}, pmid = {30140921}, issn = {1528-8951}, support = {HHSN268201000043C/HL/NHLBI NIH HHS/United States ; }, abstract = {Animal models offer a flexible experimental environment for studying atherosclerosis. The mouse is the most commonly used animal, however, the underlying hemodynamics in larger animals such as the rabbit are far closer to that of humans. The aortic arch is a vessel with complex helical flow and highly heterogeneous shear stress patterns which may influence where atherosclerotic lesions form. A better understanding of intraspecies flow variation and the impact of geometry on flow may improve our understanding of where disease forms. In this work, we use magnetic resonance angiography (MRA) and 4D phase contrast magnetic resonance imaging (PC-MRI) to image and measure blood velocity in the rabbit aortic arch. Measured flow rates from the PC-MRI were used as boundary conditions in computational fluid dynamics (CFD) models of the arches. Helical flow, cross flow index (CFI), and time-averaged wall shear stress (TAWSS) were determined from the simulated flow field. Both traditional geometric metrics and shape modes derived from statistical shape analysis were analyzed with respect to flow helicity. High CFI and low TAWSS were found to colocalize in the ascending aorta and to a lesser extent on the inner curvature of the aortic arch. The Reynolds number was linearly associated with an increase in helical flow intensity (R = 0.85, p < 0.05). Both traditional and statistical shape analyses correlated with increased helical flow symmetry. However, a stronger correlation was obtained from the statistical shape analysis demonstrating its potential for discerning the role of shape in hemodynamic studies.}, }
@article {pmid30136131, year = {2018}, author = {Krastev, VK and Amati, G and Succi, S and Falcucci, G}, title = {On the effects of surface corrugation on the hydrodynamic performance of cylindrical rigid structures.}, journal = {The European physical journal. E, Soft matter}, volume = {41}, number = {8}, pages = {95}, pmid = {30136131}, issn = {1292-895X}, mesh = {Computer Simulation ; *Hydrodynamics ; Kinetics ; Surface Properties ; }, abstract = {In this work, we perform fully three-dimensional numerical simulations of the flow field surrounding cylindrical structures characterized by different types of corrugated surface. The simulations are carried out using the Lattice Boltzmann Method (LBM), considering a flow regime with a Reynolds number [Formula: see text]. The fluid-dynamic wake structure and stability are investigated by means of PSD analyses of the velocity components and by visual inspection of the vortical coherent structure evolution. Moreover, the energy dissipation of the flow is assessed by considering an equivalent discharge coefficient [Formula: see text], which measures the total pressure losses of the flow moving around the various layout under investigation. Outcomes from our study demonstrate that the helical ridges augment energy dissipation, but might also have a role in the passive control of the characteristic frequencies of the unsteady wake flow.}, }
@article {pmid30132443, year = {2018}, author = {Lee, YJ and Lua, KB}, title = {Wing-wake interaction: comparison of 2D and 3D flapping wings in hover flight.}, journal = {Bioinspiration &amp; biomimetics}, volume = {13}, number = {6}, pages = {066003}, doi = {10.1088/1748-3190/aadc31}, pmid = {30132443}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena/physiology ; Biomimetics/methods ; Flight, Animal/*physiology ; Models, Biological ; Wings, Animal/*physiology ; }, abstract = {The wing-wake interaction of flapping wings while hovering has been investigated, with the focus on the difference in wing-wake interaction between 2D and 3D flapping wings. Numerical simulations are conducted at a Reynolds number of 100, and the flapping configurations are divided into the 2D, quasi-3D and 3D categories. Variations of the aspect ratio and Rossby number allow the flapping configuration to morph gradually between categories. The wing-wake interaction mechanisms are identified and the effect of three-dimensionality on these mechanisms is discussed. Three-dimensionality affects wing-wake interaction through four primary aerodynamic mechanisms, namely, induced jet, downwash/upwash, leading-edge vortex (LEV) shedding due to vortex pairing, and the formation of a closely attached LEV. The first two mechanisms are well-established in the literature. With regard to the LEV shedding mechanism, it is revealed that the interaction between the LEV and the residue vortex from the previous stroke plays an important role in the early vortex shedding of 2D flapping wings. This effect diminishes with increasing three-dimensionality. With regard to the mechanism of the closely attached LEV, the wake encourages the formation of an LEV that is closely attached to the wing's top surface, which is beneficial to lift generation. This closely attached LEV mechanism accounts for most of the lift enhancement that arises from wake effects. Three-dimensionality alters the efficacy of the different aerodynamic mechanisms. Consequently, the dual peak lift coefficient pattern typically seen on 2D flapping wings transforms into the single peak lift coefficient pattern of the 3D flapping wing. It is also demonstrated that the mean lift enhancement due to wing-wake interaction diminishes rapidly when three-dimensionality is introduced. Results suggest that, for wings with parameters close to those of natural flyers, wing-wake interaction yields marginal lift enhancement and a small increase in energy consumption.}, }
@article {pmid30132198, year = {2018}, author = {Espeso, DR and Martínez-García, E and Carpio, A and de Lorenzo, V}, title = {Dynamics of Pseudomonas putida biofilms in an upscale experimental framework.}, journal = {Journal of industrial microbiology &amp; biotechnology}, volume = {45}, number = {10}, pages = {899-911}, pmid = {30132198}, issn = {1476-5535}, support = {ERC-2012-ADG-322797//European Research Council/International ; EU-H2020-BIOTEC-2014-2015-6335536//Horizon 2020 Framework Programme/ ; H2020-FET-OPEN-RIA-2017-1-766975//Horizon 2020 Framework Programme/ ; }, mesh = {Algorithms ; Biofilms/*growth &amp; development ; Culture Media ; Equipment Design ; Hydrodynamics ; Image Processing, Computer-Assisted ; Industrial Microbiology/methods ; Polycarboxylate Cement/chemistry ; Pseudomonas putida/*growth &amp; development ; Software ; }, abstract = {Exploitation of biofilms for industrial processes requires them to adopt suitable physical structures for rendering them efficient and predictable. While hydrodynamics could be used to control material features of biofilms of the platform strain Pseudomonas putida KT2440 there is a dearth of experimental data on surface-associated growth behavior in such settings. Millimeter scale biofilm patterns formed by its parental strain P. putida mt-2 under different Reynolds numbers (Re) within laminar regime were analyzed using an upscale experimental continuous cultivation assembly. A tile-scan image acquisition process combined with a customized image analysis revealed patterns of dense heterogeneous structures at Re = 1000, but mostly flattened coverings sparsely patched for Re < 400. These results not only fix the somewhat narrow hydrodynamic regime under which P. putida cells form stable coatings on surfaces destined for large-scale processes, but also provide useful sets of parameters for engineering catalytic biofilms based on this important bacterium as a cell factory.}, }
@article {pmid30123895, year = {2018}, author = {Lee, J and Estlack, Z and Somaweera, H and Wang, X and Lacerda, CMR and Kim, J}, title = {A microfluidic cardiac flow profile generator for studying the effect of shear stress on valvular endothelial cells.}, journal = {Lab on a chip}, volume = {18}, number = {19}, pages = {2946-2954}, doi = {10.1039/c8lc00545a}, pmid = {30123895}, issn = {1473-0189}, mesh = {Aortic Valve/*cytology/physiology ; Endothelial Cells/*metabolism ; Equipment Design ; *Lab-On-A-Chip Devices ; *Shear Strength ; *Stress, Mechanical ; }, abstract = {To precisely investigate the mechanobiological responses of valvular endothelial cells, we developed a microfluidic flow profile generator using a pneumatically-actuated micropump consisting of microvalves of various sizes. By controlling the closing pressures and the actuation times of these microvalves, we modulated the magnitude and frequency of the shear stress to mimic mitral and aortic inflow profiles with frequencies in the range of 0.8-2 Hz and shear stresses up to 20 dyn cm-2. To demonstrate this flow profile generator, aortic inflow with an average of 5.9 dyn cm-2 shear stress at a frequency of 1.2 Hz with a Reynolds number of 2.75, a Womersley number of 0.27, and an oscillatory shear index (OSI) value of 0.2 was applied to porcine aortic valvular endothelial cells (PAVECs) for mechanobiological studies. The cell alignment, cell elongation, and alpha-smooth muscle actin (αSMA) expression of PAVECs under perfusion, steady flow, and aortic inflow conditions were analyzed to determine their shear-induced cell migration and trans-differentiation. In this morphological and immunocytochemical study, we found that the PAVECs elongated and aligned themselves perpendicular to the directions of the steady flow and the aortic inflow. In contrast, under perfusion with a fluidic shear stress of 0.47 dyn cm-2, the PAVECs elongated and aligned themselves parallel to the direction of flow. The PAVECs exposed to the aortic inflow upregulated their αSMA-protein expression to a greater degree than those exposed to perfusion and steady flow. By comparing these results to those of previous studies of pulsatile flow, we also found that the ratio of positive to negative shear stress plays an important role in determining PAVECs' trans-differentiation and adaptation to flow. This microfluidic cardiac flow profile generator will enable future valvular mechanobiological studies to determine the roles of magnitude and frequency of shear stresses.}, }
@article {pmid30119494, year = {2018}, author = {Gao, J and Katz, J}, title = {Self-calibrated microscopic dual-view tomographic holography for 3D flow measurements.}, journal = {Optics express}, volume = {26}, number = {13}, pages = {16708-16725}, doi = {10.1364/OE.26.016708}, pmid = {30119494}, issn = {1094-4087}, abstract = {This paper introduces the application of microscopic dual-view tomographic holography (M-DTH) to measure the 3D position and motion of micro-particles located in dense suspensions. Pairing of elongated traces of the same particle in the two inclined reconstructed fields requires precise matching of the entire sample volume that accounts for the inherent distortions in each view. It is achieved by an iterative volumetric self-calibration method, consisting of mapping one view onto the next, dividing the sample volume into slabs, and cross-correlating the two views. Testing of the procedures using synthetic particle fields with imposed distortion and realistic errors in particle locations shows that the self-calibration method achieves a 3D uncertainty of about 1µm, a third of the particle diameter. Multiplying the corrected intensity fields is used for truncating the elongated traces, whose centers are located within 1µm of the exact value. Without correction, only a small fraction of the traces even overlap. The distortion correction also increases the number of intersecting traces in experimental data along with their intensity. Application of this method for 3D velocity measurements is based on the centroids of the truncated/shortened particle traces. Matching of these traces in successive fields is guided by several criteria, including results of volumetric cross-correlation of the multiplied intensity fields. The resulting 3D velocity distribution is substantially more divergence-free, i.e., satisfies conservation of mass, compared to analysis performed using single-view data. Sample application of the new method shows the 3D flow structure around a pair of cubic roughness elements embedded in the inner part of a high Reynolds number turbulent boundary layer.}, }
@article {pmid30118276, year = {2018}, author = {Mathai, V and Huisman, SG and Sun, C and Lohse, D and Bourgoin, M}, title = {Dispersion of Air Bubbles in Isotropic Turbulence.}, journal = {Physical review letters}, volume = {121}, number = {5}, pages = {054501}, doi = {10.1103/PhysRevLett.121.054501}, pmid = {30118276}, issn = {1079-7114}, abstract = {Bubbles play an important role in the transport of chemicals and nutrients in many natural and industrial flows. Their dispersion is crucial to understanding the mixing processes in these flows. Here we report on the dispersion of millimetric air bubbles in a homogeneous and isotropic turbulent flow with a Taylor Reynolds number from 110 to 310. We find that the mean squared displacement (MSD) of the bubbles far exceeds that of fluid tracers in turbulence. The MSD shows two regimes. At short times, it grows ballistically (∝τ^{2}), while at larger times, it approaches the diffusive regime where the MSD∝τ. Strikingly, for the bubbles, the ballistic-to-diffusive transition occurs one decade earlier than for the fluid. We reveal that both the enhanced dispersion and the early transition to the diffusive regime can be traced back to the unsteady wake-induced motion of the bubbles. Further, the diffusion transition for bubbles is not set by the integral timescale of the turbulence (as it is for fluid tracers and microbubbles), but instead, by a timescale of eddy crossing of the rising bubbles. The present findings provide a Lagrangian perspective towards understanding mixing in turbulent bubbly flows.}, }
@article {pmid30118271, year = {2018}, author = {Oettinger, D and Ault, JT and Stone, HA and Haller, G}, title = {Invisible Anchors Trap Particles in Branching Junctions.}, journal = {Physical review letters}, volume = {121}, number = {5}, pages = {054502}, doi = {10.1103/PhysRevLett.121.054502}, pmid = {30118271}, issn = {1079-7114}, abstract = {We combine numerical simulations and an analytic approach to show that the capture of finite, inertial particles during flow in branching junctions is due to invisible, anchor-shaped three-dimensional flow structures. These Reynolds-number-dependent anchors define trapping regions that confine particles to the junction. For a wide range of Stokes numbers, these structures occupy a large part of the flow domain. For flow in a V-shaped junction, at a critical Stokes number, we observe a topological transition due to the merger of two anchors into one. From a stability analysis, we identify the parameter region of particle sizes and densities where capture due to anchors occurs.}, }
@article {pmid30117966, year = {2018}, author = {Karaminejad, S and Askari, MH and Ashjaee, M}, title = {Temperature field investigation of hydrogen/air and syngas/air axisymmetric laminar flames using Mach-Zehnder interferometry.}, journal = {Applied optics}, volume = {57}, number = {18}, pages = {5057-5067}, doi = {10.1364/AO.57.005057}, pmid = {30117966}, issn = {1539-4522}, abstract = {In this study, the optical method of Mach-Zehnder interferometry (MZI) is utilized in order to explore the flame structure and temperature field of syngas/air and hydrogen/air flames. Two axisymmetric burners with inner diameters of 4 mm and 6 mm are used for temperature field measurement of hydrogen and syngas, respectively. The effects of fuel composition, equivalence ratio, and Reynolds number (Re) are investigated at ambient condition (P=0.87 bar, T=300 K). Three different H2/CO fuel compositions with hydrogen fractions of 30%, 50%, and 100% are studied. Temperature profiles are reported at four different sections above the burner tip. Measured temperatures using the interferometry method are compared with thermocouple data and good agreement between them is observed. The results obtained in this investigation indicated that the MZI can be applied for accurate determination of flame front and temperature field, especially for high-temperature flames where other methods cannot be properly utilized. Analyses of the data reduction method revealed that the exact determination of the refractive index distribution and reference temperature is critical for accurate determination of the temperature field. The results indicated that by increasing the Re, the maximum flame temperature is enhanced. Increasing the equivalence ratio leads to expansion of the flame radial distribution (at the same distance from the burner tip). At higher distances from the burner tip, temperature increases uniformly from the flame boundary toward the flame axis, while at lower heights it shows reduction at the burner axis. By increasing the CO content of fuel, the maximum flame temperature increases at all equivalence ratios except at the stoichiometric condition, where SH100 illustrates the highest maximum flame temperature.}, }
@article {pmid30109056, year = {2018}, author = {Bhat, SS and Zhao, J and Sheridan, J and Hourigan, K and Thompson, MC}, title = {The leading-edge vortex on a rotating wing changes markedly beyond a certain central body size.}, journal = {Royal Society open science}, volume = {5}, number = {7}, pages = {172197}, pmid = {30109056}, issn = {2054-5703}, abstract = {Stable attachment of a leading-edge vortex (LEV) plays a key role in generating the high lift on rotating wings with a central body. The central body size can affect the LEV structure broadly in two ways. First, an overall change in the size changes the Reynolds number, which is known to have an influence on the LEV structure. Second, it may affect the Coriolis acceleration acting across the wing, depending on the wing-offset from the axis of rotation. To investigate this, the effects of Reynolds number and the wing-offset are independently studied for a rotating wing. The three-dimensional LEV structure is mapped using a scanning particle image velocimetry technique. The rapid acquisition of images and their correlation are carefully validated. The results presented in this paper show that the LEV structure changes mainly with the Reynolds number. The LEV-split is found to be only minimally affected by changing the central body radius in the range of small offsets, which interestingly includes the range for most insects. However, beyond this small offset range, the LEV-split is found to change dramatically.}, }
@article {pmid30089029, year = {2018}, author = {Gilmer, GG and Deshpande, VG and Chou, CL and Knepper, M}, title = {Flow resistance along the rat renal tubule.}, journal = {American journal of physiology. Renal physiology}, volume = {315}, number = {5}, pages = {F1398-F1405}, pmid = {30089029}, issn = {1522-1466}, support = {ZIA HL001285/HL/NHLBI NIH HHS/United States ; ZIA HL006129/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; *Diuresis ; *Glomerular Filtration Rate ; Hydrostatic Pressure ; Kidney Tubules/anatomy &amp; histology/*physiology ; *Models, Biological ; Rats ; Time Factors ; *Urodynamics ; Viscosity ; }, abstract = {The Reynolds number in the renal tubule is extremely low, consistent with laminar flow. Consequently, luminal flow can be described by the Hagen-Poiseuille laminar flow equation. This equation calculates the volumetric flow rate from the axial pressure gradient and flow resistance, which is dependent on the length and diameter of each renal tubule segment. Our goal was to calculate the pressure drop along each segment of the renal tubule and to determine the points of highest resistance. When the Hagen-Poiseuille equation was used for rat superficial nephrons based on known tubule flow rates, lengths, and diameters, it was found that the maximum pressure drop occurred in two segments: the thin descending limbs of Henle and the inner medullary collecting ducts. The high resistance in the thin descending limbs is due to their small diameters. The steep pressure drop observed in the inner medullary collecting ducts is due to the convergent structure of the tubules, which channels flow into fewer and fewer tubules toward the papillary tip. For short-looped nephrons, the calculated glomerular capsular pressure matched measured values, even with the high collecting duct flow rates seen in water diuresis, provided that tubule compliance was taken into account. In long-looped nephrons, the greater length of thin limb segments is likely compensated for by a larger luminal diameter. Simulation of the effect of proximal diuretics, namely acetazolamide or type 2 sodium-glucose transporter inhibitors, predicts a substantial back pressure in Bowman's capsule, which may contribute to observed decreases in glomerular filtration rate.}, }
@article {pmid30088905, year = {2018}, author = {Mateos-Maroto, A and Guerrero-Martínez, A and Rubio, RG and Ortega, F and Martínez-Pedrero, F}, title = {Magnetic Biohybrid Vesicles Transported by an Internal Propulsion Mechanism.}, journal = {ACS applied materials &amp; interfaces}, volume = {10}, number = {35}, pages = {29367-29377}, doi = {10.1021/acsami.8b09862}, pmid = {30088905}, issn = {1944-8252}, mesh = {*Hydrodynamics ; *Lipids ; *Magnetics ; *Models, Biological ; Rotation ; Transport Vesicles/metabolism ; }, abstract = {Some biological microorganisms can crawl or swim due to coordinated motions of their cytoskeleton or the flagella located inside their bodies, which push the cells forward through intracellular forces. To date, there is no demonstration of synthetic systems propelling at low Reynolds number via the precise actuation of the material confined within an enclosing lipid membrane. Here, we report lipid vesicles and other more complex self-assembled biohybrid structures able to propel due to the advection flows generated by the actuated rotation of the superparamagnetic particles they contain. The proposed swimming and release strategies, based on cooperative hydrodynamic mechanisms and near-infrared laser pulse-triggered destabilization of the phospholipid membranes, open new possibilities for the on-command transport of minute quantities of drugs, fluid or nano-objects. The lipid membranes protect the confined substances from the outside environment during transportation, thus enabling them to work in physiological conditions.}, }
@article {pmid30083106, year = {2018}, author = {Vidal, EAG and Zeidberg, LD and Buskey, EJ}, title = {Development of Swimming Abilities in Squid Paralarvae: Behavioral and Ecological Implications for Dispersal.}, journal = {Frontiers in physiology}, volume = {9}, number = {}, pages = {954}, pmid = {30083106}, issn = {1664-042X}, abstract = {This study investigates the development of swimming abilities and its relationship with morphology, growth, and nourishment of reared Doryteuthis opalescens paralarvae from hatching to 60 days of age. Paralarvae (2.5-11 mm mantle length - ML) were videotaped, and their behavior quantified throughout development using computerized motion analysis. Hatchlings swim dispersed maintaining large nearest neighbor distances (NND, 8.7 ML), with swimming speeds (SS) of 3-8 mm s[-1] and paths with long horizontal displacements, resulting in high net to gross displacement ratios (NGDR). For 15-day-old paralarvae, swimming paths are more consistent between jets, growth of fins, length, and mass increases. The swimming pattern of 18-day-old paralarvae starved for 72 h exhibited a significant reduction in mean SS and inability to perform escape jets. A key morphological, behavioral, and ecological transition occurs at about 6 mm ML (>35-day old), when there is a clear change in body shape, swimming performance, and behavior, paths are more regularly repeated and directional swimming is evident, suggesting that morphological changes incur in swimming performance. These squid are able to perform sustained swimming and hover against a current at significantly closer NND (2.0 ML), as path displacement is reduced and maneuverability increases. As paralarvae reach 6-7 mm ML, they are able to attain speeds up to 562 mm s[-1] and to form schools. Social feeding interactions (kleptoparasitism) are often observed prior to the formation of schools. Schools are always formed within areas of high flow gradient in the tanks and are dependent on squid size and current speed. Fin development is a requisite for synchronized and maneuverable swimming of schooling early juveniles. Although average speeds of paralarvae are within intermediate Reynolds numbers (Re < 100), they make the transition to the inertia-dominated realm during escape jets of high propulsion (Re > 3200), transitioning from plankton to nekton after their first month of life. The progressive development of swimming capabilities and social interactions enable juvenile squid to school, while also accelerates learning, orientation and cognition. These observations indicate that modeling of the lifecycle should include competency to exert influence over small currents and dispersal patterns after the first month of life.}, }
@article {pmid30072230, year = {2018}, author = {Gritti, F}, title = {High-resolution turbulent flow chromatography.}, journal = {Journal of chromatography. A}, volume = {1570}, number = {}, pages = {135-147}, doi = {10.1016/j.chroma.2018.07.059}, pmid = {30072230}, issn = {1873-3778}, mesh = {Benz(a)Anthracenes/*analysis/chemistry/isolation &amp; purification ; Carbon Dioxide/*chemistry ; Chromatography, High Pressure Liquid/*methods ; Chromatography, Supercritical Fluid/*methods ; Molecular Weight ; Polycyclic Compounds/*analysis/chemistry/isolation &amp; purification ; }, abstract = {The resolution power of turbulent flow chromatography using carbon dioxide as the mobile phase and coated (crosslinked methyl phenyl polysiloxane) open tube columns (OTCs) as the stationary phase was investigated under retentive conditions (0 <k< 1). The improvement in column efficiency from a laminar to a turbulent flow regime was accurately measured for small molecules (coronene and benzo[a]anthracene). This relative increase in column performance decreased from 9 to 5, 3, and to 3 with increasing the retention factor from 0 to 0.2, 0.5, and to 1.0, respectively. Despite a four to five orders of magnitude larger sample dispersion coefficient in turbulent than in laminar flow, the mass transfer in turbulent flow chromatography is still controlled and limited by the slow sample transport across the viscous layer at the column wall. The benefit of turbulent flow chromatography is then restricted to small retention factor (k< 0.2). From a practical viewpoint, turbulent flow chromatography using carbon dioxide as the mobile phase and 20 m long × 180 μm i.d. × 0.2 μm film thickness OTCs provides ultra-fast (analysis time < 10 s) and high-resolution (plate counts of 33,000) separations of weakly retained compounds (k∼0.1) at Reynolds number around 5000 (3.75 mL/min, 3000 psi back pressure).}, }
@article {pmid30069151, year = {2018}, author = {Rosti, ME and Omidyeganeh, M and Pinelli, A}, title = {Numerical Simulation of a Passive Control of the Flow Around an Aerofoil Using a Flexible, Self Adaptive Flaplet.}, journal = {Flow, turbulence and combustion}, volume = {100}, number = {4}, pages = {1111-1143}, pmid = {30069151}, issn = {1573-1987}, abstract = {Self-activated feathers are used by almost all birds to adapt their wing characteristics to delay stall or to moderate its adverse effects (e.g., during landing or sudden increase in angle of attack due to gusts). Some of the feathers are believed to pop up as a consequence of flow separation and to interact with the flow and produce beneficial modifications of the unsteady vorticity field. The use of self adaptive flaplets in aircrafts, inspired by birds feathers, requires the understanding of the physical mechanisms leading to the mentioned aerodynamic benefits and the determination of the characteristics of optimal flaps including their size, positioning and ideal fabrication material. In this framework, this numerical study is divided in two parts. Firstly, in a simplified scenario, we determine the main characteristics that render a flap mounted on an aerofoil at high angle of attack able to deliver increased lift and improved aerodynamic efficiency, by varying its length, position and its natural frequency. Later on, a detailed direct numerical simulation analysis is used to understand the origin of the aerodynamic benefits introduced by the flaplet movement induced by the interaction with the flow field. The parametric study that has been carried out, reveals that an optimal flap can deliver a mean lift increase of about 20% on a NACA0020 aerofoil at an incidence of 20 [o] degrees. The results obtained from the direct numerical simulation of the flow field around the aerofoil equipped with the optimal flap at a chord Reynolds number of 2 × 10[4] shows that the flaplet movement is mainly induced by a cyclic passage of a large recirculation bubble on the aerofoil suction side. In turns, when the flap is pushed downward, the induced plane jet displaces the trailing edge vortices further downstream, away from the wing, moderating the downforce generated by those vortices and regularising the shedding cycle that appears to be much more organised when the optimal flaplet configuration is selected.}, }
@article {pmid30069150, year = {2018}, author = {Vernet, JA and Örlü, R and Söderblom, D and Elofsson, P and Alfredsson, PH}, title = {Plasma Streamwise Vortex Generators for Flow Separation Control on Trucks: A Proof-of-concept Experiment.}, journal = {Flow, turbulence and combustion}, volume = {100}, number = {4}, pages = {1101-1109}, pmid = {30069150}, issn = {1573-1987}, abstract = {An experimental study of the effect of Dielectric Barrier Discharge plasma actuators on the flow separation on the A-pillar of a modern truck under cross-wind conditions has been carried out. The experiments were done in a wind tunnel with a 1:6 scale model of a tractor-trailer combination. The actuators were used as vortex generators positioned on the A-pillar on the leeward side of the tractor and the drag force was measured with a wind-tunnel balance. The results show that the effect at the largest yaw angle (9 degrees) can give a drag reduction of about 20% and that it results in a net power reduction. At lower yaw angles the reduction was smaller. The present results were obtained at a lower Reynolds number and a lower speed than for real driving conditions so it is still not yet confirmed if a similar positive result can be obtained in full scale.}, }
@article {pmid30069147, year = {2018}, author = {Ahmadi, S and Roccon, A and Zonta, F and Soldati, A}, title = {Turbulent Drag Reduction by a Near Wall Surface Tension Active Interface.}, journal = {Flow, turbulence and combustion}, volume = {100}, number = {4}, pages = {979-993}, pmid = {30069147}, issn = {1573-1987}, abstract = {In this work we study the turbulence modulation in a viscosity-stratified two-phase flow using Direct Numerical Simulation (DNS) of turbulence and the Phase Field Method (PFM) to simulate the interfacial phenomena. Specifically we consider the case of two immiscible fluid layers driven in a closed rectangular channel by an imposed mean pressure gradient. The present problem, which may mimic the behaviour of an oil flowing under a thin layer of different oil, thickness ratio h2/h1 = 9, is described by three main flow parameters: the shear Reynolds number Reτ (which quantifies the importance of inertia compared to viscous effects), the Weber number We (which quantifies surface tension effects) and the viscosity ratio λ = ν1/ν2 between the two fluids. For this first study, the density ratio of the two fluid layers is the same (ρ2 = ρ1), we keep Reτ and We constant, but we consider three different values for the viscosity ratio: λ = 1, λ = 0.875 and λ = 0.75. Compared to a single phase flow at the same shear Reynolds number (Reτ = 100), in the two phase flow case we observe a decrease of the wall-shear stress and a strong turbulence modulation in particular in the proximity of the interface. Interestingly, we observe that the modulation of turbulence by the liquid-liquid interface extends up to the top wall (i.e. the closest to the interface) and produces local shear stress inversions and flow recirculation regions. The observed results depend primarily on the interface deformability and on the viscosity ratio between the two fluids (λ).}, }
@article {pmid30069140, year = {2018}, author = {Sundstrom, LRJ and Cervantes, MJ}, title = {On the Similarity of Pulsating and Accelerating Turbulent Pipe Flows.}, journal = {Flow, turbulence and combustion}, volume = {100}, number = {2}, pages = {417-436}, pmid = {30069140}, issn = {1573-1987}, abstract = {The near-wall region of an unsteady turbulent pipe flow has been investigated experimentally using hot-film anemometry and two-component particle image velocimetry. The imposed unsteadiness has been pulsating, i.e., when a non-zero mean turbulent flow is perturbed by sinusoidal oscillations, and near-uniformly accelerating in which the mean flow ramped monotonically between two turbulent states. Previous studies of accelerating flows have shown that the time evolution between the two turbulent states occurs in three stages. The first stage is associated with a minimal response of the Reynolds shear stress and the ensemble-averaged mean flow evolves essentially akin to a laminar flow undergoing the same change in flow rate. During the second stage, the turbulence responds rapidly to the new flow conditions set by the acceleration and the laminar-like behavior rapidly disappears. During the final stage, the flow adapts to the conditions set by the final Reynolds number. In here, it is shown that the time-development of the ensemble-averaged wall shear stress and turbulence during the accelerating phase of a pulsating flow bears marked similarity to the first two stages of time-development exhibited by a near-uniformly accelerating flow. The stage-like time-development is observed even for a very low forcing frequency; ω+=ων/u¯τ2=0.00073 (or equivalently, ls+=2/ω+=52), at an amplitude of pulsation of 0.5. Some previous studies have considered the flow to be quasi-steady at ls+=52 ; however, the forcing amplitude has been smaller in those studies. The importance of the forcing amplitude is reinforced by the time-development of the ensemble-averaged turbulence field. For, the near-wall response of the Reynolds stresses showed a dependence on the amplitude of pulsation. Thus, it appears to exist a need to seek alternative similarity parameters, taking the amplitude of pulsation into account, if the response of different flow quantities in a pulsating flow are to be classified correctly.}, }
@article {pmid30044036, year = {2019}, author = {Dey, KK}, title = {Dynamic Coupling at Low Reynolds Number.}, journal = {Angewandte Chemie (International ed. in English)}, volume = {58}, number = {8}, pages = {2208-2228}, doi = {10.1002/anie.201804599}, pmid = {30044036}, issn = {1521-3773}, support = {IP/IITGN/PH/KD/201617-10//IIT Gandhinagar/International ; SRG 2017-18//Shastri Indo-Canadian Institute/International ; ECR/2017/002649//SERB-DST, India/International ; }, abstract = {Collective and emergent behaviors of active colloids provide useful insights into the statistical physics of out-of-equilibrium systems. Colloidal suspensions containing microscopic active swimmers have been intensively studied to understand the principles of energy transfer at low Reynolds number conditions. Studies on active enzymes and Ångström-sized organometallic catalysts have demonstrated that energy can even be transferred by molecules to their surroundings, thereby influencing the overall dynamics of the systems substantially. By monitoring the diffusion of non-reacting tracers in active solutions, it has been shown that the nature of energy transfer in systems containing different swimmers is surprisingly similar-irrespective of their size, modes of energy transduction, and propulsion strategies. This Review discusses research results obtained so far in this direction, highlighting the common features observed in the dynamic coupling of swimmers with their surroundings.}, }
@article {pmid30039801, year = {2018}, author = {Oh, S and Choi, H}, title = {A predictive model of the drag coefficient for a revolving wing at low Reynolds number.}, journal = {Bioinspiration &amp; biomimetics}, volume = {13}, number = {5}, pages = {054001}, doi = {10.1088/1748-3190/aad578}, pmid = {30039801}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena/*physiology ; Flight, Animal/physiology ; Models, Biological ; Viscosity ; Wings, Animal/*physiology ; }, abstract = {A predictive model of the drag coefficient for a revolving wing at low Reynolds number is suggested. Unlike the previous model (Wang et al 2016 J. Fluid Mech. 800 688-719), the present model includes a viscous drag on the wing from laminar boundary layer theory and thus predicts the drag force more accurately at low angles of attack and low Reynolds numbers. Also, in determining the model constants, we consider the attack angle of π/4 at which the resultant force on the wing is assumed to be perpendicular to the wing chord. The present aerodynamic model more accurately predicts drag forces of four different revolving wings than the existing ones.}, }
@article {pmid30019691, year = {2018}, author = {Dai, L and He, G and Zhang, X and Zhang, X}, title = {Intermittent locomotion of a fish-like swimmer driven by passive elastic mechanism.}, journal = {Bioinspiration &amp; biomimetics}, volume = {13}, number = {5}, pages = {056011}, doi = {10.1088/1748-3190/aad419}, pmid = {30019691}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena/physiology ; Biomimetics/*methods ; Elastic Modulus/*physiology ; Fishes/*physiology ; Locomotion/*physiology ; Models, Biological ; Swimming/*physiology ; }, abstract = {The intermittent locomotion performance of a fish-like elastic swimmer is studied numerically in this paper. The actuation is imposed only at the head and the locomotion is indirectly driven by passive elastic mechanism. For intermittent swimming, certain time durations of passive coasting are interspersed between two half-periods of active bursting. To facilitate the comparison of energy efficiencies in continuous and intermittent swimming at the same cruising speed, we consider both intermittent swimming at various duty cycles and also continuous swimming at reduced actuation frequencies. The result indicates that the intermittent style is more economical than the continuous style only when the cruising Reynolds number is sufficiently large and the duty cycle is moderate. We also explore the passive tail-beating pattern and wake structure for intermittent swimming. It is found that the kinematics of the tail contains a preparatory burst phase which lies in between the active bursting and the passive coasting phases. Three vortex streets are found in the wake structures behind the intermittent swimmers. The two oblique streets consist of strong vortex dipoles and the horizontal street is made up of weak vortices. The results of this study can provide some insight into the burst-and-coast swimming of fish and also inform the design of efficient bio-mimetic under-water vehicles.}, }
@article {pmid30016290, year = {2018}, author = {Tang, Y and Zhu, DZ and van Duin, B}, title = {Note on sediment removal efficiency in oil-grit separators.}, journal = {Water science and technology : a journal of the International Association on Water Pollution Research}, volume = {2017}, number = {3}, pages = {729-735}, doi = {10.2166/wst.2018.240}, pmid = {30016290}, issn = {0273-1223}, mesh = {*Geologic Sediments ; *Models, Theoretical ; Motion ; *Petroleum ; Water Movements ; *Water Pollutants ; Water Purification/*instrumentation/methods ; }, abstract = {Oil-grit separators (OGSs) are one type of best management practice, designed to remove oil and grit from stormwater runoff (e.g., from parking lots and paved roads). This note examines scaling parameters for OGS removal efficiency. Three dimensionless parameters are chosen as scaling parameters: Hazen number (Ha), Reynolds number (Re) and Froude number (Fr). The Hazen number is a ratio of hydraulic residence time to particle settling time. The Reynolds number measures the surrounding turbulence effects on sediment removal efficiency. The Froude number represents the ratio of inertial and gravitational forces, which indicates the influence of gravity on fluid motion. The collected data from the literature on sediment removal in OGSs can be represented by a single curve when the Hazen, Reynolds, and Froude numbers are combined into a new scaling parameter (HRF = Ha(Re/Fr)). A general form is proposed to correlate the sediment removal efficiency with this new parameter. This generalized prediction method can be used as a preliminary performance indicator for OGS units. The obtained curve can also be used to adjust raw laboratory and field measurement data to improve the evaluation of the performance of various OGSs.}, }
@article {pmid30011509, year = {2018}, author = {Fraternale, F and Domenicale, L and Staffilani, G and Tordella, D}, title = {Internal waves in sheared flows: Lower bound of the vorticity growth and propagation discontinuities in the parameter space.}, journal = {Physical review. E}, volume = {97}, number = {6-1}, pages = {063102}, doi = {10.1103/PhysRevE.97.063102}, pmid = {30011509}, issn = {2470-0053}, abstract = {This study provides sufficient conditions for the temporal monotonic decay of enstrophy for two-dimensional perturbations traveling in the incompressible, viscous, plane Poiseuille, and Couette flows. Extension of Synge's procedure [J. L. Synge, Proc. Fifth Int. Congress Appl. Mech. 2, 326 (1938); Semicentenn. Publ. Am. Math. Soc. 2, 227 (1938)] to the initial-value problem allow us to find the region of the wave-number-Reynolds-number map where the enstrophy of any initial disturbance cannot grow. This region is wider than that of the kinetic energy. We also show that the parameter space is split into two regions with clearly distinct propagation and dispersion properties.}, }
@article {pmid30009583, year = {2017}, author = {Malviya, R and Sharma, P and Dubey, S}, title = {Kheri (Acacia chundra, family: Mimosaceae) gum: Characterization using analytical, mathematical and pharmaceutical approaches.}, journal = {Polimery w medycynie}, volume = {47}, number = {2}, pages = {65-76}, doi = {10.17219/pim/76515}, pmid = {30009583}, issn = {0370-0747}, mesh = {Acacia/*chemistry ; Excipients ; Particle Size ; Plant Gums/*chemistry/isolation &amp; purification ; Polysaccharides/chemistry ; Rheology ; Spectroscopy, Fourier Transform Infrared ; Viscosity ; }, abstract = {BACKGROUND: Natural polymers have been used in medical, pharmaceutical, cosmetic and food industry. They should be characterized before their possible applications in different industries.<br><br>OBJECTIVES: The objective of this study was to characterize Kheri (Acacia chundra, family: Mimosaceae) gum using analytical, mathematical and pharmaceutical approaches.<br><br>MATERIAL AND METHODS: Crude Kheri gum (KG) was purified using distilled water as a solvent and ethanol as a precipitating agent. KG was characterized in terms of phytochemical screening, micromeritic properties, microbial load, ash value, rheological behavior, solid state 1H nuclear magnetic resonance (NMR), mass spectra and Fourier-transform infrared spectroscopy (FTIR) studies for their possible applications in food, cosmetics and pharmaceutical industry.<br><br>RESULTS: Studies show that KG contains carbohydrates, while protein, fat, volatile oils, alkaloids and glycosides are absent. 1% aqueous solution of polysaccharide showed 25.58 &#xd7; 103 kJ/kg activation energy and 1.39 Reynold's number. Viscosity average molecular weight of purified gum was found 1.73 &#xd7; 105 D. Thermodynamic parameters, i.e., change in enthalpy &#x394;Hv and change in enthalpy &#x394;Hv, were found to be 12.26 &#xd7; 103 kJ/mol and 24.47 kJ/mol, respectively. Mathematical approach also determined the rod shaped conformation of KG in aqueous solution. IR spectroscopic study shows the presence of free (COO-) and esterified (COO-R) carboxylic acid, ether (C-O stretching), galacturonic acid and mannose in polysaccharide 1H NMR study predicts presence of tetrahydropyran hydrogen in molecule. Furthermore, KG was also characterized as a suspending agent using paracetamol as a model drug. Flow rate, pH, particle size and settling behavior of suspensions were evaluated. Initial particle size of dispersed phase particles does not change significantly after 45 days.<br><br>CONCLUSIONS: From the findings of the research it can be concluded that KG can be used as an excipient in cosmaceuticals and pharmaceuticals and its characteristic rheological behavior may attract rheologists.}, }
@article {pmid29991599, year = {2018}, author = {Mutlu, BR and Edd, JF and Toner, M}, title = {Oscillatory inertial focusing in infinite microchannels.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {115}, number = {30}, pages = {7682-7687}, pmid = {29991599}, issn = {1091-6490}, support = {P41 EB002503/EB/NIBIB NIH HHS/United States ; }, mesh = {Animals ; *Blood Platelets ; *Exosomes ; Humans ; *Lab-On-A-Chip Devices ; Microfluidic Analytical Techniques/instrumentation/*methods ; *Models, Theoretical ; Particle Size ; *Staphylococcus aureus ; }, abstract = {Inertial microfluidics (i.e., migration and focusing of particles in finite Reynolds number microchannel flows) is a passive, precise, and high-throughput method for microparticle manipulation and sorting. Therefore, it has been utilized in numerous biomedical applications including phenotypic cell screening, blood fractionation, and rare-cell isolation. Nonetheless, the applications of this technology have been limited to larger bioparticles such as blood cells, circulating tumor cells, and stem cells, because smaller particles require drastically longer channels for inertial focusing, which increases the pressure requirement and the footprint of the device to the extent that the system becomes unfeasible. Inertial manipulation of smaller bioparticles such as fungi, bacteria, viruses, and other pathogens or blood components such as platelets and exosomes is of significant interest. Here, we show that using oscillatory microfluidics, inertial focusing in practically "infinite channels" can be achieved, allowing for focusing of micron-scale (i.e. hundreds of nanometers) particles. This method enables manipulation of particles at extremely low particle Reynolds number (Rep < 0.005) flows that are otherwise unattainable by steady-flow inertial microfluidics (which has been limited to Rep > ∼10[-1]). Using this technique, we demonstrated that synthetic particles as small as 500 nm and a submicron bacterium, Staphylococcus aureus, can be inertially focused. Furthermore, we characterized the physics of inertial microfluidics in this newly enabled particle size and Rep range using a Peclet-like dimensionless number (α). We experimentally observed that α >> 1 is required to overcome diffusion and be able to inertially manipulate particles.}, }
@article {pmid29987441, year = {2018}, author = {Musacchio, S and Cencini, M and Plan, ELCVM and Vincenzi, D}, title = {Enhancement of mixing by rodlike polymers.}, journal = {The European physical journal. E, Soft matter}, volume = {41}, number = {7}, pages = {84}, pmid = {29987441}, issn = {1292-895X}, abstract = {We study the mixing of a passive scalar field dispersed in a solution of rodlike polymers in two dimensions, by means of numerical simulations of a rheological model for the polymer solution. The flow is driven by a parallel sinusoidal force (Kolmogorov flow). Although the Reynolds number is lower than the critical value for inertial instabilities, the rotational dynamics of the polymers generates a chaotic flow similar to the so-called elastic-turbulence regime observed in extensible polymer solutions. The temporal decay of the variance of the scalar field and its gradients shows that this chaotic flow strongly enhances mixing.}, }
@article {pmid29974859, year = {2018}, author = {Bell, GRR and Collins, SR}, title = {"Rho"ing a Cellular Boat with Rearward Membrane Flow.}, journal = {Developmental cell}, volume = {46}, number = {1}, pages = {1-3}, doi = {10.1016/j.devcel.2018.06.008}, pmid = {29974859}, issn = {1878-1551}, support = {DP2 HD094656/HD/NICHD NIH HHS/United States ; }, mesh = {Cell Movement ; rho-Associated Kinases ; *rhoA GTP-Binding Protein ; }, abstract = {The physicist Edward Purcell wrote in 1977 about mechanisms that cells could use to propel themselves in a low Reynolds number environment. Reporting in Developmental Cell, O'Neill et al. (2018) provide direct evidence for one of these mechanisms by optogenetically driving the migration of cells suspended in liquid through RhoA activation.}, }
@article {pmid29974114, year = {2018}, author = {Bukowicki, M and Ekiel-Jeżewska, ML}, title = {Different bending models predict different dynamics of sedimenting elastic trumbbells.}, journal = {Soft matter}, volume = {14}, number = {28}, pages = {5786-5799}, doi = {10.1039/c8sm00604k}, pmid = {29974114}, issn = {1744-6848}, abstract = {The main goal of this paper is to examine theoretically and numerically the impact of a chosen bending model on the dynamics of elastic filaments settling in a viscous fluid under gravity at low-Reynolds-number. We use the bead-spring approximation of a filament and the Rotne-Prager mobility matrix to describe hydrodynamic interactions between the beads. We analyze the dynamics of trumbbells, for which bending angles are typically larger than for thin and long filaments. Each trumbbell is made of three beads connected by springs and it exhibits a bending resistance, described by the harmonic or - alternatively - by the 'cosine' (also called the Kratky-Porod) bending models, both often used in the literature. Using the harmonic bending potential, and coupling it to the spring potential by the Young's modulus, we find simple benchmark solutions: stable stationary configurations of a single elastic trumbbell and attraction of two elastic trumbbells towards a periodic long-lasting orbit. As the most significant result of this paper, we show that for very elastic trumbbells at the same initial conditions, the Kratky-Porod bending potential can lead to qualitatively and quantitatively different spurious dynamics, with artificially large bending angles and unrealistic shapes. We point out that for the bead models of an elastic filament, the range of applicability of the Kratky-Porod model might not go beyond bending angles smaller than π/2 for touching beads and beyond an even much lower value for beads well-separated from each other. The existence of stable stationary configurations of elastic trumbbells and a family of periodic oscillations of two elastic trumbbells are very important findings on their own.}, }
@article {pmid29957007, year = {2018}, author = {Kawata, T and Alfredsson, PH}, title = {Inverse Interscale Transport of the Reynolds Shear Stress in Plane Couette Turbulence.}, journal = {Physical review letters}, volume = {120}, number = {24}, pages = {244501}, doi = {10.1103/PhysRevLett.120.244501}, pmid = {29957007}, issn = {1079-7114}, abstract = {Interscale interaction between small-scale structures near the wall and large-scale structures away from the wall plays an increasingly important role with increasing Reynolds number in wall-bounded turbulence. While the top-down influence from the large- to small-scale structures is well known, it has been unclear whether the small scales near the wall also affect the large scales away from the wall. In this Letter we show that the small-scale near-wall structures indeed play a role to maintain the large-scale structures away from the wall, by showing that the Reynolds shear stress is transferred from small to large scales throughout the channel. This is in contrast to the turbulent kinetic energy transport which is from large to small scales. Such an "inverse" interscale transport of the Reynolds shear stress eventually supports the turbulent energy production at large scales.}, }
@article {pmid29925578, year = {2018}, author = {Jardin, T and Colonius, T}, title = {On the lift-optimal aspect ratio of a revolving wing at low Reynolds number.}, journal = {Journal of the Royal Society, Interface}, volume = {15}, number = {143}, pages = {}, pmid = {29925578}, issn = {1742-5662}, mesh = {Animals ; Birds/*physiology ; *Computer Simulation ; Flight, Animal/*physiology ; Insecta/*physiology ; *Models, Biological ; Wings, Animal/*physiology ; }, abstract = {Lentink &amp; Dickinson (2009 J. Exp. Biol.212, 2705-2719. (doi:10.1242/jeb.022269)) showed that rotational acceleration stabilized the leading-edge vortex on revolving, low aspect ratio (AR) wings and hypothesized that a Rossby number of around 3, which is achieved during each half-stroke for a variety of hovering insects, seeds and birds, represents a convergent high-lift solution across a range of scales in nature. Subsequent work has verified that, in particular, the Coriolis acceleration plays a key role in LEV stabilization. Implicit in these results is that there exists an optimal AR for wings revolving about their root, because it is otherwise unclear why, apart from possible morphological reasons, the convergent solution would not occur for an even lower Rossby number. We perform direct numerical simulations of the flow past revolving wings where we vary the AR and Rossby numbers independently by displacing the wing root from the axis of rotation. We show that the optimal lift coefficient represents a compromise between competing trends with competing time scales where the coefficient of lift increases monotonically with AR, holding Rossby number constant, but decreases monotonically with Rossby number, when holding AR constant. For wings revolving about their root, this favours wings of AR between 3 and 4.}, }
@article {pmid29907430, year = {2018}, author = {Maldaner, CH and Quinn, PM and Cherry, JA and Parker, BL}, title = {Improving estimates of groundwater velocity in a fractured rock borehole using hydraulic and tracer dilution methods.}, journal = {Journal of contaminant hydrology}, volume = {214}, number = {}, pages = {75-86}, doi = {10.1016/j.jconhyd.2018.05.003}, pmid = {29907430}, issn = {1873-6009}, mesh = {*Groundwater ; Models, Theoretical ; Porosity ; *Water Movements ; *Water Supply ; }, abstract = {A straddle-packer system for use in boreholes in fractured rock was modified to investigate the average linear groundwater velocity (v¯f) in fractures under ambient flow conditions. This packer system allows two different tests to be conducted in the same interval between packers without redeploying the system: (1) forced gradient hydraulic tests to determine the interval transmissivity (T), and (2) borehole dilution experiments to determine the groundwater flow rate (Qt) across the test interval. The constant head step test method provides assurance that flow is Darcian when determining T for each interval and identifies the flow rate at the onset of non-Darcian flow. The critical Reynolds number method uses this flow rate to provide the number of hydraulically active fractures (N) in each interval, the average hydraulic aperture for the test interval and the effective bulk fracture porosity. The borehole dilution method provides Qt values for the interval at the time of the test, and v¯f can be estimated from Qt using the flow area derived from the hydraulic tests. The method was assessed by application to seven test intervals in a borehole 73 m deep in a densely fractured dolostone aquifer used for municipal water supply. The critical Reynolds number method identified one or two fractures in each test interval (1.1 m long), which provided v¯f values in the range of 10 to 8000 m/day. This velocity range is consistent with values reported in the literature for ambient flow in this aquifer. However, when hydraulically active fractures in each interval is identified and measured from acoustic and optical televiewer logs, the calculated v¯f values are unreasonably low as are the calculated values of the hydraulic gradient needed to provide the Qt value for each tested interval. The combination of hydraulic and dilution tests in the same interval is an improved method to obtain values of groundwater velocity in fractured rock aquifers.}, }
@article {pmid29906944, year = {2018}, author = {Ngoma, J and Philippe, P and Bonelli, S and Radjaï, F and Delenne, JY}, title = {Two-dimensional numerical simulation of chimney fluidization in a granular medium using a combination of discrete element and lattice Boltzmann methods.}, journal = {Physical review. E}, volume = {97}, number = {5-1}, pages = {052902}, doi = {10.1103/PhysRevE.97.052902}, pmid = {29906944}, issn = {2470-0053}, abstract = {We present here a numerical study dedicated to the fluidization of a submerged granular medium induced by a localized fluid injection. To this end, a two-dimensional (2D) model is used, coupling the lattice Boltzmann method (LBM) with the discrete element method (DEM) for a relevant description of fluid-grains interaction. An extensive investigation has been carried out to analyze the respective influences of the different parameters of our configuration, both geometrical (bed height, grain diameter, injection width) and physical (fluid viscosity, buoyancy). Compared to previous experimental works, the same qualitative features are recovered as regards the general phenomenology including transitory phase, stationary states, and hysteretic behavior. We also present quantitative findings about transient fluidization, for which several dimensionless quantities and scaling laws are proposed, and about the influence of the injection width, from localized to homogeneous fluidization. Finally, the impact of the present 2D geometry is discussed, by comparison to the real three-dimensional (3D) experiments, as well as the crucial role of the prevailing hydrodynamic regime within the expanding cavity, quantified through a cavity Reynolds number, that can presumably explain some substantial differences observed regarding upward expansion process of the fluidized zone when the fluid viscosity is changed.}, }
@article {pmid29906164, year = {2018}, author = {Baker, NT and Pothérat, A and Davoust, L and Debray, F}, title = {Inverse and Direct Energy Cascades in Three-Dimensional Magnetohydrodynamic Turbulence at Low Magnetic Reynolds Number.}, journal = {Physical review letters}, volume = {120}, number = {22}, pages = {224502}, doi = {10.1103/PhysRevLett.120.224502}, pmid = {29906164}, issn = {1079-7114}, abstract = {This experimental study analyzes the relationship between the dimensionality of turbulence and the upscale or downscale nature of its energy transfers. We do so by forcing low-Rm magnetohydrodynamic turbulence in a confined channel, while precisely controlling its dimensionality by means of an externally applied magnetic field. We first identify a specific length scale l[over ^]_{⊥}^{c} that separates smaller 3D structures from larger quasi-2D ones. We then show that an inverse energy cascade of horizontal kinetic energy along horizontal scales is always observable at large scales, and that it extends well into the region of 3D structures. At the same time, a direct energy cascade confined to the smallest and strongly 3D scales is observed. These dynamics therefore appear not to be simply determined by the dimensionality of individual scales, nor by the forcing scale, unlike in other studies. In fact, our findings suggest that the relationship between kinematics and dynamics is not universal and may strongly depend on the forcing and dissipating mechanisms at play.}, }
@article {pmid29900314, year = {2018}, author = {Parise, JAR and Saboya, FEM}, title = {Experimental data on transport coefficients for developing laminar flow in isosceles triangular ducts using the naphthalene sublimation technique.}, journal = {Data in brief}, volume = {18}, number = {}, pages = {1350-1359}, pmid = {29900314}, issn = {2352-3409}, abstract = {The data presented in this article are related to the research article entitled "Transport coefficients for developing laminar flow in isosceles triangular ducts" (Parise and Saboya, 1999) [1]. The article describes an experiment involving the determination of transport coefficients in the laminar entrance region of 30°, 45°, 60° and 90° isosceles triangular ducts. Data were obtained by application of the naphthalene sublimation technique in conjunction with the heat to mass transfer analogy. Experimental conditions (duct sides made of naphthalene and base made of metal) simulated developing velocity and temperature fields in an isosceles triangular duct with isothermal lateral walls and adiabatic base. The Reynolds number ranged from 100 to 1800 and the duct length to hydraulic diameter ratio, from 2 to 40. The experiment consisted of mounting a test section (triangular duct) with the lateral walls made of naphthalene. Air was forced past the test section and naphthalene walls were weighed prior and after each data run, providing the rate of mass transfer for given flow conditions. Raw data, for a total of 77 experimental runs, include: test section geometry, air flow and mass transfer conditions. Processed data comprise the relevant non-dimensional groups, namely: Reynolds, non-dimensional axial duct length and Sherwood numbers.}, }
@article {pmid29897806, year = {2018}, author = {McCombe, D and Ackerman, JD}, title = {Collector Motion Affects Particle Capture in Physical Models and in Wind Pollination.}, journal = {The American naturalist}, volume = {192}, number = {1}, pages = {81-93}, doi = {10.1086/697551}, pmid = {29897806}, issn = {1537-5323}, mesh = {*Models, Theoretical ; Phleum/*physiology ; *Pollination ; *Wind ; }, abstract = {Particle capture is important for ecological processes in aquatic and terrestrial ecosystems. The current model is based on a stationary collector for which predictions about capture efficiency (η; flux of captured particles ∶ flux of particles) are based on the collector flow environment (i.e., collector Reynolds number, Rec; inertial force ∶ viscous force). This model does not account for the movement of collectors in nature. We examined the effect of collector motion (transverse and longitudinal to the flow) on η using a cylindrical model in the lab and the grass species Phleum pratense in the field. Collector motion increased η (up to 400% and 20% in the lab and field, respectively) and also affected the spatial distribution of particles on collectors, especially at low Rec. The effect was greatest for collectors moving transversely at large magnitude, which encountered more particles with higher relative momentum. These results, which differ from the stationary model, can be predicted by considering both Rec and the particle dynamics given by the Stokes number (Stk; particle stopping distance ∶ collector radius) and helped to resolve an existing controversy about pollination mechanisms. Collector motion should be considered in wind pollination and other ecological processes involving particle capture.}, }
@article {pmid29891403, year = {2018}, author = {Gritti, F and Fogwill, M}, title = {Molecular dispersion in pre-turbulent and sustained turbulent flow of carbon dioxide.}, journal = {Journal of chromatography. A}, volume = {1564}, number = {}, pages = {176-187}, doi = {10.1016/j.chroma.2018.06.005}, pmid = {29891403}, issn = {1873-3778}, mesh = {Acetonitriles/chemistry ; Carbon Dioxide/*chemistry ; Diffusion ; Molecular Weight ; Polycyclic Compounds/chemistry ; Pressure ; *Rheology ; Silicon Dioxide ; Viscosity ; }, abstract = {The average dispersion coefficients, Da¯, of two small molecules (acetonitrile and coronene) were measured under laminar, transient, and sustained turbulent flow regimes along fused silica open tubular capillary (OTC) columns (180 μm inner diameter by 20 m length). Carbon dioxide was used as the mobile phase at room temperature (296 K) and at average pressures in the range from 1500 to 2700 psi. The Reynolds number (Re) was increased from 600 to 5000. The measurement of Da¯ is based on the observed plate height of the non-retained analytes as a function of the applied Reynolds number. Da¯ values are directly estimated from the best fit of the general Golay HETP equation to the experimental plate height curves. The experimental data revealed that under a pre-turbulent flow regime (Re < 2000), Da¯ is 2-6 times larger (3.5 × 10[-4] cm[2]/s) than the bulk diffusion coefficients Dm of the analyte (1.6 × 10[-4] and 5.8 × 10[-5] cm[2]/s for acetonitrile and coronene, respectively). This result was explained by the random formation of decaying or vanishing turbulent puffs under pre-turbulent flow regime. Yet, the peak width remains controlled exclusively by the slow mass transfer in the mobile phase across the inner diameter (i.d.) of the OTC. Under sustained turbulent flow regime (Re > 2500), Da¯ is about four to five orders of magnitude larger than Dm. The experimental data slightly overestimated the turbulent dispersion coefficients predicted by Flint-Eisenklam model (Da¯=4 cm[2]/s). The discrepancy is explained by the approximate nature of the general Golay equation, which assumes that Da¯ is strictly uniform across the entire i.d. of the OTC. In fact, both the viscous and buffer wall layers, in which viscous effects dominate inertial effects, cannot be considered as fully developed turbulent regions. Remarkably, the mass transfer mechanism in OTC under sustained turbulent flow regime is not only controlled by longitudinal dispersion but also by a slow mass transfer in the mobile phase across the thick buffer layer and the thin viscous layer. Altogether, these layers occupy as much as 35% of the OTC volume at Re = 4000. From a theoretical viewpoint, the general Golay HETP equation is only an approximate model which should be refined based on the actual profile of the analyte dispersion coefficient across the OTC i.d. In practice, the measured plate height of non-retained analytes under sustained turbulent flow of carbon dioxide are two orders of magnitude smaller than those expected under hypothetical laminar flow regime.}, }
@article {pmid29863665, year = {2018}, author = {Kaiser, SC and Werner, S and Jossen, V and Blaschczok, K and Eibl, D}, title = {Power Input Measurements in Stirred Bioreactors at Laboratory Scale.}, journal = {Journal of visualized experiments : JoVE}, volume = {}, number = {135}, pages = {}, pmid = {29863665}, issn = {1940-087X}, mesh = {*Bioreactors ; Cell Culture Techniques/*methods ; Laboratories/*standards ; }, abstract = {The power input in stirred bioreactors is an important scaling-up parameter and can be measured through the torque that acts on the impeller shaft during rotation. However, the experimental determination of the power input in small-scale vessels is still challenging due to relatively high friction losses inside typically used bushings, bearings and/or shaft seals and the accuracy of commercially available torque meters. Thus, only limited data for small-scale bioreactors, in particular single-use systems, is available in the literature, making comparisons among different single-use systems and their conventional counterparts difficult. This manuscript provides a protocol on how to measure power inputs in benchtop scale bioreactors over a wide range of turbulence conditions, which can be described by the dimensionless Reynolds number (Re). The aforementioned friction losses are effectively reduced by the use of an air bearing. The procedure on how to set up, conduct and evaluate a torque-based power input measurement, with special focus on cell culture typical agitation conditions with low to moderate turbulence (100 < Re < 2·10[4]), is described in detail. The power input of several multi-use and single-use bioreactors is provided by the dimensionless power number (also called Newton number, P0), which is determined to be in the range of P0 ≈ 0.3 and P0 ≈ 4.5 for the maximum Reynolds numbers in the different bioreactors.}, }
@article {pmid29861812, year = {2018}, author = {Herbig, BA and Yu, X and Diamond, SL}, title = {Using microfluidic devices to study thrombosis in pathological blood flows.}, journal = {Biomicrofluidics}, volume = {12}, number = {4}, pages = {042201}, pmid = {29861812}, issn = {1932-1058}, support = {R01 HL103419/HL/NHLBI NIH HHS/United States ; T32 HL007954/HL/NHLBI NIH HHS/United States ; }, abstract = {Extreme flows can exist within pathological vessel geometries or mechanical assist devices which create complex forces and lead to thrombogenic problems associated with disease. Turbulence and boundary layer separation are difficult to obtain in microfluidics due to the low Reynolds number flow in small channels. However, elongational flows, extreme shear rates and stresses, and stagnation point flows are possible using microfluidics and small perfusion volumes. In this review, a series of microfluidic devices used to study pathological blood flows are described. In an extreme stenosis channel pre-coated with fibrillar collagen that rapidly narrows from 500 μm to 15 μm, the plasma von Willebrand Factor (VWF) will elongate and assemble into thick fiber bundles on the collagen. Using a micropost-impingement device, plasma flow impinging on the micropost generates strong elongational and wall shear stresses that trigger the growth of a VWF bundle around the post (no collagen required). Using a stagnation-point device to mimic the zone near flow reattachment, blood can be directly impinged upon a procoagulant surface of collagen and the tissue factor. Clots formed at the stagnation point of flow impingement have a classic core-shell architecture where the core is highly activated (P-selectin positive platelets and fibrin rich). Finally, within occlusive clots that fill a microchannel, the Darcy flow driven by ΔP/L > 70 mm-Hg/mm-clot is sufficient to drive NETosis of entrapped neutrophils, an event not requiring either thrombin or fibrin. Novel microfluidic devices are powerful tools to access physical environments that exist in human disease.}, }
@article {pmid29791262, year = {2018}, author = {Montoya Segnini, J and Bocanegra Evans, H and Castillo, L}, title = {Flow Recirculation in Cartilaginous Ring Cavities of Human Trachea Model.}, journal = {Journal of aerosol medicine and pulmonary drug delivery}, volume = {}, number = {}, pages = {}, doi = {10.1089/jamp.2017.1435}, pmid = {29791262}, issn = {1941-2703}, abstract = {BACKGROUND: Despite the prevailing assumption of "smooth trachea walls" in respiratory fluid dynamics research, recent investigations have demonstrated that cartilaginous rings in the trachea and main bronchi have a significant effect on the flow behavior and in particle deposition. However, there is not enough detailed information about the underlying physics of the interaction between the cartilage rings and the flow.<br><br>MATERIALS AND METHODS: This study presents an experimental observation of a simplified Weibel-based model of the human trachea and bronchi with cartilaginous rings. A transparent model and refractive index-matching methods were used to observe the flow, particularly near the wall. The flow was seeded with tracers to perform particle image velocimetry and particle tracking velocimetry to quantify the effect the rings have on the flow near the trachea and bronchi walls. The experiments were carried out with a flow rate comparable with a resting state (trachea-based Reynolds number of ReD&#x2009;=&#x2009;2650).<br><br>RESULTS: The results present a previously unknown phenomenon in the cavities between the cartilaginous rings: a small recirculation is observed in the upstream side of the cavities throughout the trachea. This recirculation is due to the adverse pressure gradient created by the expansion, which traps particles within the ring cavity, thus affecting the treatment of patients suffering from lung disease and other respiratory conditions.<br><br>CONCLUSIONS: The detection of recirculation zones in the cartilage ring cavities sheds light on the particle deposition mechanism and helps explain results from previous studies that have observed an enhancement of particle deposition in models with cartilage rings. These results bring to light the importance of including cartilage rings in experimental, numerical, and theoretical models to better understand particle deposition in the trachea and bronchi. In addition, the results provide scientists and medical staff with new insights for improving drug delivery.}, }
@article {pmid29786774, year = {2018}, author = {Bordones, AD and Leroux, M and Kheyfets, VO and Wu, YA and Chen, CY and Finol, EA}, title = {Computational Fluid Dynamics Modeling of the Human Pulmonary Arteries with Experimental Validation.}, journal = {Annals of biomedical engineering}, volume = {46}, number = {9}, pages = {1309-1324}, pmid = {29786774}, issn = {1573-9686}, support = {R01 HL121293/HL/NHLBI NIH HHS/United States ; 14GRNT19020017//American Heart Association/ ; R01HL121293//National Institutes of Health/ ; }, mesh = {Computer Simulation ; Humans ; Hydrodynamics ; *Models, Cardiovascular ; Phantoms, Imaging ; Printing, Three-Dimensional ; Pulmonary Artery/*physiology ; Rheology ; }, abstract = {Pulmonary hypertension (PH) is a chronic progressive disease characterized by elevated pulmonary arterial pressure, caused by an increase in pulmonary arterial impedance. Computational fluid dynamics (CFD) can be used to identify metrics representative of the stage of PH disease. However, experimental validation of CFD models is often not pursued due to the geometric complexity of the model or uncertainties in the reproduction of the required flow conditions. The goal of this work is to validate experimentally a CFD model of a pulmonary artery phantom using a particle image velocimetry (PIV) technique. Rapid prototyping was used for the construction of the patient-specific pulmonary geometry, derived from chest computed tomography angiography images. CFD simulations were performed with the pulmonary model with a Reynolds number matching those of the experiments. Flow rates, the velocity field, and shear stress distributions obtained with the CFD simulations were compared to their counterparts from the PIV flow visualization experiments. Computationally predicted flow rates were within 1% of the experimental measurements for three of the four branches of the CFD model. The mean velocities in four transversal planes of study were within 5.9 to 13.1% of the experimental mean velocities. Shear stresses were qualitatively similar between the two methods with some discrepancies in the regions of high velocity gradients. The fluid flow differences between the CFD model and the PIV phantom are attributed to experimental inaccuracies and the relative compliance of the phantom. This comparative analysis yielded valuable information on the accuracy of CFD predicted hemodynamics in pulmonary circulation models.}, }
@article {pmid29776113, year = {2018}, author = {Zhu, B and Ji, Z and Lou, Z and Qian, P}, title = {Torque scaling in small-gap Taylor-Couette flow with smooth or grooved wall.}, journal = {Physical review. E}, volume = {97}, number = {3-1}, pages = {033110}, doi = {10.1103/PhysRevE.97.033110}, pmid = {29776113}, issn = {2470-0053}, abstract = {The torque in the Taylor-Couette flow for radius ratios η≥0.97, with smooth or grooved wall static outer cylinders, is studied experimentally, with the Reynolds number of the inner cylinder reaching up to Re_{i}=2×10^{5}, corresponding to the Taylor number up to Ta=5×10^{10}. The grooves are perpendicular to the mean flow, and similar to the structure of a submersible motor stator. It is found that the dimensionless torque G, at a given Re_{i} and η, is significantly greater for grooved cases than smooth cases. We compare our experimental torques for the smooth cases to the fit proposed by Wendt [F. Wendt, Ing.-Arch. 4, 577 (1993)10.1007/BF02084936] and the fit proposed by Bilgen and Boulos [E. Bilgen and R. Boulos, J Fluids Eng. 95, 122 (1973)10.1115/1.3446944], which shows both fits are outside their range for small gaps. Furthermore, an additional dimensionless torque (angular velocity flux) Nu_{ω} in the smooth cases exhibits an effective scaling of Nu_{ω}∼Ta^{0.39} in the ultimate regime, which occurs at a lower Taylor number, Ta≈3.5×10^{7}, than the well-explored η=0.714 case (at Ta≈3×10^{8}). The same effective scaling exponent, 0.39, is also evident in the grooved cases, but for η=0.97 and 0.985, there is a peak before this exponent appears.}, }
@article {pmid29776082, year = {2018}, author = {Liang, H and Xu, J and Chen, J and Wang, H and Chai, Z and Shi, B}, title = {Phase-field-based lattice Boltzmann modeling of large-density-ratio two-phase flows.}, journal = {Physical review. E}, volume = {97}, number = {3-1}, pages = {033309}, doi = {10.1103/PhysRevE.97.033309}, pmid = {29776082}, issn = {2470-0053}, abstract = {In this paper, we present a simple and accurate lattice Boltzmann (LB) model for immiscible two-phase flows, which is able to deal with large density contrasts. This model utilizes two LB equations, one of which is used to solve the conservative Allen-Cahn equation, and the other is adopted to solve the incompressible Navier-Stokes equations. A forcing distribution function is elaborately designed in the LB equation for the Navier-Stokes equations, which make it much simpler than the existing LB models. In addition, the proposed model can achieve superior numerical accuracy compared with previous Allen-Cahn type of LB models. Several benchmark two-phase problems, including static droplet, layered Poiseuille flow, and spinodal decomposition are simulated to validate the present LB model. It is found that the present model can achieve relatively small spurious velocity in the LB community, and the obtained numerical results also show good agreement with the analytical solutions or some available results. Lastly, we use the present model to investigate the droplet impact on a thin liquid film with a large density ratio of 1000 and the Reynolds number ranging from 20 to 500. The fascinating phenomena of droplet splashing is successfully reproduced by the present model and the numerically predicted spreading radius exhibits to obey the power law reported in the literature.}, }
@article {pmid29776043, year = {2018}, author = {Oyama, N and Teshigawara, K and Molina, JJ and Yamamoto, R and Taniguchi, T}, title = {Reynolds-number-dependent dynamical transitions on hydrodynamic synchronization modes of externally driven colloids.}, journal = {Physical review. E}, volume = {97}, number = {3-1}, pages = {032611}, doi = {10.1103/PhysRevE.97.032611}, pmid = {29776043}, issn = {2470-0053}, abstract = {The collective dynamics of externally driven N_{p}-colloidal systems (1≤N_{p}≤4) in a confined viscous fluid have been investigated using three-dimensional direct numerical simulations with fully resolved hydrodynamics. The dynamical modes of collective particle motion are studied by changing the particle Reynolds number as determined by the strength of the external driving force and the confining wall distance. For a system with N_{p}=3, we found that at a critical Reynolds number a dynamical mode transition occurs from the doublet-singlet mode to the triplet mode, which has not been reported experimentally. The dynamical mode transition was analyzed in detail from the following two viewpoints: (1) spectrum analysis of the time evolution of a tagged particle velocity and (2) the relative acceleration of the doublet cluster with respect to the singlet particle. For a system with N_{p}=4, we found similar dynamical mode transitions from the doublet-singlet-singlet mode to the triplet-singlet mode and further to the quartet mode.}, }
@article {pmid29772223, year = {2018}, author = {Markwalter, CE and Prud'homme, RK}, title = {Design of a Small-Scale Multi-Inlet Vortex Mixer for Scalable Nanoparticle Production and Application to the Encapsulation of Biologics by Inverse Flash NanoPrecipitation.}, journal = {Journal of pharmaceutical sciences}, volume = {107}, number = {9}, pages = {2465-2471}, pmid = {29772223}, issn = {1520-6017}, mesh = {Biological Products/*chemical synthesis/metabolism ; *Chemical Precipitation ; Chemistry, Pharmaceutical/*instrumentation/methods ; Equipment Design/*instrumentation/methods ; Hydrophobic and Hydrophilic Interactions ; Nanoparticles/*chemistry/metabolism ; Particle Size ; }, abstract = {Flash NanoPrecipitation is a scalable approach to generate polymeric nanoparticles using rapid micromixing in specially designed geometries such as a confined impinging jets mixer or a Multi-Inlet Vortex Mixer (MIVM). A major limitation of formulation screening using the MIVM is that a single run requires tens of milligrams of the therapeutic. To overcome this, we have developed a scaled-down version of the MIVM, requiring as little as 0.2 mg of therapeutic, for formulation screening. The redesigned mixer can then be attached to pumps for scale-up of the identified formulation. It was shown that Reynolds number allowed accurate scaling between the 2 MIVM designs. The utility of the small-scale MIVM for formulation development was demonstrated through the encapsulation of a number of hydrophilic macromolecules using inverse Flash NanoPrecipitation with target loadings as high as 50% by mass.}, }
@article {pmid31831915, year = {2018}, author = {Coleman, GN and Rumsey, CL and Spalart, PR}, title = {Numerical study of turbulent separation bubbles with varying pressure gradient and Reynolds number.}, journal = {Journal of fluid mechanics}, volume = {847}, number = {}, pages = {28-70}, pmid = {31831915}, issn = {0022-1120}, support = {/LaRC/Langley Research Center NASA/United States ; N-999999/ImNASA/Intramural NASA/United States ; }, abstract = {A family of cases each containing a small separation bubble is treated by direct numerical simulation (DNS), varying two parameters: the severity of the pressure gradients, generated by suction and blowing across the opposite boundary, and the Reynolds number. Each flow contains a well-developed entry region with essentially zero pressure gradient, and all are adjusted to have the same value for the momentum thickness, extrapolated from the entry region to the centre of the separation bubble. Combined with fully defined boundary conditions this will make comparisons with other simulations and turbulence models rigorous; we present results for a set of eight Reynolds-averaged Navier-Stokes turbulence models. Even though the largest Reynolds number is approximately 5.5 times higher than in a similar DNS study we presented in 1997, the models have difficulties matching the DNS skin friction very closely even in the zero pressure gradient, which complicates their assessment. In the rest of the domain, the separation location per se is not particularly difficult to predict, and the most definite disagreement between DNS and models is near reattachment. Curiously, the better models tend to cluster together in their predictions of pressure and skin friction even when they deviate from the DNS, although their eddy-viscosity levels are widely different in the outer region near the bubble (or they do not rely on an eddy viscosity). Stratford's square-root law is satisfied by the velocity profiles, both at separation and reattachment. The Reynolds-number range covers a factor of two, with the Reynolds number based on the extrapolated momentum thickness equal to approximately 1500 and 3000. This allows tentative estimates of the improvements that even higher values will bring to the model comparisons. The solutions are used to assess models through pressure, skin friction and other measures; the flow fields are also used to produce effective eddy-viscosity targets for the models, thus guiding turbulence-modelling work in each region of the flow.}, }
@article {pmid29758688, year = {2018}, author = {Sanjeevi, SKP and Zarghami, A and Padding, JT}, title = {Choice of no-slip curved boundary condition for lattice Boltzmann simulations of high-Reynolds-number flows.}, journal = {Physical review. E}, volume = {97}, number = {4-1}, pages = {043305}, doi = {10.1103/PhysRevE.97.043305}, pmid = {29758688}, issn = {2470-0053}, abstract = {Various curved no-slip boundary conditions available in literature improve the accuracy of lattice Boltzmann simulations compared to the traditional staircase approximation of curved geometries. Usually, the required unknown distribution functions emerging from the solid nodes are computed based on the known distribution functions using interpolation or extrapolation schemes. On using such curved boundary schemes, there will be mass loss or gain at each time step during the simulations, especially apparent at high Reynolds numbers, which is called mass leakage. Such an issue becomes severe in periodic flows, where the mass leakage accumulation would affect the computed flow fields over time. In this paper, we examine mass leakage of the most well-known curved boundary treatments for high-Reynolds-number flows. Apart from the existing schemes, we also test different forced mass conservation schemes and a constant density scheme. The capability of each scheme is investigated and, finally, recommendations for choosing a proper boundary condition scheme are given for stable and accurate simulations.}, }
@article {pmid29758634, year = {2018}, author = {Mahalinkam, R and Gong, F and Khair, AS}, title = {Reduced-order model for inertial locomotion of a slender swimmer.}, journal = {Physical review. E}, volume = {97}, number = {4-1}, pages = {043102}, doi = {10.1103/PhysRevE.97.043102}, pmid = {29758634}, issn = {2470-0053}, abstract = {The inertial locomotion of an elongated model swimmer in a Newtonian fluid is quantified, wherein self-propulsion is achieved via steady tangential surface treadmilling. The swimmer has a length 2l and a circular cross section of longitudinal profile aR(z), where a is the characteristic width of the cross section, R(z) is a dimensionless shape function, and z is a dimensionless coordinate, normalized by l, along the centerline of the body. It is assumed that the swimmer is slender, ε=a/l≪1. Hence, we utilize slender-body theory to analyze the Navier-Stokes equations that describe the flow around the swimmer. Therefrom, we compute an asymptotic approximation to the swimming speed, U, as U/u_{s}=1-β[V(Re)-1/2∫_{-1}^{1}zlnR(z)dz]/ln(1/ε)+O[1/ln^{2}(1/ε)], where u_{s} is the characteristic speed of the surface treadmilling, Re is the Reynolds number based on the body length, and β is a dimensionless parameter that differentiates between "pusher" (propelled from the rear, β<0) and "puller" (propelled from the front, β>0) -type swimmers. The function V(Re) increases monotonically with increasing Re; hence, fluid inertia causes an increase (decrease) in the swimming speed of a pusher (puller). Next, we demonstrate that the power expenditure of the swimmer increases monotonically with increasing Re. Further, the power expenditures of a puller and pusher with the same value of |β| are equal. Therefore, pushers are superior in inertial locomotion as compared to pullers, in that they achieve a faster swimming speed for the same power expended. Finally, it is demonstrated that the flow structure predicted from our reduced-order model is consistent with that from direct numerical simulation of swimmers at intermediate Re.}, }
@article {pmid29757157, year = {2018}, author = {Daddi-Moussa-Ider, A and Lisicki, M and Mathijssen, AJTM and Hoell, C and Goh, S and Bławzdziewicz, J and Menzel, AM and Löwen, H}, title = {State diagram of a three-sphere microswimmer in a channel.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {30}, number = {25}, pages = {254004}, doi = {10.1088/1361-648X/aac470}, pmid = {29757157}, issn = {1361-648X}, abstract = {Geometric confinements are frequently encountered in soft matter systems and in particular significantly alter the dynamics of swimming microorganisms in viscous media. Surface-related effects on the motility of microswimmers can lead to important consequences in a large number of biological systems, such as biofilm formation, bacterial adhesion and microbial activity. On the basis of low-Reynolds-number hydrodynamics, we explore the state diagram of a three-sphere microswimmer under channel confinement in a slit geometry and fully characterize the swimming behavior and trajectories for neutral swimmers, puller- and pusher-type swimmers. While pushers always end up trapped at the channel walls, neutral swimmers and pullers may further perform a gliding motion and maintain a stable navigation along the channel. We find that the resulting dynamical system exhibits a supercritical pitchfork bifurcation in which swimming in the mid-plane becomes unstable beyond a transition channel height while two new stable limit cycles or fixed points that are symmetrically disposed with respect to the channel mid-height emerge. Additionally, we show that an accurate description of the averaged swimming velocity and rotation rate in a channel can be captured analytically using the method of hydrodynamic images, provided that the swimmer size is much smaller than the channel height.}, }
@article {pmid29749100, year = {2018}, author = {Tottori, S and Nelson, BJ}, title = {Controlled Propulsion of Two-Dimensional Microswimmers in a Precessing Magnetic Field.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {14}, number = {24}, pages = {e1800722}, doi = {10.1002/smll.201800722}, pmid = {29749100}, issn = {1613-6829}, abstract = {Magnetically actuated micro-/nanoswimmers can potentially be used in noninvasive biomedical applications, such as targeted drug delivery and micromanipulation. Herein, two-dimensional (2D) rigid ferromagnetic microstructures are shown to be capable of propelling themselves in three dimensions at low Reynolds numbers in a precessing field. Importantly, the above propulsion relies neither on soft structure deformation nor on the geometrical chirality of swimmers, but is rather driven by the dynamic chirality generated by field precession, which allows an almost unconstrained choice of materials and fabrication methods. Therefore, the swimming performance is systematically investigated as a function of precession angle and geometric design. One disadvantage of the described propulsion method is that the fabricated 2D swimmers are achiral, which means that the forward/backward swimming direction cannot be controlled. However, it has been found that asymmetric 2D swimmers always propel themselves toward their longer arm, which implies that dynamic chirality can be constrained to be either right-handed or left-handed by permanent magnetization. Thus, the simplicity of fabrication and possibility of dynamic chirality control make the developed method ideal for applications and fundamental studies that require a large number of swimmers.}, }
@article {pmid29745778, year = {2018}, author = {Perrin, A and Herbelin, P and Jorand, FPA and Skali-Lami, S and Mathieu, L}, title = {Design of a rotating disk reactor to assess the colonization of biofilms by free-living amoebae under high shear rates.}, journal = {Biofouling}, volume = {34}, number = {4}, pages = {368-377}, doi = {10.1080/08927014.2018.1444756}, pmid = {29745778}, issn = {1029-2454}, mesh = {Amoeba/*physiology ; *Bacteria ; Bacterial Physiological Phenomena ; *Biofilms ; Fresh Water ; Hydrodynamics ; Locomotion ; Stainless Steel ; }, abstract = {The present study was aimed at designing and optimizing a rotating disk reactor simulating high hydrodynamic shear rates (γ), which are representative of cooling circuits. The characteristics of the hydrodynamic conditions in the reactor and the complex approach used to engineer it are described. A 60 l tank was filled with freshwater containing free-living amoebae (FLA) and bacteria. Adhesion of the bacteria and formation of a biofilm on the stainless steel coupons were observed. FLA were able to establish in these biofilms under γ as high as 85,000 s[-1]. Several physical mechanisms (convection, diffusion, sedimentation) could explain the accumulation of amoeboid cells on surfaces, but further research is required to fully understand and model the fine mechanisms governing such transport under γ similar to those encountered in the industrial environment. This technological advance may enable research into these topics.}, }
@article {pmid29744606, year = {2018}, author = {Zhang, S and Luo, X and Cai, Z}, title = {Three-dimensional flows in a hyperelastic vessel under external pressure.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {17}, number = {4}, pages = {1187-1207}, doi = {10.1007/s10237-018-1022-y}, pmid = {29744606}, issn = {1617-7940}, support = {EP/N014642/1//Engineering and Physical Sciences Research Council/ ; 11172200//National Natural Science Foundation of China/ ; 2013CB035042//National Basic Research Program of China/ ; RF-2015-510//Leverhulme Trust/ ; }, mesh = {Algorithms ; Arteries/anatomy &amp; histology/*physiology ; Biomechanical Phenomena ; Blood Flow Velocity/*physiology ; Computer Simulation ; Elasticity ; Finite Element Analysis ; Humans ; Models, Anatomic ; Models, Cardiovascular ; Pressure ; Rheology ; Veins/anatomy &amp; histology/*physiology ; Viscosity ; }, abstract = {We study the collapsible behaviour of a vessel conveying viscous flows subject to external pressure, a scenario that could occur in many physiological applications. The vessel is modelled as a three-dimensional cylindrical tube of nonlinear hyperelastic material. To solve the fully coupled fluid-structure interaction, we have developed a novel approach based on the Arbitrary Lagrangian-Eulerian (ALE) method and the frontal solver. The method of rotating spines is used to enable an automatic mesh adaptation. The numerical code is verified extensively with published results and those obtained using the commercial packages in simpler cases, e.g. ANSYS for the structure with the prescribed flow, and FLUENT for the fluid flow with prescribed structure deformation. We examine three different hyperelastic material models for the tube for the first time in this context and show that at the small strain, all three material models give similar results. However, for the large strain, results differ depending on the material model used. We further study the behaviour of the tube under a mode-3 buckling and reveal its complex flow patterns under various external pressures. To understand these flow patterns, we show how energy dissipation is associated with the boundary layers created at the narrowest collapsed section of the tube, and how the transverse flow forms a virtual sink to feed a strong axial jet. We found that the energy dissipation associated with the recirculation does not coincide with the flow separation zone itself, but overlaps with the streamlines that divide the three recirculation zones. Finally, we examine the bifurcation diagrams for both mode-3 and mode-2 collapses and reveal that multiple solutions exist for a range of the Reynolds number. Our work is a step towards modelling more realistic physiological flows in collapsible arteries and veins.}, }
@article {pmid31631904, year = {2018}, author = {Yang, XIA and Abkar, M}, title = {A hierarchical random additive model for passive scalars in wall-bounded flows at high Reynolds numbers.}, journal = {Journal of fluid mechanics}, volume = {842}, number = {}, pages = {354-380}, pmid = {31631904}, issn = {0022-1120}, support = {NNX15AU93A//NASA/United States ; }, abstract = {The kinematics of a fully developed passive scalar is modelled using the hierarchical random additive process (HRAP) formalism. Here, 'a fully developed passive scalar' refers to a scalar field whose instantaneous fluctuations are statistically stationary, and the 'HRAP formalism' is a recently proposed interpretation of the Townsend attached eddy hypothesis. The HRAP model was previously used to model the kinematics of velocity fluctuations in wall turbulence: u = ∑ i = 1 N z a i , where the instantaneous streamwise velocity fluctuation at a generic wall-normal location z is modelled as a sum of additive contributions from wall-attached eddies (a i) and the number of addends is N z ~ log(δ/z). The HRAP model admits generalized logarithmic scalings including 〈ϕ [2]〉~log(δ/z), 〈ϕ(x)ϕ(x+r x)〉 ~ log(δ/r x), 〈(ϕ(x) - ϕ(x+r x))[2]〉 ~ log(r x /z), where ϕ is the streamwise velocity fluctuation, δ is an outer length scale, r x is the two-point displacement in the streamwise direction and 〈·〉 denotes ensemble averaging. If the statistical behaviours of the streamwise velocity fluctuation and the fluctuation of a passive scalar are similar, we can expect first that the above mentioned scalings also exist for passive scalars (i.e. for ϕ being fluctuations of scalar concentration) and second that the instantaneous fluctuations of a passive scalar can be modelled using the HRAP model as well. Such expectations are confirmed using large-eddy simulations. Hence the work here presents a framework for modelling scalar turbulence in high Reynolds number wall-bounded flows.}, }
@article {pmid29732048, year = {2018}, author = {Zhou, Y and Lee, C and Wang, J}, title = {The Computational Fluid Dynamics Analyses on Hemodynamic Characteristics in Stenosed Arterial Models.}, journal = {Journal of healthcare engineering}, volume = {2018}, number = {}, pages = {4312415}, pmid = {29732048}, issn = {2040-2295}, mesh = {Arterial Occlusive Diseases/*physiopathology ; Computer Simulation ; Hemodynamics/*physiology ; Humans ; *Models, Cardiovascular ; Rheology ; }, abstract = {Arterial stenosis plays an important role in the progressions of thrombosis and stroke. In the present study, a standard axisymmetric tube model of the stenotic artery is introduced and the degree of stenosis η is evaluated by the area ratio of the blockage to the normal vessel. A normal case (η = 0) and four stenotic cases of η = 0.25, 0.5, 0.625, and 0.75 with a constant Reynolds number of 300 are simulated by computational fluid dynamics (CFD), respectively, with the Newtonian and Carreau models for comparison. Results show that for both models, the poststenotic separation vortex length increases exponentially with the growth of stenosis degree. However, the vortex length of the Carreau model is shorter than that of the Newtonian model. The artery narrowing accelerates blood flow, which causes high blood pressure and wall shear stress (WSS). The pressure drop of the η = 0.75 case is nearly 8 times that of the normal value, while the WSS peak at the stenosis region of η = 0.75 case even reaches up to 15 times that of the normal value. The present conclusions are of generality and contribute to the understanding of the dynamic mechanisms of artery stenosis diseases.}, }
@article {pmid29729406, year = {2018}, author = {García-Salazar, G and de la Luz Zambrano-Zaragoza, M and Quintanar-Guerrero, D}, title = {Preparation of nanodispersions by solvent displacement using the Venturi tube.}, journal = {International journal of pharmaceutics}, volume = {545}, number = {1-2}, pages = {254-260}, doi = {10.1016/j.ijpharm.2018.05.005}, pmid = {29729406}, issn = {1873-3476}, mesh = {Acetone/*chemistry ; Drug Compounding ; Dynamic Light Scattering ; Equipment and Supplies ; Excipients/chemistry ; *Nanoparticles ; Nanotechnology ; Particle Size ; Polyesters/*chemistry ; Solvents/*chemistry ; Technology, Pharmaceutical/*instrumentation/methods ; }, abstract = {The Venturi tube (VT) is an apparatus that produces turbulence which is taken advantage of to produce nanoparticles (NP) by solvent displacement. The objective of this study was to evaluate the potential of this device for preparing NP of poly-ε-caprolactone. Response Surface Methodology was used to determine the effect of the operating conditions and optimization. The NP produced by VT were characterized by Dynamic Light-Scattering to determine their particle size distribution (PS) and polydispersity index (PDI). Results showed that the Reynolds number (Re) has a strong effect on both PS and process yield (PY).The turbulence regime is key to the efficient formation of NP. The optimal conditions for obtaining NP were a polymer concentration of 1.6 w/v, a recirculation rate of 4.8 L/min, and a stabilizer concentration of 1.1 w/v. The predicted response of the PY was 99.7%, with a PS of 333 nm, and a PDI of 0.2. Maintaining the same preparation conditions will make it possible to obtain NP using other polymers with similar properties. Our results show that VT is a reproducible and versatile method for manufacturing NP, and so may be a feasible method for industrial-scale nanoprecipitation production.}, }
@article {pmid29710732, year = {2018}, author = {Sandeep, N and Kumaran, G and Saleem, S}, title = {The influence of cross diffusion on magnetohydrodynamic flow of Carreau liquid in the presence of buoyancy force.}, journal = {Journal of integrative neuroscience}, volume = {17}, number = {3-4}, pages = {525-546}, doi = {10.3233/JIN-180086}, pmid = {29710732}, issn = {0219-6352}, abstract = {The flow of magnetohydrodynamic Carreau liquid with the Brownian moment, thermophoresis and cross diffusion effects is investigated numerically. The buoyancy persuades on the flow is contemplated in such a way that the surface is neither perpendicular/horizontal nor wedge/cone. This is very helpful in the design of jet-engine. The equations govern the flow are transmuted using acceptable similarity variables and numerically solved by recruiting Runge-Kutta based Newtons method. The graphical results are obtained to discuss the stimulus of flow, thermal and concentration fields for different parameters of interest. The wall friction, local Nusselt and Sherwood numbers are examined with the assistance of tables. It is noticed that the parabolic flow is controlled by the buoyant forces developed by the temperature difference. Since the flow is laminar, the Reynolds number considered as <1000. This study has applicable in man-made products and various industries like pumps and oil purification, petroleum production, power engineering and chemical engineering processes.}, }
@article {pmid29708343, year = {2018}, author = {Gao, S and Liao, Q and Liu, W and Liu, Z}, title = {Nanodroplets Impact on Rough Surfaces: A Simulation and Theoretical Study.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {34}, number = {20}, pages = {5910-5917}, doi = {10.1021/acs.langmuir.8b00480}, pmid = {29708343}, issn = {1520-5827}, abstract = {Impact of droplets is widespread in life, and modulating the dynamics of impinging droplets is a significant problem in production. However, on textured surfaces, the micromorphologic change and mechanism of impinging nanodroplets are not well-understood; furthermore, the accuracy of the theoretical model for nanodroplets needs to be improved. Here, considering the great challenge of conducting experiments on nanodroplets, a molecular dynamics simulation is performed to visualize the impact process of nanodroplets on nanopillar surfaces. Compared with macroscale droplets, apart from the similar relation of restitution coefficient with the Weber number, we found some distinctive results: the maximum spreading time is described as a power law of impact velocity, and the relation of maximum spreading factor with impact velocity or the Reynolds number is exponential. Moreover, the roughness of substrates plays a prominent role in the dynamics of impact nanodroplets, and on surfaces with lower solid fraction, the lower attraction force induces an easier rebound of impact nanodroplets. At last, on the basis of the energy balance, through modifying the estimation of viscous dissipation and surface energy terms, we proposed an improved model for the maximum spreading factor, which shows greater accuracy for nanodroplets, especially in the low-to-moderate velocity range. The outcome of this study demonstrates that a distinctive dynamical behavior of impinging nanodroplets, the fundamental insight, and more accurate prediction are very useful in the improvement of the hydrodynamic behavior of the nanodroplets.}, }
@article {pmid29670984, year = {2018}, author = {Vilfan, M and Osterman, N and Vilfan, A}, title = {Magnetically driven omnidirectional artificial microswimmers.}, journal = {Soft matter}, volume = {14}, number = {17}, pages = {3415-3422}, doi = {10.1039/c8sm00230d}, pmid = {29670984}, issn = {1744-6848}, abstract = {We present an experimental realisation of two new artificial microswimmers that swim at low Reynolds number. The swimmers are externally driven with a periodically modulated magnetic field that induces an alternating attractive/repulsive interaction between the swimmer parts. The field sequence also modulates the drag on the swimmer components, making the working cycle non-reciprocal. The resulting net translational displacement leads to velocities of up to 2 micrometers per second. The swimmers can be made omnidirectional, meaning that the same magnetic field sequence can drive swimmers in any direction in the sample plane. Although the direction of their swimming is determined by the momentary orientation of the swimmer, their motion can be guided by solid boundaries. We demonstrate their omnidirectionality by letting them travel through a circular microfluidic channel. We use simple scaling arguments as well as more detailed numerical simulations to explain the measured velocity as a function of the actuation frequency.}, }
@article {pmid29670148, year = {2018}, author = {Govindarajan, V and Mousel, J and Udaykumar, HS and Vigmostad, SC and McPherson, DD and Kim, H and Chandran, KB}, title = {Synergy between Diastolic Mitral Valve Function and Left Ventricular Flow Aids in Valve Closure and Blood Transport during Systole.}, journal = {Scientific reports}, volume = {8}, number = {1}, pages = {6187}, pmid = {29670148}, issn = {2045-2322}, support = {R01 HL109597/HL/NHLBI NIH HHS/United States ; UL1 TR000371/TR/NCATS NIH HHS/United States ; }, mesh = {Algorithms ; Atrial Function ; Blood Flow Velocity ; *Diastole ; Heart Atria/diagnostic imaging ; Heart Ventricles/diagnostic imaging ; *Hemodynamics ; Humans ; Imaging, Three-Dimensional ; Magnetic Resonance Imaging/methods ; Mitral Valve/diagnostic imaging/*physiology ; *Models, Cardiovascular ; *Systole ; Ventricular Function ; }, abstract = {Highly resolved three-dimensional (3D) fluid structure interaction (FSI) simulation using patient-specific echocardiographic data can be a powerful tool for accurately and thoroughly elucidating the biomechanics of mitral valve (MV) function and left ventricular (LV) fluid dynamics. We developed and validated a strongly coupled FSI algorithm to fully characterize the LV flow field during diastolic MV opening under physiologic conditions. Our model revealed that distinct MV deformation and LV flow patterns developed during different diastolic stages. A vortex ring that strongly depended on MV deformation formed during early diastole. At peak E wave, the MV fully opened, with a local Reynolds number of ~5500, indicating that the flow was in the laminar-turbulent transitional regime. Our results showed that during diastasis, the vortex structures caused the MV leaflets to converge, thus increasing mitral jet's velocity. The vortex ring became asymmetrical, with the vortex structures on the anterior side being larger than on the posterior side. During the late diastolic stages, the flow structures advected toward the LV outflow tract, enhancing fluid transport to the aorta. This 3D-FSI study demonstrated the importance of leaflet dynamics, their effect on the vortex ring, and their influence on MV function and fluid transport within the LV during diastole.}, }
@article {pmid29657749, year = {2018}, author = {Li, H and Guo, S}, title = {Aerodynamic efficiency of a bioinspired flapping wing rotor at low Reynolds number.}, journal = {Royal Society open science}, volume = {5}, number = {3}, pages = {171307}, pmid = {29657749}, issn = {2054-5703}, abstract = {This study investigates the aerodynamic efficiency of a bioinspired flapping wing rotor kinematics which combines an active vertical flapping motion and a passive horizontal rotation induced by aerodynamic thrust. The aerodynamic efficiencies for producing both vertical lift and horizontal thrust of the wing are obtained using a quasi-steady aerodynamic model and two-dimensional (2D) CFD analysis at Reynolds number of 2500. The calculated efficiency data show that both efficiencies (propulsive efficiency-ηp, and efficiency for producing lift-Pf) of the wing are optimized at Strouhal number (St) between 0.1 and 0.5 for a range of wing pitch angles (upstroke angle of attack αu less than 45°); the St for high Pf (St = 0.1 ∼ 0.3) is generally lower than for high ηp (St = 0.2 ∼ 0.5), while the St for equilibrium rotation states lies between the two. Further systematic calculations show that the natural equilibrium of the passive rotating wing automatically converges to high-efficiency states: above 85% of maximum Pf can be obtained for a wide range of prescribed wing kinematics. This study provides insight into the aerodynamic efficiency of biological flyers in cruising flight, as well as practical applications for micro air vehicle design.}, }
@article {pmid29648545, year = {2018}, author = {Wang, C and Tang, H}, title = {Enhancement of aerodynamic performance of a heaving airfoil using synthetic-jet based active flow control.}, journal = {Bioinspiration &amp; biomimetics}, volume = {13}, number = {4}, pages = {046005}, doi = {10.1088/1748-3190/aabdb9}, pmid = {29648545}, issn = {1748-3190}, mesh = {Air ; Air Movements ; *Aircraft ; Animals ; Biomechanical Phenomena ; *Biomimetic Materials ; Biomimetics ; Computer Simulation ; Equipment Design ; Flight, Animal/physiology ; Models, Biological ; Physical Phenomena ; Wings, Animal/physiology ; }, abstract = {In this study, we explore the use of synthetic jet (SJ) in manipulating the vortices around a rigid heaving airfoil, so as to enhance its aerodynamic performance. The airfoil heaves at two fixed pitching angles, with the Strouhal number, reduced frequency and Reynolds number chosen as St = 0.3, k = 0.25 and Re = 100, respectively, all falling in the ranges for natural flyers. As such, the vortex force plays a dominant role in determining the airfoil's aerodynamic performance. A pair of in-phase SJs is implemented on the airfoil's upper and lower surfaces, operating with the same strength but in opposite directions. Such a fluid-structure interaction problem is numerically solved using a lattice Boltzmann method based numerical framework. It is found that, as the airfoil heaves with zero pitching angle, its lift and drag can be improved concurrently when the SJ phase angle [Formula: see text] relative to the heave motion varies between [Formula: see text] and [Formula: see text]. But this concurrent improvement does not occur as the airfoil heaves with [Formula: see text] pitching angle. Detailed inspection of the vortex evolution and fluid stress over the airfoil surface reveals that, if at good timing, the suction and blowing strokes of the SJ pair can effectively delay or promote the shedding of leading edge vortices, and mitigate or even eliminate the generation of trailing edge vortices, so as to enhance the airfoil's aerodynamic performance. Based on these understandings, an intermittent operation of the SJ pair is then proposed to realize concurrent lift and drag improvement for the heaving airfoil with [Formula: see text] pitching angle.}, }
@article {pmid29633848, year = {2018}, author = {Bordbar, A and Taassob, A and Khojasteh, D and Marengo, M and Kamali, R}, title = {Maximum Spreading and Rebound of a Droplet Impacting onto a Spherical Surface at Low Weber Numbers.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {34}, number = {17}, pages = {5149-5158}, doi = {10.1021/acs.langmuir.8b00625}, pmid = {29633848}, issn = {1520-5827}, abstract = {The spreading and rebound patterns of low-viscous droplets upon impacting spherical solid surfaces are investigated numerically. The studied cases consider a droplet impinging onto hydrophobic and superhydrophobic surfaces with various parameters varied throughout the study, and their effects on the postimpingement behavior are discussed. These parameters include impact Weber number (through varying the surface tension and impingement velocity), the size ratio of the droplet to the solid surface, and the surface contact angle. According to the findings, the maximum spreading diameter increases with the impact velocity, with an increase of the sphere diameter, with a lower surface wettability, and with a lower surface tension. Typical outcomes of the impact include (1) complete rebound, (2) splash, and (3) a final deposition stage after a series of spreading and recoiling phases. Finally, a novel, practical model is proposed, which can reasonably predict the maximum deformation of low Reynolds number impact of droplets onto hydrophobic or superhydrophobic spherical solid surfaces.}, }
@article {pmid29608886, year = {2018}, author = {Hopgood, M and Reynolds, G and Barker, R}, title = {Using Computational Fluid Dynamics to Compare Shear Rate and Turbulence in the TIM-Automated Gastric Compartment With USP Apparatus II.}, journal = {Journal of pharmaceutical sciences}, volume = {107}, number = {7}, pages = {1911-1919}, doi = {10.1016/j.xphs.2018.03.019}, pmid = {29608886}, issn = {1520-6017}, mesh = {Chemistry, Pharmaceutical/instrumentation ; Drug Development/instrumentation ; Humans ; *Hydrodynamics ; Models, Biological ; Solubility ; Stomach/anatomy &amp; histology/*physiology ; Surface Properties ; Tablets/chemistry/*metabolism ; }, abstract = {We use computational fluid dynamics to compare the shear rate and turbulence in an advanced in vitro gastric model (TIMagc) during its simulation of fasted state Migrating Motor Complex phases I and II, with the United States Pharmacopeia paddle dissolution apparatus II (USPII). A specific focus is placed on how shear rate in these apparatus affects erosion-based solid oral dosage forms. The study finds that tablet surface shear rates in TIMagc are strongly time dependant and fluctuate between 0.001 and 360 s[-1]. In USPII, tablet surface shear rates are approximately constant for a given paddle speed and increase linearly from 9 s[-1] to 36 s[-1] as the paddle speed is increased from 25 to 100 rpm. A strong linear relationship is observed between tablet surface shear rate and tablet erosion rate in USPII, whereas TIMagc shows highly variable behavior. The flow regimes present in each apparatus are compared to in vivo predictions using Reynolds number analysis. Reynolds numbers for flow in TIMagc lie predominantly within the predicted in vivo bounds (0.01-30), whereas Reynolds numbers for flow in USPII lie above the predicted upper bound when operating with paddle speeds as low as 25 rpm (33).}, }
@article {pmid29596861, year = {2018}, author = {Prakash, J and Ramesh, K and Tripathi, D and Kumar, R}, title = {Numerical simulation of heat transfer in blood flow altered by electroosmosis through tapered micro-vessels.}, journal = {Microvascular research}, volume = {118}, number = {}, pages = {162-172}, doi = {10.1016/j.mvr.2018.03.009}, pmid = {29596861}, issn = {1095-9319}, mesh = {Blood Flow Velocity ; *Computer Simulation ; *Electroosmosis ; Energy Transfer ; Humans ; Microvessels/anatomy &amp; histology/*physiology ; *Models, Cardiovascular ; Numerical Analysis, Computer-Assisted ; Peristalsis ; Pulsatile Flow ; Regional Blood Flow ; *Temperature ; }, abstract = {A numerical simulation is presented to study the heat and flow characteristics of blood flow altered by electroosmosis through the tapered micro-vessels. Blood is assumed as non-Newtonian (micropolar) nanofluids. The flow regime is considered as asymmetric diverging (tapered) microchannel for more realistic micro-vessels which is produced by choosing the peristaltic wave train on the walls to have different amplitudes and phase. The Rosseland approximation is employed to model the radiation heat transfer and temperatures of the walls are presumed constants. The mathematical formulation of the present problem is simplified under the long-wavelength, low-Reynolds number and Debye-Hückel linearization approximations. The influence of various dominant physical parameters are discussed for axial velocity, microrotation distribution, thermal temperature distribution and nanoparticle volume fraction field. However, our foremost emphasis is to determine the effects of thermal radiation and coupling number on the axial velocity and microrotation distribution beneath electroosmotic environment. This analysis places a significant observation on the thermal radiation and coupling number which plays an influential role in hearten fluid velocity. This study is encouraged by exploring the nanofluid-dynamics in peristaltic transport as symbolized by heat transport in biological flows and also in novel pharmacodynamics pumps and gastro-intestinal motility enhancement.}, }
@article {pmid29594300, year = {2018}, author = {Jing, H and Das, S}, title = {Theory of diffusioosmosis in a charged nanochannel.}, journal = {Physical chemistry chemical physics : PCCP}, volume = {20}, number = {15}, pages = {10204-10212}, doi = {10.1039/c8cp01091a}, pmid = {29594300}, issn = {1463-9084}, abstract = {We probe the diffusioosmotic transport in a charged nanofluidic channel in the presence of an applied tangential salt concentration gradient. Ionic salt gradient driven diffusioosmosis or ionic diffusioosmosis (IDO) is characterized by the generation of an induced tangential electric field and a diffusioosmotic velocity (DOSV) that is a combination of an electroosmotic velocity (EOSV) triggered by this electric field and a chemiosmotic velocity (COSV) triggered by an induced tangential pressure gradient. We explain that unlike the existing theories on IDO, it is more appropriate to apply the zero net current conditions (formulation F2) and not more restrictive zero net local flux conditions (formulation F1) particularly for the case where one considers a nanochannel connected to two reservoirs. We pinpoint limitations in the existing literature in correctly predicting the diffusioosmotic behavior even for the case where formulation F1 is used. We address these limitations and establish that (a) the induced electric field is an interplay of the differences in ionic diffusivity, the EDL-induced imbalance in ion concentrations, and the advection effects, (b) formulation F1 may overpredict or underpredict the electric field and the EOSV leading to an overprediction/underprediction of the DOSV and (c) formulation F2 demonstrates remarkable fluid physics of localized backflows owing to a dominant local influence of the COSV, which is missed by formulation F1. We anticipate that our theory will provide the first rigorous understanding of nanofluidic IDO with applications in multiple areas of low Reynolds number transport such as biofluidics, microfluidic separation, and colloidal transport.}, }
@article {pmid29589515, year = {2018}, author = {Rigatelli, G and Zuin, M and Dell'Avvocata, F and Nguyen, T}, title = {Rheolytic effects of left main mid-shaft/distal stenting: a computational flow dynamic analysis.}, journal = {Therapeutic advances in cardiovascular disease}, volume = {12}, number = {6}, pages = {161-168}, pmid = {29589515}, issn = {1753-9455}, mesh = {Aged ; Aged, 80 and over ; Angioplasty, Balloon, Coronary/*instrumentation ; Cardiovascular Agents/administration &amp; dosage ; Computed Tomography Angiography ; Coronary Artery Disease/diagnostic imaging/physiopathology/*therapy ; *Coronary Circulation ; Coronary Stenosis/diagnostic imaging/physiopathology/*therapy ; Coronary Vessels/diagnostic imaging/*physiopathology ; *Drug-Eluting Stents ; Everolimus/administration &amp; dosage ; Female ; Humans ; Male ; Middle Aged ; *Models, Cardiovascular ; *Patient-Specific Modeling ; Prosthesis Design ; Retrospective Studies ; Rheology ; Treatment Outcome ; }, abstract = {Background The aim of this study was to evaluate the rheolytic effects of stenting a mid-shaft/distal left main coronary artery (LMCA) lesion with and without ostial coverage. Stenting of the LMCA has emerged as a valid alternative in place of traditional coronary bypass graft surgery. However, in case of mid-shaft/distal lesion, there is no consensus regarding the extension of the strut coverage up to the ostium or to stent only the culprit lesion. Methods We reconstructed a left main-left descending coronary artery (LM-LCA)-left circumflex (LCX) bifurcation after analysing 100 consecutive patients (mean age 71.4 ± 9.3, 49 males) with LM mid-shaft/distal disease. The mean diameter of proximal LM, left anterior descending (LAD) and LCX, evaluated with quantitative coronary angiography (QCA) was 4.62 ± 0.86 mm, 3.31 ± 0.92 mm, and 2.74 ± 0.93 mm, respectively. For the stent simulation, a third-generation, everolimus-eluting stent was virtually reconstructed. Results After virtual stenting, the net area averaged wall shear stress (WSS) of the model and the WSS at the LCA-LCX bifurcation resulted higher when the stent covered the culprit mid-shaft lesion only compared with the extension of the stent covering the ostium (3.68 versus 2.06 Pa, p = 0.01 and 3.97 versus 1.98 Pa, p < 0.001, respectively. Similarly, the static pressure and the Reynolds number were significantly higher after stent implantation covering up the ostium. At the ostium, the flow resulted more laminar when stenting only the mid-shaft lesion than including the ostium. Conclusions Although these findings cannot be translated directly into real practice our brief study suggests that stenting lesion 1:1 or extending the stent to cover the LM ostium impacts differently the rheolytic properties of LMCA bifurcation with potential insights for restenosis or thrombosis.}, }
@article {pmid29584651, year = {2018}, author = {Xi, J and Hu, Q and Zhao, L and Si, XA}, title = {Molecular Binding Contributes to Concentration Dependent Acrolein Deposition in Rat Upper Airways: CFD and Molecular Dynamics Analyses.}, journal = {International journal of molecular sciences}, volume = {19}, number = {4}, pages = {}, pmid = {29584651}, issn = {1422-0067}, mesh = {Acrolein/*chemistry ; Animals ; Humans ; Hydrogen Bonding ; Male ; Models, Anatomic ; Molecular Dynamics Simulation ; Particle Size ; Rats ; Rats, Sprague-Dawley ; Trachea/anatomy &amp; histology/*chemistry ; Water/*chemistry ; }, abstract = {Existing in vivo experiments show significantly decreased acrolein uptake in rats with increasing inhaled acrolein concentrations. Considering that high-polarity chemicals are prone to bond with each other, it is hypothesized that molecular binding between acrolein and water will contribute to the experimentally observed deposition decrease by decreasing the effective diffusivity. The objective of this study is to quantify the probability of molecular binding for acrolein, as well as its effects on acrolein deposition, using multiscale simulations. An image-based rat airway geometry was used to predict the transport and deposition of acrolein using the chemical species model. The low Reynolds number turbulence model was used to simulate the airflows. Molecular dynamic (MD) simulations were used to study the molecular binding of acrolein in different media and at different acrolein concentrations. MD results show that significant molecular binding can happen between acrolein and water molecules in human and rat airways. With 72 acrolein embedded in 800 water molecules, about 48% of acrolein compounds contain one hydrogen bond and 10% contain two hydrogen bonds, which agreed favorably with previous MD results. The percentage of hydrogen-bonded acrolein compounds is higher at higher acrolein concentrations or in a medium with higher polarity. Computational dosimetry results show that the size increase caused by the molecular binding reduces the effective diffusivity of acrolein and lowers the chemical deposition onto the airway surfaces. This result is consistent with the experimentally observed deposition decrease at higher concentrations. However, this size increase can only explain part of the concentration-dependent variation of the acrolein uptake and acts as a concurrent mechanism with the uptake-limiting tissue ration rate. Intermolecular interactions and associated variation in diffusivity should be considered in future dosimetry modeling of high-polarity chemicals such as acrolein.}, }
@article {pmid29557508, year = {2018}, author = {Gupta, A and Clercx, HJH and Toschi, F}, title = {Computational study of radial particle migration and stresslet distributions in particle-laden turbulent pipe flow.}, journal = {The European physical journal. E, Soft matter}, volume = {41}, number = {3}, pages = {34}, pmid = {29557508}, issn = {1292-895X}, abstract = {Particle-laden turbulent flows occur in a variety of industrial applications as well as in naturally occurring flows. While the numerical simulation of such flows has seen significant advances in recent years, it still remains a challenging problem. Many studies investigated the rheology of dense suspensions in laminar flows as well as the dynamics of point-particles in turbulence. Here we employ a fully-resolved numerical simulation based on a lattice Boltzmann scheme, to investigate turbulent flow with large neutrally buoyant particles in a pipe flow at low Reynolds number and in dilute regimes. The energy input is kept fixed resulting in a Reynolds number based on the friction velocity around 250. Two different particle radii were used giving a particle-pipe diameter ratio of 0.05 and 0.075. The number of particles is kept constant resulting in a volume fraction of 0.54% and 1.83%, respectively. We investigated Eulerian and Lagrangian statistics along with the stresslet exerted by the fluid on the spherical particles. It was observed that the high particle-to-fluid slip velocity close to the wall corresponds locally to events of high energy dissipation, which are not present in the single-phase flow. The migration of particles from the inner to the outer region of the pipe, the dependence of the stresslet on the particle radial positions and a proxy for the fragmentation rate of the particles computed using the stresslet have been investigated.}, }
@article {pmid29557347, year = {2018}, author = {Bayiz, Y and Ghanaatpishe, M and Fathy, H and Cheng, B}, title = {Hovering efficiency comparison of rotary and flapping flight for rigid rectangular wings via dimensionless multi-objective optimization.}, journal = {Bioinspiration &amp; biomimetics}, volume = {13}, number = {4}, pages = {046002}, doi = {10.1088/1748-3190/aab801}, pmid = {29557347}, issn = {1748-3190}, mesh = {Algorithms ; Animals ; Biomechanical Phenomena ; Biomimetics ; Computer Simulation ; Flight, Animal/*physiology ; Insecta/physiology ; *Models, Biological ; Torque ; Wings, Animal/*physiology ; }, abstract = {In this work, a multi-objective optimization framework is developed for optimizing low Reynolds number ([Formula: see text]) hovering flight. This framework is then applied to compare the efficiency of rigid revolving and flapping wings with rectangular shape under varying [Formula: see text] and Rossby number ([Formula: see text], or aspect ratio). The proposed framework is capable of generating sets of optimal solutions and Pareto fronts for maximizing the lift coefficient and minimizing the power coefficient in dimensionless space, explicitly revealing the trade-off between lift generation and power consumption. The results indicate that revolving wings are more efficient when the required average lift coefficient [Formula: see text] is low (<1 for [Formula: see text] and <1.6 for [Formula: see text]), while flapping wings are more efficient in achieving higher [Formula: see text]. With the dimensionless power loading as the single-objective performance measure to be maximized, rotary flight is more efficient than flapping wings for [Formula: see text] regardless of the amount of energy storage assumed in the flapping wing actuation mechanism, while flapping flight is more efficient for [Formula: see text]. It is observed that wings with low [Formula: see text] perform better when higher [Formula: see text] is needed, whereas higher [Formula: see text] cases are more efficient at [Formula: see text] regions. However, for the selected geometry and [Formula: see text], the efficiency is weakly dependent on [Formula: see text] when the dimensionless power loading is maximized.}, }
@article {pmid29555806, year = {2018}, author = {Margolin, LG}, title = {Scale matters.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {376}, number = {2118}, pages = {}, pmid = {29555806}, issn = {1471-2962}, abstract = {The applicability of Navier-Stokes equations is limited to near-equilibrium flows in which the gradients of density, velocity and energy are small. Here I propose an extension of the Chapman-Enskog approximation in which the velocity probability distribution function (PDF) is averaged in the coordinate phase space as well as the velocity phase space. I derive a PDF that depends on the gradients and represents a first-order generalization of local thermodynamic equilibrium. I then integrate this PDF to derive a hydrodynamic model. I discuss the properties of that model and its relation to the discrete equations of computational fluid dynamics.This article is part of the theme issue 'Hilbert's sixth problem'.}, }
@article {pmid29553536, year = {2018}, author = {Agudo, JR and Han, J and Park, J and Kwon, S and Loekman, S and Luzi, G and Linderberger, C and Delgado, A and Wierschem, A}, title = {Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions.}, journal = {Journal of visualized experiments : JoVE}, volume = {}, number = {132}, pages = {}, pmid = {29553536}, issn = {1940-087X}, mesh = {Computer Simulation ; Motion ; Nonlinear Dynamics ; *Stress, Mechanical ; }, abstract = {Two different experimental methods for determining the threshold of particle motion as a function of geometrical properties of the bed from laminar to turbulent flow conditions are presented. For that purpose, the incipient motion of a single bead is studied on regular substrates that consist of a monolayer of fixed spheres of uniform size that are regularly arranged in triangular and quadratic symmetries. The threshold is characterized by the critical Shields number. The criterion for the onset of motion is defined as the displacement from the original equilibrium position to the neighboring one. The displacement and the mode of motion are identified with an imaging system. The laminar flow is induced using a rotational rheometer with a parallel disk configuration. The shear Reynolds number remains below 1. The turbulent flow is induced in a low-speed wind tunnel with open jet test section. The air velocity is regulated with a frequency converter on the blower fan. The velocity profile is measured with a hot wire probe connected to a hot film anemometer. The shear Reynolds number ranges between 40 and 150. The logarithmic velocity law and the modified wall law presented by Rotta are used to infer the shear velocity from the experimental data. The latter is of special interest when the mobile bead is partially exposed to the turbulent flow in the so-called hydraulically transitional flow regime. The shear stress is estimated at onset of motion. Some illustrative results showing the strong impact of the angle of repose, and the exposure of the bead to shear flow are represented in both regimes.}, }
@article {pmid29548174, year = {2018}, author = {Kawamura, Y and Tsubaki, R}, title = {Phase reduction approach to elastohydrodynamic synchronization of beating flagella.}, journal = {Physical review. E}, volume = {97}, number = {2-1}, pages = {022212}, doi = {10.1103/PhysRevE.97.022212}, pmid = {29548174}, issn = {2470-0053}, mesh = {Flagella/*metabolism ; *Hydrodynamics ; *Models, Biological ; }, abstract = {We formulate a theory for the phase reduction of a beating flagellum. The theory enables us to describe the dynamics of a beating flagellum in a systematic manner using a single variable called the phase. The theory can also be considered as a phase reduction method for the limit-cycle solutions in infinite-dimensional dynamical systems, namely, the limit-cycle solutions to partial differential equations representing beating flagella. We derive the phase sensitivity function, which quantifies the phase response of a beating flagellum to weak perturbations applied at each point and at each time. Using the phase sensitivity function, we analyze the phase synchronization between a pair of beating flagella through hydrodynamic interactions at a low Reynolds number.}, }
@article {pmid29548159, year = {2018}, author = {Rolland, J}, title = {Extremely rare collapse and build-up of turbulence in stochastic models of transitional wall flows.}, journal = {Physical review. E}, volume = {97}, number = {2-1}, pages = {023109}, doi = {10.1103/PhysRevE.97.023109}, pmid = {29548159}, issn = {2470-0053}, abstract = {This paper presents a numerical and theoretical study of multistability in two stochastic models of transitional wall flows. An algorithm dedicated to the computation of rare events is adapted on these two stochastic models. The main focus is placed on a stochastic partial differential equation model proposed by Barkley. Three types of events are computed in a systematic and reproducible manner: (i) the collapse of isolated puffs and domains initially containing their steady turbulent fraction; (ii) the puff splitting; (iii) the build-up of turbulence from the laminar base flow under a noise perturbation of vanishing variance. For build-up events, an extreme realization of the vanishing variance noise pushes the state from the laminar base flow to the most probable germ of turbulence which in turn develops into a full blown puff. For collapse events, the Reynolds number and length ranges of the two regimes of collapse of laminar-turbulent pipes, independent collapse or global collapse of puffs, is determined. The mean first passage time before each event is then systematically computed as a function of the Reynolds number r and pipe length L in the laminar-turbulent coexistence range of Reynolds number. In the case of isolated puffs, the faster-than-linear growth with Reynolds number of the logarithm of mean first passage time T before collapse is separated in two. One finds that ln(T)=A_{p}r-B_{p}, with A_{p} and B_{p} positive. Moreover, A_{p} and B_{p} are affine in the spatial integral of turbulence intensity of the puff, with the same slope. In the case of pipes initially containing the steady turbulent fraction, the length L and Reynolds number r dependence of the mean first passage time T before collapse is also separated. The author finds that T≍exp[L(Ar-B)] with A and B positive. The length and Reynolds number dependence of T are then discussed in view of the large deviations theoretical approaches of the study of mean first passage times and multistability, where ln(T) in the limit of small variance noise is studied. Two points of view, local noise of small variance and large length, can be used to discuss the exponential dependence in L of T. In particular, it is shown how a T≍exp[L(A^{'}R-B^{'})] can be derived in a conceptual two degrees of freedom model of a transitional wall flow proposed by Dauchot and Manneville. This is done by identifying a quasipotential in low variance noise, large length limit. This pinpoints the physical effects controlling collapse and build-up trajectories and corresponding passage times with an emphasis on the saddle points between laminar and turbulent states. This analytical analysis also shows that these effects lead to the asymmetric probability density function of kinetic energy of turbulence.}, }
@article {pmid29548094, year = {2018}, author = {Nemoto, T and Alexakis, A}, title = {Method to measure efficiently rare fluctuations of turbulence intensity for turbulent-laminar transitions in pipe flows.}, journal = {Physical review. E}, volume = {97}, number = {2-1}, pages = {022207}, doi = {10.1103/PhysRevE.97.022207}, pmid = {29548094}, issn = {2470-0053}, abstract = {The fluctuations of turbulence intensity in a pipe flow around the critical Reynolds number is difficult to study but important because they are related to turbulent-laminar transitions. We here propose a rare-event sampling method to study such fluctuations in order to measure the time scale of the transition efficiently. The method is composed of two parts: (i) the measurement of typical fluctuations (the bulk part of an accumulative probability function) and (ii) the measurement of rare fluctuations (the tail part of the probability function) by employing dynamics where a feedback control of the Reynolds number is implemented. We apply this method to a chaotic model of turbulent puffs proposed by Barkley and confirm that the time scale of turbulence decay increases super exponentially even for high Reynolds numbers up to Re =2500, where getting enough statistics by brute-force calculations is difficult. The method uses a simple procedure of changing Reynolds number that can be applied even to experiments.}, }
@article {pmid29542932, year = {2018}, author = {Song, F and Ju, D and Gu, F and Liu, Y and Ji, Y and Ren, Y and He, X and Sha, B and Li, BQ and Yang, Q}, title = {Parametric Study on Electric Field-Induced Micro-/Nanopatterns in Thin Polymer Films.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {34}, number = {14}, pages = {4188-4198}, doi = {10.1021/acs.langmuir.8b00007}, pmid = {29542932}, issn = {1520-5827}, abstract = {Electric field-induced micro-/nanopatterns in thin polymer films, sometimes referred as electrohydrodynamic patterning, is a promising technique to fabricate micro-/nanostructures. Extensive attention has been attracted because of its advantages in microcontact (easy demolding) and low cost. Although considerable work has been done on this technique, including both experimental and theoretical ones, there still appears a requirement for understanding the mechanism of electrohydrodynamic patterning. Thus, we systematically studied the effect of different parameters on electrohydrodynamic patterning with a numerical phase field model. Previous researchers usually employed lubrication approximation (i.e., long-wave approximation) to simplify the numerical model. However, this approximation would lose its validity if the structure height is on the same scale or larger than the wavelength, which occurs in most cases. Thus, we abandoned the lubrication approximation and solved the full governing equations for fluid flow and electric field. In this model, the deformation of polymer film is described by the phase field model. As to the electric field, the leaky dielectric model is adopted in which both electrical permittivity and conductivity are considered. The fluid flow together with electric field is coupled together in the framework of phase field. By this model, the effect of physical parameters, such as external voltage, template structure height, and polymer conductivity, is studied in detail. After that, the governing equations are nondimesionalized to analyze the relationship between different parameters. A dimensionless parameter, electrical Reynolds number ER, is defined, for which, a large value would simplify the electric field to perfect dielectric model and a small value leads it to steady leaky model. These findings and results may enhance our understanding of electrohydrodynamic patterning and may be a meaningful guide for experiments.}, }
@article {pmid29542796, year = {2018}, author = {Du, D and Hilou, E and Biswal, SL}, title = {Reconfigurable paramagnetic microswimmers: Brownian motion affects non-reciprocal actuation.}, journal = {Soft matter}, volume = {14}, number = {18}, pages = {3463-3470}, doi = {10.1039/c8sm00069g}, pmid = {29542796}, issn = {1744-6848}, abstract = {Swimming at low Reynolds number is typically dominated by a large viscous drag, therefore microscale swimmers require non-reciprocal body deformation to generate locomotion. Purcell described a simple mechanical swimmer at the microscale consisting of three rigid components connected together with two hinges. Here we present a simple microswimmer consisting of two rigid paramagnetic particles with different sizes. When placed in an eccentric magnetic field, this simple microswimmer exhibits non-reciprocal body motion and its swimming locomotion can be directed in a controllable manner. Additional components can be added to create a multibody microswimmer, whereby the particles act cooperatively and translate in a given direction. For some multibody swimmers, the stochastic thermal forces fragment the arm, which therefore modifies the swimming strokes and changes the locomotive speed. This work offers insight into directing the motion of active systems with novel time-varying magnetic fields. It also reveals that Brownian motion not only affects the locomotion of reciprocal swimmers that are subject to the Scallop theorem, but also affects that of non-reciprocal swimmers.}, }
@article {pmid29542373, year = {2018}, author = {Oota-Ishigaki, A and Masuzawa, T and Nagayama, K}, title = {Analysis of the effect of the size of three-dimensional micro-geometric structures on physical adhesion phenomena using microprint technique.}, journal = {The International journal of artificial organs}, volume = {41}, number = {5}, pages = {277-283}, doi = {10.1177/0391398818763264}, pmid = {29542373}, issn = {1724-6040}, mesh = {Biocompatible Materials ; Heart-Assist Devices/*adverse effects ; Humans ; Hydrodynamics ; Surface Properties ; Thrombosis/*etiology ; }, abstract = {Thrombus formation on biomaterial surfaces with microstructures is complex and not fully understood. We have studied the micro-secondary flow around microstructures that causes components of blood to adhere physically in a low Reynolds number region. The purpose of this study was to investigate the effect of micro-column size on the adhesion phenomena and show a quantitative relationship between the micro-secondary flow and physical adhesion phenomena, considering microstructures of various sizes. The flow simulation and quantitative assessment of adhesion rates around micro-columns was conducted using four sizes of micro-columns. This study also calculated the vectors of micro-secondary flow and average shear rate around a micro-column using a computational fluid dynamics analysis. The simulation showed the micro-secondary flow toward the bottom surface at upstream side and low shear rate distribution generated around a micro-column. Furthermore, physical adhesion tests were conducted using microbeads and a perfusion circuit to examine the size effect of the micro-columns on the physical adhesion. The results showed that the average adhesion rate around the micro-column increases with the associated size increase of the micro-column. Our results indicate that quantification of micro-secondary flow on a material surface with microstructures of several sizes and shapes (such as in a rough surface) is important for the evaluation of the adhesion phenomenon even though the surface roughness value on the material surface is small.}, }
@article {pmid29535341, year = {2018}, author = {Rubol, S and Ling, B and Battiato, I}, title = {Universal scaling-law for flow resistance over canopies with complex morphology.}, journal = {Scientific reports}, volume = {8}, number = {1}, pages = {4430}, pmid = {29535341}, issn = {2045-2322}, abstract = {Flow resistance caused by vegetation is a key parameter to properly assess flood management and river restoration. However, quantifying the friction factor or any of its alternative metrics, e.g. the drag coefficient, in canopies with complex geometry has proven elusive. We explore the effect of canopy morphology on vegetated channels flow structure and resistance by treating the canopy as a porous medium characterized by an effective permeability, a property that describes the ease with which water can flow through the canopy layer. We employ a two-domain model for flow over and within the canopy, which couples the log-law in the free layer to the Darcy-Brinkman equation in the vegetated layer. We validate the model analytical solutions for the average velocity profile within and above the canopy, the volumetric discharge and the friction factor against data collected across a wide range of canopy morphologies encountered in riverine systems. Results indicate agreement between model predictions and data for both simple and complex plant morphologies. For low submergence canopies, we find a universal scaling law that relates friction factor with canopy permeability and a rescaled bulk Reynolds number. This provides a valuable tool to assess habitats sustainability associated with hydro-dynamical conditions.}, }
@article {pmid29527067, year = {2017}, author = {Yang, J and Wang, X and Krane, M and Zhang, LT}, title = {Fully-coupled aeroelastic simulation with fluid compressibility - For application to vocal fold vibration.}, journal = {Computer methods in applied mechanics and engineering}, volume = {315}, number = {}, pages = {584-606}, pmid = {29527067}, issn = {0045-7825}, support = {R01 DC005642/DC/NIDCD NIH HHS/United States ; }, abstract = {In this study, a fully-coupled fluid-structure interaction model is developed for studying dynamic interactions between compressible fluid and aeroelastic structures. The technique is built based on the modified Immersed Finite Element Method (mIFEM), a robust numerical technique to simulate fluid-structure interactions that has capabilities to simulate high Reynolds number flows and handles large density disparities between the fluid and the solid. For accurate assessment of this intricate dynamic process between compressible fluid, such as air and aeroelastic structures, we included in the model the fluid compressibility in an isentropic process and a solid contact model. The accuracy of the compressible fluid solver is verified by examining acoustic wave propagations in a closed and an open duct, respectively. The fully-coupled fluid-structure interaction model is then used to simulate and analyze vocal folds vibrations using compressible air interacting with vocal folds that are represented as layered viscoelastic structures. Using physiological geometric and parametric setup, we are able to obtain a self-sustained vocal fold vibration with a constant inflow pressure. Parametric studies are also performed to study the effects of lung pressure and vocal fold tissue stiffness in vocal folds vibrations. All the case studies produce expected airflow behavior and a sustained vibration, which provide verification and confidence in our future studies of realistic acoustical studies of the phonation process.}, }
@article {pmid29513310, year = {2018}, author = {Marson, RL and Huang, Y and Huang, M and Fu, T and Larson, RG}, title = {Inertio-capillary cross-streamline drift of droplets in Poiseuille flow using dissipative particle dynamics simulations.}, journal = {Soft matter}, volume = {14}, number = {12}, pages = {2267-2280}, doi = {10.1039/c7sm02294h}, pmid = {29513310}, issn = {1744-6848}, abstract = {We find using dissipative particle dynamics (DPD) simulations that a deformable droplet sheared in a narrow microchannel migrates to steady-state position that depends upon the dimensionless particle capillary number , which controls the droplet deformability (with Vmax the centerline velocity, μf the fluid viscosity, Γ the surface tension, R the droplet radius, and H the gap), the droplet (particle) Reynolds number , which controls inertia, where ρ is the fluid density, as well as on the viscosity ratio of the droplet to the suspending fluid κ = μd/μf. We find that when the Ohnesorge number is around 0.06, so that inertia is stronger than capillarity, at small capillary number Cap < 0.1, the droplet migrates to a position close to that observed for hard spheres by Segre and Silberberg, around 60% of the distance from the centerline to the wall, while for increasing Cap the droplet steady-state position moves smoothly towards the centerline, reaching around 20% of the distance from centerline to the wall when Cap reaches 0.5 or so. For higher Oh, the droplet position is much less sensitive to Cap, and remains at around 30% of the distance from centerline to the wall over the whole accessible range of Cap. The results are insensitive to viscosity ratios from unity to the highest value studied here, around 13, and the drift towards the centerline for increasing Cap is observed for ratios of droplet diameter to gap size ranging from 0.1 to 0.3. We also find consistency between our predictions and existing perturbation theory for small droplet or particle size, as well as with experimental data. Additionally, we assess the accuracy of the DPD method and conclude that with current computer resources and methods DPD is not readily able to predict cross-stream-line drift for small particle Reynolds number (much less than unity), or for droplets that are less than one tenth the gap size, owing to excessive noise and inadequate numbers of DPD particles per droplet.}, }
@article {pmid29512658, year = {2018}, author = {Hadikhani, P and Hashemi, SMH and Balestra, G and Zhu, L and Modestino, MA and Gallaire, F and Psaltis, D}, title = {Inertial manipulation of bubbles in rectangular microfluidic channels.}, journal = {Lab on a chip}, volume = {18}, number = {7}, pages = {1035-1046}, doi = {10.1039/c7lc01283g}, pmid = {29512658}, issn = {1473-0189}, abstract = {Inertial microfluidics is an active field of research that deals with crossflow positioning of the suspended entities in microflows. Until now, the majority of the studies have focused on the behavior of rigid particles in order to provide guidelines for microfluidic applications such as sorting and filtering. Deformable entities such as bubbles and droplets are considered in fewer studies despite their importance in multiphase microflows. In this paper, we show that the trajectory of bubbles flowing in rectangular and square microchannels can be controlled by tuning the balance of forces acting on them. A T-junction geometry is employed to introduce bubbles into a microchannel and analyze their lateral equilibrium position in a range of Reynolds (1 < Re < 40) and capillary numbers (0.1 < Ca < 1). We find that the Reynolds number (Re), the capillary number (Ca), the diameter of the bubble (D[combining macron]), and the aspect ratio of the channel are the influential parameters in this phenomenon. For instance, at high Re, the flow pushes the bubble towards the wall while large Ca or D[combining macron] moves the bubble towards the center. Moreover, in the shallow channels, having aspect ratios higher than one, the bubble moves towards the narrower sidewalls. One important outcome of this study is that the equilibrium position of bubbles in rectangular channels is different from that of solid particles. The experimental observations are in good agreement with the performed numerical simulations and provide insights into the dynamics of bubbles in laminar flows which can be utilized in the design of flow based multiphase flow reactors.}, }
@article {pmid29505991, year = {2018}, author = {Martínez-Pedrero, F and Tierno, P}, title = {Advances in colloidal manipulation and transport via hydrodynamic interactions.}, journal = {Journal of colloid and interface science}, volume = {519}, number = {}, pages = {296-311}, doi = {10.1016/j.jcis.2018.02.062}, pmid = {29505991}, issn = {1095-7103}, abstract = {In this review article, we highlight many recent advances in the field of micromanipulation of colloidal particles using hydrodynamic interactions (HIs), namely solvent mediated long-range interactions. At the micrsocale, the hydrodynamic laws are time reversible and the flow becomes laminar, features that allow precise manipulation and control of colloidal matter. We focus on different strategies where externally operated microstructures generate local flow fields that induce the advection and motion of the surrounding components. In addition, we review cases where the induced flow gives rise to hydrodynamic bound states that may synchronize during the process, a phenomenon essential in different systems such as those that exhibit self-assembly and swarming.}, }
@article {pmid29497820, year = {2018}, author = {Wang, Q and Othmer, HG}, title = {Analysis of a model microswimmer with applications to blebbing cells and mini-robots.}, journal = {Journal of mathematical biology}, volume = {76}, number = {7}, pages = {1699-1763}, pmid = {29497820}, issn = {1432-1416}, support = {DMS 0817529//National Science Foundation/ ; 1311974//National Science Foundation/ ; DMS1562176//National Science Foundation/ ; R01GM107264//National Institutes of Health/ ; }, mesh = {Animals ; Biophysical Phenomena ; Cell Membrane/physiology ; Cell Movement/*physiology ; Computational Biology ; Computer Simulation ; Humans ; Hydrodynamics ; Mathematical Concepts ; *Models, Biological ; Robotics ; Viscosity ; }, abstract = {Recent research has shown that motile cells can adapt their mode of propulsion depending on the environment in which they find themselves. One mode is swimming by blebbing or other shape changes, and in this paper we analyze a class of models for movement of cells by blebbing and of nano-robots in a viscous fluid at low Reynolds number. At the level of individuals, the shape changes comprise volume exchanges between connected spheres that can control their separation, which are simple enough that significant analytical results can be obtained. Our goal is to understand how the efficiency of movement depends on the amplitude and period of the volume exchanges when the spheres approach closely during a cycle. Previous analyses were predicated on wide separation, and we show that the speed increases significantly as the separation decreases due to the strong hydrodynamic interactions between spheres in close proximity. The scallop theorem asserts that at least two degrees of freedom are needed to produce net motion in a cyclic sequence of shape changes, and we show that these degrees can reside in different swimmers whose collective motion is studied. We also show that different combinations of mode sharing can lead to significant differences in the translation and performance of pairs of swimmers.}, }
@article {pmid32372770, year = {2018}, author = {Chen, H and Yao, M}, title = {A high-flow portable biological aerosol trap (HighBioTrap) for rapid microbial detection.}, journal = {Journal of aerosol science}, volume = {117}, number = {}, pages = {212-223}, pmid = {32372770}, issn = {0021-8502}, abstract = {Bioaerosols exposure can lead to many adverse health effects and even result in death if highly infectious agents involved. Apparently, there is a great need for rapid detection of bioaerosols, for which air sampling often is the first critical step. However, currently available samplers often either require an external power and/or with low sampling flow rate, thus falling short of providing a practical solution when response time is of great concern. Here, we have designed and evaluated a new portable high volume bioaerosol sampler named as HighBioTrap through optimizing its operating parameters. The sampler was operated at a sampling flow rate of 1200 L/min, with an impaction velocity of about 10.2 m/s (S/W = 1.5, T/W = 1), while the weight of the sampler is about 1.9 kg. The performances of the HighBioTrap sampler were tested both in lab controlled and natural environments (outdoor and indoor environments in a university building) along with the reference sampler-the BioStage impactor using aerosolized Polystyrene (PS) uniform microspheres of various sizes, aerosolized bacteria and also ambient air particles. The microbial community structures of collected culturable bacterial aerosol particles both by the HighBioTrap and the BioStage impactor in the natural environments were analyzed using gene sequence method. Experimental results with PS particles showed the HighBioTrap has a cutoff size of ~ 2 µm. The widely used impactor design equation was found to be not applicable for predicting the performance of the HighBioTrap due to its large Reynolds number. When sampling aerosolized individual Pseudomonas fluorescens and Bacillus subtilis bacterial particles, the HighBioTrap had physical collection efficiencies of 10% and 20%, respectively. Despite the higher desiccation effects introduced by higher flow rate, the HighBioTrap was shown to obtain a higher microbial diversity than the BioStage impactor for both in outdoor and indoor environments given the same sampling time (p < 0.01). Our data also showed that most of the desiccation effects might have occurred between 3 and 5 min of the sampling and an impaction velocity of around 10 m/s might be a close-to-optimal impaction velocity for collecting most environmental bacterial aerosols while maximally preserving their culturability. This work contributes to our understanding of microbial sampling stress (impaction velocity and sampling time), while developing a portable high volume sampler. The HighBioTrap sampler could find its great efficiencies in qualitative microbial aerosol detection and analysis, such as investigation of microbial aerosol diversity for a particular environment, or when the low level of pathogens is present and detection time is of great concern.}, }
@article {pmid29487930, year = {2018}, author = {Bao, L and Spandan, V and Yang, Y and Dyett, B and Verzicco, R and Lohse, D and Zhang, X}, title = {Flow-induced dissolution of femtoliter surface droplet arrays.}, journal = {Lab on a chip}, volume = {18}, number = {7}, pages = {1066-1074}, doi = {10.1039/c7lc01321c}, pmid = {29487930}, issn = {1473-0189}, abstract = {The dissolution of liquid nanodroplets is a crucial step in many applied processes, such as separation and dispersion in the food industry, crystal formation of pharmaceutical products, concentrating and analysis in medical diagnosis, and drug delivery in aerosols. In this work, using both experiments and numerical simulations, we quantitatively study the dissolution dynamics of femtoliter surface droplets in a highly ordered array under a uniform flow. Our results show that the dissolution of femtoliter droplets strongly depends on their spatial positions relative to the flow direction, drop-to-drop spacing in the array, and the imposed flow rate. In some particular cases, the droplet at the edge of the array can dissolve about 30% faster than the ones located near the centre. The dissolution rate of the droplet increases by 60% as the inter-droplet spacing is increased from 2.5 μm to 20 μm. Moreover, the droplets close to the front of the flow commence to shrink earlier than those droplets in the center of the array. The average dissolution rate is faster for the faster flow. As a result, the dissolution time (Ti) decreases with the Reynolds number (Re) of the flow as Ti ∝ Re-3/4. The experimental results are in good agreement with the numerical simulations where the advection-diffusion equation for the concentration field is solved and the concentration gradient on the surface of the drop is computed. The findings suggest potential approaches to manipulate nanodroplet sizes in droplet arrays simply by dissolution controlled by an external flow. The obtained droplets with varying curvatures may serve as templates for generating multifocal microlenses in one array.}, }
@article {pmid29481162, year = {2018}, author = {Nissan, A and Berkowitz, B}, title = {Inertial Effects on Flow and Transport in Heterogeneous Porous Media.}, journal = {Physical review letters}, volume = {120}, number = {5}, pages = {054504}, doi = {10.1103/PhysRevLett.120.054504}, pmid = {29481162}, issn = {1079-7114}, abstract = {We investigate the effects of high fluid velocities on flow and tracer transport in heterogeneous porous media. We simulate fluid flow and advective transport through two-dimensional pore-scale matrices with varying structural complexity. As the Reynolds number increases, the flow regime transitions from linear to nonlinear; this behavior is controlled by the medium structure, where higher complexity amplifies inertial effects. The result is, nonintuitively, increased homogenization of the flow field, which leads in the context of conservative chemical transport to less anomalous behavior. We quantify the transport patterns via a continuous time random walk, using the spatial distribution of the kinetic energy within the fluid as a characteristic measure.}, }
@article {pmid29481155, year = {2018}, author = {Cerbus, RT and Liu, CC and Gioia, G and Chakraborty, P}, title = {Laws of Resistance in Transitional Pipe Flows.}, journal = {Physical review letters}, volume = {120}, number = {5}, pages = {054502}, doi = {10.1103/PhysRevLett.120.054502}, pmid = {29481155}, issn = {1079-7114}, abstract = {As everyone knows who has opened a kitchen faucet, pipe flow is laminar at low flow velocities and turbulent at high flow velocities. At intermediate velocities, there is a transition wherein plugs of laminar flow alternate along the pipe with "flashes" of a type of fluctuating, nonlaminar flow that remains poorly understood. In the 19th century, Osborne Reynolds sought to connect these states of flow with quantitative "laws of resistance," whereby the fluid friction is determined as a function of the Reynolds number. While he succeeded for laminar and turbulent flows, the laws for transitional flows eluded him and remain unknown to this day. By properly distinguishing between laminar plugs and flashes in the transitional regime, we show experimentally and numerically that the law of resistance for laminar plugs corresponds to the laminar law and the law of resistance for flashes is identical to that of turbulence.}, }
@article {pmid29480329, year = {2018}, author = {Wu, H and de León, MAP and Othmer, HG}, title = {Getting in shape and swimming: the role of cortical forces and membrane heterogeneity in eukaryotic cells.}, journal = {Journal of mathematical biology}, volume = {77}, number = {3}, pages = {595-626}, pmid = {29480329}, issn = {1432-1416}, support = {R01 GM029123/GM/NIGMS NIH HHS/United States ; U54 CA210190/CA/NCI NIH HHS/United States ; 1311974//National Science Foundation/International ; #54-CA-210190/NH/NIH HHS/United States ; DMS 0817529//National Science Foundation/International ; }, mesh = {Algorithms ; Animals ; Biophysical Phenomena ; Cell Membrane/physiology ; Cell Movement/*physiology ; Cell Polarity/physiology ; Cell Shape/*physiology ; Cellular Microenvironment/physiology ; Computer Simulation ; Eukaryotic Cells/physiology ; Extracellular Matrix/physiology ; Humans ; Mathematical Concepts ; *Models, Biological ; }, abstract = {Recent research has shown that motile cells can adapt their mode of propulsion to the mechanical properties of the environment in which they find themselves-crawling in some environments while swimming in others. The latter can involve movement by blebbing or other cyclic shape changes, and both highly-simplified and more realistic models of these modes have been studied previously. Herein we study swimming that is driven by membrane tension gradients that arise from flows in the actin cortex underlying the membrane, and does not involve imposed cyclic shape changes. Such gradients can lead to a number of different characteristic cell shapes, and our first objective is to understand how different distributions of membrane tension influence the shape of cells in an inviscid quiescent fluid. We then analyze the effects of spatial variation in other membrane properties, and how they interact with tension gradients to determine the shape. We also study the effect of fluid-cell interactions and show how tension leads to cell movement, how the balance between tension gradients and a variable bending modulus determine the shape and direction of movement, and how the efficiency of movement depends on the properties of the fluid and the distribution of tension and bending modulus in the membrane.}, }
@article {pmid29466251, year = {2018}, author = {Arranz, G and Moriche, M and Uhlmann, M and Flores, O and García-Villalba, M}, title = {Kinematics and dynamics of the auto-rotation of a model winged seed.}, journal = {Bioinspiration &amp; biomimetics}, volume = {13}, number = {3}, pages = {036011}, doi = {10.1088/1748-3190/aab144}, pmid = {29466251}, issn = {1748-3190}, mesh = {Biomechanical Phenomena ; Biomimetics ; Computer Simulation ; *Models, Biological ; Motion ; Rotation ; Seeds/*anatomy &amp; histology/*physiology ; Wind ; }, abstract = {Numerical simulations of the auto-rotation of a model winged seed are presented. The calculations are performed by solving simultaneously the Navier-Stokes equations for the flow surrounding the seed and the rigid-body equations for the motion of the seed. The Reynolds number based on the descent speed and a characteristic chord length is varied in the range 80-240. Within this range, the seed attains an asymptotic state with finite amplitude auto-rotation, while for smaller values of the Reynolds number no auto-rotation is observed. The motion of the seed is characterized by the coning and pitch angles, the angular velocity and the horizontal translation of the seed. The values obtained for these quantities are qualitatively similar to those reported in the literature in experiments with real winged seeds. When increasing the Reynolds number, the seed tends to rotate at higher speeds, with less inclination with respect to the horizontal plane, and with a larger translation velocity. With respect to the aerodynamic forces, it is observed that, with increasing Reynolds number, the horizontal components decrease in magnitude while the vertical component increases. The force distribution along the wing span is characterized using both global and local characteristic speeds and chord lengths for the non-dimensionalisation of the force coefficients. It is found that the vertical component does not depend on the Reynolds number when using local scaling, while the chordwise component of the force does.}, }
@article {pmid29462624, year = {2018}, author = {Ishimoto, K and Gadêlha, H and Gaffney, EA and Smith, DJ and Kirkman-Brown, J}, title = {Human sperm swimming in a high viscosity mucus analogue.}, journal = {Journal of theoretical biology}, volume = {446}, number = {}, pages = {1-10}, doi = {10.1016/j.jtbi.2018.02.013}, pmid = {29462624}, issn = {1095-8541}, support = {HCS SCL-2014-05-001/DH_/Department of Health/United Kingdom ; }, mesh = {Humans ; Male ; *Models, Biological ; Mucus/metabolism ; Sperm Motility/*physiology ; Spermatozoa/cytology/*physiology ; }, abstract = {Remarkably, mammalian sperm maintain a substantive proportion of their progressive swimming speed within highly viscous fluids, including those of the female reproductive tract. Here, we analyse the digital microscopy of a human sperm swimming in a highly viscous, weakly elastic mucus analogue. We exploit principal component analysis to simplify its flagellar beat pattern, from which boundary element calculations are used to determine the time-dependent flow field around the sperm cell. The sperm flow field is further approximated in terms of regularised point forces, and estimates of the mechanical power consumption are determined, for comparison with analogous low viscosity media studies. This highlights extensive differences in the structure of the flows surrounding human sperm in different media, indicating how the cell-cell and cell-boundary hydrodynamic interactions significantly differ with the physical microenvironment. The regularised point force decomposition also provides cell-level information that may ultimately be incorporated into sperm population models. We further observe indications that the core feature in explaining the effectiveness of sperm swimming in high viscosity media is the loss of cell yawing, which is related with a greater density of regularised point force singularities along the axis of symmetry of the flagellar beat to represent the flow field. In turn this implicates a reduction of the wavelength of the distal beat pattern - and hence dynamical wavelength selection of the flagellar beat - as the dominant feature governing the effectiveness of sperm swimming in highly viscous media.}, }
@article {pmid29454239, year = {2018}, author = {Ren, LF and Adeel, M and Li, J and Xu, C and Xu, Z and Zhang, X and Shao, J and He, Y}, title = {Phenol separation from phenol-laden saline wastewater by membrane aromatic recovery system-like membrane contactor using superhydrophobic/organophilic electrospun PDMS/PMMA membrane.}, journal = {Water research}, volume = {135}, number = {}, pages = {31-43}, doi = {10.1016/j.watres.2018.02.011}, pmid = {29454239}, issn = {1879-2448}, mesh = {Dimethylpolysiloxanes/chemistry ; Equipment Design ; *Membranes, Artificial ; Methacrylates/chemistry ; Phenol/*isolation &amp; purification ; Polymethyl Methacrylate/chemistry ; Sodium Chloride ; Waste Disposal, Fluid/instrumentation/*methods ; Wastewater/chemistry ; Water Pollutants, Chemical/*isolation &amp; purification ; Water Purification/instrumentation/methods ; }, abstract = {Phenol recovery from phenol-laden saline wastewater plays an important role in the waste reclamation and pollution control. A membrane aromatic recovery system-like membrane contactor (MARS-like membrane contactor) was set up in this study using electrospun polydimethylsiloxane/polymethyl methacrylate (PDMS/PMMA) membrane with 0.0048 m[2] effective area to separate phenol from saline wastewater. Phenol and water contact angles of 0° and 162° were achieved on this membrane surface simultaneously, indicating its potential in the separation of phenol and water-soluble salt. Feed solution (500 mL) of 0.90 L/h and receiving solution (500 mL) of 1.26 L/h were investigated to be the optimum conditions for phenol separation, which corresponds to the employed Reynolds number of 14.6 and 20.5. During 108-h continuous separation for feed solution (2.0 g/L phenol, 10.0 g/L NaCl) under room temperature (20 °C), 42.6% of phenol was recycled in receiving solution with a salt rejection of 99.95%. Meanwhile, the mean phenol mass transfer coefficient (Kov) was 6.7 × 10[-7] m s[-1]. As a membrane-based process, though the permeated phenol increased with the increase of phenol concentration in feed solution, the phenol recovery ratio was determined by the membrane properties rather than the pollutant concentrations. Phenol was found to permeate this membrane via adsorption, diffusion and desorption, and therefore, the membrane fouling generated from pore blockage in other membrane separation processes was totally avoided.}, }
@article {pmid29448779, year = {2018}, author = {Fang, C and Wu, X and Yang, F and Qiao, R}, title = {Flow of quasi-two dimensional water in graphene channels.}, journal = {The Journal of chemical physics}, volume = {148}, number = {6}, pages = {064702}, doi = {10.1063/1.5017491}, pmid = {29448779}, issn = {1089-7690}, abstract = {When liquids confined in slit channels approach a monolayer, they become two-dimensional (2D) fluids. Using molecular dynamics simulations, we study the flow of quasi-2D water confined in slit channels featuring pristine graphene walls and graphene walls with hydroxyl groups. We focus on to what extent the flow of quasi-2D water can be described using classical hydrodynamics and what are the effective transport properties of the water and the channel. First, the in-plane shearing of quasi-2D water confined between pristine graphene can be described using the classical hydrodynamic equation, and the viscosity of the water is ∼50% higher than that of the bulk water in the channel studied here. Second, the flow of quasi-2D water around a single hydroxyl group is perturbed at a position of tens of cluster radius from its center, as expected for low Reynolds number flows. Even though water is not pinned at the edge of the hydroxyl group, the hydroxyl group screens the flow greatly, with a single, isolated hydroxyl group rendering drag similar to ∼90 nm[2] pristine graphene walls. Finally, the flow of quasi-2D water through graphene channels featuring randomly distributed hydroxyl groups resembles the fluid flow through porous media. The effective friction factor of the channel increases linearly with the hydroxyl groups' area density up to 0.5 nm[-2] but increases nonlinearly at higher densities. The effective friction factor of the channel can be fitted to a modified Carman equation at least up to a hydroxyl area density of 2.0 nm[-2]. These findings help understand the liquid transport in 2D material-based nanochannels for applications including desalination.}, }
@article {pmid29445037, year = {2018}, author = {Godoy-Diana, R and Thiria, B}, title = {On the diverse roles of fluid dynamic drag in animal swimming and flying.}, journal = {Journal of the Royal Society, Interface}, volume = {15}, number = {139}, pages = {}, pmid = {29445037}, issn = {1742-5662}, mesh = {Animals ; Biomechanical Phenomena ; *Hydrodynamics ; *Models, Biological ; Swimming/*physiology ; }, abstract = {Questions of energy dissipation or friction appear immediately when addressing the problem of a body moving in a fluid. For the most simple problems, involving a constant steady propulsive force on the body, a straightforward relation can be established balancing this driving force with a skin friction or form drag, depending on the Reynolds number and body geometry. This elementary relation closes the full dynamical problem and sets, for instance, average cruising velocity or energy cost. In the case of finite-sized and time-deformable bodies though, such as flapping flyers or undulatory swimmers, the comprehension of driving/dissipation interactions is not straightforward. The intrinsic unsteadiness of the flapping and deforming animal bodies complicates the usual application of classical fluid dynamic forces balance. One of the complications is because the shape of the body is indeed changing in time, accelerating and decelerating perpetually, but also because the role of drag (more specifically the role of the local drag) has two different facets, contributing at the same time to global dissipation and to driving forces. This causes situations where a strong drag is not necessarily equivalent to inefficient systems. A lot of living systems are precisely using strong sources of drag to optimize their performance. In addition to revisiting classical results under the light of recent research on these questions, we discuss in this review the crucial role of drag from another point of view that concerns the fluid-structure interaction problem of animal locomotion. We consider, in particular, the dynamic subtleties brought by the quadratic drag that resists transverse motions of a flexible body or appendage performing complex kinematics, such as the phase dynamics of a flexible flapping wing, the propagative nature of the bending wave in undulatory swimmers, or the surprising relevance of drag-based resistive thrust in inertial swimmers.}, }
@article {pmid29435817, year = {2018}, author = {Walait, A and Siddiqui, AM and Rana, MA}, title = {Analysis of a self-propelling sheet with heat transfer through non-isothermal fluid in an inclined human cervical canal.}, journal = {Journal of biological physics}, volume = {44}, number = {3}, pages = {273-300}, pmid = {29435817}, issn = {1573-0689}, mesh = {*Biophysical Phenomena ; *Cervical Vertebrae ; Computer Simulation ; *Hot Temperature ; Humans ; *Models, Theoretical ; *Numerical Analysis, Computer-Assisted ; Pressure ; *Rheology ; }, abstract = {The present theoretical analysis deals with biomechanics of the self-propulsion of a swimming sheet with heat transfer through non-isothermal fluid filling an inclined human cervical canal. Partial differential equations arising from the mathematical modeling of the proposed model are solved analytically. Flow variables like pressure gradient, propulsive velocity, fluid velocity, time mean flow rate, fluid temperature, and heat-transfer coefficients are analyzed for the pertinent parameters. Striking features of the pumping characteristics are explored. Propulsive velocity of the swimming sheet becomes faster for lower Froude number, higher Reynolds number, and for a vertical channel. Temperature and peak value of the heat-transfer coefficients below the swimming sheet showed an increase by the increment of Brinkmann number, inclination, pressure difference over wavelength, and Reynolds number whereas these quantities decrease with increasing Froude number. Aforesaid parameters have shown opposite effects on the peak value of the heat-transfer coefficients below and above the swimming sheet. Relevance of the current results to the spermatozoa transport with heat transfer through non-isothermal cervical mucus filling an inclined human cervical canal is also explored.}, }
@article {pmid29429719, year = {2018}, author = {Dehbani, M and Rahimi, M}, title = {Introducing ultrasonic falling film evaporator for moderate temperature evaporation enhancement.}, journal = {Ultrasonics sonochemistry}, volume = {42}, number = {}, pages = {689-696}, doi = {10.1016/j.ultsonch.2017.12.016}, pmid = {29429719}, issn = {1873-2828}, abstract = {In the present study, Ultrasonic Falling Film (USFF), as a novel technique has been proposed to increase the evaporation rate of moderate temperature liquid film. It is a proper method for some applications which cannot be performed at high temperature, such as foodstuff industry, due to their sensitivity to high temperatures. Evaporation rate of sodium chloride solution from an USFF on an inclined flat plate compared to that for Falling Film without ultrasonic irradiation (FF) at various temperatures was investigated. The results revealed that produced cavitation bubbles have different effects on evaporation rate at different temperatures. At lower temperatures, size fluctuation and collapse of bubbles and in consequence induced physical effects of cavitation bubbles resulted in more turbulency and evaporation rate enhancement. At higher temperatures, the behavior was different. Numerous created bubbles joined together and cover the plate surface, so not only decreased the ultrasound vibrations but also reduced the evaporation rate in comparison with FF. The highest evaporation rate enhancement of 353% was obtained at 40 °C at the lowest Reynolds number of 250. In addition, the results reveal that at temperature of 40 °C, USFF has the highest efficiency compared to FF.}, }
@article {pmid29420569, year = {2018}, author = {Tang, H and Xu, L and Hu, F}, title = {Hydrodynamic characteristics of knotted and knotless purse seine netting panels as determined in a flume tank.}, journal = {PloS one}, volume = {13}, number = {2}, pages = {e0192206}, doi = {10.1371/journal.pone.0192206}, pmid = {29420569}, issn = {1932-6203}, mesh = {*Hydrodynamics ; Models, Theoretical ; *Nylons ; }, abstract = {Nylon (PA) netting is widely used in purse seines and other fishing gears due to its high strength and good sinking performance. However, hydrodynamic properties of nylon netting of different characteristics are poorly understood. This study investigated hydrodynamic characteristics of nylon netting of different knot types and solidity ratios under different attack angles and flow velocities. It was found that the hydrodynamic coefficient of netting panels was related to Reynolds number, solidity ratio, attack angle, knot type and twine construction. The solidity ratio was found to positively correlate with drag coefficient when the netting was normal to the flow (CD90), but not the case when the netting was parallel to the flow (CD0). For netting panels inclined to the flow, the inclined drag coefficient had a negative relationship with the solidity ratio for attack angles between 0° and 50°, but a positive relationship for attack angles between 50° and 90°. The lift coefficient increased with the attack angle, reaching the culminating point at an attack angle of 50°, before subsequent decline. We found that the drag generated by knot accounted for 15-25% of total drag, and the knotted netting with higher solidity ratio exhibited a greater CD0, but it was not the case for the knotless netting. Compared to knotless polyethylene (PE) netting, the drag coefficients of knotless PA netting were dominant at higher Reynolds number (Re>2200).}, }
@article {pmid29407276, year = {2018}, author = {Mojahed, A and Rajabi, M}, title = {Self-motile swimmers: Ultrasound driven spherical model.}, journal = {Ultrasonics}, volume = {86}, number = {}, pages = {1-5}, doi = {10.1016/j.ultras.2018.01.006}, pmid = {29407276}, issn = {1874-9968}, abstract = {The concept of ultrasound acoustic driven self-motile swimmers which is the source of autonomous propulsion is the acoustic field generated by the swimmer due to the partial oscillation of its surface is investigated. Limiting the subject to a body with simple spherical geometry, it is analytically shown that the generated acoustic radiation force due to induction by asymmetric acoustic field in host medium is non-zero, which propels the device. Assuming low Reynolds number condition, the frequency-dependent swimming velocity is calculated as a function of design parameters and optimum operating condition is obtained. The proposed methodology will open a new path towards the micro- or molecular-sized self propulsive machines or mechanism with great applications in engineering, medicine and biology.}, }
@article {pmid29404782, year = {2018}, author = {Huang, JJ and Wu, J and Huang, H}, title = {An alternative method to implement contact angle boundary condition and its application in hybrid lattice-Boltzmann finite-difference simulations of two-phase flows with immersed surfaces.}, journal = {The European physical journal. E, Soft matter}, volume = {41}, number = {2}, pages = {17}, pmid = {29404782}, issn = {1292-895X}, abstract = {We propose an alternative method to implement the contact angle boundary condition on a solid wall and apply it in hybrid lattice-Boltzmann finite-difference simulations of two-phase flows with immersed surfaces in which the flow equations are solved by the lattice-Boltzmann method and the interface equations are solved by the finite-difference method. Using the hyperbolic tangent profile of the order parameter across an interface in phase-field theory, we were able to obtain its unknown value at a ghost point from the information at only one point in the fluid domain. This is in contrast with existing approaches relying on interpolations involving several points. The special feature allows it to be more easily implemented on immersed surfaces cutting through the grid lines. It was properly incorporated into the framework of the hybrid lattice-Boltzmann finite-difference simulation, and applied successfully for several problems with different levels of complexity. First, the equilibrium shapes of a droplet on a sphere with different contact angles and radii were studied under cylindrical geometry and a good agreement with theoretical predictions was found. Preliminary studies on a three-dimensional droplet spreading on a sphere were also performed and the results agreed well with the corresponding axisymmetric results. Second, the spreading of a two-dimensional drop on an embedded inclined wall with a given contact angle was investigated and the results matched those on a flat wall at the domain boundary under the same condition. Third, capillary filling in a cylindrical tube was studied and the speed of the interface in the tube was found to follow Washburn's law. Fourth, a droplet impacting on a sphere was investigated and several different outcomes were captured depending on the Reynolds number, the viscosity ratio, and the wettability and radius of the sphere. Finally, the proposed method was shown to be capable of studying even more complicated problems involving the interaction between a droplet and multiple objects of different sizes and contact angles.}, }
@article {pmid29395261, year = {2018}, author = {Mehrabian, S and Letendre, F and Cameron, CB}, title = {The mechanisms of filter feeding on oil droplets: Theoretical considerations.}, journal = {Marine environmental research}, volume = {135}, number = {}, pages = {29-42}, doi = {10.1016/j.marenvres.2018.01.006}, pmid = {29395261}, issn = {1879-0291}, mesh = {Animals ; *Feeding Behavior ; Filtration ; Hydrocarbons ; Models, Theoretical ; Water ; }, abstract = {Filter feeding animals capture food particles and oil droplets from the fluid environment using cilia or appendages composed of arrays of fibers. Here we review the theoretical models that have provided a foundation for observations on the efficiency of particle capture. We then provide the mathematical theoretical framework to characterize the efficient filtration of oil droplets. In the aquatic and marine environments oil droplets are released from the decay of organisms or as hydrocarbons. Droplet size and flow velocity, oil-to-water viscosity ratio, oil-water interfacial tension, oil and water density difference, and the surface wettability, or surface texture, of the filter fiber are the key parameters for oil droplet capture. Following capture, capillary force maintains the droplet at its location due to the oil-water interfacial tension. If the oil-coated fiber is subject to any external force such as viscous or gravitational forces, it may deform and separate from the fiber and re-enter the fluid stream. We show oil droplet capture in Daphnia and the barnacle Balanus glandula, and outline some of the ecological unknowns regarding oil capture in the oceans. Awareness of these mechanisms and their interrelationships will provide a foundation for investigations into the efficiency of various modes of filter feeding on oil droplets.}, }
@article {pmid29390777, year = {2018}, author = {Karthik, K and Vengadesan, S and Bhattacharyya, SK}, title = {Prediction of flow induced sound generated by cross flow past finite length circular cylinders.}, journal = {The Journal of the Acoustical Society of America}, volume = {143}, number = {1}, pages = {260}, doi = {10.1121/1.5021243}, pmid = {29390777}, issn = {1520-8524}, abstract = {The paper presents aeroacoustic results for the flow around finite-length circular cylinders at Reynolds number 84 770 for various length-to-diameter (L/D) ratios (= 3, 9, 20, 25, 30, and 35). The incompressible Navier-Stokes equations are solved using the large eddy simulation model of turbulence followed by acoustic predictions in the far field using Ffwocs Williams and Hawkings method. The comparisons of numerical and anechoic wind tunnel measurements show good agreement in terms of the aerodynamic forces and acoustic parameters such as tonal frequency, tonal sound pressure level, and overall sound pressure level. The cylinder L/D ratio was observed to be a significant parameter that controls vortex shedding and consequently the flow induced sound generation.}, }
@article {pmid29390714, year = {2018}, author = {Mastracci, B and Guo, W}, title = {An apparatus for generation and quantitative measurement of homogeneous isotropic turbulence in He ii.}, journal = {The Review of scientific instruments}, volume = {89}, number = {1}, pages = {015107}, doi = {10.1063/1.4997735}, pmid = {29390714}, issn = {1089-7623}, abstract = {The superfluid phase of helium-4, known as He ii, exhibits extremely small kinematic viscosity and may be a useful tool for economically producing and studying high Reynolds number turbulent flow. Such applications are not currently possible because a comprehensive understanding of the complex two-fluid behavior of He ii is lacking. This situation could be remedied by a systematic investigation of simple, well controlled turbulence that can be directly compared with theoretical models. To this end, we have developed a new apparatus that combines flow visualization with second sound attenuation to study turbulence in the wake of a mesh grid towed through a He ii filled channel. One of three mesh grids (mesh number M = 3, 3.75, or 5 mm) can be pulled at speeds between 0.1 and 60 cm/s through a cast acrylic flow channel which has a 16 mm × 16 mm cross section and measures 330 mm long. The motion of solidified deuterium tracer particles, with diameter of the order 1 μm, in the resulting flow is captured by a high speed camera, and a particle tracking velocimetry algorithm resolves the Lagrangian particle trajectories through the turbulent flow field. A pair of oscillating superleak second sound transducers installed in the channel allows complementary measurement of vortex line density in the superfluid throughout the turbulent decay process. Success in early experiments demonstrates the effectiveness of both probes, and preliminary analysis of the data shows that both measurements strongly correlate with each other. Further investigations will provide comprehensive information that can be used to address open questions about turbulence in He ii and move toward the application of this fluid to high Reynolds number fluid research.}, }
@article {pmid29390681, year = {2018}, author = {Sajjadi, S and Buelna, X and Eloranta, J}, title = {Application of time-resolved shadowgraph imaging and computer analysis to study micrometer-scale response of superfluid helium.}, journal = {The Review of scientific instruments}, volume = {89}, number = {1}, pages = {013102}, doi = {10.1063/1.5002564}, pmid = {29390681}, issn = {1089-7623}, abstract = {Application of inexpensive light emitting diodes as backlight sources for time-resolved shadowgraph imaging is demonstrated. The two light sources tested are able to produce light pulse sequences in the nanosecond and microsecond time regimes. After determining their time response characteristics, the diodes were applied to study the gas bubble formation around laser-heated copper nanoparticles in superfluid helium at 1.7 K and to determine the local cavitation bubble dynamics around fast moving metal micro-particles in the liquid. A convolutional neural network algorithm for analyzing the shadowgraph images by a computer is presented and the method is validated against the results from manual image analysis. The second application employed the red-green-blue light emitting diode source that produces light pulse sequences of the individual colors such that three separate shadowgraph frames can be recorded onto the color pixels of a charge-coupled device camera. Such an image sequence can be used to determine the moving object geometry, local velocity, and acceleration/deceleration. These data can be used to calculate, for example, the instantaneous Reynolds number for the liquid flow around the particle. Although specifically demonstrated for superfluid helium, the technique can be used to study the dynamic response of any medium that exhibits spatial variations in the index of refraction.}, }
@article {pmid29388556, year = {2018}, author = {Lynch, M and Mandadzhiev, B and Wissa, A}, title = {Bioinspired wingtip devices: a pathway to improve aerodynamic performance during low Reynolds number flight.}, journal = {Bioinspiration &amp; biomimetics}, volume = {13}, number = {3}, pages = {036003}, doi = {10.1088/1748-3190/aaac53}, pmid = {29388556}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; Biomimetic Materials ; *Biomimetics ; Computer Simulation ; Feathers/anatomy &amp; histology/physiology ; Flight, Animal/*physiology ; Hawks/anatomy &amp; histology/physiology ; Models, Anatomic ; *Models, Biological ; Wings, Animal/anatomy &amp; histology/*physiology ; }, abstract = {Birds are highly capable and maneuverable fliers, traits not currently shared with current small unmanned aerial vehicles. They are able to achieve these flight capabilities by adapting the shape of their wings during flight in a variety of complex manners. One feature of bird wings, the primary feathers, separate to form wingtip gaps at the distal end of the wing. This paper presents bio-inspired wingtip devices with varying wingtip gap sizes, defined as the chordwise distance between wingtip devices, for operation in low Reynolds number conditions of Re = 100 000, where many bird species operate. Lift and drag data was measured for planar and nonplanar wingtip devices with the total wingtip gap size ranging from 0% to 40% of the wing's mean chord. For a planar wing with a gap size of 20%, the mean coefficient of lift in the pre-stall region is increased by 7.25%, and the maximum coefficient of lift is increased by 5.6% compared to a configuration with no gaps. The nonplanar wingtip device was shown to reduce the induced drag. The effect of wingtip gap sizes is shown to be independent of the planarity/nonplanarity of the wingtip device, thereby allowing designers to decouple the wingtip parameters to tune the desired lift and drag produced.}, }
@article {pmid29377529, year = {2018}, author = {Lee, J and Burns, MA}, title = {One-Way Particle Transport Using Oscillatory Flow in Asymmetric Traps.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {14}, number = {9}, pages = {}, pmid = {29377529}, issn = {1613-6829}, support = {R01 HG004653/HG/NHGRI NIH HHS/United States ; R21 HG005077/HG/NHGRI NIH HHS/United States ; }, mesh = {Lab-On-A-Chip Devices ; Microfluidic Analytical Techniques/*methods ; Particle Size ; }, abstract = {One challenge of integrating of passive, microparticles manipulation techniques into multifunctional microfluidic devices is coupling the continuous-flow format of most systems with the often batch-type operation of particle separation systems. Here, a passive fluidic technique-one-way particle transport-that can conduct microparticle operations in a closed fluidic circuit is presented. Exploiting pass/capture interactions between microparticles and asymmetric traps, this technique accomplishes a net displacement of particles in an oscillatory flow field. One-way particle transport is achieved through four kinds of trap-particle interactions: mechanical capture of the particle, asymmetric interactions between the trap and the particle, physical collision of the particle with an obstacle, and lateral shift of the particle into a particle-trapping stream. The critical dimensions for those four conditions are found by numerically solving analytical mass balance equations formulated using the characteristics of the flow field in periodic obstacle arrays. Visual observation of experimental trap-particle dynamics in low Reynolds number flow (<0.01) confirms the validity of the theoretical predictions. This technique can transport hundreds of microparticles across trap rows in only a few fluid oscillations (<500 ms per oscillation) and separate particles by their size differences.}, }
@article {pmid29376688, year = {2018}, author = {Berera, A and Ho, RDJG}, title = {Chaotic Properties of a Turbulent Isotropic Fluid.}, journal = {Physical review letters}, volume = {120}, number = {2}, pages = {024101}, doi = {10.1103/PhysRevLett.120.024101}, pmid = {29376688}, issn = {1079-7114}, abstract = {By tracking the divergence of two initially close trajectories in phase space in an Eulerian approach to forced turbulence, the relation between the maximal Lyapunov exponent λ and the Reynolds number Re is measured using direct numerical simulations, performed on up to 2048^{3} collocation points. The Lyapunov exponent is found to solely depend on the Reynolds number with λ∝Re^{0.53} and that after a transient period the divergence of trajectories grows at the same rate at all scales. Finally a linear divergence is seen that is dependent on the energy forcing rate. Links are made with other chaotic systems.}, }
@article {pmid29376342, year = {2018}, author = {Lee, D and Nam, SM and Kim, JA and Di Carlo, D and Lee, W}, title = {Active Control of Inertial Focusing Positions and Particle Separations Enabled by Velocity Profile Tuning with Coflow Systems.}, journal = {Analytical chemistry}, volume = {90}, number = {4}, pages = {2902-2911}, doi = {10.1021/acs.analchem.7b05143}, pmid = {29376342}, issn = {1520-6882}, abstract = {Inertial microfluidics has drawn much attention not only for its diverse applications but also for counterintuitive new fluid dynamic behaviors. Inertial focusing positions are determined by two lift forces, that is, shear gradient and wall-induced lift forces, that are generally known to be opposite in direction in the flow through a channel. However, the direction of shear gradient lift force can be reversed if velocity profiles are shaped properly. We used coflows of two liquids with different viscosities to produce complex velocity profiles that lead to inflection point focusing and alteration of inertial focusing positions; the number and the locations of focusing positions could be actively controlled by tuning flow rates and viscosities of the liquids. Interestingly, 3-inlet coflow systems showed focusing mode switching between inflection point focusing and channel face focusing depending on Reynolds number and particle size. The focusing mode switching occurred at a specific size threshold, which was easily adjustable with the viscosity ratio of the coflows. This property led to different-sized particles focusing at completely different focusing positions and resulted in highly efficient particle separation of which the separation threshold was tunable. Passive separation techniques, including inertial microfluidics, generally have a limitation in the control of separation parameters. Coflow systems can provide a simple and versatile platform for active tuning of velocity profiles and subsequent inertial focusing characteristics, which was demonstrated by active control of the focusing mode using viscosity ratio tuning and temperature changes of the coflows.}, }
@article {pmid29372888, year = {2018}, author = {Fu, J and Liu, X and Shyy, W and Qiu, H}, title = {Effects of flexibility and aspect ratio on the aerodynamic performance of flapping wings.}, journal = {Bioinspiration &amp; biomimetics}, volume = {13}, number = {3}, pages = {036001}, doi = {10.1088/1748-3190/aaaac1}, pmid = {29372888}, issn = {1748-3190}, mesh = {Animals ; Biological Mimicry ; Biomechanical Phenomena ; Compliance/physiology ; Computer Simulation ; Flight, Animal/*physiology ; Insecta/anatomy &amp; histology/physiology ; *Models, Biological ; Wings, Animal/anatomy &amp; histology/*physiology ; }, abstract = {In the current study, we experimentally investigated the flexibility effects on the aerodynamic performance of flapping wings and the correlation with aspect ratio at angle of attack α = 45°. The Reynolds number based on the chord length and the wing tip velocity is maintained at Re = 5.3 × 10[3]. Our result for compliant wings with an aspect ratio of 4 shows that wing flexibility can offer improved aerodynamic performance compared to that of a rigid wing. Flexible wings are found to offer higher lift-to-drag ratios; in particular, there is significant reduction in drag with little compromise in lift. The mechanism of the flexibility effects on the aerodynamic performance is addressed by quantifying the aerodynamic lift and drag forces, the transverse displacement on the wings and the flow field around the wings. The regime of the effective stiffness that offers improved aerodynamic performance is quantified in a range of about 0.5-10 and it matches the stiffness of insect wings with similar aspect ratios. Furthermore, we find that the aspect ratio of the wing is the predominant parameter determining the flexibility effects of compliant wings. Compliant wings with an aspect ratio of two do not demonstrate improved performance compared to their rigid counterparts throughout the entire stiffness regime investigated. The correlation between wing flexibility effects and the aspect ratio is supported by the stiffness of real insect wings.}, }
@article {pmid29367420, year = {2018}, author = {Bocanegra Evans, H and Hamed, AM and Gorumlu, S and Doosttalab, A and Aksak, B and Chamorro, LP and Castillo, L}, title = {Engineered bio-inspired coating for passive flow control.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {115}, number = {6}, pages = {1210-1214}, pmid = {29367420}, issn = {1091-6490}, abstract = {Flow separation and vortex shedding are some of the most common phenomena experienced by bluff bodies under relative motion with the surrounding medium. They often result in a recirculation bubble in regions with adverse pressure gradient, which typically reduces efficiency in vehicles and increases loading on structures. Here, the ability of an engineered coating to manipulate the large-scale recirculation region was tested in a separated flow at moderate momentum thickness Reynolds number, [Formula: see text] We show that the coating, composed of uniformly distributed cylindrical pillars with diverging tips, successfully reduces the size of, and shifts downstream, the separation bubble. Despite the so-called roughness parameter, [Formula: see text], falling within the hydrodynamic smooth regime, the coating is able to modulate the large-scale recirculating motion. Remarkably, this modulation does not induce noticeable changes in the near-wall turbulence levels. Supported with experimental data and theoretical arguments based on the averaged equations of motion, we suggest that the inherent mechanism responsible for the bubble modulation is essentially unsteady suction and blowing controlled by the increasing cross-section of the tips. The coating can be easily fabricated and installed and works under dry and wet conditions, increasing its potential impact on a diverse range of applications.}, }
@article {pmid29347793, year = {2017}, author = {Zhao, Y and Tao, J and Xiong, X}, title = {Instabilities of an annulus flow between rotating cylinders in a helical magnetic field.}, journal = {Physical review. E}, volume = {96}, number = {5-1}, pages = {053101}, doi = {10.1103/PhysRevE.96.053101}, pmid = {29347793}, issn = {2470-0053}, abstract = {The stabilities of an annulus flow between the rotating inner and outer cylinders with an external helical magnetic field are studied by using the quasistatic approximation. It is shown numerically that for the spiral base flow with a zero axial pressure gradient, the helical magnetic field yields a helical traveling wave at a critical Reynolds number. This wave mode is revealed to be the most unstable mode by linear stability analysis. At higher Reynolds numbers, the first wave mode is superposed by a second antisymmetric helical wave mode, which travels with a higher phase velocity than the first mode. When the Reynolds number is increased further, the flow becomes turbulent, but the key features of the flow structure are still dominated by the first and the second wave modes. Furthermore, when a finite axial pressure gradient is applied to guarantee a zero axial flow rate, the annulus flow is found to be more unstable than the case with zero axial pressure gradient.}, }
@article {pmid29347758, year = {2017}, author = {Elperin, T and Kleeorin, N and Liberman, M and Lipatnikov, AN and Rogachevskii, I and Yu, R}, title = {Turbulent diffusion of chemically reacting flows: Theory and numerical simulations.}, journal = {Physical review. E}, volume = {96}, number = {5-1}, pages = {053111}, doi = {10.1103/PhysRevE.96.053111}, pmid = {29347758}, issn = {2470-0053}, abstract = {The theory of turbulent diffusion of chemically reacting gaseous admixtures developed previously [T. Elperin et al., Phys. Rev. E 90, 053001 (2014)PLEEE81539-375510.1103/PhysRevE.90.053001] is generalized for large yet finite Reynolds numbers and the dependence of turbulent diffusion coefficient on two parameters, the Reynolds number and Damköhler number (which characterizes a ratio of turbulent and reaction time scales), is obtained. Three-dimensional direct numerical simulations (DNSs) of a finite-thickness reaction wave for the first-order chemical reactions propagating in forced, homogeneous, isotropic, and incompressible turbulence are performed to validate the theoretically predicted effect of chemical reactions on turbulent diffusion. It is shown that the obtained DNS results are in good agreement with the developed theory.}, }
@article {pmid29347655, year = {2017}, author = {Plan, ELCVM and Musacchio, S and Vincenzi, D}, title = {Emergence of chaos in a viscous solution of rods.}, journal = {Physical review. E}, volume = {96}, number = {5-1}, pages = {053108}, doi = {10.1103/PhysRevE.96.053108}, pmid = {29347655}, issn = {2470-0053}, abstract = {It is shown that the addition of small amounts of microscopic rods in a viscous fluid at low Reynolds number causes a significant increase of the flow resistance. Numerical simulations of the dynamics of the solution reveal that this phenomenon is associated to a transition from laminar to chaotic flow. Polymer stresses give rise to flow instabilities which, in turn, perturb the alignment of the rods. This coupled dynamics results in the activation of a wide range of scales, which enhances the mixing efficiency of viscous flows.}, }
@article {pmid29347433, year = {2017}, author = {Fouxon, I and Ge, Z and Brandt, L and Leshansky, A}, title = {Integral representation of channel flow with interacting particles.}, journal = {Physical review. E}, volume = {96}, number = {6-1}, pages = {063110}, doi = {10.1103/PhysRevE.96.063110}, pmid = {29347433}, issn = {2470-0053}, abstract = {We construct a boundary integral representation for the low-Reynolds-number flow in a channel in the presence of freely suspended particles (or droplets) of arbitrary size and shape. We demonstrate that lubrication theory holds away from the particles at horizontal distances exceeding the channel height and derive a multipole expansion of the flow which is dipolar to the leading approximation. We show that the dipole moment of an arbitrary particle is a weighted integral of the stress and the flow at the particle surface, which can be determined numerically. We introduce the equation of motion that describes hydrodynamic interactions between arbitrary, possibly different, distant particles, with interactions determined by the product of the mobility matrix and the dipole moment. Further, the problem of three identical interacting spheres initially aligned in the streamwise direction is considered and the experimentally observed "pair exchange" phenomenon is derived analytically and confirmed numerically. For nonaligned particles, we demonstrate the formation of a configuration with one particle separating from a stable pair. Our results suggest that in a dilute initially homogenous particulate suspension flowing in a channel the particles will eventually separate into singlets and pairs.}, }
@article {pmid29347297, year = {2017}, author = {Hiruta, Y and Toh, S}, title = {Intermittent direction reversals of moving spatially localized turbulence observed in two-dimensional Kolmogorov flow.}, journal = {Physical review. E}, volume = {96}, number = {6-1}, pages = {063112}, doi = {10.1103/PhysRevE.96.063112}, pmid = {29347297}, issn = {2470-0053}, abstract = {We have found that in two-dimensional Kolmogorov flow a spatially localized turbulent state (SLT) exists stably and travels with a constant speed on average switching the moving direction randomly and intermittently for moderate values of the control parameters: Reynolds number and the flow rate. We define the coarse-grained position and velocity of an SLT and separate the motion of the SLT from its internal turbulent dynamics by introducing a co-moving frame. The switching process of an SLT represented by the coarse-grained velocity seems to be a random telegraph signal. Focusing on the asymmetry of the internal turbulence we introduce two coarse-grained variables characterizing the internal dynamics. These quantities follow the switching process reasonably. This suggests that the twin attracting invariant sets each of which corresponds to a one-way traveling SLT are embedded in the attractor of the moving SLT and the connection of the two sets is too complicated to be represented by a few degrees of freedom but the motion of an SLT is correlated with the internal turbulent dynamics.}, }
@article {pmid29347290, year = {2017}, author = {Schilling, O and Mueschke, NJ}, title = {Turbulent transport and mixing in transitional Rayleigh-Taylor unstable flow: A priori assessment of gradient-diffusion and similarity modeling.}, journal = {Physical review. E}, volume = {96}, number = {6-1}, pages = {063111}, doi = {10.1103/PhysRevE.96.063111}, pmid = {29347290}, issn = {2470-0053}, abstract = {Data from a 1152×760×1280 direct numerical simulation [N. J. Mueschke and O. Schilling, Phys. Fluids 21, 014106 (2009)PHFLE61070-663110.1063/1.3064120] of a Rayleigh-Taylor mixing layer modeled after a small-Atwood-number water-channel experiment is used to investigate the validity of gradient diffusion and similarity closures a priori. The budgets of the mean flow, turbulent kinetic energy, turbulent kinetic energy dissipation rate, heavy-fluid mass fraction variance, and heavy-fluid mass fraction variance dissipation rate transport equations across the mixing layer were previously analyzed [O. Schilling and N. J. Mueschke, Phys. Fluids 22, 105102 (2010)PHFLE61070-663110.1063/1.3484247] at different evolution times to identify the most important transport and mixing mechanisms. Here a methodology is introduced to systematically estimate model coefficients as a function of time in the closures of the dynamically significant terms in the transport equations by minimizing the L_{2} norm of the difference between the model and correlations constructed using the simulation data. It is shown that gradient-diffusion and similarity closures used for the turbulent kinetic energy K, turbulent kinetic energy dissipation rate ε, heavy-fluid mass fraction variance S, and heavy-fluid mass fraction variance dissipation rate χ equations capture the shape of the exact, unclosed profiles well over the nonlinear and turbulent evolution regimes. Using order-of-magnitude estimates [O. Schilling and N. J. Mueschke, Phys. Fluids 22, 105102 (2010)PHFLE61070-663110.1063/1.3484247] for the terms in the exact transport equations and their closure models, it is shown that several of the standard closures for the turbulent production and dissipation (destruction) must be modified to include Reynolds-number scalings appropriate for Rayleigh-Taylor flow at small to intermediate Reynolds numbers. The late-time, large Reynolds number coefficients are determined to be different from those used in shear flow applications and largely adopted in two-equation Reynolds-averaged Navier-Stokes (RANS) models of Rayleigh-Taylor turbulent mixing. In addition, it is shown that the predictions of the Boussinesq model for the Reynolds stress agree better with the data when additional buoyancy-related terms are included. It is shown that an unsteady RANS paradigm is needed to predict the transitional flow dynamics from early evolution times, analogous to the small Reynolds number modifications in RANS models of wall-bounded flows in which the production-to-dissipation ratio is far from equilibrium. Although the present study is specific to one particular flow and one set of initial conditions, the methodology could be applied to calibrations of other Rayleigh-Taylor flows with different initial conditions (which may give different results during the early-time, transitional flow stages, and perhaps asymptotic stage). The implications of these findings for developing high-fidelity eddy viscosity-based turbulent transport and mixing models of Rayleigh-Taylor turbulence are discussed.}, }
@article {pmid29347258, year = {2017}, author = {Adebayo, I and Xie, Z and Che, Z and Matar, OK}, title = {Doubly excited pulse waves on thin liquid films flowing down an inclined plane: An experimental and numerical study.}, journal = {Physical review. E}, volume = {96}, number = {1-1}, pages = {013118}, doi = {10.1103/PhysRevE.96.013118}, pmid = {29347258}, issn = {2470-0053}, abstract = {The interaction patterns between doubly excited pulse waves on thin liquid films flowing down an inclined plane are studied both experimentally and numerically. The effect of varying the film flow rate, interpulse interval, and substrate inclination angle on the pulse interaction patterns is examined. Our results show that different interaction patterns exist for these binary pulses, which include solitary wave behavior, partial or complete pulse coalescence, and pulse noncoalescence. A regime map of these patterns is plotted for each inclination angle examined, parametrized by the film Reynolds number and interpulse interval. Finally, the individual effect of the system parameters mentioned above on the coalescence distance of binary pulses in the "complete pulse coalescence" mode is studied; the results are compared to numerical simulations of the two-dimensional Navier-Stokes equations yielding good agreement.}, }
@article {pmid29347222, year = {2017}, author = {Huang, Y and Wang, L and Schmitt, FG and Zheng, X and Jiang, N and Liu, Y}, title = {Extremal-point density of scaling processes: From fractional Brownian motion to turbulence in one dimension.}, journal = {Physical review. E}, volume = {96}, number = {1-1}, pages = {012215}, doi = {10.1103/PhysRevE.96.012215}, pmid = {29347222}, issn = {2470-0053}, abstract = {In recent years several local extrema-based methodologies have been proposed to investigate either the nonlinear or the nonstationary time series for scaling analysis. In the present work, we study systematically the distribution of the local extrema for both synthesized scaling processes and turbulent velocity data from experiments. The results show that for the fractional Brownian motion (fBm) without intermittency correction the measured extremal-point-density (EPD) agrees well with a theoretical prediction. For a multifractal random walk (MRW) with the lognormal statistics, the measured EPD is independent of the intermittency parameter μ, suggesting that the intermittency correction does not change the distribution of extremal points but changes the amplitude. By introducing a coarse-grained operator, the power-law behavior of these scaling processes is then revealed via the measured EPD for different scales. For fBm the scaling exponent ξ(H) is found to be ξ(H)=H, where H is Hurst number, while for MRW ξ(μ) shows a linear relation with the intermittency parameter μ. Such EPD approach is further applied to the turbulent velocity data obtained from a wind tunnel flow experiment with the Taylor scale λ-based Reynolds number Re_{λ}=720, and a turbulent boundary layer with the momentum thickness θ based Reynolds number Re_{θ}=810. A scaling exponent ξ≃0.37 is retrieved for the former case. For the latter one, the measured EPD shows clearly four regimes, which agrees well with the corresponding sublayer structures inside the turbulent boundary layer.}, }
@article {pmid29347180, year = {2017}, author = {Saito, S and Abe, Y and Koyama, K}, title = {Lattice Boltzmann modeling and simulation of liquid jet breakup.}, journal = {Physical review. E}, volume = {96}, number = {1-1}, pages = {013317}, doi = {10.1103/PhysRevE.96.013317}, pmid = {29347180}, issn = {2470-0053}, abstract = {A three-dimensional color-fluid lattice Boltzmann model for immiscible two-phase flows is developed in the framework of a three-dimensional 27-velocity (D3Q27) lattice. The collision operator comprises the D3Q27 versions of three suboperators: a multiple-relaxation-time (MRT) collision operator, a generalized Liu-Valocchi-Kang perturbation operator, and a Latva-Kokko-Rothman recoloring operator. A D3Q27 version of an enhanced equilibrium distribution function is also incorporated into this model to improve the Galilean invariance. Three types of numerical tests, namely, a static droplet, an oscillating droplet, and the Rayleigh-Taylor instability, show a good agreement with analytical solutions and numerical simulations. Following these numerical tests, this model is applied to liquid-jet-breakup simulations. The simulation conditions are matched to the conditions of the previous experiments. In this case, numerical stability is maintained throughout the simulation, although the kinematic viscosity for the continuous phase is set as low as 1.8×10^{-4}, in which case the corresponding Reynolds number is 3.4×10^{3}; the developed lattice Boltzmann model based on the D3Q27 lattice enables us to perform the simulation with parameters directly matched to the experiments. The jet's liquid column transitions from an asymmetrical to an axisymmetrical shape, and entrainment occurs from the side of the jet. The measured time history of the jet's leading-edge position shows a good agreement with the experiments. Finally, the reproducibility of the regime map for liquid-liquid systems is assessed. The present lattice Boltzmann simulations well reproduce the characteristics of predicted regimes, including varicose breakup, sinuous breakup, and atomization.}, }
@article {pmid29346972, year = {2017}, author = {Coreixas, C and Wissocq, G and Puigt, G and Boussuge, JF and Sagaut, P}, title = {Recursive regularization step for high-order lattice Boltzmann methods.}, journal = {Physical review. E}, volume = {96}, number = {3-1}, pages = {033306}, doi = {10.1103/PhysRevE.96.033306}, pmid = {29346972}, issn = {2470-0053}, abstract = {A lattice Boltzmann method (LBM) with enhanced stability and accuracy is presented for various Hermite tensor-based lattice structures. The collision operator relies on a regularization step, which is here improved through a recursive computation of nonequilibrium Hermite polynomial coefficients. In addition to the reduced computational cost of this procedure with respect to the standard one, the recursive step allows to considerably enhance the stability and accuracy of the numerical scheme by properly filtering out second- (and higher-) order nonhydrodynamic contributions in under-resolved conditions. This is first shown in the isothermal case where the simulation of the doubly periodic shear layer is performed with a Reynolds number ranging from 10^{4} to 10^{6}, and where a thorough analysis of the case at Re=3×10^{4} is conducted. In the latter, results obtained using both regularization steps are compared against the Bhatnagar-Gross-Krook LBM for standard (D2Q9) and high-order (D2V17 and D2V37) lattice structures, confirming the tremendous increase of stability range of the proposed approach. Further comparisons on thermal and fully compressible flows, using the general extension of this procedure, are then conducted through the numerical simulation of Sod shock tubes with the D2V37 lattice. They confirm the stability increase induced by the recursive approach as compared with the standard one.}, }
@article {pmid29346921, year = {2017}, author = {Maleki, M and Martinuzzi, RJ and Herzog, W and Federico, S}, title = {Orthotropic hydraulic permeability of arrays of parallel cylinders.}, journal = {Physical review. E}, volume = {96}, number = {3-1}, pages = {033112}, doi = {10.1103/PhysRevE.96.033112}, pmid = {29346921}, issn = {2470-0053}, abstract = {Approximate analytical methods are presented to calculate the overall orthotropic hydraulic permeability of a flow with low Reynolds number, passing through a bundle of parallel circular cylinders. Two particular distributions are considered: (i) arrays with ordered rectangular lattices and (ii) irregular nonrandom distributions for which the unit cell cross sections are elliptical. The standard unit cell models, originally developed by Happel and Kuwabara for a random distribution of cylinders, are adapted to the case of nonrandom distributions. The drag force on a representative cylinder in a direction perpendicular to its axis is obtained based on the standard unit cell model: the actual unit cell of rectangular or elliptical cross section is replaced with an "equivalent" cylindrical unit cell of diameter equal to the maximum width of the actual unit cell. Using the obtained drag forces and referring back to the original geometry of the unit cell, closed-form approximate expressions for the overall permeabilities in the perpendicular directions are obtained. Numerical comparisons with more sophisticated approaches confirm the good efficiency of the presented approach, especially in the range of low solid volume fraction, i.e., of high porosity. Previous studies have revealed that, for the parallel fluid flow, the variation of permeability with aspect ratio (or in general the lateral arrangement) of parallel cylinders is generally weak. These observations suggest that Happel's model for parallel permeability in a random distribution of cylinders could be a good approximation for parallel permeabilities in nonrandom distributions with the same volume fraction.}, }
@article {pmid29346864, year = {2017}, author = {Yu, Z and Lin, Z and Shao, X and Wang, LP}, title = {Effects of particle-fluid density ratio on the interactions between the turbulent channel flow and finite-size particles.}, journal = {Physical review. E}, volume = {96}, number = {3-1}, pages = {033102}, doi = {10.1103/PhysRevE.96.033102}, pmid = {29346864}, issn = {2470-0053}, abstract = {A parallel direct-forcing fictitious domain method is employed to perform fully resolved numerical simulations of turbulent channel flow laden with finite-size particles. The effects of the particle-fluid density ratio on the turbulence modulation in the channel flow are investigated at the friction Reynolds number of 180, the particle volume fraction of 0.84%, and the particle-fluid density ratio ranging from 1 to 104.2. The results show that the variation of the flow drag with the particle-fluid density ratio is not monotonic, with a larger flow drag for the density ratio of 10.42, compared to those of unity and 104.2. A significant drag reduction by the particles is observed for large particle-fluid density ratios during the transient stage, but not at the statistically stationary stage. The intensity of particle velocity fluctuations generally decreases with increasing particle inertia, except that the particle streamwise root-mean-square velocity and streamwise-transverse velocity correlation in the near-wall region are largest at the density ratio of the order of 10. The averaged momentum equations are derived with the spatial averaging theorem and are used to analyze the mechanisms for the effects of the particles on the flow drag. The results indicate that the drag-reduction effect due to the decrease in the fluid Reynolds shear stress is counteracted by the drag-enhancement effect due to the increase in the total particle stress or the interphase drag force for the large particle-inertia case. The sum of the total Reynolds stress and particle inner stress contributions to the flow drag is largest at the density ratio of the order of 10, which is the reason for the largest flow drag at this density ratio. The interphase drag force obtained from the averaged momentum equation (the balance theory) is significantly smaller than (but agrees qualitatively with) that from the empirical drag formula based on the phase-averaged slip velocity for large density ratios. For the neutrally buoyant case, the balance theory predicts a positive interphase force on the particles arising from the negative gradient of the particle inner stress, which cannot be predicted by the drag formula based on the phase-averaged slip velocity. In addition, our results show that both particle collision and particle-turbulence interaction play roles in the formation of the inhomogeneous distribution of the particles at the density ratio of the order of 10.}, }
@article {pmid29343852, year = {2018}, author = {Hamilton, JK and Bryan, MT and Gilbert, AD and Ogrin, FY and Myers, TO}, title = {A new class of magnetically actuated pumps and valves for microfluidic applications.}, journal = {Scientific reports}, volume = {8}, number = {1}, pages = {933}, pmid = {29343852}, issn = {2045-2322}, abstract = {We propose a new class of magnetically actuated pumps and valves that could be incorporated into microfluidic chips with no further external connections. The idea is to repurpose ferromagnetic low Reynolds number swimmers as devices capable of generating fluid flow, by restricting the swimmers' translational degrees of freedom. We experimentally investigate the flow structure generated by a pinned swimmer in different scenarios, such as unrestricted flow around it as well as flow generated in straight, cross-shaped, Y-shaped and circular channels. This demonstrates the feasibility of incorporating the device into a channel and its capability of acting as a pump, valve and flow splitter. Different regimes could be selected by tuning the frequency and amplitude of the external magnetic field driving the swimmer, or by changing the channel orientation with respect to the field. This versatility endows the device with varied functionality which, together with the robust remote control and reproducibility, makes it a promising candidate for several applications.}, }
@article {pmid29341736, year = {2017}, author = {Yakhot, V and Donzis, D}, title = {Emergence of Multiscaling in a Random-Force Stirred Fluid.}, journal = {Physical review letters}, volume = {119}, number = {4}, pages = {044501}, doi = {10.1103/PhysRevLett.119.044501}, pmid = {29341736}, issn = {1079-7114}, abstract = {We consider the transition to strong turbulence in an infinite fluid stirred by a Gaussian random force. The transition is defined as a first appearance of anomalous scaling of normalized moments of velocity derivatives (dissipation rates) emerging from the low-Reynolds-number Gaussian background. It is shown that, due to multiscaling, strongly intermittent rare events can be quantitatively described in terms of an infinite number of different "Reynolds numbers" reflecting a multitude of anomalous scaling exponents. The theoretically predicted transition disappears at R_{λ}≤3. The developed theory is in quantitative agreement with the outcome of large-scale numerical simulations.}, }
@article {pmid29333202, year = {2017}, author = {Raffiee, AH and Dabiri, S and Ardekani, AM}, title = {Elasto-inertial migration of deformable capsules in a microchannel.}, journal = {Biomicrofluidics}, volume = {11}, number = {6}, pages = {064113}, pmid = {29333202}, issn = {1932-1058}, abstract = {In this paper, we study the dynamics of deformable cells in a channel flow of Newtonian and polymeric fluids and unravel the effects of deformability, elasticity, inertia, and size on the cell motion. We investigate the role of polymeric fluids on the cell migration behavior and the performance of inertial microfluidic devices. Our results show that the equilibrium position of the cell is on the channel diagonal, in contrast to that of rigid particles, which is on the center of the channel faces for the same range of Reynolds number. A constant-viscosity polymeric fluid, modeled using an Oldroyd-B constitutive equation, drives the cells toward the channel centerline, while a shear-thinning polymeric fluid, modeled using a Giesekus constitutive equation, pushes the cells toward the channel wall. The findings of this paper suggest that the addition of polymers in microfluidic devices can be used to enhance the throughput of cell focusing and separation devices at a low cost. This study provides an insight on the role of rheological properties of the fluid and the ways that they can be tuned to control the focal position of the cells.}, }
@article {pmid29323150, year = {2018}, author = {Mrokowska, MM}, title = {Stratification-induced reorientation of disk settling through ambient density transition.}, journal = {Scientific reports}, volume = {8}, number = {1}, pages = {412}, pmid = {29323150}, issn = {2045-2322}, abstract = {Settling due to gravity force is a basic transport mechanism of solid particles in fluids in the Earth. A large portion of particles occurring in nature and used in technical applications are non-spherical. Settling of particles is usually studied in homogeneous ambient conditions, however, stratification is inherent of natural fluids. It has been acknowledged that stratification modifies the velocity of settling spheres and amorphous aggregates. However, the effect of particle shape on the dynamics of settling through density-stratified ambient fluid has not been recognized well enough. Here I show experimental evidence that continuous density transition markedly modifies the settling dynamics of a disk in terms of settling velocity and orientation of a particle. Settling dynamics of a disk are more complex than dynamics of spheres and aggregates studied previously. I found that in a two-layer ambient with density transition, a disk settling in a low Reynolds number regime undergoes five phases of settling with the orientation varying from horizontal to vertical, and it may achieve two local minimum settling velocities in the density transition layer. Moreover, I found that the settling dynamics depends on a density difference between upper and lower homogeneous layers, stratification strength and thickness of density transition.}, }
@article {pmid29291432, year = {2018}, author = {Ranjit, NK and Shit, GC and Tripathi, D}, title = {Joule heating and zeta potential effects on peristaltic blood flow through porous micro vessels altered by electrohydrodynamic.}, journal = {Microvascular research}, volume = {117}, number = {}, pages = {74-89}, doi = {10.1016/j.mvr.2017.12.004}, pmid = {29291432}, issn = {1095-9319}, mesh = {Blood Flow Velocity ; *Computer Simulation ; *Electromagnetic Fields ; Electroosmosis ; Energy Transfer ; Hot Temperature ; Humans ; Hydrodynamics ; *Microcirculation ; Microvessels/*physiology ; *Models, Cardiovascular ; Porosity ; *Pulsatile Flow ; Regional Blood Flow ; }, abstract = {In most of the medical therapies, electromagnetic field plays important role to modulate the blood flow and to reduce the pain of human body. With this fact, this paper presents a mathematical model to study the peristaltic blood flow through porous microvessels in the presence of electrohydrodynamics. The effects of Joule heating and different zeta potential are also considered. Darcy law is employed for porous medium. The mathematical analysis is carried out in the form of electroosmosis, flow analysis and heat transfer analysis. Velocity slip conditions are imposed to solve momentum equation and thermal energy equation. Time dependent volumetric flow rate is considered which varies exponentially. Closed form solutions for potential function is obtained under Debye-Hückel approximation and velocity and temperature fields are obtained under low Reynolds number and large wavelength approximations. The influence of Hartmann number, electroosmotic parameter, slip parameters, Zeta potential, and couple stress parameter on flow characteristics, pumping characteristics and trapping phenomenon is computed. The effects of thermal slip parameters, Joule heating parameter, and Brinkman number on heat transfer characteristics are also presented graphically. Finally, the effect of Brinkman number on a graph between Nusselt number and Joule heating parameter is examined.}, }
@article {pmid31631915, year = {2018}, author = {Bose, ST and Park, GI}, title = {Wall-Modeled Large-Eddy Simulation for Complex Turbulent Flows.}, journal = {Annual review of fluid mechanics}, volume = {50}, number = {}, pages = {535-561}, pmid = {31631915}, issn = {0066-4189}, support = {NNX15AU93A//NASA/United States ; }, abstract = {Large-eddy simulation (LES) has proven to be a computationally tractable approach to simulate unsteady turbulent flows. However, prohibitive resolution requirements induced by near-wall eddies in high-Reynolds number boundary layers necessitate the use of wall models or approximate wall boundary conditions. We review recent investigations in wall-modeled LES, including the development of novel approximate boundary conditions and the application of wall models to complex flows (e.g., boundary-layer separation, shock/boundary-layer interactions, transition). We also assess the validity of underlying assumptions in wall-model derivations to elucidate the accuracy of these investigations, and offer suggestions for future studies.}, }
@article {pmid30996402, year = {2018}, author = {Ricco, P and Hicks, PD}, title = {Streamwise-travelling viscous waves in channel flows.}, journal = {Journal of engineering mathematics}, volume = {111}, number = {1}, pages = {23-49}, pmid = {30996402}, issn = {0022-0833}, abstract = {The unsteady viscous flow induced by streamwise-travelling waves of spanwise wall velocity in an incompressible laminar channel flow is investigated. Wall waves belonging to this category have found important practical applications, such as microfluidic flow manipulation via electro-osmosis and surface acoustic forcing and reduction of wall friction in turbulent wall-bounded flows. An analytical solution composed of the classical streamwise Poiseuille flow and a spanwise velocity profile described by the parabolic cylinder function is found. The solution depends on the bulk Reynolds number R, the scaled streamwise wavelength λ , and the scaled wave phase speed U. Numerical solutions are discussed for various combinations of these parameters. The flow is studied by the boundary-layer theory, thereby revealing the dominant physical balances and quantifying the thickness of the near-wall spanwise flow. The Wentzel-Kramers-Brillouin-Jeffreys (WKBJ) theory is also employed to obtain an analytical solution, which is valid across the whole channel. For positive wave speeds which are smaller than or equal to the maximum streamwise velocity, a turning-point behaviour emerges through the WKBJ analysis. Between the wall and the turning point, the wall-normal viscous effects are balanced solely by the convection driven by the wall forcing, while between the turning point and the centreline, the Poiseuille convection balances the wall-normal diffusion. At the turning point, the Poiseuille convection and the convection from the wall forcing cancel each other out, which leads to a constant viscous stress and to the break down of the WKBJ solution. This flow regime is analysed through a WKBJ composite expansion and the Langer method. The Langer solution is simpler and more accurate than the WKBJ composite solution, while the latter quantifies the thickness of the turning-point region. We also discuss how these waves can be generated via surface acoustic forcing and electro-osmosis and propose their use as microfluidic flow mixing devices. For the electro-osmosis case, the Helmholtz-Smoluchowski velocity at the edge of the Debye-Hückel layer, which drives the bulk electrically neutral flow, is obtained by matched asymptotic expansion.}, }
@article {pmid29289052, year = {2017}, author = {Hamilton, E and Bruot, N and Cicuta, P}, title = {The chimera state in colloidal phase oscillators with hydrodynamic interaction.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {27}, number = {12}, pages = {123108}, doi = {10.1063/1.4989466}, pmid = {29289052}, issn = {1089-7682}, abstract = {The chimera state is the incongruous situation where coherent and incoherent populations coexist in sets of identical oscillators. Using driven non-linear oscillators interacting purely through hydrodynamic forces at low Reynolds number, previously studied as a simple model of motile cilia supporting waves, we find concurrent incoherent and synchronised subsets in small arrays. The chimeras seen in simulation display a "breathing" aspect, reminiscent of uniformly interacting phase oscillators. In contrast to other systems where chimera has been observed, this system has a well-defined interaction metric, and we know that the emergent dynamics inherit the symmetry of the underlying Oseen tensor eigenmodes. The chimera state can thus be connected to a superposition of eigenstates, whilst considering the mean interaction strength within and across subsystems allows us to make a connection to more generic (and abstract) chimeras in populations of Kuramoto phase oscillators. From this work, we expect the chimera state to emerge in experimental observations of oscillators coupled through hydrodynamic forces.}, }
@article {pmid29286796, year = {2017}, author = {Djellouli, A and Marmottant, P and Djeridi, H and Quilliet, C and Coupier, G}, title = {Buckling Instability Causes Inertial Thrust for Spherical Swimmers at All Scales.}, journal = {Physical review letters}, volume = {119}, number = {22}, pages = {224501}, doi = {10.1103/PhysRevLett.119.224501}, pmid = {29286796}, issn = {1079-7114}, abstract = {Microswimmers, and among them aspirant microrobots, generally have to cope with flows where viscous forces are dominant, characterized by a low Reynolds number (Re). This implies constraints on the possible sequences of body motion, which have to be nonreciprocal. Furthermore, the presence of a strong drag limits the range of resulting velocities. Here, we propose a swimming mechanism which uses the buckling instability triggered by pressure waves to propel a spherical, hollow shell. With a macroscopic experimental model, we show that a net displacement is produced at all Re regimes. An optimal displacement caused by nontrivial history effects is reached at intermediate Re. We show that, due to the fast activation induced by the instability, this regime is reachable by microscopic shells. The rapid dynamics would also allow high-frequency excitation with standard traveling ultrasonic waves. Scale considerations predict a swimming velocity of order 1 cm/s for a remote-controlled microrobot, a suitable value for biological applications such as drug delivery.}, }
@article {pmid29286719, year = {2017}, author = {Atif, M and Kolluru, PK and Thantanapally, C and Ansumali, S}, title = {Essentially Entropic Lattice Boltzmann Model.}, journal = {Physical review letters}, volume = {119}, number = {24}, pages = {240602}, doi = {10.1103/PhysRevLett.119.240602}, pmid = {29286719}, issn = {1079-7114}, abstract = {The entropic lattice Boltzmann model (ELBM), a discrete space-time kinetic theory for hydrodynamics, ensures nonlinear stability via the discrete time version of the second law of thermodynamics (the H theorem). Compliance with the H theorem is numerically enforced in this methodology and involves a search for the maximal discrete path length corresponding to the zero dissipation state by iteratively solving a nonlinear equation. We demonstrate that an exact solution for the path length can be obtained by assuming a natural criterion of negative entropy change, thereby reducing the problem to solving an inequality. This inequality is solved by creating a new framework for construction of Padé approximants via quadrature on appropriate convex function. This exact solution also resolves the issue of indeterminacy in case of nonexistence of the entropic involution step. Since our formulation is devoid of complex mathematical library functions, the computational cost is drastically reduced. To illustrate this, we have simulated a model setup of flow over the NACA-0012 airfoil at a Reynolds number of 2.88×10^{6}.}, }
@article {pmid29271639, year = {2018}, author = {Kim, JA and Lee, JR and Je, TJ and Jeon, EC and Lee, W}, title = {Size-Dependent Inertial Focusing Position Shift and Particle Separations in Triangular Microchannels.}, journal = {Analytical chemistry}, volume = {90}, number = {3}, pages = {1827-1835}, doi = {10.1021/acs.analchem.7b03851}, pmid = {29271639}, issn = {1520-6882}, abstract = {A recent study of inertial microfluidics within nonrectangular cross-section channels showed that the inertial focusing positions changes with cross-sectional shapes; therefore, the cross-sectional shape can be a useful control parameter for microfluidic particle manipulations. Here, we conducted detail investigation on unique focusing position shift phenomena, which occurs strongly in channels with the cross-sectional shape of the isosceles right triangle. The top focusing positions shift along the channel walls to the direction away from the apex with increasing Reynolds number and decreasing particle size. A larger particle with its center further away from the side walls experiences shear gradient lift toward the apex, which leads to an opposite result with changes of Reynolds and particle size. The focusing position shift and the subsequent stabilization of corner focusing lead to changes in the number of focusing positions, which enables a novel method for microparticle separations with high efficiency (>95%) and resolution (<2 μm). The separation method based on equilibrium focusing; therefore, the operation is simple and no complex separation optimization is needed. Moreover, the separation threshold can be easily modulated with flow rate adjustment. Rare cell separation from blood cell was successfully demonstrated with spiked MCF-7 cells in blood by achieving the yield of ∼95% and the throughput of ∼10[6] cells/min.}, }
@article {pmid29264667, year = {2018}, author = {Oakes, JM and Roth, SC and Shadden, SC}, title = {Airflow Simulations in Infant, Child, and Adult Pulmonary Conducting Airways.}, journal = {Annals of biomedical engineering}, volume = {46}, number = {3}, pages = {498-512}, doi = {10.1007/s10439-017-1971-9}, pmid = {29264667}, issn = {1573-9686}, mesh = {Adolescent ; Adult ; Aging/*physiology ; Child ; Child, Preschool ; Female ; Humans ; Infant ; Infant, Newborn ; Lung/anatomy &amp; histology/*physiology ; Male ; *Models, Biological ; Pulmonary Ventilation/*physiology ; Respiratory Mechanics/*physiology ; Trachea/anatomy &amp; histology/*physiology ; }, abstract = {The airway structure continuously evolves from birth to adulthood, influencing airflow dynamics and respiratory mechanics. We currently know very little about how airflow patterns change throughout early life and its impact on airway resistance, namely because of experimental limitations. To uncover differences in respiratory dynamics between age groups, we performed subject-specific airflow simulations in an infant, child, and adult conducting airways. Airflow throughout the respiration cycle was calculated by coupling image-based models of the conducting airways to the global respiratory mechanics, where flow was driven by a pressure differential. Trachea diameter was 19, 9, and 4.5 mm for the adult (36 years, female), child (6 years, male), and infant (0.25 years, female), respectively. Mean Reynolds number within the trachea was nearly the same for each subject (1100) and Womersley number was above unity for all three subjects and largest for the adult, highlighting the significance of transient effects. In general, air speeds and airway resistances within the conducting airways were inversely correlated with age; the 3D pressure drop was highest in the infant model. These simulations provide new insight into age-dependent flow dynamics throughout the respiration cycle within subject-specific airways.}, }
@article {pmid29258534, year = {2017}, author = {Sass, LR and Khani, M and Natividad, GC and Tubbs, RS and Baledent, O and Martin, BA}, title = {A 3D subject-specific model of the spinal subarachnoid space with anatomically realistic ventral and dorsal spinal cord nerve rootlets.}, journal = {Fluids and barriers of the CNS}, volume = {14}, number = {1}, pages = {36}, pmid = {29258534}, issn = {2045-8118}, support = {Vandal Ideas Project//University of Idaho/ ; 1R44MH112210-01A1//National Institute of Mental Health/ ; 4U54GM104944-04TBD//National Institute of General Medical Sciences/ ; P20 GM103408/GM/NIGMS NIH HHS/United States ; P20GM1033408//National Institute of General Medical Sciences/ ; R44 MH112210/MH/NIMH NIH HHS/United States ; U54 GM104944/GM/NIGMS NIH HHS/United States ; }, mesh = {Adult ; Female ; Humans ; Imaging, Three-Dimensional ; Magnetic Resonance Imaging ; *Models, Anatomic ; *Models, Neurological ; Spinal Cord/*anatomy &amp; histology/diagnostic imaging ; Spinal Nerve Roots/*anatomy &amp; histology/diagnostic imaging ; Subarachnoid Space/*anatomy &amp; histology/diagnostic imaging ; Young Adult ; }, abstract = {BACKGROUND: The spinal subarachnoid space (SSS) has a complex 3D fluid-filled geometry with multiple levels of anatomic complexity, the most salient features being the spinal cord and dorsal and ventral nerve rootlets. An accurate anthropomorphic representation of these features is needed for development of in vitro and numerical models of cerebrospinal fluid (CSF) dynamics that can be used to inform and optimize CSF-based therapeutics.<br><br>METHODS: A subject-specific 3D model of the SSS was constructed based on high-resolution anatomic MRI. An expert operator completed manual segmentation of the CSF space with detailed consideration of the anatomy. 31 pairs of semi-idealized dorsal and ventral nerve rootlets (NR) were added to the model based on anatomic reference to the magnetic resonance (MR) imaging and cadaveric measurements in the literature. Key design criteria for each NR pair included the radicular line, descending angle, number of NR, attachment location along the spinal cord and exit through the dura mater. Model simplification and smoothing was performed to produce a final model with minimum vertices while maintaining minimum error between the original segmentation and final design. Final model geometry and hydrodynamics were characterized in terms of axial distribution of Reynolds number, Womersley number, hydraulic diameter, cross-sectional area and perimeter.<br><br>RESULTS: The final model had a total of 139,901 vertices with a total CSF volume within the SSS of 97.3&#xa0;cm[3]. Volume of the dura mater, spinal cord and NR was 123.1, 19.9 and 5.8&#xa0;cm[3]. Surface area of these features was 318.52, 112.2 and 232.1&#xa0;cm[2] respectively. Maximum Reynolds number was 174.9 and average Womersley number was 9.6, likely indicating presence of a laminar inertia-dominated oscillatory CSF flow field.<br><br>CONCLUSIONS: This study details an anatomically realistic anthropomorphic 3D model of the SSS based on high-resolution MR imaging of a healthy human adult female. The model is provided for re-use under the Creative Commons Attribution-ShareAlike 4.0 International license (CC BY-SA 4.0) and can be used as a tool for development of in vitro and numerical models of CSF dynamics for design and optimization of intrathecal therapeutics.}, }
@article {pmid29244030, year = {2018}, author = {Shidhore, TC and Christov, IC}, title = {Static response of deformable microchannels: a comparative modelling study.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {30}, number = {5}, pages = {054002}, doi = {10.1088/1361-648X/aaa226}, pmid = {29244030}, issn = {1361-648X}, abstract = {We present a comparative modelling study of fluid-structure interactions in microchannels. Through a mathematical analysis based on plate theory and the lubrication approximation for low-Reynolds-number flow, we derive models for the flow rate-pressure drop relation for long shallow microchannels with both thin and thick deformable top walls. These relations are tested against full three-dimensional two-way-coupled fluid-structure interaction simulations. Three types of microchannels, representing different elasticity regimes and having been experimentally characterized previously, are chosen as benchmarks for our theory and simulations. Good agreement is found in most cases for the predicted, simulated and measured flow rate-pressure drop relationships. The numerical simulations performed allow us to also carefully examine the deformation profile of the top wall of the microchannel in any cross section, showing good agreement with the theory. Specifically, the prediction that span-wise displacement in a long shallow microchannel decouples from the flow-wise deformation is confirmed, and the predicted scaling of the maximum displacement with the hydrodynamic pressure and the various material and geometric parameters is validated.}, }
@article {pmid29239446, year = {2018}, author = {Denn, MM and Morris, JF and Bonn, D}, title = {Shear thickening in concentrated suspensions of smooth spheres in Newtonian suspending fluids.}, journal = {Soft matter}, volume = {14}, number = {2}, pages = {170-184}, doi = {10.1039/c7sm00761b}, pmid = {29239446}, issn = {1744-6848}, abstract = {Shear thickening is a phenomenon in which the viscosity of a suspension increases with increasing stress or shear rate, sometimes in a discontinuous fashion. While the phenomenon, when observed in suspensions of corn starch in water, or Oobleck, is popular as a science experiment for children, shear thickening is actually of considerable importance for technological applications and exhibited by far simpler systems. Concentrated suspensions of smooth hard spheres will exhibit shear thickening, and understanding this behavior has required a fundamental change in the paradigm of describing low-Reynolds-number solid-fluid flows, in which contact forces have traditionally been absent. Here, we provide an overview of our understanding of shear thickening and the methods that have been developed to describe it, as well as outstanding questions.}, }
@article {pmid29219534, year = {2017}, author = {Reeves, MT and Billam, TP and Yu, X and Bradley, AS}, title = {Enstrophy Cascade in Decaying Two-Dimensional Quantum Turbulence.}, journal = {Physical review letters}, volume = {119}, number = {18}, pages = {184502}, doi = {10.1103/PhysRevLett.119.184502}, pmid = {29219534}, issn = {1079-7114}, abstract = {We report evidence for an enstrophy cascade in large-scale point-vortex simulations of decaying two-dimensional quantum turbulence. Devising a method to generate quantum vortex configurations with kinetic energy narrowly localized near a single length scale, the dynamics are found to be well characterized by a superfluid Reynolds number Re_{s} that depends only on the number of vortices and the initial kinetic energy scale. Under free evolution the vortices exhibit features of a classical enstrophy cascade, including a k^{-3} power-law kinetic energy spectrum, and constant enstrophy flux associated with inertial transport to small scales. Clear signatures of the cascade emerge for N≳500 vortices. Simulating up to very large Reynolds numbers (N=32 768 vortices), additional features of the classical theory are observed: the Kraichnan-Batchelor constant is found to converge to C^{'}≈1.6, and the width of the k^{-3} range scales as Re_{s}^{1/2}.}, }
@article {pmid29219520, year = {2017}, author = {Matsunaga, D and Meng, F and Zöttl, A and Golestanian, R and Yeomans, JM}, title = {Focusing and Sorting of Ellipsoidal Magnetic Particles in Microchannels.}, journal = {Physical review letters}, volume = {119}, number = {19}, pages = {198002}, doi = {10.1103/PhysRevLett.119.198002}, pmid = {29219520}, issn = {1079-7114}, abstract = {We present a simple method to control the position of ellipsoidal magnetic particles in microchannel Poiseuille flow at low Reynolds number using a static uniform magnetic field. The magnetic field is utilized to pin the particle orientation, and the hydrodynamic interactions between ellipsoids and channel walls allow control of the transverse position of the particles. We employ a far-field hydrodynamic theory and simulations using the boundary element method and Brownian dynamics to show how magnetic particles can be focused and segregated by size and shape. This is of importance for particle manipulation in lab-on-a-chip devices.}, }
@article {pmid30965982, year = {2017}, author = {Bhambri, P and Narain, R and Fleck, B}, title = {Drag Reduction Using Polysaccharides in a Taylor[-]Couette Flow.}, journal = {Polymers}, volume = {9}, number = {12}, pages = {}, pmid = {30965982}, issn = {2073-4360}, abstract = {Three different polysaccharides, aloe vera, Tamarind powder and pineapple fibers, are utilized as drag reducing agents in a turbulent flow. Using a Taylor[-]Couette setup, consisting of a rotating inner cylinder, for measuring the drag reduction, a range of Reynolds numbers from 4 × 10[4] to 3 × 10[5] has been explored in this study. The results are in good agreement with previous studies on polysaccharides conducted in a pipe/channel flow and a maximum drag reduction of 35% has been observed. Further, novel additives such as cellulose nanocrystals (CNC), surfactants and CNC grafted with surfactants are also examined in this study for drag reduction. CNC due to its rigid rod structure reduced the drag by 30%. Surfactant, due to its unique micelle formation showed maximum drag reduction of 80% at low Re. Further, surfactant was grafted on CNC and was examined for drag reduction. However, drag reduction property of surfactant was observed to be significantly reduced after grafting on CNC. The effect of Reynolds number on drag reduction is studied for all the additives investigated in this study.}, }
@article {pmid29201603, year = {2017}, author = {Wang, Q and Yang, L and Yu, J and Zhang, L}, title = {Characterizing dynamic behaviors of three-particle paramagnetic microswimmer near a solid surface.}, journal = {Robotics and biomimetics}, volume = {4}, number = {1}, pages = {20}, pmid = {29201603}, issn = {2197-3768}, abstract = {Particle-based magnetically actuated microswimmers have the potential to act as microrobotic tools for biomedical applications. In this paper, we report the dynamic behaviors of a three-particle paramagnetic microswimmer. Actuated by a rotating magnetic field with different frequencies, the microswimmer exhibits simple rotation and propulsion. When the input frequency is below 8 Hz, it exhibits simple rotation on the substrate, whereas it shows propulsion with varied poses when subjected to a frequency between 8 and 15 Hz. Furthermore, a solid surface that enhances swimming velocity was observed as the microswimmer is actuated near a solid surface. Our simulation results testify that the surface-enhanced swimming near a solid surface is because of the induced pressure difference in the surrounding fluid of the microagent.}, }
@article {pmid29195661, year = {2018}, author = {Tarafder, A}, title = {A study on the onset of turbulent conditions with supercritical fluid chromatography mobile-phases.}, journal = {Journal of chromatography. A}, volume = {1532}, number = {}, pages = {182-190}, doi = {10.1016/j.chroma.2017.11.056}, pmid = {29195661}, issn = {1873-3778}, mesh = {Carbon Dioxide/chemistry ; Chromatography, Supercritical Fluid/*methods ; Pressure ; *Rheology ; Solvents/*chemistry ; Temperature ; Viscosity ; }, abstract = {Following a recent publication [1], the topic of turbulent flow in SFC has generated both interest and questions. Liquid-like density, coupled with significantly low viscosity of CO2-based mobile-phases may result in high Reynolds number (Re) - higher than what represents laminar flow conditions, reaching the so-called turbulent regions. Although such turbulent flows can form only in the connecting tubings, thus not directly affecting the chromatographic process, it is important to know under many situations, whether the flow inside the tubing is laminar or turbulent. In this report a comprehensive guideline to identify the possibilities of turbulent flow conditions is provided through a series of charts. Flow properties depend on state conditions (composition, pressure and temperature) and also on the tubing material and geometry. Here guidelines to detect the onset of turbulent conditions is provided for cylindrical stainless-steel tubings of different internal diameters (i.d.) under a wide range of SFC mobile-phase conditions.}, }
@article {pmid29195464, year = {2017}, author = {Zhao, S and Cheng, E and Qiu, X and Burnett, I and Liu, JC}, title = {Wind noise spectra in small Reynolds number turbulent flows.}, journal = {The Journal of the Acoustical Society of America}, volume = {142}, number = {5}, pages = {3227}, doi = {10.1121/1.5012740}, pmid = {29195464}, issn = {1520-8524}, abstract = {Wind noise spectra caused by wind from fans in indoor environments have been found to be different from those measured in outdoor atmospheric conditions. Although many models have been developed to predict outdoor wind noise spectra under the assumption of large Reynolds number [Zhao, Cheng, Qiu, Burnett, and Liu (2016). J. Acoust. Soc. Am. 140, 4178-4182, and the references therein], they cannot be applied directly to the indoor situations because the Reynolds number of wind from fans in indoor environments is usually much smaller than that experienced in atmospheric turbulence. This paper proposes a pressure structure function model that combines the energy-containing and dissipation ranges so that the pressure spectrum for small Reynolds number turbulent flows can be calculated. The proposed pressure structure function model is validated with the experimental results in the literature, and then the obtained pressure spectrum is verified with the numerical simulation and experiment results. It is demonstrated that the pressure spectrum obtained from the proposed pressure structure function model can be utilized to estimate wind noise spectra caused by turbulent flows with small Reynolds numbers.}, }
@article {pmid29183943, year = {2017}, author = {Boselli, F and Steed, E and Freund, JB and Vermot, J}, title = {Anisotropic shear stress patterns predict the orientation of convergent tissue movements in the embryonic heart.}, journal = {Development (Cambridge, England)}, volume = {144}, number = {23}, pages = {4322-4327}, pmid = {29183943}, issn = {1477-9129}, mesh = {Animals ; Anisotropy ; Biomechanical Phenomena ; Endocardial Cushions/cytology/embryology ; Endothelial Cells/cytology/physiology ; Erythrocytes/physiology ; Heart/*embryology ; Hemodynamics ; Hydrodynamics ; Imaging, Three-Dimensional ; *Models, Cardiovascular ; Organogenesis/physiology ; Shear Strength ; Stress, Mechanical ; Zebrafish/*embryology ; }, abstract = {Myocardial contractility and blood flow provide essential mechanical cues for the morphogenesis of the heart. In general, endothelial cells change their migratory behavior in response to shear stress patterns, according to flow directionality. Here, we assessed the impact of shear stress patterns and flow directionality on the behavior of endocardial cells, the specialized endothelial cells of the heart. At the early stages of zebrafish heart valve formation, we show that endocardial cells are converging to the valve-forming area and that this behavior depends upon mechanical forces. Quantitative live imaging and mathematical modeling allow us to correlate this tissue convergence with the underlying flow forces. We predict that tissue convergence is associated with the direction of the mean wall shear stress and of the gradient of harmonic phase-averaged shear stresses, which surprisingly do not match the overall direction of the flow. This contrasts with the usual role of flow directionality in vascular development and suggests that the full spatial and temporal complexity of the wall shear stress should be taken into account when studying endothelial cell responses to flow in vivo.}, }
@article {pmid29181289, year = {2017}, author = {Li, K and Jing, D and Hu, J and Ding, X and Yao, Z}, title = {Numerical investigation of the tribological performance of micro-dimple textured surfaces under hydrodynamic lubrication.}, journal = {Beilstein journal of nanotechnology}, volume = {8}, number = {}, pages = {2324-2338}, pmid = {29181289}, issn = {2190-4286}, abstract = {Surface texturing is an important approach for controlling the tribological behavior of friction pairs used in mechanical and biological engineering. In this study, by utilizing the method of three-dimensional computational fluid dynamics (CFD) simulation, the lubrication model of a friction pair with micro-dimple array was established based on the Navier-Stokes equations. The typical pressure distribution of the lubricant film was analyzed. It was found that a positive hydrodynamic pressure is generated in the convergent part of the micro-dimple, while a negative hydrodynamic pressure is generated in the divergent part. With suitable parameters, the total integration of the pressure is positive, which can increase the load-carrying capacity of a friction pair. The effects of the micro-dimple parameters as well as fluid properties on tribological performance were investigated. It was concluded that under the condition of hydrodynamic lubrication, the main mechanism for the improvement in the tribological performance is the combined effects of wedging and recirculation. Within the range of parameters investigated in this study, the optimum texture density is 13%, while the optimum aspect ratio varies with the Reynolds number. For a given Reynolds number, there exists a combination of texture density and aspect ratio at which the optimum tribological performance could be obtained. Conclusions from this study could be helpful for the design of texture parameters in mechanical friction components and even in artificial joints.}, }
@article {pmid29178057, year = {2017}, author = {Goldobin, DS}, title = {Existence of the passage to the limit of an inviscid fluid.}, journal = {The European physical journal. E, Soft matter}, volume = {40}, number = {11}, pages = {103}, doi = {10.1140/epje/i2017-11594-4}, pmid = {29178057}, issn = {1292-895X}, mesh = {Computer Simulation ; *Hydrodynamics ; *Viscosity ; }, abstract = {In the dynamics of a viscous fluid, the case of vanishing kinematic viscosity is actually equivalent to the Reynolds number tending to infinity. Hence, in the limit of vanishing viscosity the fluid flow is essentially turbulent. On the other hand, the Euler equation, which is conventionally adopted for the description of the flow of an inviscid fluid, does not possess proper turbulent behaviour. This raises the question of the existence of the passage to the limit of an inviscid fluid for real low-viscosity fluids. To address this question, one should employ the theory of turbulent boundary layer near an inflexible boundary (e.g., rigid wall). On the basis of this theory, one can see how the solutions to the Euler equation become relevant for the description of the flow of low-viscosity fluids, and obtain the small parameter quantifying accuracy of this description for real fluids.}, }
@article {pmid29167371, year = {2017}, author = {De Canio, G and Lauga, E and Goldstein, RE}, title = {Spontaneous oscillations of elastic filaments induced by molecular motors.}, journal = {Journal of the Royal Society, Interface}, volume = {14}, number = {136}, pages = {}, pmid = {29167371}, issn = {1742-5662}, mesh = {Actin Cytoskeleton/*chemistry/physiology ; Biomechanical Phenomena ; *Models, Biological ; Molecular Motor Proteins/*physiology ; }, abstract = {It is known from the wave-like motion of microtubules in motility assays that the piconewton forces that motors produce can be sufficient to bend the filaments. In cellular phenomena such as cytosplasmic streaming, molecular motors translocate along cytoskeletal filaments, carrying cargo which entrains fluid. When large numbers of such forced filaments interact through the surrounding fluid, as in particular stages of oocyte development in Drosophila melanogaster, complex dynamics are observed, but the detailed mechanics underlying them has remained unclear. Motivated by these observations, we study here perhaps the simplest model for these phenomena: an elastic filament, pinned at one end, acted on by a molecular motor treated as a point force. Because the force acts tangential to the filament, no matter what its shape, this 'follower-force' problem is intrinsically non-variational, and thereby differs fundamentally from Euler buckling, where the force has a fixed direction, and which, in the low-Reynolds-number regime, ultimately leads to a stationary, energy-minimizing shape. Through a combination of linear stability theory, analytical study of a solvable simplified 'two-link' model and numerical studies of the full elastohydrodynamic equations of motion, we elucidate the Hopf bifurcation that occurs with increasing forcing of a filament, leading to flapping motion analogous to the high-Reynolds-number oscillations of a garden hose with a free end.}, }
@article {pmid29144304, year = {2017}, author = {Wang, Z and Dong, W and Hu, X and Sun, T and Wang, T and Sun, Y}, title = {Low energy consumption vortex wave flow membrane bioreactor.}, journal = {Water science and technology : a journal of the International Association on Water Pollution Research}, volume = {76}, number = {9-10}, pages = {2465-2472}, doi = {10.2166/wst.2017.400}, pmid = {29144304}, issn = {0273-1223}, mesh = {Bioreactors ; Membranes, Artificial ; Wastewater/*chemistry ; Water Pollutants, Chemical/chemistry ; Water Purification/instrumentation/*methods ; }, abstract = {In order to reduce the energy consumption and membrane fouling of the conventional membrane bioreactor (MBR), a kind of low energy consumption vortex wave flow MBR was exploited based on the combination of biofilm process and membrane filtration process, as well as the vortex wave flow technique. The experimental results showed that the vortex wave flow state in the membrane module could be formed when the Reynolds number (Re) of liquid was adjusted between 450 and 1,050, and the membrane flux declined more slowly in the vortex wave flow state than those in the laminar flow state and turbulent flow state. The MBR system was used to treat domestic wastewater under the condition of vortex wave flow state for 30 days. The results showed that the removal efficiency for CODcr and NH3-N was 82% and 98% respectively, and the permeate quality met the requirement of 'Water quality standard for urban miscellaneous water consumption (GB/T 18920-2002)'. Analysis of the energy consumption of the MBR showed that the average energy consumption was 1.90 ± 0.55 kWh/m[3] (permeate), which was only two thirds of conventional MBR energy consumption.}, }
@article {pmid29131890, year = {2018}, author = {Gamage, PPT and Khalili, F and Khurshidul Azad, MD and Mansy, HA}, title = {Modeling Inspiratory Flow in a Porcine Lung Airway.}, journal = {Journal of biomechanical engineering}, volume = {140}, number = {6}, pages = {0610031-06100311}, pmid = {29131890}, issn = {1528-8951}, support = {R01 EB012142/EB/NIBIB NIH HHS/United States ; R43 HL099053/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Biomechanical Phenomena ; Bronchi/physiology ; Humans ; *Inhalation ; Lung/*physiology ; *Models, Biological ; Pressure ; Swine ; Trachea/physiology ; }, abstract = {Inspiratory flow in a multigeneration pig lung airways was numerically studied at a steady inlet flow rate of 3.2 × 10-4 m3/s corresponding to a Reynolds number of 1150 in the trachea. The model was validated by comparing velocity distributions with previous measurements and simulations in simplified airway geometries. Simulation results provided detailed maps of the axial and secondary flow patterns at different cross sections of the airway tree. The vortex core regions in the airways were visualized using absolute helicity values and suggested the presence of secondary flow vortices where two counter-rotating vortices were observed at the main bifurcation and in many other bifurcations. Both laminar and turbulent flows were considered. Results showed that axial and secondary flows were comparable in the laminar and turbulent cases. Turbulent kinetic energy (TKE) vanished in the more distal airways, which indicates that the flow in these airways approaches laminar flow conditions. The simulation results suggested viscous pressure drop values comparable to earlier studies. The monopodial asymmetric nature of airway branching in pigs resulted in airflow patterns that are different from the less asymmetric human airways. The major daughters of the pig airways tended to have high airflow ratios, which may lead to different particle distribution and sound generation patterns. These differences need to be taken into consideration when interpreting the results of animal studies involving pigs before generalizing these results to humans.}, }
@article {pmid29128680, year = {2018}, author = {Han, X and Fang, H and He, G and Reible, D}, title = {Effects of roughness and permeability on solute transfer at the sediment water interface.}, journal = {Water research}, volume = {129}, number = {}, pages = {39-50}, doi = {10.1016/j.watres.2017.10.049}, pmid = {29128680}, issn = {1879-2448}, mesh = {Computer Simulation ; Friction ; *Geologic Sediments ; Models, Theoretical ; Permeability ; Solutions ; Water ; *Water Movements ; }, abstract = {Understanding the mechanisms of solute transfer across the sediment-water interface plays a crucial role in water quality prediction and management. In this study, different arranged particles are used to form typical rough and permeable beds. Large Eddy Simulation (LES) is used to model the solute transfer from the overlying water to sediment beds. Three rough wall turbulence regimes, i.e., smooth, transitional and rough regime, are separately considered and the effects of bed roughness on solute transfer are quantitatively analyzed. Results show that the classic laws related to Schmidt numbers can well reflect the solute transfer under the smooth regime with small roughness Reynolds numbers. Under the transitional regime, the solute transfer coefficient (KL[+]) is enhanced and the effect of Schmidt number is weakened by increasing roughness Reynolds number. Under the rough regime, the solute transfer is suppressed by the transition layer (Brinkman layer) and controlled by the bed permeability. Moreover, it is found that water depth, friction velocity and bed permeability can be used to estimate the solute transfer velocity (KL) under the completely rough regime.}, }
@article {pmid29117039, year = {2018}, author = {Korakianitis, T and Rezaienia, MA and Paul, G and Avital, E and Rothman, M and Mozafari, S}, title = {Optimization of Axial Pump Characteristic Dimensions and Induced Hemolysis for Mechanical Circulatory Support Devices.}, journal = {ASAIO journal (American Society for Artificial Internal Organs : 1992)}, volume = {64}, number = {6}, pages = {727-734}, pmid = {29117039}, issn = {1538-943X}, support = {II-LB-1111-20007/DH_/Department of Health/United Kingdom ; }, mesh = {*Computer Simulation ; *Equipment Design ; *Heart-Assist Devices ; Hemolysis ; Humans ; Stress, Mechanical ; }, abstract = {The application of axial pumps as ventricular assist devices (VADs) requires significant modifications to the size and characteristics of industrial pumps due to the difference in flow fields of industrial and medical pumps. Industrial pumps operate in the region of Reynolds number Re = 10, whereas axial blood pumps operate in Re < 10. The common pump design technique is to rely on the performance of previously designed pumps using the concept of fluid dynamic similarity. Such data are available for industrial pumps as specific speed-specific diameter (ns-ds) graphs. The difference between the flow fields of industrial and medical pumps makes the industrial ns-ds graphs unsuitable for medical pumps and consequently several clinically available axial blood pumps operate with low efficiencies. In this article, numerical and experimental techniques were used to design 62 axial pump impellers with different design characteristics suitable for VADs and mechanical circulatory support devices (MCSDs). The impellers were manufactured and experimentally tested in various operating conditions of flow, pressure, and rotational speed. The hemocompatibility of the impellers was numerically investigated by modeling shear stress and hemolysis. The highest efficiency of each pump impeller was plotted on an ns-ds diagram. The nondimensional results presented in this article enable preliminary design of efficient and hemocompatible axial flow pumps for VADs and MCSDs.}, }
@article {pmid29104418, year = {2017}, author = {Luo, K and Hu, C and Wu, F and Fan, J}, title = {Direct numerical simulation of turbulent boundary layer with fully resolved particles at low volume fraction.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {29}, number = {5}, pages = {053301}, pmid = {29104418}, issn = {1070-6631}, abstract = {In the present work, a direct numerical simulation (DNS) of dilute particulate flow in a turbulent boundary layer has been conducted, containing thousands of finite-sized solid rigid particles. The particle surfaces are resolved with the multi-direct forcing immersed-boundary method. This is, to the best of the authors' knowledge, the first DNS study of a turbulent boundary layer laden with finite-sized particles. The particles have a diameter of approximately 11.3 wall units, a density of 3.3 times that of the fluid, and a solid volume fraction of 1/1000. The simulation shows that the onset and the completion of the transition processes are shifted earlier with the inclusion of the solid phase and that the resulting streamwise mean velocity of the boundary layer in the particle-laden case is almost consistent with the results of the single-phase case. At the same time, relatively stronger particle movements are observed in the near-wall regions, due to the driving of the counterrotating streamwise vortexes. As a result, increased levels of dissipation occur on the particle surfaces, and the root mean square of the fluctuating velocities of the fluid in the near-wall regions is decreased. Under the present parameters, including the particle Stokes number St[+] = 24 and the particle Reynolds number Rep = 33 based on the maximum instantaneous fluid-solid velocity lag, no vortex shedding behind the particle is observed. Lastly, a trajectory analysis of the particles shows the influence of turbophoresis on particle wall-normal concentration, and the particles that originated between y[+] = 60 and 2/3 of the boundary-layer thickness are the most influenced.}, }
@article {pmid31631889, year = {2017}, author = {Park, GI}, title = {Wall-Modeled Large-Eddy Simulation of a High Reynolds Number Separating and Reattaching Flow.}, journal = {AIAA journal. American Institute of Aeronautics and Astronautics}, volume = {55}, number = {11}, pages = {}, pmid = {31631889}, issn = {1533-385X}, support = {NNX15AU93A//NASA/United States ; }, abstract = {The performance of two wall models based on Reynolds-averaged Navier-Stokes is compared in large-eddy simulation of a high Reynolds number separating and reattaching flow over the NASA wall-mounted hump. Wall modeling significantly improves flow prediction on a coarse grid where the large-eddy simulation with the no-slip wall boundary condition fails. Low-order statistics from the wall-modeled large-eddy simulation are in good agreement with the experiment. Wall-pressure fluctuations from the resolved-scale solution are in good agreement with the experiment, whereas wall shear-stress fluctuations modeled entirely through the wall models appear to be significantly underpredicted. Although the two wall models produce comparable results in the upstream attached flow region, the nonequilibrium wall model outperforms the equilibrium wall model in the separation bubble and recovery region where the key assumptions in the equilibrium model are shown to be invalid.}, }
@article {pmid29061390, year = {2017}, author = {Watson, DJ and Sazonov, I and Zawieja, DC and Moore, JE and van Loon, R}, title = {Integrated geometric and mechanical analysis of an image-based lymphatic valve.}, journal = {Journal of biomechanics}, volume = {64}, number = {}, pages = {172-179}, pmid = {29061390}, issn = {1873-2380}, support = {U01 HL123420/HL/NHLBI NIH HHS/United States ; }, mesh = {Algorithms ; Biomechanical Phenomena ; Compliance ; Computer Simulation ; Humans ; Image Processing, Computer-Assisted ; Lymph/physiology ; Lymphatic Vessels/anatomy &amp; histology/*physiology ; Microscopy, Confocal ; Models, Biological ; Pressure ; }, abstract = {Lymphatic valves facilitate the lymphatic system's role in maintaining fluid homeostasis. Malformed valves are found in several forms of primary lymphœdema, resulting in incurable swelling of the tissues and immune dysfunction. Their experimental study is complicated by their small size and operation in low pressure and low Reynolds number environments. Mathematical models of these structures can give insight and complement experimentation. In this work, we present the first valve geometry reconstructed from confocal imagery and used in the construction of a subject-specific model in a closing mode. A framework is proposed whereby an image is converted into a valve model. An FEA study was performed to identify the significance of the shear modulus, the consequences of smoothing the leaflet surface and the effect of wall motion on valve behaviour. Smoothing is inherent to any analysis from imagery. The nature of the image, segmentation and meshing all cause attenuation of high-frequency features. Smoothing not only causes loss of surface area but also the loss of high-frequency geometric features which may reduce stiffness. This work aimed to consider these effects and inform studies by taking a manual reconstruction and through manifold harmonic analysis, attenuating higher frequency features to replicate lower resolution images or lower degree-of-freedom reconstructions. In conclusion, two metrics were considered: trans-valvular pressure required to close the valve, ΔPc, and the retrograde volume displacement after closure. The higher ΔPc, the greater the volume of lymph that will pass through the valve during closure. Retrograde volume displacement after closure gives a metric of compliance of the valve and for the quality of the valve seal. In the case of the image-specific reconstructed valve, removing features with a wavelength longer than four μm caused changes in ΔPc. Varying the shear modulus from 10 kPa to 60 kPa caused a 3.85-fold increase in the retrograde volume displaced. The inclusion of a non-rigid wall caused ΔPc to increase from 1.56 to 2.52 cmH2O.}, }
@article {pmid29054787, year = {2018}, author = {Chen, Y and Li, Y and Valocchi, AJ and Christensen, KT}, title = {Lattice Boltzmann simulations of liquid CO2 displacing water in a 2D heterogeneous micromodel at reservoir pressure conditions.}, journal = {Journal of contaminant hydrology}, volume = {212}, number = {}, pages = {14-27}, doi = {10.1016/j.jconhyd.2017.09.005}, pmid = {29054787}, issn = {1873-6009}, mesh = {Carbon Dioxide/*chemistry ; *Computer Simulation ; *Microfluidics ; Porosity ; Pressure ; Viscosity ; Water/*chemistry ; }, abstract = {We employed the color-fluid lattice Boltzmann multiphase model to simulate liquid CO2 displacing water documented in experiments in a 2D heterogeneous micromodel at reservoir pressure conditions. The main purpose is to investigate whether lattice Boltzmann simulation can reproduce the CO2 invasion patterns observed in these experiments for a range of capillary numbers. Although the viscosity ratio used in the simulation matches the experimental conditions, the viscosity of the fluids in the simulation is higher than that of the actual fluids used in the experiments. Doing so is required to enhance numerical stability, and is a common strategy employed in the literature when using the lattice Boltzmann method to simulate CO2 displacing water. The simulations reproduce qualitatively similar trends of changes in invasion patterns as the capillary number is increased. However, the development of secondary CO2 pathways, a key feature of the invasion patterns in the simulations and experiments, is found to occur at a much higher capillary number in the simulations compared with the experiments. Additional numerical simulations were conducted to investigate the effect of the absolute value of viscosity on the invasion patterns while maintaining the viscosity ratio and capillary number fixed. These results indicate that the use of a high viscosity (which significantly reduces the inertial effect in the simulations) suppresses the development of secondary CO2 pathways, leading to a different fluid distribution compared with corresponding experiments at the same capillary number. Therefore, inertial effects are not negligible in drainage process with liquid CO2 and water despite the low Reynolds number based on the average velocity, as the local velocity can be much higher due to Haines jump events. These higher velocities, coupled with the low viscosity of CO2, further amplifies the inertial effect. Therefore, we conclude that caution should be taken when using proxy fluids that only rely on the capillary number and viscosity ratio in both experiment and simulation.}, }
@article {pmid29052556, year = {2017}, author = {Chen, D and Kolomenskiy, D and Nakata, T and Liu, H}, title = {Forewings match the formation of leading-edge vortices and dominate aerodynamic force production in revolving insect wings.}, journal = {Bioinspiration &amp; biomimetics}, volume = {13}, number = {1}, pages = {016009}, doi = {10.1088/1748-3190/aa94d7}, pmid = {29052556}, issn = {1748-3190}, mesh = {Animals ; Bees/*physiology ; Biomechanical Phenomena ; Drosophila melanogaster/*physiology ; Manduca/*physiology ; *Models, Biological ; Wings, Animal/anatomy &amp; histology/*physiology ; }, abstract = {In many flying insects, forewings and hindwings are coupled mechanically to achieve flapping flight synchronously while being driven by action of the forewings. How the forewings and hindwings as well as their morphologies contribute to aerodynamic force production and flight control remains unclear. Here we address the point that the forewings can produce most of the aerodynamic forces even with the hindwings removed through a computational fluid dynamic study of three revolving insect wing models, which are identical to the wing morphologies and Reynolds numbers of hawkmoth (Manduca sexta), bumblebee (Bombus ignitus) and fruitfly (Drosophila melanogaster). We find that the forewing morphologies match the formation of leading-edge vortices (LEV) and are responsible for generating sufficient lift forces at the mean angles of attack and the Reynolds numbers where the three representative insects fly. The LEV formation and pressure loading keep almost unchanged with the hindwing removed, and even lead to some improvement in power factor and aerodynamic efficiency. Moreover, our results indicate that the size and strength of the LEVs can be well quantified with introduction of a conical LEV angle, which varies remarkably with angles of attack and Reynolds numbers but within the forewing region while showing less sensitivity to the wing morphologies. This implies that the forewing morphology very likely plays a dominant role in achieving low-Reynolds number aerodynamic performance in natural flyers as well as in revolving and/or flapping micro air vehicles.}, }
@article {pmid29036075, year = {2017}, author = {Prasad, S}, title = {Extended Taylor frozen-flow hypothesis and statistics of optical phase in aero-optics.}, journal = {Journal of the Optical Society of America. A, Optics, image science, and vision}, volume = {34}, number = {6}, pages = {931-942}, doi = {10.1364/JOSAA.34.000931}, pmid = {29036075}, issn = {1520-8532}, abstract = {We present an extended Taylor frozen-flow model for the statistics of the spatiotemporal disturbances of the index of refraction of air and the phase of an optical beam propagated through the turbulent boundary and shear layers in a high-Reynolds-number flow. By incorporating rapid random fluctuations of the flow velocity about a mean convection velocity and an anisotropic spatial power spectrum for the index of refraction, we calculate both the short-delay temporal structure function and the power spectral density of these disturbances. We discuss the predicted scaling behaviors for these quantities in the context of existing experimental observations, showing specifically the agreement of these predictions with some optical phase data obtained by the Airborne Aero-Optical Laboratory.}, }
@article {pmid29027922, year = {2017}, author = {Song, Y and Zhao, K and Zuo, J and Wang, C and Li, Y and Miao, X and Zhao, X}, title = {The Detection of Water Flow in Rectangular Microchannels by Terahertz Time Domain Spectroscopy.}, journal = {Sensors (Basel, Switzerland)}, volume = {17}, number = {10}, pages = {}, pmid = {29027922}, issn = {1424-8220}, abstract = {Flow characteristics of water were tested in a rectangular microchannel for Reynolds number (Re) between 0 and 446 by terahertz time domain spectroscopy (THz-TDS). Output THz peak trough intensities and the calculated absorbances of the flow were analyzed theoretically. The results show a rapid change for Re < 250 and a slow change as Re increases, which is caused by the early transition from laminar to transition flow beginning nearly at Re = 250. Then this finding is confirmed in the plot of the flow resistant. Our results demonstrate that the THz-TDS could be a valuable tool to monitor and character the flow performance in microscale structures.}, }
@article {pmid29027748, year = {2018}, author = {Middleton, K and Kondiboyina, A and Borrett, M and Cui, Y and Mei, X and You, L}, title = {Microfluidics approach to investigate the role of dynamic similitude in osteocyte mechanobiology.}, journal = {Journal of orthopaedic research : official publication of the Orthopaedic Research Society}, volume = {36}, number = {2}, pages = {663-671}, doi = {10.1002/jor.23773}, pmid = {29027748}, issn = {1554-527X}, support = {//CIHR/Canada ; }, mesh = {*Adaptation, Physiological ; Animals ; Biomechanical Phenomena ; Female ; Microfluidic Analytical Techniques ; Osteocytes/*physiology ; *Osteogenesis ; Rats, Sprague-Dawley ; Stress, Mechanical ; }, abstract = {Fluid flow is an important regulator of cell function and metabolism in many tissues. Fluid shear stresses have been used to level the mechanical stimuli applied in vitro with what occurs in vivo. However, these experiments often lack dynamic similarity, which is necessary to ensure the validity of the model. For interstitial fluid flow, the major requirement for dynamic similarity is the Reynolds number (Re), the ratio of inertial to viscous forces, is the same between the system and model. To study the necessity of dynamic similarity for cell mechanotransduction studies, we investigated the response of osteocyte-like MLO-Y4 cells to different Re flows at the same level of fluid shear stress. Osteocytes were chosen for this study as flows applied in vitro and in vivo have Re that are orders of magnitude different. We hypothesize that osteocytes' response to fluid flow is Re dependent. We observed that cells exposed to lower and higher Re flows developed rounded and triangular morphologies, respectively. Lower Re flows also reduced apoptosis rates compared to higher Re flows. Furthermore, MLO-Y4 cells exposed to higher Re flows had stronger calcium responses compared to lower Re flows. However, by also controlling for flow rate, the lower Re flows induced a stronger calcium response; while degradation of components of the osteocyte glycocalyx reversed this effect. This work suggests that osteocytes are highly sensitive to differences in Re, independent of just shear stresses, supporting the need for improved in vitro flow platforms that better recapitulate the physiological environment. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:663-671, 2018.}, }
@article {pmid28989310, year = {2017}, author = {Manikantan, H and Squires, TM}, title = {Irreversible particle motion in surfactant-laden interfaces due to pressure-dependent surface viscosity.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {473}, number = {2205}, pages = {20170346}, pmid = {28989310}, issn = {1364-5021}, abstract = {The surface shear viscosity of an insoluble surfactant monolayer often depends strongly on its surface pressure. Here, we show that a particle moving within a bounded monolayer breaks the kinematic reversibility of low-Reynolds-number flows. The Lorentz reciprocal theorem allows such irreversibilities to be computed without solving the full nonlinear equations, giving the leading-order contribution of surface pressure-dependent surface viscosity. In particular, we show that a disc translating or rotating near an interfacial boundary experiences a force in the direction perpendicular to that boundary. In unbounded monolayers, coupled modes of motion can also lead to non-intuitive trajectories, which we illustrate using an interfacial analogue of the Magnus effect. This perturbative approach can be extended to more complex geometries, and to two-dimensional suspensions more generally.}, }
@article {pmid28982172, year = {2017}, author = {Khan, NB and Ibrahim, Z and Nguyen, LTT and Javed, MF and Jameel, M}, title = {Numerical investigation of the vortex-induced vibration of an elastically mounted circular cylinder at high Reynolds number (Re = 104) and low mass ratio using the RANS code.}, journal = {PloS one}, volume = {12}, number = {10}, pages = {e0185832}, pmid = {28982172}, issn = {1932-6203}, mesh = {*Elasticity ; Models, Theoretical ; *Vibration ; }, abstract = {This study numerically investigates the vortex-induced vibration (VIV) of an elastically mounted rigid cylinder by using Reynolds-averaged Navier-Stokes (RANS) equations with computational fluid dynamic (CFD) tools. CFD analysis is performed for a fixed-cylinder case with Reynolds number (Re) = 104 and for a cylinder that is free to oscillate in the transverse direction and possesses a low mass-damping ratio and Re = 104. Previously, similar studies have been performed with 3-dimensional and comparatively expensive turbulent models. In the current study, the capability and accuracy of the RANS model are validated, and the results of this model are compared with those of detached eddy simulation, direct numerical simulation, and large eddy simulation models. All three response branches and the maximum amplitude are well captured. The 2-dimensional case with the RANS shear-stress transport k-w model, which involves minimal computational cost, is reliable and appropriate for analyzing the characteristics of VIV.}, }
@article {pmid28981539, year = {2017}, author = {Islam, S and Nazeer, G and Ying, ZC and Islam, Z and Manzoor, R}, title = {Transitions in the flow patterns and aerodynamic characteristics of the flow around staggered rows of cylinders.}, journal = {PloS one}, volume = {12}, number = {10}, pages = {e0184169}, pmid = {28981539}, issn = {1932-6203}, mesh = {Computer Simulation ; *Models, Theoretical ; *Physical Phenomena ; }, abstract = {A two-dimensional numerical study of flow across rows of identical square cylinders arranged in staggered fashion is carried out. This study will unreveal complex flow physics depending upon the Reynolds number (Re) and gap spacing (g) between the cylinders. The combined effect of Reynolds number and gap spacing on the flow physics around staggered rows of cylinders are numerically studied for 20 ≤ Re ≤ 140 and 1 ≤ g ≤ 6. We use the lattice Boltzmann method for numerical computations. It is found that with increase in gap spacing between the cylinders the critical Reynolds number for the onset of vortex shedding also increases. We observed a strong effect of Reynolds number at g = 2 and 4. Secondary cylinder interaction frequency disappears for large Reynolds number at g = 6 and 5 and the flow around cylinders are fully dominated by the primary vortex shedding frequency. This ensures that at large gap spacing with an increase in the Reynolds number the wakes interaction between and behind the cylinders is weaken. Furthermore, it also ensures that the wake interaction behind the cylinders is strongly influenced by the jets in the gap spacing between the cylinders. We also found that g = 2 is the critical gap spacing for flow across rows of staggered square cylinders for the considered range of Reynolds number. Depending on the Reynolds number we observed; synchronous, quasi-periodic-I, quasi-periodic-II, and chaotic flow patterns. In synchronous flow pattern, an in-phase and anti-phase characteristics of consecutive cylinders has been observed. The important physical parameters are also analyzed and discussed in detail.}, }
@article {pmid28949715, year = {2017}, author = {Boffetta, G and Musacchio, S}, title = {Chaos and Predictability of Homogeneous-Isotropic Turbulence.}, journal = {Physical review letters}, volume = {119}, number = {5}, pages = {054102}, doi = {10.1103/PhysRevLett.119.054102}, pmid = {28949715}, issn = {1079-7114}, abstract = {We study the chaoticity and the predictability of a turbulent flow on the basis of high-resolution direct numerical simulations at different Reynolds numbers. We find that the Lyapunov exponent of turbulence, which measures the exponential separation of two initially close solutions of the Navier-Stokes equations, grows with the Reynolds number of the flow, with an anomalous scaling exponent, larger than the one obtained on dimensional grounds. For large perturbations, the error is transferred to larger, slower scales, where it grows algebraically generating an "inverse cascade" of perturbations in the inertial range. In this regime, our simulations confirm the classical predictions based on closure models of turbulence. We show how to link chaoticity and predictability of a turbulent flow in terms of a finite size extension of the Lyapunov exponent.}, }
@article {pmid28905060, year = {2017}, author = {Baber, R and Mazzei, L and Thanh, NTK and Gavriilidis, A}, title = {An engineering approach to synthesis of gold and silver nanoparticles by controlling hydrodynamics and mixing based on a coaxial flow reactor.}, journal = {Nanoscale}, volume = {9}, number = {37}, pages = {14149-14161}, doi = {10.1039/c7nr04962e}, pmid = {28905060}, issn = {2040-3372}, abstract = {In this work we present a detailed study of flow technology approaches that could open up new possibilities for nanoparticle synthesis. The synthesis of gold and silver nanoparticles (NPs) in a flow device based on a coaxial flow reactor (CFR) was investigated. The CFR comprised of an outer glass tube of 2 mm inner diameter (I.D.) and an inner glass tube whose I.D. varied between 0.142 and 0.798 mm. A split and recombine (SAR) mixer and coiled flow inverter (CFI) were further employed to alter the mixing conditions after the CFR. The 'Turkevich' method was used to synthesize gold NPs, with a CFR followed by a CFI. This assembly allows control over nucleation and growth through variation of residence time. Increasing the total flow rate from 0.25 ml min[-1] to 3 ml min[-1] resulted initially in a constant Au NP size, and beyond 1 ml min[-1] to a size increase of Au NPs from 17.9 ± 2.1 nm to 23.9 ± 4.7 nm. The temperature was varied between 60-100 °C and a minimum Au NP size of 17.9 ± 2.1 nm was observed at 80 °C. Silver NPs were synthesized in a CFR followed by a SAR mixer, using sodium borohydride to reduce silver nitrate in the presence of trisodium citrate. The SAR mixer provided an enhancement of the well-controlled laminar mixing in the CFR. Increasing silver nitrate concentration resulted in a decrease in Ag NP size from 5.5 ± 2.4 nm to 3.4 ± 1.4 nm. Different hydrodynamic conditions were studied in the CFR operated in isolation for silver NP synthesis. Increasing the Reynolds number from 132 to 530 in the inner tube created a vortex flow resulting in Ag NPs in the size range between 5.9 ± 1.5 nm to 7.7 ± 3.4 nm. Decreasing the inner tube I.D. from 0.798 mm to 0.142 mm resulted in a decrease in Ag NP size from 10.5 ± 4.0 nm to 4.7 ± 1.4 nm. Thus, changing the thickness of the inner stream enabled control over size of the Ag NPs.}, }
@article {pmid30400469, year = {2017}, author = {Afzal, MJ and Tayyaba, S and Ashraf, MW and Hossain, MK and Uddin, MJ and Afzulpurkar, N}, title = {Simulation, Fabrication and Analysis of Silver Based Ascending Sinusoidal Microchannel (ASMC) for Implant of Varicose Veins.}, journal = {Micromachines}, volume = {8}, number = {9}, pages = {}, pmid = {30400469}, issn = {2072-666X}, abstract = {Bioengineered veins can benefit humans needing bypass surgery, dialysis, and now, in the treatment of varicose veins. The implant of this vein in varicose veins has significant advantages over the conventional treatment methods. Deep vein thrombosis (DVT), vein patch repair, pulmonary embolus, and tissue-damaging problems can be solved with this implant. Here, the authors have proposed biomedical microdevices as an alternative for varicose veins. MATLAB and ANSYS Fluent have been used for simulations of blood flow for bioengineered veins. The silver based microchannel has been fabricated by using a micromachining process. The dimensions of the silver substrates are 51 mm, 25 mm, and 1.1 mm, in length, width, and depth respectively. The dimensions of microchannels grooved in the substrates are 0.9 mm in width and depth. The boundary conditions for pressure and velocity were considered, from 1.0 kPa to 1.50 kPa, and 0.02 m/s to 0.07 m/s, respectively. These are the actual values of pressure and velocity in varicose veins. The flow rate of 5.843 (0.1 nL/s) and velocity of 5.843 cm/s were determined at Reynolds number 164.88 in experimental testing. The graphs and results from simulations and experiments are in close agreement. These microchannels can be inserted into varicose veins as a replacement to maintain the excellent blood flow in human legs.}, }
@article {pmid28878968, year = {2017}, author = {Muir, RE and Arredondo-Galeana, A and Viola, IM}, title = {The leading-edge vortex of swift wing-shaped delta wings.}, journal = {Royal Society open science}, volume = {4}, number = {8}, pages = {170077}, pmid = {28878968}, issn = {2054-5703}, abstract = {Recent investigations on the aerodynamics of natural fliers have illuminated the significance of the leading-edge vortex (LEV) for lift generation in a variety of flight conditions. A well-documented example of an LEV is that generated by aircraft with highly swept, delta-shaped wings. While the wing aerodynamics of a manoeuvring aircraft, a bird gliding and a bird in flapping flight vary significantly, it is believed that this existing knowledge can serve to add understanding to the complex aerodynamics of natural fliers. In this investigation, a model non-slender delta-shaped wing with a sharp leading edge is tested at low Reynolds number, along with a delta wing of the same design, but with a modified trailing edge inspired by the wing of a common swift Apus apus. The effect of the tapering swift wing on LEV development and stability is compared with the flow structure over the unmodified delta wing model through particle image velocimetry. For the first time, a leading-edge vortex system consisting of a dual or triple LEV is recorded on a swift wing-shaped delta wing, where such a system is found across all tested conditions. It is shown that the spanwise location of LEV breakdown is governed by the local chord rather than Reynolds number or angle of attack. These findings suggest that the trailing-edge geometry of the swift wing alone does not prevent the common swift from generating an LEV system comparable with that of a delta-shaped wing.}, }
@article {pmid28869874, year = {2017}, author = {Xiang, J and Liu, K and Li, D and Du, J}, title = {Effects of micro-structure on aerodynamics of Coccinella septempunctata elytra (ladybird) in forward flight as assessed via electron microscopy.}, journal = {Micron (Oxford, England : 1993)}, volume = {102}, number = {}, pages = {21-34}, doi = {10.1016/j.micron.2017.08.003}, pmid = {28869874}, issn = {1878-4291}, mesh = {Animals ; Biomechanical Phenomena/*physiology ; Coleoptera/*physiology ; Flight, Animal/*physiology ; Hydrodynamics ; Microscopy, Electron ; Models, Biological ; Wings, Animal/*ultrastructure ; }, abstract = {The effects of micro-structure on aerodynamics of Coccinella septempunctata (Coleoptera: Coccinellidae) elytra in forward flight were investigated. The micro-structure was examined by a scanning electron microscope and a digital microscope. Based on the experimental results, five elytron models were constructed to separately investigate the effects of the camber and the local corrugation in both leading edge and trailing edge on aerodynamics. Computational fluid dynamic simulations of five elytron models were conducted by solving the Reynolds-Averaged Navier-Stokes equations with the Reynolds number of 245. The results show that camber and the local corrugation in the leading edge play significant roles in improving the aerodynamic performance, while the local corrugation in the trailing edge has little effect on aerodynamics.}, }
@article {pmid28862154, year = {2017}, author = {Chung, EG and Ryu, S}, title = {Stalk-length-dependence of the contractility of Vorticella convallaria.}, journal = {Physical biology}, volume = {14}, number = {6}, pages = {066002}, doi = {10.1088/1478-3975/aa89b8}, pmid = {28862154}, issn = {1478-3975}, mesh = {Biomechanical Phenomena ; Calcium/*metabolism ; Energy Metabolism ; Oligohymenophorea/*physiology ; Stress, Mechanical ; }, abstract = {Vorticella convallaria is a sessile protozoan of which the spasmoneme contracts on a millisecond timescale. Because this contraction is induced and powered by the binding of calcium ions (Ca[2+]), the spasmoneme showcases Ca[2+]-powered cellular motility. Because the isometric tension of V. convallaria increases linearly with its stalk length, it is hypothesized that the contractility of V. convallaria during unhindered contraction depends on the stalk length. In this study, the contractile force and energetics of V. convallaria cells of different stalk lengths were evaluated using a fluid dynamic drag model which accounts for the unsteadiness and finite Reynolds number of the water flow caused by contracting V. convallaria and the wall effect of the no-slip substrate. It was found that the contraction displacement, peak contraction speed, peak contractile force, total mechanical work, and peak power depended on the stalk length. The observed stalk-length-dependencies were simulated using a damped spring model, and the model estimated that the average spring constant of the contracting stalk was 1.34 nN µm[-1]. These observed length-dependencies of Vorticella's key contractility parameters reflect the biophysical mechanism of the spasmonemal contraction, and thus they should be considered in developing a theoretical model of the Vorticella spasmoneme.}, }
@article {pmid28852432, year = {2017}, author = {Malvar, S and Gontijo, RG and Carmo, BS and Cunha, FR}, title = {On the kinematics-wave motion of living particles in suspension.}, journal = {Biomicrofluidics}, volume = {11}, number = {4}, pages = {044112}, pmid = {28852432}, issn = {1932-1058}, abstract = {This work presents theoretical and experimental analyses on the kinematics-wave motion of suspended active particles in a biological fluid. The fluid is an active suspension of nematodes immersed in a gel-like biological structure, moving at a low Reynolds number. The nematode chosen for the study is Caenorhabditis elegans. Its motion is subjected to the time reversibility of creeping flows. We investigate how this worm reacts to this reversibility condition in order to break the flow symmetry and move in the surrounding fluid. We show that the relationship between the length of an individual nematode and the wavelength of its motion is linear and can be fitted by a theoretical prediction proposed in this work. We provide a deep discussion regarding the propulsion mechanics based on a scaling analysis that identifies three major forces acting on an individual nematode. These forces are a viscous force, a yield stress force due to gelification of agar molecules in the gel-like medium, and a bending force associated with the muscular tension imposed by the nematodes in the medium. By the scalings, we identify the most relevant physical parameters of the nematode's motion. In order to examine and quantify the motion, dynamical system tools such as FFT are used in the present analysis. The motion characterization is performed by examining (or studying) two different populations: (i) in the absence of food with starving nematodes and (ii) with well-fed nematodes. In addition, several kinematic quantities of the head, center of mass, and tail for a sample of nematodes are also investigated: their slip velocities, wavelengths, trajectories, frequency spectra, and mean curvatures. The main findings of this work are the confirmation of a linear relationship between the nematode's physical length and its motion wavelength, the identification of secondary movements in high frequencies that helps breaking the time-reversibility in which the worms are bonded, and the observation and interpretation of a systematic difference between the individual motion of well-fed and starving nematodes.}, }
@article {pmid28850622, year = {2017}, author = {Aftab, SMA and Ahmad, KA}, title = {CFD study on NACA 4415 airfoil implementing spherical and sinusoidal Tubercle Leading Edge.}, journal = {PloS one}, volume = {12}, number = {8}, pages = {e0183456}, pmid = {28850622}, issn = {1932-6203}, mesh = {Animal Structures/*anatomy &amp; histology ; Animals ; *Computer Simulation ; *Humpback Whale ; *Models, Biological ; }, abstract = {The Humpback whale tubercles have been studied for more than a decade. Tubercle Leading Edge (TLE) effectively reduces the separation bubble size and helps in delaying stall. They are very effective in case of low Reynolds number flows. The current Computational Fluid Dynamics (CFD) study is on NACA 4415 airfoil, at a Reynolds number 120,000. Two TLE shapes are tested on NACA 4415 airfoil. The tubercle designs implemented on the airfoil are sinusoidal and spherical. A parametric study is also carried out considering three amplitudes (0.025c, 0.05c and 0.075c), the wavelength (0.25c) is fixed. Structured mesh is utilized to generate grid and Transition SST turbulence model is used to capture the flow physics. Results clearly show spherical tubercles outperform sinusoidal tubercles. Furthermore experimental study considering spherical TLE is carried out at Reynolds number 200,000. The experimental results show that spherical TLE improve performance compared to clean airfoil.}, }
@article {pmid28837786, year = {2017}, author = {Narla, VK and Prasad, KM and Ramana Murthy, JV}, title = {Time-dependent peristaltic analysis in a curved conduit: Application to chyme movement through intestine.}, journal = {Mathematical biosciences}, volume = {293}, number = {}, pages = {21-28}, doi = {10.1016/j.mbs.2017.08.005}, pmid = {28837786}, issn = {1879-3134}, mesh = {*Gastrointestinal Contents ; *Gastrointestinal Transit ; Intestinal Mucosa/*metabolism ; Magnetic Fields ; *Models, Biological ; *Peristalsis ; Time Factors ; Viscosity ; }, abstract = {A theoretical model of time-dependent peristaltic viscous fluid flow through a curved channel in the presence of an applied magnetic field is investigated. The results for stream function, pressure distribution and mechanical efficiency are obtained under the assumptions of long wavelength and low Reynolds number approximation. Pressure fluctuations due to an integral and a non-integral number of waves along the channel length are discussed under influence of channel curvature and magnetic parameter. Two inherent characteristics of peristaltic flow regimes (trapping and reflux) are discussed numerically. The mechanical efficiency of curved magnetohydrodynamic peristaltic pumping is also examined. The magnitude of pressure increases with an increasing channel curvature and magnetic parameter. Reflex phenomenon is analyzed in the Lagrangian frame of reference. It is observed that reflex in the curved channel is higher than in the straight channel. The trapped fluid in a curved channel is studied in the Eulerian frame of reference and it contains two asymmetric boluses. The size of the lower bolus grows and the upper bolus decreases with increasing effect of magnetic strength. Pumping efficiency of the peristaltic pump is low for curved channel flow than for straight channel flow. Also, the pumping efficiency is comparatively low at the high effect of the magnetic parameter.}, }
@article {pmid28836761, year = {2017}, author = {de Anda, J and Lee, EY and Lee, CK and Bennett, RR and Ji, X and Soltani, S and Harrison, MC and Baker, AE and Luo, Y and Chou, T and O'Toole, GA and Armani, AM and Golestanian, R and Wong, GCL}, title = {High-Speed "4D" Computational Microscopy of Bacterial Surface Motility.}, journal = {ACS nano}, volume = {11}, number = {9}, pages = {9340-9351}, pmid = {28836761}, issn = {1936-086X}, support = {R37 AI083256/AI/NIAID NIH HHS/United States ; T32 GM008042/GM/NIGMS NIH HHS/United States ; U54 CA193417/CA/NCI NIH HHS/United States ; R01 AI102584/AI/NIAID NIH HHS/United States ; T32 GM008185/GM/NIGMS NIH HHS/United States ; }, mesh = {Cell Tracking/methods ; Finite Element Analysis ; Flagella/metabolism ; Hydrodynamics ; Imaging, Three-Dimensional/*methods ; Microscopy/methods ; Pseudomonas aeruginosa/*cytology/metabolism ; Single-Cell Analysis/methods ; }, abstract = {Bacteria exhibit surface motility modes that play pivotal roles in early-stage biofilm community development, such as type IV pili-driven "twitching" motility and flagellum-driven "spinning" and "swarming" motility. Appendage-driven motility is controlled by molecular motors, and analysis of surface motility behavior is complicated by its inherently 3D nature, the speed of which is too fast for confocal microscopy to capture. Here, we combine electromagnetic field computation and statistical image analysis to generate 3D movies close to a surface at 5 ms time resolution using conventional inverted microscopes. We treat each bacterial cell as a spherocylindrical lens and use finite element modeling to solve Maxwell's equations and compute the diffracted light intensities associated with different angular orientations of the bacterium relative to the surface. By performing cross-correlation calculations between measured 2D microscopy images and a library of computed light intensities, we demonstrate that near-surface 3D movies of Pseudomonas aeruginosa translational and rotational motion are possible at high temporal resolution. Comparison between computational reconstructions and detailed hydrodynamic calculations reveals that P. aeruginosa act like low Reynolds number spinning tops with unstable orbits, driven by a flagellum motor with a torque output of ∼2 pN μm. Interestingly, our analysis reveals that P. aeruginosa can undergo complex flagellum-driven dynamical behavior, including precession, nutation, and an unexpected taxonomy of surface motility mechanisms, including upright-spinning bacteria that diffuse laterally across the surface, and horizontal bacteria that follow helicoidal trajectories and exhibit superdiffusive movements parallel to the surface.}, }
@article {pmid28815228, year = {2017}, author = {Kim, J and Hong, SO and Shim, TS and Kim, JM}, title = {Inertio-elastic flow instabilities in a 90° bent microchannel.}, journal = {Soft matter}, volume = {13}, number = {34}, pages = {5656-5664}, doi = {10.1039/c7sm01355h}, pmid = {28815228}, issn = {1744-6848}, abstract = {Biological samples having viscoelastic properties are frequently tested using microfluidic devices. In addition, viscoelastic fluids such as polymer solutions have been used as a suspending medium to spatially focus particles in microchannels. The occurrence of flow instability even at low Reynolds number is a unique property of viscoelastic fluids. In this study, we report the instability in viscoelastic flow for a channel having a 90° bent geometry, which is a characteristic of many microfluidic devices. Interestingly, we observed that the flow instability in aqueous poly(ethylene oxide) (PEO) solution occurs when the concentration of PEO is as low as 50 ppm. We systematically investigated the effects of the polymer concentration, flow rate, and elasticity number on the flow instability. The results show that the flow is stabilized in shear-thinning fluids, whereas the flow instability is amplified when both elastic and inertial effects are pronounced. We believe that this study is useful to design microfluidic devices such as cell-deformability measurement devices based on viscoelastic particle focusing.}, }
@article {pmid28809710, year = {2017}, author = {Zhao, Q and Yan, S and Yuan, D and Zhang, J and Du, H and Alici, G and Li, W}, title = {Double-Mode Microparticle Manipulation by Tunable Secondary Flow in Microchannel With Arc-Shaped Groove Arrays.}, journal = {IEEE transactions on biomedical circuits and systems}, volume = {11}, number = {6}, pages = {1406-1412}, doi = {10.1109/TBCAS.2017.2722012}, pmid = {28809710}, issn = {1940-9990}, mesh = {Microfluidic Analytical Techniques/*methods ; Particle Size ; }, abstract = {In this paper, we proposed a microparticle manipulation approach, by which particles are able to be guided to different equilibrium positions through modulating the Reynolds number. In the microchannel with arc-shaped groove arrays, secondary flow vortex arisen due to the pressure gradient varies in the aspects of both magnitude and shape with the increase of Reynolds number. And the variation of secondary flow vortex brings about different focusing modes of microparticles in the microchannel. We investigated the focusing phenomenon experimentally and analyzed the mechanism through numerical simulations. At a high Reynolds number (Re = 127.27), the geometry-induced secondary flow rotates constantly along a direction, and most particles are guided to the equilibrium position near one side of the microchannel. However, at a low Reynolds number (Re = 2.39), the shapes of geometry-induced secondary flow vortices are obviously different, forming a variant Dean-like vortex that consists of two asymmetric counter-rotating streams in cross sections of the straight channel. Because of the periodical effects, suspended particles are concentrated at another equilibrium position on the opposite side of the microchannel. Meanwhile, the effects of particle size influence both the focusing position and quality in regimes.}, }
@article {pmid28805871, year = {2017}, author = {Hanasoge, S and Ballard, M and Hesketh, PJ and Alexeev, A}, title = {Asymmetric motion of magnetically actuated artificial cilia.}, journal = {Lab on a chip}, volume = {17}, number = {18}, pages = {3138-3145}, doi = {10.1039/c7lc00556c}, pmid = {28805871}, issn = {1473-0189}, mesh = {*Artificial Cells ; Biomechanical Phenomena ; Cilia/*physiology ; Equipment Design ; *Magnets ; *Microfluidics/instrumentation/methods ; *Models, Biological ; Motion ; Rotation ; Viscosity ; }, abstract = {Most microorganisms use hair-like cilia with asymmetric beating to perform vital bio-physical processes. In this paper, we demonstrate a novel fabrication method for creating magnetic artificial cilia capable of such a biologically inspired asymmetric beating pattern essential for inducing microfluidic transport at low Reynolds number. The cilia are fabricated using a lithographic process in conjunction with deposition of magnetic nickel-iron permalloy to create flexible filaments that can be manipulated by varying an external magnetic field. A rotating permanent magnet is used to actuate the cilia. We examine the kinematics of a cilium and demonstrate that the cilium motion is defined by an interplay among elastic, magnetic, and viscous forces. Specifically, the forward stroke is induced by the rotation of the magnet which bends the cilium, whereas the recovery stroke is defined by the straightening of the deformed cilium, releasing accumulated elastic potential energy. This difference in dominating forces acting during the forward stroke and the recovery stroke leads to an asymmetric beating pattern of the cilium. Such magnetic cilia can find applications in microfluidic pumping, mixing, and other fluid handling processes.}, }
@article {pmid31631903, year = {2017}, author = {Yang, XIA and Lozano-Durán, A}, title = {A multifractal model for the momentum transfer process in wall-bounded flows.}, journal = {Journal of fluid mechanics}, volume = {824}, number = {}, pages = {}, pmid = {31631903}, issn = {0022-1120}, support = {NNX15AU93A//NASA/United States ; }, abstract = {The cascading process of turbulent kinetic energy from large-scale fluid motions to small-scale and lesser-scale fluid motions in isotropic turbulence may be modelled as a hierarchical random multiplicative process according to the multifractal formalism. In this work, we show that the same formalism might also be used to model the cascading process of momentum in wall-bounded turbulent flows. However, instead of being a multiplicative process, the momentum cascade process is additive. The proposed multifractal model is used for describing the flow kinematics of the low-pass filtered streamwise wall-shear stress fluctuation τ l ' , where l is the filtering length scale. According to the multifractal formalism, 〈 τ ' 2 〉 ~ log (R e τ) and 〈 exp (p τ l ') 〉 ~ (L / l) ζ p in the log-region, where Re τ is the friction Reynolds number, p is a real number, L is an outer length scale and ζ p is the anomalous exponent of the momentum cascade. These scalings are supported by the data from a direct numerical simulation of channel flow at Re τ = 4200.}, }
@article {pmid28772551, year = {2017}, author = {Ng, WL and Yeong, WY and Naing, MW}, title = {Polyvinylpyrrolidone-Based Bio-Ink Improves Cell Viability and Homogeneity during Drop-On-Demand Printing.}, journal = {Materials (Basel, Switzerland)}, volume = {10}, number = {2}, pages = {}, pmid = {28772551}, issn = {1996-1944}, abstract = {Drop-on-demand (DOD) bioprinting has attracted huge attention for numerous biological applications due to its precise control over material volume and deposition pattern in a contactless printing approach. 3D bioprinting is still an emerging field and more work is required to improve the viability and homogeneity of printed cells during the printing process. Here, a general purpose bio-ink was developed using polyvinylpyrrolidone (PVP) macromolecules. Different PVP-based bio-inks (0%-3% w/v) were prepared and evaluated for their printability; the short-term and long-term viability of the printed cells were first investigated. The Z value of a bio-ink determines its printability; it is the inverse of the Ohnesorge number (Oh), which is the ratio between the Reynolds number and a square root of the Weber number, and is independent of the bio-ink velocity. The viability of printed cells is dependent on the Z values of the bio-inks; the results indicated that the cells can be printed without any significant impairment using a bio-ink with a threshold Z value of ≤9.30 (2% and 2.5% w/v). Next, the cell output was evaluated over a period of 30 min. The results indicated that PVP molecules mitigate the cell adhesion and sedimentation during the printing process; the 2.5% w/v PVP bio-ink demonstrated the most consistent cell output over a period of 30 min. Hence, PVP macromolecules can play a critical role in improving the cell viability and homogeneity during the bioprinting process.}, }
@article {pmid28754380, year = {2018}, author = {Grosjean, G and Hubert, M and Vandewalle, N}, title = {Magnetocapillary self-assemblies: Locomotion and micromanipulation along a liquid interface.}, journal = {Advances in colloid and interface science}, volume = {255}, number = {}, pages = {84-93}, doi = {10.1016/j.cis.2017.07.019}, pmid = {28754380}, issn = {1873-3727}, abstract = {This paper presents an overview and discussion of magnetocapillary self-assemblies. New results are presented, in particular concerning the possible development of future applications. These self-organizing structures possess the notable ability to move along an interface when powered by an oscillatory, uniform magnetic field. The system is constructed as follows. Soft magnetic particles are placed on a liquid interface, and submitted to a magnetic induction field. An attractive force due to the curvature of the interface around the particles competes with an interaction between magnetic dipoles. Ordered structures can spontaneously emerge from these conditions. Furthermore, time-dependent magnetic fields can produce a wide range of dynamic behaviours, including non-time-reversible deformation sequences that produce translational motion at low Reynolds number. In other words, due to a spontaneous breaking of time-reversal symmetry, the assembly can turn into a surface microswimmer. Trajectories have been shown to be precisely controllable. As a consequence, this system offers a way to produce microrobots able to perform different tasks. This is illustrated in this paper by the capture, transport and release of a floating cargo, and the controlled mixing of fluids at low Reynolds number.}, }
@article {pmid28749743, year = {2017}, author = {Morley, ST and Walsh, MT and Newport, DT}, title = {Opportunities for Studying the Hydrodynamic Context for Breast Cancer Cell Spread Through Lymph Flow.}, journal = {Lymphatic research and biology}, volume = {15}, number = {3}, pages = {204-219}, doi = {10.1089/lrb.2017.0005}, pmid = {28749743}, issn = {1557-8585}, mesh = {Animals ; Breast Neoplasms/diagnostic imaging/*pathology ; Cell Adhesion ; *Cell Movement ; Female ; Humans ; *Hydrodynamics ; Lymph Nodes/diagnostic imaging/pathology ; Lymphatic Metastasis ; Lymphatic System/diagnostic imaging/*pathology ; Lymphatic Vessels/diagnostic imaging/physiology ; Models, Biological ; Tumor Microenvironment ; }, abstract = {The lymphatic system serves as the primary route for the metastatic spread of breast cancer cells (BCCs). A scarcity of information exists with regard to the advection of BCCs in lymph flow and a fundamental understanding of the response of BCCs to the forces in the lymphatics needs to be established. This review summarizes the flow environment metastatic BCCs are exposed to in the lymphatics. Special attention is paid to the behavior of cells/particles in microflows in an attempt to elucidate the behavior of BCCs under lymph flow conditions (Reynolds number <1).}, }
@article {pmid31832014, year = {2017}, author = {Coleman, GN and Pirozzoli, S and Quadrio, M and Spalart, PR}, title = {Direct Numerical Simulation and Theory of a Wall-Bounded Flow with Zero Skin Friction.}, journal = {Flow, turbulence and combustion}, volume = {99}, number = {3-4}, pages = {553-564}, doi = {10.1007/s10494-017-9834-x}, pmid = {31832014}, issn = {1573-1987}, support = {/LaRC/Langley Research Center NASA/United States ; N-999999/ImNASA/Intramural NASA/United States ; }, abstract = {We study turbulent plane Couette-Poiseuille (CP) flows in which the conditions (relative wall velocity ΔU w ≡ 2U w , pressure gradient dP/dx and viscosity ν) are adjusted to produce zero mean skin friction on one of the walls, denoted by APG for adverse pressure gradient. The other wall, FPG for favorable pressure gradient, provides the friction velocity uτ , and h is the half-height of the channel. This leads to a one-dimensional family of flows of varying Reynolds number Re ≡ U w h/ν. We apply three codes, and cover three Reynolds numbers stepping by a factor of 2 each time. The agreement between codes is very good, and the Reynolds-number range is sizable. The theoretical questions revolve around Reynolds-number independence in both the core region (free of local viscous effects) and the two wall regions. The core region follows Townsend's hypothesis of universal behavior for the velocity and shear stress, when they are normalized with uτ and h; universality is not observed for all the Reynolds stresses, any more than it is in Poiseuille flow or boundary layers. The behavior at very high Re is unknown. The FPG wall region obeys the classical law of the wall, again for velocity and shear stress, but could suggest a low value for the Karman constant κ, possibly near 0.37. For the APG wall region, Stratford conjectured universal behavior when normalized with the pressure gradient, leading to a square-root law for the velocity. The literature, also covering other flows with zero skin friction, is ambiguous. Our results are very consistent with both of Stratford's conjectures, suggesting that at least in this idealized flow geometry the theory is successful like it was for the classical law of the wall. We appear to know the constants of the law within a 10% bracket. On the other hand, again that does not extend to Reynolds stresses other than the shear stress, but these stresses are passive in the momentum equation.}, }
@article {pmid28732945, year = {2017}, author = {Bulliard-Sauret, O and Ferrouillat, S and Vignal, L and Memponteil, A and Gondrexon, N}, title = {Heat transfer enhancement using 2MHz ultrasound.}, journal = {Ultrasonics sonochemistry}, volume = {39}, number = {}, pages = {262-271}, doi = {10.1016/j.ultsonch.2017.04.021}, pmid = {28732945}, issn = {1873-2828}, abstract = {The present work focuses on possible heat transfer enhancement from a heating plate towards tap water in forced convection by means of 2MHz ultrasound. The thermal approach allows to observe the increase of local convective heat transfer coefficients in the presence of ultrasound and to deduce a correlation between ultrasound power and Nusselt number. Heat transfer coefficient under ultrasound remains constant while heat transfer coefficient under silent conditions increases with Reynolds number from 900 up to 5000. Therefore, heat transfer enhancement factor ranges from 25% up to 90% for the same energy conditions (supplied ultrasonic power=110W and supplied thermal power=450W). In the same time cavitational activity due to 2MHz ultrasound emission was characterized from mechanical and chemical viewpoints without significant results. At least, Particle Image Velocimetry (PIV) measurements have been performed in order to investigate hydrodynamic modifications due to the presence of 2MHz ultrasound. It was therefore possible to propose a better understanding of heat transfer enhancement mechanism with high frequency ultrasound.}, }
@article {pmid28726415, year = {2017}, author = {Zhao, X and Dey, KK and Jeganathan, S and Butler, PJ and Córdova-Figueroa, UM and Sen, A}, title = {Enhanced Diffusion of Passive Tracers in Active Enzyme Solutions.}, journal = {Nano letters}, volume = {17}, number = {8}, pages = {4807-4812}, doi = {10.1021/acs.nanolett.7b01618}, pmid = {28726415}, issn = {1530-6992}, mesh = {Catalysis ; Diffusion ; Energy Transfer ; Enzymes/*chemistry ; Fluorescent Dyes/chemistry ; Kinetics ; Microspheres ; Particle Size ; Rhodamines/chemistry ; Spectrometry, Fluorescence ; Thermodynamics ; Urease/chemistry ; }, abstract = {Colloidal suspensions containing microscopic swimmers have been the focus of recent studies aimed at understanding the principles of energy transfer in fluidic media at low Reynolds number conditions. Going down in scale, active enzymes have been shown to be force-generating, nonequilibrium systems, thus offering opportunity to examine energy transfer at the ultralow Reynolds number regime. By monitoring the change of diffusion of inert tracers dispersed in active enzyme solutions, we demonstrate that the nature of energy transfer in these systems is similar to that reported for larger microscopic active systems, despite the large differences in scale, modes of energy transduction, and propulsion. Additionally, even an enzyme that catalyzes an endothermic reaction behaves analogously, suggesting that heat generation is not the primary factor for the observed enhanced tracer diffusion. Our results provide new insights into the mechanism of energy transfer at the molecular level.}, }
@article {pmid28725740, year = {2016}, author = {Darr, S and Dong, J and Glikin, N and Hartwig, J and Majumdar, A and Leclair, A and Chung, J}, title = {The effect of reduced gravity on cryogenic nitrogen boiling and pipe chilldown.}, journal = {NPJ microgravity}, volume = {2}, number = {}, pages = {16033}, doi = {10.1038/npjmgrav.2016.33}, pmid = {28725740}, issn = {2373-8065}, abstract = {Manned deep space exploration will require cryogenic in-space propulsion. Yet, accurate prediction of cryogenic pipe flow boiling heat transfer is lacking, due to the absence of a cohesive reduced gravity data set covering the expected flow and thermodynamic parameter ranges needed to validate cryogenic two-phase heat transfer models. This work provides a wide range of cryogenic chilldown data aboard an aircraft flying parabolic trajectories to simulate reduced gravity. Liquid nitrogen is used to quench a 1.27 cm diameter tube from room temperature. The pressure, temperature, flow rate, and inlet conditions are reported from 10 tests covering liquid Reynolds number from 2,000 to 80,000 and pressures from 80 to 810 kPa. Corresponding terrestrial gravity tests were performed in upward, downward, and horizontal flow configurations to identify gravity and flow direction effects on chilldown. Film boiling heat transfer was lessened by up to 25% in reduced gravity, resulting in longer time and more liquid to quench the pipe to liquid temperatures. Heat transfer was enhanced by increasing the flow rate, and differences between reduced and terrestrial gravity diminished at high flow rates. The new data set will enable the development of accurate and robust heat transfer models of cryogenic pipe chilldown in reduced gravity.}, }
@article {pmid28709337, year = {2017}, author = {Gürcan, &#xd6;D}, title = {Nested polyhedra model of turbulence.}, journal = {Physical review. E}, volume = {95}, number = {6-1}, pages = {063102}, doi = {10.1103/PhysRevE.95.063102}, pmid = {28709337}, issn = {2470-0053}, abstract = {A discretization of the wave-number space is proposed, using nested polyhedra, in the form of alternating dodecahedra and icosahedra that are self-similarly scaled. This particular choice allows the possibility of forming triangles using only discretized wave vectors when the scaling between two consecutive dodecahedra is equal to the golden ratio and the icosahedron between the two dodecahedra is the dual of the inner dodecahedron. Alternatively, the same discretization can be described as a logarithmically spaced (with a scaling equal to the golden ratio), nested dodecahedron-icosahedron compounds. A wave vector which points from the origin to a vertex of such a mesh, can always find two other discretized wave vectors that are also on the vertices of the mesh (which is not true for an arbitrary mesh). Thus, the nested polyhedra grid can be thought of as a reduction (or decimation) of the Fourier space using a particular set of self-similar triads arranged approximately in a spherical form. For each vertex (i.e., discretized wave vector) in this space, there are either 9 or 15 pairs of vertices (i.e., wave vectors) with which the initial vertex can interact to form a triangle. This allows the reduction of the convolution integral in the Navier-Stokes equation to a sum over 9 or 15 interaction pairs, transforming the equation in Fourier space to a network of "interacting" nodes that can be constructed as a numerical model, which evolves each component of the velocity vector on each node of the network. This model gives the usual Kolmogorov spectrum of k^{-5/3}. Since the scaling is logarithmic, and the number of nodes for each scale is constant, a very large inertial range (i.e., a very high Reynolds number) with a much lower number of degrees of freedom can be considered. Incidentally, by assuming isotropy and a certain relation between the phases, the model can be used to systematically derive shell models.}, }
@article {pmid28709335, year = {2017}, author = {Dorschner, B and Chikatamarla, SS and Karlin, IV}, title = {Entropic multirelaxation-time lattice Boltzmann method for moving and deforming geometries in three dimensions.}, journal = {Physical review. E}, volume = {95}, number = {6-1}, pages = {063306}, doi = {10.1103/PhysRevE.95.063306}, pmid = {28709335}, issn = {2470-0053}, abstract = {Entropic lattice Boltzmann methods have been developed to alleviate intrinsic stability issues of lattice Boltzmann models for under-resolved simulations. Its reliability in combination with moving objects was established for various laminar benchmark flows in two dimensions in our previous work [B. Dorschner, S. Chikatamarla, F. Bösch, and I. Karlin, J. Comput. Phys. 295, 340 (2015)JCTPAH0021-999110.1016/j.jcp.2015.04.017] as well as for three-dimensional one-way coupled simulations of engine-type geometries in B. Dorschner, F. Bösch, S. Chikatamarla, K. Boulouchos, and I. Karlin [J. Fluid Mech. 801, 623 (2016)JFLSA70022-112010.1017/jfm.2016.448] for flat moving walls. The present contribution aims to fully exploit the advantages of entropic lattice Boltzmann models in terms of stability and accuracy and extends the methodology to three-dimensional cases, including two-way coupling between fluid and structure and then turbulence and deforming geometries. To cover this wide range of applications, the classical benchmark of a sedimenting sphere is chosen first to validate the general two-way coupling algorithm. Increasing the complexity, we subsequently consider the simulation of a plunging SD7003 airfoil in the transitional regime at a Reynolds number of Re=40000 and, finally, to access the model's performance for deforming geometries, we conduct a two-way coupled simulation of a self-propelled anguilliform swimmer. These simulations confirm the viability of the new fluid-structure interaction lattice Boltzmann algorithm to simulate flows of engineering relevance.}, }
@article {pmid28698630, year = {2017}, author = {Castillo-Orozco, E and Kar, A and Kumar, R}, title = {Electrospray mode transition of microdroplets with semiconductor nanoparticle suspension.}, journal = {Scientific reports}, volume = {7}, number = {1}, pages = {5144}, pmid = {28698630}, issn = {2045-2322}, abstract = {Electrosprays operate in several modes depending on the flow rate and electric potential. This allows the deposition of droplets containing nanoparticles into discrete nanodot arrays to fabricate various electronic devices. In this study, seven different suspensions with varying properties were investigated. In the dripping mode, the normalized dropsize decreases linearly with electric capillary number, Ca e , (ratio of electric to surface tension forces) up to Ca e ≈ 1.0. The effect of viscous forces is found to be negligible in the dripping mode since the capillary number is small. For flow rates with low Reynolds number, the mode changes to microdripping mode, and then to a planar oscillating microdripping mode as Ca e increases. The normalized dropsize remains nearly constant at 0.07 for Ca e > 3.3. The microdripping mode which is important for depositing discrete array of nanodots is found to occur in the range, 2 ≤ Ca e ≤ 2.5. The droplet frequency increases steadily from dripping to microdripping mode, but stays roughly constant in the oscillating microdripping mode. This work provides a physical basis by which the flow rate and the voltage can be chosen for any nanosuspension to precisely operate in the microdripping mode at a predetermined dropsize and droplet frequency.}, }
@article {pmid28690413, year = {2017}, author = {Marques, F and Meseguer, A and Mellibovsky, F and Weidman, PD}, title = {Extensional channel flow revisited: a dynamical systems perspective.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {473}, number = {2202}, pages = {20170151}, pmid = {28690413}, issn = {1364-5021}, abstract = {Extensional self-similar flows in a channel are explored numerically for arbitrary stretching-shrinking rates of the confining parallel walls. The present analysis embraces time integrations, and continuations of steady and periodic solutions unfolded in the parameter space. Previous studies focused on the analysis of branches of steady solutions for particular stretching-shrinking rates, although recent studies focused also on the dynamical aspects of the problems. We have adopted a dynamical systems perspective, analysing the instabilities and bifurcations the base state undergoes when increasing the Reynolds number. It has been found that the base state becomes unstable for small Reynolds numbers, and a transitional region including complex dynamics takes place at intermediate Reynolds numbers, depending on the wall acceleration values. The base flow instabilities are constitutive parts of different codimension-two bifurcations that control the dynamics in parameter space. For large Reynolds numbers, the restriction to self-similarity results in simple flows with no realistic behaviour, but the flows obtained in the transition region can be a valuable tool for the understanding of the dynamics of realistic Navier-Stokes solutions.}, }
@article {pmid28688478, year = {2017}, author = {Akbar, NS and Butt, AW and Tripathi, D}, title = {Biomechanically driven unsteady non-uniform flow of Copper water and Silver water nanofluids through finite length channel.}, journal = {Computer methods and programs in biomedicine}, volume = {146}, number = {}, pages = {1-9}, doi = {10.1016/j.cmpb.2017.04.016}, pmid = {28688478}, issn = {1872-7565}, mesh = {Copper/*analysis ; Nanostructures/*analysis ; Pressure ; *Rheology ; Silver/*analysis ; Water/*analysis ; }, abstract = {BACKGROUND AND OBJECTIVES: This paper aims to investigate the unsteady flow of two types of nanofluids i.e Copper water nanofluids and Silver water nanofluids) through finite length non-uniform channel driven by peristaltic sinusoidal wave propagations.<br><br>METHODS: The governing equations are reduced in linear form using dimensional analysis and considering the low Reynolds number and large wavelength approximations. The time dependent temperature field, axial velocity, transverse velocity and pressure difference are obtained analytically in closed form solution. Trapping phenomenon is also discussed with the help of contour plots of stream function. A comparative study of pure water (Newtonian fluid), Copper water nanofluids and Silver water nanofluids under the influence of relevant physical parameters is made in graphical form and also discussed. The effects of absorption parameter and Grashof number on velocity profiles, temperature profiles and pressure distribution along the length of channel are examined.<br><br>RESULTS CONCLUSIONS: The computational results reveal that the velocity profile is maximum for Silver water nanofluids however, it is least for Copper water nanofluids. It is also concluded the temperature profile is more for pure water in comparison to Silver water and Copper water nanofluids. This model is applicable to design, micro-peristaltic pumps which help in Nanoparticle-based targeted drug delivery and to transport the sensitive or corrosive fluids, sanitary fluids, slurries and noxious fluids in nuclear industry.}, }
@article {pmid28670352, year = {2017}, author = {Zhou, J and Ryu, S and Admiraal, D}, title = {Flow and transport effect caused by the stalk contraction cycle of Vorticella convallaria.}, journal = {Biomicrofluidics}, volume = {11}, number = {3}, pages = {034119}, pmid = {28670352}, issn = {1932-1058}, abstract = {Vorticella convallaria is a protozoan attached to a substrate by a stalk which can contract in less than 10 ms, translating the zooid toward the substrate with a maximum Reynolds number of ∼1. Following contraction, the stalk slowly relaxes, moving the zooid away from the substrate, which results in creeping flow. Although Vorticella has long been believed to contract to evade danger, it has been suggested that its stalk may contract to enhance food transport near the substrate. To elucidate how Vorticella utilizes its contraction-relaxation cycle, we investigated water flow caused by the cycle, using a computational fluid dynamics model validated with an experimental scale model and particle tracking velocimetry. The simulated flow was visualized and analyzed by tracing virtual particles around the Vorticella. It is observed that one cycle can displace particles up to ∼190 μm with the maximum net vertical displacement of 3-4 μm and that the net transport effect becomes more evident over repeated cycles. This transport effect appears to be due to asymmetry of the contraction and relaxation phases of the flow field, and it can be more effective on motile food particles than non-motile ones. Therefore, our Vorticella model enabled investigating the fluid dynamics principle and ecological role of the transport effects of Vorticella's stalk contraction.}, }
@article {pmid28665292, year = {2017}, author = {Kazemi, A and Van de Riet, K and Curet, OM}, title = {Hydrodynamics of mangrove-type root models: the effect of porosity, spacing ratio and flexibility.}, journal = {Bioinspiration &amp; biomimetics}, volume = {12}, number = {5}, pages = {056003}, doi = {10.1088/1748-3190/aa7ccf}, pmid = {28665292}, issn = {1748-3190}, mesh = {*Biomimetic Materials ; Ecosystem ; Equipment Design ; *Hydrodynamics ; Plant Roots/*anatomy &amp; histology/*physiology ; *Porosity ; Rhizophoraceae/*anatomy &amp; histology/*physiology ; }, abstract = {Mangrove trees play a prominent role in coastal tropic and subtropical regions, providing habitats for many organisms and protecting shorelines against high energy flows. In particular, the species Rhizophora mangle (red mangrove) exhibits complex cluster roots interacting with different hydrological flow conditions. To better understand the resilience of mangrove trees, we modeled the roots as a collection of cylinders with a circular pattern subject to unidirectional flow. We investigated the effect of porosity and spacing ratio between roots by varying both the diameter of the patch, D, and inset cylinders, d. In addition, we modeled hanging roots of red mangroves as cantilevered rigid cylinders on a hinge. Force and velocity measurements were performed in a water tunnel (Reynolds numbers from 2200 to 11 000). Concurrently, we performed 2D flow visualization using a flowing soap film. We found that the frequency of the vortex shedding increases as the diameter of the small cylinders decreases while the patch diameter is constant, therefore increasing the Strouhal number, [Formula: see text]. By comparing the change of Strouhal numbers with a single solid cylinder, we introduced a new length scale, the effective diameter. The effective diameter of the patch decreases as the porosity increases. In addition, we found that patch drag scales linearly with the patch diameter but decreases linearly as the spacing ratio increases. After a spacing ratio of ([Formula: see text]), the force scales linearly with the free stream velocity, and the mean velocity behind the patch is independent of the Reynolds number and the patch effect disappears. For flexible cylinders, we found that a decrease in stiffness increases both patch drag and the wake deficit behind the patch in a similar fashion as increasing the blockage of the patch. This information has the potential to help in the development of methods to design resilient bio-inspired coastline structures.}, }
@article {pmid28658586, year = {2017}, author = {Qamar, A and Warnez, M and Valassis, DT and Guetzko, ME and Bull, JL}, title = {Small-bubble transport and splitting dynamics in a symmetric bifurcation.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {20}, number = {11}, pages = {1182-1194}, doi = {10.1080/10255842.2017.1340466}, pmid = {28658586}, issn = {1476-8259}, support = {R01 EB006476/EB/NIBIB NIH HHS/United States ; }, mesh = {Arteries/physiology ; Embolization, Therapeutic ; Friction ; Humans ; *Microbubbles ; *Models, Theoretical ; Numerical Analysis, Computer-Assisted ; Skin ; Stress, Mechanical ; }, abstract = {Simulations of small bubbles traveling through symmetric bifurcations are conducted to garner information pertinent to gas embolotherapy, a potential cancer treatment. Gas embolotherapy procedures use intra-arterial bubbles to occlude tumor blood supply. As bubbles pass through bifurcations in the blood stream nonhomogeneous splitting and undesirable bioeffects may occur. To aid development of gas embolotherapy techniques, a volume of fluid method is used to model the splitting process of gas bubbles passing through artery and arteriole bifurcations. The model reproduces the variety of splitting behaviors observed experimentally, including the bubble reversal phenomenon. Splitting homogeneity and maximum shear stress along the vessel walls is predicted over a variety of physical parameters. Small bubbles, having initial length less than twice the vessel diameter, were found unlikely to split in the presence of gravitational asymmetry. Maximum shear stresses were found to decrease exponentially with increasing Reynolds number. Vortex-induced shearing near the bifurcation is identified as a possible mechanism for endothelial cell damage.}, }
@article {pmid28658585, year = {2017}, author = {Qamar, A and Bull, JL}, title = {Transport and flow characteristics of an oscillating cylindrical fiber for total artificial lung application.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {20}, number = {11}, pages = {1195-1211}, doi = {10.1080/10255842.2017.1340467}, pmid = {28658585}, issn = {1476-8259}, mesh = {*Artificial Organs ; Biological Transport ; Humans ; Numerical Analysis, Computer-Assisted ; Reproducibility of Results ; *Rheology ; Stress, Mechanical ; Time Factors ; }, abstract = {Mass transport and fluid dynamics characteristics in the vicinity of an oscillating cylindrical fiber with an imposed pulsatile inflow condition are computationally investigated in the present study. The work is motivated by a recently proposed design modification to the Total Artificial Lung (TAL) device, which is expected to provide better gas exchange. Navier-Stokes computations, coupled with convection-diffusion equation are performed to assess flow dynamics and mass transport behavior around the oscillating fiber. The oscillations and the pulsatile free stream velocity are represented by two sinusoidal functions. The resulting non-dimensional parameters are Keulegan-Carpenter number (KC), Schmidt number (Sc), Reynolds number (Re), pulsatile inflow amplitude ([Formula: see text]), and amplitude of cylinder oscillation ([Formula: see text]). Results are computed for [Formula: see text], Sc = 1000, Re = 5 and 10, [Formula: see text] and 0.7 and 0.25 [Formula: see text][Formula: see text][Formula: see text] 5.25. The pulsatile inflow parameters correspond to the flow velocities found in human pulmonary artery while matching the operating TAL Reynolds number. Mass transport from the surface of the cylinder to the bulk fluid is found to be primarily dependent on the size of surface vortices created by the movement of the cylinder. Time-averaged surface Sherwood number (Sh) is dependent on the amplitude and KC of cylinder oscillation. Compared to the fixed cylinder case, a significant gain up to 380% in Sh is achieved by oscillating the cylinder even at the small displacement amplitude (AD = 0.75D). Moreover, with decrease in KC the oscillating cylinder exhibits a lower drag amplitude compared with the fixed cylinder case. Inflow pulsation amplitude has minor effects on the mass transport characteristics. However, an increase in [Formula: see text] results in an increase in the amplitude of the periodic drag force on the cylinder. This rise in the drag amplitude is similar to that measured for the fixed cylinder case. Quantifications of shear stress distribution in the bulk fluid suggest that the physiological concerns of platelet activation and injury to red blood cells due to cylinder oscillation are negligible.}, }
@article {pmid28652683, year = {2017}, author = {Qi, TY and Liu, C and Ni, MJ and Yang, JC}, title = {The linear stability of Hunt-Rayleigh-Bénard flow.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {29}, number = {6}, pages = {064103}, pmid = {28652683}, issn = {1070-6631}, abstract = {The stability of a pressure driven flow in a duct heated from below and subjected to a vertical magnetic field (Hunt-Rayleigh-Bénard flow) is studied. We use the Chebyshev collocation approach to solve the eigenvalue problem for the small-amplitude perturbations. It is demonstrated that the magnetic field can stabilize the flow, while the temperature field can disturb the flow. There exists a threshold for the Hartmann number below which the growth rate changes with the Prandtl number non-monotonously (first increases and then decreases) with a critical Prandtl number for the maximum growth rate. By comparing the [Formula: see text] neutral curves at different Rayleigh numbers, we find that the critical Reynolds number decreases with the increase in the Rayleigh number, which has an obvious influence on the long-wave instability and a little influence on the short-wave instability. The dominant mode of the long-wave instability changes from the boundary layer instability to the inflectional instability with the increase in the growth rate, which forms a new flow map. We also compare the [Formula: see text] curves and find that the critical Rayleigh number decreases with the increase in the Reynolds number. The obtained results gain an insight into the flow stability affected by the temperature field and the magnetic field.}, }
@article {pmid30400388, year = {2017}, author = {Wang, Q and Yuan, D and Li, W}, title = {Analysis of Hydrodynamic Mechanism on Particles Focusing in Micro-Channel Flows.}, journal = {Micromachines}, volume = {8}, number = {7}, pages = {}, pmid = {30400388}, issn = {2072-666X}, abstract = {In this paper, the hydrodynamic mechanism of moving particles in laminar micro-channel flows was numerically investigated. A hydrodynamic criterion was proposed to determine whether particles in channel flows can form a focusing pattern or not. A simple formula was derived to demonstrate how the focusing position varies with Reynolds number and particle size. Based on this proposed criterion, a possible hydrodynamic mechanism was discussed as to why the particles would not be focused if their sizes were too small or the channel Reynolds number was too low. The Re-λ curve (Re, λ respectively represents the channel-based Reynolds number and the particle's diameter scaled by the channel) was obtained using the data fitting with a least square method so as to obtain a parameter range of the focusing pattern. In addition, the importance of the particle rotation to the numerical modeling for the focusing of particles was discussed in view of the hydrodynamics. This research is expected to deepen the understanding of the particle transport phenomena in bounded flow, either in micro or macro fluidic scope.}, }
@article {pmid28619665, year = {2017}, author = {Tripathi, D and Borode, A and Jhorar, R and Bég, OA and Tiwari, AK}, title = {Computer modelling of electro-osmotically augmented three-layered microvascular peristaltic blood flow.}, journal = {Microvascular research}, volume = {114}, number = {}, pages = {65-83}, doi = {10.1016/j.mvr.2017.06.004}, pmid = {28619665}, issn = {1095-9319}, mesh = {Animals ; Biomimetics/methods ; Blood Viscosity ; *Computer Simulation ; *Electroosmosis ; Humans ; *Microcirculation ; Microvessels/anatomy &amp; histology/*physiology ; *Models, Cardiovascular ; *Pulsatile Flow ; Time Factors ; }, abstract = {A theoretical study is presented here for the electro-osmosis modulated peristaltic three-layered capillary flow of viscous fluids with different viscosities in the layers. The layers considered here are the core layer, the intermediate layer and the peripheral layer. The analysis has been carried out under a number of physical restrictions viz. Debye-Hückel linearization (i.e. wall zeta potential ≤25mV) is assumed sufficiently small, thin electric double layer limit (i.e. the peripheral layer is much thicker than the electric double layer thickness), low Reynolds number and large wavelength approximations. A non-dimensional analysis is used to linearize the boundary value problem. Fluid-fluid interfaces, peristaltic pumping characteristics, and trapping phenomenon are simulated. Present study also evaluates the responses of interface, pressure rise, time-averaged volume flow rate, maximum pressure rise, and the influence of Helmholtz-Smoluchowski velocity on the mechanical efficiency (with two different cases of the viscosity of fluids between the intermediate and the peripheral layer). Trapping phenomenon along with bolus dynamics evolution with thin EDL effects are analyzed. The findings of this study may ultimately be useful to control the microvascular flow during the fractionation of blood into plasma (in the peripheral layer), buffy coat (intermediate layer) and erythrocytes (core layer). This work may also contributes in electrophoresis, hematology, electrohydrodynamic therapy and, design and development of biomimetic electro-osmotic pumps.}, }
@article {pmid28618644, year = {2017}, author = {Wang, L and Huang, Y}, title = {Intrinsic flow structure and multifractality in two-dimensional bacterial turbulence.}, journal = {Physical review. E}, volume = {95}, number = {5-1}, pages = {052215}, doi = {10.1103/PhysRevE.95.052215}, pmid = {28618644}, issn = {2470-0053}, abstract = {The active interaction between the bacteria and fluid generates turbulent structures even at zero Reynolds number. The velocity of such a flow obtained experimentally has been quantitatively investigated based on streamline segment analysis. There is a clear transition at about 16 times the organism body length separating two different scale regimes, which may be attributed to the different influence of the viscous effect. Surprisingly the scaling extracted from the streamline segment indicates the existence of scale similarity even at the zero Reynolds number limit. Moreover, the multifractal feature can be quantitatively described via a lognormal formula with the Hurst number H=0.76 and the intermittency parameter μ=0.20, which is coincidentally in agreement with the three-dimensional hydrodynamic turbulence result. The direction of cascade is measured via the filter-space technique. An inverse energy cascade is confirmed. For the enstrophy, a forward cascade is observed when r/R≤3, and an inverse one is observed when r/R>3, where r and R are the separation distance and the bacteria body size, respectively. Additionally, the lognormal statistics is verified for the coarse-grained energy dissipation and enstrophy, which supports the lognormal formula to fit the measured scaling exponent.}, }
@article {pmid28618575, year = {2017}, author = {True, AC and Crimaldi, JP}, title = {Hydrodynamics of viscous inhalant flows.}, journal = {Physical review. E}, volume = {95}, number = {5-1}, pages = {053107}, doi = {10.1103/PhysRevE.95.053107}, pmid = {28618575}, issn = {2470-0053}, abstract = {Inhalant flows draw fluid into an orifice from a reservoir and are ubiquitous in engineering and biology. Surprisingly, there is a lack of quantitative information on viscous inhalant flows. We consider here laminar flows (Reynolds number Re≤100) developing after impulsive inhalation begins. We implement finite element simulations of flows with varying Re and extraction height h (orifice height above a bottom bed). Numerical results are experimentally validated using particle image velocimetry measurements in a physical model for a representative flow case in the middle of the Re-h parameter space. We use two metrics to characterize the flow in space and time: regions of influence (ROIs), which describe the spatial extent of the flow field, and inhalation volumes, which describe the initial distribution of inhaled fluid. The transient response for all Re features an inviscid sinklike component at early times followed by a viscous diffusive component. At lower Re, diffusion entrains an increasing volume of fluid over time, enlarging the ROI indefinitely. In some geometries, these flows spatially bifurcate, with some fluid being inhaled through the orifice and some bypassing into recirculation. At higher Re, inward advection dominates outward viscous diffusion and the flow remains trapped in a sinklike state. Both ROIs and inhalation volumes are strongly dependent on Re and extraction height, suggesting that organisms or engineers could tune these parameters to achieve specific inhalation criteria.}, }
@article {pmid28618505, year = {2017}, author = {Puljiz, M and Menzel, AM}, title = {Forces and torques on rigid inclusions in an elastic environment: Resulting matrix-mediated interactions, displacements, and rotations.}, journal = {Physical review. E}, volume = {95}, number = {5-1}, pages = {053002}, doi = {10.1103/PhysRevE.95.053002}, pmid = {28618505}, issn = {2470-0053}, abstract = {Embedding rigid inclusions into elastic matrix materials is a procedure of high practical relevance, for instance, for the fabrication of elastic composite materials. We theoretically analyze the following situation. Rigid spherical inclusions are enclosed by a homogeneous elastic medium under stick boundary conditions. Forces and torques are directly imposed from outside onto the inclusions or are externally induced between them. The inclusions respond to these forces and torques by translations and rotations against the surrounding elastic matrix. This leads to elastic matrix deformations, and in turn results in mutual long-ranged matrix-mediated interactions between the inclusions. Adapting a well-known approach from low-Reynolds-number hydrodynamics, we explicitly calculate the displacements and rotations of the inclusions from the externally imposed or induced forces and torques. Analytical expressions are presented as a function of the inclusion configuration in terms of displaceability and rotateability matrices. The role of the elastic environment is implicitly included in these relations. That is, the resulting expressions allow a calculation of the induced displacements and rotations directly from the inclusion configuration, without having to explicitly determine the deformations of the elastic environment. In contrast to the hydrodynamic case, compressibility of the surrounding medium is readily taken into account. We present the complete derivation based on the underlying equations of linear elasticity theory. In the future, the method will, for example, be helpful to characterize the behavior of externally tunable elastic composite materials, to accelerate numerical approaches, as well as to improve the quantitative interpretation of microrheological results.}, }
@article {pmid28618504, year = {2017}, author = {Altmeyer, S and Lueptow, RM}, title = {Wave propagation reversal for wavy vortices in wide-gap counter-rotating cylindrical Couette flow.}, journal = {Physical review. E}, volume = {95}, number = {5-1}, pages = {053103}, doi = {10.1103/PhysRevE.95.053103}, pmid = {28618504}, issn = {2470-0053}, abstract = {We present a numerical study of wavy supercritical cylindrical Couette flow between counter-rotating cylinders in which the wavy pattern propagates either prograde with the inner cylinder or retrograde opposite the rotation of the inner cylinder. The wave propagation reversals from prograde to retrograde and vice versa occur at distinct values of the inner cylinder Reynolds number when the associated frequency of the wavy instability vanishes. The reversal occurs for both twofold and threefold symmetric wavy vortices. Moreover, the wave propagation reversal only occurs for sufficiently strong counter-rotation. The flow pattern reversal appears to be intrinsic in the system as either periodic boundary conditions or fixed end wall boundary conditions for different system sizes always result in the wave propagation reversal. We present a detailed bifurcation sequence and parameter space diagram with respect to retrograde behavior of wavy flows. The retrograde propagation of the instability occurs when the inner Reynolds number is about two times the outer Reynolds number. The mechanism for the retrograde propagation is associated with the inviscidly unstable region near the inner cylinder and the direction of the global average azimuthal velocity. Flow dynamics, spatio-temporal behavior, global mean angular velocity, and torque of the flow with the wavy pattern are explored.}, }
@article {pmid28613306, year = {2017}, author = {Khojah, R and Stoutamore, R and Di Carlo, D}, title = {Size-tunable microvortex capture of rare cells.}, journal = {Lab on a chip}, volume = {17}, number = {15}, pages = {2542-2549}, doi = {10.1039/c7lc00355b}, pmid = {28613306}, issn = {1473-0189}, mesh = {Blood Cells/cytology ; Cell Line, Tumor ; Cell Separation/*instrumentation/*methods ; Cell Size ; Humans ; Image Processing, Computer-Assisted/methods ; MCF-7 Cells ; Microfluidic Analytical Techniques/*instrumentation ; Microscopy, Fluorescence ; }, abstract = {Inertial separation of particles and cells based on their size has advanced significantly over the last decade. However, size-based inertial separation methods require precise tuning of microfluidic device geometries to adjust the separation size of particles or cells. Here, we show a passive capture method that targets a wide size range of cells by controlling the flow conditions in a single device geometry. This multimodal capture device is designed to generate laminar vortices in lateral cavities that branch from long rectangular channels. Micro-vortices generated at lower Reynolds numbers capture and stabilize large particles in equilibrium orbits or limit cycles near the vortex core. Other smaller particles or cells orbit near the vortex boundaries and they are susceptible to exiting the cavity flow. In the same cavity, however, at higher Reynolds number, we observe small particles migrating inward. This evolution in limit cycle trajectories led to a corresponding evolution in the average size of captured particles, indicating that the outermost orbits are less stable. We identify three phases of capture as a function of Reynolds number that give rise to unique particle orbit trajectories. Flow-based switching overcomes a major engineering challenge to automate capture and release of polydisperse cell subpopulations. The approach can expand clinical applications of label free trapping in isolating and processing a larger subset of rare cells like circulating tumor cells (CTCs) from blood and other body fluids.}, }
@article {pmid28613157, year = {2017}, author = {Ferreira, RR and Vilfan, A and Jülicher, F and Supatto, W and Vermot, J}, title = {Physical limits of flow sensing in the left-right organizer.}, journal = {eLife}, volume = {6}, number = {}, pages = {}, pmid = {28613157}, issn = {2050-084X}, mesh = {Animals ; *Body Patterning ; Cilia/*physiology ; Embryo, Nonmammalian/cytology/*physiology ; Functional Laterality ; Gene Expression Regulation, Developmental ; Hydrodynamics ; Signal Transduction ; Zebrafish/embryology/*physiology ; Zebrafish Proteins/metabolism ; }, abstract = {Fluid flows generated by motile cilia are guiding the establishment of the left-right asymmetry of the body in the vertebrate left-right organizer. Competing hypotheses have been proposed: the direction of flow is sensed either through mechanosensation, or via the detection of chemical signals transported in the flow. We investigated the physical limits of flow detection to clarify which mechanisms could be reliably used for symmetry breaking. We integrated parameters describing cilia distribution and orientation obtained in vivo in zebrafish into a multiscale physical study of flow generation and detection. Our results show that the number of immotile cilia is too small to ensure robust left and right determination by mechanosensing, given the large spatial variability of the flow. However, motile cilia could sense their own motion by a yet unknown mechanism. Finally, transport of chemical signals by the flow can provide a simple and reliable mechanism of asymmetry establishment.}, }
@article {pmid28582613, year = {2017}, author = {Chu, X and Yu, X and Greenstein, J and Aydin, F and Uppaladadium, G and Dutt, M}, title = {Flow-Induced Shape Reconfiguration, Phase Separation, and Rupture of Bio-Inspired Vesicles.}, journal = {ACS nano}, volume = {11}, number = {7}, pages = {6661-6671}, doi = {10.1021/acsnano.7b00753}, pmid = {28582613}, issn = {1936-086X}, mesh = {1,2-Dipalmitoylphosphatidylcholine/*chemistry ; Biomimetic Materials/*chemistry ; Cell Shape ; Cholesterol/chemistry ; Computer Simulation ; Dimyristoylphosphatidylcholine/*chemistry ; Drug Carriers/*chemistry ; Erythrocytes/chemistry/cytology ; Glycolipids/chemistry ; Hydrodynamics ; Liposomes/chemistry ; Models, Molecular ; *Phase Transition ; Polyethylene Glycols/*chemistry ; }, abstract = {The structural integrity of red blood cells and drug delivery carriers through blood vessels is dependent upon their ability to adapt their shape during their transportation. Our goal is to examine the role of the composition of bio-inspired multicomponent and hairy vesicles on their shape during their transport through in a channel. Through the dissipative particle dynamics simulation technique, we apply Poiseuille flow in a cylindrical channel. We investigate the effect of flow conditions and concentration of key molecular components on the shape, phase separation, and structural integrity of the bio-inspired multicomponent and hairy vesicles. Our results show the Reynolds number and molecular composition of the vesicles impact their flow-induced deformation, phase separation on the outer monolayer due to the Marangoni effect, and rupture. The findings from this study could be used to enhance the design of drug delivery and tissue engineering systems.}, }
@article {pmid28577022, year = {2017}, author = {Huang, Y and Wang, HL and Chen, YQ and Zhang, YH and Yang, Q and Bai, ZS and Ma, L}, title = {Liquid-liquid extraction intensification by micro-droplet rotation in a hydrocyclone.}, journal = {Scientific reports}, volume = {7}, number = {1}, pages = {2678}, pmid = {28577022}, issn = {2045-2322}, abstract = {The previous literature reports that using a hydrocyclone as an extractor intensifies the mass transfer and largely reduces the consumption of extractant from 1800-2000 kg h[-1] to 30-90 kg h[-1]. However, the intensification mechanism has not been clear. This paper presents experimental and numerical methods to study the multi-scale motion of particles in hydrocyclones. In addition to the usually considered translational behavior, the high-speed rotation of dispersed micro-spheres caused by the anisotropic swirling shear flow is determined. The rotation speeds of the tested micro-spheres are above 1000 rad s[-1], which are much larger than the instantaneous rotation speed in isotropic turbulence. Due to the conical structure of a hydrocyclone, the rotation speed maintains stability along the axial direction. Numerical results show that the particle Reynolds number of micro-droplets in a hydrocyclone is equal to that in conventional extractors, but the particles have high rotation speeds of up to 10,000 rad s[-1] and long mixing lengths of more than 1000 mm. Both the rotation of micro-droplets along the spiral trajectories and the intense eddy diffusion in a hydrocyclone contribute to the extraction intensification.}, }
@article {pmid28573002, year = {2017}, author = {Petford, N and Mirhadizadeh, S}, title = {Image-based modelling of lateral magma flow: the Basement Sill, Antarctica.}, journal = {Royal Society open science}, volume = {4}, number = {5}, pages = {161083}, pmid = {28573002}, issn = {2054-5703}, abstract = {The McMurdo Dry Valleys magmatic system, Antarctica, provides a world-class example of pervasive lateral magma flow on a continental scale. The lowermost intrusion (Basement Sill) offers detailed sections through the now frozen particle microstructure of a congested magma slurry. We simulated the flow regime in two and three dimensions using numerical models built on a finite-element mesh derived from field data. The model captures the flow behaviour of the Basement Sill magma over a viscosity range of 1-10[4] Pa s where the higher end (greater than or equal to 10[2] Pa s) corresponds to a magmatic slurry with crystal fractions varying between 30 and 70%. A novel feature of the model is the discovery of transient, low viscosity (less than or equal to 50 Pa s) high Reynolds number eddies formed along undulating contacts at the floor and roof of the intrusion. Numerical tracing of particle orbits implies crystals trapped in eddies segregate according to their mass density. Recovered shear strain rates (10[-3]-10[-5] s[-1]) at viscosities equating to high particle concentrations (around more than 40%) in the Sill interior point to shear-thinning as an explanation for some types of magmatic layering there. Model transport rates for the Sill magmas imply a maximum emplacement time of ca 10[5] years, consistent with geochemical evidence for long-range lateral flow. It is a theoretically possibility that fast-flowing magma on a continental scale will be susceptible to planetary-scale rotational forces.}, }
@article {pmid28555615, year = {2017}, author = {Stieger, T and Agha, H and Schoen, M and Mazza, MG and Sengupta, A}, title = {Hydrodynamic cavitation in Stokes flow of anisotropic fluids.}, journal = {Nature communications}, volume = {8}, number = {}, pages = {15550}, pmid = {28555615}, issn = {2041-1723}, abstract = {Cavitation, the nucleation of vapour in liquids, is ubiquitous in fluid dynamics, and is often implicated in a myriad of industrial and biomedical applications. Although extensively studied in isotropic liquids, corresponding investigations in anisotropic liquids are largely lacking. Here, by combining liquid crystal microfluidic experiments, nonequilibrium molecular dynamics simulations and theoretical arguments, we report flow-induced cavitation in an anisotropic fluid. The cavitation domain nucleates due to sudden pressure drop upon flow past a cylindrical obstacle within a microchannel. For an anisotropic fluid, the inception and growth of the cavitation domain ensued in the Stokes regime, while no cavitation was observed in isotropic liquids flowing under similar hydrodynamic parameters. Using simulations we identify a critical value of the Reynolds number for cavitation inception that scales inversely with the order parameter of the fluid. Strikingly, the critical Reynolds number for anisotropic fluids can be 50% lower than that of isotropic fluids.}, }
@article {pmid28529384, year = {2017}, author = {Rosti, ME and Kamps, L and Bruecker, C and Omidyeganeh, M and Pinelli, A}, title = {The PELskin project-part V: towards the control of the flow around aerofoils at high angle of attack using a self-activated deployable flap.}, journal = {Meccanica}, volume = {52}, number = {8}, pages = {1811-1824}, pmid = {28529384}, issn = {0025-6455}, abstract = {During the flight of birds, it is often possible to notice that some of the primaries and covert feathers on the upper side of the wing pop-up under critical flight conditions, such as the landing approach or when stalking their prey (see Fig. 1) . It is often conjectured that the feathers pop up plays an aerodynamic role by limiting the spread of flow separation . A combined experimental and numerical study was conducted to shed some light on the physical mechanism determining the feathers self actuation and their effective role in controlling the flow field in nominally stalled conditions. In particular, we have considered a NACA0020 aerofoil, equipped with a flexible flap at low chord Reynolds numbers. A parametric study has been conducted on the effects of the length, natural frequency, and position of the flap. A configuration with a single flap hinged on the suction side at 70 % of the chord size c (from the leading edge), with a length of [Formula: see text] matching the shedding frequency of vortices at stall condition has been found to be optimum in delivering maximum aerodynamic efficiency and lift gains. Flow evolution both during a ramp-up motion (incidence angle from [Formula: see text] to [Formula: see text] with a reduced frequency of [Formula: see text], [Formula: see text] being the free stream velocity magnitude), and at a static stalled condition ([Formula: see text]) were analysed with and without the flap. A significant increase of the mean lift after a ramp-up manoeuvre is observed in presence of the flap. Stall dynamics (i.e., lift overshoot and oscillations) are altered and the simulations reveal a periodic re-generation cycle composed of a leading edge vortex that lift the flap during his passage, and an ejection generated by the relaxing of the flap in its equilibrium position. The flap movement in turns avoid the interaction between leading and trailing edge vortices when lift up and push the trailing edge vortex downstream when relaxing back. This cyclic behaviour is clearly shown by the periodic variation of the lift about the average value, and also from the periodic motion of the flap. A comparison with the experiments shows a similar but somewhat higher non-dimensional frequency of the flap oscillation. By assuming that the cycle frequency scales inversely with the boundary layer thickness, one can explain the higher frequencies observed in the experiments which were run at a Reynolds number about one order of magnitude higher than in the simulations. In addition, in experiments the periodic re-generation cycle decays after 3-4 periods ultimately leading to the full stall of the aerofoil. In contrast, the 2D simulations show that the cycle can become self-sustained without any decay when the flap parameters are accurately tuned.}, }
@article {pmid28508858, year = {2017}, author = {Doostmohammadi, A and Shendruk, TN and Thijssen, K and Yeomans, JM}, title = {Onset of meso-scale turbulence in active nematics.}, journal = {Nature communications}, volume = {8}, number = {}, pages = {15326}, pmid = {28508858}, issn = {2041-1723}, support = {291234/ERC_/European Research Council/International ; }, abstract = {Meso-scale turbulence is an innate phenomenon, distinct from inertial turbulence, that spontaneously occurs at low Reynolds number in fluidized biological systems. This spatiotemporal disordered flow radically changes nutrient and molecular transport in living fluids and can strongly affect the collective behaviour in prominent biological processes, including biofilm formation, morphogenesis and cancer invasion. Despite its crucial role in such physiological processes, understanding meso-scale turbulence and any relation to classical inertial turbulence remains obscure. Here we show how the motion of active matter along a micro-channel transitions to meso-scale turbulence through the evolution of locally disordered patches (active puffs) from an ordered vortex-lattice flow state. We demonstrate that the stationary critical exponents of this transition to meso-scale turbulence in a channel coincide with the directed percolation universality class. This finding bridges our understanding of the onset of low-Reynolds-number meso-scale turbulence and traditional scale-invariant turbulence in confinement.}, }
@article {pmid28505761, year = {2017}, author = {Pride, SR and Vasco, DW and Flekkoy, EG and Holtzman, R}, title = {Dispersive transport and symmetry of the dispersion tensor in porous media.}, journal = {Physical review. E}, volume = {95}, number = {4-1}, pages = {043103}, doi = {10.1103/PhysRevE.95.043103}, pmid = {28505761}, issn = {2470-0053}, abstract = {The macroscopic laws controlling the advection and diffusion of solute at the scale of the porous continuum are derived in a general manner that does not place limitations on the geometry and time evolution of the pore space. Special focus is given to the definition and symmetry of the dispersion tensor that is controlling how a solute plume spreads out. We show that the dispersion tensor is not symmetric and that the asymmetry derives from the advective derivative in the pore-scale advection-diffusion equation. When flow is spatially variable across a voxel, such as in the presence of a permeability gradient, the amount of asymmetry can be large. As first shown by Auriault [J.-L. Auriault et al. Transp. Porous Med. 85, 771 (2010)TPMEEI0169-391310.1007/s11242-010-9591-y] in the limit of low Péclet number, we show that at any Péclet number, the dispersion tensor D_{ij} satisfies the flow-reversal symmetry D_{ij}(+q)=D_{ji}(-q) where q is the mean flow in the voxel under analysis; however, Reynold's number must be sufficiently small that the flow is reversible when the force driving the flow changes sign. We also demonstrate these symmetries using lattice-Boltzmann simulations and discuss some subtle aspects of how to measure the dispersion tensor numerically. In particular, the numerical experiments demonstrate that the off-diagonal components of the dispersion tensor are antisymmetric which is consistent with the analytical dependence on the average flow gradients that we propose for these off-diagonal components.}, }
@article {pmid28505752, year = {2017}, author = {Tasaka, Y and Iima, M}, title = {Surface switching statistics of rotating fluid: Disk-rim gap effects.}, journal = {Physical review. E}, volume = {95}, number = {4-1}, pages = {043113}, doi = {10.1103/PhysRevE.95.043113}, pmid = {28505752}, issn = {2470-0053}, abstract = {We examined the influence of internal noise on the irregular switching of the shape of the free surface of fluids in an open cylindrical vessel driven by a bottom disk rotating at constant speed [Suzuki, Iima, and Hayase, Phys. Fluids 18, 101701 (2006)PHFLE61070-663110.1063/1.2359740]. A slight increase in the disk-rim gap (less than 3% of the disk radius) was established experimentally to cause significant changes in this system, specifically, frequent appearance of the surface descending event connecting a nonaxisymmetric shape in strong mixing flow (turbulent flow) and an axisymmetric shape in laminar flow, as well as a shift in critical Reynolds number that define the characteristic states. The physical mechanism underlying the change is analyzed in terms of flow characteristics in the disk-rim gap, which acts as a noise source, and a mathematical model established from measurements of the surface height fluctuations with noise term.}, }
@article {pmid28479987, year = {2017}, author = {Tank, J and Smith, L and Spedding, GR}, title = {Correction to 'On the possibility (or lack thereof) of agreement between experiment and computation of flows over wings at moderate Reynolds number'.}, journal = {Interface focus}, volume = {7}, number = {3}, pages = {20170024}, doi = {10.1098/rsfs.2017.0024}, pmid = {28479987}, issn = {2042-8898}, abstract = {[This corrects the article DOI: 10.1098/rsfs.2016.0076.].}, }
@article {pmid28479086, year = {2017}, author = {Moroni, M and Lupo, E and La Marca, F}, title = {Hydraulic separation of plastic wastes: Analysis of liquid-solid interaction.}, journal = {Waste management (New York, N.Y.)}, volume = {66}, number = {}, pages = {13-22}, doi = {10.1016/j.wasman.2017.04.045}, pmid = {28479086}, issn = {1879-2456}, mesh = {*Plastics ; Polymers ; *Recycling ; Refuse Disposal ; }, abstract = {The separation of plastic wastes in mechanical recycling plants is the process that ensures high-quality secondary raw materials. An innovative device employing a wet technology for particle separation is presented in this work. Due to the combination of the characteristic flow pattern developing within the apparatus and density, shape and size differences among two or more polymers, it allows their separation into two products, one collected within the instrument and the other one expelled through its outlet ducts. The kinematic investigation of the fluid flowing within the apparatus seeded with a passive tracer was conducted via image analysis for different hydraulic configurations. The two-dimensional turbulent kinetic energy results strictly connected to the apparatus separation efficacy. Image analysis was also employed to study the behaviour of mixtures of passive tracer and plastic particles with different physical characteristics in order to understand the coupling regime between fluid and solid phases. The two-dimensional turbulent kinetic energy analysis turned out to be fundamental to this aim. For the tested operating conditions, two-way coupling takes place, i.e., the fluid exerts an influence on the plastic particle and the opposite occurs too. Image analysis confirms the outcomes from the investigation of the two-phase flow via non-dimensional numbers (particle Reynolds number, Stokes number and solid phase volume fraction).}, }
@article {pmid28470538, year = {2017}, author = {Hosseinzadegan, H and Tafti, DK}, title = {Prediction of Thrombus Growth: Effect of Stenosis and Reynolds Number.}, journal = {Cardiovascular engineering and technology}, volume = {8}, number = {2}, pages = {164-181}, doi = {10.1007/s13239-017-0304-3}, pmid = {28470538}, issn = {1869-4098}, mesh = {Algorithms ; Heparin/*metabolism ; Humans ; Models, Theoretical ; Platelet Activation ; Platelet Adhesiveness ; Platelet Aggregation ; Shear Strength ; Thrombosis/*physiopathology ; }, abstract = {Shear stresses play a major role in platelet-substrate interactions and thrombus formation and growth in blood flow, where under both pathological and physiological conditions platelet adhesion and accumulation occur. In this study, a shear-dependent continuum model for platelet activation, adhesion and aggregation is presented. The model was first verified under three different shear conditions and at two heparin levels. Three-dimensional simulations were then carried out to evaluate the performance of the model for severely damaged (stripped) aortas with mild and severe stenosis degrees in laminar flow regime. For these cases, linear shear-dependent functions were developed for platelet-surface and platelet-platelet adhesion rates. It was confirmed that the platelet adhesion rate is not only a function of Reynolds number (or wall shear rate) but also the stenosis severity of the vessel. General correlations for adhesion rates of platelets as functions of stenosis and Reynolds number were obtained based on these cases. Finally using the new platelet adhesion rates, the model was applied to different experimental systems and shown to agree well with measured platelet deposition.}, }
@article {pmid28462417, year = {2017}, author = {Khani, M and Xing, T and Gibbs, C and Oshinski, JN and Stewart, GR and Zeller, JR and Martin, BA}, title = {Nonuniform Moving Boundary Method for Computational Fluid Dynamics Simulation of Intrathecal Cerebrospinal Flow Distribution in a Cynomolgus Monkey.}, journal = {Journal of biomechanical engineering}, volume = {139}, number = {8}, pages = {0810051-08100512}, pmid = {28462417}, issn = {1528-8951}, support = {P20 GM103408/GM/NIGMS NIH HHS/United States ; R44 MH112210/MH/NIMH NIH HHS/United States ; U54 GM104944/GM/NIGMS NIH HHS/United States ; }, mesh = {Animals ; Cerebrospinal Fluid/diagnostic imaging/*physiology ; *Computer Simulation ; *Hydrodynamics ; Macaca fascicularis ; Magnetic Resonance Imaging ; Male ; }, abstract = {A detailed quantification and understanding of cerebrospinal fluid (CSF) dynamics may improve detection and treatment of central nervous system (CNS) diseases and help optimize CSF system-based delivery of CNS therapeutics. This study presents a computational fluid dynamics (CFD) model that utilizes a nonuniform moving boundary approach to accurately reproduce the nonuniform distribution of CSF flow along the spinal subarachnoid space (SAS) of a single cynomolgus monkey. A magnetic resonance imaging (MRI) protocol was developed and applied to quantify subject-specific CSF space geometry and flow and define the CFD domain and boundary conditions. An algorithm was implemented to reproduce the axial distribution of unsteady CSF flow by nonuniform deformation of the dura surface. Results showed that maximum difference between the MRI measurements and CFD simulation of CSF flow rates was <3.6%. CSF flow along the entire spine was laminar with a peak Reynolds number of ∼150 and average Womersley number of ∼5.4. Maximum CSF flow rate was present at the C4-C5 vertebral level. Deformation of the dura ranged up to a maximum of 134 μm. Geometric analysis indicated that total spinal CSF space volume was ∼8.7 ml. Average hydraulic diameter, wetted perimeter, and SAS area were 2.9 mm, 37.3 mm and 27.24 mm2, respectively. CSF pulse wave velocity (PWV) along the spine was quantified to be 1.2 m/s.}, }
@article {pmid28452782, year = {2017}, author = {Carrera, L and Springer, F and Lipeme-Kouyi, G and Buffiere, P}, title = {Sulfide emissions in sewer networks: focus on liquid to gas mass transfer coefficient.}, journal = {Water science and technology : a journal of the International Association on Water Pollution Research}, volume = {75}, number = {7-8}, pages = {1899-1908}, doi = {10.2166/wst.2017.070}, pmid = {28452782}, issn = {0273-1223}, mesh = {Gases/chemistry ; Gravitation ; Models, Theoretical ; Phase Transition ; Sewage/*chemistry ; Sulfides/*chemistry ; Water Pollutants, Chemical/*chemistry ; }, abstract = {H2S emission dynamics in sewers are conditioned by the mass transfer coefficient at the interface. This work aims at measuring the variation of the mass transfer coefficient with the hydraulic characteristics, with the objective of estimating H2S emission in gravity pipes, and collecting data to establish models independent of the system geometry. The ratio between the H2S and O2 mass transfer coefficient was assessed in an 8 L mixed reactor under different experimental conditions. Then, oxygen mass transfer measurements were performed in a 10 m long gravity pipe. The following ranges of experimental conditions were investigated: velocity flow [0-0.61 m.s[-1]], Reynolds number [0-23,333]. The hydrodynamic parameters at the liquid/gas interface were calculated by computational fluid dynamics (CFD). In the laboratory-scale reactor, the O2 mass transfer coefficient was found to depend on the stirring rate (rph) as follows: KL,O2 = 0.016 + 0.025 N[3.85]. A KL,H2S/KL,O2 ratio of 0.64 ± 0.24 was found, in accordance with previously published data. CFD results helped in refining this correlation: the mass transfer coefficient depends on the local interface velocity ui (m.h[-1]): KL,O2 = 0.016 + 1.02 × 10[-5] ui[3.85] In the gravity pipe device, KL,O2 also exponentially increased with the mean flow velocity. These trends were found to be consistent with the increasing level of turbulence.}, }
@article {pmid28446697, year = {2017}, author = {China, V and Levy, L and Liberzon, A and Elmaliach, T and Holzman, R}, title = {Hydrodynamic regime determines the feeding success of larval fish through the modulation of strike kinematics.}, journal = {Proceedings. Biological sciences}, volume = {284}, number = {1853}, pages = {}, pmid = {28446697}, issn = {1471-2954}, mesh = {Animals ; Biomechanical Phenomena ; *Feeding Behavior ; Hydrodynamics ; Larva/physiology ; Sea Bream/*physiology ; }, abstract = {Larval fishes experience extreme mortality rates, with 99% of a cohort perishing within days after starting to actively feed. While recent evidence suggests that hydrodynamic factors contribute to constraining larval feeding during early ontogeny, feeding is a complex process that involves numerous interacting behavioural and biomechanical components. How these components change throughout ontogeny and how they contribute to feeding remain unclear. Using 339 observations of larval feeding attempts, we quantified the effects of morphological and behavioural traits on feeding success of Sparus aurata larvae during early ontogeny. Feeding success was determined using high-speed videography, under both natural and increased water viscosity treatments. Successful strikes were characterized by Reynolds numbers that were an order of magnitude higher than those of failed strikes. The pattern of increasing strike success with increasing age was driven by the ontogeny of traits that facilitate the transition to higher Reynolds numbers. Hence, the physical growth of a larva plays an important role in its transition to a hydrodynamic regime of higher Reynolds numbers, in which suction feeding is more effective.}, }
@article {pmid28443874, year = {2017}, author = {Schaaf, C and Stark, H}, title = {Inertial migration and axial control of deformable capsules.}, journal = {Soft matter}, volume = {13}, number = {19}, pages = {3544-3555}, doi = {10.1039/c7sm00339k}, pmid = {28443874}, issn = {1744-6848}, abstract = {The mechanical deformability of single cells is an important indicator for various diseases such as cancer, blood diseases and inflammation. Lab-on-a-chip devices allow to separate such cells from healthy cells using hydrodynamic forces. We perform hydrodynamic simulations based on the lattice-Boltzmann method and study the behavior of an elastic capsule in a microfluidic channel flow in the inertial regime. While inertial lift forces drive the capsule away from the channel center, its deformability favors migration in the opposite direction. Balancing both migration mechanisms, a deformable capsule assembles at a specific equilibrium distance depending on its size and deformability. We find that this equilibrium distance is nearly independent of the channel Reynolds number and falls on a single master curve when plotted versus the Laplace number. We identify a similar master curve for varying particle radius. In contrast, the actual deformation of a capsule strongly depends on the Reynolds number. The lift-force profiles behave in a similar manner as those for rigid particles. Using the Saffman effect, the capsule's equilibrium position can be controlled by an external force along the channel axis. While rigid particles move to the center when slowed down, very soft capsules show the opposite behavior. Interestingly, for a specific control force particles are focused on the same equilibrium position independent of their deformability.}, }
@article {pmid28434714, year = {2017}, author = {Gritti, F and Fogwill, M}, title = {Speed-resolution advantage of turbulent supercritical fluid chromatography in open tubular columns: II - Theoretical and experimental evidences.}, journal = {Journal of chromatography. A}, volume = {1501}, number = {}, pages = {142-150}, doi = {10.1016/j.chroma.2017.04.032}, pmid = {28434714}, issn = {1873-3778}, mesh = {Benzene Derivatives/chemistry ; Carbon Dioxide/chemistry ; Chromatography, Supercritical Fluid/*instrumentation/methods ; Kinetics ; Models, Theoretical ; Pressure ; Silicon Dioxide/chemistry ; Temperature ; }, abstract = {The potential advantage of turbulent supercritical fluid chromatography (TSFC) in open tubular columns (OTC) was evaluated on both theoretical and practical viewpoints. First, the dispersion model derived by Golay in 1958 and recently extended from laminar to turbulent flow regime is used for the predictions of the speed-resolution performance in TSFC. The average dispersion coefficient of matter in the turbulent flow regime was taken from the available experimental data over a range of Reynolds number from 2000 to 6000. Kinetic plots are built at constant pressure drop (ΔP=4500psi) and Schmidt number (Sc=15) for four inner diameters (10, 30, 100, and 300μm) of the OTC and for three retention factors (0, 1, and 10). Accordingly, in turbulent flow regime, for a Reynolds number of 4000 and a retention factor of 1 (the stationary film thickness is assumed to be negligible with respect to the OTC diameter), the theory projects that a 300μm i.d. OTC has the same speed-resolution power (200,000 theoretical plates; 2.4min hold-up time) as that of a 10μm i.d. OTC operated in laminar flow regime. Secondly, the experimental plate heights of n-butylbenzene are measured in laminar and turbulent flow regimes for a 180μm×4.8m fused silica capillary column using pure carbon dioxide as the mobile phase. The back pressure regulator was set at 1500psi, the temperature was uniform at 297K, and the flow rate was increased step-wise from 0.50 to 3.60mL/min so that the experimental Reynolds number increases from 700 to 5400. The experiments are in good agreement with the plate heights projected in TSFC at high flow rates and with those expected at low flow rates in a laminar flow regime.}, }
@article {pmid28429018, year = {2017}, author = {Menzel, AM}, title = {Force-induced elastic matrix-mediated interactions in the presence of a rigid wall.}, journal = {Soft matter}, volume = {13}, number = {18}, pages = {3373-3384}, doi = {10.1039/c7sm00459a}, pmid = {28429018}, issn = {1744-6848}, abstract = {We consider a soft elastic matrix that contains particulate inclusions and is bounded by a rigid wall, e.g., the substrate. Such a situation arises in elastic composite materials. They may serve as soft actuators when forces are imposed on or induced between the embedded particles. We investigate how the presence of the rigid wall affects the interactions between the inclusions. First, for no-slip boundary conditions, we transfer Blake's derivation of a corresponding Green's function from low-Reynolds-number hydrodynamics to the linearly elastic case. Then, we list the general expressions to describe the situation for point-like particles in the presence of no-slip and free-slip surface conditions. To compare the effect of the different surface conditions to each other and to the bulk behavior, we address the example situation of pairwise interactions between two embedded particles. The axis through both particle centers is either aligned parallel or perpendicular to the surface. Our results suggest that walls with free-slip surface conditions are preferred when they serve as substrates for soft actuators made from elastic composite materials. As we further demonstrate, the presence of a rigid wall can qualitatively change the interactions between the inclusions. In effect, it can switch attractive interactions into repulsive ones (and vice versa). It should be straightforward to observe the effects in future experiments and to combine our results, e.g., with the modeling of biological cells and tissue on rigid surfaces.}, }
@article {pmid28415285, year = {2017}, author = {Fan, WL and Pak, OS and Sandoval, M}, title = {Ellipsoidal Brownian self-driven particles in a magnetic field.}, journal = {Physical review. E}, volume = {95}, number = {3-1}, pages = {032605}, doi = {10.1103/PhysRevE.95.032605}, pmid = {28415285}, issn = {2470-0053}, abstract = {We study the two-dimensional Brownian dynamics of an ellipsoidal paramagnetic microswimmer moving at a low Reynolds number and subject to a magnetic field. Its corresponding mean-square displacement, showing the effect of a particles's shape, activity, and magnetic field on the microswimmer's diffusion, is analytically obtained. Comparison between analytical and computational results shows good agreement. In addition, the effect of self-propulsion on the transition time from anisotropic to isotropic diffusion of the ellipse is investigated.}, }
@article {pmid28415282, year = {2017}, author = {Shen, X and Marcos,  and Fu, HC}, title = {Traction reveals mechanisms of wall effects for microswimmers near boundaries.}, journal = {Physical review. E}, volume = {95}, number = {3-1}, pages = {033105}, doi = {10.1103/PhysRevE.95.033105}, pmid = {28415282}, issn = {2470-0053}, abstract = {The influence of a plane boundary on low-Reynolds-number swimmers has frequently been studied using image systems for flow singularities. However, the boundary effect can also be expressed using a boundary integral representation over the traction on the boundary. We show that examining the traction pattern on the boundary caused by a swimmer can yield physical insights into determining when far-field multipole models are accurate. We investigate the swimming velocities and the traction of a three-sphere swimmer initially placed parallel to an infinite planar wall. In the far field, the instantaneous effect of the wall on the swimmer is well approximated by that of a multipole expansion consisting of a force dipole and a force quadrupole. On the other hand, the swimmer close to the wall must be described by a system of singularities reflecting its internal structure. We show that these limits and the transition between them can be independently identified by examining the traction pattern on the wall, either using a quantitative correlation coefficient or by visual inspection. Last, we find that for nonconstant propulsion, correlations between swimming stroke motions and internal positions are important and not captured by time-averaged traction on the wall, indicating that care must be taken when applying multipole expansions to study boundary effects in cases of nonconstant propulsion.}, }
@article {pmid28413338, year = {2017}, author = {Aurnou, JM and King, EM}, title = {The cross-over to magnetostrophic convection in planetary dynamo systems.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {473}, number = {2199}, pages = {20160731}, pmid = {28413338}, issn = {1364-5021}, abstract = {Global scale magnetostrophic balance, in which Lorentz and Coriolis forces comprise the leading-order force balance, has long been thought to describe the natural state of planetary dynamo systems. This argument arises from consideration of the linear theory of rotating magnetoconvection. Here we test this long-held tenet by directly comparing linear predictions against dynamo modelling results. This comparison shows that dynamo modelling results are not typically in the global magnetostrophic state predicted by linear theory. Then, in order to estimate at what scale (if any) magnetostrophic balance will arise in nonlinear dynamo systems, we carry out a simple scaling analysis of the Elsasser number Λ, yielding an improved estimate of the ratio of Lorentz and Coriolis forces. From this, we deduce that there is a magnetostrophic cross-over length scale, [Formula: see text], where Λo is the linear (or traditional) Elsasser number, Rmo is the system scale magnetic Reynolds number and D is the length scale of the system. On scales well above [Formula: see text], magnetostrophic convection dynamics should not be possible. Only on scales smaller than [Formula: see text] should it be possible for the convective behaviours to follow the predictions for the magnetostrophic branch of convection. Because [Formula: see text] is significantly smaller than the system scale in most dynamo models, their large-scale flows should be quasi-geostrophic, as is confirmed in many dynamo simulations. Estimating Λo ≃1 and Rmo ≃10[3] in Earth's core, the cross-over scale is approximately 1/1000 that of the system scale, suggesting that magnetostrophic convection dynamics exists in the core only on small scales below those that can be characterized by geomagnetic observations.}, }
@article {pmid28413332, year = {2017}, author = {Ferrari, A}, title = {Fluid dynamics of acoustic and hydrodynamic cavitation in hydraulic power systems.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {473}, number = {2199}, pages = {20160345}, pmid = {28413332}, issn = {1364-5021}, abstract = {Cavitation is the transition from a liquid to a vapour phase, due to a drop in pressure to the level of the vapour tension of the fluid. Two kinds of cavitation have been reviewed here: acoustic cavitation and hydrodynamic cavitation. As acoustic cavitation in engineering systems is related to the propagation of waves through a region subjected to liquid vaporization, the available expressions of the sound speed are discussed. One of the main effects of hydrodynamic cavitation in the nozzles and orifices of hydraulic power systems is a reduction in flow permeability. Different discharge coefficient formulae are analysed in this paper: the Reynolds number and the cavitation number result to be the key fluid dynamical parameters for liquid and cavitating flows, respectively. The latest advances in the characterization of different cavitation regimes in a nozzle, as the cavitation number reduces, are presented. The physical cause of choked flows is explained, and an analogy between cavitation and supersonic aerodynamic flows is proposed. The main approaches to cavitation modelling in hydraulic power systems are also reviewed: these are divided into homogeneous-mixture and two-phase models. The homogeneous-mixture models are further subdivided into barotropic and baroclinic models. The advantages and disadvantages of an implementation of the complete Rayleigh-Plesset equation are examined.}, }
@article {pmid28399142, year = {2017}, author = {Potvin, J and Werth, AJ}, title = {Oral cavity hydrodynamics and drag production in Balaenid whale suspension feeding.}, journal = {PloS one}, volume = {12}, number = {4}, pages = {e0175220}, pmid = {28399142}, issn = {1932-6203}, mesh = {Animals ; Balaenoptera/*physiology ; *Feeding Behavior ; *Hydrodynamics ; Mouth/*physiology ; }, abstract = {Balaenid whales feed on large aggregates of small and slow-moving prey (predominantly copepods) through a filtration process enabled by baleen. These whales exhibit continuous filtration, namely, with the mouth kept partially opened and the baleen exposed to oncoming prey-laden waters while fluking. The process is an example of crossflow filtration (CFF) in which most of the particulates (prey) are separated from the substrate (water) without ever coming into contact with the filtering surface (baleen). This paper discusses the simulation of baleen filtration hydrodynamics based on a type of hydraulic circuit modeling commonly used in microfluidics, but adapted to the much higher Reynolds number flows typical of whale hydrodynamics. This so-called Baleen Hydraulic Circuit (BHC) model uses as input the basic characteristics of the flows moving through a section of baleen observed in a previous flume study by the authors. The model has low-spatial resolution but incorporates the effects of fluid viscosity, which doubles or more a whale's total body drag in comparison to non-feeding travel. Modeling viscous friction is crucial here since exposing the baleen system to the open ocean ends up tripling a whale's total wetted surface area. Among other findings, the BHC shows how CFF is enhanced by a large filtration surface and hence large body size; how it is carried out via the establishment of rapid anteroposterior flows transporting most of the prey-water slurry towards the oropharyngeal wall; how slower intra-baleen flows manage to transfer most of the substrate out of the mouth, all the while contributing only a fraction to overall oral cavity drag; and how these anteroposterior and intra-baleen flows lose speed as they approach the oropharyngeal wall.}, }
@article {pmid28397936, year = {2017}, author = {Reigh, SY and Zhu, L and Gallaire, F and Lauga, E}, title = {Swimming with a cage: low-Reynolds-number locomotion inside a droplet.}, journal = {Soft matter}, volume = {13}, number = {17}, pages = {3161-3173}, doi = {10.1039/c6sm01636g}, pmid = {28397936}, issn = {1744-6848}, abstract = {Inspired by recent experiments using synthetic microswimmers to manipulate droplets, we investigate the low-Reynolds-number locomotion of a model swimmer (a spherical squirmer) encapsulated inside a droplet of a comparable size in another viscous fluid. Meditated solely by hydrodynamic interactions, the encaged swimmer is seen to be able to propel the droplet, and in some situations both remain in a stable co-swimming state. The problem is tackled using both an exact analytical theory and a numerical implementation based on a boundary element method, with a particular focus on the kinematics of the co-moving swimmer and the droplet in a concentric configuration, and we obtain excellent quantitative agreement between the two. The droplet always moves slower than a swimmer which uses purely tangential surface actuation but when it uses a particular combination of tangential and normal actuations, the squirmer and droplet are able to attain the same velocity and stay concentric for all times. We next employ numerical simulations to examine the stability of their concentric co-movement, and highlight several stability scenarios depending on the particular gait adopted by the swimmer. Furthermore, we show that the droplet reverses the nature of the far-field flow induced by the swimmer: a droplet cage turns a pusher swimmer into a puller, and vice versa. Our work sheds light on the potential development of droplets as self-contained carriers of both chemical content and self-propelled devices for controllable and precise drug deliveries.}, }
@article {pmid28388112, year = {2017}, author = {Dyer, OT and Ball, RC}, title = {Wavelet Monte Carlo dynamics: A new algorithm for simulating the hydrodynamics of interacting Brownian particles.}, journal = {The Journal of chemical physics}, volume = {146}, number = {12}, pages = {124111}, doi = {10.1063/1.4978808}, pmid = {28388112}, issn = {1089-7690}, abstract = {We develop a new algorithm for the Brownian dynamics of soft matter systems that evolves time by spatially correlated Monte Carlo moves. The algorithm uses vector wavelets as its basic moves and produces hydrodynamics in the low Reynolds number regime propagated according to the Oseen tensor. When small moves are removed, the correlations closely approximate the Rotne-Prager tensor, itself widely used to correct for deficiencies in Oseen. We also include plane wave moves to provide the longest range correlations, which we detail for both infinite and periodic systems. The computational cost of the algorithm scales competitively with the number of particles simulated, N, scaling as N In N in homogeneous systems and as N in dilute systems. In comparisons to established lattice Boltzmann and Brownian dynamics algorithms, the wavelet method was found to be only a factor of order 1 times more expensive than the cheaper lattice Boltzmann algorithm in marginally semi-dilute simulations, while it is significantly faster than both algorithms at large N in dilute simulations. We also validate the algorithm by checking that it reproduces the correct dynamics and equilibrium properties of simple single polymer systems, as well as verifying the effect of periodicity on the mobility tensor.}, }
@article {pmid28373015, year = {2017}, author = {Miguel, AF}, title = {Penetration of inhaled aerosols in the bronchial tree.}, journal = {Medical engineering &amp; physics}, volume = {44}, number = {}, pages = {25-31}, doi = {10.1016/j.medengphy.2017.03.004}, pmid = {28373015}, issn = {1873-4030}, mesh = {Aerosols ; Bronchi/*anatomy &amp; histology/*metabolism/physiology ; Humans ; *Inhalation ; *Models, Anatomic ; Particle Size ; }, abstract = {It has long been recognized that the pattern of particle deposition in the respiratory tree affects how far aerosols penetrate into the deeper zones of the arterial tree, and hence contribute to either their pathogenic potential or therapeutic benefit. In this paper, we introduce an anatomically-inspired model of the human respiratory tree featuring the generations 0-7 in the Weibel model of respiratory tree (i.e., the conducting zone). This model is used to study experimentally the dynamics of inhaled aerosol particles (0.5-20µm aerodynamic diameter), in terms of the penetration fraction of particles (i.e., the fraction of inflowing particles that leave the flow system) during typical breathing patterns. Our study underline important modifications in the penetration patterns for coarse particles compared to fine particles. Our experiments suggest a significant decrease of particle penetration for large-sized particles and higher respiratory frequencies. Dimensionless numbers are also introduced to further understand the particle penetration into the respiratory tree. A decline is seen in the penetration fraction with decreasing Reynolds number and increasing Stokes number. A simple conceptual framework is presented to provide additional insights into the findings obtained.}, }
@article {pmid28364770, year = {2017}, author = {Smaoui, N and Zribi, M}, title = {On the control of the chaotic attractors of the 2-d Navier-Stokes equations.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {27}, number = {3}, pages = {033111}, doi = {10.1063/1.4978682}, pmid = {28364770}, issn = {1089-7682}, abstract = {The control problem of the chaotic attractors of the two dimensional (2-d) Navier-Stokes (N-S) equations is addressed in this paper. First, the Fourier Galerkin method based on a reduced-order modelling approach developed by Chen and Price is applied to the 2-d N-S equations to construct a fifth-order system of nonlinear ordinary differential equations (ODEs). The dynamics of the fifth-order system was studied by analyzing the system's attractor for different values of Reynolds number, Re. Then, control laws are proposed to drive the states of the ODE system to a desired attractor. Finally, an adaptive controller is designed to synchronize two reduced order ODE models having different Reynolds numbers and starting from different initial conditions. Simulation results indicate that the proposed control schemes work well.}, }
@article {pmid28342532, year = {2017}, author = {Gülan, U and Binter, C and Kozerke, S and Holzner, M}, title = {Shear-scaling-based approach for irreversible energy loss estimation in stenotic aortic flow - An in vitro study.}, journal = {Journal of biomechanics}, volume = {56}, number = {}, pages = {89-96}, doi = {10.1016/j.jbiomech.2017.03.006}, pmid = {28342532}, issn = {1873-2380}, mesh = {Aorta/physiopathology ; Aortic Valve Stenosis/*physiopathology ; Blood Flow Velocity/physiology ; Constriction, Pathologic/physiopathology ; Humans ; Magnetic Resonance Imaging/methods ; Models, Cardiovascular ; Phantoms, Imaging ; Rheology/methods ; }, abstract = {Today, the functional and risk assessment of stenosed arteries is mostly based on ultrasound Doppler blood flow velocity measurements or catheter pressure measurements, which rely on several assumptions. Alternatively, blood velocity including turbulent kinetic energy (TKE) may be measured using MRI. The aim of the present study is to validate a TKE-based approach that relies on the fact that turbulence production is dominated by the flow's shear to determine the total irreversible energy loss from MRI scans. Three-dimensional particle tracking velocimetry (3D-PTV) and phase-contrast magnetic resonance imaging (PC-MRI) simulations were performed in an anatomically accurate, compliant, silicon aortic phantom. We found that measuring only the laminar viscous losses does not reflect the true losses of stenotic flows since the contribution of the turbulent losses to the total loss become more dominant for more severe stenosis types (for example, the laminar loss is 0.0094±0.0015W and the turbulent loss is 0.0361±0.0015W for the Remax=13,800 case, where Remax is the Reynolds number based on the velocity in the vena-contracta). We show that the commonly used simplified and modified Bernoulli's approaches overestimate the total loss, while the new TKE-based method proposed here, referred to as "shear scaling" approach, results in a good agreement between 3D-PTV and simulated PC-MRI (mean error is around 10%). In addition, we validated the shear scaling approach on a geometry with post-stenotic dilatation using numerical data by Casas et al. (2016). The shear scaling-based method may hence be an interesting alternative for irreversible energy loss estimation to replace traditional approaches for clinical use. We expect that our results will evoke further research, in particular patient studies for clinical implementation of the new method.}, }
@article {pmid28337415, year = {2017}, author = {Nijp, JJ and Metselaar, K and Limpens, J and Gooren, HP and van der Zee, SE}, title = {A modification of the constant-head permeameter to measure saturated hydraulic conductivity of highly permeable media.}, journal = {MethodsX}, volume = {4}, number = {}, pages = {134-142}, pmid = {28337415}, issn = {2215-0161}, abstract = {The saturated hydraulic conductivity (Ks) is a key characteristic of porous media, describing the rate of water flow through saturated porous media. It is an indispensable parameter in a broad range of simulation models that quantify saturated and/or unsaturated water flow. The constant-head permeameter test is a common laboratory method to determine Ks on undisturbed soil samples collected from the field. In this paper we show that the application of this conventional method may result in a biased Ks in the case of highly permeable media, such as the top layer of Sphagnum peat and gravel. Tubes in the conventional permeameter, that collect water under the sample, introduce a hydraulic head-dependent resistance for highly permeable media and result in an underestimation of Ks . We present a simple and low-budget alternative of the constant-head permeameter test that overcomes the disadvantages of conventional permeameters. The new method was successfully tested on intact highly permeable peatmoss collected from a northern peatland. •Conventional constant-head permeameters underestimate Ks of highly permeable media due to flow resistance in tubing systems•We developed the low-resistance permeameter to overcome this disadvantage.•Testing of the low-resistance permeameter demonstrated no systematic bias and successful application for highly permeable media.}, }
@article {pmid28325440, year = {2017}, author = {Hayat, T and Farooq, S and Alsaedi, A}, title = {Mixed convection peristaltic motion of copper-water nanomaterial with velocity slip effects in a curved channel.}, journal = {Computer methods and programs in biomedicine}, volume = {142}, number = {}, pages = {117-128}, doi = {10.1016/j.cmpb.2017.02.006}, pmid = {28325440}, issn = {1872-7565}, mesh = {Computer Simulation ; Convection ; Copper/*chemistry ; Drug Delivery Systems ; Hot Temperature ; Metal Nanoparticles ; Models, Theoretical ; Motion ; Nanostructures/*chemistry ; *Peristalsis ; Pressure ; Rheology ; Software ; Viscosity ; Water/*chemistry ; }, abstract = {BACKGROUND AND OBJECTIVE: The primary objective of present analysis is to model the peristalsis of copper-water based nanoliquid in the presence of first order velocity and thermal slip conditions in a curved channel. Mixed convection, viscous dissipation and heat generation/absorption are also accounted.<br><br>METHOD: Mathematical formulation is simplified under the assumption of small Reynolds number and large wavelength. Regular perturbation technique is employed to find the solution of the resulting equations in terms of series for small Brinkman number. The final expression for pressure gradient, pressure rise, stream function, velocity and temperature are obtained and discussed through graphs. Mathematica software is utilized to compute the solution of the system of equations and to plot the graphical results.<br><br>RESULTS: Results indicates that insertion of 30% copper nanoparticles in the basefluid (water) velocity and temperature reduces by almost 3% and 40% respecively. Moreover it is seen that size of the trapped bolus also reduces almost 20% with the insertion of 20% nanoparticles (copper) in the basefluid (water).<br><br>CONCLUSION: It is noted that velocity and temperature are decreasing functions of nanoparticle volume fraction. Moreover the temperature rises when heat generation parameter and Brinkman number are enhanced.}, }
@article {pmid28297984, year = {2017}, author = {Hejranfar, K and Saadat, MH and Taheri, S}, title = {High-order weighted essentially nonoscillatory finite-difference formulation of the lattice Boltzmann method in generalized curvilinear coordinates.}, journal = {Physical review. E}, volume = {95}, number = {2-1}, pages = {023314}, doi = {10.1103/PhysRevE.95.023314}, pmid = {28297984}, issn = {2470-0053}, abstract = {In this work, a high-order weighted essentially nonoscillatory (WENO) finite-difference lattice Boltzmann method (WENOLBM) is developed and assessed for an accurate simulation of incompressible flows. To handle curved geometries with nonuniform grids, the incompressible form of the discrete Boltzmann equation with the Bhatnagar-Gross-Krook (BGK) approximation is transformed into the generalized curvilinear coordinates and the spatial derivatives of the resulting lattice Boltzmann equation in the computational plane are solved using the fifth-order WENO scheme. The first-order implicit-explicit Runge-Kutta scheme and also the fourth-order Runge-Kutta explicit time integrating scheme are adopted for the discretization of the temporal term. To examine the accuracy and performance of the present solution procedure based on the WENOLBM developed, different benchmark test cases are simulated as follows: unsteady Taylor-Green vortex, unsteady doubly periodic shear layer flow, steady flow in a two-dimensional (2D) cavity, steady cylindrical Couette flow, steady flow over a 2D circular cylinder, and steady and unsteady flows over a NACA0012 hydrofoil at different flow conditions. Results of the present solution are compared with the existing numerical and experimental results which show good agreement. To show the efficiency and accuracy of the solution methodology, the results are also compared with the developed second-order central-difference finite-volume lattice Boltzmann method and the compact finite-difference lattice Boltzmann method. It is shown that the present numerical scheme is robust, efficient, and accurate for solving steady and unsteady incompressible flows even at high Reynolds number flows.}, }
@article {pmid28297968, year = {2017}, author = {de Graaf, J and Stenhammar, J}, title = {Lattice-Boltzmann simulations of microswimmer-tracer interactions.}, journal = {Physical review. E}, volume = {95}, number = {2-1}, pages = {023302}, doi = {10.1103/PhysRevE.95.023302}, pmid = {28297968}, issn = {2470-0053}, abstract = {Hydrodynamic interactions in systems composed of self-propelled particles, such as swimming microorganisms and passive tracers, have a significant impact on the tracer dynamics compared to the equivalent "dry" sample. However, such interactions are often difficult to take into account in simulations due to their computational cost. Here, we perform a systematic investigation of swimmer-tracer interaction using an efficient force-counterforce-based lattice-Boltzmann (LB) algorithm [De Graaf et al., J. Chem. Phys. 144, 134106 (2016)JCPSA60021-960610.1063/1.4944962] in order to validate its ability to capture the relevant low-Reynolds-number physics. We show that the LB algorithm reproduces far-field theoretical results well, both in a system with periodic boundary conditions and in a spherical cavity with no-slip walls, for which we derive expressions here. The force-lattice coupling of the LB algorithm leads to a "smearing out" of the flow field, which strongly perturbs the tracer trajectories at close swimmer-tracer separations, and we analyze how this effect can be accurately captured using a simple renormalized hydrodynamic theory. Finally, we show that care must be taken when using LB algorithms to simulate systems of self-propelled particles, since its finite momentum transport time can lead to significant deviations from theoretical predictions based on Stokes flow. These insights should prove relevant to the future study of large-scale microswimmer suspensions using these methods.}, }
@article {pmid28297886, year = {2017}, author = {Iyer, KP and Sreenivasan, KR and Yeung, PK}, title = {Reynolds number scaling of velocity increments in isotropic turbulence.}, journal = {Physical review. E}, volume = {95}, number = {2-1}, pages = {021101}, doi = {10.1103/PhysRevE.95.021101}, pmid = {28297886}, issn = {2470-0053}, abstract = {Using the largest database of isotropic turbulence available to date, generated by the direct numerical simulation (DNS) of the Navier-Stokes equations on an 8192^{3} periodic box, we show that the longitudinal and transverse velocity increments scale identically in the inertial range. By examining the DNS data at several Reynolds numbers, we infer that the contradictory results of the past on the inertial-range universality are artifacts of low Reynolds number and residual anisotropy. We further show that both longitudinal and transverse velocity increments scale on locally averaged dissipation rate, just as postulated by Kolmogorov's refined similarity hypothesis, and that, in isotropic turbulence, a single independent scaling adequately describes fluid turbulence in the inertial range.}, }
@article {pmid28289562, year = {2017}, author = {Cheng, X and Sun, M}, title = {Aerodynamic forces and flows of the full and partial clap-fling motions in insects.}, journal = {PeerJ}, volume = {5}, number = {}, pages = {e3002}, pmid = {28289562}, issn = {2167-8359}, abstract = {Most of the previous studies on Weis-Fogh clap-fling mechanism have focused on the vortex structures and velocity fields. Detailed pressure distribution results are provided for the first time in this study to reveal the differences between the full and the partial clap-fling motions. The two motions are studied by numerically solving the Navier-Stokes equations in moving overset grids. The Reynolds number is set to 20, relevant to the tiny flying insects. The following has been shown: (1) During the clap phase, the wings clap together and create a high pressure region in the closing gap between wings, greatly increasing the positive pressure on the lower surface of wing, while pressure on the upper surface is almost unchanged by the interaction; during the fling phase, the wings fling apart and create a low pressure region in the opening gap between wings, greatly increasing the suction pressure on the upper surface of wing, while pressure on the lower surface is almost unchanged by the interaction; (2) The interference effect between wings is most severe at the end of clap phase and the start of the fling phase: two sharp force peaks (8-9 times larger than that of the one-winged case) are generated. But the total force peaks are manifested mostly as drag and barely as lift of the wing, owing to the vertical orientation of the wing section; (3) The wing-wing interaction effect in the partial clap-fling case is much weaker than that in the full clap-fling case, avoiding the generation of huge drag. Compared with a single wing flapping with the same motion, mean lift in the partial case is enhanced by 12% without suffering any efficiency degradation, indicating that partial clap-fling is a more practical choice for tiny insects to employ.}, }
@article {pmid28270051, year = {2017}, author = {Zeinoddini, M and Bakhtiari, A and Schoefs, F and Zandi, AP}, title = {Towards an understanding of marine fouling effects on the vortex-induced vibrations of circular cylinders: partial coverage issue.}, journal = {Biofouling}, volume = {33}, number = {3}, pages = {268-280}, doi = {10.1080/08927014.2017.1291803}, pmid = {28270051}, issn = {1029-2454}, mesh = {Animals ; Biofilms/*growth &amp; development ; Biofouling/*prevention &amp; control ; *Hydrodynamics ; *Models, Theoretical ; Thoracica/*physiology ; *Vibration ; }, abstract = {The results of in-water vortex-induced vibration (VIV) experiments on circular cylinders artificially covered with barnacles are reported. The paper focusses on the effects of the partial coverage and the shape of the fouling elements. An artificial barnacle typical of marine fouling was synthesised using 3-D printing. Coverage ratios of 80, 50 and 30% were examined and the results compared with those from a smooth cylinder. The Reynolds number ranged from 5.8 × 10[3] to 6.6 × 10[4]. The experimental results show that the fouling reduced the peak VIV amplitude, narrowed the synchronisation region and lowered the hydrodynamic force coefficients such as the coefficients of lift force RMS, the mean drag force and the fluctuating drag force RMS. The shape of the artificial barnacles had little effect on the maximum oscillation amplitude. The coverage ratio appeared to have a lower impact on the lift force than those on the amplitude and the frequency responses.}, }
@article {pmid28267999, year = {2017}, author = {Gritti, F}, title = {Extension of Golay's plate height equation from laminar to turbulent flow I - Theory.}, journal = {Journal of chromatography. A}, volume = {1492}, number = {}, pages = {129-135}, doi = {10.1016/j.chroma.2017.02.044}, pmid = {28267999}, issn = {1873-3778}, mesh = {Algorithms ; Chromatography, Supercritical Fluid ; *Models, Theoretical ; Temperature ; }, abstract = {The reduced plate height (RPH) equation of Golay derived in 1958 for open tubular columns (OTC) is extended from laminar to turbulent-like flow. The mass balance equation is solved under near-equilibrium conditions in the mobile phase for changing shapes of the velocity profile across the OTC diameter. The final expression of the general RPH equation is: [Formula: see text] where ν is the reduced linear velocity, k is the retention factor, Dm is the bulk diffusion coefficient in the mobile phase, Da¯ is the average axial dispersion coefficient, Dr¯ is the average radial dispersion coefficient, Ds is the diffusion coefficient of the analyte in the stationary film of thickness df, D is the OTC inner diameter, and n≥2 is a positive number controlling the shape of the flow profile (polynomial of degree n). The correctness of the derived RPH equation is verified for Poiseuille (n=2), turburlent-like (n=10), and uniformly flat (n→∞) flow profiles. The derived RPH equation is applied to predict the gain in speed-resolution of a 180μm i.d.×20m OTC (df=2μm) from laminar to turbulent flow in supercritical fluid chromatography. Using pure carbon dioxide as the mobile phase at 297K, k=1, and increasing the Reynolds number from 2000 (laminar) to 4000 (turbulent), the OTC efficiency is expected to increase from 125 to 670 (×5.4) while the hold-up time decreases from 19 to 9s (×0.5). Despite the stronger resistance to mass transfer in the stationary phase, the projected improvement of the column performance in turbulent flow is explained by the quasi-elimination of the resistance to mass transfer in the mobile phase while axial dispersion remains negligible.}, }
@article {pmid28267159, year = {2017}, author = {Peng, Z and Elfring, GJ and Pak, OS}, title = {Maximizing propulsive thrust of a driven filament at low Reynolds number via variable flexibility.}, journal = {Soft matter}, volume = {13}, number = {12}, pages = {2339-2347}, doi = {10.1039/c6sm02880b}, pmid = {28267159}, issn = {1744-6848}, abstract = {At low Reynolds numbers the locomotive capability of a body can be dramatically hindered by the absence of inertia. In this work, we show how propulsive performance in this regime can be significantly enhanced by employing spatially varying flexibility. As a prototypical example, we consider the propulsive thrust generated by a filament periodically driven at one end. The rigid case leads to zero propulsion, as so constrained by Purcell's scallop theorem, while for uniform filaments there exists a bending stiffness maximizing the propulsive force at a given frequency; here we demonstrate explicitly how considerable further improvement can be achieved by simply varying the stiffness along the filament. The optimal flexibility distribution is strongly configuration-dependent: while increasing the flexibility towards the tail-end enhances the propulsion of a clamped filament, for a hinged filament decreasing the flexibility towards the tail-end is instead favorable. The results reveal new design principles for maximizing propulsion at low Reynolds numbers, potentially useful for developing synthetic micro-swimmers requiring large propulsive force for various biomedical applications.}, }
@article {pmid28253673, year = {2017}, author = {Van Blitterswyk, J and Rocha, J}, title = {An experimental study of the wall-pressure fluctuations beneath low Reynolds number turbulent boundary layers.}, journal = {The Journal of the Acoustical Society of America}, volume = {141}, number = {2}, pages = {1257}, doi = {10.1121/1.4976341}, pmid = {28253673}, issn = {1520-8524}, abstract = {A more complete understanding of the physical relationships, between wall-pressure and turbulence, is required for modeling flow-induced noise and developing noise reduction strategies. In this study, the wall-pressure fluctuations, induced by low Reynolds number turbulent boundary layers, are experimentally studied using a high-resolution microphone array. Statistical characteristics obtained using traditional cross-correlation and cross-spectra analyses are complimented with wall-pressure-velocity cross-spectra and wavelet cross-correlations. Wall-pressure-velocity correlations revealed that turbulent activity in the buffer layer contributes at least 40% of the energy to the wall-pressure spectrum at all measured frequencies. As Reynolds number increases, the low-frequency energy shifts from the buffer layer to the logarithmic layer, as expected for regions of uniform streamwise momentum formed by hairpin packets. Conditional cross-spectra suggests that the majority of broadband wall-pressure energy is concentrated within the packets, with the pressure signatures of individual hairpin vortices estimated to decay on average within traveling ten displacement thicknesses, and the packet signature is retained for up to seven boundary layer thicknesses on average.}, }
@article {pmid28234274, year = {2017}, author = {Qin, Y and Wu, J and Hu, Q and Ghista, DN and Wong, KK}, title = {Computational evaluation of smoothed particle hydrodynamics for implementing blood flow modelling through CT reconstructed arteries.}, journal = {Journal of X-ray science and technology}, volume = {25}, number = {2}, pages = {213-232}, doi = {10.3233/XST-17255}, pmid = {28234274}, issn = {1095-9114}, mesh = {Arterial Occlusive Diseases/diagnostic imaging/pathology/physiopathology ; Blood Flow Velocity/*physiology ; *Computer Simulation ; Humans ; Hydrodynamics ; Image Processing, Computer-Assisted/*methods ; *Models, Cardiovascular ; Tomography, X-Ray Computed/*methods ; }, abstract = {Simulation of blood flow in a stenosed artery using Smoothed Particle Hydrodynamics (SPH) is a new research field, which is a particle-based method and different from the traditional continuum modelling technique such as Computational Fluid Dynamics (CFD). Both techniques harness parallel computing to process hemodynamics of cardiovascular structures. The objective of this study is to develop and test a new robust method for comparison of arterial flow velocity contours by SPH with the well-established CFD technique, and the implementation of SPH in computed tomography (CT) reconstructed arteries. The new method was developed based on three-dimensional (3D) straight and curved arterial models of millimeter range with a 25% stenosis in the middle section. In this study, we employed 1,000 to 13,000 particles to study how the number of particles influences SPH versus CFD deviation for blood-flow velocity distribution. Because further increasing the particle density has a diminishing effect on this deviation, we have determined a critical particle density of 1.45 particles/mm2 based on Reynolds number (Re = 200) at the inlet for an arterial flow simulation. Using this critical value of particle density can avoid unnecessarily big computational expenses that have no further effect on simulation accuracy. We have particularly shown that the SPH method has a big potential to be used in the virtual surgery system, such as to simulate the interaction between blood flow and the CT reconstructed vessels, especially those with stenosis or plaque when encountering vasculopathy, and for employing the simulation results output in clinical surgical procedures.}, }
@article {pmid28231298, year = {2017}, author = {Hayat, T and Aziz, A and Muhammad, T and Alsaedi, A}, title = {A revised model for Jeffrey nanofluid subject to convective condition and heat generation/absorption.}, journal = {PloS one}, volume = {12}, number = {2}, pages = {e0172518}, pmid = {28231298}, issn = {1932-6203}, mesh = {Algorithms ; Computer Simulation ; *Convection ; *Hot Temperature ; *Hydrodynamics ; Magnetic Fields ; Models, Chemical ; Motion ; Nanoparticles/*chemistry ; Nanotechnology ; Surface Properties ; }, abstract = {Here magnetohydrodynamic (MHD) boundary layer flow of Jeffrey nanofluid by a nonlinear stretching surface is addressed. Heat generation/absorption and convective surface condition effects are considered. Novel features of Brownian motion and thermophoresis are present. A non-uniform applied magnetic field is employed. Boundary layer and small magnetic Reynolds number assumptions are employed in the formulation. A newly developed condition with zero nanoparticles mass flux is imposed. The resulting nonlinear systems are solved. Convergence domains are explicitly identified. Graphs are analyzed for the outcome of sundry variables. Further local Nusselt number is computed and discussed. It is observed that the effects of Hartman number on the temperature and concentration distributions are qualitatively similar. Both temperature and concentration distributions are enhanced for larger Hartman number.}, }
@article {pmid28222160, year = {2017}, author = {Hayat, T and Zahir, H and Tanveer, A and Alsaedi, A}, title = {Soret and Dufour effects on MHD peristaltic transport of Jeffrey fluid in a curved channel with convective boundary conditions.}, journal = {PloS one}, volume = {12}, number = {2}, pages = {e0164854}, pmid = {28222160}, issn = {1932-6203}, mesh = {Convection ; Diffusion ; Electric Conductivity ; Equipment Design ; Magnetic Fields ; Osmolar Concentration ; Peristalsis ; *Rheology ; Solutions ; *Temperature ; }, abstract = {The purpose of present article is to examine the peristaltic flow of Jeffrey fluid in a curved channel. An electrically conducting fluid in the presence of radial applied magnetic field is considered. Analysis of heat and mass transfer is carried out. More generalized realistic constraints namely the convective conditions are utilized. Soret and Dufour effects are retained. Problems formulation is given for long wavelength and low Reynolds number assumptions. The expressions of velocity, temperature, heat transfer coefficient, concentration and stream function are computed. Effects of emerging parameters arising in solutions are analyzed in detail. It is found that velocity is not symmetric about centreline for curvature parameter. Also maximum velocity decreases with an increase in the strength of magnetic field. Further it is noticed that Soret and Dufour numbers have opposite behavior for temperature and concentration.}, }
@article {pmid28208335, year = {2017}, author = {Walchli, B and Thornber, B}, title = {Reynolds number effects on the single-mode Richtmyer-Meshkov instability.}, journal = {Physical review. E}, volume = {95}, number = {1-1}, pages = {013104}, doi = {10.1103/PhysRevE.95.013104}, pmid = {28208335}, issn = {2470-0053}, abstract = {The Reynolds number effects on the nonlinear growth rates of the Richtmyer-Meshkov instability are investigated using two-dimensional numerical simulations. A decrease in Reynolds number gives an increased time to reach nonlinear saturation, with Reynolds number effects only significant in the range Re<256. Within this range there is a sharp change in instability properties. The bubble and spike amplitudes move towards equal size at lower Reynolds numbers and the bubble velocities decay faster than predicted by Sohn's model [S.-I. Sohn, Phys. Rev. E 80, 055302 (2009)PLEEE81539-375510.1103/PhysRevE.80.055302]. Predicted amplitudes show reasonable agreement with the existing theory of Carles and Popinet [P. Carles and S. Popinet, Phys. Fluids Lett. 13, 1833 (2001)10.1063/1.1377863; Eur. J. Mech. B 21, 511 (2002)EJBFEV0997-754610.1016/S0997-7546(02)01199-8] and Mikaelian [K. O. Mikaelian, Phys. Rev. E 47, 375 (1993)1063-651X10.1103/PhysRevE.47.375; K. O. Mikaelian, Phys. Rev. E 87, 031003 (2013)PLEEE81539-375510.1103/PhysRevE.87.031003], with the former being the closest match to the current computations.}, }
@article {pmid28208331, year = {2017}, author = {Linkmann, M and Berera, A and Goldstraw, EE}, title = {Reynolds-number dependence of the dimensionless dissipation rate in homogeneous magnetohydrodynamic turbulence.}, journal = {Physical review. E}, volume = {95}, number = {1-1}, pages = {013102}, doi = {10.1103/PhysRevE.95.013102}, pmid = {28208331}, issn = {2470-0053}, abstract = {This paper examines the behavior of the dimensionless dissipation rate C_{ɛ} for stationary and nonstationary magnetohydrodynamic (MHD) turbulence in the presence of external forces. By combining with previous studies for freely decaying MHD turbulence, we obtain here both the most general model equation for C_{ɛ} applicable to homogeneous MHD turbulence and a comprehensive numerical study of the Reynolds number dependence of the dimensionless total energy dissipation rate at unity magnetic Prandtl number. We carry out a series of medium to high resolution direct numerical simulations of mechanically forced stationary MHD turbulence in order to verify the predictions of the model equation for the stationary case. Furthermore, questions of nonuniversality are discussed in terms of the effect of external forces as well as the level of cross- and magnetic helicity. The measured values of the asymptote C_{ɛ,∞} lie between 0.193≤C_{ɛ,∞}≤0.268 for free decay, where the value depends on the initial level of cross- and magnetic helicities. In the stationary case we measure C_{ɛ,∞}=0.223.}, }
@article {pmid28191582, year = {2017}, author = {Yasuda, S and Hayakawa, M and Onoe, H and Takinoue, M}, title = {Twisting microfluidics in a planetary centrifuge.}, journal = {Soft matter}, volume = {13}, number = {11}, pages = {2141-2147}, doi = {10.1039/c6sm02695h}, pmid = {28191582}, issn = {1744-6848}, abstract = {This paper reports a twisting microfluidic method utilising a centrifuge-based fluid extruding system in a planetary centrifuge which simultaneously generates an orbital rotation and an axial spin. In this method, fluid extrusion from a micro-scale capillary to an 'open-space' solution or air enables release of the fluid from the capillary-based microchannel, which physically means that there is a release of fluids from a confined low-Reynolds-number environment to an open non-low-Reynolds-number environment. As a result, the extruded fluids are separated from the axial spin of the capillary, and the difference in the angular rates of the axial spin between the capillary and the extruded fluids produces the 'twisting' of the fluid. In this study, we achieve control of the twist of highly viscous fluids, and we construct a simple physical model for the fluid twist. In addition, we demonstrate the formation of twisted hydrogel microstructures (stripe-patterned microbeads and multi-helical microfibres) with control over the stripe pattern and the helical pitch length. We believe that this method will enable the generation of more sophisticated microstructures which cannot easily be formed by usual channel-based microfluidic devices. This method can also provide advanced control of microfluids, as in the case of rapid mixing of highly viscous fluids. This method can contribute to a wide range of applications in materials science, biophysics, biomedical science, and microengineering in the future.}, }
@article {pmid28187884, year = {2017}, author = {Shahzadi, I and Sadaf, H and Nadeem, S and Saleem, A}, title = {Bio-mathematical analysis for the peristaltic flow of single wall carbon nanotubes under the impact of variable viscosity and wall properties.}, journal = {Computer methods and programs in biomedicine}, volume = {139}, number = {}, pages = {137-147}, doi = {10.1016/j.cmpb.2016.10.016}, pmid = {28187884}, issn = {1872-7565}, mesh = {*Nanotubes, Carbon ; *Peristalsis ; *Viscosity ; }, abstract = {OBJECTIVE: The main objective of this paper is to study the Bio-mathematical analysis for the peristaltic flow of single wall carbon nanotubes under the impact of variable viscosity and wall properties.<br><br>DESIGN/APPROACH: The right and the left walls of the curved channel possess sinusoidal wave that is travelling along the outer boundary. The features of the peristaltic motion are determined by using long wavelength and low Reynolds number approximation. Exact solutions are determined for the axial velocity and for the temperature profile.<br><br>FINDINGS: Graphical results have been presented for velocity profile, temperature and stream function for various physical parameters of interest. Symmetry of the curved channel is disturbed for smaller values of the curvature parameter. It is found that the altitude of the velocity profile increases for larger values of variable viscosity parameter for both the cases (pure blood as well as single wall carbon nanotubes). It is detected that velocity profile increases with increasing values of rigidity parameter. It is due to the fact that an increase in rigidity parameter decreases tension in the walls of the blood vessels which speeds up the blood flow for pure blood as well as single wall carbon nanotubes. Increase in Grashof number decreases the fluid velocity. This is due to the reason that viscous forces play a prominent role that's why increase in Grashof number decreases the velocity profile. It is also found that temperature drops for increasing values of nanoparticle volume fraction. Basically, higher thermal conductivity of the nanoparticles plays a key role for quick heat dissipation, and this justifies the use of the single wall carbon nanotubes in different situations as a coolant.<br><br>CONCLUSIONS: Exact solutions are calculated for the temperature and the velocity profile. Symmetry of the curved channel is destroyed due to the curvedness for velocity, temperature and contour plots. Addition of single wall carbon nanotubes shows a decrease in fluid temperature. Trapping phenomena show that the size of the trapped bolus is smaller for pure blood case as compared to the single wall carbon nanotubes.}, }
@article {pmid28176897, year = {2017}, author = {Guiffant, G and Flaud, P and Royon, L and Burnet, E and Merckx, J}, title = {Mechanical characteristics of plastic base Ports and impact on flushing efficacy.}, journal = {Medical devices (Auckland, N.Z.)}, volume = {10}, number = {}, pages = {11-15}, pmid = {28176897}, issn = {1179-1470}, abstract = {BACKGROUND: Three types of totally implantable venous access devices, Ports, are currently in use: titanium, plastic (polyoxymethylene, POM), and mixed (titanium base with a POM shell). Physics theory suggests that the interaction between a non-coring needle (NCN, made of stainless steel) and a plastic base would lead to the stronger material (steel) altering the more malleable material (plastic).<br><br>OBJECTIVES: To investigate whether needle impacts can alter a plastic base's surface, thus potentially reducing flushing efficacy.<br><br>STUDY DESIGN AND METHODS: A Port made of POM was punctured 200 times with a 19-gauge NCN. Following the existing guidelines, the needle tip pricked the base with each puncture. The Port's base was then examined using a two-dimensional optical instrument, and a bi-dimensional numerical simulation using COMSOL[&#xae;] was performed to investigate potential surface irregularities and their impact on fluid flow.<br><br>RESULTS: Each needle impact created a hole (mean depth, 0.12 mm) with a small bump beside it (mean height, 0.02 mm) the Reynolds number Rek&#x2248;10. A numerical simulation of the one hole/bump set showed that the flushing efficacy was 60% that of flushing along a flat surface.<br><br>DISCUSSION: In clinical practice, the number of times a Port is punctured depends on patient and treatment characteristics, but each needle impact on the plastic base may increase the risk of decreased flushing effectiveness. Therefore, the more a plastic Port is accessed, the greater the risk of microorganisms, blood products, and medication accumulation.<br><br>CONCLUSIONS: Multiple needle impacts created an irregular surface on the Port's base, which decreased flushing efficacy. Clinical investigation is needed to determine whether plastic base Ports are associated with an increased risk of Port infection and occlusion compared to titanium base Ports.}, }
@article {pmid28167586, year = {2017}, author = {Örlü, R and Fiorini, T and Segalini, A and Bellani, G and Talamelli, A and Alfredsson, PH}, title = {Reynolds stress scaling in pipe flow turbulence-first results from CICLoPE.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167586}, issn = {1364-503X}, abstract = {This paper reports the first turbulence measurements performed in the Long Pipe Facility at the Center for International Cooperation in Long Pipe Experiments (CICLoPE). In particular, the Reynolds stress components obtained from a number of straight and boundary-layer-type single-wire and X-wire probes up to a friction Reynolds number of 3.8×10[4] are reported. In agreement with turbulent boundary-layer experiments as well as with results from the Superpipe, the present measurements show a clear logarithmic region in the streamwise variance profile, with a Townsend-Perry constant of A2≈1.26. The wall-normal variance profile exhibits a Reynolds-number-independent plateau, while the spanwise component was found to obey a logarithmic scaling over a much wider wall-normal distance than the other two components, with a slope that is nearly half of that of the Townsend-Perry constant, i.e. A2,w≈A2/2. The present results therefore provide strong support for the scaling of the Reynolds stress tensor based on the attached-eddy hypothesis. Intriguingly, the wall-normal and spanwise components exhibit higher amplitudes than in previous studies, and therefore call for follow-up studies in CICLoPE, as well as other large-scale facilities.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, }
@article {pmid28167585, year = {2017}, author = {Klewicki, JC and Chini, GP and Gibson, JF}, title = {Prospectus: towards the development of high-fidelity models of wall turbulence at large Reynolds number.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167585}, issn = {1364-503X}, abstract = {Recent and on-going advances in mathematical methods and analysis techniques, coupled with the experimental and computational capacity to capture detailed flow structure at increasingly large Reynolds numbers, afford an unprecedented opportunity to develop realistic models of high Reynolds number turbulent wall-flow dynamics. A distinctive attribute of this new generation of models is their grounding in the Navier-Stokes equations. By adhering to this challenging constraint, high-fidelity models ultimately can be developed that not only predict flow properties at high Reynolds numbers, but that possess a mathematical structure that faithfully captures the underlying flow physics. These first-principles models are needed, for example, to reliably manipulate flow behaviours at extreme Reynolds numbers. This theme issue of Philosophical Transactions of the Royal Society A provides a selection of contributions from the community of researchers who are working towards the development of such models. Broadly speaking, the research topics represented herein report on dynamical structure, mechanisms and transport; scale interactions and self-similarity; model reductions that restrict nonlinear interactions; and modern asymptotic theories. In this prospectus, the challenges associated with modelling turbulent wall-flows at large Reynolds numbers are briefly outlined, and the connections between the contributing papers are highlighted.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, }
@article {pmid28167584, year = {2017}, author = {Dogan, E and Hearst, RJ and Ganapathisubramani, B}, title = {Modelling high Reynolds number wall-turbulence interactions in laboratory experiments using large-scale free-stream turbulence.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167584}, issn = {1364-503X}, support = {277472/ERC_/European Research Council/International ; }, abstract = {A turbulent boundary layer subjected to free-stream turbulence is investigated in order to ascertain the scale interactions that dominate the near-wall region. The results are discussed in relation to a canonical high Reynolds number turbulent boundary layer because previous studies have reported considerable similarities between these two flows. Measurements were acquired simultaneously from four hot wires mounted to a rake which was traversed through the boundary layer. Particular focus is given to two main features of both canonical high Reynolds number boundary layers and boundary layers subjected to free-stream turbulence: (i) the footprint of the large scales in the logarithmic region on the near-wall small scales, specifically the modulating interaction between these scales, and (ii) the phase difference in amplitude modulation. The potential for a turbulent boundary layer subjected to free-stream turbulence to 'simulate' high Reynolds number wall-turbulence interactions is discussed. The results of this study have encouraging implications for future investigations of the fundamental scale interactions that take place in high Reynolds number flows as it demonstrates that these can be achieved at typical laboratory scales.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, }
@article {pmid28167583, year = {2017}, author = {Chini, GP and Montemuro, B and White, CM and Klewicki, J}, title = {A self-sustaining process model of inertial layer dynamics in high Reynolds number turbulent wall flows.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167583}, issn = {1364-503X}, abstract = {Field observations and laboratory experiments suggest that at high Reynolds numbers Re the outer region of turbulent boundary layers self-organizes into quasi-uniform momentum zones (UMZs) separated by internal shear layers termed 'vortical fissures' (VFs). Motivated by this emergent structure, a conceptual model is proposed with dynamical components that collectively have the potential to generate a self-sustaining interaction between a single VF and adjacent UMZs. A large-Re asymptotic analysis of the governing incompressible Navier-Stokes equation is performed to derive reduced equation sets for the streamwise-averaged and streamwise-fluctuating flow within the VF and UMZs. The simplified equations reveal the dominant physics within-and isolate possible coupling mechanisms among-these different regions of the flow.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, }
@article {pmid28167582, year = {2017}, author = {Sharma, AS and Moarref, R and McKeon, BJ}, title = {Scaling and interaction of self-similar modes in models of high Reynolds number wall turbulence.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167582}, issn = {1364-503X}, abstract = {Previous work has established the usefulness of the resolvent operator that maps the terms nonlinear in the turbulent fluctuations to the fluctuations themselves. Further work has described the self-similarity of the resolvent arising from that of the mean velocity profile. The orthogonal modes provided by the resolvent analysis describe the wall-normal coherence of the motions and inherit that self-similarity. In this contribution, we present the implications of this similarity for the nonlinear interaction between modes with different scales and wall-normal locations. By considering the nonlinear interactions between modes, it is shown that much of the turbulence scaling behaviour in the logarithmic region can be determined from a single arbitrarily chosen reference plane. Thus, the geometric scaling of the modes is impressed upon the nonlinear interaction between modes. Implications of these observations on the self-sustaining mechanisms of wall turbulence, modelling and simulation are outlined.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, }
@article {pmid28167581, year = {2017}, author = {Cossu, C and Hwang, Y}, title = {Self-sustaining processes at all scales in wall-bounded turbulent shear flows.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167581}, issn = {1364-503X}, abstract = {We collect and discuss the results of our recent studies which show evidence of the existence of a whole family of self-sustaining motions in wall-bounded turbulent shear flows with scales ranging from those of buffer-layer streaks to those of large-scale and very-large-scale motions in the outer layer. The statistical and dynamical features of this family of self-sustaining motions, which are associated with streaks and quasi-streamwise vortices, are consistent with those of Townsend's attached eddies. Motions at each relevant scale are able to sustain themselves in the absence of forcing from larger- or smaller-scale motions by extracting energy from the mean flow via a coherent lift-up effect. The coherent self-sustaining process is embedded in a set of invariant solutions of the filtered Navier-Stokes equations which take into full account the Reynolds stresses associated with the residual smaller-scale motions.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, }
@article {pmid28167580, year = {2017}, author = {Hellström, LH and Smits, AJ}, title = {Structure identification in pipe flow using proper orthogonal decomposition.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167580}, issn = {1364-503X}, abstract = {The energetic motions in direct numerical simulations of turbulent pipe flow at Reτ=685 are investigated using proper orthogonal decomposition. The procedure is extended such that a pressure component is identified in addition to the three-component velocity field for each mode. The pressure component of the modes is shown to align with the streamwise velocity component associated with the large-scale motions, where positive pressure coincides with positive streamwise velocity, and vice versa. The streamwise evolution of structures is then visualized using a conditional mode, which exhibit a strong similarity to the large-scale, low-momentum motions. A low-pressure region is present in the downstream section of the structure, and a high-pressure region is present in the upstream section.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, }
@article {pmid28167579, year = {2017}, author = {Morrill-Winter, C and Philip, J and Klewicki, J}, title = {Statistical evidence of anasymptotic geometric structure to the momentum transporting motions in turbulent boundary layers.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167579}, issn = {1364-503X}, abstract = {The turbulence contribution to the mean flow is reflected by the motions producing the Reynolds shear stress (〈-uv〉) and its gradient. Recent analyses of the mean dynamical equation, along with data, evidence that these motions asymptotically exhibit self-similar geometric properties. This study discerns additional properties associated with the uv signal, with an emphasis on the magnitudes and length scales of its negative contributions. The signals analysed derive from high-resolution multi-wire hot-wire sensor data acquired in flat-plate turbulent boundary layers. Space-filling properties of the present signals are shown to reinforce previous observations, while the skewness of uv suggests a connection between the size and magnitude of the negative excursions on the inertial domain. Here, the size and length scales of the negative uv motions are shown to increase with distance from the wall, whereas their occurrences decrease. A joint analysis of the signal magnitudes and their corresponding lengths reveals that the length scales that contribute most to 〈-uv〉 are distinctly larger than the average geometric size of the negative uv motions. Co-spectra of the streamwise and wall-normal velocities, however, are shown to exhibit invariance across the inertial region when their wavelengths are normalized by the width distribution, W(y), of the scaling layer hierarchy, which renders the mean momentum equation invariant on the inertial domain.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, }
@article {pmid28167578, year = {2017}, author = {Schmid, PJ and Sayadi, T}, title = {Low-dimensional representation of near-wall dynamics in shear flows, with implications to wall-models.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, doi = {10.1098/rsta.2016.0082}, pmid = {28167578}, issn = {1364-503X}, abstract = {The dynamics of coherent structures near the wall of a turbulent boundary layer is investigated with the aim of a low-dimensional representation of its essential features. Based on a triple decomposition into mean, coherent and incoherent motion and a dynamic mode decomposition to recover statistical information about the incoherent part of the flow field, a driven linear system coupling first- and second-order moments of the coherent structures is derived and analysed. The transfer function for this system, evaluated for a wall-parallel plane, confirms a strong bias towards streamwise elongated structures, and is proposed as an 'impedance' boundary condition which replaces the bulk of the transport between the coherent velocity field and the coherent Reynolds stresses, thus acting as a wall model for large-eddy simulations (LES). It is interesting to note that the boundary condition is non-local in space and time. The extracted model is capable of reproducing the principal Reynolds stress components for the pretransitional, transitional and fully turbulent boundary layer.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, }
@article {pmid28167577, year = {2017}, author = {Farrell, BF and Gayme, DF and Ioannou, PJ}, title = {A statistical state dynamics approach to wall turbulence.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167577}, issn = {1364-503X}, abstract = {This paper reviews results obtained using statistical state dynamics (SSD) that demonstrate the benefits of adopting this perspective for understanding turbulence in wall-bounded shear flows. The SSD approach used in this work employs a second-order closure that retains only the interaction between the streamwise mean flow and the streamwise mean perturbation covariance. This closure restricts nonlinearity in the SSD to that explicitly retained in the streamwise constant mean flow together with nonlinear interactions between the mean flow and the perturbation covariance. This dynamical restriction, in which explicit perturbation-perturbation nonlinearity is removed from the perturbation equation, results in a simplified dynamics referred to as the restricted nonlinear (RNL) dynamics. RNL systems, in which a finite ensemble of realizations of the perturbation equation share the same mean flow, provide tractable approximations to the SSD, which is equivalent to an infinite ensemble RNL system. This infinite ensemble system, referred to as the stochastic structural stability theory system, introduces new analysis tools for studying turbulence. RNL systems provide computationally efficient means to approximate the SSD and produce self-sustaining turbulence exhibiting qualitative features similar to those observed in direct numerical simulations despite greatly simplified dynamics. The results presented show that RNL turbulence can be supported by as few as a single streamwise varying component interacting with the streamwise constant mean flow and that judicious selection of this truncated support or 'band-limiting' can be used to improve quantitative accuracy of RNL turbulence. These results suggest that the SSD approach provides new analytical and computational tools that allow new insights into wall turbulence.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, }
@article {pmid28167576, year = {2017}, author = {Duvvuri, S and McKeon, B}, title = {Phase relations in a forced turbulent boundary layer: implications for modelling of high Reynolds number wall turbulence.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167576}, issn = {1364-503X}, abstract = {Phase relations between specific scales in a turbulent boundary layer are studied here by highlighting the associated nonlinear scale interactions in the flow. This is achieved through an experimental technique that allows for targeted forcing of the flow through the use of a dynamic wall perturbation. Two distinct large-scale modes with well-defined spatial and temporal wavenumbers were simultaneously forced in the boundary layer, and the resulting nonlinear response from their direct interactions was isolated from the turbulence signal for the study. This approach advances the traditional studies of large- and small-scale interactions in wall turbulence by focusing on the direct interactions between scales with triadic wavenumber consistency. The results are discussed in the context of modelling high Reynolds number wall turbulence.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, }
@article {pmid28167575, year = {2017}, author = {Brauckmann, HJ and Eckhardt, B and Schumacher, J}, title = {Heat transport in Rayleigh-Bénard convection and angular momentum transport in Taylor-Couette flow: a comparative study.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167575}, issn = {1364-503X}, abstract = {Rayleigh-Bénard convection and Taylor-Couette flow are two canonical flows that have many properties in common. We here compare the two flows in detail for parameter values where the Nusselt numbers, i.e. the thermal transport and the angular momentum transport normalized by the corresponding laminar values, coincide. We study turbulent Rayleigh-Bénard convection in air at Rayleigh number Ra=10[7] and Taylor-Couette flow at shear Reynolds number ReS=2×10[4] for two different mean rotation rates but the same Nusselt numbers. For individual pairwise related fields and convective currents, we compare the probability density functions normalized by the corresponding root mean square values and taken at different distances from the wall. We find one rotation number for which there is very good agreement between the mean profiles of the two corresponding quantities temperature and angular momentum. Similarly, there is good agreement between the fluctuations in temperature and velocity components. For the heat and angular momentum currents, there are differences in the fluctuations outside the boundary layers that increase with overall rotation and can be related to differences in the flow structures in the boundary layer and in the bulk. The study extends the similarities between the two flows from global quantities to local quantities and reveals the effects of rotation on the transport.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, }
@article {pmid28167574, year = {2017}, author = {Deguchi, K and Hall, P}, title = {The relationship between free-stream coherent structures and near-wall streaks at high Reynolds numbers.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167574}, issn = {1364-503X}, abstract = {The present work is based on our recent discovery of a new class of exact coherent structures generated near the edge of quite general boundary layer flows. The structures are referred to as free-stream coherent structures and were found using a large Reynolds number asymptotic approach to describe equilibrium solutions of the Navier-Stokes equations. In this paper, first we present results for a new family of free-stream coherent structures existing at relatively large wavenumbers. The new results are consistent with our earlier theoretical result that such structures can generate larger amplitude wall streaks if and only if the local spanwise wavenumber is sufficiently small. In a Blasius boundary layer, the local wavenumber increases in the streamwise direction so the wall streaks can typically exist only over a finite interval. However, here it is shown that they can interact with wall curvature to produce exponentially growing Görtler vortices through the receptivity process by a novel nonparallel mechanism. The theoretical predictions found are confirmed by a hybrid numerical approach. In contrast with previous receptivity investigations, it is shown that the amplitude of the induced vortex is larger than the structures in the free-stream which generate it.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, }
@article {pmid28167573, year = {2017}, author = {Baars, WJ and Hutchins, N and Marusic, I}, title = {Reynolds number trend of hierarchies and scale interactions in turbulent boundary layers.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {375}, number = {2089}, pages = {}, pmid = {28167573}, issn = {1364-503X}, abstract = {Small-scale velocity fluctuations in turbulent boundary layers are often coupled with the larger-scale motions. Studying the nature and extent of this scale interaction allows for a statistically representative description of the small scales over a time scale of the larger, coherent scales. In this study, we consider temporal data from hot-wire anemometry at Reynolds numbers ranging from Reτ≈2800 to 22 800, in order to reveal how the scale interaction varies with Reynolds number. Large-scale conditional views of the representative amplitude and frequency of the small-scale turbulence, relative to the large-scale features, complement the existing consensus on large-scale modulation of the small-scale dynamics in the near-wall region. Modulation is a type of scale interaction, where the amplitude of the small-scale fluctuations is continuously proportional to the near-wall footprint of the large-scale velocity fluctuations. Aside from this amplitude modulation phenomenon, we reveal the influence of the large-scale motions on the characteristic frequency of the small scales, known as frequency modulation. From the wall-normal trends in the conditional averages of the small-scale properties, it is revealed how the near-wall modulation transitions to an intermittent-type scale arrangement in the log-region. On average, the amplitude of the small-scale velocity fluctuations only deviates from its mean value in a confined temporal domain, the duration of which is fixed in terms of the local Taylor time scale. These concentrated temporal regions are centred on the internal shear layers of the large-scale uniform momentum zones, which exhibit regions of positive and negative streamwise velocity fluctuations. With an increasing scale separation at high Reynolds numbers, this interaction pattern encompasses the features found in studies on internal shear layers and concentrated vorticity fluctuations in high-Reynolds-number wall turbulence.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.}, }
@article {pmid28163876, year = {2017}, author = {Phillips, N and Knowles, K and Bomphrey, RJ}, title = {Petiolate wings: effects on the leading-edge vortex in flapping flight.}, journal = {Interface focus}, volume = {7}, number = {1}, pages = {20160084}, pmid = {28163876}, issn = {2042-8898}, abstract = {The wings of many insect species including crane flies and damselflies are petiolate (on stalks), with the wing planform beginning some distance away from the wing hinge, rather than at the hinge. The aerodynamic impact of flapping petiolate wings is relatively unknown, particularly on the formation of the lift-augmenting leading-edge vortex (LEV): a key flow structure exploited by many insects, birds and bats to enhance their lift coefficient. We investigated the aerodynamic implications of petiolation P using particle image velocimetry flow field measurements on an array of rectangular wings of aspect ratio 3 and petiolation values of P = 1-3. The wings were driven using a mechanical device, the 'Flapperatus', to produce highly repeatable insect-like kinematics. The wings maintained a constant Reynolds number of 1400 and dimensionless stroke amplitude Λ* (number of chords traversed by the wingtip) of 6.5 across all test cases. Our results showed that for more petiolate wings the LEV is generally larger, stronger in circulation, and covers a greater area of the wing surface, particularly at the mid-span and inboard locations early in the wing stroke cycle. In each case, the LEV was initially arch-like in form with its outboard end terminating in a focus-sink on the wing surface, before transitioning to become continuous with the tip vortex thereafter. In the second half of the wing stroke, more petiolate wings exhibit a more detached LEV, with detachment initiating at approximately 70% and 50% span for P = 1 and 3, respectively. As a consequence, lift coefficients based on the LEV are higher in the first half of the wing stroke for petiolate wings, but more comparable in the second half. Time-averaged LEV lift coefficients show a general rise with petiolation over the range tested.}, }
@article {pmid28163871, year = {2017}, author = {Widmann, A and Tropea, C}, title = {Reynolds number influence on the formation of vortical structures on a pitching flat plate.}, journal = {Interface focus}, volume = {7}, number = {1}, pages = {20160079}, pmid = {28163871}, issn = {2042-8898}, abstract = {The impact of chord-based Reynolds number on the formation of leading-edge vortices (LEVs) on unsteady pitching flat plates is investigated. The influence of secondary flow structures on the shear layer feeding the LEV and the subsequent topological change at the leading edge as the result of viscous processes are demonstrated. Time-resolved velocity fields are measured using particle image velocimetry simultaneously in two fields of view to correlate local and global flow phenomena in order to identify unsteady boundary-layer separation and the subsequent flow structures. Finally, the Reynolds number is identified as a parameter that is responsible for the transition in mechanisms leading to LEV detachment from an aerofoil, as it determines the viscous response of the boundary layer in the vortex-wall interaction.}, }
@article {pmid28163870, year = {2017}, author = {Wagner, H and Weger, M and Klaas, M and Schröder, W}, title = {Features of owl wings that promote silent flight.}, journal = {Interface focus}, volume = {7}, number = {1}, pages = {20160078}, pmid = {28163870}, issn = {2042-8898}, abstract = {Owls are an order of birds of prey that are known for the development of a silent flight. We review here the morphological adaptations of owls leading to silent flight and discuss also aerodynamic properties of owl wings. We start with early observations (until 2005), and then turn to recent advances. The large wings of these birds, resulting in low wing loading and a low aspect ratio, contribute to noise reduction by allowing slow flight. The serrations on the leading edge of the wing and the velvet-like surface have an effect on noise reduction and also lead to an improvement of aerodynamic performance. The fringes at the inner feather vanes reduce noise by gliding into the grooves at the lower wing surface that are formed by barb shafts. The fringed trailing edge of the wing has been shown to reduce trailing edge noise. These adaptations to silent flight have been an inspiration for biologists and engineers for the development of devices with reduced noise production. Today several biomimetic applications such as a serrated pantograph or a fringed ventilator are available. Finally, we discuss unresolved questions and possible future directions.}, }
@article {pmid28163869, year = {2017}, author = {Tank, J and Smith, L and Spedding, GR}, title = {On the possibility (or lack thereof) of agreement between experiment and computation of flows over wings at moderate Reynolds number.}, journal = {Interface focus}, volume = {7}, number = {1}, pages = {20160076}, pmid = {28163869}, issn = {2042-8898}, abstract = {The flight of many birds and bats, and their robotic counterparts, occurs over a range of chord-based Reynolds numbers from 1 × 10[4] to 1.5 × 10[5]. It is precisely over this range where the aerodynamics of simple, rigid, fixed wings becomes extraordinarily sensitive to small changes in geometry and the environment, with two sets of consequences. The first is that practical lifting devices at this scale will likely not be simple, rigid, fixed wings. The second is that it becomes non-trivial to make baseline comparisons for experiment and computation, when either one can be wrong. Here we examine one ostensibly simple case of the NACA 0012 aerofoil and make careful comparison between the technical literature, and new experiments and computations. The agreement (or lack thereof) will establish one or more baseline results and some sensitivities around them. The idea is that the diagnostic procedures will help to guide comparisons and predictions in subsequent more complex cases.}, }
@article {pmid28163357, year = {2017}, author = {Wang, CY and Mercer, E and Kamranvand, F and Williams, L and Kolios, A and Parker, A and Tyrrel, S and Cartmell, E and McAdam, EJ}, title = {Tube-side mass transfer for hollow fibre membrane contactors operated in the low Graetz range.}, journal = {Journal of membrane science}, volume = {523}, number = {}, pages = {235-246}, pmid = {28163357}, issn = {0376-7388}, abstract = {Transformation of the tube-side mass transfer coefficient derived in hollow fibre membrane contactors (HFMC) of different characteristic length scales (equivalent diameter and fibre length) has been studied when operated in the low Graetz range (Gz<10). Within the low Gz range, mass transfer is generally described by the Graetz problem (Sh=3.67) which assumes that the concentration profile comprises a constant shape over the fibre radius. In this study, it is experimentally evidenced that this assumption over predicts mass transfer within the low Graetz range. Furthermore, within the low Gz range (below 2), a proportional relationship between the experimentally determined mass transfer coefficient (Kov) and the Graetz number has been identified. For Gz numbers below 2, the experimental Sh number approached unity, which suggests that mass transfer is strongly dependent upon diffusion. However, within this diffusion controlled region of mass transfer, tube-side fluid velocity remained important. For Gz numbers above 2, Sh could be satisfactorily described by extension to the Lévêque solution, which can be ascribed to the constrained growth of the concentration boundary layer adjacent to the fibre wall. Importantly this study demonstrates that whilst mass transfer in the low Graetz range does not explicitly conform to either the Graetz problem or classical Lévêque solution, it is possible to transform the experimentally derived overall mass transfer coefficient (Kov) between characteristic length scales (dh and L). T h is was corroborated by comparison of the empirical relationship determined in this study (Sh=0.36Gz) with previously published studies operated in the low Gz range. This analysis provides important insight for process design when slow tube-side flows, or low Schmidt numbers (coincident with gases) constrain operation of hollow fibre membrane contactors to the low Gz range.}, }
@article {pmid28161594, year = {2017}, author = {Tanveer, A and Hayat, T and Alsaadi, F and Alsaedi, A}, title = {Mixed convection peristaltic flow of Eyring-Powell nanofluid in a curved channel with compliant walls.}, journal = {Computers in biology and medicine}, volume = {82}, number = {}, pages = {71-79}, doi = {10.1016/j.compbiomed.2017.01.015}, pmid = {28161594}, issn = {1879-0534}, mesh = {Animals ; Computer Simulation ; Elastic Modulus/*physiology ; Humans ; *Models, Biological ; Peristalsis/*physiology ; Rheology/*methods ; Temperature ; }, abstract = {The novel features of nanofluids made them potentially significant in heat transfer mechanism occurring in medical and industrial processes like microelectronics, pharmaceutical processes, hybrid engines, thermal management of vehicles, refrigerator, chiller, gas temperature reduction and so forth. These processes bear tendency to enhance thermal conductivity and the convective heat transfer more efficiently than base fluid. This unique aspect made nanofluids the topic of interest in recent time via different fluid flow models. The problem in hand is one such application of nanofluids in peristaltic flow through curved channel. Thus peristalsis of Eyring-Powell nanofluid followed through conservation principles of mass, momentum, energy and concentration has been modeled. The whole system is made coupled via viscous dissipation, mixed convection, thermophoresis and Brownian motion. The complexity of system has been executed through a numerical approach after utilizing small Reynolds number and large wavelength concepts. A striking feature of this study is the activation of velocity and temperature with larger Brownian diffusion, whereas reduction is noticed with advancement in thermophoresis. Moreover the numerically obtained results for compliant walls are compatible with those obtained through other techniques.}, }
@article {pmid28152457, year = {2017}, author = {He, L and Hang, J and Wang, X and Lin, B and Li, X and Lan, G}, title = {Numerical investigations of flow and passive pollutant exposure in high-rise deep street canyons with various street aspect ratios and viaduct settings.}, journal = {The Science of the total environment}, volume = {584-585}, number = {}, pages = {189-206}, doi = {10.1016/j.scitotenv.2017.01.138}, pmid = {28152457}, issn = {1879-1026}, mesh = {Air Pollutants/*analysis ; *Cities ; Environmental Exposure/*analysis ; Humans ; Models, Theoretical ; Noise ; Vehicle Emissions/*analysis ; Wind ; }, abstract = {Vehicular pollutant exposure of residents and pedestrians in high-rise deep street canyons with viaducts and noise barriers requires special concerns because the ventilation capacity is weak and the literature reported inconsistent findings on flow patterns as aspect ratios (building height/street width, H/W) are larger than 2. By conducting computational fluid dynamics (CFD) simulations coupled with the intake fraction iF and the daily pollutant exposure Et, this paper investigates the impact of street aspect ratios, viaducts and noise barriers on the flow and vehicular passive pollutant exposure in full-scale street canyons (H/W=1-6, W=24m). iF represents the fraction of total emissions inhaled by a population (1ppm=10[-6]), while Et means the extent of human beings' contact with pollutants within one day. CFD methodologies of passive pollutant dispersion modeling are successfully validated by wind tunnel data in Meroney et al. (1996). As a novelty, the two-main-vortex pattern start appearing in full-scale street canyons as H/W changes from 4 to 5, however previous studies using wind-tunnel-scale models (H=6cm) reported two to five vortexes as H/W=2-5. This finding is validated by both smoke visualization in scale-model outdoor field experiments (H=1.2m, W=0.6m) and CFD simulations of Reynolds number independence. Cases with two main vortexes (H/W=5-6) experience much larger daily pollutant exposure (~10[3]-10[4]mg/m[3]/day) than those with single main vortex as H/W=1-4 (~10[1]-10[2]mg/m[3]/day). Moreover leeward-side pollutant exposures are much larger than windward-side as H/W=1-4 while oppositely as H/W=5-6. Assuming a general population density, the total iF is 485-803ppm as H/W=1, 2020-12051ppm as H/W=2-4, and 51112-794026ppm as H/W=5-6. With a single elevated pollutant source, cases with viaducts experience significantly smaller pollutant exposures than cases without viaducts. Road barriers slightly increase pollutant exposure in near-road buildings with H/W=1 while reduce a little as H/W=3 and 5. Two-source cases can experience 2.60-5.52 times pollutant exposure as great as single-source cases.}, }
@article {pmid28151968, year = {2017}, author = {Tanveer, A and Hayat, T and Alsaedi, A and Ahmad, B}, title = {Numerical simulation for peristalsis of Carreau-Yasuda nanofluid in curved channel with mixed convection and porous space.}, journal = {PloS one}, volume = {12}, number = {2}, pages = {e0170029}, pmid = {28151968}, issn = {1932-6203}, mesh = {Computer Simulation ; Convection ; Hot Temperature ; Humans ; *Hydrodynamics ; *Models, Theoretical ; Nanoparticles ; *Peristalsis/physiology ; Porosity ; Rheology ; Thermal Conductivity ; }, abstract = {Main theme of present investigation is to model and analyze the peristaltic activity of Carraeu-Yasuda nanofluid saturating porous space in a curved channel. Unlike the traditional approach, the porous medium effects are characterized by employing modified Darcy's law for Carreau-Yasuda fluid. To our knowledge this is first attempt in this direction for Carreau-Yasuda fluid. Heat and mass transfer are further considered. Simultaneous effects of heat and mass transfer are examined in presence of mixed convection, viscous dissipation and thermal radiation. The compliant characteristics for channel walls are taken into account. The resulting complex mathematical system has been discussed for small Reynolds number and large wavelength concepts. Numerical approximation to solutions are thus plotted in graphs and the physical description is presented. It is concluded that larger porosity in a medium cause an enhancement in fluid velocity and reduction in concentration.}, }
@article {pmid28141804, year = {2017}, author = {Wheeler, RJ}, title = {Use of chiral cell shape to ensure highly directional swimming in trypanosomes.}, journal = {PLoS computational biology}, volume = {13}, number = {1}, pages = {e1005353}, pmid = {28141804}, issn = {1553-7358}, support = {103261/Z/13/Z//Wellcome Trust/United Kingdom ; }, mesh = {Adaptation, Physiological/*physiology ; Cell Movement/*physiology ; *Cell Size ; Cell Tracking ; Computer Simulation ; Friction ; Hydrodynamics ; Microscopy, Video ; *Models, Biological ; Swimming/physiology ; Trypanosoma/*cytology/*physiology ; Viscosity ; }, abstract = {Swimming cells typically move along a helical path or undergo longitudinal rotation as they swim, arising from chiral asymmetry in hydrodynamic drag or propulsion bending the swimming path into a helix. Helical paths are beneficial for some forms of chemotaxis, but why asymmetric shape is so prevalent when a symmetric shape would also allow highly directional swimming is unclear. Here, I analyse the swimming of the insect life cycle stages of two human parasites; Trypanosoma brucei and Leishmania mexicana. This showed quantitatively how chirality in T. brucei cell shape confers highly directional swimming. High speed videomicrographs showed that T. brucei, L. mexicana and a T. brucei RNAi morphology mutant have a range of shape asymmetries, from wild-type T. brucei (highly chiral) to L. mexicana (near-axial symmetry). The chiral cells underwent longitudinal rotation while swimming, with more rapid longitudinal rotation correlating with swimming path directionality. Simulation indicated hydrodynamic drag on the chiral cell shape caused rotation, and the predicted geometry of the resulting swimming path matched the directionality of the observed swimming paths. This simulation of swimming path geometry showed that highly chiral cell shape is a robust mechanism through which microscale swimmers can achieve highly directional swimming at low Reynolds number. It is insensitive to random variation in shape or propulsion (biological noise). Highly symmetric cell shape can give highly directional swimming but is at risk of giving futile circular swimming paths in the presence of biological noise. This suggests the chiral T. brucei cell shape (associated with the lateral attachment of the flagellum) may be an adaptation associated with the bloodstream-inhabiting lifestyle of this parasite for robust highly directional swimming. It also provides a plausible general explanation for why swimming cells tend to have strong asymmetries in cell shape or propulsion.}, }
@article {pmid28117769, year = {2017}, author = {Kulkarni, AA and Patel, RK and Friedman, C and Leftwich, MC}, title = {A Robotic Platform to Study the Foreflipper of the California Sea Lion.}, journal = {Journal of visualized experiments : JoVE}, volume = {}, number = {119}, pages = {}, pmid = {28117769}, issn = {1940-087X}, mesh = {Animals ; Biomechanical Phenomena ; Extremities ; Female ; *Robotics ; Sea Lions/*anatomy &amp; histology ; *Swimming ; }, abstract = {The California sea lion (Zalophus californianus), is an agile and powerful swimmer. Unlike many successful swimmers (dolphins, tuna), they generate most of their thrust with their large foreflippers. This protocol describes a robotic platform designed to study the hydrodynamic performance of the swimming California sea lion (Zalophus californianus). The robot is a model of the animal's foreflipper that is actuated by motors to replicate the motion of its propulsive stroke (the 'clap'). The kinematics of the sea lion's propulsive stroke are extracted from video data of unmarked, non-research sea lions at the Smithsonian Zoological Park (SNZ). Those data form the basis of the actuation motion of the robotic flipper presented here. The geometry of the robotic flipper is based a on high-resolution laser scan of a foreflipper of an adult female sea lion, scaled to about 60% of the full-scale flipper. The articulated model has three joints, mimicking the elbow, wrist and knuckle joint of the sea lion foreflipper. The robotic platform matches dynamics properties-Reynolds number and tip speed-of the animal when accelerating from rest. The robotic flipper can be used to determine the performance (forces and torques) and resulting flowfields.}, }
@article {pmid28085475, year = {2016}, author = {Mo, CJ and Qin, LZ and Zhao, F and Yang, LJ}, title = {Application of the dissipative particle dynamics method to the instability problem of a liquid thread.}, journal = {Physical review. E}, volume = {94}, number = {6-1}, pages = {063113}, doi = {10.1103/PhysRevE.94.063113}, pmid = {28085475}, issn = {2470-0053}, abstract = {We investigate the application of the dissipative particle dynamics method to the instability problem of a long liquid thread surrounded by another fluid. The dispersion curves obtained from simulations are compared with classic theoretical predictions. The results from standard dissipative particle dynamics (DPD) simulations at first have a tendency of gradually approaching to Tomotika's Stokes flow prediction when the Reynolds number is decreased. But they then abnormally deviate again when the viscosity is very large. The same phenomenon is also confirmed in droplet retraction simulations when also compared with theoretical Stokes flow results. On the other hand, when a hard-core DPD model is used, with the decrease of the Reynolds number the simulation results did finally approach Tomotika's predictions when Re≈0.1. A combined presentation of the hard-core DPD results and the standard DPD results, excluding the abnormal ones, demonstrates that they are approximately on a continuum when labeled with Reynolds number. These results suggest that the standard DPD method is a suitable method for investigation of the instability problem of immersed liquid thread in the inertioviscous regime (0.1<Re<10), which is relevant for microfluidics applications but there is currently no theory. It cannot reach the Re≈0.1 regime because of some irregular properties of highly viscous DPD fluid, while the hard-core DPD is suitable to overcome this inferiority with standard DPD.}, }
@article {pmid28085437, year = {2016}, author = {Sampath, R and Mathur, M and Chakravarthy, SR}, title = {Lagrangian coherent structures during combustion instability in a premixed-flame backward-step combustor.}, journal = {Physical review. E}, volume = {94}, number = {6-1}, pages = {062209}, doi = {10.1103/PhysRevE.94.062209}, pmid = {28085437}, issn = {2470-0053}, abstract = {This paper quantitatively examines the occurrence of large-scale coherent structures in the flow field during combustion instability in comparison with the flow-combustion-acoustic system when it is stable. For this purpose, the features in the recirculation zone of the confined flow past a backward-facing step are studied in terms of Lagrangian coherent structures. The experiments are conducted at a Reynolds number of 18600 and an equivalence ratio of 0.9 of the premixed fuel-air mixture for two combustor lengths, the long duct corresponding to instability and the short one to the stable case. Simultaneous measurements of the velocity field using time-resolved particle image velocimetry and the CH^{*} chemiluminescence of the flame along with pressure time traces are obtained. The extracted ridges of the finite-time Lyapunov exponent (FTLE) fields delineate dynamically distinct regions of the flow field. The presence of large-scale vortical structures and their modulation over different time instants are well captured by the FTLE ridges for the long combustor where high-amplitude acoustic oscillations are self-excited. In contrast, small-scale vortices signifying Kelvin-Helmholtz instability are observed in the short duct case. Saddle-type flow features are found to separate the distinct flow structures for both combustor lengths. The FTLE ridges are found to align with the flame boundaries in the upstream regions, whereas farther downstream, the alignment is weaker due to dilatation of the flow by the flame's heat release. Specifically, the FTLE ridges encompass the flame curl-up for both the combustor lengths, and thus act as the surrogate flame boundaries. The flame is found to propagate upstream from an earlier vortex roll-up to a newer one along the backward-time FTLE ridge connecting the two structures.}, }
@article {pmid28085432, year = {2016}, author = {Jo, I and Huang, Y and Zimmermann, W and Kanso, E}, title = {Passive swimming in viscous oscillatory flows.}, journal = {Physical review. E}, volume = {94}, number = {6-1}, pages = {063116}, doi = {10.1103/PhysRevE.94.063116}, pmid = {28085432}, issn = {2470-0053}, abstract = {Fluid-based locomotion at low Reynolds number is subject to the constraints of Purcell's scallop theorem: reciprocal shape kinematics identical under a time-reversal symmetry cannot cause locomotion. In particular, a single degree-of-freedom scallop undergoing opening and closing motions cannot swim. Most strategies for symmetry breaking and locomotion rely on direct control of the swimmer's shape kinematics. Less is known about indirect control via actuation of the fluid medium. To address how such indirect actuation strategies can lead to locomotion, we analyze a Λ-shaped model system analogous to Purcell's scallop but able to deform passively in oscillatory flows. Neutrally buoyant scallops undergo no net locomotion. We show that dense, elastic scallops can exhibit passive locomotion in zero-mean oscillatory flows. We examine the efficiency of swimming parallel to the background flow and analyze the stability of these motions. We observe transitions from stable to unstable swimming, including ordered transitions from fluttering to chaoticlike motions and tumbling. Our results demonstrate that flow oscillations can be used to passively actuate and control the motion of microswimmers, which may be relevant to applications such as surgical robots and cell sorting and manipulation in microfluidic devices.}, }
@article {pmid28085295, year = {2016}, author = {Carrillo, M and Que, U and González, JA}, title = {Estimation of Reynolds number for flows around cylinders with lattice Boltzmann methods and artificial neural networks.}, journal = {Physical review. E}, volume = {94}, number = {6-1}, pages = {063304}, doi = {10.1103/PhysRevE.94.063304}, pmid = {28085295}, issn = {2470-0053}, abstract = {The present work investigates the application of artificial neural networks (ANNs) to estimate the Reynolds (Re) number for flows around a cylinder. The data required to train the ANN was generated with our own implementation of a lattice Boltzmann method (LBM) code performing simulations of a two-dimensional flow around a cylinder. As results of the simulations, we obtain the velocity field (v[over ⃗]) and the vorticity (∇[over ⃗]×v[over ⃗]) of the fluid for 120 different values of Re measured at different distances from the obstacle and use them to teach the ANN to predict the Re. The results predicted by the networks show good accuracy with errors of less than 4% in all the studied cases. One of the possible applications of this method is the development of an efficient tool to characterize a blocked flowing pipe.}, }
@article {pmid28084568, year = {2017}, author = {Fukuda, M and Yoshimura, K and Namekawa, K and Sakai, K}, title = {Technical characterization of dialysis fluid flow and mass transfer rate in dialyzers with various filtration coefficients using dimensionless correlation equation.}, journal = {Journal of artificial organs : the official journal of the Japanese Society for Artificial Organs}, volume = {20}, number = {2}, pages = {145-151}, pmid = {28084568}, issn = {1619-0904}, mesh = {*Dialysis Solutions ; Filtration ; Humans ; *Membranes, Artificial ; Models, Biological ; Permeability ; *Renal Dialysis ; }, abstract = {The objective of the present study is to evaluate the effect of filtration coefficient and internal filtration on dialysis fluid flow and mass transfer coefficient in dialyzers using dimensionless mass transfer correlation equations. Aqueous solution of vitamin B12 clearances were obtained for REXEED-15L as a low flux dialyzer, and APS-15EA and APS-15UA as high flux dialyzers. All the other design specifications were identical for these dialyzers except for filtration coefficient. The overall mass transfer coefficient was calculated, moreover, the exponents of Reynolds number (Re) and film mass transfer coefficient of the dialysis-side fluid (k D) for each flow rate were derived from the Wilson plot and dimensionless correlation equation. The exponents of Re were 0.4 for the low flux dialyzer whereas 0.5 for the high flux dialyzers. Dialysis fluid of the low flux dialyzer was close to laminar flow because of its low filtration coefficient. On the other hand, dialysis fluid of the high flux dialyzers was assumed to be orthogonal flow. Higher filtration coefficient was associated with higher k D influenced by mass transfer rate through diffusion and internal filtration. Higher filtration coefficient of dialyzers and internal filtration affect orthogonal flow of dialysis fluid.}, }
@article {pmid28069230, year = {2017}, author = {Manmi, K and Wang, Q}, title = {Acoustic microbubble dynamics with viscous effects.}, journal = {Ultrasonics sonochemistry}, volume = {36}, number = {}, pages = {427-436}, doi = {10.1016/j.ultsonch.2016.11.032}, pmid = {28069230}, issn = {1873-2828}, abstract = {Microbubble dynamics subject to ultrasound are associated with important applications in biomedical ultrasonics, sonochemistry and cavitation cleaning. The viscous effects in this phenomenon is essential since the Reynolds number Re associated is about O(10). The flow field is characterized as being an irrotational flow in the bulk volume but with a thin vorticity layer at the bubble surface. This paper investigates the phenomenon using the boundary integral method based on the viscous potential flow theory. The viscous effects are incorporated into the model through including the normal viscous stress of the irrotational flow in the dynamic boundary condition at the bubble surface. The viscous correction pressure of Joseph &amp; Wang (2004) is implemented to resolve the discrepancy between the non-zero shear stress of the irrotational flow at a free surface and the physical boundary condition of zero shear stress. The model agrees well with the Rayleigh-Plesset equation for a spherical bubble oscillating in a viscous liquid for several cycles of oscillation for Re=10. It correlates pretty closely with both the experimental data and the axisymmetric simulation based on the Navier-Stokes equations for transient bubble dynamics near a rigid boundary. We further analyze microbubble dynamics near a rigid boundary subject to ultrasound travelling perpendicular and parallel to the boundary, respectively, in parameter regions of clinical relevance. The viscous effects to acoustic microbubble dynamics are analyzed in terms of the jet velocity, bubble volume, centroid movement, Kelvin impulse and bubble energy.}, }
@article {pmid28049316, year = {2016}, author = {Jaju, SJ and Kumaran, V}, title = {System size dependence of the structure and rheology in a sheared lamellar liquid crystalline medium.}, journal = {The Journal of chemical physics}, volume = {145}, number = {24}, pages = {244901}, doi = {10.1063/1.4972132}, pmid = {28049316}, issn = {1089-7690}, abstract = {The structural and rheological evolution of an initially disordered lamellar phase system under a shear flow is examined using a mesoscale model based on a free energy functional for the concentration field, which is the scaled difference in the concentration between the hydrophilic and hydrophobic components. The dimensionless numbers which affect the shear evolution are the Reynolds number (γ˙¯L[2]/ν), the Schmidt number (ν/D), a dimensionless parameter Σ=(Aλ[2]/ρν[2]), a parameter μr which represents the viscosity contrast between the hydrophilic and hydrophobic components, and (L/λ), the ratio of system size and layer spacing. Here, ρ, ν, and D are the density, kinematic viscosity (ratio of viscosity and density), and the mass diffusivity, and A is the energy density in the free energy functional which is proportional to the compression modulus. Two distinct modes of structural evolution are observed for moderate values of the parameter Σ depending only on the combination ScΣ and independent of system size. For ScΣ less than about 10, the layers tend to form before they are deformed by the mean shear, and layered but misaligned domains are initially formed, and these are deformed and rotated by the flow. In this case, the excess viscosity (difference between the viscosity and that for an aligned state) does not decrease to zero even after 1000 strain units, but appears to plateau to a steady state value. For ScΣ greater than about 10, layers are deformed by the mean shear before they are fully formed, and a well aligned lamellar phase with edge dislocation orders completely due to the cancellation of dislocations. The excess viscosity scales as t[-1] in the long time limit. The maximum macroscopic viscosity (ratio of total stress and average strain rate over the entire sample) during the alignment process increases with the system size proportional to (L/λ)[3/2]. For large values of Σ, there is localisation of shear at the walls, and the bulk of the sample moves as a block. The thickness of the shearing region appears to be invariant with the system size, leading to an increase of viscosity proportional to L. The time for structural evolution is found to be the inverse of the strain rate γ˙[-1]. In the case of a significant viscosity contrast between the hydrophilic and hydrophobic parts, the average viscosity increases by 1-2 orders of magnitude due to the defect pinning mechanism, where the regions between defects move as a block, and shear localisation at the wall.}, }
@article {pmid28046084, year = {2017}, author = {Wei, J and Li, Y}, title = {Human Cough as a Two-Stage Jet and Its Role in Particle Transport.}, journal = {PloS one}, volume = {12}, number = {1}, pages = {e0169235}, pmid = {28046084}, issn = {1932-6203}, mesh = {Cough/*physiopathology ; Humans ; Particle Size ; *Rheology ; Time Factors ; }, abstract = {The human cough is a significant vector in the transmission of respiratory diseases in indoor environments. The cough flow is characterized as a two-stage jet; specifically, the starting jet (when the cough starts and flow is released) and interrupted jet (after the source supply is terminated). During the starting-jet stage, the flow rate is a function of time; three temporal profiles of the exit velocity (pulsation, sinusoidal and real-cough) were investigated in this study, and our results showed that the cough flow's maximum penetration distance was in the range of a 50.6-85.5 opening diameter (D) under our experimental conditions. The real-cough and sinusoidal cases exhibited greater penetration ability than the pulsation cases under the same characteristic Reynolds number (Rec) and normalized cough expired volume (Q/AD, with Q as the cough expired volume and A as the opening area). However, the effects of Rec and Q/AD on the maximum penetration distances proved to be more significant; larger values of Rec and Q/AD reflected cough flows with greater penetration distances. A protocol was developed to scale the particle experiments between the prototype in air, and the model in water. The water tank experiments revealed that although medium and large particles deposit readily, their maximum spread distance is similar to that of small particles. Moreover, the leading vortex plays an important role in enhancing particle transport.}, }
@article {pmid28040018, year = {2016}, author = {Zhao, S and Cheng, E and Qiu, X and Burnett, I and Liu, JC}, title = {Pressure spectra in turbulent flows in the inertial and the dissipation ranges.}, journal = {The Journal of the Acoustical Society of America}, volume = {140}, number = {6}, pages = {4178}, doi = {10.1121/1.4968881}, pmid = {28040018}, issn = {1520-8524}, abstract = {Based on existing studies that provide the pressure spectra in turbulent flows from the asymptotic pressure structure function in the inertial range, this paper extends the pressure spectrum to the dissipation range by proposing a pressure structure function model that incorporates both the inertial and dissipation ranges. Existing experiment results were used to validate the proposed pressure structure function model first, and then the obtained pressure spectrum was compared with the simulation and measurement data in the literature and the wind-induced noise measured outdoors. All comparisons demonstrate that the pressure spectrum obtained from the proposed pressure structure function model can be used to estimate the pressure spectra in both the inertial and dissipation ranges in turbulent flows with a sufficiently large Reynolds number.}, }
@article {pmid30174548, year = {2017}, author = {Oosterhuis, JP and Verbeek, AA and Bühler, S and Wilcox, D and van der Meer, TH}, title = {Flow Separation and Turbulence in Jet Pumps for Thermoacoustic Applications.}, journal = {Flow, turbulence and combustion}, volume = {98}, number = {1}, pages = {311-326}, pmid = {30174548}, issn = {1573-1987}, abstract = {The effect of flow separation and turbulence on the performance of a jet pump in oscillatory flows is investigated. A jet pump is a static device whose shape induces asymmetric hydrodynamic end effects when placed in an oscillatory flow. This will result in a time-averaged pressure drop which can be used to suppress acoustic streaming in closed-loop thermoacoustic devices. An experimental setup is used to measure the time-averaged pressure drop as well as the acoustic power dissipation across two different jet pump geometries in a pure oscillatory flow. The results are compared against published numerical results where flow separation was found to have a negative effect on the jet pump performance in a laminar flow. Using hot-wire anemometry the onset of flow separation is determined experimentally and the applicability of a critical Reynolds number for oscillatory pipe flows is confirmed for jet pump applications. It is found that turbulence can lead to a reduction of flow separation and hence, to an improvement in jet pump performance compared to laminar oscillatory flows.}, }
@article {pmid30069161, year = {2017}, author = {Sengupta, U and Nemati, H and Boersma, BJ and Pecnik, R}, title = {Fully Compressible Low-Mach Number Simulations of Carbon-dioxide at Supercritical Pressures and Trans-critical Temperatures.}, journal = {Flow, turbulence and combustion}, volume = {99}, number = {3}, pages = {909-931}, pmid = {30069161}, issn = {1573-1987}, abstract = {This work investigates fully developed turbulent flows of carbon-dioxide close to its vapour-liquid critical point in a channel with a hot and a cold wall. Two direct numerical simulations are performed at low Mach numbers, with the trans-critical transition near the channel centre and the cold wall, respectively. An additional simulation with constant transport properties is used to selectively investigate the effect of the non-linear equation of state on turbulence. Compared to the case where the pseudo-critical transition occurs in the channel center, the case with the pseudo-critical transition close to the cold wall reveals that compressibility effects can exist in the near-wall region even at low Mach numbers. An analysis of the velocity streaks near the hot and the cold walls also indicates a greater degree of streak coherence near the cold wall. A comparison between the constant and variable viscosity cases at the same Reynolds number, Mach number and having the same isothermal wall boundary conditions reveals that variable viscosity increases turbulence near the cold wall and also causes higher velocity gradients near the hot wall. We also show that the extended van Driest transformation results in a better agreement of the velocity profile with the log-law of the wall compared to the standard van Driest transformation. The semi-locally scaled turbulent velocity fluctuations and the turbulent kinetic energy budgets on the hot and the cold sides of the channel collapse on top of each other, thereby establishing the validity of Morkovin's hypothesis.}, }
@article {pmid30069158, year = {2017}, author = {Sanmiguel Vila, C and Örlü, R and Vinuesa, R and Schlatter, P and Ianiro, A and Discetti, S}, title = {Adverse-Pressure-Gradient Effects on Turbulent Boundary Layers: Statistics and Flow-Field Organization.}, journal = {Flow, turbulence and combustion}, volume = {99}, number = {3}, pages = {589-612}, pmid = {30069158}, issn = {1573-1987}, abstract = {This manuscripts presents a study on adverse-pressure-gradient turbulent boundary layers under different Reynolds-number and pressure-gradient conditions. In this work we performed Particle Image Velocimetry (PIV) measurements supplemented with Large-Eddy Simulations in order to have a dataset covering a range of displacement-thickness-based Reynolds-number 2300 <Reδ∗< 34000 and values of the Clauser pressure-gradient parameter β up to 2.4. The spatial resolution limits of PIV for the estimation of turbulence statistics have been overcome via ensemble-based approaches. A comparison between ensemble-correlation and ensemble Particle Tracking Velocimetry was carried out to assess the uncertainty of the two methods. The effects of β, Re and of the pressure-gradient history on turbulence statistics were assessed. A modal analysis via Proper Orthogonal Decomposition was carried out on the flow fields and showed that about 20% of the energy contribution corresponds to the first mode, while 40% of the turbulent kinetic energy corresponds to the first four modes with no appreciable dependence on β and Re within the investigated range. The topology of the spatial modes shows a dependence on the Reynolds number and on the pressure-gradient strength, in line with the results obtained from the analysis of the turbulence statistics. The contribution of the modes to the Reynolds stresses and the turbulence production was assessed using a truncated low-order reconstruction with progressively larger number of modes. It is shown that the outer peaks in the Reynolds-stress profiles are mostly due to large-scale structures in the outer part of the boundary layer.}, }
@article {pmid29606844, year = {2017}, author = {Kedzierski, MA}, title = {A Fluorescence Based Measurement Technique to Quantify Water Contaminants at Pipe Surfaces During Flow.}, journal = {International journal of transport phenomena}, volume = {14}, number = {4}, pages = {283-296}, pmid = {29606844}, issn = {1028-6578}, support = {9999-NIST//Intramural NIST DOC/United States ; }, abstract = {This paper provides a detailed account of the development of a fluorescence based measurement technique for measuring the mass of contaminant on solid surfaces in the presence of water flow. A test apparatus was designed and developed for the purpose of studying adsorption and desorption of diesel to and from a copper test surface in the presence of contaminated and fresh water flow, respectively. A calibration technique was developed to correlate the measured fluorescence intensity to the mass of diesel adsorbed per unit surface area (the excess surface density) and the bulk concentration of the diesel in the flow. Both bulk composition and the excess surface density measurements were achieved via a traverse of the fluorescent measurement probe perpendicular to the test surface. The measured diesel excess surface density varied between zero and 0.02 kg/m[2] for the variation in the bulk mass fraction and Reynolds number of the flow.}, }
@article {pmid28019677, year = {2017}, author = {Zhang, QY}, title = {Chirality-specific lift forces of helix under shear flows: Helix perpendicular to shear plane.}, journal = {Chirality}, volume = {29}, number = {2}, pages = {97-102}, doi = {10.1002/chir.22675}, pmid = {28019677}, issn = {1520-636X}, abstract = {Chiral objects in shear flow experience a chirality-specific lift force. Shear flows past helices in a low Reynolds number regime were studied using slender-body theory. The chirality-specific lift forces in the vorticity direction experienced by helices are dominated by a set of helix geometry parameters: helix radius, pitch length, number of turns, and helix phase angle. Its analytical formula is given. The chirality-specific forces are the physical reasons for the chiral separation of helices in shear flow. Our results are well supported by the latest experimental observations.}, }
@article {pmid28009203, year = {2016}, author = {Kwon, WJ and Kim, JH and Seo, SW and Shin, Y}, title = {Observation of von Kármán Vortex Street in an Atomic Superfluid Gas.}, journal = {Physical review letters}, volume = {117}, number = {24}, pages = {245301}, doi = {10.1103/PhysRevLett.117.245301}, pmid = {28009203}, issn = {1079-7114}, abstract = {We report on the experimental observation of vortex cluster shedding from a moving obstacle in an oblate atomic Bose-Einstein condensate. At low obstacle velocities v above a critical value, vortex clusters consisting of two like-sign vortices are generated to form a regular configuration like a von Kármán street, and as v is increased, the shedding pattern becomes irregular with many different kinds of vortex clusters. In particular, we observe that the Stouhal number associated with the shedding frequency exhibits saturation behavior with increasing v. The regular-to-turbulent transition of the vortex cluster shedding reveals remarkable similarities between a superfluid and a classical viscous fluid. Our work opens a new direction for experimental investigations of the superfluid Reynolds number characterizing universal superfluid hydrodynamics.}, }
@article {pmid28005133, year = {2017}, author = {Low, KW and Van Loon, R and Rolland, SA and Sienz, J}, title = {Formulation of Generalized Mass Transfer Correlations for Blood Oxygenator Design.}, journal = {Journal of biomechanical engineering}, volume = {139}, number = {3}, pages = {}, doi = {10.1115/1.4035535}, pmid = {28005133}, issn = {1528-8951}, mesh = {Blood Circulation ; Carbon Dioxide/blood/metabolism ; Equipment Design ; Models, Cardiovascular ; Oxygen/*blood/*metabolism ; *Oxygenators ; Porosity ; }, abstract = {This paper numerically investigates non-Newtonian blood flow with oxygen and carbon dioxide transport across and along an array of uniformly square and staggered arranged fibers at various porosity (ε) levels, focussing on a low Reynolds number regime (Re < 10). The objective is to establish suitable mass transfer correlations, expressed in the form of Sherwood number (Sh = f(ε, Re, Sc)), that identifies the link from local mass transfer investigations to full-device analyses. The development of a concentration field is initially investigated and expressions are established covering the range from a typical deoxygenated condition up to a full oxygenated condition. An important step is identified where a cut-off point in those expressions is required to avoid any under- or over-estimation on the Sherwood number. Geometrical features of a typical commercial blood oxygenator is adopted and results in general show that a balance in pressure drop, shear stress, and mass transfer is required to avoid potential blood trauma or clotting formation. Different definitions of mass transfer correlations are found for oxygen/carbon dioxide, parallel/transverse flow, and square/staggered configurations, respectively. From this set of correlations, it is found that transverse flow has better gas transfer than parallel flow which is consistent with reported literature. The mass transfer dependency on fiber configuration is observed to be pronounced at low porosity. This approach provides an initial platform when one is looking to improve the mass transfer performance in a blood oxygenator without the need to conduct any numerical simulations or experiments.}, }
@article {pmid27982633, year = {2016}, author = {Puljiz, M and Huang, S and Auernhammer, GK and Menzel, AM}, title = {Forces on Rigid Inclusions in Elastic Media and Resulting Matrix-Mediated Interactions.}, journal = {Physical review letters}, volume = {117}, number = {23}, pages = {238003}, doi = {10.1103/PhysRevLett.117.238003}, pmid = {27982633}, issn = {1079-7114}, abstract = {To describe many-particle systems suspended in incompressible low-Reynolds-number fluids, effective hydrodynamic interactions can be introduced. Here, we consider particles embedded in elastic media. The effective elastic interactions between spherical particles are calculated analytically, inspired by the approach in the fluid case. Our experiments on interacting magnetic particles confirm the theory. In view of the huge success of the method in hydrodynamics, we similarly expect many future applications in the elastic case, e.g., for elastic composite materials.}, }
@article {pmid27967192, year = {2016}, author = {Goto, S and Vassilicos, JC}, title = {Unsteady turbulence cascades.}, journal = {Physical review. E}, volume = {94}, number = {5-1}, pages = {053108}, doi = {10.1103/PhysRevE.94.053108}, pmid = {27967192}, issn = {2470-0053}, abstract = {We have run a total of 311 direct numerical simulations (DNSs) of decaying three-dimensional Navier-Stokes turbulence in a periodic box with values of the Taylor length-based Reynolds number up to about 300 and an energy spectrum with a wide wave-number range of close to -5/3 power-law dependence at the higher Reynolds numbers. On the basis of these runs, we have found a critical time when (i) the rate of change of the square of the integral length scale turns from increasing to decreasing, (ii) the ratio of interscale energy flux to high-pass filtered turbulence dissipation changes from decreasing to very slowly increasing in the inertial range, (iii) the signature of large-scale coherent structures disappears in the energy spectrum, and (iv) the scaling of the turbulence dissipation changes from the one recently discovered in DNSs of forced unsteady turbulence and in wind tunnel experiments of turbulent wakes and grid-generated turbulence to the classical scaling proposed by G. I. Taylor [Proc. R. Soc. London, Ser. A 151, 421 (1935)1364-502110.1098/rspa.1935.0158] and A. N. Kolmogorov [Dokl. Akad. Nauk SSSR 31, 538 (1941)]. Even though the customary theoretical basis for this Taylor-Kolmogorov scaling is a statistically stationary cascade where large-scale energy flux balances dissipation, this is not the case throughout the entire time range of integration in all our DNS runs. The recently discovered dissipation scaling can be reformulated physically as a situation in which the dissipation rates of the small and large scales evolve together. We advance two hypotheses that may form the basis of a theoretical approach to unsteady turbulence cascades in the presence of large-scale coherent structures.}, }
@article {pmid27967180, year = {2016}, author = {Zhang, J and Yao, Z and Hao, P}, title = {Drag reductions and the air-water interface stability of superhydrophobic surfaces in rectangular channel flow.}, journal = {Physical review. E}, volume = {94}, number = {5-1}, pages = {053117}, doi = {10.1103/PhysRevE.94.053117}, pmid = {27967180}, issn = {2470-0053}, abstract = {Flow in a rectangular channel with superhydrophobic (SH) top and bottom walls was investigated experimentally. Different SH surfaces, including hierarchical structured surfaces and surfaces with different micropost sizes (width and spacing) but the same solid fraction, were fabricated and measured. Pressure loss and flow rate in the channel with SH top and bottom walls were measured, with Reynolds number changing from 700 to 4700, and the corresponding friction factor for the SH surface was calculated. The statuses of the air plastron on different SH surfaces were observed during the experiment. In our experiment, compared with the experiment for the smooth surface, drag reductions were observed for all SH surfaces, with the largest drag reduction of 42.2%. It was found that the hierarchy of the microstructure can increase the drag reduction by decreasing the solid fraction and enhancing the stability of the air-water interface. With a fixed solid fraction, the drag reduction decreases as the post size (width and spacing) increases, due to the increasing curvature and instability effects of the air-water interface. A correlation parameter between the contact angle hysteresis, the air-water interface stability, and the drag reduction of the SH surfaces was found.}, }
@article {pmid27967140, year = {2016}, author = {Lycett-Brown, D and Luo, KH}, title = {Cascaded lattice Boltzmann method with improved forcing scheme for large-density-ratio multiphase flow at high Reynolds and Weber numbers.}, journal = {Physical review. E}, volume = {94}, number = {5-1}, pages = {053313}, doi = {10.1103/PhysRevE.94.053313}, pmid = {27967140}, issn = {2470-0053}, abstract = {A recently developed forcing scheme has allowed the pseudopotential multiphase lattice Boltzmann method to correctly reproduce coexistence curves, while expanding its range to lower surface tensions and arbitrarily high density ratios [Lycett-Brown and Luo, Phys. Rev. E 91, 023305 (2015)PLEEE81539-375510.1103/PhysRevE.91.023305]. Here, a third-order Chapman-Enskog analysis is used to extend this result from the single-relaxation-time collision operator, to a multiple-relaxation-time cascaded collision operator, whose additional relaxation rates allow a significant increase in stability. Numerical results confirm that the proposed scheme enables almost independent control of density ratio, surface tension, interface width, viscosity, and the additional relaxation rates of the cascaded collision operator. This allows simulation of large density ratio flows at simultaneously high Reynolds and Weber numbers, which is demonstrated through binary collisions of water droplets in air (with density ratio up to 1000, Reynolds number 6200 and Weber number 440). This model represents a significant improvement in multiphase flow simulation by the pseudopotential lattice Boltzmann method in which real-world parameters are finally achievable.}, }
@article {pmid27967048, year = {2016}, author = {Li, G and Ostace, A and Ardekani, AM}, title = {Hydrodynamic interaction of swimming organisms in an inertial regime.}, journal = {Physical review. E}, volume = {94}, number = {5-1}, pages = {053104}, doi = {10.1103/PhysRevE.94.053104}, pmid = {27967048}, issn = {2470-0053}, mesh = {Animals ; Aquatic Organisms/*physiology ; *Hydrodynamics ; *Models, Biological ; *Swimming ; }, abstract = {We numerically investigate the hydrodynamic interaction of swimming organisms at small to intermediate Reynolds number regimes, i.e., Re∼O(0.1-100), where inertial effects are important. The hydrodynamic interaction of swimming organisms in this regime is significantly different from the Stokes regime for microorganisms, as well as the high Reynolds number flows for fish and birds, which involves strong flow separation and detached vortex structures. Using an archetypal swimmer model, called a "squirmer," we find that the inertial effects change the contact time and dispersion dynamics of a pair of pusher swimmers, and trigger hydrodynamic attraction for two pullers. These results are potentially important in investigating predator-prey interactions, sexual reproduction, and the encounter rate of marine organisms such as copepods, ctenophora, and larvae.}, }
@article {pmid27967034, year = {2016}, author = {Piretto, E and Musacchio, S and De Lillo, F and Boffetta, G}, title = {Irreversibility of the two-dimensional enstrophy cascade.}, journal = {Physical review. E}, volume = {94}, number = {5-1}, pages = {053116}, doi = {10.1103/PhysRevE.94.053116}, pmid = {27967034}, issn = {2470-0053}, abstract = {We study the time irreversibility of the direct cascade in two-dimensional turbulence by looking at the time derivative of the square vorticity along Lagrangian trajectories, a quantity called metenstrophy. By means of extensive direct numerical simulations we measure the time irreversibility from the asymmetry of the probability density function of the metenstrophy and we find that it increases with the Reynolds number of the cascade, similarly to what is found in three-dimensional turbulence. A detailed analysis of the different contributions to the enstrophy budget reveals a remarkable difference with respect to what is observed for the energy cascade, in particular the role of the statistics of the forcing to determine the degree of irreversibility.}, }
@article {pmid27966980, year = {2017}, author = {Zhao, B and Wang, X and Zhang, K and Chen, L and Deng, X}, title = {Impact of Viscous Droplets on Superamphiphobic Surfaces.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {33}, number = {1}, pages = {144-151}, doi = {10.1021/acs.langmuir.6b03862}, pmid = {27966980}, issn = {1520-5827}, abstract = {The impact of a liquid droplet on a solid surface is one of the most common phenomena in nature and frequently encountered in numerous technological processes. Despite the significant progress on understanding the droplet impact phenomenon over the past century, the impact dynamics, especially the coupling effects between the properties of a liquid and surface wettability on the impact process, is still poorly understood. In this work, we experimentally investigated the impact of viscous droplets on superamphiphobic surfaces, with the viscosity of liquids ranging from 0.89 to 150 mPa s. We showed that an increase in liquid viscosity will slow down the impact process and cause bouncing droplets to rebound lower and fewer times. The critical impact velocity, above which droplets can rebound from the superamphiphobic surface, was found to linearly increase with the liquid viscosity. We also showed that the maximum spreading factor increases with Weber number or Reynolds number but decreases with the liquid viscosity. Scaling analyses based on energy conservation were carried out to explain these findings, and they were found to be in good agreement with our experimental results.}, }
@article {pmid27918493, year = {2016}, author = {Goodman, KZ and Lipford, WE and Watkins, AN}, title = {Boundary-Layer Detection at Cryogenic Conditions Using Temperature Sensitive Paint Coupled with a Carbon Nanotube Heating Layer.}, journal = {Sensors (Basel, Switzerland)}, volume = {16}, number = {12}, pages = {}, pmid = {27918493}, issn = {1424-8220}, abstract = {Detection of flow transition on aircraft surfaces and models can be vital to the development of future vehicles and computational methods for evaluating vehicle concepts. In testing at ambient conditions, IR thermography is ideal for this measurement. However, for higher Reynolds number testing, cryogenic facilities are often used, in which IR thermography is difficult to employ. In these facilities, temperature sensitive paint is an alternative with a temperature step introduced to enhance the natural temperature change from transition. Traditional methods for inducing the temperature step by changing the liquid nitrogen injection rate often change the tunnel conditions. Recent work has shown that adding a layer consisting of carbon nanotubes to the surface can be used to impart a temperature step on the model surface with little change in the operating conditions. Unfortunately, this system physically degraded at 130 K and lost heating capability. This paper describes a modification of this technique enabling operation down to at least 77 K, well below the temperature reached in cryogenic facilities. This is possible because the CNT layer is in a polyurethane binder. This was tested on a Natural Laminar Flow model in a cryogenic facility and transition detection was successfully visualized at conditions from 200 K to 110 K. Results were also compared with the traditional temperature step method.}, }
@article {pmid27913147, year = {2017}, author = {Tripathi, D and Yadav, A and Bég, OA}, title = {Electro-kinetically driven peristaltic transport of viscoelastic physiological fluids through a finite length capillary: Mathematical modeling.}, journal = {Mathematical biosciences}, volume = {283}, number = {}, pages = {155-168}, doi = {10.1016/j.mbs.2016.11.017}, pmid = {27913147}, issn = {1879-3134}, mesh = {Capillaries/*physiology ; *Electroosmosis ; Kinetics ; *Models, Theoretical ; }, abstract = {Analytical solutions are developed for the electro-kinetic flow of a viscoelastic biological liquid in a finite length cylindrical capillary geometry under peristaltic waves. The Jefferys' non-Newtonian constitutive model is employed to characterize rheological properties of the fluid. The unsteady conservation equations for mass and momentum with electro-kinetic and Darcian porous medium drag force terms are reduced to a system of steady linearized conservation equations in an axisymmetric coordinate system. The long wavelength, creeping (low Reynolds number) and Debye-Hückel linearization approximations are utilized. The resulting boundary value problem is shown to be controlled by a number of parameters including the electro-osmotic parameter, Helmholtz-Smoluchowski velocity (maximum electro-osmotic velocity), and Jefferys' first parameter (ratio of relaxation and retardation time), wave amplitude. The influence of these parameters and also time on axial velocity, pressure difference, maximum volumetric flow rate and streamline distributions (for elucidating trapping phenomena) is visualized graphically and interpreted in detail. Pressure difference magnitudes are enhanced consistently with both increasing electro-osmotic parameter and Helmholtz-Smoluchowski velocity, whereas they are only elevated with increasing Jefferys' first parameter for positive volumetric flow rates. Maximum time averaged flow rate is enhanced with increasing electro-osmotic parameter, Helmholtz-Smoluchowski velocity and Jefferys' first parameter. Axial flow is accelerated in the core (plug) region of the conduit with greater values of electro-osmotic parameter and Helmholtz-Smoluchowski velocity whereas it is significantly decelerated with increasing Jefferys' first parameter. The simulations find applications in electro-osmotic (EO) transport processes in capillary physiology and also bio-inspired EO pump devices in chemical and aerospace engineering.}, }
@article {pmid27903629, year = {2016}, author = {Jones, SK and Yun, YJ and Hedrick, TL and Griffith, BE and Miller, LA}, title = {Bristles reduce the force required to 'fling' wings apart in the smallest insects.}, journal = {The Journal of experimental biology}, volume = {219}, number = {Pt 23}, pages = {3759-3772}, doi = {10.1242/jeb.143362}, pmid = {27903629}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena/*physiology ; Flight, Animal/*physiology ; Hydrodynamics ; Hymenoptera/*anatomy &amp; histology/*physiology ; Models, Biological ; Wings, Animal/*anatomy &amp; histology ; }, abstract = {The smallest flying insects commonly possess wings with long bristles. Little quantitative information is available on the morphology of these bristles, and their functional importance remains a mystery. In this study, we (1) collected morphological data on the bristles of 23 species of Mymaridae by analyzing high-resolution photographs and (2) used the immersed boundary method to determine via numerical simulation whether bristled wings reduced the force required to fling the wings apart while still maintaining lift. The effects of Reynolds number, angle of attack, bristle spacing and wing-wing interactions were investigated. In the morphological study, we found that as the body length of Mymaridae decreases, the diameter and gap between bristles decreases and the percentage of the wing area covered by bristles increases. In the numerical study, we found that a bristled wing experiences less force than a solid wing. The decrease in force with increasing gap to diameter ratio is greater at higher angles of attack than at lower angles of attack, suggesting that bristled wings may act more like solid wings at lower angles of attack than they do at higher angles of attack. In wing-wing interactions, bristled wings significantly decrease the drag required to fling two wings apart compared with solid wings, especially at lower Reynolds numbers. These results support the idea that bristles may offer an aerodynamic benefit during clap and fling in tiny insects.}, }
@article {pmid30404389, year = {2016}, author = {Zhou, T and Wang, H and Shi, L and Liu, Z and Joo, SW}, title = {An Enhanced Electroosmotic Micromixer with an Efficient Asymmetric Lateral Structure.}, journal = {Micromachines}, volume = {7}, number = {12}, pages = {}, pmid = {30404389}, issn = {2072-666X}, abstract = {Homogeneous and rapid mixing in microfluidic devices is difficult to accomplish, owing to the low Reynolds number associated with most flows in microfluidic channels. Here, an efficient electroosmotic micromixer based on a carefully designed lateral structure is demonstrated. The electroosmotic flow in this mixer with an asymmetrical structure induces enhanced disturbance in the micro channel, helping the fluid streams' folding and stretching, thereby enabling appreciable mixing. Quantitative analysis of the mixing efficiency with respect to the potential applied and the flow rate suggests that the electroosmotic microfluidic mixer developed in the present work can achieve efficient mixing with low applied potential.}, }
@article {pmid27887729, year = {2017}, author = {Bark, DL and Johnson, B and Garrity, D and Dasi, LP}, title = {Valveless pumping mechanics of the embryonic heart during cardiac looping: Pressure and flow through micro-PIV.}, journal = {Journal of biomechanics}, volume = {50}, number = {}, pages = {50-55}, doi = {10.1016/j.jbiomech.2016.11.036}, pmid = {27887729}, issn = {1873-2380}, mesh = {Animals ; Atrial Pressure ; Embryo, Nonmammalian ; Embryonic Development/*physiology ; Heart/*embryology/*physiology ; Hemodynamics ; Rheology ; Systole ; Ventricular Pressure ; Viscosity ; Zebrafish ; }, abstract = {Cardiovascular development is influenced by the flow-induced stress environment originating from cardiac biomechanics. To characterize the stress environment, it is necessary to quantify flow and pressure. Here, we quantify the flow field in a developing zebrafish heart during the looping stage through micro-particle imaging velocimetry and by analyzing spatiotemporal plots. We further build upon previous methods to noninvasively quantify the pressure field at a low Reynolds number using flow field data for the first time, while also comparing the impact of viscosity models. Through this method, we show that the atrium builds up pressure to ~0.25mmHg relative to the ventricle during atrial systole and that atrial expansion creates a pressure difference of ~0.15mmHg across the atrium, resulting in efficient cardiac pumping. With these techniques, it is possible to noninvasively fully characterize hemodynamics during heart development.}, }
@article {pmid27886501, year = {2016}, author = {Cameron, A and Alexakis, A}, title = {Fate of Alpha Dynamos at Large Rm.}, journal = {Physical review letters}, volume = {117}, number = {20}, pages = {205101}, doi = {10.1103/PhysRevLett.117.205101}, pmid = {27886501}, issn = {1079-7114}, abstract = {At the heart of today's solar magnetic field evolution models lies the alpha dynamo description. In this work, we investigate the fate of alpha dynamos as the magnetic Reynolds number Rm is increased. Using Floquet theory, we are able to precisely quantify mean-field effects like the alpha and beta effect (i) by rigorously distinguishing dynamo modes that involve large-scale components from the ones that only involve small scales, and by (ii) providing a way to investigate arbitrary large-scale separations with minimal computational cost. We apply this framework to helical and nonhelical flows as well as to random flows with short correlation time. Our results determine that the alpha description is valid for Rm smaller than a critical value Rm_{c} at which small-scale dynamo instability starts. When Rm is above Rm_{c}, the dynamo ceases to follow the mean-field description and the growth rate of the large-scale modes becomes independent of the scale separation, while the energy in the large-scale modes is inversely proportional to the square of the scale separation. The results in this second regime do not depend on the presence of helicity. Thus, alpha-type modeling for solar and stellar models needs to be reevaluated and new directions for mean-field modeling are proposed.}, }
@article {pmid27886051, year = {2016}, author = {Habhab, MB and Ismail, T and Lo, JF}, title = {A Laminar Flow-Based Microfluidic Tesla Pump via Lithography Enabled 3D Printing.}, journal = {Sensors (Basel, Switzerland)}, volume = {16}, number = {11}, pages = {}, pmid = {27886051}, issn = {1424-8220}, abstract = {Tesla turbine and its applications in power generation and fluid flow were demonstrated by Nicholas Tesla in 1913. However, its real-world implementations were limited by the difficulty to maintain laminar flow between rotor disks, transient efficiencies during rotor acceleration, and the lack of other applications that fully utilize the continuous flow outputs. All of the aforementioned limits of Tesla turbines can be addressed by scaling to the microfluidic flow regime. Demonstrated here is a microscale Tesla pump designed and fabricated using a Digital Light Processing (DLP) based 3D printer with 43 µm lateral and 30 µm thickness resolutions. The miniaturized pump is characterized by low Reynolds number of 1000 and a flow rate of up to 12.6 mL/min at 1200 rpm, unloaded. It is capable of driving a mixer network to generate microfluidic gradient. The continuous, laminar flow from Tesla turbines is well-suited to the needs of flow-sensitive microfluidics, where the integrated pump will enable numerous compact lab-on-a-chip applications.}, }
@article {pmid27865773, year = {2017}, author = {Abdelsalam, SI and Vafai, K}, title = {Particulate suspension effect on peristaltically induced unsteady pulsatile flow in a narrow artery: Blood flow model.}, journal = {Mathematical biosciences}, volume = {283}, number = {}, pages = {91-105}, doi = {10.1016/j.mbs.2016.11.012}, pmid = {27865773}, issn = {1879-3134}, mesh = {Arteries/*physiology ; *Models, Cardiovascular ; Pulsatile Flow/*physiology ; }, abstract = {This work is concerned with theoretically investigating the pulsatile flow of a fluid with suspended particles in a flow driven by peristaltic waves that deform the wall of a small blood artery in the shape of traveling sinusoidal waves with constant velocity. The problem formulation in the wave frame of reference is presented and the governing equations are developed up to the second-order in terms of the asymptotic expansion of Womersley number which characterizes the unsteady effect in the wave frame. We suppose that the flow rate imposed, in this frame, is a function versus time. The analytical solution of the problem is achieved using the long wavelength approximation where Reynolds number is considered small with reference to the blood flow in the circulatory system. The present study inspects novelties brought about into the classic peristaltic mechanism by the inclusion of Womersley number, and the critical values of concentration and occlusion on the flow characteristics in a small artery with flexible walls. Momentum and mass equations for the fluid and particle phases are solved by means of a perturbation analysis in which the occlusion is a small parameter. Closed form solutions are obtained for the fluid/particle velocity distributions, stream function, pressure rise, friction force, wall shear stress, instantaneous mechanical efficiency, and time-averaged mechanical efficiency. The physical explanation of the Segré-Silberberg effect is introduced and the trapping phenomenon of plasma for haemodilution and haemoconcentration cases is discussed. It has been deduced that the width of the closed plasma streamlines is increased while their number is minimally reduced in case of haemoconcentration. This mathematical problem has numerous applications in various branches in science including blood flow in small blood vessels. Several results of other models can be deduced as limiting cases of our situation.}, }
@article {pmid27859372, year = {2017}, author = {Lopes, G and Bock, E and Gómez, L}, title = {Numerical Analyses for Low Reynolds Flow in a Ventricular Assist Device.}, journal = {Artificial organs}, volume = {41}, number = {6}, pages = {E30-E40}, doi = {10.1111/aor.12776}, pmid = {27859372}, issn = {1525-1594}, mesh = {Computer Simulation ; Equipment Design ; *Heart-Assist Devices ; Hemorheology ; Humans ; Hydrodynamics ; Models, Cardiovascular ; }, abstract = {Scientific and technological advances in blood pump developments have been driven by their importance in cardiac patient treatments and in the expansion of life quality in assisted people. To improve and optimize the design and development, numerical tools were incorporated into the analyses of these mechanisms and have become indispensable in their advances. This study analyzes the flow behavior with low impeller Reynolds number, for which there is no consensus on the full development of turbulence in ventricular assist devices (VAD). For supporting analyses, computational numerical simulations were carried out in different scenarios with the same rotation speed. Two modeling approaches were applied: laminar flow and turbulent flow with the standard, RNG and realizable κ - ε; the standard and SST κ - ω models; and Spalart-Allmaras models. The results agree with the literature for VAD and the range for transient flows in stirred tanks with an impeller Reynolds number around 2800 for the tested scenarios. The turbulent models were compared, and it is suggested, based on the expected physical behavior, the use of κ-ε RNG, standard and SST κ-ω, and Spalart-Allmaras models to numerical analyses for low impeller Reynolds numbers according to the tested flow scenarios.}, }
@article {pmid27855986, year = {2017}, author = {De Paolis, A and Watanabe, H and Nelson, JT and Bikson, M and Packer, M and Cardoso, L}, title = {Human cochlear hydrodynamics: A high-resolution μCT-based finite element study.}, journal = {Journal of biomechanics}, volume = {50}, number = {}, pages = {209-216}, pmid = {27855986}, issn = {1873-2380}, support = {SC1 DK103362/DK/NIDDK NIH HHS/United States ; SC2 AG034198/AG/NIA NIH HHS/United States ; }, mesh = {Contrast Media ; Ear/diagnostic imaging/*physiology ; Female ; Finite Element Analysis ; Humans ; Hydrodynamics ; Middle Aged ; Perilymph/diagnostic imaging/physiology ; X-Ray Microtomography ; }, abstract = {Measurements of perilymph hydrodynamics in the human cochlea are scarce, being mostly limited to the fluid pressure at the basal or apical turn of the scalae vestibuli and tympani. Indeed, measurements of fluid pressure or volumetric flow rate have only been reported in animal models. In this study we imaged the human ear at 6.7 and 3-µm resolution using µCT scanning to produce highly accurate 3D models of the entire ear and particularly the cochlea scalae. We used a contrast agent to better distinguish soft from hard tissues, including the auditory canal, tympanic membrane, malleus, incus, stapes, ligaments, oval and round window, scalae vestibule and tympani. Using a Computational Fluid Dynamics (CFD) approach and this anatomically correct 3D model of the human cochlea, we examined the pressure and perilymph flow velocity as a function of location, time and frequency within the auditory range. Perimeter, surface, hydraulic diameter, Womersley and Reynolds numbers were computed every 45° of rotation around the central axis of the cochlear spiral. CFD results showed both spatial and temporal pressure gradients along the cochlea. Small Reynolds number and large Womersley values indicate that the perilymph fluid flow at auditory frequencies is laminar and its velocity profile is plug-like. The pressure was found 102-106° out of phase with the fluid flow velocity at the scalae vestibule and tympani, respectively. The average flow velocity was found in the sub-µm/s to nm/s range at 20-100Hz, and below the nm/s range at 1-20kHz.}, }
@article {pmid27841571, year = {2016}, author = {Wang, P and Wang, LP and Guo, Z}, title = {Comparison of the lattice Boltzmann equation and discrete unified gas-kinetic scheme methods for direct numerical simulation of decaying turbulent flows.}, journal = {Physical review. E}, volume = {94}, number = {4-1}, pages = {043304}, doi = {10.1103/PhysRevE.94.043304}, pmid = {27841571}, issn = {2470-0053}, abstract = {The main objective of this work is to perform a detailed comparison of the lattice Boltzmann equation (LBE) and the recently developed discrete unified gas-kinetic scheme (DUGKS) methods for direct numerical simulation (DNS) of the decaying homogeneous isotropic turbulence and the Kida vortex flow in a periodic box. The flow fields and key statistical quantities computed by both methods are compared with those from the pseudospectral method at both low and moderate Reynolds numbers. The results show that the LBE is more accurate and efficient than the DUGKS, but the latter has a superior numerical stability, particularly for high Reynolds number flows. In addition, we conclude that the DUGKS can adequately resolve the flow when the minimum spatial resolution parameter k_{max}η>3, where k_{max} is the maximum resolved wave number and η is the flow Kolmogorov length. This resolution requirement can be contrasted with the requirements of k_{max}η>1 for the pseudospectral method and k_{max}η>2 for the LBE. It should be emphasized that although more validations should be conducted before the DUGKS can be called a viable tool for DNS of turbulent flows, the present work contributes to the overall assessment of the DUGKS, and it provides a basis for further applications of DUGKS in studying the physics of turbulent flows.}, }
@article {pmid27841548, year = {2016}, author = {Bhattacharya, A and Kesarkar, T}, title = {Numerical simulation of particulate flows using a hybrid of finite difference and boundary integral methods.}, journal = {Physical review. E}, volume = {94}, number = {4-1}, pages = {043309}, doi = {10.1103/PhysRevE.94.043309}, pmid = {27841548}, issn = {2470-0053}, abstract = {A combination of finite difference (FD) and boundary integral (BI) methods is used to formulate an efficient solver for simulating unsteady Stokes flow around particles. The two-dimensional (2D) unsteady Stokes equation is being solved on a Cartesian grid using a second order FD method, while the 2D steady Stokes equation is being solved near the particle using BI method. The two methods are coupled within the viscous boundary layer, a few FD grid cells away from the particle, where solutions from both FD and BI methods are valid. We demonstrate that this hybrid method can be used to accurately solve for the flow around particles with irregular shapes, even though radius of curvature of the particle surface is not resolved by the FD grid. For dilute particle concentrations, we construct a virtual envelope around each particle and solve the BI problem for the flow field located between the envelope and the particle. The BI solver provides velocity boundary condition to the FD solver at "boundary" nodes located on the FD grid, adjacent to the particles, while the FD solver provides the velocity boundary condition to the BI solver at points located on the envelope. The coupling between FD method and BI method is implicit at every time step. This method allows us to formulate an O(N) scheme for dilute suspensions, where N is the number of particles. For semidilute suspensions, where particles may cluster, an envelope formation method has been formulated and implemented, which enables solving the BI problem for each individual particle cluster, allowing efficient simulation of hydrodynamic interaction between particles even when they are in close proximity. The method has been validated against analytical results for flow around a periodic array of cylinders and for Jeffrey orbit of a moving ellipse in shear flow. Simulation of multiple force-free irregular shaped particles in the presence of shear in a 2D slit flow has been conducted to demonstrate the robustness of the FD-BI scheme. This method can also be used to solve the full Navier-Stokes equations around particles. In this case, it is shown that, below a threshold particle Reynolds number, which in turn depends on the required resolution of the particle surface, the FD-BI scheme will be more computationally efficient than a pure FD scheme solved on a multiblock grid.}, }
@article {pmid27841514, year = {2016}, author = {Kogan, E}, title = {Lift force due to odd Hall viscosity.}, journal = {Physical review. E}, volume = {94}, number = {4-1}, pages = {043111}, doi = {10.1103/PhysRevE.94.043111}, pmid = {27841514}, issn = {2470-0053}, abstract = {We study the problem of flow of a neutral gas past an infinite cylinder at right angle to its axis at low Reynolds number when the fluid is characterized by broken time-reversal invariance, and hence by odd viscosity in addition to the normal even one. We solve the Oseen approximation to Navier-Stokes equation and calculate the lift force which appears due to the odd viscosity.}, }
@article {pmid27841488, year = {2016}, author = {Suresha, S and Sujith, RI and Emerson, B and Lieuwen, T}, title = {Nonlinear dynamics and intermittency in a turbulent reacting wake with density ratio as bifurcation parameter.}, journal = {Physical review. E}, volume = {94}, number = {4-1}, pages = {042206}, doi = {10.1103/PhysRevE.94.042206}, pmid = {27841488}, issn = {2470-0053}, abstract = {The flame or flow behavior of a turbulent reacting wake is known to be fundamentally different at high and low values of flame density ratio (ρ_{u}/ρ_{b}), as the flow transitions from globally stable to unstable. This paper analyzes the nonlinear dynamics present in a bluff-body stabilized flame, and identifies the transition characteristics in the wake as ρ_{u}/ρ_{b} is varied over a Reynolds number (based on the bluff-body lip velocity) range of 1000-3300. Recurrence quantification analysis (RQA) of the experimentally obtained time series of the flame edge fluctuations reveals that the time series is highly aperiodic at high values of ρ_{u}/ρ_{b} and transitions to increasingly correlated or nearly periodic behavior at low values. From the RQA of the transverse velocity time series, we observe that periodicity in the flame oscillations are related to periodicity in the flow. Therefore, we hypothesize that this transition from aperiodic to nearly periodic behavior in the flame edge time series is a manifestation of the transition in the flow from globally stable, convective instability to global instability as ρ_{u}/ρ_{b} decreases. The recurrence analysis further reveals that the transition in periodicity is not a sudden shift; rather it occurs through an intermittent regime present at low and intermediate ρ_{u}/ρ_{b}. During intermittency, the flow behavior switches between aperiodic oscillations, reminiscent of a globally stable, convective instability, and periodic oscillations, reminiscent of a global instability. Analysis of the distribution of the lengths of the periodic regions in the intermittent time series and the first return map indicate the presence of type-II intermittency.}, }
@article {pmid27841461, year = {2016}, author = {Leclercq, C and Nguyen, F and Kerswell, RR}, title = {Connections between centrifugal, stratorotational, and radiative instabilities in viscous Taylor-Couette flow.}, journal = {Physical review. E}, volume = {94}, number = {4-1}, pages = {043103}, doi = {10.1103/PhysRevE.94.043103}, pmid = {27841461}, issn = {2470-0053}, abstract = {The "Rayleigh line" μ=η^{2}, where μ=Ω_{o}/Ω_{i} and η=r_{i}/r_{o} are respectively the rotation and radius ratios between inner (subscript i) and outer (subscript o) cylinders, is regarded as marking the limit of centrifugal instability (CI) in unstratified inviscid Taylor-Couette flow, for both axisymmetric and nonaxisymmetric modes. Nonaxisymmetric stratorotational instability (SRI) is known to set in for anticyclonic rotation ratios beyond that line, i.e., η^{2}<μ<1 for axially stably stratified Taylor-Couette flow, but the competition between CI and SRI in the range μ<η^{2} has not yet been addressed. In this paper, we establish continuous connections between the two instabilities at finite Reynolds number Re, as previously suggested by Le Bars and Le Gal [Phys. Rev. Lett. 99, 064502 (2007)PRLTAO0031-900710.1103/PhysRevLett.99.064502], making them indistinguishable at onset. Both instabilities are also continuously connected to the radiative instability at finite Re. These results demonstrate the complex impact viscosity has on the linear stability properties of this flow. Several other qualitative differences with inviscid theory were found, among which are the instability of a nonaxisymmetric mode localized at the outer cylinder without stratification and the instability of a mode propagating against the inner cylinder rotation with stratification. The combination of viscosity and stratification can also lead to a "collision" between (axisymmetric) Taylor vortex branches, causing the axisymmetric oscillatory state already observed in past experiments. Perhaps more surprising is the instability of a centrifugal-like helical mode beyond the Rayleigh line, caused by the joint effects of stratification and viscosity. The threshold μ=η^{2} seems to remain, however, an impassable instability limit for axisymmetric modes, regardless of stratification, viscosity, and even disturbance amplitude.}, }
@article {pmid27840656, year = {2016}, author = {Tian, FB}, title = {Deformation of a Capsule in a Power-Law Shear Flow.}, journal = {Computational and mathematical methods in medicine}, volume = {2016}, number = {}, pages = {7981386}, pmid = {27840656}, issn = {1748-6718}, mesh = {Algorithms ; *Blood Flow Velocity ; Computer Simulation ; Elasticity ; Erythrocytes/cytology ; Humans ; Models, Theoretical ; Motion ; Rheology/*methods ; Shear Strength ; Stress, Mechanical ; }, abstract = {An immersed boundary-lattice Boltzmann method is developed for fluid-structure interactions involving non-Newtonian fluids (e.g., power-law fluid). In this method, the flexible structure (e.g., capsule) dynamics and the fluid dynamics are coupled by using the immersed boundary method. The incompressible viscous power-law fluid motion is obtained by solving the lattice Boltzmann equation. The non-Newtonian rheology is achieved by using a shear rate-dependant relaxation time in the lattice Boltzmann method. The non-Newtonian flow solver is then validated by considering a power-law flow in a straight channel which is one of the benchmark problems to validate an in-house solver. The numerical results present a good agreement with the analytical solutions for various values of power-law index. Finally, we apply this method to study the deformation of a capsule in a power-law shear flow by varying the Reynolds number from 0.025 to 0.1, dimensionless shear rate from 0.004 to 0.1, and power-law index from 0.2 to 1.8. It is found that the deformation of the capsule increases with the power-law index for different Reynolds numbers and nondimensional shear rates. In addition, the Reynolds number does not have significant effect on the capsule deformation in the flow regime considered. Moreover, the power-law index effect is stronger for larger dimensionless shear rate compared to smaller values.}, }
@article {pmid27830719, year = {2016}, author = {Kurzthaler, C and Leitmann, S and Franosch, T}, title = {Intermediate scattering function of an anisotropic active Brownian particle.}, journal = {Scientific reports}, volume = {6}, number = {}, pages = {36702}, pmid = {27830719}, issn = {2045-2322}, mesh = {*Algorithms ; *Anisotropy ; Diffusion ; Escherichia coli/physiology ; Kinetics ; *Models, Theoretical ; *Motion ; Movement ; Particle Size ; }, abstract = {Various challenges are faced when animalcules such as bacteria, protozoa, algae, or sperms move autonomously in aqueous media at low Reynolds number. These active agents are subject to strong stochastic fluctuations, that compete with the directed motion. So far most studies consider the lowest order moments of the displacements only, while more general spatio-temporal information on the stochastic motion is provided in scattering experiments. Here we derive analytically exact expressions for the directly measurable intermediate scattering function for a mesoscopic model of a single, anisotropic active Brownian particle in three dimensions. The mean-square displacement and the non-Gaussian parameter of the stochastic process are obtained as derivatives of the intermediate scattering function. These display different temporal regimes dominated by effective diffusion and directed motion due to the interplay of translational and rotational diffusion which is rationalized within the theory. The most prominent feature of the intermediate scattering function is an oscillatory behavior at intermediate wavenumbers reflecting the persistent swimming motion, whereas at small length scales bare translational and at large length scales an enhanced effective diffusion emerges. We anticipate that our characterization of the motion of active agents will serve as a reference for more realistic models and experimental observations.}, }
@article {pmid27824053, year = {2016}, author = {Irajizad, P and Hasnain, M and Farokhnia, N and Sajadi, SM and Ghasemi, H}, title = {Magnetic slippery extreme icephobic surfaces.}, journal = {Nature communications}, volume = {7}, number = {}, pages = {13395}, pmid = {27824053}, issn = {2041-1723}, abstract = {Anti-icing surfaces have a critical footprint on daily lives of humans ranging from transportation systems and infrastructure to energy systems, but creation of these surfaces for low temperatures remains elusive. Non-wetting surfaces and liquid-infused surfaces have inspired routes for the development of icephobic surfaces. However, high freezing temperature, high ice adhesion strength, and high cost have restricted their practical applications. Here we report new magnetic slippery surfaces outperforming state-of-the-art icephobic surfaces with a ice formation temperature of -34 °C, 2-3 orders of magnitude higher delay time in ice formation, extremely low ice adhesion strength (≈2 Pa) and stability in shear flows up to Reynolds number of 10[5]. In these surfaces, we exploit the magnetic volumetric force to exclude the role of solid-liquid interface in ice formation. We show that these inexpensive surfaces are universal and can be applied to all types of solids (no required micro/nano structuring) with no compromise to their unprecedented properties.}, }
@article {pmid27816870, year = {2017}, author = {Berry, JD and Dagastine, RR}, title = {Mapping coalescence of micron-sized drops and bubbles.}, journal = {Journal of colloid and interface science}, volume = {487}, number = {}, pages = {513-522}, doi = {10.1016/j.jcis.2016.10.040}, pmid = {27816870}, issn = {1095-7103}, abstract = {Emulsion formulation, solvent extraction and multiphase microfluidics are all examples of processes that require precise control of drop or bubble collision stability. We use a previously validated numerical model to map the exact conditions under which micron-sized drops or bubbles undergo coalescence in the presence of colloidal forces and hydrodynamic effects relevant to Brownian motion and low Reynolds number flows. We demonstrate that detailed understanding of how the equilibrium surface forces vary with film thickness can be applied to make accurate predictions of the outcome of a drop or bubble collision when hydrodynamic effects are negligible. In addition, we illuminate the parameter space (i.e. interaction velocity, drop deformation, interfacial tension, etc.) at which hydrodynamic effects can stabilise collisions that are unstable at equilibrium. Further, we determine conditions for which drop or bubble collisions become unstable upon separation, caused by negative hydrodynamic pressure in the film. Lastly, we show that scaling analyses are not applicable for constant force collisions where the approach timescale is comparable to the coalescence timescale, and demonstrate that initial conditions under these circumstances cannot be ignored.}, }
@article {pmid27815242, year = {2016}, author = {Yanase, K and Saarenrinne, P}, title = {Boundary layer control by a fish: Unsteady laminar boundary layers of rainbow trout swimming in turbulent flows.}, journal = {Biology open}, volume = {5}, number = {12}, pages = {1853-1863}, pmid = {27815242}, issn = {2046-6390}, abstract = {The boundary layers of rainbow trout, Oncorhynchus mykiss [0.231±0.016 m total body length (L) (mean±s.d.); N=6], swimming at 1.6±0.09 L s[-1] (N=6) in an experimental flow channel (Reynolds number, Re=4×10[5]) with medium turbulence (5.6% intensity) were examined using the particle image velocimetry technique. The tangential flow velocity distributions in the pectoral and pelvic surface regions (arc length from the rostrum, lx=71±8 mm, N=3, and lx=110±13 mm, N=4, respectively) were approximated by a laminar boundary layer model, the Falkner-Skan equation. The flow regime over the pectoral and pelvic surfaces was regarded as a laminar flow, which could create less skin-friction drag than would be the case with turbulent flow. Flow separation was postponed until vortex shedding occurred over the posterior surface (lx=163±22 mm, N=3). The ratio of the body-wave velocity to the swimming speed was in the order of 1.2. This was consistent with the condition of the boundary layer laminarization that had been confirmed earlier using a mechanical model. These findings suggest an energy-efficient swimming strategy for rainbow trout in a turbulent environment.}, }
@article {pmid27814386, year = {2016}, author = {Kwak, TJ and Nam, YG and Najera, MA and Lee, SW and Strickler, JR and Chang, WJ}, title = {Convex Grooves in Staggered Herringbone Mixer Improve Mixing Efficiency of Laminar Flow in Microchannel.}, journal = {PloS one}, volume = {11}, number = {11}, pages = {e0166068}, pmid = {27814386}, issn = {1932-6203}, mesh = {Computer Simulation ; Equipment Design/methods ; Microfluidic Analytical Techniques/*methods ; Microfluidics/*methods ; }, abstract = {The liquid streams in a microchannel are hardly mixed to form laminar flow, and the mixing issue is well described by a low Reynolds number scheme. The staggered herringbone mixer (SHM) using repeated patterns of grooves in the microchannel have been proved to be an efficient passive micro-mixer. However, only a negative pattern of the staggered herringbone mixer has been used so far after it was first suggested, to the best of our knowledge. In this study, the mixing efficiencies from negative and positive staggered herringbone mixer patterns as well as from opposite flow directions were tested to investigate the effect of the micro-structure geometry on the surrounding laminar flow. The positive herringbone pattern showed better mixing efficiency than the conventionally used negative pattern. Also, generally used forward flow gives better mixing efficiency than reverse flow. The mixing was completed after two cycles of staggered herringbone mixer with both forward and reverse flow in a positive pattern. The traditional negative pattern showed complete mixing after four and five cycles in forward and reverse flow direction, respectively. The mixing effect in all geometries was numerically simulated, and the results confirmed more efficient mixing in the positive pattern than the negative. The results can further enable the design of a more efficient microfluidic mixer, as well as in depth understanding of the phenomena of positive and negative patterns existing in nature with regards to the surrounding fluids.}, }
@article {pmid27810627, year = {2016}, author = {Hayat, T and Zahir, H and Tanveer, A and Alsaedi, A}, title = {Numerical study for MHD peristaltic flow in a rotating frame.}, journal = {Computers in biology and medicine}, volume = {79}, number = {}, pages = {215-221}, doi = {10.1016/j.compbiomed.2016.09.021}, pmid = {27810627}, issn = {1879-0534}, mesh = {*Computer Simulation ; Hot Temperature ; Hydrodynamics ; Magnetic Fields ; *Models, Theoretical ; *Peristalsis ; Rotation ; }, abstract = {The aim of present investigation is to model and analyze the magnetohydrodynamic (MHD) peristaltic transport of Prandtl fluid in a channel with flexible walls. The whole system consisting of fluid and channel are in a rotating frame of reference with uniform angular velocity. Viscous dissipation in thermal equation is not ignored. The channel boundaries satisfy the convective conditions in terms of temperature. The arising complicated problems are reduced in solvable form using large wavelength and small Reynolds number assumptions. Numerical solution for axial and secondary velocities, temperature and heat transfer coefficient are presented. Main emphasis is given to the outcome of rotation and material parameters of Prandtl fluid on the physical quantities of interest.}, }
@article {pmid27806284, year = {2016}, author = {Guillou, L and Dahl, JB and Lin, JG and Barakat, AI and Husson, J and Muller, SJ and Kumar, S}, title = {Measuring Cell Viscoelastic Properties Using a Microfluidic Extensional Flow Device.}, journal = {Biophysical journal}, volume = {111}, number = {9}, pages = {2039-2050}, pmid = {27806284}, issn = {1542-0086}, support = {R01 NS074831/NS/NINDS NIH HHS/United States ; R21 CA174573/CA/NCI NIH HHS/United States ; R21 EB016359/EB/NIBIB NIH HHS/United States ; T32 GM098218/GM/NIGMS NIH HHS/United States ; }, mesh = {Animals ; Biomechanical Phenomena ; Cell Line, Tumor ; *Elasticity ; Glioblastoma/pathology ; *Lab-On-A-Chip Devices ; Mice ; NIH 3T3 Cells ; Viscosity ; }, abstract = {The quantification of cellular mechanical properties is of tremendous interest in biology and medicine. Recent microfluidic technologies that infer cellular mechanical properties based on analysis of cellular deformations during microchannel traversal have dramatically improved throughput over traditional single-cell rheological tools, yet the extraction of material parameters from these measurements remains quite complex due to challenges such as confinement by channel walls and the domination of complex inertial forces. Here, we describe a simple microfluidic platform that uses hydrodynamic forces at low Reynolds number and low confinement to elongate single cells near the stagnation point of a planar extensional flow. In tandem, we present, to our knowledge, a novel analytical framework that enables determination of cellular viscoelastic properties (stiffness and fluidity) from these measurements. We validated our system and analysis by measuring the stiffness of cross-linked dextran microparticles, which yielded reasonable agreement with previously reported values and our micropipette aspiration measurements. We then measured viscoelastic properties of 3T3 fibroblasts and glioblastoma tumor initiating cells. Our system captures the expected changes in elastic modulus induced in 3T3 fibroblasts and tumor initiating cells in response to agents that soften (cytochalasin D) or stiffen (paraformaldehyde) the cytoskeleton. The simplicity of the device coupled with our analytical model allows straightforward measurement of the viscoelastic properties of cells and soft, spherical objects.}, }
@article {pmid27766329, year = {2016}, author = {Li, M and Muñoz, HE and Schmidt, A and Guo, B and Lei, C and Goda, K and Di Carlo, D}, title = {Inertial focusing of ellipsoidal Euglena gracilis cells in a stepped microchannel.}, journal = {Lab on a chip}, volume = {16}, number = {22}, pages = {4458-4465}, doi = {10.1039/c6lc01118g}, pmid = {27766329}, issn = {1473-0189}, mesh = {Euglena gracilis/*cytology/genetics ; *Lab-On-A-Chip Devices ; Mutation ; }, abstract = {Euglena gracilis (E. gracilis) has recently been attracting attention as a potential renewable source for the production of biofuels, livestock feed, cosmetics, and dietary supplements. Research has focused on strain isolation, productivity improvement, nutrient and resource allocation, and co-product production, key steps that ultimately determine the economic viability and compatibility of the biomass produced. To achieve these characteristics, approaches to select E. gracilis mutants with desirable properties, such as high wax ester content, high growth rate, and high environmental tolerance for biodiesel and biomass production, are needed. Flow-based analysis and sorting can be rapid and highly automated but calls for techniques that can precisely control the position of E. gracilis with varying sizes and shapes in a tightly focused stream in a high-throughput manner. In this work, we use a stepped microchannel consisting of a low-aspect-ratio straight channel and a series of expansion regions along the channel height. We study horizontal and vertical focusing, orientation, rotational, and translational behaviors of E. gracilis as a function of aspect ratio (AR) and channel Reynolds number (Re). By making use of inertial focusing and local secondary flows, E. gracilis with diverse shapes are directed to a single equilibrium position in a single focal stream. As an application of on-chip flow cytometry, we integrate a focusing microchip with a custom laser-two-focus (L2F) optical system and demonstrate the detection of chlorophyll autofluorescence as well as the measurement of the velocity of E. gracilis cells flowing through the microchannel.}, }
@article {pmid30271109, year = {2016}, author = {Poroseva, SV and Colmenares F, JD and Murman, SM}, title = {On the accuracy of RANS simulations with DNS data.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {28}, number = {11}, pages = {}, doi = {10.1063/1.4966639}, pmid = {30271109}, issn = {1070-6631}, support = {NNX12AJ61A//NASA/United States ; }, abstract = {Simulation results conducted for incompressible planar wall-bounded turbulent flows with the Reynolds-Averaged Navier-Stokes (RANS) equations with no modeling involved are presented. Instead, all terms but the molecular diffusion are represented by the data from direct numerical simulation (DNS). In simulations, the transport equations for velocity moments through the second order (and the fourth order where the data are available) are solved in a zero-pressure gradient boundary layer over a flat plate and in a fully-developed channel flow in a wide range of Reynolds numbers using DNS data from Sillero et al. (2013), Lee &amp; Moser (2015), and Jeyapaul et al. (2015). The results obtained demonstrate that DNS data are the significant and dominant source of uncertainty in such simulations (hereafter, RANS-DNS simulations). Effects of the Reynolds number, flow geometry, and the velocity moment order as well as an uncertainty quantification technique used to collect the DNS data on the results of RANS-DNS simulations are analyzed. New criteria for uncertainty quantification in statistical data collected from DNS are proposed to guarantee the data accuracy sufficient for their use in RANS equations and for the turbulence model validation.}, }
@article {pmid27791257, year = {2016}, author = {Lee, J and Kim, S and Kim, SM and Song, R and Kim, HK and Park, JS and Park, SC}, title = {Assessing radiocephalic wrist arteriovenous fistulas of obtuse anastomosis using computational fluid dynamics and clinical application.}, journal = {The journal of vascular access}, volume = {17}, number = {6}, pages = {512-520}, doi = {10.5301/jva.5000607}, pmid = {27791257}, issn = {1724-6032}, mesh = {*Arteriovenous Shunt, Surgical/adverse effects ; Blood Flow Velocity ; *Computer Simulation ; Female ; Finite Element Analysis ; Graft Occlusion, Vascular/etiology/physiopathology ; *Hemodynamics ; Humans ; Hydrodynamics ; Kaplan-Meier Estimate ; Kidney Failure, Chronic/diagnosis/*therapy ; Male ; Middle Aged ; *Models, Cardiovascular ; Numerical Analysis, Computer-Assisted ; Radial Artery/physiopathology/*surgery ; Regional Blood Flow ; *Renal Dialysis ; Retrospective Studies ; Risk Factors ; Software ; Stress, Mechanical ; Thrombosis/etiology/physiopathology ; Time Factors ; Treatment Outcome ; Vascular Patency ; Vascular Stiffness ; Veins/physiopathology/*surgery ; Wrist/*blood supply ; }, abstract = {INTRODUCTION: A radiocephalic arteriovenous fistula (AVF) is the best choice for achieving vascular access (VA) for hemodialysis, but this AVF has high rates of early failure due to juxta-anastomotic stenosis, making it impossible to use for dialysis. Low hemodynamic shear stress contributes to the pathophysiology of VA failure due to secondary thrombosis, stenosis, and re-occlusion after percutaneous intervention.<br><br>METHODS: We used a computational fluid dynamics (CFDs) approach to evaluate the shear stress distribution and minimize its effects under various conditions including changes in the anastomosis angle. A three-dimensional computational domain was designed for arteriovenous end-to-side anastomosis based on anastomosis angles of 45&#xb0;, 90&#xb0; and including 135&#xb0; angle of an obtuse anastomosis using three-dimensional design software. COMSOL Multiphysics&#xae; simulation software was used to identify the hemodynamic factors influencing wall shear stress at the anastomosis site using a low Reynolds number k-&#x3b5; turbulence model that included non-Newtonian blood flow characteristics, the complete cardiac pulse cycle, and distention of blood vessels. In preliminary clinical study, all 201 patients who received a radiocephalic wrist AVF from January 2009 to February 2014 were divided into classic and obtuse angle groups.<br><br>RESULTS: The CFD results showed that the largest anastomosis angle (135&#xb0;) resulted in lower shear stress, which would help reduce AVF failures. This obtuse angle was preferred, as it minimized the development of anastomotic stenosis and tended to favor primary and primary-assisted patency in clinical study.<br><br>CONCLUSIONS: An obtuse radiocephalic wrist AVF shows more favorable patency compared to a classic radiocephalic AVF. Surgeons establishing a radiocephalic wrist AVF would be better to consider an AVF with an obtuse anastomosis.}, }
@article {pmid27789458, year = {2016}, author = {Miyagawa, T and Imai, Y and Ishida, S and Ishikawa, T}, title = {Relationship between gastric motility and liquid mixing in the stomach.}, journal = {American journal of physiology. Gastrointestinal and liver physiology}, volume = {311}, number = {6}, pages = {G1114-G1121}, doi = {10.1152/ajpgi.00346.2016}, pmid = {27789458}, issn = {1522-1547}, mesh = {*Computer Simulation ; *Gastric Emptying ; *Gastrointestinal Transit ; Humans ; Muscle Contraction ; Pylorus/*physiology ; }, abstract = {The relationship between gastric motility and the mixing of liquid food in the stomach was investigated with a numerical analysis. Three parameters of gastric motility were considered: the propagation velocity, frequency, and terminal acceleration of peristaltic contractions. We simulated gastric flow with an anatomically realistic geometric model of the stomach, considering free surface flow and moving boundaries. When a peristaltic contraction approaches the pylorus, retropulsive flow is generated in the antrum. Flow separation then occurs behind the contraction. The extent of flow separation depends on the Reynolds number (Re), which quantifies the inertial forces due to the peristaltic contractions relative to the viscous forces of the gastric contents; no separation is observed at low Re, while an increase in reattachment length is observed at high Re. While mixing efficiency is nearly constant for low Re, it increases with Re for high Re because of flow separation. Hence, the effect of the propagation velocity, frequency, or terminal acceleration of peristaltic contractions on mixing efficiency increases with Re.}, }
@article {pmid27722471, year = {2016}, author = {Zhao, Y and Shen, AQ and Haward, SJ}, title = {Flow of wormlike micellar solutions around confined microfluidic cylinders.}, journal = {Soft matter}, volume = {12}, number = {42}, pages = {8666-8681}, doi = {10.1039/c6sm01597b}, pmid = {27722471}, issn = {1744-6848}, abstract = {Wormlike micellar (WLM) solutions are frequently used in enhanced oil and gas recovery applications in porous rock beds where complex microscopic geometries result in mixed flow kinematics with strong shear and extensional components. Experiments with WLM solutions through model microfluidic porous media have revealed a variety of complex flow phenomena, including the formation of stable gel-like structures known as a Flow-Induced Structured Phase (FISP), which undoubtedly play an important role in applications of WLM fluids, but are still poorly understood. A first step in understanding flows of WLM fluids through porous media can be made by examining the flow around a single micro-scale cylinder aligned on the flow axis. Here we study flow behavior of an aqueous WLM solution consisting of cationic surfactant cetyltrimethylammonium bromide (CTAB) and a stable hydrotropic salt 3-hydroxy naphthalene-2-carboxylate (SHNC) in microfluidic devices with three different cylinder blockage ratios, β. We observe a rich sequence of flow instabilities depending on β as the Weissenberg number (Wi) is increased to large values while the Reynolds number (Re) remains low. Instabilities upstream of the cylinder are associated with high stresses in fluid that accelerates into the narrow gap between the cylinder and the channel wall; vortex growth upstream is reminiscent of that seen in microfluidic contraction geometries. Instability downstream of the cylinder is associated with stresses generated at the trailing stagnation point and the resulting flow modification in the wake, coupled with the onset of time-dependent flow upstream and the asymmetric division of flow around the cylinder.}, }
@article {pmid27780156, year = {2016}, author = {Lu, H and Lua, KB and Lee, YJ and Lim, TT and Yeo, KS}, title = {Ground effect on the aerodynamics of three-dimensional hovering wings.}, journal = {Bioinspiration &amp; biomimetics}, volume = {11}, number = {6}, pages = {066003}, doi = {10.1088/1748-3190/11/5/066003}, pmid = {27780156}, issn = {1748-3190}, mesh = {Animals ; Aviation ; Biomechanical Phenomena ; *Biomimetic Materials ; Biomimetics/*methods ; Computer Simulation ; Flight, Animal/*physiology ; Models, Biological ; Wings, Animal/*physiology ; }, abstract = {This paper reports the results of combined experimental and numerical studies on the ground effect on a pair of three-dimensional (3D) hovering wings. Parameters investigated include hovering kinematics, wing shapes, and Reynolds numbers (Re). The results are consistent with the observation by another study (Gao and Lu, 2008 Phys. Fluids, 20 087101) which shows that the cycle-averaged aerodynamic forces generated by two-dimensional (2D) wings in close proximity to the ground can be broadly categorized into three regimes with respect to the ground clearance; force enhancement, force reduction, and force recovery. However, the ground effect on a 3D wing is not as significant as that on a 2D flapping wing reported in (Lu et al 2014 Exp. Fluids, 55 1787); this could be attributed to a weaker wake capture effect on 3D wings. Also, unlike a 2D wing, the leading edge vortex (LEV) remains attached on a 3D wing regardless of ground clearance. For all the wing kinematics considered, the three above-mentioned regimes are closely correlated to a non-monotonic trend in the strength of downwash due to the restriction of root and tip vortex formation, and a positional shift of wake vortices. The root vortices in interaction with the ground induce an up-wash in-between the two wings, causing a strong 'fountain effect' (Maeda and Liu, 2013 J. Biomech. Sci. Eng., 8 344) that may increase the body lift of insects. The present study further shows that changes in wing planform have insignificant influence on the overall trend of ground effect except for a parallel shift in force magnitude, which is caused mainly by the difference in aspect ratio and leading edge pivot point. On the two Reynolds numbers investigated, the results for the low Re case of 100 do not deviate significantly from those of a higher Re = 5000 except for the difference in force magnitudes, since low Reynolds number generates lower downwash, weaker LEV, and lower rotational circulation. Additionally, lower Re leads to a weaker fountain effect.}, }
@article {pmid27778306, year = {2016}, author = {Qureshi, MZ and Rubbab, Q and Irshad, S and Ahmad, S and Aqeel, M}, title = {Heat and Mass Transfer Analysis of MHD Nanofluid Flow with Radiative Heat Effects in the Presence of Spherical Au-Metallic Nanoparticles.}, journal = {Nanoscale research letters}, volume = {11}, number = {1}, pages = {472}, pmid = {27778306}, issn = {1931-7573}, abstract = {Energy generation is currently a serious concern in the progress of human civilization. In this regard, solar energy is considered as a significant source of renewable energy. The purpose of the study is to establish a thermal energy model in the presence of spherical Au-metallic nanoparticles. It is numerical work which studies unsteady magnetohydrodynamic (MHD) nanofluid flow through porous disks with heat and mass transfer aspects. Shaped factor of nanoparticles is investigated using small values of the permeable Reynolds number. In order to scrutinize variation of thermal radiation effects, a dimensionless Brinkman number is introduced. The results point out that heat transfer significantly escalates with the increase of Brinkman number. Partial differential equations that govern this study are reduced into nonlinear ordinary differential equations by means of similarity transformations. Then using a shooting technique, a numerical solution of these equations is constructed. Radiative effects on temperature and mass concentration are quite opposite. Heat transfer increases in the presence of spherical Au-metallic nanoparticles.}, }
@article {pmid27771858, year = {2016}, author = {Daniels, DR}, title = {Curvature correction to the mobility of fluid membrane inclusions.}, journal = {The European physical journal. E, Soft matter}, volume = {39}, number = {10}, pages = {96}, pmid = {27771858}, issn = {1292-895X}, abstract = {Using rigorous low-Reynolds-number hydrodynamic theory on curved surfaces, we provide, via a Stokeslet-type approach, a general and concise expression for the leading-order curvature correction to the canonical, planar, Saffman-Delbrück value of the diffusion constant for a small inclusion embedded in an arbitrarily (albeit weakly) curved fluid membrane. In order to demonstrate the efficacy and utility of this general result, we apply our theory to the specific case of calculating the diffusion coefficient of a locally curvature inducing membrane inclusion. By including both the effects of inclusion and membrane elasticity, as well as their respective thermal shape fluctuations, excellent agreement is found with recently published experimental data on the surface tension dependent mobility of membrane bound inclusions.}, }
@article {pmid27643464, year = {2016}, author = {Bhatti, MM and Zeeshan, A and Ellahi, R}, title = {Endoscope analysis on peristaltic blood flow of Sisko fluid with Titanium magneto-nanoparticles.}, journal = {Computers in biology and medicine}, volume = {78}, number = {}, pages = {29-41}, doi = {10.1016/j.compbiomed.2016.09.007}, pmid = {27643464}, issn = {1879-0534}, mesh = {Endoscopy/*methods ; Hemorheology/*physiology ; Humans ; Magnetic Fields ; Magnetite Nanoparticles/*chemistry ; *Models, Biological ; Peristalsis/*physiology ; Titanium/chemistry ; }, abstract = {In this article, endoscope analysis on peristaltic blood flow of Sisko fluid having Titanium magneto-nanoparticles through a uniform tube has been analyzed. The governing flow problem consists of continuity, linear momentum and thermal energy equations. The effect of magnetic field is also taken into account with the help of ohm's law. With the help of long wavelength and zero Reynolds number approximation, the governing equations are simplified. The reduced resulting nonlinear coupled equations are solved analytically with the help of Homotopy perturbation method (HPM). The impact of all the emerging parameters is discussed with the help of graphs for pressure rise, friction forces for outer and inner tube, velocity profile, temperature profile and pressure gradient. Moreover, numerical computation has been used to evaluate the expression for pressure rise and friction forces. Trapping phenomena is also presented with the help of streamlines. The present study depicts many interesting results that provide further study on different blood flow problems.}, }
@article {pmid27757417, year = {2016}, author = {Saranadhi, D and Chen, D and Kleingartner, JA and Srinivasan, S and Cohen, RE and McKinley, GH}, title = {Sustained drag reduction in a turbulent flow using a low-temperature Leidenfrost surface.}, journal = {Science advances}, volume = {2}, number = {10}, pages = {e1600686}, pmid = {27757417}, issn = {2375-2548}, abstract = {Skin friction drag contributes a major portion of the total drag for small and large water vehicles at high Reynolds number (Re). One emerging approach to reducing drag is to use superhydrophobic surfaces to promote slip boundary conditions. However, the air layer or "plastron" trapped on submerged superhydrophobic surfaces often diminishes quickly under hydrostatic pressure and/or turbulent pressure fluctuations. We use active heating on a superhydrophobic surface to establish a stable vapor layer or "Leidenfrost" state at a relatively low superheat temperature. The continuous film of water vapor lubricates the interface, and the resulting slip boundary condition leads to skin friction drag reduction on the inner rotor of a custom Taylor-Couette apparatus. We find that skin friction can be reduced by 80 to 90% relative to an unheated superhydrophobic surface for Re in the range 26,100 ≤ Re ≤ 52,000. We derive a boundary layer and slip theory to describe the hydrodynamics in the system and show that the plastron thickness is h = 44 ± 11 μm, in agreement with expectations for a Leidenfrost surface.}, }
@article {pmid27749870, year = {2016}, author = {Longhi, S}, title = {PT-symmetric mode-locking.}, journal = {Optics letters}, volume = {41}, number = {19}, pages = {4518-4521}, doi = {10.1364/OL.41.004518}, pmid = {27749870}, issn = {1539-4794}, abstract = {Parity-time (PT) symmetry is one of the most important accomplishments in optics over the past decade. Here the concept of PT mode-locking (ML) of a laser is introduced, in which active phase-locking of cavity axial modes is realized by asymmetric mode coupling in a complex time crystal. PT ML shows a transition from single- to double-pulse emission as the PT symmetry breaking point is crossed. The transition can show a turbulent behavior, depending on a dimensionless modulation parameter that plays the same role as the Reynolds number in hydrodynamic flows.}, }
@article {pmid30404361, year = {2016}, author = {Salieb-Beugelaar, GB and Gonçalves, D and Wolf, MP and Hunziker, P}, title = {Microfluidic 3D Helix Mixers.}, journal = {Micromachines}, volume = {7}, number = {10}, pages = {}, pmid = {30404361}, issn = {2072-666X}, support = {NRP62//Schweizerischer Nationalfonds zur F&#xf6;rderung der Wissenschaftlichen Forschung/ ; 160178//Schweizerischer Nationalfonds zur F&#xf6;rderung der Wissenschaftlichen Forschung/ ; }, abstract = {Polymeric microfluidic systems are well suited for miniaturized devices with complex functionality, and rapid prototyping methods for 3D microfluidic structures are increasingly used. Mixing at the microscale and performing chemical reactions at the microscale are important applications of such systems and we therefore explored feasibility, mixing characteristics and the ability to control a chemical reaction in helical 3D channels produced by the emerging thread template method. Mixing at the microscale is challenging because channel size reduction for improving solute diffusion comes at the price of a reduced Reynolds number that induces a strictly laminar flow regime and abolishes turbulence that would be desired for improved mixing. Microfluidic 3D helix mixers were rapidly prototyped in polydimethylsiloxane (PDMS) using low-surface energy polymeric threads, twisted to form 2-channel and 3-channel helices. Structure and flow characteristics were assessed experimentally by microscopy, hydraulic measurements and chromogenic reaction, and were modeled by computational fluid dynamics. We found that helical 3D microfluidic systems produced by thread templating allow rapid prototyping, can be used for mixing and for controlled chemical reaction with two or three reaction partners at the microscale. Compared to the conventional T-shaped microfluidic system used as a control device, enhanced mixing and faster chemical reaction was found to occur due to the combination of diffusive mixing in small channels and flow folding due to the 3D helix shape. Thus, microfluidic 3D helix mixers can be rapidly prototyped using the thread template method and are an attractive and competitive method for fluid mixing and chemical reactions at the microscale.}, }
@article {pmid27742130, year = {2016}, author = {Li, P and Weng, L and Niu, H and Robinson, B and King, T and Conmy, R and Lee, K and Liu, L}, title = {Reynolds number scaling to predict droplet size distribution in dispersed and undispersed subsurface oil releases.}, journal = {Marine pollution bulletin}, volume = {113}, number = {1-2}, pages = {332-342}, doi = {10.1016/j.marpolbul.2016.10.005}, pmid = {27742130}, issn = {1879-3363}, mesh = {Alaska ; *Models, Theoretical ; Particle Size ; Petroleum/*analysis ; Petroleum Pollution/*analysis ; Viscosity ; Water Pollutants, Chemical/*analysis/*chemistry ; }, abstract = {This study was aimed at testing the applicability of modified Weber number scaling with Alaska North Slope (ANS) crude oil, and developing a Reynolds number scaling approach for oil droplet size prediction for high viscosity oils. Dispersant to oil ratio and empirical coefficients were also quantified. Finally, a two-step Rosin-Rammler scheme was introduced for the determination of droplet size distribution. This new approach appeared more advantageous in avoiding the inconsistency in interfacial tension measurements, and consequently delivered concise droplet size prediction. Calculated and observed data correlated well based on Reynolds number scaling. The relation indicated that chemical dispersant played an important role in reducing the droplet size of ANS under different seasonal conditions. The proposed Reynolds number scaling and two-step Rosin-Rammler approaches provide a concise, reliable way to predict droplet size distribution, supporting decision making in chemical dispersant application during an offshore oil spill.}, }
@article {pmid27731461, year = {2016}, author = {Beauvier, E and Bodea, S and Pocheau, A}, title = {Front propagation in a vortex lattice: dependence on boundary conditions and vortex depth.}, journal = {Soft matter}, volume = {12}, number = {43}, pages = {8935-8941}, doi = {10.1039/c6sm01547f}, pmid = {27731461}, issn = {1744-6848}, abstract = {We experimentally address the propagation of reaction-diffusion fronts in vortex lattices by combining, in a Hele-Shaw cell and at low Reynolds number, forced electroconvective flows and an autocatalytic reaction in solution. We consider both vortex chains and vortex arrays, the former referring to mixed free/rigid boundary conditions for vortices and the latter to free boundary conditions. Varying the depth of the fluid layer, we observe no variation of the mean front velocities for vortex arrays and a noticeable variation for vortex chains. This questions the two-dimensional character of front propagation in low Reynolds number vortex lattices, as well as the mechanisms of this dependence.}, }
@article {pmid27725841, year = {2016}, author = {Liu, X and Yan, W and Liu, Y and Choy, YS and Wei, Y}, title = {Numerical Investigation of Flow Characteristics in the Obstructed Realistic Human Upper Airway.}, journal = {Computational and mathematical methods in medicine}, volume = {2016}, number = {}, pages = {3181654}, pmid = {27725841}, issn = {1748-6718}, mesh = {Adult ; Airway Obstruction/diagnostic imaging/*physiopathology ; Asian People ; Biomechanical Phenomena ; China ; Computer Simulation ; Humans ; Larynx/physiopathology ; Lung/diagnostic imaging ; Male ; Models, Statistical ; Models, Theoretical ; Mouth/physiopathology ; Nasal Cavity/physiopathology ; Pharynx/physiopathology ; Respiration ; Respiration Disorders/*diagnostic imaging/physiopathology ; Respiratory Mechanics ; Respiratory System/*physiopathology ; Tomography, X-Ray Computed ; Trachea/physiopathology ; }, abstract = {The flow characteristics in the realistic human upper airway (HUA) with obstruction that resulted from pharyngeal collapse were numerically investigated. The 3D anatomically accurate HUA model was reconstructed from CT-scan images of a Chinese male patient (38 years, BMI 25.7). The computational fluid dynamics (CFD) with the large eddy simulation (LES) method was applied to simulate the airflow dynamics within the HUA model in both inspiration and expiration processes. The laser Doppler anemometry (LDA) technique was simultaneously adopted to measure the airflow fields in the HUA model for the purpose of testifying the reliability of LES approach. In the simulations, the representative respiration intensities of 16.8 L/min (slight breathing), 30 L/min (moderate breathing), and 60 L/min (severe breathing) were conducted under continuous inspiration and expiration conditions. The airflow velocity field and static pressure field were obtained and discussed in detail. The results indicated the airflow experiences unsteady transitional/turbulent flow in the HUA model under low Reynolds number. The airflow fields cause occurrence of forceful injection phenomenon due to the narrowing of pharynx caused by the respiratory illness in inspiration and expiration. There also exist strong flow separation and back flow inside obstructed HUA owing to the vigorous jet flow effect in the pharynx. The present results would provide theoretical guidance for the treatment of obstructive respiratory disease.}, }
@article {pmid27708761, year = {2016}, author = {Marth, W and Voigt, A}, title = {Collective migration under hydrodynamic interactions: a computational approach.}, journal = {Interface focus}, volume = {6}, number = {5}, pages = {20160037}, pmid = {27708761}, issn = {2042-8898}, abstract = {We consider a generic model for cell motility. Even if a comprehensive understanding of cell motility remains elusive, progress has been achieved in its modelling using a whole-cell physical model. The model takes into account the main mechanisms of cell motility, actin polymerization, actin-myosin dynamics and substrate mediated adhesion (if applicable), and combines them with steric cell-cell and hydrodynamic interactions. The model predicts the onset of collective cell migration, which emerges spontaneously as a result of inelastic collisions of neighbouring cells. Each cell here modelled as an active polar gel is accomplished with two vortices if it moves. Upon collision of two cells, the two vortices which come close to each other annihilate. This leads to a rotation of the cells and together with the deformation and the reorientation of the actin filaments in each cell induces alignment of these cells and leads to persistent translational collective migration. The effect for low Reynolds numbers is as strong as in the non-hydrodynamic model, but it decreases with increasing Reynolds number.}, }
@article {pmid27703591, year = {2016}, author = {Lee, LM and Lee, JW and Chase, D and Gebrezgiabhier, D and Liu, AP}, title = {Development of an advanced microfluidic micropipette aspiration device for single cell mechanics studies.}, journal = {Biomicrofluidics}, volume = {10}, number = {5}, pages = {054105}, pmid = {27703591}, issn = {1932-1058}, support = {DP2 HL117748/HL/NHLBI NIH HHS/United States ; T32 EB005582/EB/NIBIB NIH HHS/United States ; }, abstract = {Various micro-engineered tools or platforms have been developed recently for cell mechanics studies based on acoustic, magnetic, and optical actuations. Compared with other techniques for single cell manipulations, microfluidics has the advantages with simple working principles and device implementations. In this work, we develop a multi-layer microfluidic pipette aspiration device integrated with pneumatically actuated microfluidic control valves. This configuration enables decoupling of cell trapping and aspiration, and hence causes less mechanical perturbation on trapped single cells before aspiration. A high trapping efficiency is achieved by the microfluidic channel design based on fluid resistance model and deterministic microfluidics. Compared to conventional micropipette aspiration, the suction pressure applied on the aspirating cells is highly stable due to the viscous nature of low Reynolds number flow. As a proof-of-concept of this novel microfluidic technology, we built a microfluidic pipette aspiration device with 2 × 13 trapping arrays and used this device to measure the stiffness of a human breast cancer cell line, MDA-MB-231, through the observation of cell deformations during aspiration. As a comparison, we studied the effect of Taxol, a FDA-approved anticancer drug on single cancer cell stiffness. We found that cancer cells treated with Taxol were less deformable with a higher Young's modulus. The multi-layer microfluidic pipette aspiration device is a scalable technology for single cell mechanophenotyping studies and drug discovery applications.}, }
@article {pmid27688703, year = {2016}, author = {Dhanapal, C and Kamalakkannan, J and Prakash, J and Kothandapani, M}, title = {Analysis of Peristaltic Motion of a Nanofluid with Wall Shear Stress, Microrotation, and Thermal Radiation Effects.}, journal = {Applied bionics and biomechanics}, volume = {2016}, number = {}, pages = {4123741}, pmid = {27688703}, issn = {1176-2322}, abstract = {This paper analyzes the peristaltic flow of an incompressible micropolar nanofluid in a tapered asymmetric channel in the presence of thermal radiation and heat sources parameters. The rotation of the nanoparticles is incorporated in the flow model. The equations governing the nanofluid flow are modeled and exact solutions are managed under long wavelength and flow Reynolds number and long wavelength approximations. Explicit expressions of axial velocity, stream function, microrotation, nanoparticle temperature, and concentration have been derived. The phenomena of shear stress and trapping have also been discussed. Finally, the influences of various parameters of interest on flow variables have been discussed numerically and explained graphically. Besides, the results obtained in this paper will be helpful to those who are working on the development of various realms like fluid mechanics, the rotation, Brownian motion, thermophoresis, coupling number, micropolar parameter, and the nondimensional geometry parameters.}, }
@article {pmid27686531, year = {2016}, author = {Salimi-Kenari, H and Imani, M and Nodehi, A and Abedini, H}, title = {An engineering approach to design of dextran microgels size fabricated by water/oil emulsification.}, journal = {Journal of microencapsulation}, volume = {33}, number = {6}, pages = {511-523}, doi = {10.1080/02652048.2016.1216188}, pmid = {27686531}, issn = {1464-5246}, mesh = {Dextrans/*chemistry ; Emulsions ; Gels/chemistry ; *Models, Chemical ; Oils/*chemistry ; Particle Size ; Water/*chemistry ; }, abstract = {A correlation, based on fluid mechanics, has been investigated for the mean particle diameter of crosslinked dextran microgels (CDMs) prepared via a water/oil emulsification methodology conducted in a single-stirred vessel. To this end, non-dimensional correlations were developed to predict the mean particle size of CDMs as a function of Weber number, Reynolds number and viscosity number similar to ones introduced for liquid-liquid dispersions. Moreover, a Rosin-Rammler distribution function has been successfully applied to the microgel particle size distributions. The correlations were validated using experimentally obtained mean particle sizes for CDMs prepared at different stirring conditions. The validated correlation is especially applicable to medical and pharmaceutical applications where strict control on the mean particle size and size distribution of CDMs are extremely essential. [Formula: see text].}, }
@article {pmid27684076, year = {2016}, author = {Bachant, P and Wosnik, M and Gunawan, B and Neary, VS}, title = {Experimental Study of a Reference Model Vertical-Axis Cross-Flow Turbine.}, journal = {PloS one}, volume = {11}, number = {9}, pages = {e0163799}, pmid = {27684076}, issn = {1932-6203}, abstract = {The mechanical power, total rotor drag, and near-wake velocity of a 1:6 scale model (1.075 m diameter) of the US Department of Energy's Reference Model vertical-axis cross-flow turbine were measured experimentally in a towing tank, to provide a comprehensive open dataset for validating numerical models. Performance was measured for a range of tip speed ratios and at multiple Reynolds numbers by varying the rotor's angular velocity and tow carriage speed, respectively. A peak power coefficient CP = 0.37 and rotor drag coefficient CD = 0.84 were observed at a tip speed ratio λ0 = 3.1. A regime of weak linear Re-dependence of the power coefficient was observed above a turbine diameter Reynolds number ReD ≈ 106. The effects of support strut drag on turbine performance were investigated by covering the rotor's NACA 0021 struts with cylinders. As expected, this modification drastically reduced the rotor power coefficient. Strut drag losses were also measured for the NACA 0021 and cylindrical configurations with the rotor blades removed. For λ = λ0, wake velocity was measured at 1 m (x/D = 0.93) downstream. Mean velocity, turbulence kinetic energy, and mean kinetic energy transport were compared with results from a high solidity turbine acquired with the same test apparatus. Like the high solidity case, mean vertical advection was calculated to be the largest contributor to near-wake recovery. However, overall, lower levels of streamwise wake recovery were calculated for the RM2 case-a consequence of both the relatively low solidity and tapered blades reducing blade tip vortex shedding-responsible for mean vertical advection-and lower levels of turbulence caused by higher operating tip speed ratio and therefore reduced dynamic stall. Datasets, code for processing and visualization, and a CAD model of the turbine have been made publicly available.}, }
@article {pmid27662761, year = {2016}, author = {de Camargo, CL and Shiroma, LS and Giordano, GF and Gobbi, AL and Vieira, LC and Lima, RS}, title = {Turbulence in microfluidics: Cleanroom-free, fast, solventless, and bondless fabrication and application in high throughput liquid-liquid extraction.}, journal = {Analytica chimica acta}, volume = {940}, number = {}, pages = {73-83}, doi = {10.1016/j.aca.2016.08.052}, pmid = {27662761}, issn = {1873-4324}, abstract = {This paper addresses an important breakthrough in the deployment of ultra-high adhesion strength microfluidic technologies to provide turbulence at harsh flow rate conditions. This paper is only, to our knowledge, the second reporting on the generation of high flow rate-assisted turbulence in microchannels. This flow solves a crucial bottleneck in microfluidics: the generation of high throughput homogeneous mixings. We focused on the fabrication of bulky polydimethylsiloxane (PDMS) microchips (without any interfaces) rather than the laborious surface modifications that were employed in the first reporting about turbulence-assisted microfluidics. The fabrication is cleanroom-free, simple, low-cost, fast, solventless, and bondless requiring only a laboratory oven. More specifically, our method relies on the shaping of a nylon scaffold, cure of PDMS with embedded nylon, and removal of this scaffold. The scaffold was obtained by manually wrapping nylon threads. The withdrawing out of the scaffold was completed in few seconds using only a plier. Such microchannels endured flow rates of up to 60.0 mL min(-1) with a strikingly low elastic deformation. The importance in producing turbulence into microscale channels was successfully shown in liquid-liquid extractions. The great energy dissipation rate relative to the turbulence created high throughput and efficient extractions in microfluidics for the first time. The residence time was only 0.01 s at 25.0 mL min(-1) (total flow rate of the immiscible phases). In addition, the partition coefficient determined in a single run was similar to that obtained by the conventional batch shake-flask method that was realized in triplicate.}, }
@article {pmid27661694, year = {2016}, author = {Vakarelski, IU and Berry, JD and Chan, DY and Thoroddsen, ST}, title = {Leidenfrost Vapor Layers Reduce Drag without the Crisis in High Viscosity Liquids.}, journal = {Physical review letters}, volume = {117}, number = {11}, pages = {114503}, doi = {10.1103/PhysRevLett.117.114503}, pmid = {27661694}, issn = {1079-7114}, abstract = {The drag coefficient C_{D} of a solid smooth sphere moving in a fluid is known to be only a function of the Reynolds number Re and diminishes rapidly at the drag crisis around Re∼3×10^{5}. A Leidenfrost vapor layer on a hot sphere surface can trigger the onset of the drag crisis at a lower Re. By using a range of high viscosity perfluorocarbon liquids, we show that the drag reduction effect can occur over a wide range of Re, from as low as ∼600 to 10^{5}. The Navier slip model with a viscosity dependent slip length can fit the observed drag reduction and wake shape.}, }
@article {pmid27635104, year = {2016}, author = {Chandler, ID and Guymer, I and Pearson, JM and van Egmond, R}, title = {Vertical variation of mixing within porous sediment beds below turbulent flows.}, journal = {Water resources research}, volume = {52}, number = {5}, pages = {3493-3509}, pmid = {27635104}, issn = {0043-1397}, abstract = {River ecosystems are influenced by contaminants in the water column, in the pore water and adsorbed to sediment particles. When exchange across the sediment-water interface (hyporheic exchange) is included in modeling, the mixing coefficient is often assumed to be constant with depth below the interface. Novel fiber-optic fluorometers have been developed and combined with a modified EROSIMESS system to quantify the vertical variation in mixing coefficient with depth below the sediment-water interface. The study considered a range of particle diameters and bed shear velocities, with the permeability Péclet number, PeK between 1000 and 77,000 and the shear Reynolds number, Re*, between 5 and 600. Different parameterization of both an interface exchange coefficient and a spatially variable in-sediment mixing coefficient are explored. The variation of in-sediment mixing is described by an exponential function applicable over the full range of parameter combinations tested. The empirical relationship enables estimates of the depth to which concentrations of pollutants will penetrate into the bed sediment, allowing the region where exchange will occur faster than molecular diffusion to be determined.}, }
@article {pmid27627416, year = {2016}, author = {Ren, F and Song, B and Sukop, MC and Hu, H}, title = {Improved lattice Boltzmann modeling of binary flow based on the conservative Allen-Cahn equation.}, journal = {Physical review. E}, volume = {94}, number = {2-1}, pages = {023311}, doi = {10.1103/PhysRevE.94.023311}, pmid = {27627416}, issn = {2470-0053}, abstract = {The primary and key task of binary fluid flow modeling is to track the interface with good accuracy, which is usually challenging due to the sharp-interface limit and numerical dispersion. This article concentrates on further development of the conservative Allen-Cahn equation (ACE) [Geier et al., Phys. Rev. E 91, 063309 (2015)10.1103/PhysRevE.91.063309] under the framework of the lattice Boltzmann method (LBM), with incorporation of the incompressible hydrodynamic equations [Liang et al., Phys. Rev. E 89, 053320 (2014)10.1103/PhysRevE.89.053320]. Utilizing a modified equilibrium distribution function and an additional source term, this model is capable of correctly recovering the conservative ACE through the Chapman-Enskog analysis. We also simulate four phase-tracking benchmark cases, including one three-dimensional case; all show good accuracy as well as low numerical dispersion. By coupling the incompressible hydrodynamic equations, we also simulate layered Poiseuille flow and the Rayleigh-Taylor instability, illustrating satisfying performance in dealing with complex flow problems, e.g., high viscosity ratio, high density ratio, and high Reynolds number situations. The present work provides a reliable and efficient solution for binary flow modeling.}, }
@article {pmid27627415, year = {2016}, author = {Ba, Y and Liu, H and Li, Q and Kang, Q and Sun, J}, title = {Multiple-relaxation-time color-gradient lattice Boltzmann model for simulating two-phase flows with high density ratio.}, journal = {Physical review. E}, volume = {94}, number = {2-1}, pages = {023310}, doi = {10.1103/PhysRevE.94.023310}, pmid = {27627415}, issn = {2470-0053}, abstract = {In this paper we propose a color-gradient lattice Boltzmann (LB) model for simulating two-phase flows with high density ratio and high Reynolds number. The model applies a multirelaxation-time (MRT) collision operator to enhance the stability of the simulation. A source term, which is derived by the Chapman-Enskog analysis, is added into the MRT LB equation so that the Navier-Stokes equations can be exactly recovered. Also, a form of the equilibrium density distribution function is used to simplify the source term. To validate the proposed model, steady flows of a static droplet and the layered channel flow are first simulated with density ratios up to 1000. Small values of spurious velocities and interfacial tension errors are found in the static droplet test, and improved profiles of velocity are obtained by the present model in simulating channel flows. Then, two cases of unsteady flows, Rayleigh-Taylor instability and droplet splashing on a thin film, are simulated. In the former case, the density ratio of 3 and Reynolds numbers of 256 and 2048 are considered. The interface shapes and spike and bubble positions are in good agreement with the results of previous studies. In the latter case, the droplet spreading radius is found to obey the power law proposed in previous studies for the density ratio of 100 and Reynolds number up to 500.}, }
@article {pmid27627229, year = {2016}, author = {Heidenreich, S and Dunkel, J and Klapp, SH and Bär, M}, title = {Hydrodynamic length-scale selection in microswimmer suspensions.}, journal = {Physical review. E}, volume = {94}, number = {2-1}, pages = {020601}, doi = {10.1103/PhysRevE.94.020601}, pmid = {27627229}, issn = {2470-0053}, abstract = {A universal characteristic of mesoscale turbulence in active suspensions is the emergence of a typical vortex length scale, distinctly different from the scale invariance of turbulent high-Reynolds number flows. Collective length-scale selection has been observed in bacterial fluids, endothelial tissue, and active colloids, yet the physical origins of this phenomenon remain elusive. Here, we systematically derive an effective fourth-order field theory from a generic microscopic model that allows us to predict the typical vortex size in microswimmer suspensions. Building on a self-consistent closure condition, the derivation shows that the vortex length scale is determined by the competition between local alignment forces, rotational diffusion, and intermediate-range hydrodynamic interactions. Vortex structures found in simulations of the theory agree with recent measurements in Bacillus subtilis suspensions. Moreover, our approach yields an effective viscosity enhancement (reduction), as reported experimentally for puller (pusher) microorganisms.}, }
@article {pmid27610298, year = {2016}, author = {Maqbool, K and Shaheen, S and Mann, AB}, title = {Exact solution of cilia induced flow of a Jeffrey fluid in an inclined tube.}, journal = {SpringerPlus}, volume = {5}, number = {1}, pages = {1379}, pmid = {27610298}, issn = {2193-1801}, abstract = {The present study investigated the cilia induced flow of MHD Jeffrey fluid through an inclined tube. This study is carried out under the assumptions of long wavelength and low Reynolds number approximations. Exact solutions for the velocity profile, pressure rise, pressure gradient, volume flow rate and stream function are obtained. Effects of pertinent physical parameters on the computational results are presented graphically.}, }
@article {pmid27608508, year = {2016}, author = {Li, J and Liu, W and Li, T and Rozen, I and Zhao, J and Bahari, B and Kante, B and Wang, J}, title = {Swimming Microrobot Optical Nanoscopy.}, journal = {Nano letters}, volume = {16}, number = {10}, pages = {6604-6609}, doi = {10.1021/acs.nanolett.6b03303}, pmid = {27608508}, issn = {1530-6992}, abstract = {Optical imaging plays a fundamental role in science and technology but is limited by the ability of lenses to resolve small features below the fundamental diffraction limit. A variety of nanophotonic devices, such as metamaterial superlenses and hyperlenses, as well as microsphere lenses, have been proposed recently for subdiffraction imaging. The implementation of these micro/nanostructured lenses as practical and efficient imaging approaches requires locomotive capabilities to probe specific sites and scan large areas. However, directed motion of nanoscale objects in liquids must overcome low Reynolds number viscous flow and Brownian fluctuations, which impede stable and controllable scanning. Here we introduce a new imaging method, named swimming microrobot optical nanoscopy, based on untethered chemically powered microrobots as autonomous probes for subdiffraction optical scanning and imaging. The microrobots are made of high-refractive-index microsphere lenses and powered by local catalytic reactions to swim and scan over the sample surface. Autonomous motion and magnetic guidance of microrobots enable large-area, parallel and nondestructive scanning with subdiffraction resolution, as illustrated using soft biological samples such as neuron axons, protein microtubulin, and DNA nanotubes. Incorporating such imaging capacities in emerging nanorobotics technology represents a major step toward ubiquitous nanoscopy and smart nanorobots for spectroscopy and imaging.}, }
@article {pmid27588859, year = {2016}, author = {Ault, JT and Fani, A and Chen, KK and Shin, S and Gallaire, F and Stone, HA}, title = {Vortex-Breakdown-Induced Particle Capture in Branching Junctions.}, journal = {Physical review letters}, volume = {117}, number = {8}, pages = {084501}, doi = {10.1103/PhysRevLett.117.084501}, pmid = {27588859}, issn = {1079-7114}, abstract = {We show experimentally that a flow-induced, Reynolds number-dependent particle-capture mechanism in branching junctions can be enhanced or eliminated by varying the junction angle. In addition, numerical simulations are used to show that the features responsible for this capture have the signatures of classical vortex breakdown, including an approach flow aligned with the vortex axis and a pocket of subcriticality. We show how these recirculation regions originate and evolve and suggest a physical mechanism for their formation. Furthermore, comparing experiments and numerical simulations, the presence of vortex breakdown is found to be an excellent predictor of particle capture. These results inform the design of systems in which suspended particle accumulation can be eliminated or maximized.}, }
@article {pmid27586487, year = {2016}, author = {Hayat, T and Ahmed, B and Abbasi, FM and Ahmad, B}, title = {Mixed convective peristaltic flow of carbon nanotubes submerged in water using different thermal conductivity models.}, journal = {Computer methods and programs in biomedicine}, volume = {135}, number = {}, pages = {141-150}, doi = {10.1016/j.cmpb.2016.07.030}, pmid = {27586487}, issn = {1872-7565}, mesh = {*Models, Theoretical ; *Nanotubes, Carbon ; Water/*chemistry ; }, abstract = {BACKGROUND AND OBJECTIVE: Single Walled Carbon Nanotubes (SWCNTs) are the advanced product of nanotechnology having notable mechanical and physical properties. Peristalsis of SWCNTs suspended in water through an asymmetric channel is examined. Such mechanism is studied in the presence of viscous dissipation, velocity slip, mixed convection, temperature jump and heat generation/absorption.<br><br>METHODS: Mathematical modeling is carried out under the low Reynolds number and long wavelength approximation. Resulting nonlinear system is solved using the perturbation technique for small Brinkman's number. Physical analysis and comparison of the results in light of three different thermal conductivity models is also provided.<br><br>CONCLUSIONS: It is reported that the heat transfer rate at the boundary increases with an increase in the nanotubes volume fraction. The addition of nanotubes affects the pressure gradient during the peristaltic flow. Moreover, the maximum velocity of the fluid decreases due to addition of the nanotubes.}, }
@article {pmid27586475, year = {2016}, author = {Ramesh, K}, title = {Effects of slip and convective conditions on the peristaltic flow of couple stress fluid in an asymmetric channel through porous medium.}, journal = {Computer methods and programs in biomedicine}, volume = {135}, number = {}, pages = {1-14}, doi = {10.1016/j.cmpb.2016.07.001}, pmid = {27586475}, issn = {1872-7565}, mesh = {*Hydrodynamics ; Models, Theoretical ; Porosity ; *Stress, Mechanical ; }, abstract = {BACKGROUND: Assessment of the fluid flow pattern in a non-pregnant uterus is important for understanding embryo transport in the uterus. Fertilization occurs in the fallopian tube and the embryo enters the uterine cavity within three days of ovulation. In the uterus, the embryo is conveyed by the uterine fluid for another three to four days to a successful implantation site at the upper part of the uterus. The movements of fluid within the uterus may be induced by several mechanisms, but they seem to be dominated by myometrial contractions. The intrauterine fluid flow due to these myometrial contractions is peristaltic type motion in nature and the myometrial contractions may occur in both symmetric and asymmetric directions.<br><br>OBJECTIVE: The aim of the present article is to investigate the peristaltic transport of couple stress fluid in an asymmetric channel. The channel asymmetry is produced by choosing the peristaltic wave train on the walls to have different wave amplitudes and phase differences. The fluid is filled with a homogeneous porous medium. The effects of slip and convective boundary conditions are also taken into consideration.<br><br>METHOD: The flow is investigated in the wave frame of reference moving with constant velocity with the wave. Long wavelength and low Reynolds number approximations are utilized in problem formulation. Exact solutions are presented for the stream function, pressure gradient and temperature.<br><br>RESULTS: The graphical analysis is carried out to examine the effects of sundry parameters on flow quantities of interest. Comparative study is also made for couple stress fluid with Newtonian fluid.<br><br>CONCLUSIONS: The results revealed that the trapping fluid can be increased and the central line axial velocity can be raised to a considerable extent by increasing Darcy number. Increasing of slip parameter increases the velocity near the boundary of the walls and Brinkman number increases the temperature of the fluid.}, }
@article {pmid31534303, year = {2016}, author = {Thurman, D and Culley, D and Poinsatte, P and Raghu, S and Ameri, A and Shyam, V}, title = {INVESTIGATION OF SPIRAL AND SWEEPING HOLES.}, journal = {Journal of turbomachinery}, volume = {138}, number = {9}, pages = {}, pmid = {31534303}, issn = {0889-504X}, support = {//Glenn Research Center NASA/United States ; N-999999//Intramural NASA/United States ; }, abstract = {Surface infrared thermography, hotwire anemometry, and thermocouple surveys were performed on two new film cooling hole geometries: spiral/rifled holes and fluidic sweeping holes. The spiral holes attempt to induce large-scale vorticity to the film cooling jet as it exits the hole to prevent the formation of the kidney shaped vortices commonly associated with film cooling jets. The fluidic sweeping hole uses a passive in-hole geometry to induce jet sweeping at frequencies that scale with blowing ratios. The spiral hole performance is compared to that of round holes with and without compound angles. The fluidic hole is of the diffusion class of holes and is therefore compared to a 777 hole and Square holes. A patent-pending spiral hole design showed the highest potential of the non-diffusion type hole configurations. Velocity contours and flow temperature were acquired at discreet cross-sections of the downstream flow field. The passive fluidic sweeping hole shows the most uniform cooling distribution but suffers from low span-averaged effectiveness levels due to enhanced mixing. The data was taken at a Reynolds number of 11,000 based on hole diameter and freestream velocity. Infrared thermography was taken for blowing ratios of 1.0, 1.5, 2.0, and 2.5 at a density ratio of 1.05. The flow inside the fluidic sweeping hole was studied using 3D unsteady RANS.}, }
@article {pmid30213252, year = {2016}, author = {Tripathi, D and Akbar, NS and Khan, ZH and Bég, OA}, title = {Peristaltic transport of bi-viscosity fluids through a curved tube: A mathematical model for intestinal flow.}, journal = {Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine}, volume = {230}, number = {9}, pages = {817-828}, doi = {10.1177/0954411916658318}, pmid = {30213252}, issn = {2041-3033}, abstract = {The human intestinal tract is a long, curved tube constituting the final section of the digestive system in which nutrients and water are mostly absorbed. Motivated by the dynamics of chyme in the intestine, a mathematical model is developed to simulate the associated transport phenomena via peristaltic transport. Rheology of chyme is modelled using the Nakamura-Sawada bi-viscosity non-Newtonian formulation. The intestinal tract is considered as a curved tube geometric model. Low Reynolds number (creeping hydrodynamics) and long wavelength approximations are taken into consideration. Analytical solutions of the moving boundary value problem are derived for velocity field, pressure gradient and pressure rise. Streamline flow visualization is achieved with Mathematica symbolic software. Peristaltic pumping phenomenon and trapping of the bolus are also examined. The influence of curvature parameter, apparent viscosity coefficient (rheological parameter) and volumetric flow rate on flow characteristics is described. Validation of analytical solutions is achieved with a MAPLE17 numerical quadrature algorithm. The work is relevant to improving understanding of gastric hydrodynamics and provides a benchmark for further computational fluid dynamic simulations.}, }
@article {pmid27575234, year = {2016}, author = {Pareschi, G and Frapolli, N and Chikatamarla, SS and Karlin, IV}, title = {Conjugate heat transfer with the entropic lattice Boltzmann method.}, journal = {Physical review. E}, volume = {94}, number = {1-1}, pages = {013305}, doi = {10.1103/PhysRevE.94.013305}, pmid = {27575234}, issn = {2470-0053}, abstract = {A conjugate heat-transfer model is presented based on the two-population entropic lattice Boltzmann method. The present approach relies on the extension of Grad's boundary conditions to the two-population model for thermal flows, as well as on the appropriate exact conjugate heat-transfer condition imposed at the fluid-solid interface. The simplicity and efficiency of the lattice Boltzmann method (LBM), and in particular of the entropic multirelaxation LBM, are retained in the present approach, thus enabling simulations of turbulent high Reynolds number flows and complex wall boundaries. The model is validated by means of two-dimensional parametric studies of various setups, including pure solid conduction, conjugate heat transfer with a backward-facing step flow, and conjugate heat transfer with the flow past a circular heated cylinder. Further validations are performed in three dimensions for the case of a turbulent flow around a heated mounted cube.}, }
@article {pmid27575221, year = {2016}, author = {Sahu, S and Shankar, V}, title = {Passive manipulation of free-surface instability by deformable solid bilayers.}, journal = {Physical review. E}, volume = {94}, number = {1-1}, pages = {013111}, doi = {10.1103/PhysRevE.94.013111}, pmid = {27575221}, issn = {2470-0053}, abstract = {This study deals with the elastohydrodynamic coupling that occurs in the flow of a liquid layer down an inclined plane lined with a deformable solid bilayer and its consequences on the stability of the free surface of the liquid layer. The fluid is Newtonian and incompressible, while the linear elastic constitutive relation has been considered for the deformable solid bilayer, and the densities of the fluid and the two solids are kept equal. A temporal linear stability analysis is carried out for this coupled solid-fluid system. A long-wave asymptotic analysis is employed to obtain an analytical expression for the complex wavespeed in the low wave-number regime, and a numerical shooting method is used to solve the coupled set of governing differential equations in order to obtain the stability criterion for arbitrary values of the wave number. In a previous work on plane Couette flow past an elastic bilayer, Neelmegam et al. [Phys. Rev. E 90, 043004 (2014)PLEEE81539-375510.1103/PhysRevE.90.043004] showed that the instability of the flow can be significantly influenced by the nature of the solid layer, which is adjacent to the liquid layer. In stark contrast, for free-surface flow past a bilayer, our long-wave asymptotic analysis demonstrates that the stability of the free-surface mode is insensitive to the nature of the solid adjacent to the liquid layer. Instead, it is the effective shear modulus of the bilayer G_{eff} (given by H/G_{eff}=H_{1}/G_{1}+H_{2}/G_{2}, where H=H_{1}+H_{2} is the total thickness of the solid bilayer, H_{1} and H_{2} are the thicknesses of the two solid layers, and G_{1} and G_{2} are the shear moduli of the two solid layers) that determines the stability of the free surface in the long-wave limit. We show that for a given Reynolds number, the free-surface instability is stabilized when G_{eff} decreases below a critical value. At finite wave numbers, our numerical solution indicates that additional instabilities at the free surface and the liquid-solid interface can be induced by wall deformability and inertia in the fluid and solid. Interestingly, the onset of these additional instabilities is sensitive to the relative placements of the two solid layers comprising the bilayer. We show that it is possible to delay the onset of these additional instabilities, while still suppressing the free-surface instability, by manipulating the ratio of the shear moduli and the thicknesses of the two solid layers in the bilayer. At moderate Reynolds number and finite wave number, we demonstrate that an exchange of modes occurs between the gas-liquid and liquid-solid interfacial modes as the solid bilayer becomes more deformable. We demonstrate further that dissipative effects in the individual solid layers have an important bearing on the stability of the system, and they could also be exploited in suppressing the instability. This study thus shows that the ability to passively manipulate and control interfacial instabilities increases substantially with the use of solid bilayers.}, }
@article {pmid27575215, year = {2016}, author = {Swaminathan, RV and Ravichandran, S and Perlekar, P and Govindarajan, R}, title = {Dynamics of circular arrangements of vorticity in two dimensions.}, journal = {Physical review. E}, volume = {94}, number = {1-1}, pages = {013105}, doi = {10.1103/PhysRevE.94.013105}, pmid = {27575215}, issn = {2470-0053}, abstract = {The merger of two like-signed vortices is a well-studied problem, but in a turbulent flow, we may often have more than two like-signed vortices interacting. We study the merger of three or more identical corotating vortices initially arranged on the vertices of a regular polygon. At low to moderate Reynolds numbers, we find an additional stage in the merger process, absent in the merger of two vortices, where an annular vortical structure is formed and is long lived. Vortex merger is slowed down significantly due to this. Such annular vortices are known at far higher Reynolds numbers in studies of tropical cyclones, which have been noticed to a break down into individual vortices. In the preannular stage, vortical structures in a viscous flow are found here to tilt and realign in a manner similar to the inviscid case, but the pronounced filaments visible in the latter are practically absent in the former. Five or fewer vortices initially elongate radially, and then reorient their long axis closer to the azimuthal direction so as to form an annulus. With six or more vortices, the initial alignment is already azimuthal. Interestingly at higher Reynolds numbers, the merger of an odd number of vortices is found to proceed very differently from that of an even number. The former process is rapid and chaotic whereas the latter proceeds more slowly via pairing events. The annular vortex takes the form of a generalized Lamb-Oseen vortex (GLO), and diffuses inward until it forms a standard Lamb-Oseen vortex. For lower Reynolds number, the numerical (fully nonlinear) evolution of the GLO vortex follows exactly the analytical evolution until merger. At higher Reynolds numbers, the annulus goes through instabilities whose nonlinear stages show a pronounced difference between even and odd mode disturbances. Here again, the odd mode causes an early collapse of the annulus via decaying turbulence into a single central vortex, whereas the even mode disturbance causes a more orderly progression into a single vortex. Results from linear stability analysis agree with the nonlinear simulations, and predict the frequencies of the most unstable modes better than they predict the growth rates. It is hoped that the present findings, that multiple vortex merger is qualitatively different from the merger of two vortices, will motivate studies on how multiple vortex interactions affect the inverse cascade in two-dimensional turbulence.}, }
@article {pmid27567769, year = {2016}, author = {Tabe, R and Ghalichi, F and Hossainpour, S and Ghasemzadeh, K}, title = {Laminar-to-turbulence and relaminarization zones detection by simulation of low Reynolds number turbulent blood flow in large stenosed arteries.}, journal = {Bio-medical materials and engineering}, volume = {27}, number = {2-3}, pages = {119-129}, doi = {10.3233/BME-161574}, pmid = {27567769}, issn = {1878-3619}, mesh = {Arterial Occlusive Diseases/*physiopathology ; Arteries/*physiopathology ; Blood Flow Velocity ; Computer Simulation ; Constriction, Pathologic/*physiopathology ; Humans ; Models, Cardiovascular ; Pulsatile Flow ; Stress, Mechanical ; }, abstract = {Laminar, turbulent, transitional, or combine areas of all three types of viscous flow can occur downstream of a stenosis depending upon the Reynolds number and constriction shape parameter. Neither laminar flow solver nor turbulent models for instance the k-ω (k-omega), k-ε (k-epsilon), RANS or LES are opportune for this type of flow. In the present study attention has been focused vigorously on the effect of the constriction in the flow field with a unique way. It means that the laminar solver was employed from entry up to the beginning of the turbulent shear flow. The turbulent model (k-ω SST Transitional Flows) was utilized from starting of turbulence to relaminarization zone while the laminar model was applied again with onset of the relaminarization district. Stenotic flows, with 50 and 75% cross-sectional area, were simulated at Reynolds numbers range from 500 to 2000 employing FLUENT (v6.3.17). The flow was considered to be steady, axisymmetric, and incompressible. Achieving results were reported as axial velocity, disturbance velocity, wall shear stress and the outcomes were compared with previously experimental and CFD computations. The analogy of axial velocity profiles shows that they are in acceptable compliance with the empirical data. As well as disturbance velocity and wall shear stresses anticipated by this new approach, part by part simulation, are reasonably valid with the acceptable experimental studies.}, }
@article {pmid27552860, year = {2016}, author = {Maneshian, B and Javadi, Kh and Rahni, MT and Miller, R}, title = {Droplet dynamics in rotating flows.}, journal = {Advances in colloid and interface science}, volume = {236}, number = {}, pages = {63-82}, doi = {10.1016/j.cis.2016.07.005}, pmid = {27552860}, issn = {1873-3727}, abstract = {This paper deals with investigations of droplet dynamics in rotating flows. In many previous studies droplet dynamics was analyzed in simple unidirectional flows. To fill this gap, the focus of this study is an overview on investigations of droplet dynamics in a complex rotating flow. A Lattice Boltzmann Method with high potential in simulation of two-phase unsteady flows is applied to simulate the physics of the problem in a lid-driven cavity. In spite of its simple geometry, there is a complex rotating flow field containing different vortices and shear regions. The Reynolds number based on the cavity length scale and the upper wall velocity, ReL, is considered to be 1000. We discuss here effects of different parameters such as: density ratios (1, 5, 10, 100, and 1000), droplet sizes (D/L=0.097, 0.114, 0.131 and 0.2), and droplet initial positions (1/8, 2/8, and 3/8 of the cavity length, L, out of center). The results are discussed in terms of global flow physics and its interaction with the droplet, drop deformation during its motion along with the main flow, and droplet trajectories. It is shown that there are strong interactions between the droplet and the main carrying flow. During motion, the droplets pass through different flow regions containing acceleration/deceleration zones. Consequently, the droplets experience different shear forces resulting in stretching, shrinking, rotating and dilatation which all contribute to the dynamics of the droplet.}, }
@article {pmid27528780, year = {2016}, author = {Liu, H and Ravi, S and Kolomenskiy, D and Tanaka, H}, title = {Biomechanics and biomimetics in insect-inspired flight systems.}, journal = {Philosophical transactions of the Royal Society of London. Series B, Biological sciences}, volume = {371}, number = {1704}, pages = {}, pmid = {27528780}, issn = {1471-2970}, mesh = {*Aircraft ; Animals ; Biomechanical Phenomena ; *Biomimetics ; *Flight, Animal ; Insecta/*physiology ; }, abstract = {Insect- and bird-size drones-micro air vehicles (MAV) that can perform autonomous flight in natural and man-made environments are now an active and well-integrated research area. MAVs normally operate at a low speed in a Reynolds number regime of 10(4)-10(5) or lower, in which most flying animals of insects, birds and bats fly, and encounter unconventional challenges in generating sufficient aerodynamic forces to stay airborne and in controlling flight autonomy to achieve complex manoeuvres. Flying insects that power and control flight by flapping wings are capable of sophisticated aerodynamic force production and precise, agile manoeuvring, through an integrated system consisting of wings to generate aerodynamic force, muscles to move the wings and a control system to modulate power output from the muscles. In this article, we give a selective review on the state of the art of biomechanics in bioinspired flight systems in terms of flapping and flexible wing aerodynamics, flight dynamics and stability, passive and active mechanisms in stabilization and control, as well as flapping flight in unsteady environments. We further highlight recent advances in biomimetics of flapping-wing MAVs with a specific focus on insect-inspired wing design and fabrication, as well as sensing systems.This article is part of the themed issue 'Moving in a moving medium: new perspectives on flight'.}, }
@article {pmid27518455, year = {2016}, author = {Li, F and Jian, Y and Chang, L and Zhao, G and Yang, L}, title = {Alternating current electroosmotic flow in polyelectrolyte-grafted nanochannel.}, journal = {Colloids and surfaces. B, Biointerfaces}, volume = {147}, number = {}, pages = {234-241}, doi = {10.1016/j.colsurfb.2016.07.064}, pmid = {27518455}, issn = {1873-4367}, mesh = {Electricity ; *Electrochemistry ; Electroosmosis/*instrumentation ; *Nanotechnology ; Polyelectrolytes/*chemistry ; Static Electricity ; }, abstract = {In this work, we investigate the time periodic electroosmotic flow (EOF) of an electrolyte solution through a slit polyelectrolyte-grafted (PE-grafted) nanochannel under applied alternating current (AC) electrical field. The PE-grafted nanochannel is represented by a rigid surface covered by a polyelectrolyte layer (PEL) in a brush-like configuration. Under Debye-Hückel approximation, we obtain analytical solutions of electrical potential in decoupled regime of PE-grafted nanochannel, where the thickness of PEL is independent of the electrostatic effects triggered by polyelectrolyte charges. Based upon the electrical potential obtained above, we calculate EOF velocities with uniform and non-uniform drag coefficients for PE-grafted nanochannel and compare their results. The effects of pertinent dimensionless parameters on EOF velocity amplitude are discussed in detail. Moreover, the amplitude of EOF velocity in a PE-grafted nanochannel is compared with that in a rigid one. It is shown that larger EOF velocity and volume flow rate are found for a PE-grafted nanochannel. In addition, AC EOF velocity is further investigated. The oscillation of velocity reduces and is restricted within the region near the PEL-electrolyte interface for higher oscillating Reynolds number Re.}, }
@article {pmid27507620, year = {2016}, author = {Farutin, A and Piasecki, T and Słowicka, AM and Misbah, C and Wajnryb, E and Ekiel-Jeżewska, ML}, title = {Dynamics of flexible fibers and vesicles in Poiseuille flow at low Reynolds number.}, journal = {Soft matter}, volume = {12}, number = {35}, pages = {7307-7323}, doi = {10.1039/c6sm00819d}, pmid = {27507620}, issn = {1744-6848}, abstract = {The dynamics of flexible fibers and vesicles in unbounded planar Poiseuille flow at low Reynolds number is shown to exhibit similar basic features, when their equilibrium (moderate) aspect ratio is the same and vesicle viscosity contrast is relatively high. Tumbling, lateral migration, accumulation and shape evolution of these two types of flexible objects are analyzed numerically. The linear dependence of the accumulation position on relative bending rigidity, and other universal scalings are derived from the local shear flow approximation.}, }
@article {pmid27501748, year = {2016}, author = {Daghooghi, M and Borazjani, I}, title = {Self-propelled swimming simulations of bio-inspired smart structures.}, journal = {Bioinspiration &amp; biomimetics}, volume = {11}, number = {5}, pages = {056001}, doi = {10.1088/1748-3190/11/5/056001}, pmid = {27501748}, issn = {1748-3190}, mesh = {Animals ; Biomechanical Phenomena ; *Biomimetic Materials ; Eels/*physiology ; Locomotion ; Models, Biological ; Perciformes/*physiology ; Swimming/*physiology ; }, abstract = {This paper presents self-propelled swimming simulations of a foldable structure, whose folded configuration is a box. For self-locomotion through water the structure unfolds and undulates. To guide the design of the structure and understand how it should undulate to achieve either highest speed or maximize efficiency during locomotion, several kinematic parameters were systematically varied in the simulations: the wave type (standing wave versus traveling wave), the smoothness of undulations (smooth undulations versus undulations of rigid links), the mode of undulations (carangiform: mackerel-like versus anguilliform: eel-like undulations), and the maximum amplitude of undulations. We show that the swimmers with standing wave are slow and inefficient because they are not able to produce thrust using the added-mass mechanism. Among the tested types of undulation at low Reynolds number (Re) regime of [Formula: see text] (Strouhal number of about 1.0), structures that employ carangiform undulations can swim faster, whereas anguilliform swimmers are more economic, i.e., using less power they can swim a longer distance. Another finding of our simulations is that structures which are made of rigid links are typically less efficient (lower propulsive and power efficiencies and also lower swimming speed) compared with smoothly undulating ones because a higher added-mass force is generated by smooth undulations. The wake of all the swimmers bifurcated at the low Re regime because of the higher lateral relative to the axial velocity (high Strouhal number) that advects the vortices laterally creating a double row of vortices in the wake. In addition, we show that the wake cannot be used to predict the performance of the swimmers because the net force in each cycle is zero for self-propelled bodies and the pressure term is not negligible compared to the other terms.}, }
@article {pmid27493565, year = {2016}, author = {Smith, FT and Johnson, ER}, title = {Movement of a finite body in channel flow.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {472}, number = {2191}, pages = {20160164}, pmid = {27493565}, issn = {1364-5021}, abstract = {A body of finite size is moving freely inside, and interacting with, a channel flow. The description of this unsteady interaction for a comparatively dense thin body moving slowly relative to flow at medium-to-high Reynolds number shows that an inviscid core problem with vorticity determines much, but not all, of the dominant response. It is found that the lift induced on a body of length comparable to the channel width leads to differences in flow direction upstream and downstream on the body scale which are smoothed out axially over a longer viscous length scale; the latter directly affects the change in flow directions. The change is such that in any symmetric incident flow the ratio of slopes is found to be [Formula: see text], i.e. approximately 0.900969, independently of Reynolds number, wall shear stresses and velocity profile. The two axial scales determine the evolution of the body and the flow, always yielding instability. This unusual evolution and linear or nonlinear instability mechanism arise outside the conventional range of flow instability and are influenced substantially by the lateral positioning, length and axial velocity of the body.}, }
@article {pmid27480731, year = {2016}, author = {Akbar, NS and Butt, AW}, title = {Bio mathematical venture for the metallic nanoparticles due to ciliary motion.}, journal = {Computer methods and programs in biomedicine}, volume = {134}, number = {}, pages = {43-51}, doi = {10.1016/j.cmpb.2016.06.002}, pmid = {27480731}, issn = {1872-7565}, mesh = {Cilia/*physiology ; Computer Graphics ; Metal Nanoparticles/*chemistry ; *Models, Theoretical ; }, abstract = {BACKGROUND AND OBJECTIVES: The present investigation is associated with the contemporary study of viscous flow in a vertical tube with ciliary motion.<br><br>METHODS/RESULTS/CONCLUSIONS: The main flow problem has been modeled using cylindrical coordinates; flow equations are simplified to ordinary differential equations using longwave length and low Reynold's number approximation; and exact solutions have been obtained for velocity, pressure gradient and temperature. Results acquired are discussed graphically for better understanding. Streamlines for the velocity profile are plotted to discuss the trapping phenomenon. It is seen that with an increment in the Grashof number, the velocity of the governing fluids starts to decrease significantly.}, }
@article {pmid27475199, year = {2016}, author = {Padois, T and Laffay, P and Idier, A and Moreau, S}, title = {Tonal noise of a controlled-diffusion airfoil at low angle of attack and Reynolds number.}, journal = {The Journal of the Acoustical Society of America}, volume = {140}, number = {1}, pages = {EL113}, doi = {10.1121/1.4958916}, pmid = {27475199}, issn = {1520-8524}, abstract = {The acoustic signature of a controlled-diffusion airfoil immersed in a flow is experimentally characterized. Acoustic measurements have been carried out in an anechoic open-jet-wind-tunnel for low Reynolds numbers (from 5 × 10(4) to 4.3 × 10(5)) and several angles of attack. As with the NACA0012, the acoustic spectrum is dominated by discrete tones. These tonal behaviors are divided into three different regimes. The first one is characterized by a dominant primary tone which is steady over time, surrounded by secondary peaks. The second consists of two unsteady primary tones associated with secondary peaks and the third consists of a hump dominated by several small peaks. A wavelet study allows one to identify an amplitude modulation of the acoustic signal mainly for the unsteady tonal regime. This amplitude modulation is equal to the frequency interval between two successive tones. Finally, a bispectral analysis explains the presence of tones at higher frequencies.}, }
@article {pmid27462481, year = {2016}, author = {Zhang, W and Jiang, Y and Li, L and Chen, G}, title = {Effects of wall suction/blowing on two-dimensional flow past a confined square cylinder.}, journal = {SpringerPlus}, volume = {5}, number = {1}, pages = {985}, pmid = {27462481}, issn = {2193-1801}, abstract = {A numerical simulation is conducted to study the laminar flow past a square cylinder confined in a channel (the ratio of side length of the square to channel width is fixed at 1/4) subjected to a locally uniform blowing/suction speed placed at the top and bottom channel walls. Governing equations with boundary conditions are resolved using a finite volume method in pressure-velocity formulation. The flow patterns relevant to the critical spacing values are investigated. Numerical results show that wall blowing has a stabilizing effect on the flow, and the corresponding critical Reynolds number increases monotonically with increasing blowing velocity. Remarkably, steady asymmetric solutions and hysteretic mode transitions exist in a certain range of parameters (Reynolds number and suction speed) in the case of suction.}, }
@article {pmid27447509, year = {2016}, author = {Mathai, V and Calzavarini, E and Brons, J and Sun, C and Lohse, D}, title = {Microbubbles and Microparticles are Not Faithful Tracers of Turbulent Acceleration.}, journal = {Physical review letters}, volume = {117}, number = {2}, pages = {024501}, doi = {10.1103/PhysRevLett.117.024501}, pmid = {27447509}, issn = {1079-7114}, abstract = {We report on the Lagrangian statistics of acceleration of small (sub-Kolmogorov) bubbles and tracer particles with Stokes number St≪1 in turbulent flow. At a decreasing Reynolds number, the bubble accelerations show deviations from that of tracer particles; i.e., they deviate from the Heisenberg-Yaglom prediction and show a quicker decorrelation despite their small size and minute St. Using direct numerical simulations, we show that these effects arise due the drift of these particles through the turbulent flow. We theoretically predict this gravity-driven effect for developed isotropic turbulence, with the ratio of Stokes to Froude number or equivalently the particle drift velocity governing the enhancement of acceleration variance and the reductions in correlation time and intermittency. Our predictions are in good agreement with experimental and numerical results. The present findings are relevant to a range of scenarios encompassing tiny bubbles and droplets that drift through the turbulent oceans and the atmosphere. They also question the common usage of microbubbles and microdroplets as tracers in turbulence research.}, }
@article {pmid30404299, year = {2016}, author = {Lee, SJ and Kwon, K and Jeon, TJ and Kim, SM and Kim, D}, title = {Quantification of Vortex Generation Due to Non-Equilibrium Electrokinetics at the Micro/Nanochannel Interface: Particle Tracking Velocimetry.}, journal = {Micromachines}, volume = {7}, number = {7}, pages = {}, pmid = {30404299}, issn = {2072-666X}, support = {NRF 2014R1A2A2A01003618//National Research Foundation of Korea/ ; NRF-2016R1A2B4006987//National Research Foundation of Korea/ ; }, abstract = {We describe a quantitative study of vortex generation due to non-equilibrium electrokinetics near a micro/nanochannel interface. The microfluidic device is comprised of a microchannel with a set of nanochannels. These perm-selective nanochannels induce flow instability and thereby produce strong vortex generation. We performed tracking visualization of fluorescent microparticles to obtain velocity fields. Particle tracking enables the calculation of an averaged velocity field and the velocity fluctuations. We characterized the effect of applied voltages and electrolyte concentrations on vortex formation. The experimental results show that an increasing voltage or decreasing concentration results in a larger vortex region and a strong velocity fluctuation. We calculate the normalized velocity fluctuation-whose meaning is comparable to turbulent intensity-and we found that it is as high as 0.12. This value is indicative of very efficient mixing, albeit with a small Reynolds number.}, }
@article {pmid27436965, year = {2016}, author = {Muralidhar, SD and Pier, B and Scott, JF and Govindarajan, R}, title = {Flow around a rotating, semi-infinite cylinder in an axial stream.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {472}, number = {2190}, pages = {20150850}, pmid = {27436965}, issn = {1364-5021}, abstract = {This paper concerns steady, high-Reynolds-number flow around a semi-infinite, rotating cylinder placed in an axial stream and uses boundary-layer type of equations which apply even when the boundary-layer thickness is comparable to the cylinder radius, as indeed it is at large enough downstream distances. At large rotation rates, it is found that a wall jet appears over a certain range of downstream locations. This jet strengthens with increasing rotation, but first strengthens then weakens as downstream distance increases, eventually disappearing, so the flow recovers a profile qualitatively similar to a classical boundary layer. The asymptotic solution at large streamwise distances is obtained as an expansion in inverse powers of the logarithm of the distance. It is found that the asymptotic radial and axial velocity components are the same as for a non-rotating cylinder, to all orders in this expansion.}, }
@article {pmid27427674, year = {2016}, author = {Kristiawan, B and Kamal, S and Yanuar, }, title = {Thermo-Hydraulic Characteristics of Anatase Titania Nanofluids Flowing Through a Circular Conduit.}, journal = {Journal of nanoscience and nanotechnology}, volume = {16}, number = {6}, pages = {6078-6085}, doi = {10.1166/jnn.2016.10902}, pmid = {27427674}, issn = {1533-4880}, mesh = {*Hydrodynamics ; *Nanotechnology ; *Rheology ; *Temperature ; Titanium/*chemistry ; }, abstract = {The thermo-hydraulic characteristics of anatase titanium dioxide dispersed into distilled water with particle concentration of 0.1, 0.3, and 0.5 vol.% were investigated experimentally in this work. The influence of rheological behavior on hydrodynamic and convective heat transfer characteristics was evaluated under both laminar and turbulent flow conditions in a plain conduit and with twisted tape insert for twist ratio of 7. The nanofluids exhibited a strong shear-thinning behavior at low shear rate particularly higher particle concentration. The non-Newtonian titania nanofluids have also demonstrated a drag reduction phenomena in turbulent flow. At equal Reynolds number, the values of performance evaluation criterion in a conduit inserted a twisted tape were lower than those of in a plain conduit. It implies the unfavourable energy budget for twisted tape insert. The convective heat transfer coefficient does not gradually enhance with an increase of particle concentration. The flow features due mainly to the rheology of colloidal dispersions might be a reason for this phenomenon.}, }
@article {pmid27415315, year = {2016}, author = {Apaza, L and Sandoval, M}, title = {Ballistic behavior and trapping of self-driven particles in a Poiseuille flow.}, journal = {Physical review. E}, volume = {93}, number = {6}, pages = {062602}, doi = {10.1103/PhysRevE.93.062602}, pmid = {27415315}, issn = {2470-0053}, abstract = {We study the two- and three-dimensional dynamics of a Brownian self-driven particle at low Reynolds number in a Poiseuille flow. A deterministic analysis is also performed and we find that under certain conditions the swimmer becomes trapped, thus performing closed orbits as observed in related experiments. Further analysis enables us to provide an analytic expression to achieve this trapping phenomenon. We then turn to Brownian dynamics simulations, where we show the effect of a Poiseuille flow, self-propulsion, and confinement on the diffusion of the swimmer in both two and three dimensions. It is found that for long times the mean-square displacement (MSD) along the flow direction is always quadratic in time, whereas for shorter times (before the particle reaches the walls) its MSD has also a quartic time behavior. It is also found that self-propelled particles will spread less in a Poiseuille flow than passive ones under the same circumstances.}, }
@article {pmid27404898, year = {2016}, author = {Cole, BC and Marcus, GG and Parsa, S and Kramel, S and Ni, R and Voth, GA}, title = {Methods for Measuring the Orientation and Rotation Rate of 3D-printed Particles in Turbulence.}, journal = {Journal of visualized experiments : JoVE}, volume = {}, number = {112}, pages = {}, pmid = {27404898}, issn = {1940-087X}, mesh = {Anisotropy ; *Printing, Three-Dimensional ; }, abstract = {Experimental methods are presented for measuring the rotational and translational motion of anisotropic particles in turbulent fluid flows. 3D printing technology is used to fabricate particles with slender arms connected at a common center. Shapes explored are crosses (two perpendicular rods), jacks (three perpendicular rods), triads (three rods in triangular planar symmetry), and tetrads (four arms in tetrahedral symmetry). Methods for producing on the order of 10,000 fluorescently dyed particles are described. Time-resolved measurements of their orientation and solid-body rotation rate are obtained from four synchronized videos of their motion in a turbulent flow between oscillating grids with Rλ = 91. In this relatively low-Reynolds number flow, the advected particles are small enough that they approximate ellipsoidal tracer particles. We present results of time-resolved 3D trajectories of position and orientation of the particles as well as measurements of their rotation rates.}, }
@article {pmid27390636, year = {2016}, author = {Wang, B and Li, H}, title = {POD analysis of flow over a backward-facing step forced by right-angle-shaped plasma actuator.}, journal = {SpringerPlus}, volume = {5}, number = {1}, pages = {795}, pmid = {27390636}, issn = {2193-1801}, abstract = {PURPOSE: This study aims to present flow control over the backward-facing step with specially designed right-angle-shaped plasma actuator and analyzed the influence of various scales of flow structures on the Reynolds stress through snapshot proper orthogonal decomposition (POD).<br><br>METHODS: 2D particle image velocimetry measurements were conducted on region (x/h&#xa0;=&#xa0;0-2.25) and reattachment zone in the x-y plane over the backward-facing step at a Reynolds number of Re h &#xa0;=&#xa0;27,766 (based on step height [Formula: see text] and free stream velocity [Formula: see text]. The separated shear layer was excited by specially designed right-angle-shaped plasma actuator under the normalized excitation frequency St h &#xa0;&#x2248;&#xa0;0.345 along the 45&#xb0; direction. The spatial distribution of each Reynolds stress component was reconstructed using an increasing number of POD modes.<br><br>RESULTS: The POD analysis indicated that the flow dynamic downstream of the step was dominated by large-scale flow structures, which contributed to streamwise Reynolds stress and Reynolds shear stress. The intense Reynolds stress localized to a narrow strip within the shear layer was mainly affected by small-scale flow structures, which were responsible for the recovery of the Reynolds stress peak. With plasma excitation, a significant increase was obtained in the vertical Reynolds stress peak.<br><br>CONCLUSIONS: Under the dimensionless frequencies St h &#xa0;&#x2248;&#xa0;0.345 and [Formula: see text] which are based on the step height and momentum thickness, the effectiveness of the flow control forced by the plasma actuator along the 45&#xb0; direction was ordinary. Only the vertical Reynolds stress was significantly affected.}, }
@article {pmid27390635, year = {2016}, author = {Hossain, S and Kim, KY}, title = {Parametric investigation on mixing in a micromixer with two-layer crossing channels.}, journal = {SpringerPlus}, volume = {5}, number = {1}, pages = {794}, pmid = {27390635}, issn = {2193-1801}, abstract = {This work presents a parametric investigation on flow and mixing in a chaotic micromixer consisting of two-layer crossing channels proposed by Xia et al. (Lab Chip 5: 748-755, 2005). The flow and mixing performance were numerically analyzed using commercially available software ANSYS CFX-15.0, which solves the Navier-Stokes and mass conservation equations with a diffusion-convection model in a Reynolds number range from 0.2 to 40. A mixing index based on the variance of the mass fraction of the mixture was employed to evaluate the mixing performance of the micromixer. The flow structure in the channel was also investigated to identify the relationship with mixing performance. The mixing performance and pressure-drop were evaluated with two dimensionless geometric parameters, i.e., ratios of the sub-channel width to the main channel width and the channels depth to the main channel width. The results revealed that the mixing index at the exit of the micromixer increases with increase in the channel depth-to-width ratio, but decreases with increase in the sub-channel width to main channel width ratio. And, it was found that the mixing index could be increased up to 0.90 with variations of the geometric parameters at Re = 0.2, and the pressure drop was very sensitive to the geometric parameters.}, }
@article {pmid27378067, year = {2016}, author = {Manica, R and Klaseboer, E and Chan, DYC}, title = {The hydrodynamics of bubble rise and impact with solid surfaces.}, journal = {Advances in colloid and interface science}, volume = {235}, number = {}, pages = {214-232}, doi = {10.1016/j.cis.2016.06.010}, pmid = {27378067}, issn = {1873-3727}, abstract = {A bubble smaller than 1mm in radius rises along a straight path in water and attains a constant speed due to the balance between buoyancy and drag force. Depending on the purity of the system, within the two extreme limits of tangentially immobile or mobile boundary conditions at the air-water interface considerably different terminal speeds are possible. When such a bubble impacts on a horizontal solid surface and bounces, interesting physics can be observed. We study this physical phenomenon in terms of forces, which can be of colloidal, inertial, elastic, surface tension and viscous origins. Recent advances in high-speed photography allow for the observation of phenomena on the millisecond scale. Simultaneous use of such cameras to visualize both rise/deformation and the dynamics of the thin film drainage through interferometry are now possible. These experiments confirm that the drainage process obeys lubrication theory for the spectrum of micrometre to millimetre-sized bubbles that are covered in this review. We aim to bridge the colloidal perspective at low Reynolds numbers where surface forces are important to high Reynolds number fluid dynamics where the effect of the surrounding flow becomes important. A model that combines a force balance with lubrication theory allows for the quantitative comparison with experimental data under different conditions without any fitting parameter.}, }
@article {pmid27377152, year = {2016}, author = {Dogra, N and Izadi, H and Vanderlick, TK}, title = {Micro-motors: A motile bacteria based system for liposome cargo transport.}, journal = {Scientific reports}, volume = {6}, number = {}, pages = {29369}, pmid = {27377152}, issn = {2045-2322}, mesh = {Bacteria/metabolism ; *Bacterial Physiological Phenomena ; Biological Transport ; Fluorescence Resonance Energy Transfer ; Lipid Bilayers/*metabolism ; Unilamellar Liposomes/*metabolism ; }, abstract = {Biological micro-motors (microorganisms) have potential applications in energy utilization and nanotechnology. However, harnessing the power generated by such motors to execute desired work is extremely difficult. Here, we employ the power of motile bacteria to transport small, large, and giant unilamellar vesicles (SUVs, LUVs, and GUVs). Furthermore, we demonstrate bacteria-bilayer interactions by probing glycolipids inside the model membrane scaffold. Fluorescence Resonance Energy Transfer (FRET) spectroscopic and microscopic methods were utilized for understanding these interactions. We found that motile bacteria could successfully propel SUVs and LUVs with a velocity of 28 μm s(-1) and 13 μm s(-1), respectively. GUVs, however, displayed Brownian motion and could not be propelled by attached bacteria. Bacterial velocity decreased with the larger loaded cargo, which agrees with our calculations of loaded bacteria swimming at low Reynolds number.}, }
@article {pmid27370893, year = {2016}, author = {Takasugi, Y and Futagawa, K and Kazuhara, K and Morishita, S and Okuda, T}, title = {Roles of endotracheal tubes and slip joints in respiratory pressure loss: a laboratory study.}, journal = {Journal of anesthesia}, volume = {30}, number = {5}, pages = {789-795}, pmid = {27370893}, issn = {1438-8359}, mesh = {*Airway Resistance ; Humans ; Intubation, Intratracheal/*instrumentation ; Pressure ; }, abstract = {PURPOSE: The endotracheal tube (ETT) constitutes a significant component of total airway resistance. However, a discrepancy between measured and theoretical values has been reported in airway resistance through ETTs. The causes of the discrepancy were estimated by physical and rheological simulations.<br><br>METHODS: The pressure losses through total lengths of ETTs and slip joints under a volumetric flow rate of 30 L/min were measured, and the pressure losses through the tubular parts of ETTs with internal diameters (IDs) of 6.0-, 6.5-, 7.0-, 7.5-, and 8.0 mm were measured. The Reynolds number of each setting was calculated, and the pressure losses through the total length of the ETT, the tubular part, and the slip joint of each size of tube were estimated.<br><br>RESULTS: The Reynolds numbers were >5000 in all sizes of ETTs. Measured pressure losses were larger in small sized ETTs than in large sized ETTs-520.9 Pascals (Pa) in 6.0-mm ID and 136.4 Pa in 8.0-mm ID tubes. The measured pressure losses through the tubular part were comparable to the predicted values. The measured pressure losses through the slip joints were larger than the predicted values, and they accounted for approximately 25-40% of total pressure losses of the ETTs.<br><br>CONCLUSION: Especially in small sized tubes, the pressure loss through the slip joint accounts for a large percentage of the total pressure loss through the ETT. The pressure loss through the slip joint may play a role in the discrepancy between measured and theoretical pressure losses through ETTs.}, }
@article {pmid27344122, year = {2016}, author = {Yang, T and Wang, Q and Wu, L and Zhang, P and Zhao, G and Liu, Y}, title = {A mathematical model for the transfer of soil solutes to runoff under water scouring.}, journal = {The Science of the total environment}, volume = {569-570}, number = {}, pages = {332-341}, doi = {10.1016/j.scitotenv.2016.06.094}, pmid = {27344122}, issn = {1879-1026}, abstract = {The transfer of nutrients from soil to runoff often causes unexpected pollution in water bodies. In this study, a mathematical model that relates to the detachment of soil particles by water flow and the degree of mixing between overland flow and soil nutrients was proposed. The model assumes that the mixing depth is an integral of average water flow depth, and it was evaluated by experiments with three water inflow rates to bare soil surfaces and to surfaces with eight treatments of different stone coverages. The model predicted outflow rates were compared with the experimentally observed data to test the accuracy of the infiltration parameters obtained by curve fitting the models to the data. Further analysis showed that the comprehensive mixing coefficient (ke) was linearly correlated with Reynolds' number Re (R(2)>0.9), and this relationship was verified by comparing the simulated potassium concentration and cumulative mass with observed data, respectively. The best performance with the bias error analysis (Nash Sutcliffe coefficient of efficiency (NS), relative error (RE) and the coefficient of determination (R(2))) showed that the predicted data by the proposed model was in good agreement with the measured data. Thus the model can be used to guide soil-water and fertilization management to minimize nutrient runoff from cropland.}, }
@article {pmid30404283, year = {2016}, author = {Lee, SJ and Jeon, TJ and Kim, SM and Kim, D}, title = {Quantification of Vortex Generation Due to Non-Equilibrium Electrokinetics at the Micro/Nanochannel Interface: Spectral Analysis.}, journal = {Micromachines}, volume = {7}, number = {7}, pages = {}, pmid = {30404283}, issn = {2072-666X}, support = {2009-0083501//National Research Foundation of Korea/ ; NRF-2012-0009578//National Research Foundation of Korea/ ; Research Grant//Inha University/ ; }, abstract = {We report on our investigation of a low Reynolds number non-equilibrium electrokinetic flow in a micro/nanochannel platform. Non-equilibrium electrokinetic phenomena include so-called concentration polarization in a moderate electric field and vortex formation in a high electric field. We conducted a spectral analysis of non-equilibrium electrokinetic vortices at a micro/nanochannel interface. We found that periodic vortices are formed while the frequency varies with the applied voltages and solution concentrations. At a frequency as high as 60 Hz, vortex generation was obtained with the strongest electric field and the lowest concentration. The power spectra show increasing frequency with increasing voltage or decreasing concentration. We expect that our spectral analysis results will be useful for micromixer developers in the micromachine research field.}, }
@article {pmid27319152, year = {2016}, author = {Hahn, T and Klemm, A and Ziesse, P and Harms, K and Wach, W and Rupp, S and Hirth, T and Zibek, S}, title = {Optimization and Scale-up of Inulin Extraction from Taraxacum kok-saghyz roots.}, journal = {Natural product communications}, volume = {11}, number = {5}, pages = {689-692}, pmid = {27319152}, issn = {1934-578X}, mesh = {Chemical Fractionation/*methods ; Inulin/*isolation &amp; purification ; Plant Roots/chemistry ; Taraxacum/*chemistry ; }, abstract = {The optimization and scale-up of inulin extraction from Taraxacum kok-saghyz Rodin was successfully performed. Evaluating solubility investigations, the extraction temperature was fixed at 85 degrees C. The inulin stability regarding degradation or hydrolysis could be confirmed by extraction in the presence of model inulin. Confirming stability at the given conditions the isolation procedure was transferred from a 1 L- to a 1 m3-reactor. The Reynolds number was selected as the relevant dimensionless number that has to remain constant in both scales. The stirrer speed in the large scale was adjusted to 3.25 rpm regarding a 300 rpm stirrer speed in the 1 L-scale and relevant physical and process engineering parameters. Assumptions were confirmed by approximately homologous extraction kinetics in both scales. Since T. kok-saghyz is in the focus of research due to its rubber content side-product isolation from residual biomass it is of great economic interest. Inulin is one of these additional side-products that can be isolated in high quantity (- 35% of dry mass) and with a high average degree of polymerization (15.5) in large scale with a purity of 77%.}, }
@article {pmid27307513, year = {2016}, author = {Secchi, E and Rusconi, R and Buzzaccaro, S and Salek, MM and Smriga, S and Piazza, R and Stocker, R}, title = {Intermittent turbulence in flowing bacterial suspensions.}, journal = {Journal of the Royal Society, Interface}, volume = {13}, number = {119}, pages = {}, pmid = {27307513}, issn = {1742-5662}, mesh = {Bacillus subtilis/*physiology ; Gastrointestinal Microbiome/physiology ; Humans ; Locomotion/*physiology ; Suspensions ; }, abstract = {Dense suspensions of motile bacteria, possibly including the human gut microbiome, exhibit collective dynamics akin to those observed in classic, high Reynolds number turbulence with important implications for chemical and biological transport, yet this analogy has remained primarily qualitative. Here, we present experiments in which a dense suspension of Bacillus subtilis bacteria was flowed through microchannels and the velocity statistics of the flowing suspension were quantified using a recently developed velocimetry technique coupled with vortex identification methods. Observations revealed a robust intermittency phenomenon, whereby the average velocity profile of the suspension fluctuated between a plug-like flow and a parabolic flow profile. This intermittency is a hallmark of the onset of classic turbulence and Lagrangian tracking revealed that it here originates from the presence of transient vortices in the active, collective motion of the bacteria locally reinforcing the externally imposed flow. These results link together two entirely different manifestations of turbulence and show the potential of the microfluidic approach to mimic the environment characteristic of certain niches of the human microbiome.}, }
@article {pmid27300988, year = {2016}, author = {Lagubeau, G and Grosjean, G and Darras, A and Lumay, G and Hubert, M and Vandewalle, N}, title = {Statics and dynamics of magnetocapillary bonds.}, journal = {Physical review. E}, volume = {93}, number = {5}, pages = {053117}, doi = {10.1103/PhysRevE.93.053117}, pmid = {27300988}, issn = {2470-0053}, abstract = {When ferromagnetic particles are suspended at an interface under magnetic fields, dipole-dipole interactions compete with capillary attraction. This combination of forces has recently given promising results towards controllable self-assemblies as well as low-Reynolds-number swimming systems. The elementary unit of these assemblies is a pair of particles. Although equilibrium properties of this interaction are well described, the dynamics remain unclear. In this paper, the properties of magnetocapillary bonds are determined by probing them with magnetic perturbations. Two deformation modes are evidenced and discussed. These modes exhibit resonances whose frequencies can be detuned to generate nonreciprocal motion. A model is proposed that can become the basis for elaborate collective behaviors.}, }
@article {pmid27300987, year = {2016}, author = {Verjus, R and Angilella, JR}, title = {Critical Stokes number for the capture of inertial particles by recirculation cells in two-dimensional quasisteady flows.}, journal = {Physical review. E}, volume = {93}, number = {5}, pages = {053116}, doi = {10.1103/PhysRevE.93.053116}, pmid = {27300987}, issn = {2470-0053}, abstract = {Inertial particles are often observed to be trapped, temporarily or permanently, by recirculation cells which are ubiquitous in natural or industrial flows. In the limit of small particle inertia, determining the conditions of trapping is a challenging task, as it requires a large number of numerical simulations or experiments to test various particle sizes or densities. Here, we investigate this phenomenon analytically and numerically in the case of heavy particles (e.g., aerosols) at low Reynolds number, to derive a trapping criterion that can be used both in analytical and numerical velocity fields. The resulting criterion allows one to predict the characteristics of trapped particles as soon as single-phase simulations of the flow are performed. Our analysis is valid for two-dimensional particle-laden flows in the vertical plane, in the limit where the particle inertia, the free-fall terminal velocity, and the flow unsteadiness can be treated as perturbations. The weak unsteadiness of the flow generally induces a chaotic tangle near heteroclinic or homoclinic cycles if any, leading to the apparent diffusion of fluid elements through the boundary of the cell. The critical particle Stokes number St_{c} below which aerosols also enter and exit the cell in a complex manner has been derived analytically, in terms of the flow characteristics. It involves the nondimensional curvature-weighted integral of the squared velocity of the steady fluid flow along the dividing streamline of the recirculation cell. When the flow is unsteady and St>St_{c}, a regular motion takes place due to gravity and centrifugal effects, like in the steady case. Particles driven towards the interior of the cell are trapped permanently. In contrast, when the flow is unsteady and St<St_{c}, particles wander in a chaotic manner in the vicinity of the border of the cell, and can escape the cell.}, }
@article {pmid27300823, year = {2016}, author = {Shishkina, O}, title = {Momentum and heat transport scalings in laminar vertical convection.}, journal = {Physical review. E}, volume = {93}, number = {5}, pages = {051102}, doi = {10.1103/PhysRevE.93.051102}, pmid = {27300823}, issn = {2470-0053}, abstract = {We derive the dependence of the Reynolds number Re and the Nusselt number Nu on the Rayleigh number Ra and the Prandtl number Pr in laminar vertical convection (VC), where a fluid is confined between two differently heated isothermal vertical walls. The boundary layer equations in laminar VC yield two limiting scaling regimes: Nu∼Pr^{1/4}Ra^{1/4}, Re∼Pr^{-1/2}Ra^{1/2} for Pr≪1 and Nu∼Pr^{0}Ra^{1/4}, Re∼Pr^{-1}Ra^{1/2} for Pr≫1. These theoretical results are in excellent agreement with direct numerical simulations for Ra from 10^{5} to 10^{10} and Pr from 10^{-2} to 30. The transition between the regimes takes place for Pr around 10^{-1}.}, }
@article {pmid27289034, year = {2016}, author = {Kim, S and Ma, Y and Agrawal, P and Attinger, D}, title = {How important is it to consider target properties and hematocrit in bloodstain pattern analysis?.}, journal = {Forensic science international}, volume = {266}, number = {}, pages = {178-184}, doi = {10.1016/j.forsciint.2016.05.015}, pmid = {27289034}, issn = {1872-6283}, mesh = {*Blood Stains ; Blood Viscosity ; Forensic Sciences/*standards ; Hematocrit ; Humans ; Models, Biological ; }, abstract = {Trajectory reconstruction from inspection of bloodstain patterns is relevant to crime scene investigation. While the influence of target properties on trajectory reconstruction has been often qualitatively discussed, it has rarely been quantified. Similarly, a few impact studies measure the viscosity of the blood used in impact experiments. In this work, the impact of blood drops is investigated on targets with a range of surface roughness and surface material. The maximum spreading is characterized using a spreading correlation, which relates the ratio of stain diameter to drop diameter with the non-dimensional numbers Reynolds number and Ohnesorge number. The process for obtaining individual spreading correlations for each of the target substrates and for measuring the viscosity of the respective blood samples is described extensively. The error in estimating the drop release height, associated with using an impact correlation unspecific to the target of interest, is estimated analytically and numerically using experimental data. A similar analysis is done when the hematocrit of the blood is assumed rather than measured. Both assumptions lead to significant errors in estimating the release height of a blood droplet.}, }
@article {pmid33154603, year = {2016}, author = {Goldstein, ME and Sescu, A and Duck, PW and Choudhari, M}, title = {Nonlinear wakes behind a row of elongated roughness elements.}, journal = {Journal of fluid mechanics}, volume = {796}, number = {}, pages = {516-557}, pmid = {33154603}, issn = {0022-1120}, support = {/ARMD/Aeronautics NASA/United States ; }, abstract = {This paper is concerned with the high Reynolds number flow over a spanwise-periodic array of roughness elements with interelement spacing of the order of the local boundary-layer thickness. While earlier work by Goldstein et al. (J. Fluid Mech., vol. 644, 2010, pp. 123-163) and Goldstein et al. (J. Fluid Mech., vol. 668, 2011, pp. 236-266) was mainly concerned with smaller roughness heights that produced relatively weak distortions of the downstream flow, the focus here is on extending the analysis to larger roughness heights and streamwise elongated planform shapes that together produce a qualitatively different, nonlinear behaviour of the downstream wakes. The roughness scale flow now has a novel triple-deck structure that is somewhat different from related studies that have previously appeared in the literature. The resulting flow is formally nonlinear in the intermediate wake region, where the streamwise distance is large compared to the roughness dimensions but small compared to the downstream distance from the leading edge, as well as in the far wake region where the streamwise length scale is of the order of the downstream distance from the leading edge. In contrast, the flow perturbations in both of these wake regions were strictly linear in the earlier work by Goldstein et al. (2010, 2011). This is an important difference because the nonlinear wake flow in the present case provides an appropriate basic state for studying the secondary instability and eventual breakdown into turbulence.}, }
@article {pmid27280084, year = {2016}, author = {Mahalingam, A and Gawandalkar, UU and Kini, G and Buradi, A and Araki, T and Ikeda, N and Nicolaides, A and Laird, JR and Saba, L and Suri, JS}, title = {Numerical analysis of the effect of turbulence transition on the hemodynamic parameters in human coronary arteries.}, journal = {Cardiovascular diagnosis and therapy}, volume = {6}, number = {3}, pages = {208-220}, pmid = {27280084}, issn = {2223-3652}, abstract = {BACKGROUND: Local hemodynamics plays an important role in atherogenesis and the progression of coronary atherosclerosis disease (CAD). The primary biological effect due to blood turbulence is the change in wall shear stress (WSS) on the endothelial cell membrane, while the local oscillatory nature of the blood flow affects the physiological changes in the coronary artery. In coronary arteries, the blood flow Reynolds number ranges from few tens to several hundreds and hence it is generally assumed to be laminar while calculating the WSS calculations. However, the pulsatile blood flow through coronary arteries under stenotic condition could result in transition from laminar to turbulent flow condition.<br><br>METHODS: In the present work, the onset of turbulent transition during pulsatile flow through coronary arteries for varying degree of stenosis (i.e., 0%, 30%, 50% and 70%) is quantitatively analyzed by calculating the turbulent parameters distal to the stenosis. Also, the effect of turbulence transition on hemodynamic parameters such as WSS and oscillatory shear index (OSI) for varying degree of stenosis is quantified. The validated transitional shear stress transport (SST) k-&#x3c9; model used in the present investigation is the best suited Reynolds averaged Navier-Stokes turbulence model to capture the turbulent transition. The arterial wall is assumed to be rigid and the dynamic curvature effect due to myocardial contraction on the blood flow has been neglected.<br><br>RESULTS: Our observations shows that for stenosis 50% and above, the WSSavg, WSSmax and OSI calculated using turbulence model deviates from laminar by more than 10% and the flow disturbances seems to significantly increase only after 70% stenosis. Our model shows reliability and completely validated.<br><br>CONCLUSIONS: Blood flow through stenosed coronary arteries seems to be turbulent in nature for area stenosis above 70% and the transition to turbulent flow begins from 50% stenosis.}, }
@article {pmid32802012, year = {2016}, author = {Yu, T and Qiu, H and Yang, J and Shao, Y and Tao, L}, title = {Mixing at double-Tee junctions with unequal pipe sizes in water distribution systems.}, journal = {Water science &amp; technology, water supply}, volume = {16}, number = {6}, pages = {1595-1602}, pmid = {32802012}, issn = {1607-0798}, support = {EPA999999/ImEPA/Intramural EPA/United States ; }, abstract = {Pipe flow mixing with various solute concentrations and flow rates at pipe junctions is investigated. The degree of mixing affects contaminant spread in a water distribution system, and many studies have focused on mixing at the cross junctions; however, only a few have focused on double-Tee junctions of unequal pipe diameters. To investigate the solute mixing at such junctions, a series of experiments was conducted in a turbulent regime (Re = 12,500-50,000) with different Reynolds number ratios and connecting pipe lengths. Dimensionless outlet concentrations were found to depend on mixing mechanism at the impinging interface of junctions, where junctions with a larger pipe diameter ratio were associated with more complete mixing. Further, the inlet Reynolds number ratio affected mixing more strongly than the outlet Reynolds number ratio. Finally, the dimensionless connecting pipe length in a double-Tee played an important and complicated role in the flow mixing. The results were used to develop two-dimensional isopleth maps for the calculation of normalized north outlet concentrations.}, }
@article {pmid27190567, year = {2016}, author = {Zhou, R and Wang, C}, title = {Multiphase ferrofluid flows for micro-particle focusing and separation.}, journal = {Biomicrofluidics}, volume = {10}, number = {3}, pages = {034101}, pmid = {27190567}, issn = {1932-1058}, abstract = {Ferrofluids have demonstrated great potential for a variety of manipulations of diamagnetic (or non-magnetic) micro-particles/cells in microfluidics, including sorting, focusing, and enriching. By utilizing size dependent magnetophoresis velocity, most of the existing techniques employ single phase ferrofluids to push the particles towards the channel walls. In this work, we demonstrate a novel strategy for focusing and separating diamagnetic micro-particles by using the laminar fluid interface of two co-flowing fluids-a ferrofluid and a non-magnetic fluid. Next to the microfluidic channel, microscale magnets are fabricated to generate strong localized magnetic field gradients and forces. Due to the magnetic force, diamagnetic particles suspended in the ferrofluid phase migrate across the ferrofluid stream at the size-dependent velocities. Because of the low Reynolds number and high Péclet number associated with the flow, the fluid interface is sharp and stable. When the micro-particles migrate to the interface, they are accumulated near the interface, resulting in effective focusing and separation of particles. We investigated several factors that affect the focusing and separation efficiency, including susceptibility of the ferrofluid, distance between the microfluidic channel and microscale magnet, and width of the microfluidic channel. This concept can be extended to multiple fluid interfaces. For example, a complete separation of micro-particles was demonstrated by using a three-stream multiphase flow configuration.}, }
@article {pmid27183101, year = {2016}, author = {Wada, Y and Koyama, D and Nakamura, K}, title = {Numerical simulation of compressible fluid flow in an ultrasonic suction pump.}, journal = {Ultrasonics}, volume = {70}, number = {}, pages = {191-198}, doi = {10.1016/j.ultras.2016.05.005}, pmid = {27183101}, issn = {1874-9968}, abstract = {Characteristics of an ultrasonic suction pump that uses a vibrating piston surface and a pipe are numerically simulated and compared with experimental results. Fluid analysis based on the finite-difference time-domain (FDTD) routine is performed, where the nonlinear term and the moving fluid-surface boundary condition are considered. As a result, the suction mechanism of the pump is found to be similar to that of a check valve, where the gap is open during the inflow phase, and it is nearly closed during the outflow phase. The effects of Reynolds number, vibration amplitude and gap thickness on the pump performance are analyzed. The calculated result is in good agreement with the previously measured results.}, }
@article {pmid27176524, year = {2016}, author = {Maiden, MD and Lowman, NK and Anderson, DV and Schubert, ME and Hoefer, MA}, title = {Observation of Dispersive Shock Waves, Solitons, and Their Interactions in Viscous Fluid Conduits.}, journal = {Physical review letters}, volume = {116}, number = {17}, pages = {174501}, doi = {10.1103/PhysRevLett.116.174501}, pmid = {27176524}, issn = {1079-7114}, abstract = {Dispersive shock waves and solitons are fundamental nonlinear excitations in dispersive media, but dispersive shock wave studies to date have been severely constrained. Here, we report on a novel dispersive hydrodynamic test bed: the effectively frictionless dynamics of interfacial waves between two high viscosity contrast, miscible, low Reynolds number Stokes fluids. This scenario is realized by injecting from below a lighter, viscous fluid into a column filled with high viscosity fluid. The injected fluid forms a deformable pipe whose diameter is proportional to the injection rate, enabling precise control over the generation of symmetric interfacial waves. Buoyancy drives nonlinear interfacial self-steepening, while normal stresses give rise to the dispersion of interfacial waves. Extremely slow mass diffusion and mass conservation imply that the interfacial waves are effectively dissipationless. This enables high fidelity observations of large amplitude dispersive shock waves in this spatially extended system, found to agree quantitatively with a nonlinear wave averaging theory. Furthermore, several highly coherent phenomena are investigated including dispersive shock wave backflow, the refraction or absorption of solitons by dispersive shock waves, and the multiphase merging of two dispersive shock waves. The complex, coherent, nonlinear mixing of dispersive shock waves and solitons observed here are universal features of dissipationless, dispersive hydrodynamic flows.}, }
@article {pmid27176410, year = {2016}, author = {Mandal, S and Bandopadhyay, A and Chakraborty, S}, title = {Effect of surface charge convection and shape deformation on the dielectrophoretic motion of a liquid drop.}, journal = {Physical review. E}, volume = {93}, number = {}, pages = {043127}, doi = {10.1103/PhysRevE.93.043127}, pmid = {27176410}, issn = {2470-0053}, abstract = {The dielectrophoretic motion and shape deformation of a Newtonian liquid drop in an otherwise quiescent Newtonian liquid medium in the presence of an axisymmetric nonuniform dc electric field consisting of uniform and quadrupole components is investigated. The theory put forward by Feng [J. Q. Feng, Phys. Rev. E 54, 4438 (1996)10.1103/PhysRevE.54.4438] is generalized by incorporating the following two nonlinear effects-surface charge convection and shape deformation-towards determining the drop velocity. This two-way coupled moving boundary problem is solved analytically by considering small values of electric Reynolds number (ratio of charge relaxation time scale to the convection time scale) and electric capillary number (ratio of electrical stress to the surface tension) under the framework of the leaky dielectric model. We focus on investigating the effects of charge convection and shape deformation for different drop-medium combinations. A perfectly conducting drop suspended in a leaky (or perfectly) dielectric medium always deforms to a prolate shape and this kind of shape deformation always augments the dielectrophoretic drop velocity. For a perfectly dielectric drop suspended in a perfectly dielectric medium, the shape deformation leads to either increase (for prolate shape) or decrease (for oblate shape) in the dielectrophoretic drop velocity. Both surface charge convection and shape deformation affect the drop motion for leaky dielectric drops. The combined effect of these can significantly increase or decrease the dielectrophoretic drop velocity depending on the electrohydrodynamic properties of both the liquids and the relative strength of the electric Reynolds number and electric capillary number. Finally, comparison with the existing experiments reveals better agreement with the present theory.}, }
@article {pmid27176408, year = {2016}, author = {Koens, L and Lauga, E}, title = {Rotation of slender swimmers in isotropic-drag media.}, journal = {Physical review. E}, volume = {93}, number = {}, pages = {043125}, doi = {10.1103/PhysRevE.93.043125}, pmid = {27176408}, issn = {2470-0053}, abstract = {The drag anisotropy of slender filaments is a critical physical property allowing swimming in low-Reynolds number flows, and without it linear translation is impossible. Here we show that, in contrast, net rotation can occur under isotropic drag. We first demonstrate this result formally by considering the consequences of the force- and torque-free conditions on swimming bodies and we then illustrate it with two examples (a simple swimmers made of three rods and a model bacterium with two helical flagellar filaments). Our results highlight the different role of hydrodynamic forces in generating translational versus rotational propulsion.}, }
@article {pmid27176402, year = {2016}, author = {Hawkins, C and Angheluta, L and Krotkiewski, M and Jamtveit, B}, title = {Reynolds-number dependence of the longitudinal dispersion in turbulent pipe flow.}, journal = {Physical review. E}, volume = {93}, number = {}, pages = {043119}, doi = {10.1103/PhysRevE.93.043119}, pmid = {27176402}, issn = {2470-0053}, abstract = {In Taylor's theory, the longitudinal dispersion in turbulent pipe flows approaches, on long time scales, a diffusive behavior with a constant diffusivity K_{L}, which depends empirically on the Reynolds number Re. We show that the dependence on Re can be determined from the turbulent energy spectrum. By using the intimate connection between the friction factor and the longitudinal dispersion in wall-bounded turbulence, we predict different asymptotic scaling laws of K_{L}(Re) depending on the different turbulent cascades in two-dimensional turbulence. We also explore numerically the K_{L}(Re) dependence in turbulent channel flows with smooth and rough walls using a lattice Boltzmann method.}, }
@article {pmid27176396, year = {2016}, author = {Cappanera, L and Guermond, JL and Léorat, J and Nore, C}, title = {Two spinning ways for precession dynamo.}, journal = {Physical review. E}, volume = {93}, number = {}, pages = {043113}, doi = {10.1103/PhysRevE.93.043113}, pmid = {27176396}, issn = {2470-0053}, abstract = {It is numerically demonstrated by means of a magnetohydrodynamic code that precession can trigger dynamo action in a cylindrical container. Fixing the angle between the spin and the precession axis to be 1/2π, two limit configurations of the spinning axis are explored: either the symmetry axis of the cylinder is parallel to the spin axis (this configuration is henceforth referred to as the axial spin case), or it is perpendicular to the spin axis (this configuration is referred to as the equatorial spin case). In both cases, the centro-symmetry of the flow breaks when the kinetic Reynolds number increases. Equatorial spinning is found to be more efficient in breaking the centro-symmetry of the flow. In both cases, the average flow in the reference frame of the mantle converges to a counter-rotation with respect to the spin axis as the Reynolds number grows. We find a scaling law for the average kinetic energy in term of the Reynolds number in the axial spin case. In the equatorial spin case, the unsteady asymmetric flow is shown to be capable of sustaining dynamo action in the linear and nonlinear regimes. The magnetic field is mainly dipolar in the equatorial spin case, while it is is mainly quadrupolar in the axial spin case.}, }
@article {pmid27176354, year = {2016}, author = {Goldfriend, T and Diamant, H and Witten, TA}, title = {Hydrodynamic interactions between two forced objects of arbitrary shape. II. Relative translation.}, journal = {Physical review. E}, volume = {93}, number = {}, pages = {042609}, doi = {10.1103/PhysRevE.93.042609}, pmid = {27176354}, issn = {2470-0053}, abstract = {We study the relative translation of two arbitrarily shaped objects, caused by their hydrodynamic interaction as they are forced through a viscous fluid in the limit of zero Reynolds number. It is well known that in the case of two rigid spheres in an unbounded fluid, the hydrodynamic interaction does not produce relative translation. More generally, such an effective pair-interaction vanishes in configurations with spatial inversion symmetry; for example, an enantiomorphic pair in mirror image positions has no relative translation. We show that the breaking of inversion symmetry by boundaries of the system accounts for the interactions between two spheres in confined geometries, as observed in experiments. The same general principle also provides new predictions for interactions in other object configurations near obstacles. We examine the time-dependent relative translation of two self-aligning objects, extending the numerical analysis of our preceding publication [Goldfriend, Diamant, and Witten, Phys. Fluids 27, 123303 (2015)]PHFLE61070-663110.1063/1.4936894. The interplay between the orientational interaction and the translational one, in most cases, leads over time to repulsion between the two objects. The repulsion is qualitatively different for self-aligning objects compared to the more symmetric case of uniform prolate spheroids. The separation between the two objects increases with time t as t^{1/3} in the former case, and more strongly, as t, in the latter.}, }
@article {pmid27168523, year = {2016}, author = {Cheng, X and Sun, M}, title = {Wing-kinematics measurement and aerodynamics in a small insect in hovering flight.}, journal = {Scientific reports}, volume = {6}, number = {}, pages = {25706}, pmid = {27168523}, issn = {2045-2322}, mesh = {Animals ; Biomechanical Phenomena ; Diptera/*physiology ; Flight, Animal/*physiology ; Time Factors ; Wings, Animal/anatomy &amp; histology/*physiology ; }, abstract = {Wing-motion of hovering small fly Liriomyza sativae was measured using high-speed video and flows of the wings calculated numerically. The fly used high wingbeat frequency (≈265 Hz) and large stroke amplitude (≈182°); therefore, even if its wing-length (R) was small (R ≈ 1.4 mm), the mean velocity of wing reached ≈1.5 m/s, the same as that of an average-size insect (R ≈ 3 mm). But the Reynolds number (Re) of wing was still low (≈40), owing to the small wing-size. In increasing the stroke amplitude, the outer parts of the wings had a "clap and fling" motion. The mean-lift coefficient was high, ≈1.85, several times larger than that of a cruising airplane. The partial "clap and fling" motion increased the lift by ≈7%, compared with the case of no aerodynamic interaction between the wings. The fly mainly used the delayed stall mechanism to generate the high-lift. The lift-to-drag ratio is only 0.7 (for larger insects, Re being about 100 or higher, the ratio is 1-1.2); that is, although the small fly can produce enough lift to support its weight, it needs to overcome a larger drag to do so.}, }
@article {pmid27166813, year = {2016}, author = {Monteith, CE and Brunner, ME and Djagaeva, I and Bielecki, AM and Deutsch, JM and Saxton, WM}, title = {A Mechanism for Cytoplasmic Streaming: Kinesin-Driven Alignment of Microtubules and Fast Fluid Flows.}, journal = {Biophysical journal}, volume = {110}, number = {9}, pages = {2053-2065}, pmid = {27166813}, issn = {1542-0086}, support = {R01 GM046295/GM/NIGMS NIH HHS/United States ; }, mesh = {Biomechanical Phenomena ; *Cytoplasmic Streaming ; *Hydrodynamics ; Kinesins/*metabolism ; *Mechanical Phenomena ; Microtubules/*metabolism ; *Models, Biological ; Movement ; Oocytes/cytology ; }, abstract = {The transport of cytoplasmic components can be profoundly affected by hydrodynamics. Cytoplasmic streaming in Drosophila oocytes offers a striking example. Forces on fluid from kinesin-1 are initially directed by a disordered meshwork of microtubules, generating minor slow cytoplasmic flows. Subsequently, to mix incoming nurse cell cytoplasm with ooplasm, a subcortical layer of microtubules forms parallel arrays that support long-range, fast flows. To analyze the streaming mechanism, we combined observations of microtubule and organelle motions with detailed mathematical modeling. In the fast state, microtubules tethered to the cortex form a thin subcortical layer and undergo correlated sinusoidal bending. Organelles moving in flows along the arrays show velocities that are slow near the cortex and fast on the inward side of the subcortical microtubule layer. Starting with fundamental physical principles suggested by qualitative hypotheses, and with published values for microtubule stiffness, kinesin velocity, and cytoplasmic viscosity, we developed a quantitative coupled hydrodynamic model for streaming. The fully detailed mathematical model and its simulations identify key variables that can shift the system between disordered (slow) and ordered (fast) states. Measurements of array curvature, wave period, and the effects of diminished kinesin velocity on flow rates, as well as prior observations on f-actin perturbation, support the model. This establishes a concrete mechanistic framework for the ooplasmic streaming process. The self-organizing fast phase is a result of viscous drag on kinesin-driven cargoes that mediates equal and opposite forces on cytoplasmic fluid and on microtubules whose minus ends are tethered to the cortex. Fluid moves toward plus ends and microtubules are forced backward toward their minus ends, resulting in buckling. Under certain conditions, the buckling microtubules self-organize into parallel bending arrays, guiding varying directions for fast plus-end directed fluid flows that facilitate mixing in a low Reynolds number regime.}, }
@article {pmid27145450, year = {2016}, author = {Xi, J and Si, XA and Kim, J and Zhang, Y and Jacob, RE and Kabilan, S and Corley, RA}, title = {Anatomical Details of the Rabbit Nasal Passages and Their Implications in Breathing, Air Conditioning, and Olfaction.}, journal = {Anatomical record (Hoboken, N.J. : 2007)}, volume = {299}, number = {7}, pages = {853-868}, pmid = {27145450}, issn = {1932-8494}, support = {R01 HL073598/HL/NHLBI NIH HHS/United States ; }, mesh = {*Air Conditioning ; Animals ; Computer Simulation ; Female ; Magnetic Resonance Imaging ; Nasal Cavity/*anatomy &amp; histology/*physiology ; Pulmonary Ventilation ; Rabbits ; *Respiration ; Smell/*physiology ; }, abstract = {The rabbit is commonly used as a laboratory animal for inhalation toxicology tests and detail knowledge of the rabbit airway morphometry is needed for outcome analysis or theoretical modeling. The objective of this study is to quantify the morphometric dimension of the nasal airway of a New Zealand white rabbit and to relate the morphology and functions through analytical and computational methods. Images of high-resolution MRI scans of the rabbit were processed to measure the axial distribution of the cross-sectional areas, perimeter, and complexity level. The lateral recess, which has functions other than respiration or olfaction, was isolated from the nasal airway and its dimension was quantified separately. A low Reynolds number turbulence model was implemented to simulate the airflow, heat transfer, vapor transport, and wall shear stress. Results of this study provide detailed morphological information of the rabbit that can be used in the studies of olfaction, inhalation toxicology, drug delivery, and physiology-based pharmacokinetics modeling. For the first time, we reported a spiral nasal vestibule that splits into three paths leading to the dorsal meatus, maxilloturbinate, and ventral meatus, respectively. Both non-dimensional functional analysis and CFD simulations suggested that the airflow in the rabbit nose is laminar and the unsteady effect is only significantly during sniffing. Due to the large surface-to-volume ratio, the maxilloturbinate is highly effective in warming and moistening the inhaled air to body conditions. The unique anatomical structure and respiratory airflow pattern may have important implications for designing new odorant detectors or electronic noses. Anat Rec, 299:853-868, 2016. © 2016 Wiley Periodicals, Inc.}, }
@article {pmid27136099, year = {2016}, author = {Li, S and Huai, W}, title = {United Formula for the Friction Factor in the Turbulent Region of Pipe Flow.}, journal = {PloS one}, volume = {11}, number = {5}, pages = {e0154408}, pmid = {27136099}, issn = {1932-6203}, mesh = {*Friction ; *Models, Theoretical ; }, abstract = {Friction factor is an important element in both flow simulations and river engineering. In hydraulics, studies on the friction factor in turbulent regions have been based on the concept of three flow regimes, namely, the fully smooth regime, the fully rough regime, and the transitional regime, since the establishment of the Nikuradze's chart. However, this study further demonstrates that combining the friction factor with Reynolds number yields a united formula that can scale the entire turbulent region. This formula is derived by investigating the correlation between friction in turbulent pipe flow and its influencing factors, i.e., Reynolds number and relative roughness. In the present study, the formulae of Blasius and Stricklerare modified to rearrange the implicit model of Tao. In addition, we derive a united explicit formula that can compute the friction factor in the entire turbulent regimes based on the asymptotic behavior of the improved Tao's model. Compared with the reported formulae of Nikuradze, the present formula exhibits higher computational accuracy for the original pipe experiment data of Nikuradze.}, }
@article {pmid27131850, year = {2016}, author = {Bocanegra Evans, H and Castillo, L}, title = {Index-matched measurements of the effect of cartilaginous rings on tracheobronchial flow.}, journal = {Journal of biomechanics}, volume = {49}, number = {9}, pages = {1601-1606}, doi = {10.1016/j.jbiomech.2016.03.043}, pmid = {27131850}, issn = {1873-2380}, mesh = {Bronchi/*physiology ; Cartilage/*anatomy &amp; histology ; Humans ; Hydrodynamics ; Rheology ; Trachea/*physiology ; }, abstract = {We present a comparison of the flow characteristics in an idealized smooth trachea model and a second model which has a roughness simulating cartilaginous rings. We use refractive index-matched particle image velocimetry (PIV) to measure the velocity field in a two-generation model of the trachea and main bronchi. The flow rate has a trachea-based Reynolds number Re=2800, which is comparable to a resting state. Our results show considerable differences between both cases, the most important of which is the size and magnitude of recirculation zones at the inlet of both bronchi. The smooth case shows a larger separation bubble at the bronchi entrance, which may retain aerosols and have different effects on particles of different sizes. Furthermore, the smooth case displays a higher vorticity along the bottom walls of the bronchi, while a higher vorticity is seen along the trachea walls in the ׳ringed׳ model. These findings suggest that modeling the trachea and main bronchi as smooth tubes may not be justified, since the flow conditions in lower generations will be affected by these differences.}, }
@article {pmid27127498, year = {2016}, author = {Brkić, D and Ćojbašić, &#x17d;}, title = {Intelligent Flow Friction Estimation.}, journal = {Computational intelligence and neuroscience}, volume = {2016}, number = {}, pages = {5242596}, pmid = {27127498}, issn = {1687-5273}, mesh = {*Friction ; *Hydrodynamics ; *Neural Networks, Computer ; }, abstract = {Nowadays, the Colebrook equation is used as a mostly accepted relation for the calculation of fluid flow friction factor. However, the Colebrook equation is implicit with respect to the friction factor (λ). In the present study, a noniterative approach using Artificial Neural Network (ANN) was developed to calculate the friction factor. To configure the ANN model, the input parameters of the Reynolds Number (Re) and the relative roughness of pipe (ε/D) were transformed to logarithmic scales. The 90,000 sets of data were fed to the ANN model involving three layers: input, hidden, and output layers with, 2, 50, and 1 neurons, respectively. This configuration was capable of predicting the values of friction factor in the Colebrook equation for any given values of the Reynolds number (Re) and the relative roughness (ε/D) ranging between 5000 and 10(8) and between 10(-7) and 0.1, respectively. The proposed ANN demonstrates the relative error up to 0.07% which had the high accuracy compared with the vast majority of the precise explicit approximations of the Colebrook equation.}, }
@article {pmid27121547, year = {2016}, author = {Lee, YJ and Lua, KB and Lim, TT and Yeo, KS}, title = {A quasi-steady aerodynamic model for flapping flight with improved adaptability.}, journal = {Bioinspiration &amp; biomimetics}, volume = {11}, number = {3}, pages = {036005}, doi = {10.1088/1748-3190/11/3/036005}, pmid = {27121547}, issn = {1748-3190}, mesh = {Air ; Aircraft/*instrumentation ; Animals ; Biomimetics/*instrumentation/methods ; Computer Simulation ; *Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Friction ; Miniaturization ; *Models, Theoretical ; Oscillometry/*instrumentation/methods ; Rheology/*instrumentation/methods ; Shear Strength ; Stress, Mechanical ; }, abstract = {An improved quasi-steady aerodynamic model for flapping wings in hover has been developed. The purpose of this model is to yield rapid predictions of lift generation and efficiency during the design phase of flapping wing micro air vehicles. While most existing models are tailored for a specific flow condition, the present model is applicable over a wider range of Reynolds number and Rossby number. The effects of wing aspect ratio and taper ratio are also considered. The model was validated by comparing against numerical simulations and experimental measurements. Wings with different geometries undergoing distinct kinematics at varying flow conditions were tested during validation. Generally, model predictions of mean force coefficients were within 10% of numerical simulation results, while the deviations in power coefficients could be up to 15%. The deviation is partly due to the model not taking into consideration the initial shedding of the leading-edge vortex and wing-wake interaction which are difficult to account under quasi-steady assumption. The accuracy of this model is comparable to other models in literature, which had to be specifically designed or tuned to a narrow range of operation. In contrast, the present model has the advantage of being applicable over a wider range of flow conditions without prior tuning or calibration, which makes it a useful tool for preliminary performance evaluations.}, }
@article {pmid27118897, year = {2016}, author = {Shyy, W and Kang, CK and Chirarattananon, P and Ravi, S and Liu, H}, title = {Aerodynamics, sensing and control of insect-scale flapping-wing flight.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {472}, number = {2186}, pages = {20150712}, pmid = {27118897}, issn = {1364-5021}, abstract = {There are nearly a million known species of flying insects and 13 000 species of flying warm-blooded vertebrates, including mammals, birds and bats. While in flight, their wings not only move forward relative to the air, they also flap up and down, plunge and sweep, so that both lift and thrust can be generated and balanced, accommodate uncertain surrounding environment, with superior flight stability and dynamics with highly varied speeds and missions. As the size of a flyer is reduced, the wing-to-body mass ratio tends to decrease as well. Furthermore, these flyers use integrated system consisting of wings to generate aerodynamic forces, muscles to move the wings, and sensing and control systems to guide and manoeuvre. In this article, recent advances in insect-scale flapping-wing aerodynamics, flexible wing structures, unsteady flight environment, sensing, stability and control are reviewed with perspective offered. In particular, the special features of the low Reynolds number flyers associated with small sizes, thin and light structures, slow flight with comparable wind gust speeds, bioinspired fabrication of wing structures, neuron-based sensing and adaptive control are highlighted.}, }
@article {pmid27108375, year = {2016}, author = {Sultan, T}, title = {Numerical study of the effects of lamp configuration and reactor wall roughness in an open channel water disinfection UV reactor.}, journal = {Chemosphere}, volume = {155}, number = {}, pages = {170-179}, doi = {10.1016/j.chemosphere.2016.04.050}, pmid = {27108375}, issn = {1879-1298}, mesh = {Disinfection/*methods ; *Ultraviolet Rays ; Water Microbiology ; Water Purification/*instrumentation/methods ; }, abstract = {This article describes the assessment of a numerical procedure used to determine the UV lamp configuration and surface roughness effects on an open channel water disinfection UV reactor. The performance of the open channel water disinfection UV reactor was numerically analyzed on the basis of the performance indictor reduction equivalent dose (RED). The RED values were calculated as a function of the Reynolds number to monitor the performance. The flow through the open channel UV reactor was modelled using a k-ε model with scalable wall function, a discrete ordinate (DO) model for fluence rate calculation, a volume of fluid (VOF) model to locate the unknown free surface, a discrete phase model (DPM) to track the pathogen transport, and a modified law of the wall to incorporate the reactor wall roughness effects. The performance analysis was carried out using commercial CFD software (ANSYS Fluent 15.0). Four case studies were analyzed based on open channel UV reactor type (horizontal and vertical) and lamp configuration (parallel and staggered). The results show that lamp configuration can play an important role in the performance of an open channel water disinfection UV reactor. The effects of the reactor wall roughness were Reynolds number dependent. The proposed methodology is useful for performance optimization of an open channel water disinfection UV reactor.}, }
@article {pmid27104354, year = {2016}, author = {Aftab, SM and Mohd Rafie, AS and Razak, NA and Ahmad, KA}, title = {Turbulence Model Selection for Low Reynolds Number Flows.}, journal = {PloS one}, volume = {11}, number = {4}, pages = {e0153755}, pmid = {27104354}, issn = {1932-6203}, mesh = {*Models, Theoretical ; Viscosity ; }, abstract = {One of the major flow phenomena associated with low Reynolds number flow is the formation of separation bubbles on an airfoil's surface. NACA4415 airfoil is commonly used in wind turbines and UAV applications. The stall characteristics are gradual compared to thin airfoils. The primary criterion set for this work is the capture of laminar separation bubble. Flow is simulated for a Reynolds number of 120,000. The numerical analysis carried out shows the advantages and disadvantages of a few turbulence models. The turbulence models tested were: one equation Spallart Allmars (S-A), two equation SST K-ω, three equation Intermittency (γ) SST, k-kl-ω and finally, the four equation transition γ-Reθ SST. However, the variation in flow physics differs between these turbulence models. Procedure to establish the accuracy of the simulation, in accord with previous experimental results, has been discussed in detail.}, }
@article {pmid27078458, year = {2016}, author = {Johnson, PL and Meneveau, C}, title = {Large-deviation statistics of vorticity stretching in isotropic turbulence.}, journal = {Physical review. E}, volume = {93}, number = {3}, pages = {033118}, doi = {10.1103/PhysRevE.93.033118}, pmid = {27078458}, issn = {2470-0053}, abstract = {A key feature of three-dimensional fluid turbulence is the stretching and realignment of vorticity by the action of the strain rate. It is shown in this paper, using the cumulant-generating function, that the cumulative vorticity stretching along a Lagrangian path in isotropic turbulence obeys a large deviation principle. As a result, the relevant statistics can be described by the vorticity stretching Cramér function. This function is computed from a direct numerical simulation data set at a Taylor-scale Reynolds number of Re(λ)=433 and compared to those of the finite-time Lyapunov exponents (FTLE) for material deformation. As expected, the mean cumulative vorticity stretching is slightly less than that of the most-stretched material line (largest FTLE), due to the vorticity's preferential alignment with the second-largest eigenvalue of strain rate and the material line's preferential alignment with the largest eigenvalue. However, the vorticity stretching tends to be significantly larger than the second-largest FTLE, and the Cramér functions reveal that the statistics of vorticity stretching fluctuations are more similar to those of the largest FTLE. In an attempt to relate the vorticity stretching statistics to the vorticity magnitude probability density function in statistically stationary conditions, a model Kramers-Moyal equation is constructed using the statistics encoded in the Cramér function. The model predicts a stretched-exponential tail for the vorticity magnitude probability density function, with good agreement for the exponent but significant difference (35%) in the prefactor.}, }
@article {pmid27078456, year = {2016}, author = {De Santi, F and Fraternale, F and Tordella, D}, title = {Dispersive-to-nondispersive transition and phase-velocity transient for linear waves in plane wake and channel flows.}, journal = {Physical review. E}, volume = {93}, number = {3}, pages = {033116}, doi = {10.1103/PhysRevE.93.033116}, pmid = {27078456}, issn = {2470-0053}, abstract = {In this study we analyze the phase and group velocity of three-dimensional linear traveling waves in two sheared flows: the plane channel and the wake flows. This was carried out by varying the wave number over a large interval of values at a given Reynolds number inside the ranges 20-100, 1000-8000, for the wake and channel flow, respectively. Evidence is given about the possible presence of both dispersive and nondispersive effects which are associated with the long and short ranges of wavelength. We solved the Orr-Sommerfeld and Squire eigenvalue problem and observed the least stable mode. It is evident that, at low wave numbers, the least stable eigenmodes in the left branch of the spectrum behave in a dispersive manner. By contrast, if the wave number is above a specific threshold, a sharp dispersive-to-nondispersive transition can be observed. Beyond this transition, the dominant mode belongs to the right branch of the spectrum. The transient behavior of the phase velocity of small three-dimensional traveling waves was also considered. Having chosen the initial conditions, we then show that the shape of the transient highly depends on the transition wavelength threshold value. We show that the phase velocity can oscillate with a frequency which is equal to the frequency width of the eigenvalue spectrum. Furthermore, evidence of intermediate self-similarity is given for the perturbation field.}, }
@article {pmid27078455, year = {2016}, author = {Nedić, J and Tavoularis, S}, title = {Energy dissipation scaling in uniformly sheared turbulence.}, journal = {Physical review. E}, volume = {93}, number = {3}, pages = {033115}, doi = {10.1103/PhysRevE.93.033115}, pmid = {27078455}, issn = {2470-0053}, abstract = {The rate of turbulent kinetic energy dissipation in spatially developing, uniformly sheared turbulence is examined experimentally. In the far-downstream fully developed region of the flow, we confirm that the dissipation parameter C(ɛ) is constant. More importantly, however, we find two upstream regions where this parameter could be scaled with the local turbulent Reynolds number as C(ɛ)=ARe(λ)(α); the exponents in these two regions are, respectively, α=-0.6 and 0.5. The observed changes in scaling laws are explained by consideration of structural changes in the turbulence.}, }
@article {pmid27078453, year = {2016}, author = {Liang, H and Li, QX and Shi, BC and Chai, ZH}, title = {Lattice Boltzmann simulation of three-dimensional Rayleigh-Taylor instability.}, journal = {Physical review. E}, volume = {93}, number = {3}, pages = {033113}, doi = {10.1103/PhysRevE.93.033113}, pmid = {27078453}, issn = {2470-0053}, abstract = {In this paper, the three-dimensional (3D) Rayleigh-Taylor instability (RTI) with low Atwood number (A(t)=0.15) in a long square duct (12W × W × W) is studied by using a multiple-relaxation-time lattice Boltzmann (LB) multiphase model. The effect of the Reynolds number on the interfacial dynamics and bubble and spike amplitudes at late time is investigated in detail. The numerical results show that at sufficiently large Reynolds numbers, a sequence of stages in the 3D immiscible RTI can be observed, which includes the linear growth, terminal velocity growth, reacceleration, and chaotic development stages. At late stage, the RTI induces a very complicated topology structure of the interface, and an abundance of dissociative drops are also observed in the system. The bubble and spike velocities at late stage are unstable and their values have exceeded the predictions of the potential flow theory [V. N. Goncharov, Phys. Rev. Lett. 88, 134502 (2002)]. The acceleration of the bubble front is also measured and it is found that the normalized acceleration at late time fluctuates around a constant value of 0.16. When the Reynolds number is reduced to small values, some later stages cannot be reached sequentially. The interface becomes relatively smoothed and the bubble velocity at late time is approximate to a constant value, which coincides with the results of the extended Layzer model [S.-I. Sohn, Phys. Rev. E 80, 055302(R) (2009)] and the modified potential theory [R. Banerjee, L. Mandal, S. Roy, M. Khan, and M. R. Guptae, Phys. Plasmas 18, 022109 (2011)]. In our simulations, the Graphics Processing Unit (GPU) parallel computing is also used to relieve the massive computational cost.}, }
@article {pmid27078416, year = {2016}, author = {Jaju, SJ and Kumaran, V}, title = {Structure-rheology relationship in a sheared lamellar fluid.}, journal = {Physical review. E}, volume = {93}, number = {3}, pages = {032609}, doi = {10.1103/PhysRevE.93.032609}, pmid = {27078416}, issn = {2470-0053}, abstract = {The structure-rheology relationship in the shear alignment of a lamellar fluid is studied using a mesoscale model which provides access to the lamellar configurations and the rheology. Based on the equations and free energy functional, the complete set of dimensionless groups that characterize the system are the Reynolds number (ργL(2)/μ), the Schmidt number (μ/ρD), the Ericksen number (μγ/B), the interface sharpness parameter r, the ratio of the viscosities of the hydrophilic and hydrophobic parts μ(r), and the ratio of the system size and layer spacing (L/λ). Here, ρ and μ are the fluid density and average viscosity, γ is the applied strain rate, D is the coefficient of diffusion, B is the compression modulus, μ(r) is the maximum difference in the viscosity of the hydrophilic and hydrophobic parts divided by the average viscosity, and L is the system size in the cross-stream direction. The lattice Boltzmann method is used to solve the concentration and momentum equations for a two dimensional system of moderate size (L/λ=32) and for a low Reynolds number, and the other parameters are systematically varied to examine the qualitative features of the structure and viscosity evolution in different regimes. At low Schmidt numbers where mass diffusion is faster than momentum diffusion, there is fast local formation of randomly aligned domains with "grain boundaries," which are rotated by the shear flow to align along the extensional axis as time increases. This configuration offers a high resistance to flow, and the layers do not align in the flow direction even after 1000 strain units, resulting in a viscosity higher than that for an aligned lamellar phase. At high Schmidt numbers where momentum diffusion is fast, the shear flow disrupts layers before they are fully formed by diffusion, and alignment takes place by the breakage and reformation of layers by shear, resulting in defects (edge dislocations) embedded in a background of nearly aligned layers. At high Ericksen number where the viscous forces are large compared to the restoring forces due to layer compression and bending, shear tends to homogenize the concentration field, and the viscosity decreases significantly. At very high Ericksen number, shear even disrupts the layering of the lamellar phase. At low Ericksen number, shear results in the formation of well aligned layers with edge dislocations. However, these edge dislocations take a long time to anneal; the relatively small misalignment due to the defects results in a large increase in viscosity due to high layer stiffness and due to shear localization, because the layers between defects get pinned and move as a plug with no shear. An increase in the viscosity contrast between the hydrophilic and hydrophobic parts does not alter the structural characteristics during alignment. However, there is a significant increase in the viscosity, due to pinning of the layers between defects, which results in a plug flow between defects and a localization of the shear to a part of the domain.}, }
@article {pmid27078282, year = {2016}, author = {Haward, SJ and Poole, RJ and Alves, MA and Oliveira, PJ and Goldenfeld, N and Shen, AQ}, title = {Tricritical spiral vortex instability in cross-slot flow.}, journal = {Physical review. E}, volume = {93}, number = {3}, pages = {031101}, doi = {10.1103/PhysRevE.93.031101}, pmid = {27078282}, issn = {2470-0053}, support = {307499/ERC_/European Research Council/International ; }, abstract = {We examine fluid flow through cross-slot devices with various depth to width ratios α. At low Reynolds number, Re, flow is symmetric and a sharp boundary exists between the two incoming fluid streams. Above an α-dependent critical value, Re(c)(α), a steady symmetry-breaking bifurcation occurs and a spiral vortex structure develops. Order parameters characterizing the instability grow according to a sixth-order Landau potential, and show a progression from second- to first-order transitions as α increases beyond a tricritical value of α ≈ 0.55. Flow simulations indicate the instability is driven by vortex stretching at the stagnation point.}, }
@article {pmid27071538, year = {2016}, author = {Xiang, Y and Xue, Y and Lv, P and Li, D and Duan, H}, title = {Influence of fluid flow on the stability and wetting transition of submerged superhydrophobic surfaces.}, journal = {Soft matter}, volume = {12}, number = {18}, pages = {4241-4246}, doi = {10.1039/c6sm00302h}, pmid = {27071538}, issn = {1744-6848}, abstract = {Superhydrophobic surfaces have attracted great attention for drag reduction application. However, these surfaces are subject to instabilities, especially under fluid flow. In this work, we in situ examine the stability and wetting transition of underwater superhydrophobicity under laminar flow conditions by confocal microscopy. The absolute liquid pressure in the flow channel is regulated to acquire the pinned Cassie-Baxter and depinned metastable states. The subsequent dynamic evolution of the meniscus morphology in the two states under shear flow is monitored. It is revealed that fluid flow does not affect the pressure-mediated equilibrium states but accelerates the air exchange between entrapped air cavities and bulk water. A diffusion-based model with varying effective diffusion lengths is used to interpret the experimental data, which show a good agreement. The Sherwood number representing the convection-enhanced mass transfer coefficient is extracted from the data, and is found to follow a classic 1/3-power-law relation with the Reynolds number as has been discovered in channel flows with diffusive boundary conditions. The current work paves the way for designing durable superhydrophobic surfaces under flow conditions.}, }
@article {pmid27063642, year = {2016}, author = {Ishimoto, K}, title = {Hydrodynamic evolution of sperm swimming: Optimal flagella by a genetic algorithm.}, journal = {Journal of theoretical biology}, volume = {399}, number = {}, pages = {166-174}, doi = {10.1016/j.jtbi.2016.03.041}, pmid = {27063642}, issn = {1095-8541}, mesh = {*Algorithms ; Animals ; *Biological Evolution ; Flagella/*physiology ; *Hydrodynamics ; Male ; Models, Biological ; Sperm Motility/*physiology ; Spermatozoa/*physiology ; }, abstract = {Swimming performance of spermatozoa is an important index for the success of fertilization. For many years, numerous studies have reported the optimal swimming of flagellar organisms. Nevertheless, there is still a question as to which is optimal among planar, circular helical and ellipsoidal helical beating. In this paper, we use a genetic algorithm to investigate the beat pattern with the best swimming efficiency based on hydrodynamic dissipation and internal torque exertion. For the parameters considered, our results show that the planar beat is optimal for small heads and the helical flagellum is optimum for a larger heads, while the ellipsoidal beat is never optimal. Also, the genetic optimization reveals that the wavenumber and shape of wave envelope are relevant parameters, whereas the wave shape and head geometry have relatively minor effects on efficiency. The optimal beat with respect to the efficiency based on the internal torque exertion of an active elastic flagellum is characterized by a small-wavenumber and large-amplitude wave in a lower-viscosity medium. The obtained results on the optimal waveform are consistent with observations for planar waveforms, but in many respects, the results suggest the necessity of a detailed flagellar structure-fluid interaction to address whether real spermatozoa exhibit hydrodynamically efficient swimming. The evolutional optimization approach used in this study has distinguished biologically important parameters, and the methodology can potentially be applicable to various swimmers.}, }
@article {pmid27055766, year = {2016}, author = {Iasiello, M and Vafai, K and Andreozzi, A and Bianco, N}, title = {Analysis of non-Newtonian effects on Low-Density Lipoprotein accumulation in an artery.}, journal = {Journal of biomechanics}, volume = {49}, number = {9}, pages = {1437-1446}, doi = {10.1016/j.jbiomech.2016.03.017}, pmid = {27055766}, issn = {1873-2380}, mesh = {Arteries/*metabolism/physiology ; Diffusion ; Hemodynamics ; Humans ; Lipoproteins, LDL/*metabolism ; *Models, Cardiovascular ; Porosity ; Rheology ; Stress, Mechanical ; }, abstract = {In this work, non-Newtonian effects on Low-Density Lipoprotein (LDL) transport across an artery are analyzed with a multi-layer model. Four rheological models (Carreau, Carreau-Yasuda, power-law and Newtonian) are used for the blood flow through the lumen. For the non-Newtonian cases, the arterial wall is modeled with a generalized momentum equation. Convection-diffusion equation is used for the LDL transport through the lumen, while Staverman-Kedem-Katchalsky, combined with porous media equations, are used for the LDL transport through the wall. Results are presented in terms of filtration velocity, Wall Shear Stresses (WSS) and concentration profiles. It is shown that non-Newtonian effects on mass transport are negligible for a healthy intramural pressure value. Non-Newtonian effects increase slightly with intramural pressure, but Newtonian assumption can still be considered reliable. Effects of arterial size are also analyzed, showing that Newtonian assumption can be considered valid for both medium and large arteries, in predicting LDL deposition. Finally, non-Newtonian effects are also analyzed for an aorta-common iliac bifurcation, showing that Newtonian assumption is valid for mass transport at low Reynolds numbers. At a high Reynolds number, it has been shown that a non-Newtonian fluid model can have more impact due to the presence of flow recirculation.}, }
@article {pmid27042817, year = {2016}, author = {Beier, S and Ormiston, JA and Webster, MW and Cater, JE and Norris, SE and Medrano-Gracia, P and Young, AA and Cowan, BR}, title = {Dynamically scaled phantom phase contrast MRI compared to true-scale computational modeling of coronary artery flow.}, journal = {Journal of magnetic resonance imaging : JMRI}, volume = {44}, number = {4}, pages = {983-992}, doi = {10.1002/jmri.25240}, pmid = {27042817}, issn = {1522-2586}, mesh = {Blood Flow Velocity/*physiology ; Computer Simulation ; Coronary Circulation/*physiology ; Coronary Vessels/*diagnostic imaging/*physiology ; Equipment Design ; Equipment Failure Analysis ; Humans ; Image Interpretation, Computer-Assisted/methods ; Magnetic Resonance Angiography/*instrumentation/methods ; *Models, Cardiovascular ; *Phantoms, Imaging ; Reproducibility of Results ; Sensitivity and Specificity ; }, abstract = {PURPOSE: To examine the feasibility of combining computational fluid dynamics (CFD) and dynamically scaled phantom phase-contrast magnetic resonance imaging (PC-MRI) for coronary flow assessment.<br><br>MATERIALS AND METHODS: Left main coronary bifurcations segmented from computed tomography with bifurcation angles of 33&#xb0;, 68&#xb0;, and 117&#xb0; were scaled-up &#x223c;7&#xd7; and 3D printed. Steady coronary flow was reproduced in these phantoms using the principle of dynamic similarity to preserve the true-scale Reynolds number, using blood analog fluid and a pump circuit in a 3T MRI scanner. After PC-MRI acquisition, the data were segmented and coregistered to CFD simulations of identical, but true-scale geometries. Velocities at the inlet region were extracted from the PC-MRI to define the CFD inlet boundary condition.<br><br>RESULTS: The PC-MRI and CFD flow data agreed well, and comparison showed: 1) small velocity magnitude discrepancies (2-8%); 2) with a Spearman's rank correlation &#x2265;0.72; and 3) a velocity vector correlation (including direction) of r(2) &#x2265; 0.82. The highest agreement was achieved for high velocity regions with discrepancies being located in slow or recirculating zones with low MRI signal-to-noise ratio (SNRv) in tortuous segments and large bifurcating vessels.<br><br>CONCLUSION: Characterization of coronary flow using a dynamically scaled PC-MRI phantom flow is feasible and provides higher resolution than current in vivo or true-scale in vitro methods, and may be used to provide boundary conditions for true-scale CFD simulations. J. MAGN. RESON. IMAGING 2016;44:983-992.}, }
@article {pmid27037586, year = {2016}, author = {Barsanti, L and Coltelli, P and Evangelista, V and Frassanito, AM and Gualtieri, P}, title = {Swimming patterns of the quadriflagellate Tetraflagellochloris mauritanica (Chlamydomonadales, Chlorophyceae).}, journal = {Journal of phycology}, volume = {52}, number = {2}, pages = {209-218}, doi = {10.1111/jpy.12384}, pmid = {27037586}, issn = {1529-8817}, mesh = {Cell Tracking ; Flagella/*physiology/ultrastructure ; Movement ; Time Factors ; Volvocida/anatomy &amp; histology/*physiology/ultrastructure ; }, abstract = {Chlamydomonadales are elective subjects for the investigation of the problems related to locomotion and transport in biological fluid dynamics, whose resolution could enhance searching efficiency and assist in the avoidance of dangerous environments. In this paper, we elucidate the swimming behavior of Tetraflagellochloris mauritanica, a unicellular-multicellular alga belonging to the order Chlamydomonadales. This quadriflagellate alga has a complex swimming motion consisting of alternating swimming phases connected by in-place random reorientations and resting phases. It is capable of both forward and backward swimming, both being normal modes of swimming. The complex swimming behavior resembles the run-and-tumble motion of peritrichous bacteria, with in-place reorientation taking the place of tumbles. In the forward swimming, T. mauritanica shows a very efficient flagellar beat, with undulatory retrograde waves that run along the flagella to their tip. In the backward swimming, the flagella show a nonstereotypical synchronization mode, with a pattern that does not fit any of the modes present in the other Chlamydomonadales so far investigated.}, }
@article {pmid27036817, year = {2016}, author = {Liu, C and Du, L and Zhao, Z}, title = {A directional cylindrical anemometer with four sets of differential pressure sensors.}, journal = {The Review of scientific instruments}, volume = {87}, number = {3}, pages = {035105}, doi = {10.1063/1.4943222}, pmid = {27036817}, issn = {1089-7623}, abstract = {This paper presents a solid-state directional anemometer for simultaneously measuring the speed and direction of a wind in a plane in a speed range 1-40 m/s. This instrument has a cylindrical shape and works by detecting the pressure differences across diameters of the cylinder when exposed to wind. By analyzing our experimental data in a Reynolds number regime 1.7 × 10(3)-7 × 10(4), we figure out the relationship between the pressure difference distribution and the wind velocity. We propose a novel and simple solution based on the relationship and design an anemometer which composes of a circular cylinder with four sets of differential pressure sensors, tubes connecting these sensors with the cylinder's surface, and corresponding circuits. In absence of moving parts, this instrument is small and immune of friction. It has simple internal structures, and the fragile sensing elements are well protected. Prototypes have been fabricated to estimate performance of proposed approach. The power consumption of the prototype is less than 0.5 W, and the sample rate is up to 31 Hz. The test results in a wind tunnel indicate that the maximum relative speed measuring error is 5% and the direction error is no more than 5° in a speed range 2-40 m/s. In theory, it is capable of measuring wind up to 60 m/s. When the air stream goes slower than 2 m/s, the measuring errors of directions are slightly greater, and the performance of speed measuring degrades but remains in an acceptable range of ±0.2 m/s.}, }
@article {pmid27036184, year = {2016}, author = {Smith, SA and Warrier, S}, title = {Reynolds number effects on mixing due to topological chaos.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {26}, number = {3}, pages = {033106}, doi = {10.1063/1.4943170}, pmid = {27036184}, issn = {1089-7682}, abstract = {Topological chaos has emerged as a powerful tool to investigate fluid mixing. While this theory can guarantee a lower bound on the stretching rate of certain material lines, it does not indicate what fraction of the fluid actually participates in this minimally mandated mixing. Indeed, the area in which effective mixing takes place depends on physical parameters such as the Reynolds number. To help clarify this dependency, we numerically simulate the effects of a batch stirring device on a 2D incompressible Newtonian fluid in the laminar regime. In particular, we calculate the finite time Lyapunov exponent (FTLE) field for three different stirring protocols, one topologically complex (pseudo-Anosov) and two simple (finite-order), over a range of viscosities. After extracting appropriate measures indicative of both the amount of mixing and the area of effective mixing from the FTLE field, we see a clearly defined Reynolds number range in which the relative efficacy of the pseudo-Anosov protocol over the finite-order protocols justifies the application of topological chaos. More unexpectedly, we see that while the measures of effective mixing area increase with increasing Reynolds number for the finite-order protocols, they actually exhibit non-monotonic behavior for the pseudo-Anosov protocol.}, }
@article {pmid27033298, year = {2016}, author = {Winzen, A and Roidl, B and Schröder, W}, title = {Combined particle-image velocimetry and force analysis of the three-dimensional fluid-structure interaction of a natural owl wing.}, journal = {Bioinspiration &amp; biomimetics}, volume = {11}, number = {2}, pages = {026005}, doi = {10.1088/1748-3190/11/2/026005}, pmid = {27033298}, issn = {1748-3190}, mesh = {Air ; Animals ; Biomimetics/*methods ; Computer Simulation ; Elastic Modulus/physiology ; Feathers/anatomy &amp; histology/*physiology ; Flight, Animal/*physiology ; Friction ; *Models, Biological ; Rheology/methods ; Stress, Mechanical ; Strigiformes/anatomy &amp; histology/*physiology ; Surface Properties ; Viscosity ; Wings, Animal/anatomy &amp; histology/*physiology ; }, abstract = {Low-speed aerodynamics has gained increasing interest due to its relevance for the design process of small flying air vehicles. These small aircraft operate at similar aerodynamic conditions as, e.g. birds which therefore can serve as role models of how to overcome the well-known problems of low Reynolds number flight. The flight of the barn owl is characterized by a very low flight velocity in conjunction with a low noise emission and a high level of maneuverability at stable flight conditions. To investigate the complex three-dimensional flow field and the corresponding local structural deformation in combination with their influence on the resulting aerodynamic forces, time-resolved stereoscopic particle-image velocimetry and force and moment measurements are performed on a prepared natural barn owl wing. Several spanwise positions are measured via PIV in a range of angles of attack [Formula: see text] 6° and Reynolds numbers 40 000 [Formula: see text] 120 000 based on the chord length. Additionally, the resulting forces and moments are recorded for -10° ≤ α ≤ 15° at the same Reynolds numbers. Depending on the spanwise position, the angle of attack, and the Reynolds number, the flow field on the wing's pressure side is characterized by either a region of flow separation, causing large-scale vortical structures which lead to a time-dependent deflection of the flexible wing structure or wing regions showing no instantaneous deflection but a reduction of the time-averaged mean wing curvature. Based on the force measurements the three-dimensional fluid-structure interaction is assumed to considerably impact the aerodynamic forces acting on the wing leading to a strong mechanical loading of the interface between the wing and body. These time-depending loads which result from the flexibility of the wing should be taken into consideration for the design of future small flying air vehicles using flexible wing structures.}, }
@article {pmid27030773, year = {2016}, author = {Chin, DD and Lentink, D}, title = {Flapping wing aerodynamics: from insects to vertebrates.}, journal = {The Journal of experimental biology}, volume = {219}, number = {Pt 7}, pages = {920-932}, doi = {10.1242/jeb.042317}, pmid = {27030773}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Birds/*physiology ; Chiroptera/*physiology ; Flight, Animal/*physiology ; Insecta/*physiology ; Models, Biological ; Wings, Animal/*physiology ; }, abstract = {More than a million insects and approximately 11,000 vertebrates utilize flapping wings to fly. However, flapping flight has only been studied in a few of these species, so many challenges remain in understanding this form of locomotion. Five key aerodynamic mechanisms have been identified for insect flight. Among these is the leading edge vortex, which is a convergent solution to avoid stall for insects, bats and birds. The roles of the other mechanisms - added mass, clap and fling, rotational circulation and wing-wake interactions - have not yet been thoroughly studied in the context of vertebrate flight. Further challenges to understanding bat and bird flight are posed by the complex, dynamic wing morphologies of these species and the more turbulent airflow generated by their wings compared with that observed during insect flight. Nevertheless, three dimensionless numbers that combine key flow, morphological and kinematic parameters - the Reynolds number, Rossby number and advance ratio - govern flapping wing aerodynamics for both insects and vertebrates. These numbers can thus be used to organize an integrative framework for studying and comparing animal flapping flight. Here, we provide a roadmap for developing such a framework, highlighting the aerodynamic mechanisms that remain to be quantified and compared across species. Ultimately, incorporating complex flight maneuvers, environmental effects and developmental stages into this framework will also be essential to advancing our understanding of the biomechanics, movement ecology and evolution of animal flight.}, }
@article {pmid27009180, year = {2016}, author = {Li, G and Müller, UK and van Leeuwen, JL and Liu, H}, title = {Fish larvae exploit edge vortices along their dorsal and ventral fin folds to propel themselves.}, journal = {Journal of the Royal Society, Interface}, volume = {13}, number = {116}, pages = {}, pmid = {27009180}, issn = {1742-5662}, mesh = {Animal Fins/*physiology ; Animals ; Fishes/*physiology ; Locomotion/*physiology ; }, abstract = {Larvae of bony fish swim in the intermediate Reynolds number (Re) regime, using body- and caudal-fin undulation to propel themselves. They share a median fin fold that transforms into separate median fins as they grow into juveniles. The fin fold was suggested to be an adaption for locomotion in the intermediate Reynolds regime, but its fluid-dynamic role is still enigmatic. Using three-dimensional fluid-dynamic computations, we quantified the swimming trajectory from body-shape changes during cyclic swimming of larval fish. We predicted unsteady vortices around the upper and lower edges of the fin fold, and identified similar vortices around real larvae with particle image velocimetry. We show that thrust contributions on the body peak adjacent to the upper and lower edges of the fin fold where large left-right pressure differences occur in concert with the periodical generation and shedding of edge vortices. The fin fold enhances effective flow separation and drag-based thrust. Along the body, net thrust is generated in multiple zones posterior to the centre of mass. Counterfactual simulations exploring the effect of having a fin fold across a range of Reynolds numbers show that the fin fold helps larvae achieve high swimming speeds, yet requires high power. We conclude that propulsion in larval fish partly relies on unsteady high-intensity vortices along the upper and lower edges of the fin fold, providing a functional explanation for the omnipresence of the fin fold in bony-fish larvae.}, }
@article {pmid26986414, year = {2016}, author = {Köhler, J and Friedrich, J and Ostendorf, A and Gurevich, EL}, title = {Characterization of azimuthal and radial velocity fields induced by rotors in flows with a low Reynolds number.}, journal = {Physical review. E}, volume = {93}, number = {2}, pages = {023108}, doi = {10.1103/PhysRevE.93.023108}, pmid = {26986414}, issn = {2470-0053}, abstract = {We theoretically and experimentally investigate the flow field that emerges from a rodlike microrotor rotating about its center in a nonaxisymmetric manner. A simple theoretical model is proposed that uses a superposition of two rotlets as a fundamental solution to the Stokes equation. The predictions of this model are compared to measurements of the azimuthal and radial microfluidic velocity field components that are induced by a rotor composed of fused microscopic spheres. The rotor is driven magnetically and the fluid flow is measured with the help of a probe particle fixed by an optical tweezer. We find considerable deviations of the mere azimuthal flow pattern induced by a single rotating sphere as it has been reported by Di Leonardo et al. [Phys. Rev. Lett. 96, 134502 (2006)]. Notably, the presence of a radial velocity component that manifests itself by an oscillation of the probe particle with twice the rotor frequency is observed. These findings open up a way to discuss possible radial transport in microfluidic devices.}, }
@article {pmid26986411, year = {2016}, author = {Lavrenteva, O and Prakash, J and Nir, A}, title = {Effect of added mass on the interaction of bubbles in a low-Reynolds-number shear flow.}, journal = {Physical review. E}, volume = {93}, number = {2}, pages = {023105}, doi = {10.1103/PhysRevE.93.023105}, pmid = {26986411}, issn = {2470-0053}, mesh = {Hydrodynamics ; *Models, Theoretical ; Nonlinear Dynamics ; *Shear Strength ; }, abstract = {Equal size air bubbles that are entrapped by a Taylor vortex of the secondary flow in a Couette device, thereby defying buoyancy, slowly form a stable ordered ring with equal separation distances between all neighbors. We present two models of the process dynamics based on force balance on a bubble in the presence of other bubbles positioned on the same streamline in a simple shear flow. The forces taken into account are the viscous resistance, the added mass force, and the inertia-induced repulsing force between two bubbles in a low-Reynolds-number shear flow obtained in Prakash et al. [J. Prakash et al., Phys. Rev. E 87, 043002 (2013)]. The first model of the process assumes that each bubble interacts solely with its nearest neighbors. The second model takes into account pairwise interactions among all the bubbles in the ring. The performed dynamic simulations were compared to the experimental results reported in Prakash et al. [J. Prakash et al., Phys. Rev. E 87, 043002 (2013)] and to the results of quasistationary models (ignoring the added mass effect) suggested in that paper. It is demonstrated that taking into account the effect of added mass, the models describe the major effect of the bubbles' ordering, provide good estimation of the relaxation time, and also predict nonmonotonic behavior of the separation distance between the bubbles, which exhibit over- and undershooting of equilibrium separations. The latter effects were observed in experiments, but are not predicted by the quasistationary models.}, }
@article {pmid26951951, year = {2016}, author = {Flamini, V and DeAnda, A and Griffith, BE}, title = {Immersed boundary-finite element model of fluid-structure interaction in the aortic root.}, journal = {Theoretical and computational fluid dynamics}, volume = {30}, number = {1}, pages = {139-164}, pmid = {26951951}, issn = {0935-4964}, support = {P50 GM071558/GM/NIGMS NIH HHS/United States ; R01 HL117063/HL/NHLBI NIH HHS/United States ; }, abstract = {It has long been recognized that aortic root elasticity helps to ensure efficient aortic valve closure, but our understanding of the functional importance of the elasticity and geometry of the aortic root continues to e-volve as increasingly detailed in vivo imaging data become available. Herein, we describe a fluid-structure interaction model of the aortic root, including the aortic valve leaflets, the sinsuses of Valsalva, the aortic annulus, and the sinotubular junction, that employs a version of Peskin's immersed boundary (IB) method with a finite element (FE) description of the structural elasticity. As in earlier work, we use a fiber-based model of the valve leaflets, but this study extends earlier IB models of the aortic root by employing an incompressible hyperelastic model of the mechanics of the sinuses and ascending aorta using a constitutive law fit to experimental data from human aortic root tissue. In vivo pressure loading is accounted for by a backward displacement method that determines the unloaded configurations of the root model. Our model yields realistic cardiac output at physiological pressures, with low transvalvular pressure differences during forward flow, minimal regurgitation during valve closure, and realistic pressure loads when the valve is closed during diastole. Further, results from high-resolution computations indicate that although the detailed leaflet and root kinematics show some grid sensitivity, our IB model of the aortic root nonetheless produces essentially grid-converged flow rates and pressures at practical grid spacings for the high-Reynolds number flows of the aortic root. These results thereby clarify minimum grid resolutions required by such models when used as stand-alone models of the aortic valve as well as when used to provide models of the outflow valves in models of left ventricular fluid dynamics.}, }
@article {pmid26943538, year = {2016}, author = {Sadek, M and Alexakis, A and Fauve, S}, title = {Optimal Length Scale for a Turbulent Dynamo.}, journal = {Physical review letters}, volume = {116}, number = {7}, pages = {074501}, doi = {10.1103/PhysRevLett.116.074501}, pmid = {26943538}, issn = {1079-7114}, abstract = {We demonstrate that there is an optimal forcing length scale for low Prandtl number dynamo flows that can significantly reduce the required energy injection rate. The investigation is based on simulations of the induction equation in a periodic box of size 2πL. The flows considered are the laminar and turbulent ABC flows forced at different forcing wave numbers k_{f}, where the turbulent case is simulated using a subgrid turbulence model. At the smallest allowed forcing wave number k_{f}=k_{min}=1/L the laminar critical magnetic Reynolds number Rm_{c}^{lam} is more than an order of magnitude smaller than the turbulent critical magnetic Reynolds number Rm_{c}^{turb} due to the hindering effect of turbulent fluctuations. We show that this hindering effect is almost suppressed when the forcing wave number k_{f} is increased above an optimum wave number k_{f}L≃4 for which Rm_{c}^{turb} is minimum. At this optimal wave number, Rm_{c}^{turb} is smaller by more than a factor of 10 than the case forced in k_{f}=1. This leads to a reduction of the energy injection rate by 3 orders of magnitude when compared to the case where the system is forced at the largest scales and thus provides a new strategy for the design of a fully turbulent experimental dynamo.}, }
@article {pmid26925504, year = {2016}, author = {Hervella, P and Parra, E and Needham, D}, title = {Encapsulation and retention of chelated-copper inside hydrophobic nanoparticles: Liquid cored nanoparticles show better retention than a solid core formulation.}, journal = {European journal of pharmaceutics and biopharmaceutics : official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V}, volume = {102}, number = {}, pages = {64-76}, doi = {10.1016/j.ejpb.2016.02.015}, pmid = {26925504}, issn = {1873-3441}, mesh = {Chelating Agents/*chemistry ; Chemistry, Pharmaceutical/methods ; Copper/*chemistry ; Hydrophobic and Hydrophilic Interactions ; Lipids/chemistry ; Liposomes/chemistry ; Nanoparticles/*chemistry ; Particle Size ; Porphyrins/chemistry ; }, abstract = {MOTIVATION: In the field of imaging, (18)F-fluorodeoxyglucose (FDG) PET imaging allows evaluation of glucose metabolism and is the most widely used imaging agent clinically for metastatic cancer. While it can certainly detect the metastatic disease, in order to provide a more fully "individualized medicine" strategy of detection and pharmaceutical treatment, what is needed are additional imaging nanoparticles that resemble the subsequently-administered nanoparticle drug delivery system itself. Both of these nanoparticles must also be able to take advantage of what may well be a limited EPR effect in human tumors, which in and of itself still needs to be characterized in the clinic. Administration of FDG, followed by a nanoparticle imaging agent, followed by a therapeutic nanoparticle would constitute such an "individualized medicine strategy", especially for anti-metastasis approaches. It is here that our endogenous-inspired nanoparticle strategies for imaging and therapeutics are focused on encapsulating and retaining imaging ions such as copper inside novel hydrophobic nanoparticles. In this paper, we describe a new approach to label the core of hydrophobic nanoparticles composed of Glyceryl Trioleate (Triolein) with copper using the hydrophobic chelator Octaethyl porphyrin (OEP).<br><br>RESEARCH PLAN AND METHODS: The research plan for this study was to (1) Formulate nanoparticles and control nanoparticle size using a modification of the solvent injection technique, named fast ethanol injection; (2) Chelate copper into the octaethyl porphyrin; (3) Encapsulate OEP-Cu in nanoparticles: the encapsulation efficiency of copper into liquid nanoparticles (LNP), solid nanoparticles (SNP) and phospholipid liposomes (PL) was evaluated by UV-Vis and atomic absorption spectroscopy; (4) Retain the encapsulated OEP-Cu in the liquid or solid cores of the nanoparticles in the presence of a lipid sink.<br><br>RESULTS: (1) The size of the nanoparticles was found to be strongly dependent on the Reynolds number and the initial concentration of components for the fast injection technique. At high Reynolds number (2181), a minimum value for the particle diameter of &#x223c;30nm was measured. (2) Copper was chelated by OEP in a 1:1mol ratio with an association constant of 2.57&#xd7;10(5)M(-1). (3) The diameter of the nanoparticles was not significantly affected by the presence of OEP or OEP-Cu. The percentage of encapsulation of copper to nanoparticles was >95% at low OEP-Cu concentrations. In the absence of OEP, copper was not detected in nanoparticles demonstrating the role of the hydrophobic chelator OEP in the encapsulation of the otherwise water-soluble copper inside lipid nanoparticles. (4) The in vitro retention upon incubation at 37&#xb0;C over a 48h period in the presence of a lipid sink showed a slow transfer of OEP-Cu into the lipid sink (t1/2=7.7h) for SNP; for PL there was an almost instantaneous transfer of OEP-Cu into the lipid sink (t1/2=0.5h), while for the LNP, all OEP-Cu was retained in the LNP over the full 48h period.<br><br>CONCLUSIONS: The main conclusion of this study was that a very hydrophilic ion such as Cu(2+) can indeed be solubilized and retained in the core of hydrophobic nanoparticles when a hydrophobic molecule (OEP) is used as a chelator. The fast-injection technique was shown to provide a very convenient method to formulate both liquid and solid nanoparticles labeled with Cu (well chelated by OEP), with diameters as small as 30nm, and encapsulation efficiencies higher than 95% when the concentration of OEP-Cu loaded into the nanoparticles was equal to or below 2.5mol%. This is expected to be sufficient for PET-imaging studies.}, }
@article {pmid26889002, year = {2016}, author = {Murphy, DW and Adhikari, D and Webster, DR and Yen, J}, title = {Underwater flight by the planktonic sea butterfly.}, journal = {The Journal of experimental biology}, volume = {219}, number = {Pt 4}, pages = {535-543}, doi = {10.1242/jeb.129205}, pmid = {26889002}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Gastropoda/anatomy &amp; histology/*physiology ; Hydrodynamics ; Swimming ; Wings, Animal/anatomy &amp; histology/physiology ; Zooplankton ; }, abstract = {In a remarkable example of convergent evolution, we show that the zooplanktonic sea butterfly Limacina helicina 'flies' underwater in the same way that very small insects fly in the air. Both sea butterflies and flying insects stroke their wings in a characteristic figure-of-eight pattern to produce lift, and both generate extra lift by peeling their wings apart at the beginning of the power stroke (the well-known Weis-Fogh 'clap-and-fling' mechanism). It is highly surprising to find a zooplankter 'mimicking' insect flight as almost all zooplankton swim in this intermediate Reynolds number range (Re=10-100) by using their appendages as paddles rather than wings. The sea butterfly is also unique in that it accomplishes its insect-like figure-of-eight wing stroke by extreme rotation of its body (what we call 'hyper-pitching'), a paradigm that has implications for micro aerial vehicle (MAV) design. No other animal, to our knowledge, pitches to this extent under normal locomotion.}, }
@article {pmid26887934, year = {2016}, author = {Wang, G and Yang, F and Zhao, W and Chen, CP}, title = {On micro-electrokinetic scalar turbulence in microfluidics at a low Reynolds number.}, journal = {Lab on a chip}, volume = {16}, number = {6}, pages = {1030-1038}, doi = {10.1039/c5lc01541c}, pmid = {26887934}, issn = {1473-0189}, abstract = {We recently demonstrated the direct observation of micro-electrokinetic turbulence in a microchannel at a low Reynolds number (Re) when a pressure-driven flow was forced electrokinetically. Here, we characterize the corresponding scalar turbulence and surprisingly find that the corresponding turbulent mixing has some typical and important features of scalar turbulence, such as the Obukhov-Corrsin (O-C) -5/3 spectrum of concentration fluctuation, which can commonly be realized only at high Re in macroflows. This discovery could provide a new perspective of scalar turbulence and an avenue for control of transport phenomena in lab-on-a-chip platforms. This will deepen our fundamental understanding of transport phenomena in microfluidics.}, }
@article {pmid26886919, year = {2016}, author = {Hayat, T and Shafique, M and Tanveer, A and Alsaedi, A}, title = {Radiative Peristaltic Flow of Jeffrey Nanofluid with Slip Conditions and Joule Heating.}, journal = {PloS one}, volume = {11}, number = {2}, pages = {e0148002}, pmid = {26886919}, issn = {1932-6203}, mesh = {*Heating ; Models, Theoretical ; Nanoparticles/*chemistry ; *Peristalsis ; *Rheology ; }, abstract = {Mixed convection peristaltic flow of Jeffrey nanofluid in a channel with compliant walls is addressed here. The present investigation includes the viscous dissipation, thermal radiation and Joule heating. Whole analysis is performed for velocity, thermal and concentration slip conditions. Related problems through long wavelength and low Reynolds number are examined for stream function, temperature and concentration. Impacts of thermal radiation, Hartman number, Brownian motion parameter, thermophoresis, Joule heating and slip parameters are explored in detail. Clearly temperature is a decreasing function of Hartman number and radiation parameter.}, }
@article {pmid26883291, year = {2016}, author = {Pinto, SI and Campos, JB}, title = {Numerical study of wall shear stress-based descriptors in the human left coronary artery.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {19}, number = {13}, pages = {1443-1455}, doi = {10.1080/10255842.2016.1149575}, pmid = {26883291}, issn = {1476-8259}, mesh = {Computer Simulation ; Coronary Vessels/*physiopathology ; Hemorheology ; Humans ; Models, Cardiovascular ; *Numerical Analysis, Computer-Assisted ; Shear Strength ; *Stress, Mechanical ; Time Factors ; }, abstract = {The present work is about the application of wall shear stress descriptors - time averaged wall shear stress (TAWSS), oscillating shear index (OSI) and relative residence time (RRT) - to the study of blood flow in the left coronary artery (LCA). These descriptors aid the prediction of disturbed flow conditions in the vessels and play a significant role in the detection of potential zones of atherosclerosis development. Hemodynamic descriptors data were obtained, numerically, through ANSYS® software, for the LCA of a patient-specific geometry and for a 3D idealized model. Comparing both cases, the results are coherent, in terms of location and magnitude. Low TAWSS, high OSI and high RRT values are observed in the bifurcation - potential zone of atherosclerosis appearance. The dissimilarities observed in the TAWSS values, considering blood as a Newtonian or non-Newtonian fluid, releases the importance of the correct blood rheologic caracterization. Moreover, for a higher Reynolds number, the TAWSS values decrease in the bifurcation and along the LAD branch, increasing the probability of plaques deposition. Furthermore, for a stenotic LCA model, very low TAWSS and high RRT values in front and behind the stenosis are observed, indicating the probable extension, in the flow direction, of the lesion.}, }
@article {pmid26871181, year = {2016}, author = {Tsai, CM and Chu, HY}, title = {Evolution of a plasma vortex in air.}, journal = {Physical review. E}, volume = {93}, number = {1}, pages = {013205}, doi = {10.1103/PhysRevE.93.013205}, pmid = {26871181}, issn = {2470-0053}, mesh = {*Air ; Equipment Design ; *Helium ; Models, Theoretical ; *Motion ; *Plasma Gases ; }, abstract = {We report the generation of a vortex-shaped plasma in air by using a capacitively coupled dielectric barrier discharge system. We show that a vortex-shaped plasma can be produced inside a helium gas vortex and is capable of propagating for 3 cm. The fluctuation of the plasma ring shows a scaling relation with the Reynolds number of the vortex. The transient discharge reveals the property of corona discharge, where the conducting channel within the gas vortex and the blur plasma emission are observed at each half voltage cycle.}, }
@article {pmid26871163, year = {2016}, author = {Thiesset, F and Maurice, G and Halter, F and Mazellier, N and Chauveau, C and Gökalp, I}, title = {Geometrical properties of turbulent premixed flames and other corrugated interfaces.}, journal = {Physical review. E}, volume = {93}, number = {1}, pages = {013116}, doi = {10.1103/PhysRevE.93.013116}, pmid = {26871163}, issn = {2470-0053}, abstract = {This study focuses on the geometrical properties of turbulent flame fronts and other interfaces. Toward that end, we use an original tool based on proper orthogonal decomposition (POD), which is applied to the interface spatial coordinates. The focus is mainly on the degree of roughness of the flame front, which is quantified through the scale dependence of its coverage arclength. POD is first validated by comparing with the caliper technique. Fractal characteristics are extracted in an unambiguous fashion using a parametric expression which appears to be impressively well suited for representing Richardson plots. Then it is shown that, for the range of Reynolds numbers investigated here, the scale-by-scale contribution to the arclength does not comply with scale similarity, irrespectively of the type of similarity which is invoked. The finite ratios between large and small scales, referred to as finite Reynolds number effects, are likely to explain this observation. In this context, the Reynolds number that ought to be achieved for a proper inertial range to be discernible, and for scale similarity to be likely to apply, is calculated. Fractal characteristics of flame folding are compared to available predictions. It is confirmed that the inner cutoff satisfactorily correlates with the Kolmogorov scale while the outer cutoff appears to be proportional to the integral length scale. However, the scaling for the fractal dimension is much less obvious. It is argued that much higher Reynolds numbers have to be reached for drawing firm statements about the evolution (or constancy) of the fractal dimension with respect to flame and flow parameters. Finally, a heuristic phenomenology of corrugated interfaces is highlighted. The degree of generality of the latter phenomenology is confirmed by comparing the folding of different interfaces including a turbulent-nonturbulent interface, a liquid jet destabilized by a surrounding air jet, a cavitating flow, and an isoscalar evolving in a turbulent medium. The latter outcome is likely to have strong implications for modeling the corrugation of turbulent interfaces occurring in many physical situations.}, }
@article {pmid26871162, year = {2016}, author = {Nie, D and Lin, J and Chen, R}, title = {Grouping behavior of coaxial settling particles in a narrow channel.}, journal = {Physical review. E}, volume = {93}, number = {1}, pages = {013114}, doi = {10.1103/PhysRevE.93.013114}, pmid = {26871162}, issn = {2470-0053}, abstract = {Using numerical simulations, we studied the grouping behaviors of particles settling along their line of centers in narrow channels having a Reynolds number range of 5 ≤ Re ≤ 50. The calculations are based on our previously developed lattice Boltzmann direct-forcing-fictitious-domain method. We report the grouping behavior and investigate the dependence on the number of particles n, the initial interparticle separation h_{0}, and the Reynolds number Re. In particular, the mode of grouping is found to be independent of the number of particles when the Reynolds numbers is small. The two lowermost particles always come together first and form a vertical doublet and then the next two lowest particles form another doublet, and so on. Therefore, we observe n/2 doublets or (n-1)/2 doublets when n is even or odd, respectively. The uppermost particle is always left behind when n is odd. Furthermore, the separation between these doublets remains constant, displaying a power-law dependence decreasing from top to bottom.}, }
@article {pmid26871154, year = {2016}, author = {Wang, G and Yang, F and Zhao, W}, title = {Microelectrokinetic turbulence in microfluidics at low Reynolds number.}, journal = {Physical review. E}, volume = {93}, number = {1}, pages = {013106}, doi = {10.1103/PhysRevE.93.013106}, pmid = {26871154}, issn = {2470-0053}, mesh = {Fluorescein ; Fluorescent Dyes ; Kinetics ; Lab-On-A-Chip Devices ; *Microfluidics ; Models, Theoretical ; *Motion ; Pressure ; Solutions ; Static Electricity ; Water ; }, abstract = {There is commonly no turbulence in microfluidics, and the flows are believed to be either laminar or chaotic, since Reynolds number (Re) in microflows is usually on the order of unity or lower. However, we recently demonstrated that it is possible to achieve turbulence with low Re (based on the measured flow velocity and the width of the channel entrance) when a pressure-driven flow is electrokinetically forced in a quasi T-microchannel. To be able to measure high frequency velocity fluctuations in microchannels, a velocimeter with submicrometer spatial resolution and microsecond temporal resolution, called a laser-induced fluorescence photobleaching anemometer, is developed. Here we characterize the microelectrokinetic turbulence and observe some typical and important features of high Re flows, such as Kolmogorov -5/3 spectrum of velocity fluctuation, which usually can be realized only at very high Re in macroturbulent flows.}, }
@article {pmid26853995, year = {2016}, author = {Kim, J and Lee, J and Wu, C and Nam, S and Di Carlo, D and Lee, W}, title = {Inertial focusing in non-rectangular cross-section microchannels and manipulation of accessible focusing positions.}, journal = {Lab on a chip}, volume = {16}, number = {6}, pages = {992-1001}, doi = {10.1039/c5lc01100k}, pmid = {26853995}, issn = {1473-0189}, abstract = {Inertial focusing in microfluidic channels has been extensively studied experimentally and theoretically, which has led to various applications including microfluidic separation and enrichment of cells. Inertial lift forces are strongly dependent on the flow velocity profile and the channel cross-sectional shape. However, the channel cross-sections studied have been limited to circles and rectangles. We studied inertial focusing in non-rectangular cross-section channels to manipulate the flow profile and thus the inertial focusing of microparticles. The location and number of focusing positions are analyzed with varying cross-sectional shapes and Reynolds number. We found that the broken symmetry of non-equilateral triangular channels leads to the shifting of focusing positions with varying Reynolds number. Non-rectangular channels have unique mapping of the focusing positions and the corresponding basins of attraction. By connecting channels with different cross-sectional shapes, we were able to manipulate the accessible focusing positions and achieve focusing of microparticles to a single stream with ∼99% purity.}, }
@article {pmid26841796, year = {2016}, author = {Mathijssen, AJ and Doostmohammadi, A and Yeomans, JM and Shendruk, TN}, title = {Hotspots of boundary accumulation: dynamics and statistics of micro-swimmers in flowing films.}, journal = {Journal of the Royal Society, Interface}, volume = {13}, number = {115}, pages = {20150936}, pmid = {26841796}, issn = {1742-5662}, mesh = {*Bacteria ; *Bacterial Physiological Phenomena ; Flagella/*physiology ; Locomotion/*physiology ; *Models, Biological ; }, abstract = {Biological flows over surfaces and interfaces can result in accumulation hotspots or depleted voids of microorganisms in natural environments. Apprehending the mechanisms that lead to such distributions is essential for understanding biofilm initiation. Using a systematic framework, we resolve the dynamics and statistics of swimming microbes within flowing films, considering the impact of confinement through steric and hydrodynamic interactions, flow and motility, along with Brownian and run-tumble fluctuations. Micro-swimmers can be peeled off the solid wall above a critical flow strength. However, the interplay of flow and fluctuations causes organisms to migrate back towards the wall above a secondary critical value. Hence, faster flows may not always be the most efficacious strategy to discourage biofilm initiation. Moreover, we find run-tumble dynamics commonly used by flagellated microbes to be an intrinsically more successful strategy to escape from boundaries than equivalent levels of enhanced Brownian noise in ciliated organisms.}, }
@article {pmid26830757, year = {2016}, author = {Rosenberg, D and Marino, R and Herbert, C and Pouquet, A}, title = {Variations of characteristic time scales in rotating stratified turbulence using a large parametric numerical study.}, journal = {The European physical journal. E, Soft matter}, volume = {39}, number = {1}, pages = {8}, pmid = {26830757}, issn = {1292-895X}, abstract = {We study rotating stratified turbulence (RST) making use of numerical data stemming from a large parametric study varying the Reynolds, Froude and Rossby numbers, Re, Fr and Ro in a broad range of values. The computations are performed using periodic boundary conditions on grids of 1024(3) points, with no modeling of the small scales, no forcing and with large-scale random initial conditions for the velocity field only, and there are altogether 65 runs analyzed in this paper. The buoyancy Reynolds number defined as R(B) = ReFr2 varies from negligible values to ≈ 10(5), approaching atmospheric or oceanic regimes. This preliminary analysis deals with the variation of characteristic time scales of RST with dimensionless parameters, focusing on the role played by the partition of energy between the kinetic and potential modes, as a key ingredient for modeling the dynamics of such flows. We find that neither rotation nor the ratio of the Brunt-Väisälä frequency to the inertial frequency seem to play a major role in the absence of forcing in the global dynamics of the small-scale kinetic and potential modes. Specifically, in these computations, mostly in regimes of wave turbulence, characteristic times based on the ratio of energy to dissipation of the velocity and temperature fluctuations, T(V) and T(P), vary substantially with parameters. Their ratio γ=T(V)/T(P) follows roughly a bell-shaped curve in terms of Richardson number Ri. It reaches a plateau - on which time scales become comparable, γ≈0.6 - when the turbulence has significantly strengthened, leading to numerous destabilization events together with a tendency towards an isotropization of the flow.}, }
@article {pmid26824542, year = {2016}, author = {Shishkina, O and Wagner, S}, title = {Prandtl-Number Dependence of Heat Transport in Laminar Horizontal Convection.}, journal = {Physical review letters}, volume = {116}, number = {2}, pages = {024302}, doi = {10.1103/PhysRevLett.116.024302}, pmid = {26824542}, issn = {1079-7114}, abstract = {We report the Prandtl-number (Pr) and Rayleigh-number (Ra) dependencies of the Reynolds number (Re) and mean convective heat transport, measured by the Nusselt number (Nu), in horizontal convection (HC) systems, where the heat supply and removal are provided exclusively through a lower horizontal surface of a fluid layer. For laminar HC, we find that Re∼Ra^{2/5}Pr^{-4/5}, Nu∼Ra^{1/5}Pr^{1/10} with a transition to Re∼Ra^{1/2}Pr^{-1}, Nu∼Ra^{1/4}Pr^{0} for large Pr. The results are based on direct numerical simulations for Ra from 3×10^{8} to 5×10^{10} and Pr from 0.05 to 50 and are explained by applying the Grossmann-Lohse approach [J. Fluid Mech. 407, 27 (2000)] transferred from the case of Rayleigh-Bénard convection to the case of laminar HC.}, }
@article {pmid26821214, year = {2016}, author = {Maier, AM and Weig, C and Oswald, P and Frey, E and Fischer, P and Liedl, T}, title = {Magnetic Propulsion of Microswimmers with DNA-Based Flagellar Bundles.}, journal = {Nano letters}, volume = {16}, number = {2}, pages = {906-910}, pmid = {26821214}, issn = {1530-6992}, mesh = {Biocompatible Materials/*chemistry ; DNA/*chemistry ; Magnetic Fields ; Magnetite Nanoparticles/*chemistry ; Robotics/instrumentation ; }, abstract = {We show that DNA-based self-assembly can serve as a general and flexible tool to construct artificial flagella of several micrometers in length and only tens of nanometers in diameter. By attaching the DNA flagella to biocompatible magnetic microparticles, we provide a proof of concept demonstration of hybrid structures that, when rotated in an external magnetic field, propel by means of a flagellar bundle, similar to self-propelling peritrichous bacteria. Our theoretical analysis predicts that flagellar bundles that possess a length-dependent bending stiffness should exhibit a superior swimming speed compared to swimmers with a single appendage. The DNA self-assembly method permits the realization of these improved flagellar bundles in good agreement with our quantitative model. DNA flagella with well-controlled shape could fundamentally increase the functionality of fully biocompatible nanorobots and extend the scope and complexity of active materials.}, }
@article {pmid26802269, year = {2016}, author = {Sultan, T and Ahmad, S and Cho, J}, title = {Numerical study of the effects of surface roughness on water disinfection UV reactor.}, journal = {Chemosphere}, volume = {148}, number = {}, pages = {108-117}, doi = {10.1016/j.chemosphere.2016.01.005}, pmid = {26802269}, issn = {1879-1298}, mesh = {*Bioreactors ; *Construction Materials ; Disinfection/*methods ; Hydrodynamics ; *Models, Theoretical ; Surface Properties ; *Ultraviolet Rays ; Water Pollutants/isolation &amp; purification ; Water Purification/*methods ; }, abstract = {UV reactors are an emerging choice as a big barrier against the pathogens present in drinking water. However, the precise role of reactor's wall roughness for cross flow ultraviolet (CF-UV) and axial flow ultraviolet (AF-UV) water disinfection reactors are unknown. In this paper, the influences of reactor's wall roughness were investigated with a view to identify their role on the performance factors namely dose distribution and reduction equivalent dose (RED). Herein, the relative effects of reactor's wall roughness on the performance of CF-UV and AF-UV reactors were also highlighted. This numerical study is a first step towards the comprehensive analysis of the effects of reactor's wall roughness for UV reactor. A numerical analysis was performed using ANSYS Fluent 15 academic version. The reactor's wall roughness has a significant effect on the RED. We found that the increase in RED is Reynolds number dependent (at lower value of turbulent Reynolds number the effects are remarkable). The effects of reactor's roughness were more pronounced for AF-UV reactor. The simulation results suggest that the study of reactor's wall roughness provides valuable insight to fully understand the effects of reactor's wall roughness and its impact on the flow behavior and other features of CF-UV and AF-UV water disinfection reactors.}, }
@article {pmid26780177, year = {2016}, author = {Agbesi, MP and Naylor, S and Perkins, E and Borsuk, HS and Sykes, D and Maclaine, JS and Wang, Z and Cox, JP}, title = {Complex flow in the nasal region of guitarfishes.}, journal = {Comparative biochemistry and physiology. Part A, Molecular &amp; integrative physiology}, volume = {193}, number = {}, pages = {52-63}, doi = {10.1016/j.cbpa.2015.12.007}, pmid = {26780177}, issn = {1531-4332}, mesh = {Animals ; Fishes/metabolism/*physiology ; Nasal Cavity/metabolism/*physiology ; Respiration ; Smell/*physiology ; Swimming/physiology ; Water/metabolism ; }, abstract = {Scent detection in an aquatic environment is dependent on the movement of water. We set out to determine the mechanisms for moving water through the olfactory organ of guitarfishes (Rhinobatidae, Chondrichthyes) with open nasal cavities. We found at least two. In the first mechanism, which we identified by observing dye movement in the nasal region of a life-sized physical model of the head of Rhinobatos lentiginosus mounted in a flume, olfactory flow is generated by the guitarfish's motion relative to water, e.g. when it swims. We suggest that the pressure difference responsible for motion-driven olfactory flow is caused by the guitarfish's nasal flaps, which create a region of high pressure at the incurrent nostril, and a region of low pressure in and behind the nasal cavity. Vortical structures in the nasal region associated with motion-driven flow may encourage passage of water through the nasal cavity and its sensory channels, and may also reduce the cost of swimming. The arrangement of vortical structures is reminiscent of aircraft wing vortices. In the second mechanism, which we identified by observing dye movement in the nasal regions of living specimens of Glaucostegus typus, the guitarfish's respiratory pump draws flow through the olfactory organ in a rhythmic (0.5-2 Hz), but continuous, fashion. Consequently, the respiratory pump will maintain olfactory flow whether the guitarfish is swimming or at rest. Based on our results, we propose a model for olfactory flow in guitarfishes with open nasal cavities, and suggest other neoselachians which this model might apply to.}, }
@article {pmid26775865, year = {2015}, author = {Wang, Q and Othmer, HG}, title = {The performance of discrete models of low Reynolds number swimmers.}, journal = {Mathematical biosciences and engineering : MBE}, volume = {12}, number = {6}, pages = {1303-1320}, doi = {10.3934/mbe.2015.12.1303}, pmid = {26775865}, issn = {1551-0018}, support = {GM29123-36/GM/NIGMS NIH HHS/United States ; }, mesh = {Animals ; Cell Movement/physiology ; Cell Shape/physiology ; Computer Simulation ; Dictyostelium/cytology/physiology ; Humans ; Mathematical Concepts ; Melanoma/pathology/physiopathology ; *Models, Biological ; Movement/*physiology ; }, abstract = {Swimming by shape changes at low Reynolds number is widely used in biology and understanding how the performance of movement depends on the geometric pattern of shape changes is important to understand swimming of microorganisms and in designing low Reynolds number swimming models. The simplest models of shape changes are those that comprise a series of linked spheres that can change their separation and/or their size. Herein we compare the performance of three models in which these modes are used in different ways.}, }
@article {pmid26764831, year = {2015}, author = {Ebrahimian, M and Yekehzare, M and Ejtehadi, MR}, title = {Low-Reynolds-number predator.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {6}, pages = {063035}, doi = {10.1103/PhysRevE.92.063035}, pmid = {26764831}, issn = {1550-2376}, abstract = {To generalize simple bead-linker model of swimmers to higher dimensions and to demonstrate the chemotaxis ability of such swimmers, here we introduce a low-Reynolds predator, using a two-dimensional triangular bead-spring model. Two-state linkers as mechanochemical enzymes expand as a result of interaction with particular activator substances in the environment, causing the whole body to translate and rotate. The concentration of the chemical stimulator controls expansion versus the contraction rate of each arm and so affects the ability of the body for diffusive movements; also the variation of activator substance's concentration in the environment breaks the symmetry of linkers' preferred state, resulting in the drift of the random walker along the gradient of the density of activators. External food or danger sources may attract or repel the body by producing or consuming the chemical activators of the organism's enzymes, inducing chemotaxis behavior. Generalization of the model to three dimensions is straightforward.}, }
@article {pmid26764821, year = {2015}, author = {Iyer, KP and Sreenivasan, KR and Yeung, PK}, title = {Refined similarity hypothesis using three-dimensional local averages.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {6}, pages = {063024}, doi = {10.1103/PhysRevE.92.063024}, pmid = {26764821}, issn = {1550-2376}, abstract = {The refined similarity hypotheses of Kolmogorov, regarded as an important ingredient of intermittent turbulence, has been tested in the past using one-dimensional data and plausible surrogates of energy dissipation. We employ data from direct numerical simulations, at the microscale Reynolds number R(λ)∼650, on a periodic box of 4096(3) grid points to test the hypotheses using three-dimensional averages. In particular, we study the small-scale properties of the stochastic variable V=Δu(r)/(rε(r))(1/3), where Δu(r) is the longitudinal velocity increment and ε(r) is the dissipation rate averaged over a three-dimensional volume of linear size r. We show that V is universal in the inertial subrange. In the dissipation range, the statistics of V are shown to depend solely on a local Reynolds number.}, }
@article {pmid26764819, year = {2015}, author = {Rosén, T and Einarsson, J and Nordmark, A and Aidun, CK and Lundell, F and Mehlig, B}, title = {Numerical analysis of the angular motion of a neutrally buoyant spheroid in shear flow at small Reynolds numbers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {6}, pages = {063022}, doi = {10.1103/PhysRevE.92.063022}, pmid = {26764819}, issn = {1550-2376}, abstract = {We numerically analyze the rotation of a neutrally buoyant spheroid in a shear flow at small shear Reynolds number. Using direct numerical stability analysis of the coupled nonlinear particle-flow problem, we compute the linear stability of the log-rolling orbit at small shear Reynolds number Re(a). As Re(a)→0 and as the box size of the system tends to infinity, we find good agreement between the numerical results and earlier analytical predictions valid to linear order in Re(a) for the case of an unbounded shear. The numerical stability analysis indicates that there are substantial finite-size corrections to the analytical results obtained for the unbounded system. We also compare the analytical results to results of lattice Boltzmann simulations to analyze the stability of the tumbling orbit at shear Reynolds numbers of order unity. Theory for an unbounded system at infinitesimal shear Reynolds number predicts a bifurcation of the tumbling orbit at aspect ratio λ(c)≈0.137 below which tumbling is stable (as well as log rolling). The simulation results show a bifurcation line in the λ-Re(a) plane that reaches λ≈0.1275 at the smallest shear Reynolds number (Re(a)=1) at which we could simulate with the lattice Boltzmann code, in qualitative agreement with the analytical results.}, }
@article {pmid26764810, year = {2015}, author = {Deng, J and Sun, L and Shao, X}, title = {Dynamical features of the wake behind a pitching foil.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {6}, pages = {063013}, doi = {10.1103/PhysRevE.92.063013}, pmid = {26764810}, issn = {1550-2376}, abstract = {As an extension of the previous study on the three-dimensional transition of the wake behind a pitching foil [Deng and Caulfield, Phys. Rev. E 91, 043017 (2015)], this investigation draws a comprehensive map on the pitching frequency-amplitude phase space. First, by fixing the Reynolds number at Re=1700 and varying the pitching frequency and amplitude, we identify three key dynamical features of the wake: first, the transition from Bénard-von Kármán (BvK) vortex streets to reverse BvK vortex streets, and second, the symmetry breaking of this reverse BvK wake leading to a deflected wake, and a further transition from two-dimensional (2D) wakes to three-dimensional (3D) wakes. The transition boundary between the 2D and 3D wakes lies top right of the wake deflection boundary, implying a correlation between the wake deflection and the 2D to 3D wake transition, confirming that this transition occurs after the wake deflection. This paper supports the previous extensive numerical studies under two-dimensional assumption at low Reynolds number, since it is indeed two dimensional except for the cases at very high pitching frequencies or large amplitudes. Furthermore, by three-dimensional direct numerical simulations (DNSs), we confirm the previous statement about the physical realizability of the short wavelength mode at β=30 (or λ(z)=0.21) for Re=1500. By comparing the three-dimensional vortical structures by DNSs with that from the reconstruction of Floquet modes, we find a good consistency between them, both exhibiting clear streamwise structures in the wake.}, }
@article {pmid26764807, year = {2015}, author = {Allouche, MH and Millet, S and Botton, V and Henry, D and Ben Hadid, H and Rousset, F}, title = {Stability of a flow down an incline with respect to two-dimensional and three-dimensional disturbances for Newtonian and non-Newtonian fluids.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {6}, pages = {063010}, doi = {10.1103/PhysRevE.92.063010}, pmid = {26764807}, issn = {1550-2376}, abstract = {Squire's theorem, which states that the two-dimensional instabilities are more dangerous than the three-dimensional instabilities, is revisited here for a flow down an incline, making use of numerical stability analysis and Squire relationships when available. For flows down inclined planes, one of these Squire relationships involves the slopes of the inclines. This means that the Reynolds number associated with a two-dimensional wave can be shown to be smaller than that for an oblique wave, but this oblique wave being obtained for a larger slope. Physically speaking, this prevents the possibility to directly compare the thresholds at a given slope. The goal of the paper is then to reach a conclusion about the predominance or not of two-dimensional instabilities at a given slope, which is of practical interest for industrial or environmental applications. For a Newtonian fluid, it is shown that, for a given slope, oblique wave instabilities are never the dominant instabilities. Both the Squire relationships and the particular variations of the two-dimensional wave critical curve with regard to the inclination angle are involved in the proof of this result. For a generalized Newtonian fluid, a similar result can only be obtained for a reduced stability problem where some term connected to the perturbation of viscosity is neglected. For the general stability problem, however, no Squire relationships can be derived and the numerical stability results show that the thresholds for oblique waves can be smaller than the thresholds for two-dimensional waves at a given slope, particularly for large obliquity angles and strong shear-thinning behaviors. The conclusion is then completely different in that case: the dominant instability for a generalized Newtonian fluid flowing down an inclined plane with a given slope can be three dimensional.}, }
@article {pmid26764803, year = {2015}, author = {Anbarlooei, HR and Cruz, DO and Ramos, F and Silva Freire, AP}, title = {Phenomenological Blasius-type friction equation for turbulent power-law fluid flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {6}, pages = {063006}, doi = {10.1103/PhysRevE.92.063006}, pmid = {26764803}, issn = {1550-2376}, abstract = {We propose a friction formula for turbulent power-law fluid flows, a class of purely viscous non-Newtonian fluids commonly found in applications. Our model is derived through an extension of the friction factor analysis based on Kolmogorov's phenomenology, recently proposed by Gioia and Chakraborty. Tests against classical empirical data show excellent agreement over a significant range of Reynolds number. Limits of the model are also discussed.}, }
@article {pmid26739143, year = {2016}, author = {Low, SC and Eshtiaghi, N and Slatter, P and Baudez, JC and Parthasarathy, R}, title = {Mixing characteristics of sludge simulant in a model anaerobic digester.}, journal = {Bioprocess and biosystems engineering}, volume = {39}, number = {3}, pages = {473-483}, doi = {10.1007/s00449-015-1530-4}, pmid = {26739143}, issn = {1615-7605}, mesh = {*Models, Chemical ; Sewage/*chemistry ; }, abstract = {This study aims to investigate the mixing characteristics of a transparent sludge simulant in a mechanically agitated model digester using flow visualisation technique. Video images of the flow patterns were obtained by recording the progress of an acid-base reaction and analysed to determine the active and inactive volumes as a function of time. The doughnut-shaped inactive region formed above and below the impeller in low concentration simulant decreases in size with time and disappears finally. The 'cavern' shaped active mixing region formed around the impeller in simulant solutions with higher concentrations increases with increasing agitation time and reaches a steady state equilibrium size, which is a function of specific power input. These results indicate that the active volume is jointly determined by simulant rheology and specific power input. A mathematical correlation is proposed to estimate the active volume as a function of simulant concentration in terms of yield Reynolds number.}, }
@article {pmid26738932, year = {2016}, author = {Jawed, MK and Reis, PM}, title = {Deformation of a soft helical filament in an axial flow at low Reynolds number.}, journal = {Soft matter}, volume = {12}, number = {6}, pages = {1898-1905}, doi = {10.1039/c5sm02625c}, pmid = {26738932}, issn = {1744-6848}, mesh = {Bacterial Physiological Phenomena ; Biomechanical Phenomena ; *Elasticity ; Flagella/*chemistry/physiology ; Models, Theoretical ; Movement ; Rotation ; }, abstract = {We perform a numerical investigation of the deformation of a rotating helical filament subjected to an axial flow, under low Reynolds number conditions, motivated by the propulsion of bacteria using helical flagella. Given its slenderness, the helical rod is intrinsically soft and deforms due to the interplay between elastic forces and hydrodynamic loading. We make use of a previously developed and experimentally validated computational tool framework that models the elasticity of the filament using the discrete elastic rod method and the fluid forces are treated using Lighthill's slender body theory. Under axial flow, and in the absence of rotation, the initially helical rod is extended. Above a critical flow speed its configuration comprises a straight portion connected to a localized helix near the free end. When the rod is also rotated about its helical axis, propulsion is only possible in a finite range of angular velocity, with an upper bound that is limited by buckling of the soft helix arising due to viscous stresses. A systematic exploration of the parameter space allows us to quantify regimes for successful propulsion for a number of specific bacteria.}, }
@article {pmid26736424, year = {2015}, author = {Nita, C and Itu, L and Mihalef, V and Sharma, P and Rapaka, S}, title = {GPU-accelerated model for fast, three-dimensional fluid-structure interaction computations.}, journal = {Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference}, volume = {2015}, number = {}, pages = {965-968}, doi = {10.1109/EMBC.2015.7318524}, pmid = {26736424}, issn = {2694-0604}, mesh = {*Computer Simulation ; }, abstract = {In this paper we introduce a methodology for performing one-way Fluid-Structure interaction (FSI), i.e. where the motion of the wall boundaries is imposed. We use a Graphics Processing Unit (GPU) accelerated Lattice-Boltzmann Method (LBM) implementation and present an efficient workflow for embedding the moving geometry, given as a set of polygonal meshes, in the LBM computation. The proposed method is first validated in a synthetic experiment: a vessel which is periodically expanding and contracting. Next, the evaluation focuses on the 3D Peristaltic flow problem: a fluid flows inside a flexible tube, where a periodic wave-like deformation produces a fluid motion along the centerline of the tube. Different geometry configurations are used and results are compared against previously published solutions. The efficient approach leads to an average execution time of approx. one hour per computation, whereas 50% of it is required for the geometry update operations. Finally, we also analyse the effect of changing the Reynolds number on the flow streamlines: the flow regime is significantly affected by the Reynolds number.}, }
@article {pmid26730219, year = {2015}, author = {Huang, D and Chernyshenko, S and Goulart, P and Lasagna, D and Tutty, O and Fuentes, F}, title = {Sum-of-squares of polynomials approach to nonlinear stability of fluid flows: an example of application.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {471}, number = {2183}, pages = {20150622}, pmid = {26730219}, issn = {1364-5021}, abstract = {With the goal of providing the first example of application of a recently proposed method, thus demonstrating its ability to give results in principle, global stability of a version of the rotating Couette flow is examined. The flow depends on the Reynolds number and a parameter characterizing the magnitude of the Coriolis force. By converting the original Navier-Stokes equations to a finite-dimensional uncertain dynamical system using a partial Galerkin expansion, high-degree polynomial Lyapunov functionals were found by sum-of-squares of polynomials optimization. It is demonstrated that the proposed method allows obtaining the exact global stability limit for this flow in a range of values of the parameter characterizing the Coriolis force. Outside this range a lower bound for the global stability limit was obtained, which is still better than the energy stability limit. In the course of the study, several results meaningful in the context of the method used were also obtained. Overall, the results obtained demonstrate the applicability of the recently proposed approach to global stability of the fluid flows. To the best of our knowledge, it is the first case in which global stability of a fluid flow has been proved by a generic method for the value of a Reynolds number greater than that which could be achieved with the energy stability approach.}, }
@article {pmid26723345, year = {2015}, author = {Phong, V and Papamoschou, D}, title = {Normal incidence acoustic insertion loss of perforated plates with bias flow.}, journal = {The Journal of the Acoustical Society of America}, volume = {138}, number = {6}, pages = {3907-3921}, doi = {10.1121/1.4937602}, pmid = {26723345}, issn = {1520-8524}, abstract = {The transmission of sound at normal incidence through perforated plates with bias flow is investigated experimentally and theoretically over a large parameter space. A specially designed experimental apparatus enabled the measurement of insertion loss with bias flow Mach number up to 0.25. A theoretical model for insertion loss was constructed based on inviscid, one-dimensional wave propagation with mean flow through a single contraction/expansion chamber. The mass end correction of the contraction is modified for hole interaction effects and mean flow. Hydrodynamic losses are modeled using a vena contracta coefficient dependent on both perforation geometry and Reynolds number. Losses in acoustic energy that occur in the mixing region downstream of the perforations are modeled as fluctuations in entropy. The proposed model was validated experimentally over a range of plate thickness, porosity, and hole size. The experimental results indicate an increase in insertion loss with increasing frequency, followed by saturation and decline as resonant conditions are established in the perforations. The insertion loss at low frequency increases with increasing Mach number through the perforation. The proposed model captures these trends and its predictions are shown to be more accurate than those of past models.}, }
@article {pmid26718062, year = {2016}, author = {O Connor, J and Revell, A and Mandal, P and Day, P}, title = {Application of a lattice Boltzmann-immersed boundary method for fluid-filament dynamics and flow sensing.}, journal = {Journal of biomechanics}, volume = {49}, number = {11}, pages = {2143-2151}, doi = {10.1016/j.jbiomech.2015.11.057}, pmid = {26718062}, issn = {1873-2380}, mesh = {Cilia/metabolism ; Computer Simulation ; Cytoskeleton/metabolism ; Humans ; *Hydrodynamics ; Models, Biological ; Shear Strength ; Stress, Mechanical ; }, abstract = {Complex fluid-structure interactions between elastic filaments, or cilia, immersed in viscous flows are commonplace in nature and bear important roles. Some biological systems have evolved to interpret flow-induced motion into signals for the purpose of feedback response. Given the challenges associated with extracting meaningful experimental data at this scale, there has been particular focus on the numerical study of these effects. Porous models have proven useful where cilia arrangements are relatively dense, but for more sparse configurations the dynamic interactions of individual structures play a greater role and direct modelling becomes increasingly necessary. The present study reports efforts towards explicit modelling of regularly spaced wall-mounted cilia using a lattice Boltzmann-immersed boundary method. Both steady and forced unsteady 2D channel flows at different Reynolds numbers are investigated, with and without the presence of a periodic array of elastic inextensible filaments. It is demonstrated that the structure response depends significantly on Reynolds number. For low Reynolds flow, the recirculation vortex aft of successive filaments is small relative to the cilia spacing and does not fully bridge the gap, in which case the structure lags the flow. At higher Reynolds number, when this gap is fully bridged the structure and flow move in phase. The trapping of vortices between cilia is associated with relatively lower wall shear stress. At low to intermediate Reynolds, vortex bridging is incomplete and large deflection is still possible, which is reflected in the tip dynamics and wall shear stress profiles.}, }
@article {pmid26705658, year = {2015}, author = {Klotsa, D and Baldwin, KA and Hill, RJ and Bowley, RM and Swift, MR}, title = {Propulsion of a Two-Sphere Swimmer.}, journal = {Physical review letters}, volume = {115}, number = {24}, pages = {248102}, doi = {10.1103/PhysRevLett.115.248102}, pmid = {26705658}, issn = {1079-7114}, mesh = {Biomechanical Phenomena ; Computer Simulation ; *Models, Theoretical ; *Swimming ; }, abstract = {We describe experiments and simulations demonstrating the propulsion of a neutrally buoyant swimmer that consists of a pair of spheres attached by a spring, immersed in a vibrating fluid. The vibration of the fluid induces relative motion of the spheres which, for sufficiently large amplitudes, can lead to motion of the center of mass of the two spheres. We find that the swimming speed obtained from both experiment and simulation agree and collapse onto a single curve if plotted as a function of the streaming Reynolds number, suggesting that the propulsion is related to streaming flows. There appears to be a critical onset value of the streaming Reynolds number for swimming to occur. We observe a change in the streaming flows as the Reynolds number increases, from that generated by two independent oscillating spheres to a collective flow pattern around the swimmer as a whole. The mechanism for swimming is traced to a strengthening of a jet of fluid in the wake of the swimmer.}, }
@article {pmid26698964, year = {2015}, author = {Hay, RF and Gibson, GM and Simpson, SH and Padgett, MJ and Phillips, DB}, title = {'Lissajous-like' trajectories in optical tweezers.}, journal = {Optics express}, volume = {23}, number = {25}, pages = {31716-31727}, doi = {10.1364/OE.23.031716}, pmid = {26698964}, issn = {1094-4087}, abstract = {When a microscopic particle moves through a low Reynolds number fluid, it creates a flow-field which exerts hydrodynamic forces on surrounding particles. In this work we study the 'Lissajous-like' trajectories of an optically trapped 'probe' microsphere as it is subjected to time-varying oscillatory hydrodynamic flow-fields created by a nearby moving particle (the 'actuator'). We show a breaking of time-reversal symmetry in the motion of the probe when the driving motion of the actuator is itself time-reversal symmetric. This symmetry breaking results in a fluid-pumping effect, which arises due to the action of both a time-dependent hydrodynamic flow and a position-dependent optical restoring force, which together determine the trajectory of the probe particle. We study this situation experimentally, and show that the form of the trajectories observed is in good agreement with Stokesian dynamics simulations. Our results are related to the techniques of active micro-rheology and flow measurement, and also highlight how the mere presence of an optical trap can perturb the environment it is in place to measure.}, }
@article {pmid26684120, year = {2015}, author = {Stepanov, R and Golbraikh, E and Frick, P and Shestakov, A}, title = {Hindered Energy Cascade in Highly Helical Isotropic Turbulence.}, journal = {Physical review letters}, volume = {115}, number = {23}, pages = {234501}, doi = {10.1103/PhysRevLett.115.234501}, pmid = {26684120}, issn = {1079-7114}, abstract = {The conventional approach to the turbulent energy cascade, based on Richardson-Kolmogorov phenomenology, ignores the topology of emerging vortices, which is related to the helicity of the turbulent flow. It is generally believed that helicity can play a significant role in turbulent systems, e.g., supporting the generation of large-scale magnetic fields, but its impact on the energy cascade to small scales has never been observed. We suggest, for the first time, a generalized phenomenology for isotropic turbulence with an arbitrary spectral distribution of the helicity. We discuss various scenarios of direct turbulent cascades with new helicity effect, which can be interpreted as a hindering of the spectral energy transfer. Therefore, the energy is accumulated and redistributed so that the efficiency of nonlinear interactions will be sufficient to provide a constant energy flux. We confirm our phenomenology by high Reynolds number numerical simulations based on a shell model of helical turbulence. The energy in our model is injected at a certain large scale only, whereas the source of helicity is distributed over all scales. In particular, we found that the helical bottleneck effect can appear in the inertial interval of the energy spectrum.}, }
@article {pmid26671398, year = {2015}, author = {Zia, RN and Swan, JW and Su, Y}, title = {Pair mobility functions for rigid spheres in concentrated colloidal dispersions: Force, torque, translation, and rotation.}, journal = {The Journal of chemical physics}, volume = {143}, number = {22}, pages = {224901}, doi = {10.1063/1.4936664}, pmid = {26671398}, issn = {1089-7690}, abstract = {The formulation of detailed models for the dynamics of condensed soft matter including colloidal suspensions and other complex fluids requires accurate description of the physical forces between microstructural constituents. In dilute suspensions, pair-level interactions are sufficient to capture hydrodynamic, interparticle, and thermodynamic forces. In dense suspensions, many-body interactions must be considered. Prior analytical approaches to capturing such interactions such as mean-field approaches replace detailed interactions with averaged approximations. However, long-range coupling and effects of concentration on local structure, which may play an important role in, e.g., phase transitions, are smeared out in such approaches. An alternative to such approximations is the detailed modeling of hydrodynamic interactions utilizing precise couplings between moments of the hydrodynamic traction on a suspended particle and the motion of that or other suspended particles. For two isolated spheres, a set of these functions was calculated by Jeffrey and Onishi [J. Fluid Mech. 139, 261-290 (1984)] and Jeffrey [J. Phys. Fluids 4, 16-29 (1992)]. Along with pioneering work by Batchelor, these are the touchstone for low-Reynolds-number hydrodynamic interactions and have been applied directly in the solution of many important problems related to the dynamics of dilute colloidal dispersions [G. K. Batchelor and J. T. Green, J. Fluid Mech. 56, 375-400 (1972) and G. K. Batchelor, J. Fluid Mech. 74, 1-29 (1976)]. Toward extension of these functions to concentrated systems, here we present a new stochastic sampling technique to rapidly calculate an analogous set of mobility functions describing the hydrodynamic interactions between two hard spheres immersed in a suspension of arbitrary concentration, utilizing accelerated Stokesian dynamics simulations. These mobility functions provide precise, radially dependent couplings of hydrodynamic force and torque to particle translation and rotation, for arbitrary colloid volume fraction ϕ. The pair mobilities (describing entrainment of one particle by the disturbance flow created by another) decay slowly with separation distance: as 1/r, for volume fractions 0.05 ≤ ϕ ≤ 0.5. For the relative mobility, we find an initially rapid growth as a pair separates, followed by a slow, 1/r growth. Up to ϕ ≤ 0.4, the relative mobility does not reached the far-field value even beyond separations of many particle sizes. In the case of ϕ = 0.5, the far-field asymptote is reached but only at a separation of eight radii and after a slow 1/r growth. At these higher concentrations, the coefficients also reveal liquid-like structural effects on pair mobility at close separations. These results confirm that long-range many-body hydrodynamic interactions are an essential part of the dynamics of concentrated systems and that care must be taken when applying renormalization schemes.}, }
@article {pmid26652667, year = {2015}, author = {Schultz, MP and Walker, JM and Steppe, CN and Flack, KA}, title = {Impact of diatomaceous biofilms on the frictional drag of fouling-release coatings.}, journal = {Biofouling}, volume = {31}, number = {9-10}, pages = {759-773}, doi = {10.1080/08927014.2015.1108407}, pmid = {26652667}, issn = {1029-2454}, mesh = {Biofilms/*growth &amp; development ; Biofouling/*prevention &amp; control ; *Friction ; Models, Theoretical ; *Paint ; *Ships ; Surface Properties ; }, abstract = {Skin-friction results are presented for fouling-release (FR) hull coatings in the unexposed, clean condition and after dynamic exposure to diatomaceous biofilms for 3 and 6 months. The experiments were conducted in a fully developed turbulent channel flow facility spanning a wide Reynolds number range. The results show that the clean FR coatings tested were hydraulically smooth over much of the Reynolds number range. Biofilms, however, resulted in an increase in skin-friction of up to 70%. The roughness functions for the biofilm-covered surfaces did not display universal behavior, but instead varied with the percentage coverage by the biofilm. The effect of the biofilm was observed to scale with its mean thickness and the square root of the percentage coverage. A new effective roughness length scale (keff) for biofilms based on these parameters is proposed. Boundary layer similarity-law scaling is used to predict the impact of these biofilms on the required shaft power for a mid-sized naval surface combatant at cruising speed. The increase in power is estimated to be between 1.5% and 10.1% depending on the biofilm thickness and percentage coverage.}, }
@article {pmid26651792, year = {2015}, author = {Minier, JP and Profeta, C}, title = {Kinetic and dynamic probability-density-function descriptions of disperse turbulent two-phase flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {5}, pages = {053020}, doi = {10.1103/PhysRevE.92.053020}, pmid = {26651792}, issn = {1550-2376}, abstract = {This article analyzes the status of two classical one-particle probability density function (PDF) descriptions of the dynamics of discrete particles dispersed in turbulent flows. The first PDF formulation considers only the process made up by particle position and velocity Z(p)=(x(p),U(p)) and is represented by its PDF p(t; y(p),V(p)) which is the solution of a kinetic PDF equation obtained through a flux closure based on the Furutsu-Novikov theorem. The second PDF formulation includes fluid variables into the particle state vector, for example, the fluid velocity seen by particles Z(p)=(x(p),U(p),U(s)), and, consequently, handles an extended PDF p(t; y(p),V(p),V(s)) which is the solution of a dynamic PDF equation. For high-Reynolds-number fluid flows, a typical formulation of the latter category relies on a Langevin model for the trajectories of the fluid seen or, conversely, on a Fokker-Planck equation for the extended PDF. In the present work, a new derivation of the kinetic PDF equation is worked out and new physical expressions of the dispersion tensors entering the kinetic PDF equation are obtained by starting from the extended PDF and integrating over the fluid seen. This demonstrates that, under the same assumption of a Gaussian colored noise and irrespective of the specific stochastic model chosen for the fluid seen, the kinetic PDF description is the marginal of a dynamic PDF one. However, a detailed analysis reveals that kinetic PDF models of particle dynamics in turbulent flows described by statistical correlations constitute incomplete stand-alone PDF descriptions and, moreover, that present kinetic-PDF equations are mathematically ill posed. This is shown to be the consequence of the non-Markovian characteristic of the stochastic process retained to describe the system and the use of an external colored noise. Furthermore, developments bring out that well-posed PDF descriptions are essentially due to a proper choice of the variables selected to describe physical systems and guidelines are formulated to emphasize the key role played by the notion of slow and fast variables.}, }
@article {pmid26651790, year = {2015}, author = {Altmeyer, S and Do, Y and Lai, YC}, title = {Ring-bursting behavior en route to turbulence in narrow-gap Taylor-Couette flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {5}, pages = {053018}, doi = {10.1103/PhysRevE.92.053018}, pmid = {26651790}, issn = {1550-2376}, abstract = {We investigate the Taylor-Couette system where the radius ratio is close to unity. Systematically increasing the Reynolds number, we observe a number of previously known transitions, such as one from the classical Taylor vortex flow (TVF) to wavy vortex flow (WVF) and the transition to fully developed turbulence. Prior to the onset of turbulence, we observe intermittent bursting patterns of localized turbulent patches, confirming the experimentally observed pattern of very short wavelength bursts (VSWBs). A striking finding is that, for a Reynolds number larger than that for the onset of VSWBs, a new type of intermittently bursting behavior emerges: patterns of azimuthally closed rings of various orders. We call them ring-bursting patterns, which surround the cylinder completely but remain localized and separated in the axial direction through nonturbulent wavy structures. We employ a number of quantitative measures including the cross-flow energy to characterize the ring-bursting patterns and to distinguish them from the background flow. These patterns are interesting because they do not occur in the wide-gap Taylor-Couette flow systems. The narrow-gap regime is less studied but certainly deserves further attention to gain deeper insights into complex flow dynamics in fluids.}, }
@article {pmid26636667, year = {2016}, author = {Dey, KK and Pong, FY and Breffke, J and Pavlick, R and Hatzakis, E and Pacheco, C and Sen, A}, title = {Dynamic Coupling at the Ångström Scale.}, journal = {Angewandte Chemie (International ed. in English)}, volume = {55}, number = {3}, pages = {1113-1117}, doi = {10.1002/anie.201509237}, pmid = {26636667}, issn = {1521-3773}, abstract = {While momentum transfer from active particles to their immediate surroundings has been studied for both synthetic and biological micron-scale systems, a similar phenomenon was presumed unlikely to exist at smaller length scales due to the dominance of viscosity in the ultralow Reynolds number regime. Using diffusion NMR spectroscopy, we studied the motion of two passive tracers--tetramethylsilane and benzene--dissolved in an organic solution of active Grubbs catalyst. Significant enhancements in diffusion were observed for both the tracers and the catalyst as a function of reaction rate. A similar behavior was also observed for the enzyme urease in aqueous solution. Surprisingly, momentum transfer at the molecular scale closely resembles that reported for microscale systems and appears to be independent of swimming mechanism. Our work provides new insight into the role of active particles on advection and mixing at the Ångström scale.}, }
@article {pmid26628288, year = {2015}, author = {Wang, S and Ardekani, AM}, title = {Biogenic mixing induced by intermediate Reynolds number swimming in stratified fluids.}, journal = {Scientific reports}, volume = {5}, number = {}, pages = {17448}, pmid = {26628288}, issn = {2045-2322}, mesh = {Animals ; Humans ; *Models, Theoretical ; *Swimming ; }, abstract = {We study fully resolved motion of interacting swimmers in density stratified fluids using an archetypal swimming model called "squirmer". The intermediate Reynolds number regime is particularly important, because the vast majority of organisms in the aphotic ocean (i.e. regions that are 200 m beneath the sea surface) are small (mm-cm) and their motion is governed by the balance of inertial and viscous forces. Our study shows that the mixing efficiency and the diapycnal eddy diffusivity, a measure of vertical mass flux, within a suspension of squirmers increases with Reynolds number. The mixing efficiency is in the range of O(0.0001-0.04) when the swimming Reynolds number is in the range of O(0.1-100). The values of diapycnal eddy diffusivity and Cox number are two orders of magnitude larger for vertically swimming cells compared to horizontally swimming cells. For a suspension of squirmers in a decaying isotropic turbulence, we find that the diapycnal eddy diffusivity enhances due to the strong viscous dissipation generated by squirmers as well as the interaction of squirmers with the background turbulence.}, }
@article {pmid26621672, year = {2016}, author = {Avari, H and Savory, E and Rogers, KA}, title = {An In Vitro Hemodynamic Flow System to Study the Effects of Quantified Shear Stresses on Endothelial Cells.}, journal = {Cardiovascular engineering and technology}, volume = {7}, number = {1}, pages = {44-57}, doi = {10.1007/s13239-015-0250-x}, pmid = {26621672}, issn = {1869-4098}, support = {//Canadian Institutes of Health Research/Canada ; }, mesh = {Animals ; Biomechanical Phenomena/physiology ; Cells, Cultured ; Endothelial Cells/*physiology ; Endothelium, Vascular/cytology/*physiology ; Hemodynamics/*physiology ; Laser-Doppler Flowmetry ; *Models, Cardiovascular ; Stress, Mechanical ; Swine ; }, abstract = {Numerous in vitro systems have previously been developed and employed for studying the effects of hemodynamics on endothelial cell (EC) dysfunction. In the majority of that work, accurate flow quantification (e.g., uniformity of the flow over the ECs) remains elusive and wall shear stress (WSS) quantifications are determined using theoretical relationships (without considering the flow channel aspect ratio effects). In addition, those relationships are not applicable to flows other than steady laminar cases. The present work discusses the development of a novel hemodynamic flow system for studying the effects of various well-quantified flow regimes over ECs. The current work presents a novel hemodynamic flow system applying the concept of a parallel plate flow chamber (PPFC) with live microscopy access for studying the effects of quantified WSS on ECs. A range of steady laminar, pulsatile (carotid wave form) and low-Reynolds number turbulent WSSs were quantified through velocity field measurements by a laser Doppler velocimetry (LDV) system, to validate the functionality of the current hemodynamic flow system. Uniformity of the flow across the channel width can be analyzed with the current system (e.g., the flow was uniform across about 65-75% of the channel width for the steady cases). The WSS obtained from the experiments had higher values in almost all of the cases when compared to the most commonly-used theoretical solution (9% < error < 16%), whereas another relationship, which considers the channel dimensions, had better agreement with the experimental results (1% < error < 8%). Additionally, the latter relationship predicted the uniform flow region in the PPFC with an average difference of <5% when compared to the experimental results. The experimental data also showed that the WSS at various locations (D, E and F) at the test section differed by less than 4% for the laminar cases representing a fully developed flow. WSS was also determined for a low-Re (Re = 2750) turbulent flow using (1) the Reynolds shears stress and (2) the time-averaged velocity profile gradient at the wall, with a good agreement (differences <16%) between the two where the first method returned a higher value than the second. Porcine aortic endothelial cell (PAEC) viability in the system and morphological cell response to laminar WSS of about 11 dyne/cm(2), were observed. These results provide performance validation of this novel in vitro system with many improved features compared to previous similar prototypes for investigation of flow effects on ECs. The integration of the LDV technique in the current study and the comparison of the results with those from theory revealed that great care must be taken when using PPFCs since the commonly used theoretical relation for laminar steady flows is unable to predict the flow uniformity (which may introduce significant statistical bias in biological studies) and the predicted WSS was subjected to greater error when compared to a more comprehensive equation presented in the current work. Moreover, application of the LDV technique in the current system is essential for studies of more complex cases, such as disturbed flows, where the WSS cannot be predicted using theoretical or numerical modelling methods.}, }
@article {pmid26598001, year = {2015}, author = {Gaddam, A and Agrawal, A and Joshi, SS and Thompson, MC}, title = {Utilization of Cavity Vortex To Delay the Wetting Transition in One-Dimensional Structured Microchannels.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {31}, number = {49}, pages = {13373-13384}, doi = {10.1021/acs.langmuir.5b03666}, pmid = {26598001}, issn = {1520-5827}, abstract = {Frictional resistance across rough surfaces depends on the existence of slip on the liquid-gas interface; therefore, prolonging the existence of liquid-gas interface becomes relevant. In this work, we explore manipulation of the cavity shape in order to delay the wetting transition. We propose that liquid-driven vortices generated in the air cavity dissipate sufficient energy to delay the Cassie-Wenzel transition. Toward this, we fabricated cavities on the side walls of a polydimethylsiloxane-based microchannel for easy visualization and analysis of the dynamics of the liquid-gas interface. Two distinct flow regimes are identified in the experimental envelope. In the first regime, the liquid-gas interface is found to be protruding into the flow field, thus increasing the pressure drop at low Reynolds number. In the second regime, flow rate and geometry-based wetting transitions are established at moderate to high Reynolds numbers. We then investigate the effect of different cavity shapes (square, trapezoidal, and U-shape) in delaying the wetting transition by manipulating liquid-driven vortices. Out of the shapes considered in this study, trapezoidal cavities perform better than cavities with vertical walls in delaying the wetting transition due to geometrical squeezing of vortices toward the liquid-gas interface. Numerical simulations corroborate the experimental findings in that cavities with inclined walls exert more force on the liquid-gas interface, thus delaying their wetting transition. The proposed method being passive in nature appears more attractive than previous active methods.}, }
@article {pmid26593731, year = {2016}, author = {Sekhar, YR and Sharma, KV and Kamal, S}, title = {Nanofluid heat transfer under mixed convection flow in a tube for solar thermal energy applications.}, journal = {Environmental science and pollution research international}, volume = {23}, number = {10}, pages = {9411-9417}, doi = {10.1007/s11356-015-5715-9}, pmid = {26593731}, issn = {1614-7499}, mesh = {*Convection ; *Hot Temperature ; *Nanoparticles ; *Solar Energy ; Water ; }, abstract = {The solar flat plate collector operating under different convective modes has low efficiency for energy conversion. The energy absorbed by the working fluid in the collector system and its heat transfer characteristics vary with solar insolation and mass flow rate. The performance of the system is improved by reducing the losses from the collector. Various passive methods have been devised to aid energy absorption by the working fluid. Also, working fluids are modified using nanoparticles to improve the thermal properties of the fluid. In the present work, simulation and experimental studies are undertaken for pipe flow at constant heat flux boundary condition in the mixed convection mode. The working fluid at low Reynolds number in the mixed laminar flow range is undertaken with water in thermosyphon mode for different inclination angles of the tube. Local and average coefficients are determined experimentally and compared with theoretical values for water-based Al2O3 nanofluids. The results show an enhancement in heat transfer in the experimental range with Rayleigh number at higher inclinations of the collector tube for water and nanofluids.}, }
@article {pmid26590151, year = {2015}, author = {Rolland, J}, title = {Stochastic analysis of the time evolution of laminar-turbulent bands of plane Couette flow.}, journal = {The European physical journal. E, Soft matter}, volume = {38}, number = {11}, pages = {121}, pmid = {26590151}, issn = {1292-895X}, abstract = {This article is concerned with the time evolution of the oblique laminar-turbulent bands of transitional plane Couette flow under the influence of turbulent noise. Our study is focused on the amplitude of modulation of turbulence (the bands). In order to guide the numerical study of the flow, we first perform an analytical and numerical analysis of a Stochastic Ginzburg-Landau (GL) equation for a complex order parameter. The modulus of this order parameter models the amplitude of modulation of turbulence. Firstly, we compute the autocorrelation function of said modulus once the band is established. Secondly, we perform a calculation of average and fluctuations around the exponential growth of the order parameter. This type of analysis is similar to the Stochastic Structural Stability Theory (S3T). We then perform numerical simulations of the Navier-Stokes equations in order to confront these predictions with the actual behaviour of the bands. Computation of the autocorrelation function of the modulation of turbulence shows quantitative agreement with the model: in the established band regime, the amplitude of modulation follows an Ornstein-Uhlenbeck process. In order to test the S3T predictions, we perform quench experiments, sudden decreases of the Reynolds number from uniform turbulence, in which modulation appears. We compute the average evolution of the amplitude of modulation and the fluctuations around it. We find good agreement between numerics and modeling. The average trajectory grows exponentially, at a rate clearly smaller than that of the formation of laminar holes. Meanwhile, the actual time evolution remains in a flaring envelope, centered on the average, and expanding at the same rate. These results provide further validation of the stochastic modeling for the time evolution of the bands for further studies. Besides, they stress on the difference between the oblique band formation and the formation of laminar holes.}, }
@article {pmid26584257, year = {2016}, author = {Zhang, J and Yan, S and Yuan, D and Alici, G and Nguyen, NT and Ebrahimi Warkiani, M and Li, W}, title = {Fundamentals and applications of inertial microfluidics: a review.}, journal = {Lab on a chip}, volume = {16}, number = {1}, pages = {10-34}, doi = {10.1039/c5lc01159k}, pmid = {26584257}, issn = {1473-0189}, mesh = {Humans ; *Microfluidic Analytical Techniques ; Particle Size ; Surface Properties ; }, abstract = {In the last decade, inertial microfluidics has attracted significant attention and a wide variety of channel designs that focus, concentrate and separate particles and fluids have been demonstrated. In contrast to conventional microfluidic technologies, where fluid inertia is negligible and flow remains almost within the Stokes flow region with very low Reynolds number (Re ≪ 1), inertial microfluidics works in the intermediate Reynolds number range (~1 < Re < ~100) between Stokes and turbulent regimes. In this intermediate range, both inertia and fluid viscosity are finite and bring about several intriguing effects that form the basis of inertial microfluidics including (i) inertial migration and (ii) secondary flow. Due to the superior features of high-throughput, simplicity, precise manipulation and low cost, inertial microfluidics is a very promising candidate for cellular sample processing, especially for samples with low abundant targets. In this review, we first discuss the fundamental kinematics of particles in microchannels to familiarise readers with the mechanisms and underlying physics in inertial microfluidic systems. We then present a comprehensive review of recent developments and key applications of inertial microfluidic systems according to their microchannel structures. Finally, we discuss the perspective of employing fluid inertia in microfluidics for particle manipulation. Due to the superior benefits of inertial microfluidics, this promising technology will still be an attractive topic in the near future, with more novel designs and further applications in biology, medicine and industry on the horizon.}, }
@article {pmid26577358, year = {2015}, author = {Clark, WD and Eslahpazir, BA and Argueta-Morales, IR and Kassab, AJ and Divo, EA and DeCampli, WM}, title = {Comparison Between Bench-Top and Computational Modelling of Cerebral Thromboembolism in Ventricular Assist Device Circulation.}, journal = {Cardiovascular engineering and technology}, volume = {6}, number = {3}, pages = {242-255}, doi = {10.1007/s13239-015-0230-1}, pmid = {26577358}, issn = {1869-4098}, mesh = {Carotid Arteries/*physiopathology ; Cerebral Cortex/*blood supply ; Coronary Artery Bypass/methods ; *Heart-Assist Devices ; Hydrodynamics ; Intracranial Thrombosis/*physiopathology ; *Models, Cardiovascular ; }, abstract = {Despite improvements in ventricular assist devices (VAD) design, VAD-induced stroke rates remain remarkably high at 14-47%. We previously employed computational fluid dynamics (CFD) to propose adjustment of VAD outflow graft (VAD-OG) implantation to reduce stoke. Herein, we present an in-vitro model of cerebral vessel embolization in VAD-assisted circulation, and compare benchtop results to CFD predictions. The benchtop flow-loop consists of a 3D printed aortic bed using Accura 60 polymer driven by a continuous-flow pump. Three hundred spherical particles simulating thrombi of 2, 3.5, and 5 mm diameters were injected at the mock VAD-OG inlet. A water and glycerin mixture (3.8 cP viscosity) synthetically mimicked blood. The flowrate was adjusted to match the CFD Reynolds number. Catch cans were used to capture and count particles reaching cerebral vessels. VAD-OG geometries were evaluated using comparison of means Z-score range of -1.96 ≤ Z ≤ 1.96 to demonstrate overall agreement between computational and in-vitro techniques. Z-scores were: (i) Z = -1.05 for perpendicular (0°), (ii) Z = 0.32 for intermediate (30°), and (iii) Z = -0.52 for shallow (60°) anastomosis and confirmed agreement for all geometries. This study confirmed added benefits of using a left carotid artery bypass-graft with percent embolization reduction: 22.6% for perpendicular, 21.2% for intermediate, and 11.9% for shallow anastomoses. The shallow anastomosis demonstrated lower degrees of aortic arch flow recirculation, consistent with steady-flow computations. Quantitatively and qualitatively, contemporary steady-flow computational models for predicting VAD-induced cerebral embolization can be achieved in-vitro to validate the CFD equivalent.}, }
@article {pmid26565499, year = {2015}, author = {Gravish, N and Peters, JM and Combes, SA and Wood, RJ}, title = {Collective Flow Enhancement by Tandem Flapping Wings.}, journal = {Physical review letters}, volume = {115}, number = {18}, pages = {188101}, doi = {10.1103/PhysRevLett.115.188101}, pmid = {26565499}, issn = {1079-7114}, abstract = {We examine the fluid-mechanical interactions that occur between arrays of flapping wings when operating in close proximity at a moderate Reynolds number (Re≈100-1000). Pairs of flapping wings are oscillated sinusoidally at frequency f, amplitude θ_{M}, phase offset ϕ, and wing separation distance D^{*}, and outflow speed v^{*} is measured. At a fixed separation distance, v^{*} is sensitive to both f and ϕ, and we observe both constructive and destructive interference in airspeed. v^{*} is maximized at an optimum phase offset, ϕ_{max}, which varies with wing separation distance, D^{*}. We propose a model of collective flow interactions between flapping wings based on vortex advection, which reproduces our experimental data.}, }
@article {pmid26565366, year = {2015}, author = {Bösch, F and Chikatamarla, SS and Karlin, IV}, title = {Entropic multirelaxation lattice Boltzmann models for turbulent flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {4}, pages = {043309}, doi = {10.1103/PhysRevE.92.043309}, pmid = {26565366}, issn = {1550-2376}, abstract = {We present three-dimensional realizations of a class of lattice Boltzmann models introduced recently by the authors [I. V. Karlin, F. Bösch, and S. S. Chikatamarla, Phys. Rev. E 90, 031302(R) (2014)] and review the role of the entropic stabilizer. Both coarse- and fine-grid simulations are addressed for the Kida vortex flow benchmark. We show that the outstanding numerical stability and performance is independent of a particular choice of the moment representation for high-Reynolds-number flows. We report accurate results for low-order moments for homogeneous isotropic decaying turbulence and second-order grid convergence for most assessed statistical quantities. It is demonstrated that all the three-dimensional lattice Boltzmann realizations considered herein converge to the familiar lattice Bhatnagar-Gross-Krook model when the resolution is increased. Moreover, thanks to the dynamic nature of the entropic stabilizer, the present model features less compressibility effects and maintains correct energy and enstrophy dissipation. The explicit and efficient nature of the present lattice Boltzmann method renders it a promising candidate for both engineering and scientific purposes for highly turbulent flows.}, }
@article {pmid26565347, year = {2015}, author = {Perrin, VE and Jonker, HJ}, title = {Relative velocity distribution of inertial particles in turbulence: A numerical study.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {4}, pages = {043022}, doi = {10.1103/PhysRevE.92.043022}, pmid = {26565347}, issn = {1550-2376}, abstract = {The distribution of relative velocities between particles provides invaluable information on the rates and characteristics of particle collisions. We show that the theoretical model of Gustavsson and Mehlig [K. Gustavsson and B. Mehlig, J. Turbul. 15, 34 (2014)], within its anticipated limits of validity, can predict the joint probability density function of relative velocities and separations of identical inertial particles in isotropic turbulent flows with remarkable accuracy. We also quantify the validity range of the model. The model matches two limits (or two types) of relative motion between particles: one where pair diffusion dominates (i.e., large coherence between particle motion) and one where caustics dominate (i.e., large velocity differences between particles at small separations). By using direct numerical simulation combined with Lagrangian particle tracking, we assess the model prediction in homogeneous and isotropic turbulence. We demonstrate that, when sufficient caustics are present at a given separation and the particle response time is significantly smaller than the integral time scales of the flow, the distribution exhibits the same universal power-law form dictated by the correlation dimension as predicted by the model of Gustavsson and Mehlig. In agreement with the model, no strong dependency on the Taylor-based Reynolds number is observed.}, }
@article {pmid26565336, year = {2015}, author = {Kim, I and Wu, XL}, title = {Unified Strouhal-Reynolds number relationship for laminar vortex streets generated by different-shaped obstacles.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {4}, pages = {043011}, doi = {10.1103/PhysRevE.92.043011}, pmid = {26565336}, issn = {1550-2376}, abstract = {A structure-based Strouhal-Reynolds number relationship, St=1/(A+B/Re), has been recently proposed based on observations of laminar vortex shedding from circular cylinders in a flowing soap film. Since the new St-Re relation was derived from a general physical consideration, it raises the possibility that it may be applicable to vortex shedding from bodies other than circular ones. The work presented herein provides experimental evidence that this is the case. Our measurements also show that, in the asymptotic limit (Re→∞), St(∞)=1/A≃0.21 is constant independent of rod shapes, leaving B the only parameter that is shape dependent.}, }
@article {pmid26565330, year = {2015}, author = {Edlund, EM and Ji, H}, title = {Reynolds number scaling of the influence of boundary layers on the global behavior of laboratory quasi-Keplerian flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {4}, pages = {043005}, doi = {10.1103/PhysRevE.92.043005}, pmid = {26565330}, issn = {1550-2376}, abstract = {We present fluid velocity measurements in a modified Taylor-Couette device operated in the quasi-Keplerian regime, where it is observed that nearly ideal flows exhibit self-similarity under scaling of the Reynolds number. In contrast, nonideal flows show progressive departure from ideal Couette as the Reynolds number is increased. We present a model that describes the observed departures from ideal Couette rotation as a function of the fluxes of angular momentum across the boundaries, capturing the dependence on Reynolds number and boundary conditions.}, }
@article {pmid26565328, year = {2015}, author = {Phillips, WR}, title = {Drift and pseudomomentum in bounded turbulent shear flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {4}, pages = {043003}, doi = {10.1103/PhysRevE.92.043003}, pmid = {26565328}, issn = {1550-2376}, abstract = {This paper is concerned with the evaluation of two Lagrangian measures which arise in oscillatory or fluctuating shear flows when the fluctuating field is rotational and the spectrum of wave numbers which comprise it is continuous. The measures are the drift and pseudomomentum. Phillips [J. Fluid Mech. 430, 209 (2001)] has shown that the measures are, in such instances, succinctly expressed in terms of Lagrangian integrals of Eulerian space-time correlations. But they are difficult to interpret, and the present work begins by expressing them in a more insightful form. This is achieved by assuming the space-time correlations are separable as magnitude, determined by one-point velocity correlations, and spatial diminution. The measures then parse into terms comprised of the mean Eulerian velocity, one-point velocity correlations, and a family of integrals of spatial diminution, which in turn define a series of Lagrangian time and velocity scales. The pseudomomentum is seen to be strictly negative and related to the turbulence kinetic energy, while the drift is mixed and strongly influenced by the Reynolds stress. Both are calculated for turbulent channel flow for a range of Reynolds numbers and appear, as the Reynolds number increases, to approach a terminal form. At all Reynolds numbers studied, the pseudomomentum has a sole peak located in wall units in the low teens, while at the highest Reynolds number studied, Re(τ)=5200, the drift is negative in the vicinity of that peak, positive elsewhere, and largest near the rigid boundary. In contrast, the time and velocity scales grow almost logarithmically over much of the layer. Finally, the drift and pseudomomentum are discussed in the context of coherent wall layer structures with which they are intricately linked.}, }
@article {pmid26565230, year = {2015}, author = {Clark, AH and Shattuck, MD and Ouellette, NT and O'Hern, CS}, title = {Onset and cessation of motion in hydrodynamically sheared granular beds.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {4}, pages = {042202}, doi = {10.1103/PhysRevE.92.042202}, pmid = {26565230}, issn = {1550-2376}, abstract = {We performed molecular dynamics simulations of granular beds driven by a model hydrodynamic shear flow to elucidate general grain-scale mechanisms that determine the onset and cessation of sediment transport. By varying the Shields number (the nondimensional shear stress at the top of the bed) and particle Reynolds number (the ratio of particle inertia to viscous damping), we explore how variations of the fluid flow rate, particle inertia, and fluid viscosity affect the onset and cessation of bed motion. For low to moderate particle Reynolds numbers, a critical boundary separates mobile and static states. Transition times between these states diverge as this boundary is approached both from above and below. At high particle Reynolds number, inertial effects become dominant, and particle motion can be sustained well below flow rates at which mobilization of a static bed occurs. We also find that the onset of bed motion (for both low and high particle Reynolds numbers) is described by Weibullian weakest-link statistics and thus is crucially dependent on the packing structure of the granular bed, even deep beneath the surface.}, }
@article {pmid26563615, year = {2015}, author = {Tai, J and Lim, CP and Lam, YC}, title = {Visualization of polymer relaxation in viscoelastic turbulent micro-channel flow.}, journal = {Scientific reports}, volume = {5}, number = {}, pages = {16633}, pmid = {26563615}, issn = {2045-2322}, abstract = {In micro-channels, the flow of viscous liquids e.g. water, is laminar due to the low Reynolds number in miniaturized dimensions. An aqueous solution becomes viscoelastic with a minute amount of polymer additives; its flow behavior can become drastically different and turbulent. However, the molecules are typically invisible. Here we have developed a novel visualization technique to examine the extension and relaxation of polymer molecules at high flow velocities in a viscoelastic turbulent flow. Using high speed videography to observe the fluorescein labeled molecules, we show that viscoelastic turbulence is caused by the sporadic, non-uniform release of energy by the polymer molecules. This developed technique allows the examination of a viscoelastic liquid at the molecular level, and demonstrates the inhomogeneity of viscoelastic liquids as a result of molecular aggregation. It paves the way for a deeper understanding of viscoelastic turbulence, and could provide some insights on the high Weissenberg number problem. In addition, the technique may serve as a useful tool for the investigations of polymer drag reduction.}, }
@article {pmid26553982, year = {2015}, author = {Ni, R and Michalski, MH and Brown, E and Doan, N and Zinter, J and Ouellette, NT and Shepherd, GM}, title = {Optimal directional volatile transport in retronasal olfaction.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {112}, number = {47}, pages = {14700-14704}, pmid = {26553982}, issn = {1091-6490}, support = {R01DC 00997701/DC/NIDCD NIH HHS/United States ; }, mesh = {Female ; Humans ; Middle Aged ; Models, Anatomic ; Nose/anatomy &amp; histology/*physiology ; Smell/*physiology ; Time Factors ; Volatilization ; }, abstract = {The ability of humans to distinguish the delicate differences in food flavors depends mostly on retronasal smell, in which food volatiles entrained into the airway at the back of the oral cavity are transported by exhaled air through the nasal cavity to stimulate the olfactory receptor neurons. Little is known whether food volatiles are preferentially carried by retronasal flow toward the nasal cavity rather than by orthonasal flow into the lung. To study the differences between retronasal and orthonasal flow, we obtained computed tomography (CT) images of the orthonasal airway from a healthy human subject, printed an experimental model using a 3D printer, and analyzed the flow field inside the airway. The results show that, during inhalation, the anatomical structure of the oropharynx creates an air curtain outside a virtual cavity connecting the oropharynx and the back of the mouth, which prevents food volatiles from being transported into the main stream toward the lung. In contrast, during exhalation, the flow preferentially sweeps through this virtual cavity and effectively enhances the entrainment of food volatiles into the main retronasal flow. This asymmetrical transport efficiency is also found to have a nonmonotonic Reynolds number dependence: The asymmetry peaks at a range of an intermediate Reynolds number close to 800, because the air curtain effect during inhalation becomes strongest in this range. This study provides the first experimental evidence, to our knowledge, for adaptations of the geometry of the human oropharynx for efficient transport of food volatiles toward the olfactory receptors in the nasal cavity.}, }
@article {pmid26550904, year = {2015}, author = {Jawed, MK and Khouri, NK and Da, F and Grinspun, E and Reis, PM}, title = {Propulsion and Instability of a Flexible Helical Rod Rotating in a Viscous Fluid.}, journal = {Physical review letters}, volume = {115}, number = {16}, pages = {168101}, doi = {10.1103/PhysRevLett.115.168101}, pmid = {26550904}, issn = {1079-7114}, mesh = {*Bacterial Physiological Phenomena ; Locomotion ; *Models, Biological ; Swimming ; Viscosity ; }, abstract = {We combine experiments with simulations to investigate the fluid-structure interaction of a flexible helical rod rotating in a viscous fluid, under low Reynolds number conditions. Our analysis takes into account the coupling between the geometrically nonlinear behavior of the elastic rod with a nonlocal hydrodynamic model for the fluid loading. We quantify the resulting propulsive force, as well as the buckling instability of the originally helical filament that occurs above a critical rotation velocity. A scaling analysis is performed to rationalize the onset of this instability. A universal phase diagram is constructed to map out the region of successful propulsion and the corresponding boundary of stability is established. Comparing our results with data for flagellated bacteria suggests that this instability may be exploited in nature for physiological purposes.}, }
@article {pmid26542943, year = {2016}, author = {Ishimoto, K and Cosson, J and Gaffney, EA}, title = {A simulation study of sperm motility hydrodynamics near fish eggs and spheres.}, journal = {Journal of theoretical biology}, volume = {389}, number = {}, pages = {187-197}, doi = {10.1016/j.jtbi.2015.10.013}, pmid = {26542943}, issn = {1095-8541}, mesh = {Algorithms ; Animals ; Biophysical Phenomena ; Computer Simulation ; Female ; Flatfishes/*physiology ; Hydrodynamics ; Male ; Models, Theoretical ; Movement ; Oscillometry ; *Sperm Motility ; Sperm-Ovum Interactions/*physiology ; Spermatozoa/*physiology ; }, abstract = {For teleost fish fertilisation, sperm must proceed through a small opening on the egg surface, referred to as the micropyle. In this paper, we have used boundary element simulations to explore whether the hydrodynamic attraction between sperm and a fish egg can be a sperm guidance cue. Hydrodynamical egg-sperm interactions alone do not increase the chances of an egg encounter, nor do they induce surface swimming for virtual turbot fish sperm across smooth spheres with a diameter of 1mm, which is representative of a turbot fish egg. When a repulsive surface force between the virtual turbot sperm and the egg is introduced, as motivated by surface charge and van-der-Waals interactions for instance, we find that extended surface swimming of the virtual sperm across a model turbot egg occurs, but ultimately the sperm escapes from the egg. This is due to the small exit angle of the scattering associated with the initial sperm-egg interaction at the egg surface, leading to a weak drift away from the egg, in combination with a weak hydrodynamical attraction between both gametes, though the latter is not sufficient to prevent eventual escape. The resulting transience is not observed experimentally but is a detailed quantitative difference between theory and observation in that stable surface swimming is predicted for eggs with radii larger than about 1.8mm. Regardless, the extended sperm swimming trajectory across the egg constitutes a two-dimensional search for the micropyle and thus the egg is consistently predicted to provide a guidance cue for sperm once they are sufficiently close. In addition, the observation that the virtual turbot sperm swims stably next to a flat plane given repulsive surface interactions, but does not swim stably adjacent to a turbot-sized egg, which is extremely large by sperm-lengthscales, also highlights that the stability of sperm swimming near a boundary is very sensitive to geometry.}, }
@article {pmid26538006, year = {2015}, author = {Grosjean, G and Lagubeau, G and Darras, A and Hubert, M and Lumay, G and Vandewalle, N}, title = {Remote control of self-assembled microswimmers.}, journal = {Scientific reports}, volume = {5}, number = {}, pages = {16035}, pmid = {26538006}, issn = {2045-2322}, abstract = {Physics governing the locomotion of microorganisms and other microsystems is dominated by viscous damping. An effective swimming strategy involves the non-reciprocal and periodic deformations of the considered body. Here, we show that a magnetocapillary-driven self-assembly, composed of three soft ferromagnetic beads, is able to swim along a liquid-air interface when powered by an external magnetic field. More importantly, we demonstrate that trajectories can be fully controlled, opening ways to explore low Reynolds number swimming. This magnetocapillary system spontaneously forms by self-assembly, allowing miniaturization and other possible applications such as cargo transport or solvent flows.}, }
@article {pmid26528815, year = {2015}, author = {Ge, M and Fang, L and Tian, D}, title = {Influence of Reynolds Number on Multi-Objective Aerodynamic Design of a Wind Turbine Blade.}, journal = {PloS one}, volume = {10}, number = {11}, pages = {e0141848}, pmid = {26528815}, issn = {1932-6203}, mesh = {*Aviation ; *Models, Theoretical ; }, abstract = {At present, the radius of wind turbine rotors ranges from several meters to one hundred meters, or even more, which extends Reynolds number of the airfoil profile from the order of 105 to 107. Taking the blade for 3MW wind turbines as an example, the influence of Reynolds number on the aerodynamic design of a wind turbine blade is studied. To make the study more general, two kinds of multi-objective optimization are involved: one is based on the maximum power coefficient (CPopt) and the ultimate load, and the other is based on the ultimate load and the annual energy production (AEP). It is found that under the same configuration, the optimal design has a larger CPopt or AEP (CPopt//AEP) for the same ultimate load, or a smaller load for the same CPopt//AEP at higher Reynolds number. At a certain tip-speed ratio or ultimate load, the blade operating at higher Reynolds number should have a larger chord length and twist angle for the maximum Cpopt//AEP. If a wind turbine blade is designed by using an airfoil database with a mismatched Reynolds number from the actual one, both the load and Cpopt//AEP will be incorrectly estimated to some extent. In some cases, the assessment error attributed to Reynolds number is quite significant, which may bring unexpected risks to the earnings and safety of a wind power project.}, }
@article {pmid26521001, year = {2015}, author = {Kumar, M and Tordjeman, P and Bergez, W and Cavaro, M}, title = {Note: Void effects on eddy current distortion in two-phase liquid metal.}, journal = {The Review of scientific instruments}, volume = {86}, number = {10}, pages = {106104}, doi = {10.1063/1.4932990}, pmid = {26521001}, issn = {1089-7623}, abstract = {A model based on the first order perturbation expansion of magnetic flux in a two-phase liquid metal flow has been developed for low magnetic Reynolds number Rem. This model takes into account the distortion of the induced eddy currents due to the presence of void in the conducting medium. Specific experiments with an eddy current flow meter have been realized for two periodic void distributions. The results have shown, in agreement with the model, that the effects of velocity and void on the emf modulation are decoupled. The magnitude of the void fraction and the void spatial frequency can be determined from the spectral density of the demodulated emf.}, }
@article {pmid26519975, year = {2016}, author = {Adams, MC and Barbano, DM}, title = {Effect of ceramic membrane channel diameter on limiting retentate protein concentration during skim milk microfiltration.}, journal = {Journal of dairy science}, volume = {99}, number = {1}, pages = {167-182}, doi = {10.3168/jds.2015-9897}, pmid = {26519975}, issn = {1525-3198}, mesh = {Animals ; Blood Proteins/analysis ; Ceramics/*chemistry ; Computer Simulation ; *Filtration ; Food Handling ; Hydrodynamics ; *Membranes, Artificial ; Milk/*chemistry ; Milk Proteins/analysis ; Pilot Projects ; Viscosity ; }, abstract = {Our objective was to determine the effect of retentate flow channel diameter (4 or 6mm) of nongraded permeability 100-nm pore size ceramic membranes operated in nonuniform transmembrane pressure mode on the limiting retentate protein concentration (LRPC) while microfiltering (MF) skim milk at a temperature of 50°C, a flux of 55 kg · m(-2) · h(-1), and an average cross-flow velocity of 7 m · s(-1). At the above conditions, the retentate true protein concentration was incrementally increased from 7 to 11.5%. When temperature, flux, and average cross-flow velocity were controlled, ceramic membrane retentate flow channel diameter did not affect the LRPC. This indicates that LRPC is not a function of the Reynolds number. Computational fluid dynamics data, which indicated that both membranes had similar radial velocity profiles within their retentate flow channels, supported this finding. Membranes with 6-mm flow channels can be operated at a lower pressure decrease from membrane inlet to membrane outlet (ΔP) or at a higher cross-flow velocity, depending on which is controlled, than membranes with 4-mm flow channels. This implies that 6-mm membranes could achieve a higher LRPC than 4-mm membranes at the same ΔP due to an increase in cross-flow velocity. In theory, the higher LRPC of the 6-mm membranes could facilitate 95% serum protein removal in 2 MF stages with diafiltration between stages if no serum protein were rejected by the membrane. At the same flux, retentate protein concentration, and average cross-flow velocity, 4-mm membranes require 21% more energy to remove a given amount of permeate than 6-mm membranes, despite the lower surface area of the 6-mm membranes. Equations to predict skim milk MF retentate viscosity as a function of protein concentration and temperature are provided. Retentate viscosity, retentate recirculation pump frequency required to maintain a given cross-flow velocity at a given retentate viscosity, and retentate protein determination by mid-infrared spectrophotometry were all useful tools for monitoring the retentate protein concentration to ensure a sustainable MF process. Using 6-mm membranes instead of 4-mm membranes would be advantageous for processors who wish to reduce energy costs or maximize the protein concentration of a MF retentate.}, }
@article {pmid26504982, year = {2015}, author = {Colla, L and Marinelli, L and Fedele, L and Bobbo, S and Manca, O}, title = {Characterization and Simulation of the Heat Transfer Behaviour of Water-Based ZnO Nanofluids.}, journal = {Journal of nanoscience and nanotechnology}, volume = {15}, number = {5}, pages = {3599-3609}, doi = {10.1166/jnn.2015.9864}, pmid = {26504982}, issn = {1533-4899}, abstract = {This paper deals with the characterization and modelling of water-based nanofluids containing zinc oxide (ZnO) nanoparticles in concentrations ranging between 1 and 10 wt%. Low concentrations were chosen to reduce fouling and excessive pressure drops. First of all, the stability was verified by means of an instrument, based on the dynamic light scattering (DLS) technique, measuring mean nanoparticle diameters and Zeta potential. Moreover, nanofluids pH was measured. Then, thermal conductivities and dynamic viscosities were measured, analysing their dependence on temperature and nanoparticle concentration. Thermal conductivity was measured by means of a hot disk apparatus in the temperature range between 10 and 70 degrees C, while viscosity was measured by a magnetic suspension rheometer in the same range of temperatures. Finally, the heat transfer capability of these fluids was studied measuring their heat transfer coefficients in a dedicated apparatus between 18 and 40 degrees C. Heat transfer coefficient was evaluated at different Reynolds number, in turbulent flow regime. Reynolds and Nusselt numbers were deduced by using previously measured thermal conductivity and viscosity values. Moreover, numerical simulations in two-dimensional turbulent and steady state flow were carried out. No increase in heat transfer coefficient in the temperature range between 18 and 40 degrees C was found. Comparison between experimental and numerical simulation data, in terms of wall temperature profiles, showed a good agreement.}, }
@article {pmid26490629, year = {2015}, author = {Lenz, PH and Takagi, D and Hartline, DK}, title = {Choreographed swimming of copepod nauplii.}, journal = {Journal of the Royal Society, Interface}, volume = {12}, number = {112}, pages = {}, pmid = {26490629}, issn = {1742-5662}, mesh = {Animals ; Biomechanical Phenomena ; Copepoda/*physiology ; *Models, Biological ; Swimming/*physiology ; }, abstract = {Small metazoan paddlers, such as crustacean larvae (nauplii), are abundant, ecologically important and active swimmers, which depend on exploiting viscous forces for locomotion. The physics of micropaddling at low Reynolds number was investigated using a model of swimming based on slender-body theory for Stokes flow. Locomotion of nauplii of the copepod Bestiolina similis was quantified from high-speed video images to obtain precise measurements of appendage movements and the resulting displacement of the body. The kinematic and morphological data served as inputs to the model, which predicted the displacement in good agreement with observations. The results of interest did not depend sensitively on the parameters within the error of measurement. Model tests revealed that the commonly attributed mechanism of 'feathering' appendages during return strokes accounts for only part of the displacement. As important for effective paddling at low Reynolds number is the ability to generate a metachronal sequence of power strokes in combination with synchronous return strokes of appendages. The effect of feathering together with a synchronous return stroke is greater than the sum of each factor individually. The model serves as a foundation for future exploration of micropaddlers swimming at intermediate Reynolds number where both viscous and inertial forces are important.}, }
@article {pmid26456297, year = {2015}, author = {Schwarz, US}, title = {Physical constraints for pathogen movement.}, journal = {Seminars in cell &amp; developmental biology}, volume = {46}, number = {}, pages = {82-90}, doi = {10.1016/j.semcdb.2015.09.025}, pmid = {26456297}, issn = {1096-3634}, mesh = {Algorithms ; Amoeba/*physiology ; Animals ; Bacteria/*growth &amp; development ; Host-Pathogen Interactions ; Humans ; Models, Biological ; Movement/physiology ; Plasmodium/*physiology ; Viruses/*growth &amp; development ; }, abstract = {In this pedagogical review, we discuss the physical constraints that pathogens experience when they move in their host environment. Due to their small size, pathogens are living in a low Reynolds number world dominated by viscosity. For swimming pathogens, the so-called scallop theorem determines which kinds of shape changes can lead to productive motility. For crawling or gliding cells, the main resistance to movement comes from protein friction at the cell-environment interface. Viruses and pathogenic bacteria can also exploit intracellular host processes such as actin polymerization and motor-based transport, if they present the appropriate factors on their surfaces. Similar to cancer cells that also tend to cross various barriers, pathogens often combine several of these strategies in order to increase their motility and therefore their chances to replicate and spread.}, }
@article {pmid26452005, year = {2015}, author = {Emetere, ME and Akinyemi, ML and Akin-Ojo, O}, title = {Parametric retrieval model for estimating aerosol size distribution via the AERONET, LAGOS station.}, journal = {Environmental pollution (Barking, Essex : 1987)}, volume = {207}, number = {}, pages = {381-390}, doi = {10.1016/j.envpol.2015.09.047}, pmid = {26452005}, issn = {1873-6424}, mesh = {Aerosols ; Air Pollutants/*analysis ; Atmosphere ; Environmental Monitoring/*methods ; *Models, Theoretical ; Nigeria ; Particle Size ; Particulate Matter/*analysis ; Seasons ; Weather ; Wind ; }, abstract = {The size characteristics of atmospheric aerosol over the tropical region of Lagos, Southern Nigeria were investigated using two years of continuous spectral aerosol optical depth measurements via the AERONET station for four major bands i.e. blue, green, red and infrared. Lagos lies within the latitude of 6.465°N and longitude of 3.406°E. Few systems of dispersion model was derived upon specified conditions to solve challenges on aerosols size distribution within the Stokes regime. The dispersion model was adopted to derive an aerosol size distribution (ASD) model which is in perfect agreement with existing model. The parametric nature of the formulated ASD model shows the independence of each band to determine the ASD over an area. The turbulence flow of particulates over the area was analyzed using the unified number (Un). A comparative study via the aid of the Davis automatic weather station was carried out on the Reynolds number, Knudsen number and the Unified number. The Reynolds and Unified number were more accurate to describe the atmospheric fields of the location. The aerosols loading trend in January to March (JFM) and August to October (ASO) shows a yearly 15% retention of aerosols in the atmosphere. The effect of the yearly aerosol retention can be seen to partly influence the aerosol loadings between October and February.}, }
@article {pmid26451802, year = {2015}, author = {Phillips, N and Knowles, K and Bomphrey, RJ}, title = {The effect of aspect ratio on the leading-edge vortex over an insect-like flapping wing.}, journal = {Bioinspiration &amp; biomimetics}, volume = {10}, number = {5}, pages = {056020}, doi = {10.1088/1748-3190/10/5/056020}, pmid = {26451802}, issn = {1748-3190}, mesh = {Animals ; Biomimetics/*instrumentation ; Computer Simulation ; Computer-Aided Design ; Equipment Failure Analysis ; Flight, Animal/*physiology ; Insecta/*physiology ; *Models, Biological ; Rheology/methods ; Robotics/*instrumentation ; Shear Strength/physiology ; Stress, Mechanical ; Viscosity ; Wings, Animal/*physiology ; }, abstract = {Insect wing shapes are diverse and a renowned source of inspiration for the new generation of autonomous flapping vehicles, yet the aerodynamic consequences of varying geometry is not well understood. One of the most defining and aerodynamically significant measures of wing shape is the aspect ratio, defined as the ratio of wing length (R) to mean wing chord (c). We investigated the impact of aspect ratio, AR, on the induced flow field around a flapping wing using a robotic device. Rigid rectangular wings ranging from AR = 1.5 to 7.5 were flapped with insect-like kinematics in air with a constant Reynolds number (Re) of 1400, and a dimensionless stroke amplitude of 6.5c (number of chords traversed by the wingtip). Pseudo-volumetric, ensemble-averaged, flow fields around the wings were captured using particle image velocimetry at 11 instances throughout simulated downstrokes. Results confirmed the presence of a high-lift, separated flow field with a leading-edge vortex (LEV), and revealed that the conical, primary LEV grows in size and strength with increasing AR. In each case, the LEV had an arch-shaped axis with its outboard end originating from a focus-sink singularity on the wing surface near the tip. LEV detachment was observed for AR > 1.5 around mid-stroke at ~70% span, and initiated sooner over higher aspect ratio wings. At AR > 3 the larger, stronger vortex persisted under the wing surface well into the next half-stroke leading to a reduction in lift. Circulatory lift attributable to the LEV increased with AR up to AR = 6. Higher aspect ratios generated proportionally less lift distally because of LEV breakdown, and also less lift closer to the wing root due to the previous LEV's continuing presence under the wing. In nature, insect wings go no higher than AR ~ 5, likely in part due to architectural and physiological constraints but also because of the reducing aerodynamic benefits of high AR wings.}, }
@article {pmid26451559, year = {2015}, author = {Linkmann, MF and Morozov, A}, title = {Sudden Relaminarization and Lifetimes in Forced Isotropic Turbulence.}, journal = {Physical review letters}, volume = {115}, number = {13}, pages = {134502}, doi = {10.1103/PhysRevLett.115.134502}, pmid = {26451559}, issn = {1079-7114}, abstract = {We demonstrate an unexpected connection between isotropic turbulence and wall-bounded shear flows. We perform direct numerical simulations of isotropic turbulence forced at large scales at moderate Reynolds numbers and observe sudden transitions from a chaotic dynamics to a spatially simple flow, analogous to the laminar state in wall bounded shear flows. We find that the survival probabilities of turbulence are exponential and the typical lifetimes increase superexponentially with the Reynolds number. Our results suggest that both isotropic turbulence and wall-bounded shear flows qualitatively share the same phase-space dynamics.}, }
@article {pmid26447541, year = {2015}, author = {Lucas, KN and Thornycroft, PJ and Gemmell, BJ and Colin, SP and Costello, JH and Lauder, GV}, title = {Effects of non-uniform stiffness on the swimming performance of a passively-flexing, fish-like foil model.}, journal = {Bioinspiration &amp; biomimetics}, volume = {10}, number = {5}, pages = {056019}, doi = {10.1088/1748-3190/10/5/056019}, pmid = {26447541}, issn = {1748-3190}, mesh = {Animal Fins/*physiology ; Animals ; Biomimetics/*methods ; Computer Simulation ; Elastic Modulus/physiology ; Fishes/*physiology ; *Models, Biological ; Rheology/methods ; Robotics/*methods ; Shear Strength/physiology ; Stress, Mechanical ; Swimming/*physiology ; Viscosity ; }, abstract = {Simple mechanical models emulating fish have been used recently to enable targeted study of individual factors contributing to swimming locomotion without the confounding complexity of the whole fish body. Yet, unlike these uniform models, the fish body is notable for its non-uniform material properties. In particular, flexural stiffness decreases along the fish's anterior-posterior axis. To identify the role of non-uniform bending stiffness during fish-like propulsion, we studied four foil model configurations made by adhering layers of plastic sheets to produce discrete regions of high (5.5 × 10(-5) Nm(2)) and low (1.9 × 10(-5) Nm(2)) flexural stiffness of biologically-relevant magnitudes. This resulted in two uniform control foils and two foils with anterior regions of high stiffness and posterior regions of low stiffness. With a mechanical flapping foil controller, we measured forces and torques in three directions and quantified swimming performance under both heaving (no pitch) and constant 0° angle of attack programs. Foils self-propelled at Reynolds number 21 000-115 000 and Strouhal number ∼0.20-0.25, values characteristic of fish locomotion. Although previous models have emphasized uniform distributions and heaving motions, the combination of non-uniform stiffness distributions and 0° angle of attack pitching program was better able to reproduce the kinematics of freely-swimming fish. This combination was likewise crucial in maximizing swimming performance and resulted in high self-propelled speeds at low costs of transport and large thrust coefficients at relatively high efficiency. Because these metrics were not all maximized together, selection of the 'best' stiffness distribution will depend on actuation constraints and performance goals. These improved models enable more detailed, accurate analyses of fish-like swimming.}, }
@article {pmid26446009, year = {2016}, author = {Martin, BA and Yiallourou, TI and Pahlavian, SH and Thyagaraj, S and Bunck, AC and Loth, F and Sheffer, DB and Kröger, JR and Stergiopulos, N}, title = {Inter-operator Reliability of Magnetic Resonance Image-Based Computational Fluid Dynamics Prediction of Cerebrospinal Fluid Motion in the Cervical Spine.}, journal = {Annals of biomedical engineering}, volume = {44}, number = {5}, pages = {1524-1537}, pmid = {26446009}, issn = {1573-9686}, support = {R13 NS063446/NS/NINDS NIH HHS/United States ; R15 NS071455/NS/NINDS NIH HHS/United States ; 492 1R15NS071455-01/NS/NINDS NIH HHS/United States ; }, mesh = {*Arnold-Chiari Malformation/diagnostic imaging/physiopathology ; *Cerebrospinal Fluid ; *Cervical Cord/diagnostic imaging/physiopathology ; Female ; Humans ; *Magnetic Resonance Imaging ; Male ; Motion ; Observer Variation ; }, abstract = {For the first time, inter-operator dependence of MRI based computational fluid dynamics (CFD) modeling of cerebrospinal fluid (CSF) in the cervical spinal subarachnoid space (SSS) is evaluated. In vivo MRI flow measurements and anatomy MRI images were obtained at the cervico-medullary junction of a healthy subject and a Chiari I malformation patient. 3D anatomies of the SSS were reconstructed by manual segmentation by four independent operators for both cases. CFD results were compared at nine axial locations along the SSS in terms of hydrodynamic and geometric parameters. Intraclass correlation (ICC) assessed the inter-operator agreement for each parameter over the axial locations and coefficient of variance (CV) compared the percentage of variance for each parameter between the operators. Greater operator dependence was found for the patient (0.19 < ICC < 0.99) near the craniovertebral junction compared to the healthy subject (ICC > 0.78). For the healthy subject, hydraulic diameter and Womersley number had the least variance (CV = ~2%). For the patient, peak diastolic velocity and Reynolds number had the smallest variance (CV = ~3%). These results show a high degree of inter-operator reliability for MRI-based CFD simulations of CSF flow in the cervical spine for healthy subjects and a lower degree of reliability for patients with Type I Chiari malformation.}, }
@article {pmid26439225, year = {2015}, author = {Chen, H and Tang, T and Amirfazli, A}, title = {Fast Liquid Transfer between Surfaces: Breakup of Stretched Liquid Bridges.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {31}, number = {42}, pages = {11470-11476}, doi = {10.1021/acs.langmuir.5b03292}, pmid = {26439225}, issn = {1520-5827}, abstract = {In this work, a systematic experimental study was performed to understand the fast liquid transfer process between two surfaces. According to the value of the Reynolds number (Re), the fast transfer is divided into two different scenarios, one with negligible inertia effects (Re ≪ 1) and the other with significant inertia effects (Re > 1). For Re ≪ 1, the influences of the capillary number (Ca) and the dimensionless minimum separation (H(min)* = H(min)/V(1/3), where H(min) is the minimum separation between two surfaces and V is the volume of liquid) on the transfer ratio (α, the volume of liquid transferred to the acceptor surface over the total liquid volume) are discussed. On the basis of the roles of each physical parameter, an empirical equation is presented to predict the transfer ratio, α = f(Ca). This equation involves two coefficients which are affected only by the surface contact angles and H(min)* but not by the liquid viscosity or surface tension. When Re > 1, it is shown for the first time that the transfer ratio does not converge to 0.5 with the increase in the stretching speed.}, }
@article {pmid26429038, year = {2015}, author = {Słowicka, AM and Wajnryb, E and Ekiel-Jeżewska, ML}, title = {Dynamics of flexible fibers in shear flow.}, journal = {The Journal of chemical physics}, volume = {143}, number = {12}, pages = {124904}, doi = {10.1063/1.4931598}, pmid = {26429038}, issn = {1089-7690}, abstract = {Dynamics of flexible non-Brownian fibers in shear flow at low-Reynolds-number are analyzed numerically for a wide range of the ratios A of the fiber bending force to the viscous drag force. Initially, the fibers are aligned with the flow, and later they move in the plane perpendicular to the flow vorticity. A surprisingly rich spectrum of different modes is observed when the value of A is systematically changed, with sharp transitions between coiled and straightening out modes, period-doubling bifurcations from periodic to migrating solutions, irregular dynamics, and chaos.}, }
@article {pmid26428671, year = {2016}, author = {Costa, AP and Xu, X and Khan, MA and Burgess, DJ}, title = {Liposome Formation Using a Coaxial Turbulent Jet in Co-Flow.}, journal = {Pharmaceutical research}, volume = {33}, number = {2}, pages = {404-416}, pmid = {26428671}, issn = {1573-904X}, support = {HHSF223201310117C//PHS HHS/United States ; }, mesh = {Dynamic Light Scattering ; Equipment Design ; Ethanol/chemistry ; Lipids/chemistry ; Liposomes/*chemistry/*ultrastructure ; Particle Size ; Technology, Pharmaceutical/*instrumentation ; Water/chemistry ; }, abstract = {PURPOSE: Liposomes are robust drug delivery systems that have been developed into FDA-approved drug products for several pharmaceutical indications. Direct control in producing liposomes of a particular particle size and particle size distribution is extremely important since liposome size may impact cellular uptake and biodistribution.<br><br>METHODS: A device consisting of an injection-port was fabricated to form a coaxial turbulent jet in co-flow that produces liposomes via the ethanol injection method. By altering the injection-port dimensions and flow rates, a fluid flow profile (i.e., flow velocity ratio vs. Reynolds number) was plotted and associated with the polydispersity index of liposomes.<br><br>RESULTS: Certain flow conditions produced unilamellar, monodispersed liposomes and the mean particle size was controllable from 25 up to >465&#xa0;nm. The mean liposome size is highly dependent on the Reynolds number of the mixed ethanol/aqueous phase and independent of the flow velocity ratio.<br><br>CONCLUSIONS: The significance of this work is that the Reynolds number is predictive of the liposome particle size, independent of the injection-port dimensions. In addition, a new model describing liposome formation is outlined. The significance of the model is that it relates fluid dynamic properties and lipid-molecule physical properties to the final liposome size.}, }
@article {pmid26417381, year = {2015}, author = {Khalafvand, SS and Hung, TK and Ng, EY and Zhong, L}, title = {Kinematic, Dynamic, and Energy Characteristics of Diastolic Flow in the Left Ventricle.}, journal = {Computational and mathematical methods in medicine}, volume = {2015}, number = {}, pages = {701945}, pmid = {26417381}, issn = {1748-6718}, mesh = {Adult ; Biomechanical Phenomena ; Blood Flow Velocity ; Diastole ; Heart Ventricles/anatomy &amp; histology ; Hemodynamics ; Humans ; Hydrodynamics ; Imaging, Three-Dimensional ; Magnetic Resonance Angiography ; Mitral Valve/physiology ; *Models, Cardiovascular ; *Ventricular Function, Left ; }, abstract = {Blood flow characteristics in the normal left ventricle are studied by using the magnetic resonance imaging, the Navier-Stokes equations, and the work-energy equation. Vortices produced during the mitral valve opening and closing are modeled in a two-dimensional analysis and correlated with temporal variations of the Reynolds number and pressure drop. Low shear stress and net pressures on the mitral valve are obtained for flow acceleration and deceleration. Bernoulli energy flux delivered to blood from ventricular dilation is practically balanced by the energy influx and the rate change of kinetic energy in the ventricle. The rates of work done by shear and energy dissipation are small. The dynamic and energy characteristics of the 2D results are comparable to those of a 3D model.}, }
@article {pmid26413565, year = {2015}, author = {Prabu, PM and Padmanaban, KP}, title = {Laminar Wall Jet Flow and Heat Transfer over a Shallow Cavity.}, journal = {TheScientificWorldJournal}, volume = {2015}, number = {}, pages = {926249}, pmid = {26413565}, issn = {1537-744X}, abstract = {This paper presents the detailed simulation of two-dimensional incompressible laminar wall jet flow over a shallow cavity. The flow characteristics of wall jet with respect to aspect ratio (AR), step length (X u), and Reynolds number (Re) of the shallow cavity are expressed. For higher accuracy, third-order discretization is applied for momentum equation which is solved using QUICK scheme with SIMPLE algorithm for pressure-velocity coupling. Low Reynolds numbers 25, 50, 100, 200, 400, and 600 are assigned for simulation. Results are presented for streamline contour, velocity contour, and vorticity formation at wall and also velocity profiles are reported. The detailed study of vortex formation on shallow cavity region is presented for various AR, X u , and Re conditions which led to key findings as Re increases and vortex formation moves from leading edge to trailing edge of the wall. Distance between vortices increases when the step length (X u) increases. When Re increases, the maximum temperature contour distributions take place in shallow cavity region and highest convection heat transfer is obtained in heated walls. The finite volume code (FLUENT) is used for solving Navier-Stokes equations and GAMBIT for modeling and meshing.}, }
@article {pmid26406780, year = {2015}, author = {Shimizu, Y and Ohta, M}, title = {Influence of plaque stiffness on deformation and blood flow patterns in models of stenosis.}, journal = {Biorheology}, volume = {52}, number = {3}, pages = {171-182}, doi = {10.3233/BIR-14016}, pmid = {26406780}, issn = {1878-5034}, mesh = {Arteries/chemistry/physiopathology ; Blood Flow Velocity ; Blood Pressure ; Constriction, Pathologic/*physiopathology ; Humans ; Models, Cardiovascular ; Pulsatile Flow ; Rheology ; *Vascular Stiffness ; }, abstract = {BACKGROUND: Blood flow in stenotic vessels strongly influences the progression of vascular diseases. Plaques in stenotic blood vessels vary in stiffness, which influences plaque behavior and deformation by pressure and flow. Concurrent changes in plaque geometry can, in turn, affect blood flow conditions. Thus, simultaneous studies of blood flow and plaque deformation are needed to fully understand these interactions.<br><br>OBJECTIVES: This study aims to identify the change of flow conditions attendant to plaque deformation in a model stenotic vessel.<br><br>METHODS: Three plaques of differing stiffness were constructed on a vessel wall using poly (vinyl alcohol) hydrogels (PVA-H) with defined stiffness to facilitate simultaneous observations of blood flow and plaque deformation. Flow patterns were observed using particle image velocimetry (PIV).<br><br>RESULTS: Decreases in Reynolds number (Re) with increased plaque deformation suggest that velocity decrease is more critical to establishment of the flow pattern than expansion of the model lumen. Upon exiting the stenosis, the location of the flow reattachment point, shifted further downstream in all models as plaque stiffness decreased and depended on the increase in upstream pressure.<br><br>CONCLUSIONS: These results suggest that in addition to luminal area, plaque stiffness should be considered as a measure of the severity of the pathology.}, }
@article {pmid26406014, year = {2015}, author = {Wang, C and Si, X and Shen, Y and Zheng, L and Lin, P}, title = {The exterior unsteady viscous flow and heat transfer due to a porous expanding or contracting cylinder.}, journal = {Bio-medical materials and engineering}, volume = {26 Suppl 1}, number = {}, pages = {S279-85}, doi = {10.3233/BME-151315}, pmid = {26406014}, issn = {1878-3619}, mesh = {Body Fluids/*physiology ; Body Temperature/*physiology ; Computer Simulation ; Elastic Modulus/physiology ; Energy Transfer/*physiology ; Humans ; *Models, Biological ; Peristalsis/*physiology ; Porosity ; Pulsatile Flow/*physiology ; Rheology/methods ; Temperature ; Thermal Conductivity ; Viscosity ; }, abstract = {Since the vessels in the biological tissues are characterized by low seepage Reynolds numbers and contracting or expanding walls, more attention is paid on the viscous flow outside the porous pipe with small expansion or contraction. This paper presents a numerical solution of the flow and heat transfer outside an expanding or contracting porous cylinder. The coupled nonlinear similarity equations are solved by Bvp4c, which is a collocation method with MATLAB. The effects of the different physical parameters, namely the permeability Reynolds number,the expansion ratio and the Prandtl number, on the velocity and temperature distribution are obtained and the results are shown graphically.}, }
@article {pmid26399987, year = {2016}, author = {Sharp, MK and Diem, AK and Weller, RO and Carare, RO}, title = {Peristalsis with Oscillating Flow Resistance: A Mechanism for Periarterial Clearance of Amyloid Beta from the Brain.}, journal = {Annals of biomedical engineering}, volume = {44}, number = {5}, pages = {1553-1565}, doi = {10.1007/s10439-015-1457-6}, pmid = {26399987}, issn = {1573-9686}, mesh = {*Alzheimer Disease/blood/pathology/physiopathology ; Amyloid beta-Peptides/*blood ; *Cerebral Arteries/metabolism/pathology/physiopathology ; *Cerebrovascular Circulation ; Humans ; *Models, Cardiovascular ; *Pulsatile Flow ; }, abstract = {Alzheimer's disease is characterized by accumulation of amyloid-β (Aβ) in the brain and in the walls of cerebral arteries. The focus of this work is on clearance of Aβ along artery walls, the failure of which may explain the accumulation of Aβ in Alzheimer's disease. Periarterial basement membranes form continuous channels from cerebral capillaries to major arteries on the surface of the brain. Arterial pressure pulses drive peristaltic flow in the basement membranes in the same direction as blood flow. Here we forward the hypothesis that flexible structures within the basement membrane, if oriented such they present greater resistance to forward than retrograde flow, may cause net reverse flow, advecting Aβ along with it. A solution was obtained for peristaltic flow with low Reynolds number, long wavelength compared to channel height and small channel height compared to vessel radius in a Darcy-Brinkman medium representing a square array of cylinders. Results show that retrograde flow is promoted by high cylinder volume fraction and low peristaltic amplitude. A decrease in cylinder concentration and/or an increase in amplitude, both of which may occur during ageing, can reduce retrograde flow or even cause a transition from retrograde to forward flow. Such changes may explain the accumulation of Aβ in the brain and in artery walls in Alzheimer's disease.}, }
@article {pmid26396254, year = {2015}, author = {Ober, TJ and Foresti, D and Lewis, JA}, title = {Active mixing of complex fluids at the microscale.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {112}, number = {40}, pages = {12293-12298}, pmid = {26396254}, issn = {1091-6490}, abstract = {Mixing of complex fluids at low Reynolds number is fundamental for a broad range of applications, including materials assembly, microfluidics, and biomedical devices. Of these materials, yield stress fluids (and gels) pose the most significant challenges, especially when they must be mixed in low volumes over short timescales. New scaling relationships between mixer dimensions and operating conditions are derived and experimentally verified to create a framework for designing active microfluidic mixers that can efficiently homogenize a wide range of complex fluids. Active mixing printheads are then designed and implemented for multimaterial 3D printing of viscoelastic inks with programmable control of local composition.}, }
@article {pmid26395149, year = {2015}, author = {Sousa, PC and Pinho, FT and Oliveira, MS and Alves, MA}, title = {Purely elastic flow instabilities in microscale cross-slot devices.}, journal = {Soft matter}, volume = {11}, number = {45}, pages = {8856-8862}, doi = {10.1039/c5sm01298h}, pmid = {26395149}, issn = {1744-6848}, abstract = {We present an experimental investigation of viscoelastic fluid flow in a cross-slot microgeometry under low Reynolds number flow conditions. By using several viscoelastic fluids, we investigate the effects of the microchannel bounding walls and the polymer solution concentration on the flow patterns. We demonstrate that for concentrated polymer solutions, the flow undergoes a bifurcation above a critical Weissenberg number (Wi) at which the flow becomes asymmetric but remains steady. The appearance of this elastic instability depends on the channel aspect ratio, defined as the ratio between the depth and the width of the channels. At high aspect ratios, when bounding wall effects are reduced, two types of elastic instabilities were observed, one in which the flow becomes asymmetric and steady, followed by a second instability at higher Wi, in which the flow becomes time-dependent. When the aspect ratio decreases, the bounding walls have a stabilizing effect, preventing the occurrence of steady asymmetric flow and postponing the transition to unsteady flow to higher Wi. For less concentrated solutions, the first elastic instability to steady asymmetric flow is absent and only the time-dependent flow instability is observed.}, }
@article {pmid26383225, year = {2015}, author = {Vach, PJ and Fratzl, P and Klumpp, S and Faivre, D}, title = {Fast Magnetic Micropropellers with Random Shapes.}, journal = {Nano letters}, volume = {15}, number = {10}, pages = {7064-7070}, pmid = {26383225}, issn = {1530-6992}, abstract = {Studying propulsion mechanisms in low Reynolds number fluid has implications for many fields, ranging from the biology of motile microorganisms and the physics of active matter to micromixing in catalysis and micro- and nanorobotics. The propulsion of magnetic micropropellers can be characterized by a dimensionless speed, which solely depends on the propeller geometry for a given axis of rotation. However, this dependence has so far been only investigated for helical propeller shapes, which were assumed to be optimal. In order to explore a larger variety of shapes, we experimentally studied the propulsion properties of randomly shaped magnetic micropropellers. Surprisingly, we found that their dimensionless speeds are high on average, comparable to previously reported nanofabricated helical micropropellers. The highest dimensionless speed we observed is higher than that of any previously reported propeller moving in a low Reynolds number fluid, proving that physical random shape generation can be a viable optimization strategy.}, }
@article {pmid26382522, year = {2015}, author = {Gruca, M and Bukowicki, M and Ekiel-Jeżewska, ML}, title = {Periodic and quasiperiodic motions of many particles falling in a viscous fluid.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {2}, pages = {023026}, doi = {10.1103/PhysRevE.92.023026}, pmid = {26382522}, issn = {1550-2376}, abstract = {The dynamics of regular clusters of many nontouching particles falling under gravity in a viscous fluid at low Reynolds number are analyzed within the point-particle model. The evolution of two families of particle configurations is determined: two or four regular horizontal polygons (called "rings") centered above or below each other. Two rings fall together and periodically oscillate. Four rings usually separate from each other with chaotic scattering. For hundreds of thousands of initial configurations, a map of the cluster lifetime is evaluated in which the long-lasting clusters are centered around periodic solutions for the relative motions, and they are surrounded by regions of chaotic scattering in a similar way to what was observed by Janosi et al. [Phys. Rev. E. 56, 2858 (1997)] for three particles only. These findings suggest that we should consider the existence of periodic orbits as a possible physical mechanism of the existence of unstable clusters of particles falling under gravity in a viscous fluid.}, }
@article {pmid26382516, year = {2015}, author = {Takagi, D}, title = {Swimming with stiff legs at low Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {2}, pages = {023020}, doi = {10.1103/PhysRevE.92.023020}, pmid = {26382516}, issn = {1550-2376}, mesh = {Animals ; Crustacea/physiology ; Extremities/*physiology ; *Models, Biological ; Periodicity ; Swimming/*physiology ; Viscosity ; }, abstract = {Locomotion at low Reynolds number is not possible with cycles of reciprocal motion, an example being the oscillation of a single pair of rigid paddles or legs. Here, I demonstrate the possibility of swimming with two or more pairs of legs. They are assumed to oscillate collectively in a metachronal wave pattern in a minimal model based on slender-body theory for Stokes flow. The model predicts locomotion in the direction of the traveling wave, as commonly observed along the body of free-swimming crustaceans. The displacement of the body and the swimming efficiency depend on the number of legs, the amplitude, and the phase of oscillations. This study shows that paddling legs with distinct orientations and phases offers a simple mechanism for driving flow.}, }
@article {pmid26382506, year = {2015}, author = {Schober, J and Schleicher, DR and Federrath, C and Bovino, S and Klessen, RS}, title = {Saturation of the turbulent dynamo.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {2}, pages = {023010}, doi = {10.1103/PhysRevE.92.023010}, pmid = {26382506}, issn = {1550-2376}, abstract = {The origin of strong magnetic fields in the Universe can be explained by amplifying weak seed fields via turbulent motions on small spatial scales and subsequently transporting the magnetic energy to larger scales. This process is known as the turbulent dynamo and depends on the properties of turbulence, i.e., on the hydrodynamical Reynolds number and the compressibility of the gas, and on the magnetic diffusivity. While we know the growth rate of the magnetic energy in the linear regime, the saturation level, i.e., the ratio of magnetic energy to turbulent kinetic energy that can be reached, is not known from analytical calculations. In this paper we present a scale-dependent saturation model based on an effective turbulent resistivity which is determined by the turnover time scale of turbulent eddies and the magnetic energy density. The magnetic resistivity increases compared to the Spitzer value and the effective scale on which the magnetic energy spectrum is at its maximum moves to larger spatial scales. This process ends when the peak reaches a characteristic wave number k☆ which is determined by the critical magnetic Reynolds number. The saturation level of the dynamo also depends on the type of turbulence and differs for the limits of large and small magnetic Prandtl numbers Pm. With our model we find saturation levels between 43.8% and 1.3% for Pm≫1 and between 2.43% and 0.135% for Pm≪1, where the higher values refer to incompressible turbulence and the lower ones to highly compressible turbulence.}, }
@article {pmid26382503, year = {2015}, author = {Roisman, IV and Criscione, A and Tropea, C and Mandal, DK and Amirfazli, A}, title = {Dislodging a sessile drop by a high-Reynolds-number shear flow at subfreezing temperatures.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {2}, pages = {023007}, doi = {10.1103/PhysRevE.92.023007}, pmid = {26382503}, issn = {1550-2376}, mesh = {Air Movements ; *Models, Theoretical ; *Temperature ; Viscosity ; Wettability ; }, abstract = {The drop, exposed to an air flow parallel to the substrate, starts to dislodge when the air velocity reaches some threshold value, which depends on the substrate wetting properties and drop volume. In this study the critical air velocity is measured for different drop volumes, on substrates of various wettabilities. The substrate initial temperatures varied between the normal room temperature (24.5∘C) and subfreezing temperatures (-5∘C and -1∘C). The physics of the drop did not change at the subfreezing temperatures of the substrates, which clearly indicates that the drop does not freeze and remains liquid for a relatively long time. During this time solidification is not initiated, neither by the air flow nor by mechanical disturbances. An approximate theoretical model is proposed that allows estimation of the aerodynamic forces acting on the sessile drop. The model is valid for the case when the drop height is of the same order as the thickness of the viscous boundary in the airflow, but the inertial effects are still dominant. Such a situation, relevant to many practical applications, was never modeled before. The theoretical predictions for the critical velocity of drop dislodging agree well with the experimental data for both room temperature and lower temperatures of the substrates.}, }
@article {pmid26382501, year = {2015}, author = {Nath, SK and Mukhopadhyay, B}, title = {Origin of nonlinearity and plausible turbulence by hydromagnetic transient growth in accretion disks: Faster growth rate than magnetorotational instability.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {2}, pages = {023005}, doi = {10.1103/PhysRevE.92.023005}, pmid = {26382501}, issn = {1550-2376}, abstract = {We investigate the evolution of hydromagnetic perturbations in a small section of accretion disks. It is known that molecular viscosity is negligible in accretion disks. Hence, it has been argued that a mechanism, known as magnetorotational instability (MRI), is responsible for transporting matter in the presence of a weak magnetic field. However, there are some shortcomings, which question the effectiveness of MRI. Now the question arises, whether other hydromagnetic effects, e.g., transient growth (TG), can play an important role in bringing nonlinearity into the system, even at weak magnetic fields. In addition, it should be determined whether MRI or TG is primarily responsible for revealing nonlinearity in order to make the flow turbulent. Our results prove explicitly that the flows with a high Reynolds number (Re), which is the case for realistic astrophysical accretion disks, exhibit nonlinearity via TG of perturbation modes faster than that by modes producing MRI. For a fixed wave vector, MRI dominates over transient effects only at low Re, lower than the value expected to be in astrophysical accretion disks, and low magnetic fields. This calls into serious question the (overall) persuasiveness of MRI in astrophysical accretion disks.}, }
@article {pmid26382500, year = {2015}, author = {Man, Y and Lauga, E}, title = {Phase-separation models for swimming enhancement in complex fluids.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {2}, pages = {023004}, doi = {10.1103/PhysRevE.92.023004}, pmid = {26382500}, issn = {1550-2376}, mesh = {*Models, Biological ; Rheology ; *Swimming ; Viscosity ; }, abstract = {Swimming cells often have to self-propel through fluids displaying non-Newtonian rheology. While past theoretical work seems to indicate that stresses arising from complex fluids should systematically hinder low-Reynolds number locomotion, experimental observations suggest that locomotion enhancement is possible. In this paper we propose a physical mechanism for locomotion enhancement of microscopic swimmers in a complex fluid. It is based on the fact that microstructured fluids will generically phase-separate near surfaces, leading to the presence of low-viscosity layers, which promote slip and decrease viscous friction near the surface of the swimmer. We use two models to address the consequence of this phase separation: a nonzero apparent slip length for the fluid and then an explicit modeling of the change of viscosity in a thin layer near the swimmer. Considering two canonical setups for low-Reynolds number locomotion, namely the waving locomotion of a two-dimensional sheet and that of a three-dimensional filament, we show that phase-separation systematically increases the locomotion speeds, possibly by orders of magnitude. We close by confronting our predictions with recent experimental results.}, }
@article {pmid26382498, year = {2015}, author = {Mandal, S and Bandopadhyay, A and Chakraborty, S}, title = {Effect of interfacial slip on the cross-stream migration of a drop in an unbounded Poiseuille flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {2}, pages = {023002}, doi = {10.1103/PhysRevE.92.023002}, pmid = {26382498}, issn = {1550-2376}, abstract = {We analyze the motion and deformation of a buoyant drop suspended in an unbounded fluid which is undergoing a quadratic shearing flow at small Reynolds number in the presence of slip at the interface of the drop. The boundary condition at the interface is accounted for by means of a simple Navier slip condition. Expressions for the velocity and the shape deformation of the drop are derived considering small but finite interface deformation, and results are presented for the specific cases of sedimentation, shear flow, and Poiseuille flow with previously reported results as the limiting cases of our general expressions. The presence of interfacial slip is found to markedly affect axial as well as cross-stream migration velocity of the drop in Poiseuille flow. The effect of slip is more prominent for drops with larger viscosity wherein the drop velocity increases. The presence of significant interface slippage always leads to migration of a deformed drop towards the centerline of the channel for any drop-to-medium viscosity ratio, which is in contrast to the case of no slip at the interface, which allows drop migration towards or away from the centerline depending on the viscosity ratio. We obtain the effect of slip on the cross-stream migration time scale, which quantifies the time required to reach a final steady radial position in the channel. The presence of slip at the drop interface leads to a decrease in the cross-stream migration time scale, which further results in faster motion of the drop in the cross-stream direction. Gravity in the presence of Poiseuille flow is shown to affect not only the axial motion, but also the cross-stream migration velocity of the drop; interfacial slip always increases the drop velocities.}, }
@article {pmid26382497, year = {2015}, author = {Burnishev, Y and Steinberg, V}, title = {Turbulence and turbulent drag reduction in swirling flow: Inertial versus viscous forcing.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {2}, pages = {023001}, doi = {10.1103/PhysRevE.92.023001}, pmid = {26382497}, issn = {1550-2376}, abstract = {We report unexpected results of a drastic difference in the transition to fully developed turbulent and turbulent drag reduction (TDR) regimes and in their properties in a von Karman swirling flow with counter-rotating disks of water-based polymer solutions for viscous (by smooth disks) as well as inertial (by bladed disks) forcing and by tracking just torque Γ(t) and pressure p(t) . For the viscous forcing, just a single TDR regime is found with the transition values of the Reynolds number (Re) Re turb c =Re TDR c ≃(4.8±0.2)×10(5) independent of ϕ , whereas for the inertial forcing two turbulent regimes are revealed. The first transition is to fully developed turbulence, and the second one is to the TDR regime with both Re turb c and Re TDR c depending on polymer concentration ϕ . Both regimes differ by the values of C f and C p , by the scaling exponents of the fundamental turbulent characteristics, by the nonmonotonic dependencies of skewness and flatness of the pressure PDFs on Re, and by the different frequency power spectra of p with the different dependencies of the main vortex peak frequency in the p power spectra on ϕ and Re. Thus our experimental results show the transition to the TDR regime in a von Karman swirling flow for the viscous and inertial forcings in a sharp contrast to the recent experiments [Phys. Fluids 10, 426 (1998); Phys. Rev. E 47, R28(R) (1993); and J. Phys.: Condens. Matter 17, S1195 (2005)] where the transition to TDR is observed in the same swirling flow with counter-rotating disks only for the viscous forcing. The latter result has led its authors to the wrong conclusion that TDR is a solely boundary effect contrary to the inertial forcing associated with the bulk effect, and this conception is currently rather widely accepted in literature.}, }
@article {pmid26382334, year = {2015}, author = {Piñeirua, M and Godoy-Diana, R and Thiria, B}, title = {Resistive thrust production can be as crucial as added mass mechanisms for inertial undulatory swimmers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {2}, pages = {021001}, doi = {10.1103/PhysRevE.92.021001}, pmid = {26382334}, issn = {1550-2376}, abstract = {In this Rapid Communication, we address a crucial point regarding the description of moderate to high Reynolds numbers aquatic swimmers. For decades, swimming animals have been classified in two different families of propulsive mechanisms based on the Reynolds number: the resistive swimmers, using local friction to produce the necessary thrust force for locomotion at low Reynolds number, and the reactive swimmers, lying in the high Reynolds range, and using added mass acceleration (described by perfect fluid theory). However, inertial swimmers are also systems that dissipate energy, due to their finite size, therefore involving strong resistive contributions, even for high Reynolds numbers. Using a complete model for the hydrodynamic forces, involving both reactive and resistive contributions, we revisit here the physical mechanisms responsible for the thrust production of such swimmers. We show, for instance, that the resistive part of the force balance is as crucial as added mass effects in the modeling of the thrust force, especially for elongated species. The conclusions brought by this work may have significant contributions to the understanding of complex swimming mechanisms, especially for the future design of artificial swimmers.}, }
@article {pmid26367403, year = {2015}, author = {Mekni, MA and Achour, W and Ben Hassen, A}, title = {New Robbins device to evaluate antimicrobial activity against bacterial biofilms on central venous catheters.}, journal = {La Tunisie medicale}, volume = {93}, number = {3}, pages = {153-157}, pmid = {26367403}, issn = {0041-4131}, mesh = {Anti-Bacterial Agents/*therapeutic use ; Bacteriological Techniques/*instrumentation ; Biofilms/*growth &amp; development ; Central Venous Catheters/*microbiology ; Daptomycin/*therapeutic use ; Humans ; Staphylococcus epidermidis/*physiology ; }, abstract = {BACKGROUND: Layouts of biomedical devices were tightly related with the emergence of Staphylococcus epidermidis as a major cause of nosocomial infections because of its ability to form biofilm on the biomaterial surfaces. This fact led researchers to develop in-vitro models to simulate what is really happening during biofilm formation process in order to have a better understanding of this phenomena and then to control it and to resolve the associated problems. The aim of this paper was to develop a homemade dynamic device based on instruments used in clinical practice, easy to mount, with low coast and with no sophisticated features.<br><br>METHODS: used to evaluate this dispositive were hydrodynamic calculation and enumeration of bacterial cells on petri dishes and with real time polymerase chain reaction during simulation of Staphylococcus epidermidis biofilm eradication with daptomycin.<br><br>RESULTS: With hydrodynamic calculation, Reynolds number was estimated to be 26.62 corresponding to a perfect laminar flux giving suitable dynamic growth environment for such experiment. Data recovered from cell enumeration with the two methods showed that bacterial colonization of the tested catheter segment was significantly reduced after 24 and 48h of treatment with daptomycin (P<0.01) reflecting a considerable reliability of this device.<br><br>CONCLUSION: the simple dispositive developed in this work has shown acceptable hydrodynamic proprieties and good reliability making research on biofilm easy to reach.}, }
@article {pmid26362281, year = {2016}, author = {Wang, Q and Othmer, HG}, title = {Computational analysis of amoeboid swimming at low Reynolds number.}, journal = {Journal of mathematical biology}, volume = {72}, number = {7}, pages = {1893-1926}, pmid = {26362281}, issn = {1432-1416}, mesh = {Dictyostelium/*physiology ; *Models, Biological ; Swimming ; }, abstract = {Recent experimental work has shown that eukaryotic cells can swim in a fluid as well as crawl on a substrate. We investigate the swimming behavior of Dictyostelium discoideum amoebae who swim by initiating traveling protrusions at the front that propagate rearward. In our model we prescribe the velocity at the surface of the swimming cell, and use techniques of complex analysis to develop 2D models that enable us to study the fluid-cell interaction. Shapes that approximate the protrusions used by Dictyostelium discoideum can be generated via the Schwarz-Christoffel transformation, and the boundary-value problem that results for swimmers in the Stokes flow regime is then reduced to an integral equation on the boundary of the unit disk. We analyze the swimming characteristics of several varieties of swimming Dictyostelium discoideum amoebae, and discuss how the slenderness of the cell body and the shapes of the protrusion effect the swimming of these cells. The results may provide guidance in designing low Reynolds number swimming models.}, }
@article {pmid26353555, year = {2015}, author = {Wang, J and Wang, Y and Chen, Z and Chen, K and Li, B}, title = {The Numerical Simulation of Liquid-Vapor Stratified Flow in Horizontal Metal-Foam Tubes.}, journal = {Journal of nanoscience and nanotechnology}, volume = {15}, number = {4}, pages = {3161-3167}, doi = {10.1166/jnn.2015.9626}, pmid = {26353555}, issn = {1533-4899}, abstract = {In this paper, a boiling stratified flow model in a metal-foam tube is proposed. First, based on Branuer non-equilibrium gas-liquid interface model, a force balance on the gas-liquid interface in metal-foam is calculated. The shape of the interface of upper gas phase and lower liquid phase in metal foam tube is obtained. As for the lower liquid phase, the energy conservation equations of liquid and metal foam are formulated, which account for porosity and fiber diameter of foam on the basis of non-local thermal equilibrium model (NTEM), respectively. Therefore, a profile of temperature difference between liquid and metal foam can be obtained. For the upper gas phase, an empirical correlation developed by other researchers is utilized to obtain temperature difference between gas phase and solid wall. In addition, the variation of the Reynolds number with increasing mass quality along the flow direction is acquired. Ultimately, an average circumference heat transfer coefficient is calculated. The results of circumference heat transfer coefficient agree well with available experimental data, showing the prediction of the proposed stratified flow model is feasible. The reason resulting in discrepancies between the prediction and experiment data is also illustrated.}, }
@article {pmid26353536, year = {2015}, author = {Wei, B and Yang, M and Wang, Z and Xu, H and Zhang, Y}, title = {Flow and Thermal Performance of a Water-Cooled Periodic Transversal Elliptical Microchannel Heat Sink for Chip Cooling.}, journal = {Journal of nanoscience and nanotechnology}, volume = {15}, number = {4}, pages = {3061-3066}, doi = {10.1166/jnn.2015.9683}, pmid = {26353536}, issn = {1533-4899}, abstract = {Flow and thermal performance of transversal elliptical microchannels were investigated as a passive scheme to enhance the heat transfer performance of laminar fluid flow. The periodic transversal elliptical micro-channel is designed and its pressure drop and heat transfer characteristics in laminar flow are numerically investigated. Based on the comparison with a conventional straight micro- channel having rectangular cross section, it is found that periodic transversal elliptical microchannel not only has great potential to reduce pressure drop but also dramatically enhances heat transfer performance. In addition, when the Reynolds number equals to 192, the pressure drop of the transversal elliptical channel is 36.5% lower than that of the straight channel, while the average Nusselt number is 72.8% higher; this indicates that the overall thermal performance of the periodic transversal elliptical microchannel is superior to the conventional straight microchannel. It is suggested that such transversal elliptical microchannel are attractive candidates for cooling future electronic chips effectively with much lower pressure drop.}, }
@article {pmid26347566, year = {2015}, author = {Berthé, R and Lehmann, FO}, title = {Body appendages fine-tune posture and moments in freely manoeuvring fruit flies.}, journal = {The Journal of experimental biology}, volume = {218}, number = {Pt 20}, pages = {3295-3307}, doi = {10.1242/jeb.122408}, pmid = {26347566}, issn = {1477-9145}, mesh = {Animals ; Behavior, Animal/physiology ; Biomechanical Phenomena ; Drosophila melanogaster/*physiology ; Extremities/physiology ; *Flight, Animal ; Posture ; Wings, Animal/physiology ; }, abstract = {The precise control of body posture by turning moments is key to elevated locomotor performance in flying animals. Although elevated moments for body stabilization are typically produced by wing aerodynamics, animals also steer using drag on body appendages, shifting their centre of body mass, and changing moments of inertia caused by active alterations in body shape. To estimate the instantaneous contribution of each of these components for posture control in an insect, we three-dimensionally reconstructed body posture and movements of body appendages in freely manoeuvring fruit flies (Drosophila melanogaster) by high-speed video and experimentally scored drag coefficients of legs and body trunk at low Reynolds number. The results show that the sum of leg- and abdomen-induced yaw moments dominates wing-induced moments during 17% of total flight time but is, on average, 7.2-times (roll, 3.4-times) smaller during manoeuvring. Our data reject a previous hypothesis on synergistic moment support, indicating that drag on body appendages and mass-shift inhibit rather than support turning moments produced by the wings. Numerical modelling further shows that hind leg extension alters the moments of inertia around the three main body axes of the animal by not more than 6% during manoeuvring, which is significantly less than previously reported for other insects. In sum, yaw, pitch and roll steering by body appendages probably fine-tune turning behaviour and body posture, without providing a significant advantage for posture stability and moment support. Motion control of appendages might thus be part of the insect's trimming reflexes, which reduce imbalances in moment generation caused by unilateral wing damage and abnormal asymmetries of the flight apparatus.}, }
@article {pmid26347563, year = {2015}, author = {van Bokhorst, E and de Kat, R and Elsinga, GE and Lentink, D}, title = {Feather roughness reduces flow separation during low Reynolds number glides of swifts.}, journal = {The Journal of experimental biology}, volume = {218}, number = {Pt 20}, pages = {3179-3191}, doi = {10.1242/jeb.121426}, pmid = {26347563}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Birds/anatomy &amp; histology/*physiology ; Feathers/*anatomy &amp; histology ; *Flight, Animal ; *Models, Biological ; Wings, Animal/anatomy &amp; histology/*physiology ; }, abstract = {Swifts are aerodynamically sophisticated birds with a small arm and large hand wing that provides them with exquisite control over their glide performance. However, their hand wings have a seemingly unsophisticated surface roughness that is poised to disturb flow. This roughness of about 2% chord length is formed by the valleys and ridges of overlapping primary feathers with thick protruding rachides, which make the wing stiffer. An earlier flow study of laminar-turbulent boundary layer transition over prepared swift wings suggested that swifts can attain laminar flow at a low angle of attack. In contrast, aerodynamic design theory suggests that airfoils must be extremely smooth to attain such laminar flow. In hummingbirds, which have similarly rough wings, flow measurements on a 3D printed model suggest that the flow separates at the leading edge and becomes turbulent well above the rachis bumps in a detached shear layer. The aerodynamic function of wing roughness in small birds is, therefore, not fully understood. Here, we performed particle image velocimetry and force measurements to compare smooth versus rough 3D-printed models of the swift hand wing. The high-resolution boundary layer measurements show that the flow over rough wings is indeed laminar at a low angle of attack and a low Reynolds number, but becomes turbulent at higher values. In contrast, the boundary layer over the smooth wing forms open laminar separation bubbles that extend beyond the trailing edge. The boundary layer dynamics of the smooth surface varies non-linearly as a function of angle of attack and Reynolds number, whereas the rough surface boasts more consistent turbulent boundary layer dynamics. Comparison of the corresponding drag values, lift values and glide ratios suggests, however, that glide performance is equivalent. The increased structural performance, boundary layer robustness and equivalent aerodynamic performance of rough wings might have provided small (proto) birds with an evolutionary window to high glide performance.}, }
@article {pmid26337704, year = {2015}, author = {Lee, JS and Park, SJ and Lee, JH and Weon, BM and Fezzaa, K and Je, JH}, title = {Origin and dynamics of vortex rings in drop splashing.}, journal = {Nature communications}, volume = {6}, number = {}, pages = {8187}, pmid = {26337704}, issn = {2041-1723}, abstract = {A vortex is a flow phenomenon that is very commonly observed in nature. More than a century, a vortex ring that forms during drop splashing has caught the attention of many scientists due to its importance in understanding fluid mixing and mass transport processes. However, the origin of the vortices and their dynamics remain unclear, mostly due to the lack of appropriate visualization methods. Here, with ultrafast X-ray phase-contrast imaging, we show that the formation of vortex rings originates from the energy transfer by capillary waves generated at the moment of the drop impact. Interestingly, we find a row of vortex rings along the drop wall, as demonstrated by a phase diagram established here, with different power-law dependencies of the angular velocities on the Reynolds number. These results provide important insight that allows understanding and modelling any type of vortex rings in nature, beyond just vortex rings during drop splashing.}, }
@article {pmid26328576, year = {2015}, author = {Huhn, F and van Rees, WM and Gazzola, M and Rossinelli, D and Haller, G and Koumoutsakos, P}, title = {Quantitative flow analysis of swimming dynamics with coherent Lagrangian vortices.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {25}, number = {8}, pages = {087405}, doi = {10.1063/1.4919784}, pmid = {26328576}, issn = {1089-7682}, abstract = {Undulatory swimmers flex their bodies to displace water, and in turn, the flow feeds back into the dynamics of the swimmer. At moderate Reynolds number, the resulting flow structures are characterized by unsteady separation and alternating vortices in the wake. We use the flow field from simulations of a two-dimensional, incompressible viscous flow of an undulatory, self-propelled swimmer and detect the coherent Lagrangian vortices in the wake to dissect the driving momentum transfer mechanisms. The detected material vortex boundary encloses a Lagrangian control volume that serves to track back the vortex fluid and record its circulation and momentum history. We consider two swimming modes: the C-start escape and steady anguilliform swimming. The backward advection of the coherent Lagrangian vortices elucidates the geometry of the vorticity field and allows for monitoring the gain and decay of circulation and momentum transfer in the flow field. For steady swimming, momentum oscillations of the fish can largely be attributed to the momentum exchange with the vortex fluid. For the C-start, an additionally defined jet fluid region turns out to balance the high momentum change of the fish during the rapid start.}, }
@article {pmid26315920, year = {2015}, author = {Broderick, SP and Houston, JG and Walsh, MT}, title = {The influence of the instabilities in modelling arteriovenous junction haemodynamics.}, journal = {Journal of biomechanics}, volume = {48}, number = {13}, pages = {3591-3598}, doi = {10.1016/j.jbiomech.2015.07.038}, pmid = {26315920}, issn = {1873-2380}, mesh = {Arteriovenous Fistula/*physiopathology ; Biomechanical Phenomena ; Blood Pressure ; Computer Simulation ; Humans ; Hydrodynamics ; Models, Biological ; Regional Blood Flow ; }, abstract = {The arteriovenous junction is characterised by high flow rates, large pressure difference and typically a palpable thrill or audible bruit, associated with turbulent flow. However, the arteriovenous junction is frequently studied with the assumption of streamline flow. This assumption is based on the Reynolds number calculation, although other factors can contribute to turbulent generation. In this study, the presence of instabilities is examined and the influencing factors discussed. This was performed using a pseudo-realistic geometry with adapted graft angles, vein diameter, outflow split ratio and graft inlet velocity values. Correlation was performed between steady and unsteady averaged simulation cases with correlation performance ranked. Overall the arteriovenous junction is capable of possessing highly disturbed flows, in which strict modelling requirements are necessary to capture such instabilities and avoid erroneous conclusions. Vein diameter and flow split ratio contribute to turbulent generation, thus Reynolds number cannot be used as a sole turbulent criterion in the arteriovenous junction.}, }
@article {pmid26314259, year = {2015}, author = {Krieger, MS and Dias, MA and Powers, TR}, title = {Minimal model for transient swimming in a liquid crystal.}, journal = {The European physical journal. E, Soft matter}, volume = {38}, number = {8}, pages = {94}, pmid = {26314259}, issn = {1292-895X}, mesh = {Elasticity ; *Hydrodynamics ; Liquid Crystals/*chemistry ; *Models, Theoretical ; Rotation ; Viscosity ; }, abstract = {When a microorganism begins swimming from rest in a Newtonian fluid such as water, it rapidly attains its steady-state swimming speed since changes in the velocity field spread quickly when the Reynolds number is small. However, swimming microorganisms are commonly found or studied in complex fluids. Because these fluids have long relaxation times, the time to attain the steady-state swimming speed can also be long. In this article we study the swimming startup problem in the simplest liquid crystalline fluid: a two-dimensional hexatic liquid crystal film. We study the dependence of startup time on anchoring strength and Ericksen number, which is the ratio of viscous to elastic stresses. For strong anchoring, the fluid flow starts up immediately but the liquid crystal field and swimming velocity attain their sinusoidal steady-state values after a time proportional to the relaxation time of the liquid crystal. When the Ericksen number is high, the behavior is the same as in the strong-anchoring case for any anchoring strength. We also find that the startup time increases with the ratio of the rotational viscosity to the shear viscosity, and then ultimately saturates once the rotational viscosity is much greater than the shear viscosity.}, }
@article {pmid26314256, year = {2015}, author = {Felderhof, BU}, title = {Efficient swimming of an assembly of rigid spheres at low Reynolds number.}, journal = {The European physical journal. E, Soft matter}, volume = {38}, number = {8}, pages = {90}, pmid = {26314256}, issn = {1292-895X}, mesh = {*Hydrodynamics ; Microfluidics ; *Models, Theoretical ; Viscosity ; }, abstract = {The swimming of an assembly of rigid spheres immersed in a viscous fluid of infinite extent is studied in low-Reynolds-number hydrodynamics. The instantaneous swimming velocity and rate of dissipation are expressed in terms of the time-dependent displacements of sphere centers about their collective motion. For small-amplitude swimming with periodically oscillating displacements, optimization of the mean swimming speed at given mean power leads to an eigenvalue problem involving a velocity matrix and a power matrix. The corresponding optimal stroke permits generalization to large-amplitude motion in a model of spheres with harmonic interactions and corresponding actuating forces. The method allows straightforward calculation of the swimming performance of structures modeled as assemblies of interacting rigid spheres. A model of three collinear spheres with motion along the common axis is studied as an example.}, }
@article {pmid26298765, year = {2015}, author = {Adams, MC and Hurt, EE and Barbano, DM}, title = {Effect of ceramic membrane channel geometry and uniform transmembrane pressure on limiting flux and serum protein removal during skim milk microfiltration.}, journal = {Journal of dairy science}, volume = {98}, number = {11}, pages = {7527-7543}, doi = {10.3168/jds.2015-9753}, pmid = {26298765}, issn = {1525-3198}, mesh = {Animals ; Blood Proteins/analysis ; Caseins/analysis ; Ceramics/*chemistry ; Filtration ; *Food Handling ; Hydrodynamics ; Hydrogen-Ion Concentration ; Membranes, Artificial ; Milk/*chemistry ; Milk Proteins/analysis ; }, abstract = {Our objectives were to determine the effects of a ceramic microfiltration (MF) membrane's retentate flow channel geometry (round or diamond-shaped) and uniform transmembrane pressure (UTP) on limiting flux (LF) and serum protein (SP) removal during skim milk MF at a temperature of 50°C, a retentate protein concentration of 8.5%, and an average cross-flow velocity of 7 m·s(-1). Performance of membranes with round and diamond flow channels was compared in UTP mode. Performance of the membrane with round flow channels was compared with and without UTP. Using UTP with round flow channel MF membranes increased the LF by 5% when compared with not using UTP, but SP removal was not affected by the use of UTP. Using membranes with round channels instead of diamond-shaped channels in UTP mode increased the LF by 24%. This increase was associated with a 25% increase in Reynolds number and can be explained by lower shear at the vertices of the diamond-shaped channel's surface. The SP removal factor of the diamond channel system was higher than the SP removal factor of the round channel system below the LF. However, the diamond channel system passed more casein into the MF permeate than the round channel system. Because only one batch of each membrane was tested in our study, it was not possible to determine if the differences in protein rejection between channel geometries were due to the membrane design or random manufacturing variation. Despite the lower LF of the diamond channel system, the 47% increase in membrane module surface area of the diamond channel system produced a modular permeate removal rate that was at least 19% higher than the round channel system. Consequently, using diamond channel membranes instead of round channel membranes could reduce some of the costs associated with ceramic MF of skim milk if fewer membrane modules could be used to attain the required membrane area.}, }
@article {pmid26296866, year = {2015}, author = {Higuchi, M and Terada, K and Sugano, K}, title = {Coning phenomena under laminar flow.}, journal = {European journal of pharmaceutical sciences : official journal of the European Federation for Pharmaceutical Sciences}, volume = {80}, number = {}, pages = {53-55}, doi = {10.1016/j.ejps.2015.08.004}, pmid = {26296866}, issn = {1879-0720}, mesh = {Nuclear Proteins ; *Pharmacokinetics ; RNA-Binding Proteins ; *Rheology ; Rotation ; Technology, Pharmaceutical/*methods ; }, abstract = {The purpose of the present study was to investigate coning phenomena in the paddle dissolution test under laminar flow (Reynolds number <500). The minimum rotation speed at which the coning phenomena disappear (no coning rpm, NCrpm) was measured in viscous media (23 to 147mPa∙s) using various particles. The exponent values of particle size, density, and viscosity parameters in the Zwietering equation were found to be 0.066, 0.38, and 0.22, respectively. NCrpm was appropriately predicted by the Zwietering equation (average error: 8rpm). These values are very different from those for turbulent flow, suggesting that the main physical forces governing the motion of particles can be different between turbulent flow and laminar flow. This point should be taken into account when understanding the dissolution of drug products in viscous fluids representing the fed state.}, }
@article {pmid26278133, year = {2015}, author = {Hassanpourfard, M and Nikakhtari, Z and Ghosh, R and Das, S and Thundat, T and Liu, Y and Kumar, A}, title = {Bacterial floc mediated rapid streamer formation in creeping flows.}, journal = {Scientific reports}, volume = {5}, number = {}, pages = {13070}, pmid = {26278133}, issn = {2045-2322}, mesh = {Bacteria/*metabolism ; Bacterial Adhesion/physiology ; Biofilms ; Elasticity ; Green Fluorescent Proteins/genetics/metabolism ; Microfluidic Analytical Techniques/instrumentation/*methods ; Microscopy, Fluorescence ; Microscopy, Video ; Pseudomonas fluorescens/physiology ; }, abstract = {One of the central puzzles concerning the interaction of low Reynolds number fluid transport with bacterial biomass is the formation of filamentous structures called streamers. In this manuscript, we report our discovery of a new kind of low Re bacterial streamers, which appear from pre-formed bacterial flocs. In sharp contrast to the biofilm-mediated streamers, these streamers form over extremely small timescales (less than a second). Our experiments, carried out in a microchannel with micropillars rely on fluorescence microscopy techniques to illustrate that floc-mediated streamers form when a freely-moving floc adheres to the micropillar wall and gets rapidly sheared by the background flow. We also show that at their inception the deformation of the flocs is dominated by recoverable large strains indicating significant elasticity. These strains subsequently increase tremendously to produce filamentous streamers. Interestingly, we find that these fully formed streamers are not static structures and show viscous response at time scales larger than their formation time scales. Finally, we show that such novel streamer formation can lead to rapid clogging of microfluidic devices.}, }
@article {pmid26274284, year = {2015}, author = {Wedin, H and Cherubini, S and Bottaro, A}, title = {Effect of plate permeability on nonlinear stability of the asymptotic suction boundary layer.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {1}, pages = {013022}, doi = {10.1103/PhysRevE.92.013022}, pmid = {26274284}, issn = {1550-2376}, abstract = {The nonlinear stability of the asymptotic suction boundary layer is studied numerically, searching for finite-amplitude solutions that bifurcate from the laminar flow state. By changing the boundary conditions for disturbances at the plate from the classical no-slip condition to more physically sound ones, the stability characteristics of the flow may change radically, both for the linearized as well as the nonlinear problem. The wall boundary condition takes into account the permeability K̂ of the plate; for very low permeability, it is acceptable to impose the classical boundary condition (K̂=0). This leads to a Reynolds number of approximately Re(c)=54400 for the onset of linearly unstable waves, and close to Re(g)=3200 for the emergence of nonlinear solutions [F. A. Milinazzo and P. G. Saffman, J. Fluid Mech. 160, 281 (1985); J. H. M. Fransson, Ph.D. thesis, Royal Institute of Technology, KTH, Sweden, 2003]. However, for larger values of the plate's permeability, the lower limit for the existence of linear and nonlinear solutions shifts to significantly lower Reynolds numbers. For the largest permeability studied here, the limit values of the Reynolds numbers reduce down to Re(c)=796 and Re(g)=294. For all cases studied, the solutions bifurcate subcritically toward lower Re, and this leads to the conjecture that they may be involved in the very first stages of a transition scenario similar to the classical route of the Blasius boundary layer initiated by Tollmien-Schlichting (TS) waves. The stability of these nonlinear solutions is also investigated, showing a low-frequency main unstable mode whose growth rate decreases with increasing permeability and with the Reynolds number, following a power law Re(-ρ), where the value of ρ depends on the permeability coefficient K̂. The nonlinear dynamics of the flow in the vicinity of the computed finite-amplitude solutions is finally investigated by direct numerical simulations, providing a viable scenario for subcritical transition due to TS waves.}, }
@article {pmid26274272, year = {2015}, author = {Zhou, L and Rauh, C and Delgado, A}, title = {Multifractal-cascade model for inertial and dissipation ranges based on the wavelet reconstruction method.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {1}, pages = {013010}, doi = {10.1103/PhysRevE.92.013010}, pmid = {26274272}, issn = {1550-2376}, abstract = {The discrete wavelet is introduced to construct the turbulent velocity fields. The simple binary cascade model p model is served as the inertial range model for velocity increments. The dissipation model, which follows Foias et al. [Phys. Fluids A 2, 464 (1990)] takes the form of exp(-gk). The length of inertial and dissipation ranges is computed according to the different construction levels. Based on the binary cascade theory and the proposed dissipation model, the Reynolds number regarding to the cascade process can be estimated. The dissipation rate calculated from the proposed model not only agrees with the existing experiment data, but also suggests that the dissipation rate is not an independent variable with respect to the Reynolds number.}, }
@article {pmid26274266, year = {2015}, author = {Rorai, C and Mininni, PD and Pouquet, A}, title = {Stably stratified turbulence in the presence of large-scale forcing.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {92}, number = {1}, pages = {013003}, doi = {10.1103/PhysRevE.92.013003}, pmid = {26274266}, issn = {1550-2376}, abstract = {We perform two high-resolution direct numerical simulations of stratified turbulence for Reynolds number equal to Re≈25000 and Froude number, respectively, of Fr≈0.1 and Fr≈0.03. The flows are forced at large scale and discretized on an isotropic grid of 2048(3) points. Stratification makes the flow anisotropic and introduces two extra characteristic scales with respect to homogeneous isotropic turbulence: the buoyancy scale, L(B), and the Ozmidov scale, ℓ(oz). The former is related to the number of layers that the flow develops in the direction of gravity, and the latter is regarded as the scale at which isotropy is recovered. The values of L(B) and ℓ(oz) depend on the Froude number, and their absolute and relative amplitudes affect the repartition of energy among Fourier modes in ways that are not easy to predict. By contrasting the behavior of the two simulated flows we identify some surprising similarities: After an initial transient the two flows evolve towards comparable values of the kinetic and potential enstrophy and energy dissipation rate. This is the result of the Reynolds number being large enough in both flows for the Ozmidov scale to be resolved. When properly dimensionalized, the energy dissipation rate is compatible with atmospheric observations. Further similarities emerge at large scales: The same ratio between potential and total energy (≈0.1) is spontaneously selected by the flows, and slow modes grow monotonically in both regimes, causing a slow increase of the total energy in time. The axisymmetric total energy spectrum shows a wide variety of spectral slopes as a function of the angle between the imposed stratification and the wave vector. One-dimensional energy spectra computed in the direction parallel to gravity are flat from the forcing up to buoyancy scale. At intermediate scales a ∼k(-3) parallel spectrum develops for the Fr≈0.03 run, whereas for weaker stratification, the saturation spectrum does not have enough scales to develop and instead one observes a power law compatible with Kolmogorov scaling. Finally, the spectrum of helicity is flat until L(B), as observed in the nocturnal planetary boundary layer.}, }
@article {pmid26269230, year = {2015}, author = {van Leeuwen, JL and Voesenek, CJ and Müller, UK}, title = {How body torque and Strouhal number change with swimming speed and developmental stage in larval zebrafish.}, journal = {Journal of the Royal Society, Interface}, volume = {12}, number = {110}, pages = {0479}, pmid = {26269230}, issn = {1742-5662}, mesh = {Animals ; Biomechanical Phenomena ; *Models, Biological ; Swimming/*physiology ; Zebrafish/*physiology ; }, abstract = {Small undulatory swimmers such as larval zebrafish experience both inertial and viscous forces, the relative importance of which is indicated by the Reynolds number (Re). Re is proportional to swimming speed (vswim) and body length; faster swimming reduces the relative effect of viscous forces. Compared with adults, larval fish experience relatively high (mainly viscous) drag during cyclic swimming. To enhance thrust to an equally high level, they must employ a high product of tail-beat frequency and (peak-to-peak) amplitude fAtail, resulting in a relatively high fAtail/vswim ratio (Strouhal number, St), and implying relatively high lateral momentum shedding and low propulsive efficiency. Using kinematic and inverse-dynamics analyses, we studied cyclic swimming of larval zebrafish aged 2-5 days post-fertilization (dpf). Larvae at 4-5 dpf reach higher f (95 Hz) and Atail (2.4 mm) than at 2 dpf (80 Hz, 1.8 mm), increasing swimming speed and Re, indicating increasing muscle powers. As Re increases (60 → 1400), St (2.5 → 0.72) decreases nonlinearly towards values of large swimmers (0.2-0.6), indicating increased propulsive efficiency with vswim and age. Swimming at high St is associated with high-amplitude body torques and rotations. Low propulsive efficiencies and large yawing amplitudes are unavoidable physical constraints for small undulatory swimmers.}, }
@article {pmid26267247, year = {2015}, author = {Rashidi, MM and Freidoonimehr, N and Momoniat, E and Rostami, B}, title = {Study of Nonlinear MHD Tribological Squeeze Film at Generalized Magnetic Reynolds Numbers Using DTM.}, journal = {PloS one}, volume = {10}, number = {8}, pages = {e0135004}, pmid = {26267247}, issn = {1932-6203}, mesh = {*Models, Theoretical ; }, abstract = {In the current article, a combination of the differential transform method (DTM) and Padé approximation method are implemented to solve a system of nonlinear differential equations modelling the flow of a Newtonian magnetic lubricant squeeze film with magnetic induction effects incorporated. Solutions for the transformed radial and tangential momentum as well as solutions for the radial and tangential induced magnetic field conservation equations are determined. The DTM-Padé combined method is observed to demonstrate excellent convergence, stability and versatility in simulating the magnetic squeeze film problem. The effects of involved parameters, i.e. squeeze Reynolds number (N1), dimensionless axial magnetic force strength parameter (N2), dimensionless tangential magnetic force strength parameter (N3), and magnetic Reynolds number (Rem) are illustrated graphically and discussed in detail. Applications of the study include automotive magneto-rheological shock absorbers, novel aircraft landing gear systems and biological prosthetics.}, }
@article {pmid26252657, year = {2015}, author = {Nabawy, MR and Crowthe, WJ}, title = {A Quasi-Steady Lifting Line Theory for Insect-Like Hovering Flight.}, journal = {PloS one}, volume = {10}, number = {8}, pages = {e0134972}, pmid = {26252657}, issn = {1932-6203}, mesh = {Animals ; Biomechanical Phenomena ; Computer Simulation ; Flight, Animal/*physiology ; Insecta/*physiology ; *Models, Biological ; Time Factors ; Wings, Animal/anatomy &amp; histology/physiology ; }, abstract = {A novel lifting line formulation is presented for the quasi-steady aerodynamic evaluation of insect-like wings in hovering flight. The approach allows accurate estimation of aerodynamic forces from geometry and kinematic information alone and provides for the first time quantitative information on the relative contribution of induced and profile drag associated with lift production for insect-like wings in hover. The main adaptation to the existing lifting line theory is the use of an equivalent angle of attack, which enables capture of the steady non-linear aerodynamics at high angles of attack. A simple methodology to include non-ideal induced effects due to wake periodicity and effective actuator disc area within the lifting line theory is included in the model. Low Reynolds number effects as well as the edge velocity correction required to account for different wing planform shapes are incorporated through appropriate modification of the wing section lift curve slope. The model has been successfully validated against measurements from revolving wing experiments and high order computational fluid dynamics simulations. Model predicted mean lift to weight ratio results have an average error of 4% compared to values from computational fluid dynamics for eight different insect cases. Application of an unmodified linear lifting line approach leads on average to a 60% overestimation in the mean lift force required for weight support, with most of the discrepancy due to use of linear aerodynamics. It is shown that on average for the eight insects considered, the induced drag contributes 22% of the total drag based on the mean cycle values and 29% of the total drag based on the mid half-stroke values.}, }
@article {pmid26252016, year = {2015}, author = {Zhang, C and Hedrick, TL and Mittal, R}, title = {Centripetal Acceleration Reaction: An Effective and Robust Mechanism for Flapping Flight in Insects.}, journal = {PloS one}, volume = {10}, number = {8}, pages = {e0132093}, pmid = {26252016}, issn = {1932-6203}, mesh = {*Acceleration ; Animals ; Biomechanical Phenomena ; Computer Simulation ; Flight, Animal/*physiology ; Models, Biological ; Moths/*physiology ; Time Factors ; Wings, Animal/*physiology ; }, abstract = {Despite intense study by physicists and biologists, we do not fully understand the unsteady aerodynamics that relate insect wing morphology and kinematics to lift generation. Here, we formulate a force partitioning method (FPM) and implement it within a computational fluid dynamic model to provide an unambiguous and physically insightful division of aerodynamic force into components associated with wing kinematics, vorticity, and viscosity. Application of the FPM to hawkmoth and fruit fly flight shows that the leading-edge vortex is the dominant mechanism for lift generation for both these insects and contributes between 72-85% of the net lift. However, there is another, previously unidentified mechanism, the centripetal acceleration reaction, which generates up to 17% of the net lift. The centripetal acceleration reaction is similar to the classical inviscid added-mass in that it depends only on the kinematics (i.e. accelerations) of the body, but is different in that it requires the satisfaction of the no-slip condition, and a combination of tangential motion and rotation of the wing surface. Furthermore, the classical added-mass force is identically zero for cyclic motion but this is not true of the centripetal acceleration reaction. Furthermore, unlike the lift due to vorticity, centripetal acceleration reaction lift is insensitive to Reynolds number and to environmental flow perturbations, making it an important contributor to insect flight stability and miniaturization. This force mechanism also has broad implications for flow-induced deformation and vibration, underwater locomotion and flows involving bubbles and droplets.}, }
@article {pmid26244665, year = {2015}, author = {Yu, X and Sun, Z and Huang, R and Zhang, Y and Huang, Y}, title = {A Thermal Equilibrium Analysis of Line Contact Hydrodynamic Lubrication Considering the Influences of Reynolds Number, Load and Temperature.}, journal = {PloS one}, volume = {10}, number = {8}, pages = {e0134806}, doi = {10.1371/journal.pone.0134806}, pmid = {26244665}, issn = {1932-6203}, mesh = {Computer Simulation ; Convection ; Friction ; *Hydrodynamics ; *Lubrication ; Models, Chemical ; Temperature ; Weight-Bearing ; }, abstract = {Thermal effects such as conduction, convection and viscous dissipation are important to lubrication performance, and they vary with the friction conditions. These variations have caused some inconsistencies in the conclusions of different researchers regarding the relative contributions of these thermal effects. To reveal the relationship between the contributions of the thermal effects and the friction conditions, a steady-state THD analysis model was presented. The results indicate that the contribution of each thermal effect sharply varies with the Reynolds number and temperature. Convective effect could be dominant under certain conditions. Additionally, the accuracy of some simplified methods of thermo-hydrodynamic analysis is further discussed.}, }
@article {pmid26226349, year = {2015}, author = {Maertens, AP and Triantafyllou, MS and Yue, DK}, title = {Efficiency of fish propulsion.}, journal = {Bioinspiration &amp; biomimetics}, volume = {10}, number = {4}, pages = {046013}, doi = {10.1088/1748-3190/10/4/046013}, pmid = {26226349}, issn = {1748-3190}, mesh = {Animals ; Computer Simulation ; Energy Metabolism/*physiology ; Energy Transfer/*physiology ; Fishes/*physiology ; Friction ; *Models, Biological ; Rheology/*methods ; Shear Strength/physiology ; Stress, Mechanical ; Viscosity ; }, abstract = {The system efficiency of a self-propelled flexible body is ill-defined, hence we introduce the concept of quasi-propulsive efficiency, defined as the ratio of the power needed to tow a body in rigid-straight condition over the power it requires for self-propulsion, both measured for the same speed. Through examples we show that the quasi-propulsive efficiency is a rational non-dimensional metric of the propulsive fitness of fish and fish-like mechanisms, consistent with the goal to minimize fuel consumption under size and velocity constraints. We perform two-dimensional viscous simulations and apply the concept of quasi-propulsive efficiency to illustrate and discuss the efficiency of two-dimensional undulating foils employing first carangiform and then anguilliform kinematics. We show that low efficiency may be due to adverse body-propulsor hydrodynamic interactions, which cannot be accounted for by an increase in friction drag, as done previously, since at the Reynolds number Re = 5 000 considered in the simulations, pressure is a major contributor to both thrust and drag.}, }
@article {pmid26196807, year = {2015}, author = {Linkmann, MF and Berera, A and McComb, WD and McKay, ME}, title = {Nonuniversality and Finite Dissipation in Decaying Magnetohydrodynamic Turbulence.}, journal = {Physical review letters}, volume = {114}, number = {23}, pages = {235001}, doi = {10.1103/PhysRevLett.114.235001}, pmid = {26196807}, issn = {1079-7114}, abstract = {A model equation for the Reynolds number dependence of the dimensionless dissipation rate in freely decaying homogeneous magnetohydrodynamic turbulence in the absence of a mean magnetic field is derived from the real-space energy balance equation, leading to Cϵ=Cϵ,∞+C/R-+O(1/R-(2)), where R- is a generalized Reynolds number. The constant Cϵ,∞ describes the total energy transfer flux. This flux depends on magnetic and cross helicities, because these affect the nonlinear transfer of energy, suggesting that the value of Cϵ,∞ is not universal. Direct numerical simulations were conducted on up to 2048(3) grid points, showing good agreement between data and the model. The model suggests that the magnitude of cosmological-scale magnetic fields is controlled by the values of the vector field correlations. The ideas introduced here can be used to derive similar model equations for other turbulent systems.}, }
@article {pmid26195761, year = {2015}, author = {Wang, J and Li, Q and E, W}, title = {Study of the instability of the Poiseuille flow using a thermodynamic formalism.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {112}, number = {31}, pages = {9518-9523}, pmid = {26195761}, issn = {1091-6490}, mesh = {Friction ; Kinetics ; Magnetic Phenomena ; Models, Theoretical ; *Rheology ; Skin Physiological Phenomena ; Solutions ; Thermodynamics ; }, abstract = {The stability of the plane Poiseuille flow is analyzed using a thermodynamic formalism by considering the deterministic Navier-Stokes equation with Gaussian random initial data. A unique critical Reynolds number, Rec ≈ 2,332, at which the probability of observing puffs in the solution changes from 0 to 1, is numerically demonstrated to exist in the thermodynamic limit and is found to be independent of the noise amplitude. Using the puff density as the macrostate variable, the free energy of such a system is computed and analyzed. The puff density approaches zero as the critical Reynolds number is approached from above, signaling a continuous transition despite the fact that the bifurcation is subcritical for a finite-sized system. An action function is found for the probability of observing puffs in a small subregion of the flow, and this action function depends only on the Reynolds number. The strategy used here should be applicable to a wide range of other problems exhibiting subcritical instabilities.}, }
@article {pmid26180066, year = {2015}, author = {Gemmell, BJ and Jiang, H and Buskey, EJ}, title = {A tale of the ciliate tail: investigation into the adaptive significance of this sub-cellular structure.}, journal = {Proceedings. Biological sciences}, volume = {282}, number = {1812}, pages = {20150770}, pmid = {26180066}, issn = {1471-2954}, mesh = {Biomechanical Phenomena ; Ciliophora/*physiology ; *Escape Reaction ; *Hydrodynamics ; Species Specificity ; Swimming ; Video Recording ; }, abstract = {Ciliates can form an important link between the microbial loop and higher trophic levels primarily through consumption by copepods. This high predation pressure has resulted in a number of ciliate species developing rapid escape swimming behaviour. Several species of these escaping ciliates also possess a long contractile tail for which the functionality remains unresolved. We use high-speed video, specialized optics and novel fluid visualization tools to evaluate the role of this contractile appendage in two free-swimming ciliates, Pseudotontonia sp. and Tontonia sp., and compare the performance to escape swimming behaviour of a non-tailed species, Strobilidium sp. Here, we show that 'tailed' species respond to hydrodynamic disturbances with extremely short response latencies (less than or equal to 0.89 ms) by rapidly contracting the tail which carries the cell body 2-4 cell diameters within a few milliseconds. This provides an advantage over non-tailed species during the critical first 10-30 ms of an escape. Two small, short-lived vortex rings are created during contraction of the tail. The flow imposed by the ciliate jumping can be described as two well-separated impulsive Stokeslets and the overall flow attenuates spatially as r(-3). The high initial velocities and spatio-temporal arrangement of vortices created by tail contractions appear to provide a means for rapid escape as well as hydrodynamic 'camouflage' against fast striking, mechanoreceptive predators such as copepods.}, }
@article {pmid26179936, year = {2015}, author = {Murakami, R and Tsai, CH and Kaneko, M and Sakuma, S and Arai, F}, title = {Cell pinball: phenomenon and mechanism of inertia-like cell motion in a microfluidic channel.}, journal = {Lab on a chip}, volume = {15}, number = {16}, pages = {3307-3313}, doi = {10.1039/c5lc00535c}, pmid = {26179936}, issn = {1473-0189}, mesh = {Biomechanical Phenomena ; Cell Movement ; Erythrocytes/*cytology/metabolism ; Humans ; Microfluidic Analytical Techniques/instrumentation/*methods ; Microscopy, Confocal ; Microspheres ; Sodium Chloride/chemistry ; }, abstract = {An unexpected phenomenon of red blood cells bouncing back and forth between the walls inside a microfluidic channel was observed during experiments, and is presented as "Cell Pinball" in this paper. In general, cells in a microfluidic environment are supposed to move along the streamlines parallel to the channel walls when the Reynolds number is small, and the inertia of the cells becomes negligible. However, the cell pinball presented in this paper does not only move along the streamlines but also moves across the channel with the velocity component perpendicular to the streamlines while the Reynolds number is only 0.74. Furthermore, the motion in the direction perpendicular to the streamlines reverses when the cell pinball hits a wall as it "bounces" at the wall. This phenomenon caught our attention and is investigated with both microbead visualization and confocal microscopy. Consistent patterns of rotation with respect to the direction of motion are observed. A kinematic model is proposed to interpret the phenomenon, and it is believed that the phenomenon is caused by the separation of the centroid of the cell and the contact point. The model successfully interprets the features of cell pinball, and the estimated separation between the centroid and the contact point is presented.}, }
@article {pmid26172798, year = {2015}, author = {Piedra, S and Ramos, E and Herrera, JR}, title = {Dynamics of two-dimensional bubbles.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {6}, pages = {063013}, doi = {10.1103/PhysRevE.91.063013}, pmid = {26172798}, issn = {1550-2376}, abstract = {The dynamics of two-dimensional bubbles ascending under the influence of buoyant forces is numerically studied with a one-fluid model coupled with the front-tracking technique. The bubble dynamics are described by recording the position, shape, and orientation of the bubbles as functions of time. The qualitative properties of the bubbles and their terminal velocities are described in terms of the Eötvos (ratio of buoyancy to surface tension) and Archimedes numbers (ratio of buoyancy to viscous forces). The terminal Reynolds number result from the balance of buoyancy and drag forces and, consequently, is not an externally fixed parameter. In the cases that yield small Reynolds numbers, the bubbles follow straight paths and the wake is steady. A more interesting behavior is found at high Reynolds numbers where the bubbles follow an approximately periodic zigzag trajectory and an unstable wake with properties similar to the Von Karman vortex street is formed. The dynamical features of the motion of single bubbles are compared to experimental observations of air bubbles ascending in a water-filled Hele-Shaw cell. Although the comparison is not strictly valid in the sense that the effect of the lateral walls is not incorporated in the model, most of the dynamical properties observed are in good qualitative agreement with the numerical calculations. Hele-Shaw cells with different gaps have been used to determine the degree of approximation of the numerical calculation. It is found that for the relation between the terminal Reynolds number and the Archimedes number, the numerical calculations are closer to the observations of bubble dynamics in Hele-Shaw cells of larger gaps.}, }
@article {pmid26172790, year = {2015}, author = {Cadot, O and Evrard, A and Pastur, L}, title = {Imperfect supercritical bifurcation in a three-dimensional turbulent wake.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {6}, pages = {063005}, doi = {10.1103/PhysRevE.91.063005}, pmid = {26172790}, issn = {1550-2376}, abstract = {The turbulent wake of a square-back body exhibits a strong bimodal behavior. The wake randomly undergoes symmetry-breaking reversals between two mirror asymmetric steady modes [reflectional symmetry-breaking (RSB) modes]. The characteristic time for reversals is about 2 or 3 orders of magnitude larger than the natural time for vortex shedding. Studying the effects of the proximity of a ground wall together with the Reynolds number, it is shown that the bimodal behavior is the result of an imperfect pitchfork bifurcation. The RSB modes correspond to the two stable bifurcated branches resulting from an instability of the stable symmetric wake. An attempt to stabilize the unstable symmetric wake is investigated using a passive control technique. Although the controlled wake still exhibits strong fluctuations, the bimodal behavior is suppressed and the drag reduced. This promising experiment indicates the possible existence of an unstable solution branch corresponding to a reflectional symmetry preserved (RSP) mode. This work is encouraging to develop a control strategy based on a stabilization of this RSP mode to reduce mean drag and lateral force fluctuations.}, }
@article {pmid26163996, year = {2016}, author = {Elcner, J and Lizal, F and Jedelsky, J and Jicha, M and Chovancova, M}, title = {Numerical investigation of inspiratory airflow in a realistic model of the human tracheobronchial airways and a comparison with experimental results.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {15}, number = {2}, pages = {447-469}, doi = {10.1007/s10237-015-0701-1}, pmid = {26163996}, issn = {1617-7940}, mesh = {Biomechanical Phenomena ; Bronchi/*physiology ; Humans ; *Models, Biological ; *Numerical Analysis, Computer-Assisted ; Pulmonary Ventilation/*physiology ; *Respiration ; Time Factors ; Trachea/*physiology ; }, abstract = {In this article, the results of numerical simulations using computational fluid dynamics (CFD) and a comparison with experiments performed with phase Doppler anemometry are presented. The simulations and experiments were conducted in a realistic model of the human airways, which comprised the throat, trachea and tracheobronchial tree up to the fourth generation. A full inspiration/expiration breathing cycle was used with tidal volumes 0.5 and 1 L, which correspond to a sedentary regime and deep breath, respectively. The length of the entire breathing cycle was 4 s, with inspiration and expiration each lasting 2 s. As a boundary condition for the CFD simulations, experimentally obtained flow rate distribution in 10 terminal airways was used with zero pressure resistance at the throat inlet. CCM+ CFD code (Adapco) was used with an SST k-ω low-Reynolds Number RANS model. The total number of polyhedral control volumes was 2.6 million with a time step of 0.001 s. Comparisons were made at several points in eight cross sections selected according to experiments in the trachea and the left and right bronchi. The results agree well with experiments involving the oscillation (temporal relocation) of flow structures in the majority of the cross sections and individual local positions. Velocity field simulation in several cross sections shows a very unstable flow field, which originates in the tracheal laryngeal jet and propagates far downstream with the formation of separation zones in both left and right airways. The RANS simulation agrees with the experiments in almost all the cross sections and shows unstable local flow structures and a quantitatively acceptable solution for the time-averaged flow field.}, }
@article {pmid26160306, year = {2015}, author = {Carugo, D and Capretto, L and Roy, B and Carboni, M and Caine, M and Lewis, AL and Hill, M and Chakraborty, S and Zhang, X}, title = {Spatiotemporal dynamics of doxorubicin elution from embolic beads within a microfluidic network.}, journal = {Journal of controlled release : official journal of the Controlled Release Society}, volume = {214}, number = {}, pages = {62-75}, doi = {10.1016/j.jconrel.2015.07.003}, pmid = {26160306}, issn = {1873-4995}, mesh = {Algorithms ; Antibiotics, Antineoplastic/*administration &amp; dosage/*chemistry ; Capillaries/metabolism ; Chemoembolization, Therapeutic/*methods ; Doxorubicin/*administration &amp; dosage/*chemistry ; Drug Delivery Systems ; Drug Design ; Injections, Intravenous ; Kinetics ; Lab-On-A-Chip Devices ; Microfluidics ; Microspheres ; Models, Biological ; Spectrometry, Fluorescence ; }, abstract = {Anticancer treatment using embolic drug-eluting beads (DEBs) has shown multifarious advantages compared to systemic chemotherapy. However, there is a growing need for a better understanding of the physical parameters governing drug-elution from embolic devices under physiologically relevant fluidic conditions. In the present study, we investigated the spatiotemporal dynamics of doxorubicin hydrochloride elution from drug-loaded hydrogel embolic beads within a microfluidic device consisting of a network of interconnected microchannels which replicates the architectural properties of microvascular systems. Drug-elution has been investigated experimentally at a single-bead level, using in-house developed microscopy- and spectrofluorimetry-based methods. Results demonstrated that the kinetics of drug-elution and the amount of eluted drug strongly depended on the location of the embolic event within the embolised channel (e.g. fractional amount of eluted drug after 3h was equal to ~0.2 and ~0.6 for completely-confined and partially-confined bead, respectively). Drug-elution from partially-confined bead showed a counterintuitive dependence on the local Reynolds number (and thus on the mean fluid velocity), as a result of dynamic changes in bead compressibility causing the displacement of the bead from the primary embolic site. Conversely, the kinetics of drug-elution from fully-confined bead was less affected by the local Reynolds number and bead displayed faster elution from the surface area exposed to the systemic flow, which was associated with the formation of fluid eddies nearby the bead post embolisation.}, }
@article {pmid26158210, year = {2016}, author = {Ali, N and Javid, K and Sajid, M and Anwar Bég, O}, title = {Numerical simulation of peristaltic flow of a biorheological fluid with shear-dependent viscosity in a curved channel.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {19}, number = {6}, pages = {614-627}, doi = {10.1080/10255842.2015.1055257}, pmid = {26158210}, issn = {1476-8259}, mesh = {Body Fluids/physiology ; Humans ; *Models, Theoretical ; Peristalsis/*physiology ; Reproducibility of Results ; Rheology ; Viscosity ; }, abstract = {Peristaltic motion of a non-Newtonian Carreau fluid is analyzed in a curved channel under the long wavelength and low Reynolds number assumptions, as a simulation of digestive transport. The flow regime is shown to be governed by a dimensionless fourth-order, nonlinear, ordinary differential equation subject to no-slip wall boundary conditions. A well-tested finite difference method based on an iterative scheme is employed for the solution of the boundary value problem. The important phenomena of pumping and trapping associated with the peristaltic motion are investigated for various values of rheological parameters of Carreau fluid and curvature of the channel. An increase in Weissenberg number is found to generate a small eddy in the vicinity of the lower wall of the channel, which is enhanced with further increase in Weissenberg number. For shear-thinning bio-fluids (power-law rheological index, n < 1) greater Weissenberg number displaces the maximum velocity toward the upper wall. For shear-thickening bio-fluids, the velocity amplitude is enhanced markedly with increasing Weissenberg number.}, }
@article {pmid26154384, year = {2015}, author = {Arrieta, J and Cartwright, JH and Gouillart, E and Piro, N and Piro, O and Tuval, I}, title = {Geometric Mixing, Peristalsis, and the Geometric Phase of the Stomach.}, journal = {PloS one}, volume = {10}, number = {7}, pages = {e0130735}, pmid = {26154384}, issn = {1932-6203}, mesh = {Animals ; Computer Simulation ; Gastric Juice/*physiology ; Humans ; Models, Anatomic ; Models, Biological ; Nonlinear Dynamics ; Peristalsis/*physiology ; Stomach/*physiology ; }, abstract = {Mixing fluid in a container at low Reynolds number--in an inertialess environment--is not a trivial task. Reciprocating motions merely lead to cycles of mixing and unmixing, so continuous rotation, as used in many technological applications, would appear to be necessary. However, there is another solution: movement of the walls in a cyclical fashion to introduce a geometric phase. We show using journal-bearing flow as a model that such geometric mixing is a general tool for using deformable boundaries that return to the same position to mix fluid at low Reynolds number. We then simulate a biological example: we show that mixing in the stomach functions because of the "belly phase," peristaltic movement of the walls in a cyclical fashion introduces a geometric phase that avoids unmixing.}, }
@article {pmid27057133, year = {2015}, author = {Ebrahimi, M and Abbaspour, M}, title = {A Comparative Numerical Study on the Performances and Vortical Patterns of Two Bioinspired Oscillatory Mechanisms: Undulating and Pure Heaving.}, journal = {Applied bionics and biomechanics}, volume = {2015}, number = {}, pages = {325934}, pmid = {27057133}, issn = {1176-2322}, abstract = {The hydrodynamics and energetics of bioinspired oscillating mechanisms have received significant attentions by engineers and biologists to develop the underwater and air vehicles. Undulating and pure heaving (or plunging) motions are two significant mechanisms which are utilized in nature to provide propulsive, maneuvering, and stabilization forces. This study aims to elucidate and compare the propulsive vortical signature and performance of these two important natural mechanisms through a systematic numerical study. Navier-Stokes equations are solved, by a pressure-based finite volume method solver, in an arbitrary Lagrangian-Eulerian (ALE) framework domain containing a 2D NACA0012 foil moving with prescribed kinematics. Some of the important findings are (1) the thrust production of the heaving foil begins at lower St and has a greater growing slope with respect to the St; (2) the undulating mechanism has some limitations to produce high thrust forces; (3) the undulating foil shows a lower power consumption and higher efficiency; (4) changing the Reynolds number (Re) in a constant St affects the performance of the oscillations; and (5) there is a distinguishable appearance of leading edge vortices in the wake of the heaving foil without observable ones in the wake of the undulating foil, especially at higher St.}, }
@article {pmid27057132, year = {2015}, author = {Chaube, MK and Tripathi, D and Bég, OA and Sharma, S and Pandey, VS}, title = {Peristaltic Creeping Flow of Power Law Physiological Fluids through a Nonuniform Channel with Slip Effect.}, journal = {Applied bionics and biomechanics}, volume = {2015}, number = {}, pages = {152802}, pmid = {27057132}, issn = {1176-2322}, abstract = {A mathematical study on creeping flow of non-Newtonian fluids (power law model) through a nonuniform peristaltic channel, in which amplitude is varying across axial displacement, is presented, with slip effects included. The governing equations are simplified by employing the long wavelength and low Reynolds number approximations. The expressions for axial velocity, stream function, pressure gradient, and pressure difference are obtained. Computational and numerical results for velocity profile, pressure gradient, and trapping under the effects of slip parameter, fluid behavior index, angle between the walls, and wave number are discussed with the help of Mathematica graphs. The present model is applicable to study the behavior of intestinal flow (chyme movement from small intestine to large intestine). It is also relevant to simulations of biomimetic pumps conveying hazardous materials, polymers, and so forth.}, }
@article {pmid27041980, year = {2015}, author = {Pandey, SK and Chaube, MK and Tripathi, D}, title = {Flow Characteristics of Distinctly Viscous Multilayered Intestinal Fluid Motion.}, journal = {Applied bionics and biomechanics}, volume = {2015}, number = {}, pages = {515241}, pmid = {27041980}, issn = {1176-2322}, abstract = {The goal of this investigation is to study the three layered (core layer, intermediate layer, and peripheral layer) tubular flow of power law fluids with variable viscosity by peristalsis in order to investigate the strength of the role played by an artificially generated intermediate layer to ease constipation. The solution is carried out under the long wavelength and low Reynolds number approximations in the wave frame of reference as the flow is creeping one. The stream functions for each layer such as core layer, intermediate layer, and peripheral layer are determined. The expressions for axial pressure gradient, interfaces, trapping, and reflux limits are obtained. The effects of power law index and viscosities on pressure across one wavelength, mechanical efficiency, and trapping are discussed numerically. It is found that the pressure required to restrain flow rates and the mechanical efficiency increase with the viscosities of the intermediate and peripheral layers as well as with the flow behaviour index. It is observed that the axisymmetric flow in intestines is less prone to constipation than two-dimensional flow and may be more easily overcome with introducing a viscous intermediate layer.}, }
@article {pmid30514019, year = {2014}, author = {Mendoza, U and Candella, RN and Assad, LPF and Castillo, FV and Azevedo, L and Knoppers, BA and Albuquerque, ALS}, title = {A Model Analysis for the Design and Deployment of an Eulerian Sediment Trap Mooring Array in a Western Boundary Upwelling System from Southeast Brazil.}, journal = {Anais da Academia Brasileira de Ciencias}, volume = {86}, number = {2}, pages = {589-600}, pmid = {30514019}, issn = {1678-2690}, abstract = {This work addresses the design and configuration of a Eulerian sediment trap mooring array, which was deployed at the shelf edge (zm ≈ 140 m) 80 km off Cabo Frio, SE- Brazil (23° S). The site was subject to interplay between the Tropical Waters (TW) of the Brazil Current (BC), intrusions from the South Atlantic Central Waters (SACW), which are the source of upwelling in the region, and other oceanographic processes. Detailed computations were used to optimize the total weight, buoyancy balance, and maximum acceptable tilt to avoid hydrodynamic bias in the trapping efficiency and array adaptation to the local oceanographic conditions with the assistance of Matlab and Muringa programs and Modular Ocean Model 4.0 (MOM; i.e., to assert the vertical distribution of the meridional current component). The velocity range of the current component was determined by short term measurements to be between 0.1 and 0.5 m/s. Projections led to a resulting minimum anchor weight of 456 kg. The necessary line tension was ascertained by using the appropriate distribution of a series of buoys along the array, which finally attained a high vertical load of 350 kg because of the attached oceanographic equipment. Additional flotation devices resulted in a stable mooring array as reflected by their low calculated tilt (2.6° ± 0.6°). A low drag of 16 N was computed for the maximum surface current velocity of 0.5 m/s. The Reynolds number values ranged from 4 × 104 to 2 × 105 and a cone-trap aspect ratio of 1.75 was used to assess the trap sampling efficiency upon exposure to different current velocities.}, }
@article {pmid30245535, year = {2014}, author = {Poroseva, SV}, title = {The Effect of a Pressure-Containing Correlation Model on Near-Wall Flow Simulations with RST Models.}, journal = {Journal of fluids engineering}, volume = {136}, number = {6}, pages = {}, doi = {10.1115/1.4025936}, pmid = {30245535}, issn = {0098-2202}, support = {NNX12AJ61A//NASA/United States ; }, abstract = {It is accustomed to think that turbulence models based on solving the Reynolds-Averaged Navier-Stokes equations require empirical functions to accurately reproduce the behavior of flow characteristics of interest, particularly near a wall. The current paper analyzes how choosing a model for pressure-strain correlations in second-order closures affects the need for introducing empirical functions in model equations to reproduce the flow behavior near a wall correctly. An axially-rotating pipe flow is used as a test flow for the analysis. Results of simulations demonstrate that by using more physics-based models to represent pressure-strain correlations, one can eliminate wall functions associated with such models. The higher the Reynolds number or the strength of imposed rotation on a flow, the less need there is for empirical functions regardless of the choice of a pressure-strain correlation model.}, }
@article {pmid27355040, year = {2014}, author = {Srivastava, N}, title = {MHD Flow of the Micropolar Fluid between Eccentrically Rotating Disks.}, journal = {International scholarly research notices}, volume = {2014}, number = {}, pages = {317075}, pmid = {27355040}, issn = {2356-7872}, abstract = {This analytical investigation examines the magnetohydrodynamic flow problem of an incompressible micropolar fluid between the two eccentrically placed disks. Employing suitable transformations, the flow governing partial differential equations is reduced to ordinary differential equations. An exact solution representing the different flow characteristic of micropolar fluid has been derived by solving the ordinary differential equations. Analysis of the flow characteristics of the micropolar fluid has been done graphically by varying the Reynolds number and the Hartmann number. This analysis has been carried out for the weak and strong interactions.}, }
@article {pmid27524855, year = {2011}, author = {Briguglio, A and Hohenegger, J}, title = {How to react to shallow water hydrodynamics: The larger benthic foraminifera solution.}, journal = {Marine micropaleontology}, volume = {81}, number = {1-2}, pages = {63-76}, pmid = {27524855}, issn = {0377-8398}, support = {P 23459/FWF_/Austrian Science Fund FWF/Austria ; }, abstract = {Symbiont-bearing larger benthic foraminifera inhabit the photic zone to provide their endosymbiotic algae with light. Because of the hydrodynamic conditions of shallow water environments, tests of larger foraminifera can be entrained and transported by water motion. To resist water motion, these foraminifera have to build a test able to avoid transport or have to develop special mechanisms to attach themselves to substrate or to hide their test below sediment grains. For those species which resist transport by the construction of hydrodynamic convenient shapes, the calculation of hydrodynamic parameters of their test defines the energetic input they can resist and therefore the scenario where they can live in. Measuring the density, size and shape of every test, combined with experimental data, helps to define the best mathematical approach for the settling velocity and Reynolds number of every shell. The comparison between water motion at the sediment-water interface and the specimen-specific settling velocity helps to calculate the water depths at which, for a certain test type, transport, deposition and accumulation may occur. The results obtained for the investigated taxa show that the mathematical approach gives reliable results and can discriminate the hydrodynamic behaviour of different shapes. Furthermore, the study of the settling velocities, calculated for all the investigated taxa, shows that several species are capable to resist water motion and therefore they appear to be functionally adapted to the hydrodynamic condition of its specific environment. The same study is not recommended on species which resist water motion by adopting hiding or anchoring strategies to avoid the effect of water motion.}, }
@article {pmid28509944, year = {2010}, author = {Kumar, MS and Philominathan, P}, title = {The physics of flagellar motion of E. coli during chemotaxis.}, journal = {Biophysical reviews}, volume = {2}, number = {1}, pages = {13-20}, pmid = {28509944}, issn = {1867-2450}, abstract = {Flagellar motion has been an active area of study right from the discovery of bacterial chemotaxis in 1882. During chemotaxis, E. coli moves with the help of helical flagella in an aquatic environment. Helical flagella are rotated in clockwise or counterclockwise direction using reversible flagellar motors situated at the base of each flagellum. The swimming of E. coli is characterized by a low Reynolds number that is unique and time reversible. The random motion of E. coli is influenced by the viscosity of the fluid and the Brownian motion of molecules of fluid, chemoattractants, and chemorepellants. This paper reviews the literature about the physics involved in the propulsion mechanism of E. coli. Starting from the resistive-force theory, various theories on flagellar hydrodynamics are critically reviewed. Expressions for drag force, elastic force and velocity of flagellar elements are derived. By taking the elastic nature of flagella into account, linear and nonlinear equations of motions are derived and their solutions are presented.}, }
@article {pmid32646073, year = {2005}, author = {Nisisako, T and Okushima, S and Torii, T}, title = {Controlled formulation of monodisperse double emulsions in a multiple-phase microfluidic system.}, journal = {Soft matter}, volume = {1}, number = {1}, pages = {23-27}, doi = {10.1039/b501972a}, pmid = {32646073}, issn = {1744-6848}, abstract = {This paper gives an overview of our recent work on the use of microfluidic devices to formulate double emulsions. Key issues in the controlled encapsulation of highly monodisperse drops include: (a) regular periodicity in the formation of micro droplets due to the interplay between viscous shearing and interfacial tension in low Reynolds number streams; (b) serially connected hydrophobic and hydrophilic microchannels to form aqueous and organic drops consecutively. Water-in-oil-in-water emulsions and oil-in-water-in-oil emulsions can both be produced by reversing the order of hydrophobic and hydrophilic junctions. Alternating formation of aqueous droplets at a cross junction has enabled the production of organic droplets that encase two aqueous droplets of differing compositions.}, }
@article {pmid28868711, year = {1996}, author = {Tamagawa, M and Akamatsu, T and Saitoh, K}, title = {Prediction of Hemolysis in Turbulent Shear Orifice Flow.}, journal = {Artificial organs}, volume = {20}, number = {5}, pages = {553-559}, doi = {10.1111/j.1525-1594.1996.tb04479.x}, pmid = {28868711}, issn = {1525-1594}, abstract = {This study proposes a method of predicting hemolysis induced by turbulent shear stress (Reynolds stress) in a simplified orifice pipe flow. In developing centrifugal blood pumps, there has been a serious problem with hemolysis at the impeller or casing edge; because of flow separation and turbulence in these regions. In the present study, hemolysis caused by turbulent shear stress must occur at high shear stress levels in regions near the edge of an orifice pipe flow. We have computed turbulent shear flow using the low-Reynolds number k -ε model. We found that the computed turbulent shear stress near the edge was several hundreds times that of the laminar shear stress (molecular shear stress). The peak turbulent shear stress is much greater than that obtained in conventional hemolysis testing using a viscometer apparatus. Thus, these high turbulent shear stresses should not be ignored in estimating hemolysis in this blood flow. Using an integrated power by shear force, it is optimimal to determine the threshold of the turbulent shear stress by comparing computed stress levels with those of hemolysis experiments of pipe orifice blood flow.}, }
@article {pmid29281382, year = {1994}, author = {Williams, TA}, title = {A Model of Rowing Propulsion and the Ontogeny of Locomotion in Artemia Larvae.}, journal = {The Biological bulletin}, volume = {187}, number = {2}, pages = {164-173}, doi = {10.2307/1542239}, pmid = {29281382}, issn = {1939-8697}, abstract = {Newly hatched Artemia larvae use one pair of limbs to locomote. During development they gradually add additional limbs along the elongating trunk. As larvae grow, body length increases from about 0.4 mm to 4 mm, mean swimming speed increases from 1.8 mm s-1 to 9.9 mm s-1, and frequency of antennal beat decreases from 9.5 to 6.7 Hz. As new limbs are added, they become active in the metachronal rhythm of pre-existing limbs. The body velocity oscillates as early larvae swim; later larvae swim without a cyclic acceleration and deceleration of the body. The change in the pattern of swimming is correlated with the addition of propulsors and a transition in the relative importance of viscous and inertial effects that determine the propulsion in subsequent stages. Reynolds number (based on body length) increases from 2 to 37. A theoretical analysis of rowing propulsion at these intermediate Reynolds numbers shows that initial development of new limbs in Artemia larvae is unimportant for propulsion. Rowing propulsion at the low Reynolds numbers is drag-based; as Reynolds number increases, inertial effects become more important, and unsteady forces on the body become significant in the balance between limb and body. A glide of the body develops at the end of the powerstroke, and relative limb velocity changes.}, }
@article {pmid29281381, year = {1994}, author = {Williams, TA}, title = {Locomotion in Developing Artemia Larvae: Mechanical Analysis of Antennal Propulsors Based on Large-Scale Physical Models.}, journal = {The Biological bulletin}, volume = {187}, number = {2}, pages = {156-163}, doi = {10.2307/1542238}, pmid = {29281381}, issn = {1939-8697}, abstract = {A physical model of the swimming appendage (second antenna) of a larval Artemia was oscillated and translated through a tank of glycerine to determine how such a shape may be used to generate thrust at the intermediate Reynolds numbers at which it operates. Force on the model was measured by strain gauges and used to calculate coefficients of drag at a series of speeds and frequencies that represented flow regimes of different larval stages. Measured coefficients of drag (Cd) over this Reynolds number range ({approx}1-10) suggest that an expression for a cylinder perpendicular to flow at intermediate Reynolds number (Cd = 1 + 10 Re-2/3) best represents the changes in drag coefficients for this geometry. Unsteady forces were found to be a negligible portion of the force on the model in spite of a high ratio of frequency of oscillation to forward translational velocity (i.e., Strouhal number). Comparison of the thrust generated by the model with its fan of setae rigidly fixed versus passively flexing suggests that passive extension of setae can be influenced by relative limb and body speed.}, }
@article {pmid30139156, year = {1993}, author = {Andersen, MC}, title = {DIASPORE MORPHOLOGY AND SEED DISPERSAL IN SEVERAL WIND-DISPERSED ASTERACEAE.}, journal = {American journal of botany}, volume = {80}, number = {5}, pages = {487-492}, doi = {10.1002/j.1537-2197.1993.tb13830.x}, pmid = {30139156}, issn = {1537-2197}, abstract = {I made measurements of morphology and settling velocity on seeds of 19 species of wind-dispersed Asteraceae. From the morphological measurements I calculated Reynolds numbers and approximate plume loadings for the species. Diaspore settling velocity increases linearly with the square root of plume loading. This relationship varies among species and among subfamilies, but not among life history types. Reynolds number is highly variable among subfamilies, less so within subfamilies. Diaspores with beaked achenes have significantly lower settling velocities than diaspores with unbeaked achenes, even though beaked and unbeaked achenes do not differ in plume loading or in Reynolds number. Reynolds numbers of all diaspores examined are well above the range in which Stokes' Law applies. I recommend that the use of formulae based on Stokes' Law be curtailed in studies of the relationship between plume loading and settling velocity. The results suggest that many seed characters may have evolved due to selection on dispersal ability. This is in spite of phyletic constraints on morphology reflected in the relative uniformity of Reynolds numbers within subfamilies.}, }
@article {pmid31071803, year = {1992}, author = {Goff, HD and Davidson, VJ}, title = {Flow Characteristics and Holding Time Calculations of Ice Cream Mixes in HTST Holding Tubes.}, journal = {Journal of food protection}, volume = {55}, number = {1}, pages = {34-37}, doi = {10.4315/0362-028X-55.1.34}, pmid = {31071803}, issn = {1944-9097}, abstract = {In order to determine the potential for development of laminar flow and consequential underholding in the holding tubes of HTST pasteurizers, a study on the relationship between ice cream mix viscosity and shear rate at 80°C has been conducted. Typical shear rates at the wall were calculated for HTST holding tubes of standard industry sizes and flow rates. Shear rates in the holding tube were found to vary from 50 to 180 s[-1], depending on the conditions. Viscosity of ice cream mixes as a function of shear rate, stabilizer type, and stabilizer concentration were measured. Ice cream mix was found to be non-Newtonian and pseudoplastic. Viscosities ranged from 8.7 cP in an unstabilized mix at high shear rate (relative to the inside of the holding tube) to 103 cP for 0.25% carboxymethyl cellulose at low shear rate. Generalized Reynolds numbers inside the holding tubes varied from 100 to 1700, indicating a strong potential for the development of laminar flow. The apparent viscosities required to result in a minimum generalized Reynolds number of 2100 are very near to or less than the actual viscosities of stabilized ice cream mixes, and thus the potential for a laminar flow pattern within the holding tube needs to be addressed in determining holding tube lengths for a required holding time.}, }
@article {pmid29303631, year = {1991}, author = {Patterson, MR}, title = {The Effects of Flow on Polyp-Level Prey Capture in an Octocoral, Alcyonium siderium.}, journal = {The Biological bulletin}, volume = {180}, number = {1}, pages = {93-102}, doi = {10.2307/1542432}, pmid = {29303631}, issn = {1939-8697}, abstract = {Particle capture by individual polyps and tentacles of the octocoral, Alcyonium siderium, was investigated in flows of different speed and turbulence intensity. In low flow (Umean = 2.7 cm/s; u' = 1.2 cm/s, where u' is the root mean square of the fluctuations from Umean), tentacles on the upstream side of a polyp capture the most prey. In intermediate flow (Umean = 12.2 cm/s; u' = 6.0 cm/s), downstream tentacles within a polyp catch the most prey. In high flow (Umean = 19.8 cm/s; u'= 4.0 cm/s), polyps are bent downstream, eddies form over the tentacular surfaces, and the capture distribution over tentacles becomes radially symmetric. At all flow speeds tested, particles are caught with increasing frequency nearer the tip of the tentacle relative to locations near the pharynx. At the highest flow speed tested, no particles are caught on the segment of each tentacle closest to the pharynx. The per polyp capture efficiency is low and drops markedly with increasing Reynolds number. The capture mechanism for this species appears to be direct interception; inertial impaction is shown to be unimportant. Flow modulation of particle capture by polyps is probably a general phenomenon among octocorals.}, }
@article {pmid28312353, year = {1989}, author = {Statzner, B and Holm, TF}, title = {Morphological adaptation of shape to flow: Microcurrents around lotic macroinvertebrates with known Reynolds numbers at quasi-natural flow conditions.}, journal = {Oecologia}, volume = {78}, number = {2}, pages = {145-157}, pmid = {28312353}, issn = {1432-1939}, abstract = {Using Laser Doppler Anemometry we measured current velocities in the median plane around dead lotic macroinvertebrates in a flume which reproduced natural near bottom hydraulics. We investigated specimens of the gastropods Ancylus, Acroloxus, and Potamopyrgus, the amphipod Gammarus, and the larval caddisflies Anabolia, Micrasema, and Silo of various size, various alignment to the flow or which were otherwise manipulated in order to clarify certain questions of adaptation of shape or case building style to flow, or the effects of flow on field distribution patterns. The steepest velocity gradients close to the animals were found near areas of their bodies protruding furthest into the flow. In such regions the rates of potential diffusive exchange processes, the potential corrasion (abrasion through suspended solids), and, for larger specimens, the lift forces (directed towards the water surface) must be highest. Posterior of these areas growing boundary layers formed above those species whose upper contour was approximately parallel to the upstream-downstream direction of the flow. All specimens removed momentum from the flow and thus experience a drag force (directed downstream). From the complete data set we derived the following general conclusions about the physical effects of potential morphological adaptations, taking into consideration diffusion through boundary layers, corrasion, lift forces, friction and pressure drag forces: The physical significance of these five factors generally depends on the Reynolds number of an animal and is largely affected by flow separation, which was significantly related to the ratio of body length to height and the slope of the posterior contour. A simultaneous effective morphological adaptation to all five factors is physically impossible and, in addition, would have to change from life at low (e.g. a young, small specimen of a species) to life at high (e.g. a fully grown specimen of the same species) Reynolds number.}, }
@article {pmid28310857, year = {1985}, author = {Gilbert, JJ}, title = {Escape response of the rotifer Polyarthra: a high-speed cinematographic analysis.}, journal = {Oecologia}, volume = {66}, number = {3}, pages = {322-331}, pmid = {28310857}, issn = {1432-1939}, abstract = {Cinefilms of unconstrained P. vulgaris at 17°C were taken at a low magnification (∼2x) and 120-200 fps to analyze body movements during swimming and escape responses mediated by movements of the 12 lateral, bladelike appendages or paddles. Cinefilms of partially constrained P. vulgaris and P. dolichoptera at 16°C were taken at a higher magnification (∼10x) and 300 fps, using interference contrast optics, to resolve paddle movements during escape responses. When swimming, P. vulgaris moved at a velocity of 0.348±0,025 (S.E.) mm·s[-1] (2.64 body lenghs·s[-1]), having a Reynolds number of 0.05. During escape responses, P. vulgaris traveled 1.947±0.124 (S.E.) mm (15 body lengths) during 0.0564±0.0038 (S.E.) s, continuously moving at a velocity of 35.7±1.2 (S.E.) mm·s[-1] (270 body lengths·s[-1]) and having a Reynolds number of 5. During these responses, P. vulgaris tumbled sinuously but mostly-88.9±2.3 (S.E.) %-in a constant direction; the angular change in direction from one frame to the next was 28±2 (S.E.) degrees, but the sign of the change in direction frequently alternated. Escape responses are caused by 1-3 cycles of paddle movements. In each cycle, the rigid paddles move up asynchronously until they are all directly overhead, and then they move downwards to their original resting positions, again asynchronously. Polyarthra's body moves along the flight path during all phases of this cycle. A single cycle may take as little as 26 ms, 13 ms for the paddles to elevate and 13 ms for them to descend. The asynchronous upward and downward movements of each of the 12 paddles explain why Polyarthra's body tumbles continuously through its low Reynolds number, viscous environment. Escape responses generally were initiated by contact with another rotifer. In one P. dolichoptera response, the time lag between such contact and the initiation of paddle elevation was about 7 ms. The very short lag time, great velocity, considerable displacement, and unpredictable directionality of Polyarthra's escape response make it a very effective defense against capture by some invertebrate predators.}, }
@article {pmid28310572, year = {1983}, author = {Porter, KG and Feig, YS and Vetter, EF}, title = {Morphology, flow regimes, and filtering rates of Daphnia, Ceriodaphnia, and Bosmina fed natural bacteria.}, journal = {Oecologia}, volume = {58}, number = {2}, pages = {156-163}, pmid = {28310572}, issn = {1432-1939}, abstract = {Body size is the best overall indicator of the abilities of the cladocerans Daphnia magna, D. parvula, Ceriodaphnia lacustris and Bosmina longirostris to filter natural bacteria (<1.0 μm). However, species differences exist which cannot be inferred from differences in size, behavior, or morphology alone. The relationship between filtering rate (FR in ml animal[-1]h[-1]) and body length (L in mm) for the cladocerans studied can be described by the power function: [Formula: see text] In D. parvula, algal filtering rates are higher and increase more rapidly with increasing body size than do bacterial filtering rates which are 26 to 33% of algal rates. This suggests that different processes may be involved in the capture of these ultrafine particles and that ultrafine particle capture efficiency decreases with increasing body size within a species. Weight specific filtering rates (in μl μg dry wt[-1]h[-1]) have a strong negative relationship to body size and show species specific differences. Appendage beat rates intersetular distances, setule diameter, appendage, area, % open space on the filtering appendage, Reynolds number, and boundary layer thickness do not provide simple predictions of bacterial filtering rates for the cladocerans studied. Filtering rates on cultured laboratory bacteria and algae may not indicate filtering rates on natural bacterioplankton because of differences in bacterial size, motility, and surface properties. Uptake of ultrafine particles may be enhanced by the presence of larger, more readily filtered particles through a "piggybacking" phenomenon.}, }
@article {pmid28310599, year = {1982}, author = {Kingsolver, JG and Moffat, RJ}, title = {Thermoregulation and the determinants of heat transfer in Colias butterflies.}, journal = {Oecologia}, volume = {53}, number = {1}, pages = {27-33}, pmid = {28310599}, issn = {1432-1939}, abstract = {As a means of exploring behavioral and morphological adaptations for thermoregulation in Colias butterflies, convective heat transfer coefficients of real and model butterflies were measured in a wind tunnel as a function of wind speed and body orientation (yaw angle). Results are reported in terms of a dimensionless heat transfer coefficient (Nusselt number, Nu) and a dimensionless wind speed (Reynolds number, Re), for a wind speed range typical of that experienced by basking Colias in the field. The resultant Nusselt-Reynolds (Nu-Re) plots thus indicate the rates of heat transfer by forced convection as a function of wind speed for particular model geometries.For Reynolds numbers throughout the measured range, Nusselt numbers for C. eurytheme butterflies are consistently lower than those for long cylinders, and are independent of yaw angle. There is significant variation among individual butterflies in heat transfer coefficients throughout the Re range. Model butterflies without artificial fur have Nu-Re relations similar to those for cylinders. Heat transfer in these models depends upon yaw angle, with higher heat transfer at intermediate yaw angles (30-60°); these yaw effects increase with increasing Reynolds number. Models with artificial fur, like real Colias, have Nusselt numbers which are consistently lower than those for models without fur at given Reynolds numbers throughout the Re range. Unlike real Colias, however, the models with fur do show yaw angle effects similar to those for models without fur.The independence of heat loss from yaw angle for real Colias is consistent with field observations indicating no behavioral orientation to wind direction. The presence of fur on the models reduces heat loss but does not affect yaw dependence. The large individual variation in heat transfer coefficients among butterflies is probably due to differences in fur characteristics rather than to differences in wing morphology.Finally, a physical model of a butterfly was constructed which accurately simulates the body temperatures of basking Colias in the field for a variety of radiation and wind velocity conditions. The success of the butterfly simulator in mimicking Colias thermal characteristics confirms our preliminary understanding of the physical bases for and heat transfer mechanisms underlying thermoregulatory adaptations in these butterflies.}, }
@article {pmid32196167, year = {1960}, author = {Sherlin, GC}, title = {Behavior of Isolated Disturbances Superimposed on Laminar Flow in a Rectangular Pipe.}, journal = {Journal of research of the National Bureau of Standards. Section A, Physics and chemistry}, volume = {64A}, number = {4}, pages = {281-289}, doi = {10.6028/jres.064A.027}, pmid = {32196167}, issn = {0022-4332}, abstract = {An investigation was conducted in a horizontal transparent rectangular pipe to study the behavior, in laminar flow, of an isolated turbulent-like disturbance produced by injecting a quantity of dye into the pipe 39 feet from the entrance. As the resulting mass of colored water moved downstream, time-distance measurements were made for the front of the dye mass and for the rear of the disturbance. The experimental setup, which is described in some detail, permitted reasonable control over the mean flow rate from which Reynolds number was calculated. The utilization of the data unfolded a functional relationship among three quantities: The ratio of the velocity of the rear of the disturbance to the velocity of the front of the dye UR/UF ; the distance from the origin, XF ; and the Reynolds number R. The similarity of this work to that being done by Lindgren in Stockholm is mentioned.}, }
@article {pmid26135361, year = {2015}, author = {Alexandrov, DV and Galenko, PK}, title = {Thermo-solutal and kinetic regimes of an anisotropic dendrite growing under forced convective flow.}, journal = {Physical chemistry chemical physics : PCCP}, volume = {17}, number = {29}, pages = {19149-19161}, doi = {10.1039/c5cp03018h}, pmid = {26135361}, issn = {1463-9084}, abstract = {A thermo-diffusional problem of a free dendrite growing in a binary mixture is considered analytically. Effects of the anisotropy and convective flow on the stable mode of the dendrite with four-fold crystal symmetry are studied. Special analysis is given for the parabolic dendrite growing at arbitrary Péclet numbers and with small anisotropy of surface energy and atomic kinetics. The stable growth mode is analyzed through the solvability condition giving the stability criterion for the dendrite tip velocity V and dendrite tip diameter ρ as a function of growth Péclet number, Pg, flow Péclet number, Pf, and Reynolds number, Re. Using the obtained criterion of stability, a complete sequence of transitions in growth regimes (namely, from solute diffusion-limited to thermally controlled and further to kinetically-limited regimes) of the anisotropic dendrite is derived and revealed. Limiting cases to known criteria for small and high growth Péclet numbers of the solidifying system with and without convective fluid flow are found. Two-dimensional solidification regimes and scalings obtained are discussed for their extension to three-dimensional dendritic growth.}, }
@article {pmid26133874, year = {2015}, author = {Huisman, SG and van der Veen, RC and Bruggert, GW and Lohse, D and Sun, C}, title = {The boiling Twente Taylor-Couette (BTTC) facility: Temperature controlled turbulent flow between independently rotating, coaxial cylinders.}, journal = {The Review of scientific instruments}, volume = {86}, number = {6}, pages = {065108}, doi = {10.1063/1.4923082}, pmid = {26133874}, issn = {1089-7623}, abstract = {A new Taylor-Couette system has been designed and constructed with precise temperature control. Two concentric independently rotating cylinders are able to rotate at maximum rates of f(i) = ± 20 Hz for the inner cylinder and f(o) = ± 10 Hz for the outer cylinder. The inner cylinder has an outside radius of r(i) = 75 mm, and the outer cylinder has an inside radius of r(o) = 105 mm, resulting in a gap of d = 30 mm. The height of the gap is L = 549 mm, giving a volume of V = 9.3 L. The geometric parameters are η = r(i)/r(o) = 0.714 and Γ = L/d = 18.3. With water as working fluid at room temperature, the Reynolds numbers that can be achieved are Re(i) = ω(i)r(i)(r(o) - r(i))/ν = 2.8 × 10(5) and Re(o) = ω(o)r(o)(r(o) - r(i))/ν = 2 × 10(5) or a combined Reynolds number of up to Re = (ω(i)r(i) - ω(o)r(o))(r(o) - r(i))/ν = 4.8 × 10(5). If the working fluid is changed to the fluorinated liquid FC-3284 with kinematic viscosity 0.42 cSt, the combined Reynolds number can reach Re = 1.1 × 10(6). The apparatus features precise temperature control of the outer and inner cylinders separately and is fully optically accessible from the side and top. The new facility offers the possibility to accurately study the process of boiling inside a turbulent flow and its effect on the flow.}, }
@article {pmid26116202, year = {2015}, author = {Vasey, G and Lukeman, R and Wyeth, RC}, title = {Additional Navigational Strategies Can Augment Odor-Gated Rheotaxis for Navigation under Conditions of Variable Flow.}, journal = {Integrative and comparative biology}, volume = {55}, number = {3}, pages = {447-460}, doi = {10.1093/icb/icv073}, pmid = {26116202}, issn = {1557-7023}, mesh = {Animals ; *Chemotaxis ; Fishes/*physiology ; Invertebrates/*physiology ; Models, Biological ; *Movement ; *Odorants ; Rheology ; *Spatial Navigation ; }, abstract = {The navigation strategies animals use to find sources of odor depend on the olfactory stimuli, the properties of flowing fluids, and the locomotory capabilities of the animal. In high Reynolds number environments, animals typically use odor-gated rheotaxis to find the source of turbulent odor plumes. This strategy succeeds because, although turbulence creates an intermittent chemical cue, the animal follows the (continuous) directional cue created by the flow that is transporting the chemical. However, in nature, animals may lose all contact with an odor plume as variations in the direction of bulk flow cause the plume to be rotated away before the animal reaches the source of the odor. Our goal was to use a mathematical model to test the hypothesis that strategies that augment odor-gated rheotaxis would be beneficial for finding the source of an odor plume in such variable flow. The model links a stochastic variable-direction odor plume with a turbulence-based intermittent chemical signal and four different movement strategies, including: odor-gated rheotaxis alone (as a control), odor-gated rheotaxis augmented by further rheotaxis in the absence of odor, odor-gated rheotaxis augmented by a random walk, and odor-gated rheotaxis augmented by movement actively guided by the heading of the flow when the odor was still present. We found that any of the three augmented strategies could improve on strict odor-gated rheotaxis. Moreover, variations in performance caused the best strategy to depend on the speed of movement of the animal and the magnitude of the variation in flow, and more subtly on the duration over which the augmented strategy was performed. For most combinations of parameters in the model, either augmenting with a random walk or following the last-known heading were the best-performing strategies. Overall, our results suggest that marine animals that rely on odor cues to navigate in turbulent environments may augment odor-gated rheotaxis with additional movements that will increase the probability of finding the sources of odors. Moreover, we believe our approach to modeling odor plumes in variable flows is a valuable step toward mathematically capturing the key conditions experienced by animals navigating on the basis of odors carried by flows.}, }
@article {pmid26100535, year = {2015}, author = {Mirbod, P and Meng, D}, title = {Analysis of bolus formation in micropipette ejection systems.}, journal = {The European physical journal. E, Soft matter}, volume = {38}, number = {6}, pages = {59}, pmid = {26100535}, issn = {1292-895X}, mesh = {*Hydrodynamics ; Injections/*instrumentation ; Microfluidics ; Models, Theoretical ; }, abstract = {The ejection of drugs from micropipettes is practiced frequently in biomedical research and clinical studies however, little is known about the dynamics of this process. The fundamentals of disperse fluid injection via a capillary into an ambient immiscible fluid have been investigated extensively. Here, we experimentally investigate the bolus formation in micropipette ejection systems, where the injection and ambient fluid are the same. We experimentally measure the temporal evolution of the bolus formation in the same fluid. There are three different bolus formation mechanisms that arise from different Re t regimes: a) a nearly spherical bolus, b) a pear-like bolus, and c) a large distortion or axial jet. We examine the scaled dimensions of the bolus, R b/D t, L b/D t, H/D t, and α, as a function of the dimensionless parameters such as tip Reynolds number, Re t, dimensionless value of g/(D t (.) V t), the dimensionless time, tV t/D t, and the distance between the edge of the micropipette and the free surface, D/D t. The bolus radius for 0.2 < Re t < 30 grows according to t (1/2) in the entire time range, which allows us to estimate the time for complete bolus formation.}, }
@article {pmid26098511, year = {2015}, author = {Yadav, V and Duan, W and Butler, PJ and Sen, A}, title = {Anatomy of Nanoscale Propulsion.}, journal = {Annual review of biophysics}, volume = {44}, number = {}, pages = {77-100}, doi = {10.1146/annurev-biophys-060414-034216}, pmid = {26098511}, issn = {1936-1238}, mesh = {Animals ; Bacteria/chemistry/cytology ; Bacterial Physiological Phenomena ; Chemotaxis ; Cilia/physiology/ultrastructure ; Flagella/physiology ; Locomotion ; Molecular Motor Proteins/chemistry ; *Motion ; Nanotechnology/instrumentation/*methods ; }, abstract = {Nature supports multifaceted forms of life. Despite the variety and complexity of these forms, motility remains the epicenter of life. The applicable laws of physics change upon going from macroscales to microscales and nanoscales, which are characterized by low Reynolds number (Re). We discuss motion at low Re in natural and synthetic systems, along with various propulsion mechanisms, including electrophoresis, electrolyte diffusiophoresis, and nonelectrolyte diffusiophoresis. We also describe the newly uncovered phenomena of motility in non-ATP-driven self-powered enzymes and the directional movement of these enzymes in response to substrate gradients. These enzymes can also be immobilized to function as fluid pumps in response to the presence of their substrates. Finally, we review emergent collective behavior arising from interacting motile species, and we discuss the possible biomedical applications of the synthetic nanobots and microbots.}, }
@article {pmid26084355, year = {2015}, author = {Pan, R and Geng, J and Cai, J and Tyree, MT}, title = {A comparison of two methods for measuring vessel length in woody plants.}, journal = {Plant, cell &amp; environment}, volume = {38}, number = {12}, pages = {2519-2526}, doi = {10.1111/pce.12566}, pmid = {26084355}, issn = {1365-3040}, mesh = {Acer/*anatomy &amp; histology ; Plant Stems/anatomy &amp; histology ; Populus/*anatomy &amp; histology ; Quercus/*anatomy &amp; histology ; Vitis/*anatomy &amp; histology ; Wood/anatomy &amp; histology ; }, abstract = {Vessel lengths are important to plant hydraulic studies, but are not often reported because of the time required to obtain measurements. This paper compares the fast dynamic method (air injection method) with the slower but traditional static method (rubber injection method). Our hypothesis was that the dynamic method should yield a larger mean vessel length than the static method. Vessel length was measured by both methods in current year stems of Acer, Populus, Vitis and Quercus representing short- to long-vessel species. The hypothesis was verified. The reason for the consistently larger values of vessel length is because the dynamic method measures air flow rates in cut open vessels. The Hagen-Poiseuille law predicts that the air flow rate should depend on the product of number of cut open vessels times the fourth power of vessel diameter. An argument is advanced that the dynamic method is more appropriate because it measures the length of the vessels that contribute most to hydraulic flow. If all vessels had the same vessel length distribution regardless of diameter, then both methods should yield the same average length. This supports the hypothesis that large-diameter vessels might be longer than short-diameter vessels in most species.}, }
@article {pmid26083027, year = {2015}, author = {Noreen, S and Qasim, M}, title = {Influence of Hall Current and Viscous Dissipation on Pressure Driven Flow of Pseudoplastic Fluid with Heat Generation: A Mathematical Study.}, journal = {PloS one}, volume = {10}, number = {6}, pages = {e0129588}, pmid = {26083027}, issn = {1932-6203}, mesh = {Body Fluids/*physiology ; Body Temperature ; Hot Temperature ; Humans ; Hydrodynamics ; Models, Biological ; Motion ; *Peristalsis ; Pressure ; *Rheology ; Viscosity ; }, abstract = {In this paper, we study the influence of heat sink (or source) on the peristaltic motion of pseudoplastic fluid in the presence of Hall current, where channel walls are non-conducting in nature. Flow analysis has been carried out under the approximations of a low Reynolds number and long wavelength. Coupled equations are solved using shooting method for numerical solution for the axial velocity function, temperature and pressure gradient distributions. We analyze the influence of various interesting parameters on flow quantities. The present study can be considered as a mathematical presentation of the dynamics of physiological organs with stones.}, }
@article {pmid26066439, year = {2015}, author = {Bos, WJ and Kadoch, B and Schneider, K}, title = {Angular statistics of Lagrangian trajectories in turbulence.}, journal = {Physical review letters}, volume = {114}, number = {21}, pages = {214502}, doi = {10.1103/PhysRevLett.114.214502}, pmid = {26066439}, issn = {1079-7114}, abstract = {The angle between subsequent particle displacement increments is evaluated as a function of the time lag in isotropic turbulence. It is shown that the evolution of this angle contains two well-defined power laws, reflecting the multiscale dynamics of high-Reynolds number turbulence. The probability density function of the directional change is shown to be self-similar and well approximated by an analytically derived model assuming Gaussianity and independence of the velocity and the Lagrangian acceleration.}, }
@article {pmid26066263, year = {2015}, author = {Low, R and Pothérat, A}, title = {Bounds on the attractor dimension for magnetohydrodynamic channel flow with parallel magnetic field at low magnetic Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {5}, pages = {053022}, doi = {10.1103/PhysRevE.91.053022}, pmid = {26066263}, issn = {1550-2376}, abstract = {We investigate aspects of low-magnetic-Reynolds-number flow between two parallel, perfectly insulating walls in the presence of an imposed magnetic field parallel to the bounding walls. We find a functional basis to describe the flow, well adapted to the problem of finding the attractor dimension and which is also used in subsequent direct numerical simulation of these flows. For given Reynolds and Hartmann numbers, we obtain an upper bound for the dimension of the attractor by means of known bounds on the nonlinear inertial term and this functional basis for the flow. Three distinct flow regimes emerge: a quasi-isotropic three-dimensional (3D) flow, a nonisotropic 3D flow, and a 2D flow. We find the transition curves between these regimes in the space parametrized by Hartmann number Ha and attractor dimension d(att). We find how the attractor dimension scales as a function of Reynolds and Hartmann numbers (Re and Ha) in each regime. We also investigate the thickness of the boundary layer along the bounding wall and find that in all regimes this scales as 1/Re, independently of the value of Ha, unlike Hartmann boundary layers found when the field is normal to the channel. The structure of the set of least dissipative modes is indeed quite different between these two cases but the properties of turbulence far from the walls (smallest scales and number of degrees of freedom) are found to be very similar.}, }
@article {pmid26066258, year = {2015}, author = {Rosén, T and Do-Quang, M and Aidun, CK and Lundell, F}, title = {Effect of fluid and particle inertia on the rotation of an oblate spheroidal particle suspended in linear shear flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {5}, pages = {053017}, doi = {10.1103/PhysRevE.91.053017}, pmid = {26066258}, issn = {1550-2376}, mesh = {*Hydrodynamics ; *Mechanical Phenomena ; *Models, Theoretical ; Rheology ; *Rotation ; }, abstract = {This work describes the inertial effects on the rotational behavior of an oblate spheroidal particle confined between two parallel opposite moving walls, which generate a linear shear flow. Numerical results are obtained using the lattice Boltzmann method with an external boundary force. The rotation of the particle depends on the particle Reynolds number, Re(p)=Gd(2)ν(-1) (G is the shear rate, d is the particle diameter, ν is the kinematic viscosity), and the Stokes number, St=αRe(p) (α is the solid-to-fluid density ratio), which are dimensionless quantities connected to fluid and particle inertia, respectively. The results show that two inertial effects give rise to different stable rotational states. For a neutrally buoyant particle (St=Re(p)) at low Re(p), particle inertia was found to dominate, eventually leading to a rotation about the particle's symmetry axis. The symmetry axis is in this case parallel to the vorticity direction; a rotational state called log-rolling. At high Re(p), fluid inertia will dominate and the particle will remain in a steady state, where the particle symmetry axis is perpendicular to the vorticity direction and has a constant angle ϕ(c) to the flow direction. The sequence of transitions between these dynamical states were found to be dependent on density ratio α, particle aspect ratio r(p), and domain size. More specifically, the present study reveals that an inclined rolling state (particle rotates around its symmetry axis, which is not aligned in the vorticity direction) appears through a pitchfork bifurcation due to the influence of periodic boundary conditions when simulated in a small domain. Furthermore, it is also found that a tumbling motion, where the particle symmetry axis rotates in the flow-gradient plane, can be a stable motion for particles with high r(p) and low α.}, }
@article {pmid26066247, year = {2015}, author = {Mishra, PK and Herault, J and Fauve, S and Verma, MK}, title = {Dynamics of reversals and condensates in two-dimensional Kolmogorov flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {5}, pages = {053005}, doi = {10.1103/PhysRevE.91.053005}, pmid = {26066247}, issn = {1550-2376}, abstract = {We present numerical simulations of the different two-dimensional flow regimes generated by a constant spatially periodic forcing balanced by viscous dissipation and large-scale drag with a dimensionless damping rate 1/Rh. The linear response to the forcing is a 6×6 square array of counterrotating vortices, which is stable when the Reynolds number Re or Rh are small. After identifying the sequence of bifurcations that lead to a spatially and temporally chaotic regime of the flow when Re and Rh are increased, we study the transitions between the different turbulent regimes observed for large Re by varying Rh. A large-scale circulation at the box size (the condensate state) is the dominant mode in the limit of vanishing large-scale drag (Rh large). When Rh is decreased, the condensate becomes unstable and a regime with random reversals between two large-scale circulations of opposite signs is generated. It involves a bimodal probability density function of the large-scale velocity that continuously bifurcates to a Gaussian distribution when Rh is decreased further.}, }
@article {pmid26066225, year = {2015}, author = {Joglekar, M and Feudel, U and Yorke, JA}, title = {Geometry of the edge of chaos in a low-dimensional turbulent shear flow model.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {5}, pages = {052903}, doi = {10.1103/PhysRevE.91.052903}, pmid = {26066225}, issn = {1550-2376}, abstract = {We investigate the geometry of the edge of chaos for a nine-dimensional sinusoidal shear flow model and show how the shape of the edge of chaos changes with increasing Reynolds number. Furthermore, we numerically compute the scaling of the minimum perturbation required to drive the laminar attracting state into the turbulent region. We find this minimum perturbation to scale with the Reynolds number as Re(-2).}, }
@article {pmid26064617, year = {2015}, author = {Montenegro-Johnson, TD and Gadêlha, H and Smith, DJ}, title = {Spermatozoa scattering by a microchannel feature: an elastohydrodynamic model.}, journal = {Royal Society open science}, volume = {2}, number = {3}, pages = {140475}, pmid = {26064617}, issn = {2054-5703}, abstract = {Sperm traverse their microenvironment through viscous fluid by propagating flagellar waves; the waveform emerges as a consequence of elastic structure, internal active moments and low Reynolds number fluid dynamics. Engineered microchannels have recently been proposed as a method of sorting and manipulating motile cells; the interaction of cells with these artificial environments therefore warrants investigation. A numerical method is presented for large-amplitude elastohydrodynamic interaction of active swimmers with domain features. This method is employed to examine hydrodynamic scattering by a model microchannel backstep feature. Scattering is shown to depend on backstep height and the relative strength of viscous and elastic forces in the flagellum. In a 'high viscosity' parameter regime corresponding to human sperm in cervical mucus analogue, this hydrodynamic contribution to scattering is comparable in magnitude to recent data on contact effects, being of the order of 5°-10°. Scattering can be positive or negative depending on the relative strength of viscous and elastic effects, emphasizing the importance of viscosity on the interaction of sperm with their microenvironment. The modulation of scattering angle by viscosity is associated with variations in flagellar asymmetry induced by the elastohydrodynamic interaction with the boundary feature.}, }
@article {pmid26037711, year = {2015}, author = {Krujatz, F and Illing, R and Krautwer, T and Liao, J and Helbig, K and Goy, K and Opitz, J and Cuniberti, G and Bley, T and Weber, J}, title = {Light-field-characterization in a continuous hydrogen-producing photobioreactor by optical simulation and computational fluid dynamics.}, journal = {Biotechnology and bioengineering}, volume = {112}, number = {12}, pages = {2439-2449}, doi = {10.1002/bit.25667}, pmid = {26037711}, issn = {1097-0290}, mesh = {*Chemical Phenomena ; *Hydrodynamics ; Hydrogen/*metabolism ; *Light ; Photobioreactors/*microbiology ; Rhodobacter sphaeroides/*growth &amp; development/*metabolism ; }, abstract = {Externally illuminated photobioreactors (PBRs) are widely used in studies on the use of phototrophic microorganisms as sources of bioenergy and other photobiotechnology research. In this work, straightforward simulation techniques were used to describe effects of varying fluid flow conditions in a continuous hydrogen-producing PBR on the rate of photofermentative hydrogen production (rH2) by Rhodobacter sphaeroides DSM 158. A ZEMAX optical ray tracing simulation was performed to quantify the illumination intensity reaching the interior of the cylindrical PBR vessel. 24.2% of the emitted energy was lost through optical effects, or did not reach the PBR surface. In a dense culture of continuously producing bacteria during chemostatic cultivation, the illumination intensity became completely attenuated within the first centimeter of the PBR radius as described by an empirical three-parametric model implemented in Mathcad. The bacterial movement in chemostatic steady-state conditions was influenced by varying the fluid Reynolds number. The "Computational Fluid Dynamics" and "Particle Tracing" tools of COMSOL Multiphysics were used to visualize the fluid flow pattern and cellular trajectories through well-illuminated zones near the PBR periphery and dark zones in the center of the PBR. A moderate turbulence (Reynolds number = 12,600) and fluctuating illumination of 1.5 Hz were found to yield the highest continuous rH2 by R. sphaeroides DSM 158 (170.5 mL L(-1) h(-1)) in this study.}, }
@article {pmid26030270, year = {2015}, author = {Walker, D and Kübler, M and Morozov, KI and Fischer, P and Leshansky, AM}, title = {Optimal Length of Low Reynolds Number Nanopropellers.}, journal = {Nano letters}, volume = {15}, number = {7}, pages = {4412-4416}, doi = {10.1021/acs.nanolett.5b01925}, pmid = {26030270}, issn = {1530-6992}, abstract = {Locomotion in fluids at the nanoscale is dominated by viscous drag. One efficient propulsion scheme is to use a weak rotating magnetic field that drives a chiral object. From bacterial flagella to artificial drills, the corkscrew is a universally useful chiral shape for propulsion in viscous environments. Externally powered magnetic micro- and nanomotors have been recently developed that allow for precise fuel-free propulsion in complex media. Here, we combine analytical and numerical theory with experiments on nanostructured screw-propellers to show that the optimal length is surprisingly short-only about one helical turn, which is shorter than most of the structures in use to date. The results have important implications for the design of artificial actuated nano- and micropropellers and can dramatically reduce fabrication times, while ensuring optimal performance.}, }
@article {pmid26029795, year = {2015}, author = {Jang, B and Gutman, E and Stucki, N and Seitz, BF and Wendel-García, PD and Newton, T and Pokki, J and Ergeneman, O and Pané, S and Or, Y and Nelson, BJ}, title = {Undulatory Locomotion of Magnetic Multilink Nanoswimmers.}, journal = {Nano letters}, volume = {15}, number = {7}, pages = {4829-4833}, doi = {10.1021/acs.nanolett.5b01981}, pmid = {26029795}, issn = {1530-6992}, support = {336456/ERC_/European Research Council/International ; }, abstract = {Micro- and nanorobots operating in low Reynolds number fluid environments require specialized swimming strategies for efficient locomotion. Prior research has focused on designs mimicking the rotary corkscrew motion of bacterial flagella or the planar beating motion of eukaryotic flagella. These biologically inspired designs are typically of uniform construction along their flagellar axis. This work demonstrates for the first time planar undulations of composite multilink nanowire-based chains (diameter 200 nm) induced by a planar-oscillating magnetic field. Those chains comprise an elastic eukaryote-like polypyrrole tail and rigid magnetic nickel links connected by flexible polymer bilayer hinges. The multilink design exhibits a high swimming efficiency. Furthermore, the manufacturing process enables tuning the geometrical and material properties to specific applications.}, }
@article {pmid26015833, year = {2015}, author = {Kim, H and Cheang, UK and Kim, D and Ali, J and Kim, MJ}, title = {Hydrodynamics of a self-actuated bacterial carpet using microscale particle image velocimetry.}, journal = {Biomicrofluidics}, volume = {9}, number = {2}, pages = {024121}, pmid = {26015833}, issn = {1932-1058}, abstract = {Microorganisms can effectively generate propulsive force at the microscale where viscous forces overwhelmingly dominate inertia forces; bacteria achieve this task through flagellar motion. When swarming bacteria, cultured on agar plates, are blotted onto the surface of a microfabricated structure, a monolayer of bacteria forms what is termed a "bacterial carpet," which generates strong flows due to the combined motion of their freely rotating flagella. Furthermore, when the bacterial carpet coated microstructure is released into a low Reynolds number fluidic environment, the propulsive force of the bacterial carpet is able to give the microstructure motility. In our previous investigations, we demonstrated motion control of these bacteria powered microbiorobots (MBRs). Without any external stimuli, MBRs display natural rotational and translational movements on their own; this MBR self-actuation is due to the coordination of flagella. Here, we investigate the flow fields generated by bacterial carpets, and compare this flow to the flow fields observed in the bulk fluid at a series of locations above the bacterial carpet. Using microscale particle image velocimetry, we characterize the flow fields generated from the bacterial carpets of MBRs in an effort to understand their propulsive flow, as well as the resulting pattern of flagella driven self-actuated motion. Comparing the velocities between the bacterial carpets on fixed and untethered MBRs, it was found that flow velocities near the surface of the microstructure were strongest, and at distances far above, the surface flow velocities were much smaller.}, }
@article {pmid26005774, year = {2015}, author = {Lu, X and Xuan, X}, title = {Continuous Microfluidic Particle Separation via Elasto-Inertial Pinched Flow Fractionation.}, journal = {Analytical chemistry}, volume = {87}, number = {12}, pages = {6389-6396}, doi = {10.1021/acs.analchem.5b01432}, pmid = {26005774}, issn = {1520-6882}, mesh = {Chemical Fractionation ; *Microfluidic Analytical Techniques ; Particle Size ; }, abstract = {Many of the fluids encountered in chemical and biomedical applications exhibit non-Newtonian behavior. However, the majority of current particle separation methods have been demonstrated in Newtonian fluids only. This work presents an experimental study of continuous particle separation in viscoelastic solutions via a combined action of elastic and inertial lift forces, which we term elasto-inertial pinched flow fractionation (eiPFF). The parametric effects on eiPFF are systematically investigated in terms of dimensionless numbers. It is found that eiPFF offers much higher particle throughput and separation resolution than the traditional steric effects-based PFF. Moreover, eiPFF works most efficiently when the Reynolds number, Re, is of order 1 and hence fills perfectly into the gap of our recently proposed inertia-enhanced PFF (iPFF) technique (Anal. Chem. 2015, 87, 4560-4565) that favors Re of the order 10 or more. However, the particle separation via eiPFF does not increase monotonically with the elasticity number at higher polymer concentrations and is strongly affected by the aspect ratio of channel width to height, both of which have not been previously reported. More surprisingly, the elasto-inertial deflection of small particles can be even greater than that of large particles in a high-aspect-ratio channel for Re less than 1.}, }
@article {pmid26004808, year = {2015}, author = {Hu, R and Li, F and Lv, J and He, Y and Lu, D and Yamada, T and Ono, N}, title = {Microfluidic analysis of pressure drop and flow behavior in hypertensive micro vessels.}, journal = {Biomedical microdevices}, volume = {17}, number = {3}, pages = {9959}, doi = {10.1007/s10544-015-9959-4}, pmid = {26004808}, issn = {1572-8781}, mesh = {Animals ; *Blood Flow Velocity ; Computer Simulation ; Humans ; Microcirculation ; Microfluidics/*methods ; Microvessels/*physiopathology ; *Models, Cardiovascular ; Retinal Artery/*physiopathology ; Retinal Artery Occlusion/*physiopathology ; }, abstract = {The retinal arterial network is the only source of the highly nutrient-consumptive retina, thus any insult on the arteries can impair the retinal oxygen and nutrient supply and affect its normal function. The aim of this work is to study the influences of vascular structure variation on the flow and pressure characteristics via microfluidic devices. Two sets of micro-channel were designed to mimic the stenosed microvessels and dichotomous branching structure in the retinal arteries. Three working fluids including red blood cell (RBC) suspension were employed to investigate the pressure drop in the stenosed channel. The flow behaviors of RBC suspensions inside the micro channels were observed using high speed camera system. Pressure drop of different working fluids and RBC velocity profiles in the stenosed channel were obtained. Moreover, hematocrit levels of RBC suspensions inside the bifurcated channels were analyzed from the sequential images of RBC flow. The results of the flow in the stenosed channel show that RBCs drift from the center of the channels, and RBC velocity is influenced not only by the inlet flow rate but also the interaction between RBCs. The measured pressure drops in the stenosed channel increase notably with the increase of fluid viscosity. Furthermore, the dimensionless pressure drop due to the stenosis decreases with Reynolds number. On the other hand, the results of flow through the bifurcated channels show that as the ratio of the daughter-branch width to the mother-channel width increases, the ratio of hematocrit in two connected branches (Ht/Hd) decreases, which is in favorable agreement with the available analysis results.}, }
@article {pmid25998171, year = {2015}, author = {Dasgupta, R and Tomar, G and Govindarajan, R}, title = {Numerical study of laminar, standing hydraulic jumps in a planar geometry.}, journal = {The European physical journal. E, Soft matter}, volume = {38}, number = {5}, pages = {130}, doi = {10.1140/epje/i2015-15045-0}, pmid = {25998171}, issn = {1292-895X}, abstract = {We solve the two-dimensional, planar Navier-Stokes equations to simulate a laminar, standing hydraulic jump using a Volume-of-Fluid method. The geometry downstream of the jump has been designed to be similar to experimental conditions by including a pit at the edge of the platform over which liquid film flows. We obtain jumps with and without separation. Increasing the inlet Froude number pushes the jump downstream and makes the slope of the jump weaker, consistent with experimental observations of circular jumps, and decreasing the Reynolds number brings the jump upstream while making it steeper. We study the effect of the length of the domain and that of a downstream obstacle on the structure and location of the jump. The transient flow which leads to a final steady jump is described for the first time to our knowledge. In the moderate Reynolds number regime, we obtain steady undular jumps with a separated bubble underneath the first few undulations. Interestingly, surface tension leads to shortening of wavelength of these undulations. We show that the undulations can be explained using the inviscid theory of Benjamin and Lighthill (Proc. R. Soc. London, Ser. A, 1954). We hope this new finding will motivate experimental verification.}, }
@article {pmid26001019, year = {2015}, author = {Henríquez Rivera, RG and Sinha, K and Graham, MD}, title = {Margination regimes and drainage transition in confined multicomponent suspensions.}, journal = {Physical review letters}, volume = {114}, number = {18}, pages = {188101}, doi = {10.1103/PhysRevLett.114.188101}, pmid = {26001019}, issn = {1079-7114}, mesh = {Blood ; *Blood Chemical Analysis ; Hydrodynamics ; *Models, Biological ; *Models, Chemical ; Suspensions/*chemistry ; }, abstract = {A mechanistic theory is developed to describe segregation in confined multicomponent suspensions such as blood. It incorporates the two key phenomena arising in these systems at low Reynolds number: hydrodynamic pair collisions and wall-induced migration. In simple shear flow, several regimes of segregation arise, depending on the value of a "margination parameter" M. Most importantly, there is a critical value of M below which a sharp "drainage transition" occurs: one component is completely depleted from the bulk flow to the vicinity of the walls. Direct simulations also exhibit this transition as the size or flexibility ratio of the components changes.}, }
@article {pmid25990633, year = {2015}, author = {Montino, A and DeSimone, A}, title = {Three-sphere low-Reynolds-number swimmer with a passive elastic arm.}, journal = {The European physical journal. E, Soft matter}, volume = {38}, number = {5}, pages = {127}, pmid = {25990633}, issn = {1292-895X}, abstract = {One of the simplest model swimmers at low Reynolds number is the three-sphere swimmer by Najafi and Golestanian. It consists of three spheres connected by two rods which change their lengths periodically in non-reciprocal fashion. Here we investigate a variant of this model in which one rod is periodically actuated while the other is replaced by an elastic spring. We show that the competition between the elastic restoring force and the hydrodynamic drag produces a delay in the response of the passive elastic arm with respect to the active one. This leads to non-reciprocal shape changes and self-propulsion. After formulating the equations of motion, we study their solutions qualitatively and numerically. The leading-order term of the solution is computed analytically. We then address questions of optimization with respect to both actuation frequency and swimmer's geometry. Our results can provide valuable conceptual guidance in the engineering of robotic microswimmers.}, }
@article {pmid25974595, year = {2015}, author = {Grafke, T and Frishman, A and Falkovich, G}, title = {Time irreversibility of the statistics of a single particle in compressible turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {4}, pages = {043022}, doi = {10.1103/PhysRevE.91.043022}, pmid = {25974595}, issn = {1550-2376}, abstract = {We investigate time irreversibility from the point of view of a single particle in Burgers turbulence. Inspired by the recent work for incompressible flows [Xu et al., Proc. Natl. Acad. Sci. USA 111, 7558 (2014)], we analyze the evolution of the kinetic energy for fluid markers and use the fluctuations of the instantaneous power as a measure of time irreversibility. For short times, starting from a uniform distribution of markers, we find the scaling 〈[E(t)-E(0)](n)〉∝t and 〈p(n)〉∝Re(n-1) for the power as a function of the Reynolds number. Both observations can be explained using the "flight-crash" model, suggested by Xu et al. Furthermore, we use a simple model for shocks that reproduces the moments of the energy difference, including the pre-factor for 〈E(t)-E(0)〉. To complete the single-particle picture for Burgers we compute the moments of the Lagrangian velocity difference and show that they are bifractal. This arises in a similar manner to the bifractality of Eulerian velocity differences. In the above setting, time irreversibility is directly manifest as particles eventually end up in shocks. We additionally investigate time irreversibility in the long-time limit when all particles are located inside shocks and the Lagrangian velocity statistics are stationary. We find the same scalings for the power and energy differences as at short times and argue that this is also a consequence of rare "flight-crash" events related to shock collisions.}, }
@article {pmid25974591, year = {2015}, author = {Felderhof, BU}, title = {Stokesian spherical swimmers and active particles.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {4}, pages = {043018}, doi = {10.1103/PhysRevE.91.043018}, pmid = {25974591}, issn = {1550-2376}, abstract = {The net steady state flow pattern of a distorting sphere is studied in the framework of the bilinear theory of swimming at low Reynolds number. It is argued that the starting point of a theory of interacting active particles should be based on such a calculation, since any arbitrarily chosen steady state flow pattern is not necessarily the result of a swimming motion. Furthermore, it is stressed that as a rule the phase of stroke is relevant in hydrodynamic interactions, so that the net flow pattern must be used with caution.}, }
@article {pmid25974590, year = {2015}, author = {Deng, J and Caulfield, CP}, title = {Three-dimensional transition after wake deflection behind a flapping foil.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {4}, pages = {043017}, doi = {10.1103/PhysRevE.91.043017}, pmid = {25974590}, issn = {1550-2376}, abstract = {We report the inherently three-dimensional linear instabilities of a propulsive wake, produced by a flapping foil, mimicking the caudal fin of a fish or the wing of a flying animal. For the base flow, three sequential wake patterns appear as we increase the flapping amplitude: Bénard-von Kármán (BvK) vortex streets; reverse BvK vortex streets; and deflected wakes. Imposing a three-dimensional spanwise periodic perturbation, we find that the resulting Floquet multiplier |μ| indicates an unstable "short wavelength" mode at wave number β=30, or wavelength λ=0.21 (nondimensionalized by the chord length) at sufficiently high flow Reynolds number Re=Uc/ν≃600, where U is the upstream flow velocity, c is the chord length, and ν is the kinematic viscosity of the fluid. Another, "long wavelength" mode at β=6 (λ=1.05) becomes critical at somewhat higher Reynolds number, although we do not expect that this mode would be observed physically because its growth rate is always less than the short wavelength mode, at least for the parameters we have considered. The long wavelength mode has certain similarities with the so-called mode A in the drag wake of a fixed bluff body, while the short wavelength mode appears to have a period of the order of twice that of the base flow, in that its structure seems to repeat approximately only every second cycle of the base flow. Whether it is appropriate to classify this mode as a truly subharmonic mode or as a quasiperiodic mode is still an open question however, worthy of a detailed parametric study with various flapping amplitudes and frequencies.}, }
@article {pmid25974586, year = {2015}, author = {McComb, WD and Berera, A and Yoffe, SR and Linkmann, MF}, title = {Energy transfer and dissipation in forced isotropic turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {4}, pages = {043013}, doi = {10.1103/PhysRevE.91.043013}, pmid = {25974586}, issn = {1550-2376}, abstract = {A model for the Reynolds-number dependence of the dimensionless dissipation rate C(ɛ) was derived from the dimensionless Kármán-Howarth equation, resulting in C(ɛ)=C(ɛ,∞)+C/R(L)+O(1/R(L)(2)), where R(L) is the integral scale Reynolds number. The coefficients C and C(ɛ,∞) arise from asymptotic expansions of the dimensionless second- and third-order structure functions. This theoretical work was supplemented by direct numerical simulations (DNSs) of forced isotropic turbulence for integral scale Reynolds numbers up to R(L)=5875 (R(λ)=435), which were used to establish that the decay of dimensionless dissipation with increasing Reynolds number took the form of a power law R(L)(n) with exponent value n=-1.000±0.009 and that this decay of C(ɛ) was actually due to the increase in the Taylor surrogate U(3)/L. The model equation was fitted to data from the DNS, which resulted in the value C=18.9±1.3 and in an asymptotic value for C(ɛ) in the infinite Reynolds-number limit of C(ɛ,∞)=0.468±0.006.}, }
@article {pmid25974583, year = {2015}, author = {Beaume, C and Chini, GP and Julien, K and Knobloch, E}, title = {Reduced description of exact coherent states in parallel shear flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {4}, pages = {043010}, doi = {10.1103/PhysRevE.91.043010}, pmid = {25974583}, issn = {1550-2376}, abstract = {A reduced description of exact coherent structures in the transition regime of plane parallel shear flows is developed, based on the Reynolds number scaling of streamwise-averaged (mean) and streamwise-varying (fluctuation) velocities observed in numerical simulations. The resulting system is characterized by an effective unit Reynolds number mean equation coupled to linear equations for the fluctuations, regularized by formally higher-order diffusion. Stationary coherent states are computed by solving the resulting equations simultaneously using a robust numerical algorithm developed for this purpose. The algorithm determines self-consistently the amplitude of the fluctuations for which the associated mean flow is just such that the fluctuations neither grow nor decay. The procedure is used to compute exact coherent states of a flow introduced by Drazin and Reid [Hydrodynamic Stability (Cambridge University Press, Cambridge, UK, 1981)] and studied by Waleffe [Phys. Fluids 9, 883 (1997)]: a linearly stable, plane parallel shear flow confined between stationary stress-free walls and driven by a sinusoidal body force. Numerical continuation of the lower-branch states to lower Reynolds numbers reveals the presence of a saddle node; the saddle node allows access to upper-branch states that are, like the lower-branch states, self-consistently described by the reduced equations. Both lower- and upper-branch states are characterized in detail.}, }
@article {pmid25974578, year = {2015}, author = {Chantry, M and Kerswell, RR}, title = {Localization in a spanwise-extended model of plane Couette flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {4}, pages = {043005}, doi = {10.1103/PhysRevE.91.043005}, pmid = {25974578}, issn = {1550-2376}, abstract = {We consider a nine-partial-differential-equation (1-space and 1-time) model of plane Couette flow in which the degrees of freedom are severely restricted in the streamwise and cross-stream directions to study spanwise localization in detail. Of the many steady Eckhaus (spanwise modulational) instabilities identified of global steady states, none lead to a localized state. Spatially localized, time-periodic solutions were found instead, which arise in saddle node bifurcations in the Reynolds number. These solutions appear global (domain filling) in narrow (small spanwise) domains yet can be smoothly continued out to fully spanwise-localized states in very wide domains. This smooth localization behavior, which has also been seen in fully resolved duct flow (S. Okino, Ph.D. thesis, Kyoto University, Kyoto, 2011), indicates that an apparently global flow structure does not have to suffer a modulational instability to localize in wide domains.}, }
@article {pmid25974576, year = {2015}, author = {Cerbus, RT and Goldburg, WI}, title = {Predicting two-dimensional turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {4}, pages = {043003}, doi = {10.1103/PhysRevE.91.043003}, pmid = {25974576}, issn = {1550-2376}, abstract = {Prediction is a fundamental objective of science. It is more difficult for chaotic and complex systems like turbulence. Here we use information theory to quantify spatial prediction using experimental data from a turbulent soap film. At high Reynolds number, Re, where a cascade exists, turbulence becomes easier to predict as the inertial range broadens. The development of a cascade at low Re is also detected.}, }
@article {pmid25974574, year = {2015}, author = {Verma, MK and Kumaran, V}, title = {Stability of the flow in a soft tube deformed due to an applied pressure gradient.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {4}, pages = {043001}, doi = {10.1103/PhysRevE.91.043001}, pmid = {25974574}, issn = {1550-2376}, abstract = {A linear stability analysis is carried out for the flow through a tube with a soft wall in order to resolve the discrepancy of a factor of 10 for the transition Reynolds number between theoretical predictions in a cylindrical tube and the experiments of Verma and Kumaran [J. Fluid Mech. 705, 322 (2012)]. Here the effect of tube deformation (due to the applied pressure difference) on the mean velocity profile and pressure gradient is incorporated in the stability analysis. The tube geometry and dimensions are reconstructed from experimental images, where it is found that there is an expansion and then a contraction of the tube in the streamwise direction. The mean velocity profiles at different downstream locations and the pressure gradient, determined using computational fluid dynamics, are found to be substantially modified by the tube deformation. The velocity profiles are then used in a linear stability analysis, where the growth rates of perturbations are calculated for the flow through a tube with the wall modeled as a neo-Hookean elastic solid. The linear stability analysis is carried out for the mean velocity profiles at different downstream locations using the parallel flow approximation. The analysis indicates that the flow first becomes unstable in the downstream converging section of the tube where the flow profile is more pluglike when compared to the parabolic flow in a cylindrical tube. The flow is stable in the upstream diverging section where the deformation is maximum. The prediction for the transition Reynolds number is in good agreement with experiments, indicating that the downstream tube convergence and the consequent modification in the mean velocity profile and pressure gradient could reduce the transition Reynolds number by an order of magnitude.}, }
@article {pmid25974532, year = {2015}, author = {Andersen, A and Wadhwa, N and Kiørboe, T}, title = {Quiet swimming at low Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {4}, pages = {042712}, doi = {10.1103/PhysRevE.91.042712}, pmid = {25974532}, issn = {1550-2376}, mesh = {Animals ; Biomechanical Phenomena ; Chlamydomonas reinhardtii/physiology ; Ciliophora/physiology ; Copepoda/physiology ; Crustacea/physiology ; Flagella/physiology ; Hydrodynamics ; *Models, Biological ; *Swimming/physiology ; }, abstract = {The stresslet provides a simple model of the flow created by a small, freely swimming and neutrally buoyant aquatic organism and shows that the far field fluid disturbance created by such an organism in general decays as one over distance squared. Here we discuss a quieter swimming mode that eliminates the stresslet component of the flow and leads to a faster spatial decay of the fluid disturbance described by a force quadrupole that decays as one over distance cubed. Motivated by recent experimental results on fluid disturbances due to small aquatic organisms, we demonstrate that a three-Stokeslet model of a swimming organism which uses breast stroke type kinematics is an example of such a quiet swimmer. We show that the fluid disturbance in both the near field and the far field is significantly reduced by appropriately arranging the propulsion apparatus, and we find that the far field power laws are valid surprisingly close to the organism. Finally, we discuss point force models as a general framework for hypothesis generation and experimental exploration of fluid mediated predator-prey interactions in the planktonic world.}, }
@article {pmid25967293, year = {2015}, author = {Mishra, GK and Kumar, A and Prakash, O and Biswal, R and Dixit, SK and Nakhe, SV}, title = {Flow and thermal characteristics of high Reynolds number (2800-17,000) dye cell: simulation and experiment.}, journal = {Applied optics}, volume = {54}, number = {11}, pages = {3106-3114}, doi = {10.1364/AO.54.003106}, pmid = {25967293}, issn = {1539-4522}, abstract = {This paper presents computational and experimental studies on wavelength/frequency fluctuation characteristics of a high pulse repetition rate (18 kHz) dye laser pumped by a frequency-doubled Nd:YAG laser (532 nm). The temperature gradient in the dye solution is found to be responsible for wavelength fluctuations of the dye laser at low flow rates (2800<Re(d)<5600). The turbulence Reynolds number (ReT) and the range of eddy sizes present in the turbulent flow are found to be responsible for the fluctuations at high flow rates (8400<Re(d)<17,000). A new dimensionless parameter, dimensionless eddy size (l(+)), has been defined to correlate the range of eddy sizes with the experimentally observed wavelength fluctuations. It was found that fluctuations can be controlled by keeping ReT≈10 and lmax(+)≈1. The simulated result explains the experimental observation and provides a basis for optimizing the dye solution flow rate for high PRR pumping.}, }
@article {pmid25963226, year = {2015}, author = {Chen, J and Kang, Z and Wang, G and Loo, J and Kong, SK and Ho, HP}, title = {Optofluidic guiding, valving, switching and mixing based on plasmonic heating in a random gold nanoisland substrate.}, journal = {Lab on a chip}, volume = {15}, number = {11}, pages = {2504-2512}, doi = {10.1039/c5lc00406c}, pmid = {25963226}, issn = {1473-0189}, mesh = {Equipment Design ; Escherichia coli ; Gold/*chemistry ; Hot Temperature ; Microbial Viability ; Microfluidic Analytical Techniques/*instrumentation ; Nanostructures/*chemistry ; Optics and Photonics/*instrumentation ; }, abstract = {We present a versatile optofluidic flow manipulation scheme based on plasmonic heating in a random gold nanoisland substrate (Au-NIS). With its highly efficient conversion of optical power to hydrodynamic actuation, the reported substrate is used for laser-controlled optofluidic manipulation. It is the first time that microfluidic flow guiding, valving, and mixing within the same functional substrate has been realised. Plasmonic heating provides power for guiding the sample flow inside a microfluidic channel at controlled speed and transport of small particles or living cells is demonstrated. We have also made a laser-actuated microfluidic valve through controlling the surface wettability of the sample/Au-NIS interface. When the laser power density is sufficiently high to generate a bubble, localized convection around the bubble can lead to efficient sample mixing within a microfluidic chamber. The reported Au-NIS scheme practically offers a programmable functional surface on which users have the freedom to control the wetting characteristics with a focused laser beam. We have verified that this optofluidic approach induces insignificant degradation in cell viability. The reported scheme therefore offers a wide range of application possibilities in microfluidics and biomedical engineering, particularly those operated under a low Reynolds number.}, }
@article {pmid25946079, year = {2015}, author = {Sridhar, M and Kang, CK}, title = {Aerodynamic performance of two-dimensional, chordwise flexible flapping wings at fruit fly scale in hover flight.}, journal = {Bioinspiration &amp; biomimetics}, volume = {10}, number = {3}, pages = {036007}, doi = {10.1088/1748-3190/10/3/036007}, pmid = {25946079}, issn = {1748-3190}, mesh = {Animals ; Biological Clocks/*physiology ; Computer Simulation ; Drosophila/*physiology ; Elastic Modulus/physiology ; Energy Transfer/physiology ; Flight, Animal/*physiology ; *Models, Biological ; Wings, Animal/*physiology ; }, abstract = {Fruit flies have flexible wings that deform during flight. To explore the fluid-structure interaction of flexible flapping wings at fruit fly scale, we use a well-validated Navier-Stokes equation solver, fully-coupled with a structural dynamics solver. Effects of chordwise flexibility on a two dimensional hovering wing is studied. Resulting wing rotation is purely passive, due to the dynamic balance between aerodynamic loading, elastic restoring force, and inertial force of the wing. Hover flight is considered at a Reynolds number of Re = 100, equivalent to that of fruit flies. The thickness and density of the wing also corresponds to a fruit fly wing. The wing stiffness and motion amplitude are varied to assess their influences on the resulting aerodynamic performance and structural response. Highest lift coefficient of 3.3 was obtained at the lowest-amplitude, highest-frequency motion (reduced frequency of 3.0) at the lowest stiffness (frequency ratio of 0.7) wing within the range of the current study, although the corresponding power required was also the highest. Optimal efficiency was achieved for a lower reduced frequency of 0.3 and frequency ratio 0.35. Compared to the water tunnel scale with water as the surrounding fluid instead of air, the resulting vortex dynamics and aerodynamic performance remained similar for the optimal efficiency motion, while the structural response varied significantly. Despite these differences, the time-averaged lift scaled with the dimensionless shape deformation parameter γ. Moreover, the wing kinematics that resulted in the optimal efficiency motion was closely aligned to the fruit fly measurements, suggesting that fruit fly flight aims to conserve energy, rather than to generate large forces.}, }
@article {pmid25940836, year = {2015}, author = {Piskin, S and Ündar, A and Pekkan, K}, title = {Computational Modeling of Neonatal Cardiopulmonary Bypass Hemodynamics With Full Circle of Willis Anatomy.}, journal = {Artificial organs}, volume = {39}, number = {10}, pages = {E164-75}, doi = {10.1111/aor.12468}, pmid = {25940836}, issn = {1525-1594}, mesh = {Aorta, Thoracic/anatomy &amp; histology/physiology/surgery ; Cardiac Catheterization/methods ; *Cardiopulmonary Bypass/methods ; Cerebral Arteries/anatomy &amp; histology/physiology ; Circle of Willis/*anatomy &amp; histology/physiology ; *Computer Simulation ; Heart Defects, Congenital/pathology/physiopathology/surgery ; Hemodynamics/*physiology ; Humans ; Imaging, Three-Dimensional ; Infant, Newborn ; }, abstract = {Cardiopulmonary bypass (CPB) procedure is employed to repair most congenital heart defects (CHD). Cannulation is a critical component of this procedure where the location and diameter of cannula controls the hemodynamic performance. State-of-the-art computational studies of neonatal CPB employed an isolated aortic arch region by truncating the three-dimensional (3D) patient-specific cerebral system. The present work expanded these studies where the 3D patient-specific MRI reconstruction of the cerebral system, including the Circle of Willis (CoW), is integrated with a hypoplastic neonatal aortic arch. The inlet of the arterial cannula is assigned a steady velocity boundary condition of the CPB pump, while all outlets are modeled as resistance boundary conditions, thus allowing acute comparisons between different cannula configurations. Three-dimensional (3D) flow simulations in the aortic arch model are performed at a Reynolds number of 2150 using an experimentally validated commercial solver. Results demonstrate that the inclusion of 3D CoW is essential to predict the accurate head-neck blood perfusion and therefore critical in deciding the neonatal aortic cannulation strategy preoperatively. Using this integrated model two CPB configurations are studied, where the cannulas were placed at innominate artery (IA) (IA-cannula configuration) and ductus arteriosus (DA) (DA-cannula configuration). Configuration change produced significant differences in flow splits and local hemodynamics of blood flow throughout the whole aortic arch, neck and cerebral arteries. Percent flow rate differences between the IA- and DA-cannula configurations are computed to be: 19%, for descending aorta, 198% for ascending aorta (perfusing coronary arteries), 91% for right anterior cerebral artery, and 68% for left anterior cerebral artery. Another important finding is the retrograde flow at vertebral arteries for IA-cannula configuration, but not for DA-cannula. These results may help to translate better neonatal arterial cannulae design for minimizing cerebral complications during CPB procedures.}, }
@article {pmid25938331, year = {2015}, author = {Guo, Y and Green, S}, title = {Visualization of high speed liquid jet impaction on a moving surface.}, journal = {Journal of visualized experiments : JoVE}, volume = {}, number = {98}, pages = {}, doi = {10.3791/52603}, pmid = {25938331}, issn = {1940-087X}, mesh = {Friction ; Glycerol/*chemistry ; Polyethylene Glycols/*chemistry ; Rheology/*methods ; Robotics/methods ; Surface Properties ; Video Recording/methods ; Water/*chemistry ; }, abstract = {Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds between 0 and 25 m/sec) and a spinning disk device (for examining surface speeds between 15 and 100 m/sec). The air cannon linear traverse is a pneumatic energy-powered system that is designed to accelerate a metal rail surface mounted on top of a wooden projectile. A pressurized cylinder fitted with a solenoid valve rapidly releases pressurized air into the barrel, forcing the projectile down the cannon barrel. The projectile travels beneath a spray nozzle, which impinges a liquid jet onto its metal upper surface, and the projectile then hits a stopping mechanism. A camera records the jet impingement, and a pressure transducer records the spray nozzle backpressure. The spinning disk set-up consists of a steel disk that reaches speeds of 500 to 3,000 rpm via a variable frequency drive (VFD) motor. A spray system similar to that of the air cannon generates a liquid jet that impinges onto the spinning disc, and cameras placed at several optical access points record the jet impingement. Video recordings of jet impingement processes are recorded and examined to determine whether the outcome of impingement is splash, splatter, or deposition. The apparatuses are the first that involve the high speed impingement of low-Reynolds-number liquid jets on high speed moving surfaces. In addition to its rail industry applications, the described technique may be used for technical and industrial purposes such as steelmaking and may be relevant to high-speed 3D printing.}, }
@article {pmid25937803, year = {2015}, author = {Anyoji, M and Numata, D and Nagai, H and Asai, K}, title = {Pressure-sensitive paint technique for surface pressure measurements in a low-density wind tunnel.}, journal = {Journal of visualization}, volume = {18}, number = {2}, pages = {297-309}, pmid = {25937803}, issn = {1343-8875}, abstract = {ABSTRACT: A low-density wind tunnel called the Mars wind tunnel, has been developed at Tohoku University that can produce a high subsonic flow at low pressures for aerodynamic measurements of low-Reynolds-number aircraft wings aimed at developing aircraft applicable to the atmosphere on the planet Mars. Accurate surface pressure measurements on the wing are essential for analysis of not only aerodynamic performance, including lift and drag, but also the flow fields around the wing. This paper presents a surface pressure measurement technique using pressure-sensitive paint (PSP) applicable for Mars wind tunnel tests under low-pressure conditions. The results show that a PSP composed of palladium tetra(pentafluorophenyl) porphyrin (PdTFPP) and poly[1-(trimethylsilyl)-propyne] [poly(TMSP)] exhibits a high-pressure sensitivity at pressures as low as 1 kPa, and the absolute values of the static pressures measured by the PSP accorded well with the values derived from static pressure sensors used as a reference. A calibration methodology for the non-uniform pressure sensitivity on the test model, including a temperature calibration, is also established. The PSP technique clearly demonstrated pressure sensitivity over a distinctive low-pressure region inside a leading edge separation bubble on a flat plate at low Reynolds numbers.}, }
@article {pmid25933320, year = {2015}, author = {Reeves, MT and Billam, TP and Anderson, BP and Bradley, AS}, title = {Identifying a Superfluid Reynolds Number via Dynamical Similarity.}, journal = {Physical review letters}, volume = {114}, number = {15}, pages = {155302}, doi = {10.1103/PhysRevLett.114.155302}, pmid = {25933320}, issn = {1079-7114}, abstract = {The Reynolds number provides a characterization of the transition to turbulent flow, with wide application in classical fluid dynamics. Identifying such a parameter in superfluid systems is challenging due to their fundamentally inviscid nature. Performing a systematic study of superfluid cylinder wakes in two dimensions, we observe dynamical similarity of the frequency of vortex shedding by a cylindrical obstacle. The universality of the turbulent wake dynamics is revealed by expressing shedding frequencies in terms of an appropriately defined superfluid Reynolds number, Re(s), that accounts for the breakdown of superfluid flow through quantum vortex shedding. For large obstacles, the dimensionless shedding frequency exhibits a universal form that is well-fitted by a classical empirical relation. In this regime the transition to turbulence occurs at Re(s)≈0.7, irrespective of obstacle width.}, }
@article {pmid25933066, year = {2015}, author = {Uddin, MJ and Khan, WA and Ismail, AI}, title = {G-jitter induced magnetohydrodynamics flow of nanofluid with constant convective thermal and solutal boundary conditions.}, journal = {PloS one}, volume = {10}, number = {5}, pages = {e0122663}, pmid = {25933066}, issn = {1932-6203}, mesh = {*Convection ; Friction ; Hot Temperature ; *Hydrodynamics ; *Magnetic Phenomena ; Models, Theoretical ; Nanoparticles/*chemistry ; *Rheology ; Skin ; *Temperature ; Time Factors ; }, abstract = {Taking into account the effect of constant convective thermal and mass boundary conditions, we present numerical solution of the 2-D laminar g-jitter mixed convective boundary layer flow of water-based nanofluids. The governing transport equations are converted into non-similar equations using suitable transformations, before being solved numerically by an implicit finite difference method with quasi-linearization technique. The skin friction decreases with time, buoyancy ratio, and thermophoresis parameters while it increases with frequency, mixed convection and Brownian motion parameters. Heat transfer rate decreases with time, Brownian motion, thermophoresis and diffusion-convection parameters while it increases with the Reynolds number, frequency, mixed convection, buoyancy ratio and conduction-convection parameters. Mass transfer rate decreases with time, frequency, thermophoresis, conduction-convection parameters while it increases with mixed convection, buoyancy ratio, diffusion-convection and Brownian motion parameters. To the best of our knowledge, this is the first paper on this topic and hence the results are new. We believe that the results will be useful in designing and operating thermal fluids systems for space materials processing. Special cases of the results have been compared with published results and an excellent agreement is found.}, }
@article {pmid25917201, year = {2015}, author = {Fortuny, G and Herrero, J and Puigjaner, D and Olivé, C and Marimon, F and Garcia-Bennett, J and Rodríguez, D}, title = {Effect of anticoagulant treatment in deep vein thrombosis: A patient-specific computational fluid dynamics study.}, journal = {Journal of biomechanics}, volume = {48}, number = {10}, pages = {2047-2053}, doi = {10.1016/j.jbiomech.2015.03.026}, pmid = {25917201}, issn = {1873-2380}, mesh = {Aged, 80 and over ; Anticoagulants/*pharmacology/therapeutic use ; Hemodynamics/drug effects ; Humans ; *Hydrodynamics ; Male ; Models, Cardiovascular ; *Patient-Specific Modeling ; Stress, Mechanical ; Venous Thrombosis/*drug therapy/*physiopathology ; Viscosity ; }, abstract = {A methodology that might help physicians to establish a diagnostic and treatment tailored for each specific patient with a pathological thrombus is presented. A realistic model for the geometry of a popliteal vein with a thrombus just above the knee was reconstructed from in vivo computed tomography images acquired from one specific patient and then it was used to perform computational fluid dynamics (CFD) simulations. The wall shear stress (WSS) response to the administration of anticoagulant drugs and the influence of viscosity on the shape of the velocity distribution were investigated. Both a Newtonian and a non-Newtonian viscosity model were implemented for different blood flow rates in the range 3-7 cm(3)/s. The effect of anticoagulants on the blood was simulated by setting three different levels of viscosity in the Newtonian model (μ/μ∞=0.60, 0.80 and 1 with μ∞=3.45×10(-3) Pas). A reduction of μ by a given amount always led to a more modest reduction, typically by a factor of two, of the resulting WSS levels. Moreover, for a given flow rate the calculation with the non-Newtonian viscosity model yielded WSS levels between 20% and 40% larger than those obtained in the corresponding Newtonian fluid simulation. It was also found that blood moves slowly in the region between the thrombus and the vein wall, a fact that will favor the growth of the thrombotic mass. Both the mean WSS levels and the degree of sluggishness of the blood flow can be described by functions of the Reynolds number.}, }
@article {pmid25897758, year = {2015}, author = {Weddell, JC and Kwack, J and Imoukhuede, PI and Masud, A}, title = {Hemodynamic analysis in an idealized artery tree: differences in wall shear stress between Newtonian and non-Newtonian blood models.}, journal = {PloS one}, volume = {10}, number = {4}, pages = {e0124575}, pmid = {25897758}, issn = {1932-6203}, mesh = {Atherosclerosis/metabolism/pathology/*physiopathology ; Blood Flow Velocity ; Blood Platelets/metabolism/pathology ; Cell Adhesion Molecules/genetics/metabolism ; Computer Simulation ; Drug Delivery Systems ; Endothelial Cells/metabolism/pathology ; Femoral Artery/metabolism/pathology/*physiopathology ; Gene Expression ; Humans ; Integrins/genetics/metabolism ; Magnetite Nanoparticles/chemistry ; *Mechanotransduction, Cellular ; *Models, Cardiovascular ; Monocytes/metabolism/pathology ; Pulsatile Flow ; Stress, Mechanical ; }, abstract = {Development of many conditions and disorders, such as atherosclerosis and stroke, are dependent upon hemodynamic forces. To accurately predict and prevent these conditions and disorders hemodynamic forces must be properly mapped. Here we compare a shear-rate dependent fluid (SDF) constitutive model, based on the works by Yasuda et al in 1981, against a Newtonian model of blood. We verify our stabilized finite element numerical method with the benchmark lid-driven cavity flow problem. Numerical simulations show that the Newtonian model gives similar velocity profiles in the 2-dimensional cavity given different height and width dimensions, given the same Reynolds number. Conversely, the SDF model gave dissimilar velocity profiles, differing from the Newtonian velocity profiles by up to 25% in velocity magnitudes. This difference can affect estimation in platelet distribution within blood vessels or magnetic nanoparticle delivery. Wall shear stress (WSS) is an important quantity involved in vascular remodeling through integrin and adhesion molecule mechanotransduction. The SDF model gave a 7.3-fold greater WSS than the Newtonian model at the top of the 3-dimensional cavity. The SDF model gave a 37.7-fold greater WSS than the Newtonian model at artery walls located immediately after bifurcations in the idealized femoral artery tree. The pressure drop across arteries reveals arterial sections highly resistive to flow which correlates with stenosis formation. Numerical simulations give the pressure drop across the idealized femoral artery tree with the SDF model which is approximately 2.3-fold higher than with the Newtonian model. In atherosclerotic lesion models, the SDF model gives over 1 Pa higher WSS than the Newtonian model, a difference correlated with over twice as many adherent monocytes to endothelial cells from the Newtonian model compared to the SDF model.}, }
@article {pmid25879052, year = {2015}, author = {Paria, S and Sarhan, AA and Goodarzi, MS and Baradaran, S and Rahmanian, B and Yarmand, H and Alavi, MA and Kazi, SN and Metselaar, HS}, title = {Indoor solar thermal energy saving time with phase change material in a horizontal shell and finned-tube heat exchanger.}, journal = {TheScientificWorldJournal}, volume = {2015}, number = {}, pages = {291657}, pmid = {25879052}, issn = {1537-744X}, abstract = {An experimental as well as numerical investigation was conducted on the melting/solidification processes of a stationary phase change material (PCM) in a shell around a finned-tube heat exchanger system. The PCM was stored in the horizontal annular space between a shell and finned-tube where distilled water was employed as the heat transfer fluid (HTF). The focus of this study was on the behavior of PCM for storage (charging or melting) and removal (discharging or solidification), as well as the effect of flow rate on the charged and discharged solar thermal energy. The impact of the Reynolds number was determined and the results were compared with each other to reveal the changes in amount of stored thermal energy with the variation of heat transfer fluid flow rates. The results showed that, by increasing the Reynolds number from 1000 to 2000, the total melting time decreases by 58%. The process of solidification also will speed up with increasing Reynolds number in the discharging process. The results also indicated that the fluctuation of gradient temperature decreased and became smooth with increasing Reynolds number. As a result, by increasing the Reynolds number in the charging process, the theoretical efficiency rises.}, }
@article {pmid25878133, year = {2015}, author = {Ishimoto, K and Gaffney, EA}, title = {Fluid flow and sperm guidance: a simulation study of hydrodynamic sperm rheotaxis.}, journal = {Journal of the Royal Society, Interface}, volume = {12}, number = {106}, pages = {}, pmid = {25878133}, issn = {1742-5662}, mesh = {Biological Clocks/*physiology ; Cells, Cultured ; Computer Simulation ; Humans ; Hydrodynamics ; Male ; Microfluidics/*methods ; *Models, Biological ; Shear Strength/physiology ; Sperm Motility/*physiology ; Spermatozoa/*physiology ; Stress, Mechanical ; }, abstract = {How does a sperm find its way? The study of guidance cues has fascinated sperm biologists and in particular the prospect of rheotaxis, that is a fluid flow orienting the direction of sperm swimming, has been the subject of extensive recent study, as readily motivated by the prospect that such guidance may be active in the mammalian female reproductive tract. For instance, it has been hypothesized that helical sperm flagellar beating is necessary for such guidance, whereas there is an extensive diversity of flagellar beating patterns, with planar sperm beating readily observed in human cells for example. In particular, such cells will not be guided by fluid flow according to hypothesized mechanisms for rheotaxis presented thus far. Here, using simulation methods, we investigate rheotaxis for a wide range of flagellar beat patterns. Providing the virtual sperm firstly does not possess a tightly circling trajectory in the absence of a background flow and secondly, remains within a region of low shear to prevent being washed away by the background flow, rheotaxis is generally observed with the sperm swimming into the flow together with a possible transverse velocity. Tight circling sperm motility, as observed in select hyperactivated sperm and CatSper mutants, is predicted to disrupt the rheotactic response, whereas confinement to low shear regions generally requires boundary accumulation, thus introducing subtleties in the relationship between rheotactic behaviours and the flagellar waveform and sperm characteristics. Nonetheless, such predictions suggest such rheotactic guidance may be more common and robust than previously thought, and we document simple criteria for the presence of rheotaxis that are consistent with our simulations and understanding, as well as reported observations to date.}, }
@article {pmid25871215, year = {2015}, author = {Nizkaya, TV and Asmolov, ES and Zhou, J and Schmid, F and Vinogradova, OI}, title = {Flows and mixing in channels with misaligned superhydrophobic walls.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {3}, pages = {033020}, doi = {10.1103/PhysRevE.91.033020}, pmid = {25871215}, issn = {1550-2376}, abstract = {Aligned superhydrophobic surfaces with the same texture orientation reduce drag in the channel and generate secondary flows transverse to the direction of the applied pressure gradient. Here we show that a transverse shear can be easily generated by using superhydrophobic channels with misaligned textured surfaces. We propose a general theoretical approach to quantify this transverse flow by introducing the concept of an effective shear tensor. To illustrate its use, we present approximate theoretical solutions and Dissipative Particle Dynamics simulations for striped superhydrophobic channels. Our results demonstrate that the transverse shear leads to complex flow patterns, which provide a new mechanism of a passive vertical mixing at the scale of a texture period. Depending on the value of Reynolds number two different scenarios occur. At relatively low Reynolds number the flow represents a transverse shear superimposed with two corotating vortices. For larger Reynolds number these vortices become isolated, by suppressing fluid transport in the transverse direction.}, }
@article {pmid25871207, year = {2015}, author = {Shum, H and Gaffney, EA}, title = {Hydrodynamic analysis of flagellated bacteria swimming near one and between two no-slip plane boundaries.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {3}, pages = {033012}, doi = {10.1103/PhysRevE.91.033012}, pmid = {25871207}, issn = {1550-2376}, mesh = {*Flagella ; *Hydrodynamics ; *Models, Biological ; *Movement ; Rhodobacter sphaeroides/*cytology/*physiology ; }, abstract = {The motility of swimming bacteria near solid surfaces has implications in a wide range of scenarios, including water treatment facilities, microfluidics, and biomedical implants. Using the boundary element method to numerically solve the equations of low Reynolds number fluid flow, we investigate the dynamics of a model swimmer propelled by rotating a single helical flagellum. Building on previous simulation results for swimmers near a single plane boundary, we introduce a second, parallel boundary and show that the bacterial trajectories change as the two plates are brought closer together. Analysis of this dynamical system shows that the configuration in the center of the channel and parallel to the walls is an unstable equilibrium state for large plate separations, but it becomes the only stable position for swimmers when the plate separation is reduced to three to four times the cell width. Our model also predicts that transient trajectories, i.e., those not at steady states, can exhibit curvature in the opposite sense to that expected from the well-known explanation for circular bacterial paths near a single wall.}, }
@article {pmid25871197, year = {2015}, author = {Oliveira, RS and Andrade, JS and Andrade, RF}, title = {Fluid flow through packings of rotating obstacles.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {3}, pages = {033002}, doi = {10.1103/PhysRevE.91.033002}, pmid = {25871197}, issn = {1550-2376}, mesh = {*Computer Simulation ; *Hydrodynamics ; Porosity ; *Rotation ; }, abstract = {We investigate through numerical simulation the nonstationary flow of a Newtonian fluid through a two-dimensional channel filled with an array of circular obstacles of distinct sizes. The disks may rotate around their respective centers, modeling a nonstationary, inhomogeneous porous medium. Obstacle sizes and positions are defined by the geometry of an Apollonian packing (AP). To allow for fluid flow, the radii of the disks are uniformly reduced by a factor 0.6≤s≤0.8 for assemblies corresponding to the four first AP generations. The investigation is targeted to elucidate the main features of the rotating regime as compared to the fixed disk condition. It comprises the evaluation of the region of validity of Darcy's law as well as the study of the nonlinear hydraulic resistance as a function of the channel Reynolds number, the reduction factor s, and the AP generation. Depending on a combination of these factors, the resistance of rotating disks may be larger or smaller than that of the corresponding static case. We also analyze the flow redistribution in the interdisk channels as a result of the rotation pattern and characterize the angular velocity of the disks. Here, the striking feature is the emergence of a stable oscillatory behavior of the angular velocity for almost all disks that are inserted into the assemblies after the second generation.}, }
@article {pmid25852431, year = {2015}, author = {Meng, X and Li, Y}, title = {Numerical study of natural convection in a horizontal cylinder filled with water-based alumina nanofluid.}, journal = {Nanoscale research letters}, volume = {10}, number = {}, pages = {142}, pmid = {25852431}, issn = {1931-7573}, abstract = {Natural heat convection of water-based alumina (Al2O3/water) nanofluids (with volume fraction 1% and 4%) in a horizontal cylinder is numerically investigated. The whole three-dimensional computational fluid dynamics (CFD) procedure is performed in a completely open-source way. Blender, enGrid, OpenFOAM and ParaView are employed for geometry creation, mesh generation, case simulation and post process, respectively. Original solver 'buoyantBoussinesqSimpleFoam' is selected for the present study, and a temperature-dependent solver 'buoyantBoussinesqSimpleTDFoam' is developed to ensure the simulation is more realistic. The two solvers are used for same cases and compared to corresponding experimental results. The flow regime in these cases is laminar (Reynolds number is 150) and the Rayleigh number range is 0.7 × 10(7) ~ 5 × 10(7). By comparison, the average natural Nusselt numbers of water and Al2O3/water nanofluids are found to increase with the Rayleigh number. At the same Rayleigh number, the Nusselt number is found to decrease with nanofluid volume fraction. The temperature-dependent solver is found better for water and 1% Al2O3/water nanofluid cases, while the original solver is better for 4% Al2O3/water nanofluid cases. Furthermore, due to strong three-dimensional flow features in the horizontal cylinder, three-dimensional CFD simulation is recommended instead of two-dimensional simplifications.}, }
@article {pmid25851515, year = {2015}, author = {Rao, KJ and Li, F and Meng, L and Zheng, H and Cai, F and Wang, W}, title = {A Force to Be Reckoned With: A Review of Synthetic Microswimmers Powered by Ultrasound.}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = {11}, number = {24}, pages = {2836-2846}, doi = {10.1002/smll.201403621}, pmid = {25851515}, issn = {1613-6829}, mesh = {*Acoustics ; *Ultrasonics ; }, abstract = {Synthetic microswimmers are a class of artificial nano- or microscale particle capable of converting external energy into motion. They are similar to natural microswimmers such as bacteria in behavior and are, therefore, of great interest to the study of active matter. Additionally, microswimmers show promise in applications ranging from bioanalytics and environmental monitoring to particle separation and drug delivery. However, since their sizes are on the nano-/microscale and their speeds are in the μm s(-1) range, they fall into a low Reynolds number regime where viscosity dominates. Therefore, new propulsion schemes are needed for these microswimmers to be able to efficiently move. Furthermore, many of the hotly pursued applications call for innovations in the next phase of development of biocompatible microswimmers. In this review, the latest developments of microswimmers powered by ultrasound are presented. Ultrasound, especially at MHz frequencies, does little harm to biological samples and provides an advantageous and well-controlled means to efficiently power microswimmers. By critically reviewing the recent progress in this research field, an introduction of how ultrasound propels colloidal particles into autonomous motion is presented, as well as how this propulsion can be used to achieve preliminary but promising applications.}, }
@article {pmid25837725, year = {2015}, author = {Lu, X and Xuan, X}, title = {Inertia-enhanced pinched flow fractionation.}, journal = {Analytical chemistry}, volume = {87}, number = {8}, pages = {4560-4565}, doi = {10.1021/acs.analchem.5b00752}, pmid = {25837725}, issn = {1520-6882}, mesh = {Chemical Fractionation/*methods ; *Microfluidic Analytical Techniques ; Particle Size ; }, abstract = {Separating target particles or cells from a heterogeneous mixture is often critical to many chemical and biomedical applications. Pinched flow fractionation (PFF) is a microfluidic technique that utilizes the laminar flow profile to continuously separate particles by size. We demonstrate that the flow-induced inertial lift force in microchannels can be exploited to significantly increase the particle displacement in PFF due to its strong size dependence. This inertia-enhanced PFF (iPFF) technique can offer at least one-order-of-magnitude higher particle throughput than PFF does at the same sheath flow rate. Moreover, it is able to work effectively in a large range of Reynolds number that spans more than 1 order of magnitude in the current study. In addition, iPFF is found to work most effectively in a rectangular microchannel with a width-to-height aspect ratio of around 2.}, }
@article {pmid25835787, year = {2015}, author = {Farbos de Luzan, C and Chen, J and Mihaescu, M and Khosla, SM and Gutmark, E}, title = {Computational study of false vocal folds effects on unsteady airflows through static models of the human larynx.}, journal = {Journal of biomechanics}, volume = {48}, number = {7}, pages = {1248-1257}, pmid = {25835787}, issn = {1873-2380}, support = {R01 DC009435/DC/NIDCD NIH HHS/United States ; R01DC009435/DC/NIDCD NIH HHS/United States ; }, mesh = {Biomechanical Phenomena ; Computer Simulation ; Glottis/*physiology/physiopathology ; Humans ; Larynx/*physiology/physiopathology ; *Models, Anatomic ; Motion ; *Phonation ; Pressure ; Speech ; Vocal Cords/*physiology/physiopathology ; }, abstract = {Compressible large eddy simulation is employed to numerically investigate the laryngeal flow. Symmetric static models of the human larynx with a divergent glottis are considered, with the presence of false vocal folds (FVFs). The compressible study agrees well with that of the incompressible study. Due to the high enough Reynolds number, the flow is unsteady and develops asymmetric states downstream of the glottis. The glottal jet curvature decreases with the presence of FVFs or the ventricular folds. The gap between the FVFs stretches the flow structure and reduces the jet curvature. The presence of FVFs has a significant effect on the laryngeal flow resistance. The intra-glottal vortex structures are formed on the divergent wall of the glottis, immediately downstream of the separation point. The vortices are then convected downstream and characterized by a significant negative static pressure. The FVFs are a main factor in the generation of stronger vortices, and thus on the closure of the TVFs. The direct link between the FVFs geometry and the motion of the TVFs, and by extension to the voice production, is of interest for medical applications as well as future research works. The presence of the FVFs also changes the dominant frequencies in the velocity and pressure spectra.}, }
@article {pmid25816074, year = {2016}, author = {Al-Azawy, MG and Turan, A and Revell, A}, title = {Assessment of turbulence models for pulsatile flow inside a heart pump.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {19}, number = {3}, pages = {271-285}, doi = {10.1080/10255842.2015.1015527}, pmid = {25816074}, issn = {1476-8259}, mesh = {Cardiovascular System ; Computational Biology ; Equipment Design ; *Heart-Assist Devices ; Humans ; Hydrodynamics ; *Models, Theoretical ; *Pulsatile Flow ; Stress, Mechanical ; }, abstract = {Computational fluid dynamics (CFD) is applied to study the unsteady flow inside a pulsatile pump left ventricular assist device, in order to assess the sensitivity to a range of commonly used turbulence models. Levels of strain and wall shear stress are directly relevant to the evaluation of risk from haemolysis and thrombosis, and thus understanding the sensitivity to these turbulence models is important in the assessment of uncertainty in CFD predictions. The study focuses on a positive displacement or pulsatile pump, and the CFD model includes valves and moving pusher plate. An unstructured dynamic layering method was employed to capture this cyclic motion, and valves were simulated in their fully open position to mimic the natural scenario, with in/outflow triggered at control planes away from the valves. Six turbulence models have been used, comprising three relevant to the low Reynolds number nature of this flow and three more intended to investigate different transport effects. In the first group, we consider the shear stress transport (SST) [Formula: see text] model in both its standard and transition-sensitive forms, and the 'laminar' model in which no turbulence model is used. In the second group, we compare the one equation Spalart-Almaras model, the standard two equation [Formula: see text] and the full Reynolds stress model (RSM). Following evaluation of spatial and temporal resolution requirements, results are compared with available experimental data. The model was operated at a systolic duration of 40% of the pumping cycle and a pumping rate of 86 BPM (beats per minute). Contrary to reasonable preconception, the 'transition' model, calibrated to incorporate additional physical modelling specifically for these flow conditions, was not noticeably superior to the standard form of the model. Indeed, observations of turbulent viscosity ratio reveal that the transition model initiates a premature increase of turbulence in this flow, when compared with both experimental and higher order numerical results previously reported in the literature. Furthermore, the RSM is indicated to provide the most accurate prediction over much of the flow, due to its ability to more correctly account for three-dimensional effects. Finally, the clinical relevance of the results is reported along with a discussion on the impact of such modelling uncertainties.}, }
@article {pmid25813605, year = {2015}, author = {Zeitz, M and Gurevich, P and Stark, H}, title = {Feedback control of flow vorticity at low Reynolds numbers.}, journal = {The European physical journal. E, Soft matter}, volume = {38}, number = {3}, pages = {22}, pmid = {25813605}, issn = {1292-895X}, abstract = {Our aim is to explore strategies of feedback control to design and stabilize novel dynamic flow patterns in model systems of complex fluids. To introduce the control strategies, we investigate the simple Newtonian fluid at low Reynolds number in a circular geometry. Then, the fluid vorticity satisfies a diffusion equation. We determine the mean vorticity in the sensing area and use two control strategies to feed it back into the system by controlling the angular velocity of the circular boundary. Hysteretic feedback control generates self-regulated stable oscillations in time, the frequency of which can be adjusted over several orders of magnitude by tuning the relevant feedback parameters. Time-delayed feedback control initiates unstable vorticity modes for sufficiently large feedback strength. For increasing delay time, we first observe oscillations with beats and then regular trains of narrow pulses. Close to the transition line between the resting fluid and the unstable modes, these patterns are relatively stable over long times.}, }
@article {pmid25805919, year = {2014}, author = {Tao, Z and Zhang, D and Luo, X and Xu, G and Han, J}, title = {Windage Heating in a Shrouded Rotor-Stator System.}, journal = {Journal of engineering for gas turbines and power}, volume = {136}, number = {6}, pages = {0626021-6260210}, doi = {10.1115/1.4026429}, pmid = {25805919}, issn = {0742-4795}, abstract = {This paper has experimentally and numerically studied the windage heating in a shrouded rotor-stator disk system with superimposed flow. Temperature rise in the radius direction on the rotating disk is linked to the viscous heating process when cooling air flows through the rotating component. A test rig has been developed to investigate the effect of flow parameters and the gap ratio on the windage heating, respectively. Experimental results were obtained from a 0.45 m diameter disk rotating at up to 12,000 rpm with gap ratio varying from 0.02 to 0.18 and a stator of the same diameter. Infrared temperature measurement technology has been proposed to measure the temperature rise on the rotor surface directly. The PIV technique was adapted to allow for tangential velocity measurements. The tangential velocity data along the radial direction in the cavity was compared with the results obtained by CFD simulation. The comparison between the free disk temperature rise data and an associated theoretical analysis for the windage heating indicates that the adiabatic disk temperature can be measured by infrared method accurately. For the small value of turbulence parameter, the gap ratio has limited influence on the temperature rise distribution along the radius. As turbulence parameter increases, the temperature rise difference is independent of the gap ratio, leaving that as a function of rotational Reynolds number and throughflow Reynolds number only. The PIV results show that the swirl ratio of the rotating core between the rotor and the stator has a key influence on the windage heating.}, }
@article {pmid25791159, year = {2015}, author = {Roisman, IV and Lembach, A and Tropea, C}, title = {Drop splashing induced by target roughness and porosity: The size plays no role.}, journal = {Advances in colloid and interface science}, volume = {222}, number = {}, pages = {615-621}, doi = {10.1016/j.cis.2015.02.004}, pmid = {25791159}, issn = {1873-3727}, abstract = {Drop splash as a result of an impact onto a dry substrate is governed by the impact parameters, gas properties and the substrate properties. The splash thresholds determine the boundaries between various splash modes. Various existing models for the splash threshold are reviewed in this paper. It is shown that our understanding of splash is not yet complete. The most popular, widely used models for splash threshold do not describe well the available experimental data. The scientific part of this paper is focused on the description of drop prompt splash on rough and porous substrates. It is found that the absolute length scales of the substrate roughness, like Ra or Rz, do not have any significant effect on the splash threshold. It is discovered that on rough substrates the main influencing splash parameters are the impact Weber number and the characteristic slope of the roughness of the substrate. The drop deposition without splash on porous substrates is enhanced by the liquid modified Reynolds number. Surprisingly, it is not influenced by the pore size, at least for the impact parameters used in the experiments. Finally, an empirical correlation for the prompt splash on rough and porous substrates is proposed, based on a rather amount of experimental data.}, }
@article {pmid25789334, year = {2015}, author = {Siddiqui, AM and Farooq, AA and Rana, MA}, title = {A mathematical model for the flow of a Casson fluid due to metachronal beating of cilia in a tube.}, journal = {TheScientificWorldJournal}, volume = {2015}, number = {}, pages = {487819}, pmid = {25789334}, issn = {1537-744X}, mesh = {Cilia/*physiology ; Genitalia, Male/physiology ; Humans ; Male ; *Models, Statistical ; }, abstract = {A mathematical model is developed to study the transport mechanism of a Casson fluid flow inspired by the metachronal coordination between the beating cilia in a cylindrical tube. A two-dimensional system of nonlinear equations governing the flow problem is formulated by using axisymmetric cylindrical coordinates and then simplified by employing the long wavelength and low Reynolds number assumptions. Exact solutions are derived for the velocity components, the axial pressure gradient, and the stream function. However, the expressions for the pressure rise and the volume flow rate are evaluated numerically. The features of the flow characteristics such as pumping and trapping are illustrated and discussed with the help of graphs. It is observed that the volume flow rate is influenced significantly by the width of plug flow region H p as well as the cilia length parameter ε. The analysis is also applied and compared with the estimated value of the volume flow rate of epididymal fluid in the ductus efferentes of the human male reproductive tract.}, }
@article {pmid25785396, year = {2015}, author = {Drews, AM and Cartier, CA and Bishop, KJ}, title = {Contact charge electrophoresis: experiment and theory.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {31}, number = {13}, pages = {3808-3814}, doi = {10.1021/acs.langmuir.5b00342}, pmid = {25785396}, issn = {1520-5827}, abstract = {Contact charge electrophoresis (CCEP) uses steady electric fields to drive the continuous, oscillatory motion of conductive particles and droplets between two or more electrodes. These rapid oscillations can be rectified to direct the motion of objects within microfluidic environments using low-power, dc voltage. Here, we compare high precision experimental measurements of CCEP within a microfluidic system to equally detailed theoretical predictions on the motion of a conductive particle between parallel electrodes. We use a simple, capillary microfluidic platform that combines high-speed imaging with precision electrical measurements to enable the synchronized acquisition of both the particle location and the electric current due to particle motion. The experimental results are compared to those of a theoretical model, which relies on a Stokesian dynamics approach to accurately describe both the electrostatic and hydrodynamic problems governing particle motion. We find remarkable agreement between theory and experiment, suggesting that particle motion can be accurately captured by a combination of classical electrostatics and low-Reynolds number hydrodynamics. Building on this agreement, we offer new insight into the charge transfer process that occurs when the particle nears contact with an electrode surface. In particular, we find that the particle does not make mechanical contact with the electrode but rather that charge transfer occurs at finite surface separations of >0.1 μm by means of an electric discharge through a thin lubricating film. We discuss the implications of these findings on the charging of the particle and its subsequent dynamics.}, }
@article {pmid25775552, year = {2015}, author = {Yuan, J and Raizen, DM and Bau, HH}, title = {Propensity of undulatory swimmers, such as worms, to go against the flow.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {112}, number = {12}, pages = {3606-3611}, pmid = {25775552}, issn = {1091-6490}, support = {5R03AG042690-02/AG/NIA NIH HHS/United States ; R01 NS088432/NS/NINDS NIH HHS/United States ; P40 OD010440/OD/NIH HHS/United States ; R01 NS064030/NS/NINDS NIH HHS/United States ; R03 AG042690/AG/NIA NIH HHS/United States ; R01NS064030/NS/NINDS NIH HHS/United States ; }, mesh = {Animals ; *Behavior, Animal ; Caenorhabditis elegans/*physiology ; Ecosystem ; Hydrodynamics ; Microfluidics ; *Orientation ; Rheology ; Swimming ; Temperature ; }, abstract = {The ability to orient oneself in response to environmental cues is crucial to the survival and function of diverse organisms. One such orientation behavior is the alignment of aquatic organisms with (negative rheotaxis) or against (positive rheotaxis) fluid current. The questions of whether low-Reynolds-number, undulatory swimmers, such as worms, rheotax and whether rheotaxis is a deliberate or an involuntary response to mechanical forces have been the subject of conflicting reports. To address these questions, we use Caenorhabditis elegans as a model undulatory swimmer and examine, in experiment and theory, the orientation of C. elegans in the presence of flow. We find that when close to a stationary surface the animal aligns itself against the direction of the flow. We elucidate for the first time to our knowledge the mechanisms of rheotaxis in worms and show that rheotaxis can be explained solely by mechanical forces and does not require sensory input or deliberate action. The interaction between the flow field induced by the swimmer and a nearby surface causes the swimmer to tilt toward the surface and the velocity gradient associated with the flow rotates the animal to face upstream. Fluid mechanical computer simulations faithfully mimic the behavior observed in experiments, supporting the notion that rheotaxis behavior can be fully explained by hydrodynamics. Our study highlights the important role of hydrodynamics in the behavior of small undulating swimmers and may assist in developing control strategies to affect the animals' life cycles.}, }
@article {pmid25768609, year = {2015}, author = {Davoust, L and Achard, JL and Drazek, L}, title = {Low-to-moderate Reynolds number swirling flow in an annular channel with a rotating end wall.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {2}, pages = {023019}, doi = {10.1103/PhysRevE.91.023019}, pmid = {25768609}, issn = {1550-2376}, abstract = {This paper presents a new method for solving analytically the axisymmetric swirling flow generated in a finite annular channel from a rotating end wall, with no-slip boundary conditions along stationary side walls and a slip condition along the free surface opposite the rotating floor. In this case, the end-driven swirling flow can be described from the coupling between an azimuthal shear flow and a two-dimensional meridional flow driven by the centrifugal force along the rotating floor. A regular asymptotic expansion based on a small but finite Reynolds number is used to calculate centrifugation-induced first-order correction to the azimuthal Stokes flow obtained as the solution at leading order. For solving the first-order problem, the use of an integral boundary condition for the vorticity is found to be a convenient way to attribute boundary conditions in excess for the stream function to the vorticity. The annular geometry is characterized by both vertical and horizontal aspect ratios, whose respective influences on flow patterns are investigated. The vertical aspect ratio is found to involve nontrivial changes in flow patterns essentially due to the role of corner eddies located on the left and right sides of the rotating floor. The present analytical method can be ultimately extended to cylindrical geometries, irrespective of the surface opposite the rotating floor: a wall or a free surface. It can also serve as an analytical tool for monitoring confined rotating flows in applications related to surface viscosimetry or crystal growth from the melt.}, }
@article {pmid25768597, year = {2015}, author = {Chokshi, P and Bhade, P and Kumaran, V}, title = {Wall-mode instability in plane shear flow of viscoelastic fluid over a deformable solid.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {91}, number = {2}, pages = {023007}, doi = {10.1103/PhysRevE.91.023007}, pmid = {25768597}, issn = {1550-2376}, mesh = {Computer Simulation ; Linear Models ; *Models, Theoretical ; Pliability ; Polymers/chemistry ; Solutions ; *Viscoelastic Substances/chemistry ; Viscosity ; }, abstract = {The linear stability analysis of a plane Couette flow of an Oldroyd-B viscoelastic fluid past a flexible solid medium is carried out to investigate the role of polymer addition in the stability behavior. The system consists of a viscoelastic fluid layer of thickness R, density ρ, viscosity η, relaxation time λ, and retardation time βλ flowing past a linear elastic solid medium of thickness HR, density ρ, and shear modulus G. The emphasis is on the high-Reynolds-number wall-mode instability, which has recently been shown in experiments to destabilize the laminar flow of Newtonian fluids in soft-walled tubes and channels at a significantly lower Reynolds number than that for flows in rigid conduits. For Newtonian fluids, the linear stability studies have shown that the wall modes become unstable when flow Reynolds number exceeds a certain critical value Re(c) which scales as Σ(3/4), where Reynolds number Re=ρVR/η,V is the top-plate velocity, and dimensionless parameter Σ=ρGR(2)/η(2) characterizes the fluid-solid system. For high-Reynolds-number flow, the addition of polymer tends to decrease the critical Reynolds number in comparison to that for the Newtonian fluid, indicating a destabilizing role for fluid viscoelasticity. Numerical calculations show that the critical Reynolds number could be decreased by up to a factor of 10 by the addition of small amount of polymer. The critical Reynolds number follows the same scaling Re(c)∼Σ(3/4) as the wall modes for a Newtonian fluid for very high Reynolds number. However, for moderate Reynolds number, there exists a narrow region in β-H parametric space, corresponding to very dilute polymer solution (0.9≲β<1) and thin solids (H≲1.1), in which the addition of polymer tends to increase the critical Reynolds number in comparison to the Newtonian fluid. Thus, Reynolds number and polymer properties can be tailored to either increase or decrease the critical Reynolds number for unstable modes, thus providing an additional degree of control over the laminar-turbulent transition.}, }
@article {pmid25752537, year = {2015}, author = {Johansen, &#xd8; and Reed, M and Bodsberg, NR}, title = {Natural dispersion revisited.}, journal = {Marine pollution bulletin}, volume = {93}, number = {1-2}, pages = {20-26}, doi = {10.1016/j.marpolbul.2015.02.026}, pmid = {25752537}, issn = {1879-3363}, mesh = {*Models, Chemical ; Norway ; Petroleum ; Petroleum Pollution/*statistics &amp; numerical data ; Water Pollutants, Chemical/*analysis ; Water Pollution, Chemical/*statistics &amp; numerical data ; }, abstract = {This paper presents a new semi-empirical model for oil droplet size distributions generated by single breaking wave events. Empirical data was obtained from laboratory experiments with different crude oils at different stages of weathering. The paper starts with a review of the most commonly used model for natural dispersion, which is followed by a presentation of the laboratory study on oil droplet size distributions formed by breaking waves conducted by SINTEF on behalf of the NOAA/UNH Coastal Response Research Center. The next section presents the theoretical and empirical foundation for the new model. The model is based on dimensional analysis and contains two non-dimensional groups; the Weber and Reynolds number. The model was validated with data from a full scale experimental oil spill conducted in the Haltenbanken area offshore Norway in July 1982, as described in the last section of the paper.}, }
@article {pmid25750412, year = {2015}, author = {Yanase, K and Saarenrinne, P}, title = {Unsteady turbulent boundary layers in swimming rainbow trout.}, journal = {The Journal of experimental biology}, volume = {218}, number = {Pt 9}, pages = {1373-1385}, doi = {10.1242/jeb.108043}, pmid = {25750412}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Friction ; Oncorhynchus mykiss/*physiology ; Pressure ; Rheology ; *Swimming ; }, abstract = {The boundary layers of rainbow trout, Oncorhynchus mykiss, swimming at 1.02±0.09 L s(-1) (mean±s.d., N=4), were measured by the particle image velocimetry (PIV) technique at a Reynolds number of 4×10(5). The boundary layer profile showed unsteadiness, oscillating above and beneath the classical logarithmic law of the wall with body motion. Across the entire surface regions that were measured, local Reynolds numbers based on momentum thickness, which is the distance that is perpendicular to the fish surface through which the boundary layer momentum flows at free-stream velocity, were greater than the critical value of 320 for the laminar-to-turbulent transition. The skin friction was dampened on the convex surface while the surface was moving towards a free-stream flow and increased on the concave surface while retreating. These observations contradict the result of a previous study using different species swimming by different methods. Boundary layer compression accompanied by an increase in local skin friction was not observed. Thus, the overall results may not support absolutely the Bone-Lighthill boundary layer thinning hypothesis that the undulatory motions of swimming fish cause a large increase in their friction drag because of the compression of the boundary layer. In some cases, marginal flow separation occurred on the convex surface in the relatively anterior surface region, but the separated flow reattached to the fish surface immediately downstream. Therefore, we believe that a severe impact due to induced drag components (i.e. pressure drag) on the swimming performance, an inevitable consequence of flow separation, was avoided.}, }
@article {pmid25750148, year = {2015}, author = {Launder, BE}, title = {First steps in modelling turbulence and its origins: a commentary on Reynolds (1895) 'On the dynamical theory of incompressible viscous fluids and the determination of the criterion'.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {373}, number = {2039}, pages = {}, pmid = {25750148}, issn = {1471-2962}, abstract = {Reynolds' paper sought to explain the change in character of flow through a pipe from laminar to turbulent that his earlier experiments had shown to occur when the dimensionless group that today bears his name exceeded approximately 2000. This he did by decomposing the velocity into mean and fluctuating components and noting how the average kinetic energy generation and dissipation rates changed with Reynolds number. The paper was only grudgingly accepted by two very distinguished referees and initially raised little external interest. As years went by, however, the averaged form of the equations of motion, known as the Reynolds equations (which were an intermediate stage in Reynolds' analysis) became the acknowledged starting point for computing turbulent flows. Moreover, some 50 years after his paper, a refinement of his strategy for predicting transition was also successfully taken up. For some engineering problems, the continual rapid growth of computing resources has meant that more detailed approaches for computing turbulent flow phenomena can nowadays be employed. However, this growth of computing power likewise makes possible a Reynolds-averaging strategy for complex flow systems in industry or the environment which formerly had to adopt less comprehensive analyses. Thus, Reynolds' approach may well remain in use throughout the present century. This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society.}, }
@article {pmid25737365, year = {2015}, author = {Marschewski, J and Jung, S and Ruch, P and Prasad, N and Mazzotti, S and Michel, B and Poulikakos, D}, title = {Mixing with herringbone-inspired microstructures: overcoming the diffusion limit in co-laminar microfluidic devices.}, journal = {Lab on a chip}, volume = {15}, number = {8}, pages = {1923-1933}, doi = {10.1039/c5lc00045a}, pmid = {25737365}, issn = {1473-0189}, abstract = {Enhancing mixing is of uttermost importance in many laminar microfluidic devices, aiming at overcoming the severe performance limitation of species transport by diffusion alone. Here we focus on the significant category of microscale co-laminar flows encountered in membraneless redox flow cells for power delivery. The grand challenge is to achieve simultaneously convective mixing within each individual reactant, to thin the reaction depletion boundary layers, while maintaining separation of the co-flowing reactants, despite the absence of a membrane. The concept presented here achieves this goal with the help of optimized herringbone flow promoting microstructures with an integrated separation zone. Our electrochemical experiments using a model redox couple show that symmetric flow promoter designs exhibit laminar to turbulent flow behavior, the latter at elevated flow rates. This change in flow regime is accompanied by a significant change in scaling of the Sherwood number with respect to the Reynolds number from Sh ~ Re(0.29) to Sh ~ Re(0.58). The stabilized continuous laminar flow zone along the centerline of the channel allows operation in a co-laminar flow regime up to Re ~325 as we demonstrate by micro laser-induced fluorescence (μLIF) measurements. Micro particle image velocimetry (μPIV) proves the maintenance of a stratified flow along the centerline, mitigating reactant cross-over effectively. The present work paves the way toward improved performance in membraneless microfluidic flow cells for electrochemical energy conversion.}, }
@article {pmid25711100, year = {2014}, author = {Filatova, OV and Sidorenko, AA and Skorobogatov, IuIu}, title = {[The study of hemodynamic parameters of human internal carotid arteries depending on the age considering the sex and the localization of the artery].}, journal = {Fiziologiia cheloveka}, volume = {40}, number = {5}, pages = {93-102}, pmid = {25711100}, issn = {0131-1646}, mesh = {Adolescent ; Adult ; *Age Factors ; Aged ; Aged, 80 and over ; Blood Flow Velocity/*physiology ; Carotid Artery, Internal/*physiology ; Child ; Child, Preschool ; Female ; *Hemodynamics ; Humans ; Infant ; Infant, Newborn ; Male ; Middle Aged ; Sex Characteristics ; }, abstract = {The research of the ultrasound diameter, linear velocity and the resistance of internal carotid arteries of 647 people of both sexes aged from one to 74 years was conducted. Additionally, shear stress and the Reynolds number were calculated. During the period from early childhood to adolescence and from the first mature to old age there is an increase in the diameter of the internal carotid arteries. The phases of increased vascular resistance by the first period of childhood, adolescence and old age are observed. Volumetric flow rate has relatively stable parameters till adolescence, then it declines by old age. The average linear velocity, shear stress, and the Reynolds number diminish progressively twice with age. Laminar blood flow with local twists in the early stages of postnatal ontogenesis is characteristic of internal carotid arteries. The diameter of internal carotid arteries, vascular resistance index, blood flow velocity are higher in males than in females during most age periods. Shear stress in both internal carotid arteries during the age periods studied is symmetrical and has no sex differences.}, }
@article {pmid25680212, year = {2015}, author = {Nadeem, S and Sadaf, H}, title = {Theoretical Analysis of Cu-Blood Nanofluid for Metachronal Wave of Cilia Motion in a Curved Channel.}, journal = {IEEE transactions on nanobioscience}, volume = {14}, number = {4}, pages = {447-454}, doi = {10.1109/TNB.2015.2401972}, pmid = {25680212}, issn = {1558-2639}, abstract = {In this paper, the mechanism of cilia-induced flow is discussed through a mathematical model. In this study two dimensional flow of a viscous fluid in the presence of nanoparticles are observed in a curved channel with ciliated walls. Cilia have a distinctive pattern of motion by which they can set fluid into motion at low Reynolds number. The flow is modeled in both fixed and wave frame of reference. Exact solution is calculated for the velocity as well as for temperature profile and the flow properties for the Cu-blood nanofluid is determined as a function of the cilia and metachronal wave velocity. Results for temperature profile, velocity, pressure rise, pressure gradient and stream function are constructed and evaluated graphically.}, }
@article {pmid25672601, year = {2015}, author = {Gibbs, JG and Fischer, P}, title = {Active colloidal microdrills.}, journal = {Chemical communications (Cambridge, England)}, volume = {51}, number = {20}, pages = {4192-4195}, doi = {10.1039/c5cc00565e}, pmid = {25672601}, issn = {1364-548X}, mesh = {Catalysis ; Colloids/*chemistry ; *Hydrodynamics ; Movement ; Platinum/chemistry ; Rotation ; Torque ; }, abstract = {We demonstrate a chemically driven, autonomous catalytic microdrill. An asymmetric distribution of catalyst causes the helical swimmer to twist while it undergoes directed propulsion. A driving torque and hydrodynamic coupling between translation and rotation at low Reynolds number leads to drill-like swimming behaviour.}, }
@article {pmid25671438, year = {2015}, author = {You, JB and Kang, K and Tran, TT and Park, H and Hwang, WR and Kim, JM and Im, SG}, title = {PDMS-based turbulent microfluidic mixer.}, journal = {Lab on a chip}, volume = {15}, number = {7}, pages = {1727-1735}, doi = {10.1039/c5lc00070j}, pmid = {25671438}, issn = {1473-0189}, abstract = {Over the past decade, homogeneous mixing in microfluidic devices has been a critical challenge, because of the inherently low flow rates in microfluidic channels. Although several mixer designs have been suggested to achieve efficient mixing, most of them involve intricate structures requiring a series of laborious fabrication processes. Operation at high flow rates can greatly enhance mixing by induction of turbulence, but devices that can resist such a high pressure drop to induce turbulence in microfluidic channels are difficult to fabricate, especially for commonly used poly(dimethylsiloxane) (PDMS)-based microfluidic devices. We have developed a Y-shaped, turbulent microfluidic mixer made of PDMS and a glass substrate by strong bonding of the substrates to a nanoadhesive layer deposited via initiated chemical vapor deposition. The high bonding strength of the nanoadhesive layer enables safe operation of the PDMS/glass turbulent microfluidic mixer at a total water flow rate of 40 mL min(-1), corresponding to a Reynolds number, Re, of ~4423, one of the highest values achieved in a microfluidic channel. The turbulence generated as a result of the high Re allows rapid mixing of the input fluids on contact. Image analysis showed that mixing started as soon as the fluids were introduced into the mixer. The experimental results matched the numerical predictions well, demonstrating that convective mixing was dominant as a result of turbulence induced in the microfluidic channel. Using the turbulent microfluidic mixer, we have demonstrated high throughput formation of emulsions with narrower size distribution. It was shown that as the flow rate increases inside the microfluidic channel, the size distribution of resulting emulsions decreases owing to the increase in the turbulent energy dissipation. The turbulent microfluidic mixer developed in this work not only enables rapid mixing of streams, but also increases throughputs of microfluidic reactors.}, }
@article {pmid25659002, year = {2015}, author = {Sinhuber, M and Bodenschatz, E and Bewley, GP}, title = {Decay of turbulence at high reynolds numbers.}, journal = {Physical review letters}, volume = {114}, number = {3}, pages = {034501}, doi = {10.1103/PhysRevLett.114.034501}, pmid = {25659002}, issn = {1079-7114}, abstract = {Turbulent motions in a fluid decay at a certain rate once stirring has stopped. The role of the most basic parameter in fluid mechanics, the Reynolds number, in setting the decay rate is not generally known. This Letter concerns the high-Reynolds-number limit of the process. In a classical grid-turbulence wind-tunnel experiment that both reaches higher Reynolds numbers than ever before and covers a wide range of them (10^{4}<Re=UM/ν<5×10^{6}), we measure the decay rate with the unprecedented precision of about 2%. Here U is the mean speed of the flow, M is the forcing scale, and ν is the kinematic viscosity of the fluid. We observe that the decay rate is Reynolds-number independent, which contradicts some models and supports others.}, }
@article {pmid25650274, year = {2015}, author = {Feng, J and Yuan, J and Cho, SK}, title = {Micropropulsion by an acoustic bubble for navigating microfluidic spaces.}, journal = {Lab on a chip}, volume = {15}, number = {6}, pages = {1554-1562}, doi = {10.1039/c4lc01266f}, pmid = {25650274}, issn = {1473-0189}, mesh = {*Acoustics ; Computer Simulation ; *Hydrodynamics ; *Lab-On-A-Chip Devices ; }, abstract = {This paper describes an underwater micropropulsion principle where a gaseous bubble trapped in a suspended microchannel and oscillated by external acoustic excitation generates a propelling force. The propelling swimmer is designed and microfabricated from parylene on the microscale (the equivalent diameter of the cylindrical bubble is around 60 μm) using microphotolithography. The propulsion mechanism is studied and verified by computational fluid dynamics (CFD) simulations as well as experiments. The acoustically excited and thus periodically oscillating bubble generates alternating flows of intake and discharge through an opening of the microchannel. As the Reynolds number of oscillating flow increases, the difference between the intake and discharge flows becomes significant enough to generate a net flow (microstreaming flow) and a propulsion force against the channel. As the size of the device is reduced, however, the Reynolds number is also reduced. To maintain the Reynolds number in a certain range and thus generate a strong propulsion force in the fabricated device, the oscillation amplitude of the bubble is maximized (resonated) and the oscillation frequency is set high (over 10 kHz). Propelling motions by a single bubble as well as an array of bubbles are achieved on the microscale. In addition, the microswimmer demonstrates payload carrying. This propulsion mechanism may be applied to microswimmers that navigate microfluidic environments and possibly narrow passages in human bodies to perform biosensing, drug delivery, imaging, and microsurgery.}, }
@article {pmid25643048, year = {2015}, author = {Weymouth, GD and Subramaniam, V and Triantafyllou, MS}, title = {Ultra-fast escape maneuver of an octopus-inspired robot.}, journal = {Bioinspiration &amp; biomimetics}, volume = {10}, number = {1}, pages = {016016}, doi = {10.1088/1748-3190/10/1/016016}, pmid = {25643048}, issn = {1748-3190}, mesh = {Animals ; Biomimetics/*instrumentation ; Computer Simulation ; Equipment Design ; Equipment Failure Analysis ; Escape Reaction/*physiology ; *Models, Biological ; Octopodiformes/*physiology ; Robotics/*instrumentation ; Ships ; Swimming/*physiology ; }, abstract = {We design and test an octopus-inspired flexible hull robot that demonstrates outstanding fast-starting performance. The robot is hyper-inflated with water, and then rapidly deflates to expel the fluid so as to power the escape maneuver. Using this robot we verify for the first time in laboratory testing that rapid size-change can substantially reduce separation in bluff bodies traveling several body lengths, and recover fluid energy which can be employed to improve the propulsive performance. The robot is found to experience speeds over ten body lengths per second, exceeding that of a similarly propelled optimally streamlined rigid rocket. The peak net thrust force on the robot is more than 2.6 times that on an optimal rigid body performing the same maneuver, experimentally demonstrating large energy recovery and enabling acceleration greater than 14 body lengths per second squared. Finally, over 53% of the available energy is converted into payload kinetic energy, a performance that exceeds the estimated energy conversion efficiency of fast-starting fish. The Reynolds number based on final speed and robot length is [Formula: see text]. We use the experimental data to establish a fundamental deflation scaling parameter [Formula: see text] which characterizes the mechanisms of flow control via shape change. Based on this scaling parameter, we find that the fast-starting performance improves with increasing size.}, }
@article {pmid25642947, year = {2015}, author = {Temel, FZ and Yesilyurt, S}, title = {Confined swimming of bio-inspired microrobots in rectangular channels.}, journal = {Bioinspiration &amp; biomimetics}, volume = {10}, number = {1}, pages = {016015}, doi = {10.1088/1748-3190/10/1/016015}, pmid = {25642947}, issn = {1748-3190}, mesh = {*Bacterial Physiological Phenomena ; Biomimetics/*instrumentation/methods ; Computer Simulation ; Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Miniaturization ; *Models, Biological ; Rheology/instrumentation/methods ; Robotics/*instrumentation/methods ; Swimming/*physiology ; }, abstract = {Controlled swimming of bio-inspired microrobots in confined spaces needs to be understood well for potential use in medical applications in conduits and vessels inside the body. In this study, experimental and computational studies are performed for analysis of swimming modes of a bio-inspired microrobot in rectangular channels at low Reynolds number. Experiments are performed on smooth and rough surfaces using a magnetic helical swimmer (MHS), having 0.5 mm diameter and 2 mm length, with left-handed helical tail and radially polarized magnetic head within rotating magnetic field obtained by two electromagnetic coil pairs. Experiments indicate three motion modes of the MHS with respect to the rotation frequency: (i) lateral motion under the effect of a perpendicular force such as gravity and the surface traction at low frequencies, (ii) lateral motion under the effect of fluid forces and gravity at transition frequencies, and (iii) circular motion under the effect of fluid forces at high frequencies. Observed modes of motion for the MHS are investigated with computational fluid dynamics simulations by calculating translational and angular velocities and studying the induced flow fields for different radial positions inside the channel. Results indicate the importance of rotation frequency, surface roughness and flow field on the swimming modes and behaviour of the MHS inside the rectangular channel.}, }
@article {pmid25629213, year = {2015}, author = {Goto, Y and Tanaka, H}, title = {Purely hydrodynamic ordering of rotating disks at a finite Reynolds number.}, journal = {Nature communications}, volume = {6}, number = {}, pages = {5994}, doi = {10.1038/ncomms6994}, pmid = {25629213}, issn = {2041-1723}, abstract = {Self-organization of moving objects in hydrodynamic environments has recently attracted considerable attention in connection to natural phenomena and living systems. However, the underlying physical mechanism is much less clear due to the intrinsically nonequilibrium nature, compared with self-organization of thermal systems. Hydrodynamic interactions are believed to play a crucial role in such phenomena. To elucidate the fundamental physical nature of many-body hydrodynamic interactions at a finite Reynolds number, here we study a system of co-rotating hard disks in a two-dimensional viscous fluid at zero temperature. Despite the absence of thermal noise, this system exhibits rich phase behaviours, including a fluid state with diffusive dynamics, a cluster state, a hexatic state, a glassy state, a plastic crystal state and phase demixing. We reveal that these behaviours are induced by the off-axis and many-body nature of nonlinear hydrodynamic interactions and the finite time required for propagating the interactions by momentum diffusion.}, }
@article {pmid25615472, year = {2015}, author = {Srinivasan, S and Kleingartner, JA and Gilbert, JB and Cohen, RE and Milne, AJ and McKinley, GH}, title = {Sustainable drag reduction in turbulent Taylor-Couette flows by depositing sprayable superhydrophobic surfaces.}, journal = {Physical review letters}, volume = {114}, number = {1}, pages = {014501}, doi = {10.1103/PhysRevLett.114.014501}, pmid = {25615472}, issn = {1079-7114}, abstract = {We demonstrate a reduction in the measured inner wall shear stress in moderately turbulent Taylor-Couette flows by depositing sprayable superhydrophobic microstructures on the inner rotor surface. The magnitude of reduction becomes progressively larger as the Reynolds number increases up to a value of 22% at Re=8.0×10(4). We show that the mean skin friction coefficient C(f) in the presence of the superhydrophobic coating can be fitted to a modified Prandtl-von Kármán-type relationship of the form (C(f)/2)(-1/2)=Mln (Re(C(f)/2)(1/2))+N+(b/Δr)Re(C(f)/2)(1/2) from which we extract an effective slip length of b≈19 μm. The dimensionless effective slip length b(+)=b/δ(ν), where δ(ν) is the viscous length scale, is the key parameter that governs the drag reduction and is shown to scale as b(+)∼Re(1/2) in the limit of high Re.}, }
@article {pmid25615195, year = {2014}, author = {Klewicki, J and Philip, J and Marusic, I and Chauhan, K and Morrill-Winter, C}, title = {Self-similarity in the inertial region of wall turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {6}, pages = {063015}, doi = {10.1103/PhysRevE.90.063015}, pmid = {25615195}, issn = {1550-2376}, abstract = {The inverse of the von Kármán constant κ is the leading coefficient in the equation describing the logarithmic mean velocity profile in wall bounded turbulent flows. Klewicki [J. Fluid Mech. 718, 596 (2013)] connects the asymptotic value of κ with an emerging condition of dynamic self-similarity on an interior inertial domain that contains a geometrically self-similar hierarchy of scaling layers. A number of properties associated with the asymptotic value of κ are revealed. This is accomplished using a framework that retains connection to invariance properties admitted by the mean statement of dynamics. The development leads toward, but terminates short of, analytically determining a value for κ. It is shown that if adjacent layers on the hierarchy (or their adjacent positions) adhere to the same self-similarity that is analytically shown to exist between any given layer and its position, then κ≡Φ(-2)=0.381966..., where Φ=(1+√5)/2 is the golden ratio. A number of measures, derived specifically from an analysis of the mean momentum equation, are subsequently used to empirically explore the veracity and implications of κ=Φ(-2). Consistent with the differential transformations underlying an invariant form admitted by the governing mean equation, it is demonstrated that the value of κ arises from two geometric features associated with the inertial turbulent motions responsible for momentum transport. One nominally pertains to the shape of the relevant motions as quantified by their area coverage in any given wall-parallel plane, and the other pertains to the changing size of these motions in the wall-normal direction. In accord with self-similar mean dynamics, these two features remain invariant across the inertial domain. Data from direct numerical simulations and higher Reynolds number experiments are presented and discussed relative to the self-similar geometric structure indicated by the analysis, and in particular the special form of self-similarity shown to correspond to κ=Φ(-2).}, }
@article {pmid25615188, year = {2014}, author = {Katul, GG and Manes, C}, title = {Cospectral budget of turbulence explains the bulk properties of smooth pipe flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {6}, pages = {063008}, doi = {10.1103/PhysRevE.90.063008}, pmid = {25615188}, issn = {1550-2376}, abstract = {Connections between the wall-normal turbulent velocity spectrum E(ww)(k) at wave number k and the mean velocity profile (MVP) are explored in pressure-driven flows confined within smooth walls at moderate to high bulk Reynolds numbers (Re). These connections are derived via a cospectral budget for the longitudinal (u') and wall-normal (w') velocity fluctuations, which include a production term due to mean shear interacting with E(ww)(k), viscous effects, and a decorrelation between u' and w' by pressure-strain effects [=π(k)]. The π(k) is modeled using a conventional Rotta-like return-to-isotropy closure but adjusted to include the effects of isotropization of the production term. The resulting cospectral budget yields a generalization of a previously proposed "spectral link" between the MVP and the spectrum of turbulence. The proposed cospectral budget is also shown to reproduce the measured MVP across the pipe with changing Re including the MVP shapes in the buffer and wake regions. Because of the links between E(ww)(k) and the MVP, the effects of intermittency corrections to inertial subrange scales and the so-called spectral bottleneck reported as k approaches viscous dissipation eddy sizes (η) on the MVP shapes are investigated and shown to be of minor importance. Inclusion of a local Reynolds number correction to a parameter associated with the spectral exponential cutoff as kη→1 appears to be more significant to the MVP shape in the buffer region. While the bulk shape of the MVP is reasonably reproduced in all regions of the pipe, the solution to the cospectral budget systematically underestimates the negative curvature of the MVP within the buffer layer.}, }
@article {pmid25615182, year = {2014}, author = {Wu, F and Speetjens, MF and Vainchtein, DL and Trieling, RR and Clercx, HJ}, title = {Comparative numerical-experimental analysis of the universal impact of arbitrary perturbations on transport in three-dimensional unsteady flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {6}, pages = {063002}, doi = {10.1103/PhysRevE.90.063002}, pmid = {25615182}, issn = {1550-2376}, abstract = {Numerical studies of three-dimensional (3D) time-periodic flow inside a lid-driven cylinder revealed that a weak perturbation of the noninertial state (Reynolds number Re=0) has a strong impact on the Lagrangian flow structure by inducing transition of a global family of nested spheroidal invariant surfaces into intricate coherent structures consisting of adiabatic invariant surfaces connected by tubes. These tubes provide paths for passive tracers to escape from one invariant surface to another. Perturbation is introduced in two ways: (i) weak fluid inertia by nonzero Re∼O(10(-3)); (ii) small disturbance of the external flow forcing. Both induce essentially the same dynamics, implying a universal response in the limit of a weak perturbation. Moreover, we show that the motion inside tubes possesses an adiabatic invariant. Long-term experiments were conducted using 3D particle-tracking velocimetry and relied on experimental imperfections as natural weak perturbations. This provided first experimental evidence of the tube formation and revealed close agreement with numerical simulations. We experimentally validated the universality of the perturbation response and, given the inevitability of imperfections, exposed the weakly perturbed state as the true "unperturbed state" in realistic systems.}, }
@article {pmid25615181, year = {2014}, author = {Tritschler, VK and Zubel, M and Hickel, S and Adams, NA}, title = {Evolution of length scales and statistics of Richtmyer-Meshkov instability from direct numerical simulations.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {6}, pages = {063001}, doi = {10.1103/PhysRevE.90.063001}, pmid = {25615181}, issn = {1550-2376}, abstract = {In this study we present direct numerical simulation results of the Richtmyer-Meshkov instability (RMI) initiated by Ma=1.05,Ma=1.2, and Ma=1.5 shock waves interacting with a perturbed planar interface between air and SF(6). At the lowest shock Mach number the fluids slowly mix due to viscous diffusion, whereas at the highest shock Mach number the mixing zone becomes turbulent. When a minimum critical Taylor microscale Reynolds number is exceeded, an inertial range spectrum emerges, providing further evidence of transition to turbulence. The scales of turbulent motion, i.e., the Kolmogorov length scale, the Taylor microscale, and the integral length, scale are presented. The separation of these scales is found to increase as the Reynolds number is increased. Turbulence statistics, i.e., the probability density functions of the velocity and its longitudinal and transverse derivatives, show a self-similar decay and thus that turbulence evolving from RMI is not fundamentally different from isotropic turbulence, though nominally being only isotropic and homogeneous in the transverse directions.}, }
@article {pmid25615103, year = {2014}, author = {Lee, YK and Ahn, KH and Lee, SJ}, title = {Local shear stress and its correlation with local volume fraction in concentrated non-Brownian suspensions: lattice Boltzmann simulation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {6}, pages = {062317}, doi = {10.1103/PhysRevE.90.062317}, pmid = {25615103}, issn = {1550-2376}, abstract = {The local shear stress of non-Brownian suspensions was investigated using the lattice Boltzmann method coupled with the smoothed profile method. Previous studies have only focused on the bulk rheology of complex fluids because the local rheology of complex fluids was not accessible due to technical limitations. In this study, the local shear stress of two-dimensional solid particle suspensions in Couette flow was investigated with the method of planes to correlate non-Newtonian fluid behavior with the structural evolution of concentrated particle suspensions. Shear thickening was successfully captured for highly concentrated suspensions at high particle Reynolds number, and both the local rheology and local structure of the suspensions were analyzed. It was also found that the linear correlation between the local particle stress and local particle volume fraction was dramatically reduced during shear thickening. These results clearly show how the change in local structure of suspensions influences the local and bulk rheology of the suspensions.}, }
@article {pmid25615081, year = {2014}, author = {Xu, Y and Padding, JT and Kuipers, JA}, title = {Numerical investigation of the vertical plunging force of a spherical intruder into a prefluidized granular bed.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {6}, pages = {062203}, doi = {10.1103/PhysRevE.90.062203}, pmid = {25615081}, issn = {1550-2376}, abstract = {The plunging of a large intruder sphere into a prefluidized granular bed with various constant velocities and various sphere diameters is investigated using a state-of-the-art hybrid discrete particle and immersed boundary method, in which both the gas-induced drag force and the contact force exerted on the intruder can be investigated separately. We investigate low velocities, where velocity dependent effects first begin to appear. The results show a concave-to-convex dependence of the plunging force as a function of intruder depth. In the concave region the force fits to a power law with an exponent around 1.3, which is in good agreement with existing experimental observations. Our simulation results further show that the force exerted on the frontal hemisphere of the intruder is dominant. At larger intruder velocities, friction with the granular medium causes a velocity-dependent drag force. As long as the granular particles have not yet closed the gap behind the intruder, this drag force is independent of the actual intruder depth. In this regime, the drag force experienced by intruders of different diameter moving at different velocities all fall onto a single master curve if plotted against the Reynolds number, using a single value for the effective viscosity of the granular medium. This master curve corresponds well to the Schiller-Naumann correlation for the drag force between a sphere and a Newtonian fluid. After the gap behind the intruder has closed, the drag force increases not only with velocity but also with depth. We attribute this to the effect of increasing hydrostatic particle pressure in the granular medium, leading to an increase in effective viscosity.}, }
@article {pmid25602685, year = {2015}, author = {Chen, Y and Xiong, Y and Jiang, W and Yan, F and Guo, M and Wang, Q and Fan, Y}, title = {Numerical simulation on the effects of drug eluting stents at different Reynolds numbers on hemodynamic and drug concentration distribution.}, journal = {Biomedical engineering online}, volume = {14 Suppl 1}, number = {Suppl 1}, pages = {S16}, pmid = {25602685}, issn = {1475-925X}, mesh = {Blood Vessels/drug effects/physiology ; Dose-Response Relationship, Drug ; *Drug-Eluting Stents/adverse effects ; Graft Occlusion, Vascular/chemically induced/physiopathology ; Hemodynamics/*drug effects ; Hydrodynamics ; *Models, Biological ; Shear Strength/drug effects ; Stress, Mechanical ; }, abstract = {BACKGROUND: The changes of hemodynamics and drug concentration distribution caused by the implantation of drug eluting stents (DESs) in curved vessels have significant effects on In-Stent Restenosis.<br><br>METHODS: A 3D virtual stent with 90&#xb0; curvature was modelled and the distribution of wall shear stress (WSS) and drug concentration in this model were numerically studied at Reynolds numbers of 200, 400, 600, 800.<br><br>RESULTS: The results showed that (1) the intensity of secondary flow at the 45&#xb0; cross-section was stronger than that at the 90&#xb0; cross-section; (2) As the Reynolds number increases, the WSS decreases. When the Reynolds number reaches 600, the low-WSS region only accounts for 3% of the total area. (3) The effects of Reynolds number on drug concentration in the vascular wall decreases in proportionally and then the blood velocity increased 4 times, the drug concentration in the vascular wall decreased by about 30%. (4) The size of the high drug concentration region is inversely proportional to the Reynolds number. As the blood velocity increases, the drug concentration in the DES decreases, especially at the outer bend.<br><br>CONCLUSIONS: It is beneficial for the patient to decrease vigorous activities and keep calm at the beginning of the stent implantation, because a substantial amount of the drug is released in the first two months of stent implantation, thus a calm status is conducive to drug release and absorption; Subsequently, appropriate exercise which increases the blood velocity is helpful in decreasing regions of low-WSS.}, }
@article {pmid25598070, year = {2014}, author = {Bit, A and Chattopadhyay, H}, title = {Numerical investigations of pulsatile flow in stenosed artery.}, journal = {Acta of bioengineering and biomechanics}, volume = {16}, number = {4}, pages = {33-44}, pmid = {25598070}, issn = {2450-6303}, mesh = {Blood Flow Velocity ; Coronary Stenosis/pathology/*physiopathology ; Coronary Vessels/pathology/*physiopathology ; Humans ; Models, Cardiovascular ; *Numerical Analysis, Computer-Assisted ; Pressure ; Pulsatile Flow/*physiology ; Stress, Mechanical ; Time Factors ; }, abstract = {PURPOSE: Abnormalities in blood vessels by virtue of complex blood flow dynamics is being supported by non-Newtonian behavior of blood. Thus it becomes a focus of research to most of the researchers. Additionally, consideration of real life patient specific model of vessel as well as patient specific inlet flow boundary condition implementation was limited in literature. Thus a thorough implementation of these considerations was done here.<br><br>METHOD: In this work, a numerical investigation of hemodynamic flow in stenosed artery has been carried out with realistic pulsating profile at the inlet. Flow has been considered to be laminar due to arresting condition of cardiovascular state of the subject. Two non- Newtonian rheological models namely, Power Law viscosity model and Quemada viscosity model have been used. Two different patient- specific pulsatile profiles are considered at the inlet of a long stenosed artery with varying degree of stenoses from 25% to 80%.<br><br>RESULTS: Transient form of Navier-Stokes equation is solved in an axi-symmetric domain to calculate the detailed flow structure of the flow field. From the simulation data, temporal and time averaged wall shear stress, oscillatory shear index and pressure drop are calculated.<br><br>CONCLUSIONS: The results demonstrate that oscillatory shear index and wall shear stresses are extensively governed by the degree of stenoses. The position and movement of recirculation bubbles are found to vary with flow Reynolds number.}, }
@article {pmid25573580, year = {2015}, author = {Ekiel-Jeżewska, ML and Felderhof, BU}, title = {Hydrodynamic interactions between a sphere and a number of small particles.}, journal = {The Journal of chemical physics}, volume = {142}, number = {1}, pages = {014904}, doi = {10.1063/1.4904981}, pmid = {25573580}, issn = {1089-7690}, abstract = {Exact expressions are derived for the pair and three-body hydrodynamic interactions between a sphere and a number of small particles immersed in a viscous incompressible fluid. The analysis is based on the Stokes equations of low Reynolds number hydrodynamics. The results follow by a combination of the solutions for flow about a sphere with no-slip boundary condition derived by Stokes and Kirchhoff and the result derived by Oseen for the Green tensor of Stokes equations in the presence of a fixed sphere.}, }
@article {pmid25564849, year = {2015}, author = {Visser, CW and Gielen, MV and Hao, Z and Le Gac, S and Lohse, D and Sun, C}, title = {Quantifying cell adhesion through impingement of a controlled microjet.}, journal = {Biophysical journal}, volume = {108}, number = {1}, pages = {23-31}, pmid = {25564849}, issn = {1542-0086}, mesh = {*Cell Adhesion ; Computer Simulation ; Cytological Techniques/*instrumentation ; HeLa Cells ; Humans ; Microtechnology/*instrumentation/*methods ; Models, Biological ; Stress, Mechanical ; }, abstract = {The impingement of a submerged, liquid jet onto a cell-covered surface allows assessing cell attachment on surfaces in a straightforward and quantitative manner and in real time, yielding valuable information on cell adhesion. However, this approach is insufficiently characterized for reliable and routine use. In this work, we both model and measure the shear stress exerted by the jet on the impingement surface in the micrometer-domain, and subsequently correlate this to jet-induced cell detachment. The measured and numerically calculated shear stress data are in good agreement with each other, and with previously published values. Real-time monitoring of the cell detachment reveals the creation of a circular cell-free area upon jet impingement, with two successive detachment regimes: 1), a dynamic regime, during which the cell-free area grows as a function of both the maximum shear stress exerted by the jet and the jet diameter; followed by 2), a stationary regime, with no further evolution of the cell-free area. For the latter regime, which is relevant for cell adhesion strength assessment, a relationship between the jet Reynolds number, the cell-free area, and the cell adhesion strength is proposed. To illustrate the capability of the technique, the adhesion strength of HeLa cervical cancer cells is determined ((34 ± 14) N/m(2)). Real-time visualization of cell detachment in the dynamic regime shows that cells detach either cell-by-cell or by collectively (for which intact parts of the monolayer detach as cell sheets). This process is dictated by the cell monolayer density, with a typical threshold of (1.8 ± 0.2) × 10(9) cells/m(2), above which the collective behavior is mostly observed. The jet impingement method presents great promises for the field of tissue engineering, as the influence of both the shear stress and the surface characteristics on cell adhesion can be systematically studied.}, }
@article {pmid25563524, year = {2015}, author = {Liu, C and Hu, G and Jiang, X and Sun, J}, title = {Inertial focusing of spherical particles in rectangular microchannels over a wide range of Reynolds numbers.}, journal = {Lab on a chip}, volume = {15}, number = {4}, pages = {1168-1177}, doi = {10.1039/c4lc01216j}, pmid = {25563524}, issn = {1473-0189}, mesh = {Equipment Design ; *Lab-On-A-Chip Devices ; Particle Size ; }, abstract = {Inertial microfluidics has emerged as an important tool for manipulating particles and cells. For a better design of inertial microfluidic devices, we conduct 3D direct numerical simulations (DNS) and experiments to determine the complicated dependence of focusing behaviour on the particle size, channel aspect ratio, and channel Reynolds number. We find that the well-known focusing of the particles at the two centers of the long channel walls occurs at a relatively low Reynolds number, whereas additional stable equilibrium positions emerge close to the short walls with increasing Reynolds number. Based on the numerically calculated trajectories of particles, we propose a two-stage particle migration which is consistent with experimental observations. We further present a general criterion to secure good focusing of particles for high flow rates. This work thus provides physical insight into the multiplex focusing of particles in rectangular microchannels with different geometries and Reynolds numbers, and paves the way for efficiently designing inertial microfluidic devices.}, }
@article {pmid25554885, year = {2014}, author = {Lashgari, I and Picano, F and Breugem, WP and Brandt, L}, title = {Laminar, turbulent, and inertial shear-thickening regimes in channel flow of neutrally buoyant particle suspensions.}, journal = {Physical review letters}, volume = {113}, number = {25}, pages = {254502}, doi = {10.1103/PhysRevLett.113.254502}, pmid = {25554885}, issn = {1079-7114}, abstract = {The aim of this Letter is to characterize the flow regimes of suspensions of finite-size rigid particles in a viscous fluid at finite inertia. We explore the system behavior as a function of the particle volume fraction and the Reynolds number (the ratio of flow and particle inertia to viscous forces). Unlike single-phase flows, where a clear distinction exists between the laminar and the turbulent states, three different regimes can be identified in the presence of a particulate phase, with smooth transitions between them. At low volume fractions, the flow becomes turbulent when increasing the Reynolds number, transitioning from the laminar regime dominated by viscous forces to the turbulent regime characterized by enhanced momentum transport by turbulent eddies. At larger volume fractions, we identify a new regime characterized by an even larger increase of the wall friction. The wall friction increases with the Reynolds number (inertial effects) while the turbulent transport is weakly affected, as in a state of intense inertial shear thickening. This state may prevent the transition to a fully turbulent regime at arbitrary high speed of the flow.}, }
@article {pmid25554059, year = {2014}, author = {Sikiö, P and Jalali, P}, title = {Study of turbulent energy dissipation rate of fluid flow in the vicinity of dispersed phase boundary using spatiotemporal tree model.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {24}, number = {4}, pages = {043139}, doi = {10.1063/1.4903818}, pmid = {25554059}, issn = {1089-7682}, abstract = {The hierarchical shell models of turbulence including a spatial dimension, namely, spatiotemporal tree models, reproduce the intermittent behavior of Navier-Stokes equations in both space and time dimensions corresponding to high Reynolds number turbulent flows. This model is used, for the first time in this paper, in a one-dimensional flow zone containing a dispersed-phase particle that can be used in the study of dispersed-phase flows. In this paper, a straightforward method has been used to introduce discrete phase into the spatiotemporal tree model that leads to an increased amount of turbulent energy dissipation rate in the vicinity of the discrete phase. The effects of particle insertion and particle size on the turbulent energy dissipation rate are demonstrated. Moreover, the space-scale behavior of the time-averaged turbulent energy dissipation rate in the presence of dispersed phase is demonstrated by means of continuous wavelet transform.}, }
@article {pmid25553185, year = {2014}, author = {Song, J and Song, M and Kang, T and Kim, D and Lee, LP}, title = {Label-free density difference amplification-based cell sorting.}, journal = {Biomicrofluidics}, volume = {8}, number = {6}, pages = {064108}, pmid = {25553185}, issn = {1932-1058}, abstract = {The selective cell separation is a critical step in fundamental life sciences, translational medicine, biotechnology, and energy harvesting. Conventional cell separation methods are fluorescent activated cell sorting and magnetic-activated cell sorting based on fluorescent probes and magnetic particles on cell surfaces. Label-free cell separation methods such as Raman-activated cell sorting, electro-physiologically activated cell sorting, dielectric-activated cell sorting, or inertial microfluidic cell sorting are, however, limited when separating cells of the same kind or cells with similar sizes and dielectric properties, as well as similar electrophysiological phenotypes. Here we report a label-free density difference amplification-based cell sorting (dDACS) without using any external optical, magnetic, electrical forces, or fluidic activations. The conceptual microfluidic design consists of an inlet, hydraulic jump cavity, and multiple outlets. Incoming particles experience gravity, buoyancy, and drag forces in the separation chamber. The height and distance that each particle can reach in the chamber are different and depend on its density, thus allowing for the separation of particles into multiple outlets. The separation behavior of the particles, based on the ratio of the channel heights of the inlet and chamber and Reynolds number has been systematically studied. Numerical simulation reveals that the difference between the heights of only lighter particles with densities close to that of water increases with increasing the ratio of the channel heights, while decreasing Reynolds number can amplify the difference in the heights between the particles considered irrespective of their densities.}, }
@article {pmid25533171, year = {2014}, author = {Astumian, RD}, title = {Enhanced diffusion, chemotaxis, and pumping by active enzymes: progress toward an organizing principle of molecular machines.}, journal = {ACS nano}, volume = {8}, number = {12}, pages = {11917-11924}, doi = {10.1021/nn507039b}, pmid = {25533171}, issn = {1936-086X}, mesh = {*Chemotaxis ; Enzymes/*isolation &amp; purification ; *Microfluidic Analytical Techniques ; }, abstract = {Active enzymes diffuse more rapidly than inactive enzymes. This phenomenon may be due to catalysis-driven conformational changes that result in "swimming" through the aqueous solution. Recent additional work has demonstrated that active enzymes can undergo chemotaxis toward regions of high substrate concentration, whereas inactive enzymes do not, and, further, that active enzymes immobilized at surfaces can directionally pump liquids. In this Perspective, I will discuss these phenomena in light of Purcell's work on directed motion at low Reynold's number and in the context of microscopic reversibility. The conclusions suggest that a deep understanding of catalytically driven enhanced diffusion of enzymes and related phenomena can lead toward a general organizing principle for the design, characterization, and operation of molecular machines.}, }
@article {pmid25527319, year = {2015}, author = {Wang, S and Vafai, K}, title = {Analysis of Low Density Lipoprotein (LDL) Transport Within a Curved Artery.}, journal = {Annals of biomedical engineering}, volume = {43}, number = {7}, pages = {1571-1584}, doi = {10.1007/s10439-014-1219-x}, pmid = {25527319}, issn = {1573-9686}, mesh = {Arteries/*anatomy &amp; histology/*physiology ; Atherosclerosis/physiopathology ; Humans ; Lipoproteins, LDL/*physiology ; *Models, Cardiovascular ; }, abstract = {To elucidate the mechanism of the effect of LDL concentration on the thickening of intima in a curved artery, LDL transport in each layer of the curved arterial wall is studied analytically. A comprehensive concentration distribution expression of LDL in each layer of the curved artery wall is presented along with the characterization and estimation of the effect of curvature on the growth of atherosclerosis within the arterial wall. The effect of curvature on species concentration distribution is analyzed and the results are thoroughly benchmarked against prior pertinent works. The concentration at the interface of lumen and endothelium will directly affect the concentration profile inside the arterial wall layers. The results show that the average concentration in the circumferential direction is actually decreasing in the axial direction for a curved artery compared with a straight artery. Small radius ratio and Reynolds number will augment the LDL accumulation at the lumen endothelium interface. The increase in concentration at the lumen/endothelium interface in the axial direction has a minor effect on the concentration profile at the other wall interface layers.}, }
@article {pmid25526130, year = {2014}, author = {Dennis, DJ and Sogaro, FM}, title = {Distinct organizational States of fully developed turbulent pipe flow.}, journal = {Physical review letters}, volume = {113}, number = {23}, pages = {234501}, doi = {10.1103/PhysRevLett.113.234501}, pmid = {25526130}, issn = {1079-7114}, abstract = {Organizational states of turbulence are identified through novel analysis of large scale pipe flow experiments at a Reynolds number of 35 000. The distinct states are revealed by an azimuthal decomposition of the two-point spatial correlation of the streamwise velocity fluctuation. States with dominant azimuthal wave numbers corresponding to k_{θ}=2,3,4,5,6 are discovered and their structure revealed as a series of alternately rotating quasistreamwise vortices. Such organizational states are highly reminiscent of the nonlinear traveling wave solutions previously identified at Reynolds numbers an order of magnitude lower.}, }
@article {pmid25512586, year = {2015}, author = {Bourguet, R and Triantafyllou, MS}, title = {Vortex-induced vibrations of a flexible cylinder at large inclination angle.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {373}, number = {2033}, pages = {}, pmid = {25512586}, issn = {1471-2962}, abstract = {The free vibrations of a flexible circular cylinder inclined at 80° within a uniform current are investigated by means of direct numerical simulation, at Reynolds number 500 based on the body diameter and inflow velocity. In spite of the large inclination angle, the cylinder exhibits regular in-line and cross-flow vibrations excited by the flow through the lock-in mechanism, i.e. synchronization of body motion and vortex formation. A profound reconfiguration of the wake is observed compared with the stationary body case. The vortex-induced vibrations are found to occur under parallel, but also oblique vortex shedding where the spanwise wavenumbers of the wake and structural response coincide. The shedding angle and frequency increase with the spanwise wavenumber. The cylinder vibrations and fluid forces present a persistent spanwise asymmetry which relates to the asymmetry of the local current relative to the body axis, owing to its in-line bending. In particular, the asymmetrical trend of flow-body energy transfer results in a monotonic orientation of the structural waves. Clockwise and counter-clockwise figure eight orbits of the body alternate along the span, but the latter are found to be more favourable to structure excitation. Additional simulations at normal incidence highlight a dramatic deviation from the independence principle, which states that the system behaviour is essentially driven by the normal component of the inflow velocity.}, }
@article {pmid25502616, year = {2015}, author = {Khodarahmi, I}, title = {Comparing velocity and fluid shear stress in a stenotic phantom with steady flow: phase-contrast MRI, particle image velocimetry and computational fluid dynamics.}, journal = {Magma (New York, N.Y.)}, volume = {28}, number = {4}, pages = {385-393}, pmid = {25502616}, issn = {1352-8661}, mesh = {Constriction, Pathologic ; Hydrodynamics ; In Vitro Techniques ; Magnetic Resonance Imaging/*methods ; Phantoms, Imaging ; Pulsatile Flow ; Reproducibility of Results ; Rheology/*methods ; }, abstract = {OBJECT: This study aims to validate phase-contrast magnetic resonance imaging (PC-MRI) measurements of a steady flow through a severe stenotic phantom using particle image velocimetry (PIV) and computational fluid dynamics (CFD).<br><br>MATERIALS AND METHODS: The study was performed in an axisymmetric 87 % area stenosis model using an inlet Reynolds number (Re) of 160, corresponding to a jet Re of 444. Velocity patterns and estimated fluid shear stresses from three modalities were analyzed and compared qualitatively and quantitatively.<br><br>RESULTS: Visual analysis via contour subtraction and Bland-Altman plots showed good agreement for flow velocities and less agreement for maximum shear stress (MSS). The Pearson's coefficients of correlation between PC-MRI and PIV were 0.97 for the velocity field and 0.82 for the MSS. The corresponding parameters between PC-MRI and CFD were 0.96 and 0.84, respectively.<br><br>CONCLUSION: Findings indicate that PC-MRI can be implemented to estimate velocity flow fields and MSS; however, this method is not sufficiently accurate to quantify the MSS at regions of high shear rate.}, }
@article {pmid25497311, year = {2015}, author = {Ziffels, S and Bemelmans, NL and Durham, PG and Hickey, AJ}, title = {In vitro dry powder inhaler formulation performance considerations.}, journal = {Journal of controlled release : official journal of the Controlled Release Society}, volume = {199}, number = {}, pages = {45-52}, doi = {10.1016/j.jconrel.2014.11.035}, pmid = {25497311}, issn = {1873-4995}, mesh = {Albuterol/administration &amp; dosage/pharmacokinetics ; Anti-Asthmatic Agents/administration &amp; dosage/pharmacokinetics ; Budesonide/administration &amp; dosage/pharmacokinetics ; Chemistry, Pharmaceutical/*methods ; Drug Carriers ; Drug Delivery Systems ; *Dry Powder Inhalers ; Excipients ; In Vitro Techniques ; Lactose ; Particle Size ; Powders ; }, abstract = {It has long been desired to match airflow conditions during formulation evaluation to those of relevance to lung deposition. In this context several strategies have been adopted involving sampling at different: flow rate (without consideration of flow conditions, e.g. shear, Reynolds number, work function); pressure drop (with and without consideration of flow conditions) and; flow rate and pressure drop. Performance testing has focused on the influence of these sampling conditions on delivered dose uniformity and aerodynamic particle size distribution. However, in order to be physiologically relevant it is also important to know when the drug was delivered with respect to initiation of airflow as variation in this parameter would influence lung deposition. A light obscuration method of detecting the dose delivered from a dry powder inhaler while sampling for aerodynamic particle size distributions (APSD) by inertial impaction has been developed. Four formulations of albuterol sulfate and budesonide in sieved and milled lactose, respectively, were dispersed and their rate of delivery monitored. The differences observed have the potential to impact the site of delivery in the lungs. The rate of delivery of drug is clearly an important companion measurement to delivered dose and APSD if the intent is to predict the similarity of in vivo performance of dry powder inhaler products.}, }
@article {pmid25496731, year = {2015}, author = {Krick, J and Ackerman, JD}, title = {Adding ecology to particle capture models: numerical simulations of capture on a moving cylinder in crossflow.}, journal = {Journal of theoretical biology}, volume = {368}, number = {}, pages = {13-26}, doi = {10.1016/j.jtbi.2014.12.003}, pmid = {25496731}, issn = {1095-8541}, mesh = {Algorithms ; Computer Simulation ; *Ecological and Environmental Phenomena ; *Hydrodynamics ; *Models, Biological ; Particle Size ; Pollination ; Rheology/methods ; }, abstract = {The particle capture efficiency, η, of systems that remove suspended particles from ambient flow (e.g. suspension feeding, abiotic pollination) has been studied using static collectors in steady flows. Particle deposition on collectors moving due to fluid flow remains largely unknown, despite its ecological relevance. We used numerical modeling to simulate particle deposition on a 2D circular cylinder subject to flow-induced oscillation in a cross flow. Using parameter values relevant to wind pollination and other natural biological systems, we examined the influence of the direction, amplitude and frequency of the oscillation, the Stokes number (Stk=0.01-5, characterizing particle behavior), as well as the Reynolds number (Re=662 and 3309, characterizing flow regime) in steady and unsteady flow, on η. The numerical model was validated with empirical results for parts of the parameter space. Particle capture occurred via "inertial impaction", "direct interception" and "leeward deposition", as well as via a new mechanism, "collector chasing" for moving collectors. The η of an oscillating cylinder varied significantly relative to a static cylinder, depending on the parameters used, and on the magnitude of a numerical error that caused loss of particles. This variance of η was due to a change in relative momentum between the particle and the moving collector, which depends on Re, Stk and the oscillation parameters. Collector oscillation transverse to oncoming flow direction strongly increased η, whereas collector motion parallel to flow had little effect on capture efficiency. The oscillation also changed leeward capture significantly in some cases. For most conditions, however, leeward deposition was small. Results suggest that collector motion could have significant influence on the particle capture efficiency of natural systems, which indicates the need to incorporate these ecologically more relevant findings into current models. Empirical studies, however, are still necessary to validate these results and provide reliable data.}, }
@article {pmid25493887, year = {2014}, author = {Felderhof, BU}, title = {Collinear swimmer propelling a cargo sphere at low Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {5-1}, pages = {053013}, doi = {10.1103/PhysRevE.90.053013}, pmid = {25493887}, issn = {1550-2376}, abstract = {The swimming velocity and rate of dissipation of a linear chain consisting of two or three little spheres and a big sphere is studied on the basis of low Reynolds number hydrodynamics. The big sphere is treated as a passive cargo, driven by the tail of little spheres via hydrodynamic and direct elastic interaction. The fundamental solution of Stokes equations in the presence of a sphere with a no-slip boundary condition, as derived by Oseen, is used to model the hydrodynamic interactions between the big sphere and the little spheres.}, }
@article {pmid25493884, year = {2014}, author = {McComb, WD and Yoffe, SR and Linkmann, MF and Berera, A}, title = {Spectral analysis of structure functions and their scaling exponents in forced isotropic turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {5-1}, pages = {053010}, doi = {10.1103/PhysRevE.90.053010}, pmid = {25493884}, issn = {1550-2376}, abstract = {The pseudospectral method, in conjunction with a technique for obtaining scaling exponents ζ_{n} from the structure functions S_{n}(r), is presented as an alternative to the extended self-similarity (ESS) method and the use of generalized structure functions. We propose plotting the ratio |S_{n}(r)/S_{3}(r)| against the separation r in accordance with a standard technique for analyzing experimental data. This method differs from the ESS technique, which plots S_{n}(r) against S_{3}(r), with the assumption S_{3}(r)∼r. Using our method for the particular case of S_{2}(r) we obtain the result that the exponent ζ_{2} decreases as the Taylor-Reynolds number increases, with ζ_{2}→0.679±0.013 as R_{λ}→∞. This supports the idea of finite-viscosity corrections to the K41 prediction for S_{2}, and is the opposite of the result obtained by ESS. The pseudospectral method also permits the forcing to be taken into account exactly through the calculation of the energy input in real space from the work spectrum of the stirring forces.}, }
@article {pmid25493880, year = {2014}, author = {Jalali, MA and Alam, MR and Mousavi, S}, title = {Versatile low-Reynolds-number swimmer with three-dimensional maneuverability.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {5-1}, pages = {053006}, doi = {10.1103/PhysRevE.90.053006}, pmid = {25493880}, issn = {1550-2376}, abstract = {We design and simulate the motion of a swimmer, the Quadroar, with three-dimensional translation and reorientation capabilities in low-Reynolds-number conditions. The Quadroar is composed of an I-shaped frame whose body link is a simple linear actuator and four disks that can rotate about the axes of flange links. The time symmetry is broken by a combination of disk rotations and the one-dimensional expansion or contraction of the body link. The Quadroar propels on forward and transverse straight lines and performs full three-dimensional reorientation maneuvers, which enable it to swim along arbitrary trajectories. We find continuous operation modes that propel the swimmer on planar and three-dimensional periodic and quasiperiodic orbits. Precessing quasiperiodic orbits consist of slow lingering phases with cardioid or multiloop turns followed by directional propulsive phases. Quasiperiodic orbits allow the swimmer to access large parts of its neighboring space without using complex control strategies. We also discuss the feasibility of fabricating a nanoscale Quadroar by photoactive molecular rotors.}, }
@article {pmid25483750, year = {2014}, author = {Rossen, NS and Tarp, JM and Mathiesen, J and Jensen, MH and Oddershede, LB}, title = {Long-range ordered vorticity patterns in living tissue induced by cell division.}, journal = {Nature communications}, volume = {5}, number = {}, pages = {5720}, pmid = {25483750}, issn = {2041-1723}, mesh = {Biophysics ; Blood Flow Velocity ; *Cell Division ; Cytoplasm/metabolism ; Endothelial Cells/*cytology ; Fourier Analysis ; Hemodynamics ; Human Umbilical Vein Endothelial Cells ; Humans ; Hydrodynamics ; Microscopy, Phase-Contrast ; Models, Cardiovascular ; Models, Theoretical ; Stress, Mechanical ; }, abstract = {In healthy blood vessels with a laminar blood flow, the endothelial cell division rate is low, only sufficient to replace apoptotic cells. The division rate significantly increases during embryonic development and under halted or turbulent flow. Cells in barrier tissue are connected and their motility is highly correlated. Here we investigate the long-range dynamics induced by cell division in an endothelial monolayer under non-flow conditions, mimicking the conditions during vessel formation or around blood clots. Cell divisions induce long-range, well-ordered vortex patterns extending several cell diameters away from the division site, in spite of the system's low Reynolds number. Our experimental results are reproduced by a hydrodynamic continuum model simulating division as a local pressure increase corresponding to a local tension decrease. Such long-range physical communication may be crucial for embryonic development and for healing tissue, for instance around blood clots.}, }
@article {pmid25480040, year = {2014}, author = {Van Hirtum, A and Fujiso, Y and Nozaki, K}, title = {The role of initial flow conditions for sibilant fricative production.}, journal = {The Journal of the Acoustical Society of America}, volume = {136}, number = {6}, pages = {2922}, doi = {10.1121/1.4900595}, pmid = {25480040}, issn = {1520-8524}, abstract = {Sibilant fricative sound production depends on the geometric and flow properties of the production system. Nevertheless, few studies deal with the potential impact of flow properties other than the inlet volume flow rate on the noise produced. In this work, an experimental study is presented using a replica based on a reconstructed oral cavity for the phoneme /s/. Initial flow conditions upstream from the sibilant groove are altered by varying the method of air supply. Statistical moments of the initial velocity distribution are characterized using hot-film anemometry and related to spectral features of the radiated acoustic pressure. Discrepancies in the dynamic amplitude (≤25%) and negative spectral slope (≤35%) observed at a constant Reynolds number but different initial upstream flow conditions are of the same order of magnitude as those previously reported in humans. This suggests that consideration of the upstream flow conditions is important in the study of sibilant fricative sound production.}, }
@article {pmid25474212, year = {2014}, author = {Hina, S and Mustafa, M and Hayat, T}, title = {Peristaltic motion of Johnson-Segalman fluid in a curved channel with slip conditions.}, journal = {PloS one}, volume = {9}, number = {12}, pages = {e114168}, pmid = {25474212}, issn = {1932-6203}, mesh = {Body Fluids/*physiology ; Computer Graphics ; *Hydrodynamics ; *Models, Biological ; *Movement ; *Peristalsis ; Software ; }, abstract = {Slip effects on the peristaltic transport of Johnson-Segalman fluid through a curved channel have been addressed. The influence of wall properties is also analyzed. Long wavelength and low Reynolds number assumptions have been utilized in the mathematical formulation of the problem. The equations so formed have been solved numerically by shooting method through computational software Mathematica 8. In addition the analytic solution for small Weissenberg number (elastic parameter) is computed through a regular perturbation method. An excellent agreement is noticed between the two solutions. The results indicate an increase in the magnitude of velocity with an intensification in the slip effect. Moreover the size and circulation of the trapped boluses increase with an increase in the slip parameter. Unlike the planar channel, the profiles of axial velocity are not symmetric about the central line of the channel.}, }
@article {pmid25460608, year = {2014}, author = {Hayat, T and Tanveer, A and Yasmin, H and Alsaedi, A}, title = {Homogeneous-heterogeneous reactions in peristaltic flow with convective conditions.}, journal = {PloS one}, volume = {9}, number = {12}, pages = {e113851}, pmid = {25460608}, issn = {1932-6203}, mesh = {*Convection ; Models, Theoretical ; *Peristalsis ; *Rheology ; Solutions ; Temperature ; }, abstract = {This article addresses the effects of homogeneous-heterogeneous reactions in peristaltic transport of Carreau fluid in a channel with wall properties. Mathematical modelling and analysis have been carried out in the presence of Hall current. The channel walls satisfy the more realistic convective conditions. The governing partial differential equations along with long wavelength and low Reynolds number considerations are solved. The results of temperature and heat transfer coefficient are analyzed for various parameters of interest.}, }
@article {pmid25455807, year = {2015}, author = {Dukhin, SS and Kovalchuk, VI and Gochev, GG and Lotfi, M and Krzan, M and Malysa, K and Miller, R}, title = {Dynamics of Rear Stagnant Cap formation at the surface of spherical bubbles rising in surfactant solutions at large Reynolds numbers under conditions of small Marangoni number and slow sorption kinetics.}, journal = {Advances in colloid and interface science}, volume = {222}, number = {}, pages = {260-274}, doi = {10.1016/j.cis.2014.10.002}, pmid = {25455807}, issn = {1873-3727}, abstract = {On the surface of bubbles rising in a surfactant solution the adsorption process proceeds and leads to the formation of a so called Rear Stagnant Cap (RSC). The larger this RSC is the stronger is the retardation of the rising velocity. The theory of a steady RSC and steady retarded rising velocity, which sets in after a transient stage, has been generally accepted. However, a non-steady process of bubble rising starting from the initial zero velocity represents an important portion of the trajectory of rising, characterized by a local velocity profile (LVP). As there is no theory of RSC growth for large Reynolds numbers Re » 1 so far, the interpretation of LVPs measured in this regime was impossible. It turned out, that an analytical theory for a quasi-steady growth of RSC is possible for small Marangoni numbers Ma « 1, i.e. when the RSC is almost completely compressed, which means a uniform surface concentration Γ(θ)=Γ(∞) within the RSC. Hence, the RSC angle ψ(t) is obtained as a function of the adsorption isotherm parameters and time t. From the steady velocity v(st)(ψ), the dependence of non-steady velocity on time is obtained by employing v(st)[ψ(t)] via a quasi-steady approximation. The measurement of LVP creates a promising new opportunity for investigation of the RSC dynamics and adsorption kinetics. While adsorption and desorption happen at the same localization in the classical methods, in rising bubble experiments desorption occurs mainly within RSC while adsorption on the mobile part of the bubble surface. The desorption flux from RSC is proportional to αΓ(∞), while it is usually αΓ. The adsorption flux at the mobile surface above RSC can be assumed proportional to βC0, while it is usually βC0(1-Γ/Γ(∞)). These simplifications may become favorable in investigations of the adsorption kinetics for larger molecules, in particular for globular proteins, which essentially stay at an interface once adsorbed.}, }
@article {pmid25434694, year = {2016}, author = {Chen, Z and Zhan, F and Ding, J and Zhang, X and Deng, X}, title = {A new stent with streamlined cross-section can suppress monocyte cell adhesion in the flow disturbance zones of the endovascular stent.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {19}, number = {1}, pages = {60-66}, doi = {10.1080/10255842.2014.984701}, pmid = {25434694}, issn = {1476-8259}, mesh = {Cell Adhesion ; *Hemorheology ; Humans ; Monocytes/*cytology ; Perfusion ; *Stents ; Stress, Mechanical ; U937 Cells ; }, abstract = {We proposed a new stent with streamlined cross-sectional wires, which is different from the clinical coronary stents with square or round cross-sections. We believe the new stent might have better hemodynamic performance than the clinical metal stents. To test the hypothesis, we designed an experimental study to compare the performance of the new stent with the clinical stents in terms of monocyte (U-937 cells) adhesion. The results showed that when compared with the clinical stents, the adhesion of U-937 cells were much less in the new stent. The results also showed that, when Reynolds number increased from 180 (the rest condition for the coronary arteries) to 360 (the strenuous exercise condition for the coronary arteries), the flow disturbance zones in the clinical stents became larger, while they became smaller with the new stent. The present experimental study therefore suggests that the optimization of the cross-sectional shape of stent wires ought to be taken into consideration in the design of endovascular stents.}, }
@article {pmid25430137, year = {2014}, author = {Krynkin, A and Horoshenkov, KV and Nichols, A and Tait, SJ}, title = {A non-invasive acoustical method to measure the mean roughness height of the free surface of a turbulent shallow water flow.}, journal = {The Review of scientific instruments}, volume = {85}, number = {11}, pages = {114902}, doi = {10.1063/1.4901932}, pmid = {25430137}, issn = {1089-7623}, abstract = {In this paper, the directivity of the airborne sound field scattered by a dynamically rough free flow surface in a flume is used to determine the mean roughness height for six hydraulic conditions in which the uniform depth of the turbulent flow. The nonlinear curve fitting method is used to minimize the error between the predicted directivity and directivity data. The data fitting algorithm is based on the averaged solution for the scattered sound pressure as a function of angle which is derived through the Kirchhoff integral and its approximations. This solution takes into account the directivity of the acoustic source. For the adopted source and receiver geometry and acoustic frequency it is shown that the contribution from the stationary phase point (single specular point on the rough surface) yields similar results to those which can be obtained through the full Kirchhoff's integral. The accuracy in the inverted mean roughness height is comparable to that achieved with an array of conductive wave probes. This method enables non-invasive estimation of the flow Reynolds number and uniform flow depth.}, }
@article {pmid25410423, year = {2014}, author = {Das, S and Kumar, A}, title = {Formation and post-formation dynamics of bacterial biofilm streamers as highly viscous liquid jets.}, journal = {Scientific reports}, volume = {4}, number = {}, pages = {7126}, pmid = {25410423}, issn = {2045-2322}, mesh = {Biofilms/*growth &amp; development ; Elasticity ; *Models, Statistical ; Pseudomonas aeruginosa/chemistry/*physiology ; Pseudomonas fluorescens/chemistry/*physiology ; Rheology ; Shear Strength ; Staphylococcus epidermidis/chemistry/*physiology ; Stress, Mechanical ; Viscosity ; }, abstract = {It has been recently reported that in presence of low Reynolds number (Re ≪ 1) transport, preformed bacterial biofilms, several hours after their formation, may degenerate in form of filamentous structures, known as streamers. In this work, we explain that such streamers form as the highly viscous liquid states of the intrinsically viscoelastic biofilms. Such "viscous liquid" state can be hypothesized by noting that the time of appearance of the streamers is substantially larger than the viscoelastic relaxation time scale of the biofilms, and this appearance is explained by the inability of a viscous liquid to withstand external shear. Further, by identifying the post formation dynamics of the streamers as that of a viscous liquid jet in a surrounding flow field, we can interpret several unexplained issues associated with the post-formation dynamics of streamers, such as the clogging of the flow passage or the exponential time growth of streamer dimensions. Overall our manuscript provides a biophysical basis for understanding the evolution of biofilm streamers in creeping flows.}, }
@article {pmid25403834, year = {2014}, author = {Felderhof, BU}, title = {Swimming of an assembly of rigid spheres at low Reynolds number.}, journal = {The European physical journal. E, Soft matter}, volume = {37}, number = {11}, pages = {110}, pmid = {25403834}, issn = {1292-895X}, abstract = {A matrix formulation is derived for the calculation of the swimming speed and the power required for swimming of an assembly of rigid spheres immersed in a viscous fluid of infinite extent. The spheres may have arbitrary radii and may interact with elastic forces. The analysis is based on the Stokes mobility matrix of the set of spheres, defined in low Reynolds number hydrodynamics. For small amplitude, swimming optimization of the swimming speed at given power leads to an eigenvalue problem. The method allows straightforward calculation of the swimming performance of structures modeled as assemblies of interacting rigid spheres.}, }
@article {pmid25381677, year = {2014}, author = {Han, JS and Chang, JW and Kim, ST}, title = {Reynolds number dependency of an insect-based flapping wing.}, journal = {Bioinspiration &amp; biomimetics}, volume = {9}, number = {4}, pages = {046012}, doi = {10.1088/1748-3182/9/4/046012}, pmid = {25381677}, issn = {1748-3190}, mesh = {Aircraft/*instrumentation ; Animals ; Biological Clocks/physiology ; Biomimetics/*instrumentation/methods ; Computer Simulation ; Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Flight, Animal/*physiology ; Insecta/*physiology ; *Models, Biological ; Rheology/*methods ; Viscosity ; Wings, Animal/*physiology ; }, abstract = {Aerodynamic characteristics depending on Reynolds number (Re) ranges were studied to investigate the suitable design parameters of an insect-based micro air vehicle (MAV). The tests centered on the wing rotation timing and Re ranges, and were conducted to understand the lift augmentations and unsteady effects. A dynamically scaled-up flapping wing controlled by a pair of servos was installed underwater with a micro force/torque sensor. A high-speed camera and a laser sheet were also put in front of the water tank for the time-resolved digital particle image velocimetry (DPIV). The lift augmentations clearly appeared at low Re and were well reflected on the insect's flight range. In the case of the high Re, however, the peak standing for the wing–wake interaction was delayed, and the pitching-up rotation was not able to lead to another lift enhancement, i.e., rotational lift. In such Re, the mean CL and the L/D of the advanced rotation were substantially decreased from those of the other rotations. The DPIV results at high Re well described turbulent characteristics such as the irregular, unstable, and high-intensity vortex structures with a short temporal delay. In the advanced rotation, the LEV in the rotational phase could not maintain the attachment. Thus, the rotational lift was not able to work. On the contrary, the temporal response delay benefitted the wing in the delayed rotation. Therefore, the wing in the delayed rotation had both a similar level of the mean CL and a higher marked L/D than those of the advanced rotation. Such results indicate that the high Re could interrupt lift augmentation mechanisms, and these augmentations would not be suitable for a heavier MAV. In conclusion, using adequate wing kinematics to acquire estimations of the weight and range of the Re is highly recommended at the aerodynamic design step.}, }
@article {pmid25379087, year = {2014}, author = {Shi, Y and Fox, RO and Olsen, MG}, title = {Micromixing visualization and quantification in a microscale multi-inlet vortex nanoprecipitation reactor using confocal-based reactive micro laser-induced fluorescence.}, journal = {Biomicrofluidics}, volume = {8}, number = {4}, pages = {044102}, pmid = {25379087}, issn = {1932-1058}, abstract = {A technique for visualizing and quantifying reactive mixing for laminar and turbulent flow in a microscale chemical reactor using confocal-based microscopic laser induced fluorescence (confocal μ-LIF) was demonstrated in a microscale multi-inlet vortex nanoprecipitation reactor. Unlike passive scalar μ-LIF, the reactive μ-LIF technique is able to visualize and quantify micromixing effects. The confocal imaging results indicated that the flow in the reactor was laminar and steady for inlet Reynolds numbers of 10, 53, and 93. Mixing and reaction were incomplete at each of these Reynolds numbers. The results also suggested that although mixing by diffusion was enhanced near the midplane of the reactor at Rej = 53 and 93 due to very thin bands of acidic and basic fluid forming as the fluid spiraled towards the center of the reactor, near the top, and bottom walls of the reactor, the lower velocities due to fluid friction with the walls hindered the formation of these thin bands, and, thus, resulted in large regions of unmixed and unreacted fluid. At Rej = 240, the flow was turbulent and unsteady. The mixing and reaction processes were still found to be incomplete even at this highest Reynolds number. At the reactor midplane, the flow images at Rej = 240 showed unmixed base fluid near the center of the reactor, suggesting that just as in the Rej = 53 and 93 cases, lower velocities near the top and bottom walls of the reactor hinder the mixing and rection of the acidic and basic streams. Ensemble averages of line-scan profiles for the Rej = 240 were then calculated to provide statistical quantification of the microscale mixing in the reactor. These results further demonstrate that even at this highest Reynolds number investigated, mixing and reaction are incomplete. Visualization and quantification of micromixing using this reactive μ-LIF technique can prove useful in the validation of computational fluid dynamics models of micromixing within microscale chemical reactors.}, }
@article {pmid25378709, year = {2014}, author = {Huang, H and He, X}, title = {Interfacial tension based on-chip extraction of microparticles confined in microfluidic Stokes flows.}, journal = {Applied physics letters}, volume = {105}, number = {14}, pages = {143704}, pmid = {25378709}, issn = {0003-6951}, support = {R01 EB012108/EB/NIBIB NIH HHS/United States ; }, abstract = {Microfluidics involving two immiscible fluids (oil and water) has been increasingly used to produce hydrogel microparticles with wide applications. However, it is difficult to extract the microparticles out of the microfluidic Stokes flows of oil that have a Reynolds number (the ratio of inertia to viscous force) much less than one, where the dominant viscous force tends to drive the microparticles to move together with the surrounding oil. Here, we present a passive method for extracting hydrogel microparticles in microfluidic Stokes flow from oil into aqueous extracting solution on-chip by utilizing the intrinsic interfacial tension between oil and the microparticles. We further reveal that the thickness of an "extended confining layer" of oil next to the interface between oil and aqueous extracting solution must be smaller than the radius of microparticles for effective extraction. This method uses a simple planar merging microchannel design that can be readily fabricated and further integrated into a fluidic system to extract microparticles for wide applications.}, }
@article {pmid25378268, year = {2014}, author = {Ishihara, D and Horie, T and Niho, T}, title = {An experimental and three-dimensional computational study on the aerodynamic contribution to the passive pitching motion of flapping wings in hovering flies.}, journal = {Bioinspiration &amp; biomimetics}, volume = {9}, number = {4}, pages = {046009}, doi = {10.1088/1748-3182/9/4/046009}, pmid = {25378268}, issn = {1748-3190}, mesh = {Animals ; Biological Clocks/*physiology ; Biomimetics/*methods ; Computer Simulation ; Diptera/*physiology ; Flight, Animal/*physiology ; *Models, Biological ; Rheology/*methods ; Stress, Mechanical ; Wings, Animal/anatomy &amp; histology/*physiology ; }, abstract = {The relative importance of the wing's inertial and aerodynamic forces is the key to revealing how the kinematical characteristics of the passive pitching motion of insect flapping wings are generated, which is still unclear irrespective of its importance in the design of insect-like micro air vehicles. Therefore, we investigate three species of flies in order to reveal this, using a novel fluid-structure interaction analysis that consists of a dynamically scaled experiment and a three-dimensional finite element analysis. In the experiment, the dynamic similarity between the lumped torsional flexibility model as a first approximation of the dipteran wing and the actual insect is measured by the Reynolds number Re, the Strouhal number St, the mass ratio M, and the Cauchy number Ch. In the computation, the three-dimension is important in order to simulate the stable leading edge vortex and lift force in the present Re regime over 254. The drawback of the present experiment is the difficulty in satisfying the condition of M due to the limitation of available solid materials. The novelty of the present analysis is to complement this drawback using the computation. We analyze the following two cases: (a) The equilibrium between the wing's elastic and fluid forces is dynamically similar to that of the actual insect, while the wing's inertial force can be ignored. (b) All forces are dynamically similar to those of the actual insect. From the comparison between the results of cases (a) and (b), we evaluate the contributions of the equilibrium between the aerodynamic and the wing's elastic forces and the wing's inertial force to the passive pitching motion as 80-90% and 10-20%, respectively. It follows from these results that the dipteran passive pitching motion will be based on the equilibrium between the wing's elastic and aerodynamic forces, while it will be enhanced by the wing's inertial force.}, }
@article {pmid25375605, year = {2014}, author = {Yakhot, V}, title = {Reynolds number of transition and self-organized criticality of strong turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {4}, pages = {043019}, doi = {10.1103/PhysRevE.90.043019}, pmid = {25375605}, issn = {1550-2376}, abstract = {A turbulent flow is characterized by velocity fluctuations excited in an extremely broad interval of wave numbers k>Λf, where Λf is a relatively small set of the wave vectors where energy is pumped into fluid by external forces. Iterative averaging over small-scale velocity fluctuations from the interval Λf<k≤Λ0, where η=2π/Λ0 is the dissipation scale, leads to an infinite number of "relevant" scale-dependent coupling constants (Reynolds numbers) Ren(k)=O(1). It is shown that in the infrared limit k→Λf, the Reynolds numbers Re(k)→Retr, where Retr is the recently numerically and experimentally discovered universal Reynolds number of "smooth" transition from Gaussian to anomalous statistics of spatial velocity derivatives. The calculated relation Re(Λf)=Retr "selects" the lowest-order nonlinearity as the only relevant one. This means that in the infrared limit k→Λf, all high-order nonlinearities generated by the scale elimination sum up to zero.}, }
@article {pmid25375600, year = {2014}, author = {Illingworth, SJ and Naito, H and Fukagata, K}, title = {Active control of vortex shedding: an explanation of the gain window.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {4}, pages = {043014}, doi = {10.1103/PhysRevE.90.043014}, pmid = {25375600}, issn = {1550-2376}, abstract = {This paper explains the gain window phenomenon seen in early experimental and computational studies on active, closed-loop control of vortex shedding, whereby shedding is completely suppressed only if the feedback gain lies within some narrow window of stabilizing gains. Using two-dimensional direct numerical simulations and reduced-order modeling techniques, a low-order, linear model of the cylinder wake is formed at a Reynolds number of 60. This model is used to reproduce and to explain the gain window seen in previous studies. It is shown that the gain window is not caused by the destabilization of a higher mode but rather is determined entirely by the behavior of the open-loop unstable mode under the action of the closed-loop controller. It is demonstrated that the time taken for actuated fluid to convect to the sensor location plays an important part in explaining this gain window. A similar analysis at a higher Reynolds number of 80 reveals that the wake remains unstable for all choices of the feedback gain. The study illustrates the limitations of closed-loop suppression of vortex shedding when a very simple control strategy is used.}, }
@article {pmid25375588, year = {2014}, author = {de la Cruz, JM and Vassilicos, JC and Rossi, L}, title = {Topologies of velocity-field stagnation points generated by a single pair of magnets in free-surface electromagnetic experiments.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {4}, pages = {043001}, doi = {10.1103/PhysRevE.90.043001}, pmid = {25375588}, issn = {1550-2376}, abstract = {The velocity fields generated by a static pair of magnets in free-surface electromagnetically forced flows are analyzed for different magnet attitudes, ionic currents, and brine depths. A wide range of laminar velocity fields is obtained despite the forcing simplicity. The velocity fields are classified according to their temporal mean flow topology, which strongly depends on the forcing geometry but barely on its strength, even through the bifurcation to unsteady regimes. The mean flow topology possesses a major influence on the critical Reynolds number Rec under which the steady velocity fields remain stable. The qualitative comparison of the dependence of Rec on the topology is in agreement with previous works. The unsteady configurations evidence the advection of smaller flow structures by the largest scales, commonly known as "sweeping."}, }
@article {pmid25373110, year = {2015}, author = {Kothandapani, M and Prakash, J}, title = {Influence of Heat Source, Thermal Radiation, and Inclined Magnetic Field on Peristaltic Flow of a Hyperbolic Tangent Nanofluid in a Tapered Asymmetric Channel.}, journal = {IEEE transactions on nanobioscience}, volume = {14}, number = {4}, pages = {385-392}, doi = {10.1109/TNB.2014.2363673}, pmid = {25373110}, issn = {1558-2639}, abstract = {In the present analytic thinking, we have modeled the governing equations of a two dimensional peristaltic transport of a Hyperbolic tangent nanofluid in the presence of a heat source/sink with the combined effects of thermal radiation and inclined magnetic field in a tapered asymmetric channel. The propagation of waves on the non-uniform walls to have different amplitudes and phase but the same wave speed is produced the tapered asymmetric channel. The equations of dimensionless temperature and nanoparticle concentration are solved analytically under assumptions of long wavelength and low Reynolds number. The governing equations of momentum of a hyperbolic tangent nanofluid for the tapered asymmetric channel have also been solved analytically using the regular perturbation method. The expression for average rise in pressure has been figured using numerical integrations. The effects of various physical parameters entering into the problem are discussed numerically and graphically. The phenomenon of trapping is also investigated. Furthermore, the received results show that the maximum pressure rise gets increased in case of non-Newtonian fluid when equated with Newtonian fluid.}, }
@article {pmid25369018, year = {2014}, author = {Qiu, T and Lee, TC and Mark, AG and Morozov, KI and Münster, R and Mierka, O and Turek, S and Leshansky, AM and Fischer, P}, title = {Swimming by reciprocal motion at low Reynolds number.}, journal = {Nature communications}, volume = {5}, number = {}, pages = {5119}, pmid = {25369018}, issn = {2041-1723}, mesh = {Animals ; Biomechanical Phenomena ; Cell Movement ; Models, Biological ; Pectinidae/*chemistry/*physiology ; Swimming ; Viscosity ; }, abstract = {Biological microorganisms swim with flagella and cilia that execute nonreciprocal motions for low Reynolds number (Re) propulsion in viscous fluids. This symmetry requirement is a consequence of Purcell's scallop theorem, which complicates the actuation scheme needed by microswimmers. However, most biomedically important fluids are non-Newtonian where the scallop theorem no longer holds. It should therefore be possible to realize a microswimmer that moves with reciprocal periodic body-shape changes in non-Newtonian fluids. Here we report a symmetric 'micro-scallop', a single-hinge microswimmer that can propel in shear thickening and shear thinning (non-Newtonian) fluids by reciprocal motion at low Re. Excellent agreement between our measurements and both numerical and analytical theoretical predictions indicates that the net propulsion is caused by modulation of the fluid viscosity upon varying the shear rate. This reciprocal swimming mechanism opens new possibilities in designing biomedical microdevices that can propel by a simple actuation scheme in non-Newtonian biological fluids.}, }
@article {pmid25353903, year = {2014}, author = {Weber, CR and Clark, DS and Cook, AW and Busby, LE and Robey, HF}, title = {Inhibition of turbulence in inertial-confinement-fusion hot spots by viscous dissipation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {5}, pages = {053106}, doi = {10.1103/PhysRevE.89.053106}, pmid = {25353903}, issn = {1550-2376}, abstract = {Achieving ignition in inertial confinement fusion (ICF) requires the formation of a high-temperature (>10 keV) central hot spot. Turbulence has been suggested as a mechanism for degrading the hot-spot conditions by altering transport properties, introducing colder, mixed material, or reducing the conversion of radially directed kinetic energy to hot-spot heating. We show, however, that the hot spot is very viscous, and the assumption of turbulent conditions in the hot spot is incorrect. This work presents the first high-resolution, three-dimensional simulations of National Ignition Facility (NIF) implosion experiments using detailed knowledge of implosion dynamics and instability seeds and including an accurate model of physical viscosity. We find that when viscous effects are neglected, the hot spot can exhibit a turbulent kinetic energy cascade. Viscous effects, however, are significant and strongly damp small-scale velocity structures, with a hot-spot Reynolds number in the range of only 10-100.}, }
@article {pmid25353889, year = {2014}, author = {Honey, RE and Hershberger, R and Donnelly, RJ and Bolster, D}, title = {Oscillating-grid experiments in water and superfluid helium.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {5}, pages = {053016}, doi = {10.1103/PhysRevE.89.053016}, pmid = {25353889}, issn = {1550-2376}, abstract = {Passing a fluid through a grid is a well-known mechanism used to study the properties of turbulence. Oscillating a horizontal grid vertically in a tank has also been used extensively and is considered to be a source of almost homogenous isotropic turbulence. When the oscillating grid is turned on a turbulent flow is induced. A front translates into the experimental tank, behind which the flow is highly turbulent. Long predicted that the growth of such a front would grow diffusively as the square root of time (i.e., d ∼ sqrt[t]) and Dickinson and Long presented experimental evidence for the diffusive result at a low mesh Reynolds number of 555. This paper revisits these experiments and attempts a set of two models for the advancing front in both square and round tanks. We do not observe significant differences between runs in square and round tanks. The experiments in water reach mesh Reynolds numbers of order 30000. Using some data from superfluid helium experiments we are able to explore mesh Reynolds numbers to about 43000. We find the power law for the advancing front decreases weakly with the mesh Reynolds number. Using a very long tank we find that the turbulent front stops completely at a certain depth and attempt a simple explanation for that behavior. We study the propagation of the turbulent front into tubes of different diameters inserted into the main tank. We show that these tubes exclude wavelengths much larger than the tube diameter. We explore the variation of the position of the steady-state boundary H on tube diameter D and find that H = cD with c ∼ 2. We suggest this may be explained by saturation of the energy-containing length scale ℓ(e). We also report on the effect of plugging up just one hole of the grid. Finally, we recall some earlier oscillating grid experiments in superfluid (4)He in the light of the present results.}, }
@article {pmid25353601, year = {2014}, author = {Nash, RW and Carver, HB and Bernabeu, MO and Hetherington, J and Groen, D and Krüger, T and Coveney, PV}, title = {Choice of boundary condition for lattice-Boltzmann simulation of moderate-Reynolds-number flow in complex domains.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {2}, pages = {023303}, doi = {10.1103/PhysRevE.89.023303}, pmid = {25353601}, issn = {1550-2376}, support = {//British Heart Foundation/United Kingdom ; }, mesh = {*Algorithms ; Animals ; Blood Flow Velocity/*physiology ; Blood Vessels/*physiology ; Blood Viscosity/physiology ; Computer Simulation ; Humans ; *Models, Cardiovascular ; *Numerical Analysis, Computer-Assisted ; Rheology/*methods ; }, abstract = {Modeling blood flow in larger vessels using lattice-Boltzmann methods comes with a challenging set of constraints: a complex geometry with walls and inlets and outlets at arbitrary orientations with respect to the lattice, intermediate Reynolds (Re) number, and unsteady flow. Simple bounce-back is one of the most commonly used, simplest, and most computationally efficient boundary conditions, but many others have been proposed. We implement three other methods applicable to complex geometries [Guo, Zheng, and Shi, Phys. Fluids 14, 2007 (2002); Bouzidi, Firdaouss, and Lallemand, Phys. Fluids 13, 3452 (2001); Junk and Yang, Phys. Rev. E 72, 066701 (2005)] in our open-source application hemelb. We use these to simulate Poiseuille and Womersley flows in a cylindrical pipe with an arbitrary orientation at physiologically relevant Re number (1-300) and Womersley (4-12) numbers and steady flow in a curved pipe at relevant Dean number (100-200) and compare the accuracy to analytical solutions. We find that both the Bouzidi-Firdaouss-Lallemand (BFL) and Guo-Zheng-Shi (GZS) methods give second-order convergence in space while simple bounce-back degrades to first order. The BFL method appears to perform better than GZS in unsteady flows and is significantly less computationally expensive. The Junk-Yang method shows poor stability at larger Re number and so cannot be recommended here. The choice of collision operator (lattice Bhatnagar-Gross-Krook vs multiple relaxation time) and velocity set (D3Q15 vs D3Q19 vs D3Q27) does not significantly affect the accuracy in the problems studied.}, }
@article {pmid25353575, year = {2014}, author = {Taghavi, SM and Larson, RG}, title = {Regularized thin-fiber model for nanofiber formation by centrifugal spinning.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {2}, pages = {023011}, doi = {10.1103/PhysRevE.89.023011}, pmid = {25353575}, issn = {1550-2376}, abstract = {We propose a regularized thin-fiber (string) model that overcomes past numerical limitations and allows determination of the steady fiber velocity and diameter of a semi-infinite Newtonian viscous fiber emerging from a nozzle rotating about an axis in the presence of centrifugal, inertial, and viscous forces of arbitrary magnitudes. The results are controlled by two dimensionless groups, namely, the Rossby number Rb expressing the ratio of inertial to centrifugal forces and the Reynolds number Re, the ratio of inertial to viscous forces. We find that for Rb < 0.5 and Re < 1, regularization of the string-model equations is required to provide numerical stability, which we achieve. Solutions are thereby obtained in which viscosity reduces curvature in the fiber trajectory; these solutions asymptotically approach the inviscid solution at large distances along the spin line. Thus, long spin lines reach a diameter that is independent of viscosity, as long as the fiber is sufficiently long, a criterion that is made clear in the paper. At Rb > 0.5, regularization is not required, the curvature in fiber trajectory is increased by viscosity, and the solution at large distances along the spin line does not converge to the inviscid result. Regimes of behavior in the plane formed by Re and Rb are mapped out and example behavior is given for each regime.}, }
@article {pmid25353568, year = {2014}, author = {Musacchio, S and Boffetta, G}, title = {Turbulent channel without boundaries: the periodic Kolmogorov flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {2}, pages = {023004}, doi = {10.1103/PhysRevE.89.023004}, pmid = {25353568}, issn = {1550-2376}, abstract = {The Kolmogorov flow provides an ideal instance of a virtual channel flow: It has no boundaries, but it possesses well defined mean flow in each half wavelength. We exploit this remarkable feature for the purpose of investigating the interplay between the mean flow and the turbulent drag of the bulk flow. By means of a set of direct numerical simulations at increasing Reynolds number, we show the dependence of the bulk turbulent drag on the amplitude of the mean flow. Further, we present a detailed analysis of the scale-by-scale energy balance, which describes how kinetic energy is redistributed among different regions of the flow while being transported toward small dissipative scales. Our results allow us to obtain an accurate prediction for the spatial energy transport at large scales.}, }
@article {pmid25353409, year = {2014}, author = {Gupta, A and Vincenzi, D and Pandit, R}, title = {Elliptical tracers in two-dimensional, homogeneous, isotropic fluid turbulence: the statistics of alignment, rotation, and nematic order.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {2}, pages = {021001}, doi = {10.1103/PhysRevE.89.021001}, pmid = {25353409}, issn = {1550-2376}, abstract = {We study the statistical properties of orientation and rotation dynamics of elliptical tracer particles in two-dimensional, homogeneous, and isotropic turbulence by direct numerical simulations. We consider both the cases in which the turbulent flow is generated by forcing at large and intermediate length scales. We show that the two cases are qualitatively different. For large-scale forcing, the spatial distribution of particle orientations forms large-scale structures, which are absent for intermediate-scale forcing. The alignment with the local directions of the flow is much weaker in the latter case than in the former. For intermediate-scale forcing, the statistics of rotation rates depends weakly on the Reynolds number and on the aspect ratio of particles. In contrast with what is observed in three-dimensional turbulence, in two dimensions the mean-square rotation rate increases as the aspect ratio increases.}, }
@article {pmid25338940, year = {2014}, author = {Bandyopadhyay, PR and Hellum, AM}, title = {Modeling how shark and dolphin skin patterns control transitional wall-turbulence vorticity patterns using spatiotemporal phase reset mechanisms.}, journal = {Scientific reports}, volume = {4}, number = {}, pages = {6650}, pmid = {25338940}, issn = {2045-2322}, mesh = {Animals ; Diffusion ; Dolphins/*physiology ; Movement/*physiology ; Nonlinear Dynamics ; Pigmentation/physiology ; Sharks/*physiology ; Skin Physiological Phenomena ; *Spatio-Temporal Analysis ; Zebrafish ; }, abstract = {Many slow-moving biological systems like seashells and zebrafish that do not contend with wall turbulence have somewhat organized pigmentation patterns flush with their outer surfaces that are formed by underlying autonomous reaction-diffusion (RD) mechanisms. In contrast, sharks and dolphins contend with wall turbulence, are fast swimmers, and have more organized skin patterns that are proud and sometimes vibrate. A nonlinear spatiotemporal analytical model is not available that explains the mechanism underlying control of flow with such proud patterns, despite the fact that shark and dolphin skins are major targets of reverse engineering mechanisms of drag and noise reduction. Comparable to RD, a minimal self-regulation model is given for wall turbulence regeneration in the transitional regime--laterally coupled, diffusively--which, although restricted to pre-breakdown durations and to a plane close and parallel to the wall, correctly reproduces many experimentally observed spatiotemporal organizations of vorticity in both laminar-to-turbulence transitioning and very low Reynolds number but turbulent regions. We further show that the onset of vorticity disorganization is delayed if the skin organization is treated as a spatiotemporal template of olivo-cerebellar phase reset mechanism. The model shows that the adaptation mechanisms of sharks and dolphins to their fluid environment have much in common.}, }
@article {pmid25314537, year = {2014}, author = {Herault, J and Pétrélis, F}, title = {Optimum reduction of the dynamo threshold by a ferromagnetic layer located in the flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {3}, pages = {033015}, doi = {10.1103/PhysRevE.90.033015}, pmid = {25314537}, issn = {1550-2376}, mesh = {*Electromagnetic Phenomena ; *Magnets ; *Models, Theoretical ; Motion ; }, abstract = {We consider a fluid dynamo model generated by the flow on both sides of a moving layer. The magnetic permeability of the layer is larger than that of the flow. We show that there exists an optimum value of magnetic permeability for which the critical magnetic Reynolds number for dynamo onset is smaller than for a nonmagnetic material and also smaller than for a layer of infinite magnetic permeability. We present a mechanism that provides an explanation for recent experimental results. A similar effect occurs when the electrical conductivity of the layer is large.}, }
@article {pmid25314534, year = {2014}, author = {Lee, W and Kim, Y and Olson, SD and Lim, S}, title = {Nonlinear dynamics of a rotating elastic rod in a viscous fluid.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {3}, pages = {033012}, doi = {10.1103/PhysRevE.90.033012}, pmid = {25314534}, issn = {1550-2376}, mesh = {*Elasticity ; Nonlinear Dynamics ; *Rotation ; *Viscosity ; }, abstract = {The dynamics of an elastic rod in a viscous fluid at zero Reynolds number is investigated when the bottom end of the rod is tethered at a point in space and rotates at a prescribed angular frequency, while the other part of the rod freely moves through the fluid. A rotating elastic rod, which is intrinsically straight, exhibits three dynamical motions: twirling, overwhirling, and whirling. The first two motions are stable, whereas the last motion is unstable. The stability of dynamical motions is determined by material and geometrical properties of the rod, fluid properties, and the angular frequency of the rod. We employ the regularized Stokes flow to describe the fluid motion and the Kirchhoff rod model to describe the elastic rod. Our simulation results display subcritical Hopf bifurcation diagrams indicating the bistability region. We also investigate the whirling motion generated by the rotation of an intrinsically bent rod. It is observed that the angular frequency determines the handedness of the whirling rod and thus the flow direction and that there is a critical frequency which separates the positive (upward) flow at frequencies above it from the negative (downward) flow at frequencies below it.}, }
@article {pmid25314533, year = {2014}, author = {Aouane, O and Thiébaud, M and Benyoussef, A and Wagner, C and Misbah, C}, title = {Vesicle dynamics in a confined Poiseuille flow: from steady state to chaos.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {3}, pages = {033011}, doi = {10.1103/PhysRevE.90.033011}, pmid = {25314533}, issn = {1550-2376}, mesh = {Cell Shape ; Elasticity ; *Erythrocytes/cytology ; Lipid Bilayers ; *Models, Cardiovascular ; Motion ; Nonlinear Dynamics ; }, abstract = {Red blood cells (RBCs) are the major component of blood, and the flow of blood is dictated by that of RBCs. We employ vesicles, which consist of closed bilayer membranes enclosing a fluid, as a model system to study the behavior of RBCs under a confined Poiseuille flow. We extensively explore two main parameters: (i) the degree of confinement of vesicles within the channel and (ii) the flow strength. Rich and complex dynamics for vesicles are revealed, ranging from steady-state shapes (in the form of parachute and slipper shapes) to chaotic dynamics of shape. Chaos occurs through a cascade of multiple periodic oscillations of the vesicle shape. We summarize our results in a phase diagram in the parameter plane (degree of confinement and flow strength). This finding highlights the level of complexity of a flowing vesicle in the small Reynolds number where the flow is laminar in the absence of vesicles and can be rendered turbulent due to elasticity of vesicles.}, }
@article {pmid25314529, year = {2014}, author = {Cheang, UK and Meshkati, F and Kim, D and Kim, MJ and Fu, HC}, title = {Minimal geometric requirements for micropropulsion via magnetic rotation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {3}, pages = {033007}, doi = {10.1103/PhysRevE.90.033007}, pmid = {25314529}, issn = {1550-2376}, mesh = {Algorithms ; Elasticity ; Linear Models ; *Magnetic Phenomena ; Magnets ; Models, Theoretical ; Nanostructures ; Robotics ; *Rotation ; Swimming ; Torque ; }, abstract = {Controllable propulsion of microscale and nanoscale devices enhanced with additional functionality would enable the realization of miniaturized robotic swimmers applicable to transport and assembly, actuators, and drug delivery systems. Following biological examples, existing magnetically actuated microswimmers have been designed to use flexibility or chirality, presenting fabrication challenges. Here we show that, contrary to biomimetic expectations, magnetically actuated geometries with neither flexibility nor chirality can produce propulsion, through both experimental demonstration and a theoretical analysis, which elucidates the fundamental constraints on micropropulsion via magnetetic rotation. Our results advance existing paradigms of low-Reynolds-number propulsion, possibly enabling simpler fabrication and design of microswimmers and nanoswimmers.}, }
@article {pmid25314388, year = {2014}, author = {Karlin, IV and Bösch, F and Chikatamarla, SS}, title = {Gibbs' principle for the lattice-kinetic theory of fluid dynamics.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {3}, pages = {031302}, doi = {10.1103/PhysRevE.90.031302}, pmid = {25314388}, issn = {1550-2376}, mesh = {*Hydrodynamics ; Kinetics ; Mechanical Phenomena ; *Models, Theoretical ; }, abstract = {Gibbs' seminal prescription for constructing optimal states by maximizing the entropy under pertinent constraints is used to derive a lattice kinetic theory for the computation of high Reynolds number flows. The notion of modifying the viscosity to stabilize subgrid simulations is challenged in this kinetic framework. A lattice Boltzmann model for direct simulation of turbulent flows is presented without any need for tunable parameters and turbulent viscosity. Simulations at very high Reynolds numbers demonstrate a major extension of the operation range for fluid dynamics.}, }
@article {pmid25309949, year = {2014}, author = {Tisa, F and Raman, AA and Daud, WM}, title = {Simulation for supporting scale-up of a fluidized bed reactor for advanced water oxidation.}, journal = {TheScientificWorldJournal}, volume = {2014}, number = {}, pages = {348974}, pmid = {25309949}, issn = {1537-744X}, mesh = {Computer Simulation ; Hydrodynamics ; Hydrogen Peroxide/chemistry ; Kinetics ; Oxidation-Reduction ; Phenols/*chemistry/isolation &amp; purification ; Waste Disposal, Fluid ; Wastewater/*chemistry ; Water Pollutants, Chemical/*chemistry/isolation &amp; purification ; Water Purification/instrumentation/*methods ; }, abstract = {Simulation of fluidized bed reactor (FBR) was accomplished for treating wastewater using Fenton reaction, which is an advanced oxidation process (AOP). The simulation was performed to determine characteristics of FBR performance, concentration profile of the contaminants, and various prominent hydrodynamic properties (e.g., Reynolds number, velocity, and pressure) in the reactor. Simulation was implemented for 2.8 L working volume using hydrodynamic correlations, continuous equation, and simplified kinetic information for phenols degradation as a model. The simulation shows that, by using Fe(3+) and Fe(2+) mixtures as catalyst, TOC degradation up to 45% was achieved for contaminant range of 40-90 mg/L within 60 min. The concentration profiles and hydrodynamic characteristics were also generated. A subsequent scale-up study was also conducted using similitude method. The analysis shows that up to 10 L working volume, the models developed are applicable. The study proves that, using appropriate modeling and simulation, data can be predicted for designing and operating FBR for wastewater treatment.}, }
@article {pmid25283952, year = {2014}, author = {Yeh, PH and Hsu, JP and Tseng, S}, title = {Influence of polyelectrolyte shape on its sedimentation behavior: effect of relaxation electric field.}, journal = {Soft matter}, volume = {10}, number = {44}, pages = {8864-8874}, doi = {10.1039/c4sm01351d}, pmid = {25283952}, issn = {1744-6848}, abstract = {The sedimentation of an isolated, charged polyelectrolyte (PE) subjected to an applied field is modeled theoretically, taking into account the variation of its shape. In particular, the effects of double-layer relaxation, effective charge density, and strength of the induced relaxation electric field are examined. We show that the interaction of these effects yields complex and interesting sedimentation behaviors. For example, the behavior of the electric force acting on a loosely structured PE can be different from that on a compactly structured one; the former is dominated mainly by the convective fluid flow. For thick double layers, electric force has a local maximum as the Reynolds number varies, but tends to increase monotonically with increasing Reynolds number if the layer is thin. The drag factor is found to behave differently from literature results. The shape of a PE significantly influences its sedimentation behavior by affecting the amount of counterions attracted to its interior and the associated local electric field. Interestingly, a more stretched PE has a higher effective charge density but experiences a weaker electric force.}, }
@article {pmid25279733, year = {2014}, author = {Ismadi, MZ and Gupta, P and Fouras, A and Verma, P and Jadhav, S and Bellare, J and Hourigan, K}, title = {Flow characterization of a spinner flask for induced pluripotent stem cell culture application.}, journal = {PloS one}, volume = {9}, number = {10}, pages = {e106493}, pmid = {25279733}, issn = {1932-6203}, mesh = {Animals ; Batch Cell Culture Techniques ; Bioreactors ; Cell Culture Techniques/*instrumentation/*methods ; Cell Proliferation ; Induced Pluripotent Stem Cells/*cytology ; Mice ; Rheology ; }, abstract = {We present detailed quantitative measurement analyses for flow in a spinner flask with spinning rates between 20 to 45 RPM, utilizing the optical velocimetry measurement technique of Particle Image Velocimetry (PIV). A partial section of the impeller was immersed in the working fluid to reduce the shear forces induced on the cells cultured on microcarriers. Higher rotational speeds improved the mixing effect in the medium at the expense of a higher shear environment. It was found that the mouse induced pluripotent stem (iPS) cells achieved the optimum number of cells over 7 days in 25 RPM suspension culture. This condition translates to 0.0984 Pa of maximum shear stress caused by the interaction of the fluid flow with the bottom surface. However, inverse cell growth was obtained at 28 RPM culture condition. Such a narrow margin demonstrated that mouse iPS cells cultured on microcarriers are very sensitive to mechanical forces. This study provides insight to biomechanical parameters, specifically the shear stress distribution, for a commercially available spinner flask over a wide range of Reynolds number.}, }
@article {pmid25278637, year = {2014}, author = {Jus, Y and Longatte, E and Chassaing, JC and Sagaut, P}, title = {Low Mass-Damping Vortex-Induced Vibrations of a Single Cylinder at Moderate Reynolds Number.}, journal = {Journal of pressure vessel technology}, volume = {136}, number = {5}, pages = {0513051-0513057}, pmid = {25278637}, issn = {0094-9930}, abstract = {The feasibility and accuracy of large eddy simulation is investigated for the case of three-dimensional unsteady flows past an elastically mounted cylinder at moderate Reynolds number. Although these flow problems are unconfined, complex wake flow patterns may be observed depending on the elastic properties of the structure. An iterative procedure is used to solve the structural dynamic equation to be coupled with the Navier-Stokes system formulated in a pseudo-Eulerian way. A moving mesh method is involved to deform the computational domain according to the motion of the fluid structure interface. Numerical simulations of vortex-induced vibrations are performed for a freely vibrating cylinder at Reynolds number 3900 in the subcritical regime under two low mass-damping conditions. A detailed physical analysis is provided for a wide range of reduced velocities, and the typical three-branch response of the amplitude behavior usually reported in the experiments is exhibited and reproduced by numerical simulation.}, }
@article {pmid25273740, year = {2014}, author = {Bodenschatz, E and Bewley, GP and Nobach, H and Sinhuber, M and Xu, H}, title = {Variable density turbulence tunnel facility.}, journal = {The Review of scientific instruments}, volume = {85}, number = {9}, pages = {093908}, doi = {10.1063/1.4896138}, pmid = {25273740}, issn = {1089-7623}, abstract = {The Variable Density Turbulence Tunnel at the Max Planck Institute for Dynamics and Self-Organization in Göttingen, Germany, produces very high turbulence levels at moderate flow velocities, low power consumption, and adjustable kinematic viscosity between 10(-4) m(2)/s and 10(-7) m(2)/s. The Reynolds number can be varied by changing the pressure or flow rate of the gas or by using different non-flammable gases including air. The highest kinematic viscosities, and hence lowest Reynolds numbers, are reached with air or nitrogen at 0.1 bar. To reach the highest Reynolds numbers the tunnel is pressurized to 15 bars with the dense gas sulfur hexafluoride (SF6). Turbulence is generated at the upstream ends of two measurement sections with grids, and the evolution of this turbulence is observed as it moves down the length of the sections. We describe the instrumentation presently in operation, which consists of the tunnel itself, classical grid turbulence generators, and state-of-the-art nano-fabricated hot-wire anemometers provided by Princeton University [M. Vallikivi, M. Hultmark, S. C. C. Bailey, and A. J. Smits, Exp. Fluids 51, 1521 (2011)]. We report measurements of the characteristic scales of the flow and of turbulent spectra up to Taylor Reynolds number R(λ) ≈ 1600, higher than any other grid-turbulence experiment. We also describe instrumentation under development, which includes an active grid and a Lagrangian particle tracking system that moves down the length of the tunnel with the mean flow. In this configuration, the properties of the turbulence are adjustable and its structure is resolvable up to R(λ) ≈ 8000.}, }
@article {pmid25266059, year = {2015}, author = {Zhou, D and Xu, Z and Wang, Y and Wang, J and Hou, D and Dong, S}, title = {Simultaneous removal of multi-pollutants in an intimate integrated flocculation-adsorption fluidized bed.}, journal = {Environmental science and pollution research international}, volume = {22}, number = {5}, pages = {3794-3802}, pmid = {25266059}, issn = {1614-7499}, mesh = {Adsorption ; Aluminum Chloride ; Aluminum Compounds ; Aluminum Silicates ; Charcoal ; Chlorides ; Clay ; Flocculation ; Kaolin ; Microscopy, Electron, Scanning ; Phenols ; Polymers ; Silicon Dioxide ; Waste Disposal, Fluid/*methods ; *Water Movements ; Water Pollutants, Chemical/analysis/*isolation &amp; purification ; Water Purification/*methods ; }, abstract = {A novel intimate integrated flocculation-adsorption fluidized bed (IFAFB) was designed based on the hydraulic classification theory, and the operation, performance, characterization, and mechanisms of the novel process were developed. In this system, 150 mg · L(-1) kaolin clay and 100 mg · L(-1) phenol were used to simulate multi-pollutants in synthetic influent; resin beads and silica beads were the solid phases for the fluidized flocculator, and polymer aluminum chloride (PAC) and granular activated carbon were the flocculant and the adsorbent, respectively. The results showed that the Euler numeral was the most suitable dynamic parameter for flocculation in the fluidized bed when compared with the velocity gradient (G), Reynolds number (Re), and GRe (-1/2) . Additionally, the adsorption capacities of the fluidized regime were 8.77 and 24.70 mg · g(-1) greater than those of the fixed regime at superficial velocities of 6 and 8 mm · s(-1), respectively. In the IFAFB, the removal efficiencies of kaolin clay and phenol in the IFAFB reached 95 and 80 % simultaneously at total initial bed height of 35 mm. Flocs size, fractal dimension, and scanning electron microscopy (SEM) confirmed that the relationship of flocculation and adsorption in the IFAFB was mutually beneficial. Adsorption favored continuous growth of flocs and protected flocs from breakage, while flocculation removed fine particles as the first stage to prevent the adsorption of kaolin clay.}, }
@article {pmid25254236, year = {2014}, author = {Yarmand, H and Gharehkhani, S and Kazi, SN and Sadeghinezhad, E and Safaei, MR}, title = {Numerical investigation of heat transfer enhancement in a rectangular heated pipe for turbulent nanofluid.}, journal = {TheScientificWorldJournal}, volume = {2014}, number = {}, pages = {369593}, pmid = {25254236}, issn = {1537-744X}, mesh = {*Algorithms ; Aluminum Oxide/chemistry ; Computer Simulation ; Copper/chemistry ; *Hot Temperature ; Hydrodynamics ; Models, Chemical ; Nanoparticles/*chemistry ; Silicon Dioxide/chemistry ; *Thermal Conductivity ; Water/*chemistry ; Zinc Oxide/chemistry ; }, abstract = {Thermal characteristics of turbulent nanofluid flow in a rectangular pipe have been investigated numerically. The continuity, momentum, and energy equations were solved by means of a finite volume method (FVM). The symmetrical rectangular channel is heated at the top and bottom at a constant heat flux while the sides walls are insulated. Four different types of nanoparticles Al2O3, ZnO, CuO, and SiO2 at different volume fractions of nanofluids in the range of 1% to 5% are considered in the present investigation. In this paper, effect of different Reynolds numbers in the range of 5000 < Re < 25000 on heat transfer characteristics of nanofluids flowing through the channel is investigated. The numerical results indicate that SiO2-water has the highest Nusselt number compared to other nanofluids while it has the lowest heat transfer coefficient due to low thermal conductivity. The Nusselt number increases with the increase of the Reynolds number and the volume fraction of nanoparticles. The results of simulation show a good agreement with the existing experimental correlations.}, }
@article {pmid25252883, year = {2014}, author = {Bergmann, M and Iollo, A and Mittal, R}, title = {Effect of caudal fin flexibility on the propulsive efficiency of a fish-like swimmer.}, journal = {Bioinspiration &amp; biomimetics}, volume = {9}, number = {4}, pages = {046001}, doi = {10.1088/1748-3182/9/4/046001}, pmid = {25252883}, issn = {1748-3190}, mesh = {Animal Fins/*physiology ; Animals ; Biomimetics/*instrumentation ; Computer Simulation ; Computer-Aided Design ; Elastic Modulus/physiology ; Energy Transfer/*physiology ; Equipment Design ; Equipment Failure Analysis ; *Models, Biological ; Physical Exertion/physiology ; Rheology/methods ; Robotics/*instrumentation ; *Ships ; Stress, Mechanical ; Swimming/*physiology ; }, abstract = {A computational model is used to examine the effect of caudal fin flexibility on the propulsive efficiency of a self-propelled swimmer. The computational model couples a penalization method based Navier-Stokes solver with a simple model of flow induced deformation and self-propelled motion at an intermediate Reynolds number of about 1000. The results indicate that a significant increase in efficiency is possible by careful choice of caudal fin rigidity. The flow-physics underlying this observation is explained through the use of a simple hydrodynamic force model and guidelines for bioinspired designs of flexible fin propulsors are proposed.}, }
@article {pmid25250384, year = {2014}, author = {Wan Mohtar, WH and ElShafie, A}, title = {Characteristics of low reynolds number shear-free turbulence at an impermeable base.}, journal = {TheScientificWorldJournal}, volume = {2014}, number = {}, pages = {683537}, doi = {10.1155/2014/683537}, pmid = {25250384}, issn = {1537-744X}, mesh = {*Permeability ; Rheology/instrumentation/*methods ; *Shear Strength ; }, abstract = {Shear-free turbulence generated from an oscillating grid in a water tank impinging on an impermeable surface at varying Reynolds number 74 ≤ Re(l) ≤ 570 was studied experimentally, where the Reynolds number is defined based on the root-mean-square (r.m.s) horizontal velocity and the integral length scale. A particular focus was paid to the turbulence characteristics for low Re(l) < 150 to investigate the minimum limit of Re l obeying the profiles of rapid distortion theory. The measurements taken at near base included the r.m.s turbulent velocities, evolution of isotropy, integral length scales, and energy spectra. Statistical analysis of the velocity data showed that the anisotropic turbulence structure follows the theory for flows with Re(l) ≥ 117. At low Re(l) < 117, however, the turbulence profile deviated from the prediction where no amplification of horizontal velocity components was observed and the vertical velocity components were seen to be constant towards the tank base. Both velocity components sharply decreased towards zero at a distance of ≈ 1/3 of the integral length scale above the base due to viscous damping. The lower limit where Re(l) obeys the standard profile was found to be within the range 114 ≤ Re(l) ≤ 116.}, }
@article {pmid25238401, year = {2014}, author = {Zizzari, A and Bianco, M and Miglietta, R and del Mercato, LL and Carraro, M and Sorarù, A and Bonchio, M and Gigli, G and Rinaldi, R and Viola, I and Arima, V}, title = {Catalytic oxygen production mediated by smart capsules to modulate elastic turbulence under a laminar flow regime.}, journal = {Lab on a chip}, volume = {14}, number = {22}, pages = {4391-4397}, doi = {10.1039/c4lc00791c}, pmid = {25238401}, issn = {1473-0189}, abstract = {Liquid flow in microchannels is completely laminar and uniaxial, with a very low Reynolds number regime and long mixing lengths. To increase fluid mixing and solubility of reactants, as well as to reduce reaction time, complex three-dimensional networks inducing chaotic advection have to be designed. Alternatively, turbulence in the liquid can be generated by active mixing methods (magnetic, acoustic waves, etc.) or adding small quantities of elastic materials to the working liquid. Here, polyelectrolyte multilayer capsules embodying a catalytic polyoxometalate complex have been suspended in an aqueous solution and used to create elastic turbulence and to propel fluids inside microchannels as an alternative to viscoelastic polymers. The overall effect is enhanced and controlled by feeding the polyoxometalate-modified capsules with hydrogen peroxide, H2O2, thus triggering an on-demand propulsion due to oxygen evolution resulting from H2O2 decomposition. The quantification of the process is done by analysing some structural parameters of motion such as speed, pressure, viscosity, and Reynolds and Weissenberg numbers, directly obtained from the capillary dynamics of the aqueous mixtures with different concentrations of H2O2. The increases in fluid speed as well as the capsule-induced turbulence effects are proportional to the H2O2 added and therefore dependent on the kinetics of H2O2 dismutation.}, }
@article {pmid25226956, year = {2014}, author = {Ma, J and Xu, Y and Tian, F and Tang, X}, title = {IB-LBM study on cell sorting by pinched flow fractionation.}, journal = {Bio-medical materials and engineering}, volume = {24}, number = {6}, pages = {2547-2554}, doi = {10.3233/BME-141069}, pmid = {25226956}, issn = {1878-3619}, mesh = {Animals ; *Cell Physiological Phenomena ; Cell Separation/*instrumentation/methods ; Computer Simulation ; Equipment Design ; Equipment Failure Analysis ; Flow Cytometry/*instrumentation/methods ; Humans ; Microfluidic Analytical Techniques/*instrumentation/methods ; *Models, Biological ; }, abstract = {Separation of two categories of cells in pinched flow fractionation(PFF) device is simulated by employing IB-LBM. The separation performances at low Reynolds number (about 1) under different pinched segment widths, flow ratios, cell features, and distances between neighboring cells are studied and the results are compared with those predicted by the empirical formula. The simulation indicates that the diluent flow rate should approximate to or more than the flow rate of particle solution in order to get a relatively ideal separation performance. The discrepancy of outflow position between numerical simulation and the empirical prediction enlarges, when the cells become more flexible. Too short distance between two neighboring cells could lead to cell banding which would result in incomplete separation, and the relative position of two neighboring cells influences the banding of cells. The present study will probably provide some new applications of PFF, and make some suggestions on the design of PFF devices.}, }
@article {pmid25226942, year = {2014}, author = {Yu, CH and Kwon, TK}, title = {Study of parameters for evaluating flow reduction with stents in a sidewall aneurysm phantom model.}, journal = {Bio-medical materials and engineering}, volume = {24}, number = {6}, pages = {2417-2424}, doi = {10.3233/BME-141055}, pmid = {25226942}, issn = {1878-3619}, mesh = {Biomimetics/instrumentation ; Blood Flow Velocity ; Blood Pressure ; *Blood Vessel Prosthesis ; *Cerebrovascular Circulation ; *Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Humans ; Intracranial Aneurysm/*physiopathology/*therapy ; Laser-Doppler Flowmetry ; Phantoms, Imaging ; Shear Strength ; *Stents ; Treatment Outcome ; }, abstract = {The effect of stent design parameters such as porosity, pore density, number of strands, and strut angle to the artery were studied in vitro using particle image velocimetry (PIV). Five mesh stents were implanted into a sidewall aneurysm model. The flow features in a sidewall aneurysm silicone phantom model were investigated at a Reynolds number of 300. It was found that the lowest porosity stent had the best value for velocity and vorticity reduction in an aneurysm pocket. The stent with higher pore density had a tendency to decrease the mean and maximum velocities, but it was not superior to the effects of porosity. In addition, investigation of the evaluation system confirmed that higher stent strut angles to the parent artery had a tendency to lower mean velocity, as shown by PIV and CFD. However, this effect was relatively smaller compared to porosity and pore density. Our evaluation system suggested the best combinations of parameters for the development of an ideal stent would be lower porosity, higher pore density, and higher strut angle. The results obtained in this study indicated that our evaluation system could be useful for various purposes related to evaluation of endovascular interventional devices.}, }
@article {pmid25215821, year = {2014}, author = {Felderhof, BU and Jones, RB}, title = {Optimal translational swimming of a sphere at low Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {2}, pages = {023008}, doi = {10.1103/PhysRevE.90.023008}, pmid = {25215821}, issn = {1550-2376}, mesh = {*Models, Theoretical ; *Motion ; Swimming ; Viscosity ; }, abstract = {Swimming velocity and rate of dissipation of a sphere with surface distortions are discussed on the basis of the Stokes equations of low-Reynolds-number hydrodynamics. At first the surface distortions are assumed to cause an irrotational axisymmetric flow pattern. The efficiency of swimming is optimized within this class of flows. Subsequently, more general axisymmetric polar flows with vorticity are considered. This leads to a considerably higher maximum efficiency. An additional measure of swimming performance is proposed based on the energy consumption for given amplitude of stroke.}, }
@article {pmid25189373, year = {2014}, author = {Yaniv, S and Elad, D and Holzman, R}, title = {Suction feeding across fish life stages: flow dynamics from larvae to adults and implications for prey capture.}, journal = {The Journal of experimental biology}, volume = {217}, number = {Pt 20}, pages = {3748-3757}, doi = {10.1242/jeb.104331}, pmid = {25189373}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Computer Simulation ; Feeding Behavior/*physiology ; Larva/growth &amp; development/physiology ; Mouth/physiology ; Predatory Behavior ; Rheology ; Sea Bream/growth &amp; development/*physiology ; Sucking Behavior/physiology ; Swimming/physiology ; }, abstract = {Suction feeding is thought to be the primary mode of prey capture in most larval fishes. Similar to adult suction feeders, larvae swim towards their prey while rapidly expanding their mouth cavity to generate an inward flow of water that draws the prey into the mouth. Although larvae are known to experience flows with lower Reynolds numbers than adults, it is unclear how the suction-induced flow field changes throughout ontogeny, and how such changes relate to prey capture performance. To address these questions, we determined mouth dimensions and opening speeds in Sparus aurata from first-feeding larvae to adults. We proceeded to develop a computational model of mouth expansion in order to analyze the scaling of suction flows under the observed parameters. Larval fish produced suction flows that were around two orders of magnitude slower than those of adults. Compared with adult fish, in which flow speed decays steeply with distance in front of the mouth, flow speed decayed more gradually in larval fish. This difference indicates that viscous forces in low Reynolds number flows modify the spatial distribution flow speed in front of the mouth. Consequently, simulated predator-prey encounters showed that larval fish could capture inert prey from a greater distance compared with adults. However, if prey attempted to escape then larval fish performed poorly: simulations inferred capture success in only weakly escaping prey immediately in front of the mouth. These ontogenetic changes in Reynolds number, suction-induced flow field and feeding performance could explain a widespread ontogenetic diet shift from passive prey at early life stages to evasive prey as larvae mature.}, }
@article {pmid25170908, year = {2014}, author = {Abbasi, FM and Hayat, T and Ahmad, B and Chen, GQ}, title = {Slip effects on mixed convective peristaltic transport of copper-water nanofluid in an inclined channel.}, journal = {PloS one}, volume = {9}, number = {8}, pages = {e105440}, pmid = {25170908}, issn = {1932-6203}, mesh = {Copper/*chemistry ; Hot Temperature ; Metal Nanoparticles/*chemistry ; Models, Chemical ; Motion ; Rheology ; Water/*chemistry ; }, abstract = {Peristaltic transport of copper-water nanofluid in an inclined channel is reported in the presence of mixed convection. Both velocity and thermal slip conditions are considered. Mathematical modelling has been carried out using the long wavelength and low Reynolds number approximations. Resulting coupled system of equations is solved numerically. Quantities of interest are analyzed through graphs. Numerical values of heat transfer rate at the wall for different parameters are obtained and examined. Results showed that addition of copper nanoparticles reduces the pressure gradient, axial velocity at the center of channel, trapping and temperature. Velocity slip parameter has a decreasing effect on the velocity near the center of channel. Temperature of nanofluid increases with increase in the Grashoff number and channel inclination angle. It is further concluded that the heat transfer rate at the wall increases considerably in the presence of copper nanoparticles.}, }
@article {pmid25152217, year = {2014}, author = {Sen, S and Voorheis, HP}, title = {Protein folding: understanding the role of water and the low Reynolds number environment as the peptide chain emerges from the ribosome and folds.}, journal = {Journal of theoretical biology}, volume = {363}, number = {}, pages = {169-187}, doi = {10.1016/j.jtbi.2014.07.025}, pmid = {25152217}, issn = {1095-8541}, mesh = {Hydrodynamics ; Hydrophobic and Hydrophilic Interactions ; *Models, Biological ; Peptides/*chemistry ; Protein Biosynthesis/*physiology ; *Protein Folding ; Water/*chemistry ; }, abstract = {The mechanism of protein folding during early stages of the process has three determinants. First, moving water molecules obey the rules of low Reynolds number physics without an inertial component. Molecular movement is instantaneous and size insensitive. Proteins emerging from the ribosome move and rotate without an external force if they change shape, forming and propagating helical structures that increases translocational efficiency. Forward motion ceases when the shape change or propelling force ceases. Second, application of quantum field theory to water structure predicts the spontaneous formation of low density coherent units of fixed size that expel dissolved atmospheric gases. Structured water layers with both coherent and non-coherent domains, form a sheath around the new protein. The surface of exposed hydrophobic amino acids is protected from water contact by small nanobubbles of dissolved atmospheric gases, 5 or 6 molecules on average, that vibrate, attracting even widely separated resonating nanobubbles. This force results from quantum effects, appearing only when the system is within and interacts with an oscillating electromagnetic field. The newly recognized quantum force sharply bends the peptide and is part of a dynamic field determining the pathway of protein folding. Third, the force initiating the tertiary folding of proteins arises from twists at the position of each hydrophobic amino acid, that minimizes surface exposure of the hydrophobic amino acids and propagates along the protein. When the total bend reaches 360°, the leading segment of water sheath intersects the trailing segment. This steric self-intersection expels water from overlapping segments of the sheath and by Newton׳s second law moves the polypeptide chain in an opposite direction. Consequently, with very few exceptions that we enumerate and discuss, tertiary structures are absent from proteins without hydrophobic amino acids, which control the early stages of protein folding and the overall shape of protein. Consequently, proteins only adopt a limited number of forms. The formation of quaternary structures is not necessarily prevented by the absence of hydrophobic amino acids.}, }
@article {pmid25148210, year = {2014}, author = {Saini, R and Garg, A and Barz, DP}, title = {Streaming potential revisited: the influence of convection on the surface conductivity.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {30}, number = {36}, pages = {10950-10961}, doi = {10.1021/la501426c}, pmid = {25148210}, issn = {1520-5827}, abstract = {Electrokinetic phenomena play an important role in the electrical characterization of surfaces. In terms of planar or porous substrates, streaming potential and/or streaming current measurements can be used to determine the zeta potential of the substrates in contact with aqueous electrolytes. In this work, we perform electrical impedance spectroscopy measurements to infer the electrical resistance in a microchannel with the same conditions as for a streaming potential experiment. Novel correlations are derived to relate the streaming current and streaming potential to the Reynolds number of the channel flow. Our results not only quantify the influence of surface conductivity, and here especially the contribution of the stagnant layer, but also reveal that channel resistance and therefore zeta potential are influenced by the flow in the case of low ionic strengths. We conclude that convection can have a significant impact on the electrical double layer configuration which is reflected by changes in the surfaces conductivity.}, }
@article {pmid25145564, year = {2014}, author = {De Pauw, R and Choikhet, K and Desmet, G and Broeckhoven, K}, title = {Occurrence of turbulent flow conditions in supercritical fluid chromatography.}, journal = {Journal of chromatography. A}, volume = {1361}, number = {}, pages = {277-285}, doi = {10.1016/j.chroma.2014.07.088}, pmid = {25145564}, issn = {1873-3778}, mesh = {Chromatography, Supercritical Fluid/instrumentation/*methods ; Diffusion ; Kinetics ; Pressure ; Time Factors ; Viscosity ; }, abstract = {Having similar densities as liquids but with viscosities up to 20 times lower (higher diffusion coefficients), supercritical CO2 is the ideal (co-)solvent for fast and/or highly efficient separations without mass-transfer limitations or excessive column pressure drops. Whereas in liquid chromatography the flow remains laminar in both the packed bed and tubing, except in extreme cases (e.g. in a 75 μm tubing, pure acetonitrile at 5 ml/min), a supercritical fluid can experience a transition from laminar to turbulent flow in more typical operation modes. Due to the significant lower viscosity, this transition for example already occurs at 1.3 ml/min for neat CO2 when using connection tubing with an ID of 127 μm. By calculating the Darcy friction factor, which can be plotted versus the Reynolds number in a so-called Moody chart, typically used in fluid dynamics, higher values are found for stainless steel than PEEK tubing, in agreement with their expected higher surface roughness. As a result turbulent effects are more pronounced when using stainless steel tubing. The higher than expected extra-column pressure drop limits the kinetic performance of supercritical fluid chromatography and complicates the optimization of tubing ID, which is based on a trade-off between extra-column band broadening and pressure drop. One of the most important practical consequences is the non-linear increase in extra-column pressure drop over the tubing downstream of the column which leads to an unexpected increase in average column pressure and mobile phase density, and thus decrease in retention. For close eluting components with a significantly different dependence of retention on density, the selectivity can significantly be affected by this increase in average pressure. In addition, the occurrence of turbulent flow is also observed in the detector cell and connection tubing. This results in a noise-increase by a factor of four when going from laminar to turbulent flow (e.g. going from 0.5 to 2.5 ml/min for neat CO2).}, }
@article {pmid25122841, year = {2014}, author = {Maraj, EN and Akbar, NS and Nadeem, S}, title = {Biological analysis of Jeffrey nanofluid in a curved channel with heat dissipation.}, journal = {IEEE transactions on nanobioscience}, volume = {13}, number = {4}, pages = {431-437}, doi = {10.1109/TNB.2014.2338891}, pmid = {25122841}, issn = {1558-2639}, mesh = {Animals ; Computer Simulation ; *Energy Transfer ; Humans ; *Models, Biological ; Nanoparticles/*chemistry ; Peristalsis/*physiology ; Pressure ; Pulsatile Flow/*physiology ; Rheology/*methods ; }, abstract = {This study examines the peristaltic flow of Jeffrey nanofluid in a curved channel. The governing equations of Jeffrey nanofluid model for curved channel are derived including the effects of curvature. The highly nonlinear partial differential equations are simplified by using the long wave length and low Reynolds number assumptions. The reduced nonlinear partial differential equations are solved analytically with the help of homotopy perturbation method. The expression for pressure rise is computed through numerical integration. The physical features of pertinent parameters have been discussed by plotting the graphs of pressure rise, velocity, temperature, nanoparticle volume fraction and stream functions. It is observed that the curve-ness of the channel decreases the pressure rise in the peristaltic pumping region. Moreover, curve-ness of the channel effects the fluid flow by decreasing the fluid velocity near inner wall and increasing the velocity near the outer wall of the channel.}, }
@article {pmid25122386, year = {2014}, author = {Parra-Rojas, C and Soto, R}, title = {Casimir effect in swimmer suspensions.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {1}, pages = {013024}, doi = {10.1103/PhysRevE.90.013024}, pmid = {25122386}, issn = {1550-2376}, mesh = {*Models, Theoretical ; *Motion ; Suspensions ; }, abstract = {We show that the Casimir effect can emerge in microswimmer suspensions. In principle, two effects conspire against the development of Casimir effects in swimmer suspensions. First, at low Reynolds number, the force on any closed volume vanishes, but here the relevant effect is the drag by the flow produced by the swimmers, which can be finite. Second, the fluid velocity and the pressure are linear on the swimmer force dipoles, and averaging over the swimmer orientations would lead to a vanishing effect. However, being that the suspension is a discrete system, the noise terms of the coarse-grained equations depend on the density, which itself fluctuates, resulting in effective nonlinear dynamics. Applying the tools developed for other nonequilibrium systems to general coarse-grained equations for swimmer suspensions, the Casimir drag is computed on immersed objects, and it is found to depend on the correlation function between the rescaled density and dipolar density fields. By introducing a model correlation function with medium-range order, explicit expressions are obtained for the Casimir drag on a body. When the correlation length is much larger than the microscopic cutoff, the average drag is independent of the correlation length, with a range that depends only on the size of the immersed bodies.}, }
@article {pmid25122373, year = {2014}, author = {Jardin, T and David, L}, title = {Spanwise gradients in flow speed help stabilize leading-edge vortices on revolving wings.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {1}, pages = {013011}, doi = {10.1103/PhysRevE.90.013011}, pmid = {25122373}, issn = {1550-2376}, mesh = {Air ; Animals ; Biomechanical Phenomena ; Flight, Animal ; Kinetics ; *Mechanical Phenomena ; *Models, Biological ; *Wings, Animal/physiology ; }, abstract = {While a leading-edge vortex on an infinite translating wing is shed after a short distance of travel, its counterpart on a finite span revolving insect wing or maple seed membrane exhibits robust attachment. The latter explains the aerodynamic lift generated by such biological species. Here we analyze the mechanisms responsible for leading-edge vortex attachment. We compute the Navier-Stokes solution of the flow past a finite span wing (i) embedded in a uniform oncoming flow, (ii) embedded in a spanwise varying oncoming flow, and (iii) revolving about its root. We show that over flapping amplitudes typical of insect flight (ϕ = 120°), the spanwise gradient of the local wing speed may suffice in maintaining leading-edge vortex attachment. We correlate this result with the development of spanwise flow, driven by the spanwise gradient of pressure, and we evaluate the sensitivity of such a mechanism to the Reynolds number. It is noted, however, that leading-edge vortex attachment through the spanwise gradient of the local wing speed does not promote large lift, which ultimately arises from centrifugal and Coriolis effects.}, }
@article {pmid25122372, year = {2014}, author = {Li, GJ and Ardekani, AM}, title = {Hydrodynamic interaction of microswimmers near a wall.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {1}, pages = {013010}, pmid = {25122372}, issn = {1550-2376}, support = {UL1 TR000006/TR/NCATS NIH HHS/United States ; UL1 TR001108/TR/NCATS NIH HHS/United States ; }, mesh = {*Hydrodynamics ; *Models, Theoretical ; Motion ; }, abstract = {The hydrodynamics of an archetypal low-Reynolds number swimmer, called "squirmer," near a wall has been numerically studied. For a single squirmer, depending on the swimming mechanism, three different modes are distinguished: (a) the squirmer escaping from the wall, (b) the squirmer swimming along the wall at a constant distance and orientation angle, and (c) the squirmer swimming near the wall in a periodic trajectory. The role of inertial effects on the near-wall motion of the squirmer is quantified. The dynamics of multiple squirmers swimming between two walls is found to be very different from a single squirmer. Near-wall accumulation of squirmers are observed. At a relatively small concentration c = 0.1, around 60-80% of the squirmers are accumulated near the walls and attraction of pushers and pullers toward the wall is stronger than neutral squirmers. Near-wall squirmers orient normal to the wall, while in the bulk region, the squirmers are mostly oriented parallel to the wall. At a high concentration c = 0.4, the percentage of the near-wall squirmers is around 40%. The orientation angle of squirmers in the bulk region is more uniformly distributed at high concentrations. In the near-wall region, pullers repel each other, while pushers are attracted to each other and form clusters.}, }
@article {pmid25122366, year = {2014}, author = {Tilgner, A}, title = {Magnetic energy dissipation and mean magnetic field generation in planar convection-driven dynamos.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {1}, pages = {013004}, doi = {10.1103/PhysRevE.90.013004}, pmid = {25122366}, issn = {1550-2376}, mesh = {*Convection ; *Hydrodynamics ; *Magnetic Phenomena ; *Models, Theoretical ; Rotation ; }, abstract = {A numerical study of dynamos in rotating convecting plane layers is presented which focuses on magnetic energies and dissipation rates and the generation of mean fields (where the mean is taken over horizontal planes). The scaling of the magnetic energy with the flux Rayleigh number is different from the scaling proposed in spherical shells, whereas the same dependence of the magnetic dissipation length on the magnetic Reynolds number is found for the two geometries. Dynamos both with and without mean field exist in rapidly rotating convecting plane layers.}, }
@article {pmid25122298, year = {2014}, author = {Risbud, SR and Drazer, G}, title = {Directional locking in deterministic lateral-displacement microfluidic separation systems.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {90}, number = {1}, pages = {012302}, doi = {10.1103/PhysRevE.90.012302}, pmid = {25122298}, issn = {1550-2376}, mesh = {*Microfluidics ; Models, Molecular ; Molecular Conformation ; }, abstract = {We analyze the trajectory of suspended spherical particles moving through a square array of obstacles, in the deterministic limit and at zero Reynolds number. We show that in the dilute approximation of widely separated obstacles, the average motion of the particles is equivalent to the trajectory followed by a point particle moving through an array of obstacles with an effective radius. The effective radius accounts for the hydrodynamic as well as short-range repulsive nonhydrodynamic interactions between the suspended particles and the obstacles, and is equal to the critical offset at which particle trajectories become irreversible. Using this equivalent system we demonstrate the presence of directional locking in the trajectory of the particles and derive an inequality that accurately describes the "devil's staircase" type of structure observed in the migration angle as a function of the forcing direction. We use these results to determine the optimum resolution in the fractionation of binary mixtures using deterministic lateral-displacement microfluidic separation systems as well as to comment on the collision frequencies when the arrays of posts are utilized as immunocapture devices.}, }
@article {pmid25118607, year = {2014}, author = {Liangjie, M and Qingyou, L and Shouwei, Z}, title = {Experimental study of the vortex-induced vibration of drilling risers under the shear flow with the same shear parameter at the different Reynolds numbers.}, journal = {PloS one}, volume = {9}, number = {8}, pages = {e104806}, doi = {10.1371/journal.pone.0104806}, pmid = {25118607}, issn = {1932-6203}, mesh = {Computer Simulation ; Extraction and Processing Industry/*instrumentation ; *Models, Theoretical ; Oceans and Seas ; *Shear Strength ; *Vibration ; *Water Movements ; }, abstract = {A considerable number of studies for VIV under the uniform flow have been performed. However, research on VIV under shear flow is scarce. An experiment for VIV under the shear flow with the same shear parameter at the two different Reynolds numbers was conducted in a deep-water offshore basin. Various measurements were obtained by the fiber bragg grating strain sensors. Experimental data were analyzed by modal analysis method. Results show several valuable features. First, the corresponding maximum order mode of the natural frequency for shedding frequency is the maximum dominant vibration mode and multi-modal phenomenon is appeared in VIV under the shear flow, and multi-modal phenomenon is more apparent at the same shear parameter with an increasing Reynolds number under the shear flow effect. Secondly, the riser vibrates at the natural frequency and the dominant vibration frequency increases for the effect of the real-time tension amplitude under the shear flow and the IL vibration frequency is the similar with the CF vibration frequency at the Reynolds number of 1105 in our experimental condition and the IL dominant frequency is twice the CF dominant frequency with an increasing Reynolds number. In addition, the displacement trajectories at the different locations of the riser appear the same shape and the shape is changed at the same shear parameter with an increasing Reynolds number under the shear flow. The diagonal displacement trajectories are observed at the low Reynolds number and the crescent-shaped displacement trajectories appear with an increasing Reynolds number under shear flow in the experiment.}, }
@article {pmid25110161, year = {2014}, author = {Arun, RK and Chaudhury, K and Ghosh, M and Biswas, G and Chanda, N and Chakraborty, S}, title = {Controlled splitting and focusing of a stream of nanoparticles in a converging-diverging microchannel.}, journal = {Lab on a chip}, volume = {14}, number = {19}, pages = {3800-3808}, doi = {10.1039/c4lc00542b}, pmid = {25110161}, issn = {1473-0189}, abstract = {We demonstrate the potential of a converging-diverging microchannel to split a stream of nanoparticles towards the interfacial region of the dispersed and the carrier phases, introduced through the middle inlet and through the remaining two inlets respectively, while maintaining a low Reynolds number limit (<10) for the flow of both phases. In addition to the splitting of passive tracer particles, such as polystyrene beads as used herein, the present setup has the potential to be utilized for a controlled reaction and thereby the separation of products towards an intended location, as observed from the experimentation with silver-nanoparticles and hydrogen-peroxide solution. Moreover, the microscale dimension of the channel allows controlled deposition of the reaction product over the bottom surface of the channel, allowing the possibility of bottom-up fabrication of microscale features. We unveil the underlying hydrodynamics that lead to such behaviours through numerical simulations, which are consistent with the experimental observations. The phenomenological features are found to be guided by the splitting of the intrinsic streamlines conforming to the flow geometry under consideration.}, }
@article {pmid25109407, year = {2014}, author = {Maxwell, AD and Park, S and Vaughan, BL and Cain, CA and Grotberg, JB and Xu, Z}, title = {Trapping of embolic particles in a vessel phantom by cavitation-enhanced acoustic streaming.}, journal = {Physics in medicine and biology}, volume = {59}, number = {17}, pages = {4927-4943}, pmid = {25109407}, issn = {1361-6560}, support = {R01 EB008998/EB/NIBIB NIH HHS/United States ; }, mesh = {*Acoustics ; Embolism/*therapy ; Humans ; Phantoms, Imaging ; *Rheology ; Ultrasonic Therapy/*methods ; }, abstract = {Cavitation clouds generated by short, high-amplitude, focused ultrasound pulses were previously observed to attract, trap, and erode thrombus fragments in a vessel phantom. This phenomenon may offer a noninvasive method to capture and eliminate embolic fragments flowing through the bloodstream during a cardiovascular intervention. In this article, the mechanism of embolus trapping was explored by particle image velocimetry (PIV). PIV was used to examine the fluid streaming patterns generated by ultrasound in a vessel phantom with and without crossflow of blood-mimicking fluid. Cavitation enhanced streaming, which generated fluid vortices adjacent to the focus. The focal streaming velocity, uf, was as high as 120 cm/s, while mean crossflow velocities, uc, were imposed up to 14 cm/s. When a solid particle 3-4 mm diameter was introduced into crossflow, it was trapped near the focus. Increasing uf promoted particle trapping while increasing uc promoted particle escape. The maximum crossflow Reynolds number at which particles could be trapped, Rec, was approximately linear with focal streaming number, Ref, i.e. Rec = 0.25Ref + 67.44 (R(2) = 0.76) corresponding to dimensional velocities uc = 0.084uf + 3.122 for 20 < uf < 120 cm/s. The fluidic pressure map was estimated from PIV and indicated a negative pressure gradient towards the focus, trapping the embolus near this location.}, }
@article {pmid25105872, year = {2014}, author = {Lázaro, GR and Hernández-Machado, A and Pagonabarraga, I}, title = {Rheology of red blood cells under flow in highly confined microchannels: I. effect of elasticity.}, journal = {Soft matter}, volume = {10}, number = {37}, pages = {7195-7206}, doi = {10.1039/c4sm00894d}, pmid = {25105872}, issn = {1744-6848}, mesh = {Biophysical Phenomena ; Elasticity ; Erythrocyte Membrane/metabolism ; Erythrocytes/*cytology ; Humans ; Models, Biological ; Oscillometry ; Rheology/*methods ; Stress, Mechanical ; Surface Properties ; Viscosity ; }, abstract = {We analyze the rheology of dilute red blood cell suspensions in pressure driven flows at low Reynolds number, in terms of the morphologies and elasticity of the cells. We focus on narrow channels of width similar to the cell diameter, when the interactions with the walls dominate the cell dynamics. The suspension presents a shear-thinning behaviour, with a Newtonian-behaviour at low shear rates, an intermediate region of strong decay of the suspension viscosity, and an asymptotic regime at high shear rates in which the effective viscosity converges to that of the solvent. We identify the relevant aspects of cell elasticity that contribute to the rheological response of blood at high confinement. In a second paper, we will explore the focusing of red blood cells while flowing at high shear rates and how this effect is controlled by the geometry of the channel.}, }
@article {pmid25085867, year = {2014}, author = {Hall, CL and Calt, M}, title = {Computational modeling of thrombotic microparticle deposition in nonparallel flow regimes.}, journal = {Journal of biomechanical engineering}, volume = {136}, number = {11}, pages = {}, doi = {10.1115/1.4028134}, pmid = {25085867}, issn = {1528-8951}, mesh = {Biomechanical Phenomena ; *Blood Circulation ; Cell-Derived Microparticles/*pathology ; *Computer Simulation ; Constriction, Pathologic/pathology/physiopathology ; *Mechanical Phenomena ; Models, Biological ; Thrombosis/*pathology/*physiopathology ; }, abstract = {Thrombotic microparticles (MPs) released from cells and platelets in response to various stimuli are present in elevated numbers in various disease states that increase the risk for thrombotic events. In order to understand how particles of this size may localize in nonparallel flow regimes and increase thrombotic risk, a computational analysis of flow and MP deposition was performed for 3 deg of stenosis at moderate Reynolds number (20<Re<80) and for recirculation zones at low Reynolds (1) number. The results indicate that MP deposition results primarily from impaction and not by diffusive flux.}, }
@article {pmid25081386, year = {2014}, author = {Wu, D and Tawhai, MH and Hoffman, EA and Lin, CL}, title = {A numerical study of heat and water vapor transfer in MDCT-based human airway models.}, journal = {Annals of biomedical engineering}, volume = {42}, number = {10}, pages = {2117-2131}, pmid = {25081386}, issn = {1573-9686}, support = {S10-RR022421/RR/NCRR NIH HHS/United States ; U01 HL114494/HL/NHLBI NIH HHS/United States ; P30 DK054759/DK/NIDDK NIH HHS/United States ; R01-HL094315/HL/NHLBI NIH HHS/United States ; S10 RR022421/RR/NCRR NIH HHS/United States ; U01-HL114494/HL/NHLBI NIH HHS/United States ; R01 HL094315/HL/NHLBI NIH HHS/United States ; R01 HL112986/HL/NHLBI NIH HHS/United States ; P30 ES005605/ES/NIEHS NIH HHS/United States ; }, mesh = {Adult ; Aged ; Female ; *Hot Temperature ; Humans ; Humidity ; Male ; *Models, Biological ; *Respiratory Physiological Phenomena ; Respiratory System/*diagnostic imaging ; Tomography, X-Ray Computed ; *Water Loss, Insensible ; Young Adult ; }, abstract = {A three-dimensional (3D) thermo-fluid model is developed to study regional distributions of temperature and water vapor in three multi-detector row computed-tomography-based human airways with minute ventilations of 6, 15 and 30 L/min. A one-dimensional (1D) model is also solved to provide necessary initial and boundary conditions for the 3D model. Both 3D and 1D predicted temperature distributions agree well with available in vivo measurement data. On inspiration, the 3D cold high-speed air stream is split at the bifurcation to form secondary flows, with its cold regions biased toward the inner wall. The cold air flowing along the wall is warmed up more rapidly than the air in the lumen center. The repeated splitting pattern of air streams caused by bifurcations acts as an effective mechanism for rapid heat and mass transfer in 3D. This provides a key difference from the 1D model, where heating relies largely on diffusion in the radial direction, thus significantly affecting gradient-dependent variables, such as energy flux and water loss rate. We then propose the correlations for respective heat and mass transfer in the airways of up to 6 generations: [Formula: see text] and [Formula: see text], where Nu is the Nusselt number, Sh is the Sherwood number, Re is the branch Reynolds number, D a is the airway equivalent diameter, and [Formula: see text] is the tracheal equivalent diameter.}, }
@article {pmid25059738, year = {2015}, author = {Tripathi, D and Anwar Bég, O}, title = {Mathematica numerical simulation of peristaltic biophysical transport of a fractional viscoelastic fluid through an inclined cylindrical tube.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {18}, number = {15}, pages = {1648-1657}, doi = {10.1080/10255842.2014.940332}, pmid = {25059738}, issn = {1476-8259}, mesh = {Biological Transport ; *Biophysical Phenomena ; *Computer Simulation ; *Elasticity ; Friction ; Models, Biological ; Models, Theoretical ; *Numerical Analysis, Computer-Assisted ; Peristalsis/*physiology ; Pressure ; *Rheology ; Viscosity ; }, abstract = {This paper studies the peristaltic transport of a viscoelastic fluid (with the fractional second-grade model) through an inclined cylindrical tube. The wall of the tube is modelled as a sinusoidal wave. The flow analysis is presented under the assumptions of long wave length and low Reynolds number. Caputo's definition of fractional derivative is used to formulate the fractional differentiation. Analytical solutions are developed for the normalized momentum equations. Expressions are also derived for the pressure, frictional force, and the relationship between the flow rate and pressure gradient. Mathematica numerical computations are then performed. The results are plotted and analysed for different values of fractional parameter, material constant, inclination angle, Reynolds number, Froude number and peristaltic wave amplitude. It is found that fractional parameter and Froude number resist the flow pattern while material constant, Reynolds number, inclination of angle and amplitude aid the peristaltic flow. Furthermore, frictional force and pressure demonstrate the opposite behaviour under the influence of the relevant parameters emerging in the equations of motion. The study has applications in uretral biophysics, and also potential use in peristaltic pumping of petroleum viscoelastic bio-surfactants in chemical engineering and astronautical applications involving conveyance of non-Newtonian fluids (e.g. lubricants) against gravity and in conduits with deformable walls.}, }
@article {pmid25053861, year = {2014}, author = {Nevmerzhitskiy, NV and Sotskov, EA and Sen'kovskiy, ED and Krivonos, OL and Polovnikov, AA and Levkina, EV and Frolov, SV and Abakumov, SA and Marmyshev, VV}, title = {Study of the Reynolds Number Effect on the Process of Instability Transition Into the Turbulent Stage.}, journal = {Journal of fluids engineering}, volume = {136}, number = {9}, pages = {0912071-0912079}, pmid = {25053861}, issn = {0098-2202}, abstract = {The results of the experimental study of the Reynolds number effect on the process of the Rayleigh-Taylor (R-T) instability transition into the turbulent stage are presented. The experimental liquid layer was accelerated by compressed gas. Solid particles were scattered on the layer free surface to specify the initial perturbations in some experiments. The process was recorded with the use of a high-speed motion picture camera. The following results were obtained in experiments: (1) Long-wave perturbation is developed at the interface at the Reynolds numbers Re < 10[4]. If such perturbation growth is limited by a hard wall, the jet directed in gas is developed. If there is no such limitation, this perturbation is resolved into the short-wave ones with time, and their growth results in gas-liquid mixing. (2) Short-wave perturbations specified at the interface significantly reduce the Reynolds number Re for instability to pass into the turbulent mixing stage.}, }
@article {pmid25034393, year = {2014}, author = {Nadal, F and Pak, OS and Zhu, L and Brandt, L and Lauga, E}, title = {Rotational propulsion enabled by inertia.}, journal = {The European physical journal. E, Soft matter}, volume = {37}, number = {7}, pages = {16}, pmid = {25034393}, issn = {1292-895X}, mesh = {Biophysical Phenomena ; Cell Movement ; Hydrodynamics ; Models, Biological ; Models, Theoretical ; *Motion ; *Rotation ; Viscosity ; }, abstract = {The fluid mechanics of small-scale locomotion has recently attracted considerable attention, due to its importance in cell motility and the design of artificial micro-swimmers for biomedical applications. Most studies on the topic consider the ideal limit of zero Reynolds number. In this paper, we investigate a simple propulsion mechanism --an up-down asymmetric dumbbell rotating about its axis of symmetry-- unable to propel in the absence of inertia in a Newtonian fluid. Inertial forces lead to continuous propulsion for all finite values of the Reynolds number. We study computationally its propulsive characteristics as well as analytically in the small-Reynolds-number limit. We also derive the optimal dumbbell geometry. The direction of propulsion enabled by inertia is opposite to that induced by viscoelasticity.}, }
@article {pmid25024422, year = {2014}, author = {Gourdain, N and Sicot, F and Duchaine, F and Gicquel, L}, title = {Large eddy simulation of flows in industrial compressors: a path from 2015 to 2035.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2022}, pages = {20130323}, pmid = {25024422}, issn = {1364-503X}, abstract = {A better understanding of turbulent unsteady flows is a necessary step towards a breakthrough in the design of modern compressors. Owing to high Reynolds numbers and very complex geometry, the flow that develops in such industrial machines is extremely hard to predict. At this time, the most popular method to simulate these flows is still based on a Reynolds-averaged Navier-Stokes approach. However, there is some evidence that this formalism is not accurate for these components, especially when a description of time-dependent turbulent flows is desired. With the increase in computing power, large eddy simulation (LES) emerges as a promising technique to improve both knowledge of complex physics and reliability of flow solver predictions. The objective of the paper is thus to give an overview of the current status of LES for industrial compressor flows as well as to propose future research axes regarding the use of LES for compressor design. While the use of wall-resolved LES for industrial multistage compressors at realistic Reynolds number should not be ready before 2035, some possibilities exist to reduce the cost of LES, such as wall modelling and the adaptation of the phase-lag condition. This paper also points out the necessity to combine LES to techniques able to tackle complex geometries. Indeed LES alone, i.e. without prior knowledge of such flows for grid construction or the prohibitive yet ideal use of fully homogeneous meshes to predict compressor flows, is quite limited today.}, }
@article {pmid25024418, year = {2014}, author = {Tafti, DK and He, L and Nagendra, K}, title = {Large eddy simulation for predicting turbulent heat transfer in gas turbines.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2022}, pages = {20130322}, pmid = {25024418}, issn = {1364-503X}, abstract = {Blade cooling technology will play a critical role in the next generation of propulsion and power generation gas turbines. Accurate prediction of blade metal temperature can avoid the use of excessive compressed bypass air and allow higher turbine inlet temperature, increasing fuel efficiency and decreasing emissions. Large eddy simulation (LES) has been established to predict heat transfer coefficients with good accuracy under various non-canonical flows, but is still limited to relatively simple geometries and low Reynolds numbers. It is envisioned that the projected increase in computational power combined with a drop in price-to-performance ratio will make system-level simulations using LES in complex blade geometries at engine conditions accessible to the design process in the coming one to two decades. In making this possible, two key challenges are addressed in this paper: working with complex intricate blade geometries and simulating high-Reynolds-number (Re) flows. It is proposed to use the immersed boundary method (IBM) combined with LES wall functions. A ribbed duct at Re=20 000 is simulated using the IBM, and a two-pass ribbed duct is simulated at Re=100 000 with and without rotation (rotation number Ro=0.2) using LES with wall functions. The results validate that the IBM is a viable alternative to body-conforming grids and that LES with wall functions reproduces experimental results at a much lower computational cost.}, }
@article {pmid25024417, year = {2014}, author = {Lele, SK and Nichols, JW}, title = {A second golden age of aeroacoustics?.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2022}, pages = {20130321}, doi = {10.1098/rsta.2013.0321}, pmid = {25024417}, issn = {1364-503X}, abstract = {In 1992, Sir James Lighthill foresaw the dawn of a second golden age in aeroacoustics enabled by computer simulations (Hardin JC, Hussaini MY (eds) 1993 Computational aeroacoustics, New York, NY: Springer (doi:10.1007/978-1-4613-8342-0)). This review traces the progress in large-scale computations to resolve the noise-source processes and the methods devised to predict the far-field radiated sound using this information. Keeping focus on aviation-related noise sources a brief account of the progress in simulations of jet noise, fan noise and airframe noise is given highlighting the key technical issues and challenges. The complex geometry of nozzle elements and airframe components as well as the high Reynolds number of target applications require careful assessment of the discretization algorithms on unstructured grids and modelling compromises. High-fidelity simulations with 200-500 million points are not uncommon today and are used to improve scientific understanding of the noise generation process in specific situations. We attempt to discern where the future might take us, especially if exascale computing becomes a reality in 10 years. A pressing question in this context concerns the role of modelling in the coming era. While the sheer scale of the data generated by large-scale simulations will require new methods for data analysis and data visualization, it is our view that suitable theoretical formulations and reduced models will be even more important in future.}, }
@article {pmid25024414, year = {2014}, author = {Fujii, K}, title = {High-performance computing-based exploration of flow control with micro devices.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2022}, pages = {20130326}, pmid = {25024414}, issn = {1364-503X}, abstract = {The dielectric barrier discharge (DBD) plasma actuator that controls flow separation is one of the promising technologies to realize energy savings and noise reduction of fluid dynamic systems. However, the mechanism for controlling flow separation is not clearly defined, and this lack of knowledge prevents practical use of this technology. Therefore, large-scale computations for the study of the DBD plasma actuator have been conducted using the Japanese Petaflops supercomputer 'K' for three different Reynolds numbers. Numbers of new findings on the control of flow separation by the DBD plasma actuator have been obtained from the simulations, and some of them are presented in this study. Knowledge of suitable device parameters is also obtained. The DBD plasma actuator is clearly shown to be very effective for controlling flow separation at a Reynolds number of around 10(5), and several times larger lift-to-drag ratio can be achieved at higher angles of attack after stall. For higher Reynolds numbers, separated flow is partially controlled. Flow analysis shows key features towards better control. DBD plasma actuators are a promising technology, which could reduce fuel consumption and contribute to a green environment by achieving high aerodynamic performance. The knowledge described above can be obtained only with high-end computers such as the supercomputer 'K'.}, }
@article {pmid25024175, year = {2014}, author = {Schumacher, J and Scheel, JD and Krasnov, D and Donzis, DA and Yakhot, V and Sreenivasan, KR}, title = {Small-scale universality in fluid turbulence.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {111}, number = {30}, pages = {10961-10965}, pmid = {25024175}, issn = {1091-6490}, abstract = {Turbulent flows in nature and technology possess a range of scales. The largest scales carry the memory of the physical system in which a flow is embedded. One challenge is to unravel the universal statistical properties that all turbulent flows share despite their different large-scale driving mechanisms or their particular flow geometries. In the present work, we study three turbulent flows of systematically increasing complexity. These are homogeneous and isotropic turbulence in a periodic box, turbulent shear flow between two parallel walls, and thermal convection in a closed cylindrical container. They are computed by highly resolved direct numerical simulations of the governing dynamical equations. We use these simulation data to establish two fundamental results: (i) at Reynolds numbers Re ∼ 10(2) the fluctuations of the velocity derivatives pass through a transition from nearly Gaussian (or slightly sub-Gaussian) to intermittent behavior that is characteristic of fully developed high Reynolds number turbulence, and (ii) beyond the transition point, the statistics of the rate of energy dissipation in all three flows obey the same Reynolds number power laws derived for homogeneous turbulence. These results allow us to claim universality of small scales even at low Reynolds numbers. Our results shed new light on the notion of when the turbulence is fully developed at the small scales without relying on the existence of an extended inertial range.}, }
@article {pmid25019897, year = {2014}, author = {Clark di Leoni, P and Cobelli, PJ and Mininni, PD}, title = {Wave turbulence in shallow water models.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {6}, pages = {063025}, doi = {10.1103/PhysRevE.89.063025}, pmid = {25019897}, issn = {1550-2376}, mesh = {Computer Simulation ; *Hydrodynamics ; *Models, Chemical ; Models, Statistical ; *Nonlinear Dynamics ; Rheology/*methods ; Water/*chemistry ; *Water Movements ; }, abstract = {We study wave turbulence in shallow water flows in numerical simulations using two different approximations: the shallow water model and the Boussinesq model with weak dispersion. The equations for both models were solved using periodic grids with up to 2048{2} points. In all simulations, the Froude number varies between 0.015 and 0.05, while the Reynolds number and level of dispersion are varied in a broader range to span different regimes. In all cases, most of the energy in the system remains in the waves, even after integrating the system for very long times. For shallow flows, nonlinear waves are nondispersive and the spectrum of potential energy is compatible with ∼k{-2} scaling. For deeper (Boussinesq) flows, the nonlinear dispersion relation as directly measured from the wave and frequency spectrum (calculated independently) shows signatures of dispersion, and the spectrum of potential energy is compatible with predictions of weak turbulence theory, ∼k{-4/3}. In this latter case, the nonlinear dispersion relation differs from the linear one and has two branches, which we explain with a simple qualitative argument. Finally, we study probability density functions of the surface height and find that in all cases the distributions are asymmetric. The probability density function can be approximated by a skewed normal distribution as well as by a Tayfun distribution.}, }
@article {pmid25019884, year = {2014}, author = {Vega, EJ and Acero, AJ and Montanero, JM and Herrada, MA and Gañán-Calvo, AM}, title = {Production of microbubbles from axisymmetric flow focusing in the jetting regime for moderate Reynolds numbers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {6}, pages = {063012}, doi = {10.1103/PhysRevE.89.063012}, pmid = {25019884}, issn = {1550-2376}, mesh = {Computer Simulation ; Gases/*chemistry ; *Microbubbles ; *Models, Chemical ; Rheology/*methods ; Shear Strength ; Solutions/*chemistry ; Viscosity ; }, abstract = {We analyze both experimentally and numerically the formation of microbubbles in the jetting regime reached when a moderately viscous liquid stream focuses a gaseous meniscus inside a converging micronozzle. If the total (stagnation) pressure of the injected gas current is fixed upstream, then there are certain conditions on which a quasisteady gas meniscus forms. The meniscus tip is sharpened by the liquid stream down to the gas molecular scale. On the other side, monodisperse collections of microbubbles can be steadily produced in the jetting regime if the feeding capillary is appropriately located inside the nozzle. In this case, the microbubble size depends on the feeding capillary position. The numerical simulations for an imposed gas flow rate show that a recirculation cell appears in the gaseous meniscus for low enough values of that parameter. The experiments allow one to conclude that the bubble pinch-off comprises two phases: (i) a stretching motion of the precursor jet where the neck radius versus the time before the pinch essentially follows a potential law, and (ii) a final stage where a very thin and slender gaseous thread forms and eventually breaks apart into a number of micron-sized bubbles. Because of the difference between the free surface and core velocities, the gaseous jet breakage differs substantially from that of liquid capillary jets and gives rise to bubbles with diameters much larger than those expected from the Rayleigh-type capillary instability. The dependency of the bubble diameter upon the flow-rate ratio agrees with the scaling law derived by A. M. Gañán-Calvo [Phys. Rev. E 69, 027301 (2004)], although a slight influence of the Reynolds number can be observed in our experiments.}, }
@article {pmid25016321, year = {2014}, author = {Semião, AJ and Habimana, O and Casey, E}, title = {Bacterial adhesion onto nanofiltration and reverse osmosis membranes: effect of permeate flux.}, journal = {Water research}, volume = {63}, number = {}, pages = {296-305}, doi = {10.1016/j.watres.2014.06.031}, pmid = {25016321}, issn = {1879-2448}, mesh = {*Bacterial Adhesion ; *Biofouling ; Osmosis ; Permeability ; Pseudomonas fluorescens/*physiology ; Pseudomonas putida/*physiology ; Surface Properties ; Ultrafiltration ; *Water Purification ; }, abstract = {The influence of permeate flux on bacterial adhesion to NF and RO membranes was examined using two model Pseudomonas species, namely Pseudomonas fluorescens and Pseudomonas putida. To better understand the initial biofouling profile during NF/RO processes, deposition experiments were conducted in cross flow under permeate flux varying from 0.5 up to 120 L/(h m(2)), using six NF and RO membranes each having different surface properties. All experiments were performed at a Reynolds number of 579. Complementary adhesion experiments were performed using Pseudomonas cells grown to early-, mid- and late-exponential growth phases to evaluate the effect of bacterial cell surface properties during cell adhesion under permeate flux conditions. Results from this study show that initial bacterial adhesion is strongly dependent on the permeate flux conditions, where increased adhesion was obtained with increased permeate flux, until a maximum of 40% coverage was reached. Membrane surface properties or bacterial growth stages was further found to have little impact on bacterial adhesion to NF and RO membrane surfaces under the conditions tested. These results emphasise the importance of conducting adhesion and biofouling experiments under realistic permeate flux conditions, and raises questions about the efficacy of the methods for the evaluation of antifouling membranes in which bacterial adhesion is commonly assessed under zero-flux or low flux conditions, unrepresentative of full-scale NF/RO processes.}, }
@article {pmid25015666, year = {2014}, author = {Bahramian, F and Mohammadi, H}, title = {A novel periodic boundary condition for computational hemodynamics studies.}, journal = {Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine}, volume = {228}, number = {7}, pages = {643-651}, doi = {10.1177/0954411914542170}, pmid = {25015666}, issn = {2041-3033}, mesh = {*Algorithms ; Animals ; Blood Flow Velocity/*physiology ; Blood Pressure/*physiology ; Blood Vessels/*physiology ; Computer Simulation ; Humans ; *Models, Cardiovascular ; Oscillometry/*methods ; Shear Strength/physiology ; Vascular Resistance/physiology ; }, abstract = {In computational fluid dynamics models for hemodynamics applications, boundary conditions remain one of the major issues in obtaining accurate fluid flow predictions. For major cardiovascular models, the realistic boundary conditions are not available. In order to address this issue, the whole computational domain needs to be modeled, which is practically impossible. For simulating fully developed turbulent flows using the large eddy simulation and dynamic numerical solution methods, which are very popular in hemodynamics studies, periodic boundary conditions are suitable. This is mainly because the computational domain can be reduced considerably. In this study, a novel periodic boundary condition is proposed, which is based on mass flow condition. The proposed boundary condition is applied on a square duct for the sake of validation. The mass-based condition was shown to obtain the solution in 15% less time. As such, the mass-based condition has two decisive advantages: first, the solution for a given Reynolds number can be obtained in a single simulation because of the direct specification of the mass flow, and second, simulations can be made more quickly.}, }
@article {pmid25014474, year = {2014}, author = {Ishimoto, K and Gaffney, EA}, title = {A study of spermatozoan swimming stability near a surface.}, journal = {Journal of theoretical biology}, volume = {360}, number = {}, pages = {187-199}, doi = {10.1016/j.jtbi.2014.06.034}, pmid = {25014474}, issn = {1095-8541}, mesh = {Biomechanical Phenomena ; Cell Movement/*physiology ; Cell Shape/*physiology ; Computer Simulation ; Flagella/physiology ; Humans ; Male ; Microscopy/methods ; *Models, Biological ; Spermatozoa/*cytology/*physiology ; *Surface Properties ; Systems Biology/*methods ; }, abstract = {The swimming stability of spermatozoa with a specified planar beat pattern in the presence of a no-slip flat surface is explored in a modelling study exploiting direct numerical computation via the boundary element method and dynamical systems theory. Parameter sweeps varying the sperm head morphology and flagellar beat pattern wavenumber are conducted and reveal that stable surface swimming is a robust hydrodynamical phenomenon across extensive parameter values, emphasising that diverse sperm will readily swim adjacent to a surface without detailed feedback. There is little sensitivity to the details of the sperm head morphologies considered and, in particular, cells with human sperm head geometries are well approximated by those with prolate ellipsoid heads. However, surface accumulation is predicted to be inhibited by changes associated with mammalian sperm hyperactivation and quantitative aspects, such as the accumulation height associated with surface swimming, are sensitive to the flagellar beat pattern wavenumber and even to the asymptotically small modelling approximations of slender body theory. In particular, the predicted sensitivity of the accumulation height of swimming sperm to the beat pattern wavenumber is sufficient to suggest the possibility that the limited focal depth of typical microscopy studies analysing flagellar patterns with a fixed focal plane may inadvertently bias the wavenumber of the sperm that are observed.}, }
@article {pmid25011003, year = {2014}, author = {Theers, M and Winkler, RG}, title = {Effects of thermal fluctuations and fluid compressibility on hydrodynamic synchronization of microrotors at finite oscillatory Reynolds number: a multiparticle collision dynamics simulation study.}, journal = {Soft matter}, volume = {10}, number = {32}, pages = {5894-5904}, doi = {10.1039/c4sm00770k}, pmid = {25011003}, issn = {1744-6848}, abstract = {We investigate the emergent dynamical behavior of hydrodynamically coupled microrotors by means of multiparticle collision dynamics (MPC) simulations. The two rotors are confined in a plane and move along circles driven by active forces. Comparing simulations to theoretical results based on linearized hydrodynamics, we demonstrate that time-dependent hydrodynamic interactions lead to synchronization of the rotational motion. Thermal noise implies large fluctuations of the phase-angle difference between the rotors, but synchronization prevails and the ensemble-averaged time dependence of the phase-angle difference agrees well with analytical predictions. Moreover, we demonstrate that compressibility effects lead to longer synchronization times. In addition, the relevance of the inertia terms of the Navier-Stokes equation are discussed, specifically the linear unsteady acceleration term characterized by the oscillatory Reynolds number ReT. We illustrate the continuous breakdown of synchronization with the Reynolds number ReT, in analogy to the continuous breakdown of the scallop theorem with decreasing Reynolds number.}, }
@article {pmid24987981, year = {2014}, author = {Xi, J and Kim, J and Si, XA and Su, WC and Zhou, Y}, title = {Effects of the facial interface on inhalation and deposition of micrometer particles in calm air in a child airway model.}, journal = {Inhalation toxicology}, volume = {26}, number = {8}, pages = {492-505}, doi = {10.3109/08958378.2014.925992}, pmid = {24987981}, issn = {1091-7691}, mesh = {Administration, Inhalation ; Aerosols/*administration &amp; dosage ; Air ; Child, Preschool ; *Face ; Humans ; Hydrodynamics ; Male ; *Models, Biological ; Particle Size ; Respiration ; Respiratory System/*metabolism ; }, abstract = {CONTEXT: How the facial interface affects particle inhalability and depositions within the airway is not well understood. Previous studies of inhalation dosimetry are limited to either inhalability or deposition, rather than the two studied in a systematic way.<br><br>OBJECTIVE: To systematically evaluate the effects of the facial interface on aerosol inhalability, nasal deposition and thoracic dose in a 5-year-old child airway model using a coupled imaging-computational fluid dynamics approach.<br><br>METHODS: A face-nose-throat model was developed from magnetic resonance imaging scans of a 5-year-old boy. Respiration airflows and particle transport were simulated with the low Reynolds number k-&#x3c9; turbulence model and the Lagrangian tracking approach. Particles ranging from 1 to 70 &#xb5;m were considered in a calm air.<br><br>RESULTS: Retaining the facial interface in the computational model induced substantial variations in flow dynamics, aerosol inhalability and thoracic doses. The nasal and thoracic deposition fractions were much lower with the facial interface due to the low inhalability into downward-facing nostrils and facial deposition losses. For a given inhalation rate of 10 L/min, including the facial interface reduced the thoracic dose by 5% for 2.5-&#xb5;m particles and by 50% for 10&#x2009;&#xb5;m particles in the child model. Considering localized conditions, facial interface substantially increased depositions at the turbinate region and dorsal pharynx.<br><br>CONCLUSION: This study highlighted the need to include facial interface in future numerical and in vitro studies. Findings of this study have practical implications in the design of aerosol samplers and interpretation of deposition data from studies without facial interfaces.}, }
@article {pmid24987735, year = {2014}, author = {Xu, Y and Wu, Y and Sun, Q}, title = {Flow characteristics of the raw sewage for the design of sewage-source heat pump systems.}, journal = {TheScientificWorldJournal}, volume = {2014}, number = {}, pages = {503624}, doi = {10.1155/2014/503624}, pmid = {24987735}, issn = {1537-744X}, mesh = {Algorithms ; *Models, Theoretical ; *Rheology ; Sewage/*chemistry ; }, abstract = {The flow characteristics of raw sewage directly affect the technical and economic performance of sewage-source heat pump systems. The purpose of this research is to characterize the flow characteristics of sewage by experimental means. A sophisticated and flexible experimental apparatus was designed and constructed. Then the flow characteristics of the raw sewage were studied through laboratorial testing and theoretical analyses. Results indicated that raw sewage could be characterized as a power-law fluid with the rheological exponent n being 0.891 and the rheological coefficient k being 0.00175. In addition, the frictional loss factor formula in laminar flow for raw sewage was deduced by theoretical analysis of the power-law fluid. Furthermore, an explicit empirical formula for the frictional loss factor in turbulent flow was obtained through curve fitting of the experimental data. Finally, the equivalent viscosity of the raw sewage is defined in order to calculate the Reynolds number in turbulent flow regions; it was found that sewage had two to three times the viscosity of water at the same temperature. These results contributed to appropriate parameters of fluid properties when designing and operating sewage-source heat pump systems.}, }
@article {pmid24985873, year = {2014}, author = {Venugopal, A and Agrawal, A and Prabhu, SV}, title = {Note: A vortex cross-correlation flowmeter with enhanced turndown ratio.}, journal = {The Review of scientific instruments}, volume = {85}, number = {6}, pages = {066109}, doi = {10.1063/1.4884078}, pmid = {24985873}, issn = {1089-7623}, abstract = {In the present study, a novel dual sensor vortex cross correlation technique is suggested and implemented to extend the lower operating range of the flowmeter. The first sensor located at an optimum streamwise location of 0.85 times the width of the bluff body is employed to compute the vortex shedding frequency under high Reynolds number conditions. Under low Reynolds number conditions, when the strength of the vortex signal is poor, the outputs from the two piezoelectric sensors are correlated to compute the vortex convection velocity. This vortex convection velocity is used to compute the volume flow rate. This novel dual flow rate estimation technique has demonstrated its robustness under low Reynolds number flow conditions with a remarkable turndown ratio of 1:66 as compared to 1:20 for conventional vortex flowmeters.}, }
@article {pmid24984071, year = {2014}, author = {Alizadeh, A and Zhang, L and Wang, M}, title = {Mixing enhancement of low-Reynolds electro-osmotic flows in microchannels with temperature-patterned walls.}, journal = {Journal of colloid and interface science}, volume = {431}, number = {}, pages = {50-63}, doi = {10.1016/j.jcis.2014.05.070}, pmid = {24984071}, issn = {1095-7103}, mesh = {*Electroosmosis ; *Models, Chemical ; }, abstract = {Mixing becomes challenging in microchannels because of the low Reynolds number. This study aims to present a mixing enhancement method for electro-osmotic flows in microchannels using vortices caused by temperature-patterned walls. Since the fluid is non-isothermal, the conventional form of Nernst-Planck equation is modified by adding a new migration term which is dependent on both temperature and internal electric potential gradient. This term results in the so-called thermo-electrochemical migration phenomenon. The coupled Navier-Stokes, Poisson, modified Nernst-Planck, energy and advection-diffusion equations are iteratively solved by multiple lattice Boltzmann methods to obtain the velocity, internal electric potential, ion distribution, temperature and species concentration fields, respectively. To enhance the mixing, three schemes of temperature-patterned walls have been considered with symmetrical or asymmetrical arrangements of blocks with surface charge and temperature. Modeling results show that the asymmetric arrangement scheme is the most efficient scheme and enhances the mixing of species by 39% when the Reynolds number is on the order of 10(-3). Current results may help improve the design of micro-mixers at low Reynolds number.}, }
@article {pmid24975756, year = {2015}, author = {Barbosa, TM and Morais, JE and Marques, MC and Silva, AJ and Marinho, DA and Kee, YH}, title = {Hydrodynamic profile of young swimmers: changes over a competitive season.}, journal = {Scandinavian journal of medicine &amp; science in sports}, volume = {25}, number = {2}, pages = {e184-96}, doi = {10.1111/sms.12281}, pmid = {24975756}, issn = {1600-0838}, mesh = {Adolescent ; Athletic Performance/*physiology ; Biomechanical Phenomena ; Child ; Female ; Humans ; *Hydrodynamics ; Longitudinal Studies ; Male ; Models, Biological ; Seasons ; Swimming/*physiology ; }, abstract = {The aim of this study was to analyze the changes in the hydrodynamic profile of young swimmers over a competitive season and to compare the variations according to a well-designed training periodization. Twenty-five swimmers (13 boys and 12 girls) were evaluated in (a) October (M1); (b) March (M2); and (c) June (M3). Inertial and anthropometrical measures included body mass, swimmer's added water mass, height, and trunk transverse surface area. Swimming efficiency was estimated by the speed fluctuation, stroke index, and approximate entropy. Active drag was estimated with the velocity perturbation method and the passive drag with the gliding decay method. Hydrodynamic dimensionless numbers (Froude and Reynolds numbers) and hull velocity (i.e., speed at Froude number = 0.42) were also calculated. No variable presented a significant gender effect. Anthropometrics and inertial parameters plus dimensionless numbers increased over time. Swimming efficiency improved between M1 and M3. There was a trend for both passive and active drag increase from M1 to M2, but being lower at M3 than at M1. Intra-individual changes between evaluation moments suggest high between- and within-subject variations. Therefore, hydrodynamic changes over a season occur in a non-linear fashion way, where the interplay between growth and training periodization explain the unique path flow selected by each young swimmer.}, }
@article {pmid24973704, year = {2014}, author = {Slominski, CG and Kraynik, AM and Brady, JF}, title = {The Einstein shear viscosity correction for non no-slip hyperspheres.}, journal = {Journal of colloid and interface science}, volume = {430}, number = {}, pages = {302-304}, doi = {10.1016/j.jcis.2014.05.052}, pmid = {24973704}, issn = {1095-7103}, abstract = {We calculate the effective shear viscosity of a dilute dispersion of n-dimensional non no-slip hyperspheres, first for hyperdrops, second for slippery hyperspheres, and third for porous hyperspheres.}, }
@article {pmid24973405, year = {2014}, author = {Rembold, CM and Suratt, PM}, title = {Airway turbulence and changes in upper airway hydraulic diameter can be estimated from the intensity of high frequency inspiratory sounds in sleeping adults.}, journal = {The Journal of physiology}, volume = {592}, number = {17}, pages = {3831-3839}, pmid = {24973405}, issn = {1469-7793}, support = {M01 RR00847/RR/NCRR NIH HHS/United States ; }, mesh = {Adult ; Humans ; *Inhalation ; Larynx/pathology/*physiopathology ; Models, Biological ; Nose/pathology/*physiopathology ; Sleep Apnea, Obstructive/pathology/*physiopathology ; *Snoring ; }, abstract = {Obstructive sleep disordered breathing can cause death and significant morbidity in adults and children. We previously found that children with smaller upper airways (measured by magnetic resonance imaging while awake) generated loud high frequency inspiratory sounds (HFIS, defined as inspiratory sounds > 2 kHz) while they slept. The purpose of this study was (1) to determine what characteristics of airflow predicted HFIS intensity, and (b) to determine if we could calculate changes in hydraulic diameter (D) in both an in vitro model and in the upper airways of sleeping humans. In an in vitro model, high frequency sound intensity was an estimate of airflow turbulence as reflected by the Reynold's number (Re). D of the in vitro model was calculated using Re, the pressure gradient, Swamee-Jain formula and Darcy formula. D was proportional to but smaller than the actual diameters (r(2) = 0.94). In humans, we measured HFIS intensity and the pressure gradient across the upper airway (estimated with oesophageal pressure, Pes) during polysomnography in four adult volunteers and applied the same formulae to calculate D. At apnoea termination when the airway opens, we observed (1) an increase in HFIS intensity suggesting an increase in turbulence (higher Re), and (2) a larger calculated D. This method allows dynamic estimation of changes in relative upper airway hydraulic diameter (D) in sleeping humans with narrowed upper airways.}, }
@article {pmid24960397, year = {2014}, author = {Hong, J and Toloui, M and Chamorro, LP and Guala, M and Howard, K and Riley, S and Tucker, J and Sotiropoulos, F}, title = {Natural snowfall reveals large-scale flow structures in the wake of a 2.5-MW wind turbine.}, journal = {Nature communications}, volume = {5}, number = {}, pages = {4216}, doi = {10.1038/ncomms5216}, pmid = {24960397}, issn = {2041-1723}, abstract = {To improve power production and structural reliability of wind turbines, there is a pressing need to understand how turbines interact with the atmospheric boundary layer. However, experimental techniques capable of quantifying or even qualitatively visualizing the large-scale turbulent flow structures around full-scale turbines do not exist today. Here we use snowflakes from a winter snowstorm as flow tracers to obtain velocity fields downwind of a 2.5-MW wind turbine in a sampling area of ~36 × 36 m(2). The spatial and temporal resolutions of the measurements are sufficiently high to quantify the evolution of blade-generated coherent motions, such as the tip and trailing sheet vortices, identify their instability mechanisms and correlate them with turbine operation, control and performance. Our experiment provides an unprecedented in situ characterization of flow structures around utility-scale turbines, and yields significant insights into the Reynolds number similarity issues presented in wind energy applications.}, }
@article {pmid24948628, year = {2014}, author = {Wadhwa, N and Andersen, A and Kiørboe, T}, title = {Hydrodynamics and energetics of jumping copepod nauplii and copepodids.}, journal = {The Journal of experimental biology}, volume = {217}, number = {Pt 17}, pages = {3085-3094}, doi = {10.1242/jeb.105676}, pmid = {24948628}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Copepoda/growth &amp; development/*physiology ; *Hydrodynamics ; Larva ; Rheology ; *Swimming ; Video Recording ; Viscosity ; }, abstract = {Within its life cycle, a copepod goes through drastic changes in size, shape and swimming mode. In particular, there is a stark difference between the early (nauplius) and later (copepodid) stages. Copepods inhabit an intermediate Reynolds number regime (between ~1 and 100) where both viscosity and inertia are potentially important, and the Reynolds number changes by an order of magnitude during growth. Thus we expect the life stage related changes experienced by a copepod to result in hydrodynamic and energetic differences, ultimately affecting the fitness. To quantify these differences, we measured the swimming kinematics and fluid flow around jumping Acartia tonsa at different stages of its life cycle, using particle image velocimetry and particle tracking velocimetry. We found that the flow structures around nauplii and copepodids are topologically different, with one and two vortex rings, respectively. Our measurements suggest that copepodids cover a larger distance compared to their body size in each jump and are also hydrodynamically quieter, as the flow disturbance they create attenuates faster with distance. Also, copepodids are energetically more efficient than nauplii, presumably due to the change in hydrodynamic regime accompanied with a well-adapted body form and swimming stroke.}, }
@article {pmid24936020, year = {2014}, author = {Scheichl, B}, title = {Gross separation approaching a blunt trailing edge as the turbulence intensity increases.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2020}, pages = {}, doi = {10.1098/rsta.2014.0001}, pmid = {24936020}, issn = {1364-503X}, abstract = {A novel rational description of incompressible two-dimensional time-mean turbulent boundary layer (BL) flow separating from a bluff body at an arbitrarily large globally formed Reynolds number, Re, is devised. Partly in contrast to and partly complementing previous approaches, it predicts a pronounced delay of massive separation as the turbulence intensity level increases. This is bounded from above by a weakly decaying Re-dependent gauge function (hence, the BL approximation stays intact locally), and thus the finite intensity level characterizing fully developed turbulence. However, it by far exceeds the moderate level found in a preceding study which copes with the associated moderate delay of separation. Thus, the present analysis bridges this self-consistent and another forerunner theory, proposing extremely retarded separation by anticipating a fully attached external potential flow. Specifically, it is shown upon formulation of a respective distinguished limit at which rate the separation point and the attached-flow trailing edge collapse as [Formula: see text] and how on a short streamwise scale the typical small velocity deficit in the core region of the incident BL evolves to a large one. Hence, at its base, the separating velocity profile varies generically with the one-third power of the wall distance, and the classical triple-deck problem describing local viscous-inviscid interaction crucial for moderately retarded separation is superseded by a Rayleigh problem, governing separation of that core layer. Its targeted solution proves vital for understanding the separation process more close to the wall. Most importantly, the analysis does not resort to any specific turbulence closure. A first comparison with the available experimentally found positions of separation for the canonical flow past a circular cylinder is encouraging.}, }
@article {pmid24936018, year = {2014}, author = {Rothmayer, AP}, title = {Magnetohydrodynamic channel flows with weak transverse magnetic fields.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2020}, pages = {}, doi = {10.1098/rsta.2013.0344}, pmid = {24936018}, issn = {1364-503X}, abstract = {Magnetohydrodynamic flow of an incompressible fluid through a plane channel with slowly varying walls and a magnetic field applied transverse to the channel is investigated in the high Reynolds number limit. It is found that the magnetic field can first influence the hydrodynamic flow when the Hartmann number reaches a sufficiently large value. The magnetic field is found to suppress the steady and unsteady viscous flow near the channel walls unless the wall shapes become large.}, }
@article {pmid24936016, year = {2014}, author = {Logue, RP and Gajjar, JS and Ruban, AI}, title = {Instability of supersonic compression ramp flow.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2020}, pages = {}, doi = {10.1098/rsta.2013.0342}, pmid = {24936016}, issn = {1364-503X}, abstract = {The instability of supersonic compression ramp flow is investigated. It is assumed that the Reynolds number is large and that the governing equations are the unsteady triple-deck equations. The mean flow is first calculated by solving the steady equations for various scaled ramp angles α, and the numerical results suggest that there is no singularity for increasing ramp angles. The stability of the flow is investigated using two approaches, first by solving the linearized unsteady equations and looking for global modes proportional to e(λt). In the second approach, the linearized unsteady equations are solved numerically with various initial conditions. Whereas no globally unsteady modes could be found for the range of ramp angles studied, the numerical simulations show the formation of wavepacket type disturbances which grow and convect and reach large amplitudes. However, the numerical results show large variations with grid size even on very fine grids.}, }
@article {pmid24936013, year = {2014}, author = {Braun, S and Scheichl, S}, title = {On recent developments in marginal separation theory.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2020}, pages = {}, pmid = {24936013}, issn = {1364-503X}, abstract = {Thin aerofoils are prone to localized flow separation at their leading edge if subjected to moderate angles of attack α. Although 'laminar separation bubbles' at first do not significantly alter the aerofoil performance, they tend to 'burst' if α is increased further or if perturbations acting upon the flow reach a certain intensity. This then either leads to global flow separation (stall) or triggers the laminar-turbulent transition process within the boundary layer flow. This paper addresses the asymptotic analysis of the early stages of the latter phenomenon in the limit as the characteristic Reynolds number [Formula: see text], commonly referred to as marginal separation theory. A new approach based on the adjoint operator method is presented that enables the fundamental similarity laws of marginal separation theory to be derived and the analysis to be extended to higher order. Special emphasis is placed on the breakdown of the flow description, i.e. the formation of finite-time singularities (a manifestation of the bursting process), and on its resolution being based on asymptotic arguments. The passage to the subsequent triple-deck stage is described in detail, which is a prerequisite for carrying out a future numerical treatment of this stage in a proper way. Moreover, a composite asymptotic model is developed in order for the inherent ill-posedness of the Cauchy problems associated with the current flow description to be resolved.}, }
@article {pmid24936012, year = {2014}, author = {Wu, X}, title = {On the role of acoustic feedback in boundary-layer instability.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2020}, pages = {}, doi = {10.1098/rsta.2013.0347}, pmid = {24936012}, issn = {1364-503X}, abstract = {In this paper, the classical triple-deck formalism is employed to investigate two instability problems in which an acoustic feedback loop plays an essential role. The first concerns a subsonic boundary layer over a flat plate on which two well-separated roughness elements are present. A spatially amplifying Tollmien-Schlichting (T-S) wave between the roughness elements is scattered by the downstream roughness to emit a sound wave that propagates upstream and impinges on the upstream roughness to regenerate the T-S wave, thereby forming a closed feedback loop in the streamwise direction. Numerical calculations suggest that, at high Reynolds numbers and for moderate roughness heights, the long-range acoustic coupling may lead to absolute instability, which is characterized by self-sustained oscillations at discrete frequencies. The dominant peak frequency may jump from one value to another as the Reynolds number, or the distance between the roughness elements, is varied gradually. The second problem concerns the supersonic 'twin boundary layers' that develop along two well-separated parallel flat plates. The two boundary layers are in mutual interaction through the impinging and reflected acoustic waves. It is found that the interaction leads to a new instability that is absent in the unconfined boundary layer.}, }
@article {pmid24936011, year = {2014}, author = {Cassel, KW and Conlisk, AT}, title = {Unsteady separation in vortex-induced boundary layers.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2020}, pages = {}, doi = {10.1098/rsta.2013.0348}, pmid = {24936011}, issn = {1364-503X}, abstract = {This paper provides a brief review of the analytical and numerical developments related to unsteady boundary-layer separation, in particular as it relates to vortex-induced flows, leading up to our present understanding of this important feature in high-Reynolds-number, surface-bounded flows in the presence of an adverse pressure gradient. In large part, vortex-induced separation has been the catalyst for pulling together the theory, numerics and applications of unsteady separation. Particular attention is given to the role that Prof. Frank T. Smith, FRS, has played in these developments over the course of the past 35 years. The following points will be emphasized: (i) unsteady separation plays a pivotal role in a wide variety of high-Reynolds-number flows, (ii) asymptotic methods have been instrumental in elucidating the physics of both steady and unsteady separation, (iii) Frank T. Smith has served as a catalyst in the application of asymptotic methods to high-Reynolds-number flows, and (iv) there is still much work to do in articulating a complete theoretical understanding of unsteady boundary-layer separation.}, }
@article {pmid24936010, year = {2014}, author = {Kluwick, A and Kornfeld, M}, title = {Triple-deck analysis of transonic high Reynolds number flow through slender channels.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2020}, pages = {}, doi = {10.1098/rsta.2013.0346}, pmid = {24936010}, issn = {1364-503X}, abstract = {In this work, laminar transonic weakly three-dimensional flows at high Reynolds numbers in slender channels, as found in microsupersonic nozzles and turbomachines of micro-electro-mechanical systems, are considered. The channel height is taken so small that the viscous wall layers forming at the channel walls start to interact strongly rather than weakly with the inviscid core flow and, therefore, the classical boundary layer approach fails. The resulting viscous-inviscid interaction problem is formulated using matched asymptotic expansions and found to be governed by a triple-deck structure. As a consequence, the properties of the predominantly inviscid core region and the viscous wall layers have to be calculated simultaneously in the interaction region. Weakly three-dimensional effects caused by surface roughness, upstream propagating flow perturbations, boundary layer separation as well as bifurcating solutions are discussed. Representative results for subsonic as well as supersonic conditions are presented, and the importance of these flow phenomena in technical applications as, for example, a means to reduce shock losses through the use of deformed geometry is addressed.}, }
@article {pmid24936008, year = {2014}, author = {Goldstein, ME}, title = {Effect of free-stream turbulence on boundary layer transition.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2020}, pages = {}, doi = {10.1098/rsta.2013.0354}, pmid = {24936008}, issn = {1364-503X}, abstract = {This paper is concerned with the transition to turbulence in flat plate boundary layers due to moderately high levels of free-stream turbulence. The turbulence is assumed to be generated by an (idealized) grid and matched asymptotic expansions are used to analyse the resulting flow over a finite thickness flat plate located in the downstream region. The characteristic Reynolds number Rλ based on the mesh size λ and free-stream velocity is assumed to be large, and the turbulence intensity ε is assumed to be small. The asymptotic flow structure is discussed for the generic case where the turbulence Reynolds number εRλ and the plate thickness and are held fixed (at O(1) and O(λ), respectively) in the limit as [Formula: see text] and ε→0. But various limiting cases are considered in order to explain the relevant transition mechanisms. It is argued that there are two types of streak-like structures that can play a role in the transition process: (i) those that appear in the downstream region and are generated by streamwise vorticity in upstream flow and (ii) those that are concentrated near the leading edge and are generated by plate normal vorticity in upstream flow. The former are relatively unaffected by leading edge geometry and are usually referred to as Klebanoff modes while the latter are strongly affected by leading edge geometry and are more streamwise vortex-like in appearance.}, }
@article {pmid24936006, year = {2014}, author = {Deguchi, K and Hall, P}, title = {Canonical exact coherent structures embedded in high Reynolds number flows.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {372}, number = {2020}, pages = {}, doi = {10.1098/rsta.2013.0352}, pmid = {24936006}, issn = {1364-503X}, abstract = {The applications and implications of two recently addressed asymptotic descriptions of exact coherent structures in shear flows are discussed. The first type of asymptotic framework to be discussed was introduced in a series of papers by Hall &amp; Smith in the 1990s and was referred to as vortex-wave interaction theory (VWI). New results are given here for the canonical VWI problem in an infinite region; the results confirm and extend the results for the infinite problem inferred the recent VWI computation of plane Couette flow. The results given define for the first time exact coherent structures in unbounded flows. The second type of canonical structure described here is that recently found for asymptomatic suction boundary layer and corresponds to freestream coherent structures (FCS), in boundary layer flows. Here, it is shown that the FCS can also occur in flows such as Burgers vortex sheet. It is concluded that both canonical problems can be locally embedded in general shear flows and thus have widespread applicability.}, }
@article {pmid24931649, year = {2014}, author = {Kozu, H and Kobayashi, I and Neves, MA and Nakajima, M and Uemura, K and Sato, S and Ichikawa, S}, title = {PIV and CFD studies on analyzing intragastric flow phenomena induced by peristalsis using a human gastric flow simulator.}, journal = {Food &amp; function}, volume = {5}, number = {8}, pages = {1839-1847}, doi = {10.1039/c4fo00041b}, pmid = {24931649}, issn = {2042-650X}, mesh = {*Computer Simulation ; Humans ; *Models, Biological ; Peristalsis/*physiology ; *Rheology ; }, abstract = {This study quantitatively analyzed the flow phenomena in model gastric contents induced by peristalsis using a human gastric flow simulator (GFS). Major functions of the GFS include gastric peristalsis simulation by controlled deformation of rubber walls and direct observation of inner flow through parallel transparent windows. For liquid gastric contents (water and starch syrup solutions), retropulsive flow against the direction of peristalsis was observed using both particle image velocimetry (PIV) and computational fluid dynamics (CFD). The maximum flow velocity was obtained in the region occluded by peristalsis. The maximum value was 9 mm s(-1) when the standard value of peristalsis speed in healthy adults (UACW = 2.5 mm s(-1)) was applied. The intragastric flow-field was laminar with the maximum Reynolds number (Re = 125). The viscosity of liquid gastric contents hardly affected the maximum flow velocity in the applied range of this study (1 to 100 mPa s). These PIV results agreed well with the CFD results. The maximum shear rate in the liquid gastric contents was below 20 s(-1) at UACW = 2.5 mm s(-1). We also measured the flow-field in solid-liquid gastric contents containing model solid food particles (plastic beads). The direction of velocity vectors was influenced by the presence of the model solid food particle surface. The maximum flow velocity near the model solid food particles ranged from 8 to 10 mm s(-1) at UACW = 2.5 mm s(-1). The maximum shear rate around the model solid food particles was low, with a value of up to 20 s(-1).}, }
@article {pmid24910525, year = {2014}, author = {Pihler-Puzović, D and Pedley, TJ}, title = {Flutter in a quasi-one-dimensional model of a collapsible channel.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {470}, number = {2166}, pages = {20140015}, pmid = {24910525}, issn = {1364-5021}, abstract = {The effects of wall inertia on instabilities in a collapsible channel with a long finite-length flexible wall containing a high Reynolds number flow of incompressible fluid are studied. Using the ideas of interactive boundary layer theory, the system is described by a one-dimensional model that couples inviscid flow outside the boundary layers formed on the channel walls with the deformation of the flexible wall. The observed instability is a form of flutter, which is superposed on the behaviour of the system when the wall mass is neglected. We show that the flutter has a positive growth rate because the fluid loading acts as a negative damping in the system. We discuss these findings in relation to other work on self-excited oscillations in collapsible channels.}, }
@article {pmid24895466, year = {2013}, author = {Benmouhoub, D and Mataoui, A}, title = {Turbulent Heat Transfer From a Slot Jet Impinging on a Flat Plate.}, journal = {Journal of heat transfer}, volume = {135}, number = {10}, pages = {1022011-1022019}, pmid = {24895466}, issn = {0022-1481}, abstract = {The flow field and heat transfer of a plane impinging jet on a hot moving wall were investigated using one point closure turbulence model. Computations were carried out by means of a finite volume method. The evolutions of mean velocity components, vorticity, skin friction coefficient, Nusselt number and pressure coefficient are examined in this paper. Two parameters of this type of interaction are considered for a given impinging distance of 8 times the nozzle thickness (H/e = 8): the jet-surface velocity ratio and the jet exit Reynolds number. The flow field structure at a given surface-to-jet velocity ratio is practically independent to the jet exit Reynolds number. A slight modification of the flow field is observed for weak surface-to-jet velocity ratios while the jet is strongly driven for higher velocity ratio. The present results satisfactorily compare to the experimental data available in the literature for Rsj ≤ 1.The purpose of this paper is to investigate this phenomenon for higher Rsj values (0 ≤ Rsj ≤ 4). It follows that the variation of the mean skin friction and the Nusselt number can be correlated according to the surface-to-jet velocity ratios and the Reynolds numbers.}, }
@article {pmid24864128, year = {2014}, author = {Odeleye, AO and Marsh, DT and Osborne, MD and Lye, GJ and Micheletti, M}, title = {On the fluid dynamics of a laboratory scale single-use stirred bioreactor.}, journal = {Chemical engineering science}, volume = {111}, number = {100}, pages = {299-312}, pmid = {24864128}, issn = {0009-2509}, abstract = {The commercial success of mammalian cell-derived recombinant proteins has fostered an increase in demand for novel single-use bioreactor (SUB) systems that facilitate greater productivity, increased flexibility and reduced costs (Zhang et al., 2010). These systems exhibit fluid flow regimes unlike those encountered in traditional glass/stainless steel bioreactors because of the way in which they are designed. With such disparate hydrodynamic environments between SUBs currently on the market, traditional scale-up approaches applied to stirred tanks should be revised. One such SUB is the Mobius[®] 3 L CellReady, which consists of an upward-pumping marine scoping impeller. This work represents the first experimental study of the flow within the CellReady using a Particle Image Velocimetry (PIV) approach, combined with a biological study into the impact of these fluid dynamic characteristics on cell culture performance. The PIV study was conducted within the actual vessel, rather than using a purpose-built mimic. PIV measurements conveyed a degree of fluid compartmentalisation resulting from the up-pumping impeller. Both impeller tip speed and fluid working volume had an impact upon the fluid velocities and spatial distribution of turbulence within the vessel. Cell cultures were conducted using the GS-CHO cell-line (Lonza) producing an IgG4 antibody. Disparity in cellular growth and viability throughout the range of operating conditions used (80-350 rpm and 1-2.4 L working volume) was not substantial, although a significant reduction in recombinant protein productivity was found at 350 rpm and 1 L working volume (corresponding to the highest Reynolds number tested in this work). The study shows promise in the use of PIV to improve understanding of the hydrodynamic environment within individual SUBs and allows identification of the critical hydrodynamic parameters under the different flow regimes for compatibility and scalability across the range of bioreactor platforms.}, }
@article {pmid24855668, year = {2014}, author = {Ngo, V and McHenry, MJ}, title = {The hydrodynamics of swimming at intermediate Reynolds numbers in the water boatman (Corixidae).}, journal = {The Journal of experimental biology}, volume = {217}, number = {Pt 15}, pages = {2740-2751}, doi = {10.1242/jeb.103895}, pmid = {24855668}, issn = {1477-9145}, mesh = {Acceleration ; Animals ; Biomechanical Phenomena ; Extremities/physiology ; Heteroptera/*physiology ; *Hydrodynamics ; Models, Theoretical ; Swimming/*physiology ; Video Recording ; Viscosity ; }, abstract = {The fluid forces that govern propulsion determine the speed and energetic cost of swimming. These hydrodynamics are scale dependent and it is unclear what forces matter to the tremendous diversity of aquatic animals that are between a millimeter and a centimeter in length. Animals at this scale generally operate within the regime of intermediate Reynolds numbers, where both viscous and inertial fluid forces have the potential to play a role in propulsion. The present study aimed to resolve which forces create thrust and drag in the paddling of the water boatman (Corixidae), an animal that spans much of the intermediate regime (10<Re<200). By measuring the force generated by tethered water boatmen, we found that thrust is generated primarily by drag on the paddling appendages, with a negligible contribution from the acceleration reaction force. Based on these findings, we developed a forward-dynamic model of propulsion in free swimming that accurately predicted changes in the body's center of mass over time. For both tethered and free swimming, we used non-linear optimization algorithms to determine the force coefficients that best matched our measurements. With this approach, the drag coefficients on the body and paddle were found to be up to three times greater than on static structures in fully developed flow at the same Reynolds numbers. This is likely a partial consequence of unsteady interactions between the paddles or between the paddles and the body. In addition, the maximum values for these coefficients were inversely related to the Reynolds number, which suggests that viscous forces additionally play an important role in the hydrodynamics of small water boatmen. This understanding for the major forces that operate at intermediate Reynolds numbers offers a basis for interpreting the mechanics, energetics and functional morphology of swimming in many small aquatic animals.}, }
@article {pmid24849267, year = {2014}, author = {Vakarelski, IU and Chan, DY and Thoroddsen, ST}, title = {Leidenfrost vapour layer moderation of the drag crisis and trajectories of superhydrophobic and hydrophilic spheres falling in water.}, journal = {Soft matter}, volume = {10}, number = {31}, pages = {5662-5668}, doi = {10.1039/c4sm00368c}, pmid = {24849267}, issn = {1744-6848}, abstract = {We investigate the dynamic effects of a Leidenfrost vapour layer sustained on the surface of heated steel spheres during free fall in water. We find that a stable vapour layer sustained on the textured superhydrophobic surface of spheres falling through 95 °C water can reduce the hydrodynamic drag by up to 75% and stabilize the sphere trajectory for the Reynolds number between 10(4) and 10(6), spanning the drag crisis in the absence of the vapour layer. For hydrophilic spheres under the same conditions, the transition to drag reduction and trajectory stability occurs abruptly at a temperature different from the static Leidenfrost point. The observed drag reduction effects are attributed to the disruption of the viscous boundary layer by the vapour layer whose thickness depends on the water temperature. Both the drag reduction and the trajectory stabilization effects are expected to have significant implications for development of sustainable vapour layer based technologies.}, }
@article {pmid24827344, year = {2014}, author = {Lapa, MF and Hughes, TL}, title = {Swimming at low Reynolds number in fluids with odd, or Hall, viscosity.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {4}, pages = {043019}, doi = {10.1103/PhysRevE.89.043019}, pmid = {24827344}, issn = {1550-2376}, mesh = {Animals ; Biological Clocks/*physiology ; Computer Simulation ; Friction/physiology ; Humans ; *Models, Biological ; Rheology/*methods ; Shear Strength/physiology ; Swimming/*physiology ; Viscosity ; Water/*chemistry ; }, abstract = {We apply the geometric theory of swimming at low Reynolds number to the study of nearly circular swimmers in two-dimensional fluids with nonvanishing "odd," or Hall, viscosity. The odd viscosity gives an off-diagonal contribution to the fluid stress tensor, which results in a number of striking effects. In particular, we find that a swimmer whose area is changing will experience a torque proportional to the rate of change of the area, with the constant of proportionality given by the coefficient ηo of odd viscosity. After working out the general theory of swimming in fluids with odd viscosity for a class of simple swimmers, we give a number of example swimming strokes which clearly demonstrate the differences between swimming in a fluid with conventional viscosity and a fluid which also has an odd viscosity. We also include a discussion of the extension of the famous Scallop theorem of low Reynolds number swimming to the case where the fluid has a nonzero odd viscosity. A number of more technical results, including a proof of the torque-area relation for swimmers of more general shape, are explained in a set of Appendixes.}, }
@article {pmid24827337, year = {2014}, author = {Scagliarini, A and Gylfason, &#xc1; and Toschi, F}, title = {Heat-flux scaling in turbulent Rayleigh-Bénard convection with an imposed longitudinal wind.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {4}, pages = {043012}, doi = {10.1103/PhysRevE.89.043012}, pmid = {24827337}, issn = {1550-2376}, abstract = {We present a numerical study of Rayleigh-Bénard convection disturbed by a longitudinal wind. Our results show that under the action of the wind, the vertical heat flux through the cell initially decreases, due to the mechanism of plume sweeping, and then increases again when turbulent forced convection dominates over the buoyancy. As a result, the Nusselt number is a nonmonotonic function of the shear Reynolds number. We provide simple models that capture with good accuracy all the dynamical regimes observed. We expect that our findings can lead the way to a more fundamental understanding of the complex interplay between mean wind and plume ejection in the Rayleigh-Bénard phenomenology.}, }
@article {pmid24821393, year = {2015}, author = {Sera, T and Uesugi, K and Yagi, N and Yokota, H}, title = {Numerical simulation of airflow and microparticle deposition in a synchrotron micro-CT-based pulmonary acinus model.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {18}, number = {13}, pages = {1427-1435}, doi = {10.1080/10255842.2014.915030}, pmid = {24821393}, issn = {1476-8259}, mesh = {Adult ; Animals ; Computer Simulation ; Gravitation ; Humans ; Mice ; *Models, Biological ; Pulmonary Alveoli/*diagnostic imaging ; Radiographic Image Interpretation, Computer-Assisted ; Respiration ; Synchrotrons ; *X-Ray Microtomography ; }, abstract = {The acinus consists of complex, branched alveolar ducts and numerous surrounding alveoli, and so in this study, we hypothesized that the particle deposition can be much influenced by the complex acinar geometry, and simulated the airflow and particle deposition (density = 1.0 g/cm(3), diameter = 1 and 3 μm) numerically in a pulmonary acinar model based on synchrotron micro-CT of the mammalian lung. We assumed that the fluid-structure interaction was neglected and that alveolar flow was induced by the expansion and contraction of the acinar model with the volume changing sinusoidally with time as the moving boundary conditions. The alveolar flow was dominated by radial flows, and a weak recirculating flow was observed at the proximal side of alveoli during the entire respiratory cycle, despite the maximum Reynolds number at the inlet being 0.029. Under zero gravity, the particle deposition rate after single breathing was less than 0.01, although the particles were transported deeply into the acinus after inspiration. Under a gravitational field, the deposition rate and map were influenced strongly by gravity orientation. In the case of a particle diameter of 1 μm, the rate increased dramatically and mostly non-deposited particles remained in the model, indicating that the rate would increase further after repeated breathing. At a particle diameter of 3 μm, the rate was 1.0 and all particles were deposited during single breathing. Our results show that the particle deposition rate in realistic pulmonary acinar model is higher than in an idealized model.}, }
@article {pmid24819059, year = {2014}, author = {Huisman, SG and van der Veen, RC and Sun, C and Lohse, D}, title = {Multiple states in highly turbulent Taylor-Couette flow.}, journal = {Nature communications}, volume = {5}, number = {}, pages = {3820}, doi = {10.1038/ncomms4820}, pmid = {24819059}, issn = {2041-1723}, abstract = {The ubiquity of turbulent flows in nature and technology makes it of utmost importance to fundamentally understand turbulence. Kolmogorov's 1941 paradigm suggests that for strongly turbulent flows with many degrees of freedom and large fluctuations, there would only be one turbulent state as the large fluctuations would explore the entire higher dimensional phase space. Here we report the first conclusive evidence of multiple turbulent states for large Reynolds number, Re = O(10(6)) (Taylor number Ta = O(10(12))) Taylor-Couette flow in the regime of ultimate turbulence, by probing the phase space spanned by the rotation rates of the inner and outer cylinder. The manifestation of multiple turbulent states is exemplified by providing combined global torque- and local-velocity measurements. This result verifies the notion that bifurcations can occur in high-dimensional flows (that is, very large Re) and questions Kolmogorov's paradigm.}, }
@article {pmid24811136, year = {2014}, author = {Prohm, C and Stark, H}, title = {Feedback control of inertial microfluidics using axial control forces.}, journal = {Lab on a chip}, volume = {14}, number = {12}, pages = {2115-2123}, doi = {10.1039/c4lc00145a}, pmid = {24811136}, issn = {1473-0189}, mesh = {*Microfluidic Analytical Techniques ; *Models, Theoretical ; }, abstract = {Inertial microfluidics is a promising tool for many lab-on-a-chip applications. Particles in channel flows with Reynolds numbers above one undergo cross-streamline migration to a discrete set of equilibrium positions in square and rectangular channel cross sections. This effect has been used extensively for particle sorting and the analysis of particle properties. Using the lattice Boltzmann method, we determined the equilibrium positions in square and rectangular cross sections and classify their types of stability for different Reynolds numbers, particle sizes, and channel aspect ratios. Our findings thereby help to design microfluidic channels for particle sorting. Furthermore, we demonstrated how an axial control force, which slows down the particles and shifts the stable equilibrium position towards the channel center. Ultimately, the particles then stay on the centerline for forces exceeding the threshold value. This effect is sensitive to the particle size and channel Reynolds number and therefore suggests an efficient method for particle separation. In combination with a hysteretic feedback scheme, we can even increase the particle throughput.}, }
@article {pmid24805351, year = {2014}, author = {Taylor, JO and Witmer, KP and Neuberger, T and Craven, BA and Meyer, RS and Deutsch, S and Manning, KB}, title = {In vitro quantification of time dependent thrombus size using magnetic resonance imaging and computational simulations of thrombus surface shear stresses.}, journal = {Journal of biomechanical engineering}, volume = {136}, number = {7}, pages = {}, doi = {10.1115/1.4027613}, pmid = {24805351}, issn = {1528-8951}, mesh = {Animals ; Blood Circulation ; Cattle ; *Computer Simulation ; *Hydrodynamics ; *Magnetic Resonance Imaging ; Models, Biological ; *Shear Strength ; *Stress, Mechanical ; Thrombosis/pathology/*physiopathology ; Time Factors ; }, abstract = {Thrombosis and thromboembolization remain large obstacles in the design of cardiovascular devices. In this study, the temporal behavior of thrombus size within a backward-facing step (BFS) model is investigated, as this geometry can mimic the flow separation which has been found to contribute to thrombosis in cardiac devices. Magnetic resonance imaging (MRI) is used to quantify thrombus size and collect topographic data of thrombi formed by circulating bovine blood through a BFS model for times ranging between 10 and 90 min at a constant upstream Reynolds number of 490. Thrombus height, length, exposed surface area, and volume are measured, and asymptotic behavior is observed for each as the blood circulation time is increased. Velocity patterns near, and wall shear stress (WSS) distributions on, the exposed thrombus surfaces are calculated using computational fluid dynamics (CFD). Both the mean and maximum WSS on the exposed thrombus surfaces are much more dependent on thrombus topography than thrombus size, and the best predictors for asymptotic thrombus length and volume are the reattachment length and volume of reversed flow, respectively, from the region of separated flow downstream of the BFS.}, }
@article {pmid24801556, year = {2014}, author = {Pal, A and Anupindi, K and Delorme, Y and Ghaisas, N and Shetty, DA and Frankel, SH}, title = {Large eddy simulation of transitional flow in an idealized stenotic blood vessel: evaluation of subgrid scale models.}, journal = {Journal of biomechanical engineering}, volume = {136}, number = {7}, pages = {0710091-0710098}, pmid = {24801556}, issn = {1528-8951}, support = {R01 HL098353/HL/NHLBI NIH HHS/United States ; HL098353/HL/NHLBI NIH HHS/United States ; }, mesh = {Blood Vessels/*physiopathology ; Constriction, Pathologic ; *Hemodynamics ; *Hydrodynamics ; *Models, Cardiovascular ; }, abstract = {In the present study, we performed large eddy simulation (LES) of axisymmetric, and 75% stenosed, eccentric arterial models with steady inflow conditions at a Reynolds number of 1000. The results obtained are compared with the direct numerical simulation (DNS) data (Varghese et al., 2007, "Direct Numerical Simulation of Stenotic Flows. Part 1. Steady Flow," J. Fluid Mech., 582, pp. 253-280). An inhouse code (WenoHemo) employing high-order numerical methods for spatial and temporal terms, along with a 2nd order accurate ghost point immersed boundary method (IBM) (Mark, and Vanwachem, 2008, "Derivation and Validation of a Novel Implicit Second-Order Accurate Immersed Boundary Method," J. Comput. Phys., 227(13), pp. 6660-6680) for enforcing boundary conditions on curved geometries is used for simulations. Three subgrid scale (SGS) models, namely, the classical Smagorinsky model (Smagorinsky, 1963, "General Circulation Experiments With the Primitive Equations," Mon. Weather Rev., 91(10), pp. 99-164), recently developed Vreman model (Vreman, 2004, "An Eddy-Viscosity Subgrid-Scale Model for Turbulent Shear Flow: Algebraic Theory and Applications," Phys. Fluids, 16(10), pp. 3670-3681), and the Sigma model (Nicoud et al., 2011, "Using Singular Values to Build a Subgrid-Scale Model for Large Eddy Simulations," Phys. Fluids, 23(8), 085106) are evaluated in the present study. Evaluation of SGS models suggests that the classical constant coefficient Smagorinsky model gives best agreement with the DNS data, whereas the Vreman and Sigma models predict an early transition to turbulence in the poststenotic region. Supplementary simulations are performed using Open source field operation and manipulation (OpenFOAM) ("OpenFOAM," http://www.openfoam.org/) solver and the results are inline with those obtained with WenoHemo.}, }
@article {pmid24794529, year = {2014}, author = {Xu, H and Pumir, A and Falkovich, G and Bodenschatz, E and Shats, M and Xia, H and Francois, N and Boffetta, G}, title = {Flight-crash events in turbulence.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {111}, number = {21}, pages = {7558-7563}, pmid = {24794529}, issn = {1091-6490}, mesh = {*Acceleration ; *Air Movements ; Computer Simulation ; *Hydrodynamics ; *Models, Chemical ; }, abstract = {The statistical properties of turbulence differ in an essential way from those of systems in or near thermal equilibrium because of the flux of energy between vastly different scales at which energy is supplied and at which it is dissipated. We elucidate this difference by studying experimentally and numerically the fluctuations of the energy of a small fluid particle moving in a turbulent fluid. We demonstrate how the fundamental property of detailed balance is broken, so that the probabilities of forward and backward transitions are not equal for turbulence. In physical terms, we found that in a large set of flow configurations, fluid elements decelerate faster than accelerate, a feature known all too well from driving in dense traffic. The statistical signature of rare "flight-crash" events, associated with fast particle deceleration, provides a way to quantify irreversibility in a turbulent flow. Namely, we find that the third moment of the power fluctuations along a trajectory, nondimensionalized by the energy flux, displays a remarkable power law as a function of the Reynolds number, both in two and in three spatial dimensions. This establishes a relation between the irreversibility of the system and the range of active scales. We speculate that the breakdown of the detailed balance characterized here is a general feature of other systems very far from equilibrium, displaying a wide range of spatial scales.}, }
@article {pmid24792975, year = {2014}, author = {Cui, Y and Schmalfuß, S and Zellnitz, S and Sommerfeld, M and Urbanetz, N}, title = {Towards the optimisation and adaptation of dry powder inhalers.}, journal = {International journal of pharmaceutics}, volume = {470}, number = {1-2}, pages = {120-132}, doi = {10.1016/j.ijpharm.2014.04.065}, pmid = {24792975}, issn = {1873-3476}, mesh = {Drug Carriers/chemistry ; *Dry Powder Inhalers ; Hydrodynamics ; Microscopy, Atomic Force ; Microscopy, Electron, Scanning ; Models, Theoretical ; Pharmaceutical Preparations/chemistry ; Powders ; }, abstract = {Pulmonary drug delivery by dry powder inhalers is becoming more and more popular. Such an inhalation device must insure that during the inhalation process the drug powder is detached from the carrier due to fluid flow stresses. The goal of the project is the development of a drug powder detachment model to be used in numerical computations (CFD, computational fluid dynamics) of fluid flow and carrier particle motion through the inhaler and the resulting efficiency of drug delivery. This programme will be the basis for the optimisation of inhaler geometry and dry powder inhaler formulation. For this purpose a multi-scale approach is adopted. First the flow field through the inhaler is numerically calculated with OpenFOAM(®) and the flow stresses experienced by the carrier particles are recorded. This information is used for micro-scale simulations using the Lattice-Boltzmann method where only one carrier particle covered with drug powder is placed in cubic flow domain and exposed to the relevant flow situations, e.g. plug and shear flow with different Reynolds numbers. Therefrom the fluid forces on the drug particles are obtained. In order to allow the determination of the drug particle detachment possibility by lift-off, sliding or rolling, also measurements by AFM (atomic force microscope) were conducted for different carrier particle surface structures. The contact properties, such as van der Waals force, friction coefficient and adhesion surface energy were used to determine, from a force or moment balance (fluid forces versus contact forces), the detachment probability by the three mechanisms as a function of carrier particle Reynolds number. These results will be used for deriving the drug powder detachment model.}, }
@article {pmid24777527, year = {2014}, author = {Hu, C and Morris, JE and Hartman, RL}, title = {Microfluidic investigation of the deposition of asphaltenes in porous media.}, journal = {Lab on a chip}, volume = {14}, number = {12}, pages = {2014-2022}, doi = {10.1039/c4lc00192c}, pmid = {24777527}, issn = {1473-0189}, abstract = {The deposition of asphaltenes in porous media, an important problem in science and macromolecular engineering, was for the first time investigated in a transparent packed-bed microreactor (μPBR) with online analytics to generate high-throughput information. Residence time distributions of the μPBR before and after loading with ~29 μm quartz particles were measured using inline UV-Vis spectroscopy. Stable packings of quartz particles with porosity of ~40% and permeability of ~500 mD were obtained. The presence of the packing materials reduced dispersion under the same velocity via estimation of dispersion coefficients and the Bodenstein number. Reynolds number was observed to influence the asphaltene deposition mechanism. For larger Reynolds numbers, mechanical entrapment likely resulted in significant pressure drops for less pore volumes injected and less mass of asphaltenes being retained under the same maximum dimensionless pressure drop. The innovation of packed-bed microfluidics for investigations on asphaltene deposition mechanisms could contribute to society by bridging macromolecular science with microsystems.}, }
@article {pmid24771243, year = {2014}, author = {Khapko, T and Duguet, Y and Kreilos, T and Schlatter, P and Eckhardt, B and Henningson, DS}, title = {Complexity of localised coherent structures in a boundary-layer flow.}, journal = {The European physical journal. E, Soft matter}, volume = {37}, number = {4}, pages = {32}, pmid = {24771243}, issn = {1292-895X}, abstract = {We study numerically transitional coherent structures in a boundary-layer flow with homogeneous suction at the wall (the so-called asymptotic suction boundary layer ASBL). The dynamics restricted to the laminar-turbulent separatrix is investigated in a spanwise-extended domain that allows for robust localisation of all edge states. We work at fixed Reynolds number and study the edge states as a function of the streamwise period. We demonstrate the complex spatio-temporal dynamics of these localised states, which exhibits multistability and undergoes complex bifurcations leading from periodic to chaotic regimes. It is argued that in all regimes the dynamics restricted to the edge is essentially low-dimensional and non-extensive.}, }
@article {pmid24771239, year = {2014}, author = {Wedin, H and Bottaro, A and Hanifi, A and Zampogna, G}, title = {Unstable flow structures in the Blasius boundary layer.}, journal = {The European physical journal. E, Soft matter}, volume = {37}, number = {4}, pages = {34}, pmid = {24771239}, issn = {1292-895X}, abstract = {Finite amplitude coherent structures with a reflection symmetry in the spanwise direction of a parallel boundary layer flow are reported together with a preliminary analysis of their stability. The search for the solutions is based on the self-sustaining process originally described by Waleffe (Phys. Fluids 9, 883 (1997)). This requires adding a body force to the Navier-Stokes equations; to locate a relevant nonlinear solution it is necessary to perform a continuation in the nonlinear regime and parameter space in order to render the body force of vanishing amplitude. Some states computed display a spanwise spacing between streaks of the same length scale as turbulence flow structures observed in experiments (S.K. Robinson, Ann. Rev. Fluid Mech. 23, 601 (1991)), and are found to be situated within the buffer layer. The exact coherent structures are unstable to small amplitude perturbations and thus may be part of a set of unstable nonlinear states of possible use to describe the turbulent transition. The nonlinear solutions survive down to a displacement thickness Reynolds number Re * = 496 , displaying a 4-vortex structure and an amplitude of the streamwise root-mean-square velocity of 6% scaled with the free-stream velocity. At this Re* the exact coherent structure bifurcates supercritically and this is the point where the laminar Blasius flow starts to cohabit the phase space with alternative simple exact solutions of the Navier-Stokes equations.}, }
@article {pmid24770612, year = {2014}, author = {Ranjith, SK and Patnaik, BS and Vedantam, S}, title = {Transport of DNA in hydrophobic microchannels: a dissipative particle dynamics simulation.}, journal = {Soft matter}, volume = {10}, number = {23}, pages = {4184-4191}, doi = {10.1039/c3sm53035c}, pmid = {24770612}, issn = {1744-6848}, mesh = {Computer Simulation ; DNA/*chemistry/metabolism ; Hydrophobic and Hydrophilic Interactions ; Models, Molecular ; }, abstract = {In this work, we numerically study a new means of manipulating single DNA chains in microchannels. The method is based on the effect of finite slip at hydrophobic walls on the hydrodynamics and, consequently, on the dynamics of the DNA in microchannels. We use dissipative particle dynamics to study DNA transport as a function of chain length and the Reynolds number in two dimensional parallel plate channels. We show how an asymmetric velocity profile in a channel with hydrophobic and hydrophilic walls can be used to manipulate the location of the DNA molecules. Using this effect, we propose a simple arrangement of hydrophobic and hydrophilic strips which can be exploited to separate long and short DNA chains.}, }
@article {pmid24756029, year = {2014}, author = {Bejan, A and Ziaei, S and Lorente, S}, title = {Evolution: why all plumes and jets evolve to round cross sections.}, journal = {Scientific reports}, volume = {4}, number = {}, pages = {4730}, pmid = {24756029}, issn = {2045-2322}, abstract = {Turbulent curtains of smoke rise initially as flat plumes and, above a certain height, they become round plumes. The same evolution of cross-sectional shape is exhibited by jets issuing from flat nozzles. Here we predict based on principle that all such flows should evolve their cross-sectional shapes from flat to round (and not the other way) at a critical distance downstream, which is predictable. The principle is that the prevailing flow architecture provides greater access to the flow of momentum from the moving core (plume, jet) to the still surroundings. For turbulent plumes and jets, the transition distance scales with the long dimensions (L) of the two-dimensional (flat) heat sources and nozzles that drive them. For laminar jets, the transition distance scales with L Re, where Re is the Reynolds number based on nozzle velocity and the smaller dimension of the nozzle cross section. These predictions are confirmed by full numerical experiments of the three-dimensional flow fields of turbulent and laminar jets covering the Re range 10-10(4).}, }
@article {pmid24754496, year = {2014}, author = {Ozcelik, A and Ahmed, D and Xie, Y and Nama, N and Qu, Z and Nawaz, AA and Huang, TJ}, title = {An acoustofluidic micromixer via bubble inception and cavitation from microchannel sidewalls.}, journal = {Analytical chemistry}, volume = {86}, number = {10}, pages = {5083-5088}, pmid = {24754496}, issn = {1520-6882}, support = {1DP2OD007209-01/OD/NIH HHS/United States ; }, mesh = {Chemistry/instrumentation/methods ; Microfluidic Analytical Techniques/*instrumentation ; Polyethylene Glycols ; Viscosity ; }, abstract = {During the deep reactive ion etching process, the sidewalls of a silicon mold feature rough wavy structures, which can be transferred onto a polydimethylsiloxane (PDMS) microchannel through the soft lithography technique. In this article, we utilized the wavy structures of PDMS microchannel sidewalls to initiate and cavitate bubbles in the presence of acoustic waves. Through bubble cavitation, this acoustofluidic approach demonstrates fast, effective mixing in microfluidics. We characterized its performance by using viscous fluids such as poly(ethylene glycol) (PEG). When two PEG solutions with a resultant viscosity 54.9 times higher than that of water were used, the mixing efficiency was found to be 0.92, indicating excellent, homogeneous mixing. The acoustofluidic micromixer presented here has the advantages of simple fabrication, easy integration, and capability to mix high-viscosity fluids (Reynolds number: ~0.01) in less than 100 ms.}, }
@article {pmid24745238, year = {2014}, author = {Rathnakumar, P and Mayilsamy, K and Suresh, S and Murugesan, P}, title = {Laminar heat transfer and friction factor characteristics of carbon nano tube/water nanofluids.}, journal = {Journal of nanoscience and nanotechnology}, volume = {14}, number = {3}, pages = {2400-2407}, doi = {10.1166/jnn.2014.8505}, pmid = {24745238}, issn = {1533-4880}, abstract = {This paper presents an experimental investigation on the convective heat transfer and friction factor characteristics of CNT/water nanofluid through a circular tube fitted with helical screw tape inserts with constant heat flux under laminar flow condition. Nanofluids of 0.1% and 0.2% volume fractions are prepared by two step method. Thermo-physical properties like thermal conductivity and viscosity are measured by using KD2 thermal property analyzer and Brooke field cone and plate viscometer respectively. From the measurements, it is found that the viscosity increase is substantially higher than the increase in the thermal conductivity. The helical screw tape insets with twist ratios Y = 3, 2.44 and 1.78 are used to study the convective heat transfer and friction factor characteristics under laminar flow in the Reynolds number range of 520-2500. It is observed that, in a plain tube, maximum enhancement in Nusselt number for 0.1% and 0.2% volume fractions of nanofluids compared to pure water is 15% and 32% respectively. With the use of inserts, maximum enhancement in Nusselt number corresponding to twist ratios of 1.78, 2.44 and 3 are obtained as 8%, 16% and 4.6% for 0.1% volume fraction of nanofluid and 5%, 4% and 12% for 0.2% volume fraction of nanofluid when compared with water in plain tube. Thermal performance factor evaluation revealed that the values at all Reynolds number for all twist ratios and both concentration of CNT nanofluid are greater than unity which indicates that helical screw tape inserts with twist ratios considered are feasible in terms of energy saving in laminar flow.}, }
@article {pmid24745233, year = {2014}, author = {Dominic, A and Sarangan, J and Suresh, S and Sai, M}, title = {Heat transfer performance of Al2O3/water nanofluids in a mini channel heat sink.}, journal = {Journal of nanoscience and nanotechnology}, volume = {14}, number = {3}, pages = {2368-2376}, doi = {10.1166/jnn.2014.8543}, pmid = {24745233}, issn = {1533-4880}, abstract = {The high density heat removal in electronic packaging is a challenging task of modern days. Finding compact, energy efficient and cost effective methods of heat removal is being the interest of researchers. In the present work, mini channel with forced convective heat transfer in simultaneously developing regime is investigated as the heat transfer coefficient is inversely proportional to hydraulic diameter. Mini channel heat sink is made from the aluminium plate of 30 mm square with 8 mm thickness. It has 15 mini channel of 0.9 mm width, 1.3 mm height and 0.9 mm of pitch. DI water and water based 0.1% and 0.2% volume fractions of Al2O3/water nanofluids are used as coolant. The flow rates of the coolants are maintained in such a way that it is simultaneously developing. Reynolds number is varied from 400 to 1600 and heat input is varied from 40 W to 70 W. The results showed that heat transfer coefficient is more than the heat transfer coefficient of fully developed flow. Also the heat transfer is more for nanofluids compared to DI water.}, }
@article {pmid24744905, year = {2014}, author = {Nakamura, Y and Awa, S}, title = {Radius exponent in elastic and rigid arterial models optimized by the least energy principle.}, journal = {Physiological reports}, volume = {2}, number = {2}, pages = {e00236}, pmid = {24744905}, issn = {2051-817X}, abstract = {It was analyzed in normal physiological arteries whether the least energy principle would suffice to account for the radius exponent x. The mammalian arterial system was modeled as two types, the elastic or the rigid, to which Bernoulli's and Hagen-Poiseuille's equations were applied, respectively. We minimized the total energy function E, which was defined as the sum of kinetic, pressure, metabolic and thermal energies, and loss of each per unit time in a single artery transporting viscous incompressible blood. Assuming a scaling exponent α between the vessel radius (r) and length (l) to be 1.0, x resulted in 2.33 in the elastic model. The rigid model provided a continuously changing x from 2.33 to 3.0, which corresponded to Uylings' and Murray's theories, respectively, through a function combining Reynolds number with a proportional coefficient of the l - r relationship. These results were expanded to an asymmetric arterial fractal tree with the blood flow preservation rule. While x in the optimal elastic model accounted for around 2.3 in proximal systemic (r >1 mm) and whole pulmonary arteries (r ≥0.004 mm), optimal x in the rigid model explained 2.7 in elastic-muscular (0.1 < r ≤1 mm) and 3.0 in peripheral resistive systemic arteries (0.004 ≤ r ≤0.1 mm), in agreement with data obtained from angiographic, cast-morphometric, and in vivo experimental studies in the literature. The least energy principle on the total energy basis provides an alternate concept of optimality relating to mammalian arterial fractal dimensions under α = 1.0.}, }
@article {pmid24738015, year = {2014}, author = {Fan, LL and He, XK and Han, Y and Du, L and Zhao, L and Zhe, J}, title = {Continuous size-based separation of microparticles in a microchannel with symmetric sharp corner structures.}, journal = {Biomicrofluidics}, volume = {8}, number = {2}, pages = {024108}, pmid = {24738015}, issn = {1932-1058}, abstract = {A new microchannel with a series of symmetric sharp corner structures is reported for passive size-dependent particle separation. Micro particles of different sizes can be completely separated based on the combination of the inertial lift force and the centrifugal force induced by the sharp corner structures in the microchannel. At appropriate flow rate and Reynolds number, the centrifugal force effect on large particles, induced by the sharp corner structures, is stronger than that on small particles; hence after passing a series of symmetric sharp corner structures, large particles are focused to the center of the microchannel, while small particles are focused at two particle streams near the two side walls of the microchannel. Particles of different sizes can then be completely separated. Particle separation with this device was demonstrated using 7.32 μm and 15.5 μm micro particles. Experiments show that in comparison with the prior multi-orifice flow fractionation microchannel and multistage-multiorifice flow fractionation microchannel, this device can completely separate two-size particles with narrower particle stream band and larger separation distance between particle streams. In addition, it requires no sheath flow and complex multi-stage separation structures, avoiding the dilution of analyte sample and complex operations. The device has potentials to be used for continuous, complete particle separation in a variety of lab-on-a-chip and biomedical applications.}, }
@article {pmid24736320, year = {2014}, author = {Hayat, T and Abbasi, FM and Ahmad, B and Alsaedi, A}, title = {Peristaltic transport of Carreau-Yasuda fluid in a curved channel with slip effects.}, journal = {PloS one}, volume = {9}, number = {4}, pages = {e95070}, pmid = {24736320}, issn = {1932-6203}, mesh = {Algorithms ; *Models, Theoretical ; }, abstract = {The wide occurrence of peristaltic pumping should not be surprising at all since it results physiologically from neuro-muscular properties of any tubular smooth muscle. Of special concern here is to predict the rheological effects on the peristaltic motion in a curved channel. Attention is focused to develop and simulate a nonlinear mathematical model for Carreau-Yasuda fluid. The progressive wave front of peristaltic flow is taken sinusoidal (expansion/contraction type). The governing problem is challenge since it has nonlinear differential equation and nonlinear boundary conditions even in the long wavelength and low Reynolds number regime. Numerical solutions for various flow quantities of interest are presented. Comparison for different flow situations is also made. Results of physical quantities are interpreted with particular emphasis to rheological characteristics.}, }
@article {pmid24730943, year = {2014}, author = {Okamoto, N and Yoshimatsu, K and Schneider, K and Farge, M}, title = {Small-scale anisotropic intermittency in magnetohydrodynamic turbulence at low magnetic Reynolds numbers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {3}, pages = {033013}, doi = {10.1103/PhysRevE.89.033013}, pmid = {24730943}, issn = {1550-2376}, abstract = {Small-scale anisotropic intermittency is examined in three-dimensional incompressible magnetohydrodynamic turbulence subjected to a uniformly imposed magnetic field. Orthonormal wavelet analyses are applied to direct numerical simulation data at moderate Reynolds number and for different interaction parameters. The magnetic Reynolds number is sufficiently low such that the quasistatic approximation can be applied. Scale-dependent statistical measures are introduced to quantify anisotropy in terms of the flow components, either parallel or perpendicular to the imposed magnetic field, and in terms of the different directions. Moreover, the flow intermittency is shown to increase with increasing values of the interaction parameter, which is reflected in strongly growing flatness values when the scale decreases. The scale-dependent anisotropy of energy is found to be independent of scale for all considered values of the interaction parameter. The strength of the imposed magnetic field does amplify the anisotropy of the flow.}, }
@article {pmid24730940, year = {2014}, author = {Ding, Z and Wong, TN}, title = {Electrohydrodynamic instability in an annular liquid layer with radial conductivity gradients.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {3}, pages = {033010}, doi = {10.1103/PhysRevE.89.033010}, pmid = {24730940}, issn = {1550-2376}, abstract = {In this paper, the electrohydrodynamic stability in an annular liquid layer with a radial electrical conductivity gradient is investigated. A weak shear flow arises from a constant pressure gradient in the axial direction. In the radial direction, an electric field is applied. The three-dimensional linear instability analysis is implemented to study the influence of the inner radius, electrical conductivity gradient, shear flow, and ionic diffusion on the dynamics of the fluid layer. It is found that the critical unstable mode may either be oscillatory or stationary. The system becomes more unstable as the dimensionless inner radius a increases. When the inner radius a is small, the critical unstable mode is stationary, while it is given by three-dimensional oblique waves when a is large. When the conductivity gradient is small, the critical unstable mode is the three-dimensional oblique wave, while when the conductivity gradient is large, it would switch to the stationary mode rather than the oscillatory mode. The system becomes more unstable when the Reynolds number is slightly increased from zero. Additionally, it is found that the electrical Schmidt number has dual effects. The liquid layer becomes either more unstable or stable as the electric Schmidt number increases.}, }
@article {pmid24730939, year = {2014}, author = {Rüdiger, G and Brandenburg, A}, title = {α effect in a turbulent liquid-metal plane Couette flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {3}, pages = {033009}, doi = {10.1103/PhysRevE.89.033009}, pmid = {24730939}, issn = {1550-2376}, abstract = {We calculate the mean electromotive force in plane Couette flows of a nonrotating conducting fluid under the influence of a large-scale magnetic field for driven turbulence. A vertical stratification of the turbulence intensity results in an α effect owing to the presence of horizontal shear. Here we discuss the possibility of an experimental determination of the components of the α tensor using both quasilinear theory and nonlinear numerical simulations. For magnetic Prandtl numbers of the order of unity, we find that in the high-conductivity limit the α effect in the direction of the flow clearly exceeds the component in spanwise direction. In this limit, α runs linearly with the magnetic Reynolds number Rm, while in the low-conductivity limit it runs with the product Rm·Re, where Re is the kinetic Reynolds number, so that for a given Rm the α effect grows with decreasing magnetic Prandtl number. For the small magnetic Prandtl numbers of liquid metals, a common value for the horizontal elements of the α tensor appears, which makes it unimportant whether the α effect is measured in the spanwise or the streamwise directions. The resulting effect should lead to an observable voltage of about 0.5 mV in both directions for magnetic fields of 1 kG and velocity fluctuations of about 1 m/s in a channel of 50-cm height (independent of its width).}, }
@article {pmid24724653, year = {2014}, author = {du Puits, R and Li, L and Resagk, C and Thess, A and Willert, C}, title = {Turbulent boundary layer in high Rayleigh number convection in air.}, journal = {Physical review letters}, volume = {112}, number = {12}, pages = {124301}, doi = {10.1103/PhysRevLett.112.124301}, pmid = {24724653}, issn = {1079-7114}, abstract = {Flow visualizations and particle image velocimetry measurements in the boundary layer of a Rayleigh-Bénard experiment are presented for the Rayleigh number Ra=1.4×1010. Our visualizations indicate that the appearance of the flow structures is similar to ordinary (isothermal) turbulent boundary layers. Our particle image velocimetry measurements show that vorticity with both positive and negative sign is generated and that the smallest flow structures are 1 order of magnitude smaller than the boundary layer thickness. Additional local measurements using laser Doppler velocimetry yield turbulence intensities up to I=0.4 as in turbulent atmospheric boundary layers. From our observations, we conclude that the convective boundary layer becomes turbulent locally and temporarily although its Reynolds number Re≈200 is considerably smaller than the value 420 underlying existing phenomenological theories. We think that, in turbulent Rayleigh-Bénard convection, the transition of the boundary layer towards turbulence depends on subtle details of the flow field and is therefore not universal.}, }
@article {pmid24721664, year = {2014}, author = {Phuntsho, S and Lotfi, F and Hong, S and Shaffer, DL and Elimelech, M and Shon, HK}, title = {Membrane scaling and flux decline during fertiliser-drawn forward osmosis desalination of brackish groundwater.}, journal = {Water research}, volume = {57}, number = {}, pages = {172-182}, doi = {10.1016/j.watres.2014.03.034}, pmid = {24721664}, issn = {1879-2448}, mesh = {Fertilizers/*analysis ; Groundwater/*chemistry ; Microscopy, Electron, Scanning ; *Osmosis ; *Salinity ; Spectrometry, X-Ray Emission ; Water Purification/*methods ; X-Ray Diffraction ; }, abstract = {Fertiliser-drawn forward osmosis (FDFO) desalination has been recently studied as one feasible application of forward osmosis (FO) for irrigation. In this study, the potential of membrane scaling in the FDFO process has been investigated during the desalination of brackish groundwater (BGW). While most fertilisers containing monovalent ions did not result in any scaling when used as an FO draw solution (DS), diammonium phosphate (DAP or (NH4)2HPO4) resulted in significant scaling, which contributed to severe flux decline. Membrane autopsy using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD) analysis indicated that the reverse diffusion of DAP from the DS to the feed solution was primarily responsible for scale formation during the FDFO process. Physical cleaning of the membrane with deionised water at varying crossflow velocities was employed to evaluate the reversibility of membrane scaling and the extent of flux recovery. For the membrane scaled using DAP as DS, 80-90% of the original flux was recovered when the crossflow velocity for physical cleaning was the same as the crossflow velocity during FDFO desalination. However, when a higher crossflow velocity or Reynolds number was used, the flux was recovered almost completely, irrespective of the DS concentration used. This study underscores the importance of selecting a suitable fertiliser for FDFO desalination of brackish groundwater to avoid membrane scaling and severe flux decline.}, }
@article {pmid24718997, year = {2014}, author = {Anzai, H and Falcone, JL and Chopard, B and Hayase, T and Ohta, M}, title = {Optimization of strut placement in flow diverter stents for four different aneurysm configurations.}, journal = {Journal of biomechanical engineering}, volume = {136}, number = {6}, pages = {061006}, doi = {10.1115/1.4027411}, pmid = {24718997}, issn = {1528-8951}, mesh = {Algorithms ; *Blood Circulation ; Intracranial Aneurysm/pathology/*physiopathology ; Models, Anatomic ; *Prosthesis Design ; *Stents ; }, abstract = {A modern technique for the treatment of cerebral aneurysms involves insertion of a flow diverter stent. Flow stagnation, produced by the fine mesh structure of the diverter, is thought to promote blood clotting in an aneurysm. However, apart from its effect on flow reduction, the insertion of the metal device poses the risk of occlusion of a parent artery. One strategy for avoiding the risk of arterial occlusion is the use of a device with a higher porosity. To aid the development of optimal stents in the view point of flow reduction maintaining a high porosity, we used lattice Boltzmann flow simulations and simulated annealing optimization to investigate the optimal placement of stent struts. We constructed four idealized aneurysm geometries that resulted in four different inflow characteristics and employed a stent model with 36 unconnected struts corresponding to the porosity of 80%. Assuming intracranial flow, steady flow simulation with Reynolds number of 200 was applied for each aneurysm. Optimization of strut position was performed to minimize the average velocity in an aneurysm while maintaining the porosity. As the results of optimization, we obtained nonuniformed structure as optimized stent for each aneurysm geometry. And all optimized stents were characterized by denser struts in the inflow area. The variety of inflow patterns that resulted from differing aneurysm geometries led to unique strut placements for each aneurysm type.}, }
@article {pmid24704879, year = {2014}, author = {Eltsov, V and Hänninen, R and Krusius, M}, title = {Quantum turbulence in superfluids with wall-clamped normal component.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {111 Suppl 1}, number = {Suppl 1}, pages = {4711-4718}, pmid = {24704879}, issn = {1091-6490}, abstract = {In Fermi superfluids, such as superfluid (3)He, the viscous normal component can be considered to be stationary with respect to the container. The normal component interacts with the superfluid component via mutual friction, which damps the motion of quantized vortex lines and eventually couples the superfluid component to the container. With decreasing temperature and mutual friction, the internal dynamics of the superfluid component becomes more important compared with the damping and coupling effects from the normal component. As a result profound changes in superfluid dynamics are observed: the temperature-dependent transition from laminar to turbulent vortex motion and the decoupling from the reference frame of the container at even lower temperatures.}, }
@article {pmid24700264, year = {2014}, author = {Nason, F and Pennati, G and Dubini, G}, title = {Computational modeling of passive furrowed channel micromixers for lab-on-a-chip applications.}, journal = {Journal of applied biomaterials &amp; functional materials}, volume = {12}, number = {3}, pages = {278-285}, doi = {10.5301/jabfm.5000191}, pmid = {24700264}, issn = {2280-8000}, mesh = {Computer Simulation ; Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Microfluidic Analytical Techniques/*instrumentation/methods ; *Models, Chemical ; Solutions/*chemistry ; }, abstract = {BACKGROUND: Effective micromixers represent essential components for micro total analysis systems or lab-on-a-chip. Indeed, mixing is a key process for the success of all chemical or biochemical reactions. Most microfluidic systems operate in a laminar flow regime dominated by molecular diffusion, which is not favorable to mixing. In the present work, numerical analyses of mixing in 3-dimensional channels with obstacles on the walls were performed to investigate mixing behavior and flow characteristics with geometric parameters as well as Reynolds number.<br><br>METHODS: Several channel wall geometries were numerically modeled, and the influence of obstacle height, phase shift between the walls, channel cross-section shape (aspect ratio) and Reynolds number on mixer performances was investigated. Wall geometries were evaluated comparatively in terms of index of mixing and pressure drops caused.<br><br>RESULTS: Results indicated that furrowed channels with proper triangle-shaped obstacles show good performances in terms of achieving complete mixing in a very short length of channel, and at the same time offer low pressure losses. Convective motions are the main influences responsible for successful mixing, and micromixers with triangle-shaped obstacles show an improvement in the mixing performances for increasing Reynolds numbers. Moreover, short times are required for the mixing process. Finally, depending on the Reynolds number that one works at, there is also some flexibility in the choice of the channel geometry, as the occurrence of effective chaotic advection was obtained for several conformations of the channels proposed in this study.<br><br>CONCLUSIONS: Mixing enhancement can be achieved by optimizing the shape of the furrowed channel.}, }
@article {pmid24671449, year = {2014}, author = {Battiato, I}, title = {Effective medium theory for drag-reducing micro-patterned surfaces in turbulent flows.}, journal = {The European physical journal. E, Soft matter}, volume = {37}, number = {3}, pages = {19}, pmid = {24671449}, issn = {1292-895X}, abstract = {Many studies in the last decade have revealed that patterns at the microscale can reduce skin drag. Yet, the mechanisms and parameters that control drag reduction, e.g. Reynolds number and pattern geometry, are still unclear. We propose an effective medium representation of the micro-features, that treats the latter as a porous medium, and provides a framework to model turbulent flow over patterned surfaces. Our key result is a closed-form expression for the skin friction coefficient in terms of frictional Reynolds (or Kármán) number in turbulent regime, the viscosity ratio between the fluid in and above the features, and their geometrical properties. We apply the proposed model to turbulent flows over superhydrophobic ridged surfaces. The model predictions agree with laboratory experiments for Reynolds numbers ranging from 3000 to 10000.}, }
@article {pmid24671019, year = {2014}, author = {Wickramarathna, LN and Noss, C and Lorke, A}, title = {Hydrodynamic trails produced by Daphnia: size and energetics.}, journal = {PloS one}, volume = {9}, number = {3}, pages = {e92383}, pmid = {24671019}, issn = {1932-6203}, mesh = {Animals ; Biomechanical Phenomena ; Daphnia/*physiology ; *Hydrodynamics ; Swimming ; Viscosity ; Zooplankton ; }, abstract = {This study focuses on quantifying hydrodynamic trails produced by freely swimming zooplankton. We combined volumetric tracking of swimming trajectories with planar observations of the flow field induced by Daphnia of different size and swimming in different patterns. Spatial extension of the planar flow field along the trajectories was used to interrogate the dimensions (length and volume) and energetics (dissipation rate of kinetic energy and total dissipated power) of the trails. Our findings demonstrate that neither swimming pattern nor size of the organisms affect the trail width or the dissipation rate. However, we found that the trail volume increases with increasing organism size and swimming velocity, more precisely the trail volume is proportional to the third power of Reynolds number. This increase furthermore results in significantly enhanced total dissipated power at higher Reynolds number. The biggest trail volume observed corresponds to about 500 times the body volume of the largest daphnids. Trail-averaged viscous dissipation rate of the swimming daphnids vary in the range of 1.8 x 10(-6) W/kg to 3.4 x 10(-6) W/kg and the observed magnitudes of total dissipated power between 1.3 x 10(-9) W and 1 x 10(-8) W, respectively. Among other zooplankton species, daphnids display the highest total dissipated power in their trails. These findings are discussed in the context of fluid mixing and transport by organisms swimming at intermediate Reynolds numbers.}, }
@article {pmid24647804, year = {2014}, author = {Dey, R and Raj M, K and Bhandaru, N and Mukherjee, R and Chakraborty, S}, title = {Tunable hydrodynamic characteristics in microchannels with biomimetic superhydrophobic (lotus leaf replica) walls.}, journal = {Soft matter}, volume = {10}, number = {19}, pages = {3451-3462}, doi = {10.1039/c4sm00037d}, pmid = {24647804}, issn = {1744-6848}, mesh = {Biomimetic Materials/*chemistry ; *Hydrodynamics ; Hydrophobic and Hydrophilic Interactions ; Lotus/*chemistry ; Microscopy, Fluorescence ; Plant Leaves/chemistry ; Surface Properties ; }, abstract = {The present work comprehensively addresses the hydrodynamic characteristics through microchannels with lotus leaf replica (exhibiting low adhesion and superhydrophobic properties) walls. The lotus leaf replica is fabricated following an efficient, two-step, soft-molding process and is then integrated with rectangular microchannels. The inherent biomimetic, superhydrophobic surface-liquid interfacial hydrodynamics, and the consequential bulk flow characteristics, are critically analyzed by the micro-particle image velocimetry technique. It is observed that the lotus leaf replica mediated microscale hydrodynamics comprise of two distinct flow regimes even within the low Reynolds number paradigm, unlike the commonly perceived solely apparent slip-stick dominated flows over superhydrophobic surfaces. While the first flow regime is characterized by an apparent slip-stick flow culminating in an enhanced bulk throughput rate, the second flow regime exhibits a complete breakdown of the aforementioned laminar and uni-axial flow model, leading to a predominantly no-slip flow. Interestingly, the critical flow condition dictating the transition between the two hydrodynamic regimes is intrinsically dependent on the micro-confinement effect. In this regard, an energetically consistent theoretical model is also proposed to predict the alterations in the critical flow condition with varying microchannel configurations, by addressing the underlying biomimetic surface-liquid interfacial conditions. Hence, the present research endeavour provides a new design-guiding paradigm for developing multi-functional microfluidic devices involving biomimetic, superhydrophobic surfaces, by judicious exploitation of the tunable hydrodynamic characteristics in the two regimes.}, }
@article {pmid24633506, year = {2014}, author = {Jachero, L and Ahumada, I and Richter, P}, title = {Rotating-disk sorptive extraction: effect of the rotation mode of the extraction device on mass transfer efficiency.}, journal = {Analytical and bioanalytical chemistry}, volume = {406}, number = {12}, pages = {2987-2992}, doi = {10.1007/s00216-014-7693-z}, pmid = {24633506}, issn = {1618-2650}, abstract = {The extraction device used in rotating-disk sorptive extraction consists of a Teflon disk in which a sorptive phase is fixed on one of its surfaces. Depending on the configuration, the rotation axis of the disk device can be either perpendicular or parallel to its radius, giving rise to two different mass transfer patterns when rotating-disk sorptive extraction is applied in liquid samples. In the perpendicular case (configuration 1), which is the typical configuration, the disk contains an embedded miniature stir bar that allows the disk rotation to be driven using a common laboratory magnetic stirrer. In the parallel case (configuration 2), the disk is driven by a rotary rod connected to an electric stirrer. In this study, triclosan and its degradation product methyl triclosan were used as analyte models to demonstrate the significant effect of the rotation configuration of the disk on the efficiency of analyte mass transfer from water to a sorptive phase of polydimethylsiloxane. Under the same experimental conditions and at a rotation velocity of 1,250 rpm, extraction equilibrium was reached at 80 min when the disk was rotated in configuration 1 and at 30 min when the disk was rotated in configuration 2. The extraction equilibration time decreased to 14 min when the rotation velocity was increased to 2,000 rpm in configuration 2. Because the rotation pattern affects the mass transfer efficiency, each rotation configuration was characterized through the Reynolds number; Re values of 6,875 and 16,361 were achieved with configurations 1 and 2, respectively, at 1,250 rpm.}, }
@article {pmid24632825, year = {2014}, author = {Horstmann, JT and Henningsson, P and Thomas, AL and Bomphrey, RJ}, title = {Wake development behind paired wings with tip and root trailing vortices: consequences for animal flight force estimates.}, journal = {PloS one}, volume = {9}, number = {3}, pages = {e91040}, pmid = {24632825}, issn = {1932-6203}, support = {BB/J001244/2/BB_/Biotechnology and Biological Sciences Research Council/United Kingdom ; BB/J001244/1/BB_/Biotechnology and Biological Sciences Research Council/United Kingdom ; }, mesh = {Animals ; Flight, Animal/*physiology ; Models, Biological ; Rheology ; Wings, Animal/*physiology ; }, abstract = {Recent experiments on flapping flight in animals have shown that a variety of unrelated species shed a wake behind left and right wings consisting of both tip and root vortices. Here we present an investigation using Particle Image Velocimetry (PIV) of the behaviour and interaction of trailing vortices shed by paired, fixed wings that simplify and mimic the wake of a flying animal with a non-lifting body. We measured flow velocities at five positions downstream of two adjacent NACA 0012 aerofoils and systematically varied aspect ratio, the gap between the wings (corresponding to the width of a non-lifting body), angle of attack, and the Reynolds number. The range of aspect ratios and Reynolds number where chosen to be relevant to natural fliers and swimmers, and insect flight in particular. We show that the wake behind the paired wings deformed as a consequence of the induced flow distribution such that the wingtip vortices convected downwards while the root vortices twist around each other. Vortex interaction and wake deformation became more pronounced further downstream of the wing, so the positioning of PIV measurement planes in experiments on flying animals has an important effect on subsequent force estimates due to rotating induced flow vectors. Wake deformation was most severe behind wings with lower aspect ratios and when the distance between the wings was small, suggesting that animals that match this description constitute high-risk groups in terms of measurement error. Our results, therefore, have significant implications for experimental design where wake measurements are used to estimate forces generated in animal flight. In particular, the downstream distance of the measurement plane should be minimised, notwithstanding the animal welfare constraints when measuring the wake behind flying animals.}, }
@article {pmid24632685, year = {2014}, author = {Sochol, RD and Lu, A and Lei, J and Iwai, K and Lee, LP and Lin, L}, title = {Microfluidic bead-based diodes with targeted circular microchannels for low Reynolds number applications.}, journal = {Lab on a chip}, volume = {14}, number = {9}, pages = {1585-1594}, doi = {10.1039/c3lc51069g}, pmid = {24632685}, issn = {1473-0189}, mesh = {Dimethylpolysiloxanes/chemistry ; Microfluidic Analytical Techniques/*instrumentation ; *Microspheres ; Models, Theoretical ; Pressure ; }, abstract = {Self-regulating fluidic components are critical to the advancement of microfluidic processors for chemical and biological applications, such as sample preparation on chip, point-of-care molecular diagnostics, and implantable drug delivery devices. Although researchers have developed a wide range of components to enable flow rectification in fluidic systems, engineering microfluidic diodes that function at the low Reynolds number (Re) flows and smaller scales of emerging micro/nanofluidic platforms has remained a considerable challenge. Recently, researchers have demonstrated microfluidic diodes that utilize high numbers of suspended microbeads as dynamic resistive elements; however, using spherical particles to block fluid flow through rectangular microchannels is inherently limited. To overcome this issue, here we present a single-layer microfluidic bead-based diode (18 μm in height) that uses a targeted circular-shaped microchannel for the docking of a single microbead (15 μm in diameter) to rectify fluid flow under low Re conditions. Three-dimensional simulations and experimental results revealed that adjusting the docking channel geometry and size to better match the suspended microbead greatly increased the diodicity (Di) performance. Arraying multiple bead-based diodes in parallel was found to adversely affect system efficacy, while arraying multiple diodes in series was observed to enhance device performance. In particular, systems consisting of four microfluidic bead-based diodes with targeted circular-shaped docking channels in series revealed average Di's ranging from 2.72 ± 0.41 to 10.21 ± 1.53 corresponding to Re varying from 0.1 to 0.6.}, }
@article {pmid24605055, year = {2014}, author = {Salman, SD and Kadhum, AA and Takriff, MS and Mohamad, AB}, title = {Heat transfer enhancement of laminar nanofluids flow in a circular tube fitted with parabolic-cut twisted tape inserts.}, journal = {TheScientificWorldJournal}, volume = {2014}, number = {}, pages = {543231}, pmid = {24605055}, issn = {1537-744X}, mesh = {Algorithms ; *Models, Theoretical ; }, abstract = {Numerical investigation has been carried out on heat transfer and friction factor characteristics of copper-water nanofluid flow in a constant heat-fluxed tube with the existence of new configuration of vortex generator using Computational Fluid Dynamics (CFD) simulation. Two types of swirl flow generator: Classical twisted tape (CTT) and Parabolic-cut twisted tape (PCT) with a different twist ratio (y = 2.93, 3.91 and 4.89) and different cut depth (w = 0.5, 1.0 and 1.5 cm) with 2% and 4% volume concentration of CuO nanofluid were used for simulation. The effect of different parameters such as flow Reynolds number, twist ratio, cut depth and nanofluid were considered. The results show that the enhancement of heat transfer rate and the friction factor induced by the Classical (CTT) and Parabolic-cut (PCT) inserts increases with twist ratio and cut depth decreases. The results also revealed that the heat transfer enhancement increases with an increase in the volume fraction of the CuO nanoparticle. Furthermore, the twisted tape with twist ratio (y = 2.93) and cut depth w = 0.5 cm offered 10% enhancement of the average Nusselt number with significant increases in friction factor than those of Classical twisted tape.}, }
@article {pmid24599543, year = {2014}, author = {Wang, GR and Yang, F and Zhao, W}, title = {There can be turbulence in microfluidics at low Reynolds number.}, journal = {Lab on a chip}, volume = {14}, number = {8}, pages = {1452-1458}, doi = {10.1039/c3lc51403j}, pmid = {24599543}, issn = {1473-0189}, mesh = {Diffusion ; *Hydrodynamics ; Kinetics ; *Microfluidics ; Pressure ; }, abstract = {Turbulence is commonly viewed as a type of macroflow, where the Reynolds number (Re) has to be sufficiently high. In microfluidics, when Re is below or on the order of 1 and fast mixing is required, so far only chaotic flow has been reported to enhance mixing based on previous publications since turbulence is believed not to be possible to generate in such a low Re microflow. There is even a lack of velocimeter that can measure turbulence in microchannels. In this work, we report a direct observation of the existence of turbulence in microfluidics with Re on the order of 1 in a pressure driven flow under electrokinetic forcing using a novel velocimeter having ultrahigh spatiotemporal resolution. The work could provide a new method to control flow and transport phenomena in lab-on-a-chip and a new perspective on turbulence.}, }
@article {pmid24592153, year = {2014}, author = {Wu, PS and Tsai, ST and Jhuo, YH}, title = {Effect of turbulence intensity on cross-injection film cooling at a stepped or smooth endwall of a gas turbine vane passage.}, journal = {TheScientificWorldJournal}, volume = {2014}, number = {}, pages = {256136}, doi = {10.1155/2014/256136}, pmid = {24592153}, issn = {1537-744X}, mesh = {Liquid Crystals ; *Natural Gas ; Power Plants/*instrumentation ; Temperature ; }, abstract = {This study is concerned with a film cooling technique applicable to the protection of the endwalls of a gas turbine vane. In the experiments, cross-injection coolant flow from two-row, paired, inclined holes with nonintersecting centerlines was utilized. The test model is a scaled two-half vane. The levels of turbulence intensity used in the experiments are T.I. = 1.8%, 7%, and 12%. Other parameters considered in the film cooling experiments include three inlet Reynolds numbers (9.20 × 10(4), 1.24 × 10(5), and 1.50 × 10(5)), three blowing ratios (0.5, 1.0, and 2.0), and three endwall conditions (smooth endwall and stepped endwall with forward-facing or backward-facing step). Thermochromic liquid crystal (TLC) technique with steady-state heat transfer experiments was used to obtain the whole-field film cooling effectiveness. Results show that, at low turbulence intensity, increasing Reynolds number decreases the effectiveness in most of the vane passage. There is no monotonic trend of influence by Reynolds number at high turbulence intensity. The effect of blowing ratio on the effectiveness has opposite trends at low and high turbulence levels. Increasing turbulent intensity decreases the effectiveness, especially near the inlet of the vane passage. With a stepped endwall, turbulence intensity has only mild effect on the film cooling effectiveness.}, }
@article {pmid24587561, year = {2014}, author = {Anupindi, K and Lai, W and Frankel, S}, title = {Characterization of oscillatory instability in lid driven cavity flows using lattice Boltzmann method.}, journal = {Computers &amp; fluids}, volume = {92}, number = {}, pages = {7-21}, pmid = {24587561}, issn = {0045-7930}, support = {R01 HL098353/HL/NHLBI NIH HHS/United States ; }, abstract = {In the present work, lattice Boltzmann method (LBM) is applied for simulating flow in a three-dimensional lid driven cubic and deep cavities. The developed code is first validated by simulating flow in a cubic lid driven cavity at 1000 and 12000 Reynolds numbers following which we study the effect of cavity depth on the steady-oscillatory transition Reynolds number in cavities with depth aspect ratio equal to 1, 2 and 3. Turbulence modeling is performed through large eddy simulation (LES) using the classical Smagorinsky sub-grid scale model to arrive at an optimum mesh size for all the simulations. The simulation results indicate that the first Hopf bifurcation Reynolds number correlates negatively with the cavity depth which is consistent with the observations from two-dimensional deep cavity flow data available in the literature. Cubic cavity displays a steady flow field up to a Reynolds number of 2100, a delayed anti-symmetry breaking oscillatory field at a Reynolds number of 2300, which further gets restored to a symmetry preserving oscillatory flow field at 2350. Deep cavities on the other hand only attain an anti-symmetry breaking flow field from a steady flow field upon increase of the Reynolds number in the range explored. As the present work involved performing a set of time-dependent calculations for several Reynolds numbers and cavity depths, the parallel performance of the code is evaluated a priori by running the code on up to 4096 cores. The computational time required for these runs shows a close to linear speed up over a wide range of processor counts depending on the problem size, which establishes the feasibility of performing a thorough search process such as the one presently undertaken.}, }
@article {pmid24584155, year = {2014}, author = {Tay, WB and van Oudheusden, BW and Bijl, H}, title = {Numerical simulation of X-wing type biplane flapping wings in 3D using the immersed boundary method.}, journal = {Bioinspiration &amp; biomimetics}, volume = {9}, number = {3}, pages = {036001}, doi = {10.1088/1748-3182/9/3/036001}, pmid = {24584155}, issn = {1748-3190}, mesh = {Aircraft/*instrumentation ; Algorithms ; Animals ; Biological Clocks/physiology ; Biomimetics/*instrumentation ; Computer Simulation ; *Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Flight, Animal/*physiology ; *Models, Biological ; Movement/*physiology ; Numerical Analysis, Computer-Assisted ; Oscillometry/methods ; Wings, Animal/*physiology ; }, abstract = {The numerical simulation of an insect-sized 'X-wing' type biplane flapping wing configuration is performed in 3D using an immersed boundary method solver at Reynolds numbers equal to 1000 (1 k) and 5 k, based on the wing's root chord length. This X-wing type flapping configuration draws its inspiration from Delfly, a bio-inspired ornithopter MAV which has two pairs of wings flapping in anti-phase in a biplane configuration. The objective of the present investigation is to assess the aerodynamic performance when the original Delfly flapping wing micro-aerial vehicle (FMAV) is reduced to the size of an insect. Results show that the X-wing configuration gives more than twice the average thrust compared with only flapping the upper pair of wings of the X-wing. However, the X-wing's average thrust is only 40% that of the upper wing flapping at twice the stroke angle. Despite this, the increased stability which results from the smaller lift and moment variation of the X-wing configuration makes it more suited for sharp image capture and recognition. These advantages make the X-wing configuration an attractive alternative design for insect-sized FMAVS compared to the single wing configuration. In the Reynolds number comparison, the vorticity iso-surface plot at a Reynolds number of 5 k revealed smaller, finer vortical structures compared to the simulation at 1 k, due to vortices' breakup. In comparison, the force output difference is much smaller between Re = 1 k and 5 k. Increasing the body inclination angle generates a uniform leading edge vortex instead of a conical one along the wingspan, giving higher lift. Understanding the force variation as the body inclination angle increases will allow FMAV designers to optimize the thrust and lift ratio for higher efficiency under different operational requirements. Lastly, increasing the spanwise flexibility of the wings increases the thrust slightly but decreases the efficiency. The thrust result is similar to one of the spanwise studies, but the efficiency result contradicts it, indicating that other flapping parameters are involved as well. Results from this study provide a deeper understanding of the underlying aerodynamics of the X-wing type, which will help to improve the performance of insect-sized FMAVs using this unique configuration.}, }
@article {pmid24580458, year = {2014}, author = {Kreilos, T and Eckhardt, B and Schneider, TM}, title = {Increasing lifetimes and the growing saddles of shear flow turbulence.}, journal = {Physical review letters}, volume = {112}, number = {4}, pages = {044503}, doi = {10.1103/PhysRevLett.112.044503}, pmid = {24580458}, issn = {1079-7114}, abstract = {In linearly stable shear flows, turbulence spontaneously decays with a characteristic lifetime that varies with Reynolds number. The lifetime sharply increases with Reynolds number so that a possible divergence marking the transition to sustained turbulence at a critical point has been discussed. We present a mechanism by which the lifetimes increase: in the system's state space, turbulent motion is supported by a chaotic saddle. Inside this saddle a locally attracting periodic orbit is created and undergoes a traditional bifurcation sequence generating chaos. The formed new "turbulent bubble" is initially an attractor supporting persistent chaotic dynamics. Soon after its creation, it collides with its own boundary, by which it becomes leaky and dynamically connected with the surrounding structures. The complexity of the chaotic saddle that supports transient turbulence hence increases by incorporating the remnant of a new bubble. As a a result, the time it takes for a trajectory to leave the saddle and decay to the laminar state is increased. We demonstrate this phenomenon in plane Couette flow and show that characteristic lifetimes vary nonsmoothly and nonmonotonically with Reynolds number.}, }
@article {pmid24580356, year = {2014}, author = {Zhou, Y and Grinstein, FF and Wachtor, AJ and Haines, BM}, title = {Estimating the effective Reynolds number in implicit large-eddy simulation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {1}, pages = {013303}, doi = {10.1103/PhysRevE.89.013303}, pmid = {24580356}, issn = {1550-2376}, abstract = {In implicit large-eddy simulation (ILES), energy-containing large scales are resolved, and physics capturing numerics are used to spatially filter out unresolved scales and to implicitly model subgrid scale effects. From an applied perspective, it is highly desirable to estimate a characteristic Reynolds number (Re)-and therefore a relevant effective viscosity-so that the impact of resolution on predicted flow quantities and their macroscopic convergence can usefully be characterized. We argue in favor of obtaining robust Re estimates away from the smallest scales of the simulated flow-where numerically controlled dissipation takes place and propose a theoretical basis and framework to determine such measures. ILES examples include forced turbulence as a steady flow case, the Taylor-Green vortex to address transition and decaying turbulence, and simulations of a laser-driven reshock experiment illustrating a fairly complex turbulence problem of current practical interest.}, }
@article {pmid24580339, year = {2014}, author = {Niebling, MJ and Tallakstad, KT and Toussaint, R and Måløy, KJ}, title = {Direct velocity measurement of a turbulent shear flow in a planar Couette cell.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {1}, pages = {013026}, doi = {10.1103/PhysRevE.89.013026}, pmid = {24580339}, issn = {1550-2376}, abstract = {In a plane Couette cell a thin fluid layer consisting of water is sheared between the sides of a transparent band at Reynolds numbers ranging from 300 to 1400. The length of the cell's flow channel is large compared to the film separation. To extract the flow velocity in the experiments, a correlation image velocimetry method is used on pictures recorded with a high-speed camera. The flow is recorded at a resolution that allows us to analyze flow patterns similar in size to the film separation. The fluid flow is then studied by calculating flow velocity autocorrelation functions. The turbulent patterns that arise on this scale above a critical Reynolds number of Re=360 display characteristic patterns that are proven by use of the calculated velocity autocorrelation functions. The patterns are metastable and reappear at different positions and times throughout the experiments. Typically these patterns are turbulent rolls which are elongated in the stream direction, which is the direction in which the band is moving. Although the flow states are metastable they possess similarities to the steady Taylor vortices known to appear in circular Taylor Couette cells.}, }
@article {pmid24580328, year = {2014}, author = {Joung, YS and Buie, CR}, title = {Scaling laws for drop impingement on porous films and papers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {1}, pages = {013015}, doi = {10.1103/PhysRevE.89.013015}, pmid = {24580328}, issn = {1550-2376}, abstract = {This study investigates drop impingement on highly wetting porous films and papers. Experiments reveal previously unexplored impingement modes on porous surfaces designated as necking, spreading, and jetting. Dimensional analysis yields a nondimensional parameter, denoted the Washburn-Reynolds number, relating droplet kinetic energy and surface energy. The impingement modes correlate with Washburn-Reynolds number variations spanning four orders of magnitude and a corresponding energy conservation analysis for droplet spreading shows good agreement with the experimental results. The simple scaling laws presented will inform the investigation of dynamic interactions between porous surfaces and liquid drops.}, }
@article {pmid24580325, year = {2014}, author = {Xu, M}, title = {Effect of soft-iron impellers on the von Kármán-sodium dynamo.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {89}, number = {1}, pages = {013012}, doi = {10.1103/PhysRevE.89.013012}, pmid = {24580325}, issn = {1550-2376}, abstract = {The explanation for the observed axisymmetric magnetic field in the von Kármán-sodium (VKS) dynamo experiment is still an unresolved question. In this paper, the integral equation approach is extended to investigate the VKS dynamo action by taking into account the discontinuity of the magnetic permeability and electrical conductivity in the conducting region. When the relative magnetic permeability of the soft-iron impellers is set to 65, a steady toroidal field that is apparently axisymmetric is excited at the critical magnetic Reynolds number, Rmc≈27.23, which is close to the experimental result, Rmc≈30. Our results show that the critical magnetic Reynolds number declines as the relative magnetic permeability of the impellers increases. Furthermore, when the relative magnetic permeability is not greater than 37, an equatorial magnetic field with an azimuthal wave number m=1 is the dominant mode, otherwise a steady toroidal field with an azimuthal wave number m=0 predominates the magnetic field generated by the VKS dynamo action.}, }
@article {pmid24563612, year = {2013}, author = {Zhao, C and Oztekin, A and Cheng, X}, title = {Gravity-induced swirl of nanoparticles in microfluidics.}, journal = {Journal of nanoparticle research : an interdisciplinary forum for nanoscale science and technology}, volume = {15}, number = {}, pages = {1611}, pmid = {24563612}, issn = {1388-0764}, support = {R21 AI081638/AI/NIAID NIH HHS/United States ; }, abstract = {Parallel flows of two fluids in microfluidic devices are used for miniaturized chemistry, physics, biology and bioengineering studies, and the streams are often considered to remain parallel. However, as the two fluids do not always have the same density, interface reorientation induced by density stratification is unavoidable. In this paper, flow characteristics of an aqueous polystyrene nanofluid and a sucrose-densified aqueous solution flowing parallel in microchannels are examined. Nanoparticles 100 nm in diameter are used in the study. The motion of the nanoparticles is simulated using the Lagrangian description and directly observed by a confocal microscope. Matched results are obtained from computational and empirical analysis. Although solution density homogenizes rapidly resulting from a fast diffusion of sucrose in water, the nanofluid is observed to rotate for an extended period. Angular displacement of the nanofluid depends on the ratio of gravitational force to viscous force, Re/Fr[2], where Re is the Reynolds number and Fr is the Froude number. In the developing region at the steady state, the angular displacement is related to y/Dh, the ratio between distance from the inlet and the hydraulic diameter of the microfluidic channel. The development of nanofluid flow feature also depends on h/w, the ratio of microfluidic channel's height to width. The quantitative description of the angular displacement of nanofluid will aid rational designs of microfluidic devices utilizing multistream, multiphase flows.}, }
@article {pmid24561349, year = {2014}, author = {Janiga, G}, title = {Large eddy simulation of the FDA benchmark nozzle for a Reynolds number of 6500.}, journal = {Computers in biology and medicine}, volume = {47}, number = {}, pages = {113-119}, doi = {10.1016/j.compbiomed.2014.01.004}, pmid = {24561349}, issn = {1879-0534}, mesh = {Computer Simulation/*standards ; *Hydrodynamics ; *Models, Theoretical ; }, abstract = {This work investigates the flow in a benchmark nozzle model of an idealized medical device proposed by the FDA using computational fluid dynamics (CFD). It was in particular shown that a proper modeling of the transitional flow features is particularly challenging, leading to large discrepancies and inaccurate predictions from the different research groups using Reynolds-averaged Navier-Stokes (RANS) modeling. In spite of the relatively simple, axisymmetric computational geometry, the resulting turbulent flow is fairly complex and non-axisymmetric, in particular due to the sudden expansion. The resulting flow cannot be well predicted with simple modeling approaches. Due to the varying diameters and flow velocities encountered in the nozzle, different typical flow regions and regimes can be distinguished, from laminar to transitional and to weakly turbulent. The purpose of the present work is to re-examine the FDA-CFD benchmark nozzle model at a Reynolds number of 6500 using large eddy simulation (LES). The LES results are compared with published experimental data obtained by Particle Image Velocimetry (PIV) and an excellent agreement can be observed considering the temporally averaged flow velocities. Different flow regimes are characterized by computing the temporal energy spectra at different locations along the main axis.}, }
@article {pmid24532222, year = {2014}, author = {Whitfield, CA and Marenduzzo, D and Voituriez, R and Hawkins, RJ}, title = {Active polar fluid flow in finite droplets.}, journal = {The European physical journal. E, Soft matter}, volume = {37}, number = {2}, pages = {8}, pmid = {24532222}, issn = {1292-895X}, mesh = {Actin Cytoskeleton/*chemistry/metabolism ; Cell Movement ; *Models, Biological ; *Motion ; }, abstract = {We present a continuum level analytical model of a droplet of active contractile fluid consisting of filaments and motors. We calculate the steady state flows that result from a splayed polarisation of the filaments. We account for interaction with the external medium by imposing a viscous friction at the fixed droplet boundary. We then show that the droplet has non-zero force dipole and quadrupole moments, the latter of which is essential for self-propelled motion of the droplet at low Reynolds' number. Therefore, this calculation describes a simple mechanism for the motility of a droplet of active contractile fluid embedded in a three-dimensional environment, which is relevant to cell migration in confinement (for example, embedded within a gel or tissue). Our analytical results predict how the system depends on various parameters such as the effective friction coefficient, the phenomenological activity parameter and the splay of the imposed polarisation.}, }
@article {pmid24529910, year = {2014}, author = {Helgeland, A and Mardal, KA and Haughton, V and Reif, BA}, title = {Numerical simulations of the pulsating flow of cerebrospinal fluid flow in the cervical spinal canal of a Chiari patient.}, journal = {Journal of biomechanics}, volume = {47}, number = {5}, pages = {1082-1090}, doi = {10.1016/j.jbiomech.2013.12.023}, pmid = {24529910}, issn = {1873-2380}, mesh = {Arnold-Chiari Malformation/*physiopathology ; Cerebrospinal Fluid/*physiology ; Cervical Vertebrae ; Computer Simulation ; Diastole ; Humans ; Male ; *Models, Biological ; *Pulsatile Flow ; Spinal Canal/*physiopathology ; Subarachnoid Space ; Systole ; }, abstract = {The flow of cerebrospinal fluid (CSF) in a patient-specific model of the subarachnoid space in a Chiari I patient was investigated using numerical simulations. The pulsating CSF flow was modeled using a time-varying velocity pulse based on peak velocity measurements (diastole and systole) derived from a selection of patients with Chiari I malformation. The present study introduces the general definition of the Reynolds number to provide a measure of CSF flow instability to give an estimate of the possibility of turbulence occurring in CSF flow. This was motivated by the fact that the combination of pulsating flow and the geometric complexity of the spinal canal may result in local Reynolds numbers that are significantly higher than the commonly used global measure such that flow instabilities may develop into turbulent flow in these regions. The local Reynolds number was used in combination with derived statistics to characterize the flow. The results revealed the existence of both local unstable regions and local regions with velocity fluctuations similar in magnitude to what is observed in fully turbulent flows. The results also indicated that the fluctuations were not self-sustained turbulence, but rather flow instabilities that may develop into turbulence. The case considered was therefore believed to represent a CSF flow close to transition.}, }
@article {pmid24522785, year = {2014}, author = {Nabawy, MR and Crowther, WJ}, title = {On the quasi-steady aerodynamics of normal hovering flight part I: the induced power factor.}, journal = {Journal of the Royal Society, Interface}, volume = {11}, number = {93}, pages = {20131196}, pmid = {24522785}, issn = {1742-5662}, mesh = {Animals ; Flight, Animal/*physiology ; *Models, Biological ; Wings, Animal/*physiology ; }, abstract = {An analytical treatment to quantify the losses captured in the induced power factor, k, is provided for flapping wings in normal hover, including the effects of non-uniform downwash, tip losses and finite flapping amplitude. The method is based on a novel combination of actuator disc and lifting line blade theories that also takes into account the effect of advance ratio. The model has been evaluated against experimental results from the literature and qualitative agreement obtained for the effect of advance ratio on the lift coefficient of revolving wings. Comparison with quantitative experimental data for the circulation as a function of span for a fruitfly wing shows that the model is able to correctly predict the circulation shape of variation, including both the magnitude of the peak circulation and the rate of decay in circulation towards zero. An evaluation of the contributions to induced power factor in normal hover for eight insects is provided. It is also shown how Reynolds number can be accounted for in the induced power factor, and good agreement is obtained between predicted span efficiency as a function of Reynolds number and numerical results from the literature. Lastly, it is shown that for a flapping wing in hover k owing to the non-uniform downwash effect can be reduced to 1.02 using an arcsech chord distribution. For morphologically realistic wing shapes based on beta distributions, it is shown that a value of 1.07 can be achieved for a radius of first moment of wing area at 40% of wing length.}, }
@article {pmid24520175, year = {2014}, author = {Moffatt, HK}, title = {Helicity and singular structures in fluid dynamics.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {111}, number = {10}, pages = {3663-3670}, pmid = {24520175}, issn = {1091-6490}, mesh = {*Hydrodynamics ; *Magnetic Fields ; Models, Theoretical ; Physics ; *Planets ; }, abstract = {Helicity is, like energy, a quadratic invariant of the Euler equations of ideal fluid flow, although, unlike energy, it is not sign definite. In physical terms, it represents the degree of linkage of the vortex lines of a flow, conserved when conditions are such that these vortex lines are frozen in the fluid. Some basic properties of helicity are reviewed, with particular reference to (i) its crucial role in the dynamo excitation of magnetic fields in cosmic systems; (ii) its bearing on the existence of Euler flows of arbitrarily complex streamline topology; (iii) the constraining role of the analogous magnetic helicity in the determination of stable knotted minimum-energy magnetostatic structures; and (iv) its role in depleting nonlinearity in the Navier-Stokes equations, with implications for the coherent structures and energy cascade of turbulence. In a final section, some singular phenomena in low Reynolds number flows are briefly described.}, }
@article {pmid24511253, year = {2014}, author = {Namdeo, S and Khaderi, SN and Onck, PR}, title = {Numerical modelling of chirality-induced bi-directional swimming of artificial flagella.}, journal = {Proceedings. Mathematical, physical, and engineering sciences}, volume = {470}, number = {2162}, pages = {20130547}, pmid = {24511253}, issn = {1364-5021}, abstract = {Biomimetic micro-swimmers can be used for various medical applications, such as targeted drug delivery and micro-object (e.g. biological cells) manipulation, in lab-on-a-chip devices. Bacteria swim using a bundle of flagella (flexible hair-like structures) that form a rotating cork-screw of chiral shape. To mimic bacterial swimming, we employ a computational approach to design a bacterial (chirality-induced) swimmer whose chiral shape and rotational velocity can be controlled by an external magnetic field. In our model, we numerically solve the coupled governing equations that describe the system dynamics (i.e. solid mechanics, fluid dynamics and magnetostatics). We explore the swimming response as a function of the characteristic dimensionless parameters and put special emphasis on controlling the swimming direction. Our results provide fundamental physical insight on the chirality-induced propulsion, and it provides guidelines for the design of magnetic bi-directional micro-swimmers.}, }
@article {pmid24503612, year = {2014}, author = {Bahraseman, H and Hassani, K and Khosravi, A and Navidbakhsh, M and Espino, D and Fatouraee, N and Kazemi-Saleh, D}, title = {Combining numerical and clinical methods to assess aortic valve hemodynamics during exercise.}, journal = {Perfusion}, volume = {29}, number = {4}, pages = {340-350}, doi = {10.1177/0267659114521103}, pmid = {24503612}, issn = {1477-111X}, abstract = {Computational simulations have the potential to aid understanding of cardiovascular hemodynamics under physiological conditions, including exercise. Therefore, blood hemodynamic parameters during different heart rates, rest and exercise have been investigated, using a numerical method. A model was developed for a healthy subject. Using geometrical data acquired by echo-Doppler, a two-dimensional model of the chamber of aortic sinus valsalva and aortic root was created. Systolic ventricular and aortic pressures were applied as boundary conditions computationally. These pressures were the initial physical conditions applied to the model to predict valve deformation and changes in hemodynamics. They were the clinically measured brachial pressures plus differences between brachial, central and left ventricular pressures. Echocardiographic imaging was also used to acquire different ejection times, necessary for pressure waveform equations of blood flow during exercise. A fluid-structure interaction simulation was performed, using an arbitrary Lagrangian-Eulerian mesh. During exercise, peak vorticity increased by 14.8%, peak shear rate by 15.8%, peak cell Reynolds number by 20%, peak leaflet tip velocity increased by 47% and the blood velocity increased by 3% through the leaflets, whereas full opening time decreased by 11%. Our results show that numerical methods can be combined with clinical measurements to provide good estimates of patient-specific hemodynamics at different heart rates.}, }
@article {pmid24501132, year = {2014}, author = {Staaf, DJ and Gilly, WF and Denny, MW}, title = {Aperture effects in squid jet propulsion.}, journal = {The Journal of experimental biology}, volume = {217}, number = {Pt 9}, pages = {1588-1600}, doi = {10.1242/jeb.082271}, pmid = {24501132}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Decapodiformes/anatomy &amp; histology/*physiology ; Models, Theoretical ; Swimming/*physiology ; }, abstract = {Squid are the largest jet propellers in nature as adults, but as paralarvae they are some of the smallest, faced with the inherent inefficiency of jet propulsion at a low Reynolds number. In this study we describe the behavior and kinematics of locomotion in 1 mm paralarvae of Dosidicus gigas, the smallest squid yet studied. They swim with hop-and-sink behavior and can engage in fast jets by reducing the size of the mantle aperture during the contraction phase of a jetting cycle. We go on to explore the general effects of a variable mantle and funnel aperture in a theoretical model of jet propulsion scaled from the smallest (1 mm mantle length) to the largest (3 m) squid. Aperture reduction during mantle contraction increases propulsive efficiency at all squid sizes, although 1 mm squid still suffer from low efficiency (20%) because of a limited speed of contraction. Efficiency increases to a peak of 40% for 1 cm squid, then slowly declines. Squid larger than 6 cm must either reduce contraction speed or increase aperture size to maintain stress within maximal muscle tolerance. Ecological pressure to maintain maximum velocity may lead them to increase aperture size, which reduces efficiency. This effect might be ameliorated by nonaxial flow during the refill phase of the cycle. Our model's predictions highlight areas for future empirical work, and emphasize the existence of complex behavioral options for maximizing efficiency at both very small and large sizes.}, }
@article {pmid24500609, year = {2014}, author = {Dhital, S and Dolan, G and Stokes, JR and Gidley, MJ}, title = {Enzymatic hydrolysis of starch in the presence of cereal soluble fibre polysaccharides.}, journal = {Food &amp; function}, volume = {5}, number = {3}, pages = {579-586}, doi = {10.1039/c3fo60506j}, pmid = {24500609}, issn = {2042-650X}, mesh = {Animals ; Biocatalysis ; Dietary Fiber/*analysis/metabolism ; Digestion ; Glucan 1,4-alpha-Glucosidase/*chemistry ; Hydrolysis ; Pancreatin/*chemistry ; Polysaccharides/*chemistry/metabolism ; Starch/*chemistry/metabolism ; Swine ; Viscosity ; Zea mays/*chemistry/metabolism ; }, abstract = {The in vitro amylolysis of both granular and cooked maize starch and the diffusion of glucose in the presence of 1% and 2% cereal soluble fibre polysaccharides (arabinoxylan and mixed linkage beta-glucan) were studied at various levels of shear mixing in order to identify potential molecular mechanisms underlying observed glycemia-reducing effects of soluble fibres in vivo. The presence of soluble fibres increased viscosity by ca. 10× and 100× for 1% and 2% concentrations respectively. Despite this large difference in viscosity, measured digestion and mass transfer coefficients were only reduced by a factor of 1.5 to 2.5 at the same mixing speed. In contrast, introduction of mixing in the digesting and diffusing medium significantly increased the rate of amylolytic starch digestion and mass transfer of glucose. This effect is such that mixing at high speeds negates the hindering effect of the 100× increased viscosity imparted by the presence of 2% soluble fibre; this is essentially captured by the Reynolds number (the ratio of inertial and viscous forces) that defines the flow kinematics. The modest reduction of in vitro starch hydrolysis and glucose diffusion at increased viscosity suggests that the established benefits of soluble fibres on post-prandial glycaemia, in terms of attenuation of the overall rate and extent of dietary starch conversion to blood glucose, are not primarily due to a direct effect of viscosity. Alternative hypotheses are proposed based on gastric emptying, restriction of turbulent flow, and/or stimulation of mucus turnover.}, }
@article {pmid24483567, year = {2013}, author = {Dallas, V and Alexakis, A}, title = {Symmetry breaking of decaying magnetohydrodynamic Taylor-Green flows and consequences for universality.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {6}, pages = {063017}, doi = {10.1103/PhysRevE.88.063017}, pmid = {24483567}, issn = {1550-2376}, abstract = {We investigate the evolution and stability of a decaying magnetohydrodynamic Taylor-Green flow, using pseudospectral simulations with resolutions up to 2048(3). The chosen flow has been shown to result in a steep total energy spectrum with power law behavior k(-2). We study the symmetry breaking of this flow by exciting perturbations of different amplitudes. It is shown that for any finite amplitude perturbation there is a high enough Reynolds number for which the perturbation will grow enough at the peak of dissipation rate resulting in a nonlinear feedback into the flow and subsequently break the Taylor-Green symmetries. In particular, we show that symmetry breaking at large scales occurs if the amplitude of the perturbation is σ(crit)∼Re(-1) and at small scales occurs if σ(crit)∼Re(-3/2). This symmetry breaking modifies the scaling laws of the energy spectra at the peak of dissipation rate away from the k(-2) scaling and towards the classical k(-5/3) and k(-3/2) power laws.}, }
@article {pmid24483558, year = {2013}, author = {Vosskuhle, M and Lévêque, E and Wilkinson, M and Pumir, A}, title = {Multiple collisions in turbulent flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {6}, pages = {063008}, doi = {10.1103/PhysRevE.88.063008}, pmid = {24483558}, issn = {1550-2376}, abstract = {In turbulent suspensions, collision rates determine how rapidly particles coalesce or react with each other. To determine the collision rate, many numerical studies rely on the ghost collision approximation (GCA), which simply records how often pairs of point particles come within a threshold distance. In many applications, the suspended particles stick (or in the case of liquid droplets, coalesce) upon collision, and it is the frequency of first contact which is of interest. If a pair of "ghost" particles undergoes multiple collisions, the GCA may overestimate the true collision rate. Here, using fully resolved direct numerical simulations of turbulent flows at moderate Reynolds number (Re(λ)=130), we investigate the prevalence and properties of multiple collisions. We find the probability P(N(c)) for a given pair of ghost particles to collide N(c) times to be of the form P(N(c))=βα(N(c)) for N(c)>1, where α and β are coefficients which depend upon the particle inertia. We also investigate the statistics of the times that ghost particles remain in contact. We show that the probability density function of the contact time is different for the first collision. The difference is explained by the effect of caustics in the phase space of the suspended particles. We demonstrate that, as a result of multiple collisions, the GCA leads to a small, but systematic overestimate of the collision rate, which is of the order of ∼15% when the particle inertia is small, and slowly decreases when inertia increases.}, }
@article {pmid24483556, year = {2013}, author = {Chen, P}, title = {Dynamics of finite-symmetry and general-shaped objects under shear and shear alignment of uniaxial objects at finite temperatures.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {6}, pages = {063006}, doi = {10.1103/PhysRevE.88.063006}, pmid = {24483556}, issn = {1550-2376}, abstract = {We prove that, for an object with a finitefold rotational symmetry (except for a twofold one) around an axis and mirror symmetries (such as a square rod or pentagonal slab, etc.), dynamics of the symmetry axis in low Reynolds number shear flow exactly follows the same form as that of a uniaxial object (e.g., a circular rod or symmetric ellipsoid) as the so-called Jeffery orbits. We use the formulation in which the dynamics of the rigid body follows first-order ordinary differential equations in time [Phys. Rev. E 84, 056309 (2011)]. Interaction between the object and the shear flow enters through a set of scalar coefficients, and the flow field does not need to be solved dynamically. Results of numerical simulations for general-shaped objects also are discussed. In the second part, Brownian dynamics of a uniaxial object is studied numerically. With D as the rotational diffusion constant, α as a parameter characterizing the aspect ratio, and γ as the shear rate, the object starts to align with the flow when the value of D/(γα) decreases near 1. At large α (the long object limit), the results suggest much lower flow alignment when D/(γα)>1.}, }
@article {pmid24481172, year = {2014}, author = {Xi, J and Si, X and Longest, W}, title = {Electrostatic charge effects on pharmaceutical aerosol deposition in human nasal-laryngeal airways.}, journal = {Pharmaceutics}, volume = {6}, number = {1}, pages = {26-35}, pmid = {24481172}, issn = {1999-4923}, abstract = {Electrostatic charging occurs in most aerosol generation processes and can significantly influence subsequent particle deposition rates and patterns in the respiratory tract through the image and space forces. The behavior of inhaled aerosols with charge is expected to be most affected in the upper airways, where particles come in close proximity to the narrow turbinate surface, and before charge dissipation occurs as a result of high humidity. The objective of this study was to quantitatively evaluate the deposition of charged aerosols in an MRI-based nasal-laryngeal airway model. Particle sizes of 5 nm-30 µm and charge levels ranging from neutralized to ten times the saturation limit were considered. A well-validated low Reynolds number (LRN) k-ω turbulence model and a discrete Lagrangian tracking approach that accounted for electrostatic image force were employed to simulate the nasal airflow and aerosol dynamics. For ultrafine aerosols, electrostatic charge was observed to exert a discernible but insignificant effect. In contrast, remarkably enhanced depositions were observed for micrometer particles with charge, which could be one order of magnitude larger than no-charge depositions. The deposition hot spots shifted towards the anterior part of the upper airway as the charge level increased. Results of this study have important implications for evaluating nasal drug delivery devices and for assessing doses received from pollutants, which often carry a certain level of electric charges.}, }
@article {pmid24477611, year = {2014}, author = {Holden, D and Socha, JJ and Cardwell, ND and Vlachos, PP}, title = {Aerodynamics of the flying snake Chrysopelea paradisi: how a bluff body cross-sectional shape contributes to gliding performance.}, journal = {The Journal of experimental biology}, volume = {217}, number = {Pt 3}, pages = {382-394}, doi = {10.1242/jeb.090902}, pmid = {24477611}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Colubridae/anatomy &amp; histology/*physiology ; *Flight, Animal ; Rheology ; }, abstract = {A prominent feature of gliding flight in snakes of the genus Chrysopelea is the unique cross-sectional shape of the body, which acts as the lifting surface in the absence of wings. When gliding, the flying snake Chrysopelea paradisi morphs its circular cross-section into a triangular shape by splaying its ribs and flattening its body in the dorsoventral axis, forming a geometry with fore-aft symmetry and a thick profile. Here, we aimed to understand the aerodynamic properties of the snake's cross-sectional shape to determine its contribution to gliding at low Reynolds numbers. We used a straight physical model in a water tunnel to isolate the effects of 2D shape, analogously to studying the profile of an airfoil of a more typical flyer. Force measurements and time-resolved (TR) digital particle image velocimetry (DPIV) were used to determine lift and drag coefficients, wake dynamics and vortex-shedding characteristics of the shape across a behaviorally relevant range of Reynolds numbers and angles of attack. The snake's cross-sectional shape produced a maximum lift coefficient of 1.9 and maximum lift-to-drag ratio of 2.7, maintained increases in lift up to 35 deg, and exhibited two distinctly different vortex-shedding modes. Within the measured Reynolds number regime (Re=3000-15,000), this geometry generated significantly larger maximum lift coefficients than many other shapes including bluff bodies, thick airfoils, symmetric airfoils and circular arc airfoils. In addition, the snake's shape exhibited a gentle stall region that maintained relatively high lift production even up to the highest angle of attack tested (60 deg). Overall, the cross-sectional geometry of the flying snake demonstrated robust aerodynamic behavior by maintaining significant lift production and near-maximum lift-to-drag ratios over a wide range of parameters. These aerodynamic characteristics help to explain how the snake can glide at steep angles and over a wide range of angles of attack, but more complex models that account for 3D effects and the dynamic movements of aerial undulation are required to fully understand the gliding performance of flying snakes.}, }
@article {pmid24476281, year = {2013}, author = {Li, CK and Ryutov, DD and Hu, SX and Rosenberg, MJ and Zylstra, AB and Séguin, FH and Frenje, JA and Casey, DT and Johnson, MG and Manuel, MJ and Rinderknecht, HG and Petrasso, RD and Amendt, PA and Park, HS and Remington, BA and Wilks, SC and Betti, R and Froula, DH and Knauer, JP and Meyerhofer, DD and Drake, RP and Kuranz, CC and Young, R and Koenig, M}, title = {Structure and dynamics of colliding plasma jets.}, journal = {Physical review letters}, volume = {111}, number = {23}, pages = {235003}, doi = {10.1103/PhysRevLett.111.235003}, pmid = {24476281}, issn = {1079-7114}, abstract = {Monoenergetic-proton radiographs of laser-generated, high-Mach-number plasma jets colliding at various angles shed light on the structures and dynamics of these collisions. The observations compare favorably with results from 2D hydrodynamic simulations of multistream plasma jets, and also with results from an analytic treatment of electron flow and magnetic field advection. In collisions of two noncollinear jets, the observed flow structure is similar to the analytic model's prediction of a characteristic feature with a narrow structure pointing in one direction and a much thicker one pointing in the opposite direction. Spontaneous magnetic fields, largely azimuthal around the colliding jets and generated by the well-known ∇T(e)×∇n(e) Biermann battery effect near the periphery of the laser spots, are demonstrated to be "frozen in" the plasma (due to high magnetic Reynolds number Re(M)∼5×10(4)) and advected along the jet streamlines of the electron flow. These studies provide novel insight into the interactions and dynamics of colliding plasma jets.}, }
@article {pmid24461848, year = {2014}, author = {Dalili, A and Chandra, S and Mostaghimi, J and Fan, HT and Simmer, JC}, title = {Formation of liquid sheets by deposition of droplets on a surface.}, journal = {Journal of colloid and interface science}, volume = {418}, number = {}, pages = {292-299}, doi = {10.1016/j.jcis.2013.12.033}, pmid = {24461848}, issn = {1095-7103}, abstract = {Experiments were done to observe the coalescence of highly viscous liquid droplets (87 wt% glycerin-in-water solutions) deposited onto a flat, solid steel plate. Droplets were deposited sequentially in straight lines or square droplet arrays. Droplet center-to-center distance was varied and the final dimensions of lines and sheets measured from photographs. When overlapping droplets were deposited surface tension forces pulled impacting droplets towards those already on the surface, a phenomena known as drawback. A dimensionless drawback index, quantifying the extent of droplet displacement, was calculated from experimental measurements for different values of droplet overlap. At large overlaps droplets deposited in a line or square array coalesced to form a circular film. When the droplet center-to-center distance increased, leading to less interaction, long, thin lines and square sheets were formed. As overlap was further decreased lines and sheets became discontinuous. A simple model was developed to predict the conditions under which rupture occurred. The lowest droplet overlap ratio (defined as droplet overlap distance divided by droplet spread diameter) at which a continuous liquid film could be formed was λ=0.293. At large overlap ratios (λ>0.6) droplets deposited in a square array formed a circular film. The minimum thickness of a continuous film formed by coalescence of droplets was shown to vary from 5% to 70% of the initial droplet diameter while increasing impact Weber and Reynolds number reduced the film thickness.}, }
@article {pmid24437742, year = {2014}, author = {Reyt, I and Bailliet, H and Valière, JC}, title = {Experimental investigation of acoustic streaming in a cylindrical wave guide up to high streaming Reynolds numbers.}, journal = {The Journal of the Acoustical Society of America}, volume = {135}, number = {1}, pages = {27-37}, doi = {10.1121/1.4837855}, pmid = {24437742}, issn = {1520-8524}, mesh = {*Acoustics ; Laser-Doppler Flowmetry ; *Models, Theoretical ; Motion ; Nonlinear Dynamics ; Pressure ; *Signal Processing, Computer-Assisted ; *Sound ; Sound Spectrography ; Time Factors ; }, abstract = {Measurements of streaming velocity are performed by means of Laser Doppler Velocimetry and Particle Image Velociimetry in an experimental apparatus consisting of a cylindrical waveguide having one loudspeaker at each end for high intensity sound levels. The case of high nonlinear Reynolds number ReNL is particularly investigated. The variation of axial streaming velocity with respect to the axial and to the transverse coordinates are compared to available Rayleigh streaming theory. As expected, the measured streaming velocity agrees well with the Rayleigh streaming theory for small ReNL but deviates significantly from such predictions for high ReNL. When the nonlinear Reynolds number is increased, the outer centerline axial streaming velocity gets distorted towards the acoustic velocity nodes until counter-rotating additional vortices are generated near the acoustic velocity antinodes. This kind of behavior is followed by outer streaming cells only and measurements in the near wall region show that inner streaming vortices are less affected by this substantial evolution of fast streaming pattern. Measurements of the transient evolution of streaming velocity provide an additional insight into the evolution of fast streaming.}, }
@article {pmid24435099, year = {2014}, author = {Williams, BJ and Anand, SV and Rajagopalan, J and Saif, MT}, title = {A self-propelled biohybrid swimmer at low Reynolds number.}, journal = {Nature communications}, volume = {5}, number = {}, pages = {3081}, doi = {10.1038/ncomms4081}, pmid = {24435099}, issn = {2041-1723}, mesh = {Animals ; Biocompatible Materials ; Biomechanical Phenomena/physiology ; Cell Movement/*physiology ; Cells, Cultured ; *Dimethylpolysiloxanes ; Fibroblasts/cytology/physiology ; *Hydrodynamics ; *Models, Biological ; Myocytes, Cardiac/cytology/*physiology ; Rats ; Rats, Sprague-Dawley ; }, abstract = {Many microorganisms, including spermatozoa and forms of bacteria, oscillate or twist a hair-like flagella to swim. At this small scale, where locomotion is challenged by large viscous drag, organisms must generate time-irreversible deformations of their flagella to produce thrust. To date, there is no demonstration of a self propelled, synthetic flagellar swimmer operating at low Reynolds number. Here we report a microscale, biohybrid swimmer enabled by a unique fabrication process and a supporting slender-body hydrodynamics model. The swimmer consists of a polydimethylsiloxane filament with a short, rigid head and a long, slender tail on which cardiomyocytes are selectively cultured. The cardiomyocytes contract and deform the filament to propel the swimmer at 5-10 μm s(-1), consistent with model predictions. We then demonstrate a two-tailed swimmer swimming at 81 μm s(-1). This small-scale, elementary biohybrid swimmer can serve as a platform for more complex biological machines.}, }
@article {pmid24430733, year = {2014}, author = {Boyd, DA and Adams, AA and Daniele, MA and Ligler, FS}, title = {Microfluidic fabrication of polymeric and biohybrid fibers with predesigned size and shape.}, journal = {Journal of visualized experiments : JoVE}, volume = {}, number = {83}, pages = {e50958}, pmid = {24430733}, issn = {1940-087X}, mesh = {Click Chemistry ; Hydrogels/chemistry ; Hydrophobic and Hydrophilic Interactions ; Liquid Crystals/chemistry ; Microfluidic Analytical Techniques/instrumentation/*methods ; Photochemical Processes ; Polymers/*chemistry ; Viscosity ; }, abstract = {A "sheath" fluid passing through a microfluidic channel at low Reynolds number can be directed around another "core" stream and used to dictate the shape as well as the diameter of a core stream. Grooves in the top and bottom of a microfluidic channel were designed to direct the sheath fluid and shape the core fluid. By matching the viscosity and hydrophilicity of the sheath and core fluids, the interfacial effects are minimized and complex fluid shapes can be formed. Controlling the relative flow rates of the sheath and core fluids determines the cross-sectional area of the core fluid. Fibers have been produced with sizes ranging from 300 nm to ~1 mm, and fiber cross-sections can be round, flat, square, or complex as in the case with double anchor fibers. Polymerization of the core fluid downstream from the shaping region solidifies the fibers. Photoinitiated click chemistries are well suited for rapid polymerization of the core fluid by irradiation with ultraviolet light. Fibers with a wide variety of shapes have been produced from a list of polymers including liquid crystals, poly(methylmethacrylate), thiol-ene and thiol-yne resins, polyethylene glycol, and hydrogel derivatives. Minimal shear during the shaping process and mild polymerization conditions also makes the fabrication process well suited for encapsulation of cells and other biological components.}, }
@article {pmid24414062, year = {2014}, author = {Bermejo, J and Benito, Y and Alhama, M and Yotti, R and Martínez-Legazpi, P and Del Villar, CP and Pérez-David, E and González-Mansilla, A and Santa-Marta, C and Barrio, A and Fernández-Avilés, F and Del Álamo, JC}, title = {Intraventricular vortex properties in nonischemic dilated cardiomyopathy.}, journal = {American journal of physiology. Heart and circulatory physiology}, volume = {306}, number = {5}, pages = {H718-29}, pmid = {24414062}, issn = {1522-1539}, support = {1-R21-HL-108268-01/HL/NHLBI NIH HHS/United States ; }, mesh = {Adult ; Aged ; Biomechanical Phenomena ; Cardiomyopathy, Dilated/diagnostic imaging/*physiopathology ; Case-Control Studies ; Echocardiography, Doppler, Color ; Echocardiography, Doppler, Pulsed ; Female ; Heart Ventricles/diagnostic imaging/*physiopathology ; Humans ; Image Interpretation, Computer-Assisted ; Magnetic Resonance Imaging ; Male ; Middle Aged ; Models, Cardiovascular ; Predictive Value of Tests ; Stroke Volume ; Time Factors ; *Ventricular Function, Left ; Ventricular Pressure ; Ventricular Remodeling ; }, abstract = {Vortices may have a role in optimizing the mechanical efficiency and blood mixing of the left ventricle (LV). We aimed to characterize the size, position, circulation, and kinetic energy (KE) of LV main vortex cores in patients with nonischemic dilated cardiomyopathy (NIDCM) and analyze their physiological correlates. We used digital processing of color-Doppler images to study flow evolution in 61 patients with NIDCM and 61 age-matched control subjects. Vortex features showed a characteristic biphasic temporal course during diastole. Because late filling contributed significantly to flow entrainment, vortex KE reached its maximum at the time of the peak A wave, storing 26 ± 20% of total KE delivered by inflow (range: 1-74%). Patients with NIDCM showed larger and stronger vortices than control subjects (circulation: 0.008 ± 0.007 vs. 0.006 ± 0.005 m(2)/s, respectively, P = 0.02; KE: 7 ± 8 vs. 5 ± 5 mJ/m, P = 0.04), even when corrected for LV size. This helped confining the filling jet in the dilated ventricle. The vortex Reynolds number was also higher in the NIDCM group. By multivariate analysis, vortex KE was related to the KE generated by inflow and to chamber short-axis diameter. In 21 patients studied head to head, Doppler measurements of circulation and KE closely correlated with phase-contract magnetic resonance values (intraclass correlation coefficient = 0.82 and 0.76, respectively). Thus, the biphasic nature of filling determines normal vortex physiology. Vortex formation is exaggerated in patients with NIDCM due to chamber remodeling, and enlarged vortices are helpful for ameliorating convective pressure losses and facilitating transport. These findings can be accurately studied using ultrasound.}, }
@article {pmid24404073, year = {2013}, author = {Yaginuma, T and Oliveira, MS and Lima, R and Ishikawa, T and Yamaguchi, T}, title = {Human red blood cell behavior under homogeneous extensional flow in a hyperbolic-shaped microchannel.}, journal = {Biomicrofluidics}, volume = {7}, number = {5}, pages = {54110}, pmid = {24404073}, issn = {1932-1058}, abstract = {It is well known that certain pathological conditions result in a decrease of red blood cells (RBCs) deformability and subsequently can significantly alter the blood flow in microcirculation, which may block capillaries and cause ischemia in the tissues. Microfluidic systems able to obtain reliable quantitative measurements of RBC deformability hold the key to understand and diagnose RBC related diseases. In this work, a microfluidic system composed of a microchannel with a hyperbolic-shaped contraction followed by a sudden expansion is presented. We provide a detailed quantitative description of the degree of deformation of human RBCs under a controlled homogeneous extensional flow field. We measured the deformation index (DI) as well as the velocity of the RBCs travelling along the centerline of the channel for four different flow rates and analyze the impact of the particle Reynolds number. The results show that human RBC deformation tends to reach a plateau value in the region of constant extensional rate, the value of which depends on the extension rate. Additionally, we observe that the presence of a sudden expansion downstream of the hyperbolic contraction modifies the spatial distribution of cells and substantially increases the cell free layer (CFL) downstream of the expansion plane similarly to what is seen in other expansion flows. Beyond a certain value of flow rate, there is only a weak effect of inlet flow rates on the enhancement of the downstream CFL. These in vitro experiments show the potential of using microfluidic systems with hyperbolic-shaped microchannels both for the separation of the RBCs from plasma and to assess changes in RBC deformability in physiological and pathological situations for clinical purposes. However, the selection of the geometry and the identification of the most suitable region to evaluate the changes on the RBC deformability under extensional flows are crucial if microfluidics is to be used as an in vitro clinical methodology to detect circulatory diseases.}, }
@article {pmid24404068, year = {2013}, author = {Mbaye, S and Séchet, P and Pignon, F and Martins, JM}, title = {Influence of hydrodynamics on the growth kinetics of glass-adhering Pseudomonas putida cells through a parallel plate flow chamber.}, journal = {Biomicrofluidics}, volume = {7}, number = {5}, pages = {54105}, pmid = {24404068}, issn = {1932-1058}, abstract = {The objective of this work was to investigate the influence of hydrodynamics on the growth kinetics of surface-adhering Pseudomonas putida cells. The results showed in particular that under non substrate-limiting conditions, the early step of bacterial apparent growth rate is lower than those measured with suspended cells. Contrary to previously cited authors which explain this behavior to the different adhesive properties of the "daughter"-cells (which makes more probable the detachment of these daughter-cells), in our experimental conditions, that explanation does not hold and we show a clear dependence of growth kinetics with flow conditions, due to the formation of boundary layer concentration at low Reynolds number. These results revealed that using Monod law in the modeling of biofilm growth in fixed-biomass processes should be performed with care.}, }
@article {pmid24404053, year = {2013}, author = {Geislinger, TM and Franke, T}, title = {Sorting of circulating tumor cells (MV3-melanoma) and red blood cells using non-inertial lift.}, journal = {Biomicrofluidics}, volume = {7}, number = {4}, pages = {44120}, pmid = {24404053}, issn = {1932-1058}, abstract = {We demonstrate the method of non-inertial lift induced cell sorting (NILICS), a continuous, passive, and label-free cell sorting approach in a simple single layer microfluidic device at low Reynolds number flow conditions. In the experiments, we exploit the non-inertial lift effect to sort circulating MV3-melanoma cells from red blood cell suspensions at different hematocrits as high as 9%. We analyze the separation process and the influence of hematocrit and volume flow rates. We achieve sorting efficiencies for MV3-cells up to EMV3 = 100% at Hct = 9% and demonstrate cell viability by recultivation of the sorted cells.}, }
@article {pmid24399860, year = {2013}, author = {Boghosian, ME and Cassel, KW}, title = {A pressure-gradient mechanism for vortex shedding in constricted channels.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {25}, number = {12}, pages = {123603}, pmid = {24399860}, issn = {1070-6631}, support = {R01 DK090769/DK/NIDDK NIH HHS/United States ; }, abstract = {Numerical simulations of the unsteady, two-dimensional, incompressible Navier-Stokes equations are performed for a Newtonian fluid in a channel having a symmetric constriction modeled by a two-parameter Gaussian distribution on both channel walls. The Reynolds number based on inlet half-channel height and mean inlet velocity ranges from 1 to 3000. Constriction ratios based on the half-channel height of 0.25, 0.5, and 0.75 are considered. The results show that both the Reynolds number and constriction geometry have a significant effect on the behavior of the post-constriction flow field. The Navier-Stokes solutions are observed to experience a number of bifurcations: steady attached flow, steady separated flow (symmetric and asymmetric), and unsteady vortex shedding downstream of the constriction depending on the Reynolds number and constriction ratio. A sequence of events is described showing how a sustained spatially growing flow instability, reminiscent of a convective instability, leads to the vortex shedding phenomenon via a proposed streamwise pressure-gradient mechanism.}, }
@article {pmid24397384, year = {2014}, author = {Dudani, JS and Go, DE and Gossett, DR and Tan, AP and Di Carlo, D}, title = {Mediating millisecond reaction time around particles and cells.}, journal = {Analytical chemistry}, volume = {86}, number = {3}, pages = {1502-1510}, doi = {10.1021/ac402920m}, pmid = {24397384}, issn = {1520-6882}, support = {//Howard Hughes Medical Institute/United States ; }, mesh = {Cell Survival ; Equipment Design ; HeLa Cells ; Humans ; MCF-7 Cells ; Microfluidic Analytical Techniques/instrumentation/*methods ; Permeability ; Staining and Labeling ; Time Factors ; }, abstract = {Precise spatiotemporal control of how particles and cells interact with reagents is critical for numerous laboratory and industrial processes. Novel tools for exerting this control at shorter time scales will enable development of new chemical processes and biomedical assays. Previously, we have developed a generalized approach to manipulate cells and particles across fluid streams termed rapid inertial solution exchange (RInSE), which utilizes inertial lift forces at finite Reynolds number and high Peclet number to transfer particles from an initial solution to another within a millisecond. Here, we apply these principles toward developing a continuous flow microfluidic platform that enables transient chemical treatments of cells and particles (on the order of 1 ms). We also demonstrate how the reactant stream can be employed as a diffusion barrier, preventing adverse reactions between coflowing solutions. In order to demonstrate the utility of the method, we applied it to various operations in molecular biology and automated cell staining including cell permeabilization, fluorescent staining, and molecular delivery to viable cells. We expect this method will enable previously unexplored studies of the dynamics of molecular events, improve uniformity of reactions carried on the surface of beads, and increase uniformity in cell-based assays through automation.}, }
@article {pmid24396530, year = {2013}, author = {Feng, X and Ren, Y and Jiang, H}, title = {An effective splitting-and-recombination micromixer with self-rotated contact surface for wide Reynolds number range applications.}, journal = {Biomicrofluidics}, volume = {7}, number = {5}, pages = {54121}, pmid = {24396530}, issn = {1932-1058}, abstract = {It is difficult to mix two liquids on a microfluidic chip because the small dimensions and velocities effectively prevent the turbulence. This paper describes two 2-layer PDMS passive micromixers based on the concept of splitting and recombining the flow that exploits a self-rotated contact surface to increase the concentration gradients to obtain fast and efficient mixing. The designed micromixers were simulated and the mixing performance was assessed. The mixers have shown excellent mixing efficiency over a wide range of Reynolds number. The mixers were reasonably fabricated by multilayer soft lithography, and the experimental measurements were performed to qualify the mixing performance of the realized mixer. The results show that the mixing efficiency for one realized mixer is from 91.8% to 87.7% when the Reynolds number increases from 0.3 to 60, while the corresponding value for another mixer is from 89.4% to 72.9%. It is rather interesting that the main mechanism for the rapid mixing is from diffusion to chaotic advection when the flow rate increases, but the mixing efficiency has not obvious decline. The smart geometry of the mixers with total length of 10.25 mm makes it possible to be integrated with many microfluidic devices for various applications in μ-TAS and Lab-on-a-chip systems.}, }
@article {pmid24353347, year = {2012}, author = {Deng, M and Li, X and Liang, H and Caswell, B and Karniadakis, GE}, title = {Simulation and modelling of slip flow over surfaces grafted with polymer brushes and glycocalyx fibres.}, journal = {Journal of fluid mechanics}, volume = {711}, number = {}, pages = {}, pmid = {24353347}, issn = {0022-1120}, support = {R01 HL094270/HL/NHLBI NIH HHS/United States ; }, abstract = {Fabrication of functionalized surfaces using polymer brushes is a relatively simple process and parallels the presence of glycocalyx filaments coating the luminal surface of our vasculature. In this paper, we perform atomistic-like simulations based on dissipative particle dynamics (DPD) to study both polymer brushes and glycocalyx filaments subject to shear flow, and we apply mean-field theory to extract useful scaling arguments on their response. For polymer brushes, a weak shear flow has no effect on the brush density profile or its height, while the slip length is independent of the shear rate and is of the order of the brush mesh size as a result of screening by hydrodynamic interactions. However, for strong shear flow, the polymer brush is penetrated deeper and is deformed, with a corresponding decrease of the brush height and an increase of the slip length. The transition from the weak to the strong shear regime can be described by a simple 'blob' argument, leading to the scaling γ̇0 ∝ σ[3/2], where γ̇0 is the critical transition shear rate and σ is the grafting density. Furthermore, in the strong shear regime, we observe a cyclic dynamic motion of individual polymers, causing a reversal in the direction of surface flow. To study the glycocalyx layer, we first assume a homogeneous flow that ignores the discrete effects of blood cells, and we simulate microchannel flows at different flow rates. Surprisingly, we find that, at low Reynolds number, the slip length decreases with the mean flow velocity, unlike the behaviour of polymer brushes, for which the slip length remains constant under similar conditions. (The slip length and brush height are measured with respect to polymer mesh size and polymer contour length, respectively.) We also performed additional DPD simulations of blood flow in a tube with walls having a glycocalyx layer and with the deformable red blood cells modelled accurately at the spectrin level. In this case, a plasma cell-free layer is formed, with thickness more than three times the glycocalyx layer. We then find our scaling arguments based on the homogeneous flow assumption to be valid for this physiologically correct case as well. Taken together, our findings point to the opposing roles of conformational entropy and bending rigidity - dominant effects for the brush and glycocalyx, respectively - which, in turn, lead to different flow characteristics, despite the apparent similarity of the two systems.}, }
@article {pmid24329356, year = {2013}, author = {Cerbus, RT and Goldburg, WI}, title = {Information content of turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {5}, pages = {053012}, doi = {10.1103/PhysRevE.88.053012}, pmid = {24329356}, issn = {1550-2376}, abstract = {We treat a turbulent velocity field as a message in the same way as a book or a picture. All messages can be described by their entropy per symbol h, defined as in Shannon's theory of communication. In a turbulent flow, as the Reynolds number Re increases, more correlated degrees of freedom are excited and participate in the turbulent cascade. Experiments in a turbulent soap film suggest that the spatial entropy density h is a decreasing function of Re, namely h[proportionality]-logRe + const. In the logistic map, also analyzed here, increasing the control parameter r increases h. A modified logistic map with additional coupling to past iterations suggests the significance of correlations.}, }
@article {pmid24329355, year = {2013}, author = {Favier, B and Proctor, MR}, title = {Kinematic dynamo action in square and hexagonal patterns.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {5}, pages = {053011}, doi = {10.1103/PhysRevE.88.053011}, pmid = {24329355}, issn = {1550-2376}, abstract = {We consider kinematic dynamo action in rapidly rotating Boussinesq convection just above onset. The velocity is constrained to have either a square or a hexagonal pattern. For the square pattern, large-scale dynamo action is observed at onset, with most of the magnetic energy being contained in the horizontally averaged component. As the magnetic Reynolds number increases, small-scale dynamo action becomes possible, reducing the overall growth rate of the dynamo. For the hexagonal pattern, the breaking of symmetry between up and down flows results in an effective pumping velocity. For intermediate rotation rates, this additional effect can prevent the growth of any mean-field dynamo, so that only a small-scale dynamo is eventually possible at large enough magnetic Reynolds number. For very large rotation rates, this pumping term becomes negligible, and the dynamo properties of square and hexagonal patterns are qualitatively similar. These results hold for both perfectly conducting and infinite magnetic permeability boundary conditions.}, }
@article {pmid24329354, year = {2013}, author = {Guervilly, C and Wood, TS and Brummell, NH}, title = {Effect of metallic walls on dynamos generated by laminar boundary-driven flow in a spherical domain.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {5}, pages = {053010}, doi = {10.1103/PhysRevE.88.053010}, pmid = {24329354}, issn = {1550-2376}, abstract = {We present a numerical study of dynamo action in a conducting fluid encased in a metallic spherical shell. Motions in the fluid are driven by differential rotation of the outer metallic shell, which we refer to as "the wall." The two hemispheres of the wall are held in counter-rotation, producing a steady, axisymmetric interior flow consisting of differential rotation and a two-cell meridional circulation with radial inflow in the equatorial plane. From previous studies, this type of flow is known to maintain a stationary equatorial dipole by dynamo action if the magnetic Reynolds number is larger than about 300 and if the outer boundary is electrically insulating. We vary independently the thickness, electrical conductivity, and magnetic permeability of the wall to determine their effect on the dynamo action. The main results are the following: (a) Increasing the conductivity of the wall hinders the dynamo by allowing eddy currents within the wall, which are induced by the relative motion of the equatorial dipole field and the wall. This processes can be viewed as a skin effect or, equivalently, as the tearing apart of the dipole by the differential rotation of the wall, to which the field lines are anchored by high conductivity. (b) Increasing the magnetic permeability of the wall favors dynamo action by constraining the magnetic field lines in the fluid to be normal to the wall, thereby decoupling the fluid from any induction in the wall. (c) Decreasing the wall thickness limits the amplitude of the eddy currents, and is therefore favorable for dynamo action, provided that the wall is thinner than the skin depth. We explicitly demonstrate these effects of the wall properties on the dynamo field by deriving an effective boundary condition in the limit of vanishing wall thickness.}, }
@article {pmid24329353, year = {2013}, author = {Mizuta, A and Matsumoto, T and Toh, S}, title = {Transition of the scaling law in inverse energy cascade range caused by a nonlocal excitation of coherent structures observed in two-dimensional turbulent fields.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {5}, pages = {053009}, doi = {10.1103/PhysRevE.88.053009}, pmid = {24329353}, issn = {1550-2376}, abstract = {We numerically investigate the inverse energy cascade range of two-dimensional Navier-Stokes turbulence. Our focus is on the universality of the Kolmogorov's phenomenology. In our direct numerical simulations, two types of forcing processes, the random forcing and the deterministic forcing, are employed besides the systematically varied numerical parameters. We first calculate the two-dimensional Navier-Stokes equations and confirm that results in the quasi steady state are consistent with the classical phenomenology for both types of forcing processes. It is also found that the difference in forcing process appears after the inverse energy cascade range reaches the system size; the dipole coherent vortices emerge and grow only when the random forcing is adopted. Then we add a large-scale drag term to the Navier-Stokes equations to obtain the statistically stationary state. When the random forcing is used, the scaling exponent of the energy spectrum in the stationary state starts to differ from the predicted -5/3 in the inverse energy cascade range as the infrared Reynolds number Re(d) increases, where Re(d) is defined as k(f)/k(d) with the forcing wave number k(f) and the large-scale drag wave number k(d). That can be interpreted as a transition phenomenon in which the local maximum vorticity grows like an order parameter caused by excitation of strong coherent vortices. Strong coherent vortices emerge and grow after the quasi steady state and destroy the scaling law when Re(d) is over a critical value. These coherent vortices are not due to the finite-size effect, unlike the dipole coherent vortices. On the other hand, when the deterministic forcing is adopted, strong coherent vortices are hardly seen and the -5/3 scaling law holds independently of Re(d). We examine the cases of the combination of both types of forcing processes and find that formation of such coherent vortices is sensitive to the mechanism of the external forcing process as well as the numerical parameters. Several types of large-scale drag terms are also tested and their insignificant influence on these qualitative properties is revealed.}, }
@article {pmid24329352, year = {2013}, author = {Huang, W and Liu, H and Wang, F and Wu, J and Zhang, HP}, title = {Experimetal study of a freely falling plate with an inhomogeneous mass distribution.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {5}, pages = {053008}, doi = {10.1103/PhysRevE.88.053008}, pmid = {24329352}, issn = {1550-2376}, abstract = {A homogeneous thin plate often flutters while falling through a fluid under gravity. The center of gravity of the plate moves back-and-forth horizontally and the plate tilting angle oscillates symmetrically from the horizontal. Here we show that such a scenario is qualitatively changed for a plate with noncoinciding centers of gravity and buoyancy due to an inhomogeneous mass distribution. Mismatch of the centers causes an external torque that breaks the symmetry of rotational motion, shifts the mean tilting position from the horizontal, and leads to a net horizontal plate displacement. In laboratory experiments with a Reynolds number around 1500, we found that the net horizontal displacement scales linearly with the separation between the centers up to a critical value, beyond which the plate falls vertically in an edge-on configuration with the heavier side downward. Experimental results are compared to predictions of a quasi-steady numerical model. Our work demonstrates that motion of freely moving objects in a fluid depends sensitively on external torques, which potentially can be used as an effective control method.}, }
@article {pmid24329346, year = {2013}, author = {Samanta, A}, title = {Shear wave instability for electrified falling films.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {5}, pages = {053002}, doi = {10.1103/PhysRevE.88.053002}, pmid = {24329346}, issn = {1550-2376}, abstract = {The effect of an electric field on the shear wave instability pertaining to a gravity driven conducting liquid film is studied based on the Chebyshev-Tau method. The shear wave appears at very large values of the Reynolds number when the inclination angle is sufficiently small. The presence of an electric field shows peculiar behavior on the critical Reynolds number corresponding to the shear mode. It suppresses shear wave instability through the amplification of the critical Reynolds number and leads to a nontrivial stabilizing effect when inclination angle B≥3'. On the other hand, the reduction of the critical Reynolds number is found if the inclination angle is further lowered in magnitude.}, }
@article {pmid24329198, year = {2013}, author = {Kraft, DJ and Wittkowski, R and ten Hagen, B and Edmond, KV and Pine, DJ and Löwen, H}, title = {Brownian motion and the hydrodynamic friction tensor for colloidal particles of complex shape.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {5}, pages = {050301}, doi = {10.1103/PhysRevE.88.050301}, pmid = {24329198}, issn = {1550-2376}, abstract = {We synthesize colloidal particles with various anisotropic shapes and track their orientationally resolved Brownian trajectories using confocal microscopy. An analysis of appropriate short-time correlation functions provides direct access to the hydrodynamic friction tensor of the particles revealing nontrivial couplings between the translational and rotational degrees of freedom. The results are consistent with calculations of the hydrodynamic friction tensor in the low-Reynolds-number regime for the experimentally determined particle shapes.}, }
@article {pmid24312547, year = {2013}, author = {Sagong, W and Jeon, WP and Choi, H}, title = {Hydrodynamic characteristics of the sailfish (Istiophorus platypterus) and swordfish (Xiphias gladius) in gliding postures at their cruise speeds.}, journal = {PloS one}, volume = {8}, number = {12}, pages = {e81323}, pmid = {24312547}, issn = {1932-6203}, mesh = {Animals ; *Hydrodynamics ; Kinetics ; *Movement ; Perciformes/anatomy &amp; histology/*physiology ; *Posture ; Skin/anatomy &amp; histology ; }, abstract = {The sailfish and swordfish are known as the fastest sea animals, reaching their maximum speeds of around 100 km/h. In the present study, we investigate the hydrodynamic characteristics of these fishes in their cruise speeds of about 1 body length per second. We install a taxidermy specimen of each fish in a wind tunnel, and measure the drag on its body and boundary-layer velocity above its body surface at the Reynolds number corresponding to its cruising condition. The drag coefficients of the sailfish and swordfish based on the free-stream velocity and their wetted areas are measured to be 0.0075 and 0.0091, respectively, at their cruising conditions. These drag coefficients are very low and comparable to those of tuna and pike and smaller than those of dogfish and small-size trout. On the other hand, the long bill is one of the most distinguished features of these fishes from other fishes, and we study its role on the ability of drag modification. The drag on the fish without the bill or with an artificially-made shorter one is slightly smaller than that with the original bill, indicating that the bill itself does not contribute to any drag reduction at its cruise speed. From the velocity measurement near the body surface, we find that at the cruise speed flow separation does not occur over the whole body even without the bill, and the boundary layer flow is affected only at the anterior part of the body by the bill.}, }
@article {pmid24307870, year = {2013}, author = {Guarendi, AN and Chandy, AJ}, title = {Magnetohydrodynamic simulations of hypersonic flow over a cylinder using axial- and transverse-oriented magnetic dipoles.}, journal = {TheScientificWorldJournal}, volume = {2013}, number = {}, pages = {438381}, doi = {10.1155/2013/438381}, pmid = {24307870}, issn = {1537-744X}, mesh = {*Air Movements ; Computer Simulation ; *Hydrodynamics ; Magnetics ; *Models, Theoretical ; *Spacecraft ; }, abstract = {Numerical simulations of magnetohydrodynamic (MHD) hypersonic flow over a cylinder are presented for axial- and transverse-oriented dipoles with different strengths. ANSYS CFX is used to carry out calculations for steady, laminar flows at a Mach number of 6.1, with a model for electrical conductivity as a function of temperature and pressure. The low magnetic Reynolds number (<<1) calculated based on the velocity and length scales in this problem justifies the quasistatic approximation, which assumes negligible effect of velocity on magnetic fields. Therefore, the governing equations employed in the simulations are the compressible Navier-Stokes and the energy equations with MHD-related source terms such as Lorentz force and Joule dissipation. The results demonstrate the ability of the magnetic field to affect the flowfield around the cylinder, which results in an increase in shock stand-off distance and reduction in overall temperature. Also, it is observed that there is a noticeable decrease in drag with the addition of the magnetic field.}, }
@article {pmid24300568, year = {2014}, author = {Tripathi, D and Anwar Bég, O}, title = {Peristaltic propulsion of generalized Burgers' fluids through a non-uniform porous medium: a study of chyme dynamics through the diseased intestine.}, journal = {Mathematical biosciences}, volume = {248}, number = {}, pages = {67-77}, doi = {10.1016/j.mbs.2013.11.006}, pmid = {24300568}, issn = {1879-3134}, mesh = {Biophysical Phenomena ; Body Fluids/physiology ; Elasticity ; Gastrointestinal Contents ; Humans ; Intestinal Diseases/*physiopathology ; Mathematical Concepts ; *Models, Biological ; Peristalsis/*physiology ; Porosity ; Rheology ; Viscosity ; }, abstract = {A mathematical study of the peristaltic flow of complex rheological viscoelastic fluids using the generalized fractional Burgers' model through a non-uniform channel is presented. This model is designed to study the movement of chyme and undigested chyme (biophysical waste materials) through the small intestine to the large intestine. To simulate blockages and impedance of debris generated by cell shedding, infections, adhesions on the wall and undigested material, a drag force porous media model is utilized. This effectively mimicks resistance to chyme percolation generated by solid matrix particles in the regime. The conduit geometry is mathematically simulated as a sinusoidal propagation with linear increment in shape of the bolus along the length of channel. A modified Darcy-Brinkman model is employed to simulate the generalized flows through isotropic, homogenous porous media, a simplified but physically robust approximation to actual clinical situations. To model the rheological properties of chyme, a viscoelastic Burgers' fluid formulation is adopted. The governing equations are simplified by assuming long wavelength and low Reynolds number approximations. Numerical and approximate analytical solutions are obtained with two semi-numerical techniques, namely the homotopy perturbation method and the variational iteration method. Visualization of the results is achieved with Mathematica software. The influence of the dominant hydromechanical and geometric parameters such as fractional viscoelastic parameters, wave number, non-uniformity constant, permeability parameter, and material constants on the peristaltic flow characteristics are depicted graphically.}, }
@article {pmid24292011, year = {2014}, author = {Tripathi, D and Bég, OA}, title = {Mathematical modelling of peristaltic propulsion of viscoplastic bio-fluids.}, journal = {Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine}, volume = {228}, number = {1}, pages = {67-88}, doi = {10.1177/0954411913511584}, pmid = {24292011}, issn = {2041-3033}, mesh = {Biomechanical Phenomena/*physiology ; Body Fluids ; Friction ; Humans ; *Models, Biological ; Peristalsis/*physiology ; Pressure ; Rheology/*methods ; Viscosity ; }, abstract = {This article studies theoretically the transportation of rheological viscoplastic fluids through physiological vessels by continuous muscle contraction and relaxation, that is, peristalsis. Both cases of planar and cylindrical physiological vessels are considered. A mathematical model is developed under long wavelength and low Reynolds number approximations. Expressions for axial velocity in core region, axial velocity in plug flow region, volume flow rate and pressure gradient in non-dimensional form are obtained. A comparative study of velocity profiles, pressure distribution, friction force and mechanical efficiency for different viscoplastic liquids is conducted. The influence of width of plug flow region, shear rate strain index and yield stress index on the pressure distribution, friction force and mechanical efficiency is elaborated. The study is relevant to gastric fluid mechanics and also non-Newtonian biomimetic pump hazardous waste systems exploiting peristaltic mechanisms.}, }
@article {pmid24260130, year = {2013}, author = {Noreen, S}, title = {Mixed convection peristaltic flow of third order nanofluid with an induced magnetic field.}, journal = {PloS one}, volume = {8}, number = {11}, pages = {e78770}, pmid = {24260130}, issn = {1932-6203}, mesh = {*Magnetic Fields ; *Models, Theoretical ; Nanoparticles/*chemistry ; *Rheology ; }, abstract = {This research is concerned with the peristaltic flow of third order nanofluid in an asymmetric channel. The governing equations of third order nanofluid are modelled in wave frame of reference. Effect of induced magnetic field is considered. Long wavelength and low Reynolds number situation is tackled. Numerical solutions of the governing problem are computed and analyzed. The effects of Brownian motion and thermophoretic diffusion of nano particles are particularly emphasized. Physical quantities such as velocity, pressure rise, temperature, induced magnetic field and concentration distributions are discussed.}, }
@article {pmid24237566, year = {2013}, author = {Pushkin, DO and Yeomans, JM}, title = {Fluid mixing by curved trajectories of microswimmers.}, journal = {Physical review letters}, volume = {111}, number = {18}, pages = {188101}, doi = {10.1103/PhysRevLett.111.188101}, pmid = {24237566}, issn = {1079-7114}, mesh = {Chlamydomonas reinhardtii/physiology ; Escherichia coli/physiology ; *Models, Biological ; *Swimming ; }, abstract = {We consider the tracer diffusion D(rr) that arises from the run-and-tumble motion of low Reynolds number swimmers, such as bacteria. Assuming a dilute suspension, where the bacteria move in uncorrelated runs of length λ, we obtain an exact expression for D(rr) for dipolar swimmers in three dimensions, hence explaining the surprising result that this is independent of λ. We compare D(rr) to the contribution to tracer diffusion from entrainment.}, }
@article {pmid24229310, year = {2013}, author = {Najafi, A and Raad, SS and Yousefi, R}, title = {Self-propulsion in a low-Reynolds-number fluid confined by two walls of a microchannel.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {4}, pages = {045001}, doi = {10.1103/PhysRevE.88.045001}, pmid = {24229310}, issn = {1550-2376}, abstract = {The problem of hydrodynamic interactions with confining walls is examined for a model of a microswimmer composed of three connected beads. Two parallel walls of a narrow microfluidic channel confine the fluid flow. We show that different trajectories for this linear swimmer emerge because of long-range hydrodynamic interactions with the walls of the channel. The possibility of space-spanning trajectories for this swimmer can potentially introduce it as a candidate for constructing a mixing device for working at the laminar flow conditions in microfluidic channels.}, }
@article {pmid24229281, year = {2013}, author = {Paul, MR and Clark, MT and Cross, MC}, title = {Coupled motion of microscale and nanoscale elastic objects in a viscous fluid.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {4}, pages = {043012}, doi = {10.1103/PhysRevE.88.043012}, pmid = {24229281}, issn = {1550-2376}, abstract = {We study the coupled dynamics of two closely spaced micron or nanoscale elastic objects immersed in a viscous fluid. The dynamics of the elastic objects are coupled through the motion of the surrounding viscous fluid. We consider two cases: (i) one object is driven externally by an imposed harmonic actuation force and the second object is passive and (ii) both objects are driven by a Brownian force to yield stochastic dynamics. Using a harmonic oscillator approximation for the elastic objects and the unsteady Stokes equations to describe the fluid dynamics, we develop analytical expressions for the amplitude and phase of the displacement of the oscillating objects. For the case of an imposed actuation we use an impulse in force to determine the resulting dynamics over all frequencies. For the Brownian-driven objects the stochastic dynamics are found using the fluctuation-dissipation theorem. We validate our theoretical expressions by comparison with results from finite-element numerical simulations of the complete fluid-solid interaction problem. Our results yield interesting features in the amplitude and phase of the displacement of the elastic objects due to the fluid motion. We find that the dynamics depend on the separation of the objects, a measure of the mass loading due to the fluid, and the frequency parameter which acts as a frequency-based Reynolds number. Our results are valid over the range of parameters typical of micron and nanoscale elastic objects in fluid. The range of dynamics found can be understood in terms of the interplay between the viscous and potential components of the fluid flow field described by the unsteady Stokes equation for an oscillating cylinder. For small values of the frequency parameter, typical of nanoscale elastic objects, the dynamics are overdamped due to the dominance of viscous forces over inertial forces. For moderate and large values of the frequency parameter, typical of micron-scale elastic objects, we find that the dynamics of the fluid-coupled objects exhibits an interesting mode splitting to yield a bimodal signature in the amplitude-frequency plots. We find that the mode splitting can be described using a normal mode analysis containing only potential fluid interactions between the cylinders.}, }
@article {pmid24223445, year = {2013}, author = {Wang, X and Zhang, LT}, title = {Modified Immersed Finite Element Method For Fully-Coupled Fluid-Structure Interations.}, journal = {Computer methods in applied mechanics and engineering}, volume = {267}, number = {}, pages = {}, pmid = {24223445}, issn = {0045-7825}, support = {R01 DC005642/DC/NIDCD NIH HHS/United States ; }, abstract = {In this paper, we develop a "modified" immersed finite element method (mIFEM), a non-boundary-fitted numerical technique, to study fluid-structure interactions. Using this method, we can more precisely capture the solid dynamics by solving the solid governing equation instead of imposing it based on the fluid velocity field as in the original immersed finite element (IFEM). Using the IFEM may lead to severe solid mesh distortion because the solid deformation is been over-estimated, especially for high Reynolds number flows. In the mIFEM, the solid dynamics is solved using appropriate boundary conditions generated from the surrounding fluid, therefore produces more accurate and realistic coupled solutions. We show several 2-D and 3-D testing cases where the mIFEM has a noticeable advantage in handling complicated fluid-structure interactions when the solid behavior dominates the fluid flow.}, }
@article {pmid24222752, year = {2013}, author = {Yadav, AS and Bhagoria, JL}, title = {Modeling and simulation of turbulent flows through a solar air heater having square-sectioned transverse rib roughness on the absorber plate.}, journal = {TheScientificWorldJournal}, volume = {2013}, number = {}, pages = {827131}, doi = {10.1155/2013/827131}, pmid = {24222752}, issn = {1537-744X}, mesh = {*Air ; Computer Simulation ; Heating/*instrumentation/methods ; *Hydrodynamics ; *Models, Theoretical ; *Solar Energy ; Thermodynamics ; }, abstract = {Solar air heater is a type of heat exchanger which transforms solar radiation into heat energy. The thermal performance of conventional solar air heater has been found to be poor because of the low convective heat transfer coefficient from the absorber plate to the air. Use of artificial roughness on a surface is an effective technique to enhance the rate of heat transfer. A CFD-based investigation of turbulent flow through a solar air heater roughened with square-sectioned transverse rib roughness has been performed. Three different values of rib-pitch (P) and rib-height (e) have been taken such that the relative roughness pitch (P/e = 14.29) remains constant. The relative roughness height, e/D, varies from 0.021 to 0.06, and the Reynolds number, Re, varies from 3800 to 18,000. The results predicted by CFD show that the average heat transfer, average flow friction, and thermohydraulic performance parameter are strongly dependent on the relative roughness height. A maximum value of thermohydraulic performance parameter has been found to be 1.8 for the range of parameters investigated. Comparisons with previously published work have been performed and found to be in excellent agreement.}, }
@article {pmid24194551, year = {2013}, author = {Wilson, LG and Carter, LM and Reece, SE}, title = {High-speed holographic microscopy of malaria parasites reveals ambidextrous flagellar waveforms.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {110}, number = {47}, pages = {18769-18774}, pmid = {24194551}, issn = {1091-6490}, support = {/WT_/Wellcome Trust/United Kingdom ; 082234MA/WT_/Wellcome Trust/United Kingdom ; }, mesh = {Animals ; Axoneme/physiology ; Biomechanical Phenomena ; Flagella/*physiology/*ultrastructure ; Germ Cells/*physiology ; Holography/*methods ; Male ; Microscopy/*methods ; *Models, Biological ; Plasmodium berghei/*cytology ; }, abstract = {Axonemes form the core of eukaryotic flagella and cilia, performing tasks ranging from transporting fluid in developing embryos to the propulsion of sperm. Despite their abundance across the eukaryotic domain, the mechanisms that regulate the beating action of axonemes remain unknown. The flagellar waveforms are 3D in general, but current understanding of how axoneme components interact stems from 2D data; comprehensive measurements of flagellar shape are beyond conventional microscopy. Moreover, current flagellar model systems (e.g., sea urchin, human sperm) contain accessory structures that impose mechanical constraints on movement, obscuring the "native" axoneme behavior. We address both problems by developing a high-speed holographic imaging scheme and applying it to the (male) microgametes of malaria (Plasmodium) parasites. These isolated flagella are a unique, mathematically tractable model system for the physics of microswimmers. We reveal the 3D flagellar waveforms of these microorganisms and map the differential shear between microtubules in their axonemes. Furthermore, we overturn claims that chirality in the structure of the axoneme governs the beat pattern [Hirokawa N, et al. (2009) Ann Rev Fluid Mech 41:53-72], because microgametes display a left- or right-handed character on alternate beats. This breaks the link between structural chirality in the axoneme and larger scale symmetry breaking (e.g., in developing embryos), leading us to conclude that accessory structures play a critical role in shaping the flagellar beat.}, }
@article {pmid24187531, year = {2013}, author = {Zhou, J and Kasper, S and Papautsky, I}, title = {Enhanced size-dependent trapping of particles using microvortices.}, journal = {Microfluidics and nanofluidics}, volume = {15}, number = {5}, pages = {}, pmid = {24187531}, issn = {1613-4982}, support = {R01 DK060957/DK/NIDDK NIH HHS/United States ; }, abstract = {Inertial microfluidics has been attracting considerable interest for size-based separation of particles and cells. The inertial forces can be manipulated by expanding the microchannel geometry, leading to formation of microvortices which selectively isolate and trap particles or cells from a mixture. In this work, we aim to enhance our understanding of particle trapping in such microvortices by developing a model of selective particle trapping. Design and operational parameters including flow conditions, size of the trapping region, and target particle concentration are explored to elucidate their influence on trapping behavior. Our results show that the size dependence of trapping is characterized by a threshold Reynolds number, which governs the selective entry of particles into microvortices from the main flow. We show that concentration enhancement on the order of 100,000× and isolation of targets at concentrations in the 1/mL is possible. Ultimately, the insights gained from our systematic investigation suggest optimization solutions that enhance device performance (efficiency, size selectivity, and yield) and are applicable to selective isolation and trapping of large rare cells as well as other applications.}, }
@article {pmid24182136, year = {2013}, author = {Si, J and Colgate, SA and Li, H and Martinic, J and Westpfahl, D}, title = {Data acquisition in a high-speed rotating frame for New Mexico Institute of Mining and Technology liquid sodium αω dynamo experiment.}, journal = {The Review of scientific instruments}, volume = {84}, number = {10}, pages = {104501}, doi = {10.1063/1.4825354}, pmid = {24182136}, issn = {1089-7623}, abstract = {New Mexico Institute of Mining and Technology liquid sodium αω-dynamo experiment models the magnetic field generation in the universe as discussed in detail by Colgate, Li, and Pariev [Phys. Plasmas 8, 2425 (2001)]. To obtain a quasi-laminar flow with magnetic Reynolds number R(m) ~ 120, the dynamo experiment consists of two co-axial cylinders of 30.5 cm and 61 cm in diameter spinning up to 70 Hz and 17.5 Hz, respectively. During the experiment, the temperature of the cylinders must be maintained to 110 °C to ensure that the sodium remains fluid. This presents a challenge to implement a data acquisition (DAQ) system in such high temperature, high-speed rotating frame, in which the sensors (including 18 Hall sensors, 5 pressure sensors, and 5 temperature sensors, etc.) are under the centrifugal acceleration up to 376g. In addition, the data must be transmitted and stored in a computer 100 ft away for safety. The analog signals are digitized, converted to serial signals by an analog-to-digital converter and a field-programmable gate array. Power is provided through brush/ring sets. The serial signals are sent through ring/shoe sets capacitively, then reshaped with cross-talk noises removed. A microcontroller-based interface circuit is used to decode the serial signals and communicate with the data acquisition computer. The DAQ accommodates pressure up to 1000 psi, temperature up to more than 130 °C, and magnetic field up to 1000 G. First physics results have been analyzed and published. The next stage of the αω-dynamo experiment includes the DAQ system upgrade.}, }
@article {pmid24180752, year = {2013}, author = {Vladimirov, VA and Ilin, K}, title = {An asymptotic model in acoustics: acoustic drift equations.}, journal = {The Journal of the Acoustical Society of America}, volume = {134}, number = {5}, pages = {3419-3424}, doi = {10.1121/1.4821211}, pmid = {24180752}, issn = {1520-8524}, mesh = {*Acoustics ; *Models, Theoretical ; Motion ; *Sound ; Time Factors ; }, abstract = {A rigorous asymptotic procedure with the Mach number as a small parameter is used to derive the equations of mean flows which coexist and are affected by the background acoustic waves in the limit of very high Reynolds number.}, }
@article {pmid24173367, year = {2013}, author = {Mendoza, M and Succi, S and Herrmann, HJ}, title = {Flow through randomly curved manifolds.}, journal = {Scientific reports}, volume = {3}, number = {}, pages = {3106}, pmid = {24173367}, issn = {2045-2322}, abstract = {We present a computational study of the transport properties of campylotic (intrinsically curved) media. It is found that the relation between the flow through a campylotic media, consisting of randomly located curvature perturbations, and the average Ricci scalar of the system, exhibits two distinct functional expressions, depending on whether the typical spatial extent of the curvature perturbation lies above or below the critical value maximizing the overall scalar of curvature. Furthermore, the flow through such systems as a function of the number of curvature perturbations is found to present a sublinear behavior for large concentrations, due to the interference between curvature perturbations leading to an overall less curved space. We have also characterized the flux through such media as a function of the local Reynolds number and the scale of interaction between impurities. For the purpose of this study, we have also developed and validated a new lattice Boltzmann model.}, }
@article {pmid24160630, year = {2013}, author = {Leptos, KC and Wan, KY and Polin, M and Tuval, I and Pesci, AI and Goldstein, RE}, title = {Antiphase synchronization in a flagellar-dominance mutant of Chlamydomonas.}, journal = {Physical review letters}, volume = {111}, number = {15}, pages = {158101}, pmid = {24160630}, issn = {1079-7114}, support = {/WT_/Wellcome Trust/United Kingdom ; 097855/WT_/Wellcome Trust/United Kingdom ; BB/F021844/1/BB_/Biotechnology and Biological Sciences Research Council/United Kingdom ; }, mesh = {Chlamydomonas reinhardtii/genetics/*physiology ; Flagella/genetics/*physiology ; *Models, Biological ; Oscillometry ; Stochastic Processes ; }, abstract = {Groups of beating flagella or cilia often synchronize so that neighboring filaments have identical frequencies and phases. A prime example is provided by the unicellular biflagellate Chlamydomonas reinhardtii, which typically displays synchronous in-phase beating in a low-Reynolds number version of breaststroke swimming. We report the discovery that ptx1, a flagellar-dominance mutant of C. reinhardtii, can exhibit synchronization in precise antiphase, as in the freestyle swimming stroke. High-speed imaging shows that ptx1 flagella switch stochastically between in-phase and antiphase states, and that the latter has a distinct waveform and significantly higher frequency, both of which are strikingly similar to those found during phase slips that stochastically interrupt in-phase beating of the wild-type. Possible mechanisms underlying these observations are discussed.}, }
@article {pmid26029774, year = {2013}, author = {Luo, ZY and Wang, SQ and He, L and Xu, F and Bai, BF}, title = {Inertia-dependent dynamics of three-dimensional vesicles and red blood cells in shear flow.}, journal = {Soft matter}, volume = {9}, number = {40}, pages = {9651-9660}, doi = {10.1039/c3sm51823j}, pmid = {26029774}, issn = {1744-6848}, mesh = {*Blood Viscosity ; Computer Simulation ; Elasticity ; Erythrocyte Membrane/physiology ; Erythrocytes/*physiology ; Humans ; Microfluidic Analytical Techniques ; Microscopy, Confocal ; Models, Biological ; *Shear Strength ; *Stress, Mechanical ; }, abstract = {A three-dimensional (3D) simulation study of the effect of inertia on the dynamics of vesicles and red blood cells (RBCs) has not been reported. Here, we developed a 3D model based on the front tracking method to investigate how inertia affects the dynamics of spherical/non-spherical vesicles and biconcave-shaped RBCs with the Reynolds number ranging from 0.1 to 10. The results showed that inertia induced non-spherical vesicles transitioned from tumbling to swinging, which was not observed in previous 2D models. The critical viscosity ratio of inner/outer fluids for the tumbling–swinging transition remarkably increased with an increasing Reynolds number. The deformation of vesicles was greatly enhanced by inertia, and the frequency of tumbling and tank-treading was significantly decreased by inertia. We also found that RBCs can transit from tumbling to steady tank-treading through the swinging regime when the Reynolds number increased from 0.1 to 10. These results indicate that inertia needs to be considered at moderate Reynolds number (Re ~ 1) in the study of blood flow in the human body and the flow of deformable particle suspension in inertial microfluidic devices. The developed 3D model provided new insights into the dynamics of RBCs under shear flow, thus holding great potential to better understand blood flow behaviors under normal/disease conditions.}, }
@article {pmid24146013, year = {2013}, author = {Nevmerzhitskiy, NV}, title = {Some peculiarities of turbulent mixing growth and perturbations at hydrodynamic instabilities.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {371}, number = {2003}, pages = {20120291}, doi = {10.1098/rsta.2012.0291}, pmid = {24146013}, issn = {1364-503X}, abstract = {The author presents a review of some experimental works devoted to the research of evolution of large-scale perturbations and turbulent mixing (TM) in liquid and gaseous media during the growth of hydrodynamic instabilities. In particular, it is shown that growth of perturbations and TM in gases is sensitive to the Mach number of shock wave; character of gas front penetration into liquid is not changed as the Reynolds number of flow increases from 5×10(5) to 10(7); and change of the Atwood number sign from positive to negative causes stopping of gas front penetration into liquid, but mixing zone width is expanded under inertia.}, }
@article {pmid24146005, year = {2013}, author = {Youngs, DL}, title = {The density ratio dependence of self-similar Rayleigh-Taylor mixing.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {371}, number = {2003}, pages = {20120173}, doi = {10.1098/rsta.2012.0173}, pmid = {24146005}, issn = {1364-503X}, abstract = {Previous research on self-similar mixing caused by Rayleigh-Taylor (RT) instability is summarized and a recent series of high resolution large eddy simulations is described. Mesh sizes of approximately 2000 ×1000 × 1000 are used to investigate the properties of high Reynolds number self-similar RT mixing at a range of density ratios from 1.5 : 1 to 20 : 1. In some cases, mixing evolves from 'small random perturbations'. In other cases, random long wavelength perturbations (k(-3) spectrum) are added to give self-similar mixing at an enhanced rate, more typical of that observed in experiments. The properties of the turbulent mixing zone (volume fraction distributions, turbulence kinetic energy, molecular mixing parameter, etc.) are related to the RT growth rate parameter, α. Comparisons are made with experimental data on the internal structure and the asymmetry of the mixing zone (spike distance/bubble distance). The main purpose of this series of simulations is to provide data for calibration of engineering models (e.g. Reynolds-averaged Navier-Stokes models). It is argued that the influence of initial conditions is likely to be significant in most applications and the implications of this for engineering modelling are discussed.}, }
@article {pmid24145440, year = {2013}, author = {Geyer, VF and Jülicher, F and Howard, J and Friedrich, BM}, title = {Cell-body rocking is a dominant mechanism for flagellar synchronization in a swimming alga.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {110}, number = {45}, pages = {18058-18063}, pmid = {24145440}, issn = {1091-6490}, mesh = {Biomechanical Phenomena ; Chlamydomonas/*physiology ; Flagella/*physiology ; Hydrodynamics ; Locomotion/*physiology ; Microscopy, Video ; *Models, Biological ; }, abstract = {The unicellular green alga Chlamydomonas swims with two flagella that can synchronize their beat. Synchronized beating is required to swim both fast and straight. A long-standing hypothesis proposes that synchronization of flagella results from hydrodynamic coupling, but the details are not understood. Here, we present realistic hydrodynamic computations and high-speed tracking experiments of swimming cells that show how a perturbation from the synchronized state causes rotational motion of the cell body. This rotation feeds back on the flagellar dynamics via hydrodynamic friction forces and rapidly restores the synchronized state in our theory. We calculate that this "cell-body rocking" provides the dominant contribution to synchronization in swimming cells, whereas direct hydrodynamic interactions between the flagella contribute negligibly. We experimentally confirmed the two-way coupling between flagellar beating and cell-body rocking predicted by our theory.}, }
@article {pmid24125344, year = {2013}, author = {Boi, S and Mazzino, A and Pralits, JO}, title = {Minimal model for zero-inertia instabilities in shear-dominated non-Newtonian flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {3}, pages = {033007}, doi = {10.1103/PhysRevE.88.033007}, pmid = {24125344}, issn = {1550-2376}, abstract = {The emergence of fluid instabilities in the relevant limit of vanishing fluid inertia (i.e., arbitrarily close to zero Reynolds number) has been investigated for the well-known Kolmogorov flow. The finite-time shear-induced order-disorder transition of the non-Newtonian microstructure and the corresponding viscosity change from lower to higher values are the crucial ingredients for the instabilities to emerge. The finite-time low-to-high viscosity change for increasing shear characterizes the rheopectic fluids. The instability does not emerge in shear-thinning or -thickening fluids where viscosity adjustment to local shear occurs instantaneously. The lack of instabilities arbitrarily close to zero Reynolds number is also observed for thixotropic fluids, in spite of the fact that the viscosity adjustment time to shear is finite as in rheopectic fluids. Renormalized perturbative expansions (multiple-scale expansions), energy-based arguments (on the linearized equations of motion), and numerical results (of suitable eigenvalue problems from the linear stability analysis) are the main tools leading to our conclusions. Our findings may have important consequences in all situations where purely hydrodynamic fluid instabilities or mixing are inhibited due to negligible inertia, as in microfluidic applications. To trigger mixing in these situations, suitable (not necessarily viscoelastic) non-Newtonian fluid solutions appear as a valid answer. Our results open interesting questions and challenges in the field of smart (fluid) materials.}, }
@article {pmid24125342, year = {2013}, author = {Chaudhuri, S and Wu, F and Law, CK}, title = {Scaling of turbulent flame speed for expanding flames with Markstein diffusion considerations.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {3}, pages = {033005}, doi = {10.1103/PhysRevE.88.033005}, pmid = {24125342}, issn = {1550-2376}, abstract = {In this paper we clarify the role of Markstein diffusivity, which is the product of the planar laminar flame speed and the Markstein length, on the turbulent flame speed and its scaling, based on experimental measurements on constant-pressure expanding turbulent flames. Turbulent flame propagation data are presented for premixed flames of mixtures of hydrogen, methane, ethylene, n-butane, and dimethyl ether with air, in near-isotropic turbulence in a dual-chamber, fan-stirred vessel. For each individual fuel-air mixture presented in this work and the recently published iso-octane data from Leeds, normalized turbulent flame speed data of individual fuel-air mixtures approximately follow a Re_{T,f}^{0.5} scaling, for which the average radius is the length scale and thermal diffusivity is the transport property of the turbulence Reynolds number. At a given Re_{T,f}^{}, it is experimentally observed that the normalized turbulent flame speed decreases with increasing Markstein number, which could be explained by considering Markstein diffusivity as the leading dissipation mechanism for the large wave number flame surface fluctuations. Consequently, by replacing thermal diffusivity with the Markstein diffusivity in the turbulence Reynolds number definition above, it is found that normalized turbulent flame speeds could be scaled by Re_{T,M}^{0.5} irrespective of the fuel, equivalence ratio, pressure, and turbulence intensity for positive Markstein number flames.}, }
@article {pmid24125340, year = {2013}, author = {Lovecchio, S and Marchioli, C and Soldati, A}, title = {Time persistence of floating-particle clusters in free-surface turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {3}, pages = {033003}, doi = {10.1103/PhysRevE.88.033003}, pmid = {24125340}, issn = {1550-2376}, abstract = {We study the dispersion of light particles floating on a flat shear-free surface of an open channel in which the flow is turbulent. This configuration mimics the motion of buoyant matter (e.g., phytoplankton, pollutants, or nutrients) in water bodies when surface waves and ripples are smooth or absent. We perform direct numerical simulation of turbulence coupled with Lagrangian particle tracking, considering different values of the shear Reynolds number (Re_{τ}=171 and 509) and of the Stokes number (0.06<St<1 in viscous units). Results show that particle buoyancy induces clusters that evolve towards a long-term fractal distribution in a time much longer than the Lagrangian integral fluid time scale, indicating that such clusters overlive the surface turbulent structures which produced them. We quantify cluster dynamics, crucial when modeling dispersion in free-surface flow turbulence, via the time evolution of the cluster correlation dimension.}, }
@article {pmid24110751, year = {2013}, author = {Wu, J and Chui, CK and Binh, PN and Teo, CL}, title = {Real-time rendering of drug injection and interactive simulation of vessel deformation using GPU.}, journal = {Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference}, volume = {2013}, number = {}, pages = {4569-4572}, doi = {10.1109/EMBC.2013.6610564}, pmid = {24110751}, issn = {2694-0604}, mesh = {Algorithms ; Antineoplastic Agents/*administration &amp; dosage ; Blood Vessels/*drug effects ; *Computer Simulation ; Humans ; Imaging, Three-Dimensional/*methods ; Injections ; Liver/*blood supply/pathology ; Models, Anatomic ; Models, Theoretical ; Time Factors ; Tomography, X-Ray Computed ; User-Computer Interface ; }, abstract = {Developing patient specific model for the simulation of chemotherapy drug injection is important in medical application. This paper proposed a two-phase fluidic method to simulate chemotherapy drug injection and an improved lumped element method to simulate deformation of vessel at real-time by using GPU for general computing. Firstly, a three-dimensional (3-D) model of hepatic vessels is reconstructed from clinical CT-images using multi-layer method. A 3-D thinning algorithm based on Valence Driven Spatial Median (VDSM) is applied to generate unit-width skeleton of the vessel tree. The two-phase flow simulation of drug injection is based on Hagen-Poiseuille model by introducing a friction factor using bubbly flow Reynolds number. The improved lumped element method achieves good simulation realism at high computational speed to simulate deformable object. Real-time rendering and interaction of vessel deformation, self collision, and surface tearing has been realized and demonstrated in a virtual experiment.}, }
@article {pmid24103844, year = {2013}, author = {Palagi, S and Jager, EW and Mazzolai, B and Beccai, L}, title = {Propulsion of swimming microrobots inspired by metachronal waves in ciliates: from biology to material specifications.}, journal = {Bioinspiration &amp; biomimetics}, volume = {8}, number = {4}, pages = {046004}, doi = {10.1088/1748-3182/8/4/046004}, pmid = {24103844}, issn = {1748-3190}, mesh = {Biological Clocks/physiology ; Biomimetic Materials/*chemical synthesis ; Biomimetics/*instrumentation/methods ; Cilia/*physiology ; Computer Simulation ; Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Hydrodynamics ; Miniaturization ; Models, Biological ; Paramecium caudatum/chemistry/*physiology ; Robotics/*instrumentation ; *Ships ; Swimming/*physiology ; }, abstract = {The quest for swimming microrobots originates from possible applications in medicine, especially involving navigation in bodily fluids. Swimming microorganisms have become a source of inspiration because their propulsion mechanisms are effective in the low-Reynolds number regime. In this study, we address a propulsion mechanism inspired by metachronal waves, i.e. the spontaneous coordination of cilia leading to the fast swimming of ciliates. We analyse the biological mechanism (referring to its particular embodiment in Paramecium caudatum), and we investigate the contribution of its main features to the swimming performance, through a three-dimensional finite-elements model, in order to develop a simplified, yet effective artificial design. We propose a bioinspired propulsion mechanism for a swimming microrobot based on a continuous cylindrical electroactive surface exhibiting perpendicular wave deformations travelling longitudinally along its main axis. The simplified propulsion mechanism is conceived specifically for microrobots that embed a micro-actuation system capable of executing the bioinspired propulsion (self-propelled microrobots). Among the available electroactive polymers, we select polypyrrole as the possible actuation material and we assess it for this particular embodiment. The results are used to appoint target performance specifications for the development of improved or new electroactive materials to attain metachronal-waves-like propulsion.}, }
@article {pmid24089969, year = {2013}, author = {Narayanan, S and Gunaratne, GH and Hussain, F}, title = {A dynamical systems approach to the control of chaotic dynamics in a spatiotemporal jet flow.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {23}, number = {3}, pages = {033133}, doi = {10.1063/1.4820819}, pmid = {24089969}, issn = {1089-7682}, abstract = {We present a strategy for control of chaos in open flows and provide its experimental validation in the near field of a transitional jet flow system. The low-dimensional chaotic dynamics studied here results from vortex ring formation and their pairings over a spatially extended region of the flow that was excited by low level periodic forcing of the primary instability. The control method utilizes unstable periodic orbits (UPO) embedded within the chaotic attractor. Since hydrodynamic instabilities in the open flow system are convective, both monitoring and control can be implemented at a few locations, resulting in a simple and effective control algorithm. Experiments were performed in an incompressible, initially laminar, 4 cm diameter circular air jet, at a Reynolds number of 23,000, housed in a low-noise, large anechoic chamber. Distinct trajectory bundles surrounding the dominant UPOs were found from experimentally derived, time-delayed embedding of the chaotic attractor. Velocity traces from a pair of probes placed at the jet flow exit and farther downstream were used to empirically model the UPOs and compute control perturbations to be applied at the jet nozzle lip. Open loop control was used to sustain several nearly periodic states.}, }
@article {pmid24089943, year = {2013}, author = {Miranda, RA and Rempel, EL and Chian, AC and Seehafer, N and Toledo, BA and Muñoz, PR}, title = {Lagrangian coherent structures at the onset of hyperchaos in the two-dimensional Navier-Stokes equations.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {23}, number = {3}, pages = {033107}, doi = {10.1063/1.4811297}, pmid = {24089943}, issn = {1089-7682}, abstract = {We study a transition to hyperchaos in the two-dimensional incompressible Navier-Stokes equations with periodic boundary conditions and an external forcing term. Bifurcation diagrams are constructed by varying the Reynolds number, and a transition to hyperchaos (HC) is identified. Before the onset of HC, there is coexistence of two chaotic attractors and a hyperchaotic saddle. After the transition to HC, the two chaotic attractors merge with the hyperchaotic saddle, generating random switching between chaos and hyperchaos, which is responsible for intermittent bursts in the time series of energy and enstrophy. The chaotic mixing properties of the flow are characterized by detecting Lagrangian coherent structures. After the transition to HC, the flow displays complex Lagrangian patterns and an increase in the level of Lagrangian chaoticity during the bursty periods that can be predicted statistically by the hyperchaotic saddle prior to HC transition.}, }
@article {pmid24089734, year = {2013}, author = {Ando, T and Chow, E and Skolnick, J}, title = {Dynamic simulation of concentrated macromolecular solutions with screened long-range hydrodynamic interactions: algorithm and limitations.}, journal = {The Journal of chemical physics}, volume = {139}, number = {12}, pages = {121922}, pmid = {24089734}, issn = {1089-7690}, support = {R01 GM037408/GM/NIGMS NIH HHS/United States ; GM-37408/GM/NIGMS NIH HHS/United States ; }, mesh = {*Algorithms ; *Hydrodynamics ; Macromolecular Substances/*chemistry ; *Molecular Dynamics Simulation ; Solutions ; }, abstract = {Hydrodynamic interactions exert a critical effect on the dynamics of macromolecules. As the concentration of macromolecules increases, by analogy to the behavior of semidilute polymer solutions or the flow in porous media, one might expect hydrodynamic screening to occur. Hydrodynamic screening would have implications both for the understanding of macromolecular dynamics as well as practical implications for the simulation of concentrated macromolecular solutions, e.g., in cells. Stokesian dynamics (SD) is one of the most accurate methods for simulating the motions of N particles suspended in a viscous fluid at low Reynolds number, in that it considers both far-field and near-field hydrodynamic interactions. This algorithm traditionally involves an O(N(3)) operation to compute Brownian forces at each time step, although asymptotically faster but more complex SD methods are now available. Motivated by the idea of hydrodynamic screening, the far-field part of the hydrodynamic matrix in SD may be approximated by a diagonal matrix, which is equivalent to assuming that long range hydrodynamic interactions are completely screened. This approximation allows sparse matrix methods to be used, which can reduce the apparent computational scaling to O(N). Previously there were several simulation studies using this approximation for monodisperse suspensions. Here, we employ newly designed preconditioned iterative methods for both the computation of Brownian forces and the solution of linear systems, and consider the validity of this approximation in polydisperse suspensions. We evaluate the accuracy of the diagonal approximation method using an intracellular-like suspension. The diffusivities of particles obtained with this approximation are close to those with the original method. However, this approximation underestimates intermolecular correlated motions, which is a trade-off between accuracy and computing efficiency. The new method makes it possible to perform large-scale and long-time simulation with an approximate accounting of hydrodynamic interactions.}, }
@article {pmid24089470, year = {2013}, author = {Anton, H and Harlepp, S and Ramspacher, C and Wu, D and Monduc, F and Bhat, S and Liebling, M and Paoletti, C and Charvin, G and Freund, JB and Vermot, J}, title = {Pulse propagation by a capacitive mechanism drives embryonic blood flow.}, journal = {Development (Cambridge, England)}, volume = {140}, number = {21}, pages = {4426-4434}, doi = {10.1242/dev.096768}, pmid = {24089470}, issn = {1477-9129}, mesh = {Animals ; Arteries/*embryology ; Biomechanical Phenomena ; Blood Viscosity ; Embryo, Nonmammalian/*physiology ; Hemodynamics/*physiology ; Microscopy, Confocal ; *Models, Biological ; Optical Tweezers ; Pulsatile Flow/*physiology ; Video Recording ; Zebrafish/*embryology ; }, abstract = {Pulsatile flow is a universal feature of the blood circulatory system in vertebrates and can lead to diseases when abnormal. In the embryo, blood flow forces stimulate vessel remodeling and stem cell proliferation. At these early stages, when vessels lack muscle cells, the heart is valveless and the Reynolds number (Re) is low, few details are available regarding the mechanisms controlling pulses propagation in the developing vascular network. Making use of the recent advances in optical-tweezing flow probing approaches, fast imaging and elastic-network viscous flow modeling, we investigated the blood-flow mechanics in the zebrafish main artery and show how it modifies the heart pumping input to the network. The movement of blood cells in the embryonic artery suggests that elasticity of the network is an essential factor mediating the flow. Based on these observations, we propose a model for embryonic blood flow where arteries act like a capacitor in a way that reduces heart effort. These results demonstrate that biomechanics is key in controlling early flow propagation and argue that intravascular elasticity has a role in determining embryonic vascular function.}, }
@article {pmid24086276, year = {2013}, author = {Noreen, S and Ahmad, B and Hayat, T}, title = {Mixed convection flow of nanofluid in presence of an inclined magnetic field.}, journal = {PloS one}, volume = {8}, number = {9}, pages = {e73248}, pmid = {24086276}, issn = {1932-6203}, mesh = {*Magnetics ; Models, Theoretical ; Temperature ; }, abstract = {This research is concerned with the mixed convection peristaltic flow of nanofluid in an inclined asymmetric channel. The fluid is conducting in the presence of inclined magnetic field. The governing equations are modelled. Mathematical formulation is completed through long wavelength and low Reynolds number approach. Numerical solution to the nonlinear analysis is made by shooting technique. Attention is mainly focused to the effects of Brownian motion and thermophoretic diffusion of nanoparticle. Results for velocity, temperature, concentration, pumping and trapping are obtained and analyzed in detail.}, }
@article {pmid24078795, year = {2013}, author = {Salman, SD and Kadhum, AA and Takriff, MS and Mohamad, AB}, title = {Numerical investigation of heat transfer and friction factor characteristics in a circular tube fitted with V-cut twisted tape inserts.}, journal = {TheScientificWorldJournal}, volume = {2013}, number = {}, pages = {492762}, doi = {10.1155/2013/492762}, pmid = {24078795}, issn = {1537-744X}, mesh = {Friction ; *Hot Temperature ; *Models, Theoretical ; *Thermodynamics ; }, abstract = {Numerical investigation of the heat transfer and friction factor characteristics of a circular fitted with V-cut twisted tape (VCT) insert with twist ratio (y = 2.93) and different cut depths (w = 0.5, 1, and 1.5 cm) were studied for laminar flow using CFD package (FLUENT-6.3.26). The data obtained from plain tube were verified with the literature correlation to ensure the validation of simulation results. Classical twisted tape (CTT) with different twist ratios (y = 2.93, 3.91, 4.89) were also studied for comparison. The results show that the enhancement of heat transfer rate induced by the classical and V-cut twisted tape inserts increases with the Reynolds number and decreases with twist ratio. The results also revealed that the V-cut twisted tape with twist ratio y = 2.93 and cut depth w = 0.5 cm offered higher heat transfer rate with significant increases in friction factor than other tapes. In addition the results of V-cut twist tape compared with experimental and simulated data of right-left helical tape inserts (RLT), it is found that the V-cut twist tape offered better thermal contact between the surface and the fluid which ultimately leads to a high heat transfer coefficient. Consequently, 107% of maximum heat transfer was obtained by using this configuration.}, }
@article {pmid24036239, year = {2014}, author = {Radwan, A and Wagner, M and Amidon, GL and Langguth, P}, title = {Bio-predictive tablet disintegration: effect of water diffusivity, fluid flow, food composition and test conditions.}, journal = {European journal of pharmaceutical sciences : official journal of the European Federation for Pharmaceutical Sciences}, volume = {57}, number = {}, pages = {273-279}, doi = {10.1016/j.ejps.2013.08.038}, pmid = {24036239}, issn = {1879-0720}, mesh = {Benzilates/*chemistry ; Biopharmaceutics/methods ; Chemistry, Pharmaceutical ; Diffusion ; *Food-Drug Interactions ; Gastric Juice/chemistry ; *Gastrointestinal Motility ; Gastrointestinal Tract/*physiology ; Humans ; Hydrodynamics ; Kinetics ; Models, Chemical ; Nortropanes/*chemistry ; Osmolar Concentration ; *Postprandial Period ; Solubility ; Tablets, Enteric-Coated ; Technology, Pharmaceutical/methods ; Viscosity ; Water/*chemistry ; }, abstract = {Food intake may delay tablet disintegration. Current in vitro methods have little predictive potential to account for such effects. The effect of a variety of factors on the disintegration of immediate release tablets in the gastrointestinal tract has been identified. They include viscosity of the media, precipitation of food constituents on the surface of the tablet and reduction of water diffusivity in the media as well as changes in the hydrodynamics in the surrounding media of the solid dosage form. In order to improve the predictability of food affecting the disintegration of a dosage form, tablet disintegration in various types of a liquefied meal has been studied under static vs. dynamic (agitative) conditions. Viscosity, water diffusivity, osmolality and Reynolds numbers for the different media were characterized. A quantitative model is introduced which predicts the influence of the Reynolds number in the tablet disintegration apparatus on the disintegration time. Viscosity, water diffusivity and media flow velocity are shown to be important factors affecting dosage form disintegration. The results suggest the necessity of considering these parameters when designing a predictive model for simulating the in vivo conditions. Based on these experiments and knowledge on in vivo hydrodynamics in the GI tract, it is concluded that the disintegration tester under current pharmacopoeial conditions is operated in an unphysiological mode and no bioprediction may be derived. Recommendations regarding alternative mode of operation are made.}, }
@article {pmid24032937, year = {2013}, author = {Prakash, J and Lavrenteva, OM and Nir, A}, title = {Interaction of bubbles in an inviscid and low-viscosity shear flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {2}, pages = {023021}, doi = {10.1103/PhysRevE.88.023021}, pmid = {24032937}, issn = {1550-2376}, abstract = {The pressure loads on two identical spherical bubbles impulsively introduced in an inviscid simple shear flow are calculated. The interaction force due to these pressure loads is employed to model the dynamics of air bubbles injected to a low-viscosity fluid sheared in a Couette device at the first shear flow instability where the bubbles are trapped inside the stable Taylor vortex. It was shown that the interaction between the bubbles in the primary shear flow drives them away from each other. The performed simulations revealed that in an inviscid flow the separation distances between equal size bubbles undergo complex periodic motion. The presence of low-viscosity results in a qualitative change of the interaction pattern: The bubbles either eventually assume an ordered string with equal separation distances between all neighbors or some of them collide. The first regime is qualitatively similar to the behavior of bubbles at low Reynolds number [Prakash et al., Phys. Rev. E 87, 043002 (2013)]. Furthermore, if the Reynolds number exceeds some critical value the temporal behavior of the separations becomes nonmonotonic and exhibits over- and undershooting of the equilibrium separations. The latter effects were observed in the experiments, but are not predicted by the low Reynolds number model of the process [Prakash et al., Phys. Rev. E 87, 043002 (2013)].}, }
@article {pmid24032926, year = {2013}, author = {Jiang, R and Lin, J and Chen, Z}, title = {Vibrations of cylindrical objects obstructing a Poiseuille-type flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {2}, pages = {023009}, doi = {10.1103/PhysRevE.88.023009}, pmid = {24032926}, issn = {1550-2376}, abstract = {Using the lattice Boltzmann equation, we numerically studied the dynamics of a physical model system, the Poiseuille flow-induced vibrations (PFIV). At a moderate Reynolds number, for flows past a cylinder that is free to move in the cross-flow direction while being fixed in the streamwise direction, between two parallel walls, a variety of distinct vibration regimes involving symmetrical periodic vibration, deflective quasiperiodic vibration, and deflective periodic vibration with corresponding wake states were observed. The data analysis shows that the distribution of the lift coefficient depending on the blockage ratio plays an important role in such a system. A further study of the case of two side-by-side identical cylinders demonstrates the existence of two distinct cooperative vibrations of the cylinders, e.g., in-phase-synchronized vibration (IPSV) and anti-phase-synchronized vibration (APSV). The result reveals that there is a critical blockage ratio, beyond which a phase transition between IPSV and APSV occurs. For the phenomena observed here, PFIV can be considered a new type of vortex-induced vibration, and such a system is expected to find applications in fluid mixing.}, }
@article {pmid24032925, year = {2013}, author = {Taghiloo, M and Miri, M}, title = {Three-sphere magnetic swimmer in a shear flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {2}, pages = {023008}, doi = {10.1103/PhysRevE.88.023008}, pmid = {24032925}, issn = {1550-2376}, abstract = {We consider a low-Reynolds-number swimmer made from three spheres linked by two slender arms, and explore its motion in a shear flow. This rodlike three-sphere swimmer finally follows the direction dictated by the shear flow. To overcome this shortcoming, we propose a model in which the two outer spheres have permanent magnetic moments along the arms. This magnetic swimmer can be navigated to a desired direction by applying an external static and uniform magnetic field.}, }
@article {pmid24032922, year = {2013}, author = {López Carranza, SN and Jenny, M and Nouar, C}, title = {Instability of streaks in pipe flow of shear-thinning fluids.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {2}, pages = {023005}, doi = {10.1103/PhysRevE.88.023005}, pmid = {24032922}, issn = {1550-2376}, abstract = {This study is motivated by recent experimental results dealing with the transition to turbulence in a pipe flow of shear-thinning fluids, where a streaky flow with an azimuthal wave number n=1 is observed in the transitional regime. Here, a linear stability analysis of pipe flow of shear-thinning fluids modulated azimuthally by finite amplitude streaks is performed. The shear-thinning behavior of the fluid is described by the Carreau model. The streaky base flows considered are obtained from two-dimensional direct numerical simulation using finite amplitude longitudinal rolls as the initial condition and by extracting the velocity field at time t(max), where the amplitude of the streaks reaches its maximum, denoted by A(max). It is found that the amplitude A(max) increases with increasing Reynolds number as well as with increasing amplitude E(0) of the initial longitudinal rolls. For sufficiently large streaks amplitude, streamwise velocity profiles develop inflection points, leading to instabilities. Depending on the threshold amplitude A(c), two different modes may trigger the instability of the streaks. If A(c) exceeds approximately 41.5% of the centerline velocity, the instability mode is located near the axis of the pipe, i.e., it is a "center mode." For weaker amplitude A(c), the instability mode is located near the pipe wall, in the region of highest wall normal shear, i.e., it is a "wall mode." The threshold amplitude A(c) decreases with increasing shear-thinning effects. The energy equation analysis indicates that (i) wall modes are driven mainly by the work of the Reynolds stress against the wall normal shear and (ii) for center modes, the contribution of the normal wall shear remains dominant; however, it is noted that the contribution of the Reynolds stress against the azimuthal shear increases with increasing shear-thinning effects.}, }
@article {pmid24032837, year = {2013}, author = {Kaiser, A and Popowa, K and Wensink, HH and Löwen, H}, title = {Capturing self-propelled particles in a moving microwedge.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {2}, pages = {022311}, doi = {10.1103/PhysRevE.88.022311}, pmid = {24032837}, issn = {1550-2376}, abstract = {Catching fish with a fishing net is typically done either by dragging a fishing net through quiescent water or by placing a stationary basket trap into a stream. We transfer these general concepts to micron-sized self-motile particles moving in a solvent at low Reynolds number and study their collective trapping behavior by means of computer simulations of a two-dimensional system of self-propelled rods. A chevron-shaped obstacle is dragged through the active suspension with a constant speed v and acts as a trapping "net." Three trapping states can be identified corresponding to no trapping, partial trapping, and complete trapping and their relative stability is studied as a function of the apex angle of the wedge, the swimmer density, and the drag speed v. When the net is dragged along the inner wedge, complete trapping is facilitated and a partially trapped state changes into a complete trapping state if the drag speed exceeds a certain value. Reversing the drag direction leads to a reentrant transition from no trapping to complete trapping and then back to no trapping upon increasing the drag speed along the outer wedge contour. The transition to complete trapping is marked by a templated self-assembly of rods forming polar smectic structures anchored onto the inner contour of the wedge. Our predictions can be verified in experiments of artificial or microbial swimmers confined in microfluidic trapping devices.}, }
@article {pmid24006976, year = {2013}, author = {Zhao, T and Wang, X and Jiang, L and Larson, RG}, title = {Assessment of mesoscopic particle-based methods in microfluidic geometries.}, journal = {The Journal of chemical physics}, volume = {139}, number = {8}, pages = {084109}, doi = {10.1063/1.4819124}, pmid = {24006976}, issn = {1089-7690}, abstract = {We assess the accuracy and efficiency of two particle-based mesoscopic simulation methods, namely, Dissipative Particle Dynamics (DPD) and Stochastic Rotation Dynamics (SRD) for predicting a complex flow in a microfluidic geometry. Since both DPD and SRD use soft or weakly interacting particles to carry momentum, both methods contain unavoidable inertial effects and unphysically high fluid compressibility. To assess these effects, we compare the predictions of DPD and SRD for both an exact Stokes-flow solution and nearly exact solutions at finite Reynolds numbers from the finite element method for flow in a straight channel with periodic slip boundary conditions. This flow represents a periodic electro-osmotic flow, which is a complex flow with an analytical solution for zero Reynolds number. We find that SRD is roughly ten-fold faster than DPD in predicting the flow field, with better accuracy at low Reynolds numbers. However, SRD has more severe problems with compressibility effects than does DPD, which limits the Reynolds numbers attainable in SRD to around 25-50, while DPD can achieve Re higher than this before compressibility effects become too large. However, since the SRD method runs much faster than DPD does, we can afford to enlarge the number of grid cells in SRD to reduce the fluid compressibility at high Reynolds number. Our simulations provide a method to estimate the range of conditions for which SRD or DPD is preferable for mesoscopic simulations.}, }
@article {pmid23981650, year = {2013}, author = {Liu, W and Xiao, Q and Cheng, F}, title = {A bio-inspired study on tidal energy extraction with flexible flapping wings.}, journal = {Bioinspiration &amp; biomimetics}, volume = {8}, number = {3}, pages = {036011}, doi = {10.1088/1748-3182/8/3/036011}, pmid = {23981650}, issn = {1748-3190}, mesh = {Animals ; Biomimetics/*instrumentation ; Birds/*physiology ; Computer Simulation ; Computer-Aided Design ; Elastic Modulus ; *Electric Power Supplies ; Energy Transfer/*physiology ; Equipment Design ; Equipment Failure Analysis ; Flight, Animal/*physiology ; Models, Biological ; Rheology/instrumentation ; *Tidal Waves ; Wings, Animal/*physiology ; }, abstract = {Previous research on the flexible structure of flapping wings has shown an improved propulsion performance in comparison to rigid wings. However, not much is known about this function in terms of power efficiency modification for flapping wing energy devices. In order to study the role of the flexible wing deformation in the hydrodynamics of flapping wing energy devices, we computationally model the two-dimensional flexible single and twin flapping wings in operation under the energy extraction conditions with a large Reynolds number of 106. The flexible motion for the present study is predetermined based on a priori structural result which is different from a passive flexibility solution. Four different models are investigated with additional potential local distortions near the leading and trailing edges. Our simulation results show that the flexible structure of a wing is beneficial to enhance power efficiency by increasing the peaks of lift force over a flapping cycle, and tuning the phase shift between force and velocity to a favourable trend. Moreover, the impact of wing flexibility on efficiency is more profound at a low nominal effective angle of attack (AoA). At a typical flapping frequency f * = 0.15 and nominal effective AoA of 10°, a flexible integrated wing generates 7.68% higher efficiency than a rigid wing. An even higher increase, around six times that of a rigid wing, is achievable if the nominal effective AoA is reduced to zero degrees at feathering condition. This is very attractive for a semi-actuated flapping energy system, where energy input is needed to activate the pitching motion. The results from our dual-wing study found that a parallel twin-wing device can produce more power compared to a single wing due to the strong flow interaction between the two wings.}, }
@article {pmid23975383, year = {2014}, author = {Walker, AM and Johnston, CR and Rival, DE}, title = {On the characterization of a non-Newtonian blood analog and its response to pulsatile flow downstream of a simplified stenosis.}, journal = {Annals of biomedical engineering}, volume = {42}, number = {1}, pages = {97-109}, doi = {10.1007/s10439-013-0893-4}, pmid = {23975383}, issn = {1573-9686}, mesh = {Animals ; Blood Substitutes/*chemistry ; Constriction, Pathologic/physiopathology ; Humans ; *Models, Cardiovascular ; Polysaccharides, Bacterial/*chemistry ; *Pulsatile Flow ; Swine ; }, abstract = {Particle image velocimetry (PIV) was used to investigate the influence of a non-Newtonian blood analog of aqueous xanthan gum on flow separation in laminar and transitional environments and in both steady and pulsatile flow. Initial steady pressure drop measurements in laminar and transitional flow for a Newtonian analog showed an extension of laminar behavior to Reynolds number (Re) ~ 2900 for the non-Newtonian case. On a macroscale level, this showed good agreement with porcine blood. Subsequently, PIV was used to measure flow patterns and turbulent statistics downstream of an axisymmetric stenosis in the aqueous xanthan gum solution and for a Newtonian analog at Re ~ 520 and Re ~ 1250. The recirculation length for the non-Newtonian case was reduced at Re ~ 520 resultant from increased viscosity at low shear strain rates. At Re ~ 1250, peak turbulent intensities and turbulent shear stresses were dampened by the non-Newtonian fluid in close proximity to the blockage outlet. Although the non-Newtonian case's recirculation length was increased at peak pulsatile flow, turbulent shear stress was found to be elevated for the Newtonian case downstream from the blockage, suggesting shear layer fragmentation and radial transport. Our findings conclude that the xanthan gum elastic polymer prolongs flow stabilization, which in turn emphasizes the importance of non-Newtonian blood characteristics on the resulting flow patterns in such cardiovascular environments.}, }
@article {pmid23971551, year = {2013}, author = {Kirillov, ON and Stefani, F}, title = {Extending the range of the inductionless magnetorotational instability.}, journal = {Physical review letters}, volume = {111}, number = {6}, pages = {061103}, doi = {10.1103/PhysRevLett.111.061103}, pmid = {23971551}, issn = {1079-7114}, abstract = {The magnetorotational instability (MRI) can destabilize hydrodynamically stable rotational flows, thereby allowing angular momentum transport in accretion disks. A notorious problem for the MRI is its questionable applicability in regions with low magnetic Reynolds number. Using the WKB method, we extend the range of applicability of the MRI by showing that the inductionless versions of the MRI, such as the helical MRI and the azimuthal MRI, can easily destabilize Keplerian profiles ∝r(-3/2) if the radial profile of the azimuthal magnetic field is only slightly modified from the current-free profile ∝r(-1). This way we further show how the formerly known lower Liu limit of the critical Rossby number Ro≈-0.828 connects naturally with the upper Liu limit Ro≈+4.828.}, }
@article {pmid23970568, year = {2013}, author = {Abadeh, A and Lew, RR}, title = {Mass flow and velocity profiles in Neurospora hyphae: partial plug flow dominates intra-hyphal transport.}, journal = {Microbiology (Reading, England)}, volume = {159}, number = {Pt 11}, pages = {2386-2394}, doi = {10.1099/mic.0.071191-0}, pmid = {23970568}, issn = {1465-2080}, mesh = {*Biological Transport ; Genes, Reporter ; Green Fluorescent Proteins/analysis/genetics ; Hyphae/metabolism/*physiology ; Microscopy, Fluorescence ; Neurospora crassa/metabolism/*physiology ; Organelles/metabolism/*physiology ; Osmotic Pressure ; Staining and Labeling/methods ; }, abstract = {Movement of nuclei, mitochondria and vacuoles through hyphal trunks of Neurospora crassa were vector-mapped using fluorescent markers and green fluorescent protein tags. The vectorial movements of all three were strongly correlated, indicating the central role of mass (bulk) flow in cytoplasm movements in N. crassa. Profiles of velocity versus distance from the hyphal wall did not match the parabolic shape predicted by the ideal Hagen-Poiseuille model of flow at low Reynolds number. Instead, the profiles were flat, consistent with a model of partial plug flow due to the high concentration of organelles in the flowing cytosol. The intra-hyphal pressure gradients were manipulated by localized external osmotic treatments to demonstrate the dependence of velocity (and direction) on pressure gradients within the hyphae. The data support the concept that mass transport, driven by pressure gradients, dominates intra-hyphal transport. The transport occurs by partial plug flow due to the organelles in the cytosol.}, }
@article {pmid23949178, year = {2013}, author = {Javadzadegan, A and Shimizu, Y and Behnia, M and Ohta, M}, title = {Correlation between Reynolds number and eccentricity effect in stenosed artery models.}, journal = {Technology and health care : official journal of the European Society for Engineering and Medicine}, volume = {21}, number = {4}, pages = {357-367}, doi = {10.3233/THC-130736}, pmid = {23949178}, issn = {1878-7401}, mesh = {Blood Flow Velocity/physiology ; Coronary Stenosis/*physiopathology ; Hemorheology/physiology ; Humans ; *Models, Cardiovascular ; Rheology/instrumentation/methods ; }, abstract = {BACKGROUND: Flow recirculation and shear strain are physiological processes within coronary arteries which are associated with pathogenic biological pathways. Distinct Quite apart from coronary stenosis severity, lesion eccentricity can cause flow recirculation and affect shear strain levels within human coronary arteries.<br><br>OBJECTIVE: The aim of this study is to analyse the effect of lesion eccentricity on the transient flow behaviour in a model of a coronary artery and also to investigate the correlation between Reynolds number (Re) and the eccentricity effect on flow behaviour.<br><br>METHODS: A transient particle image velocimetry (PIV) experiment was implemented in two silicone based models with 70% diameter stenosis, one with eccentric stenosis and one with concentric stenosis.<br><br>RESULTS: At different times throughout the flow cycle, the eccentric model was always associated with a greater recirculation zone length, maximum shear strain rate and maximum axial velocity; however, the highest and lowest impacts of eccentricity were on the recirculation zone length and maximum shear strain rate, respectively. Analysis of the results revealed a negative correlation between the Reynolds number (Re) and the eccentricity effect on maximum axial velocity, maximum shear strain rate and recirculation zone length.<br><br>CONCLUSIONS: As Re number increases the eccentricity effect on the flow behavior becomes negligible.}, }
@article {pmid23944553, year = {2013}, author = {Horne, E and Mininni, PD}, title = {Sign cancellation and scaling in the vertical component of velocity and vorticity in rotating turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {1}, pages = {013011}, doi = {10.1103/PhysRevE.88.013011}, pmid = {23944553}, issn = {1550-2376}, abstract = {We study sign changes and scaling laws in the Cartesian components of the velocity and vorticity of rotating turbulence, in the helicity, and in the components of vertically averaged fields. Data for the analysis are provided by high-resolution direct numerical simulations of rotating turbulence with different forcing functions, with up to 1536(3) grid points, with Reynolds numbers between ≈1100 and ≈5100, and with moderate Rossby numbers between ≈0.06 and ≈8. When rotation is negligible, all Cartesian components of the velocity show similar scaling, in agreement with the expected isotropy of the flow. However, in the presence of rotation, only the vertical components of the fields show clear scaling laws, with evidence of possible sign singularity in the limit of an infinite Reynolds number. Horizontal components of the velocity are smooth and do not display rapid fluctuations for arbitrarily small scales. The vertical velocity and vorticity, as well as the vertically averaged vertical velocity and vorticity, show the same scaling within error bars, in agreement with theories that predict that these quantities have the same dynamical equation for very strong rotation.}, }
@article {pmid23944548, year = {2013}, author = {Marques, F and Mellibovsky, F and Meseguer, A}, title = {Fold-pitchfork bifurcation for maps with Z(2) symmetry in pipe flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {1}, pages = {013006}, doi = {10.1103/PhysRevE.88.013006}, pmid = {23944548}, issn = {1550-2376}, abstract = {This study aims to provide a better understanding of recently identified transition scenarios exhibited by traveling wave solutions in pipe flow. This particular family of solutions are invariant under certain reflectional symmetry transformations and they emerge from saddle-node bifurcations within a two-dimensional parameter space characterized by the length of the pipe and the Reynolds number. The present work precisely provides a detailed analysis of a codimension-two saddle-node bifurcation arising in discrete dynamical systems (maps) with Z(2) symmetry. Normal form standard techniques are applied in order to obtain the reduced map up to cubic order. All possible bifurcation scenarios exhibited by this normal form are analyzed in detail. Finally, a qualitative comparison of these scenarios with the ones observed in the aforementioned hydrodynamic problem is provided.}, }
@article {pmid23944544, year = {2013}, author = {Miralles, S and Bonnefoy, N and Bourgoin, M and Odier, P and Pinton, JF and Plihon, N and Verhille, G and Boisson, J and Daviaud, F and Dubrulle, B}, title = {Dynamo threshold detection in the von Kármán sodium experiment.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {88}, number = {1}, pages = {013002}, doi = {10.1103/PhysRevE.88.013002}, pmid = {23944544}, issn = {1550-2376}, abstract = {Predicting dynamo self-generation in liquid metal experiments has been an ongoing question for many years. In contrast to simple dynamical systems for which reliable techniques have been developed, the ability to predict the dynamo capacity of a flow and the estimate of the corresponding critical value of the magnetic Reynolds number (the control parameter of the instability) has been elusive, partly due to the high level of turbulent fluctuations of flows in such experiments (with kinetic Reynolds numbers in excess of 10(6)). We address these issues here, using the von Kármán sodium experiment and studying its response to an externally applied magnetic field. We first show that a dynamo threshold can be estimated from analysis related to critical slowing down and susceptibility divergence, in configurations for which dynamo action is indeed observed. These approaches are then applied to flow configurations that have failed to self-generate magnetic fields within operational limits, and we quantify the dynamo capacity of these configurations.}, }
@article {pmid23933985, year = {2013}, author = {Saha, S and Salin, D and Talon, L}, title = {Low Reynolds number suspension gravity currents.}, journal = {The European physical journal. E, Soft matter}, volume = {36}, number = {8}, pages = {85}, pmid = {23933985}, issn = {1292-895X}, mesh = {Extracellular Fluid/*chemistry ; *Gravitation ; *Hydrodynamics ; *Models, Chemical ; *Rheology ; Surface Properties ; Viscosity ; }, abstract = {The extension of a gravity current in a lock-exchange problem, proceeds as square root of time in the viscous-buoyancy phase, where there is a balance between gravitational and viscous forces. In the presence of particles however, this scenario is drastically altered, because sedimentation reduces the motive gravitational force and introduces a finite distance and time at which the gravity current halts. We investigate the spreading of low Reynolds number suspension gravity currents using a novel approach based on the Lattice-Boltzmann (LB) method. The suspension is modeled as a continuous medium with a concentration-dependent viscosity. The settling of particles is simulated using a drift flux function approach that enables us to capture sudden discontinuities in particle concentration that travel as kinematic shock waves. Thereafter a numerical investigation of lock-exchange flows between pure fluids of unequal viscosity, reveals the existence of wall layers which reduce the spreading rate substantially compared to the lubrication theory prediction. In suspension gravity currents, we observe that the settling of particles leads to the formation of two additional fronts: a horizontal front near the top that descends vertically and a sediment layer at the bottom which aggrandises due to deposition of particles. Three phases are identified in the spreading process: the final corresponding to the mutual approach of the two horizontal fronts while the laterally advancing front halts indicating that the suspension current stops even before all the particles have settled. The first two regimes represent a constant and a decreasing spreading rate respectively. Finally we conduct experiments to substantiate the conclusions of our numerical and theoretical investigation.}, }
@article {pmid23931372, year = {2013}, author = {de Silva, CM and Philip, J and Chauhan, K and Meneveau, C and Marusic, I}, title = {Multiscale geometry and scaling of the turbulent-nonturbulent interface in high Reynolds number boundary layers.}, journal = {Physical review letters}, volume = {111}, number = {4}, pages = {044501}, doi = {10.1103/PhysRevLett.111.044501}, pmid = {23931372}, issn = {1079-7114}, abstract = {The scaling and surface area properties of the wrinkled surface separating turbulent from nonturbulent regions in open shear flows are important to our understanding of entrainment mechanisms at the boundaries of turbulent flows. Particle image velocimetry data from high Reynolds number turbulent boundary layers covering three decades in scale are used to resolve the turbulent-nonturbulent interface experimentally and, for the first time, determine unambiguously whether such surfaces exhibit fractal scaling. Box counting of the interface intersection with the measurement plane exhibits power-law scaling, with an exponent between -1.3 and -1.4. A complementary analysis based on spatial filtering of the velocity fields also shows power-law behavior of the coarse-grained interface length as a function of filter width, with an exponent between -0.3 and -0.4. These results establish that the interface is fractal-like with a multiscale geometry and fractal dimension of Df≈2.3-2.4.}, }
@article {pmid23930807, year = {2013}, author = {Basiri Parsa, A and Rashidi, MM and Anwar Bég, O and Sadri, SM}, title = {Semi-computational simulation of magneto-hemodynamic flow in a semi-porous channel using optimal homotopy and differential transform methods.}, journal = {Computers in biology and medicine}, volume = {43}, number = {9}, pages = {1142-1153}, doi = {10.1016/j.compbiomed.2013.05.019}, pmid = {23930807}, issn = {1879-0534}, mesh = {Blood Flow Velocity ; *Blood Viscosity ; *Computer Simulation ; Humans ; *Magnetic Fields ; *Models, Cardiovascular ; Porosity ; }, abstract = {In this paper, the semi-numerical techniques known as the optimal homotopy analysis method (HAM) and Differential Transform Method (DTM) are applied to study the magneto-hemodynamic laminar viscous flow of a conducting physiological fluid in a semi-porous channel under a transverse magnetic field. The two-dimensional momentum conservation partial differential equations are reduced to ordinary form incorporating Lorentizian magnetohydrodynamic body force terms. These ordinary differential equations are solved by the homotopy analysis method, the differential transform method and also a numerical method (fourth-order Runge-Kutta quadrature with a shooting method), under physically realistic boundary conditions. The homotopy analysis method contains the auxiliary parameter ℏ, which provides us with a simple way to adjust and control the convergence region of solution series. The differential transform method (DTM) does not require an auxiliary parameter and is employed to compute an approximation to the solution of the system of nonlinear differential equations governing the problem. The influence of Hartmann number (Ha) and transpiration Reynolds number (mass transfer parameter, Re) on the velocity profiles in the channel are studied in detail. Interesting fluid dynamic characteristics are revealed and addressed. The HAM and DTM solutions are shown to both correlate well with numerical quadrature solutions, testifying to the accuracy of both HAM and DTM in nonlinear magneto-hemodynamics problems. Both these semi-numerical techniques hold excellent potential in modeling nonlinear viscous flows in biological systems.}, }
@article {pmid23930806, year = {2013}, author = {Ghodsi, SR and Esfahanian, V and Shamsodini, R and Ghodsi, SM and Ahmadi, G}, title = {Blood flow vectoring control in aortic arch using full and partial clamps.}, journal = {Computers in biology and medicine}, volume = {43}, number = {9}, pages = {1134-1141}, doi = {10.1016/j.compbiomed.2013.05.016}, pmid = {23930806}, issn = {1879-0534}, mesh = {Aorta, Thoracic/pathology/*physiopathology ; Aortic Aneurysm/pathology/*physiopathology ; Blood Flow Velocity ; Humans ; *Models, Cardiovascular ; *Stress, Physiological ; }, abstract = {BACKGROUND: Early diagnosis and treatment of aneurysm plays an important role in reducing the mortality risk of rupture. The aneurysm is a complex phenomenon and caused by different reasons, such as arteriosclerosis and heredity. In addition, pressure and Wall Shear Stress are two known factors influencing the establishment of an aneurysm. The aim of this study is to investigate the effect of using a full or partial clamp to control the blood flow streamlines and hence the location of stress concentration in a clean configuration of aorta. The main question is how to control the stresses distribution in order to reduce the possibility of aneurysm growth with less negative effects on the other sides.<br><br>METHODS AND RESULTS: A simple form of aortic arch with three branches is considered to simulate the effect of changing blood flow streamlines directions. A parameter study has been performed on the main characteristics of clamp, i.e. size, location, and the percentage of coverage. The Shear Stress Transport model is employed to simulate steady-state Newtonian blood flow when the Reynolds number is about 6500. Simulations are conducted using the commercial CFD solver ANSYS Fluent. The obtained results show that the location of clamp is more effective than the size. It is also found that increasing the depth of clamp has a negative impact on mean velocity field and hence on stress concentration.<br><br>CONCLUSION: The present results demonstrate that the Blood Flow Vectoring Control (BFVC) can change the main form of flow streamlines and consequently the distributions of pressure and Wall Shear Stress. A partial clamp leads to better results.}, }
@article {pmid23930803, year = {2013}, author = {Tian, FB and Zhu, L and Fok, PW and Lu, XY}, title = {Simulation of a pulsatile non-Newtonian flow past a stenosed 2D artery with atherosclerosis.}, journal = {Computers in biology and medicine}, volume = {43}, number = {9}, pages = {1098-1113}, doi = {10.1016/j.compbiomed.2013.05.023}, pmid = {23930803}, issn = {1879-0534}, mesh = {*Atherosclerosis/blood/pathology/physiopathology ; *Blood Viscosity ; Constriction, Pathologic/blood/pathology/physiopathology ; Endothelial Cells/metabolism/pathology ; Humans ; *Models, Cardiovascular ; Myocytes, Smooth Muscle/metabolism/pathology ; *Plaque, Atherosclerotic/blood/pathology/physiopathology ; *Pulsatile Flow ; *Stress, Physiological ; }, abstract = {Atherosclerotic plaque can cause severe stenosis in the artery lumen. Blood flow through a substantially narrowed artery may have different flow characteristics and produce different forces acting on the plaque surface and artery wall. The disturbed flow and force fields in the lumen may have serious implications on vascular endothelial cells, smooth muscle cells, and circulating blood cells. In this work a simplified model is used to simulate a pulsatile non-Newtonian blood flow past a stenosed artery caused by atherosclerotic plaques of different severity. The focus is on a systematic parameter study of the effects of plaque size/geometry, flow Reynolds number, shear-rate dependent viscosity and flow pulsatility on the fluid wall shear stress and its gradient, fluid wall normal stress, and flow shear rate. The computational results obtained from this idealized model may shed light on the flow and force characteristics of more realistic blood flow through an atherosclerotic vessel.}, }
@article {pmid23911695, year = {2013}, author = {Tripathi, D and Anwar Bég, O}, title = {Transient magneto-peristaltic flow of couple stress biofluids: a magneto-hydro-dynamical study on digestive transport phenomena.}, journal = {Mathematical biosciences}, volume = {246}, number = {1}, pages = {72-83}, doi = {10.1016/j.mbs.2013.07.012}, pmid = {23911695}, issn = {1879-3134}, mesh = {Animals ; Biological Transport ; *Hydrodynamics ; Magnetic Fields ; *Models, Biological ; Peristalsis/*physiology ; Rheology/*statistics &amp; numerical data ; }, abstract = {Magnetic fields are increasingly being utilized in endoscopy and gastric transport control. In this regard, the present study investigates the influence of a transverse magnetic field in the transient peristaltic rheological transport. An electrically-conducting couple stress non-Newtonian model is employed to accurately simulate physiological fluids in peristaltic flow through a sinusoidally contracting channel of finite length. This model is designed for computing the intra-bolus oesophageal and intestinal pressures during the movement of food bolus in the digestive system under magneto-hydro-dynamic effects. Long wavelength and low Reynolds number approximations have been employed to reduce the governing equations from nonlinear to linear form, this being a valid approach for creeping flows which characterizes physiological dynamics. Analytical approximate solutions for axial velocity, transverse velocity, pressure gradient, local wall shear stress and volumetric flow rate are obtained for the non-dimensional conservation equations subject to appropriate boundary conditions. The effects of couple stress parameter and transverse magnetic field on the velocity profile, pressure distribution, local wall shear stress and the averaged flow rate are discussed with the aid of computational results. The comparative study of non-integral and integral number of waves propagating along the finite length channel is also presented. Magnetic field and non-Newtonian properties are found to strongly influence peristaltic transport.}, }
@article {pmid23909127, year = {2013}, author = {Park, YR and Kim, SJ and Kim, SJ and Kim, JS and Kang, HS and Kim, GB}, title = {A study on hemodynamic characteristics at the stenosed blood vessel using computational fluid dynamics simulations.}, journal = {Journal of biomedical nanotechnology}, volume = {9}, number = {7}, pages = {1137-1145}, doi = {10.1166/jbn.2013.1516}, pmid = {23909127}, issn = {1550-7033}, mesh = {Aneurysm, Ruptured/etiology/*physiopathology ; Animals ; Arterial Occlusive Diseases/complications/*physiopathology ; Arterial Pressure ; Arteries/*physiopathology ; Blood Flow Velocity ; Computer Simulation ; Humans ; *Models, Cardiovascular ; Rheology/*methods ; Shear Strength ; Vascular Resistance ; }, abstract = {In this study, we have used computational fluid dynamics to investigate the blood flow in the stenosed blood vessels. The numerical simulation using commercial software ADINA 8.6 were solved about the stenosed blood vessel according to the percent of stenosis and Reynolds number. The blood flow in the normal and stenosed blood vessel was grasped for the validity of the model. The characteristic of the pulsatile flow changed through the steady state flow and analysis of the pulsatile flow according to the time was grasped. The computational model with the characteristics of the fluid-structure interaction is introduced to investigate the wall shear stress, pressure distribution and axial flow velocity. The results show that axial flow velocity and wall shear stress in the region of stenosis was increased by increasing percent of stenosis and Reynolds number. Also, we can know that in the stenosed blood vessel the possibility of the generation of the aneurysm was increased by increasing Reynolds number and percent of stenosis.}, }
@article {pmid23906281, year = {2013}, author = {Teodósio, JS and Silva, FC and Moreira, JM and Simões, M and Melo, LF and Alves, MA and Mergulhão, FJ}, title = {Flow cells as quasi-ideal systems for biofouling simulation of industrial piping systems.}, journal = {Biofouling}, volume = {29}, number = {8}, pages = {953-966}, doi = {10.1080/08927014.2013.821467}, pmid = {23906281}, issn = {1029-2454}, mesh = {*Biofilms ; Biofouling ; Environmental Monitoring/*methods ; Escherichia coli/*physiology ; *Hydrodynamics ; Models, Theoretical ; Plankton/physiology ; *Water Supply ; }, abstract = {Semi-circular flow cells are often used to simulate the formation of biofilms in industrial pipes with circular section because their planar surface allows easy sampling using coupons. Computational fluid dynamics was used to assess whether the flow in pipe systems can be emulated by the semi-circular flow cells that are used to study biofilm formation. The results show that this is the case for Reynolds numbers (Re) ranging from 10 to 1000 and 3500 to 10,000. A correspondence involving the friction factor was obtained in order to correlate any semi-circular flow cell to any circular pipe for Re between 10 and 100,000. The semi-circular flow cell was then used to assess experimentally the effect of Reynolds number (Re = 4350 and 6720) on planktonic cell concentration and biofilm formation using Escherichia coli JM109 (DE3). Lower planktonic cell concentrations and thicker biofilms (>1.2 mm) were obtained with the lower Re.}, }
@article {pmid23897065, year = {2013}, author = {Haber, S and Clark, A and Tawhai, M}, title = {Blood flow in capillaries of the human lung.}, journal = {Journal of biomechanical engineering}, volume = {135}, number = {10}, pages = {101006-101011}, doi = {10.1115/1.4025092}, pmid = {23897065}, issn = {1528-8951}, mesh = {Blood Pressure ; Capillaries/*physiology/*physiopathology ; Emphysema/physiopathology ; Humans ; Lung/*blood supply ; Models, Biological ; *Regional Blood Flow ; }, abstract = {A novel model for the blood system is postulated focusing on the flow rate and pressure distribution inside the arterioles and venules of the pulmonary acinus. Based upon physiological data it is devoid of any ad hoc constants. The model comprises nine generations of arterioles, venules, and capillaries in the acinus, the gas exchange unit of the lung. Blood is assumed incompressible and Newtonian and the blood vessels are assumed inextensible. Unlike previous models of the blood system, the venules and arterioles open up to the capillary network in numerous locations along each generation. The large number of interconnected capillaries is perceived as a porous medium in which the flow is macroscopically unidirectional from arterioles to venules openings. In addition, the large number of capillaries extending from each arteriole and venule allows introduction of a continuum theory and formulation of a novel system of ordinary, nonlinear differential equations which governs the blood flow and pressure fields along the arterioles, venules, and capillaries. The solution of the differential equations is semianalytical and requires the inversion of three diagonal, 9 × 9 matrices only. The results for the total flow rate of blood through the acinus are within the ballpark of physiological observations despite the simplifying assumptions used in our model. The results also manifest that the contribution of the nonlinear convection term of the Navier-Stokes equations has little effect (less than 2%) on the total blood flow entering/leaving the acinus despite the fact that the Reynolds number is not much smaller than unity at the proximal generations. The model makes it possible to examine some pathological cases. Here, centri-acinar and distal emphysema were investigated yielding a reduction in inlet blood flow rate.}, }
@article {pmid23893860, year = {2013}, author = {Rani, SD and Park, T and You, BH and Soper, SA and Murphy, MC and Nikitopoulos, DE}, title = {Modeling of misalignment effects in microfluidic interconnects for modular bio-analytical chip applications.}, journal = {Electrophoresis}, volume = {34}, number = {20-21}, pages = {2988-2995}, pmid = {23893860}, issn = {1522-2683}, support = {R24 EB002115/EB/NIBIB NIH HHS/United States ; NIH R24-EB002115/EB/NIBIB NIH HHS/United States ; }, mesh = {Computer Simulation ; Equipment Design ; Microfluidic Analytical Techniques/*instrumentation ; Models, Theoretical ; }, abstract = {Minimizing misalignments during the interconnection of microfluidic modules is extremely critical to develop a fully integrated microfluidic device. Misalignments arising during chip-to-chip or world-to-chip interconnections can be greatly detrimental to efficient functioning of microfluidic devices. To address this problem, we have performed numerical simulations to investigate the effect of misalignments arising in three types of interconnection methods: (i) end-to-end interconnection (ii) channel overlap when chips are stacked on top of each other, and (iii) tube-in-reservoir misalignment occurring due to the offset between the external tubing and the reservoir. For the case of end-to-end interconnection, the effect of misalignment was investigated for 0, 13, 50, 58, and 75% reduction in the available flow area at the location of geometrical misalignment. In the channel overlap interconnection method, various possible misalignment configurations were simulated by maintaining the same amount of misalignment (75% flow area reduction). The effect of misalignment in a tube-in-reservoir interconnection was investigated by positioning the tube at an offset of 164 μm from the reservoir center. All the results were evaluated in terms of the equivalent length of a straight pipe. The effect of Reynolds number (Re) was also taken into account by performing additional simulations of aforementioned cases at Re ranging between 0.075 ≤ Re ≤ 75. Correlations were developed and the results were interpreted in terms of equivalent length (Le). Equivalent length calculations revealed that the effect of misalignment in tube-in-reservoir interconnection method was the least significant when compared to the other two methods of interconnection.}, }
@article {pmid23891174, year = {2013}, author = {Sayed Razavi, M and Shirani, E}, title = {Development of a general method for designing microvascular networks using distribution of wall shear stress.}, journal = {Journal of biomechanics}, volume = {46}, number = {13}, pages = {2303-2309}, doi = {10.1016/j.jbiomech.2013.06.005}, pmid = {23891174}, issn = {1873-2380}, mesh = {Blood Flow Velocity ; Computer Simulation ; Microvessels/*physiology ; *Models, Cardiovascular ; Rheology ; Stress, Mechanical ; Viscosity ; }, abstract = {In the present study, theoretical formulations for calculation of optimal bifurcation angle and relationship between the diameters of mother and daughter vessels using the power law model for non-Newtonian fluids are developed. The method is based on the distribution of wall shear stress in the mother and daughter vessels. Also, the effect of distribution of wall shear stress on the minimization of energy loss and flow resistance is considered. It is shown that constant wall shear stress in the mother and daughter vessels provides the minimum flow resistance and energy loss of biological flows. Moreover, the effects of different wall shear stresses in the mother and daughter branches, different lengths of daughter branches in the asymmetric bifurcations and non-Newtonian effect of biological fluid flows on the bifurcation angle and the relationship between the diameters of mother and daughter branches are considered. Using numerical simulations for non-Newtonian models such as power law and Carreau models, the effects of optimal bifurcation angle on the pressure drop and flow resistance of blood flow in the symmetric bifurcation are investigated. Numerical simulations show that optimal bifurcation angle decreases the pressure drop and flow resistance especially for bifurcations at large Reynolds number.}, }
@article {pmid23887878, year = {2013}, author = {M'rabet Bensalah, K and Uehlinger, D and Kalicki, R and Czerwinska, J}, title = {Hemodynamic modeling of the intrarenal circulation.}, journal = {Annals of biomedical engineering}, volume = {41}, number = {12}, pages = {2630-2644}, doi = {10.1007/s10439-013-0865-8}, pmid = {23887878}, issn = {1573-9686}, mesh = {Arteries/physiology ; Computer Simulation ; Constriction, Pathologic/physiopathology ; Hemodynamics ; Humans ; Kidney/*blood supply ; *Models, Cardiovascular ; Renal Circulation ; Software ; Veins/physiology ; }, abstract = {Three dimensional, time dependent numerical simulations of healthy and pathological conditions in a model kidney were performed. Blood flow in a kidney is not commonly investigated by computational approach, in contrast for example, to the flow in a heart. The flow in a kidney is characterized by relatively small Reynolds number (100 < Re < 0.01-laminar regime). The presented results give insight into the structure of such flow, which is hard to measure in vivo. The simulations have suggested that venous thrombosis is more likely than arterial thrombosis-higher shear rate observed. The obtained maximum velocity, as a result of the simulations, agrees with the observed in vivo measurements. The time dependent simulations show separation regimes present in the vicinity of the maximum pressure value. The pathological constriction introduced to the arterial geometry leads to the changes in separation structures. The constriction of a single vessel affects flow in the whole kidney. Pathology results in different flow rate values in healthy and affected branches, as well as, different pulsate cycle characteristic for the whole system.}, }
@article {pmid23886851, year = {2013}, author = {Imamoglu, E and Sukan, FV}, title = {Scale-up and kinetic modeling for bioethanol production.}, journal = {Bioresource technology}, volume = {144}, number = {}, pages = {311-320}, doi = {10.1016/j.biortech.2013.06.118}, pmid = {23886851}, issn = {1873-2976}, mesh = {*Biofuels ; Bioreactors ; Biotechnology/*methods ; Escherichia coli/metabolism ; Ethanol/*metabolism ; Glucose/analysis ; Kinetics ; Lactic Acid/biosynthesis ; *Models, Theoretical ; Oryza/chemistry ; Rheology ; Waste Products/analysis ; Xylose/analysis ; }, abstract = {Bioethanol was produced from acidic hydrolysate of rice hulls using recombinant Escherichia coli KO11. Two different issues (scale-up and kinetic modeling) were evaluated simultaneously and concomitantly for bioethanol production. During the step-wise scale-up process from 100 mL shaken flask to 10 L stirred-tank bioreactor, the constant Reynolds number and the constant impeller tip speed were evaluated as scale-up methodologies under laboratory conditions. It was determined that the volumetric bioethanol productivity was 88% higher in 10 L bioreactor in comparison to the value of 0.21 g L(-1) h(-1) in shaken flask. The modified Monod and Luedeking-Piret models provided an accurate approach for the modeling of the experimental data. Ethanol concentration reached the maximum level of 29.03 g/L, which was 5% higher than the value of model prediction in 10 L bioreactor. The findings of this research could contribute to the industrial scale productions especially from lignocellulosic raw materials.}, }
@article {pmid23872180, year = {2013}, author = {Hadinoto, K and Sundaresan, A and Cheow, WS}, title = {Lipid-polymer hybrid nanoparticles as a new generation therapeutic delivery platform: a review.}, journal = {European journal of pharmaceutics and biopharmaceutics : official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V}, volume = {85}, number = {3 Pt A}, pages = {427-443}, doi = {10.1016/j.ejpb.2013.07.002}, pmid = {23872180}, issn = {1873-3441}, mesh = {Animals ; *Drug Delivery Systems ; Drug Stability ; High-Throughput Screening Assays/methods ; Humans ; Lipids/*chemistry ; Liposomes ; *Nanoparticles ; Polyethylene Glycols/chemistry ; Polymers/*chemistry ; }, abstract = {Lipid-polymer hybrid nanoparticles (LPNs) are core-shell nanoparticle structures comprising polymer cores and lipid/lipid-PEG shells, which exhibit complementary characteristics of both polymeric nanoparticles and liposomes, particularly in terms of their physical stability and biocompatibility. Significantly, the LPNs have recently been demonstrated to exhibit superior in vivo cellular delivery efficacy compared to that obtained from polymeric nanoparticles and liposomes. Since their inception, the LPNs have advanced significantly in terms of their preparation strategy and scope of applications. Their preparation strategy has undergone a shift from the conceptually simple two-step method, involving preformed polymeric nanoparticles and lipid vesicles, to the more principally complex, yet easier to perform, one-step method, relying on simultaneous self-assembly of the lipid and polymer, which has resulted in better products and higher production throughput. The scope of LPNs' applications has also been extended beyond single drug delivery for anticancer therapy, to include combinatorial and active targeted drug deliveries, and deliveries of genetic materials, vaccines, and diagnostic imaging agents. This review details the current state of development for the LPNs preparation and applications from which we identify future research works needed to bring the LPNs closer to its clinical realization.}, }
@article {pmid23870271, year = {2013}, author = {Bark, DL and Ku, DN}, title = {Platelet transport rates and binding kinetics at high shear over a thrombus.}, journal = {Biophysical journal}, volume = {105}, number = {2}, pages = {502-511}, pmid = {23870271}, issn = {1542-0086}, mesh = {Animals ; Blood Platelets/*physiology ; *Cell Movement ; Coronary Thrombosis/*pathology ; Erythrocytes/physiology ; Hemodynamics ; Humans ; Kinetics ; *Models, Biological ; *Platelet Adhesiveness ; *Platelet Aggregation ; }, abstract = {Thrombus formation over a ruptured atherosclerotic plaque cap can occlude an artery with fatal consequences. We describe a computational model of platelet transport and binding to interpret rate-limiting steps seen in experimental thrombus formation over a collagen-coated stenosis. The model is used to compute shear rates in stenoses with growing boundaries. In the model, moving erythrocytes influence platelet transport based on shear-dependent enhanced diffusivity and a nonuniform platelet distribution. Adhesion is modeled as platelet-platelet binding kinetics. The results indicate that observed thrombus growth rates are limited by platelet transport to the wall for shear rates up to 6000 s(-1). Above 7000 s(-1), the thrombus growth rate is likely limited by binding kinetics (10(-4) m/s). Thrombus growth computed from these rate-limiting steps match the thrombus location and occlusion times for experimental conditions if a lag time for platelet activation is included. Using fitted parameters, the model is then used to predict thrombus size and shape at a higher Reynolds number flow consistent with coronary artery disease.}, }
@article {pmid23860724, year = {2014}, author = {Walther, C and Mayer, S and Trefilov, A and Sekot, G and Hahn, R and Jungbauer, A and Dürauer, A}, title = {Prediction of inclusion body solubilization from shaken to stirred reactors.}, journal = {Biotechnology and bioengineering}, volume = {111}, number = {1}, pages = {84-94}, doi = {10.1002/bit.24998}, pmid = {23860724}, issn = {1097-0290}, mesh = {Bioreactors/*microbiology ; *Biotechnology/instrumentation/methods ; Escherichia coli/metabolism ; High-Throughput Screening Assays/instrumentation/methods ; Inclusion Bodies/*chemistry/*metabolism ; Kinetics ; Solubility ; }, abstract = {Inclusion bodies (IBs) were solubilized in a µ-scale system using shaking microtiter plates or a stirred tank reactor in a laboratory setting. Characteristic dimensionless numbers for mixing, the Phase number Ph and Reynolds number Re did not correlate with the kinetics and equilibrium of protein solubilization. The solubilization kinetics was independent of the mixing system, stirring or shaking rate, shaking diameter, and energy input. Good agreement was observed between the solubilization kinetics and yield on the µ-scale and laboratory setting. We show that the IB solubilization process is controlled predominantly by pore diffusion. Thus, for the process it is sufficient to keep the IBs homogeneously suspended, and additional power input will not improve the process. The high-throughput system developed on the µ-scale can predict solubilization in stirred reactors up to a factor of 500 and can therefore be used to determine optimal solubilization conditions on laboratory and industrial scale.}, }
@article {pmid23851658, year = {2013}, author = {Sobh, AM}, title = {Combined effect of couple stresses and heat and mass transfer on peristaltic flow with slip conditions in a tube.}, journal = {Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine}, volume = {227}, number = {10}, pages = {1073-1082}, doi = {10.1177/0954411913487852}, pmid = {23851658}, issn = {2041-3033}, mesh = {Animals ; Body Fluids/*physiology ; Computer Simulation ; Energy Transfer/*physiology ; Friction ; Hot Temperature ; Humans ; *Models, Biological ; Peristalsis/*physiology ; Rheology/*methods ; Shear Strength/physiology ; Stress, Mechanical ; Thermal Conductivity ; Thermodynamics ; }, abstract = {In this article, the influence of heat and mass transfer on peristaltic transport of a couple stress fluid in a uniform tube with slip conditions on the wall is studied. The problem can model the blood flow in living creatures. Under long wavelength approximation and zero Reynolds number, exact solutions for the axial velocity component, pressure gradient, and both temperature and concentration fields are derived. The pressure rise is computed numerically and explained graphically. Moreover, effects of various physical parameters of the problem on temperature distribution, concentration field, and trapping are studied and discussed graphically.}, }
@article {pmid23848775, year = {2013}, author = {Wang, S and Ardekani, AM}, title = {Swimming of a model ciliate near an air-liquid interface.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {6}, pages = {063010}, doi = {10.1103/PhysRevE.87.063010}, pmid = {23848775}, issn = {1550-2376}, mesh = {Air ; Biological Clocks/*physiology ; Ciliophora/*physiology ; Computer Simulation ; Lubrication ; *Models, Biological ; Rheology/*methods ; Shear Strength/physiology ; Solutions ; Swimming/*physiology ; }, abstract = {In this work, the role of the hydrodynamic forces on a swimming microorganism near an air-liquid interface is studied. The lubrication theory is utilized to analyze hydrodynamic effects within the narrow gap between a flat interface and a small swimmer. By using an archetypal low-Reynolds-number swimming model called "squirmer," we find that the magnitude of the vertical swimming velocity is on the order of O(εlnε), where ε is the ratio of the gap width to the swimmer's body size. The reduced swimming velocity near an interface can explain experimental observations of the aggregation of microorganisms near a liquid interface.}, }
@article {pmid23848693, year = {2013}, author = {Alexandrov, DV and Galenko, PK}, title = {Selection criterion of stable dendritic growth at arbitrary Péclet numbers with convection.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {6}, pages = {062403}, doi = {10.1103/PhysRevE.87.062403}, pmid = {23848693}, issn = {1550-2376}, mesh = {Computer Simulation ; Convection ; Crystallization/*methods ; Dendrimers/*chemical synthesis ; *Models, Chemical ; *Models, Molecular ; Nanoparticles/*chemistry/*ultrastructure ; }, abstract = {A free dendrite growth under forced fluid flow is analyzed for solidification of a nonisothermal binary system. Using an approach to dendrite growth developed by Bouissou and Pelcé [Phys. Rev. A 40, 6673 (1989)], the analysis is presented for the parabolic dendrite interface with small anisotropy of surface energy growing at arbitrary Péclet numbers. The stable growth mode is obtained from the solvability condition giving the stability criterion for the dendrite tip velocity V and dendrite tip radius ρ as a function of the growth Péclet number, flow Péclet number, and Reynolds number. In limiting cases, the obtained stability criterion presents known criteria for small and high growth Péclet numbers of the solidifying system with and without convective fluid flow.}, }
@article {pmid23848659, year = {2013}, author = {Anvari, M and Aghamohammadi, C and Dashti-Naserabadi, H and Salehi, E and Behjat, E and Qorbani, M and Nezhad, MK and Zirak, M and Hadjihosseini, A and Peinke, J and Tabar, MR}, title = {Stochastic nature of series of waiting times.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {6}, pages = {062139}, doi = {10.1103/PhysRevE.87.062139}, pmid = {23848659}, issn = {1550-2376}, abstract = {Although fluctuations in the waiting time series have been studied for a long time, some important issues such as its long-range memory and its stochastic features in the presence of nonstationarity have so far remained unstudied. Here we find that the "waiting times" series for a given increment level have long-range correlations with Hurst exponents belonging to the interval 1/2<H<1. We also study positive-negative level asymmetry of the waiting time distribution. We find that the logarithmic difference of waiting times series has a short-range correlation, and then we study its stochastic nature using the Markovian method and determine the corresponding Kramers-Moyal coefficients. As an example, we analyze the velocity fluctuations in high Reynolds number turbulence and determine the level dependence of Markov time scales, as well as the drift and diffusion coefficients. We show that the waiting time distributions exhibit power law tails, and we were able to model the distribution with a continuous time random walk.}, }
@article {pmid23838468, year = {2013}, author = {Herrera-Velarde, S and Euán-Díaz, EC and Córdoba-Valdés, F and Castañeda-Priego, R}, title = {Hydrodynamic correlations in three-particle colloidal systems in harmonic traps.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {25}, number = {32}, pages = {325102}, doi = {10.1088/0953-8984/25/32/325102}, pmid = {23838468}, issn = {1361-648X}, abstract = {We report on the hydrodynamic correlations between colloids immersed in a low Reynolds number fluid. We consider colloidal arrays composed of three particles; each colloid is trapped in a single harmonic potential and interacts with the other colloids only via hydrodynamic forces. We focus on the role of a third body in the two-body correlation functions. We give special attention to a collinear configuration of particles, although the salient features of an equilateral triangle configuration are outlined. The correlation functions are computed both by means of Brownian dynamics simulations, and by solving analytically and numerically the Langevin equation under the assumption of constant diffusion tensor; this approximation is validated through computer simulations. We explicitly show that the presence of a third body affects the auto- and cross-correlation functions and that their behaviour, in some specific conditions, can be different from that commonly seen in a two-particle system. In particular, we have found that the auto-correlation functions show a slower decay, while the cross-correlation ones exhibit a temporal shift and a weaker amplitude. Moreover, an unexpected behaviour related to a positive correlation and associated with the appearance of new dynamical modes is observed in the case of the collinear array of three particles. This interesting effect might be used to tune the degree of hydrodynamic correlation in few-body colloidal systems.}, }
@article {pmid23837306, year = {2013}, author = {Rodríguez, FA and Mateo, MN and Aceves, JM and Rivero, EP and González, I}, title = {Electrochemical oxidation of bio-refractory dye in a simulated textile industry effluent using DSA electrodes in a filter-press type FM01-LC reactor.}, journal = {Environmental technology}, volume = {34}, number = {5-8}, pages = {573-583}, doi = {10.1080/09593330.2012.706645}, pmid = {23837306}, issn = {0959-3330}, mesh = {Electrochemistry/*instrumentation ; *Electrodes ; Equipment Design ; Equipment Failure Analysis ; Filtration/*instrumentation ; Indigo Carmine/*isolation &amp; purification ; Oxidation-Reduction ; Pressure ; Rheology/instrumentation ; Textile Industry/*instrumentation ; Water Pollutants, Chemical/*isolation &amp; purification ; Water Purification/*methods ; }, abstract = {This work presents a study on degradation of indigo carmine dye in a filter-press type FM01-LC reactor using Sb2O5-doped Ti/IrO2-SnO2 dimensionally stable anode (DSA) electrodes. Micro- and macroelectrolysis studies were carried out using solutions of 0.8 mM indigo carmine in 0.05 M NaCl, which resemble blue denim laundry industrial wastewater. Microelectrolysis results show the behaviour of DSA electrodes in comparison with the behaviour of boron-doped diamond (BDD) electrodes. In general, dye degradation reactions are carried out indirectly through active chlorine generated on DSA, whereas in the case of BDD electrodes more oxidizing species are formed, mainly OH radicals, on the electrode surface. The well-characterized geometry, flow pattern and mass transport of the FM01-LC reactor used in macroelectrolysis experiments allowed the evaluation of the effect of hydrodynamic conditions on the chlorine-mediated degradation rate. Four values of Reynolds number (Re) (93, 371, 464 and 557) at four current densities (50, 100, 150 and 200 A/m2) were tested. The results show that the degradation rate is independent of Re at low current density (50 A/m2) but becomes dependent on the Re at high current density (200 A/m2). This behaviour shows the central role of mass transport and the reactor parameters and design. The low energy consumption (2.02 and 9.04 kWh/m3 for complete discolouration and chemical oxygen demand elimination at 50 A/m2, respectively) and the low cost of DSA electrodes compared to BDD make DSA electrodes promising for practical application in treating industrial textile effluents. In the present study, chlorinated organic compounds were not detected.}, }
@article {pmid23834834, year = {2013}, author = {Stumpo, M and Anselmi, C and Vauthier, C and Mitri, K and Hanno, I and Huang, N and Bouchemal, K}, title = {Scale-up of polyamide and polyester Parsol® MCX nanocapsules by interfacial polycondensation and solvent diffusion method.}, journal = {International journal of pharmaceutics}, volume = {454}, number = {2}, pages = {678-685}, doi = {10.1016/j.ijpharm.2013.06.062}, pmid = {23834834}, issn = {1873-3476}, mesh = {2-Propanol/chemistry ; Acetone/chemistry ; Cinnamates/*chemistry ; Diffusion ; Microscopy, Electron, Transmission ; Nanocapsules/*chemistry/ultrastructure ; Nylons/*chemistry ; Particle Size ; Polyesters/*chemistry ; Solvents/chemistry ; Spectroscopy, Fourier Transform Infrared ; Sunscreening Agents/*chemistry ; }, abstract = {The scale-up of oil-containing polyamide nanocapsules produced by simultaneous interfacial polycondensation and solvent diffusion was successfully achieved. Up to 1,500 mL were produced by using a Y-shaped mixer device. The sizes of nanocapsules containing olive oil were modulated from 646 to 211 nm by changing process parameters without modification of the formulation composition. All the results of nanocapsule diameters (dsc) expressed as a function of the Reynolds number (Re) showed the existence of a typical power-law relationship. It was demonstrated that the high turbulences created upon nanocapsule formation are the most important parameter allowing to nanocapsule size to be controlled without modifying the formulation composition. Finally, the power-law relationship was used to predict the size of nanocapsules composed of polyamide or polyester and loaded with Parsol(®) MCX. The physico-chemical properties of both polyamide and polyester nanocapsules at the laboratory scale were compared to the ones obtained at the pilot scale. The encapsulation efficiency was higher than 98% in both types of nanocapsules at the laboratory and the pilot scales. The in vitro releases of Parsol(®) MCX from polyester nanocapsules were reproducible at both scales. This is the first time such a power-law was described for the preparation of nanocapsules by interfacial polycondensation and solvent diffusion.}, }
@article {pmid23826109, year = {2013}, author = {Tang, JW and Nicolle, A and Pantelic, J and Klettner, CA and Su, R and Kalliomaki, P and Saarinen, P and Koskela, H and Reijula, K and Mustakallio, P and Cheong, DK and Sekhar, C and Tham, KW}, title = {Different types of door-opening motions as contributing factors to containment failures in hospital isolation rooms.}, journal = {PloS one}, volume = {8}, number = {6}, pages = {e66663}, pmid = {23826109}, issn = {1932-6203}, mesh = {Hospital Design and Construction ; *Hospitals ; Humans ; Infection Control/*instrumentation ; *Motion ; *Patient Isolation ; *Patients' Rooms ; }, abstract = {Hospital isolation rooms are vital for the containment (when under negative pressure) of patients with, or the protection (when under positive pressure) of patients, from airborne infectious agents. Such facilities were essential for the management of highly contagious patients during the 2003 severe acute respiratory syndrome (SARS) outbreaks and the more recent 2009 A/H1N1 influenza pandemic. Many different types of door designs are used in the construction of such isolation rooms, which may be related to the space available and affordability. Using colored food dye as a tracer, the qualitative effects of door-opening motions on the dissemination of potentially contaminated air into and out of a single isolation room were visualized and filmed using Reynolds-number-equivalent, small-scale, water-tank models fitted with programmable door-opening and moving human figure motions. Careful scaling considerations involved in the design and construction of these water-tank models enabled these results to be accurately extrapolated to the full-scale situation. Four simple types of door design were tested: variable speed single and double, sliding and hinged doors, in combination with the moving human figure. The resulting video footage was edited, synchronized and presented in a series of split-screen formats. From these experiments, it is clear that double-hinged doors pose the greatest risk of leakage into or out of the room, followed by (in order of decreasing risk) single-hinged, double-sliding and single-sliding doors. The relative effect of the moving human figure on spreading any potential contamination was greatest with the sliding doors, as the bulk airflows induced were large relative to those resulting from these door-opening motions. However, with the hinged doors, the airflows induced by these door-opening motions were significantly greater. Further experiments involving a simulated ventilated environment are required, but from these findings alone, it appears that sliding-doors are far more effective for hospital isolation room containment.}, }
@article {pmid23823920, year = {2013}, author = {Balla, HH and Abdullah, S and Mohdfaizal, W and Zulkifli, R and Sopian, K}, title = {Numerical study of the enhancement of heat transfer for hybrid CuO-Cu Nanofluids flowing in a circular pipe.}, journal = {Journal of oleo science}, volume = {62}, number = {7}, pages = {533-539}, doi = {10.5650/jos.62.533}, pmid = {23823920}, issn = {1347-3352}, mesh = {Copper/*chemistry ; *Hot Temperature ; *Models, Chemical ; Nanoparticles/*chemistry ; }, abstract = {A numerical simulation model for laminar flow of nanofluids in a pipe with constant heat flux on the wall was built to study the effect of the Reynolds number on convective heat transfer and pressure loss. The investigation was performed for hybrid nanofluids consisting of CuO-Cu nanoparticles and compared with CuO and Cu in which the nanoparticles have a spherical shape with size 50, 50, 50nm respectively. The nanofluids were prepared, following which the thermal conductivity and dynamic viscosity were measured for a range of temperatures (10 -60°C). The numerical results obtained were compared with the existing well-established correlation. The prediction of the Nusselt number for nanofluids agrees well with the Shah correlation. The comparison of heat transfer coefficients for CuO, Cu and CuO-Cu presented an increase in thermal conductivity of the nanofluid as the convective heat transfer coefficient increased. It was found that the pressure loss increases with an increase in the Reynolds number, nanoparticle density and particle volume fraction. However, the flow demonstrates enhancement in heat transfer which becomes greater with an increase in the Reynolds number for the nanofluid flow.}, }
@article {pmid23822377, year = {2013}, author = {Avila, K and Hof, B}, title = {High-precision Taylor-Couette experiment to study subcritical transitions and the role of boundary conditions and size effects.}, journal = {The Review of scientific instruments}, volume = {84}, number = {6}, pages = {065106}, doi = {10.1063/1.4807704}, pmid = {23822377}, issn = {1089-7623}, abstract = {A novel Taylor-Couette system has been constructed for investigations of transitional as well as high Reynolds number turbulent flows in very large aspect ratios. The flexibility of the setup enables studies of a variety of problems regarding hydrodynamic instabilities and turbulence in rotating flows. The inner and outer cylinders and the top and bottom endplates can be rotated independently with rotation rates of up to 30 Hz, thereby covering five orders of magnitude in Reynolds numbers (Re = 10(1)-10(6)). The radius ratio can be easily changed, the highest realized one is η = 0.98 corresponding to an aspect ratio of 260 gap width in the vertical and 300 in the azimuthal direction. For η < 0.98 the aspect ratio can be dynamically changed during measurements and complete transparency in the radial direction over the full length of the cylinders is provided by the usage of a precision glass inner cylinder. The temperatures of both cylinders are controlled independently. Overall this apparatus combines an unmatched variety in geometry, rotation rates, and temperatures, which is provided by a sophisticated high-precision bearing system. Possible applications are accurate studies of the onset of turbulence and spatio-temporal intermittent flow patterns in very large domains, transport processes of turbulence at high Re, the stability of Keplerian flows for different boundary conditions, and studies of baroclinic instabilities.}, }
@article {pmid23808762, year = {2014}, author = {Kim, J and Xi, J and Si, X and Berlinski, A and Su, WC}, title = {Hood nebulization: effects of head direction and breathing mode on particle inhalability and deposition in a 7-month-old infant model.}, journal = {Journal of aerosol medicine and pulmonary drug delivery}, volume = {27}, number = {3}, pages = {209-218}, doi = {10.1089/jamp.2013.1051}, pmid = {23808762}, issn = {1941-2703}, mesh = {Administration, Inhalation ; Aerosols ; Computer Simulation ; Drug Delivery Systems/*instrumentation ; Equipment Design ; Female ; Head/*anatomy &amp; histology/diagnostic imaging ; *Head Movements ; Humans ; Infant ; Models, Anatomic ; Motion ; *Nebulizers and Vaporizers ; Numerical Analysis, Computer-Assisted ; Particle Size ; Pharmaceutical Preparations/*administration &amp; dosage/chemistry ; Radiography ; *Respiration ; Respiratory System/*anatomy &amp; histology/diagnostic imaging ; Rheology ; }, abstract = {BACKGROUND: Aerosol drug delivery to infants is a strong function of their behavior. Infants can be active during medication administration, changing head position or breathing mode. The objective was to evaluate the influence of the head direction and breathing mode on the hood drug delivery in a 7-month-old girl airway model by using an approach that couples imaging with computational fluid dynamics (CFD). Three head directions, i.e., face up, face side, and sitting (face front), and two breathing modes, i.e., oronasal and nasal breathing, were studied.<br><br>METHODS: The face-airway model was developed from computed tomography scans of a 7-month-old girl. Respiratory airflows and particle transport were simulated with the low Reynolds number &#x3ba;-&#x3c9; turbulence model and Lagrangian tracking approach. Three pharmaceutical aerosol sizes (1, 2.5, and 5 &#x3bc;m) via hood nebulization were considered under quiet breathing conditions (5 L/min).<br><br>RESULTS: Both head direction and breathing mode can noticeably affect aerosol inhalability and lung delivery efficiency. A maximum of 20% difference in inhalability is observed among the three head positions. Facial-ocular depositions are predominantly influenced by head position, but not breathing mode. The facial-ocular deposition rate with the face-up position is about threefold that with the sitting position for 5-&#x3bc;m particles. Nasal breathing gives about 17.8% lower lung deposition and about 65% higher facial-ocular deposition than the oronasal breathing.<br><br>CONCLUSION: The face-side position has less facial-ocular deposition than the face-up position, while still achieving similar lung delivery efficiency. Because aerosols deposited around the eyes may cause irritation to the eyes, the face-side position appears to be a better option than the face-up position for comfort and safety reasons.}, }
@article {pmid23804440, year = {2013}, author = {Pennycuick, CJ and Åkesson, S and Hedenström, A}, title = {Air speeds of migrating birds observed by ornithodolite and compared with predictions from flight theory.}, journal = {Journal of the Royal Society, Interface}, volume = {10}, number = {86}, pages = {20130419}, pmid = {23804440}, issn = {1742-5662}, mesh = {Animal Migration/*physiology ; Animals ; Birds/*physiology ; Female ; Flight, Animal/*physiology ; Male ; *Models, Biological ; }, abstract = {We measured the air speeds of 31 bird species, for which we had body mass and wing measurements, migrating along the east coast of Sweden in autumn, using a Vectronix Vector 21 ornithodolite and a Gill WindSonic anemometer. We expected each species' average air speed to exceed its calculated minimum-power speed (Vmp), and to fall below its maximum-range speed (Vmr), but found some exceptions to both limits. To resolve these discrepancies, we first reduced the assumed induced power factor for all species from 1.2 to 0.9, attributing this to splayed and up-turned primary feathers, and then assigned body drag coefficients for different species down to 0.060 for small waders, and up to 0.12 for the mute swan, in the Reynolds number range 25 000-250 000. These results will be used to amend the default values in existing software that estimates fuel consumption in migration, energy heights on arrival and other aspects of flight performance, using classical aeronautical theory. The body drag coefficients are central to range calculations. Although they cannot be measured on dead bird bodies, they could be checked against wind tunnel measurements on living birds, using existing methods.}, }
@article {pmid23802980, year = {2013}, author = {Reddig, S and Stark, H}, title = {Nonlinear dynamics of spherical particles in Poiseuille flow under creeping-flow condition.}, journal = {The Journal of chemical physics}, volume = {138}, number = {23}, pages = {234902}, doi = {10.1063/1.4809989}, pmid = {23802980}, issn = {1089-7690}, mesh = {Colloids/*chemistry ; Computer Simulation ; Hydrodynamics ; *Nonlinear Dynamics ; Solvents/*chemistry ; }, abstract = {We study the nonlinear dynamics of spherical colloids under the influence of a pressure driven flow at vanishing Reynolds number. The colloids are confined between two parallel planar walls with a distance comparable to the particle diameter and they interact hydrodynamically via the solvent. We show that the bounded Poiseuille flow gives rise to new classes of trajectories resulting in cross-streamline migration. Two particles moving on these new trajectories exhibit either bound or unbound states. In the first case they oscillate on closed trajectories in the center-of-mass frame. In the second case, they exhibit cross-swapping trajectories in addition to swapping trajectories which were already observed in unbounded or bounded linear shear flow. The different classes of trajectories occur depending on the initial positions of the two particles and their size. We present state diagrams in the lateral positions, where we categorize the trajectories and color code the oscillation frequencies of the bound states. Finally we discuss how the results on the two-particle system help to understand the stability of particle trains composed of several particles.}, }
@article {pmid23781125, year = {2013}, author = {Yang, J and Wolgemuth, CW and Huber, G}, title = {Force and torque on a cylinder rotating in a narrow gap at low Reynolds number: Scaling and lubrication analyses.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {25}, number = {5}, pages = {51901}, pmid = {23781125}, issn = {1070-6631}, support = {R01 GM072004/GM/NIGMS NIH HHS/United States ; }, abstract = {The hydrodynamic forces and torques on a rotating cylinder in a narrow channel are investigated in this paper using lubrication analysis and scaling analysis. To explore the effect of the shape of the gap, three different geometries are considered. The force and torque expressions from lubrication analysis agree well with numerical solutions when the gap between cylinder and wall is small. The solutions from scaling analysis can be applied over a broader range, but only if the scaling coefficients are properly deduced from numerical solution or lubrication analysis. Self-similarity in the solutions is discussed as well.}, }
@article {pmid23767651, year = {2013}, author = {Li, Q and Luo, KH and Li, XJ}, title = {Lattice Boltzmann modeling of multiphase flows at large density ratio with an improved pseudopotential model.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {5}, pages = {053301}, doi = {10.1103/PhysRevE.87.053301}, pmid = {23767651}, issn = {1550-2376}, mesh = {Computer Simulation ; *Membranes, Artificial ; *Models, Chemical ; *Models, Molecular ; Rheology/*methods ; Solutions/*chemistry ; }, abstract = {Owing to its conceptual simplicity and computational efficiency, the pseudopotential multiphase lattice Boltzmann (LB) model has attracted significant attention since its emergence. In this work, we aim to extend the pseudopotential LB model to simulate multiphase flows at large density ratio and relatively high Reynolds number. First, based on our recent work [Q. Li, K. H. Luo, and X. J. Li, Phys. Rev. E 86, 016709 (2012)], an improved forcing scheme is proposed for the multiple-relaxation-time pseudopotential LB model in order to achieve thermodynamic consistency and large density ratio in the model. Next, through investigating the effects of the parameter a in the Carnahan-Starling equation of state, we find that the interface thickness is approximately proportional to 1/√a. Using a smaller a will lead to a wider interface thickness, which can reduce the spurious currents and enhance the numerical stability of the pseudopotential model at large density ratio. Furthermore, it is found that a lower liquid viscosity can be gained in the pseudopotential model by increasing the kinematic viscosity ratio between the vapor and liquid phases. The improved pseudopotential LB model is numerically validated via the simulations of stationary droplet and droplet oscillation. Using the improved model as well as the above treatments, numerical simulations of droplet splashing on a thin liquid film are conducted at a density ratio in excess of 500 with Reynolds numbers ranging from 40 to 1000. The dynamics of droplet splashing is correctly reproduced and the predicted spread radius is found to obey the power law reported in the literature.}, }
@article {pmid23767635, year = {2013}, author = {Parra-Rojas, C and Soto, R}, title = {Active temperature and velocity correlations produced by a swimmer suspension.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {5}, pages = {053022}, doi = {10.1103/PhysRevE.87.053022}, pmid = {23767635}, issn = {1550-2376}, mesh = {Animals ; Anisotropy ; Cell Movement/*physiology ; Computer Simulation ; Humans ; Microfluidics/*methods ; *Models, Biological ; Swimming/*physiology ; Temperature ; }, abstract = {The agitation produced in a fluid by a suspension of microswimmers in the low Reynolds number limit is studied. In this limit, swimmers are modeled as force dipoles all with equal strength. The agitation is characterized by the active temperature defined, as in kinetic theory, as the mean square velocity, and by the equal-time spatial correlations. Considering the phase in which the swimmers are homogeneously and isotropically distributed in the fluid, it is shown that the active temperature and velocity correlations depend on a single scalar correlation function of the dipole-dipole correlation function. By making a simple medium-range order model, in which the dipole-dipole correlation function is characterized by a single correlation length k(0)(-1) it is possible to make quantitative predictions. It is found that the active temperature depends on the system size, scaling as L(4-d) at large correlation lengths L<<k(0)(-1), while in the opposite limit it saturates in three dimensions and diverges logarithmically with the system size in two dimensions. In three dimensions the velocity correlations decay as 1/r for small correlation lengths, while at large correlation lengths the transverse correlation function becomes negative at maximum separation r~L/2, an effect that disappears as the system increases in size.}, }
@article {pmid23767633, year = {2013}, author = {Hollerbach, R and Nore, C and Marti, P and Vantieghem, S and Luddens, F and Léorat, J}, title = {Parity-breaking flows in precessing spherical containers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {5}, pages = {053020}, doi = {10.1103/PhysRevE.87.053020}, pmid = {23767633}, issn = {1550-2376}, mesh = {Computer Simulation ; *Computer-Aided Design ; *Models, Theoretical ; Rheology/*instrumentation/*methods ; }, abstract = {We present numerical solutions of the flow in precessing spheres and spherical shells with small (r(i)/r(o)=0.1) inner cores and either stress-free or no-slip inner boundary conditions. For each of these three cases we consider the sequence of bifurcations as the Reynolds number Re=r(o)(2)Ω/ν is increased up to ~1280, focusing particular attention on bifurcations that break the antipodal symmetry U(-r)=-U(r). All three cases have steady and time-periodic symmetric solutions at smaller Re, and quasiperiodic asymmetric solutions at larger Re, but the details of the transitions differ, and include also periodic asymmetric and quasiperiodic symmetric solutions in some of the cases.}, }
@article {pmid23767622, year = {2013}, author = {Zhang, J and Xu, M and Pollard, A and Mi, J}, title = {Effects of external intermittency and mean shear on the spectral inertial-range exponent in a turbulent square jet.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {5}, pages = {053009}, doi = {10.1103/PhysRevE.87.053009}, pmid = {23767622}, issn = {1550-2376}, mesh = {Computer Simulation ; *Models, Theoretical ; *Nonlinear Dynamics ; Rheology/*methods ; Shear Strength ; }, abstract = {This study investigates by experiment the dependence of the inertial-range exponent m of the streamwise velocity spectrum on the external intermittency factor γ (≡ the fraction of time the flow is fully turbulent) and the mean shear S in a turbulent square jet. Velocity measurements were made using hot-wire anemometry in the jet at 15 < x/D(e) < 40, where D(e) denotes the exit equivalent diameter, and for an exit Reynolds number of Re = 50,000. The Taylor microscale Reynolds number R(λ) varies from about 70 to 450 in the present study. The TERA (turbulent energy recognition algorithm) method proposed by Falco and Gendrich [in Near-Wall Turbulence: 1988 Zoran Zariç Memorial Conference, edited by S. J. Kline and N. H. Afgan (Hemisphere Publishing Corp., Washington, DC, 1990), pp. 911-931] is discussed and applied to estimate the intermittency factor from velocity signals. It is shown that m depends strongly on γ but negligibly on S. More specifically, m varies with γ following m=m(t)+(lnγ(-0.0173))(1/2), where m(t) denotes the spectral exponent found in fully turbulent regions.}, }
@article {pmid23767618, year = {2013}, author = {Potomkin, M and Gyrya, V and Aranson, I and Berlyand, L}, title = {Collision of microswimmers in a viscous fluid.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {5}, pages = {053005}, doi = {10.1103/PhysRevE.87.053005}, pmid = {23767618}, issn = {1550-2376}, mesh = {Cell Communication/*physiology ; Cell Movement/*physiology ; Computer Simulation ; Microfluidics/*methods ; *Models, Biological ; Shear Strength ; Solutions/*chemistry ; Surface Properties ; Swimming/*physiology ; Viscosity ; }, abstract = {We investigate the effects of boundary conditions on the surface of self-propelled spherical swimmers moving in a viscous fluid with a low Reynolds number. We first show that collisions between the swimmers are impossible under the commonly used no-slip conditions. Next we demonstrate that collisions do occur if the more general Navier boundary conditions, allowing for a finite slip on the surface that produces drag, are imposed on the boundary of swimmers. The presence of a small inertia for each swimmer does not influence whether collisions occur between swimmers.}, }
@article {pmid23767615, year = {2013}, author = {Khali, S and Nebbali, R and Ameziani, DE and Bouhadef, K}, title = {Numerical investigation of non-Newtonian fluids in annular ducts with finite aspect ratio using lattice Boltzmann method.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {5}, pages = {053002}, doi = {10.1103/PhysRevE.87.053002}, pmid = {23767615}, issn = {1550-2376}, mesh = {Computer Simulation ; *Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; *Models, Theoretical ; Rheology/*instrumentation/*methods ; }, abstract = {In this work the instability of the Taylor-Couette flow for Newtonian and non-Newtonian fluids (dilatant and pseudoplastic fluids) is investigated for cases of finite aspect ratios. The study is conducted numerically using the lattice Boltzmann method (LBM). In many industrial applications, the apparatuses and installations drift away from the idealized case of an annulus of infinite length, and thus the end caps effect can no longer be ignored. The inner cylinder is rotating while the outer one and the end walls are maintained at rest. The lattice two-dimensional nine-velocity (D2Q9) Boltzmann model developed from the Bhatnagar-Gross-Krook approximation is used to obtain the flow field for fluids obeying the power-law model. The combined effects of the Reynolds number, the radius ratio, and the power-law index n on the flow characteristics are analyzed for an annular space of finite aspect ratio. Two flow modes are obtained: a primary Couette flow (CF) mode and a secondary Taylor vortex flow (TVF) mode. The flow structures so obtained are different from one mode to another. The critical Reynolds number Re(c) for the passage from the primary to the secondary mode exhibits the lowest value for the pseudoplastic fluids and the highest value for the dilatant fluids. The findings are useful for studies of the swirling flow of non-Newtonians fluids in axisymmetric geometries using LBM. The flow changes from the CF to TVF and its structure switches from the two-cells to four-cells regime for both Newtonian and dilatant fluids. Contrariwise for pseudoplastic fluids, the flow exhibits 2-4-2 structure passing from two-cells to four cells and switches again to the two-cells configuration. Furthermore, the critical Reynolds number presents a monotonic increase with the power-law index n of the non-Newtonian fluid, and as the radius ratio grows, the transition flow regimes tend to appear for higher critical Reynolds numbers.}, }
@article {pmid23762212, year = {2012}, author = {Hu, SW and Sheng, YJ and Tsao, HK}, title = {Polymer stretch in two-phase microfluidics: Effect of wall wettability.}, journal = {Biomicrofluidics}, volume = {6}, number = {2}, pages = {24130}, pmid = {23762212}, issn = {1932-1058}, abstract = {Polymer stretching in two-phase microfluidics is investigated by dissipative particle dynamics. The flow patterns can be controlled by wall wettability, flowrate ratio between two phases, and Reynolds number (Re). For neutral and partially wettable walls, segmented flows are formed and polymer stretching can be controlled by Re and segment length. At high Re, stratified flows are observed and the extension ratio can be tuned by the flowrate ratio. For nonwettable walls, slug flows are formed and polymer stretching can be controlled by Re and slug length. At high Re or flowrate ratio, annular flows are observed and high extension ratio can be easily attained.}, }
@article {pmid23746596, year = {2013}, author = {Lantz, J and Ebbers, T and Engvall, J and Karlsson, M}, title = {Numerical and experimental assessment of turbulent kinetic energy in an aortic coarctation.}, journal = {Journal of biomechanics}, volume = {46}, number = {11}, pages = {1851-1858}, doi = {10.1016/j.jbiomech.2013.04.028}, pmid = {23746596}, issn = {1873-2380}, mesh = {Angioplasty, Balloon ; Aortic Coarctation/*physiopathology/therapy ; Biomechanical Phenomena ; Blood Flow Velocity/physiology ; Computer Simulation ; Female ; Hemorheology/physiology ; Humans ; Magnetic Resonance Angiography ; Middle Aged ; *Models, Cardiovascular ; }, abstract = {The turbulent blood flow through an aortic coarctation in a 63-year old female patient was studied experimentally using magnetic resonance imaging (MRI), and numerically using computational fluid dynamics (CFD), before and after catheter intervention. Turbulent kinetic energy (TKE) was computed in the numerical model using large eddy simulation and compared with direct in vivo MRI measurements. Despite the two totally different methods to obtain TKE values, both quantitative and qualitative results agreed very well. The results showed that even though both blood flow rate and Reynolds number increased after intervention, total turbulent kinetic energy levels decreased in the coarctation. Therefore, the use of the Reynolds number alone as a measure of turbulence in cardiovascular flows should be used with caution. Furthermore, the change in flow field and kinetic energy were assessed, and it was found that before intervention a jet formed in the throat of the coarctation, which impacted the arterial wall just downstream the constriction. After intervention the jet was significantly weaker and broke up almost immediately, presumably resulting in less stress on the wall. As there was a good agreement between measurements and numerical results (the increase and decrease of integrated TKE matched measurements almost perfectly while peak values differed by approximately 1mJ), the CFD results confirmed the MRI measurements while at the same time providing high-resolution details about the flow. Thus, this preliminary study indicates that MR-based TKE measurements might be useful as a diagnostic tool when evaluating intervention outcome, while the detailed numerical results might be useful for further understanding of the flow for treatment planning.}, }
@article {pmid23741525, year = {2013}, author = {Hamadneh, N and Khan, WA and Sathasivam, S and Ong, HC}, title = {Design optimization of pin fin geometry using particle swarm optimization algorithm.}, journal = {PloS one}, volume = {8}, number = {5}, pages = {e66080}, pmid = {23741525}, issn = {1932-6203}, mesh = {*Algorithms ; *Computer Simulation ; *Models, Theoretical ; Reproducibility of Results ; }, abstract = {Particle swarm optimization (PSO) is employed to investigate the overall performance of a pin fin.The following study will examine the effect of governing parameters on overall thermal/fluid performance associated with different fin geometries, including, rectangular plate fins as well as square, circular, and elliptical pin fins. The idea of entropy generation minimization, EGM is employed to combine the effects of thermal resistance and pressure drop within the heat sink. A general dimensionless expression for the entropy generation rate is obtained by considering a control volume around the pin fin including base plate and applying the conservations equations for mass and energy with the entropy balance. Selected fin geometries are examined for the heat transfer, fluid friction, and the minimum entropy generation rate corresponding to different parameters including axis ratio, aspect ratio, and Reynolds number. The results clearly indicate that the preferred fin profile is very dependent on these parameters.}, }
@article {pmid23724953, year = {2013}, author = {Lee, MG and Shin, JH and Bae, CY and Choi, S and Park, JK}, title = {Label-free cancer cell separation from human whole blood using inertial microfluidics at low shear stress.}, journal = {Analytical chemistry}, volume = {85}, number = {13}, pages = {6213-6218}, doi = {10.1021/ac4006149}, pmid = {23724953}, issn = {1520-6882}, mesh = {Blood Cells/*chemistry ; Cell Line, Tumor ; Cell Movement/physiology ; Cell Separation/*methods ; Humans ; MCF-7 Cells ; Microfluidics/*methods ; Neoplastic Cells, Circulating/chemistry ; *Shear Strength/physiology ; *Stress, Mechanical ; }, abstract = {We report a contraction-expansion array (CEA) microchannel device that performs label-free high-throughput separation of cancer cells from whole blood at low Reynolds number (Re). The CEA microfluidic device utilizes hydrodynamic field effect for cancer cell separation, two kinds of inertial effects: (1) inertial lift force and (2) Dean flow, which results in label-free size-based separation with high throughput. To avoid cell damages potentially caused by high shear stress in conventional inertial separation techniques, the CEA microfluidic device isolates the cells with low operational Re, maintaining high-throughput separation, using nondiluted whole blood samples (hematocrit ~45%). We characterized inertial particle migration and investigated the migration of blood cells and various cancer cells (MCF-7, SK-BR-3, and HCC70) in the CEA microchannel. The separation of cancer cells from whole blood was demonstrated with a cancer cell recovery rate of 99.1%, a blood cell rejection ratio of 88.9%, and a throughput of 1.1 × 10(8) cells/min. In addition, the blood cell rejection ratio was further improved to 97.3% by a two-step filtration process with two devices connected in series.}, }
@article {pmid23719764, year = {2013}, author = {Glavan, AC and Martinez, RV and Maxwell, EJ and Subramaniam, AB and Nunes, RM and Soh, S and Whitesides, GM}, title = {Rapid fabrication of pressure-driven open-channel microfluidic devices in omniphobic R(F) paper.}, journal = {Lab on a chip}, volume = {13}, number = {15}, pages = {2922-2930}, doi = {10.1039/c3lc50371b}, pmid = {23719764}, issn = {1473-0189}, mesh = {Equipment Design ; Gases/chemistry ; Halogenation ; Microfluidic Analytical Techniques/*instrumentation ; Paper ; Permeability ; Pressure ; Silanes/chemistry ; }, abstract = {This paper describes the fabrication of pressure-driven, open-channel microfluidic systems with lateral dimensions of 45-300 microns carved in omniphobic paper using a craft-cutting tool. Vapor phase silanization with a fluorinated alkyltrichlorosilane renders paper omniphobic, but preserves its high gas permeability and mechanical properties. When sealed with tape, the carved channels form conduits capable of guiding liquid transport in the low-Reynolds number regime (i.e. laminar flow). These devices are compatible with complex fluids such as droplets of water in oil. The combination of omniphobic paper and a craft cutter enables the development of new types of valves and switches, such as "fold valves" and "porous switches," which provide new methods to control fluid flow.}, }
@article {pmid23705104, year = {2013}, author = {Asai, T and Seo, K}, title = {Aerodynamic drag of modern soccer balls.}, journal = {SpringerPlus}, volume = {2}, number = {1}, pages = {171}, pmid = {23705104}, issn = {2193-1801}, abstract = {Soccer balls such as the Adidas Roteiro that have been used in soccer tournaments thus far had 32 pentagonal and hexagonal panels. Recently, the Adidas Teamgeist II and Adidas Jabulani, respectively having 14 and 8 panels, have been used at tournaments; the aerodynamic characteristics of these balls have not yet been verified. Now, the Adidas Tango 12, having 32 panels, has been developed for use at tournaments; therefore, it is necessary to understand its aerodynamic characteristics. Through a wind tunnel test and ball trajectory simulations, this study shows that the aerodynamic resistance of the new 32-panel soccer ball is larger in the high-speed region and lower in the middle-speed region than that of the previous 14- and 8-panel balls. The critical Reynolds number of the Roteiro, Teamgeist II, Jabulani, and Tango 12 was ~2.2 × 10(5) (drag coefficient, C d ≈ 0.12), ~2.8 × 10(5) (C d ≈ 0.13), ~3.3 × 10(5) (C d ≈ 0.13), and ~2.4 × 10(5) (C d ≈ 0.15), respectively. The flight trajectory simulation suggested that the Tango 12, one of the newest soccer balls, has less air resistance in the medium-speed region than the Jabulani and can thus easily acquire large initial velocity in this region. It is considered that the critical Reynolds number of a soccer ball, as considered within the scope of this experiment, depends on the extended total distance of the panel bonds rather than the small designs on the panel surfaces.}, }
@article {pmid23698444, year = {2013}, author = {Tobias, SM and Cattaneo, F}, title = {Shear-driven dynamo waves at high magnetic Reynolds number.}, journal = {Nature}, volume = {497}, number = {7450}, pages = {463-465}, pmid = {23698444}, issn = {1476-4687}, abstract = {Astrophysical magnetic fields often display remarkable organization, despite being generated by dynamo action driven by turbulent flows at high conductivity. An example is the eleven-year solar cycle, which shows spatial coherence over the entire solar surface. The difficulty in understanding the emergence of this large-scale organization is that whereas at low conductivity (measured by the magnetic Reynolds number, Rm) dynamo fields are well organized, at high Rm their structure is dominated by rapidly varying small-scale fluctuations. This arises because the smallest scales have the highest rate of strain, and can amplify magnetic field most efficiently. Therefore most of the effort to find flows whose large-scale dynamo properties persist at high Rm has been frustrated. Here we report high-resolution simulations of a dynamo that can generate organized fields at high Rm; indeed, the generation mechanism, which involves the interaction between helical flows and shear, only becomes effective at large Rm. The shear does not enhance generation at large scales, as is commonly thought; instead it reduces generation at small scales. The solution consists of propagating dynamo waves, whose existence was postulated more than 60 years ago and which have since been used to model the solar cycle.}, }
@article {pmid23695000, year = {2013}, author = {Mizota, T and Kurogi, K and Ohya, Y and Okajima, A and Naruo, T and Kawamura, Y}, title = {The strange flight behaviour of slowly spinning soccer balls.}, journal = {Scientific reports}, volume = {3}, number = {}, pages = {1871}, doi = {10.1038/srep01871}, pmid = {23695000}, issn = {2045-2322}, abstract = {The strange three-dimensional flight behaviour of slowly spinning soccer balls is one of the most interesting and unknown phenomenon associated with the trajectories of sports balls. Many spectators have experienced numerous exciting and emotional instances while observing the curious flight behaviour of these balls. We examine the aerodynamic mechanisms of erratic ball behaviours through real flight observations, unsteady force measurements and flow pattern visualisations. The strange behaviour is elucidated by the relationship between the unsteady forces on the ball and the wake flow. The irregular changes in position for twin longitudinal vortices have already been discovered in the supercritical Reynolds number region of a sphere with a smooth surface. This finding is applicable to the strange behaviour of the flight of soccer balls with this supercritical flow. The players, spectators, and television viewers will gain greater insight into the effects of soccer ball flights.}, }
@article {pmid23687629, year = {2013}, author = {Davarnejad, R and Barati, S and Kooshki, M}, title = {CFD simulation of the effect of particle size on the nanofluids convective heat transfer in the developed region in a circular tube.}, journal = {SpringerPlus}, volume = {2}, number = {1}, pages = {192}, pmid = {23687629}, issn = {2193-1801}, abstract = {The CFD simulation of heat transfer characteristics of a nanofluid in a circular tube under constant heat flux was considered using Fluent software (version 6.3.26) in the laminar flow. Al2O3 nanoparticles in water with concentrations of 0.5%, 1.0%, 1.5%, 2% and 2.5% were used in this simulation. All of the thermo-physical properties of nanofluids were assumed to be temperature independent. Two particle sizes with average size of 20 and 50 nm were used in this research. It was concluded that heat transfer coefficient increased by increasing the Reynolds number and the concentration of nanoparticles. The maximum convective heat transfer coefficient was observed at the highest concentration of nano-particles in water (2.5%). Furthermore, the two nanofluids showed higher heat transfer than the base fluid (water) although the nanofluid with particles size of 20 nm had the highest heat transfer coefficient.}, }
@article {pmid23679518, year = {2013}, author = {Xu, Q and Brown, E and Jaeger, HM}, title = {Impact dynamics of oxidized liquid metal drops.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {4}, pages = {043012}, doi = {10.1103/PhysRevE.87.043012}, pmid = {23679518}, issn = {1550-2376}, abstract = {With exposure to air, many liquid metals spontaneously generate an oxide layer on their surface. In oscillatory rheological tests, this skin is found to introduce a yield stress that typically dominates the elastic response but can be tuned by exposing the metal to hydrochloric acid solutions of different concentration. We systematically studied the normal impact of eutectic gallium-indium (eGaIn) drops under different oxidation conditions and show how this leads to two different dynamical regimes. At low impact velocity (or low Weber number), eGaIn droplets display strong recoil and rebound from the impacted surface when the oxide layer is removed. In addition, the degree of drop deformation or spreading during impact is controlled by the oxide skin. We show that the scaling law known from ordinary liquids for the maximum spreading radius as a function of impact velocity can still be applied to the case of oxidized eGaIn if an effective Weber number We* is employed that uses an effective surface tension factoring in the yield stress. In contrast, no influence on spreading from different oxidations conditions is observed for high impact velocity. This suggests that the initial kinetic energy is mostly damped by bulk viscous dissipation. Results from both regimes can be collapsed in an impact phase diagram controlled by two variables, the maximum spreading factor P(m)=R(0)/R(m), given by the ratio of initial to maximum drop radius, and the impact number K=We*/Re(4/5), which scales with the effective Weber number We* as well as the Reynolds number Re. The data exhibit a transition from capillary to viscous behavior at a critical impact number K(c)≈0.1.}, }
@article {pmid23679512, year = {2013}, author = {Curtis, MP and Gaffney, EA}, title = {Three-sphere swimmer in a nonlinear viscoelastic medium.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {4}, pages = {043006}, doi = {10.1103/PhysRevE.87.043006}, pmid = {23679512}, issn = {1550-2376}, mesh = {*Hydrodynamics ; *Motion ; *Nonlinear Dynamics ; Rheology ; *Viscoelastic Substances ; }, abstract = {A simple model for a swimmer consisting of three colinearly linked spheres attached by rods and oscillating out of phase to break reciprocal motion is analyzed. With a prescribed forcing of the rods acting on the three spheres, the swimming dynamics are determined analytically in both a Newtonian Stokes fluid and a zero Reynolds number, nonlinear, Oldroyd-B viscoelastic fluid with Deborah numbers of order one (or less), highlighting the effects of viscoelasticity on the net displacement of swimmer. For instance, the model predicts that the three-sphere swimmer with a sinusoidal, but nonreciprocal, forcing cycle within an Oldroyd-B representation of a polymeric Boger fluid moves a greater distance with enhanced efficiency in comparison with its motility in a Newtonian fluid of the same viscosity. Furthermore, the nonlinear contributions to the viscoelastic constitutive relation, while dynamically nontrivial, are predicted a posteriori to have no effect on swimmer motility at leading order, given a prescribed forcing between spheres.}, }
@article {pmid23679508, year = {2013}, author = {Prakash, J and Lavrenteva, OM and Byk, L and Nir, A}, title = {Interaction of equal-size bubbles in shear flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {4}, pages = {043002}, doi = {10.1103/PhysRevE.87.043002}, pmid = {23679508}, issn = {1550-2376}, abstract = {The inertia-induced forces on two identical spherical bubbles in a simple shear flow at small but finite Reynolds number, for the case when the bubbles are within each other's inner viscous region, are calculated making use of the reciprocal theorem. This interaction force is further employed to model the dynamics of air bubbles injected to a viscous fluid sheared in a Couette device at the first shear flow instability where the bubbles are trapped inside the stable Taylor vortex. It was shown that, during a long time scale, the inertial interaction between the bubbles in the primary shear flow drives them away from each other and, as a result, equal-size bubbles eventually assume an ordered string with equal separation distances between all neighbors. We report on experiments showing the dynamic evolution of various numbers of bubbles. The results of the theory are in good agreement with the experimental observations.}, }
@article {pmid23679418, year = {2013}, author = {Guzmán-Lastra, F and Soto, R}, title = {Subdiffusive behavior of a dilute non-Brownian suspension under shear.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {4}, pages = {042311}, doi = {10.1103/PhysRevE.87.042311}, pmid = {23679418}, issn = {1550-2376}, abstract = {Shear-induced self-diffusion in a dilute suspension of non-Brownian spheres under a simple shear flow is studied in the limit of zero Reynolds number, for different volume fractions φ. Particles are simulated considering the first term in the multipolar expansion to take into account the long-range hydrodynamic interactions, and a repulsive force is added to avoid interpenetration. The final diffusive regime is established after a long time (t(diffusion)~φ(-1.5)), and the diffusion coefficient is proportional to φ(2), as expected in the presence of the short-range repulsive force. Before the diffusive regime is established, there is a rich subdiffusive behavior, particularly in the gradient direction. Each pairwise hydrodynamic interaction is reversible, not leading to streamline migration. Due to the incoherence of the different pair interactions, a plateau in the mean square displacement is first observed, lasting for a period that increases as φ is decreased. Then, a first diffusive regime is established due to three-particle interactions, with a diffusion coefficient of D((1))~φ(2.4). At longer times, a phenomenon similar to caging is observed. Particles diffuse for long times in the vicinity of some positions, and eventually large displacements are produced, moving the particle to a new position and resulting in transient large values of the kurtosis of the displacement distribution. This migration is produced by collisions through the repulsive potential. After several of those large displacements, the final diffusive regime is established.}, }
@article {pmid23642079, year = {2013}, author = {Shardt, O and Derksen, JJ and Mitra, SK}, title = {Simulations of droplet coalescence in simple shear flow.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {29}, number = {21}, pages = {6201-6212}, doi = {10.1021/la304919p}, pmid = {23642079}, issn = {1520-5827}, abstract = {Simulating droplet coalescence is challenging because small-scale (tens of nanometers) phenomena determine the behavior of much larger (micrometer- to millimeter-scale) droplets. In general, liquid droplets colliding in a liquid medium coalesce when the capillary number is less than a critical value. We present simulations of droplet collisions and coalescence in simple shear flow using the free-energy binary-liquid lattice Boltzmann method. In previous simulations of low-speed collisions, droplets coalesced at unrealistically high capillary numbers. Simulations of noncoalescing droplets have not been reported, and therefore, the critical capillary number for simulated collisions was unknown. By simulating droplets with radii up to 100 lattice nodes, we determine the critical capillary number for coalescence and quantify the effects of several numerical and geometric parameters. The simulations were performed with a well-resolved interface, a Reynolds number of one, and capillary numbers from 0.01 to 0.2. The ratio of the droplet radius and interface thickness has the greatest effect on the critical capillary number. As in experiments, the critical capillary number decreases with increasing droplet size. A second numerical parameter, the interface diffusivity (Péclet number) also influences the conditions for coalescence: coalescence occurs at higher capillary numbers with lower Péclet numbers (higher diffusivity). The effects of the vertical offset between the droplets and the confinement of the droplets were also studied. Physically reasonable results were obtained and provide insight into the conditions for coalescence. Simulations that match the conditions of experiments reported in the literature remain computationally impractical. However, the scale of the simulations is now sufficiently large that a comparison with experiments involving smaller droplets (≈10 μm) and lower viscosities (≈10(-6) m(2)/s, the viscosity of water) may be possible. Experiments at these conditions are therefore needed to determine the interface thickness and Péclet number that should be used for predictive simulations of coalescence phenomena.}, }
@article {pmid23641116, year = {2013}, author = {Dorfman, KD}, title = {The Fluid Mechanics of Genome Mapping.}, journal = {AIChE journal. American Institute of Chemical Engineers}, volume = {59}, number = {2}, pages = {346-354}, pmid = {23641116}, issn = {0001-1541}, support = {R01 HG005216/HG/NHGRI NIH HHS/United States ; }, }
@article {pmid23630622, year = {2013}, author = {Bredlau, JP and Mohajer, YJ and Cameron, TM and Kester, KM and Fine, ML}, title = {Characterization and generation of male courtship song in Cotesia congregata (Hymenoptera: Braconidae).}, journal = {PloS one}, volume = {8}, number = {4}, pages = {e62051}, pmid = {23630622}, issn = {1932-6203}, mesh = {Animals ; Biomechanical Phenomena ; Female ; Male ; Movement/physiology ; Sexual Behavior, Animal ; Singing/*physiology ; Video Recording ; Wasps/*physiology ; Wings, Animal/physiology ; }, abstract = {BACKGROUND: Male parasitic wasps attract females with a courtship song produced by rapid wing fanning. Songs have been described for several parasitic wasp species; however, beyond association with wing fanning, the mechanism of sound generation has not been examined. We characterized the male courtship song of Cotesia congregata (Hymenoptera: Braconidae) and investigated the biomechanics of sound production.<br><br>Courtship songs were recorded using high-speed videography (2,000 fps) and audio recordings. The song consists of a long duration amplitude-modulated "buzz" followed by a series of pulsatile higher amplitude "boings," each decaying into a terminal buzz followed by a short inter-boing pause while wings are stationary. Boings have higher amplitude and lower frequency than buzz components. The lower frequency of the boing sound is due to greater wing displacement. The power spectrum is a harmonic series dominated by wing repetition rate &#x223c;220 Hz, but the sound waveform indicates a higher frequency resonance &#x223c;5 kHz. Sound is not generated by the wings contacting each other, the substrate, or the abdomen. The abdomen is elevated during the first several wing cycles of the boing, but its position is unrelated to sound amplitude. Unlike most sounds generated by volume velocity, the boing is generated at the termination of the wing down stroke when displacement is maximal and wing velocity is zero. Calculation indicates a low Reynolds number of &#x223c;1000.<br><br>CONCLUSIONS AND SIGNIFICANCE: Acoustic pressure is proportional to velocity for typical sound sources. Our finding that the boing sound was generated at maximal wing displacement coincident with cessation of wing motion indicates that it is caused by acceleration of the wing tips, consistent with a dipole source. The low Reynolds number requires a high wing flap rate for flight and predisposes wings of small insects for sound production.}, }
@article {pmid23594696, year = {2013}, author = {Sidik, NA and Khakbaz, M and Jahanshaloo, L and Samion, S and Darus, AN}, title = {Simulation of forced convection in a channel with nanofluid by the lattice Boltzmann method.}, journal = {Nanoscale research letters}, volume = {8}, number = {1}, pages = {178}, pmid = {23594696}, issn = {1931-7573}, abstract = {This paper presents a numerical study of the thermal performance of fins mounted on the bottom wall of a horizontal channel and cooled with either pure water or an Al2O3-water nanofluid. The bottom wall of the channel is heated at a constant temperature and cooled by mixed convection of laminar flow at a relatively low temperature. The results of the numerical simulation indicate that the heat transfer rate of fins is significantly affected by the Reynolds number (Re) and the thermal conductivity of the fins. The influence of the solid volume fraction on the increase of heat transfer is more noticeable at higher values of the Re.}, }
@article {pmid23592394, year = {2013}, author = {Miloh, T}, title = {Dipolophoresis of Janus nanoparticles in a microchannel.}, journal = {Electrophoresis}, volume = {34}, number = {13}, pages = {1939-1949}, doi = {10.1002/elps.201300037}, pmid = {23592394}, issn = {1522-2683}, mesh = {Electrophoresis/*instrumentation/methods ; Hydrodynamics ; Microfluidic Analytical Techniques/*instrumentation ; *Models, Chemical ; Nanoparticles/*chemistry ; Static Electricity ; }, abstract = {A nonlinear dipolophoretic analysis is applied to analytically explain the counterintuitive experimental results of Gangwal et al. that an uncharged micro/nanosize dielectric Janus particle is attracted to the wall of a microchannel when exposed to an AC-uniform electric field in the direction parallel to the no-slip boundaries. We employ the so-called "weak" field assumption and consider a metallodielectric Janus colloid comprising two semispheres of distinct dielectric properties subject to an oscillating-uniform electric field with moderate frequency (below the Maxwell-Wagner limit). The Debye scale (ratio of electric double layer thickness to particle size) is considered unrestricted. Under the low Reynolds number hypothesis, Faxén's theorem and the Green's function (Stokeslet) method of singularities, including appropriate images with respect to the no-slip boundary, are applied under the remote-field approximation to determine the dynamics and trajectory of a small colloid moving near a wall. When assuming maximum dielectric contrasts between hemispheres and relatively low Debye scale (compared to particle radius), a rather simple relation for the equilibrium position of the colloid (i.e. tilt angle and distance from the wall) is obtained and found to be in qualitative good agreement with the experimental observations of Gangwal et al. and the predictions of Kilic and Bazant.}, }
@article {pmid25167273, year = {2013}, author = {Pacheco-Martinez, HA and Liao, L and Hill, RJ and Swift, MR and Bowley, RM}, title = {Spontaneous orbiting of two spheres levitated in a vibrated liquid.}, journal = {Physical review letters}, volume = {110}, number = {15}, pages = {154501}, doi = {10.1103/PhysRevLett.110.154501}, pmid = {25167273}, issn = {1079-7114}, abstract = {In the absence of gravity, particles can form a suspension in a liquid irrespective of the difference in density between the solid and the liquid. If such a suspension is subjected to vibration, there is relative motion between the particles and the fluid which can lead to self-organization and pattern formation. Here, we describe experiments carried out to investigate the behavior of two identical spheres suspended magnetically in a fluid, mimicking weightless conditions. Under vibration, the spheres mutually attract and, for sufficiently large vibration amplitudes, the spheres are observed to spontaneously orbit each other. The collapse of the experimental data onto a single curve indicates that the instability occurs at a critical value of the streaming Reynolds number. Simulations reproduce the observed behavior qualitatively and quantitatively, and are used to identify the features of the flow that are responsible for this instability.}, }
@article {pmid23576069, year = {2013}, author = {Kim, J and Kim, HS and Han, S and Lee, JY and Oh, JE and Chung, S and Park, HD}, title = {Hydrodynamic effects on bacterial biofilm development in a microfluidic environment.}, journal = {Lab on a chip}, volume = {13}, number = {10}, pages = {1846-1849}, doi = {10.1039/c3lc40802g}, pmid = {23576069}, issn = {1473-0189}, mesh = {Biofilms/*growth &amp; development ; Hydrodynamics ; *Microfluidic Analytical Techniques ; Models, Biological ; Pseudomonas aeruginosa/*physiology ; }, abstract = {In aquatic environments, microorganisms tend to form biofilms on surfaces to protect them from harsh conditions. The biofilms then accumulate into multilayered mat-like structures. In this study, we evaluated the effects of the hydrodynamic conditions on the ecology of biofilms produced by Pseudomonas aeruginosa (PA14). In microfluidic channels, we found that the development of biofilms was regulated by hydrodynamic conditions, but the developed biofilms also changed flow velocity by narrowing flow width. The coupled growing conditions were simplified by a new concept of consequent variables, and the dimensionless biofilm development (Ab/h(2) &amp; Ab/w(cs)(2)) was successfully expressed by the Reynolds number (Re) and the dimension of the channel (r). At low Re, higher flow rates encouraged growth of biofilms, while higher flow rates with high Re suppressed growth of biofilms. These results provide a simple model as a theoretical basis for understanding development of biofilms in microfluidic channels.}, }
@article {pmid23568531, year = {2013}, author = {Tanaka, Y and Koghure, T and Ueno, M and Sugiyama, H and Hamamoto, Y and Tamai, M and Taguchi, N and Sakamoto, H}, title = {Effects of flow patterns and hemodynamic force on vascular endothelium in the temporary arteriovenous shunt loop in rabbits.}, journal = {Journal of reconstructive microsurgery}, volume = {29}, number = {5}, pages = {331-340}, doi = {10.1055/s-0033-1343500}, pmid = {23568531}, issn = {1098-8947}, mesh = {Animals ; *Arteriovenous Shunt, Surgical/adverse effects ; Blood Flow Velocity ; Blood Viscosity ; Endothelium, Vascular/*physiopathology ; Femoral Artery/*physiopathology ; Hemodynamics/*physiology ; Heparin/pharmacology ; Male ; Rabbits ; Risk Factors ; Stress, Mechanical ; Thrombosis/*etiology ; Vascular Patency ; }, abstract = {The purpose of this study was to investigate whether there is a risk of thrombosis in the temporary arteriovenous shunt loop (TAVSL). The authors established a TAVSL model in the rabbit. Experimental groups were divided into non-heparin treated and heparin treated. The maximum blood flow volume, blood viscosity, and radius of curvature were measured, and the Reynolds number and the sheer stress were calculated. Computational fluid dynamics (CFD) was used to predict the flow pattern in the TAVSL, and these predicted data were compared with histological results. Early occlusion was noted in 70% (7/10) of the non-heparin-treated group and 22% (2/9) of the heparin-treated group. CFD analysis predicted a high shear stress at the arterial anastomosis region and the outer luminal surface of the curved section. The intimal structure at the luminal surface of the curved section was extensively lost histologically. In the patent group, severe stenosis of the lumen was noted at the apex of the loop due to an organized thrombus. Thus, thrombosis is likely to occur in the TAVSL due to endothelium injury caused by high shear stress, and this results in the formation of white thrombi at an early stage and an organized thrombus at a late stage.}, }
@article {pmid23563437, year = {2013}, author = {Nunes, MA and Fernandes, PC and Ribeiro, MH}, title = {Microtiter plates versus stirred mini-bioreactors in biocatalysis: a scalable approach.}, journal = {Bioresource technology}, volume = {136}, number = {}, pages = {30-40}, doi = {10.1016/j.biortech.2013.02.057}, pmid = {23563437}, issn = {1873-2976}, mesh = {*Biocatalysis ; *Bioreactors ; Biotechnology/*instrumentation/*methods ; Enzymes, Immobilized/metabolism ; Flavanones/metabolism ; Hydrolysis ; Kinetics ; Multienzyme Complexes/metabolism ; Polyvinyl Alcohol/chemistry ; Rheology ; beta-Glucosidase/metabolism ; }, abstract = {To place the application of miniaturized vessels as microbioreactors on a firm footing, focus has been given to engineering characterization. Studies on this matter have mostly involved carrier-free biological systems, while support-based systems have been overlooked. The present work aims to contribute to fill in such gap. Thus, it intended to establish a robust scaled down approach to identify and optimize relevant operational conditions of naringin hydrolysis by naringinase in PVA lens-shaped particles. The influence of geometric and dynamic (viz. Reynolds number) parameters was evaluated. Naringin hydrolysis in round, flat bottom MTP proved more effective than in square, pyramidal bottom. The bioconversion at MTP and stirred tank reactors scales showed that, given the 12.5-fold scale difference was in agreement between the bioconversion rates. The external mass transfer resistances were negligible as deduced from Damkohler modulus ≤1. The bioconversion was effectively scaled-up 200-fold from shaken microtiter plates to stirred tank reactors.}, }
@article {pmid23556981, year = {2013}, author = {Chekmarev, SF}, title = {Tendency to occupy a statistically dominant spatial state of the flow as a driving force for turbulent transition.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {23}, number = {1}, pages = {013144}, doi = {10.1063/1.4795279}, pmid = {23556981}, issn = {1089-7682}, mesh = {*Elementary Particles ; Entropy ; Hydrodynamics ; *Models, Statistical ; Motion ; Particle Size ; Rheology ; Time Factors ; Uncertainty ; Viscosity ; }, abstract = {The transition from laminar to turbulent fluid motion occurring at large Reynolds numbers is generally associated with the instability of the laminar flow. On the other hand, since the turbulent flow characteristically appears in the form of spatially localized structures (e.g., eddies) filling the flow field, a tendency to occupy such a structured state of the flow cannot be ruled out as a driving force for turbulent transition. To examine this possibility, we propose a simple analytical model that treats the flow as a collection of localized spatial structures, each of which consists of elementary cells in which the behavior of the particles (atoms or molecules) is uncorrelated. This allows us to introduce the Reynolds number, associating it with the ratio between the total phase volume for the system and that for the elementary cell. Using the principle of maximum entropy to calculate the most probable size distribution of the localized structures, we show that as the Reynolds number increases, the elementary cells group into the localized structures, which successfully explains turbulent transition and some other general properties of turbulent flows. An important feature of the present model is that a bridge between the spatial-statistical description of the flow and hydrodynamic equations is established. We show that the basic assumptions underlying the model, i.e., that the particles are indistinguishable and elementary volumes of phase space exist in which the state of the particles is uncertain, are involved in the derivation of the Navier-Stokes equation. Taking into account that the model captures essential features of turbulent flows, this suggests that the driving force for the turbulent transition is basically the same as in the present model, i.e., the tendency of the system to occupy a statistically dominant state plays a key role. The instability of the flow at high Reynolds numbers can then be a mechanism to initiate structural rearrangement of the flow to find this state.}, }
@article {pmid25166810, year = {2013}, author = {Wadhwa, N and Vlachos, P and Jung, S}, title = {Noncoalescence in the oblique collision of fluid jets.}, journal = {Physical review letters}, volume = {110}, number = {12}, pages = {124502}, doi = {10.1103/PhysRevLett.110.124502}, pmid = {25166810}, issn = {1079-7114}, abstract = {When two jets of fluid collide, they can "bounce" off each other, due to a thin film of air which keeps them separated. We describe the phenomenon of stable noncoalescence between two jets of the same fluid, colliding obliquely with each other. Using a simple experimental setup, we carry out a parametric study of the bouncing jets by varying the jet diameter, velocity, angle of inclination, and fluid viscosity, which suggests that the contact time of bouncing jets scales as the square root of the normal Weber number We. A dimensionless parameter K = (We sqrt[Re]/sinα)(1/2), where Re is the normal Reynolds number and α the angle of inclination of the jets, quantitatively captures the transition of colliding jets from bouncing to coalescence. This parameter draws parallels between jet coalescence and droplet splashing and indicates that the transition is governed by a surface instability. Stable and continuous noncoalescence between fluid jets makes it a good platform for experimental studies of the interaction between fluid interfaces and the properties of the interfacial air films.}, }
@article {pmid23496636, year = {2013}, author = {Fakhari, A and Lee, T}, title = {Multiple-relaxation-time lattice Boltzmann method for immiscible fluids at high Reynolds numbers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {2}, pages = {023304}, doi = {10.1103/PhysRevE.87.023304}, pmid = {23496636}, issn = {1550-2376}, mesh = {*Algorithms ; Computer Simulation ; *Models, Theoretical ; Rheology/*methods ; }, abstract = {The lattice Boltzmann method for immiscible multiphase flows with large density ratio is extended to high Reynolds number flows using a multiple-relaxation-time (MRT) collision operator, and its stability and accuracy are assessed by simulating the Kelvin-Helmholtz instability. The MRT model is successful at damping high-frequency oscillations in the kinetic energy emerging from traveling waves generated by the inclusion of curvature. Numerical results are shown to be in good agreement with prior studies using adaptive mesh refinement techniques applied to the Navier-Stokes equations. Effects of viscosity and surface tension, as well as density ratio, are investigated in terms of the Reynolds and Weber numbers. It is shown that increasing the Reynolds number results in a more chaotic interface evolution and eventually shattering of the interface, while surface tension is shown to have a stabilizing effect.}, }
@article {pmid23496617, year = {2013}, author = {Merbold, S and Brauckmann, HJ and Egbers, C}, title = {Torque measurements and numerical determination in differentially rotating wide gap Taylor-Couette flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {2}, pages = {023014}, doi = {10.1103/PhysRevE.87.023014}, pmid = {23496617}, issn = {1550-2376}, mesh = {Computer Simulation ; *Energy Transfer ; *Models, Theoretical ; Rheology/*methods ; Rotation ; Torque ; }, abstract = {We investigate experimentally and numerically turbulent Taylor-Couette flow with independently rotating cylinders and radius ratio η=0.5. The torque acting on the inner wall is measured to analyze the transverse current of azimuthal motion J(ω). The scaling of the torque with shear Reynolds number is determined for the outer cylinder at rest. For constant shear Reynolds number we investigate various ratios of angular velocities and find a torque maximum for counter-rotating cylinders that deviates from the prediction suggested by van Gils et al. [J. Fluid Mech. 706, 118 (2012)]. The direct comparison between the experiment and the numerical simulation shows a good agreement in the torques.}, }
@article {pmid23496605, year = {2013}, author = {Ni, R and Xia, KQ}, title = {Kolmogorov constants for the second-order structure function and the energy spectrum.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {2}, pages = {023002}, doi = {10.1103/PhysRevE.87.023002}, pmid = {23496605}, issn = {1550-2376}, mesh = {Computer Simulation ; *Energy Transfer ; *Models, Theoretical ; Rheology/*methods ; }, abstract = {We examine the behavior of the Kolmogorov constants C(2), C(k), and C(k1), which are, respectively, the prefactors of the second-order longitudinal structure function and the three-dimensional and one-dimensional longitudinal energy spectrum in the inertial range. We show that their ratios, C(2)/C(k1) and C(k)/C(k1), exhibit clear dependence on the microscale Reynolds number R(λ), implying that they cannot all be independent of R(λ). In particular, it is found that (C(k1)/C(2)-0.25)=1.95R(λ)(-0.68). The study further reveals that the widely used relation C(2)=4.02C(k1) holds only asymptotically when R(λ)>/~10(5). It is also found that C(2) has much stronger R(λ) dependence than either C(k) or C(k1) if the latter indeed has a systematic dependence on R(λ). We further show that the varying dependence on R(λ) of these three numbers can be attributed to the difference of the inertial range in real- and wave-number space, with the inertial range in real-space known to be much shorter than that in wave-number space.}, }
@article {pmid23487740, year = {2013}, author = {Gemmell, BJ and Sheng, J and Buskey, EJ}, title = {Compensatory escape mechanism at low Reynolds number.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {110}, number = {12}, pages = {4661-4666}, pmid = {23487740}, issn = {1091-6490}, mesh = {Animals ; Biomechanical Phenomena/physiology ; Copepoda/*physiology ; Locomotion/*physiology ; *Models, Biological ; Phytoplankton/physiology ; Predatory Behavior/*physiology ; Zooplankton/*physiology ; }, abstract = {Despite high predation pressure, planktonic copepods remain one of the most abundant groups on the planet. Their escape response provides one of most effective mechanisms to maximize evolutionary fitness. Owing to their small size (100 µm) compared with their predators (>1 mm), increasing viscosity is believed to have detrimental effects on copepods' fitness at lower temperature. Using high-speed digital holography we acquire 3D kinematics of the nauplius escape including both location and detailed appendage motion. By independently varying temperature and viscosity we demonstrate that at natural thermal extremes, contrary to conventional views, nauplii achieve equivalent escape distance while maintaining optimal velocity. Using experimental results and kinematic simulations from a resistive force theory propulsion model, we demonstrate that a shift in appendage timing creates an increase in power stroke duration relative to recovery stroke duration. This change allows the nauplius to limit losses in velocity and maintain distance during escapes at the lower bound of its natural thermal range. The shift in power stroke duration relative to recovery stroke duration is found to be regulated by the temperature dependence of swimming appendage muscle groups, not a dynamic response to viscosity change. These results show that copepod nauplii have natural adaptive mechanisms to compensate for viscosity variations with temperature but not in situations in which viscosity varies independent of temperature, such as in some phytoplankton blooms. Understanding the robustness of escapes in the wake of environmental changes such as temperature and viscosity has implications in assessing the future health of performance compensation.}, }
@article {pmid23480363, year = {2013}, author = {Bukiet, F and Soler, T and Guivarch, M and Camps, J and Tassery, H and Cuisinier, F and Candoni, N}, title = {Factors affecting the viscosity of sodium hypochlorite and their effect on irrigant flow.}, journal = {International endodontic journal}, volume = {46}, number = {10}, pages = {954-961}, doi = {10.1111/iej.12086}, pmid = {23480363}, issn = {1365-2591}, mesh = {Hot Temperature ; *Root Canal Irrigants ; Sodium Hypochlorite/*chemistry ; Surface-Active Agents/chemistry ; *Viscosity ; }, abstract = {AIM: To assess the influence of concentration, temperature and surfactant addition to a sodium hypochlorite solution on its dynamic viscosity and to calculate the corresponding Reynolds number to determine the corresponding flow regimen.<br><br>METHODOLOGY: The dynamic viscosity of the irrigant was assessed using a rotational viscometer. Sodium hypochlorite with concentrations ranging from 0.6% to 9.6% was tested at 37 and 22 &#xb0;C. A wide range of concentrations of three different surfactants was mixed in 2.4% sodium hypochlorite for viscosity measurements. The Reynolds number was calculated under each condition. Data were analysed using two-way anova.<br><br>RESULTS: There was a significant influence of sodium hypochlorite concentration (P < 0.001) and temperature (P < 0.001) on dynamic viscosity: the latter significantly increased with sodium hypochlorite concentration and decreased with temperature. A significant influence of surfactant concentration on dynamic viscosity (P < 0.001) occurred, especially for high surfactant concentrations: 6.25% for benzalkonium chloride, 15% for Tween 80 and 6.25% for Triton X-100. Reynolds number values calculated for a given flow rate (0.14 mL s(-1)), and root canal diameter (sizes 45 and 70) clearly qualified the irrigant flow regimen as laminar.<br><br>CONCLUSIONS: Dynamic viscosity increased with sodium hypochlorite and surfactant concentration but decreased with temperature. Under clinical conditions, all viscosities measured led to laminar flow. The transition between laminar and turbulent flow may be reached by modifying different parameters at the same time: increasing flow rate and temperature whilst decreasing irrigant viscosity by adding surfactants with a high value of critical micellar concentration.}, }
@article {pmid23473153, year = {2013}, author = {Alexakis, A}, title = {Large-scale magnetic fields in magnetohydrodynamic turbulence.}, journal = {Physical review letters}, volume = {110}, number = {8}, pages = {084502}, doi = {10.1103/PhysRevLett.110.084502}, pmid = {23473153}, issn = {1079-7114}, abstract = {High Reynolds number magnetohydrodynamic turbulence in the presence of zero-flux large-scale magnetic fields is investigated as a function of the magnetic field strength. For a variety of flow configurations, the energy dissipation rate [symbol: see text] follows the scaling [Symbol: see text] proportional U(rms)(3)/ℓ even when the large-scale magnetic field energy is twenty times larger than the kinetic energy. A further increase of the magnetic energy showed a transition to the [Symbol: see text] proportional U(rms)(2) B(rms)/ℓ scaling implying that magnetic shear becomes more efficient at this point at cascading the energy than the velocity fluctuations. Strongly helical configurations form nonturbulent helicity condensates that deviate from these scalings. Weak turbulence scaling was absent from the investigation. Finally, the magnetic energy spectra support the Kolmogorov spectrum k(-5/3) while kinetic energy spectra are closer to the Iroshnikov-Kraichnan spectrum k(-3/2) as observed in the solar wind.}, }
@article {pmid23464237, year = {2013}, author = {Hindasageri, V and Vedula, RP and Prabhu, SV}, title = {Thermocouple error correction for measuring the flame temperature with determination of emissivity and heat transfer coefficient.}, journal = {The Review of scientific instruments}, volume = {84}, number = {2}, pages = {024902}, doi = {10.1063/1.4790471}, pmid = {23464237}, issn = {1089-7623}, abstract = {Temperature measurement by thermocouples is prone to errors due to conduction and radiation losses and therefore has to be corrected for precise measurement. The temperature dependent emissivity of the thermocouple wires is measured by the use of thermal infrared camera. The measured emissivities are found to be 20%-40% lower than the theoretical values predicted from theory of electromagnetism. A transient technique is employed for finding the heat transfer coefficients for the lead wire and the bead of the thermocouple. This method does not require the data of thermal properties and velocity of the burnt gases. The heat transfer coefficients obtained from the present method have an average deviation of 20% from the available heat transfer correlations in literature for non-reacting convective flow over cylinders and spheres. The parametric study of thermocouple error using the numerical code confirmed the existence of a minimum wire length beyond which the conduction loss is a constant minimal. Temperature of premixed methane-air flames stabilised on 16 mm diameter tube burner is measured by three B-type thermocouples of wire diameters: 0.15 mm, 0.30 mm, and 0.60 mm. The measurements are made at three distances from the burner tip (thermocouple tip to burner tip/burner diameter = 2, 4, and 6) at an equivalence ratio of 1 for the tube Reynolds number varying from 1000 to 2200. These measured flame temperatures are corrected by the present numerical procedure, the multi-element method, and the extrapolation method. The flame temperatures estimated by the two-element method and extrapolation method deviate from numerical results within 2.5% and 4%, respectively.}, }
@article {pmid23456695, year = {2013}, author = {Krishnakumar, S and Gaudana, SB and Viswanathan, GA and Pakrasi, HB and Wangikar, PP}, title = {Rhythm of carbon and nitrogen fixation in unicellular cyanobacteria under turbulent and highly aerobic conditions.}, journal = {Biotechnology and bioengineering}, volume = {110}, number = {9}, pages = {2371-2379}, doi = {10.1002/bit.24882}, pmid = {23456695}, issn = {1097-0290}, mesh = {Biotechnology ; Carbon/*metabolism ; Carbon Dioxide/metabolism ; Cell Culture Techniques/*methods ; Chemical Phenomena ; Cyanothece/genetics/metabolism/*physiology ; Glycogen/metabolism ; *Light ; Nitrogen/metabolism ; Nitrogen Fixation/*physiology ; Oxygen/metabolism ; Transcriptome/physiology ; }, abstract = {Nitrogen fixing cyanobacteria are being increasingly explored for nitrogenase-dependent hydrogen production. Commercial success however will depend on the ability to grow these cultures at high cell densities. Photo-limitation at high cell densities leads to hindered photoautotrophic growth while turbulent conditions, which simulate flashing light effect, can lead to oxygen toxicity to the nitrogenase enzyme. Cyanothece sp. strain ATCC 51142, a known hydrogen producer, is reported to grow and fix nitrogen under moderately oxic conditions in shake flasks. In this study, we explore the growth and nitrogen fixing potential of this organism under turbulent conditions with volumetric oxygen mass transfer coefficient (KL a) values that are up to 20-times greater than in shake flasks. In a stirred vessel, the organism grows well in turbulent regime possibly due to a simulated flashing light effect with optimal growth at Reynolds number of approximately 35,000. A respiratory burst lasting for about 4 h creates anoxic conditions intracellularly with near saturating levels of dissolved oxygen in the extracellular medium. This is concomitant with complete exhaustion of intracellular glycogen storage and upregulation of nifH and nifX, the genes encoding proteins of the nitrogenase complex. Further, the rhythmic oscillations in exhaust gas CO2 and O2 profiles synchronize faithfully with those in biochemical parameters and gene expression thereby serving as an effective online monitoring tool. These results will have important implications in potential commercial success of nitrogenase-dependent hydrogen production by cyanobacteria.}, }
@article {pmid23430990, year = {2013}, author = {Salcedo, E and Treviño, C and Vargas, RO and Martínez-Suástegui, L}, title = {Stereoscopic particle image velocimetry measurements of the three-dimensional flow field of a descending autorotating mahogany seed (Swietenia macrophylla).}, journal = {The Journal of experimental biology}, volume = {216}, number = {Pt 11}, pages = {2017-2030}, doi = {10.1242/jeb.085407}, pmid = {23430990}, issn = {1477-9145}, mesh = {Biomechanical Phenomena ; Meliaceae/*anatomy &amp; histology ; Models, Biological ; Rheology ; Seeds/*anatomy &amp; histology ; Wind ; }, abstract = {An experimental investigation of near field aerodynamics of wind dispersed rotary seeds has been performed using stereoscopic digital particle image velocimetry (DPIV). The detailed three-dimensional flow structure of the leading-edge vortex (LEV) of autorotating mahogany seeds (Swietenia macrophylla) in a low-speed vertical wind tunnel is revealed for the first time. The results confirm that the presence of strong spanwise flow and strain produced by centrifugal forces through a spiral vortex are responsible for the attachment and stability of the LEV, with its core forming a cone pattern with a gradual increase in vortex size. The LEV appears at 25% of the wingspan, increases in size and strength outboard along the wing, and reaches its maximum stability and spanwise velocity at 75% of the wingspan. At a region between 90 and 100% of the wingspan, the strength and stability of the vortex core decreases and the LEV re-orientation/inflection with the tip vortex takes place. In this study, the instantaneous flow structure and the instantaneous velocity and vorticity fields measured in planes parallel to the free stream direction are presented as contour plots using an inertial and a non-inertial frame of reference. Results for the mean aerodynamic thrust coefficients as a function of the Reynolds number are presented to supplement the DPIV data.}, }
@article {pmid23427919, year = {2013}, author = {Hoppe, TJ and Moorjani, SG and Shear, JB}, title = {Generating arbitrary chemical patterns for multipoint dosing of single cells.}, journal = {Analytical chemistry}, volume = {85}, number = {7}, pages = {3746-3751}, pmid = {23427919}, issn = {1520-6882}, support = {R21 GM078228/GM/NIGMS NIH HHS/United States ; R43 MH085396/MH/NIMH NIH HHS/United States ; 1R43MH085396-01/MH/NIMH NIH HHS/United States ; }, mesh = {Animals ; Cell Culture Techniques/methods ; Cell Line, Tumor ; Fluorescent Dyes/analysis ; Laser Therapy/methods ; Microfluidic Analytical Techniques/*methods ; Microscopy/*methods ; Single-Cell Analysis/*methods ; }, abstract = {Living cells reside within anisotropic microenvironments that orchestrate a broad range of polarized responses through physical and chemical cues. To unravel how localized chemical signals influence complex behaviors, tools must be developed for establishing patterns of chemical gradients that vary over subcellular dimensions. Here, we present a strategy for addressing this critical need in which an arbitrary number of chemically distinct, subcellular dosing streams are created in real time within a microfluidic environment. In this approach, cells are cultured on a thin polymer membrane that serves as a barrier between the cell-culture environment and a reagent chamber containing multiple reagent species flowing in parallel under low Reynolds number conditions. Focal ablation of the membrane creates pores that allow solution to flow from desired regions within this reagent pattern into the cell-culture chamber, resulting in narrow, chemically distinct dosing streams. Unlike previous dosing strategies, this system provides the capacity to tailor arbitrary patterns of reagents on the fly to suit the geometry and orientation of specific cells.}, }
@article {pmid23427094, year = {2013}, author = {Yagi, T and Sato, A and Shinke, M and Takahashi, S and Tobe, Y and Takao, H and Murayama, Y and Umezu, M}, title = {Experimental insights into flow impingement in cerebral aneurysm by stereoscopic particle image velocimetry: transition from a laminar regime.}, journal = {Journal of the Royal Society, Interface}, volume = {10}, number = {82}, pages = {20121031}, pmid = {23427094}, issn = {1742-5662}, mesh = {Blood Flow Velocity ; Female ; Humans ; Intracranial Aneurysm/pathology/*physiopathology ; Middle Aged ; *Models, Cardiovascular ; Pulsatile Flow ; Rheology ; }, abstract = {This study experimentally investigated the instability of flow impingement in a cerebral aneurysm, which was speculated to promote the degradation of aneurysmal wall. A patient-specific, full-scale and elastic-wall replica of cerebral artery was fabricated from transparent silicone rubber. The geometry of the aneurysm corresponded to that found at 9 days before rupture. The flow in a replica was analysed by quantitative flow visualization (stereoscopic particle image velocimetry) in a three-dimensional, high-resolution and time-resolved manner. The mid-systolic and late-diastolic flows with a Reynolds number of 450 and 230 were compared. The temporal and spatial variations of near-wall velocity at flow impingement delineated its inherent instability at a low Reynolds number. Wall shear stress (WSS) at that site exhibited a combination of temporal fluctuation and spatial divergence. The frequency range of fluctuation was found to exceed significantly that of the heart rate. The high-frequency-fluctuating WSS appeared only during mid-systole and disappeared during late diastole. These results suggested that the flow impingement induced a transition from a laminar regime. This study demonstrated that the hydrodynamic instability of shear layer could not be neglected even at a low Reynolds number. No assumption was found to justify treating the aneurysmal haemodynamics as a fully viscous laminar flow.}, }
@article {pmid23419503, year = {2013}, author = {Wagner, GL and Lauga, E}, title = {Crawling scallop: friction-based locomotion with one degree of freedom.}, journal = {Journal of theoretical biology}, volume = {324}, number = {}, pages = {42-51}, doi = {10.1016/j.jtbi.2013.01.021}, pmid = {23419503}, issn = {1095-8541}, mesh = {Animals ; Biomechanical Phenomena ; *Friction ; *Locomotion ; *Models, Biological ; }, abstract = {Fluid-based locomotion at low Reynolds number is subject to the constraints of the scallop theorem, which dictate that body kinematics identical under a time-reversal symmetry (in particular, those with a single degree of freedom) cannot display locomotion on average. The implications of the theorem naturally compel one to ask whether similar symmetry constraints exist for locomotion in different environments. In this work we consider locomotion along a surface where forces are described by isotropic Coulomb friction. To address whether motions with a single degree of freedom can lead to transport, we analyze a model system consisting of two bodies whose separation distance undergoes periodic time variations. The behavior of the two-body system is entirely determined by the kinematic specification of their separation, the friction forces, and the mass of each body. We show that the constraints of the scallop theorem can be escaped in frictional media if two asymmetry conditions are met at the same time: the frictional forces of each body against the surface must be distinct and the time-variation of the body-body separation must vary asymmetrically in time (so quick-slow or slow-quick in the extension-contraction phases). Our results are demonstrated numerically and interpreted using asymptotic expansions.}, }
@article {pmid23410462, year = {2013}, author = {Clausen, JR}, title = {Entropically damped form of artificial compressibility for explicit simulation of incompressible flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {1}, pages = {013309}, doi = {10.1103/PhysRevE.87.013309}, pmid = {23410462}, issn = {1550-2376}, mesh = {*Algorithms ; Computer Simulation ; Elastic Modulus ; Energy Transfer ; *Models, Theoretical ; *Numerical Analysis, Computer-Assisted ; Rheology/*methods ; Viscosity ; }, abstract = {An alternative artificial compressibility (AC) scheme is proposed to allow the explicit simulation of the incompressible Navier-Stokes (INS) equations. Traditional AC schemes rely on an artificial equation of state that gives the pressure as a function of the density, which is known to enforce isentropic behavior. This behavior is nonideal, especially in viscously dominated flows. An alternative, the entropically damped artificial compressibility (EDAC) method, is proposed that employs a thermodynamic constraint to damp the pressure oscillations inherent to AC methods. The EDAC method converges to the INS in the low-Mach limit, and is consistent in both the low- and high-Reynolds-number limits, unlike standard AC schemes. The proposed EDAC method is discretized using a simple finite-difference scheme and is compared with traditional AC schemes as well as the lattice-Boltzmann method for steady lid-driven cavity flow and a transient traveling-wave problem. The EDAC method is shown to be beneficial in damping pressure and velocity-divergence oscillations when performing transient simulations. The EDAC method follows a similar derivation to the kinetically reduced local Navier-Stokes (KRLNS) method [Borok et al., Phys. Rev. E 76, 066704 (2007)]; however, the EDAC method does not rely on the grand potential as the thermodynamic variable, but instead uses the more common pressure-velocity system. Additionally, a term neglected in the KRLNS is identified that is important for accurately approximating the INS equations.}, }
@article {pmid23410432, year = {2013}, author = {Bailey, PR and Abbá, A and Tordella, D}, title = {Pressure and kinetic energy transport across the cavity mouth in resonating cavities.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {87}, number = {1}, pages = {013013}, doi = {10.1103/PhysRevE.87.013013}, pmid = {23410432}, issn = {1550-2376}, mesh = {*Algorithms ; Computer Simulation ; *Energy Transfer ; Kinetics ; *Models, Theoretical ; Pressure ; Rheology/*methods ; }, abstract = {Basic properties of the incompressible fluid motion in a rectangular cavity located along one wall of a plane channel are considered. For Mach numbers of the order of 1×10(-3) and using the incompressible formulation, we look for observable properties that can be associated with acoustic emission, which is normally observed in this kind of flow beyond a critical value of Reynolds number. The focus is put on the energy dynamics, in particular on the accumulation of energy in the cavity which takes place in the form of pressure and kinetic energy. By increasing the external forcing, we observe that the pressure flow into the cavity increases very rapidly, then peaks. However, the flow of kinetic energy, which is many orders of magnitude lower than that of the pressure, slowly but continuously grows. This leads to the pressure-kinetic energy flows ratio reaching an asymptotic state around the value 1000 for the channel bulk speed Reynolds number. It is interesting to note that beyond this threshold when the channel flow is highly unsteady-a sort of coarse turbulent flow-a sequence of high and low pressure spots is seen to depart from the downward cavity step in the statistically averaged field. The set of spots forms a steady spatial structure, a sort of damped standing wave stretching along the spanwise direction. The line joining the centers of the spots has an inclination similar to the normal to the fronts of density or pressure waves, which are observed to propagate from the downstream cavity edge in compressible cavity flows (at Mach numbers of 1×10(2) to 1×10(3), larger than those considered here). The wavelength of the standing wave is of the order of 1/8 the cavity depth and observed at the channel bulk Reynolds number, Re~2900. In this condition, the measure of the maximum pressure differences in the cavity field shows values of the order of 1×10(-1) Pa. We interpret the presence of this sort of wave as the fingerprint of the noise emission spots which could be observed in simulations where the full compressible formulation is used. The flow is studied by means of a sequence of direct numerical simulations in the Reynolds number range 25-2900. This allows the study to span across the steady laminar regime up to a first coarse turbulent regime. These results are confirmed by the good agreement with a set of laboratory results obtained at a Reynolds number one order of magnitude larger in a different cavity geometry [M. Gharib and A. Roshko, J. Fluid Mech. 177, 501 (1987)]. This leaves room for a certain degree of qualitative universality to be associated with the present findings.}, }
@article {pmid23368468, year = {2012}, author = {Soulard, O}, title = {Implications of the Monin-Yaglom relation for Rayleigh-Taylor turbulence.}, journal = {Physical review letters}, volume = {109}, number = {25}, pages = {254501}, doi = {10.1103/PhysRevLett.109.254501}, pmid = {23368468}, issn = {1079-7114}, abstract = {The aim of this letter is to assess existing theories for Rayleigh-Taylor small turbulent scales. For this purpose, we propose to adapt the Monin-Yaglom relation to the Rayleigh-Taylor turbulence context. A special emphasis is put on the inhomogeneity of the flow and on the effect of buoyancy forces. This relation is then used to show that, among existing theories, the standard Kolmogorov-Obukhov theory should apply to Rayleigh-Taylor turbulence in the limit of a large Reynolds number, large times, and small scales.}, }
@article {pmid23368443, year = {2012}, author = {Willis, AP}, title = {Optimization of the magnetic dynamo.}, journal = {Physical review letters}, volume = {109}, number = {25}, pages = {251101}, doi = {10.1103/PhysRevLett.109.251101}, pmid = {23368443}, issn = {1079-7114}, abstract = {In stars and planets, magnetic fields are believed to originate from the motion of electrically conducting fluids in their interior, through a process known as the dynamo mechanism. In this Letter, an optimization procedure is used to simultaneously address two fundamental questions of dynamo theory: "Which velocity field leads to the most magnetic energy growth?" and "How large does the velocity need to be relative to magnetic diffusion?" In general, this requires optimization over the full space of continuous solenoidal velocity fields possible within the geometry. Here the case of a periodic box is considered. Measuring the strength of the flow with the root-mean-square amplitude, an optimal velocity field is shown to exist, but without limitation on the strain rate, optimization is prone to divergence. Measuring the flow in terms of its associated dissipation leads to the identification of a single optimal at the critical magnetic Reynolds number necessary for a dynamo. This magnetic Reynolds number is found to be only 15% higher than that necessary for transient growth of the magnetic field.}, }
@article {pmid23368064, year = {2012}, author = {Schober, J and Schleicher, D and Bovino, S and Klessen, RS}, title = {Small-scale dynamo at low magnetic Prandtl numbers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {6 Pt 2}, pages = {066412}, doi = {10.1103/PhysRevE.86.066412}, pmid = {23368064}, issn = {1550-2376}, abstract = {The present-day Universe is highly magnetized, even though the first magnetic seed fields were most probably extremely weak. To explain the growth of the magnetic field strength over many orders of magnitude, fast amplification processes need to operate. The most efficient mechanism known today is the small-scale dynamo, which converts turbulent kinetic energy into magnetic energy leading to an exponential growth of the magnetic field. The efficiency of the dynamo depends on the type of turbulence indicated by the slope of the turbulence spectrum v(ℓ)∝ℓ^{ϑ}, where v(ℓ) is the eddy velocity at a scale ℓ. We explore turbulent spectra ranging from incompressible Kolmogorov turbulence with ϑ=1/3 to highly compressible Burgers turbulence with ϑ=1/2. In this work, we analyze the properties of the small-scale dynamo for low magnetic Prandtl numbers Pm, which denotes the ratio of the magnetic Reynolds number, Rm, to the hydrodynamical one, Re. We solve the Kazantsev equation, which describes the evolution of the small-scale magnetic field, using the WKB approximation. In the limit of low magnetic Prandtl numbers, the growth rate is proportional to Rm^{(1-ϑ)/(1+ϑ)}. We furthermore discuss the critical magnetic Reynolds number Rm_{crit}, which is required for small-scale dynamo action. The value of Rm_{crit} is roughly 100 for Kolmogorov turbulence and 2700 for Burgers. Furthermore, we discuss that Rm_{crit} provides a stronger constraint in the limit of low Pm than it does for large Pm. We conclude that the small-scale dynamo can operate in the regime of low magnetic Prandtl numbers if the magnetic Reynolds number is large enough. Thus, the magnetic field amplification on small scales can take place in a broad range of physical environments and amplify week magnetic seed fields on short time scales.}, }
@article {pmid23368052, year = {2012}, author = {Kim, Y and Lai, MC}, title = {Numerical study of viscosity and inertial effects on tank-treading and tumbling motions of vesicles under shear flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {6 Pt 2}, pages = {066321}, doi = {10.1103/PhysRevE.86.066321}, pmid = {23368052}, issn = {1550-2376}, mesh = {Biophysics/*methods ; Computer Simulation ; Models, Theoretical ; *Motion ; Movement ; Shear Strength ; Stress, Mechanical ; *Viscosity ; }, abstract = {An inextensible vesicle under shear flow experiences a tank-treading motion on its membrane if the viscosity contrast between the interior and exterior fluids is small. Above a critical threshold of viscosity contrast, the vesicle undergoes a tumbling bifurcation. In this paper, we extend our previous work [Kim and Lai, J. Comput. Phys. 229, 4840 (2010)] to the case of different viscosity and investigate the transition between the tank-treading and tumbling motions in detail. The present numerical results are in a good agreement with other numerical and theoretical studies qualitatively. In addition, we study the inertial effect on this transition and find that the inertial effect might inhibit the tumbling motion in favor of the tank-treading motion, which is observed recently in the literature. The critical viscosity contrast for the transition to the tumbling motion usually increases as the reduced area increases in the Stokes regime. However, we surprisingly observe that the critical viscosity contrast decreases as the reduced area increases to some point in the flow of slightly higher Reynolds number. Our numerical result also shows that the inertial effect has stronger inhibition to tumbling motion when the reduced area is small.}, }
@article {pmid23368040, year = {2012}, author = {Brouwers, JJ}, title = {Statistical description of turbulent dispersion.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {6 Pt 2}, pages = {066309}, doi = {10.1103/PhysRevE.86.066309}, pmid = {23368040}, issn = {1550-2376}, abstract = {We derive a comprehensive statistical model for dispersion of passive or almost passive admixture particles such as fine particulate matter, aerosols, smoke, and fumes in turbulent flow. The model rests on the Markov limit for particle velocity. It is in accordance with the asymptotic structure of turbulence at large Reynolds number as described by Kolmogorov. The model consists of Langevin and diffusion equations in which the damping and diffusivity are expressed by expansions in powers of the reciprocal Kolmogorov constant C_{0}. We derive solutions of O(C_{0}^{0}) and O(C_{0}^{-1}). We truncate at O(C_{0}^{-2}) which is shown to result in an error of a few percentages in predicted dispersion statistics for representative cases of turbulent flow. We reveal analogies and remarkable differences between the solutions of classical statistical mechanics and those of statistical turbulence.}, }
@article {pmid23363214, year = {2013}, author = {Kousera, CA and Wood, NB and Seed, WA and Torii, R and O'Regan, D and Xu, XY}, title = {A numerical study of aortic flow stability and comparison with in vivo flow measurements.}, journal = {Journal of biomechanical engineering}, volume = {135}, number = {1}, pages = {011003}, doi = {10.1115/1.4023132}, pmid = {23363214}, issn = {1528-8951}, mesh = {Adult ; Aorta/*physiology ; *Blood Circulation ; Female ; Humans ; *Hydrodynamics ; Models, Anatomic ; *Models, Biological ; Stress, Mechanical ; }, abstract = {The development of an engineering transitional turbulence model and its subsequent evaluation and validation for some diseased cardiovascular flows have been suggestive of its likely utility in normal aortas. The existence of experimental data from human aortas, acquired in the early 1970s with catheter-mounted hot film velocimeters, provided the opportunity to compare the performance of the model on such flows. A generic human aorta, derived from magnetic resonance anatomical and velocity images of a young volunteer, was used as the basis for varying both Reynolds number (Re) and Womersley parameter (α) to match four experimental data points from human ascending aortas, comprising two with disturbed flow and two with apparently undisturbed flow. Trials were made with three different levels of inflow turbulence intensity (Tu) to find if a single level could represent the four different cases with 4000 < Re < 10,000 and 17 < α < 26. A necessary boundary condition includes the inflow "turbulence" level, and convincing results were obtained for all four cases with inflow Tu = 1.0%, providing additional confidence in the application of the transitional model in flows in larger arteries. The Reynolds-averaged Navier-Stokes (RANS)-based shear stress transport (SST) transitional model is capable of capturing the correct flow state in the human aorta when low inflow turbulence intensity (1.0%) is specified.}, }
@article {pmid23363125, year = {2013}, author = {Vaik, I and Paál, G}, title = {Flow simulations on an organ pipe foot model.}, journal = {The Journal of the Acoustical Society of America}, volume = {133}, number = {2}, pages = {1102-1110}, doi = {10.1121/1.4773861}, pmid = {23363125}, issn = {1520-8524}, mesh = {*Acoustics ; *Computer Simulation ; *Models, Theoretical ; Motion ; *Music ; *Numerical Analysis, Computer-Assisted ; Oscillometry ; *Sound ; Time Factors ; }, abstract = {The present paper shows numerical simulations of the flow responsible for the sound generation in an organ pipe. Only the foot model of the organ pipe (i.e., with the resonator detached) is investigated by two-dimensional incompressible CFD simulations. It is shown that in spite of the moderately high Reynolds number (Re≈2350) no turbulence modeling is necessary. Free jet simulation (foot model without the upper lip) showed that the jet oscillates due to its natural instability. The velocity profile, the centerline and the width of the jet is determined at different heights above the flue. Edge tone simulations (foot model with the upper lip) were carried out having the upper lip at a constant height but at different x positions. It was found that the strongest and most stable edge tone oscillation occurs if the lower left corner of the upper lip is in the centerline of the jet (optimum position). When the upper lip is far from its optimum position the oscillation of the jet is rather due to the natural instability of the jet than the edge tone phenomenon. The results agree well with the experimental results of Außerlechner et al. [J. Acoust. Soc. Am. 126, 878-886 (2009)] and Außerlechner (Ph.D. thesis, Universität Stuttgart, Stuttgart, Germany) and with former results of the authors [Paál and Vaik, Int. J. Heat Fluid Flow 28, 575-586 (2007); Paál and Vaik, in Conference on Modelling Fluid Flow (CMFF'09), Budapest, Hungary].}, }
@article {pmid23363089, year = {2013}, author = {Lam, GC and Leung, RC and Tang, SK}, title = {Aeroacoustics of T-junction merging flow.}, journal = {The Journal of the Acoustical Society of America}, volume = {133}, number = {2}, pages = {697-708}, doi = {10.1121/1.4773351}, pmid = {23363089}, issn = {1520-8524}, mesh = {*Acoustics/instrumentation ; Computer Simulation ; Equipment Design ; *Models, Theoretical ; Motion ; Noise/prevention &amp; control ; Numerical Analysis, Computer-Assisted ; Pressure ; Rheology ; *Sound ; Time Factors ; }, abstract = {This paper reports a numerical study of the aeroacoustics of merging flow at T-junction. The primary focus is to elucidate the acoustic generation by the flow unsteadiness. The study is conducted by performing direct aeroacoustic simulation approach, which solves the unsteady compressible Navier-Stokes equations and the perfect gas equation of state simultaneously using the conservation element and solution element method. For practical flows, the Reynolds number based on duct width is usually quite high (>10(5)). In order to properly account for the effects of flow turbulence, a large eddy simulation methodology together with a wall modeling derived from the classical logarithm wall law is adopted. The numerical simulations are performed in two dimensions and the acoustic generation physics at different ratios of side-branch to main duct flow velocities VR (=0.5,0.67,1.0,2.0) are studied. Both the levels of unsteady interactions of merging flow structures and the efficiency of acoustic generation are observed to increase with VR. Based on Curle's analogy, the major acoustic source is found to be the fluctuating wall pressure induced by the flow unsteadiness occurred in the downstream branch. A scaling between the wall fluctuating force and the efficiency of the acoustic generation is also derived.}, }
@article {pmid23326222, year = {2013}, author = {Chindapol, N and Kaandorp, JA and Cronemberger, C and Mass, T and Genin, A}, title = {Modelling growth and form of the scleractinian coral Pocillopora verrucosa and the influence of hydrodynamics.}, journal = {PLoS computational biology}, volume = {9}, number = {1}, pages = {e1002849}, pmid = {23326222}, issn = {1553-7358}, mesh = {Animals ; Anthozoa/*growth &amp; development ; Finite Element Analysis ; *Hydrodynamics ; *Models, Biological ; Tomography, X-Ray Computed ; }, abstract = {The growth of scleractinian corals is strongly influenced by the effect of water motion. Corals are known to have a high level of phenotypic variation and exhibit a diverse range of growth forms, which often contain a high level of geometric complexity. Due to their complex shape, simulation models represent an important option to complement experimental studies of growth and flow. In this work, we analyzed the impact of flow on coral's morphology by an accretive growth model coupled with advection-diffusion equations. We performed simulations under no-flow and uni-directional flow setup with the Reynolds number constant. The relevant importance of diffusion to advection was investigated by varying the diffusion coefficient, rather than the flow speed in Péclet number. The flow and transport equations were coupled and solved using COMSOL Multiphysics. We then compared the simulated morphologies with a series of Computed Tomography (CT) scans of scleractinian corals Pocillopora verrucosa exposed to various flow conditions in the in situ controlled flume setup. As a result, we found a similar trend associated with the increasing Péclet for both simulated forms and in situ corals; that is uni-directional current tends to facilitate asymmetrical growth response resulting in colonies with branches predominantly developed in the upstream direction. A closer look at the morphological traits yielded an interesting property about colony symmetry and plasticity induced by uni-directional flow. Both simulated and in situ corals exhibit a tendency where the degree of symmetry decreases and compactification increases in conjunction with the augmented Péclet thus indicates the significant importance of hydrodynamics.}, }
@article {pmid23325520, year = {2014}, author = {Nocke, H and Meyer, F and Lessmann, V}, title = {[Aspects of vascular physiology in clinical and vascular surgical practice: basic principles of vascular mechanics].}, journal = {Zentralblatt fur Chirurgie}, volume = {139}, number = {5}, pages = {499-507}, doi = {10.1055/s-0032-1327967}, pmid = {23325520}, issn = {1438-9592}, mesh = {Blood Pressure/*physiology ; Cardiovascular Diseases/*physiopathology/*surgery ; *Cardiovascular Physiological Phenomena ; Hemodynamics/*physiology ; Humans ; Models, Cardiovascular ; Muscle, Smooth, Vascular/*physiopathology ; Pulsatile Flow/*physiology ; Reference Values ; Vascular Stiffness/*physiology ; }, abstract = {To be able to evaluate properly a vascular problem, basic concepts of vascular physiology need to be considered, as they have been taught in physiology for a long time. This article deals with selected definitions and laws of passive vascular mechanics, subdivided into parameters of vascular filling and parameters of vascular flow. PARAMETERS OF VASCULAR FILLING: During vascular filling the transmural pressure distends the vascular wall until it is balanced by the wall tension. The extent of this distension up to the point of balance depends on the elasticity of the wall. Transmural pressure, wall tension and elasticity are defined, and their respective importance is described by clinical examples, e.g. aneurysm and varix. PARAMETERS OF VASCULAR FLOW: The vascular flow can be divided into stationary and pulsating components. Both components are relevant for the bloodstream. Since the blood flow is directed in the circuit, it can be understood in first approximation as stationary ("direct current").The direct current model uses only the average values of the pulsating variables. The great advantage of the direct current model is that it can be described with simple laws, which are not valid without reservation, but often allow a first theoretical approach to a vascular problem: Ohm's law, driving pressure, flow resistance, Hagen-Poiseuille law, wall shear stress, law of continuity, Bernoulli's equation and Reynold's number are described and associated with clinical examples.The heart is a pressure-suction pump and produces a pulsating flow, the pulse. The pulse runs with pulse wave velocity, which is much larger than the blood flow velocity, through the arterial vascular system. During propagation, the pulse has to overcome the wave resistance (impedance). Wherever the wave resistance changes, e.g., at vascular bifurcations and in the periphery, it comes to reflections. The incident (forward) and reflected (backward) waves are superimposed to yield the resulting pulse wave. This pulse wave allows one to distinguish pressure and flow pulse by measurement. Both are described separately, and their respective clinical meaning is illustrated by appropriate examples, e.g., arterial stiffness and pre-/postocclusive high/low resistance flow, respectively.}, }
@article {pmid23319607, year = {2013}, author = {Rodenborn, B and Chen, CH and Swinney, HL and Liu, B and Zhang, HP}, title = {Propulsion of microorganisms by a helical flagellum.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {110}, number = {5}, pages = {E338-47}, pmid = {23319607}, issn = {1091-6490}, mesh = {*Algorithms ; *Bacterial Physiological Phenomena ; Computer Simulation ; Flagella/*physiology ; *Models, Biological ; Movement/physiology ; Rotation ; Torque ; }, abstract = {The swimming of a bacterium or a biomimetic nanobot driven by a rotating helical flagellum is often interpreted using the resistive force theory developed by Gray and Hancock and by Lighthill, but this theory has not been tested for a range of physically relevant parameters. We test resistive force theory in experiments on macroscopic swimmers in a fluid that is highly viscous so the Reynolds number is small compared to unity, just as for swimming microorganisms. The measurements are made for the range of helical wavelengths λ, radii R, and lengths L relevant to bacterial flagella. The experiments determine thrust, torque, and drag, thus providing a complete description of swimming driven by a rotating helix at low Reynolds number. Complementary numerical simulations are conducted using the resistive force theories, the slender body theories of Lighthill and Johnson, and the regularized Stokeslet method. The experimental results differ qualitatively and quantitatively from the predictions of resistive force theory. The difference is especially large for and/or , parameter ranges common for bacteria. In contrast, the predictions of Stokeslet and slender body analyses agree with the laboratory measurements within the experimental uncertainty (a few percent) for all λ, R, and L. We present code implementing the slender body, regularized Stokeslet, and resistive force theories; thus readers can readily compute force, torque, and drag for any bacterium or nanobot driven by a rotating helical flagellum.}, }
@article {pmid23315132, year = {2012}, author = {Uchida, N and Golestanian, R}, title = {Hydrodynamic synchronization between objects with cyclic rigid trajectories.}, journal = {The European physical journal. E, Soft matter}, volume = {35}, number = {12}, pages = {9813}, pmid = {23315132}, issn = {1292-895X}, mesh = {Cilia ; Flagella ; *Hydrodynamics ; *Models, Theoretical ; Rotation ; }, abstract = {Synchronization induced by long-range hydrodynamic interactions is attracting attention as a candidate mechanism behind coordinated beating of cilia and flagella. Here we consider a minimal model of hydrodynamic synchronization in the low Reynolds number limit. The model consists of rotors, each of which assumed to be a rigid bead making a fixed trajectory under periodically varying driving force. By a linear analysis, we derive the necessary and sufficient conditions for a pair of rotors to synchronize in phase. We also derive a non-linear evolution equation for their phase difference, which is reduced to minimization of an effective potential. The effective potential is calculated for a variety of trajectory shapes and geometries (either bulk or substrated), for which the stable and metastable states of the system are identified. Finite size of the trajectory induces asymmetry of the potential, which also depends sensitively on the tilt of the trajectory. Our results show that flexibility of cilia or flagella is not a requisite for their synchronized motion, in contrast to previous expectations. We discuss the possibility to directly implement the model and verify our results by optically driven colloids.}, }
@article {pmid23293067, year = {2013}, author = {Kim, JW and Xi, J and Si, XA}, title = {Dynamic growth and deposition of hygroscopic aerosols in the nasal airway of a 5-year-old child.}, journal = {International journal for numerical methods in biomedical engineering}, volume = {29}, number = {1}, pages = {17-39}, doi = {10.1002/cnm.2490}, pmid = {23293067}, issn = {2040-7947}, mesh = {Administration, Intranasal ; Aerosols/*pharmacology ; Child, Preschool ; Humans ; Male ; *Models, Biological ; *Nasal Cavity ; }, abstract = {Hygroscopic growth within the human respiratory tract can be significant, which may notably alter the behavior and fate of the inhaled aerosols. The objective of this study is to evaluate the hygroscopic effects upon the transport and deposition of nasally inhaled fine-regime aerosols in children. A physiologically realistic nasal-laryngeal airway model was developed based on magnetic resonance imaging of a 5-year-old boy. Temperature and relative humidity field were simulated using the low Reynolds number k - ε turbulence model and chemical specie transport model under a spectrum of four thermo-humidity conditions. Particle growth and transport were simulated using a well validated Lagrangian tracking model coupled with a user-defined hygroscopic growth module. The subsequent aerosol depositions for the four inhalation scenarios were evaluated on a multiscale basis such as total, subregional, and cellular-level depositions. Results of this study show that a supersaturated humid environment is possible in the nasal turbinate region and can lead to significant condensation growth (d / d(0) > 10) of nasally inhaled aerosols. Depositions in the nasal airway can also be greatly enhanced by condensation growth with appropriate inhalation temperature and humidity. For subsaturated and mild inhalation conditions, the hygroscopic effects were found to be nonsignificant for total depositions, while exerting a large impact upon localized depositions.}, }
@article {pmid23280552, year = {2013}, author = {Spruell, C and Baker, AB}, title = {Analysis of a high-throughput cone-and-plate apparatus for the application of defined spatiotemporal flow to cultured cells.}, journal = {Biotechnology and bioengineering}, volume = {110}, number = {6}, pages = {1782-1793}, pmid = {23280552}, issn = {1097-0290}, support = {DP2 OD008716/OD/NIH HHS/United States ; }, mesh = {Cell Culture Techniques/*instrumentation/*methods ; Cells, Cultured ; Computer Simulation ; Endothelial Cells/cytology ; High-Throughput Screening Assays/*instrumentation ; Humans ; Stress, Mechanical ; Viscosity ; }, abstract = {The shear stresses derived from blood flow regulate many aspects of vascular and immunobiology. In vitro studies on the shear stress-mediated mechanobiology of endothelial cells have been carried out using systems analogous to the cone-and-plate viscometer in which a rotating, low-angle cone applies fluid shear stress to cells grown on an underlying, flat culture surface. We recently developed a device that could perform high-throughput studies on shear-mediated mechanobiology through the rotation of cone-tipped shafts in a standard 96-well culture plate. Here, we present a model of the three-dimensional flow within the culture wells with a rotating, cone-tipped shaft. Using this model we examined the effects of modifying the design parameters of the system to allow the device to create a variety of flow profiles. We first examined the case of steady-state flow with the shaft rotating at constant angular velocity. By varying the angular velocity and distance of the cone from the underlying plate we were able to create flow profiles with controlled shear stress gradients in the radial direction within the plate. These findings indicate that both linear and non-linear spatial distributions in shear stress can be created across the bottom of the culture plate. In the transition and "parallel shaft" regions of the system, the angular velocities needed to provide high levels of physiological shear stress (5 Pa) created intermediate Reynolds number Taylor-Couette flow. In some cases, this led to the development of a flow regime in which stable helical vortices were created within the well. We also examined the system under oscillatory and pulsatile motion of the shaft and demonstrated minimal time lag between the rotation of the cone and the shear stress on the cell culture surface.}, }
@article {pmid24957058, year = {2013}, author = {Ochando-Pulido, JM and Hodaifa, G and Victor-Ortega, MD and Martinez-Ferez, A}, title = {Performance modeling and cost analysis of a pilot-scale reverse osmosis process for the final purification of olive mill wastewater.}, journal = {Membranes}, volume = {3}, number = {4}, pages = {285-297}, pmid = {24957058}, issn = {2077-0375}, abstract = {A secondary treatment for olive mill wastewater coming from factories working with the two-phase olive oil production process (OMW-2) has been set-up on an industrial scale in an olive oil mill in the premises of Jaén (Spain). The secondary treatment comprises Fenton-like oxidation followed by flocculation-sedimentation and filtration through olive stones. In this work, performance modelization and preliminary cost analysis of a final reverse osmosis (RO) process was examined on pilot scale for ulterior purification of OMW-2 with the goal of closing the loop of the industrial production process. Reduction of concentration polarization on the RO membrane equal to 26.3% was provided upon increment of the turbulence over the membrane to values of Reynolds number equal to 2.6 × 104. Medium operating pressure (25 bar) should be chosen to achieve significant steady state permeate flux (21.1 L h-1 m-2) and minimize membrane fouling, ensuring less than 14.7% flux drop and up to 90% feed recovery. Under these conditions, irreversible fouling below 0.08 L h-2 m-2 bar-1 helped increase the longevity of the membrane and reduce the costs of the treatment. For 10 m3 day-1 OMW-2 on average, 47.4 m2 required membrane area and 0.87 € m-3 total costs for the RO process were estimated.}, }
@article {pmid24891756, year = {2013}, author = {Siddique, W and El-Gabry, L and Shevchuk, IV and Fransson, TH}, title = {Validation and Analysis of Numerical Results for a Two-Pass Trapezoidal Channel With Different Cooling Configurations of Trailing Edge.}, journal = {Journal of turbomachinery}, volume = {135}, number = {1}, pages = {0110271-0110278}, pmid = {24891756}, issn = {0889-504X}, abstract = {High inlet temperatures in a gas turbine lead to an increase in the thermal efficiency of the gas turbine. This results in the requirement of cooling of gas turbine blades/vanes. Internal cooling of the gas turbine blade/vanes with the help of two-pass channels is one of the effective methods to reduce the metal temperatures. In particular, the trailing edge of a turbine vane is a critical area, where effective cooling is required. The trailing edge can be modeled as a trapezoidal channel. This paper describes the numerical validation of the heat transfer and pressure drop in a trapezoidal channel with and without orthogonal ribs at the bottom surface. A new concept of ribbed trailing edge has been introduced in this paper which presents a numerical study of several trailing edge cooling configurations based on the placement of ribs at different walls. The baseline geometries are two-pass trapezoidal channels with and without orthogonal ribs at the bottom surface of the channel. Ribs induce secondary flow which results in enhancement of heat transfer; therefore, for enhancement of heat transfer at the trailing edge, ribs are placed at the trailing edge surface in three different configurations: first without ribs at the bottom surface, then ribs at the trailing edge surface in-line with the ribs at the bottom surface, and finally staggered ribs. Heat transfer and pressure drop is calculated at Reynolds number equal to 9400 for all configurations. Different turbulent models are used for the validation of the numerical results. For the smooth channel low-Re k-ɛ model, realizable k-ɛ model, the RNG k-ω model, low-Re k-ω model, and SST k-ω models are compared, whereas for ribbed channel, low-Re k-ɛ model and SST k-ω models are compared. The results show that the low-Re k-ɛ model, which predicts the heat transfer in outlet pass of the smooth channels with difference of +7%, underpredicts the heat transfer by -17% in case of ribbed channel compared to experimental data. Using the same turbulence model shows that the height of ribs used in the study is not suitable for inducing secondary flow. Also, the orthogonal rib does not strengthen the secondary flow rotational momentum. The comparison between the new designs for trailing edge shows that if pressure drop is acceptable, staggered arrangement is suitable for the outlet pass heat transfer. For the trailing edge wall, the thermal performance for the ribbed trailing edge only was found about 8% better than other configurations.}, }
@article {pmid23229757, year = {2012}, author = {Seto, R and Botet, R and Auernhammer, GK and Briesen, H}, title = {Restructuring of colloidal aggregates in shear flow: coupling interparticle contact models with Stokesian dynamics.}, journal = {The European physical journal. E, Soft matter}, volume = {35}, number = {12}, pages = {9805}, pmid = {23229757}, issn = {1292-895X}, abstract = {A method to couple interparticle contact models with Stokesian dynamics (SD) is introduced to simulate colloidal aggregates under flow conditions. The contact model mimics both the elastic and plastic behavior of the cohesive connections between particles within clusters. Owing to this, clusters can maintain their structures under low stress while restructuring or even breakage may occur under sufficiently high stress conditions. SD is an efficient method to deal with the long-ranged and many-body nature of hydrodynamic interactions for low Reynolds number flows. By using such a coupled model, the restructuring of colloidal aggregates under shear flows with stepwise increasing shear rates was studied. Irreversible compaction occurs due to the increase of hydrodynamic stress on clusters. Results show that the greater part of the fractal clusters are compacted to rod-shaped packed structures, while the others show isotropic compaction.}, }
@article {pmid23224111, year = {2012}, author = {Leoni, M and Liverpool, TB}, title = {Translations and rotations at low Reynolds number: a study of simple model swimmers with finite amplitude strokes.}, journal = {The European physical journal. E, Soft matter}, volume = {35}, number = {12}, pages = {9803}, pmid = {23224111}, issn = {1292-895X}, mesh = {Humans ; *Models, Theoretical ; Rotation ; Swimming/*physiology ; }, abstract = {We present a simple dynamical model of self-propeller at low Reynolds number in which self-propulsion is achieved via rotary elements (rotors). In this model by changing the sense of rotation of the rotors, the self-propeller can switch between a "linear swimming" phase where it swims in a straight line and a "tumbling" phase in which it can change direction in a controllable way via a global rotation of its body. We study the dynamics of this propeller in detail. To do this we provide an analytic framework within which the non-perturbative aspects of the internal dynamics can be treated allowing us to study the swimming process for arbitrary values of the swimmer deformations. Using it, we compute the averages (over a deformation cycle) of a number of characteristic properties of the swimmer such as its self-propulsion velocity, the dissipated power, its efficiency and the fluid flow patterns it generates. We compare these results to the corresponding average quantities for another class of model swimmers, where self-propulsion is achieved via periodic translations. Finally, we provide an explanation of why non-perturbative results can be obtained for these models using the geometrical language of gauge theory.}, }
@article {pmid23215676, year = {2013}, author = {Mattei, TA and Morris, M and Nowak, K and Smith, D and Yee, J and Goulart, CR and Zborowski, A and Lin, JJ}, title = {Addressing the siphoning effect in new shunt designs by decoupling the activation pressure and the pressure gradient across the valve.}, journal = {Journal of neurosurgery. Pediatrics}, volume = {11}, number = {2}, pages = {181-187}, doi = {10.3171/2012.10.PEDS11561}, pmid = {23215676}, issn = {1933-0715}, mesh = {*Cerebrospinal Fluid ; Cerebrospinal Fluid Shunts/*instrumentation/methods ; *Computer Simulation ; Equipment Design ; Humans ; Hydrocephalus/*physiopathology/*surgery ; *Hydrodynamics ; *Intracranial Pressure ; }, abstract = {OBJECT: Although several improvements have been observed in the past few years in shunt technology, currently available systems still present several associated problems. Among these, overdrainage along with its complications remains one of the great challenges for new shunt designs. To address the so-called siphoning effect, the authors provide a practical example of how it is possible to decouple the activation pressure and the pressure gradient across the valve through a 3-key component system. In this new shunt design, the flow is expected to depend only on the intracranial pressure and not on the pressure gradient across the valve, thus avoiding the so-called siphoning effect.<br><br>METHODS: The authors used computer models to theoretically evaluate the mechanical variables involved in the operation of the newly designed valve, such as the fluid's Reynolds number, proximal pressure, distal pressure, pressure gradient, actual flow rate, and expected flow rate. After fabrication of the first superscaled model, the authors performed benchmark tests to analyze the performance of the new shunt prototype, and the obtained data were compared with the results predicted by the previous mathematical models.<br><br>RESULTS: The final design of the new paddle wheel valve with the 3-key component antisiphoning system was tested in the hydrodynamics laboratory to prove that the siphoning effect did not occur. According to the calculations obtained using the LabVIEW program during the experiments, each time the distal pressure decreased without an increase in the proximal pressure (despite the range of the pressure gradient), the pin blocked the spinning of the paddle wheels, and the calculated fluid velocity through the system tended to zero. Such a situation was significantly different from the expected flow rate for such a pressure gradient in a siphoning situation without the new antisiphon system.<br><br>CONCLUSIONS: The design of this new prototype with a 3-key component antisiphoning system demonstrated that it is possible to decouple the activation pressure and the pressure gradient across the valve, avoiding the siphoning effect. Although further developments are necessary to provide a model compatible to clinical use, the authors believe that this new prototype illustrates the possibility of successfully addressing the siphoning effect by using a simple 3-key component system that is able to decouple the activation pressure and the pressure gradient across the valve by using a separate pressure chamber. It is expected that such proof of concept may significantly contribute to future shunt designs attempting to address the problem of overdrainage due to the siphoning effect.}, }
@article {pmid23214882, year = {2012}, author = {Urzhumov, YA and Smith, DR}, title = {Flow stabilization with active hydrodynamic cloaks.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {5 Pt 2}, pages = {056313}, doi = {10.1103/PhysRevE.86.056313}, pmid = {23214882}, issn = {1550-2376}, mesh = {Computer Simulation ; *Hydrodynamics ; *Models, Theoretical ; Refractometry/*methods ; Rheology/*methods ; }, abstract = {We demonstrate that fluid flow cloaking solutions, based on active hydrodynamic metamaterials, exist for two-dimensional flows past a cylinder in a wide range of Reynolds numbers (Re's), up to approximately 200. Within the framework of the classical Brinkman equation for homogenized porous flow, we demonstrate using two different methods that such cloaked flows can be dynamically stable for Re's in the range of 5-119. The first highly efficient method is based on a linearization of the Brinkman-Navier-Stokes equation and finding the eigenfrequencies of the least stable eigenperturbations; the second method is a direct numerical integration in the time domain. We show that, by suppressing the von Kármán vortex street in the weakly turbulent wake, porous flow cloaks can raise the critical Reynolds number up to about 120 or five times greater than for a bare uncloaked cylinder.}, }
@article {pmid23214877, year = {2012}, author = {Shi, L and Pan, TW and Glowinski, R}, title = {Lateral migration and equilibrium shape and position of a single red blood cell in bounded Poiseuille flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {5 Pt 2}, pages = {056308}, doi = {10.1103/PhysRevE.86.056308}, pmid = {23214877}, issn = {1550-2376}, mesh = {Animals ; Blood Flow Velocity/*physiology ; Cell Movement/*physiology ; Cell Polarity ; Cell Size ; Cells, Cultured ; Computer Simulation ; Erythrocytes/*physiology ; Humans ; Membrane Fluidity/*physiology ; *Models, Cardiovascular ; Shear Strength/physiology ; }, abstract = {Lateral migration and equilibrium shape and position of a single red blood cell (RBC) in bounded two-dimensional Poiseuille flows are investigated by using an immersed boundary method. An elastic spring model is applied to simulate the skeleton structure of a RBC membrane. We focus on studying the properties of lateral migration of a single RBC in Poiseuille flows by varying the initial position, the initial angle, the swelling ratio (s), the membrane bending stiffness of RBC (k{b}), the maximum velocity of fluid flow (u{max}), and the degree of confinement. The combined effect of the deformability, the degree of confinement, and the shear gradient of the Poiseuille flow make the RBCs migrate toward a certain cross-sectional equilibrium position, which lies either on the center line of the channel or off center line. For s>0.8, the speed of the migration at the beginning decreases as one increases the swelling ratio s. But for s<0.8, the speed of the migration at the beginning is an increasing function of the swelling ratio s. Two motions of oscillation and vacillating breathing (swing) of RBCs are observed. The distance Y{d} between the cell mass center of the equilibrium position and the center line of the channel increases with increasing the Reynolds number Re and reaches a peak, then decreases with increasing Re. The peak of Re is a decreasing function of the swelling ratio (s<1.0). The cell membrane energy of the equilibrium position is an increasing function as Re increases. The slipper-shaped cell is more stable than the parachute-shaped one in the sense that the energy stored in the former is lower than that in the latter. For a given Re, the bigger the swelling ratio (s<1.0), the lower the cell membrane energy.}, }
@article {pmid23214698, year = {2012}, author = {Wei, T and Livescu, D}, title = {Late-time quadratic growth in single-mode Rayleigh-Taylor instability.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {4 Pt 2}, pages = {046405}, doi = {10.1103/PhysRevE.86.046405}, pmid = {23214698}, issn = {1550-2376}, abstract = {The growth of the two-dimensional single-mode Rayleigh-Taylor instability (RTI) at low Atwood number (A=0.04) is investigated using Direct Numerical Simulations. The main result of the paper is that, at long times and sufficiently high Reynolds numbers, the bubble acceleration becomes stationary, indicating mean quadratic growth. This is contrary to the general belief that single-mode Rayleigh-Taylor instability reaches a constant bubble velocity at long times. At unity Schmidt number, the development of the instability is strongly influenced by the perturbation Reynolds number, defined as Rep≡λsqrt[Agλ/(1+A)]/ν. Thus, the instability undergoes different growth stages at low and high Rep. A new stage, chaotic development, was found at sufficiently high Rep values, after the reacceleration stage. During the chaotic stage, the instability experiences seemingly random acceleration and deceleration phases, as a result of complex vortical motions, with strong dependence on the initial perturbation shape (i.e., wavelength, amplitude, and diffusion thickness). Nevertheless, our results show that the mean acceleration of the bubble front becomes constant at late times, with little influence from the initial shape of the interface. As Rep is lowered to small values, the later instability stages, chaotic development, reacceleration, potential flow growth, and even the exponential growth described by linear stability theory, are subsequently no longer reached. Therefore, the results suggest a minimum Reynolds number and a minimum development time necessary to achieve all stages of single-mode RTI development, requirements which were not satisfied in the previous studies of single-mode RTI.}, }
@article {pmid23214675, year = {2012}, author = {Huang, H and Wu, Y and Lu, X}, title = {Shear viscosity of dilute suspensions of ellipsoidal particles with a lattice Boltzmann method.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {4 Pt 2}, pages = {046305}, doi = {10.1103/PhysRevE.86.046305}, pmid = {23214675}, issn = {1550-2376}, abstract = {The intrinsic viscosities for prolate and oblate spheroidal suspensions in a dilute Newtonian fluid are studied using a three-dimensional lattice Boltzmann method. Through directly calculated viscous dissipation, the minimum and maximum intrinsic viscosities and the period of the tumbling state all agree well with the analytical solution for particles with different aspect ratios. This numerical test verifies the analysis on maximum and minimum intrinsic viscosities. Different behavior patterns of transient intrinsic viscosity in a period are analyzed in detail. A phase lag between the transient intrinsic viscosity and the orientation of the particle at finite Reynolds number (Re) is found and attributed to fluid and particle inertia. At lower Re, the phase lag increases with Re. There exists a critical Reynolds number Rea at which the phase lag begins to decrease with Re. The Rea depends on the aspect ratio of the particle. We found that both the intrinsic viscosity and the period change linearly with Re when Re<Rea (low-Re regime) and nonlinearly when Re>Rea (high-Re regime). In the high-Re regime, the dependence of the period on Re is consistent with a scaling law, and the dependence of the intrinsic viscosity on Re is well described by second-degree polynomial fits.}, }
@article {pmid23214641, year = {2012}, author = {Castrejón-Pita, AA and Castrejón-Pita, JR and Hutchings, IM}, title = {Experimental observation of von Kármán vortices during drop impact.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {4 Pt 2}, pages = {045301}, doi = {10.1103/PhysRevE.86.045301}, pmid = {23214641}, issn = {1550-2376}, abstract = {The observation of von Kármán type vortices during the impact of water droplets onto a pool of water is reported. Shadowgraph imaging and laser-sheet visualization are used to document these events. The appearance of these vortices occurs within theoretically predicted regions in a Reynolds-splash number parameter space. In addition, and also in agreement with theoretical predictions, smooth splashing, with vortices absent, is found for smaller Reynolds number.}, }
@article {pmid23205152, year = {2012}, author = {McCormick, SM and Seil, JT and Smith, DS and Tan, F and Loth, F}, title = {Transitional Flow in a Cylindrical Flow Chamber for Studies at the Cellular Level.}, journal = {Cardiovascular engineering and technology}, volume = {3}, number = {4}, pages = {439-449}, pmid = {23205152}, issn = {1869-4098}, support = {R01 HL055296/HL/NHLBI NIH HHS/United States ; }, abstract = {Fluid shear stress is an important regulator of vascular and endothelial cell (EC) functions. Its effect is dependent not only on magnitude but also on flow type. Although laminar flow predominates in the vasculature, transitional flow can occur and is thought to play a role in vascular diseases. While a great deal is known about the mechanisms and signaling cascades through which laminar shear stress regulates cells, little is known on how transitional shear stress regulates cells. To better understand the response of endothelial cells to transitional shear stress, a novel cylindrical flow chamber was designed to expose endothelial cells to a transitional flow environment similar to that found in vivo. The velocity profiles within the transitional flow chamber at Reynolds numbers 2200 and 3000 were measured using laser Doppler anemometry (LDA). At both Reynolds numbers, the velocity profiles are blunt (non-parabolic) with fluctuations larger than 5% of the velocity at the center of the pipe indicating the flows are transitional. Based on near wall velocity measurements and well established data for flow at these Reynolds numbers, the wall shear stress was estimated to be 3-4 and 5-6 dynes/cm(2) for Reynolds number 2200 and 3000, respectively. In contrast to laminar shear stress, no cell alignment was observed under transitional shear stress at both Reynolds numbers. However, transitional shear stress at the higher Reynolds number caused cell elongation similar to that of laminar shear stress at 3 dynes/cm(2). The fluctuating component of the wall shear stress may be responsible for these differences. The transitional flow chamber will facilitate cellular studies to identify the mechanisms through which transitional shear stress alters EC biology, which will assist in the development of vascular therapeutic treatments.}, }
@article {pmid25552745, year = {2012}, author = {Attia, JA and McKinley, IM and Moreno-Magana, D and Pilon, L}, title = {Convective heat transfer in foams under laminar flow in pipes and tube bundles.}, journal = {International journal of heat and mass transfer}, volume = {55}, number = {25-26}, pages = {7823-7831}, pmid = {25552745}, issn = {0017-9310}, support = {R25 GM055052/GM/NIGMS NIH HHS/United States ; }, abstract = {The present study reports experimental data and scaling analysis for forced convection of foams and microfoams in laminar flow in circular and rectangular tubes as well as in tube bundles. Foams and microfoams are pseudoplastic (shear thinning) two-phase fluids consisting of tightly packed bubbles with diameters ranging from tens of microns to a few millimeters. They have found applications in separation processes, soil remediation, oil recovery, water treatment, food processes, as well as in fire fighting and in heat exchangers. First, aqueous solutions of surfactant Tween 20 with different concentrations were used to generate microfoams with various porosity, bubble size distribution, and rheological behavior. These different microfoams were flowed in uniformly heated circular tubes of different diameter instrumented with thermocouples. A wide range of heat fluxes and flow rates were explored. Experimental data were compared with analytical and semi-empirical expressions derived and validated for single-phase power-law fluids. These correlations were extended to two-phase foams by defining the Reynolds number based on the effective viscosity and density of microfoams. However, the local Nusselt and Prandtl numbers were defined based on the specific heat and thermal conductivity of water. Indeed, the heated wall was continuously in contact with a film of water controlling convective heat transfer to the microfoams. Overall, good agreement between experimental results and model predictions was obtained for all experimental conditions considered. Finally, the same approach was shown to be also valid for experimental data reported in the literature for laminar forced convection of microfoams in rectangular minichannels and of macrofoams across aligned and staggered tube bundles with constant wall heat flux.}, }
@article {pmid23194395, year = {2013}, author = {Atlar, M and Unal, B and Unal, UO and Politis, G and Martinelli, E and Galli, G and Davies, C and Williams, D}, title = {An experimental investigation of the frictional drag characteristics of nanostructured and fluorinated fouling-release coatings using an axisymmetric body.}, journal = {Biofouling}, volume = {29}, number = {1}, pages = {39-52}, doi = {10.1080/08927014.2012.745856}, pmid = {23194395}, issn = {1029-2454}, mesh = {Biofouling/*prevention &amp; control ; Dimethylpolysiloxanes/*chemistry ; Fluorine/chemistry ; Friction ; Hydrodynamics ; Laser-Doppler Flowmetry ; Nanostructures/*chemistry ; Polymers/*chemistry ; Surface Properties ; }, abstract = {The hydrodynamic performance of two, recently developed, nanostructured and fluorinated polymer coatings was explored in a systematic experimental study using the Newcastle University Cavitation Tunnel. The experiments consisted of testing the two coatings on an axisymmetric body apparatus to measure their boundary layer flow and frictional drag simultaneously. The tests also included a smooth reference surface as well as a state-of-the-art commercial fouling-release coating (Intersleek(®) 900). The boundary layer measurements were performed using a two-dimensional Laser Doppler Velocimetry (LDV) system whilst the direct frictional force measurements were taken using a special load cell installed in the testing body. Careful surface roughness measurements of the test surfaces were also performed including the use of a non-contact high precision laser profilometer. The tests and subsequent analysis of the data highlighted the exceptionally good frictional properties of all the coatings tested as well as some of the drag benefits of the new polymer coatings in the investigated Reynolds number range.}, }
@article {pmid23192329, year = {2013}, author = {Mikhal, J and Geurts, BJ}, title = {Development and application of a volume penalization immersed boundary method for the computation of blood flow and shear stresses in cerebral vessels and aneurysms.}, journal = {Journal of mathematical biology}, volume = {67}, number = {6-7}, pages = {1847-1875}, pmid = {23192329}, issn = {1432-1416}, mesh = {Blood Flow Velocity/*physiology ; Brain/*blood supply ; Cerebral Arteries/*physiology ; Computer Simulation ; Hemodynamics/physiology ; Humans ; Intracranial Aneurysm/*physiopathology ; *Models, Cardiovascular ; }, abstract = {A volume-penalizing immersed boundary method is presented for the simulation of laminar incompressible flow inside geometrically complex blood vessels in the human brain. We concentrate on cerebral aneurysms and compute flow in curved brain vessels with and without spherical aneurysm cavities attached. We approximate blood as an incompressible Newtonian fluid and simulate the flow with the use of a skew-symmetric finite-volume discretization and explicit time-stepping. A key element of the immersed boundary method is the so-called masking function. This is a binary function with which we identify at any location in the domain whether it is 'solid' or 'fluid', allowing to represent objects immersed in a Cartesian grid. We compare three definitions of the masking function for geometries that are non-aligned with the grid. In each case a 'staircase' representation is used in which a grid cell is either 'solid' or 'fluid'. Reliable findings are obtained with our immersed boundary method, even at fairly coarse meshes with about 16 grid cells across a velocity profile. The validation of the immersed boundary method is provided on the basis of classical Poiseuille flow in a cylindrical pipe. We obtain first order convergence for the velocity and the shear stress, reflecting the fact that in our approach the solid-fluid interface is localized with an accuracy on the order of a grid cell. Simulations for curved vessels and aneurysms are done for different flow regimes, characterized by different values of the Reynolds number (Re). The validation is performed for laminar flow at Re = 250, while the flow in more complex geometries is studied at Re = 100 and Re = 250, as suggested by physiological conditions pertaining to flow of blood in the circle of Willis.}, }
@article {pmid23188458, year = {2013}, author = {Beas-Catena, A and Sánchez-Mirón, A and García-Camacho, F and Contreras-Gómez, A and Molina-Grima, E}, title = {Adaptation of the Spodoptera exigua Se301 insect cell line to grow in serum-free suspended culture. Comparison of SeMNPV productivity in serum-free and serum-containing media.}, journal = {Applied microbiology and biotechnology}, volume = {97}, number = {8}, pages = {3373-3381}, doi = {10.1007/s00253-012-4576-0}, pmid = {23188458}, issn = {1432-0614}, mesh = {Animals ; Baculoviridae/*growth &amp; development ; Cell Culture Techniques/*methods ; Cell Line ; Culture Media, Serum-Free ; *Genetic Vectors ; Spodoptera ; }, abstract = {Spodoptera exigua Se301 cells have been successfully adapted to two different commercial serum-free media (SFM; Ex-Cell 420 and Serum-Free Insect Medium-1) by gradually reducing the 10 %-added serum-containing medium content from 100 % to 0 % (v/v) in suspended cultures. Both direct adaptation to a serum-free medium and cell growth in the absence of protective additives against fluid dynamic stress [polyvinyl pyrrolidone and polyvinyl alcohol] and disaggregation [dextran sulfate] proved impossible. Cells grew reproducibly in both SFMs once the serum had been completely removed, although the use of Ex-Cell 420 resulted in higher growth rates and cell densities. Turbulence was sufficiently high to reduce growth rates and final cell densities at the highest Reynolds number investigated, although no clear influence of agitation was observed on virus productivity. Both attached and suspended Se301 cell cultures were successfully infected with the SeMNPV baculovirus. Cells adapted to different conditions (attached or suspended culture, serum-containing or serum-free medium) showed different occlusion bodies productivities at the two multiplicities of infection assayed (0.1 and 0.5).}, }
@article {pmid23185060, year = {2013}, author = {Lozovatsky, ID and Fernando, HJ}, title = {Mixing efficiency in natural flows.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {371}, number = {1982}, pages = {20120213}, doi = {10.1098/rsta.2012.0213}, pmid = {23185060}, issn = {1364-503X}, abstract = {It is argued that the mixing efficiency of naturally occurring stratified shear flows, γ=Rf/(1-Rf), where Rf is the flux Richardson number, is dependent on at least two governing parameters: the gradient Richardson number Ri and the buoyancy Reynolds number Re(b)=ε/vN(2). It is found that, in the range approximately 0.03<Ri<0.4, which spans 10(4)<Re(b)<10(6), the mixing efficiency obtained via direct measurements of fluxes and property gradients in the stable atmospheric boundary layer and homogeneous/stationary balance equations of turbulent kinetic energy (TKE) is nominally similar to that evaluated using the scalar balance equations. Outside these Ri and Re(b) ranges, the commonly used flux-estimation methodology based on homogeneity and stationarity of TKE equations breaks down (e.g. buoyancy effects are unimportant, energy flux divergence is significant or flow is non-stationary). In a wide range, 0.002<Ri<1, the mixing efficiency increases with Ri, but decreases with Re(b). When Ri is in the proximity of Ri(cr)∼0.1-0.25, γ can be considered a constant γ≈0.16-0.2. The results shed light on the wide variability of γ noted in previous studies.}, }
@article {pmid23179247, year = {2013}, author = {Bedkihal, S and Kumaradas, JC and Rohlf, K}, title = {Steady flow through a constricted cylinder by multiparticle collision dynamics.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {12}, number = {5}, pages = {929-939}, doi = {10.1007/s10237-012-0454-z}, pmid = {23179247}, issn = {1617-7940}, mesh = {Computer Simulation ; Hemorheology/*physiology ; Humans ; *Models, Cardiovascular ; }, abstract = {The flow characterization of blood through healthy and diseased flow geometries is of interest to researchers and clinicians alike, as it may allow for early detection, and monitoring, of cardiovascular disease. In this paper, we use a numerically efficient particle-based flow model called multiparticle collision dynamics (MPC for short) to study the effect of compressibility and slip of flow of a Newtonian fluid through a cylinder with a local constriction. We use a cumulative averaging method to compare our MPC results to the finite-element solution of the incompressible no-slip Navier-Stokes equations in the same geometry. We concentrate on low Reynolds number flows [[Formula: see text]] and quantify important differences observed between the MPC results and the Navier-Stokes solution in constricted geometries. In particular, our results show that upstream recirculating zones can form with the inclusion of slip and compressibility, which are not observed in the flow of an incompressible Newtonian fluid using the no-slip assumption, but have been observed experimentally for blood. Important flow features are also presented that could be used as indicators to observe compressibility and slip in experimental data where near-wall data may be difficult to obtain. Finally, we found that the cumulative averaging method used is ideal for steady particle-based flow methods, as macroscopic no-slip is readily obtained using the MPC bounce-back rule. Generally, a small spurious slip is seen using other averaging methods such as weighted spatial averages or averages over several runs, and the bounce-back rule has to be modified so as to achieve macroscopic no-slip. No modifications of the bounce-back rule were required for our simulations.}, }
@article {pmid23178038, year = {2013}, author = {Sznitman, J}, title = {Respiratory microflows in the pulmonary acinus.}, journal = {Journal of biomechanics}, volume = {46}, number = {2}, pages = {284-298}, doi = {10.1016/j.jbiomech.2012.10.028}, pmid = {23178038}, issn = {1873-2380}, mesh = {Animals ; Humans ; *Models, Biological ; Pulmonary Alveoli/*physiology ; Pulmonary Ventilation/*physiology ; }, abstract = {Over the past few decades, our understanding of the fluid mechanics characterizing the pulmonary acinus of the lungs has been fundamentally revisited. In the present paper, we review the current knowledge of acinar convective airflows and their role in determining the fate of inhaled aerosols in the distal regions of the lungs. We discuss the influential body of computational and experimental efforts following the revealing bolus studies initiated by Heyder et al. (1988) that have dramatically advanced our description of acinar flow phenomena. In particular, we characterize the range of complex flow topologies that exist locally in alveolar cavities and describe the ensuing convective mechanisms known to generate kinematic irreversibility in the acinus, despite low-Reynolds-number flows. By using dimensional analysis, we shed some light on the intimate coupling that arises in the pulmonary acinus between diffusive, convective and sedimentation mechanisms for aerosol deposition. Finally, we evoke some of the critical challenges that lie ahead in predicting accurately the deposition of inhaled particles across the acinar region and give a brief outlook toward novel approaches for resolving acinar flow dynamics at the real scale.}, }
@article {pmid23155481, year = {2012}, author = {Itoh, SI and Itoh, K}, title = {New thermodynamical force in plasma phase space that controls turbulence and turbulent transport.}, journal = {Scientific reports}, volume = {2}, number = {}, pages = {860}, pmid = {23155481}, issn = {2045-2322}, abstract = {Physics of turbulence and turbulent transport has been developed on the central dogma that spatial gradients constitute the controlling parameters, such as Reynolds number and Rayleigh number. Recent experiments with the nonequilibrium plasmas in magnetic confinement devices, however, have shown that the turbulence and transport change much faster than global parameters, after an abrupt change of heating power. Here we propose a theory of turbulence in inhomogeneous magnetized plasmas, showing that the heating power directly influences the turbulence. New mechanism, that an external source couples with plasma fluctuations in phase space so as to affect turbulence, is investigated. A new thermodynamical force in phase-space, i.e., the derivative of heating power by plasma pressure, plays the role of new control parameter, in addition to spatial gradients. Following the change of turbulence, turbulent transport is modified accordingly. The condition under which this new effect can be observed is also evaluated.}, }
@article {pmid23127040, year = {2012}, author = {Keiter, PA and Gamboa, EJ and Huntington, CM and Kuranz, CC}, title = {Concept to diagnose mix with imaging x-ray Thomson scattering.}, journal = {The Review of scientific instruments}, volume = {83}, number = {10}, pages = {10E534}, doi = {10.1063/1.4732185}, pmid = {23127040}, issn = {1089-7623}, abstract = {Turbulent mixing of two fluid species is a ubiquitous problem, prevalent in systems such as inertial confinement fusion (ICF) capsule implosions, supernova remnants, and other astrophysical systems. In complex, high Reynolds number compressible high energy density (HED) flows such as these, hydrodynamic instabilities initiate the turbulent mixing process, which can then feedback and alter the mean hydrodynamic motion through nonlinear processes. In order to predict how these systems evolve under turbulent conditions, models are used. However, these models require detailed quantitative data to validate and constrain their detailed physics models as well as improve them. Providing this much needed data is currently at the forefront of HED research but is proving elusive due to a lack of available diagnostics capable of directly measuring detailed flow variables. Thomson scattering is a promising technique in this regard as it provides fundamental conditions of the flow (ρ, T, Zbar) due to its direct interaction with the small scales of the fluid or plasma and was recently considered as a possible mix diagnostic. With the development of imaging x-ray Thomson scattering (IXRTS) obtaining spatial profiles of these variables is within reach. We propose a novel use of the IXRTS technique that will provide more detailed quantitative data required for model validation in mix experiments.}, }
@article {pmid23109382, year = {2012}, author = {Shahriari, S and Kadem, L and Rogers, BD and Hassan, I}, title = {Smoothed particle hydrodynamics method applied to pulsatile flow inside a rigid two-dimensional model of left heart cavity.}, journal = {International journal for numerical methods in biomedical engineering}, volume = {28}, number = {11}, pages = {1121-1143}, doi = {10.1002/cnm.2482}, pmid = {23109382}, issn = {2040-7947}, mesh = {Biomedical Engineering ; Computer Simulation ; Heart Ventricles/*anatomy &amp; histology ; Hemorheology/physiology ; Humans ; Hydrodynamics ; Mathematical Concepts ; *Models, Cardiovascular ; Pulsatile Flow ; Ventricular Function, Left/*physiology ; }, abstract = {This paper aims to extend the application of smoothed particle hydrodynamics (SPH), a meshfree particle method, to simulate flow inside a model of the heart's left ventricle (LV). This work is considered the first attempt to simulate flow inside a heart cavity using a meshfree particle method. Simulating this kind of flow, characterized by high pulsatility and moderate Reynolds number using SPH is challenging. As a consequence, validation of the computational code using benchmark cases is required prior to simulating the flow inside a model of the LV. In this work, this is accomplished by simulating an unsteady oscillating flow (pressure amplitude: A = 2500 N ∕ m(3) and Womersley number: W(o) = 16) and the steady lid-driven cavity flow (Re = 3200, 5000). The results are compared against analytical solutions and reference data to assess convergence. Then, both benchmark cases are combined and a pulsatile jet in a cavity is simulated and the results are compared with the finite volume method. Here, an approach to deal with inflow and outflow boundary conditions is introduced. Finally, pulsatile inlet flow in a rigid model of the LV is simulated. The results demonstrate the ability of SPH to model complex cardiovascular flows and to track the history of fluid properties. Some interesting features of SPH are also demonstrated in this study, including the relation between particle resolution and sound speed to control compressibility effects and also order of convergence in SPH simulations, which is consistently demonstrated to be between first-order and second-order at the moderate Reynolds numbers investigated.}, }
@article {pmid23097503, year = {2013}, author = {Sareh, S and Rossiter, J and Conn, A and Drescher, K and Goldstein, R}, title = {Swimming like algae: biomimetic soft artificial cilia.}, journal = {Journal of the Royal Society, Interface}, volume = {10}, number = {78}, pages = {20120666}, pmid = {23097503}, issn = {1742-5662}, mesh = {Cilia/metabolism ; *Motion ; Volvox/cytology/*physiology ; }, abstract = {Cilia are used effectively in a wide variety of biological systems from fluid transport to thrust generation. Here, we present the design and implementation of artificial cilia, based on a biomimetic planar actuator using soft-smart materials. This actuator is modelled on the cilia movement of the alga Volvox, and represents the cilium as a piecewise constant-curvature robotic actuator that enables the subsequent direct translation of natural articulation into a multi-segment ionic polymer metal composite actuator. It is demonstrated how the combination of optimal segmentation pattern and biologically derived per-segment driving signals reproduce natural ciliary motion. The amenability of the artificial cilia to scaling is also demonstrated through the comparison of the Reynolds number achieved with that of natural cilia.}, }
@article {pmid23083247, year = {2012}, author = {Scatamacchia, R and Biferale, L and Toschi, F}, title = {Extreme events in the dispersions of two neighboring particles under the influence of fluid turbulence.}, journal = {Physical review letters}, volume = {109}, number = {14}, pages = {144501}, doi = {10.1103/PhysRevLett.109.144501}, pmid = {23083247}, issn = {1079-7114}, abstract = {We present a numerical study of two-particle dispersion from point sources in three-dimensional incompressible homogeneous and isotropic turbulence at Reynolds number Re≃300. Tracer particles are emitted in bunches from localized sources smaller than the Kolmogorov scale. We report the first quantitative evidence, supported by an unprecedented statistics, of the deviations of relative dispersion from Richardson's picture. Deviations are due to extreme events of pairs separating much faster than average, and of pairs remaining close for long time. The two classes of events are the fingerprints of complete different physics, the former dominated by inertial subrange and large-scale fluctuations, and the latter by dissipation subrange. A comparison of the relative separation in surrogate white-in-time velocity field, with correct viscous-, inertial-, and integral-scale properties, allows us to assess the importance of temporal correlations along tracer trajectories.}, }
@article {pmid23076403, year = {2013}, author = {Gurovich, AN and Braith, RW}, title = {Enhanced external counterpulsation creates acute blood flow patterns responsible for improved flow-mediated dilation in humans.}, journal = {Hypertension research : official journal of the Japanese Society of Hypertension}, volume = {36}, number = {4}, pages = {297-305}, doi = {10.1038/hr.2012.169}, pmid = {23076403}, issn = {1348-4214}, mesh = {Adult ; Algorithms ; Analysis of Variance ; Blood Flow Velocity/physiology ; Blood Pressure/physiology ; Brachial Artery/anatomy &amp; histology/physiology ; Counterpulsation/*methods ; Data Interpretation, Statistical ; Echocardiography, Doppler ; Endothelium, Vascular/physiology ; Femoral Artery/anatomy &amp; histology/physiology ; Humans ; Hyperemia/physiopathology ; Male ; Regional Blood Flow/*physiology ; Vasodilation/*physiology ; Young Adult ; }, abstract = {Enhanced external counterpulsation (EECP) is a FDA-approved treatment for patients with coronary artery disease and unstable angina. Although beneficial effects of EECP have been linked to central/cardiac adaptations, recent findings have shown peripheral/vascular effects. Here, we sought to determine EECP-induced blood flow patterns and their association with vascular function. The present study was designed to investigate endothelium-mediated arterial vasodilation changes after one 45-min session of either EECP or Sham EECP in 18 randomly assigned apparently healthy, young men (25±4 years). Brachial (b) and femoral (f) flow-mediated dilation (FMD) were assessed before and within 10 min after completing EECP or Sham. After 20 min of EECP, peak blood flow velocity (V) and brachial and femoral artery diameters (D) were recorded live for 2 min. In addition, a blood sample was drawn from the earlobe to determine hematocrit and then to calculate blood viscosity (μ) and density (ρ), Reynolds number (Re=V*D*ρ/μ), and endothelial shear stress (ESS=2μ*V/D). EECP increased retrograde shear stress and retrograde-turbulent blood flow in the femoral artery and antegrade-laminar shear stress in the brachial artery. fFMD was increased after EECP compared with Sham and baseline (fFMD=13.1±3.7 vs. 7.9±4.6% and 7.8±4.5%, respectively, P<0.05) and bFMD was increased after EECP compared with baseline (bFMD=10.6±4.8 vs. 7.0±3.5%, P<0.05), despite different blood flow patterns. These results provide novel evidence that a single session of EECP-induced blood flow patterns improve endothelial function in peripheral muscular conduit arteries.}, }
@article {pmid23057236, year = {2012}, author = {Tripathi, D and Bég, OA}, title = {A study of unsteady physiological magneto-fluid flow and heat transfer through a finite length channel by peristaltic pumping.}, journal = {Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine}, volume = {226}, number = {8}, pages = {631-644}, doi = {10.1177/0954411912449946}, pmid = {23057236}, issn = {0954-4119}, mesh = {Animals ; Body Fluids/*physiology ; Computer Simulation ; Humans ; Magnetic Fields ; *Models, Biological ; Peristalsis/*physiology ; Pulsatile Flow/*physiology ; Rheology/*methods ; }, abstract = {Magnetohydrodynamic peristaltic flows arise in controlled magnetic drug targeting, hybrid haemodynamic pumps and biomagnetic phenomena interacting with the human digestive system. Motivated by the objective of improving an understanding of the complex fluid dynamics in such flows, we consider in the present article the transient magneto-fluid flow and heat transfer through a finite length channel by peristaltic pumping. Reynolds number is small enough and the wavelength to diameter ratio is large enough to negate inertial effects. Analytical solutions for temperature field, axial velocity, transverse velocity, pressure gradient, local wall shear stress, volume flowrate and averaged volume flowrate are obtained. The effects of the transverse magnetic field, Grashof number and thermal conductivity on the flow patterns induced by peristaltic waves (sinusoidal propagation along the length of channel) are studied using graphical plots. The present study identifies that greater pressure is required to propel the magneto-fluid by peristaltic pumping in comparison to a non-conducting Newtonian fluid, whereas, a lower pressure is required if heat transfer is effective. The analytical solutions further provide an important benchmark for future numerical simulations.}, }
@article {pmid23053449, year = {2012}, author = {Sahari, A and Headen, D and Behkam, B}, title = {Effect of body shape on the motile behavior of bacteria-powered swimming microrobots (BacteriaBots).}, journal = {Biomedical microdevices}, volume = {14}, number = {6}, pages = {999-1007}, doi = {10.1007/s10544-012-9712-1}, pmid = {23053449}, issn = {1572-8781}, mesh = {Biomechanical Phenomena ; Drug Carriers ; *Equipment Design ; Escherichia coli/*cytology ; Models, Theoretical ; Nanoparticles/*chemistry ; Robotics/*instrumentation/methods ; Viscosity ; }, abstract = {Swimming microrobots are envisioned to impact minimally invasive diagnosis, localized treatment of diseases, and environmental monitoring. Dynamics of micro-scale swimming robots falls in the realm of low Reynolds number, where viscous forces exerted on the robots are dominant over inertia. Viscous forces developed at the interface of the swimming microrobots and the surrounding fluid are a strong function of the body geometry. In this work, a collection of bacteria-powered micro-robots (BacteriaBots) with prolate spheroid, barrel, and bullet-shaped bodies is fabricated and the influence of body shape on the dynamics of the BacteriaBots is investigated. We have experimentally demonstrated that using non-spherical geometries increases the mean directionality of the motion of the BacteriaBots but does not significantly affect their average speed compared with their spherical counterparts. We have also demonstrated that directionality of non-spherical BacteriaBots depends on the aspect ratio of the body and for the case of prolate spheroid, a higher aspect ratio of two led to a larger directionality compared to their low aspect ratio counterparts.}, }
@article {pmid23047705, year = {2012}, author = {Arroyo, M and Heltai, L and Millán, D and DeSimone, A}, title = {Reverse engineering the euglenoid movement.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {109}, number = {44}, pages = {17874-17879}, pmid = {23047705}, issn = {1091-6490}, support = {240487/ERC_/European Research Council/International ; }, mesh = {Biomechanical Phenomena ; Biophysics ; *Euglenida/physiology ; }, abstract = {Euglenids exhibit an unconventional motility strategy amongst unicellular eukaryotes, consisting of large-amplitude highly concerted deformations of the entire body (euglenoid movement or metaboly). A plastic cell envelope called pellicle mediates these deformations. Unlike ciliary or flagellar motility, the biophysics of this mode is not well understood, including its efficiency and molecular machinery. We quantitatively examine video recordings of four euglenids executing such motions with statistical learning methods. This analysis reveals strokes of high uniformity in shape and pace. We then interpret the observations in the light of a theory for the pellicle kinematics, providing a precise understanding of the link between local actuation by pellicle shear and shape control. We systematically understand common observations, such as the helical conformations of the pellicle, and identify previously unnoticed features of metaboly. While two of our euglenids execute their stroke at constant body volume, the other two exhibit deviations of about 20% from their average volume, challenging current models of low Reynolds number locomotion. We find that the active pellicle shear deformations causing shape changes can reach 340%, and estimate the velocity of the molecular motors. Moreover, we find that metaboly accomplishes locomotion at hydrodynamic efficiencies comparable to those of ciliates and flagellates. Our results suggest new quantitative experiments, provide insight into the evolutionary history of euglenids, and suggest that the pellicle may serve as a model for engineered active surfaces with applications in microfluidics.}, }
@article {pmid23041872, year = {2012}, author = {He, S and Chen, F and Liu, K and Yang, Q and Liu, H and Bian, H and Meng, X and Shan, C and Si, J and Zhao, Y and Hou, X}, title = {Fabrication of three-dimensional helical microchannels with arbitrary length and uniform diameter inside fused silica.}, journal = {Optics letters}, volume = {37}, number = {18}, pages = {3825-3827}, doi = {10.1364/ol.37.003825}, pmid = {23041872}, issn = {1539-4794}, mesh = {Equipment Design ; Equipment Failure Analysis ; Flow Injection Analysis/*instrumentation ; *Lasers ; Microfluidic Analytical Techniques/*instrumentation ; Silicon Dioxide/*chemistry/*radiation effects ; }, abstract = {We demonstrate an improved femtosecond laser irradiation followed by chemical etching process to create complex three-dimensional (3D) microchannels with arbitrary length and uniform diameter inside fused silica. A segmented chemical etching method of introducing extra access ports and a secondary power compensation is presented, which enables the fabrication of uniform 3D helical microchannels with length of 1.140 cm and aspect-ratio of 522. Based on this method, a micromixer which consists of a long helical microchannel and a y-tape microchannel was created inside the fused silica. We measured the mixing properties of the micromixer by injecting the phenolphthalein and NaOH solution through the two inlets of the y-tape microchannel. A rapid and efficient mixing was achieved in the 3D micromixer at a low Reynolds number.}, }
@article {pmid23031025, year = {2012}, author = {Sen, A and Mininni, PD and Rosenberg, D and Pouquet, A}, title = {Anisotropy and nonuniversality in scaling laws of the large-scale energy spectrum in rotating turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {3 Pt 2}, pages = {036319}, doi = {10.1103/PhysRevE.86.036319}, pmid = {23031025}, issn = {1550-2376}, mesh = {*Algorithms ; *Anisotropy ; Computer Simulation ; *Energy Transfer ; *Models, Chemical ; *Nonlinear Dynamics ; Rheology/*methods ; }, abstract = {Rapidly rotating turbulent flow is characterized by the emergence of columnar structures that are representative of quasi-two-dimensional behavior of the flow. It is known that when energy is injected into the fluid at an intermediate scale Lf, it cascades towards smaller as well as larger scales. In this paper we analyze the flow in the inverse cascade range at a small but fixed Rossby number, Rof≈0.05. Several numerical simulations with helical and nonhelical forcing functions are considered in periodic boxes with unit aspect ratio. In order to resolve the inverse cascade range with reasonably large Reynolds number, the analysis is based on large eddy simulations which include the effect of helicity on eddy viscosity and eddy noise. Thus, we model the small scales and resolve explicitly the large scales. We show that the large-scale energy spectrum has at least two solutions: one that is consistent with Kolmogorov-Kraichnan-Batchelor-Leith phenomenology for the inverse cascade of energy in two-dimensional (2D) turbulence with a ∼k⊥-5/3 scaling, and the other that corresponds to a steeper ∼k⊥-3 spectrum in which the three-dimensional (3D) modes release a substantial fraction of their energy per unit time to the 2D modes. The spectrum that emerges depends on the anisotropy of the forcing function, the former solution prevailing for forcings in which more energy is injected into the 2D modes while the latter prevails for isotropic forcing. In the case of anisotropic forcing, whence the energy goes from the 2D to the 3D modes at low wave numbers, large-scale shear is created, resulting in a time scale τsh, associated with shear, thereby producing a ∼k-1 spectrum for the total energy with the horizontal energy of the 2D modes still following a ∼k⊥-5/3 scaling.}, }
@article {pmid23031013, year = {2012}, author = {Stawarz, JE and Pouquet, A and Brachet, ME}, title = {Long-time properties of magnetohydrodynamic turbulence and the role of symmetries.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {3 Pt 2}, pages = {036307}, doi = {10.1103/PhysRevE.86.036307}, pmid = {23031013}, issn = {1550-2376}, mesh = {Computer Simulation ; *Hydrodynamics ; *Magnetic Fields ; *Models, Chemical ; Nonlinear Dynamics ; Rheology/*methods ; Solutions/*chemistry/*radiation effects ; }, abstract = {Using direct numerical simulations with grids of up to 512(3) points, we investigate long-time properties of three-dimensional magnetohydrodynamic turbulence in the absence of forcing and examine in particular the roles played by the quadratic invariants of the system and the symmetries of the initial configurations. We observe that when sufficient accuracy is used, initial conditions with a high degree of symmetries, as in the absence of helicity, do not travel through parameter space over time, whereas by perturbing these solutions either explicitly or implicitly using, for example, single precision for long times, the flows depart from their original behavior and can either become strongly helical or have a strong alignment between the velocity and the magnetic field. When the symmetries are broken, the flows evolve towards different end states, as already predicted by statistical arguments for nondissipative systems with the addition of an energy minimization principle. Increasing the Reynolds number by an order of magnitude when using grids of 64(3)-512(3) points does not alter these conclusions. Furthermore, the alignment properties of these flows, between velocity, vorticity, magnetic potential, induction, and current, correspond to the dominance of two main regimes, one helically dominated and one in quasiequipartition of kinetic and magnetic energies. We also contrast the scaling of the ratio of magnetic energy to kinetic energy as a function of wave number to the ratio of eddy turnover time to Alfvén time as a function of wave number. We find that the former ratio is constant with an approximate equipartition for scales smaller than the largest scale of the flow, whereas the ratio of time scales increases with increasing wave number.}, }
@article {pmid23030941, year = {2012}, author = {Strawbridge, EM and Wolgemuth, CW}, title = {Surface traction and the dynamics of elastic rods at low Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {3 Pt 1}, pages = {031904}, pmid = {23030941}, issn = {1550-2376}, support = {R01 GM072004/GM/NIGMS NIH HHS/United States ; }, mesh = {*Elasticity ; Hydrodynamics ; *Models, Theoretical ; *Surface Properties ; }, abstract = {Molecular and cell biological processes often use proteins and structures that are significantly longer in one dimension than they are in the other two, for example, DNA, actin, and bacterial flagella. The dynamics of these structures are the consequence of the balance between the elastic forces from the structure itself and viscous forces from the surrounding fluid. Typically, the motion of these filamentary objects is described using variations of the Kirchhoff rod equations with resistive forces from the fluid treated as body forces acting on the centerline. In reality, though, these forces are applied to the surface of the filament; however, the standard derivation of the Kirchhoff equations ignores surface traction stresses. Here, we rederive the Kirchhoff rod equations in the presence of resistive traction stresses and determine the conditions under which treating the drag forces as body forces is reasonable. We show that in most biologically relevant cases the standard implementation of resistive forces into the Kirchhoff rod equations is applicable; however, we note one particular biological system where the Kirchhoff rod formalism may not apply.}, }
@article {pmid23030935, year = {2012}, author = {Santos-Oliván, D and Fiasconaro, A and Falo, F}, title = {Directional motion of forced polymer chains with hydrodynamic interaction.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {3 Pt 1}, pages = {031804}, doi = {10.1103/PhysRevE.86.031804}, pmid = {23030935}, issn = {1550-2376}, mesh = {*Hydrodynamics ; Models, Molecular ; *Motion ; Polymers/*chemistry ; }, abstract = {We study the propulsion of a one-dimensional (1D) polymer chain under sinusoidal external forces in the overdamped (low Reynolds number) regime. We show that, when hydrodynamical interactions are included, the polymer presents directional motion which depends on the phase differences of the external force applied along the chain. Moreover, the velocity shows a maximum as a function of the frequency. We discuss the relevance of all these results in light of recent nanotechnology experiments.}, }
@article {pmid23030122, year = {2012}, author = {Friedrich, BM and Jülicher, F}, title = {Flagellar synchronization independent of hydrodynamic interactions.}, journal = {Physical review letters}, volume = {109}, number = {13}, pages = {138102}, doi = {10.1103/PhysRevLett.109.138102}, pmid = {23030122}, issn = {1079-7114}, mesh = {Chlamydomonas/*physiology ; Flagella/*physiology ; *Models, Theoretical ; Motion ; Swimming ; }, abstract = {Inspired by the coordinated beating of the flagellar pair of the green algae Chlamydomonas, we study theoretically a simple, mirror-symmetric swimmer, which propels itself at low Reynolds number by a revolving motion of a pair of spheres. We show that perfect synchronization between these two driven spheres can occur due to the motion of the swimmer and local hydrodynamic friction forces. Hydrodynamic interactions, though crucial for net propulsion, contribute little to synchronization for this free-moving swimmer.}, }
@article {pmid23029455, year = {2012}, author = {Stanley, R and Snelgrove, PV and Deyoung, B and Gregory, RS}, title = {Dispersal patterns, active behaviour, and flow environment during early life history of coastal cold water fishes.}, journal = {PloS one}, volume = {7}, number = {9}, pages = {e46266}, pmid = {23029455}, issn = {1932-6203}, mesh = {*Animal Distribution ; Animals ; Behavior, Animal/*physiology ; Body Size ; Fishes/*physiology ; Fresh Water ; Hydrodynamics ; Newfoundland and Labrador ; Swimming/*physiology ; Water Movements ; Zooplankton/physiology ; }, abstract = {During the pelagic larval phase, fish dispersal may be influenced passively by surface currents or actively determined by swimming behaviour. In situ observations of larval swimming are few given the constraints of field sampling. Active behaviour is therefore often inferred from spatial patterns in the field, laboratory studies, or hydrodynamic theory, but rarely are these approaches considered in concert. Ichthyoplankton survey data collected during 2004 and 2006 from coastal Newfoundland show that changes in spatial heterogeneity for multiple species do not conform to predictions based on passive transport. We evaluated the interaction of individual larvae with their environment by calculating Reynolds number as a function of ontogeny. Typically, larvae hatch into a viscous environment in which swimming is inefficient, and later grow into more efficient intermediate and inertial swimming environments. Swimming is therefore closely related to length, not only because of swimming capacity but also in how larvae experience viscosity. Six of eight species sampled demonstrated consistent changes in spatial patchiness and concomitant increases in spatial heterogeneity as they transitioned into more favourable hydrodynamic swimming environments, suggesting an active behavioural element to dispersal. We propose the tandem assessment of spatial heterogeneity and hydrodynamic environment as a potential approach to understand and predict the onset of ecologically significant swimming behaviour of larval fishes in the field.}, }
@article {pmid23005541, year = {2012}, author = {Teitelbaum, T and Mininni, PD}, title = {Thermalization and free decay in surface quasigeostrophic flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {1 Pt 2}, pages = {016323}, doi = {10.1103/PhysRevE.86.016323}, pmid = {23005541}, issn = {1550-2376}, mesh = {Computer Simulation ; Hot Temperature ; *Models, Statistical ; *Nonlinear Dynamics ; Rheology/*methods ; *Thermodynamics ; }, abstract = {We derive statistical equilibrium solutions of the truncated inviscid surface quasigeostrophic (SQG) equations, and verify the validity of these solutions at late times in numerical simulations. The results indicate the pseudoenstrophy thermalizes while the pseudoenergy can condense at the gravest modes, in agreement with previous indications of a direct cascade of pseudoenstrophy and an inverse cascade of pseudoenergy in forced-dissipative SQG systems. At early times, the truncated inviscid SQG simulations show a behavior reminiscent of forced-dissipative SQG turbulence, and we identify spectral scaling laws for the pseudoenergy and pseudoenstrophy spectra. More importantly, a comparison between viscous and inviscid simulations allows us to identify free-decay laws for the pseudoenstrophy in SQG turbulence at very large Reynolds number.}, }
@article {pmid23005526, year = {2012}, author = {Liu, G and Yu, YL and Tong, BG}, title = {Optimal energy-utilization ratio for long-distance cruising of a model fish.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {1 Pt 2}, pages = {016308}, doi = {10.1103/PhysRevE.86.016308}, pmid = {23005526}, issn = {1550-2376}, mesh = {Animals ; Computer Simulation ; Energy Transfer/*physiology ; *Models, Biological ; Physical Exertion/*physiology ; Salmon/*physiology ; Swimming/*physiology ; }, abstract = {The efficiency of total energy utilization and its optimization for long-distance migration of fish have attracted much attention in the past. This paper presents theoretical and computational research, clarifying the above well-known classic questions. Here, we specify the energy-utilization ratio (f(η)) as a scale of cruising efficiency, which consists of the swimming speed over the sum of the standard metabolic rate and the energy consumption rate of muscle activities per unit mass. Theoretical formulation of the function f(η) is made and it is shown that based on a basic dimensional analysis, the main dimensionless parameters for our simplified model are the Reynolds number (Re) and the dimensionless quantity of the standard metabolic rate per unit mass (R(pm)). The swimming speed and the hydrodynamic power output in various conditions can be computed by solving the coupled Navier-Stokes equations and the fish locomotion dynamic equations. Again, the energy consumption rate of muscle activities can be estimated by the quotient of dividing the hydrodynamic power by the muscle efficiency studied by previous researchers. The present results show the following: (1) When the value of f(η) attains a maximum, the dimensionless parameter R(pm) keeps almost constant for the same fish species in different sizes. (2) In the above cases, the tail beat period is an exponential function of the fish body length when cruising is optimal, e.g., the optimal tail beat period of Sockeye salmon is approximately proportional to the body length to the power of 0.78. Again, the larger fish's ability of long-distance cruising is more excellent than that of smaller fish. (3) The optimal swimming speed we obtained is consistent with previous researchers' estimations.}, }
@article {pmid23005522, year = {2012}, author = {Tian, FB and Lu, XY and Luo, H}, title = {Propulsive performance of a body with a traveling-wave surface.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {1 Pt 2}, pages = {016304}, doi = {10.1103/PhysRevE.86.016304}, pmid = {23005522}, issn = {1550-2376}, mesh = {Animals ; Computer Simulation ; Humans ; *Models, Biological ; Rheology/*methods ; Swimming/*physiology ; }, abstract = {A body with a traveling-wave surface (TWS) is investigated by solving the incompressible Navier-Stokes equation numerically to understand the mechanisms of a novel propulsive strategy. In this study, a virtual model of a foil with a flexible surface which performs a traveling-wave movement is used as a free swimming body. Based on the simulations by varying the traveling-wave Reynolds number and the amplitude and wave number of the TWS, some propulsive properties including the forward speed, the swimming efficiency, and the flow field are analyzed in detail. It is found that the mean forward velocity increases with the traveling-wave Reynolds number, the amplitude, and the wave number of the TWS. A weak wake behind the free swimming body is identified and the propulsive mechanisms are discussed. Moreover, the TWS is a "quiet" propulsive approach, which is an advantage when preying. The results obtained in this study provide a novel propulsion concept, which may also lead to an important design capability for underwater vehicles.}, }
@article {pmid23005407, year = {2012}, author = {Gollwitzer, F and Rehberg, I and Kruelle, CA and Huang, K}, title = {Coefficient of restitution for wet particles.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {86}, number = {1 Pt 1}, pages = {011303}, doi = {10.1103/PhysRevE.86.011303}, pmid = {23005407}, issn = {1550-2376}, mesh = {Colloids/*chemistry ; Computer Simulation ; *Models, Chemical ; *Models, Molecular ; Rheology/*methods ; *Shear Strength ; Solutions/*chemistry ; Wettability ; }, abstract = {The influence of a liquid film on the coefficient of restitution (COR) is investigated experimentally by tracing freely falling particles bouncing on a wet surface. The dependence of the COR on the impact velocity and various properties of the particle and liquid is presented and discussed in terms of dimensionless numbers that characterize the interplay between inertial, viscous, and surface forces. In the Reynolds number regime where lubrication theory does not apply, the ratio of the film thickness to the particle size is found to be a crucial parameter determining the COR.}, }
@article {pmid23005222, year = {2012}, author = {Tran, CV and Yu, X}, title = {Bounds for the number of degrees of freedom of incompressible magnetohydrodynamic turbulence in two and three dimensions.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {6 Pt 2}, pages = {066323}, doi = {10.1103/PhysRevE.85.066323}, pmid = {23005222}, issn = {1550-2376}, mesh = {Compressive Strength ; Computer Simulation ; *Hydrodynamics ; *Magnetic Fields ; *Models, Chemical ; Nonlinear Dynamics ; Rheology/*methods ; }, abstract = {We study incompressible magnetohydrodynamic turbulence in both two and three dimensions, with an emphasis on the number of degrees of freedom N. This number is estimated in terms of the magnetic Prandtl number Pr, kinetic Reynolds number Re, and magnetic Reynolds number Rm. Here Re and Rm are dynamic in nature, defined in terms of the kinetic and magnetic energy dissipation rates (or averages of the velocity and magnetic field gradients), viscosity and magnetic diffusivity, and the system size. It is found that for the two-dimensional case, N satisfies N≤PrRe(3/2)+Rm(3/2) for Pr>1 and N≤Re(3/2)+Pr(-1)Rm(3/2) for Pr≤1. In three dimensions, on the other hand, N satisfies N≤(PrRe(3/2)+Rm(3/2))(3/2) for Pr>1 and N≤(Re(3/2)+Pr(-1)Rm(3/2))(3/2) for Pr≤1. In the limit Pr→0, Re(3/2) dominates Pr(-1)Rm(3/2), and the present estimate for N appropriately reduces to Re(9/4) as in the case of usual Navier-Stokes turbulence. For Pr≈1, our results imply the classical spectral scaling of the energy inertial range and dissipation wave number (in the form of upper bounds). These bounds are consistent with the existing predictions in the literature for turbulence with or without Alfvén wave effects. We discuss the possibility of solution regularity, with an emphasis on the two-dimensional case in the absence of either one or both of the dissipation terms.}, }
@article {pmid23005217, year = {2012}, author = {Liu, R and Liu, QS}, title = {Nonmodal stability in Hagen-Poiseuille flow of a shear thinning fluid.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {6 Pt 2}, pages = {066318}, doi = {10.1103/PhysRevE.85.066318}, pmid = {23005217}, issn = {1550-2376}, mesh = {Computer Simulation ; *Models, Chemical ; Rheology/*methods ; Shear Strength ; Viscosity ; }, abstract = {Linear stability in Hagen-Poiseuille flow of a shear-thinning fluid is considered. The non-Newtonian viscosity is described by the Carreau rheological law. The effects of shear thinning on the stability are investigated using the energy method and the nonmodal stability theory. The energy analysis shows that the nonaxisymmetric disturbance with the azimuthal wave number m=1 has the lowest critical energy Reynolds number for both the Newtonian and shear-thinning cases. With the increase of shear thinning, the critical energy Reynolds number decreases for both the axisymmetric and nonaxisymmetric cases. For the nonmodal stability, we focus on two problems: response to external excitations and response to initial conditions. The former is studied by examining the ε pseudospectrum, and the latter by examining the energy growth function G(t). For both Newtonian and shear-thinning fluids, it is found that there can be a rather large transient growth even though the linear operator of the Hagen-Poiseuille flow has no unstable eigenvalue. For the problem of response to external excitations, the optimal response is achieved by disturbance with m=1 for both the Newtonian and non-Newtonian cases. For the problem of response to initial conditions, the optimal disturbance is in the form of streamwise uniform streaks. Being different from the Newtonian case, the azimuthal wave number of the optimal disturbance may be greater than 1 for strongly shear-thinning cases.}, }
@article {pmid23005207, year = {2012}, author = {Tanino, Y and Moisy, F and Hulin, JP}, title = {Laminar-turbulent cycles in inclined lock-exchange flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {6 Pt 2}, pages = {066308}, doi = {10.1103/PhysRevE.85.066308}, pmid = {23005207}, issn = {1550-2376}, mesh = {Computer Simulation ; *Models, Chemical ; Nonlinear Dynamics ; Rheology/*methods ; }, abstract = {We consider strongly confined, stably stratified shear flows generated as a lock exchange in a tube inclined at an angle of θ=45(∘). This paper focuses on a transitional regime, in which the flow alternates between two distinct states: laminar, parallel shear flow and intense transverse motion characteristic of turbulence. Laminar-turbulent cycles were captured at Atwood numbers At≡(ρ(2)-ρ(1))/(ρ(1)+ρ(2)) ranging from 2.45×10(-3) to 4.0×10(-3), where (ρ(1),ρ(2)) are the initial densities of the two fluids, with multiple cycles observed at At=2.55×10(-3). The evolution of the density and velocity fields in these flows was measured simultaneously using laser-induced fluorescence and particle image velocimetry. During each laminar-turbulent cycle, the axial velocity exhibits a distinctive ramp-cliff pattern, indicating that the flow accelerates as it relaminarizes, then decelerates rapidly as the Kelvin-Helmholtz billows break down. Within the range of experimental conditions, transverse stratification does not directly determine the onset of instability. Instead, the data suggest that a necessary criterion for the onset of instability is for the local Reynolds number to exceed 2200, with only a weak dependence on the Richardson number.}, }
@article {pmid23005203, year = {2012}, author = {Setter, E and Bucher, I and Haber, S}, title = {Low-Reynolds-number swimmer utilizing surface traveling waves: analytical and experimental study.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {6 Pt 2}, pages = {066304}, doi = {10.1103/PhysRevE.85.066304}, pmid = {23005203}, issn = {1550-2376}, mesh = {Biomimetics/*methods ; Computer Simulation ; *Models, Theoretical ; Motion ; Rheology/*methods ; Robotics/*methods ; *Swimming ; }, abstract = {Microscale slender swimmers are frequently encountered in nature and are now used in microrobotic applications. The swimming mechanism examined in this paper is based on small transverse axisymmetric traveling wave deformations of a cylindrical long shell. The thin-shelled device is assumed to be inextensible at the middle surface and extensible at the surface wetted by the fluid. Assuming low-Reynolds-number hydrodynamics, an analytical solution is derived for waves of small amplitudes compared with the cylinder diameter. We show that swimming velocity increases with β(1) (the ratio of cylinder radius to wavelength) and that swimming velocity is linearly dependent on wave propagation velocity, increasing to leading order with the square of the ratio of wave amplitude to wavelength β(2) and decreasing with the wall thickness. A fourth-order correction in β(2) was also calculated and was found to have a negative effect on the swimming velocity. The results for a shell of negligible-wall thickness were compared with Taylor's solution for an inextensible two-dimensional flat membrane undergoing a waving motion and Felderhof's results [Phys. Fluids 22, 113604 (2010)] for an unbounded flow field and negligible-wall thickness. We show that Taylor's analytic solution is a particular limiting case of the present solution, assuming zero wall thickness and infinite values of β(1). The present mechanism was also compared with Taylor's well known solutions of waving planar and helical circular tails. We show that the present approach yields higher velocities as β(1) increases, whereas, the opposite occurs for waving tails. Indeed, in the region where β(1)>15, the present approach yields velocities nearly as fast as Taylor's helical waving tail while consuming less power and with a design that is considerably more compact. In this regime, the axisymmetric swimmer is twice as fast as Taylor's planar-tail swimmer for an additional investment of only one-third of the power. Experiments were conducted using a macroscale autonomous model immersed in highly viscous silicone fluid. We outlined how the proposed mechanism was realized to propel an elongated, yet finite, swimmer. Measured data demonstrate the effects of wave velocity and wavelength on swimming speed, showing good agreement with analytical results.}, }
@article {pmid23005134, year = {2012}, author = {Farzin, M and Ronasi, K and Najafi, A}, title = {General aspects of hydrodynamic interactions between three-sphere low-Reynolds-number swimmers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {6 Pt 1}, pages = {061914}, doi = {10.1103/PhysRevE.85.061914}, pmid = {23005134}, issn = {1550-2376}, mesh = {Animals ; Biological Clocks/*physiology ; Computer Simulation ; Humans ; *Models, Biological ; Rheology/*methods ; Stress, Mechanical ; Swimming/*physiology ; }, abstract = {We investigate hydrodynamic interactions between two three-sphere swimmers analytically and numerically. Hydrodynamic forces exerted on the swimmers as well as the translational and angular velocities of them are obtained in the far field regime. We demonstrate that the active term of the translational velocity is along the intrinsic direction of swimming (n) and has no component along the direction of relative positions of swimmers (r[over ̂]) as reported in previous papers. Using numerical simulations we investigate the long-time swimming paths of swimmers in two general situations of swimming in the same and opposite directions. The former reveals four swimming states for symmetric swimmers-attractive, repulsive, parallel, and oscillatory-and only three swimming states for asymmetric swimmers-attractive, repulsive, and contracting-oscillatory, confirming that the expanding-oscillatory state reported in previous papers is not stable. The latter shows that there are rotative bound states in hydrodynamic scattering of the swimmers.}, }
@article {pmid23004865, year = {2012}, author = {Mohammadzadeh, A and Roohi, E and Niazmand, H and Stefanov, S and Myong, RS}, title = {Thermal and second-law analysis of a micro- or nanocavity using direct-simulation Monte Carlo.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {5 Pt 2}, pages = {056310}, doi = {10.1103/PhysRevE.85.056310}, pmid = {23004865}, issn = {1550-2376}, abstract = {In this study the direct-simulation Monte Carlo (DSMC) method is utilized to investigate thermal characteristics of micro- or nanocavity flow. The rarefied cavity flow shows unconventional behaviors which cannot be predicted by the Fourier law, the constitutive relation for the continuum heat transfer. Our analysis in this study confirms some recent observations and shows that the gaseous flow near the top-left corner of the cavity is in a strong nonequilibrium state even within the early slip regime, Kn=0.005. As we obtained slip velocity and temperature jump on the driven lid of the cavity, we reported meaningful discrepancies between the direct and macroscopic sampling of rarefied flow properties in the DSMC method due to existence of nonequilibrium effects in the corners of cavity. The existence of unconventional nonequilibrium heat transfer mechanisms in the middle of slip regime, Kn=0.05, results in the appearance of cold-to-hot heat transfer in the microcavity. In the current study we demonstrate that existence of such unconventional heat transfer is strongly dependent on the Reynolds number and it vanishes in the large values of the lid velocity. As we compared DSMC solution with the results of regularized 13 moments (R13) equations, we showed that the thermal characteristic of the microcavity obtained by the R13 method coincides with the DSMC prediction. Our investigation also includes the analysis of molecular entropy in the microcavity to explain the heat transfer mechanism with the aid of the second law of thermodynamics. To this aim, we obtained the two-dimensional velocity distribution functions to report the molecular-based entropy distribution, and show that the cold-to-hot heat transfer in the cavity is well in accordance with the second law of thermodynamics and takes place in the direction of increasing entropy. At the end we introduce the entropy density for the rarefied flow and show that it can accurately illustrate departure from the equilibrium state.}, }
@article {pmid23004662, year = {2012}, author = {Or, Y}, title = {Asymmetry and stability of shape kinematics in microswimmers' motion.}, journal = {Physical review letters}, volume = {108}, number = {25}, pages = {258101}, doi = {10.1103/PhysRevLett.108.258101}, pmid = {23004662}, issn = {1079-7114}, mesh = {Biomechanical Phenomena ; Eukaryota/*physiology ; Flagella/chemistry/*physiology ; *Models, Biological ; Structure-Activity Relationship ; Swimming ; }, abstract = {Many swimming microorganisms governed by low Reynolds number hydrodynamics utilize flagellar undulations for self-propulsion. Most of the existing theoretical models assume that the shape kinematics is directly controlled, while in reality, eukaryotes actuate internal bending moments along their flagellum. Under this control, the shape is dynamically evolving and periodic gaits may become unstable. This Letter addresses the problem by revisiting Purcell's three-link swimmer model where joint torques are controlled, and the geometric symmetries underlying the dynamics of the swimmer are analyzed. It is found that one has to break the front-back symmetry of the swimmer's structure and/or actuation profile in order to induce stable shape kinematics. The results may explain why most of the flagellated eukaryotes swim with their head forward.}, }
@article {pmid23004333, year = {2012}, author = {Hendrix, MH and Manica, R and Klaseboer, E and Chan, DY and Ohl, CD}, title = {Spatiotemporal evolution of thin liquid films during impact of water bubbles on glass on a micrometer to nanometer scale.}, journal = {Physical review letters}, volume = {108}, number = {24}, pages = {247803}, doi = {10.1103/PhysRevLett.108.247803}, pmid = {23004333}, issn = {1079-7114}, abstract = {Collisions between millimeter-size bubbles in water against a glass plate are studied using high-speed video. Bubble trajectory and shape are tracked simultaneously with laser interferometry between the glass and bubble surfaces that monitors spatial-temporal evolution of the trapped water film. Initial bubble bounces and the final attachment of the bubble to the surface have been quantified. While the global Reynolds number is large (∼10(2)), the film Reynolds number remains small and permits analysis with lubrication theory with tangentially immobile boundary condition at the air-water interface. Accurate predictions of dimple formation and subsequent film drainage are obtained.}, }
@article {pmid23003602, year = {2012}, author = {Matsuda, K and Onishi, R and Kurose, R and Komori, S}, title = {Turbulence effect on cloud radiation.}, journal = {Physical review letters}, volume = {108}, number = {22}, pages = {224502}, doi = {10.1103/PhysRevLett.108.224502}, pmid = {23003602}, issn = {1079-7114}, abstract = {The effect of turbulent clustering of water droplets on radiative transfer is investigated by means of both a three-dimensional direct numerical simulation of particle-laden homogeneous isotropic turbulence and a radiative transfer simulation based on a Monte Carlo photon tracing method. The results show that turbulent clustering causes the formation of void regions of droplets and hence increases the direct transmittance. This effect decreases as the turbulent Reynolds number increases and is estimated to be negligibly small under the conditions in real clouds.}, }
@article {pmid23003267, year = {2012}, author = {Valente, PC and Vassilicos, JC}, title = {Universal dissipation scaling for nonequilibrium turbulence.}, journal = {Physical review letters}, volume = {108}, number = {21}, pages = {214503}, doi = {10.1103/PhysRevLett.108.214503}, pmid = {23003267}, issn = {1079-7114}, abstract = {It is experimentally shown that the nonclassical high Reynolds number energy dissipation behavior, C(ε)≡εL/u(3)=f(Re(M))/Re(L), observed during the decay of fractal square grid-generated turbulence (where Re(M) is a global inlet Reynolds number and Re(L) is a local turbulence Reynolds number) is also manifested in decaying turbulence originating from various regular grids. For sufficiently high values of the global Reynolds numbers Re(M), f(Re(M))~Re(M).}, }
@article {pmid22996450, year = {2013}, author = {Elimelech, Y and Ellington, CP}, title = {Analysis of the transitional flow field over a fixed hummingbird wing.}, journal = {The Journal of experimental biology}, volume = {216}, number = {Pt 2}, pages = {303-318}, doi = {10.1242/jeb.075341}, pmid = {22996450}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Birds/anatomy &amp; histology/*physiology ; *Flight, Animal ; Male ; Models, Biological ; Wings, Animal/anatomy &amp; histology/*physiology ; }, abstract = {We analyzed the flow fields characterized by chord-based Reynolds numbers of 5000 to 15,000 over a stationary model of a hummingbird (Calypte anna) wing. Utilizing two experimental techniques, constant-temperature anemometry and stereo particle image velocimetry, the high-fidelity results depict a laminar-to-turbulent transition process that develops over the wing. At both zero and non-zero angles of attack the spectrum of the velocity signals is wide. At non-zero angles of attack the flow separates from the wing surface and a shear layer forms. As a result, unsteady flow disturbances amplify at a chord-based Reynolds numbers as low as 5000. Nevertheless, only at a Reynolds number of 15,000 is the flow disturbance growth rate sufficient to bring enough momentum from the outer region of the boundary layer to reattach the flow to the wing surface. For a Reynolds number of 5000, a comparison between the observed growth rates and a theoretical approximation concludes that flow disturbances of a Strouhal number of unity (and above) are no longer two-dimensional. In view of these conclusions, this study could serve as the first step towards a better understanding of the flow mechanisms over steady revolving and periodically flapping wings at this Reynolds number regime.}, }
@article {pmid22972227, year = {2012}, author = {DeSimone, A and Tatone, A}, title = {Crawling motility through the analysis of model locomotors: two case studies.}, journal = {The European physical journal. E, Soft matter}, volume = {35}, number = {9}, pages = {85}, pmid = {22972227}, issn = {1292-895X}, mesh = {Animals ; Bacteria/*cytology ; *Cell Movement ; Friction ; *Locomotion ; *Models, Theoretical ; Robotics ; Snails/*physiology ; }, abstract = {We study model locomotors on a substrate, which derive their propulsive capabilities from the tangential (viscous or frictional) resistance offered by the substrate. Our aim is to develop new tools and insight for future studies of cellular motility by crawling and of collective bacterial motion. The purely viscous case (worm) is relevant for cellular motility by crawling of individual cells. We re-examine some recent results on snail locomotion in order to assess the role of finely regulated adhesion mechanisms in crawling motility. Our main conclusion is that such regulation, although well documented in several biological systems, is not indispensable to accomplish locomotion driven by internal deformations, provided that the crawler may execute sufficiently large body deformations. Thus, there is no snail theorem. Namely, the crawling analog of the scallop theorem of low Reynolds number hydrodynamics does not hold for snail-like crawlers. The frictional case is obtained by assuming that the viscous coefficient governing tangential resistance forces, which act parallel and in the direction opposite to the velocity of the point to which they are applied, depends on the normal force acting at that point. We combine these surface interactions with inertial effects in order to investigate the mechanisms governing the motility of a bristle-robot. This model locomotor is easily manufactured and has been proposed as an effective tool to replicate and study collective bacterial motility.}, }
@article {pmid22960952, year = {2012}, author = {Martel, S}, title = {Bacterial microsystems and microrobots.}, journal = {Biomedical microdevices}, volume = {14}, number = {6}, pages = {1033-1045}, doi = {10.1007/s10544-012-9696-x}, pmid = {22960952}, issn = {1572-8781}, mesh = {Bacteria/*metabolism ; Bacterial Adhesion ; Chemotaxis ; Microfluidics/methods ; Robotics/*instrumentation/methods ; Systems Biology/*methods ; }, abstract = {Microorganisms and specifically motile bacteria have been recently added to the list of micro-actuators typically considered for the implementation of microsystems and microrobots. Such trend has been motivated by the fact these microorganisms are self-powered actuators with overall sizes at the lower end of the micrometer range and which have proven to be extremely effective in low Reynolds number hydrodynamic regime of usually less than 10(-2). Furthermore, the various sensors or taxes in bacteria influencing their movements can also be exploited to perform tasks that were previously considered only for futuristic artificial microrobots. Bacterial implementations and related issues are not only reviewed, but this paper also proposes many techniques and approaches that can be considered as building blocks for the implementations of more sophisticated microsystems and microrobots.}, }
@article {pmid22938326, year = {2012}, author = {Fonda, E and Sreenivasan, KR and Lathrop, DP}, title = {Liquid nitrogen in fluid dynamics: visualization and velocimetry using frozen particles.}, journal = {The Review of scientific instruments}, volume = {83}, number = {8}, pages = {085101}, doi = {10.1063/1.4739837}, pmid = {22938326}, issn = {1089-7623}, abstract = {High-Reynolds-number flows are common both in nature and industrial applications, but are difficult to attain in laboratory settings using standard test fluids such as air and water. To extend the Reynolds number range, water and air have been replaced at times by low-viscosity fluids such as pressurized air, sulfur hexafluoride, and cryogenic nitrogen gas, as well as liquid and gaseous helium. With a few exceptions, liquid nitrogen has been neglected despite the fact that it has a kinematic viscosity of about a fifth of that of water at room temperature. We explore the use of liquid nitrogen here. In particular, we study the use of frozen particles for flow visualization and velocimetry in liquid nitrogen. We create particles in situ by injecting a gaseous mixture of room-temperature nitrogen and an additional seeding gas into the flow. We present a systematic study of potential seeding gases to determine which create particles with the best fidelity and optical properties. The technique has proven capable of producing sub-micrometer sized tracers that allow particle tracking and particle image velocimetry. We review possible high-Reynolds-number experiments using this technique, and discuss the merits and challenges of using liquid nitrogen as a test fluid.}, }
@article {pmid22926809, year = {2012}, author = {Prohm, C and Gierlak, M and Stark, H}, title = {Inertial microfluidics with multi-particle collision dynamics.}, journal = {The European physical journal. E, Soft matter}, volume = {35}, number = {8}, pages = {80}, pmid = {22926809}, issn = {1292-895X}, abstract = {Using the method of multi-particle collision dynamics (MPCD), we investigate inertial focussing in microfluidic channels that gives rise to the Segré-Silberberg effect. At intermediate Reynolds numbers, we model the motion of a spherical colloid in a circular microchannel under pressure-driven flow. We determine the radial distribution function and show how its width and the location of its maximum are strongly influenced by the colloid size and the Reynolds number of the Poiseuille flow. We demonstrate that MPCD is well suited for calculating mean values for the lift force acting on the colloid in the cross-sectional plane and for its mean axial velocity. We introduce a Langevin equation for the cross-sectional motion whose steady state is the Boltzmann distribution that contains the integrated lift force as potential energy. It perfectly coincides with the simulated radial distribution function.}, }
@article {pmid22925874, year = {2012}, author = {de Cassia Feroni, R and Santos, JM and Reis, NC}, title = {Volatilization of hydrogen sulfide from a quiescent surface.}, journal = {Water science and technology : a journal of the International Association on Water Pollution Research}, volume = {66}, number = {9}, pages = {1991-1996}, doi = {10.2166/wst.2012.382}, pmid = {22925874}, issn = {0273-1223}, mesh = {Hydrogen Sulfide/*chemistry ; *Models, Theoretical ; Volatilization ; }, abstract = {Air-water mass transfer of hydrogen sulfide from a shallow tank with a quiescent surface under the influence of weak wind stress on the water surface was studied numerically using a two-dimensional model. The flow field in the tank was investigated using a computational code based on a finite volume, which is used to numerically solve momentum, mass and continuity conservation equations. The results show that water phase flow field is strongly dependent on the wind-induced surface velocity and the aspect ratio of the tank. Based on the numerical study, the liquid-side mass transfer coefficient is correlated with Reynolds number (R(e)), tank aspect ratio (AR) and Schmidt number (S(c)). Overall mass transfer coefficient (K(L)) values extend further downstream as the R(e) number increases.}, }
@article {pmid22923592, year = {2012}, author = {Wang, W and Jiang, Z and Westermann, M and Ping, L}, title = {Three mutations in Escherichia coli that generate transformable functional flagella.}, journal = {Journal of bacteriology}, volume = {194}, number = {21}, pages = {5856-5863}, pmid = {22923592}, issn = {1098-5530}, mesh = {Escherichia coli/chemistry/*genetics/physiology ; Escherichia coli Proteins/chemistry/genetics/metabolism ; Flagella/chemistry/*genetics/physiology ; Flagellin ; *Locomotion ; Models, Molecular ; *Mutation, Missense ; *Point Mutation ; Protein Conformation ; }, abstract = {Hydrodynamics predicts that swimming bacteria generate a propulsion force when a helical flagellum rotates because rotating helices necessarily translate at a low Reynolds number. It is generally believed that the flagella of motile bacteria are semirigid helices with a fixed pitch determined by hydrodynamic principles. Here, we report the characterization of three mutations in laboratory strains of Escherichia coli that produce different steady-state flagella without losing cell motility. E. coli flagella rotate counterclockwise during forward swimming, and the normal form of the flagella is a left-handed helix. A single amino acid exchange A45G and a double mutation of A48S and S110A change the resting flagella to right-handed helices. The stationary flagella of the triple mutant were often straight or slightly curved at neutral pH. Deprotonation facilitates the helix formation of it. The helical and curved flagella can be transformed to the normal form by torsion upon rotation and thus propel the cell. These mutations arose in the long-term laboratory cultivation. However, flagella are under strong selection pressure as extracellular appendages, and similar transformable flagella would be common in natural environments.}, }
@article {pmid22908251, year = {2012}, author = {Posner, JD and Pérez, CL and Santiago, JG}, title = {Electric fields yield chaos in microflows.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {109}, number = {36}, pages = {14353-14356}, pmid = {22908251}, issn = {1091-6490}, mesh = {Electric Conductivity ; Electrochemistry/*methods ; *Electromagnetic Fields ; *Hydrodynamics ; Microfluidics/*methods ; *Models, Chemical ; *Nonlinear Dynamics ; }, abstract = {We present an investigation of chaotic dynamics of a low Reynolds number electrokinetic flow. Electrokinetic flows arise due to couplings of electric fields and electric double layers. In these flows, applied (steady) electric fields can couple with ionic conductivity gradients outside electric double layers to produce flow instabilities. The threshold of these instabilities is controlled by an electric Rayleigh number, Ra(e). As Ra(e) increases monotonically, we show here flow dynamics can transition from steady state to a time-dependent periodic state and then to an aperiodic, chaotic state. Interestingly, further monotonic increase of Ra(e) shows a transition back to a well-ordered state, followed by a second transition to a chaotic state. Temporal power spectra and time-delay phase maps of low dimensional attractors graphically depict the sequence between periodic and chaotic states. To our knowledge, this is a unique report of a low Reynolds number flow with such a sequence of periodic-to-aperiodic transitions. Also unique is a report of strange attractors triggered and sustained through electric fluid body forces.}, }
@article {pmid22907616, year = {2012}, author = {Passov, E and Or, Y}, title = {Dynamics of Purcell's three-link microswimmer with a passive elastic tail.}, journal = {The European physical journal. E, Soft matter}, volume = {35}, number = {8}, pages = {78}, pmid = {22907616}, issn = {1292-895X}, mesh = {*Elasticity ; *Microbiology ; *Models, Biological ; *Movement ; }, abstract = {One of the few possible mechanisms for self-propulsion at low Reynolds number is undulations of a passive elastic tail, as proposed in the classical work of Purcell (1977). This effect is studied here by investigating a variant of Purcell's three-link swimmer model where the front joint angle is periodically actuated while the rear joint is driven by a passive torsional spring. The dynamic equations of motion are formulated and explicit expressions for the leading-order solution are derived by using perturbation expansion. The dependence of the motion on the actuation amplitude and frequency is analyzed, and optimization with respect to the swimmer's geometry is conducted.}, }
@article {pmid22901062, year = {2012}, author = {Abbas, F and Sudarsan, R and Eberl, HJ}, title = {Longtime behavior of one-dimensional biofilm models with shear dependent detachment rates.}, journal = {Mathematical biosciences and engineering : MBE}, volume = {9}, number = {2}, pages = {215-239}, doi = {10.3934/mbe.2012.9.215}, pmid = {22901062}, issn = {1551-0018}, mesh = {Bacteria/growth &amp; development ; Bacterial Adhesion ; *Biofilms ; Bioreactors ; Computer Simulation ; Hydrodynamics ; *Models, Biological ; *Shear Strength ; *Stress, Mechanical ; }, abstract = {We investigate the role of non shear stress and shear stressed based detachment rate functions for the longterm behavior of one-dimensional biofilm models. We find that the particular choice of a detachment rate function can affect the model prediction of persistence or washout of the biofilm. Moreover, by comparing biofilms in three settings: (i) Couette flow reactors, (ii) Poiseuille flow with fixed flow rate and (iii) Poiseuille flow with fixed pressure drop, we find that not only the bulk flow Reynolds number but also the particular mechanism driving the flow can play a crucial role for longterm behavior. We treat primarily the single species-case that can be analyzed with elementary ODE techniques. But we show also how the results, to some extent, can be carried over to multi-species biofilm models, and to biofilm models that are embedded in reactor mass balances.}, }
@article {pmid22891974, year = {2014}, author = {Xinhui, S and Liancun, Z and Xinxin, Z and Xinyi, S and Min, L}, title = {Asymmetric viscoelastic flow through a porous channel with expanding or contracting walls: a model for transport of biological fluids through vessels.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {17}, number = {6}, pages = {623-631}, doi = {10.1080/10255842.2012.708341}, pmid = {22891974}, issn = {1476-8259}, mesh = {Biological Transport ; Body Fluids/*metabolism ; Elasticity ; *Models, Biological ; Porosity ; Viscosity ; }, abstract = {In this article, the asymmetric viscoelastic fluid in a rectangular domain bounded by two porous moving channels with expanding or contracting walls is investigated. The governing equations are reduced to an ordinary equation by using suitable similar transformations. Homotopy analysis method is used to obtain the expression for velocity fields. The analytical solutions are influenced by the permeation Reynolds number Re, the wall expansion ratio [Formula: see text] and viscoelastic parameter [Formula: see text]. Graphs are sketched and the effects of some values of parameters, especially the expansion ratio and viscoelastic parameter, on the velocity fields are discussed in detail.}, }
@article {pmid22886565, year = {2012}, author = {Vilfan, A}, title = {Generic flow profiles induced by a beating cilium.}, journal = {The European physical journal. E, Soft matter}, volume = {35}, number = {8}, pages = {72}, pmid = {22886565}, issn = {1292-895X}, mesh = {Cilia/*metabolism ; *Hydrodynamics ; *Mechanical Phenomena ; Models, Biological ; }, abstract = {We describe a multipole expansion for the low-Reynolds-number fluid flows generated by a localized source embedded in a plane with a no-slip boundary condition. It contains 3 independent terms that fall quadratically with the distance and 6 terms that fall with the third power. Within this framework we discuss the flows induced by a beating cilium described in different ways: a small particle circling on an elliptical trajectory, a thin rod and a general ciliary beating pattern. We identify the flow modes present based on the symmetry properties of the ciliary beat.}, }
@article {pmid22886515, year = {2012}, author = {Mitri, K and Vauthier, C and Huang, N and Menas, A and Ringard-Lefebvre, C and Anselmi, C and Stambouli, M and Rosilio, V and Vachon, JJ and Bouchemal, K}, title = {Scale-up of nanoemulsion produced by emulsification and solvent diffusion.}, journal = {Journal of pharmaceutical sciences}, volume = {101}, number = {11}, pages = {4240-4247}, doi = {10.1002/jps.23291}, pmid = {22886515}, issn = {1520-6017}, mesh = {Diffusion ; *Emulsions ; *Nanotechnology ; *Solvents ; Viscosity ; }, abstract = {The scale-up of nanoemulsions (NEs) produced by emulsification and solvent diffusion process was successfully achieved in the present work. Up to 1500 mL of NEs were produced with olive oil, castor oil, almond oil, or Arlamol™ E by using a Y-shaped mixer device. NE droplet sizes were significantly modulated from 290 to 185 nm by changing the process parameters without modification of the formulation composition. Smaller NE droplet sizes were obtained by (1) decreasing the internal diameter of the Y-mixer from 5 to 0.8 mm, (2) increasing the flow rates of the organic and the aqueous phases upon mixing, and (3) increasing the temperature of the experiment from 5°C to 40°C. All the results of NE diameters (d(sc)) expressed as a function of the Reynolds number (Re) and the shear rate inside the Y-mixer (\documentclass{article}\usepackage{amssymb}\begin{document}\pagestyle{empty}$\dot \gamma$\end{document}) showed the existence of typical power-law relationships: d(sc) = 10(2.82) Re(- 0.14) and \documentclass{article}\usepackage{amssymb}\begin{document}\pagestyle{empty}$d_{{\rm sc}} = 10^{2.60} \dot \gamma ^{- 0.06}$\end{document}, respectively. The existence of these power-laws for NE formation by emulsification and solvent diffusion process has never been reported in the literature yet and constitutes a new finding in this work. We definitely proved that the high turbulences created upon NE formation are the most important parameter allowing to decrease droplet size.}, }
@article {pmid22864542, year = {2012}, author = {Ledesma-Aguilar, R and Löwen, H and Yeomans, JM}, title = {A circle swimmer at low Reynolds number.}, journal = {The European physical journal. E, Soft matter}, volume = {35}, number = {8}, pages = {70}, pmid = {22864542}, issn = {1292-895X}, abstract = {Swimming in circles occurs in a variety of situations at low Reynolds number. Here we propose a simple model for a swimmer that undergoes circular motion, generalising the model of a linear swimmer proposed by Najafi and Golestanian (Phys. Rev. E 69, 062901 (2004)). Our model consists of three solid spheres arranged in a triangular configuration, joined by two links of time-dependent length. For small strokes, we discuss the motion of the swimmer as a function of the separation angle between its links. We find that swimmers describe either clockwise or anticlockwise circular motion depending on the tilting angle in a non-trivial manner. The symmetry of the swimmer leads to a quadrupolar decay of the far flow field. We discuss the potential extensions and experimental realisation of our model.}, }
@article {pmid22852428, year = {2012}, author = {Karadagli, F and Rittmann, BE and McAvoy, DC and Richardson, JE}, title = {Effect of turbulence on the disintegration rate of flushable consumer products.}, journal = {Water environment research : a research publication of the Water Environment Federation}, volume = {84}, number = {5}, pages = {424-433}, doi = {10.2175/106143012x13354606450960}, pmid = {22852428}, issn = {1061-4303}, mesh = {*Environmental Restoration and Remediation ; *Household Products ; Hydrodynamics ; *Waste Disposal, Fluid ; }, abstract = {A previously developed model for the physical disintegration of flushable consumer products is expanded by investigating the effects of turbulence on the rate of physical disintegration. Disintegration experiments were conducted with cardboard tampon applicators at 100, 150, and 200 rotations per minute, corresponding to Reynold's numbers of 25,900, 39,400, and 52,900, respectively, which were estimated by using computational fluid dynamics modeling. The experiments were simulated with the disintegration model to obtain best-fit values of the kinetic and distribution parameters. Computed rate coefficients (ki) for all solid sizes (i.e., greater than 8, 4 to 8, 2 to 4, and 1 to 2 mm) increased strongly with Reynold's number or rotational speed. Thus, turbulence strongly affected the disintegration rate of flushable products, and the relationship of the ki values to Reynold's number can be included in mathematical representations of physical disintegration.}, }
@article {pmid22817394, year = {2014}, author = {Tripathi, D and Pandey, SK and Siddiqui, A and Bég, OA}, title = {Non-steady peristaltic propulsion with exponential variable viscosity: a study of transport through the digestive system.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {17}, number = {6}, pages = {591-603}, doi = {10.1080/10255842.2012.703660}, pmid = {22817394}, issn = {1476-8259}, mesh = {Body Fluids/metabolism ; Humans ; Intestines/physiology ; *Models, Biological ; *Peristalsis ; Pressure ; Stress, Mechanical ; Viscosity ; }, abstract = {A theoretical study is presented for transient peristaltic flow of an incompressible fluid with variable viscosity in a finite length cylindrical tube as a simulation of transport in physiological vessels and biomimetic peristaltic pumps. The current axisymmetric analysis is qualitatively similar to two-dimensional analysis but exhibits quantitative variations. The current analysis is motivated towards further elucidating the physiological migration of gastric suspensions (food bolus) in the human digestive system. It also applies to variable viscosity industrial fluid (waste) peristaltic pumping systems. First, an axisymmetric model is analysed in the limit of large wavelength ([Formula: see text]) and low Reynolds number ([Formula: see text]) for axial velocity, radial velocity, pressure, hydromechanical efficiency and stream function in terms of radial vibration of the wall ([Formula: see text]), amplitude of the wave ([Formula: see text]), averaged flow rate ([Formula: see text]) and variable viscosity ([Formula: see text]). Subsequently, the peristaltic flow of a fluid with an exponential viscosity model is examined, which is based on the analytical solutions for pressure, wall shear stress, hydromechanical efficiency and streamline patterns in the finite length tube. The results are found to correlate well with earlier studies using a constant viscosity formulation. This study reveals some important features in the flow characteristics including the observation that pressure as well as both number and size of lower trapped bolus increases. Furthermore, the study indicates that hydromechanical efficiency reduces with increasing magnitude of viscosity parameter.}, }
@article {pmid22779677, year = {2012}, author = {Raghu, RC and Schofield, J}, title = {Simulation of tethered oligomers in nanochannels using multi-particle collision dynamics.}, journal = {The Journal of chemical physics}, volume = {137}, number = {1}, pages = {014901}, doi = {10.1063/1.4731662}, pmid = {22779677}, issn = {1089-7690}, abstract = {The effect of a high Reynold's number, pressure-driven flow of a compressible gas on the conformation of an oligomer tethered to the wall of a square channel is studied under both ideal solvent and poor solvent conditions using a hybrid multiparticle collision dynamics and molecular dynamics algorithm. Unlike previous studies, the flow field contains an elongational component in addition to a shear component as well as fluid slip near the walls and results in a Schmidt number for the polymer beads that is less than unity. In both solvent regimes the oligomer is found to extend in the direction of flow. Under the ideal solvent conditions, torsional twisting of the chain and aperiodic cyclical dynamics are observed for the end of the oligomer. Under poor solvent conditions, a metastable helix forms in the end of the chain despite the lack of any attractive potential between beads in the oligomeric chain. The formation of the helix is postulated to be the result of a solvent induced chain collapse that has been confined to a single dimension by a strong flow field.}, }
@article {pmid22761309, year = {2012}, author = {Amini, H and Sollier, E and Weaver, WM and Di Carlo, D}, title = {Intrinsic particle-induced lateral transport in microchannels.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {109}, number = {29}, pages = {11593-11598}, pmid = {22761309}, issn = {1091-6490}, mesh = {Convection ; Microfluidics/*methods ; *Models, Chemical ; Particle Size ; Rheology/*methods ; }, abstract = {In microfluidic systems at low Reynolds number, the flow field around a particle is assumed to maintain fore-aft symmetry, with fluid diverted by the presence of a particle, returning to its original streamline downstream. This current model considers particles as passive components of the system. However, we demonstrate that at finite Reynolds number, when inertia is taken into consideration, particles are not passive elements in the flow but significantly disturb and modify it. In response to the flow field, particles translate downstream while rotating. The combined effect of the flow of fluid around particles, particle rotation, channel confinement (i.e., particle dimensions approaching those of the channel), and finite fluid inertia creates a net recirculating flow perpendicular to the primary flow direction within straight channels that resembles the well-known Dean flow in curved channels. Significantly, the particle generating this flow remains laterally fixed as it translates downstream and only the fluid is laterally transferred. Therefore, as the particles remain inertially focused, operations can be performed around the particles in a way that is compatible with downstream assays such as flow cytometry. We apply this particle-induced transfer to perform fluid switching and mixing around rigid microparticles as well as deformable cells. This transport phenomenon, requiring only a simple channel geometry with no external forces to operate, offers a practical approach for fluid transfer at high flow rates with a wide range of applications, including sample preparation, flow reaction, and heat transfer.}, }
@article {pmid22757491, year = {2012}, author = {Zheng, LY and Farnam, DS and Homentcovschi, D and Sammakia, BG}, title = {A porous elastic model for bacterial biofilms: application to the simulation of deformation of bacterial biofilms under microfluidic jet impingement.}, journal = {Journal of biomechanical engineering}, volume = {134}, number = {5}, pages = {051003}, doi = {10.1115/1.4006683}, pmid = {22757491}, issn = {1528-8951}, mesh = {Anti-Bacterial Agents/pharmacology ; *Biofilms/drug effects/growth &amp; development ; Cell Line ; *Elasticity ; Extracellular Matrix/drug effects/metabolism ; *Microfluidic Analytical Techniques ; Models, Biological ; Porosity ; Pressure ; Streptococcus mutans/cytology/drug effects/*physiology ; }, abstract = {The presence of bacterial biofilms is detrimental in a wide range of healthcare situations especially wound healing. Physical debridement of biofilms is a method widely used to remove them. This study evaluates the use of microfluidic jet impingement to debride biofilms. In this case, a biofilm is treated as a saturated porous medium also having linear elastic properties. A numerical modeling approach is used to calculate the von Mises stress distribution within a porous medium under fluid-structure interaction (FSI) loading to determine the initial rupture of the biofilm structure. The segregated model first simulates the flow field to obtain the FSI interface loading along the fluid-solid interface and body force loading within the porous medium. A stress-strain model is consequently used to calculate the von Mises stress distribution to obtain the biofilm deformation. Under a vertical jet, 60% of the deformation of the porous medium can be accounted for by treating the medium as if it was an impermeable solid. However, the maximum deformation in the porous medium corresponds to the point of maximum shear stress which is a different position in the porous medium than that of the maximum normal stress in an impermeable solid. The study shows that a jet nozzle of 500 μm internal diameter (ID) with flow of Reynolds number (Re) of 200 can remove the majority of biofilm species.}, }
@article {pmid22750570, year = {2012}, author = {Zhu, JH and Lee, HP and Lim, KM and Gordon, BR and Wang, de Y}, title = {Effect of accessory ostia on maxillary sinus ventilation: a computational fluid dynamics (CFD) study.}, journal = {Respiratory physiology &amp; neurobiology}, volume = {183}, number = {2}, pages = {91-99}, doi = {10.1016/j.resp.2012.06.026}, pmid = {22750570}, issn = {1878-1519}, mesh = {Adult ; Air ; Female ; Humans ; *Hydrodynamics ; Imaging, Three-Dimensional ; Maxillary Sinus/diagnostic imaging/*physiopathology ; Models, Biological ; Rhinitis, Allergic ; Rhinitis, Allergic, Perennial/diagnostic imaging/physiopathology ; Sinusitis/diagnostic imaging/physiopathology ; Tomography, X-Ray Computed ; }, abstract = {We evaluated, by CFD simulation, effects of accessory ostium (AO) on maxillary sinus ventilation. A three-dimensional nasal model was constructed from an adult CT scan with two left maxillary AOs (sinus I) and one right AO (sinus II), then compared to an identical control model with all AOs sealed (sinuses III and IV). Transient simulations of quiet inspiration and expiration at 15 L/min, and nasal blow at 48 L/min, were calculated for both models using low-Reynolds-number turbulent analysis. At low flows, ventilation rates in sinuses with AOs (I ≈ 0.46 L/min, II ≈ 0.54 L/min), were both more than a magnitude higher than sinuses without AOs (II I ≈ 0.019 L/min, IV ≈ 0.020 L/min). Absence of AO almost completely prevented sinus ventilation. Increased ventilation of sinuses with AOs is complex. Under high flow conditions mimicking nose blowing, in sinuses II, III, and IV, the sinus flow rate increased. In contrast, the airflow direction through sinus I reversed between inspiration and expiration, while it remained almost constant throughout the respiration cycle in sinus II. CFD simulation demonstrated that AOs markedly increase maxillary sinus airflow rates and alter sinus air circulation patterns. Whether these airflow changes impact maxillary sinus physiology or pathophysiology is unknown.}, }
@article {pmid22736305, year = {2012}, author = {Deng, Y and Liu, Z and Zhang, P and Liu, Y and Gao, Q and Wu, Y}, title = {A flexible layout design method for passive micromixers.}, journal = {Biomedical microdevices}, volume = {14}, number = {5}, pages = {929-945}, doi = {10.1007/s10544-012-9672-5}, pmid = {22736305}, issn = {1572-8781}, mesh = {Equipment Design ; Microfluidics/*instrumentation/*methods ; Models, Theoretical ; Software ; Spatial Analysis ; }, abstract = {This paper discusses a flexible layout design method of passive micromixers based on the topology optimization of fluidic flows. Being different from the trial and error method, this method obtains the detailed layout of a passive micromixer according to the desired mixing performance by solving a topology optimization problem. Therefore, the dependence on the experience of the designer is weaken, when this method is used to design a passive micromixer with acceptable mixing performance. Several design disciplines for the passive micromixers are considered to demonstrate the flexibility of the layout design method for passive micromixers. These design disciplines include the approximation of the real 3D micromixer, the manufacturing feasibility, the spacial periodic design, and effects of the Péclet number and Reynolds number on the designs obtained by this layout design method. The capability of this design method is validated by several comparisons performed between the obtained layouts and the optimized designs in the recently published literatures, where the values of the mixing measurement is improved up to 40.4% for one cycle of the micromixer.}, }
@article {pmid22733254, year = {2012}, author = {Lagus, TP and Edd, JF}, title = {High throughput single-cell and multiple-cell micro-encapsulation.}, journal = {Journal of visualized experiments : JoVE}, volume = {}, number = {64}, pages = {e4096}, pmid = {22733254}, issn = {1940-087X}, mesh = {HL-60 Cells ; High-Throughput Screening Assays/*methods ; Humans ; Microfluidic Analytical Techniques/*methods ; Single-Cell Analysis/*methods ; }, abstract = {UNLABELLED: Microfluidic encapsulation methods have been previously utilized to capture cells in picoliter-scale aqueous, monodisperse drops, providing confinement from a bulk fluid environment with applications in high throughput screening, cytometry, and mass spectrometry. We describe a method to not only encapsulate single cells, but to repeatedly capture a set number of cells (here we demonstrate one- and two-cell encapsulation) to study both isolation and the interactions between cells in groups of controlled sizes. By combining drop generation techniques with cell and particle ordering, we demonstrate controlled encapsulation of cell-sized particles for efficient, continuous encapsulation. Using an aqueous particle suspension and immiscible fluorocarbon oil, we generate aqueous drops in oil with a flow focusing nozzle. The aqueous flow rate is sufficiently high to create ordering of particles which reach the nozzle at integer multiple frequencies of the drop generation frequency, encapsulating a controlled number of cells in each drop. For representative results, 9.9 μm polystyrene particles are used as cell surrogates. This study shows a single-particle encapsulation efficiency P(k=1) of 83.7% and a double-particle encapsulation efficiency P(k=2) of 79.5% as compared to their respective Poisson efficiencies of 39.3% and 33.3%, respectively. The effect of consistent cell and particle concentration is demonstrated to be of major importance for efficient encapsulation, and dripping to jetting transitions are also addressed.<br><br>INTRODUCTION: Continuous media aqueous cell suspensions share a common fluid environment which allows cells to interact in parallel and also homogenizes the effects of specific cells in measurements from the media. High-throughput encapsulation of cells into picoliter-scale drops confines the samples to protect drops from cross-contamination, enable a measure of cellular diversity within samples, prevent dilution of reagents and expressed biomarkers, and amplify signals from bioreactor products. Drops also provide the ability to re-merge drops into larger aqueous samples or with other drops for intercellular signaling studies. The reduction in dilution implies stronger detection signals for higher accuracy measurements as well as the ability to reduce potentially costly sample and reagent volumes. Encapsulation of cells in drops has been utilized to improve detection of protein expression, antibodies, enzymes, and metabolic activity for high throughput screening, and could be used to improve high throughput cytometry. Additional studies present applications in bio-electrospraying of cell containing drops for mass spectrometry and targeted surface cell coatings. Some applications, however, have been limited by the lack of ability to control the number of cells encapsulated in drops. Here we present a method of ordered encapsulation which increases the demonstrated encapsulation efficiencies for one and two cells and may be extrapolated for encapsulation of a larger number of cells. To achieve monodisperse drop generation, microfluidic "flow focusing" enables the creation of controllable-size drops of one fluid (an aqueous cell mixture) within another (a continuous oil phase) by using a nozzle at which the streams converge. For a given nozzle geometry, the drop generation frequency f and drop size can be altered by adjusting oil and aqueous flow rates Q(oil) and Q(aq). As the flow rates increase, the flows may transition from drop generation to unstable jetting of aqueous fluid from the nozzle. When the aqueous solution contains suspended particles, particles become encapsulated and isolated from one another at the nozzle. For drop generation using a randomly distributed aqueous cell suspension, the average fraction of drops D(k) containing k cells is dictated by Poisson statistics, where D(k) = &#x3bb;(k) exp(-&#x3bb;)/(k!) and &#x3bb; is the average number of cells per drop. The fraction of cells which end up in the "correctly" encapsulated drops is calculated using P(k) = (k x D(k))/&#x3a3;(k' x D(k)'). The subtle difference between the two metrics is that D(k) relates to the utilization of aqueous fluid and the amount of drop sorting that must be completed following encapsulation, and P(k) relates to the utilization of the cell sample. As an example, one could use a dilute cell suspension (low &#x3bb;) to encapsulate drops where most drops containing cells would contain just one cell. While the efficiency metric P(k) would be high, the majority of drops would be empty (low D(k)), thus requiring a sorting mechanism to remove empty drops, also reducing throughput. Combining drop generation with inertial ordering provides the ability to encapsulate drops with more predictable numbers of cells per drop and higher throughputs than random encapsulation. Inertial focusing was first discovered by Segre and Silberberg and refers to the tendency of finite-sized particles to migrate to lateral equilibrium positions in channel flow. Inertial ordering refers to the tendency of the particles and cells to passively organize into equally spaced, staggered, constant velocity trains. Both focusing and ordering require sufficiently high flow rates (high Reynolds number) and particle sizes (high Particle Reynolds number). Here, the Reynolds number Re =uD(h)/&#x3bd; and particle Reynolds number Rep =Re(a/D(h))&#xb2;, where u is a characteristic flow velocity, D(h) [=2wh/(w+h)] is the hydraulic diameter, &#x3bd; is the kinematic viscosity, a is the particle diameter, w is the channel width, and h is the channel height. Empirically, the length required to achieve fully ordered trains decreases as Re and Re(p) increase. Note that the high Re and Re(p) requirements (for this study on the order of 5 and 0.5, respectively) may conflict with the need to keep aqueous flow rates low to avoid jetting at the drop generation nozzle. Additionally, high flow rates lead to higher shear stresses on cells, which are not addressed in this protocol. The previous ordered encapsulation study demonstrated that over 90% of singly encapsulated HL60 cells under similar flow conditions to those in this study maintained cell membrane integrity. However, the effect of the magnitude and time scales of shear stresses will need to be carefully considered when extrapolating to different cell types and flow parameters. The overlapping of the cell ordering, drop generation, and cell viability aqueous flow rate constraints provides an ideal operational regime for controlled encapsulation of single and multiple cells. Because very few studies address inter-particle train spacing, determining the spacing is most easily done empirically and will depend on channel geometry, flow rate, particle size, and particle concentration. Nonetheless, the equal lateral spacing between trains implies that cells arrive at predictable, consistent time intervals. When drop generation occurs at the same rate at which ordered cells arrive at the nozzle, the cells become encapsulated within the drop in a controlled manner. This technique has been utilized to encapsulate single cells with throughputs on the order of 15 kHz, a significant improvement over previous studies reporting encapsulation rates on the order of 60-160 Hz. In the controlled encapsulation work, over 80% of drops contained one and only one cell, a significant efficiency improvement over Poisson (random) statistics, which predicts less than 40% efficiency on average. In previous controlled encapsulation work, the average number of particles per drop &#x3bb; was tuned to provide single-cell encapsulation. We hypothesize that through tuning of flow rates, we can efficiently encapsulate any number of cells per drop when &#x3bb; is equal or close to the number of desired cells per drop. While single-cell encapsulation is valuable in determining individual cell responses from stimuli, multiple-cell encapsulation provides information relating to the interaction of controlled numbers and types of cells. Here we present a protocol, representative results using polystyrene microspheres, and discussion for controlled encapsulation of multiple cells using a passive inertial ordering channel and drop generation nozzle.}, }
@article {pmid22729901, year = {2012}, author = {Pandey, A and Simha, RA}, title = {Minimal polar swimmer at low Reynolds number.}, journal = {The European physical journal. E, Soft matter}, volume = {35}, number = {6}, pages = {52}, pmid = {22729901}, issn = {1292-895X}, abstract = {We propose a minimal model for a polar swimmer, consisting of two spheres connected by a rigid slender arm, at low Reynolds number. The propulsive velocity for the proposed model is the maximum for any swimming cycle with the same variations in its two degrees of freedom and its displacement in a cycle is achieved entirely in one step. The stroke averaged flow field generated by the contractile swimmer at large distances is found to be dipolar. In addition, the changing radius of one of the spheres generates the field of a potential doublet centered at its initial position.}, }
@article {pmid22723904, year = {2012}, author = {Furlan, S and Comparini, D and Ciszak, M and Beccai, L and Mancuso, S and Mazzolai, B}, title = {Origin of polar order in dense suspensions of phototactic micro-swimmers.}, journal = {PloS one}, volume = {7}, number = {6}, pages = {e38895}, pmid = {22723904}, issn = {1932-6203}, mesh = {*Cyanobacteria ; Microfluidics ; *Models, Theoretical ; *Motion ; Rheology ; Suspensions ; }, abstract = {A main question for the study of collective motion in living organisms is the origin of orientational polar order, i.e., how organisms align and what are the benefits of such collective behaviour. In the case of micro-organisms swimming at a low Reynolds number, steric repulsion and long-range hydrodynamic interactions are not sufficient to explain a homogeneous polar order state in which the direction of motion is aligned. An external symmetry-breaking guiding field such as a mechanism of taxis appears necessary to understand this phonemonon. We have investigated the onset of polar order in the velocity field induced by phototaxis in a suspension of a motile micro-organism, the algae Chlamydomonas reinhardtii, for density values above the limit provided by the hydrodynamic approximation of a force dipole model. We show that polar order originates from a combination of both the external guiding field intensity and the population density. In particular, we show evidence for a linear dependence of a phototactic guiding field on cell density to determine the polar order for dense suspensions and demonstrate the existence of a density threshold for the origin of polar order. This threshold represents the density value below which cells undergoing phototaxis are not able to maintain a homogeneous polar order state and marks the transition to ordered collective motion. Such a transition is driven by a noise dominated phototactic reorientation where the noise is modelled as a normal distribution with a variance that is inversely proportional to the guiding field strength. Finally, we discuss the role of density in dense suspensions of phototactic micro-swimmers.}, }
@article {pmid22716029, year = {2012}, author = {Kim, Y and Lee Chung, B and Ma, M and Mulder, WJ and Fayad, ZA and Farokhzad, OC and Langer, R}, title = {Mass production and size control of lipid-polymer hybrid nanoparticles through controlled microvortices.}, journal = {Nano letters}, volume = {12}, number = {7}, pages = {3587-3591}, pmid = {22716029}, issn = {1530-6992}, support = {HHSN268201000045C/HL/NHLBI NIH HHS/United States ; U54 CA151884/CA/NCI NIH HHS/United States ; R01 CA155432/CA/NCI NIH HHS/United States ; CA151884/CA/NCI NIH HHS/United States ; 268201000045C//PHS HHS/United States ; }, mesh = {Lipids/*chemistry ; *Microfluidic Analytical Techniques ; Molecular Weight ; Nanoparticles/*chemistry ; Particle Size ; Polymers/*chemistry ; Surface Properties ; }, abstract = {Lipid-polymer hybrid (LPH) nanoparticles can deliver a wide range of therapeutic compounds in a controlled manner. LPH nanoparticle syntheses using microfluidics improve the mixing process but are restricted by a low throughput. In this study, we present a pattern-tunable microvortex platform that allows mass production and size control of LPH nanoparticles with superior reproducibility and homogeneity. We demonstrate that by varying flow rates (i.e., Reynolds number (30-150)) we can control the nanoparticle size (30-170 nm) with high productivity (∼3 g/hour) and low polydispersity (∼0.1). Our approach may contribute to efficient development and optimization of a wide range of multicomponent nanoparticles for medical imaging and drug delivery.}, }
@article {pmid22711456, year = {2012}, author = {Pennella, F and Rossi, M and Ripandelli, S and Rasponi, M and Mastrangelo, F and Deriu, MA and Ridolfi, L and Kähler, CJ and Morbiducci, U}, title = {Numerical and experimental characterization of a novel modular passive micromixer.}, journal = {Biomedical microdevices}, volume = {14}, number = {5}, pages = {849-862}, doi = {10.1007/s10544-012-9665-4}, pmid = {22711456}, issn = {1572-8781}, mesh = {Computer Simulation ; Equipment Design ; Microfluidic Analytical Techniques/*instrumentation/methods ; Microfluidics/*instrumentation/*methods ; Models, Theoretical ; }, abstract = {This paper reports a new low-cost passive microfluidic mixer design, based on a replication of identical mixing units composed of microchannels with variable curvature (clothoid) geometry. The micromixer presents a compact and modular architecture that can be easily fabricated using a simple and reliable fabrication process. The particular clothoid-based geometry enhances the mixing by inducing transversal secondary flows and recirculation effects. The role of the relevant fluid mechanics mechanisms promoting the mixing in this geometry were analysed using computational fluid dynamics (CFD) for Reynolds numbers ranging from 1 to 110. A measure of mixing potency was quantitatively evaluated by calculating mixing efficiency, while a measure of particle dispersion was assessed through the lacunarity index. The results show that the secondary flow arrangement and recirculation effects are able to provide a mixing efficiency equal to 80 % at Reynolds number above 70. In addition, the analysis of particles distribution promotes the lacunarity as powerful tool to quantify the dispersion of fluid particles and, in turn, the overall mixing. On fabricated micromixer prototypes the microscopic-Laser-Induced-Fluorescence (μLIF) technique was applied to characterize mixing. The experimental results confirmed the mixing potency of the microdevice.}, }
@article {pmid22687444, year = {2012}, author = {Lorente, S and Cetkin, E and Bello-Ochende, T and Meyer, JP and Bejan, A}, title = {The constructal-law physics of why swimmers must spread their fingers and toes.}, journal = {Journal of theoretical biology}, volume = {308}, number = {}, pages = {141-146}, doi = {10.1016/j.jtbi.2012.05.033}, pmid = {22687444}, issn = {1095-8541}, mesh = {Animals ; Athletes ; Biomechanical Phenomena/physiology ; Computer Simulation ; Fingers/*physiology ; Humans ; Hydrodynamics ; *Models, Biological ; Swimming/*physiology ; Time Factors ; Toes/*physiology ; }, abstract = {Here we show theoretically that swimming animals and athletes gain an advantage in force and speed by spreading their fingers and toes optimally. The larger force means larger body mass lifted and greater speed, in accord with the constructal theory of all animal locomotion. The spacing between fingers must be twice the thickness of the boundary layer around one finger. This theoretical prediction is confirmed by computational fluid dynamics simulations of flow across two and four cylinders of diameter D. The optimal spacing is in the range 0.2D-0.4D, and decreases slightly as the Reynolds number (Re) increases from 20 to 100. For example, the total force exerted by two optimally spaced cylinders exceeds by 53% the total force of two cylinders with no spacing when Re=20. These design features hold for both time-dependent and steady-state flows.}, }
@article {pmid22680576, year = {2012}, author = {Liu, H and Valocchi, AJ and Kang, Q}, title = {Three-dimensional lattice Boltzmann model for immiscible two-phase flow simulations.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {4 Pt 2}, pages = {046309}, doi = {10.1103/PhysRevE.85.046309}, pmid = {22680576}, issn = {1550-2376}, abstract = {We present an improved three-dimensional 19-velocity lattice Boltzmann model for immisicible binary fluids with variable viscosity and density ratios. This model uses a perturbation step to generate the interfacial tension and a recoloring step to promote phase segregation and maintain surfaces. A generalized perturbation operator is derived using the concept of a continuum surface force together with the constraints of mass and momentum conservation. A theoretical expression for the interfacial tension is determined directly without any additional analysis and assumptions. The recoloring algorithm proposed by Latva-Kokko and Rothman is applied for phase segregation, which minimizes the spurious velocities and removes lattice pinning. This model is first validated against the Laplace law for a stationary bubble. It is found that the interfacial tension is predicted well for density ratios up to 1000. The model is then used to simulate droplet deformation and breakup in simple shear flow. We compute droplet deformation at small capillary numbers in the Stokes regime and find excellent agreement with the theoretical Taylor relation for the segregation parameter β=0.7. In the limit of creeping flow, droplet breakup occurs at a critical capillary number 0.35<Ca(c)<0.4 for the viscosity ratio of unity, consistent with previous numerical simulations and experiments. Droplet breakup can also be promoted by increasing the Reynolds number. Finally, we numerically investigate a single bubble rising under buoyancy force in viscous fluids for a wide range of Eötvös and Morton numbers. Numerical results are compared with theoretical predictions and experimental results, and satisfactory agreement is shown.}, }
@article {pmid22680531, year = {2012}, author = {Brosten, TR and Vogt, SJ and Seymour, JD and Codd, SL and Maier, RS}, title = {Preasymptotic hydrodynamic dispersion as a quantitative probe of permeability.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {4 Pt 2}, pages = {045301}, doi = {10.1103/PhysRevE.85.045301}, pmid = {22680531}, issn = {1550-2376}, mesh = {Biophysics/*methods ; Diffusion ; Electrochemistry/methods ; *Hydrodynamics ; Linear Models ; Magnetic Resonance Spectroscopy/*methods ; Models, Statistical ; *Permeability ; Porosity ; Stochastic Processes ; Time Factors ; Viscosity ; }, abstract = {We interpret a generalized short-time expansion of stochastic hydrodynamic dispersion dynamics in the case of small Reynolds number flow through macroscopically homogenous permeable porous media to directly determine hydrodynamic permeability. The approach allows determination of hydrodynamic permeability from pulsed field gradient spin-echo nuclear magnetic resonance measurement of the short-time effective hydrodynamic dispersion coefficient. The analytical expansion of asymptotic dynamics agrees with experimental NMR data and lattice Boltzmann simulation of hydrodynamic dispersion in consolidated random sphere pack media.}, }
@article {pmid22680412, year = {2012}, author = {Leoni, M and Liverpool, TB}, title = {Hydrodynamic synchronization of nonlinear oscillators at low Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {4 Pt 1}, pages = {040901}, doi = {10.1103/PhysRevE.85.040901}, pmid = {22680412}, issn = {1550-2376}, mesh = {Computer Simulation ; *Models, Chemical ; *Models, Molecular ; *Nonlinear Dynamics ; Oscillometry/*methods ; Rheology/*methods ; Water/*chemistry ; }, abstract = {We introduce a generic model of a weakly nonlinear self-sustained oscillator as a simplified tool to study synchronization in a fluid at low Reynolds number. By averaging over the fast degrees of freedom, we examine the effect of hydrodynamic interactions on the slow dynamics of two oscillators and show that they can lead to synchronization. Furthermore, we find that synchronization is strongly enhanced when the oscillators are nonisochronous, which on the limit cycle means the oscillations have an amplitude-dependent frequency. Nonisochronity is determined by a nonlinear coupling α being nonzero. We find that its (α) sign determines if they synchronize in phase or antiphase. We then study an infinite array of oscillators in the long-wavelength limit, in the presence of noise. For α>0, hydrodynamic interactions can lead to a homogeneous synchronized state. Numerical simulations for a finite number of oscillators confirm this and, when α<0, show the propagation of waves, reminiscent of metachronal coordination.}, }
@article {pmid22671425, year = {2012}, author = {Berendsen, CW and Zeegers, JC and Kruis, GC and Riepen, M and Darhuber, AA}, title = {Rupture of thin liquid films induced by impinging air-jets.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {28}, number = {26}, pages = {9977-9985}, doi = {10.1021/la301353f}, pmid = {22671425}, issn = {1520-5827}, mesh = {*Air ; Models, Theoretical ; *Pressure ; *Surface-Active Agents ; Time Factors ; }, abstract = {Thin liquid films on partially wetting substrates are subjected to laminar axisymmetric air-jets impinging at normal incidence. We measured the time at which film rupture occurs and dewetting commences as a function of diameter and Reynolds number of the air-jet. We developed numerical models for the air flow as well as the height evolution of the thin liquid film. The experimental results were compared with numerical simulations based on the lubrication approximation and a phenomenological expression for the disjoining pressure. We achieved quantitative agreement for the rupture times. We found that the film thickness profiles were highly sensitive to the presence of minute quantities of surface-active contaminants.}, }
@article {pmid22662054, year = {2011}, author = {Berry, JD and Davidson, MR and Bharti, RP and Harvie, DJ}, title = {Effect of wall permittivity on electroviscous flow through a contraction.}, journal = {Biomicrofluidics}, volume = {5}, number = {4}, pages = {44102-4410217}, pmid = {22662054}, issn = {1932-1058}, abstract = {The electroviscous flow at low Reynolds number through a two-dimensional slit contraction with electric double-layer overlap is investigated numerically for cases where the permittivity of the wall material is significant in comparison with the permittivity of the liquid. The liquid-solid interface is assumed to have uniform surface-charge density. It is demonstrated that a finite wall permittivity has a marked effect on the distribution of ions in and around the contraction, with a significant build-up of counter-ions observed at the back-step. The development length of the flow increases substantially as the wall permittivity becomes significant, meaning that the electric double-layers require a longer distance to develop within the contraction. Consequently, there is a corresponding decrease in the hydrodynamic and electro-potential resistance caused by the contraction. The effect of wall-region width on the flow characteristics is also quantified, demonstrating that the development length increases with increasing wall-region width for widths up to 5 channel widths.}, }
@article {pmid22639553, year = {2012}, author = {Hao, J and Li, Z and Lubkin, SR}, title = {AN AUGMENTED IMMERSED INTERFACE METHOD FOR MOVING STRUCTURES WITH MASS.}, journal = {Discrete and continuous dynamical systems. Series B}, volume = {17}, number = {4}, pages = {1175-1184}, pmid = {22639553}, issn = {1531-3492}, support = {R01 GM096195/GM/NIGMS NIH HHS/United States ; R01 GM096195-02/GM/NIGMS NIH HHS/United States ; }, abstract = {We present an augmented immersed interface method for simulating the dynamics of a deformable structure with mass in an incompressible fluid. The fluid is modeled by the Navier-Stokes equations in two dimensions. The acceleration of the structure due to mass is coupled with the flow velocity and the pressure. The surface tension of the structure is assumed to be a constant for simplicity. In our method, we treat the unknown acceleration as the only augmented variable so that the augmented immersed interface method can be applied. We use a modified projection method that can enforce the pressure jump conditions corresponding to the unknown acceleration. The acceleration must match the flow acceleration along the interface. The proposed augmented method is tested against an exact solution with a stationary interface. It shows that the augmented method has a second order of convergence in space. The dynamics of a deformable circular structure with mass is also investigated. It shows that the fluid-structure system has bi-stability: a stationary state for a smaller Reynolds number and an oscillatory state for a larger Reynolds number. The observation agrees with those in the literature.}, }
@article {pmid22616875, year = {2014}, author = {Tripathi, D and Bég, OA and Curiel-Sosa, JL}, title = {Homotopy semi-numerical simulation of peristaltic flow of generalised Oldroyd-B fluids with slip effects.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {17}, number = {4}, pages = {433-442}, doi = {10.1080/10255842.2012.688109}, pmid = {22616875}, issn = {1476-8259}, mesh = {Body Fluids/*physiology ; Hydrodynamics ; *Models, Biological ; Peristalsis ; Pressure ; }, abstract = {This investigation deals with the peristaltic flow of generalised Oldroyd-B fluids (with the fractional model) through a cylindrical tube under the influence of wall slip conditions. The analysis is carried out under the assumptions of long wavelength and low Reynolds number. Analytical approximate solutions are obtained by using the highly versatile and rigorous semi-numerical procedure known as the homotopy analysis method. It is assumed that the cross section of the tube varies sinusoidally along the length of the tube. The effects of the dominant hydromechanical parameters, i.e. fractional parameters, material constants, slip parameter, time and amplitude on the pressure difference across one wavelength, are studied. Graphical plots reveal that the influence of both fractional parameters on pressure is opposite to each other. Interesting responses to a variation in the constants are obtained. Pressure is shown to be reduced by increasing the slip parameter. Furthermore, the pressure in the case of fractional models (fractional Oldroyd-B model and fractional Maxwell model) of viscoelastic fluids is considerably more substantial than that in the corresponding classical viscoelastic models (Oldroyd-B and Maxwell models). Applications of the study arise in biophysical food processing, embryology and gastro-fluid dynamics.}, }
@article {pmid22587177, year = {2012}, author = {Du, J and Keener, JP and Guy, RD and Fogelson, AL}, title = {Low-Reynolds-number swimming in viscous two-phase fluids.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {3 Pt 2}, pages = {036304}, doi = {10.1103/PhysRevE.85.036304}, pmid = {22587177}, issn = {1550-2376}, mesh = {Elasticity ; *Hydrodynamics ; Models, Theoretical ; *Motion ; Viscosity ; }, abstract = {The fluid media surrounding many microorganisms are often mixtures of multiple materials with very different physical properties. The composition and rheology of the mixture may strongly affect the related locomotive behaviors. We study the classical Taylor's swimming sheet problem within a two-fluid model, which consists of two intermixed viscous fluids with different viscosities, with both numerical experiments and analysis. Our results indicate that both the swimming speed and efficiency may be decreased substantially relative to those for a single-phase fluid.}, }
@article {pmid22549087, year = {2012}, author = {Nichols, JT and Krueger, PS}, title = {Effect of vehicle configuration on the performance of a submersible pulsed-jet vehicle at intermediate Reynolds number.}, journal = {Bioinspiration &amp; biomimetics}, volume = {7}, number = {3}, pages = {036010}, doi = {10.1088/1748-3182/7/3/036010}, pmid = {22549087}, issn = {1748-3190}, mesh = {Animals ; Biomimetic Materials ; Biomimetics/*instrumentation ; Computer Simulation ; Computer-Aided Design ; Decapodiformes/*physiology ; Equipment Design ; Equipment Failure Analysis ; Immersion ; *Models, Biological ; Rheology/*instrumentation ; *Ships ; Swimming/*physiology ; }, abstract = {Recent results have demonstrated that pulsed-jet propulsion can achieve propulsive efficiency greater than that for steady jets when short, high frequency pulses are used, and the pulsed-jet advantage increases as Reynolds number decreases into the intermediate range (∼50). An important aspect of propulsive performance, however, is the vehicle configuration. The nozzle configuration influences the jet speed and, in the case of pulsed-jets, the formation of the vortex rings with each jet pulse, which have important effects on thrust. Likewise, the hull configuration influences the vehicle speed through its effect on drag. To investigate these effects, several flow inlet, nozzle, and hull tail configurations were tested on a submersible, self-propelled pulsed-jet vehicle ('Robosquid' for short) for jet pulse length-to-diameter ratios (L/D) in the range 0.5-6 and pulsing duty cycles (St(L)) of 0.2 and 0.5. For the configurations tested, the vehicle Reynolds number (Re(υ)) ranged from 25 to 110. In terms of propulsive efficiency, changing between forward and aft-facing inlets had little effect for the conditions considered, but changing from a smoothly tapered aft hull section to a blunt tail increased propulsive efficiency slightly due to reduced drag for the blunt tail at intermediate Re(υ). Sharp edged orifices also showed increased vehicle velocity and propulsive efficiency in comparison to smooth nozzles, which was associated with stronger vortex rings being produced by the flow contraction through the orifice. Larger diameter orifices showed additional gains in propulsive efficiency over smaller orifices if the rate of mass flow was matched with the smaller diameter cases, but using the same maximum jet velocity with the larger diameter decreased the propulsive efficiency relative to the smaller diameter cases.}, }
@article {pmid22540703, year = {2012}, author = {Jakiela, S and Korczyk, PM and Makulska, S and Cybulski, O and Garstecki, P}, title = {Discontinuous transition in a laminar fluid flow: a change of flow topology inside a droplet moving in a micron-size channel.}, journal = {Physical review letters}, volume = {108}, number = {13}, pages = {134501}, doi = {10.1103/PhysRevLett.108.134501}, pmid = {22540703}, issn = {1079-7114}, abstract = {Even at moderate values of Reynolds number [e.g., Re=O(1)] a curved interface between liquids can induce an abrupt transition between topologically different configurations of laminar flow. Here we show for the first time direct evidence of a sharp transition in the speed of flow of a droplet upon a small increase of the value of the capillary number above a threshold and the associated change of topology of flow. The quantitative results on the dependence of the threshold capillary number on the contrast of viscosities and on the direction of transition cannot be explained by any of the existing theories and call for a new description.}, }
@article {pmid22538166, year = {2012}, author = {Banerjee, S and Sutanto, S and Kleijn, JM and van Roosmalen, MJ and Witkamp, GJ and Stuart, MA}, title = {Colloidal interactions in liquid CO2--a dry-cleaning perspective.}, journal = {Advances in colloid and interface science}, volume = {175}, number = {}, pages = {11-24}, doi = {10.1016/j.cis.2012.03.005}, pmid = {22538166}, issn = {1873-3727}, mesh = {Carbon Dioxide/*chemistry ; *Clothing ; Colloids/chemistry ; Detergents/*chemistry ; Soil/analysis/chemistry ; Solvents/chemistry ; Surface-Active Agents/chemistry ; Tetrachloroethylene/*chemistry ; Water/chemistry ; }, abstract = {Liquid CO(2) is a viable alternative for the toxic and environmentally harmful solvents traditionally used in dry-cleaning industry. Although liquid CO(2) dry-cleaning is being applied already at a commercial scale, it is still a relatively young technique which poses many challenges. The focus of this review is on the causes of the existing problems and directions to solve them. After presenting an overview of the state-of-the-art, we analyze the detergency challenges from the fundamentals of colloid and interface science. The properties of liquid CO(2) such as dielectric constant, density, Hamaker constant, refractive index, viscosity and surface tension are presented and in the subsequent chapters their effects on CO(2) dry-cleaning operation are delineated. We show, based on theory, that the van der Waals forces between a model soil (silica) and model fabric (cellulose) through liquid CO(2) are much stronger compared to those across water or the traditional dry-cleaning solvent PERC (perchloroethylene). Prevention of soil particle redeposition in liquid CO(2) by electrostatic stabilization is challenging and the possibility of using electrolytes having large anionic parts is discussed. Furthermore, the role of different additives used in dry-cleaning, such as water, alcohol and surfactants, is reviewed. Water is not only used as an aid to remove polar soils, but also enhances adhesion between fabric and soil by forming capillary bridges. Its role as a minor component in liquid CO(2) is complex as it depends on many factors, such as the chemical nature of fabrics and soil, and also on the state of water itself, whether present as molecular solution in liquid CO(2) or phase separated droplets. The phenomena of wicking and wetting in liquid CO(2) systems are predicted from the Washburn-Lucas equation for fabrics of various surface energies and pore sizes. It is shown that nearly complete wetting is desirable for good detergency. The effect of mechanical action and fluid dynamic conditions on dry-cleaning is analyzed theoretically. From this it follows that in liquid CO(2) an order of magnitude higher Reynold's number is required to exceed the binding forces between fabric and soil as opposed to PERC or water, mainly due to the strong van der Waals forces and the low viscosity of CO(2) at dry-cleaning operational conditions.}, }
@article {pmid22533995, year = {2012}, author = {Siddiqui, SW and Norton, IT}, title = {Oil-in-water emulsification using confined impinging jets.}, journal = {Journal of colloid and interface science}, volume = {377}, number = {1}, pages = {213-221}, doi = {10.1016/j.jcis.2012.03.062}, pmid = {22533995}, issn = {1095-7103}, mesh = {Emulsions/chemistry ; Hexoses/chemistry ; Lecithins/chemistry ; *Microfluidic Analytical Techniques ; Milk Proteins/chemistry ; Plant Oils/*chemistry ; Polysorbates/chemistry ; Sodium Dodecyl Sulfate/chemistry ; Sunflower Oil ; Water/chemistry ; Whey Proteins ; }, abstract = {A confined impinging jet mixing device has been used to investigate the continuous sunflower oil/water emulsification process under turbulent flow conditions with oil contents between 5% (v/v) and 10% (v/v). Various emulsifiers (Tween20, Span80, Whey Protein, Lecithin and Sodium Dodecylsulphate) varying in molecular weights have been studied. Mean droplet sizes varied with the emulsifiers used and smallest droplets were obtained under fully turbulent flow regime, i.e. at the highest jet flow rate and highest jet Reynolds Number conditions. Sodium Dodecylsulfate (SDS) produced droplets in the range of 3.8 μm while 6 μm droplets were obtained with Whey Protein. Similar droplet sizes were obtained under fully turbulent flow conditions (610 mL/min; Reynolds Number=13,000) for oil content varying between 5% (v/v) and 10% (v/v). To investigate the smallest droplet size possible in the device, the emulsion was passed through the geometry multiple times. Multi-pass emulsification resulted in reduction in droplet size indicating that longer residence in the flow field under high shear condition allowed for breakage of droplets as well as the time for the emulsifier to stabilize the newly formed droplets, decreasing the impact of coalescence. This was confirmed by timescale analysis of the involved process steps for the droplet data obtained via experiments. Dependence of mean droplet size on the o/w interfacial tension and peak energy dissipation was also investigated.}, }
@article {pmid22531992, year = {2012}, author = {Valente, I and Stella, B and Marchisio, DL and Dosio, F and Barresi, AA}, title = {Production of PEGylated nanocapsules through solvent displacement in confined impinging jet mixers.}, journal = {Journal of pharmaceutical sciences}, volume = {101}, number = {7}, pages = {2490-2501}, doi = {10.1002/jps.23167}, pmid = {22531992}, issn = {1520-6017}, mesh = {Cyanoacrylates/chemistry ; Equipment Design ; Nanocapsules/*chemistry ; Nanotechnology/instrumentation ; Particle Size ; Polyethylene Glycols/*chemistry ; }, abstract = {The growth of importance of nanocapsules (and other particulate systems) in different fields requires fast and reproducible methods for their production. Confined impinging jet mixers were successfully used for the production of nanospheres and are now tested for the first time for the production of nanocapsules. This work focuses on the understanding of formation mechanisms and on the quantification of the effect of the most important operating parameters involved in their production. Solvent displacement is employed here for the assembly of the nanocapsules by using a PEGylated derivative of cyanoacrylate as copolymer. A comparison with nanospheres obtained under the same operating conditions is also reported. Results show that the oil-to-copolymer mass ratio (MR) is the main factor affecting the final size distribution and that small nanocapsules are obtained only at low oil-to-copolymer MR. The effect of mixing is significant, proving that mixing of solvent and antisolvent also affects the final size distribution; this depends mainly on the inlet jet velocity, but the size of the mixer is also important. The Reynolds number may be useful to take this into account for geometrically similar systems. Quenching by dilution allows to stabilize the nanocapsules, evidencing the role of aggregation and ripening.}, }
@article {pmid22529933, year = {2012}, author = {Lichter, S and Rafferty, B and Flohr, Z and Martini, A}, title = {Protein high-force pulling simulations yield low-force results.}, journal = {PloS one}, volume = {7}, number = {4}, pages = {e34781}, pmid = {22529933}, issn = {1932-6203}, mesh = {Hydrodynamics ; *Molecular Dynamics Simulation ; Protein Conformation ; *Protein Unfolding ; Proteins/*chemistry ; }, abstract = {All-atom explicit-solvent molecular dynamics simulations are used to pull with extremely large constant force (750-3000 pN) on three small proteins. The introduction of a nondimensional timescale permits direct comparison of unfolding across all forces. A crossover force of approximately 1100 pN divides unfolding dynamics into two regimes. At higher forces, residues sequentially unfold from the pulling end while maintaining the remainder of the protein force-free. Measurements of hydrodynamic viscous stresses are made easy by the high speeds of unfolding. Using an exact low-Reynolds-number scaling, these measurements can be extrapolated to provide, for the first time, an estimate of the hydrodynamic force on low-force unfolding. Below 1100 pN, but surprisingly still at extremely large applied force, intermediate states and cooperative unfoldings as seen at much lower forces are observed. The force-insensitive persistence of these structures indicates that decomposition into unfolded fragments requires a large fluctuation. This finding suggests how proteins are constructed to resist transient high force. The progression of [Formula: see text] helix and [Formula: see text] sheet unfolding is also found to be insensitive to force. The force-insensitivity of key aspects of unfolding opens the possibility that numerical simulations can be accelerated by high applied force while still maintaining critical features of unfolding.}, }
@article {pmid22517056, year = {2012}, author = {McFaul, SM and Lin, BK and Ma, H}, title = {Cell separation based on size and deformability using microfluidic funnel ratchets.}, journal = {Lab on a chip}, volume = {12}, number = {13}, pages = {2369-2376}, doi = {10.1039/c2lc21045b}, pmid = {22517056}, issn = {1473-0189}, support = {//Canadian Institutes of Health Research/Canada ; }, mesh = {Animals ; Cell Line, Tumor ; *Cell Separation ; Cell Size ; Humans ; Leukocytes, Mononuclear/*cytology ; Mice ; Microfluidic Analytical Techniques/*instrumentation/methods ; }, abstract = {The separation of biological cells by filtration through microstructured constrictions is limited by unpredictable variations of the filter hydrodynamic resistance as cells accumulate in the microstructure. Applying a reverse flow to unclog the filter will undo the separation and reduce filter selectivity because of the reversibility of low-Reynolds number flow. We introduce a microfluidic structural ratchet mechanism to separate cells using oscillatory flow. Using model cells and microparticles, we confirmed the ability of this mechanism to sort and separate cells and particles based on size and deformability. We further demonstrate that the spatial distribution of cells after sorting is repeatable and that the separation process is irreversible. This mechanism can be applied generally to separate cells that differ based on size and deformability.}, }
@article {pmid22498691, year = {2012}, author = {Johnston, J and Gopalarathnam, A}, title = {Investigation of a bio-inspired lift-enhancing effector on a 2D airfoil.}, journal = {Bioinspiration &amp; biomimetics}, volume = {7}, number = {3}, pages = {036003}, doi = {10.1088/1748-3182/7/3/036003}, pmid = {22498691}, issn = {1748-3190}, mesh = {*Aircraft ; Animals ; *Biomimetic Materials ; Biomimetics/*instrumentation ; Birds/*physiology ; Computer Simulation ; Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Flight, Animal/*physiology ; *Models, Biological ; Movement/*physiology ; Wings, Animal/*physiology ; }, abstract = {A flap mounted on the upper surface of an airfoil, called a 'lift-enhancing effector', has been shown in wind tunnel tests to have a similar function to a bird's covert feathers, which rise off the wing's surface in response to separated flows. The effector, fabricated from a thin Mylar sheet, is allowed to rotate freely about its leading edge. The tests were performed in the NCSU subsonic wind tunnel at a chord Reynolds number of 4 × 10(5). The maximum lift coefficient with the effector was the same as that for the clean airfoil, but was maintained over an angle-of-attack range from 12° to almost 20°, resulting in a very gentle stall behavior. To better understand the aerodynamics and to estimate the deployment angle of the free-moving effector, fixed-angle effectors fabricated out of stiff wood were also tested. A progressive increase in the stall angle of attack with increasing effector angle was observed, with diminishing returns beyond the effector angle of 60°. Drag tests on both the free-moving and fixed effectors showed a marked improvement in drag at high angles of attack. Oil flow visualization on the airfoil with and without the fixed-angle effectors proved that the effector causes the separation point to move aft on the airfoil, as compared to the clean airfoil. This is thought to be the main mechanism by which an effector improves both lift and drag. A comparison of the fixed-effector results with those from the free-effector tests shows that the free effector's deployment angle is between 30° and 45°. When operating at and beyond the clean airfoil's stall angle, the free effector automatically deploys to progressively higher angles with increasing angles of attack. This slows down the rapid upstream movement of the separation point and avoids the severe reduction in the lift coefficient and an increase in the drag coefficient that are seen on the clean airfoil at the onset of stall. Thus, the effector postpones the stall by 4-8° and makes the stall behavior more gentle. The benefits of using the effector could include care-free operations at high angles of attack during perching and maneuvering flight, especially in gusty conditions.}, }
@article {pmid22463643, year = {2012}, author = {Hultmark, M and Vallikivi, M and Bailey, SC and Smits, AJ}, title = {Turbulent pipe flow at extreme Reynolds numbers.}, journal = {Physical review letters}, volume = {108}, number = {9}, pages = {094501}, doi = {10.1103/PhysRevLett.108.094501}, pmid = {22463643}, issn = {1079-7114}, abstract = {Both the inherent intractability and complex beauty of turbulence reside in its large range of physical and temporal scales. This range of scales is captured by the Reynolds number, which in nature and in many engineering applications can be as large as 10(5)-10(6). Here, we report turbulence measurements over an unprecedented range of Reynolds numbers using a unique combination of a high-pressure air facility and a new nanoscale anemometry probe. The results reveal previously unknown universal scaling behavior for the turbulent velocity fluctuations, which is remarkably similar to the well-known scaling behavior of the mean velocity distribution.}, }
@article {pmid22463354, year = {2012}, author = {Li, Q and Luo, KH and Gao, YJ and He, YL}, title = {Additional interfacial force in lattice Boltzmann models for incompressible multiphase flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {2 Pt 2}, pages = {026704}, doi = {10.1103/PhysRevE.85.026704}, pmid = {22463354}, issn = {1550-2376}, abstract = {The existing lattice Boltzmann models for incompressible multiphase flows are mostly constructed with two distribution functions: one is the order parameter distribution function, which is used to track the interface between different phases, and the other is the pressure distribution function for solving the velocity field. In this paper, it is shown that in these models the recovered momentum equation is inconsistent with the target one: an additional force is included in the recovered momentum equation. The additional force has the following features. First, it is proportional to the macroscopic velocity. Second, it is zero in every single-phase region but is nonzero in the interface. Therefore it can be interpreted as an interfacial force. To investigate the effects of the additional interfacial force, numerical simulations are carried out for the problem of Rayleigh-Taylor instability, droplet splashing on a thin liquid film, and the evolution of a falling droplet under gravity. Numerical results demonstrate that, with the increase of the velocity or the Reynolds number, the additional interfacial force will gradually have an important influence on the interface and affect the numerical accuracy.}, }
@article {pmid22463328, year = {2012}, author = {Tamayol, A and Wong, KW and Bahrami, M}, title = {Effects of microstructure on flow properties of fibrous porous media at moderate Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {2 Pt 2}, pages = {026318}, doi = {10.1103/PhysRevE.85.026318}, pmid = {22463328}, issn = {1550-2376}, mesh = {*Hydrodynamics ; Microtechnology/*methods ; Models, Theoretical ; Porosity ; }, abstract = {In this study, effects of microstructure on the viscous permeability and Forchheimer coefficient of monodispersed fibers are investigated. The porous material is represented by a unit cell which is assumed to be repeated throughout the medium. Based on the orientation of the fibers in the space, fibrous media are divided into three categories: one-, two-, and three-directional (1D, 2D, and 3D) structures. Parallel and transverse flow through square arrangements of 1D fibers, simple 2D mats, and 3D simple cubic structures are solved numerically over a wide range of porosity (0.35 < ε < 0.95) and Reynolds number (0.01 < Re < 200). The results are used to calculate the permeability and the inertial coefficient of the considered geometries. An experimental study is performed; the flow coefficients of three different ordered tube banks in the moderate range of Reynolds number (0.001 < Re < 15) are determined. The numerical results are successfully compared with the present and the existing experimental data in the literature. The results suggest that the permeability and Forchheimer coefficient are functions of porosity and fiber orientation. A comparison of the experimental and numerical results with the Ergun equation reveals that this equation is not suitable for highly porous materials. As such, accurate correlations are proposed for determining the Forchheimer coefficient in fibrous porous media.}, }
@article {pmid22463313, year = {2012}, author = {Schober, J and Schleicher, D and Federrath, C and Klessen, R and Banerjee, R}, title = {Magnetic field amplification by small-scale dynamo action: dependence on turbulence models and Reynolds and Prandtl numbers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {2 Pt 2}, pages = {026303}, doi = {10.1103/PhysRevE.85.026303}, pmid = {22463313}, issn = {1550-2376}, abstract = {The small-scale dynamo is a process by which turbulent kinetic energy is converted into magnetic energy, and thus it is expected to depend crucially on the nature of the turbulence. In this paper, we present a model for the small-scale dynamo that takes into account the slope of the turbulent velocity spectrum v(ℓ)proportional ℓ([symbol see text])V}, where ℓ and v(ℓ) are the size of a turbulent fluctuation and the typical velocity on that scale. The time evolution of the fluctuation component of the magnetic field, i.e., the small-scale field, is described by the Kazantsev equation. We solve this linear differential equation for its eigenvalues with the quantum-mechanical WKB approximation. The validity of this method is estimated as a function of the magnetic Prandtl number Pm. We calculate the minimal magnetic Reynolds number for dynamo action, Rm_{crit}, using our model of the turbulent velocity correlation function. For Kolmogorov turbulence ([symbol see text] = 1/3), we find that the critical magnetic Reynolds number is Rm(crit) (K) ≈ 110 and for Burgers turbulence ([symbol see text] = 1/2) Rm(crit)(B) ≈ 2700. Furthermore, we derive that the growth rate of the small-scale magnetic field for a general type of turbulence is Γ proportional Re((1-[symbol see text])/(1+[symbol see text])) in the limit of infinite magnetic Prandtl number. For decreasing magnetic Prandtl number (down to Pm >/~ 10), the growth rate of the small-scale dynamo decreases. The details of this drop depend on the WKB approximation, which becomes invalid for a magnetic Prandtl number of about unity.}, }
@article {pmid22463271, year = {2012}, author = {Lemoult, G and Aider, JL and Wesfreid, JE}, title = {Experimental scaling law for the subcritical transition to turbulence in plane Poiseuille flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {2 Pt 2}, pages = {025303}, doi = {10.1103/PhysRevE.85.025303}, pmid = {22463271}, issn = {1550-2376}, abstract = {We present an experimental study of the transition to turbulence in a plane Poiseuille flow. Using a well-controlled perturbation, we analyze the flow by using extensive particle image velocimetry and flow visualization (using laser-induced fluorescence) measurements, and use the deformation of the mean velocity profile as a criterion to characterize the state of the flow. From a large parametric study, four different states are defined, depending on the values of the Reynolds number and the amplitude of the perturbation. We discuss the role of coherent structures, such as hairpin vortices, in the transition. We find that the minimal amplitude of the perturbation triggering transition scales asymptotically as Re(-1).}, }
@article {pmid22463269, year = {2012}, author = {Babler, MU and Biferale, L and Lanotte, AS}, title = {Breakup of small aggregates driven by turbulent hydrodynamical stress.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {2 Pt 2}, pages = {025301}, doi = {10.1103/PhysRevE.85.025301}, pmid = {22463269}, issn = {1550-2376}, abstract = {The breakup of small solid aggregates in homogeneous and isotropic turbulence is studied theoretically and by using direct numerical simulations at high Reynolds number, Reλ =/~ 400. We show that turbulent fluctuations of the hydrodynamic stress along the aggregate trajectory play a key role in determining the aggregate mass distribution function. The differences between turbulent and laminar flows are discussed. A definition of the fragmentation rate is proposed in terms of the typical frequency at which the hydrodynamic stress becomes sufficiently high to cause breakup along each Lagrangian path. We also define an Eulerian proxy of the real fragmentation rate, based on the joint statistics of the stress and its time derivative, which should be easier to measure in any experimental setup. Both our Eulerian and Lagrangian formulations define a clear procedure for the computation of the mass distribution function due to fragmentation. Contrary, previous estimates based only on single point statistics of the hydrodynamic stress exhibit some deficiencies. These are discussed by investigating the evolution of an ensemble of aggregates undergoing breakup and aggregation.}, }
@article {pmid22463238, year = {2012}, author = {Reid, DA and Hildenbrandt, H and Padding, JT and Hemelrijk, CK}, title = {Fluid dynamics of moving fish in a two-dimensional multiparticle collision dynamics model.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {2 Pt 1}, pages = {021901}, doi = {10.1103/PhysRevE.85.021901}, pmid = {22463238}, issn = {1550-2376}, mesh = {Animals ; Computer Simulation ; Fishes/*physiology ; *Models, Biological ; Particle Size ; Rheology/*methods ; Swimming/*physiology ; }, abstract = {The fluid dynamics of animal locomotion, such as that of an undulating fish, are of great interest to both biologists and engineers. However, experimentally studying these fluid dynamics is difficult and time consuming. Model studies can be of great help because of their simpler and more detailed analysis. Their insights may guide empirical work. Particularly the recently introduced multiparticle collision dynamics method may be suitable for the study of moving organisms because it is computationally fast, simple to implement, and has a continuous representation of space. As regards the study of hydrodynamics of moving organisms, the method has only been applied at low Reynolds numbers (below 120) for soft, permeable bodies, and static fishlike shapes. In the present paper we use it to study the hydrodynamics of an undulating fish at Reynolds numbers 1100-1500, after confirming its performance for a moving insect wing at Reynolds number 75. We measure (1) drag, thrust, and lift forces, (2) swimming efficiency and spatial structure of the wake, and (3) distribution of forces along the fish body. We confirm the resemblance between the simulated undulating fish and empirical data. In contrast to theoretical predictions, our model shows that for steadily undulating fish, thrust is produced by the rear 2/3 of the body and that the slip ratio U/V (with U the forward swimming speed and V the rearward speed of the body wave) correlates negatively (instead of positively) with the actual Froude efficiency of swimming. Besides, we show that the common practice of modeling individuals while constraining their sideways acceleration causes them to resemble unconstrained fish with a higher tailbeat frequency.}, }
@article {pmid22443967, year = {2012}, author = {Sun, ZH and Zhang, X and Guo, M and Pandelaers, L and Vleugels, J and Van der Biest, O and Van Reusel, K and Blanpain, B}, title = {Strong magnetic field effects on solid-liquid and particle-particle interactions during the processing of a conducting liquid containing non-conducting particles.}, journal = {Journal of colloid and interface science}, volume = {375}, number = {1}, pages = {203-212}, doi = {10.1016/j.jcis.2012.02.059}, pmid = {22443967}, issn = {1095-7103}, abstract = {The behavior of micrometer-sized weak magnetic insulating particles migrating in a conductive liquid metal is of broad interest during strong magnetic field processing of materials. In the present paper, we develop a numerical method to investigate the solid-liquid and particle-particle interactions by using a computational fluid dynamics (CFDs) modeling. By applying a strong magnetic field, for example, 10 Tesla, the drag forces of a single spherical particle can be increased up to around 15% at a creeping flow limit. However, magnetic field effects are reduced when the Reynolds number becomes higher. For two identical particles migrating along their centerline in a conductive liquid, both the drag forces and the magnetic interaction will be influenced. Factors such as interparticle distance, Reynolds number and magnetic flux density are investigated. Shielding effects are found from the leading particle, which will subsequently induce a hydrodynamic interaction between two particles. Strong magnetic fields however do not appear to have a significant influence on the shielding effects. In addition, the magnetic interaction forces of magnetic dipole-dipole interaction and induced magneto-hydrodynamic interaction are considered. It can be found that the induced magneto-hydrodynamic interaction force highly depends on the flow field and magnetic flux density. Therefore, the interaction between insulating particles can be controlled by applying a strong magnetic field and modifying the flow field. The present research provides a better understanding of the magnetic field induced interaction during liquid metal processing, and a method of non-metallic particles manipulation for metal/ceramic based materials preparation may be proposed.}, }
@article {pmid22438496, year = {2012}, author = {Gemmell, BJ and Jiang, H and Strickler, JR and Buskey, EJ}, title = {Plankton reach new heights in effort to avoid predators.}, journal = {Proceedings. Biological sciences}, volume = {279}, number = {1739}, pages = {2786-2792}, pmid = {22438496}, issn = {1471-2954}, mesh = {Animals ; Biomechanical Phenomena ; Copepoda/*physiology ; *Escape Reaction ; Fishes/*physiology ; *Motor Activity ; *Predatory Behavior ; Video Recording ; }, abstract = {The marine environment associated with the air-water interface (neuston) provides an important food source to pelagic organisms where subsurface prey is limited. However, studies on predator-prey interactions within this environment are lacking. Copepods are known to produce strong escape jumps in response to predators, but must contend with a low-Reynolds-number environment where viscous forces limit escape distance. All previous work on copepod interaction with predators has focused on a liquid environment. Here, we describe a novel anti-predator behaviour in two neustonic copepod species, where individuals frequently exit the water surface and travel many times their own body length through air to avoid predators. Using both field recordings with natural predators and high-speed laboratory recordings, we obtain detailed kinematics of this behaviour, and estimate energetic cost associated with this behaviour. We demonstrate that despite losing up to 88 per cent of their initial kinetic energy, copepods that break the water surface travel significantly further than those escaping underwater and successfully exit the perceptive field of the predator. This behaviour provides an effective defence mechanism against subsurface-feeding visual predators and the results provide insight into trophic interactions within the neustonic environment.}, }
@article {pmid22428106, year = {2012}, author = {Vilfan, M and Kokot, G and Vilfan, A and Osterman, N and Kavčič, B and Poberaj, I and Babič, D}, title = {Analysis of fluid flow around a beating artificial cilium.}, journal = {Beilstein journal of nanotechnology}, volume = {3}, number = {}, pages = {163-171}, pmid = {22428106}, issn = {2190-4286}, abstract = {Biological cilia are found on surfaces of some microorganisms and on surfaces of many eukaryotic cells where they interact with the surrounding fluid. The periodic beating of the cilia is asymmetric, resulting in directed swimming of unicellular organisms or in generation of a fluid flow above a ciliated surface in multicellular ones. Following the biological example, externally driven artificial cilia have recently been successfully implemented as micropumps and mixers. However, biomimetic systems are useful not only in microfluidic applications, but can also serve as model systems for the study of fundamental hydrodynamic phenomena in biological samples. To gain insight into the basic principles governing propulsion and fluid pumping on a micron level, we investigated hydrodynamics around one beating artificial cilium. The cilium was composed of superparamagnetic particles and driven along a tilted cone by a varying external magnetic field. Nonmagnetic tracer particles were used for monitoring the fluid flow generated by the cilium. The average flow velocity in the pumping direction was obtained as a function of different parameters, such as the rotation frequency, the asymmetry of the beat pattern, and the cilium length. We also calculated the velocity field around the beating cilium by using the analytical far-field expansion. The measured average flow velocity and the theoretical prediction show an excellent agreement.}, }
@article {pmid22426194, year = {2012}, author = {Zhang, L and Petit, T and Peyer, KE and Nelson, BJ}, title = {Targeted cargo delivery using a rotating nickel nanowire.}, journal = {Nanomedicine : nanotechnology, biology, and medicine}, volume = {8}, number = {7}, pages = {1074-1080}, doi = {10.1016/j.nano.2012.03.002}, pmid = {22426194}, issn = {1549-9642}, mesh = {Blood Cells/cytology ; Humans ; Magnetic Fields ; Micromanipulation/*methods ; Microspheres ; Motion ; Nanowires/*chemistry/ultrastructure ; Nickel/*chemistry ; Rotation ; Single-Cell Analysis/*methods ; }, abstract = {UNLABELLED: This paper reports an approach to perform basic noncontact and contact manipulation tasks using rotating nickel nanowires driven by a rotating magnetic field. A rotating nanowire is capable of propulsion and steering near a solid surface by a tumbling motion. The FEM simulation shows that fluid flow is induced around the rotating nanowire, which was applied to manipulate micro-objects in a noncontact fashion. Pushing, pulling, and rotation tests of individual polystyrene microbeads are conducted on a solid surface. In addition, targeted delivery tasks of biological samples, e.g., individual flagellated microorganisms and human blood cells, are demonstrated. The results imply that rotating magnetic nanowires are good tools for handling cellular and subcellular objects in an aqueous low-Reynolds-number environment and have potential for single-cell analysis.<br><br>FROM THE CLINICAL EDITOR: In this study, the authors report the ability to push, pull, and rotate individual polystyrene microbeads on a solid surface. Furthermore, they demonstrate targeted delivery of biological samples, implying that rotating magnetic nanowires are good tools for handling cellular and subcellular objects.}, }
@article {pmid22418895, year = {2012}, author = {Butler, CJ and Ryan, K and Sheard, GJ}, title = {Haemodynamic forces on in vitro thrombi: a numerical analysis.}, journal = {Medical &amp; biological engineering &amp; computing}, volume = {50}, number = {5}, pages = {493-502}, pmid = {22418895}, issn = {1741-0444}, mesh = {Blood Platelets/*physiology ; Hemorheology/physiology ; Humans ; *Models, Cardiovascular ; Platelet Adhesiveness/physiology ; Stress, Mechanical ; Thrombosis/*blood ; }, abstract = {The flow of blood past an axisymmetric thrombus analogue, within an in vitro geometry, is computed via solution of the discrete three-dimensional (3D) Navier-Stokes equations. Particle tracking is used to model the behaviour of thrombocytes (platelets) moving throughout the domain and to investigate behaviour with respect to the platelets. The system is explored using shear rate to quantify the effects an idealised thrombus has with respect to an undisturbed in vitro geometry over 'Poiseuille flow' shear rate conditions applicable to in vivo and in vitro experiments (1,200-10,000 s[-1]). Local shear rate variations show peaks in shear rate greater than double that of Poiseuille flow conditions. These local shear rate variations are observed to be non-linear, despite the low Reynolds number (5.2-43.4) within the system. Topological transitions of shear rate are observed, limiting the height of peak shear rate within the system, suggesting a thrombus growth limiting behaviour. Temporal gradients of shear rate, measured with respect to individual platelets, were calculated. Multiple regions of peak shear rate gradient were observed throughout the flow, suggesting that platelet-platelet interaction may not be limited to regions near to the surface of the thrombus.}, }
@article {pmid22400849, year = {2012}, author = {Chaudhuri, S and Wu, F and Zhu, D and Law, CK}, title = {Flame speed and self-similar propagation of expanding turbulent premixed flames.}, journal = {Physical review letters}, volume = {108}, number = {4}, pages = {044503}, doi = {10.1103/PhysRevLett.108.044503}, pmid = {22400849}, issn = {1079-7114}, abstract = {In this Letter we present turbulent flame speeds and their scaling from experimental measurements on constant-pressure, unity Lewis number expanding turbulent flames, propagating in nearly homogeneous isotropic turbulence in a dual-chamber, fan-stirred vessel. It is found that the normalized turbulent flame speed as a function of the average radius scales as a turbulent Reynolds number to the one-half power, where the average radius is the length scale and the thermal diffusivity is the transport property, thus showing self-similar propagation. Utilizing this dependence it is found that the turbulent flame speeds from the present expanding flames and those from the Bunsen geometry in the literature can be unified by a turbulent Reynolds number based on flame length scales using recent theoretical results obtained by spectral closure of the transformed G equation.}, }
@article {pmid22400654, year = {2012}, author = {Noskov, V and Denisov, S and Stepanov, R and Frick, P}, title = {Turbulent viscosity and turbulent magnetic diffusivity in a decaying spin-down flow of liquid sodium.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {1 Pt 2}, pages = {016303}, doi = {10.1103/PhysRevE.85.016303}, pmid = {22400654}, issn = {1550-2376}, abstract = {The free decay of a strong flow of liquid sodium (at Reynolds number defined via the maximal mean velocity and the radius of the channel cross section up to Re≈3×10(60) and the corresponding magnetic Reynolds number up to Rm≈30) generated by the sudden stop of a rapidly rotating toroidal channel is studied experimentally. The toroidal and poloidal components of velocity are measured using a potential probe. We describe the onset of motion, the evolution of strongly anisotropic fluctuations, and the homogenization and decay of turbulence in the final period. We analyze the statistical characteristics of velocity fields in relation to the behavior of effective magnetic diffusivity estimated from measurements of the phase shift between the induced and applied magnetic fields. For the late (self-similar) decay of turbulent flow, turbulent viscosity is shown to be dependent on the root-mean-square velocity pulsations and can be expressed as νt∼νRe1.3. The behavior of turbulent magnetic diffusivity depends on the magnetic Reynolds number defined in terms of the root-mean-square velocity pulsations. At low magnetic Reynolds numbers (Rmrms<1), turbulent magnetic diffusivity grows rapidly with increasing velocity pulsations (ηt∼ηRmrms2). If the magnetic Reynolds number exceeds unity, the behavior of turbulent magnetic diffusivity becomes similar to the behavior of turbulent viscosity. The highest values of turbulent magnetic diffusivity are achieved at the end of braking, which corresponds to the transient stage of a strongly anisotropic turbulent flow in which the poloidal velocity oscillations prevail.}, }
@article {pmid22400615, year = {2012}, author = {Chakraborty, S and Frisch, U and Pauls, W and Ray, SS}, title = {Nelkin scaling for the Burgers equation and the role of high-precision calculations.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {85}, number = {1 Pt 2}, pages = {015301}, doi = {10.1103/PhysRevE.85.015301}, pmid = {22400615}, issn = {1550-2376}, abstract = {Nelkin scaling, the scaling of moments of velocity gradients in terms of the Reynolds number, is an alternative way of obtaining inertial-range information. It is shown numerically and theoretically for the Burgers equation that this procedure works already for Reynolds numbers of the order of 100 (or even lower when combined with a suitable extended self-similarity technique). At moderate Reynolds numbers, for the accurate determination of scaling exponents, it is crucial to use higher than double precision. Similar issues are likely to arise for three-dimensional Navier-Stokes simulations.}, }
@article {pmid22393813, year = {2012}, author = {Huang, CH and Alonso, M}, title = {Influence of particle location on the number of charges per charged nanoparticle at the outlet of a needle charger.}, journal = {Journal of the Air &amp; Waste Management Association (1995)}, volume = {62}, number = {1}, pages = {87-91}, doi = {10.1080/10473289.2011.617609}, pmid = {22393813}, issn = {1096-2247}, mesh = {Air Pollutants/*chemistry ; *Electrochemistry ; Environmental Monitoring/instrumentation ; *Nanoparticles ; Particulate Matter/*chemistry ; *Static Electricity ; }, abstract = {This study has investigated numerically the influence of particle location on the number of charges per charged particle in the 10-40 nm size range at the outlet of a needle charger by simulating flow field, electric field, particle charging, and particle trajectory at various conditions. The results show that the total (i.e., diffusion + field charging) number of charges per particle increase with decreasing ratio values of radial location at the outlet of the charger due to the particle position close to the needle tip. It has also been shown that in the outlet region of the charger there is a critical radial location at which the number of charges per particle is a maximum; this critical radial location represents the point at which the charged particle trajectory becomes closest to the needle electrode. The maximum value of number of charges increases with increasing Reynolds number and slightly increases with decreasing applied voltage for particle diameter larger than 20 nm. The maximum number of charges per charged nanoparticle increases with increasing particle diameter. In addition, the minimum ratio value of radial particle location decreases with increasing Reynolds number for various particle diameters.}, }
@article {pmid22382672, year = {2012}, author = {Gurovich, AN and Braith, RW}, title = {Analysis of both pulsatile and streamline blood flow patterns during aerobic and resistance exercise.}, journal = {European journal of applied physiology}, volume = {112}, number = {11}, pages = {3755-3764}, pmid = {22382672}, issn = {1439-6327}, mesh = {Adult ; Blood Flow Velocity/*physiology ; Brachial Artery/physiology ; Exercise/*physiology ; Femoral Artery/physiology ; Hemodynamics ; Humans ; Male ; Pulsatile Flow/*physiology ; Stress, Mechanical ; }, abstract = {Blood flow-induced endothelial shear stress (ESS) during aerobic (AX) and resistance (RX) exercise can regulate endothelial function. However, non-invasive in vivo ESS estimation is normally obtained only according to Poiseuille's laws for streamline flow, rather than using Womersley's approximation for pulsatile flows. Here, we sought to determine brachial and femoral artery blood flow patterns, based on ESS, flow direction, and flow turbulence, using both pulsatile and streamline flow approximations during low- and moderate-intensity AX and RX. We performed high-resolution ultrasound imaging and Doppler peak blood flow velocity (V) measurements of the brachial and femoral arteries in eight young, healthy men during rest and two intensities of AX and RX at 40 and 70% of VO2max and 1-RM, respectively. Microhematocrit measurement was used to determine blood density (ρ) and viscosity (μ). ESS was calculated using Poiseuille's law, ESS = 2μ × SR (V/artery diameter), and Womersley's approximation, ESS = 2 Kμ × SR, where K is a function of Womersley's parameter α. Turbulence was determined using Reynolds number (Re). Re was calculated using Re = V × artery diameter × ρ/μ and normalized to resting steady-state values (nRe). ESS increases in a dose-dependent manner in the femoral and brachial arteries during both AX and RX when using either streamline or pulsatile approximations. However, our findings indicate that ESS is underestimated when using Poiseuille's law. Secondly, turbulence increases in conduit arteries with exercise intensity in a dose-dependent manner in both retrograde and antegrade flows during both AX and RX.}, }
@article {pmid22380105, year = {2012}, author = {Chien, SH and Hsieh, MK and Li, H and Monnell, J and Dzombak, D and Vidic, R}, title = {Pilot-scale cooling tower to evaluate corrosion, scaling, and biofouling control strategies for cooling system makeup water.}, journal = {The Review of scientific instruments}, volume = {83}, number = {2}, pages = {024101}, doi = {10.1063/1.3680563}, pmid = {22380105}, issn = {1089-7623}, mesh = {Biofouling/*prevention &amp; control ; Corrosion ; Equipment Design ; Industry/*instrumentation ; Pilot Projects ; *Temperature ; Thermodynamics ; Volatilization ; Water/*chemistry ; }, abstract = {Pilot-scale cooling towers can be used to evaluate corrosion, scaling, and biofouling control strategies when using particular cooling system makeup water and particular operating conditions. To study the potential for using a number of different impaired waters as makeup water, a pilot-scale system capable of generating 27,000 kJ∕h heat load and maintaining recirculating water flow with a Reynolds number of 1.92 × 10(4) was designed to study these critical processes under conditions that are similar to full-scale systems. The pilot-scale cooling tower was equipped with an automatic makeup water control system, automatic blowdown control system, semi-automatic biocide feeding system, and corrosion, scaling, and biofouling monitoring systems. Observed operational data revealed that the major operating parameters, including temperature change (6.6 °C), cycles of concentration (N = 4.6), water flow velocity (0.66 m∕s), and air mass velocity (3660 kg∕h m(2)), were controlled quite well for an extended period of time (up to 2 months). Overall, the performance of the pilot-scale cooling towers using treated municipal wastewater was shown to be suitable to study critical processes (corrosion, scaling, biofouling) and evaluate cooling water management strategies for makeup waters of complex quality.}, }
@article {pmid22378463, year = {2013}, author = {Zierenberg, JR and Halpern, D and Filoche, M and Sapoval, B and Grotberg, JB}, title = {An asymptotic model of particle deposition at an airway bifurcation.}, journal = {Mathematical medicine and biology : a journal of the IMA}, volume = {30}, number = {2}, pages = {131-156}, pmid = {22378463}, issn = {1477-8602}, support = {R01 HL085156/HL/NHLBI NIH HHS/United States ; HL85156/HL/NHLBI NIH HHS/United States ; }, mesh = {Aerosols ; Biological Transport, Active ; Humans ; Hydrodynamics ; Mathematical Concepts ; *Models, Biological ; Particle Size ; Particulate Matter/*pharmacokinetics ; *Respiratory Physiological Phenomena ; Respiratory System/*anatomy &amp; histology ; Tissue Distribution ; }, abstract = {Particle transport and deposition associated with flow over a wedge is investigated as a model for particle transport and flow at the carina of an airway bifurcation during inspiration. Using matched asymptotics, a uniformly valid solution is obtained to represent the high Reynolds number flow over a wedge that considers the viscous boundary layer near the wedge and the outer inviscid region and is then used to solve the particle transport equations. Sometimes particle impaction on the wedge is prevented due to the boundary layer. We call this boundary layer shielding (BLS). This effect can be broken down into different types: rejection, trapping and deflection that are described by what happens to the particle's initial negative velocity normal to the wall either changing sign, reaching zero, or remaining negative in the boundary layer region. The deposition efficiency depends on the critical Stokes number but exhibits a weak dependence on Reynolds number. Deposition efficiency for S(c) in the range 0 < S(c) < 0.4 yields the following relationship De ≈ (1.867S(c)[1]·[78]-0.016) sin(βπ/2) at large Reynolds numbers, where βπ is the wedge angle. For a specific deposition efficiency, S(c) decreases as βπ increases. The distribution of impacted particles was also computed and revealed that particles primarily impact within one airway diameter of the carina, consistent with computational fluid dynamics approaches. This work provides a new insight that the BLS inherent to the wedge component of the structure is the dominant reason for the particle distribution. This finding is important in linking aerosol deposition to the location of airway disease as well as target sites for therapeutic deposition.}, }
@article {pmid22372464, year = {2012}, author = {Park, CS and Jeon, SW and Lee, KJ and Kim, JS and Oh, JG and Park, JC and Lee, HS and Choi, YS}, title = {Wind-drag estimation in a traffic accident involving a motor scooter and a tractor-trailer.}, journal = {Journal of forensic sciences}, volume = {57}, number = {4}, pages = {1108-1113}, doi = {10.1111/j.1556-4029.2012.02082.x}, pmid = {22372464}, issn = {1556-4029}, abstract = {This case report describes a noncontact traffic accident involving a motor scooter and a tractor-trailer with a focus on the wind-drag effect. We used load cells to measure the drag force acting on a substantially similar motor scooter when a substantially similar tractor-trailer passes by it, taking into consideration various speeds of the tractor-trailer and distances between the two vehicles. A three-dimensional steady-state flow analysis was also performed by using the CFX program for computational fluid dynamics to examine the streamlines and the pressure distribution around the tractor-trailer at various speeds. From the experiment, for a separation distance of 1.0 m (3.28 ft) and a speed of 90 km/h (55.9 mph), the maximum resultant drag force is 124.5 N (28 lb); this constitutes a degree of force that could abruptly disrupt the stability in maneuvering by an operator who is unaware of the approaching tractor-trailer. In addition, a single equation that relates the tractor-trailer speed to the drag force that acts on the motor scooter was derived on the basis of the Reynolds number (Re) and the wind-drag coefficient (C(d)): C(d) = 1.298 × 10(-7) Re.}, }
@article {pmid22357360, year = {2012}, author = {Malcher, T and Gzyl-Malcher, B}, title = {Influence of polymer-surfactant aggregates on fluid flow.}, journal = {Bioelectrochemistry (Amsterdam, Netherlands)}, volume = {87}, number = {}, pages = {42-49}, doi = {10.1016/j.bioelechem.2012.01.011}, pmid = {22357360}, issn = {1878-562X}, mesh = {Cations ; Cetrimonium ; Cetrimonium Compounds/*chemistry ; Computer Simulation ; Micelles ; Models, Chemical ; Polyethylene Glycols/*chemistry ; Rheology ; Salicylates/chemistry ; *Software ; Static Electricity ; Surface-Active Agents/*chemistry ; Viscosity ; Water ; }, abstract = {This paper describes the influence of interactions of poly(ethylene oxide) (PEO) with cationic cetyltrimethylammonium bromide (CTAB) micelles on drag reduction. Since the interactions between PEO and CTAB micelles alone are weak, salicylate ions were used as CTAB counterions. They facilitate formation of polymer-micelle aggregates by screening the electrostatic repulsions between the charged surfactant headgroups. The influence of polymer-surfactant interactions on drag reduction is of biomedical engineering importance. Drag reducing additives introduced to blood produce beneficial effects on blood circulation, representing a novel way to treat cardiovascular disorders. PEO is a blood-compatible polymer. However, it quickly mechanically degrades when subjected to high shear stresses. Thus, there is a need to search for other additives able to reduce drag, which would be more mechanically stable, e.g. polymer-surfactant aggregates. Numerical simulations of the flow were performed using the CFX software. Based on the internal structure of the polymer-surfactant solution, a hypothesis explaining the reason of increase of drag reduction and decrease in dynamic viscosity with increasing shear rate was proposed. It was suggested that the probable reason for the abrupt increase in friction factor, observed when the critical Reynolds number was exceeded, was the disappearance of the difference in the dynamic viscosity.}, }
@article {pmid22355147, year = {2012}, author = {Doostmohammadi, A and Stocker, R and Ardekani, AM}, title = {Low-Reynolds-number swimming at pycnoclines.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {109}, number = {10}, pages = {3856-3861}, pmid = {22355147}, issn = {1091-6490}, mesh = {Algorithms ; Bacterial Physiological Phenomena ; Computer Simulation ; Diffusion ; Ecology ; Ecosystem ; Lakes ; Models, Biological ; Models, Statistical ; *Movement ; Oceans and Seas ; Oscillometry/methods ; Salts ; Temperature ; Viscosity ; Water/chemistry ; *Water Microbiology ; }, abstract = {Microorganisms play pivotal functions in the trophic dynamics and biogeochemistry of aquatic ecosystems. Their concentrations and activities often peak at localized hotspots, an important example of which are pycnoclines, where water density increases sharply with depth due to gradients in temperature or salinity. At pycnoclines organisms are exposed to different environmental conditions compared to the bulk water column, including reduced turbulence, slow mass transfer, and high particle and predator concentrations. Here we show that, at an even more fundamental level, the density stratification itself can affect microbial ecology at pycnoclines, by quenching the flow signature, increasing the energetic expenditure, and stifling the nutrient uptake of motile organisms. We demonstrate this through numerical simulations of an archetypal low-Reynolds-number swimmer, the "squirmer." We identify the Richardson number--the ratio of buoyancy forces to viscous forces--as the fundamental parameter that quantifies the effects of stratification. These results demonstrate an unexpected effect of buoyancy on low-Reynolds-number swimming, potentially affecting a broad range of abundant organisms living at pycnoclines in oceans and lakes.}, }
@article {pmid22340669, year = {2012}, author = {Zeitoun, O and Ali, M}, title = {Nanofluid impingement jet heat transfer.}, journal = {Nanoscale research letters}, volume = {7}, number = {1}, pages = {139}, pmid = {22340669}, issn = {1556-276X}, abstract = {Experimental investigation to study the heat transfer between a vertical round alumina-water nanofluid jet and a horizontal circular round surface is carried out. Different jet flow rates, jet nozzle diameters, various circular disk diameters and three nanoparticles concentrations (0, 6.6 and 10%, respectively) are used. The experimental results indicate that using nanofluid as a heat transfer carrier can enhance the heat transfer process. For the same Reynolds number, the experimental data show an increase in the Nusselt numbers as the nanoparticle concentration increases. Size of heating disk diameters shows reverse effect on heat transfer. It is also found that presenting the data in terms of Reynolds number at impingement jet diameter can take into account on both effects of jet heights and nozzle diameter. Presenting the data in terms of Peclet numbers, at fixed impingement nozzle diameter, makes the data less sensitive to the percentage change of the nanoparticle concentrations. Finally, general heat transfer correlation is obtained verses Peclet numbers using nanoparticle concentrations and the nozzle diameter ratio as parameters.}, }
@article {pmid22326047, year = {2012}, author = {Alvarez, NJ and Vogus, DR and Walker, LM and Anna, SL}, title = {Using bulk convection in a microtensiometer to approach kinetic-limited surfactant dynamics at fluid-fluid interfaces.}, journal = {Journal of colloid and interface science}, volume = {372}, number = {1}, pages = {183-191}, doi = {10.1016/j.jcis.2011.12.034}, pmid = {22326047}, issn = {1095-7103}, abstract = {The impact of transport of surfactants to fluid-fluid interfaces is complex to assess and model, as many processes are in the regime where kinetics, diffusion and convection are comparable. Using the principle that the timescale for diffusion decreases with increasing curvature, we previously developed a microtensiometer to accurately measure fundamental transport coefficients via dynamic surface tension at spherical microscale liquid-fluid interfaces. In the present study, we use a low Reynolds number flow in the bulk solution to further increase the rate of diffusion. Dynamic surface tension is measured as a function of Peclet number and the results are compared with a simplified convection-diffusion model. Although a transition from diffusion to kinetic-limited transport is not observed experimentally for the surfactants considered, lower bounds on the adsorption and desorption rate constants are determined that are much larger than previously reported rate constants. The results show that the details of the flow field do not need to be controlled as long as the local Reynolds number is low. Aside from other pragmatic advantages, this experimental tool and analysis allows the governing mechanisms of surfactant transport at liquid-fluid interfaces to be quantified using flow near the interface to decrease the length scale for diffusion, separating the relevant timescales.}, }
@article {pmid22324715, year = {2012}, author = {Xi, L and Graham, MD}, title = {Dynamics on the laminar-turbulent boundary and the origin of the maximum drag reduction asymptote.}, journal = {Physical review letters}, volume = {108}, number = {2}, pages = {028301}, doi = {10.1103/PhysRevLett.108.028301}, pmid = {22324715}, issn = {1079-7114}, abstract = {Dynamical trajectories on the boundary in state space between laminar and turbulent plane channel flow-edge states-are computed for Newtonian and viscoelastic fluids. Viscoelasticity has a negligible effect on the properties of these solutions, and, at least at a low Reynolds number, their mean velocity profiles correspond closely to experimental observations for polymer solutions in the maximum drag reduction regime. These results confirm the existence of weak turbulence states that cannot be suppressed by polymer additives, explaining the fact that there is an upper limit for polymer-induced drag reduction.}, }
@article {pmid22324688, year = {2012}, author = {He, X and Funfschilling, D and Nobach, H and Bodenschatz, E and Ahlers, G}, title = {Transition to the ultimate state of turbulent Rayleigh-Bénard convection.}, journal = {Physical review letters}, volume = {108}, number = {2}, pages = {024502}, doi = {10.1103/PhysRevLett.108.024502}, pmid = {22324688}, issn = {1079-7114}, abstract = {Measurements of the Nusselt number Nu and of a Reynolds number Re(eff) for Rayleigh-Bénard convection (RBC) over the Rayleigh-number range 10(12)≲Ra≲10(15) and for Prandtl numbers Pr near 0.8 are presented. The aspect ratio Γ≡D/L of a cylindrical sample was 0.50. For Ra≲10(13) the data yielded Nu∝Ra(γ(eff)) with γ(eff)≃0.31 and Re(eff)∝Ra(ζ(eff)) with ζ(eff)≃0.43, consistent with classical turbulent RBC. After a transition region for 10(13)≲Ra≲5×10(14), where multistability occurred, we found γ(eff)≃0.38 and ζ(eff)=ζ≃0.50, in agreement with the results of Grossmann and Lohse for the large-Ra asymptotic state with turbulent boundary layers which was first predicted by Kraichnan.}, }
@article {pmid22311121, year = {2012}, author = {Wurm, M and Zeng, AP}, title = {Mechanical disruption of mammalian cells in a microfluidic system and its numerical analysis based on computational fluid dynamics.}, journal = {Lab on a chip}, volume = {12}, number = {6}, pages = {1071-1077}, doi = {10.1039/c2lc20918g}, pmid = {22311121}, issn = {1473-0189}, mesh = {Animals ; CHO Cells ; Cell Fractionation/*instrumentation ; Computer Simulation ; Cricetinae ; Cricetulus ; Equipment Design ; Hydrodynamics ; Microfluidics/*instrumentation ; Models, Biological ; Pressure ; Stress, Mechanical ; }, abstract = {The lysis of mammalian cells is an essential part of different lab-on-a-chip sample preparation methods, which aim at the release, separation, and subsequent analysis of DNA, proteins, or metabolites. Particularly for the analysis of compartmented in vivo metabolism of mammalian cells, such a method must be very fast compared to the metabolic turnover-rates, it should not affect the native metabolite concentrations, and should ideally leave cell organelles undamaged. So far, no such a method is available. We have developed a microfluidic system for the effective rapid mechanical cell disruption and established a mathematical model to describe the efficiency of the system. Chinese hamster ovary (CHO) cells were disrupted with high efficiency by passing through two consecutive micronozzle arrays. Simultaneous cell compression and shearing led to a disruption rate of ≥90% at a sample flow rate of Q = 120 μL min(-1) per nozzle passage, which corresponds to a mean fluid velocity of 13.3 m s(-1) and a mean Reynolds number of 22.6 in the nozzle gap. We discussed the problem of channel clogging by cellular debris and the resulting flow instability at the micronozzle arrays. The experimental results were compared to predictions from Computational Fluid Dynamics (CFD) simulations and the critical energy dissipation rate for the disruption of the CHO cell population with known size distribution was determined to be 4.7 × 10(8) W m(-3). Our model for the calculation of cell disruption on the basis of CFD-data could be applied to other microgeometries to predict intended disruption or undesired cell damage.}, }
@article {pmid22304214, year = {2011}, author = {Zhou, G and Wang, L and Wang, X and Ge, W}, title = {Galilean-invariant algorithm coupling immersed moving boundary conditions and Lees-Edwards boundary conditions.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {84}, number = {6 Pt 2}, pages = {066701}, doi = {10.1103/PhysRevE.84.066701}, pmid = {22304214}, issn = {1550-2376}, abstract = {Many investigators have coupled the Lees-Edwards boundary conditions (LEBCs) and suspension methods in the framework of the lattice Boltzmann method to study the pure bulk properties of particle-fluid suspensions. However, these suspension methods are all link-based and are more or less exposed to the disadvantages of violating Galilean invariance. In this paper, we have coupled LEBCs with a node-based suspension method, which is demonstrated to be Galilean invariant in benchmark simulations. We use the coupled algorithm to predict the viscosity of a particle-fluid suspension at very low Reynolds number, and the simulation results are in good agreement with the semiempirical Krieger-Dougherty formula.}, }
@article {pmid22304198, year = {2011}, author = {Duguet, Y and Le Maître, O and Schlatter, P}, title = {Stochastic and deterministic motion of a laminar-turbulent front in a spanwisely extended Couette flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {84}, number = {6 Pt 2}, pages = {066315}, doi = {10.1103/PhysRevE.84.066315}, pmid = {22304198}, issn = {1550-2376}, abstract = {We investigate numerically the dynamics of a laminar-turbulent interface in a spanwisely extended and streamwisely minimal plane Couette flow. The chosen geometry allows one to suppress the large-scale secondary flow and to focus on the nucleation of streaks near the interface. It is shown that the resulting spanwise motion of the interface is essentially stochastic and can be modeled as a continuous-time random walk. This model corresponds here to a Gaussian diffusion process. The average speed of the interface and the corresponding diffusion coefficient are determined as functions of the Reynolds number Re, as well as the threshold value above which turbulence contaminates the whole domain. For the lowest values of Re, the stochastic dynamics competes with another deterministic regime of growth of the localized perturbations. The latter is interpreted as a depinning process from the homoclinic snaking region of the system.}, }
@article {pmid22300354, year = {2012}, author = {Qazi, SJ and Rennie, AR and Cockcroft, JK}, title = {Orientation of a dispersion of kaolinite flowing in a jet.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {28}, number = {8}, pages = {3704-3713}, doi = {10.1021/la204864p}, pmid = {22300354}, issn = {1520-5827}, abstract = {Orientational alignment in a dilute dispersion of kaolinite particles has been investigated in a flow pattern that combines both shear and elongational stress, namely flow at a jet created by a 2 mm diameter nozzle inserted in a 6 mm diameter pipe. Spatially-resolved X-ray diffraction with synchrotron radiation permits detailed maps of the alignment to be deduced and compared with fluid mechanics calculations of the flow. The angular distribution of diffracted intensity from a given position in the pipe provides information about the orientation distribution of the particles. This is quantified and presented in terms of order parameters. The cone-shaped nozzle provides a jet of liquid giving a high degree of alignment of the particles that is uniform along lines across the conical section and constant in the small straight-sided region at the exit of the nozzle. The vortex motion that arises from the flow with a modest Reynolds number could be determined as well as the tendency for some particles to align with their large faces perpendicular to the overall flow direction at the flat surface of the nozzle outlet.}, }
@article {pmid24910780, year = {2012}, author = {Ito, K and Li, Z and Qiao, Z}, title = {The Sensitivity Analysis for the Flow Past Obstacles Problem with Respect to the Reynolds Number.}, journal = {Advances in applied mathematics and mechanics}, volume = {4}, number = {1}, pages = {21-35}, doi = {10.4208/aamm.11-m1110}, pmid = {24910780}, issn = {2070-0733}, support = {R01 GM096195/GM/NIGMS NIH HHS/United States ; }, abstract = {In this paper, numerical sensitivity analysis with respect to the Reynolds number for the flow past obstacle problem is presented. To carry out such analysis, at each time step, we need to solve the incompressible Navier-Stokes equations on irregular domains twice, one for the primary variables; the other is for the sensitivity variables with homogeneous boundary conditions. The Navier-Stokes solver is the augmented immersed interface method for Navier-Stokes equations on irregular domains. One of the most important contribution of this paper is that our analysis can predict the critical Reynolds number at which the vortex shading begins to develop in the wake of the obstacle. Some interesting experiments are shown to illustrate how the critical Reynolds number varies with different geometric settings.}, }
@article {pmid22276579, year = {2012}, author = {Lieu, VH and House, TA and Schwartz, DT}, title = {Hydrodynamic tweezers: impact of design geometry on flow and microparticle trapping.}, journal = {Analytical chemistry}, volume = {84}, number = {4}, pages = {1963-1968}, doi = {10.1021/ac203002z}, pmid = {22276579}, issn = {1520-6882}, abstract = {Here we explore the role of microfabricated device geometry on frequency-dependent low Reynolds number steady streaming flow and particle trapping behavior. In our system, flow and particle trapping is induced near an obstruction or cavity located in an otherwise rectilinear oscillating flow of frequency ω and amplitude s in a fluid of kinematic viscosity ν. This work expands prior studies to characterize nine distinct obstruction/cavity geometries. The imaged microeddy flows show that the device geometry affects the eddy number, shape, structure, and strength. Comparison of measured particle trap locations with the computed eddy flow structure shows that particles trap closer to the wall than the eddy core. Trapping strength and location are controlled by the geometry and the oscillation frequency. In most cases, the trapping behavior is linearly proportional to the Stokes layer thickness, δ(AC) ~ O((ν/ω)(1/2)). We show that steady streaming in microfluidic eddies can be a flexible and versatile method for noncontact microparticle trapping, and hence we call this class of devices "hydrodynamic tweezers".}, }
@article {pmid22246469, year = {2012}, author = {Miyawaki, S and Tawhai, MH and Hoffman, EA and Lin, CL}, title = {Effect of carrier gas properties on aerosol distribution in a CT-based human airway numerical model.}, journal = {Annals of biomedical engineering}, volume = {40}, number = {7}, pages = {1495-1507}, pmid = {22246469}, issn = {1573-9686}, support = {R01 HL112986/HL/NHLBI NIH HHS/United States ; R01-EB005823/EB/NIBIB NIH HHS/United States ; R01-HL064368/HL/NHLBI NIH HHS/United States ; S10-RR022421/RR/NCRR NIH HHS/United States ; R01-HL094315/HL/NHLBI NIH HHS/United States ; S10 RR022421/RR/NCRR NIH HHS/United States ; R01 EB005823-03/EB/NIBIB NIH HHS/United States ; R01 HL094315-06/HL/NHLBI NIH HHS/United States ; R01 EB005823/EB/NIBIB NIH HHS/United States ; R01 HL064368-10/HL/NHLBI NIH HHS/United States ; S10 RR022421-01A2/RR/NCRR NIH HHS/United States ; R01 HL094315/HL/NHLBI NIH HHS/United States ; R01 HL064368/HL/NHLBI NIH HHS/United States ; }, mesh = {Aerosols ; Helium/*administration &amp; dosage ; Humans ; *Lung/diagnostic imaging/physiology ; *Models, Biological ; Oxygen/*administration &amp; dosage ; Respiratory Transport/*physiology ; *Tomography, X-Ray Computed ; Trachea/diagnostic imaging/physiology ; Xenon/*administration &amp; dosage ; }, abstract = {The effect of carrier gas properties on particle transport in the human lung is investigated numerically in an imaging based airway model. The airway model consists of multi-detector row computed tomography (MDCT)-based upper and intra-thoracic central airways. The large-eddy simulation technique is adopted for simulation of transitional and turbulent flows. The image-registration-derived boundary condition is employed to match regional ventilation of the whole lung. Four different carrier gases of helium (He), a helium-oxygen mixture (He-O(2)), air, and a xenon-oxygen mixture (Xe-O(2)) are considered. A steady inspiratory flow rate of 342 mL/s is imposed at the mouthpiece inlet to mimic aerosol delivery on inspiration, resulting in the Reynolds number at the trachea of Re(t) ≈ 190, 460, 1300, and 2800 for the respective gases of He, He-O(2), air, and Xe-O(2). Thus, the flow for the He case is laminar, transitional for He-O(2), and turbulent for air and Xe-O(2). The instantaneous and time-averaged flow fields and the laminar/transitional/turbulent characteristics resulting from the four gases are discussed. With increasing Re(t), the high-speed jet formed at the glottal constriction is more dispersed around the peripheral region of the jet and its length becomes shorter. In the laminar flow the distribution of 2.5-μm particles in the central airways depends on the particle release location at the mouthpiece inlet, whereas in the turbulent flow the particles are well mixed before reaching the first bifurcation and their distribution is strongly correlated with regional ventilation.}, }
@article {pmid22243329, year = {2011}, author = {Schnitzer, O and Khair, AS and Yariv, E}, title = {Irreversible electrokinetic repulsion at zero-Reynolds-number sedimentation.}, journal = {Physical review letters}, volume = {107}, number = {27}, pages = {278301}, doi = {10.1103/PhysRevLett.107.278301}, pmid = {22243329}, issn = {1079-7114}, abstract = {Stokes-flow reversibility is violated in electrolyte solutions by a streaming-potential mechanism, where nonuniform convective currents within Debye layers surrounding charged particles induce electric fields in the electroneutral Ohmic bulk. We demonstrate the irreversibility consequences of this phenomenon for the problem of particle-pair sedimentation, where the two particles experience a repulsive force driven by bulk Maxwell stresses. At small separations the force scales inversely with the third power of separation distance. This singular behavior is associated with the counterrotation of the two torque-free particles, which leads through a lubrication mechanism to an intense electric field in the narrow gap between them. At large separations the force follows an inverse dependence upon the fourth power of separation, now associated with rectilinear particle motion.}, }
@article {pmid22243085, year = {2011}, author = {Heinemann, T and McWilliams, JC and Schekochihin, AA}, title = {Large-scale magnetic field generation by randomly forced shearing waves.}, journal = {Physical review letters}, volume = {107}, number = {25}, pages = {255004}, doi = {10.1103/PhysRevLett.107.255004}, pmid = {22243085}, issn = {1079-7114}, abstract = {A rigorous theory for the generation of a large-scale magnetic field by random nonhelically forced motions of a conducting fluid combined with a linear shear is presented in the analytically tractable limit of low magnetic Reynolds number (Rm) and weak shear. The dynamo is kinematic and due to fluctuations in the net (volume-averaged) electromotive force. This is a minimal proof-of-concept quasilinear calculation aiming to put the shear dynamo, a new effect recently found in numerical experiments, on a firm theoretical footing. Numerically observed scalings of the wave number and growth rate of the fastest-growing mode, previously not understood, are derived analytically. The simplicity of the model suggests that shear dynamo action may be a generic property of sheared magnetohydrodynamic turbulence.}, }
@article {pmid23956497, year = {2012}, author = {Scherr, T and Quitadamo, C and Tesvich, P and Park, DS and Tiersch, T and Hayes, D and Choi, JW and Nandakumar, K and Monroe, WT}, title = {A Planar Microfluidic Mixer Based on Logarithmic Spirals.}, journal = {Journal of micromechanics and microengineering : structures, devices, and systems}, volume = {22}, number = {5}, pages = {55019}, pmid = {23956497}, issn = {0960-1317}, support = {R24 OD010441/OD/NIH HHS/United States ; R24 RR023998/RR/NCRR NIH HHS/United States ; }, abstract = {A passive, planar micromixer design based on logarithmic spirals is presented. The device was fabricated using polydimethylsiloxane soft photolithography techniques, and mixing performance was characterized via numerical simulation and fluorescent microscopy. Mixing efficiency initially declined as Reynolds number increased, and this trend continued until a Reynolds number of 15 where a minimum was reached at 53%. Mixing efficiency then began to increase reaching a maximum mixing efficiency of 86% at Re = 67. Three-dimensional simulations of fluid mixing in this design were compared to other planar geometries such as the Archimedes spiral and Meandering-S mixers. The implementation of logarithmic curvature offers several unique advantages that enhance mixing, namely a variable cross-sectional area and a logarithmically varying radius of curvature that creates 3-D Dean vortices. These flow phenomena were observed in simulations with multilayered fluid folding and validated with confocal microscopy. This design provides improved mixing performance over a broader range of Reynolds numbers than other reported planar mixers, all while avoiding external force fields, more complicated fabrication processes, and the introduction of flow obstructions or cavities that may unintentionally affect sensitive or particulate-containing samples. Due to the planar design requiring only single-step lithographic features, this compact geometry could be easily implemented into existing micro-total analysis systems requiring effective rapid mixing.}, }
@article {pmid23471191, year = {2012}, author = {Khanafer, K and Cook, K and Marafie, A}, title = {THE ROLE OF POROUS MEDIA IN MODELING FLUID FLOW WITHIN HOLLOW FIBER MEMBRANES OF THE TOTAL ARTIFICIAL LUNG.}, journal = {Journal of porous media}, volume = {15}, number = {2}, pages = {113-122}, pmid = {23471191}, issn = {1091-028X}, support = {R01 HL089043/HL/NHLBI NIH HHS/United States ; }, abstract = {A numerical study was conducted to analyze fluid flow within hollow fiber membranes of the artificial lungs. The hollow fiber bundle was approximated using a porous media model. In addition, the transport equations were solved using the finite-element formulation based on the Galerkin method of weighted residuals. Comparisons with previously published work on the basis of special cases were performed and found to be in excellent agreement. A Newtonian viscous fluid model for the blood was used. Different flow models for porous media, such as the Brinkman-extended Darcy model, Darcy's law model, and the generalized flow model, were considered. Results were obtained in terms of streamlines, velocity vectors, and pressure distribution for various Reynolds numbers and Darcy numbers. The results from this investigation showed that the pressure drop across the artificial lung device increased with an increase in the Reynolds number. In addition, the pressure drop was found to increase significantly for small Darcy numbers.}, }
@article {pmid22207186, year = {2012}, author = {Al-Shannag, M}, title = {Mass transport enhancement in annular-shaped lid-driven bioreactor.}, journal = {Bioprocess and biosystems engineering}, volume = {35}, number = {6}, pages = {875-884}, doi = {10.1007/s00449-011-0672-2}, pmid = {22207186}, issn = {1615-7605}, mesh = {Biological Transport/physiology ; *Bioreactors ; *Models, Biological ; }, abstract = {The current study investigated numerically the two-dimensional (2D) incompressible flow and mass transfer in a lid-driven cavity of annular geometry accompanied by enzymatic surface-reactions. The lid-driven bioreactor had a square cross-section of (H × H) and a radius of curvature of r (c). This flow configuration gives the opportunity to evaluate effects of curvature as well as operational parameters on the bioreactor performance. For forced-convection, conservation equations were solved numerically, using fourth-order finite volume schemes, to identify the 2D flow structure and concentration distribution of substrate within the bioreactor. For pure diffusion, analytical solution was obtained. Substrate transfer rates were presented in terms of Sherwood number. While, effectiveness factor was computed to evaluate the force-convection contribution over pure molecular diffusion. Mass-transfer against surface-reaction resistance was estimated via Damkohler number. Results indicate the positive role of increasing Peclet number, Reynolds number, and radius of curvature in enhancing the substrate transport process.}, }
@article {pmid22185614, year = {2012}, author = {Dimakopoulos, Y and Bogaerds, AC and Anderson, PD and Hulsen, MA and Baaijens, FP}, title = {Direct numerical simulation of a 2D-stented aortic heart valve at physiological flow rates.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {15}, number = {11}, pages = {1157-1179}, doi = {10.1080/10255842.2011.581238}, pmid = {22185614}, issn = {1476-8259}, mesh = {Algorithms ; Aortic Valve/*physiology/surgery ; Biomedical Engineering ; Computer Simulation ; Finite Element Analysis ; Heart Valve Prosthesis ; Hemodynamics/physiology ; Hemorheology/physiology ; Humans ; *Models, Cardiovascular ; Stents ; }, abstract = {We study the nonlinear interaction of an aortic heart valve, composed of hyperelastic corrugated leaflets of finite density attached to a stented vessel under physiological flow conditions. In our numerical simulations, we use a 2D idealised representation of this arrangement. Blood flow is caused by a time-varying pressure gradient that mimics that of the aortic valve and corresponds to a peak Reynolds number equal to 4050. Here, we fully account for the shear-thinning behaviour of the blood and large deformations and contact between the leaflets by solving the momentum and mass balances for blood and leaflets. The mixed finite element/Galerkin method along with linear discontinuous Lagrange multipliers for coupling the fluid and elastic domains is adopted. Moreover, a series of challenging numerical issues such as the finite length of the computational domain and the conditions that should be imposed on its inflow/outflow boundaries, the accurate time integration of the parabolic and hyperbolic momentum equations, the contact between the leaflets and the non-conforming mesh refinement in part of the domain are successfully resolved. Calculations for the velocity and the shear stress fields of the blood reveal that boundary layers appear on both sides of a leaflet. The one along the ventricular side transfers blood with high momentum from the core region of the vessel to the annulus or the sinusoidal expansion, causing the continuous development of flow instabilities. At peak systole, vortices are convected in the flow direction along the annulus of the vessel, whereas during the closure stage of the valve, an extremely large vortex develops in each half of the flow domain.}, }
@article {pmid22181500, year = {2011}, author = {Chen, P and Zhang, Q}, title = {Dynamical solutions for migration of chiral DNA-type objects in shear flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {84}, number = {5 Pt 2}, pages = {056309}, doi = {10.1103/PhysRevE.84.056309}, pmid = {22181500}, issn = {1550-2376}, mesh = {Algorithms ; Biophysics/*methods ; Computer Simulation ; DNA/*chemistry ; Models, Statistical ; Motion ; Nucleic Acid Conformation ; Reproducibility of Results ; Shear Strength ; Stereoisomerism ; Stress, Mechanical ; Surface Properties ; Torque ; }, abstract = {We present a dynamical analysis of chiral object motions to explain physical mechanisms and give quantitative predictions on the shear-induced drift motions of chiral objects and the chiral separation of enantiomers using shear flows. For objects well represented by the uniaxial approximation, such as DNA and chiral disk hexamers, dynamical motions in low-Reynolds-number shear flows are solved analytically, in terms of steady-state object-flow interacting parameters, which can be calculated numerically by well-established methods. The shear-induced drifting speed of long helices are evaluated. Good agreements are found between our results and those obtained from dynamical simulations [Makino and Doi, Phys. Fluids 17, 103605 (2005)]. We also compare our results with those obtained experimentally [Marcos, Fu, Powers, and Stocker, Phys. Rev. Lett. 102, 158103 (2009)]. The analysis may also be extended to study other important chiral-flow interactions in nature environments and microfluidic devices, such as the particle-wall and interparticle interactions.}, }
@article {pmid22181275, year = {2011}, author = {Rädler, KH and Brandenburg, A and Del Sordo, F and Rheinhardt, M}, title = {Mean-field diffusivities in passive scalar and magnetic transport in irrotational flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {84}, number = {4 Pt 2}, pages = {046321}, doi = {10.1103/PhysRevE.84.046321}, pmid = {22181275}, issn = {1550-2376}, abstract = {Certain aspects of the mean-field theory of turbulent passive scalar transport and of mean-field electrodynamics are considered with particular emphasis on aspects of compressible fluids. It is demonstrated that the total mean-field diffusivity for passive scalar transport in a compressible flow may well be smaller than the molecular diffusivity. This is in full analogy to an old finding regarding the magnetic mean-field diffusivity in an electrically conducting turbulently moving compressible fluid. These phenomena occur if the irrotational part of the motion dominates the vortical part, the Péclet or magnetic Reynolds number is not too large, and, in addition, the variation of the flow pattern is slow. For both the passive scalar and the magnetic cases several further analytical results on mean-field diffusivities and related quantities found within the second-order correlation approximation are presented, as well as numerical results obtained by the test-field method, which applies independently of this approximation. Particular attention is paid to nonlocal and noninstantaneous connections between the turbulence-caused terms and the mean fields. Two examples of irrotational flows, in which interesting phenomena in the above sense occur, are investigated in detail. In particular, it is demonstrated that the decay of a mean scalar in a compressible fluid under the influence of these flows can be much slower than without any flow, and can be strongly influenced by the so-called memory effect, that is, the fact that the relevant mean-field coefficients depend on the decay rates themselves.}, }
@article {pmid22181268, year = {2011}, author = {Chen, C and Ma, M and Jin, K and Liu, JZ and Shen, L and Zheng, Q and Xu, Z}, title = {Nanoscale fluid-structure interaction: flow resistance and energy transfer between water and carbon nanotubes.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {84}, number = {4 Pt 2}, pages = {046314}, doi = {10.1103/PhysRevE.84.046314}, pmid = {22181268}, issn = {1550-2376}, abstract = {We investigate here water flow passing a single-walled carbon nanotube (CNT), through analysis based on combined atomistic and continuum mechanics simulations. The relation between drag coefficient C(D) and Reynolds number Re is obtained for a wide range of flow speed u from 5 to 600 m/s. The results suggest that Stokes law for creep flow works well for small Reynolds numbers up to 0.1 (u ≈ 100 m/s), and indicates a linear dependence between drag force and flow velocity. Significant deviation is observed at elevated Re values, which is discussed by considering the interfacial slippage, reduction of viscosity due to friction-induced local heating, and flow-induced structural vibration. We find that interfacial slippage has a limited contribution to the reduction of the resistance, and excitations of low-frequency vibration modes in the carbon nanotube play an important role in energy transfer between water and carbon nanotubes, especially at high flow speeds where drastic enhancement of the carbon nanotube vibration is observed. The results reported here reveal nanoscale fluid-structure interacting mechanisms, and lay the ground for rational design of nanofluidics and nanoelectromechanical devices operating in a fluidic environment.}, }
@article {pmid22181266, year = {2011}, author = {Gravanis, E and Akylas, E}, title = {Stationarity of linearly forced turbulence in finite domains.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {84}, number = {4 Pt 2}, pages = {046312}, doi = {10.1103/PhysRevE.84.046312}, pmid = {22181266}, issn = {1550-2376}, abstract = {A simple scheme of forcing turbulence away from decay was introduced by Lundgren some time ago, the "linear forcing," which amounts to a force term that is linear in the velocity field with a constant coefficient. The evolution of linearly forced turbulence toward a stationary final state, as indicated by direct numerical simulations (DNS), is examined from a theoretical point of view based on symmetry arguments. In order to follow closely the DNS, the flow is assumed to live in a cubic domain with periodic boundary conditions. The simplicity of the linear forcing scheme allows one to rewrite the problem as one of decaying turbulence with a decreasing viscosity. Its late-time behavior can then be studied by scaling symmetry considerations. The evolution of the system in the description of "decaying" turbulence can be understood as the gradual symmetry breaking of a larger approximate symmetry to a smaller symmetry that is exact at late times. The latter symmetry implies a stationary state: In the original description all correlators are constant in time, while, in the "decaying" turbulence description, that state possesses constant Reynolds number and integral length scale. The finiteness of the domain is intimately related to the evolution of the system to a stationary state at late times: In linear forcing there is no other large scale than the domain size, therefore, it is the only scale available to set the magnitude of the necessarily constant integral length scale in the stationary state. A high degree of local isotropy is implied by the late-time exact symmetry, the symmetries of the domain itself, and the solenoidal nature of the velocity field. The fluctuations observed in the DNS for all quantities in the stationary state can be associated with deviations from isotropy that is necessarily broken at the large scale by the finiteness of the domain. Indeed, to strengthen this conclusion somewhat, self-preserving isotropic turbulence models are used to study evolution from a direct dynamical point of view. Simultaneously, the naturalness of the Taylor microscale as a self-similarity scale in this system is emphasized. In this context the stationary state emerges as a stable fixed point. We also note that self-preservation seems to be the reason behind a noted similarity of the third-order structure function between the linearly forced and freely decaying turbulence, where, again, the finiteness of the domain plays a significant role.}, }
@article {pmid22181264, year = {2011}, author = {Martínez-Suástegui, L and Treviño, C and Cajas, JC}, title = {Thermal nonlinear oscillator in mixed convection.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {84}, number = {4 Pt 2}, pages = {046310}, doi = {10.1103/PhysRevE.84.046310}, pmid = {22181264}, issn = {1550-2376}, abstract = {A detailed numerical simulation is carried out for transient laminar flow opposing mixed convection in a downward vertical channel flow with both walls suddenly subjected to isothermal heat sources over a finite portion of the channel walls, by solving the unsteady two-dimensional Navier-Stokes and energy equations. The dynamical behavior of the system is influenced by, in addition to the geometrical parameters, three nondimensional parameters: the Reynolds, Richardson, and Prandtl numbers. Numerical experiments were performed for fixed values of the geometrical parameters, the Reynolds number (Re=100) and the Prandtl number (Pr=7). With variation in the value of the buoyancy (Richardson number), the nonlinear dynamical response of the system can reach (i) a stationary solution, (ii) a local and then a global periodic solution where the system executes self-sustained relaxation oscillations, or (iii) a solution in which the relaxation oscillation is destroyed leading to a chaotic state. In this study, bifurcations between different states, phase-space plots of the self-oscillatory system, characteristic times of temperature oscillations, and an exact description of the oscillations are presented quantitatively for a range of values of the buoyancy parameter. The results include the effects of the Reynolds and Prandtl numbers on the evolution of the different transitions.}, }
@article {pmid22181261, year = {2011}, author = {Ding, Z and Liu, Q}, title = {Stability of liquid films on a porous vertical cylinder.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {84}, number = {4 Pt 2}, pages = {046307}, doi = {10.1103/PhysRevE.84.046307}, pmid = {22181261}, issn = {1550-2376}, abstract = {The stability of liquid films flowing down a vertical porous cylinder is investigated in this paper. Fluids in the porous medium are assumed to be governed by Darcy's law. The Beaver-Joseph conditions on the liquid-porous surface are applied, and the influence of the porous medium reduces as a slip condition on the cylinder, which leads to the one-sided model. A Benney-type equation governing the interfacial shape is derived to study the nonlinear behavior of liquid films. Linear stability analysis shows that the film flow system on a porous vertical cylinder is more unstable than that on a solid impermeable vertical cylinder and that increasing the permeability of the porous medium enhances the destabilizing effect. Nonlinear studies examine our linear stability analysis. We find that, for Reynolds number Re=0, as the permeability parameter increases, the rupture time of film decreases; for Re>0, Rayleigh-Plateau instability is suppressed, and disturbances evolve to saturated traveling waves. By increasing the permeability parameter, the amplitude of traveling wave increases, and the wave speed increases too. Aside from that, the wave speed increases with increasing Re.}, }
@article {pmid22181260, year = {2011}, author = {Shtern, VN and del Mar Torregrosa, M and Herrada, MA}, title = {Development of colliding swirling counterflows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {84}, number = {4 Pt 2}, pages = {046306}, doi = {10.1103/PhysRevE.84.046306}, pmid = {22181260}, issn = {1550-2376}, abstract = {This numerical study of the axisymmetric motion of a viscous incompressible fluid in an elongated cylindrical container explains how colliding counterflows develop. Two swirling flows enter the container through peripheral inlets and leave it through central exhausts symmetrically from both ends. Different flow rates, characterized by the Reynolds number Re, are studied for a fixed swirl number. For small Re, the throughflow (TF) is limited to the inlet-exhaust vicinities and a few circulation cells occupy the rest of the interior. As Re grows, (i) the circulation cells disappear while the TF reaches the container's midsection and becomes U shaped, moving near the sidewall inward and going back near the container axis; elongated circulation regions develop separating the TF branches; (ii) the flow convergence to the axis focuses near the container's midsection, resulting in the vortex breakdown development; (iii) the swirl-induced low pressure causes suction of the ambient fluid through the central parts of the exhausts; (iv) the suction flow reaches the container's midsection, turns around, mixes with the driving TF, forms an annular outflow, and leaves through the exhaust periphery. The two factors, (a) swirl decay due to friction at the sidewall and (b) the focused flow convergence to the axis, constitute the physical mechanism of the colliding counterflows. Such flow pattern is favorable for a vortex solid-fuel combustor.}, }
@article {pmid22181216, year = {2011}, author = {Bonn, D and Ingremeau, F and Amarouchene, Y and Kellay, H}, title = {Large velocity fluctuations in small-Reynolds-number pipe flow of polymer solutions.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {84}, number = {4 Pt 2}, pages = {045301}, doi = {10.1103/PhysRevE.84.045301}, pmid = {22181216}, issn = {1550-2376}, abstract = {The flow of polymer solutions is examined in a flow geometry where a jet is used to inject the viscoelastic solution into a cylindrical tube. We show that this geometry allows for the generation of a "turbulentlike" flow at very low Reynolds numbers with a fluctuation level which can be as high as 30%. The fluctuations increase with an increase in solution polymer concentration and flow velocity. The turbulent fluctuations decay downstream for small flow velocities but persist for high velocities. The statistical properties of the generated fluctuations indicate that this turbulentlike flow is different from previously studied flows displaying elastic turbulence and shows a direct cascade of energy to small scales with practically no intermittency.}, }
@article {pmid22168737, year = {2011}, author = {Kojic, M and Butler, JP and Vlastelica, I and Stojanovic, B and Rankovic, V and Tsuda, A}, title = {Geometric hysteresis of alveolated ductal architecture.}, journal = {Journal of biomechanical engineering}, volume = {133}, number = {11}, pages = {111005}, pmid = {22168737}, issn = {1528-8951}, support = {R01 HL054885/HL/NHLBI NIH HHS/United States ; R01 HL070542/HL/NHLBI NIH HHS/United States ; R01 HL074022/HL/NHLBI NIH HHS/United States ; R01 HL094567/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Biomechanical Phenomena ; Finite Element Analysis ; Models, Anatomic ; Models, Biological ; Muscle, Smooth/anatomy &amp; histology/physiology ; Pulmonary Alveoli/*anatomy &amp; histology/*physiology ; Rabbits ; Respiratory Mechanics ; }, abstract = {Low Reynolds number airflow in the pulmonary acinus and aerosol particle kinetics therein are significantly conditioned by the nature of the tidal motion of alveolar duct geometry. At least two components of the ductal structure are known to exhibit stress-strain hysteresis: smooth muscle within the alveolar entrance rings, and surfactant at the air-tissue interface. We hypothesize that the geometric hysteresis of the alveolar duct is largely determined by the interaction of the amount of smooth muscle and connective tissue in ductal rings, septal tissue properties, and surface tension-surface area characteristics of surfactant. To test this hypothesis, we have extended the well-known structural model of the alveolar duct by Wilson and Bachofen (1982, "A Model for Mechanical Structure of the Alveolar Duct," J. Appl. Physiol. 52(4), pp. 1064-1070) by adding realistic elastic and hysteretic properties of (1) the alveolar entrance ring, (2) septal tissue, and (3) surfactant. With realistic values for tissue and surface properties, we conclude that: (1) there is a significant, and underappreciated, amount of geometric hysteresis in alveolar ductal architecture; and (2) the contribution of smooth muscle and surfactant to geometric hysteresis are of opposite senses, tending toward cancellation. Quantitatively, the geometric hysteresis found experimentally by Miki et al. (1993, "Geometric Hysteresis in Pulmonary Surface-to-Volume Ratio during Tidal Breathing," J. Appl. Physiol. 75(4), pp. 1630-1636) is consistent with little or no smooth muscle tone in anesthetized rabbits in control conditions, and with substantial smooth muscle activation following methacholine challenge. The observed local hysteretic boundary motion of the acinar duct would result in irreversible acinar flow fields, which might be important mechanistic contributors to aerosol mixing and deposition deep in the lung.}, }
@article {pmid22129015, year = {2011}, author = {Duri, D and Baudet, C and Charvin, P and Virone, J and Rousset, B and Poncet, JM and Diribarne, P}, title = {Liquid helium inertial jet for comparative study of classical and quantum turbulence.}, journal = {The Review of scientific instruments}, volume = {82}, number = {11}, pages = {115109}, doi = {10.1063/1.3661127}, pmid = {22129015}, issn = {1089-7623}, abstract = {We present a new cryogenic wind tunnel facility developed to study the high Reynolds number developed classical or quantum turbulence in liquid (4)He. A stable inertial round jet flow with a Reynolds number of 4 × 10(6) can be sustained in both He I and He II down to a minimum temperature of 1.7 K. The circuit can be pressurized up to 3.5 × 10(5) Pa. The system has been designed to exploit the self-similar properties of the jet far field in order to adapt to the spatial resolution of the existing probes. Multiple and complementary sensors can be simultaneously installed to obtain spatial and time resolved measurements. The technical difficulties and design details are described and the system performance is presented.}, }
@article {pmid23555330, year = {2011}, author = {Barber, JO and Restrepo, JM and Secomb, TW}, title = {Simulated Red Blood Cell Motion in Microvessel Bifurcations: Effects of Cell-Cell Interactions on Cell Partitioning.}, journal = {Cardiovascular engineering and technology}, volume = {2}, number = {4}, pages = {349-360}, pmid = {23555330}, issn = {1869-4098}, support = {R01 HL034555/HL/NHLBI NIH HHS/United States ; }, abstract = {Partitioning of red blood cell (RBC) fluxes between the branches of a diverging microvessel bifurcation is generally not proportional to the flow rates, as RBCs preferentially enter the higher-flow branch. A two-dimensional model for RBC motion and deformation is used to investigate the effects of cell-cell mechanical interactions on RBC partitioning in bifurcations. The RBC membrane and cytoplasm are represented by sets of viscoelastic elements immersed in a low Reynolds number flow. Several types of two-cell interactions that can affect partitioning are found. In the most frequent interactions, a `trade-off' occurs, in which a cell entering one branch causes a following cell to enter the other branch. Other types of interactions include `herding,' where the leading cell is caused to enter the same branch as the following cell, and `following,' where the trailing cell is caused to enter the same branch as the leading cell. The combined effect of these cell-cell interactions is a tendency towards more uniform partitioning, which results from the trade-off effect but is reduced by the herding and following effects. With increasing hematocrit, the frequency of interactions increases, and more uniform partitioning results. This prediction is consistent with experimental observations on how hematocrit affects RBC partitioning.}, }
@article {pmid22128305, year = {2011}, author = {Carpi, F and Erb, R and Jeronimidis, G}, title = {Special section on biomimetics of movement.}, journal = {Bioinspiration &amp; biomimetics}, volume = {6}, number = {4}, pages = {040201}, doi = {10.1088/1748-3182/6/4/040201}, pmid = {22128305}, issn = {1748-3190}, abstract = {Movement in biology is an essential aspect of survival for many organisms, animals and plants. Implementing movement efficiently to meet specific needs is a key attribute of natural living systems, and can provide ideas for man-made developments. If we had to find a subtitle able to essentially convey the aim of this special section, it could read as follows: 'taking inspiration from nature for new materials, actuators, structures and controls for systems that move'. Our world is characterized by a huge variety of technical, engineering systems that move. They surround us in countless products that integrate actuators for different kinds of purposes. Basically, any kind of mechatronic system, such as those used for consumer products, machines, vehicles, industrial systems, robots, etc, is based on one or more devices that move, according to different implementations and motion ranges, often in response to external and internal stimuli. Despite this, technical solutions to develop systems that move do not evolve very quickly as they rely on traditional and well consolidated actuation technologies, which are implemented according to known architectures and with established materials. This fact limits our capability to overcome challenges related to the needs continuously raised by new fields of application, either at small or at large scales. Biomimetics-based approaches may provide innovative thinking and technologies in the field, taking inspiration from nature for smart and effective solutions. In an effort to disseminate current advances in this field, this special section collects some papers that cover different topics. A brief synopsis of the content of each contribution is presented below. The first paper, by Lienhard et al [1], deals with bioinspiration for the realization of structural parts in systems that passively move. It presents a bioinspired hingeless flapping mechanism, considered as a solution to the kinematics of deployable systems for architectural structures. The approach relies on structural elasticity to replace the need for local hinges. To this end, the authors have used fibre-reinforced polymers combining high tensile strength with low bending stiffness. The solution favours lower structural complexity as well as higher design versatility. Bioinspiration from the elastic kinetics of plants is a central pillar of the paper, which highlights the interrelation of form, actuation and kinematics in those natural systems. The second paper, by Nakata et al [2], deals with bioinspired systems that actively move, and, more specifically, fly. The paper is about the aerodynamics of a bio-inspired flexible flapping-wing micro air vehicle conceived to fly in a Reynolds number regime used by most natural flyers, including insects, bats and birds. The paper presents a study of the flexible wing aerodynamics of the flapping vehicle by combining an in-house computational fluid dynamic model with wind tunnel experiments. In particular, the developed model is shown to be able to predict unsteady aerodynamics in terms of vortex and wake structures and their relationship with aerodynamic force generation. Simulations are validated by wind tunnel experiments, confirming the effectiveness of the adopted design solutions, as well as the importance of wing flexibility in designing small flapping-wing vehicles. The third paper, by Annunziata et al [3], deals with bioinspired control strategies for systems that move. In particular, the paper describes approaches to increase the stiffness variability in multi-muscle driven joints. Different strategies for simultaneous control of torque and stiffness in a hinge joint actuated by two antagonistic muscle pairs are presented. The proposed strategies combine torque and stiffness control by co-activation with approaches based on activation overflow and inverse modelling. Extensive simulations are performed and described to assess the control efficacy. In the fourth paper, Merker et al [4] present a study on stable walking with asymmetric legs. The authors are concerned with the need to clarify to what extent differences in the leg function of contralateral limbs can be tolerated during walking or running. A bipedal spring-mass model simulating walking with compliant legs is used to show that even remarkable differences between contralateral legs can not only be tolerated, but may also introduce advantages to the robustness of the system dynamics. This study might contribute to shedding light on the stability of asymmetric leg walking, including the potential benefits of asymmetry, with possible implications for design of prosthetic or orthotic systems. The last two papers of this special section deal with active bioinspired systems driven by new actuators made of smart materials. In particular, the paper authored by Rossi et al [5] presents an underwater fish-like robot based on bending structures driven by shape memory alloys. These kinds of actuators are used to bend the backbone of the fish, which in turn causes a change in the curvature of the fish body. The paper describes the mechanisms by which standard swimming patterns can be reproduced with the proposed design, and show characterizations in terms of the actuation speed and position accuracy of prototype systems. The last paper, by Carpi et al [6], presents an overview on ionic- and electronic-type electromechanically active polymer actuators as artificial muscles for bioinspired applications. The electrical responsiveness and numerous functional and structural properties that these materials and actuators have in common with natural muscles are shown to be the key motivation by which they are studied as artificial muscles for a huge variety of possible uses. The authors describe the fundamental aspects of relevant technologies and emphasize how after several years of basic research, electromechanically active polymer actuators are today facing their important initial transition from academia into commercialization. In conclusion, we hope that the selection of papers in this special section might help to provide readers with a balanced overview, through examples on the relevant fundamental aspects, materials, actuators, structures, controls and on their effective integration, in order to develop approaches which will be successful in 'taking inspiration from nature for systems that move'. References [1] Lienhard J, Schleicher S, Poppinga S, Masselter T, Milwich M, Speck T and Knippers J 2011 Flectofin: a hingeless flapping mechanism inspired by nature Bioinsp. Biomim. 6 045001 [2] Nakata T, Liu H, Tanaka Y, Nishihashi N, Wang X and Sato A 2011 Aerodynamics of a bio-inspired flexible flapping-wing micro air vehicle Bioinsp. Biomim. 6 045002 [3] Annunziata S, Paskarbeit J and Schneider A 2011 Novel bioinspired control approaches to increase the stiffness variability in multi-muscle driven joints Bioinsp. Biomim. 6 045003 [4] Merker A, Rummel J and Seyfarth A 2011 Stable walking with asymmetric legs Bioinsp. Biomim. 6 045004 [5] Rossi C, Colorado J, Coral W and Barrientos A 2011 Bending continuous structures with SMAs: a novel robotic fish design Bioinsp. Biomim. 6 045005 [6] Carpi F, Kornbluh R, Sommer-Larsen P and Alici G 2011 Electroactive polymer actuators as artificial muscles: are they ready for bioinspired applications? Bioinsp. Biomim. 6 045006.}, }
@article {pmid22126793, year = {2011}, author = {Nakata, T and Liu, H and Tanaka, Y and Nishihashi, N and Wang, X and Sato, A}, title = {Aerodynamics of a bio-inspired flexible flapping-wing micro air vehicle.}, journal = {Bioinspiration &amp; biomimetics}, volume = {6}, number = {4}, pages = {045002}, doi = {10.1088/1748-3182/6/4/045002}, pmid = {22126793}, issn = {1748-3190}, mesh = {*Aircraft ; Animals ; *Biomimetic Materials ; Birds/*physiology ; Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Flight, Animal/*physiology ; Miniaturization ; Wings, Animal/*physiology ; }, abstract = {MAVs (micro air vehicles) with a maximal dimension of 15 cm and nominal flight speeds of around 10 m s[-1], operate in a Reynolds number regime of 10[5] or lower, in which most natural flyers including insects, bats and birds fly. Furthermore, due to their light weight and low flight speed, the MAVs' flight characteristics are substantially affected by environmental factors such as wind gust. Like natural flyers, the wing structures of MAVs are often flexible and tend to deform during flight. Consequently, the aero/fluid and structural dynamics of these flyers are closely linked to each other, making the entire flight vehicle difficult to analyze. We have recently developed a hummingbird-inspired, flapping flexible wing MAV with a weight of 2.4-3.0 g and a wingspan of 10-12 cm. In this study, we carry out an integrated study of the flexible wing aerodynamics of this flapping MAV by combining an in-house computational fluid dynamic (CFD) method and wind tunnel experiments. A CFD model that has a realistic wing planform and can mimic realistic flexible wing kinematics is established, which provides a quantitative prediction of unsteady aerodynamics of the four-winged MAV in terms of vortex and wake structures and their relationship with aerodynamic force generation. Wind tunnel experiments further confirm the effectiveness of the clap and fling mechanism employed in this bio-inspired MAV as well as the importance of the wing flexibility in designing small flapping-wing MAVs.}, }
@article {pmid22121605, year = {2011}, author = {Kwon, YH and Kim, D and Li, CG and Lee, JK and Hong, DS and Lee, JG and Lee, SH and Cho, YH and Kim, SH}, title = {Heat transfer and pressure drop characteristics of nanofluids in a plate heat exchanger.}, journal = {Journal of nanoscience and nanotechnology}, volume = {11}, number = {7}, pages = {5769-5774}, doi = {10.1166/jnn.2011.4399}, pmid = {22121605}, issn = {1533-4880}, abstract = {In this paper, the heat transfer characteristics and pressure drop of the ZnO and Al2O3 nanofluids in a plate heat exchanger were studied. The experimental conditions were 100-500 Reynolds number and the respective volumetric flow rates. The working temperature of the heat exchanger was within 20-40 degrees C. The measured thermophysical properties, such as thermal conductivity and kinematic viscosity, were applied to the calculation of the convective heat transfer coefficient of the plate heat exchanger employing the ZnO and Al2O3 nanofluids made through a two-step method. According to the Reynolds number, the overall heat transfer coefficient for 6 vol% Al2O3 increased to 30% because at the given viscosity and density of the nanofluids, they did not have the same flow rates. At a given volumetric flow rate, however, the performance did not improve. After the nanofluids were placed in the plate heat exchanger, the experimental results pertaining to nanofluid efficiency seemed inauspicious.}, }
@article {pmid22119230, year = {2012}, author = {Johnson, BN and Mutharasan, R}, title = {Biosensing using dynamic-mode cantilever sensors: a review.}, journal = {Biosensors &amp; bioelectronics}, volume = {32}, number = {1}, pages = {1-18}, doi = {10.1016/j.bios.2011.10.054}, pmid = {22119230}, issn = {1873-4235}, mesh = {Animals ; Biosensing Techniques/*instrumentation/methods ; Equipment Design ; Humans ; Microtechnology/methods ; Surface Properties ; }, abstract = {Current progress on the use of dynamic-mode cantilever sensors for biosensing applications is critically reviewed. We summarize their use in biosensing applications to date with focus given to: cantilever size (milli-, micro-, and nano-cantilevers), their geometry, and material used in fabrication. The review also addresses techniques investigated for both exciting and measuring cantilever resonance in various environments (vacuum, air, and liquid). Biological targets that have been detected to date are summarized with attention to bio-recognition chemistry, surface functionalization method, limit of detection, resonant frequency mode type, and resonant frequency measurement scheme. Applications published to date are summarized in a comprehensive table with description of the aforementioned details including comparison of sensitivities. Further, the general theory of cantilever resonance is discussed including fluid-structure interaction and its dependence on the Reynolds number for Newtonian fluids. The review covers designs with frequencies ranging from ∼1 kHz to 10 MHz and cantilever size ranging from millimeters to nanometers. We conclude by identifying areas that require further investigation.}, }
@article {pmid22107391, year = {2011}, author = {Würger, A}, title = {Leidenfrost gas ratchets driven by thermal creep.}, journal = {Physical review letters}, volume = {107}, number = {16}, pages = {164502}, doi = {10.1103/PhysRevLett.107.164502}, pmid = {22107391}, issn = {1079-7114}, abstract = {We show that thermal creep is at the origin of the recently discovered Leidenfrost ratchet, where liquid droplets float on a vapor layer along a heated sawtooth surface and accelerate to velocities of up to 40 cm/s. As the active element, the asymmetric temperature profile at each ratchet summit rectifies the vapor flow in the boundary layer. This mechanism works at low Reynolds number and provides a novel tool for controlling gas flow at nanostructured surfaces.}, }
@article {pmid22106263, year = {2011}, author = {Liu, B and Powers, TR and Breuer, KS}, title = {Force-free swimming of a model helical flagellum in viscoelastic fluids.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {108}, number = {49}, pages = {19516-19520}, pmid = {22106263}, issn = {1091-6490}, mesh = {Algorithms ; Animals ; Body Fluids/chemistry/*physiology ; Caenorhabditis elegans/physiology ; Elasticity ; Female ; Flagella/*physiology ; Humans ; Male ; Models, Biological ; Movement/*physiology ; Sperm Motility/physiology ; Swimming/*physiology ; Viscosity ; }, abstract = {We precisely measure the force-free swimming speed of a rotating helix in viscous and viscoelastic fluids. The fluids are highly viscous to replicate the low Reynolds number environment of microorganisms. The helix, a macroscopic scale model for the bacterial flagellar filament, is rigid and rotated at a constant rate while simultaneously translated along its axis. By adjusting the translation speed to make the net hydrodynamic force vanish, we measure the force-free swimming speed as a function of helix rotation rate, helix geometry, and fluid properties. We compare our measurements of the force-free swimming speed of a helix in a high-molecular weight silicone oil with predictions for the swimming speed in a Newtonian fluid, calculated using slender-body theories and a boundary-element method. The excellent agreement between theory and experiment in the Newtonian case verifies the high accuracy of our experiments. For the viscoelastic fluid, we use a polymer solution of polyisobutylene dissolved in polybutene. This solution is a Boger fluid, a viscoselastic fluid with a shear-rate-independent viscosity. The elasticity is dominated by a single relaxation time. When the relaxation time is short compared to the rotation period, the viscoelastic swimming speed is close to the viscous swimming speed. As the relaxation time increases, the viscoelastic swimming speed increases relative to the viscous speed, reaching a peak when the relaxation time is comparable to the rotation period. As the relaxation time is further increased, the viscoelastic swimming speed decreases and eventually falls below the viscous swimming speed.}, }
@article {pmid22101507, year = {2011}, author = {Gilbert, AD and Ogrin, FY and Petrov, PG and Winlove, CP}, title = {Motion and mixing for multiple ferromagnetic microswimmers.}, journal = {The European physical journal. E, Soft matter}, volume = {34}, number = {11}, pages = {121}, pmid = {22101507}, issn = {1292-895X}, abstract = {This paper concerns the interaction of several ferromagnetic microswimmers, their motion and the resulting fluid mixing. Each swimmer consists of two ferromagnetic beads joined by an elastic link, and is driven by an external, time-dependent magnetic field. The external field provides a torque on a swimmer and, together with the varying attraction between the magnetic beads, generates a time-irreversible motion leading to persistent swimming in a low Reynolds number environment. The aim of the present paper is to consider the interactions between several swimmers. A regime is considered in which identical swimmers move in the same overall direction, and their motion is synchronised because of driving by the external field. It is found that two swimmers tend to encircle one another while three undergo more complicated motion that may involve the braiding of swimmer trajectories. By means of approximations it is established that the interaction between pairs of swimmers gives circulatory motion which falls off with an inverse square law and is linked to their overall speed of motion through the fluid. As groups of two or more swimmers move through the fluid they process fluid, leaving behind a trail of fluid that has undergone mixing: this is investigated by following streak lines numerically.}, }
@article {pmid22087893, year = {2011}, author = {Lacombe, R and Moussou, P and Aurégan, Y}, title = {Whistling of an orifice in a reverberating duct at low Mach number.}, journal = {The Journal of the Acoustical Society of America}, volume = {130}, number = {5}, pages = {2662-2672}, doi = {10.1121/1.3641427}, pmid = {22087893}, issn = {1520-8524}, mesh = {Acoustics/*instrumentation ; Equipment Design ; Models, Theoretical ; Motion ; *Noise ; Oscillometry ; *Sound ; Time Factors ; Vibration ; }, abstract = {An experimental investigation of the parameters controlling the whistling frequency and amplitude of an orifice in a confined turbulent flow is undertaken. A circular single hole orifice with sharp edges, a hole diameter equal to 0.015 m and a thickness equal to 0.005 m, is arranged in an air test rig with an inner diameter equal to 0.03 m. The Mach number ranges around 0.02 and the Reynolds number around 10(4). Variable reflecting boundary conditions are arranged upstream and downstream, and several flow velocities are tested. It is found that the Bode-Nyquist criterion accurately predicts the conditions of self-sustained oscillation and the value of the whistling frequency. Furthermore, it is found that the acoustic velocity in whistling regime varies from 1% to 15% of the steady flow velocity, and that it depends on the overall acoustic reflection of the surrounding pipe and on the Strouhal number.}, }
@article {pmid22086090, year = {2012}, author = {Naemi, R and Psycharakis, SG and McCabe, C and Connaboy, C and Sanders, RH}, title = {Relationships between glide efficiency and swimmers' size and shape characteristics.}, journal = {Journal of applied biomechanics}, volume = {28}, number = {4}, pages = {400-411}, doi = {10.1123/jab.28.4.400}, pmid = {22086090}, issn = {1543-2688}, mesh = {Body Size/*physiology ; Computer Simulation ; Energy Transfer/*physiology ; Female ; Humans ; Male ; *Models, Biological ; Posture/*physiology ; Swimming/*physiology ; Young Adult ; }, abstract = {Glide efficiency, the ability of a body to minimize deceleration over the glide, can change with variations in the body's size and shape. The purpose of this study was to investigate the relationships between glide efficiency and the size and shape characteristics of swimmers. Eight male and eight female swimmers performed a series of horizontal glides at a depth of 70 cm below the surface. Glide efficiency parameters were calculated for velocities ranging from 1.4 to 1.6 m/s for female swimmers (and at the Reynolds number of 3.5 million) and from 1.6 to 1.8 m/s for male swimmers (and at the Reynolds number of 4.5 million). Several morphological indices were calculated to account for the shape characteristics, with the use of a photogrammetric method. Relationships between the variables of interest were explored with correlations, while repeated-measures ANOVA was used to assess within-group differences between different velocities for each gender group. Glide efficiency of swimmers increased when velocity decreased. Some morphological indices and postural angles showed a significant correlation with glide efficiency. The glide coefficient was significantly correlated to the chest to waist taper index for both gender groups. For the male group, the glide coefficient correlated significantly to the fineness ratio of upper body, the chest to hip cross-section. For the female group the glide coefficient had a significant correlation with the waist to hip taper index. The findings suggested that gliding efficiency was more dependent on shape characteristics and appropriate postural angles rather than being dependent on size characteristics.}, }
@article {pmid22077402, year = {2012}, author = {Sharma, V and Szymusiak, M and Shen, H and Nitsche, LC and Liu, Y}, title = {Formation of polymeric toroidal-spiral particles.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {28}, number = {1}, pages = {729-735}, doi = {10.1021/la203338v}, pmid = {22077402}, issn = {1520-5827}, mesh = {Biocompatible Materials/chemistry ; Kinetics ; Polymers/*chemistry ; }, abstract = {Compared to spherical matrices, particles with well-defined internal structure provide large surface to volume ratio and predictable release kinetics for the encapsulated payloads. We describe self-assembly of polymeric particles, whereby competitive kinetics of viscous sedimentation, diffusion, and cross-linking yield a controllable toroidal-spiral (T-S) structure. Precursor polymeric droplets are splashed through the surface of a less dense, miscible solution, after which viscous forces entrain the surrounding bulk solution into the sedimenting polymer drop to form T-S channels. The intricate structure forms because low interfacial tension between the two miscible solutions is dominated by viscous forces. The biocompatible polymer, poly(ethylene glycol) diacrylate (PEG-DA), is used to demonstrate the solidification of the T-S shapes at various configurational stages by UV-triggered cross-linking. The dimensions of the channels are controlled by Weber number during impact on the surface, and Reynolds number and viscosity ratio during subsequent sedimentation. We anticipate applications of the T-S particle in drug delivery, wherein diffusion through these T-S channels and the polymer matrix would offer parallel release pathways for molecules of different sizes. Polyphosphate, as a model macromolecule, is entrained in T-S particles during their formation. The in vitro release kinetics of polyphosphate from the T-S particles with various channel length and width is reported. In addition, self-assembly of T-S particles occurs in a single step under benign conditions for delicate macromolecules, and appears conducive to scaleup.}, }
@article {pmid22071184, year = {2011}, author = {Szymik, BG and Satterlie, RA}, title = {Changes in wingstroke kinematics associated with a change in swimming speed in a pteropod mollusk, Clione limacina.}, journal = {The Journal of experimental biology}, volume = {214}, number = {Pt 23}, pages = {3935-3947}, doi = {10.1242/jeb.058461}, pmid = {22071184}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena/physiology ; Clione/*anatomy &amp; histology/*physiology ; Swimming/*physiology ; Time Factors ; }, abstract = {In pteropod mollusks, the gastropod foot has evolved into two broad, wing-like structures that are rhythmically waved through the water for propulsion. The flexibility of the wings lends a tremendous range of motion, an advantage that could be exploited when changing locomotory speed. Here, we investigated the kinematic changes that take place during an increase in swimming speed in the pteropod mollusk Clione limacina. Clione demonstrates two distinct swim speeds: a nearly constant slow swimming behavior and a fast swimming behavior used for escape and hunting. The neural control of Clione's swimming is well documented, as are the neuromuscular changes that bring about Clione's fast swimming. This study examined the kinematics of this swimming behavior at the two speeds. High speed filming was used to obtain 3D data from individuals during both slow and fast swimming. Clione's swimming operates at a low Reynolds number, typically under 200. Within a given swimming speed, we found that wing kinematics are highly consistent from wingbeat to wingbeat, but differ between speeds. The transition to fast swimming sees a significant increase in wing velocity and angle of attack, and range of motion increases as the wings bend more during fast swimming. Clione likely uses a combination of drag-based and unsteady mechanisms for force production at both speeds. The neuromuscular control of Clione's speed change points to a two-gaited swimming behavior, and we consider the kinematic evidence for Clione's swim speeds being discrete gaits.}, }
@article {pmid22060486, year = {2011}, author = {Liu, YH and Kuo, CY and Chang, CC and Wang, CY}, title = {Electro-osmotic flow through a two-dimensional screen-pump filter.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {84}, number = {3 Pt 2}, pages = {036301}, doi = {10.1103/PhysRevE.84.036301}, pmid = {22060486}, issn = {1550-2376}, mesh = {Electricity ; Electroosmosis/*instrumentation ; Filtration/*instrumentation ; Models, Theoretical ; }, abstract = {The electro-osmotic flow driven by a screen pump, composed of a line array of evenly spaced identical rectangular solid blocks, is investigated under the Debye-Hückel approximation. The geometry of the screen pump is determined by the spacing and aspect ratio of the solid blocks. A constant surface zeta potential is assumed on the block surface. The method of eigenfunction series expansion is applied to solve analytically for the applied electric field, electric charge potential in the fluid, and flow field. Because of the low Reynolds number, Stokes equations are applied for the flow. The analytic result is first confirmed by comparing with the exact solution of the electro-osmotic flow in an infinite channel. Then different geometries of the screen pump and the effect of the electrokinetic width are computed for their influence on the flow rate. Recirculating eddies and reversing flow are found even though the applied electric driving field is unidirectional.}, }
@article {pmid22060447, year = {2011}, author = {Sipos, M and Goldenfeld, N}, title = {Directed percolation describes lifetime and growth of turbulent puffs and slugs.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {84}, number = {3 Pt 2}, pages = {035304}, doi = {10.1103/PhysRevE.84.035304}, pmid = {22060447}, issn = {1550-2376}, abstract = {We show that directed percolation (DP) simulations in a pipe geometry in 3+1 dimensions capture the observed complex phenomenology of the transition to turbulence. At low Reynolds numbers (Re), turbulent puffs form and spontaneously relaminarize. At high Re, turbulent slugs expand uniformly into the laminar regions. In a spatiotemporally intermittent state between these two regimes of Re, puffs split and turbulent regions exhibit laminar patches. DP also captures some of the quantitative features of the transition, with a superexponentially diverging characteristic lifetime below the transition. Above the percolation threshold, active (turbulent) clusters expand into the inactive (laminar) phase with a well-defined velocity whose scaling with control parameter (Reynolds number or percolation probability) is consistent with experimental results. Our results provide strong evidence in favor of a conjecture of Pomeau.}, }
@article {pmid22049736, year = {2011}, author = {Njau, KN and Gastory, L and Eshton, B and Katima, JH and Minja, RJ and Kimwaga, R and Shaaban, M}, title = {Effect of diffusional mass transfer on the performance of horizontal subsurface flow constructed wetlands in tropical climate conditions.}, journal = {Water science and technology : a journal of the International Association on Water Pollution Research}, volume = {63}, number = {12}, pages = {3039-3045}, doi = {10.2166/wst.2011.640}, pmid = {22049736}, issn = {0273-1223}, mesh = {Biological Oxygen Demand Analysis ; Facility Design and Construction ; Hydrodynamics ; Models, Theoretical ; Tanzania ; *Tropical Climate ; *Water Movements ; Water Pollutants, Chemical/isolation &amp; purification ; Water Purification/*methods/standards ; *Wetlands ; }, abstract = {The effect of mass transfer on the removal rate constants of BOD5, NH3, NO3 and TKN has been investigated in a Horizontal Subsurface Flow Constructed Wetland (HSSFCW) planted with Phragmites mauritianus. The plug flow model was assumed and the inlet and outlet concentrations were used to determine the observed removal rate constants. Mass transfer effects were studied by assessing the influence of interstitial velocity on pollutant removal rates in CW cells of different widths. The flow velocities varied between 3-46 m/d. Results indicate that the observed removal rate constants are highly influenced by the flow velocity. Correlation of dimensionless groups namely Reynolds Number (Re), Sherwood Number (Sh) and Schmidt Number (Sc) were applied and log-log plots of rate constants against velocity yielded straight lines with values beta = 0.87 for BOD5, 1.88 for NH3, 1.20 for NO3 and 0.94 for TKN. The correlation matched the expected for packed beds although the constant beta was higher than expected for low Reynolds numbers. These results indicate that the design values of rate constants used to size wetlands are influenced by flow velocity. This paper suggests the incorporation of mass transfer into CW design procedures in order to improve the performance of CW systems and reduce land requirements.}, }
@article {pmid22034325, year = {2011}, author = {Koehler, C and Wischgoll, T and Dong, H and Gaston, Z}, title = {Vortex visualization in ultra low Reynolds number insect flight.}, journal = {IEEE transactions on visualization and computer graphics}, volume = {17}, number = {12}, pages = {2071-2079}, doi = {10.1109/TVCG.2011.260}, pmid = {22034325}, issn = {1941-0506}, mesh = {Animals ; *Computer Graphics ; Computer Simulation ; Flight, Animal/*physiology ; Hydrodynamics ; Imaging, Three-Dimensional/statistics &amp; numerical data ; Insecta/*physiology ; Models, Biological ; }, abstract = {We present the visual analysis of a biologically inspired CFD simulation of the deformable flapping wings of a dragonfly as it takes off and begins to maneuver, using vortex detection and integration-based flow lines. The additional seed placement and perceptual challenges introduced by having multiple dynamically deforming objects in the highly unsteady 3D flow domain are addressed. A brief overview of the high speed photogrammetry setup used to capture the dragonfly takeoff, parametric surfaces used for wing reconstruction, CFD solver and underlying flapping flight theory is presented to clarify the importance of several unsteady flight mechanisms, such as the leading edge vortex, that are captured visually. A novel interactive seed placement method is used to simplify the generation of seed curves that stay in the vicinity of relevant flow phenomena as they move with the flapping wings. This method allows a user to define and evaluate the quality of a seed's trajectory over time while working with a single time step. The seed curves are then used to place particles, streamlines and generalized streak lines. The novel concept of flowing seeds is also introduced in order to add visual context about the instantaneous vector fields surrounding smoothly animate streak lines. Tests show this method to be particularly effective at visually capturing vortices that move quickly or that exist for a very brief period of time. In addition, an automatic camera animation method is used to address occlusion issues caused when animating the immersed wing boundaries alongside many geometric flow lines. Each visualization method is presented at multiple time steps during the up-stroke and down-stroke to highlight the formation, attachment and shedding of the leading edge vortices in pairs of wings. Also, the visualizations show evidence of wake capture at stroke reversal which suggests the existence of previously unknown unsteady lift generation mechanisms that are unique to quad wing insects.}, }
@article {pmid22026857, year = {2011}, author = {Galtier, S and Banerjee, S}, title = {Exact relation for correlation functions in compressible isothermal turbulence.}, journal = {Physical review letters}, volume = {107}, number = {13}, pages = {134501}, doi = {10.1103/PhysRevLett.107.134501}, pmid = {22026857}, issn = {1079-7114}, abstract = {Compressible isothermal turbulence is analyzed under the assumption of homogeneity and in the asymptotic limit of a high Reynolds number. An exact relation is derived for some two-point correlation functions which reveals a fundamental difference with the incompressible case. The main difference resides in the presence of a new type of term which acts on the inertial range similarly as a source or a sink for the mean energy transfer rate. When isotropy is assumed, compressible turbulence may be described by the relation -2/3ε(eff)r = F(r)(r), where F(r) is the radial component of the two-point correlation functions and ε(eff) is an effective mean total energy injection rate. By dimensional arguments, we predict that a spectrum in k(-5/3) may still be preserved at small scales if the density-weighted fluid velocity ρ(1/3)u is used.}, }
@article {pmid22010758, year = {2011}, author = {Shim, EB and Hong, SB and Lim, KM and Leem, CH and Youn, CH and Pak, HN and Earm, YE and Noble, D}, title = {New index for categorising cardiac reentrant wave: in silico evaluation.}, journal = {IET systems biology}, volume = {5}, number = {5}, pages = {317-323}, doi = {10.1049/iet-syb.2011.0019}, pmid = {22010758}, issn = {1751-8849}, mesh = {Action Potentials ; Arrhythmias, Cardiac/physiopathology ; Biomarkers/metabolism ; Cardiology/methods ; Computational Biology ; Computer Simulation ; Electrophysiology/methods ; Heart/*physiology ; Heart Conduction System/*physiology ; Humans ; *Models, Cardiovascular ; Models, Theoretical ; Reference Standards ; Rheology/methods ; Systems Biology/methods ; }, abstract = {Based on the similarity between a reentrant wave in cardiac tissue and a vortex in fluid dynamics, the authors hypothesised that a new non-dimensional index, like the Reynolds number in fluid dynamics, may play a critical role in categorising reentrant wave dynamics. Therefore the goal of the present study is to devise a new index to characterise electric wave conduction in cardiac tissue and examined whether this index can be used as a biomarker for categorising the reentrant wave pattern in cardiac tissue. Similar to the procedure used to derive the Reynolds number in fluid dynamics, the authors used a non-dimensionalisation technique to obtain the new index. Its usefulness was verified using a two-dimensional simulation model of electrical wave propagation in cardiac tissue. The simulation results showed that electrical waves in cardiac tissue move into an unstable region when the index exceeds a threshold value.}, }
@article {pmid21976022, year = {2011}, author = {Gaensler, BM and Haverkorn, M and Burkhart, B and Newton-McGee, KJ and Ekers, RD and Lazarian, A and McClure-Griffiths, NM and Robishaw, T and Dickey, JM and Green, AJ}, title = {Low-Mach-number turbulence in interstellar gas revealed by radio polarization gradients.}, journal = {Nature}, volume = {478}, number = {7368}, pages = {214-217}, doi = {10.1038/nature10446}, pmid = {21976022}, issn = {1476-4687}, abstract = {The interstellar medium of the Milky Way is multiphase, magnetized and turbulent. Turbulence in the interstellar medium produces a global cascade of random gas motions, spanning scales ranging from 100 parsecs to 1,000 kilometres (ref. 4). Fundamental parameters of interstellar turbulence such as the sonic Mach number (the speed of sound) have been difficult to determine, because observations have lacked the sensitivity and resolution to image the small-scale structure associated with turbulent motion. Observations of linear polarization and Faraday rotation in radio emission from the Milky Way have identified unusual polarized structures that often have no counterparts in the total radiation intensity or at other wavelengths, and whose physical significance has been unclear. Here we report that the gradient of the Stokes vector (Q, U), where Q and U are parameters describing the polarization state of radiation, provides an image of magnetized turbulence in diffuse, ionized gas, manifested as a complex filamentary web of discontinuities in gas density and magnetic field. Through comparison with simulations, we demonstrate that turbulence in the warm, ionized medium has a relatively low sonic Mach number, M(s) ≲ 2. The development of statistical tools for the analysis of polarization gradients will allow accurate determinations of the Mach number, Reynolds number and magnetic field strength in interstellar turbulence over a wide range of conditions.}, }
@article {pmid21975086, year = {2012}, author = {Arfaoui, A and Popa, CV and Taïar, R and Polidori, G and Fohanno, S}, title = {Numerical streamline patterns at swimmer's surface using RANS equations.}, journal = {Journal of applied biomechanics}, volume = {28}, number = {3}, pages = {279-283}, doi = {10.1123/jab.28.3.279}, pmid = {21975086}, issn = {1543-2688}, mesh = {Adult ; Computer Simulation ; Female ; Humans ; *Models, Biological ; Rheology/*methods ; Shear Strength/physiology ; Swimming/*physiology ; }, abstract = {The objective of this article is to perform a numerical modeling on the flow dynamics around a competitive female swimmer during the underwater swimming phase for a velocity of 2.2 m/s corresponding to national swimming levels. Flow around the swimmer is assumed turbulent and simulated with a computational fluid dynamics method based on a volume control approach. The 3D numerical simulations have been carried out with the code ANSYS FLUENT and are presented using the standard k-ω turbulence model for a Reynolds number of 6.4 × 10(6). To validate the streamline patterns produced by the simulation, experiments were performed in the swimming pools of the National Institute of Sports and Physical Education in Paris (INSEP) by using the tufts method.}, }
@article {pmid21956206, year = {2012}, author = {Suzuki, I and Shiraishi, Y and Yabe, S and Tsuboko, Y and Sugai, TK and Matsue, K and Kameyama, T and Saijo, Y and Tanaka, T and Okamoto, Y and Feng, Z and Miyazaki, T and Yamagishi, M and Yoshizawa, M and Umezu, M and Yambe, T}, title = {Engineering analysis of the effects of bulging sinuses in a newly designed pediatric pulmonary heart valve on hemodynamic function.}, journal = {Journal of artificial organs : the official journal of the Japanese Society for Artificial Organs}, volume = {15}, number = {1}, pages = {49-56}, pmid = {21956206}, issn = {1619-0904}, mesh = {Child ; Heart/*physiology ; *Heart Valve Prosthesis ; Hemodynamics/*physiology ; Humans ; Materials Testing ; *Models, Cardiovascular ; Polytetrafluoroethylene ; Pulsatile Flow/physiology ; }, abstract = {The purpose of this study was to examine the hemodynamic characteristics of expanded polytetrafluoroethylene (ePTFE) pulmonary valves with bulging sinuses quantitatively in a pediatric pulmonary mechanical circulatory system designed by us, in order to propose the optimal design for clinical applications. In this study, we developed a pediatric pulmonary mock circulation system, which consisted of a pneumatic right ventricular model, a pulmonary heart valve chamber, and a pulmonary elastic compliance tubing with resistive units. The hemodynamic characteristics of four different types of ePTFE valves and a monoleaflet mechanical heart valve were examined. Relationships between the leaflet movements and fluid characteristics were evaluated based on engineering analyses using echocardiography and a high-speed video camera under the pediatric circulatory conditions of the mock system. We successfully performed hemodynamic simulations in our pediatric pulmonary circulatory system that could be useful for quantitatively evaluating the pediatric heart valves. In the simulation study, the ePTFE valve with bulging sinuses exhibited a large eddy in the vicinity of the leaflets, whereas the straight tubing exhibited turbulent flow. The Reynolds number obtained in the valve with bulging sinuses was calculated to be 1667, which was smaller than that in the straight tubing (R (e) = 2454).The hemodynamic characteristics of ePTFE pediatric pulmonary heart valves were examined in our mock circulatory system. The presence of the bulging sinuses in the pulmonary heart valve decreased the hydrodynamic energy loss and increased the systolic opening area. Based on an in vitro experiment, we were able to propose an optimal selection of pulmonary valve design parameters that could yield a more sophisticated pediatric ePTFE valve shape.}, }
@article {pmid21952728, year = {2012}, author = {Golden, JP and Justin, GA and Nasir, M and Ligler, FS}, title = {Hydrodynamic focusing--a versatile tool.}, journal = {Analytical and bioanalytical chemistry}, volume = {402}, number = {1}, pages = {325-335}, pmid = {21952728}, issn = {1618-2650}, support = {U01 AI075489/AI/NIAID NIH HHS/United States ; U01 AI075489-05/AI/NIAID NIH HHS/United States ; }, mesh = {Biosensing Techniques/*instrumentation ; Equipment Design ; Flow Cytometry/instrumentation ; *Hydrodynamics ; Microfluidic Analytical Techniques/*instrumentation ; Microtechnology/*instrumentation ; }, abstract = {The control of hydrodynamic focusing in a microchannel has inspired new approaches for microfluidic mixing, separations, sensors, cell analysis, and microfabrication. Achieving a flat interface between the focusing and focused fluids is dependent on Reynolds number and device geometry, and many hydrodynamic focusing systems can benefit from this understanding. For applications where a specific cross-sectional shape is desired for the focused flow, advection generated by grooved structures in the channel walls can be used to define the shape of the focused flow. Relative flow rates of the focused flow and focusing streams can be manipulated to control the cross-sectional area of the focused flows. This paper discusses the principles for defining the shape of the interface between the focused and focusing fluids and provides examples from our lab that use hydrodynamic focusing for impedance-based sensors, flow cytometry, and microfabrication to illustrate the breadth of opportunities for introducing new capabilities into microfluidic systems. We evaluate each example for the advantages and limitations integral to utilization of hydrodynamic focusing for that particular application.}, }
@article {pmid21937045, year = {2011}, author = {Cui, XG and Gutheil, E}, title = {Large eddy simulation of the unsteady flow-field in an idealized human mouth-throat configuration.}, journal = {Journal of biomechanics}, volume = {44}, number = {16}, pages = {2768-2774}, doi = {10.1016/j.jbiomech.2011.08.019}, pmid = {21937045}, issn = {1873-2380}, mesh = {Computer Simulation ; Humans ; Larynx/anatomy &amp; histology/*physiology ; *Models, Biological ; Palate, Soft/anatomy &amp; histology/*physiology ; Pharynx/anatomy &amp; histology/*physiology ; *Respiratory Physiological Phenomena ; Trachea/anatomy &amp; histology/*physiology ; }, abstract = {The present study concerns the simulation and analysis of the flow field in the upper human respiratory system in order to gain an improved understanding of the complex flow field with respect to the process affecting drug delivery for medical treatment of the human air system. For this purpose, large eddy simulation (LES) is chosen because of its powerful performance in the transitional range of laminar and turbulent flow fields. The average gas velocity in a constricted tube is compared with experimental data (Ahmed and Giddens, 1983) and numerical data from Reynolds-averaged Navier-Stokes (RANS) equations coupled with low Reynolds number (LRN) κ-ω model (Zhang and Kleinstreuer, 2003) and LRN shear-stress transport κ-ω model (Jayaraju et al., 2007), for model validation. The present study emphasizes on the instantaneous flow field, where the simulations capture different scales of secondary vortices in different flow zones including recirculation zones, the laryngeal jet zone, the mixing zone, and the wall shear layer. It is observed that the laryngeal jet tail breaks up, and the unsteady motion of laryngeal jet is coupled with the unsteady distribution of secondary vortices in the jet boundary. The present results show that it is essential to study the unsteady flow field since it strongly affects the particle flow in the human upper respiratory system associated with drug delivery for medical treatment.}, }
@article {pmid21929104, year = {2011}, author = {Alexakis, A}, title = {Searching for the fastest dynamo: laminar ABC flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {84}, number = {2 Pt 2}, pages = {026321}, doi = {10.1103/PhysRevE.84.026321}, pmid = {21929104}, issn = {1550-2376}, abstract = {The growth rate of the dynamo instability as a function of the magnetic Reynolds number R(M) is investigated by means of numerical simulations for the family of the Arnold-Beltrami-Childress (ABC) flows and for two different forcing scales. For the ABC flows that are driven at the largest available length scale, it is found that, as the magnetic Reynolds number is increased: (a) The flow that results first in a dynamo is the 2 1/2-dimensional flow for which A=B and C=0 (and all permutations). (b) The second type of flow that results in a dynamo is the one for which A=B≃2C/5 (and permutations). (c) The most symmetric flow, A=B=C, is the third type of flow that results in a dynamo. (d) As R(M) is increased, the A=B=C flow stops being a dynamo and transitions from a local maximum to a third-order saddle point. (e) At larger R(M), the A=B=C flow reestablishes itself as a dynamo but remains a saddle point. (f) At the largest examined R(M), the growth rate of the 2 1/2-dimensional flows starts to decay, the A=B=C flow comes close to a local maximum again, and the flow A=B≃2C/5 (and permutations) results in the fastest dynamo with growth rate γ≃0.12 at the largest examined R(M). For the ABC flows that are driven at the second largest available length scale, it is found that (a) the 2 1/2-dimensional flows A=B,C=0 (and permutations) are again the first flows that result in a dynamo with a decreased onset. (b) The most symmetric flow, A=B=C, is the second type of flow that results in a dynamo. It is, and it remains, a local maximum. (c) At larger R(M), the flow A=B≃2C/5 (and permutations) appears as the third type of flow that results in a dynamo. As R(M) is increased, it becomes the flow with the largest growth rate. The growth rates appear to have some correlation with the Lyapunov exponents, but constructive refolding of the field lines appears equally important in determining the fastest dynamo flow.}, }
@article {pmid21885152, year = {2011}, author = {Quinn, PM and Parker, BL and Cherry, JA}, title = {Using constant head step tests to determine hydraulic apertures in fractured rock.}, journal = {Journal of contaminant hydrology}, volume = {126}, number = {1-2}, pages = {85-99}, doi = {10.1016/j.jconhyd.2011.07.002}, pmid = {21885152}, issn = {1873-6009}, mesh = {Calcium Carbonate ; *Geological Phenomena ; Groundwater ; Hydrodynamics ; Magnesium ; Porosity ; *Water Movements ; *Water Supply ; }, abstract = {The initial step in the analysis of contaminant transport in fractured rock requires the consideration of groundwater velocity. Practical methods for estimating the average linear groundwater velocity (v¯) in fractured rock require determination of hydraulic apertures which are commonly calculated by applying the cubic law using transmissivity (T) values and the number of hydraulically active fractures in the test interval. High-resolution, constant-head step injection testing of cored boreholes in a 100 m thick fractured dolostone aquifer was conducted using inflatable packers to isolate specific test intervals from the rest of the borehole. The steps in each test interval were gradually increased from very low to much higher injection rates. At smaller injection rates, the flow rate vs. applied pressure graph projects through the origin and indicates Darcian flow; non Darcian flow is evident at higher injection rates. Non-Darcian flow results in significantly lower calculated T values, which translates to smaller hydraulic aperture values. Further error in the calculated hydraulic aperture stems from uncertainty in the number of hydraulically active fractures in each test interval. This estimate can be inferred from borehole image and core logs, however, all of the fractures identified are not necessarily hydraulically active. This study proposes a method based on Reynolds number calculations aimed at improving confidence in the selection of the number of active fractures in each test interval.}, }
@article {pmid21867314, year = {2011}, author = {Nore, C and Léorat, J and Guermond, JL and Luddens, F}, title = {Nonlinear dynamo action in a precessing cylindrical container.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {84}, number = {1 Pt 2}, pages = {016317}, doi = {10.1103/PhysRevE.84.016317}, pmid = {21867314}, issn = {1550-2376}, abstract = {It is numerically demonstrated by means of a magnetohydrodynamics code that precession can trigger the dynamo effect in a cylindrical container. When the Reynolds number, based on the radius of the cylinder and its angular velocity, increases, the flow, which is initially centrosymmetric, loses its stability and bifurcates to a quasiperiodic motion. This unsteady and asymmetric flow is shown to be capable of sustaining dynamo action in the linear and nonlinear regimes. The magnetic field thus generated is unsteady and quadrupolar. These numerical evidences of dynamo action in a precessing cylindrical container may be useful for an experiment now planned at the Dresden sodium facility for dynamo and thermohydraulic studies in Germany.}, }
@article {pmid21867311, year = {2011}, author = {Graham, JP and Mininni, PD and Pouquet, A}, title = {High Reynolds number magnetohydrodynamic turbulence using a Lagrangian model.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {84}, number = {1 Pt 2}, pages = {016314}, doi = {10.1103/PhysRevE.84.016314}, pmid = {21867311}, issn = {1550-2376}, abstract = {With the help of a model of magnetohydrodynamic (MHD) turbulence tested previously, we explore high Reynolds number regimes up to equivalent resolutions of 6000(3) grid points in the absence of forcing and with no imposed uniform magnetic field. For the given initial condition chosen here, with equal kinetic and magnetic energy, the flow ends up being dominated by the magnetic field, and the dynamics leads to an isotropic Iroshnikov-Kraichnan energy spectrum. However, the locally anisotropic magnetic field fluctuations perpendicular to the local mean field follow a Kolmogorov law. We find that the ratio of the eddy turnover time to the Alfvén time increases with wave number, contrary to the so-called critical balance hypothesis. Residual energy and helicity spectra are also considered; the role played by the conservation of magnetic helicity is studied, and scaling laws are found for the magnetic helicity and residual helicity spectra. We put these results in the context of the dynamics of a globally isotropic MHD flow that is locally anisotropic because of the influence of the strong large-scale magnetic field, leading to a partial equilibration between kinetic and magnetic modes for the energy and the helicity.}, }
@article {pmid21867274, year = {2011}, author = {Huang, YX and Schmitt, FG and Hermand, JP and Gagne, Y and Lu, ZM and Liu, YL}, title = {Arbitrary-order Hilbert spectral analysis for time series possessing scaling statistics: comparison study with detrended fluctuation analysis and wavelet leaders.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {84}, number = {1 Pt 2}, pages = {016208}, doi = {10.1103/PhysRevE.84.016208}, pmid = {21867274}, issn = {1550-2376}, mesh = {Calibration ; Fourier Analysis ; Fractals ; Motion ; Nonlinear Dynamics ; Reproducibility of Results ; *Signal Processing, Computer-Assisted ; Time Factors ; }, abstract = {In this paper we present an extended version of Hilbert-Huang transform, namely arbitrary-order Hilbert spectral analysis, to characterize the scale-invariant properties of a time series directly in an amplitude-frequency space. We first show numerically that due to a nonlinear distortion, traditional methods require high-order harmonic components to represent nonlinear processes, except for the Hilbert-based method. This will lead to an artificial energy flux from the low-frequency (large scale) to the high-frequency (small scale) part. Thus the power law, if it exists, is contaminated. We then compare the Hilbert method with structure functions (SF), detrended fluctuation analysis (DFA), and wavelet leader (WL) by analyzing fractional Brownian motion and synthesized multifractal time series. For the former simulation, we find that all methods provide comparable results. For the latter simulation, we perform simulations with an intermittent parameter μ=0.15. We find that the SF underestimates scaling exponent when q>3. The Hilbert method provides a slight underestimation when q>5. However, both DFA and WL overestimate the scaling exponents when q>5. It seems that Hilbert and DFA methods provide better singularity spectra than SF and WL. We finally apply all methods to a passive scalar (temperature) data obtained from a jet experiment with a Taylor's microscale Reynolds number Re(λ)≃250. Due to the presence of strong ramp-cliff structures, the SF fails to detect the power law behavior. For the traditional method, the ramp-cliff structure causes a serious artificial energy flux from the low-frequency (large scale) to the high-frequency (small scale) part. Thus DFA and WL underestimate the scaling exponents. However, the Hilbert method provides scaling exponents ξ(θ)(q) quite close to the one for longitudinal velocity, indicating a less intermittent passive scalar field than what was believed before.}, }
@article {pmid21867241, year = {2011}, author = {Kitahata, H and Yoshinaga, N and Nagai, KH and Sumino, Y}, title = {Spontaneous motion of a droplet coupled with a chemical wave.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {84}, number = {1 Pt 2}, pages = {015101}, doi = {10.1103/PhysRevE.84.015101}, pmid = {21867241}, issn = {1550-2376}, mesh = {*Hydrodynamics ; *Models, Theoretical ; *Motion ; }, abstract = {We propose a framework for the spontaneous motion of a droplet coupled with internal dynamic patterns generated in a reaction-diffusion system. The spatiotemporal order of the chemical reaction gives rise to inhomogeneous surface tension and results in self-propulsion driven by the surrounding flow due to the Marangoni effect. Numerical calculations of internal patterns together with theoretical results of the flow fields at low Reynolds number reproduce well the experimental results obtained using a droplet of the Belousov-Zhabotinsky reaction medium.}, }
@article {pmid21867044, year = {2011}, author = {Seguin, A and Bertho, Y and Gondret, P and Crassous, J}, title = {Dense granular flow around a penetrating object: experiment and hydrodynamic model.}, journal = {Physical review letters}, volume = {107}, number = {4}, pages = {048001}, doi = {10.1103/PhysRevLett.107.048001}, pmid = {21867044}, issn = {1079-7114}, mesh = {*Hydrodynamics ; Kinetics ; Mechanical Phenomena ; *Models, Theoretical ; *Rheology ; }, abstract = {We present in this Letter experimental results on the bidimensional flow field around a cylinder penetrating into dense granular matter, together with drag force measurements. A hydrodynamic model based on extended kinetic theory for dense granular flow reproduces well the flow localization close to the cylinder and the corresponding scalings of the drag force, which is found to not depend on velocity, but linearly on the pressure and on the cylinder diameter and weakly on the grain size. Such a regime is found to be valid at a low enough "granular" Reynolds number.}, }
@article {pmid21865627, year = {2011}, author = {Truong, QT and Nguyen, QV and Truong, VT and Park, HC and Byun, DY and Goo, NS}, title = {A modified blade element theory for estimation of forces generated by a beetle-mimicking flapping wing system.}, journal = {Bioinspiration &amp; biomimetics}, volume = {6}, number = {3}, pages = {036008}, doi = {10.1088/1748-3182/6/3/036008}, pmid = {21865627}, issn = {1748-3190}, mesh = {*Aircraft ; Animals ; *Biomimetic Materials ; Biomimetics/*instrumentation/*methods ; Coleoptera/*physiology ; Computer Simulation ; Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Flight, Animal/*physiology ; Miniaturization ; Models, Biological ; Stress, Mechanical ; Wings, Animal/*physiology ; }, abstract = {We present an unsteady blade element theory (BET) model to estimate the aerodynamic forces produced by a freely flying beetle and a beetle-mimicking flapping wing system. Added mass and rotational forces are included to accommodate the unsteady force. In addition to the aerodynamic forces needed to accurately estimate the time history of the forces, the inertial forces of the wings are also calculated. All of the force components are considered based on the full three-dimensional (3D) motion of the wing. The result obtained by the present BET model is validated with the data which were presented in a reference paper. The difference between the averages of the estimated forces (lift and drag) and the measured forces in the reference is about 5.7%. The BET model is also used to estimate the force produced by a freely flying beetle and a beetle-mimicking flapping wing system. The wing kinematics used in the BET calculation of a real beetle and the flapping wing system are captured using high-speed cameras. The results show that the average estimated vertical force of the beetle is reasonably close to the weight of the beetle, and the average estimated thrust of the beetle-mimicking flapping wing system is in good agreement with the measured value. Our results show that the unsteady lift and drag coefficients measured by Dickinson et al are still useful for relatively higher Reynolds number cases, and the proposed BET can be a good way to estimate the force produced by a flapping wing system.}, }
@article {pmid21856147, year = {2011}, author = {Ashford, RL and White, P and Indramohan, V}, title = {The aerodynamics of running socks: Reality or rhetoric?.}, journal = {Foot (Edinburgh, Scotland)}, volume = {21}, number = {4}, pages = {184-187}, doi = {10.1016/j.foot.2011.06.002}, pmid = {21856147}, issn = {1532-2963}, mesh = {*Air Movements ; Clothing/*standards ; Equipment Design ; Humans ; Materials Testing/*methods ; Models, Theoretical ; *Running ; }, abstract = {AIM: The primary objective of this study was to test the aerodynamic properties of a selection of running and general sports socks.<br><br>METHODS AND PROCEDURES: Eleven pairs of socks were tested in a specially constructed rig which was inserted into a fully calibrated wind tunnel. Wind test speeds included 3, 4, 5, 6, 12 and 45m/s.<br><br>RESULTS: There was no significant difference between any of the socks tested for their aerodynamic properties. The drag coefficients calculated for each sock varied proportionally with the Reynolds number. No particular sock was more aerodynamic than any of the socks tested.<br><br>CONCLUSION: There is no evidence that a sock that is "aerodynamically designed" will help an athlete go faster. This may be more product rhetoric than reality, and further work is justified if such claims are being made.}, }
@article {pmid21852407, year = {2011}, author = {Persak, SC and Sin, S and McDonough, JM and Arens, R and Wootton, DM}, title = {Noninvasive estimation of pharyngeal airway resistance and compliance in children based on volume-gated dynamic MRI and computational fluid dynamics.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {111}, number = {6}, pages = {1819-1827}, pmid = {21852407}, issn = {1522-1601}, support = {HD-053693/HD/NICHD NIH HHS/United States ; HL-62408/HL/NHLBI NIH HHS/United States ; }, mesh = {Airway Resistance/*physiology ; Case-Control Studies ; Child ; Child, Preschool ; Compliance/physiology ; Computer Simulation ; Humans ; Hydrodynamics ; Imaging, Three-Dimensional ; Magnetic Resonance Imaging/*methods ; Models, Biological ; Pharynx/*physiology/physiopathology ; Respiratory Mechanics/physiology ; Sleep Apnea, Obstructive/*physiopathology ; }, abstract = {Computational fluid dynamics (CFD) analysis was used to model the effect of collapsing airway geometry on internal pressure and velocity in the pharyngeal airway of three sedated children with obstructive sleep apnea syndrome (OSAS) and three control subjects. Model geometry was reconstructed from volume-gated magnetic resonance images during normal tidal breathing at 10 increments of tidal volume through the respiratory cycle. Each geometry was meshed with an unstructured grid and solved using a low-Reynolds number k-ω turbulence model driven by flow data averaged over 12 consecutive breathing cycles. Combining gated imaging with CFD modeling created a dynamic three-dimensional view of airway anatomy and mechanics, including the evolution of airway collapse and flow resistance and estimates of the local effective compliance. The upper airways of subjects with OSAS were generally much more compliant during tidal breathing. Compliance curves (pressure vs. cross-section area), derived for different locations along the airway, quantified local differences along the pharynx and between OSAS subjects. In one subject, the distal oropharynx was more compliant than the nasopharynx (1.028 vs. 0.450 mm(2)/Pa) and had a lower theoretical limiting flow rate, confirming the distal oropharynx as the flow-limiting segment of the airway in this subject. Another subject had a more compliant nasopharynx (0.053 mm(2)/Pa) during inspiration and apparent stiffening of the distal oropharynx (C = 0.0058 mm(2)/Pa), and the theoretical limiting flow rate indicated the nasopharynx as the flow-limiting segment. This new method may help to differentiate anatomical and functional factors in airway collapse.}, }
@article {pmid21818636, year = {2012}, author = {Yan, WW and Cai, B and Liu, Y and Fu, BM}, title = {Effects of wall shear stress and its gradient on tumor cell adhesion in curved microvessels.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {11}, number = {5}, pages = {641-653}, pmid = {21818636}, issn = {1617-7940}, support = {SC1 CA153325/CA/NCI NIH HHS/United States ; 1SC1CA153325-01/CA/NCI NIH HHS/United States ; }, mesh = {Animals ; *Cell Adhesion ; Female ; Microvessels/*pathology ; Models, Theoretical ; Neoplasms, Experimental/*blood/blood supply ; Rats ; Rats, Sprague-Dawley ; *Stress, Physiological ; }, abstract = {Tumor cell adhesion to vessel walls in the microcirculation is one critical step in cancer metastasis. In this paper, the hypothesis that tumor cells prefer to adhere at the microvessels with localized shear stresses and their gradients, such as in the curved microvessels, was examined both experimentally and computationally. Our in vivo experiments were performed on the microvessels (post-capillary venules, 30-50 μm diameter) of rat mesentery. A straight or curved microvessel was cannulated and perfused with tumor cells by a glass micropipette at a velocity of ~1mm/s. At less than 10 min after perfusion, there was a significant difference in cell adhesion to the straight and curved vessel walls. In 60 min, the averaged adhesion rate in the curved vessels (n = 14) was ~1.5-fold of that in the straight vessels (n = 19). In 51 curved segments, 45% of cell adhesion was initiated at the inner side, 25% at outer side, and 30% at both sides of the curved vessels. To investigate the mechanical mechanism by which tumor cells prefer adhering at curved sites, we performed a computational study, in which the fluid dynamics was carried out by the lattice Boltzmann method , and the tumor cell dynamics was governed by the Newton's law of translation and rotation. A modified adhesive dynamics model that included the influence of wall shear stress/gradient on the association/dissociation rates of tumor cell adhesion was proposed, in which the positive wall shear stress/gradient jump would enhance tumor cell adhesion while the negative wall shear stress/gradient jump would weaken tumor cell adhesion. It was found that the wall shear stress/gradient, over a threshold, had significant contribution to tumor cell adhesion by activating or inactivating cell adhesion molecules. Our results elucidated why the tumor cell adhesion prefers to occur at the positive curvature of curved microvessels with very low Reynolds number (in the order of 10(-2)) laminar flow.}, }
@article {pmid21809854, year = {2011}, author = {Wu, L and Gao, B and Muñoz-Carpena, R}, title = {Experimental analysis of colloid capture by a cylindrical collector in laminar overland flow.}, journal = {Environmental science &amp; technology}, volume = {45}, number = {18}, pages = {7777-7784}, doi = {10.1021/es201578n}, pmid = {21809854}, issn = {1520-5851}, mesh = {*Colloids ; Fluorescence ; Microspheres ; *Models, Theoretical ; Particle Size ; *Plant Stems ; *Water Movements ; *Water Pollutants ; }, abstract = {Although colloid-facilitated contaminant transport in water flow is a well-known contamination process, little research has been conducted to investigate the transport of colloidal particles through emergent vegetation in overland flow. In this work, a series of laboratory experiments were conducted to measure the single-collector contact efficiency (η(0)) of colloid capture by a simulated plant stem in laminar lateral flow. Fluorescent microspheres of various sizes were used as experimental colloids. The colloid suspensions were applied to a glass cylinder installed in a small size flow chamber at different flow rates. Two cylinder sizes were tested in the experiment and silicone grease was applied to the cylinder surface to make it favorable for colloid deposition. Our results showed that increases in flow rate and collector size reduced the value of η(0) and a minimum value of η(0) might exist for a colloid size. The experimental data were compared to theoretical predictions of different single-collector contact efficiency models. The results indicated that existing single-collector contact efficiency models underestimated the η(0) of colloid capture by the cylinders in laminar overland flow. A regression equation of η(0) as a function of collector Reynolds number (Re(c)) and Peclet number (N(Pe)) was developed and fit the experimental data very well (R(2) > 0.98). This regression equation can be used to help construct and refine mathematical models of colloid transport and filtration in laminar overland flow on vegetated surfaces.}, }
@article {pmid21802431, year = {2011}, author = {Tripathi, D}, title = {A mathematical model for the peristaltic flow of chyme movement in small intestine.}, journal = {Mathematical biosciences}, volume = {233}, number = {2}, pages = {90-97}, doi = {10.1016/j.mbs.2011.06.007}, pmid = {21802431}, issn = {1879-3134}, mesh = {Computer Simulation ; Gastrointestinal Contents ; Humans ; Intestine, Small/*physiology ; *Models, Biological ; Peristalsis/*physiology ; }, abstract = {A mathematical model based on viscoelastic fluid (fractional Oldroyd-B model) flow is considered for the peristaltic flow of chyme in small intestine, which is assumed to be in the form of an inclined cylindrical tube. The peristaltic flow of chyme is modeled more realistically by assuming that the peristaltic rush wave is a sinusoidal wave, which propagates along the tube. The governing equations are simplified by making the assumptions of long wavelength and low Reynolds number. Analytical approximate solutions of problem are obtained by using homotopy analysis method and convergence of the obtained series solution is properly checked. For the realistic values of the emerging parameters such as fractional parameters, relaxation time, retardation time, Reynolds number, Froude number and inclination of tube, the numerical results for the pressure difference and the frictional force across one wavelength are computed and discussed the roles played by these parameters during the peristaltic flow. On the basis of this study, it is found that the first fractional parameter, relaxation time and Froude number resist the movement of chyme, while, the second fractional parameter, retardation time, Reynolds number and inclination of tube favour the movement of chyme through the small intestine during pumping. It is further revealed that size of trapped bolus reduces with increasing the amplitude ratio whereas it is unaltered with other parameters.}, }
@article {pmid21801733, year = {2011}, author = {Tsuda, A and Laine-Pearson, FE and Hydon, PE}, title = {Why chaotic mixing of particles is inevitable in the deep lung.}, journal = {Journal of theoretical biology}, volume = {286}, number = {1}, pages = {57-66}, pmid = {21801733}, issn = {1095-8541}, support = {HL074022/HL/NHLBI NIH HHS/United States ; HL054885/HL/NHLBI NIH HHS/United States ; R01 HL074022/HL/NHLBI NIH HHS/United States ; R01 HL054885/HL/NHLBI NIH HHS/United States ; HL070542/HL/NHLBI NIH HHS/United States ; R01 HL070542/HL/NHLBI NIH HHS/United States ; }, mesh = {Administration, Inhalation ; Aerosols ; Humans ; *Models, Biological ; Nonlinear Dynamics ; Particle Size ; Pulmonary Alveoli/*physiology ; Pulmonary Gas Exchange/physiology ; Respiratory Transport/*physiology ; }, abstract = {Fine/ultrafine particles can easily reach the pulmonary acinus, where gas is exchanged, but they need to mix with alveolar residual air to land on the septal surface. Classical fluid mechanics theory excludes flow-induced mixing mechanisms because of the low Reynolds number nature of the acinar flow. For more than a decade, we have been challenging this classical view, proposing the idea that chaotic mixing is a potent mechanism in determining the transport of inhaled particles in the pulmonary acinus. We have demonstrated this in numerical simulations, experimental studies in both physical models and in animals, and mathematical modeling. However, the mathematical theory that describes chaotic mixing in small airways and alveoli is highly complex; it not readily accessible by non-mathematicians. The purpose of this paper is to make the basic mechanisms that operate in acinar chaotic mixing more accessible, by translating the key mathematical ideas into physics-oriented language. The key to understanding chaotic mixing is to identify two types of frequency in the system, each of which is induced by a different mechanism. The way in which their interplay creates chaos is explained with instructive illustrations but without any equations. We also explain why self-similarity occurs in the alveolar system and was indeed observed as a fractal pattern deep in rat lungs (Proc. Natl. Acad. Sci. USA. 99:10173-10178, 2002).}, }
@article {pmid21797480, year = {2011}, author = {Brito, D and Alboussière, T and Cardin, P and Gagnière, N and Jault, D and La Rizza, P and Masson, JP and Nataf, HC and Schmitt, D}, title = {Zonal shear and super-rotation in a magnetized spherical Couette-flow experiment.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {6 Pt 2}, pages = {066310}, doi = {10.1103/PhysRevE.83.066310}, pmid = {21797480}, issn = {1550-2376}, abstract = {We present measurements performed in a spherical shell filled with liquid sodium, where a 74-mm-radius inner sphere is rotated while a 210-mm-radius outer sphere is at rest. The inner sphere holds a dipolar magnetic field and acts as a magnetic propeller when rotated. In this experimental setup called "Derviche Tourneur Sodium" (DTS), direct measurements of the velocity are performed by ultrasonic Doppler velocimetry. Differences in electric potential and the induced magnetic field are also measured to characterize the magnetohydrodynamic flow. Rotation frequencies of the inner sphere are varied between -30 Hz and +30 Hz, the magnetic Reynolds number based on measured sodium velocities and on the shell radius reaching to about 33. We have investigated the mean axisymmetric part of the flow, which consists of differential rotation. Strong super-rotation of the fluid with respect to the rotating inner sphere is directly measured. It is found that the organization of the mean flow does not change much throughout the entire range of parameters covered by our experiment. The direct measurements of zonal velocity give a nice illustration of Ferraro's law of isorotation in the vicinity of the inner sphere, where magnetic forces dominate inertial ones. The transition from a Ferraro regime in the interior to a geostrophic regime, where inertial forces predominate, in the outer regions has been well documented. It takes place where the local Elsasser number is about 1. A quantitative agreement with nonlinear numerical simulations is obtained when keeping the same Elsasser number. The experiments also reveal a region that violates Ferraro's law just above the inner sphere.}, }
@article {pmid21797471, year = {2011}, author = {Burgener, T and Kadau, D and Herrmann, HJ}, title = {Simulation of particle mixing in turbulent channel flow due to intrinsic fluid velocity fluctuation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {6 Pt 2}, pages = {066301}, doi = {10.1103/PhysRevE.83.066301}, pmid = {21797471}, issn = {1550-2376}, abstract = {We combine a discrete-element-method simulation with a stochastic process to model the movement of spherical particles in a turbulent channel flow. With this model we investigate the mixing properties of two species of particles flowing through the channel. We find a linear increase of the mixing zone with the length of the pipe. Flows at different Reynolds number are studied. Below a critical Reynolds number at the Taylor microscale of around Rc ≈ 300 the mixing rate is strongly dependent on the Reynolds number. Above Rc the mixing rate stays nearly constant.}, }
@article {pmid21797295, year = {2011}, author = {Najafi, A}, title = {Hydrodynamics of a microhunter: a chemotactic scenario.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {6 Pt 1}, pages = {060902}, doi = {10.1103/PhysRevE.83.060902}, pmid = {21797295}, issn = {1550-2376}, mesh = {*Chemotaxis ; Flagella/physiology ; *Hydrodynamics ; *Models, Biological ; Movement ; Swimming ; }, abstract = {Inspired by biological chemotaxis along circular paths, we propose a hydrodynamic molecular scale hunter that can swim and can find its target. The system is essentially a stochastic low-Reynolds-number swimmer with the ability to move in two-dimensional space and to sense the local value of the chemical concentration emitted by a target. We show that, by adjusting the geometrical and dynamical variables of the swimmer, we can always achieve a swimmer that can navigate and can search for the region with a higher concentration of a chemical emitted by a source.}, }
@article {pmid21737736, year = {2011}, author = {Avila, K and Moxey, D and de Lozar, A and Avila, M and Barkley, D and Hof, B}, title = {The onset of turbulence in pipe flow.}, journal = {Science (New York, N.Y.)}, volume = {333}, number = {6039}, pages = {192-196}, doi = {10.1126/science.1203223}, pmid = {21737736}, issn = {1095-9203}, abstract = {Shear flows undergo a sudden transition from laminar to turbulent motion as the velocity increases, and the onset of turbulence radically changes transport efficiency and mixing properties. Even for the well-studied case of pipe flow, it has not been possible to determine at what Reynolds number the motion will be either persistently turbulent or ultimately laminar. We show that in pipes, turbulence that is transient at low Reynolds numbers becomes sustained at a distinct critical point. Through extensive experiments and computer simulations, we were able to identify and characterize the processes ultimately responsible for sustaining turbulence. In contrast to the classical Landau-Ruelle-Takens view that turbulence arises from an increase in the temporal complexity of fluid motion, here, spatial proliferation of chaotic domains is the decisive process and intrinsic to the nature of fluid turbulence.}, }
@article {pmid21728696, year = {2011}, author = {Luo, LS and Liao, W and Chen, X and Peng, Y and Zhang, W}, title = {Numerics of the lattice Boltzmann method: effects of collision models on the lattice Boltzmann simulations.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {5 Pt 2}, pages = {056710}, doi = {10.1103/PhysRevE.83.056710}, pmid = {21728696}, issn = {1550-2376}, abstract = {We conduct a comparative study to evaluate several lattice Boltzmann (LB) models for solving the near incompressible Navier-Stokes equations, including the lattice Boltzmann equation with the multiple-relaxation-time (MRT), the two-relaxation-time (TRT), the single-relaxation-time (SRT) collision models, and the entropic lattice Boltzmann equation (ELBE). The lid-driven square cavity flow in two dimensions is used as a benchmark test. Our results demonstrate that the ELBE does not improve the numerical stability of the SRT or the lattice Bhatnagar-Gross-Krook (LBGK) model. Our results also show that the MRT and TRT LB models are superior to the ELBE and LBGK models in terms of accuracy, stability, and computational efficiency and that the ELBE scheme is the most inferior among the LB models tested in this study, thus is unfit for carrying out numerical simulations in practice. Our study suggests that, to optimize the accuracy, stability, and efficiency in the MRT model, it requires at least three independently adjustable relaxation rates: one for the shear viscosity ν (or the Reynolds number Re), one for the bulk viscosity ζ, and one to satisfy the criterion imposed by the Dirichlet boundary conditions which are realized by the bounce-back-type boundary conditions.}, }
@article {pmid21728673, year = {2011}, author = {Eyink, GL}, title = {Stochastic flux freezing and magnetic dynamo.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {5 Pt 2}, pages = {056405}, doi = {10.1103/PhysRevE.83.056405}, pmid = {21728673}, issn = {1550-2376}, abstract = {Magnetic flux conservation in turbulent plasmas at high magnetic Reynolds numbers is argued neither to hold in the conventional sense nor to be entirely broken, but instead to be valid in a statistical sense associated to the "spontaneous stochasticity" of Lagrangian particle trajectories. The latter phenomenon is due to the explosive separation of particles undergoing turbulent Richardson diffusion, which leads to a breakdown of Laplacian determinism for classical dynamics. Empirical evidence is presented for spontaneous stochasticity, including numerical results. A Lagrangian path-integral approach is then exploited to establish stochastic flux freezing for resistive hydromagnetic equations and to argue, based on the properties of Richardson diffusion, that flux conservation must remain stochastic at infinite magnetic Reynolds number. An important application of these results is the kinematic, fluctuation dynamo in nonhelical, incompressible turbulence at magnetic Prandtl number (Pr(m)) equal to unity. Numerical results on the Lagrangian dynamo mechanisms by a stochastic particle method demonstrate a strong similarity between the Pr(m)=1 and 0 dynamos. Stochasticity of field-line motion is an essential ingredient of both. Finally, some consequences for nonlinear magnetohydrodynamic turbulence, dynamo, and reconnection are briefly considered.}, }
@article {pmid21728649, year = {2011}, author = {Singh, NK and Sridhar, S}, title = {Transport coefficients for the shear dynamo problem at small Reynolds numbers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {5 Pt 2}, pages = {056309}, doi = {10.1103/PhysRevE.83.056309}, pmid = {21728649}, issn = {1550-2376}, abstract = {We build on the formulation developed in S. Sridhar and N. K. Singh [J. Fluid Mech. 664, 265 (2010)] and present a theory of the shear dynamo problem for small magnetic and fluid Reynolds numbers, but for arbitrary values of the shear parameter. Specializing to the case of a mean magnetic field that is slowly varying in time, explicit expressions for the transport coefficients α(il) and η(il) are derived. We prove that when the velocity field is nonhelical, the transport coefficient α(il) vanishes. We then consider forced, stochastic dynamics for the incompressible velocity field at low Reynolds number. An exact, explicit solution for the velocity field is derived, and the velocity spectrum tensor is calculated in terms of the Galilean-invariant forcing statistics. We consider forcing statistics that are nonhelical, isotropic, and delta correlated in time, and specialize to the case when the mean field is a function only of the spatial coordinate X(3) and time τ; this reduction is necessary for comparison with the numerical experiments of A. Brandenburg, K. H. Rädler, M. Rheinhardt, and P. J. Käpylä [Astrophys. J. 676, 740 (2008)]. Explicit expressions are derived for all four components of the magnetic diffusivity tensor η(il)(τ). These are used to prove that the shear-current effect cannot be responsible for dynamo action at small Re and Rm, but for all values of the shear parameter.}, }
@article {pmid21728574, year = {2011}, author = {Guo, Q and McFaul, SM and Ma, H}, title = {Deterministic microfluidic ratchet based on the deformation of individual cells.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {5 Pt 1}, pages = {051910}, doi = {10.1103/PhysRevE.83.051910}, pmid = {21728574}, issn = {1550-2376}, mesh = {Biomechanical Phenomena ; *Mechanical Phenomena ; *Microfluidic Analytical Techniques ; Pressure ; Single-Cell Analysis/*instrumentation ; }, abstract = {We present a microfluidic ratchet that exploits the deformation of individual cells through microscale funnel constrictions. The threshold pressure required to transport single cells through such constrictions is greater against the direction of taper than along the direction of taper. This physical asymmetry combined with an oscillatory excitation can enable selective and irreversible transport of individual cells in low Reynolds number flow. We devised a microfluidic device to measure the pressure asymmetry across various geometries of funnel constrictions. Using a chain of funnel constrictions, we showed that oscillatory pressure enables ratcheting transport when the pressure amplitude and oscillation period exceeds the threshold required to transport single cells. These experiments demonstrate the potential of using this mechanism to selectively transport biological cells based on their internal mechanics, and the potential to separate cells based on cell morphology or disease state.}, }
@article {pmid21728530, year = {2011}, author = {Dalbe, MJ and Cosic, D and Berhanu, M and Kudrolli, A}, title = {Aggregation of frictional particles due to capillary attraction.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {5 Pt 1}, pages = {051403}, doi = {10.1103/PhysRevE.83.051403}, pmid = {21728530}, issn = {1550-2376}, abstract = {Capillary attraction between identical millimeter-sized spheres floating at a liquid-air interface and the resulting aggregation are investigated at low Reynolds number. We show that the measured capillary forces between two spheres as a function of distance can be described by expressions obtained using the Nicolson approximation at low Bond numbers for far greater particle sizes than previously assumed. We find that viscous hydrodynamic interactions between the spheres needs to be included to describe the dynamics close to contact. We then consider the aggregates formed when a third sphere is added after the initial two spheres are already in contact. In this case, we find that linear superposition of capillary forces describes the observed approach qualitatively but not quantitatively. Further, we observe an angular dependence of the structure due to a rapid decrease of capillary force with distance of separation, which has a tendency to align the particles before contact. When the three particles come into contact, they may preserve their shape or rearrange to form an equilateral triangle cluster-the lowest-energy state-depending on the competition between attraction between particles and friction. Using these observations, we demonstrate that a linear particle chain can be built from frictional particles with capillary attraction.}, }
@article {pmid21711785, year = {2011}, author = {Bianco, V and Nardini, S and Manca, O}, title = {Enhancement of heat transfer and entropy generation analysis of nanofluids turbulent convection flow in square section tubes.}, journal = {Nanoscale research letters}, volume = {6}, number = {1}, pages = {252}, pmid = {21711785}, issn = {1556-276X}, abstract = {In this article, developing turbulent forced convection flow of a water-Al2O3 nanofluid in a square tube, subjected to constant and uniform wall heat flux, is numerically investigated. The mixture model is employed to simulate the nanofluid flow and the investigation is accomplished for particles size equal to 38 nm.An entropy generation analysis is also proposed in order to find the optimal working condition for the given geometry under given boundary conditions. A simple analytical procedure is proposed to evaluate the entropy generation and its results are compared with the numerical calculations, showing a very good agreement.A comparison of the resulting Nusselt numbers with experimental correlations available in literature is accomplished. To minimize entropy generation, the optimal Reynolds number is determined.}, }
@article {pmid21711743, year = {2011}, author = {Manca, O and Mesolella, P and Nardini, S and Ricci, D}, title = {Numerical study of a confined slot impinging jet with nanofluids.}, journal = {Nanoscale research letters}, volume = {6}, number = {1}, pages = {188}, pmid = {21711743}, issn = {1556-276X}, abstract = {BACKGROUND: Heat transfer enhancement technology concerns with the aim of developing more efficient systems to satisfy the increasing demands of many applications in the fields of automotive, aerospace, electronic and process industry. A solution for obtaining efficient cooling systems is represented by the use of confined or unconfined impinging jets. Moreover, the possibility of increasing the thermal performances of the working fluids can be taken into account, and the introduction of nanoparticles in a base fluid can be considered.<br><br>RESULTS: In this article, a numerical investigation on confined impinging slot jet working with a mixture of water and Al2O3 nanoparticles is described. The flow is turbulent and a constant temperature is applied on the impinging. A single-phase model approach has been adopted. Different geometric ratios, particle volume concentrations and Reynolds number have been considered to study the behavior of the system in terms of average and local Nusselt number, convective heat transfer coefficient and required pumping power profiles, temperature fields and stream function contours.<br><br>CONCLUSIONS: The dimensionless stream function contours show that the intensity and size of the vortex structures depend on the confining effects, given by H/W ratio, Reynolds number and particle concentrations. Furthermore, for increasing concentrations, nanofluids realize increasing fluid bulk temperature, as a result of the elevated thermal conductivity of mixtures. The local Nusselt number profiles show the highest values at the stagnation point, and the lowest at the end of the heated plate. The average Nusselt number increases for increasing particle concentrations and Reynolds numbers; moreover, the highest values are observed for H/W = 10, and a maximum increase of 18% is detected at a concentration equal to 6%. The required pumping power as well as Reynolds number increases and particle concentrations grow, which is almost 4.8 times greater than the values calculated in the case of base fluid.List of symbols.}, }
@article {pmid21711694, year = {2011}, author = {Zeinali Heris, S and Noie, SH and Talaii, E and Sargolzaei, J}, title = {Numerical investigation of Al2O3/water nanofluid laminar convective heat transfer through triangular ducts.}, journal = {Nanoscale research letters}, volume = {6}, number = {1}, pages = {179}, pmid = {21711694}, issn = {1556-276X}, abstract = {In this article, laminar flow-forced convective heat transfer of Al2O3/water nanofluid in a triangular duct under constant wall temperature condition is investigated numerically. In this investigation, the effects of parameters, such as nanoparticles diameter, concentration, and Reynolds number on the enhancement of nanofluids heat transfer is studied. Besides, the comparison between nanofluid and pure fluid heat transfer is achieved in this article. Sometimes, because of pressure drop limitations, the need for non-circular ducts arises in many heat transfer applications. The low heat transfer rate of non-circular ducts is one the limitations of these systems, and utilization of nanofluid instead of pure fluid because of its potential to increase heat transfer of system can compensate this problem. In this article, for considering the presence of nanoparticl: es, the dispersion model is used. Numerical results represent an enhancement of heat transfer of fluid associated with changing to the suspension of nanometer-sized particles in the triangular duct. The results of the present model indicate that the nanofluid Nusselt number increases with increasing concentration of nanoparticles and decreasing diameter. Also, the enhancement of the fluid heat transfer becomes better at high Re in laminar flow with the addition of nanoparticles.}, }
@article {pmid21698321, year = {2011}, author = {Hutzler, NR and Parsons, MF and Gurevich, YV and Hess, PW and Petrik, E and Spaun, B and Vutha, AC and DeMille, D and Gabrielse, G and Doyle, JM}, title = {A cryogenic beam of refractory, chemically reactive molecules with expansion cooling.}, journal = {Physical chemistry chemical physics : PCCP}, volume = {13}, number = {42}, pages = {18976-18985}, doi = {10.1039/c1cp20901a}, pmid = {21698321}, issn = {1463-9084}, abstract = {Cryogenically cooled buffer gas beam sources of the molecule thorium monoxide (ThO) are optimized and characterized. Both helium and neon buffer gas sources are shown to produce ThO beams with high flux, low divergence, low forward velocity, and cold internal temperature for a variety of stagnation densities and nozzle diameters. The beam operates with a buffer gas stagnation density of ∼10(15)-10(16) cm(-3) (Reynolds number ∼1-100), resulting in expansion cooling of the internal temperature of the ThO to as low as 2 K. For the neon (helium) based source, this represents cooling by a factor of about 10 (2) from the initial nozzle temperature of about 20 K (4 K). These sources deliver ∼10(11) ThO molecules in a single quantum state within a 1-3 ms long pulse at 10 Hz repetition rate. Under conditions optimized for a future precision spectroscopy application [A. C. Vutha et al., J. Phys. B: At., Mol. Opt. Phys., 2010, 43, 074007], the neon-based beam has the following characteristics: forward velocity of 170 m s(-1), internal temperature of 3.4 K, and brightness of 3 × 10(11) ground state molecules per steradian per pulse. Compared to typical supersonic sources, the relatively low stagnation density of this source and the fact that the cooling mechanism relies only on collisions with an inert buffer gas make it widely applicable to many atomic and molecular species, including those which are chemically reactive, such as ThO.}, }
@article {pmid21671959, year = {2011}, author = {Turri, F and Yanagihara, JI}, title = {Computer-assisted numerical analysis for oxygen and carbon dioxide mass transfer in blood oxygenators.}, journal = {Artificial organs}, volume = {35}, number = {6}, pages = {579-592}, doi = {10.1111/j.1525-1594.2010.01150.x}, pmid = {21671959}, issn = {1525-1594}, mesh = {Carbon Dioxide/*blood ; Computer Simulation ; Equipment Design ; Extracorporeal Membrane Oxygenation/instrumentation/*methods ; Humans ; Hydrogen-Ion Concentration ; Models, Biological ; *Numerical Analysis, Computer-Assisted ; Oxygen/*blood ; *Oxygenators, Membrane ; }, abstract = {A two-dimensional numeric simulator is developed to predict the nonlinear, convective-reactive, oxygen mass exchange in a cross-flow hollow fiber blood oxygenator. The numeric simulator also calculates the carbon dioxide mass exchange, as hemoglobin affinity to oxygen is affected by the local pH value, which depends mostly on the local carbon dioxide content in blood. Blood pH calculation inside the oxygenator is made by the simultaneous solution of an equation that takes into account the blood buffering capacity and the classical Henderson-Hasselbach equation. The modeling of the mass transfer conductance in the blood comprises a global factor, which is a function of the Reynolds number, and a local factor, which takes into account the amount of oxygen reacted to hemoglobin. The simulator is calibrated against experimental data for an in-line fiber bundle. The results are: (i) the calibration process allows the precise determination of the mass transfer conductance for both oxygen and carbon dioxide; (ii) very alkaline pH values occur in the blood path at the gas inlet side of the fiber bundle; (iii) the parametric analysis of the effect of the blood base excess (BE) shows that (.)V(CO2) is similar in the case of blood metabolic alkalosis, metabolic acidosis, or normal BE, for a similar blood inlet P(CO2), although the condition of metabolic alkalosis is the worst case, as the pH in the vicinity of the gas inlet is the most alkaline; (iv) the parametric analysis of the effect of the gas flow to blood flow ratio (QG/QB) shows that (.)V(CO2) variation with the gas flow is almost linear up to QG/QB = 2.0. (.)V(O2) is not affected by the gas flow as it was observed that by increasing the gas flow up to eight times, the (.)V(O2) grows only 1%. The mass exchange of carbon dioxide uses the full length of the hollow-fiber only if Q(G) /Q(B)> 2.0, as it was observed that only in this condition does the local variation of pH and blood P(CO2) comprise the whole fiber bundle.}, }
@article {pmid21669208, year = {2011}, author = {Herschlag, G and Miller, L}, title = {Reynolds number limits for jet propulsion: a numerical study of simplified jellyfish.}, journal = {Journal of theoretical biology}, volume = {285}, number = {1}, pages = {84-95}, doi = {10.1016/j.jtbi.2011.05.035}, pmid = {21669208}, issn = {1095-8541}, mesh = {Animals ; Hydrodynamics ; *Models, Biological ; Rheology/methods ; Scyphozoa/anatomy &amp; histology/*physiology ; Swimming/*physiology ; Viscosity ; }, abstract = {The Scallop theorem states that reciprocal methods of locomotion, such as jet propulsion or paddling, will not work in Stokes flow (Reynolds number=0). In nature the effective limit of jet propulsion is still in the range where inertial forces are significant. It appears that almost all animals that use jet propulsion swim at Reynolds numbers (Re) of about 5 or more. Juvenile squid and octopods hatch from the egg already swimming in this inertial regime. Juvenile jellyfish, or ephyrae, break off from polyps swimming at Re greater than 5. Many other organisms, such as scallops, rarely swim at Re less than 100. The limitations of jet propulsion at intermediate Re is explored here using the immersed boundary method to solve the 2D Navier-Stokes equations coupled to the motion of a simplified jellyfish. The contraction and expansion kinematics are prescribed, but the forward and backward swimming motions of the idealized jellyfish are emergent properties determined by the resulting fluid dynamics. Simulations are performed for both an oblate bell shape using a paddling mode of swimming and a prolate bell shape using jet propulsion. Average forward velocities and work put into the system are calculated for Re between 1 and 320. The results show that forward velocities rapidly decay with decreasing Re for all bell shapes when Re<10. Similarly, the work required to generate the pulsing motion increases significantly for Re<10. When compared to actual organisms, the swimming velocities and vortex separation patterns for the model prolate agree with those observed in Nemopsis bachei. The forward swimming velocities of the model oblate jellyfish after two pulse cycles are comparable to those reported for Aurelia aurita, but discrepancies are observed in the vortex dynamics between when the 2D model oblate jellyfish and the organism. This discrepancy is likely due to a combination of the differences between the 3D reality of the jellyfish and the 2D simplification, as well as the rigidity of the time varying geometry imposed by the idealized model.}, }
@article {pmid21657203, year = {2011}, author = {Donner, JS and Baffou, G and McCloskey, D and Quidant, R}, title = {Plasmon-assisted optofluidics.}, journal = {ACS nano}, volume = {5}, number = {7}, pages = {5457-5462}, doi = {10.1021/nn200590u}, pmid = {21657203}, issn = {1936-086X}, abstract = {We study the ability of a plasmonic structure under illumination to release heat and induce fluid convection at the nanoscale. We first introduce the unified formalism associated with this multidisciplinary problem combining optics, thermodynamics, and hydrodynamics. On this basis, numerical simulations were performed to compute the temperature field and velocity field evolutions of the surrounding fluid for a gold disk on glass while illuminated at its plasmon resonance. We show that the velocity amplitude of the surrounding fluid has a linear dependence on the structure temperature and a quadratic dependence on the structure size (for a given temperature). The fluid velocity remains negligible for single nanometer-sized plasmonic structures (<1 nm/s) due to a very low Reynolds number. However thermal-induced fluid convection can play a significant role when considering either micrometer-size structures or an assembly of nanostructures.}, }
@article {pmid21653822, year = {2011}, author = {Kim, D and Gharib, M}, title = {Characteristics of vortex formation and thrust performance in drag-based paddling propulsion.}, journal = {The Journal of experimental biology}, volume = {214}, number = {Pt 13}, pages = {2283-2291}, doi = {10.1242/jeb.050716}, pmid = {21653822}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Biophysical Phenomena ; Biophysics ; *Energy Metabolism ; Locomotion ; Movement ; Stress, Mechanical ; Swimming/*physiology ; }, abstract = {Several characteristics of drag-based paddling propulsion are studied with a simple mechanical model and a measurement technique for mapping three-dimensional flow fields. In drag-based propulsion, the temporal change of the vortex strength is an important parameter in the relationship between vortex formation and thrust generation. Our results indicate that spanwise flow behind the paddling propulsor significantly affects tip vortex development and thrust generation. The distribution of spanwise flow is dependent on the propulsor shape and the Reynolds number. A delta-shaped propulsor generates strong spanwise flow compared with a rectangular propulsor. For the low Reynolds number case, spanwise flow is not as strong as that for the high Reynolds number case. Without sacrificing total impulse, the flexible propulsor can smooth out thrust peaks during sudden stroke motions, which is favorable for avoiding structural failures and stabilizing body motion. We also explored the role of stopping vortex shedding in efficient thrust generation by determining the relationship between stroke angles and total impulses generated by paddling propulsors.}, }
@article {pmid21641317, year = {2011}, author = {Bayly, PV and Lewis, BL and Ranz, EC and Okamoto, RJ and Pless, RB and Dutcher, SK}, title = {Propulsive forces on the flagellum during locomotion of Chlamydomonas reinhardtii.}, journal = {Biophysical journal}, volume = {100}, number = {11}, pages = {2716-2725}, pmid = {21641317}, issn = {1542-0086}, support = {R01 GM032843/GM/NIGMS NIH HHS/United States ; }, mesh = {Algorithms ; Bacterial Proteins/metabolism ; Biomechanical Phenomena ; Chlamydomonas reinhardtii/*cytology/genetics/metabolism ; Dyneins/metabolism ; Flagella/*metabolism ; Genotype ; Hydrodynamics ; Kinetics ; *Mechanical Phenomena ; *Movement ; Mutation ; }, abstract = {The distributed propulsive forces exerted on the flagellum of the swimming alga Chlamydomonas reinhardtii by surrounding fluid were estimated from experimental image data. Images of uniflagellate mutant Chlamydomonas cells were obtained at 350 frames/s with 125-nm spatial resolution, and the motion of the cell body and the flagellum were analyzed in the context of low-Reynolds-number fluid mechanics. Wild-type uniflagellate cells, as well as uniflagellate cells lacking inner dynein arms (ida3) or outer dynein arms (oda2) were studied. Ida3 cells exhibit stunted flagellar waveforms, whereas oda2 cells beat with lower frequency. Image registration and sorting algorithms provided high-resolution estimates of the motion of the cell body, as well as detailed kinematics of the flagellum. The swimming cell was modeled as an ellipsoid in Stokes flow, propelled by viscous forces on the flagellum. The normal and tangential components of force on the flagellum (f(N) and f(T)) were related by resistive coefficients (C(N) and C(T)) to the corresponding components of velocity (V(N) and V(T)).The values of these coefficients were estimated by satisfying equilibrium requirements for force and torque on the cell. The estimated values of the resistive coefficients are consistent among all three genotypes and similar to theoretical predictions.}, }
@article {pmid21635091, year = {2011}, author = {Nguyen van Yen, R and Farge, M and Schneider, K}, title = {Energy dissipating structures produced by walls in two-dimensional flows at vanishing viscosity.}, journal = {Physical review letters}, volume = {106}, number = {18}, pages = {184502}, doi = {10.1103/PhysRevLett.106.184502}, pmid = {21635091}, issn = {1079-7114}, abstract = {We perform numerical experiments of a dipole crashing into a wall, a generic event in two-dimensional incompressible flows with solid boundaries. The Reynolds number (Re) is varied from 985 to 7880, and no-slip boundary conditions are approximated by Navier boundary conditions with a slip length proportional to Re(-1). Energy dissipation is shown to first set up within a vorticity sheet of thickness proportional to Re(-1) in the neighborhood of the wall, and to continue as this sheet rolls up into a spiral and detaches from the wall. The energy dissipation rate integrated over these regions appears to converge towards Re-independent values, indicating the existence of energy dissipating structures that persist in the vanishing viscosity limit.}, }
@article {pmid21635041, year = {2011}, author = {Colgate, SA and Beckley, H and Si, J and Martinic, J and Westpfahl, D and Slutz, J and Westrom, C and Klein, B and Schendel, P and Scharle, C and McKinney, T and Ginanni, R and Bentley, I and Mickey, T and Ferrel, R and Li, H and Pariev, V and Finn, J}, title = {High magnetic shear gain in a liquid sodium stable Couette flow experiment: a prelude to an α-Ω dynamo.}, journal = {Physical review letters}, volume = {106}, number = {17}, pages = {175003}, doi = {10.1103/PhysRevLett.106.175003}, pmid = {21635041}, issn = {1079-7114}, abstract = {The Ω phase of the liquid sodium α-Ω dynamo experiment at New Mexico Institute of Mining and Technology in cooperation with Los Alamos National Laboratory has demonstrated a high toroidal field B(ϕ) that is ≃8×B(r), where B(r) is the radial component of an applied poloidal magnetic field. This enhanced toroidal field is produced by the rotational shear in stable Couette flow within liquid sodium at a magnetic Reynolds number Rm≃120. Small turbulence in stable Taylor-Couette flow is caused by Ekman flow at the end walls, which causes an estimated turbulence energy fraction of (δv/v)(2)∼10(-3).}, }
@article {pmid21635038, year = {2011}, author = {Aluie, H}, title = {Compressible turbulence: the cascade and its locality.}, journal = {Physical review letters}, volume = {106}, number = {17}, pages = {174502}, doi = {10.1103/PhysRevLett.106.174502}, pmid = {21635038}, issn = {1079-7114}, abstract = {We prove that interscale transfer of kinetic energy in compressible turbulence is dominated by local interactions. In particular, our results preclude direct transfer of kinetic energy from large-scales to dissipation scales, such as into shocks, in high Reynolds number turbulence as is commonly believed. Our assumptions on the scaling of structure functions are weak and enjoy compelling empirical support. Under a stronger assumption on pressure dilatation cospectrum, we show that mean kinetic and internal energy budgets statistically decouple beyond a transitional conversion range. Our analysis establishes the existence of an ensuing inertial range over which mean subgrid scale kinetic energy flux becomes constant, independent of scale. Over this inertial range, mean kinetic energy cascades locally and in a conservative fashion despite not being an invariant.}, }
@article {pmid21622046, year = {2011}, author = {Pavan, TZ and Almeida, TW and Carneiro, AA}, title = {Magnetic tracking of acoustic radiation force-induced micro-order displacement.}, journal = {IEEE transactions on ultrasonics, ferroelectrics, and frequency control}, volume = {58}, number = {5}, pages = {909-915}, doi = {10.1109/TUFFC.2011.1891}, pmid = {21622046}, issn = {1525-8955}, abstract = {The dynamic behavior of a rigid magnetic sphere induced by an acoustic radiation force was investigated. The sphere was suspended in water in a simple pendulum configuration. The drag force acting on the pendulum during its motion was considered to follow a modified Stokes law for a low Reynolds number, accounting for phenomena related to its oscillatory movement. Steady forces of long (a few seconds) and short (a few milliseconds) durations were used. The movement of the magnetic sphere was tracked using a magnetoresistive sensor. From the new equilibrium position of the sphere in response to the long-duration static radiation force, the amplitude of this force was estimated. To assess the water viscosity, the relaxation movement after the acoustic force had stopped was fitted to a harmonic-motion model. Based on the results for the acoustic force and water viscosity, a theoretical profile of the sphere's micro-order displacement as a function of time caused by short-duration acoustic radiation force agreed well with experimental results.}, }
@article {pmid21609687, year = {2011}, author = {Yuan, L and Zheng, YF}, title = {A microdevice for the mixing of a highly viscous biosample with water/membrane protein solution using microchannel and centrifugation.}, journal = {Journal of laboratory automation}, volume = {16}, number = {1}, pages = {68-81}, doi = {10.1016/j.jala.2010.04.007}, pmid = {21609687}, issn = {2211-0690}, mesh = {Biological Products/*chemistry ; Centrifugation/*methods ; Glycerides/chemistry ; Hydrodynamics ; Membrane Proteins/chemistry ; Microfluidics/*methods ; Models, Theoretical ; Solutions/chemistry ; *Viscosity ; Water/chemistry ; X-Ray Diffraction ; }, abstract = {A mechanism for controlling the mixing of highly viscous biosamples at the microliter scale is presented. Existing methods for mixing biosamples using microstirrers or shaking microwells are only effective for non-highly viscous materials. The proposed mechanism mixes monoolein, a highly viscous biosample, with water/membrane protein solution in a microdevice called microcapsule using a microchannel and centrifugation. To achieve effective mixing, the design of the microcapsule along with the microchannel is presented and so is the hydrodynamic model describing the flow of viscous materials in the microchannel. The mixing process is analyzed according to the Reynolds number of the biosamples using computer simulation, which is observed during the experiment using digital images for further analysis. Finally, the new approach is verified by X-ray diffraction experiments with water and the Rh membrane protein solution, which are used to evaluate the effectiveness of mixing. Experimental results not only validate the proposed method but also determine the flow oscillation time in the microchannel to achieve effective and efficient mixing.}, }
@article {pmid21605565, year = {2011}, author = {Cohen-Krausz, S and Cabahug, PC and Trachtenberg, S}, title = {The monomeric, tetrameric, and fibrillar organization of Fib: the dynamic building block of the bacterial linear motor of Spiroplasma melliferum BC3.}, journal = {Journal of molecular biology}, volume = {410}, number = {2}, pages = {194-213}, doi = {10.1016/j.jmb.2011.04.067}, pmid = {21605565}, issn = {1089-8638}, mesh = {Bacterial Proteins/*chemistry/ultrastructure ; Cytoskeletal Proteins/*chemistry/ultrastructure ; Models, Molecular ; Molecular Dynamics Simulation ; Molecular Motor Proteins/*chemistry/ultrastructure ; Pentosyltransferases/chemistry/ultrastructure ; Phosphorylation ; Protein Structure, Secondary ; Protein Structure, Tertiary ; Spiroplasma/*enzymology/ultrastructure ; }, abstract = {Spiroplasmas belong to the class Mollicutes, representing the minimal, free-living, and self-replicating forms of life. Spiroplasmas are helical wall-less bacteria and the only ones known to swim by means of a linear motor (rather than the near-universal rotary bacterial motor). The linear motor follows the shortest path along the cell's helical membranal tube. The motor is composed of a flat monolayered ribbon of seven parallel fibrils and is believed to function in controlling cell helicity and motility through dynamic, coordinated, differential length changes in the fibrils. The latter cause local perturbations of helical symmetry, which are essential for net directional displacement in environments with a low Reynolds number. The underlying fibrils' core building block is a circular tetramer of the 59-kDa protein Fib. The fibrils' differential length changes are believed to be driven by molecular switching of Fib, leading consequently to axial ratio and length changes in tetrameric rings. Using cryo electron microscopy, diffractometry, single-particle analysis of isolated ribbons, and sequence analyses of Fib, we determined the overall molecular organization of the Fib monomer, tetramer, fibril, and linear motor of Spiroplasma melliferum BC3 that underlies cell geometry and motility. Fib appears to be a bidomained molecule, of which the N-terminal half is apparently a globular phosphorylase. By a combination of reversible rotation and diagonal shift of Fib monomers, the tetramer adopts either a cross-like nonhanded conformation or a ring-like handed conformation. The sense of Fib rotation may determine the handedness of the linear motor and, eventually, of the cell. A further change in the axial ratio of the ring-like tetramers controls fibril lengths and the consequent helical geometry. Analysis of tetramer quadrants from adjacent fibrils clearly demonstrates local differential fibril lengths.}, }
@article {pmid21599309, year = {2011}, author = {Shin, SJ and Sung, HJ}, title = {Inertial migration of an elastic capsule in a Poiseuille flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {4 Pt 2}, pages = {046321}, doi = {10.1103/PhysRevE.83.046321}, pmid = {21599309}, issn = {1550-2376}, abstract = {The inertial migration of a two-dimensional elastic capsule in a Poiseuille flow was studied over the Reynolds number range 1 ≤ Re ≤ 100. The lateral migration velocity, slip velocity, and the deformation and inclination angle of the capsule were investigated by varying the lateral position, Reynolds number, capsule-to-channel size ratio (λ), membrane stretching coefficient (ϕ), and membrane bending coefficient (γ). During the initial transient motion, the lateral migration velocity increased with increasing Re and λ, but decreased with increases in ϕ, γ, and the lateral distance from the wall. On the other hand, the deformation of the capsule increased and the inclination angle became smaller as Re, ϕ, γ, and the distance from the wall decreased. The initial behavior of the capsule was influenced by variation in the initial lateral position (y(0)), but the equilibrium position of the capsule was not affected by such variation. The balance between the wall effect and the shear gradient effect determined the equilibrium position. As Re increased, the equilibrium position initially shifted closer to the wall and then moved toward the channel center. A peak in the equilibrium position was observed near Re = 30 for λ = 0.1, and the peak shifted to higher Re as λ increased. Depending on the lateral migration velocity, the equilibrium position moved toward the centerline for larger λ, but moved toward the wall for larger ϕ and γ.}, }
@article {pmid21599301, year = {2011}, author = {Chiang, TP and Sau, A and Hwang, RR}, title = {Asymmetry and bifurcations in three-dimensional sudden-contraction channel flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {4 Pt 2}, pages = {046313}, doi = {10.1103/PhysRevE.83.046313}, pmid = {21599301}, issn = {1550-2376}, abstract = {This study reports the presence of two different stable modes of bifurcation in the near field of a three-dimensional sudden contraction. To be precise, flow downstream of a symmetric sudden contraction undergoes a transition from a symmetric state to an asymmetric state through a symmetry-breaking pitchfork bifurcation following an increase in the channel aspect ratio or the Reynolds number. In addition, the oncoming (upstream) symmetry-plane flow exhibits spanwise bifurcations along the topological core lines of each of the salient roof and floor eddies. Small aspect-ratio (contraction) channels are noted to facilitate interesting splitting of the salient roof and floor eddies into multicore forms with accompanying spanwise flow bifurcations along the respective vortical core lines. Herein extensive three-dimensional simulations performed with various aspect and contraction ratios and Reynolds numbers clearly suggest that flow transition in the sudden-contraction channels should indeed occur primarily through these two generically distinct modes of bifurcation.}, }
@article {pmid21599299, year = {2011}, author = {Dias, EO and Miranda, JA}, title = {Inertial effects on rotating Hele-Shaw flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {4 Pt 2}, pages = {046311}, doi = {10.1103/PhysRevE.83.046311}, pmid = {21599299}, issn = {1550-2376}, abstract = {We examine the finite surface tension radial viscous fingering problem in a rotating Hele-Shaw cell, and focus on the action of inertial effects on the stability and morphology of the emerging patterns. To study such a flow we use an alternative version of the usual Darcy's law derived by gap-averaging the Navier-Stokes equation, but retaining its inertial terms. The importance of inertial forces is pertinently characterized by a rotational Reynolds number. Linear and weakly nonlinear stages of the dynamics are described analytically through a mode coupling approach. The linear stability results indicate that inertia has a stabilizing role. However, the characteristic number of fingers and the width of the band of linearly unstable modes are not altered by inertia. In the early nonlinear regime we find that inertia acts to favor the development of fingers with narrower tips than those obtained in its absence. We have also verified that finger competition events are affected by inertial effects which tend to restrain finger length variability among inward-moving fingers.}, }
@article {pmid21599289, year = {2011}, author = {Ghanbari, A and Bahrami, M and Nobari, MR}, title = {Methodology for artificial microswimming using magnetic actuation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {4 Pt 2}, pages = {046301}, doi = {10.1103/PhysRevE.83.046301}, pmid = {21599289}, issn = {1550-2376}, abstract = {We propose a methodology for swimming at low-Reynolds-number flows based on ciliary motion of a microswimmer using magnetic actuation of artificial cilia. By solving the coupled magnetic-elastic-hydrodynamic problem, we demonstrate nonreciprocal effective and recovery strokes for cilia that nicely mimic natural cilia beating. Cilia drag forces, microswimmer net displacement, velocity, and efficiency are calculated, and we show the model can swim using a prespecified magnetic actuation. The proposed methodology can be used for devising biomedical microdevices that swim in viscous flows inside the human body.}, }
@article {pmid21598915, year = {2011}, author = {Gibbs, JG and Kothari, S and Saintillan, D and Zhao, YP}, title = {Geometrically designing the kinematic behavior of catalytic nanomotors.}, journal = {Nano letters}, volume = {11}, number = {6}, pages = {2543-2550}, doi = {10.1021/nl201273n}, pmid = {21598915}, issn = {1530-6992}, mesh = {Catalysis ; Hydrogen Peroxide/chemistry ; Nanostructures/*chemistry ; Particle Size ; Platinum/chemistry ; Silicon Dioxide/chemistry ; Surface Properties ; Titanium/chemistry ; }, abstract = {Catalytic nanomotors with silica microbead heads and TiO(2) arms are systematically designed by dynamic shadowing growth. The swimming trajectories are fine tuned by altering the arm length and orientation exploiting geometry-dependent hydrodynamic interactions at low Reynolds number. The curvature, angular frequency, and radius of curvature of the trajectories change as a function of arm length. Simulations based on the method of regularized Stokeslets are also described and correctly capture the trends observed in the experiments.}, }
@article {pmid21580804, year = {2011}, author = {Qamar, A and Seda, R and Bull, JL}, title = {Pulsatile flow past an oscillating cylinder.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {23}, number = {4}, pages = {41903}, pmid = {21580804}, issn = {1070-6631}, support = {R01 HL069420/HL/NHLBI NIH HHS/United States ; R01 HL089043/HL/NHLBI NIH HHS/United States ; }, abstract = {A fundamental study to characterize the flow around an oscillating cylinder in a pulsatile flow environment is investigated. This work is motivated by a new proposed design of the total artificial lung (TAL), which is envisioned to provide better gas exchange. The Navier-Stokes computations in a moving frame of reference were performed to compute the dynamic flow field surrounding the cylinder. Cylinder oscillations and pulsatile free-stream velocity were represented by two sinusoidal waves with amplitudes A and B and frequencies ω(c) and ω, respectively. The Keulegan-Carpenter number (K(c)=U(o)∕Dω(c)) was used to describe the frequency of the oscillating cylinder while the pulsatile free-stream velocity was fixed by imposing ω∕K(c)=1 for all cases investigated. The parameters of interest and their values were amplitude (0.5D<A<D), the Keulegan-Carpenter number (0.33<K(c)<1), and the Reynolds number (5<Re<20) corresponding to operating conditions of the TAL. It was observed that an increase in amplitude and a decrease in K(c) are associated with an increase in vorticity (up to 246%) for every Re suggesting that mixing could be enhanced by the proposed TAL design. The drag coefficient was found to decrease for higher amplitudes and lower K(c) for all cases investigated. In some cases the drag coefficient values were found to be lower than the stationary cylinder values (A=0.5, K(c)=0.3, and Re=10 and 20). A lock-in phenomenon (cylinder oscillating frequency matched the vortex shedding frequency) was found when K(c)=1 for all cases. This lock-in condition was attributed to be the cause of the rise in drag observed in that operating regime. For optimal performance of the modified TAL design it is recommended to operate the device at higher fiber oscillation amplitudes and lower K(c) (avoiding the lock-in regime).}, }
@article {pmid21580803, year = {2011}, author = {Kumar, H and Tawhai, MH and Hoffman, EA and Lin, CL}, title = {Steady streaming: A key mixing mechanism in low-Reynolds-number acinar flows.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {23}, number = {4}, pages = {41902}, pmid = {21580803}, issn = {1070-6631}, support = {R01 EB005823/EB/NIBIB NIH HHS/United States ; R01 HL064368/HL/NHLBI NIH HHS/United States ; R01 HL094315/HL/NHLBI NIH HHS/United States ; S10 RR022421/RR/NCRR NIH HHS/United States ; }, abstract = {Study of mixing is important in understanding transport of submicron sized particles in the acinar region of the lung. In this article, we investigate transport in view of advective mixing utilizing Lagrangian particle tracking techniques: tracer advection, stretch rate and dispersion analysis. The phenomenon of steady streaming in an oscillatory flow is found to hold the key to the origin of kinematic mixing in the alveolus, the alveolar mouth and the alveolated duct. This mechanism provides the common route to folding of material lines and surfaces in any region of the acinar flow, and has no bearing on whether the geometry is expanding or if flow separates within the cavity or not. All analyses consistently indicate a significant decrease in mixing with decreasing Reynolds number (Re). For a given Re, dispersion is found to increase with degree of alveolation, indicating that geometry effects are important. These effects of Re and geometry can also be explained by the streaming mechanism. Based on flow conditions and resultant convective mixing measures, we conclude that significant convective mixing in the duct and within an alveolus could originate only in the first few generations of the acinar tree as a result of nonzero inertia, flow asymmetry, and large Keulegan-Carpenter (K(C)) number.}, }
@article {pmid21576168, year = {2011}, author = {Kataoka, Y and Inamuro, T}, title = {Numerical simulations of the behaviour of a drop in a square pipe flow using the two-phase lattice Boltzmann method.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {369}, number = {1945}, pages = {2528-2536}, doi = {10.1098/rsta.2011.0041}, pmid = {21576168}, issn = {1364-503X}, mesh = {*Models, Theoretical ; }, abstract = {The lattice Boltzmann method for multi-component immiscible fluids is applied to simulations of the behaviour of a drop in a square pipe flow for various Reynolds numbers of 10<Re<500, Weber numbers of 0<We<250 and viscosity ratios of η=1/5, 1, 2 and 5. It is found that, for low Weber numbers, the drop moves straight along a stable position on the diagonal line of the pipe section, and it moves along the centre axis of the pipe for larger Weber numbers. We obtain the boundary of the two different behaviours of the drop in terms of Reynolds number, Weber number and viscosity ratio.}, }
@article {pmid21576157, year = {2011}, author = {Inoue, Y and Gotoh, T}, title = {Effects of finite mass ratio and inelastic reflection on the interaction between graphene and laminar flow.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {369}, number = {1945}, pages = {2431-2438}, doi = {10.1098/rsta.2011.0094}, pmid = {21576157}, issn = {1364-503X}, abstract = {A modified boundary condition for the distribution function in the Lattice Boltzmann method at the interface between solid and fluid that takes into account a finite mass ratio between two phases and an inelastic reflection is proposed. The new boundary condition is built into the immersed boundary method to compute the interaction between graphene and laminar flow. Numerical simulations are carried out at a Reynolds number of 40, and drag and lift acting on the graphene and its deformation are examined by changing the mass ratio and the coefficient of restitution. It is found that the amplitude of the oscillating motion of the graphene is enhanced when compared with the case of infinite mass ratio with perfect collision.}, }
@article {pmid21568386, year = {2011}, author = {Moreau, DJ and Brooks, LA and Doolan, CJ}, title = {Broadband trailing edge noise from a sharp-edged strut.}, journal = {The Journal of the Acoustical Society of America}, volume = {129}, number = {5}, pages = {2820-2829}, doi = {10.1121/1.3569698}, pmid = {21568386}, issn = {1520-8524}, mesh = {Aircraft ; Equipment Design ; Models, Theoretical ; *Noise ; Noise, Transportation ; Sound Spectrography ; Wind ; }, abstract = {This paper presents experimental data concerning the flow and noise generated by a sharp-edged flat plate at low-to-moderate Reynolds number (Reynolds number based on chord of 2.0 × 10(5) to 5.0 × 10(5)). The data are used to evaluate a variety of semi-empirical trailing edge noise prediction methods. All were found to under-predict noise at lower frequencies. Examination of the velocity spectra in the near wake reveals that there are energetic velocity fluctuations at low frequency about the trailing edge. A semi-empirical model of the surface pressure spectrum is derived for predicting the trailing edge noise at low-to-moderate Reynolds number.}, }
@article {pmid21560814, year = {2011}, author = {Adams, JC and Jiamsripong, P and Belohlavek, M and McMahon, EM and Marupakula, V and Heys, J and Chaliki, HP}, title = {Potential role of Reynolds number in resolving Doppler- and catheter-based transvalvular gradient discrepancies in aortic stenosis.}, journal = {The Journal of heart valve disease}, volume = {20}, number = {2}, pages = {159-164}, pmid = {21560814}, issn = {0966-8519}, mesh = {Analysis of Variance ; Aortic Valve/*diagnostic imaging/*physiopathology/surgery ; Aortic Valve Stenosis/*diagnosis/diagnostic imaging/physiopathology ; *Bioprosthesis ; *Cardiac Catheterization ; *Echocardiography, Doppler ; Friction ; *Heart Valve Prosthesis ; Humans ; Linear Models ; Models, Cardiovascular ; Predictive Value of Tests ; Pressure ; *Pulsatile Flow ; Suture Techniques ; Viscosity ; }, abstract = {Discrepancies in mean transvalvular gradient have been observed between Doppler echocardiography and catheter-based techniques in the assessment of aortic stenosis (AS). The Reynolds number (RE) has been shown to influence Doppler-derived gradients, and may be useful in resolving Doppler- and catheter-based gradient discrepancies in AS. The study aim was to assess the influence of the RE on such discrepancies.<br><br>METHODS: A pulsatile in-vitro heart model using a bioprosthetic aortic valve with leaflets sutured together was used to simulate AS. Simultaneous gradients were measured using Doppler echocardiography and high-fidelity catheters while the RE was varied, by testing solutions of different density and viscosity across a range of cardiac outputs.<br><br>RESULTS: The echocardiographic and catheter-derived mean gradient (MG) values were correlated (r = 0.89; p < 0.0001); however, significant differences in the MG were observed across hemodynamic states. A direct linear relationship was identified between RE and the absolute difference in MG measured using the two techniques (r = 0.94, p < 0.0001). Relative to catheter-based measurements, the MG was underestimated by Doppler (range: 13-16 mmHg) at low RE (median 6,999) and overestimated (7-33 mmHg) at high RE (median 34,268). However, agreement between catheter- and Doppler-derived gradients was within 5 mmHg at intermediate RE (median 17,284) (p < 0.0001).<br><br>CONCLUSION: The underestimation of Doppler-derived MGs at low RE relative to catheter-based measurements may be due to an exclusion of viscous friction from the simplified Bernoulli equation, while the overestimation of Doppler-derived MGs at high RE may be due to a pressure recovery effect. However, within an intermediate range of RE, where the effects of viscous and inertial forces are balanced, the agreement between catheter- and Doppler-derived gradients was excellent.}, }
@article {pmid21538925, year = {2011}, author = {Holmes, WM and Cotton, R and Xuan, VB and Rygg, AD and Craven, BA and Abel, RL and Slack, R and Cox, JP}, title = {Three-dimensional structure of the nasal passageway of a hagfish and its implications for olfaction.}, journal = {Anatomical record (Hoboken, N.J. : 2007)}, volume = {294}, number = {6}, pages = {1045-1056}, doi = {10.1002/ar.21382}, pmid = {21538925}, issn = {1932-8494}, mesh = {Animals ; *Hagfishes ; Imaging, Three-Dimensional/*methods ; Magnetic Resonance Imaging/methods ; *Models, Anatomic ; Nasal Cavity/*anatomy &amp; histology/*physiology ; Odorants ; Olfactory Mucosa/anatomy &amp; histology/physiology ; Smell/*physiology ; }, abstract = {From high-resolution (65 μm) data acquired by magnetic resonance imaging, we have reconstructed the nasal passageway of a single adult hagfish specimen (probably Eptatretus stoutii). We have used this reconstruction to investigate how the anatomy and morphometry of the nasal passageway influence the olfactory ability of the hagfish. We found that the long, broad section of the passageway preceding the nasal chamber will delay the response to an odor by 1-2 s. Diffusion of odorant to the olfactory epithelium, on which the olfactory sensitivity of an animal depends, will be favored by the relatively large surface area of the olfactory epithelium (∼140 mm(2)) and a modest expansion in the nasal chamber. Oscillating flow (0.3-0.4 Hz) within the narrow (65-130 μm) sensory channels of the nasal chamber is laminar (Reynolds number ∼ 5) and quasi-steady (Womersley number generally less than one). Distribution of flow over the olfactory epithelium may be aided by: (a) a narrowing before the nasal chamber; (b) partial blockage of the nasal passageway by a protrusion on the central olfactory lamella; and (c) the inward inclination of the olfactory lamellae.}, }
@article {pmid21523785, year = {2011}, author = {Lengsfeld, CS and Munson, L and Lentz, YK and Anchordoquy, TJ}, title = {DNA hydrodynamic degradation controlled by Kolomogorov length scales in pipe flow.}, journal = {Journal of pharmaceutical sciences}, volume = {100}, number = {8}, pages = {3088-3095}, doi = {10.1002/jps.22582}, pmid = {21523785}, issn = {1520-6017}, mesh = {Computer Simulation ; DNA, Bacterial/chemistry/genetics ; DNA, Superhelical/*chemistry/genetics ; Drug Stability ; Escherichia coli/genetics ; Hydrodynamics ; *Models, Chemical ; Plasmids/chemistry/genetics ; Stress, Mechanical ; }, abstract = {Strict US Food and Drug Administration regulations on contamination levels for DNA therapeutics acceptable for human use complicate the manufacturing process. This study aims to improve therapeutic production through the investigation of the molecular effects of hydrodynamic forces encountered during processing. Results suggest that the strain rate and residence time were not solely responsible for degradation within the system. Instead, turbulent flows at the entrance or developing flow regions dominate especially when the Kolmogorov length scale approaches the stretched molecular length scale. We specifically suggest this for linear genomic DNA and supercoiled plasmid DNA when the ratio of the molecular length to the Kolmogorov length scale must remain smaller than unity to minimize loss of the desired structure. These findings suggest that bioprocessing systems should design expansions and contractions to minimize recirculation and turbulent mixing zones, although, not always possible, careful attention should be paid to pipe surface roughness to ensure that turbulent eddies are not generated in low Reynolds number flows.}, }
@article {pmid21517588, year = {2011}, author = {Philip, J and Manneville, P}, title = {From temporal to spatiotemporal dynamics in transitional plane Couette flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {3 Pt 2}, pages = {036308}, doi = {10.1103/PhysRevE.83.036308}, pmid = {21517588}, issn = {1550-2376}, abstract = {Laboratory experiments point out the existence of patterns made of alternately laminar and turbulent oblique bands in plane Couette flow (PCF) on its way to or from turbulence as the Reynolds number R is varied. Many previous theoretical and numerical works on the problem have considered small-aspect-ratio systems subjected to periodic boundary conditions, while experiments correspond to the opposite limit of large aspect ratio. Here, by means of fully resolved direct numerical simulations of the Navier-Stokes equations at decreasing R, we scrutinize the transition from temporal to spatiotemporal behavior in systems of intermediate sizes. We show that there exists a streamwise crossover size of order L{x}~70-80 h (where 2 h is the gap between the plates driving the flow) beyond which the transition to or from turbulence in PCF is undoubtedly a spatiotemporal process, with typical scenario turbulent flow→riddled regime→oblique pattern→ laminar flow, whereas below that size it is more a temporal process describable in terms of finite-dimensional dynamical systems with the scenario chaotic flow→laminar flow (via chaotic transients). In the crossover region, the oblique pattern stage is skipped, which leads us to suggest that an appropriate rendering of the patterns observed in experiments needs a faithful account of streamwise correlations at scales at least of the order of that crossover size.}, }
@article {pmid21517581, year = {2011}, author = {Alexakis, A}, title = {Nonlinear dynamos at infinite magnetic Prandtl number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {3 Pt 2}, pages = {036301}, doi = {10.1103/PhysRevE.83.036301}, pmid = {21517581}, issn = {1550-2376}, abstract = {The dynamo instability is investigated in the limit of infinite magnetic Prandtl number. In this limit the fluid is assumed to be very viscous so that the inertial terms can be neglected and the flow is enslaved to the forcing. The forcing consist of an external forcing function that drives the dynamo flow and the resulting Lorentz force caused by the back reaction of the magnetic field. The flows under investigation are the Archontis flow and the ABC flow forced at two different scales. The investigation covers roughly 3 orders of magnitude of the magnetic Reynolds number above onset. All flows show a weak increase of the averaged magnetic energy as the magnetic Reynolds number is increased. Most of the magnetic energy is concentrated in flat elongated structures that produce a Lorentz force with small solenoidal projection so that the resulting magnetic field configuration is almost force free. Although the examined system has zero kinetic Reynolds number at sufficiently large magnetic Reynolds number the structures are unstable to small scale fluctuations that result in a chaotic temporal behavior.}, }
@article {pmid21517551, year = {2011}, author = {Garcia, M and Berti, S and Peyla, P and Rafaï, S}, title = {Random walk of a swimmer in a low-Reynolds-number medium.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {3 Pt 2}, pages = {035301}, doi = {10.1103/PhysRevE.83.035301}, pmid = {21517551}, issn = {1550-2376}, mesh = {*Cell Movement ; Chlamydomonas reinhardtii/*cytology ; *Hydrodynamics ; Probability ; Stochastic Processes ; Time Factors ; Viscosity ; }, abstract = {Swimming at a micrometer scale demands particular strategies. When inertia is negligible compared to viscous forces, hydrodynamics equations are reversible in time. To achieve propulsion, microswimmers must therefore deform in a way that is not invariant under time reversal. Here, we investigate dispersal properties of the microalga Chlamydomonas reinhardtii by means of microscopy and cell tracking. We show that tracked trajectories are well modeled by a correlated random walk. This process is based on short time correlations in the direction of movement called persistence. At longer times, correlation is lost and a standard random walk characterizes the trajectories. Moreover, high-speed imaging enables us to show how the back-and-forth motion of flagella at very short times affects the statistical description of the dynamics. Finally, we show how drag forces modify the characteristics of this particular random walk.}, }
@article {pmid21511259, year = {2011}, author = {Wu, D and Ganatos, P and Spray, DC and Weinbaum, S}, title = {On the electrophysiological response of bone cells using a Stokesian fluid stimulus probe for delivery of quantifiable localized picoNewton level forces.}, journal = {Journal of biomechanics}, volume = {44}, number = {9}, pages = {1702-1708}, pmid = {21511259}, issn = {1873-2380}, support = {R01 AR057139-02/AR/NIAMS NIH HHS/United States ; AR057139/AR/NIAMS NIH HHS/United States ; R01 AR057139-01A2/AR/NIAMS NIH HHS/United States ; R01 AR057139/AR/NIAMS NIH HHS/United States ; R01 AR041210/AR/NIAMS NIH HHS/United States ; }, mesh = {Actins/chemistry ; Bone and Bones/physiology ; Electrochemistry/methods ; Electrophysiology/*methods ; Equipment Design ; Humans ; Hydrodynamics ; Materials Testing ; Neurons/*physiology ; Osteocytes/cytology ; Patch-Clamp Techniques ; Pressure ; Signal Processing, Computer-Assisted ; Signal Transduction ; Stress, Mechanical ; }, abstract = {A Stokesian fluid stimulus probe (SFSP), capable of delivering quantifiable pN level hydrodynamic forces, is developed to distinguish the electrophysiological response of the cell process and cell body of osteocyte-like MLO-Y4 cells without touching the cell or its substrate. The hydrodynamic disturbance is a short lived (100 ms), constant strength pressure pulse that propagates nearly instantaneously through the medium creating a nearly spherical expanding fluid bolus surrounding a 0.8 μm micropipette tip. Laboratory model experiments show that the growth of the bolus and the pressure field can be closely modeled by quasi-steady Stokes flow through a circular orifice provided the tip Reynolds number, Re(t)<0.03. By measuring the deflection of the dendritic processes between discrete attachment sites, and applying a detailed ultrastructural model for the central actin filament bundle within the process, one is able to calculate the forces produced by the probe using elastic beam theory. One finds that forces between 1 and 2.3 pN are sufficient to initiate electrical signaling when applied to the cell process, but not the much softer cell body. Even more significantly, cellular excitation by the process only occurs when the probe is directed at discrete focal attachment sites along the cell process. This suggests that electrical signaling is initiated at discrete focal attachments along the cell process and that these sites are likely integrin-mediated complexes associated with stretch-activated ion channels though their molecular structure is unknown.}, }
@article {pmid21508011, year = {2011}, author = {Kazakidi, A and Plata, AM and Sherwin, SJ and Weinberg, PD}, title = {Effect of reverse flow on the pattern of wall shear stress near arterial branches.}, journal = {Journal of the Royal Society, Interface}, volume = {8}, number = {64}, pages = {1594-1603}, pmid = {21508011}, issn = {1742-5662}, mesh = {Arteries/*physiopathology ; Atherosclerosis/*physiopathology ; Blood Flow Velocity/*physiology ; Computational Biology/methods ; Humans ; *Models, Biological ; Pulsatile Flow/*physiology ; *Shear Strength ; *Stress, Mechanical ; }, abstract = {Atherosclerotic lesions have a patchy distribution within arteries that suggests a controlling influence of haemodynamic stresses on their development. The distribution near aortic branches varies with age and species, perhaps reflecting differences in these stresses. Our previous work, which assumed steady flow, revealed a dependence of wall shear stress (WSS) patterns on Reynolds number and side-branch flow rate. Here, we examine effects of pulsatile flow. Flow and WSS patterns were computed by applying high-order unstructured spectral/hp element methods to the Newtonian incompressible Navier-Stokes equations in a geometrically simplified model of an aorto-intercostal junction. The effect of pulsatile but non-reversing side-branch flow was small; the aortic WSS pattern resembled that obtained under steady flow conditions, with high WSS upstream and downstream of the branch. When flow in the side branch or in the aortic near-wall region reversed during part of the cycle, significantly different instantaneous patterns were generated, with low WSS appearing upstream and downstream. Time-averaged WSS was similar to the steady flow case, reflecting the short duration of these events, but patterns of the oscillatory shear index for reversing aortic near-wall flow were profoundly altered. Effects of reverse flow may help explain the different distributions of lesions.}, }
@article {pmid21505818, year = {2011}, author = {Feng, Z and Fukuda, S and Yokoyama, M and Kitajima, T and Nakamura, T and Umezu, M}, title = {Flux characteristics of cell culture medium in rectangular microchannels.}, journal = {Journal of artificial organs : the official journal of the Japanese Society for Artificial Organs}, volume = {14}, number = {3}, pages = {238-244}, pmid = {21505818}, issn = {1619-0904}, mesh = {Albumins ; Animals ; Cell Culture Techniques ; *Culture Media ; Fibroblasts/cytology ; Friction ; Microfluidics/*methods ; Rats ; }, abstract = {Rectangular microchannels 50 μm high and 30, 40, 50, 60, or 70 μm wide were fabricated by adjusting the width of a gap cut in a polyethylene sheet 50 μm thick and sandwiching the sheet between an acrylic plate and a glass plate. Flux in the microchannels was measured under three different inner surface conditions: uncoated, albumin-coated, and confluent growth of rat fibroblasts on the bottom of the microchannels. The normalized flux in microchannels with cultured fibroblasts or albumin coating was significantly larger than that in the uncoated channels. The experimental data for all microchannels deviated from that predicted by classical hydrodynamic theory. At small aspect ratio the flux in the microchannels was larger than that predicted theoretically, whereas it became smaller at large aspect ratio. The aspect ratio rather than Reynolds number is the correct property for predicting the variation of the normalized friction factor. We postulate that two counteracting effects, rotation of large molecules and slip velocity at the corners of the microchannels, are responsible for the deviation. From these results we conclude that albumin coating should be carried out in the same way as when fabricating our integrating cell-culture system. The outcomes of this study are not only important for the design of our culture system, but also quite informative for general microfluidics.}, }
@article {pmid21497817, year = {2011}, author = {Defraeye, T and Blocken, B and Koninckx, E and Hespel, P and Carmeliet, J}, title = {Computational fluid dynamics analysis of drag and convective heat transfer of individual body segments for different cyclist positions.}, journal = {Journal of biomechanics}, volume = {44}, number = {9}, pages = {1695-1701}, doi = {10.1016/j.jbiomech.2011.03.035}, pmid = {21497817}, issn = {1873-2380}, mesh = {Bicycling/*physiology ; Body Temperature Regulation/*physiology ; Computer Simulation ; Hot Temperature ; Humans ; Hydrodynamics ; Models, Theoretical ; Posture ; Software ; Wind ; }, abstract = {This study aims at investigating drag and convective heat transfer for cyclists at a high spatial resolution. Such an increased spatial resolution, when combined with flow-field data, can increase insight in drag reduction mechanisms and in the thermo-physiological response of cyclists related to heat stress and hygrothermal performance of clothing. Computational fluid dynamics (steady Reynolds-averaged Navier-Stokes) is used to evaluate the drag and convective heat transfer of 19 body segments of a cyclist for three different cyclist positions. The influence of wind speed on the drag is analysed, indicating a pronounced Reynolds number dependency on the drag, where more streamlined positions show a dependency up to higher Reynolds numbers. The drag and convective heat transfer coefficient (CHTC) of the body segments and the entire cyclist are compared for all positions at racing speeds, showing high drag values for the head, legs and arms and high CHTCs for the legs, arms, hands and feet. The drag areas of individual body segments differ markedly for different cyclist positions whereas the convective heat losses of the body segments are found to be less sensitive to the position. CHTC-wind speed correlations are derived, in which the power-law exponent does not differ significantly for the individual body segments for all positions, where an average value of 0.84 is found. Similar CFD studies can be performed to assess drag and CHTCs at a higher spatial resolution for applications in other sport disciplines, bicycle equipment design or to assess convective moisture transfer.}, }
@article {pmid21491262, year = {2011}, author = {Nadeem, S and Akbar, NS and Hayat, T and Hendi, AA}, title = {Numerical and series solutions of the peristaltic motion of an Oldroyd 8-constant fluid in an endoscope.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {14}, number = {11}, pages = {987-993}, doi = {10.1080/10255842.2010.503960}, pmid = {21491262}, issn = {1476-8259}, mesh = {*Endoscopes ; *Models, Theoretical ; *Peristalsis ; }, abstract = {In the present article, we have presented the peristaltic flow of an Oldroyd 8-constant fluid in an endoscope. The governing equations for the flow problem are simplified using long wavelength and low Reynold's number approximations. The solutions of the simplified problem are calculated using (i) Homotopy analysis method and (ii) Shooting method. The comparison of both the solutions shows a very good agreement between the results. The graphical results for the velocity field and stresses are presented to show the physical behaviour of all the parameters appearing in the problem.}, }
@article {pmid21476669, year = {2011}, author = {Zheng, X and Mittal, R and Bielamowicz, S}, title = {A computational study of asymmetric glottal jet deflection during phonation.}, journal = {The Journal of the Acoustical Society of America}, volume = {129}, number = {4}, pages = {2133-2143}, pmid = {21476669}, issn = {1520-8524}, support = {R0IDC007125//PHS HHS/United States ; }, mesh = {*Computer Simulation ; Glottis/*physiology ; Humans ; Larynx/physiology ; *Models, Biological ; Phonation/*physiology ; }, abstract = {Two-dimensional numerical simulations are used to explore the mechanism for asymmetric deflection of the glottal jet during phonation. The model employs the full Navier-Stokes equations for the flow but a simple laryngeal geometry and vocal-fold motion. The study focuses on the effect of Reynolds number and glottal opening angle with a particular emphasis on examining the importance of the so-called "Coanda effect" in jet deflection. The study indicates that the glottal opening angle has no substantial effect on glottal jet deflection. Deflection in the glottal jet is always preceded by large-scale asymmetry in the downstream portion of the glottal jet. A detailed analysis of the velocity and vorticity fields shows that these downstream asymmetric vortex structures induce a flow at the glottal exit which is the primary driver for glottal jet deflection.}, }
@article {pmid21476631, year = {2011}, author = {Xu, Y and Zheng, ZC and Wilson, DK}, title = {A computational study of the effect of windscreen shape and flow resistivity on turbulent wind noise reduction.}, journal = {The Journal of the Acoustical Society of America}, volume = {129}, number = {4}, pages = {1740-1747}, doi = {10.1121/1.3552886}, pmid = {21476631}, issn = {1520-8524}, mesh = {Acoustics/*instrumentation ; Equipment Design ; *Models, Theoretical ; Noise/*prevention &amp; control ; Signal Detection, Psychological ; *Wind ; }, abstract = {In this paper, numerical simulations are used to study the turbulent wind noise reduction effect of microphone windscreens with varying shapes and flow resistivities. Typical windscreen shapes consisting of circular, elliptical, and rectangular cylinders are investigated. A turbulent environment is generated by placing a solid circular cylinder upstream of the microphone. An immersed-boundary method with a fifth-order weighted essentially non-oscillatory scheme is implemented to enhance the simulation accuracy for high-Reynolds number flow around the solid cylinder as well as at the interface between the open air and the porous material comprising the windscreen. The Navier-Stokes equations for incompressible flow are solved in the open air. For the flow inside the porous material, a modified form of the Zwikker-Kosten equation is solved. The results show that, on average, the circular and horizontal ellipse windscreens have similar overall wind noise reduction performance, while the horizontal ellipse windscreen with medium flow resistivity provides the most effective wind noise reduction among all the considered cases. The vertical ellipse windscreen with high flow resistivity, in particular, increases the wind noise because of increased self-generation of turbulence.}, }
@article {pmid21476623, year = {2011}, author = {Moreau, DJ and Brooks, LA and Doolan, CJ}, title = {On the aeroacoustic tonal noise generation mechanism of a sharp-edged plate.}, journal = {The Journal of the Acoustical Society of America}, volume = {129}, number = {4}, pages = {EL154-60}, doi = {10.1121/1.3565472}, pmid = {21476623}, issn = {1520-8524}, mesh = {*Acoustics ; Aircraft/*instrumentation ; Humans ; *Models, Theoretical ; *Noise, Transportation ; *Wind ; }, abstract = {This letter presents an experimental study on the tonal noise generated by a sharp-edged flat plate at low-to-moderate Reynolds number. Flow and far-field noise data reveal that, in this particular case, the tonal noise appears to be governed by vortex shedding processes. Also related to the existence of the tonal noise is a region of separated flow slightly upstream of the trailing edge. Hydrodynamic fluctuations at selected vortex shedding frequencies are strongly amplified by the inflectional mean velocity profile in the separated shear layer. The amplified hydrodynamic fluctuations are diffracted by the trailing edge, producing strong tonal noise.}, }
@article {pmid21455535, year = {2011}, author = {Baby, TT and Ramaprabhu, S}, title = {Experimental investigation of the thermal transport properties of a carbon nanohybrid dispersed nanofluid.}, journal = {Nanoscale}, volume = {3}, number = {5}, pages = {2208-2214}, doi = {10.1039/c0nr01024c}, pmid = {21455535}, issn = {2040-3372}, mesh = {Colloids/*chemistry ; Energy Transfer ; Materials Testing ; Microfluidics/*methods ; Nanotubes, Carbon/*chemistry/*ultrastructure ; Particle Size ; Solutions/*chemistry ; Thermal Conductivity ; }, abstract = {A hybrid nanostructure consisting of 1D carbon nanotubes and 2D graphene was successfully synthesized. Nanofluids were made by dispersing the hybrid nanostructure in deionized (DI) water and ethylene glycol (EG) separately, without any surfactant. Later the thermal conductivity and heat transfer coefficient of the nanofluids were experimentally measured. Meanwhile, multiwalled carbon nanotubes (MWNT) were prepared by catalytic chemical vapor deposition (CCVD), and hydrogen exfoliated graphene (HEG) was synthesized by exfoliating graphite oxide in a hydrogen atmosphere. The hybrid nanostructure (f-MWNT+f-HEG) of functionalized MWNT (f-MWNT) and functionalized HEG (f-HEG) was prepared by a post mixing technique, and the sample was characterized by powder X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy and transmission electron microscopy. Thermal conductivity of the nanofluids was measured for different volume fractions of f-MWNT+f-HEG at different temperatures. The hybrid nanostructure dispersed in the DI water based nanofluid shows a thermal conductivity enhancement of 20% for a volume fraction of 0.05%. Similarly, for a Reynolds number of 15,500, the enhancement of the heat transfer coefficient is about 289% for a 0.01% volume fraction of f-MWNT+f-HEG.}, }
@article {pmid21448976, year = {2011}, author = {Lee, GS and Filipovic, N and Lin, M and Gibney, BC and Simpson, DC and Konerding, MA and Tsuda, A and Mentzer, SJ}, title = {Intravascular pillars and pruning in the extraembryonic vessels of chick embryos.}, journal = {Developmental dynamics : an official publication of the American Association of Anatomists}, volume = {240}, number = {6}, pages = {1335-1343}, pmid = {21448976}, issn = {1097-0177}, support = {R01 HL075426/HL/NHLBI NIH HHS/United States ; HL75426/HL/NHLBI NIH HHS/United States ; HL94567/HL/NHLBI NIH HHS/United States ; R01 HL094567-03/HL/NHLBI NIH HHS/United States ; R01 HL094567/HL/NHLBI NIH HHS/United States ; R01 HL094567-02/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Blood Vessels/*embryology/metabolism/physiology/ultrastructure ; Chick Embryo/*blood supply/metabolism ; Computer Simulation ; Endothelial Cells/cytology/physiology ; Extraembryonic Membranes/*blood supply/metabolism ; Neovascularization, Physiologic/*physiology ; Periodicity ; Regional Blood Flow/physiology ; Stress, Mechanical ; }, abstract = {To investigate the local mechanical forces associated with intravascular pillars and vessel pruning, we studied the conducting vessels in the extraembryonic circulation of the chick embryo. During the development days 13-17, intravascular pillars and blood flow parameters were identified using fluorescent vascular tracers and digital time-series video reconstructions. The geometry of selected vessels was confirmed by corrosion casting and scanning electron microscopy. Computational simulations of pruning vessels suggested that serial pillars form along pre-existing velocity streamlines; blood pressure demonstrated no obvious spatial relationship with the intravascular pillars. Modeling a Reynolds number of 0.03 produced 4 pillars at approximately 20-μm intervals matching the observed periodicity. In contrast, a Reynolds number of 0.06 produced only 2 pillars at approximately 63-μm intervals. Our modeling data indicated that the combination of wall shear stress and gradient of shear predicted the location, direction, and periodicity of developing pillars.}, }
@article {pmid21448948, year = {2011}, author = {Stalder, AF and Frydrychowicz, A and Russe, MF and Korvink, JG and Hennig, J and Li, K and Markl, M}, title = {Assessment of flow instabilities in the healthy aorta using flow-sensitive MRI.}, journal = {Journal of magnetic resonance imaging : JMRI}, volume = {33}, number = {4}, pages = {839-846}, doi = {10.1002/jmri.22512}, pmid = {21448948}, issn = {1522-2586}, mesh = {Adult ; Algorithms ; Aorta/*pathology ; Aorta, Thoracic/pathology ; Blood Flow Velocity/physiology ; Cohort Studies ; Diagnostic Imaging/*methods ; Female ; Humans ; Image Processing, Computer-Assisted/methods ; Magnetic Resonance Imaging/*methods ; Male ; Models, Statistical ; Prevalence ; *Pulsatile Flow ; }, abstract = {PURPOSE: To assess blood flow velocities and spatial distribution of aortic Reynolds numbers in vivo using flow-sensitive magnetic resonance imaging (MRI) and probe for flow instabilities along the aorta based on an empirical model for physiological pulsatile blood flow.<br><br>MATERIALS AND METHODS: Thirty young healthy volunteers were examined by flow-sensitive MRI at eight imaging planes distributed along the thoracic aorta. Flow, Womersley, Strouhal, Reynolds, and critical Reynolds numbers were calculated and used to assess the presence of flow instabilities.<br><br>RESULTS: The average peak Reynolds number was higher in the ascending (&#x2248;4500) and descending aorta (&#x2248;4200) than in the aortic arch (&#x2248;3400). According to the calculated critical Reynolds numbers, flow instabilities were prominent in the ascending (14/30 volunteers) and descending aorta (22/30 volunteers) but not in the aortic arch (3/30 volunteers). A significant difference (P < 0.05) in supracritical peak Reynolds numbers was observed between genders. The supracritical Reynolds number, indicating flow instabilities, significantly correlated (P < 0.05) with body weight (r = 0.34), aortic diameter (r = 0.48), and cardiac output (r = 0.53).<br><br>CONCLUSION: Flow-sensitive MRI was used to indirectly assess the presence of flow instabilities in vivo. The results in volunteers indicate the presence of flow instabilities in the young healthy aorta with a higher prevalence for men than women.}, }
@article {pmid21416230, year = {2011}, author = {Zhang, Z and Zhang, X}, title = {Mechanical behavior of the erythrocyte in microvessel stenosis.}, journal = {Science China. Life sciences}, volume = {54}, number = {5}, pages = {450-458}, doi = {10.1007/s11427-011-4152-3}, pmid = {21416230}, issn = {1869-1889}, mesh = {Blood Viscosity ; Cell Membrane/metabolism ; Computational Biology/methods ; Computer Simulation ; Constriction, Pathologic ; Cytoplasm/metabolism ; Erythrocyte Aggregation ; Erythrocytes/*physiology ; Humans ; Leukocytes/cytology ; *Microcirculation ; Microvessels/*pathology ; Rheology/methods ; Time Factors ; Viscosity ; }, abstract = {The passage of red blood cells (RBCs) through capillaries is essential for human blood microcirculation. This study used a moving mesh technology that incorporated leader-follower pairs to simulate the fluid-structure and structure-structure interactions between the RBC and a microvessel stenosis. The numerical model consisted of plasma, cytoplasm, the erythrocyte membrane, and the microvessel stenosis. Computational results showed that the rheology of the RBC is affected by the Reynolds number of the plasma flow as well as the surface-to-volume ratio of the erythrocyte. At a constant inlet flow rate, an increased plasma viscosity will improve the transit of the RBC through the microvessel stenosis. For the above reasons, we consider that the decreased hemorheology in microvessels in a pathological state may primarily be attributed to an increase in the number of white blood cells. This leads to the aggregation of RBCs and a change in the blood flow structure. The present fundamental study of hemorheology aimed at providing theoretical guidelines for clinical hemorheology.}, }
@article {pmid21405774, year = {2011}, author = {Schumacher, KR and Riley, JJ and Finlayson, BA}, title = {Turbulence in ferrofluids in channel flow with steady and oscillating magnetic fields.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {1 Pt 2}, pages = {016307}, doi = {10.1103/PhysRevE.83.016307}, pmid = {21405774}, issn = {1550-2376}, abstract = {The turbulent flow of a ferrofluid in channel flow is studied using direct numerical simulation. The method of analysis is an extension of that used for Newtonian fluids, with additional features necessary to model the ferrofluid. The analysis is applied to low Reynolds number turbulence in the range of existing experimental data in a capillary. For steady and oscillating magnetic fields, comparisons are made between a Newtonian fluid and a ferrofluid by comparing the pressure drop, turbulent Reynolds number, turbulent kinetic energy (k), Reynolds stress, velocity, and spin profiles. The results are also compared with predictions of a k-ɛ model to show the accuracy of that model when applied to ferrofluids, where ɛ is the rate of viscous dissipation of turbulent kinetic energy.}, }
@article {pmid21405773, year = {2011}, author = {Duran-Matute, M and Trieling, RR and van Heijst, GJ}, title = {Scaling and asymmetry in an electromagnetically forced dipolar flow structure.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {1 Pt 2}, pages = {016306}, doi = {10.1103/PhysRevE.83.016306}, pmid = {21405773}, issn = {1550-2376}, abstract = {A dipolar flow structure is experimentally studied in a layer of salt solution driven by time-independent electromagnetic forcing. In particular, the response of the flow to the forcing is quantified by measuring the Reynolds number Re as a function of the Chandrasekhar number Ch (the ratio of Lorentz forces to viscous forces) and δ (the ratio of vertical to horizontal length scales of the flow domain). In agreement with theoretical predictions, two scaling regimes are found: Re~Ch/π(2) (viscous regime) and Re~Ch(1/2)δ(-1) (advective regime). The transition between the two regimes at Ch(1/2)δ~π(2) is reflected in the flow geometry in the form of an asymmetry of the dipolar flow structure.}, }
@article {pmid21405711, year = {2011}, author = {Zhou, H and Gabilondo, BB and Losert, W and van de Water, W}, title = {Stretching and relaxation of vesicles.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {1 Pt 1}, pages = {011905}, doi = {10.1103/PhysRevE.83.011905}, pmid = {21405711}, issn = {1550-2376}, mesh = {Hydrodynamics ; Optical Phenomena ; Phosphatidylcholines/chemistry ; Time Factors ; Unilamellar Liposomes/*chemistry ; }, abstract = {We study the shape relaxation of spherical giant unilamellar vesicles which have been deformed far from equilibrium into ellipsoids using optical tweezers. The relaxation back to a sphere is determined by elastic constants of the vesicles, and their excess area, parameters that are obtained for each stretched vesicle from shape fluctuations in thermal equilibrium, as well as low Reynolds number fluid flow. The relaxation time could be compared favorably to a simple formula which encompasses the joint effect of membrane rigidity and fluid flow. The time constant of the stretched vesicle is slower than that of its thermal fluctuations, which agrees with a recent theory; however, it is one order of magnitude faster than predicted.}, }
@article {pmid21405707, year = {2011}, author = {Zhu, L and Do-Quang, M and Lauga, E and Brandt, L}, title = {Locomotion by tangential deformation in a polymeric fluid.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {83}, number = {1 Pt 1}, pages = {011901}, doi = {10.1103/PhysRevE.83.011901}, pmid = {21405707}, issn = {1550-2376}, mesh = {*Cell Movement ; Elasticity ; *Models, Biological ; Polymers/*chemistry ; }, abstract = {In several biologically relevant situations, cell locomotion occurs in polymeric fluids with Weissenberg number larger than 1. Here we present results of three-dimensional numerical simulations for the steady locomotion of a self-propelled body in a model polymeric (Giesekus) fluid at low Reynolds number. Locomotion is driven by steady tangential deformation at the surface of the body (the so-called squirming motion). In the case of a spherical squirmer, we show that the swimming velocity is systematically less than that in a Newtonian fluid, with a minimum occurring for Weissenberg numbers of order 1. The rate of work done by the swimmer always goes up compared to that occurring in the Newtonian solvent alone but is always lower than the power necessary to swim in a Newtonian fluid with the same viscosity. The swimming efficiency, defined as the ratio between the rate of work necessary to pull the body at the swimming speed in the same fluid and the rate of work done by swimming, is found to always be increased in a polymeric fluid. Further analysis reveals that polymeric stresses break the Newtonian front-back symmetry in the flow profile around the body. In particular, a strong negative elastic wake is present behind the swimmer, which correlates with strong polymer stretching, and its intensity increases with Weissenberg number and viscosity contrasts. The velocity induced by the squirmer is found to decay in space faster than in a Newtonian flow, with a strong dependence on the polymer relaxation time and viscosity. Our computational results are also extended to prolate spheroidal swimmers and smaller polymer stretching are obtained for slender shapes compared to bluff swimmers. The swimmer with an aspect ratio of two is found to be the most hydrodynamically efficient.}, }
@article {pmid21405520, year = {2011}, author = {Beresnyak, A}, title = {Spectral slope and Kolmogorov constant of MHD turbulence.}, journal = {Physical review letters}, volume = {106}, number = {7}, pages = {075001}, doi = {10.1103/PhysRevLett.106.075001}, pmid = {21405520}, issn = {1079-7114}, abstract = {The spectral slope of strong MHD turbulence has recently been a matter of controversy. While the Goldreich-Sridhar model predicts a -5/3 slope, shallower slopes have been observed in numerics. We argue that earlier numerics were affected by driving due to a diffuse locality of energy transfer. Our highest-resolution simulation (3072(2)×1024) exhibited the asymptotic -5/3 scaling. We also discover that the dynamic alignment, proposed in models with -3/2 slope, saturates and cannot modify the asymptotic, high Reynolds number slope. From the observed -5/3 scaling we measure the Kolmogorov constant C(KA)=3.27±0.07 for Alfvénic turbulence and C(K)=4.2±0.2 for full MHD turbulence, which is higher than the hydrodynamic value of 1.64. This larger C(K) indicates inefficient energy transfer in MHD turbulence, which is in agreement with diffuse locality.}, }
@article {pmid21405441, year = {2011}, author = {Uchida, N and Golestanian, R}, title = {Generic conditions for hydrodynamic synchronization.}, journal = {Physical review letters}, volume = {106}, number = {5}, pages = {058104}, doi = {10.1103/PhysRevLett.106.058104}, pmid = {21405441}, issn = {1079-7114}, mesh = {*Hydrodynamics ; *Models, Theoretical ; }, abstract = {Synchronization of actively oscillating organelles such as cilia and flagella facilitates self-propulsion of cells and pumping fluid in low Reynolds number environments. To understand the key mechanism behind synchronization induced by hydrodynamic interaction, we study a model of rigid-body rotors making fixed trajectories of arbitrary shape under driving forces that are arbitrary functions of the phase. For a wide class of geometries, we obtain the necessary and sufficient conditions for synchronization of a pair of rotors. We also find a novel synchronized pattern with an oscillating phase shift. Our results shed light on the role of hydrodynamic interactions in biological systems, and could help in developing efficient mixing and transport strategies in microfluidic devices.}, }
@article {pmid21403848, year = {2011}, author = {Tsai, RT and Wu, CY}, title = {An efficient micromixer based on multidirectional vortices due to baffles and channel curvature.}, journal = {Biomicrofluidics}, volume = {5}, number = {1}, pages = {14103}, pmid = {21403848}, issn = {1932-1058}, abstract = {An efficient planar micromixer based on multidirectional vortices in a curved channel with radial baffles is proposed and examined in this work. The curvature of the microchannel and the radial baffles induce vortices in different directions. The multidirectional vortices and the converging-diverging flow caused by the baffles contribute together to the enhancement of mixing. The micromixer is fabricated with polydimethylsiloxane by a single planar microlithography process and the mixing behaviors are observed by a confocal spectral microscope imaging system to validate the simulation obtained by a commercial code. The simulation and experimental results are in reasonable agreement. The concentration distributions and flow patterns obtained reveal the following trends. (i) The mixing efficiency of the basic C-shaped micromixer with the first baffle attached to the internal cylinder and the second attached to the external cylinder is better than that of the C-shaped micromixer with inverted arrangement of baffles. (ii) When the radius of the curved channel and the width of the passage between the baffle and the cylindrical wall are small enough and the Reynolds number (Re) is large enough, an extra separation vortex develops in the downstream of the second baffle. This phenomenon is one of the reasons of trend (i). (iii) A micromixer consisting of a few basic C-shaped micromixers connected by straight channels may generate a high degree of mixing for the case with a large Re.}, }
@article {pmid21402020, year = {2011}, author = {Rusconi, R and Lecuyer, S and Autrusson, N and Guglielmini, L and Stone, HA}, title = {Secondary flow as a mechanism for the formation of biofilm streamers.}, journal = {Biophysical journal}, volume = {100}, number = {6}, pages = {1392-1399}, pmid = {21402020}, issn = {1542-0086}, mesh = {*Biofilms ; *Hydrodynamics ; Microfluidic Analytical Techniques ; *Models, Biological ; Pseudomonas aeruginosa/physiology ; Time Factors ; Viscosity ; }, abstract = {In most environments, such as natural aquatic systems, bacteria are found predominantly in self-organized sessile communities known as biofilms. In the presence of a significant flow, mature multispecies biofilms often develop into long filamentous structures called streamers, which can greatly influence ecosystem processes by increasing transient storage and cycling of nutrients. However, the interplay between hydrodynamic stresses and streamer formation is still unclear. Here, we show that suspended thread-like biofilms steadily develop in zigzag microchannels with different radii of curvature. Numerical simulations of a low-Reynolds-number flow around these corners indicate the presence of a secondary vortical motion whose intensity is related to the bending angle of the turn. We demonstrate that the formation of streamers is directly proportional to the intensity of the secondary flow around the corners. In addition, we show that a model of an elastic filament in a two-dimensional corner flow is able to explain how the streamers can cross fluid streamlines and connect corners located at the opposite sides of the channel.}, }
@article {pmid21392770, year = {2011}, author = {Tovar-Lopez, FJ and Rosengarten, G and Khoshmanesh, K and Westein, E and Jackson, SP and Nesbitt, WS and Mitchell, A}, title = {Structural and hydrodynamic simulation of an acute stenosis-dependent thrombosis model in mice.}, journal = {Journal of biomechanics}, volume = {44}, number = {6}, pages = {1031-1039}, doi = {10.1016/j.jbiomech.2011.02.006}, pmid = {21392770}, issn = {1873-2380}, mesh = {Animals ; *Blood Platelets ; Constriction, Pathologic/complications/*physiopathology ; Disease Models, Animal ; Mesenteric Arteries/*physiopathology ; Mice ; *Models, Cardiovascular ; *Platelet Activation ; Thrombosis/etiology/*physiopathology ; }, abstract = {Platelet activation under blood flow is thought to be critically dependent on the autologous secretion of soluble platelet agonists (chemical activators) such as ADP and thromboxane. However, recent evidence challenging this model suggests that platelet activation can occur independent of soluble agonist signalling, in response to the mechanical effects of micro-scale shear gradients. A key experimental tool utilized to define the effect of shear gradients on platelet aggregation is the murine intravital microscopy model of platelet thrombosis under conditions of acute controlled arteriolar stenosis. This paper presents a computational structural and hydrodynamic simulation of acute stenotic blood flow in the small bowel mesenteric vessels of mice. Using a homogeneous fluid at low Reynolds number (0.45) we investigated the relationship between the local hydrodynamic strain-rates and the severity of arteriolar stensosis. We conclude that the critical rates of blood flow acceleration and deceleration at sites of artificially induced stenosis (vessel side-wall compression or ligation) are a function of tissue elasticity. By implementing a structural simulation of arteriolar side wall compression, we present a mechanistic model that provides accurate simulations of stenosis in vivo and allows for predictions of the effects on local haemodynamics in the murine small bowel mesenteric thrombosis model.}, }
@article {pmid21385952, year = {2011}, author = {Blough, T and Colin, SP and Costello, JH and Marques, AC}, title = {Ontogenetic changes in the bell morphology and kinematics and swimming behavior of rowing medusae: the special case of the limnomedusa Liriope tetraphylla.}, journal = {The Biological bulletin}, volume = {220}, number = {1}, pages = {6-14}, doi = {10.1086/BBLv220n1p6}, pmid = {21385952}, issn = {1939-8697}, mesh = {Animals ; Hydrozoa/growth &amp; development/*physiology ; Locomotion ; }, abstract = {Swimming animals may experience significant changes in the Reynolds number (Re) of their surrounding fluid flows throughout ontogeny. Many medusae experience Re environments with significant viscous forces as small juveniles but inertially dominated Re environments as adults. These different environments may affect their propulsive strategies. In particular, rowing, a propulsive strategy with ecological advantages for large adults, may be constrained by viscosity for small juvenile medusae. We examined changes in the bell morphology and swimming kinematics of the limnomedusa Liriope tetraphylla at different stages of development. L. tetraphylla maintained an oblate bell (fineness ratio ≈ 0.5-0.6), large velar aperture ratio (R(v) ≈ 0.5-0.8), and rapid bell kinematics throughout development. These traits enabled it to use rowing propulsion at all stages except the very smallest sizes observed (diameter = 0.14 cm). During the juvenile stage, very rapid bell kinematics served to increase Re sufficiently for rowing propulsion. Other taxa that use rowing propulsion as adults, such as leptomedusae and scyphomedusae, typically utilize different propulsive strategies as small juveniles to function in low Re environments. We compared the performance values of the different propulsive modes observed among juvenile medusae.}, }
@article {pmid21382831, year = {2011}, author = {Spalart, PR and McLean, JD}, title = {Drag reduction: enticing turbulence, and then an industry.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {369}, number = {1940}, pages = {1556-1569}, doi = {10.1098/rsta.2010.0369}, pmid = {21382831}, issn = {1364-503X}, abstract = {We examine drag-reduction proposals, as presented in this volume and in general, first with concrete examples of how to bridge the distance from pure science through engineering to what makes inventions go into service; namely, the value to the public. We point out that the true drag reduction can be markedly different from an estimate based simply on the difference between turbulent and laminar skin friction over the laminarized region, or between the respective skin frictions of the baseline and the riblet-treated flow. In some situations, this difference is favourable, and is due to secondary differences in pressure drag. We reiterate that the benefit of riblets, if it is expressed as a percentage in skin-friction reduction, is unfortunately lower at full-size Reynolds numbers than in a small-scale experiment or simulation. The Reynolds number-independent measure of such benefits is a shift of the logarithmic law, or 'ΔU(+)'. Anticipating the design of a flight test and then a product, we note the relative ease in representing riblets or laminarization in computational fluid dynamics, in contrast with the huge numerical and turbulence-modelling challenge of resolving active flow control systems in a calculation of the full flow field. We discuss in general terms the practical factors that have limited applications of concepts that would appear more than ready after all these years, particularly riblets and laminar-flow control.}, }
@article {pmid21382823, year = {2011}, author = {Quadrio, M}, title = {Drag reduction in turbulent boundary layers by in-plane wall motion.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {369}, number = {1940}, pages = {1428-1442}, doi = {10.1098/rsta.2010.0366}, pmid = {21382823}, issn = {1364-503X}, abstract = {Drag-reduction techniques capable of reducing the level of turbulent friction through wall-parallel movement of the wall are described, with special emphasis placed on spanwise movement. The discussion is confined to active open-loop control strategies, although feedback control is briefly mentioned with regard to peculiarities of spanwise sensing and/or actuation. Theoretical considerations are first given to explain why spanwise motion is expected to be particularly effective in skin-friction drag reduction. A review of the spanwise oscillating-wall technique is given next, with discussion of recent results and prospects. Last, waves of spanwise velocity are addressed, either spanwise- or streamwise-travelling. The latter include the oscillating wall as a special case. The generalized Stokes layer--i.e. the laminar, transverse oscillating boundary layer that develops under the action of the streamwise-travelling waves--is described, and its importance in determining turbulent drag reduction discussed. Finally, open issues like energetic efficiency and its dependence on Reynolds number are addressed.}, }
@article {pmid21382820, year = {2011}, author = {Erdmann, R and Pätzold, A and Engert, M and Peltzer, I and Nitsche, W}, title = {On active control of laminar-turbulent transition on two-dimensional wings.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {369}, number = {1940}, pages = {1382-1395}, doi = {10.1098/rsta.2010.0364}, pmid = {21382820}, issn = {1364-503X}, abstract = {This paper gives an overview of drag reduction on aerofoils by means of active control of Tollmien-Schlichting (TS) waves. Wind-tunnel experiments at Mach numbers of up to M(x)=0.42 and model Reynolds numbers of up to Re(c)=2 × 10(6), as well as in-flight experiments on a wing glove at Mach numbers of M<0.1 and at a Reynolds number of Re(c)=2.4 × 10(6), are presented. Surface hot wires were used to detect the linearly growing TS waves in the transitional boundary layer. Different types of voice-coil- and piezo-driven membrane actuators, as well as active-wall actuators, located between the reference and error sensors, were demonstrated to be effective in introducing counter-waves into the boundary layer to cancel the travelling TS waves. A control algorithm based on the filtered-x least mean square (FxLMS) approach was employed for in-flight and high-speed wind-tunnel experiments. A model-predictive control algorithm was tested in low-speed experiments on an active-wall actuator system. For the in-flight experiments, a reduction of up to 12 dB (75% TS amplitude) was accomplished in the TS frequency range between 200 and 600 Hz. A significant reduction of up to 20 dB (90% TS amplitude) in the flow disturbance amplitude was achieved in high-speed wind-tunnel experiments in the fundamental TS frequency range between 3 and 8 kHz. A downstream shift of the laminar-turbulent transition of up to seven TS wavelengths is presented. The cascaded sensor-actuator arrangement given by Sturzebecher &amp; Nitsche in 2003 for low-speed wind-tunnel experiments was able to shift the transition Δx=240 mm (18% x/c) downstream by a TS amplitude reduction of 96 per cent (30 dB). By using an active-wall actuator, which is much shorter than the cascaded system, a transition delay of seven TS wavelengths (16 dB TS amplitude reduction) was reached.}, }
@article {pmid21377477, year = {2011}, author = {Pandey, SK and Chaube, MK and Tripathi, D}, title = {Peristaltic transport of multilayered power-law fluids with distinct viscosities: a mathematical model for intestinal flows.}, journal = {Journal of theoretical biology}, volume = {278}, number = {1}, pages = {11-19}, doi = {10.1016/j.jtbi.2011.02.027}, pmid = {21377477}, issn = {1095-8541}, mesh = {*Biological Transport ; Intestines/*physiology ; *Models, Biological ; Peristalsis/*physiology ; Pressure ; *Rheology ; Viscosity ; }, abstract = {This paper is concerned with the theoretical study of two-dimensional peristaltic flow of power-law fluids in three layers with different viscosities. The analysis is carried out under low Reynolds number and long wavelength approximations. The shapes of the interfaces are described by a system of non-linear algebraic equations which are solved numerically as streamlines. It is found that the non-uniformity in the intermediate and peripheral layers diminishes when the viscosity of the intermediate layer is increased and that of the outermost layer is kept unaltered for both the pseudo-plastic and dilatant fluids. Similar are the observations when the viscosity of the outermost layer is increased and that of the intermediate layer is kept fixed. The flow rate increases with the viscosities of the peripheral and the intermediate layers but the viscosity of the outermost layer is more effective. However, the knowledge of the effect of the viscosity of the intermediate layer facilitates us to achieve the required flow rate without disturbing the outermost layer. An increase in the flow behaviour index too favours larger flow rates. The trapping limits increase with the viscosity of the intermediate layer but decrease with the viscosity of the outermost layer and the flow behaviour index. Thus, a medicinal intervention that creates a more viscous intermediate layer and reduces pseudo plasticity may reduce constipation.}, }
@article {pmid21364256, year = {2011}, author = {Moslemi, AA and Krueger, PS}, title = {The effect of Reynolds number on the propulsive efficiency of a biomorphic pulsed-jet underwater vehicle.}, journal = {Bioinspiration &amp; biomimetics}, volume = {6}, number = {2}, pages = {026001}, doi = {10.1088/1748-3182/6/2/026001}, pmid = {21364256}, issn = {1748-3190}, mesh = {Animals ; *Biomimetic Materials ; Computer Simulation ; Computer-Aided Design ; Decapodiformes/*physiology ; Equipment Design ; Equipment Failure Analysis ; *Models, Biological ; *Ships ; Swimming/*physiology ; Viscosity ; }, abstract = {The effect of Reynolds number on the propulsive efficiency of pulsed-jet propulsion was studied experimentally on a self-propelled, pulsed-jet underwater vehicle, dubbed Robosquid due to the similarity of its propulsion system with squid. Robosquid was tested for jet slug length-to-diameter ratios (L/D) in the range 2-6 and dimensionless frequency (St(L)) in the range 0.2-0.6 in a glycerin-water mixture. Digital particle image velocimetry was used for measuring the impulse and energy of jet pulses from the velocity and vorticity fields of the jet flow to calculate the pulsed-jet propulsive efficiency, and compare it with an equivalent steady jet system. Robosquid's Reynolds number (Re) based on average vehicle velocity and vehicle diameter ranged between 37 and 60. The current results for propulsive efficiency were compared to the previously published results in water where Re ranged between 1300 and 2700. The results showed that the average propulsive efficiency decreased by 26% as the average Re decreased from 2000 to 50 while the ratio of pulsed-jet to steady jet efficiency (η(P)/η(P, ss)) increased up to 0.15 (26%) as the Re decreased over the same range and for similar pulsing conditions. The improved η(P)/η(P, ss) at lower Re suggests that pulsed-jet propulsion can be used as an efficient propulsion system for millimeter-scale propulsion applications. The Re = 37-60 conditions in the present investigation, showed a reduced dependence of η(P) and η(P)/η(P, ss)on L/D compared to higher Re results. This may be due to the lack of clearly observed vortex ring pinch-off as L/D increased for this Re regime.}, }
@article {pmid21361631, year = {2011}, author = {van Gils, DP and Bruggert, GW and Lathrop, DP and Sun, C and Lohse, D}, title = {The Twente turbulent Taylor-Couette (T3C) facility: strongly turbulent (multiphase) flow between two independently rotating cylinders.}, journal = {The Review of scientific instruments}, volume = {82}, number = {2}, pages = {025105}, doi = {10.1063/1.3548924}, pmid = {21361631}, issn = {1089-7623}, abstract = {A new turbulent Taylor-Couette system consisting of two independently rotating cylinders has been constructed. The gap between the cylinders has a height of 0.927 m, an inner radius of 0.200 m, and a variable outer radius (from 0.279 to 0.220 m). The maximum angular rotation rates of the inner and outer cylinder are 20 and 10 Hz, respectively, resulting in Reynolds numbers up to 3.4 × 10(6) with water as working fluid. With this Taylor-Couette system, the parameter space (Re(i), Re(o), η) extends to (2.0 × 10(6), ±1.4 × 10(6), 0.716-0.909). The system is equipped with bubble injectors, temperature control, skin-friction drag sensors, and several local sensors for studying turbulent single-phase and two-phase flows. Inner cylinder load cells detect skin-friction drag via torque measurements. The clear acrylic outer cylinder allows the dynamics of the liquid flow and the dispersed phase (bubbles, particles, fibers, etc.) inside the gap to be investigated with specialized local sensors and nonintrusive optical imaging techniques. The system allows study of both Taylor-Couette flow in a high-Reynolds-number regime, and the mechanisms behind skin-friction drag alterations due to bubble injection, polymer injection, and surface hydrophobicity and roughness.}, }
@article {pmid21354574, year = {2011}, author = {Kang, MY and Hwang, J and Lee, JW}, title = {Effect of geometric variations on pressure loss for a model bifurcation of the human lung airway.}, journal = {Journal of biomechanics}, volume = {44}, number = {6}, pages = {1196-1199}, doi = {10.1016/j.jbiomech.2011.02.011}, pmid = {21354574}, issn = {1873-2380}, mesh = {Humans ; Lung/anatomy &amp; histology/*physiology ; *Models, Biological ; Pressure ; Respiratory Mechanics/*physiology ; Respiratory Rate/*physiology ; }, abstract = {Characteristics of pressure loss (ΔP) in human lung airways were numerically investigated using a realistic model bifurcation. Flow equations were numerically solved for the steady inspiratory condition with the tube length, the branching angle and flow velocity being varied over a wide range. In general, the ΔP coefficient K showed a power-law dependence on Reynolds number (Re) and length-to-diameter ratio with a different exponent for Re≥100 than for Re<100. The effect of different branching angles on pressure loss was very weak in the smooth-branching airways.}, }
@article {pmid21347910, year = {2011}, author = {Dinarvand, S}, title = {Viscous flow through slowly expanding or contracting porous walls with low seepage Reynolds number: a model for transport of biological fluids through vessels.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {14}, number = {10}, pages = {853-862}, doi = {10.1080/10255842.2010.497490}, pmid = {21347910}, issn = {1476-8259}, mesh = {Biological Transport ; Blood Vessels/*metabolism ; Body Fluids/*metabolism ; Pressure ; Viscosity ; }, abstract = {In this article, the problem of laminar, isothermal, incompressible and viscous flow in a rectangular domain bounded by two moving porous walls, which enable the fluid to enter or exit during successive expansions or contractions, is investigated. The governing non-linear equations and their associated boundary conditions are transformed into a highly non-linear ordinary differential equation. The series solution of the problem is obtained by utilising the homotopy perturbation method. Graphical results are presented to investigate the influence of the non-dimensional wall dilation rate and seepage Reynolds number (Re) on the velocity, normal pressure distribution and wall shear stress. Since the transport of biological fluids through contracting or expanding vessels is characterised by low seepage Res, the current study focuses on the viscous flow driven by small wall contractions and expansions of two weakly permeable walls.}, }
@article {pmid21320911, year = {2011}, author = {Gibbon, JD and Holm, DD}, title = {Extreme events in solutions of hydrostatic and non-hydrostatic climate models.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {369}, number = {1939}, pages = {1156-1179}, doi = {10.1098/rsta.2010.0244}, pmid = {21320911}, issn = {1364-503X}, abstract = {Initially, this paper reviews the mathematical issues surrounding hydrostatic primitive equations (HPEs) and non-hydrostatic primitive equations (NPEs) that have been used extensively in numerical weather prediction and climate modelling. A new impetus has been provided by a recent proof of the existence and uniqueness of solutions of viscous HPEs on a cylinder with Neumann-like boundary conditions on the top and bottom. In contrast, the regularity of solutions of NPEs remains an open question. With this HPE regularity result in mind, the second issue examined in this paper is whether extreme events are allowed to arise spontaneously in their solutions. Such events could include, for example, the sudden appearance and disappearance of locally intense fronts that do not involve deep convection. Analytical methods are used to show that for viscous HPEs, the creation of small-scale structures is allowed locally in space and time at sizes that scale inversely with the Reynolds number.}, }
@article {pmid21308417, year = {2011}, author = {Li, Z and Kleinstreuer, C}, title = {Airflow analysis in the alveolar region using the lattice-Boltzmann method.}, journal = {Medical &amp; biological engineering &amp; computing}, volume = {49}, number = {4}, pages = {441-451}, pmid = {21308417}, issn = {1741-0444}, mesh = {Humans ; Inhalation/physiology ; *Models, Biological ; Pulmonary Alveoli/anatomy &amp; histology/*physiology ; Respiratory Mechanics/*physiology ; Rheology ; }, abstract = {A validated lattice-Boltzmann code has been developed based on the Bhatnagar-Gross-Krook formulation to simulate and analyze transient laminar two-dimensional airflow in alveoli and bifurcating alveolated ducts with moving walls, representative of the human respiratory zone. A physically more realistic pressure boundary condition has been implemented, considering a physiological Reynolds number range, i.e., 0 < Re < 11, which covers the inhalation scenarios from resting mode to moderate exercise. Axial velocity contours, vortex propagation, and streamlines as well as mid-plane pressure variations in different alveolar geometries and shapes are illustrated and discussed. The results show that the influence of the geometric structure on the airflow fields in the human alveolar region is very important. Furthermore, the effect of a moving alveolus wall is significant, i.e., the vortices in the duct or alveolar sacs may change in size. In summary, for a given set of realistic inlet conditions, the airflow velocity and vortical flows are greatly dependent on the different alveolar sac shapes, local geometric structures, and sac expansion rates. The pressure distributions are less influenced by the alveolus shape and wall movement. The present results provide new physical insight and are important for the simulation of particle transport/deposition in the deep lung region.}, }
@article {pmid21301636, year = {2011}, author = {Forbes, TP and Degertekin, FL and Fedorov, AG}, title = {Droplet charging regimes for ultrasonic atomization of a liquid electrolyte in an external electric field.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {23}, number = {1}, pages = {12104}, pmid = {21301636}, issn = {1070-6631}, support = {R21 RR021474/RR/NCRR NIH HHS/United States ; }, abstract = {Distinct regimes of droplet charging, determined by the dominant charge transport process, are identified for an ultrasonic droplet ejector using electrohydrodynamic computational simulations, a fundamental scale analysis, and experimental measurements. The regimes of droplet charging are determined by the relative magnitudes of the dimensionless Strouhal and electric Reynolds numbers, which are a function of the process (pressure forcing), advection, and charge relaxation time scales for charge transport. Optimal (net maximum) droplet charging has been identified to exist for conditions in which the electric Reynolds number is of the order of the inverse Strouhal number, i.e., the charge relaxation time is on the order of the pressure forcing (droplet formation) time scale. The conditions necessary for optimal droplet charging have been identified as a function of the dimensionless Debye number (i.e., liquid conductivity), external electric field (magnitude and duration), and atomization drive signal (frequency and amplitude). The specific regime of droplet charging also determines the functional relationship between droplet charge and charging electric field strength. The commonly expected linear relationship between droplet charge and external electric field strength is only found when either the inverse of the Strouhal number is less than the electric Reynolds number, i.e., the charge relaxation is slower than both the advection and external pressure forcing, or in the electrostatic limit, i.e., when charge relaxation is much faster than all other processes. The analysis provides a basic understanding of the dominant physics of droplet charging with implications to many important applications, such as electrospray mass spectrometry, ink jet printing, and drop-on-demand manufacturing.}, }
@article {pmid21283217, year = {2011}, author = {Jiang, N and Webster, M and Lempert, WR and Miller, JD and Meyer, TR and Ivey, CB and Danehy, PM}, title = {MHz-rate nitric oxide planar laser-induced fluorescence imaging in a Mach 10 hypersonic wind tunnel.}, journal = {Applied optics}, volume = {50}, number = {4}, pages = {A20-8}, doi = {10.1364/AO.50.000A20}, pmid = {21283217}, issn = {1539-4522}, abstract = {Nitric oxide planar laser-induced fluorescence (NO PLIF) imaging at repetition rates as high as 1 MHz is demonstrated in the NASA Langley 31 in. Mach 10 hypersonic wind tunnel. Approximately 200 time-correlated image sequences of between 10 and 20 individual frames were obtained over eight days of wind tunnel testing spanning two entries in March and September of 2009. The image sequences presented were obtained from the boundary layer of a 20° flat plate model, in which transition was induced using a variety of different shaped protuberances, including a cylinder and a triangle. The high-speed image sequences captured a variety of laminar and transitional flow phenomena, ranging from mostly laminar flow, typically at a lower Reynolds number and/or in the near wall region of the model, to highly transitional flow in which the temporal evolution and progression of characteristic streak instabilities and/or corkscrew-shaped vortices could be clearly identified.}, }
@article {pmid21231507, year = {2010}, author = {Leoni, M and Liverpool, TB}, title = {Swimmers in thin films: from swarming to hydrodynamic instabilities.}, journal = {Physical review letters}, volume = {105}, number = {23}, pages = {238102}, doi = {10.1103/PhysRevLett.105.238102}, pmid = {21231507}, issn = {1079-7114}, abstract = {We investigate theoretically the collective dynamics of a suspension of low Reynolds number swimmers that are confined to two dimensions by a thin fluid film. Our model swimmer is characterized by internal degrees of freedom which locally exert active stresses on the fluid. We find that hydrodynamic interactions mediated by the film can give rise to spontaneous continuous symmetry breaking (swarming), to states with either polar or nematic homogeneous order. For dipolar swimmers, the stroke averaged dynamics are enough to determine the leading contributions to the collective behavior. In contrast, for quadrupolar swimmers, details of the internal dynamics are important in determining the bulk behavior. In the broken symmetry phases, fluctuations of hydrodynamic variables destabilize order. Interestingly, this instability is not generic and depends on the length scale.}, }
@article {pmid21231308, year = {2010}, author = {Cortet, PP and Chiffaudel, A and Daviaud, F and Dubrulle, B}, title = {Experimental evidence of a phase transition in a closed turbulent flow.}, journal = {Physical review letters}, volume = {105}, number = {21}, pages = {214501}, doi = {10.1103/PhysRevLett.105.214501}, pmid = {21231308}, issn = {1079-7114}, abstract = {We experimentally study the susceptibility to symmetry breaking of a closed turbulent von Kármán swirling flow from Re=150 to Re≃10[6]. We report a divergence of this susceptibility at an intermediate Reynolds number Re=Re(χ)≃90,000 which gives experimental evidence that such a highly space and time fluctuating system can undergo a "phase transition." This transition is furthermore associated with a peak in the amplitude of fluctuations of the instantaneous flow symmetry corresponding to intermittencies between spontaneously symmetry breaking metastable states.}, }
@article {pmid21231108, year = {2010}, author = {Frick, P and Noskov, V and Denisov, S and Stepanov, R}, title = {Direct measurement of effective magnetic diffusivity in turbulent flow of liquid sodium.}, journal = {Physical review letters}, volume = {105}, number = {18}, pages = {184502}, doi = {10.1103/PhysRevLett.105.184502}, pmid = {21231108}, issn = {1079-7114}, abstract = {The first direct measurements of effective magnetic diffusivity in turbulent flow of electroconductive fluids (the so-called β effect) under the magnetic Reynolds number Rm≫1 are reported. The measurements are performed in a nonstationary turbulent flow of liquid sodium, generated in a closed toroidal channel. The peak level of the Reynolds number reached Re≈3×10(6), which corresponds to the magnetic Reynolds number Rm≈30. The magnetic diffusivity of the liquid metal was determined by measuring the phase shift between the induced and the applied magnetic fields. The maximal deviation of magnetic diffusivity from its laminar value reaches about 50%.}, }
@article {pmid21230837, year = {2010}, author = {Kadoch, B and Bos, WJ and Schneider, K}, title = {Origin of lagrangian intermittency in drift-wave turbulence.}, journal = {Physical review letters}, volume = {105}, number = {14}, pages = {145001}, doi = {10.1103/PhysRevLett.105.145001}, pmid = {21230837}, issn = {1079-7114}, abstract = {The Lagrangian velocity statistics of dissipative drift-wave turbulence are investigated. For large values of the adiabaticity (or small collisionality), the probability density function of the Lagrangian acceleration shows exponential tails, as opposed to the stretched exponential or algebraic tails, generally observed for the highly intermittent acceleration of Navier-Stokes turbulence. This exponential distribution is shown to be a robust feature independent of the Reynolds number. For small adiabaticity, algebraic tails are observed, suggesting the strong influence of point-vortex-like dynamics on the acceleration. A causal connection is found between the shape of the probability density function and the autocorrelation of the norm of the acceleration.}, }
@article {pmid21230833, year = {2010}, author = {Perlekar, P and Benzi, R and Nelson, DR and Toschi, F}, title = {Population dynamics at high Reynolds number.}, journal = {Physical review letters}, volume = {105}, number = {14}, pages = {144501}, doi = {10.1103/PhysRevLett.105.144501}, pmid = {21230833}, issn = {1079-7114}, abstract = {We study the statistical properties of population dynamics evolving in a realistic two-dimensional compressible turbulent velocity field. We show that the interplay between turbulent dynamics and population growth and saturation leads to quasilocalization and a remarkable reduction in the carrying capacity. The statistical properties of the population density are investigated and quantified via multifractal scaling analysis. We also investigate numerically the singular limit of negligibly small growth rates and delocalization of population ridges triggered by uniform advection.}, }
@article {pmid21230732, year = {2010}, author = {Zhan, JM and Chen, ZW and Li, YS and Nie, YH}, title = {Three-dimensional double-diffusive Marangoni convection in a cubic cavity with horizontal temperature and concentration gradients.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {6 Pt 2}, pages = {066305}, doi = {10.1103/PhysRevE.82.066305}, pmid = {21230732}, issn = {1550-2376}, abstract = {Three-dimensional double-diffusive Marangoni convection in a cubic cavity is studied in the present paper. Both the temperature and solute concentration gradients are applied horizontally. Direct numerical simulations are carried out for surface-tension Reynolds number 10≤Re≤500, surface-tension ratio -2≤R(σ)≤1, and Lewis number 1<Le≤200. Symmetry-breaking pitchfork bifurcation is observed, which does not exist in the pure thermocapillary case, and the flow field is essentially three dimensional. The evolution of the flow structure, as well as the dependence of the heat and mass transfer rates on the different parameters, is investigated systematically. The simulations are performed until the temporal chaotic flow regime is reached and an atypical bifurcation sequence is identified. Namely, as the thermal forcing of the system increases, the flow can undergo a reverse transition from a temporal chaotic to a steady state. Multiple solution branches exist in some parameter ranges, and these are depicted in terms of the heat and mass transfer rates. Corresponding two-dimensional simulations are also performed to clearly illustrate the deviations from the three-dimensional model. The onset of oscillatory flow from the quiescent equilibrium state is also considered. The present work intends to initiate the study of double-diffusive Marangoni convection in three-dimensional confined cavities with horizontal temperature and concentration gradients.}, }
@article {pmid21230728, year = {2010}, author = {Carini, M and Quadrio, M}, title = {Direct-numerical-simulation-based measurement of the mean impulse response of homogeneous isotropic turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {6 Pt 2}, pages = {066301}, doi = {10.1103/PhysRevE.82.066301}, pmid = {21230728}, issn = {1550-2376}, abstract = {A technique for measuring the mean impulse response function of stationary homogeneous isotropic turbulence is proposed. Such a measurement is carried out here on the basis of direct numerical simulation (DNS). A zero-mean white-noise volume forcing is used to probe the turbulent flow, and the response function is obtained by accumulating the space-time correlation between the white forcing and the velocity field. This technique to measure the turbulent response in a DNS numerical experiment is a research tool in that field of spectral closures where the linear-response concept is invoked either by resorting to renormalized perturbations theories or by introducing the well-known fluctuation-dissipation relation (FDR). Although the results obtained in the present work are limited to relatively low values of the Reynolds number, a preliminary analysis is possible. Both the characteristic form and the time scaling properties of the response function are investigated in the universal subrange of dissipative wave numbers; a comparison with the response approximation given by the FDR is proposed through the independent DNS measurement of the correlation function. Very good agreement is found between the measured response and Kraichnan's description of random energy-range advection effects.}, }
@article {pmid21230621, year = {2010}, author = {Kataoka, T and Tsutahara, M}, title = {Accuracy of the lattice Boltzmann method for describing the behavior of a gas in the continuum limit.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {5 Pt 2}, pages = {056709}, doi = {10.1103/PhysRevE.82.056709}, pmid = {21230621}, issn = {1550-2376}, abstract = {The accuracy of the lattice Boltzmann method (LBM) for describing the behavior of a gas in the continuum limit is systematically investigated. The asymptotic analysis for small Knudsen numbers is carried out to derive the corresponding fluid-dynamics-type equations, and the errors of the LBM are estimated by comparing them with the correct fluid-dynamics-type equations. We discuss the following three important cases: (I) the Mach number of the flow is much smaller than the Knudsen number, (II) the Mach number is of the same order as the Knudsen number, and (III) the Mach number is finite. From the von Karman relation, the above three cases correspond to the flows of (I) small Reynolds number, (II) finite Reynolds number, and (III) large Reynolds number, respectively. The analysis is made with the information only of the fundamental properties of the lattice Boltzmann models without stepping into their detailed form. The results are therefore applicable to various lattice Boltzmann models that satisfy the fundamental properties used in the analysis.}, }
@article {pmid21230595, year = {2010}, author = {Uritsky, VM and Pouquet, A and Rosenberg, D and Mininni, PD and Donovan, EF}, title = {Structures in magnetohydrodynamic turbulence: detection and scaling.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {5 Pt 2}, pages = {056326}, doi = {10.1103/PhysRevE.82.056326}, pmid = {21230595}, issn = {1550-2376}, abstract = {We present a systematic analysis of statistical properties of turbulent current and vorticity structures at a given time using cluster analysis. The data stem from numerical simulations of decaying three-dimensional magnetohydrodynamic turbulence in the absence of an imposed uniform magnetic field; the magnetic Prandtl number is taken equal to unity, and we use a periodic box with grids of up to 1536[3] points and with Taylor Reynolds numbers up to 1100. The initial conditions are either an X -point configuration embedded in three dimensions, the so-called Orszag-Tang vortex, or an Arn'old-Beltrami-Childress configuration with a fully helical velocity and magnetic field. In each case two snapshots are analyzed, separated by one turn-over time, starting just after the peak of dissipation. We show that the algorithm is able to select a large number of structures (in excess of 8000) for each snapshot and that the statistical properties of these clusters are remarkably similar for the two snapshots as well as for the two flows under study in terms of scaling laws for the cluster characteristics, with the structures in the vorticity and in the current behaving in the same way. We also study the effect of Reynolds number on cluster statistics, and we finally analyze the properties of these clusters in terms of their velocity-magnetic-field correlation. Self-organized criticality features have been identified in the dissipative range of scales. A different scaling arises in the inertial range, which cannot be identified for the moment with a known self-organized criticality class consistent with magnetohydrodynamics. We suggest that this range can be governed by turbulence dynamics as opposed to criticality and propose an interpretation of intermittency in terms of propagation of local instabilities.}, }
@article {pmid21230594, year = {2010}, author = {Deguchi, K and Nagata, M}, title = {Traveling hairpin-shaped fluid vortices in plane Couette flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {5 Pt 2}, pages = {056325}, doi = {10.1103/PhysRevE.82.056325}, pmid = {21230594}, issn = {1550-2376}, abstract = {Traveling-wave solutions are discovered in plane Couette flow. They are obtained when the so-called steady hairpin vortex state found recently by Gibson [J. Fluid Mech. 638, 243 (2009)] and Itano and Generalis [Phys. Rev. Lett. 102, 114501 (2009)] is continued to sliding Couette flow geometry between two concentric cylinders by using the radius ratio as a homotopy parameter. It turns out that in the plane Couette flow geometry two traveling waves having the phase velocities with opposite signs are associated with their appearance from the steady hairpin vortex state, where the amplitude of the phase velocities increases gradually from zero as the Reynolds number is increased. The solutions obviously inherit the streaky structure of the hairpin vortex state, but shape preserving flow patterns propagate in the streamwise direction. Other striking features of the solution are asymmetric mean flow profiles and strong quasistreamwise vortices which occupy the vicinity of only the top or bottom moving boundary, depending on the sign of the phase velocity. Furthermore, we find that the pitchfork bifurcation associated with the appearance of the solution becomes imperfect when the flow is perturbed by a Poiseuille flow component.}, }
@article {pmid21230585, year = {2010}, author = {Takemoto, Y and Mizushima, J}, title = {Mechanism of sustained oscillations in a fluid flowing past a circular cylinder obstacle.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {5 Pt 2}, pages = {056316}, doi = {10.1103/PhysRevE.82.056316}, pmid = {21230585}, issn = {1550-2376}, abstract = {The mechanism of sustained oscillation in the flow past a circular cylinder is investigated numerically, in which impulsive force is given at a certain point in the flow and subsequent spatiotemporal development of induced disturbance is observed. The impulsive force generates an intense localized disturbance at the point of forcing, which is transmitted immediately up to a region just behind the cylinder, and there it yields an transient and eigen modes of disturbance having a packet form. Extending the conventional notions of convective and absolute modes of instability established on the parallel flow approximation to nonparallel flows, we define "passive" and "active" modes of instability, respectively, and evaluate the growth rate of each mode. It was found that the entire flow field is stable to active mode below the critical Reynolds number for the global instability though some extent of the flow behind the cylinder is unstable to passive mode, while the flow becomes unstable to active mode everywhere simultaneously when the Reynolds number exceeds the critical value. The numerical analysis brought us a conclusion that the oscillation is sustained by superiority of the growth of disturbance due to instability over the decrease due to advection of the packet.}, }
@article {pmid21230397, year = {2010}, author = {Eyink, GL}, title = {Fluctuation dynamo and turbulent induction at small Prandtl number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {4 Pt 2}, pages = {046314}, doi = {10.1103/PhysRevE.82.046314}, pmid = {21230397}, issn = {1550-2376}, abstract = {We study the Lagrangian mechanism of the fluctuation dynamo at zero Prandtl number and infinite magnetic Reynolds number, in the Kazantsev-Kraichnan model of white-noise advection. With a rough velocity field corresponding to a turbulent inertial range, flux freezing holds only in a stochastic sense. We show that field lines arriving to the same point which were initially separated by many resistive lengths are important to the dynamo. Magnetic vectors of the seed field that point parallel to the initial separation vector arrive anticorrelated and produce an "antidynamo" effect. We also study the problem of "magnetic induction" of a spatially uniform seed field. We find no essential distinction between this process and fluctuation dynamo, both producing the same growth rates and small-scale magnetic correlations. In the regime of very rough velocity fields where fluctuation dynamo fails, we obtain the induced magnetic energy spectra. We use these results to evaluate theories proposed for magnetic spectra in laboratory experiments of turbulent induction.}, }
@article {pmid21230392, year = {2010}, author = {Banerjee, A and Gore, RA and Andrews, MJ}, title = {Development and validation of a turbulent-mix model for variable-density and compressible flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {4 Pt 2}, pages = {046309}, doi = {10.1103/PhysRevE.82.046309}, pmid = {21230392}, issn = {1550-2376}, abstract = {The modeling of buoyancy driven turbulent flows is considered in conjunction with an advanced statistical turbulence model referred to as the BHR (Besnard-Harlow-Rauenzahn) k-S-a model. The BHR k-S-a model is focused on variable-density and compressible flows such as Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM), and Kelvin-Helmholtz (KH) driven mixing. The BHR k-S-a turbulence mix model has been implemented in the RAGE hydro-code, and model constants are evaluated based on analytical self-similar solutions of the model equations. The results are then compared with a large test database available from experiments and direct numerical simulations (DNS) of RT, RM, and KH driven mixing. Furthermore, we describe research to understand how the BHR k-S-a turbulence model operates over a range of moderate to high Reynolds number buoyancy driven flows, with a goal of placing the modeling of buoyancy driven turbulent flows at the same level of development as that of single phase shear flows.}, }
@article {pmid21230186, year = {2010}, author = {Demekhin, EA and Kalaidin, EN and Kalliadasis, S and Vlaskin, SY}, title = {Three-dimensional localized coherent structures of surface turbulence: Model validation with experiments and further computations.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {3 Pt 2}, pages = {036322}, doi = {10.1103/PhysRevE.82.036322}, pmid = {21230186}, issn = {1550-2376}, abstract = {We validate experimentally the Kapitsa-Shkadov model utilized in the theoretical studies by Demekhin [Phys. Fluids 19, 114103 (2007)10.1063/1.2793148; Phys. Fluids 19, 114104 (2007)]10.1063/1.2793149 of surface turbulence on a thin liquid film flowing down a vertical planar wall. For water at 15° , surface turbulence typically occurs at an inlet Reynolds number of ≃40 . Of particular interest is to assess experimentally the predictions of the model for three-dimensional nonlinear localized coherent structures, which represent elementary processes of surface turbulence. For this purpose we devise simple experiments to investigate the instabilities and transitions leading to such structures. Our experimental results are in good agreement with the theoretical predictions of the model. We also perform time-dependent computations for the formation of coherent structures and their interaction with localized structures of smaller amplitude on the surface of the film.}, }
@article {pmid21230185, year = {2010}, author = {Willis, AP and Hwang, Y and Cossu, C}, title = {Optimally amplified large-scale streaks and drag reduction in turbulent pipe flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {3 Pt 2}, pages = {036321}, doi = {10.1103/PhysRevE.82.036321}, pmid = {21230185}, issn = {1550-2376}, abstract = {The optimal amplifications of small coherent perturbations within turbulent pipe flow are computed for Reynolds numbers up to one million. Three standard frameworks are considered: the optimal growth of an initial condition, the response to harmonic forcing and the Karhunen-Loève (proper orthogonal decomposition) analysis of the response to stochastic forcing. Similar to analyses of the turbulent plane channel flow and boundary layer, it is found that streaks elongated in the streamwise direction can be greatly amplified from quasistreamwise vortices, despite linear stability of the mean flow profile. The most responsive perturbations are streamwise uniform and, for sufficiently large Reynolds number, the most responsive azimuthal mode is of wave number m=1 . The response of this mode increases with the Reynolds number. A secondary peak, where m corresponds to azimuthal wavelengths λ_{θ}^{+}≈70-90 in wall units, also exists in the amplification of initial conditions and in premultiplied response curves for the forced problems. Direct numerical simulations at Re=5300 confirm that the forcing of m=1,2 and m=4 optimal structures results in the large response of coherent large-scale streaks. For moderate amplitudes of the forcing, low-speed streaks become narrower and more energetic, whereas high-speed streaks become more spread. It is further shown that drag reduction can be achieved by forcing steady large-scale structures, as anticipated from earlier investigations. Here the energy balance is calculated. At Re=5300 it is shown that, due to the small power required by the forcing of optimal structures, a net power saving of the order of 10% can be achieved following this approach, which could be relevant for practical applications.}, }
@article {pmid21230174, year = {2010}, author = {Yatou, H}, title = {Flow pattern transition accompanied with sudden growth of flow resistance in two-dimensional curvilinear viscoelastic flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {3 Pt 2}, pages = {036310}, doi = {10.1103/PhysRevE.82.036310}, pmid = {21230174}, issn = {1550-2376}, abstract = {We numerically find three types of steady solutions of viscoelastic flows and flow pattern transitions between them in a two-dimensional wavy-walled channel for low to moderate Weissenberg (Wi) and Reynolds (Re) numbers using a spectral element method. The solutions are called "convective," "transition," and "elastic" in ascending order of Wi. In the convective region in the Wi-Re parameter space, convective effect and pressure gradient balance on average. As Wi increases, elastic effect becomes comparable, and the first transition sets in. Through the transition, a separation vortex disappears, and a jet flow induced close to the wall by the viscoelasticity moves into the bulk; the viscous drag significantly drops, and the elastic wall friction rises sharply. This transition is caused by an elastic force in the streamwise direction due to the competition of the convective and elastic effects. In the transition region, the convective and elastic effects balance. When the elastic effect becomes greater than the convective effect, the second transition occurs but it is relatively moderate. The second transition seems to be governed by the so-called Weissenberg effect. These transitions are not sensitive to driving forces. By a scaling analysis, it is shown that the stress component is proportional to the Reynolds number on the boundary of the first transition in the Wi-Re space. This scaling coincides well with the numerical result.}, }
@article {pmid21216428, year = {2011}, author = {Wu, B}, title = {CFD investigation of turbulence models for mechanical agitation of non-Newtonian fluids in anaerobic digesters.}, journal = {Water research}, volume = {45}, number = {5}, pages = {2082-2094}, doi = {10.1016/j.watres.2010.12.020}, pmid = {21216428}, issn = {1879-2448}, mesh = {Algorithms ; Anaerobiosis ; *Computer Simulation ; Hydrodynamics ; Kinetics ; Mechanical Phenomena ; *Models, Chemical ; Reproducibility of Results ; Rheology/*methods ; Water Pollutants/*chemistry ; }, abstract = {This study evaluates six turbulence models for mechanical agitation of non-Newtonian fluids in a lab-scale anaerobic digestion tank with a pitched blade turbine (PBT) impeller. The models studied are: (1) the standard k-ɛ model, (2) the RNG k-ɛ model, (3) the realizable k-ɛ model, (4) the standard k-ω model, (5) the SST k-ω model, and (6) the Reynolds stress model. Through comparing power and flow numbers for the PBT impeller obtained from computational fluid dynamics (CFD) with those from the lab specifications, the realizable k-ɛ and the standard k-ω models are found to be more appropriate than the other turbulence models. An alternative method to calculate the Reynolds number for the moving zone that characterizes the impeller rotation is proposed to judge the flow regime. To check the effect of the model setup on the predictive accuracy, both discretization scheme and numerical approach are investigated. The model validation is conducted by comparing the simulated velocities with experimental data in a lab-scale digester from literature. Moreover, CFD simulation of mixing in a full-scale digester with two side-entry impellers is performed to optimize the installation.}, }
@article {pmid21198093, year = {2010}, author = {Kamil, SM and Menon, GI and Sinha, S}, title = {A coupled map lattice model for rheological chaos in sheared nematic liquid crystals.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {20}, number = {4}, pages = {043123}, doi = {10.1063/1.3504435}, pmid = {21198093}, issn = {1089-7682}, abstract = {A variety of complex fluids under shear exhibit complex spatiotemporal behavior, including what is now termed rheological chaos, at moderate values of the shear rate. Such chaos associated with rheological response occurs in regimes where the Reynolds number is very small. It must thus arise as a consequence of the coupling of the flow to internal structural variables describing the local state of the fluid. We propose a coupled map lattice model for such complex spatiotemporal behavior in a passively sheared nematic liquid crystal using local maps constructed so as to accurately describe the spatially homogeneous case. Such local maps are coupled diffusively to nearest and next-nearest neighbors to mimic the effects of spatial gradients in the underlying equations of motion. We investigate the dynamical steady states obtained as parameters in the map and the strength of the spatial coupling are varied, studying local temporal properties at a single site as well as spatiotemporal features of the extended system. Our methods reproduce the full range of spatiotemporal behavior seen in earlier one-dimensional studies based on partial differential equations. We report results for both the one- and two-dimensional cases, showing that spatial coupling favors uniform or periodically time-varying states, as intuitively expected. We demonstrate and characterize regimes of spatiotemporal intermittency out of which chaos develops. Our work indicates that similar simplified lattice models of the dynamics of complex fluids under shear should provide useful ways to access and quantify spatiotemporal complexity in such problems, in addition to representing a fast and numerically tractable alternative to continuum representations.}, }
@article {pmid21192705, year = {2011}, author = {Yang, L and Gao, K and Luo, Y and Luo, J and Li, D and Meng, Q}, title = {In situ observation and measurement of evaporation-induced self-assembly under controlled pressure and temperature.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {27}, number = {5}, pages = {1700-1706}, doi = {10.1021/la104338a}, pmid = {21192705}, issn = {1520-5827}, abstract = {In situ observations of evaporation-induced colloidal self-assembly and in situ measurement of mass transfer process were carried out under a temperature and pressure controlling system. The growth processes of colloidal crystals in different cuvettes recorded by direct video observations revealed that solvent flow around the pore space of the crystal played a key role. By changing the circumstances (temperature and pressure) of the self-assembly system and properties of fluid (viscosity), different evaporation rate of solvent and growth rate of colloidal crystals were measured directly. It turned out that both evaporation rate and growth rate as functions of temperature and pressure fit Stefan's law well. Furthermore, the transfer process of particles in the fluid flow was determined by the fluid-dynamic characteristics, which can be analyzed by the Reynolds number. The results obtained provide an insight into the growth mechanisms of self-assembly and theoretical basis for optimizing the experimental growth conditions of colloidal crystals.}, }
@article {pmid21151737, year = {2010}, author = {Wang, Y and Zhang, J}, title = {Fast and Robust Sixth Order Multigrid Computation for 3D Convection Diffusion Equation.}, journal = {Journal of computational and applied mathematics}, volume = {234}, number = {12}, pages = {3496-3506}, doi = {10.1016/j.cam.2010.05.022}, pmid = {21151737}, issn = {0377-0427}, support = {R01 HL086644/HL/NHLBI NIH HHS/United States ; R01 HL086644-01/HL/NHLBI NIH HHS/United States ; }, abstract = {We present a sixth order explicit compact finite difference scheme to solve the three dimensional (3D) convection diffusion equation. We first use multiscale multigrid method to solve the linear systems arising from a 19-point fourth order discretization scheme to compute the fourth order solutions on both the coarse grid and the fine grid. Then an operator based interpolation scheme combined with an extrapolation technique is used to approximate the sixth order accurate solution on the fine grid. Since the multigrid method using a standard point relaxation smoother may fail to achieve the optimal grid independent convergence rate for solving convection diffusion equation with a high Reynolds number, we implement the plane relaxation smoother in the multigrid solver to achieve better grid independency. Supporting numerical results are presented to demonstrate the efficiency and accuracy of the sixth order compact scheme (SOC), compared with the previously published fourth order compact scheme (FOC).}, }
@article {pmid21132115, year = {2010}, author = {Laine-Pearson, FE and Hydon, PE}, title = {Alternating Flow in a Moving Corner.}, journal = {European journal of mechanics. B, Fluids}, volume = {29}, number = {4}, pages = {278-284}, pmid = {21132115}, issn = {0997-7546}, support = {R01 HL070542-05/HL/NHLBI NIH HHS/United States ; R01 HL070542/HL/NHLBI NIH HHS/United States ; R01 HL074022-05/HL/NHLBI NIH HHS/United States ; R01 HL054885-13/HL/NHLBI NIH HHS/United States ; R01 HL074022/HL/NHLBI NIH HHS/United States ; R01 HL054885/HL/NHLBI NIH HHS/United States ; }, abstract = {Recent experiments have shown that rapid kinematic mixing occurs in the pulmonary alveoli. Here the Reynolds number is very small, there is recirculation in the alveolar cavity and the alveolar walls move periodically. We have recently shown that non-diffusing particles move chaotically in a two-dimensional model flow with the above features. In parts of the lung, however, there is asynchrony between the wall motion and the ductal flow immediately outside the alveolus. The extent to which this asynchrony affects kinematic mixing in real alveoli is not yet known. The purpose of this paper is to describe the effect of asynchrony on chaotic advection in our two-dimensional model, in order to understand the circumstances in which this becomes significant.}, }
@article {pmid21112999, year = {2010}, author = {Ruck, S and Oertel, H}, title = {Fluid-structure interaction simulation of an avian flight model.}, journal = {The Journal of experimental biology}, volume = {213}, number = {Pt 24}, pages = {4180-4192}, doi = {10.1242/jeb.041285}, pmid = {21112999}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Birds/*physiology ; *Flight, Animal ; *Models, Biological ; Wings, Animal/physiology ; }, abstract = {A three-dimensional numerical avian model was developed to investigate the unsteady and turbulent aerodynamic performance of flapping wings for varying wingbeat frequencies and flow velocities (up to 12 Hz and 9 m s(-1)), corresponding to a reduced frequency range of k=0.22 to k=1.0 and a Reynolds number range of Re=16,000 to Re=50,000. The wings of the bird-inspired model consist of an elastic membrane. Simplifying the complicated locomotion kinematics to a sinusoidal wing rotation about two axes, the main features of dynamic avian flight were approximated. Numerical simulation techniques of fluid-structure interaction (FSI) providing a fully resolved flow field were applied to calculate the aerodynamic performance of the flapping elastic wings with the Reynolds averaged Navier-Stokes (RANS) approach. The results were used to characterize and describe the macroscopic flow configurations in terms of starting, stopping, trailing and bound vortices. For high reduced frequencies up to k=0.67 it was shown that the wake does not consist of individual vortex rings known as the discrete vortex ring gait. Rather, the wake is dominated by a chain of elliptical vortex rings on each wing. The structures are interlocked at the starting and stopping vortices, which are shed in pairs at the reversal points of the wingbeat cycle. For decreasing reduced frequency, the results indicate a transition to a continuous vortex gait. The upstroke becomes more aerodynamically active, leading to a consistent circulation of the bound vortex on the wing and a continuous spanwise shedding of small scale vortices. The formation of the vortices shed spanwise in pairs at the reversal points is reduced and the wake is dominated by the tip and root vortices, which form long drawn-out vortex structures.}, }
@article {pmid21096448, year = {2010}, author = {Khodarahmi, I and Shakeri, M and Sharp, M and Amini, AA}, title = {Using PIV to determine relative pressures in a stenotic phantom under steady flow based on the pressure-poisson equation.}, journal = {Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference}, volume = {2010}, number = {}, pages = {2594-2597}, doi = {10.1109/IEMBS.2010.5626676}, pmid = {21096448}, issn = {2375-7477}, mesh = {Aged ; Algorithms ; Angiography/methods ; Blood Flow Velocity/physiology ; Constriction, Pathologic/*pathology ; Equipment Design ; Humans ; Hydrodynamics ; Models, Cardiovascular ; Normal Distribution ; Phantoms, Imaging ; Poisson Distribution ; Pressure ; Reproducibility of Results ; Rheology/methods ; }, abstract = {Pressure gradient across a Gaussian-shaped 87% area stenosis phantom was estimated by solving the pressure Poisson equation (PPE) for a steady flow mimicking the blood flow through the human iliac artery. The velocity field needed to solve the pressure equation was obtained using particle image velocimetry (PIV). A steady flow rate of 46.9 ml/s was used, which corresponds to a Reynolds number of 188 and 595 at the inlet and stenosis throat, respectively (in the range of mean Reynolds number encountered in-vivo). In addition, computational fluid dynamics (CFD) simulation of the same flow was performed. Pressure drops across the stenosis predicted by PPE/PIV and CFD were compared with those measured by a pressure catheter transducer. RMS errors relative to the measurements were 17% and 10% for PPE/PIV and CFD, respectively.}, }
@article {pmid21095819, year = {2010}, author = {Garcia, J and Kadem, L and Pibarot, P}, title = {Silicone rubber trileaflet valve assessment using cardiovascular magnetic resonance imaging.}, journal = {Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference}, volume = {2010}, number = {}, pages = {5169-5172}, doi = {10.1109/IEMBS.2010.5626141}, pmid = {21095819}, issn = {2375-7477}, mesh = {Blood Flow Velocity/physiology ; Blood Pressure/physiology ; *Heart Valve Prosthesis ; Humans ; Magnetic Resonance Imaging/*methods ; Pulsatile Flow/physiology ; Silicone Elastomers/*chemistry ; }, abstract = {Hydrodynamic valve performance is usually evaluated by effective orifice area (EOA), geometric orifice area (GOA) and transvalvular pressure gradients (PG). Magnetic resonance imaging (MRI) is a very efficient tool for assessing these parameters. In this study, we evaluated a silicone rubber trileaflet valve using MRI. EOA, GOA and PG were evaluated under steady (12 l/min - 20 l/min) and pulsatile (5 l/min) flow conditions using continuity equation, planimetry and simplified Bernoulli's equation respectively; the contraction coefficient (Cc) and Reynolds number (Re) were also evaluated as hydrodynamic parameters. The highest EOAs were 0.75 cm(2) for steady flow conditions and 0.98 cm(2) for pulsatile flow. For pulsatile flow conditions greater GOA by planimetry was 1.43 cm(2). For both flow conditions the highest PGs were > 40 mmHg. Cc was on range from 0.8 to 0.86 under steady flow conditions and 0.68 for pulsatile flow at peak sytole. The Re was much greater than 2200 for all flow conditions. This study allowed the non invasive evaluation of a silicone rubber trileaflet valve under steady and pulsatile conditions with MRI in order to understand valve opening.}, }
@article {pmid21091515, year = {2011}, author = {Chen, Y and Sharp, MK}, title = {A strain-based flow-induced hemolysis prediction model calibrated by in vitro erythrocyte deformation measurements.}, journal = {Artificial organs}, volume = {35}, number = {2}, pages = {145-156}, doi = {10.1111/j.1525-1594.2010.01050.x}, pmid = {21091515}, issn = {1525-1594}, mesh = {Equipment Design ; *Erythrocyte Deformability ; Erythrocytes/*cytology/ultrastructure ; *Hemolysis ; Hemorheology ; Humans ; Microscopy/instrumentation ; Models, Biological ; Stress, Mechanical ; }, abstract = {Hemolysis is caused by fluid stresses in flows within hypodermic needles, blood pumps, artificial hearts, and other cardiovascular devices. Developers of cardiovascular devices may expend considerable time and effort in testing of prototypes, because there is currently insufficient understanding of how flow-induced cell damage occurs to accurately predict hemolysis. The objective of this project was to measure cell deformation in response to a range of flow conditions, and to develop a constitutive model correlating cell damage to fluid stresses. An experimental system was constructed to create Poiseuille flow under a microscope with velocities up to 4 m/s, Reynolds number to 200, and fluid stresses to 5000 dyn/cm(2). Pulsed laser illumination and a digital camera captured images of cells deformed by the flow. Equilibrium equations were developed to relate fluid stresses to cell membrane tension, and a viscoelastic membrane model was used to predict cell strain. Measurements of aspect ratio as a function of shear stress and duration of shear were used to calibrate the cell deformation model. Hemolysis prediction was incorporated with a threshold strain value for cell rupture. The new model provides an improved match to experimentally observed hemolytic stress thresholds, particularly at long exposure times, and may reduce the empiricism of hemolysis prediction.}, }
@article {pmid21087769, year = {2011}, author = {Wu, Y and Sun, D and Huang, W}, title = {Mechanical force characterization in manipulating live cells with optical tweezers.}, journal = {Journal of biomechanics}, volume = {44}, number = {4}, pages = {741-746}, doi = {10.1016/j.jbiomech.2010.10.034}, pmid = {21087769}, issn = {1873-2380}, mesh = {Computer Simulation ; Elastic Modulus/physiology ; *Models, Biological ; *Optical Tweezers ; Saccharomyces cerevisiae/*cytology/*physiology ; Stress, Mechanical ; }, abstract = {Laser trapping with optical tweezers is a noninvasive manipulation technique and has received increasing attentions in biological applications. Understanding forces exerted on live cells is essential to cell biomechanical characterizations. Traditional numerical or experimental force measurement assumes live cells as ideal objects, ignoring their complicated inner structures and rough membranes. In this paper, we propose a new experimental method to calibrate the trapping and drag forces acted on live cells. Binding a micro polystyrene sphere to a live cell and moving the mixture with optical tweezers, we can obtain the drag force on the cell by subtracting the drag force on the sphere from the total drag force on the mixture, under the condition of extremely low Reynolds number. The trapping force on the cell is then obtained from the drag force when the cell is in force equilibrium state. Experiments on numerous live cells demonstrate the effectiveness of the proposed force calibration approach.}, }
@article {pmid21082456, year = {2011}, author = {Teodósio, JS and Simões, M and Melo, LF and Mergulhão, FJ}, title = {Flow cell hydrodynamics and their effects on E. coli biofilm formation under different nutrient conditions and turbulent flow.}, journal = {Biofouling}, volume = {27}, number = {1}, pages = {1-11}, doi = {10.1080/08927014.2010.535206}, pmid = {21082456}, issn = {1029-2454}, mesh = {Biofilms/drug effects/*growth &amp; development ; Culture Media/chemistry ; Escherichia coli/*growth &amp; development/physiology ; Flow Cytometry/instrumentation ; Glucose/metabolism/*pharmacology ; Hydrodynamics ; Microscopy, Confocal ; Models, Biological ; Plankton/growth &amp; development ; Software ; Stress, Mechanical ; Water Movements ; }, abstract = {Biofilm formation is a major factor in the growth and spread of both desirable and undesirable bacteria as well as in fouling and corrosion. In order to simulate biofilm formation in industrial settings a flow cell system coupled to a recirculating tank was used to study the effect of a high (550 mg glucose l[-1]) and a low (150 mg glucose l[-1]) nutrient concentration on the relative growth of planktonic and attached biofilm cells of Escherichia coli JM109(DE3). Biofilms were obtained under turbulent flow (a Reynolds number of 6000) and the hydrodynamic conditions of the flow cell were simulated by using computational fluid dynamics. Under these conditions, the flow cell was subjected to wall shear stresses of 0.6 Pa and an average flow velocity of 0.4 m s[-1] was reached. The system was validated by studying flow development on the flow cell and the applicability of chemostat model assumptions. Full development of the flow was assessed by analysis of velocity profiles and by monitoring the maximum and average wall shear stresses. The validity of the chemostat model assumptions was performed through residence time analysis and identification of biofilm forming areas. These latter results were obtained through wall shear stress analysis of the system and also by assessment of the free energy of interaction between E. coli and the surfaces. The results show that when the system was fed with a high nutrient concentration, planktonic cell growth was favored. Additionally, the results confirm that biofilms adapt their architecture in order to cope with the hydrodynamic conditions and nutrient availability. These results suggest that until a certain thickness was reached nutrient availability dictated biofilm architecture but when that critical thickness was exceeded mechanical resistance to shear stress (ie biofilm cohesion) became more important.}, }
@article {pmid21082068, year = {2010}, author = {Tytell, ED and Borazjani, I and Sotiropoulos, F and Baker, TV and Anderson, EJ and Lauder, GV}, title = {Disentangling the functional roles of morphology and motion in the swimming of fish.}, journal = {Integrative and comparative biology}, volume = {50}, number = {6}, pages = {1140-1154}, pmid = {21082068}, issn = {1557-7023}, support = {FS32 NS054367/NS/NINDS NIH HHS/United States ; R01 NS054274/NS/NINDS NIH HHS/United States ; }, mesh = {Animal Fins/anatomy &amp; histology/physiology ; Animals ; Biomechanical Phenomena ; Body Size ; Computer Simulation ; Fishes/*anatomy &amp; histology/*physiology ; *Hydrodynamics ; Models, Biological ; Species Specificity ; *Swimming ; }, abstract = {In fishes the shape of the body and the swimming mode generally are correlated. Slender-bodied fishes such as eels, lampreys, and many sharks tend to swim in the anguilliform mode, in which much of the body undulates at high amplitude. Fishes with broad tails and a narrow caudal peduncle, in contrast, tend to swim in the carangiform mode, in which the tail undulates at high amplitude. Such fishes also tend to have different wake structures. Carangiform swimmers generally produce two staggered vortices per tail beat and a strong downstream jet, while anguilliform swimmers produce a more complex wake, containing at least two pairs of vortices per tail beat and relatively little downstream flow. Are these differences a result of the different swimming modes or of the different body shapes, or both? Disentangling the functional roles requires a multipronged approach, using experiments on live fishes as well as computational simulations and physical models. We present experimental results from swimming eels (anguilliform), bluegill sunfish (carangiform), and rainbow trout (subcarangiform) that demonstrate differences in the wakes and in swimming performance. The swimming of mackerel and lamprey was also simulated computationally with realistic body shapes and both swimming modes: the normal carangiform mackerel and anguilliform lamprey, then an anguilliform mackerel and carangiform lamprey. The gross structure of simulated wakes (single versus double vortex row) depended strongly on Strouhal number, while body shape influenced the complexity of the vortex row, and the swimming mode had the weakest effect. Performance was affected even by small differences in the wakes: both experimental and computational results indicate that anguilliform swimmers are more efficient at lower swimming speeds, while carangiform swimmers are more efficient at high speed. At high Reynolds number, the lamprey-shaped swimmer produced a more complex wake than the mackerel-shaped swimmer, similar to the experimental results. Finally, we show results from a simple physical model of a flapping fin, using fins of different flexural stiffness. When actuated in the same way, fins of different stiffnesses propel themselves at different speeds with different kinematics. Future experimental and computational work will need to consider the mechanisms underlying production of the anguilliform and carangiform swimming modes, because anguilliform swimmers tend to be less stiff, in general, than are carangiform swimmers.}, }
@article {pmid21080093, year = {2011}, author = {Hutchison, C and Sullivan, P and Ethier, CR}, title = {Measurements of steady flow through a bileaflet mechanical heart valve using stereoscopic PIV.}, journal = {Medical &amp; biological engineering &amp; computing}, volume = {49}, number = {3}, pages = {325-335}, pmid = {21080093}, issn = {1741-0444}, mesh = {Algorithms ; Blood Flow Velocity/physiology ; Coronary Circulation/physiology ; *Heart Valve Prosthesis ; Humans ; Models, Cardiovascular ; Prosthesis Design ; }, abstract = {Computational modeling of bileaflet mechanical heart valve (BiMHV) flow requires experimentally validated datasets and improved knowledge of BiMHV fluid mechanics. In this study, flow was studied downstream of a model BiMHV in an axisymmetric aortic sinus using stereoscopic particle image velocimetry. The inlet flow was steady and the Reynolds number based on the aortic diameter was 7600. Results showed the out-of-plane velocity was of similar magnitude as the transverse velocity. Although additional studies are needed for confirmation, analysis of the out-of-plane velocity showed the possible presence of a four-cell streamwise vortex structure in the mean velocity field. Spatial data for all six Reynolds stress components were obtained. Reynolds normal stress profiles revealed similarities between the central jet and free jets. These findings are important to BiMHV flow modeling, though clinical relevance is limited due to the idealized conditions chosen. To this end, the dataset is publicly available for CFD validation purposes.}, }
@article {pmid21072415, year = {2011}, author = {Choi, YS and Seo, KW and Lee, SJ}, title = {Lateral and cross-lateral focusing of spherical particles in a square microchannel.}, journal = {Lab on a chip}, volume = {11}, number = {3}, pages = {460-465}, doi = {10.1039/c0lc00212g}, pmid = {21072415}, issn = {1473-0189}, mesh = {Flow Cytometry ; Hydrodynamics ; *Lab-On-A-Chip Devices ; Microfluidic Analytical Techniques/*instrumentation/methods ; *Particle Size ; }, abstract = {The inertial migration of particles in micro-scale flows has received much attention due to its promising applications, such as the membrane-free passive separation of particles or cells. The particles suspended in rectangular channels are known to be focused near the center of each channel face as the channel Reynolds number (R(C)) increases due to the lift force balance and the hydrodynamic interactions of the particles with the wall. In this study, the three-dimensional positions of neutrally buoyant spherical particles inside a square microchannel are measured using the digital holographic microscopy technique, and a transition from the lateral tubular pinch to the cross-lateral focusing with increasing R(C) is reported. The particles are found to migrate first in the lateral direction and then cross-laterally toward the four equilibrium positions. A general criterion that can be used to secure the fully developed state of particle focusing in Lab-on-a-Chip applications is also derived. This criterion could be helpful for the accurate estimation of the design parameters of inertial microfluidic devices, such as R(C), channel length and width, and particle diameter.}, }
@article {pmid21047058, year = {2010}, author = {Wu, B}, title = {Computational fluid dynamics investigation of turbulence models for non-newtonian fluid flow in anaerobic digesters.}, journal = {Environmental science &amp; technology}, volume = {44}, number = {23}, pages = {8989-8995}, doi = {10.1021/es1010016}, pmid = {21047058}, issn = {1520-5851}, mesh = {Anaerobiosis ; Biodegradation, Environmental ; Flocculation ; Friction ; *Hydrodynamics ; Kinetics ; Manure ; *Models, Biological ; Models, Chemical ; Pressure ; Rheology ; Water Pollutants/*chemistry ; }, abstract = {In this paper, 12 turbulence models for single-phase non-newtonian fluid flow in a pipe are evaluated by comparing the frictional pressure drops obtained from computational fluid dynamics (CFD) with those from three friction factor correlations. The turbulence models studied are (1) three high-Reynolds-number k-ε models, (2) six low-Reynolds-number k-ε models, (3) two k-ω models, and (4) the Reynolds stress model. The simulation results indicate that the Chang-Hsieh-Chen version of the low-Reynolds-number k-ε model performs better than the other models in predicting the frictional pressure drops while the standard k-ω model has an acceptable accuracy and a low computing cost. In the model applications, CFD simulation of mixing in a full-scale anaerobic digester with pumped circulation is performed to propose an improvement in the effective mixing standards recommended by the U.S. EPA based on the effect of rheology on the flow fields. Characterization of the velocity gradient is conducted to quantify the growth or breakage of an assumed floc size. Placement of two discharge nozzles in the digester is analyzed to show that spacing two nozzles 180° apart with each one discharging at an angle of 45° off the wall is the most efficient. Moreover, the similarity rules of geometry and mixing energy are checked for scaling up the digester.}, }
@article {pmid21037110, year = {2010}, author = {Tytell, ED and Hsu, CY and Williams, TL and Cohen, AH and Fauci, LJ}, title = {Interactions between internal forces, body stiffness, and fluid environment in a neuromechanical model of lamprey swimming.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {107}, number = {46}, pages = {19832-19837}, pmid = {21037110}, issn = {1091-6490}, support = {F32 NS054367/NS/NINDS NIH HHS/United States ; R01 NS054271/NS/NINDS NIH HHS/United States ; }, mesh = {Animals ; Biomechanical Phenomena/physiology ; Computer Simulation ; *Environment ; Lampreys/*physiology ; *Models, Biological ; Muscle Contraction/physiology ; *Nervous System Physiological Phenomena ; *Rheology ; Swimming/*physiology ; Tail/physiology ; Viscosity ; }, abstract = {Animal movements result from a complex balance of many different forces. Muscles produce force to move the body; the body has inertial, elastic, and damping properties that may aid or oppose the muscle force; and the environment produces reaction forces back on the body. The actual motion is an emergent property of these interactions. To examine the roles of body stiffness, muscle activation, and fluid environment for swimming animals, a computational model of a lamprey was developed. The model uses an immersed boundary framework that fully couples the Navier-Stokes equations of fluid dynamics with an actuated, elastic body model. This is the first model at a Reynolds number appropriate for a swimming fish that captures the complete fluid-structure interaction, in which the body deforms according to both internal muscular forces and external fluid forces. Results indicate that identical muscle activation patterns can produce different kinematics depending on body stiffness, and the optimal value of stiffness for maximum acceleration is different from that for maximum steady swimming speed. Additionally, negative muscle work, observed in many fishes, emerges at higher tail beat frequencies without sensory input and may contribute to energy efficiency. Swimming fishes that can tune their body stiffness by appropriately timed muscle contractions may therefore be able to optimize the passive dynamics of their bodies to maximize peak acceleration or swimming speed.}, }
@article {pmid21036338, year = {2010}, author = {Fischer, MW and Stolze-Rybczynski, JL and Davis, DJ and Cui, Y and Money, NP}, title = {Solving the aerodynamics of fungal flight: how air viscosity slows spore motion.}, journal = {Fungal biology}, volume = {114}, number = {11-12}, pages = {943-948}, pmid = {21036338}, issn = {1878-6146}, support = {R15 ES016425/ES/NIEHS NIH HHS/United States ; 1R15 ES016425/ES/NIEHS NIH HHS/United States ; }, mesh = {Fungi/*chemistry/cytology ; Models, Biological ; Spores, Fungal/*chemistry/cytology ; Viscosity ; }, abstract = {Viscous drag causes the rapid deceleration of fungal spores after high-speed launches and limits discharge distance. Stokes' law posits a linear relationship between drag force and velocity. It provides an excellent fit to experimental measurements of the terminal velocity of free-falling spores and other instances of low Reynolds number motion (Re<1). More complex, non-linear drag models have been devised for movements characterized by higher Re, but their effectiveness for modeling the launch of fast-moving fungal spores has not been tested. In this paper, we use data on spore discharge processes obtained from ultra-high-speed video recordings to evaluate the effects of air viscosity predicted by Stokes' law and a commonly used non-linear drag model. We find that discharge distances predicted from launch speeds by Stokes' model provide a much better match to measured distances than estimates from the more complex drag model. Stokes' model works better over a wide range projectile sizes, launch speeds, and discharge distances, from microscopic mushroom ballistospores discharged at <1 m s(-1) over a distance of <0.1mm (Re<1.0), to macroscopic sporangia of Pilobolus that are launched at >10 m s(-1) and travel as far as 2.5m (Re>100).}, }
@article {pmid20957273, year = {2011}, author = {Sim, TS and Kwon, K and Park, JC and Lee, JG and Jung, HI}, title = {Multistage-multiorifice flow fractionation (MS-MOFF): continuous size-based separation of microspheres using multiple series of contraction/expansion microchannels.}, journal = {Lab on a chip}, volume = {11}, number = {1}, pages = {93-99}, doi = {10.1039/c0lc00109k}, pmid = {20957273}, issn = {1473-0189}, mesh = {Chemical Fractionation/*instrumentation ; Equipment Design ; Microfluidic Analytical Techniques/*instrumentation ; *Microspheres ; Particle Size ; }, abstract = {Previously we introduced a novel hydrodynamic method using a multi-orifice microchannel for size-based particle separation, which is called a multi-orifice flow fractionation (MOFF). The MOFF has several advantages such as continuous, non-intrusive, and minimal power consumption. However, it has a limitation that the recovery yield is relatively low. Although the recovery may be increased by adjusting parameters such as the Reynolds number and central collecting region, poor purity inevitably followed. We newly designed and fabricated a microfluidic channel for multi-stage multi-orifice flow fractionation (MS-MOFF), which is made by combining three multi-orifice segments, and consists of 3 inlets, 3 filters, 3 multi-orifice segments and 5 outlets. The structure and dimensions of the MS-MOFF were determined by the hydrodynamic principles to have constant Reynolds numbers at each multi-orifice segment. Polystyrene microspheres of two different sizes (7 μm and 15 μm) were tested. With this device, we made an attempt to improve recovery and minimize loss of purity by collecting and re-separating non-selected particles of the first separation. The final recovery successfully increased from 73.2% to 88.7% while the final purity slightly decreased from 91.4% to 89.1% (for 15 μm). These values were never achievable with the single-stage MOFF (SS-MOFF) having only one multi-orifice segment in our previous work. The MS-MOFF channel will be useful for clinical applications, such as separation of circulating tumor cells (CTC) or rare cells from human blood samples.}, }
@article {pmid20951576, year = {2011}, author = {Yu, L and Ma, J and Chen, S}, title = {Numerical simulation of mechanical mixing in high solid anaerobic digester.}, journal = {Bioresource technology}, volume = {102}, number = {2}, pages = {1012-1018}, doi = {10.1016/j.biortech.2010.09.079}, pmid = {20951576}, issn = {1873-2976}, mesh = {Anaerobiosis ; *Computer Simulation ; *Mechanical Phenomena ; *Numerical Analysis, Computer-Assisted ; Refuse Disposal/*instrumentation ; Rheology/*instrumentation ; Temperature ; }, abstract = {Computational fluid dynamics (CFD) was employed to study mixing performance in high solid anaerobic digester (HSAD) with A-310 impeller and helical ribbon. A mathematical model was constructed to assess flow fields. Good agreement of the model results with experimental data was obtained for the A-310 impeller. A systematic comparison for the interrelationship of power number, flow number and Reynolds number was simulated in a digester with less than 5% TS and 10% TS (total solids). The simulation results suggested a great potential for using the helical ribbon mixer in the mixing of high solids digester. The results also provided quantitative confirmation for minimum power consumption in HSAD and the effect of share rate on bio-structure.}, }
@article {pmid20887004, year = {2010}, author = {Johnson, TJ and Lang, AW and Wheelus, JN and Westcott, M}, title = {Low Reynolds number Couette flow facility for drag measurements.}, journal = {The Review of scientific instruments}, volume = {81}, number = {9}, pages = {095103}, doi = {10.1063/1.3480993}, pmid = {20887004}, issn = {1089-7623}, abstract = {For this study a new low Reynolds number Couette facility was constructed to investigate surface drag. In this facility, mineral oil was used as the working fluid to increase the shear stress across the surface of the experimental models. A mounted conveyor inside a tank creates a flow above which an experimental model of a flat plate was suspended. The experimental plate was attached to linear bearings on a slide system that connects to a force gauge used to measure the drag. Within the gap between the model and moving belt a Couette flow with a linear velocity profile was created. Digital particle image velocimetry was used to confirm the velocity profile. The drag measurements agreed within 5% of the theoretically predicted Couette flow value.}, }
@article {pmid20883758, year = {2011}, author = {Bai, G and Wang, Y and Armenante, PM}, title = {Velocity profiles and shear strain rate variability in the USP Dissolution Testing Apparatus 2 at different impeller agitation speeds.}, journal = {International journal of pharmaceutics}, volume = {403}, number = {1-2}, pages = {1-14}, doi = {10.1016/j.ijpharm.2010.09.022}, pmid = {20883758}, issn = {1873-3476}, mesh = {Chemistry, Pharmaceutical/*instrumentation ; Computer Simulation ; *Laser-Doppler Flowmetry ; Models, Chemical ; *Pharmaceutical Preparations/chemistry/standards ; Pharmacopoeias as Topic ; *Shear Strength ; Solubility ; Solutions ; United States ; }, abstract = {The fluid velocity profiles at different locations inside a standard USP Dissolution Testing Apparatus 2 were experimentally obtained via Laser Doppler Velocimetry (LDV) at three impeller agitations speeds, namely 50rpm, 75rpm and 100rpm. The experimental results were compared with the predictions obtained with Computational Fluid Dynamics (CFD) where the κ-ω model with low Reynolds number correction was used to account for turbulence effects. In general, good agreement was found between the experimental LDV velocity measurements and the CFD simulation predictions. The non-dimensional tangential, axial and radial velocity profiles (scaled with the impeller tip speed) and the flow pattern were found to be nearly independent of the agitation speed in most regions of the vessel, implying that increasing the agitation speed generally produced a corresponding increase in the local values of the velocity. However, the velocity profiles and flow pattern in the inner core region just below the impeller, where the dissolving tablet is usually located, were found to be much less sensitive to agitation speed. In this region, the axial and radial velocities were especially low and were not significantly affected by agitation increases. This inner core region at the center of the vessel bottom persisted irrespective of agitation intensity. The CFD predictions also indicated that increasing the agitation speed resulted in a higher shear strain rate distribution along the vessel bottom, although the strain rate was always very low at the center of the vessel bottom, even when the agitation speed was increased.}, }
@article {pmid20873764, year = {2010}, author = {Zhang, L and Petit, T and Lu, Y and Kratochvil, BE and Peyer, KE and Pei, R and Lou, J and Nelson, BJ}, title = {Controlled propulsion and cargo transport of rotating nickel nanowires near a patterned solid surface.}, journal = {ACS nano}, volume = {4}, number = {10}, pages = {6228-6234}, doi = {10.1021/nn101861n}, pmid = {20873764}, issn = {1936-086X}, mesh = {Colloids/chemistry ; *Drug Delivery Systems ; Electrochemistry/methods ; Magnetics ; Microscopy, Electron, Scanning/methods ; Microscopy, Electron, Transmission/methods ; Nanowires/*chemistry ; Nickel/chemistry ; Silicon/chemistry ; Software ; Surface Properties ; Water/chemistry ; }, abstract = {We show that rotating Ni nanowires are capable of propulsion and transport of colloidal cargo near a complex surface. When dissimilar boundary conditions exist at the two ends of a nanowire, such as when a nanowire is near a wall, tumbling motion can be generated that leads to propulsion of the nanowire. The motion of the nanowire can be precisely controlled using a uniform rotating magnetic field. We investigate the propulsion mechanism and the trajectory of the nanowire during the tumbling motion and demonstrate cargo transport of a polystyrene microbead by the nanowire over a flat surface or across an open microchannel. The results imply that functionalized, ferromagnetic one-dimensional, tumbling nanostructures can be used for cell manipulation and targeted drug delivery in a low Reynolds number aqueous environment.}, }
@article {pmid20868101, year = {2010}, author = {Ardekani, AM and Stocker, R}, title = {Stratlets: low Reynolds number point-force solutions in a stratified fluid.}, journal = {Physical review letters}, volume = {105}, number = {8}, pages = {084502}, doi = {10.1103/PhysRevLett.105.084502}, pmid = {20868101}, issn = {1079-7114}, mesh = {*Hydrodynamics ; *Models, Theoretical ; }, abstract = {We present fundamental solutions of low Reynolds number flows in a stratified fluid, including the case of a point force (Stokeslet) and a doublet. Stratification dramatically alters the flow by creating toroidal eddies, and velocity decays much faster than in a homogeneous fluid. The fundamental length scale is set by the competition of buoyancy, diffusion and viscosity, and is O(100 μm-1 mm) in aquatic environments. Stratification can therefore affect the swimming of small organisms and the sinking of marine snow particles, and diminish the effectiveness of mechanosensing in the ocean.}, }
@article {pmid20867846, year = {2010}, author = {Rempel, EL and Lesur, G and Proctor, MR}, title = {Supertransient magnetohydrodynamic turbulence in Keplerian shear flows.}, journal = {Physical review letters}, volume = {105}, number = {4}, pages = {044501}, doi = {10.1103/PhysRevLett.105.044501}, pmid = {20867846}, issn = {1079-7114}, abstract = {A subcritical transition to turbulence in magnetized Keplerian shear flows is investigated by using a statistical approach. Three-dimensional numerical simulations of the shearing box equations with zero net magnetic flux are employed to determine the transition from decaying to sustained turbulence as a function of the magnetic Reynolds number R{m}. The results reveal no clear transition to sustained turbulence as the average lifetime of the transients grows as an exponential function of R{m}, in accordance with a type-II supertransient law.}, }
@article {pmid20867483, year = {2010}, author = {Golestanian, R}, title = {Synthetic mechanochemical molecular swimmer.}, journal = {Physical review letters}, volume = {105}, number = {1}, pages = {018103}, doi = {10.1103/PhysRevLett.105.018103}, pmid = {20867483}, issn = {1079-7114}, mesh = {*Biomimetics ; Catalysis ; Hydrodynamics ; *Mechanical Phenomena ; Models, Chemical ; Molecular Conformation ; *Motion ; Static Electricity ; Stochastic Processes ; Thermodynamics ; }, abstract = {A minimal design for a molecular swimmer is proposed that is based on a mechanochemical propulsion mechanism. Conformational changes are induced by electrostatic actuation when specific parts of the molecule temporarily acquire net charges through catalyzed chemical reactions involving ionic components. The mechanochemical cycle is designed such that the resulting conformational changes would be sufficient for achieving low Reynolds number propulsion. The system is analyzed within the recently developed framework of stochastic swimmers to take account of the noisy environment at the molecular scale. The swimming velocity of the device is found to depend on the concentration of the fuel molecule according to the Michaelis-Menten rule in enzymatic reactions.}, }
@article {pmid20867145, year = {2010}, author = {Roullet, G and Klein, P}, title = {Cyclone-anticyclone asymmetry in geophysical turbulence.}, journal = {Physical review letters}, volume = {104}, number = {21}, pages = {218501}, doi = {10.1103/PhysRevLett.104.218501}, pmid = {20867145}, issn = {1079-7114}, abstract = {We address the problem of cyclone-anticyclone asymmetry in geophysical turbulence using a direct numerical simulation with high Reynolds number Re∼15,000 that includes an active upper boundary and interior dynamics. The regime, characterized by a finite Rossby number (Ro∼0.6) strongly departs from the classical quasigeostrophic regime. The numerical resolution is pushed to the limit of today's supercomputer capabilities ensuring more than two decades free of viscous effects. The results show a strong cyclonic dominance in the upper layers that is stronger for filaments than for vortices. This is in contrast with similar studies that have no active upper boundary which reported either anticyclone dominance or a symmetry between cyclones and anticyclones in the upper layers. This highlights the impact of boundary dynamics on geophysical turbulence.}, }
@article {pmid20866944, year = {2010}, author = {Khaderi, SN and Baltussen, MG and Anderson, PD and den Toonder, JM and Onck, PR}, title = {Breaking of symmetry in microfluidic propulsion driven by artificial cilia.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {2 Pt 2}, pages = {027302}, doi = {10.1103/PhysRevE.82.027302}, pmid = {20866944}, issn = {1550-2376}, mesh = {Biomimetics/*methods ; Cilia/*physiology ; *Hydrodynamics ; *Microfluidics ; Models, Biological ; }, abstract = {In this Brief Report we investigate biomimetic fluid propulsion due to an array of periodically beating artificial cilia. A generic model system is defined in which the effects of inertial fluid forces and the spatial, temporal, and orientational asymmetries of the ciliary motion can be individually controlled. We demonstrate that the so-far unexplored orientational asymmetry plays an important role in generating flow and that the flow increases sharply with Reynolds number and eventually becomes unidirectional. We introduce the concept of configurational symmetry that unifies the spatial, temporal, and orientational symmetries. The breaking of configurational symmetry leads to fluid propulsion in microfluidic channels.}, }
@article {pmid20866925, year = {2010}, author = {Grappin, R and Müller, WC}, title = {Scaling and anisotropy in magnetohydrodynamic turbulence in a strong mean magnetic field.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {2 Pt 2}, pages = {026406}, doi = {10.1103/PhysRevE.82.026406}, pmid = {20866925}, issn = {1550-2376}, abstract = {We present an analysis of the anisotropic spectral energy distribution in incompressible magnetohydrodynamic turbulence permeated by a strong mean magnetic field. The turbulent flow is generated by high-resolution pseudospectral direct numerical simulations with large-scale isotropic forcing. Examining the radial energy distribution for various angles θ with respect to B0 reveals a specific structure which remains hidden when not taking axial symmetry with respect to B0 into account. For each direction, starting at the forced large scales, the spectrum first exhibits an amplitude drop around a wave number k0 which marks the start of a scaling range and goes on up to a dissipative wave number k(d)(θ). The three-dimensional spectrum for k≥k0 is described by a single θ-independent functional form F(k/k(d)), with the scaling law being the same in every direction. The previous properties still hold when increasing the mean field from B0=5 up to B0=10b(rms), as well as when passing from resistive to ideal flows. We conjecture that at fixed B0 the direction-independent scaling regime is reached when increasing the Reynolds number above a threshold which raises with increasing B0. Below that threshold critically balanced turbulence is expected.}, }
@article {pmid20866914, year = {2010}, author = {Duguet, Y and Brandt, L and Larsson, BR}, title = {Towards minimal perturbations in transitional plane Couette flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {2 Pt 2}, pages = {026316}, doi = {10.1103/PhysRevE.82.026316}, pmid = {20866914}, issn = {1550-2376}, abstract = {For parallel shear flows, transition to turbulence occurs only for perturbations of sufficiently large amplitude. It is therefore relevant to study the shape, amplitude, and dynamics of the least energetic initial disturbances leading to transition. We suggest a numerical approach to find such minimal perturbations, applied here to the case of plane Couette flow. The optimization method seeks such perturbations at initial time as a linear combination of a finite number of linear optimal modes. The energy threshold of the minimal perturbation for a Reynolds number Re=400 is only 2% less than for a pair of symmetric oblique waves. The associated transition scenario shows a long transient approach to a steady state solution with special symmetries. Modal analysis shows how the oblique-wave mechanism can be optimized by the addition of other oblique modes breaking the flow symmetry and whose nonlinear interaction generates spectral components of the edge state. The Re dependence of energy thresholds is revisited, with evidence for a O(Re(-2)) -scaling for both oblique waves and streamwise vortices scenarios.}, }
@article {pmid20866913, year = {2010}, author = {Cantwell, CD and Barkley, D}, title = {Computational study of subcritical response in flow past a circular cylinder.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {2 Pt 2}, pages = {026315}, doi = {10.1103/PhysRevE.82.026315}, pmid = {20866913}, issn = {1550-2376}, abstract = {Flow past a circular cylinder is investigated in the subcritical regime, below the onset of Bénard-von Kármán vortex shedding at Reynolds number Re(c)≃47 . The transient response of infinitesimal perturbations is computed. The domain requirements for obtaining converged results is discussed at length. It is shown that energy amplification occurs as low as Re=2.2 . Throughout much of the subcritical regime the maximum energy amplification increases approximately exponentially in the square of Re reaching 6800 at Re(c). The spatiotemporal structure of the optimal transient dynamics is shown to be transitory Bénard-von Kármán vortex streets. At Re≃42 the long-time structure switches from exponentially increasing downstream to exponentially decaying downstream. Three-dimensional computations show that two-dimensional structures dominate the energy growth except at short times.}, }
@article {pmid20866901, year = {2010}, author = {Belan, M and De Ponte, S and Tordella, D}, title = {Highly underexpanded jets in the presence of a density jump between an ambient gas and a jet.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {2 Pt 2}, pages = {026303}, doi = {10.1103/PhysRevE.82.026303}, pmid = {20866901}, issn = {1550-2376}, abstract = {An experimental research concerning highly underexpanded jets made of different gases from the surrounding ambient is here described. By selecting different species of gases, it was possible to vary the jet-to-ambient density ratio in the 0.04-12 range and observe its effect on the jet morphology. By adjusting the stagnation and ambient pressures, it has been possible to select the Mach number of the jets, independently from the density ratio. Each jet is therefore characterized by its maximum Mach number, ranging from 10 to 50. The Reynolds number range of the nozzle is 10(3)-5×10(4). The spatial evolution of the jets was observed over a much larger scale than the nozzle diameter. The gas densities were evaluated from the light emission induced by an electron beam and the gas concentrations were obtained by analyzing the color of the emitted light. The results have shown that the morphology of the jets depends to a greater extent on the density ratio. Jets that are lighter than the ambient exhibit a more intense jet-ambient mixing than jets that are heavier than the ambient, while the effects of changing the jet Mach number do not seem to be too large in the explored range. These results can be expressed by means of two simple scaling laws relevant to the near field (pre-Mach-disk) and the mid-long term field (post-Mach-disk), respectively.}, }
@article {pmid20866899, year = {2010}, author = {Tian, FB and Luo, H and Zhu, L and Lu, XY}, title = {Interaction between a flexible filament and a downstream rigid body.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {2 Pt 2}, pages = {026301}, doi = {10.1103/PhysRevE.82.026301}, pmid = {20866899}, issn = {1550-2376}, abstract = {A filament flapping in the bow wake of a rigid body is considered in order to study the hydrodynamic interaction between flexible and rigid bodies in tandem arrangement. Both numerical and experimental methods are adopted to analyze the motion of the filament, and the drag force on both bodies is computed. It is shown that the results largely depend on the gap between the two objects and the Reynolds number. The flexible body may have larger vibration amplitude but meanwhile experience a reduced drag force. On the other hand, the trailing rigid body enjoys a drag reduction. The qualitative behavior of the filament is independent of the filament's length and mass ratio or the shape of the rigid body for the parameter regime considered. The result is in contrast with the interaction between two rigid or two flexible objects in tandem arrangement, and it may provide a physical insight into the understanding of the aquatic animals swimming in the bow wake of ships or staying in the bow wake of stationary structures.}, }
@article {pmid20866737, year = {2010}, author = {Rüdiger, G and Gellert, M and Schultz, M and Hollerbach, R}, title = {Dissipative Taylor-Couette flows under the influence of helical magnetic fields.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {1 Pt 2}, pages = {016319}, doi = {10.1103/PhysRevE.82.016319}, pmid = {20866737}, issn = {1550-2376}, abstract = {The linear stability of magnetohydrodynamic Taylor-Couette flows in axially unbounded cylinders is considered for magnetic Prandtl number unity. Magnetic background fields varying from purely axial to purely azimuthal are imposed, with a general helical field parametrized by β=B(ϕ)/B(z). We map out the transition from the standard magnetorotational instability (MRI) for β=0 to the nonaxisymmetric azimuthal magnetorotational instability for β→∞. For finite β, positive and negative wave numbers m , corresponding to right and left spirals, are no longer degenerate. For the nonaxisymmetric modes, the most unstable mode spirals in the opposite direction to the background field. The standard (β=0) MRI is axisymmetric for weak fields (including the instability with the lowest Reynolds number) but is nonaxisymmetric for stronger fields. If the azimuthal field is due in part to an axial current flowing through the fluid itself (and not just along the central axis), then it is also unstable to the nonaxisymmetric Tayler instability which is most effective without rotation. For purely toroidal fields the solutions for m=±1 are identical so that in this case no preferred helicity results. For large β the wave number m=-1 is preferred, whereas for β≲1 the mode with m=-2 is most unstable. The most unstable modes always spiral in the same direction as the background field. For background fields with positive and not too large β the kinetic helicity of the fluctuations proves to be negative for all the magnetic instabilities considered.}, }
@article {pmid20866723, year = {2010}, author = {Uma, B and Usha, R}, title = {Electrified film on a porous inclined plane: dynamics and stability.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {1 Pt 2}, pages = {016305}, doi = {10.1103/PhysRevE.82.016305}, pmid = {20866723}, issn = {1550-2376}, abstract = {The time evolution of a thin conducting liquid film flowing down a porous inclined substrate is investigated when an electric field acts normal to the substrate. It is assumed that the flow through the porous medium is governed by Darcy's law together with Beavers-Joseph condition. Under the assumption of small permeability relative to the thickness of the overlying fluid layer, the flow is decoupled from the filtration flow through the porous medium. A slip condition at the bottom is used to incorporate the effects of the permeability of the substrate. From the set of exact averaged equations derived using integral boundary method for the film thickness and for the flow rate, a nonlinear evolution equation for the film thickness is derived through a long-wave approximation. A linear stability analysis of the base flow is performed and the critical Reynolds number is obtained. The results reveal that the substrate porosity in general destabilizes the liquid film flow and the presence of the electric field enhances this destabilizing effect. A weakly nonlinear stability analysis divulges the existence of supercritical stable and subcritical unstable zones in the wave number/Reynolds number parameter space and the results demonstrate how the neutral curves change as the intensity of the electric filed or the permeability of the porous medium is varied. The numerical solution of the nonlinear evolution equation in a periodic domain reveals that the base flow yields to surface structures that are either time independent waves of permanent form that propagate or time-dependent modes that oscillate slightly in the amplitude. Further, it is observed that the shape and amplitude of long-time waveforms are influenced by the permeability of the porous medium as well as by the applied electric field. The results reveal that the destabilization induced by the electric field in an otherwise stable film over a porous medium is exhibited in the form of traveling waves of finite amplitude. The presence of the porous substrate promotes the oscillatory behavior of the long-time waveform; however, the electric field has a tendency to suppress this oscillatory behavior.}, }
@article {pmid20866679, year = {2010}, author = {Olla, P}, title = {Passive swimming in low-Reynolds-number flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {1 Pt 2}, pages = {015302}, doi = {10.1103/PhysRevE.82.015302}, pmid = {20866679}, issn = {1550-2376}, abstract = {The possibility of microscopic swimming by extraction of energy from an external flow is discussed, focusing on the migration of a simple trimer across a linear shear flow. The geometric properties of swimming, together with the possible generalization to the case of a vesicle, are analyzed. The mechanism of energy extraction from the flow appears to be the generalization to a discrete swimmer of the tank-treading regime of a vesicle. The swimmer takes advantage of the external flow by both extracting energy for swimming and "sailing" through it. The migration velocity is found to scale linearly in the stroke amplitude, and not quadratically as in a quiescent fluid. This effect turns out to be connected with the nonapplicability of the scallop theorem in the presence of external flow fields.}, }
@article {pmid20866556, year = {2010}, author = {Kulkarni, SD and Metzger, B and Morris, JF}, title = {Particle-pressure-induced self-filtration in concentrated suspensions.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {82}, number = {1 Pt 1}, pages = {010402}, doi = {10.1103/PhysRevE.82.010402}, pmid = {20866556}, issn = {1550-2376}, abstract = {Gravity-driven flow of concentrated suspensions (solid volume fraction ϕ>0.50) of non-brownian spherical particles through a channel contraction at low Reynolds number is studied experimentally. The abrupt change in the flow area at the contraction forms distinct shear-rate regions having different fluid pressures, which are related to the concept of particle pressure. A model involving particle pressure variation coupled to a Darcy-like behavior for the fluid captures the phenomenon of "self-filtration," in which the effluent material has lower solid fraction than the input suspension. For ϕ≐ϕ crit ≈ 0.58, under added load from a weighted piston, the flow periodically alternates between fast and slow motions.}, }
@article {pmid20866546, year = {2010}, author = {Ohkitani, K and Al Sulti, F}, title = {Quantification of topological changes of vorticity contours in two-dimensional Navier-Stokes flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {6 Pt 2}, pages = {067302}, doi = {10.1103/PhysRevE.81.067302}, pmid = {20866546}, issn = {1550-2376}, abstract = {A characterization of reconnection of vorticity contours is made by direct numerical simulations of the two-dimensional Navier-Stokes flow at a relatively low Reynolds number. We identify all the critical points of the vorticity field and classify them by solving an eigenvalue problem of its Hessian matrix on the basis of critical-point theory. The numbers of hyperbolic (saddles) and elliptic (minima and maxima) points are confirmed to satisfy Euler's index theorem numerically. Time evolution of these indices is studied for a simple initial condition. Generally speaking, we have found that the indices are found to decrease in number with time. This result is discussed in connection with related works on streamline topology, in particular, the relationship between stagnation points and the dissipation. Associated elementary procedures in physical space, the merging of vortices, are studied in detail for a number of snapshots. A similar analysis is also done using the stream function.}, }
@article {pmid20866545, year = {2010}, author = {Najafi, A and Zargar, R}, title = {Two-sphere low-Reynolds-number propeller.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {6 Pt 2}, pages = {067301}, doi = {10.1103/PhysRevE.81.067301}, pmid = {20866545}, issn = {1550-2376}, mesh = {Bacterial Physiological Phenomena ; *Hydrodynamics ; Kinetics ; *Models, Biological ; *Motion ; Swimming ; }, abstract = {A three-dimensional model of a low-Reynolds-number swimmer is introduced and analyzed in this Brief Report. This model consists of two large and small spheres connected by two perpendicular thin rods. The geometry of this system is motivated by the microorganisms that use a single tail to swim; the large sphere represents the head of microorganism and the small sphere resembles its tail. Each rod changes its length and orientation in a nonreciprocal manner that effectively propels the system. Translational and rotational velocities of the swimmer are studied for different values of parameters. Our findings show that by changing the parameters we can adjust both the velocity and the direction of motion of the swimmer.}, }
@article {pmid20866523, year = {2010}, author = {Kang, CW and Quan, S and Lou, J}, title = {Numerical study of a Taylor bubble rising in stagnant liquids.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {6 Pt 2}, pages = {066308}, doi = {10.1103/PhysRevE.81.066308}, pmid = {20866523}, issn = {1550-2376}, abstract = {The dynamics of a Taylor bubble rising in stagnant liquids is numerically investigated using a front tracking coupled with finite difference method. Parametric studies on the dynamics of the rising Taylor bubble including the final shape, the Reynolds number (Re(T)), the Weber number (We(T)), the Froude number (Fr), the thin liquid film thickness (w/D), and the wake length (l(w)/D) are carried out. The effects of density ratio (η), viscosity ratio (λ), Eötvös number (Eo), and Archimedes number (Ar) are examined. The simulations demonstrate that the density ratio and the viscosity ratio under consideration have minimal effect on the dynamics of the Taylor bubble. Eötvös number and Archimedes number influence the elongation of the tail and the wake structures, where higher Eo and Ar result in longer wake. To explain the sudden extension of the tail, a Weber number (We(l)) based on local curvature and velocity is evaluated and a critical We(l) is detected around unity. The onset of flow separation at the wake occurs in between Ar=2×10(3) and Ar=1×10(4), which corresponds to Re(T) between 13.39 and 32.55. Archimedes number also drastically affects the final shape of Taylor bubble, the terminal velocity, the thickness of thin liquid film, as well as the wall shear stress. It is found that w/D=0.32 Ar(-0.1).}, }
@article {pmid20866330, year = {2010}, author = {Rimbert, N}, title = {Simple model for turbulence intermittencies based on self-avoiding random vortex stretching.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {5 Pt 2}, pages = {056315}, doi = {10.1103/PhysRevE.81.056315}, pmid = {20866330}, issn = {1550-2376}, abstract = {Whether statistics of intermittencies (between small and large eddies) in homogeneous and isotropic turbulence should be described by a logarithmic-Poisson, a logarithmic-stable probability density function, or other is still debated nowadays. In this paper, a bridge between polymer physics, self-avoiding walk, and random vortex stretching is established which may help to obtain new insights on this topic. A very simple relationship between the stability index of the Lévy stable law and Flory's exponent stemming from statistics of linear polymer growth is established. Moreover, the scaling of turbulence intermittencies with Reynolds number is also explained and the overall picture is given of smallest vortex tubes of Kolmogorov length width (i.e., the smallest dissipative eddies) bent by bigger vortices of Taylor length scale (i.e., the mean dissipative eddies), themselves stretched by the bigger eddies in a continuous cascade. This results in both a simple and sound model with no fitting parameters required.}, }
@article {pmid20866319, year = {2010}, author = {Masoud, H and Alexeev, A}, title = {Resonance of flexible flapping wings at low Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {5 Pt 2}, pages = {056304}, doi = {10.1103/PhysRevE.81.056304}, pmid = {20866319}, issn = {1550-2376}, abstract = {Using three-dimensional computer simulations, we examine hovering aerodynamics of flexible planar wings oscillating at resonance. We model flexible wings as tilted elastic plates whose sinusoidal plunging motion is imposed at the plate root. Our simulations reveal that large-amplitude resonance oscillations of elastic wings drastically enhance aerodynamic lift and efficiency of low-Reynolds-number plunging. Driven by a simple sinusoidal stroke, flexible wings at resonance generate a hovering force comparable to that of small insects that employ a very efficient but much more complicated stroke kinematics. Our results indicate the feasibility of using flexible wings driven by a simple harmonic stroke for designing efficient microscale flying machines.}, }
@article {pmid20855154, year = {2010}, author = {Dizge, N and Tansel, B}, title = {External mass transfer analysis for simultaneous removal of carbohydrate and protein by immobilized activated sludge culture in a packed bed batch bioreactor.}, journal = {Journal of hazardous materials}, volume = {184}, number = {1-3}, pages = {671-677}, doi = {10.1016/j.jhazmat.2010.08.090}, pmid = {20855154}, issn = {1873-3336}, mesh = {*Bioreactors ; Carbohydrates/*isolation &amp; purification ; Proteins/*isolation &amp; purification ; *Sewage ; }, abstract = {External mass transfer effects were analyzed for removal of carbohydrate and protein by immobilized activated sludge culture in a packed bed bioreactor. The bioreactor was made from 52 cm glass tubing with 5.0 cm inner diameter (with a total volume of 1020 cm(3)). The microbial culture was immobilized on microporus polyurethane cut into cubic pieces of approximately 1.5 cm in length. The effect of flow rate on mass transfer and removal of carbohydrate and protein were analyzed theoretically and compared with experimental data. The rate constants were estimated using external film diffusion models at different flow rates (900, 1200, 1800 cm(3)h(-1)). Based on the experimental data, correlations between the Colburn factor (J(D)) and Reynolds number (Re) as J(D)=5.7 × Re(-0.90) and J(D)=5.7 × Re(-0.18) were found to be adequate to predict the removal of carbohydrate and protein, respectively.}, }
@article {pmid20839859, year = {2010}, author = {Liu, L and Li, WW and Sheng, GP and Liu, ZF and Zeng, RJ and Liu, JX and Yu, HQ and Lee, DJ}, title = {Microscale hydrodynamic analysis of aerobic granules in the mass transfer process.}, journal = {Environmental science &amp; technology}, volume = {44}, number = {19}, pages = {7555-7560}, doi = {10.1021/es1021608}, pmid = {20839859}, issn = {1520-5851}, mesh = {Aerobiosis ; Microscopy, Confocal ; Solubility ; *Water Movements ; Water Pollutants/chemistry ; }, abstract = {The internal structure of aerobic granules has a significant impact on the hydrodynamic performance and mass transfer process, and severely affects the efficiency and stability of granules-based reactors for wastewater treatment. In this study, for the first time the granule complex structure was correlated with the hydrodynamic performance and substrates reactions process. First, a series of multiple fluorescence stained confocal laser scanning microscopy images of aerobic granules were obtained. Then, the form and structure of the entire granule was reconstructed. A three-dimensional computational fluid dynamics study was carried out for the hydrodynamic analysis. Two different models were developed on the basis of different fluorescence stained confocal laser scanning microscopy images to elucidate the roles of the granule structure in the hydrodynamic and mass transfer processes of aerobic granules. The fluid flow behavior, such as the velocity profiles, the pathlines and hence the hydrodynamic drag force, exerted on the granule in a Newtonian fluid, was studied by varying the Reynolds number. Furthermore, the spatial distribution of dissolved nutrients (e.g., oxygen) was acquired by solving the convection-diffusion equations on the basis of the reconstructed granule structure. This study demonstrates that the reconstructed granule model could offer a better understanding to the mass transfer process of aerobic granules than simply considering the granule structure to be homogeneous.}, }
@article {pmid20838481, year = {2010}, author = {Tasoglu, S and Kaynak, G and Szeri, AJ and Demirci, U and Muradoglu, M}, title = {Impact of a compound droplet on a flat surface: A model for single cell epitaxy.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {22}, number = {8}, pages = {}, pmid = {20838481}, issn = {1070-6631}, support = {R21 EB007707/EB/NIBIB NIH HHS/United States ; }, abstract = {The impact and spreading of a compound viscous droplet on a flat surface are studied computationally using a front-tracking method as a model for the single cell epitaxy. This is a technology developed to create two-dimensional and three-dimensional tissue constructs cell by cell by printing cell-encapsulating droplets precisely on a substrate using an existing ink-jet printing method. The success of cell printing mainly depends on the cell viability during the printing process, which requires a deeper understanding of the impact dynamics of encapsulated cells onto a solid surface. The present study is a first step in developing a model for deposition of cell-encapsulating droplets. The inner droplet representing the cell, the encapsulating droplet, and the ambient fluid are all assumed to be Newtonian. Simulations are performed for a range of dimensionless parameters to probe the deformation and rate of deformation of the encapsulated cell, which are both hypothesized to be related to cell damage. The deformation of the inner droplet consistently increases: as the Reynolds number increases; as the diameter ratio of the encapsulating droplet to the cell decreases; as the ratio of surface tensions of the air-solution interface to the solution-cell interface increases; as the viscosity ratio of the cell to encapsulating droplet decreases; or as the equilibrium contact angle decreases. It is observed that maximum deformation for a range of Weber numbers has (at least) one local minimum at We=2. Thereafter, the effects of cell deformation on viability are estimated by employing a correlation based on the experimental data of compression of cells between parallel plates. These results provide insight into achieving optimal parameter ranges for maximal cell viability during cell printing.}, }
@article {pmid20802127, year = {2010}, author = {Hansen, BW and Jakobsen, HH and Andersen, A and Almeda, R and Pedersen, TM and Christensen, AM and Nilsson, B}, title = {Swimming behavior and prey retention of the polychaete larvae Polydora ciliata (Johnston).}, journal = {The Journal of experimental biology}, volume = {213}, number = {Pt 18}, pages = {3237-3246}, doi = {10.1242/jeb.038810}, pmid = {20802127}, issn = {1477-9145}, mesh = {Animals ; Hydrodynamics ; Larva/anatomy &amp; histology/*physiology ; Particle Size ; Polychaeta/anatomy &amp; histology/*physiology ; Predatory Behavior/*physiology ; Swimming/*physiology ; }, abstract = {The behavior of the ubiquitous estuarine planktotrophic spionid polychaete larvae Polydora ciliata was studied. We describe ontogenetic changes in morphology, swimming speed and feeding rates and have developed a simple swimming model using low Reynolds number hydrodynamics. In the model we assumed that the ciliary swimming apparatus is primarily composed of the prototroch and secondarily by the telotroch. The model predicted swimming speeds and feeding rates that corresponded well with the measured speeds and rates. Applying empirical data to the model, we were able to explain the profound decrease in specific feeding rates and the observed increase in the difference between upward and downward swimming speeds with larval size. We estimated a critical larval length above which the buoyancy-corrected weight of the larva exceeds the propulsion force generated by the ciliary swimming apparatus and thus forces the larva to the bottom. This modeled critical larval length corresponded to approximately 1 mm, at which, according to the literature, competence for metamorphosis and no more length increase is observed. These findings may have general implications for all planktivorous polychaete larvae that feed without trailing threads. We observed bell shaped particle retention spectra with a minimum prey size of approximately 4 microm equivalent spherical diameter, and we found that an ontogenetic increase in maximum prey size add to a reduction in intra-specific food competition in the various larval stages. In a grazing experiment using natural seawater, ciliates were cleared approximately 50% more efficiently than similar sized dinoflagellates. The prey sizes retainable for P. ciliata larvae covers the microplankton fraction and includes non-motile as well as motile prey items, which is why the larvae are trophically positioned among the copepods and dinoflagellates. Not only do larval morphology and behavior govern larval feeding, prey behavior also influences the feeding efficiency of Polydora ciliata.}, }
@article {pmid20710067, year = {2010}, author = {Moslemi, AA and Krueger, PS}, title = {Propulsive efficiency of a biomorphic pulsed-jet underwater vehicle.}, journal = {Bioinspiration &amp; biomimetics}, volume = {5}, number = {3}, pages = {036003}, doi = {10.1088/1748-3182/5/3/036003}, pmid = {20710067}, issn = {1748-3190}, mesh = {Animals ; Biomimetic Materials ; Decapodiformes/*physiology ; Equipment Design ; Kinetics ; *Models, Biological ; *Robotics ; Swimming/*physiology ; }, abstract = {The effect of the velocity program and duty cycle (St(L)) on the propulsive efficiency of pulsed-jet propulsion was studied experimentally on a self-propelled, pulsed-jet underwater vehicle, dubbed Robosquid due to the similarity of essential elements of its propulsion system with squid jet propulsion. Robosquid was tested for jet slug length-to-diameter ratios (L/D) in the range 2-6 and St(L) in the range 0.2-0.6 with jet velocity programs commanded to be triangular or trapezoidal. Digital particle image velocimetry was used for measuring the impulse and energy of jet pulses to calculate the pulsed-jet propulsive efficiency and compare it with an equivalent steady jet system. Robosquid's Reynolds number (Re) based on average vehicle velocity and vehicle diameter ranged between 1300 and 2700 for the conditions tested. The results indicated better propulsive efficiency of the trapezoidal velocity program (up to 20% higher) compared to the triangular velocity program. Also, an increase in the ratio of the pulsed-jet propulsive efficiency to the equivalent steady jet propulsive efficiency (eta(P)/eta(P, ss)) was observed as St(L) increased and L/D decreased. For cases of short L/D and high St(L), eta(P)/eta(P, ss) was found to be as high as 1.2, indicating better performance of pulsed jets. This result demonstrates a case where propulsion using essential elements of a biological locomotion system can outperform the traditional mechanical system equivalent in terms of efficiency. It was also found that changes in St(L) had a proportionately larger effect on propulsive efficiency compared to changes in L/D. A simple model is presented to explain the results in terms of the contribution of over-pressure at the nozzle exit plane associated with the formation of vortex rings with each jet pulse.}, }
@article {pmid20709931, year = {2010}, author = {Borazjani, I and Sotiropoulos, F and Malkiel, E and Katz, J}, title = {On the role of copepod antennae in the production of hydrodynamic force during hopping.}, journal = {The Journal of experimental biology}, volume = {213}, number = {Pt 17}, pages = {3019-3035}, doi = {10.1242/jeb.043588}, pmid = {20709931}, issn = {1477-9145}, mesh = {Animals ; Arthropod Antennae/*physiology ; Biomechanical Phenomena/physiology ; Copepoda/*physiology ; Holography ; *Hydrodynamics ; Models, Biological ; Movement/*physiology ; Rheology ; Video Recording ; }, abstract = {We integrate high-resolution experimental observations of a freely hopping copepod with three-dimensional numerical simulations to investigate the role of the copepod antennae in production of hydrodynamic force during hopping. The experimental observations revealed a distinctive asymmetrical deformation of the antennae during the power and return strokes, which lead us to the hypothesis that the antennae are active contributors to the production of propulsive force with kinematics selected in nature in order to maximize net thrust. To examine the validity of this hypothesis we carried out numerical experiments using an anatomically realistic, tethered, virtual copepod, by prescribing two sets of antenna kinematics. In the first set, each antenna moves as a rigid, oar-like structure in a reversible manner, whereas in the second set, the antenna is made to move asymmetrically as a deformable structure as revealed by the experiments. The computed results show that for both cases the antennae are major contributors to the net thrust force during hopping, and the results also clearly demonstrate the significant hydrodynamic benefit in terms of thrust enhancement and drag reduction derived from the biologically realistic, asymmetric antenna motion. This finding is not surprising given the low local Reynolds number environment within which the antenna operates, and points to striking similarities between the copepod antenna motion and ciliary propulsion. Finally, the simulations provide the first glimpse into the complex, highly 3-D structure of copepod wakes.}, }
@article {pmid20707548, year = {2010}, author = {Sadlej, K and Wajnryb, E and Ekiel-Jezewska, ML}, title = {Hydrodynamic interactions suppress deformation of suspension drops in Poiseuille flow.}, journal = {The Journal of chemical physics}, volume = {133}, number = {5}, pages = {054901}, doi = {10.1063/1.3457154}, pmid = {20707548}, issn = {1089-7690}, mesh = {Microfluidic Analytical Techniques/*methods ; *Molecular Dynamics Simulation ; Suspensions/*chemistry ; *Thermodynamics ; }, abstract = {Evolution of a suspension drop entrained by Poiseuille flow is studied numerically at a low Reynolds number. A suspension drop is modeled by a cloud of many nontouching particles, initially randomly distributed inside a spherical volume of a viscous fluid which is identical to the host fluid outside the drop. Evolution of particle positions and velocities is evaluated by the accurate multipole method corrected for lubrication, implemented in the HYDROMULTIPOLE numerical code. Deformation of the drop is shown to be smaller for a larger volume fraction. At high concentrations, hydrodynamic interactions between close particles significantly decrease elongation of the suspension drop along the flow in comparison to the corresponding elongation of the pure-fluid drop. Owing to hydrodynamic interactions, the particles inside a dense-suspension drop tend to stay for a long time together in the central part of the drop; later on, small clusters occasionally separate out from the drop, and are stabilized by quasiperiodic orbits of the constituent nontouching particles. Both effects significantly reduce the drop spreading along the flow. At large volume fractions, suspension drops destabilize by fragmentation, and at low volume fractions, by dispersing into single particles.}, }
@article {pmid20706891, year = {2010}, author = {Magin, CM and Long, CJ and Cooper, SP and Ista, LK and López, GP and Brennan, AB}, title = {Engineered antifouling microtopographies: the role of Reynolds number in a model that predicts attachment of zoospores of Ulva and cells of Cobetia marina.}, journal = {Biofouling}, volume = {26}, number = {6}, pages = {719-727}, doi = {10.1080/08927014.2010.511198}, pmid = {20706891}, issn = {1029-2454}, mesh = {*Bacterial Adhesion ; Biofilms ; *Biofouling ; *Cell Adhesion ; Engineering ; Halomonadaceae/cytology/*physiology ; Image Processing, Computer-Assisted ; Marine Biology ; Microscopy, Electron, Scanning ; *Models, Biological ; Predictive Value of Tests ; Spores/*physiology ; Surface Properties ; Ulva/*physiology ; }, abstract = {A correlation between the attachment density of cells from two phylogenetic groups (prokaryotic Bacteria and eukaryotic Plantae), with surface roughness is reported for the first time. The results represent a paradigm shift in the understanding of cell attachment, which is a critical step in the biofouling process. The model predicts that the attachment densities of zoospores of the green alga, Ulva, and cells of the marine bacterium, Cobetia marina, scale inversely with surface roughness. The size and motility of the bacterial cells and algal spores were incorporated into the attachment model by multiplying the engineered roughness index (ERI(II)), which is a representation of surface energy, by the Reynolds number (Re) of the cells. The results showed a negative linear correlation of normalized, transformed attachment density for both organisms with ERI(II) x Re (R(2) = 0.77). These studies demonstrate for the first time that organisms respond in a uniform manner to a model, which incorporates surface energy and the Reynolds number of the organism.}, }
@article {pmid20696887, year = {2010}, author = {Sutherland, KR and Madin, LP and Stocker, R}, title = {Filtration of submicrometer particles by pelagic tunicates.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {107}, number = {34}, pages = {15129-15134}, pmid = {20696887}, issn = {1091-6490}, mesh = {Animals ; Cyanobacteria/ultrastructure ; Eating/physiology ; Ecosystem ; Filtration ; Marine Biology ; Models, Biological ; Particle Size ; Phytoplankton/ultrastructure ; Urochordata/*physiology/ultrastructure ; Zooplankton/ultrastructure ; }, abstract = {Salps are common in oceanic waters and have higher per-individual filtration rates than any other zooplankton filter feeder. Although salps are centimeters in length, feeding via particle capture occurs on a fine, mucous mesh (fiber diameter d approximately 0.1 microm) at low velocity (U = 1.6 +/- 0.6 cmxs(-1), mean +/- SD) and is thus a low Reynolds-number (Re approximately 10(-3)) process. In contrast to the current view that particle encounter is dictated by simple sieving of particles larger than the mesh spacing, a low-Re mathematical model of encounter rates by the salp feeding apparatus for realistic oceanic particle-size distributions shows that submicron particles, due to their higher abundances, are encountered at higher rates (particles per time) than larger particles. Data from feeding experiments with 0.5-, 1-, and 3-microm diameter polystyrene spheres corroborate these findings. Although particles larger than 1 microm (e.g., flagellates, small diatoms) represent a larger carbon pool, smaller particles in the 0.1- to 1-microm range (e.g., bacteria, Prochlorococcus) may be more quickly digestible because they present more surface area, and we find that particles smaller than the mesh size (1.4 microm) can fully satisfy salp energetic needs. Furthermore, by packaging submicrometer particles into rapidly sinking fecal pellets, pelagic tunicates can substantially change particle-size spectra and increase downward fluxes in the ocean.}, }
@article {pmid20696550, year = {2010}, author = {Lin, BA and Forouhar, AS and Pahlevan, NM and Anastassiou, CA and Grayburn, PA and Thomas, JD and Gharib, M}, title = {Color Doppler jet area overestimates regurgitant volume when multiple jets are present.}, journal = {Journal of the American Society of Echocardiography : official publication of the American Society of Echocardiography}, volume = {23}, number = {9}, pages = {993-1000}, doi = {10.1016/j.echo.2010.06.011}, pmid = {20696550}, issn = {1097-6795}, mesh = {Humans ; Image Processing, Computer-Assisted ; Mitral Valve Insufficiency/*diagnostic imaging/physiopathology ; Models, Cardiovascular ; Phantoms, Imaging ; Pulsatile Flow ; Severity of Illness Index ; *Ultrasonography, Doppler, Color ; }, abstract = {BACKGROUND: Color Doppler jet area (CDJA) is an important measure used to classify mitral regurgitation (MR) severity. The investigators hypothesized that the presence and configuration of multiple regurgitant jets can alter CDJA quantification for fixed regurgitant volumes. This has relevance to MR assessment prior to the treatment of valves with multiple regurgitant orifices or after surgical or percutaneous double-orifice mitral valve repair.<br><br>METHODS: An in vitro model was developed to create jets flowing through a simulated mitral orifice into an imaging chamber. The flow loop was driven with a pulsatile pump at 60 beats/min containing a water-glycerol solution approximating the viscosity of blood. At the orifice, simulated regurgitant stroke volumes of 2.5 to 25 mL were created through plates having either single openings with orifice areas from 0.125 to 0.50 cm(2) or two to four openings with total orifice area of 0.25 cm(2) and varied linear spacing. An 8-MHz transthoracic two-dimensional ultrasound probe was used to acquire jet velocities by continuous-wave Doppler as well as color Doppler for offline analysis. CDJA values were obtained with custom automated pixel-counting software.<br><br>RESULTS: Peak jet velocities ranged from 30 to 550 cm/sec. For single jets, normalized average CDJA values increased nonlinearly as a function of average Reynolds number. Peak CDJA values were up to 62% higher for multiple jets compared with single jets with similar total orifice areas and simulated regurgitant stroke volumes. The presence or absence of multiple jets, rather than the total number of jets, appeared to have a greater effect on maximum CDJA. In addition, peak CDJA values for multiple jets increased with increased linear spacing.<br><br>CONCLUSIONS: A fixed regurgitant volume involving multiple jets will have a larger CDJA value than the same total volume from a single jet. The source of this discrepancy appears to be increased ambient fluid entrainment from adjacent regurgitant jets. This potential overestimation of MR severity using color Doppler flow jets should be taken into consideration when assessing MR prior to treatment or when assessing residual MR after double-orifice mitral valve repair.}, }
@article {pmid20673771, year = {2010}, author = {Levy, DE and Seifert, A}, title = {Parameter study of simplified dragonfly airfoil geometry at Reynolds number of 6000.}, journal = {Journal of theoretical biology}, volume = {266}, number = {4}, pages = {691-702}, doi = {10.1016/j.jtbi.2010.07.016}, pmid = {20673771}, issn = {1095-8541}, mesh = {Animals ; Biomechanical Phenomena ; Flight, Animal/*physiology ; Insecta/*anatomy &amp; histology/*physiology ; *Models, Biological ; Wings, Animal/*anatomy &amp; histology/*physiology ; }, abstract = {Aerodynamic study of a simplified Dragonfly airfoil in gliding flight at Reynolds numbers below 10,000 is motivated by both pure scientific interest and technological applications. At these Reynolds numbers, the natural insect flight could provide inspiration for technology development of Micro UAV's and more. Insect wings are typically characterized by corrugated airfoils. The present study follows a fundamental flow physics study (Levy and Seifert, 2009), that revealed the importance of flow separation from the first corrugation, the roll-up of the separated shear layer to discrete vortices and their role in promoting flow reattachment to the aft arc, as the leading mechanism enabling high-lift, low drag performance of the Dragonfly gliding flight. This paper describes the effect of systematic airfoil geometry variations on the aerodynamic properties of a simplified Dragonfly airfoil at Reynolds number of 6000. The parameter study includes a detailed analysis of small variations of the nominal geometry, such as corrugation placement or height, rear arc and trailing edge shape. Numerical simulations using the 2D laminar Navier-Stokes equations revealed that the flow accelerating over the first corrugation slope is followed by an unsteady pressure recovery, combined with vortex shedding. The latter allows the reattachment of the flow over the rear arc. Also, the drag values are directly linked to the vortices' magnitude. This parametric study shows that geometric variations which reduce the vortices' amplitude, as reduction of the rear cavity depth or the reduction of the rear arc and trailing edge curvature, will reduce the drag values. Other changes will extend the flow reattachment over the rear arc for a larger mean lift coefficients range; such as the negative deflection of the forward flat plate. These changes consequently reduce the drag values at higher mean lift coefficients. The detailed geometry study enabled the definition of a corrugated airfoil geometry with enhanced aerodynamic properties, such as range and endurance factors, as compared to the nominal airfoil studied in the literature.}, }
@article {pmid20662600, year = {2010}, author = {Sewatkar, CM and Sharma, A and Agrawal, A}, title = {A first attempt to numerically compute forces on birds in V formation.}, journal = {Artificial life}, volume = {16}, number = {3}, pages = {245-258}, doi = {10.1162/artl_a_00005}, pmid = {20662600}, issn = {1064-5462}, mesh = {Animals ; Behavior, Animal/physiology ; Biomechanical Phenomena ; Birds/*physiology ; Flight, Animal/*physiology ; Mechanical Phenomena ; Models, Biological ; Space Perception ; Stress, Physiological ; }, abstract = {A model for studying the flow forces experienced by cylinders placed in V formation is presented, and an elementary comparison with flocking birds is made. The cylinders are modeled as two-dimensional square bodies exposed to incoming flow at Reynolds number 100. The effects of angle of formation (alpha), streamwise spacing (S(s)), and number of cylinders (N) on parameters such as the coefficient of drag, coefficient of lateral force, and Strouhal number are studied. It is observed that the drag experienced by the cylinders decreases with a decrease in the angle of formation. The leading cylinder experiences the smallest drag, irrespective of the angle. The drag becomes less than the drag on an isolated cylinder at certain angles depending on the position of the cylinder in the formation. The average drag on cylinders in V formation is found to be less than on an isolated cylinder, leading to energy saving when flying in formation. It is also noted that the cylinders experience a substantial lateral force. Study of this simple model may help better understand certain features of flocking birds.}, }
@article {pmid20646710, year = {2010}, author = {Zhang, H and Papadakis, G}, title = {Computational analysis of flow structure and particle deposition in a single asthmatic human airway bifurcation.}, journal = {Journal of biomechanics}, volume = {43}, number = {13}, pages = {2453-2459}, doi = {10.1016/j.jbiomech.2010.05.031}, pmid = {20646710}, issn = {1873-2380}, support = {//Department of Health/United Kingdom ; //Medical Research Council/United Kingdom ; }, mesh = {Asthma/*physiopathology ; *Computer Simulation ; Humans ; *Models, Anatomic ; Models, Theoretical ; Particle Size ; Pressure ; Respiratory System/*anatomy &amp; histology ; }, abstract = {This paper aims to improve current understanding of flow structure and particle deposition in asthmatic human airways. A single, symmetric airway bifurcation, corresponding to generations 10-11 of Weibel's model, is investigated through validated numerical simulations. The parent airway segment is modelled as a smooth circular tube. The child segments are considered asthmatic and their cross-section is modelled as a constricted tube with sinusoidal folds uniformly distributed along the circumference. The flow structure and particle deposition pattern for normal (i.e., healthy) and asthmatic airway bifurcations are compared and discussed. The numerical results reveal that the secondary flow in the asthmatic airway bifurcation is much stronger than in the healthy one, resulting in higher particle deposition. The effects of size of the lumen area and number of folds on particle deposition and pressure drop are also investigated. It is found that particle deposition efficiency is significantly affected by lumen area of the asthmatic segment (the smaller the lumen area, the higher the particle deposition efficiency). The effect of number of folds is small. Particle deposition efficiency also increases with Reynolds number. The pressure drop in the asthmatic airway bifurcation depends mainly on size of the lumen area. The effect of number of folds becomes important for strongly collapsed airways.}, }
@article {pmid20643152, year = {2010}, author = {Ye, T and Li, H and Lam, KY}, title = {Modeling and simulation of microfluid effects on deformation behavior of a red blood cell in a capillary.}, journal = {Microvascular research}, volume = {80}, number = {3}, pages = {453-463}, doi = {10.1016/j.mvr.2010.07.002}, pmid = {20643152}, issn = {1095-9319}, mesh = {Algorithms ; Animals ; Blood Flow Velocity ; Blood Viscosity ; Capillaries/*physiology ; *Computer Simulation ; Elastic Modulus ; *Erythrocyte Deformability ; Erythrocytes/*physiology ; Hemorheology ; Humans ; *Microcirculation ; *Microfluidic Analytical Techniques ; *Models, Cardiovascular ; Numerical Analysis, Computer-Assisted ; Reproducibility of Results ; }, abstract = {A modified SIMPER algorithm is developed for analysis of microfluid effects on the motion and deformation of a red blood cell (RBC) in a capillary. With consideration of very small Reynolds number in microfluidics, this algorithm not only speeds up the convergence of the momentum equations by combining the advantages of the SIMPLEC and SIMPLER algorithms together, but also satisfies the continuity equation with higher accuracy by integrating a fine adjustment technique. In order to validate the modified SIMPLER algorithm, the behavior of RBC in a capillary is simulated at different velocities. When the mean RBC velocity is 0.1mm/s, the RBC exhibits a characteristic parachute shape in the steady state, which agrees well with the numerical results previously reported. Apart from that, a quantitative validation with the experimental data is performed by examining the relationship between the mean velocity and deformation index of the RBC, showing an excellent agreement. The effects of crucial parameters are investigated systematically on the motion and deformation of the RBC, including the RBC radius, elastic modulus and bending stiffness of RBC membrane, initial velocity of suspending fluid, as well as the density and viscosity ratios of the suspending fluid to RBC. The simulation results demonstrate that all of the parameters have influences on the RBC behavior by changing the interaction between the RBC and suspending fluid.}, }
@article {pmid20635204, year = {2010}, author = {Lee, MG and Choi, S and Park, JK}, title = {Rapid multivortex mixing in an alternately formed contraction-expansion array microchannel.}, journal = {Biomedical microdevices}, volume = {12}, number = {6}, pages = {1019-1026}, doi = {10.1007/s10544-010-9456-8}, pmid = {20635204}, issn = {1572-8781}, mesh = {Erythrocytes ; Fluorescein/chemistry ; Humans ; Hydrodynamics ; Microfluidic Analytical Techniques/*instrumentation ; Phosphates/chemistry ; Spectrometry, Fluorescence ; Time Factors ; }, abstract = {We report a contraction-expansion array (CEA) microchannel for rapidly and homogeneously mixing different types of fluids by multivortex induced in alternately formed rectangular structures of the channel. Rapid mixing can be achieved in a topologically simple and easily fabricated CEA microchannel, employing a synergetic combination of two kinds of vortices: (1) expansion-vortices being induced by flow separation due to an abrupt change of cross-sectional area of the channel in its expansion region, and (2) Dean-vortices being induced by centrifugal forces acting on a cornering fluid through the channel. We experimentally and numerically investigated expansion- and Dean-vortices, and demonstrated rapid mixing of an aqueous solution containing fluorescein or human red blood cells (RBCs) at different flow rates corresponding to Reynolds number (Re) ranging from 7.2 to 43.0. Over 90% mixing efficiency at a channel length of 14.4 and 19.5 mm was achieved at Re ≥ 28.6 (fluorescein solution and deionized water) and Re ≥ 21.5 (RBC suspension and phosphate buffered saline), respectively. The proposed CEA channel is expected to be useful for a wide range of applications where particles, cells and reagents must be rapidly and homogeneously mixed in microchannels.}, }
@article {pmid20615983, year = {2010}, author = {Lim, H and Iwerks, J and Glimm, J and Sharp, DH}, title = {Nonideal Rayleigh-Taylor mixing.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {107}, number = {29}, pages = {12786-12792}, pmid = {20615983}, issn = {1091-6490}, abstract = {Rayleigh-Taylor mixing is a classical hydrodynamic instability that occurs when a light fluid pushes against a heavy fluid. The two main sources of nonideal behavior in Rayleigh-Taylor (RT) mixing are regularizations (physical and numerical), which produce deviations from a pure Euler equation, scale invariant formulation, and nonideal (i.e., experimental) initial conditions. The Kolmogorov theory of turbulence predicts stirring at all length scales for the Euler fluid equations without regularization. We interpret mathematical theories of existence and nonuniqueness in this context, and we provide numerical evidence for dependence of the RT mixing rate on nonideal regularizations; in other words, indeterminacy when modeled by Euler equations. Operationally, indeterminacy shows up as nonunique solutions for RT mixing, parametrized by Schmidt and Prandtl numbers, in the large Reynolds number (Euler equation) limit. Verification and validation evidence is presented for the large eddy simulation algorithm used here. Mesh convergence depends on breaking the nonuniqueness with explicit use of the laminar Schmidt and Prandtl numbers and their turbulent counterparts, defined in terms of subgrid scale models. The dependence of the mixing rate on the Schmidt and Prandtl numbers and other physical parameters will be illustrated. We demonstrate numerically the influence of initial conditions on the mixing rate. Both the dominant short wavelength initial conditions and long wavelength perturbations are observed to play a role. By examination of two classes of experiments, we observe the absence of a single universal explanation, with long and short wavelength initial conditions, and the various physical and numerical regularizations contributing in different proportions in these two different contexts.}, }
@article {pmid20603370, year = {2010}, author = {Karabasov, SA}, title = {Understanding jet noise.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {368}, number = {1924}, pages = {3593-3608}, doi = {10.1098/rsta.2010.0086}, pmid = {20603370}, issn = {1364-503X}, abstract = {Jets are one of the most fascinating topics in fluid mechanics. For aeronautics, turbulent jet-noise modelling is particularly challenging, not only because of the poor understanding of high Reynolds number turbulence, but also because of the extremely low acoustic efficiency of high-speed jets. Turbulent jet-noise models starting from the classical Lighthill acoustic analogy to state-of-the art models were considered. No attempt was made to present any complete overview of jet-noise theories. Instead, the aim was to emphasize the importance of sound generation and mean-flow propagation effects, as well as their interference, for the understanding and prediction of jet noise.}, }
@article {pmid20596461, year = {2010}, author = {Guo, SZ and Li, Y and Jiang, JS and Xie, HQ}, title = {Nanofluids Containing γ-Fe2O3 Nanoparticles and Their Heat Transfer Enhancements.}, journal = {Nanoscale research letters}, volume = {5}, number = {7}, pages = {1222-1227}, pmid = {20596461}, issn = {1556-276X}, abstract = {Homogeneous and stable magnetic nanofluids containing γ-Fe2O3 nanoparticles were prepared using a two-step method, and their thermal transport properties were investigated. Thermal conductivities of the nanofluids were measured to be higher than that of base fluid, and the enhanced values increase with the volume fraction of the nanoparticles. Viscosity measurements showed that the nanofluids demonstrated Newtonian behavior and the viscosity of the nanofluids depended strongly on the tested temperatures and the nanoparticles loadings. Convective heat transfer coefficients tested in a laminar flow showed that the coefficients increased with the augment of Reynolds number and the volume fraction.}, }
@article {pmid20541796, year = {2010}, author = {Ballyns, JJ and Wright, TM and Bonassar, LJ}, title = {Effect of media mixing on ECM assembly and mechanical properties of anatomically-shaped tissue engineered meniscus.}, journal = {Biomaterials}, volume = {31}, number = {26}, pages = {6756-6763}, pmid = {20541796}, issn = {1878-5905}, support = {P30 AR046121/AR/NIAMS NIH HHS/United States ; P30 AR046121-10/AR/NIAMS NIH HHS/United States ; }, mesh = {Animals ; Cattle ; Collagen/metabolism ; Culture Media/*pharmacology ; DNA/metabolism ; Extracellular Matrix/*drug effects/*metabolism ; Glycosaminoglycans/metabolism ; Implants, Experimental ; Materials Testing/*methods ; Mechanical Phenomena/*drug effects ; Menisci, Tibial/*drug effects ; Tensile Strength/drug effects ; Tissue Engineering/*methods ; Tissue Scaffolds/chemistry ; }, abstract = {This study investigated the hypothesis that controlled media mixing will enhance tissue formation and increase mechanical properties of anatomically-shaped tissue engineered menisci. Bovine meniscal fibrochondrocytes were seeded in 2% w/v alginate, cross-linked with 0.02 g/mL CaSO(4), and injected into molds of menisci. Engineered menisci were incubated for up to 6 weeks. A mixing media bioreactor was designed to ensure proper mixing of culture medium while protecting constructs from the spinning impeller. Impeller speeds were calibrated to produce Reynolds number (Re) of 0.5, 2.9, 5.8, 10.2, and 21.8. Constructs were divided a tested in confined compression and in tension to determine the equilibrium and tensile moduli, respectively. Media stimulation resulted in a 2-5 fold increase in mechanical properties and a 2-3 fold increase in matrix accumulation in constructs over 6 weeks in culture. Benefits from mixing stimulation for collagen accumulation and compressive modulus appeared to peak near Re 2.9, and decreased with increased mixing intensity. This study suggests that fluid mixing can be optimized to enhance mechanical properties of anatomically-shaped engineered constructs.}, }
@article {pmid20534502, year = {2010}, author = {Barry, NP and Bretscher, MS}, title = {Dictyostelium amoebae and neutrophils can swim.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {107}, number = {25}, pages = {11376-11380}, pmid = {20534502}, issn = {1091-6490}, mesh = {Amoeba/*metabolism ; Cell Adhesion ; Cell Movement ; Chemotaxis ; Cyclic AMP/metabolism ; Dictyostelium/*metabolism ; Green Fluorescent Proteins/metabolism ; Humans ; Microscopy, Confocal/methods ; Models, Biological ; Movement ; N-Formylmethionine Leucyl-Phenylalanine/metabolism ; Needles ; Neutrophils/*metabolism ; }, abstract = {Animal cells migrating over a substratum crawl in amoeboid fashion; how the force against the substratum is achieved remains uncertain. We find that amoebae and neutrophils, cells traditionally used to study cell migration on a solid surface, move toward a chemotactic source while suspended in solution. They can swim and do so with speeds similar to those on a solid substrate. Based on the surprisingly rapidly changing shape of amoebae as they swim and earlier theoretical schemes for how suspended microorganisms can migrate (Purcell EM (1977) Life at low Reynolds number. Am J Phys 45:3-11), we suggest the general features these cells use to gain traction with the medium. This motion requires either the movement of the cell's surface from the cell's front toward its rear or protrusions that move down the length of the elongated cell. Our results indicate that a solid substratum is not a prerequisite for these cells to produce a forward thrust during movement and suggest that crawling and swimming are similar processes, a comparison we think is helpful in understanding how cells migrate.}, }
@article {pmid20525003, year = {2010}, author = {Knoblauch, M and Peters, WS}, title = {Münch, morphology, microfluidics - our structural problem with the phloem.}, journal = {Plant, cell &amp; environment}, volume = {33}, number = {9}, pages = {1439-1452}, doi = {10.1111/j.1365-3040.2010.02177.x}, pmid = {20525003}, issn = {1365-3040}, mesh = {Biological Transport ; Microfluidics ; *Models, Biological ; Phloem/*anatomy &amp; histology/physiology ; Plant Stems/*anatomy &amp; histology/physiology ; }, abstract = {The sieve tubes of the phloem are enigmatic structures. Their role as channels for the distribution of assimilates was established in the 19th century, but their sensitivity to disturbations has hampered the elucidation of their transport mechanisms and its regulation ever since. Ernst Münch's classical monograph of 1930 is generally regarded as the first coherent theory of phloem transport, but the 'Münchian' pressure flow mechanism had been discussed already before the turn of the century. Münch's impact rather rested on his simple physical models of the phloem that visualized pressure flow in an intuitive way, and we argue that the downscaling of such models to realistic, low-Reynolds-number sizes will boost our understanding of phloem transport in this century just as Münch's models did in the previous one. However, biologically meaningful physical models that could be used to test predictions of the many existing mathematical models would have to be designed in analogy with natural phloem structures. Unfortunately, the study of phloem anatomy seems in decline, and we still lack basic quantitative data required for evaluating the plausibility of our theoretical deductions. In this review, we provide a subjective overview of unresolved problems in angiosperm phloem structure research within a functional context.}, }
@article {pmid20515156, year = {2010}, author = {Yuan, L and Zheng, YF and Chen, W}, title = {Efficient micromixing of a highly viscous biosample with water using orbital shaking and microchannels.}, journal = {The Review of scientific instruments}, volume = {81}, number = {5}, pages = {054301}, doi = {10.1063/1.3422244}, pmid = {20515156}, issn = {1089-7623}, mesh = {Biopolymers/chemistry ; Complex Mixtures/*chemistry ; Equipment Design ; Equipment Failure Analysis ; Flow Injection Analysis/*instrumentation ; Microfluidic Analytical Techniques/*instrumentation ; Reproducibility of Results ; Sensitivity and Specificity ; Vibration ; Viscosity ; }, abstract = {Micromixing of a highly viscous biosample with water using orbital shaking and microchannels is considered. Existing methods mix biosamples by only shaking microwells or by specially designed microstirrers which are ineffective or inapplicable for highly viscous materials, let alone small volumes at microliter or nanoliter levels. Our method mixes a viscous biosample with water in microwells using orbital shaking plus an innovative block which divides the microwells into two compartments and is built in with microchannels. The mixing method with the block in the microwell is efficient compared to mixing in the microwell without the block. In this paper, the design of the block is presented, the model of the flow of the biosamples in the microchannel is developed, the Reynolds number of the flow in the microchannel is calculated, and the dynamics of the mixing process is analyzed. Furthermore, a miniature wireless video sensor system is used to observe the mixing process which verifies the model of the flow in the analysis. Finally, x-ray diffraction experiments on mixing monoolein with water are presented. In each trial, x-ray diffraction is used to evaluate the results of mixing which confirms that the proposed approach is effective for mixing a highly viscous biosample with water.}, }
@article {pmid20513401, year = {2010}, author = {Ryu, S and Matsudaira, P}, title = {Unsteady motion, finite Reynolds numbers, and wall effect on Vorticella convallaria contribute contraction force greater than the stokes drag.}, journal = {Biophysical journal}, volume = {98}, number = {11}, pages = {2574-2581}, pmid = {20513401}, issn = {1542-0086}, mesh = {Algorithms ; *Computer Simulation ; Microfluidics ; *Models, Biological ; Motion ; Oligohymenophorea/*physiology ; Time Factors ; Torsion, Mechanical ; Video Recording ; Viscosity ; Water ; }, abstract = {Contraction of Vorticella convallaria, a sessile ciliated protozoan, is completed within a few milliseconds and results in a retraction of its cell body toward the substratum by coiling its stalk. Previous studies have modeled the cell body as a sphere and assumed a drag force that satisfies Stokes' law. However, the contraction-induced flow of the medium is transient and bounded by the substrate, and the maximum Reynolds number is larger than unity. Thus, calculations of contractile force from the drag force are incomplete. In this study, we analyzed fluid flow during contraction by the particle tracking velocimetry and computational fluid dynamics simulations to estimate the contractile force. Particle paths show that the induced flow is limited by the substrate. Simulation-based force estimates suggest that the combined effect of the flow unsteadiness, the finite Reynolds number, and the substrate comprises 35% of the total force. The work done in the early stage of contraction and the maximum power output are similar regardless of the medium viscosity. These results suggest that, during the initial development of force, V. convallaria uses a common mechanism for performing mechanical work irrespective of viscous loading conditions.}, }
@article {pmid20488446, year = {2010}, author = {Defraeye, T and Blocken, B and Koninckx, E and Hespel, P and Carmeliet, J}, title = {Computational fluid dynamics analysis of cyclist aerodynamics: performance of different turbulence-modelling and boundary-layer modelling approaches.}, journal = {Journal of biomechanics}, volume = {43}, number = {12}, pages = {2281-2287}, doi = {10.1016/j.jbiomech.2010.04.038}, pmid = {20488446}, issn = {1873-2380}, mesh = {Bicycling/*physiology ; Biomechanical Phenomena ; Computer Simulation ; Humans ; Hydrodynamics ; Manikins ; *Models, Biological ; Pressure ; Wind ; }, abstract = {This study aims at assessing the accuracy of computational fluid dynamics (CFD) for applications in sports aerodynamics, for example for drag predictions of swimmers, cyclists or skiers, by evaluating the applied numerical modelling techniques by means of detailed validation experiments. In this study, a wind-tunnel experiment on a scale model of a cyclist (scale 1:2) is presented. Apart from three-component forces and moments, also high-resolution surface pressure measurements on the scale model's surface, i.e. at 115 locations, are performed to provide detailed information on the flow field. These data are used to compare the performance of different turbulence-modelling techniques, such as steady Reynolds-averaged Navier-Stokes (RANS), with several k-epsilon and k-omega turbulence models, and unsteady large-eddy simulation (LES), and also boundary-layer modelling techniques, namely wall functions and low-Reynolds number modelling (LRNM). The commercial CFD code Fluent 6.3 is used for the simulations. The RANS shear-stress transport (SST) k-omega model shows the best overall performance, followed by the more computationally expensive LES. Furthermore, LRNM is clearly preferred over wall functions to model the boundary layer. This study showed that there are more accurate alternatives for evaluating flow around bluff bodies with CFD than the standard k-epsilon model combined with wall functions, which is often used in CFD studies in sports.}, }
@article {pmid20482210, year = {2010}, author = {Rojas, NO and Argentina, M and Cerda, E and Tirapegui, E}, title = {Inertial lubrication theory.}, journal = {Physical review letters}, volume = {104}, number = {18}, pages = {187801}, doi = {10.1103/PhysRevLett.104.187801}, pmid = {20482210}, issn = {1079-7114}, abstract = {Thin fluid films can have surprising behavior depending on the boundary conditions enforced, the energy input and the specific Reynolds number of the fluid motion. Here we study the equations of motion for a thin fluid film with a free boundary and its other interface in contact with a solid wall. Although shear dissipation increases for thinner layers and the motion can generally be described in the limit as viscous, inertial modes can always be excited for a sufficiently high input of energy. We derive the minimal set of equations containing inertial effects in this strongly dissipative regime.}, }
@article {pmid20481863, year = {2010}, author = {Oliveira, RS and Andrade, JS and Andrade, RF}, title = {Fluid flow through Apollonian packings.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {4 Pt 2}, pages = {047302}, doi = {10.1103/PhysRevE.81.047302}, pmid = {20481863}, issn = {1550-2376}, abstract = {This work considers the flow of a Newtonian fluid in a two-dimensional channel filled with an array of obstacles of distinct sizes that models an inhomogeneous medium. Obstacle sizes and positions are defined by the geometry of an Apollonian packing (AP). The radii of the circles are uniformly reduced by a factor s<1 for assemblies corresponding to the five first AP generations. The region of validity of Darcy's law as a function of the channel Reynolds number is investigated for different values of s and the dependency of the flow pattern and permeability with respect to porosity is established. Our results show that the semiempirical Kozeny-Carman scaling relation is satisfied provided the effects of the apparent porosity and s-dependent formation factor are properly considered.}, }
@article {pmid20481832, year = {2010}, author = {Gurbatov, SN and Moshkov, AY and Noullez, A}, title = {Evolution of anisotropic structures and turbulence in the multidimensional Burgers equation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {4 Pt 2}, pages = {046312}, doi = {10.1103/PhysRevE.81.046312}, pmid = {20481832}, issn = {1550-2376}, abstract = {The goal of the present paper is the investigation of the final evolution of anisotropic regular structures and turbulence at large Reynolds number in the multidimensional Burgers equation. We show that we have local isotropization at small scales of the velocity and potential fields inside cellular zones. For periodic waves, we have simple decay inside a frozen structure. The global structure at large times is determined by the initial correlations and for short range correlated fields we have isotropization of turbulence. Finally, we consider the final behavior of the field, when the processes of nonlinear beating interactions become frozen, and the evolution of the field is determined only by the linear dissipation.}, }
@article {pmid20454540, year = {2010}, author = {Lee, P and Griffith, BE and Peskin, CS}, title = {The immersed boundary method for advection-electrodiffusion with implicit timestepping and local mesh refinement.}, journal = {Journal of computational physics}, volume = {229}, number = {13}, pages = {5208-5227}, pmid = {20454540}, issn = {0021-9991}, support = {P50 GM071558/GM/NIGMS NIH HHS/United States ; P50 GM071558-01A2/GM/NIGMS NIH HHS/United States ; }, abstract = {We describe an immersed boundary method for problems of fluid-solute-structure interaction. The numerical scheme employs linearly implicit timestepping, allowing for the stable use of timesteps that are substantially larger than those permitted by an explicit method, and local mesh refinement, making it feasible to resolve the steep gradients associated with the space charge layers as well as the chemical potential, which is used in our formulation to control the permeability of the membrane to the (possibly charged) solute. Low Reynolds number fluid dynamics are described by the time-dependent incompressible Stokes equations, which are solved by a cell-centered approximate projection method. The dynamics of the chemical species are governed by the advection-electrodiffusion equations, and our semi-implicit treatment of these equations results in a linear system which we solve by GMRES preconditioned via a fast adaptive composite-grid (FAC) solver. Numerical examples demonstrate the capabilities of this methodology, as well as its convergence properties.}, }
@article {pmid20437777, year = {2010}, author = {Rong, L and Nielsen, PV and Zhang, G}, title = {Experimental and numerical study on effects of airflow and aqueous ammonium solution temperature on ammonia mass transfer coefficient.}, journal = {Journal of the Air &amp; Waste Management Association (1995)}, volume = {60}, number = {4}, pages = {419-428}, doi = {10.3155/1047-3289.60.4.419}, pmid = {20437777}, issn = {1096-2247}, mesh = {Air Movements ; Ammonia/*chemistry ; *Models, Chemical ; Quaternary Ammonium Compounds/*chemistry ; Temperature ; Validation Studies as Topic ; Volatilization ; }, abstract = {This paper reports the results of an investigation, based on fundamental fluid dynamics and mass transfer theory, carried out to obtain a general understanding of ammonia mass transfer from an emission surface. The effects of airflow and aqueous ammonium solution temperature on ammonia mass transfer are investigated by using computational fluid dynamics (CFD) modeling and by a mechanism modeling using dissociation constant and Henry's constant models based on the parameters measured in the experiments performed in a wind tunnel. The validated CFD model by experimental data is used to investigate the surface concentration distribution and mass transfer coefficient at different temperatures and velocities for which the Reynolds number is from 1.36 x 10(4) to 5.43 x 10(4) (based on wind tunnel length). The surface concentration increases as velocity decreases and varies greatly along the airflow direction on the emission surface. The average mass transfer coefficient increases with higher velocity and turbulence intensity. However, the mass transfer coefficient estimated by CFD simulation is consistently larger than the calculated one by the method using dissociation constant and Henry's constant models. In addition, the results show that the liquid-air temperature difference has little impact on the simulated mass transfer coefficient by CFD modeling, whereas the mass transfer coefficient increases with higher liquid temperature using the other method under the conditions that the liquid temperature is lower than the air temperature. Although there are differences of mass transfer coefficients between these two methods, the mass transfer coefficients determined by these two methods are significantly related.}, }
@article {pmid20433964, year = {2010}, author = {Bhattacharya, S and Gurung, D}, title = {Derivation of governing equation describing time-dependent penetration length in channel flows driven by non-mechanical forces.}, journal = {Analytica chimica acta}, volume = {666}, number = {1-2}, pages = {51-54}, doi = {10.1016/j.aca.2010.02.019}, pmid = {20433964}, issn = {1873-4324}, abstract = {Several past attempts were made to describe the penetration length in microchannels as a function of time for electroosmotic or capillary flow. In all of these studies, a complex governing equation is derived by taking into account the inertial contributions along with other forces. The system being unsteady, this derivation requires the consideration of proper unsteady flow-profile inside the channel. However, the past theories introduced an inconsistency by using parabolic velocity-field valid only for steady systems. This discrepancy creates an error of the same order as the inertial contribution leading to two consequences. Firstly, the inherent inaccuracy makes the past theories inapplicable when Reynolds number is greater than unity. Secondly, it renders the inclusion of inertial terms pointless for low Reynolds number systems-the additional complexity due to inertia does not serve any purpose because error of similar order is already present in the formulation. In this paper, we address this problem by rectifying the mathematical derivation where instead of the parabolic velocity-profile, proper analytical expression for unsteady flow is used. As a result, the correct governing equation is derived for the penetration length for any laminar system with arbitrary Reynolds number. We also simplify the equation for low Reynolds number cases by considering appropriate limiting conditions. The equation for low Reynolds number flow, while being as accurate as the ones obtained in the earlier studies, is much simpler than the previous versions.}, }
@article {pmid20428951, year = {2010}, author = {Niazmand, H and Rajabi Jaghargh, E}, title = {Bend sweep angle and Reynolds number effects on hemodynamics of s-shaped arteries.}, journal = {Annals of biomedical engineering}, volume = {38}, number = {9}, pages = {2817-2828}, doi = {10.1007/s10439-010-0043-1}, pmid = {20428951}, issn = {1573-9686}, mesh = {Arteries/*physiology ; Blood Flow Velocity/physiology ; *Computer Simulation ; Hemodynamics/*physiology ; Humans ; *Models, Cardiovascular ; Numerical Analysis, Computer-Assisted ; }, abstract = {The purpose of this study is to investigate the effects of the Reynolds number and the bend sweep angle on the blood flow patterns of S-shaped bends. The numerical simulations of steady flows in S-shaped bends with sweep angles of 45 degrees , 90 degrees , and 135 degrees are performed at Reynolds numbers of 125, 500, and 960. Hemodynamic characteristics such as secondary flows, vorticity, and axial velocity profiles are analyzed in detail. Flow patterns in S-shaped bends are strongly dependent on both Reynolds number and bend sweep angle, which can be categorized into three groups based on the first bend secondary flow effects on the transverse flow of the second bend. For low Reynolds numbers and any sweep angles, secondary flows in the second bend eliminate the first bend effects in the early sections of the second bend and therefore the axial velocity profile is consistent with the bend curvature, while for high Reynolds numbers depending on the bend sweep angles the secondary vortex pattern of the first bend may persist partially or totally throughout the second bend leading to a four-vortex secondary structure. Moreover, an interesting flow feature observed at the Reynolds number of 960 is that the secondary flow asymmetrical behavior occurred around the second bend exit and along the outflow straight section. This symmetry-breaking phenomenon which has not been reported in the previous studies is shown to be more pronounced in the 90 degrees S-shaped bend as compared to other models considered here. The probability of flow separation as one of the important flow features contributing to the onset and development of arterial wall diseases is also studied. It is observed that the second bend outer wall of gentle bends with sweep angles from 20 degrees to 30 degrees at high enough Reynolds numbers are prone to flow separation.}, }
@article {pmid20422105, year = {2010}, author = {Xia, HM and Wang, ZP and Koh, YX and May, KT}, title = {A microfluidic mixer with self-excited 'turbulent' fluid motion for wide viscosity ratio applications.}, journal = {Lab on a chip}, volume = {10}, number = {13}, pages = {1712-1716}, doi = {10.1039/b925025e}, pmid = {20422105}, issn = {1473-0197}, abstract = {In micromixer studies, compared with the design, modeling and characterization, the influence of the fluid properties on mixing has been less discussed. This topic is of practical significance as the properties of diverse biological and chemical liquids to be mixed have large variations. Here, we report a microfluidic mixer for mixing fluids with widely different viscosities. It contains an interconnected multi-channel network through which the bulk fluid volumes are divided into smaller ones and chaotically reorganized. Then, the multiple fluid streams are driven into an expansion chamber which triggers viscous flow instabilities. Experiments with the co-flow of glycerol and aqueous solutions show an automatic transition of the flow from a steady state to a 'turbulent' state, significantly enhancing the mixing. This observation is rather interesting considering that it occurs in a passive flow and the average Reynolds number involved is small. Further testing indicates that this mixer works well at viscosity ratio (chi) up to the order of 10(4).}, }
@article {pmid20390133, year = {2010}, author = {Srivastava, N and Din, C and Judson, A and MacDonald, NC and Meinhart, CD}, title = {A unified scaling model for flow through a lattice of microfabricated posts.}, journal = {Lab on a chip}, volume = {10}, number = {9}, pages = {1148-1152}, doi = {10.1039/b919942j}, pmid = {20390133}, issn = {1473-0197}, mesh = {Computer Simulation ; Equipment Design ; Equipment Failure Analysis ; Microfluidic Analytical Techniques/*instrumentation/*methods ; Miniaturization ; *Models, Chemical ; Solutions/*chemistry ; }, abstract = {A scaling model is presented for low Reynolds number viscous flow within an array of microfabricated posts. Such posts are widely used in several lab-on-a-chip applications such as heat pipes, antibody arrays and biomolecule separation columns. Finite element simulations are used to develop a predictive model for pressure driven viscous flow through posts. The results indicate that the flow rate per unit width scales as approximately h1.17g1.33/d0.5 where h is the post height, d post diameter and g is the spacing between the posts. These results compare favorably to theoretical limits. The scaling is extended to capillary pressure driven viscous flows. This unified model is the first report of a scaling that incorporates both viscous and capillary forces in the microfabricated post geometry. The model is consistent with Washburn dynamics and was experimentally validated to within 8% using wetting on microfabricated silicon posts.}, }
@article {pmid20387966, year = {2010}, author = {Al-Atabi, M and Chin, SB and Luo, XY}, title = {Experimental investigation of the flow of bile in patient specific cystic duct models.}, journal = {Journal of biomechanical engineering}, volume = {132}, number = {4}, pages = {041003}, doi = {10.1115/1.4001043}, pmid = {20387966}, issn = {1528-8951}, mesh = {Bile/*physiology ; Cystic Duct/*physiology ; Humans ; *Models, Anatomic ; *Models, Biological ; Rheology/methods ; }, abstract = {Three-dimensional scaled-up transparent models of three human cystic ducts were prepared on the basis of anatomical specimens. The measurement of pressure drop across the cystic duct models and visualization of the flow structures within these ducts were performed at conditions replicating the physiological state. The flow visualization study confirmed the laminar nature of the flow of bile inside the cystic duct and values of pressure drop coefficient (Cp) decreased as the Reynolds number (Re) increased. The three tested models showed comparable behavior for the curve of Reynolds number versus the pressure drop coefficient. The results show that the tested cystic ducts have both increased pressure drop and complicated flow structures when compared with straight conduits. High resistance in a cystic duct may indicate that the gallbladder has to exert large force in expelling bile to the cystic duct. For patients with diseased gallbladder, and even in healthy persons, gallbladder is known to stiffen with age and it may lose its compliance or flexibility. A high resistance cystic duct coupled with a stiffened gallbladder may result in prolonged stasis of bile in the gallbladder, which is assumed to encourage the formation of gallstones.}, }
@article {pmid20385399, year = {2010}, author = {Foteinopoulou, K and Laso, M}, title = {Numerical simulation of bubble dynamics in a Phan-Thien-Tanner liquid: non-linear shape and size oscillatory response under periodic pressure.}, journal = {Ultrasonics}, volume = {50}, number = {8}, pages = {758-776}, doi = {10.1016/j.ultras.2010.03.002}, pmid = {20385399}, issn = {1874-9968}, abstract = {We study non-linear bubble oscillations driven by an acoustic pressure with the bubble being immersed in a viscoelastic, Phan-Thien-Tanner liquid. Solution is provided numerically through a method which is based on a finite element discretization of the Navier-Stokes flow equations. The proposed computational approach does not rely on the solution of the simplified Rayleigh-Plesset equation, is not limited in studying only spherically symmetric bubbles and provides coupled solutions for the velocity, stress fields and bubble interface. We present solutions for non-spherical bubbles, with asphericity being addressed by means of Legendre polynomials or associated Legendre functions. A parametric investigation of the bubble dynamical oscillatory response as a function of the fluid rheological properties shows that the amplitude of bubble oscillations drastically increases as liquid elasticity (quantified by the Deborah number) increases or as liquid viscosity decreases (quantified by the Reynolds number). Extensive numerical calculations demonstrate that increasing elasticity and/or viscosity of the surrounding liquid tend to stabilize the shape anisotropy of an initially non-spherical bubble. Results are shown for pressure amplitudes 0.2-2MPa and Deborah, Reynolds numbers in the intervals of 1-8 and 0.094-1.256, respectively.}, }
@article {pmid20372989, year = {2010}, author = {Wong, W and Fletcher, DF and Traini, D and Chan, HK and Crapper, J and Young, PM}, title = {Particle aerosolisation and break-up in dry powder inhalers 1: evaluation and modelling of venturi effects for agglomerated systems.}, journal = {Pharmaceutical research}, volume = {27}, number = {7}, pages = {1367-1376}, pmid = {20372989}, issn = {1573-904X}, mesh = {Aerosols/*chemistry ; *Computer Simulation ; Mannitol/chemistry ; *Models, Biological ; *Nebulizers and Vaporizers ; Particle Size ; Powders/*chemistry ; Viscosity ; Water/chemistry ; }, abstract = {PURPOSE: This study utilized a combination of computational fluid dynamics (CFD) and standardized entrainment tubes to investigate the influence of turbulence on the break-up and aerosol performance of a model inhalation formulation.<br><br>METHODS: Agglomerates (642.8 mum mean diameter) containing 3.91 mum median diameter primary spherical mannitol particles were prepared by spheronisation. A series of entrainment tubes with different Venturi sections were constructed in silico, and the flow pattern and turbulence/impaction parameters were predicted using CFD. The entrainment models were constructed from the in silico model using three-dimensional printing. The aerosol performance of the mannitol was assessed by entraining the agglomerates into the experimental tubes at a series of flow rates and assessing the size distribution downstream of the venturi via in-line laser diffraction.<br><br>RESULTS: A series of parameters (including Reynolds number (Re), turbulence kinetic energy, turbulence eddy frequency, turbulence length-scale, velocity and pressure drop) were calculated from the CFD simulation. The venturi diameter and volumetric flow rate were varied systematically. The particle size data of the agglomerated powders were then correlated with the CFD measurements. No correlation between turbulence and aerosol performance could be made (i.e. at a Reynolds number of 8,570, the d(0.1) was 52.5 mum +/- 19.7 mum, yet at a Reynolds number of 12,000, the d(0.1) was 429.1 mum +/- 14.8 mum). Lagrangian particle tracking indicated an increase in the number of impactions and the normal velocity component at the wall, with increased volumetric airflow and reduced venturi diameter. Chemical analysis of the mannitol deposited on the walls showed a linear relationship with respect to the theoretical number of impactions (R(2) = 0.9620). Analysis of the relationship between the CFD results and the experimental size data indicated a critical impact velocity was required to initiate agglomerate break-up (approximately 0.4 m.s(-1)).<br><br>CONCLUSION: While this study focussed on the effect of turbulence on agglomerate break-up, the small amount of impaction, which inevitably occurs in the venturi assembly, appeared to dominate agglomerate break-up in this dry powder system.}, }
@article {pmid20370303, year = {2010}, author = {O'Farrell, C and Dabiri, JO}, title = {A Lagrangian approach to identifying vortex pinch-off.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {20}, number = {1}, pages = {017513}, doi = {10.1063/1.3275499}, pmid = {20370303}, issn = {1089-7682}, mesh = {Algorithms ; Animals ; Biophysics/*methods ; Humans ; Hydrodynamics ; Models, Theoretical ; Movement ; Physics/methods ; Swimming ; }, abstract = {A criterion for identifying vortex ring pinch-off based on the Lagrangian coherent structures (LCSs) in the flow is proposed and demonstrated for a piston-cylinder arrangement with a piston stroke to diameter (L/D) ratio of approximately 12. It is found that the appearance of a new disconnected LCS and the termination of the original LCS are indicative of the initiation of vortex pinch-off. The subsequent growth of new LCSs, which tend to roll into spirals, indicates the formation of new vortex cores in the trailing shear layer. Using this criterion, the formation number is found to be 4.1+/-0.1, which is consistent with the predicted formation number of approximately 4 of Gharib et al. [Gharib et al. J. Fluid Mech. 360, 121 (1998)]. The results obtained using the proposed LCS criterion are compared with those obtained using the circulation criterion of Gharib et al. and are found to be in excellent agreement. The LCS approach is also compared against other metrics, both Lagrangian and Eulerian, and is found to yield insight into the pinch-off process that these do not. Furthermore, the LCS analysis reveals a consistent pattern of coalescing or "pairing" of adjacent vortices in the trailing shear layer, a process which has been extensively documented in circular jets. Given that LCSs are objective and insensitive to local errors in the velocity field, the proposed criterion has the potential to be a robust tool for pinch-off identification. In particular, it may prove useful in the study of unsteady and low Reynolds number flows, where conventional methods based on vorticity prove difficult to use.}, }
@article {pmid20370299, year = {2010}, author = {Eldredge, JD and Chong, K}, title = {Fluid transport and coherent structures of translating and flapping wings.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {20}, number = {1}, pages = {017509}, doi = {10.1063/1.3273036}, pmid = {20370299}, issn = {1089-7682}, mesh = {Algorithms ; Animals ; Biomechanical Phenomena ; Biophysics/*methods ; Flight, Animal/*physiology ; Models, Statistical ; Oscillometry ; Surface Properties ; Swimming ; Wings, Animal/*physiology ; }, abstract = {The Lagrangian coherent structures (LCSs) of simple wing cross sections in various low Reynolds number motions are extracted from high-fidelity numerical simulation data and examined in detail. The entrainment process in the wake of a translating ellipse is revealed by studying the relationship between attracting structures in the wake and upstream repelling structures, with the help of blocks of tracer particles. It is shown that a series of slender lobes in the repelling LCS project upstream from the front of the ellipse and "pull" fluid into the wake. Each lobe is paired with a corresponding wake vortex, into which the constituent fluid particles are folded. Flexible and rigid foils in flapping motion are studied, and the resulting differences in coherent structures are used to elucidate their differences in force generation. The clarity with which these flow structures are revealed, compared to the vorticity or velocity fields, provides new insight into the vortex shedding mechanisms that play an important role in unsteady aerodynamics.}, }
@article {pmid20370293, year = {2010}, author = {Brunton, SL and Rowley, CW}, title = {Fast computation of finite-time Lyapunov exponent fields for unsteady flows.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {20}, number = {1}, pages = {017503}, doi = {10.1063/1.3270044}, pmid = {20370293}, issn = {1089-7682}, mesh = {Algorithms ; Computers ; Models, Theoretical ; Nonlinear Dynamics ; Physics/*methods ; Reproducibility of Results ; Software ; }, abstract = {This paper presents new efficient methods for computing finite-time Lyapunov exponent (FTLE) fields in unsteady flows. The methods approximate the particle flow map, eliminating redundant particle integrations in neighboring flow map calculations. Two classes of flow map approximations are investigated based on composition of intermediate flow maps; unidirectional approximation constructs a time-T map by composing a number of smaller time-h maps, while bidirectional approximation constructs a flow map by composing both positive- and negative-time maps. The unidirectional method is shown to be fast and accurate, although it is memory intensive. The bidirectional method is also fast and uses significantly less memory; however, it is prone to error which is large in regions where the opposite-time FTLE field is large, rendering it unusable. The algorithms are implemented and compared on three example fluid flows: a double gyre, a low Reynolds number pitching flat plate, and an unsteady ABC flow.}, }
@article {pmid20370277, year = {2010}, author = {Wu, ZB}, title = {Generalization of the JTZ model to open plane wakes.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {20}, number = {1}, pages = {013122}, doi = {10.1063/1.3339818}, pmid = {20370277}, issn = {1089-7682}, mesh = {Algorithms ; Biophysics/*methods ; Computer Simulation ; Models, Theoretical ; Nonlinear Dynamics ; Normal Distribution ; Particle Size ; Time Factors ; }, abstract = {The JTZ model [C. Jung, T. Tel, and E. Ziemniak, Chaos 3, 555 (1993)], as a theoretical model of a plane wake behind a circular cylinder in a narrow channel at a moderate Reynolds number, has previously been employed to analyze phenomena of chaotic scattering. It is extended here to describe an open plane wake without the confined narrow channel by incorporating a double row of shedding vortices into the intermediate and far wake. The extended JTZ model is found in qualitative agreement with both direct numerical simulations and experimental results in describing streamlines and vorticity contours. To further validate its applications to particle transport processes, the interaction between small spherical particles and vortices in an extended JTZ model flow is studied. It is shown that the particle size has significant influences on the features of particle trajectories, which have two characteristic patterns: one is rotating around the vortex centers and the other accumulating in the exterior of vortices. Numerical results based on the extended JTZ model are found in qualitative agreement with experimental ones in the normal range of particle sizes.}, }
@article {pmid20366935, year = {2010}, author = {Yu, H and Meneveau, C}, title = {Lagrangian refined Kolmogorov similarity hypothesis for gradient time evolution and correlation in turbulent flows.}, journal = {Physical review letters}, volume = {104}, number = {8}, pages = {084502}, doi = {10.1103/PhysRevLett.104.084502}, pmid = {20366935}, issn = {1079-7114}, abstract = {We study time evolution of velocity and pressure gradients in isotropic turbulence by quantifying their autocorrelation functions and decorrelation time scales. The Lagrangian analysis uses data in a public database generated by direct numerical simulation at a Reynolds number Re{lambda} approximately 433. It is confirmed that when averaging over the entire domain, correlation functions decay on time scales on the order of the global Kolmogorov turnover time scale. However, when performing the analysis in different subregions of the flow, turbulence intermittency leads to large spatial variability in the decay time scales. Remarkably, excellent collapse of the autocorrelation functions is recovered when using a locally defined Kolmogorov time scale. This provides new evidence for the validity of Kolmogorov's refined similarity hypothesis, but from a Lagrangian viewpoint that provides a natural frame to describe the dynamics of turbulence.}, }
@article {pmid20366768, year = {2010}, author = {Gopalan, B and Katz, J}, title = {Turbulent shearing of crude oil mixed with dispersants generates long microthreads and microdroplets.}, journal = {Physical review letters}, volume = {104}, number = {5}, pages = {054501}, doi = {10.1103/PhysRevLett.104.054501}, pmid = {20366768}, issn = {1079-7114}, abstract = {Using cinematic digital holography, we demonstrate that turbulent breakup of crude oil mixed with dispersants into microdroplets starts with the formation of very long and quite stable, single or multiple microthreads that trail behind 300-1400 microm droplets. These threads extend from Reynolds number dependent regions with high surfactant concentration, which, along with associated viscosities and stretching by turbulence stabilizes the threads. The subsequent breakup, producing 2.8 microm droplets, is due to an increasing surface area and diffusion of dispersants into the continuous phase.}, }
@article {pmid20366100, year = {2009}, author = {Boldyrev, S and Perez, JC}, title = {Spectrum of weak magnetohydrodynamic turbulence.}, journal = {Physical review letters}, volume = {103}, number = {22}, pages = {225001}, doi = {10.1103/PhysRevLett.103.225001}, pmid = {20366100}, issn = {1079-7114}, abstract = {Turbulence of magnetohydrodynamic waves in nature and in the laboratory is generally cross-helical or nonbalanced, in that the energies of Alfvén waves moving in opposite directions along the guide magnetic field are unequal. Based on high-resolution numerical simulations it is proposed that such turbulence spontaneously generates a condensate of the residual energy E(v) - E(b) at small field-parallel wave numbers. As a result, the energy spectra of Alfvén waves are generally not scale invariant in an inertial interval of limited extent. In the limit of an infinite Reynolds number, the universality is asymptotically restored at large wave numbers, and both spectra attain the scaling E(k) proportional to k(perpendicular)(-2). The generation of a condensate is apparently related to the breakdown of mirror symmetry in nonbalanced turbulence.}, }
@article {pmid20365926, year = {2009}, author = {Morais, AF and Seybold, H and Herrmann, HJ and Andrade, JS}, title = {Non-newtonian fluid flow through three-dimensional disordered porous media.}, journal = {Physical review letters}, volume = {103}, number = {19}, pages = {194502}, doi = {10.1103/PhysRevLett.103.194502}, pmid = {20365926}, issn = {1079-7114}, mesh = {*Models, Chemical ; Porosity ; *Rheology ; Water/chemistry ; }, abstract = {We investigate the flow of various non-newtonian fluids through three-dimensional disordered porous media by direct numerical simulation of momentum transport and continuity equations. Remarkably, our results for power-law (PL) fluids indicate that the flow, when quantified in terms of a properly modified permeability-like index and Reynolds number, can be successfully described by a single (universal) curve over a broad range of Reynolds conditions and power-law exponents. We also study the flow behavior of Bingham fluids described in terms of the Herschel-Bulkley model. In this case, our simulations reveal that the interplay of (i) the disordered geometry of the pore space, (ii) the fluid rheological properties, and (iii) the inertial effects on the flow is responsible for a substantial enhancement of the macroscopic hydraulic conductance of the system at intermediate Reynolds conditions.}, }
@article {pmid20365904, year = {2010}, author = {Fakhari, A and Rahimian, MH}, title = {Phase-field modeling by the method of lattice Boltzmann equations.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {3 Pt 2}, pages = {036707}, doi = {10.1103/PhysRevE.81.036707}, pmid = {20365904}, issn = {1550-2376}, abstract = {In this paper, at first, a lattice Boltzmann method for binary fluids, which is applicable at low viscosity values, is developed. The presented scheme is extension of the free-energy-based approach to a multi-relaxation-time collision model. Various benchmark problems such as the well-known Laplace law for stationary bubbles and capillary-wave test are conducted for validation. As an appealing application, instability of a rising bubble in an enclosed duct is studied and irregular behavior of the bubble is observed at very high Reynolds numbers. In order to highlight its capability to simulate high Reynolds number flows, which is a challenge for many other models, a typical wobbling bubble in the turbulent regime is simulated successfully. Then, in the context of phase-field modeling, a lattice Boltzmann method is proposed for multiphase flows with a density contrast. Unlike most of the previous models based on the phase-field theory, the proposed scheme not only tolerates very low viscosity values but also emerges as a promising method for investigation of two-phase flow problems with moderate density ratios. In addition to comparison to the kinetic-based model, the proposed approach is further verified by judging against the theoretical solutions and experimental data. Various case studies including the rising bubble, droplet splashing on a wet surface, and falling droplet are conducted to show the versatility of the presented lattice Boltzmann model.}, }
@article {pmid20365875, year = {2010}, author = {Bryce, RM and Freeman, MR}, title = {Extensional instability in electro-osmotic microflows of polymer solutions.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {3 Pt 2}, pages = {036328}, doi = {10.1103/PhysRevE.81.036328}, pmid = {20365875}, issn = {1550-2376}, abstract = {Fluid transport in microfluidic systems typically is laminar due to the low Reynolds number characteristic of the flow. The inclusion of suspended polymers imparts elasticity to fluids, allowing instabilities to be excited when substantial polymer stretching occurs. For high molecular weight polymer chains we find that flow velocities achievable by standard electro-osmotic pumping are sufficient to excite extensional instabilities in dilute polymer solutions. We observe a dependence in measured fluctuations on polymer concentration which plateaus at a threshold corresponding to the onset of significant molecular crowding in macromolecular solutions; plateauing occurs well below the overlap concentration. Our results show that electro-osmotic flows of complex fluids are disturbed from the steady regime, suggesting potential for enhanced mixing and requiring care in modeling the flow of complex liquids such as biopolymer suspensions.}, }
@article {pmid20365869, year = {2010}, author = {Bordja, L and Tuckerman, LS and Witkowski, LM and Navarro, MC and Barkley, D and Bessaih, R}, title = {Influence of counter-rotating von Kármán flow on cylindrical Rayleigh-Bénard convection.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {3 Pt 2}, pages = {036322}, doi = {10.1103/PhysRevE.81.036322}, pmid = {20365869}, issn = {1550-2376}, abstract = {The axisymmetric flow in an aspect-ratio-one cylinder whose upper and lower bounding disks are maintained at different temperatures and rotate at equal and opposite velocities is investigated. In this combined Rayleigh-Bénard/von Kármán problem, the imposed temperature gradient is measured by the Rayleigh number Ra and the angular velocity by the Reynolds number Re. Although fluid motion is present as soon as Re not equal 0 , a symmetry-breaking transition analogous to the onset of convection takes place at a finite Rayleigh number higher than that for Re=0 . For Re<95 , the transition is a pitchfork bifurcation to a pair of steady states, while for Re>95 , it is a Hopf bifurcation to a limit cycle. The steady states and limit cycle are connected via a pair of saddle-node infinite-period bifurcations except very near the Takens-Bogdanov codimension-two point, where the scenario includes global bifurcations. Detailed phase portraits and bifurcation diagrams are presented, as well as the evolution of the leading part of the spectrum, over the parameter ranges 0<or=Re<or=120 and 0<or=Ra<or=30 000 .}, }
@article {pmid20365864, year = {2010}, author = {Sahoo, G and Mitra, D and Pandit, R}, title = {Dynamo onset as a first-order transition: lessons from a shell model for magnetohydrodynamics.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {3 Pt 2}, pages = {036317}, doi = {10.1103/PhysRevE.81.036317}, pmid = {20365864}, issn = {1550-2376}, abstract = {We carry out systematic and high-resolution studies of dynamo action in a shell model for magnetohydrodynamic (MHD) turbulence over wide ranges of the magnetic Prandtl number PrM and the magnetic Reynolds number ReM. Our study suggests that it is natural to think of dynamo onset as a nonequilibrium first-order phase transition between two different turbulent, but statistically steady, states. The ratio of the magnetic and kinetic energies is a convenient order parameter for this transition. By using this order parameter, we obtain the stability diagram (or nonequilibrium phase diagram) for dynamo formation in our MHD shell model in the (PrM-1,ReM) plane. The dynamo boundary, which separates dynamo and no-dynamo regions, appears to have a fractal character. We obtain a hysteretic behavior of the order parameter across this boundary and suggestions of nucleation-type phenomena.}, }
@article {pmid20365860, year = {2010}, author = {Crowdy, DG and Or, Y}, title = {Two-dimensional point singularity model of a low-Reynolds-number swimmer near a wall.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {3 Pt 2}, pages = {036313}, doi = {10.1103/PhysRevE.81.036313}, pmid = {20365860}, issn = {1550-2376}, mesh = {Algorithms ; Animals ; Environment ; *Locomotion ; *Models, Biological ; Motion ; Motor Activity ; Nonlinear Dynamics ; Robotics ; }, abstract = {This paper studies a simple two-dimensional model of a swimmer at low-Reynolds-number near a no-slip wall by utilizing methods of complex analysis. The swimmer is propelled by purely tangential surface deformations and is modeled by moving point singularities. The nonlinear dynamics of the swimmer is formulated explicitly, and its motion near the wall is fully characterized. The results show qualitative agreement with predictions of three-dimensional models and with motion experiments on a robotic swimmer. The success and simplicity of the model suggest that it will provide a simple way to study the dynamics of low-Reynolds-number swimmers in more complicated geometries.}, }
@article {pmid20365857, year = {2010}, author = {Goddard, C and Hess, O and Hess, S}, title = {Low Reynolds number turbulence in nonlinear Maxwell-model fluids.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {3 Pt 2}, pages = {036310}, doi = {10.1103/PhysRevE.81.036310}, pmid = {20365857}, issn = {1550-2376}, abstract = {A generalized nonlinear Maxwell model which had previously been analyzed for plane Couette geometry is here applied to a lid-driven cavity flow. The full three-dimensional hydrodynamical problem is treated numerically. Depending on the relevant model parameters, both smooth laminar and low Reynolds number turbulent flows are found, strikingly similar to the experimentally observed elastic turbulence phenomena in polymer solutions. Representative results of the calculated flow patterns, as well as measures for the turbulent nature of the flow are presented graphically.}, }
@article {pmid20365856, year = {2010}, author = {Beltrán, A and Ramos, E and Cuevas, S and Brøns, M}, title = {Bifurcation analysis in a vortex flow generated by an oscillatory magnetic obstacle.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {3 Pt 2}, pages = {036309}, doi = {10.1103/PhysRevE.81.036309}, pmid = {20365856}, issn = {1550-2376}, abstract = {A numerical simulation and a theoretical model of the two-dimensional flow produced by the harmonic oscillation of a localized magnetic field (magnetic obstacle) in a quiescent viscous, electrically conducting fluid are presented. Nonuniform Lorentz forces produced by induced currents interacting with the oscillating magnetic field create periodic laminar flow patterns that can be characterized by three parameters: the oscillation Reynolds number, Reomega, the Hartmann number, Ha, and the dimensionless amplitude of the magnetic obstacle oscillation, D. The analysis is restricted to oscillations of small amplitude and Ha=100. The resulting flow patterns are described and interpreted in terms of position and evolution of the critical points of the instantaneous streamlines. It is found that in most of the cycle, the flow is dominated by a pair of counter rotating vortices that switch their direction of rotation twice per cycle. The transformation of the flow field present in the first part of the cycle into the pattern displayed in the second half occurs via the generation of hyperbolic and elliptic critical points. The numerical solution of the flow indicates that for low frequencies (v.e. Reomega=1), two elliptic and two hyperbolic points are generated, while for high frequencies (v.e. Reomega=100), a more complex topology involving four elliptic and two hyperbolic points appear. The bifurcation map for critical points of the instantaneous streamline is obtained numerically and a theoretical model based on a local analysis that predicts most of the qualitative properties calculated numerically is proposed.}, }
@article {pmid20365853, year = {2010}, author = {Sugioka, H}, title = {Chaotic mixer using electro-osmosis at finite Péclet number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {3 Pt 2}, pages = {036306}, doi = {10.1103/PhysRevE.81.036306}, pmid = {20365853}, issn = {1550-2376}, abstract = {Two pressure-driven streams of two miscible liquids can only mix by diffusion in microfluidic channels because of the low Reynolds number. We present an idea to generate mixing by "chaotic advection" in microscale geometries. That is, we consider using induced-charge electro-osmosis to generate a second flow and then modulate between the pressure-driven and induced-charge flows. By using the combined method consisting of the boundary element method, the Lagrangian particle tracking method, and the random-walk method, we analyze mixing efficiency, mixing time, and mixing length, with the effects of modulation frequency and molecular diffusivity, and compare our proposed mixer with other mixers. By this analysis, we find that chaotic mixing can be produced efficiently in a microfluidic channel by switching between pressure-driven and induced-charge flows in a wide range of Péclet number under the specific condition of Strouhal number. By using our proposed mixer, we can expect to realize efficient chaotic mixing with minimum voltage in an ordinary flow channel with a simple structure without an oblique electric field even at large Péclet number.}, }
@article {pmid20365852, year = {2010}, author = {Wang, SY and Tian, FB and Jia, LB and Lu, XY and Yin, XZ}, title = {Secondary vortex street in the wake of two tandem circular cylinders at low Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {3 Pt 2}, pages = {036305}, doi = {10.1103/PhysRevE.81.036305}, pmid = {20365852}, issn = {1550-2376}, abstract = {The experiments on two tandem circular cylinders were conducted in a horizontal soap film tunnel for the Reynolds number Re=60 , 80, and 100 and the nondimensional center-to-center spacing Gamma ranging in 1 approximately 12. The flow patterns were recorded by a high-speed camera and the vortex shedding frequency was obtained by a spatiotemporal evolution method. The secondary vortex formation (SVF) mode characterized by the formation of a secondary vortex street in the wake of the downstream cylinder was found at large gamma. Moreover, some typical modes predicted by previous investigations, including the single bluff-body, shear layer reattachment, and synchronization of vortex shedding modes, were also revisited in our experiments. Further, numerical simulations were carried out using a space-time finite-element method and the results confirmed the existence of the SVF mode. The mechanism of SVF mode was analyzed in terms of the numerical results. The dependence of the Strouhal number Sr on Gamma was given and the flow characteristics relevant to the critical spacing values and the hysteretic mode transitions were investigated.}, }
@article {pmid20365851, year = {2010}, author = {Leoni, M and Bassetti, B and Kotar, J and Cicuta, P and Cosentino Lagomarsino, M}, title = {Minimal two-sphere model of the generation of fluid flow at low Reynolds numbers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {3 Pt 2}, pages = {036304}, doi = {10.1103/PhysRevE.81.036304}, pmid = {20365851}, issn = {1550-2376}, abstract = {Locomotion and generation of flow at low Reynolds number are subject to severe limitations due to the irrelevance of inertia: the "scallop theorem" requires that the system have at least two degrees of freedom, which move in non-reciprocal fashion, i.e. breaking time-reversal symmetry. We show here that a minimal model consisting of just two spheres driven by harmonic potentials is capable of generating flow. In this pump system the two degrees of freedom are the mean and relative positions of the two spheres. We have performed and compared analytical predictions, numerical simulation and experiments, showing that a time-reversible drive is sufficient to induce flow.}, }
@article {pmid20365807, year = {2010}, author = {Goldenfeld, N and Guttenberg, N and Gioia, G}, title = {Extreme fluctuations and the finite lifetime of the turbulent state.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {3 Pt 2}, pages = {035304}, doi = {10.1103/PhysRevE.81.035304}, pmid = {20365807}, issn = {1550-2376}, abstract = {We argue that the transition to turbulence is controlled by large amplitude events that follow extreme distribution theory. The theory suggests an explanation for recent observations of the turbulent state lifetime which exhibit superexponential scaling behavior with Reynolds number.}, }
@article {pmid20365804, year = {2010}, author = {Fransson, JH}, title = {Turbulent spot evolution in spatially invariant boundary layers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {3 Pt 2}, pages = {035301}, doi = {10.1103/PhysRevE.81.035301}, pmid = {20365804}, issn = {1550-2376}, abstract = {A demanding task, for successful fluid dynamic design in many industrial applications, is being able to predict the transition to turbulence location in boundary layer flows. The focus of the present experimental study is on the late stage of transition scenarios where turbulent spots are borne. We report on a natural stabilizing mechanism on the growth rate of turbulent spots, which takes place in a specific bypass transition scenario, and show that there is a palpable history effect of the origin of the turbulent spot on the streamwise evolution. Furthermore, experimental evidence on Reynolds number effects on the spot evolution in boundary layers is put forward. This has been made possible by setting up an idealized experiment, which usually only is considered as a schoolbook example.}, }
@article {pmid20365653, year = {2010}, author = {Bychkov, V and Akkerman, V and Valiev, D and Law, CK}, title = {Role of compressibility in moderating flame acceleration in tubes.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {2 Pt 2}, pages = {026309}, doi = {10.1103/PhysRevE.81.026309}, pmid = {20365653}, issn = {1550-2376}, abstract = {The effect of gas compression on spontaneous flame acceleration leading to deflagration-to-detonation transition is studied theoretically for small Reynolds number flame propagation from the closed end of a tube. The theory assumes weak compressibility through expansion in small Mach number. Results show that the flame front accelerates exponentially during the initial stage of propagation when the Mach number is negligible. With continuous increase in the flame velocity with respect to the tube wall, the flame-generated compression waves subsequently moderate the acceleration process by affecting the flame shape and velocity, as well as the flow driven by the flame.}, }
@article {pmid20365648, year = {2010}, author = {Shayeganfar, F and Javidpour, L and Taghavinia, N and Rahimi Tabar, MR and Sahimi, M and Bagheri-Tar, F}, title = {Controlled nucleation and growth of CdS nanoparticles by turbulent dispersion.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {2 Pt 2}, pages = {026304}, doi = {10.1103/PhysRevE.81.026304}, pmid = {20365648}, issn = {1550-2376}, abstract = {We propose and test a method for controlling the size of nanoparticles, which plays a fundamental role in their electrical, optical, and mechanical properties. The method utilizes turbulent mixing, and is applicable to the fabrication of any type of nanoparticle that uses a solution environment in the preparation process. We show by well-controlled experiments on the CdS nanoparticles, which are semiconducting materials, that the average size d of the particles decreases with Reynolds number Re.}, }
@article {pmid20365623, year = {2010}, author = {Borrero-Echeverry, D and Schatz, MF and Tagg, R}, title = {Transient turbulence in Taylor-Couette flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {2 Pt 2}, pages = {025301}, doi = {10.1103/PhysRevE.81.025301}, pmid = {20365623}, issn = {1550-2376}, abstract = {Recent studies have brought into question the view that at sufficiently high Reynolds number turbulence is an asymptotic state. We present direct observation of the decay of turbulent states in Taylor-Couette flow with lifetimes spanning five orders of magnitude. We also show that there is a regime where Taylor-Couette flow shares many of the decay characteristics observed in other shear flows, including Poisson statistics and the coexistence of laminar and turbulent patches. Our data suggest that for a range of Reynolds numbers characteristic decay times increase superexponentially with increasing Reynolds number but remain bounded in agreement with the most recent data from pipe flow. Our data are also consistent with recent theoretical predictions of lifetime scaling in transitional flows.}, }
@article {pmid20365507, year = {2010}, author = {Chakraborty, S and Jensen, MH and Madsen, BS}, title = {Three-dimensional turbulent relative dispersion by the Gledzer-Ohkitani-Yamada shell model.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {1 Pt 2}, pages = {017301}, doi = {10.1103/PhysRevE.81.017301}, pmid = {20365507}, issn = {1550-2376}, abstract = {We study pair dispersion in a three-dimensional incompressible high Reynolds number turbulent flow generated by Fourier transforming the dynamics of the Gledzer-Ohkitani-Yamada (GOY) shell model into real space. We show that GOY shell model can successfully reproduce both the Batchelor and the Richardson-Obukhov regimes of turbulent relative dispersion. We also study how the crossover time scales with the initial separations of a particle pair and compare it to the prediction by Batchelor.}, }
@article {pmid20365471, year = {2010}, author = {Lee, E and Brachet, ME and Pouquet, A and Mininni, PD and Rosenberg, D}, title = {Lack of universality in decaying magnetohydrodynamic turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {1 Pt 2}, pages = {016318}, doi = {10.1103/PhysRevE.81.016318}, pmid = {20365471}, issn = {1550-2376}, abstract = {Using computations of three-dimensional magnetohydrodynamic (MHD) turbulence with a Taylor-Green flow, whose inherent time-independent symmetries are implemented numerically, and in the absence of either a forcing function or an imposed uniform magnetic field, we show that three different inertial ranges for the energy spectrum may emerge for three different initial magnetic fields, the selecting parameter being the ratio of nonlinear eddy to Alfvén time. Equivalent computational grids range from 128(3) to 2048(3) points with a unit magnetic Prandtl number and a Taylor Reynolds number of up to 1500 at the peak of dissipation. We also show a convergence of our results with Reynolds number. Our study is consistent with previous findings of a variety of energy spectra in MHD turbulence by studies performed in the presence of both a forcing term with a given correlation time and a strong, uniform magnetic field. However, in contrast to the previous studies, here the ratio of characteristic time scales can only be ascribed to the intrinsic nonlinear dynamics of the paradigmatic flows under study.}, }
@article {pmid20365470, year = {2010}, author = {Schumacher, KR and Riley, JJ and Finlayson, BA}, title = {Effects of an oscillating magnetic field on homogeneous ferrofluid turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {1 Pt 2}, pages = {016317}, doi = {10.1103/PhysRevE.81.016317}, pmid = {20365470}, issn = {1550-2376}, abstract = {This paper presents the results from direct numerical simulations of homogeneous ferrofluid turbulence with a spatially uniform, applied oscillating magnetic field. Due to the strong coupling that exists between the magnetic field and the ferrofluid, we find that the oscillating field can affect the characteristics of the turbulent flow. The magnetic field does work on the turbulent flow and typically leads to an increased rate of energy loss via two dissipation modes specific to ferrofluids. However, under certain conditions this magnetic work results in injection, or a forcing, of turbulent kinetic energy into the flow. For the cases considered here, there is no mean shear and the mean components of velocity, vorticity, and particle spin rate are all zero. Thus, the effects shown are entirely due to the interactions between the turbulent fluctuations of the ferrofluid and the magnetic field. In addition to the effects of the oscillation frequency, we also investigate the effects of the choice of magnetization equation. The calculations focus on the approximate centerline conditions of the relatively low Reynolds number turbulent ferrofluid pipe flow experiments described previously [K. R. Schumacher, Phys. Rev. E 67, 026308 (2003)].}, }
@article {pmid20365463, year = {2010}, author = {Martin, LN and Mininni, PD}, title = {Intermittency in the isotropic component of helical and nonhelical turbulent flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {1 Pt 2}, pages = {016310}, doi = {10.1103/PhysRevE.81.016310}, pmid = {20365463}, issn = {1550-2376}, abstract = {We analyze the isotropic component of turbulent flows spanning a broad range or Reynolds numbers. The aim is to identify scaling laws and their Reynolds number dependence in flows under different mechanical forcings. To this end, we applied an SO(3) decomposition to data stemming from direct numerical simulations with spatial resolutions ranging from 64(3) to 1024(3) grid points, and studied the scaling of high order moments of the velocity field. The study was carried out for two different flows obtained forcing the system with a Taylor-Green vortex or the Arn'old-Beltrami-Childress flow. Our results indicate that helicity has no significant impact on the scaling exponents as obtained from the generalized structure functions. Intermittency effects increase with the Reynolds number in the range of parameters studied, and in some cases are larger than what can be expected from several models of intermittency in the literature. The observed dependence of intermittency with the Reynolds number decreases if extended self-similarity is used to estimate the exponents.}, }
@article {pmid20365423, year = {2010}, author = {Schneider, TM and De Lillo, F and Buehrle, J and Eckhardt, B and Dörnemann, T and Dörnemann, K and Freisleben, B}, title = {Transient turbulence in plane Couette flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {81}, number = {1 Pt 2}, pages = {015301}, doi = {10.1103/PhysRevE.81.015301}, pmid = {20365423}, issn = {1550-2376}, abstract = {Plane Couette flow, the flow between two parallel plates moving in opposite directions, belongs to the group of shear flows where turbulence occurs while the laminar profile is stable. Experimental and numerical studies show that at intermediate Reynolds numbers turbulence is transient and that the lifetimes are distributed exponentially. However, these studies have remained inconclusive about a divergence in lifetimes above a critical Reynolds number. The extensive numerical results for flow in a box of width 2pi and length 8pi presented here cover observation times up to 12,000 units and show that while the lifetimes increase rapidly with Reynolds number, they do not indicate a divergence and therefore no transition to persistent turbulence.}, }
@article {pmid20365276, year = {2009}, author = {Blanchette, F}, title = {Flow lines and mixing within drops in microcapillaries.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {80}, number = {6 Pt 2}, pages = {066316}, doi = {10.1103/PhysRevE.80.066316}, pmid = {20365276}, issn = {1550-2376}, mesh = {Algorithms ; Biophysics/*methods ; Computer Simulation ; Microfluidic Analytical Techniques/*instrumentation ; *Microfluidics ; Stress, Mechanical ; }, abstract = {We present a theoretical and numerical investigation of streamlines and mixing within drops flowing in capillaries. We first study theoretically the limit case of purely viscous flow around a drop of negligible radius, and find that, owing to geometrical constraints, recirculating regions are always present at the front and back of such drops. Using two-dimensional simulations, we visualize streamlines for larger drops, showing that the extent of these recirculating torii increases with drop size and decreases with Reynolds number. We study the mixing within drops as they are subjected to time-dependent shear, thus modeling a sinusoidal channel, and find that while cross-stream mixing is efficient, streamwise mixing is hindered by the front and back recirculating regions.}, }
@article {pmid20365222, year = {2009}, author = {Cartellier, A and Andreotti, M and Sechet, P}, title = {Induced agitation in homogeneous bubbly flows at moderate particle Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {80}, number = {6 Pt 2}, pages = {065301}, doi = {10.1103/PhysRevE.80.065301}, pmid = {20365222}, issn = {1550-2376}, abstract = {We investigated the agitation induced in a liquid by quasimonodispersed spherical bubbles. For Re(p) about 10 and for void fractions ranging from 0.002 to 0.1, the axial velocity fluctuation probability density functions happen to be uniquely determined by the velocity variance. In addition, the variance experiences a rupture from a nonlinear to a quasilinear increase with the volumic concentration. It is shown that the presence of a deficit of neighbors in the wake of any test inclusion forces the screening of velocity disturbances at a finite distance X-of order Re(p)/alpha-and that the velocity variance does not depend on the system size when the later is large compared with X. Finally, the bubble-induced agitation happens to be much stronger for quasimonodispersed than for polydispersed size distributions because of the longer interaction duration between pairs in the former case.}, }
@article {pmid20365073, year = {2009}, author = {Ng, CO and Ma, Y}, title = {Lagrangian transport induced by peristaltic pumping in a closed channel.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {80}, number = {5 Pt 2}, pages = {056307}, doi = {10.1103/PhysRevE.80.056307}, pmid = {20365073}, issn = {1550-2376}, mesh = {Algorithms ; Biomechanical Phenomena ; Biophysics/*methods ; Motion ; Oscillometry ; *Peristalsis ; Rheology/methods ; Time Factors ; }, abstract = {Lagrangian transport induced by peristaltic waves traveling on the boundaries of a two-dimensional rectangular closed channel is studied analytically. Based on the Lagrangian description, an asymptotic analysis is performed to generate explicit expressions for the leading-order oscillatory as well as the higher-order time-mean mass transport (or steady streaming) velocities as functions of the wave properties. Two cases are considered. The first case, which is for slow wave frequency or very small wave amplitude such that the steady-streaming Reynolds number (Re_(s)) is very small, recovers the one studied previously in the literature, but with all the results fully presented in the Lagrangian sense. The second case, corresponding to high-frequency pumping such as Re_(s) is order unity, is where it has been handled analytically. It is found that the overall mixing resulting from the mass transport can depend on the phase shift of the two waves, the wave number, the frequency, as well as the amplitude of the waves.}, }
@article {pmid20365010, year = {2009}, author = {Leshansky, AM}, title = {Enhanced low-Reynolds-number propulsion in heterogeneous viscous environments.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {80}, number = {5 Pt 1}, pages = {051911}, doi = {10.1103/PhysRevE.80.051911}, pmid = {20365010}, issn = {1550-2376}, mesh = {Animals ; Cell Movement/*physiology ; Cilia/*physiology ; Computer Simulation ; *Ecosystem ; Flagella/*physiology ; *Models, Biological ; Swimming/*physiology ; Viscosity ; }, abstract = {It has been known for some time that some microorganisms can swim faster in high-viscosity gel-forming polymer solutions. These gel-like media come to mimic highly viscous heterogeneous environment that these microorganisms encounter in-vivo. The qualitative explanation of this phenomena first offered by Berg and Turner [Nature (London) 278, 349 (1979)], suggests that propulsion enhancement is a result of flagellum pushing on quasi-rigid loose polymer network formed in some polymer solutions. Inspired by these observations, inertia-less propulsion in a heterogeneous viscous medium composed of sparse array of stationary obstacles embedded into a incompressible Newtonian liquid is considered. It is demonstrated that for prescribed propulsion gaits, including propagating surface distortions and rotating helical filament, the propulsion speed is enhanced when compared to swimming in purely viscous solvent. It is also shown that the locomotion in heterogenous viscous media is characterized by improved hydrodynamic efficiency. The results of the rigorous numerical simulation of the rotating helical filament propelled through a random sparse array of stationary obstructions are in close agreement with predictions of the proposed resistive force theory based on effective media approximation.}, }
@article {pmid20358453, year = {2010}, author = {Karaismail, E and Celik, I}, title = {On the inconsistencies related to prediction of flow into an enclosing hood obstructed by a worker.}, journal = {Journal of occupational and environmental hygiene}, volume = {7}, number = {6}, pages = {315-325}, doi = {10.1080/15459621003717854}, pmid = {20358453}, issn = {1545-9632}, support = {1 R01 OH008165/OH/NIOSH CDC HHS/United States ; }, mesh = {*Air Movements ; Humans ; Inhalation Exposure ; Occupational Exposure ; *Occupational Health ; *Ventilation ; }, abstract = {The recirculating flow structures formed in the wake of a worker standing in front of an enclosing fume hood were numerically investigated. Two- and three-dimensional, unsteady, laminar/turbulent computations were performed for a Reynolds number (Re) range of 1.0 x 10(3)-1.0 x 10(5). The standard k-epsilon, Renormalization group (RNG) k-epsilon, and Shear Stress Transport (SST) k-omega models were used in Unsteady Reynolds Averaged Navier-Stokes (URANS) computations, and the results were compared with each other and also with the previous predictions reported in the literature. Numerical issues regarding the grid convergence and the inadequacies of turbulence models that may come into play at low Reynolds numbers were addressed. On the whole, SST k-omega model was found to be promising for qualitatively accurate prediction of both steady and unsteady recirculatory flow patterns in the wake of the worker. On the other hand, the standard and RNG k-epsilon models failed in prediction of anticipated unsteadiness at low Reynolds numbers. In a more realistic three-dimensional simulation with SST k-omega model, the anticipated unsteady and recirculating flow field in the wake of the worker was captured. Present results seem to qualitatively agree with the deductions made from experimental analyses in the literature while conflicting with some aspects of the previously reported numerical results. The apparent inconsistencies observed between the current results and those published in the literature were elucidated.}, }
@article {pmid20211881, year = {2010}, author = {Orlov, SS and Abarzhi, SI and Oh, SB and Barbastathis, G and Sreenivasan, KR}, title = {High-performance holographic technologies for fluid-dynamics experiments.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {368}, number = {1916}, pages = {1705-1737}, pmid = {20211881}, issn = {1364-503X}, mesh = {Algorithms ; Equipment Design ; Fourier Analysis ; Holography/*methods ; Image Interpretation, Computer-Assisted/*methods ; Imaging, Three-Dimensional/*methods ; Models, Statistical ; Nitrogen/chemistry ; Optics and Photonics ; Oxygen/chemistry ; Pattern Recognition, Automated/methods ; Rheology/*instrumentation ; Signal Processing, Computer-Assisted ; Xenon ; }, abstract = {Modern technologies offer new opportunities for experimentalists in a variety of research areas of fluid dynamics. Improvements are now possible in the state-of-the-art in precision, dynamic range, reproducibility, motion-control accuracy, data-acquisition rate and information capacity. These improvements are required for understanding complex turbulent flows under realistic conditions, and for allowing unambiguous comparisons to be made with new theoretical approaches and large-scale numerical simulations. One of the new technologies is high-performance digital holography. State-of-the-art motion control, electronics and optical imaging allow for the realization of turbulent flows with very high Reynolds number (more than 10(7)) on a relatively small laboratory scale, and quantification of their properties with high space-time resolutions and bandwidth. In-line digital holographic technology can provide complete three-dimensional mapping of the flow velocity and density fields at high data rates (over 1000 frames per second) over a relatively large spatial area with high spatial (1-10 microm) and temporal (better than a few nanoseconds) resolution, and can give accurate quantitative description of the fluid flows, including those of multi-phase and unsteady conditions. This technology can be applied in a variety of problems to study fundamental properties of flow-particle interactions, rotating flows, non-canonical boundary layers and Rayleigh-Taylor mixing. Some of these examples are discussed briefly.}, }
@article {pmid20206000, year = {2010}, author = {Waghmare, PR and Mitra, SK}, title = {Modeling of combined electroosmotic and capillary flow in microchannels.}, journal = {Analytica chimica acta}, volume = {663}, number = {2}, pages = {117-126}, doi = {10.1016/j.aca.2010.01.055}, pmid = {20206000}, issn = {1873-4324}, mesh = {Chromatography, Micellar Electrokinetic Capillary/*methods ; Electrolytes/chemistry ; Electroosmosis/*methods ; Microfluidic Analytical Techniques/*methods ; *Models, Chemical ; Surface Tension ; Time Factors ; }, abstract = {In the present study, theoretical model for the transient response of a capillary flow under the combined effects of electroosmotic and capillary forces at low Reynolds number is presented. The governing equation is derived based on the balance among the electrokinetic, surface, viscous and gravity forces. A non-dimensional transient governing equation for the penetration depth as a function of time is obtained by normalizing the viscous, gravity and electroosmotic forces with surface tension force. A new non-dimensional group for the electroosmotic force, E(o), is obtained through the non-dimensional analysis. This new non-dimensional group is a representation of combined electroosmosis and surface tension, i.e., capillarity. The numerical solution of governing equation is obtained to study the effect of different operating parameters on the flow front transport. In a combined flow, it is observed that the flow with positive and low negative magnitude E(o) numbers, the attainment of equilibrium penetration depth is similar to a capillary flow. In case of high negative magnitude E(o) numbers, complete filling of the channel is observed. The electrolyte with lower permittivity delays the progress of the flow front whereas a large EDL transports the electrolyte quickly. Higher viscous and gravity forces also delay the transport process in the combined flow. This model suggests that in combined flow the electrokinetic parameters also play an important role on the capillary flow and experiments are required to confirm this electrokinetic effect on capillary transport.}, }
@article {pmid20171640, year = {2010}, author = {Defraeye, T and Blocken, B and Koninckx, E and Hespel, P and Carmeliet, J}, title = {Aerodynamic study of different cyclist positions: CFD analysis and full-scale wind-tunnel tests.}, journal = {Journal of biomechanics}, volume = {43}, number = {7}, pages = {1262-1268}, doi = {10.1016/j.jbiomech.2010.01.025}, pmid = {20171640}, issn = {1873-2380}, mesh = {*Bicycling ; Humans ; *Models, Theoretical ; *Posture ; }, abstract = {Three different cyclist positions were evaluated with Computational Fluid Dynamics (CFD) and wind-tunnel experiments were used to provide reliable data to evaluate the accuracy of the CFD simulations. Specific features of this study are: (1) both steady Reynolds-averaged Navier-Stokes (RANS) and unsteady flow modelling, with more advanced turbulence modelling techniques (Large-Eddy Simulation - LES), were evaluated; (2) the boundary layer on the cyclist's surface was resolved entirely with low-Reynolds number modelling, instead of modelling it with wall functions; (3) apart from drag measurements, also surface pressure measurements on the cyclist's body were performed in the wind-tunnel experiment, which provided the basis for a more detailed evaluation of the predicted flow field by CFD. The results show that the simulated and measured drag areas differed about 11% (RANS) and 7% (LES), which is considered to be a close agreement in CFD studies. A fair agreement with wind-tunnel data was obtained for the predicted surface pressures, especially with LES. Despite the higher accuracy of LES, its much higher computational cost could make RANS more attractive for practical use in some situations. CFD is found to be a valuable tool to evaluate the drag of different cyclist positions and to investigate the influence of small adjustments in the cyclist's position. A strong advantage of CFD is that detailed flow field information is obtained, which cannot easily be obtained from wind-tunnel tests. This detailed information allows more insight in the causes of the drag force and provides better guidance for position improvements.}, }
@article {pmid20162357, year = {2010}, author = {Xia, G and Tawhai, MH and Hoffman, EA and Lin, CL}, title = {Airway wall stiffening increases peak wall shear stress: a fluid-structure interaction study in rigid and compliant airways.}, journal = {Annals of biomedical engineering}, volume = {38}, number = {5}, pages = {1836-1853}, pmid = {20162357}, issn = {1573-9686}, support = {R01-HL-064368/HL/NHLBI NIH HHS/United States ; R01 EB005823-01/EB/NIBIB NIH HHS/United States ; R01 EB005823/EB/NIBIB NIH HHS/United States ; R01 HL064368-10/HL/NHLBI NIH HHS/United States ; S10 RR022421/RR/NCRR NIH HHS/United States ; R01-EB-005823/EB/NIBIB NIH HHS/United States ; S10 RR022421-01A2/RR/NCRR NIH HHS/United States ; R01 HL064368/HL/NHLBI NIH HHS/United States ; S10-RR-022421/RR/NCRR NIH HHS/United States ; UL1 RR024979/RR/NCRR NIH HHS/United States ; }, mesh = {*Airway Remodeling ; Humans ; Stress, Mechanical ; }, abstract = {The airflow characteristics in a computed tomography (CT) based human airway bifurcation model with rigid and compliant walls are investigated numerically. An in-house three-dimensional (3D) fluid-structure interaction (FSI) method is applied to simulate the flow at different Reynolds numbers and airway wall stiffness. As the Reynolds number increases, the airway wall deformation increases and the secondary flow becomes more prominent. It is found that the peak wall shear stress on the rigid airway wall can be five times stronger than that on the compliant airway wall. When adding tethering forces to the model, we find that these forces, which produce larger airway deformation than without tethering, lead to more skewed velocity profiles in the lower branches and further reduced wall shear stresses via a larger airway lumen. This implies that pathologic changes in the lung such as fibrosis or remodeling of the airway wall-both of which can serve to restrain airway wall motion-have the potential to increase wall shear stress and thus can form a positive feed-back loop for the development of altered flow profiles and airway remodeling. These observations are particularly interesting as we try to understand flow and structural changes seen in, for instance, asthma, emphysema, cystic fibrosis, and interstitial lung disease.}, }
@article {pmid20160939, year = {2009}, author = {Hoskins, MH and Kunz, RF and Bistline, JE and Dong, C}, title = {Coupled Flow-Structure-Biochemistry Simulations of Dynamic Systems of Blood Cells Using an Adaptive Surface Tracking Method.}, journal = {Journal of fluids and structures}, volume = {25}, number = {5}, pages = {936-953}, pmid = {20160939}, issn = {0889-9746}, support = {R01 CA125707/CA/NCI NIH HHS/United States ; R01 CA125707-01A1/CA/NCI NIH HHS/United States ; R01 CA125707-02/CA/NCI NIH HHS/United States ; R01 CA125707-03/CA/NCI NIH HHS/United States ; }, abstract = {A method for the computation of low Reynolds number dynamic blood cell systems is presented. The specific system of interest here is interaction between cancer cells and white blood cells in an experimental flow system. Fluid dynamics, structural mechanics, six-degree-of freedom motion control and surface biochemistry analysis components are coupled in the context of adaptive octree-based grid generation. Analytical and numerical verification of the quasi-steady assumption for the fluid mechanics is presented. The capabilities of the technique are demonstrated by presenting several three-dimensional cell system simulations, including the collision/interaction between a cancer cell and an endothelium adherent polymorphonuclear leukocyte (PMN) cell in a shear flow.}, }
@article {pmid20159158, year = {2010}, author = {Sznitman, J and Purohit, PK and Krajacic, P and Lamitina, T and Arratia, PE}, title = {Material properties of Caenorhabditis elegans swimming at low Reynolds number.}, journal = {Biophysical journal}, volume = {98}, number = {4}, pages = {617-626}, pmid = {20159158}, issn = {1542-0086}, support = {R01 AA017580/AA/NIAAA NIH HHS/United States ; }, mesh = {Animals ; Biomechanical Phenomena ; Caenorhabditis elegans/genetics/*physiology ; Elastic Modulus ; *Models, Biological ; Muscular Dystrophy, Animal/physiopathology ; Mutation ; Swimming/*physiology ; Viscosity ; }, abstract = {Undulatory locomotion, as seen in the nematode Caenorhabditis elegans, is a common swimming gait of organisms in the low Reynolds number regime, where viscous forces are dominant. Although the nematode's motility is expected to be a strong function of its material properties, measurements remain scarce. Here, the swimming behavior of C. elegans is investigated in experiments and in a simple model. Experiments reveal that nematodes swim in a periodic fashion and generate traveling waves that decay from head to tail. The model is able to capture the experiments' main features and is used to estimate the nematode's Young's modulus E and tissue viscosity eta. For wild-type C. elegans, we find E approximately 3.77 kPa and eta approximately -860 Pa.s; values of eta for live C. elegans are negative because the tissue is generating rather than dissipating energy. Results show that material properties are sensitive to changes in muscle functional properties, and are useful quantitative tools with which to more accurately describe new and existing muscle mutants.}, }
@article {pmid20148347, year = {2010}, author = {Van Doormaal, MA and Ethier, CR}, title = {Design optimization of a helical endothelial cell culture device.}, journal = {Biomechanics and modeling in mechanobiology}, volume = {9}, number = {5}, pages = {523-531}, doi = {10.1007/s10237-010-0192-z}, pmid = {20148347}, issn = {1617-7940}, mesh = {Cell Culture Techniques ; Endothelium/*chemistry ; *Equipment Design ; }, abstract = {The specific roles of mass transfer and fluid dynamic stresses on endothelial function, important in atherogenesis, are not known. Further, the effects of mass transfer and fluid dynamic stresses are difficult to separate because areas of "abnormal" mass transfer and "abnormal" wall shear stress tend to co-localize (where abnormal is defined as any deviation from the mass transfer rate or wall shear stress present in a long straight artery with the same flow rate and diameter). Our goal was to design a cell culture device which gives maximum separation between areas of abnormal shear stress and areas of abnormal mass transfer. We used design optimization principles to design a helical cell culture device. Using shear stress and mass transfer fields predicted by solving the governing equations, the area of the device which was exposed to low rates of mass transfer and normal levels of wall shear stress was determined. The design optimization method then maximized this area by varying the design variables, resulting in the optimum design. The optimum design had Reynolds number = 50, helical radius = 3.23 and helical pitch = 3.82. The area of the device which was exposed to low rates of mass transfer and regular levels of wall shear stress was about 4.5 times the inlet cross-sectional area of the device or about 5% of the device total internal surface area. An optimum design was successfully determined and the methodology used was shown to be robust. The area of the device which was exposed to low rates of mass transfer and regular levels of wall shear stress occurred in a defined region which should aid further experimental work.}, }
@article {pmid20097350, year = {2010}, author = {Keller, F and Feist, M and Nirschl, H and Dörfler, W}, title = {Investigation of the nonlinear effects during the sedimentation process of a charged colloidal particle by direct numerical simulation.}, journal = {Journal of colloid and interface science}, volume = {344}, number = {1}, pages = {228-236}, doi = {10.1016/j.jcis.2009.12.032}, pmid = {20097350}, issn = {1095-7103}, mesh = {Centrifugation ; Colloids/*chemistry ; Computer Simulation ; Gravitation ; Models, Chemical ; }, abstract = {In this article we study the settling process of a colloidal particle under the influence of a gravitational or centrifugal field in an unbounded electrolyte solution. Since particles in aqueous solutions normally carry a non-zero surface charge, a microscopic electric field develops which alters the sedimentation process compared to an uncharged particle. This process can be mathematically modelled via the Stokes-Poisson-Nernst-Planck system, a system of coupled partial differential equations that have to be solved in an exterior domain. After a dimensional analysis we investigate the influence of the various characteristic dimensionless numbers on the sedimentation velocity. Thereby the linear-response (weak-field) approximation that underpins almost all existing theoretical work on classical electrokinetic phenomena is relaxed, such that no additional assumption on the thickness of the double layer as well as on its displacement is needed. We show that there exists a strong influence of the fluid Reynolds number and the ionic strength on the sedimentation velocity. Further we have developed an asymptotic expansion to describe the limit of small values of the surface potential of a single particle. This expansion incorporates all nonlinear effects and extends the well-known results of Booth (1954) [1] and Ohshima et al. (1984) [2] to higher fluid Reynolds numbers.}, }
@article {pmid20063880, year = {2010}, author = {Kim, Y and Pekkan, K and Messner, WC and Leduc, PR}, title = {Three-dimensional chemical profile manipulation using two-dimensional autonomous microfluidic control.}, journal = {Journal of the American Chemical Society}, volume = {132}, number = {4}, pages = {1339-1347}, doi = {10.1021/ja9079572}, pmid = {20063880}, issn = {1520-5126}, mesh = {Equipment Design ; Microchemistry/*instrumentation/methods ; Microfluidics/*instrumentation/methods ; }, abstract = {The ability to specify or control spatiotemporal chemical environments is critical for controlling diverse processes from chemical synthesis to cellular responses. When established by microfluidics methods, this chemical control has largely been limited to two dimensions and by the need for using complex approaches. The ability to create three-dimensional (3D) chemical patterns is becoming more critical as microfluidics is beginning to have novel applications at larger millifluidic scales, including model organism behavior, embryonic development, and optofluidics. Here, we present a simple approach to create 3D chemical patterns that can be controlled in space and time via two-dimensional (2D), single-layer fluidic modules. Not only can we employ autonomous flow in a 2D fluidic configuration to produce a 3D pattern, but with very simple changes in the 2D configuration, the chemical pattern can be "focused and defocused" within the 3D cross section. We also show that these chemical patterns can be predicted by computational fluid dynamics simulations with high experimental correlation. These simulations allow analyses of the characteristics of interface behaviors with respect to three basic yet critical parameters that need to be thoroughly considered in scaling-up from microfluidic to millifluidic research: Reynolds number (Re), inlet geometry, and channel height. The findings not only indicate proof of concept for 3D pattern creation but also reveal that a number of fluidic experiments may have inherent limitations resulting from unrecognized 3D profiles that depend on these parameter choices. These results will be useful for research areas including embryonic development, cellular stimulation, and chemical fabrication approaches.}, }
@article {pmid20018696, year = {2009}, author = {Torney, C and Neufeld, Z and Couzin, ID}, title = {Context-dependent interaction leads to emergent search behavior in social aggregates.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {106}, number = {52}, pages = {22055-22060}, pmid = {20018696}, issn = {1091-6490}, mesh = {Algorithms ; Animals ; *Appetitive Behavior ; Cooperative Behavior ; Ecosystem ; Fourier Analysis ; Memory ; *Models, Biological ; Signal Transduction ; *Social Behavior ; Stochastic Processes ; }, abstract = {Locating the source of an advected chemical signal is a common challenge facing many living organisms. When the advecting medium is characterized by either high Reynolds number or high Peclet number, the task becomes highly nontrivial due to the generation of heterogeneous, dynamically changing filamental concentrations that do not decrease monotonically with distance to the source. Defining search strategies that are effective in these environments has important implications for the understanding of animal behavior and for the design of biologically inspired technology. Here we present a strategy that is able to solve this task without the higher intelligence required to assess spatial gradient direction, measure the diffusive properties of the flow field, or perform complex calculations. Instead, our method is based on the collective behavior of autonomous individuals following simple social interaction rules which are modified according to the local conditions they are experiencing. Through these context-dependent interactions, the group is able to locate the source of a chemical signal and in doing so displays an awareness of the environment not present at the individual level. This behavior illustrates an alternative pathway to the evolution of higher cognitive capacity via the emergent, group-level intelligence that can result from local interactions.}, }
@article {pmid20008363, year = {2010}, author = {Licht, SC and Wibawa, MS and Hover, FS and Triantafyllou, MS}, title = {In-line motion causes high thrust and efficiency in flapping foils that use power downstroke.}, journal = {The Journal of experimental biology}, volume = {213}, number = {1}, pages = {63-71}, doi = {10.1242/jeb.031708}, pmid = {20008363}, issn = {1477-9145}, mesh = {Animals ; Biomechanical Phenomena ; Flight, Animal ; Locomotion ; Models, Anatomic ; *Models, Biological ; *Movement ; }, abstract = {We show experimentally that flapping foil kinematics consisting of a power downstroke and a feathering upstroke together with a properly timed in-line motion, similar to those employed in forelimb propulsion of sea turtles, can produce high thrust and be hydrodynamically as efficient as symmetrically flapping foils. The crucial parameter for such asymmetrically flapping foils is a properly sized and timed in-line motion, whose effect is quantified by a new parameter, the advance angle, defined as the angle of the foil trajectory with respect to the horizontal, evaluated at the middle of the power downstroke. We show, in particular, that optimal efficiency in high aspect ratio rigid foils, accompanied by significant thrust production, is obtained for Strouhal numbers in the range 0.2-0.6 for Reynolds number equal to 13,000, and for values of the advance angle around 0.55pi (100 deg.). The optimized kinematics consist of the foil moving back axially during the downstroke, in the direction of the oncoming flow, and rotating with a large pitch angle. This causes the force vector to rotate and become nearly parallel to the steady flow, thus providing a large thrust and a smaller transverse force. During the upstroke, the foil is feathering while it moves axially forward, i.e. away from the vorticity shed during the power stroke; as a result, the transverse force remains relatively small and no large drag force is produced. Observations from turtles confirm qualitatively the findings from the foil experiments.}, }
@article {pmid20004514, year = {2010}, author = {Qian, F and Wang, H}, title = {Study of the filtration performance of a plain wave fabric filter using response surface methodology.}, journal = {Journal of hazardous materials}, volume = {176}, number = {1-3}, pages = {559-568}, doi = {10.1016/j.jhazmat.2009.11.065}, pmid = {20004514}, issn = {1873-3336}, mesh = {*Computer Simulation ; Equipment Design ; Filtration ; *Membranes, Artificial ; Methods ; Models, Theoretical ; Pressure ; Rheology ; }, abstract = {The gas-solid two-phase flows in the plain wave fabric filter were simulated by computational fluid dynamics (CFD) technology, and the warps and wefts of the fabric filter were made of filaments with different dimensions. The numerical solutions were carried out using commercial computational fluid dynamics (CFD) code Fluent 6.1. The filtration performances of the plain wave fabric filter with different geometry parameters and operating condition, including the horizontal distance, the vertical distance and the face velocity were calculated. The effects of geometry parameters and operating condition on filtration efficiency and pressure drop were studied using response surface methodology (RSM) by means of the statistical software (Minitab V14), and two second-order polynomial models were obtained with regard to the effect of the three factors as stated above. Moreover, the models were modified by dismissing the insignificant terms. The results show that the horizontal distance, vertical distance and the face velocity all play an important role in influencing the filtration efficiency and pressure drop of the plane wave fabric filters. The horizontal distance of 3.8 times the fiber diameter, the vertical distance of 4.0 times the fiber diameter and Reynolds number of 0.98 are found to be the optimal conditions to achieve the highest filtration efficiency at the same face velocity, while maintaining an acceptable pressure drop.}, }
@article {pmid19956555, year = {2009}, author = {Kolachalama, VB and Levine, EG and Edelman, ER}, title = {Luminal flow amplifies stent-based drug deposition in arterial bifurcations.}, journal = {PloS one}, volume = {4}, number = {12}, pages = {e8105}, pmid = {19956555}, issn = {1932-6203}, support = {R01 GM049039/GM/NIGMS NIH HHS/United States ; }, mesh = {Coronary Circulation/*physiology ; Coronary Vessels/*pathology/*physiopathology ; *Drug-Eluting Stents ; Humans ; Models, Biological ; }, abstract = {BACKGROUND: Treatment of arterial bifurcation lesions using drug-eluting stents (DES) is now common clinical practice and yet the mechanisms governing drug distribution in these complex morphologies are incompletely understood. It is still not evident how to efficiently determine the efficacy of local drug delivery and quantify zones of excessive drug that are harbingers of vascular toxicity and thrombosis, and areas of depletion that are associated with tissue overgrowth and luminal re-narrowing.<br><br>METHODS AND RESULTS: We constructed two-phase computational models of stent-deployed arterial bifurcations simulating blood flow and drug transport to investigate the factors modulating drug distribution when the main-branch (MB) was treated using a DES. Simulations predicted extensive flow-mediated drug delivery in bifurcated vascular beds where the drug distribution patterns are heterogeneous and sensitive to relative stent position and luminal flow. A single DES in the MB coupled with large retrograde luminal flow on the lateral wall of the side-branch (SB) can provide drug deposition on the SB lumen-wall interface, except when the MB stent is downstream of the SB flow divider. In an even more dramatic fashion, the presence of the SB affects drug distribution in the stented MB. Here fluid mechanic effects play an even greater role than in the SB especially when the DES is across and downstream to the flow divider and in a manner dependent upon the Reynolds number.<br><br>CONCLUSIONS: The flow effects on drug deposition and subsequent uptake from endovascular DES are amplified in bifurcation lesions. When only one branch is stented, a complex interplay occurs - drug deposition in the stented MB is altered by the flow divider imposed by the SB and in the SB by the presence of a DES in the MB. The use of DES in arterial bifurcations requires a complex calculus that balances vascular and stent geometry as well as luminal flow.}, }
@article {pmid19945138, year = {2010}, author = {Chatelain, M and Guizien, K}, title = {Modelling coupled turbulence - dissolved oxygen dynamics near the sediment-water interface under wind waves and sea swell.}, journal = {Water research}, volume = {44}, number = {5}, pages = {1361-1372}, doi = {10.1016/j.watres.2009.11.010}, pmid = {19945138}, issn = {1879-2448}, mesh = {Diffusion ; Geologic Sediments/*chemistry ; *Models, Chemical ; Oceans and Seas ; Oxygen/*analysis ; Solubility ; Time Factors ; Water/*chemistry ; *Water Movements ; *Wind ; }, abstract = {A one-dimensional vertical unsteady numerical model for diffusion-consumption of dissolved oxygen (DO) above and below the sediment-water interface was developed to investigate DO profile dynamics under wind waves and sea swell (high-frequency oscillatory flows with periods ranging from 2 to 30s). We tested a new approach to modelling DO profiles that coupled an oscillatory turbulent bottom boundary layer model with a Michaelis-Menten based consumption model. The flow regime controls both the mean value and the fluctuations of the oxygen mass transfer efficiency during a wave cycle, as expressed by the non-dimensional Sherwood number defined with the maximum shear velocity (Sh). The Sherwood number was found to be non-dependent on the sediment biogeochemical activity (mu). In the laminar regime, both cycle-averaged and variance of the Sherwood number are very low (Sh <0.05, VAR(Sh)<0.1%). In the turbulent regime, the cycle-averaged Sherwood number is larger (Sh approximately 0.2). The Sherwood number also has intra-wave cycle fluctuations that increase with the wave Reynolds number (VAR(Sh) up to 30%). Our computations show that DO mass transfer efficiency under high-frequency oscillatory flows in the turbulent regime are water-side controlled by: (a) the diffusion time across the diffusive boundary layer and (b) diffusive boundary layer dynamics during a wave cycle. As a result of these two processes, when the wave period decreases, the Sh minimum increases and the Sh maximum decreases. Sh values vary little, ranging from 0.17 to 0.23. For periods up to 30s, oxygen penetration depth into the sediment did not show any intra-wave fluctuations. Values for the laminar regime are small (<or=1mm for mu=2000gm(-3)d(-1)) and decrease when the flow period increases. In the turbulent regime, the oxygen penetration depth reaches values up to five times larger than those in the laminar regime, becoming asymptotic as the maximum shear velocity increases.}, }
@article {pmid19941326, year = {2010}, author = {Hortsch, R and Weuster-Botz, D}, title = {Power consumption and maximum energy dissipation in a milliliter-scale bioreactor.}, journal = {Biotechnology progress}, volume = {26}, number = {2}, pages = {595-599}, doi = {10.1002/btpr.338}, pmid = {19941326}, issn = {1520-6033}, mesh = {*Bioreactors ; Biotechnology/*methods ; Fermentation ; Thermodynamics ; Torque ; }, abstract = {Mean power consumption and maximum local energy dissipation were measured as function of operating conditions of a milliliter-scale stirred tank bioreactor (V = 12 mL) with a gas-inducing impeller. A standard laboratory-scale stirred tank bioreactor (V = 1,200 mL) with Rushton turbines was used as reference. The measured power characteristics (Newton number as function of Reynolds number) were the same on both scales. The changeover between laminar and turbulent flow regime was observed at a Reynolds number of 3,000 with the gas-inducing stirrer on a milliliter-scale. The Newton number (power number) in the turbulent flow regime was 3.3 on a milliliter-scale, which is close to values reported for six-blade Rushton turbines of standard bioreactors. Maximum local energy dissipation (epsilon(max)) was measured using a clay/polymer flocculation system. The maximum local energy dissipation in the milliliter-scale stirred tank bioreactor was reduced compared with the laboratory-scale stirred tank at the same mean power input per unit mass (epsilon(ø)), yielding epsilon(max)/epsilon(ø) approximately 10 compared with epsilon(max)/epsilon(ø) approximately 16. Hence, the milliliter-scale stirred tank reactor distributes power more uniformly in the reaction medium. These results are in good agreement with literature data, where a decreasing epsilon(max)/epsilon(ø) with increasing ratio of impeller diameter to reactor diameter is found (d/D = 0.7 compared with d/D = 0.4). Based on these data, impeller speeds can now be easily adjusted to achieve the same maximum local energy dissipation at different scales. This enables a more reliable and robust scale-up of bioprocesses from milliliter-scale to liter-scale reactors.}, }
@article {pmid19934055, year = {2010}, author = {Vilfan, M and Potocnik, A and Kavcic, B and Osterman, N and Poberaj, I and Vilfan, A and Babic, D}, title = {Self-assembled artificial cilia.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {107}, number = {5}, pages = {1844-1847}, pmid = {19934055}, issn = {1091-6490}, mesh = {Bioengineering ; Biophysical Phenomena ; Cilia/*physiology ; Colloids ; Equipment Design ; Magnetics ; Microfluidic Analytical Techniques/*instrumentation ; Models, Theoretical ; Rheology ; }, abstract = {Due to their small dimensions, microfluidic devices operate in the low Reynolds number regime. In this case, the hydrodynamics is governed by the viscosity rather than inertia and special elements have to be introduced into the system for mixing and pumping of fluids. Here we report on the realization of an effective pumping device that mimics a ciliated surface and imitates its motion to generate fluid flow. The artificial biomimetic cilia are constructed as long chains of spherical superparamagnetic particles, which self-assemble in an external magnetic field. Magnetic field is also used to actuate the cilia in a simple nonreciprocal manner, resulting in a fluid flow. We prove the concept by measuring the velocity of a cilia-pumped fluid as a function of height above the ciliated surface and investigate the influence of the beating asymmetry on the pumping performance. A numerical simulation was carried out that successfully reproduced the experimentally obtained data.}, }
@article {pmid19932019, year = {2010}, author = {Nasir, M and Ateya, DA and Burk, D and Golden, JP and Ligler, FS}, title = {Hydrodynamic focusing of conducting fluids for conductivity-based biosensors.}, journal = {Biosensors &amp; bioelectronics}, volume = {25}, number = {6}, pages = {1363-1369}, doi = {10.1016/j.bios.2009.10.033}, pmid = {19932019}, issn = {1873-4235}, mesh = {Biosensing Techniques/*instrumentation ; Computer-Aided Design ; Electric Conductivity ; Electrochemistry/*instrumentation ; Equipment Design ; Equipment Failure Analysis ; Flow Injection Analysis/*instrumentation ; Microfluidic Analytical Techniques/*instrumentation ; Pressure ; Solutions/*chemistry ; }, abstract = {Hydrodynamic focusing of a conducting fluid by a non-conducting fluid to form a constricted current path between two sensing electrodes is implemented in order to enhance the sensitivity of a 4-electrode conductance-based biosensor. The sensor has a simple two-inlet T-junction design and performs four-point conductivity measurements to detect particles immobilized between the sensing electrode pair. Computational simulations conducted in conjunction with experimental flow studies using confocal microscopy show that a flat profile for the focused layer is dependent on the Reynolds number for the chosen flow parameters. The results also indicate that a flat focused layer is desirable for both increased sensitivity as well as surface-binding efficiency. Proof of concept for conductance measurements in a hydrodynamically focused conducting fluid was demonstrated with entrapped magnetic beads.}, }
@article {pmid21715897, year = {2009}, author = {Shen, J and Liburdy, JA and Pence, DV and Narayanan, V}, title = {Droplet impingement dynamics: effect of surface temperature during boiling and non-boiling conditions.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {21}, number = {46}, pages = {464133}, doi = {10.1088/0953-8984/21/46/464133}, pmid = {21715897}, issn = {1361-648X}, abstract = {This study investigates the hydrodynamic characteristics of droplet impingement on heated surfaces and compares the effect of surface temperature when using water and a nanofluid on a polished and nanostructured surface. Results are obtained for an impact Reynolds number and Weber number of approximately 1700 and 25, respectively. Three discs are used: polished silicon, nanostructured porous silicon and gold-coated polished silicon. Seven surface temperatures, including single-phase (non-boiling) and two-phase (boiling) conditions, are included. Droplet impact velocity, transient spreading diameter and dynamic contact angle are measured. Results of water and a water-based single-wall carbon-nanotube nanofluid impinging on a polished silicon surface are compared to determine the effects of nanoparticles on impinging dynamics. The nanofluid results in larger spreading velocities, larger spreading diameters and an increase in early-stage dynamic contact angle. Results of water impinging on both polished silicon and nanostructured silicon show that the nanostructured surface enhances the heat transfer for evaporative cooling at lower surface temperatures, which is indicated by a shorter evaporation time. Using a nanofluid or a nanostructured surface can reduce the total evaporation time up to 20% and 37%, respectively. Experimental data are compared with models that predict dynamic contact angle and non-dimensional maximum spreading diameter. Results show that the molecular-kinetic theory's dynamic contact angle model agrees well with current experimental data for later times, but over-predicts at early times. Predictions of maximum spreading diameter based on surface energy analyses indicate that these models over-predict unless empirical coefficients are adjusted to fit the test conditions. This is a consequence of underestimates of the dissipative energy for the conditions studied.}, }
@article {pmid22949744, year = {2009}, author = {Padaki, A and Ultman, JS and Borhan, A}, title = {Ozone Uptake During Inspiratory Flow in a Model of the Larynx, Trachea and Primary Bronchial Bifurcation.}, journal = {Chemical engineering science}, volume = {64}, number = {22}, pages = {4640-4648}, pmid = {22949744}, issn = {0009-2509}, support = {P01 ES011617/ES/NIEHS NIH HHS/United States ; P01 ES011617-04/ES/NIEHS NIH HHS/United States ; }, abstract = {Three-dimensional simulations of the transport and uptake of a reactive gas such as O(3) were compared between an idealized model of the larynx, trachea, and first bifurcation and a second "control" model in which the larynx was replaced by an equivalent, cylindrical, tube segment. The Navier-Stokes equations, Spalart-Allmaras turbulence equation, and convection-diffusion equation were implemented at conditions reflecting inhalation into an adult human lung. Simulation results were used to analyze axial velocity, turbulent viscosity, local fractional uptake, and regional uptake. Axial velocity data revealed a strong laryngeal jet with a reattachment point in the proximal trachea. Turbulent viscosity data indicated that jet turbulence occurred only at high Reynolds numbers and was attenuated by the first bifurcation. Local fractional uptake data affirmed hotspots previously reported at the first carina, and suggested additional hotspots at the glottal constriction and jet reattachment point in the proximal trachea. These laryngeal effects strongly depended on inlet Reynolds number, with maximal effects (approaching 15%) occurring at maximal inlet flow rates. While the increase in the regional uptake caused by the larynx subsided by the end of the model, the effect of the larynx on cumulative uptake persisted further downstream. These results suggest that with prolonged exposure to a reactive gas, entire regions of the larynx and proximal trachea could show signs of tissue injury.}, }
@article {pmid19905642, year = {2009}, author = {Kinet, M and Knaepen, B and Molokov, S}, title = {Instabilities and transition in magnetohydrodynamic flows in ducts with electrically conducting walls.}, journal = {Physical review letters}, volume = {103}, number = {15}, pages = {154501}, doi = {10.1103/PhysRevLett.103.154501}, pmid = {19905642}, issn = {1079-7114}, abstract = {This Letter presents a numerical study of a magnetohydrodynamic flow in a square duct with electrically conducting walls subject to a uniform, transverse magnetic field. Two regimes of instability and transition of Hunt's jets at the walls parallel to the magnetic field have been identified. The first one occurs for relatively low values of the Reynolds number Re and is associated with weak, periodic, counterrotating vortices discovered previously in linear stability studies. The second is a new regime taking place for higher values of Re. It is associated with trains of small-scale vortices enveloped into larger structures, and involves partial detachment of jets from parallel walls. Once this regime sets in, the kinetic energy of perturbations increases by 2 orders of magnitude.}, }
@article {pmid19905571, year = {2009}, author = {Duriez, T and Aider, JL and Wesfreid, JE}, title = {Self-sustaining process through streak generation in a flat-plate boundary layer.}, journal = {Physical review letters}, volume = {103}, number = {14}, pages = {144502}, doi = {10.1103/PhysRevLett.103.144502}, pmid = {19905571}, issn = {1079-7114}, abstract = {The existence of a self-sustaining process between streamwise vortices and streaks has been suggested at moderate Reynolds numbers. Such a mechanism has never been demonstrated experimentally. Using small cylinders as vortex generators to create streamwise counterrotating vortices, we show, through the characterization of the spatial transient growth of the energy of the longitudinal and spanwise velocity perturbations, that such a mechanism exists above a given Reynolds number. From instantaneous particle image velocimetry fields in a horizontal plane, we show that the self-sustaining process can also be associated with the longitudinal destabilization of streamwise streaks.}, }
@article {pmid19905544, year = {2009}, author = {Kaya, T and Koser, H}, title = {Characterization of hydrodynamic surface interactions of Escherichia coli cell bodies in shear flow.}, journal = {Physical review letters}, volume = {103}, number = {13}, pages = {138103}, doi = {10.1103/PhysRevLett.103.138103}, pmid = {19905544}, issn = {0031-9007}, mesh = {Escherichia coli/chemistry/*physiology ; *Models, Biological ; Surface Properties ; }, abstract = {We experimentally demonstrate that nonflagellated Escherichia coli strains follow modified Jeffery orbits in shear flow near a surface. We fully characterize their Jeffery orbits as a function of their aspect ratios and distance from that surface. Thanks to the linearity of Navier-Stokes equations under low-Reynolds-number conditions, the hydrodynamic body-wall interactions described here can be superimposed with flagellar motility and Brownian motion to construct models that explain the full picture of bacterial motility near a surface under shear flow.}, }
@article {pmid19905477, year = {2009}, author = {Liao, W and Peng, Y and Luo, LS}, title = {Gas-kinetic schemes for direct numerical simulations of compressible homogeneous turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {80}, number = {4 Pt 2}, pages = {046702}, doi = {10.1103/PhysRevE.80.046702}, pmid = {19905477}, issn = {1550-2376}, mesh = {Computer Simulation ; Gases/*chemistry ; Kinetics ; *Models, Theoretical ; *Nonlinear Dynamics ; *Numerical Analysis, Computer-Assisted ; Pressure ; Rheology/*methods ; }, abstract = {We apply the gas-kinetic scheme (GKS) for the direct numerical simulations (DNSs) of compressible decaying homogeneous isotropic turbulence (DHIT). We intend to study the accuracy, stability, and efficiency of the gas-kinetic scheme for DNS of compressible homogeneous turbulence depending on both flow conditions and numerics. In particular, we study the GKS with multidimensional, quasi-one-dimensional, dimensional-splitting, and smooth-flow approximations. We simulate the compressible DHIT with the Taylor microscale Reynolds number Re(lambda)=72.0 and the turbulence Mach number Ma(t) between 0.1 and 0.6. We compute the low-order statistical quantities including the total kinetic energy K(t), the dissipation rate epsilon(t), the skewness S(u)(t), and the flatness F(u)(t) of the velocity field u(x,t). We assess the effects on the turbulence statistics due to the approximations made in the treatment of fluxes, the flux limiter, the accuracy of the interpolation, and the bulk viscosity. Our results show that the GKS is adequate for DNS of compressible homogeneous turbulence as far as the low-order turbulence statistics are concerned.}, }
@article {pmid19905440, year = {2009}, author = {Hamlington, PE and Dahm, WJ}, title = {Nonlocal form of the rapid pressure-strain correlation in turbulent flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {80}, number = {4 Pt 2}, pages = {046311}, doi = {10.1103/PhysRevE.80.046311}, pmid = {19905440}, issn = {1550-2376}, mesh = {Computer Simulation ; Elastic Modulus ; *Models, Theoretical ; *Nonlinear Dynamics ; Pressure ; Rheology/*methods ; Statistics as Topic ; Stress, Mechanical ; }, abstract = {A new fundamentally based formulation of nonlocal effects in the rapid pressure-strain correlation in turbulent flows has been obtained. The resulting explicit form for the rapid pressure-strain correlation accounts for nonlocal effects produced by spatial variations in the mean-flow velocity gradients and is derived through Taylor expansion of the mean velocity gradients appearing in the exact integral relation for the rapid pressure-strain correlation. The integrals in the resulting series expansion are solved for high- and low-Reynolds number forms of the longitudinal correlation function f(r), and the resulting nonlocal rapid pressure-strain correlation is expressed as an infinite series in terms of Laplacians of the mean strain rate tensor. This formulation is used to obtain a nonlocal transport equation for the turbulence anisotropy that is expected to provide improved predictions of the anisotropy in strongly inhomogeneous flows.}, }
@article {pmid19905223, year = {2009}, author = {du Puits, R and Resagk, C and Thess, A}, title = {Structure of viscous boundary layers in turbulent Rayleigh-Bénard convection.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {80}, number = {3 Pt 2}, pages = {036318}, doi = {10.1103/PhysRevE.80.036318}, pmid = {19905223}, issn = {1550-2376}, mesh = {*Air ; *Air Movements ; Computer Simulation ; *Models, Theoretical ; *Nonlinear Dynamics ; Rheology/*methods ; Viscosity ; }, abstract = {Highly resolved profiles of the mean velocity in turbulent Rayleigh-Bénard convection in air are presented and discussed. The present work extends our recently performed experiments at constant aspect ratio [Phys. Rev. Lett. 99, 234504 (2007)] to variable aspect ratios. The experiments cover a range of Rayleigh numbers 10(9)<Ra<10(12) and aspect ratios 1.13<Gamma<11.3 whereas the Prandtl number is fixed at Pr=0.7. The major finding of the present work is that the profiles of the mean horizontal velocity and its fluctuations are virtually invariant against the variation in Ra or Gamma if the wall distance is scaled by the displacement thickness of the boundary layer. Furthermore we have studied typical length scales of the boundary layer and their scaling with Ra and Gamma. Regarding a potential transition of the heat transport toward the ultimate regime we found that the boundary layer Reynolds number remains below Redelta=250 which is significantly lower than the predicted limit.}, }
@article {pmid19905216, year = {2009}, author = {Kholmyansky, M and Moriconi, L and Pereira, RM and Tsinober, A}, title = {Log-Poisson cascade description of turbulent velocity-gradient statistics.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {80}, number = {3 Pt 2}, pages = {036311}, doi = {10.1103/PhysRevE.80.036311}, pmid = {19905216}, issn = {1550-2376}, mesh = {Computer Simulation ; *Models, Statistical ; *Nonlinear Dynamics ; Poisson Distribution ; Rheology/*methods ; }, abstract = {The Log-Poisson phenomenological description of the turbulent energy cascade is evoked to discuss high-order statistics of velocity derivatives and the mapping between their probability distribution functions at different Reynolds numbers. The striking confirmation of theoretical predictions suggests that numerical solutions of the flow obtained at low/moderate Reynolds numbers can play an important quantitative role in the analysis of experimental high Reynolds number phenomena, where small scales fluctuations are in general inaccessible from direct numerical simulations.}, }
@article {pmid19901999, year = {2009}, author = {Choi, J and Tawhai, MH and Hoffman, EA and Lin, CL}, title = {On intra- and intersubject variabilities of airflow in the human lungs.}, journal = {Physics of fluids (Woodbury, N.Y. : 1994)}, volume = {21}, number = {10}, pages = {101901}, pmid = {19901999}, issn = {1070-6631}, support = {R01 EB005823/EB/NIBIB NIH HHS/United States ; R01 HL064368/HL/NHLBI NIH HHS/United States ; S10 RR022421/RR/NCRR NIH HHS/United States ; UL1 RR024979/RR/NCRR NIH HHS/United States ; }, abstract = {The effects of intra- and intersubject variabilities in airway geometry on airflow in the human lungs are investigated by large eddy simulation. The airway models of two human subjects consisting of extra- and intrathoracic airways are reconstructed from CT images. For intrasubject study, airflows at two inspiratory flow rates are simulated on the airway geometries of the same subject with four different levels of truncation. These airway models are the original complete geometry and three geometries obtained by truncating the original one at the subglottis, the supraglottis, and the laryngopharynx, respectively. A comparison of the airflows in the complete geometry model shows that the characteristics of the turbulent laryngeal jet in the trachea are similar regardless of Reynolds number in terms of mean velocities, turbulence statistics, coherent structures, and pressure distribution. The truncated airway models, however, do not produce the similar flow structures observed in the complete geometry. An improved inlet boundary condition is then proposed for the airway model truncated at the laryngopharynx to improve the accuracy of solution. The new boundary condition significantly improves the mean flow. The spectral analysis shows that turbulent characteristics are captured downstream away from the glottis. For intersubject study, although the overall flow characteristics are similar, two morphological factors are found to significantly affect the flows between subjects. These are the constriction ratio of the glottis with respect to the trachea and the curvature and shape of the airways.}, }
@article {pmid19850445, year = {2010}, author = {Sundberg, J and Scherer, R and Hess, M and Müller, F}, title = {Whispering--a single-subject study of glottal configuration and aerodynamics.}, journal = {Journal of voice : official journal of the Voice Foundation}, volume = {24}, number = {5}, pages = {574-584}, doi = {10.1016/j.jvoice.2009.01.001}, pmid = {19850445}, issn = {1873-4588}, mesh = {Adult ; Air Pressure ; Fiber Optic Technology ; Glottis/anatomy &amp; histology/*physiology ; Humans ; Loudness Perception ; Male ; *Phonation ; Signal Processing, Computer-Assisted ; *Speech Acoustics ; Transducers, Pressure ; Video Recording ; *Voice Quality ; }, abstract = {Whisper productions were produced by a single adult male subject over a wide range of subglottal pressures, glottal areas, and glottal flows. Dimensional measurements were made of these three variables, including glottal perimeter. Subglottal pressure was directly obtained by a pressure transducer in a tracheal catheter, and wide-band flow with a pneumotach mask. Four types of whispers were used-hyperfunctional, hypofunctional, neutral, and postphonation-in addition to three levels of loudness (soft, medium, loud). Sequences of the /pae/ syllable were used. Video recordings of the larynx were made. The glottis was outlined by hand with extrapolation for unseen parts, and area and perimeter were obtained through image analysis software. The whisper tokens resulted in the following wide ranges: subglottal pressure: 1.3-17 cm H2O; glottal flow: 0.9-1.71 L/s; glottal area: 0.065-1.76 m2; and glottal perimeter: 1.09-6.55 cm. Hyperfunctional whisper tended to have higher subglottal pressures and lower areas and flows than hypofunctional whisper, with neutral and postphonation whisper values in between. An important finding is that glottal flow changed more for small changes of area when the area was already small, and did not create much flow change when area was changed for already larger areas; that is, whisper is "more sensitive" to airflow changes for smaller glottal areas. A general equation for whisper aerodynamics was obtained, namely, P (subglottal pressure [cm H2O])=C X F (glottal flow [cm(3)/s]), where C = 0.052 x A(4) - 0.1913 x A(3) + 0.2577 x A(2) - 0.1523 x A+0.0388, where A is the glottal area (cm(2)). Another general equation for nondimensional terms (pressure coefficient vs Reynolds number) also is offered. Implications for whisper flow resistance and aerodynamic power are given. These results give insight into whisper aerodynamics and offer equations relevant to speech synthesis.}, }
@article {pmid19811997, year = {2009}, author = {Qin, L and Zeng, Z and Cheng, H and Wang, QM}, title = {Acoustic wave flow sensor using quartz thickness shear mode resonator.}, journal = {IEEE transactions on ultrasonics, ferroelectrics, and frequency control}, volume = {56}, number = {9}, pages = {1945-1954}, doi = {10.1109/TUFFC.2009.1270}, pmid = {19811997}, issn = {1525-8955}, abstract = {A quartz thickness shear mode (TSM) bulk acoustic wave resonator was used for in situ and real-time detection of liquid flow rate in this study. A special flow chamber made of 2 parallel acrylic plates was designed for flow measurement. The flow chamber has a rectangular flow channel, 2 flow reservoirs for stabilizing the fluid flow, a sensor mounting port for resonator holding, one inlet port, and one outlet port for pipe connection. A 5-MHz TSM quartz resonator was edge-bonded to the sensor mounting port with one side exposed to the flowing liquid and other side exposed to air. The electrical impedance spectra of the quartz resonator at different volumetric flow rate conditions were measured by an impedance analyzer for the extraction of the resonant frequency through a data-fitting method. The fundamental, 3rd, 5th, 7th, and 9th resonant frequency shifts were found to be around 920, 3572, 5947, 8228, and 10,300 Hz for flow rate variation from 0 to 3000 mL/min, which had a corresponding Reynolds number change from 0 to 822. The resonant frequency shifts of different modes are found to be quadratic with flow rate, which is attributed to the nonlinear effect of quartz resonator due to the effective normal pressure imposing on the resonator sensor by the flowing fluid. The results indicate that quartz TSM resonators can be used for flow sensors with characteristics of simplicity, fast response, and good repeatability.}, }
@article {pmid19792800, year = {2009}, author = {Thomases, B and Shelley, M}, title = {Transition to mixing and oscillations in a Stokesian viscoelastic flow.}, journal = {Physical review letters}, volume = {103}, number = {9}, pages = {094501}, doi = {10.1103/PhysRevLett.103.094501}, pmid = {19792800}, issn = {0031-9007}, abstract = {In seeking to understand experiments on low-Reynolds-number mixing and flow transitions in viscoelastic fluids, we simulate the dynamics of the Oldroyd-B model, with a simple background force driving the flow. We find that at small Weissenberg number, flows are "slaved" to the extensional geometry imposed by forcing. For large Weissenberg number, such solutions become unstable and transit to a structurally dissimilar state dominated by a single large vortex. This new state can show persistent oscillatory behavior with the production and destruction of smaller-scale vortices that drive mixing.}, }
@article {pmid19792377, year = {2009}, author = {Beatus, T and Tlusty, T and Bar-Ziv, R}, title = {Burgers shock waves and sound in a 2D microfluidic droplets ensemble.}, journal = {Physical review letters}, volume = {103}, number = {11}, pages = {114502}, doi = {10.1103/PhysRevLett.103.114502}, pmid = {19792377}, issn = {0031-9007}, abstract = {We investigate the collective motion of a two-dimensional disordered ensemble of droplets in a microfluidic channel far from equilibrium and at Reynolds number approximately 10(-4). The ensemble carries ultraslow shock waves and sound, propagating at approximately 100 microm s(-1) and superposed on diffusive droplets motion. These modes are induced by long-range hydrodynamic dipolar interactions between droplets, the result of the symmetry breaking flow. The modes obey the Burgers equation due to a local coupling between droplets velocity and number density. This stems from a singular effect of the channel sidewall boundaries upon summation of the hydrodynamic interaction in two dimensions.}, }
@article {pmid19792258, year = {2009}, author = {Berg, J and Ott, S and Mann, J and Lüthi, B}, title = {Experimental investigation of Lagrangian structure functions in turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {80}, number = {2 Pt 2}, pages = {026316}, doi = {10.1103/PhysRevE.80.026316}, pmid = {19792258}, issn = {1539-3755}, abstract = {Lagrangian properties obtained from a particle tracking velocimetry experiment in a turbulent flow at intermediate Reynolds number are presented. Accurate sampling of particle trajectories is essential in order to obtain the Lagrangian structure functions and to measure intermittency at small temporal scales. The finiteness of the measurement volume can bias the results significantly. We present a robust way to overcome this obstacle. Despite no fully developed inertial range, we observe strong intermittency at the scale of dissipation. The multifractal model is only partially able to reproduce the results.}, }
@article {pmid19792250, year = {2009}, author = {Zargar, R and Najafi, A and Miri, M}, title = {Three-sphere low-Reynolds-number swimmer near a wall.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {80}, number = {2 Pt 2}, pages = {026308}, doi = {10.1103/PhysRevE.80.026308}, pmid = {19792250}, issn = {1539-3755}, abstract = {We study the influence of a wall on the dynamics of a low-Reynolds-number three-sphere swimmer. A far swimmer whose arm makes an angle theta with the horizon experiences the wall presence as an angle-dependent quadrupole force proportional to (a/L)(2)(L/z)(2)cos theta, where a, L, and z are the radius of spheres, the arm length, and the swimmer distance to the wall, respectively. The wall-induced translational velocity of swimmer is perpendicular to the arms. A far swimmer prefers to orient its arms parallel to the plate. This state is stable. Remarkably, the parallel state is unstable when the swimmer is close to the wall. In this regime, the velocity of swimmer decreases as (z/L)(2). Numerical solution of the equations of motion for arbitrary initial z/L and theta reveals four different phases of locomotion.}, }
@article {pmid19792243, year = {2009}, author = {Chen, Y and Zhang, C and Shi, M and Peterson, GP}, title = {Role of surface roughness characterized by fractal geometry on laminar flow in microchannels.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {80}, number = {2 Pt 2}, pages = {026301}, doi = {10.1103/PhysRevE.80.026301}, pmid = {19792243}, issn = {1539-3755}, abstract = {A three-dimensional model of laminar flow in microchannels is numerically analyzed incorporating surface roughness effects as characterized by fractal geometry. The Weierstrass-Mandelbrot function is proposed to characterize the multiscale self-affine roughness. The effects of Reynolds number, relative roughness, and fractal dimension on laminar flow are all investigated and discussed. The results indicate that unlike flow in smooth microchannels, the Poiseuille number in rough microchannels increases linearly with the Reynolds number, Re, and is larger than what is typically observed in smooth channels. For these situations, the flow over surfaces with high relative roughness induces recirculation and flow separation, which play an important role in single-phase pressure drop. More specifically, surfaces with the larger fractal dimensions yield more frequent variations in the surface profile, which result in a significantly larger incremental pressure loss, even though at the same relative roughness. The accuracy of the predicted Poiseuille number as calculated by the present model is verified using experimental data available in the literature.}, }
@article {pmid19792189, year = {2009}, author = {Mininni, PD and Pouquet, A}, title = {Finite dissipation and intermittency in magnetohydrodynamics.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {80}, number = {2 Pt 2}, pages = {025401}, doi = {10.1103/PhysRevE.80.025401}, pmid = {19792189}, issn = {1539-3755}, abstract = {We present an analysis of data stemming from numerical simulations of decaying magnetohydrodynamic (MHD) turbulence up to grid resolution of 1536(3) points and up to Taylor Reynolds number of approximately 1200 . The initial conditions are such that the initial velocity and magnetic fields are helical and in equipartition, while their correlation is negligible. Analyzing the data at the peak of dissipation, we show that the dissipation in MHD seems to asymptote to a constant as the Reynolds number increases, thereby strengthening the possibility of fast reconnection events in the solar environment for very large Reynolds numbers. Furthermore, intermittency of MHD flows, as determined by the spectrum of anomalous exponents of structure functions of the velocity and the magnetic field, is stronger than that of fluids, confirming earlier results; however, we also find that there is a measurable difference between the exponents of the velocity and those of the magnetic field, reminiscent of recent solar wind observations. Finally, we discuss the spectral scaling laws that arise in this flow.}, }
@article {pmid19792147, year = {2009}, author = {Dunkel, J and Zaid, IM}, title = {Noisy swimming at low Reynolds numbers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {80}, number = {2 Pt 1}, pages = {021903}, doi = {10.1103/PhysRevE.80.021903}, pmid = {19792147}, issn = {1539-3755}, mesh = {Diffusion ; *Models, Biological ; *Movement ; }, abstract = {Small organisms (e.g., bacteria) and artificial microswimmers move due to a combination of active swimming and passive Brownian motion. Considering a simplified linear three-sphere swimmer, we study how the swimmer size regulates the interplay between self-driven and diffusive behavior at low Reynolds number. Starting from the Kirkwood-Smoluchowski equation and its corresponding Langevin equation, we derive formulas for the orientation correlation time, the mean velocity and the mean-square displacement in three space dimensions. The validity of the analytical results is illustrated through numerical simulations. Tuning the swimmer parameters to values that are typical of bacteria, we find three characteristic regimes: (i) Brownian motion at small times, (ii) quasiballistic behavior at intermediate time scales, and (iii) quasidiffusive behavior at large times due to noise-induced rotation. Our analytical results can be useful for a better quantitative understanding of optimal foraging strategies in bacterial systems, and they can help to construct more efficient artificial microswimmers in fluctuating fluids.}, }
@article {pmid19775116, year = {2009}, author = {Park, JS and Jung, HI}, title = {Multiorifice flow fractionation: continuous size-based separation of microspheres using a series of contraction/expansion microchannels.}, journal = {Analytical chemistry}, volume = {81}, number = {20}, pages = {8280-8288}, doi = {10.1021/ac9005765}, pmid = {19775116}, issn = {1520-6882}, mesh = {Fractionation, Field Flow/*instrumentation ; Microfluidic Analytical Techniques ; *Microspheres ; Polystyrenes/chemistry/isolation &amp; purification ; }, abstract = {We designed a new microfluidic method, multiorifice flow fractionation (MOFF), for continuous size-based separation of spherical microparticles. This method utilizes inertial lift force and momentum-change-induced inertial force generated in a series of contraction/expansion microchannels. The particles were concentrated gradually along the walls of microchannels by those inertial forces as they passed through the channels. The particle trajectory was deflected from the carrier fluid by means of numerous sudden turns formed in a multiorifice channel. The inertial force was induced by this trajectory mismatching between fluid and particle that resulted from the momentum change. The trajectory mismatching induces the lateral drift of the equilibrium position of particle distribution, and its extent is variable according to particle size and flow rate. In the case of polydispersion, the size-based particle separation could be achieved in the specific range of the channel Reynolds number (Re(c)). It was found that, at Re(c) of 63-91, large polymer particles (approximately 15 microm) were aligned along the centerline of outlet channel, whereas small particles (approximately 7 microm) remained near both sidewalls. This method has potential in continuous separation without using a sheath flow.}, }
@article {pmid19761190, year = {2009}, author = {Gossett, DR and Di Carlo, D}, title = {Particle focusing mechanisms in curving confined flows.}, journal = {Analytical chemistry}, volume = {81}, number = {20}, pages = {8459-8465}, doi = {10.1021/ac901306y}, pmid = {19761190}, issn = {1520-6882}, mesh = {Microfluidic Analytical Techniques/instrumentation/methods ; *Microfluidics ; Motion ; }, abstract = {Particles in finite-inertia confined channel flows are known to segregate and focus to equilibrium positions whose number corresponds with the fold of symmetry of the channel's cross section. The addition of curvature into channels presumably modifies these equilibrium inertial focusing positions, because of the secondary flow induced in curved channels. Here, we identify the critical interaction of the secondary flow field with inertial lift forces to create complex sets of particle focusing positions that vary with the channel Reynolds number (Re(C)) and the inertial force ratio, which is a new dimensionless parameter that is based on the ratio of inertial lift to drag forces from the secondary flow. We use these results to identify microfluidic channel geometries to focus particles at rates an order of magnitude higher than previously shown (channel Reynolds number, Re(C) = 270) and develop design criteria for the focusing of potentially arbitrary-sized particles. In addition, our results indicate that channel curvature can lead to microfluidic designs with reduced fluidic resistance, useful for lower power inertial focusing or separation. These results will enable design of practical particle/cell separation, filtration, and focusing systems for critical applications in biomedicine and environmental cleanup.}, }
@article {pmid19746726, year = {2009}, author = {Zhang, P and Devries, SL and Dathe, A and Bagtzoglou, AC}, title = {Enhanced mixing and plume containment in porous media under time-dependent oscillatory flow.}, journal = {Environmental science &amp; technology}, volume = {43}, number = {16}, pages = {6283-6288}, doi = {10.1021/es900854r}, pmid = {19746726}, issn = {0013-936X}, mesh = {1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium Salt/chemistry ; Calibration ; *Environmental Restoration and Remediation ; Fluorescein/chemistry ; Molybdenum/chemistry ; Porosity ; Rheology ; Time Factors ; Water Supply ; }, abstract = {Solute transport experiments were conducted in a decimeter scale flow cell packed with sand to study the potential for enhanced mixing of solutes in porous media and improved containment of injected plumes under multiple pumping-well driven, time-dependent oscillatory flow with respect to constant flow. Real-time imaging of the colorimetric reaction of Tiron (1,2-dihydroxybenzene-3,5-disulfonic acid) and molybdate was used to quantify mixing, whereas fluorescein was used to better examine plume size. Results from the small scale experiments clearly demonstrated the enhanced mixing of solutes under low Reynolds number oscillatory flow (a factor of 2 with respect to constant flow in homogeneous sand and a factor of 3 in layered sand), as the result of increased contact interface for solute diffusion. Further, the injected solute plume was better contained under oscillatory flow (25% less area with respect to constant flow in homogeneous sand) due to the cancellation of advective transport at each well over time. Enhanced mixing under oscillatory flow may enhance the processes of chemical and biological remediation. Furthermore, improved plume containment under oscillatory flow may require smaller amounts of chemicals to be injected during aquifer remediation.}, }
@article {pmid19743538, year = {2009}, author = {Chin, DA and Price, RM and DiFrenna, VJ}, title = {Nonlinear flow in karst formations.}, journal = {Ground water}, volume = {47}, number = {5}, pages = {669-674}, doi = {10.1111/j.1745-6584.2009.00574.x}, pmid = {19743538}, issn = {1745-6584}, mesh = {*Models, Theoretical ; *Water Movements ; }, abstract = {The variation of effective hydraulic conductivity as a function of specific discharge in several 0.2-m and 0.3-m cubes of Key Largo Limestone was investigated. The experimental results closely match the Forchheimer equation. Defining the pore-size length scale in terms of Forchheimer parameters, it is demonstrated that significant deviations from Darcian flow will occur when the Reynolds number exceeds 0.11. A particular threshold model previously proposed for use in karstic formations does not show strong agreement with the data near the onset of nonlinear flow.}, }
@article {pmid19716332, year = {2009}, author = {Nagels, MA and Cater, JE}, title = {Large eddy simulation of high frequency oscillating flow in an asymmetric branching airway model.}, journal = {Medical engineering &amp; physics}, volume = {31}, number = {9}, pages = {1148-1153}, doi = {10.1016/j.medengphy.2009.07.013}, pmid = {19716332}, issn = {1873-4030}, mesh = {Adult ; Algorithms ; Computer Simulation ; *High-Frequency Ventilation ; Humans ; Lung/*physiology ; Models, Theoretical ; Nonlinear Dynamics ; Oscillometry/*methods ; Pressure ; Respiratory Mechanics ; Respiratory System ; Software ; Temperature ; Viscosity ; }, abstract = {The implementation of artificial ventilation schemes is necessary when respiration fails. One approach involves the application of high frequency oscillatory ventilation (HFOV) to the respiratory system. Oscillatory airflow in the upper bronchial tree can be characterized by Reynolds numbers as high as 10(4), hence, the flow presents turbulent features. In this study, transitional and turbulent flow within an asymmetric bifurcating model of the upper airway during HFOV are studied using large eddy simulation (LES) methods. The flow, characterized by a peak Reynolds number of 8132, is analysed using a validated LES model of a three-dimensional branching geometry. The pressures, velocities, and vorticity within the flow are presented and compared with prior models for branching flow systems. The results demonstrate how pendelluft occurs at asymmetric branches within the respiratory system. These results may be useful in optimising treatments using HFOV methods.}, }
@article {pmid19693399, year = {2009}, author = {Lam, YC and Gan, HY and Nguyen, NT and Lie, H}, title = {Micromixer based on viscoelastic flow instability at low Reynolds number.}, journal = {Biomicrofluidics}, volume = {3}, number = {1}, pages = {14106}, pmid = {19693399}, issn = {1932-1058}, abstract = {We exploited the viscoelasticity of biocompatible dilute polymeric solutions, namely, dilute poly(ethylene oxide) solutions, to significantly enhance mixing in microfluidic devices at a very small Reynolds number, i.e., Re approximately 0.023, but large Peclet and elasticity numbers. With an abrupt contraction microgeometry (8:1 contraction ratio), two different dilute poly(ethylene oxide) solutions were successfully mixed with a short flow length at a relatively fast mixing time of <10 mus. Microparticle image velocimetry was employed in our investigations to characterize the flow fields. The increase in velocity fluctuation with an increase in flow rate and Deborah number indicates the increase in viscoelastic flow instability. Mixing efficiency was characterized by fluorescent concentration measurements. Our results showed that enhanced mixing can be achieved through viscoelastic flow instability under situations where molecular-diffusion and inertia effects are negligible. This approach bypasses the laminar flow limitation, usually associated with a low Reynolds number, which is not conducive to mixing.}, }
@article {pmid19693348, year = {2009}, author = {Jain, M and Yeung, A and Nandakumar, K}, title = {Induced charge electro osmotic mixer: Obstacle shape optimization.}, journal = {Biomicrofluidics}, volume = {3}, number = {2}, pages = {22413}, pmid = {19693348}, issn = {1932-1058}, abstract = {Efficient mixing is difficult to achieve in miniaturized devices due to the nature of low Reynolds number flow. Mixing can be intentionally induced, however, if conducting or nonconducting obstacles are embedded within the microchannel. In the case of conducting obstacles, vortices can be generated in the vicinity of the obstacle due to induced charge electro-osmosis (ICEO) which enhances mixing of different streams: the obstacle shape affects the induced zeta potential on the conducting surface, which in turn influences the flow profile near the obstacle. This study deals with optimization of the geometric shape of a conducting obstacle for the purpose of micromixing. The obstacle boundary is parametrically represented by nonuniform rational B-spline curves. The optimal obstacle shape, which maximizes the mixing for given operating conditions, is found using genetic algorithms. Various case studies at different operating conditions demonstrated that the near right triangle shape provides optimal mixing in the ICEO flow dominant regime, whereas rectangular shape is the optimal shape in diffusion dominant regime. The tradeoff between mixing and transport is examined for symmetric and nonsymmetric obstacle shapes.}, }
@article {pmid19693281, year = {2009}, author = {Borazjani, I and Sotiropoulos, F}, title = {Vortex-induced vibrations of two cylinders in tandem arrangement in the proximity-wake interference region.}, journal = {Journal of fluid mechanics}, volume = {621}, number = {}, pages = {321-364}, pmid = {19693281}, issn = {0022-1120}, support = {R01 HL070262/HL/NHLBI NIH HHS/United States ; R01 HL070262-05A1/HL/NHLBI NIH HHS/United States ; T32 HL007262/HL/NHLBI NIH HHS/United States ; }, abstract = {We investigate numerically vortex-induced vibrations (VIV) of two identical two-dimensional elastically mounted cylinders in tandem in the proximity-wake interference regime at Reynolds number Re = 200 for systems having both one (transverse vibrations) and two (transverse and in-line) degrees of freedom (1-DOF and 2-DOF, respectively). For the 1-DOF system the computed results are in good qualitative agreement with available experiments at higher Reynolds numbers. Similar to these experiments our simulations reveal: (1) larger amplitudes of motion and a wider lock-in region for the tandem arrangement when compared with an isolated cylinder; (2) that at low reduced velocities the vibration amplitude of the front cylinder exceeds that of the rear cylinder; and (3) that above a threshold reduced velocity, large-amplitude VIV are excited for the rear cylinder with amplitudes significantly larger than those of the front cylinder. By analysing the simulated flow patterns we identify the VIV excitation mechanisms that lead to such complex responses and elucidate the near-wake vorticity dynamics and vortex-shedding modes excited in each case. We show that at low reduced velocities vortex shedding provides the initial excitation mechanism, which gives rise to a vertical separation between the two cylinders. When this vertical separation exceeds one cylinder diameter, however, a significant portion of the incoming flow is able to pass through the gap between the two cylinders and the gap-flow mechanism starts to dominate the VIV dynamics. The gap flow is able to periodically force either the top or the bottom shear layer of the front cylinder into the gap region, setting off a series of very complex vortex-to-vortex and vortex-to-cylinder interactions, which induces pressure gradients that result in a large oscillatory force in phase with the vortex shedding and lead to the experimentally observed larger vibration amplitudes. When the vortex shedding is the dominant mechanism the front cylinder vibration amplitude is larger than that of the rear cylinder. The reversing of this trend above a threshold reduced velocity is associated with the onset of the gap flow. The important role of the gap flow is further illustrated via a series of simulations for the 2-DOF system. We show that when the gap-flow mechanism is triggered, the 2-DOF system can develop and sustain large VIV amplitudes comparable to those observed in the corresponding (same reduced velocity) 1-DOF system. For sufficiently high reduced velocities, however, the two cylinders in the 2-DOF system approach each other, thus significantly reducing the size of the gap region. In such cases the gap flow is entirely eliminated, and the two cylinders vibrate together as a single body with vibration amplitudes up to 50% lower than the amplitudes of the corresponding 1-DOF in which the gap flow is active. Three-dimensional simulations are also carried out to examine the adequacy of two-dimensional simulations for describing the dynamic response of the tandem system at Re = 200. It is shown that even though the wake transitions to a weakly three-dimensional state when the gap flow is active, the three-dimensional modes are too weak to affect the dynamic response of the system, which is found to be identical to that obtained from the two-dimensional computations.}, }
@article {pmid19680583, year = {2009}, author = {Fung, WT and Beyzavi, A and Abgrall, P and Nguyen, NT and Li, HY}, title = {Microfluidic platform for controlling the differentiation of embryoid bodies.}, journal = {Lab on a chip}, volume = {9}, number = {17}, pages = {2591-2595}, doi = {10.1039/b903753e}, pmid = {19680583}, issn = {1473-0197}, mesh = {Animals ; Blotting, Western ; *Cell Differentiation ; Embryonic Stem Cells/*cytology ; Fluorescent Antibody Technique ; Mice ; Microfluidics/*instrumentation ; }, abstract = {Embryonic stem (ES) cells are pluripotent cells, which can differentiate into any cell type. This cell type has often been implicated as an eminent source of renewable cells for tissue regeneration and cellular replacement therapies. Studies on manipulation of the various differentiation pathways have been at the forefront of research. There are many ways in which ES cells can be differentiated. One of the most common techniques is to initiate the development of embryoid bodies (EBs) by in vitro aggregation of ES cells. Thereafter, EBs can be induced to undergo differentiation into various cell lineages. In this article, we present a microfluidic platform using biocompatible materials, which is suitable for culturing EBs. The platform is based on a Y-channel device with two inlets for two different culturing media. An EB is located across both streams. Using the laminar characteristics at low Reynolds number and high Peclet numbers, we have induced cell differentiation on half of the EB while maintaining the other half in un-induced stages. The results prove the potential of using microfluidic technology for manipulation of EBs and ES cells in tissue engineering.}, }
@article {pmid19674925, year = {2009}, author = {Paul, MC and Larman, A}, title = {Investigation of spiral blood flow in a model of arterial stenosis.}, journal = {Medical engineering &amp; physics}, volume = {31}, number = {9}, pages = {1195-1203}, doi = {10.1016/j.medengphy.2009.07.008}, pmid = {19674925}, issn = {1873-4030}, mesh = {Arteries/pathology/*physiopathology ; Blood Flow Velocity/*physiology ; Computer Simulation ; Constriction, Pathologic/pathology/*physiopathology ; Finite Element Analysis ; Hemodynamics ; Hemorheology ; Humans ; Kinetics ; Models, Anatomic ; *Models, Cardiovascular ; Pressure ; Pulsatile Flow ; Stress, Mechanical ; }, abstract = {The spiral component of blood flow has both beneficial and detrimental effects in human circulatory system [Stonebridge PA, Brophy CM. Spiral laminar flow in arteries? Lancet 1991; 338: 1360-1]. We investigate the effects of the spiral blood flow in a model of three-dimensional arterial stenosis with a 75% cross-sectional area reduction at the centre by means of computational fluid dynamics (CFD) techniques. The standard k-omega model is employed for simulation of the blood flow for the Reynolds number of 500 and 1000. We find that for Re=500 the spiral component of the blood flow increases both the total pressure and velocity of the blood, and some significant differences are found between the wall shear stresses of the spiral and non-spiral induced flow downstream of the stenosis. The turbulent kinetic energy is reduced by the spiral flow as it induces the rotational stabilities in the forward flow. For Re=1000 the tangential component of the blood velocity is most influenced by the spiral speed, but the effect of the spiral flow on the centreline turbulent kinetic energy and shear stress is mild. The results of the effects of the spiral flow are discussed in the paper along with the relevant pathological issues.}, }
@article {pmid19671796, year = {2010}, author = {Lambert, AR and Lin, CL and Mardorf, E and O'Shaughnessy, P}, title = {CFD simulation of contaminant decay for high reynolds flow in a controlled environment.}, journal = {The Annals of occupational hygiene}, volume = {54}, number = {1}, pages = {88-99}, pmid = {19671796}, issn = {1475-3162}, support = {P30 ES05605/ES/NIEHS NIH HHS/United States ; }, mesh = {*Air Movements ; Air Pollutants/*analysis/chemistry ; Air Pollution, Indoor/statistics &amp; numerical data ; Carbon Dioxide/analysis ; *Computer Simulation ; Diffusion ; *Environment, Controlled ; Environmental Exposure/prevention &amp; control/statistics &amp; numerical data ; Humans ; *Hydrodynamics ; Kinetics ; Models, Chemical ; Time Factors ; Ventilation ; }, abstract = {This study examines the usage of computational fluid dynamics (CFDs) for estimating the time-elapsed decay of contaminants within a chamber experiencing high Reynolds flow. CFD results were compared with measurements taken at a controlled facility. In addition, parameters of the CFD simulation were examined; namely the effects of turbulence and inertial transport at high Reynolds number ventilating flows, as well as inlet duct configuration and its effect on the inlet velocity profile. The agreement between the computational and experimental clearance times was quite good, with percent errors as low as -5.32% at high flow rate and -11.8% at the lower flow rate. This study determined that for high Reynolds flow, diffusive transport effects may be ignored as the majority of mass is transported via the bulk stream, i.e. momentum transport. In addition, resolving the inlet velocity profile was of prime importance for accurate simulation of ventilating flows and prediction of contaminant washout. This was done by including the inlet duct geometry in the computational domain. In addition, it was found that despite different flow rates, the predicted contaminant washout took approximately 12-13% longer than predicted assuming instantaneous mixing. Furthermore, percent error between computational and experimental data as low as -5.32% shows that CFD is a useful tool for studying ventilation phenomena.}, }
@article {pmid19659285, year = {2009}, author = {Lepore, J and Mydlarski, L}, title = {Effect of the scalar injection mechanism on passive scalar structure functions in a turbulent flow.}, journal = {Physical review letters}, volume = {103}, number = {3}, pages = {034501}, doi = {10.1103/PhysRevLett.103.034501}, pmid = {19659285}, issn = {0031-9007}, abstract = {Higher-order passive scalar (temperature) structure functions are measured in the turbulent wake of a circular cylinder at a Taylor-microscale Reynolds number (Rlambda) of 370. The scalar is injected by two different means: (i) heating of the cylinder and (ii) use of a mandoline. Even though the second-order statistics (e.g., power spectra, second-order structure functions) of the scalar field are experimentally indistinguishable in the inertial and dissipative ranges, we observe notable differences in the inertial-range scaling exponents (xin) of the scalar structure functions at higher orders. The implication is therefore that the variations in previous estimates of xin may be attributable to differences in the scalar field initial conditions (and may not be deemed characteristic of a universal nature of the small-scale statistics of turbulent passive scalars).}, }
@article {pmid19659030, year = {2009}, author = {Watari, N and Larson, RG}, title = {Shear-induced chiral migration of particles with anisotropic rigidity.}, journal = {Physical review letters}, volume = {102}, number = {24}, pages = {246001}, doi = {10.1103/PhysRevLett.102.246001}, pmid = {19659030}, issn = {0031-9007}, mesh = {Anisotropy ; Cell Physiological Phenomena ; Models, Biological ; Models, Chemical ; Models, Molecular ; *Models, Theoretical ; Molecular Conformation ; Polymers/chemistry ; Shear Strength ; }, abstract = {We report that an achiral particle with anisotropic rigidity can migrate in the vorticity direction in shear flow. A minimal "tetrumbbell" model of such a particle is constructed from four beads and six springs to make a tetrahedral structure. A combination of two different spring constants corresponding to "hard" and "soft" springs yields ten distinguishable tetrumbbells, which when simulated in shear flow with hydrodynamic interactions between beads but no Brownian motion at zero Reynolds number, produces five different types of behavior in which seven out of ten tetrumbbell structures migrate in the vorticity direction due to shear-induced chirality. Some of the structures migrate in the same direction along the vorticity direction even when the shear flow is reversed, which is impossible for permanently chiral objects.}, }
@article {pmid19658812, year = {2009}, author = {Pietarila Graham, J and Mininni, PD and Pouquet, A}, title = {Lagrangian-averaged model for magnetohydrodynamic turbulence and the absence of bottlenecks.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {80}, number = {1 Pt 2}, pages = {016313}, doi = {10.1103/PhysRevE.80.016313}, pmid = {19658812}, issn = {1539-3755}, abstract = {We demonstrate that, for the case of quasiequipartition between the velocity and the magnetic field, the Lagrangian-averaged magnetohydrodynamics (LAMHD) alpha model reproduces well both the large-scale and the small-scale properties of turbulent flows; in particular, it displays no increased (superfilter) bottleneck effect with its ensuing enhanced energy spectrum at the onset of the subfilter scales. This is in contrast to the case of the neutral fluid in which the Lagrangian-averaged Navier-Stokes alpha model is somewhat limited in its applications because of the formation of spatial regions with no internal degrees of freedom and subsequent contamination of superfilter-scale spectral properties. We argue that, as the Lorentz force breaks the conservation of circulation and enables spectrally nonlocal energy transfer (associated with Alfvén waves), it is responsible for the absence of a viscous bottleneck in magnetohydrodynamics (MHD), as compared to the fluid case. As LAMHD preserves Alfvén waves and the circulation properties of MHD, there is also no (superfilter) bottleneck found in LAMHD, making this method capable of large reductions in required numerical degrees of freedom; specifically, we find a reduction factor of approximately 200 when compared to a direct numerical simulation on a large grid of 1536;{3} points at the same Reynolds number.}, }
@article {pmid19658805, year = {2009}, author = {Lishchuk, SV and Halliday, I}, title = {Effective surface viscosities of a particle-laden fluid interface.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {80}, number = {1 Pt 2}, pages = {016306}, doi = {10.1103/PhysRevE.80.016306}, pmid = {19658805}, issn = {1539-3755}, abstract = {The Einstein formula for the effective shear viscosity of low Reynolds number suspension flows is generalized to the case of flat, low-concentration, particle-laden interfaces separating two immiscible fluids. The effective surface shear and dilational viscosities of this system is found to be eta{s}=5/3(eta{1}+eta{2})R phi and zeta{s}=5(eta_{1}+eta_{2})R phi , correspondingly, where eta{1} and eta{2} are the shear viscosities of two bulk fluids and phi is the surface concentration of spherical particles of radius R . The formula is found to be in excellent agreement with data obtained using multicomponent lattice Boltzmann equation simulation.}, }
@article {pmid19658619, year = {2009}, author = {Liu, B and Khalili, A}, title = {Lattice Boltzmann model for exterior flows with an annealing preconditioning method.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {79}, number = {6 Pt 2}, pages = {066701}, doi = {10.1103/PhysRevE.79.066701}, pmid = {19658619}, issn = {1539-3755}, abstract = {In this paper we propose a highly efficient and stable lattice Boltzmann method for solving low Reynolds number exterior flows using a preconditioning technique. The present method is based on replacing the constant preconditioning parameter (gamma) within uniform grids [Guo, Phys. Rev. E 70, 066706 (2004)] by a space- and time-dependent one in a nested mesh-refined domain. To do this, for the transition from a fine to the neighboring coarser grid, gamma has been divided by a factor K , which is large initially and anneals stepwise to a small value after some iterations. With this technique, more than one order of magnitude larger convergence rate can be achieved, and several orders of magnitude larger system size can be treated.}, }
@article {pmid19658604, year = {2009}, author = {Mazzitelli, IM and Lohse, D}, title = {Evolution of energy in flow driven by rising bubbles.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {79}, number = {6 Pt 2}, pages = {066317}, doi = {10.1103/PhysRevE.79.066317}, pmid = {19658604}, issn = {1539-3755}, abstract = {We investigate by direct numerical simulations the flow that rising bubbles cause in an originally quiescent fluid. We employ the Eulerian-Lagrangian method with two-way coupling and periodic boundary conditions. In order to be able to treat up to 288000 bubbles, the following approximations and simplifications had to be introduced, as done before, e.g., by Climent and Magnaudet, Phys. Rev. Lett. 82, 4827 (1999). (i) The bubbles were treated as point particles, thus (ii) disregarding the near-field interactions among them, and (iii) effective force models for the lift and the drag forces were used. In particular, the lift coefficient was assumed to be 1/2, independent of the bubble Reynolds number and the local flow field. The results suggest that large-scale motions are generated, owing to an inverse energy cascade from the small to the large scales. However, as the Taylor-Reynolds number is only in the range of 1, the corresponding scaling of the energy spectrum with an exponent of -5/3 cannot develop over a pronounced range. In the long term, the property of local energy transfer, characteristic of real turbulence, is lost and the input of energy equals the viscous dissipation at all scales. Due to the lack of strong vortices, the bubbles spread rather uniformly in the flow. The mechanism for uniform spreading is as follows. Rising bubbles induce a velocity field behind them that acts on the following bubbles. Owing to the shear, those bubbles experience a lift force, which makes them spread to the left or right, thus preventing the formation of vertical bubble clusters and therefore of efficient forcing. Indeed, when the lift is artificially put to zero in the simulations, the flow is forced much more efficiently and a more pronounced energy that accumulation at large scales (due to the inverse energy cascade) is achieved.}, }
@article {pmid19658596, year = {2009}, author = {Willmott, GR}, title = {Slip-induced dynamics of patterned and Janus-like spheres in laminar flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {79}, number = {6 Pt 2}, pages = {066309}, doi = {10.1103/PhysRevE.79.066309}, pmid = {19658596}, issn = {1539-3755}, abstract = {Calculations of force and torque on a sphere with inhomogeneous slip boundary conditions are presented. A theoretical approach introduced previously is employed to explicitly explore two types of azimuthally symmetric boundary-condition patterning of high practical importance. The first is a discontinuous binary surface while the second involves continuously varying slip patterned in stripes, with arbitrary periodicity. These geometries mimic anisotropic spheres, as well as superhydrophobic surfaces applied to a sphere. The dynamics apply for unbounded uniform flow and pure rotational flow of a Newtonian fluid at low Reynolds number. In unbounded uniform flow, torque is maximized for an ideal Janus sphere with a discontinuous equatorial transition between regions of slip and no slip.}, }
@article {pmid19658591, year = {2009}, author = {Alboussière, T}, title = {Bound of dissipation on a plane Couette dynamo.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {79}, number = {6 Pt 2}, pages = {066304}, doi = {10.1103/PhysRevE.79.066304}, pmid = {19658591}, issn = {1539-3755}, abstract = {Variational turbulence is among the few approaches providing rigorous results in turbulence. In addition, it addresses a question of direct practical interest, namely, the rate of energy dissipation. Unfortunately, only an upper bound is obtained as a larger functional space than the space of solutions to the Navier-Stokes equations is searched. Yet, in some cases, this upper bound is in good agreement with experimental results in terms of order of magnitude and power law of the imposed Reynolds number. In this paper, the variational approach to turbulence is extended to the case of dynamo action and an upper bound is obtained for the global dissipation rate (viscous and Ohmic). A simple plane Couette flow is investigated. For low magnetic Prandtl number P_{m} fluids, the upper bound of energy dissipation is that of classical turbulence (i.e., proportional to the cubic power of the shear velocity) for magnetic Reynolds numbers below P_{m};{-1} and follows a steeper evolution for magnetic Reynolds numbers above P_{m};{-1} (i.e., proportional to the shear velocity to the power of 4) in the case of electrically insulating walls. However, the effect of wall conductance is crucial: for a given value of wall conductance, there is a value for the magnetic Reynolds number above which energy dissipation cannot be bounded. This limiting magnetic Reynolds number is inversely proportional to the square root of the conductance of the wall. Implications in terms of energy dissipation in experimental and natural dynamos are discussed.}, }
@article {pmid19658555, year = {2009}, author = {Guttenberg, N and Goldenfeld, N}, title = {Friction factor of two-dimensional rough-boundary turbulent soap film flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {79}, number = {6 Pt 2}, pages = {065306}, doi = {10.1103/PhysRevE.79.065306}, pmid = {19658555}, issn = {1539-3755}, abstract = {We use momentum-transfer arguments to predict the friction factor f in two-dimensional turbulent soap film flows with rough boundaries (an analog of three-dimensional pipe flow) as a function of Reynolds number Re and roughness r , considering separately the inverse energy cascade and the forward enstrophy cascade. At intermediate Re, we predict a Blasius-like friction factor scaling of f proportional, variant Re{-1/2} in flows dominated by the enstrophy cascade, distinct from the energy cascade scaling of Re{-1/4} . For large Re, f approximately r in the enstrophy-dominated case. We use conformal map techniques to perform direct numerical simulations that are in satisfactory agreement with theory and exhibit data collapse scaling of roughness-induced criticality, previously shown to arise in the three-dimensional pipe data of Nikuradse.}, }
@article {pmid19658550, year = {2009}, author = {Boffetta, G and Mazzino, A and Musacchio, S and Vozella, L}, title = {Kolmogorov scaling and intermittency in Rayleigh-Taylor turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {79}, number = {6 Pt 2}, pages = {065301}, doi = {10.1103/PhysRevE.79.065301}, pmid = {19658550}, issn = {1539-3755}, abstract = {Turbulence induced by Rayleigh-Taylor instability is a ubiquitous phenomenon with applications ranging from atmospheric physics and geophysics to supernova explosions and plasma confinement fusion. Despite its fundamental character, a phenomenological theory has been proposed only recently and several predictions are untested. In this Rapid Communication we confirm spatiotemporal predictions of the theory by means of direct numerical simulations at high resolution and we extend the phenomenology to take into account intermittency effects. We show that scaling exponents are indistinguishable from those of Navier-Stokes turbulence at comparable Reynolds number, a result in support of the universality of turbulence with respect to the forcing mechanism. We also show that the time dependence of Rayleigh, Reynolds, and Nusselt numbers realizes the Kraichnan scaling regime associated with the ultimate state of thermal convection.}, }
@article {pmid19658474, year = {2009}, author = {Menon, GI and Ramaswamy, S}, title = {Universality class of the reversible-irreversible transition in sheared suspensions.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {79}, number = {6 Pt 1}, pages = {061108}, doi = {10.1103/PhysRevE.79.061108}, pmid = {19658474}, issn = {1539-3755}, abstract = {Collections of non-Brownian particles suspended in a viscous fluid and subjected to oscillatory shear at very low Reynolds number have recently been shown to exhibit a remarkable dynamical phase transition separating reversible from irreversible behavior as the strain amplitude or volume fraction are increased. We present a simple model for this phenomenon, based on which we argue that this transition lies in the universality class of the conserved directed percolation models. This leads to predictions for the scaling behavior of a large number of experimental observables. Non-Brownian suspensions under oscillatory shear may thus constitute the first experimental realization of an inactive-active phase transition which is not in the universality class of conventional directed percolation.}, }
@article {pmid19657797, year = {2010}, author = {Molla, MM and Paul, MC and Roditi, G}, title = {LES of additive and non-additive pulsatile flows in a model arterial stenosis.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {13}, number = {1}, pages = {105-120}, doi = {10.1080/10255842.2010.495582}, pmid = {19657797}, issn = {1476-8259}, mesh = {Arterial Occlusive Diseases/*pathology/*physiopathology ; Arteries/*pathology/*physiopathology ; Biomechanical Phenomena ; Computer Simulation ; Constriction, Pathologic ; Hemorheology ; Humans ; *Models, Cardiovascular ; Pulsatile Flow ; }, abstract = {Transition of additive and non-additive pulsatile flows through a simple 3D model of arterial stenosis is investigated by using a large eddy simulation (LES) technique. We find in both the pulsatile cases that the interaction of the two shear layers, one of which separates from the nose of the stenosis and the another one from its opposite wall, causes recirculation in the flow downstream of the stenosis where the nature of the transient flow becomes turbulent. The strength of this recirculation is found to be quite high from the non-additive pulsations when the flow Reynolds numbers, Re>or=1500, for which both the pressure and shearing stresses take on an oscillating form at the post-stenotic region. Potential medical consequences of these results are discussed in the paper. In addition, some comparisons of the non-additive pulsatile results are given with those of both the additive pulsatile and steady flows. The capability of using LES to simulate the pulsatile transitional flow is also assessed, and the present results show that the smaller (subgrid) scales (SGS) contributes about 78% energy dissipation to the flow when the Reynolds number is taken as 2000. The level of SGS dissipation decreases as the Reynolds number is decreased. The numerical results are validated with the experimental data available in literature where a quite good agreement is found.}, }
@article {pmid19648415, year = {2009}, author = {Lentink, D and Dickinson, MH}, title = {Rotational accelerations stabilize leading edge vortices on revolving fly wings.}, journal = {The Journal of experimental biology}, volume = {212}, number = {Pt 16}, pages = {2705-2719}, doi = {10.1242/jeb.022269}, pmid = {19648415}, issn = {0022-0949}, mesh = {Air ; Animals ; Biomechanical Phenomena/physiology ; Coriolis Force ; Drosophila melanogaster/anatomy &amp; histology/*physiology ; Flight, Animal/*physiology ; Models, Animal ; Movement/physiology ; Robotics ; Stress, Mechanical ; Weight-Bearing/physiology ; Wings, Animal/anatomy &amp; histology/*physiology ; }, abstract = {The aerodynamic performance of hovering insects is largely explained by the presence of a stably attached leading edge vortex (LEV) on top of their wings. Although LEVs have been visualized on real, physically modeled, and simulated insects, the physical mechanisms responsible for their stability are poorly understood. To gain fundamental insight into LEV stability on flapping fly wings we expressed the Navier-Stokes equations in a rotating frame of reference attached to the wing's surface. Using these equations we show that LEV dynamics on flapping wings are governed by three terms: angular, centripetal and Coriolis acceleration. Our analysis for hovering conditions shows that angular acceleration is proportional to the inverse of dimensionless stroke amplitude, whereas Coriolis and centripetal acceleration are proportional to the inverse of the Rossby number. Using a dynamically scaled robot model of a flapping fruit fly wing to systematically vary these dimensionless numbers, we determined which of the three accelerations mediate LEV stability. Our force measurements and flow visualizations indicate that the LEV is stabilized by the ;quasi-steady' centripetal and Coriolis accelerations that are present at low Rossby number and result from the propeller-like sweep of the wing. In contrast, the unsteady angular acceleration that results from the back and forth motion of a flapping wing does not appear to play a role in the stable attachment of the LEV. Angular acceleration is, however, critical for LEV integrity as we found it can mediate LEV spiral bursting, a high Reynolds number effect. Our analysis and experiments further suggest that the mechanism responsible for LEV stability is not dependent on Reynolds number, at least over the range most relevant for insect flight (100<Re<14,000). LEVs are stable and continue to augment force even when they burst. These and similar findings for propellers and wind turbines at much higher Reynolds numbers suggest that even large flying animals could potentially exploit LEV-based force augmentation during slow hovering flight, take-offs or landing. We calculated the Rossby number from single-wing aspect ratios of over 300 insects, birds, bats, autorotating seeds, and pectoral fins of fish. We found that, on average, wings and fins have a Rossby number close to that of flies (Ro=3). Theoretically, many of these animals should therefore be able to generate a stable LEV, a prediction that is supported by recent findings for several insects, one bat, one bird and one fish. This suggests that force augmentation through stably attached (leading edge) vortices could represent a convergent solution for the generation of high fluid forces over a quite large range in size.}, }
@article {pmid19648414, year = {2009}, author = {Lentink, D and Dickinson, MH}, title = {Biofluiddynamic scaling of flapping, spinning and translating fins and wings.}, journal = {The Journal of experimental biology}, volume = {212}, number = {Pt 16}, pages = {2691-2704}, doi = {10.1242/jeb.022251}, pmid = {19648414}, issn = {0022-0949}, mesh = {Animals ; Biomechanical Phenomena/physiology ; Diptera/physiology ; Fishes/*physiology ; Flight, Animal/*physiology ; Insecta/*physiology ; Models, Biological ; Motor Activity/physiology ; Movement/*physiology ; Swimming/*physiology ; Wings, Animal/anatomy &amp; histology/*physiology ; }, abstract = {Organisms that swim or fly with fins or wings physically interact with the surrounding water and air. The interactions are governed by the morphology and kinematics of the locomotory system that form boundary conditions to the Navier-Stokes (NS) equations. These equations represent Newton's law of motion for the fluid surrounding the organism. Several dimensionless numbers, such as the Reynolds number and Strouhal number, measure the influence of morphology and kinematics on the fluid dynamics of swimming and flight. There exists, however, no coherent theoretical framework that shows how such dimensionless numbers of organisms are linked to the NS equation. Here we present an integrated approach to scale the biological fluid dynamics of a wing that flaps, spins or translates. Both the morphology and kinematics of the locomotory system are coupled to the NS equation through which we find dimensionless numbers that represent rotational accelerations in the flow due to wing kinematics and morphology. The three corresponding dimensionless numbers are (1) the angular acceleration number, (2) the centripetal acceleration number, and (3) the Rossby number, which measures Coriolis acceleration. These dimensionless numbers consist of length scale ratios, which facilitate their geometric interpretation. This approach gives fundamental insight into the physical mechanisms that explain the differences in performance among flapping, spinning and translating wings. Although we derived this new framework for the special case of a model fly wing, the method is general enough to make it applicable to other organisms that fly or swim using wings or fins.}, }
@article {pmid23133151, year = {2009}, author = {Srivastava, A and Sood, A and Joy, SP and Woodcock, J}, title = {Principles of physics in surgery: the laws of flow dynamics physics for surgeons - Part 1.}, journal = {The Indian journal of surgery}, volume = {71}, number = {4}, pages = {182-187}, pmid = {23133151}, issn = {0972-2068}, abstract = {In the field of medicine and surgery many principles of physics find numerous applications. In this article we have summarized some prominent applications of the laws of fluid mechanics and hydrodynamics in surgery. Poiseuille's law sets the limits of isovolaemic haemodilution, enumerates limiting factors during fluid resuscitation and is a guiding principle in surgery for vascular stenoses. The equation of continuity finds use in non-invasive measurement of blood flow. Bernoulli's theorem explains the formation of post-stenotic dilatation. Reynolds number explains the origin of murmurs, haemolysis and airflow disturbances. Various forms of oxygen therapy are a direct application of the gas laws. Doppler effect is used in ultrasonography to find the direction and velocity of blood flow. In this first part of a series of articles we describe some applications of the laws of hydrodynamics governing the flow of blood and other body fluids.}, }
@article {pmid19631665, year = {2009}, author = {Kim, WK and Ko, JH and Park, HC and Byun, D}, title = {Effects of corrugation of the dragonfly wing on gliding performance.}, journal = {Journal of theoretical biology}, volume = {260}, number = {4}, pages = {523-530}, doi = {10.1016/j.jtbi.2009.07.015}, pmid = {19631665}, issn = {1095-8541}, mesh = {Animals ; Biomechanical Phenomena ; Flight, Animal/*physiology ; Insecta/*anatomy &amp; histology/physiology ; Models, Biological ; Surface Properties ; Wings, Animal/*anatomy &amp; histology/physiology ; }, abstract = {We investigate the aerodynamic performance of the dragonfly wing, which has cross-sectional corrugation, via a static 2-dimensional unsteady simulation. Computational conditions are Re=150, 1400, and 10,000 with angles of attack ranging from 0 degrees to 40 degrees . From the computational results, lift coefficients are increased by the wing corrugation at all Reynolds number. However, the corrugation has little influence on the drag coefficients. The flows such as vortex in the valley of corrugation and near the edge of the corrugation are locally different from those of an elliptic wing. However, such local flows have little influence on the time averaged wing performance. From the numerical experiment presented in this study, it is determined that suction side corrugations of the wing have very little influence on increase of the lift coefficient at a positive angle of attack.}, }
@article {pmid19615495, year = {2009}, author = {Fortes, PR and Feres, MA and Sasaki, MK and Alves, ER and Zagatto, EA and Prior, JA and Santos, JL and Lima, JL}, title = {Evidences of turbulent mixing in multi-pumping flow systems.}, journal = {Talanta}, volume = {79}, number = {4}, pages = {978-983}, doi = {10.1016/j.talanta.2009.01.062}, pmid = {19615495}, issn = {1873-3573}, abstract = {Multi-pumping flow systems exploit pulsed flows delivered by solenoid pumps. Their improved performance rely on the enhanced radial mass transport inherent to the pulsed flow, which is a consequence of the establishment of vortices thus a tendency towards turbulent mixing. This paper presents several evidences of turbulent mixing in relation to pulsed flows, such as recorded peak shape, establishment of fluidized beds, exploitation of flow reversal, implementation of relatively slow chemical reactions and/or heating of the reaction medium. In addition, Reynolds number associated with the GO period of a pulsed flow is estimated and photographic images of dispersing samples flowing under laminar regime and pulsed flow conditions are presented.}, }
@article {pmid19567970, year = {2009}, author = {Chung, MH}, title = {On burst-and-coast swimming performance in fish-like locomotion.}, journal = {Bioinspiration &amp; biomimetics}, volume = {4}, number = {3}, pages = {036001}, doi = {10.1088/1748-3182/4/3/036001}, pmid = {19567970}, issn = {1748-3190}, mesh = {Animals ; Biomimetics/*methods ; Computer Simulation ; Energy Metabolism/*physiology ; Fishes/*physiology ; *Models, Biological ; Physical Exertion/*physiology ; Swimming/*physiology ; }, abstract = {Burst-and-coast swimming performance in fish-like locomotion is studied via two-dimensional numerical simulation. The numerical method used is the collocated finite-volume adaptive Cartesian cut-cell method developed previously. The NACA00xx airfoil shape is used as an equilibrium fish-body form. Swimming in a burst-and-coast style is computed assuming that the burst phase is composed of a single tail-beat. Swimming efficiency is evaluated in terms of the mass-specific cost of transport instead of the Froude efficiency. The effects of the Reynolds number (based on the body length and burst time), duty cycle and fineness ratio (the body length over the largest thickness) on swimming performance (momentum capacity and the mass-specific cost of transport) are studied quantitatively. The results lead to a conclusion consistent with previous findings that a larval fish seldom swims in a burst-and-coast style. Given mass and swimming speed, a fish needs the least cost if it swims in a burst-and-coast style with a fineness ratio of 8.33. This energetically optimal fineness ratio is larger than that derived from the simple hydromechanical model proposed in literature. The calculated amount of energy saving in burst-and-coast swimming is comparable with the real-fish estimation in the literature. Finally, the predicted wake-vortex structures of both continuous and burst-and-coast swimming are biologically relevant.}, }
@article {pmid19544384, year = {2009}, author = {Sahu, AK and Conneely, T and Nüsslein, K and Ergas, SJ}, title = {Hydrogenotrophic denitrification and perchlorate reduction in ion exchange brines using membrane biofilm reactors.}, journal = {Biotechnology and bioengineering}, volume = {104}, number = {3}, pages = {483-491}, doi = {10.1002/bit.22414}, pmid = {19544384}, issn = {1097-0290}, mesh = {Bacteroidetes/classification/isolation &amp; purification/metabolism ; *Biofilms ; Cluster Analysis ; DNA, Bacterial/chemistry/genetics ; DNA, Ribosomal/chemistry/genetics ; Gammaproteobacteria/classification/isolation &amp; purification/metabolism ; Hydrogen/*metabolism ; Ion Exchange ; Membranes/*microbiology ; Molecular Sequence Data ; Nitrites/*metabolism ; Oxidation-Reduction ; Perchlorates/*metabolism ; Phylogeny ; RNA, Ribosomal, 16S/genetics ; Sequence Analysis, DNA ; Water Pollutants, Chemical/*metabolism ; Water Purification/methods ; }, abstract = {Halophilic (salt loving), hydrogenotrophic (H(2) oxidizing) denitrifying bacteria were investigated for treatment of nitrate (NO3-) and perchlorate (ClO4-) contaminated groundwater and ion exchange (IX) brines. Hydrogenotrophic denitrifying bacteria were enriched from a denitrifying wastewater seed under both halophilc and non-halophilc conditions. The cultures were inoculated into bench-scale membrane biofilm reactors (MBfRs) with an "outside in" configuration, with contaminated water supplied to the lumen of the membranes and H(2) supplied to the shell. Abiotic mass transfer tests showed that H(2) mass transfer coefficients were lower in brines than in tap water at highest Reynolds number, possibly due to increased transport of salts and decreased H(2) solubility at the membrane/liquid interface. An average NO3- removal efficiency of 93% was observed for the MBfR operated in continuous flow mode with synthetic contaminated groundwater. Removal efficiencies of 30% for NO3- and 42% for ClO4- were observed for the MBfR operated with synthetic IX brine in batch operating mode with a reaction time of 53 h. Phylogenetic analysis focused on the active microbial community and revealed that halotolerant, NO3- -reducing bacteria of the bacterial classes Gamma-Proteobacteria and Sphingobacteria were the metabolically dominant members within the stabilized biofilm. This study shows that, despite decreased H(2) transfer under high salt conditions, hydrogenotrophic biological reduction may be successfully used for the treatment of NO3- and ClO- in a MBfR.}, }
@article {pmid19531512, year = {2009}, author = {Krajnovic, S}, title = {Large eddy simulation of flows around ground vehicles and other bluff bodies.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {367}, number = {1899}, pages = {2917-2930}, doi = {10.1098/rsta.2009.0021}, pmid = {19531512}, issn = {1364-503X}, abstract = {A brief review of large eddy simulation (LES) applications for different bluff-body flows performed by the author and his co-workers is presented. Examples of flows range from simple cube flows characterized by sharp edge separation over a three-dimensional hill where LES relies on good near-wall resolution, to complex flows of a tall, finite cylinder that contains several flow regimes that cause different challenges to LES. The second part of the paper is devoted to flows around ground vehicles at moderate Reynolds numbers. Although the present review proves the applicability of LES for various bluff-body flows, an increase of the Reynolds number towards the operational speeds of ground vehicles requires accurate near-wall modelling for a successful LES.}, }
@article {pmid19531510, year = {2009}, author = {Leschziner, M and Li, N and Tessicini, F}, title = {Simulating flow separation from continuous surfaces: routes to overcoming the Reynolds number barrier.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {367}, number = {1899}, pages = {2885-2903}, doi = {10.1098/rsta.2009.0002}, pmid = {19531510}, issn = {1364-503X}, abstract = {This paper provides a discussion of several aspects of the construction of approaches that combine statistical (Reynolds-averaged Navier-Stokes, RANS) models with large eddy simulation (LES), with the objective of making LES an economically viable method for predicting complex, high Reynolds number turbulent flows. The first part provides a review of alternative approaches, highlighting their rationale and major elements. Next, two particular methods are introduced in greater detail: one based on coupling near-wall RANS models to the outer LES domain on a single contiguous mesh, and the other involving the application of the RANS and LES procedures on separate zones, the former confined to a thin near-wall layer. Examples for their performance are included for channel flow and, in the case of the zonal strategy, for three separated flows. Finally, a discussion of prospects is given, as viewed from the writer's perspective.}, }
@article {pmid19531509, year = {2009}, author = {Geurts, BJ}, title = {Analysis of errors occurring in large eddy simulation.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {367}, number = {1899}, pages = {2873-2883}, doi = {10.1098/rsta.2009.0001}, pmid = {19531509}, issn = {1364-503X}, abstract = {We analyse the effect of second- and fourth-order accurate central finite-volume discretizations on the outcome of large eddy simulations of homogeneous, isotropic, decaying turbulence at an initial Taylor-Reynolds number Re(lambda)=100. We determine the implicit filter that is induced by the spatial discretization and show that a higher order discretization also induces a higher order filter, i.e. a low-pass filter that keeps a wider range of flow scales virtually unchanged. The effectiveness of the implicit filtering is correlated with the optimal refinement strategy as observed in an error-landscape analysis based on Smagorinsky's subfilter model. As a point of reference, a finite-volume method that is second-order accurate for both the convective and the viscous fluxes in the Navier-Stokes equations is used. We observe that changing to a fourth-order accurate convective discretization leads to a higher value of the Smagorinsky coefficient C(S) required to achieve minimal total error at given resolution. Conversely, changing only the viscous flux discretization to fourth-order accuracy implies that optimal simulation results are obtained at lower values of C(S). Finally, a fully fourth-order discretization yields an optimal C(S) that is slightly lower than the reference fully second-order method.}, }
@article {pmid19531507, year = {2009}, author = {Sagaut, P and Deck, S}, title = {Large eddy simulation for aerodynamics: status and perspectives.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {367}, number = {1899}, pages = {2849-2860}, doi = {10.1098/rsta.2008.0269}, pmid = {19531507}, issn = {1364-503X}, abstract = {The present paper provides an up-to-date survey of the use of large eddy simulation (LES) and sequels for engineering applications related to aerodynamics. Most recent landmark achievements are presented. Two categories of problem may be distinguished whether the location of separation is triggered by the geometry or not. In the first case, LES can be considered as a mature technique and recent hybrid Reynolds-averaged Navier-Stokes (RANS)-LES methods do not allow for a significant increase in terms of geometrical complexity and/or Reynolds number with respect to classical LES. When attached boundary layers have a significant impact on the global flow dynamics, the use of hybrid RANS-LES remains the principal strategy to reduce computational cost compared to LES. Another striking observation is that the level of validation is most of the time restricted to time-averaged global quantities, a detailed analysis of the flow unsteadiness being missing. Therefore, a clear need for detailed validation in the near future is identified. To this end, new issues, such as uncertainty and error quantification and modelling, will be of major importance. First results dealing with uncertainty modelling in unsteady turbulent flow simulation are presented.}, }
@article {pmid19518958, year = {2009}, author = {Meyer, RF and Crocker, JC}, title = {Universal dripping and jetting in a transverse shear flow.}, journal = {Physical review letters}, volume = {102}, number = {19}, pages = {194501}, doi = {10.1103/PhysRevLett.102.194501}, pmid = {19518958}, issn = {0031-9007}, abstract = {One particularly efficient approach to making emulsions having monosized droplets is to push a fluid through an orifice into a transverse flow of a second immiscible fluid. We find that, at an intermediate particle Reynolds number, the final droplet size can be readily computed using a simple force balance. Remarkably like the well-known dripping faucet, this system displays both dripping and jetting behavior, controlled by the capillary, Weber and Ohnesorge numbers of the relevant fluids, and interesting nonlinear behavior such as period doubling near the transition between these two regimes.}, }
@article {pmid19518563, year = {2009}, author = {Tran, CV and Blackbourn, L}, title = {Number of degrees of freedom of two-dimensional turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {79}, number = {5 Pt 2}, pages = {056308}, doi = {10.1103/PhysRevE.79.056308}, pmid = {19518563}, issn = {1539-3755}, abstract = {We derive upper bounds for the number of degrees of freedom of two-dimensional Navier-Stokes turbulence freely decaying from a smooth initial vorticity field omega(x,y,0)=omega0. This number denoted by N is defined as the minimum dimension such that for n>or=N, arbitrary n-dimensional balls in phase space centered on the solution trajectory omega(x,y,t); for t>0, contract under the dynamics of the system linearized about omega(x,y,t). In other words, N is the minimum number of greatest Lyapunov exponents whose sum becomes negative. It is found that N<or=C1Re when the phase space is endowed with the energy norm and N<or=C2Re(1+ln Re)1/3 when the phase space is endowed with the enstrophy norm. Here C1 and C2 are constant and Re is the Reynolds number defined in terms of omega0, the system length scale, and the viscosity nu. The linear (or nearly linear) dependence of N on Re is consistent with the estimate for the number of active modes deduced from a recent mathematical bound for the viscous dissipation wave number. This result is in a sharp contrast to the forced case, for which well-known estimates for the Hausdorff dimension DH of the global attractor scale highly superlinearly with nu(-1). We argue that the "extra" dependence of DH on nu(-1) is not an intrinsic property of the turbulent dynamics. Rather, it is a "removable artifact" brought about by the use of a time-independent forcing as a model for energy and enstrophy injection that drives the turbulence.}, }
@article {pmid19518562, year = {2009}, author = {Krapf, NW and Witten, TA and Keim, NC}, title = {Chiral sedimentation of extended objects in viscous media.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {79}, number = {5 Pt 2}, pages = {056307}, doi = {10.1103/PhysRevE.79.056307}, pmid = {19518562}, issn = {1539-3755}, abstract = {We study theoretically the chirality of a generic rigid object's sedimentation in a fluid under gravity in the low Reynolds number regime. We represent the object as a collection of small Stokes spheres or stokeslets and the gravitational force as a constant point force applied at an arbitrary point of the object. For a generic configuration of stokeslets and forcing point, the motion takes a simple form in the nearly free draining limit where the stokeslet radius is arbitrarily small. In this case, the internal hydrodynamic interactions between stokeslets are weak, and the object follows a helical path while rotating at a constant angular velocity omega about a fixed axis. This omega is independent of initial orientation and thus constitutes a chiral response for the object. Even though there can be no such chiral response in the absence of hydrodynamic interactions between the stokeslets, the angular velocity obtains a fixed nonzero limit as the stokeslet radius approaches zero. We characterize empirically how omega depends on the placement of the stokeslets, concentrating on three-stokeslet objects with the external force applied far from the stokeslets. Objects with the largest omega are aligned along the forcing direction. In this case, the limiting omega varies as the inverse square of the minimum distance between stokeslets. We illustrate the prevalence of this robust chiral motion with experiments on small macroscopic objects of arbitrary shape.}, }
@article {pmid19518454, year = {2009}, author = {Keaveny, EE and Shelley, MJ}, title = {Hydrodynamic mobility of chiral colloidal aggregates.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {79}, number = {5 Pt 1}, pages = {051405}, doi = {10.1103/PhysRevE.79.051405}, pmid = {19518454}, issn = {1539-3755}, abstract = {A recent advance in colloidal technology [Zerrouki, Nature (London) 455, 380 (2008)] uses magnetic aggregation to enable the formation of micron-scale particle clusters with helical symmetry. The basic building blocks of these aggregates are doublets composed of two micron-scale beads of different radii bonded together by a magnetic cement. Such self-assembled structures offer potential for controllable transport and separation in a low Reynolds number environment using externally applied magnetic or electric fields. Establishing the hydrodynamic properties of the aggregates, in particular the coupling between rotation and translation afforded by the cluster geometry, is an essential initial step toward the design of microfluidic devices employing these aggregates. To quantify this coupling, we first determine parametrized expressions that describe the positions of the beads in an aggregate as a function of size ratio of the two beads composing the doublets. With the geometry of the structure known, we perform hydrodynamic calculations to ascertain entries of the mobility matrix for the aggregate and establish the relationship between the applied torque about the helical axis and translations parallel to this direction. We find that for larger values of the particle radius ratio the coupling between rotations and translations changes sign as the number of doublets in the aggregate increases. This feature indicates that the clusters possess a more complex superhelical structure.}, }
@article {pmid19518377, year = {2009}, author = {Krüger, T and Varnik, F and Raabe, D}, title = {Shear stress in lattice Boltzmann simulations.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {79}, number = {4 Pt 2}, pages = {046704}, doi = {10.1103/PhysRevE.79.046704}, pmid = {19518377}, issn = {1539-3755}, abstract = {A thorough study of shear stress within the lattice Boltzmann method is provided. Via standard multiscale Chapman-Enskog expansion we investigate the dependence of the error in shear stress on grid resolution showing that the shear stress obtained by the lattice Boltzmann method is second-order accurate. This convergence, however, is usually spoiled by the boundary conditions. It is also investigated which value of the relaxation parameter minimizes the error. Furthermore, for simulations using velocity boundary conditions, an artificial mass increase is often observed. This is a consequence of the compressibility of the lattice Boltzmann fluid. We investigate this issue and derive an analytic expression for the time dependence of the fluid density in terms of the Reynolds number, Mach number, and a geometric factor for the case of a Poiseuille flow through a rectangular channel in three dimensions. Comparison of the analytic expression with results of lattice Boltzmann simulations shows excellent agreement.}, }
@article {pmid19518348, year = {2009}, author = {Rinoshika, A and Zhou, Y}, title = {Reynolds number effects on wavelet components of self-preserving turbulent structures.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {79}, number = {4 Pt 2}, pages = {046322}, doi = {10.1103/PhysRevE.79.046322}, pmid = {19518348}, issn = {1539-3755}, abstract = {The effect of the Reynolds number on the wavelet-decomposed turbulent structures in a self-preserving plane wake has been investigated for Re_{theta} (based on the free-stream velocity and momentum thickness, theta, of the wake) =1350 and 4600. Measurements were made at x/theta (x is the streamwise distance downstream of the cylinder) =580 for the circular cylinder using two orthogonal arrays of 16 X wires, eight in the (x,y) plane, and eight in the (x,z) plane. A wavelet multiresolution technique is used to analyze the measured hot-wire data. This technique decomposes turbulence structures into a number of components based on their central frequencies, which are linked with the turbulence scales. Sectional streamlines and vorticity contours at the same central frequency, i.e., the comparable scales of turbulent structures, are examined and compared between the two Reynolds numbers. Discernible differences are observed in the turbulent structures of relatively large to intermediate scales. The differences are further quantified in terms of contributions from the turbulent structures of different scales to the Reynolds stresses, vorticity variance, and probability density functions of the fluctuating velocities. The large-scale structure contributes most to the Reynolds stresses and this contribution drops for the higher Re_{theta}.}, }
@article {pmid19518289, year = {2009}, author = {L'vov, VS and Procaccia, I and Rudenko, O}, title = {Velocity and energy profiles in two- versus three-dimensional channels: Effects of an inverse- versus a direct-energy cascade.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {79}, number = {4 Pt 2}, pages = {045304}, doi = {10.1103/PhysRevE.79.045304}, pmid = {19518289}, issn = {1539-3755}, abstract = {In light of some recent experiments on quasi two-dimensional (2D) turbulent channel flow we provide here a model of the ideal case, for the sake of comparison. The ideal 2D channel flow differs from its three-dimensional (3D) counterpart by having a second quadratic conserved variable in addition to the energy and the latter has an inverse rather than a direct cascade. The resulting qualitative differences in profiles of velocity V and energy K as a function of the distance from the wall are highlighted and explained. The most glaring difference is that the 2D channel is much more energetic, with K in wall units increasing logarithmically with the Reynolds number Re_{tau} instead of being Re_{tau} independent in 3D channels.}, }
@article {pmid19518287, year = {2009}, author = {Or, Y and Murray, RM}, title = {Dynamics and stability of a class of low Reynolds number swimmers near a wall.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {79}, number = {4 Pt 2}, pages = {045302}, doi = {10.1103/PhysRevE.79.045302}, pmid = {19518287}, issn = {1539-3755}, abstract = {We study the dynamic stability of low Reynolds number swimming near a plane wall from a control-theoretic viewpoint. We consider a special class of swimmers having a constant shape, focus on steady motion parallel to the wall, and derive conditions under which it is passively stable without sensing or feedback. We study the geometric structure of the swimming equation and highlight the relation between stability and reversing symmetry of the dynamical system. Finally, our numerical simulations reveal the existence of stable periodic motion. The results have implications for design of miniature robotic swimmers, as well as for explaining the attraction of micro-organisms to surfaces.}, }
@article {pmid19493531, year = {2009}, author = {Luo, HY and Liu, Y}, title = {Particle deposition in a CT-scanned human lung airway.}, journal = {Journal of biomechanics}, volume = {42}, number = {12}, pages = {1869-1876}, doi = {10.1016/j.jbiomech.2009.05.004}, pmid = {19493531}, issn = {1873-2380}, mesh = {Bronchi ; Humans ; *Lung/diagnostic imaging ; Male ; Middle Aged ; Particle Size ; Particulate Matter/*analysis ; Pulmonary Ventilation ; *Respiratory Mechanics ; *Tomography, X-Ray Computed ; Trachea ; }, abstract = {The particle deposition in a computerized tomography (CT)-scanned human lung was numerically investigated. The five-generation airway is extracted from the trachea to segmental bronchi of a 60-year-old Chinese male patient. Computations were carried out in the flow rate range of 210-630 ml/s (Reynolds number range of 1000-3000) and particle size of 2-10 microm (Stokes number range of 0.0007-0.049). To count the effect of laryngeal jet on trachea inlet, the trachea was extended and modified to simulate the larynx, consequently the inlet velocity profile is biased towards the rear wall. The laryngeal jet-induced turbulence was simulated using low Reynolds number (LRN) kappa-omega turbulent model. Particle deposition patterns, deposition efficiency and deposition factor were studied in detail. The turbulent flow has significant effect on the particle deposition, and the present deposition factor is compared well with the available data.}, }
@article {pmid19482288, year = {2009}, author = {Kumar, H and Tawhai, MH and Hoffman, EA and Lin, CL}, title = {The effects of geometry on airflow in the acinar region of the human lung.}, journal = {Journal of biomechanics}, volume = {42}, number = {11}, pages = {1635-1642}, pmid = {19482288}, issn = {1873-2380}, support = {R01 HL064368-06A1/HL/NHLBI NIH HHS/United States ; R01 EB005823-03/EB/NIBIB NIH HHS/United States ; R01 EB005823-01/EB/NIBIB NIH HHS/United States ; R01 EB005823/EB/NIBIB NIH HHS/United States ; R01 EB005823-02/EB/NIBIB NIH HHS/United States ; R01-EB-005823/EB/NIBIB NIH HHS/United States ; R01 HL064368/HL/NHLBI NIH HHS/United States ; R01 HL064368-07/HL/NHLBI NIH HHS/United States ; R01 HL064368-09/HL/NHLBI NIH HHS/United States ; R01 HL064368-08/HL/NHLBI NIH HHS/United States ; R01-HL-064368/HL/NHLBI NIH HHS/United States ; }, mesh = {Biomechanical Phenomena ; Computer Simulation ; Finite Element Analysis ; Humans ; Lung/*anatomy &amp; histology/physiology ; Models, Anatomic ; Models, Statistical ; Pulmonary Alveoli/metabolism ; Pulmonary Ventilation ; Respiration ; *Respiratory Mechanics ; Time Factors ; }, abstract = {Understanding flow phenomena in the pulmonary acinus is important for predicting particle transport and deposition and hence, in designing effective drug delivery strategies for the lung. In the current study, a three-dimensional honeycomb-like geometry involving a central airspace and surrounding alveoli is used to represent an alveolar duct and sacs. Numerical results predict that flow in the presence of wall motion is characterized by the presence of a developing recirculation region within the cavity and by a flow entrainment region indicative of the weak nature of interaction between duct and cavity. Under the normal breathing condition (2.5 s) and volumetric expansion (approximately 25%) considered here, recirculation disappears for Re<0.6. Alveolar flow in higher generations (at lower Reynolds number) results from significantly higher entrainment of the ductal flow, and does not exhibit any recirculation. In an asymmetric arrangement of the alveolar cluster, topological differences in cavity result in significant differences in the size of recirculation and the size of entrainment region within the alveoli of the same acinar generation, indicative of a non-uniform alveolar ventilation. The flow in the terminal alveolar sac is non-recirculating and not affected by variation in geometrical features.}, }
@article {pmid19481190, year = {2009}, author = {Sankey, M and Yang, Z and Gladden, L and Johns, ML and Lister, D and Newling, B}, title = {SPRITE MRI of bubbly flow in a horizontal pipe.}, journal = {Journal of magnetic resonance (San Diego, Calif. : 1997)}, volume = {199}, number = {2}, pages = {126-135}, doi = {10.1016/j.jmr.2009.01.034}, pmid = {19481190}, issn = {1096-0856}, mesh = {*Algorithms ; Gases/*chemistry ; Image Interpretation, Computer-Assisted/*methods ; Magnetic Resonance Imaging/*methods ; Rheology/*methods ; }, abstract = {Bubble flow is characterised by numerous phase interfaces and turbulence, leading to fast magnetic resonance signal decay and artefacts in spin-warp imaging. In this paper, the SPRITE MRI pulse sequence, with its potential for very short encoding times, is demonstrated as an ideal technique for studying such dynamic systems. It has been used to acquire liquid velocity and relative intensity maps of two-phase gas-liquid dispersed bubble flow in a horizontal pipe at a liquid Reynolds number of 14,500. The fluids were air and water and a turbulence grid was used to generate a dispersed bubble flow pattern. The SPRITE technique shows promise for future research in gas-liquid flow.}, }
@article {pmid19464694, year = {2009}, author = {Hsu, JP and Chou, CH and Tseng, S and Wu, RM}, title = {3D simulations of hydrodynamic drag on a nonhomogeneously structured permeable sphere and advective flow thereof.}, journal = {Journal of colloid and interface science}, volume = {336}, number = {2}, pages = {850-856}, doi = {10.1016/j.jcis.2009.04.045}, pmid = {19464694}, issn = {1095-7103}, abstract = {The influence of the structure of a permeable sphere on the flow field and the hydrodynamic drag acting on it are investigated theoretically under the conditions of low to medium large Reynolds number. The anisotropic nature of the permeability of the sphere is taken into account by considering a three-dimensional permeability model. We show that although the permeability in the main flow direction dominates, the permeability in the other directions cannot be neglected. If Reynolds number is small, the larger the permeability in the main flow direction the more significant the influence of the permeability in the other directions. If Reynolds number takes a medium large value, the influence of the permeability in the other directions may decrease if the permeability in the main flow direction is sufficiently large. Depending on the levels of Reynolds number and the permeability, the extent of that influence can be on the order of 10%.}, }
@article {pmid19457490, year = {2009}, author = {Ai, L and Yu, H and Takabe, W and Paraboschi, A and Yu, F and Kim, ES and Li, R and Hsiai, TK}, title = {Optimization of intravascular shear stress assessment in vivo.}, journal = {Journal of biomechanics}, volume = {42}, number = {10}, pages = {1429-1437}, pmid = {19457490}, issn = {1873-2380}, support = {R01 HL118650/HL/NHLBI NIH HHS/United States ; R01 HL083015-01A1/HL/NHLBI NIH HHS/United States ; K08 HL068689/HL/NHLBI NIH HHS/United States ; R01 HL083015/HL/NHLBI NIH HHS/United States ; K08 HL068689-01A1/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Aorta, Abdominal/diagnostic imaging/*physiology ; Biomechanical Phenomena ; Biomedical Engineering ; *Hemorheology ; Imaging, Three-Dimensional ; *Models, Cardiovascular ; Rabbits ; Radiography ; Stress, Mechanical ; Ultrasonography ; }, abstract = {The advent of microelectromechanical systems (MEMS) sensors has enabled real-time wall shear stress (WSS) measurements with high spatial and temporal resolution in a 3-D bifurcation model. To optimize intravascular shear stress assessment, we evaluated the feasibility of catheter/coaxial wire-based MEMS sensors in the abdominal aorta of the New Zealand white (NZW) rabbits. Theoretical and computational fluid dynamics (CFD) analyses were performed. Fluoroscope and angiogram provided the geometry of aorta, and the Doppler ultrasound system provided the pulsatile flow velocity for the boundary conditions. The physical parameters governing the shear stress assessment in NZW rabbits included (1) the position and distance from which the MEMS sensors were mounted to the terminal end of coaxial wire or the entrance length, (L(e)), (2) diameter ratios of aorta to the coaxial wire (D(aorta) /D(coaxial wire)=1.5-9.5), and (3) the range of Reynolds numbers (116-1550). At an aortic diameter of 2.4mm and a maximum Reynolds number of 212 (a mean Reynolds number of 64.2), the time-averaged shear stress (tau(ave)) was computed to be 10.06 dyn cm(-2) with a systolic peak at 33.18 dyn cm(-2). In the presence of a coaxial wire (D(aorta)/D(coaxial wire)=6 and L(e)=1.18 cm), the tau(ave) value increased to 15.54 dyn cm(-2) with a systolic peak at 51.25 dyn cm(-2). Real-time intravascular shear stress assessment by the MEMS sensor revealed an tau(ave) value of 11.92 dyn cm(-2) with a systolic peak at 47.04 dyn cm(-2). The difference between CFD and experimental tau(ave) was 18.5%. These findings provided important insights into packaging the MEMS sensors to optimize in vivo shear stress assessment.}, }
@article {pmid21825518, year = {2009}, author = {Coq, N and Roure, Od and Fermigier, M and Bartolo, D}, title = {Helical beating of an actuated elastic filament.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {21}, number = {20}, pages = {204109}, doi = {10.1088/0953-8984/21/20/204109}, pmid = {21825518}, issn = {0953-8984}, abstract = {We investigate the propulsive force resulting from the rotation of a flexible filament in the low Reynolds number regime. Using a simple linear model, we establish the nonlinear torque-force relations for two torque-driven actuation modes. When the rotation of the filament is induced by two perpendicular transverse oscillating torques, the propulsive force increases monotonically with the torque amplitude. Conversely, when a constant axial torque is applied, the torque-force characteristics displays an unstable branch, related to a discontinuous transition in the shape of the filament. We characterize this shape transition using two geometrical parameters, quantifying the wrapping around and the collapse on the axis of the filament. The proposed theoretical description correctly accounts for our experimental observations and reveals a strong dependence of the filament dynamics on the anchoring conditions.}, }
@article {pmid21825516, year = {2009}, author = {Hernandez-Ortiz, JP and Underhill, PT and Graham, MD}, title = {Dynamics of confined suspensions of swimming particles.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {21}, number = {20}, pages = {204107}, doi = {10.1088/0953-8984/21/20/204107}, pmid = {21825516}, issn = {0953-8984}, abstract = {Low Reynolds number direct simulations of large populations of hydrodynamically interacting swimming particles confined between planar walls are performed. The results of simulations are compared with a theory that describes dilute suspensions of swimmers. The theory yields scalings with concentration for diffusivities and velocity fluctuations as well as a prediction of the fluid velocity spatial autocorrelation function. Even for uncorrelated swimmers, the theory predicts anticorrelations between nearby fluid elements that correspond to vortex-like swirling motions in the fluid with length scale set by the size of a swimmer and the slit height. Very similar results arise from the full simulations indicating either that correlated motion of the swimmers is not significant at the concentrations considered or that the fluid phase autocorrelation is not a sensitive measure of the correlated motion. This result is in stark contrast with results from unconfined systems, for which the fluid autocorrelation captures large-scale collective fluid structures. The additional length scale (screening length) introduced by the confinement seems to prevent these large-scale structures from forming.}, }
@article {pmid21825515, year = {2009}, author = {Felderhof, BU}, title = {Swimming and peristaltic pumping between two plane parallel walls.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {21}, number = {20}, pages = {204106}, doi = {10.1088/0953-8984/21/20/204106}, pmid = {21825515}, issn = {0953-8984}, abstract = {Swimming at low Reynolds number in a fluid confined between two plane walls is studied for an infinite plane sheet located midway between the walls and distorted with a transverse propagating wave. It is shown that the flow pattern is closely related to that for peristaltic pumping. The hydrodynamic interaction between two flexible sheets swimming parallel in infinite space is related to the problem of peristaltic pumping in a planar channel with two wavy walls.}, }
@article {pmid21825514, year = {2009}, author = {Wilson, MM and Peng, J and Dabiri, JO and Eldredge, JD}, title = {Lagrangian coherent structures in low Reynolds number swimming.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {21}, number = {20}, pages = {204105}, doi = {10.1088/0953-8984/21/20/204105}, pmid = {21825514}, issn = {0953-8984}, abstract = {This work explores the utility of the finite-time Lyapunov exponent (FTLE) field for revealing flow structures in low Reynolds number biological locomotion. Previous studies of high Reynolds number unsteady flows have demonstrated that ridges of the FTLE field coincide with transport barriers within the flow, which are not shown by a more classical quantity such as vorticity. In low Reynolds number locomotion (O(1)-O(100)), in which viscous diffusion rapidly smears the vorticity in the wake, the FTLE field has the potential to add new insight to locomotion mechanics. The target of study is an articulated two-dimensional model for jellyfish-like locomotion, with swimming Reynolds number of order 1. The self-propulsion of the model is numerically simulated with a viscous vortex particle method, using kinematics adapted from previous experimental measurements on a live medusan swimmer. The roles of the ridges of the computed forward- and backward-time FTLE fields are clarified by tracking clusters of particles both backward and forward in time. It is shown that a series of ridges in front of the jellyfish in the forward-time FTLE field transport slender fingers of fluid toward the lip of the bell orifice, which are pulled once per contraction cycle into the wake of the jellyfish, where the fluid remains partitioned. A strong ridge in the backward-time FTLE field reveals a persistent barrier between fluid inside and outside the subumbrellar cavity. The system is also analyzed in a body-fixed frame subject to a steady free stream, and the FTLE field is used to highlight differences in these frames of reference.}, }
@article {pmid21825513, year = {2009}, author = {Golestanian, R and Ajdari, A}, title = {Stochastic low Reynolds number swimmers.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {21}, number = {20}, pages = {204104}, doi = {10.1088/0953-8984/21/20/204104}, pmid = {21825513}, issn = {0953-8984}, abstract = {As technological advances allow us to fabricate smaller autonomous self-propelled devices, it is clear that at some point directed propulsion could not come from pre-specified deterministic periodic deformation of the swimmer's body and we need to develop strategies for extracting a net directed motion from a series of random transitions in the conformation space of the swimmer. We present a theoretical formulation for describing the 'stochastic motor' that drives the motion of low Reynolds number swimmers based on this concept, and use it to study the propulsion of a simple low Reynolds number swimmer, namely, the three-sphere swimmer model. When the detailed balanced is broken and the motor is driven out of equilibrium, it can propel the swimmer in the required direction. The formulation can be used to study optimal design strategies for molecular scale low Reynolds number swimmers.}, }
@article {pmid21825512, year = {2009}, author = {Gonzalez-Rodriguez, D and Lauga, E}, title = {Reciprocal locomotion of dense swimmers in Stokes flow.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {21}, number = {20}, pages = {204103}, doi = {10.1088/0953-8984/21/20/204103}, pmid = {21825512}, issn = {0953-8984}, abstract = {Due to the kinematic reversibility of Stokes flow, a body executing a reciprocal motion (a motion in which the sequence of body configurations remains identical under time reversal) cannot propel itself in a viscous fluid in the limit of negligible inertia; this result is known as Purcell's scallop theorem. In this limit, the Reynolds numbers based on the fluid inertia and on the body inertia are all zero. Previous studies characterized the breakdown of the scallop theorem with fluid inertia. In this paper we show that, even in the absence of fluid inertia, certain dense bodies undergoing reciprocal motion are able to swim. Using Lorentz's reciprocal theorem, we first derive the general differential equations that govern the locomotion kinematics of a dense swimmer. We demonstrate that no reciprocal swimming is possible if the body motion consists only of tangential surface deformation (squirming). We then apply our general formulation to compute the locomotion of four simple swimmers, each with a different spatial asymmetry, that perform normal surface deformations. We show that the resulting swimming speeds (or rotation rates) scale as the first power of a properly defined 'swimmer Reynolds number', demonstrating thereby a continuous breakdown of the scallop theorem with body inertia.}, }
@article {pmid19426988, year = {2009}, author = {Zhao, CX and Xu, YL and He, CH}, title = {Axial dispersion coefficient in high-speed counter-current chromatography.}, journal = {Journal of chromatography. A}, volume = {1216}, number = {24}, pages = {4841-4846}, doi = {10.1016/j.chroma.2009.04.020}, pmid = {19426988}, issn = {1873-3778}, mesh = {Countercurrent Distribution/*methods ; Organic Chemicals/*chemistry ; *Physical Phenomena ; }, abstract = {Experimental measurements of axial dispersion coefficients in high-speed counter-current chromatography have been carried out in the single-phase and two-phase modes. Axial dispersion coefficients were calculated from the residence time distribution curve (or the elution profile). The experimental data obtained were used to develop a model involving Peclet number Pe, Reynolds number and the ratio of flow velocity u to linear angular velocity u(theta) for predicting the axial dispersion coefficient. Furthermore, the models obtained from the single-phase and two-phase modes were compared, and a counterintuitive phenomenon was found in that the effects of the flow rate and the rotation speed on the axial dispersion coefficients are inconsistent: the axial dispersion coefficient decreases with the rotation speed and increases with the flow rate in the single-phase mode, but increases with rotation speed and decreases slightly with the flow rate in the two-phase mode.}, }
@article {pmid19426338, year = {2009}, author = {Grassi, W and Testi, D}, title = {Electrohydrodynamic convective heat transfer in a square duct.}, journal = {Annals of the New York Academy of Sciences}, volume = {1161}, number = {}, pages = {452-462}, doi = {10.1111/j.1749-6632.2008.04330.x}, pmid = {19426338}, issn = {1749-6632}, abstract = {Laminar to weakly turbulent forced convection in a square duct heated from the bottom is strengthened by ion injection from an array of high-voltage points opposite the heated strip. Both positive and negative ion injection are activated within the working liquid HFE-7100 (C(4)F(9)OCH(3)), with transiting electrical currents on the order of 0.1 mA. Local temperatures on the heated wall are measured by liquid crystal thermography. The tests are conducted in a Reynolds number range from 510 to 12,100. In any case, heat transfer is dramatically augmented, almost independently from the flow rate. The pressure drop increase caused by the electrohydrodynamically induced flow is also measured. A profitable implementation of the technique in the design of heat sinks and heat exchangers is foreseen; possible benefits are pumping power reduction, size reduction, and heat exchange capability augmentation.}, }
@article {pmid19426325, year = {2009}, author = {Asavatesanupap, C and Sadhal, SS}, title = {Fluid dynamical analysis of a particle with large vapor transport in poiseuille flow.}, journal = {Annals of the New York Academy of Sciences}, volume = {1161}, number = {}, pages = {268-276}, doi = {10.1111/j.1749-6632.2008.04079.x}, pmid = {19426325}, issn = {1749-6632}, abstract = {The fluid dynamics of a particle with vapor transport in the presence of gaseous Poiseuille flow is examined in detail for low translational Reynolds number. Poiseuille flow is used to represent an undisturbed steady flow in a cylindrical tube. The particle has a dominant radial field of condensation, evaporation, sublimation, or other form of gasification, with a corresponding radial Reynolds number of order unity. An analysis is carried out by using the perturbation method in which the purely radial flow is used as the leading order, and Poiseuille flow together with particle translation is a perturbation of higher order. Whereas the leading order motion may be described by potential flow, the higher order involves nonlinear interaction of viscous and inertial forces. With the perturbation process bringing about linearization of this interaction, an Oseen-like solution is obtained. However, with the dominant radial flow being strongly diminishing in the far field, a regular perturbation (instead of singular) is sufficient for the perturbed flow description. Presently, the axisymmetric case of a particle along the centerline of the cylinder is considered. The asymmetric case of the off-center particle is also under examination. The results show that the drag components decrease as the radial Reynolds number increases. The influence of the paraboloidal component of Poiseuille flow is a slight increase in the pressure drag as the ratio of the particle size and the tube radius (a/R(0)) increases for moderate values of the radial Reynolds number (Re(R) < 5). For higher values of Re(R), the pressure drag decreases with increasing (a/R(0)). The viscous drag, on the other hand, consistently decreases as the ratio (a/R(0)) increases.}, }
@article {pmid19426324, year = {2009}, author = {Mukundakrishnan, K and Eckmann, DM and Ayyaswamy, PS}, title = {Bubble motion through a generalized power-law fluid flowing in a vertical tube.}, journal = {Annals of the New York Academy of Sciences}, volume = {1161}, number = {}, pages = {256-267}, pmid = {19426324}, issn = {1749-6632}, support = {R01 HL067986/HL/NHLBI NIH HHS/United States ; R01 HL067986-05A2/HL/NHLBI NIH HHS/United States ; R01 HL 67986-01 A1/HL/NHLBI NIH HHS/United States ; }, mesh = {Chemistry Techniques, Analytical/*methods ; Gases/*chemistry ; *Motion ; }, abstract = {Intravascular gas embolism may occur with decompression in space flight, as well as during cardiac and vascular surgery. Intravascular bubbles may be deposited into any end organ, such as the heart or the brain. Surface interactions between the bubble and the endothelial cells lining the vasculature result in serious impairment of blood flow and can lead to heart attack, stroke, or even death. To develop effective therapeutic strategies, there is a need for understanding the dynamics of bubble motion through blood and its interaction with the vessel wall through which it moves. Toward this goal, we numerically investigate the axisymmetric motion of a bubble moving through a vertical circular tube in a shear-thinning generalized power-law fluid, using a front-tracking method. The formulation is characterized by the inlet Reynolds number, capillary number, Weber number, and Froude number. The flow dynamics and the associated wall shear stresses are documented for a combination of two different inlet flow conditions (inlet Reynolds numbers) and three different effective bubble radii (ratio of the undeformed bubble radii to the tube radii). The results of the non-Newtonian model are then compared with that of the model assuming a Newtonian blood viscosity. Specifically, for an almost occluding bubble (effective bubble radius = 0.9), the wall shear stress and the bubble residence time are compared for both Newtonian and non-Newtonian cases. Results show that at low shear rates, for a given pressure gradient the residence time for a non-Newtonian flow is higher than that for a Newtonian flow.}, }
@article {pmid19416879, year = {2009}, author = {Humphries, S}, title = {Filter feeders and plankton increase particle encounter rates through flow regime control.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {106}, number = {19}, pages = {7882-7887}, pmid = {19416879}, issn = {1091-6490}, mesh = {Algorithms ; Animals ; Computer Simulation ; Ecosystem ; Eukaryota/physiology ; Filtration ; Models, Biological ; Models, Statistical ; Models, Theoretical ; Particle Size ; Plankton/*physiology ; Software ; }, abstract = {Collisions between particles or between particles and other objects are fundamental to many processes that we take for granted. They drive the functioning of aquatic ecosystems, the onset of rain and snow precipitation, and the manufacture of pharmaceuticals, powders and crystals. Here, I show that the traditional assumption that viscosity dominates these situations leads to consistent and large-scale underestimation of encounter rates between particles and of deposition rates on surfaces. Numerical simulations reveal that the encounter rate is Reynolds number dependent and that encounter efficiencies are consistent with the sparse experimental data. This extension of aerosol theory has great implications for understanding of selection pressure on the physiology and ecology of organisms, for example filter feeders able to gather food at rates up to 5 times higher than expected. I provide evidence that filter feeders have been strongly selected to take advantage of this flow regime and show that both the predicted peak concentration and the steady-state concentrations of plankton during blooms are approximately 33% of that predicted by the current models of particle encounter. Many ecological and industrial processes may be operating at substantially greater rates than currently assumed.}, }
@article {pmid19406427, year = {2009}, author = {Davis, RH and Zinchenko, AZ}, title = {Motion of deformable drops through granular media and other confined geometries.}, journal = {Journal of colloid and interface science}, volume = {334}, number = {2}, pages = {113-123}, doi = {10.1016/j.jcis.2009.02.062}, pmid = {19406427}, issn = {1095-7103}, mesh = {Computer Simulation ; Elasticity ; Emulsions/*chemistry ; Models, Chemical ; *Motion ; Rheology ; Viscosity ; }, abstract = {This article features recent simulation studies of the flow of emulsions containing deformable drops through pores, constrictions, and granular media. The flow is assumed to be at low Reynolds number, so that viscous forces dominate, and boundary-integral methods are used to determine interfacial velocities and, hence, track the drop motion and shapes. A single drop in a flat channel migrates to the channel centerplane due to deformation-induced drift, which increases its steady-state velocity along the channel. A drop moving towards a smaller interparticle constriction squeezes through the constriction if the capillary number (ratio of viscous deforming forces and interfacial tension forces) is large enough, but it becomes trapped when the capillary number is below a critical value. These concepts then influence the flow of an emulsion through a granular medium, for which the drop phase moves faster than the suspending liquid at large capillary numbers but slower than the suspending liquid at smaller capillary numbers. The permeabilities of the granular medium to both phases increase with increasing capillary number, due to the reduced resistance to squeezing of easily deformed drops, though drop breakup must also be considered at large capillary numbers.}, }
@article {pmid19404437, year = {2008}, author = {Austin, RH}, title = {Nanoscale hydrodynamics in the cell: balancing motorized transport with diffusion.}, journal = {HFSP journal}, volume = {2}, number = {5}, pages = {262-265}, pmid = {19404437}, issn = {1955-2068}, abstract = {One of the central problems in the cell is how to transport molecules around the cell to desired locations. Since low Reynolds number conditions apply and diffusional times are large, without the aid of molecular motors to transport the fluid quickly cells could not survive, yet diffusion is still essential for the ultimate delivery of the goods. This paradox of low Reynolds numberlarge Peclet number has been solved by the algal weed Chara corallina in ingenious ways, as the recent paper by Goldstein, et al. [Proc. Natl. Acad. Sci. 105, 3663-3667 (2008)] discusses at a deep but accessible way using modern hydrodynamic modeling.}, }
@article {pmid19394941, year = {2009}, author = {Wang, CY and Li, CF and Adhikari, S}, title = {Dynamic behaviors of microtubules in cytosol.}, journal = {Journal of biomechanics}, volume = {42}, number = {9}, pages = {1270-1274}, doi = {10.1016/j.jbiomech.2009.03.027}, pmid = {19394941}, issn = {1873-2380}, mesh = {Animals ; Anisotropy ; Biomechanical Phenomena ; Cell Polarity/physiology ; Computer Simulation ; Cytosol/chemistry/*physiology ; Humans ; Microtubules/chemistry/*physiology ; *Models, Biological ; Vibration ; }, abstract = {Highly anisotropic microtubules (MTs) immersed in cytosol are a central part of the cytoskeleton in eukaryotic cells. The dynamic behaviors of an MT-cytosol system are of major interest in biomechanics community. Such a solid-fluid system is characterized by a Reynolds number of the order 10(-3) and a slip ionic layer formed at the MT-cytosol interface. In view of these unique features, an orthotropic shell-Stokes flow model with a slip boundary condition has been developed to explore the distinctive dynamic behaviors of MTs in cytosol. Three types of motions have been identified, i.e., (a) undamped and damped torsional vibration, (b) damped longitudinal vibration, and (c) overdamped bending and radial motions. The exponentially decaying bending motion given by the present model is found to be in qualitative agreement with the existing experimental observation [Felgner et al., 1996. Flexural rigidity of microtubules measured with the use of optical tweezers, Journal of Cell Science 109, 509-516 ].}, }
@article {pmid19394624, year = {2009}, author = {Tabakova, SS and Danov, KD}, title = {Effect of disjoining pressure on the drainage and relaxation dynamics of liquid films with mobile interfaces.}, journal = {Journal of colloid and interface science}, volume = {336}, number = {1}, pages = {273-284}, doi = {10.1016/j.jcis.2009.03.084}, pmid = {19394624}, issn = {1095-7103}, abstract = {This work presents a generalized lubrication approximation of the drainage and relaxation of thin liquid films with tangentially mobile surfaces. The proposed model accounts for the dynamic effects and the role of surface forces of intermolecular origin. The van der Waals and hydrophobic attractive and the electrostatic and steric repulsive components of the disjoining pressure are included in the numerical calculations of the dynamics and relaxation of one-dimensional films. Different regimes of film drainage are discussed: regular and unstable mechanisms of thinning depending on the magnitude of the Reynolds number; pimple formation in the presence of large enough attractive surface forces; and stabilizing effects of the disjoining pressure repulsive components. In the case of relaxation, it is proven that the disturbances in the film thickness: decrease exponentially to the equilibrium state without taking into account the role of the disjoining pressure; increase very fast to the point of film rupture in the presence of attractive surface forces; oscillate with exponentially decreasing amplitudes towards the state of stable equilibrium when the electrostatic and steric repulsive forces are significant.}, }
@article {pmid19392526, year = {2009}, author = {Di Carlo, D and Edd, JF and Humphry, KJ and Stone, HA and Toner, M}, title = {Particle segregation and dynamics in confined flows.}, journal = {Physical review letters}, volume = {102}, number = {9}, pages = {094503}, pmid = {19392526}, issn = {0031-9007}, support = {F32 EB007901/EB/NIBIB NIH HHS/United States ; P41 EB002503/EB/NIBIB NIH HHS/United States ; }, mesh = {*Microfluidics ; *Models, Chemical ; *Nonlinear Dynamics ; Particle Size ; }, abstract = {Nonlinearity in finite-Reynolds-number flow results in particle migration transverse to fluid streamlines, producing the well-known "tubular pinch effect" in cylindrical pipes. Here we investigate these nonlinear effects in highly confined systems where the particle size approaches the channel dimensions. Experimental and numerical results reveal distinctive dynamics, including complex scaling of lift forces with channel and particle geometry. The unique behavior described in this Letter has broad implications for confined particulate flows.}, }
@article {pmid19392360, year = {2009}, author = {Odier, P and Chen, J and Rivera, MK and Ecke, RE}, title = {Fluid mixing in stratified gravity currents: the Prandtl mixing length.}, journal = {Physical review letters}, volume = {102}, number = {13}, pages = {134504}, doi = {10.1103/PhysRevLett.102.134504}, pmid = {19392360}, issn = {0031-9007}, abstract = {Shear-induced vertical mixing in a stratified flow is a key ingredient of thermohaline circulation. We experimentally determine the vertical flux of momentum and density of a forced gravity current using high-resolution velocity and density measurements. A constant eddy-viscosity model provides a poor description of the physics of mixing, but a Prandtl mixing length model relating momentum and density fluxes to mean velocity and density gradients works well. For the average gradient Richardson number Ri(g) approximately 0.08 and a Taylor Reynolds number Re(lambda) approximately 100, the mixing lengths are fairly constant, about the same magnitude, comparable to the turbulent shear length.}, }
@article {pmid19392287, year = {2009}, author = {Taylor, JB and Borchardt, M and Helander, P}, title = {Interacting vortices and spin-up in two-dimensional turbulence.}, journal = {Physical review letters}, volume = {102}, number = {12}, pages = {124505}, doi = {10.1103/PhysRevLett.102.124505}, pmid = {19392287}, issn = {0031-9007}, abstract = {In simulations of decaying two-dimensional turbulence, Clercx and co-workers discovered the unexpected phenomenon of "spin-up." (This is the spontaneous acquisition of angular momentum by a turbulent two-dimensional fluid in a rigid container.) Here we show that this phenomenon can readily be interpreted in terms of statistical models of two-dimensional turbulence. When the net vorticity is zero in a bounded system, there are two distinct types of statistical equilibrium. The first has the expected property that its angular momentum is zero. However, the second type has a nonzero angular momentum even though its circulation vanishes. The relative probability of the two types of equilibrium depends strongly on the shape of the boundary and weakly on the energy. The angular momentum predicted for the second type of equilibrium is in good agreement with that found in simulations at high Reynolds number.}, }
@article {pmid19392203, year = {2009}, author = {Itano, T and Generalis, SC}, title = {Hairpin vortex solution in planar couette flow: a tapestry of knotted vortices.}, journal = {Physical review letters}, volume = {102}, number = {11}, pages = {114501}, doi = {10.1103/PhysRevLett.102.114501}, pmid = {19392203}, issn = {0031-9007}, abstract = {A numerical continuation method has been carried out seeking solutions for two distinct flow configurations, planar Couette flow (PCF) and laterally heated flow in a vertical slot (LHF). We found that the spanwise vortex solution in LHF identifies a new solution in PCF. The vortical structure of our new solution has the shape of a hairpin observed ubiquitously in high-Reynolds-number turbulent flow, and we believe this discovery may provide the paradigm for a hierarchical organization of coherent structures in turbulent shear layers.}, }
@article {pmid19391871, year = {2009}, author = {Pattison, MJ and Premnath, KN and Banerjee, S}, title = {Computation of turbulent flow and secondary motions in a square duct using a forced generalized lattice Boltzmann equation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {79}, number = {2 Pt 2}, pages = {026704}, doi = {10.1103/PhysRevE.79.026704}, pmid = {19391871}, issn = {1539-3755}, abstract = {Turbulent flow in a straight square duct driven by a pressure gradient exhibits remarkable flow structures such as the presence of mean streamwise vorticity or secondary flows. These secondary circulations take the form of two counter-rotating vortices near each corner of the duct. Even though their magnitudes are small compared with primary streamwise motions, they have a significant influence on flow and scalar transport and are challenging to accurately predict using computational approaches. In this paper, we employ a recently developed formulation of the generalized lattice Boltzmann equation (GLBE) with forcing term to perform large eddy simulation of fully developed turbulent flow in a square duct at a shear Reynolds number based on duct width equal to 300. Subgrid scale effects are represented by the Smagorinsky eddy viscosity model, which is modified by the van Driest damping function in the near-wall regions, in this GLBE approach, which is based on multiple relaxation times. It was found that the GLBE is able to correctly reproduce the existence of mean secondary motions and the computed detailed structure of first- and second-order statistics of main and secondary motions are in good agreement with prior direct numerical simulations based on the solution of the Navier-Stokes equations and experimental data.}, }
@article {pmid19391870, year = {2009}, author = {Premnath, KN and Pattison, MJ and Banerjee, S}, title = {Generalized lattice Boltzmann equation with forcing term for computation of wall-bounded turbulent flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {79}, number = {2 Pt 2}, pages = {026703}, doi = {10.1103/PhysRevE.79.026703}, pmid = {19391870}, issn = {1539-3755}, abstract = {In this paper, we present a framework based on the generalized lattice Boltzmann equation (GLBE) using multiple relaxation times with forcing term for eddy capturing simulation of wall-bounded turbulent flows. Due to its flexibility in using disparate relaxation times, the GLBE is well suited to maintaining numerical stability on coarser grids and in obtaining improved solution fidelity of near-wall turbulent fluctuations. The subgrid scale (SGS) turbulence effects are represented by the standard Smagorinsky eddy viscosity model, which is modified by using the van Driest wall-damping function to account for reduction of turbulent length scales near walls. In order to be able to simulate a wider class of problems, we introduce forcing terms, which can represent the effects of general nonuniform forms of forces, in the natural moment space of the GLBE. Expressions for the strain rate tensor used in the SGS model are derived in terms of the nonequilibrium moments of the GLBE to include such forcing terms, which comprise a generalization of those presented in a recent work [Yu, Comput. Fluids 35, 957 (2006)]. Variable resolutions are introduced into this extended GLBE framework through a conservative multiblock approach. The approach, whose optimized implementation is also discussed, is assessed for two canonical flow problems bounded by walls, viz., fully developed turbulent channel flow at a shear or friction Reynolds number (Re) of 183.6 based on the channel half-width and three-dimensional (3D) shear-driven flows in a cubical cavity at a Re of 12 000 based on the side length of the cavity. Comparisons of detailed computed near-wall turbulent flow structure, given in terms of various turbulence statistics, with available data, including those from direct numerical simulations (DNS) and experiments showed good agreement. The GLBE approach also exhibited markedly better stability characteristics and avoided spurious near-wall turbulent fluctuations on coarser grids when compared with the single-relaxation-time (SRT)-based approach. Moreover, its implementation showed excellent parallel scalability on a large parallel cluster with over a thousand processors.}, }
@article {pmid19391795, year = {2009}, author = {Manneville, P}, title = {Spatiotemporal perspective on the decay of turbulence in wall-bounded flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {79}, number = {2 Pt 2}, pages = {025301}, doi = {10.1103/PhysRevE.79.025301}, pmid = {19391795}, issn = {1539-3755}, abstract = {By use of a reduced model focusing on the in-plane dependence of plane Couette flow, it is shown that the turbulent-->laminar relaxation process can be understood as a nucleation problem similar to that occurring at a thermodynamic first-order phase transition. The approach, apt to deal with the large extension of the system considered, challenges the current interpretation in terms of chaotic transients typical of temporal chaos. The study of the distribution of the sizes of laminar domains embedded in turbulent flow proves that an abrupt transition from sustained spatiotemporal chaos to laminar flow can take place at some given value of the Reynolds number Rlow, whether or not the local chaos lifetime, as envisioned within low-dimensional dynamical systems theory, diverges at finite R beyond Rlow.}, }
@article {pmid19370236, year = {2009}, author = {Wu, Z and Willing, B and Bjerketorp, J and Jansson, JK and Hjort, K}, title = {Soft inertial microfluidics for high throughput separation of bacteria from human blood cells.}, journal = {Lab on a chip}, volume = {9}, number = {9}, pages = {1193-1199}, doi = {10.1039/b817611f}, pmid = {19370236}, issn = {1473-0197}, mesh = {Blood Component Removal/*instrumentation ; Blood-Borne Pathogens/*isolation &amp; purification ; Candida albicans/*isolation &amp; purification ; Centrifugation/*instrumentation/methods ; Computer-Aided Design ; Disinfection/*instrumentation/methods ; Equipment Design ; Equipment Failure Analysis ; Hemofiltration/*instrumentation ; Humans ; Micro-Electrical-Mechanical Systems/*instrumentation ; Microfluidic Analytical Techniques/*instrumentation ; Reproducibility of Results ; Sensitivity and Specificity ; }, abstract = {We developed a new approach to separate bacteria from human blood cells based on soft inertial force induced migration with flow defined curved and focused sample flow inside a microfluidic device. This approach relies on a combination of an asymmetrical sheath flow and proper channel geometry to generate a soft inertial force on the sample fluid in the curved and focused sample flow segment to deflect larger particles away while the smaller ones are kept on or near the original flow streamline. The curved and focused sample flow and inertial effect were visualized and verified using a fluorescent dye primed in the device. First the particle behaviour was studied in detail using 9.9 and 1.0 microm particles with a polymer-based prototype. The prototype device is compact with an active size of 3 mm(2). The soft inertial effect and deflection distance were proportional to the fluid Reynolds number (Re) and particle Reynolds number (Re(p)), respectively. We successfully demonstrated separation of bacteria (Escherichia coli) from human red blood cells at high cell concentrations (above 10(8)/mL), using a sample flow rate of up to 18 microL/min. This resulted in at least a 300-fold enrichment of bacteria at a wide range of flow rates with a controlled flow spreading. The separated cells were proven to be viable. Proteins from fractions before and after cell separation were analyzed by gel electrophoresis and staining to verify the removal of red blood cell proteins from the bacterial cell fraction. This novel microfluidic process is robust, reproducible, simple to perform, and has a high throughput compared to other cell sorting systems. Microfluidic systems based on these principles could easily be manufactured for clinical laboratory and biomedical applications.}, }
@article {pmid19368186, year = {2009}, author = {Schaefer, CE and Callaghan, AV and King, JD and McCray, JE}, title = {Dense nonaqueous phase liquid architecture and dissolution in discretely fractured sandstone blocks.}, journal = {Environmental science &amp; technology}, volume = {43}, number = {6}, pages = {1877-1883}, doi = {10.1021/es8011172}, pmid = {19368186}, issn = {0013-936X}, mesh = {Geological Phenomena ; Models, Chemical ; Solubility ; Tetrachloroethylene/*chemistry ; Water Pollutants, Chemical/chemistry ; }, abstract = {Laboratory experiments were performed in discretely fractured sandstone blocks to evaluate residual dense nonaqueous phase liquid (DNAPL) architecture and dissolution. Tetrachloroethene (PCE) DNAPL residual saturations (DNAPL volume/ fracture volume) ranged between 0.18 and 0.52 for the rocks studied. DNAPL-water specific interfacial areas ranged between 19 and 57 cm2/cm3. No measurable correlation was observed between DNAPL-water interfacial area and aperture, aperture ratio, or residual saturation. DNAPL-water interfacial areas were comparable to those reported in sands with grain diameters similar to the rock apertures. However, the DNAPL residual saturation in the fractures were 2-4 times greater than in the sands, suggesting that PCE dissolution rates in rock fractures may be substantially less than in unconsolidated media, as the effective interfacial area per volume of DNAPL in rock fractures was less than in sands. Comparison of dissolution mass transfer coefficients in the bedrock fractures to corresponding mass transfer coefficients measured in sands indicated that dissolution rates in bedrock fractures were substantially less than dissolution rates measured in sands, even after normalization to DNAPL-water interfacial area. The presence of preferential water and DNAPL flow paths within the discrete fractures was shown to have a significant impact on observed DNAPL dissolution rates. DNAPL dissolution was reasonably described by a Reynolds number correlation that incorporated flow characteristics and the DNAPL-water interfacial area.}, }
@article {pmid19357496, year = {2009}, author = {Kunikata, S and Fukuda, M and Yamamoto, K and Yagi, Y and Matsuda, M and Sakai, K}, title = {Technical characterization of dialysis fluid flow of newly developed dialyzers using mass transfer correlation equations.}, journal = {ASAIO journal (American Society for Artificial Internal Organs : 1992)}, volume = {55}, number = {3}, pages = {231-235}, doi = {10.1097/MAT.0b013e318198d870}, pmid = {19357496}, issn = {1538-943X}, mesh = {Equipment Design ; Membranes, Artificial ; Renal Dialysis/*instrumentation/*methods ; }, abstract = {Dialysis fluid flow and mass transfer rate of newly developed dialyzers were evaluated using mass transfer correlation equations of dialysis fluid-side film coefficient. Aqueous creatinine clearance and overall mass transfer coefficient for APS-15S (Asahi Kasei Kuraray) as a conventional dialyzer, and APS-15SA (Asahi Kasei Kuraray), PES-150Salpha (Nipro), FPX140 (Fresenius), and CS-1.6U (Toray) as newly developed dialyzers were obtained at a blood-side flow rate (QB) of 200 ml/min, dialysis fluid-side flow rates (QD) of 200-800 ml/min and a net filtration rate (QF) of 0 ml/min. Mass transfer correlation equations between Sherwood number (Sh) containing dialysis fluid-side mass transfer film coefficient and Reynolds number (Re) were formed for each dialyzer. The exponents of Re were 0.62 for APS-15S whereas approximately 0.5 for the newly developed dialyzers. The dialysis fluid-side mass transfer film coefficients of the newly developed dialyzers were higher than those of the conventional dialyzer. Based on the mass transfer correlation equations, introduction of short taper, full baffle of dialyzer jacket and further wave-shaped hollow fiber improves the dialysis fluid flow of the newly developed dialyzers.}, }
@article {pmid19335410, year = {2009}, author = {Shu, F and Parks, R and Maholtz, J and Ash, S and Antaki, JF}, title = {Multimodal flow visualization and optimization of pneumatic blood pump for sorbent hemodialysis system.}, journal = {Artificial organs}, volume = {33}, number = {4}, pages = {334-345}, doi = {10.1111/j.1525-1594.2009.00724.x}, pmid = {19335410}, issn = {1525-1594}, mesh = {Dye Dilution Technique ; Equipment Design ; Equipment Safety ; *Heart-Assist Devices/adverse effects ; Hemorheology ; Materials Testing ; Renal Dialysis/adverse effects/*instrumentation ; Thrombosis/etiology/prevention &amp; control ; }, abstract = {Renal Solutions Allient Sorbent Hemodialysis System utilizes a two-chambered pneumatic pump (Pulsar Blood Pump, Renal Solutions, Inc., Warrendale, PA, USA) to avoid limitations associated with peristaltic pumping systems. Single-needle access is enabled by counter-pulsing the two pump chambers, thereby obviating compliance chambers or blood reservoirs. Each chamber propels 20 cc per pulse of 3 s (dual access) or 6 s (single access) duration, corresponding to a peak Reynolds number of approximately 8000 (based on inlet velocity and chamber diameter). A multimodal series of flow visualization studies (tracer particle, dye washout, and dye erosion) was conducted on a sequence of pump designs with varying port locations and diaphragms to improve the geometry with respect to risk of thrombogenesis. Experiments were conducted in a simplified flow loop using occluders to simulate flow resistance induced by tubing and dialyzer. Tracer visualization revealed flow patterns and qualitatively indicated turbulence intensity. Dye washout identified dwell volume and areas of flow stagnation for each design. Dye erosion results indicated the effectiveness and homogeneity of surface washing. Compared to a centered inlet which resulted in a fluid jet that produced two counter-rotating vortices, a tangential inlet introduced a single vortex, and kept the flow laminar. It also provided better surface washing on the pump inner surface. However, a tangential outlet did not present as much benefit as expected. On the contrary, it created a sharp defection to the flow when transiting from filling to ejection.}, }
@article {pmid19324562, year = {2009}, author = {Sugiharto, S and Su'ud, Z and Kurniadi, R and Wibisono, W and Abidin, Z}, title = {Radiotracer method for residence time distribution study in multiphase flow system.}, journal = {Applied radiation and isotopes : including data, instrumentation and methods for use in agriculture, industry and medicine}, volume = {67}, number = {7-8}, pages = {1445-1448}, doi = {10.1016/j.apradiso.2009.02.073}, pmid = {19324562}, issn = {1872-9800}, mesh = {Extraction and Processing Industry/*methods ; Iodine Radioisotopes ; *Petroleum ; Radioactive Tracers ; Rheology ; }, abstract = {[(131)I] isotope in different chemical compounds have been injected into 24in hydrocarbon transmission pipeline containing approximately 95% water, 3% crude oil, 2% gas and negligible solid material, respectively. The system is operated at the temperature around 70 degrees C enabling fluids flow is easier in the pipeline. The segment of measurement was chosen far from the junction point of the pipeline, therefore, it was reasonably to assume that the fluids in such multiphase system were separated distinctively. Expandable tubing of injector was used to ensure that the isotopes were injected at the proper place in the sense that [(131)I]Na isotope was injected into water layer and iodo-benzene, ([131])IC(6)H(5,) was injected into crude oil regime. The radiotracer selection was based on the compatibility of radiotracer with each of fluids under investigation. [(131)I]Na was used for measuring flow of water while iodo-benzene, ([131])IC(6)H(5,) was used for measuring flow of crude oil. Two scintillation detectors were used and they are put at the distances 80 and 100m, respectively, from injection point. The residence time distribution data were utilized for calculation water and crude oil flows. Several injections were conducted in the experiments. Although the crude oil density is lighter than the density of water, the result of measurement shows that the water flow is faster than the crude oil flow. As the system is water-dominated, water may act as carrier and the movement of crude oil is slowed due to friction between crude oil with water and crude oil with gas at top layer. Above of all, this result was able to give answer on the question why crude oil always arrives behind water as it is checked at gathering station. In addition, the flow patterns of the water in the pipeline calculated by Reynolds number and predicted by simple tank-in-series model is turbulence in character.}, }
@article {pmid19299786, year = {2009}, author = {McPherson, D and Adekanye, O and Wilkes, AR and Hall, JE}, title = {Fluid flow through intravenous cannulae in a clinical model.}, journal = {Anesthesia and analgesia}, volume = {108}, number = {4}, pages = {1198-1202}, doi = {10.1213/ane.0b013e3181966451}, pmid = {19299786}, issn = {1526-7598}, mesh = {Catheterization/*instrumentation/standards ; Equipment Design ; Hemorheology ; Infusions, Intravenous/*instrumentation/standards ; Models, Cardiovascular ; Pressure ; Time Factors ; }, abstract = {BACKGROUND: Predicting flow through an IV cannula is useful to clinicians if changes in flow are required and to guide selection of cannula. We sought the usefulness of manufacturers' quoted flows in predicting actual flow and to characterize that flow.<br><br>METHODS: We built a vein model and inserted cannulae between 14 and 20-gauge. In the first experiment, we compared the manufacturer's quoted flows using deionized water, Hartmann's solution and Gelofusine. In the second experiment, we varied the pressure feeding the cannula and measured the resulting flow.<br><br>RESULTS: Flow through a cannula is not a simple ratio of the manufacturers' quoted flow rate, even controlling for fluid type and feeding pressure. Flow is neither fully laminar, nor fully turbulent in the range of rates we have measured and in the International Organization for Standardization test. The Reynolds number is often below 2000.<br><br>CONCLUSIONS: Flow through cannulae is not laminar at the upper range of clinically used flows, therefore Poiseuille's law is not useful in predicting flow and the effect of changing radius is less than commonly believed. The quoted maximum flows are also not useful. There are many conditions for laminar flow apart from Reynolds number. Further work would determine useful predictors of flow.}, }
@article {pmid19294305, year = {2009}, author = {Park, JS and Song, SH and Jung, HI}, title = {Continuous focusing of microparticles using inertial lift force and vorticity via multi-orifice microfluidic channels.}, journal = {Lab on a chip}, volume = {9}, number = {7}, pages = {939-948}, doi = {10.1039/b813952k}, pmid = {19294305}, issn = {1473-0197}, mesh = {Microfluidic Analytical Techniques/*instrumentation/methods ; Microfluidics/*instrumentation/methods ; Particle Size ; }, abstract = {We developed a new microfluidic method for focusing microparticles through the combined use of inertial lift forces and turbulent secondary flows generated in a topographically patterned microchannel. The mechanism of particle focusing is based on the hydrodynamic inertial forces exerted on particles migrating along a non-circular microchannel, i.e.tubular pinch effect and wall effect, which induce particle movement away from walls and along a specific lateral position in the microchannel. With the extraordinary geometry of multi-orifice microchannel, an ordered and focused particle distribution was achieved at central or side regions according to a particle Reynolds number (Re(p)) range. The focusing of particles was controlled by the particle Reynolds number, microchannel length, and volume fraction of particles in suspension. This method will be beneficial in particle focusing processes in a microfluidic device since it offers continuous, high-throughput performance and simple operation.}, }
@article {pmid19263268, year = {2009}, author = {Hikita, H and Sato, A and Nozato, T and Kawashima, T and Takahashi, Y and Kuwahara, T and Takahashi, A}, title = {Low coronary flow velocity and shear stress predict restenosis after sirolimus-eluting stent implantation.}, journal = {Scandinavian cardiovascular journal : SCJ}, volume = {43}, number = {5}, pages = {298-303}, doi = {10.1080/14017430902785493}, pmid = {19263268}, issn = {1651-2006}, mesh = {Aged ; Angioplasty, Balloon, Coronary/*adverse effects/*instrumentation ; Blood Flow Velocity ; Cardiovascular Agents/*administration &amp; dosage ; Chi-Square Distribution ; Coronary Angiography ; Coronary Artery Disease/diagnostic imaging/physiopathology/*therapy ; *Coronary Circulation ; Coronary Restenosis/diagnostic imaging/*etiology/physiopathology ; *Drug-Eluting Stents ; Female ; Humans ; Japan ; Male ; Middle Aged ; Prosthesis Design ; Regression Analysis ; Risk Assessment ; Risk Factors ; Sirolimus/*administration &amp; dosage ; Stress, Mechanical ; Time Factors ; Treatment Outcome ; }, abstract = {OBJECTIVES: This study sought to assess predictive values of coronary flow velocity and an index of shear stress throughout the vessel for angiographic restenosis after sirolimus-eluting stent implantation.<br><br>DESIGN: The study patients underwent successful implantation of a sirolimus-eluting stent for de novo lesions located in native coronary vessels and underwent follow-up angiography 6-9 months later. The TIMI frame count method and quantitative digital angiographic analysis were performed based on the post-stenting angiogram. Coronary flow velocity and Reynolds number, an index of shear stress, were measured.<br><br>RESULTS: Post-stenting digital angiograms from 267 patients were analyzed. We divided the study patients into two groups: a Restenosis group with 21 patients and a Non-Restenosis group with 246 patients. The Restenosis group indicated significantly lower coronary flow velocity (137.7+/-35.6 mm/sec versus 241.1+/-72.9 mm/sec, p = 0.0001) and lower Reynolds number (107.0+/-35.8 versus 199.2+/-67.1, p = 0.0001) than did the Non-Restenosis group.<br><br>CONCLUSIONS: Lowered coronary flow velocity and shear stress after sirolimus-eluting stenting may predict the risk of restenosis.}, }
@article {pmid19258689, year = {2009}, author = {Blake, RW}, title = {Biological implications of the hydrodynamics of swimming at or near the surface and in shallow water.}, journal = {Bioinspiration &amp; biomimetics}, volume = {4}, number = {1}, pages = {015004}, doi = {10.1088/1748-3182/4/1/015004}, pmid = {19258689}, issn = {1748-3190}, mesh = {Animals ; Computer Simulation ; Ducks/*physiology ; Energy Transfer/*physiology ; *Models, Biological ; Rheology/*methods ; Species Specificity ; Swimming/*physiology ; *Water ; }, abstract = {The origins and effects of wave drag at and near the surface and in shallow water are discussed in terms of the dispersive waves generated by streamlined technical bodies of revolution and by semi-aquatic and aquatic animals with a view to bearing on issues regarding the design and function of autonomous surface and underwater vehicles. A simple two-dimensional model based on energy flux, allowing assessment of drag and its associated wave amplitude, is applied to surface swimming in Lesser Scaup ducks and is in good agreement with measured values. It is argued that hydrodynamic limitations to swimming at speeds associated with the critical Froude number (approximately 0.5) and hull speed do not necessarily set biological limitations as most behaviours occur well below the hull speed. From a comparative standpoint, the need for studies on the hull displacement of different forms is emphasized. For forms in surface proximity, drag is a function of both Froude and Reynolds numbers. Whilst the depth dependence of wave drag is not particularly sensitive to Reynolds number, its magnitude is, with smaller and slower forms subject to relatively less drag augmentation than larger, faster forms that generate additional resistance due to ventilation and spray. A quasi-steady approach to the hydrodynamics of swimming in shallow water identifies substantial drag increases relative to the deeply submerged case at Froude numbers of about 0.9 that could limit the performance of semi-aquatic and aquatic animals and autonomous vehicles. A comparative assessment of fast-starting trout and upside down catfish shows that the energy losses of fast-starting fish are likely to be less for fish in surface proximity in deep water than for those in shallow water. Further work on unsteady swimming in both circumstances is encouraged. Finally, perspectives are offered as to how autonomous surface and underwater vehicles in surface proximity and shallow water could function to avoid prohibitive hydrodynamic resistance, thereby increasing their operational life.}, }
@article {pmid19258688, year = {2009}, author = {Liu, H and Aono, H}, title = {Size effects on insect hovering aerodynamics: an integrated computational study.}, journal = {Bioinspiration &amp; biomimetics}, volume = {4}, number = {1}, pages = {015002}, doi = {10.1088/1748-3182/4/1/015002}, pmid = {19258688}, issn = {1748-3190}, mesh = {Animals ; *Computer Simulation ; Energy Transfer/*physiology ; Flight, Animal/*physiology ; Insecta/*physiology ; *Models, Biological ; Systems Integration ; Wings, Animal/*physiology ; }, abstract = {Hovering is a miracle of insects that is observed for all sizes of flying insects. Sizing effect in insect hovering on flapping-wing aerodynamics is of interest to both the micro-air-vehicle (MAV) community and also of importance to comparative morphologists. In this study, we present an integrated computational study of such size effects on insect hovering aerodynamics, which is performed using a biology-inspired dynamic flight simulator that integrates the modelling of realistic wing-body morphology, the modelling of flapping-wing and body kinematics and an in-house Navier-Stokes solver. Results of four typical insect hovering flights including a hawkmoth, a honeybee, a fruit fly and a thrips, over a wide range of Reynolds numbers from O(10(4)) to O(10(1)) are presented, which demonstrate the feasibility of the present integrated computational methods in quantitatively modelling and evaluating the unsteady aerodynamics in insect flapping flight. Our results based on realistically modelling of insect hovering therefore offer an integrated understanding of the near-field vortex dynamics, the far-field wake and downwash structures, and their correlation with the force production in terms of sizing and Reynolds number as well as wing kinematics. Our results not only give an integrated interpretation on the similarity and discrepancy of the near- and far-field vortex structures in insect hovering but also demonstrate that our methods can be an effective tool in the MAVs design.}, }
@article {pmid19257437, year = {2009}, author = {Loutherback, K and Puchalla, J and Austin, RH and Sturm, JC}, title = {Deterministic microfluidic ratchet.}, journal = {Physical review letters}, volume = {102}, number = {4}, pages = {045301}, doi = {10.1103/PhysRevLett.102.045301}, pmid = {19257437}, issn = {0031-9007}, support = {HG01506/HG/NHGRI NIH HHS/United States ; }, mesh = {Microfluidic Analytical Techniques/instrumentation/*methods ; Particle Size ; Polystyrenes/chemistry ; }, abstract = {We present a deterministic, nonthermal ratchet where the trajectory of particles in a certain size range is not reversible when the sign of the pressure gradient is reversed at a low Reynolds number. This effect is produced by employing triangular rather than the conventional circular posts in an array that selectively displaces particles transported through the array. The ratchet irreversibly moves particles of a certain size range in a direction orthogonal to an oscillating flow, with no net displacement of the fluid itself. The underlying mechanism of this ratchet is shown to be connected to irreversible particle-post interactions and the asymmetric fluid velocity distribution through the gap between the triangular posts. Diffusion plays no role in this ratchet, and hence the device parameters presented here can be scaled up to high rates of flow, of clear importance in separation technologies.}, }
@article {pmid19256864, year = {2008}, author = {Yang, Y and Elgeti, J and Gompper, G}, title = {Cooperation of sperm in two dimensions: synchronization, attraction, and aggregation through hydrodynamic interactions.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {6 Pt 1}, pages = {061903}, doi = {10.1103/PhysRevE.78.061903}, pmid = {19256864}, issn = {1539-3755}, mesh = {Animals ; Biophysical Phenomena ; Cell Aggregation/physiology ; Energy Metabolism ; Humans ; Male ; *Models, Biological ; Sperm Motility/*physiology ; Spermatozoa/cytology/*physiology ; }, abstract = {Sperm swimming at low Reynolds number have strong hydrodynamic interactions when their concentration is high in vivo or near substrates in vitro. The beating tails not only propel the sperm through a fluid, but also create flow fields through which sperm interact with each other. We study the hydrodynamic interaction and cooperation of sperm embedded in a two-dimensional fluid by using a particle-based mesoscopic simulation method, multiparticle collision dynamics. We analyze the sperm behavior by investigating the relationship between the beating-phase difference and the relative sperm position, as well as the energy consumption. Two effects of hydrodynamic interaction are found, synchronization and attraction. With these hydrodynamic effects, a multisperm system shows swarm behavior with a power-law dependence of the average cluster size on the width of the distribution of beating frequencies.}, }
@article {pmid19224024, year = {2009}, author = {Cieslicki, K and Piechna, A}, title = {Investigations of mixing process in microfluidic manifold designed according to biomimetic rule.}, journal = {Lab on a chip}, volume = {9}, number = {5}, pages = {726-732}, doi = {10.1039/b811005k}, pmid = {19224024}, issn = {1473-0197}, mesh = {Algorithms ; Biomimetics/*instrumentation ; Computer Simulation ; Diffusion ; Equipment Design ; Microfluidics/*instrumentation ; Models, Statistical ; Shear Strength ; }, abstract = {The paper is focused on the mechanism of mixing process in a manifold which mimics the geometrical properties of vascular systems. The relationship governing the optimum ratio between the diameters of the parent and daughter branches in vascular systems was first discovered by Murray using the principle of minimum work. However, in contrast to biological vascular networks, which are composed of circular pipes, microfluidic manifolds are fabricated using a range of processes (photolithography, wet or dry etching, surface micromachining), which result in channels of rectangular or trapezoidal sections and constant depth throughout the device. The paper focuses on constant-depth rectangular channels often employed in lab-on-a-chip systems and provides comprehensive numerical studies of mixing in such geometry. It also presents simplified analytical estimation on how the coefficient of mixing depends on the number of generations and Reynolds number. The main goal of the paper is to describe the concept of a mixer which provides almost perfect mixing at the outlet regardless of the value of Re and for a minimal number of manifold's generations.}, }
@article {pmid19211800, year = {2009}, author = {Roper, M and Brenner, MP}, title = {A nonperturbative approximation for the moderate Reynolds number Navier-Stokes equations.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {106}, number = {9}, pages = {2977-2982}, pmid = {19211800}, issn = {1091-6490}, mesh = {Nonlinear Dynamics ; *Physics ; Viscosity ; }, abstract = {The nonlinearity of the Navier-Stokes equations makes predicting the flow of fluid around rapidly moving small bodies highly resistant to all approaches save careful experiments or brute force computation. Here, we show how a linearization of the Navier-Stokes equations captures the drag-determining features of the flow and allows simplified or analytical computation of the drag on bodies up to Reynolds number of order 100. We illustrate the utility of this linearization in 2 practical problems that normally can only be tackled with sophisticated numerical methods: understanding flow separation in the flow around a bluff body and finding drag-minimizing shapes.}, }
@article {pmid19211110, year = {2009}, author = {Bhalla, G and Deen, WM}, title = {Effects of charge on osmotic reflection coefficients of macromolecules in porous membranes.}, journal = {Journal of colloid and interface science}, volume = {333}, number = {1}, pages = {363-372}, doi = {10.1016/j.jcis.2009.01.019}, pmid = {19211110}, issn = {1095-7103}, abstract = {A computational model was developed to predict the effects of solute and pore charge on the osmotic reflection coefficients (sigma(o)) of spherical macromolecules in cylindrical pores. Results were obtained for particles and pores of like charge and fixed surface charge densities, using a theory that combined low Reynolds number hydrodynamics with a continuum, point-charge description of the electrical double layers. In this formulation steric and/or electrostatic exclusion of macromolecules from the vicinity of the pore wall creates radial variations in osmotic pressure. These, in turn, lead to the axial pressure gradient that drives the osmotic flow. Due to the stronger exclusion that results from repulsive electrostatic interactions, sigma(o) with charge effects always exceeded that for an uncharged system with the same solute and pore size. The effects of charge stemmed almost entirely from particle positions within a pore being energetically unfavorable. It was found that the required potential energy could be computed with sufficient accuracy using the linearized Poisson-Boltzmann equation, high charge densities notwithstanding. In principle, another factor that might influence sigma(o) in charged pores is the electrical body force due to the streaming potential. However, the streaming potential was shown to have little effect on sigma(o), even when it markedly reduced the apparent hydraulic permeability.}, }
@article {pmid19191328, year = {2009}, author = {Böl, M and Möhle, RB and Haesner, M and Neu, TR and Horn, H and Krull, R}, title = {3D finite element model of biofilm detachment using real biofilm structures from CLSM data.}, journal = {Biotechnology and bioengineering}, volume = {103}, number = {1}, pages = {177-186}, doi = {10.1002/bit.22235}, pmid = {19191328}, issn = {1097-0290}, mesh = {Biofilms/*growth &amp; development ; Bioreactors ; *Computer Simulation ; *Microscopy, Confocal ; Shear Strength ; Stress, Mechanical ; *Water Microbiology ; }, abstract = {In this work, a three-dimensional model of fluid-structure interactions (FSI) in biofilm systems is developed in order to simulate biofilm detachment as a result of mechanical processes. Therein, fluid flow past the biofilm surface results in a mechanical load on the structure which in turn causes internal stresses in the biofilm matrix. When the strength of the matrix is exceeded parts of the structure are detached. The model is used to investigate the influence of several parameters related to the mechanical strength of the biofilm matrix, Young's modulus, Reynolds number, and biofilm structure on biofilm detachment. Variations in biofilm strength and flow conditions significantly influence the simulation outcome. With respect to structural properties the model is widely independent from a change of Young's modulus. A further result of this work indicates that the change of biofilm structure due to growth or other processes will significantly change the stress distribution in the biofilm and thereby the detachment rate. An increase of the mechanical load by increasing fluid flow results in a flat surface of the remaining biofilm structure. It is concluded that the change of structure during biofilm development is the key determinant in terms of the detachment behavior.}, }
@article {pmid19181905, year = {2009}, author = {Borazjani, I and Sotiropoulos, F}, title = {Numerical investigation of the hydrodynamics of anguilliform swimming in the transitional and inertial flow regimes.}, journal = {The Journal of experimental biology}, volume = {212}, number = {Pt 4}, pages = {576-592}, doi = {10.1242/jeb.025007}, pmid = {19181905}, issn = {0022-0949}, mesh = {Animals ; Biomechanical Phenomena ; Eels/*physiology ; Models, Biological ; Rheology ; *Swimming ; Tail/physiology ; }, abstract = {We employ numerical simulation to investigate the hydrodynamic performance of anguilliform locomotion and compare it with that of carangiform swimming as the Reynolds number (Re) and the tail-beat frequency (Strouhal number, St) are systematically varied. The virtual swimmer is a 3-D lamprey-like flexible body undulating with prescribed experimental kinematics of anguilliform type. Simulations are carried out for three Reynolds numbers spanning the transitional and inertial flow regimes, Re=300, 4000 (viscous flow), and infinity (inviscid flow). The net mean force is found to be mainly dependent on the tail-beat frequency rather than the tail-beat amplitude. The critical Strouhal number, St, at which the net mean force becomes zero (constant-speed self-propulsion) is, similar to carangiform swimming, a decreasing function of Re and approaches the range of St numbers at which most anguilliform swimmers swim in nature (St approximately 0.45) only as Re increases. The anguilliform swimmer's force time series is characterized by significantly smaller fluctuations above the mean than that for carangiform swimmers. In stark contrast with carangiform swimmers, the propulsive efficiency of anguilliform swimmers at St is not an increasing function of Re but instead is maximized in the transitional regime. Furthermore, the power required for anguilliform swimming is less than that for the carangiform swimmer at the same Re. We also show that the form drag decreases while viscous drag increases as St increases. Finally, our simulations reinforce our previous finding for carangiform swimmers that the 3-D wake structure depends primarily on the Strouhal number.}, }
@article {pmid19177174, year = {2008}, author = {Ma, Y and Sun, CP and Fields, M and Li, Y and Haake, DA and Churchill, BM and Ho, CM}, title = {An unsteady microfluidic T-form mixer perturbed by hydrodynamic pressure.}, journal = {Journal of micromechanics and microengineering : structures, devices, and systems}, volume = {18}, number = {}, pages = {45015}, pmid = {19177174}, issn = {0960-1317}, support = {U01 AI075565/AI/NIAID NIH HHS/United States ; R33 DK070328/DK/NIDDK NIH HHS/United States ; R01 EB000127/EB/NIBIB NIH HHS/United States ; U01 AI075565-01/AI/NIAID NIH HHS/United States ; U54 AI065359/AI/NIAID NIH HHS/United States ; R33 DK070328-02/DK/NIDDK NIH HHS/United States ; U54 AI065359-030019/AI/NIAID NIH HHS/United States ; }, abstract = {An unsteady microfluidic T-form mixer driven by pressure disturbances was designed and investigated. The performance of the mixer was examined both through numerical simulation and experimentation. Linear Stokes equations were used for these low Reynolds number flows. Unsteady mixing in a micro-channel of two aqueous solutions differing in concentrations of chemical species was described using a convection-dominated diffusion equation. The task was greatly simplified by employing linear superimposition of a velocity field for solving a scalar species concentration equation. Low-order-based numerical codes were found not to be suitable for simulation of a convection-dominated mixing process due to erroneous computational dissipation. The convection-dominated diffusion problem was addressed by designing a numerical algorithm with high numerical accuracy and computational-cost effectiveness. This numerical scheme was validated by examining a test case prior to being applied to the mixing simulation. Parametric analysis was performed using this newly developed numerical algorithm to determine the best mixing conditions. Numerical simulation identified the best mixing condition to have a Strouhal number (St)of 0.42. For a T-junction mixer (with channel width = 196 μm), about 75% mixing can be finished within a mixing distance of less than 3 mm (i.e. 15 channel width) at St = 0.42 for flow with a Reynolds number less than 0.24. Numerical results were validated experimentally by mixing two aqueous solutions containing yellow and blue dyes. Visualization of the flow field under the microscope revealed a high level of agreement between numerical simulation and experimental results.}, }
@article {pmid19173426, year = {2009}, author = {Kaburagi, T and Tanabe, Y}, title = {Low-dimensional models of the glottal flow incorporating viscous-inviscid interaction.}, journal = {The Journal of the Acoustical Society of America}, volume = {125}, number = {1}, pages = {391-404}, doi = {10.1121/1.3021436}, pmid = {19173426}, issn = {1520-8524}, mesh = {Glottis/*physiology ; Humans ; Models, Biological ; Phonation/*physiology ; Vocal Cords/physiology ; }, abstract = {The behavior of glottal flow can, to a large extent, be characterized by development and separation of the boundary layer. The point of flow separation is known to vary during the phonatory cycle due to change in channel configuration. To take the movable nature of the separation point into account, the boundary-layer equation is solved numerically, and the values of the characteristic quantities are determined as well as the point of separation. Development of the boundary layer in general reduces the effective size of the channel, and, therefore, increases the core flow velocity, which, in turn provides the boundary condition of the boundary-layer equation. The interaction between the viscous (boundary layer) and inviscid (core flow) parts of the glottal flow is, therefore, strongly indicated. To apply this viscous-inviscid interaction, the expression of the core flow is derived for a two-dimensional flow field, and is solved jointly with the boundary-layer equation. Numerical results are shown to examine the effect of the Reynolds number and glottal configuration, with special emphasis on the comparison of flow models developed for one- and two-dimensional flow fields. Numerical results are also quantitatively compared with data obtained from flow measurement experiments.}, }
@article {pmid19169723, year = {2009}, author = {Alouges, F and DeSimone, A and Lefebvre, A}, title = {Optimal strokes for axisymmetric microswimmers.}, journal = {The European physical journal. E, Soft matter}, volume = {28}, number = {3}, pages = {279-284}, pmid = {19169723}, issn = {1292-895X}, mesh = {*Bacterial Physiological Phenomena ; Biophysics/methods ; Mathematics ; Models, Biological ; Models, Statistical ; Models, Theoretical ; Motion ; *Movement ; Physics/methods ; }, abstract = {We present a theory for low-Reynolds-number axisymmetric swimmers and a general strategy for the computation of strokes of maximal efficiency. An explicit equation characterizing optimal strokes is derived, and numerical strategies to obtain solutions are discussed. The merits of this approach are demonstrated by applying it to two concrete examples: the three linked spheres of Najafi and Golestanian and the pushmepullyou of Avron, Kenneth, and Oakmin.}, }
@article {pmid19148753, year = {2009}, author = {Cookson, AN and Doorly, DJ and Sherwin, SJ}, title = {Mixing through stirring of steady flow in small amplitude helical tubes.}, journal = {Annals of biomedical engineering}, volume = {37}, number = {4}, pages = {710-721}, doi = {10.1007/s10439-009-9636-y}, pmid = {19148753}, issn = {1573-9686}, mesh = {Animals ; Computer Simulation ; Entropy ; *Models, Biological ; *Models, Theoretical ; Particle Size ; *Physical Phenomena ; Rotation ; }, abstract = {In this paper we numerically simulate flow in a helical tube for physiological conditions using a co-ordinate mapping of the Navier-Stokes equations. Helical geometries have been proposed for use as bypass grafts, arterial stents and as an idealized model for the out-of-plane curvature of arteries. Small amplitude helical tubes are also currently being investigated for possible application as A-V shunts, where preliminary in vivo tests suggest a possibly lower risk of thrombotic occlusion. In-plane mixing induced by the geometry is hypothesized to be an important mechanism. In this work, we focus mainly on a Reynolds number of 250 and investigate both the flow structure and the in-plane mixing in helical geometries with fixed pitch of 6 tube diameters (D), and centerline helical radius ranging from 0.1 D to 0.5 D. High-order particle tracking, and an information entropy measure is used to analyze the in-plane mixing. A combination of translational and rotational reference frames are shown to explain the apparent discrepancy between flow field and particle trajectories, whereby particle paths display a pattern characteristic of a double vortex, though the flow field reveals only a single dominant vortex. A radius of 0.25 D is found to provide the best trade-off between mixing and pressure loss, with little increase in mixing above R=0.25 D, whereas pressure continues to increase linearly.}, }
@article {pmid19135462, year = {2009}, author = {Pindera, MZ and Ding, H and Athavale, MM and Chen, Z}, title = {Accuracy of 1D microvascular flow models in the limit of low Reynolds numbers.}, journal = {Microvascular research}, volume = {77}, number = {3}, pages = {273-280}, doi = {10.1016/j.mvr.2008.11.006}, pmid = {19135462}, issn = {1095-9319}, support = {5R44CA097827-03/CA/NCI NIH HHS/United States ; }, mesh = {Blood Flow Velocity/physiology ; Capillaries/anatomy &amp; histology/*physiology ; Computer Simulation ; *Models, Cardiovascular ; Reproducibility of Results ; }, abstract = {We describe results of numerical simulations of steady flows in tubes with branch bifurcations using fully 3D and reduced 1D geometries. The intent is to delineate the range of validity of reduced models used for simulations of flows in microcapillary networks, as a function of the flow Reynolds number Re. Results from model problems indicate that for Re less than 1 and possibly as high as 10, vasculatures may be represented by strictly 1D Poiseuille flow geometries with flow variation in the axial dimensions only. In that range flow rate predictions in the different branches generated by 1D and 3D models differ by a constant factor, independent of Re. When the cross-sectional areas of the branches are constant these differences are generally small and appear to stem from an uncertainty of how the individual branch lengths are defined. This uncertainty can be accounted for by a simple geometrical correction. For non-constant cross-sections the differences can be much more significant. If additional corrections for the presence of branch junctions and flow area variations are not taken into account in 1D models of complex vasculatures, the resultant flow predictions should be interpreted with caution.}, }
@article {pmid19134043, year = {2009}, author = {Boutsioukis, C and Lambrianidis, T and Kastrinakis, E}, title = {Irrigant flow within a prepared root canal using various flow rates: a Computational Fluid Dynamics study.}, journal = {International endodontic journal}, volume = {42}, number = {2}, pages = {144-155}, doi = {10.1111/j.1365-2591.2008.01503.x}, pmid = {19134043}, issn = {1365-2591}, mesh = {*Computer Simulation ; Dental Pulp Cavity/*pathology ; Equipment Design ; Humans ; Image Processing, Computer-Assisted ; *Models, Chemical ; Needles ; Rheology ; Root Canal Irrigants/*chemistry ; Root Canal Preparation/instrumentation ; Software ; Surface Properties ; Syringes ; Therapeutic Irrigation/instrumentation ; Tooth Apex/pathology ; }, abstract = {AIM: To study using computer simulation the effect of irrigant flow rate on the flow pattern within a prepared root canal, during final irrigation with a syringe and needle.<br><br>METHODOLOGY: Geometrical characteristics of a side-vented endodontic needle and clinically realistic flow rate values were obtained from previous and preliminary studies. A Computational Fluid Dynamics (CFD) model was created using FLUENT 6.2 software. Calculations were carried out for five selected flow rates (0.02-0.79 mL sec(-1)) and velocity and turbulence quantities along the domain were evaluated.<br><br>RESULTS: Irrigant replacement was limited to 1-1.5 mm apical to the needle tip for all flow rates tested. Low-Reynolds number turbulent flow was detected near the needle outlet. Irrigant flow rate affected significantly the flow pattern within the root canal.<br><br>CONCLUSIONS: Irrigation needles should be placed to within 1 mm from working length to ensure fluid exchange. Turbulent flow of irrigant leads to more efficient irrigant replacement. CFD represents a powerful tool for the study of irrigation.}, }
@article {pmid19117273, year = {2009}, author = {Moore, SK and Kleis, SJ and Geng, YJ}, title = {Assessment of fetal canine cardiac myocyte survival in a dual-side flow bioreactor with modeled hypoxia/reperfusion injury.}, journal = {Biotechnology and bioengineering}, volume = {103}, number = {1}, pages = {199-206}, doi = {10.1002/bit.22216}, pmid = {19117273}, issn = {1097-0290}, mesh = {Animals ; Cell Culture Techniques ; *Cell Survival ; Cells, Cultured ; Dogs ; *Hypoxia ; Myocytes, Cardiac/*physiology ; *Reperfusion Injury ; }, abstract = {The present study introduces a new experimental model of hypoxia/reperfusion injury using a newly developed bioreactor system. The injury is introduced and kept localized via fluid dynamic manipulation. Using low Reynolds number fluid flow, regions of the culture can be injured while maintaining physiological conditions in the remaining culture. This approach enables both normal and injured cells within the same monolayer to be investigated side-by-side. The current study evaluated the ability of the model to induce localized reperfusion injury in a monolayer of fetal canine cardiomyocytes (FCCs). Significant apoptosis was found in the hypoxia/reperfusion-injured but not normal-flow regions of the myocyte cultures. The model holds the potential to help elucidate the fundamental mechanisms of hypoxic/reperfusion insults in myocardium.}, }
@article {pmid22400004, year = {2009}, author = {Lee, HW and Azid, IH}, title = {Neuro-genetic optimization of the diffuser elements for applications in a valveless diaphragm micropumps system.}, journal = {Sensors (Basel, Switzerland)}, volume = {9}, number = {9}, pages = {7481-7497}, doi = {10.3390/s90907481}, pmid = {22400004}, issn = {1424-8220}, abstract = {In this study, a hybridized neuro-genetic optimization methodology realized by embedding numerical simulations trained artificial neural networks (ANN) into a genetic algorithm (GA) is used to optimize the flow rectification efficiency of the diffuser element for a valveless diaphragm micropump application. A higher efficiency ratio of the diffuser element consequently yields a higher flow rate for the micropump. For that purpose, optimization of the diffuser element is essential to determine the maximum pumping rate that the micropump is able to generate. Numerical simulations are initially carried out using CoventorWare® to analyze the effects of varying parameters such as diffuser angle, Reynolds number and aspect ratio on the volumetric flow rate of the micropump. A limited range of simulation results will then be used to train the neural network via back-propagation algorithm and optimization process commence subsequently by embedding the trained ANN results as a fitness function into GA. The objective of the optimization is to maximize the efficiency ratio of the diffuser element for the range of parameters investigated. The optimized efficiency ratio obtained from the neuro-genetic optimization is 1.38, which is higher than any of the maximum efficiency ratio attained from the overall parametric studies, establishing the superiority of the optimization method.}, }
@article {pmid22346704, year = {2009}, author = {Wang, CT and Hu, YC and Hu, TY}, title = {Biophysical micromixer.}, journal = {Sensors (Basel, Switzerland)}, volume = {9}, number = {7}, pages = {5379-5389}, pmid = {22346704}, issn = {1424-8220}, abstract = {In this study a biophysical passive micromixer with channel anamorphosis in a space of 370 μm, which is shorter than traditional passive micromixers, could be created by mimicing features of vascular flow networks and executed with Reynolds numbers ranging from 1 to 90. Split and recombination (SAR) was the main mixing method for enhancing the convection effect and promoting the mixing performance in the biophysical channel. The 2D numerical results reveal that good mixing efficiency of the mixer was possible, with ε(mixing) = 0.876 at Reynolds number ration Re(r) = 0.85. Generally speaking, increasing the Reynolds number will enhance the mixing. In addition, the sidewall effect will influence the mixing performance and an optimal mixing performance with ε(mixing) = 0.803 will occur at an aspect ratio of AR = 2. These findings will be useful for enhancing mixing performance for passive micromixers.}, }
@article {pmid19113623, year = {2008}, author = {Boeck, T and Krasnov, D and Thess, A and Zikanov, O}, title = {Large-scale intermittency of liquid-metal channel flow in a magnetic field.}, journal = {Physical review letters}, volume = {101}, number = {24}, pages = {244501}, doi = {10.1103/PhysRevLett.101.244501}, pmid = {19113623}, issn = {0031-9007}, abstract = {We predict a novel flow regime in liquid metals under the influence of a magnetic field. It is characterized by long periods of nearly steady, two-dimensional flow interrupted by violent three-dimensional bursts. Our prediction has been obtained from direct numerical simulations in a channel geometry at low magnetic Reynolds number and translates into physical parameters which are amenable to experimental verification under laboratory conditions. The new regime occurs in a wide range of parameters and may have implications for metallurgical applications.}, }
@article {pmid19113216, year = {2008}, author = {Mayo, JR and Kerstein, AR}, title = {Fronts in randomly advected and heterogeneous media and nonuniversality of Burgers turbulence: theory and numerics.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {5 Pt 2}, pages = {056307}, doi = {10.1103/PhysRevE.78.056307}, pmid = {19113216}, issn = {1539-3755}, abstract = {A recently established mathematical equivalence-between weakly perturbed Huygens fronts (e.g., flames in weak turbulence or geometrical-optics wave fronts in slightly nonuniform media) and the inviscid limit of white-noise-driven Burgers turbulence-motivates theoretical and numerical estimates of Burgers-turbulence properties for specific types of white-in-time forcing. Existing mathematical relations between Burgers turbulence and the statistical mechanics of directed polymers, allowing use of the replica method, are exploited to obtain systematic upper bounds on the Burgers energy density, corresponding to the ground-state binding energy of the directed polymer and the speedup of the Huygens front. The results are complementary to previous studies of both Burgers turbulence and directed polymers, which have focused on universal scaling properties instead of forcing-dependent parameters. The upper-bound formula can be heuristically understood in terms of renormalization of a different kind from that previously used in combustion models, and also shows that the burning velocity of an idealized turbulent flame does not diverge with increasing Reynolds number at fixed turbulence intensity, a conclusion that applies even to strong turbulence. Numerical simulations of the one-dimensional inviscid Burgers equation using a Lagrangian finite-element method confirm that the theoretical upper bounds are sharp within about 15% for various forcing spectra (corresponding to various two-dimensional random media). These computations provide a quantitative test of the replica method. The inferred nonuniversality (spectrum dependence) of the front speedup is of direct importance for combustion modeling.}, }
@article {pmid19102569, year = {2009}, author = {Gupta, S and Soellinger, M and Boesiger, P and Poulikakos, D and Kurtcuoglu, V}, title = {Three-dimensional computational modeling of subject-specific cerebrospinal fluid flow in the subarachnoid space.}, journal = {Journal of biomechanical engineering}, volume = {131}, number = {2}, pages = {021010}, doi = {10.1115/1.3005171}, pmid = {19102569}, issn = {0148-0731}, mesh = {Cerebral Ventricles/*physiology ; Cerebrospinal Fluid/*physiology ; Fourth Ventricle/*physiology ; Humans ; *Models, Biological ; Spinal Canal/physiology ; Subarachnoid Space/*physiology ; }, abstract = {This study aims at investigating three-dimensional subject-specific cerebrospinal fluid (CSF) dynamics in the inferior cranial space, the superior spinal subarachnoid space (SAS), and the fourth cerebral ventricle using a combination of a finite-volume computational fluid dynamics (CFD) approach and magnetic resonance imaging (MRI) experiments. An anatomically accurate 3D model of the entire SAS of a healthy volunteer was reconstructed from high resolution T2 weighted MRI data. Subject-specific pulsatile velocity boundary conditions were imposed at planes in the pontine cistern, cerebellomedullary cistern, and in the spinal subarachnoid space. Velocimetric MRI was used to measure the velocity field at these boundaries. A constant pressure boundary condition was imposed at the interface between the aqueduct of Sylvius and the fourth ventricle. The morphology of the SAS with its complex trabecula structures was taken into account through a novel porous media model with anisotropic permeability. The governing equations were solved using finite-volume CFD. We observed a total pressure variation from -42 Pa to 40 Pa within one cardiac cycle in the investigated domain. Maximum CSF velocities of about 15 cms occurred in the inferior section of the aqueduct, 14 cms in the left foramen of Luschka, and 9 cms in the foramen of Magendie. Flow velocities in the right foramen of Luschka were found to be significantly lower than in the left, indicating three-dimensional brain asymmetries. The flow in the cerebellomedullary cistern was found to be relatively diffusive with a peak Reynolds number (Re)=72, while the flow in the pontine cistern was primarily convective with a peak Re=386. The net volumetric flow rate in the spinal canal was found to be negligible despite CSF oscillation with substantial amplitude with a maximum volumetric flow rate of 109 mlmin. The observed transient flow patterns indicate a compliant behavior of the cranial subarachnoid space. Still, the estimated deformations were small owing to the large parenchymal surface. We have integrated anatomic and velocimetric MRI data with computational fluid dynamics incorporating the porous SAS morphology for the subject-specific reconstruction of cerebrospinal fluid flow in the subarachnoid space. This model can be used as a basis for the development of computational tools, e.g., for the optimization of intrathecal drug delivery and computer-aided evaluation of cerebral pathologies such as syrinx development in syringomelia.}, }
@article {pmid19101568, year = {2009}, author = {Okamoto, M and Sunada, S and Tokutake, H}, title = {Stability analysis of gliding flight of a swallowtail butterfly Papilio xuthus.}, journal = {Journal of theoretical biology}, volume = {257}, number = {2}, pages = {191-202}, doi = {10.1016/j.jtbi.2008.11.012}, pmid = {19101568}, issn = {1095-8541}, mesh = {Aircraft ; Animals ; Biomechanical Phenomena ; Butterflies/anatomy &amp; histology/*physiology ; Flight, Animal/*physiology ; Models, Biological ; Movement ; Wings, Animal/anatomy &amp; histology/*physiology ; }, abstract = {Preliminary observation of the flights of swallowtail butterfly Papilio xuthus revealed that its dihedral angle is larger than 30 degrees and that the section of its left hind wing close to its body and the counterpart of its right hind wing actually clap and form a "vertical tail". In this study, the effects of these two features on the lateral-directional dynamic flight stability of these butterflies were analyzed theoretically and revealed the following: (a) when the dihedral angle is larger than 30 degrees , the lateral-directional motion of the swallowtail becomes stable; (b) the vertical tail stabilizes the dutch roll mode; (c) the effects of the dihedral angle on the roll and spiral modes of a swallowtail are qualitatively the same as those of a meter-sized airplane; and (d) with increasing dihedral angle, the stability of the dutch roll mode decreases for a meter-sized airplane with vertical and horizontal tails but increases for the swallowtail. A possible explanation for the latter effect is the smaller Reynolds number of the insect that causes the drag coefficient of the swallowtail wings to increase more rapidly with an increasing angle of attack compared to a large airplane.}, }
@article {pmid19088215, year = {2009}, author = {Vanella, M and Fitzgerald, T and Preidikman, S and Balaras, E and Balachandran, B}, title = {Influence of flexibility on the aerodynamic performance of a hovering wing.}, journal = {The Journal of experimental biology}, volume = {212}, number = {Pt 1}, pages = {95-105}, doi = {10.1242/jeb.016428}, pmid = {19088215}, issn = {0022-0949}, mesh = {Animals ; Biomechanical Phenomena ; Flight, Animal/*physiology ; *Models, Anatomic ; *Models, Theoretical ; Pliability ; Wings, Animal/*physiology ; }, abstract = {In the present study, a computational investigation was carried out to understand the influence of flexibility on the aerodynamic performance of a hovering wing. A flexible, two-dimensional, two-link model moving within a viscous fluid was considered. The Navier-Stokes equations governing the fluid dynamics were solved together with the equations governing the structural dynamics by using a strongly coupled fluid-structure interaction scheme. Harmonic kinematics was used to prescribe the motions of one of the links, thus effectively reducing the wing to a single degree-of-freedom oscillator. The wing's flexibility was characterized by the ratio of the flapping frequency to the natural frequency of the structure. Apart from the rigid case, different values of this frequency ratio (only in the range of 1/2 to 1/6) were considered at the Reynolds numbers of 75, 250 and 1000. It was found that flexibility can enhance aerodynamic performance and that the best performance is realized when the wing is excited by a non-linear resonance at 1/3 of the natural frequency. Specifically, at Reynolds numbers of 75, 250 and 1000, the aerodynamic performance that is characterized by the ratio of lift coefficient to drag coefficient is respectively increased by 28%, 23% and 21% when compared with the corresponding ratios of a rigid wing driven with the same kinematics. For all Reynolds numbers, the lift generated per unit driving power is also enhanced in a similar manner. The wake capture mechanism is enhanced, due to a stronger flow around the wing at stroke reversal, resulting from a stronger end of stroke vortex at the trailing edge. The present study provides some clues about how flexibility affects the aerodynamic performance in low Reynolds number flapping flight. In addition, it points to the importance of considering non-linear resonances for enhancing aerodynamic performance.}, }
@article {pmid19051936, year = {2008}, author = {Zhao, S and Povitsky, A}, title = {Method of submerged Stokeslets for slip flow about ensembles of particles.}, journal = {Journal of nanoscience and nanotechnology}, volume = {8}, number = {7}, pages = {3790-3801}, pmid = {19051936}, issn = {1533-4880}, abstract = {A boundary singularity method with submerged Stokeslets is applied to the low Reynolds number flows about a set of spheres. Newtonian fluid is considered with no slip or partial slip boundary conditions at the wall. The validity of the method for Stokes flows about representative sets of spheres is investigated. The considered cases include (i) a uniform flow about a stationary set of particles typical for filtration and chemical vapor deposition, (ii) a flow induced by particles moving toward each other typical for self-assembly processes and (iii) a flow induced by spinning particles typical for micro-pump applications. The dependence of the flowfield on the number of Stokeslets is investigated in order to establish the needed number of Stokeslets. Comparison of flow field for the no-slip (Kn = 0) and partial-slip boundary conditions (Kn = 0.1) shows that the partial slip at the particles' surface significantly affect the velocity field and pressure distribution.}, }
@article {pmid19045926, year = {2009}, author = {Naire, S}, title = {Dynamics of voluntary cough maneuvers: a theoretical model.}, journal = {Journal of biomechanical engineering}, volume = {131}, number = {1}, pages = {011010}, doi = {10.1115/1.3005168}, pmid = {19045926}, issn = {0148-0731}, mesh = {Airway Resistance ; Computer Simulation ; Cough/*physiopathology ; Humans ; Lung/*physiopathology ; *Models, Biological ; *Respiratory Mechanics ; Rheology/*methods ; *Volition ; }, abstract = {Voluntary cough maneuvers are characterized by transient peak expiratory flows (PEFs) exceeding the maximum expiratory flow-volume (MEFV) curve. In some cases, these flows can be well in excess of the MEFV, generally referred to as supramaximal flows. Understanding the flow-structure interaction involved in these maneuvers is the main goal of this study. We present a simple theoretical model for investigating the dynamics of voluntary cough and forced expiratory maneuvers. The core modeling idea is based on a 1D model of high Reynolds number flow through flexible-walled tubes. The model incorporates key ingredients involved in these maneuvers: the expiratory effort generated by the abdominal and expiratory muscles, the glottis, and the flexibility and compliance of the lung airways. Variations in these allow investigation of the expiratory flows generated by a variety of single cough maneuvers. The model successfully reproduces the transient PEFs, reported in cough studies. The amplitude of the PEFs is shown to depend on the cough generation protocol, the glottis reopening time, and the compliance of the airways. The particular highlight is in simulating supramaximal PEFs for very compliant tubes. The flow-structure interaction mechanisms behind these are discussed. The wave-speed theory of flow limitation is used to characterize the PEFs. Existing hypotheses of the origin of PEFs, from cough and forced expiration experiments, are also tested using this model. This modeling framework could be a first step toward more sophisticated cough models as well as in developing ideas for new bench-top experiments.}, }
@article {pmid19045922, year = {2009}, author = {Henry, FS and Laine-Pearson, FE and Tsuda, A}, title = {Hamiltonian chaos in a model alveolus.}, journal = {Journal of biomechanical engineering}, volume = {131}, number = {1}, pages = {011006}, doi = {10.1115/1.2953559}, pmid = {19045922}, issn = {0148-0731}, support = {HL074022/HL/NHLBI NIH HHS/United States ; HL054885/HL/NHLBI NIH HHS/United States ; R01 HL074022/HL/NHLBI NIH HHS/United States ; R01 HL054885/HL/NHLBI NIH HHS/United States ; HL070542/HL/NHLBI NIH HHS/United States ; R01 HL070542/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Computer Simulation ; Humans ; *Models, Biological ; *Nonlinear Dynamics ; Pulmonary Alveoli/*physiology ; Respiratory Mechanics/*physiology ; Rheology/*methods ; }, abstract = {In the pulmonary acinus, the airflow Reynolds number is usually much less than unity and hence the flow might be expected to be reversible. However, this does not appear to be the case as a significant portion of the fine particles that reach the acinus remains there after exhalation. We believe that this irreversibility is at large a result of chaotic mixing in the alveoli of the acinar airways. To test this hypothesis, we solved numerically the equations for incompressible, pulsatile, flow in a rigid alveolated duct and tracked numerous fluid particles over many breathing cycles. The resulting Poincare sections exhibit chains of islands on which particles travel. In the region between these chains of islands, some particles move chaotically. The presence of chaos is supported by the results of an estimate of the maximal Lyapunov exponent. It is shown that the streamfunction equation for this flow may be written in the form of a Hamiltonian system and that an expansion of this equation captures all the essential features of the Poincare sections. Elements of Kolmogorov-Arnol'd-Moser theory, the Poincare-Birkhoff fixed-point theorem, and associated Hamiltonian dynamics theory are then employed to confirm the existence of chaos in the flow in a rigid alveolated duct.}, }
@article {pmid19045764, year = {2008}, author = {Hong, C and Shin, KK and Jeon, JJ and Kim, SY}, title = {Transitional wall pressure fluctuations on axisymmetric bodies.}, journal = {The Journal of the Acoustical Society of America}, volume = {124}, number = {5}, pages = {2767-2773}, doi = {10.1121/1.2988291}, pmid = {19045764}, issn = {1520-8524}, mesh = {*Computer Simulation ; Manometry ; *Noise ; Nonlinear Dynamics ; *Pressure ; Sound ; }, abstract = {This paper reports the characteristics of wall pressure fluctuations in the transition region of the flow over axisymmetric bodies. Measurements are conducted in a low noise wind tunnel to obtain the boundary-layer flow field, the local static pressures, and the wall pressure fluctuations using hot wires, micromanometers and flush-mounted microphones. The spatial and the temporal developments of Tollmien-Schlichting (T-S) waves were first observed in the time domain. The wall pressure fluctuations in the transitional boundary-layer flows were of intermittent pulses and intensified as they were convected downstream at typically 63% of the upstream velocity. The Wigner-Ville distributions are then obtained to examine the energy evolution jointly in time and in frequency. The center frequency of the T-S wave is decreased with increases of the boundary-layer thickness and the bandwidth of the energy distribution is broadened as the local Reynolds number is increased. Finally the nondimensional spectra of the transitional wall pressure fluctuations scaled on the outer variables was obtained and it was then found that the characteristic frequency of the T-S wave was related to the outer variables as omegadelta(*)/U(infinity) approximately 0.2. The peak level of the pressure fluctuations during late transition at the characteristic frequency is about 10 dB higher than that of the fully developed flow.}, }
@article {pmid19045679, year = {2008}, author = {Kandula, M}, title = {Spectral attenuation of sound in dilute suspensions with nonlinear particle relaxation.}, journal = {The Journal of the Acoustical Society of America}, volume = {124}, number = {5}, pages = {EL284-90}, doi = {10.1121/1.2987463}, pmid = {19045679}, issn = {1520-8524}, mesh = {*Acoustics ; Air ; Elementary Particle Interactions ; Hot Temperature ; Predictive Value of Tests ; *Sound ; Thermodynamics ; }, abstract = {Previous studies on the sound attenuation in particle-laden flows under Stokesian drag and conduction-controlled heat transfer have been extended to accommodate the nonlinear drag and heat transfer. It has been shown that for large particle-to-fluid density ratio, the particle Reynolds number bears a cubic relationship with omegatau(d) (where omega is the circular frequency and tau(d) is the Stokesian particle relaxation time). This dependence leads to the existence of a peak value in the linear absorption coefficient occurring at a finite value of omegatau(d). Comparison of the predictions with the test data for the spectral attenuation of sound with water injection in a perfectly expanded supersonic air jet shows a satisfactory trend of the theory accounting for nonlinear particle relaxation processes.}, }
@article {pmid19045545, year = {2008}, author = {Naemi, R and Sanders, RH}, title = {A "hydrokinematic" method of measuring the glide efficiency of a human swimmer.}, journal = {Journal of biomechanical engineering}, volume = {130}, number = {6}, pages = {061016}, doi = {10.1115/1.3002764}, pmid = {19045545}, issn = {0148-0731}, mesh = {Computer Simulation ; Energy Transfer/*physiology ; Female ; Humans ; Male ; *Models, Biological ; Rheology/*methods ; Swimming/*physiology ; *Task Performance and Analysis ; Young Adult ; }, abstract = {The aim of this study was to develop and test a method of quantifying the glide efficiency, defined as the ability of the body to maintain its velocity over time and to minimize deceleration through a rectilinear glide. The glide efficiency should be determined in a way that accounts for both the inertial and resistive characteristics of the gliding body as well as the instantaneous velocity. A displacement function (parametric curve) was obtained from the equation of motion of the body during a horizontal rectilinear glide. The values of the parameters in the displacement curve that provide the best fit to the displacement-time data of a body during a rectilinear horizontal glide represent the glide factor and the initial velocity of the particular glide interval. The glide factor is a measure of glide efficiency and indicates the ability of the body to minimize deceleration at each corresponding velocity. The glide efficiency depends on the hydrodynamic characteristic of the body, which is influenced by the body's shape as well as by the body's size. To distinguish the effects of size and shape on the glide efficiency, a size-related glide constant and a shape-related glide coefficient were determined as separate entities. The glide factor is the product of these two parameters. The goodness of fit statistics indicated that the representative displacement function found for each glide interval closely represents the real displacement data of a body in a rectilinear horizontal glide. The accuracy of the method was indicated by a relative standard error of calculation of less than 2.5%. Also the method was able to distinguish between subjects in their glide efficiency. It was found that the glide factor increased with decreasing velocity. The glide coefficient also increased with decreasing Reynolds number. The method is sufficiently accurate to distinguish between individual swimmers in terms of their glide efficiency. The separation of glide factor to a size-related glide constant and a shape-related glide coefficient enabled the effect of size and shape to be quantified.}, }
@article {pmid19045379, year = {2008}, author = {Ekiel-Jezewska, ML and Wajnryb, E and Bławzdziewicz, J and Feuillebois, F}, title = {Lubrication approximation for microparticles moving along parallel walls.}, journal = {The Journal of chemical physics}, volume = {129}, number = {18}, pages = {181102}, doi = {10.1063/1.3009251}, pmid = {19045379}, issn = {1089-7690}, abstract = {Lubrication expressions for the friction coefficients of a spherical particle moving in a fluid between and along two parallel solid walls are explicitly evaluated in the low-Reynolds-number regime. They are used to determine lubrication expression for the particle free motion under an ambient Poiseuille flow. The range of validity and the accuracy of the lubrication approximation are determined by comparing with the corresponding results of the accurate multipole procedure. The results are applicable for thin, wide, and long microchannels, or quasi-two-dimensional systems.}, }
@article {pmid19030903, year = {2009}, author = {Gauger, EM and Downton, MT and Stark, H}, title = {Fluid transport at low Reynolds number with magnetically actuated artificial cilia.}, journal = {The European physical journal. E, Soft matter}, volume = {28}, number = {2}, pages = {231-242}, pmid = {19030903}, issn = {1292-895X}, mesh = {Biomechanical Phenomena ; Biomimetic Materials/*metabolism ; Cilia/*metabolism ; Flagella/metabolism ; *Hydrodynamics ; Kinetics ; *Magnetics ; *Models, Biological ; Movement ; Surface Properties ; }, abstract = {By numerical modeling we investigate fluid transport in low-Reynolds-number flow achieved with a special elastic filament or artificIal cilium attached to a planar surface. The filament is made of superparamagnetic particles linked together by DNA double strands. An external magnetic field induces dipolar interactions between the beads of the filament which provides a convenient way of actuating the cilium in a well-controlled manner. The filament has recently been used to successfully construct the first artificial micro-swimmer (R. Dreyfus et al., Nature 437, 862 (2005)). In our numerical study we introduce a measure, which we call pumping performance, to quantify the fluid transport induced by the magnetically actuated cilium and identify an optimum stroke pattern of the filament. It consists of a slow transport stroke and a fast recovery stroke. Our detailed parameter study also reveals that for sufficiently large magnetic fields the artificial cilium is mainly governed by the Mason number that compares frictional to magnetic forces. Initial studies on multi-cilia systems show that the pumping performance is very sensitive to the imposed phase lag between neighboring cilia, i.e., to the details of the initiated metachronal wave.}, }
@article {pmid19019406, year = {2009}, author = {Wagner, M and Ivleva, NP and Haisch, C and Niessner, R and Horn, H}, title = {Combined use of confocal laser scanning microscopy (CLSM) and Raman microscopy (RM): investigations on EPS-Matrix.}, journal = {Water research}, volume = {43}, number = {1}, pages = {63-76}, doi = {10.1016/j.watres.2008.10.034}, pmid = {19019406}, issn = {0043-1354}, mesh = {Biofilms/growth &amp; development ; Biopolymers/*analysis ; Bioreactors ; Culture Media ; Extracellular Space/*metabolism ; Glycoconjugates/analysis ; Image Processing, Computer-Assisted ; Microscopy, Confocal ; Reference Standards ; *Spectrum Analysis, Raman ; Time Factors ; }, abstract = {Confocal laser scanning microscopy (CLSM) was applied in combination with Raman microscopy (RM) for the characterization of heterotrophic biofilms. Compared to CLSM, RM allows for a deeper insight into the chemical structure of extracellular polymeric substances (EPS) of the biofilm matrix. A low load of glucose (2 g m(-2)d(-1)) was applied as substrate to ensure small growth rates of the heterotrophic biofilm. To investigate the influence of hydrodynamic conditions on the chemical composition of EPS, a three funnel flow system was used, wherein biofilms were grown at Reynolds numbers of 1000, 2500 and 4000, respectively. 31 and 92 days after inoculation with activated sludge supernatant RM was applied as an additional technique to standard CLSM measurements for a more detailed analysis of the biofilm matrix. Polysaccharide-related Raman bands are in good agreement with the lectin binding analysis from CLSM. For the older biofilm, lectin binding analysis showed no change in the composition of EPS, whereas Raman spectra pointed out a change of EPS composition from predominantly polysaccharides to predominantly (glyco) proteins. For the applied substrate condition no significant influence of the Reynolds number on the chemical properties was observed.}, }
@article {pmid19016893, year = {2009}, author = {Jardani, A and Revil, A and Barrash, W and Crespy, A and Rizzo, E and Straface, S and Cardiff, M and Malama, B and Miller, C and Johnson, T}, title = {Reconstruction of the water table from self-potential data: a bayesian approach.}, journal = {Ground water}, volume = {47}, number = {2}, pages = {213-227}, doi = {10.1111/j.1745-6584.2008.00513.x}, pmid = {19016893}, issn = {1745-6584}, mesh = {*Bayes Theorem ; Models, Theoretical ; *Water Movements ; }, abstract = {Ground water flow associated with pumping and injection tests generates self-potential signals that can be measured at the ground surface and used to estimate the pattern of ground water flow at depth. We propose an inversion of the self-potential signals that accounts for the heterogeneous nature of the aquifer and a relationship between the electrical resistivity and the streaming current coupling coefficient. We recast the inversion of the self-potential data into a Bayesian framework. Synthetic tests are performed showing the advantage in using self-potential signals in addition to in situ measurements of the potentiometric levels to reconstruct the shape of the water table. This methodology is applied to a new data set from a series of coordinated hydraulic tomography, self-potential, and electrical resistivity tomography experiments performed at the Boise Hydrogeophysical Research Site, Idaho. In particular, we examine one of the dipole hydraulic tests and its reciprocal to show the sensitivity of the self-potential signals to variations of the potentiometric levels under steady-state conditions. However, because of the high pumping rate, the response was also influenced by the Reynolds number, especially near the pumping well for a given test. Ground water flow in the inertial laminar flow regime is responsible for nonlinearity that is not yet accounted for in self-potential tomography. Numerical modeling addresses the sensitivity of the self-potential response to this problem.}, }
@article {pmid19012900, year = {2009}, author = {Chang, YC and Keh, HJ}, title = {Translation and rotation of slightly deformed colloidal spheres experiencing slip.}, journal = {Journal of colloid and interface science}, volume = {330}, number = {1}, pages = {201-210}, doi = {10.1016/j.jcis.2008.10.055}, pmid = {19012900}, issn = {1095-7103}, mesh = {Colloids/*chemistry ; Rheology ; Viscosity ; }, abstract = {The steady translation and rotation of a rigid, slightly deformed colloidal sphere in arbitrary directions in a viscous fluid are analyzed in the limit of small Reynolds number. The fluid is allowed to slip frictionally at the surface of the particle, and the Stokes equations are solved asymptotically using a method of perturbed expansions. To the second order in the small parameter characterizing the deformation of the particle from the spherical shape, the resistance problem is formulated for the general case and explicit expressions for the hydrodynamic drag force and torque exerted on the particle are obtained for the special cases of prolate and oblate spheroids. The agreement between our asymptotic results for a slip-surface spheroid and the relevant exact solutions in the literature is very good, even if the particle deformation from the spherical shape is not very small. As expected, the second-order expansions for the translational and rotational resistances in powers of the small deformation parameter make better consistency with the available exact results than the first-order expansions do. Depending on the value of the slip parameter, the hydrodynamic drag force and torque acting on a moving spheroid normalized by the corresponding values for a spherical particle with equal equatorial radius are not necessarily monotonic functions of the aspect ratio of the spheroid. Noticeable behavior of the drag force and torque is grasped in the second-order expansions; e.g., the torque exerted on a perfect-slip rotating spheroid is not necessarily zero. For a moving spheroid with a fixed aspect ratio, its normalized hydrodynamic drag force and torque decrease monotonically with an increase in the slip capability of the particle.}, }
@article {pmid18999672, year = {2008}, author = {Bychkov, V and Valiev, D and Eriksson, LE}, title = {Physical mechanism of ultrafast flame acceleration.}, journal = {Physical review letters}, volume = {101}, number = {16}, pages = {164501}, doi = {10.1103/PhysRevLett.101.164501}, pmid = {18999672}, issn = {0031-9007}, abstract = {We explain the physical mechanism of ultrafast flame acceleration in obstructed channels used in modern experiments on detonation triggering. It is demonstrated that delayed burning between the obstacles creates a powerful jetflow, driving the acceleration. This mechanism is much stronger than the classical Shelkin scenario of flame acceleration due to nonslip at the channel walls. The mechanism under study is independent of the Reynolds number, with turbulence playing only a supplementary role. The flame front accelerates exponentially; the analytical formula for the growth rate is obtained. The theory is validated by extensive direct numerical simulations and comparison to previous experiments.}, }
@article {pmid18999560, year = {2008}, author = {Pan, W and Fedosov, DA and Karniadakis, GE and Caswell, B}, title = {Hydrodynamic interactions for single dissipative-particle-dynamics particles and their clusters and filaments.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {4 Pt 2}, pages = {046706}, doi = {10.1103/PhysRevE.78.046706}, pmid = {18999560}, issn = {1539-3755}, abstract = {We have investigated low Reynolds number flow past single dissipative-particle-dynamics particles (point centers of repulsion), their clusters, and their filaments using dissipative-particle-dynamics (DPD) simulations. The objective of our study was to verify whether DPD particles immersed in a sea of DPD particles behave like Langevin particles suspended in a continuous Newtonian fluid solvent, the basis of Brownian dynamics. Our principal test is to compare two effective DPD radii calculated by independent means. From the calculated coefficients of self-diffusion and viscosity the Stokes-Einstein equation yields an intrinsic radius, and from simulations of flow past a single fixed DPD particle a second radius is calculated from Stokes law. In the limit of small Reynolds number the two radii were found to approach each other. Hydrodynamic interactions were studied with Stokes flow past two DPD particles, and single DPD particles in bounded uniform flow and in-plane Poiseuille flow. Additional simulations examined closely spaced multiparticle clusters (straight-chains and hexagonal-packed aggregates). For all cases of rigid bodies the simulation results are in good agreement with predictions derived analytically from the continuum Stokes system. Elastic filaments, DPD-particle chains with bending resistance, were also simulated to examine hydrodynamically induced distortions, and the results show that the model captures the correct hydrodynamic interactions among filament beads.}, }
@article {pmid18999536, year = {2008}, author = {Chen, X and Fried, E}, title = {Influence of the dispersive and dissipative scales alpha and beta on the energy spectrum of the Navier-Stokes alphabeta equations.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {4 Pt 2}, pages = {046317}, doi = {10.1103/PhysRevE.78.046317}, pmid = {18999536}, issn = {1539-3755}, abstract = {Lundgren's vortex model for the intermittent fine structure of high-Reynolds-number turbulence is applied to the Navier-Stokes alphabeta equations and specialized to the Navier-Stokes alpha equations. The Navier-Stokes alphabeta equations involve dispersive and dissipative length scales alpha and beta, respectively. Setting beta equal to alpha reduces the Navier-Stokes alphabeta equations to the Navier-Stokes alpha equations. For the Navier-Stokes alpha equations, the energy spectrum is found to obey Kolmogorov's -5/3 law in a range of wave numbers identical to that determined by Lundgren for the Navier-Stokes equations. For the Navier-Stokes alphabeta equations, Kolmogorov's -5/3 law is also recovered. However, granted that beta < alpha, the range of wave numbers for which this law holds is extended by a factor of alphabeta . This suggests that simulations based on the Navier-Stokes alphabeta equations may have the potential to resolve features smaller than those obtainable using the Navier-Stokes alpha equations.}, }
@article {pmid18999533, year = {2008}, author = {Xu, Y and Liu, Y and Xia, Y and Wu, F}, title = {Lattice-Boltzmann simulation of two-dimensional flow over two vibrating side-by-side circular cylinders.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {4 Pt 2}, pages = {046314}, doi = {10.1103/PhysRevE.78.046314}, pmid = {18999533}, issn = {1539-3755}, abstract = {A numerical simulation using the multiple relaxation time lattice-Boltzmann method is carried out for the purpose of investigating fluid flow over two vibrating side-by-side circular cylinders and the effect of moving the cylinders on the wake characteristics. As a benchmark problem to assess the validity and efficiency of the model, the calculation was carried out at Reynolds number of 200 and four pitch ratios (T/D , where D is the cylinder diameter while T is the center-to-center spacing between the two cylinders) of 1.2, 1.6, 2.2, and 3.2, respectively. The calculated results indicate that the vibration of the cylinder pair has significant influence on the wake patterns. When the amplitude of vibration is big enough, the vibration locks up the vortex shedding and formation. For each cylinder vibration frequency, there exists a threshold of vibration amplitude for the lock-up phenomenon. With the vibration frequency is increased, the threshold of vibration amplitude decreases.}, }
@article {pmid18999531, year = {2008}, author = {Herrada, MA and Gañán-Calvo, AM and Guillot, P}, title = {Spatiotemporal instability of a confined capillary jet.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {4 Pt 2}, pages = {046312}, doi = {10.1103/PhysRevE.78.046312}, pmid = {18999531}, issn = {1539-3755}, abstract = {Recent experimental studies on the instability of capillary jets have revealed the suitability of a linear spatiotemporal instability analysis to ascertain the parametrical conditions for specific flow regimes such as steady jetting or dripping. In this work, an extensive analytical, numerical, and experimental description of confined capillary jets is provided, leading to an integrated picture both in terms of data and interpretation. We propose an extended, accurate analytic model in the low Reynolds number limit, and introduce a numerical scheme to predict the system response when the liquid inertia is not negligible. Theoretical predictions show remarkable accuracy when compared with the extensive experimental mapping.}, }
@article {pmid18999525, year = {2008}, author = {Nicolleau, F and Sung, KS and Vassilicos, JC}, title = {Depletion of horizontal pair diffusion in strongly stratified turbulence: comparison with plane two-dimensional flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {4 Pt 2}, pages = {046306}, doi = {10.1103/PhysRevE.78.046306}, pmid = {18999525}, issn = {1539-3755}, abstract = {In this paper different arguments are put forward to explain why two-particle diffusion is depleted in the direction of stratification of a stably stratified turbulence. Kinematic simulations (KSs) which reproduce that depletion are used to shed light on the responsible mechanisms. The local horizontal divergence is studied and comparisons are made with two-dimensional kinematic simulation. The probability density function of the horizontal divergence of the velocity field is not a Dirac distribution in the presence of stratification but a Gaussian and this Gaussian does not depend on the Froude number. The number of stagnation points in the KS of three-dimensional strongly stratified turbulence is found virtually identical to what it is in KS of three-dimensional isotropic turbulence. However, the root mean square horizontal and vertical stagnation point velocities of the stratified turbulence are both larger than their counterparts in isotropic turbulence that latter getting progressively smaller as the Reynolds number increases. Therefore, the strong stratification destroys the persistence of the stagnation points. The main reason for the depletion, however, seems to have to be sought in the effect of stratification on the strain rate tensor. The stratification does lead to a depletion of the average square strain rate tensor, as well as of all average square strain rate eigenvalues. We conclude that it is these effects of stratification on the strain rate tensor that explain the depletion of the horizontal turbulent pair diffusion.}, }
@article {pmid18999482, year = {2008}, author = {Alexander, GP and Pooley, CM and Yeomans, JM}, title = {Scattering of low-Reynolds-number swimmers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {4 Pt 2}, pages = {045302}, doi = {10.1103/PhysRevE.78.045302}, pmid = {18999482}, issn = {1539-3755}, mesh = {Bacteria/metabolism ; Bacterial Physiological Phenomena ; Biophysics/methods ; Flagella/metabolism ; Mathematics ; *Models, Biological ; Motion ; *Movement ; }, abstract = {We describe the consequences of time-reversal invariance of the Stokes equations for the hydrodynamic scattering of two low-Reynolds-number swimmers. For swimmers that are related to each other by a time-reversal transformation, this leads to the striking result that the angle between the two swimmers is preserved by the scattering. The result is illustrated for the particular case of a linked-sphere model swimmer. For more general pairs of swimmers, not related to each other by time reversal, we find that hydrodynamic scattering can alter the angle between their trajectories by several tens of degrees. For two identical contractile swimmers, this can lead to the formation of a bound state.}, }
@article {pmid18995877, year = {2009}, author = {Burke, EN and Wadzuk, BM}, title = {The effect of field conditions on low Reynolds number flow in a wetland.}, journal = {Water research}, volume = {43}, number = {2}, pages = {508-514}, doi = {10.1016/j.watres.2008.10.027}, pmid = {18995877}, issn = {0043-1354}, mesh = {Conservation of Energy Resources ; Environmental Monitoring ; Models, Theoretical ; Water/chemistry ; *Water Movements ; Water Pollution, Chemical/prevention &amp; control ; *Wetlands ; }, abstract = {Stormwater runoff has been an environmental concern since the 1980s. Green infrastructure, such as constructed stormwater wetlands (CSWs), is a tool in stormwater management, however, little is known about the hydraulic diffusion processes that impact water quality in low flow, laminar (i.e. baseflow) conditions. Diffusion provides the mechanisms that distribute and mix water through a CSW and therefore how pollutants will be spread through the CSW impacting the water quality. Laboratory experiments were performed by Nepf, H.M., Sullivan, J.A., Zavistoski, R.A. [1997. A model for diffusion within emergent vegetation. Limnology and Oceanography, 42(8), 1735-1745], and Serra, T., Fernando, H.J.S., Rodriquez, R.V. [2004. Effects of emergent vegetation on lateral diffusion in wetland. Water Research, 38(1), 139-147] to examine the effect of plant density on diffusion in laminar flow conditions. Nepf, H.M. [1999. Drag, turbulence, and diffusion in flow through emergent vegetation. Water Resources Research, 35(2), 479-489] proposed a model predicting the diffusion coefficient based upon the plant density for both laminar and turbulent flow conditions. The present study examines the effect of field conditions on diffusion in a laminar flow field and verifies the diffusion model created by Nepf, H.M. [1999. Drag, turbulence, and diffusion in flow through emergent vegetation. Water Resources Research, 35(2), 479-489]. The results from the present study show that the laminar flow model, based solely on mechanical diffusion, is not sufficient for field conditions and the total diffusion model must be used. The variability in flow conditions and stem diameter found in the field produce pockets of turbulence and dead zones that must be considered to predict the diffusion coefficients in low flow CSWs. A sensitivity analysis of the dead zone term shows that the laboratory, field and diffusion models lie within an acceptable theoretical range for the observed or predicted diffusion coefficient. In addition, a model was created using the Danish Hydraulic Institutes Mike 21 software. Model results indicate that non-uniform velocities significantly affect the diffusion coefficient and a range of diffusion coefficients should be considered when designing CSWs.}, }
@article {pmid18990664, year = {2009}, author = {de Lozar, A and Hof, B}, title = {An experimental study of the decay of turbulent puffs in pipe flow.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {367}, number = {1888}, pages = {589-599}, doi = {10.1098/rsta.2008.0199}, pmid = {18990664}, issn = {1364-503X}, abstract = {As reported in a number of recent studies, turbulence in pipe flow is transient for Re<2000 and the flow eventually always returns to the laminar state. Generally, the lifetime of turbulence has been observed to increase rapidly with Reynolds number but there is currently no accord on the exact scaling behaviour. In particular, it is not clear whether a critical point exists where turbulence becomes sustained or if it remains transient. We here aim to clarify if these conflicting results may have been caused by the different experimental and numerical protocols used to trigger turbulence in these studies.}, }
@article {pmid18990662, year = {2009}, author = {Schneider, TM and Eckhardt, B}, title = {Edge states intermediate between laminar and turbulent dynamics in pipe flow.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {367}, number = {1888}, pages = {577-587}, doi = {10.1098/rsta.2008.0216}, pmid = {18990662}, issn = {1364-503X}, abstract = {We studied the dynamics near the boundary between laminar and turbulent dynamics in pipe flow. This boundary contains invariant dynamical states that are attracting when the dynamics is confined to the boundary. These states can be found by controlling a single quantity, in our case the energy content. The edge state is dominated by two downstream vortices and shows intrinsic chaotic dynamics. With increasing Reynolds number the separation between the edge state and turbulence increases. We can track it down to Re=1900, where the turbulent lifetimes are short enough that spontaneous decay can also be seen in experiments.}, }
@article {pmid18990661, year = {2009}, author = {Viswanath, D}, title = {The critical layer in pipe flow at high Reynolds number.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {367}, number = {1888}, pages = {561-576}, doi = {10.1098/rsta.2008.0225}, pmid = {18990661}, issn = {1364-503X}, abstract = {We report the computation of a family of travelling wave solutions of pipe flow up to Re=75000. As in all lower branch solutions, streaks and rolls feature prominently in these solutions. For large Re, these solutions develop a critical layer away from the wall. Although the solutions are linearly unstable, the two unstable eigenvalues approach 0 as Re-->infinity at rates given by Re-0.41 and Re-0.87; surprisingly, the solutions become more stable as the flow becomes less viscous. The formation of the critical layer and other aspects of the Re-->infinity limit could be universal to lower branch solutions of shear flows. We give implementation details of the GMRES-hookstep and Arnoldi iterations used for computing these solutions and their spectra, while pointing out the new aspects of our method.}, }
@article {pmid18990660, year = {2009}, author = {van Doorne, CW and Westerweel, J}, title = {The flow structure of a puff.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {367}, number = {1888}, pages = {489-507}, doi = {10.1098/rsta.2008.0227}, pmid = {18990660}, issn = {1364-503X}, abstract = {From time-resolved stereoscopic particle image velocimetry measurements over the entire circular cross section of a pipe, a first-of-its-kind quasi-instantaneous three-dimensional velocity field of a turbulent puff at a low Reynolds number is reconstructed. At the trailing edge of the puff, where the laminar flow undergoes transition to turbulence, pairs of counterrotating streamwise vortices are observed that form the legs of large hairpin vortices. At the upstream end of the puff, a quasi-periodic regeneration of streamwise vortices takes place. Initially, the vortex structure resembles a travelling wave solution, but as the vortices propagate into the turbulent region of the puff, they continue to develop into strong hairpin vortices. These hairpin vortices extract so much energy from the mean flow that they cannot be sustained. This structure provides a possible explanation for the intermittent character of the puffs in pipe flow at low Reynolds numbers.}, }
@article {pmid18990659, year = {2009}, author = {Cohen, J and Philip, J and Ben-Dov, G}, title = {Aspects of linear and nonlinear instabilities leading to transition in pipe and channel flows.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {367}, number = {1888}, pages = {509-527}, doi = {10.1098/rsta.2008.0189}, pmid = {18990659}, issn = {1364-503X}, abstract = {The failure of normal-mode linear stability analysis to predict a transition Reynolds number (Retr) in pipe flow and subcritical transition in plane Poiseuille flow (PPF) has led to the search of other scenarios to explain transition to turbulence in both flows. In this work, various results associated with linear and nonlinear mechanisms of both flows are presented. The results that combine analytical and experimental approaches indicate the strong link between the mechanisms governing the transition of both flows. It is demonstrated that the linear transient growth mechanism is based on the existence of a pair of least stable nearly parallel modes (having opposite phases and almost identical amplitude distributions). The analysis that has been applied previously to pipe flow is extended here to a fully developed channel flow predicting the shape of the optimized initial disturbance (a pair of counter-rotating vortices, CVP), time for maximum energy amplification and the dependence of the latter on Re. The results agree with previous predictions based on many modes. Furthermore, the shape of the optimized initial disturbance is similar in both flows and has been visualized experimentally. The analysis reveals that in pipe flow, the transient growth is a consequence of two opposite running modes decaying with an equal decay rate whereas in PPF it is due to two stationary modes decaying with different decay rates. In the first nonlinear scenario, the breakdown of the CVPs (produced by the linear transient growth mechanism) into hairpin vortices is followed experimentally. The associated scaling laws, relating the minimal disturbance amplitude required for the initiation of hairpins and the Re, are found experimentally for both PPF and pipe flow. The scaling law associated with PPF agrees well with the previous predictions of Chapman, whereas the scaling of the pipe flow is the same as the one previously obtained by Hof et al. indicating transition to a turbulent state. In the second nonlinear scenario, the base flow of pipe when it is mildly deviated from the Poiseuille profile by an axisymmetric distortion is examined. The nonlinear features reveal a Retr of approximately 2000 associated with the bifurcation between two deviation solutions.}, }
@article {pmid18990657, year = {2009}, author = {Duggleby, A and Ball, KS and Schwaenen, M}, title = {Structure and dynamics of low Reynolds number turbulent pipe flow.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {367}, number = {1888}, pages = {473-488}, doi = {10.1098/rsta.2008.0241}, pmid = {18990657}, issn = {1364-503X}, abstract = {Using large-scale numerical calculations, we explore the proper orthogonal decomposition of low Reynolds number turbulent pipe flow, using both the translational invariant (Fourier) method and the method of snapshots. Each method has benefits and drawbacks, making the 'best' choice dependent on the purpose of the analysis. Owing to its construction, the Fourier method includes all the flow fields that are translational invariants of the simulated flow fields. Thus, the Fourier method converges to an estimate of the dimension of the chaotic attractor in less total simulation time than the method of snapshots. The converse is that for a given simulation, the method of snapshots yields a basis set that is more optimal because it does not include all of the translational invariants that were not a part of the simulation. Using the Fourier method yields smooth structures with definable subclasses based upon Fourier wavenumber pairs, and results in a new dynamical systems insight into turbulent pipe flow. These subclasses include a set of modes that propagate with a nearly constant phase speed, act together as a wave packet and transfer energy from streamwise rolls. It is these interactions that are responsible for bursting events and Reynolds stress generation. These structures and dynamics are similar to those found in turbulent channel flow. A comparison of structures and dynamics in turbulent pipe and channel flows is reported to emphasize the similarities and differences.}, }
@article {pmid18977505, year = {2009}, author = {Simões, M and Simões, LC and Vieira, MJ}, title = {Species association increases biofilm resistance to chemical and mechanical treatments.}, journal = {Water research}, volume = {43}, number = {1}, pages = {229-237}, doi = {10.1016/j.watres.2008.10.010}, pmid = {18977505}, issn = {0043-1354}, mesh = {Bacillus cereus/cytology/drug effects/physiology ; Bacterial Adhesion/drug effects ; Biofilms/*drug effects ; Bioreactors ; Cetrimonium ; Cetrimonium Compounds/*pharmacology ; Glutaral/*pharmacology ; Microbial Viability/drug effects ; Phenotype ; Pseudomonas fluorescens/cytology/drug effects/physiology ; Species Specificity ; }, abstract = {The study of biofilm ecology and interactions might help to improve our understanding of their resistance mechanisms to control strategies. Concerns that the diversity of the biofilm communities can affect disinfection efficacy have led us to examine the effect of two antimicrobial agents on two important spoilage bacteria. Studies were conducted on single and dual species biofilms of Bacillus cereus and Pseudomonas fluorescens. Biofilms were formed on a stainless steel rotating device, in a bioreactor, at a constant Reynolds number of agitation (Re(A)). Biofilm phenotypic characterization showed significant differences, mainly in the metabolic activity and both extracellular proteins and polysaccharides content. Cetyl trimethyl ammonium bromide (CTAB) and glutaraldehyde (GLUT) solutions in conjunction with increasing Re(A) were used to treat biofilms in order to assess their ability to kill and remove biofilms. B. cereus and P. fluorescens biofilms were stratified in a layered structure with each layer having differential tolerance to chemical and mechanical stresses. Dual species biofilms and P. fluorescens single biofilms had both the highest resistance to removal when pre-treated with CTAB and GLUT, respectively. B. cereus biofilms were the most affected by hydrodynamic disturbance and the most susceptible to antimicrobials. Dual biofilms were more resistant to antimicrobials than each single species biofilm, with a significant proportion of the population remaining in a viable state after exposure to CTAB or GLUT. Moreover, the species association increased the proportion of viable cells of both bacteria, comparatively to the single species scenarios, enhancing each other's survival to antimicrobials and the biofilm shear stress stability.}, }
@article {pmid18968783, year = {2002}, author = {Costin, CD and Synovec, RE}, title = {Measuring the transverse concentration gradient between adjacent laminar flows in a microfluidic device by a laser-based refractive index gradient detector.}, journal = {Talanta}, volume = {58}, number = {3}, pages = {551-560}, doi = {10.1016/s0039-9140(02)00321-1}, pmid = {18968783}, issn = {1873-3573}, abstract = {A detection scheme that probes the refractive index gradient (RIG) between adjacent laminar flows in microfluidic devices has been developed and evaluated. The behavior of low Reynolds number flows has been well documented and shows that molecular transport (mixing) between adjacent laminar flows occurs by molecular diffusion between the flow boundaries. A diode laser has been used to probe the transverse concentration gradient at a selected position along a microchannel. The concentration gradient is affected by the transverse diffusion from a flow with analyte into a flow initially without analyte. To optimize sensitivity, the RIG is probed at a position in which molecular diffusion across the boundary of the two flows has been minimal, i.e. just after the flow initially without analyte merges with the flow initially containing the analyte at a given concentration. The RIG formed causes the laser beam, impinging orthogonal to the RIG through the microchannel, to be deflected. The angle of deflection is then monitored on a position sensitive detector (PSD). Currently, this detection scheme is demonstrated to provide quantitative detection of sucrose, as a test analyte, with a concentration limit of detection (LOD) of 96 ppm (w/v) or 280 muM, corresponding to 1.3x10(-5) DeltaRI units using 3sigma baseline noise. A dynamic range of 96 ppm to 50% sucrose is obtained. This detection method provides universal detection selectivity for microfluidic analysis systems that are becoming increasingly useful in monitoring chemical systems, particularly for the polymer, pharmaceutical and life sciences fields. For a larger molecular weight analyte with a smaller diffusion coefficient, lower concentration and RI LODs were achieved since detection sensitivity is a function of analyte diffusion. For example, for the polymer poly (ethylene glycol) with a molar mass of 11 840 g mol(-1), the LOD was experimentally determined to be 56 ppm (4.7 muM), equivalent to a RI LOD of 4.5x10(-6) DeltaRI (3sigma). The detection limit for proteins was also found to be favorable. For example, with the current configuration, ribonuclease A (RNAse) had a LOD of 46 ppm (3.4 muM), and bovine serum albumin (BSA) had a LOD of 54 ppm (780 nM).}, }
@article {pmid18931316, year = {2008}, author = {Martone, PT and Denny, MW}, title = {To break a coralline: mechanical constraints on the size and survival of a wave-swept seaweed.}, journal = {The Journal of experimental biology}, volume = {211}, number = {Pt 21}, pages = {3433-3441}, doi = {10.1242/jeb.020495}, pmid = {18931316}, issn = {0022-0949}, mesh = {Biomechanical Phenomena ; *Models, Biological ; Rhodophyta/*physiology ; Seaweed/*physiology ; *Stress, Mechanical ; Water Movements ; }, abstract = {Previous studies have hypothesized that wave-induced drag forces may constrain the size of intertidal organisms by dislodging or breaking organisms that exceed some critical dimension. In this study, we explored constraints on the size of the articulated coralline alga Calliarthron, which thrives in wave-exposed intertidal habitats. Its ability to survive depends critically upon its segmented morphology (calcified segments separated by flexible joints or ;genicula'), which allows otherwise rigid fronds to bend and thereby reduce drag. However, bending also amplifies stress within genicula near the base of fronds. We quantified breakage of genicula in bending by applying known forces to fronds until they broke. Using a mathematical model, we demonstrate the mitigating effect of neighboring fronds on breakage and show that fronds growing within dense populations are no more likely to break in bending than in tension, suggesting that genicular morphology approaches an engineering optimum, possibly reflecting adaptation to hydrodynamic stress. We measured drag in a re-circulating water flume (0.23-3.6 m s(-1)) and a gravity-accelerated water flume, which generates jets of water that mimic the impact of breaking waves (6-10 m s(-1)). We used frond Reynolds number to extrapolate drag coefficients in the field and to predict water velocities necessary to break fronds of given sizes. Laboratory data successfully predicted frond sizes found in the field, suggesting that, although Calliarthron is well adapted to resist breakage, wave forces may ultimately limit the size of intertidal fronds.}, }
@article {pmid18926966, year = {2009}, author = {Humphrey, JA}, title = {Drag force acting on a neuromast in the fish lateral line trunk canal. II. Analytical modelling of parameter dependencies.}, journal = {Journal of the Royal Society, Interface}, volume = {6}, number = {36}, pages = {641-653}, pmid = {18926966}, issn = {1742-5662}, mesh = {Animals ; Biomechanical Phenomena ; Biophysics ; Fishes/*physiology ; Lateral Line System/*physiology ; Mechanoreceptors/*physiology ; *Models, Theoretical ; Pressure ; }, abstract = {In Part I of this two-part study, the coupled flows external and internal to the fish lateral line trunk canal were consecutively calculated by solving the Navier-Stokes (N-S) equations numerically in each domain. With the external flow known, the solution for the internal flow was obtained using a parallelepiped to simulate the neuromast cupula present between a pair of consecutive pores, allowing the calculation of the drag force acting on the neuromast cupula. While physically rigorous and accurate, the numerical approach is tedious and inefficient since it does not readily reveal the parameter dependencies of the drag force. In Part II of this work we present an analytically based physical-mathematical model for rapidly calculating the drag force acting on a neuromast cupula. The cupula is well approximated as an immobile sphere located inside a tube-shaped canal segment of circular cross section containing a constant property fluid in a steady-periodic oscillating state of motion. The analytical expression derived for the dimensionless drag force is of the form |F(N)/(|P(L) - P(R)|pi(D/2)(2) = f(d/D, L(t)/D, omega(*)(D), where |F(N)| is the amplitude of the drag force; |P(L)-P(R)| is the amplitude of the pressure difference driving the flow in the interpore tube segment; d/D is the ratio of sphere diameter to tube diameter; L(t)/D is the ratio of interpore tube segment length to tube diameter; and omega(*)(D) = omega(D/2)(2) /v is the oscillating flow kinetic Reynolds number (a dimensionless frequency). Present results show that the dimensionless drag force amplitude increases with decreasing L(t)/D and maximizes in the range 0.65< or =d/D< or =0.85, depending on the values of L(t)/D and omega(*)(D). It is also found that in the biologically relevant range of dimensionless frequencies 1< or = omega(*)(D) < or =20 and segment lengths 4< or =L(t)/D< or =16, the sphere tube (neuromast-canal) system acts as a low-pass filter for values d/D< or =0.75, approximately. For larger values of d/D the system is equally sensitive to all frequencies, but the drag force is significantly decreased. Comparisons with N-S calculations of the drag force show good agreement with the analytical model results. By revealing the parameter dependencies of the drag force, the model serves to guide biological understanding and the optimized design of corresponding bioinspired artificial sensors.}, }
@article {pmid18851218, year = {2008}, author = {Laguerre, R and Nore, C and Ribeiro, A and Léorat, J and Guermond, JL and Plunian, F}, title = {Impact of impellers on the axisymmetric magnetic mode in the VKS2 dynamo experiment.}, journal = {Physical review letters}, volume = {101}, number = {10}, pages = {104501}, doi = {10.1103/PhysRevLett.101.104501}, pmid = {18851218}, issn = {0031-9007}, abstract = {In the von Kármán Sodium 2 (VKS2) successful dynamo experiment of September 2006, the observed magnetic field showed a strong axisymmetric component, implying that nonaxisymmetric components of the flow field were acting. By modeling the induction effect of the spiraling flow between the blades of the impellers in a kinematic dynamo code, we find that the axisymmetric magnetic mode is excited. The control parameters are the magnetic Reynolds number of the mean flow, the coefficient measuring the induction effect alpha, and the type of boundary conditions. We show that using realistic values of alpha, the observed critical magnetic Reynolds number, Rm;{c} approximately 32, can be reached easily with ferromagnetic boundary conditions. We conjecture that the dynamo action achieved in this experiment may not be related to the turbulence in the bulk of the flow, but rather to the alpha effect induced by the impellers.}, }
@article {pmid18851156, year = {2008}, author = {Alam, MM and Zhou, Y}, title = {Alternative drag coefficient in the wake of an isolated bluff body.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {3 Pt 2}, pages = {036320}, doi = {10.1103/PhysRevE.78.036320}, pmid = {18851156}, issn = {1539-3755}, abstract = {An alternative drag coefficient Cda [=F[over]/(1/2rhoUinfinity2UinfinityTs)] , is proposed for an isolated bluff-body wake, where F[over] is the drag force on the body per unit length, U_{infinity} is the free-stream velocity, rho is the density of fluid, and Ts is the vortex shedding period. Theoretical analysis presently conducted indicates that, while the conventional drag coefficient Cd [=F[over]/(1/2rhoUinfinity2d)] may be interpreted as the intensity of the mean kinetic energy deficit distributed over the characteristic length of cylinder height d , Cda is the intensity of the mean kinetic energy deficit distributed over the characteristic length of the Karman vortex wavelength UinfinityTs . Therefore, Cda may be considered to be a drag coefficient with the characteristic length given by UinfinityTs , instead of d . As long as a bluff body is isolated, without energy exchange between the cylinder and its support, this drag coefficient is invariant, as confirmed by our experimental data as well as those in the literature, with respect to the bluff-body geometry, angle of attack, and Reynolds number, with a caveat of limited cases examined presently.}, }
@article {pmid18851145, year = {2008}, author = {Ching, ES and Ko, TC}, title = {Ultimate-state scaling in a shell model for homogeneous turbulent convection.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {3 Pt 2}, pages = {036309}, doi = {10.1103/PhysRevE.78.036309}, pmid = {18851145}, issn = {1539-3755}, abstract = {An interesting question in turbulent convection is how the heat transport depends on the strength of thermal forcing in the limit of very large thermal forcing. Kraichnan predicted [Phys. Fluids 5, 1374 (1962)] that for fluids with low Prandtl number (Pr), the heat transport measured by the Nusselt number (Nu) would depend on the strength of thermal forcing measured by the Rayleigh number (Ra) as Nu approximately Ra(1/2) with logarithmic corrections at very high Ra. According to Kraichnan, the shear boundary layers play a crucial role in giving rise to this so-called ultimate-state scaling. A similar scaling result is predicted by the Grossmann-Lohse theory [J. Fluid Mech. 407, 27 (2000)], but with the assumption that the ultimate state is a bulk-dominated state in which both the average kinetic and thermal dissipation rates are dominated by contributions from the bulk of the flow with the boundary layers either broken down or playing no role in the heat transport. In this paper, we study the dependence of Nu and the Reynolds number (Re) measuring the root-mean-squared velocity fluctuations on Ra and Pr, for low Pr, using a shell model for homogeneous turbulent convection where buoyancy is acting directly on most of the scales. We find that Nu approximately Ra(1/2)Pr(1/2) and Re approximately Ra(1/2)Pr(-1/2) , which resemble the ultimate-state scaling behavior for fluids with low Pr, and show that the presence of a drag acting on the large scales is crucial in giving rise to such scaling. As a large-scale drag cannot exist by itself in the bulk of turbulent thermal convection, our results indicate that if buoyancy acts on most of the scales in the bulk of turbulent convection at very high Ra, then the ultimate state cannot be bulk dominated.}, }
@article {pmid18851137, year = {2008}, author = {Keetels, GH and Clercx, HJ and van Heijst, GJ}, title = {Spontaneous angular momentum generation of two-dimensional fluid flow in an elliptic geometry.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {3 Pt 2}, pages = {036301}, doi = {10.1103/PhysRevE.78.036301}, pmid = {18851137}, issn = {1539-3755}, abstract = {Spontaneous spin-up, i.e., the significant increase of the total angular momentum of a flow that initially has no net angular momentum, is very characteristic for decaying two-dimensional turbulence in square domains bounded by rigid no-slip walls. In contrast, spontaneous spin-up is virtually absent for such flows in a circular domain with a no-slip boundary. In order to acquire an understanding of this strikingly different behavior observed on the square and the circle, we consider a set of elliptic geometries with a gradual increase of the eccentricity. It is shown that a variation of the eccentricity can be used as a control parameter to tune the relative contribution of the pressure and viscous stresses in the angular momentum balance. Direct numerical simulations demonstrate that the magnitude of the torque can be related to the relative contribution of the pressure. As a consequence, the number of spin-up events in an ensemble of slightly different initial conditions depends strongly on the eccentricity. For small eccentricities, strong and rapid spin-up events are observed occasionally, whereas the majority of the runs do not show significant spin-up. Small differences in the initial condition can result in a completely different evolution of the flow and an appearance of the end state of the decay process. For sufficiently large eccentricities, all the runs in the ensemble demonstrate strong and rapid spin-up, which is consistent with the flow development on the square. It is verified that the number of spin-up events for a given eccentricity does not depend on the Reynolds number of the flow. This observation is consistent with the conjecture that it is the pressure on the domain boundaries that drives the spin-up processes.}, }
@article {pmid18850986, year = {2008}, author = {Lauga, E and Bartolo, D}, title = {No many-scallop theorem: collective locomotion of reciprocal swimmers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {3 Pt 1}, pages = {030901}, doi = {10.1103/PhysRevE.78.030901}, pmid = {18850986}, issn = {1539-3755}, abstract = {To achieve propulsion at low Reynolds number, a swimmer must deform in a way that is not invariant under time-reversal symmetry; this result is known as the scallop theorem. However, there is no many-scallop theorem. We demonstrate here that two active particles undergoing reciprocal deformations can swim collectively; moreover, polar particles also experience effective long-range interactions. These results are derived for a minimal dimers model, and generalized to more complex geometries on the basis of symmetry and scaling arguments. We explain how such cooperative locomotion can be realized experimentally by shaking a collection of soft particles with a homogeneous external field.}, }
@article {pmid18850938, year = {2008}, author = {Wei, X and Hollerbach, R}, title = {Instabilities of Shercliffe and Stewartson layers in spherical Couette flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {2 Pt 2}, pages = {026309}, doi = {10.1103/PhysRevE.78.026309}, pmid = {18850938}, issn = {1539-3755}, abstract = {We explore numerically the flow induced in a spherical shell by differentially rotating the inner and outer spheres. The fluid is also taken to be electrically conducting (in the low magnetic Reynolds number limit), and a magnetic field is imposed parallel to the axis of rotation. If the outer sphere is stationary, the magnetic field induces a Shercliffe layer on the tangent cylinder, the cylinder just touching the inner sphere and parallel to the field. If the magnetic field is absent, but a strong overall rotation is present, Coriolis effects induce a Stewartson layer on the tangent cylinder. The nonaxisymmetric instabilities of both types of layer separately have been studied before; here, we consider the two cases side by side, as well as the mixed case, and investigate how magnetic and rotational effects interact. We find that if the differential rotation and the overall rotation are in the same direction, the overall rotation may have a destabilizing influence, whereas if the differential rotation and the overall rotation are in the opposite direction, the overall rotation always has a stabilizing influence.}, }
@article {pmid18850933, year = {2008}, author = {Gañán-Calvo, AM}, title = {Unconditional jetting.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {2 Pt 2}, pages = {026304}, doi = {10.1103/PhysRevE.78.026304}, pmid = {18850933}, issn = {1539-3755}, abstract = {Capillary jetting of a fluid dispersed into another immiscible phase is usually limited by a critical capillary number, a function of the Reynolds number and the fluid property ratios. Critical conditions are set when the minimum spreading velocity of small perturbations v_{-};{*} along the jet (marginal stability velocity) is zero. Here we identify and describe parametric regions of high technological relevance, where v_{-};{*}>0 and the jet flow is always supercritical independently of the dispersed liquid flow rate; within these relatively broad regions, the jet does not undergo the usual dripping-jetting transition, so that either the jet can be made arbitrarily thin (yielding droplets of any imaginably small size), or the issuing flow rate can be made arbitrarily small. In this work, we provide illustrative analytical studies of asymptotic cases for both negligible and dominant inertia forces. In this latter case, requiring a nonzero jet surface velocity, axisymmetric perturbation waves "surf" downstream for all given wave numbers, while the liquid bulk can remain static. In the former case (implying small Reynolds flow) we found that the jet profile small slope is limited by a critical value; different published experiments support our predictions.}, }
@article {pmid18850932, year = {2008}, author = {Ching, ES and Guo, H and Lo, TS}, title = {Refined similarity hypotheses in shell models of homogeneous turbulence and turbulent convection.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {2 Pt 2}, pages = {026303}, doi = {10.1103/PhysRevE.78.026303}, pmid = {18850932}, issn = {1539-3755}, abstract = {A major challenge in turbulence research is to understand from first principles the origin of the anomalous scaling of velocity fluctuations in high-Reynolds-number turbulent flows. One important idea was proposed by Kolmogorov [J. Fluid Mech. 13, 82 (1962)], which attributes the anomaly to variations of the locally averaged energy dissipation rate. Kraichnan later pointed out [J. Fluid Mech. 62, 305 (1973)] that the locally averaged energy dissipation rate is not an inertial-range quantity and a proper inertial-range quantity would be the local energy transfer rate. As a result, Kraichnan's idea attributes the anomaly to variations of the local energy transfer rate. These ideas, generally known as refined similarity hypotheses, can also be extended to study the anomalous scaling of fluctuations of an active scalar, such as the temperature in turbulent convection. We examine the validity of these refined similarity hypotheses and their extensions to an active scalar in shell models of homogeneous turbulence and turbulent convection. We find that Kraichnan's refined similarity hypothesis and its extension are valid.}, }
@article {pmid18850886, year = {2008}, author = {Shukurov, A and Stepanov, R and Sokoloff, D}, title = {Dynamo action in Möbius flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {2 Pt 2}, pages = {025301}, doi = {10.1103/PhysRevE.78.025301}, pmid = {18850886}, issn = {1539-3755}, abstract = {We demonstrate that flows of conducting fluid along a Möbius strip and related surfaces are hydromagnetic dynamos, i.e., they can produce an exponentially growing magnetic field from an infinitesimal seed. The critical magnetic Reynolds number in one of our models is as low as about 16. Together with other attractive features, this makes this flow an interesting candidate for a laboratory dynamo experiment.}, }
@article {pmid18850271, year = {2008}, author = {Zhang, Z and Kleinstreuer, C and Kim, CS}, title = {Airflow and nanoparticle deposition in a 16-generation tracheobronchial airway model.}, journal = {Annals of biomedical engineering}, volume = {36}, number = {12}, pages = {2095-2110}, doi = {10.1007/s10439-008-9583-z}, pmid = {18850271}, issn = {1573-9686}, mesh = {Algorithms ; Bronchi/*physiology ; Computer Simulation ; Humans ; *Models, Biological ; *Nanoparticles ; Particle Size ; *Pulmonary Ventilation ; Reproducibility of Results ; Trachea/*physiology ; }, abstract = {In order to achieve both manageable simulation and local accuracy of airflow and nanoparticle deposition in a representative human tracheobronchial (TB) region, the complex airway network was decomposed into adjustable triple-bifurcation units, spreading axially and laterally. Given Q(in) = 15 and 30 L/min and a realistic inlet velocity profile, the experimentally validated computer simulation model provided some interesting 3-D airflow patterns, i.e., for each TB-unit they depend on the upstream condition, local geometry and local Reynolds number. Directly coupled to the local airflow fields are the convective-diffusive transport and deposition of nanoparticles, i.e., 1 nm < or = d(p) < or = 100 nm. The CFD modeling predictions were compared to experimental observations as well as analytical modeling results. The CFD-simulated TB deposition values agree astonishingly well with analytical modeling results. However, measurable differences can be observed for bifurcation-by-bifurcation deposition fractions obtained with these two different approaches due to the effects of more realistic inlet conditions and geometric features incorporated in the CFD model. Specifically, while the difference between the total TB deposition fraction (DF) is less than 16%, it may be up to 70% for bifurcation-by-bifurcation DFs. In addition, it was found that fully developed flow and uniform nanoparticle concentrations can be assumed beyond generation G12. For nanoparticles with d(p) > 10 nm, the geometric effects, including daughter-branch rotation, are minor. Furthermore, the deposition efficiencies at each individual bifurcation in the TB region can be well correlated as a function of an effective diffusion parameter.}, }
@article {pmid21832623, year = {2008}, author = {Sun, L and Keshoju, K and Xing, H}, title = {Magnetic field mediated nanowire alignment in liquids for nanocomposite synthesis.}, journal = {Nanotechnology}, volume = {19}, number = {40}, pages = {405603}, doi = {10.1088/0957-4484/19/40/405603}, pmid = {21832623}, issn = {0957-4484}, abstract = {The motion of magnetic nanowires can be manipulated by a magnetic field in liquids so that their distribution, alignment and orientation can be effectively controlled. The small dimensions of nanoscale entities result in an extremely low Reynolds number, and a steady state Stokes flow approximation was adopted to analyze the nanowire motion under the influences of applied field. The effects of fluid viscosity and external field on the motion of different sized nanowires were investigated. Polydimethylsiloxane composites with nickel nanowires as reinforcing fillers were synthesized as a demonstration of the effectiveness of magnetic alignment. Anisotropic magnetic properties and mechanical strengthening effects were explored.}, }
@article {pmid18813391, year = {2008}, author = {Rosenfeld, C and Serra, C and Brochon, C and Hadziioannou, G}, title = {Influence of micromixer characteristics on polydispersity index of block copolymers synthesized in continuous flow microreactors.}, journal = {Lab on a chip}, volume = {8}, number = {10}, pages = {1682-1687}, doi = {10.1039/b803885f}, pmid = {18813391}, issn = {1473-0197}, abstract = {The influence of interdigital multilamination micromixer characteristics on monomer conversions, molecular weights and especially on the polydispersity index of block copolymers synthesized continuously in two microtube reactors is investigated. The micromixers are used to mix, before copolymerization, a polymer solution with different viscosities and the second monomer. Different geometries of micromixer (number of microchannels, characteristic lengths) have been studied. It was found that polydispersity indices of the copolymers follow a linear relationship with the Reynolds number in the micromixer, represented by a form factor. Thus, beside the operating conditions (nature of the first block and comonomer flow rate), the choice of the micromixer geometry and dimension is essential to control the copolymerization in terms of molecular weights and polydispersity indices. This linear correlation allows the prediction of copolymer features. It can also be a new method to optimize existing micromixers or design other geometries so that mixing could be more efficient.}, }
@article {pmid18812285, year = {2009}, author = {Kazakidi, A and Sherwin, SJ and Weinberg, PD}, title = {Effect of Reynolds number and flow division on patterns of haemodynamic wall shear stress near branch points in the descending thoracic aorta.}, journal = {Journal of the Royal Society, Interface}, volume = {6}, number = {35}, pages = {539-548}, pmid = {18812285}, issn = {1742-5662}, mesh = {Animals ; Aorta/physiology ; Aorta, Thoracic/*physiology ; Computer Simulation ; *Hemodynamics ; Humans ; Mice ; Models, Cardiovascular ; Rabbits ; *Regional Blood Flow ; Shear Strength ; }, abstract = {Atherosclerotic lesions are non-uniformly distributed at arterial bends and branch sites, suggesting an important role for haemodynamic factors, particularly wall shear stress (WSS), in their development. The pattern of lesions at aortic branch sites depends on age and species. Using computational flow simulations in an idealized model of an intercostal artery emerging perpendicularly from the thoracic aorta, we studied the effects of Reynolds number and flow division under steady conditions. Patterns of flow and WSS were strikingly dependent on these haemodynamic parameters. With increasing Reynolds number, WSS, normalized by the fully developed aortic value, was lowered at the sides of the ostium and increased upstream and downstream of it. Increasing flow into the side branch exacerbated these patterns and gave rise to a reversing flow region downstream of the ostium. Incorporation of more realistic geometric features had only minor effects and patterns of mean WSS under pulsatile conditions were similar to the steady flow results. Aspects of the observed WSS patterns correlate with, and may explain, some but not all of the lesion patterns in human, rabbit and mouse aortas.}, }
@article {pmid18800971, year = {2009}, author = {Sepúlveda, N}, title = {Analysis of methods to estimate spring flows in a karst aquifer.}, journal = {Ground water}, volume = {47}, number = {3}, pages = {337-349}, doi = {10.1111/j.1745-6584.2008.00498.x}, pmid = {18800971}, issn = {1745-6584}, mesh = {Florida ; Geography ; *Models, Theoretical ; United States ; *Water Movements ; *Water Supply ; }, abstract = {Hydraulically and statistically based methods were analyzed to identify the most reliable method to predict spring flows in a karst aquifer. Measured water levels at nearby observation wells, measured spring pool altitudes, and the distance between observation wells and the spring pool were the parameters used to match measured spring flows. Measured spring flows at six Upper Floridan aquifer springs in central Florida were used to assess the reliability of these methods to predict spring flows. Hydraulically based methods involved the application of the Theis, Hantush-Jacob, and Darcy-Weisbach equations, whereas the statistically based methods were the multiple linear regressions and the technology of artificial neural networks (ANNs). Root mean square errors between measured and predicted spring flows using the Darcy-Weisbach method ranged between 5% and 15% of the measured flows, lower than the 7% to 27% range for the Theis or Hantush-Jacob methods. Flows at all springs were estimated to be turbulent based on the Reynolds number derived from the Darcy-Weisbach equation for conduit flow. The multiple linear regression and the Darcy-Weisbach methods had similar spring flow prediction capabilities. The ANNs provided the lowest residuals between measured and predicted spring flows, ranging from 1.6% to 5.3% of the measured flows. The model prediction efficiency criteria also indicated that the ANNs were the most accurate method predicting spring flows in a karst aquifer.}, }
@article {pmid18764367, year = {2008}, author = {Trouilloud, R and Yu, TS and Hosoi, AE and Lauga, E}, title = {Soft swimming: exploiting deformable interfaces for low reynolds number locomotion.}, journal = {Physical review letters}, volume = {101}, number = {4}, pages = {048102}, doi = {10.1103/PhysRevLett.101.048102}, pmid = {18764367}, issn = {0031-9007}, mesh = {Locomotion ; Membranes/chemistry ; *Models, Biological ; *Swimming ; Viscosity ; }, abstract = {Reciprocal movement cannot be used for locomotion at low Reynolds number in an infinite fluid or near a rigid surface. Here we show that this limitation is relaxed for a body performing reciprocal motions near a deformable interface. Using physical arguments and scaling relationships, we show that the nonlinearities arising from reciprocal flow-induced interfacial deformation rectify the periodic motion of the swimmer, leading to locomotion. Such a strategy can be used to move toward, away from, and parallel to any deformable interface as long as the length scales involved are smaller than intrinsic scales, which we identify. A macroscale experiment of flapping motion near a free surface illustrates this new result.}, }
@article {pmid18764053, year = {2008}, author = {Abou El-Azm Aly, A and Nicolleau, F}, title = {Dispersion of heavy particle sets in isotropic turbulence using kinematic simulation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {1 Pt 2}, pages = {016310}, doi = {10.1103/PhysRevE.78.016310}, pmid = {18764053}, issn = {1539-3755}, abstract = {We study the dispersion of heavy particle sets, triangle and tetrahedron, in an isotropic and incompressible three-dimensional turbulent flow. The turbulent velocity field is generated using kinematic simulation, which allows us to vary the inertial range and to reach large values of the Reynolds numbers. We study the time evolution of the parameters characterizing the geometry, the size and shape of the triangle and tetrahedron. The Lagrangian correlations of the sets' size, area or volume, are also studied. Different initial separations between particles, inertial ranges, Stokes numbers, and particle drift velocities are considered. We found that the Reynolds number has no effect on the shape evolution of the triangle and tetrahedron provided that the initial distance between the particles is larger than the Kolmogorov length scale.}, }
@article {pmid18764050, year = {2008}, author = {Guillot, P and Colin, A and Ajdari, A}, title = {Stability of a jet in confined pressure-driven biphasic flows at low Reynolds number in various geometries.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {1 Pt 2}, pages = {016307}, doi = {10.1103/PhysRevE.78.016307}, pmid = {18764050}, issn = {1539-3755}, abstract = {We adress the question of the stability of a confined coflowing jet at low Reynolds number in various geometries. Our study is motivated by recent experiments in microfluidic devices. When immiscible fluids flow in microchannels, either monodisperse droplets or parallel flows are obtained depending upon the flow rate of the aqueous phase and the oil phase. In these experiments, the confining and the shape of the geometry play a fundamental role. In a previous paper [Guillot, Phys. Rev. Lett 99, 104502 (2007)], we analyzed the stability of the jet in the framework of the lubrication approximation at low Reynolds number in a cylindrical geometry, and we related the transition between the droplets regime and the jet regime to the absolute-convective transition of the Rayleigh plateau instability. In this work, the effect of the channel geometry and the jet position within the microfluidic device are discussed. New flow patterns are pointed out. Bidimensional jets are encountered in square and rectangular geometry. Contrary to jets occuring in circular geometry, these two-dimensional jets are absolutely stable. Focusing on situations where the inner fluid is more viscous than the outer one, we evidence a range of parameters where droplets are produced through a blocking and pinching mechanism. In this particular case, the flow is unstable, the growing perturbations are convected upstream. This induces the clogging of the channel by the internal phase and its pinching by the external one. In a future presentation we will give a comparison between this model and experimental data.}, }
@article {pmid18764045, year = {2008}, author = {Rousseaux, G and Kruithof, J and Jenffer, P and Wesfreid, JE}, title = {Oscillation-induced sand ripples in a circular geometry.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {78}, number = {1 Pt 2}, pages = {016302}, doi = {10.1103/PhysRevE.78.016302}, pmid = {18764045}, issn = {1539-3755}, abstract = {This study deals with the observation of sand ripples in a circular geometry under oscillatory flow. We characterize the observed patterns as a function of the excitation parameters. We report the time evolution of the corrugated front invading the flat bed. These experiments reveal unambiguously, because of the gradient of shear stress, the existence of two separated thresholds: one for grain motion and the other for the appearance of ripples. In addition, we display the phase diagram of this instability as a function of the Froude number and a Reynolds number.}, }
@article {pmid18754463, year = {2008}, author = {Trivedi, J and Babadagli, T}, title = {Efficiency analysis of greenhouse gas sequestration during miscible CO2 injection in fractured oil reservoirs.}, journal = {Environmental science &amp; technology}, volume = {42}, number = {15}, pages = {5473-5479}, doi = {10.1021/es703264r}, pmid = {18754463}, issn = {0013-936X}, mesh = {Carbon Dioxide/*analysis/chemistry ; Chemical Industry/*methods ; Diffusion ; *Greenhouse Effect ; Kinetics ; Models, Chemical ; Oils/*analysis ; Solvents/chemistry ; }, abstract = {During CO2 injection into naturally fractured oil reservoirs for enhanced oil recovery, the great portion of oil is recovered by matrix-fracture interaction. Diffusive mass transfer between matrix and fracture controls this process if CO2 is miscible with matrix oil. Oil expelled from matrix is replaced by CO2, and the matrix could be potentially a good storage medium for the long-term. For the cooptimization of the oil recovery and CO2 storage, i.e., maximizing the oil recovery while maximizing the amount of CO2 stored, we propose an efficiency analysis using a dimensionless term defined as the global effectiveness factor. The Biot number and Thiele modulus were incorporated in the development of the global effectiveness factor. Diffusion coefficients and the rate of mass-transfer constants were obtained from our previous finite element modeling study. We first defined and derived the dimensionless groups to be used in the efficiency analysis and then formulated a relationship between the dimensionless groups and the efficiency indicators, i.e., the ratios of total solute (oil) produced to total solvent injected and total solvent stored to total solvent injected. It was shown that the efficiency of the process can be represented by a dimensionless group that consists of well-known dimensionless numbers such as the Reynolds number, the Peclet number, the Sherwood number, and the global effectiveness factor.}, }
@article {pmid18712605, year = {2008}, author = {Xi, J and Longest, PW}, title = {Evaluation of a drift flux model for simulating submicrometer aerosol dynamics in human upper tracheobronchial airways.}, journal = {Annals of biomedical engineering}, volume = {36}, number = {10}, pages = {1714-1734}, doi = {10.1007/s10439-008-9552-6}, pmid = {18712605}, issn = {1573-9686}, mesh = {Aerosols/*pharmacokinetics/toxicity ; Bronchi/anatomy &amp; histology/*physiology ; Humans ; *Inhalation Exposure ; *Models, Biological ; Particle Size ; Particulate Matter/*pharmacokinetics/toxicity ; Pulmonary Ventilation/physiology ; Respiratory Mechanics/*physiology ; Trachea/anatomy &amp; histology/*physiology ; }, abstract = {In this study, a hybrid drift flux velocity correction (DF-VC) model that accounts for both submicrometer particle diffusion and inertia was extended to transient conditions and was tested against existing experimental deposition data measured in a replica cast of the human tracheobronchial (TB) region for laminar and turbulent flow. To evaluate the effectiveness of the DF-VC model, deposition results were compared with a standard chemical species (CS) approach that neglects particle inertia. A numerical model of the TB cast was constructed from CT images and extended from the larynx to approximately the sixth respiratory generation. Experimentally determined inlet and outlet flow conditions were implemented in the computational model to ensure direct comparisons between simulations and measurements for the deposition of 40 and 200 nm particles. A low Reynolds number k-omega turbulence model was employed to resolve the laminar and turbulent flow regimes that coexist in the TB geometry. Interesting flow characteristics were observed due to the presence of the larynx, asymmetrical ventilation, and left-right asymmetry, which created a right-skewed laryngeal jet and flow reversal in the trachea that persist over a majority of the transient flow cycle. In comparison with the CS model, deposition results of the DF-VC approach persistently agreed better with experimental findings on a total and sub-branch basis, which indicated that the DF-VC model effectively captured the influence of finite particle inertia. For the submicrometer aerosols considered, transient flows were observed to increase deposition arising from impaction and decrease deposition arising from diffusion on a total and segmental basis compared with steady state conditions. However, the maximum deposition enhancement factor was significantly increased under transient conditions for both 40 nm (factor of 2) and 200 nm (factor of 7) aerosols. Results of this study indicate that a drift flux particle transport model with near-wall velocity corrections can provide an effective continuous-field approach for simulating the transport and deposition of submicrometer respiratory aerosols in human upper TB airways.}, }
@article {pmid18681626, year = {2008}, author = {Ekiel-Jezewska, ML and Sadlej, K and Wajnryb, E}, title = {Friction of rodlike particles adsorbed to a planar surface in shear flow.}, journal = {The Journal of chemical physics}, volume = {129}, number = {4}, pages = {041104}, doi = {10.1063/1.2957492}, pmid = {18681626}, issn = {1089-7690}, abstract = {A planar hard surface covered with elongated stiff rodlike particles in shear flow is considered in the low-Reynolds-number regime assuming low particle surface coverage. The particles are modeled as straight chains of spherical beads. Multipole expansion of the Stokes equations (the accurate HYDROMULTIPOLE algorithm) is applied to evaluate the hydrodynamic force exerted by the fluid on the rodlike particles, depending on their shape, i.e., on the number of beads and their orientation with respect to the wall and to the ambient shear flow.}, }
@article {pmid18681605, year = {2008}, author = {Park, JB and Mongeau, L}, title = {Experimental investigation of the influence of a posterior gap on glottal flow and sound.}, journal = {The Journal of the Acoustical Society of America}, volume = {124}, number = {2}, pages = {1171-1179}, doi = {10.1121/1.2945116}, pmid = {18681605}, issn = {1520-8524}, mesh = {Glottis/*anatomy &amp; histology/*physiology ; Humans ; *Models, Anatomic ; *Models, Biological ; Oscillometry ; *Phonation ; Pressure ; Rheology ; Speech Acoustics ; Time Factors ; Vocal Cords/anatomy &amp; histology/physiology ; Voice Quality ; }, abstract = {The influence of a posterior gap on the airflow through the human glottis was investigated using a driven synthetic model. Instantaneous orifice discharge coefficient of a glottal shaped orifice was obtained from the time-varying orifice area and the velocity distribution of the pulsated jet measured on the axial plane using a single hot-wire probe. Instantaneous orifice discharge coefficient values were found to undergo a cyclic hysteresis loop when plotted versus Reynolds number and time, indicating a pressure head increase and a net energy transfer from the air flow to the orifice wall. The net energy transferred was estimated to be around 10% of the value presumably required to achieve self-sustained oscillation. The radiated sound pressure was measured to characterize the influence of the minimum flow through the posterior gap on the broadband component of the radiated sound. The presence of a posterior gap was found to significantly increase the broadband sound level produced over the frequency range in which human hearing is most sensitive.}, }
@article {pmid18675985, year = {2008}, author = {Duffadar, RD and Davis, JM}, title = {Dynamic adhesion behavior of micrometer-scale particles flowing over patchy surfaces with nanoscale electrostatic heterogeneity.}, journal = {Journal of colloid and interface science}, volume = {326}, number = {1}, pages = {18-27}, doi = {10.1016/j.jcis.2008.07.004}, pmid = {18675985}, issn = {1095-7103}, abstract = {The dynamic adhesion behavior of micrometer-scale silica particles is investigated numerically for a low Reynolds number shear flow over a planar collecting wall with randomly distributed electrostatic heterogeneity at the 10-nanometer scale. The hydrodynamic forces and torques on a particle are coupled to spatially varying colloidal interactions between the particle and wall. Contact and frictional forces are included in the force and torque balances to capture particle skipping, rolling, and arrest. These dynamic adhesion signatures are consistent with experimental results and are reminiscent of motion signatures observed in cell adhesion under flowing conditions, although for the synthetic system the particle-wall interactions are controlled by colloidal forces rather than physical bonds between cells and a functionalized surface. As the fraction of the surface (Theta) covered by the cationic patches is increased from zero, particle behavior sequentially transitions from no contact with the surface to skipping, rolling, and arrest, with the threshold patch density for adhesion (Theta(crit)) always greater than zero and in quantitative agreement with experimental results. The ionic strength of the flowing solution determines the extent of the electrostatic interactions and can be used to tune selectively the dynamic adhesion behavior by modulating two competing effects. The extent of electrostatic interactions in the plane of the wall, or electrostatic zone of influence, governs the importance of spatial fluctuations in the cationic patch density and thus determines if flowing particles contact the wall. The distance these interactions extend into solution normal to the wall determines the strength of the particle-wall attraction, which governs the transition from skipping and rolling to arrest. The influence of Theta, particle size, Debye length, and shear rate is quantified through the construction of adhesion regime diagrams, which delineate the regions in parameter space that give rise to different dynamic adhesion signatures and illustrate selective adhesion based on particle size or curvature. The results of this study are suggestive of novel ways to control particle-wall interactions using randomly distributed surface heterogeneity.}, }
@article {pmid18667205, year = {2008}, author = {Luo, HY and Liu, Y}, title = {Modeling the bifurcating flow in a CT-scanned human lung airway.}, journal = {Journal of biomechanics}, volume = {41}, number = {12}, pages = {2681-2688}, doi = {10.1016/j.jbiomech.2008.06.018}, pmid = {18667205}, issn = {0021-9290}, mesh = {Bronchi/*physiology ; Bronchography/*methods ; Computer Simulation ; Humans ; Male ; Middle Aged ; *Models, Biological ; Pulmonary Ventilation/*physiology ; Respiratory Mechanics/*physiology ; Rheology/*methods ; Tomography, X-Ray Computed/*methods ; }, abstract = {The inspiratory flow characteristics in a CT-scanned human lung model were numerically investigated using low Reynolds number (LRN) kappa-omega turbulent model. The five-generation airway is extracted from the trachea to segmental bronchi of a 60-year-old Chinese male patient. Computations were carried out in the Reynolds number range of 900-2100, corresponding to mouth-air breathing rates of 190-440 ml/s. Flow patterns on the Re=2100 and flow rate distribution were presented. In this model, the flow pattern is very complex. To count the effect of laryngeal jet on trachea inlet, the trachea was extended and modified to simulate the larynx, consequently the inlet velocity profile is biased towards the rear wall. In the inferior lobar bronchi, there are two stems in which the axial velocity is stronger but secondary velocity is weaker. Secondary flow in the lateral bronchi is stronger than the medial ones. With increasing Re, the air flow increases in the middle, inferior lobes and left main bronchus, i.e., flow biases to left and downward.}, }
@article {pmid18663613, year = {2009}, author = {Mayeed, MS and Al-Mekhnaqi, AM and Auner, GW and Newaz, GM}, title = {A surface accumulator of Escherichia coli in water flow.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {12}, number = {1}, pages = {109-112}, doi = {10.1080/10255840903077394}, pmid = {18663613}, issn = {1025-5842}, mesh = {Acoustics/instrumentation ; Biosensing Techniques/*instrumentation/methods ; Colony Count, Microbial/*instrumentation/methods ; Computer Simulation ; Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Escherichia coli/*isolation &amp; purification/physiology ; Flow Cytometry/*instrumentation/methods ; Microfluidic Analytical Techniques/*instrumentation/methods ; Models, Biological ; Ultrafiltration/*instrumentation/methods ; *Water Microbiology ; Water Movements ; }, abstract = {The objective of this research is to design and optimise a mini/micro-channel based surface accumulator of Escherichia coli to be detected by acoustic wave biosensors. A computational research has been carried out using the state of the art software, CFD-ACE with water as bacteria bearing fluid. E. coli bacteria have been modelled as random discrete particles tracked by solving the Lagrangian equations. The design challenges are to achieve low shear force (pico-N), high concentration at accumulation and high enough Reynolds number to avoid bacteria swimming. A range of low Reynolds number (Re) from 28.2 to 58.3 has been considered along with the effects of particle-boundary interactions, gravity, Saffman lift and Magnus lift. About four orders of magnitude higher concentration at accumulation than the inlet concentration and lower shear force in the order of less than pico-N have been achieved in the optimised design with particles accumulating at a specific location under random particle-boundary interactions.}, }
@article {pmid18646956, year = {2008}, author = {Bae, Y and Moon, YJ}, title = {Aerodynamic sound generation of flapping wing.}, journal = {The Journal of the Acoustical Society of America}, volume = {124}, number = {1}, pages = {72-81}, doi = {10.1121/1.2932340}, pmid = {18646956}, issn = {1520-8524}, abstract = {The unsteady flow and acoustic characteristics of the flapping wing are numerically investigated for a two-dimensional model of Bombus terrestris bumblebee at hovering and forward flight conditions. The Reynolds number Re, based on the maximum translational velocity of the wing and the chord length, is 8800 and the Mach number M is 0.0485. The computational results show that the flapping wing sound is generated by two different sound generation mechanisms. A primary dipole tone is generated at wing beat frequency by the transverse motion of the wing, while other higher frequency dipole tones are produced via vortex edge scattering during a tangential motion. It is also found that the primary tone is directional because of the torsional angle in wing motion. These features are only distinct for hovering, while in forward flight condition, the wing-vortex interaction becomes more prominent due to the free stream effect. Thereby, the sound pressure level spectrum is more broadband at higher frequencies and the frequency compositions become similar in all directions.}, }
@article {pmid18643199, year = {2008}, author = {Esmael, A and Nouar, C}, title = {Transitional flow of a yield-stress fluid in a pipe: evidence of a robust coherent structure.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {5 Pt 2}, pages = {057302}, doi = {10.1103/PhysRevE.77.057302}, pmid = {18643199}, issn = {1539-3755}, abstract = {In two independent articles, Escudier and Presti [J. Non-Newtonian Fluid Mech. 62, 291 (1996)] and Peixinho [J. Non-Newtonian Fluid Mech. 128, 172 (2005)] studied experimentally the flow structure of a yield stress fluid in a cylindrical pipe. It was observed that the mean, i.e., time-averaged, velocity profiles were axisymmetric in the laminar and turbulent regimes, and presented an increasing asymmetry with increasing Reynolds number in the transitional regime. The present paper provides a three-dimensional description of this asymmetry from axial velocity profiles measurements at three axial positions and different azimuthal positions. The observed transitional flow suggests the existence of a robust nonlinear coherent structure characterized by two weakly modulated counter-rotating longitudinal vortices. This new state mediates the transition between laminar and turbulent flow.}, }
@article {pmid18643198, year = {2008}, author = {Chupin, A and Stepanov, R}, title = {Full perturbation solution for the flow in a rotating torus.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {5 Pt 2}, pages = {057301}, doi = {10.1103/PhysRevE.77.057301}, pmid = {18643198}, issn = {1539-3755}, abstract = {We present a perturbation solution for a pressure-driven fluid flow in a rotating toroidal channel. The analysis shows the difference between the solutions of full and simplified equations studied earlier. The result is found to be reliable for low Reynolds number (Re), as was the case for a previously studied solution for high Re. The convergence conditions are defined for the whole range of governing parameters. The viscous flow exhibits some interesting features in flow pattern and hydrodynamic characteristics.}, }
@article {pmid18643191, year = {2008}, author = {Latt, J and Chopard, B and Malaspinas, O and Deville, M and Michler, A}, title = {Straight velocity boundaries in the lattice Boltzmann method.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {5 Pt 2}, pages = {056703}, doi = {10.1103/PhysRevE.77.056703}, pmid = {18643191}, issn = {1539-3755}, abstract = {Various ways of implementing boundary conditions for the numerical solution of the Navier-Stokes equations by a lattice Boltzmann method are discussed. Five commonly adopted approaches are reviewed, analyzed, and compared, including local and nonlocal methods. The discussion is restricted to velocity Dirichlet boundary conditions, and to straight on-lattice boundaries which are aligned with the horizontal and vertical lattice directions. The boundary conditions are first inspected analytically by applying systematically the results of a multiscale analysis to boundary nodes. This procedure makes it possible to compare boundary conditions on an equal footing, although they were originally derived from very different principles. It is concluded that all five boundary conditions exhibit second-order accuracy, consistent with the accuracy of the lattice Boltzmann method. The five methods are then compared numerically for accuracy and stability through benchmarks of two-dimensional and three-dimensional flows. None of the methods is found to be throughout superior to the others. Instead, the choice of a best boundary condition depends on the flow geometry, and on the desired trade-off between accuracy and stability. From the findings of the benchmarks, the boundary conditions can be classified into two major groups. The first group comprehends boundary conditions that preserve the information streaming from the bulk into boundary nodes and complete the missing information through closure relations. Boundary conditions in this group are found to be exceptionally accurate at low Reynolds number. Boundary conditions of the second group replace all variables on boundary nodes by new values. They exhibit generally much better numerical stability and are therefore dedicated for use in high Reynolds number flows.}, }
@article {pmid18643169, year = {2008}, author = {Twardos, MJ and Arratia, PE and Rivera, MK and Voth, GA and Gollub, JP and Ecke, RE}, title = {Stretching fields and mixing near the transition to nonperiodic two-dimensional flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {5 Pt 2}, pages = {056315}, doi = {10.1103/PhysRevE.77.056315}, pmid = {18643169}, issn = {1539-3755}, abstract = {Although time-periodic fluid flows sometimes produce mixing via Lagrangian chaos, the additional contribution to mixing caused by nonperiodicity has not been quantified experimentally. Here, we do so for a quasi-two-dimensional flow generated by electromagnetic forcing. Several distinct measures of mixing are found to vary continuously with the Reynolds number, with no evident change in magnitude or slope at the onset of nonperiodicity. Furthermore, the scaled probability distributions of the mean Lyapunov exponent have the same form in the periodic and nonperiodic flow states.}, }
@article {pmid18643168, year = {2008}, author = {Liu, W}, title = {Magnetized Ekman layer and Stewartson layer in a magnetized Taylor-Couette flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {5 Pt 2}, pages = {056314}, doi = {10.1103/PhysRevE.77.056314}, pmid = {18643168}, issn = {1539-3755}, abstract = {In this paper we present axisymmetric nonlinear simulations of magnetized Ekman and Stewartson layers in a magnetized Taylor-Couette flow with a centrifugally stable angular-momentum profile and with a magnetic Reynolds number below the threshold of magnetorotational instability. The magnetic field is found to inhibit the Ekman suction. The width of the Ekman layer is reduced with increased magnetic field normal to the end plate. A uniformly rotating region forms near the outer cylinder. A strong magnetic field leads to a steady Stewartson layer emanating from the junction between differentially rotating rings at the endcaps. The Stewartson layer becomes thinner with larger Reynolds number and penetrates deeper into the bulk flow with stronger magnetic field and larger Reynolds number. However, at Reynolds number larger than a critical value approximately 600 , axisymmetric, and perhaps also nonaxisymmetric, instabilities occur and result in a less prominent Stewartson layer that extends less far from the boundary.}, }
@article {pmid18643162, year = {2008}, author = {Alexakis, A and Ponty, Y}, title = {Effect of the Lorentz force on on-off dynamo intermittency.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {5 Pt 2}, pages = {056308}, doi = {10.1103/PhysRevE.77.056308}, pmid = {18643162}, issn = {1539-3755}, abstract = {An investigation of the dynamo instability close to the threshold produced by an ABC forced flow is presented. We focus on the on-off intermittency behavior of the dynamo and the countereffect of the Lorentz force in the nonlinear stage of the dynamo. The Lorentz force drastically alters the statistics of the turbulent fluctuations of the flow and reduces their amplitude. As a result, much longer bursts (on phases) are observed than is expected based on the amplitude of the fluctuations in the kinematic regime of the dynamo. For large Reynolds numbers, the duration time of the on phase follows a power law distribution, while for smaller Reynolds numbers the Lorentz force completely kills the noise and the system transits from a chaotic state into a laminar time periodic flow. The behavior of the on-off intermittency as the Reynolds number is increased is also examined. The connections with dynamo experiments and theoretical modeling are discussed.}, }
@article {pmid18643123, year = {2008}, author = {Willmott, G}, title = {Dynamics of a sphere with inhomogeneous slip boundary conditions in Stokes flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {5 Pt 2}, pages = {055302}, doi = {10.1103/PhysRevE.77.055302}, pmid = {18643123}, issn = {1539-3755}, abstract = {The dynamic resistance of a sphere with a general inhomogeneous slip boundary condition is analyzed in Newtonian unbounded uniform flow at low Reynolds number. The boundary condition is treated as a perturbation to a homogeneous sphere, assuming that the slip length magnitude b is much smaller than the sphere radius a . To first order, the effect of inhomogeneous slip is the same as that of a radial deformity of magnitude b . Full resistance tensors are presented and the dynamics of a hemispherical inhomogeneous sphere, such as a Janus particle, are explicitly calculated.}, }
@article {pmid18642340, year = {1997}, author = {Stoodley, P and Yang, S and Lappin-Scott, H and Lewandowski, Z}, title = {Relationship between mass transfer coefficient and liquid flow velocity in heterogenous biofilms using microelectrodes and confocal microscopy.}, journal = {Biotechnology and bioengineering}, volume = {56}, number = {6}, pages = {681-688}, doi = {10.1002/(SICI)1097-0290(19971220)56:6&lt;681::AID-BIT11&gt;3.0.CO;2-B}, pmid = {18642340}, issn = {0006-3592}, abstract = {The relationship between local mass transfer coefficient and fluid velocity in heterogenous biofilms was investigated by combining microelectrodes and confocal scanning laser microscopy (CSLM). The biofilms were grown for up to 7 days and consisted of cell clusters separated by interstitial channels. Mass transfer coefficient depth profiles were measured at specific locations in the cell clusters and channels at average flow velocities of 2.3 and 4.0 cm/s. Liquid flow velocity profiles were measured in the same locations using a particle tracking technique. The velocity profiles showed that flow in the open channel was laminar. There was no flow at the top surface of the biofilm cell clusters but the mass transfer coefficient was 0.01 cm/s. At the same depth in a biofilm channel, the flow velocity was 0.3 cm/s and the mass transfer coefficient was 0.017 cm/s. The mass transfer coefficient profiles in the channels were not influenced by the surrounding cell clusters. Local flow velocities were correlated with local mass transfer coefficients using a semi-theoretical mass transfer equation. The relationship between the Sherwood number (Sh,) the Reynolds number (Re,) and the Schmidt number (Sc) was found using the experimental data to find the dimensionless empirical constants (n1, n2, and m) in the equation Sh = n(1) + n(2)Re(m) Sc(1/3). The values of the constants ranged from 1.45 to 2.0 for n(1), 0.22 to 0.28 for n(2), and 0.21 to 0.60 for m. These values were similar to literature values for mass transfer in porous media. The Sherwood number for the entire flow cell was 10 when the bulk flow velocity was 2.3 cm/s and 11 when the bulk flow velocity was 4.0 cm/s. (c) 1997 John Wiley &amp; Sons, Inc. Biotechnol Bioeng 56: 681-688, 1997.}, }
@article {pmid18614172, year = {2008}, author = {Freitas, RK and Schröder, W}, title = {Numerical investigation of the three-dimensional flow in a human lung model.}, journal = {Journal of biomechanics}, volume = {41}, number = {11}, pages = {2446-2457}, doi = {10.1016/j.jbiomech.2008.05.016}, pmid = {18614172}, issn = {0021-9290}, mesh = {Artificial Organs ; Biomechanical Phenomena ; Humans ; Imaging, Three-Dimensional ; Lung/*physiology ; *Models, Biological ; Silicon ; }, abstract = {The flow field at inspiration and expiration in the upper human airways consisting of the trachea down to the sixth generation of the bronchial tree is numerically simulated. The three-dimensional steady flow at a hydraulic diameter-based Reynolds number Re(D)=1250 is computed via a lattice-Boltzmann method (LBM). The simulation is validated by the experimental data based on particle-image velocimetry (PIV) measurements. The good agreement between numerical and experimental results is evidenced by comparing velocity contours and distributions in a defined reference plane. The results show the LBM to be an accurate tool to numerically predict flow structures in the human lung. Using an automatic Cartesian grid generator, the overall process time from meshing to a steady-state solution is <12h. Moreover, the numerical simulation allows a closer analysis of the secondary flow structures than in the experimental investigation. The three-dimensional streamline patterns reveal some insight on the air exchange mechanism at inspiration and expiration. At inspiration, the slower near-wall tracheal flow enters through the right principal bronchus into the right upper lobar bronchus. The bulk mass flux in the trachea is nearly evenly distributed over the left upper, center and lower lobar bronchi and the right center and lower bronchi. At expiration, the air from the right upper lobar bronchus enters the right center of the trachea and displaces the airflow from the lower and center right bronchi such that the tracheal positions of the streamlines at inspiration and expiration are switched. The flow in the left bronchi does not show this kind of switching. The findings emphasize the impact of the asymmetry of the lung geometry on the respiratory air exchange mechanism.}, }
@article {pmid21694272, year = {2008}, author = {Korlie, MS and Mukherjee, A and Nita, BG and Stevens, JG and Trubatch, AD and Yecko, P}, title = {Modeling bubbles and droplets in magnetic fluids.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {20}, number = {20}, pages = {204143}, doi = {10.1088/0953-8984/20/20/204143}, pmid = {21694272}, issn = {0953-8984}, abstract = {We develop, test and apply a volume of fluid (VOF) type code for the direct numerical simulation of two-fluid configurations of magnetic fluids with dynamic interfaces. Equilibrium magnetization and linear magnetic material are assumed and uniform imposed magnetic fields are considered, although extensions to nonlinear materials and to fields with spatio-temporal variability are possible. Models are computed for configurations of bubbles of non-magnetic fluid rising in ferrofluid and droplets of ferrofluid falling through non-magnetic fluid. Bubbles and droplets exhibit similar changes of shape in the presence of vertical fields, due to a combination of elongation along the field lines and the fluid dynamics of ordinary rising or falling at small Bond number. Bubbles become more prolate than droplets under the same parameters and are accordingly found to break up more readily than droplets in stronger fields. Indirect effects are observed, such as the change in rise time and the consequent changes in the flow due to increased Reynolds number.}, }
@article {pmid21694258, year = {2008}, author = {Cunha, FR and Couto, HL}, title = {Transverse gradient diffusion in a polydisperse dilute suspension of magnetic spheres during sedimentation.}, journal = {Journal of physics. Condensed matter : an Institute of Physics journal}, volume = {20}, number = {20}, pages = {204129}, doi = {10.1088/0953-8984/20/20/204129}, pmid = {21694258}, issn = {0953-8984}, abstract = {In this work we investigate the pair interaction of magnetic particles in a dilute polydisperse sedimenting suspension. The suspension is composed of magnetic spherical forms of different radii and densities immersed in a Newtonian fluid, settling due to the gravity. When in close contact, the particles may exert on each other a magnetic force due to a permanent magnetization. We restrict our attention to dispersions of micromagnetic composite with negligible Brownian motion. The calculations of the relative particle trajectories are based on direct computations of the hydrodynamic interactions among rigid spheres in the regime of low particle Reynolds number. Depending on the relative importance of the interparticle forces and gravity, the collisions may result in aggregation or simply in a breaking of the particle relative trajectory time reversibility. After summing over all possible encounters, the transverse self-diffusion and down-gradient diffusion coefficients that describe the cross-flow migration of the particles are calculated. Our calculation shows first evidence and the significance of the diffusion process arising from magnetic interactions in dilute non-Brownian suspensions.}, }
@article {pmid19746195, year = {2008}, author = {Buchholz, JH and Smits, AJ}, title = {The wake structure and thrust performance of a rigid low-aspect-ratio pitching panel.}, journal = {Journal of fluid mechanics}, volume = {603}, number = {}, pages = {331-365}, pmid = {19746195}, issn = {0022-1120}, support = {R01 NS054271/NS/NINDS NIH HHS/United States ; R01 NS054271-01/NS/NINDS NIH HHS/United States ; }, abstract = {Thrust performance and wake structure were investigated for a rigid rectangular panel pitching about its leading edge in a free stream. For Re(C) = O(10(4)), thrust coefficient was found to depend primarily on Strouhal number St and the aspect ratio of the panel AR. Propulsive efficiency was sensitive to aspect ratio only for AR less than 0.83; however, the magnitude of the peak efficiency of a given panel with variation in Strouhal number varied inversely with the amplitude to span ratio A/S, while the Strouhal number of optimum efficiency increased with increasing A/S. Peak efficiencies between 9 % and 21 % were measured. Wake structures corresponding to a subset of the thrust measurements were investigated using dye visualization and digital particle image velocimetry. In general, the wakes divided into two oblique jets; however, when operating at or near peak efficiency, the near wake in many cases represented a Kármán vortex street with the signs of the vortices reversed. The three-dimensional structure of the wakes was investigated in detail for AR = 0.54, A/S = 0.31 and Re(C) = 640. Three distinct wake structures were observed with variation in Strouhal number. For approximately 0.20 < St < 0.25, the main constituent of the wake was a horseshoe vortex shed by the tips and trailing edge of the panel. Streamwise variation in the circulation of the streamwise horseshoe legs was consistent with a spanwise shear layer bridging them. For St > 0.25, a reorganization of some of the spanwise vorticity yielded a bifurcating wake formed by trains of vortex rings connected to the tips of the horseshoes. For St > 0.5, an additional structure formed from a perturbation of the streamwise leg which caused a spanwise expansion. The wake model paradigm established here is robust with variation in Reynolds number and is consistent with structures observed for a wide variety of unsteady flows. Movies are available with the online version of the paper.}, }
@article {pmid20569602, year = {2006}, author = {Konishi, Y and Fukasaku, K and Kobori, T and Takakura, Y and Arai, N and Yazaki, H and Shiokawa, Y}, title = {Flow in a tube with an aneurysmal sac: effect of aneurysm and stent.}, journal = {Interventional neuroradiology : journal of peritherapeutic neuroradiology, surgical procedures and related neurosciences}, volume = {12}, number = {Suppl 1}, pages = {53-56}, pmid = {20569602}, issn = {1591-0199}, abstract = {Ruptured saccular aneurysms were severe condition for intracerebral Condition. And the cause for their rupture is not yet clear. In this study (I), since the configurations of aneurysms are considered to be a factor for the rupture of aneurysms, several shapes has been modeled using Aspect ratio AR and inclination angle of saccular aneurysms. In vitro the parametric study has been conducted on the range of Reynolds Number in human blood flow for aneurismal models of AR=2.1 and 1.3 and q=90 degrees and 70 degrees , As results, it was con firme d that there are characteristic flow patterns with Reynolds Number, And that the aneurismal configuration has effects on the shear stress and pressure losses. II) The object of this paper is to study the effects of STENTS.We made the model of aneurysm and performed in vitro study in range of Reynolds number of human blood flows using three kinds of STENTS. As results, it was confirmed that flow pattern and pressure loss changes with the kinds of STENTS. This study aims the accumulation of data to predict the hazard of aneurysmal rupture by their shapes and STENTS.}, }
@article {pmid21680386, year = {2002}, author = {Daniel, TL and Combes, SA}, title = {Flexible wings and fins: bending by inertial or fluid-dynamic forces?.}, journal = {Integrative and comparative biology}, volume = {42}, number = {5}, pages = {1044-1049}, doi = {10.1093/icb/42.5.1044}, pmid = {21680386}, issn = {1540-7063}, abstract = {Flapping flight and swimming in many organisms is accompanied by significant bending of flexible wings and fins. The instantaneous shape of wings and fins has, in turn, a profound effect on the fluid dynamic forces they can generate, with non-monotonic relationships between the pattern of deformation waves passing along the wing and the thrust developed. Many of these deformations arise, in part, from the passive mechanics of oscillating a flexible air- or hydrofoil. At the same time, however, their instantaneous shape may well emerge from details of the fluid loading. This issue-the extent to which there is feedback between the instantaneous wing shape and the fluid dynamic loading-is core to understanding flight control. We ask to what extent surface shape of wings and fins is controlled by structural mechanics versus fluid dynamic loading. To address this issue, we use a combination of computational and analytic methods to explore how bending stresses arising from inertial-elastic mechanisms compare to those stresses that arise from fluid pressure forces. Our analyses suggest that for certain combinations of wing stiffness, wing motions, and fluid density, fluid pressure stresses play a relatively minor role in determining wing shape. Nearly all of these combinations correspond to wings moving in air. The exciting feature provided by this analysis is that, for high Reynolds number motions where linear potential flow equations provide reasonable estimates of lift and thrust, we can finally examine how wing structure affects flight performance. Armed with this approach, we then show how modest levels of passive elasticity can affect thrust for a given level of energy input in the form of an inertial oscillation of a compliant foil.}, }
@article {pmid21708714, year = {2002}, author = {Hernández, LP and Barresi, MJ and Devoto, SH}, title = {Functional morphology and developmental biology of zebrafish: reciprocal illumination from an unlikely couple.}, journal = {Integrative and comparative biology}, volume = {42}, number = {2}, pages = {222-231}, doi = {10.1093/icb/42.2.222}, pmid = {21708714}, issn = {1540-7063}, abstract = {Functional morphology has benefited greatly from the input of techniques and thinking from other disciplines. This has been especially productive in situations where each discipline has made significant contributions to a particular research topic. A combination of methodologies from functional morphology and developmental biology has allowed us to characterize feeding mechanics of first-feeding larval zebrafish (Danio rerio). Contrary to kinematic patterns commonly seen in adult teleosts, larval zebrafish showed no lateral abduction during the expansive phase of a suction-feeding event. Instead, dorsoventral expansion of the buccal chamber, more typical of patterns seen in primitive fishes, characterized the expansive phase. Moreover, a pronounced preparatory phase during which the buccal chamber is constricted by the protractor hyoideus was consistently seen in first-feeding larval kinematics. Key kinematic variables associated with first feeding correlated significantly with the hydrodynamic regime as measured by the Reynolds number. Using the tools of both functional morphology and developmental biology we have not only determined which cranial muscles are important for successful feeding but also uncovered important physiological differences in muscle structure. Muscles necessary for the rapid dorsoventral expansion of the head are composed primarily of fast-twitch fibers while those involved in more tonic contractions such as hyoid protraction have more slow-twitch muscle fibers. While most evolutionary developmental studies have examined mechanisms responsible for large evolutionary changes in morphology, we propose that the type of data uncovered in functional studies can lead to the generation of hypotheses concerning the developmental mechanisms responsible for smaller intra- and/or interspecific changes.}, }
@article {pmid23345732, year = {2001}, author = {Ramadan, QM and Hamid, O and Lim, KO}, title = {Steady flow visualization in a rigid model of the aortic bifurcation: application to atherosclerosis.}, journal = {Journal of biological physics}, volume = {27}, number = {1}, pages = {35-57}, pmid = {23345732}, issn = {0092-0606}, abstract = {Hemodynamics have long been implicated in atherogenesis. The studiesreported here seek to explain the mechanisms for the formation ofatherosclerotic plaque in an aortic bifurcation. Flow studies were made ina model constructed from plexiglass to represent an aortic bifurcation. Under steady flow conditions at inflow Reynolds numbers of 80-1250,the streamline flow patterns and the boundary layer separation zones wereinvestigated in relation to the location of atherosclerotic plaques clinicallyfound at regions in the human aortic bifurcation. The streamline flowswere visualized by a slow injection of dye over the cross section of the tubeentrance and along the tube walls. The studies revealed a complex flowfield where secondary flows, induced by the centrifugal and viscous forces,cause the fluid to move towards the inner walls of the aortic bifurcation. The effect was more clearly seen with increasing Reynolds number. Boundary layer separation zones were observed to occur at the outercorners of the branching. The nature of the separation zone formed wasfound to be dependent on Reynolds number. The residence time of fluidparticles within such a separation zone was estimated by measuring thewashout time of a bolus of dye injected at strategic locations along the tubewalls. The residence time was found to decrease exponentially withincreasing Reynolds number. These observations provide strong support forthe role of flow separation in the accumulation of LDL and plateletaggregation within the aortic bifurcation.}, }
@article {pmid20336175, year = {2000}, author = {Loosmore, GA and Hunt, JR}, title = {Dust resuspension without saltation.}, journal = {Journal of geophysical research}, volume = {105}, number = {D16}, pages = {20663-20672}, pmid = {20336175}, issn = {0148-0227}, support = {P42 ES004705/ES/NIEHS NIH HHS/United States ; P42 ES004705-180026/ES/NIEHS NIH HHS/United States ; }, abstract = {Wind resuspension (or entrainment) provides a source of dust and contaminants for the atmosphere. Conventional wind erosion models parameterize dust resuspension flux with a threshold velocity or with a horizontal abrasion flux; in the absence of abrasion the models assume dust flux is transient only. Our experiments with an uncrusted, fine material at relative humidities exceeding 40% show a long-term steady dust flux in the absence of abrasion, which fits the approximate form: F(d) = 3.6(u*)(3), where F(d) is the dust flux (in mug/m(2) s), and u* is the friction velocity (in m/s). These fluxes are generally too small to be significant sources of dust in most models of dust emission. However, they provide a potential route to transport contaminants into the atmosphere. In addition, dust release is substantial during the initial transient phase. Comparison with field data suggests that the particle friction Reynolds number may prove a better parameter than u* for correlating fluxes and understanding the potential for abrasion.}, }
@article {pmid21182690, year = {1998}, author = {Kerr, CJ and Osborn, KS and Robson, GD and Handley, PS}, title = {The relationship between pipe material and biofilm formation in a laboratory model system.}, journal = {Journal of applied microbiology}, volume = {85 Suppl 1}, number = {}, pages = {29S-38S}, doi = {10.1111/j.1365-2672.1998.tb05280.x}, pmid = {21182690}, issn = {1365-2672}, mesh = {Bacteria/growth &amp; development/isolation &amp; purification ; *Bacterial Physiological Phenomena ; *Biofilms/drug effects ; Chlorine/pharmacology ; Colony Count, Microbial ; Disinfectants/pharmacology ; Iron ; Manufactured Materials/*microbiology ; Polyethylene ; Polyvinyl Chloride ; Temperature ; Time Factors ; *Water Microbiology ; Water Supply/*standards ; }, abstract = {The aim of this study was to compare biofilm accumulation and heterotrophic bacterial diversity on three pipe materials-cast iron, medium density polyethylene (MDPE), and unplasticised polyvinyl chloride (uPVC) - using a laboratory model system run over a short period (21 d) and a longer period (7 months). Newly Modified Robbins Devices (nMRD) were run in parallel, each containing 25 discs of one material with cold tap water flowing through the devices at 3 ml min(-1) (Reynolds Number 9.05) for 21 d. The numbers of bacteria on each material increased exponentially between 0 and 11 d when the biofilm viable count remained constant. The mean doubling times of the heterotrophic population on the materials during the exponential phase was 13.2 h for cast iron and 15.6 h for MDPE and uPVC. The same experiment was repeated under different environmental conditions with a lower temperature, higher free chlorine and lower number of organisms ml(-1) of incoming water. The exponential phase lengthened to 16 d but the steady state count remained the same. The mean viable count after 21 d and after 7 months was on average 97% higher on cast iron than on the other materials. Very few different colony types were isolated from each material with the largest number (nine) recovered from cast iron. The numbers of planktonic bacteria in the effluent water leaving each of the nMRDs directly correlated with the numbers in the biofilm phase on each of the materials. In addition the distribution and thickness of the biofilms on the MDPE and uPVC were observed using confocal scanning laser microscopy. In conclusion, MDPE and uPVC support the lowest numbers of bacteria in a steady state biofilm in the short term (21 d) and over a longer term (7 months). The diversity of heterotrophic bacteria was greatest on cast iron.}, }
@article {pmid18636572, year = {1997}, author = {Goldstein, AS and Dimilla, PA}, title = {Application of fluid mechanic and kinetic models to characterize mammalian cell detachment in a radial-flow chamber.}, journal = {Biotechnology and bioengineering}, volume = {55}, number = {4}, pages = {616-629}, doi = {10.1002/(SICI)1097-0290(19970820)55:4&lt;616::AID-BIT4&gt;3.0.CO;2-K}, pmid = {18636572}, issn = {0006-3592}, abstract = {The strength of adhesion and dynamics of detachment of murine 3T3 fibroblasts from self-assembled monolayers were measured in a radial-flow chamber (RFC) by applying models for fluid mechanics, adhesion strength probability distributions, and detachment kinetics. Four models for predicting fluid mechanics in a RFC were compared to evaluate the accuracy of each model and the significance of inlet effects. Analysis of these models indicated an outer region at large radial positions consistent with creeping flow, an intermediate region influenced by inertial dampening, and an inner region dominated by entrance effects from the axially-oriented inlet. In accompanying experiments patterns of the fraction of cells resisting detachment were constructed for individual surfaces as a function of the applied shear stress and evaluated by comparison with integrals of both a normal and a log-normal distribution function. The two functions were equally appropriate, yielding similar estimates of the mean strength of adhesion. Further, varying the Reynolds number in the inlet, Re(d), between 630 and 1480 (corresponding to volumetric flow rates between 0.9 and 2.1 mL/s) did not affect the mean strength of adhesion. For these same experiments, analysis of the dynamics of detachment revealed three temporal phases: 1) rapid detachment of cells at the onset of flow, consistent with a first-order homogeneous kinetic model; 2) time-dependent rate of detachment during the first 30 sec. of exposure to hydrodynamic shear, consistent with the first-order heterogeneous kinetic model proposed by Dickinson and Cooper (1995); and 3) negligible detachment, indicative of pseudo-steady state after 60 sec. of flow. Our results provide rigorous guidelines for the measurement of adhesive interactions between mammalian cells and prospective biomaterial surfaces using a RFC. (c) 1997 John Wiley &amp; Sons, Inc. Biotechnol Bioeng 55: 616-629, 1997.}, }
@article {pmid21708665, year = {1997}, author = {Ackerman, J}, title = {Submarine pollination in the marine angiosperm Zostera marina (Zosteraceae). I. The influence of floral morphology on fluid flow.}, journal = {American journal of botany}, volume = {84}, number = {8}, pages = {1099}, pmid = {21708665}, issn = {0002-9122}, abstract = {An understanding of the process of submarine pollination should provide insight into the evolutionary and reproductive ecology of the marine angiosperms (seagrasses). The flow around the reproductive organs of the seagrass Zostera marina L. (Potamogetonales) was, therefore, examined in a flow chamber. The phenological emergence of flowers during (1) pollen capture and (2) pollen release, and by fruit during (3) seed release, led to a reduction in flow rate toward the inflorescence. This change in flow due to floral emergence was associated with a 50% increase in the fluid shear stress [tau = (2.2 _ 0.3) x 10-3 Pa for an immature flower vs. tau = (3.1 _ 0.5) x 10-3 Pa for a receptive flower]. The Reynolds number (Re) and fluid shear stress around inflorescences and infructescences were comparable, indicating a dynamic similarity in the processes of pollen capture and fruit dehiscence [Re = 47 _ 5, tau = (1.6 _ 0.3) x 10-3 Pa for inflorescences; Re = 38 _ 5, tau = (1.3 _ 0.1) x 10-3 Pa for infructescences]. These results indicate that the emergence of reproductive organs leads to changes in fluid shear stress, which will affect the release, transport, and capture of particles including pollen. Theoretical considerations of these observations using aerosol-filtration theory suggest that pollen capture in Z. marina occurs through direct interception of pollen by stigmas.}, }
@article {pmid18629815, year = {1996}, author = {Wang, SJ and Zhong, JJ}, title = {A novel centrifugal impeller bioreactor. II. Oxygen transfer and power consumption.}, journal = {Biotechnology and bioengineering}, volume = {51}, number = {5}, pages = {520-527}, doi = {10.1002/(SICI)1097-0290(19960905)51:5&lt;520::AID-BIT3&gt;3.0.CO;2-E}, pmid = {18629815}, issn = {0006-3592}, abstract = {The effects of the impeller configuration, aeration rate, and agitation speed on oxygen transfer coefficient K(L)a were studied in a newly designed centrifugal impeller bioreactor (5-L). The oxygen transfer rates in the novel bioreactor were also compared with those in a cell-lift bioreactor with comparable dimensions. The cell-lift impeller produced much higher surface oxygen transfer rates than the centrifugal one at an agitation speed over 200 rpm. This result was in good agreement with our observation that the cell-lift impeller produced much higher unfavorable turbulence. In addition, the experiments using granulated agar particles as pseudo plant cells indicated that the K(L)a value decreased steadily with an increase in agar particle concentration, and the centrifugal impeller still demonstrated a larger K(L)a than the cell lift up to a high pseudo cell concentration of 19.5 g dry weight (DW)/L (under 150 rpm and 0.20 vvm) or 22.3 g DW/L (under 200 rpm and 0.20 vvm). Furthermore, the correlation between power number and impeller Reynolds number for both the centrifugal and the cell-lift impellers was successfully obtained, which could be used for predicting the power input required by each impeller. From the results obtained, the centrifugal impeller bioreactor is expected to have great potential in its application to shear-sensitive biological systems.}, }
@article {pmid21060570, year = {1995}, author = {Ni, T and Pinson, JA and Gupta, S and Santoro, RJ}, title = {Two-dimensional imaging of soot volume fraction by the use of laser-induced incandescence.}, journal = {Applied optics}, volume = {34}, number = {30}, pages = {7083-7091}, doi = {10.1364/AO.34.007083}, pmid = {21060570}, issn = {1559-128X}, abstract = {A recently developed laser-induced incandescence technique is used to make novel planar measurements of soot volume fraction within turbulent diffusion flames and droplet flames. The two-dimensional imaging technique is developed and assessed by systematic experiments in a coannular laminar diffusion flame, in which the soot characteristics have been well established. With a single point calibration procedure, agreement to within 10% was found between the values of soot volume fraction measured by this technique and those determined by conventional laser scattering-extinction methods in the flame. As a demonstration of the wide range of applicability of the technique, soot volume fraction images are also obtained from both turbulent ethene diffusion flames and from a freely falling droplet flame that burns the mixture of 75% benzene and 25% methanol. For the turbulent diffusion flames, approximately an 80% reduction in soot volume fraction was found when the Reynolds number of the fuel jet increased from 4000 to 8000. In the droplet flame case, the distribution of soot field was found to be similar to that observed in coannular laminar diffusion flames.}, }
@article {pmid18613137, year = {1993}, author = {Torzillo, G and Carlozzi, P and Pushparaj, B and Montaini, E and Materassi, R}, title = {A two-plane tubular photobioreactor for outdoor culture of Spirulina.}, journal = {Biotechnology and bioengineering}, volume = {42}, number = {7}, pages = {891-898}, doi = {10.1002/bit.260420714}, pmid = {18613137}, issn = {0006-3592}, abstract = {A photobioreactor in the form of a 245-m-long loop made of plexiglass tubes having an inner diameter of 2.6 cm was designed and constructed for outdoor culture of Spirulina. The loop was arranged in two planes, with 15 8-m-long tubes in each plane. In the upper plane, the tubes were placed in the vacant space between the ones of the lower plane. The culture recycle was performed either with two airlifts, one per plane, or with two peristaltic pumps. The power required for water recycle in the tubular photobioreactor, with a Reynolds number of 4000, was 3.93 x 10(-2) W m(-2). The photobioreactor contained 145 L of culture and covered an overall area of 7.8 m(2). The photobioreactor operation was computer controlled. Viscosity measurements performed on Spirulina cultures having different biomass concentrations showed non-Newtonian behavior displaying decreasing viscosity with an increasing shear rate. The performance of the two-plane photobioreactor was tested under the climatic conditions of central Italy (latitude 43.8 degrees N, longitude 11.3 degrees E). A biomass concentration of 3.5 g L(-1) was found to be adequate for outdoor culture of Spirulina. With a biomass concentration of 6.3 g L(-1), the biomass output rate significantly decreased. The net biomass output rate reached a mean value of 27.8 g m(-2) d(-1) in July; this corresponded to a net photosynthetic efficiency of 6.6% (based on visible irradiance).}, }
@article {pmid18965707, year = {1993}, author = {Underhill, DW}, title = {Convective transport in diffusive samplers.}, journal = {Talanta}, volume = {40}, number = {6}, pages = {785-790}, doi = {10.1016/0039-9140(93)80031-l}, pmid = {18965707}, issn = {0039-9140}, abstract = {Convective transport in diffusive samplers was determined by the loss of a dilute dye solution from these samplers while held in a water bath. The water flow in the bath was adjusted to give the same Reynolds number had the diffusive sampler been exposed to an airborne analyte at a predetermined flow velocity. By numerical analysis, estimates were made of the degree of interference of convection on sampler performance. The results indicate an enormous difference between commercial diffusive samplers with respect to the effect of convection on the transport of analyte into the sampler.}, }
@article {pmid18610620, year = {2008}, author = {Qiao, A and Liu, Y and Zhang, S}, title = {[Influences of graft diameter on the blood flow in 2-way bypassing surgery].}, journal = {Sheng wu yi xue gong cheng xue za zhi = Journal of biomedical engineering = Shengwu yixue gongchengxue zazhi}, volume = {25}, number = {2}, pages = {346-50, 377}, pmid = {18610620}, issn = {1001-5515}, mesh = {*Anastomosis, Surgical ; Arterial Occlusive Diseases/surgery ; Blood Flow Velocity/physiology ; *Blood Vessel Prosthesis ; Blood Vessel Prosthesis Implantation/*methods ; Femoral Artery/physiopathology/*surgery ; Humans ; *Models, Cardiovascular ; Shear Strength ; Stress, Mechanical ; }, abstract = {The graft diameter plays a critically important role in the long-term patency rates of bypass surgery. To clarify the influence of graft diameter on the blood flows in the femoral 2-way bypass surgery, the physiologically pulsatile flows in two femoral bypass models were simulated with numerical methods. For the sake of comparison, the models were constructed with identical geometry parameters except the different diameters of grafts. Two models with small and large grafts were studied. The boundary conditions for the simulation of blood flow were constant for both models. The maximum Reynolds number was 832.8, and the Womersley number was 6.14. The emphases of results were on the analysis of flow fields in the vicinity of the distal anastomosis. The temporal-spatial distributions of velocity vectors, pressure drop between the proximal and distal toe, wall shear stresses, wall shear stress gradients and oscillating shear index were compared. The present study indicated that femoral artery bypassed with a large graft demonstrated disturbed axial flow and secondary flow at the distal anastomosis while the axial flow at its downstream of toe was featured with larger and more uniform longitudinal velocities. Meanwhile, the large model exhibits less refluences, relatively uniform wall shear stresses, lower pressure and smaller wall shear stress gradients, whereas it does not have any advantages in the distributions of secondary flow and the oscillating shear index. In general, the large model exhibits better and more uniform hemodynamic phenomena near the vessel wall and may be effective in preventing the initiation and development of postoperative intimal hyperplasia and restenosis.}, }
@article {pmid18574310, year = {2008}, author = {Liou, TM and Li, YC and Wang, TC}, title = {Hemodynamics altered by placing helix stents in an aneurysm at a 45 degrees angle to the curved vessel.}, journal = {Physics in medicine and biology}, volume = {53}, number = {14}, pages = {3763-3776}, doi = {10.1088/0031-9155/53/14/004}, pmid = {18574310}, issn = {0031-9155}, mesh = {Coronary Aneurysm/*physiopathology ; Coronary Vessels/*pathology/*physiopathology ; *Hemodynamics ; Humans ; Intracranial Aneurysm/physiopathology ; Porosity ; Pressure ; *Stents ; Time Factors ; }, abstract = {Flow visualization, particle image velocimetry and numerical computation have been complementarily performed to study the fluid flow inside a stented lateral aneurysm. The curved afferent vessel had an inner diameter of 5 mm. The diameters of the aneurysmal orifice, neck and fundus were 7 mm, 5 mm and 7.5 mm, respectively, and the distance between the orifice and dome measured 10 mm. Stents with various porosities were examined. A volume-flow rate waveform of the internal carotid artery was reconstructed with a Wormersley number of 4 and Reynolds number ranging from 202 to 384 in a cardiac cycle. Results are presented in terms of the main and secondary flow velocity vector fields, the inflow rates into the aneurysm and the intra-aneurysmal wall shear stress and pressure. Some comparisons of the computed results with the experimental results and the data available from the literature are also made. It is found that the placement of stents for endovascular treatment is more critical for an unstented parent vessel with curvature than without since the maximum inflow rate of the former is 15 times the latter. The critical porosity of 70% below which an inhibition of intra-aneurysmal thrombus formation will not occur is identified for the first time.}, }
@article {pmid18562236, year = {2009}, author = {Paul, MC and Mamun Molla, M and Roditi, G}, title = {Large-Eddy simulation of pulsatile blood flow.}, journal = {Medical engineering &amp; physics}, volume = {31}, number = {1}, pages = {153-159}, doi = {10.1016/j.medengphy.2008.04.014}, pmid = {18562236}, issn = {1350-4533}, mesh = {Arteries/pathology/physiopathology ; Computer Simulation ; Constriction, Pathologic/physiopathology ; *Models, Biological ; Pressure ; *Pulsatile Flow ; Time Factors ; }, abstract = {Large-Eddy simulation (LES) is performed to study pulsatile blood flow through a 3D model of arterial stenosis. The model is chosen as a simple channel with a biological type stenosis formed on the top wall. A sinusoidal non-additive type pulsation is assumed at the inlet of the model to generate time dependent oscillating flow in the channel and the Reynolds number of 1200, based on the channel height and the bulk velocity, is chosen in the simulations. We investigate in detail the transition-to-turbulent phenomena of the non-additive pulsatile blood flow downstream of the stenosis. Results show that the high level of flow recirculation associated with complex patterns of transient blood flow have a significant contribution to the generation of the turbulent fluctuations found in the post-stenosis region. The importance of using LES in modelling pulsatile blood flow is also assessed in the paper through the prediction of its sub-grid scale contributions. In addition, some important results of the flow physics are achieved from the simulations, these are presented in the paper in terms of blood flow velocity, pressure distribution, vortices, shear stress, turbulent fluctuations and energy spectra, along with their importance to the relevant medical pathophysiology.}, }
@article {pmid18553503, year = {2008}, author = {Venkiteshwaran, A and Heider, P and Teysseyre, L and Belfort, G}, title = {Selective precipitation-assisted recovery of immunoglobulins from bovine serum using controlled-fouling crossflow membrane microfiltration.}, journal = {Biotechnology and bioengineering}, volume = {101}, number = {5}, pages = {957-966}, doi = {10.1002/bit.21964}, pmid = {18553503}, issn = {1097-0290}, mesh = {Adsorption ; Ammonium Sulfate/chemistry ; Animals ; Biotechnology/methods ; Cattle ; Fractional Precipitation ; Immunoglobulins/*analysis/chemistry ; Serum/chemistry ; Serum Albumin, Bovine/analysis/chemistry ; Ultrafiltration/*methods ; }, abstract = {Efficient and economic recovery of immunoglobulins (Igs) from complex biological fluids such as serum, cell culture supernatant or fermentation cell lysate or supernatant, represents a substantial challenge in biotechnology. Methods such as protein A affinity chromatography and anion exchange chromatography are limited by cost and selectivity, respectively, while membrane chromatography is limited by low adsorptive area, flow distribution problems and scale-up difficulties. By combining the traditional salt-assisted precipitation process for selective removal of Igs from serum followed by constant-permeate flux membrane microfiltration for low fouling, we demonstrate an exciting new, efficient and economic hybrid method. The high selectivity of an ammonium sulfate-induced precipitation step was used to precipitate the Igs leaving the major undesirable impurity, the bovine serum albumin (BSA), in solution. Crossflow membrane microfiltration in diafiltration mode was then employed to retain the precipitate, while using axial flow rates to optimize removal of residual soluble BSA to the permeate. The selectivity between immunoglobulin G (IgG) and BSA obtained from the precipitation step was approximately 36, with 97% removal of the BSA with diafiltration in 5 diavolumes with resulting purity of the IgG of approximately 93% after the membrane microfiltration step. Complete resolubilization of the IgG was obtained without any aggregation at the concentrations of ammonium sulfate employed in this work. Further, membrane pore size and axial Reynolds number (recirculation rate) were shown to be important for minimizing fouling and loss of protein precipitate.}, }
@article {pmid18532860, year = {2008}, author = {Rakesh, V and Datta, AK and Ducharme, NG and Pease, AP}, title = {Simulation of turbulent airflow using a CT based upper airway model of a racehorse.}, journal = {Journal of biomechanical engineering}, volume = {130}, number = {3}, pages = {031011}, doi = {10.1115/1.2913338}, pmid = {18532860}, issn = {0148-0731}, mesh = {Airway Resistance/physiology ; Anatomy, Comparative ; Animals ; Computer Simulation ; Finite Element Analysis ; Horses/anatomy &amp; histology/*physiology ; Humans ; Kinetics ; *Mathematical Computing ; Models, Anatomic ; *Models, Biological ; Muscle Strength/physiology ; Nonlinear Dynamics ; Pharynx/anatomy &amp; histology/*physiology ; Physiology, Comparative ; Pressure ; Respiratory Mechanics/*physiology ; *Rheology ; Tomography, X-Ray Computed ; }, abstract = {Computational model for airflow through the upper airway of a horse was developed. Previous flow models for human airway do not hold true for horses due to significant differences in anatomy and the high Reynolds number of flow in the equine airway. Moreover, models that simulate the entire respiratory cycle and emphasize on pressures inside the airway in relation to various anatomical diseases are lacking. The geometry of the airway was created by reconstructing images obtained from computed tomography scans of a thoroughbred racehorse. Different geometries for inhalation and exhalation were used for the model based on the difference in the nasopharynx size during the two phases of respiration. The Reynolds averaged Navier-Stokes equations were solved for the isothermal flow with the standard k-epsilon model for turbulence. Transient pressure boundary conditions for the entire breathing cycle were obtained from past experimental studies on live horses. The flow equations were solved in a commercial finite volume solver. The flow rates, computed based on the applied pressure conditions, were compared to experimentally measured flow rates for model validation. Detailed analysis of velocity, pressure, and turbulence characteristics of the flow was done. Velocity magnitudes at various slices during inhalation were found to be higher than corresponding velocity magnitudes during exhalation. The front and middle parts of the nasopharynx were found to have minimum intraluminal pressure in the airway during inhalation. During exhalation, the pressures in the soft palate were higher compared to those in the larynx, epiglottis, and nasopharynx. Turbulent kinetic energy was found to be maximum at the entry to the airway and gradually decreased as the flow moved inside the airway. However, turbulent kinetic energy increased in regions of the airway with abrupt change in area. Based on the analysis of pressure distribution at different sections of the airway, it was concluded that the front part of the nasopharynx requires maximum muscular activity to support it during inhalation. During exhalation, the soft palate is susceptible to displacements due to presence of high pressures. These can serve as critical information for diagnosis and treatment planning of diseases known to affect the soft palate and nasopharynx in horses, and can potentially be useful for human beings.}, }
@article {pmid18529171, year = {2008}, author = {Winkel, ES and Elbing, BR and Ceccio, SL and Perlin, M and Dowling, DR}, title = {High-Reynolds-number turbulent-boundary-layer wall pressure fluctuations with skin-friction reduction by air injection.}, journal = {The Journal of the Acoustical Society of America}, volume = {123}, number = {5}, pages = {2522-2530}, doi = {10.1121/1.2902169}, pmid = {18529171}, issn = {1520-8524}, mesh = {Air/*analysis ; *Friction ; Humans ; Injections ; Kinetics ; Microbubbles ; Models, Biological ; Pressure ; *Skin Physiological Phenomena ; }, abstract = {The hydrodynamic pressure fluctuations that occur on the solid surface beneath a turbulent boundary layer are a common source of flow noise. This paper reports multipoint surface pressure fluctuation measurements in water beneath a high-Reynolds-number turbulent boundary layer with wall injection of air to reduce skin-friction drag. The experiments were conducted in the U.S. Navy's Large Cavitation Channel on a 12.9-m-long, 3.05-m-wide hydrodynamically smooth flat plate at freestream speeds up to 20 ms and downstream-distance-based Reynolds numbers exceeding 200 x 10(6). Air was injected from one of two spanwise slots through flush-mounted porous stainless steel frits (approximately 40 microm mean pore diameter) at volume flow rates from 17.8 to 142.5 l/s per meter span. The two injectors were located 1.32 and 9.78 m from the model's leading edge and spanned the center 87% of the test model. Surface pressure measurements were made with 16 flush-mounted transducers in an "L-shaped" array located 10.7 m from the plate's leading edge. When compared to no-injection conditions, the observed wall-pressure variance was reduced by as much as 87% with air injection. In addition, air injection altered the inferred convection speed of pressure fluctuation sources and the streamwise coherence of pressure fluctuations.}, }
@article {pmid18518640, year = {2008}, author = {Ogrin, FY and Petrov, PG and Winlove, CP}, title = {Ferromagnetic microswimmers.}, journal = {Physical review letters}, volume = {100}, number = {21}, pages = {218102}, doi = {10.1103/PhysRevLett.100.218102}, pmid = {18518640}, issn = {0031-9007}, mesh = {Anisotropy ; DNA/chemistry ; Elasticity ; *Ferric Compounds ; Flagella/physiology ; *Models, Theoretical ; Polymers/chemistry ; Proteins/chemistry ; }, abstract = {We propose a model for a novel artificial low Reynolds number swimmer, based on the magnetic interactions of a pair of ferromagnetic particles: one with hard and the other with soft magnetic properties, connected by a linear spring. Using a computational model, we analyze the behavior of the system and demonstrate that for realistic values of the parameters involved, the swimmer is capable of self-propelling with average speeds of the order of hundreds of micrometers per second.}, }
@article {pmid18518606, year = {2008}, author = {Saw, EW and Shaw, RA and Ayyalasomayajula, S and Chuang, PY and Gylfason, A}, title = {Inertial clustering of particles in high-Reynolds-number turbulence.}, journal = {Physical review letters}, volume = {100}, number = {21}, pages = {214501}, doi = {10.1103/PhysRevLett.100.214501}, pmid = {18518606}, issn = {0031-9007}, abstract = {We report experimental evidence of spatial clustering of dense particles in homogenous, isotropic turbulence at high Reynolds numbers. The dissipation-scale clustering becomes stronger as the Stokes number increases and is found to exhibit similarity with respect to the droplet Stokes number over a range of experimental conditions (particle diameter and turbulent energy dissipation rate). These findings are in qualitative agreement with recent theoretical and computational studies of inertial particle clustering in turbulence. Because of the large Reynolds numbers a broad scaling range of particle clustering due to turbulent mixing is present, and the inertial clustering can clearly be distinguished from that due to mixing of fluid particles.}, }
@article {pmid18517734, year = {2008}, author = {Benzi, R and Ching, ES and De Angelis, E and Procaccia, I}, title = {Comparison of theory and direct numerical simulations of drag reduction by rodlike polymers in turbulent channel flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {4 Pt 2}, pages = {046309}, doi = {10.1103/PhysRevE.77.046309}, pmid = {18517734}, issn = {1539-3755}, abstract = {Numerical simulations of turbulent channel flows, with or without additives, are limited in the extent of the Reynolds number (Re) and Deborah number (De). The comparison of such simulations to theories of drag reduction, which are usually derived for asymptotically high Re and De, calls for some care. In this paper we present a study of drag reduction by rodlike polymers in a turbulent channel flow using direct numerical simulation and illustrate how these numerical results should be related to the recently developed theory.}, }
@article {pmid18517728, year = {2008}, author = {Baerenzung, J and Politano, H and Ponty, Y and Pouquet, A}, title = {Spectral modeling of turbulent flows and the role of helicity.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {4 Pt 2}, pages = {046303}, doi = {10.1103/PhysRevE.77.046303}, pmid = {18517728}, issn = {1539-3755}, abstract = {We present a version of a dynamical spectral model for large eddy simulation based on the eddy damped quasinormal Markovian approximation [S. A. Orszag, in, edited by R. Balian, Proceedings of Les Houches Summer School, 1973 (Gordon and Breach, New York, 1977), p. 237; J. P. Chollet and M. Lesievr, J. Atmos. Sci. 38, 2747 (1981)]. Three distinct modifications are implemented and tested. On the one hand, whereas in current approaches, a Kolmogorov-like energy spectrum is usually assumed in order to evaluate the non-local transfer, in our method the energy spectrum of the subgrid scales adapts itself dynamically to the large-scale resolved spectrum; this first modification allows in particular for a better treatment of transient phases and instabilities, as shown on one specific example. Moreover, the model takes into account the phase relationships of the small scales, embodied, for example, in strongly localized structures such as vortex filaments. To that effect, phase information is implemented in the treatment of the so-called eddy noise in the closure model. Finally, we also consider the role that helical small scales may play in the evaluation of the transfer of energy and helicity, the two invariants of the primitive equations in the inviscid case; this leads as well to intrinsic variations in the development of helicity spectra. Therefore, our model allows for simulations of flows for a variety of circumstances and a priori at any given Reynolds number. Comparisons with direct numerical simulations of the three-dimensional Navier-Stokes equation are performed on fluids driven by an Arnold-Beltrami-Childress (ABC) flow which is a prototype of fully helical flows (velocity and vorticity fields are parallel). Good agreements are obtained for physical and spectral behavior of the large scales.}, }
@article {pmid18517659, year = {2008}, author = {Keaveny, EE and Maxey, MR}, title = {Interactions between comoving magnetic microswimmers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {4 Pt 1}, pages = {041910}, doi = {10.1103/PhysRevE.77.041910}, pmid = {18517659}, issn = {1539-3755}, mesh = {Computer Simulation ; Flagella/*physiology ; *Magnetics ; *Models, Biological ; Motion ; *Movement ; *Swimming ; }, abstract = {The artificial microswimmer [R. Dreyfus, Nature (London) 437, 862 (2005)] whose mechanism of propulsion is the magnetically driven undulation of a flagellum-like tail composed of chemically linked paramagnetic beads can be used as a physical model with which to study low-Reynolds-number swimming. Understanding how such swimmers interact provides insight into the related problem of quantifying the hydrodynamic interactions between microorganisms. In this study, particle-based numerical simulations are conducted of two comoving artificial swimmers. The resulting swimming speeds are determined over a range of separations for swimmers driven by planar and rotational magnetic fields. The far-field hydrodynamic interactions are analyzed and found to decay as h(-2) where h is the separation distance. Additionally, the role of the interswimmer magnetic forces is determined.}, }
@article {pmid18517526, year = {2008}, author = {Malik, M and Dey, J and Alam, M}, title = {Linear stability, transient energy growth, and the role of viscosity stratification in compressible plane Couette flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {3 Pt 2}, pages = {036322}, doi = {10.1103/PhysRevE.77.036322}, pmid = {18517526}, issn = {1539-3755}, abstract = {Linear stability and the nonmodal transient energy growth in compressible plane Couette flow are investigated for two prototype mean flows: (a) the uniform shear flow with constant viscosity, and (b) the nonuniform shear flow with stratified viscosity. Both mean flows are linearly unstable for a range of supersonic Mach numbers (M). For a given M , the critical Reynolds number (Re) is significantly smaller for the uniform shear flow than its nonuniform shear counterpart; for a given Re, the dominant instability (over all streamwise wave numbers, alpha) of each mean flow belongs to different modes for a range of supersonic M . An analysis of perturbation energy reveals that the instability is primarily caused by an excess transfer of energy from mean flow to perturbations. It is shown that the energy transfer from mean flow occurs close to the moving top wall for "mode I" instability, whereas it occurs in the bulk of the flow domain for "mode II." For the nonmodal transient growth analysis, it is shown that the maximum temporal amplification of perturbation energy, G(max), and the corresponding time scale are significantly larger for the uniform shear case compared to those for its nonuniform counterpart. For alpha=0 , the linear stability operator can be partitioned into L ~ L+Re(2) L(p), and the Re-dependent operator L(p) is shown to have a negligibly small contribution to perturbation energy which is responsible for the validity of the well-known quadratic-scaling law in uniform shear flow: G(t/Re) ~ Re(2). In contrast, the dominance of L(p) is responsible for the invalidity of this scaling law in nonuniform shear flow. An inviscid reduced model, based on Ellingsen-Palm-type solution, has been shown to capture all salient features of transient energy growth of full viscous problem. For both modal and nonmodal instability, it is shown that the viscosity stratification of the underlying mean flow would lead to a delayed transition in compressible Couette flow.}, }
@article {pmid18517519, year = {2008}, author = {Yan, Y and Koplik, J}, title = {Flow of power-law fluids in self-affine fracture channels.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {3 Pt 2}, pages = {036315}, doi = {10.1103/PhysRevE.77.036315}, pmid = {18517519}, issn = {1539-3755}, abstract = {The two-dimensional pressure driven flow of non-Newtonian power-law fluids in self-affine fracture channels at finite Reynolds number is calculated. The channels have constant mean aperture and two values zeta=0.5 and 0.8 of the Hurst exponent are considered. The calculation is based on the lattice-Boltzmann method, using a different technique to obtain a power-law variation in viscosity, and the behavior of shear-thinning, Newtonian, and shear-thickening liquids is compared. Local aspects of the flow fields, such as maximum velocity and pressure fluctuations, are studied, and the non-Newtonian fluids are compared to the (previously studied) Newtonian case. We find a scaling relation between permeability and mean aperture in the low Reynolds number regime, generalizing an earlier result for Newtonian fluids. As the Reynolds number increases, we observe the same sequence of transitions to nonlinearity found in intergranular porous media. Furthermore, the permeability results may be collapsed into a master curve of friction factor vs Reynolds number, using a scaling similar to that employed for power-law fluids in porous media.}, }
@article {pmid18517516, year = {2008}, author = {van Reeuwijk, M and Jonker, HJ and Hanjalić, K}, title = {Wind and boundary layers in Rayleigh-Bénard convection. II. Boundary layer character and scaling.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {3 Pt 2}, pages = {036312}, doi = {10.1103/PhysRevE.77.036312}, pmid = {18517516}, issn = {1539-3755}, abstract = {The scaling of the kinematic boundary layer thickness lambda(u) and the friction factor C(f) at the top and bottom walls of Rayleigh-Bénard convection is studied by direct numerical simulation (DNS). By a detailed analysis of the friction factor, a new parameterisation for C(f) and lambda(u) is proposed. The simulations were made of an L/H=4 aspect-ratio domain with periodic lateral boundary conditions at Ra=(10(5), 10(6), 10(7), 10(8)) and Pr=1. The continuous spectrum, as well as significant forcing due to Reynolds stresses, clearly indicates a turbulent character of the boundary layer, while viscous effects cannot be neglected, judging from the scaling of classical integral boundary layer parameters with Reynolds number. Using a conceptual wind model, we find that the friction factor C(f) should scale proportionally to the thermal boundary layer thickness as C(f) proportional variant lambda(Theta)/H, while the kinetic boundary layer thickness lambda(u) scales inversely proportionally to the thermal boundary layer thickness and wind Reynolds number lambda(u)/H proportional variant (lambda(Theta)/H)(-1)Re(-1). The predicted trends for C(f) and lambda(u) are in agreement with DNS results.}, }
@article {pmid18517515, year = {2008}, author = {van Reeuwijk, M and Jonker, HJ and Hanjalić, K}, title = {Wind and boundary layers in Rayleigh-Bénard convection. I. Analysis and modeling.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {3 Pt 2}, pages = {036311}, doi = {10.1103/PhysRevE.77.036311}, pmid = {18517515}, issn = {1539-3755}, abstract = {The aim of this paper is to contribute to the understanding of and to model the processes controlling the amplitude of the wind of Rayleigh-Bénard convection. We analyze results from direct simulation of an L/H=4 aspect-ratio domain with periodic sidewalls at Ra=(10(5), 10(6), 10(7), 10(8)) and at Pr=1 by decomposing independent realizations into wind and fluctuations. It is shown that, deep inside the thermal boundary layer, horizontal heat fluxes exceed the average vertical heat flux by a factor of 3 due to the interaction between the wind and the mean temperature field. These large horizontal heat fluxes are responsible for spatial temperature differences that drive the wind by creating pressure gradients. The wall fluxes and turbulent mixing in the bulk provide damping. Using the direct numerical simulation results to parametrize the unclosed terms, a simple model capturing the essential processes governing the wind structure is derived. The model consists of two coupled differential equations for wind velocity and temperature amplitude. The equations indicate that the formation of a wind structure is inevitable due to the positive feedback resulting from the interaction between the wind and temperature field. Furthermore, the wind velocity is largely determined by the turbulence in the bulk rather than by the wall-shear stress. The model reproduces the Ra dependence of wind Reynolds number and temperature amplitude.}, }
@article {pmid18517514, year = {2008}, author = {Djenidi, L}, title = {Structure of a turbulent crossbar near-wake studied by means of lattice Boltzmann simulation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {3 Pt 2}, pages = {036310}, doi = {10.1103/PhysRevE.77.036310}, pmid = {18517514}, issn = {1539-3755}, abstract = {The turbulent near-wake of a crossbar is investigated numerically with the lattice Boltzmann method (LBM). The crossbar is made up of two perpendicular square bars arranged in a biplane configuration and is included in the computational domain. The Reynolds number based on a bar diameter is about 1600. The numerical results are first tested against results of both particle image velocimetry (PIV) and laser Doppler velocimetry (LDV). The LBM data compare well with the PIV and LDV data. In particular, the LBM reproduces the generation of vortical structures at the crossbar as observed in the PIV data. The numerical results reveal the presence of intermittent lateral motions along the span of the two bars, yielding fingerlike structures. It is argued that these motions contribute to the formation of streamwise vortical structures just behind the crossbar. These streamwise structures interlace with lateral structures also generated at the crossbar. The region over which this activity takes place is about four diameters. Within this region, the turbulent kinetic energy at the crossbar centerline increases and reaches a maximum at a distance of about three diameters. As the downstream distance increases, the individual wakes merge to form a single wake with features, for x/D> or =20 , similar to those observed in grid-generated turbulence.}, }
@article {pmid18517512, year = {2008}, author = {Golestanian, R and Ajdari, A}, title = {Analytic results for the three-sphere swimmer at low Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {3 Pt 2}, pages = {036308}, doi = {10.1103/PhysRevE.77.036308}, pmid = {18517512}, issn = {1539-3755}, abstract = {The simple model of a low Reynolds number swimmer made from three spheres that are connected by two arms is considered in its general form and analyzed. The swimming velocity, force-velocity response, power consumption, and efficiency of the swimmer are calculated both for general deformations and also for specific model prescriptions. The role of noise and coherence in the stroke cycle is also discussed.}, }
@article {pmid18517511, year = {2008}, author = {Kleeorin, N and Rogachevskii, I}, title = {Mean-field dynamo in a turbulence with shear and kinetic helicity fluctuations.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {3 Pt 2}, pages = {036307}, doi = {10.1103/PhysRevE.77.036307}, pmid = {18517511}, issn = {1539-3755}, abstract = {We study the effects of kinetic helicity fluctuations in a turbulence with large-scale shear using two different approaches: the spectral tau approximation and the second-order correlation approximation (or first-order smoothing approximation). These two approaches demonstrate that homogeneous kinetic helicity fluctuations alone with zero mean value in a sheared homogeneous turbulence cannot cause a large-scale dynamo. A mean-field dynamo is possible when the kinetic helicity fluctuations are inhomogeneous, which causes a nonzero mean alpha effect in a sheared turbulence. On the other hand, the shear-current effect can generate a large-scale magnetic field even in a homogeneous nonhelical turbulence with large-scale shear. This effect was investigated previously for large hydrodynamic and magnetic Reynolds numbers. In this study we examine the threshold required for the shear-current dynamo versus Reynolds number. We demonstrate that there is no need for a developed inertial range in order to maintain the shear-current dynamo (e.g., the threshold in the Reynolds number is of the order of 1).}, }
@article {pmid18517510, year = {2008}, author = {Mininni, PD and Alexakis, A and Pouquet, A}, title = {Nonlocal interactions in hydrodynamic turbulence at high Reynolds numbers: the slow emergence of scaling laws.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {3 Pt 2}, pages = {036306}, doi = {10.1103/PhysRevE.77.036306}, pmid = {18517510}, issn = {1539-3755}, abstract = {We analyze the data stemming from a forced incompressible hydrodynamic simulation on a grid of 2048(3) regularly spaced points, with a Taylor Reynolds number of R(lambda) ~ 1300. The forcing is given by the Taylor-Green vortex, which shares similarities with the von Kàrmàn flow used in several laboratory experiments; the computation is run for ten turnover times in the turbulent steady state. At this Reynolds number the anisotropic large scale flow pattern, the inertial range, the bottleneck, and the dissipative range are clearly visible, thus providing a good test case for the study of turbulence as it appears in nature. Triadic interactions, the locality of energy fluxes, and longitudinal structure functions of the velocity increments are computed. A comparison with runs at lower Reynolds numbers is performed and shows the emergence of scaling laws for the relative amplitude of local and nonlocal interactions in spectral space. Furthermore, the scaling of the Kolmogorov constant, and of skewness and flatness of velocity increments is consistent with previous experimental results. The accumulation of energy in the small scales associated with the bottleneck seems to occur on a span of wave numbers that is independent of the Reynolds number, possibly ruling out an inertial range explanation for it. Finally, intermittency exponents seem to depart from standard models at high R(lambda), leaving the interpretation of intermittency an open problem.}, }
@article {pmid18517505, year = {2008}, author = {Smolka, LB and North, J and Guerra, BK}, title = {Dynamics of free surface perturbations along an annular viscous film.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {3 Pt 2}, pages = {036301}, doi = {10.1103/PhysRevE.77.036301}, pmid = {18517505}, issn = {1539-3755}, abstract = {It is known that the free surface of an axisymmetric viscous film flowing down the outside of a thin vertical fiber under the influence of gravity becomes unstable to interfacial perturbations. We present an experimental study using fluids with different densities, surface tensions, and viscosities to investigate the growth and dynamics of these interfacial perturbations and to test the assumptions made by previous authors. We find that the initial perturbation growth is exponential, followed by a slower phase as the amplitude and wavelength saturate in size. Measurements of the perturbation growth for experiments conducted at low and moderate Reynolds numbers are compared to theoretical predictions developed from linear stability theory. Excellent agreement is found between predictions from a long-wave Stokes flow model [Craster and Matar, J. Fluid Mech. 553, 85 (2006)] and data, while fair to excellent agreement (depending on fiber size) is found between predictions from a moderate-Reynolds-number model [Sisoev, Chem. Eng. Sci. 61, 7279 (2006)] and data. Furthermore, we find that a known transition in the longer-time perturbation dynamics from unsteady to steady behavior at a critical flow rate Q(c) is correlated with a transition in the rate at which perturbations naturally form along the fiber. For Q<Q(c) (steady case), the rate of perturbation formation is constant. As a result, the position along the fiber where perturbations form is nearly fixed, and the spacing between consecutive perturbations remains constant as they travel 2 m down the fiber. For Q>Q(c) (unsteady case), the rate of perturbation formation is modulated. As a result, the position along the fiber where perturbations form oscillates irregularly, and the initial speed and spacing between perturbations varies, resulting in the coalescence of neighboring perturbations further down the fiber.}, }
@article {pmid18517436, year = {2008}, author = {Kuriabova, T and Levine, AJ}, title = {Nanorheology of viscoelastic shells: applications to viral capsids.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {3 Pt 1}, pages = {031921}, doi = {10.1103/PhysRevE.77.031921}, pmid = {18517436}, issn = {1539-3755}, mesh = {Biophysics/*methods ; Capsid/*chemistry ; Computer Simulation ; Elasticity ; Kinetics ; Microscopy, Atomic Force ; Models, Biological ; Models, Statistical ; Nanoparticles/*chemistry ; Nanotechnology/*methods ; Pressure ; Rheology/*methods ; Solvents/chemistry ; Viruses/*metabolism ; Viscosity ; }, abstract = {We study the microrheology of nanoparticle shells [A. D. Dinsmore, Science 298, 1006 (2002)] and viral capsids [I. L. Ivanovska, Proc. Natl. Acad. Sci. U.S.A. 101, 7600 (2004)] by computing the mechanical response function and thermal fluctuation spectrum of a viscoelastic spherical shell that is permeable to the surrounding solvent. We determine analytically the damped dynamics of bend and compression modes of the shell coupled to the solvent both inside and outside the sphere in the zero Reynolds number limit. We identify fundamental length and time scales in the system, and compute the thermal correlation function of displacements of antipodal points on the sphere and the mechanical response to pinching forces applied at these points. We describe how such a frequency-dependent antipodal correlation and/or response function, which should be measurable in new AFM-based microrheology experiments, can probe the viscoelasticity of these synthetic and biological shells constructed of nanoparticles.}, }
@article {pmid18517379, year = {2008}, author = {Başağaoğlu, H and Meakin, P and Succi, S and Redden, GR and Ginn, TR}, title = {Two-dimensional lattice Boltzmann simulation of colloid migration in rough-walled narrow flow channels.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {3 Pt 1}, pages = {031405}, doi = {10.1103/PhysRevE.77.031405}, pmid = {18517379}, issn = {1539-3755}, abstract = {A lattice Boltzmann model was used to simulate the accelerated transport of dense inert particles in low Reynolds number flows in smooth- and rough-walled narrow channels. The simulations showed that, after an initial transient, an initially immobile particle migrated faster than the average fluid velocity. The sensitivity of the particle residence time to wall roughness increased with decreasing Reynolds numbers. The relationship between the exit position and residence time of a particle was sensitive to the release position, flow strength, and the wall roughness. A particle with a density 5% larger than the density of the fluid migrated to an equilibrium position between the centerline and the wall for the slowest flow rates in rough-walled channels, displaying the Segre-Silberberg effect that a rigid neutrally buoyant spherical particle exhibits in small Reynolds number flows. However, a particle that was 35% denser than the density of the fluid drifted to the centerline in the slowest flows due to the gravitational settling effect. The difference in the residence time of the less-dense and dense particles was most sensitive to the surface roughness at the smallest Reynolds number investigated.}, }
@article {pmid18508062, year = {2008}, author = {Dasi, LP and Pekkan, K and Katajima, HD and Yoganathan, AP}, title = {Functional analysis of Fontan energy dissipation.}, journal = {Journal of biomechanics}, volume = {41}, number = {10}, pages = {2246-2252}, pmid = {18508062}, issn = {0021-9290}, support = {P41 RR006009-185541/RR/NCRR NIH HHS/United States ; HL67622/HL/NHLBI NIH HHS/United States ; R01 HL067622/HL/NHLBI NIH HHS/United States ; R01 HL067622-02/HL/NHLBI NIH HHS/United States ; P41 RR006009/RR/NCRR NIH HHS/United States ; }, mesh = {Biomechanical Phenomena/*methods ; Blood Flow Velocity ; Cardiac Output ; Computer Simulation ; Fontan Procedure/*methods ; Heart/*anatomy &amp; histology ; Humans ; Models, Anatomic ; Models, Biological ; Models, Cardiovascular ; Models, Statistical ; Pulmonary Artery/physiology/surgery ; Reproducibility of Results ; Venae Cavae/surgery ; }, abstract = {We formalize the hydrodynamic energy dissipation in the total cavopulmonary connection (TCPC) using dimensional analysis and examine the effect of governing flow variables; namely, cardiac output, flow split, body surface area, Reynolds number, and certain geometric characteristics. A simplistic and clinically useful mathematical model of the dependence of energy dissipation on the governing variables is developed. In vitro energy loss data corresponding to six patients' anatomies validated the predicted dependency of each variable and was used to develop a predictive, semi-empirical energy dissipation model of the TCPC. It is shown that energy dissipation is a cubic function of pulmonary flow split in the physiological range. Furthermore, non-dimensional energy dissipation, which is a measure of resistance of the connection, is dependent on Reynolds number and geometrical factors alone. Non-dimensional energy dissipation decreases with Reynolds number as Re(-0.25) (R(2)>0.95). In addition, for high Reynolds numbers, within physiological exercise limits, dissipation strongly correlates to minimum PA area as a power law decay with an exponent of -5/4 (R(2)>0.88). This study presents a simple analytical form of energy dissipation rate in complex patient-specific TCPCs that accurately captures the effect of cardiac output, flow split, body surface area, Reynolds number, and pulmonary artery size within physiological limits. Further studies with larger sample sizes are necessary for incorporating finer geometrical parameters such as vessel curvatures and offsets.}, }
@article {pmid18495624, year = {2008}, author = {Fraenkel, LE}, title = {On Kelvin-Stuart vortices in a viscous fluid.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {366}, number = {1876}, pages = {2717-2728}, doi = {10.1098/rsta.2008.0064}, pmid = {18495624}, issn = {1364-503X}, abstract = {When one contemplates the one-parameter family of steady inviscid shear flows discovered by J. T. Stuart in 1967, an obvious thought is that these flows resemble a row of vortices diffusing in a viscous fluid, with the parameter playing the role of a reversed time. In this paper, we ask how close this resemblance is. Accordingly, the paper begins to explore Navier-Stokes solutions having as initial condition the classical, irrotational flow due to a row of point vortices. However, since we seek explicit answers, such exploration seems possible only in two relatively easy cases: that of small time and arbitrary Reynolds number and that of small Reynolds number and arbitrary time.}, }
@article {pmid18487124, year = {2008}, author = {Blennerhassett, PJ and Bassom, AP}, title = {On the linear stability of Stokes layers.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {366}, number = {1876}, pages = {2685-2697}, doi = {10.1098/rsta.2008.0055}, pmid = {18487124}, issn = {1364-503X}, abstract = {Oscillatory flows occur naturally, with applications ranging across many disciplines from engineering to physiology. Transition to turbulence in such flows is a topic of practical interest and this article discusses some recent work that has furthered our understanding of the stability of a class of time-periodic fluid motions. Our study starts with an examination of the linear stability of a classical flat Stokes layer. Although experiments conducted over many years have demonstrated conclusively that this layer is unstable at a sufficiently large Reynolds number, it has only been relatively recently that rigorous theoretical confirmation of this behaviour has been obtained. The analysis and numerical calculations for the planar Stokes layer were subsequently extended to flows in channels and pipes and for the flow within a torsionally oscillating circular cylinder. We discuss why our predictions for the onset of instability in these geometries are in disappointingly poor agreement with experimental results. Finally, some suggestions for future experimental work are given and some areas for future theoretical analysis outlined.}, }
@article {pmid18487120, year = {2008}, author = {Willis, AP and Peixinho, J and Kerswell, RR and Mullin, T}, title = {Experimental and theoretical progress in pipe flow transition.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {366}, number = {1876}, pages = {2671-2684}, doi = {10.1098/rsta.2008.0063}, pmid = {18487120}, issn = {1364-503X}, abstract = {There have been many investigations of the stability of Hagen-Poiseuille flow in the 125 years since Osborne Reynolds' famous experiments on the transition to turbulence in a pipe, and yet the pipe problem remains the focus of attention of much research. Here, we discuss recent results from experimental and numerical investigations obtained in this new century. Progress has been made on three fundamental issues: the threshold amplitude of disturbances required to trigger a transition to turbulence from the laminar state; the threshold Reynolds number flow below which a disturbance decays from turbulence to the laminar state, with quantitative agreement between experimental and numerical results; and understanding the relevance of recently discovered families of unstable travelling wave solutions to transitional and turbulent pipe flow.}, }
@article {pmid18476411, year = {2007}, author = {Kumar, A and Gupta, SK and Kale, SR}, title = {Effects of drop acceleration and deceleration on particle capture in a cross-flow gravity tower at intermediate drop Reynolds numbers.}, journal = {Journal of environmental science &amp; engineering}, volume = {49}, number = {2}, pages = {157-163}, pmid = {18476411}, mesh = {Acceleration ; Air ; Air Movements ; Air Pollutants/*analysis ; Chemistry, Physical/methods ; Deceleration ; Dust ; Environmental Monitoring/*methods ; Gravitation ; Models, Theoretical ; }, abstract = {Cross-flow gravity towers are particle scrubbing devices in which water is sprayed from the top into particle-laden flow moving horizontally. Models for predicting particle capture assume drops traveling at terminal velocity and potential flow (ReD > 1000) around it, however, Reynolds numbers in the intermediate range of 1 to 1000 are common in gravity towers. Drops are usually injected at velocities greater than their terminal velocities (as in nozzles) or from near rest (perforated tray) and they accelerate/decelerate to their terminal velocity in the tower. Also, the effects of intermediate drop Reynolds number on capture efficiency have been simulated for (a) drops at their terminal velocity and (b) drops accelerating/decelerating to their terminal velocity. Tower efficiency based on potential flow about the drop is 40%-50% greater than for 200 mm drops traveling at their terminal velocity. The corresponding values for 500 mm drops are about 10%-20%. The drop injection velocity is important operating parameter. Increase in tower efficiency by about 40% for particles smaller than 5 mm is observed for increase in injection velocity from 0 to 20 m/s for 200 and 500mm drops.}, }
@article {pmid18471808, year = {2008}, author = {Jayalalitha, G and Shanthoshini Deviha, V and Uthayakumar, R}, title = {Fractal model for blood flow in cardiovascular system.}, journal = {Computers in biology and medicine}, volume = {38}, number = {6}, pages = {684-693}, doi = {10.1016/j.compbiomed.2008.03.002}, pmid = {18471808}, issn = {0010-4825}, mesh = {Algorithms ; Blood Flow Velocity/physiology ; Blood Pressure/physiology ; *Computer Simulation ; Coronary Circulation/*physiology ; Elasticity ; *Fractals ; Heart/anatomy &amp; histology ; Humans ; Models, Anatomic ; *Models, Cardiovascular ; Vascular Resistance/physiology ; }, abstract = {Blood flow in the cardiovascular system is the central point of experimental and theoretical investigation. The objective of the study is to determine the blood flow in the cardiovascular system using Darcy's law, Reynold's number and Poiseuille's equation. A possible way of modeling of self-similar biological tree-like structure is proposed. Special attention is paid to the blood vessel system, with elaboration on a model with certain spatial arrangement of the vessels and reasonable dependence of the blood pressure on the vessels diameter such that the organism has a homogeneous oxygen supply. Flow analysis in the above systems is analyzed by invasion percolation. The blood flow in the cardiovascular system has been numerically calculated for both normal and abnormal patients. A new algorithm has been introduced to visit the blood vessels in a robust manner which avoids loops and provides us the results in a simple manner.}, }
@article {pmid18456881, year = {2008}, author = {Borazjani, I and Sotiropoulos, F}, title = {Numerical investigation of the hydrodynamics of carangiform swimming in the transitional and inertial flow regimes.}, journal = {The Journal of experimental biology}, volume = {211}, number = {Pt 10}, pages = {1541-1558}, doi = {10.1242/jeb.015644}, pmid = {18456881}, issn = {0022-0949}, mesh = {Animals ; Biomechanical Phenomena ; Fishes/*physiology ; Models, Biological ; Swimming/*physiology ; Tail/*physiology ; Viscosity ; }, abstract = {We employ numerical simulation to investigate the hydrodynamics of carangiform locomotion as the relative magnitude of viscous and inertial forces, i.e. the Reynolds number (Re), and the tail-beat frequency, i.e. the Strouhal number (St), are systematically varied. The model fish is a three-dimensional (3D) mackerel-like flexible body undulating with prescribed experimental kinematics of carangiform type. Simulations are carried out for three Re spanning the transitional and inertial flow regimes, Re=300 and 4000 (viscous flow), and infinity (inviscid flow). For each Re there is a critical Strouhal number, St*, at which the net mean force becomes zero, making constant-speed self-propulsion possible. St* is a decreasing function of Re and approaches the range of St at which most carangiform swimmers swim in nature (St approximately 0.25) only as Re approaches infinity. The propulsive efficiency at St* is an increasing function of Re while the power required for swimming is decreasing with Re. For all Re, however, the swimming power is shown to be significantly greater than that required to tow the rigid body at the same speed. We also show that the variation of the total drag and its viscous and form components with St depend on the Re. For Re=300, body undulations increase the drag over the rigid body level, while significant drag reduction is observed for Re=4000. This difference is shown to be due to the fact that at sufficiently high Re the drag force variation with St is dominated by its form component variation, which is reduced by undulatory swimming for St>0.2. Finally, our simulations clarify the 3D structure of various wake patterns observed in experiments--single and double row vortices--and suggest that the wake structure depends primarily on the St. Our numerical findings help elucidate the results of previous experiments with live fish, underscore the importance of scale (Re) effects on the hydrodynamic performance of carangiform swimming, and help explain why in nature this mode of swimming is typically preferred by fast swimmers.}, }
@article {pmid18446441, year = {2008}, author = {Chung, CK and Shih, TR and Chen, TC and Wu, BH}, title = {Mixing behavior of the rhombic micromixers over a wide Reynolds number range using Taguchi method and 3D numerical simulations.}, journal = {Biomedical microdevices}, volume = {10}, number = {5}, pages = {739-748}, doi = {10.1007/s10544-008-9185-4}, pmid = {18446441}, issn = {1387-2176}, mesh = {Computer Simulation ; Diffusion ; Equipment Design ; *Image Processing, Computer-Assisted ; Microchemistry/*instrumentation/methods ; *Numerical Analysis, Computer-Assisted ; Sensitivity and Specificity ; Software ; Time Factors ; }, abstract = {A planar micromixer with rhombic microchannels and a converging-diverging element has been systematically investigated by the Taguchi method, CFD-ACE simulations and experiments. To reduce the footprint and extend the operation range of Reynolds number, Taguchi method was used to numerically study the performance of the micromixer in a L(9) orthogonal array. Mixing efficiency is prominently influenced by geometrical parameters and Reynolds number (Re). The four factors in a L(9) orthogonal array are number of rhombi, turning angle, width of the rhombic channel and width of the throat. The degree of sensitivity by Taguchi method can be ranked as: Number of rhombi > Width of the rhombic channel > Width of the throat > Turning angle of the rhombic channel. Increasing the number of rhombi, reducing the width of the rhombic channel and throat and lowering the turning angle resulted in better fluid mixing efficiency. The optimal design of the micromixer in simulations indicates over 90% mixing efficiency at both Re > or = 80 and Re < or = 0.1. Experimental results in the optimal simulations are consistent with the simulated one. This planar rhombic micromixer has simplified the complex fabrication process of the multi-layer or three-dimensional micromixers and improved the performance of a previous rhombic micromixer at a reduced footprint and lower Re.}, }
@article {pmid18441754, year = {2008}, author = {Zeiser, T and Bashoor-Zadeh, M and Darabi, A and Baroud, G}, title = {Pore-scale analysis of Newtonian flow in the explicit geometry of vertebral trabecular bones using lattice Boltzmann simulation.}, journal = {Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine}, volume = {222}, number = {2}, pages = {185-194}, doi = {10.1243/09544119JEIM261}, pmid = {18441754}, issn = {0954-4119}, mesh = {*Algorithms ; Body Fluids/*physiology ; Computer Simulation ; Humans ; Microfluidics/*methods ; *Models, Biological ; Porosity ; Spine/*physiology ; }, abstract = {The geometric and transport properties of trabecular bone are of particular interest for medical engineers active in orthopaedic applications and more specifically in hard tissue implantations. This article resorts to computational methods to provide some understanding of the geometric and transport properties of vertebral trabecular bone. A fuzzy distance transform algorithm was used for geometric analysis on the pore scale, and a lattice Boltzmann method (LBM) for the simulation of flow on the same scale. The transport properties of bone including the pressure drop, elongation, and shear component of dissipated energy, and the tortuosity of the bone geometry were extracted from the results of the LBM flow simulations. Whenever suitable, dimensionless numbers were used for the analysis of the data. The average pore size and distribution of the bone were found to be 746 microm and between 75 and 2940 microm, respectively. The permeability of the flow in the cavities of the specific bone sample was found to be 5.05 x 10(-8) m2 for the superior-inferior direction which was by a factor of 1.5-1.7 higher than the permeability in the other two anatomical directions (anterior-posterior). These findings are consistent with experimental results found 3 years prior independently. Tortuosity values approached 1.05 for the superior-inferior direction, and 1.13 and 1.11 for the other two perpendicular directions. The low tortuosities result mainly from the large bone porosity of 0.92. The flow on the pore scale seems to be shear dominated but 30 per cent of the energy dissipation was because of elongational effects. The converging and diverging geometry of the bone explains the significant elongation and deformation of the fluid elements. The transition from creeping flow (the Darcy regime), which is of interest to vertebral augmentation and this study, to the laminar region with significant inertia effects took place at a Reynolds number of about 1-10, as usual for porous media. Finally, the authors wish to advise the readers on the significant computational requirements to be allocated to such a virtual test bench.}, }
@article {pmid18416571, year = {2008}, author = {Allison, S and Pei, H and Haynes, M and Xin, Y and Law, L and Labrum, J and Augustin, D}, title = {Translational diffusion of macromolecules and nanoparticles modeled as non-overlapping bead arrays in an effective medium.}, journal = {The journal of physical chemistry. B}, volume = {112}, number = {18}, pages = {5858-5866}, doi = {10.1021/jp710700n}, pmid = {18416571}, issn = {1520-6106}, abstract = {There are three objectives to the present work. First, starting from a boundary element (BE) formulation of low Reynolds number hydrodynamics, model the translational diffusion of macromolecules modeled as an array of non-overlapping beads, and show how this approach is equivalent to previous formulations of "bead hydrodynamics" and under what conditions. Second, show how this approach can be improved upon by accounting for the variation in forces over the surfaces of individual beads and also extending the approach to a gel modeled as an effective medium, EM. Third, develop a "combined obstruction and hydrodynamic effect" model of the translational diffusion of irregularly shaped macromolecules in a gel. In one of the cases studied, the BE approach is shown to be equivalent to previous "bead model" formulations in which intersubunit hydrodynamic interaction is modeled using the Rotne-Prager tensor. A bead model that accounts for the variation in hydrodynamic stress forces over the individual bead surfaces is shown to be in best agreement with exact results for simple bead arrays made up of 2-4 subunits. The translational diffusion of rods, modeled as strings of from 2 to 100 touching beads in dilute gels is examined. Interpolation formulas valid over a range of gel concentrations and rod lengths are derived for the parallel and perpendicular components of the diffusion tensor as well as the orientationally averaged diffusion tensor. The EM model accounts for the long-range hydrodynamic interaction exerted by the gel support matrix on the diffusing particle of interest but does not account for the reduction in diffusion caused by the direct obstruction of the gel, or steric effect. Both effects are accounted for by writing the translational diffusion in a gel as the product of two terms representing long-range hydrodynamic interaction and steric effects. Finally, the diffusion of a 564 base pair DNA in a 2% agarose gel is examined and model results are compared to experiment (Pluen, A.; Netti, P. A.; Jain, R. K.; Berk, D. A. Biophys. J. 1999, 77, 542-552). For reasonable choices of model parameters, fair agreement between theory and experiment is achieved.}, }
@article {pmid18412512, year = {2008}, author = {Wang, CY}, title = {Heat transfer to blood flow in a small tube.}, journal = {Journal of biomechanical engineering}, volume = {130}, number = {2}, pages = {024501}, doi = {10.1115/1.2898722}, pmid = {18412512}, issn = {0148-0731}, mesh = {Animals ; *Blood Circulation ; Friction ; *Hot Temperature ; Humans ; *Models, Cardiovascular ; Thermal Conductivity ; }, abstract = {Blood flow in a small tube (30-1000 mum) can be successfully modeled by the two-fluid model. The fully developed, constant heat flux convective heat transfer problem is studied. The velocity and temperature profiles are determined in closed form. Formulas for friction-factor-Reynolds number product, axial temperature gradient, and Nusselt number are found.}, }
@article {pmid18412478, year = {2008}, author = {Fedosov, DA and Em Karniadakis, G and Caswell, B}, title = {Dissipative particle dynamics simulation of depletion layer and polymer migration in micro- and nanochannels for dilute polymer solutions.}, journal = {The Journal of chemical physics}, volume = {128}, number = {14}, pages = {144903}, doi = {10.1063/1.2897761}, pmid = {18412478}, issn = {0021-9606}, mesh = {Computer Simulation ; Diffusion ; Microfluidics/*methods ; *Models, Chemical ; *Models, Molecular ; Molecular Conformation ; Nanoparticles/*chemistry/*ultrastructure ; Particle Size ; Polymers/*chemistry ; Porosity ; Surface Properties ; }, abstract = {The flows of dilute polymer solutions in micro- and nanoscale channels are of both fundamental and practical importance in variety of applications in which the channel gap is of the same order as the size of the suspended particles or macromolecules. In such systems depletion layers are observed near solid-fluid interfaces, even in equilibrium, and the imposition of flow results in further cross-stream migration of the particles. In this work we employ dissipative particle dynamics to study depletion and migration in dilute polymer solutions in channels several times larger than the radius of gyration (Rg) of bead-spring chains. We compare depletion layers for different chain models and levels of chain representation, solvent quality, and relative wall-solvent-polymer interactions. By suitable scaling the simulated depletion layers compare well with the asymptotic lattice theory solution of depletion near a repulsive wall. In Poiseuille flow, polymer migration across the streamlines increases with the Peclet and the Reynolds number until the center-of-mass distribution develops two symmetric off-center peaks which identify the preferred chain positions across the channel. These appear to be governed by the balance of wall-chain repulsive interactions and an off-center driving force of the type known as the Segre-Silberberg effect.}, }
@article {pmid18397000, year = {2008}, author = {Toilliez, JO and Szeri, AJ}, title = {Optimized translation of microbubbles driven by acoustic fields.}, journal = {The Journal of the Acoustical Society of America}, volume = {123}, number = {4}, pages = {1916-1930}, doi = {10.1121/1.2887413}, pmid = {18397000}, issn = {1520-8524}, mesh = {*Acoustics ; *Models, Statistical ; Pressure ; Viscosity ; }, abstract = {The problem of a single acoustically driven bubble translating unsteadily in a fluid is considered. The investigation of the translation equation identifies the inverse Reynolds number as a small perturbation parameter. The objective is to obtain a closed-form, leading order solution for the translation of the bubble, assuming nonlinear radial oscillations and a pressure field as the forcing term. In a second part, the periodic attractor of the Rayleigh-Plesset equation serves as basis for an optimal acoustic forcing designed to achieve maximized bubble translation over one dimensionless period. At near-resonant or super-resonant driving frequencies, it seems one cannot improve much on sinusoidal forcing. However at moderate acoustic intensity and sub-resonant frequencies, acoustic wave forms that enhance bubble collapse lead to displacement many times larger than the case of purely sinusoidal forcing. The survey covers a wide spectrum of driving ratios and bubble diameters including those relevant to biomedical applications. Shape stability issues are considered. Together, these results suggest new ways to predict some of the direct and indirect effects of the acoustic radiation force in applications such as targeted drug delivery, selective bubble driving, and accumulation.}, }
@article {pmid18377914, year = {2008}, author = {Liou, TM and Li, YC}, title = {Effects of stent porosity on hemodynamics in a sidewall aneurysm model.}, journal = {Journal of biomechanics}, volume = {41}, number = {6}, pages = {1174-1183}, doi = {10.1016/j.jbiomech.2008.01.025}, pmid = {18377914}, issn = {0021-9290}, mesh = {Cerebrovascular Circulation ; Hemorheology ; Humans ; Intracranial Aneurysm/*physiopathology ; *Models, Cardiovascular ; Porosity ; *Stents ; }, abstract = {Computation and experiment have been complementarily performed to study the fluid flow inside a stented lateral aneurysm anchored on the straight parent vessel. The implicit solver was based on the time-dependent incompressible Navier-Stokes equations of laminar flow. Solutions were generated by a cell-center finite-volume method that used second-order upwind and second-order center flux difference splitting for the convection and diffusion term, respectively. The second-order Crank-Nicolson method was used in the time integration term. Experimental techniques used were flow visualization (FV) and particle tracking velocimetry (PTV). Experimentally, the straight afferent vessel had an inner diameter 10mm. The diameters of the aneurysmal orifice, neck, and fundus were 14, 10, and 15 mm, respectively, and the distance between the orifice and dome measured 20mm. A 30 mm long helix-shaped stent was tested. Four stent porosities of 100%, 70%, 50%, and 25% were examined. Volume-flow rate waveform of a cerebral artery was considered with a maximum Reynolds number of 250 and Womersley number of 3.9. Results are presented in terms of the pulsatile main and secondary flow velocity vector fields, the volume inflow rates into the aneurysm, and the wall shear stress (WSS) and wall pressure at the aneurysm dome. Some comparisons of computed results with the present FV and PTV results and with the data available from the literature are also made. The maximum flow velocity inside the aneurysm ostium and the WSS in the dome region at the peak flow can, respectively, be suppressed to less than 5% of the parent vessel bulk velocity (or 20% of the unstented case) and 8% of the unstented case if the stent porosity is smaller than 40% (about the porosity of the two-layer stents). In general, the three-layer stents seem not as effective as the two-layer stents in reducing the magnitude of aneurysm inflow rate and WSS.}, }
@article {pmid18375846, year = {2008}, author = {Lu, Y and Shen, GX}, title = {Three-dimensional flow structures and evolution of the leading-edge vortices on a flapping wing.}, journal = {The Journal of experimental biology}, volume = {211}, number = {Pt 8}, pages = {1221-1230}, doi = {10.1242/jeb.010652}, pmid = {18375846}, issn = {0022-0949}, mesh = {Animals ; *Biological Evolution ; Flight, Animal/*physiology ; Insecta/*physiology ; Models, Biological ; Rheology ; Wings, Animal/*physiology ; }, abstract = {Following the identification and confirmation of the substructures of the leading-edge vortex (LEV) system on flapping wings, it is apparent that the actual LEV structures could be more complex than had been estimated in previous investigations. In this experimental study, we reveal for the first time the detailed three-dimensional (3-D) flow structures and evolution of the LEVs on a flapping wing in the hovering condition at high Reynolds number (Re=1624). This was accomplished by utilizing an electromechanical model dragonfly wing flapping in a water tank (mid-stroke angle of attack=60 degrees) and applying phase-lock based multi-slice digital stereoscopic particle image velocimetry (DSPIV) to measure the target flow fields at three typical stroke phases: at 0.125 T (T=stroke period), when the wing was accelerating; at 0.25 T, when the wing had maximum speed; and at 0.375 T, when the wing was decelerating. The result shows that the LEV system is a collection of four vortical elements: one primary vortex and three minor vortices, instead of a single conical or tube-like vortex as reported or hypothesized in previous studies. These vortical elements are highly time-dependent in structure and show distinct ;stay properties' at different spanwise sections. The spanwise flows are also time-dependent, not only in the velocity magnitude but also in direction.}, }
@article {pmid18352377, year = {2008}, author = {L'vov, VS and Procaccia, I and Rudenko, O}, title = {Universal model of finite reynolds number turbulent flow in channels and pipes.}, journal = {Physical review letters}, volume = {100}, number = {5}, pages = {054504}, doi = {10.1103/PhysRevLett.100.054504}, pmid = {18352377}, issn = {0031-9007}, abstract = {In this Letter, we suggest a simple and physically transparent analytical model of pressure driven turbulent wall-bounded flows at high but finite Reynolds numbers Re. The model provides an accurate quantitative description of the profiles of the mean-velocity and Reynolds stresses (second order correlations of velocity fluctuations) throughout the entire channel or pipe, for a wide range of Re, using only three Re-independent parameters. The model sheds light on the long-standing controversy between supporters of the century-old log-law theory of von Kàrmàn and Prandtl and proposers of a newer theory promoting power laws to describe the intermediate region of the mean velocity profile.}, }
@article {pmid18352121, year = {2008}, author = {de Zárate, JM and Sengers, JV}, title = {Transverse-velocity fluctuations in a liquid under steady shear.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {2 Pt 2}, pages = {026306}, doi = {10.1103/PhysRevE.77.026306}, pmid = {18352121}, issn = {1539-3755}, abstract = {We present an analysis of the transverse-velocity fluctuations in an isothermal liquid layer with a uniform shear rate between two parallel horizontal boundaries as a function of the wave number and the Reynolds number. The results were obtained by solving a stochastic version of the Orr-Sommerfeld equation subject to no-slip boundary conditions in a second-order Galerkin approximation. We find that the spatial Fourier transform of the transverse-velocity fluctuations exhibits a maximum as a function of the (horizontal) wave number q(parallels). This maximum is associated with a crossover from a q(parallels)(-4) dependence for larger q(parallels) to a q(parallels)(2) dependence for small q(parallels). The q(parallels)(-4) dependence at larger wave numbers is independent of the boundary conditions, but the small- q(parallels) behavior is strongly affected by the boundary conditions. The nonequilibrium enhancement of the intensity of the transverse-velocity fluctuations remains finite for all values of the Reynolds number, but increases approximately with the square of the Reynolds number. The relation between our results and those obtained by previous authors in the absence of boundary conditions is elucidated.}, }
@article {pmid18352117, year = {2008}, author = {Hu, J and Yin, XY and Ben Hadid, H and Henry, D}, title = {Linear temporal and spatiotemporal stability analysis of two-layer falling films with density stratification.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {2 Pt 2}, pages = {026302}, doi = {10.1103/PhysRevE.77.026302}, pmid = {18352117}, issn = {1539-3755}, abstract = {A detailed temporal and spatiotemporal stability analysis of two-layer falling films with density and viscosity stratification is performed by using the Chebyshev collocation method to solve the full system of linear stability equations. From the neutral curves Re(k) for the surface mode and the interface mode of instability, obtained for different density ratios gamma of the upper layer to the lower layer, it is found that smaller density ratios make the surface mode and the short-wave interface mode much more stable, and can even make the short-wave interfacial instability disappear. Moreover, through the study of the local growth rates of the spatiotemporal instability as a function of the ray velocity V , it is found that for not too small incline angles like theta=0.2, the two-layer flow is always convectively unstable, and there is a transition between long- and short-wave instabilities which is determined by the Briggs-Bers collision criterion. Due to the existence of the absolute Rayleigh-Taylor instability for gamma>0 and theta=0, a transition from convective to absolute instability can be detected at small incline angles, and the corresponding boundary curves are plotted for different Reynolds numbers, viscosity ratios, and incline angles. It is found that there exists a limit Reynolds number above which the two-layer film flow can only be convectively unstable for a fixed small incline angle. The spatial amplification properties of the convective waves are finally presented for both surface and interface modes.}, }
@article {pmid18352047, year = {2008}, author = {Kaoui, B and Ristow, GH and Cantat, I and Misbah, C and Zimmermann, W}, title = {Lateral migration of a two-dimensional vesicle in unbounded Poiseuille flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {77}, number = {2 Pt 1}, pages = {021903}, doi = {10.1103/PhysRevE.77.021903}, pmid = {18352047}, issn = {1539-3755}, mesh = {Computer Simulation ; Lipid Bilayers/*chemistry ; *Membrane Fluidity ; Microfluidics/*methods ; *Models, Chemical ; Molecular Conformation ; Motion ; Unilamellar Liposomes/*chemistry ; }, abstract = {The migration of a suspended vesicle in an unbounded Poiseuille flow is investigated numerically in the low Reynolds number limit. We consider the situation without viscosity contrast between the interior of the vesicle and the exterior. Using the boundary integral method we solve the corresponding hydrodynamic flow equations and track explicitly the vesicle dynamics in two dimensions. We find that the interplay between the nonlinear character of the Poiseuille flow and the vesicle deformation causes a cross-streamline migration of vesicles toward the center of the Poiseuille flow. This is in a marked contrast with a result [L. G. Leal, Annu. Rev. Fluid Mech. 12, 435 (1980)] according to which the droplet moves away from the center (provided there is no viscosity contrast between the internal and the external fluids). The migration velocity is found to increase with the local capillary number (defined by the time scale of the vesicle relaxation toward its equilibrium shape times the local shear rate), but reaches a plateau above a certain value of the capillary number. This plateau value increases with the curvature of the parabolic flow profile. We present scaling laws for the migration velocity.}, }
@article {pmid18348974, year = {2008}, author = {Risso, F and Roig, V and Amoura, Z and Riboux, G and Billet, AM}, title = {Wake attenuation in large Reynolds number dispersed two-phase flows.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {366}, number = {1873}, pages = {2177-2190}, doi = {10.1098/rsta.2008.0002}, pmid = {18348974}, issn = {1364-503X}, abstract = {The dynamics of high Reynolds number-dispersed two-phase flow strongly depends on the wakes generated behind the moving bodies that constitute the dispersed phase. The length of these wakes is considerably reduced compared with those developing behind isolated bodies. In this paper, this wake attenuation is studied from several complementary experimental investigations with the aim of determining how it depends on the body Reynolds number and the volume fraction alpha. It is first shown that the wakes inside a homogeneous swarm of rising bubbles decay exponentially with a characteristic length that scales as the ratio of the bubble diameter d to the drag coefficient Cd, and surprisingly does not depend on alpha for 10(-2)<or=alpha<or=10(-1). The attenuation of the wakes in a fixed array of spheres randomly distributed in space (alpha=2 x 10(-2)) is observed to be stronger than that of the wake of an isolated sphere in a turbulent incident flow, but similar to that of bubbles within a homogeneous swarm. It thus appears that the wakes in dispersed two-phase flows are controlled by multi-body interactions, which cause a much faster decay than turbulent fluctuations having the same energy and integral length scale. Decomposition of velocity fluctuations into a contribution related to temporal variations and that associated to the random character of the body positions is proposed as a perspective for studying the mechanisms responsible for multi-body interactions.}, }
@article {pmid18323947, year = {1999}, author = {Renfro, MW and King, GB and Laurendeau, NM}, title = {Quantitative hydroxyl concentration time-series measurements in turbulent nonpremixed flames.}, journal = {Applied optics}, volume = {38}, number = {21}, pages = {4596-4608}, doi = {10.1364/ao.38.004596}, pmid = {18323947}, issn = {1559-128X}, abstract = {Quantitative hydroxyl concentration time-series measurements have been obtained by picosecond time-resolved laser-induced fluorescence in a series of methane-air and hydrogen-argon-air nonpremixed flames. The recovery of a quantitative time series is complicated by the need to account for fluctuations in the fluorescence lifetime. We have recently developed instrumentation that enables the simultaneous measurement of fluorescence signal and lifetime. The present research represents the first application of this technique to turbulent flames. The correction for hydroxyl lifetime fluctuations is shown to be significant for mean concentrations and thus probability density functions but negligible for power spectral densities (PSD's). The hydroxyl PSD's were found to vary slightly with radial and axial location in the flames and to vary significantly with Reynolds number. However, the PSD's in the H(2)-Ar-air flames are nearly identical to those in the CH(4)-air flames.}, }
@article {pmid18314890, year = {2008}, author = {Sheng, JJ and Sirois, PJ and Dressman, JB and Amidon, GL}, title = {Particle diffusional layer thickness in a USP dissolution apparatus II: a combined function of particle size and paddle speed.}, journal = {Journal of pharmaceutical sciences}, volume = {97}, number = {11}, pages = {4815-4829}, doi = {10.1002/jps.21345}, pmid = {18314890}, issn = {1520-6017}, support = {GM07767/GM/NIGMS NIH HHS/United States ; }, mesh = {*Chemistry, Pharmaceutical ; Diffusion ; Fenofibrate/*chemistry ; Particle Size ; Solubility ; Viscosity ; }, abstract = {This work was to investigate the effects of particle size and paddle speed on the particle diffusional layer thickness h(app) in a USP dissolution apparatus II. After the determination of the powder dissolution rates of five size fractions of fenofibrate, including <20, 20-32, 32-45, 63-75, and 90-106 microm, the present work shows that the dependence of h(app) on particle size follows different functions in accordance with the paddle speed. At 50 rpm, the function of h(app) is best described by a linear plot of h{app} = 9.91sqrt d-23.31 (R(2) = 0.98) throughout the particle diameter, d, from 6.8 to 106 microm. In contrast, at 100 rpm a transitional particle radius, r, of 23.7 microm exists, under which linear relationship h(app) = 1.59r (R(2) = 0.98) occurs, but above which h(app) becomes a constant of 43.5 microm. Thus, h(app) changes not only with particle size, but also with the hydrodynamics under standard USP configurations, which has been overlooked in the past. Further, the effects of particle size and paddle speed on h(app) were combined using dimensionless analysis. Within certain fluid velocity/particle regime, linear correlation of h(app)/d with the square-root of Reynolds number (d\varpi/upsilon){1/2}, that is, h{app}/d = 1.5207 - 9.25 x 10{- 4} (d\varpi/n){1/2} (R(2) = 0.9875), was observed.}, }
@article {pmid18298194, year = {2008}, author = {Varghese, SS and Frankel, SH and Fischer, PF}, title = {Modeling transition to turbulence in eccentric stenotic flows.}, journal = {Journal of biomechanical engineering}, volume = {130}, number = {1}, pages = {014503}, doi = {10.1115/1.2800832}, pmid = {18298194}, issn = {0148-0731}, mesh = {Blood Flow Velocity ; Blood Pressure ; Carotid Stenosis/*physiopathology ; Computer Simulation ; Humans ; *Models, Cardiovascular ; *Nonlinear Dynamics ; Pulsatile Flow ; }, abstract = {Mean flow predictions obtained from a host of turbulence models were found to be in poor agreement with recent direct numerical simulation results for turbulent flow distal to an idealized eccentric stenosis. Many of the widely used turbulence models, including a large eddy simulation model, were unable to accurately capture the poststenotic transition to turbulence. The results suggest that efforts toward developing more accurate turbulence models for low-Reynolds number, separated transitional flows are necessary before such models can be used confidently under hemodynamic conditions where turbulence may develop.}, }
@article {pmid18298191, year = {2008}, author = {Fresconi, FE and Prasad, AK}, title = {Convective dispersion during steady flow in the conducting airways of the human lung.}, journal = {Journal of biomechanical engineering}, volume = {130}, number = {1}, pages = {011015}, doi = {10.1115/1.2838042}, pmid = {18298191}, issn = {0148-0731}, mesh = {Aerosols/*pharmacokinetics ; Computer Simulation ; Humans ; Lung/*metabolism ; *Models, Biological ; Respiratory Mechanics/*physiology ; Rheology/*methods ; }, abstract = {The adverse health effects of inhaled particulate matter from the environment depend on its dispersion, transport, and deposition in the human airways. Similarly, precise targeting of deposition sites by pulmonary drug delivery systems also relies on characterizing the dispersion and transport of therapeutic aerosols in the respiratory tract. A variety of mechanisms may contribute to convective dispersion in the lung; simple axial streaming, augmented dispersion, and steady streaming are investigated in this effort. Flow visualization of a bolus during inhalation and exhalation, and dispersion measurements were conducted during steady flow in a three-generational, anatomically accurate in vitro model of the conducting airways to support this goal. Control variables included Reynolds number, flow direction, generation, and branch. Experiments illustrate transport patterns in the lumen cross section and map their relation to dispersion metrics. These results indicate that simple axial streaming, rather than augmented dispersion, is the dominant steady convective dispersion mechanism in symmetric Weibel generations 7-13 during normal respiration. Experimental evidence supports the branching nature of the airways as a possible contributor to steady streaming in the lung.}, }
@article {pmid18298184, year = {2008}, author = {Xi, J and Longest, PW}, title = {Effects of oral airway geometry characteristics on the diffusional deposition of inhaled nanoparticles.}, journal = {Journal of biomechanical engineering}, volume = {130}, number = {1}, pages = {011008}, doi = {10.1115/1.2838039}, pmid = {18298184}, issn = {0148-0731}, mesh = {Aerosols/*chemistry/*pharmacokinetics ; Computer Simulation ; Diffusion ; Humans ; Inhalation/*physiology ; *Models, Biological ; Mouth/anatomy &amp; histology/*chemistry/physiology ; Nanoparticles/administration &amp; dosage/*chemistry ; }, abstract = {The deposition of ultrafine aerosols in the respiratory tract presents a significant health risk due to the increased cellular-level response that these particles may invoke. However, the effects of geometric simplifications on local and regional nanoparticle depositions remain unknown for the oral airway and throughout the respiratory tract. The objective of this study is to assess the effects of geometric simplifications on diffusional transport and deposition characteristics of inhaled ultrafine aerosols in models of the extrathoracic oral airway. A realistic model of the oral airway with the nasopharynx (NP) included has been constructed based on computed tomography scans of a healthy adult in conjunction with measurements reported in the literature. Three other geometries with descending degrees of physical realism were then constructed with successive geometric simplifications of the realistic model. A validated low Reynolds number k-omega turbulence model was employed to simulate laminar, transitional, and fully turbulent flow regimes for the transport of 1-200 nm particles. Results of this study indicate that the geometric simplifications considered did not significantly affect the total deposition efficiency or maximum local deposition enhancement of nanoparticles. However, particle transport dynamics and the underlying flow characteristics such as separation, turbulence intensity, and secondary motions did show an observable sensitivity to the geometric complexity. The orientation of the upper trachea was shown to be a major factor determining local deposition downstream of the glottis and should be retained in future models of the respiratory tract. In contrast, retaining the NP produced negligible variations in airway dynamics and could be excluded for predominantly oral breathing conditions. Results of this study corroborate the use of existing diffusion correlations based on a circular oral airway model. In comparison to previous studies, an improved correlation for the deposition of nanoparticles was developed based on a wider range of particle sizes and flow rates, which captures the dependence of the Sherwood number on both Reynolds and Schmidt numbers.}, }
@article {pmid18297492, year = {2008}, author = {Howden, L and Giddings, D and Power, H and Aroussi, A and Vloeberghs, M and Garnett, M and Walker, D}, title = {Three-dimensional cerebrospinal fluid flow within the human ventricular system.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {11}, number = {2}, pages = {123-133}, doi = {10.1080/10255840701492118}, pmid = {18297492}, issn = {1025-5842}, mesh = {Cerebrospinal Fluid/*physiology ; Computer Simulation ; Humans ; Imaging, Three-Dimensional/*methods ; *Models, Biological ; Rheology/*methods ; *Ventricular Function ; }, abstract = {Cerebrospinal fluid (CSF) is a Newtonian fluid and can, therefore, be modelled using computational fluid dynamics (CFD). Previous modelling of the CSF has been limited to simplified geometric models. This work describes a geometrically accurate three dimensional (3D) computational model of the human ventricular system (HVS) constructed from magnetic resonance images (MRI) of the human brain. It is an accurate and full representation of the HVS and includes appropriately positioned CSF production and drainage locations. It was used to investigate the pulsatile motion of CSF within the human brain. During this investigation CSF flow rate was set at a constant 500 ml/day, to mimic real life secretion of CSF into the system, and a pulsing velocity profile was added to the inlets to incorporate the effect of cardiac pulsations on the choroid plexus and their subsequent influence on CSF motion in the HVS. Boundary conditions for the CSF exits from the ventricles (foramina of Magendie and Lushka) were found using a "nesting" approach, in which a simplified model of the entire central nervous system (CNS) was used to examine the effects of the CSF surrounding the ventricular system (VS). This model provided time varying pressure data for the exits from the VS nested within it. The fastest flow was found in the cerebral aqueduct, where a maximum velocity of 11.38 mm/s was observed over five cycles. The maximum Reynolds number recorded during the simulation was 15 with an average Reynolds number of the order of 0.39, indicating that CSF motion is creeping flow in most of the computational domain and consequently will follow the geometry of the model. CSF pressure also varies with geometry with a maximum pressure drop of 1.14 Pa occurring through the cerebral aqueduct. CSF flow velocity is substantially slower in the areas that are furthest away from the inlets; in some areas flow is nearly stagnant.}, }
@article {pmid18273551, year = {2008}, author = {Golestanian, R}, title = {Three-sphere low-Reynolds-number swimmer with a cargo container.}, journal = {The European physical journal. E, Soft matter}, volume = {25}, number = {1}, pages = {1-4}, pmid = {18273551}, issn = {1292-8941}, mesh = {*Algorithms ; Biomechanical Phenomena ; Computer Simulation ; Forearm/physiology ; Hand/physiology ; Humans ; *Models, Biological ; Molecular Motor Proteins/chemistry/physiology ; Movement/*physiology ; Swimming/*physiology ; }, abstract = {A recently introduced model for an autonomous swimmer at low Reynolds number that is comprised of three spheres connected by two arms is considered when one of the spheres has a large radius. The Stokes hydrodynamic flow associated with the swimming strokes and net motion of this system can be studied analytically using the Stokes Green's function of a point force in front of a sphere of arbitrary radius R provided by Oseen. The swimming velocity is calculated, and shown to scale as 1/R3 with the radius of the sphere.}, }
@article {pmid18273548, year = {2008}, author = {Yamaguchi, R and Ujiie, H and Haida, S and Nakazawa, N and Hori, T}, title = {Velocity profile and wall shear stress of saccular aneurysms at the anterior communicating artery.}, journal = {Heart and vessels}, volume = {23}, number = {1}, pages = {60-66}, pmid = {18273548}, issn = {0910-8327}, mesh = {Blood Flow Velocity/*physiology ; Cerebrovascular Circulation/*physiology ; Humans ; Intracranial Aneurysm/*physiopathology ; Laser-Doppler Flowmetry ; Models, Theoretical ; Severity of Illness Index ; Shear Strength ; Stress, Mechanical ; }, abstract = {It has recently been shown that the aspect ratio (dome/neck) of an aneurysm correlates well with intraaneurysmal blood flow. Aneurysms with an aspect ratio larger than 1.6 carry a higher risk of rupture. We examined the effect of aspect ratio (AR) on intra-aneurysmal flow using experimental models. Flow visualization with particle imaging velocimetry and measurement of wall shear stress using laser Doppler anemometry were performed on three different aneurysm models: AR 0.5, 1.0, and 2.0. Intraaneurysmal flow consists of inflow, circulation, and outflow. Rapid inflow impinged on the distal neck creating a stagnant point. Rapid flow and maximum wall shear stress were observed in the vicinity of the stagnant point. By changing the Reynold's number, the stagnant point moved. By increasing the AR of the aneurysm, vortices inside the aneurysm sac closed and very slow flow was observed, resulting in very low shear stress markedly at a Reynold's number of 250, compatible with the diastolic phase. In the aneurysm model AR 2.0, both rapid flow at the neck and vortices inside the aneurysm are sufficient to activate platelets, making a thrombus that may anchor on the dome where very slow flow takes place. Hemodynamics in aneurysms larger than AR 2.0 definitely contribute to thrombus formation.}, }
@article {pmid18264314, year = {1997}, author = {Nozhat, WM}, title = {Measurement of liquid-film thickness by laser interferometry.}, journal = {Applied optics}, volume = {36}, number = {30}, pages = {7864-7869}, doi = {10.1364/ao.36.007864}, pmid = {18264314}, issn = {1559-128X}, abstract = {Here the variation of a liquid-film thickness at small Reynolds numbers is discussed. The film thickness measurement by laser interferometry corresponds to the liquid flowing on the inner surface of a small-bore glass tube. An adequate theoretical background for the techniques used in this experiment is discussed to demonstrate the capability of the experimental technique. An advantage of this method is that it shows the shape of the thin film on the inner surface of the vertical tube at a point in a horizontal cross section. The results obtained from this experiment show that the flow of liquid films on vertical surfaces is inherently unstable and three dimensional even at a Reynolds number smaller than 1.}, }
@article {pmid18260678, year = {2008}, author = {Son, Y and Kim, C and Yang, DH and Ahn, DJ}, title = {Spreading of an inkjet droplet on a solid surface with a controlled contact angle at low Weber and Reynolds numbers.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {24}, number = {6}, pages = {2900-2907}, doi = {10.1021/la702504v}, pmid = {18260678}, issn = {0743-7463}, mesh = {Adsorption ; *Membranes, Artificial ; Silanes/*chemistry ; Silicon/*chemistry ; Silicon Dioxide/*chemistry ; Surface Properties ; Water/*chemistry ; Wettability ; }, abstract = {Even though the inkjet technology has been recognized as one of the most promising technologies for electronic and bio industries, the full understanding of the dynamics of an inkjet droplet at its operating conditions is still lacking. In this study, the normal impact of water droplets on solid substrates was investigated experimentally. The size of water droplets studied here was 46 microm and was much smaller than the most of the previous studies on drop impact. The Weber number (We) and Reynolds number (Re) were 0.05-2 and 10-100, respectively, and the Ohnesorge number was fixed at 0.017. The wettability of the solid substrate was varied by adsorbing a self-assembled monolayer of octadecyltrichlorosilane followed by the exposure to UV-ozone plasma. The impact scenarios for low We impacts were found to be qualitatively different from the high to moderate We impacts. Neither the development of a thin film and lamella under the traveling sphere nor the entrapment of small bubbles was observed. The dynamics of droplet impact at the conditions studied here is found to proceed under the combined influences of inertia, surface tension, and viscosity without being dominated by one specific mechanism. The maximum spreading factor (beta), the ratio of the diameter of the wetted surface and the drop diameter before impact, was correlated well with the relationship ln beta=0.090 ln We/(fs-cos theta)+0.151 for three decades of We/(fs-cos theta), where theta is the equilibrium contact angle, and fs is the ratio between the surface areas contacting the air and the solid substrate. The result implies that the final shape of the droplet is determined by the surface phenomenon rather than fluid mechanical effects.}, }
@article {pmid18247868, year = {2008}, author = {Moreau, S and Bailliet, H and Valière, JC}, title = {Measurements of inner and outer streaming vortices in a standing waveguide using laser doppler velocimetry.}, journal = {The Journal of the Acoustical Society of America}, volume = {123}, number = {2}, pages = {640-647}, doi = {10.1121/1.2828059}, pmid = {18247868}, issn = {1520-8524}, abstract = {Measurements of the axial streaming velocity are performed by means of laser doppler velocimetry in an experimental apparatus consisting of a waveguide having loudspeakers at each end for high intensity sound levels. Streaming is characterized by an appropriate Reynolds number Re(NL), the case Re(NL)<<1 corresponding to the so-called slow streaming and the case Re(NL)>/=1 being referred to as fast streaming. The variation of axial streaming velocity with respect to the transverse coordinate is compared to the available slow streaming theory. Streaming fluid flow is measured both in the core region and in the near wall region. Streaming velocity in the center of the guide agrees reasonably well with the slow streaming theory for small Re(NL) but deviates significantly from such predictions for Re(NL)>20 and its evolution for further increasing Re(NL) is discussed. Then streaming behavior in the near wall region is particularly studied. For Re(NL)<70, two vortices are present across the guide section as predicted by slow streaming theory. Then it appears that, when the Reynolds number is increased, two other vortices become visible in the near wall region. Different stages for the generation and evolution of these inner streaming vortices are presented.}, }
@article {pmid18247773, year = {2007}, author = {Krane, M and Barry, M and Wei, T}, title = {Unsteady behavior of flow in a scaled-up vocal folds model.}, journal = {The Journal of the Acoustical Society of America}, volume = {122}, number = {6}, pages = {3659-3670}, pmid = {18247773}, issn = {1520-8524}, support = {R01 DC005642/DC/NIDCD NIH HHS/United States ; R01 DC005642-01/DC/NIDCD NIH HHS/United States ; 1R01DC054642-0L/DC/NIDCD NIH HHS/United States ; }, mesh = {Biomechanical Phenomena ; Glottis/anatomy &amp; histology/*physiology ; Humans ; *Models, Anatomic ; *Models, Biological ; Motion ; *Phonation ; Pressure ; *Rheology ; Signal Processing, Computer-Assisted ; Time Factors ; Vocal Cords/anatomy &amp; histology/*physiology ; }, abstract = {Measurements of the fluid flow through a scaled-up model of the human glottis are presented to determine whether glottal flow may be approximated as unsteady. Time- and space-resolved velocity vector fields from digital particle image velocimetry (DPIV) measurements of the flow through the gap between two moving, rigid walls are presented in four cases, over a range of Strouhal numbers: 0.010, 0.018, 0.035, 0.040, corresponding to life-scale f(0) of 30, 58, 109, and 126 Hz, respectively, at a Reynolds number of 8000. It is observed that (1) glottal flow onset is delayed after glottal opening and (2) glottal flow shutoff occurs prior to closure. A comparison between flow through a fully open, nonmoving glottis and that through the moving vocal folds shows a marked difference in spatial structure of the glottal jet. The following features of the flow are seen to exhibit strong dependence on cycle frequency: (a) glottal exit plane velocity, (b) volume flow, (c) vortex shedding rates, and (d) vortex amplitude. Vortex shedding appears to be a factor both in controlling flow resistance and in cycle-to-cycle volume flow variations. All these observations strongly suggest that glottal flow is inherently unsteady.}, }
@article {pmid18241875, year = {2008}, author = {Hartley, WH and Banerjee, S}, title = {Imaging c-PAM-induced flocculation of paper fibers.}, journal = {Journal of colloid and interface science}, volume = {320}, number = {1}, pages = {159-162}, doi = {10.1016/j.jcis.2007.12.036}, pmid = {18241875}, issn = {0021-9797}, abstract = {The flocculation of paper fibers by cationic polyacrylamides (c-PAM) was studied by imaging the fibers that remain free during flocculation. Studies with fibers of different lengths showed that the degree of flocculation increases with fiber length, with the best flocs being formed with mixtures of short and long fibers. Short fibers did not flocculate by themselves but were captured by flocs formed with longer fibers. The short fibers strengthen the floc and give it shear resistance. Shear had the expected effect of promoting flocculation at low Reynolds number but disrupting it at higher values. For a given polymer the maximum floc size for a mixture of fibers is dictated by the length distribution of the fibers. The polymer dose governs the rate of flocculation. The technique is especially useful in following the tail end of the flocculation process. At this stage a floc is almost fully grown and a small increase in its size would be very difficult to measure by conventional techniques. In contrast, the number of free fibers measured by single fiber imaging decreases rapidly at this point.}, }
@article {pmid18238238, year = {2003}, author = {Farrell, JA and Pang, S and Li, W}, title = {Plume mapping via hidden Markov methods.}, journal = {IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics : a publication of the IEEE Systems, Man, and Cybernetics Society}, volume = {33}, number = {6}, pages = {850-863}, doi = {10.1109/TSMCB.2003.810873}, pmid = {18238238}, issn = {1083-4419}, abstract = {This paper addresses the problem of mapping likely locations of a chemical source using an autonomous vehicle operating in a fluid flow. The paper reviews biological plume-tracing concepts, reviews previous strategies for vehicle-based plume tracing, and presents a new plume mapping approach based on hidden Markov methods (HMM). HMM provide efficient algorithms for predicting the likelihood of odor detection versus position, the likelihood of source location versus position, the most likely path taken by the odor to a given location, and the path between two points most likely to result in odor detection. All four are useful for solving the odor source localization problem using an autonomous vehicle. The vehicle is assumed to be capable of detecting above threshold chemical concentration and sensing the fluid flow velocity at the vehicle location. The fluid flow is assumed to vary with space and time, and to have a high Reynolds number (Re>10).}, }
@article {pmid18233947, year = {2007}, author = {Candelier, F and Souhar, M}, title = {Time-dependent lift force acting on a particle moving arbitrarily in a pure shear flow, at small Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {76}, number = {6 Pt 2}, pages = {067301}, doi = {10.1103/PhysRevE.76.067301}, pmid = {18233947}, issn = {1539-3755}, abstract = {In this paper we seek an approximate expression for the time-dependent lift force, initially derived by Saffman in the steady case, by using the Asmolov and McLaughlin frequential results. The single-frequency expression derived by these authors can indeed be used to obtain a temporal expression of the lift force acting on a sphere with arbitrary motion, since the problem is linear. The major difficulty lies in the fact that their frequential results are given under a very complicated algebraic expression. Therefore, no analytical inverse Fourier transform can be carried out and the expression of the time-dependent lift force acting on a particle cannot be obtained in the general case. In the present paper, however, it is shown that a closed temporal expression for this force can be found, provided one makes additional approximations. This expression takes the form of a convolution product involving an empirical kernel as well as the slip velocity of the particle.}, }
@article {pmid18233759, year = {2007}, author = {Pietarila Graham, J and Holm, DD and Mininni, PD and Pouquet, A}, title = {Highly turbulent solutions of the Lagrangian-averaged Navier-Stokes alpha model and their large-eddy-simulation potential.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {76}, number = {5 Pt 2}, pages = {056310}, doi = {10.1103/PhysRevE.76.056310}, pmid = {18233759}, issn = {1539-3755}, abstract = {We compute solutions of the Lagrangian-averaged Navier-Stokes alpha - (LANS alpha) model for significantly higher Reynolds numbers (up to Re approximately 8300) than have previously been accomplished. This allows sufficient separation of scales to observe a Navier-Stokes inertial range followed by a second inertial range specific to the LANS alpha model. Both fully helical and nonhelical flows are examined, up to Reynolds numbers of approximately 1300. Analysis of the third-order structure function scaling supports the predicted l3 scaling; it corresponds to a k-1 scaling of the energy spectrum for scales smaller than alpha. The energy spectrum itself shows a different scaling, which goes as k1. This latter spectrum is consistent with the absence of stretching in the subfilter scales due to the Taylor frozen-in hypothesis employed as a closure in the derivation of the LANS alpha model. These two scalings are conjectured to coexist in different spatial portions of the flow. The l3 [E(k) approximately k-1] scaling is subdominant to k1 in the energy spectrum, but the l3 scaling is responsible for the direct energy cascade, as no cascade can result from motions with no internal degrees of freedom. We demonstrate verification of the prediction for the size of the LANS alpha attractor resulting from this scaling. From this, we give a methodology either for arriving at grid-independent solutions for the LANS alpha model, or for obtaining a formulation of the large eddy simulation optimal in the context of the alpha models. The fully converged grid-independent LANS alpha model may not be the best approximation to a direct numerical simulation of the Navier-Stokes equations, since the minimum error is a balance between truncation errors and the approximation error due to using the LANS alpha instead of the primitive equations. Furthermore, the small-scale behavior of the LANS alpha model contributes to a reduction of flux at constant energy, leading to a shallower energy spectrum for large alpha. These small-scale features, however, do not preclude the LANS alpha model from reproducing correctly the intermittency properties of the high-Reynolds-number flow.}, }
@article {pmid18233758, year = {2007}, author = {Rüdiger, G and Schultz, M and Shalybkov, D and Hollerbach, R}, title = {Theory of current-driven instability experiments in magnetic Taylor-Couette flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {76}, number = {5 Pt 2}, pages = {056309}, doi = {10.1103/PhysRevE.76.056309}, pmid = {18233758}, issn = {1539-3755}, abstract = {We consider the linear stability of dissipative magnetic Taylor-Couette flow with imposed toroidal magnetic fields. The inner and outer cylinders can be either insulating or conducting; the inner one rotates, the outer one is stationary. The magnetic Prandtl number can be as small as 10(-5) , approaching realistic liquid-metal values. The magnetic field destabilizes the flow, except for radial profiles of B(phi)(R) close to the current-free solution. The profile with B(in)=B(out) (the most uniform field) is considered in detail. For weak fields the Taylor-Couette flow is stabilized, until for moderately strong fields the m=1 azimuthal mode dramatically destabilizes the flow again so that a maximum value for the critical Reynolds number exists. For sufficiently strong fields (as measured by the Hartmann number) the toroidal field is always unstable, even for the nonrotating case with Re=0 . The electric currents needed to generate the required toroidal fields in laboratory experiments are a few kA if liquid sodium is used, somewhat more if gallium is used. Weaker currents are needed for wider gaps, so a wide-gap apparatus could succeed even with gallium. The critical Reynolds numbers are only somewhat larger than the nonmagnetic values; hence such experiments would work with only modest rotation rates.}, }
@article {pmid18233756, year = {2007}, author = {Rogachevskii, I and Kleeorin, N}, title = {Magnetic fluctuations and formation of large-scale inhomogeneous magnetic structures in a turbulent convection.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {76}, number = {5 Pt 2}, pages = {056307}, doi = {10.1103/PhysRevE.76.056307}, pmid = {18233756}, issn = {1539-3755}, abstract = {Magnetic fluctuations generated by a tangling of the mean magnetic field by velocity fluctuations are studied in a developed turbulent convection with large magnetic Reynolds numbers. We show that the energy of magnetic fluctuations depends on the magnetic Reynolds number only when the mean magnetic field is smaller than B(eq)/4Rm(1/4), where B(eq) is the equipartition mean magnetic field determined by the turbulent kinetic energy and Rm is the magnetic Reynolds number. Generation of magnetic fluctuations in a turbulent convection with a nonzero mean magnetic field results in a decrease of the total turbulent pressure and may cause the formation of large-scale inhomogeneous magnetic structures even in an originally uniform mean magnetic field. This effect is caused by a negative contribution of the turbulent convection to the effective mean Lorentz force. The inhomogeneous large-scale magnetic fields are formed due to excitation of the large-scale instability. The energy for this instability is supplied by small-scale turbulent convection. The discussed effects might be useful for understanding the origin of solar nonuniform magnetic fields: e.g., sunspots.}, }
@article {pmid18233676, year = {2007}, author = {Lehtola, V and Punkkinen, O and Ala-Nissila, T}, title = {Polymer scaling and dynamics in steady-state sedimentation at infinite Péclet number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {76}, number = {5 Pt 1}, pages = {051802}, doi = {10.1103/PhysRevE.76.051802}, pmid = {18233676}, issn = {1539-3755}, abstract = {We consider the static and dynamical behavior of a flexible polymer chain under steady-state sedimentation using analytic arguments and computer simulations. The model system comprises a single coarse-grained polymer chain of N segments, which resides in a Newtonian fluid as described by the Navier-Stokes equations. The chain is driven into nonequilibrium steady state by gravity acting on each segment. The equations of motion for the segments and the Navier-Stokes equations are solved simultaneously using an immersed boundary method, where thermal fluctuations are neglected. To characterize the chain conformation, we consider its radius of gyration RG(N). We find that the presence of gravity explicitly breaks the spatial symmetry leading to anisotropic scaling of the components of RG with N along the direction of gravity RG, parallel and perpendicular to it RG, perpendicular, respectively. We numerically estimate the corresponding anisotropic scaling exponents nu parallel approximately 0.79 and nu perpendicular approximately 0.45, which differ significantly from the equilibrium scaling exponent nue=0.588 in three dimensions. This indicates that on the average, the chain becomes elongated along the sedimentation direction for large enough N. We present a generalization of the Flory scaling argument, which is in good agreement with the numerical results. It also reveals an explicit dependence of the scaling exponents on the Reynolds number. To study the dynamics of the chain, we compute its effective diffusion coefficient D(N), which does not contain Brownian motion. For the range of values of N used here, we find that both the parallel and perpendicular components of D increase with the chain length N, in contrast to the case of thermal diffusion in equilibrium. This is caused by the fluid-driven fluctuations in the internal configuration of the polymer that are magnified as polymer size becomes larger.}, }
@article {pmid18233525, year = {2007}, author = {Mininni, PD and Pouquet, A}, title = {Energy spectra stemming from interactions of Alfvén waves and turbulent eddies.}, journal = {Physical review letters}, volume = {99}, number = {25}, pages = {254502}, doi = {10.1103/PhysRevLett.99.254502}, pmid = {18233525}, issn = {0031-9007}, abstract = {We present a numerical analysis of an incompressible decaying magnetohydrodynamic turbulence run on a grid of 1536{3} points. The Taylor Reynolds number at the maximum of dissipation is approximately 1100, and the initial condition is a superposition of large-scale Arn'old-Beltrami-Childress flows and random noise at small scales, with no uniform magnetic field. The initial kinetic and magnetic energies are equal, with negligible correlation. The resulting energy spectrum is a combination of two components, each moderately resolved. Isotropy obtains in the large scales, with a spectral law compatible with the Iroshnikov-Kraichnan theory stemming from the weakening of nonlinear interactions due to Alfvén waves; scaling of structure functions confirms the non-Kolmogorovian nature of the flow in this range. At small scales, weak turbulence emerges with a k{perpendicular}{-2} spectrum, the perpendicular direction referring to the local quasiuniform magnetic field.}, }
@article {pmid18233332, year = {2007}, author = {Pooley, CM and Alexander, GP and Yeomans, JM}, title = {Hydrodynamic interaction between two swimmers at low Reynolds number.}, journal = {Physical review letters}, volume = {99}, number = {22}, pages = {228103}, doi = {10.1103/PhysRevLett.99.228103}, pmid = {18233332}, issn = {0031-9007}, mesh = {Animals ; *Models, Biological ; Movement/*physiology ; Paramecium/physiology ; }, abstract = {We investigate the hydrodynamic interactions between micro-organisms swimming at low Reynolds number. By considering simple model swimmers, and combining analytic and numerical approaches, we investigate the time-averaged flow field around a swimmer. At short distances the swimmer behaves like a pump. At large distances the velocity field depends on whether the swimming stroke is invariant under a combined time-reversal and parity transformation. We then consider two swimmers and find that the interaction between them consists of two parts: a passive term, independent of the motion of the second swimmer, and an active term resulting from the simultaneous swimming action of both swimmers. The swimmer-swimmer interaction is a complicated function of their relative displacement, orientation, and phase, leading to motion that can be attractive, repulsive, or oscillatory.}, }
@article {pmid18233291, year = {2007}, author = {Keating, SR and Diamond, PH}, title = {Turbulent diffusion of magnetic fields in two-dimensional magnetohydrodynamic turbulence with stable stratification.}, journal = {Physical review letters}, volume = {99}, number = {22}, pages = {224502}, doi = {10.1103/PhysRevLett.99.224502}, pmid = {18233291}, issn = {0031-9007}, abstract = {We calculate the correction, due to nonlinear wave-wave interactions, to the Zel'dovich estimate for the turbulent diffusivity of magnetic fields in a model of two-dimensional magnetohydrodynamic turbulence in the presence of stable stratification. Such a model has some relevance to hydromagnetic turbulence in stellar interiors. The significance of this correction is that, unlike the lowest-order Zel'dovich balance, it is independent of the molecular resistivity eta and so will not vanish in the limit of a large magnetic Reynolds number, although the correction is O(sigma;{4}), where sigma is the wave slope, which necessarily is small. Thus, we are led to the counterintuitive result that the presence of stable stratification can actually increase the vertical flux of magnetic fields relative to that in 2D MHD turbulence without stratification.}, }
@article {pmid18233145, year = {2007}, author = {Xu, H and Ouellette, NT and Vincenzi, D and Bodenschatz, E}, title = {Acceleration correlations and pressure structure functions in high-reynolds number turbulence.}, journal = {Physical review letters}, volume = {99}, number = {20}, pages = {204501}, doi = {10.1103/PhysRevLett.99.204501}, pmid = {18233145}, issn = {0031-9007}, abstract = {We present measurements of fluid particle accelerations in turbulent water flow between counterrotating disks using three-dimensional Lagrangian particle tracking. By simultaneously following multiple particles with sub-Kolmogorov-time-scale temporal resolution, we measured the spatial correlation of fluid particle acceleration at Taylor microscale Reynolds numbers between 200 and 690. We also obtained indirect, nonintrusive measurements of the Eulerian pressure structure functions by integrating the acceleration correlations. Our measurements are in good agreement with the theoretical predictions of the acceleration correlations and the pressure structure function in isotropic high-Reynolds number turbulence by Obukhov and Yaglom in 1951 [Prikl. Mat. Mekh. 15, 3 (1951)]. The measured pressure structure functions display K41 scaling in the inertial range.}, }
@article {pmid18233039, year = {2008}, author = {Golestanian, R and Ajdari, A}, title = {Mechanical response of a small swimmer driven by conformational transitions.}, journal = {Physical review letters}, volume = {100}, number = {3}, pages = {038101}, doi = {10.1103/PhysRevLett.100.038101}, pmid = {18233039}, issn = {0031-9007}, abstract = {A conformation space kinetic model is constructed to drive the deformation cycle of a three-sphere swimmer to achieve propulsion at low Reynolds number. We analyze the effect of an external load on the performance of this kinetic swimmer and show that it depends sensitively on where the force is exerted, so that there is no general force-velocity relation. We discuss how the conformational cycle of such swimmers should be designed to increase their performance in resisting forces applied at specific points.}, }
@article {pmid18232667, year = {2008}, author = {Cabooter, D and Lynen, F and Sandra, P and Desmet, G}, title = {Turbulence as a source of excessive baseline noise during high-speed isocratic and gradient separations using absorption detection.}, journal = {Analytical chemistry}, volume = {80}, number = {5}, pages = {1679-1688}, doi = {10.1021/ac701906j}, pmid = {18232667}, issn = {0003-2700}, abstract = {The occurrence of turbulent flow conditions in the connection tubing or at the entrance of the detection flow cell has been identified as a potential source of excessive detector noise in the signal of the diode array UV-absorption detector flow cell of a commercial HPLC system used to perform high-speed separations on wide-bore columns (4.6 mm i.d.). This excessive noise was found to occur abruptly if the flow rate is increased beyond a certain critical value or during gradient runs, if the mobile phase viscosity falls below a certain critical value. Several detector cells of different dimensions were studied to investigate the dependency of the effect on the detector cell design and the system tubing. Evidence for the turbulent flow origin of this noise is that its onset always occurred at a given fixed value of the Reynolds number. This critical Reynolds number could also be used to predict the onset of detector noise during gradient elution runs. Second, evidence for the turbulent flow origin of the noise was that it could be reliably eliminated using a flow splitter after the column to reduce the flow rate below its critical value before entering the detector. The loss in separation efficiency and detection sensitivity accompanying this flow splitting solution was found to be so small that it does not weigh up against the huge advantage of the possibility to eliminate the excessive detector noise.}, }
@article {pmid18178623, year = {2008}, author = {Cotrell, DL and McFadden, GB and Alder, BJ}, title = {Instability in pipe flow.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {105}, number = {2}, pages = {428-430}, pmid = {18178623}, issn = {1091-6490}, abstract = {The long-puzzling, unphysical result that linear stability analyses lead to no transition in pipe flow, even at infinite Reynolds number, is ascribed to the use of stick boundary conditions, because they ignore the amplitude variations associated with the roughness of the wall. Once that length scale is introduced (here, crudely, through a corrugated pipe), linear stability analyses lead to stable vortex formation at low Reynolds number above a finite amplitude of the corrugation and unsteady flow at a higher Reynolds number, where indications are that the vortex dislodges. Remarkably, extrapolation to infinite Reynolds number of both of these transitions leads to a finite and nearly identical value of the amplitude, implying that below this amplitude, the vortex cannot form because the wall is too smooth and, hence, stick boundary results prevail.}, }
@article {pmid18165254, year = {2008}, author = {Lentink, D and Muijres, FT and Donker-Duyvis, FJ and van Leeuwen, JL}, title = {Vortex-wake interactions of a flapping foil that models animal swimming and flight.}, journal = {The Journal of experimental biology}, volume = {211}, number = {Pt 2}, pages = {267-273}, doi = {10.1242/jeb.006155}, pmid = {18165254}, issn = {0022-0949}, mesh = {Animals ; Biomechanical Phenomena ; Extremities/*physiology ; Flight, Animal/*physiology ; *Models, Biological ; Swimming/*physiology ; }, abstract = {The fluid dynamics of many swimming and flying animals involves the generation and shedding of vortices into the wake. Here we studied the dynamics of similar vortices shed by a simple two-dimensional flapping foil in a soap-film tunnel. The flapping foil models an animal wing, fin or tail in forward locomotion. The vortical flow induced by the foil is correlated to (the resulting) thickness variations in the soap film. We visualized these thickness variations through light diffraction and recorded it with a digital high speed camera. This set-up enabled us to study the influence of foil kinematics on vortex-wake interactions. We varied the dimensionless wavelength of the foil (lambda*=4-24) at a constant dimensionless flapping amplitude (A*=1.5) and geometric angle of attack amplitude (A(alpha,geo)=15 degrees). The corresponding Reynolds number was of the order of 1000. Such values are relevant for animal swimming and flight. We found that a significant leading edge vortex (LEV) was generated by the foil at low dimensionless wavelengths (lambda*<10). The LEV separated from the foil for all dimensionless wavelengths. The relative time (compared with the flapping period) that the unstable LEV stayed above the flapping foil increased for decreasing dimensionless wavelengths. As the dimensionless wavelength decreased, the wake dynamics evolved from a wavy von Kármán-like vortex wake shed along the sinusoidal path of the foil into a wake densely packed with large interacting vortices. We found that strongly interacting vortices could change the wake topology abruptly. This occurred when vortices were close enough to merge or tear each other apart. Our experiments show that relatively small changes in the kinematics of a flapping foil can alter the topology of the vortex wake drastically.}, }
@article {pmid18071827, year = {2008}, author = {Cogan, NG}, title = {Two-fluid model of biofilm disinfection.}, journal = {Bulletin of mathematical biology}, volume = {70}, number = {3}, pages = {800-819}, doi = {10.1007/s11538-007-9280-3}, pmid = {18071827}, issn = {0092-8240}, mesh = {Bacterial Physiological Phenomena ; Biofilms/*drug effects/*growth &amp; development ; Computer Simulation ; Disinfectants/*pharmacology ; *Models, Biological ; }, abstract = {We consider a dynamic model of biofilm disinfection in two dimensions. The biofilm is treated as a viscous fluid immersed in a fluid of less viscosity. The bulk fluid moves due to an imposed external parabolic flow. The motion of the fluid is coupled to the biofilm inducing motion of the biofilm. Both the biofilm and the bulk fluid are dominated by viscous forces, hence the Reynolds number is negligible and the appropriate equations are Stokes equations. The governing partial differential equations are recast as boundary integral equations using a version of the Lorenz reciprocal relationship. This allows for robust treatment of the simplified fluid/biofilm motion. The transport of nutrients and antimicrobials, which depends directly on the velocities of the fluid and biofilm, is also included. Disinfection of the bacteria is considered under the assumption that the biofilm growth is overwhelmed by disinfection.}, }
@article {pmid18025564, year = {2007}, author = {Singh, JP and Ghaly, AE}, title = {Effect of flow characteristics on online sterilization of cheese whey in UV reactors.}, journal = {Applied biochemistry and biotechnology}, volume = {142}, number = {1}, pages = {1-16}, doi = {10.1007/s12010-007-0004-9}, pmid = {18025564}, issn = {0273-2289}, mesh = {*Bioreactors ; Biotechnology/*methods ; Cheese ; Equipment Design ; Filtration ; Food ; Food Microbiology ; Microbiological Techniques ; Models, Chemical ; Sterilization ; Temperature ; Ultraviolet Rays ; }, abstract = {An ultraviolet (UV) coil reactor was designed and used for the online sterilization of cheese whey. Its microbial destruction efficiency was compared to that of the conventionally used UV reactor. Both reactors have the same geometry (840 ml volume and 17 mm gap size) and were tested at 11 flow rates of 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, and 70 ml/min. The results obtained from this study showed that despite of its high turbidity, cheese whey could be sterilized using UV radiation if the proper reactor design and flow rate are used. The performances of the UV reactors were governed by the flow rate and the hydraulics of flow inside the reactor. The flow was laminar in both the reactors, as the Reynolds number was in the range of 1.39-20.10. The phenomenon of Dean Flow was observed in the coil reactor and the Dean number was in the range of 1.09-15.41. Dean vortices resulted in higher microbial destruction efficiency in the coil reactor in a shorter retention time. The rate of microbial destruction was found to be exponential in the conventional reactor and polynomial in the coil reactor. Increasing the flow rate from 5 ml/min to 70 ml/min decreased the microbial destruction efficiency of the conventional reactor from 99.40 to 31.58%, while the microbial destruction efficiency in the coil reactor increased from 60.77% at the flow rate of 5 ml/min to 99.98% at the flow rate of 30 ml/min and then decreased with further increases in flow rate reaching 46.2% at the flow rate of 70 ml/min. The maximum effluent temperatures in the conventional and coil reactors were 45.8 and 46.1 degrees C, respectively. Fouling in the coil reactor was significantly less compared to the conventional reactor. The extent of fouling was influenced by flow rate and reactor's hydraulics.}, }
@article {pmid17995340, year = {2007}, author = {Materassi, M and Consolini, G}, title = {Magnetic reconnection rate in space plasmas: a fractal approach.}, journal = {Physical review letters}, volume = {99}, number = {17}, pages = {175002}, doi = {10.1103/PhysRevLett.99.175002}, pmid = {17995340}, issn = {0031-9007}, abstract = {Magnetic reconnection is generally discussed via a fluid description. Here, we evaluate the reconnection rate assuming a fractal topology of the reconnection region. The central idea is that the fluid hypothesis may be violated at the scales where reconnection takes place. The reconnection rate, expressed as the Alfvén Mach number of the plasma moving toward the diffusion region, is shown to depend on the fractal dimension and on the sizes of the reconnection or diffusion region. This mechanism is more efficient than prediction of the Sweet-Parker model and even Petschek's model for finite magnetic Reynolds number. A good agreement also with rates given by Hall MHD models is found. A discussion of the fractal assumption on the diffusion region in terms of current microstructures is proposed. The comparison with in-situ satellite observations suggests the reconnection region to be a filamentary domain.}, }
@article {pmid17995113, year = {2007}, author = {Jain, A and Shankar, V}, title = {Instability suppression in viscoelastic film flows down an inclined plane lined with a deformable solid layer.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {76}, number = {4 Pt 2}, pages = {046314}, doi = {10.1103/PhysRevE.76.046314}, pmid = {17995113}, issn = {1539-3755}, abstract = {The linear stability of viscoelastic (Oldroyd-B) film flow down an inclined plane lined with a deformable (neo-Hookean) solid layer is analyzed using low-wave-number asymptotic analysis and the Chebyshev-Tau spectral numerical method. The free surface of film flows of viscoelastic liquids, unlike that of their Newtonian counterparts, becomes unstable in flow down a rigid inclined surface even in the absence of fluid inertia, due to the elastic nature of the liquids. For film flow past a deformable solid, our low-wave-number asymptotic analysis reveals that the solid deformability has a stabilizing effect on the free-surface instability, and, remarkably, this prediction is insensitive to rheology of the liquid film, be it viscoelastic or Newtonian. Using the spectral numerical method, we demonstrate that the free-surface instability can be completely suppressed at all wave numbers when the solid becomes sufficiently deformable. For the case of pure polymeric liquids without any solvent, when the solid layer is made further deformable, both the free surface and the liquid-solid interface are destabilized at finite wave numbers. We also demonstrate a type of mode exchange phenomenon between the modes corresponding to the two interfaces. Importantly, our numerical results show that there is a sufficient range of shear modulus of the solid where both the modes are stable at all wave numbers. For polymer solutions described by the Oldroyd-B model, while the free-surface instability is suppressed by the deformable solid, a host of new unstable modes appear at finite Reynolds number and wave number because of the coupling between liquid flow and free shear waves in the solid. Our study thus demonstrates that the elastohydrodynamic coupling between liquid flow and solid deformation can be exploited either to suppress the free-surface instability (present otherwise in rigid inclines) in viscoelastic film flows, or to induce new instabilities that are absent in flow adjacent to rigid surfaces.}, }
@article {pmid17952569, year = {2008}, author = {Raula, J and Lähde, A and Kauppinen, EI}, title = {A novel gas phase method for the combined synthesis and coating of pharmaceutical particles.}, journal = {Pharmaceutical research}, volume = {25}, number = {1}, pages = {242-245}, pmid = {17952569}, issn = {0724-8741}, mesh = {Aerosols ; Albuterol/administration &amp; dosage/chemistry ; Bronchodilator Agents/administration &amp; dosage/chemistry ; Drug Compounding ; Gases ; Leucine/chemistry ; Microscopy, Electron, Scanning ; Nanoparticles/*chemistry ; Particle Size ; }, abstract = {PURPOSE: A novel aerosol flow reactor method for the combined gas phase synthesis and coating of particles for drug delivery has been developed.<br><br>MATERIALS AND METHODS: As an example, micron-sized salbutamol sulfate particles were produced via droplet-to-particle conversion and in-situ coated by the physical vapor deposition (PVD) of L-leucine vapor.<br><br>RESULTS: During the deposition, L-leucine vapor crystallized on the surfaces of amorphous salbutamol particles. The size of L-leucine crystallites increased with increasing vapor concentration of L-leucine. The salbutamol particles with rough L-leucine surfaces exhibited good flowability enabling to them to be dispersed into air flow without the delivery aid of coarse lactose carriers.<br><br>CONCLUSIONS: The fraction of particles smaller than 5 micrometers varied between 0.35 and 0.48 when dispersed into 60 l/min air flow having a jet Reynolds number of 30700. When the coated fine particles were blended with lactose carriers, the fine particle fraction was as high as 90%. The L-leucine coating also improved the stability of salbutamol particles when stored at 45% relative humidity atmosphere.}, }
@article {pmid17946781, year = {2006}, author = {Lin, Q and Mirc, D and Fu, BM}, title = {Mechanical mechanisms for thrombosis in microvessels.}, journal = {Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference}, volume = {2006}, number = {}, pages = {83-86}, doi = {10.1109/IEMBS.2006.259976}, pmid = {17946781}, issn = {1557-170X}, mesh = {Animals ; *Blood Flow Velocity ; *Blood Pressure ; Computer Simulation ; Female ; *Mechanotransduction, Cellular ; Microcirculation/*physiopathology ; *Models, Cardiovascular ; Rats ; Rats, Sprague-Dawley ; Shear Strength ; *Splanchnic Circulation ; Stress, Mechanical ; Thrombosis/*physiopathology ; }, abstract = {The hypothesis that thrombus can be induced in curved vessels due to mechanical stimuli was tested both experimentally and computationally. Our in vivo experiments on the mesentery of Sprague-Dawley rats (250-300 g) showed that thrombi were formed in non-injured curved microvessels (post-capillary venules, 20-50 micrometer in diameter), and they were initiated at the inner side of the vessel. We observed thrombus formation in 7 out of 32 microvessels after they were stretched and curved for 10-60 mm. To investigate the mechanical mechanisms of thrombus induction, we performed 3-D computational simulation using commercial software, FLUENT. The blood flow was approximated as a Newtonian laminar flow with Reynolds number around 0.01 in this type of microvessels. We considered the vessels with different curvatures (90 degrees and 180 degrees) as well as different shaped-cross sections (circular and elliptic). Computational results demonstrated that the shear rate and shear rate gradient and at the inner side of the vessel were higher than those at the opposite side. The differences became larger in more bended and elliptic-shaped microvessels. This suggested that higher shear rate and shear rate gradient are two of the factors that initiate the thrombosis in curved post-capillary venules. Our results are consistent with others in branched venules.}, }
@article {pmid17939698, year = {2007}, author = {Fornés, JA and de Zárate, JM}, title = {Low-frequency velocity correlation spectrum of fluid in a rectangular microcapillary.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {23}, number = {23}, pages = {11917-11923}, doi = {10.1021/la702502q}, pmid = {17939698}, issn = {0743-7463}, abstract = {In addition to the fast correlation for local stochastic motion, the velocity correlation function in a fluid enclosed within the pore boundaries features a slow long time-tail decay. At late times, the flow approaches that of an incompressible fluid. Here, we consider the motion of a viscous fluid, at constant temperature, in a rectangular semipermeable channel. The fluid is driven through the rectangular capillary by a uniform main pressure gradient. Tiny pressure gradients are allowed perpendicular to the main flux. We solve numerically the three-dimensional Navier-Stokes equations for the velocity field to obtain the steady solution. We then set and solve the Langevin equation for the fluid velocity. We report hydrodynamic fluctuations for the center-line velocity together with the corresponding relaxation times as a function of the size of the observing region and the Reynolds number. The effective diffusion coefficient for the fluid in the microchannel is also estimated (Deff = 1.43 x 10(-10) m2.s-1 for Re = 2), which is in accordance with measurements reported for a similar system (Stepisnik, J.; Callaghan, P. T. Physica B 2000, 292, 296-301; Stepisnik, J.; Callaghan, P. T. Magn. Reson. Imaging 2001, 19, 469-472).}, }
@article {pmid17930759, year = {2007}, author = {de la Torre, A and Burguete, J}, title = {Slow dynamics in a turbulent von Kármán swirling flow.}, journal = {Physical review letters}, volume = {99}, number = {5}, pages = {054101}, doi = {10.1103/PhysRevLett.99.054101}, pmid = {17930759}, issn = {1079-7114}, abstract = {An experimental study of a turbulent von Kármán flow in a cylinder is presented. The mean flow is stationary up to a Reynolds number Re=10(4) where a bifurcation takes place. The new regime breaks some symmetries of the problem and becomes time dependent because of equatorial vortices moving with a precession movement. In the exact counterrotating case, a bistable regime appears and spontaneous reversals of the azimuthal velocity are registered. A three-well potential model with additive noise reproduces this dynamic. A regime of periodic response is observed when a very weak forcing is applied.}, }
@article {pmid17930596, year = {2007}, author = {Wilkin, SL and Barenghi, CF and Shukurov, A}, title = {Magnetic structures produced by the small-scale dynamo.}, journal = {Physical review letters}, volume = {99}, number = {13}, pages = {134501}, doi = {10.1103/PhysRevLett.99.134501}, pmid = {17930596}, issn = {0031-9007}, abstract = {Small-scale dynamo action has been obtained for a flow previously used to model fluid turbulence, where the sensitivity of the magnetic field parameters to the kinetic energy spectrum can be explored. We apply quantitative morphology diagnostics, based on the Minkowski functionals, to magnetic fields produced by the kinematic small-scale dynamo to show that magnetic structures are predominantly filamentary rather than sheetlike. Our results suggest that the thickness, width, and length of the structures scale differently with magnetic Reynolds number as R(m)(-2/(1-s)) and R(m)(-0.55} for the former two, whereas the latter is independent of R(m), with s the slope of the energy spectrum.}, }
@article {pmid17930444, year = {2007}, author = {Marusic, I and Heuer, WD}, title = {Reynolds number invariance of the structure inclination angle in wall turbulence.}, journal = {Physical review letters}, volume = {99}, number = {11}, pages = {114504}, doi = {10.1103/PhysRevLett.99.114504}, pmid = {17930444}, issn = {0031-9007}, abstract = {Cross correlations of the fluctuating wall-shear stress and the streamwise velocity in the logarithmic region of turbulent boundary layers are reported over 3 orders of magnitude change in Reynolds number. These results are obtained using hot-film and hot-wire anemometry in a wind tunnel facility, and sonic anemometers and a purpose-built wall-shear stress sensor in the near-neutral atmospheric surface layer on the salt flats of Utah's western desert. The direct measurement of fluctuating wall-shear stress in the atmospheric surface layer has not been available before. Structure inclination angles are inferred from the cross correlation results and are found to be invariant over the large range of Reynolds number. The findings justify the prior use of low Reynolds number experiments for obtaining structure angles for near-wall models in the large-eddy simulation of atmospheric surface layer flows.}, }
@article {pmid17930390, year = {2007}, author = {Guillot, P and Colin, A and Utada, AS and Ajdari, A}, title = {Stability of a jet in confined pressure-driven biphasic flows at low reynolds numbers.}, journal = {Physical review letters}, volume = {99}, number = {10}, pages = {104502}, doi = {10.1103/PhysRevLett.99.104502}, pmid = {17930390}, issn = {0031-9007}, abstract = {Motivated by its importance for microfluidic applications, we study the stability of jets formed by pressure-driven concentric biphasic flows in cylindrical capillaries. The specificity of this variant of the classical Rayleigh-Plateau instability is the role of the geometry which imposes confinement and Poiseuille flow profiles. We experimentally evidence a transition between situations where the flow takes the form of a jet and regimes where drops are produced. We describe this as the transition from convective to absolute instability, within a simple linear analysis using lubrication theory for flows at low Reynolds number, and reach remarkable agreement with the data.}, }
@article {pmid17930342, year = {2007}, author = {Mukundakrishnan, K and Quan, S and Eckmann, DM and Ayyaswamy, PS}, title = {Numerical study of wall effects on buoyant gas-bubble rise in a liquid-filled finite cylinder.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {76}, number = {3 Pt 2}, pages = {036308}, pmid = {17930342}, issn = {1539-3755}, support = {R01 HL067986/HL/NHLBI NIH HHS/United States ; R01 HL067986-04/HL/NHLBI NIH HHS/United States ; R01 HL 67986-01A1/HL/NHLBI NIH HHS/United States ; }, mesh = {Computer Simulation ; Gases/*chemistry ; Gravitation ; Microfluidics/*methods ; *Models, Theoretical ; Solutions/*chemistry ; Surface Properties ; }, abstract = {The wall effects on the axisymmetric rise and deformation of an initially spherical gas bubble released from rest in a liquid-filled, finite circular cylinder are numerically investigated. The bulk and gas phases are considered incompressible and immiscible. The bubble motion and deformation are characterized by the Morton number (Mo), Eötvös number (Eo), Reynolds number (Re), Weber number (We), density ratio, viscosity ratio, the ratios of the cylinder height and the cylinder radius to the diameter of the initially spherical bubble (H*=H/d0, R*=R/d0). Bubble rise in liquids described by Eo and Mo combinations ranging from (1,0.01) to (277.5,0.092), as appropriate to various terminal state Reynolds numbers (ReT) and shapes have been studied. The range of terminal state Reynolds numbers includes 0.02<ReT<70 . Bubble shapes at terminal states vary from spherical to intermediate spherical-cap-skirted. The numerical procedure employs a front tracking finite difference method coupled with a level contour reconstruction of the front. This procedure ensures a smooth distribution of the front points and conserves the bubble volume. For the wide range of Eo and Mo examined, bubble motion in cylinders of height H*=8 and R*> or =3 , is noted to correspond to the rise in an infinite medium, both in terms of Reynolds number and shape at terminal state. In a thin cylindrical vessel (small R*), the motion of the bubble is retarded due to increased total drag and the bubble achieves terminal conditions within a short distance from release. The wake effects on bubble rise are reduced, and elongated bubbles may occur at appropriate conditions. For a fixed volume of the bubble, increasing the cylinder radius may result in the formation of well-defined rear recirculatory wakes that are associated with lateral bulging and skirt formation. The paper includes figures of bubble shape regimes for various values of R*, Eo, Mo, and ReT. Our predictions agree with existing results reported in the literature.}, }
@article {pmid17930189, year = {2007}, author = {Stratford, K and Desplat, JC and Stansell, P and Cates, ME}, title = {Binary fluids under steady shear in three dimensions.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {76}, number = {3 Pt 1}, pages = {030501}, doi = {10.1103/PhysRevE.76.030501}, pmid = {17930189}, issn = {1539-3755}, abstract = {We simulate by the lattice Boltzmann method the steady shearing of a binary fluid mixture with full hydrodynamics in three dimensions. Contrary to some theoretical scenarios, a dynamical steady state is attained with finite correlation lengths in all three spatial directions. Using large simulations, we obtain at moderately high Reynolds numbers apparent scaling exponents comparable to those found by us previously in two dimensions (2D). However, in 3D there may be a crossover to different behavior at low Reynolds number: accessing this regime requires even larger computational resources than used here.}, }
@article {pmid17930175, year = {2007}, author = {Halliday, I and Hollis, AP and Care, CM}, title = {Lattice Boltzmann algorithm for continuum multicomponent flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {76}, number = {2 Pt 2}, pages = {026708}, doi = {10.1103/PhysRevE.76.026708}, pmid = {17930175}, issn = {1539-3755}, abstract = {We present a multicomponent lattice Boltzmann simulation for continuum fluid mechanics, paying particular attention to the component segregation part of the underlying algorithm. In the principal result of this paper, the dynamics of a component index, or phase field, is obtained for a segregation method after U. D'Ortona [Phys. Rev. E 51, 3718 (1995)], due to Latva-Kokko and Rothman [Phys. Rev. E 71 056702 (2005)]. The said dynamics accord with a simulation designed to address multicomponent flow in the continuum approximation and underwrite improved simulation performance in two main ways: (i) by reducing the interfacial microcurrent activity considerably and (ii) by facilitating simulational access to regimes of flow with a low capillary number and drop Reynolds number [I. Halliday, R. Law, C. M. Care, and A. Hollis, Phys. Rev. E 73, 056708 (2006)]. The component segregation method studied, used in conjunction with Lishchuk's method [S. V. Lishchuk, C. M. Care, and I. Halliday, Phys. Rev. E 67, 036701 (2003)], produces an interface, which is distributed in terms of its component index; however, the hydrodynamic boundary conditions which emerge are shown to support the notion of a sharp, unstructured, continuum interface.}, }
@article {pmid17930151, year = {2007}, author = {Mininni, PD}, title = {Inverse cascades and alpha effect at a low magnetic Prandtl number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {76}, number = {2 Pt 2}, pages = {026316}, doi = {10.1103/PhysRevE.76.026316}, pmid = {17930151}, issn = {1539-3755}, abstract = {Dynamo action in a fully helical Arn'old-Beltrami-Childress flow is studied using both direct numerical simulations and subgrid modeling. Sufficient scale separation is given in order to allow for large-scale magnetic energy buildup. Growth of magnetic energy obtains down to a magnetic Prandtl number P(M) = R(M)/R(V) close to 0.005, where R(V) and R(M) are the kinetic and magnetic Reynolds numbers. The critical magnetic Reynolds number for dynamo action R(M)(c) seems to saturate at values close to 20. Detailed studies of the dependence of the amplitude of the saturated magnetic energy with P(M) are presented. When P(M) is decreased, numerical experiments are conducted with either R(V) or R(M) kept constant. In the former case, the ratio of magnetic to kinetic energy saturates to a value slightly below unity as P(M) decreases. Examination of energy spectra and structures in real space reveals that quenching of the velocity by a large-scale magnetic field takes place, with an inverse cascade of magnetic helicity and a force-free field at large scale in the saturated regime.}, }
@article {pmid17930145, year = {2007}, author = {Yu, Z and Phan-Thien, N and Tanner, RI}, title = {Rotation of a spheroid in a Couette flow at moderate Reynolds numbers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {76}, number = {2 Pt 2}, pages = {026310}, doi = {10.1103/PhysRevE.76.026310}, pmid = {17930145}, issn = {1539-3755}, abstract = {The rotation of a single spheroid in a planar Couette flow as a model for simple shear flow is numerically simulated with the distributed Lagrangian multiplier based fictitious domain method. The study is focused on the effects of inertia on the orbital behavior of prolate and oblate spheroids. The numerical orbits are found to be well described by a simple empirical model, which states that the rate of the spheroid rotation about the vorticity axis is a sinusoidal function of the corresponding projection angle in the flow-gradient plane, and that the exponential growth rate of the orbit function is a constant. The following transitions in the steady state with increasing Reynolds number are identified: Jeffery orbit, tumbling, quasi-Jeffery orbit, log rolling, and inclined rolling for a prolate spheroid; and Jeffery orbit, log rolling, inclined rolling, and motionless state for an oblate spheroid. In addition, it is shown that the orbit behavior is sensitive to the initial orientation in the case of strong inertia and there exist different steady states for certain shear Reynolds number regimes.}, }
@article {pmid17930142, year = {2007}, author = {Kholmyansky, M and Moriconi, L and Tsinober, A}, title = {Large-scale intermittency in the atmospheric boundary layer.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {76}, number = {2 Pt 2}, pages = {026307}, doi = {10.1103/PhysRevE.76.026307}, pmid = {17930142}, issn = {1539-3755}, abstract = {We find actual evidence, relying upon vorticity time series taken in a high-Reynolds-number atmospheric experiment, that to a very good approximation the surface boundary layer flow may be described, in a statistical sense and under certain regimes, as an advected ensemble of homogeneous turbulent systems, characterized by a log-normal distribution of fluctuating intensities. Our analysis suggests that the usual direct numerical simulations of homogeneous and isotropic turbulence, performed at moderate Reynolds numbers, may play an important role in the study of turbulent boundary layer flows, if supplemented with appropriate statistical information concerned with the structure of large-scale fluctuations.}, }
@article {pmid17930139, year = {2007}, author = {Boy, DA and Storey, BD}, title = {Electrohydrodynamic instabilities in microchannels with time periodic forcing.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {76}, number = {2 Pt 2}, pages = {026304}, doi = {10.1103/PhysRevE.76.026304}, pmid = {17930139}, issn = {1539-3755}, abstract = {In microfluidic applications it has been observed that flows with spatial gradients in electrical conductivity are unstable under the application of sufficiently strong electric fields. These electrohydrodynamic instabilities can drive a nonlinear flow despite the low Reynolds number. Such flows hold promise as a simple mechanism for mixing fluids. In this work, the effect of a time periodic electric field on the instability is explored. The case where an electric field is applied across a diffuse interface of two fluids with varying electrical conductivity is considered. Frequency-dependent behavior is found only in the regime where the instability growth rates are very slow and cannot outpace mixing by molecular diffusion. Improving mixing by modulation of the electric body force is not a viable strategy in this geometry.}, }
@article {pmid17887898, year = {2007}, author = {Fresconi, FE and Prasad, AK}, title = {Secondary velocity fields in the conducting airways of the human lung.}, journal = {Journal of biomechanical engineering}, volume = {129}, number = {5}, pages = {722-732}, doi = {10.1115/1.2768374}, pmid = {17887898}, issn = {0148-0731}, mesh = {Administration, Inhalation ; Aerosols/administration &amp; dosage ; Biological Transport/physiology ; Convection ; Diffusion ; Drug Delivery Systems ; Humans ; Lung/anatomy &amp; histology/*physiology ; *Models, Biological ; Oscillometry ; Pulmonary Gas Exchange/*physiology ; Pulmonary Ventilation/*physiology ; Rheology ; Viscosity ; }, abstract = {An understanding of flow and dispersion in the human respiratory airways is necessary to assess the toxicological impact of inhaled particulate matter as well as to optimize the design of inhalable pharmaceutical aerosols and their delivery systems. Secondary flows affect dispersion in the lung by mixing solute in the lumen cross section. The goal of this study is to measure and interpret these secondary velocity fields using in vitro lung models. Particle image velocimetry experiments were conducted in a three-generational, anatomically accurate model of the conducting region of the lung. Inspiration and expiration flows were examined under steady and oscillatory flow conditions. Results illustrate secondary flow fields as a function of flow direction, Reynolds number, axial location with respect to the bifurcation junction, generation, branch, phase in the oscillatory cycle, and Womersley number. Critical Dean number for the formation of secondary vortices in the airways, as well as the strength and development length of secondary flow, is characterized. The normalized secondary velocity magnitude was similar on inspiration and expiration and did not vary appreciably with generation or branch. Oscillatory flow fields were not significantly different from corresponding steady flow fields up to a Womersley number of 1 and no instabilities related to shear were detected on flow reversal. These observations were qualitatively interpreted with respect to the simple streaming, augmented dispersion, and steady streaming convective dispersion mechanisms.}, }
@article {pmid17887893, year = {2007}, author = {Chan, KY and Fujioka, H and Hirshl, RB and Bartlett, RH and Grotberg, JB}, title = {Pulsatile blood flow and gas exchange across a cylindrical fiber array.}, journal = {Journal of biomechanical engineering}, volume = {129}, number = {5}, pages = {676-687}, doi = {10.1115/1.2768105}, pmid = {17887893}, issn = {0148-0731}, support = {R01 HL069420/HL/NHLBI NIH HHS/United States ; }, mesh = {Artificial Organs ; Biological Transport, Active/physiology ; Blood Flow Velocity/physiology ; Computational Biology/methods ; Computer Simulation ; Humans ; Lung/*blood supply/*physiology ; *Models, Cardiovascular ; Pulmonary Circulation/physiology ; Pulmonary Gas Exchange/*physiology ; Pulsatile Flow/*physiology ; Respiratory Transport/physiology ; }, abstract = {The pulsatile blood flow and gas transport of oxygen and carbon dioxide through a cylindrical array of microfibers are numerically simulated. Blood is modeled as a homogeneous Casson fluid, and hemoglobin molecules in blood are assumed to be in local equilibrium with oxygen and carbon dioxide. It is shown that flow pulsatility enhances gas transport and the amount of gas exchange is sensitive to the blood flow field across the fibers. The steady Sherwood number dependence on Reynolds number was shown to have a linear relation consistent with experimental findings. For most cases, an enhancement in gas transport is accompanied with an increase in flow resistance. Maximum local shear stress is provided as a possible indicator of thrombosis, and the computed shear stress is shown to be below the threshold value for thrombosis formation for all cases evaluated.}, }
@article {pmid17887891, year = {2007}, author = {Sznitman, J and Heimsch, F and Heimsch, T and Rusch, D and Rösgen, T}, title = {Three-dimensional convective alveolar flow induced by rhythmic breathing motion of the pulmonary acinus.}, journal = {Journal of biomechanical engineering}, volume = {129}, number = {5}, pages = {658-665}, doi = {10.1115/1.2768109}, pmid = {17887891}, issn = {0148-0731}, mesh = {Airway Resistance/physiology ; Computer Simulation ; Humans ; Models, Biological ; Pulmonary Alveoli/*physiology ; *Respiration ; }, abstract = {Low Reynolds number flows (Re<1) in the human pulmonary acinus are often difficult to assess due to the submillimeter dimensions and accessibility of the region. In the present computational study, we simulated three-dimensional alveolar flows in an alveolated duct at each generation of the pulmonary acinar tree using recent morphometric data. Rhythmic lung expansion and contraction motion was modeled using moving wall boundary conditions to simulate realistic sedentary tidal breathing. The resulting alveolar flow patterns are largely time independent and governed by the ratio of the alveolar to ductal flow rates, Qa/Qd. This ratio depends uniquely on geometrical configuration such that alveolar flow patterns may be entirely determined by the location of the alveoli along the acinar tree. Although flows within alveoli travel very slowly relative to those in acinar ducts, 0.021%<or=Ua/Ud<or=9.1%, they may exhibit complex patterns linked to the three-dimensional nature of the flow and confirm findings from earlier three-dimensional simulations. Such patterns are largely determined by the interplay between recirculation in the cavity induced by ductal shear flow over the alveolar opening and radial flows induced by wall displacement. Furthermore, alveolar flow patterns under rhythmic wall motion contrast sharply with results obtained in a rigid alveolus, further confirming the importance of including inherent wall motion to understand realistic acinar flow phenomena. The present findings may give further insight into the role of convective alveolar flows in determining aerosol kinematics and deposition in the pulmonary acinus.}, }
@article {pmid17727270, year = {2007}, author = {Lee, J and Lim, KG and Palmore, GT and Tripathi, A}, title = {Optimization of microfluidic fuel cells using transport principles.}, journal = {Analytical chemistry}, volume = {79}, number = {19}, pages = {7301-7307}, doi = {10.1021/ac070812e}, pmid = {17727270}, issn = {0003-2700}, mesh = {Electrodes ; Microfluidics/*instrumentation ; Models, Theoretical ; }, abstract = {Microfluidic fuel cells exploit the lack of convective mixing at low Reynolds number to eliminate the need for a physical membrane to separate the fuel from the oxidant. Slow transport of reactants in combination with high catalytic surface-to-volume ratios often inhibit the efficiency of a microfluidic fuel cell. The performance of microfluidic devices that rely on surface electrochemical reactions is controlled by the interplay between reaction kinetics and the rate of mass transfer to the reactive surfaces. This paper presents theoretical and experimental work to describe the role of flow rate, microchannel geometry, and location of electrodes within a microfluidic fuel cell on its performance. A transport model, based on the convective-diffusive flux of reactants, is developed that describes the optimal conditions for maximizing both the average current density and the percentage of fuel utilized. The results show that the performance can be improved when the design of the device includes electrodes smaller than a critical length. The results of this study advance current approaches to the design of microfluidic fuel cells and other electrochemically-coupled microfluidic devices.}, }
@article {pmid17701258, year = {2008}, author = {Cattoni, DI and Chara, O}, title = {Vacuum effects over the closing of enterocutaneous fistulae: a mathematical modeling approach.}, journal = {Bulletin of mathematical biology}, volume = {70}, number = {1}, pages = {281-296}, doi = {10.1007/s11538-007-9258-1}, pmid = {17701258}, issn = {0092-8240}, mesh = {Computer Simulation ; Humans ; Intestinal Fistula/*therapy ; *Models, Biological ; *Vacuum ; }, abstract = {Enterocutaneous fistulae are pathological communications between the intestinal lumen and the abdominal skin. Under surgery the mortality of this pathology is very high, therefore a vacuum applying system has been carried previously on attempting to close these fistulae. The objective of this article is the understanding of how these treatments might work through deterministic mathematical modelling. Four models are here proposed based on several assumptions involving: the conservation of the flow in the fistula, a low enough Reynolds number justifying a laminar flow, the use of Poiseuille law to model the movement of the fistulous liquid, as well as phenomenological equations including the fistula tissue and intermediate chamber compressibility. Interestingly, the four models show fistulae closing behaviour during experimental time (t<60 sec). To compare the models, both, simulations and pressure measurements, carried out on the vacuum connected to the patients, are performed. Time course of pressure are then simulated (from each model) and fitted to the experimental data. The model which best describes actual measurements shows exponential pumping flux kinetics. Applying this model, numerical relationship between the fistula compressibility and closure time is presented. The models here developed would contribute to clarify the treatment mechanism and, eventually, improve the fistulae treatment.}, }
@article {pmid17677745, year = {2007}, author = {Iskakov, AB and Schekochihin, AA and Cowley, SC and McWilliams, JC and Proctor, MR}, title = {Numerical demonstration of fluctuation dynamo at low magnetic Prandtl numbers.}, journal = {Physical review letters}, volume = {98}, number = {20}, pages = {208501}, doi = {10.1103/PhysRevLett.98.208501}, pmid = {17677745}, issn = {0031-9007}, mesh = {*Magnetics ; *Models, Theoretical ; Rheology ; }, abstract = {Direct numerical simulations of incompressible nonhelical randomly forced MHD turbulence are used to demonstrate for the first time that the fluctuation dynamo exists in the limit of large magnetic Reynolds number Rm>>1 and small magnetic Prandtl number Pm<<1. The dependence of the critical Rmc for dynamo on the hydrodynamic Reynolds number Re is obtained for 1 less than or similar Re less than or similar 6700. In the limit Pm<<1, Rmc is about 3 times larger than for the previously well-established dynamo at large and moderate Prandtl numbers: Rmc less than or similar 200 for Re greater than or similar 6000 compared to Rmc approximately 60 for Pm>or=1. It is not yet possible to determine numerically whether the growth rate of the magnetic energy is proportional, Rm1/2 in the limit Rm-->infinity, as it should be if the dynamo is driven by the inertial-range motions at the resistive scale.}, }
@article {pmid17677701, year = {2007}, author = {Wang, J and Gibson, J and Waleffe, F}, title = {Lower branch coherent states in shear flows: transition and control.}, journal = {Physical review letters}, volume = {98}, number = {20}, pages = {204501}, doi = {10.1103/PhysRevLett.98.204501}, pmid = {17677701}, issn = {0031-9007}, abstract = {Lower branch coherent states in plane Couette flow have an asymptotic structure that consists of O(1) streaks, O(R(-1)) streamwise rolls and a weak sinusoidal wave that develops a critical layer, for large Reynolds number R. Higher harmonics become negligible. These unstable lower branch states appear to have a single unstable eigenvalue at all Reynolds numbers. These results suggest that lower branch coherent states control transition to turbulence and that they may be promising targets for new turbulence prevention strategies.}, }
@article {pmid17677566, year = {2007}, author = {Liu, W and Goodman, J and Ji, H}, title = {Traveling waves in a magnetized Taylor-Couette flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {76}, number = {1 Pt 2}, pages = {016310}, doi = {10.1103/PhysRevE.76.016310}, pmid = {17677566}, issn = {1539-3755}, abstract = {We investigate numerically a traveling wave pattern observed in experimental magnetized Taylor-Couette flow at low magnetic Reynolds number. By accurately modeling viscous and magnetic boundaries in all directions, we reproduce the experimentally measured wave patterns and their amplitudes. Contrary to previous claims, the waves are shown to be transiently amplified disturbances launched by viscous boundary layers, rather than globally unstable magnetorotational modes.}, }
@article {pmid17677560, year = {2007}, author = {Ou, J and Moss, GR and Rothstein, JP}, title = {Enhanced mixing in laminar flows using ultrahydrophobic surfaces.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {76}, number = {1 Pt 2}, pages = {016304}, doi = {10.1103/PhysRevE.76.016304}, pmid = {17677560}, issn = {1539-3755}, abstract = {Under laminar, microscale flow conditions, rapid mixing can be difficult to achieve. In these low Reynolds number flows, mixing rates are governed by molecular diffusion, and in the absence of enhanced mixing techniques, mixing lengths and residence times can be much longer than most applications will allow. A number of active mixing techniques have been developed to improve mixing; however, they can be complex to implement and expensive to fabricate. In this paper, we describe a passive mixing method that utilizes a series of ultrahydrophobic surfaces. Our previous experiments have demonstrated that a shear-free air-water interface supported between hydrophobic microridges results in large slip velocities along these ultrahydrophobic surfaces, and significant drag reduction. By aligning the microridges and therefore the air-water interface at an oblique angle to the flow direction, a secondary flow is generated, which is shown to efficiently stretch and fold the fluid elements and reduce the mixing length by more than an order of magnitude compared to that of a smooth microchannel. The designs of the ultrahydrophobic surfaces were optimized through experiments and numerical simulations. A Y-shaped channel was used to bring two streams of water together, one tagged with a fluorescent dye. A confocal microscope was used to measure fluorescence intensity and dye concentration. Quantitative agreement between the experiments and the numerical simulations was achieved for both the flow patterns and degree of mixing. Increasing the angle of the microridges was found to reduce the mixing length up to a critical angle of about 60 degrees , beyond which the mixing length was found to increase with further increases to the angle of the microridge. The mixing enhancement was found to be much less sensitive to changes in microridge width or separation.}, }
@article {pmid17677557, year = {2007}, author = {De Lillo, F and Eckhardt, B}, title = {Shear turbulence on a sparse spectral grid.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {76}, number = {1 Pt 2}, pages = {016301}, doi = {10.1103/PhysRevE.76.016301}, pmid = {17677557}, issn = {1539-3755}, abstract = {We simulate turbulence in a plane Couette geometry by a spectral method intermediate between full resolution and the complete elimination of small modes common in large eddy simulations. The wave number grid is sparse in spanwise and downstream direction, with a total number of modes proportional to Re(3/4) lnRe. At a Reynolds number of 2000 we could suppress more than 80% of the modes and still obtain a fairly accurate resolution of the boundary layer structures and friction factors. For a wide range of resolutions, the mean velocities are described by logarithmic profiles, with von Karman constant near a value of 0.4.}, }
@article {pmid17677389, year = {2007}, author = {Dupin, MM and Halliday, I and Care, CM and Alboul, L and Munn, LL}, title = {Modeling the flow of dense suspensions of deformable particles in three dimensions.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {75}, number = {6 Pt 2}, pages = {066707}, pmid = {17677389}, issn = {1539-3755}, support = {R21 CA126761-01/CA/NCI NIH HHS/United States ; R21 CA126761/CA/NCI NIH HHS/United States ; R01 HL064240-07/HL/NHLBI NIH HHS/United States ; R21 CA126761-02/CA/NCI NIH HHS/United States ; R01 HL064240-08/HL/NHLBI NIH HHS/United States ; R01 HL064240/HL/NHLBI NIH HHS/United States ; }, abstract = {We describe here a rigorous and accurate model for the simulation of three-dimensional deformable particles (DPs). The method is very versatile, easily simulating various types of deformable particles such as vesicles, capsules, and biological cells. Each DP is resolved explicitly and advects within the surrounding Newtonian fluid. The DPs have a preferred rest shape (e.g., spherical for vesicles, or biconcave for red blood cells). The model uses a classic hybrid system: an Eulerian approach is used for the Navier-Stokes solver (the lattice Boltzmann method) and a Lagrangian approach for the evolution of the DP mesh. Coupling is accomplished through the lattice Boltzmann velocity field, which transmits force to the membranes of the DPs. The novelty of this method resides in its ability (by design) to simulate a large number of DPs within the bounds of current computational limitations: our simple and efficient approach is to (i) use the lattice Boltzmann method because of its acknowledged efficiency at low Reynolds number and its ease of parallelization, and (ii) model the DP dynamics using a coarse mesh (approximately 500 nodes) and a spring model constraining (if necessary) local area, total area, cell volume, local curvature, and local primary stresses. We show that this approach is comparable to the more common - yet numerically expensive - approach of membrane potential function, through a series of quantitative comparisons. To demonstrate the capabilities of the model, we simulate the flow of 200 densely packed red blood cells - a computationally challenging task. The model is very efficient, requiring of the order of minutes for a single DP in a 50 microm x 40 microm x 40 microm simulation domain and only hours for 200 DPs in 80 microm x 30 microm x 30 microm . Moreover, the model is highly scalable and efficient compared to other models of blood cells in flow, making it an ideal and unique tool for studying blood flow in microvessels or vesicle or capsule flow (or a mixture of different particles). In addition to directly predicting fluid dynamics in complex suspension in any geometry, the model allows determination of accurate, empirical rules which may improve existing macroscopic, continuum models.}, }
@article {pmid17677365, year = {2007}, author = {Kleeorin, N and Rogachevskii, I}, title = {Nonlinear turbulent magnetic diffusion and effective drift velocity of a large-scale magnetic field in two-dimensional magnetohydrodynamic turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {75}, number = {6 Pt 2}, pages = {066315}, doi = {10.1103/PhysRevE.75.066315}, pmid = {17677365}, issn = {1539-3755}, abstract = {We study a nonlinear quenching of turbulent magnetic diffusion and effective drift velocity of large-scale magnetic field in a developed two-dimensional MHD turbulence at large magnetic Reynolds numbers. We show that transport of the mean-square magnetic potential strongly changes quenching of turbulent magnetic diffusion. In particularly, the catastrophic quenching of turbulent magnetic diffusion does not occur for the large-scale magnetic fields B >> B(eq)/square root[Rm] when a divergence of the flux of the mean-square magnetic potential is not zero, where B(eq) is the equipartition mean magnetic field determined by the turbulent kinetic energy and Rm is the magnetic Reynolds number. In this case the quenching of turbulent magnetic diffusion is independent of magnetic Reynolds number. The situation is similar to three-dimensional MHD turbulence at large magnetic Reynolds numbers whereby the catastrophic quenching of the alpha effect does not occur when a divergence of the flux of the small-scale magnetic helicity is not zero.}, }
@article {pmid17677363, year = {2007}, author = {Schneider, TM and Eckhardt, B and Vollmer, J}, title = {Statistical analysis of coherent structures in transitional pipe flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {75}, number = {6 Pt 2}, pages = {066313}, doi = {10.1103/PhysRevE.75.066313}, pmid = {17677363}, issn = {1539-3755}, abstract = {Numerical and experimental studies of transitional pipe flow have shown the prevalence of coherent flow structures that are dominated by downstream vortices. They attract special attention because they contribute predominantly to the increase of the Reynolds stresses in turbulent flow. In the present study we introduce a convenient detector for these coherent states, calculate the fraction of time the structures appear in the flow, and present a Markov model for the transition between the structures. The fraction of states that show vortical structures exceeds 24% for a Reynolds number of about Re=2200 , and it decreases to about 20% for Re=2500 . The Markov model for the transition between these states is in good agreement with the observed fraction of states, and in reasonable agreement with the prediction for their persistence. It provides insight into dominant qualitative changes of the flow when increasing the Reynolds number.}, }
@article {pmid17677163, year = {2007}, author = {Fried, E and Gurtin, ME}, title = {Turbulent kinetic energy and a possible hierarchy of length scales in a generalization of the Navier-Stokes alpha theory.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {75}, number = {5 Pt 2}, pages = {056306}, doi = {10.1103/PhysRevE.75.056306}, pmid = {17677163}, issn = {1539-3755}, abstract = {We present a continuum-mechanical formulation and generalization of the Navier-Stokes alpha theory based on a general framework for fluid-dynamical theories with gradient dependencies. Our flow equation involves two additional problem-dependent length scales alpha and beta. The first of these scales enters the theory through the internal kinetic energy, per unit mass, alpha2|D|2, where D is the symmetric part of the gradient of the filtered velocity. The remaining scale is associated with a dissipative hyperstress which depends linearly on the gradient of the filtered vorticity. When alpha and beta are equal, our flow equation reduces to the Navier-Stokes alpha equation. In contrast to the original derivation of the Navier-Stokes alpha equation, which relies on Lagrangian averaging, our formulation delivers boundary conditions. For a confined flow, our boundary conditions involve an additional length scale l characteristic of the eddies found near walls. Based on a comparison with direct numerical simulations for fully developed turbulent flow in a rectangular channel of height 2h, we find that alphabeta approximately Re(0.470) and lh approximately Re(-0.772), where Re is the Reynolds number. The first result, which arises as a consequence of identifying the internal kinetic energy with the turbulent kinetic energy, indicates that the choice alpha=beta required to reduce our flow equation to the Navier-Stokes alpha equation is likely to be problematic. The second result evinces the classical scaling relation eta/L approximately Re(-3/4) for the ratio of the Kolmogorov microscale eta to the integral length scale L . The numerical data also suggests that l < or = beta . We are therefore led to conjecture a tentative hierarchy, l < or = beta < alpha , involving the three length scales entering our theory.}, }
@article {pmid17671314, year = {2006}, author = {Eldredge, JD}, title = {Numerical simulations of undulatory swimming at moderate Reynolds number.}, journal = {Bioinspiration &amp; biomimetics}, volume = {1}, number = {4}, pages = {S19-24}, doi = {10.1088/1748-3182/1/4/S03}, pmid = {17671314}, issn = {1748-3190}, mesh = {Animals ; Biological Clocks/*physiology ; Biomechanical Phenomena/methods ; Biomimetics/methods ; Computer Simulation ; Fishes/*physiology ; Humans ; *Models, Biological ; Rheology/*methods ; Swimming/*physiology ; }, abstract = {We perform numerical simulations of the swimming of a three-linkage articulated system in a moderately viscous regime. The computational methodology focuses on the creation, diffusion and transport of vorticity from the surface of the bodies into the fluid. The simulations are dynamically coupled, in that the motion of the three-linkage swimmer is computed simultaneously with the dynamics of the fluid. The novel coupling scheme presented in this work is the first to exploit the relationship between vorticity creation and body dynamics. The locomotion of the system, when subject to undulatory inputs of the hinges, is computed at Reynolds numbers of 200 and 1000. It is found that the forward swimming speed increases with the Reynolds number, and that in both cases the swimming is slower than in an inviscid medium. The vortex shedding is examined, and found to exhibit behavior consistent with experimental flow visualizations of fish.}, }
@article {pmid17662993, year = {2007}, author = {Szyk-Warszynska, L and Trybala, A}, title = {Deposition of core latex particles encapsulated in polyelectrolyte shells at modified mica surfaces.}, journal = {Journal of colloid and interface science}, volume = {314}, number = {2}, pages = {398-404}, doi = {10.1016/j.jcis.2007.06.002}, pmid = {17662993}, issn = {0021-9797}, abstract = {We used an oblique impinging jet (OIJ) cell to determine the initial deposition rates of model microcapsules at bare and modified by multilayer polyelectrolyte (PE) film mica surfaces. The transport conditions in the cell were quantitatively established by studying the kinetics of deposition of negatively charged latex at mica surfaces converted to positively charged by adsorption of (3-aminoprolyl)triethoxysilane. The dependence of reduced particle flux on the Reynolds number of the flow in the OIJ cell was determined by a direct counting of particles deposited on the mica surface. The results are described in terms of convective-diffusion theory taking into account hydrodynamic, dispersive, and electrostatic interactions, between the charged particles/capsules and the mica plate. In this way, transport conditions in the cell were characterized and they were used to interpret the results concerning the deposition of microcapsules with PE shells of various thickness obtained by layer-by-layer polyelectrolyte adsorption on colloidal cores. We demonstrated that the initial deposition rate of capsules is governed by the charge of the solid/liquid interface and the outermost layer of the capsule shell, and is largely independent of the thickness of the capsule shell or the number of PE layers at the mica surface. The deposition rates were in good agreement with theoretical predictions derived from the convective-diffusion theory.}, }
@article {pmid17653925, year = {2007}, author = {Boyle, JD and Lappin-Scott, H}, title = {The effect of flow direction and magnitude on the initial distribution of Pseudomonas aeruginosa cells attached to glass.}, journal = {Biofouling}, volume = {23}, number = {3-4}, pages = {139-150}, doi = {10.1080/08927010701218051}, pmid = {17653925}, issn = {0892-7014}, mesh = {*Bacterial Adhesion ; *Glass ; Pseudomonas aeruginosa/*cytology ; Surface Properties ; }, abstract = {The effect of flowrate and Reynolds Number, Re, on the spatial distribution of individual Pseudomonas aeruginosa cells during their initial attachment to glass flowcells was observed in a series of time-lapse images obtained over a 56-h period. It was shown that flow affected the distribution at Re > 245. Under laminar flow conditions, Re = 96, the distribution of bacterial cells in 200 sub-areas was accurately predicted by using the Poisson distribution and was not dependent on the orientation or shape of the sub-areas. Under turbulent flow conditions, Re = 2220, cells initially attached in streaks along the line of flow. As bacterial cells accumulated on the surface, the streaks broadened and the distribution became more uniform. Analyses showed that, initially, flow had an effect on cell distribution in the flowcell with Re = 245, with significantly greater effects at higher Re. As the cell surface densities increased, the effect of flow direction on cell distribution decreased. It is concluded that the visco-elastic properties of the extracellular polymeric substances (EPS) in which the cells are embedded, significantly affect the distribution of attaching cells.}, }
@article {pmid17645741, year = {2007}, author = {Knock, C and Davison, M}, title = {Predicting the position of the source of blood stains for angled impacts.}, journal = {Journal of forensic sciences}, volume = {52}, number = {5}, pages = {1044-1049}, doi = {10.1111/j.1556-4029.2007.00505.x}, pmid = {17645741}, issn = {0022-1198}, mesh = {Animals ; Biophysical Phenomena ; Biophysics ; *Blood Stains ; Forensic Medicine/*methods ; *Models, Biological ; Photography ; Swine ; }, abstract = {Droplets of pig's blood were dropped onto paper at different angles to the horizontal to produce blood stains. Impact velocities varied from 1.82 to 5.76 m/sec, drop size from 3.7 to 5.0 mm in diameter, and the surface sloped at angles between 22.7 degrees and 90 degrees to the horizontal. From the data a single equation relating stain size to drop size and velocity for all impact angles was produced; ab = 111.74 (Re(1/2)We(1/4))(0.75)D(o)D(o) + 0.00084 with R(2) = 0.88, where a is the stain width, b the stain length, Re the Reynolds number, and We the Weber number. A second equation related the number of spines, N, to drop size, velocity, and surface slope for all impact angles as N = 0.76 We(0.5) sin(3)theta with R(2) = 0.9, where theta is the impact angle. Combining these equations the impact velocity can be determined and hence the position of the stain's source.}, }
@article {pmid17614472, year = {2007}, author = {Nagem, RJ and Sandri, G and Uminsky, D}, title = {Vorticity dynamics and sound generation in two-dimensional fluid flow.}, journal = {The Journal of the Acoustical Society of America}, volume = {122}, number = {1}, pages = {128-134}, doi = {10.1121/1.2736513}, pmid = {17614472}, issn = {1520-8524}, mesh = {Computer Simulation ; *Models, Theoretical ; Normal Distribution ; Pressure ; Reproducibility of Results ; *Rheology ; Rotation ; *Sound ; Viscosity ; }, abstract = {An approximate solution to the two-dimensional incompressible fluid equations is constructed by expanding the vorticity field in a series of derivatives of a Gaussian vortex. The expansion is used to analyze the motion of a corotating Gaussian vortex pair, and the spatial rotation frequency of the vortex pair is derived directly from the fluid vorticity equation. The resulting rotation frequency includes the effects of finite vortex core size and viscosity and reduces, in the appropriate limit, to the rotation frequency of the Kirchhoff point vortex theory. The expansion is then used in the low Mach number Lighthill equation to derive the far-field acoustic pressure generated by the Gaussian vortex pair. This pressure amplitude is compared with that of a previous fully numerical simulation in which the Reynolds number is large and the vortex core size is significant compared to the vortex separation. The present analytic result for the far-field acoustic pressure is shown to be substantially more accurate than previous theoretical predictions. The given example suggests that the vorticity expansion is a useful tool for the prediction of sound generated by a general distributed vorticity field.}, }
@article {pmid17614471, year = {2007}, author = {Chakravarthy, SR and Shreenivasan, OJ and Boehm, B and Dreizler, A and Janicka, J}, title = {Experimental characterization of onset of acoustic instability in a nonpremixed half-dump combustor.}, journal = {The Journal of the Acoustical Society of America}, volume = {122}, number = {1}, pages = {120-127}, doi = {10.1121/1.2741374}, pmid = {17614471}, issn = {1520-8524}, mesh = {Air Movements ; Equipment Design ; Gases ; Hot Temperature ; Incineration/*instrumentation ; *Methane ; *Models, Theoretical ; Motion ; *Noise ; Pressure ; Time Factors ; }, abstract = {This paper reports work on a nonpremixed half-dump combustor, in which methane is injected at the backward-facing step, and mixes and burns with the air flowing past the step in the unsteady recirculation zone. The flow and geometric parameters are widely varied, to gradually change from conditions of low-amplitude noise to excitation of high-amplitude discrete tones. The purpose of the work is to focus on the transition from the former condition to the latter, and to mark the onset of instability. Dimensionless groups such as the Helmholtz and Strouhal numbers are formed based on the observed dominant frequencies, whose variation with the air flow Reynolds number is used to identify the oscillations as those due to the natural acoustic modes or the vortex shedding process. High-speed chemiluminescence imaging reveals shedding of vortical structures in the flame zone. With variation in the conditions, flow-acoustic lock-on and transition from one vortex shedding mode to another is marked by nonlinearity in the corresponding amplitude variations. Such conditions are identified as the onset of instability in terms of the ratio of the flow time scale to the acoustic time scale and mapped against the operating fuel-air equivalence ratio of the combustor.}, }
@article {pmid17568552, year = {2007}, author = {Zimmerman, WB and Rees, JM and Hewakandamby, BN}, title = {Numerical analysis of solutocapillary Marangoni-induced interfacial waves.}, journal = {Advances in colloid and interface science}, volume = {134-135}, number = {}, pages = {346-359}, doi = {10.1016/j.cis.2007.04.015}, pmid = {17568552}, issn = {0001-8686}, abstract = {Spreading problems and solutocapillary waves are now routinely treated by semi-analytic lubrication theory leading to a 1D spatiotemporal system to be integrated numerically. In this review, such theories have been shown to be robust predictors of the pseudo-steady propagation at long times with only an initial transient period when the lubrication assumptions breakdown and the wave front is retarded due to bottom friction. Linear stability theory for bottom friction effects leads to 1D evolution equations that predict the scale of Marangoni stresses needed to excite waves and the solitary wave structure of their propagation. In general, applications which are sensitive to Marangoni effects naturally have high values of the Marangoni number (at least hundreds and potentially much higher in evaporation problems). Even when the Marangoni-induced effects are small amplitude, the gradients in stresses are such that numerical resolution requirements are steep. The idealization of interfacial dynamics to a domain with zero thickness (molecular effects) is computationally more demanding than the boundary layers induced in say high Reynolds number laminar flows. Therefore, specialized computational methods for treating open deformable interfaces with high transverse gradients are both required and are being successfully developed as reported here.}, }
@article {pmid17547019, year = {2007}, author = {Simões, M and Cleto, S and Pereira, MO and Vieira, MJ}, title = {Influence of biofilm composition on the resistance to detachment.}, journal = {Water science and technology : a journal of the International Association on Water Pollution Research}, volume = {55}, number = {8-9}, pages = {473-480}, doi = {10.2166/wst.2007.293}, pmid = {17547019}, issn = {0273-1223}, mesh = {Bacillus cereus/*physiology/ultrastructure ; Bacterial Adhesion ; Bacterial Proteins/analysis ; *Biofilms ; Bioreactors ; Colony Count, Microbial ; Microscopy, Electron, Scanning ; Oxygen/metabolism ; Polysaccharides/analysis ; Pseudomonas fluorescens/*physiology/ultrastructure ; Stress, Mechanical ; }, abstract = {Bacillus cereus and Pseudomonas fluorescens were used to develop monoculture biofilms in a bioreactor rotating system using a stainless steel cylinder for biofilm formation. The biofilms were allowed to grow for 7 days, exposed continuously to a Reynolds number of agitation (ReA) of 2,400. Afterwards, the biofilms were characterised in terms of respiratory activity, amount of biomass, cellular density, cellular size and total and extracellular proteins and polysaccharides. The biofilm mechanical stability was assessed by sequential submission of the biofilms to increasing ReA, respectively, 4,000, 8,100, 12,100 and 16,100. The results showed that P. fluorescens biofilms were five times more active, had a higher amount of biomass, cellular density, a reduced cellular size and a four-fold higher amount of extracellular proteins and polysaccharides than B. cereus biofilms. The application of shear stress forces higher than the one under which the biofilm was formed (ReA = 2,400) caused biomass removal. The high percentage of removal occurred with the implementation of a ReA of 8,100 for both B. cereus and P. fluorescens biofilms. The total series of ReA did not give rise to total biofilm removal, as only about 76% of P. fluorescens biofilm mass and 53% of B. cereus biofilm mass were detached from the cylinders. This latter result evidences that B. cereus had a higher mechanical stability than P. fluorescens biofilms. The overall results demonstrate that P. fluorescens and B. cereus formed physiologically distinct biofilms, B. cereus biofilms mainly being constituted by cells and P. fluorescens biofilms largely constituted by extracellular proteins and polysaccharides. B. cereus biofilms had a substantially higher mechanical stability than P. fluorescens biofilms.}, }
@article {pmid17538203, year = {2007}, author = {Ali, N and Hayat, T and Sajid, M}, title = {Peristaltic flow of a couple stress fluid in an asymmetric channel.}, journal = {Biorheology}, volume = {44}, number = {2}, pages = {125-138}, pmid = {17538203}, issn = {0006-355X}, mesh = {Animals ; Body Fluids/physiology ; Humans ; *Models, Theoretical ; Peristalsis/*physiology ; Viscosity ; }, abstract = {This paper presents an analysis of the peristaltic flow of a couple stress fluid in an asymmetric channel. The asymmetric nature of the flow is introduced through the peristaltic waves of different amplitudes and phases on the channel walls. Mathematical modelling corresponding to a two-dimensional flow has been carried out. The flow analysis is presented under long wavelength and low Reynolds number approximations. Closed form solutions for the axial velocity, stream function and the axial pressure gradient are given. Numerical computations have been carried out for the pressure rise per wavelength, friction forces and trapping. It is noted that there is a decrease in the pressure when the couple stress fluid parameter increases. The variation of the couple stress fluid parameter with the size of the trapped bolus is also similar to that of pressure. Furthermore, the friction force on the lower channel wall is greater than that on the upper channel wall.}, }
@article {pmid17530868, year = {2007}, author = {Serra, C and Berton, N and Bouquey, M and Prat, L and Hadziioannou, G}, title = {A predictive approach of the influence of the operating parameters on the size of polymer particles synthesized in a simplified microfluidic system.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {23}, number = {14}, pages = {7745-7750}, doi = {10.1021/la063289s}, pmid = {17530868}, issn = {0743-7463}, abstract = {Monodisperse and size-controlled spherical polymer particles were synthesized by in situ photopolymerization of O/W monomer emulsions. Monomer droplets were produced without surfactant or pretreatment at a needle tip in a simplified axisymmetric microfluidic device. The effect of the viscosity of the continuous phase on the particle size was studied. The system operated in the dripping mode, at a low Reynolds number. A dimensionless master curve describes the particle diameter as a function of the needle inner diameter as well as velocity and viscosity ratios of continuous and dispersed phases. An empirical law predicts the particle size. The normalized particle diameter depends upon the ratio of the capillary numbers of continuous and dispersed phases with an exponent equal to -0.22.}, }
@article {pmid17524505, year = {2007}, author = {Buckingham-Meyer, K and Goeres, DM and Hamilton, MA}, title = {Comparative evaluation of biofilm disinfectant efficacy tests.}, journal = {Journal of microbiological methods}, volume = {70}, number = {2}, pages = {236-244}, doi = {10.1016/j.mimet.2007.04.010}, pmid = {17524505}, issn = {0167-7012}, mesh = {Biofilms/*drug effects ; Chlorine/pharmacology ; Colony Count, Microbial ; Disinfectants/*pharmacology ; Microbial Sensitivity Tests/*methods ; Phenols/pharmacology ; Pseudomonas aeruginosa/drug effects/physiology ; Quaternary Ammonium Compounds/pharmacology ; Staphylococcus aureus/drug effects/physiology ; }, abstract = {Regulatory agencies are receiving registration applications for unprecedented, antibiofilm label claims for disinfectants. Reliable, practical, and relevant laboratory biofilm test methods are required to support such claims. This investigation describes the influence of fluid dynamics on the relevancy of a laboratory test. Several disinfectant formulations were tested using three different biofilm testing systems run side-by-side: the CDC biofilm reactor system that created turbulent flow (Reynolds number between 800 and 1850), the drip flow biofilm reactor system that created slow laminar flow (Reynolds number between 12 and 20), and the static biofilm system that involved no fluid flow. Each comparative experiment also included a dried surface carrier test and a dried biofilm test. All five disinfectant tests used glass coupons and followed the same steps for treatment, neutralization, viable cell counting, and calculating the log reduction (LR). Three different disinfectants, chlorine, a quaternary ammonium compound, and a phenolic, were each applied at two concentrations. Experiments were conducted separately with Pseudomonas aeruginosa and Staphylococcus aureus and every experiment was independently repeated. The results showed that biofilm grown in the CDC reactor produced the smallest LR, the static biofilm produced the largest LR, and biofilm grown in the drip flow reactor produced an intermediate LR. The differences were large enough to be of practical importance. The dried surface test often produced a significantly higher LR than the tests against hydrated or dried biofilm. The dried biofilm test produced LR values similar to those for the corresponding hydrated biofilm test. These results show that the efficacy of a disinfectant must be measured by using a laboratory method where biofilm is grown under fluid flow conditions similar to the environment where the disinfectant will be applied.}, }
@article {pmid17519201, year = {2007}, author = {Carpenter, PW and Kudar, KL and Ali, R and Sen, PK and Davies, C}, title = {A deterministic model for the sublayer streaks in turbulent boundary layers for application to flow control.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {365}, number = {1859}, pages = {2419-2441}, doi = {10.1098/rsta.2007.2016}, pmid = {17519201}, issn = {1364-503X}, abstract = {We present a relatively simple, deterministic, theoretical model for the sublayer streaks in a turbulent boundary layer based on an analogy with Klebanoff modes. Our approach is to generate the streamwise vortices found in the buffer layer by means of a vorticity source in the form of a fictitious body force. It is found that the strongest streaks correspond to a spanwise wavelength that lies within the range of the experimentally observed values for the statistical mean streak spacing. We also present results showing the effect of streamwise pressure gradient, Reynolds number and wall compliance on the sublayer streaks. The theoretical predictions for the effects of wall compliance on the streak characteristics agree well with experimental data. Our proposed theoretical model for the quasi-periodic bursting cycle is also described, which places the streak modelling in context. The proposed bursting process is as follows: (i) streamwise vortices generate sublayer streaks and other vortical elements generate propagating plane waves, (ii) when the streaks reach a sufficient amplitude, they interact nonlinearly with the plane waves to produce oblique waves that exhibit transient growth, and (iii) the oblique waves interact nonlinearly with the plane wave to generate streamwise vortices; these in turn generate the sublayer streaks and so the cycle is renewed.}, }
@article {pmid17508821, year = {2007}, author = {Cichocki, B and Ekiel-Jezewska, ML and Wajnryb, E}, title = {Hydrodynamic interactions between spheres in a viscous fluid with a flat free surface or hard wall.}, journal = {The Journal of chemical physics}, volume = {126}, number = {18}, pages = {184704}, doi = {10.1063/1.2724815}, pmid = {17508821}, issn = {0021-9606}, abstract = {Hydrodynamic interactions between spheres immersed in a low-Reynolds-number fluid flow close to a flat free surface or hard wall are investigated. The spheres may have different or equal radii, and may be separated from the boundary or at contact with the free surface. A simple and useful expression is derived for the propagator (Green operator) connecting centers of two spheres. In the derivation, the method of images and the displacement theorems are used. Symmetry of the displacement operators is explicitly shown. The significance of these results in efficient Stokesian and Brownian dynamics simulations is outlined. An example of an application is shown.}, }
@article {pmid17505888, year = {2007}, author = {Tseng, HY and Wang, CH and Lin, WY and Lee, GB}, title = {Membrane-activated microfluidic rotary devices for pumping and mixing.}, journal = {Biomedical microdevices}, volume = {9}, number = {4}, pages = {545-554}, doi = {10.1007/s10544-007-9062-6}, pmid = {17505888}, issn = {1387-2176}, mesh = {Membranes, Artificial ; Microfluidic Analytical Techniques/*instrumentation ; }, abstract = {Microfluidic devices are operated at a low-Reynolds-number flow regime such that the transportation and mixing of fluids are naturally challenging. There is still a great need to integrate fluid control systems such as pumps, valves and mixers with other functional microfluidic devices to form a micro-total-analysis-system. This study presents a new pneumatic microfluidic rotary device capable of transporting and mixing two different kinds of samples in an annular microchannel by using MEMS (Micro-electro-mechanical-systems) technology. Pumping and mixing can be achieved using a single device with different operation modes. The micropump has four membranes with an annular layout and is compact in size. The new device has a maximum pumping rate of 165.7 microL/min at a driving frequency of 17 Hz and an air pressure of 30 psi. Experimental data show that the pumping rate increases as higher air pressure and driving frequency are applied. In addition, not only can the microfluidic rotary device work as a peristaltic pumping device, but it also is an effective mixing device. The performance of the micromixer is extensively characterized. Experimental data indicate that a mixing index as high as 96.3% can be achieved. The developed microfluidic rotary device can be easily integrated with other microfluidic devices due to its simple and reliable PDMS fabrication process. The development of the microfluidic rotary device can be promising for micro-total-analysis-systems.}, }
@article {pmid17501357, year = {2007}, author = {Philip, J and Svizher, A and Cohen, J}, title = {Scaling law for a subcritical transition in plane Poiseuille flow.}, journal = {Physical review letters}, volume = {98}, number = {15}, pages = {154502}, doi = {10.1103/PhysRevLett.98.154502}, pmid = {17501357}, issn = {0031-9007}, abstract = {The scaling law for the threshold amplitude of perturbations to initiate a transition in subcritical plane Poiseuille flow as a function of the Reynolds number is demonstrated experimentally. The disturbances are introduced through an almost streamwise independent slot drilled at the bottom wall of a horizontal air-channel flow. Following the two stages of transition, linear transient growth and nonlinear secondary instability, it is found that the normalized critical injection rate (v0) scales with the Reynolds number (R) as v0 approximately R-3/2. This scaling law agrees with the theoretical predictions of Chapman [J. Fluid Mech. 451, 34 (2002).].}, }
@article {pmid17501019, year = {2007}, author = {Dutcher, CS and Muller, SJ}, title = {Explicit analytic formulas for Newtonian Taylor-Couette primary instabilities.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {75}, number = {4 Pt 2}, pages = {047301}, doi = {10.1103/PhysRevE.75.047301}, pmid = {17501019}, issn = {1539-3755}, abstract = {In this study, existing primary stability boundary data for flow between concentric cylinders, for the broad range of radius and rotation ratios examined, were found to be self-similar in a properly chosen parameter space. The experimental results for the primary transitions to both Taylor vortex flow and spiral vortex flow collapsed onto a single curve using a combination of variables technique, for both counter-rotating and co-rotating cylinders. The curves were then empirically fit, yielding explicit analytic formulas for the critical Reynolds number for any radius ratio (eta) and rotation ratio (micro) . For counter-rotating flows, the primary critical Reynolds number is determined by a single variable: the ratio of the nodal gap fraction to a known function of the radius ratio. The existence and influence of a nodal surface is shown experimentally for micro approximately equal -1.7. For co-rotating flows, the important scaled variable was found to be the radius ratio divided by the nodal radius ratio. Comparisons of the resulting explicit stability formulas were made to existing analytic stability expressions and experimental data. Excellent quantitative agreement was found with data across the entire parameter space.}, }
@article {pmid17500987, year = {2007}, author = {Scott, RK}, title = {Nonrobustness of the two-dimensional turbulent inverse cascade.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {75}, number = {4 Pt 2}, pages = {046301}, doi = {10.1103/PhysRevE.75.046301}, pmid = {17500987}, issn = {1539-3755}, abstract = {The inverse energy cascade in two-dimensional Navier-Stokes turbulence is examined in the quasisteady regime, with small-scale, band-limited forcing at scale kf-1, with particular attention to the influence of forcing Reynolds number Re on the energy distribution at large scales. The strength of the inverse energy cascade, or fraction of energy input that is transferred to larger scales, increases monotonically toward unity with increasing Re proportional, variantkmax2kf2, where kmax is the maximum resolved wave number. Moreover, as Re increases beyond a critical value, for which a direct enstrophy cascade to small scales is first realized, the energy spectrum in the energy-cascading range steepens from a k-53 to k-2 dependence. The steepening is interpreted as the result of a greater tendency for coherent vortex formation in cases when forcing scales are adequately resolved. In spectral space, it is associated with nonlocality of the inverse energy transfer.}, }
@article {pmid17500890, year = {2007}, author = {Bickel, T}, title = {Hindered mobility of a particle near a soft interface.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {75}, number = {4 Pt 1}, pages = {041403}, doi = {10.1103/PhysRevE.75.041403}, pmid = {17500890}, issn = {1539-3755}, abstract = {The translational motion of a solid sphere near a deformable fluid interface is studied in the low Reynolds number regime. In this problem, the fluid flow driven by the sphere is dynamically coupled to the instantaneous conformation of the interface. Using a two-dimensional Fourier transform technique, we are able to account for the multiple backflows scattered from the interface. The correction to the mobility tensor is then obtained from the matrix elements of the relevant Green's function. Our perturbative analysis allows us to express the explicit position and frequency dependence of the mobility for small particles. We recover in the steady limit the result for a sphere near a perfectly flat interface. At intermediate time scales, the mobility exhibits an imaginary part which is a signature of the elastic response of the interface. In the short time limit, we find that the perpendicular mobility may, under some circumstances, become lower than the bulk value. All the results can be explained using the definition of the relaxation time of the soft interface.}, }
@article {pmid17500830, year = {2007}, author = {Brownlee, RA and Gorban, AN and Levesley, J}, title = {Stability and stabilization of the lattice Boltzmann method.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {75}, number = {3 Pt 2}, pages = {036711}, doi = {10.1103/PhysRevE.75.036711}, pmid = {17500830}, issn = {1539-3755}, abstract = {We revisit the classical stability versus accuracy dilemma for the lattice Boltzmann methods (LBM). Our goal is a stable method of second-order accuracy for fluid dynamics based on the lattice Bhatnager-Gross-Krook method (LBGK). The LBGK scheme can be recognized as a discrete dynamical system generated by free flight and entropic involution. In this framework the stability and accuracy analysis are more natural. We find the necessary and sufficient conditions for second-order accurate fluid dynamics modeling. In particular, it is proven that in order to guarantee second-order accuracy the distribution should belong to a distinguished surface--the invariant film (up to second order in the time step). This surface is the trajectory of the (quasi)equilibrium distribution surface under free flight. The main instability mechanisms are identified. The simplest recipes for stabilization add no artificial dissipation (up to second order) and provide second-order accuracy of the method. Two other prescriptions add some artificial dissipation locally and prevent the system from loss of positivity and local blowup. Demonstration of the proposed stable LBGK schemes are provided by the numerical simulation of a one-dimensional (1D) shock tube and the unsteady 2D flow around a square cylinder up to Reynolds number Re approximately 20,000.}, }
@article {pmid17495331, year = {2007}, author = {Song, OY and Kim, D and Ko, HS}, title = {Derivative particles for simulating detailed movements of fluids.}, journal = {IEEE transactions on visualization and computer graphics}, volume = {13}, number = {4}, pages = {711-719}, doi = {10.1109/TVCG.2007.1022}, pmid = {17495331}, issn = {1077-2626}, mesh = {*Algorithms ; *Computer Graphics ; Computer Simulation ; Image Enhancement/*methods ; Image Interpretation, Computer-Assisted/*methods ; Imaging, Three-Dimensional/*methods ; Information Storage and Retrieval/methods ; *Models, Theoretical ; Numerical Analysis, Computer-Assisted ; Particle Size ; Rheology/*methods ; User-Computer Interface ; }, abstract = {We present a new fluid simulation technique that significantly reduces the nonphysical dissipation of velocity. The proposed method is based on an apt use of particles and derivative information. We note that a major source of numerical dissipation in the conventional Navier-Stokes equations solver lies in the advection step. Hence, starting with the conventional grid-based simulator, when the details of fluid movements need to be simulated, we replace the advection part with a particle simulator. When swapping between the grid-based and particle-based simulators, the physical quantities such as the level set and velocity must be converted. For this purpose, we develop a novel dissipation-suppressing conversion procedure that utilizes the derivative information stored in the particles, as well as in the grid points. For the fluid regions where such details are not needed, the advection is simulated using an octree-based constrained interpolation profile (CIP) solver, which we develop in this work. Through several experiments, we show that the proposed technique can reproduce the detailed movements of high-Reynolds-number fluids such as droplets/bubbles, thin water sheets, and whirlpools. The increased accuracy in the advection, which forms the basis of the proposed technique, can also be used to produce better results in larger scale fluid simulations.}, }
@article {pmid17489611, year = {2007}, author = {Daniels, DR and Turner, MS}, title = {Diffusion on membrane tubes: a highly discriminatory test of the Saffman-Delbruck theory.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {23}, number = {12}, pages = {6667-6670}, doi = {10.1021/la0635000}, pmid = {17489611}, issn = {0743-7463}, support = {HL 58512/HL/NHLBI NIH HHS/United States ; }, mesh = {Diffusion ; *Membranes, Artificial ; *Models, Theoretical ; }, abstract = {The efficient transport of membrane proteins is vital in maintaining life. In this work, we investigate the transport of such membrane proteins along long thin membrane tubes or tethers. We calculate the diffusion constant to leading order in the low Reynolds number regime to be D = (4 pi eta)-1 log(r/a), with r and a being the tube and protein radii, respectively, and eta being the membrane viscosity. Thus we propose an exact limiting form for the controversial logarithmic correction, such as originally introduced by Saffman and Delbruck, that involves the tube radius rather than some "frame size". Our work suggests a test of this logarithmic correction could be achieved by measuring diffusion on membrane tubes, exploiting the fact that the equilibrium tube radius can be controlled by the membrane tension and varied over several orders of magnitude. We analyze the time taken for a protein to transit a membrane tube between cells and find that this can vary by an order of magnitude over physiological tensions. This is a strong effect in biological terms and suggests a possible regulatory coupling between membrane tension and signaling.}, }
@article {pmid17471715, year = {2007}, author = {Sabra, KG and Winkel, ES and Bourgoyne, DA and Elbing, BR and Ceccio, SL and Perlin, M and Dowling, DR}, title = {Using cross correlations of turbulent flow-induced ambient vibrations to estimate the structural impulse response. Application to structural health monitoring.}, journal = {The Journal of the Acoustical Society of America}, volume = {121}, number = {4}, pages = {1987-1995}, doi = {10.1121/1.2710463}, pmid = {17471715}, issn = {0001-4966}, mesh = {Acoustics ; Earth, Planet ; *Environment ; *Vibration ; Water ; }, abstract = {It has been demonstrated theoretically and experimentally that an estimate of the impulse response (or Green's function) between two receivers can be obtained from the cross correlation of diffuse wave fields at these two receivers in various environments and frequency ranges: ultrasonics, civil engineering, underwater acoustics, and seismology. This result provides a means for structural monitoring using ambient structure-borne noise only, without the use of active sources. This paper presents experimental results obtained from flow-induced random vibration data recorded by pairs of accelerometers mounted within a flat plate or hydrofoil in the test section of the U.S. Navy's William B. Morgan Large Cavitation Channel. The experiments were conducted at high Reynolds number (Re > 50 million) with the primary excitation source being turbulent boundary layer pressure fluctuations on the upper and lower surfaces of the plate or foil. Identical deterministic time signatures emerge from the noise cross-correlation function computed via robust and simple processing of noise measured on different days by a pair of passive sensors. These time signatures are used to determine and/or monitor the structural response of the test models from a few hundred to a few thousand Hertz.}, }
@article {pmid17445820, year = {2007}, author = {Harrison, SE and Smith, SM and Bernsdorf, J and Hose, DR and Lawford, PV}, title = {Application and validation of the lattice Boltzmann method for modelling flow-related clotting.}, journal = {Journal of biomechanics}, volume = {40}, number = {13}, pages = {3023-3028}, doi = {10.1016/j.jbiomech.2007.01.026}, pmid = {17445820}, issn = {0021-9290}, mesh = {Animals ; Biomechanical Phenomena ; Milk ; *Models, Biological ; Rheology ; }, abstract = {The purpose of this paper is to present a simple clotting model, based on residence time and shear stress distribution, that can simulate the deposition over time of enzyme-activated milk in an in vitro system. Results for the model are compared with experiments exhibiting clot deposition in the region of a sharp-edged stenosis. The milk experiments have been shown to be a valuable analogue for the experimental representation of flow-induced blood clotting, particularly in the context of separation of hydrodynamic from biochemical factors. The facility to predict the flow-induced clotting of the blood analogue, in which the chemistry reduces to what is effectively a zeroth order reaction, gives confidence in this physics-based approach to simulation of the final part of the coagulation cascade. This type of study is a necessary precursor to the development of a complex, multi-factorial, biochemical model of the process of thrombosis. In addition to the clotting simulations, comparisons are reported between the computed flow patterns prior to clot deposition and flow visualisation studies. Excellent agreement of hydrodynamic parameters is reported for a Reynolds number of 100, and qualitative agreement is seen for the complex, disturbed flow occurring at a physiologically relevant Reynolds number of 550. The explicit, time-stepping lattice Boltzmann approach may have particular merit for the transitional flow at this higher Reynolds number.}, }
@article {pmid17442332, year = {2007}, author = {Chen, CK and Cho, CC}, title = {Electrokinetically-driven flow mixing in microchannels with wavy surface.}, journal = {Journal of colloid and interface science}, volume = {312}, number = {2}, pages = {470-480}, doi = {10.1016/j.jcis.2007.03.033}, pmid = {17442332}, issn = {0021-9797}, mesh = {Computer Simulation ; Electroosmosis/*methods ; Mathematics ; Microfluidics/*instrumentation/methods ; Models, Theoretical ; }, abstract = {This paper investigates the mixing characteristics of electrokinetically-driven flow in microchannels with different wavy surface configurations. Numerical simulations are performed to analyze the influence of the wave amplitude and the length of the wavy section on the mixing efficiency within the microchannel. Typically, straight channels have a poor mixing performance because the fluid flow is restricted to the low Reynolds number regime, and hence mixing takes place primarily as a result of diffusion effects. However, the wavy surfaces employed in the current microchannels increase the interfacial contact area between the two species in the microchannel and therefore improve the mixing efficiency. The mixing performance is further enhanced by the application of a heterogeneous charge pattern on the wavy surfaces. The numerical results show that the heterogeneous charge pattern generates flow circulations near the microchannel walls. These circulations are shown to provide an effective enhancement in the mixing performance. Overall, the present results show that the mixing performance is improved by increasing the magnitude of the heterogeneous surface zeta potential upon the wavy surface or by increasing the wave amplitude or the length of the wavy section in the microchannel.}, }
@article {pmid17426938, year = {2007}, author = {Langlois, V and Valance, A}, title = {Initiation and evolution of current ripples on a flat sand bed under turbulent water flow.}, journal = {The European physical journal. E, Soft matter}, volume = {22}, number = {3}, pages = {201-208}, pmid = {17426938}, issn = {1292-8941}, abstract = {We investigate the formation and dynamics of sand ripples under a turbulent water flow. Our experiments were conducted in an open flume with spherical glass beads between 100 and 500 microm in diameter. The flow Reynolds number is of the order of 10,000 and the particle Reynolds number of the order of 1 to 10. We study the development of ripples by measuring their wavelength and amplitude in course of time and investigate the influence of the grain size and the flow properties. In particular, we demonstrate two different regimes according to the grain size. For fine grains, a slow coarsening process (i.e., a logarithmic increase of the wavelength and amplitude) takes place, while for coarser grains, this process occurs at a much faster rate (i.e., with a linear growth) and stops after a finite time. In the later case, a stable pattern is eventually observed. Besides, we carefully analyze the wavelength of ripples in the first stages of the instability as a function of the grain size and the shear velocity of the flow, and compare our results with other available experimental data and with theoretical predictions based on linear stability analyses.}, }
@article {pmid17408325, year = {2007}, author = {Zierenberg, JR and Fujioka, H and Hirschl, RB and Bartlett, RH and Grotberg, JB}, title = {Pulsatile blood flow and oxygen transport past a circular cylinder.}, journal = {Journal of biomechanical engineering}, volume = {129}, number = {2}, pages = {202-215}, doi = {10.1115/1.2485961}, pmid = {17408325}, issn = {0148-0731}, support = {R01 HL069420/HL/NHLBI NIH HHS/United States ; HL69420/HL/NHLBI NIH HHS/United States ; }, mesh = {Biological Transport ; Blood Flow Velocity ; Humans ; *Models, Cardiovascular ; *Pulsatile Flow ; *Respiratory Transport ; Rheology ; Stress, Mechanical ; }, abstract = {The fundamental study of blood flow past a circular cylinder filled with an oxygen source is investigated as a building block for an artificial lung. The Casson constitutive equation is used to describe the shear-thinning and yield stress properties of blood. The presence of hemoglobin is also considered. Far from the cylinder, a pulsatile blood flow in the x direction is prescribed, represented by a time periodic (sinusoidal) component superimposed on a steady velocity. The dimensionless parameters of interest for the characterization of the flow and transport are the steady Reynolds number (Re), Womersley parameter (alpha), pulsation amplitude (A), and the Schmidt number (Sc). The Hill equation is used to describe the saturation curve of hemoglobin with oxygen. Two different feed-gas mixtures were considered: pure O(2) and air. The flow and concentration fields were computed for Re=5, 10, and 40, 0< or =A< or =0.75, alpha=0.25, 0.4, and Schmidt number, Sc=1000. The Casson fluid properties result in reduced recirculations (when present) downstream of the cylinder as compared to a Newtonian fluid. These vortices oscillate in size and strength as A and alpha are varied. Hemoglobin enhances mass transport and is especially important for an air feed which is dominated by oxyhemoglobin dispersion near the cylinder. For a pure O(2) feed, oxygen transport in the plasma dominates near the cylinder. Maximum oxygen transport is achieved by operating near steady flow (small A) for both feed-gas mixtures. The time averaged Sherwood number, Sh, is found to be largely influenced by the steady Reynolds number, increasing as Re increases and decreasing with A. Little change is observed with varying alpha for the ranges investigated. The effect of pulsatility on Sh is greater at larger Re. Increasing Re aids transport, but yields a higher cylinder drag force and shear stresses on the cylinder surface which are potentially undesirable.}, }
@article {pmid17408321, year = {2007}, author = {Li, WG and Luo, XY and Johnson, AG and Hill, NA and Bird, N and Chin, SB}, title = {One-dimensional models of the human biliary system.}, journal = {Journal of biomechanical engineering}, volume = {129}, number = {2}, pages = {164-173}, doi = {10.1115/1.2472379}, pmid = {17408321}, issn = {0148-0731}, mesh = {Bile/physiology ; Biliary Tract/*anatomy &amp; histology ; Biophysical Phenomena ; Biophysics ; Cystic Duct/anatomy &amp; histology/pathology ; Gallstones/etiology/pathology/physiopathology ; Humans ; *Models, Biological ; Pressure ; Viscosity ; }, abstract = {This paper studies two one-dimensional models to estimate the pressure drop in the normal human biliary system for Reynolds number up to 20. Excessive pressure drop during bile emptying and refilling may result in incomplete bile emptying, leading to stasis and subsequent formation of gallbladder stones. The models were developed following the group's previous work on the cystic duct using numerical simulations. Using these models, the effects of the biliary system geometry, elastic property of the cystic duct, and bile viscosity on the pressure drop can be studied more efficiently than with full numerical approaches. It was found that the maximum pressure drop occurs during bile emptying immediately after a meal, and is greatly influenced by the viscosity of the bile and the geometric configuration of the cystic duct, i.e., patients with more viscous bile or with a cystic duct containing more baffles or a longer length, have the greatest pressure drop. It is found that the most significant parameter is the diameter of the cystic duct; a 1% decrease in the diameter increases the pressure drop by up to 4.3%. The effects of the baffle height ratio and number of baffles on the pressure drop are reflected in the fact that these effectively change the equivalent diameter and length of the cystic duct. The effect of the Young's modulus on the pressure drop is important only if it is lower than 400 Pa; above this value, a rigid-walled model gives a good estimate of the pressure drop in the system for the parameters studied.}, }
@article {pmid17407871, year = {2007}, author = {Takaishi, T and Miyazawa, M and Kato, C}, title = {A computational method of evaluating noncompact sound based on vortex sound theory.}, journal = {The Journal of the Acoustical Society of America}, volume = {121}, number = {3}, pages = {1353-1361}, doi = {10.1121/1.2431345}, pmid = {17407871}, issn = {0001-4966}, abstract = {A numerical investigation is made of the production of sound by turbulence interacting with a noncompact body. The problem is formulated in the frequency domain by extending the theory of vortex sound proposed by Howe. The anomalous "numerical" generation of sound by the sudden termination of Lighthill's stress tensor at the outer boundary of a finite computational domain is avoided by identification of "scattered" sound sources that generate sound principally by interaction with the solid surface. It is argued that the boundary element method is the most efficient means of computing the aeroacoustic Green's function for the problem, because it requires a minimum of CPU time, is not prone to numerical errors such as dispersion and dissipation during propagation, and the radiation condition is easily applied at the outer boundary. The method is applied to the problem of sound generation by high Reynolds number flow past a circular cylinder. The "scattered" sources are shown to be confined to the vicinity of the cylinder surface. At low frequencies the radiation has a dipole-like directivity in agreement with the compact approximation. However, the directivity is quite different at high frequencies, where our noncompact method predicts a more complicated "leaf-like" radiation pattern.}, }
@article {pmid17399723, year = {2007}, author = {Lima, R and Wada, S and Takeda, M and Tsubota, K and Yamaguchi, T}, title = {In vitro confocal micro-PIV measurements of blood flow in a square microchannel: the effect of the haematocrit on instantaneous velocity profiles.}, journal = {Journal of biomechanics}, volume = {40}, number = {12}, pages = {2752-2757}, doi = {10.1016/j.jbiomech.2007.01.012}, pmid = {17399723}, issn = {0021-9290}, mesh = {*Blood Flow Velocity ; Erythrocytes/*cytology ; *Hematocrit ; Hemorheology/instrumentation/methods ; Humans ; *Microfluidic Analytical Techniques ; Microscopy, Confocal ; Microspheres ; }, abstract = {A confocal microparticle image velocimetry (micro-PIV) system was used to obtain detailed information on the velocity profiles for the flow of pure water (PW) and in vitro blood (haematocrit up to 17%) in a 100-microm-square microchannel. All the measurements were made in the middle plane of the microchannel at a constant flow rate and low Reynolds number (Re=0.025). The averaged ensemble velocity profiles were found to be markedly parabolic for all the working fluids studied. When comparing the instantaneous velocity profiles of the three fluids, our results indicated that the profile shape depended on the haematocrit. Our confocal micro-PIV measurements demonstrate that the root mean square (RMS) values increase with the haematocrit implying that it is important to consider the information provided by the instantaneous velocity fields, even at low Re. The present study also examines the potential effect of the RBCs on the accuracy of the instantaneous velocity measurements.}, }
@article {pmid17396416, year = {2007}, author = {Ganesan, MV and Saravanan, V and Sreekrishnan, TR}, title = {Formation and hydrodynamic characteristics of aerobic granules in an activated sludge system.}, journal = {Environmental technology}, volume = {28}, number = {2}, pages = {217-224}, doi = {10.1080/09593332808618784}, pmid = {17396416}, issn = {0959-3330}, mesh = {Aerobiosis ; Bacteria, Aerobic/*chemistry/metabolism ; *Bioreactors ; Carbon/*chemistry ; Glucose/metabolism ; Sewage ; Waste Disposal, Fluid/*methods ; }, abstract = {Development of aerobic granules in the aeration tank of an activated sludge system has been studied. The introduction of activated carbon particles into the aeration tank resulted in the formation of biogranules containing activated carbon as core nuclei. The presence of activated carbon also induced the formation of self-immobilized granules, which did not have any carrier particle at their core. The presence of aerobic granules enhanced the treatment efficiency of the reactor. At an organic loading rate of 32.8 kg COD m(-3)d(-1) and 0.78 h hydraulic retention time (HRT), the reactor showed 96% COD removal efficiency. At an HRT of 0.272 h and organic loading rate of 46.7 kg COD m(-3)d(-1), the reactor outlet COD remained below 100 mg l(-1). Settling velocity studies carried out on the biogranules showed that the drag coefficient of biogranules is greater than that of the rigid particle at the same Reynolds number.}, }
@article {pmid17368472, year = {2007}, author = {Oh, JM and Kang, KH}, title = {Conditions for similitude and the effect of finite Debye length in electroosmotic flows.}, journal = {Journal of colloid and interface science}, volume = {310}, number = {2}, pages = {607-616}, doi = {10.1016/j.jcis.2007.01.087}, pmid = {17368472}, issn = {0021-9797}, mesh = {Electrochemistry ; *Models, Theoretical ; Osmosis ; *Rheology ; }, abstract = {Under certain conditions, the velocity field is similar to the electric field for electroosmotic flow (EOF) inside a channel. There was a disagreement between investigators on the necessity of the infinitesimal-Reynolds-number condition for the similarity when the Helmholtz-Smoluchowski relation is applied throughout the boundaries. What is puzzling is a recent numerical result that showed, contrary to the conventional belief, an evident Reynolds number dependence of the EOF. We show here that the notion that the infinitesimal-Reynolds-number condition is required originates from the misunderstanding that the EOF is the Stokes flow. We point out that the EOF becomes the potential flow when the Helmholtz-Smoluchowski relation is applied at the boundaries. We carry out a numerical simulation to investigate the effect of finiteness of the Debye length and the vorticity layer inherently existing at the channel wall. We show that the Reynolds number dependence of the previous numerical simulation resulted from the finiteness of the Debye length and subsequent convective transport of vorticity toward the bulk flow. We discuss in detail how the convection of vorticity occurs and what factors are involved in the transport process, after carrying out the simulation for different Reynolds numbers, Debye lengths, corner radii, and geometries.}, }
@article {pmid17361052, year = {2007}, author = {Fukui, T and Parker, KH and Tsubota, K and Wada, S and Yamaguchi, T}, title = {Differentiation of stenosed and aneurysmal arteries by pulse wave propagation analysis based on a fluid-solid interaction computational method.}, journal = {Technology and health care : official journal of the European Society for Engineering and Medicine}, volume = {15}, number = {2}, pages = {79-90}, pmid = {17361052}, issn = {0928-7329}, mesh = {Aortic Aneurysm/blood/*diagnosis/physiopathology ; Aortic Valve Stenosis/blood/*diagnosis/physiopathology ; Biomedical Engineering ; Blood Flow Velocity/*physiology ; Cardiovascular Diseases/*diagnosis/physiopathology ; Elasticity ; Humans ; *Models, Cardiovascular ; Pulsatile Flow/*physiology ; Severity of Illness Index ; }, abstract = {Pulse Wave Velocity (PWV) is recognized by clinicians as an index of the mechanical properties of human blood vessels. However, the measured PWV of real human blood vessels will not always obey the Moens-Korteweg equation, which describes the PWV in ideal elastic tubes. Waveform analysis has been studied as an alternative diagnosis for cardiovascular disease, and reflected waves that occur in the diseased region may be a key for the estimation of the severity of disease. In this study, we modeled stenosed and aneurysmal arteries in a three-dimensional coupled fluid-solid interaction scheme, and analyzed the pulse wave propagation in order to assess the reflected waves that occurred in the diseased region. A commercial code (Radioss, MECALOG, France) was used to solve the fluid-solid interactions. A steady flow with Reynolds number 1000 was imposed at the inlet of the artery as the basic flow, then a single rectangular pulse with Reynolds number 4000 was imposed upon the basic flow to produce a propagating wave. We showed that the reflected waves from the stenosis and the aneurysm are different in their phase, and the wavelength of the reflected waves from the aneurysm is affected by the aneurysm length.}, }
@article {pmid17359102, year = {2007}, author = {Bec, J and Biferale, L and Cencini, M and Lanotte, A and Musacchio, S and Toschi, F}, title = {Heavy particle concentration in turbulence at dissipative and inertial scales.}, journal = {Physical review letters}, volume = {98}, number = {8}, pages = {084502}, doi = {10.1103/PhysRevLett.98.084502}, pmid = {17359102}, issn = {0031-9007}, abstract = {Spatial distributions of heavy particles suspended in an incompressible isotropic and homogeneous turbulent flow are investigated by means of high resolution direct numerical simulations. In the dissipative range, it is shown that particles form fractal clusters with properties independent of the Reynolds number. Clustering is there optimal when the particle response time is of the order of the Kolmogorov time scale tau(eta). In the inertial range, the particle distribution is no longer scale invariant. It is, however, shown that deviations from uniformity depend on a rescaled contraction rate, which is different from the local Stokes number given by dimensional analysis. Particle distribution is characterized by voids spanning all scales of the turbulent flow; their signature in the coarse-grained mass probability distribution is an algebraic behavior at small densities.}, }
@article {pmid17359101, year = {2007}, author = {van den Berg, TH and van Gils, DP and Lathrop, DP and Lohse, D}, title = {Bubbly turbulent drag reduction is a boundary layer effect.}, journal = {Physical review letters}, volume = {98}, number = {8}, pages = {084501}, doi = {10.1103/PhysRevLett.98.084501}, pmid = {17359101}, issn = {0031-9007}, abstract = {In turbulent Taylor-Couette flow, the injection of bubbles reduces the overall drag. On the other hand, rough walls enhance the overall drag. In this work, we inject bubbles into turbulent Taylor-Couette flow with rough walls (with a Reynolds number up to 4 x 10(5), finding an enhancement of the dimensionless drag as compared to the case without bubbles. The dimensional drag is unchanged. As in the rough-wall case no smooth boundary layers can develop, the results demonstrate that bubbly drag reduction is a pure boundary layer effect.}, }
@article {pmid17358948, year = {2007}, author = {Ben-Dov, G and Cohen, J}, title = {Critical Reynolds number for a natural transition to turbulence in pipe flows.}, journal = {Physical review letters}, volume = {98}, number = {6}, pages = {064503}, doi = {10.1103/PhysRevLett.98.064503}, pmid = {17358948}, issn = {0031-9007}, abstract = {Experimental results obtained over more than a century have shown that laminar flow in a circular pipe becomes naturally turbulent at a critical Reynolds number of Re approximately 2000. In this Letter a theoretical explanation, based on the minimum energy of an axisymmetric deviation (from the developed pipe flow profile), is suggested for this critical value. It is shown that for Re>1840 the minimum energy of the deviation, associated with the central part of the pipe, becomes a global minimum for triggering secondary instabilities. For Re<1840 the global minimum energy deviation is located next to the pipe wall. Previous experimental observations support this explanation.}, }
@article {pmid17358947, year = {2007}, author = {Beck, C}, title = {Statistics of three-dimensional lagrangian turbulence.}, journal = {Physical review letters}, volume = {98}, number = {6}, pages = {064502}, doi = {10.1103/PhysRevLett.98.064502}, pmid = {17358947}, issn = {0031-9007}, abstract = {We consider a superstatistical model for a Lagrangian tracer particle in a high-Reynolds-number turbulent flow. The analytical model predictions are in excellent agreement with recent experimental data for flow between counter-rotating disks. In particular, the predicted Lagrangian scaling exponents zeta_{j} agree well with the measured exponents reported in H. Xu et al. [Phys. Rev. Lett.10.1103/PhysRevLett.96.114503 96, 114503 (2006)]. The model also correctly predicts the shape of acceleration probability densities, correlation functions, statistical dependencies between components, and explains the fact that enstrophy lags behind dissipation.}, }
@article {pmid17358779, year = {2007}, author = {Monchaux, R and Berhanu, M and Bourgoin, M and Moulin, M and Odier, P and Pinton, JF and Volk, R and Fauve, S and Mordant, N and Pétrélis, F and Chiffaudel, A and Daviaud, F and Dubrulle, B and Gasquet, C and Marié, L and Ravelet, F}, title = {Generation of a magnetic field by dynamo action in a turbulent flow of liquid sodium.}, journal = {Physical review letters}, volume = {98}, number = {4}, pages = {044502}, doi = {10.1103/PhysRevLett.98.044502}, pmid = {17358779}, issn = {0031-9007}, abstract = {We report the observation of dynamo action in the von Kármán sodium experiment, i.e., the generation of a magnetic field by a strongly turbulent swirling flow of liquid sodium. Both mean and fluctuating parts of the field are studied. The dynamo threshold corresponds to a magnetic Reynolds number R(m) approximately 30. A mean magnetic field of the order of 40 G is observed 30% above threshold at the flow lateral boundary. The rms fluctuations are larger than the corresponding mean value for two of the components. The scaling of the mean square magnetic field is compared to a prediction previously made for high Reynolds number flows.}, }
@article {pmid17358686, year = {2007}, author = {Umurhan, OM and Menou, K and Regev, O}, title = {Weakly nonlinear analysis of the magnetorotational instability in a model channel flow.}, journal = {Physical review letters}, volume = {98}, number = {3}, pages = {034501}, doi = {10.1103/PhysRevLett.98.034501}, pmid = {17358686}, issn = {0031-9007}, abstract = {We show by means of a perturbative weakly nonlinear analysis that the axisymmetric magnetorotational instability (MRI) of a viscous, resistive, incompressible rotating shear flow subject to a background vertical magnetic field in a thin channel gives rise to a Ginzburg-Landau equation for the disturbance amplitude. For small magnetic Prandtl number (P(m)), the saturation amplitude is proportional square root P(m) and the resulting momentum transport scales as R(-1), where R is the hydrodynamic Reynolds number. Simplifying assumptions, such as linear shear base flow, mathematically expedient boundary conditions, and continuous spectrum of the vertical linear modes, are used to facilitate this analysis. The asymptotic results are shown to comply with numerical calculations using a spectral code. They suggest that the transport due to the nonlinearly developed MRI may be very small in experimental setups with P(m)<<1.}, }
@article {pmid17358478, year = {2007}, author = {Willis, AP and Kerswell, RR}, title = {Critical behavior in the relaminarization of localized turbulence in pipe flow.}, journal = {Physical review letters}, volume = {98}, number = {1}, pages = {014501}, doi = {10.1103/PhysRevLett.98.014501}, pmid = {17358478}, issn = {0031-9007}, abstract = {The statistics of the relaminarization of localized turbulence in a pipe are examined by direct numerical simulation. As in recent experimental data [J. Peixinho and T. Mullin, Phys. Rev. Lett. 96, 094501 (2006)10.1103/PhysRevLett.96.094501], the half-life for the decaying turbulence is consistent with the scaling (Rec-Re) -1, indicating a boundary crisis of the localized turbulent state familiar in low-dimensional dynamical systems. The crisis Reynolds number is estimated as Rec=1870, a value within 7% of the experimental value 1750. We argue that the frequently asked question, of which initial disturbances at a given Re trigger sustained turbulence in a pipe, is really two separate questions: the "local phase space" question (local to the laminar state) of what threshold disturbance at a given Re is needed to initially trigger turbulence, followed by the "global phase space" question of whether Re exceeds Rec at which point the turbulent state becomes an attractor.}, }
@article {pmid17358420, year = {2007}, author = {Abu-Ramadan, E and Khayat, RE}, title = {Stability of vortex flow in a modulated channel.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {75}, number = {2 Pt 2}, pages = {026305}, doi = {10.1103/PhysRevE.75.026305}, pmid = {17358420}, issn = {1539-3755}, abstract = {Linear stability analysis of a fully developed two-dimensional periodic steady flow in a spatially modulated symmetric channel is investigated numerically. Both walls are sinusoidally modulated. The modulation amplitude is assumed to be small. The base steady flow is calculated using a regular perturbation expansion of the flow field coupled to a variable-step finite-difference scheme. The disturbance flow equations are derived within the framework of Floquet theory and solved using a two-point boundary value method. The implemented procedure is simple, direct, and very efficient. The accuracy of this method is established. The influence of geometric parameters on the threshold for the onset of instability is systematically investigated. It is established that the critical Reynolds number for the onset of hydrodynamic instability decreases as the wall modulation amplitude or wave number increases. Modulated channel flow is characterized by the formation of a recirculation region or vortices beneath the modulation crest as the Reynolds number exceeds a certain critical threshold. The relation between the thresholds for the onset of instability and vortex flow is examined over a wide range of geometric parameters. Vortex flow effects on the conditions for the onset of instability are systematically investigated. The parameter regime of stable vortex flow is established. It is found that the parameter regime of stable vortex flow increases significantly with the wall modulation wave number for small wave numbers. This increase become less pronounced as the wave number is further increased.}, }
@article {pmid17358418, year = {2007}, author = {Bayliss, RA and Forest, CB and Nornberg, MD and Spence, EJ and Terry, PW}, title = {Numerical simulations of current generation and dynamo excitation in a mechanically forced turbulent flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {75}, number = {2 Pt 2}, pages = {026303}, doi = {10.1103/PhysRevE.75.026303}, pmid = {17358418}, issn = {1539-3755}, abstract = {The role of turbulence in current generation and self-excitation of magnetic fields has been studied in the geometry of a mechanically driven, spherical dynamo experiment, using a three-dimensional numerical computation. A simple impeller model drives a flow that can generate a growing magnetic field, depending on the magnetic Reynolds number Rm=micro0sigmaVa and the fluid Reynolds number Re=Vanu of the flow. For Re<420, the flow is laminar and the dynamo transition is governed by a threshold of Rmcrit=100, above which a growing magnetic eigenmode is observed that is primarily a dipole field transverse to the axis of symmetry of the flow. In saturation, the Lorentz force slows the flow such that the magnetic eigenmode becomes marginally stable. For Re>420 and Rm approximately 100 the flow becomes turbulent and the dynamo eigenmode is suppressed. The mechanism of suppression is a combination of a time varying large-scale field and the presence of fluctuation driven currents (such as those predicted by the mean-field theory), which effectively enhance the magnetic diffusivity. For higher Rm, a dynamo reappears; however, the structure of the magnetic field is often different from the laminar dynamo. It is dominated by a dipolar magnetic field aligned with the axis of symmetry of the mean-flow, which is apparently generated by fluctuation-driven currents. The magnitude and structure of the fluctuation-driven currents have been studied by applying a weak, axisymmetric seed magnetic field to laminar and turbulent flows. An Ohm's law analysis of the axisymmetric currents allows the fluctuation-driven currents to be identified. The magnetic fields generated by the fluctuations are significant: a dipole moment aligned with the symmetry axis of the mean-flow is generated similar to those observed in the experiment, and both toroidal and poloidal flux expulsion are observed.}, }
@article {pmid17358387, year = {2007}, author = {Blazková, M and Schmoranzer, D and Skrbek, L}, title = {Transition from laminar to turbulent drag in flow due to a vibrating quartz fork.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {75}, number = {2 Pt 2}, pages = {025302}, doi = {10.1103/PhysRevE.75.025302}, pmid = {17358387}, issn = {1539-3755}, abstract = {Flow due to a commercially available vibrating quartz fork is studied in gaseous helium, He I and He II, over a wide range of temperatures and pressures. On increasing the driving force applied to the fork, the drag changes in character from laminar (characterized by a linear drive vs velocity dependence) to turbulent (characterized by a quadratic drive vs velocity dependence). We characterize this transition by a critical Reynolds number Recrdelta=Ucrdelta/nu, where Ucr is the critical velocity, nu stands for the kinematic viscosity, delta=sqrt[2nu/omega] is the viscous penetration depth, and omega is the angular frequency of oscillations. We have experimentally verified that the corresponding scaling Ucr proportional, sqrt[nuomega] holds in a classical viscous fluid over two decades of nu.}, }
@article {pmid17358251, year = {2007}, author = {Gadêlha, H and Brito, N and Miranda, JA}, title = {Dynamics of viscous fingers in rotating Hele-Shaw cells with Coriolis effects.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {75}, number = {1 Pt 2}, pages = {016305}, doi = {10.1103/PhysRevE.75.016305}, pmid = {17358251}, issn = {1539-3755}, abstract = {A growing number of experimental and theoretical works have been addressing various aspects of the viscous fingering formation in rotating Hele-Shaw cells. However, only a few of them consider the influence of Coriolis forces. The studies including Coriolis effects are mostly restricted to the high-viscosity-contrast limit and rely on either purely linear stability analyses or intensive numerical simulations. We approach the problem analytically and use a modified Darcy's law including the exact form of the Coriolis effects to execute a mode-coupling analysis of the system. By imposing no restrictions on the viscosity contrast A (dimensionless viscosity difference) we go beyond linear stages and examine the onset of nonlinearities. Our results indicate that when Coriolis effects are taken into account, an interesting interplay between the Reynolds number Re and A arises. This leads to important changes in the stability and morphological features of the emerging interfacial patterns. We contrast our mode-coupling approach with previous theoretical models proposed in the literature.}, }
@article {pmid17330174, year = {2007}, author = {Bottausci, F and Cardonne, C and Meinhart, C and Mezić, I}, title = {An ultrashort mixing length micromixer: the shear superposition micromixer.}, journal = {Lab on a chip}, volume = {7}, number = {3}, pages = {396-398}, doi = {10.1039/b616104a}, pmid = {17330174}, issn = {1473-0197}, mesh = {Equipment Design ; Microfluidics/*instrumentation ; }, abstract = {We report for the first time a laminar high-performance continuous micromixing process of two fluids over a length of 200 microns in under 10 milliseconds achieved by an optimization of the control parameters amplitude and frequency in the mixing device denoted as 'Shear Superposition Micromixer'. We improve mixing time by approximately 5 orders of magnitude over diffusion-limited mixing. The data indicate that rapid mixing is a result of the combined action of Taylor-Aris dispersion in the main and secondary microchannels and unsteady vortex motion that occurs at finite Reynolds number, which occurs above a threshold amplitude and frequency. The mixing performance is quantified using micron-resolution particle image velocimetry (micro-PIV) and computational fluid dynamics (CFD) simulations.}, }
@article {pmid17313234, year = {2007}, author = {Earl, DJ and Pooley, CM and Ryder, JF and Bredberg, I and Yeomans, JM}, title = {Modeling microscopic swimmers at low Reynolds number.}, journal = {The Journal of chemical physics}, volume = {126}, number = {6}, pages = {064703}, doi = {10.1063/1.2434160}, pmid = {17313234}, issn = {0021-9606}, mesh = {*Bacterial Physiological Phenomena ; Mathematics ; *Models, Biological ; Motion ; }, abstract = {The authors employ three numerical methods to explore the motion of low Reynolds number swimmers, modeling the hydrodynamic interactions by means of the Oseen tensor approximation, lattice Boltzmann simulations, and multiparticle collision dynamics. By applying the methods to a three bead linear swimmer, for which exact results are known, the authors are able to compare and assess the effectiveness of the different approaches. They then propose a new class of low Reynolds number swimmers, generalized three bead swimmers that can change both the length of their arms and the angle between them. Hence they suggest a design for a microstructure capable of moving in three dimensions. They discuss multiple bead, linear microstructures and show that they are highly efficient swimmers. They then turn to consider the swimming motion of elastic filaments. Using multiparticle collision dynamics the authors show that a driven filament behaves in a qualitatively similar way to the micron-scale swimming device recently demonstrated by Dreyfus et al. [Nature (London) 437, 862 (2005)].}, }
@article {pmid17306819, year = {2007}, author = {Chang, YI and Liao, KY}, title = {Effect of particle size distribution on the collection efficiency of Brownian particles.}, journal = {Journal of colloid and interface science}, volume = {309}, number = {2}, pages = {236-244}, doi = {10.1016/j.jcis.2007.01.043}, pmid = {17306819}, issn = {0021-9797}, abstract = {The main purpose of the present paper is to investigate the effect of the normal Gaussian size distribution on the deposition of Brownian particles onto a spherical collector, by applying the Brownian dynamic simulation method and the Kuwabara flow field model with different types of DLVO interaction energy curves and the shadow effect. The simulation results show that the collection efficiency of Brownian particles always increases with a wider particle size distribution region. The same increased tendencies are also observed for the case of increasing Reynolds number and for the case of increasing the particle size to the collector size ratio. When compared to the available experimental data, the present simulation method fits well with the experimental data when the specific deposit per collector is not large.}, }
@article {pmid17304557, year = {2007}, author = {Mannall, GJ and Titchener-Hooker, NJ and Dalby, PA}, title = {Factors affecting protein refolding yields in a fed-batch and batch-refolding system.}, journal = {Biotechnology and bioengineering}, volume = {97}, number = {6}, pages = {1523-1534}, doi = {10.1002/bit.21377}, pmid = {17304557}, issn = {0006-3592}, mesh = {Bioreactors/microbiology ; Combinatorial Chemistry Techniques/*methods ; Computer Simulation ; Escherichia coli/chemistry/genetics/*metabolism ; Escherichia coli Proteins/*chemistry/genetics/*metabolism ; Inclusion Bodies/chemistry/*metabolism ; *Models, Biological ; Protein Engineering/methods ; Protein Folding ; Recombinant Proteins/*chemistry/metabolism ; }, abstract = {The refolding of recombinant protein from inclusion bodies expressed in Escherichia coli can present a process bottleneck. Yields at industrially relevant concentrations are restricted by aggregation of protein upon dilution of the denatured form. This article studies the effect of five factors upon the dilution refolding of protein in a twin impeller fed-batch system using refold buffer containing only the oxidized form of the redox reagent. Such a buffer is easier to prepare and more stable than a buffer containing both reduced and oxidized forms. The five factors chosen were: bulk impeller Reynolds number, mini-impeller Reynolds number, injection rate of denatured protein, redox ratio, and guanidine hydrochloride (GdHCl) concentration. A 2(5) factorial experiment was conducted at an industrially relevant protein concentration using lysozyme as the test system. The study identified that in the system used, the guanidine hydrochloride concentration, redox ratio, and injection rate were the most important factors in determining refolding yields. Two interactions were found to be important: redox ratio/guanidine hydrochloride concentration and guanidine hydrochloride concentration/injection rate. Conditions were also found at which high refolding yields could be achieved even with rapid injection and poor mixing efficiency. Therefore, a comparative assessment was carried out with minimal mixing in a simple batch-refolding mode of operation, which revealed different behavior to that of fed-batch. A graphical (windows of operation) analysis of the batch data suggested that optimal yields and productivity are obtained at high guanidine hydrochloride concentrations (1.2 M) and redox ratios of unity or greater.}, }
@article {pmid17297799, year = {2007}, author = {Park, JB and Mongeau, L}, title = {Instantaneous orifice discharge coefficient of a physical, driven model of the human larynx.}, journal = {The Journal of the Acoustical Society of America}, volume = {121}, number = {1}, pages = {442-455}, doi = {10.1121/1.2401652}, pmid = {17297799}, issn = {0001-4966}, support = {R01 DC 05788/DC/NIDCD NIH HHS/United States ; R01 DC03577/DC/NIDCD NIH HHS/United States ; }, mesh = {Humans ; Larynx/anatomy &amp; histology/*physiology ; *Models, Biological ; *Phonetics ; Pressure ; *Speech Acoustics ; }, abstract = {The quasisteady approximation is often made in the study of phonatory aerodynamics to facilitate the modeling of time-varying air flows through the self-oscillating vocal folds. The unsteady, pulsating flow is approximated by a sequence of steady flows through representative configurations of the vocal folds at rest. Previous studies have discussed the accuracy of this approximation for a range of orifice geometries, and flow conditions. The purpose of the present study was to further evaluate the quasisteady approximation experimentally using an improved procedure, from a direct comparison between the discharge coefficients of steady jets through fixed orifices and unsteady jets through modulated orifices of identical shape, area, and transglottal pressures at a given time. Life-scale convergent and divergent glottis-shaped rubber orifices were used in a rigid-walled tube and a low Mach number flow representative of human phonation. It was found that the quasisteady approximation is valid during 70% of the duty cycle, when the Reynolds number was above 3000, for a frequency of oscillations of 100 Hz. The steady form of Bernoulli's equation along a streamline, and Bernoulli's flow obstruction theory were found to be reasonably accurate for the unsteady flows. These models break down at low Reynolds numbers, near the beginning and the end of the duty cycle, due to viscous effects and to the influence of flow displaced by the motion of the walls.}, }
@article {pmid17293522, year = {2007}, author = {Krauter, P and Biermann, A}, title = {Reaerosolization of fluidized spores in ventilation systems.}, journal = {Applied and environmental microbiology}, volume = {73}, number = {7}, pages = {2165-2172}, pmid = {17293522}, issn = {0099-2240}, mesh = {Aerosols ; *Air Microbiology ; Bacillus/*isolation &amp; purification ; Spores, Bacterial ; *Ventilation ; }, abstract = {This project examined dry, fluidized spore reaerosolization in a heating, ventilating, and air conditioning duct system. Experiments using spores of Bacillus atrophaeus, a nonpathogenic surrogate for Bacillus anthracis, were conducted to delineate the extent of spore reaerosolization behavior under normal indoor airflow conditions. Short-term (five air-volume exchanges), long-term (up to 21,000 air-volume exchanges), and cycled (on-off) reaerosolization tests were conducted using two common duct materials. Spores were released into the test apparatus in turbulent airflow (Reynolds number, 26,000). After the initial pulse of spores (approximately 10(10) to 10(11) viable spores) was released, high-efficiency particulate air filters were added to the air intake. Airflow was again used to perturb the spores that had previously deposited onto the duct. Resuspension rates on both steel and plastic duct materials were between 10(-3) and 10(-5) per second, which decreased to 10 times less than initial rates within 30 min. Pulsed flow caused an initial spike in spore resuspension concentration that rapidly decreased. The resuspension rates were greater than those predicted by resuspension models for contamination in the environment, a result attributed to surface roughness differences. There was no difference between spore reaerosolization from metal and that from plastic duct surfaces over 5 hours of constant airflow. The spores that deposited onto the duct remained a persistent source of contamination over a period of several hours.}, }
@article {pmid17289994, year = {2007}, author = {Prakash, M and Gershenfeld, N}, title = {Microfluidic bubble logic.}, journal = {Science (New York, N.Y.)}, volume = {315}, number = {5813}, pages = {832-835}, doi = {10.1126/science.1136907}, pmid = {17289994}, issn = {1095-9203}, mesh = {Capillary Action ; Chemical Phenomena ; Chemistry, Physical ; *Computing Methodologies ; Logic ; Mathematics ; Microchip Analytical Procedures ; *Microfluidic Analytical Techniques ; *Microfluidics ; Nonlinear Dynamics ; Surface Tension ; }, abstract = {We demonstrate universal computation in an all-fluidic two-phase microfluidic system. Nonlinearity is introduced into an otherwise linear, reversible, low-Reynolds number flow via bubble-to-bubble hydrodynamic interactions. A bubble traveling in a channel represents a bit, providing us with the capability to simultaneously transport materials and perform logical control operations. We demonstrate bubble logic AND/OR/NOT gates, a toggle flip-flop, a ripple counter, timing restoration, a ring oscillator, and an electro-bubble modulator. These show the nonlinearity, gain, bistability, synchronization, cascadability, feedback, and programmability required for scalable universal computation. With increasing complexity in large-scale microfluidic processors, bubble logic provides an on-chip process control mechanism integrating chemistry and computation.}, }
@article {pmid17289906, year = {2007}, author = {de Rochefort, L and Vial, L and Fodil, R and Maître, X and Louis, B and Isabey, D and Caillibotte, G and Thiriet, M and Bittoun, J and Durand, E and Sbirlea-Apiou, G}, title = {In vitro validation of computational fluid dynamic simulation in human proximal airways with hyperpolarized 3He magnetic resonance phase-contrast velocimetry.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {102}, number = {5}, pages = {2012-2023}, doi = {10.1152/japplphysiol.01610.2005}, pmid = {17289906}, issn = {8750-7587}, mesh = {Bronchi/anatomy &amp; histology/*physiology ; Bronchography ; *Computer Simulation ; *Helium ; Humans ; Image Processing, Computer-Assisted ; Isotopes ; Magnetic Resonance Imaging/*methods ; Male ; Middle Aged ; Models, Anatomic ; Models, Biological ; Reproducibility of Results ; *Respiration ; Respiratory Mechanics ; *Rheology ; Tomography, X-Ray Computed ; Trachea/anatomy &amp; histology/diagnostic imaging/*physiology ; }, abstract = {Computational fluid dynamics (CFD) and magnetic resonance (MR) gas velocimetry were concurrently performed to study airflow in the same model of human proximal airways. Realistic in vivo-based human airway geometry was segmented from thoracic computed tomography. The three-dimensional numerical description of the airways was used for both generation of a physical airway model using rapid prototyping and mesh generation for CFD simulations. Steady laminar inspiratory experiments (Reynolds number Re = 770) were performed and velocity maps down to the fourth airway generation were extracted from a new velocity mapping technique based on MR velocimetry using hyperpolarized (3)He gas. Full two-dimensional maps of the velocity vector were measured within a few seconds. Numerical simulations were carried out with the experimental flow conditions, and the two sets of data were compared between the two modalities. Flow distributions agreed within 3%. Main and secondary flow velocity intensities were similar, as were velocity convective patterns. This work demonstrates that experimental and numerical gas velocity data can be obtained and compared in the same complex airway geometry. Experiments validated the simulation platform that integrates patient-specific airway reconstruction process from in vivo thoracic scans and velocity field calculation with CFD, hence allowing the results of this numerical tool to be used with confidence in potential clinical applications for lung characterization. Finally, this combined numerical and experimental approach of flow assessment in realistic in vivo-based human airway geometries confirmed the strong dependence of airway flow patterns on local and global geometrical factors, which could contribute to gas mixing.}, }
@article {pmid17282684, year = {2005}, author = {Amili, O and Fatouraee, N}, title = {Lipoprotein transport in the blood stream to the arterial wall in a carotid artery bifurcation.}, journal = {Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference}, volume = {2005}, number = {}, pages = {2264-2267}, doi = {10.1109/IEMBS.2005.1616915}, pmid = {17282684}, issn = {1557-170X}, abstract = {The carotid arteries are a common site of atherosclerotic plaque formation, which has been linked to the blood flow patterns and the mass transport phenomenon. The purpose of this research was to study the lipid transport in a human carotid artery model, focusing on the effects of local geometric and hemodynamic factors on mass transfer from blood flow to vessel wall and its concentration at the luminal surface of the artery. The Reynolds number, 250, and the Schmidt number, 6.66x10[5], were selected to model the mass transfer of LDL macro molecules, and in order to see the effect of Reynolds and Schmidt numbers to mass transport, the model was analyzed with different conditions. The steady state flow was used for two dimensional carotid geometry. At the inlet, the blood flow was assumed a steady fully developed laminar velocity profile with a uniform LDL concentration. The vessel wall was assumed permeable to water and semi-permeable to LDL macro molecules. The problem was analyzed with the finite element method. The results show 26% increase of LDL concentration from inlet value at the luminal surface of the artery located in the separated flow region. The maximum value of LDL concentration occurred at the separation point.}, }
@article {pmid17280293, year = {2006}, author = {Mininni, PD and Pouquet, AG and Montgomery, DC}, title = {Small-scale structures in three-dimensional magnetohydrodynamic turbulence.}, journal = {Physical review letters}, volume = {97}, number = {24}, pages = {244503}, doi = {10.1103/PhysRevLett.97.244503}, pmid = {17280293}, issn = {0031-9007}, abstract = {We investigate using direct numerical simulations with grids up to 1536(3) points, the rate at which small scales develop in a decaying three-dimensional MHD flow both for deterministic and random initial conditions. Parallel current and vorticity sheets form at the same spatial locations, and further destabilize and fold or roll up after an initial exponential phase. At high Reynolds numbers, a self-similar evolution of the current and vorticity maxima is found, in which they grow as a cubic power of time; the flow then reaches a finite dissipation rate independent of the Reynolds number.}, }
@article {pmid17280143, year = {2006}, author = {Eyink, GL}, title = {Cascade of circulations in fluid turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {74}, number = {6 Pt 2}, pages = {066302}, doi = {10.1103/PhysRevE.74.066302}, pmid = {17280143}, issn = {1539-3755}, abstract = {Kelvin's theorem on conservation of circulations is an essential ingredient of Taylor's theory of turbulent energy dissipation by the process of vortex-line stretching. In previous work, we have proposed a nonlinear mechanism for the breakdown of Kelvin's theorem in ideal turbulence at infinite Reynolds number. We develop here a detailed physical theory of this cascade of circulations. Our analysis is based upon an effective equation for large-scale coarse-grained velocity, which contains a turbulent-induced vortex force that can violate Kelvin's theorem. We show that singularities of sufficient strength, which are observed to exist in turbulent flow, can lead to nonvanishing dissipation of circulation for an arbitrarily small coarse-graining length in the effective equations. This result is an analog for circulation of Onsager's theorem on energy dissipation for singular Euler solutions. The physical mechanism of the breakdown of Kelvin's theorem is diffusion of lines of large-scale vorticity out of the advected loop. This phenomenon can be viewed as a classical analog of the Josephson-Anderson phase-slip phenomenon in superfluids due to quantized vortex lines. We show that the circulation cascade is local in scale and use this locality to develop concrete expressions for the turbulent vortex force by a multiscale gradient expansion. We discuss implications for Taylor's theory of turbulent dissipation and we point out some related cascade phenomena, in particular for magnetic flux in magnetohydrodynamic turbulence.}, }
@article {pmid17280111, year = {2006}, author = {Frank, AM}, title = {Shear driven solitary waves on a liquid film.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {74}, number = {6 Pt 2}, pages = {065301}, doi = {10.1103/PhysRevE.74.065301}, pmid = {17280111}, issn = {1539-3755}, abstract = {Long nonlinear two-dimensional traveling waves on a film driven by laminar gas flow are investigated numerically via solving Navier-Stokes equations. The evolution of their shape, amplitude, and speed with increasing Reynolds number is studied. The existence of solitary waves is demonstrated. A comparison between shear driven and gravity-capillary waves is made and discussed. It is shown that shear driven waves as compared to gravity driven waves are much higher for equal film Reynolds numbers and much slower for equal wave amplitudes.}, }
@article {pmid17279993, year = {2006}, author = {Frank, X and Li, HZ}, title = {Negative wake behind a sphere rising in viscoelastic fluids: a lattice Boltzmann investigation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {74}, number = {5 Pt 2}, pages = {056307}, doi = {10.1103/PhysRevE.74.056307}, pmid = {17279993}, issn = {1539-3755}, abstract = {We investigate the complex flow field around a sphere rising in a Maxwell fluid by means of the lattice Boltzmann simulation to provide insights into the strange negative wake experimentally observed behind a bubble or particle in non Newtonian fluids. The influence of the rise velocity, sphere diameter, and fluid's rheology is considered through two dimensionless numbers: the Deborah number De and the Reynolds number Re. Our simulation shows that the negative wake appears behind the sphere when De>2 . On the other hand, the shape of the negative wake described by the opening angle theta of the upward flow cone surrounding the negative wake is mainly determined by the Reynolds number Re. These results reveal that the physical origin of the negative wake stems mainly from the competition between the elastic and viscous stresses in the fluid.}, }
@article {pmid17279987, year = {2006}, author = {Cuevas, S and Smolentsev, S and Abdou, M}, title = {Vorticity generation in creeping flow past a magnetic obstacle.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {74}, number = {5 Pt 2}, pages = {056301}, doi = {10.1103/PhysRevE.74.056301}, pmid = {17279987}, issn = {1539-3755}, abstract = {The generation of vorticity in the two-dimensional creeping flow of an incompressible, electrically conducting viscous fluid past a localized magnetic field distribution is analyzed under the low magnetic Reynolds number approximation. It is shown that the Lorentz force produced by the interaction of the induced electric currents with the nonuniform magnetic field acts as an obstacle for the flow, creating different steady flow patterns that are reminiscent of those observed in the flow past bluff bodies. First, analytic solutions are obtained for a creeping flow past a magnetic point dipole, modeled as a Gaussian distribution. Using a perturbation scheme, the vorticity is expressed as an expansion in the small Reynolds number, and first- and second-order approximations are calculated. The induced magnetic field, pressure, and stream function are also determined. Further, full numerical finite difference solutions are obtained for a uniform creeping flow past a finite size magnetic field distribution produced by a square magnetized plate. Hartmann numbers in the range 1< or =Ha< or =100 are explored. Depending on the strength of the magnetic force, stagnation zones or steady vortical structures are obtained. The analysis contributes to the understanding of flows in nonuniform magnetic fields and flows produced by localized forces.}, }
@article {pmid17279919, year = {2006}, author = {Zheng, R and Witten, TA}, title = {Feasibility of large free-standing liquid films in space.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {74}, number = {5 Pt 1}, pages = {051602}, doi = {10.1103/PhysRevE.74.051602}, pmid = {17279919}, issn = {1539-3755}, abstract = {We consider the feasibility of large-scale free-standing thin liquid film experiment in the space environment as a new realization to study two-dimensional hydrodynamics. We identify material and environmental criteria necessary to avoid freezing, evaporation, chemical degradation, and spontaneous collapse of the film. These criteria pose no obstacles to achieving films of kilometer scale and lifetime of many months, with attainable Reynolds number up to 10(7). However, impacts from meteoroids pose a serious threat to the film, and require substantial shielding or unproven self-healing properties in the film. Current theoretical and experimental studies of two-dimensional turbulence are briefly reviewed. We also describe a specific candidate liquid for the film.}, }
@article {pmid17270760, year = {2004}, author = {Soundararajan, G and Hsiai, TK and DeMaio, L and Chang, M and Chang, S}, title = {MEMS shear stress sensors for cardiovascular diagnostics.}, journal = {Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference}, volume = {2004}, number = {}, pages = {2420-2423}, doi = {10.1109/IEMBS.2004.1403700}, pmid = {17270760}, issn = {1557-170X}, abstract = {Coronary artery disease is the leading cause of morbidity and mortality in the industrialized nations. Both biochemical and biomechanical stimuli modulate the pathogenesis of coronary artery diseases. Shear stress acting on the lumen of blood vessels intimately modulates the biological activities of vascular endothelial cells (ECs). We hereby develop microelectro mechanical system (MEMS)-based sensors at the dimension comparable to a single EC to monitor realtime shear stress in fluidic channel. Our goal is to fabricate sensors for ex vivo or in vivo shear stress measurement at Reynolds number commonly encountered in human circulation. The MEMS sensors were designed based on the previously described heat transfer principles. The polysilicon was doped with phosphorous to render the sensing element a high resistivity at 2.5 KOmega. The development of backside wire bonding enabled the application for the vascular geometry. The small dimension (80x2 mum) and the gain amplitude at 71 KHz offered an entry point to measure shear stress with high spatial and temporal resolution.}, }
@article {pmid17254594, year = {2007}, author = {Duffadar, RD and Davis, JM}, title = {Interaction of micrometer-scale particles with nanotextured surfaces in shear flow.}, journal = {Journal of colloid and interface science}, volume = {308}, number = {1}, pages = {20-29}, doi = {10.1016/j.jcis.2006.12.068}, pmid = {17254594}, issn = {0021-9797}, abstract = {Dynamic particle adhesion from flow over collecting surfaces with nanoscale heterogeneity occurs in important natural systems and current technologies. Accurate modeling and prediction of the dynamics of particles interacting with such surfaces will facilitate their use in applications for sensing, separating, and sorting colloidal-scale objects. In this paper, the interaction of micrometer-scale particles with electrostatically heterogeneous surfaces is analyzed. The deposited polymeric patches that provide the charge heterogeneity in experiments are modeled as 11-nm disks randomly distributed on a planar surface. A novel technique based on surface discretization is introduced to facilitate computation of the colloidal interactions between a particle and the heterogeneous surface based on expressions for parallel plates. Combining these interactions with hydrodynamic forces and torques on a particle in a low Reynolds number shear flow allows particle dynamics to be computed for varying net surface coverage. Spatial fluctuations in the local surface density of the deposited patches are shown responsible for the dynamic adhesion phenomena observed experimentally, including particle capture on a net-repulsive surface.}, }
@article {pmid17252612, year = {2007}, author = {Chavarría-Hernández, N and Sanjuan-Galindo, R and Rodríguez-Pastrana, BR and Medina-Torres, L and Rodríguez-Hernández, AI}, title = {Submerged monoxenic culture of the entomopathogenic nematode Steinernema carpocapsae in an internal-loop airlift bioreactor using two configurations of the inner tube.}, journal = {Biotechnology and bioengineering}, volume = {98}, number = {1}, pages = {167-176}, doi = {10.1002/bit.21356}, pmid = {17252612}, issn = {0006-3592}, mesh = {Air Movements ; Animals ; *Bioreactors ; Cell Culture Techniques/*instrumentation/methods ; Cell Proliferation ; Coculture Techniques/*instrumentation/methods ; Equipment Design ; Equipment Failure Analysis ; Nematoda/*growth &amp; development/*microbiology ; Symbiosis/physiology ; Xenorhabdus/*physiology ; }, abstract = {This article reports the submerged culture of the entomopathogenic nematode Steinernema carpocapsae and its symbiotic bacterium, Xenorhabdus nematophila, within an internal-loop airlift bioreactor. Two configurations of the inner cylinder were tested: a standard draft tube (SDT) and a static mixer (SM), as well as two production media: MP1 (500 mL/L whey, among other ingredients) and MP2 (82 mL/L agave-juice from Agave spp., among other ingredients). Three fermentations were carried out: F1 --> SDT-MP1, F2 --> SM-MP1 and F3 --> SM-MP2. The operating conditions were expressed on the basis of dimensionless Reynolds number (Re) and volumetric oxygen transfer coefficient (k(L)a), both of them determined on riser and downcomer sections within the bioreactor. The experiments began with fewer than 1,000 infective juvenile nematode stages (IJ) per mL and at t = 20 d, they achieved (nematodes/mL-%IJ) 222,000-87%, 62,200-23% and 114,600-80%, within F1, F2 and F3 experiments, respectively. Nonetheless, the achieved maximum nematode biomass concentrations (g/L) were F1 --> 408, F2 --> 557 and F3 --> 613, and occurred at t = 16, 10 and 12 d, respectively. The fermentation operating conditions involved 0.042 (-) < Re < 647 (-) and 2.8 x 10(-4) s(-1) < k(L)a < 0.0447 s(-1), as functions of 0.004 m/s < superficial gas velocity (within the riser) < 0.079 m/s, 0.001 m/s < mean downcomer velocity < 0.014 m/s, and culture broth rheological properties which evolved from nearly the Newtonian behaviour to the pseudoplastic one. The maximum IJ concentration was achieved within F1 experiment (193,406 IJ/mL). Also, fermentation conditions involving higher riser-Re and lower downcomer-Re as well as higher nutriment concentrations in culture medium, promote higher nematode biomass concentrations but lower %IJ, maybe as a result of better conditions for the nematode population development.}, }
@article {pmid17244593, year = {2007}, author = {Jiménez, J and Moser, RD}, title = {What are we learning from simulating wall turbulence?.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {365}, number = {1852}, pages = {715-732}, doi = {10.1098/rsta.2006.1943}, pmid = {17244593}, issn = {1364-503X}, abstract = {The study of turbulence near walls has experienced a renaissance in the last decade, largely owing to the availability of high-quality numerical simulations. The viscous and buffer layers over smooth walls are essentially independent of the outer flow, and there is a family of numerically exact nonlinear structures that account for about half of the energy production and dissipation. The rest can be modelled by their unsteady bursting. Many characteristics of the wall layer, such as the dimensions of the dominant structures, are well predicted by those models, which were essentially completed in the 1990s after the increase in computer power made the kinematic simulations of the late 1980s cheap enough to undertake dynamic experiments.Today, we are at the early stages of simulating the logarithmic (or overlap) layer, and a number of details regarding its global properties are becoming clear. For instance, a finite Reynolds number correction to the logarithmic law has been validated in turbulent channels. This has allowed upper and lower limits of the overlap region to be clarified, with both upper and lower bounds occurring at much larger distances from the wall than commonly assumed. A kinematic picture of the various cascades present in this part of the flow is also beginning to emerge. Dynamical understanding can be expected in the next decade.}, }
@article {pmid17244589, year = {2007}, author = {Metzger, M and McKeon, BJ and Holmes, H}, title = {The near-neutral atmospheric surface layer: turbulence and non-stationarity.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {365}, number = {1852}, pages = {859-876}, doi = {10.1098/rsta.2006.1946}, pmid = {17244589}, issn = {1364-503X}, abstract = {The neutrally stable atmospheric surface layer is used as a physical model of a very high Reynolds number, canonical turbulent boundary layer. Challenges and limitations with this model are addressed in detail, including the inherent thermal stratification, surface roughness and non-stationarity of the atmosphere. Concurrent hot-wire and sonic anemometry data acquired in Utah's western desert provide insight to Reynolds number trends in the axial velocity statistics and spectra.}, }
@article {pmid17244588, year = {2007}, author = {Nickels, TB and Marusic, I and Hafez, S and Hutchins, N and Chong, MS}, title = {Some predictions of the attached eddy model for a high Reynolds number boundary layer.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {365}, number = {1852}, pages = {807-822}, doi = {10.1098/rsta.2006.1950}, pmid = {17244588}, issn = {1364-503X}, abstract = {Many flows of practical interest occur at high Reynolds number, at which the flow in most of the boundary layer is turbulent, showing apparently random fluctuations in velocity across a wide range of scales. The range of scales over which these fluctuations occur increases with the Reynolds number and hence high Reynolds number flows are difficult to compute or predict. In this paper, we discuss the structure of these flows and describe a physical model, based on the attached eddy hypothesis, which makes predictions for the statistical properties of these flows and their variation with Reynolds number. The predictions are shown to compare well with the results from recent experiments in a new purpose-built high Reynolds number facility. The model is also shown to provide a clear physical explanation for the trends in the data. The limits of applicability of the model are also discussed.}, }
@article {pmid17244586, year = {2007}, author = {McKeon, BJ and Sreenivasan, KR}, title = {Introduction: scaling and structure in high Reynolds number wall-bounded flows.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {365}, number = {1852}, pages = {635-646}, doi = {10.1098/rsta.2006.1952}, pmid = {17244586}, issn = {1364-503X}, }
@article {pmid17244585, year = {2007}, author = {Allen, JJ and Shockling, MA and Kunkel, GJ and Smits, AJ}, title = {Turbulent flow in smooth and rough pipes.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {365}, number = {1852}, pages = {699-714}, doi = {10.1098/rsta.2006.1939}, pmid = {17244585}, issn = {1364-503X}, abstract = {Recent experiments at Princeton University have revealed aspects of smooth pipe flow behaviour that suggest a more complex scaling than previously noted. In particular, the pressure gradient results yield a new friction factor relationship for smooth pipes, and the velocity profiles indicate the presence of a power-law region near the wall and, for Reynolds numbers greater than about 400x103 (R+>9x103), a logarithmic region further out. New experiments on a rough pipe with a honed surface finish with krms/D=19.4x10-6, over a Reynolds number range of 57x103-21x106, show that in the transitionally rough regime this surface follows an inflectional friction factor relationship rather than the monotonic relationship given in the Moody diagram. Outer-layer scaling of the mean velocity data and streamwise turbulence intensities for the rough pipe show excellent collapse and provide strong support for Townsend's outer-layer similarity hypothesis for rough-walled flows. The streamwise rough-wall spectra also agree well with the corresponding smooth-wall data. The pipe exhibited smooth behaviour for ks+ < or =3.5, which supports the suggestion that the original smooth pipe was indeed hydraulically smooth for ReD< or =24x106. The relationship between the velocity shift, DeltaU/utau, and the roughness Reynolds number, ks+, has been used to generalize the form of the transition from smooth to fully rough flow for an arbitrary relative roughness krms/D. These predictions apply for honed pipes when the separation of pipe diameter to roughness height is large, and they differ significantly from the traditional Moody curves.}, }
@article {pmid17244584, year = {2007}, author = {Hutchins, N and Marusic, I}, title = {Large-scale influences in near-wall turbulence.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {365}, number = {1852}, pages = {647-664}, doi = {10.1098/rsta.2006.1942}, pmid = {17244584}, issn = {1364-503X}, abstract = {Hot-wire data acquired in a high Reynolds number facility are used to illustrate the need for adequate scale separation when considering the coherent structure in wall-bounded turbulence. It is found that a large-scale motion in the log region becomes increasingly comparable in energy to the near-wall cycle as the Reynolds number increases. Through decomposition of fluctuating velocity signals, it is shown that this large-scale motion has a distinct modulating influence on the small-scale energy (akin to amplitude modulation). Reassessment of DNS data, in light of these results, shows similar trends, with the rate and intensity of production due to the near-wall cycle subject to a modulating influence from the largest-scale motions.}, }
@article {pmid17244583, year = {2007}, author = {Morrison, JF}, title = {The interaction between inner and outer regions of turbulent wall-bounded flow.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {365}, number = {1852}, pages = {683-698}, doi = {10.1098/rsta.2006.1947}, pmid = {17244583}, issn = {1364-503X}, abstract = {The nature of the interaction between the inner and outer regions of turbulent wall-bounded flow is examined. Townsend's theory of inactive motion is shown to be a first-order, linear approximation of the effect of the large eddies at the surface that acts as a quasi-inviscid, low-frequency modulation of the shear-stress-bearing motion. This is shown to be a 'strong' asymptotic condition that directly expresses the decoupling of the inner-scale active motion from the outer-scale inactive motion. It is further shown that such a decoupling of the inner and outer vorticity fields near the wall is inappropriate, even at high Reynolds numbers, and that a 'weak' asymptotic condition is required to represent the increasing effect of outer-scale influences as the Reynolds number increases. High Reynolds number data from a fully developed pipe flow and the atmospheric surface layer are used to show that the large-scale motion penetrates to the wall, the inner-outer interaction is not describable as a linear process and the interaction should more generally be accepted as an intrinsically nonlinear one.}, }
@article {pmid17244582, year = {2007}, author = {Nagib, HM and Chauhan, KA and Monkewitz, PA}, title = {Approach to an asymptotic state for zero pressure gradient turbulent boundary layers.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {365}, number = {1852}, pages = {755-770}, doi = {10.1098/rsta.2006.1948}, pmid = {17244582}, issn = {1364-503X}, abstract = {Flat plate turbulent boundary layers under zero pressure gradient at high Reynolds numbers are studied to reveal appropriate scale relations and asymptotic behaviour. Careful examination of the skin-friction coefficient results confirms the necessity for direct and independent measurement of wall shear stress. We find that many of the previously proposed empirical relations accurately describe the local Cf behaviour when modified and underpinned by the same experimental data. The variation of the integral parameter, H, shows consistent agreement between the experimental data and the relation from classical theory. In accordance with the classical theory, the ratio of Delta and delta asymptotes to a constant. Then, the usefulness of the ratio of appropriately defined mean and turbulent time-scales to define and diagnose equilibrium flow is established. Next, the description of mean velocity profiles is revisited, and the validity of the logarithmic law is re-established using both the mean velocity profile and its diagnostic function. The wake parameter, Pi, is shown to reach an asymptotic value at the highest available experimental Reynolds numbers if correct values of logarithmic-law constants and an appropriate skin-friction estimate are used. The paper closes with a discussion of the Reynolds number trends of the outer velocity defect which are important to establish a consistent similarity theory and appropriate scaling.}, }
@article {pmid17237991, year = {2007}, author = {Xi, J and Longest, PW}, title = {Transport and deposition of micro-aerosols in realistic and simplified models of the oral airway.}, journal = {Annals of biomedical engineering}, volume = {35}, number = {4}, pages = {560-581}, doi = {10.1007/s10439-006-9245-y}, pmid = {17237991}, issn = {0090-6964}, mesh = {*Aerosols ; Humans ; Larynx/anatomy &amp; histology/*physiology ; *Models, Biological ; Mouth/anatomy &amp; histology/*physiology ; Particle Size ; }, abstract = {A number of in vivo, in vitro and numerical studies have considered flow field characteristics and micro-particle deposition in the oral airway extending from the mouth through the larynx. These studies have highlighted the effects of flow rates, turbulence and particle characteristics on deposition values in realistic and simplified geometries. However, the effect of geometry simplifications on regional and local deposition patterns remains largely un-quantified for the oral airway and throughout the respiratory tract. The objective of this study is to assess the effects of geometry simplifications on regionally averaged and local micro-aerosol deposition characteristics in models of the extrathoracic oral airway. To achieve this objective, a realistic model of the oral airway has been constructed based on CT scans of a healthy adult in conjunction with measurements reported in the literature. Three other geometries with descending degrees of physical realism were constructed based on successive geometric simplifications of the realistic model. A validated low Reynolds number (LRN) k-omega turbulence model was employed to simulate laminar, transitional and fully turbulent flow regimes for 1-31 microm particles. Geometric simplifications were found to have a significant effect on aerosol dynamics, hot spot formations and cellular-level deposition values in the extrathoracic airway models considered. For all models, regional deposition efficiency results were found to be approximately within one standard deviation of available experimental data when plotted as a function of Stokes number. The realistic geometry provided the best predictions of regional deposition in comparison to experimental data as a function of particle diameter. Considering localized deposition, maximum deposition enhancement factors, which represent the ratio of local to total deposition, were one to two orders of magnitude higher for the realistic model. Geometric factors that significantly contributed to enhanced particle localization in the realistic model include a triangular-shaped glottis and a dorsal-sloped trachea. Therefore, highly realistic models of the oral airway geometry may be necessary to evaluate localized deposition patterns and hot spot formations, which are critical for accurately predicting cellular-level dose.}, }
@article {pmid17234203, year = {2007}, author = {Chang, YR and Chang, HM and Lin, CF and Liu, TJ and Wu, PY}, title = {Three minimum wet thickness regions of slot die coating.}, journal = {Journal of colloid and interface science}, volume = {308}, number = {1}, pages = {222-230}, doi = {10.1016/j.jcis.2006.11.054}, pmid = {17234203}, issn = {0021-9797}, abstract = {An experimental study was carried out to determine the minimum wet thickness of slot die coating for low-viscosity solutions. There exist three distinct coating regions (I, II, and III), depending on the physical properties of the coating fluid, die geometry, and flow conditions. A critical Reynolds number was found, below which viscous and surface tension effects are important. In Region I, the minimum wet thickness increases with increasing capillary number and becomes independent of capillary number in Region II. Region III exists above the critical Reynolds number where fluid inertia is dominant. In this region, the minimum wet thickness decreases as Reynolds number increases. Flow visualization on the coating bead reveals that the position of the downstream meniscus of the coating bead determines the types of coating region, whereas the shape and position of the upstream meniscus determine the type of coating defects. It was also observed that the downstream meniscus was not located at the die lip corner and both the static and dynamic contact angles varied under different conditions. These findings are critical for realistic theoretical study of slot die coating.}, }
@article {pmid17216661, year = {2007}, author = {Singh, H and Ang, ES and Lim, TT and Hutmacher, DW}, title = {Flow modeling in a novel non-perfusion conical bioreactor.}, journal = {Biotechnology and bioengineering}, volume = {97}, number = {5}, pages = {1291-1299}, doi = {10.1002/bit.21327}, pmid = {17216661}, issn = {0006-3592}, mesh = {*Bioreactors ; Cell Culture Techniques/*instrumentation ; Computer Simulation ; *Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Flow Injection Analysis/instrumentation/methods ; *Models, Biological ; Rheology/*instrumentation/*methods ; Tissue Engineering/*instrumentation ; }, abstract = {We have developed a bioreactor vessel design which has the advantages of simplicity and ease of assembly and disassembly, and with the appropriately determined flow rate, even allows for a scaffold to be suspended freely regardless of its weight. This article reports our experimental and numerical investigations to evaluate the performance of a newly developed non-perfusion conical bioreactor by visualizing the flow through scaffolds with 45 degrees and 90 degrees fiber lay down patterns. The experiments were conducted at the Reynolds numbers (Re) 121, 170, and 218 based on the local velocity and width of scaffolds. The flow fields were captured using short-time exposures of 60 microm particles suspended in the bioreactor and illuminated using a thin laser sheet. The effects of scaffold fiber lay down pattern and Reynolds number were obtained and correspondingly compared to results obtained from a computational fluid dynamics (CFD) software package. The objectives of this article are twofold: to investigate the hypothesis that there may be an insufficient exchange of medium within the interior of the scaffold when using our non-perfusion bioreactor, and second, to compare the flows within and around scaffolds of 45 degrees and 90 degrees fiber lay down patterns. Scaffold porosity was also found to influence flow patterns. It was therefore shown that fluidic transport could be achieved within scaffolds with our bioreactor design, being a non-perfusion vessel. Fluid velocities were generally same of the same or one order lower in magnitude as compared to the inlet flow velocity. Additionally, the 90 degrees fiber lay down pattern scaffold was found to allow for slightly higher fluid velocities within, as compared to the 45 degrees fiber lay down pattern scaffold. This was due to the architecture and pore arrangement of the 90 degrees fiber lay down pattern scaffold, which allows for fluid to flow directly through (channel-like flow).}, }
@article {pmid17182927, year = {2006}, author = {Berguer, R and Bull, JL and Khanafer, K}, title = {Refinements in mathematical models to predict aneurysm growth and rupture.}, journal = {Annals of the New York Academy of Sciences}, volume = {1085}, number = {}, pages = {110-116}, doi = {10.1196/annals.1383.033}, pmid = {17182927}, issn = {0077-8923}, mesh = {Aneurysm/*pathology ; Computer Simulation ; Humans ; *Models, Biological ; Regional Blood Flow ; }, abstract = {The growth of aneurysms and eventually their likelihood of rupture depend on the determination of the stress and strain within the aneurysm wall and the exact reproduction of its geometry. A numerical model is developed to analyze pulsatile flow in abdominal aortic aneurysm (AAA) models using real physiological resting and exercise waveforms. Both laminar and turbulent flows are considered. Interesting features of the flow field resulting from using realistic physiological waveforms are obtained for various parameters using finite element methods. Such parameters include Reynolds number, size of the aneurysm (D/d), and flexibility of the aneurysm wall. The effect of non-Newtonian behavior of blood on hemodynamic stresses is compared with Newtonian behavior, and the non-Newtonian effects are demonstrated to be significant in realistic flow situations. Our results show that maximum turbulent fluid shear stress occurs at the distal end of the AAA model. Furthermore, turbulence is found to have a significant effect on the pressure distribution along AAA wall for both physiological waveforms. Related experimental work in which a bench top aneurysm model is developed is also discussed. The experimental model provides a platform to validate the numerical model. This work is part of our ongoing development of a patient-specific tool to guide clinician decision making and to elucidate the contribution of blood flow-induced stresses to aneurysm growth and eventual rupture. These studies indicate that accurately modeling the physiologic features of real aneurysms and blood is paramount to achieving our goal.}, }
@article {pmid17165126, year = {2007}, author = {Lin, YC and Chung, YC and Wu, CY}, title = {Mixing enhancement of the passive microfluidic mixer with J-shaped baffles in the tee channel.}, journal = {Biomedical microdevices}, volume = {9}, number = {2}, pages = {215-221}, doi = {10.1007/s10544-006-9023-5}, pmid = {17165126}, issn = {1387-2176}, mesh = {Computer Simulation ; *Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Microfluidics/*instrumentation/*methods ; *Models, Theoretical ; }, abstract = {This study proposed a new design of a passive micromixer employing several J-shaped baffles in the tee channel to enhance mixing. The mixing performance of the device was investigated experimentally and by numerical simulation. The in-plane structured micromixer was fabricated using micromolding of SU-8 photoresist and PDMS. The mixing performance was demonstrated using image analysis to quantify the concentration distribution in the microchannel. The percentage of mixing increased as the number of baffles increased. The simulated and experimental results showed that the mixer with J-shaped baffles exhibited better mixing performance, and the percentage of mixing was about 1.2 to 2.2 times higher when compared to those without baffles, in the range of Reynolds number (Re) 5 to 350. The improvement in mixing performance was especially apparent at the short axial distance and at the lower Reynolds numbers. The results revealed that the J-shaped baffles could result in lateral convection in the main channel, resulting in improved mixing.}, }
@article {pmid17164598, year = {2007}, author = {Han, T and O'Neal, DL and Ortiz, CA}, title = {A generic-tee-plenum mixing system for application to single point aerosol sampling in stacks and ducts.}, journal = {Health physics}, volume = {92}, number = {1}, pages = {40-49}, doi = {10.1097/01.HP.0000234674.68338.a2}, pmid = {17164598}, issn = {0017-9078}, mesh = {Aerosols/*analysis ; Air Pollutants, Radioactive/*analysis ; *Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Flow Injection Analysis/*instrumentation/methods ; Radiation Monitoring/*instrumentation/methods ; Radiation Protection/*instrumentation ; Rheology/*instrumentation/methods ; }, abstract = {The ANSI/HPS-N13.1-1999 standard is based on the concept of obtaining a single point representative sample from a location where the velocity and contaminant profiles are relatively uniform. It is difficult to predict the level of mixing in an arbitrary stack or duct without experimental data to meet the ANSI/HPS N13.1-1999 requirements. The goal of this study was to develop experimental data for a range of conditions in "S" (S-shaped configuration) duct systems with different mixing elements and "S" systems having one or two mixing elements. Results were presented in terms of the coefficients of variation (COVs) for velocity, tracer gas, and 10-mum aerodynamic diameter (AD) aerosol particle profiles at different downstream locations for each mixing element. Five mixing elements were tested, including a 90 degrees elbow, a commercial static mixer, a Small-Horizontal Generic-Tee-Plenum (SH-GTP), a Small-Vertical Generic-Tee-Plenum (SV-GTP), and a Large-Horizontal Generic-Tee-Plenum (LH-GTP) system. The COVs for velocity, gas concentration, and aerosol particles for the three GTP systems were all determined to be less than 8%. Tests with two different sizes of GTPs were conducted, and the results showed the performance of the GTPs was relatively unaffected by either size or velocity as reflected by the Reynolds number. The pressure coefficients were 0.59, 0.57, and 0.65, respectively, for the SH-GTP, SV-GTP, and LH-GTP. The pressure drop for the GTPs was approximately twice that of the round elbow, but a factor of 5 less than a Type IV Air Blender. The GTP was developed to provide a sampling location less than 4-duct diameters downstream of a mixing element with low pressure drop condition. The object of the developmental effort was to provide a system that could be employed in new stack; however, the concept of GTPs could also be retrofitted onto existing system applications as well. Results from these tests show that the system performance is well within the ANSI/HPS N13.1-1999 mixing criteria--the COVs for velocity, tracer gas, and 10-microm AD aerosol particles are less than the 20% criteria levels.}, }
@article {pmid17161843, year = {2007}, author = {Huynh, TN and Chacko, BK and Teng, X and Brott, BC and Allon, M and Kelpke, SS and Thompson, JA and Patel, RP and Anayiotos, AS}, title = {Effects of venous needle turbulence during ex vivo hemodialysis on endothelial morphology and nitric oxide formation.}, journal = {Journal of biomechanics}, volume = {40}, number = {10}, pages = {2158-2166}, doi = {10.1016/j.jbiomech.2006.10.028}, pmid = {17161843}, issn = {0021-9290}, support = {HL 70146/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Aorta/metabolism/pathology ; *Blood Vessel Prosthesis/adverse effects ; Cattle ; Cells, Cultured ; Endothelial Cells/*metabolism/*pathology ; Humans ; Hyperplasia/etiology/metabolism/pathology ; *Models, Cardiovascular ; Needles/*adverse effects ; Nitric Oxide/*biosynthesis ; *Renal Dialysis/adverse effects ; Tunica Intima/*metabolism/*pathology ; }, abstract = {Arteriovenous grafts used for hemodialysis frequently develop intimal hyperplasia (IH), which ultimately leads to graft failure. Although the turbulent jet from the dialysis needle may contribute to vessel wall injury, its role in the pathogenesis of IH is relatively unexplored. In the current study, using bovine aortic endothelial cells (BAEC) cultured on the inner surface of a compliant tube, we evaluated the effects of simulated hemodialysis conditions on morphology and nitric oxide (NO) production. The flows via the graft and needle were 500 ml/min (Reynolds number=819) and 100ml/min (Reynolds number=954), respectively. In the presence of the needle jet for 6h, 19.3% (+/-1.53%) of BAEC were sheared off, whereas no loss of BAEC was observed in the presence of graft flow alone (P<0.05). In the presence of graft flow alone, assessment of cell orientation by the Saltykov method revealed that BAEC were oriented along the flow direction. This alignment, however, was lost in the presence of needle flow. Finally, NO production was also significantly decreased in the presence of the needle flow compared to the presence of graft flow alone (16+/-3.1 vs 34.7+/-1.9 nmol/10(6)cells/h, P<0.05). NO is a key player in vascular homeostasis mechanisms modulating vasomotor tone, inhibiting inflammation and smooth muscle cell proliferation. Thus, the loss of NO signaling and the loss of endothelial integrity caused by needle jet turbulence may contribute to the cascade of events leading to IH formation during hemodialysis.}, }
@article {pmid17155261, year = {2006}, author = {Ayyalasomayajula, S and Gylfason, A and Collins, LR and Bodenschatz, E and Warhaft, Z}, title = {Lagrangian measurements of inertial particle accelerations in grid generated wind tunnel turbulence.}, journal = {Physical review letters}, volume = {97}, number = {14}, pages = {144507}, doi = {10.1103/PhysRevLett.97.144507}, pmid = {17155261}, issn = {0031-9007}, abstract = {We describe Lagrangian measurements of water droplets in grid generated wind tunnel turbulence at a Taylor Reynolds number of R(lambda)=250 and an average Stokes number (St) of approximately 0.1. The inertial particles are tracked by a high speed camera moving along the side of the tunnel at the mean flow speed. The standardized acceleration probability density functions of the particles have spread exponential tails that are narrower than those of a fluid particles (St approximately 0) and there is a decrease in the acceleration variance with increasing Stokes number. A simple vortex model shows that the inertial particles selectively sample the fluid field and are less likely to experience regions of the fluid undergoing the largest accelerations. Recent direct numerical simulations compare favorably with these first measurements of Lagrangian statistics of inertial particles in highly turbulent flows.}, }
@article {pmid17155260, year = {2006}, author = {Villermaux, E and Duplat, J}, title = {Coarse grained scale of turbulent mixtures.}, journal = {Physical review letters}, volume = {97}, number = {14}, pages = {144506}, doi = {10.1103/PhysRevLett.97.144506}, pmid = {17155260}, issn = {0031-9007}, abstract = {What is the physical length scale which supports the concentration content in a stirred mixture? Among the length scales familiar in stirred mixtures is the dissipation scale which equilibrates substrate deformation and diffusive smearing rates. That scale is a decreasing function of the deformation rate and is, thus, a decreasing function of the Reynolds number in turbulent flows. Experiments show that the mixture concentration content is defined on a support whose elementary brick eta=LSc(-2/5) is much larger. It scales like the stirring scale L, depends on the Schmidt number Sc, and is independent of the Reynolds number. The above law is supported by measurements covering two decades in L and three decades in Sc. We suggest that this scale results from the aggregation of bundles of elementary stretched scalar sheets merging under large-scale substrate deformation.}, }
@article {pmid17155259, year = {2006}, author = {Chen, S and Eyink, GL and Wan, M and Xiao, Z}, title = {Is the Kelvin theorem valid for high Reynolds number turbulence?.}, journal = {Physical review letters}, volume = {97}, number = {14}, pages = {144505}, doi = {10.1103/PhysRevLett.97.144505}, pmid = {17155259}, issn = {0031-9007}, abstract = {The Kelvin-Helmholtz theorem on conservation of circulation is supposed to hold for ideal inviscid fluids and is believed to be play a crucial role in turbulent phenomena. However, this expectation does not take into account singularities in turbulent velocity fields at infinite Reynolds number. We present evidence from numerical simulations for the breakdown of the classical Kelvin theorem in the three-dimensional turbulent energy cascade. Although violated in individual realizations, we find that circulation is still conserved in some average sense. For comparison, we show that Kelvin's theorem holds for individual realizations in the two-dimensional enstrophy cascade, in agreement with theory. The turbulent "cascade of circulations" is shown to be a classical analogue of phase slip due to quantized vortices in superfluids, and various applications in geophysics and astrophysics are outlined.}, }
@article {pmid17155168, year = {2006}, author = {Nicolleau, F and Elmaihy, A}, title = {Effect of the Reynolds number on three- and four-particle diffusion in three-dimensional turbulence using kinematic simulation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {74}, number = {4 Pt 2}, pages = {046302}, doi = {10.1103/PhysRevE.74.046302}, pmid = {17155168}, issn = {1539-3755}, abstract = {We study the evolution of three- and four-particle diffusion at large Reynolds numbers using kinematic simulation (KS) in isotropic turbulent flows. We vary the Reynolds number and find that the geometrical characteristics of triangles and tetrahedrons as functions of time do not depend on the Reynolds number but only on the ratio Delta0/L1 that is on the portion of the inertial range that was contained within the triangle or tetrahedron at the initial time. We also study the effect of the modeling of the unsteadiness term in the KS.}, }
@article {pmid17145184, year = {2007}, author = {Moreira, RM and Pinto, AM and Mesnier, R and Leclerc, JP}, title = {Influence of inlet positions on the flow behavior inside a photoreactor using radiotracers and colored tracer investigations.}, journal = {Applied radiation and isotopes : including data, instrumentation and methods for use in agriculture, industry and medicine}, volume = {65}, number = {4}, pages = {419-427}, doi = {10.1016/j.apradiso.2006.09.012}, pmid = {17145184}, issn = {0969-8043}, mesh = {Coloring Agents ; Enterobacteriaceae/radiation effects ; Escherichia coli/radiation effects ; Models, Theoretical ; Photochemistry/*instrumentation ; Radioisotopes ; Rheology/*methods ; *Ultraviolet Rays ; Water Purification/*instrumentation/*methods ; }, abstract = {The influence of the inlet positions on the flow behavior inside a photoreactor has been studied using colored tracer and radiotracer investigations. The photoreactor for water disinfection is a tubular reactor inside which UV emitting lamps are placed. The key to its good performance is a combination of optimum irradiation dose and fluid residence time distributions (RTD). The inlet system is one of the better possibilities of controling the fluid RTD. Three configurations have been tested. In the first step, colored tracer experiments help us to raise the mean trends of the flow behavior for the different configurations. When the inlet is located at the central bottom of the reactor, the flow is closed to a perfect mixing whereas lateral inlets lead to a plug flow with axial dispersion behavior. RTD measurements using radiotracer was carried out in a wide range of flowrates. The axial dispersion coefficient increases linearly with the Reynolds number. It is lower when the lateral inlet is divided in three inlets uniformly distributed around the bottom of the reactor. This paper shows the usefulness of radioactive isotopes as tracers in the field of wastewater treatment.}, }
@article {pmid17131171, year = {2007}, author = {Taylor, AB and Borhan, A and Ultman, JS}, title = {Three-dimensional simulations of reactive gas uptake in single airway bifurcations.}, journal = {Annals of biomedical engineering}, volume = {35}, number = {2}, pages = {235-249}, doi = {10.1007/s10439-006-9195-4}, pmid = {17131171}, issn = {0090-6964}, support = {P01 ES 11617/ES/NIEHS NIH HHS/United States ; }, mesh = {Air Pollutants/*chemistry ; Animals ; Computer Simulation ; Diffusion ; Humans ; Imaging, Three-Dimensional/methods ; Lung/*chemistry ; Microfluidics/*methods ; *Models, Biological ; Models, Chemical ; Ozone/*chemistry ; *Pulmonary Gas Exchange ; *Respiratory Mechanics ; }, abstract = {The pattern of lung injury induced by the inhalation of ozone (O(3)) depends on the dose delivered to different tissues in the airways. This study examined the distribution of O(3) uptake in a single, symmetrically branched airway bifurcation. Reaction in the epithelial lining fluid was assumed to be so rapid that O(3) concentration was negligible along the entire surface of the bifurcation wall. Three-dimensional numerical solutions of the continuity, Navier-Stokes and convection-diffusion equations were obtained for steady inspiratory and expiratory flows at Reynolds numbers ranging from 100 to 500. The total rate of O(3) uptake was found to increase with increasing flow rate during both inspiration and expiration. Hot spots of O(3) flux appeared at the carina of the bifurcation for virtually all inspiratory and expiratory Reynolds numbers considered in the simulations. At the lowest expiratory Reynolds number, however, the location of the maximum flux was shifted to the outer wall of the daughter branch. For expiratory flow, additional hot spots of flux were found on the parent branch wall just downstream of the branching region. In all cases, O(3) uptake in the single bifurcation was larger than that in a straight tube of equal inlet radius and wall surface area. This study provides insight into the effect of flow conditions on O(3) uptake and dose distribution in individual bifurcations.}, }
@article {pmid17109876, year = {2007}, author = {Wengeler, R and Nirschl, H}, title = {Turbulent hydrodynamic stress induced dispersion and fragmentation of nanoscale agglomerates.}, journal = {Journal of colloid and interface science}, volume = {306}, number = {2}, pages = {262-273}, doi = {10.1016/j.jcis.2006.10.065}, pmid = {17109876}, issn = {0021-9797}, abstract = {High pressure dispersion nozzles of 2.5-10 mm length and 125 microm diameter have been characterized in terms of fluid dynamics and dispersion experiments at 100-1400 bar. Elongational stresses at the nozzle entry (5 x 10(5) Pa) and turbulent stresses up to 10(5) Pa at a Reynolds number of 25,000 in turbulent channel flow are identified crucial for desagglomeration and aggregate fragmentation. Maximum stresses are calculated on representative particle tracks and related to agglomerate breakage. Agglomerates in the experimental study are in the range of the Kolmogorov micro scale (100-400 nm) and therefore break due to turbulent energy dissipation in viscous flow. Bond strength distributions could be determined experimentally from particle size distributions and fluid dynamics simulations, with primary particle erosion determined as dispersion mechanism for diffusion flame silica particles. Nanoscale agglomerates show a power law scaling for breakage with scaling exponents diverging from theory of floc dispersion. This is attributed to their strong bonding by sinter necks.}, }
@article {pmid17106640, year = {2007}, author = {Lin, CH and Tsai, CH and Pan, CW and Fu, LM}, title = {Rapid circular microfluidic mixer utilizing unbalanced driving force.}, journal = {Biomedical microdevices}, volume = {9}, number = {1}, pages = {43-50}, doi = {10.1007/s10544-006-9009-3}, pmid = {17106640}, issn = {1387-2176}, mesh = {Chemistry Techniques, Analytical/*instrumentation/methods ; Complex Mixtures/*chemistry ; Equipment Design ; Equipment Failure Analysis ; Microfluidics/*instrumentation/methods ; Motion ; Stress, Mechanical ; }, abstract = {This paper proposes a novel rapid circular microfluidic mixer for micro-total-analysis-systems (mu-TAS) applications in which an unbalanced driving force is used to mix fluids in a circular chamber at low Reynolds numbers (Re). The microfluidic mixer has a three-layered structure and is fabricated on low-cost glass slides using a simple and reliable fabrication process. Using hydrodynamic pumps, fluids are driven from two inlet ports into a circular mixing chamber. Each inlet port separates into two separate channels, which are then attached to opposite sides of the 3-dimensional (3-D) circular mixing chamber. The unequal lengths of these inlet channels generate an unbalanced driving force, which enhances the mixing effect in the mixing chamber. Numerical simulations are performed to predict the fluid phenomena in the mixing chamber and to estimate the mixing performance under various Reynolds number conditions. The numerical results are verified by performing flow visualization experiments. A good agreement is found between the two sets of results. The numerical and experimental results reveal that the mixing performance can reach 91% within a mixing chamber of 1 mm diameter at a Reynolds number of Re=3. Additionally, the results confirm that the unbalanced driving force produces a flow rotation in the circular mixer at low Reynolds numbers, which significantly enhances the mixing performance. The novel micromixing method presented in this study provides a simple solution for mixing problems in Lab-on-a-chip systems.}, }
@article {pmid17106078, year = {2006}, author = {Fillaudeau, L and Winterton, P and Leuliet, JC and Tissier, JP and Maury, V and Semet, F and Debreyne, P and Berthou, M and Chopard, F}, title = {Heat treatment of whole milk by the direct joule effect--experimental and numerical approaches to fouling mechanisms.}, journal = {Journal of dairy science}, volume = {89}, number = {12}, pages = {4475-4489}, doi = {10.3168/jds.S0022-0302(06)72496-1}, pmid = {17106078}, issn = {1525-3198}, mesh = {Animals ; Dairying/instrumentation/*methods ; Electric Conductivity ; Food Handling/instrumentation/*methods ; *Hot Temperature ; Milk/*chemistry ; Models, Theoretical ; Sterilization/instrumentation/*methods ; }, abstract = {The development of alternative technologies such as the direct Joule effect to pasteurize and sterilize food products is of great scientific and industrial interest. Our objective was 1) to gain insight into the ability to ensure ultra-high-temperature treatment of milk and 2) to investigate the links among thermal, hydraulic, and electrical phenomena in relation to fouling in a direct Joule effect heater. The ohmic heater [OH; E perpendicular to v (where E is the electrical field and v is the velocity); P (power) = 15 kW] was composed of 5 flat rectangular cells [e (space between the plate and electrode) = 15 mm, w (wall) = 76 mm, and L (length of the plate in plate heat exchanger or electrode) = 246 mm]--3 active cells to ensure heating and 2 (at the extremities) for electrical insulation and the recovery of leakage currents. In the first step, the thermal performance of the OH was investigated vs. the flow regimen [50 < Re (Reynolds number) < 5,000], supplied power (0 < P < 15 kW), and electrical conductivity of fluids (0.1 < sigma(20 degrees C) < 2 S/m) under clean conditions with model fluids. This protocol enabled a global thermal approach (thermal and electrical balance, modeling of the temperature profile of a fluid) and local analysis of the wall temperature of the electrode. An empirical correlation was established to estimate the temperature gradient, T(w)-T(b) (where T(w) is the wall temperature and T(b) is the product temperature) under clean conditions (without fouling) and was used to define operating conditions for pure-volume and direct-resistance heating. In the second step, the ability of OH to ensure the ultra-high-temperature treatment of whole milk was investigated and compared with a plate heat exchanger. Special care was taken to investigate the heat transfer phenomena occurring over a range of temperatures from 105 to 138 degrees C. This temperature range corresponds to the part of the process made critical by protein and mineral fouling. The objectives were 1) to demonstrate the ability of an OH to ensure heat treatment of milk, 2) to study the thermal and hydraulic performance with an increasing power and temperature difference between the inlet and outlet of the OH, 3) to define and validate a criterion to follow heat dissipation efficiency, and 4) to compare the fouling propensity with the different configurations. A heat dissipation coefficient, Rh(CO), was defined and validated to monitor the fouling propensity through global electrical and thermal parameters. Finally, a numerical simulation was developed to analyze heat profiles (wall, deposit, bulk). Because of an increasing Joule effect in the static deposit, the simulation showed how wall overheating would definitively cause fouling to spiral out of control.}, }
@article {pmid17086658, year = {2006}, author = {Jayaraman, B and Kristoffersen, AH and Finlayson, EU and Gadgil, AJ}, title = {CFD investigation of room ventilation for improved operation of a downdraft table: novel concepts.}, journal = {Journal of occupational and environmental hygiene}, volume = {3}, number = {11}, pages = {583-591}, doi = {10.1080/15459620600932551}, pmid = {17086658}, issn = {1545-9624}, mesh = {*Air Movements ; Air Pollutants, Occupational ; Air Pollution, Indoor/*prevention &amp; control ; Computer Simulation ; Hazardous Substances ; *Models, Theoretical ; Occupational Exposure/*prevention &amp; control ; *Ventilation ; }, abstract = {We report a computational fluid dynamics (CFD) study of containment of airborne hazardous materials in a ventilated room containing a downdraft table. Specifically, we investigated the containment of hazardous airborne material obtainable under a range of ventilation configurations. The desirable ventilation configuration should ensure excellent containment of the hazardous material released from the workspace above the downdraft table. However, increased airflow raises operation costs, so the airflow should be as low as feasible without compromising containment. The airflow is modeled using Reynolds Averaged Navier Stokes equations with a high Reynolds number k-epsilon turbulence model. CFD predictions are examined for several ventilation configurations. Based on this study, we find that substantial improvements in containment are possible concurrent with reduction in airflow, compared with the existing design of ventilation configuration.}, }
@article {pmid17069826, year = {2007}, author = {Crespy, A and Bolève, A and Revil, A}, title = {Influence of the Dukhin and Reynolds numbers on the apparent zeta potential of granular porous media.}, journal = {Journal of colloid and interface science}, volume = {305}, number = {1}, pages = {188-194}, doi = {10.1016/j.jcis.2006.09.038}, pmid = {17069826}, issn = {0021-9797}, abstract = {The Helmholtz-Smoluchowski (HS) equation is widely used to determine the apparent zeta potential of porous materials using the streaming potential method. We present a model able to correct this apparent zeta potential of granular media of the influence of the Dukhin and Reynolds numbers. The Dukhin number represents the ratio between the surface conductivity (mainly occurring in the Stern layer) and the pore water conductivity. The Reynolds number represents the ratio between inertial and viscous forces in the Navier-Stokes equation. We show here that the HS equation can lead to serious errors if it is used to predict the dependence of zeta potential on flow in the inertial laminar flow regime without taking into account these corrections. For indifferent 1:1 electrolytes (such as sodium chloride), we derived two simple scaling laws for the dependence of the streaming potential coupling coefficient (or the apparent zeta potential) on the Dukhin and Reynolds numbers. Our model is compared with a new set of experimental data obtained on glass bead packs saturated with NaCl solutions at different salinities and pH. We find fairly good agreement between the model and these experimental data.}, }
@article {pmid17064809, year = {2007}, author = {Yu, P and Lee, TS and Zeng, Y and Low, HT}, title = {A 3D analysis of oxygen transfer in a low-cost micro-bioreactor for animal cell suspension culture.}, journal = {Computer methods and programs in biomedicine}, volume = {85}, number = {1}, pages = {59-68}, doi = {10.1016/j.cmpb.2006.09.008}, pmid = {17064809}, issn = {0169-2607}, mesh = {Animals ; *Bioreactors/economics ; Cells, Cultured ; *Costs and Cost Analysis ; Oxygen/*metabolism ; }, abstract = {A 3D numerical model was developed to study the flow field and oxygen transport in a micro-bioreactor with a rotating magnetic bar on the bottom to mix the culture medium. The Reynolds number (Re) was kept in the range of 100-716 to ensure laminar environment for animal cell culture. The volumetric oxygen transfer coefficient (k(L)a) was determined from the oxygen concentration distribution. It was found that the effect of the cell consumption on k(L)a could be negligible. A correlation was proposed to predict the liquid-phase oxygen transfer coefficient (k(Lm)) as a function of Re. The overall oxygen transfer coefficient (k(L)) was obtained by the two-resistance model. Another correlation, within an error of 15%, was proposed to estimate the minimum oxygen concentration to avoid cell hypoxia. By combination of the correlations, the maximum cell density, which the present micro-bioreactor could support, was predicted to be in the order of 10(12) cells m(-3). The results are comparable with typical values reported for animal cell growth in mechanically stirred bioreactors.}, }
@article {pmid17049904, year = {2007}, author = {Jeong, SJ and Kim, WS and Sung, SJ}, title = {Numerical investigation on the flow characteristics and aerodynamic force of the upper airway of patient with obstructive sleep apnea using computational fluid dynamics.}, journal = {Medical engineering &amp; physics}, volume = {29}, number = {6}, pages = {637-651}, doi = {10.1016/j.medengphy.2006.08.017}, pmid = {17049904}, issn = {1350-4533}, mesh = {Adult ; Computer Simulation ; Humans ; Male ; *Models, Biological ; Pharynx/*physiopathology ; Pressure ; *Pulmonary Ventilation ; *Respiratory Mechanics ; Rheology/methods ; Sleep Apnea, Obstructive/*physiopathology ; Stress, Mechanical ; }, abstract = {Developing a mathematical model to predict the abnormal flow characteristics that are produced by obstructive sleep apnea is an important step in learning the pathophysiology of the obstructive sleep apnea (OSA) disease. The present study provides detailed calculations of flow in the pharyngeal airway of a patient with obstructive sleep apnea. To achieve this goal, a computational fluid dynamics model was constructed using raw data from three-dimensional computed tomogram (CT) images of an OSA patient. To reproduce the important transition from laminar to turbulent flow in the pharyngeal airway, the low Reynolds number k-epsilon model was adopted and successfully validated using previous open literature. The results show that the flow in the pharyngeal airway of patients with OSA comprises a turbulent jet formed by area restriction at the velopharynx. This turbulent jet causes higher shear and pressure forces in the vicinity of the velopharynx. From the results, It may be deduced that the most collapsible area in the pharyngeal airway of OSA patients is the velopharynx where minimum intraluminal pressure and maximum aerodynamic force lie.}, }
@article {pmid17047283, year = {2006}, author = {Khanafer, KM and Gadhoke, P and Berguer, R and Bull, JL}, title = {Modeling pulsatile flow in aortic aneurysms: effect of non-Newtonian properties of blood.}, journal = {Biorheology}, volume = {43}, number = {5}, pages = {661-679}, pmid = {17047283}, issn = {0006-355X}, mesh = {Aortic Aneurysm, Abdominal/*physiopathology ; Blood Flow Velocity ; Blood Viscosity ; *Hemorheology ; Humans ; *Models, Cardiovascular ; Pulsatile Flow ; Stress, Mechanical ; Systole ; }, abstract = {Pulsatile flow in an axisymmetric rigid-walled model of an abdominal aorta aneurysm was analyzed numerically for various aneurysm dilations using physiologically realistic resting waveform at time-averaged Reynolds number of 300 and peak Reynolds number of 1607. Discretization of the governing equations was achieved using a finite element scheme based on the Galerkin method of weighted residuals. Comparisons with previously published work on the basis of special cases were performed and found to be in excellent agreement. Our findings indicate that the velocity fields are significantly affected by non-Newtonian properties in pathologically altered configurations. Non-Newtonian fluid shear stress is found to be greater than Newtonian fluid shear stress during peak systole. Further, the maximum shear stress is found to occur near the distal end of AAA during peak systole. The impact of non-Newtonian blood flow characteristics on pressure compared to Newtonian model is found insignificant under resting conditions. Viscous and inertial forces associated with blood flow are responsible for the changes in the wall that result in thrombus deposition and dilation while rupture of AAA is more likely determined by much larger mechanical stresses imposed by pulsatile pressure on the wall of AAA.}, }
@article {pmid17036813, year = {2006}, author = {Pang, S and Farrell, JA}, title = {Chemical plume source localization.}, journal = {IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics : a publication of the IEEE Systems, Man, and Cybernetics Society}, volume = {36}, number = {5}, pages = {1068-1080}, doi = {10.1109/tsmcb.2006.874689}, pmid = {17036813}, issn = {1083-4419}, mesh = {Air Pollution/*analysis ; *Algorithms ; *Artificial Intelligence ; Bayes Theorem ; Computer Simulation ; Diffusion ; Environmental Monitoring/*methods ; Microfluidics/methods ; *Models, Chemical ; Models, Statistical ; Pattern Recognition, Automated/*methods ; Principal Component Analysis ; Robotics/methods ; Smell ; Water Pollutants, Chemical/*analysis ; }, abstract = {This paper addresses the problem of estimating a likelihood map for the location of the source of a chemical plume using an autonomous vehicle as a sensor probe in a fluid flow. The fluid flow is assumed to have a high Reynolds number. Therefore, the dispersion of the chemical is dominated by turbulence, resulting in an intermittent chemical signal. The vehicle is capable of detecting above-threshold chemical concentration and sensing the fluid flow velocity at the vehicle location. This paper reviews instances of biological plume tracing and reviews previous strategies for a vehicle-based plume tracing. The main contribution is a new source-likelihood mapping approach based on Bayesian inference methods. Using this Bayesian methodology, the source-likelihood map is propagated through time and updated in response to both detection and nondetection events. Examples are included that use data from in-water testing to compare the mapping approach derived herein with the map derived using a previously existing technique.}, }
@article {pmid17026233, year = {2006}, author = {Volk, R and Ravelet, F and Monchaux, R and Berhanu, M and Chiffaudel, A and Daviaud, F and Odier, P and Pinton, JF and Fauve, S and Mordant, N and Pétrélis, F}, title = {Transport of magnetic field by a turbulent flow of liquid sodium.}, journal = {Physical review letters}, volume = {97}, number = {7}, pages = {074501}, doi = {10.1103/PhysRevLett.97.074501}, pmid = {17026233}, issn = {0031-9007}, abstract = {We study the effect of a turbulent flow of liquid sodium generated in the von Kármán geometry, on the localized field of a magnet placed close to the frontier of the flow. We observe that the field can be transported by the flow on distances larger than its integral length scale. In the most turbulent configurations, the mean value of the field advected at large distance vanishes. However, the rms value of the fluctuations increases linearly with the magnetic Reynolds number. The advected field is strongly intermittent.}, }
@article {pmid17025630, year = {2006}, author = {Padding, JT and Louis, AA}, title = {Hydrodynamic interactions and Brownian forces in colloidal suspensions: coarse-graining over time and length scales.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {74}, number = {3 Pt 1}, pages = {031402}, doi = {10.1103/PhysRevE.74.031402}, pmid = {17025630}, issn = {1539-3755}, abstract = {We describe in detail how to implement a coarse-grained hybrid molecular dynamics and stochastic rotation dynamics simulation technique that captures the combined effects of Brownian and hydrodynamic forces in colloidal suspensions. The importance of carefully tuning the simulation parameters to correctly resolve the multiple time and length scales of this problem is emphasized. We systematically analyze how our coarse-graining scheme resolves dimensionless hydrodynamic numbers such as the Reynolds number Re, which indicates the importance of inertial effects, the Schmidt number Sc, which indicates whether momentum transport is liquidlike or gaslike, the Mach number, which measures compressibility effects, the Knudsen number, which describes the importance of noncontinuum molecular effects, and the Peclet number, which describes the relative effects of convective and diffusive transport. With these dimensionless numbers in the correct regime the many Brownian and hydrodynamic time scales can be telescoped together to maximize computational efficiency while still correctly resolving the physically relevant processes. We also show how to control a number of numerical artifacts, such as finite-size effects and solvent-induced attractive depletion interactions. When all these considerations are properly taken into account, the measured colloidal velocity autocorrelation functions and related self-diffusion and friction coefficients compare quantitatively with theoretical calculations. By contrast, these calculations demonstrate that, notwithstanding its seductive simplicity, the basic Langevin equation does a remarkably poor job of capturing the decay rate of the velocity autocorrelation function in the colloidal regime, strongly underestimating it at short times and strongly overestimating it at long times. Finally, we discuss in detail how to map the parameters of our method onto physical systems and from this extract more general lessons-keeping in mind that there is no such thing as a free lunch-that may be relevant for other coarse-graining schemes such as lattice Boltzmann or dissipative particle dynamics.}, }
@article {pmid17025542, year = {2006}, author = {Li, Y and Meneveau, C and Chen, S and Eyink, GL}, title = {Subgrid-scale modeling of helicity and energy dissipation in helical turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {74}, number = {2 Pt 2}, pages = {026310}, doi = {10.1103/PhysRevE.74.026310}, pmid = {17025542}, issn = {1539-3755}, abstract = {The subgrid-scale (SGS) modeling of helical, isotropic turbulence in large eddy simulation is investigated by quantifying rates of helicity and energy cascade. Assuming Kolmogorov spectra, the Smagorinsky model with its traditional coefficient is shown to underestimate the helicity dissipation rate by about 40%. Several two-term helical models are proposed with the model coefficients calculated from simultaneous energy and helicity dissipation balance. The helical models are also extended to include dynamic determination of their coefficients. The models are tested a priori in isotropic steady helical turbulence. Together with the dynamic Smagorinsky model and the dynamic mixed model, they are also tested a posteriori in both decaying and steady isotropic helical turbulence by comparing results to direct numerical simulations (DNS). The a priori tests confirm that the Smagorinsky model underestimates SGS helicity dissipation, although quantitative differences with the predictions are observed due to the finite Reynolds number of the DNS. Also, in a posteriori tests improvement can be achieved for the helicity decay rate with the proposed models, compared with the Smagorinsky model. Overall, however, the effect of the new helical terms added to obtain the correct rate of global helicity dissipation is found to be quite small. Within the small differences, the various versions of the dynamic model provide the results closest to the DNS. The dynamic model's good performance in capturing mean kinetic energy dissipation at the finite Reynolds number of the simulations appears to be the most important aspect in accounting also for accurate prediction of the helicity dissipation.}, }
@article {pmid17025538, year = {2006}, author = {Lepreti, F and Carbone, V and Veltri, P}, title = {Model for intermittency of energy dissipation in turbulent flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {74}, number = {2 Pt 2}, pages = {026306}, doi = {10.1103/PhysRevE.74.026306}, pmid = {17025538}, issn = {1539-3755}, abstract = {Modeling the intermittent behavior of turbulent energy dissipation processes in both space and time is often a relevant problem when dealing with phenomena occurring in high-Reynolds-number flows, especially in astrophysical and space fluids. In this paper, a dynamical model is proposed to describe the intermittency of the energy dissipation rate in a turbulent system. This is done by using a shell model to simulate the time evolution of the turbulent cascade and introducing some heuristic rules, partly inspired by the well-known p model, to construct a spatial structure of the energy dissipation rate. In order to validate the model and to study its spatial intermittency properties, a series of numerical simulations have been performed. These show that the level of spatial intermittency of the system can be simply tuned by varying a single parameter of the model and that scaling laws in agreement with those obtained from experiments on fully turbulent hydrodynamic flows can be recovered. It is finally suggested that the model could represent a useful tool to simulate the intermittent structure of turbulent energy dissipation in those high-Reynolds-number astrophysical fluids where impulsive energy release processes can be associated with the dynamics of the turbulent cascade.}, }
@article {pmid17014140, year = {2006}, author = {Matteucci, ME and Hotze, MA and Johnston, KP and Williams, RO}, title = {Drug nanoparticles by antisolvent precipitation: mixing energy versus surfactant stabilization.}, journal = {Langmuir : the ACS journal of surfaces and colloids}, volume = {22}, number = {21}, pages = {8951-8959}, doi = {10.1021/la061122t}, pmid = {17014140}, issn = {0743-7463}, mesh = {Itraconazole/*chemistry ; Microscopy, Electron, Scanning ; Nanoparticles/*chemistry/*ultrastructure ; Particle Size ; Solvents/*chemistry ; Surface-Active Agents/*chemistry ; Temperature ; }, abstract = {Organic itraconazole (ITZ) solutions were mixed with aqueous solutions to precipitate sub-300 nm particles over a wide range of energy dissipation rates, even for drug loadings as high as 86% (ITZ weight/total weight). The small particle sizes were produced with the stabilizer poloxamer 407, which lowered the interfacial tension, increasing the nucleation rate while inhibiting growth by coagulation and condensation. The highest nucleation rates and slowest growth rates were found at temperatures below 20 degrees C and increased with surfactant concentration and Reynolds number (Re). This increase in the time scale for growth reduced the Damkohler number (Da) (mixing time/precipitation time) to low values even for modest mixing energies. As the stabilizer concentration increased, the average particle size decreased and reached a threshold where Da may be considered to be unity. Da was maintained at a low value by compensating for a change in one variable away from optimum conditions (for small particles) by manipulating another variable. This tradeoff in compensation variables was demonstrated for organic flow rate vs Re, Re vs stabilizer concentration, stabilizer feed location (organic phase vs aqueous phase) vs stabilizer concentration, and stabilizer feed location vs Re. A decrease in the nucleation rate with particle density in the aqueous suspension indicated that secondary nucleation was minimal. A fundamental understanding of particle size control in antisolvent precipitation is beneficial for designing mixing systems and surfactant stabilizers for forming nanoparticles of poorly water soluble drugs with the potential for high dissolution rates.}, }
@article {pmid17006510, year = {2006}, author = {Furukawa, A and Tanaka, H}, title = {Violation of the incompressibility of liquid by simple shear flow.}, journal = {Nature}, volume = {443}, number = {7110}, pages = {434-438}, doi = {10.1038/nature05119}, pmid = {17006510}, issn = {1476-4687}, abstract = {In standard fluid dynamics, the density change associated with flow is often assumed to be negligible, implying that the fluid is incompressible. For example, this has been established for simple shear flows, where no pressure change is associated with flow: there is no volume deformation due to viscous stress and inertial effects can be neglected. Accordingly, any flow-induced instabilities (such as cavitation) are unexpected for simple shear flows. Here we demonstrate that the incompressibility condition can be violated even for simple shear flows, by taking into account the coupling between the flow and density fluctuations, which arises owing to the density dependence of the viscosity. We show that a liquid can become mechanically unstable above a critical shear rate that is given by the inverse of the derivative of viscosity with respect to pressure. Our model predicts that, for very viscous liquids, this shear-induced instability should occur at moderate shear rates that are experimentally accessible. Our results explain the unusual shear-induced instability observed in viscous lubricants, and may illuminate other poorly understood phenomena associated with mechanical instability of liquids at low Reynolds number; for example, shear-induced cavitation and bubble growth, and shear-banding of very viscous liquids such as metallic glasses and the Earth's mantle.}, }
@article {pmid17002099, year = {2006}, author = {Zhang, C and Wen, S and Liu, Y}, title = {[Numerical study on inspiratory flows in two and three generation bronchi of human lung airways].}, journal = {Sheng wu yi xue gong cheng xue za zhi = Journal of biomedical engineering = Shengwu yixue gongchengxue zazhi}, volume = {23}, number = {4}, pages = {748-752}, pmid = {17002099}, issn = {1001-5515}, mesh = {Bronchi/anatomy &amp; histology/*physiology ; Finite Element Analysis ; Humans ; Inhalation/*physiology ; *Models, Biological ; }, abstract = {The main physiological function of respiratory system is exchange of oxygen and carbon dioxide between atmosphere and blood. Its physiological process is closely related with air flow and transport in respiratory airway. This paper studies numerically the inspiratory flows in a two generation and a three generation bronchial airway. The numerical results of the two generation bronchi show that the present computations fit the available experiments very well. For three generation bronchi, no separation appears within the whole airway under normal breathing rate, which is contrary to the occurrence of separation at even low Reynolds number by the previous two dimensional models. Strong secondary flow phenomenon, skew and m-shaped main flow velocity profiles are found in the airways due to geometrical curvature and bifurcation. These increase shear stress acting on the inner wall as well as on the anterior and posterior wall in the bifurcating airways. In the end bronchi of the three generation airway, the mass flow rates in medial and lateral bronchi are unequal, and the mass flow ratio between the medial and the lateral bronchi is 1.2 at the flow conditions considered.}, }
@article {pmid16999505, year = {2006}, author = {Qi, D}, title = {Direct simulations of flexible cylindrical fiber suspensions in finite Reynolds number flows.}, journal = {The Journal of chemical physics}, volume = {125}, number = {11}, pages = {114901}, doi = {10.1063/1.2336777}, pmid = {16999505}, issn = {0021-9606}, abstract = {Direct simulations of flexible cylindrical fiber suspensions in a finite Reynolds number flow are reported. The simulation method is based on a lattice Boltzmann equation and a flexible fiber model. A slender solid body is discretized into a chain of cylindrical segments contacting each other at the their ends through ball and socket joints that allow adjacent segments to rotate around the joints in three dimensional space. A constraint force is imposed at each joint. In general, motion and rotational matrices of each segment are functions of constraint forces. It is necessary to linearize the rotational matrices in forces and torques so that constraint forces could be solved using joint contacting conditions. Therefore, quaternion parameters as well as rotational matrix could be expanded in a power series of the length of time step up to a second order. A half leapfrog algorithm D. Fincham, [CCP5 Quarterly, 2, 6 (1981)] is modified to ensure the ball and socket joint conditions to be satisfied at each time step. The validation of the present flexible fiber method is tested by using a rigid particle method. It is shown that the computational results are consistent with the existing experimental and theoretical results at finite Reynolds number flows. With the present method, nonlinear inertial interactions between fluid and flexible filaments can be naturally studied. A few applications are included.}, }
@article {pmid16995757, year = {2006}, author = {Zheng, Y and Fujioka, H and Grotberg, JC and Grotberg, JB}, title = {Effects of inertia and gravity on liquid plug splitting at a bifurcation.}, journal = {Journal of biomechanical engineering}, volume = {128}, number = {5}, pages = {707-716}, doi = {10.1115/1.2246235}, pmid = {16995757}, issn = {0148-0731}, support = {HL-41126/HL/NHLBI NIH HHS/United States ; HL64373/HL/NHLBI NIH HHS/United States ; }, mesh = {*Acceleration ; Body Fluids/*physiology ; Bronchi/*physiology ; *Gravitation ; Humans ; Liquid Ventilation/*methods ; Microfluidics/methods ; Pressure ; Pulmonary Surfactants/*metabolism ; Respiratory Mechanics/*physiology ; }, abstract = {Liquid plugs may form in pulmonary airways during the process of liquid instillation or removal in many clinical treatments. During inspiration the plug may split at airway bifurcations and lead to a nonuniform final liquid distribution, which can adversely affect treatment outcomes. In this paper, a combination of bench top experimental and theoretical studies is presented to study the effects of inertia and gravity on plug splitting in an airway bifurcation model to simulate the liquid distributions in large airways. The splitting ratio, Rs, is defined as the ratio of the plug volume entering the upper (gravitationally opposed) daughter tube to the lower (gravitationally favored) one. Rs is measured as a function of parent tube Reynolds number, Rep; gravitational orientations for roll angle, phi, and pitch angle, gamma; parent plug length LP; and the presence of pre-existing plug blockages in downstream daughter tubes. Results show that increasing Rep causes more homogeneous splitting. A critical Reynolds number Rec is found to exist so that when Rep < or = Rec, Rs = 0, i.e., no liquid enters the upper daughter tube. Rec increases while Rs decreases with increasing the gravitational effect, i.e., increasing phi and gamma. When a blockage exists in the lower daughter, Rec is only found at phi = 60 deg in the range of Rep studied, and the resulting total mass ratio can be as high as 6, which also asymptotes to a finite value for different phi as Rep increases. Inertia is further demonstrated to cause more homogeneous plug splitting from a comparison study of Rs versus Cap (another characteristic speed) for three liquids: water, glycerin, and LB-400X. A theoretical model based on entrance flow for the plug in the daughters is developed and predicts Rs versus Rep. The frictional pressure drop, as a part of the total pressure drop, is estimated by two fitting parameters and shows a linear relationship with Rep. The theory provides a good prediction on liquid plug splitting and well simulates the liquid distributions in the large airways of human lungs.}, }
@article {pmid16983201, year = {2006}, author = {Trachtenberg, S}, title = {The cytoskeleton of spiroplasma: a complex linear motor.}, journal = {Journal of molecular microbiology and biotechnology}, volume = {11}, number = {3-5}, pages = {265-283}, doi = {10.1159/000094060}, pmid = {16983201}, issn = {1464-1801}, mesh = {Bacterial Proteins/metabolism ; Cell Membrane/metabolism ; Contractile Proteins/metabolism ; Cryoelectron Microscopy ; Cytoskeletal Proteins/metabolism ; Cytoskeleton/metabolism/*ultrastructure ; Models, Biological ; Phosphorylation ; Spiroplasma/cytology/metabolism/*ultrastructure ; }, abstract = {Spiroplasma are wall-less, helical bacteria from the class Mollicutes. The Mollicutes (Mycoplasma, Acholeplasma, Spiroplasma) evolved by regressive evolution to generate one of the simplest and minimal free-living and self-replicating forms of life. The spiroplasmas are the more advanced members in the class and are the closest to their clostridial ancestors. Spiroplasmas were discovered and identified as such only in 1972 and the finding of a unique and well-defined internal cytoskeleton, believed to be uncommon in bacteria, followed in 1973. Structural analysis suggests that the core of the spiroplasmal cytoskeleton is a flat, monolayered ribbon comprised of the 59-kDa fib gene product. The ribbon follows the shortest helical line of the polar cell from end to end. The structural building blocks of the cytoskeletal ribbon are fibrils assembling into a structure with approximately 10-nm axial and lateral repeats. Differential length changes of the fibrils may generate a wide dynamic spectrum of helical and non-helical geometries allowing for directional motility in low Reynolds number environments. The presence of other cytoskeletal elements (FtsZ, FtsA, EF-TU, MreB) has been demonstrated only recently in Spiroplasma cells. The cellular and molecular structure and dynamics of spiroplasmas and their cytoskeletal elements are reviewed.}, }
@article {pmid16957725, year = {2006}, author = {Hof, B and Westerweel, J and Schneider, TM and Eckhardt, B}, title = {Finite lifetime of turbulence in shear flows.}, journal = {Nature}, volume = {443}, number = {7107}, pages = {59-62}, doi = {10.1038/nature05089}, pmid = {16957725}, issn = {1476-4687}, abstract = {Generally, the motion of fluids is smooth and laminar at low speeds but becomes highly disordered and turbulent as the velocity increases. The transition from laminar to turbulent flow can involve a sequence of instabilities in which the system realizes progressively more complicated states, or it can occur suddenly. Once the transition has taken place, it is generally assumed that, under steady conditions, the turbulent state will persist indefinitely. The flow of a fluid down a straight pipe provides a ubiquitous example of a shear flow undergoing a sudden transition from laminar to turbulent motion. Extensive calculations and experimental studies have shown that, at relatively low flow rates, turbulence in pipes is transient, and is characterized by an exponential distribution of lifetimes. They also suggest that for Reynolds numbers exceeding a critical value the lifetime diverges (that is, becomes infinitely large), marking a change from transient to persistent turbulence. Here we present experimental data and numerical calculations covering more than two decades of lifetimes, showing that the lifetime does not in fact diverge but rather increases exponentially with the Reynolds number. This implies that turbulence in pipes is only a transient event (contrary to the commonly accepted view), and that the turbulent and laminar states remain dynamically connected, suggesting avenues for turbulence control.}, }
@article {pmid16938987, year = {2006}, author = {Erath, BD and Plesniak, MW}, title = {The occurrence of the Coanda effect in pulsatile flow through static models of the human vocal folds.}, journal = {The Journal of the Acoustical Society of America}, volume = {120}, number = {2}, pages = {1000-1011}, doi = {10.1121/1.2213522}, pmid = {16938987}, issn = {0001-4966}, support = {R01 DC03577/DC/NIDCD NIH HHS/United States ; }, mesh = {Air Pressure ; Algorithms ; Computer Simulation ; Fourier Analysis ; Humans ; Models, Biological ; Phonation/*physiology ; Pulmonary Ventilation/*physiology ; Pulsatile Flow/*physiology ; Signal Processing, Computer-Assisted ; Vocal Cords/*physiology ; }, abstract = {Pulsatile flow through a one-sided diffuser and static divergent vocal-fold models is investigated to ascertain the relevance of viscous-driven flow asymmetries in the larynx. The models were 7.5 times real size, and the flow was scaled to match Reynolds and Strouhal numbers, as well as the translaryngeal pressure drop. The Reynolds number varied from 0-2000, for flow oscillation frequencies corresponding to 100 and 150 Hz life-size. Of particular interest was the development of glottal flow skewing by attachment to the bounding walls, or Coanda effect, in a pulsatile flow field, and its impact on speech. The vocal folds form a divergent passage during phases of the phonation cycle when viscous effects such as flow separation are important. It was found that for divergence angles of less than 20 degrees, the attachment of the flow to the vocal-fold walls occurred when the acceleration of the forcing function was zero, and the flow had reached maximum velocity. For a divergence angle of 40 degrees, the fully separated central jet never attached to the vocal-fold walls. Inferences are made regarding the impact of the Coanda effect on the sound source contribution in speech.}, }
@article {pmid16937405, year = {2006}, author = {Francis, P and Martinez, DM and Taghipour, F and Bowen, BD and Haynes, CA}, title = {Optimizing the rotor design for controlled-shear affinity filtration using computational fluid dynamics.}, journal = {Biotechnology and bioengineering}, volume = {95}, number = {6}, pages = {1207-1217}, doi = {10.1002/bit.21090}, pmid = {16937405}, issn = {0006-3592}, mesh = {Animals ; CHO Cells ; Cell Culture Techniques/*methods ; Chromatography ; Computer Simulation ; Computers ; Cricetinae ; *Equipment Design ; Models, Theoretical ; Proteins/chemistry/*isolation &amp; purification ; Rheology ; Software ; Stress, Mechanical ; }, abstract = {Controlled shear affinity filtration (CSAF) is a novel integrated processing technology that positions a rotor directly above an affinity membrane chromatography column to permit protein capture and purification directly from cell culture. The conical rotor is intended to provide a uniform and tunable shear stress at the membrane surface that inhibits membrane fouling and cell cake formation by providing a hydrodynamic force away from and a drag force parallel to the membrane surface. Computational fluid dynamics (CFD) simulations are used to show that the rotor in the original CSAF device (Vogel et al., 2002) does not provide uniform shear stress at the membrane surface. This results in the need to operate the system at unnecessarily high rotor speeds to reach a required shear stress of at least 0.17 Pa at every radial position of the membrane surface, compromising the scale-up of the technology. Results from CFD simulations are compared with particle image velocimetry (PIV) experiments and a numerical solution for low Reynolds number conditions to confirm that our CFD model accurately describes the hydrodynamics in the rotor chamber of the CSAF device over a range of rotor velocities, filtrate fluxes, and (both laminar and turbulent) retentate flows. CFD simulations were then carried out in combination with a root-finding method to optimize the shape of the CSAF rotor. The optimized rotor geometry produces a nearly constant shear stress of 0.17 Pa at a rotational velocity of 250 rpm, 60% lower than the original CSAF design. This permits the optimized CSAF device to be scaled up to a maximum rotor diameter 2.5 times larger than is permissible in the original device, thereby providing more than a sixfold increase in volumetric throughput.}, }
@article {pmid16935949, year = {2006}, author = {Gebremichael, Y and Ayton, GS and Voth, GA}, title = {Mesoscopic modeling of bacterial flagellar microhydrodynamics.}, journal = {Biophysical journal}, volume = {91}, number = {10}, pages = {3640-3652}, pmid = {16935949}, issn = {0006-3495}, support = {R01 GM053148/GM/NIGMS NIH HHS/United States ; GM053148/GM/NIGMS NIH HHS/United States ; }, mesh = {*Bacterial Physiological Phenomena ; Computer Simulation ; Flagella/*physiology ; Microfluidics/*methods ; *Models, Biological ; Motion ; }, abstract = {A particle-based hybrid method of elastic network model and smooth-particle hydrodynamics has been employed to describe the propulsion of bacterial flagella in a viscous hydrodynamic environment. The method explicitly models the two aspects of bacterial propulsion that involve flagellar flexibility and long-range hydrodynamic interaction of low-Reynolds-number flow. The model further incorporates the molecular organization of the flagellar filament at a coarse-grained level in terms of the 11 protofilaments. Each of these protofilaments is represented by a collection of material points that represent the flagellin proteins. A computational model of a single flexible helical segment representing the filament of a bacterial flagellum is presented. The propulsive dynamics and the flow fields generated by the motion of the model filament are examined. The nature of flagellar deformation and the influence of hydrodynamics in determining the shape of deformations are examined based on the helical filament.}, }
@article {pmid16919667, year = {2006}, author = {Khair, AS}, title = {The 'Einstein correction' to the bulk viscosity in n dimensions.}, journal = {Journal of colloid and interface science}, volume = {302}, number = {2}, pages = {702-703}, doi = {10.1016/j.jcis.2006.07.076}, pmid = {16919667}, issn = {0021-9797}, abstract = {We calculate the effective bulk viscosity of a dilute dispersion of rigid n-dimensional hyperspheres in a compressible Newtonian fluid at zero Reynolds number.}, }
@article {pmid16917931, year = {2007}, author = {Rao, AR and Kumar, B}, title = {Scale-up criteria of square tank surface aerator.}, journal = {Biotechnology and bioengineering}, volume = {96}, number = {3}, pages = {464-470}, doi = {10.1002/bit.21149}, pmid = {16917931}, issn = {0006-3592}, mesh = {*Bioreactors ; *Models, Theoretical ; *Oxygen/chemistry ; }, abstract = {Oxygen transfer rate and the corresponding power requirement to operate the rotor are vital for design and scale-up of surface aerators. Present study develops simulation or scale-up criterion correlating the oxygen transfer coefficient and power number along with a parameter governing theoretical power per unit volume (X, which is defined as equal to F(4/3)R(1/3), where F and R are impellers' Froude and Reynolds number, respectively). Based on such scale-up criteria, design considerations are developed to save energy requirements while designing square tank surface aerators. It has been demonstrated that energy can be saved substantially if the aeration tanks are run at relatively higher input powers. It is also demonstrated that smaller sized tanks are more energy conservative and economical when compared to big sized tanks, while aerating the same volume of water, and at the same time by maintaining a constant input power in all the tanks irrespective of their size. An example illustrating how energy can be reduced while designing different sized aerators is given. The results presented have a wide application in biotechnology and bioengineering areas with a particular emphasis on the design of appropriate surface aeration systems.}, }
@article {pmid16907578, year = {2006}, author = {Truesdell, R and Mammoli, A and Vorobieff, P and van Swol, F and Brinker, CJ}, title = {Drag reduction on a patterned superhydrophobic surface.}, journal = {Physical review letters}, volume = {97}, number = {4}, pages = {044504}, doi = {10.1103/PhysRevLett.97.044504}, pmid = {16907578}, issn = {0031-9007}, abstract = {We present an experimental study of a low-Reynolds number shear flow between two surfaces, one of which has a regular grooved texture augmented with a superhydrophobic coating. The combination reduces the effective fluid-surface contact area, thereby appreciably decreasing the drag on the surface and effectively changing the macroscopic boundary condition on the surface from no slip to limited slip. We measure the force on the surface and the velocity field in the immediate vicinity on the surface (and thus the wall shear) simultaneously. The latter facilitates a direct assessment of the effective slip length associated with the drag reduction.}, }
@article {pmid16907217, year = {2006}, author = {Lishchuk, SV and Halliday, I and Care, CM}, title = {Shear viscosity of bulk suspensions at low Reynolds number with the three-dimensional lattice Boltzmann method.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {74}, number = {1 Pt 2}, pages = {017701}, doi = {10.1103/PhysRevE.74.017701}, pmid = {16907217}, issn = {1539-3755}, abstract = {We report three-dimensional parallel Lagrangian particle simulations using the lattice Boltzmann method, conducted at a low Reynolds number. Using modified Lees-Edwards boundary conditions and directly calculated viscous dissipation, we show that it is possible to recover excellent agreement with the Einstein viscosity formula in the low concentration limit and to predict viscosity corrections for larger concentrations.}, }
@article {pmid16907210, year = {2006}, author = {Nahum, A and Seifert, A}, title = {Technique for backward particle tracking in a flow field.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {74}, number = {1 Pt 2}, pages = {016701}, doi = {10.1103/PhysRevE.74.016701}, pmid = {16907210}, issn = {1539-3755}, abstract = {A numerical method to determine the history of particle paths is presented and its application for mixing quantification is illustrated. When more than one source exists in a flow field, the current technique can reveal the particle's identity found in any time and place in the field, by backward tracking its origin. Since the particle position at a preceding time is not known, the velocity vector is implicit. To resolve this uncertainty, a three-stage iterative procedure is developed and implemented. The current particle velocity is multiplied by the time increment and the product is used to estimate the previous time increment particle position. Two velocity matrices are generated on a mesh around the estimated position. The first matrix is the Eulerian velocity field interpolated on the mesh. The second matrix contains velocity vectors that point to the current particle position. A correlation matrix is calculated from the two velocity matrices in order to resolve the actual particle position in the previous time increment. Determination of the time increments' size is performed by checking the maximum of the correlation matrix. The new algorithm was validated using a numerical solution of the confined twin-jet flow at low Reynolds number. This flow performs a Hopf bifurcation at a Reynolds number of about 30, therefore chaotic trajectories might exist in the flow. First, the convergence of the backward particle path to the streamlines in steady flow was demonstrated. Convergence of the particle paths for various time increments was achieved also at the unsteady two-dimensional confined twin-jet flow. When the flow has more than one source, the proposed tracking method can be applied to generate complete and ordered particle source images in any desired position and time in the flow field. Maps of particle sources are used to visualize the flow patterns and the stretched interface between the two fluid sources. Those maps are demonstrated as a powerful tool for mixing quantification and can be implemented also for pollution source detection and many other fluid dynamics applications.}, }
@article {pmid16907188, year = {2006}, author = {Berg, J and Lüthi, B and Mann, J and Ott, S}, title = {Backwards and forwards relative dispersion in turbulent flow: an experimental investigation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {74}, number = {1 Pt 2}, pages = {016304}, doi = {10.1103/PhysRevE.74.016304}, pmid = {16907188}, issn = {1539-3755}, abstract = {From particle tracking velocimetry we present an experimental measure of the ratio between backwards and forwards relative dispersion in an intermediate Reynolds number turbulent flow. Lack of time-reversal symmetry implies that their ratio may be different from 1. From a stochastic model, this has recently been studied by Sawford et al [Phys. Fluids 17, 095109 (2005)] giving ratios between 5 and 20. We find a value of approximately 2 and discuss it in the context of the characteristics of the rate of strain tensor s(ij). An analysis of a direct numerical simulation by Biferale et al [Phys. Rev. Lett. 93, 064502 (2004) and Phys. Fluids 17, 021701 (2004)] gives the same result.}, }
@article {pmid16907024, year = {2006}, author = {Fan, H and Zhang, R and Chen, H}, title = {Extended volumetric scheme for lattice Boltzmann models.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {73}, number = {6 Pt 2}, pages = {066708}, doi = {10.1103/PhysRevE.73.066708}, pmid = {16907024}, issn = {1539-3755}, abstract = {An extended volumetric scheme is proposed for lattice Boltzmann (LB) models. This scheme is particularly desirable for multispeed LB models due to its removal of nonlocal advection. It recovers the same macroscopic hydrodynamics as the standard lattice Boltzmann method without any further treatments. This scheme achieves an effectively reduced Courant-Friedrichs-Lewy number so that numerical stability is significantly enhanced for high Reynolds number simulations while maintaining the same order of numerical accuracy.}, }
@article {pmid16907021, year = {2006}, author = {Geier, M and Greiner, A and Korvink, JG}, title = {Cascaded digital lattice Boltzmann automata for high Reynolds number flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {73}, number = {6 Pt 2}, pages = {066705}, doi = {10.1103/PhysRevE.73.066705}, pmid = {16907021}, issn = {1539-3755}, abstract = {Lattice Boltzmann methods are of limited applicability for direct numerical simulation of turbulent flow due to instabilities in the zero viscosity limit. We observe that this is caused by an insufficient degree of Galilean invariance of the relaxation-type Lattice Boltzmann collision operator. The cascaded digital lattice Boltzmann automata described here, provides a method with which to achieve stable collision operators down to the limit of zero viscosity.}, }
@article {pmid16906973, year = {2006}, author = {Burattini, P and Lavoie, P and Agrawal, A and Djenidi, L and Antonia, RA}, title = {Power law of decaying homogeneous isotropic turbulence at low Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {73}, number = {6 Pt 2}, pages = {066304}, doi = {10.1103/PhysRevE.73.066304}, pmid = {16906973}, issn = {1539-3755}, abstract = {We focus on an estimate of the decay exponent (m) in the initial period of decay of homogeneous isotropic turbulence at low Taylor microscale Reynolds number R lambda (approximately equal to 20-50). Lattice Boltzmann simulations in a periodic box of 256(3) points are performed and compared with measurements in grid turbulence at similar R lambda. Good agreement is found between measured and calculated energy spectra. The exponent m is estimated in three different ways: from the decay of the turbulent kinetic energy, the decay of the mean energy dissipation rate, and the rate of growth of the Taylor microscale. Although all estimates are close, as prescribed by theory, that from the Taylor microscale has the largest variability. It is then suggested that the virtual origin for the decay rate be determined from the Taylor microscale, but the actual value of m be estimated from the decay rate of the kinetic energy. The dependence of m on R lambda(0) (the value of R lambda at the beginning of the simulation) is also analyzed, using the present data as well as data from the literature. The results confirmed that m approaches 1, as R lambda(0) increases.}, }
@article {pmid16906900, year = {2006}, author = {Barba, LA}, title = {Nonshielded multipolar vortices at high Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {73}, number = {6 Pt 2}, pages = {065303}, doi = {10.1103/PhysRevE.73.065303}, pmid = {16906900}, issn = {1539-3755}, abstract = {Vortex multipoles--consisting of a core of vorticity closely surrounded by several smaller vorticity concentrations of opposite sign--are obtained from the evolution of vorticity in two-dimensional simulations. Using a meshless vortex method, we obtained triangular and square vortices, surrounded by three and four satellites, respectively. These structures have only been observed before to emerge from zero-circulation initial conditions. We also observed a pentagon vortex. Here, we obtain compound vortices of nonzero total circulation, and suggest a gamut of multipolar asymptotic solutions to the Navier-Stokes equations.}, }
@article {pmid16906800, year = {2006}, author = {Holzer, L and Zimmermann, W}, title = {Particles held by springs in a linear shear flow exhibit oscillatory motion.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {73}, number = {6 Pt 1}, pages = {060801}, doi = {10.1103/PhysRevE.73.060801}, pmid = {16906800}, issn = {1539-3755}, abstract = {The dynamics of small spheres that are held by linear springs in a low Reynolds number shear flow at neighboring locations is investigated. The flow elongates the beads, and the interplay of the shear gradient with the nonlinear behavior of the hydrodynamic interaction among the spheres causes in a large range of parameters a bifurcation to a surprising oscillatory bead motion. The parameter ranges wherein this bifurcation is either super- or subcritical are determined.}, }
@article {pmid16905426, year = {2006}, author = {Leis, JM}, title = {Are larvae of demersal fishes plankton or nekton?.}, journal = {Advances in marine biology}, volume = {51}, number = {}, pages = {57-141}, doi = {10.1016/S0065-2881(06)51002-8}, pmid = {16905426}, issn = {0065-2881}, mesh = {Animals ; Behavior, Animal/physiology ; Feeding Behavior/physiology ; Fishes/*physiology ; Larva/classification/physiology ; Models, Biological ; Movement/*physiology ; Orientation/physiology ; Predatory Behavior/physiology ; Swimming/physiology ; }, abstract = {A pelagic larval stage is found in nearly all demersal marine teleost fishes, and it is during this pelagic stage that the geographic scale of dispersal is determined. Marine biologists have long made a simplifying assumption that behaviour of larvae--with the possible exception of vertical distribution--has negligible influence on larval dispersal. Because advection by currents can take place over huge scales during a pelagic larval stage that typically lasts for several days to several weeks, this simplifying assumption leads to the conclusion that populations of marine demersal fishes operate over, and are connected over, similar huge scales. This conclusion has major implications for our perception of how marine fish populations operate and for our management of them. Recent (and some older) behavioural research-reviewed here-reveals that for a substantial portion of the pelagic larval stage of perciform fishes, the simplifying assumption is invalid. Near settlement, and for a considerable portion of the pelagic stage prior to that, larvae of many fish species are capable of swimming at speeds faster than mean ambient currents over long periods, travelling tens of kilometres. Only the smallest larvae of perciform fishes swim in an energetically costly viscous hydrodynamic environment (i.e., low Reynolds number). Vertical distribution is under strong behavioural control from the time of hatching, if not before, and can have a decisive, if indirect, influence on dispersal trajectories. Larvae of some species avoid currents by occupying the epibenthic boundary layer. Larvae are able to swim directionally in the pelagic environment, with some species apparently orientating relative to the sun and others to settlement sites. These abilities develop relatively early, and ontogenetic changes in orientation are seemingly common. Larvae of some species can use sound to navigate, and others can use odour to find settlement habitat, at least over small scales. Other senses may also be important to orientation. Larvae are highly aware of their environment and of potential predators, and some school during the pelagic larval stage. Larvae are selective about where they settle at both meso and micro scales, and settlement is strongly influenced by interactions with resident fishes. Most of these behaviours are flexible; for example, swimming speeds and depth may vary among locations, and speed may vary with swimming direction. In direct tests, these behaviours result in dispersal different from that predicted by currents alone. Work with both tropical and temperate species shows that these behaviours begin to be significant relatively early in larval development, but much more needs to be learned about the ontogeny of behaviour and sensory abilities in larvae of marine fishes. As a preliminary rule of thumb, behaviour must be taken into account in considerations of dispersal after the preflexion stage, and vertical distribution behaviour can influence dispersal from hatching. Larvae of perciform fishes are close to being planktonic at the start of the pelagic period and are clearly nektonic at its end, and for a substantial period prior to that. All these things differ among species. Larvae of clupeiform, gadiform and pleuronectiform fishes may be less capable behaviourally than perciform fishes, but this remains to be confirmed. Clearly, these behaviours, along with hydrography, must be included in modelling dispersal and retention and may provide explanations for recent demonstrations of self-recruitment in marine fish populations. Current work is directed at understanding the ontogeny of the gradual transition from planktonic to nektonic behaviour. Although it is clear that larvae of perciform fishes have the ability to strongly influence their dispersal trajectories, it is less clear whether or how these abilities are applied.}, }
@article {pmid16904117, year = {2007}, author = {Kurtcuoglu, V and Soellinger, M and Summers, P and Boomsma, K and Poulikakos, D and Boesiger, P and Ventikos, Y}, title = {Computational investigation of subject-specific cerebrospinal fluid flow in the third ventricle and aqueduct of Sylvius.}, journal = {Journal of biomechanics}, volume = {40}, number = {6}, pages = {1235-1245}, doi = {10.1016/j.jbiomech.2006.05.031}, pmid = {16904117}, issn = {0021-9290}, mesh = {Adult ; Cerebral Aqueduct/*physiology ; Cerebrospinal Fluid/*physiology ; Computer Simulation ; Humans ; Image Interpretation, Computer-Assisted/methods ; Magnetic Resonance Imaging/*methods ; Male ; *Models, Biological ; Rheology/methods ; Third Ventricle/*physiology ; }, abstract = {The cerebrospinal fluid flow in the third ventricle of the brain and the aqueduct of Sylvius was studied using computational fluid dynamics (CFD) based on subject-specific boundary conditions derived from magnetic resonance imaging (MRI) scans. The flow domain geometry was reconstructed from anatomical MRI scans by manual image segmentation. The movement of the domain boundary was derived from MRI brain motion scans. Velocimetric MRI scans were used to reconstruct the velocity field at the inferior end of the aqueduct of Sylvius based on the theory of pulsatile flow in pipes. A constant pressure boundary condition was assigned at the foramina of Monro. Three main flow features were observed: a fluid jet emerging from the aqueduct of Sylvius, a moderately mobile recirculation zone above the jet and a mobile recirculation below the jet. The flow in the entire domain was laminar with a maximum Reynolds number of 340 in the aqueduct. The findings demonstrate that by combining MRI scans and CFD simulations, subject-specific detailed quantitative information of the flow field in the third ventricle and the aqueduct of Sylvius can be obtained.}, }
@article {pmid16883682, year = {2006}, author = {Wu, Y and Ghaly, ES}, title = {Effect of hydrodynamic environment on tablet dissolution using flow-through dissolution apparatus.}, journal = {Puerto Rico health sciences journal}, volume = {25}, number = {1}, pages = {75-83}, pmid = {16883682}, issn = {0738-0658}, mesh = {Solubility ; *Tablets ; Water ; }, abstract = {The main objective of this research is to investigate the principles underlying the dissolution process, study the phenomena of drug release in laminar flow, and better understand the effect of hydrodynamic condition on drug dissolution, in order to predict drug dissolution from a solid dosage form. Two drug models were selected, theophylline (Class I) and naproxen (Class II), and were formulated into conventional tablets containing 105 mg theophylline or 300 mg naproxen using wet granulation method. Additionally theophylline (105 mg) and naproxen (300 mg) matrices containing 30% hydroxypropylmethylcellulose (HPMC) polymer were prepared by direct compression and tested for dissolution using both USP II and IV dissolution apparatus. Tablets were tested for dissolution (USP IV) using different cell diameter, flow rate, and different position of the tablet inside the cell. In general, the drug dissolution at a given time is a direct function of the flow rate, increasing the flow rate increases drug release. The use of a small cell resulted in faster drug dissolution and higher Reynold's Number than using a large cell. Tablet position in the cell, also has an effect on drug dissolution, inserting the tablet in a horizontal position inside the cell gave faster dissolution than a vertical position. The hydrodynamic conditions did not affect the drug dissolution from HPMC controlled release tablets indicating that the drug dissolution is controlled by the matrix. An equation to predict drug dissolution from conventional tablets was established: Sh=-21.36+10.58Re(1/2) where R2=0.98. This study demonstrated that hydrodynamic conditions, and type of dissolution testing apparatus used have an effect on dissolution rate, mass transfer rate, and film thickness underlying dissolution process.}, }
@article {pmid16882152, year = {2006}, author = {Liu, Z and Lin, YE and Stout, JE and Hwang, CC and Vidic, RD and Yu, VL}, title = {Effect of flow regimes on the presence of Legionella within the biofilm of a model plumbing system.}, journal = {Journal of applied microbiology}, volume = {101}, number = {2}, pages = {437-442}, doi = {10.1111/j.1365-2672.2006.02970.x}, pmid = {16882152}, issn = {1364-5072}, mesh = {Bacterial Adhesion ; Biofilms ; Colony Count, Microbial ; Fluorescent Antibody Technique, Direct ; Legionella pneumophila/immunology/isolation &amp; purification/*physiology ; Models, Biological ; Plankton ; *Sanitary Engineering ; Stress, Mechanical ; *Water Microbiology ; Water Movements ; Water Supply ; }, abstract = {AIMS: Stagnation is widely believed to predispose water systems to colonization by Legionella. A model plumbing system was constructed to determine the effect of flow regimes on the presence of Legionella within microbial biofilms.<br><br>METHODS AND RESULTS: The plumbing model contained three parallel pipes where turbulent, laminar and stagnant flow regimes were established. Four sets of experiments were carried out with Reynolds number from 10,000 to 40,000 and from 355 to 2,000 in turbulent and laminar pipes, respectively. Legionella counts recovered from biofilm and planktonic water samples of the three sampling pipes were compared with to determine the effect of flow regime on the presence of Legionella. Significantly higher colony counts of Legionella were recovered from the biofilm of the pipe with turbulent flow compared with the pipe with laminar flow. The lowest counts were in the pipe with stagnant flow.<br><br>CONCLUSIONS: We were unable to demonstrate that stagnant conditions promoted Legionella colonization.<br><br>Plumbing modifications to remove areas of stagnation including deadlegs are widely recommended, but these modifications are tedious and expensive to perform. Controlled studies in large buildings are needed to validate this unproved hypothesis.}, }
@article {pmid16874678, year = {2006}, author = {Del Gaudio, C and Morbiducci, U and Grigioni, M}, title = {Time dependent non-Newtonian numerical study of the flow field in a realistic model of aortic arch.}, journal = {The International journal of artificial organs}, volume = {29}, number = {7}, pages = {709-718}, doi = {10.1177/039139880602900711}, pmid = {16874678}, issn = {0391-3988}, mesh = {Aorta, Thoracic/*physiology ; Atherosclerosis/physiopathology ; Blood Flow Velocity/*physiology ; Computer Simulation ; *Hemorheology ; Humans ; *Models, Cardiovascular ; Pulsatile Flow/physiology ; *Shear Strength ; Stress, Mechanical ; }, abstract = {A three-dimensional time dependent numerical simulation was performed in a geometric model of aortic arch complete with a realistic aortic root and major branches originating from the arch, for a peak Reynolds number set at 2200 and Womersley number set at 20.4. The computational fluid dynamic analysis was aimed to provide spatial and temporal distribution of the shear stress all along the entire model together with the velocity patterns, related both to the non planar geometry of the aortic system here considered and to the pulsatility imposed on the numerical model to simulate physiologic conditions. A non-Newtonian evolving fluid was considered to account for the actual rheological nature of blood; a comparison on the incidence of wall shear stress, implementing a Newtonian fluid, was also made as reference. The spatial shear stress pattern, within the cardiac cycle, was shown to have higher values in correspondence to the inner wall of the aortic arch and the sites where the major vessels originated from the arch itself. The velocity patterns, on transversal sections of the aorta, resulted in highly skewed morphology. The resulting complex fluid dynamics, established in the aortic arch and in its branches, can be related to the possible endothelium response to mechanical stimuli, induced by wall shear stress, in the promotion of inflammatory events.}, }
@article {pmid16822029, year = {2006}, author = {Chen, W}, title = {A speculative study of 23-order fractional Laplacian modeling of turbulence: some thoughts and conjectures.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {16}, number = {2}, pages = {023126}, doi = {10.1063/1.2208452}, pmid = {16822029}, issn = {1054-1500}, abstract = {This study makes the first attempt to use the 23-order fractional Laplacian modeling of Kolmogorov -53 scaling of fully developed turbulence and enhanced diffusing movements of random turbulent particles. Nonlinear inertial interactions and molecular Brownian diffusivity are considered to be the bifractal mechanism behind multifractal scaling of moderate Reynolds number turbulence. Accordingly, a stochastic equation is proposed to describe turbulence intermittency. The 23-order fractional Laplacian representation is also used to model nonlinear interactions of fluctuating velocity components, and then we conjecture a fractional Reynolds equation, underlying fractal spacetime structures of Levy 23 stable distribution and the Kolmogorov scaling at inertial scales. The new perspective of this study is that the fractional calculus is an effective approach to modeling the chaotic fractal phenomena induced by nonlinear interactions.}, }
@article {pmid16813448, year = {2006}, author = {Hazel, AL and Heil, M}, title = {Finite-Reynolds-number effects in steady, three-dimensional airway reopening.}, journal = {Journal of biomechanical engineering}, volume = {128}, number = {4}, pages = {573-578}, doi = {10.1115/1.2206203}, pmid = {16813448}, issn = {0148-0731}, mesh = {Airway Obstruction/*physiopathology ; Computer Simulation ; Elasticity ; Finite Element Analysis ; Humans ; Imaging, Three-Dimensional/*methods ; Lung/*physiopathology ; *Models, Biological ; *Respiratory Mechanics ; Rheology/*methods ; }, abstract = {Motivated by the physiological problem of pulmonary airway reopening, we study the steady propagation of an air finger into a buckled elastic tube, initially filled with viscous fluid. The system is modeled using geometrically non-linear, Kirchhoff-Love shell theory, coupled to the free-surface Navier-Stokes equations. The resulting three-dimensional, fluid-structure-interaction problem is solved numerically by a fully coupled finite element method. Our study focuses on the effects of fluid inertia, which has been neglected in most previous studies. The importance of inertial forces is characterized by the ratio of the Reynolds and capillary numbers, ReCa, a material parameter. Fluid inertia has a significant effect on the system's behavior, even at relatively small values of ReCa. In particular, compared to the case of zero Reynolds number, fluid inertia causes a significant increase in the pressure required to drive the air finger at a given speed.}, }
@article {pmid16806240, year = {2006}, author = {Hlushkou, D and Tallarek, U}, title = {Transition from creeping via viscous-inertial to turbulent flow in fixed beds.}, journal = {Journal of chromatography. A}, volume = {1126}, number = {1-2}, pages = {70-85}, doi = {10.1016/j.chroma.2006.06.011}, pmid = {16806240}, issn = {0021-9673}, mesh = {*Chromatography, Liquid/methods ; Models, Theoretical ; Rheology ; }, abstract = {This review is concerned with the analysis of flow regimes in porous media, in particular, in fixed beds of spherical particles used as reactors in engineering applications, or as separation units in liquid chromatography. A transition from creeping via viscous-inertial to turbulent flow is discussed based on macro-scale transport behaviour with respect to the pressure drop-flow rate dependence, in particular, the deviation from Darcy's law, as well as direct microscopic data which reflect concomitant changes in the pore-level hydrodynamics. In contrast to the flow behaviour in straight pipes, the transition from laminar to turbulent flow in fixed particulate beds is not sharp, but proceeds gradually through a viscous-inertial flow regime. The onset of this steady, nonlinear regime and increasing role of inertial forces is macroscopically manifested in the failure of Darcy's law to describe flow through fixed beds at higher Reynolds numbers. While the physical reasons for this failure still are not completely understood, it is not caused by turbulence which occurs at Reynolds numbers about two orders of magnitude above those for which a deviation from Darcy's law is observed. Microscopic analysis shows that this steady, nonlinear flow regime is characterized by the development of an inertial core in the pore-level profile, i.e., at increasing Reynolds number velocity profiles in individual pores become flatter towards the center of the pores, while the velocity gradient increases close to the solid-liquid interface. Further, regions with local backflow and stationary eddies are demonstrated for the laminar flow regime in fixed beds. The onset of local fluctuations (end of laminar regime) is observed at superficial Reynolds numbers on the order of 100. Complementary analysis of hydrodynamic dispersion suggests that this unsteady flow accelerates lateral equilibration between different velocities in fixed beds which, in turn, reduces spreading in the longitudial (macroscopic flow) direction.}, }
@article {pmid16805400, year = {2006}, author = {Clack, HL}, title = {Mass transfer within electrostatic precipitators: trace gas adsorption by sorbent-covered plate electrodes.}, journal = {Journal of the Air &amp; Waste Management Association (1995)}, volume = {56}, number = {6}, pages = {759-766}, doi = {10.1080/10473289.2006.10464489}, pmid = {16805400}, issn = {1096-2247}, mesh = {Adsorption ; Air Pollutants/analysis/*chemistry ; Air Pollution/*prevention &amp; control ; Coal ; Electrodes ; Mercury/analysis/*chemistry ; *Power Plants ; }, abstract = {Varying degrees of mercury (Hg) capture have been reported within the electrostatic precipitators (ESPs) of coal-fired electric utility boilers. There has been some speculation that the adsorption takes place on the particulate-covered plate electrodes. This convective mass transfer analysis of laminar and turbulent channel flows provides the maximum potential for Hg adsorption by the plate electrodes within an ESP under those conditions. Mass transfer calculations, neglecting electrohydrodynamic (EHD) effects, reveal 65% removal of elemental Hg for a laminar flow within a 15-m-long channel of 0.2-m spacing and 42% removal for turbulent flow within a similar configuration. Both configurations represent specific collection areas (SCAs) that are significantly larger than conventional ESPs in use. Results reflecting more representative SCA values generally returned removal efficiencies of <20%. EHD effects, although potentially substantial at low Reynolds numbers, diminish rapidly with increasing Reynolds number and become negligible at typical ESP operating conditions. The present results indicate maximum Hg removal efficiencies for ESPs that are much less than those observed in practice for comparable ESP operating conditions. Considering Hg adsorption kinetics and finite sorbent capacity in addition to the present mass transfer analyses would yield even lower adsorption efficiencies than the present results. In a subsequent paper, the author addresses the mass transfer potential presented by the charged, suspended particulates during their collection within an ESP and the role they potentially play in Hg capture within ESPs.}, }
@article {pmid16803177, year = {2006}, author = {Ding, EJ and Aidun, CK}, title = {Cluster size distribution and scaling for spherical particles and red blood cells in pressure-driven flows at small Reynolds number.}, journal = {Physical review letters}, volume = {96}, number = {20}, pages = {204502}, doi = {10.1103/PhysRevLett.96.204502}, pmid = {16803177}, issn = {0031-9007}, mesh = {*Cell Aggregation ; Cluster Analysis ; Erythrocytes/*cytology ; *Models, Biological ; Particle Size ; Viscosity ; }, abstract = {The clustering characteristic of purely hydrodynamically interacting particles suspended in pressure-driven flow in a circular cylinder is studied using direct numerical simulation based on the solution of the lattice-Boltzmann equation. We find a universal scaling relation for the cluster size distribution in the subcritical regime for all of the cases considered in this study. This scaling relation is independent of particle shape and concentration.}, }
@article {pmid16803075, year = {2006}, author = {Halliday, I and Law, R and Care, CM and Hollis, A}, title = {Improved simulation of drop dynamics in a shear flow at low Reynolds and capillary number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {73}, number = {5 Pt 2}, pages = {056708}, doi = {10.1103/PhysRevE.73.056708}, pmid = {16803075}, issn = {1539-3755}, abstract = {The simulation of multicomponent fluids at low Reynolds number and low capillary number is of interest in a variety of applications such as the modeling of venule scale blood flow and microfluidics; however, such simulations are computationally demanding. An improved multicomponent lattice Boltzmann scheme, designed to represent interfaces in the continuum approximation, is presented and shown (i) significantly to reduce common algorithmic artifacts and (ii) to recover full Galilean invariance. The method is used to model drop dynamics in shear flow in two dimensions where it recovers correct results over a range of Reynolds and capillary number greater than that which may be addressed with previous methods.}, }
@article {pmid16802991, year = {2006}, author = {Dupin, MM and Halliday, I and Care, CM}, title = {Simulation of a microfluidic flow-focusing device.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {73}, number = {5 Pt 2}, pages = {055701}, doi = {10.1103/PhysRevE.73.055701}, pmid = {16802991}, issn = {1539-3755}, abstract = {We present a model of microfluidic flow of several completely immiscible fluids and use it to simulate a whole flow focusing device chamber. Our efficient, practical model supports a large parameter space, spanned by surface wetting, surface tension, liquid-liquid wetting, viscosity ratio, and inlet velocity. It is based upon an N-component lattice Boltzmann method with interrupted coalescence [Dupin, Philos. Trans. R. Soc. London, Ser. A 362, 1885 (2004)], here adapted for calculations at low capillary and Reynolds numbers, with wetting and significantly reduced spurious flow. Results over 2 orders of magnitude in Reynolds number are presented.}, }
@article {pmid16801561, year = {2006}, author = {Bernard, PS}, title = {Turbulent flow properties of large-scale vortex systems.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {103}, number = {27}, pages = {10174-10179}, doi = {10.1073/pnas.0604159103}, pmid = {16801561}, issn = {0027-8424}, abstract = {Large-scale computations of dynamically interacting vortex tubes forming filaments are performed with a view toward investigating their relationship to turbulent fluid flow. It is shown that the statistical properties of the tubes are consistent with commonly accepted observations about turbulence such as the Kolmogorov inertial range spectrum and lognormality of the vorticity distribution. A loop-removal algorithm is demonstrated to reduce the nominally exponential growth rate in the number of tubes to linear growth without apparent harm to the underlying physics. In this form, a vortex tube method may become a practical means for simulating high Reynolds number turbulent flows.}, }
@article {pmid16783935, year = {2004}, author = {Valencia, A}, title = {Flow dynamics in models of intracranial terminal aneurysms.}, journal = {Mechanics &amp; chemistry of biosystems : MCB}, volume = {1}, number = {3}, pages = {221-231}, pmid = {16783935}, issn = {1546-2048}, mesh = {Basilar Artery/*physiopathology ; Humans ; Intracranial Aneurysm/*physiopathology ; *Models, Biological ; }, abstract = {Flow dynamics play an important role in the pathogenesis and treatment of intracranial aneurysms. The evaluation of the velocity field in the aneurysm dome and neck is important for the correct placement of endovascular coils, and the temporal and spatial variations of wall shear stress in the aneurysm are correlated with its growth and rupture. This numerical investigation describes the hemodynamic in two models of terminal aneurysm of the basilar artery. Aneurysm models with a aspect ratio of 1.0 and 1.67 were studied. Each model was subject to physiological representative waveform of inflow for a mean Reynolds number of 560. The effects of symmetric and asymmetric outflow conditions in the branches were studied. The three dimensional continuity and Navier-Stokes equations for incompressible, unsteady laminar flow with Newtonian properties were solved with a commercial software using non structured fine grids with 197807 and 202515 tetrahedral cells for the model 1 and 2 respectively. The flow shows complex vortex structure in both models, the inflow and outflow zones in the aneurysm neck were determined. The wall shear stress on the aneurysm showed big temporal and spatial variations. The asymmetric outflow increased the wall shear stress on the aneurysm only in model 1.}, }
@article {pmid16777127, year = {2006}, author = {Mullins, BJ and Braddock, RD and Agranovski, IE and Cropp, RA}, title = {Observation and modelling of barrel droplets on vertical fibres subjected to gravitational and drag forces.}, journal = {Journal of colloid and interface science}, volume = {300}, number = {2}, pages = {704-712}, doi = {10.1016/j.jcis.2006.02.059}, pmid = {16777127}, issn = {0021-9797}, abstract = {Extensive experimental investigation of the wetting processes of fibre/liquid systems during air filtration (when drag and gravitational forces are acting) has shown many important features, including droplet extension, oscillatory motion, and detachment or flow of drops from fibres as airflow velocity increases. A detailed experimental study of the aforementioned processes was conducted using glass filter fibres and H(2)O aerosol, which coalesce on the fibre to form barrel droplets with small contact angles. The droplets were predominantly observed in the Reynolds transition (or unsteady laminar) flow region. The droplet oscillation appears to be induced by the onset of vortexes in the flow field around the droplet as the increasing droplet size increases the Reynolds number. Flow in this region is usually modelled using the classical two-dimensional Karman vortex street, and there exist no 3D equivalents. Therefore to model such oscillation it was necessary to create a new conceptual model to account for the forces both inducing and inhibiting such oscillation. The agreement between the model and experimental results is acceptable for both the radial and transverse oscillations.}, }
@article {pmid16774865, year = {2006}, author = {Longest, PW and Oldham, MJ}, title = {Mutual enhancements of CFD modeling and experimental data: a case study of 1-mum particle deposition in a branching airway model.}, journal = {Inhalation toxicology}, volume = {18}, number = {10}, pages = {761-771}, doi = {10.1080/08958370600748653}, pmid = {16774865}, issn = {1091-7691}, mesh = {Aerosols/*chemistry ; *Computer Simulation ; Humans ; *Models, Anatomic ; *Models, Biological ; Particle Size ; Respiratory Mechanics ; Respiratory System/*anatomy &amp; histology ; }, abstract = {In order to better understand aerosol dynamics and deposition in the complex flow field of the respiratory tract, both in vitro experiments and numerical modeling techniques have widely been employed. Computational fluid dynamics (CFD) modeling offers the flexibility of easily modifying system parameters such as flow rates, particle sizes, system geometry, and heterogeneous outlet conditions. However, a number of numerical errors and artifacts can lead to nonphysical CFD results. Experimental methods offer the advantage of physical realism; however, parameter variation is often difficult. The objective of this study is to illustrate the use of CFD to enhance the understanding of experimental results. In parallel, the selected experimental results have been used to partially validate the CFD predictions. A specific case study has been considered focusing on 1-mum particle depositions in a physiologically realistic bifurcation (PRB) model of respiratory generations 3-5. Previous experiments in this system report a deposition rate of approximately 0.01%. An in-depth CFD analysis has been employed to evaluate two cases of the empirical model. The first case consists of only the PRB double bifurcation geometry. The second case includes a portion of the experimental particle delivery system, which may influence the entering velocity and particle profiles. To assess the influence of upstream transition and turbulence, each of the two cases considered has been evaluated using laminar and low Reynolds number k-omega approximations. Results indicate that both upstream flow effects and turbulent or transitional flow play a significant role in determining the deposition of 1-mum particles in the model considered. Simulating upstream flow effects and laminar flow was required to match the empirically reported deposition fraction and provided a two orders of magnitude improvement over initial CFD estimates. This study highlights the need to consider the effects of experimental particle generation systems on velocity and particle profiles entering respiratory models. Future work is necessary to investigate the mechanisms responsible for the experimentally observed local deposition patterns.}, }
@article {pmid16753293, year = {2007}, author = {Lim, KG and Palmore, GT}, title = {Microfluidic biofuel cells: the influence of electrode diffusion layer on performance.}, journal = {Biosensors &amp; bioelectronics}, volume = {22}, number = {6}, pages = {941-947}, doi = {10.1016/j.bios.2006.04.019}, pmid = {16753293}, issn = {0956-5663}, mesh = {*Bioelectric Energy Sources ; *Electrodes ; Equipment Design ; Equipment Failure Analysis ; Microfluidics/*instrumentation/methods ; }, abstract = {Microfluidic biofuel cells exploit the lack of convective mixing at low Reynolds number to eliminate the need for a physical membrane to separate fuel from oxidant. This paper demonstrates how the length and spacing of electrodes within a microchannel, and thus thickness of the diffusion layer, affects the performance of a microfluidic biofuel cell. It was found that splitting a single electrode into two (or more) smaller electrodes and separating them by a distance equal to three times their length prevents the continuous increase in thickness of a diffusion layer. This change results in a 25% increase in maximum power density compared to a single electrode device with identical electroactive area. Furthermore, we found that the maximum current density of a microfluidic biofuel cell operated with different electrode configurations (i.e., length of cathode) closely matches that predicted by theory.}, }
@article {pmid16730892, year = {2006}, author = {Pełech, R and Milchert, E and Wróbel, R}, title = {Adsorption dynamics of chlorinated hydrocarbons from multi-component aqueous solution onto activated carbon.}, journal = {Journal of hazardous materials}, volume = {137}, number = {3}, pages = {1479-1487}, doi = {10.1016/j.jhazmat.2006.04.023}, pmid = {16730892}, issn = {0304-3894}, mesh = {Adsorption ; Carbon/*chemistry ; Chlorine/*chemistry ; Hydrocarbons/*chemistry ; Models, Chemical ; Solutions ; }, abstract = {The results and a numerical simulation of studies on dynamics of the adsorption from seven-component aqueous solution of light chlorinated hydrocarbons on activated carbon have been presented. Aqueous solution of 1,2-dichloroethane (12DCE), 1,1,2,2-tetrachloroethane (S-TET), chloroform (CHCl(3)), carbon tetrachloride (CCl(4)), 1,1-dichloroethene (VDC), perchloroethene (PER) and 1,1,2-trichloroethene (TRI) was used. Concentrations of chlorohydrocarbons were similar as in wastewater from vinyl chloride plant. A cell model that incorporates the diffusion through a laminar layer of liquid around a particle was used to describe the experimental results. The applied calculation methods, which take kinetics into account, allows to well describe a phenomenon of dynamic adsorption. Mean relative deviations between the experimental and calculated values amounted 17%. The breakthrough curves become steeper along with an increase of the bed height. A consistency of the experimental results with those calculated indicates for a negligible contribution of the axial diffusion on the dynamic adsorption process of light chlorinated hydrocarbons from aqueous solution under the hydrodynamic conditions corresponding to the Reynolds number equal to 1.3. Determined optimal bed height for waste linear flow rate-15 cm/min is in the range 80-120 cm.}, }
@article {pmid16730016, year = {2006}, author = {Wu, RM and Lin, MH and Lin, HY and Hsu, RY}, title = {3D simulations of hydrodynamic drag forces on two porous spheres moving along their centerline.}, journal = {Journal of colloid and interface science}, volume = {301}, number = {1}, pages = {227-235}, doi = {10.1016/j.jcis.2006.04.049}, pmid = {16730016}, issn = {0021-9797}, abstract = {This paper numerically evaluates the hydrodynamic drag force exerted on two highly porous spheres moving steadily along their centerline through a quiescent Newtonian fluid over a Reynolds number ranging from 0.1 to 40. At creeping-flow limit, the drag forces exerted on both spheres were approximately identical. At higher Reynolds numbers the drag force on the leading sphere (sphere #1) was higher than the following sphere (sphere #2), revealing the shading effects produced by sphere #1 on sphere #2. At dimensionless diameter beta<2 (beta=d(f)/2k(0.5), d(f) and k are sphere diameter and interior permeability, respectively), the spheres can be regarded as "no-spheres" limit. At increasing beta for both spheres, the drag force on sphere #2 was increased because of the more difficult advective flow through its interior, and at the same time the drag was reduced owing to the stronger wake flow produced by the denser sphere #1. The competition between these two effects leads to complicated dependence of drag force on sphere #2 on beta value. These effects were minimal when beta became low.}, }
@article {pmid16723037, year = {2006}, author = {Hess, DR and Fink, JB and Venkataraman, ST and Kim, IK and Myers, TR and Tano, BD}, title = {The history and physics of heliox.}, journal = {Respiratory care}, volume = {51}, number = {6}, pages = {608-612}, pmid = {16723037}, issn = {0020-1324}, mesh = {Animals ; Biophysics ; *Helium/history/pharmacology/therapeutic use ; History, 19th Century ; Humans ; Hypoxia/*physiopathology ; *Oxygen/history/pharmacology/therapeutic use ; Respiratory Tract Diseases/drug therapy ; Rheology ; Thermal Conductivity ; Viscosity ; Voice/drug effects ; }, abstract = {Since the discovery of helium in 1868, it has found numerous applications in industry and medicine. Its low density makes helium potentially valuable in respiratory care applications, to reduce work of breathing, improve distribution of ventilation, reduce minute volume requirement, and improve aerosol delivery. This review includes a brief history of the use of heliox (a mixture of helium and oxygen) and addresses issues related to the physics of gas flow when heliox is used. Specifically covered are the Hagen-Poiseuille equation, laminar versus turbulent flow, the Reynolds number, orifice flow, Bernoulli's principle, Graham's law, wave speed, and thermal conductivity.}, }
@article {pmid16712081, year = {2006}, author = {Arratia, PE and Thomas, CC and Diorio, J and Gollub, JP}, title = {Elastic instabilities of polymer solutions in cross-channel flow.}, journal = {Physical review letters}, volume = {96}, number = {14}, pages = {144502}, doi = {10.1103/PhysRevLett.96.144502}, pmid = {16712081}, issn = {0031-9007}, abstract = {When polymer molecules pass near the hyperbolic point of a microchannel cross flow, they are strongly stretched. As the strain rate is varied at low Reynolds number (< 10(-2)), tracer and particle-tracking experiments show that molecular stretching produces two flow instabilities: one in which the velocity field becomes strongly asymmetric, and a second in which it fluctuates nonperiodically in time. The flow is strongly perturbed even far from the region of instability, and this phenomenon can be used to produce mixing.}, }
@article {pmid16711993, year = {2006}, author = {Subramanian, G and Koch, DL}, title = {Centrifugal forces alter streamline topology and greatly enhance the rate of heat and mass transfer from neutrally buoyant particles to a shear flow.}, journal = {Physical review letters}, volume = {96}, number = {13}, pages = {134503}, doi = {10.1103/PhysRevLett.96.134503}, pmid = {16711993}, issn = {0031-9007}, abstract = {Centrifugal forces break the degenerate closed-streamline configuration that occurs in simple shear flow past a neutrally buoyant torque-free particle in the inertialess limit. The broken symmetry allows heat or mass to be convected away in an efficient manner in sharp contrast to the inertialess diffusion-limited scenario. The dimensionless transfer rate, characterized by the Nusselt number, is found to be Nu = 0.33(RePe)(1/3) + O(1) for small but finite Re when RePe >> 1. Here, the particle Reynolds number (Re) is a dimensionless measure of the inertial forces, while the Peclet number (Pe) measures the relative importance of the convective and the diffusive transfer mechanisms. The symmetry-breaking bifurcation is expected to occur in generic shearing flows, and represents a possible means for heat or mass transfer enhancement from the dispersed phase in multiphase systems.}, }
@article {pmid16711991, year = {2006}, author = {Nie, X and Robbins, MO and Chen, S}, title = {Resolving singular forces in cavity flow: multiscale modeling from atomic to millimeter scales.}, journal = {Physical review letters}, volume = {96}, number = {13}, pages = {134501}, doi = {10.1103/PhysRevLett.96.134501}, pmid = {16711991}, issn = {0031-9007}, abstract = {Flow driven by moving a wall that bounds a fluid-filled cavity is a classic example of a multiscale problem. Continuum equations predict that every scale contributes roughly equally to the total force on the moving wall, leading to a logarithmic divergence, and that there is an infinite hierarchy of vortices at the stationary corners. A multiscale approach is developed that retains an atomistic description in key regions. Following the stress over more than six decades in length in systems with characteristic scales of up to millimeters and milliseconds allows us to resolve the singularities and determine the force for the first time. We find a universal dependence on the macroscopic Reynolds number, and large atomistic effects that depend on wall velocity and interactions.}, }
@article {pmid16711931, year = {2006}, author = {Ekiel-Jezewska, ML and Wajnryb, E}, title = {Equilibria for the relative motion of three heavy spheres in Stokes fluid flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {73}, number = {4 Pt 2}, pages = {046309}, doi = {10.1103/PhysRevE.73.046309}, pmid = {16711931}, issn = {1539-3755}, abstract = {Dynamics of three identical solid spheres falling under gravity in low-Reynolds-number fluid flow is investigated. Stationary solutions are found. Their stability is discussed. Phase portraits for two types of symmetric motions are calculated.}, }
@article {pmid16711810, year = {2006}, author = {Aradian, A and Cates, ME}, title = {Minimal model for chaotic shear banding in shear thickening fluids.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {73}, number = {4 Pt 1}, pages = {041508}, doi = {10.1103/PhysRevE.73.041508}, pmid = {16711810}, issn = {1539-3755}, abstract = {We present a minimal model for spatiotemporal oscillation and rheochaos in shear thickening complex fluids at zero Reynolds number. In the model, a tendency towards inhomogeneous flows in the form of shear bands combines with a slow structural dynamics, modeled by delayed stress relaxation. Using Fourier-space numerics, we study the nonequilibrium "phase diagram" of the fluid as a function of a steady mean (spatially averaged) stress, and of the relaxation time for structural relaxation. We find several distinct regions of periodic behavior (oscillating bands, traveling bands, and more complex oscillations) and also regions of spatiotemporal rheochaos. A low-dimensional truncation of the model retains the important physical features of the full model (including rheochaos) despite the suppression of sharply defined interfaces between shear bands. Our model maps onto the FitzHugh-Nagumo model for neural network dynamics, with an unusual form of long-range coupling.}, }
@article {pmid16706596, year = {2006}, author = {Mayeed, MS and Mian, A and Auner, GW and Newaz, GM}, title = {Accumulation of E. Coli bacteria in mini-channel flow.}, journal = {Journal of biomechanical engineering}, volume = {128}, number = {3}, pages = {458-461}, doi = {10.1115/1.2187049}, pmid = {16706596}, issn = {0148-0731}, mesh = {Cell Aggregation/physiology ; Cell Culture Techniques/*instrumentation/methods ; Cell Separation/*instrumentation/methods ; Colony Count, Microbial/*instrumentation/methods ; Computer Simulation ; *Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis ; Escherichia coli/*isolation &amp; purification/physiology ; Flow Cytometry/*instrumentation/methods ; Flow Injection Analysis/instrumentation/methods ; Microfluidic Analytical Techniques/*instrumentation ; Models, Biological ; }, abstract = {The objective of this research is to design and optimize a mini/micro-channel based surface-accumulator of E. coli bacteria to be detected by acoustic wave biosensors. A computational approach has been carried out using the state of the art software, CFD-ACE with water as bacteria bearing fluid. E. coli bacteria have been modeled as random discrete particles tracked by solving the Lagrangian equations. The design challenges are to achieve low shear force (pico-N), high concentration at accumulation, and high enough Reynolds number to avoid bacteria swimming. A range of low Reynolds number (Re) has been considered along with the effects of particle boundary interactions, gravity, Saffman lift, etc. More than two orders of magnitude higher concentration at the accumulation than the inlet concentration, and lower shear force of less than pico-N have been achieved in the optimized designs.}, }
@article {pmid16700024, year = {2006}, author = {de Rochefort, L and Maître, X and Fodil, R and Vial, L and Louis, B and Isabey, D and Croce, C and Darrasse, L and Apiou, G and Caillibotte, G and Bittoun, J and Durand, E}, title = {Phase-contrast velocimetry with hyperpolarized 3He for in vitro and in vivo characterization of airflow.}, journal = {Magnetic resonance in medicine}, volume = {55}, number = {6}, pages = {1318-1325}, doi = {10.1002/mrm.20899}, pmid = {16700024}, issn = {0740-3194}, mesh = {Contrast Media ; *Helium/administration &amp; dosage ; Humans ; Image Enhancement/*methods ; Image Interpretation, Computer-Assisted/*methods ; Isotopes/administration &amp; dosage ; Lung/anatomy &amp; histology/*physiology ; Magnetic Resonance Imaging/instrumentation/*methods ; Phantoms, Imaging ; Pulmonary Ventilation/*physiology ; Rheology/instrumentation/*methods ; }, abstract = {This paper describes a technique that combines radial MRI and phase contrast (PC) to map the velocities of hyperpolarized gases ((3)He) in respiratory airways. The method was evaluated on well known geometries (straight and U-shaped pipes) before it was applied in vivo. Dynamic 2D maps of the three velocity components were obtained from a 10-mm slice with an in-plane spatial resolution of 1.6 mm within 1 s. Integration of the in vitro through-plane velocity over the slice matched the input flow within a relative precision of 6.4%. As expected for the given Reynolds number, a parabolic velocity profile was obtained in the straight pipe. In the U-shaped pipe the three velocity components were measured and compared to a fluid-dynamics simulation so the precision was evaluated as fine as 0.025 m s(-1). The technique also demonstrated its ability to visualize vortices and localize characteristic points, such as the maximum velocity and vortex-center positions. Finally, in vivo feasibility was demonstrated in the human trachea during inhalation.}, }
@article {pmid16688571, year = {2006}, author = {Wu, CH and Yang, RJ}, title = {Improving the mixing performance of side channel type micromixers using an optimal voltage control model.}, journal = {Biomedical microdevices}, volume = {8}, number = {2}, pages = {119-131}, doi = {10.1007/s10544-006-7707-5}, pmid = {16688571}, issn = {1387-2176}, mesh = {Complex Mixtures/*analysis/*chemistry ; Computer Simulation ; *Computer-Aided Design ; Electrochemistry/*instrumentation/methods ; Equipment Design ; Equipment Failure Analysis ; Feedback ; Microfluidic Analytical Techniques/*instrumentation/methods ; Miniaturization ; *Models, Chemical ; Motion ; }, abstract = {Electroosmotic flow in microchannels is restricted to low Reynolds number regimes. Since the inertia forces are extremely weak in such regimes, turbulent conditions do not readily develop, and hence species mixing occurs primarily as a result of diffusion. Consequently, achieving a thorough species mixing generally relies upon the use of extended mixing channels. This paper aims to improve the mixing performance of conventional side channel type micromixers by specifying the optimal driving voltages to be applied to each channel. In the proposed approach, the driving voltages are identified by constructing a simple theoretical scheme based on a 'flow-rate-ratio' model and Kirchhoff's law. The numerical and experimental results confirm that the optimal voltage control approach provides a better mixing performance than the use of a single driving voltage gradient.}, }
@article {pmid16683952, year = {2006}, author = {Chan, WK and Wong, YW}, title = {A review of leakage flow in centrifugal blood pumps.}, journal = {Artificial organs}, volume = {30}, number = {5}, pages = {354-359}, doi = {10.1111/j.1525-1594.2006.00225.x}, pmid = {16683952}, issn = {0160-564X}, mesh = {Centrifugation ; Heart, Artificial/*standards ; Mechanics ; Prosthesis Design ; }, abstract = {This article presents a new approach in determining the functional relationship between the leakage flow in a centrifugal blood pump and various parameters that affect it. While high leakage flow in a blood pump is essential for good washout and can help prevent thrombus formation, excessive leakage flow will result in higher fluid shear stress that may lead to hemolysis. Dimensional analysis is employed to provide a functional relationship between leakage flow rate and other important parameters governing the operation of a centrifugal blood pump. Results showed that pump performance with a smaller gap clearance is clearly superior compared to those of two other similar pumps with larger gap clearances. It was also observed that the nondimensional leakage flow rate varies almost linearly with dimensionless pump head. It also decreases with increasing volume flow rate. A smaller gap clearance will also increase the flow resistance and hence, decrease the nondimensional leakage flow rate. Increasing surface roughness, length of the gap clearance passage, or loss coefficient of the gap geometry will increase losses and hence, decrease the leakage flow rate. It is also interesting to note that for a given pump and gap clearance geometry, the nondimensional leakage flow rate is almost independent of the Reynolds number when specific speed is constant.}, }
@article {pmid16683267, year = {2006}, author = {Dusting, J and Sheridan, J and Hourigan, K}, title = {A fluid dynamics approach to bioreactor design for cell and tissue culture.}, journal = {Biotechnology and bioengineering}, volume = {94}, number = {6}, pages = {1196-1208}, doi = {10.1002/bit.20960}, pmid = {16683267}, issn = {0006-3592}, mesh = {*Bioreactors ; Cell Culture Techniques/*instrumentation ; Computer Simulation ; *Computer-Aided Design ; Equipment Design/methods ; Microfluidics/*instrumentation/methods ; *Models, Theoretical ; Tissue Culture Techniques/*instrumentation/methods ; }, abstract = {The problem of controlling cylindrical tank bioreactor conditions for cell and tissue culture purposes has been considered from a flow dynamics perspective. Simple laminar flows in the vortex breakdown region are proposed as being a suitable alternative to turbulent spinner flask flows and horizontally oriented rotational flows. Vortex breakdown flows have been measured using three-dimensional Stereoscopic particle image velocimetry, and non-dimensionalized velocity and stress distributions are presented. Regions of locally high principal stress occur in the vicinity of the impeller and the lower sidewall. Topological changes in the vortex breakdown region caused by an increase in Reynolds number are reflected in a redistribution of the peak stress regions. The inclusion of submerged scaffold models adds complexity to the flow, although vortex breakdown may still occur. Relatively large stresses occur along the edge of disks jutting into the boundary of the vortex breakdown region.}, }
@article {pmid16606268, year = {2006}, author = {Peixinho, J and Mullin, T}, title = {Decay of turbulence in pipe flow.}, journal = {Physical review letters}, volume = {96}, number = {9}, pages = {094501}, doi = {10.1103/PhysRevLett.96.094501}, pmid = {16606268}, issn = {0031-9007}, abstract = {A novel experiment has been devised which provides direct evidence for critical point behavior in the longstanding problem of the transition to turbulence in a pipe. The novelty lies in the quenching of turbulence by reducing the Reynolds number and observing the decay of disordered motion. Divergence of the time scales implies underlying deterministic dynamics which are analogous to those found in boundary crises in dynamical systems. A modulated wave packet emerges from the long term transients and this coherent state provides evidence for connections with recent theoretical developments.}, }
@article {pmid16605912, year = {2006}, author = {Gañán-Calvo, AM and Herrada, MA and Garstecki, P}, title = {Bubbling in unbounded coflowing liquids.}, journal = {Physical review letters}, volume = {96}, number = {12}, pages = {124504}, doi = {10.1103/PhysRevLett.96.124504}, pmid = {16605912}, issn = {0031-9007}, abstract = {An investigation of the stability of low density and viscosity fluid jets and spouts in unbounded coflowing liquids is presented. A full parametrical analysis from low to high Weber and Reynolds numbers shows that the presence of any fluid of finite density and viscosity inside the hollow jet elicits a transition from an absolute to a convective instability at a finite value of the Weber number, for any value of the Reynolds number. Below that critical value of the Weber number, the absolute character of the instability leads to local breakup, and consequently to local bubbling. Experimental data support our model.}, }
@article {pmid16605910, year = {2006}, author = {Monchaux, R and Ravelet, F and Dubrulle, B and Chiffaudel, A and Daviaud, F}, title = {Properties of steady states in turbulent axisymmetric flows.}, journal = {Physical review letters}, volume = {96}, number = {12}, pages = {124502}, doi = {10.1103/PhysRevLett.96.124502}, pmid = {16605910}, issn = {0031-9007}, abstract = {We experimentally study the properties of mean and most probable velocity fields in a turbulent von Kármán flow. These fields are found to be described by two families of functions, as predicted by a recent statistical mechanics study of 3D axisymmetric flows. We show that these functions depend on the viscosity and on the forcing. Furthermore, when the Reynolds number is increased, we exhibit a tendency for Beltramization of the flow, i.e., a velocity-vorticity alignment. This result provides a first experimental evidence of nonlinearity depletion in nonhomogeneous nonisotropic turbulent flow.}, }
@article {pmid16605651, year = {2006}, author = {Zhou, T and Rinoshika, A and Hao, Z and Zhou, Y and Chua, LP}, title = {Wavelet multiresolution analysis of the three vorticity components in a turbulent far wake.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {73}, number = {3 Pt 2}, pages = {036307}, doi = {10.1103/PhysRevE.73.036307}, pmid = {16605651}, issn = {1539-3755}, abstract = {The main objective of the present study is to examine the characteristics of the vortical structures in a turbulent far wake using the wavelet multiresolution technique by decomposing the vorticity into a number of orthogonal wavelet components based on different central frequencies. The three vorticity components were measured simultaneously using an eight-wire probe at three Reynolds numbers, namely 2000, 4000, and 6000. It is found that the dominant contributions to the vorticity variances are from the intermediate and relatively small-scale structures. The contributions from the large and intermediate-scale structures to the vorticity variances decrease with the increase of Reynolds number. The contributions from the small-scale structures to all three vorticity variances jump significantly when Reynolds number is changed from 2000 to 4000, which is connected to previous observations in the near wake that there is a significant increase in the generation of small-scale structures once the Reynolds number reaches about 5000. This result reinforces the conception that turbulence "remembers" its origin.}, }
@article {pmid16605647, year = {2006}, author = {Guala, M and Liberzon, A and Lüthi, B and Kinzelbach, W and Tsinober, A}, title = {Stretching and tilting of material lines in turbulence: the effect of strain and vorticity.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {73}, number = {3 Pt 2}, pages = {036303}, doi = {10.1103/PhysRevE.73.036303}, pmid = {16605647}, issn = {1539-3755}, abstract = {The Lagrangian evolution of infinitesimal material lines is investigated experimentally through three dimensional particle tracking velocimetry (3D-PTV) in quasihomogeneous turbulence with the Taylor microscale Reynolds number Re(lambda)=50. Through 3D-PTV we access the full tensor of velocity derivatives du(i)/dx(j) along particle trajectories, which is necessary to monitor the Lagrangian evolution of infinitesimal material lines l. By integrating the effect on l of (i) the tensor du(i)/dx(j), (ii) its symmetric part s(ij), (iii) its antisymmetric part r(ij), along particle trajectories, we study the evolution of three sets of material lines driven by a genuine turbulent flow, by "strain only," or by "vorticity only," respectively. We observe that, statistically, vorticity reduces the stretching rate l(i)l(j)s(ij)/l2, altering (by tilting material lines) the preferential orientation between l and the first (stretching) eigenvector lambda1 of the rate of strain tensor. In contrast, s(ij), in "absence" of vorticity, significantly contributes to both tilting and stretching, resulting in an enhanced stretching rate compared to the case of material lines driven by the full tensor du(i)/dx(j). The same trend is observed for the deformation of material volumes.}, }
@article {pmid16605455, year = {2006}, author = {Bandi, MM and Goldburg, WI and Cressman, JR and Pumir, A}, title = {Energy flux fluctuations in a finite volume of turbulent flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {73}, number = {2 Pt 2}, pages = {026308}, doi = {10.1103/PhysRevE.73.026308}, pmid = {16605455}, issn = {1539-3755}, abstract = {The flux of turbulent kinetic energy from large to small spatial scales is measured in a small domain of varying size . The probability distribution function of the flux is obtained using a time-local version of Kolmogorov four-fifths law. The measurements, made at a moderate Reynolds number, show frequent events where the flux is backscattered from small to large scales, their frequency increasing as is decreased. The observations are corroborated by a numerical simulation based on the motion of many particles and on an explicit form of the eddy damping.}, }
@article {pmid16605450, year = {2006}, author = {McComb, WD}, title = {Asymptotic freedom, non-Gaussian perturbation theory, and the application of renormalization group theory to isotropic turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {73}, number = {2 Pt 2}, pages = {026303}, doi = {10.1103/PhysRevE.73.026303}, pmid = {16605450}, issn = {1539-3755}, abstract = {A model equation with an extended range of asymptotic freedom is used as the basis of a non-Gaussian perturbation expansion in powers of the control parameter of the conditional average. Re-expansion in the local Reynolds number allows the systematic rederivation of an earlier, heuristic theory [W. D. McComb and A. G. Watt, Phys. Rev. Lett. 65, 3281 (1990)].}, }
@article {pmid16605448, year = {2006}, author = {Yin, X and Koch, DL and Verberg, R}, title = {Lattice-Boltzmann method for simulating spherical bubbles with no tangential stress boundary conditions.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {73}, number = {2 Pt 2}, pages = {026301}, doi = {10.1103/PhysRevE.73.026301}, pmid = {16605448}, issn = {1539-3755}, abstract = {A lattice-Boltzmann boundary rule has been developed to recover the slip boundary condition at a liquid-gas interface. This rule enables one to use a single-component lattice-Boltzmann model to simulate bubbly flows where bubbles are nearly spherical and coalescence is prohibited. Numerical tests showed this method to be robust and accurate in simulating both steady and unsteady flows around spherical bubbles in the Reynolds number range 0<Re<30.}, }
@article {pmid16578875, year = {2002}, author = {Barenblatt, GI and Chorin, AJ and Prostokishin, VM}, title = {A model of a turbulent boundary layer with a nonzero pressure gradient.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {99}, number = {9}, pages = {5772-5776}, pmid = {16578875}, issn = {0027-8424}, abstract = {According to a model of the turbulent boundary layer that we propose, in the absence of external turbulence the intermediate region between the viscous sublayer and the external flow consists of two sharply separated self-similar structures. The velocity distribution in these structures is described by two different scaling laws. The mean velocity u in the region adjacent to the viscous sublayer is described by the previously obtained Reynolds-number-dependent scaling law Φ = u / u(*) = Aη(α), A = 1/√3 In ReΛ + 5/2, α = 3/2 in ReΛ η = u(*)y/v. (Here u(*) is the dynamic or friction velocity, y is the distance from the wall, ν the kinetic viscosity of the fluid, and the Reynolds number ReΛ is well defined by the data.) In the region adjacent to the external flow, the scaling law is different: Φ = Bη(β). The power β for zero-pressure-gradient boundary layers was found by processing various experimental data and is close (with some scatter) to 0.2. We show here that for nonzero-pressure-gradient boundary layers, the power β is larger than 0.2 in the case of an adverse pressure gradient and less than 0.2 for a favorable pressure gradient. Similarity analysis suggests that both the coefficient Β and the power β depend on ReΛ and on a new dimensionless parameter P proportional to the pressure gradient. Recent experimental data of Perry, Marušić, and Jones were analyzed, and the results are in agreement with the model we propose.}, }
@article {pmid16573094, year = {2006}, author = {Wang, R and Lin, J}, title = {Numerical analysis on a passive chaotic micromixer with helical microchannel.}, journal = {Journal of nanoscience and nanotechnology}, volume = {6}, number = {1}, pages = {190-194}, pmid = {16573094}, issn = {1533-4880}, mesh = {Computer Simulation ; Diffusion ; Models, Molecular ; Models, Theoretical ; Nanostructures/*chemistry ; Nonlinear Dynamics ; }, abstract = {In order to improve the mixing efficiency, the diffusion and mixing of species in the helical micro-mixer are simulated numerically. The results show that the mixing efficiency in the helical micromixer is much higher than that in the straight micro-channel and obviously higher than that in the serpentine micro-channel when Reynolds number is low. At high Reynolds number, even though the mixing efficiency in the helical micro-mixer is still much higher than that in the straight micro-channel, no obvious difference of mixing efficiency in the helical micro-mixer and serpentine micro-channel is found. The conclusions are helpful to optimize the structure of the micro-mixer.}, }
@article {pmid16572217, year = {2006}, author = {Mott, DR and Howell, PB and Golden, JP and Kaplan, CR and Ligler, FS and Oran, ES}, title = {Toolbox for the design of optimized microfluidic components.}, journal = {Lab on a chip}, volume = {6}, number = {4}, pages = {540-549}, doi = {10.1039/b516459a}, pmid = {16572217}, issn = {1473-0197}, mesh = {Microfluidic Analytical Techniques/*instrumentation/*methods ; Microfluidics ; Models, Theoretical ; Viscosity ; }, abstract = {A computational "toolbox" for the a priori design of optimized microfluidic components is presented. These components consist of a microchannel under low-Reynolds number, pressure-driven flow, with an arrangement of grooves cut into the top and bottom to generate a tailored cross-channel flow. An advection map for each feature (i.e., groove of a particular shape and orientation) predicts the lateral transport of fluid within the channel due to that feature. We show that applying these maps in sequence generates an excellent representation of the outflow distribution for complex designs that combine these basic features. The effect of the complex three-dimensional flow field can therefore be predicted without solving the governing flow equations through the composite geometry, and the resulting distribution of fluids in the channel is used to evaluate how well a component performs a specified task. The generation and use of advection maps is described, and the toolbox is applied to determine optimal combinations of features for specified mixer sizes and mixing metrics.}, }
@article {pmid16553954, year = {2006}, author = {Ferrari, M and Werner, GS and Bahrmann, P and Richartz, BM and Figulla, HR}, title = {Turbulent flow as a cause for underestimating coronary flow reserve measured by Doppler guide wire.}, journal = {Cardiovascular ultrasound}, volume = {4}, number = {}, pages = {14}, pmid = {16553954}, issn = {1476-7120}, mesh = {Artifacts ; *Blood Flow Velocity ; *Coronary Circulation ; Coronary Vessels/*diagnostic imaging/*physiopathology ; Echocardiography, Doppler/*instrumentation/*methods ; Equipment Design ; Equipment Failure Analysis ; Female ; Humans ; Image Interpretation, Computer-Assisted/instrumentation/*methods ; Male ; Middle Aged ; Nonlinear Dynamics ; Reproducibility of Results ; Sensitivity and Specificity ; }, abstract = {BACKGROUND: Doppler-tipped coronary guide-wires (FW) are well-established tools in interventional cardiology to quantitatively analyze coronary blood flow. Doppler wires are used to measure the coronary flow velocity reserve (CFVR). The CFVR remains reduced in some patients despite anatomically successful coronary angioplasty. It was the aim of our study to test the influence of changes in flow profile on the validity of intra-coronary Doppler flow velocity measurements in vitro. It is still unclear whether turbulent flow in coronary arteries is of importance for physiologic studies in vivo.<br><br>METHODS: We perfused glass pipes of defined inner diameters (1.5-5.5 mm) with heparinized blood in a pulsatile flow model. Laminar and turbulent flow profiles were achieved by varying the flow velocity. The average peak velocity (APV) was recorded using 0.014 inch FW. Flow velocity measurements were also performed in 75 patients during coronary angiography. Coronary hyperemia was induced by intra-coronary injection of adenosine. The APV maximum was taken for further analysis. The mean luminal diameter of the coronary artery at the region of flow velocity measurement was calculated by quantitative angiography in two orthogonal planes.<br><br>RESULTS: In vitro, the measured APV multiplied with the luminal area revealed a significant correlation to the given perfusion volumes in all diameters under laminar flow conditions (r2 > 0.85). Above a critical Reynolds number of 500--indicating turbulent flow--the volume calculation derived by FW velocity measurement underestimated the actual rate of perfusion by up to 22.5 % (13 +/- 4.6 %). In vivo, the hyperemic APV was measured irrespectively of the inherent deviation towards lower velocities. In 15 of 75 patients (20%) the maximum APV exceeded the velocity of the critical Reynolds number determined by the in vitro experiments.<br><br>CONCLUSION: Doppler guide wires are a valid tool for exact measurement of coronary flow velocity below a critical Reynolds number of 500. Reaching a coronary flow velocity above the velocity of the critical Reynolds number may result in an underestimation of the CFVR caused by turbulent flow. This underestimation of the flow velocity may reach up to 22.5 % compared to the actual volumetric flow. Cardiologists should consider this phenomena in at least 20 % of patients when measuring CFVR for clinical decision making.}, }
@article {pmid16543642, year = {2006}, author = {Seki, J and Satomura, Y and Ooi, Y and Yanagida, T and Seiyama, A}, title = {Velocity profiles in the rat cerebral microvessels measured by optical coherence tomography.}, journal = {Clinical hemorheology and microcirculation}, volume = {34}, number = {1-2}, pages = {233-239}, pmid = {16543642}, issn = {1386-0291}, mesh = {Animals ; Arterioles ; *Blood Flow Velocity ; Cerebrovascular Circulation/*physiology ; Male ; Microcirculation ; Pulsatile Flow ; Rats ; Rats, Wistar ; Time Factors ; *Tomography, Optical Coherence ; }, abstract = {In order to analyze cerebral hemodynamics and its change following neural activation, the cross-sectional profiles of blood flow velocity in the rat pial microvessels and their temporal changes were measured in vivo using Doppler OCT technique (Doppler optical coherence tomography). The OCT system used in this study has axial resolution of 11 microm and lateral resolution about 14 microm in the cortical tissue. The velocity distributions along the vertical diameter of pial microvessels in a cranial window of the rats were measured at short time intervals by scanning the OCT sampling point repeatedly. The velocity profiles obtained in the pial arterioles were parabolic at any phase, although the centerline velocity pulsated following heart beats with amplitude as large as 50% of the temporal mean velocity. It indicates that the blood flow in the pial microvessels is a quasi-steady laminar flow, which is consistent with the flow expected for the case of a small Reynolds number and a small frequency parameter. The stimulus-induced increase in velocity pulsation was much larger than the increase in the mean velocity, which places a restriction on the mechanism of regulating the regional cerebral blood flow and blood volume. The results obtained in this study showed that the Doppler OCT has a potential of measuring velocity profiles and their temporal changes with both high temporal and spatial resolutions for the pial microvessels with diameter up to 200 microm.}, }
@article {pmid16536493, year = {2006}, author = {Muruganathan, R and Zhang, Y and Fischer, TM}, title = {Interfacial thermocapillary vortical flow for microfluidic mixing.}, journal = {Journal of the American Chemical Society}, volume = {128}, number = {11}, pages = {3474-3475}, doi = {10.1021/ja0566883}, pmid = {16536493}, issn = {0002-7863}, mesh = {1,2-Dipalmitoylphosphatidylcholine/*chemistry ; Microfluidic Analytical Techniques/*methods ; Phosphatidylserines/*chemistry ; Surface-Active Agents/*chemistry ; Temperature ; Viscosity ; }, abstract = {We present a method for the mixing of fluids in a quasi two-dimensional system with low Reynolds number by means of generating a vortical flow. A two-dimensional cavitation bubble is induced in liquid-expanded phase by locally heating a Langmuir monolayer at the air/liquid interface with an IR laser. The laser-induced cavitation bubble works as a microfluidic pump and generates a thermocapillary flow around the pump. As a result, the surrounding liquid-expanded phase flows in one direction. Perturbing the thermocapillary flow with solid folds that are created by compression and reexpansion of the monolayer induces the vortical flow behind the folds. Applying the equation of creeping flow, we find a torque halfway from the center causing the vortical flow. The vorticity created in this way stretches the liquid-expanded and gaseous phase in the azimuthal direction and at the same time thins both phases in the radial direction. If the vortical flow could be maintained long enough to reach a radial thinning that would allow the interdiffusion of surfactants at the surface, then this technique would open a route for the effective two-dimensional microfluidic mixing at low Reynolds numbers.}, }
@article {pmid16533511, year = {2007}, author = {Worth Longest, P and Vinchurkar, S}, title = {Validating CFD predictions of respiratory aerosol deposition: effects of upstream transition and turbulence.}, journal = {Journal of biomechanics}, volume = {40}, number = {2}, pages = {305-316}, doi = {10.1016/j.jbiomech.2006.01.006}, pmid = {16533511}, issn = {0021-9290}, mesh = {*Aerosols ; Animals ; *Biomechanical Phenomena ; Exhalation/*physiology ; Humans ; *Models, Biological ; Predictive Value of Tests ; }, abstract = {A number of computational fluid dynamics (CFD) studies have explored local deposition patterns of inhaled aerosols in the respiratory tract. These studies have highlighted the effects of multiple physiologic, geometric, and particle characteristics on deposition. However, very few studies have reported local or sub-branch quantitative comparisons to in vitro particle deposition data. The objective of this study is to numerically investigate the effects of transition and turbulence on highly localized particle deposition in a respiratory double bifurcation model in order to quantitatively validate CFD results. To perform the validations, local comparisons have been made to a specific in vitro case study of 10 microm particles depositing in a model of respiratory generations G3-G5. To achieve this objective, two geometric cases have been considered. The first case includes only the double bifurcation model. The second case includes a portion of the experimental particle delivery geometry, where transitional flow is expected. To evaluate the effectiveness of two-equation turbulence models in this system, the flow field solutions have been computed using laminar, standard k-omega, and low Reynolds number (LRN) k-omega approximations. Results indicate that even though the Reynolds number remained below the critical limit required for full turbulence, transition and turbulence have a significant impact on the flow field and local particle deposition patterns. For the experimental case considered, turbulence impacted the local deposition of 10 microm particles primarily by influencing the initial velocity and particle profiles. As such, both the laminar and LRN k-omega flow models provided good local quantitative matches to the in vitro deposition data, provided that the correct initial particle profile was specified. Implications of this study include the need for local quantitative validations of particle deposition results, the importance of correct inlet conditions, and the need to consider upstream effects in experimental and computational studies of the respiratory tract. Applications of these results to realistic respiratory geometries will require consideration on upstream flow conditions in the lung, transient flow, and intermittent turbulent structures.}, }
@article {pmid16532621, year = {2006}, author = {Chan, KY and Fujioka, H and Bartlett, RH and Hirschl, RB and Grotberg, JB}, title = {Pulsatile flow and mass transport over an array of cylinders: gas transfer in a cardiac-driven artificial lung.}, journal = {Journal of biomechanical engineering}, volume = {128}, number = {1}, pages = {85-96}, doi = {10.1115/1.2133761}, pmid = {16532621}, issn = {0148-0731}, support = {HL69420/HL/NHLBI NIH HHS/United States ; }, mesh = {*Artificial Organs ; Biological Transport, Active/physiology ; Blood Flow Velocity/physiology ; Computer Simulation ; Equipment Failure Analysis/methods ; Gases/*metabolism ; Heart/*physiology ; Humans ; Lung/*blood supply/*physiology/surgery ; *Models, Cardiovascular ; Pulmonary Circulation/physiology ; Pulmonary Gas Exchange/*physiology ; Pulsatile Flow/physiology ; Respiratory Transport/physiology ; }, abstract = {The pulsatile flow and gas transport of a Newtonian passive fluid across an array of cylindrical microfibers are numerically investigated. It is related to an implantable, artificial lung where the blood flow is driven by the right heart. The fibers are modeled as either squared or staggered arrays. The pulsatile flow inputs considered in this study are a steady flow with a sinusoidal perturbation and a cardiac flow. The aims of this study are twofold: identifying favorable array geometry/spacing and system conditions that enhance gas transport; and providing pressure drop data that indicate the degree of flow resistance or the demand on the right heart in driving the flow through the fiber bundle. The results show that pulsatile flow improves the gas transfer to the fluid compared to steady flow. The degree of enhancement is found to be significant when the oscillation frequency is large, when the void fraction of the fiber bundle is decreased, and when the Reynolds number is increased; the use of a cardiac flow input can also improve gas transfer. In terms of array geometry, the staggered array gives both a better gas transfer per fiber (for relatively large void fraction) and a smaller pressure drop (for all cases). For most cases shown, an increase in gas transfer is accompanied by a higher pressure drop required to power the flow through the device.}, }
@article {pmid16486712, year = {2006}, author = {Courvoisier, A and Hughes, DW and Tobias, SM}, title = {Alpha effect in a family of chaotic flows.}, journal = {Physical review letters}, volume = {96}, number = {3}, pages = {034503}, doi = {10.1103/PhysRevLett.96.034503}, pmid = {16486712}, issn = {0031-9007}, abstract = {We perform numerical experiments to calculate the kinematic alpha effect for a family of maximally helical, chaotic flows with a range of correlation times. We find that the value of depends on the structure of the flow, on its correlation time and on the magnetic Reynolds number in a nontrivial way. Furthermore, it seems that there is no clear relation between alpha and the helicity of the flow, contrary to what is often assumed for the parametrization of mean-field dynamo models.}, }
@article {pmid16486587, year = {2006}, author = {Xu, H and Bourgoin, M and Ouellette, NT and Bodenschatz, E and , }, title = {High order Lagrangian velocity statistics in turbulence.}, journal = {Physical review letters}, volume = {96}, number = {2}, pages = {024503}, doi = {10.1103/PhysRevLett.96.024503}, pmid = {16486587}, issn = {0031-9007}, abstract = {We report measurements of the Lagrangian velocity structure functions of orders 1 through 10 in a high Reynolds number (Taylor microscale Reynolds numbers of up to R(lambda) = 815) turbulence experiment. Passive tracer particles are tracked optically in three dimensions and in time, and velocities are calculated from the particle tracks. The structure function anomalous scaling exponents are measured both directly and using extended self-similarity and are found to be more intermittent than their Eulerian counterparts. Classical Kolmogorov inertial range scaling is also found for all structure function orders at times that trend downward as the order increases. The temporal shift of this classical scaling behavior is observed to saturate as the structure function order increases at times shorter than the Kolmogorov time scale.}, }
@article {pmid16486585, year = {2006}, author = {Arratia, PE and Gollub, JP}, title = {Predicting the progress of diffusively limited chemical reactions in the presence of chaotic advection.}, journal = {Physical review letters}, volume = {96}, number = {2}, pages = {024501}, doi = {10.1103/PhysRevLett.96.024501}, pmid = {16486585}, issn = {0031-9007}, abstract = {The effects of chaotic advection and diffusion on fast chemical reactions in two-dimensional fluid flows are investigated using experimentally measured stretching fields and fluorescent monitoring of the local concentration. Flow symmetry, Reynolds number, and mean path length affect the spatial distribution and time dependence of the reaction product. A single parameter lambdaN , where lambda is the mean Lyapunov exponent N and is the number of mixing cycles, can be used to predict the time-dependent total product for flows having different dynamical features.}, }
@article {pmid16486361, year = {2005}, author = {Cichowlas, C and Bonaïti, P and Debbasch, F and Brachet, M}, title = {Effective dissipation and turbulence in spectrally truncated euler flows.}, journal = {Physical review letters}, volume = {95}, number = {26}, pages = {264502}, doi = {10.1103/PhysRevLett.95.264502}, pmid = {16486361}, issn = {0031-9007}, abstract = {A new transient regime in the relaxation towards absolute equilibrium of the conservative and time-reversible 3D Euler equation with a high-wave-number spectral truncation is characterized. Large-scale dissipative effects, caused by the thermalized modes that spontaneously appear between a transition wave number and the maximum wave number, are calculated using fluctuation dissipation relations. The large-scale dynamics is found to be similar to that of high-Reynolds number Navier-Stokes equations and thus obeys (at least approximately) Kolmogorov scaling.}, }
@article {pmid16486271, year = {2006}, author = {Shankar, V and Sahu, AK}, title = {Suppression of instability in liquid flow down an inclined plane by a deformable solid layer.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {73}, number = {1 Pt 2}, pages = {016301}, doi = {10.1103/PhysRevE.73.016301}, pmid = {16486271}, issn = {1539-3755}, abstract = {The linear stability of a liquid layer flowing down an inclined plane lined with a deformable, viscoelastic solid layer is analyzed in order to determine the effect of the elastohydrodynamic coupling between the liquid flow and solid deformation on the free-surface instability in the liquid layer. The stability of this two-layer system is characterized by two qualitatively different interfacial instability modes: In the absence of the deformable solid layer, the free surface of the liquid film undergoes a long-wave instability due to fluid inertia. With the presence of the deformable solid layer, the interface between the fluid and the solid undergoes a finite-wavelength instability when the deformable solid becomes sufficiently soft. The effect of the solid layer deformability on the free-surface instability of the liquid film flow is analyzed using a long-wave asymptotic analysis. The asymptotic results show that for a fixed Reynolds number and inclination angle, the free-surface instability is completely suppressed in the long-wave limit when the nondimensional (inverse) solid elasticity parameter Gamma=Va eta/(GR)increases beyond a critical value. Here, Va is the average velocity of the liquid film flow, eta is the viscosity of the liquid, G is the shear modulus of the solid layer, and is R the thickness of the liquid layer. The predictions of the asymptotic analysis are verified and extended to finite wavelengths using a numerical solution, and this indicates that the suppression of the free-surface instability indeed continues to finite wavelength disturbances. Further increase of Gamma is found to have two consequences: first, the interface between the liquid and the deformable solid layer could become unstable at finite wavelengths; second, the free-surface interfacial mode could also become unstable at finite wavelengths due to an increase in solid layer deformability. However, our numerical results demonstrate that, for a given average velocity, there exists a sufficient window in the value of shear modulus G where both the unstable modes are absent at all wavelengths. Our study therefore suggests that soft solid layer coatings could potentially provide a passive method of suppressing free-surface instabilities in liquid film flows.}, }
@article {pmid16486102, year = {2005}, author = {Sun, C and Xia, KQ}, title = {Scaling of the Reynolds number in turbulent thermal convection.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {72}, number = {6 Pt 2}, pages = {067302}, doi = {10.1103/PhysRevE.72.067302}, pmid = {16486102}, issn = {1539-3755}, abstract = {A riddle in turbulent thermal convection is the apparent dispersion from 0.42 to 0.5 in the value of the scaling exponent of experimentally measured Reynolds number Re approximately Ragamma, where Ra is the Rayleigh number. The measured Re may be divided into two groups: one based on the circulation frequency of the mean wind and the other based on a directly measured velocity. With new experimental results we show that in frequency measurements the dispersion in gamma is a result of the evolution in the circulation path of the wind, and that in the velocity measurements it is caused by the inclusion of a counterflow in the mean velocity. When these factors are properly accounted for both groups give gamma=0.5, which may imply that a single mechanism is driving the flow for both low and high values of Ra.}, }
@article {pmid16486063, year = {2005}, author = {Chu, AK}, title = {Linear stability of acoustic streaming flows in microchannels.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {72}, number = {6 Pt 2}, pages = {066311}, doi = {10.1103/PhysRevE.72.066311}, pmid = {16486063}, issn = {1539-3755}, abstract = {We study the stability of acoustic streaming flows of fluids induced by a small-amplitude surface acoustic wave propagating along the walls of a confined parallel-plane microchannel or microslab in the incompressible flow regime. The secondary (Navier) slip flows are of negligible effect on the stability characteristic compared with the primary (Navier) slip flow. The governing equation, which was derived by considering the weakly nonlinear coupling between the wavy interface and the viscous fluid, is obtained by taking into account the (Navier) slip conditions and then the eigenvalue problem is solved by a verified numerical code together with the associated dynamic and kinematic conditions. The value of the critical Reynolds number was found to be near 1441 which is smaller than the value 5772 for conventional pressure-driven flows.}, }
@article {pmid16486059, year = {2005}, author = {Bergthorson, JM and Sone, K and Mattner, TW and Dimotakis, PE and Goodwin, DG and Meiron, DI}, title = {Impinging laminar jets at moderate Reynolds numbers and separation distances.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {72}, number = {6 Pt 2}, pages = {066307}, doi = {10.1103/PhysRevE.72.066307}, pmid = {16486059}, issn = {1539-3755}, abstract = {An experimental and numerical study of impinging, incompressible, axisymmetric, laminar jets is described, where the jet axis of symmetry is aligned normal to the wall. Particle streak velocimetry (PSV) is used to measure axial velocities along the centerline of the flow field. The jet-nozzle pressure drop is measured simultaneously and determines the Bernoulli velocity. The flow field is simulated numerically by an axisymmetric Navier-Stokes spectral-element code, an axisymmetric potential-flow model, and an axisymmetric one-dimensional stream-function approximation. The axisymmetric viscous and potential-flow simulations include the nozzle in the solution domain, allowing nozzle-wall proximity effects to be investigated. Scaling the centerline axial velocity by the Bernoulli velocity collapses the experimental velocity profiles onto a single curve that is independent of the nozzle-to-plate separation distance. Axisymmetric direct numerical simulations yield good agreement with experiment and confirm the velocity profile scaling. Potential-flow simulations reproduce the collapse of the data; however, viscous effects result in disagreement with experiment. Axisymmetric one-dimensional stream-function simulations can predict the flow in the stagnation region if the boundary conditions are correctly specified. The scaled axial velocity profiles are well characterized by an error function with one Reynolds-number-dependent parameter. Rescaling the wall-normal distance by the boundary-layer displacement-thickness-corrected diameter yields a collapse of the data onto a single curve that is independent of the Reynolds number. These scalings allow the specification of an analytical expression for the velocity profile of an impinging laminar jet over the Reynolds number range investigated of .}, }
@article {pmid16470882, year = {2006}, author = {Peter, CP and Suzuki, Y and Büchs, J}, title = {Hydromechanical stress in shake flasks: correlation for the maximum local energy dissipation rate.}, journal = {Biotechnology and bioengineering}, volume = {93}, number = {6}, pages = {1164-1176}, doi = {10.1002/bit.20827}, pmid = {16470882}, issn = {0006-3592}, mesh = {*Algorithms ; *Bioreactors ; Culture Media/chemistry ; Rheology ; Stress, Mechanical ; Viscosity ; }, abstract = {Shake flasks are widely used in biotechnological process research. Bioprocesses for which hydromechanical stress may become the rate controlling parameter include those where oils are applied as carbon sources, biotransformation of compounds with low solubility in the aqueous phase, or processes employing animal, plant, or filamentous microorganisms. In this study, the maximum local energy dissipation rate as the measure for hydromechanical stress is characterized in shake flasks by measuring the maximum stable drop size. The theoretical basis for the method is that the maximum stable drop diameter in a coalescence inhibited liquid/liquid dispersion is only a function of the maximum local energy dissipation rate and not of the dispersing apparatus. The maximum local energy dissipation rate is obtained by comparing the drop diameters in shake flasks to those in a stirred tank reactor. At the same volumetric power consumption, the maximum energy dissipation rate in shake flasks is about 10 times lower than in stirred tank reactors explaining the common observation of considerable differences in the morphology of hydromechanically sensitive cells between these two reactor types. At the same volumetric power consumption, the maximum local energy dissipation rate in baffled and in unbaffled shake flasks is very similar. A correlation is presented to quantify the maximum local energy dissipation rate in shake flasks as a function of the operating conditions. Non-negligible drop viscosity may be considered by known literature correlations. Further, from dispersion experiments a critical Reynolds number of about 60,000 is proposed for turbulent flow in unbaffled shake flasks.}, }
@article {pmid16468925, year = {2003}, author = {Kwang-Hua Chu, A}, title = {Theoretical study of stability problems for transport in a deformable microfabricated channel.}, journal = {IEE proceedings. Nanobiotechnology}, volume = {150}, number = {1}, pages = {21-23}, doi = {10.1049/ip-nbt:20030570}, pmid = {16468925}, issn = {1478-1581}, abstract = {We investigate the stability problem related to the basic flows induced by peristaltic transport within the bounded deformable walls which are common in micro- andor nanobiotechnological applications. The neutral stability boundary is obtained by solving the relevant Orr-Sommerfeld equation via a verified preconditioned complex-matrix solver. The critical Reynolds number (when the wall is deformable) is 2886.5 which is much less than the conventional rigid-wall case (approximately 5772, obtained by Orszag based on the spectral method).}, }
@article {pmid16465875, year = {2005}, author = {Lin, JZ and Wang, YL and Zhang, WF}, title = {Sedimentation of short cylindrical pollutants with mechanical contacts.}, journal = {Journal of environmental sciences (China)}, volume = {17}, number = {6}, pages = {906-911}, pmid = {16465875}, issn = {1001-0742}, mesh = {Computer Simulation ; *Environmental Pollutants ; *Models, Theoretical ; Particle Size ; }, abstract = {Lattice Boltzmann method and elastic particle collision model were used to investigate the sedimentation of short cylindrical pollutant particles with mechanical contacts for varying bulk number density epsilon and terminal Reynolds number ReT. The corresponding experiments were performed as a comparison. The clusters of pollutant particles with an inverted "T" structure were observed, the pollutant particles for high epsilon and large ReT scattered wider than that for low epsilon and small ReT. The sedimentation velocities increased suddenly at the initial stage, then decreased drastically, after that swayed around and approached to a steady value. The time to steady state did not depend on epsilon and ReT. The effect of particle interactions was to hinder the average sedimentation velocity, and hindrance was directly proportional to epsilon. The orientation distributions of pollutant particles depended on ReT and epsilon, especially on the former. Both the standard deviations of vertical and horizontal velocity, the former was larger than the latter, were nearly independent on epsilon and ReT.}, }
@article {pmid16391346, year = {2006}, author = {Bejan, A and Marden, JH}, title = {Unifying constructal theory for scale effects in running, swimming and flying.}, journal = {The Journal of experimental biology}, volume = {209}, number = {Pt 2}, pages = {238-248}, doi = {10.1242/jeb.01974}, pmid = {16391346}, issn = {0022-0949}, mesh = {Animals ; Biomechanical Phenomena ; Biophysical Phenomena ; *Biophysics ; Body Size ; Flight, Animal/*physiology ; *Models, Theoretical ; Running/*physiology ; Swimming/*physiology ; }, abstract = {Biologists have treated the view that fundamental differences exist between running, flying and swimming as evident, because the forms of locomotion and the animals are so different: limbs and wings vs body undulations, neutrally buoyant vs weighted bodies, etc. Here we show that all forms of locomotion can be described by a single physics theory. The theory is an invocation of the principle that flow systems evolve in such a way that they destroy minimum useful energy (exergy, food). This optimization approach delivers in surprisingly direct fashion the observed relations between speed and body mass (M(b)) raised to 1/6, and between frequency (stride, flapping) and M(b)(-1/6), and shows why these relations hold for running, flying and swimming. Animal locomotion is an optimized two-step intermittency: an optimal balance is achieved between the vertical loss of useful energy (lifting the body weight, which later drops), and the horizontal loss caused by friction against the surrounding medium. The theory predicts additional features of animal design: the Strouhal number constant, which holds for running as well as flying and swimming, the proportionality between force output and mass in animal motors, and the fact that undulating swimming and flapping flight occur only if the body Reynolds number exceeds approximately 30. This theory, and the general body of work known as constructal theory, together now show that animal movement (running, flying, swimming) and fluid eddy movement (turbulent structure) are both forms of optimized intermittent movement.}, }
@article {pmid16389077, year = {2006}, author = {Yang, XL and Liu, Y and So, RM and Yang, JM}, title = {The effect of inlet velocity profile on the bifurcation COPD airway flow.}, journal = {Computers in biology and medicine}, volume = {36}, number = {2}, pages = {181-194}, doi = {10.1016/j.compbiomed.2004.11.002}, pmid = {16389077}, issn = {0010-4825}, mesh = {*Computer Simulation ; Humans ; Lung/pathology/physiopathology ; Models, Anatomic ; *Models, Biological ; Pressure ; Pulmonary Disease, Chronic Obstructive/pathology/*physiopathology ; Respiratory Mechanics ; }, abstract = {The effect of inlet velocity profile on the flow features in obstructed airways is investigated in this study. In reality, the inlet velocity distributions on such models, which are extracted from medial branches of natural human lung, should be neither uniform, nor symmetric parabolic, but skewed-parabolic due to having been skewed by the upper carina ridges. Four different three-dimensional three-generation models based on the 23 generations model of Weibel have been considered, respectively. The fully three-dimensional incompressible laminar Navier-Stokes equations and continuity equation have been solved using CFD solver on unstructured tetrahedral meshes. To reduce the complexity of the simulations, only one Reynolds number of 900 was used in this calculation. Four types of inlet boundary conditions, namely uniform, parabolic, positive-skewed parabolic (skewed to the positive x-direction), and negative-skewed parabolic, were imposed on the obstructed airway models, which were considered to be obstructed at either the second generation or the third generation airways, respectively. The results show that the inlet velocity profile has significant influence on the flow patterns, mass distributions, and pressure drops in either the symmetric model, or the three obstructed models. The three generation airways may not be enough to study the bifurcation flow in chronic obstructive pulmonary disease (COPD) airways, and a four-generation or more airway model is necessary to get better predictive results.}, }
@article {pmid16384384, year = {2005}, author = {Schneider, K and Farge, M}, title = {Decaying two-dimensional turbulence in a circular container.}, journal = {Physical review letters}, volume = {95}, number = {24}, pages = {244502}, doi = {10.1103/PhysRevLett.95.244502}, pmid = {16384384}, issn = {0031-9007}, abstract = {We present direct numerical simulations of two-dimensional decaying turbulence at initial Reynolds number 5 x 10(4) in a circular container with no-slip boundary conditions. Starting with random initial conditions the flow rapidly exhibits self-organization into coherent vortices. We study their formation and the role of the viscous boundary layer on the production and decay of integral quantities. The no-slip wall produces vortices which are injected into the bulk flow and tend to compensate the enstrophy dissipation. The self-organization of the flow is reflected by the transition of the initially Gaussian vorticity probability density function (PDF) towards a distribution with exponential tails. Because of the presence of coherent vortices the pressure PDF become strongly skewed with exponential tails for negative values.}, }
@article {pmid16384145, year = {2005}, author = {Davidson, PA and Pearson, BR}, title = {Identifying turbulent energy distributions in real, rather than fourier, space.}, journal = {Physical review letters}, volume = {95}, number = {21}, pages = {214501}, doi = {10.1103/PhysRevLett.95.214501}, pmid = {16384145}, issn = {0031-9007}, abstract = {It has been suggested that the equilibrium-range properties of high-Reynolds number turbulence are more readily observed in spectral space, using E(k) or T(k), than in real space, using second- or third-order structure functions. For example, the -5/3 law is usually easier to see in experimental data than the equivalent 2/3 law. We argue that this is not an implicit feature of a real-space description of turbulence. Rather, it is because the second-order structure function mixes small and large-scale information. To remedy this problem we adopt a real-space function, the signature function, which plays the role of an energy density, somewhat analogous to E(k). In this Letter we determine the form of the signature function in a variety of turbulent flows. We find that dissipation-range phenomena, such as the so-called bottleneck effect, are evident in the signature function, while absent in the structure function.}, }
@article {pmid16384062, year = {2005}, author = {Hernandez-Ortiz, JP and Stoltz, CG and Graham, MD}, title = {Transport and collective dynamics in suspensions of confined swimming particles.}, journal = {Physical review letters}, volume = {95}, number = {20}, pages = {204501}, doi = {10.1103/PhysRevLett.95.204501}, pmid = {16384062}, issn = {0031-9007}, abstract = {Direct simulations of large populations of confined hydrodynamically interacting swimming particles at low Reynolds number are performed. Hydrodynamic coupling between the swimmers leads to large-scale coherent vortex motions in the flow and regimes of anomalous diffusion that are consistent with experimental observations. At low concentrations, swimmers propelled from behind (like spermatazoa) strongly migrate toward solid surfaces in agreement with simple theoretical considerations; at higher concentrations this localization is disrupted by the large-scale coherent motions.}, }
@article {pmid16383758, year = {2005}, author = {Mininni, PD and Montgomery, DC}, title = {Low magnetic Prandtl number dynamos with helical forcing.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {72}, number = {5 Pt 2}, pages = {056320}, doi = {10.1103/PhysRevE.72.056320}, pmid = {16383758}, issn = {1539-3755}, abstract = {We present direct numerical simulations of dynamo action in a forced Roberts flow. The behavior of the dynamo is followed as the mechanical Reynolds number is increased, starting from the laminar case until a turbulent regime is reached. The critical magnetic Reynolds for dynamo action is found, and in the turbulent flow it is observed to be nearly independent on the magnetic Prandtl number in the range from approximately 0.3 to approximately 0.1. Also the dependence of this threshold with the amount of mechanical helicity in the flow is studied. For the different regimes found, the configuration of the magnetic and velocity fields in the saturated steady state are discussed.}, }
@article {pmid16383434, year = {2005}, author = {Biben, T and Kassner, K and Misbah, C}, title = {Phase-field approach to three-dimensional vesicle dynamics.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {72}, number = {4 Pt 1}, pages = {041921}, doi = {10.1103/PhysRevE.72.041921}, pmid = {16383434}, issn = {1539-3755}, mesh = {Computer Simulation ; Elasticity ; Liposomes/*chemistry ; *Membrane Fluidity ; *Membranes, Artificial ; Microfluidics/methods ; *Models, Chemical ; *Models, Molecular ; Motion ; Stress, Mechanical ; }, abstract = {We extend our recent phase-field [T. Biben and C. Misbah, Phys. Rev. E 67, 031908 (2003)] approach to 3D vesicle dynamics. Unlike the boundary-integral formulations, based on the use of the Oseen tensor in the small Reynolds number limit, this method offers several important flexibilities. First, there is no need to track the membrane position; rather this is automatically encoded in dynamics of the phase field to which we assign a finite width representing the membrane extent. Secondly, this method allows naturally for any topology change, like vesicle budding, for example. Thirdly, any non-Newtonian constitutive law, that is generically nonlinear, can be naturally accounted for, a fact which is precluded by the boundary integral formulation. The phase-field approach raises, however, a complication due to the local membrane incompressibility, which, unlike usual interfacial problems, imposes a nontrivial constraint on the membrane. This problem is solved by introducing dynamics of a tension field. The first purpose of this paper is to show how to write adequately the advected-field model for 3D vesicles. We shall then perform a singular expansion of the phase field equation to show that they reduce, in the limit of a vanishing membrane extent, to the sharp boundary equations. Then, we present some results obtained by the phase-field model. We consider two examples; (i) kinetics towards equilibrium shapes and (ii) tanktreading and tumbling. We find a very good agreement between the two methods. We also discuss briefly how effects, such as the membrane shear elasticity and stretching elasticity, and the relative sliding of monolayers, can be accounted for in the phase-field approach.}, }
@article {pmid16379621, year = {2005}, author = {Zhang, Y and Finlay, WH}, title = {Experimental measurements of particle deposition in three proximal lung bifurcation models with an idealized mouth-throat.}, journal = {Journal of aerosol medicine : the official journal of the International Society for Aerosols in Medicine}, volume = {18}, number = {4}, pages = {460-473}, doi = {10.1089/jam.2005.18.460}, pmid = {16379621}, issn = {0894-2684}, mesh = {Administration, Inhalation ; Aerosols ; Chemistry, Pharmaceutical/*methods ; Decanoic Acids/administration &amp; dosage/*pharmacokinetics ; Humans ; Larynx/physiology ; Lung/*metabolism ; *Models, Anatomic ; Mouth/*metabolism ; Oils ; Particle Size ; Pharynx/*metabolism ; Respiratory Mechanics/physiology ; Trachea/metabolism ; }, abstract = {In this paper, particle deposition in three idealized proximal lung bifurcation models with an idealized mouth-throat were investigated experimentally. These bifurcation models included (1) a small symmetric bifurcation, (2) an intermediate asymmetric bifurcation, and (3) a large symmetric bifurcation. An idealized mouth-throat geometry (the "Alberta geometry") was used as the inlet to these bifurcation models. Monodisperse aerosol particles of DEHS (di-2-ethylhexyl-sebecate) oil with mass median diameters in the range of 2.5-7.5 microm were employed at steady flow rates of 30-90 L/min. Particle deposition measurements were conducted by gravimetry. The results show that particle deposition in the mouth-throat and trachea accounts for the major portion of total deposition in the entire models used, and particle deposition fraction in the proximal lung bifurcations is lower compared with that deposited in the regions upstream (the mouth-throat and the trachea). Total particle deposition efficiency increases with increasing either inertial parameter or Stokes number. Total particle deposition varies appreciably from model to model. The laryngeal jet is the key factor dominating particle deposition within the trachea. An effect of Reynolds number on particle deposition efficiency in the trachea is observed. In addition, particle deposition in the bifurcation region is influenced little by the upstream flow condition, and therefore the effect of the laryngeal jet on deposition seemingly does not propagate to the bifurcations downstream.}, }
@article {pmid16371336, year = {2005}, author = {Stoodley, P and Dodds, I and De Beer, D and Scott, HL and Boyle, JD}, title = {Flowing biofilms as a transport mechanism for biomass through porous media under laminar and turbulent conditions in a laboratory reactor system.}, journal = {Biofouling}, volume = {21}, number = {3-4}, pages = {161-168}, doi = {10.1080/08927010500375524}, pmid = {16371336}, issn = {0892-7014}, mesh = {Biofilms/*growth &amp; development ; Image Processing, Computer-Assisted ; Microscopy, Fluorescence ; Porosity ; Time Factors ; *Water Movements ; }, abstract = {Fluid flow has been shown to be important in influencing biofilm morphology and causing biofilms to flow over surfaces in flow cell experiments. However, it is not known whether similar effects may occur in porous media. Generally, it is assumed that the primary transport mechanism for biomass in porous media is through convection, as suspended particulates (cells and flocs) carried by fluid flowing through the interstices. However, the flow of biofilms over the surfaces of soils and sediment particles, may represent an important flux of biomass, and subsequently affect both biological activity and permeability. Mixed species bacterial biofilms were grown in glass flow cells packed with 1 mm diameter glass beads, under laminar or turbulent flow (porous media Reynolds number = 20 and 200 respectively). The morphology and dynamic behavior reflected those of biofilms grown in the open flow cells. The laminar biofilm was relatively uniform and after 23 d had inundated the majority of the pore spaces. Under turbulent flow the biofilm accumulated primarily in protected regions at contact points between the beads and formed streamers that trailed from the leeward face. Both biofilms caused a 2 to 3-fold increase in friction factor and in both cases there were sudden reductions in friction factor followed by rapid recovery, suggesting periodic sloughing and regrowth events. Time-lapse microscopy revealed that under both laminar and turbulent conditions biofilms flowed over the surface of the porous media. In some instances ripple structures formed. The velocity of biofilm flow was on the order of 10 mum h(-1) in the turbulent flow cell and 1.0 mum h(-1) in the laminar flow cell.}, }
@article {pmid16355220, year = {2005}, author = {Pine, DJ and Gollub, JP and Brady, JF and Leshansky, AM}, title = {Chaos and threshold for irreversibility in sheared suspensions.}, journal = {Nature}, volume = {438}, number = {7070}, pages = {997-1000}, doi = {10.1038/nature04380}, pmid = {16355220}, issn = {1476-4687}, abstract = {Systems governed by time reversible equations of motion often give rise to irreversible behaviour. The transition from reversible to irreversible behaviour is fundamental to statistical physics, but has not been observed experimentally in many-body systems. The flow of a newtonian fluid at low Reynolds number can be reversible: for example, if the fluid between concentric cylinders is sheared by boundary motion that is subsequently reversed, then all fluid elements return to their starting positions. Similarly, slowly sheared suspensions of solid particles, which occur widely in nature and science, are governed by time reversible equations of motion. Here we report an experiment showing precisely how time reversibility fails for slowly sheared suspensions. We find that there is a concentration dependent threshold for the deformation or strain beyond which particles do not return to their starting configurations after one or more cycles. Instead, their displacements follow the statistics of an anisotropic random walk. By comparing the experimental results with numerical simulations, we demonstrate that the threshold strain is associated with a pronounced growth in the Lyapunov exponent (a measure of the strength of chaotic particle interactions). The comparison illuminates the connections between chaos, reversibility and predictability.}, }
@article {pmid16351878, year = {2002}, author = {Lehmann, FO}, title = {The constraints of body size on aerodynamics and energetics in flying fruit flies: an integrative view.}, journal = {Zoology (Jena, Germany)}, volume = {105}, number = {4}, pages = {287-295}, doi = {10.1078/0944-2006-00083}, pmid = {16351878}, issn = {0944-2006}, abstract = {Reynolds number and thus body size may potentially limit aerodynamic force production in flying insects due to relative changes of viscous forces on the beating wings. By comparing four different species of fruit flies similar in shape but with different body mass, we have investigated how small insects cope with changes in fluid mechanical constraints on power requirements for flight and the efficiency with which chemical energy is turned into aerodynamic flight forces. The animals were flown in a flight arena in which stroke kinematics, aerodynamic force production, and carbon dioxide release were measured within the entire working range of the flight motor. The data suggest that during hovering performance mean lift coefficient for flight is higher in smaller animals than in their larger relatives. This result runs counter to predictions based on conventional aerodynamic theory and suggests subtle differences in stroke kinematics between the animals. Estimates in profile power requirements based on high drag coefficient suggest that among all tested species of fruit flies elastic energy storage might not be required to minimize energetic expenditures during flight. Moreover, muscle efficiency significantly increases with increasing body size whereas aerodynamic efficiency tends to decrease with increasing size or Reynolds number. As a consequence of these two opposite trends, total flight efficiency tends to increase only slightly within the 6-fold range of body sizes. Surprisingly, total flight efficiency in fruit flies is broadly independent of different profile power estimates and typically yields mean values between 2-4%.}, }
@article {pmid16317892, year = {2005}, author = {Takiguchi, H and Odake, T and Umemura, T and Hotta, H and Tsunoda, K}, title = {Characteristics of a liquid/liquid optical waveguide using sheath flow and its application to detect molecules at a liquid/liquid interface.}, journal = {Analytical sciences : the international journal of the Japan Society for Analytical Chemistry}, volume = {21}, number = {11}, pages = {1269-1274}, doi = {10.2116/analsci.21.1269}, pmid = {16317892}, issn = {0910-6340}, mesh = {Anilino Naphthalenesulfonates/chemistry ; Chemistry Techniques, Analytical/*methods ; Ether/chemistry ; Furans/chemistry ; Kinetics ; Microfluidics/*methods ; Rheology/methods ; Rhodamines/chemistry ; Solvents/*chemistry ; Spectrometry, Fluorescence ; Spectrophotometry ; Toluene/chemistry ; Water/chemistry ; }, abstract = {The formation conditions and characteristics of a liquid/liquid optical waveguide (LLW) were studied using a two-phase sheath flow, where the inner organic phase flow acted as the core and the outer aqueous flow acted as the clad. In immiscible solvent systems, i.e., toluene/water and diethyl ether/water systems, the LLWs were formed in the range of higher than ca. 600 of the Reynolds number (Re), where the linear velocity of the organic solvent was much higher than that of the aqueous solution. On the other hand, in a miscible solvent system, i.e., a tetrahydrofuran/water system, a stable LLW was formed in the range of a much lower Re than in immiscible systems. Moreover, the molecules at the toluene/water interface of the LLW were observed with both fluorescence and absorbance measurement systems. In particular, the change in the fluorescence spectrum of 1-anilino-8-naphthalenesulfonate (ANS) at the interface within 1 ms was observed by this method, indicating the usefulness of the LLW for a fast kinetic study of a liquid/liquid interface.}, }
@article {pmid16317764, year = {2006}, author = {Vallejos, JR and Kostov, Y and Ram, A and French, JA and Marten, MR and Rao, G}, title = {Optical analysis of liquid mixing in a minibioreactor.}, journal = {Biotechnology and bioengineering}, volume = {93}, number = {5}, pages = {906-911}, doi = {10.1002/bit.20785}, pmid = {16317764}, issn = {0006-3592}, support = {RR018608/RR/NCRR NIH HHS/United States ; }, mesh = {Algorithms ; *Bioreactors ; Biosensing Techniques/instrumentation/*methods ; Equipment Design ; Signal Processing, Computer-Assisted ; }, abstract = {A novel optical sensor was used to study mixing and mean circulation time in a model minibioreactor (12.5 mL stirred vessel, equipped with a paddle impeller). Rotational rates in the range of 10-1,000 rpm corresponding to Reynolds number between 14 and 1,350 were studied. Results suggest that depending on the impeller rotational speed, mixing times up to 214 +/- 87 s can be reproducibly achieved. The minibioreactor was operated in the transitional regime, and it was determined that the non-dimensional form for mixing time, NTheta(M) was linearly dependent on Reynolds number. A linear correlation between mean circulation time and the inverse of rotational speed was also determined. The mean circulation time dependence on rotational speed in the 12.5 mL stirred vessel is similar to those found in large-scale stirred vessels. These results suggest that mixing and circulation times found in large-scale reactors can be replicated in minibioreactors.}, }
@article {pmid16294973, year = {2005}, author = {Bhatnagar, R and Chaube, R and Singh, N}, title = {Effect of optical turbulence in the dye medium on the bandwidth of a narrowband, high-repetition-rate dye laser.}, journal = {Applied optics}, volume = {44}, number = {32}, pages = {6962-6970}, doi = {10.1364/ao.44.006962}, pmid = {16294973}, issn = {1559-128X}, abstract = {An analysis of turbulence in the dye medium of a high-repetition-rate narrowband dye laser is presented, and it is shown that the output bandwidth is proportional to the turbulence length scale, which depends on the Reynolds number. The length scale and the bandwidth both first decrease and then increase as the Reynolds number is increased from -200 to -20,000. The observed bandwidth, as we report and as in the published literature, confirms the validity of the analysis. A Rhodamine 6G grazing-incidence grating, stable dye laser transversely pumped by a copper-vapor laser was used in the experiments.}, }
@article {pmid16294730, year = {2005}, author = {Liu, X and Huang, H and Chen, H}, title = {[Coupling between adherent leukocytes and blood flow].}, journal = {Sheng wu yi xue gong cheng xue za zhi = Journal of biomedical engineering = Shengwu yixue gongchengxue zazhi}, volume = {22}, number = {5}, pages = {956-60, 994}, pmid = {16294730}, issn = {1001-5515}, mesh = {Blood Circulation/*physiology ; *Cell Adhesion ; Hemodynamics ; Humans ; Leukocytes/cytology/*physiology ; Models, Biological ; Regional Blood Flow ; Shear Strength ; }, abstract = {A theoretical model was developed to simulate the coupling between the adhered leukocyte and blood flow. Methods of computational fluid dynamics (CFD) were introduced to analyze the distributions of the shear stress and the pressure on the cell surface. Meanwhile, the hemodynamical parameters were measured with laser Doppler velocimetry. The results showed that the deformation index of the leukocyte was increased with initial contact angle and Reynolds number. The blood flow induced the redistributions of the shear stress and pressure on the surface of the cell, but the maximum shear stress was on the top point of the cell. It suggests that the non-uniform distribution of shear stress on the cell surface may play a particular role in the change of cell shape and functions.}, }
@article {pmid16290624, year = {2002}, author = {Rust, AC and Manga, M}, title = {Bubble shapes and orientations in low Re simple shear flow.}, journal = {Journal of colloid and interface science}, volume = {249}, number = {2}, pages = {476-480}, doi = {10.1006/jcis.2002.8292}, pmid = {16290624}, issn = {0021-9797}, abstract = {We present measurements of shape and orientation of air bubbles in a viscous Newtonian fluid deformed by simple shear. The apparatus is a variation of the "parallel band" device developed by G. I. Taylor. Previous experimental studies on low viscosity ratio, low Reynolds number (Re << 1) bubble deformation have focussed on either small or large deformations (mostly small deformation) and have only qualitatively examined the orientation of bubbles except for small deformations. Our data set spans both the theoretical small deformation and high deformation limits. With these data we confirm theoretical relationships and assess the range of capillary numbers (Ca) over which theoretical relationships for shape and orientation of bubbles are appropriate. We also examine the geometry of deformed bubbles as they relax to a spherical shape once shear stresses are removed. Our data indicate that for extremely small Reynolds numbers and viscosity ratios, the small deformation theoretical relationship first developed by Taylor, is a good approximation for Ca<0.5. The large deformation results for both shape and bubble orientation derived by Hinch and Acrivos agree with our data for Ca>1 and Ca>0.5, respectively.}, }
@article {pmid16290589, year = {2002}, author = {Gleeson, JP}, title = {Electroosmotic flows with random zeta potential.}, journal = {Journal of colloid and interface science}, volume = {249}, number = {1}, pages = {217-226}, doi = {10.1006/jcis.2002.8256}, pmid = {16290589}, issn = {0021-9797}, abstract = {The hydrodynamic problem of electroosmotic flow in a cylindrical capillary with random zeta potential is solved in the limit of small Deybe length and low Reynolds number. Averages are defined over multiple experiments and the mean axial velocity is found to be a plug flow. The variance of the velocity exhibits parabolic-like variation across the capillary. Average concentrations of samples transported by the flow are approximated by defining an effective diffusivity coefficient. Theoretical formulas for the average concentration are supported by numerical experiments.}, }
@article {pmid16290528, year = {2002}, author = {Adamczyk, Z and Siwek, B and Warszyński, P}, title = {Deposition of particles in the impinging-jet cell for the high coverage regime.}, journal = {Journal of colloid and interface science}, volume = {248}, number = {2}, pages = {244-254}, doi = {10.1006/jcis.2002.8243}, pmid = {16290528}, issn = {0021-9797}, abstract = {Particle deposition in the radial impinging-jet cell for the high coverage regime was studied theoretically and experimentally. A detailed description of the flow distribution in the cell was attained by solving the governing Navier-Stokes equation numerically. The macroscopic flow pattern was decomposed into simpler local flows. It was demonstrated that for tangential distances r/R>0.5 the overall flow at the interface was dominated by the simple shear. The intensity of this flow was calculated numerically as a function of the Reynolds number and the distance from the cell center. Knowing the fluid velocity field the convective diffusion equation was formulated describing a two-dimensional transport of particles. As a result of nonlinearity of the boundary condition this equation was solved in an exact manner for low coverage only. For higher coverage, approximate methods were proposed exploiting the random sequential adsorption (RSA) approach. The validity of the theoretical predictions was verified experimentally using the direct microscope observation method and polystyrene latex particles of the size 0.87 mum. Particle coverage distribution was studied in detail as a function of the Re number governing the local shear rate. It was demonstrated that for low Re number (Re<4) uniform particle monolayers of high coverage can be attained. On the other hand, for Re>8 the particle coverage distribution became nonuniform as a result of the hydrodynamic scattering. This effect, leading to an apparent kinetic saturation of the surface at coverages of a few percents, was quantitatively interpreted in terms of the theoretical model.}, }
@article {pmid16290509, year = {2002}, author = {Lopez, JM and Miraghaie, R and Hirsa, AH}, title = {Non-newtonian behavior of an insoluble monolayer: effects of inertia.}, journal = {Journal of colloid and interface science}, volume = {248}, number = {1}, pages = {103-110}, doi = {10.1006/jcis.2001.8198}, pmid = {16290509}, issn = {0021-9797}, abstract = {Interfacial velocity measurements were performed in an optical annular channel, consisting of stationary inner and outer cylinders, a floor rotating at a constant rate, and a flat free surface on which an insoluble monolayer was initially spread. Measurements for essentially inviscid monolayers and some viscous monolayers on water show good agreement with numerical predictions for a Newtonian interface (Boussinesq-Scriven surface model) coupled to a bulk flow described by the Navier-Stokes equations. Here, we consider in detail a viscous monolayer, namely hemicyanine, and find that above a certain concentration, the monolayer does not behave Newtonian at a Reynolds number of about 250. We show that the discrepancies between the measurements and predicted Newtonian behavior are not due to compositional effects (i.e., nonuniform monolayer distribution), Reynolds number (i.e., inertia and/or secondary flows), or surface dilatational viscosity (which does not play any role in the parameter regime investigated). We show prima facie evidence that the observed shear thinning nature of the velocity profile is associated with a phase transition at C approximately 0.9 mg/m(2) at low Reynolds numbers. At large Reynolds numbers (Re=8500), hemicyanine is found to flow like a viscous Newtonian monolayer on the air/water interface, with viscosity dependent only on the local concentration.}, }
@article {pmid16290389, year = {2002}, author = {Nguyen, AV and Evans, GM}, title = {The liquid flow force on a particle in the bubble-particle interaction in flotation.}, journal = {Journal of colloid and interface science}, volume = {246}, number = {1}, pages = {100-104}, doi = {10.1006/jcis.2001.8010}, pmid = {16290389}, issn = {0021-9797}, abstract = {In this paper the problem of calculating the liquid flow force on a particle in interaction with an air bubble with a mobile surface in flotation as a function of the separation distance was solved. The force equation was obtained by first deriving the disturbed flow confined between the surfaces. The model for the force includes the separation distance between the bubble and the particle, the particle size, the bubble's Reynolds number, the bubble rise velocity, and the polar position of the particle on the bubble surface. The proposed equations provide an exact solution to the situation where the particle and the bubble are very close together. The attractive flow force and the surface forces are of similar orders of magnitude. Consequently, the models presented in this paper should provide a better estimate for calculating the forces on particles interacting with air bubbles in mineral flotation and other separation operations involving colloidal interactions.}, }
@article {pmid16289205, year = {2005}, author = {Simões, M and Pereira, MO and Vieira, MJ}, title = {Effect of mechanical stress on biofilms challenged by different chemicals.}, journal = {Water research}, volume = {39}, number = {20}, pages = {5142-5152}, doi = {10.1016/j.watres.2005.09.028}, pmid = {16289205}, issn = {0043-1354}, mesh = {Bacterial Proteins/metabolism ; Benzalkonium Compounds/pharmacology ; Biofilms/*growth &amp; development ; Cetrimonium ; Cetrimonium Compounds/pharmacology ; Disinfectants/pharmacology ; Glucose/metabolism ; Glutaral/pharmacology ; Oxygen/metabolism ; Polysaccharides/metabolism ; Pseudomonas fluorescens/drug effects/*physiology ; Sodium Dodecyl Sulfate/pharmacology ; Sodium Hydroxide/pharmacology ; Sodium Hypochlorite/pharmacology ; Stainless Steel ; Stress, Mechanical ; Surface-Active Agents/pharmacology ; o-Phthalaldehyde/pharmacology ; }, abstract = {In this study a methodology was applied in order to ascertain the mechanical stability of biofilms, by using a stainless-steel (SS) rotating device immersed in a biological reactor where biofilms formed by Pseudomonas fluorescens were allowed to grow for 7 days at a Reynolds number of agitation of 2400. The biofilms developed with this system were characterised in terms of amount of total, extracellular and intracellular proteins and polysaccharides, amount of mass, metabolic activity and mechanical stability, showing that the biofilms were active, had a high content of extracellular constituents and an inherent mechanical stability. In order to assess the role of chemical agents on the mechanical stability, the biofilms were exposed to chemical agents followed by mechanical treatments by submission to increase Reynolds number of agitation. Seven different chemical agents were tested (two non-oxidising biocides, three surfactants and two oxidising biocides) and their effects on the biofilm mechanical stability were evaluated. The increase in the Reynolds number increased the biofilm removal, but total biofilm removal was not found for all the conditions tested. For the experiment without chemical addition (only mechanical treatment), the biofilm remaining on the surface was about 76%. The chemical treatment followed by the subsequent mechanical treatment did not remove all the biofilms from the surface. The biofilm remaining on the SS cylinder ranged from 3% to 62%, depending on the chemical treatment, showing that the chemical treatment is far from being a cause that induces massive biofilm detachment and even the synergistic chemical and mechanical treatments did not promote biofilm removal. Some chemical agents promoted an increase in the biofilm mechanical stability such as glutaraldehyde (GTA), benzalkonium chloride (BC), except for the lower concentration tested, and sodium dodecyl sulphate (SDS), except for the higher concentration tested. Treatments that promoted biofilm removal, to an extent similar to the control experiment (without chemical treatment), were BC, for the lower and the higher concentration of SDS. Cetyltrimethyl ammonium bromide (CTAB), ortho-phthalaldehyde (OPA), sodium hydroxide (NaOH) and sodium hypochlorite (SHC) promoted the weakening of the biofilm mechanical stability.}, }
@article {pmid16269629, year = {2005}, author = {Bushi, D and Grad, Y and Einav, S and Yodfat, O and Nishri, B and Tanne, D}, title = {Hemodynamic evaluation of embolic trajectory in an arterial bifurcation: an in-vitro experimental model.}, journal = {Stroke}, volume = {36}, number = {12}, pages = {2696-2700}, doi = {10.1161/01.STR.0000190097.08862.9a}, pmid = {16269629}, issn = {1524-4628}, mesh = {Animals ; Blood Flow Velocity ; Cerebrovascular Circulation ; *Hemodynamics ; Humans ; Intracranial Embolism/*physiopathology ; *Models, Cardiovascular ; Particle Size ; Pulsatile Flow ; Research Design/standards ; }, abstract = {BACKGROUND AND PURPOSE: Despite the importance of embolism as a major cause of brain infarction, little is known about the hemodynamic factors governing the path large emboli tend to follow. Our aim was to test in vitro, whether hemodynamic parameters other than flow ratios between bifurcation branches may affect the distribution of embolic particles in a Y-shaped bifurcation model, used as an analogue to an arterial bifurcation.<br><br>METHODS: In vitro experiments were conducted using suspensions of sphere-shaped particles (0.6, 1.6, and 3.2 mm) in water-glycerin mixture, using steady and pulsatile laminar flow regimes in a Y-shaped bifurcation model (identical branching angles [theta1=theta2=45 degrees] with one daughter branch diameter wider than the other [D1=6 mm, D2=4 mm]; average Reynolds number 500).<br><br>RESULTS: Experiments using naturally buoyant particles under steady flow conditions and four outlet-flow ratios revealed that small (0.6 mm) and mid-sized (1.6 mm) particles entered into either the narrower or wider bifurcation daughter branch nonpreferentially, proportionally to the flow ratios. Large particles (3.2 mm), however, preferentially entered the wider daughter branch. Moreover, as the flow ratio increases this phenomenon was augmented. Further experiments revealed that the preference of the wider daughter branch for high particle-to-branch diameter-ratios further increases under pulsatile flow and by the density ratio between particles and fluid.<br><br>CONCLUSIONS: Particles' distribution in a bifurcation is affected, beyond its outlets-flow-ratios, by the particle-to-branch diameter-ratio. The tendency of large particles to preferentially enter the wider bifurcation branch, beyond the flow ratio, is augmented under pulsatile flow conditions and is affected by particle-to-fluid density-ratio. These findings may have important implications for understanding the hemodynamic mechanisms underlying the trajectory of large emboli.}, }
@article {pmid16256673, year = {2003}, author = {Hsu, JP and Hsieh, YH}, title = {Boundary effect on the drag force on a nonhomogeneous floc.}, journal = {Journal of colloid and interface science}, volume = {264}, number = {2}, pages = {517-525}, doi = {10.1016/S0021-9797(03)00506-X}, pmid = {16256673}, issn = {0021-9797}, abstract = {The boundary effect on the drag force acting on a spherical floc having a nonhomogeneous structure is examined by considering a spherical floc at the centerline of a cylindrical tube. The floc is simulated by an entity having a two-layer structure, and its porous nature mimicked by varying the relative magnitude of the permeability of its inner and outer layers. The results of numerical simulation reveal that the tube wall has the effect of compressing the streamlines and vorticity contours. Also, as in the case of a rigid entity, the wake in the rear region of a floc, which arises from the convective motion of the fluid, is depressed. For fixed volume-averaged permeability, the influence of the tube wall on the behavior of a heterogeneous floc is more significant than that on the behavior of a homogeneous floc, and the influence varies with the structure of the former. The heterogeneous structure of a floc leads to a deviation in the modified drag coefficient-Reynolds number relation from a Stokes-law-like correlation. The smaller the average permeability of a floc the greater the deviation, but the presence of the tube wall has the effect of reducing the deviation.}, }
@article {pmid16256565, year = {2003}, author = {Johnson, RA and Borhan, A}, title = {Pressure-driven motion of surfactant-laden drops through cylindrical capillaries: effect of surfactant solubility.}, journal = {Journal of colloid and interface science}, volume = {261}, number = {2}, pages = {529-541}, doi = {10.1016/S0021-9797(03)00031-6}, pmid = {16256565}, issn = {0021-9797}, abstract = {The effect of bulk-soluble surfactants on the dynamics of a drop translating through a cylindrical tube under low-Reynolds-number conditions is investigated. Interfacial surfactant adsorption/desorption is modeled according to the Frumkin adsorption framework, and the bulk-insoluble surfactant limit is recovered as the rate of surfactant sorption becomes large compared to that of bulk diffusion. As the equilibrium surface coverage is increased, the mechanism by which drop mobility is reduced changes from uniform retardation at low surface coverage to the formation of a stagnant cap at high surface coverage. For large capillary numbers, the drop does not achieve a steady shape, and eventually it breaks up either through the formation of a penetrating viscous jet of suspending fluid, or by continuous elongation and pinch-off. Surfactants have a destabilizing effect on transient drop shapes by accelerating the formation and development of the penetrating viscous jet that leads to drop breakup. The critical conditions for drop breakup, as well as the mode of breakup, depend on the manner in which the strength of the flow (i.e., the capillary number) is increased.}, }
@article {pmid16256510, year = {2003}, author = {Hsu, JP and Hsieh, YH}, title = {Drag force on a porous, non-homogeneous spheroidal floc in a uniform flow field.}, journal = {Journal of colloid and interface science}, volume = {259}, number = {2}, pages = {301-308}, doi = {10.1016/S0021-9797(02)00132-7}, pmid = {16256510}, issn = {0021-9797}, abstract = {The force acting on a porous spheroidal floc having a nonhomogeneous structure in a uniform flow field is evaluated theoretically. Here, the floc is simulated by an entity having a two-layer type of structure, and its porous nature is mimicked by varying the relative magnitudes of the permeabilities of its inner and outer layers. The results of numerical simulation reveal that, for the same volume-averaged permeability, the drag coefficient of a spheroidal floc with a nonhomogeneous structure is much larger than that of a floc with a homogeneous structure for both prolate and oblate spheroids. This is true regardless of the relative magnitudes of the permeability of the inner layer and that of the outer layer. While the drag coefficient of a homogeneous prolate is the same as that of a homogeneous oblate the drag coefficient of a nonhomogeneous prolate is larger than that of a nonhomogeneous oblate. For the same volume-averaged size, the more nonhomogeneous the structure of a spheroidal floc the easier for the relation between the drag coefficient and the Reynolds number to deviate from a Stokes-law-like relation. For a fixed volume-averaged permeability, the effective drag coefficient increases with the increase in the ratio (polar radius of inner layer/polar radius of floc), regardless of whether its inner layer is less permeable than its outer layer or not.}, }
@article {pmid16241808, year = {2005}, author = {Metzger, B and Guazzelli, E and Butler, JE}, title = {Large-scale streamers in the sedimentation of a dilute fiber suspension.}, journal = {Physical review letters}, volume = {95}, number = {16}, pages = {164506}, doi = {10.1103/PhysRevLett.95.164506}, pmid = {16241808}, issn = {0031-9007}, abstract = {We experimentally characterize structures formed during the sedimentation of rigid fibers of high aspect ratio at small Reynolds number using particle image velocimetry. Measurements show the existence of large-scale streamers during early stages of the sedimentation process, consistent with previously published theory and numerical simulations. At longer times, the cell-wide inhomogeneities evolve into smaller-scale streamers. Measurements of spatially averaged fiber velocities and velocity fluctuations are also presented.}, }
@article {pmid16241805, year = {2005}, author = {Aarts, DG and Lekkerkerker, HN and Guo, H and Wegdam, GH and Bonn, D}, title = {Hydrodynamics of droplet coalescence.}, journal = {Physical review letters}, volume = {95}, number = {16}, pages = {164503}, doi = {10.1103/PhysRevLett.95.164503}, pmid = {16241805}, issn = {0031-9007}, abstract = {We study droplet coalescence in a molecular system with a variable viscosity and a colloid-polymer mixture with an ultralow surface tension. When either the viscosity is large or the surface tension is small enough, we observe that the opening of the liquid bridge initially proceeds at a constant speed set by the capillary velocity. In the first system we show that inertial effects become dominant at a Reynolds number of about 1.5+/- 0.5 and the neck then grows as the square root of time. In the second system we show that decreasing the surface tension by a factor of 10(5) opens the way to a more complete understanding of the hydrodynamics involved.}, }
@article {pmid16241569, year = {2005}, author = {Parras, L and Fernandez-Feria, R}, title = {Nonparallel spatial stability of the boundary layer induced by Long's vortex on a solid plane perpendicular to its axis.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {72}, number = {3 Pt 2}, pages = {036305}, doi = {10.1103/PhysRevE.72.036305}, pmid = {16241569}, issn = {1539-3755}, abstract = {We consider the linear, viscous stability of the boundary layer induced by an unbounded vortex whose outer inviscid structure coincides near the axis with Long's vortex. The viscous boundary layer induced by the interaction of such a vortex with a solid plane perpendicular to the axis has a known self-similar structure. The spatial stability of this self-similar solution is analyzed here for axisymmetric and nonaxisymmetric perturbations propagating towards the axis of rotation. Viscous and nonparallel effects on the stability of the perturbations are retained up to their first order in the inverse of the local Reynolds number (nondimensional radius). The resulting parabolic stability equations are solved numerically using a spectral collocation method varying both the nondimensional frequency and radius. It is found that the flow is unstable to axisymmetric perturbations far away from the axis (inviscid instability). The growth rate of this inertial instability mode first increases and then decreases as the Reynolds number decreases (as the axis is approached). However, before this inviscid mode becomes stabilized, new viscous instabilities for both axisymmetric and nonaxisymmetric perturbations show up, which finally become stabilized at moderate Reynolds numbers. We characterize the critical Reynolds numbers and frequencies for the stability of these unstable perturbations as functions of their azimuthal wave number. It is found that the last perturbations that become stable as the axis is approached are nonaxisymmetric, corotating, perturbations with an azimuthal wave number n=4 .}, }
@article {pmid16241352, year = {2003}, author = {Białecki, J and Hołyst, JA}, title = {Linear stability analysis in a liquid layer with a surface velocity gradient.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {67}, number = {6 Pt 2}, pages = {066311}, doi = {10.1103/PhysRevE.67.066311}, pmid = {16241352}, issn = {1539-3755}, abstract = {A case of combined planar Couette-Poiseuille flow corresponding to vanishing horizontal flux has been generalized by the introduction of a model for the surface velocity gradient. A relation corresponding to the Orr-Sommerfeld equation has been derived for this model. The critical value of the surface velocity gradient has been obtained. At the critical point, the corresponding critical Reynolds number equals infinity. Using an approximated method we estimated the behavior of the critical Reynolds number for a slightly overcritical surface velocity gradient.}, }
@article {pmid16241345, year = {2003}, author = {Truesdell, RA and Vorobieff, PV and Sklar, LA and Mammoli, AA}, title = {Mixing of a continuous flow of two fluids due to unsteady flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {67}, number = {6 Pt 2}, pages = {066304}, doi = {10.1103/PhysRevE.67.066304}, pmid = {16241345}, issn = {1539-3755}, support = {EB00264/EB/NIBIB NIH HHS/United States ; GM60799/GM/NIGMS NIH HHS/United States ; }, mesh = {Biophysics/*methods ; Flow Cytometry/instrumentation ; Models, Statistical ; Models, Theoretical ; Rheology ; }, abstract = {In many low-Reynolds number mixing applications, the absence of turbulence makes it difficult to achieve proper mixing of two fluids. In this paper, flow visualization is used to obtain quantitative measurements of mixing that occurs when combining two pulsatile fluid streams at a Y-connection. Mixing results from the interface distortion created by the pulsatile flow. This is generated by combining the action a peristaltic pump, which provides the mean flow, with the action of two pinch valves, one on each arm of the Y-connection, to generate strong pulsations. The action of the pinch valves is be controlled via pulse generators. Apparently chaotic conditions were realized in the confluence region, superimposed with the mean flow. The valve action was optimized to maximize mixing, the latter quantified via image analysis. This work demonstrates a low cost, efficient mixing device for low-Reynolds number conditions, which is therefore suitable for miniaturization.}, }
@article {pmid16240195, year = {2005}, author = {Kumar, PR and Singh, DN}, title = {A novel technique for monitoring contaminant transport through soils.}, journal = {Environmental monitoring and assessment}, volume = {109}, number = {1-3}, pages = {147-160}, pmid = {16240195}, issn = {0167-6369}, mesh = {Calibration ; Chlorides/analysis ; Diffusion ; Electric Conductivity ; Electrodes ; Environmental Monitoring/instrumentation/*methods ; Minerals/analysis ; Sodium Chloride/chemistry ; Soil/analysis ; *Soil Pollutants ; *Water Movements ; }, abstract = {An experimental setup which is capable of simulation as well as monitoring contaminant transport through soil mass has been developed. Efficiency of the experimental setup has been demonstrated by comparing the results obtained from the argentometric method. Reynolds number (R(e)) and the Peclet number (P(e)) have been found to be less than unity. This indicates that flow of the solute through soil mass is laminar and the dominant contaminant transport mechanism is diffusion.}, }
@article {pmid16240085, year = {2005}, author = {Rouhanizadeh, M and Lin, TC and Arcas, D and Hwang, J and Hsiai, TK}, title = {Spatial variations in shear stress in a 3-D bifurcation model at low Reynolds numbers.}, journal = {Annals of biomedical engineering}, volume = {33}, number = {10}, pages = {1360-1374}, doi = {10.1007/s10439-005-6542-9}, pmid = {16240085}, issn = {0090-6964}, support = {HL 068689-01A1/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Arteries/*physiology ; Blood Flow Velocity/*physiology ; Blood Pressure/*physiology ; Computer Simulation ; Elasticity ; Hemodynamics/physiology ; Humans ; *Models, Cardiovascular ; Shear Strength ; Stress, Mechanical ; }, abstract = {Real-time wall shear stress is difficult to monitor precisely because it varies in space and time. Microelectromechanical systems sensor provides high spatial resolution to resolve variations in shear stress in a 3-D bifurcation model for small-scaled hemodynamics. At low Reynolds numbers from 1.34 to 6.7 skin friction coefficients (C(f)) varied circumferentially by a factor of two or more within the bifurcation. At a Reynolds number of 6.7, the C(f) value at the lateral wall of the bifurcation along the 270 degree plane was 7.1, corresponding to a shear stress value of 0.0061 dyn/cm(2). Along the 180 degree plane, C(f) was 13 or 0.0079 dyn/cm(2), and at the medial wall along the 90 degree plane, C(f) was 10.3 or 0.0091 dyn/cm(2). The experimental skin friction coefficients correlated with values derived from the Navier-Stokes solutions.}, }
@article {pmid16236305, year = {2006}, author = {Lin, J and Zhang, L and Zhang, W}, title = {Rheological behavior of fiber suspensions in a turbulent channel flow.}, journal = {Journal of colloid and interface science}, volume = {296}, number = {2}, pages = {721-728}, doi = {10.1016/j.jcis.2005.09.038}, pmid = {16236305}, issn = {0021-9797}, abstract = {Rheological behavior of fiber suspensions in a turbulent channel flow was investigated theoretically and numerically. A model of turbulent fiber suspensions was proposed to predict the orientation distribution of fibers. The fluctuating equation for the orientation distribution function (ODF) of fibers was theoretically solved using the method of characteristics. The self-governed mean equation for orientation distribution function (ODF) was derived by relating the fluctuating ODF and angular velocities-correlated terms to the gradient of mean ODF. Then the ODF of fibers was predicted by numerically solving the mean equation for ODF. Finally the shear stress and first normal stress difference of suspensions were obtained. The results, some of which agree with the available relevant experimental data, show that the orientation distribution of fibers in the vicinity of the center of the flow is relatively broad in turbulent regime, and becomes broader with the increase of Reynolds number. The shear stress of fiber suspensions increases, while the first normal stress difference decreases, from the wall to the center of the flow for varying Reynolds number.}, }
@article {pmid16214693, year = {2002}, author = {Tölke, J and Krafczyk, M and Schulz, M and Rank, E}, title = {Lattice Boltzmann simulations of binary fluid flow through porous media.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {360}, number = {1792}, pages = {535-545}, doi = {10.1098/rsta.2001.0944}, pmid = {16214693}, issn = {1364-503X}, mesh = {Biological Transport ; Colloids/*chemistry ; Computer Simulation ; *Diffusion ; Kinetics ; *Models, Chemical ; Motion ; Numerical Analysis, Computer-Assisted ; Particle Size ; Porosity ; Pressure ; Quantum Theory ; Rheology/*methods ; Solutions/*chemistry ; }, abstract = {The lattice Boltzmann equation is often advocated as a simulation tool that is particularly effective for complex fluids such as multiphase and multicomponent flows through porous media. We construct a three-dimensional 19 velocity lattice Boltzmann model for immiscible binary fluids with variable viscosities and density ratio based on the model proposed by Gunstensen. The model is tested for the following binary fluid flow problems: a stationary planar interface among two fluids; channel flow of immiscible binary fluids; the Laplace problem; and a rising bubble. The results agree well with semi-analytic results in a range of the Eötvös, Morton and Reynolds number. We also present preliminary simulation results for two large-scale realistic applications: the flow of an air-water mixture in a waste-water batch reactor and the saturation hysteresis effect in soil flow. We discuss some limitations of the lattice Boltzmann method in the simulation of realistic and difficult multiphase problems.}, }
@article {pmid16210181, year = {2002}, author = {Zbikowski, R}, title = {On aerodynamic modelling of an insect-like flapping wing in hover for micro air vehicles.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {360}, number = {1791}, pages = {273-290}, doi = {10.1098/rsta.2001.0930}, pmid = {16210181}, issn = {1364-503X}, mesh = {Animals ; Biomechanical Phenomena ; Flight, Animal/*physiology ; Insecta/*physiology ; Models, Biological ; Wings, Animal/*physiology ; }, abstract = {This theoretical paper discusses recent advances in the fluid dynamics of insect and micro air vehicle (MAV) flight and considers theoretical analyses necessary for their future development. The main purpose is to propose a new conceptual framework and, within this framework, two analytic approaches to aerodynamic modelling of an insect-like flapping wing in hover in the context of MAVs. The motion involved is periodic and is composed of two half-cycles (downstroke and upstroke) which, in hover, are mirror images of each other. The downstroke begins with the wing in the uppermost and rearmost position and then sweeps forward while pitching up and plunging down. At the end of the half-cycle, the wing flips, so that the leading edge points backwards and the wing's lower surface becomes its upper side. The upstroke then follows by mirroring the downstroke kinematics and executing them in the opposite direction. Phenomenologically, the interpretation of the flow dynamics involved, and adopted here, is based on recent experimental evidence obtained by biologists from insect flight and related mechanical models. It is assumed that the flow is incompressible, has low Reynolds number and is laminar, and that two factors dominate: (i) forces generated by the bound leading-edge vortex, which models flow separation; and (ii) forces due to the attached part of the flow generated by the periodic pitching, plunging and sweeping. The first of these resembles the analogous phenomenon observed on sharp-edged delta wings and is treated as such. The second contribution is similar to the unsteady aerodynamics of attached flow on helicopter rotor blades and is interpreted accordingly. Theoretically, the fluid dynamic description is based on: (i) the superposition of the unsteady contributions of wing pitching, plunging and sweeping; and (ii) adding corrections due to the bound leading-edge vortex and wake distortion. Viscosity is accounted for indirectly by imposing the Kutta condition on the trailing edge and including the influence of the vortical structure on the leading edge. Mathematically, two analytic approaches are proposed. The first derives all the quantities of interest from the notion of circulation and leads to tractable integral equations. This is an application of the von Kármán-Sears unsteady wing theory and its nonlinear extensions due to McCune and Tavares; the latter can account for the bound leading-edge vortex and wake distortion. The second approach uses the velocity potential as the central concept and leads to relatively simple ordinary differential equations. It is a combination of two techniques: (i) unsteady aerodynamic modelling of attached flow on helicopter rotor blades; and (ii) Polhamus's leading-edge suction analogy. The first of these involves both frequency-domain (Theodorsen style) and time-domain (indicial) methods, including the effects of wing sweeping and returning wake. The second is a nonlinear correction accounting for the bound leading-edge vortex. Connections of the proposed framework with control engineering and aeroelasticity are pointed out.}, }
@article {pmid16197079, year = {2005}, author = {Hollerbach, R and Rüdiger, G}, title = {New type of magnetorotational instability in cylindrical taylor-couette flow.}, journal = {Physical review letters}, volume = {95}, number = {12}, pages = {124501}, doi = {10.1103/PhysRevLett.95.124501}, pmid = {16197079}, issn = {0031-9007}, abstract = {We study the stability of cylindrical Taylor-Couette flow in the presence of combined axial and azimuthal magnetic fields, and show that adding an azimuthal field profoundly alters the previous results for purely axial fields. For small magnetic Prandtl numbers Pm, the critical Reynolds number Re(c) for the onset of the magnetorotational instability becomes independent of Pm, whereas for purely axial fields it scales as Pm-1. For typical liquid metals, Re(c) is then reduced by several orders of magnitude, enough that this new design should succeed in realizing this instability in the laboratory.}, }
@article {pmid16196862, year = {2005}, author = {Araujo, FF and Grossmann, S and Lohse, D}, title = {Wind reversals in turbulent Rayleigh-Bénard convection.}, journal = {Physical review letters}, volume = {95}, number = {8}, pages = {084502}, doi = {10.1103/PhysRevLett.95.084502}, pmid = {16196862}, issn = {0031-9007}, abstract = {The phenomenon of irregular cessation and subsequent reversal of the large-scale circulation in turbulent Rayleigh-Bénard convection is theoretically analyzed. The force and thermal balance on a single plume detached from the thermal boundary layer yields a set of coupled nonlinear equations, whose dynamics is related to the Lorenz equations. For Prandtl and Rayleigh numbers in the range 10(-2) < or = Pr < or = 10(3) and 10(7) < or = Ra < or = 10(12), the model has the following features: (i) chaotic reversals may be exhibited at Ra > or = 10(7); (ii) the Reynolds number based on the root mean square velocity scales as Re(rms) approximately Ra([0.41...0.47]) (depending on Pr), and as Re(rms) approximately Pr(-[0.66...0.76]) (depending on Ra); and (iii) the mean reversal frequency follows an effective scaling law omega/(nu L(-2)) approximately Pr(-(0.64 +/- 0.01))Ra(0.44 +/- 0.01). The phase diagram of the model is sketched, and the observed transitions are discussed.}, }
@article {pmid16196785, year = {2005}, author = {Nickels, TB and Marusic, I and Hafez, S and Chong, MS}, title = {Evidence of the kappa1-1 law in a high-Reynolds-number turbulent boundary layer.}, journal = {Physical review letters}, volume = {95}, number = {7}, pages = {074501}, doi = {10.1103/PhysRevLett.95.074501}, pmid = {16196785}, issn = {0031-9007}, abstract = {Dimensional analysis and overlap arguments lead to a prediction of a region in the streamwise velocity spectrum of wall-bounded turbulent flows in which the dependence on the streamwise wave number, kappa(1), is given by kappa(1)(-1). Some recent experiments have questioned the existence of this region. In this Letter, experimental spectra are presented which support the existence of the kappa(1)(-1) law in a high-Reynolds-number boundary layer. This Letter presents the experimental results and discusses the theoretical and experimental issues involved in examining the existence of the kappa(1)(-1) law and the reasons why it has proved so elusive.}, }
@article {pmid16196708, year = {2005}, author = {Jung, S and Swinney, HL}, title = {Velocity difference statistics in turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {72}, number = {2 Pt 2}, pages = {026304}, doi = {10.1103/PhysRevE.72.026304}, pmid = {16196708}, issn = {1539-3755}, abstract = {We unify two approaches that have been taken to explain the non-Gaussian probability distribution functions (PDFs) obtained in measurements of longitudinal velocity differences in turbulence, and we apply our approach to Couette-Taylor turbulence data. The first approach we consider was developed by Castaing and co-workers, who obtained the non-Gaussian velocity difference PDF from a superposition of Gaussian distributions for subsystems that have a particular energy dissipation rate at a fixed length scale [Castaing, Physica D 46, 177 (1990)]. Another approach was proposed by Beck and Cohen, who showed that the observed PDFs can be obtained from a superposition of Gaussian velocity difference PDFs in subsystems conditioned on the value of an intensive variable (inverse "effective temperature") in each subsystem [Beck and Cohen, Physica A 322, 267 (2003)]. The intensive variable was defined for subsystems assuming local thermodynamic equilibrium, but no method was proposed for determining the size of a subsystem. We show that the Castaing and Beck-Cohen methods are related, and we present a way to determine subsystem size in the Beck-Cohen method. The application of our approach to Couette-Taylor turbulence (Reynolds number 540,000) yields a log-normal distribution of the intensive parameter, and the resultant velocity difference PDF agrees well the observed non-Gaussian velocity difference PDFs.}, }
@article {pmid16193993, year = {2005}, author = {Wang, R and Lin, J and Li, ZH}, title = {Study on the impacting factors of transverse diffusion in the micro-channels of T-sensors.}, journal = {Journal of nanoscience and nanotechnology}, volume = {5}, number = {8}, pages = {1281-1286}, doi = {10.1166/jnn.2005.208}, pmid = {16193993}, issn = {1533-4880}, mesh = {Algorithms ; Diffusion ; Equipment Design ; Mathematics ; Microfluidic Analytical Techniques/*instrumentation/statistics &amp; numerical data ; Models, Statistical ; Nanotechnology ; Pressure ; }, abstract = {A diffusion-based microfluidic T-sensor with three inlets in which various species are injected was simulated numerically. The results show that the Reynolds number, the dimension, and shape of the micro-channel of the T-sensor, play an important role in the diffusion of flow. The smaller the channel width is, the wider the species diffuse. The inlet angle larger than 45 degrees will not exert any influence on the diffusion. The serpentine channel is a better structure for transverse diffusion and mixing in the micro-channel. These conclusions are helpful for the design and fabrication of micro-fluidic devices as well as the analysis of data collected from such devices.}, }
@article {pmid16139841, year = {2006}, author = {Nitin, S and Chhabra, RP}, title = {Sedimentation of a circular disk in power law fluids.}, journal = {Journal of colloid and interface science}, volume = {295}, number = {2}, pages = {520-527}, doi = {10.1016/j.jcis.2005.08.024}, pmid = {16139841}, issn = {0021-9797}, abstract = {The continuity and momentum equations have been solved numerically for the two-dimensional steady flow of power law fluids over a thin circular disk oriented normal to the direction of flow. Extensive results on the individual and total drag coefficients are obtained as functions of the power law flow behavior index (0.4 < or = n < or = 1.0), Reynolds number (1 < or = Re < or = 100) and the blockage ratio, disk-to-cylinder diameter ratio (0.02 < or = e < or = 0.5), which can be used to estimate the settling velocity of a circular disk. The numerical predictions of drag are consistent with the scant experimental results available in the literature.}, }
@article {pmid16121530, year = {2005}, author = {Chung, CA and Tzou, MR and Ho, RW}, title = {Oscillatory flow in a cone-and-plate bioreactor.}, journal = {Journal of biomechanical engineering}, volume = {127}, number = {4}, pages = {601-610}, doi = {10.1115/1.1933964}, pmid = {16121530}, issn = {0148-0731}, mesh = {*Bioreactors ; Cell Culture Techniques/*instrumentation/methods ; Computer Simulation ; Computer-Aided Design ; Equipment Design ; Equipment Failure Analysis/methods ; Microfluidics/*methods ; *Models, Theoretical ; Motion ; Oscillometry/*instrumentation/*methods ; Stress, Mechanical ; Tissue Engineering/*instrumentation/methods ; }, abstract = {Motivated by biometric applications, we analyze oscillatory flow in a cone-and-plate geometry. The cone is rotated in a simple harmonic way on a stationary plate. Based on assuming that the angle between the cone and plate is small, we describe the flow analytically by a perturbation method in terms of two small parameters, the Womersley number and the Reynolds number, which account for the influences of the local acceleration and centripetal force, respectively. Working equations for the shear stresses induced both by laminar primary and secondary flows on the plate surface are presented.}, }
@article {pmid16105782, year = {2005}, author = {Walton, AG}, title = {The linear and nonlinear stability of thread-annular flow.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {363}, number = {1830}, pages = {1223-1233}, doi = {10.1098/rsta.2005.1564}, pmid = {16105782}, issn = {1364-503X}, mesh = {Humans ; Minimally Invasive Surgical Procedures ; *Models, Theoretical ; *Prostheses and Implants ; }, abstract = {The surgical technique of thread injection of medical implants is modelled by the axial pressure-gradient-driven flow between concentric cylinders with a moving core. The linear stability of the flow to both axisymmetric and asymmetric perturbations is analysed asymptotically at large Reynolds number, and computationally at finite Reynolds number. The existence of multiple regions of instability is predicted and their dependence upon radius ratio and thread velocity is determined. A discrepancy in critical Reynolds numbers and cut-off velocity is found to exist between experimental results and the predictions of the linear theory. In order to account for this discrepancy, the high Reynolds number, nonlinear stability properties of the flow are analysed and a nonlinear, equilibrium critical layer structure is found, which leads to an enhanced correction to the basic flow. The predictions of the nonlinear theory are found to be in good agreement with the experimental data.}, }
@article {pmid16105778, year = {2005}, author = {Mackerrell, SO}, title = {Stability of Bödewadt flow.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {363}, number = {1830}, pages = {1181-1187}, doi = {10.1098/rsta.2005.1559}, pmid = {16105778}, issn = {1364-503X}, abstract = {The stability of the flow produced over an infinite stationary plane in a fluid rotating with uniform angular velocity at an infinite distance from the plane is considered. The basic flow is an exact solution of the Navier-Stokes equations making it amenable to theoretical study. An asymptotic investigation is presented in the limit of large Reynolds number. It is shown that the stationary spiral instabilities observed experimentally can be described by a linear inviscid stability analysis. The prediction obtained for the wave angle of the disturbances is found to agree well with the available experimental and numerical results.}, }
@article {pmid16105775, year = {2005}, author = {Kerimbekov, RM and Ruban, AI}, title = {Receptivity of boundary layers to distributed wall vibrations.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {363}, number = {1830}, pages = {1145-1155}, doi = {10.1098/rsta.2005.1556}, pmid = {16105775}, issn = {1364-503X}, abstract = {Linear three-dimensional receptivity of boundary layers to distributed wall vibrations in the large Reynolds number limit (Re-->infinity) is studied in this paper. The fluid motion is analysed by means of the multiscale asymptotic technique combined with the method of matched asymptotic expansions. The body surface is assumed to be perturbed by small-amplitude oscillations being tuned in resonance with the neutral Tollmien-Schlichting wave at a certain point on the wall. The characteristic length of the resonance region is found to be O(Re-3/16), which follows from the condition that the boundary-layer non-parallelism and the wave amplitude growth have the same order of magnitude. The amplitude equation is derived as a solvability condition for the inhomogeneous boundary-value problem. Investigating detuning effects, we consider perturbations in the form of a wave packet with a narrow O(Re-3/16) discrete or continuous spectrum concentrated near the resonant wavenumber and frequency. The boundary-layer laminarization based on neutralizing the oncoming Tollmien-Schlichting waves (or wave packets) is also discussed.}, }
@article {pmid16105770, year = {2005}, author = {Choudhari, M and Chang, CL and Jiang, L}, title = {Towards transition modelling for supersonic laminar flow control based on spanwise periodic roughness elements.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {363}, number = {1830}, pages = {1079-1096}, doi = {10.1098/rsta.2005.1551}, pmid = {16105770}, issn = {1364-503X}, abstract = {Laminar flow control (LFC) is one of the key enabling technologies for quiet and efficient supersonic aircraft. Recent work at Arizona State University (ASU) has led to a novel concept for passive LFC, which employs distributed leading edge roughness to limit the growth of naturally dominant crossflow instabilities in a swept-wing boundary layer. Predicated on nonlinear modification of the mean boundary-layer flow via controlled receptivity, the ASU concept requires a holistic prediction approach that accounts for all major stages within transition in an integrated manner. As a first step in developing an engineering methodology for the design and optimization of roughness-based supersonic LFC, this paper reports on canonical findings related to receptivity plus linear and nonlinear development of stationary crossflow instabilities on a Mach 2.4, 73 degrees swept airfoil with a chord Reynolds number of 16.3 million.}, }
@article {pmid16098533, year = {2006}, author = {Xu, C and Sin, S and McDonough, JM and Udupa, JK and Guez, A and Arens, R and Wootton, DM}, title = {Computational fluid dynamics modeling of the upper airway of children with obstructive sleep apnea syndrome in steady flow.}, journal = {Journal of biomechanics}, volume = {39}, number = {11}, pages = {2043-2054}, doi = {10.1016/j.jbiomech.2005.06.021}, pmid = {16098533}, issn = {0021-9290}, support = {HL-62408/HL/NHLBI NIH HHS/United States ; M01-RR00240/RR/NCRR NIH HHS/United States ; }, mesh = {Biomechanical Phenomena ; Child ; Child, Preschool ; *Computer Simulation ; Female ; Humans ; Male ; *Models, Biological ; Pressure ; Respiratory System/*physiopathology ; Rheology ; Sleep Apnea, Obstructive/*physiopathology ; }, abstract = {Computational fluid dynamic (CFD) analysis was used to model the effect of airway geometry on internal pressure in the upper airway of three children with obstructive sleep apnea syndrome (OSAS), and three controls. Model geometry was reconstructed from magnetic resonance images obtained during quiet tidal breathing, meshed with an unstructured grid, and solved at normative peak resting flow. The unsteady Reynolds-averaged Navier-Stokes equations were solved with steady flow boundary conditions in inspiration and expiration, using a two-equation low-Reynolds number turbulence model. Model results were validated using an in-vitro scale model, unsteady flow simulation, and reported nasal resistance measurements in children. Pharynx pressure drop strongly correlated to airway area restriction. Inspiratory pressure drop was primarily proportional to the square of flow, consistent with pressure losses due to convective acceleration caused by area restriction. On inspiration, in OSAS pressure drop occurred primarily between the choanae and the region where the adenoids overlap the tonsils (overlap region) due to airway narrowing, rather than in the nasal passages; in controls the majority of pressure drop was in the nasal passages. On expiration, in OSAS the majority of pressure drop occurred between the oropharynx (posterior to the tongue) and overlap region, and local minimum pressure in the overlap region was near atmospheric due to pressure recovery in the anterior nasopharynx. The results suggest that pharyngeal airway shape in children with OSAS significantly affects internal pressure distribution compared to nasal resistance. The model may also help explain regional dynamic airway narrowing during expiration.}, }
@article {pmid16097742, year = {2005}, author = {Ke, K and Hasselbrink, EF and Hunt, AJ}, title = {Rapidly prototyped three-dimensional nanofluidic channel networks in glass substrates.}, journal = {Analytical chemistry}, volume = {77}, number = {16}, pages = {5083-5088}, doi = {10.1021/ac0505167}, pmid = {16097742}, issn = {0003-2700}, support = {T32 GM145304/GM/NIGMS NIH HHS/United States ; }, mesh = {Glass/*chemistry ; Imaging, Three-Dimensional ; Microscopy, Electron, Scanning ; Nanostructures/*chemistry/ultrastructure ; Solutions ; Time Factors ; }, abstract = {Microfluidic and nanofluidic technologies have long sought a fast, reliable method to overcome the creative limitations of planar fabrication methods, the resolution limits of lithography, and the materials limitations for fast prototyping. In the present work, we demonstrate direct 3D machining of submicrometer diameter, subsurface fluidic channels in glass, via optical breakdown near critical intensity, using a femtosecond pulsed laser. No postexposure etching or bonding is required; the channel network (or almost any arbitrary-shaped cavity below the surface) is produced directly from "art-to-part". The key to this approach is to use very low energy, highly focused, pulses in the presence of liquid. Microbubbles that result from laser energy deposition gently expand and extrude machining debris from the channels. These bubbles are in a highly damped, low Reynolds number regime, implying that surface spalling due to bubble collapse is unimportant. We demonstrate rapid prototyping of three-dimensional "jumpers", mixers, and other key components of complex 3D microscale analysis systems in glass substrates.}, }
@article {pmid16090687, year = {2005}, author = {Casciola, CM and Gualtieri, P and Jacob, B and Piva, R}, title = {Scaling properties in the production range of shear dominated flows.}, journal = {Physical review letters}, volume = {95}, number = {2}, pages = {024503}, doi = {10.1103/PhysRevLett.95.024503}, pmid = {16090687}, issn = {0031-9007}, abstract = {In large Reynolds number turbulence, isotropy is recovered as the scale is reduced and homogeneous-isotropic scalings are eventually observed. This picture is violated in many cases, e.g., wall bounded flows, where, due to the shear, different scaling laws emerge. This effect has been ascribed to the contamination of the inertial range by the larger anisotropic scales. The issue is addressed here by analyzing both numerical and experimental data for a homogeneous shear flow. In fact, under strong shear, the alteration of the scaling exponents is not induced by the contamination from the anisotropic sectors. Actually, the exponents are universal properties of the isotropic component of the structure functions of shear dominated flows. The implications are discussed in the context of turbulence near solid walls, where improved closure models would be advisable.}, }
@article {pmid16090685, year = {2005}, author = {Morozov, AN and van Saarloos, W}, title = {Subcritical finite-amplitude solutions for plane Couette flow of viscoelastic fluids.}, journal = {Physical review letters}, volume = {95}, number = {2}, pages = {024501}, doi = {10.1103/PhysRevLett.95.024501}, pmid = {16090685}, issn = {0031-9007}, abstract = {Plane Couette flow of viscoelastic fluids is shown to exhibit a purely elastic subcritical instability at a very small-Reynolds number in spite of being linearly stable. The mechanism of this instability is proposed and the nonlinear stability analysis of plane Couette flow of the Upper-Convected Maxwell fluid is presented. Above a critical Weissenberg number, a small finite-size perturbation is sufficient to create a secondary flow, and the threshold value for the amplitude of the perturbation decreases as the Weissenberg number increases. The results suggest a scenario for weakly turbulent viscoelastic flow which is similar to the one for Newtonian fluids as a function of Reynolds number.}, }
@article {pmid16090474, year = {2005}, author = {Zhang, J and Wu, XL}, title = {Velocity intermittency in a buoyancy subrange in a two-dimensional soap film convection experiment.}, journal = {Physical review letters}, volume = {94}, number = {23}, pages = {234501}, doi = {10.1103/PhysRevLett.94.234501}, pmid = {16090474}, issn = {0031-9007}, abstract = {In a two-dimensional soap film convection experiment, the velocity fields are found to be strongly intermittent in the buoyancy subrange, which was reported to be nonintermittent in a recent numerical simulation. The structure functions Sq(l)(= <delta(upsilon)l(q)>) exhibit self-similar structures and can be described by power laws l(zetaq) for integers 8 > or = q < or = 1. By extending Kolmogorov's refined similarity hypothesis to our system, an analytical form is derived for the scaling exponent zeta(q) = q/2 + (mu/18)(3q - q2). Our measurements yield mu = 0.42, which is significantly greater than 0.2 found in high Reynolds number turbulence in wind tunnels.}, }
@article {pmid16090136, year = {2005}, author = {Sanyasiraju, YV and Manjula, V}, title = {Flow past an impulsively started circular cylinder using a higher-order semicompact scheme.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {72}, number = {1 Pt 2}, pages = {016709}, doi = {10.1103/PhysRevE.72.016709}, pmid = {16090136}, issn = {1539-3755}, abstract = {In the present investigation an attempt has been made to solve the two-dimensional incompressible viscous flow past an impulsively started circular cylinder for Reynolds numbers ranging from 20 to 5000 using higher-order semicompact scheme (HOSC). Unlike conventional higher-order compact schemes the HOSC scheme has been developed to handle the circular geometry of the chosen problem and the intensive algebraic manipulations have been reduced considerably by relaxing the compactness of the computational stencil for few terms (but retained for most of the terms) of the discretized equations. For the flow past an impulsively started circular cylinder the results obtained at low and moderate Reynolds numbers have been validated with the experimental and numerical observations available in the literature. For high Reynolds number flows, the present scheme rightly captures the alpha phenomenon at Re=1000 and both beta and alpha phenomena one after the other at Re=5000 .}, }
@article {pmid16090088, year = {2005}, author = {McComb, WD and Kiyani, K}, title = {Eulerian spectral closures for isotropic turbulence using a time-ordered fluctuation-dissipation relation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {72}, number = {1 Pt 2}, pages = {016309}, doi = {10.1103/PhysRevE.72.016309}, pmid = {16090088}, issn = {1539-3755}, abstract = {Procedures for time-ordering the covariance function, as given in a previous paper [K. Kiyani and W. D. McComb, Phys. Rev. E 70, 066303 (2004)], are extended and used to show that the response function associated at second order with the Kraichnan-Wyld perturbation series can be determined by a local (in wave number) energy balance. These time-ordering procedures also allow the two-time formulation to be reduced to time-independent form by means of exponential approximations and it is verified that the response equation does not have an infrared divergence at infinite Reynolds number. Last, single-time Markovianized closure equations (stated in our previous paper) are derived and shown to be compatible with the Kolmogorov distribution without the need to introduce an ad hoc constant.}, }
@article {pmid16089576, year = {2005}, author = {Balter, A and Tang, JX}, title = {Hydrodynamic stability of helical growth at low Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {71}, number = {5 Pt 1}, pages = {051912}, doi = {10.1103/PhysRevE.71.051912}, pmid = {16089576}, issn = {1539-3755}, mesh = {Actins/analysis/*chemistry ; Colloids/analysis/*chemistry ; Computer Simulation ; Crystallization/*methods ; Microfluidics/*methods ; *Models, Chemical ; *Models, Molecular ; Multiprotein Complexes/analysis/chemistry ; Protein Conformation ; Solutions ; Water/*chemistry ; }, abstract = {A cylindrical object growing at a low Reynolds number can spontaneously develop a helical shape. We have studied this phenomenon numerically, and our results may shed some light on the spontaneous formation of helical tails of a dense protein network observed in experiments on actin based motility. We also identify an unstable critical pitch angle which separates helices that straighten into rods from helices that flatten into planar curves as they grow. At the critical angle the pitch angle remains constant, whereas both helical diameter and pitch increase with the helical contour length.}, }
@article {pmid16081606, year = {2005}, author = {Lehmann, FO and Sane, SP and Dickinson, M}, title = {The aerodynamic effects of wing-wing interaction in flapping insect wings.}, journal = {The Journal of experimental biology}, volume = {208}, number = {Pt 16}, pages = {3075-3092}, doi = {10.1242/jeb.01744}, pmid = {16081606}, issn = {0022-0949}, mesh = {Animals ; Biomechanical Phenomena ; Drosophila melanogaster/anatomy &amp; histology/*physiology ; Flight, Animal/*physiology ; *Models, Anatomic ; Rheology ; Time Factors ; Wings, Animal/*physiology ; }, abstract = {We employed a dynamically scaled mechanical model of the small fruit fly Drosophila melanogaster (Reynolds number 100-200) to investigate force enhancement due to contralateral wing interactions during stroke reversal (the ;clap-and-fling'). The results suggest that lift enhancement during clap-and-fling requires an angular separation between the two wings of no more than 10-12 degrees . Within the limitations of the robotic apparatus, the clap-and-fling augmented total lift production by up to 17%, but depended strongly on stroke kinematics. The time course of the interaction between the wings was quite complex. For example, wing interaction attenuated total force during the initial part of the wing clap, but slightly enhanced force at the end of the clap phase. We measured two temporally transient peaks of both lift and drag enhancement during the fling phase: a prominent peak during the initial phase of the fling motion, which accounts for most of the benefit in lift production, and a smaller peak of force enhancement at the end fling when the wings started to move apart. A detailed digital particle image velocimetry (DPIV) analysis during clap-and-fling showed that the most obvious effect of the bilateral ;image' wing on flow occurs during the early phase of the fling, due to a strong fluid influx between the wings as they separate. The DPIV analysis revealed, moreover, that circulation induced by a leading edge vortex (LEV) during the early fling phase was smaller than predicted by inviscid two-dimensional analytical models, whereas circulation of LEV nearly matched the predictions of Weis-Fogh's inviscid model at late fling phase. In addition, the presence of the image wing presumably causes subtle modifications in both the wake capture and viscous forces. Collectively, these effects explain some of the changes in total force and lift production during the fling. Quite surprisingly, the effect of clap-and-fling is not restricted to the dorsal part of the stroke cycle but extends to the beginning of upstroke, suggesting that the presence of the image wing distorts the gross wake structure throughout the stroke cycle.}, }
@article {pmid16079346, year = {2005}, author = {Lew, RR}, title = {Mass flow and pressure-driven hyphal extension in Neurospora crassa.}, journal = {Microbiology (Reading, England)}, volume = {151}, number = {Pt 8}, pages = {2685-2692}, doi = {10.1099/mic.0.27947-0}, pmid = {16079346}, issn = {1350-0872}, mesh = {Cytoplasm/*metabolism ; Hyphae/*growth &amp; development ; Neurospora crassa/cytology/*growth &amp; development ; Pressure ; }, abstract = {Mass flow of cytoplasm in Neurospora crassa trunk hyphae was directly confirmed by injecting oil droplets into the hyphae. The droplets move in a manner similar to cytoplasmic particles and vacuoles within the hyphae. The direction of mass flow is towards the growing hyphal tips at the colony edge. Based on flow velocities (about 5 microm s(-1)), hyphal radius and estimates of cytoplasm viscosity, the Reynolds number is about 10(-4), indicating that mass flow is laminar. Therefore, the Poiseulle equation can be used to calculate the pressure gradient required for mass flow: 0.0005-0.1 bar cm(-1) (depending on the values used for septal pore radius and cytoplasmic viscosity). These values are very small compared to the normal hydrostatic pressure of the hyphae (4-5 bar). Mass flow stops after respiratory inhibition with cyanide, or creation of an extracellular osmotic gradient. The flow is probably caused by internal osmotic gradients created by differential ion transport along the hyphae. Apical cytoplasm migrates at the same rate as tip extension, as do oil droplets injected near the tip. Thus, in addition to organelle positioning mediated by molecular motors, pressure-driven mass flow may be an integral part of hyphal extension.}, }
@article {pmid16078131, year = {2005}, author = {Abrahamsson, B and Pal, A and Sjöberg, M and Carlsson, M and Laurell, E and Brasseur, JG}, title = {A novel in vitro and numerical analysis of shear-induced drug release from extended-release tablets in the fed stomach.}, journal = {Pharmaceutical research}, volume = {22}, number = {8}, pages = {1215-1226}, pmid = {16078131}, issn = {0724-8741}, mesh = {Algorithms ; Chemistry, Pharmaceutical/instrumentation ; Computer Simulation ; *Delayed-Action Preparations ; Gastric Mucosa/*metabolism ; Models, Statistical ; Pharmaceutical Preparations/*metabolism ; Rheology ; Solubility ; Solutions ; Surface Properties ; Tablets ; }, abstract = {PURPOSE: To design an in vitro apparatus that could simulate the in vivo range of surface shear stresses relevant for the human stomach under fed conditions.<br><br>METHODS: Computer simulations were combined with in vitro experiments to quantify tablet erosion rate vs. surface shear stress. From two separate computer models, of tablets in the fed stomach and of tablets in vitro, we first estimated the intragastric range of surface stress and Reynolds number (Re), and then designed a dissolution apparatus and parameter space to replicate the in vivo conditions. The in vitro tablet erosion was determined by a new rotating beaker apparatus that provided predictable surface shear on tablets. Tablet mass erosion rates were measured for two different extended-release tablets at a range of in vivo relevant surface shear stresses obtained by varying viscosity of test media and rotation rate of the beaker.<br><br>RESULTS: Mass erosion rate and surface shear were found to be highly correlated. Erosion rate increased with surface shear more rapidly at "low" stresses (<35 dyne/cm2) independent of tablet material. At higher surface stress, erosion was strongly material dependent.<br><br>CONCLUSIONS: Shear force effects on drug release from matrix tablets relevant for fed state are for the first time possible to predict by in vitro dissolution testing.}, }
@article {pmid16061240, year = {2006}, author = {Wang, X and Wu, J}, title = {Flow behavior of periodical electroosmosis in microchannel for biochips.}, journal = {Journal of colloid and interface science}, volume = {293}, number = {2}, pages = {483-488}, doi = {10.1016/j.jcis.2005.06.080}, pmid = {16061240}, issn = {0021-9797}, mesh = {Electroosmosis/*methods ; Microarray Analysis/*instrumentation/*methods ; }, abstract = {This paper presents an analytical solution for periodical electroosmotic flows in two-dimensional uniform microchannel based on Poisson-Boltzmann equations for electric double layer (EDL) and Navier-Stokes equation for incompressible viscous fluid. Analytical results indicate that the velocity of periodical electroosmosis strongly depends on Reynolds number Re=omegah(2)/nu, as well as on EDL properties and applied electric field. Slip velocity of EDL decreases as the Reynolds number increases. Electroosmotic velocity outside the EDL decreases, and lag phase angle of velocity increases as distance away from the channel wall increases. A wavelike velocity profile across the channel is found. An asymptotic solution for low Reynolds number is given in this paper. Periodical electroosmosis with low Reynolds has same velocity amplitude and a pluglike velocity profile as that of steady electroosmosis. Based on Debye-Hückel approximation, this paper also obtains a solution of periodical electroosmosis applicable to cases where the thickness of EDL is of the same order as half of channel width.}, }
@article {pmid16060347, year = {2005}, author = {Guzmán, AM and Escobar, RA and Amon, CH}, title = {Flow mixing enhancement from balloon pulsations in an intravenous oxygenator.}, journal = {Journal of biomechanical engineering}, volume = {127}, number = {3}, pages = {400-415}, doi = {10.1115/1.1894260}, pmid = {16060347}, issn = {0148-0731}, mesh = {Blood Flow Velocity/physiology ; *Blood Vessel Prosthesis ; Catheterization/*instrumentation/methods ; Computer Simulation ; Equipment Design ; Equipment Failure Analysis/*methods ; Humans ; *Models, Cardiovascular ; Oxygen/*blood ; *Oxygenators, Membrane ; Pulsatile Flow/*physiology ; Venae Cavae/*physiology/surgery ; }, abstract = {Computational investigations of flow mixing and oxygen transfer characteristics in an intravenous membrane oxygenator (IMO) are performed by direct numerical simulations of the conservation of mass, momentum, and species equations. Three-dimensional computational models are developed to investigate flow-mixing and oxygen-transfer characteristics for stationary and pulsating balloons, using the spectral element method. For a stationary balloon, the effect of the fiber placement within the fiber bundle and the number of fiber rings is investigated. In a pulsating balloon, the flow mixing characteristics are determined and the oxygen transfer rate is evaluated. For a stationary balloon, numerical simulations show two well-defined flow patterns that depend on the region of the IMO device. Successive increases of the Reynolds number raise the longitudinal velocity without creating secondary flow. This characteristic is not affected by staggered or non-staggered fiber placement within the fiber bundle. For a pulsating balloon, the flow mixing is enhanced by generating a three-dimensional time-dependent flow characterized by oscillatory radial, pulsatile longitudinal, and both oscillatory and random tangential velocities. This three-dimensional flow increases the flow mixing due to an active time-dependent secondary flow, particularly around the fibers. Analytical models show the fiber bundle placement effect on the pressure gradient and flow pattern. The oxygen transport from the fiber surface to the mean flow is due to a dominant radial diffusion mechanism, for the stationary balloon. The oxygen transfer rate reaches an asymptotic behavior at relatively low Reynolds numbers. For a pulsating balloon, the time-dependent oxygen-concentration field resembles the oscillatory and wavy nature of the time-dependent flow. Sherwood number evaluations demonstrate that balloon pulsations enhance the oxygen transfer rate, even for smaller flow rates.}, }
@article {pmid16055551, year = {2005}, author = {Alben, S and Shelley, M}, title = {Coherent locomotion as an attracting state for a free flapping body.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {102}, number = {32}, pages = {11163-11166}, pmid = {16055551}, issn = {0027-8424}, mesh = {Animals ; Biomechanical Phenomena ; Computer Simulation ; *Flight, Animal ; *Models, Theoretical ; Rheology ; }, abstract = {A recent experiment [Vandenberghe, N., Zhang, J. &amp; Childress, S. (2004) J. Fluid Mech. 506, 147-155] has shown that an axle-mounted blade can spontaneously rotate when oscillated (or "flapped") above a critical frequency in a fluid. To understand the nature of flapping locomotion we study numerically the dynamics of a simple body, flapped up and down within a viscous fluid and free to move horizontally. We show here that, at sufficiently large "frequency Reynolds number," unidirectional locomotion emerges as an attracting state for an initially nonlocomoting body. Locomotion is generated in two stages: first, the fluid field loses symmetry by an instability similar to the classical von Kármán instability; and second, precipitous interactions with previously shed vortical structures "push" the body into locomotion. Body mass and slenderness play central and unexpected roles in each stage. Conceptually, this work demonstrates how locomotion can be transduced from the simple oscillations of a body through an interaction with its fluid environment.}, }
@article {pmid16045331, year = {2005}, author = {Quevedo, E and Steinbacher, J and McQuade, DT}, title = {Interfacial polymerization within a simplified microfluidic device: capturing capsules.}, journal = {Journal of the American Chemical Society}, volume = {127}, number = {30}, pages = {10498-10499}, doi = {10.1021/ja0529945}, pmid = {16045331}, issn = {0002-7863}, abstract = {A simple approach to a microfluidic device is described. The device is composed of flexible tubing and a needle inserted orthogonal to the long axis of the tubing. This design is well suited to creating oil-water interfaces allowing the formation of laminar flows and monodisperse emulsions. The system is characterized by mapping the phases observed as a function of organic phase flow and Reynolds number. In addition, the device allows interfacial polymerization reactions to capture low coefficient of variation capsules. The shell structure and surface are examined by scanning electron microscopy.}, }
@article {pmid16024032, year = {2005}, author = {Hsu, JP and Yeh, SJ and Lee, DJ}, title = {Drag on two coaxial, nonuniformly structured flocs in a uniform flow field.}, journal = {Journal of colloid and interface science}, volume = {292}, number = {1}, pages = {290-298}, doi = {10.1016/j.jcis.2005.05.078}, pmid = {16024032}, issn = {0021-9797}, abstract = {The drag on two coaxial flocs of nonuniform structure in a Newtonian fluid is evaluated for Reynolds number ranges from 0.1 to 40. A two-layer model is adopted to simulate various possible structures of a floc. The influences of the key parameters of the problem under consideration, including the separation distance between two flocs, the Reynolds number, and the ratios (inner radius/outer radius) and (permeability of outer layer/permeability of inner layer), on the drag acting on two flocs are investigated. We show that if Reynolds number is small, the drag on the leading floc is about the same as that on the rear floc. However, if Reynolds number is sufficiently large, because wakes are formed in the rear region of the leading floc, the drag on it is greater than that on the rear floc. For a fixed mean permeability, the more nonuniform the floc structure is, the more important is its influence on the drag, and the more appreciable the deviation of the drag coefficient-Reynolds number curve from a Stokes'-law-like relation.}, }
@article {pmid16006519, year = {2005}, author = {Bell, JB and Day, MS and Shepherd, IG and Johnson, MR and Cheng, RK and Grcar, JF and Beckner, VE and Lijewski, MJ}, title = {Numerical simulation of a laboratory-scale turbulent V-flame.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {102}, number = {29}, pages = {10006-10011}, pmid = {16006519}, issn = {0027-8424}, abstract = {We present a three-dimensional, time-dependent simulation of a laboratory-scale rod-stabilized premixed turbulent V-flame. The experimental parameters correspond to a turbulent Reynolds number, Re(t) = 40, and to a Damköhler number, D(a) = 6. The simulations are performed using an adaptive time-dependent low-Mach-number model with detailed chemical kinetics and a mixture model for differential species diffusion. The algorithm is based on a second-order projection formulation and does not require an explicit subgrid model for turbulence or turbulence/chemistry interaction. Adaptive mesh refinement is used to dynamically resolve the flame and turbulent structures. Here, we briefly discuss the numerical procedure and present detailed comparisons with experimental measurements showing that the computation is able to accurately capture the basic flame morphology and associated mean velocity field. Finally, we discuss key issues that arise in performing these types of simulations and the implications of these issues for using computation to form a bridge between turbulent flame experiments and basic combustion chemistry.}, }
@article {pmid15981275, year = {2005}, author = {Saravanan, V and Sreekrishnan, TR}, title = {Hydrodynamic study of biogranules obtained from an anaerobic hybrid reactor.}, journal = {Biotechnology and bioengineering}, volume = {91}, number = {6}, pages = {715-721}, doi = {10.1002/bit.20567}, pmid = {15981275}, issn = {0006-3592}, mesh = {Anaerobiosis ; *Bioreactors ; Biotechnology/*methods ; Linear Models ; Particle Size ; }, abstract = {The bed expansion characteristics of a fluidized bed containing bacterial granules have been studied. These biogranules were obtained from an anaerobic hybrid reactor, which uses biogranules (without carrier particle) in fluidized condition. The settling velocity study of biogranules has shown that the drag coefficient of biogranule is greater than that of the rigid particle at the same Reynolds number. A new correlation based on this finding has been developed. The bed expansion study has demonstrated that a linear relationship exists between the natural logarithm of bed porosity and the natural logarithm of upflow superficial liquid velocity for the bed containing either a particular fraction of biogranule size or biogranules with wide size distribution. For a fluidized bed having a particular granule size, the bed porosity, and liquid superficial velocity could be related by the classic equation suggested by Richardson and Zaki (1954). The characteristic parameter of this correlation, the slope of the line n, has been related with Reynolds number. The intercept of the line gave a smaller value than the unhindered settling velocity of the particle. For fluidized bed having wide size distribution, the characteristic parameter n could not be related to Reynolds number. But the correlation suggested for single biogranule size has been found to predict n value with an average error of 2.3%.}, }
@article {pmid15974788, year = {2005}, author = {Felderhof, BU}, title = {Sedimentation of spheres at small Reynolds number.}, journal = {The Journal of chemical physics}, volume = {122}, number = {21}, pages = {214905}, doi = {10.1063/1.1905583}, pmid = {15974788}, issn = {0021-9606}, abstract = {The effect of fluid inertia on the settling of spheres in a viscous incompressible fluid is studied in the limit of small Reynolds number. The kinetic energy of flow depends on the positions of the spheres, and gives rise to forces on the spheres. In the dilute limit it suffices to study the corresponding pair interaction. The interaction is calculated from the Stokes flow for two spheres settling between plane walls in the point particle limit. The dissipative interaction between a pair of spheres is calculated from the Proudman-Pearson [I. Proudman and J. R. A. Pearson, J. Fluid Mech. 2, 237 (1957)] solution of the Navier-Stokes equations for flow about a sphere in unbounded geometry. The combination of kinetic and dissipative interaction gives rise to a repulsive force of range of the order of the sphere diameter divided by the Reynolds number.}, }
@article {pmid15970967, year = {2005}, author = {Kim, DS and Lee, SH and Kwon, TH and Ahn, CH}, title = {A serpentine laminating micromixer combining splitting/recombination and advection.}, journal = {Lab on a chip}, volume = {5}, number = {7}, pages = {739-747}, doi = {10.1039/b418314b}, pmid = {15970967}, issn = {1473-0197}, abstract = {Mixing enhancement has drawn great attention from designers of micromixers, since the flow in a microchannel is usually characterized by a low Reynolds number (Re) which makes the mixing quite a difficult task to accomplish. In this paper, a novel integrated efficient micromixer named serpentine laminating micromixer (SLM) has been designed, simulated, fabricated and fully characterized. In the SLM, a high level of efficient mixing can be achieved by combining two general chaotic mixing mechanisms: splitting/recombination and chaotic advection. The splitting and recombination (in other terms, lamination) mechanism is obtained by the successive arrangement of "F"-shape mixing units in two layers. The advection is induced by the overall three-dimensional serpentine path of the microchannel. The SLM was realized by SU-8 photolithography, nickel electroplating, injection molding and thermal bonding. Mixing performance of the SLM was fully characterized numerically and experimentally. The numerical mixing simulations show that the advection acts favorably to realize the ideal vertical lamination of fluid flow. The mixing experiments based on an average mixing color intensity change of phenolphthalein show a high level of mixing performance was obtained with the SLM. Numerical and experimental results confirm that efficient mixing is successfully achieved from the SLM over the wide range of Re. Due to the simple and mass producible geometry of the efficient micromixer, SLM proposed in this study, the SLM can be easily applied to integrated microfluidic systems, such as micro-total-analysis-systems or lab-on-a-chip systems.}, }
@article {pmid15936286, year = {2005}, author = {Dukhin, S and Zhu, C and Dave, RN and Yu, Q}, title = {Hydrodynamic fragmentation of nanoparticle aggregates at orthokinetic coagulation.}, journal = {Advances in colloid and interface science}, volume = {114-115}, number = {}, pages = {119-131}, doi = {10.1016/j.cis.2004.07.012}, pmid = {15936286}, issn = {0001-8686}, mesh = {Kinetics ; Models, Statistical ; Nanotechnology/*methods ; Particle Size ; Physics/methods ; *Static Electricity ; Surface Properties ; Time Factors ; Water/chemistry ; }, abstract = {Hydrodynamic forces on a doublet of large particles or aggregates during sedimentation cause the non-inertial fragmentation of the doublet, if the doublet Reynolds number and Stokes number are small. In lio-dispersed systems, this non-inertial fragmentation is known to promote the wet classification of large particles whereas the small particles are aggregated (in the secondary minimum) and hence cannot be separated despite the electrostatic repulsion. In aero-dispersed systems with negligible electrostatic repulsion, it is possible to have a narrower separation between two interacting particles so that the attractive surface forces such as van der Waals force could increase in orders of magnitude. As a result, the doublet fragmentation by the aerodynamic detaching force becomes very difficult or even impossible in sedimentation at a small Re. However, this study shows that, when extending above analysis for the interacting fractal aggregates of nanoparticles in a suspension, it is still possible to have aggregate (doublet of two nano-aggregates) fragmentation by the aerodynamic detaching force because the surface forces for nanoparticle contact between two aggregates may be in orders of magnitude smaller than that for micron-sized particles. Even with multiple contacts between two interacting nanoparticle aggregates, this prediction of aggregate fragmentation may still be valid because the contacts may break step by step due to the aggregate rolling along each other caused by a short-range aerodynamic interaction during their differential settling. The aerodynamics of aero-dispersed nanoparticle aggregates is analogous to the hydrodynamics of lio-dispersed solid particles. Therefore the hydrodynamic fragmentation model may be used to partially interpret the stability of nanoparticle fluidization process. Our model indicates that, without continued doublet fragmentation of nano-aggregates, the fluidized nanoparticle suspension would be de-fluidized within minutes via the cascading aggregation. However, the experimental evidence of a sustained operation of fluidization of nanoparticle aggregates over a very long time period without changing the size of nanoparticle aggregates indicates that there is a dynamic balance between the aggregation and fragmentation of nano-aggregates in nanoparticle fluidization. The prediction of critical size of nanoparticle aggregates caused by fragmentation in stabilized fluidization agrees with our in situ measurements.}, }
@article {pmid15927627, year = {2005}, author = {Sánchez, M and Luna, E and Medina, A and Méndez, F}, title = {Simultaneous imbibition-heat convection process in a non-Darcian porous medium.}, journal = {Journal of colloid and interface science}, volume = {288}, number = {2}, pages = {562-569}, doi = {10.1016/j.jcis.2005.03.016}, pmid = {15927627}, issn = {0021-9797}, abstract = {In the present work, the nonisothermal imbibition process in a porous medium was numerically analyzed using a non-Darcian model for the momentum equation and energy equations for the wetting and dry zones. In order to show the thermal character of the problem, we assume initially that the porous medium is found at a uniform temperature T0 and suddenly begins the imbibition process into the porous medium with a penetrating fluid at temperature T1. The physical influence of nondimensional parameters such as Peclet number, Pe, effective heat capacity number, beta(w), porous Reynolds number, Re(p), and the inertial coefficient of the porous medium, F, serve us to evaluate the position and velocity of the imbibition front as well as temperature profiles in both zones. In particular, for values of Re(p)F/beta(w)>>1, we recover a type of nonisothermal Washburn law. The numerical predictions show that the imbibition front and the temperature fields strongly depend on the above nondimensional parameters, revealing a clear deviation of the simple Washburn law.}, }
@article {pmid15909650, year = {2005}, author = {Seo, T and Schachter, LG and Barakat, AI}, title = {Computational study of fluid mechanical disturbance induced by endovascular stents.}, journal = {Annals of biomedical engineering}, volume = {33}, number = {4}, pages = {444-456}, doi = {10.1007/s10439-005-2499-y}, pmid = {15909650}, issn = {0090-6964}, mesh = {Animals ; Biomechanical Phenomena/methods ; Blood Flow Velocity/*physiology ; Blood Pressure/physiology ; *Blood Vessel Prosthesis ; Blood Vessels/*physiology ; Computer Simulation ; Computer-Aided Design ; Equipment Failure Analysis/*methods ; Hemorheology/*methods ; Humans ; *Models, Cardiovascular ; Nonlinear Dynamics ; Prosthesis Design ; Pulsatile Flow/physiology ; Shear Strength ; *Stents ; Vascular Surgical Procedures/instrumentation/methods ; }, abstract = {Arterial restenosis following stent deployment may be influenced by the local flow environment within and around the stent. We have used computational fluid dynamics to investigate the flow field in the vicinity of model stents positioned within straight and curved vessels. Our simulations have revealed the presence of flow separation and recirculation immediately downstream of stents. In steady flow within straight vessels, the extent of flow disturbance downstream of the stent increases with both Reynolds number and stent wire thickness but is relatively insensitive to stent interwire spacing. In curved vessels, flow disturbance downstream of the stent occurs along both the inner and outer vessel walls with the extent of disturbance dependent on the angle of vessel curvature. In pulsatile flow, the regions of flow disturbance periodically increase and decrease in size. Non-Newtonian fluid properties lead to a modest reduction in flow disturbance downstream of the stent. In more realistic stent geometries such as stents modeled as spirals or as intertwined rings, the nature of stent-induced flow disturbance is exquisitely sensitive to stent design. These results provide an understanding of the flow physics in the vicinity of stents and suggest strategies for stent design optimization to minimize flow disturbance.}, }
@article {pmid15904232, year = {2005}, author = {Ponty, Y and Mininni, PD and Montgomery, DC and Pinton, JF and Politano, H and Pouquet, A}, title = {Numerical study of dynamo action at low magnetic Prandtl numbers.}, journal = {Physical review letters}, volume = {94}, number = {16}, pages = {164502}, doi = {10.1103/PhysRevLett.94.164502}, pmid = {15904232}, issn = {0031-9007}, abstract = {We present a three-pronged numerical approach to the dynamo problem at low magnetic Prandtl numbers P(M). The difficulty of resolving a large range of scales is circumvented by combining direct numerical simulations, a Lagrangian-averaged model and large-eddy simulations. The flow is generated by the Taylor-Green forcing; it combines a well defined structure at large scales and turbulent fluctuations at small scales. Our main findings are (i) dynamos are observed from P(M)=1 down to P(M)=10(-2), (ii) the critical magnetic Reynolds number increases sharply with P(M)(-1) as turbulence sets in and then it saturates, and (iii) in the linear growth phase, unstable magnetic modes move to smaller scales as P(M) is decreased. Then the dynamo grows at large scales and modifies the turbulent velocity fluctuations.}, }
@article {pmid15903994, year = {2005}, author = {Simonnet, C and Groisman, A}, title = {Chaotic mixing in a steady flow in a microchannel.}, journal = {Physical review letters}, volume = {94}, number = {13}, pages = {134501}, doi = {10.1103/PhysRevLett.94.134501}, pmid = {15903994}, issn = {0031-9007}, abstract = {We report experiments on mixing of a passively advected fluorescent dye in a low Reynolds number flow in a microscopic channel. The channel is a chain of repeating segments with a custom designed profile that generates a steady three-dimensional flow with stretching and folding, and chaotic mixing. A few statistical characteristics of mixing in the flow are studied and are all found to agree with theoretical and experimental results for the flows in the Batchelor regime of mixing that are chaotic in time. The proposed microchannel provides fast and efficient mixing and is simple to fabricate.}, }
@article {pmid15903786, year = {2005}, author = {ElMaihy, A and Nicolleau, F}, title = {Investigation of the dispersion of heavy-particle pairs and Richardson's law using kinematic simulation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {71}, number = {4 Pt 2}, pages = {046307}, doi = {10.1103/PhysRevE.71.046307}, pmid = {15903786}, issn = {1539-3755}, abstract = {In this paper we investigate the dispersion of heavy-particle pairs (particles with inertia in a gravity field). We vary the particles' inertia when there is no gravity, and the particles' drift at constant inertia. We use kinematic simulation (KS) for which large values of the Reynolds number can be achieved. We investigate the pair diffusivity to discuss Richardson's law, and the locality-in-scale hypothesis that underlies that law, for different particle drifts and Stokes numbers. The effect of inertia and gravity on Richardson's law and the autocorrelation in time of the pair's separation are studied for an inertial scale ratio of 1000 and different initial separations delta0 . We extend results from F. Nicolleau and J. C. Vassilicos, Phys. Rev. Lett. 90, 024503 (2003) to three-dimensional (3D) KS and the diffusivity-based analysis of F. Nicolleau and G. Yu, Phys. Fluids 16, 2309 (2004) to particles with inertia and gravity. We find that inertia impedes the locality-in-scale hypothesis whereas gravity improves it. However, the overall effect of gravity and inertia is to decrease the pair's diffusivity in the inertial range.}, }
@article {pmid15903577, year = {2005}, author = {Panga, MK and Mudunuri, RR and Balakotaiah, V}, title = {Long-wavelength equation for vertically falling films.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {71}, number = {3 Pt 2B}, pages = {036310}, doi = {10.1103/PhysRevE.71.036310}, pmid = {15903577}, issn = {1539-3755}, abstract = {An equation is derived for describing wave evolution on the surface of a vertically falling viscous film. The traditional long-wavelength scaling is replaced by a new scaling to reduce the (We) must be used instead of the Reynolds number (Re) to distinguish between viscous and inertia dominated regimes for vertically falling films. This equation includes viscous dissipation and pressure correction terms that are missing in the existing single evolution equations at the same order. Comparison of the neutral stability curves and growth rates predicted by different models to that of the Orr-Sommerfeld (OS) equation shows that our equation matches with the OS results better than the existing single evolution equations. However, our equation is not free from finite time blowup. Selective regularization leads to a two mode model in flow rate and film thickness. The regularized equation is free from finite time blowup and predicts two families of solitary waves. Numerical simulations of the derived equation and its regularized version in the traveling wave coordinate show the transition of wave structure from regular (periodic) to chaotic profiles. Model predictions on maximum wave amplitude on the low celerity branch show good agreement with experimental data.}, }
@article {pmid15903574, year = {2005}, author = {Boffetta, G and Celani, A and Mazzino, A}, title = {Drag reduction in the turbulent Kolmogorov flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {71}, number = {3 Pt 2B}, pages = {036307}, doi = {10.1103/PhysRevE.71.036307}, pmid = {15903574}, issn = {1539-3755}, abstract = {We investigate the phenomenon of drag reduction in a viscoelastic fluid model of dilute polymer solutions. By means of direct numerical simulations of the three-dimensional turbulent Kolmogorov flow we show that drag reduction takes place above a critical Reynolds number Re(c). An explicit expression for the dependence of Re(c) on polymer elasticity and diffusivity is derived. The values of the drag coefficient obtained for different fluid parameters collapse onto a universal curve when plotted as a function of the rescaled Reynolds number Re/ Re(c). The analysis of the momentum budget allows us to gain some insight on the physics of drag reduction, and suggests the existence of a Re-independent value of the drag cofficient--lower than the Newtonian one--for large Reynolds numbers.}, }
@article {pmid15903570, year = {2005}, author = {Pearson, BR and van de Water, W}, title = {Inverse structure functions.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {71}, number = {3 Pt 2B}, pages = {036303}, doi = {10.1103/PhysRevE.71.036303}, pmid = {15903570}, issn = {1539-3755}, abstract = {While the ordinary structure function in turbulence is concerned with the statistical moments of the velocity increment Deltau measured over a distance r , the inverse structure function is related to the distance r where the turbulent velocity exits the interval Deltau. We study inverse structure functions of wind-tunnel turbulence which covers a range of Reynolds numbers Re(lambda) = 400-1100. We test a recently proposed relation between the scaling exponents of the ordinary structure functions and those of the inverse structure functions [S. Roux and M. H. Jensen, Phys. Rev. E 69, 16309 (2004)]. The relatively large range of Reynolds numbers in our experiment also enables us to address the scaling with Reynolds number that is expected to highlight the intermediate dissipative range. While we firmly establish the (relative) scaling of inverse structure functions, our experimental results fail both predictions. Therefore, the question of the significance of inverse structure functions remains open.}, }
@article {pmid15886673, year = {2005}, author = {Dardik, A and Chen, L and Frattini, J and Asada, H and Aziz, F and Kudo, FA and Sumpio, BE}, title = {Differential effects of orbital and laminar shear stress on endothelial cells.}, journal = {Journal of vascular surgery}, volume = {41}, number = {5}, pages = {869-880}, doi = {10.1016/j.jvs.2005.01.020}, pmid = {15886673}, issn = {0741-5214}, support = {R01-HL47345-05/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Aorta/cytology ; Apoptosis/physiology ; Arteriosclerosis/prevention &amp; control ; Cattle ; Cell Count ; Cell Division/physiology ; Cells, Cultured ; Endothelium, Vascular/*cytology/physiology ; Flow Cytometry ; Fluorescent Antibody Technique, Indirect ; Humans ; Immunoblotting ; Immunohistochemistry ; In Vitro Techniques ; Laser-Doppler Flowmetry ; Rotation ; Stress, Mechanical ; Umbilical Veins/cytology ; }, abstract = {OBJECTIVE: Laminar shear stress is atheroprotective for endothelial cells (ECs), whereas nonlaminar, disturbed, or oscillatory shear stress correlates with development of atherosclerosis and neointimal hyperplasia. The effects of orbital and laminar shear stress on EC morphology, proliferation, and apoptosis were compared.<br><br>METHODS: ECs were exposed to orbital shear stress with an orbital shaker (210 rpm) or laminar shear stress (14 dyne/cm 2) with a parallel plate. Shear stress in the orbital shaker was measured with optical velocimetry. Cell proliferation was assessed with direct counting and proliferating cell nuclear antigen staining; apoptosis was assessed with transferase-mediated deoxyuridine triphosphate nick end labeling staining. Cell surface E-selectin and intercellular adhesion molecule expression were assessed with fluorescence-activated cell sorting. Akt phosphorylation was assessed with Western blotting.<br><br>RESULTS: Orbital shear stress increased EC proliferation by 29% and 3 [H]thymidine incorporation two-fold compared to 16% and 38% decreases, respectively, in ECs treated with laminar shear stress (P < .0001 and P = .03, analysis of variance). Cells in the periphery of the culture well aligned to the direction of shear stress similar to the shape change seen with laminar shear stress, whereas ECs in the center of the well appeared unaligned similar to ECs not exposed to shear stress. Shear stress at the bottom surface of the culture well was reduced in the center of the well (5 dyne/cm 2) compared to the periphery (11 dyne/cm 2); the Reynolds' number was 2066. ECs were seeded differentially in the center and periphery of the wells. ECs in the center of the well had increased proliferation, increased apoptosis, reduced Akt phosphorylation, increased intercelluar adhesion molecule expression, and reduced E-selectin down-regulation, compared with ECs in the periphery of the well.<br><br>CONCLUSION: Although the orbital shaker does not apply uniform shear stress throughout the culture well, arterial magnitudes of shear stress are present in the periphery of the well. ECs cultured in the center of the well exposed to low magnitudes of orbital shear stress might be a model of the "activated" EC phenotype.<br><br>CLINICAL RELEVANCE: The perfect in vitro model to study and assess treatments for atherosclerosis and neointimal hyperplasia does not exists. An extensive body of literature describing effects of laminar shear stress on endothelial cells has contributed to our understanding of the interactions between shear stress and blood vessels. Laminar shear stress is atheroprotective, whereas oscillatory or disturbed shear stress correlates with areas of atherosclerosis and neointimal hyperplasia in vivo. This study describes the orbital shear stress model, its effects on endothelial cell proliferation and apoptosis, and suggests that activation of the intracellular Akt pathway is associated with these differing effects of laminar and orbital shear stress on endothelial cells.}, }
@article {pmid15871263, year = {2005}, author = {Weber, WJ and Kim, HS}, title = {Optimizing contaminant desorption and bioavailability in dense slurry systems. 1. Rheology, mechanical mixing, and PAH desorption.}, journal = {Environmental science &amp; technology}, volume = {39}, number = {7}, pages = {2267-2273}, doi = {10.1021/es049565b}, pmid = {15871263}, issn = {0013-936X}, mesh = {Adsorption ; Chromatography, High Pressure Liquid ; Environmental Pollution/*prevention &amp; control ; Polycyclic Aromatic Hydrocarbons/*chemistry ; Rheology/*methods ; Soil Pollutants/*analysis ; Viscosity ; }, abstract = {Intermittently mixed batch reactor (IMBR) systems were employed to evaluate the effects of mechanical mixing and corresponding power consumption on rates of phenanthrene desorption from natural and synthetic model sorbent phases to the aqueous phase in dense slurry reactors. Sorbent slurries comprising 57-67% (w/w) solids exhibited non-Newtonian (pseudoplastic) fluid behaviors, with apparent viscosities varying with shear rate. Dimensionless power numbers varied inversely with the Reynolds number under laminar flow conditions, indicating that small increases in mixing revolution number and auger size effect significant increases in power and torque requirements for the mechanical mixing of dense slurries. Rates of release of phenanthrene associated with rapidly desorbing or labile fractions of sorbent organic matter (SOM) to the aqueous phase were markedly enhanced by relatively low-level auger mixing, but significantly less further enhancement was observed as higher levels of mixing were applied. Conversely, desorption of phenanthrene associated with slowly desorbing or resistant fractions of SOM was relatively unaffected by auger mixing, being limited as it is by slow intraparticle-scale diffusion processes that are not enhanced by reactor-scale mixing. The experimental results lead to and support a conclusion that auger mixing at relatively low intensity is an attractive strategy for optimizing dense slurry reactor systems for remediation of hydrophobic organic contaminants associated with labile (rapidly desorbing) fractions of SOM with respect to performance efficiency and cost-effectiveness.}, }
@article {pmid15868787, year = {2005}, author = {Bertram, CD and Nugent, AH}, title = {The flow field downstream of an oscillating collapsed tube.}, journal = {Journal of biomechanical engineering}, volume = {127}, number = {1}, pages = {39-45}, doi = {10.1115/1.1835351}, pmid = {15868787}, issn = {0148-0731}, mesh = {Animals ; Biological Clocks/*physiology ; Computer Simulation ; Elasticity ; Humans ; *Models, Biological ; Movement/*physiology ; Oscillometry/*methods ; Rheology/*methods ; Shear Strength ; Stress, Mechanical ; }, abstract = {A two-component laser Doppler anemometer was used to determine the velocity of aqueous flow in the region from 0.25 to 2.5 diameters downstream of a collapsible tube while the tube was executing vigorous repetitive flow-induced oscillations. The Reynolds number for the time-averaged flow was 10,750. A simultaneous measurement of the pressure at the downstream end of the tube was used to align all the results in time at sixty locations in each of the two principal planes defined by the axes of collapse of the flexible tube upstream. The raw data of seed-particle velocity were used to create a periodic waveform for each measured velocity component at each location by least-squares fitting of a Fourier series. The results are presented as both velocity vectors and interpolated contours, for each of ten salient instants during the cycle of oscillation. In the plane of the collapse major axis, the dominant feature is the jet which emerges from each of the two tube lobes when it collapses, but transient retrograde flow is observed on both the central and lateral edges of this jet. In the orthogonal, minor-axis plane, the dominant feature is the retrograde flow, which during part of the cycle extends over the whole plane. All these features are essentially confined to the first 1.5 diameters of the rigid pipe downstream of the flexible tube. These data map the temporal and spatial extent of the highly three-dimensional reversing flow just downstream of an oscillating collapsed tube.}, }
@article {pmid15855397, year = {2005}, author = {Marden, JH}, title = {Scaling of maximum net force output by motors used for locomotion.}, journal = {The Journal of experimental biology}, volume = {208}, number = {Pt 9}, pages = {1653-1664}, doi = {10.1242/jeb.01483}, pmid = {15855397}, issn = {0022-0949}, mesh = {Animals ; Biomechanical Phenomena ; Biophysical Phenomena ; *Biophysics ; Energy Metabolism/*physiology ; Engineering ; Locomotion/*physiology ; *Models, Biological ; Molecular Motor Proteins/*physiology ; Muscle, Skeletal/*physiology ; }, abstract = {Biological and engineered motors are surprisingly similar in their adherence to two or possibly three fundamental regimes for the mass scaling of maximum force output (Fmax). One scaling regime (Group 1: myosin, kinesin, dynein and RNA polymerase molecules; muscle cells; whole muscles; winches; linear actuators) comprises motors that create slow translational motion with force outputs limited by the axial stress capacity of the motor, which results in Fmax scaling as motor mass0.67 (M0.67). Another scaling regime (Group 2: flying birds, bats and insects; swimming fish; running animals; piston engines; electric motors; jets) comprises motors that cycle rapidly, with significant internal and external accelerations, and for whom inertia and fatigue life appear to be important constraints. The scaling of inertial loads and fatigue life both appear to enforce Fmax scaling as M1.0 in these motors. Despite great differences in materials and mechanisms, the mass specific Fmax of Group 2 motors clusters tightly around a mean of 57 N kg(-1), a region of specific force loading where there appears to be a common transition from high- to low-cycle fatigue. For motors subject to multi-axial stresses, the steepness of the load-life curve in the neighborhood of 50-100 N kg(-1) may overwhelm other material and mechanistic factors, thereby homogenizing the mass specific Fmax of grossly dissimilar animals and machines. Rockets scale with Group 1 motors but for different mechanistic reasons; they are free from fatigue constraints and their thrust is determined by mass flow rates that depend on cross sectional area of the exit nozzle. There is possibly a third scaling regime of Fmax for small motors (bacterial and spermatazoan flagella; a protozoan spring) where viscosity dominates over inertia. Data for force output of viscous regime motors are scarce, but the few data available suggest a gradually increasing scaling slope that converges with the Group 2 scaling relationship at a Reynolds number of about 10(2). The Group 1 and Group 2 scaling relationships intersect at a motor mass of 4400 kg, which restricts the force output and design of Group 2 motors greater than this mass. Above 4400 kg, all motors are limited by stress and have Fmax that scales as M0.67; this results in a gradual decline in mass specific Fmax at motor mass greater than 4400 kg. Because of declining mass specific Fmax, there is little or no potential for biological or engineered motors or rockets larger than those already in use.}, }
@article {pmid15848443, year = {2005}, author = {Hsu, JP and Shie, CF and Tseng, S}, title = {Sedimentation of a cylindrical particle in a Carreau fluid.}, journal = {Journal of colloid and interface science}, volume = {286}, number = {1}, pages = {392-399}, doi = {10.1016/j.jcis.2005.01.041}, pmid = {15848443}, issn = {0021-9797}, abstract = {The drag coefficient of an isolated, rigid cylindrical particle in a Carreau fluid is evaluated. The result of numerical simulation reveals that, in general, the shear-thinning nature of a Carreau fluid yields a drag coefficient smaller than that for the corresponding Newtonian fluid. Also, the smaller the Reynolds number, the more appreciable the decrease of the drag coefficient as the relaxation time constant of the Carreau fluid increases. The influence of the index parameter of a Carreau fluid on the drag coefficient depends largely on the magnitude of the relaxation time constant and is insensitive to the Reynolds number. Only if the relaxation time constant is sufficiently large is the influence of the index parameter on the drag coefficient significant. If the Reynolds number and/or the relaxation time constant is sufficiently large, the flow field upstream of a particle becomes asymmetric to that downstream. In general, the influence of the index parameter, the relaxation time constant, and the Reynolds number on the flow field follows the order index parameter<relaxation time constant<Reynolds number.}, }
@article {pmid15812001, year = {2005}, author = {McDonald, WL and O'Riley, KJ and Schroen, CJ and Condron, RJ}, title = {Heat inactivation of Mycobacterium avium subsp. paratuberculosis in milk.}, journal = {Applied and environmental microbiology}, volume = {71}, number = {4}, pages = {1785-1789}, pmid = {15812001}, issn = {0099-2240}, mesh = {Animals ; Cattle ; Colony Count, Microbial ; Culture Media ; Food Contamination ; Food Handling/instrumentation/methods ; *Hot Temperature ; Milk/*microbiology ; Mycobacterium avium subsp. paratuberculosis/*growth &amp; development ; Sensitivity and Specificity ; Sterilization/*instrumentation/*methods ; }, abstract = {The effectiveness of pasteurization and the concentration of Mycobacterium avium subsp. paratuberculosis in raw milk have been identified in quantitative risk analysis as the most critical factors influencing the potential presence of viable Mycobacterium paratuberculosis in dairy products. A quantitative assessment of the lethality of pasteurization was undertaken using an industrial pasteurizer designed for research purposes with a validated Reynolds number of 62,112 and flow rates of 3,000 liters/h. M. paratuberculosis was artificially added to raw whole milk, which was then homogenized, pasteurized, and cultured, using a sensitive technique capable of detecting one organism per 10 ml of milk. Twenty batches of milk containing 10(3) to 10(4) organisms/ml were processed with combinations of three temperatures of 72, 75, and 78 degrees C and three time intervals of 15, 20, and 25 s. Thirty 50-ml milk samples from each processed batch were cultured, and the logarithmic reduction in M. paratuberculosis organisms was determined. In 17 of the 20 runs, no viable M. paratuberculosis organisms were detected, which represented > 6-log10 reductions during pasteurization. These experiments were conducted with very heavily artificially contaminated milk to facilitate the measurement of the logarithmic reduction. In three of the 20 runs of milk, pasteurized at 72 degrees C for 15 s, 75 degrees C for 25 s, and 78 degrees C for 15 s, a few viable organisms (0.002 to 0.004 CFU/ml) were detected. Pasteurization at all temperatures and holding times was found to be very effective in killing M. paratuberculosis, resulting in a reduction of > 6 log10 in 85% of runs and > 4 log10 in 14% of runs.}, }
@article {pmid15801780, year = {2005}, author = {Carlozzi, P and Ena, A and Carnevale, S}, title = {Hydrodynamic alterations during cyanobacteria (Arthrospira platensis) growth from low to high biomass concentration inside tubular photobioreactors.}, journal = {Biotechnology progress}, volume = {21}, number = {2}, pages = {416-422}, doi = {10.1021/bp049665l}, pmid = {15801780}, issn = {8756-7938}, mesh = {*Bioreactors ; Cyanobacteria/*growth &amp; development ; Kinetics ; Photochemistry ; }, abstract = {The rheological behavior of an Arthrospira culture was studied from low to high biomass concentration. Two tubular undulating row photobioreactors (TURP-5r and TURP-10r), with a very short light path of 1.0 cm, were used during batch growth. In TURP-5r, the biomass concentration increased to 14.5 g(dw) L(-1), and alterations of the physical properties and hydrodynamic behavior occurred as a result. In the past, the rheological characteristics of photosynthetic-microbe cultures were rarely investigated because of the low biomass concentration attained in the systems. Developing closed photobioreactor technologies, the optimum biomass concentration rises and the viscosity, the generalized Reynolds number (N'(Re)), and the power required for culture recycling are also subject to alteration. Starting from a biomass concentration of 4.1 g(dw) L(-1), the Arthrospira culture already exhibits the characteristics of a non-Newtonian fluid. As a result of culture recycling from 2.0 to 20.5 g(dw) L(-1) and an available power of 1.67 W row(-1), we demonstrated that N'(Re) is reduced from 6265 to 1148. Our experimental results showed that N'(Re) of 2345 can be reached only at a cell concentration below 11.1 g(dw) L(-1), while at a cell concentration below 4.1 g(dw) L(-1) N'(Re) = 4080 was reached. The power consumption (P(c)) for culture recycling increased noticeably when the cell concentration rose; the highest P(c) increase attained was from 2.0 to 4.1 g(dw) L(-1). This is the range within which the Arthrospira culture changes from a Newtonian to a non-Newtonian fluid.}, }
@article {pmid15783649, year = {2005}, author = {Roushan, P and Wu, XL}, title = {Structure-based interpretation of the Strouhal-Reynolds number relationship.}, journal = {Physical review letters}, volume = {94}, number = {5}, pages = {054504}, doi = {10.1103/PhysRevLett.94.054504}, pmid = {15783649}, issn = {0031-9007}, abstract = {The wake in the flow past a circular cylinder has posed a long-standing challenge to scientists since the late 19th century. Many aspects of this seemingly simple phenomenon remain unexplained. Of particular interest is the relationship between the dimensionless vortex shedding frequency (the Strouhal number St) and the ratio of inertial to viscous forces in the fluid (the Reynolds number Re). We propose a new St-Re relation based on the observations of the structure of a vortex street in flowing soap films. The measurements suggest a simple two-parameter form St=1/(A+B/Re) that describes laminar vortex shedding remarkably well for bulk fluids as well as for two-dimensional flowing soap films.}, }
@article {pmid15783076, year = {2005}, author = {Schalper, K and Harnisch, S and Müller, RH and Hildebrand, GE}, title = {Preparation of microparticles by micromixers: characterization of oil/water process and prediction of particle size.}, journal = {Pharmaceutical research}, volume = {22}, number = {2}, pages = {276-284}, pmid = {15783076}, issn = {0724-8741}, mesh = {*Microspheres ; Oils/*chemistry ; Particle Size ; Predictive Value of Tests ; Technology, Pharmaceutical/*instrumentation/*methods ; Viscosity ; Water/*chemistry ; }, abstract = {PURPOSE: A descriptive model for microparticle preparation by micromixers was developed to allow prediction of nascent microsphere size and provide a better understanding of a microscale oil/water (O/W) emulsion process.<br><br>METHODS: Nascent blank microparticles were prepared by an O/W emulsion method using a micromixer. Seven dimensionless groups were derived from the relevant process parameters. A multiple linear regression model was established on an empirical basis to describe the relationship between the key process parameters and the resulting Sauter particle diameter.<br><br>RESULTS: The investigated micromixer is particularly suitable for processing of low-viscosity systems. The particle size is mainly controlled by flow velocity. Reynolds number and the viscosity ratio were found to be the most important dimensionless groups regarding the preparation procedure. Particle size was predicted with an accuracy up to 100% applying the empirically derived equations.<br><br>CONCLUSIONS: An O/W process using micromixers for microparticle preparation with a multitude of influencing parameters was successfully characterized by application of dimensional analysis. Dimensionless groups turned out to be suitable for prediction of microparticle size with high precision.}, }
@article {pmid15780316, year = {2005}, author = {Hsu, JP and Hsieh, YH and Tseng, S}, title = {Drag force on a rigid spheroidal particle in a cylinder filled with Carreau fluid.}, journal = {Journal of colloid and interface science}, volume = {284}, number = {2}, pages = {729-741}, doi = {10.1016/j.jcis.2004.08.124}, pmid = {15780316}, issn = {0021-9797}, abstract = {The boundary effect on the drag acting on a rigid particle is investigated by considering a spheroid on the axis of a cylinder filled with a Carreau fluid. The result of numerical simulation reveals that the ratio (drag coefficient in Carreau fluid/drag coefficient in Newtonian fluid) has a maximum as the ratio (semiaxis in radial direction/radius of cylinder) varies. The presence of a wall has the effect of enhancing the convective motion in the rear part of a particle, and therefore, the formation of wakes. The influence of the shape of a particle on the drag force acting on it can be decreased either by increasing the shear-thinning effect of the fluid or by increasing the Reynolds number. The Reynolds number at which flow separation occurs is found to increase roughly linearly with the increase in the power-law exponent of the Carreau fluid.}, }
@article {pmid15752821, year = {2005}, author = {Hsu, JP and Li, MC and Chang, AC}, title = {Drag of a dispersion of nonhomogeneously structured flocs in a flow field.}, journal = {Journal of colloid and interface science}, volume = {284}, number = {1}, pages = {332-338}, doi = {10.1016/j.jcis.2004.09.070}, pmid = {15752821}, issn = {0021-9797}, abstract = {The influence of floc structure and floc concentration on the drag acting on a floc is investigated theoretically. A two-layer model is adopted to describe floc structure, and a cell model is used to simulate a floc dispersion. The influences of the key parameters of the problem under consideration, including floc concentration, Reynolds number, the ratio (permeability of outer layer/permeability of inner layer), and the ratio (thickness of outer layer/thickness of inner layer), on the drag coefficient are discussed. We show that the more heterogeneous the floc structure is, the greater the drag and the more significant the deviation of curve of variation of drag coefficient against Reynolds number from a Stokes-law-like relation. The drag on a floc declines with the decrease in floc concentration, and, due to the convective flow of the fluid, the distortion of streamlines surrounding a floc becomes more serious and the deviation of the variation of the curve of drag against Reynolds number from a Stokes-law-like relation is more significant.}, }
@article {pmid15752809, year = {2005}, author = {Mullins, BJ and Braddock, RD and Agranovski, IE and Cropp, RA and O'Leary, RA}, title = {Observation and modelling of clamshell droplets on vertical fibres subjected to gravitational and drag forces.}, journal = {Journal of colloid and interface science}, volume = {284}, number = {1}, pages = {245-254}, doi = {10.1016/j.jcis.2004.10.013}, pmid = {15752809}, issn = {0021-9797}, abstract = {Extensive experimental investigation of the wetting processes of fibre-liquid systems during air filtration (when drag and gravitational forces are acting) has shown many important features, including droplet extension, oscillatory motion, and detachment of drops from fibres as airflow velocity increases, and also movement or flow of droplets along fibres. A detailed experimental study of the processes was conducted using stainless steel filter fibres and H2O aerosol, which coalesce on the fibre to form clamshell droplets. The droplets were predominantly observed in the Reynolds transition flow region, since this is the region where most of the above features occur. The droplet oscillation is believed to be induced by the onset of the transition from laminar to turbulent flow as the increasing droplet size increases Reynolds number for the flow around the droplet. Two-dimensional flow in this region is usually modelled using the classical Karman vortex street, however there exist no 3D equivalents. Therefore to model such oscillation it was necessary to create a new conceptual model to account for the forces both inducing and preventing such oscillation. The agreement between the model and experimental results is very good for both the radial and transverse oscillations.}, }
@article {pmid15721036, year = {2005}, author = {Azuma, A and Okamoto, M}, title = {Theoretical study on two-dimensional aerodynamic characteristics of unsteady wings.}, journal = {Journal of theoretical biology}, volume = {234}, number = {1}, pages = {67-78}, doi = {10.1016/j.jtbi.2004.11.016}, pmid = {15721036}, issn = {0022-5193}, mesh = {Animals ; Biomechanical Phenomena ; Flight, Animal/*physiology ; *Models, Biological ; Rheology ; Wings, Animal/*physiology ; }, abstract = {A simple computing method based on a potential theory is developed for two-dimensional steady and unsteady deflected wings. This method of theoretical analysis is essentially related to thin and angular airfoils. Thus, the method is very simple but is effective to forecast aerodynamic forces for deflected or angular airfoils with a small camber operating in high Reynolds number flow, specifically in unsteady motion. The suction force acting on the leading edge of steady airfoils is theoretically obtained by using the Blasius formula. By Polhamus's leading edge suction analogy, the suction force is considered to be directed upward in partially separated flow for real thin airfoil with sharp leading edge. The theory can also be applied to obtain the aerodynamic characteristics of thin airfoils operating on low Reynolds number flow under some degree of approximation. This is very useful for the unsteady aerodynamic analysis because the Navier-Stokes equation can be solved by neither analytical nor numerical method for the thin and angular airfoils, which are common in the insect wing.}, }
@article {pmid15713299, year = {2005}, author = {Mishra, M and Rao, AR}, title = {Peristaltic transport in a channel with a porous peripheral layer: model of a flow in gastrointestinal tract.}, journal = {Journal of biomechanics}, volume = {38}, number = {4}, pages = {779-789}, doi = {10.1016/j.jbiomech.2004.05.017}, pmid = {15713299}, issn = {0021-9290}, mesh = {Biological Transport ; Body Fluids ; Duodenogastric Reflux ; Gastrointestinal Tract/metabolism/*physiology ; Humans ; Models, Biological ; Peristalsis/*physiology ; Porosity ; *Rheology ; Stress, Mechanical ; }, abstract = {Peristaltic transport in a two dimensional channel, filled with a porous medium in the peripheral region and a Newtonian fluid in the core region, is studied under the assumptions of long wavelength and low Reynolds number. The fluid flow is investigated in the waveframe of reference moving with the velocity of the peristaltic wave. Brinkman extended Darcy equation is utilized to model the flow in the porous layer. The interface is determined as a part of the solution using the conservation of mass in both the porous and fluid regions independently. A shear-stress jump boundary condition is used at the interface. The physical quantities of importance in peristaltic transport like pumping, trapping, reflux and axial velocity are discussed for various parameters of interest governing the flow like Darcy number, porosity, permeability, effective viscosity etc. It is observed that the peristalsis works as a pump against greater pressure in two-layered model with a porous medium compared with a viscous fluid in the peripheral layer. Increasing Darcy number Da decreases the pumping and increasing shear stress jump constant beta results in increasing the pumping. The limits on the time averaged flux Q for trapping in the core layer are obtained. The discussion on pumping, trapping and reflux may be helpful in understanding some of the fluid dynamic aspects of the transport of chyme in gastrointestinal tract.}, }
@article {pmid15698178, year = {2005}, author = {Crawford, AM and Mordant, N and Bodenschatz, E}, title = {Joint statistics of the Lagrangian acceleration and velocity in fully developed turbulence.}, journal = {Physical review letters}, volume = {94}, number = {2}, pages = {024501}, doi = {10.1103/PhysRevLett.94.024501}, pmid = {15698178}, issn = {0031-9007}, abstract = {We report experimental results on the joint statistics of the Lagrangian acceleration and velocity in highly turbulent flows. The acceleration was measured up to a microscale Reynolds number R(lambda)=690 using high speed silicon strip detectors from high energy physics. The acceleration variance was observed to be strongly dependent on the velocity, following a Heisenberg-Yaglom-like u(9/2) increase. However, the shape of the probability density functions of the acceleration component conditioned on the same component of the velocity when normalized by the acceleration variance was observed to be independent of velocity and to coincide with the unconditional probability density function of the acceleration components. This observation imposes a strong mathematical constraint on the possible functional form of the acceleration probability distribution function.}, }
@article {pmid15697717, year = {2005}, author = {Frenkel, AL and Halpern, D}, title = {Effect of inertia on the insoluble-surfactant instability of a shear flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {71}, number = {1 Pt 2}, pages = {016302}, doi = {10.1103/PhysRevE.71.016302}, pmid = {15697717}, issn = {1539-3755}, abstract = {We study, for the case of the two-layer plane Couette flow, the effects of inertia on the recently found instability due to insoluble surfactants. The insoluble-surfactant instability takes place even when inertia is absent provided an interface or a free surface under a nonzero shear is laden with an insoluble surfactant. Considering a normal mode of the streamwise wave number alpha , the perturbation theory we construct is good for any alpha provided the Reynolds number is correspondingly small. Inertia is responsible for some notable effects, including the appearance of new regions of instability and stability. For long--and only for long--waves, the following growth-rate additivity property for the inertia and interfacial instabilities holds: the growth rate corresponding to some nonzero values of the Marangoni number M and the Reynolds number Re is the sum of two contributions, one corresponding to the same value of M but zero Re, and the other corresponding to the same (nonzero) Re but zero M. This violation of the additivity property is in contrast to the case of a surfactantless Couette flow where this property holds for all wave numbers. Thus these results provide a counterexample to a conjecture that this additivity property is a universal principle. Among other results, when the thinner layer is the less viscous one, there is a nonzero critical Marangoni number Mc for the onset of instability; this (long-wave) threshold Mc grows from zero with the Reynolds number. Also, varying the ratio of viscosities through certain characteristic values leads to changes in the topology of marginal-stability curves.}, }
@article {pmid15697500, year = {2004}, author = {Mouri, H and Hori, A and Kawashima, Y}, title = {Vortex tubes in turbulence velocity fields at Reynolds numbers Re lambda approximately equal to 300-1300.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {70}, number = {6 Pt 2}, pages = {066305}, doi = {10.1103/PhysRevE.70.066305}, pmid = {15697500}, issn = {1539-3755}, abstract = {The most elementary structures of turbulence, i.e., vortex tubes, are studied using velocity data obtained in a laboratory experiment for boundary layers with Reynolds numbers Re(lambda) =295-1258 . We conduct conditional averaging for enhancements of a small-scale velocity increment and obtain the typical velocity profile for vortex tubes. Their radii are of the order of the Kolmogorov length. Their circulation velocities are of the order of the root-mean-square velocity fluctuation. We also obtain the distribution of the interval between successive enhancements of the velocity increment as the measure of the spatial distribution of vortex tubes. They tend to cluster together below about the integral length and more significantly below about the Taylor microscale. These properties are independent of the Reynolds number and are hence expected to be universal.}, }
@article {pmid15696514, year = {2005}, author = {Curran, SJ and Black, RA}, title = {Oxygen transport and cell viability in an annular flow bioreactor: comparison of laminar Couette and Taylor-vortex flow regimes.}, journal = {Biotechnology and bioengineering}, volume = {89}, number = {7}, pages = {766-774}, doi = {10.1002/bit.20361}, pmid = {15696514}, issn = {0006-3592}, mesh = {Aerobiosis ; Animals ; *Bioreactors ; Cell Culture Techniques/*instrumentation/methods ; Cell Survival ; Fibroblasts/metabolism ; L Cells ; Mice ; Oxygen/analysis/*metabolism ; Rheology ; Shear Strength ; *Water Movements ; }, abstract = {Rotating wall vessel bioreactors have been proposed as a means of controlling the fluid dynamic environment during long-term culture of mammalian cells and engineered tissues. In this study, we show how the delivery of oxygen to cells in an annular flow bioreactor is enhanced by the forced convective transport afforded by Taylor vortex flows. A fiberoptic oxygen probe with negligible lag time was used to measure the dissolved oxygen concentration in real time and under carefully controlled aeration conditions. From these data, the overall mass transfer coefficients were calculated and mass transport correlations determined under laminar Couette flow conditions and discrete Taylor vortex flow regimes, including laminar, wavy, and turbulent flows. While oxygen transport in Taylor vortex flows was significantly greater, and the available oxygen exceeded that consumed by murine fibroblasts in free suspension, the proportion of cells that remained viable decreased with increasing Reynolds number (101.8 < Rei < 1018), which we attribute to the action of fluid shear stresses on the cells as opposed to any limitation in mass transport. Nevertheless, the results of this study suggest that laminar Taylor-vortex flow regimes provide an effective means of maintaining the levels of oxygen transport required for long-term cell culture.}, }
@article {pmid15648813, year = {2004}, author = {Allen, GM and Shortall, BP and Gemci, T and Corcoran, TE and Chigier, NA}, title = {Computational simulations of airflow in an in vitro model of the pediatric upper airways.}, journal = {Journal of biomechanical engineering}, volume = {126}, number = {5}, pages = {604-613}, doi = {10.1115/1.1800554}, pmid = {15648813}, issn = {0148-0731}, mesh = {Air ; Airway Resistance/physiology ; Child, Preschool ; Computer Simulation ; Humans ; Larynx/*physiology ; Male ; *Models, Biological ; Pediatrics/methods ; Pharynx/*physiology ; Pulmonary Ventilation/*physiology ; Respiratory Mechanics/*physiology ; Respiratory System ; Trachea/*physiology ; }, abstract = {In order to understand mechanisms of gas and aerosol transport in the human respiratory system airflow in the upper airways of a pediatric subject (male aged 5) was calculated using Computational Fluid Dynamic techniques. An in vitro reconstruction of the subject's anatomy was produced from MRI images. Flow fields were solved for steady inhalation at 6.4 and 8 LPM. For validation of the numerical solution, airflow in an adult cadaver based trachea was solved using identical numerical methods. Comparisons were made between experimental results and computational data of the adult model to determine solution validity. It was found that numerical simulations can provide an accurate representation of axial velocities and turbulence intensity. Data on flow resistance, axial velocities, secondary velocity vectors, and turbulent kinetic energy are presented for the pediatric case. Turbulent kinetic energy and axial velocities were heavily dependant on flow rate, whereas turbulence intensity varied less over the flow rates studied. The laryngeal jet from an adult model was compared to the laryngeal jet in the pediatric model based on Tracheal Reynolds number. The pediatric case indicated that children show axial velocities in the laryngeal jet comparable to adults, who have much higher tracheal Reynolds numbers than children due to larger characteristic dimensions. The intensity of turbulence follows a similar trend, with higher turbulent kinetic energy levels in the pediatric model than would be expected from measurements in adults at similar tracheal Reynolds numbers. There was reasonable agreement between the location of flow structures between adults and children, suggesting that an unknown length scale correlation factor could exist that would produce acceptable predictions of pediatric velocimetry based off of adult data sets. A combined scale for turbulent intensity as well may not exist due to the complex nature of turbulence production and dissipation.}, }
@article {pmid15648810, year = {2004}, author = {Younis, BA and Berger, SA}, title = {A turbulence model for pulsatile arterial flows.}, journal = {Journal of biomechanical engineering}, volume = {126}, number = {5}, pages = {578-584}, doi = {10.1115/1.1798032}, pmid = {15648810}, issn = {0148-0731}, mesh = {Animals ; Arteries/*physiology ; Blood Flow Velocity/*physiology ; Blood Pressure/*physiology ; Computer Simulation ; Humans ; *Models, Cardiovascular ; *Nonlinear Dynamics ; Pulsatile Flow/*physiology ; }, abstract = {Difficulties in predicting the behavior of some high Reynolds number flows in the circulatory system stem in part from the severe requirements placed on the turbulence model chosen to close the time-averaged equations of fluid motion. In particular, the successful turbulence model is required to (a) correctly capture the "nonequilibrium" effects wrought by the interactions of the organized mean-flow unsteadiness with the random turbulence, (b) correctly reproduce the effects of the laminar-turbulent transitional behavior that occurs at various phases of the cardiac cycle, and (c) yield good predictions of the near-wall flow behavior in conditions where the universal logarithmic law of the wall is known to be not valid. These requirements are not immediately met by standard models of turbulence that have been developed largely with reference to data from steady, fully turbulent flows in approximate local equilibrium. The purpose of this paper is to report on the development of a turbulence model suited for use in arterial flows. The model is of the two-equation eddy-viscosity variety with dependent variables that are zero-valued at a solid wall and vary linearly with distance from it. The effects of transition are introduced by coupling this model to the local value of the intermittency and obtaining the latter from the solution of a modeled transport equation. Comparisons with measurements obtained in oscillatory transitional flows in circular tubes show that the model produces substantial improvements over existing closures. Further pulsatile-flow predictions, driven by a mean-flow wave form obtained in a diseased human carotid artery, indicate that the intermittency-modified model yields much reduced levels of wall shear stress compared to the original, unmodified model. This result, which is attributed to the rapid growth in the thickness of the viscous sublayer arising from the severe acceleration of systole, argues in favor of the use of the model for the prediction of arterial flows.}, }
@article {pmid15648809, year = {2004}, author = {Fujioka, H and Grotberg, JB}, title = {Steady propagation of a liquid plug in a two-dimensional channel.}, journal = {Journal of biomechanical engineering}, volume = {126}, number = {5}, pages = {567-577}, doi = {10.1115/1.1798051}, pmid = {15648809}, issn = {0148-0731}, support = {HL41126/HL/NHLBI NIH HHS/United States ; }, mesh = {*Algorithms ; Animals ; Computer Simulation ; Humans ; Lung/*physiology ; *Models, Biological ; Movement/*physiology ; Pulmonary Surfactants/*chemistry ; Rheology/*methods ; Solutions ; }, abstract = {In this study, we investigate the steady propagation of a liquid plug within a two-dimensional channel lined by a uniform, thin liquid film. The Navier-Stokes equations with free-surface boundary conditions are solved using the finite volume numerical scheme. We examine the effect of varying plug propagation speed and plug length in both the Stokes flow limit and for finite Reynolds number (Re). For a fixed plug length, the trailing film thickness increases with plug propagation speed. If the plug length is greater than the channel width, the trailing film thickness agrees with previous theories for semi-infinite bubble propagation. As the plug length decreases below the channel width, the trailing film thickness decreases, and for finite Re there is significant interaction between the leading and trailing menisci and their local flow effects. A recirculation flow forms inside the plug core and is skewed towards the rear meniscus as Re increases. The recirculation velocity between both tips decreases with the plug length. The macroscopic pressure gradient, which is the pressure drop between the leading and trailing gas phases divided by the plug length, is a function of U and U2, where U is the plug propagation speed, when the fluid property and the channel geometry are fixed. The U2 term becomes dominant at small values of the plug length. A capillary wave develops at the front meniscus, with an amplitude that increases with Re, and this causes large local changes in wall shear stresses and pressures.}, }
@article {pmid15644364, year = {2004}, author = {Rashidnia, N and Balasubramaniam, R and Schroer, RT}, title = {The formation of spikes in the displacement of miscible fluids.}, journal = {Annals of the New York Academy of Sciences}, volume = {1027}, number = {}, pages = {311-316}, doi = {10.1196/annals.1324.025}, pmid = {15644364}, issn = {0077-8923}, mesh = {Diffusion ; Models, Theoretical ; Nonlinear Dynamics ; Pressure ; Rheology/*methods ; Silicon/chemistry ; Stress, Mechanical ; Time Factors ; Viscosity ; }, abstract = {We report on experiments in which a more viscous fluid displaces a less viscous one in a vertical cylindrical tube. These experiments were performed using silicone oils in a vertical pipette of small diameter. The more viscous fluid also had a slightly larger density than the less viscous fluid. In the initial configuration, the fluids were at rest, and the interface was nominally flat. A dye was added to the more viscous fluid for ease of observation of the interface between the fluids. The flow was initiated by pumping the more viscous fluid into the less viscous one. The displacement velocity was such that the Reynolds number was smaller than unity and the Peclet number for mass transfer between the fluids was large compared to unity. For upward displacement of the more viscous fluid from an initially stable configuration, an axisymmetric finger was observed under all conditions. However, a needle-shaped spike was seen to propagate from the main finger in many cases, similar to that observed by Petitjeans and Maxworthy for the displacement of a more viscous fluid by a less viscous one.}, }
@article {pmid15644363, year = {2004}, author = {Balasubramaniam, R and Subramanian, RS}, title = {Thermocapillary migration of a drop: an exact solution with Newtonian interfacial rheology and stretching/shrinkage of interfacial area elements for small Marangoni numbers.}, journal = {Annals of the New York Academy of Sciences}, volume = {1027}, number = {}, pages = {303-310}, doi = {10.1196/annals.1324.024}, pmid = {15644363}, issn = {0077-8923}, mesh = {Hot Temperature ; Models, Theoretical ; Motion ; Physical Phenomena ; Physics ; Rheology/*methods ; Temperature ; Viscosity ; }, abstract = {In this paper we analyze the effects of the following phenomena associated with the thermocapillary migration of a drop. The first is the influence of Newtonian surface rheology of the interface and the second is that of the energy changes associated with stretching and shrinkage of the interfacial area elements, when the drop is in motion. The former occurs because of dissipative processes in the interfacial region, such as when surfactant molecules are adsorbed at the interface in sufficient concentration. The interface is typically modeled in this instance by ascribing to it a surface viscosity. This is a different effect from that of interfacial tension gradients arising from surfactant concentration gradients. The stretching and shrinkage of interfacial area elements leads to changes in the internal energy of these elements that affects the transport of energy in the fluids adjoining the interface. When an element on the interface is stretched, its internal energy increases because of the increase in its area. This energy is supplied by the neighboring fluids that are cooled as a consequence. Conversely, when an element on the interface shrinks, the adjoining fluids are warmed. In the case of a moving drop, elements of interfacial area are stretched in the forward half of the drop, and are shrunk in the rear half. Consequently, the temperature variation on the surface of the drop and its migration speed are modified. The analysis of the motion of a drop including these effects was first performed by LeVan in 1981, in the limit when convective transport of momentum and energy are negligible. We extend the analysis of LeVan to include the convective transport of momentum by demonstrating that an exact solution of the momentum equation is obtained for an arbitrary value of the Reynolds number. This solution is then used to calculate the slightly deformed shape of the drop from a sphere.}, }
@article {pmid15619364, year = {2005}, author = {Zacarias, GD and Ferreira, CP and Velasco-Hernández, JX}, title = {Porosity and tortuosity relations as revealed by a mathematical model of biofilm structure.}, journal = {Journal of theoretical biology}, volume = {233}, number = {2}, pages = {245-251}, doi = {10.1016/j.jtbi.2004.10.006}, pmid = {15619364}, issn = {0022-5193}, mesh = {Animals ; *Biofilms ; *Computer Simulation ; Models, Biological ; Porosity ; Viscosity ; }, abstract = {A biofilm is assumed to be submerged in a fluid with given viscosity and low Reynolds number. The interaction between fluid and bacteria is modeled through streamlines. We use finite-difference and boundary element numerical schemes to predict streamlines within the biofilm. The results show that this approach can provide information about prior distribution and geometry of the biofilm structure. Theoretical values of porosity and tortuosity are computed and compared with published data.}, }
@article {pmid15614359, year = {2005}, author = {Isetun, S and Nilsson, U}, title = {Dynamic field sampling of airborne organophosphate triesters using solid-phase microextraction under equilibrium and non-equilibrium conditions.}, journal = {The Analyst}, volume = {130}, number = {1}, pages = {94-98}, doi = {10.1039/b410597d}, pmid = {15614359}, issn = {0003-2654}, mesh = {Air Pollutants, Occupational/*analysis ; Environmental Monitoring/instrumentation/*methods ; Organophosphates/*analysis ; Specimen Handling ; Time Factors ; }, abstract = {A simple setup for dynamic air sampling using a solid-phase microextraction (SPME) device designed for use in the field was evaluated for organophosphate triester vapour under both equilibrium and non-equilibrium conditions. The effects of varying the applied airflows in the sampling device were evaluated in order to optimise the system with respect to the Reynolds number and magnitude of the boundary layer that developed near the surface. Further, the storage stability of the analytes was studied for both capped and uncapped 100-microm PDMS fibres. Organophosphate triesters are utilized on large scales as flame-retardants and/or plasticizers, for instance in upholstered furniture. In indoor working environments these compounds have become common components in the surrounding air. Measurements were performed in a recently furnished working environment and the concentration of tris(2-choropropyl) phosphate was found to be 7 microg m(-3).}, }
@article {pmid15601618, year = {2004}, author = {Miguel, AF and Reis, AH and Aydin, M}, title = {Aerosol particle deposition and distribution in bifurcating ventilation ducts.}, journal = {Journal of hazardous materials}, volume = {116}, number = {3}, pages = {249-255}, doi = {10.1016/j.jhazmat.2004.09.013}, pmid = {15601618}, issn = {0304-3894}, mesh = {*Aerosols/chemistry ; Environmental Monitoring/*methods ; Equipment Design ; Humans ; *Humidity ; Microspheres ; Particle Size ; Ventilation/*instrumentation ; }, abstract = {The quantitative information gained from detailed studies of particle deposition in ducts is important, for example, to evaluate human exposure to particles within buildings, implement cleaning strategies for ventilation ducts and also understand particulate deposition in the respiratory tree. For this purpose, an experimental study for aerosol particles of diameters ranging from 8.1 to 23.2 microm was conducted in a curved bifurcating ventilation duct. At the bend segment of the duct, the particle size, bend angle, curvature ratio and Reynolds number affect aerosol deposition significantly. On the other hand, tests conducted on the bifurcating segments show that deposition increases with particle size and Reynolds number. Accumulation of particles occurs mainly around the bend segment and the ridge of carina of the bifurcation. In all segments of the duct models, particle deposition is found to be enhanced with increasing humidity which increases from 66 to 95% (i.e., close the saturation). A physical interpretation of the results obtained is also presented.}, }
@article {pmid15600932, year = {2004}, author = {Subramanian, K and Brandenburg, A}, title = {Nonlinear current helicity fluxes in turbulent dynamos and alpha quenching.}, journal = {Physical review letters}, volume = {93}, number = {20}, pages = {205001}, doi = {10.1103/PhysRevLett.93.205001}, pmid = {15600932}, issn = {0031-9007}, abstract = {Large scale dynamos produce small scale current helicity as a waste product that quenches the large scale dynamo process (alpha effect). This quenching can be catastrophic (i.e., intensify with magnetic Reynolds number) unless one has fluxes of small scale magnetic (or current) helicity out of the system. We derive the form of helicity fluxes in turbulent dynamos, taking also into account the nonlinear effects of Lorentz forces due to fluctuating fields. We confirm the form of an earlier derived magnetic helicity flux term, and also show that it is not renormalized by the small scale magnetic field, just like turbulent diffusion. Additional nonlinear fluxes are identified, which are driven by the anisotropic and antisymmetric parts of the magnetic correlations. These could provide further ways for turbulent dynamos to transport out small scale magnetic helicity, so as to avoid catastrophic quenching.}, }
@article {pmid15600747, year = {2004}, author = {Pearson, BR and Yousef, TA and Haugen, NE and Brandenburg, A and Krogstad, PA}, title = {Delayed correlation between turbulent energy injection and dissipation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {70}, number = {5 Pt 2}, pages = {056301}, doi = {10.1103/PhysRevE.70.056301}, pmid = {15600747}, issn = {1539-3755}, abstract = {The dimensionless kinetic energy dissipation rate C(epsilon) is estimated from numerical simulations of statistically stationary isotropic box turbulence that is slightly compressible. The Taylor microscale Reynolds number (Re(lambda)) range is 20< or approximately equal to Re(lambda) < or approximately equal to 220 and the statistical stationarity is achieved with a random phase forcing method. The strong Re(lambda) dependence of C(epsilon) abates when Re(lambda) approximately 100 after which C(epsilon) slowly approaches approximately 0.5, a value slightly different from previously reported simulations but in good agreement with experimental results. If C(epsilon) is estimated at a specific time step from the time series of the quantities involved it is necessary to account for the time lag between energy injection and energy dissipation. Also, the resulting value can differ from the ensemble averaged value by up to +/-30%. This may explain the spread in results from previously published estimates of C(epsilon).}, }
@article {pmid15576103, year = {2005}, author = {Allison, S}, title = {Electrophoretic mobility and primary electroviscous effect of dilute "hard" prolate ellipsoids.}, journal = {Journal of colloid and interface science}, volume = {282}, number = {1}, pages = {231-237}, doi = {10.1016/j.jcis.2004.08.055}, pmid = {15576103}, issn = {0021-9797}, abstract = {Electrophoretic mobilities and primary electroviscous coefficients are determined for "hard" prolate ellipsoids of axial ratio less than or equal to 4 in KCl, NaCl, and Tris-glycine salt solutions. Account is taken of the steady state distortion of the ion atmosphere around the ellipsoid by numerical solution of the coupled Poisson, low-Reynolds-number Navier-Stokes, and ion transport equations. This is accomplished by a boundary element procedure. Results are presented as ratios of mobilities and primary electroviscous coefficients of ellipsoids to those of corresponding spheres. It is shown that the electrophoretic mobility of an ellipsoid is very similar to that of a sphere under similar conditions of size, ionic strength, salt type, and zeta potential. Other factors being equal, shape has little effect on electrophoretic mobility. For the primary electroviscous coefficient, on the other hand, there is a substantial shape effect. It is argued that the complementary techniques of electrophoresis and viscosity together provide an effective means of studying the size, charge, and shape of macroions and colloidal particles.}, }
@article {pmid15570371, year = {2004}, author = {Atencia, J and Beebe, DJ}, title = {Magnetically-driven biomimetic micro pumping using vortices.}, journal = {Lab on a chip}, volume = {4}, number = {6}, pages = {598-602}, doi = {10.1039/b407710e}, pmid = {15570371}, issn = {1473-0197}, mesh = {Biomimetics/*instrumentation/methods ; Equipment Design ; Equipment Failure Analysis ; Magnetics/*instrumentation ; Microfluidic Analytical Techniques/*instrumentation/methods ; Microfluidics/*instrumentation/methods ; }, abstract = {Planar micropumps utilizing vortices shed by an oscillating ferromagnetic bar are presented. The movement of the bar is induced by magnetic coupling with an external spinning magnet. Thus, energy transfer is achieved without physical contact or need of any on-chip power source. To create vortices inside the chip, the Reynolds number is locally increased with the oscillation of the bar. The utilization of the vortices as a tool for efficient transfer of energy is inspired by the behaviour of swimming animals and flying insects in nature. The pumps operate in two different scales (milli-scale and micro-scale) in order to take advantage of both. Experiments are presented characterizing the pumps and their flow patterns. The range of operation of the pumps is from 3 microl min(-1) to 600 microl min(-1), though smaller flow rates are also possible.}, }
@article {pmid15553839, year = {2004}, author = {Liu, Y and Xu, S and Yan, J and Shen, G and Sun, W and Chew, Y and Low, H and Xu, J}, title = {[Capillary blood flow with dynamical change of tissue pressure caused by exterior force].}, journal = {Sheng wu yi xue gong cheng xue za zhi = Journal of biomedical engineering = Shengwu yixue gongchengxue zazhi}, volume = {21}, number = {5}, pages = {699-703}, pmid = {15553839}, issn = {1001-5515}, mesh = {Biomechanical Phenomena ; Blood Flow Velocity ; Blood Viscosity ; Capillaries/*physiology ; Hematocrit ; *Hemodynamics ; Humans ; *Massage ; Models, Cardiovascular ; Pressure ; Regional Blood Flow ; }, abstract = {A hemodynamic model of capillary and tissue, in which tissue pressure changed with swing manipulation of Traditional Chinese Medical Massage (TCMM), is presented in this paper to explain the hemodynamic mechanism of swing manipulation. Blood flowed in capillary with low Reynolds number. Plasma exuded through capillary according to the Starling's Law. Tissue pressure changed linearly with the massage force measured. Blood apparent viscosity, plasma protein concentration and red cell's hematocrit were taken into account. Capillary flow rate, blood apparent viscosity, filtration rate and filtration fraction with dynamical change of tissue pressure were calculated numerically, and were compared with those in static tissue pressure condition. Results showed that, dynamical change of tissue pressure led to the increase of capillary flow rate and the decrease of blood apparent viscosity, which qualitatively explained the hemodynamic mechanism of "promoting blood circulation and removing blood stasis" in swing manipulation of TCMM.}, }
@article {pmid15543859, year = {2004}, author = {Karl, A and Henry, FS and Tsuda, A}, title = {Low reynolds number viscous flow in an alveolated duct.}, journal = {Journal of biomechanical engineering}, volume = {126}, number = {4}, pages = {420-429}, doi = {10.1115/1.1784476}, pmid = {15543859}, issn = {0148-0731}, support = {HL54885/HL/NHLBI NIH HHS/United States ; HL70542/HL/NHLBI NIH HHS/United States ; HL74022/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; *Bronchoalveolar Lavage Fluid ; Computer Simulation ; Humans ; *Models, Biological ; Pulmonary Alveoli/*physiology ; Rheology/instrumentation/*methods ; Viscosity ; }, abstract = {Flow visualization studies and supplementary numerical simulations are carried out on slow flow through a model alveolated duct. The results reveal that the type of flow that develops in the alveoli, or cavities, is controlled by the ratio of the depth to the width of the cavity and by the ratio of cavity volume to duct volume. While weak, the slowly rotating flow in the cavity is thought to be important to the convective transport of heat and mass transfer to, or from, the walls of the cavity. The relevance of these finding to particle transport and deposition deep in the lung is discussed.}, }
@article {pmid15524627, year = {2004}, author = {Aringazin, AK}, title = {Conditional Lagrangian acceleration statistics in turbulent flows with Gaussian-distributed velocities.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {70}, number = {3 Pt 2}, pages = {036301}, doi = {10.1103/PhysRevE.70.036301}, pmid = {15524627}, issn = {1539-3755}, abstract = {The random intensity of noise approach to the one-dimensional Laval-Dubrulle-Nazarenko-type model having deductive support from the three-dimensional Navier-Stokes equation is used to describe Lagrangian acceleration statistics of a fluid particle in developed turbulent flows. Intensity of additive noise and cross correlation between multiplicative and additive noises entering a nonlinear Langevin equation are assumed to depend on random velocity fluctuations in an exponential way. We use an exact analytic result for the acceleration probability density function obtained as a stationary solution of the associated Fokker-Planck equation. We give a complete quantitative description of the available experimental data on conditional and unconditional acceleration statistics within the framework of a single model with a single set of fit parameters. The acceleration distribution and variance conditioned on Lagrangian velocity fluctuations and the marginal distribution calculated by using independent Gaussian velocity statistics are found to be in a good agreement with the recent high-Reynolds-number Lagrangian experimental data. The fitted conditional mean acceleration is very small, that is, in agreement with direct numerical simulations, and increases for higher velocities but it departs from the experimental data, which exhibit anisotropy of the studied flow.}, }
@article {pmid15519598, year = {2004}, author = {Chen, J and Lu, XY}, title = {Numerical investigation of the non-Newtonian blood flow in a bifurcation model with a non-planar branch.}, journal = {Journal of biomechanics}, volume = {37}, number = {12}, pages = {1899-1911}, doi = {10.1016/j.jbiomech.2004.02.030}, pmid = {15519598}, issn = {0021-9290}, mesh = {Arteries/*anatomy &amp; histology/*physiology ; Arteriosclerosis/etiology/pathology/physiopathology ; Biomechanical Phenomena ; Blood Flow Velocity/physiology ; Hemodynamics ; Hemorheology ; Humans ; Models, Anatomic ; *Models, Cardiovascular ; Models, Statistical ; }, abstract = {The non-Newtonian fluid flow in a bifurcation model with a non-planar daughter branch is investigated by using finite element method to solve the three-dimensional Navier-Stokes equations coupled with a non-Newtonian constitutive model, in which the shear thinning behavior of the blood fluid is incorporated by the Carreau-Yasuda model. The objective of this study is to investigate the influence of the non-Newtonian property of fluid as well as of curvature and out-of-plane geometry in the non-planar daughter vessel on wall shear stress (WSS) and flow phenomena. In the non-planar daughter vessel, the flows are typified by the skewing of the velocity profile towards the outer wall, creating a relatively low WSS at the inner wall. In the downstream of the bifurcation, the velocity profiles are shifted towards the flow divider. The low WSS is found at the inner walls of the curvature and the lateral walls of the bifurcation. Secondary flow patterns that swirl fluid from the inner wall of curvature to the outer wall in the middle of the vessel are also well documented for the curved and bifurcating vessels. The numerical results for the non-Newtonian fluid and the Newtonian fluid with original Reynolds number and the corresponding rescaled Reynolds number are presented. Significant difference between the non-Newtonian flow and the Newtonian flow is revealed; however, reasonable agreement between the non-Newtonian flow and the rescaled Newtonian flow is found. Results of this study support the view that the non-planarity of blood vessels and the non-Newtonian properties of blood are an important factor in hemodynamics and may play a significant role in vascular biology and pathophysiology.}, }
@article {pmid15495975, year = {2004}, author = {Chen, YX and Yin, J and Fang, S}, title = {Biological removal of air loaded with a hydrogen sulfide and ammonia mixture.}, journal = {Journal of environmental sciences (China)}, volume = {16}, number = {4}, pages = {656-661}, pmid = {15495975}, issn = {1001-0742}, mesh = {Air Pollutants/*isolation &amp; purification ; Ammonia/*isolation &amp; purification ; Biodegradation, Environmental ; China ; Filtration ; Hydrogen Sulfide/*isolation &amp; purification ; Odorants/*prevention &amp; control ; Waste Disposal, Fluid ; }, abstract = {The nuisance impact of air pollutant emissions from wastewater pumping stations is a major issue of concern to China. Hydrogen sulfide and ammonia are commonly the primary odor and are important targets for removal. An alternative control technology, biofiltration, was studied. The aim of this study is to investigate the potential of unit systems packed with compost in terms of ammonia and hydrogen sulfide emissions treatment, and to establish optimal operating conditions for a full-scale conceptual design. The laboratory scale biofilter packed with compost was continuously supplied with hydrogen sulfide and ammonia gas mixtures. A volumetric load of less than 150 gH2S/(m3 x d) and 230 gNH3/(m3 x d) was applied for about fifteen weeks. Hydrogen sulfide and ammonia elimination occurred in the biofilter simultaneously. The removal efficiency, removal capacity and removal kinetics in the biofilter were studied. The hydrogen sulfide removal efficiency reached was very high above 99%, and ammonia removal efficiency was about 80%. Hydrogen sulfide was oxidized into sulphate. The ammonia oxidation products were nitrite and nitrate. Ammonia in the biofilter was mainly removed by adsorption onto the carrier material and by absorption into the water fraction of the carrier material. High percentages of hydrogen sulfide or ammonia were oxidized in the first section of the column. Through kinetics analysis, the presence of ammonia did not hinder the hydrogen sulfide removal. According to the relationship between pressure drop and gas velocity for the biofilter and Reynolds number, non-Darcy flow can be assumed to represent the flow in the medium.}, }
@article {pmid15478438, year = {2004}, author = {Alipour, F and Scherer, RC}, title = {Flow separation in a computational oscillating vocal fold model.}, journal = {The Journal of the Acoustical Society of America}, volume = {116}, number = {3}, pages = {1710-1719}, doi = {10.1121/1.1779274}, pmid = {15478438}, issn = {0001-4966}, support = {R01 DC003566/DC/NIDCD NIH HHS/United States ; DC03566-05/DC/NIDCD NIH HHS/United States ; }, mesh = {Air Pressure ; *Computer Simulation ; Glottis/*physiology ; Humans ; Manometry ; *Models, Biological ; Phonation/*physiology ; Pulmonary Ventilation/*physiology ; }, abstract = {A finite-volume computational model that solves the time-dependent glottal airflow within a forced-oscillation model of the glottis was employed to study glottal flow separation. Tracheal input velocity was independently controlled with a sinusoidally varying parabolic velocity profile. Control parameters included flow rate (Reynolds number), oscillation frequency and amplitude of the vocal folds, and the phase difference between the superior and inferior glottal margins. Results for static divergent glottal shapes suggest that velocity increase caused glottal separation to move downstream, but reduction in velocity increase and velocity decrease moved the separation upstream. At the fixed frequency, an increase of amplitude of the glottal walls moved the separation further downstream during glottal closing. Increase of Reynolds number caused the flow separation to move upstream in the glottis. The flow separation cross-sectional ratio ranged from approximately 1.1 to 1.9 (average of 1.47) for the divergent shapes. Results suggest that there may be a strong interaction of rate of change of airflow, inertia, and wall movement. Flow separation appeared to be "delayed" during the vibratory cycle, leading to movement of the separation point upstream of the glottal end only after a significant divergent angle was reached, and to persist upstream into the convergent phase of the cycle.}, }
@article {pmid15462586, year = {2004}, author = {Rani, PN and Sarojamma, G}, title = {Peristaltic transport of a Casson fluid in an asymmetric channel.}, journal = {Australasian physical &amp; engineering sciences in medicine}, volume = {27}, number = {2}, pages = {49-59}, doi = {10.1007/BF03178376}, pmid = {15462586}, issn = {0158-9938}, mesh = {Biological Transport, Active/physiology ; Computer Simulation ; *Models, Biological ; Peristalsis/*physiology ; Pulsatile Flow/*physiology ; Rheology/*methods ; Viscosity ; }, abstract = {The peristaltic transport of a Casson fluid in a two-dimensional asymmetric channel is studied under long- wavelength and low-Reynolds number assumption. The asymmetry in the channel is created by considering the peristaltic waves imposed on the boundary walls to possess different amplitude and phase. The analysis of the flow is carried out in a wave frame of reference moving with the velocity of the wave. Due to the asymmetry in the channel two yield planes exist and they are calculated by solving the transcendental equation in terms of the core width. In an asymmetric channel the yield planes are skewed towards the boundary with higher amplitude or a phase difference in relation to the other boundary. While in a symmetric channel the yield planes are located symmetrically on either side of the axis of the channel. The phenomena of trapping and reflux have been discussed in the symmetric case of the channel. It is noticed that trapping of fluid occurs and the trapping zone extends for an increase in the time average flux. It is found that reflux occurs for higher values of amplitude of the peristaltic wave and the reflux zone extends for increased amplitudes.}, }
@article {pmid15447583, year = {2004}, author = {Cohen, I}, title = {Scaling and transition structure dependence on the fluid viscosity ratio in the selective withdrawal transition.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {70}, number = {2 Pt 2}, pages = {026302}, doi = {10.1103/PhysRevE.70.026302}, pmid = {15447583}, issn = {1539-3755}, abstract = {In the selective withdrawal experiment, fluid is withdrawn through a tube with its tip suspended above a two-fluid interface. At sufficiently high flow rates, the interface undergoes a transition so that the lower fluid is entrained with the upper one, forming a spout. Previous experiments address the scalings and similarity profiles characterizing steady states of the system near the transition for one combination of fluids. In the present study, we show that these scalings and similarity profiles extend to systems with different viscosity ratios. Surprisingly, we find no dependence of the scalings and similarity profiles on the lower fluid viscosity. We use the results of a low-Reynolds-number flow dimensional analysis to show that for different fluid combinations the curves denoting the transition straw height as a function of flow rate can be collapsed. Finally, these results are used to argue that in the low-Reynolds-number regime, the capillary length sets the scale for the final curvature of the interface before the transition.}, }
@article {pmid15447537, year = {2004}, author = {Moriconi, L}, title = {Statistics of intense turbulent vorticity events.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {70}, number = {2 Pt 2}, pages = {025302}, doi = {10.1103/PhysRevE.70.025302}, pmid = {15447537}, issn = {1539-3755}, abstract = {We investigate statistical properties of vorticity fluctuations in fully developed turbulence, which are known to exhibit a strong intermittent behavior. Taking as the starting point the Navier-Stokes equations with a random force term correlated at large scales, we obtain in the high Reynolds number regime a closed analytical expression for the probability distribution function of an arbitrary component of the vorticity field. The central idea underlying the analysis consists in the restriction of the velocity configurational phase-space to a particular sector where the rate of strain and the rotation tensors can be locally regarded as slow and fast degrees of freedom, respectively. This prescription is implemented along the Martin-Siggia-Rose functional framework, whereby instantons and perturbations around them are taken into account within a steepest-descent approach.}, }
@article {pmid15447193, year = {2004}, author = {Ponta, FL and Aref, H}, title = {Strouhal-Reynolds number relationship for vortex streets.}, journal = {Physical review letters}, volume = {93}, number = {8}, pages = {084501}, doi = {10.1103/PhysRevLett.93.084501}, pmid = {15447193}, issn = {0031-9007}, abstract = {A rationale for the empirically observed Strouhal-Reynolds number relation for vortex shedding in the wake of a cylinder is provided. This rationale derives from a mechanism of vortex formation observed in numerical simulations of two-dimensional vortex shedding coupled with an order of magnitude estimate of the terms in the vorticity transport equation based on this mechanism.}, }
@article {pmid15379249, year = {2004}, author = {Liu, X and Wang, X and Yin, H and Chen, H}, title = {Deformation mechanism of leukocyte adhering to vascular surface under steady shear flow.}, journal = {Science in China. Series C, Life sciences}, volume = {47}, number = {2}, pages = {165-174}, doi = {10.1360/02yc0255}, pmid = {15379249}, issn = {1006-9305}, mesh = {Cell Adhesion/*physiology ; Cell Nucleus/physiology ; Endothelium, Vascular/*physiology ; Kinetics ; Leukocytes/*cytology/physiology ; Models, Biological ; Stress, Mechanical ; }, abstract = {The adhesion of leukocytes to vascular surface is an important biomedical problem and has drawn extensive attention. In this study, we propose a compound drop model to simulate a leukocyte with a nucleus adhering to the surface of blood vessel under steady shear flow. A two-dimensional computational fluid dynamics (CFD) is conducted to determine the local distribution of pressure on the surface of the adherent model cell. By introducing the parameter of deformation index (DI), we investigate the deformation of the leukocyte and its nucleus under controlled conditions. Our numerical results show that: (i) the leukocyte is capable of deformation under external exposed flow field. The deformation index increases with initial contact angle and Reynolds number of external exposed flow. (ii) The nucleus deforms with the cell, and the deformation index of the leukocyte is greater than that of the nucleus. The leukocyte is more deformable while the nucleus is more capable of resisting external shear flow. (iii) The leukocyte and the nucleus are not able to deform infinitely with the increase of Reynolds number because the deformation index reaches a maximum. (iv) Pressure distribution confirms that there exists a region downstream of the cell, which produces high pressure to retard continuous deformation and provide a positive lift force on the cell. Meanwhile, we have measured the deformation of human leukocytes exposed to shear flow by using a flow chamber system. We found that the numerical results are well consistent with those of experiment. We conclude that the nucleus with high viscosity plays a particular role in leukocyte deformation.}, }
@article {pmid15375688, year = {2004}, author = {Abrusán, G}, title = {Filamentous cyanobacteria, temperature and Daphnia growth: the role of fluid mechanics.}, journal = {Oecologia}, volume = {141}, number = {3}, pages = {395-401}, pmid = {15375688}, issn = {0029-8549}, mesh = {Animals ; Cyanobacteria/*physiology ; Daphnia/*growth &amp; development ; Physical Phenomena ; Physics ; Population Dynamics ; *Temperature ; Water/chemistry ; *Water Movements ; }, abstract = {Viscosity increases significantly with a fall in water temperature, thus temperature change affects not only the metabolic rates of aquatic suspension feeders, but also the physical properties of the surrounding fluid. This mechanistic effect of water temperature change on growth was separated from the effect of metabolism by using culture media with modified viscosity, while the temperature was kept constant. The effect of water viscosity on growth rate and feeding of four Daphnia species (D. magna, D. pulicaria, D. hyalina, D. galeata) was investigated. Increased viscosity decreased the growth rate significantly for three species, with the exception of D. galeata. Changing viscosity also affects growth qualitatively: the filamentous blue-green Cylindrospermopsis raciborskii reduces the growth rate of D. pulicaria at low viscosity, but its negative effect disappears when viscosity is higher. The findings are consistent with the hypothesis that it is the Reynolds number of the filtering appendages that determines the qualitative features of Daphnia filtration. The edibility of C. raciborskii at high water viscosity is most probably caused by lack of interference with filtering combs, and explains the coexistence of D. pulicaria with filamentous blue-green species in the field, and also the observed temperature dependence of growth inhibition of filaments.}, }
@article {pmid15341850, year = {2004}, author = {Chu, CP and Lee, DJ}, title = {Advective flow in a sludge floc.}, journal = {Journal of colloid and interface science}, volume = {277}, number = {2}, pages = {387-395}, doi = {10.1016/j.jcis.2004.04.036}, pmid = {15341850}, issn = {0021-9797}, abstract = {The interior of sludge floc is highly heterogeneous, while the large pores in the floc control the advective flow. This work for the first time numerically details fluid flow and mass transfer processes in pores of activated sludge floc. The dimensionless permeabilities and mass dispersion coefficients were contoured against pore size ratio and the floc Reynolds number. With a pore size less than 20% of the floc size, the commonly adopted homogeneous model overestimates the floc permeability, and pore velocity is less than 2% of the bulk velocity. This is particularly true for flocs with low porosity. Although the convective flux is low, the dispersive mass transfer rate can be much higher than the diffusional rate, attributable to the strong Taylor dispersion effect. The three-dimensional pore structures in waste activated-sludge floc were identified using confocal laser scanning microscope (CLSM) images. Large pores were used to numerically estimate the permeability and dispersion coefficient for these pores. The permeability and the dispersion coefficient of the tortuous pores can be one order of magnitude lower than those for the equivalent straight pores. Besides the dispersion effect, the pore tortuosity appeared as the most important geometrical factor retarding the advective flow in the sludge pores. In addition, the small side pores connected to the large pore had only a mild effect on the flow process, and can be neglected in analysis.}, }
@article {pmid15324209, year = {2004}, author = {Reynolds, AM and Yeo, K and Lee, C}, title = {Anisotropy of acceleration in turbulent flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {70}, number = {1 Pt 2}, pages = {017302}, doi = {10.1103/PhysRevE.70.017302}, pmid = {15324209}, issn = {1539-3755}, abstract = {Third-order Lagrangian stochastic models for the evolution of fluid-particle hyperaccelerations (material derivatives of Lagrangian accelerations) are shown to account naturally for the anisotropy of acceleration variances in low-Reynolds-number turbulent flows and for their dependency upon the energy-containing scales of motion. Model predictions are shown to be in close accord with the results of direct numerical simulations for a turbulent channel flow and with previously acquired simulation data for a homogeneous turbulent shear flow.}, }
@article {pmid15324170, year = {2004}, author = {Haugen, NE and Brandenburg, A and Dobler, W}, title = {Simulations of nonhelical hydromagnetic turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {70}, number = {1 Pt 2}, pages = {016308}, doi = {10.1103/PhysRevE.70.016308}, pmid = {15324170}, issn = {1539-3755}, abstract = {Nonhelical hydromagnetic forced turbulence is investigated using large scale simulations on up to 256 processors and 1024(3) mesh points. The magnetic Prandtl number is varied between 1/8 and 30, although in most cases it is unity. When the magnetic Reynolds number is based on the inverse forcing wave number, the critical value for dynamo action is shown to be around 35 for magnetic Prandtl number of unity. For small magnetic Prandtl numbers we find the critical magnetic Reynolds number to increase with decreasing magnetic Prandtl number. The Kazantsev k(3/2) spectrum for magnetic energy is confirmed for the kinematic regime, i.e., when nonlinear effects are still unimportant and when the magnetic Prandtl number is unity. In the nonlinear regime, the energy budget converges for large Reynolds numbers (around 1000) such that for our parameters about 70% is in kinetic energy and about 30% is in magnetic energy. The energy dissipation rates are converged to 30% viscous dissipation and 70% resistive dissipation. Second-order structure functions of the Elsasser variables give evidence for a k(-5/3) spectrum. Nevertheless, the three-dimensional spectrum is close to k(-3/2), but we argue that this is due to the bottleneck effect. The bottleneck effect is shown to be equally strong both for magnetic and nonmagnetic turbulence, but it is far weaker in one-dimensional spectra that are normally studied in laboratory turbulence. Structure function exponents for other orders are well described by the She-Leveque formula, but the velocity field is significantly less intermittent and the magnetic field is more intermittent than the Elsasser variables.}, }
@article {pmid15313659, year = {2004}, author = {Eggert, MD and Kumar, S}, title = {Observations of instability, hysteresis, and oscillation in low-Reynolds-number flow past polymer gels.}, journal = {Journal of colloid and interface science}, volume = {278}, number = {1}, pages = {234-242}, doi = {10.1016/j.jcis.2004.05.043}, pmid = {15313659}, issn = {0021-9797}, mesh = {Cross-Linking Reagents/chemistry ; Dimethylpolysiloxanes/*chemistry ; Gels/*chemistry ; Polymers/chemistry ; Polypropylenes/chemistry ; Rheology ; Stress, Mechanical ; Viscosity ; }, abstract = {We perform a set of experiments to study the nonlinear nature of an instability that arises in low-Reynolds-number flow past polymer gels. A layer of a viscous liquid is placed on a polydimethylsiloxane (PDMS) gel in a parallel-plate rheometer which is operated in stress-controlled mode. As the shear stress on the top plate increases, the apparent viscosity stays relatively constant until a transition stress where it sharply increases. If the stress is held at a level slightly above the transition stress, the apparent viscosity oscillates with time. If the stress is increased to a value above the transition stress and then decreased back to zero, the apparent viscosity shows hysteretic behavior. If the stress is instead decreased to a constant value and held there, the apparent viscosity is different from its pretransition value and exhibits sustained oscillations. This can happen even if the stress is held at values below the transition stress. Our observations suggest that the instability studied here is subcritical and leads to a flow that is oscillatory and far from viscometric. The phenomena reported here may be useful in applications such as microfluidics, membrane separations, and polymer processing. They may also provide insight into the rheological behavior of complex fluids that undergo flow-induced gelation.}, }
@article {pmid15306421, year = {2004}, author = {Dupin, MM and Spencer, TJ and Halliday, I and Care, CM}, title = {A many-component lattice Boltzmann equation simulation for transport of deformable particles.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {362}, number = {1822}, pages = {1885-1914}, doi = {10.1098/rsta.2004.1422}, pmid = {15306421}, issn = {1364-503X}, abstract = {We review the analysis of single and N-component lattice Boltzmann methods for fluid flow simulation. Results are presented for the emergent pressure field of a single phase incompressible liquid flowing over a backward-facing step, at moderate Reynolds Number, which is compared with the experimental data of Denham &amp; Patrick (1974 Trans. IChE 52, 361-367). We then access the potential of the N-component method for transport of high volume fraction suspensions of deformable particles in pressure-driven flow. The latter are modelled as incompressible, closely packed liquid drops. We demonstrate the technique by investigating the particles' transverse migration in a uniform shear ('lift'), and profile blunting and chaining.}, }
@article {pmid15282812, year = {2004}, author = {Nasiraei-Moghaddam, A and Behrens, G and Fatouraee, N and Agarwal, R and Choi, ET and Amini, AA}, title = {Factors affecting the accuracy of pressure measurements in vascular stenoses from phase-contrast MRI.}, journal = {Magnetic resonance in medicine}, volume = {52}, number = {2}, pages = {300-309}, doi = {10.1002/mrm.20152}, pmid = {15282812}, issn = {0740-3194}, mesh = {Algorithms ; Blood Flow Velocity ; Blood Pressure/*physiology ; Constriction, Pathologic/physiopathology ; Hemorheology ; Magnetic Resonance Imaging/*methods ; *Models, Cardiovascular ; Phantoms, Imaging ; Poisson Distribution ; Viscosity ; }, abstract = {In this work the effects of noise, resolution, and velocity (flow) on the measurement of intravascular pressure from phase-contrast (PC) MRI are discussed. To elucidate these effects, we employed an axisymmetric geometry that enabled us to calculate pressures in <2 min on a Sun Ultra SPARC 10 workstation. To determine the effects of vascular stenoses, we fabricated several stenotic phantom geometries (with 50%, 75%, and 90% area stenoses), and performed both MRI and computational fluid dynamics (CFD) simulations for various flow rates for these phantom geometries. Noise with Gaussian statistics was added to the velocity field obtained from the CFD simulations. The pressure maps obtained directly from CFD simulations for our phantom geometries were compared with pressure maps derived by our algorithm when 1) the input was noise-corrupted velocity data from CFD, and 2) the input was PC-MRI data collected from the phantoms. The quantitative effects of noise, resolution, and flow rate on the accuracy of pressure measurements were determined. We found that for flow rates below the Reynolds number for turbulent flow, resolution is a more significant determinant of accuracy than SNR. Furthermore, if other parameters remain constant, increased flow rates may result in decreased accuracy.}, }
@article {pmid15281102, year = {2004}, author = {Baruah, GL and Belfort, G}, title = {Optimized recovery of monoclonal antibodies from transgenic goat milk by microfiltration.}, journal = {Biotechnology and bioengineering}, volume = {87}, number = {3}, pages = {274-285}, doi = {10.1002/bit.20112}, pmid = {15281102}, issn = {0006-3592}, mesh = {Algorithms ; Animals ; Animals, Genetically Modified/*metabolism ; Antibodies, Monoclonal/chemistry/genetics/isolation &amp; purification ; Goats/genetics ; Hydrogen-Ion Concentration ; Immunoglobulin G/chemistry/*genetics/immunology/*isolation &amp; purification ; Microfluidics/instrumentation/*methods ; Milk/*chemistry/*immunology ; Porosity ; Ultrafiltration/instrumentation/*methods ; }, abstract = {The Predictive Aggregate Transport Model for microfiltration is used in combination with optimum fluid mechanics and electrostatics to maximize recovery of a heterologous immunoglobulin (IgG) from transgenic goat milk. The optimization algorithm involved varying pH (6.8-9), transmembrane pressure (2-4.5 psi), milk feed concentration (1-2X), membrane module type (linear vs. helical design), and axial velocity (Reynolds number: 830-1170). Operation in the pressure-dependent regime at low uniform transmembrane pressures (approximately 2 psi) using permeate circulation in co-flow, at the pI of the protein (9 in this case) was used to increase IgG recovery from less than 1% to over 95%. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and attenuated total reflection Fourier transform infrared spectroscopy of the microfiltration permeate samples confirmed that all the fat globules and most of the casein micelles were retained in the MF membrane whereas a large amount of the target IgG was transported through the membrane. Transmembrane pressure and hence permeation flux was kept low (approximately 15 lmh) to maximize IgG membrane transport and thus recovery, due to a sparse deposit on the membrane which facilitated high solute transport. Next, an analytical method was used to optimize the diafiltration process using the aggregate transport model, experimental target protein sieving coefficients and permeation flux (Baruah and Belfort, 2003). The methodology reported here should be generalizable to the recovery of target proteins found in other complex suspensions of biological origin using the microfiltration process.}, }
@article {pmid15244735, year = {2004}, author = {Cleve, J and Greiner, M and Pearson, BR and Sreenivasan, KR}, title = {Intermittency exponent of the turbulent energy cascade.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {69}, number = {6 Pt 2}, pages = {066316}, doi = {10.1103/PhysRevE.69.066316}, pmid = {15244735}, issn = {1539-3755}, abstract = {We consider the turbulent energy dissipation from one-dimensional records in experiments using air and gaseous helium at cryogenic temperatures, and obtain the intermittency exponent via the two-point correlation function of the energy dissipation. The air data are obtained in a number of flows in a wind tunnel and the atmospheric boundary layer at a height of about 35 m above the ground. The helium data correspond to the centerline of a jet exhausting into a container. The air data on the intermittency exponent are consistent with each other and with a trend that increases with the Taylor microscale Reynolds number, R(lambda), of up to about 1000 and saturates thereafter. On the other hand, the helium data cluster around a constant value at nearly all R(lambda), this being about half of the asymptotic value for the air data. Some possible explanation is offered for this anomaly.}, }
@article {pmid15244734, year = {2004}, author = {Aivalis, KG and Kurien, S and Schumacher, J and Sreenivasan, KR}, title = {Sign-symmetry of temperature structure functions.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {69}, number = {6 Pt 2}, pages = {066315}, doi = {10.1103/PhysRevE.69.066315}, pmid = {15244734}, issn = {1539-3755}, abstract = {New scalar structure functions with different sign-symmetry properties are defined. These structure functions possess different scaling exponents even when their order is the same. Their scaling properties are investigated for second and third orders, using data from high-Reynolds-number atmospheric boundary layer. It is only when structure functions with disparate sign-symmetry properties are compared can the extended self-similarity detect two different scaling ranges that may exist, as in the example of convective turbulence.}, }
@article {pmid15244732, year = {2004}, author = {Kurien, S and Taylor, MA and Matsumoto, T}, title = {Cascade time scales for energy and helicity in homogeneous isotropic turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {69}, number = {6 Pt 2}, pages = {066313}, doi = {10.1103/PhysRevE.69.066313}, pmid = {15244732}, issn = {1539-3755}, abstract = {We extend the Kolmogorov phenomenology for the scaling of energy spectra in high-Reynolds-number turbulence, to explicitly include the effect of helicity. There exists a time scale tau(H) for helicity transfer in homogeneous, isotropic turbulence with helicity. We arrive at this time scale using the phenomenological arguments used by Kraichnan to derive the time scale tau(E) for energy transfer [J. Fluid Mech. 47, 525 (1971)]]. We show that in general tau(H) may not be neglected compared to tau(E), even for rather low relative helicity. We then deduce an inertial range joint cascade of energy and helicity in which the dynamics are dominated by tau(E) in the low wave numbers with both energy and helicity spectra scaling as k(-5/3); and by tau(H) at larger wave numbers with spectra scaling as k(-4/3). We demonstrate how, within this phenomenology, the commonly observed "bottleneck" in the energy spectrum might be explained. We derive a wave number k(h) which is less than the Kolmogorov dissipation wave number, at which both energy and helicity cascades terminate due to dissipation effects. Data from direct numerical simulations are used to check our predictions.}, }
@article {pmid15244724, year = {2004}, author = {Burghelea, T and Segre, E and Bar-Joseph, I and Groisman, A and Steinberg, V}, title = {Chaotic flow and efficient mixing in a microchannel with a polymer solution.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {69}, number = {6 Pt 2}, pages = {066305}, doi = {10.1103/PhysRevE.69.066305}, pmid = {15244724}, issn = {1539-3755}, abstract = {Microscopic flows are almost universally linear, laminar, and stationary because the Reynolds number, Re, is usually very small. That impedes mixing in microfluidic devices, which sometimes limits their performance. Here, we show that truly chaotic flow can be generated in a smooth microchannel of a uniform width at arbitrarily low Re, if a small amount of flexible polymers is added to the working liquid. The chaotic flow regime is characterized by randomly fluctuating three-dimensional velocity field and significant growth of the flow resistance. Although the size of the polymer molecules extended in the flow may become comparable to the microchannel width, the flow behavior is fully compatible with that in a macroscopic channel in the regime of elastic turbulence. The chaotic flow leads to quite efficient mixing, which is almost diffusion independent. For macromolecules, mixing time in this microscopic flow can be three to four orders of magnitude shorter than due to molecular diffusion.}, }
@article {pmid15244721, year = {2004}, author = {Sau, A and Sheu, TW and Hwang, RR and Yang, WC}, title = {Three-dimensional simulation of square jets in cross-flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {69}, number = {6 Pt 2}, pages = {066302}, doi = {10.1103/PhysRevE.69.066302}, pmid = {15244721}, issn = {1539-3755}, abstract = {Direct numerical simulations are performed to predict the three-dimensional unsteady flow interactions in the near-field of a square jet issuing normal to a cross-flow. The simulated flow features reveal the formation of an upstream horseshoe vortex system, which is the result of an interaction between the oncoming channel floor shear layer and the transverse jet; the growth of a sequence of Kelvin-Helmholtz instability-induced vortical rollers in the mixing layer between the jet and the cross-flow, which wrap around the front side of the jet; and the inception process of the counter-rotating vortex pair (CVP), which is initiated through the folding of the lateral jet shear layers. It has been observed that for a square jet in cross-flow, the developed Kelvin-Helmholtz instability induced shear layer rollers do not form closed circumferential vortex rings. Along the downstream side of the jet, the extended tails of such rollers gradually join the locally evolving CVP. The very inception of the CVP is, however, observed to take place within the cross-flow-induced skewed lateral jet shear layers, and such inception was seen to occur slightly below the jet orifice. The simulated results also reveal the growth of the upright wake vortices from the topological singular points that developed on the cross-flow floor boundary layer. The accumulated floor vortices are seen to spiral around the critical points and subsequently leave the channel floor uprightly. During upward motion these vortices eventually get entrained into the CVP core. It has been made clear topologically that the unstable local surface excitations are the seeds from which upright vortices grow. Interestingly, such findings remain quite consistent with the existing experimental predictions for a round jet. Simulations were performed for two moderate values of the Reynolds number 225 and 300, based on the jet width and the average cross-flow inlet velocity, and for two different values of the jet to cross-stream velocity ratio, 2.5 and 3.5.}, }
@article {pmid15244646, year = {2004}, author = {Najafi, A and Golestanian, R}, title = {Simple swimmer at low Reynolds number: three linked spheres.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {69}, number = {6 Pt 1}, pages = {062901}, doi = {10.1103/PhysRevE.69.062901}, pmid = {15244646}, issn = {1539-3755}, mesh = {Animals ; Biological Clocks/*physiology ; Computer Simulation ; Humans ; Microfluidics/*methods ; *Models, Biological ; *Models, Chemical ; Molecular Motor Proteins/*chemistry/*physiology ; Swimming/*physiology ; }, abstract = {We propose a very simple one-dimensional swimmer consisting of three spheres that are linked by rigid rods whose lengths can change between two values. With a periodic motion in a nonreciprocal fashion, which breaks the time-reversal symmetry as well as the translational symmetry, we show that the model device can swim at low Reynolds number. This model system could be used in constructing molecular-sized machines.}, }
@article {pmid15240335, year = {2004}, author = {Peters, TM and Leith, D}, title = {Particle deposition in industrial duct bends.}, journal = {The Annals of occupational hygiene}, volume = {48}, number = {5}, pages = {483-490}, doi = {10.1093/annhyg/meh031}, pmid = {15240335}, issn = {0003-4878}, support = {T42/CCT410423-09/CC/ODCDC CDC HHS/United States ; }, mesh = {Dust/*analysis ; Equipment Design ; Kinetics ; Models, Structural ; Particle Size ; Suspensions ; Ventilation ; }, abstract = {A study of particle deposition in industrial duct bends is presented. Particle deposition by size was measured by comparing particle size distributions upstream and downstream of bends that had geometries and flow conditions similar to those used in industrial ventilation. As the interior surface of the duct bend was greased to prevent particle bounce, the results are applicable to liquid drops and solid particles where duct walls are sticky. Factors investigated were: (i) flow Reynolds number (Re = 203 000, 36 000); (ii) particle Reynolds number (10 < Repinfinity < 200); (iii) particle Stokes number (0.08 < Stk < 16); (iv) bend angle (theta = 45 degrees, 90 degrees, 180 degrees); (v) bend curvature ratio (1.7 < R0 < 12); (vi) orientation (horizontal-to-horizontal and horizontal-to-vertical); and (vii) construction technique (smooth, gored, segmented). Measured deposition was compared with models developed for bends in small diameter sampling lines (Re < 20 000; Repinfinity < 13). Whereas deposition measured in this work generally agreed with that estimated with models for particles <30 microm (Stk < 0.7), it was significantly lower than that estimated for larger particles. As the flow around larger particles became increasingly turbulent, the models progressively under-represented drag forces and over-estimated deposition. For particles >20 microm, deposition was slightly greater in the horizontal-to-horizontal orientation than in the horizontal-to-vertical orientation due to gravitational settling. Penetration was not a multiplicative function of bend angle as theory predicts, due to the developing nature of turbulent flow in bends. Deposition in a smooth bend was similar to that in a gored bend; however, a tight radius segmented bend (R0 = 1.7) exhibited much lower deposition. For more gradual bends (3 < R0 < 12), curvature ratio had negligible effect on deposition.}, }
@article {pmid15217480, year = {2004}, author = {Finlayson, EU and Gadgil, AJ and Thatcher, TL and Sextro, RG}, title = {Pollutant dispersion in a large indoor space. Part 2: Computational fluid dynamics predictions and comparison with a scale model experiment for isothermal flow.}, journal = {Indoor air}, volume = {14}, number = {4}, pages = {272-283}, doi = {10.1111/j.1600-0668.2004.00243.x}, pmid = {15217480}, issn = {0905-6947}, mesh = {*Air Movements ; Air Pollutants/*analysis ; Air Pollution, Indoor/*analysis ; Environmental Monitoring/*methods ; Humans ; Models, Theoretical ; Vehicle Emissions/*analysis ; *Water ; }, abstract = {UNLABELLED: This paper reports on an investigation of the adequacy of computational fluid dynamics (CFD), using a standard Reynolds Averaged Navier-Stokes (RANS) model, for predicting dispersion of neutrally buoyant gas in a large indoor space. We used CFD to predict pollutant (dye) concentration distribution in a water-filled scale model of an atrium with a continuous pollutant source in the absence of furniture and occupants. Predictions from the RANS formulation are comparable with an ensemble average of independent identical experiments. Model results were compared with pollutant concentration data in a horizontal plane from experiments in a scale model atrium. Predictions were made for steady-state (fully developed) and transient (developing) pollutant concentrations. Agreement between CFD predictions and ensemble averaged experimental measurements is quantified using the ratios of CFD-predicted and experimentally measured dye concentration at a large number of points in the measurement plane. Agreement is considered good if these ratios fall between 0.5 and 2.0 at all points in the plane. The standard k-epsilon two-equation turbulence model obtains this level of agreement and predicts pollutant arrival time to the measurement plane within a few seconds. These results suggest that this modeling approach is adequate for predicting isothermal pollutant transport in a large room with simple geometry.<br><br>PRACTICAL IMPLICATIONS: CFD modeling of pollutant transport is becoming increasingly common but high quality comparisons between CFD and experiment remain rare. Our results provide such a comparison. We demonstrate that the standard k-epsilon model provides good predictions for both transient and fully developed pollutant concentrations for an isothermal large space where furnishings are unimportant. This model is less computationally intensive than a large eddy simulation or low Reynolds number k-epsilon model.}, }
@article {pmid15217479, year = {2004}, author = {Thatcher, TL and Wilson, DJ and Wood, EE and Craig, MJ and Sextro, RG}, title = {Pollutant dispersion in a large indoor space: Part 1 -- Scaled experiments using a water-filled model with occupants and furniture.}, journal = {Indoor air}, volume = {14}, number = {4}, pages = {258-271}, doi = {10.1111/j.1600-0668.2004.00242.x}, pmid = {15217479}, issn = {0905-6947}, mesh = {*Air Movements ; Air Pollutants/*analysis ; Air Pollution, Indoor/*analysis ; Environmental Monitoring/*methods ; Humans ; Models, Theoretical ; Vehicle Emissions/*analysis ; *Water ; }, abstract = {Scale modeling is a useful tool for analyzing complex indoor spaces. Scale model experiments can reduce experimental costs, improve control of flow and temperature conditions, and provide a practical method for pretesting full-scale system modifications. However, changes in physical scale and working fluid (air or water) can complicate interpretation of the equivalent effects in the full-scale structure. This paper presents a detailed scaling analysis of a water tank experiment designed to model a large indoor space, and experimental results obtained with this model to assess the influence of furniture and people in the pollutant concentration field at breathing height. Theoretical calculations are derived for predicting the effects from losses of molecular diffusion, small scale eddies, turbulent kinetic energy, and turbulent mass diffusivity in a scale model, even without Reynolds number matching. Pollutant dispersion experiments were performed in a water-filled 30:1 scale model of a large room, using uranine dye injected continuously from a small point source. Pollutant concentrations were measured in a plane, using laser-induced fluorescence techniques, for three interior configurations: unobstructed, table-like obstructions, and table-like and figure-like obstructions. Concentrations within the measurement plane varied by more than an order of magnitude, even after the concentration field was fully developed. Objects in the model interior had a significant effect on both the concentration field and fluctuation intensity in the measurement plane. PRACTICAL IMPLICATION: This scale model study demonstrates both the utility of scale models for investigating dispersion in indoor environments and the significant impact of turbulence created by furnishings and people on pollutant transport from floor level sources. In a room with no furniture or occupants, the average concentration can vary by about a factor of 3 across the room. Adding furniture and occupants can increase this spatial variation by another factor of 3.}, }
@article {pmid15207478, year = {2004}, author = {Verhagen, JH}, title = {Hydrodynamics of burst swimming fish larvae; a conceptual model approach.}, journal = {Journal of theoretical biology}, volume = {229}, number = {2}, pages = {235-248}, doi = {10.1016/j.jtbi.2004.03.022}, pmid = {15207478}, issn = {0022-5193}, mesh = {Animals ; Carps/physiology ; Fishes/*physiology ; Larva ; Models, Biological ; Swimming/*physiology ; }, abstract = {Burst swimming of fish larvae is analysed from a hydrodynamic point of view. A picture of the expected flow pattern is presented based on information in literature on unsteady-flow patterns around obstacles in the intermediate Reynolds number region. It is shown that the acceleration stage of burst swimming under restricted conditions can be treated as a frictionless impulsive motion. The stream pattern resulting from this motion is presented and the efficiency of locomotion during the acceleration stage is calculated. The flow pattern in the post-acceleration stage is sketched and the origin of an interaction between the viscous and the reactive force contribution to the propulsive force in this stage is discussed. It is explained how this interaction can lead to an increase in propulsive efficiency. A conceptual model is developed describing the three stages in burst swimming locomotion: the acceleration stage, the post-acceleration stage and the gliding stage. Data from literature of the travel distance versus time relation of the common carp larva (Cyprinus carpio) of 5.5-mm length has been used to test the model results. The test appeared remarkably successful, and the model results for larger larvae up to 22 mm length are presented. The gliding distance as a function of larval length resulting from the model has been compared with experimental data from literature.}, }
@article {pmid15179173, year = {2004}, author = {Mollendorf, JC and Termin, AC and Oppenheim, E and Pendergast, DR}, title = {Effect of swim suit design on passive drag.}, journal = {Medicine and science in sports and exercise}, volume = {36}, number = {6}, pages = {1029-1035}, doi = {10.1249/01.mss.0000128179.02306.57}, pmid = {15179173}, issn = {0195-9131}, mesh = {Adult ; *Clothing ; Equipment Design ; Friction ; Humans ; *Swimming ; }, abstract = {INTRODUCTION: The drag (D) of seven (7) male swimmers wearing five (5) swimsuits was investigated.<br><br>METHODS: The drag was measured during passive surface tows at speeds from 0.2 up to 2.2 m x s and during starts and push-offs. The swimsuits varied in body coverage from shoulder-to-ankle (SA), shoulder-to-knee (SK), waist-to-ankle (WA) and waist-to-knee (WK) and briefs (CS).<br><br>RESULTS: Differences in total drag among the suits were small, but significant. In terms of least drag at 2.2 m x s, the swimsuits ranked: SK, SA, WA, WK and CS. The drag was decomposed into its pressure drag (DP), skin friction drag (DSF) and wave drag (DW) components using nonlinear regression and classical formulations for each drag component. The transition-to-turbulence Reynolds number and decreasing frontal area with speed were taken into account. The transition-to-turbulence Reynolds number location was found to be very close to the swimmers' "leading edge," i.e. the head. Flow was neither completely laminar, nor completely turbulent; but rather, it was transitional over most of the body. The DP contributed the most to drag at low speeds (<1.0 m x s) and DW the least at all speeds. DSF contributed the most at higher speeds for SA and SK suits, whereas DP and DW were reduced compared with the other suits.<br><br>CONCLUSION: The decomposition of swimmer drag into DSF, DP and DW suggests that increasing DSF on the upper-body of a swimmer reduces DP and DW by tripping the boundary layer and attaching the flow to the body from the shoulder to the knees. It is possible that body suits that cover the torso and legs may reduce drag and improve performance of swimmers.}, }
@article {pmid15169289, year = {2004}, author = {Lucor, D and Karniadakis, GE}, title = {Noisy inflows cause a shedding-mode switching in flow past an oscillating cylinder.}, journal = {Physical review letters}, volume = {92}, number = {15}, pages = {154501}, doi = {10.1103/PhysRevLett.92.154501}, pmid = {15169289}, issn = {0031-9007}, abstract = {Vortex streets formed behind oscillating bluff bodies consist of arrays of groups of two, three, or four vortices classified as 2S, P+S, and 2P shedding modes, respectively. The prevailing dominant mode depends primarily on the amplitude and the frequency of the oscillation and on the Reynolds number. We investigate the effect of noise at the inflow on the stability of these vortex modes in laminar flow past a circular cylinder. We employ stochastic simulations based on a new polynomial chaos method to study the shedding-mode switching from a P+S pattern to a 2S mode in the presence of noise.}, }
@article {pmid15169130, year = {2004}, author = {Schumacher, J}, title = {Scalar gradient fields by geometric measure theory.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {69}, number = {4 Pt 2}, pages = {047301}, doi = {10.1103/PhysRevE.69.047301}, pmid = {15169130}, issn = {1539-3755}, abstract = {Upper bounds of the Hausdorff volume of scalar gradient field graphs are derived by means of geometric measure theory. The approach reproduces that scalar gradient fields along a mean imposed scalar gradient become space filling for sufficiently high values of Schmidt numbers Sc. The bounds are consistent with findings from recent high-resolution numerical experiments for 1< or =Sc< or =64, but too rough when compared with numerical simulations. A Reynolds number dependence of the bounds is found due to the additional scalar gradient stretching term in the equation of motion.}, }
@article {pmid15167803, year = {2004}, author = {Biddiss, E and Erickson, D and Li, D}, title = {Heterogeneous surface charge enhanced micromixing for electrokinetic flows.}, journal = {Analytical chemistry}, volume = {76}, number = {11}, pages = {3208-3213}, doi = {10.1021/ac035451r}, pmid = {15167803}, issn = {0003-2700}, abstract = {Enhancing the species mixing in microfluidic applications is key to reducing analysis time and increasing device portability. The mixing in electroosmotic flow is usually diffusion-dominated. Recent numerical studies have indicated that the introduction of electrically charged surface heterogeneities may augment mixing efficiencies by creating localized regions of flow circulation. In this study, we experimentally visualized the effects of surface charge patterning and developed an optimized electrokinetic micromixer applicable to the low Reynolds number regime. Using the optimized micromixer, mixing efficiencies were improved between 22 and 68% for the applied potentials ranging from 70 to 555 V/cm when compared with the negatively charged homogeneous case. For producing a 95% mixture, this equates to a potential decrease in the required mixing channel length of up to 88% for flows with Péclet numbers between 190 and 1500.}, }
@article {pmid15165878, year = {2004}, author = {Liu, XH and Wang, X}, title = {The deformation of an adherent leukocyte under steady shear flow: a numerical study.}, journal = {Journal of biomechanics}, volume = {37}, number = {7}, pages = {1079-1085}, doi = {10.1016/j.jbiomech.2003.11.015}, pmid = {15165878}, issn = {0021-9290}, mesh = {Capillaries ; *Cell Adhesion ; Hemodynamics ; Leukocytes/*cytology ; Models, Biological ; Stress, Mechanical ; }, abstract = {Leukocyte adhesion is a pathophysiological process in which the balance between hemodynamic and adhesion forces (molecular bonds) plays a key role. In this work, we studied the deformation of an adherent leukocyte and calculated the forces exerted on it. Three model cells were proposed, considering the leukocyte as a single drop, a compound drop, and a nucleus drop, representing a cell without nucleus, a cell with a nucleus, and a nucleus only, respectively. These model cells were supposedly adherent to a smooth substrate under steady shear flow. Our numerical results showed that all three model cells deformed in function of the initial contact angle, capillary number, and Reynolds number. The single drop was the most deformable, while the nucleus drop was the most resistant to the external flow. Each of the model cells showed maximum cell deformation at a high Reynolds number. The distribution of pressure on the cell confirmed the existence of a high-pressure region downstream of the drop, which retarded further deformation of the cell and provided a positive lift force on the drop. The consideration of a highly viscous nucleus can correct the over evaluation of the cell deformation in a flow.}, }
@article {pmid15159779, year = {2004}, author = {Vuppu, AK and Garcia, AA and Saha, SK and Phelan, PE and Hayes, MA and Calhoun, R}, title = {Modeling microflow and stirring around a microrotor in creeping flow using a quasi-steady-state analysis.}, journal = {Lab on a chip}, volume = {4}, number = {3}, pages = {201-208}, doi = {10.1039/b314007e}, pmid = {15159779}, issn = {1473-0197}, support = {R21:EB000679-1/EB/NIBIB NIH HHS/United States ; }, mesh = {Microfluidic Analytical Techniques/*instrumentation ; *Microfluidics ; Models, Theoretical ; Motion ; }, abstract = {The microflow and stirring around paramagnetic particle microchains, referred to as microrotors, are modeled as a circular cylinder rotating about its radial axis at very low Reynolds number. Time scales for momentum transfer under these conditions are determined to be much smaller than those for boundary movement, hence a quasi-steady approximation can be used. The flow is derived at every instant from the case of a steady motion of a horizontally translating cylinder, with the rotation approximated to a series of differential incremental translations. A numerical simulation is used to determine the pathlines and material lines of virtual point fluid elements, which were analyzed to understand the behavior of the flow around the microrotor. The results indicate the flow to be unsteady, with chaotic advection observed in the system. The fluid motion is primarily two-dimensional, parallel to the rotational plane, with mixing limited to the immediate area around the rotating cylinder. Fluid layers, up to many cylinder diameters, in the axial direction experience the disturbance. Elliptic and star shaped pathlines, including periodic orbits, are observed depending on the fluid element's initial location. The trajectories and phase angles compare well with the experimental results, as well as with data from particle dynamics simulations. Material lines and streaklines display stretching and folding, which are indicative of the chaotic behavior and stirring characteristics of the system. The material lines have similar lengths for the same amount of rotation at different speeds, and the effect of rotational speeds appears to be primarily to change the time of mixing. The results are expected to help in the design of a particle microrotor based sensing technique.}, }
@article {pmid15158418, year = {2004}, author = {Reynolds, AM}, title = {Stokes number effects in Lagrangian stochastic models of dispersed two-phase flows.}, journal = {Journal of colloid and interface science}, volume = {275}, number = {1}, pages = {328-335}, doi = {10.1016/j.jcis.2004.02.039}, pmid = {15158418}, issn = {0021-9797}, abstract = {The statistical properties of fluid velocities along particle trajectories in turbulent flows have a conditional dependency upon particle velocity. It is shown that the formulation of Lagrangian stochastic (LS) models for particle trajectories in terms of the well-mixed condition for these conditional velocity statistics is exactly analogous to the formulation of second-order LS models for fluid-particle trajectories. The particle aerodynamic response time is shown to be incorporated at second order, which together with the Lagrangian timescale introduced at first order, defines the Stokes number. Reynolds-number effects can be incorporated at third order. The corresponding Fokker-Planck equation is shown to be identical to that advocated by Pozorski and Minier [Phys. Rev. E 59 (1999) 855], who included the fluid velocities "seen" by a particle in the probability density function (pdf) formalism of Reeks and co-workers as a means of circumventing the closure problem (prescribing a closure for the particle flux induced by the fluid) associated with that approach. It is demonstrated that the neglect of Stokes-number effects accounts, in part, for the tendency of first-order LS models to underpredict particle deposition velocities in the diffusion-impaction regime.}, }
@article {pmid15158415, year = {2004}, author = {Hsu, JP and Hsieh, YH}, title = {Moving of a nonhomogeneous, porous floc normal to a rigid plate.}, journal = {Journal of colloid and interface science}, volume = {275}, number = {1}, pages = {309-316}, doi = {10.1016/j.jcis.2004.01.025}, pmid = {15158415}, issn = {0021-9797}, abstract = {The boundary effect on the moving of a porous, nonhomogeneous, spherical floc normal to a rigid plate is analyzed theoretically for the case of low to medium Reynolds number. In particular, the drag force acting on the floc under various conditions is evaluated. A two-layer structure is adopted to simulate the nonhomogeneous nature of a floc. We show that if a floc is away from the plate, the streamlines surrounding the floc are distorted, but the degree of distortion becomes less significant if the floc is near the plate. The modified drag coefficient of a porous floc is orders of magnitude smaller than that of the corresponding rigid particle. For a fixed volume-averaged permeability, the effect of the presence of the plate on the behavior of a nonhomogeneous floc is more significant than that of a homogeneous floc, and this effect depends largely on the structure of a floc. The nonhomogeneous structure of a floc leads to a positive deviation from a Stokes-law-like correlation in the modified drag coefficient, and the smaller the volume-averaged permeability of a floc the greater the deviation. The presence of the plate has the effect of reducing this deviation. The nonhomogeneous structure of a floc on its modified drag coefficient is pronounced when it is close to a boundary.}, }
@article {pmid15147748, year = {2004}, author = {Luo, XY and Hinton, JS and Liew, TT and Tan, KK}, title = {LES modelling of flow in a simple airway model.}, journal = {Medical engineering &amp; physics}, volume = {26}, number = {5}, pages = {403-413}, doi = {10.1016/j.medengphy.2004.02.008}, pmid = {15147748}, issn = {1350-4533}, mesh = {Computer Simulation ; Finite Element Analysis ; Humans ; Inhalation/*physiology ; Lung/*physiology ; *Models, Biological ; *Nonlinear Dynamics ; Reproducibility of Results ; Rheology/*methods ; Sensitivity and Specificity ; Trachea/*physiology ; }, abstract = {Detailed information about the flow field pattern is highly important in accurately predicting particle deposition sites in the human airway. Flow in the upper airway during heavy breathing can have a Reynolds number as high as 9300, and therefore presents turbulent features. Although turbulence is believed to have an important effect on the airflow and other transport processes in the bronchial tree, to date both theoretical and numerical studies have predominantly assumed the flow to be laminar. In this paper, transitional/turbulent flow during inspiration is studied using a large eddy simulation (LES) in a single asymmetric bifurcation model of human upper airway. The influence of the non-laminar flow on the patterns and the particle paths is investigated in both 2D and 3D models. Throughout the investigation, comparisons with the laminar and conventional k- models for the same configuration and flow conditions are made. The LES model is also carefully validated against published experimental data in a stenotic tube model. The results demonstrate that the LES model is capable of capturing instantaneous eddy formation and flow separation in (almost) laminar, transitional and turbulent flow regimes, and hence may be used as a powerful and practical tool to provide much of the detailed flow information required for tracing the particle trajectories and particle deposition in human airways.}, }
@article {pmid15142586, year = {2004}, author = {Chau, SW and Hsu, KL and Chen, SC and Liou, TM and Shih, KC}, title = {The fluid property dependency on micro-fluidic characteristics in the deposition process for microfabrication.}, journal = {Biosensors &amp; bioelectronics}, volume = {20}, number = {1}, pages = {133-138}, doi = {10.1016/j.bios.2003.11.031}, pmid = {15142586}, issn = {0956-5663}, mesh = {Computer Simulation ; *Computer-Aided Design ; Equipment Design/*methods ; Equipment Failure Analysis/*instrumentation/methods ; Microfluidic Analytical Techniques/*instrumentation/methods ; Microfluidics/*instrumentation/*methods ; Miniaturization/methods ; *Models, Theoretical ; }, abstract = {The droplet impingement into a cavity at micrometer-scale is one of important fluidic issues for microfabrications, e.g. the inkjet deposition process in the PLED display manufacturing. The related micro-fluidic behaviors in the deposition process should be carefully treated to ensure the desired quality of microfabrication. The droplets generally dispensing from an inkjet head, which contains an array of nozzles, have a volume in several picoliters, while each nozzle responds very quickly and jets the droplets into cavities on substrates with micrometer size. The nature of droplet impingement depends on the fluid properties, the initial state of droplet, the impact parameters and the surface characteristics. The commonly chosen non-dimensional numbers to describe this process are the Weber number, the Reynolds number, the Ohnesorge number, and the Bond number. This paper discusses the influences of fluid properties of a Newtonian fluid, such as surface tension and fluid viscosity, on micro-fluidic characteristics for a certain jetting speed in the deposition process via a numerical approach, which indicates the impingement process consists of four different phases. In the first phase, the droplet stretching outwards rapidly, where inertia force is dominated. In the second phase, the recoiling of droplet is observed, where surface tension becomes the most important force. In the third phase, the gravitational force pulls the droplet surface towards cavity walls. The fourth phase begins when the droplet surface touches cavity walls and ends when the droplet obtains a stable shape. If the fluid viscosity is relatively small, the droplet surface touches cavity walls in the second phase. A stable fluid layer would not form if the viscosity is relatively small.}, }
@article {pmid15141208, year = {2004}, author = {Christensen, UR and Tilgner, A}, title = {Power requirement of the geodynamo from ohmic losses in numerical and laboratory dynamos.}, journal = {Nature}, volume = {429}, number = {6988}, pages = {169-171}, doi = {10.1038/nature02508}, pmid = {15141208}, issn = {1476-4687}, abstract = {In the Earth's fluid outer core, a dynamo process converts thermal and gravitational energy into magnetic energy. The power needed to sustain the geomagnetic field is set by the ohmic losses (dissipation due to electrical resistance). Recent estimates of ohmic losses cover a wide range, from 0.1 to 3.5 TW, or roughly 0.3-10% of the Earth's surface heat flow. The energy requirement of the dynamo puts constraints on the thermal budget and evolution of the core through Earth's history. Here we use a set of numerical dynamo models to derive scaling relations between the core's characteristic dissipation time and the core's magnetic and hydrodynamic Reynolds numbers--dimensionless numbers that measure the ratio of advective transport to magnetic and viscous diffusion, respectively. The ohmic dissipation of the Karlsruhe dynamo experiment supports a simple dependence on the magnetic Reynolds number alone, indicating that flow turbulence in the experiment and in the Earth's core has little influence on its characteristic dissipation time. We use these results to predict moderate ohmic dissipation in the range of 0.2-0.5 TW, which removes the need for strong radioactive heating in the core and allows the age of the solid inner core to exceed 2.5 billion years.}, }
@article {pmid15136742, year = {2004}, author = {Xi, C and Marks, DL and Parikh, DS and Raskin, L and Boppart, SA}, title = {Structural and functional imaging of 3D microfluidic mixers using optical coherence tomography.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {101}, number = {20}, pages = {7516-7521}, pmid = {15136742}, issn = {0027-8424}, mesh = {Microfluidics/*methods ; Microscopy ; *Tomography, Optical Coherence ; }, abstract = {To achieve high mixing efficiency in microfluidic devices, complex designs are often required. Microfluidic devices have been evaluated with light and confocal microscopy, but fluid-flow characteristics at different depths are difficult to separate from the en face images produced. By using optical coherence tomography (OCT), an imaging modality capable of imaging 3D microstructures at micrometer-scale resolutions over millimeter-size scales, we obtained 3D dynamic functional and structural data for three representative microfluidic mixers: a Y channel mixer, a 3D serpentine mixer, and a vortex mixer. In the serpentine mixer, OCT image analysis revealed that the mixing efficiency was linearly dependent on the Reynolds number, whereas it appeared to have exponential dependence when imaged with light microscopy. The visual overlap of fluid flows in light-microscopy images leads to an overestimation of the mixing efficiency, an effect that was eliminated with OCT imaging. Doppler OCT measurements determined velocity profiles at various points in the serpentine mixer. Mixing patterns in the vortex mixer were compared with light-microscopy and OCT image analysis. These results demonstrate that OCT can significantly improve the characterization of 3D microfluidic device structure and function.}, }
@article {pmid15132311, year = {2004}, author = {Liew, TT and How, TV}, title = {In vitro assessment of a continuous cardiac output catheter system.}, journal = {Physiological measurement}, volume = {25}, number = {2}, pages = {455-465}, doi = {10.1088/0967-3334/25/2/005}, pmid = {15132311}, issn = {0967-3334}, mesh = {Cardiac Catheterization/instrumentation/*methods ; Cardiac Output/*physiology ; *Models, Biological ; }, abstract = {Continuous measurement of cardiac output (CCO) is useful in assessing the cardiovascular status of patients during cardiac surgery and in intensive care. Recently, a CCO system (truCCOMS, Aortech, UK), capable of detecting rapid changes in cardiac output (CO) was introduced. The method is based on the energy required to maintain an integral heat-transfer device at constant temperature above the ambient value. The aim of this study was to assess the performance of this CCO system in vitro under in steady as well as pulsatile flow conditions representative of those in the pulmonary artery. In order to determine the sensitivity of the system to changes in vessel cross-sectional area and therefore local flow velocity, the catheter was deployed in a linear-tapered tube. Steady and pulsatile flows were generated, and the electrical power at various locations along the tapered tube was recorded. The results show significant differences in the performance under the two different flow conditions. In steady flow, the CO was highly dependent on the local velocity whereas in pulsatile flow, CO varied much less with local velocity. The sensitivity expressed as a percentage increase in CO per 100% increase in velocity at a CO of 5 l min(-1) was 87% in steady flow and 24% in pulsatile flow. Experiments carried out with three fluids with different viscosity show that the errors in determining CO in the tapered tube were also dependent on the Reynolds number and flow regime. The mean errors ranged from about 50% at 2 l min(-1) to less than 10% at 8 l min(-1). The correlation between the predicted and actual CO was generally good. In conclusion, the pulmonary artery catheter is not recommended in situations where blood flow is expected to be steady or of low pulsatility. It may, however, be suitable under normal pulsatile flow conditions in the pulmonary artery.}, }
@article {pmid15120306, year = {2004}, author = {Ren, CL and Li, D}, title = {Electroviscous effects on pressure-driven flow of dilute electrolyte solutions in small microchannels.}, journal = {Journal of colloid and interface science}, volume = {274}, number = {1}, pages = {319-330}, doi = {10.1016/j.jcis.2003.10.036}, pmid = {15120306}, issn = {0021-9797}, abstract = {A fundamental understanding of the flow characteristics of electrolyte solutions in microchannels is critical to the design and control of microfluidic devices. Experimental studies have shown that the electroviscous effect is appreciable for a dilute solution in a small microchannel. However, the experimentally observed electroviscous effects cannot be predicted by the traditional theoretical model, which involves the use of the Boltzmann distribution for the ionic concentration field. It has been found that the Boltzmann distribution is not applicable to systems with dilute electrolyte solutions in small microchannels because it violates the ion number conservation condition. A new theoretical model is developed in this paper using the Nernst equation and the ion number conservation, instead of the Boltzmann distribution, to obtain the ionic concentration field. The ionic concentration field, electrical potential field, and flow field in small microchannels are studied using the model developed here. In order to verify this model, the model-predicted dP/dx (applied pressure gradient) Re (Reynolds number) relationship is compared with the experimentally determined dP/dx approximately Re relationship. Strong agreement between the model predictions and the experimental results supports this model.}, }
@article {pmid15100792, year = {2003}, author = {Glasgow, I and Aubry, N}, title = {Enhancement of microfluidic mixing using time pulsing.}, journal = {Lab on a chip}, volume = {3}, number = {2}, pages = {114-120}, doi = {10.1039/b302569a}, pmid = {15100792}, issn = {1473-0197}, mesh = {Computer Simulation ; Microfluidics/instrumentation/*methods ; Numerical Analysis, Computer-Assisted ; Periodicity ; }, abstract = {Many microfluidic applications require the mixing of reagents, but efficient mixing in these laminar (i.e., low Reynolds number) systems is typically difficult. Instead of using complex geometries and/or relatively long channels, we demonstrate the merits of flow rate time dependency through periodic forcing. We illustrate the technique by studying mixing in a simple "T" channel intersection by means of computational fluid dynamics (CFD) as well as physically mixing two aqueous reagents. The "T" geometry selected consists of two inlet channel segments merging at 90 degrees to each other, the outlet segment being an extension of one of the inlet segments. All channel segments are 200 microm wide by 120 microm deep, a practical scale for mass-produced disposable devices. The flow rate and average velocity after the confluence of the two reagents are 48 nl s(-1) and 2 mm s(-1) respectively, which, for aqueous solutions at room temperature, corresponds to a Reynolds number of 0.3. We use a mass diffusion constant of 10(-10) m(2) s(-1), typical of many BioMEMS applications, and vary the flow rates of the reagents such that the average flow rate remains unchanged but the instantaneous flow rate is sinusoidal (with a DC bias) with respect to time. We analyze the effect of pulsing the flow rate in one inlet only as well as in the two inlets, and demonstrate that the best results occur when both inlets are pulsed out of phase. In this case, the interface is shown to stretch, retain one fold, and sweep through the confluence zone, leading to good mixing within 2 mm downstream of the confluence, i.e. about 1 s of contact. From a practical viewpoint, the case where the inlets are 180 degrees out of phase is of particular interest as the outflow is constant.}, }
@article {pmid15093212, year = {2004}, author = {Mautner, T}, title = {Application of the synthetic jet concept to low Reynolds number biosensor microfluidic flows for enhanced mixing: a numerical study using the lattice Boltzmann method.}, journal = {Biosensors &amp; bioelectronics}, volume = {19}, number = {11}, pages = {1409-1419}, doi = {10.1016/j.bios.2003.12.023}, pmid = {15093212}, issn = {0956-5663}, mesh = {*Biosensing Techniques ; Computer Simulation ; *Microfluidics ; Models, Theoretical ; }, abstract = {The concept of macro scale synthetic jets has been applied to the low Reynolds number (Re=10), two-dimensional channel flows which may be found in biosensor microfluidic systems. The current numerical investigation utilizes a hybrid approach of the lattice Boltzmann (LB) method for flow field computations and a finite-difference, convection-diffusion equation for passive scalar transport. The study presents the modified main channel flow results for various wall jet geometries (derived from synthetic jets), jet inlet conditions, scaling issues and Reynolds numbers. The results indicate limited effects due to jet cavity-slot geometry, and that the forced jet imparts momentum to the channel flow thus enhancing fluid mixing.}, }
@article {pmid15089546, year = {2004}, author = {Ponty, Y and Politano, H and Pinton, JF}, title = {Simulation of induction at low magnetic Prandtl number.}, journal = {Physical review letters}, volume = {92}, number = {14}, pages = {144503}, doi = {10.1103/PhysRevLett.92.144503}, pmid = {15089546}, issn = {0031-9007}, abstract = {We consider the induction of a magnetic field in flows of an electrically conducting fluid at low magnetic Prandtl number and large kinetic Reynolds number. Using the separation between the magnetic and kinetic diffusive length scales, we propose a new numerical approach. The coupled magnetic and fluid equations are solved using a mixed scheme, where the magnetic field fluctuations are fully resolved and the velocity fluctuations at small scale are modeled using a large eddy simulation (LES) scheme. We study the response of a forced Taylor-Green flow to an externally applied field: topology of the mean induction and time fluctuations at fixed locations. The results are in remarkable agreement with existing experimental data; a global 1/f behavior at long times is also evidenced.}, }
@article {pmid15089544, year = {2004}, author = {Boldyrev, S and Cattaneo, F}, title = {Magnetic-field generation in Kolmogorov turbulence.}, journal = {Physical review letters}, volume = {92}, number = {14}, pages = {144501}, doi = {10.1103/PhysRevLett.92.144501}, pmid = {15089544}, issn = {0031-9007}, abstract = {We analyze the initial, kinematic stage of magnetic field evolution in an isotropic and homogeneous turbulent conducting fluid with a rough velocity field, v(l) approximately l(alpha), alpha<1. This regime is relevant to the problem of magnetic field generation in fluids with small magnetic Prandtl number, i.e., with Ohmic resistivity much larger than viscosity. We propose that the smaller the roughness exponent alpha, the larger the magnetic Reynolds number that is needed to excite magnetic fluctuations. This implies that numerical or experimental investigations of magnetohydrodynamic turbulence with small Prandtl numbers need to achieve extremely high resolution in order to describe magnetic phenomena adequately.}, }
@article {pmid15089471, year = {2004}, author = {Groisman, A and Quake, SR}, title = {A microfluidic rectifier: anisotropic flow resistance at low Reynolds numbers.}, journal = {Physical review letters}, volume = {92}, number = {9}, pages = {094501}, doi = {10.1103/PhysRevLett.92.094501}, pmid = {15089471}, issn = {0031-9007}, abstract = {It is one of the basic concepts of Newtonian fluid dynamics that at low Reynolds number (Re) the Navier-Stokes equation is linear and flows are reversible. In microfluidic devices, where Re is essentially always low, this implies that flow resistance in microchannels is isotropic. Here we present a microfluidic rectifier: a microscopic channel of a special shape whose flow resistance is strongly anisotropic, differing by up to a factor of 2 for opposite flow directions. Its nonlinear operation at arbitrary small Re is due to non-Newtonian elastic properties of the working fluid, which is a 0.01% aqueous solution of a high molecular weight polymer. The rectifier works as a dynamic valve and may find applications in microfluidic pumps and other integrated devices.}, }
@article {pmid15052351, year = {2004}, author = {Stiles, PJ and Fletcher, DF}, title = {Hydrodynamic control of the interface between two liquids flowing through a horizontal or vertical microchannel.}, journal = {Lab on a chip}, volume = {4}, number = {2}, pages = {121-124}, doi = {10.1039/b315524b}, pmid = {15052351}, issn = {1473-0197}, abstract = {We derive a Fourier expansion for estimating laminar hydrodynamic spreading when two immiscible liquids flow steadily, side by side, at low Reynolds number, in a horizontal microchannel of rectangular cross-section. When the aspect ratio of the height of the channel to its width is small this expansion can be truncated after a couple of terms and solved to yield the steady-state position of the boundary in terms of the constant volumetric flow rates, the aspect ratio and the viscosities of the two liquids. Our formula shows that we can control the location of the liquid boundary at the outlet of the microchannel by adjusting the relative volumetric flow rates of the two inlet streams. If the microchannel is oriented vertically and the volumetric flow rates are very low, the position of the boundary is also influenced by gravitational forces that depend on the relative densities of the two liquids. We have tested solutions to our analytical expansions by running computational fluid dynamics simulations and have found excellent agreement. When the aspect ratio is 0.01 the leading term in the Fourier expansion for the spreading has an accuracy of about 1%. This accuracy deteriorates to about 12% when the aspect ratio is 0.1. An understanding of these spreading mechanisms is fundamental to the design of T-sensors and related microfluidic devices.}, }
@article {pmid15015119, year = {2002}, author = {Betat, A and Kruelle, CA and Frette, V and Rehberg, I}, title = {Long-time behavior of sand ripples induced by water shear flow.}, journal = {The European physical journal. E, Soft matter}, volume = {8}, number = {5}, pages = {465-476}, doi = {10.1140/epje/i2001-10110-y}, pmid = {15015119}, issn = {1292-8941}, abstract = {The formation of sand ripples under water shear flow in a narrow annular channel and the approach of the ripple pattern towards a steady state were studied experimentally. Four results are obtained: i) The mean amplitude, the average drift velocity and the mean sediment transport rate of the evolving bed shape are strongly related. A quantitative characterization of this relation is given. ii) The ripple pattern reaches a stationary state with a finite ripple amplitude and wavelength. The time needed to reach the state depends on the shear stress and may be several days. iii) The onset of ripple formation is determined by the bed shear stress, but it seems neither to depend on the grain diameter nor on the depth of the water layer. iv) The ripple amplitude, drift velocity and sediment transport in this stationary state depend on the grain size. This dependency is neither captured by the particle Reynolds number nor by the Shields parameter: an empirical scaling law is presented instead.}, }
@article {pmid15008372, year = {2004}, author = {Cooke, J and Hertzberg, J and Boardman, M and Shandas, R}, title = {Characterizing vortex ring behavior during ventricular filling with Doppler echocardiography: an in vitro study.}, journal = {Annals of biomedical engineering}, volume = {32}, number = {2}, pages = {245-256}, doi = {10.1023/b:abme.0000012744.97413.01}, pmid = {15008372}, issn = {0090-6964}, mesh = {Blood Flow Velocity/*physiology ; Echocardiography, Doppler/instrumentation/*methods ; Heart Ventricles/*diagnostic imaging ; Hemorheology/*methods ; Humans ; Image Interpretation, Computer-Assisted/*methods ; Models, Cardiovascular ; Phantoms, Imaging ; *Ventricular Function ; Ventricular Function, Left/*physiology ; }, abstract = {Doppler ultrasound color M-mode imaging (CMM) has been proposed as a noninvasive means of quantifying diastolic function by measuring flow propagation into the left ventricle. However, the relationship between CMM-derived parameters and underlying fluid dynamics is still unclear. The purpose of this study was to couple high-resolution velocimetry measurements with ultrasound Doppler and CMM measurements in order to shed light on the relationship between CMM flow propagation and inflow dynamics using a simple yet highly reproducible in vitro model of left ventricular inflow. Two Reynolds number conditions were analyzed: 4000 and 6000. Both conditions produced starting jets that formed vortex rings. Average (N = 5) CMM centerline velocities were in agreement with DPIV centerline velocities, although large uncertainty in CMM data was present (uncertainty +/- 10 cm s(-1)). Two flow propagation parameters were extracted from the CMM data: the first utilized an isovelocity as the marker of flow propagation; the second used local peak velocity as the marker. The isovelocity technique followed the flow proximal to the vortex (wavefront) while the peak velocity method followed peak vorticity, and therefore vortex propagation, closely. We conclude that CMM imaging, while limited in measuring absolute velocities, can be utilized to assess inflow vortex ring properties, and thereby provide useful information on diastolic function.}, }
@article {pmid15008367, year = {2004}, author = {Hsiai, TK and Cho, SK and Wong, PK and Ing, MH and Salazar, A and Hama, S and Navab, M and Demer, LL and Ho, CM}, title = {Micro sensors: linking real-time oscillatory shear stress with vascular inflammatory responses.}, journal = {Annals of biomedical engineering}, volume = {32}, number = {2}, pages = {189-201}, doi = {10.1023/b:abme.0000012739.88554.01}, pmid = {15008367}, issn = {0090-6964}, support = {HL07895/HL/NHLBI NIH HHS/United States ; K08 HL068689-01A1/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Cattle ; Cell Adhesion/physiology ; Cell Movement/*physiology ; Cells, Cultured ; Coculture Techniques ; Cytokines/metabolism ; Endothelium, Vascular/*physiology ; Equipment Design ; Equipment Failure Analysis ; Flow Cytometry/*instrumentation/methods ; Humans ; Lymphocyte Activation/*physiology ; Microfluidics/instrumentation/methods ; Miniaturization ; Monocytes/*physiology ; Online Systems ; Oscillometry/instrumentation/methods ; Pulsatile Flow/*physiology ; Shear Strength ; *Transducers ; }, abstract = {The important interplay between blood circulation and vascular cell behavior warrants the development of highly sensitive but small sensing systems. The emerging micro electro mechanical systems (MEMS) technology, thus, provides the high spatiotemporal resolution to link biomechanical forces on the microscale with large-scale physiology. We fabricated MEMS sensors, comparable to the endothelial cells (ECs) in size, to link real-time shear stress with monocyte/EC interactions in an oscillatory flow environment, simulating the moving and unsteady separation point at arterial bifurcations. In response to oscillatory shear stress (tau) at +/- 2.6 dyn/cm2, time-averaged shear stress (tauave) = 0 at 0.5 Hz, individual monocytes displayed unique to-and-fro trajectories, undergoing rolling, binding, and dissociation with other monocyte, followed by solid adhesion on EC. Incorporating with cell-tracking velocimetry, we visualized that these real-time events occurred over a dynamic range of oscillating shear stress between +/- 2.6 dyn/cm2 and Reynolds number between 0 and 22.2 in the presence of activated adhesion molecule and chemokine mRNA expression.}, }
@article {pmid15007458, year = {2003}, author = {El Moctar, AO and Aubry, N and Batton, J}, title = {Electro-hydrodynamic micro-fluidic mixer.}, journal = {Lab on a chip}, volume = {3}, number = {4}, pages = {273-280}, doi = {10.1039/b306868b}, pmid = {15007458}, issn = {1473-0197}, abstract = {Fluid mixing in microchannels is needed for many applications ranging from bio-arrays to micro-reactors, but is typically difficult to achieve. A simple geometry micro-mixer is proposed based on the electro-hydrodynamic (EHD) force present when the fluids to be mixed have different electrical properties and are subjected to an electric field. The electrodes are arranged so that the electric field is perpendicular to the interface between the two fluids, creating a transversal secondary flow. The technique is demonstrated experimentally using the flow of two liquids with identical viscosity and density, but different electrical properties. The volume flow rate and average velocity are 0.26 microl s(-1) and 4.2 mm s(-1), respectively, corresponding to a Reynolds number Re= 0.0174. The effect of a continuous (DC) electric field and two alternating (AC)- sinusoidal and square - electric fields is explored. At the appropriate parameter values, very good mixing takes place in less than 0.1 s, over a very short distance (within a fraction of the width 250 microm of the electrodes).}, }
@article {pmid15005109, year = {2004}, author = {Liu, XH and Wang, X and Yin, HM}, title = {Effects of steady shear flow on the deformation of leukocyte adhered to vascular endothelial surface.}, journal = {Hang tian yi xue yu yi xue gong cheng = Space medicine &amp; medical engineering}, volume = {17}, number = {1}, pages = {7-11}, pmid = {15005109}, issn = {1002-0837}, mesh = {Biomechanical Phenomena ; Cell Adhesion/physiology ; Cell Nucleus ; Endothelium, Vascular ; Leukocytes/*cytology/*physiology ; Models, Biological ; Stress, Mechanical ; }, abstract = {OBJECTIVE: To investigate the effects of steady shear flow on the deformation properties of an adherent leukocyte and its nucleus.<br><br>METHOD: A compound drop model was developed to simulate the leukocyte adhered to the inner surface of a blood vessel, and a two dimensional computational fluid dynamics (CFD) was conducted to solve the model equations.<br><br>RESULT: The results show: 1) The Reynolds number of the external shear flow plays a crucial role in leukocyte deformation. Leukocyte deformation increases with Reynolds number; 2) The nucleus deforms together with the leukocyte, and the deformation index of the leukocyte is greater than that of the nucleus. The leukocyte is more deformable while the nucleus is more capable of resisting external shear flow; 3) The leukocyte and the nucleus will not deform infinitely when the Reynolds number increases beyond a certain value where the deformation index reaches its maximum; 4) Pressure distribution over the surface demonstrated that there exists a region downstream of the cell, where is high pressure produced to retard continuous deformation and to provide a positive lift force on the cell.<br><br>CONCLUSION: The nucleus with high viscosity plays a particular role in leukocyte deformation under shear flow.}, }
@article {pmid14995310, year = {2004}, author = {Schekochihin, AA and Cowley, SC and Maron, JL and McWilliams, JC}, title = {Critical magnetic Prandtl number for small-scale dynamo.}, journal = {Physical review letters}, volume = {92}, number = {5}, pages = {054502}, doi = {10.1103/PhysRevLett.92.054502}, pmid = {14995310}, issn = {0031-9007}, abstract = {We report a series of numerical simulations showing that the critical magnetic Reynolds number Rm(c) for the nonhelical small-scale dynamo depends on the Reynolds number Re. Namely, the dynamo is shut down if the magnetic Prandtl number Pr(m)=Rm/Re is less than some critical value Pr(m,c)< approximately 1 even for Rm for which dynamo exists at Pr(m)> or =1. We argue that, in the limit of Re-->infinity, a finite Pr(m,c) may exist. The second possibility is that Pr(m,c)-->0 as Re--> infinity, while Rm(c) tends to a very large constant value inaccessible at current resolutions. If there is a finite Pr(m,c), the dynamo is sustainable only if magnetic fields can exist at scales smaller than the flow scale, i.e., it is always effectively a large-Pr(m) dynamo. If there is a finite Rm(c), our results provide a lower bound: Rm(c) greater, similar 220 for Pr(m)< or =1/8. This is larger than Rm in many planets and in all liquid-metal experiments.}, }
@article {pmid14995893, year = {2004}, author = {Benzi, R and Ching, ES and Horesh, N and Procaccia, I}, title = {Theory of concentration dependence in drag reduction by polymers and of the maximum drag reduction asymptote.}, journal = {Physical review letters}, volume = {92}, number = {7}, pages = {078302}, doi = {10.1103/PhysRevLett.92.078302}, pmid = {14995893}, issn = {0031-9007}, abstract = {A simple model of the effect of polymer concentration on the amount of drag reduction in turbulence is presented, simulated, and analyzed. The qualitative phase diagram of drag coefficient versus Reynolds number (Re) is recaptured in this model, including the theoretically elusive onset of drag reduction and the maximum drag reduction (MDR) asymptote. The Re-dependent drag and the MDR are analytically explained, and the dependence of the amount of drag on material parameters is rationalized.}, }
@article {pmid14995717, year = {2004}, author = {Shtern, V and Mi, J}, title = {Hysteresis and precession of a swirling jet normal to a wall.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {69}, number = {1 Pt 2}, pages = {016312}, doi = {10.1103/PhysRevE.69.016312}, pmid = {14995717}, issn = {1539-3755}, abstract = {Interaction of a swirling jet with a no-slip surface has striking features of fundamental and practical interest. Different flow states and transitions among them occur at the same conditions in combustors, vortex tubes, and tornadoes. The jet axis can undergo precession and bending in combustors; this precession enhances large-scale mixing and reduces emissions of NOx. To explore the mechanisms of these phenomena, we address conically similar swirling jets normal to a wall. In addition to the Serrin model of tornadolike flows, a new model is developed where the flow is singularity free on the axis. New analytical and numerical solutions of the Navier-Stokes equations explain occurrence of multiple states and show that hysteresis is a common feature of wall-normal vortices or swirling jets no matter where sources of motion are located. Then we study the jet stability with the aid of a new approach accounting for deceleration and nonparallelism of the base flow. An appropriate transformation of variables reduces the stability problem for this strongly nonparallel flow to a set of ordinary differential equations. A particular flow whose stability is studied in detail is a half-line vortex normal to a rigid plane-a model of a tornado and of a swirling jet issuing from a nozzle in a combustor. Helical counter-rotating disturbances appear to be first growing as Reynolds number increases. Disturbance frequency changes its sign along the neutral curve while the wave number remains positive. Short disturbance waves propagate downstream and long waves propagate upstream. This helical instability causes bending of the vortex axis and its precession-the effects observed in technological flows and in tornadoes.}, }
@article {pmid14995711, year = {2004}, author = {Brunet, E and Ajdari, A}, title = {Generalized Onsager relations for electrokinetic effects in anisotropic and heterogeneous geometries.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {69}, number = {1 Pt 2}, pages = {016306}, doi = {10.1103/PhysRevE.69.016306}, pmid = {14995711}, issn = {1539-3755}, abstract = {We lay down a general formalism to describe the linear electrohydrodynamic response of systems of arbitrary topology, symmetry and heterogeneity, and through an explicit proof, we demonstrate a set of general Onsager relations between the corresponding electrokinetic coefficients. This generalizes a classical result of Mazur and Overbeek [P. Mazur and J.T.G. Overbeek, Recl. Trav. Chim. Pays-Bas. 70, 83 (1951)] to situations that may become of practical relevance in particular in the field of microfluidic devices. Technically, our proof of the symmetry of the generalized conductance matrix relies on an adaptation of the reciprocal theorem of low-Reynolds-number hydrodynamics.}, }
@article {pmid14995554, year = {2004}, author = {Breuer, M and Wessling, S and Schmalzl, J and Hansen, U}, title = {Effect of inertia in Rayleigh-Bénard convection.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {69}, number = {2 Pt 2}, pages = {026302}, doi = {10.1103/PhysRevE.69.026302}, pmid = {14995554}, issn = {1539-3755}, abstract = {We have investigated the influence of the Prandtl number on the dynamics of high Rayleigh number thermal convection. A numerical parameter study in a three-dimensional Rayleigh-Bénard configuration was carried out, where we varied the Prandtl number between 10(-3)< or =Pr< or =10(2). The Rayleigh number was fixed at a value of Ra=10(6). Our main focus lay on the question how the value of the Prandtl number affects the spatial structure of the flow. We investigated the functional dependence of the Nusselt number and the Reynolds number and compared our results with a recent theoretical approach of Grossmann and Lohse [J. Fluid Mech. 407, 27 (2000); Phys. Rev. Lett. 86, 3316 (2001)].}, }
@article {pmid14979546, year = {2004}, author = {Martínez, SA and Rodríguez, MG and Aguilar, R and Soto, G}, title = {Removal of chromium hexavalent from rinsing chromating waters electrochemical reduction in a laboratory pilot plant.}, journal = {Water science and technology : a journal of the International Association on Water Pollution Research}, volume = {49}, number = {1}, pages = {115-122}, pmid = {14979546}, issn = {0273-1223}, mesh = {Carcinogens, Environmental/chemistry/*isolation &amp; purification ; Chromium/chemistry/*isolation &amp; purification ; Electrochemistry ; Kinetics ; *Models, Theoretical ; Oxidation-Reduction ; Water Pollutants/*isolation &amp; purification ; Water Purification/methods ; }, abstract = {In this work, experiments in a 16 L operating volume laboratory pilot plant with ring iron rotary electrodes were performed, obtaining an overall kinetic equation rate of hexavalent chromium reduction concentration and current density-dependent. Other scale-up criteria such as Reynolds' number were also evaluated to ensure a completely stirred reactor at low energy expenditure. A dimensionless N(E) is a relationship between liquid properties and the electric charge supplied to the system. The number, which depends on the rotation iron ring electrode speed number and the current density, is proposed to be used as scale-up criterion. It was found that at N(Re) = 42,179 (130 rpm rotation electrodes rate) and at N(E) = 9.8 x 10(5) (current density of 113 A/m2), complete mixing was reached at minimum energy spent and the process becomes more efficient. In addition, it was found that the higher the current density, the less treatment time and less energy spent on agitation. After the electrochemical treatment the Cr(VI) concentration in the rinsing wastewater was less than 0.5 mg/L.}, }
@article {pmid14978056, year = {2004}, author = {Wu, JH and Sun, M}, title = {Unsteady aerodynamic forces of a flapping wing.}, journal = {The Journal of experimental biology}, volume = {207}, number = {Pt 7}, pages = {1137-1150}, doi = {10.1242/jeb.00868}, pmid = {14978056}, issn = {0022-0949}, mesh = {Animals ; Biomechanical Phenomena ; Computer Simulation ; *Flight, Animal ; Insecta ; *Models, Biological ; Rotation ; *Wings, Animal ; }, abstract = {The unsteady aerodynamic forces of a model fruit fly wing in flapping motion were investigated by numerically solving the Navier-Stokes equations. The flapping motion consisted of translation and rotation [the translation velocity (u(t)) varied according to the simple harmonic function (SHF), and the rotation was confined to a short period around stroke reversal]. First, it was shown that for a wing of given geometry with u(t) varying as the SHF, the aerodynamic force coefficients depended only on five non-dimensional parameters, i.e. Reynolds number (Re), stroke amplitude (Phi), mid-stroke angle of attack (alpha(m)), non-dimensional duration of wing rotation (Delta tau(r)) and rotation timing [the mean translation velocity at radius of the second moment of wing area (U), the mean chord length (c) and c/U were used as reference velocity, length and time, respectively]. Next, the force coefficients were investigated for a case in which typical values of these parameters were used (Re=200; Phi=150 degrees; alpha(m)=40 degrees; Delta tau(r) was 20% of wingbeat period; rotation was symmetrical). Finally, the effects of varying these parameters on the force coefficients were investigated. In the Re range considered (20-1800), when Re was above approximately 100, the lift ((L)) and drag ((D)) coefficients were large and varied only slightly with Re (in agreement with results previously published for revolving wings); the large force coefficients were mainly due to the delayed stall mechanism. However, when Re was below approximately 100, (L) decreased and (D) increased greatly. At such low Re, similar to the case of higher Re, the leading edge vortex existed and attached to the wing in the translatory phase of a half-stroke; but it was very weak and its vorticity rather diffused, resulting in the small (L) and large (D). Comparison of the calculated results with available hovering flight data in eight species (Re ranging from 13 to 1500) showed that when Re was above approximately 100, lift equal to insect weight could be produced but when Re was lower than approximately 100, additional high-lift mechanisms were needed. In the range of Re above approximately 100, Phi from 90 degrees to 180 degrees and Delta tau(r) from 17% to 32% of the stroke period (symmetrical rotation), the force coefficients varied only slightly with Re, Phi and Delta tau(r). This meant that the forces were approximately proportional to the square of Phi n (n is the wingbeat frequency); thus, changing Phi and/or n could effectively control the magnitude of the total aerodynamic force. The time course of (L) (or (D)) in a half-stroke for u(t) varying according to the SHF resembled a half sine-wave. It was considerably different from that published previously for u(t), varying according to a trapezoidal function (TF) with large accelerations at stroke reversal, which was characterized by large peaks at the beginning and near the end of the half-stroke. However, the mean force coefficients and the mechanical power were not so different between these two cases (e.g. the mean force coefficients for u(t) varying as the TF were approximately 10% smaller than those for u(t) varying as the SHF except when wing rotation is delayed).}, }
@article {pmid14754343, year = {2003}, author = {Ginzburg, I and d'Humières, D}, title = {Multireflection boundary conditions for lattice Boltzmann models.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {68}, number = {6 Pt 2}, pages = {066614}, doi = {10.1103/PhysRevE.68.066614}, pmid = {14754343}, issn = {1539-3755}, abstract = {We present a general framework for several previously introduced boundary conditions for lattice Boltzmann models, such as the bounce-back rule and the linear and quadratic interpolations. The objectives are twofold: first to give theoretical tools to study the existing link-type boundary conditions and their corresponding accuracy; second to design boundary conditions for general flows which are third-order kinetic accurate. Using these new boundary conditions, Couette and Poiseuille flows are exact solutions of the lattice Boltzmann models for a Reynolds number Re=0 (Stokes limit) for arbitrary inclination with the lattice directions. Numerical comparisons are given for Stokes flows in periodic arrays of spheres and cylinders, linear periodic array of cylinders between moving plates, and for Navier-Stokes flows in periodic arrays of cylinders for Re<200. These results show a significant improvement of the overall accuracy when using the linear interpolations instead of the bounce-back reflection (up to an order of magnitude on the hydrodynamics fields). Further improvement is achieved with the new multireflection boundary conditions, reaching a level of accuracy close to the quasianalytical reference solutions, even for rather modest grid resolutions and few points in the narrowest channels. More important, the pressure and velocity fields in the vicinity of the obstacles are much smoother with multireflection than with the other boundary conditions. Finally the good stability of these schemes is highlighted by some simulations of moving obstacles: a cylinder between flat walls and a sphere in a cylinder.}, }
@article {pmid14754319, year = {2003}, author = {Shevtsova, VM and Melnikov, DE and Legros, JC}, title = {Multistability of oscillatory thermocapillary convection in a liquid bridge.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {68}, number = {6 Pt 2}, pages = {066311}, doi = {10.1103/PhysRevE.68.066311}, pmid = {14754319}, issn = {1539-3755}, abstract = {A parametric investigation of the onset of chaos in a liquid bridge was numerically carried out for a medium Prandtl number liquid, Pr = 4, and unit aspect ratio under zero-gravity conditions. Spatiotemporal patterns of thermocapillary flow were successively studied beginning from the onset of instability up to the appearance of the nonperiodic flow and further on. Well-tested numerical code is used for solving the three-dimensional time-dependent Navier-Stokes equations in cylindrical coordinate system. Two-dimensional steady flow becomes oscillatory with azimuthal wave number m=2 as a result of Hopf bifurcation at Re(cr)(1)=630. A second independent solution with wave number m=3 was found to appear at Reynolds number Re(cr)(2) approximately 810. Two branches of three-dimensional periodic orbits, traveling waves with m=2 and m=3, coexist for Re>Re(cr)(2). Additional stable branches do not connect them. The different flow organizations reveal different behaviors in the supercritical area. The m=2 traveling wave always remains periodic, but the mode m=3 starts exhibiting chaotic features at Re approximately 4200. The onset of temporal nonperiodicity was shown to be associated with development of broadband noise in spectra and preceded by a quasiperiodicity. The flow stabilizes back to periodic with single frequency when Re exceeds a value Re approximately 5100. The window of periodicity exists up to at least Re=6000, the largest investigated value of the Reynolds number.}, }
@article {pmid14754200, year = {2003}, author = {Raiskinmäki, P and Aström, JA and Kataja, M and Latva-Kokko, M and Koponen, A and Jäsberg, A and Shakib-Manesh, A and Timonen, J}, title = {Clustering and viscosity in a shear flow of a particulate suspension.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {68}, number = {6 Pt 1}, pages = {061403}, doi = {10.1103/PhysRevE.68.061403}, pmid = {14754200}, issn = {1539-3755}, abstract = {A shear flow of particulate suspension is analyzed for the qualitative effect of particle clustering on viscosity using a simple kinetic clustering model and direct numerical simulations. The clusters formed in a Couette flow can be divided into rotating chainlike clusters and layers of particles at the channel walls. The size distribution of the rotating clusters is scale invariant in the small-cluster regime and decreases rapidly above a characteristic length scale that diverges at a jamming transition. The behavior of the suspension can qualitatively be divided into three regimes. For particle Reynolds number Re(p) less than or approximately equal 0.1, viscosity is controlled by the characteristic cluster size deduced from the kinetic clustering model. For Re(p) approximately 1, clustering is maximal, but the simple kinetic model becomes inapplicable presumably due to onset of instabilities. In this transition regime viscosity begins to increase. For Re(p) greater than or approximately equal 10, inertial effects become important, clusters begin to breakup, and suspension displays shear thickening. This phenomenon may be attributed to enhanced contribution of solid phase in the total shear stress.}, }
@article {pmid14695302, year = {2004}, author = {Shankaran, H and Neelamegham, S}, title = {Hydrodynamic forces applied on intercellular bonds, soluble molecules, and cell-surface receptors.}, journal = {Biophysical journal}, volume = {86}, number = {1 Pt 1}, pages = {576-588}, pmid = {14695302}, issn = {0006-3495}, support = {R01 HL063014/HL/NHLBI NIH HHS/United States ; HL63014/HL/NHLBI NIH HHS/United States ; }, mesh = {Blood Platelets/*physiology ; Blood Vessels/physiology ; Cell Adhesion/*physiology ; Cell Movement/*physiology ; Computer Simulation ; Hemorheology/*methods ; *Models, Cardiovascular ; Motion ; Receptors, Cell Surface/*physiology ; Shear Strength ; Solubility ; Stress, Mechanical ; }, abstract = {Cells and biomolecules exposed to blood circulation experience hydrodynamic forces that affect their function. We present a methodology to estimate fluid forces and force loading rates applied on cellular aggregates, cell-surface proteins, and soluble molecules. Low Reynolds-number hydrodynamic theory is employed. Selected results are presented for biological cases involving platelets, neutrophils, tumor cells, GpIb-like cell-surface receptors, and plasma von Willebrand factor (vWF)-like soluble proteins. Calculations reveal the following: 1), upon application of constant linear shear, cell aggregates and biomolecules experience time-varying forces due to their tumbling motion. 2), In comparison to neutrophil homotypic aggregates, the maximum force applied on neutrophil-platelet aggregates is approximately threefold lower. Thus, alterations in cell size may dramatically alter adhesion molecule requirement for efficient cell binding. Whereas peak forces on homotypic cell doublets are tensile, shear forces dominate in heterotypic doublets with radius ratio <0.3. 3), The peak forces on platelet GpIb and von Willebrand factor are of comparable magnitude. However, they are orders-of-magnitude lower than those applied on intercellular bonds. Charts are provided to rapidly evaluate the magnitude of hydrodynamic force and rotation time-period occurring in any given experiment. The calculation scheme may find application in studies of vascular biology and receptor biophysics.}, }
@article {pmid14691093, year = {2004}, author = {Wang, ZJ and Birch, JM and Dickinson, MH}, title = {Unsteady forces and flows in low Reynolds number hovering flight: two-dimensional computations vs robotic wing experiments.}, journal = {The Journal of experimental biology}, volume = {207}, number = {Pt 3}, pages = {449-460}, doi = {10.1242/jeb.00739}, pmid = {14691093}, issn = {0022-0949}, mesh = {Animals ; Biomechanical Phenomena ; Computer Simulation ; *Flight, Animal ; *Models, Biological ; Rotation ; Wings, Animal/*physiology ; }, abstract = {We compare computational, experimental and quasi-steady forces in a generic hovering wing undergoing sinusoidal motion along a horizontal stroke plane. In particular, we investigate unsteady effects and compare two-dimensional (2D) computations and three-dimensional (3D) experiments in several qualitatively different kinematic patterns. In all cases, the computed drag compares well with the experiments. The computed lift agrees in the cases in which the sinusoidal changes in angle of attack are symmetrical or advanced with respect to stroke positions, but lags behind the measured 3D lift in the delayed case. In the range of amplitudes studied here, 3-5 chords, the force coefficients have a weak dependence on stroke amplitude. As expected, the forces are sensitive to the phase between stroke angle and angle of attack, a result that can be explained by the orientation of the wing at reversal. This dependence on amplitude and phase suggests a simple maneuver strategy that could be used by a flapping wing device. In all cases the unsteady forces quickly reach an almost periodic state with continuous flapping. The fluid forces are dominated by the pressure contribution. The force component directly proportional to the linear acceleration is smaller by a factor proportional to the ratio of wing thickness and stroke amplitude; its net contribution is zero in hovering. The ratio of wing inertia and fluid force is proportional to the product of the ratio of wing and fluid density and the ratio of wing thickness and stroke amplitude; it is negligible in the robotic wing experiment, but need not be in insect flight. To identify unsteady effects associated with wing acceleration, and coupling between rotation and translation, as well as wake capture, we examine the difference between the unsteady forces and the estimates based on translational velocities, and compare them against the estimate of the coupling between rotation and translation, which have simple analytic forms for sinusoidal motions. The agreement and disagreement between the computed forces and experiments offer further insight into when the 3D effects are important. A main difference between a 3D revolving wing and a 2D translating wing is the absence of vortex shedding by a revolving wing over a distance much longer than the typical stroke length of insects. No doubt such a difference in shedding dynamics is responsible in part for the differences in steady state force coefficients measured in 2D and 3D. On the other hand, it is unclear whether such differences would have a significant effect on transient force coefficients before the onset of shedding. While the 2D steady state force coefficients underpredict 3D forces, the transient 2D forces measured prior to shedding are much closer to the 3D forces. In the cases studied here, the chord is moving between 3 to 5 chords, typical of hovering insect stroke length, and the flow does not appear to separate during each stroke in the cases of advanced and symmetrical rotation. In these cases, the wing reverses before the leading edge vortex would have time to separate even in 2D. This suggests that the time scale for flow separation in these strokes is dictated by the flapping frequency, which is dimensionally independent. In such cases, the 2D unsteady forces turn out to be good approximations of 3D experiments.}, }
@article {pmid14683309, year = {2003}, author = {Chevillard, L and Roux, SG and Levêque, E and Mordant, N and Pinton, JF and Arneodo, A}, title = {Lagrangian velocity statistics in turbulent flows: effects of dissipation.}, journal = {Physical review letters}, volume = {91}, number = {21}, pages = {214502}, doi = {10.1103/PhysRevLett.91.214502}, pmid = {14683309}, issn = {0031-9007}, abstract = {We use the multifractal formalism to describe the effects of dissipation on Lagrangian velocity statistics in turbulent flows. We analyze high Reynolds number experiments and direct numerical simulation data. We show that this approach reproduces the shape evolution of velocity increment probability density functions from Gaussian to stretched exponentials as the time lag decreases from integral to dissipative time scales. A quantitative understanding of the departure from scaling exhibited by the magnitude cumulants, early in the inertial range, is obtained with a free parameter function D(h) which plays the role of the singularity spectrum in the asymptotic limit of infinite Reynolds number. We observe that numerical and experimental data are accurately described by a unique quadratic D(h) spectrum which is found to extend from h(min) approximately 0.18 to h(max) approximately 1.}, }
@article {pmid14683129, year = {2003}, author = {Hof, B and Juel, A and Mullin, T}, title = {Scaling of the turbulence transition threshold in a pipe.}, journal = {Physical review letters}, volume = {91}, number = {24}, pages = {244502}, doi = {10.1103/PhysRevLett.91.244502}, pmid = {14683129}, issn = {0031-9007}, abstract = {We report the results of an experimental investigation of the transition to turbulence in a pipe over approximately an order of magnitude range in the Reynolds number Re. A novel scaling law is uncovered using a systematic experimental procedure which permits contact to be made with modern theoretical thinking. The principal result we uncover is a scaling law which indicates that the amplitude of perturbation required to cause transition scales as O(Re-1).}, }
@article {pmid14683081, year = {2003}, author = {Zhang, YT and Shi, J and Shu, CW and Zhou, Y}, title = {Numerical viscosity and resolution of high-order weighted essentially nonoscillatory schemes for compressible flows with high Reynolds numbers.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {68}, number = {4 Pt 2}, pages = {046709}, doi = {10.1103/PhysRevE.68.046709}, pmid = {14683081}, issn = {1539-3755}, abstract = {A quantitative study is carried out in this paper to investigate the size of numerical viscosities and the resolution power of high-order weighted essentially nonoscillatory (WENO) schemes for solving one- and two-dimensional Navier-Stokes equations for compressible gas dynamics with high Reynolds numbers. A one-dimensional shock tube problem, a one-dimensional example with parameters motivated by supernova and laser experiments, and a two-dimensional Rayleigh-Taylor instability problem are used as numerical test problems. For the two-dimensional Rayleigh-Taylor instability problem, or similar problems with small-scale structures, the details of the small structures are determined by the physical viscosity (therefore, the Reynolds number) in the Navier-Stokes equations. Thus, to obtain faithful resolution to these small-scale structures, the numerical viscosity inherent in the scheme must be small enough so that the physical viscosity dominates. A careful mesh refinement study is performed to capture the threshold mesh for full resolution, for specific Reynolds numbers, when WENO schemes of different orders of accuracy are used. It is demonstrated that high-order WENO schemes are more CPU time efficient to reach the same resolution, both for the one-dimensional and two-dimensional test problems.}, }
@article {pmid14683045, year = {2003}, author = {L'vov, VS and Pomyalov, A and Tiberkevich, V}, title = {Multizone shell model for turbulent wall bounded flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {68}, number = {4 Pt 2}, pages = {046308}, doi = {10.1103/PhysRevE.68.046308}, pmid = {14683045}, issn = {1539-3755}, abstract = {We suggested a multizone shell (MZS) model for wall-bounded flows accounting for the space inhomogeneity in a piecewise approximation, in which the cross-sectional area of the flow, S, is subdivided into j zones. The area of the first zone, responsible for the core of the flow, S1 approximately S/2, and the areas of the next j zones, S(j), decrease toward the wall like S(j) proportional, variant 2(-j). In each j zone the statistics of turbulence is assumed to be space homogeneous and is described by the set of shell velocities u(nj)(t) for turbulent fluctuations of the scale proportional to 2(-n). The MZS model includes a set of complex variables V(j)(t), j=1,2, em leader, infinity, describing the amplitudes of the near-wall coherent structures of the scale s(j) approximately 2(-j) and responsible for the mean velocity profile. The suggested MZS equations of motion for u(nj)(t) and V(j)(t) preserve the actual conservation laws (energy, mechanical, and angular momenta), respect the existing symmetries (including Galilean and scale invariance), and account for the type of nonlinearity in the Navier-Stokes equation, dimensional reasoning, etc. The MZS model qualitatively describes important characteristics of the wall-bounded turbulence, e.g., evolution of the mean velocity profile with increasing Reynolds number Re from the laminar profile toward the universal logarithmic profile near the flat-plane boundary layer as Re--> infinity.}, }
@article {pmid14683042, year = {2003}, author = {Chu, AK}, title = {Stability of acoustic streaming flows in plane channels.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {68}, number = {4 Pt 2}, pages = {046305}, doi = {10.1103/PhysRevE.68.046305}, pmid = {14683042}, issn = {1539-3755}, abstract = {We study the stability of acoustic streaming flows of normal fluids induced by a small-amplitude surface acoustic wave propagating along the walls of a confined parallel-plane channel or slab in the incompressible flow regime. The secondary flows derived are of negligible effect to the stability characteristic after comparing with the primary flow. The governing equation which was derived by considering the weakly nonlinear coupling between the wavy wall and viscous fluid is obtained and then the eigenvalue problem is solved by a numerical code together with the associated dynamic and kinematic conditions. The value of the critical Reynolds number was found to be near 4873 which is smaller than the case 5772 for conventional pressure-driven flows.}, }
@article {pmid14682993, year = {2003}, author = {Wagner, AJ and Wilson, LM and Cates, ME}, title = {Role of inertia in two-dimensional deformation and breakdown of a droplet.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {68}, number = {4 Pt 2}, pages = {045301}, doi = {10.1103/PhysRevE.68.045301}, pmid = {14682993}, issn = {1539-3755}, abstract = {We investigate by lattice Boltzmann methods the effect of inertia on the deformation and breakdown of stability of a two-dimensional fluid droplet surrounded by fluid of equal viscosity (in a confined geometry) whose shear rate is increased very slowly. We give evidence that in two dimensions inertia is necessary for the loss of stability, so that at zero Reynolds number there is always a stable stationary droplet shape. We identify two different routes to breakdown, via two-lobed and three-lobed structures and give evidence for a sharp transition between these routes as parameters are varied.}, }
@article {pmid14682882, year = {2003}, author = {Pesci, AI and Porter, MA and Goldstein, RE}, title = {Inertially driven buckling and overturning of jets in a Hele-Shaw cell.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {68}, number = {5 Pt 2}, pages = {056305}, doi = {10.1103/PhysRevE.68.056305}, pmid = {14682882}, issn = {1539-3755}, abstract = {We study a fluid jet descending through stratified surroundings at low Reynolds number in Hele-Shaw flow. The jet buckles and overturns inside a conduit of entrained fluid which supports smooth or unstable traveling waves. A model of the recirculating flow within the conduit shows that buckling and waves arise from Kelvin-Helmholtz instabilities and quantitatively accounts for the main experimental observations. Beyond the onset of the instability, a damped, forced Burgers' equation obtained from corrections to Darcy's law for small Reynolds number governs the interface dynamics and supports singularities corresponding to the observed jet overturning and unstable waves.}, }
@article {pmid14682839, year = {2003}, author = {Ravoux, JF and Provansal, M and Nadim, A and Schouveiler, L}, title = {Strouhal-Reynolds number relationship for bluff-body flows numerically simulated by an artificial boundary method.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {68}, number = {5 Pt 2}, pages = {055702}, doi = {10.1103/PhysRevE.68.055702}, pmid = {14682839}, issn = {1539-3755}, abstract = {The incidence of the numerical resolution and the blockage effect are investigated in an embedding method for solving bidimensional bluff body flows. This method consists of using an artificial boundary instead of imposing exact conditions on the body surface. It requires us to define a blur frontier ratio and a blockage effect ratio. The blockage effect ratio is found using the mean flow of a circular cylinder directly. The blur frontier ratio is obtained by comparison of the present method with another numerical method where explicit boundary conditions on the body are imposed. For this ratio, the investigations are based on the flow past a square cylinder which discard the uncertainty on the surface of the body for the embedding method. Hence, the two factors allow the transformations of the Strouhal and the Reynolds numbers for the flow past a circular cylinder. The universal Strouhal-Reynolds number relationship of the circular cylinder is finally recovered.}, }
@article {pmid14671319, year = {2003}, author = {Kim, M and Bird, JC and Van Parys, AJ and Breuer, KS and Powers, TR}, title = {A macroscopic scale model of bacterial flagellar bundling.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {100}, number = {26}, pages = {15481-15485}, pmid = {14671319}, issn = {0027-8424}, mesh = {Escherichia coli/*physiology ; Flagella/*physiology/ultrastructure ; Models, Biological ; Movement/physiology ; Salmonella typhimurium/*physiology ; }, abstract = {Escherichia coli and other bacteria use rotating helical filaments to swim. Each cell typically has about four filaments, which bundle or disperse depending on the sense of motor rotation. To study the bundling process, we built a macroscopic scale model consisting of stepper motor-driven polymer helices in a tank filled with a high-viscosity silicone oil. The Reynolds number, the ratio of viscous to elastic stresses, and the helix geometry of our experimental model approximately match the corresponding quantities of the full-scale E. coli cells. We analyze digital video images of the rotating helices to show that the initial rate of bundling is proportional to the motor frequency and is independent of the characteristic relaxation time of the filament. We also determine which combinations of helix handedness and sense of motor rotation lead to bundling.}, }
@article {pmid14663862, year = {2004}, author = {Shao, XM and Lin, JZ and Yu, ZS}, title = {Sedimentation of a single particle between two parallel walls.}, journal = {Journal of Zhejiang University. Science}, volume = {5}, number = {1}, pages = {111-116}, doi = {10.1007/BF02839322}, pmid = {14663862}, issn = {1009-3095}, mesh = {Colloids/*chemistry ; Complex Mixtures/*chemistry ; Computer Simulation ; Geologic Sediments/*chemistry ; Membranes, Artificial ; Microfluidics/*methods ; *Models, Chemical ; Motion ; *Numerical Analysis, Computer-Assisted ; Particle Size ; }, abstract = {The sedimentation of a single circular particle between two parallel walls was studied by means of direct numerical simulation (DNS) and experiment. The improved implementation of distributed Lagrange multiplier/fictitious domain method used in our DNS is a promising new way for simulation of particulate flows. The settling behaviors of the particle are presented ranging in Reynolds number from 0 to about 700, which showed that our results for low Reynolds numbers agreed well with that reported before. Nevertheless, for higher Reynolds numbers our results were different from theirs. The long-term mean equilibrium positions in our results were all on the centerline, but not at off-center position as reported before. In order to validate our simulation, experiments were also conducted. The results showed that the sedimenting behavior simulated in this paper agreed well with our experiment result.}, }
@article {pmid14649496, year = {2003}, author = {David, T}, title = {Wall shear stress modulation of ATP/ADP concentration at the endothelium.}, journal = {Annals of biomedical engineering}, volume = {31}, number = {10}, pages = {1231-1237}, doi = {10.1114/1.1615574}, pmid = {14649496}, issn = {0090-6964}, mesh = {Adenosine Diphosphate/*metabolism ; Adenosine Triphosphate/*metabolism ; Animals ; Blood Flow Velocity ; Computer Simulation ; Endothelium, Vascular/*physiology ; Hemostasis/*physiology ; Humans ; *Models, Cardiovascular ; Pulsatile Flow ; Shear Strength ; Stress, Mechanical ; }, abstract = {A mathematical model of ATP/ADP reaction at the surface of the endothelium for any two-dimensional or axisymmetric nonsingular functional form of the wall shear stress has been presented. Excellent agreement is obtained with the numerical solution for the parallel plate case. For spatially varying wall shear stress, such as the stagnation point flow and a backward facing step the ATP concentrations are shown to have a maximum at the stagnation point streamline and the reattachment point respectively. Increasing the Reynolds number increases both the ATP and ADP concentrations. For the backward facing step significant spatial variations occur in the concentration. Hence, a strong controlling factor for physiological kinetic values is the geometry of the arterial vessel since this determines the wall shear stress and thence the transport to the reactive surface. The area of high concentration also occurs where the wall shear stress is low (limiting case is zero shear stress). Atherosclerotic plaques are known to occur in areas of low wall shear stress and at vessel bifurcations where the wall shear stress is spatially varying. The ATP/ADP concentrations at these particular points may very well contribute to the formation of plaques.}, }
@article {pmid14630111, year = {2004}, author = {Serra, T and Fernando, HJ and Rodríguez, RV}, title = {Effects of emergent vegetation on lateral diffusion in wetlands.}, journal = {Water research}, volume = {38}, number = {1}, pages = {139-147}, doi = {10.1016/j.watres.2003.09.009}, pmid = {14630111}, issn = {0043-1354}, mesh = {Diffusion ; *Ecosystem ; *Models, Theoretical ; Plant Development ; Waste Disposal, Fluid/*methods ; *Water Movements ; }, abstract = {Constructed wetlands are widely used for a variety of environmental applications, such as wastewater treatment and recharge, and their efficacy is largely determined by the hydrodynamic characteristics of the flow system. An experimental study was carried out to quantify the lateral dispersion of passive substances in shallow zones of a constructed wetland wherein water flows though the interstices of the distributed vegetation. The experimental set up was designed to mimic the Tres Rios constructed wetland located in Phoenix, Arizona. The major emphasis was on the lateral diffusivity K(t) of a shallow zone with randomly distributed vegetation. The results are presented in the context of a simple theoretical model where K(t) is expressed in terms of the diameter of the plant stalk D(v), the characteristic distance between the plants d(v), the flow velocity U and the drag coefficient C(D) as (K(t)/UD(v))(d(v)/D(v))=betaC(D), where beta is a dimensionless constant. Fitting of data to the above model indicate that C(D), in general, is a function of the Reynolds number (Re). The data are also compared with a model proposed by Nepf et al. (Water Res 35 (1999) 479).}, }
@article {pmid14618930, year = {2003}, author = {Ge, L and Jones, SC and Sotiropoulos, F and Healy, TM and Yoganathan, AP}, title = {Numerical simulation of flow in mechanical heart valves: grid resolution and the assumption of flow symmetry.}, journal = {Journal of biomechanical engineering}, volume = {125}, number = {5}, pages = {709-718}, doi = {10.1115/1.1614817}, pmid = {14618930}, issn = {0148-0731}, support = {R01-HL-07262/HL/NHLBI NIH HHS/United States ; }, mesh = {Blood Flow Velocity/*physiology ; *Blood Physiological Phenomena ; Blood Pressure ; Computer Simulation ; Equipment Failure Analysis/*methods ; Finite Element Analysis ; *Heart Valve Prosthesis ; Heart Valves/*physiology ; Hemorheology/*methods ; Humans ; *Models, Cardiovascular ; }, abstract = {A numerical method is developed for simulating unsteady, 3-D, laminar flow through a bileaflet mechanical heart valve with the leaflets fixed. The method employs a dual-time-stepping artificial-compressibility approach together with overset (Chimera) grids and is second-order accurate in space and time. Calculations are carried out for the full 3-D valve geometry under steady inflow conditions on meshes with a total number of nodes ranging from 4 x 10(5) to 1.6 x 10(6). The computed results show that downstream of the leaflets the flow is dominated by two pairs of counter-rotating vortices, which originate on either side of the central orifice in the aortic sinus and rotate such that the common flow of each pair is directed away from the aortic wall. These vortices intensify with Reynolds number, and at a Reynolds number of approximately 1200 their complex interaction leads to the onset of unsteady flow and the break of symmetry with respect to both geometric planes of symmetry. Our results show the highly 3-D structure of the flow; question the validity of computationally expedient assumptions of flow symmetry; and demonstrate the need for highly resolved, fully 3-D simulations if computational fluid dynamics is to accurately predict the flow in prosthetic mechanical heart valves.}, }
@article {pmid14618924, year = {2003}, author = {Hangan, H and Bekele, S}, title = {Numerical simulation of the flow and concentration fields for oxygen delivery systems.}, journal = {Journal of biomechanical engineering}, volume = {125}, number = {5}, pages = {648-662}, doi = {10.1115/1.1613296}, pmid = {14618924}, issn = {0148-0731}, mesh = {Computer Simulation ; Computer-Aided Design ; Drug Delivery Systems/*instrumentation ; Equipment Failure Analysis/*methods ; Humans ; *Masks ; *Models, Theoretical ; Oxygen/*administration &amp; dosage/analysis ; Oxygen Inhalation Therapy/*instrumentation ; Respiration, Artificial/*instrumentation ; Rheology/*methods ; }, abstract = {The flow and concentration fields for various medical oxygen delivery devices are numerically investigated. Simulations are performed for a classical Venturi mask and two new OxyArm portable devices. The velocity and oxygen concentration fields are investigated for: (i) a constant (steady-state) inhalation and (ii) a complete respiratory cycle (unsteady). The numerical results are qualitatively compared with clinical trials. It is found that the optimal functioning of these medical devices implies a balance between oxygen delivery by advection and the mixing process that allows for reliable CO2 monitoring (capnographic capability). Also, at the typical scales associated with these devices the flow is found to be Reynolds number dependent.}, }
@article {pmid14618922, year = {2003}, author = {Sugihara-Seki, M and Schmid-Schönbein, GW}, title = {The fluid shear stress distribution on the membrane of leukocytes in the microcirculation.}, journal = {Journal of biomechanical engineering}, volume = {125}, number = {5}, pages = {628-638}, doi = {10.1115/1.1611515}, pmid = {14618922}, issn = {0148-0731}, support = {HL 43026/HL/NHLBI NIH HHS/United States ; }, mesh = {Blood Flow Velocity ; Blood Pressure ; Cell Adhesion/*physiology ; Cell Membrane/*physiology ; Cell Movement/*physiology ; Computer Simulation ; Hemorheology/*methods ; Leukocytes/*physiology ; Microcirculation/*physiopathology ; *Models, Cardiovascular ; Shear Strength ; Surface Tension ; }, abstract = {Recent in-vivo and in-vitro evidence indicates that fluid shear stress on the membrane of leukocytes has a powerful control over several aspects of their cell function. This evidence raises a question about the magnitude of the fluid shear stress on leukocytes in the circulation. The flow of plasma on the surface of a leukocyte at a very low Reynolds number is governed by the Stokes equation for the motion of a Newtonian fluid. We numerically estimated the distribution of fluid shear stress on a leukocyte membrane in a microvessel for the cases when the leukocyte is freely suspended, as well as rolling along or attached to a microvessel wall. The results indicate that the fluid shear stress distribution on the leukocyte membrane is nonuniform with a sharp increase when the leukocyte makes membrane attachment to the microvessel wall. In a microvessel (10 microns diameter), the fluid shear stress on the membrane of a freely suspended leukocyte (8 microns diameter) is estimated to be several times larger than the wall shear stress exerted by the undisturbed Poiseuille flow, and increases on an adherent leukocyte up to ten times. High temporal stress gradients are present in freely suspended leukocytes in shear flow due to cell rotation, which are proportional to the local shear rate. In comparison, the temporal stress gradients are reduced on the membrane of leukocytes that are rolling or firmly adhered to the endothelium. High temporal gradients of shear stress are also present on the endothelial wall. At a plasma viscosity of 1 cPoise, the peak shear stresses for suspended and adherent leukocytes are of the order of 10 dyn/cm2 and 100 dyn/cm2, respectively.}, }
@article {pmid14610313, year = {2003}, author = {Ghalichi, F and Deng, X}, title = {Turbulence detection in a stenosed artery bifurcation by numerical simulation of pulsatile blood flow using the low-Reynolds number turbulence model.}, journal = {Biorheology}, volume = {40}, number = {6}, pages = {637-654}, pmid = {14610313}, issn = {0006-355X}, mesh = {Blood Flow Velocity ; Carotid Stenosis/pathology/*physiopathology ; Finite Element Analysis ; *Hemorheology ; Humans ; *Models, Cardiovascular ; Pulsatile Flow ; Stress, Mechanical ; }, abstract = {The pulsatile blood flow in a partially blocked artery is significantly altered as the flow regime changes through the cardiac cycle. This paper reports on the application of a low-Reynolds turbulence model for computation of physiological pulsatile flow in a healthy and stenosed carotid artery bifurcation. The human carotid artery was chosen since it has received much attention because atherosclerotic lesions are frequently observed. The Wilcox low-Re k-omega turbulence model was used for the simulation since it has proven to be more accurate in describing transition from laminar to turbulent flow. Using the FIDAP finite element code a validation showed very good agreement between experimental and numerical results for a steady laminar to turbulent flow transition as reported in a previous publication by the same authors. Since no experimental or numerical results were available in the literature for a pulsatile and turbulent flow regime, a comparison between laminar and low-Re turbulent calculations was made to further validate the turbulence model. The results of this study showed a very good agreement for velocity profiles and wall shear stress values for this imposed pulsatile laminar flow regime. To explore further the medical aspect, the calculations showed that even in a healthy or non-stenosed artery, small instabilities could be found at least for a portion of the pulse cycle and in different sections. The 40% and 55% diameter reduction stenoses did not significantly change the turbulence characteristics. Further results showed that the presence of 75% stenoses changed the flow properties from laminar to turbulent flow for a good portion of the cardiac pulse. A full 3D simulation with this low-Re-turbulence model, coupled with Doppler ultrasound, can play a significant role in assessing the degree of stenosis for cardiac patients with mild conditions.}, }
@article {pmid14582876, year = {2003}, author = {Etemad, SG and Thibault, J and Hashemabadi, SH}, title = {Calculation of the Pitot tube correction factor for Newtonian and non-Newtonian fluids.}, journal = {ISA transactions}, volume = {42}, number = {4}, pages = {505-512}, doi = {10.1016/s0019-0578(07)60001-9}, pmid = {14582876}, issn = {0019-0578}, mesh = {*Algorithms ; Calibration ; Computer Simulation ; Kinetics ; *Models, Theoretical ; *Neural Networks, Computer ; Nonlinear Dynamics ; Pressure ; Quality Control ; Reproducibility of Results ; Rheology/*instrumentation/*methods ; Sensitivity and Specificity ; Transducers ; }, abstract = {This paper presents the numerical investigation performed to calculate the correction factor for Pitot tubes. The purely viscous non-Newtonian fluids with the power-law model constitutive equation were considered. It was shown that the power-law index, the Reynolds number, and the distance between the impact and static tubes have a major influence on the Pitot tube correction factor. The problem was solved for a wide range of these parameters. It was shown that employing Bernoulli's equation could lead to large errors, which depend on the magnitude of the kinetic energy and energy friction loss terms. A neural network model was used to correlate the correction factor of a Pitot tube as a function of these three parameters. This correlation is valid for most Newtonian, pseudoplastic, and dilatant fluids at low Reynolds number.}, }
@article {pmid14574699, year = {2003}, author = {Manz, B and Volke, F and Goll, D and Horn, H}, title = {Measuring local flow velocities and biofilm structure in biofilm systems with magnetic resonance imaging (MRI).}, journal = {Biotechnology and bioengineering}, volume = {84}, number = {4}, pages = {424-432}, doi = {10.1002/bit.10782}, pmid = {14574699}, issn = {0006-3592}, mesh = {*Algorithms ; Bacteria/*cytology ; *Bacterial Physiological Phenomena ; Biofilms/*growth &amp; development ; Bioreactors/*microbiology ; Cell Culture Techniques/*methods ; Image Interpretation, Computer-Assisted ; Magnetic Resonance Imaging/*methods ; Microfluidics/*methods ; Movement ; Surface Properties ; }, abstract = {The characterization of substrate transport in the bulk phase and in the biofilm matrix is one of the problems which has to be solved for the verification of biofilm models. Additionally, the surface structure of biofilms has to be described with appropriate parameters. Magnetic resonance imaging (MRI) is one of the promising methods for the investigation of transport phenomena and structure in biofilm systems. The MRI technique allows the noninvasive determination of flow velocities and biofilm structures with a high resolution on the sub-millimeter scale. The presented investigations were carried out for defined heterotrophic biofilms which were cultivated in a tube reactor at a Reynolds number of 2000 and 8000 and a substrate load of 6 and 4 g/m2d glucose. Magnetic resonance imaging provides both structure data of the biofilm surface and flow velocities in the bulk phase and at the bulk/biofilm interface. It is shown that the surface roughness of the biofilms can be determined in one experiment for the complete cross section of the test tubes both under flow and stagnant conditions. Furthermore, the local shear stress was calculated from the measured velocity profiles. In the investigated biofilm systems the local shear stress at the biofilm surface was up to 3 times higher compared to the mean wall shear stress calculated on the base of the mean flow velocity.}, }
@article {pmid14561347, year = {2003}, author = {Tytell, ED and Ellington, CP}, title = {How to perform measurements in a hovering animal's wake: physical modelling of the vortex wake of the hawkmoth, Manduca sexta.}, journal = {Philosophical transactions of the Royal Society of London. Series B, Biological sciences}, volume = {358}, number = {1437}, pages = {1559-1566}, pmid = {14561347}, issn = {0962-8436}, mesh = {Air Movements ; Animals ; Flight, Animal/*physiology ; Manduca/*physiology ; *Models, Biological ; Rheology ; Time Factors ; }, abstract = {The vortex wake structure of the hawkmoth, Manduca sexta, was investigated using a vortex ring generator. Based on existing kinematic and morphological data, a piston and tube apparatus was constructed to produce circular vortex rings with the same size and disc loading as a hovering hawkmoth. Results show that the artificial rings were initially laminar, but developed turbulence owing to azimuthal wave instability. The initial impulse and circulation were accurately estimated for laminar rings using particle image velocimetry; after the transition to turbulence, initial circulation was generally underestimated. The underestimate for turbulent rings can be corrected if the transition time and velocity profile are accurately known, but this correction will not be feasible for experiments on real animals. It is therefore crucial that the circulation and impulse be estimated while the wake vortices are still laminar. The scaling of the ring Reynolds number suggests that flying animals of about the size of hawkmoths may be the largest animals whose wakes stay laminar for long enough to perform such measurements during hovering. Thus, at low advance ratios, they may be the largest animals for which wake circulation and impulse can be accurately measured.}, }
@article {pmid14525244, year = {2003}, author = {Reynolds, AM}, title = {Superstatistical mechanics of tracer-particle motions in turbulence.}, journal = {Physical review letters}, volume = {91}, number = {8}, pages = {084503}, doi = {10.1103/PhysRevLett.91.084503}, pmid = {14525244}, issn = {0031-9007}, abstract = {The Lagrangian stochastic model of Reynolds [Phys. Fluids 15, L1-4 (2003)]] for the accelerations of fluid particles in turbulence is shown to predict precisely the observed Reynolds-number dependency of the distribution of Lagrangian accelerations and the exponents characterizing the observed extended self-similarity scaling of the Lagrangian velocity structure functions. Departures from superstatistics of the log-normal kind are accounted for and their impact upon model predictions is quantified.}, }
@article {pmid14525111, year = {2003}, author = {Khan, MA and Pumir, A and Vassilicos, JC}, title = {Kinematic simulation of turbulent dispersion of triangles.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {68}, number = {2 Pt 2}, pages = {026313}, doi = {10.1103/PhysRevE.68.026313}, pmid = {14525111}, issn = {1539-3755}, abstract = {As three particles are advected by a turbulent flow, they separate from each other and develop nontrivial geometries, which effectively reflect the structure of the turbulence. We investigate here the geometry, in a statistical sense, of three Lagrangian particles advected, in two dimensions, by kinematic simulation (KS). KS is a Lagrangian model of turbulent diffusion that makes no use of any delta correlation in time at any level. With this approach, situations with a very large range of inertial scales and varying persistence of spatial flow structure can be studied. We first demonstrate that the model flow reproduces recent experimental results at low Reynolds numbers. The statistical properties of the shape distribution at a much higher Reynolds number is then considered. The numerical results support the existence of nontrivial shape statistics, with a high probability of having elongated triangles. Even at the highest available inertial range of scales, corresponding to a ratio between large and small scale L/eta=17,000, a perfect self-similar regime is not found. The effects of the parameters of the synthetic flow, such as the exponent of the spectrum and the effect of the sweeping affect our results, are also discussed. Special attention is given to the effects of persistence of spatial flow structure.}, }
@article {pmid14525108, year = {2003}, author = {Taylor, MA and Kurien, S and Eyink, GL}, title = {Recovering isotropic statistics in turbulence simulations: the Kolmogorov 4/5th law.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {68}, number = {2 Pt 2}, pages = {026310}, doi = {10.1103/PhysRevE.68.026310}, pmid = {14525108}, issn = {1539-3755}, abstract = {One of the main benchmarks in direct numerical simulations of three-dimensional turbulence is the Kolmogorov prediction for third-order structure functions with homogeneous and isotropic statistics in the infinite Reynolds number limit. Previous direct numerical simulations (DNS) techniques to obtain isotropic statistics have relied on time-averaging structure functions in a few directions over many eddy-turnover times, using forcing schemes carefully constructed to generate isotropic data. Motivated by recent theoretical work, which removes isotropy requirements by spherically averaging the structure functions over all directions, we will present results which supplement long-time averaging by angle-averaging over up to 73 directions from a single flow snapshot. The directions are among those natural to a square computational grid, and are weighted to approximate the spherical average. We use this angle-averaging procedure to compare the statistically steady flows generated by two different forcing schemes in a periodic box. Our results show that despite the apparent differences in the two flows, their isotropic components, as measured by the Kolmogorov laws, are essentially identical. This procedure may be used to investigate the isotropic part of the small-scale statistics of any quantity of interest. The averaging process is inexpensive, and for the Kolmogorov 4/5 law, reasonable results can be obtained from a single snapshot of data. This implies consistency with the recently derived local versions of the Kolmogorov laws, which do not require long-time averages.}, }
@article {pmid14525035, year = {2003}, author = {Boghosian, BM and Love, PJ and Coveney, PV and Karlin, IV and Succi, S and Yepez, J}, title = {Galilean-invariant lattice-Boltzmann models with H theorem.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {68}, number = {2 Pt 2}, pages = {025103}, doi = {10.1103/PhysRevE.68.025103}, pmid = {14525035}, issn = {1539-3755}, abstract = {We demonstrate that the requirement of Galilean invariance determines the choice of H function for a wide class of entropic lattice-Boltzmann models for the incompressible Navier-Stokes equations. The required H function has the form of the Burg entropy for D=2, and of a Tsallis entropy with q=1-(2/D) for D>2, where D is the number of spatial dimensions. We use this observation to construct a fully explicit, unconditionally stable, Galilean-invariant, lattice-Boltzmann model for the incompressible Navier-Stokes equations, for which attainable Reynolds number is limited only by grid resolution.}, }
@article {pmid14525007, year = {2003}, author = {Cosentino Lagomarsino, M and Jona, P and Bassetti, B}, title = {Metachronal waves for deterministic switching two-state oscillators with hydrodynamic interaction.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {68}, number = {2 Pt 1}, pages = {021908}, doi = {10.1103/PhysRevE.68.021908}, pmid = {14525007}, issn = {1539-3755}, abstract = {We employ a model system, called rowers, as a generic physical framework to define the problem of the coordinated motion of cilia (the metachronal wave) as a far from equilibrium process. Rowers are active (two-state) oscillators in a low Reynolds number fluid, and interact solely through the forces of hydrodynamic origin. In this work, we consider the case of fully deterministic dynamics, find analytical solutions of the equation of motion in the long-wavelength (continuum) limit, and investigate numerically the short-wavelength limit. We prove the existence of metachronal waves below a characteristic wavelength. Such waves are unstable and become stable only if the sign of the coupling is reversed. We also find that with normal hydrodynamic interaction, the metachronal pattern has the form of stable trains of traveling wave packets sustained by the onset of anti-coordinated beating of consecutive rowers.}, }
@article {pmid14524891, year = {2003}, author = {Laval, JP and McWilliams, JC and Dubrulle, B}, title = {Forced stratified turbulence: successive transitions with Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {68}, number = {3 Pt 2}, pages = {036308}, doi = {10.1103/PhysRevE.68.036308}, pmid = {14524891}, issn = {1539-3755}, abstract = {Numerical simulations are made for forced turbulence at a sequence of increasing values of Reynolds number Re keeping fixed a strongly stable, volume-mean density stratification. At smaller values of Re, the turbulent velocity is mainly horizontal, and the momentum balance is approximately cyclostrophic and hydrostatic. This is a regime dominated by so-called pancake vortices, with only a weak excitation of internal gravity waves and large values of the local Richardson number Ri everywhere. At higher values of Re there are successive transitions to (a) overturning motions with local reversals in the density stratification and small or negative values of Ri; (b) growth of a horizontally uniform vertical shear flow component; and (c) growth of a large-scale vertical flow component. Throughout these transitions, pancake vortices continue to dominate the large-scale part of the turbulence, and the gravity wave component remains weak except at small scales.}, }
@article {pmid12968569, year = {2003}, author = {Varghese, SS and Frankel, SH}, title = {Numerical modeling of pulsatile turbulent flow in stenotic vessels.}, journal = {Journal of biomechanical engineering}, volume = {125}, number = {4}, pages = {445-460}, doi = {10.1115/1.1589774}, pmid = {12968569}, issn = {0148-0731}, mesh = {Animals ; Arterial Occlusive Diseases/*physiopathology ; Arteries/*physiopathology ; *Blood Flow Velocity ; Computer Simulation ; Constriction, Pathologic ; Hemorheology/*methods ; Humans ; *Models, Cardiovascular ; *Nonlinear Dynamics ; *Pulsatile Flow ; }, abstract = {Pulsatile turbulent flow in stenotic vessels has been numerically modeled using the Reynolds-averaged Navier-Stokes equation approach. The commercially available computational fluid dynamics code (CFD), FLUENT, has been used for these studies. Two different experiments were modeled involving pulsatile flow through axisymmetric stenoses. Four different turbulence models were employed to study their influence on the results. It was found that the low Reynolds number k-omega turbulence model was in much better agreement with previous experimental measurements than both the low and high Reynolds number versions of the RNG (renormalization-group theory) k-epsilon turbulence model and the standard k-epsilon model, with regard to predicting the mean flow distal to the stenosis including aspects of the vortex shedding process and the turbulent flow field. All models predicted a wall shear stress peak at the throat of the stenosis with minimum values observed distal to the stenosis where flow separation occurred.}, }
@article {pmid12968292, year = {2003}, author = {Ramirez, LE and Lim, EA and Coimbra, CF and Kobayashi, MH}, title = {On the dynamics of a spherical scaffold in rotating bioreactors.}, journal = {Biotechnology and bioengineering}, volume = {84}, number = {3}, pages = {382-389}, doi = {10.1002/bit.10778}, pmid = {12968292}, issn = {0006-3592}, mesh = {Acceleration ; *Bioreactors ; Cell Culture Techniques/methods ; *Cell Physiological Phenomena ; Cells, Cultured ; Computer Simulation ; Extracellular Matrix/*physiology ; Mechanotransduction, Cellular/*physiology ; Membranes, Artificial ; *Models, Biological ; Physical Stimulation/instrumentation/*methods ; Rheology/*methods ; *Rotation ; Shear Strength ; Stress, Mechanical ; }, abstract = {We analyze the dynamics of a spherical scaffold in rotating bioreactors (or clinostats). The idealized clinostat environment consists of a purely rotational flow that is perpendicular to a gravitational field. We confirm through a detailed analytical study that lift effects considerably alter the position of the equilibrium point reached by the scaffolds in the (vertical) direction collinear to the gravitational field. This result holds for small particle and shear Reynolds numbers. Our analysis shows that the inertial lift effect is negligible in the horizontal direction. We show that for all rotations of practical interest, and for the range of particle Reynolds number smaller than unity, the vertical coordinate of the equilibrium point is strongly affected by consideration of lift effects. For light (heavy) particles, inclusion of lift in the formation forces the equilibrium position to be below (above) the horizontal plane that contains the axis of rotation. The equilibrium point for light particles is stable and therefore is observable experimentally. The equilibrium point for heavy particles is unstable. We also estimate the stress level applied to the scaffold and derive an algebraic expression that indicates that the stress level acting on the scaffold decreases with increasing shear Reynolds number.}, }
@article {pmid12964754, year = {2003}, author = {Kohara, Y}, title = {Hybridization reaction kinetics of DNA probes on beads arrayed in a capillary enhanced by turbulent flow.}, journal = {Analytical chemistry}, volume = {75}, number = {13}, pages = {3079-3085}, doi = {10.1021/ac0341214}, pmid = {12964754}, issn = {0003-2700}, mesh = {Base Sequence ; DNA Probes/*chemistry/genetics ; Kinetics ; Microscopy, Fluorescence ; Microspheres ; Nucleic Acid Hybridization ; Oligonucleotide Array Sequence Analysis/instrumentation/*methods ; Rheology ; }, abstract = {The hybridization reaction kinetics of DNA probes on beads arrayed in a capillary was investigated experimentally and theoretically by using fluid mechanical methods. A device was prepared to contain DNA probes conjugated on 103-microm-diameter beads that were queued in a 150-microm-diameter capillary. The hybridization experiments were performed by introducing sample into the capillary and moving it with a one-way or a reciprocal flow. From the relation between Reynolds number and the resistance coefficient of the system, we found that the flow in the system was turbulent and not laminar as has been said of other microfluidic devices. The reaction efficiency was estimated using a mass-transfer coefficient derived from Chilton-Colburn's analogy. The estimate agreed well with the experimental data. A diffusion equation under laminar assumption was also solved, but this estimated value was 4.0-10.4 times smaller than the experimental data. Using the device achieved a hybridization efficiency as high as approximately 90% in 10 min. It was concluded that the high hybridization performance of the device resulted from turbulent flow and that the flow compensated the slow molecular diffusion. Using this bead-included structure resulted in a rapid and effective reaction at the solid-liquid interface, and the device seems very promising for many future applications.}, }
@article {pmid12953884, year = {2003}, author = {Lee, S and Liang, L and Riestenberg, D and West, OR and Tsouris, C and Adams, E}, title = {CO2 hydrate composite for ocean carbon sequestration.}, journal = {Environmental science &amp; technology}, volume = {37}, number = {16}, pages = {3701-3708}, doi = {10.1021/es026301l}, pmid = {12953884}, issn = {0013-936X}, mesh = {Carbon Dioxide/analysis/*chemistry ; Environmental Monitoring ; Greenhouse Effect ; *Models, Theoretical ; Seawater/*chemistry ; Solubility ; }, abstract = {Rapid CO2 hydrate formation was investigated with the objective of producing a negatively buoyant CO2-seawater mixture under high-pressure and low-temperature conditions, simulating direct CO2 injection at intermediate ocean depths of 1.0-1.3 km. A coflow reactor was developed to maximize CO2 hydrate production by injecting water droplets (e.g., approximately 267 microm average diameter) from a capillary tube into liquid CO2. The droplets were injected in the mixing zone of the reactor where CO2 hydrate formed at the surface of the water droplets. The water-encased hydrate particles aggregated in the liquid CO2, producing a paste-like composite containing CO2 hydrate, liquid CO2, and water phases. This composite was extruded into ambient water from the coflow reactor as a coherent cylindrical mass, approximately 6 mm in diameter, which broke into pieces 5-10 cm long. Both modeling and experiments demonstrated that conversion from liquid CO2 to CO2 hydrate increased with water flow rate, ambient pressure, and residence time and decreased with CO2 flow rate. Increased mixing intensity, as expressed by the Reynolds number, enhanced the mass transfer and increased the conversion of liquid CO2 into CO2 hydrate. Using a plume model, we show that hydrate composite particles (for a CO2 loading of 1000 kg/s and 0.25 hydrate conversion) will dissolve and sink through a total depth of 350 m. This suggests significantly better CO2 dispersal and potentially reduced environmental impacts than would be possible by simply discharging positively buoyant liquid CO2 droplets. Further studies are needed to address hydrate conversion efficiency, scale-up criteria, sequestration longevity, and impact on the ocean biota before in-situ production of sinking CO2 hydrate composite can be applied to oceanic CO2 storage and sequestration.}, }
@article {pmid12935251, year = {2003}, author = {Xiang, Y and Bau, HH}, title = {Complex magnetohydrodynamic low-Reynolds-number flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {68}, number = {1 Pt 2}, pages = {016312}, doi = {10.1103/PhysRevE.68.016312}, pmid = {12935251}, issn = {1539-3755}, abstract = {The interaction between electric currents and a magnetic field is used to produce body (Lorentz) forces in electrolyte solutions. By appropriate patterning of the electrodes, one can conveniently control the direction and magnitude of the electric currents and induce spatially and temporally complicated flow patterns. This capability is useful, not only for fundamental flow studies, but also for inducing fluid flow and stirring in minute devices in which the incorporation of moving components may be difficult. This paper focuses on a theoretical and experimental study of magnetohydrodynamic flows in a conduit with a rectangular cross section. The conduit is equipped with individually controlled electrodes uniformly spaced at a pitch L. The electrodes are aligned transversely to the conduit's axis. The entire device is subjected to a uniform magnetic field. The electrodes are divided into two groups A and C in such a way that there is an electrode of group C between any two electrodes of group A. We denote the various A and C electrodes with subscripts, i.e., A(i) and C(i), where i=0,+/-1,+/-2, .... When positive and negative potentials are, respectively, applied to the even and odd numbered A electrodes, opposing electric currents are induced on the right and left hand sides of each A electrode. These currents generate transverse forces that drive cellular convection in the conduit. We refer to the resulting flow pattern as A. When electrodes of group C are activated, a similar flow pattern results, albeit shifted in space. We refer to this flow pattern as C. By alternating periodically between patterns A and C, one induces Lagrangian chaos. Such chaotic advection may be beneficial for stirring fluids, particularly in microfluidic devices. Since the flow patterns A and C are shifted in space, they also provide a mechanism for Lagrangian drift that allows net migration of passive tracers along the conduit's length.}, }
@article {pmid12935247, year = {2003}, author = {Benzi, R and De Angelis, E and Govindarajan, R and Procaccia, I}, title = {Shell model for drag reduction with polymer additives in homogeneous turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {68}, number = {1 Pt 2}, pages = {016308}, doi = {10.1103/PhysRevE.68.016308}, pmid = {12935247}, issn = {1539-3755}, abstract = {Recent direct numerical simulations of the finite-extensibility nonlinear elastic dumbbell model with the Peterlin approximation of non-Newtonian hydrodynamics revealed that the phenomenon of drag reduction by polymer additives exists (albeit in reduced form) also in homogeneous turbulence. We use here a simple shell model for homogeneous viscoelastic flows, which recaptures the essential observations of the full simulations. The simplicity of the shell model allows us to offer a transparent explanation of the main observations. It is shown that the mechanism for drag reduction operates mainly on large scales. Understanding the mechanism allows us to predict how the amount of drag reduction depends on the various parameters in the model. The main conclusion is that drag reduction is not a universal phenomenon; it peaks in a window of parameters such as the Reynolds number and the relaxation rate of the polymer.}, }
@article {pmid12935145, year = {2003}, author = {Kuksenok, O and Balazs, AC}, title = {Simulating the dynamic behavior of immiscible binary fluids in three-dimensional chemically patterned microchannels.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {68}, number = {1 Pt 1}, pages = {011502}, doi = {10.1103/PhysRevE.68.011502}, pmid = {12935145}, issn = {1539-3755}, abstract = {Using computer simulations, we investigate the behavior of an immiscible binary AB fluid that is driven to flow through a microchannel, which is decorated with a checkerboard pattern of chemically distinct A- and B-like patches on the top and bottom walls. We isolate conditions where the coupling between the imposed flow field and thermodynamic interactions yields a rich interfacial behavior between the A and B fluids and complex velocity patterns over the checkerboard domains. In effect, the A and B fluids undergo extensive mixing in specific regions of the channel, even for low Reynolds number flow. Decreasing the height-to-width ratio of the patterned microchannel enhances the extent of mixing between these two components. On the other hand, the length of the A/B interfaces is optimized in microchannels that have a square cross section. The results provide guidelines for designing microfluidic devices that can be used to effectively intermix multicomponent fluids.}, }
@article {pmid12929240, year = {2003}, author = {Kalse, SG and Bijl, H and van Oudheusden, BW}, title = {A one-dimensional viscous-inviscid strong interaction model for flow in indented channels with separation and reattachment.}, journal = {Journal of biomechanical engineering}, volume = {125}, number = {3}, pages = {355-362}, doi = {10.1115/1.1580524}, pmid = {12929240}, issn = {0148-0731}, mesh = {Blood Flow Velocity/*physiology ; *Blood Physiological Phenomena ; Computer Simulation ; Hemorheology/*methods ; *Models, Cardiovascular ; *Nonlinear Dynamics ; Viscosity ; }, abstract = {A new one-dimensional model is presented for the calculation of steady and unsteady flow through an indented two-dimensional channel with separation and reattachment. It is based on an interactive boundary layer approach, where the equations for the boundary layer flow near the channel walls and for an inviscid core flow are solved simultaneously. This approach requires no semi-empirical inputs, such as the location of separation and reattachment, which is an advantage over other existing one-dimensional models. Because of the need of an inviscid core alongside the boundary layers, the type of inflow as well as the length of the channel and the value of the Reynolds number poses some limitations on the use of the new model. Results have been obtained for steady flow through the indented channel of Ikeda and Matsuzaki. In further perspective, it is discussed how the present model, in contrast to other one-dimensional flow models, can be extended to calculate the flow in nonsymmetrical channels, by considering different boundary layers on each of the walls.}, }
@article {pmid12909040, year = {2003}, author = {Chung, HY and Ju, SP and Lee, DJ}, title = {Hydrodynamic drag force exerted on activated sludge floc at intermediate Reynolds number.}, journal = {Journal of colloid and interface science}, volume = {263}, number = {2}, pages = {498-505}, doi = {10.1016/s0021-9797(03)00404-1}, pmid = {12909040}, issn = {0021-9797}, abstract = {We hung the activated sludge flocs on an elastic nylon stick and then subjected it to a uniform water flow and measured its displacement. The hydrodynamic drag force exerted on the floc was subsequently estimated, both for cationic flocculated flocs and for flocculated and then frozen/thawed flocs. A confocal laser scanning microscope (CLSM) was employed to probe the interior structure of flocs. Polyelectrolyte flocculation leads to a compact global structure, and hence high drag force exerted on the floc by water. The corresponding C(D)Omega value at Re=12-27 for flocs ranges from 1.58 to 3.61. Fast freezing would little affect the hydrodynamic drag force. Slow freezing, in contrast, considerably consolidated the floc structure and hence presented impermeable sphere-like behavior of the slowly frozen/thawed flocs.}, }
@article {pmid12885538, year = {2003}, author = {Fujimatsu, T and Fujita, H and Hirota, M and Okada, O}, title = {Interfacial deformation between an impacting water drop and a silicone-oil surface.}, journal = {Journal of colloid and interface science}, volume = {264}, number = {1}, pages = {212-220}, doi = {10.1016/s0021-9797(03)00402-8}, pmid = {12885538}, issn = {0021-9797}, abstract = {Detailed observations have been conducted on the interfacial deformation of a silicone oil surface and a water drop falling on it. Eleven kinds of silicone oils with wide variations of kinematic viscosity, nu(T)=1-10(5) mm(2)/s, have been tested. The oil surface is disturbed by a water drop with a diameter d(L)=3.1 mm, which falls freely on it from a height of 100-1000 mm. Special attention has been directed to the maximum depth of the cavity formed on the oil surface D(M) and to the maximum diameter of the water drop spreading on the oil surface d(M). We have categorized the configurations of the oil cavity into seven patterns, and those of the water drop at the oil-water interface into five patterns. The maximum cavity depth D(M)/d(L) can be well correlated by a dimensionless group Re(TL)We(TL), where Re(TL) is Reynolds number based on d(L) and nu(T) and We(TL) is Weber number with the water density and surface tension of oil. The maximum diameter of the impacting water drop d(M)/d(L) can be correlated by the Reynolds number with a viscosity of water (Re(L)) and the Ohnesorge number (Oh). Moreover, the condition under which the impacting water drop is smashed into pieces has been also examined based on Re(L) and Oh.}, }
@article {pmid12877610, year = {2003}, author = {Greil, O and Pflugbeil, G and Weigand, K and Weiss, W and Liepsch, D and Maurer, PC and Berger, H}, title = {Changes in carotid artery flow velocities after stent implantation: a fluid dynamics study with laser Doppler anemometry.}, journal = {Journal of endovascular therapy : an official journal of the International Society of Endovascular Specialists}, volume = {10}, number = {2}, pages = {275-284}, doi = {10.1177/152660280301000217}, pmid = {12877610}, issn = {1526-6028}, mesh = {Blood Flow Velocity/*physiology ; Blood Vessel Prosthesis Implantation ; Carotid Artery, External/*physiology/surgery ; Carotid Artery, Internal/*physiology/surgery ; Humans ; *Laser-Doppler Flowmetry ; Models, Cardiovascular ; Pulsatile Flow/*physiology ; *Stents ; }, abstract = {PURPOSE: To study the influence of stent size and location on flow patterns in a physiological carotid model.<br><br>METHODS: Wallstents were positioned in silicon models of the carotid artery at various locations: 2 stents appropriately sized to the anatomy were placed in (1) the internal carotid artery (ICA) and (2) the ICA extending completely into the common carotid artery so as to cover the external carotid artery (ECA) orifice. Another 2 stents were placed in the ICA extending (1) partially and (2) completely into the bulb to simulate stent displacement and disproportion between stent size and the original vessel geometry. Measurements were performed with laser Doppler anemometry (LDA) using pulsatile flow conditions (Reynolds number=250; flow 0.431 L/min; ICA:ECA flow rate ratio 70:30) in hemodynamically relevant cross sections. The hemodynamic changes were analyzed with 1-dimensional flow profiles.<br><br>RESULTS: With the stent in the ICA, no changes of the normal flow profile were seen. For stents positioned in the ICA and extending partially or completely into the carotid bulb, the flow behavior was affected by the resistance of the stent to flow in the ECA. Hemodynamically relevant disturbances were seen in the ICA and ECA, especially in the separation zones (regions along the walls just after a bifurcation, bend, or curve). The ICA:ECA flow rate ratios shifted from 70:30 to 71.3:28.7 and from 70:30 to 75.1:24.9, respectively, in the 2 malpositioned stent models. With the stent placed in the ICA extending completely into the CCA, the ICA:ECA flow rate ratio shifted from 70:30 to 72.4:27.6. In this configuration, there were no notable flow changes in the ICA, but a clear diminishing of the separation zones in the ECA separation zones.<br><br>CONCLUSIONS: Anatomically correct positioning of appropriately sized stents does not lead to relevant flow disturbances in the ICA. In the ECA, depending on the position, size, and interstices of the stent, the physiological flow was considerably disturbed when any part of the stent covered the inflow of the vessel. Disturbances were seen when the stent was positioned into the bulb. For clinical application, stent location and size must be carefully determined so that the stent covers the bifurcation completely or is in the ICA only.}, }
@article {pmid12861614, year = {2003}, author = {Lin, JZ and Zhang, LX}, title = {On the structural features of fiber suspensions in converging channel flow.}, journal = {Journal of Zhejiang University. Science}, volume = {4}, number = {4}, pages = {400-406}, doi = {10.1631/jzus.2003.0400}, pmid = {12861614}, issn = {1009-3095}, mesh = {Computer Simulation ; Elasticity ; *Manufactured Materials ; Microfluidics/*methods ; *Models, Chemical ; Motion ; Particle Size ; Shear Strength ; Suspensions/chemical synthesis/*chemistry ; *Textiles ; Viscosity ; }, abstract = {The structural features of fiber suspensions are dependent on the fiber alignment in the flows. In this work the orientation distribution function and orientation tensors for semi-concentrated fiber suspensions in converging channel flow were calculated, and the evolutions of the fiber alignment and the bulk effective viscosity were analyzed. The results showed that the bulk stress and the effective viscosity were functions of the rate-of-strain tensor and the fiber orientation state; and that the fiber suspensions evolved to steady alignment and tended to concentrate to some preferred directions close to but not same as the directions of local streamlines. The bulk effective viscosity depended on the product of Reynolds number and time. The decrease of effective viscosity near the boundary benefited the increase of the rate of flow. Finally when the fiber alignment went into steady state, the structural features of fiber suspensions were not dependent on the Reynolds number but on the converging channel angle.}, }
@article {pmid12827700, year = {2003}, author = {Wu, JY and Chen, KC and Chen, CT and Hwang, SC}, title = {Hydrodynamic characteristics of immobilized cell beads in a liquid-solid fluidized-bed bioreactor.}, journal = {Biotechnology and bioengineering}, volume = {83}, number = {5}, pages = {583-594}, doi = {10.1002/bit.10710}, pmid = {12827700}, issn = {0006-3592}, mesh = {Acinetobacter baumannii/physiology/ultrastructure ; Aeromonas hydrophila/physiology/ultrastructure ; Bacterial Adhesion/*physiology ; Bioreactors/*microbiology ; Cell Culture Techniques/*methods ; Cell Movement/physiology ; Cells, Immobilized/physiology ; Comamonas testosteroni/physiology/ultrastructure ; Computer Simulation ; Gram-Negative Bacteria/*physiology/*ultrastructure ; Microfluidics/*methods ; Microspheres ; *Models, Biological ; *Polyvinyl Alcohol ; Species Specificity ; }, abstract = {This study examined the hydrodynamic characteristics of a liquid-solid fluidized-bed bioreactor using elastic particles (PVA gel beads) of various diameters as carriers. The drag coefficient-Reynolds number, velocity-voidage, and expansion index-Reynolds number relationships observed during fluidization of PVA gel beads in a fluidized bed in our experiments were compared with the published results. Predictions made from previous correlations were examined with our new experimental findings, revealing the inadequacy of most of these correlations. Thus, new correlations describing the above-mentioned relationships are suggested. The drag coefficient of immobilized cell beads is larger than that of free cell ones at the same Reynolds number because the surface of the immobilized cell beads is rougher. For multiparticle systems, the correction factor, f(epsilon), is a function of the falling gel bead properties (Reynolds number) as well as the fluidized gel bead properties (Archimedes number), and depend strongly on the bed voidage (epsilon). A new simple relation was developed to predict easily the epsilon value from 0.5-0.9 at 4,986 < A(r) < 40,745 or 34 < Re(t) < 186. For all the immobilized cell beads used in this study, the prediction error of the bed voidage was less than 5% at epsilon > 0.5. The prediction equations in this study can be further applied to analyzing the hydrodynamic characteristics of a fluidized-bed reactor using similar entrapped elastic particles as carriers.}, }
@article {pmid12822781, year = {2003}, author = {Karthik, B and Chakravarthy, SR and Sujith, RI}, title = {Jet forking driven by pipe tone.}, journal = {The Journal of the Acoustical Society of America}, volume = {113}, number = {6}, pages = {3091-3094}, doi = {10.1121/1.1573636}, pmid = {12822781}, issn = {0001-4966}, abstract = {The present work deals with an experimental investigation of flow of air through a square-edged circular orifice at the downstream end of a circular duct. Self-excited acoustic oscillations at the natural duct modes are observed for certain flow velocities when the orifice is sufficiently thick. For a specific Reynolds number based on the orifice diameter and the mean jet velocity (9150 < Re < 9850), the jet forks into two trains, with the alternating vortices falling into the same branch of the forked train. Whereas this phenomenon has been reported earlier to have occurred when the density ratio of the jet is less than 0.72, the present results show that it is possible for a jet having the same density as the ambient atmosphere. The jet forking is coincident with jump in the acoustic frequency from one natural acoustic mode to another with comparable amplitudes of both the modes.}, }
@article {pmid12804889, year = {2003}, author = {Allison, S and Wall, S and Rasmusson, M}, title = {A general gel layer model for the transport of colloids and macroions in dilute solution.}, journal = {Journal of colloid and interface science}, volume = {263}, number = {1}, pages = {84-98}, doi = {10.1016/s0021-9797(03)00188-7}, pmid = {12804889}, issn = {0021-9797}, abstract = {A general boundary element methodology for studying the dilute solution transport of rigid macroions that contain gel layers on their outer surfaces is developed and applied to several model systems. The methodology can be applied to particles of arbitrary size, shape, charge distribution, and gel layer geometry. Account is also taken of the steady state distortion of the ion atmosphere from equilibrium, which makes it applicable to the transport of highly charged structures. The coupled field equations (Poisson, ion-transport, low-Reynolds-number Navier-Stokes, and Brinkman) are solved numerically and from this, transport properties (diffusion constants, electrophoretic mobilities, excess viscosities) can be computed. In the present work, the methodology is first applied to a gel sphere model over a wide range of particle charge and the resulting transport properties are found to be in excellent agreement with independent theory under those conditions where independent theory is available. It is then applied to several prolate spheroidal models of a particular silica sol sample in an attempt to identify possible solution structures. A single model, that is able to account simultaneously for all of the transport behavior, which does not undergo significant conformational change with salt concentration, could not be found. A model with a thin (</=1-nm) gel layer at high salt content that expands on going to low salt content is able to explain the salt dependence of the intrinsic viscosity, but not the electrophoretic mobility. However, a model with a fairly thick (2-nm) gel layer at high salt content, which expands slightly (2.5-nm) at low salt content, is in fairly good agreement with experiment. In addition, the influence of particle charge and the presence of a gel layer on the Scheraga-Mandelkern parameter are examined. This parameter is proportional to the product of the translational diffusion constant and the cube root of the intrinsic viscosity. It is found to be very robust with regard to net particle charge as well as properties of the gel layer.}, }
@article {pmid12804218, year = {2003}, author = {Li, X and Pozrikidis, C}, title = {Film flow of a suspension down an inclined plane.}, journal = {Philosophical transactions. Series A, Mathematical, physical, and engineering sciences}, volume = {361}, number = {1806}, pages = {847-869}, doi = {10.1098/rsta.2003.1171}, pmid = {12804218}, issn = {1364-503X}, mesh = {*Computer Simulation ; Gravitation ; *Microspheres ; *Models, Theoretical ; Motion ; Particle Size ; Rheology/*methods ; Shear Strength ; Stress, Mechanical ; *Suspensions ; Torque ; Viscosity ; }, abstract = {A method is developed for simulating the film flow of a suspension of rigid particles with arbitrary shapes down an inclined plane in the limit of vanishing Reynolds number. The problem is formulated in terms of a system of integral equations of the first and second kind for the free-surface velocity and the traction distribution along the particle surfaces involving the a priori unknown particle linear velocity of translation and angular velocity of rotation about designated centres. The problem statement is completed by introducing scalar constraints that specify the force and torque exerted on the individual particles. A boundary-element method is implemented for solving the governing equations for the case of a two-dimensional periodic suspension. The system of linear equations arising from numerical discretization is solved using a preconditioner based on a particle-cluster iterative method recently developed by Pozrikidis (2000 Engng Analysis Bound. Elem. 25, 19-30). Numerical investigations show that the generalized minimal residual (GMRES) method with this preconditioner is significantly more efficient than the plain GMRES method used routinely in boundary-element implementations. Extensive numerical simulations for solitary particles and random suspensions illustrate the effect of the particle shape, size and aspect ratio in semi-finite shear flow, and the effect of free-surface deformability in film flow.}, }
@article {pmid12786492, year = {2003}, author = {Rüdiger, G and Schultz, M and Shalybkov, D}, title = {Linear magnetohydrodynamic Taylor-Couette instability for liquid sodium.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {67}, number = {4 Pt 2}, pages = {046312}, doi = {10.1103/PhysRevE.67.046312}, pmid = {12786492}, issn = {1539-3755}, abstract = {The linear stability of MHD Taylor-Couette flow of infinite vertical extension is considered for liquid sodium with its small magnetic Prandtl number Pm of order 10(-5). The calculations are performed for a container with R(out)=2R(in), with an axial uniform magnetic field and with boundary conditions for both vacuum and perfect conductions. For resting outer cylinder subcritical excitation in comparison to the hydrodynamical case occurs for large Pm but it disappears for small Pm. For rotating outer cylinder the Rayleigh line plays an exceptional role. The hydromagnetic instability exists with Reynolds numbers exactly scaling with Pm(-1/2) so that the moderate values of order 10(4) (for Pm=10(-5)) result. For the smallest step beyond the Rayleigh line, however, the Reynolds numbers scale as 1/Pm leading to much higher values of order 10(6). Then it is the magnetic Reynolds number Rm that directs the excitation of the instability. It results as lower for insulating than for conducting walls. The magnetic Reynolds number has to exceed here values of order 10 leading to frequencies of about 20 Hz for the rotation of the inner cylinder if containers with (say) 10 cm radius are considered. With vacuum boundary conditions the excitation of nonaxisymmetric modes is always more difficult than the excitation of axisymmetric modes. For conducting walls, however, crossovers of the lines of marginal stability exist for both resting and rotating outer cylinders, and this might be essential for future dynamo experiments. In this case the instability also can onset as an overstability.}, }
@article {pmid12786270, year = {2003}, author = {Zhou, Y and Robey, HF and Buckingham, AC}, title = {Onset of turbulence in accelerated high-Reynolds-number flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {67}, number = {5 Pt 2}, pages = {056305}, doi = {10.1103/PhysRevE.67.056305}, pmid = {12786270}, issn = {1539-3755}, abstract = {A new criterion, flow drive time, is identified here as a necessary condition for transition to turbulence in accelerated, unsteady flows. Compressible, high-Reynolds-number flows initiated, for example, in shock tubes, supersonic wind tunnels with practical limitations on dimensions or reservoir capacity, and high energy density pulsed laser target vaporization experimental facilities may not provide flow duration adequate for turbulence development. In addition, for critical periods of the overall flow development, the driving background flow is often unsteady in the experiments as well as in the physical flow situations they are designed to mimic. In these situations transition to fully developed turbulence may not be realized despite achievement of flow Reynolds numbers associated with or exceeding stationary flow transitional criteria. Basically our transitional criterion and prediction procedure extends to accelerated, unsteady background flow situations the remarkably universal mixing transition criterion proposed by Dimotakis [P. E. Dimotakis, J. Fluid Mech. 409, 69 (2000)] for stationary flows. This provides a basis for the requisite space and time scaling. The emphasis here is placed on variable density flow instabilities initiated by constant acceleration Rayleigh-Taylor instability (RTI) or impulsive (shock) acceleration Richtmyer-Meshkov instability (RMI) or combinations of both. The significant influences of compressibility on these developing transitional flows are discussed with their implications on the procedural model development. A fresh perspective for predictive modeling and design of experiments for the instability growth and turbulent mixing transitional interval is provided using an analogy between the well-established buoyancy-drag model with applications of a hierarchy of single point turbulent transport closure models. Experimental comparisons with the procedural results are presented where use is made of three distinctly different types of acceleration driven instability experiments: (1) classical, relatively low speed, constant acceleration RTI experiments; (2) shock tube, shockwave driven RMI flow mixing experiments; (3) laser target vaporization RTI and RMI mixing experiments driven at very high energy density. These last named experiments are of special interest as they provide scaleable flow conditions simulating those of astrophysical magnitude such as shock-driven hydrodynamic mixing in supernova evolution research.}, }
@article {pmid12786075, year = {2003}, author = {Pétrélis, F and Bourgoin, M and Marié, L and Burguete, J and Chiffaudel, A and Daviaud, F and Fauve, S and Odier, P and Pinton, JF}, title = {Nonlinear magnetic induction by helical motion in a liquid sodium turbulent flow.}, journal = {Physical review letters}, volume = {90}, number = {17}, pages = {174501}, doi = {10.1103/PhysRevLett.90.174501}, pmid = {12786075}, issn = {0031-9007}, abstract = {We report an experimental study of the magnetic field B--> induced by a turbulent swirling flow of liquid sodium submitted to a transverse magnetic field B-->(0). We show that the induced field can behave nonlinearly as a function of the magnetic Reynolds number, R(m). At low R(m), the induced mean field along the axis of the flow, <Bx>, and the one parallel to B-->(0), <B(y)>, first behave like R(2)(m), whereas the third component, <B(z)>, is linear in R(m). The sign of <Bx> is determined by the flow helicity. At higher R(m), B--> strongly depends on the local geometry of the mean flow: <Bx> decreases to zero in the core of the swirling flow but remains finite outside. We compare the experimental results with the computed magnetic induction due to the mean flow alone.}, }
@article {pmid12779521, year = {2001}, author = {Finn, JM and Del-Castillo-Negrete, D}, title = {Lagrangian chaos and Eulerian chaos in shear flow dynamics.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {11}, number = {4}, pages = {816-832}, doi = {10.1063/1.1418762}, pmid = {12779521}, issn = {1089-7682}, abstract = {Shear flow dynamics described by the two-dimensional incompressible Navier-Stokes equations is studied for a one-dimensional equilibrium vorticity profile having two minima. These lead to two linear Kelvin-Helmholtz instabilities; the resulting nonlinear waves corresponding to the two minima have different phase velocities. The nonlinear behavior is studied as a function of two parameters, the Reynolds number and a parameter lambda specifying the width of the minima in the vorticity profile. For parameters such that the instabilities grow to a sufficient level, there is Lagrangian chaos, leading to mixing of vorticity, i.e., momentum transport, between the chains of vortices or cat's eyes. Lagrangian chaos is quantified by plotting the finite time Lyapunov exponents on a grid of initial points, and by the probability distribution of these exponents. For moderate values of lambda, there is Lagrangian chaos everywhere except near the centers of the vortices and near the boundaries, and there are competing effects of homogenization of vorticity and formation of structures associated with secondary resonances. For smaller values of lambda Lagrangian chaos occurs in the regions in the centers of the vortices, and the Eulerian behavior of the flow undergoes bifurcations leading to Eulerian chaos, as measured by the time series of several Galilean invariant quantities. A discussion of Lagrangian chaos and its relation to Eulerian chaos is given.(c) 2001 American Institute of Physics.}, }
@article {pmid12775911, year = {2003}, author = {Banerjee, RK and Back, LH and Back, MR and Cho, YI}, title = {Physiological flow analysis in significant human coronary artery stenoses.}, journal = {Biorheology}, volume = {40}, number = {4}, pages = {451-476}, pmid = {12775911}, issn = {0006-355X}, mesh = {Blood Flow Velocity ; Blood Pressure ; Coronary Stenosis/pathology/*physiopathology ; Hemodynamics ; *Hemorheology ; Humans ; Models, Cardiovascular ; Pulsatile Flow ; Stress, Mechanical ; }, abstract = {To evaluate the local hemodynamics in flow limiting coronary lesions, computational hemodynamics was applied to a group of patients previously reported by Wilson et al. (1988) with representative pre-angioplasty stenosis geometry (minimal lesion size d(m)=0.95 mm; 68% mean diameter stenosis) and with measured values of coronary flow reserve (CFR) in the abnormal range (2.3+/-0.1). The computations were at mean flow rates (Q) of 50, 75 and 100 ml/min (the limit of our converged calculations). Computed mean pressure drops Deltap were approximately 9 mmHg for basal flow (50 ml/min), approximately 27 mmHg for elevated flow (100 ml/min) and increased to an extrapolated value of approximately 34 mmHg for hyperemic flow (115 ml/min), which led to a distal mean coronary pressure p(rh) of approximately 55 mmHg, a level known to cause ischemia in the subendocardium (Brown et al., 1984), and consistent with the occurrence of angina in the patients. Relatively high levels of wall shear stress were computed in the narrow throat region and ranged from about 600 to 1500 dyn/cm(2), with periodic (phase shifted) peak systolic values of about 3500 dyn/cm(2). In the distal vessel, the interaction between the separated shear layer wave, convected downstream by the core flow, and the wall shear layer flow, led to the formation of vortical flow cells along the distal vessel wall during the systolic phase where Reynolds numbers Re(e)(t) were higher. During the phasic vortical mode observed at both basal and elevated mean flow rates, wide variations in distal wall shear stress occurred, distal transmural pressures were depressed below throat levels, and pressure recovery was larger farther along the distal vessel. Along the constriction (convergent) and throat segments of the lesion the pulsatile flow field was principally quasi-steady before flow separation occurred. The flow regimes were complex in the narrow mean flow Reynolds number range Re(e)=100-230 and a frequency parameter of alphae=2.25. The shear layer flow disturbances diminished in strength due to viscous damping along the distal vessel at these relatively low values of Re(e), typical of flow through diseased epicardial coronary vessels. The distal hyperemic flow field was likely to be in an early stage of turbulent flow development during the peak systolic phase.}, }
@article {pmid12757804, year = {2003}, author = {Liu, Y and So, RM and Zhang, CH}, title = {Modeling the bifurcating flow in an asymmetric human lung airway.}, journal = {Journal of biomechanics}, volume = {36}, number = {7}, pages = {951-959}, doi = {10.1016/s0021-9290(03)00064-2}, pmid = {12757804}, issn = {0021-9290}, mesh = {Bronchi/*anatomy &amp; histology/*physiology ; Computer Simulation ; Humans ; Lung/anatomy &amp; histology/physiology ; *Models, Biological ; Motion ; Pressure ; Pulmonary Ventilation/*physiology ; Reproducibility of Results ; Respiration ; Respiratory Mechanics/*physiology ; Rheology/*methods ; Sensitivity and Specificity ; }, abstract = {In a former paper, the inspiratory flow characteristics in a three-generation symmetric bifurcation airway have been numerically investigated using a control volume method to solve the fully three-dimensional laminar Navier-Stokes equations. The present paper extends the work to deal with asymmetric airway extracted from the 5th-11th branches of the model of Weibel (Morphometry of the Human Lung. New York Academic Press, Verlag, 1963) in order to more appropriately model human air passage. Computations are carried out in the Reynolds number range 200-1600, corresponding to mouth-air breathing rates ranging from 0.27 to 2.16l/s, representative for an averaged height man breathing from quiet to vigorous state. Particular attentions are paid to establishing relations between the Reynolds number and the overall flow characteristics, including flow patterns and pressure drop. The study shows that the ratios of airflow rate through the medial branches to that of their mother branches are the same, and this is also true for the ratios of airflow rate through the lateral branches. This partially explains why regular human breathing is not affected by airways of different sizes.}, }
@article {pmid12751282, year = {2003}, author = {Finol, EA and Keyhani, K and Amon, CH}, title = {The effect of asymmetry in abdominal aortic aneurysms under physiologically realistic pulsatile flow conditions.}, journal = {Journal of biomechanical engineering}, volume = {125}, number = {2}, pages = {207-217}, doi = {10.1115/1.1543991}, pmid = {12751282}, issn = {0148-0731}, mesh = {Anisotropy ; Aorta, Abdominal/anatomy &amp; histology/physiopathology ; Aortic Aneurysm, Abdominal/*physiopathology ; Blood Flow Velocity ; Blood Pressure ; Computer Simulation ; Elasticity ; Finite Element Analysis ; Hemorheology/methods ; Humans ; *Models, Cardiovascular ; Pulsatile Flow ; Shear Strength ; Stress, Mechanical ; }, abstract = {In the abdominal segment of the human aorta under a patient's average resting conditions, pulsatile blood flow exhibits complex laminar patterns with secondary flows induced by adjacent branches and irregular vessel geometries. The flow dynamics becomes more complex when there is a pathological condition that causes changes in the normal structural composition of the vessel wall, for example, in the presence of an aneurysm. This work examines the hemodynamics of pulsatile blood flow in hypothetical three-dimensional models of abdominal aortic aneurysms (AAAs). Numerical predictions of blood flow patterns and hemodynamic stresses in AAAs are performed in single-aneurysm, asymmetric, rigid wall models using the finite element method. We characterize pulsatile flow dynamics in AAAs for average resting conditions by means of identifying regions of disturbed flow and quantifying the disturbance by evaluating flow-induced stresses at the aneurysm wall, specifically wall pressure and wall shear stress. Physiologically realistic abdominal aortic blood flow is simulated under pulsatile conditions for the range of time-average Reynolds numbers 50 < or = Rem < or = 300, corresponding to a range of peak Reynolds numbers 262.5 < or = Repeak < or = 1575. The vortex dynamics induced by pulsatile flow in AAAs is depicted by a sequence of four different flow phases in one period of the cardiac pulse. Peak wall shear stress and peak wall pressure are reported as a function of the time-average Reynolds number and aneurysm asymmetry. The effect of asymmetry in hypothetically shaped AAAs is to increase the maximum wall shear stress at peak flow and to induce the appearance of secondary flows in late diastole.}, }
@article {pmid12751280, year = {2003}, author = {Lutostansky, EM and Karner, G and Rappitsch, G and Ku, DN and Perktold, K}, title = {Analysis of hemodynamic fluid phase mass transport in a separated flow region.}, journal = {Journal of biomechanical engineering}, volume = {125}, number = {2}, pages = {189-196}, doi = {10.1115/1.1543547}, pmid = {12751280}, issn = {0148-0731}, support = {R01 HL39437-07/HL/NHLBI NIH HHS/United States ; }, mesh = {Adenosine Diphosphate/*pharmacokinetics ; Adsorption ; Arteries/metabolism/*physiology ; Biological Transport, Active/physiology ; Blood Flow Velocity ; Blood Pressure ; Endothelium, Vascular/metabolism ; Hemorheology/*methods ; Humans ; *Models, Cardiovascular ; Sensitivity and Specificity ; }, abstract = {The mass transfer behavior in the recirculation region downstream of an axisymmetric sudden expansion was examined. The Reynolds number, 500, and Schmidt number, 3200, were selected to model the mass transfer of molecules, such as ADP, in the arterial system. In a first step the transient mass transport applying zero diffusive flux at the wall was analyzed using experiments and two computational codes. The two codes were FLUENT, a commercially available finite volume method, and FTSP, a finite element code developed at Graz University of Technology. The comparison of the transient wall concentration values determined by the three methods was excellent and provides a measure of confidence for computational mass transfer calculations in convection dominated, separated flows. In a second step the effect of the flow separation on the stationary mass transport applying a permeability boundary condition at the water-permeable wall was analyzed using the finite element code FTSP. The results show an increase of luminal ADP surface concentration in the upstream and in the downstream tube of the sudden expansion geometry in the range of six and twelve percent of the bulk flow concentration. The effect of flow separation in the downstream tube on the wall concentration is a decrease of about ten percent of the difference between wall concentration and bulk concentration occurring at nearly fully developed flow at the downstream region at a distance of 66 downstream tube diameters from the expansion. The decrease of ADP flux into the wall is in the range of three percent of the flux at the downstream region.}, }
@article {pmid12744156, year = {2003}, author = {Liu, X and Wang, X and Huang, H and Chen, H}, title = {[A biomechanical model for simulating the deformation of a leukocyte adhered to the surface of a blood vessel under steady shear flow].}, journal = {Sheng wu yi xue gong cheng xue za zhi = Journal of biomedical engineering = Shengwu yixue gongchengxue zazhi}, volume = {20}, number = {1}, pages = {30-34}, pmid = {12744156}, issn = {1001-5515}, mesh = {Biomechanical Phenomena ; Blood Vessels/*cytology/physiology ; Cell Adhesion/physiology ; Cell Nucleus/physiology ; Leukocytes/*physiology ; *Models, Cardiovascular ; Numerical Analysis, Computer-Assisted ; }, abstract = {The adhesion of leukocytes to substrate is an important biomedical engineering problem and has drawn extensive research. In this study, we have proposed a compound drop model to simulate a leukocyte with a nucleus adhered to the surface of a blood vessel under steady shear flow. A two-dimensional computational fluid dynamics (CFD) is conducted to determine the local distribution of pressure on the surface of the adherent model cell. By introducing the parameter of deformation index (DI), we have investigated the deformation of the model cell and it's nucleus under controlled conditions. Our numerical results show that: (1) the model cell is capable of deformation with the increase of initial contact angle, capillary number, and Reynolds number, and that the cytoplasm is more deformable while the nucleus is more capable of resisting external imposed shear flow; (2) the model cell is not able to deform infinitely with the increase of external shear flow because the deformation index reaches a maximum; (3) pressure distribution confirms that there exists a region downstream of the cell, which produces high pressure to retard continuous deformation and provide a positive lift force on the cell. Our results of nucleus deformation may help to develop a better understanding of how leukocytes transduce external mechanical signal like shear stress into nucleus.}, }
@article {pmid12731949, year = {2003}, author = {Mauroy, B and Filoche, M and Andrade, JS and Sapoval, B}, title = {Interplay between geometry and flow distribution in an airway tree.}, journal = {Physical review letters}, volume = {90}, number = {14}, pages = {148101}, doi = {10.1103/PhysRevLett.90.148101}, pmid = {12731949}, issn = {0031-9007}, mesh = {Animals ; Bronchi/*anatomy &amp; histology/*physiology ; Humans ; Lung/anatomy &amp; histology/physiology ; *Models, Anatomic ; *Models, Biological ; Respiratory Mechanics ; }, abstract = {Uniform flow distribution in a symmetric volume can be realized through a symmetric branched tree. It is shown here, however, by 3D numerical simulation of the Navier-Stokes equations, that the flow partitioning can be highly sensitive to deviations from exact symmetry if inertial effects are present. The flow asymmetry is quantified and found to depend on the Reynolds number. Moreover, for a given Reynolds number, we show that the flow distribution depends on the aspect ratio of the branching elements as well as their angular arrangement. Our results indicate that physiological variability should be severely restricted in order to ensure adequate fluid distribution through a tree.}, }
@article {pmid12711175, year = {2003}, author = {Kim, JW and Ulrich, J}, title = {Prediction of degree of deformation and crystallization time of molten droplets in pastillation process.}, journal = {International journal of pharmaceutics}, volume = {257}, number = {1-2}, pages = {205-215}, doi = {10.1016/s0378-5173(03)00141-8}, pmid = {12711175}, issn = {0378-5173}, mesh = {*Chemistry, Pharmaceutical ; *Crystallization ; Particle Size ; Time Factors ; Viscosity ; }, abstract = {The direct solidification process of a melt into a particulate solid is studied to achieve the desired size and shape of the product and to predict the required crystallization time. For an example, a Bisacodyl melt is chosen. The role of the contact angle of the droplet is investigated as a function of Reynolds number, degree of subcooling and characteristic of used cooled surface (substrate). The static contact angle increases with increasing degree of surface roughness of the substrate. The contact angle, however, decreases with increasing Reynolds number and degree of subcooling. The phenomena of spreading and rebouncing of droplets are used in the discussion of the deformation process. By the model of Madejski the degree of deformation is found to be proportional to the Reynolds number to the power of 0.2. On the basis of a simple droplet solidification model and experimental data, a numerical study is presented. The equations allow to estimate the normalized deformation and crystallization times, which are proportional to the Reynolds number to the power of 1.23 and help the design of solidification processes.}, }
@article {pmid12689111, year = {2003}, author = {Ambjörnsson, T and Apell, SP}, title = {Ellipsoidal particles driven by intensity gradients through viscous fluids.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {67}, number = {3 Pt 1}, pages = {031917}, doi = {10.1103/PhysRevE.67.031917}, pmid = {12689111}, issn = {1539-3755}, abstract = {We investigate the drift velocity v(drift) of ellipsoidal polarizable particles (ellipsoids and coated ellipsoids), driven through a viscous fluid by an electric or electromagnetic field intensity gradient. At low Reynolds number and in the dipole approximation v(drift) is proportional to the square of the principal axis along the direction of motion multiplied by a form factor, which is weakly depending on the shape of the particle, and by a frequency and shape dependent factor f(omega). Near frequencies where the real part of epsilon (m)f(omega) changes sign (epsilon (m) is the relative dielectric function of the medium in which the partcle is immersed), v(drift) is sensitive to the shape of the particle. We suggest that our results can be used for the experimental separation of neutral polarizable particles with respect to size or shape.}, }
@article {pmid12688999, year = {2003}, author = {Portelli, B and Holdsworth, PC and Pinton, JF}, title = {Intermittency and non-Gaussian fluctuations of the global energy transfer in fully developed turbulence.}, journal = {Physical review letters}, volume = {90}, number = {10}, pages = {104501}, doi = {10.1103/PhysRevLett.90.104501}, pmid = {12688999}, issn = {0031-9007}, abstract = {We address the experimentally observed non-Gaussian fluctuations for the energy injected into a closed turbulent flow at fixed Reynolds number. We propose that the power fluctuations mirror the internal kinetic energy fluctuations. Using a stochastic cascade model, we construct the excess kinetic energy as the sum over the energy transfers at different levels of the cascade. We find an asymmetric distribution that strongly resembles the experimental data. The asymmetry is an explicit consequence of intermittency and the global measure is dominated by small scale events correlated over the entire system. Our calculation is consistent with the statistical analogy recently made between a confined turbulent flow and a critical system of finite size.}, }
@article {pmid12680733, year = {2003}, author = {Foo, JJ and Liu, KK and Chan, V}, title = {Thermal effect on a viscously deformed liposome in a laser trap.}, journal = {Annals of biomedical engineering}, volume = {31}, number = {3}, pages = {354-362}, doi = {10.1114/1.1555626}, pmid = {12680733}, issn = {0090-6964}, mesh = {1,2-Dipalmitoylphosphatidylcholine/chemistry/radiation effects ; Computer Simulation ; Elasticity ; *Hot Temperature ; Lasers ; Lipid Bilayers/chemistry/radiation effects ; Liposomes/*chemistry/*radiation effects ; *Membrane Fluidity ; Micromanipulation/*methods ; *Models, Theoretical ; Motion ; Rheology/methods ; Temperature ; Viscosity ; }, abstract = {The viscous drag and mechanical deformation of a single vesicle under hydrodynamics flow during the phase transition of a lipid bilayer is determined by optical tweezers experiments with the aid of computational fluid dynamics simulations. Based on the experimental geometry of the vesicle under hydrodynamics flow, the surface stresses and drag force are numerically calculated. It is found that the vesicle is less rigid and the viscous drag force of the vesicle decreases with the increase of temperature at low Reynolds number flow during sample heating. Interestingly, these mechanical properties are reversible and depend strongly on the liposome's thermotropic phase transition temperature. Overall, this study provides new insights into highly coupled thermal and hydrodynamics effects on the biomechanical properties of model membrane vesicle in physiological flow systems.}, }
@article {pmid12686186, year = {2003}, author = {Leneweit, G and Roesner, KG and Koehler, R}, title = {Effect of surfactants on the stability of thin liquid film flow on a rotating disk.}, journal = {Journal of colloid and interface science}, volume = {260}, number = {2}, pages = {349-360}, doi = {10.1016/s0021-9797(02)00023-1}, pmid = {12686186}, issn = {0021-9797}, abstract = {The effect of surfactants on surface instabilities of thin liquid film flow on a rotating disk was studied at different flow rates Q (0.5<or=Q<or=2 ml/s), rotation rates f (33<or=f<or=100 Hz), and volume concentrations rho(s) of the surface active protein BSA (10(-4)<or=rho(s)<or=4 x 10(-4) wt%) in the far field of large radii r (11<or=r<or=25 cm). With these parameters, ranges of the Reynolds number Re (0.48<or=Re<or=4.3), Weber number We (22.3<or=We<or=1410), and surface elasticity numbers zeta or E (0.02<or=zeta<or=62; 0.1<or=E<or=1.4) were covered. The ratio Re/Re(crit) varied between values <<1 and 15000. Surface waves were induced with a constant gas jet directed onto the rotating liquid film in order to investigate their propagation velocities. Measured data are in fairly good agreement with linear and nonlinear theories. The damping effect of surfactants was studied using self-excited waves. It could be shown that the adsorbing monolayer is not in thermodynamic equilibrium at small radii r, but approaches equilibrium at larger r. Assuming the validity of linear stability theory with respect to wave damping, the adsorption kinetics of BSA on the flowing film could be traced. The determination of the transition radius from wavy to smooth film surfaces provides a tool to estimate local film pressures in situ.}, }
@article {pmid12636802, year = {2003}, author = {Madadi, M and Sahimi, M}, title = {Lattice Boltzmann simulation of fluid flow in fracture networks with rough, self-affine surfaces.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {67}, number = {2 Pt 2}, pages = {026309}, doi = {10.1103/PhysRevE.67.026309}, pmid = {12636802}, issn = {1539-3755}, abstract = {Using the lattice Boltzmann method, we study fluid flow in a two-dimensional (2D) model of fracture network of rock. Each fracture in a square network is represented by a 2D channel with rough, self-affine internal surfaces. Various parameters of the model, such as the connectivity and the apertures of the fractures, the roughness profile of their surface, as well as the Reynolds number for flow of the fluid, are systematically varied in order to assess their effect on the effective permeability of the fracture network. The distribution of the fractures' apertures is approximated well by a log-normal distribution, which is consistent with experimental data. Due to the roughness of the fractures' surfaces, and the finite size of the networks that can be used in the simulations, the fracture network is anisotropic. The anisotropy increases as the connectivity of the network decreases and approaches the percolation threshold. The effective permeability K of the network follows the power law K approximately <delta>(beta), where <delta> is the average aperture of the fractures in the network and the exponent beta may depend on the roughness exponent. A crossover from linear to nonlinear flow regime is obtained at a Reynolds number Re approximately O(1), but the precise numerical value of the crossover Re depends on the roughness of the fractures' surfaces.}, }
@article {pmid12636801, year = {2003}, author = {Schumacher, KR and Sellien, I and Knoke, GS and Cader, T and Finlayson, BA}, title = {Experiment and simulation of laminar and turbulent ferrofluid pipe flow in an oscillating magnetic field.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {67}, number = {2 Pt 2}, pages = {026308}, doi = {10.1103/PhysRevE.67.026308}, pmid = {12636801}, issn = {1539-3755}, abstract = {Laminar and turbulent pipe flow of a ferrofluid with an imposed linearly polarized, oscillating, magnetic field is examined here. Experimental results show a fractional pressure drop dependence on flow rate, magnetic field strength, and oscillation frequency. Calculations are presented, which show that ferrofluid theory can explain the flow phenomena in laminar and turbulent pipe flow. The model requires an initial fit of key parameters but then shows predictive capability in both laminar and turbulent flow. Simulation results are found to be essentially independent of the spin boundary condition due to an approximation of spin viscosity that is very small. A low Reynolds number k-epsilon model is used to model the turbulent pipe flow.}, }
@article {pmid12636600, year = {2003}, author = {Mouri, H and Hori, A and Kawashima, Y}, title = {Vortex tubes in velocity fields of laboratory isotropic turbulence: dependence on the Reynolds number.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {67}, number = {1 Pt 2}, pages = {016305}, doi = {10.1103/PhysRevE.67.016305}, pmid = {12636600}, issn = {1539-3755}, abstract = {The streamwise and transverse velocities are measured simultaneously in isotropic grid turbulence at relatively high Reynolds numbers Re(lambda) approximately 110-330. Using a conditional averaging technique, we extract typical intermittency patterns that are consistent with velocity profiles of a model for a vortex tube, i.e., Burgers vortex. The radii of the vortex tubes are several of the Kolmogorov length, regardless of the Reynolds number. Using the distribution of an interval between successive enhancements of a small-scale velocity increment, we study the spatial distribution of vortex tubes. The vortex tubes tend to cluster together. This tendency is increasingly significant with the Reynolds number. Using statistics of velocity increments, we also study the energetical importance of vortex tubes as a function of the scale. The vortex tubes are important over the background flow at small scales especially below the Taylor microscale. At a fixed scale, the importance is increasingly significant with the Reynolds number.}, }
@article {pmid12633362, year = {2003}, author = {Chatelain, P and Kivotides, D and Leonard, A}, title = {Reconnection of colliding vortex rings.}, journal = {Physical review letters}, volume = {90}, number = {5}, pages = {054501}, doi = {10.1103/PhysRevLett.90.054501}, pmid = {12633362}, issn = {0031-9007}, abstract = {We investigate numerically the Navier-Stokes dynamics of reconnecting vortex rings at small Reynolds number for a variety of configurations. We find that reconnections are dissipative due to the smoothing of vorticity gradients at reconnection kinks and to the formation of secondary structures of stretched antiparallel vorticity which transfer kinetic energy to small scales where it is subsequently dissipated efficiently. In addition, the relaxation of the reconnection kinks excites Kelvin waves which due to strong damping are of low wave number and affect directly only large scale properties of the flow.}, }
@article {pmid12618099, year = {2003}, author = {Allison, S and Rasmusson, M and Wall, S}, title = {The primary electroviscous effect, free solution electrophoretic mobility, and diffusion of dilute prolate ellipsoid particles (minor axis = 3 nm) in monovalent salt solution.}, journal = {Journal of colloid and interface science}, volume = {258}, number = {2}, pages = {289-297}, doi = {10.1016/s0021-9797(02)00215-1}, pmid = {12618099}, issn = {0021-9797}, abstract = {The principal objective of the present work is the modeling of the primary electroviscous effect of charged prolate ellipsoid models of low axial ratio. Other transport properties examined include (free solution) electrophoretic mobilities and translational diffusion constants. A numerical boundary element method is employed to solve the coupled Poisson, low Reynolds number Navier-Stokes, and ion transport equations. The methodology is first applied to the primary electroviscous effect of spheres with a centrosymmetric charge distribution and excellent agreement with independent theory is obtained. Specific model studies are also carried out for prolate ellipsoid models with axial ratios less than 4 and a minor axis equal to 3 nm. Most studies are carried out in aqueous NaCl solution (2 to 50 mM) at 20 degrees C for a range of different particle charges, although limited results are also presented in LiCl and KCl solution. The primary electroviscous effect for weakly charged prolate ellipsoids is smaller than that of a sphere under similar conditions. These studies are also carried out at high absolute particle charge. A comparison is made between the primary electroviscous effect and electrophoretic mobilities of prolate ellipsoids and corresponding spherical models.}, }
@article {pmid12607185, year = {2002}, author = {Miller, KL and Polse, KA and Radke, CJ}, title = {Black-line formation and the "perched" human tear film.}, journal = {Current eye research}, volume = {25}, number = {3}, pages = {155-162}, doi = {10.1076/ceyr.25.3.155.13478}, pmid = {12607185}, issn = {0271-3683}, mesh = {Adult ; Biomechanical Phenomena ; Blinking/*physiology ; Drainage ; Female ; Fluorescein/administration &amp; dosage ; Gravitation ; Humans ; Male ; Models, Biological ; Models, Theoretical ; Surface Tension ; Tears/*metabolism ; Time Factors ; Wettability ; }, abstract = {Introduction. McDonald and Brubaker(1) observed that after instillation of fluorescein, dark lines appear near the upper and lower lid margins of the human eye immediately following a blink. Methods. This paper numerically models the dynamic black-line formation under the lubrication approximation at low Reynolds number, including gravity and surface tension forces. Results. The hydrodynamic model predicts that menisci at the lid margins draw liquid from the tear film, resulting in local thinning close to the lids (i.e., black lines) due to capillary suction. Once the film thins locally, resistance to further thinning increases. No vertical gravity-induced drainage occurs between blinks, and the tear film is trapped in its initially deposited state or "perched" between the two black lines. Conclusions. We demonstrate quantitatively that due to rapid formation of black lines, the tear film is trapped for extended periods. Lid action is therefore required to disturb the perched tear film.}, }
@article {pmid12583563, year = {2003}, author = {Clough, AV and Haworth, ST and Roerig, DL and Hoffman, EA and Dawson, CA}, title = {Influence of gravity on radiographic contrast material-based measurements of regional blood flow distribution.}, journal = {Academic radiology}, volume = {10}, number = {2}, pages = {128-138}, doi = {10.1016/s1076-6332(03)80036-3}, pmid = {12583563}, issn = {1076-6332}, support = {HL19298/HL/NHLBI NIH HHS/United States ; HL64368/HL/NHLBI NIH HHS/United States ; }, mesh = {Angiography ; *Contrast Media ; *Gravitation ; Humans ; Lung/*blood supply/diagnostic imaging ; *Models, Cardiovascular ; Phantoms, Imaging ; Regional Blood Flow ; Tomography, X-Ray Computed/instrumentation ; }, abstract = {RATIONALE AND OBJECTIVES: Radiographic measurement of regional blood flow distribution in the lungs is potentially biased because the contrast material used to track flow is denser than blood. The authors performed this study to evaluate the effect of gravity on flow estimates by using an experimental test phantom and numeric simulations.<br><br>MATERIALS AND METHODS: Cross-sectionally uniform boluses of radiopaque contrast material were delivered at the upstream end of a horizontal inlet tube connected to a downstream axisymmetric bifuration attached to collecting tubing spirals. The phantom was imaged by using both planar angiography and dynamic multi-detector row computed tomography (CT) during the passage of the bolus through the phantom. The images were analyzed to determine the relative amounts of contrast material traveling through the top and bottom branches of the bifurcation by using varying Reynolds numbers and ratios of inlet tube volume to bolus volume. Numeric simulations of flow within a straight channeL with use of a dispersion operator intended to simulate settling of the bolus due to gravity, were performed under conditions representative of those in the experiments.<br><br>RESULTS: When the plane of the bifurcation was vertical and actual flow through the two branches was equal, the fraction of contrast material passing through the downward-directed branch increased with decreasing Reynolds number and increasing inlet tube-bolus volume ratio. This occurred in both the experiments and the simulations.<br><br>CONCLUSION: Because in the circulation Reynolds number decreases and pathway length increases with decreasing vessel diameter, the accuracy of regional flow measurements obtained with angiography or CT within the lungs may be limited by density differences between contrast material and blood.}, }
@article {pmid12570619, year = {2003}, author = {Matas, JP and Morris, JF and Guazzelli, E}, title = {Transition to turbulence in particulate pipe flow.}, journal = {Physical review letters}, volume = {90}, number = {1}, pages = {014501}, doi = {10.1103/PhysRevLett.90.014501}, pmid = {12570619}, issn = {0031-9007}, abstract = {We investigate experimentally the influence of suspended particles on the transition to turbulence. The particles are monodisperse and neutrally buoyant with the liquid. The role of the particles on the transition depends upon both the pipe to particle diameter ratios and the concentration. For large pipe-to-particle diameter ratios the transition is delayed while it is lowered for small ratios. A scaling is proposed to collapse the departure from the critical Reynolds number for pure fluid as a function of concentration into a single master curve.}, }
@article {pmid12558256, year = {2003}, author = {Zheng, ZC and Tan, BK}, title = {Reynolds number effects on flow/acoustic mechanisms in spherical windscreens.}, journal = {The Journal of the Acoustical Society of America}, volume = {113}, number = {1}, pages = {161-166}, doi = {10.1121/1.1527927}, pmid = {12558256}, issn = {0001-4966}, abstract = {There is a practical need to fully understand the mechanisms involved in the flow/pressure fluctuations around a screened microphone. A stream of uniform flow with low-frequency turbulence encountering a rigid, impermeable spherical windscreen is considered in this study. Pressure distributions on the surface of the sphere are determined by the flow structure. Pressure fluctuations at the center of the sphere are then calculated based on the integration of surface pressure distributions. Because of the low-frequency assumption, results from steady-state laminar flows can be used to investigate the Reynolds number effects on wind noise reduction. Three types of flow have been studied in this paper: an inviscid case, a low-Reynolds-number Stokes flow, and intermediate- and high-Reynolds-number flows. A Reynolds-number/wind-noise-reduction correlation shows that the wind noise reduction increases with decreasing Reynolds number.}, }
@article {pmid12557508, year = {2002}, author = {Qan, K and Guo, B and Liu, B and Liu, Z}, title = {[A perturbation solution of pulsatile Casson flow in the parallel-plate flow chamber].}, journal = {Sheng wu yi xue gong cheng xue za zhi = Journal of biomedical engineering = Shengwu yixue gongchengxue zazhi}, volume = {19}, number = {3}, pages = {402-407}, pmid = {12557508}, issn = {1001-5515}, mesh = {*Algorithms ; In Vitro Techniques ; Models, Cardiovascular ; *Pulsatile Flow ; Stress, Mechanical ; }, abstract = {The parallel-plate flow chamber (PPFC) with rectangular shape, of which the height is far smaller than its own length and width, is one of the main apparatus for in vitro studies of the mechanical behavior of the cells. Considering that the Reynolds numbers of flows in the usually used PPFCs are small, a perturbation solution of laminar pulsatile Casson fluid in the PPFC is presented using Reynolds number as perturbation parameter. Furthermore, the velocities and shear stresses in the PPFC are given. The numerical results demonstrate that under the same pressure gradient the shear stresses are almost identical between Casson fluid and Newtonian fluid, whereas under the same flux the shear stresses are obviously different between Casson fluid and Newtonian fluid. The results in this paper provide a theoretical way to determine the shear stresses in the parallel-plate flow chamber under pulsatile Casson fluid.}, }
@article {pmid12536593, year = {2001}, author = {Lin, K and Shi, Y and Liu, S and Jiang, W}, title = {[Quantitative detection of flow indices in tubal flow via pulsed Doppler ultrasound, in vitro].}, journal = {Hua xi yi ke da xue xue bao = Journal of West China University of Medical Sciences = Huaxi yike daxue xuebao}, volume = {32}, number = {3}, pages = {454-458}, pmid = {12536593}, issn = {0257-7712}, mesh = {Biomechanical Phenomena ; Blood Flow Velocity ; Blood Vessels/pathology ; Constriction, Pathologic/diagnostic imaging ; *Models, Cardiovascular ; *Ultrasonography, Doppler, Pulsed ; }, abstract = {OBJECTIVE: This paper deals with the method and feasibility of quantitative detection of flow indices via commercially available Pulsed Doppler Ultrasound.<br><br>METHODS: The indices, such as Reynolds number, relative spectral broadening (RSB), laminar shear stress and Reynolds normal stress (RNS) were selected and evaluated. Detection was done temporally and spatially, upstream and downstream of the stenosis. The data were evaluated qualitatively and quantitatively.<br><br>RESULTS: The roughest turbulence was met at 1/2R sample volume, 1.0 cm downstream of the stenosis.<br><br>CONCLUSION: The methodology in this study is proved to be feasible and may have good prospects in clinical use.}, }
@article {pmid12535068, year = {2003}, author = {Gilad, R and Porat, A and Trachtenberg, S}, title = {Motility modes of Spiroplasma melliferum BC3: a helical, wall-less bacterium driven by a linear motor.}, journal = {Molecular microbiology}, volume = {47}, number = {3}, pages = {657-669}, doi = {10.1046/j.1365-2958.2003.03200.x}, pmid = {12535068}, issn = {0950-382X}, mesh = {Culture Media ; Image Processing, Computer-Assisted/methods ; Microscopy/methods ; Movement ; Optics and Photonics/instrumentation ; Spiroplasma/growth &amp; development/*physiology/*ultrastructure ; Viscosity ; }, abstract = {Spiroplasma are members of the Mollicutes (Mycoplasma, Acholeplasma and Spiroplasma) - the simplest, minimal, free-living and self-replicating forms of life. The mollicutes are unique among bacteria in completely lacking cell walls and flagella and in having an internal, contractile cytoskeleton, which also functions as a linear motor. Spiroplasma are helical, chemotactic and viscotactic active swimmers. The Spiroplasmal cytoskeleton is a flat ribbon composed of seven pairs of fibrils. The ribbon is attached to the inner side of the cell membrane along its innermost (shortest) helical line. The cell's geometry and dynamic helical parameters, and consequently motility, can be controlled by changing differentially and in a co-ordinated manner, the length of the fibrils. We identified several consistent modes of cell movements and motility originating, most likely, as a result of co-operative or local molecular switching of fibrils: (i). regular extension and contraction within the limits of helical symmetry (this mode also includes straightening, beyond what is allowed by helical symmetry, and reversible change of helical sense); (ii). spontaneous and random change of helical sense originating at random sites along the cell (these changes propagate along the cell in either direction and hand switching is completed within approximately 0.08 second); (iii). forming a deformation on one of the helical turns and propagating it along the cell (these helical deformations may travel along the cell at a speed of up to approximately 40 microm s-1); (iv). random bending, flexing and twitching (equivalent to tumbling). In standard medium (viscosity = 1.147 centipoise) the cells run at approximately 1.5 microm s-1, have a Reynolds number of approximately 3.5 x 10-6 and consume approximately 30 ATP molecules s-1. Running velocity, duration, persistence and efficiency increase with viscosity upon adding ficoll, dextran and methylcellulose to standard media. Relative force measurements using optical tweezers confirm these findings.}, }
@article {pmid12528042, year = {2003}, author = {Demokritou, P and Gupta, T and Ferguson, S and Koutrakis, P}, title = {Development of a high-volume concentrated ambient particles system (CAPS) for human and animal inhalation toxicological studies.}, journal = {Inhalation toxicology}, volume = {15}, number = {2}, pages = {111-129}, doi = {10.1080/08958370304475}, pmid = {12528042}, issn = {0895-8378}, mesh = {Aerosols ; Air Pollutants/*toxicity ; Animals ; Equipment Design ; Humans ; Particle Size ; Toxicity Tests/*methods ; }, abstract = {A two-stage, high-volume, ambient particle concentrator was developed and characterized. This versatile system, depending on its operational parameters, can be used to fractionate and concentrate particles in three size ranges (PM(10-2.5), PM(10-1), PM(2.5-1)). The performance of this concentrated ambient particle system (CAPS), as well as its individual virtual impaction stages, was investigated as a function of several parameters, including minor-to-total flow ratios and acceleration nozzle Reynolds number. During these laboratory tests, performance parameters such as concentration enrichment factor (CF), particle losses, collection efficiency curves, cutpoint, and pressure drop were measured. The main objective of these investigations was to optimize the ability of the system to concentrate ambient PM(2.5-10) and PM(1-10) particles. PM(2.5-10) particles were concentrated by a factor of 70 to 150. The flow rate of the concentrated aerosol can range between 12.5 and 50 LPM (L/min). Other features of the system include relatively low-pressure drops in the major and minor flows, low particle losses, and a compact design. Performance evaluation of the system also confirmed that separation and concentration of the PM(2.5-10) particles occurred without any significant distortion of the size distribution, during the concentration process. Similar results were obtained for the PM(1-10) size range. For this size range, concentration enrichment was 70 times, and again, no particle size distribution distortion was observed. The overall performance of this versatile system makes it suitable for inhalation toxicological studies.}, }
@article {pmid12513491, year = {2002}, author = {Ekiel-Jezewska, ML and Lecoq, N and Anthore, R and Bostel, F and Feuillebois, F}, title = {Rotation due to hydrodynamic interactions between two spheres in contact.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {66}, number = {5 Pt 1}, pages = {051504}, doi = {10.1103/PhysRevE.66.051504}, pmid = {12513491}, issn = {1539-3755}, abstract = {We analyze the rotational and translational motion of two close spheres in a fluid at low Reynolds number to investigate if their surfaces come into mechanical contact. The rotational motion of a sphere settling close to another fixed ball is calculated from a model in which contact interactions between the spheres are added to the gravitational and hydrodynamic forces. The model predicts a transition from pure rolling to rolling with slip, determined by the Coulomb's law, when the ratio of the mechanical friction to the load increases up to the static friction coefficient. The dependence of the angular and translational velocities on the kinetic friction coefficient and on the separation between the particle surfaces is analyzed. The angular and translational velocities of a millimeter size bead in a viscous oil, close to a fixed bead of a similar size, are measured from video images. Interferometric data on translational motion are also collected according to the method introduced in our earlier studies. A systematic fitting procedure of the model to the experiment is developed and applied to the rotational and translational measurements. The model parameters are determined.}, }
@article {pmid12513403, year = {2002}, author = {Lin, W and Armfield, SW}, title = {Weak fountains in a stratified fluid.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {66}, number = {6 Pt 2}, pages = {066308}, doi = {10.1103/PhysRevE.66.066308}, pmid = {12513403}, issn = {1539-3755}, abstract = {The behavior of weak axisymmetric and plane fountains resulting from the injection of denser fluid upwards into large containers containing a stably stratified fluid has been explored using dimensional analysis, scaling analysis, and direct numerical simulation. For weak fountains, with Froude number Fr approximately 1.0, dimensional and scaling analyses have been used to derive scaling relations for the dimensionless fountain height, width, thickness of the temperature layer, and development times in terms of the Froude number Fr, Reynolds number Re, Prandtl number Pr, and ambient stratification number s. Numerical simulations have been carried out for a series of Fr, Re, Pr, and s for both axisymmetric and plane fountains to validate and quantify the scaling relations obtained by the dimensional and scaling analyses. The numerical results have been found to agree well with the analytical scaling relations.}, }
@article {pmid12507313, year = {2002}, author = {Manjunatha, M and Singh, M}, title = {Computerised visualisation from images of blood flow through frog mesenteric microvessels with multiple complexities.}, journal = {Medical &amp; biological engineering &amp; computing}, volume = {40}, number = {6}, pages = {634-640}, pmid = {12507313}, issn = {0140-0118}, mesh = {Animals ; *Hemorheology ; Image Processing, Computer-Assisted ; Microcirculation ; Microscopy, Video ; Ranidae ; Splanchnic Circulation/*physiology ; }, abstract = {Blood flow through a frog mesenteric microvessel, consisting of one loop and two successive bends, was recorded by a video-microscopic system and analysed by a PC-based image processing system. After preprocessing, these images were analysed by the image velocimetry, axial tomography and image processing procedures. The blood flow in the microvessel had a Reynolds number of 0.033, and the Dean number varied from 0.004 in the loop to 0.007 in the bend, showing an increase in secondary flow in the bend region. These changes led to outward shifts in the peaks of velocity and concentration profiles, with an increase in the thickness of the outer walls (of about three times) compared with that of the inner walls. The mean velocity and mean cellular concentration showed a similar pattern. The variation in the cellular concentration in the microvessel was visualised by concentration contours and grey-scale images of the cellular distribution. At the inner wall of the complex geometry, the velocity reduced to zero, whereas the cellular concentration varied from 2 to 5%. In the high shear stress regions in the complex geometry, the vessel wall thickness was two-three times more than that in low shear stress regions.}, }
@article {pmid12498520, year = {2003}, author = {Anand, M and McFarland, AR and Rajagopal, KR}, title = {Gas mixing for achieving suitable conditions for single point aerosol sampling in a straight tube: experimental and numerical results.}, journal = {Health physics}, volume = {84}, number = {1}, pages = {82-91}, doi = {10.1097/00004032-200301000-00007}, pmid = {12498520}, issn = {0017-9078}, mesh = {Aerosols ; Equipment Design ; Gases/*analysis ; *Nuclear Reactors ; Radiation Monitoring/instrumentation/*methods ; }, abstract = {Experimental measurements of velocity and tracer gas concentration are taken in a straight tube to evaluate the effectiveness of mixing in achieving conditions as required by ANSI N13.1-1999 for single point extractive sampling from stacks and ducts of nuclear facilities. Mixing is evaluated for inlet turbulent intensities of 1.5%, 10%, and 20%, achieved by introducing various bi-plane grids, and for conditions generated by a commercial static gas mixer. The data obtained (at Reynolds number = 15,000) highlight the importance of inlet turbulence intensity in the process of turbulent dispersion of a dilute gas. The gas mixer does not introduce significant pressure losses and unlike bi-plane grids, the turbulence downstream of the mixer is not homogenous. A judicious choice of the release location that uses the large scale eddies and inhomogeneity of the turbulence ensures that the specified ANSI N13.1-1999 criteria are attained within 7 diameters downstream of the duct inlet. This is significantly more effective than a bi-plane grid where even with 20% inlet intensity the criteria are met only at 21 diameters downstream. The predictions of a proposed semi-empirical correlation match favorably with data. For example, at 18 diameters downstream with inlet intensities of 1.5% and 10%, the predicted coefficients of variation (COVs) of 150% and 65% are close to the actual values of 154% and 50%; where the COV of a set of measurements is the ratio of the standard deviation of the set to its mean value. The corresponding results obtained using commercially available software are 141% and 12%. Results from a particle-tracking model show good qualitative trends, but they should not be used to determine compliance with the requirements of the ANSI standard.}, }
@article {pmid12498196, year = {2002}, author = {Schure, MR and Maier, RS and Kroll, DM and Davis, HT}, title = {Simulation of packed-bed chromatography utilizing high-resolution flow fields: comparison with models.}, journal = {Analytical chemistry}, volume = {74}, number = {23}, pages = {6006-6016}, doi = {10.1021/ac0204101}, pmid = {12498196}, issn = {0003-2700}, abstract = {A computer simulation of a section of the interior region of a liquid chromatographic column is performed. The detailed fluid flow profile is provided from a microscopic calculation of low Reynolds number flow through a random packed bed of nonporous spherical particles. The fluid mechanical calculations are performed on a parallel processor computer utilizing the lattice Boltzmann technique. Convection, diffusion, and retention in this flow field are calculated using a stochastic-based algorithm. This computational scheme provides for the ability to reproduce the essential dynamics of the chromatographic process from the fundamental considerations of particle geometry, particle size, flow velocity, solute diffusion coefficient, and solute retention parameters when retention is utilized. The simulation data are fit to semiempirical models. The best agreement is found for the "coupling" model of Giddings and the four-parameter Knox model. These models are verified over a wide range of particle sizes and flow velocities at both low and high velocity. The simulations appear to capture the essential dynamics of the chromatographic flow process for non-dimensional flow velocities (Péclet number) less than 500. Since the same packing geometry is utilized for different particle size studies, the interpretation of the parameter estimates from these models can be extended to the physical column model. The simulations reported here agree very well with a number of experiments reported previously.}, }
@article {pmid12484833, year = {2002}, author = {Blackman, EG and Field, GB}, title = {New dynamical mean-field dynamo theory and closure approach.}, journal = {Physical review letters}, volume = {89}, number = {26}, pages = {265007}, doi = {10.1103/PhysRevLett.89.265007}, pmid = {12484833}, issn = {0031-9007}, abstract = {We develop a new nonlinear mean field dynamo theory that couples field growth to the time evolution of the magnetic helicity and the turbulent electromotive force, E. We show that the difference between kinetic and current helicities emerges naturally as the growth driver when the time derivative of E is coupled into the theory. The solutions predict significant field growth in a kinematic phase and a saturation rate/strength that is magnetic Reynolds number dependent/independent in agreement with numerical simulations. The amplitude of early time oscillations provides a diagnostic for the closure.}, }
@article {pmid12483477, year = {2002}, author = {Dunsmore, BC and Jacobsen, A and Hall-Stoodley, L and Bass, CJ and Lappin-Scott, HM and Stoodley, P}, title = {The influence of fluid shear on the structure and material properties of sulphate-reducing bacterial biofilms.}, journal = {Journal of industrial microbiology &amp; biotechnology}, volume = {29}, number = {6}, pages = {347-353}, doi = {10.1038/sj.jim.7000302}, pmid = {12483477}, issn = {1367-5435}, support = {R01 GM60052-02/GM/NIGMS NIH HHS/United States ; }, mesh = {Biofilms/*growth &amp; development ; Desulfovibrio/cytology/*growth &amp; development/*metabolism ; Rheology ; Stress, Mechanical ; Sulfates/*metabolism ; Time Factors ; }, abstract = {Biofilms of sulphate-reducing Desulfovibrio sp. EX265 were grown in square section glass capillary flow cells under a range of fluid flow velocities from 0.01 to 0.4 m/s (wall shear stress, tau(w), from 0.027 to 1.0 N/m(2)). In situ image analysis and confocal scanning laser microscopy revealed biofilm characteristics similar to those reported for aerobic biofilms. Biofilms in both flow cells were patchy and consisted of cell clusters separated by voids. Length-to-width ratio measurements (l(c):w(c)) of biofilm clusters demonstrated the formation of more "streamlined" biofilm clusters (l(c):w(c)=3.03) at high-flow velocity (Reynolds number, Re, 1200), whereas at low-flow velocity (Re 120), the l(c):w(c) of the clusters was approximately 1 (l(c):w(c) of 1 indicates no elongation in the flow direction). Cell clusters grown under high flow were more rigid and had a higher yield point (the point at which the biofilm began to flow like a fluid) than those established at low flow and some biofilm cell aggregates were able to relocate within a cluster, by travelling in the direction of flow, before attaching more firmly downstream.}, }
@article {pmid12454794, year = {2002}, author = {Zhang, Z and Kleinstreuer, C and Kim, CS and Hickey, AJ}, title = {Aerosol transport and deposition in a triple bifurcation bronchial airway model with local tumors.}, journal = {Inhalation toxicology}, volume = {14}, number = {11}, pages = {1111-1133}, doi = {10.1080/08958370290084809}, pmid = {12454794}, issn = {0895-8378}, mesh = {Administration, Inhalation ; Aerosols/administration &amp; dosage/*pharmacokinetics ; Airway Obstruction/pathology/physiopathology ; Biological Availability ; Bronchi/*metabolism ; Computer Simulation ; Humans ; *Models, Anatomic ; *Models, Biological ; Neoplasms/*metabolism/pathology ; Particle Size ; Pulmonary Ventilation ; }, abstract = {Airflow characteristics and particle deposition have been numerically simulated in a triple bifurcation lung airway model (from generation 3-6 airways) with local tumors protruded from the sidewalls of generation 5 airways. The effects of tumors in terms of size and location on airflow, particle transport, and deposition patterns were analyzed for constant inspiratory flow rates with inlet Reynolds (Re(match) = 463 and 1882) and Stokes number (St(match) = 0.02-0.12) combinations that match different cyclic inhalation waveforms. The size of tumors was varied to induce an obstruction of airway lumen by 16-74%. Extreme conditions, 2 and 100% obstruction, were also examined. The results show that enhanced deposition occurs in the carina region at each bifurcation, and deposition increases with increasing Stokes and Reynolds number as expected from earlier studies. In addition, deposition increases at the tumor site until the tumor blocks about half of the airway lumen and then decreases with a further obstruction. In other words, there exists a maximum particle deposition fraction (DF) for a protruding tumor that occludes the lumen. The maximum DF at the tumor was 10.2% within the test conditions used. Deposition occurs mainly on the frontal surface of the tumors, but spreads out to the opposite wall, or upstream sections, or sister branches of the tumor at high flow rates and Stokes number. The present results (1) help in the understanding of the complex toxic or therapeutic aerosol dynamics in the lung with local airways obstruction, and (2) provide quantitative information on critical tumor size and particle deposition to health care specialists.}, }
@article {pmid12454441, year = {2002}, author = {Mekheimer, KhS}, title = {Peristaltic transport of a couple stress fluid in a uniform and non-uniform channels.}, journal = {Biorheology}, volume = {39}, number = {6}, pages = {755-765}, pmid = {12454441}, issn = {0006-355X}, mesh = {Blood Flow Velocity/physiology ; Blood Pressure/physiology ; Blood Viscosity/physiology ; Friction ; Humans ; Mathematics ; *Models, Cardiovascular ; Pulsatile Flow/physiology ; Regional Blood Flow/*physiology ; }, abstract = {The problem of peristaltic transport of a couple stress fluid in uniform and non-uniform two-dimensional channels has been investigated under zero Reynolds number with long wavelength approximation. Blood is represented by a couple stress fluid (a fluid which its particles size are taken into account, a special case of a non-Newtonian fluid). It is found that the pressure rise decreases as the couple stress fluid parameter gamma increases (i.e., small size fluid particle). So the pressure rise for a couple stress fluid (as a blood model) is greater than that for a Newtonian fluid. Also the pressure rise increases as the amplitude ratio phi increases for different values of gamma. Further, the pressure rise in the case of non-uniform geometry is found to be much smaller than the corresponding value in the case of uniform geometry. Finally, the maximum pressure rise when the mean flow rate over one period of the wave, Q = 0, increases as phi increases and gamma decreases.}, }
@article {pmid12432011, year = {2002}, author = {Goldman, JA and Patek, SN}, title = {Two sniffing strategies in palinurid lobsters.}, journal = {The Journal of experimental biology}, volume = {205}, number = {Pt 24}, pages = {3891-3902}, doi = {10.1242/jeb.205.24.3891}, pmid = {12432011}, issn = {0022-0949}, mesh = {Animals ; Behavior, Animal/*physiology ; Nephropidae/anatomy &amp; histology/physiology ; Odorants ; Palinuridae/*anatomy &amp; histology/classification/*physiology ; Phylogeny ; Seawater ; Sense Organs/physiology/ultrastructure ; Smell/*physiology ; Videotape Recording ; }, abstract = {Most studies of lobster chemoreception have focused on the model systems of Panulirus argus (Palinuridae) and Homarus americanus (Nephropidae). We compare antennule morphology across lobsters and conduct the first kinematic study of antennule flicking in a palinurid species other than P. argus. High-speed video analysis shows that Palinurus elephas flicks at a rate more than an order of magnitude higher than in P. argus. However, both species flick their antennular flagella at a Reynolds number (Re) of approximately one, such that an asymmetry in the speed of the flick phases causes both species to have a leaky closing flick phase and a non-leaky opening phase. The antennular flagella of P. argus are nearly seven times longer than those of P. elephas, and, when compared across palinurid genera, Panulirus species sample far greater areas of water over greater spatial and time scales than do any other palinurid genera. Palinurid lobsters appear to have two sniffing strategies: low flick rates over a large area of water (e.g. P. argus) or high flick rates over a small area of water (e.g. P. elephas). P. argus is a highly informative model system in which to study aquatic chemoreception; however, its antennule anatomy and kinematics suggest a separate strategy, unique to Panulirus species, for sensing chemical plumes in fluid environments.}, }
@article {pmid12408223, year = {2002}, author = {Canning, CR and Greaney, MJ and Dewynne, JN and Fitt, AD}, title = {Fluid flow in the anterior chamber of a human eye.}, journal = {IMA journal of mathematics applied in medicine and biology}, volume = {19}, number = {1}, pages = {31-60}, pmid = {12408223}, issn = {0265-0746}, mesh = {Anterior Chamber/*physiology ; Eye/anatomy &amp; histology ; Humans ; Intraocular Pressure/physiology ; *Models, Biological ; *Ocular Physiological Phenomena ; }, abstract = {A simple model is presented to analyse fluid flow in the anterior chamber of a human eye. It is shown that under normal conditions such flow inevitably occurs. The flow, whose reduced Reynolds number is small, is viscosity dominated and is driven by buoyancy effects which are present because of the temperature difference between the front and back of the anterior chamber. In cases of severe eye trauma or as a result of certain diseases and medical conditions, particulate matter may be introduced into the anterior chamber. The motion and distribution of such particles is analysed and it is shown that the model is capable of predicting well-established and observed features that may be present in a traumatized eye such as hyphemas, keratic precipitates, hypopyons and Krukenberg spindles.}, }
@article {pmid12366257, year = {2002}, author = {Herrada, MA and Barrero, A}, title = {Self-rotation in electrocapillary flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {66}, number = {3 Pt 2B}, pages = {036311}, doi = {10.1103/PhysRevE.66.036311}, pmid = {12366257}, issn = {1539-3755}, abstract = {The mechanism of appearance of swirl in a certain class of converging flows is investigated numerically. The analysis is motivated by the spontaneous generation of swirl, which has been observed in electrified menisci (Taylor cones). The electrical stress acting on the cone surface drives these electrified millimetric fluid flows. Numerical results show that the primarily swirl-free meridian flow is unstable within an interval of values of the Reynolds number based on the surface stress. For values of the Reynolds number outside this interval, which depends on the forcing conditions and the geometry of the flow, the nonswirling meridian flow is stable. The instability mechanism of circulation amplification, which has nothing to do with the well-known increase of swirl velocity due to the vortex stretching mechanism, is due to a convection-diffusion effect. The circulation accumulated at the axis zone by the converging meridian motion is pumped by diffusion toward the conical surface. This feedback loop mechanism shoots the circulation amplification for values of the Reynolds number larger than a critical one. The same instability mechanism of swirl amplification could also appear in other converging flows generated by body forces (natural convection, electrical forces, etc.).}, }
@article {pmid12322758, year = {2002}, author = {Dionysiou, DD and Burbano, AA and Suidan, MT and Baudin, I and Laîné, JM}, title = {Effect of oxygen in a thin-film rotating disk photocatalytic reactor.}, journal = {Environmental science &amp; technology}, volume = {36}, number = {17}, pages = {3834-3843}, doi = {10.1021/es0113605}, pmid = {12322758}, issn = {0013-936X}, mesh = {Biodegradation, Environmental ; *Bioreactors ; Catalysis ; Chlorobenzoates/analysis/chemistry ; *Computer Simulation ; Oxygen/*chemistry ; Titanium/chemistry ; Ultraviolet Rays ; Water Purification/instrumentation/*methods ; }, abstract = {A novel experimental procedure was developed to measure oxygen mass transfer during the oxygenation of water in a thin film of a rotating disk photocatalytic reactor (RDPR). The increase in dissolved oxygen (DO) of initially deaerated water was monitored with time in the reactor vessel at different disk angular velocities after exposure of the reactor to the atmosphere. Oxygenation was predominantly achieved by oxygen mass transport through the thin liquid film carried by the disk and to a much lesser extent by direct oxygenation of the water in the reactor vessel via a surface renewal mechanism. A mathematical model was developed to simulate the phenomenon considering both cases of presence and absence of oxygen mass transport limitations. In the latter case, the model considered that the amount of liquid carried by the disk was saturated with oxygen when returning to the reactor vessel. On the basis of the model and the experimental data, it was proven that mass-transfer limitations existed until the water in the reactor vessel became saturated with oxygen. Results obtained from the model were validated by an alternative analysis using dimensionless groups characteristic to the system. The study revealed that the mass-transfer coefficient increased linearly with disk angular velocity and thus disk Reynolds number. The results showed that oxygen mass-transfer limitations decreased with increasing disk angular velocity, mainly due to an increase in the overall mass-transfer coefficient. In the presence of UV radiation, the influence of oxygen on the photocatalytic oxidation of 4-chlorobenzoic acid was investigated in the RDPR operated in batch and continuous mode. The photocatalytic reactions occurred in a thin film of liquid carried by the disk in the presence of UV radiation and ST-B01 composite spherical ceramic (SiO2/Al2O3) balls coated with anatase TiO2 catalyst. It was found that the initial degradation rate followed Langmuir kinetics with respect to oxygen concentration in the gas phase. When the oxygen concentration in the gas phase surpassed that in air, the degradation rates did not improve significantly, suggesting that operation with air instead of oxygen is most probably a more realistic practical choice. Measurements of DO during the presence and absence of UV radiation suggested that the photocatalytic reactions were mainly oxygen concentration-limited rather than oxygen mass-transfer-limited.}, }
@article {pmid12241481, year = {2002}, author = {Rüdiger, G and Shalybkov, D}, title = {Stability of axisymmetric Taylor-Couette flow in hydromagnetics.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {66}, number = {1 Pt 2}, pages = {016307}, doi = {10.1103/PhysRevE.66.016307}, pmid = {12241481}, issn = {1539-3755}, abstract = {The linear marginal instability of an axisymmetric magnetohydrodynamics Taylor-Couette flow of infinite vertical extension is considered. We are only interested in those vertical wave numbers for which the characteristic Reynolds number is minimum. For hydrodynamically unstable flows minimum Reynolds numbers exist even without a magnetic field, but there are also solutions with smaller characteristic Reynolds numbers for certain weak magnetic fields. The magnetic field, therefore, destabilizes the rotating flow by the so-called magnetorotational instability (MRI). The MRI, however, can only exist for hydrodynamically unstable flow if the magnetic Prandtl number, Pr, is not too small. For too small magnetic Prandtl numbers (and too strong magnetic fields) only the well-known magnetic suppression of the Taylor-Couette instability can be found. The MRI is even more pronounced for hydrodynamically stable flows. In this case we can always find a magnetic field amplitude where the characteristic Reynolds number is minimum. These critical values are computed for different magnetic Prandtl numbers and for three types of geometry (small, medium, and wide gaps between the rotating cylinders). In all cases the minimum Reynolds numbers are running with 1/Pr for small enough Pr so that the critical Reynolds numbers may easily exceed values of 10(6) for the magnetic Prandtl number of sodium (10(-5)) or gallium (10(-6)). The container walls are considered either electrically conducting or insulating. For insulating walls with small and medium-size gaps between the cylinders (i) the critical Reynolds number is smaller, (ii) the critical Hartmann number is higher, and (iii) the Taylor vortices are longer in the direction of the rotation axis. For wider gaps the differences in the results between both sets of boundary conditions become smaller and smaller.}, }
@article {pmid12241479, year = {2002}, author = {Grossmann, S and Lohse, D}, title = {Prandtl and Rayleigh number dependence of the Reynolds number in turbulent thermal convection.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {66}, number = {1 Pt 2}, pages = {016305}, doi = {10.1103/PhysRevE.66.016305}, pmid = {12241479}, issn = {1539-3755}, abstract = {The Prandtl and Rayleigh number dependences of the Reynolds number in turbulent thermal convection following from the unifying theory by Grossmann and Lohse [J. Fluid Mech. 407, 27 (2000); Phys. Rev. Lett. 86, 3316 (2001)] are presented and compared with various recent experimental findings. This dependence Re(Ra,Pr) is more complicated than a simple global power law. For Pr=5.5 and 10(8)<Ra<10(10) the effective or local power law exponent of Re as a function of Ra is definitely less than 0.50, namely, Re approximately Ra(0.45), in agreement with Qiu and Tong's experimental findings [Phys. Rev. E 64, 036304 (2001)]. We also calculated the kinetic boundary layer width. Both in magnitude and in Ra scaling it is consistent with the data.}, }
@article {pmid12241411, year = {2002}, author = {Daya, ZA and Deyirmenjian, VB and Morris, SW}, title = {Sequential bifurcations in sheared annular electroconvection.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {66}, number = {1 Pt 2}, pages = {015201}, doi = {10.1103/PhysRevE.66.015201}, pmid = {12241411}, issn = {1539-3755}, abstract = {A sequence of bifurcations is studied in a one-dimensional pattern forming system subject to the variation of two experimental control parameters: a dimensionless electrical forcing number R and a shear Reynolds number Re. The pattern is an azimuthally periodic array of traveling vortices with integer mode number m. Varying R and Re permits the passage through several codimension-two (CoD2) points. We find that the coefficients of the nonlinear terms in a generic Landau equation for the primary bifurcation are discontinuous at the CoD2 points. Further, we map the stability boundaries in the space of the two parameters by studying the subcritical secondary bifurcations in which m-->m+1 when R is increased at constant Re.}, }
@article {pmid12241290, year = {2002}, author = {Cook, AW and Zhou, Y}, title = {Energy transfer in Rayleigh-Taylor instability.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {66}, number = {2 Pt 2}, pages = {026312}, doi = {10.1103/PhysRevE.66.026312}, pmid = {12241290}, issn = {1539-3755}, abstract = {The spatial structure and energy budget for Rayleigh-Taylor instability are examined using results from a 512 x 512 x 2040 point direct numerical simulation. The outer-scale Reynolds number of the flow follows a rough t(3) power law and reaches a final value of about 5500. Taylor microscales and Reynolds numbers are plotted to characterize anisotropy in the flow and document progress towards the mixing transition. A mixing parameter is defined which characterizes the relative rates of entrainment and mixing in the flow. The spectrum of each term in the kinetic energy equation is plotted, at regular time intervals, as a function of the inhomogeneous direction and the two-dimensional wave number for the homogeneous directions. The energy spectrum manifests the beginning of an inertial range by the latter stages of the simulation. The production and dissipation spectra become increasingly opposite and separate in wave space as the flow evolves. The transfer spectrum depends strongly on the inhomogeneous direction, with the net transfer being from large to small scales. Energy transfer at the bubble/spike fronts is strictly positive. Extensive cancellation occurs between the pressure and advection terms. The dilatation term produces negligible energy transfer, but its overall effect is to move energy from high to low density regions.}, }
@article {pmid12241288, year = {2002}, author = {Zaytsev, M and Bychkov, V}, title = {Effect of the Darrieus-Landau instability on turbulent flame velocity.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {66}, number = {2 Pt 2}, pages = {026310}, doi = {10.1103/PhysRevE.66.026310}, pmid = {12241288}, issn = {1539-3755}, abstract = {The propagation of turbulent premixed flames influenced by the intrinsic hydrodynamic flame instability (the Darrieus-Landau instability) is considered in a two-dimensional case using the model nonlinear equation proposed recently by Bychkov [Phys. Rev. Lett. 84, 6122 (2000)]. The nonlinear equation takes into account both the influence of external turbulence and the intrinsic properties of a flame front, such as small but finite flame thickness and realistically large density variations across the flame front. Dependence of the flame velocity on the turbulent length scale, turbulent intensity, and density variations is investigated in the case of weak nonlinearity and weak external turbulence. It is shown that the Darrieus-Landau instability influences the flamelet velocity considerably. The obtained results are in agreement with experimental data on the turbulent burning of moderate values of the Reynolds number.}, }
@article {pmid12241226, year = {2002}, author = {Cates, ME and Head, DA and Ajdari, A}, title = {Rheological chaos in a scalar shear-thickening model.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {66}, number = {2 Pt 2}, pages = {025202}, doi = {10.1103/PhysRevE.66.025202}, pmid = {12241226}, issn = {1539-3755}, abstract = {We study a simple scalar constitutive equation for a shear-thickening material at zero Reynolds number, in which the shear stress sigma is driven at a constant shear rate gamma; and relaxes by two parallel decay processes: a nonlinear decay at a nonmonotonic rate R(sigma(1)) and a linear decay at rate lambda sigma(2). Here sigma(1,2)(t)= tau(-1)(1,2) integral (t)(0)sigma(t')exp[-(t-t')/tau(1,2)]dt' are two retarded stresses. For suitable parameters, the steady state flow curve is monotonic but unstable; this arises when tau(2)>tau(1) and 0>R'(sigma)>-lambda so that monotonicity is restored only through the strongly retarded term (which might model a slow evolution of the material structure under stress). Within the unstable region we find a period-doubling sequence leading to chaos. Instability, but not chaos, persists even for the case tau(1)-->0. A similar generic mechanism might also arise in shear thinning systems and in some banded flows.}, }
@article {pmid12237479, year = {2002}, author = {Manjunatha, M and Singh, M}, title = {Digital blood flow analysis from microscopic images of mesenteric microvessel with multiple branching.}, journal = {Clinical hemorheology and microcirculation}, volume = {27}, number = {2}, pages = {91-106}, pmid = {12237479}, issn = {1386-0291}, mesh = {Animals ; Capillaries/physiology ; Cell Size ; Erythrocytes/cytology ; Image Processing, Computer-Assisted/*methods ; Microcirculation ; Microscopy, Video/*methods ; Ranidae ; Regional Blood Flow ; *Splanchnic Circulation ; }, abstract = {Blood flow through frog mesenteric microvessel with multiple branching, at Reynolds number 0.022, is analyzed. After pre-processing the images the velocity and erythrocyte distribution profiles by image velocimetry and axial tomography are obtained, respectively. The vascular parameters and shape descriptors are obtained by image processing techniques. The axial velocity shows the variation around branching areas associated with an increase in radial velocity, which is up to 10% of axial velocity. From the erythrocyte distribution profiles at various locations in the microvessel the tomograms are reconstructed. Based on these the contours of equal concentration are reconstructed. From these contours the point-to-point variation in cell concentration throughout the microvessel is observed and regions where the cellular concentration varies from 3 to 5%, at zero axial velocity, are identified. The change in erythrocyte shape, determined by the shape descriptors, while passing through the capillary is significant. This passage of cells, depending on their orientation, also displaces the capillary walls by 1.5 to 2.5 microm.}, }
@article {pmid12236369, year = {2002}, author = {Costin, CD and Synovec, RE}, title = {A microscale-molecular weight sensor: probing molecular diffusion between adjacent laminar flows by refractive index gradient detection.}, journal = {Analytical chemistry}, volume = {74}, number = {17}, pages = {4558-4565}, doi = {10.1021/ac020143z}, pmid = {12236369}, issn = {0003-2700}, abstract = {A detection scheme that measures the refractive index gradient (RIG) between adjacent laminar flows in a microfluidic device has been used to develop a microscale-molecular weight sensor. The behavior of low Reynolds number flows has been well documented and shows that molecular transport (mixing) between adjacent laminar flows occurs by molecular diffusion between flow boundaries. A diode laser beam, incident upon and illuminating the entire width of a microchannel, measured the transverse concentration gradient at two different positions along a microchannel. The concentration gradient is impacted by the transverse diffusion from a flow with analyte into a flow initially without analyte. The RIG that forms as analyte diffuses from one adjacent flow to the other causes the laser beam, impinging orthogonal to the RIG through the microchannel, to be deflected. The angle of deflection is then monitored on a position-sensitive detector (PSD) at two different positions along the axis of flow to provide a measurement of analyte diffusion. The two positions are just after the flow initially without analyte merges with the flow initially containing all of the analyte (upstream) and then after the two streams have had more time to diffuse together (downstream). The ratio of the PSD signals obtained at the two positions along the flow, downstream signal divided by the upstream signal, is readily correlated to the analyte diffusion coefficient and, thus, the analyte molecular weight for a given class of compounds. The device was evaluated as a molecular weight sensor for poly(ethylene glycol) (PEG) solutions over a molar mass range from 106 to 22,800 g/mol. The ratio signal was found to be both independent of PEG concentration and sensitive to molecular weight changes for samples ranging from 960 to 22,800 g/mol. Independence of concentration is important for obtaining a reliable molecular weight measurement. The limit of detection for 11,840 g/mol PEG measured at the upstream detection position was determined to be 56 ppm, equivalent to 4.5 x 10(-6) RI (3sigma). This technique provides a much needed universal detection method, without requiring analyte derivatization chemistry (e.g., fluorescence), for microfluidic analyses that are becoming increasingly useful in monitoring chemical systems such as continuous-flow reactors or batch polymerization processes. Thus, the molecular weight determination capability is potentially applicable to other compound classes, such as DNA or proteins.}, }
@article {pmid12231285, year = {2002}, author = {Majdalani, J and Zhou, C and Dawson, CA}, title = {Two-dimensional viscous flow between slowly expanding or contracting walls with weak permeability.}, journal = {Journal of biomechanics}, volume = {35}, number = {10}, pages = {1399-1403}, doi = {10.1016/s0021-9290(02)00186-0}, pmid = {12231285}, issn = {0021-9290}, mesh = {Computer Simulation ; Elasticity ; *Models, Biological ; Peristalsis/physiology ; Permeability ; Pulsatile Flow/physiology ; Rheology/*methods ; Viscosity ; }, abstract = {Since the transport of biological fluids through contracting or expanding vessels is characterized by low seepage Reynolds numbers, the current study focuses on the viscous flow driven by small wall contractions and expansions of two weakly permeable walls. The scope is limited to two-dimensional symmetrical solutions inside a simulated channel with moving porous walls. In seeking an exact solution, similarity transformations are used in both space and time. The problem is first reduced to a nonlinear differential equation that is later solved both numerically and analytically. The analytical procedure is based on double perturbations in the permeation Reynolds number R and the wall expansion ratio alpha. Results are correlated and compared via variations in R and alpha. Under the auspices of small [R] and [alpha], the analytical result constitutes a practical equivalent to the numerical solution. We find that, when suction is coupled with wall contraction, rapid flow turning is precipitated near the wall where the boundary layer is formed. Conversely, when injection is paired with wall expansion, the flow adjacent to the wall is delayed. In this case, the viscous boundary layer thickens as injection or expansion rates are reduced. Furthermore, the pressure drop along the plane of symmetry increases when the rate of contraction is increased and when either the rate of expansion or permeation is reduced. As nonlinearity is retained, our solutions are valid from a large cross-section down to the state of a completely collapsed system.}, }
@article {pmid12230199, year = {2002}, author = {Fang, Y and Hozalski, RM and Clapp, LW and Novak, PJ and Semmens, MJ}, title = {Passive dissolution of hydrogen gas into groundwater using hollow-fiber membranes.}, journal = {Water research}, volume = {36}, number = {14}, pages = {3533-3542}, doi = {10.1016/s0043-1354(02)00046-5}, pmid = {12230199}, issn = {0043-1354}, mesh = {Biodegradation, Environmental ; Chlorine Compounds/*metabolism ; Hydrogen/*chemistry ; Membranes, Artificial ; Solubility ; Solvents/*metabolism ; Water Movements ; Water Pollutants/*metabolism ; Water Purification/*methods ; }, abstract = {A new hollow-fiber membrane remediation system has recently been developed to passively supply groundwater with dissolved hydrogen (H2) to stimulate the biodegradation of chlorinated solvents. Understanding the mass transfer behavior of membranes under conditions of creeping flow is critical for the design of such systems. Therefore, the objectives of this research were to evaluate the gas transfer behavior of hollow-fiber membranes under conditions typical of groundwater flow and to assess the effect of membrane configuration on gas transfer performance. Membrane gas transfer was evaluated using laboratory-scale glass columns operated at low flow velocities (8.6-12,973 cm/d). H2 was supplied to the inside of the membrane fibers while water flowed on the outside and normal to the fibers (i.e. cross-flow). Membrane configuration (single fiber and fabric) and membrane spacing for the fabric modules did not affect gas transfer performance. Therefore, the results from all of the experiments were combined to obtain the following dimensionless Sherwood number (Sh) correlation expressed as a function of Reynolds number (Re) and Schmidt number (Sc): Sh = 0.824Re(0.39)Sc(0.33) (0.0004<Re<0.6). This correlation is useful for predicting the rate of transfer of any gas from clean membranes to flowing water at low Re. This correlation provides a basis for estimating the membrane surface area requirements for groundwater remediation as illustrated by a simple example.}, }
@article {pmid12228727, year = {2002}, author = {Balkovsky, E and Shraiman, BI}, title = {Olfactory search at high Reynolds number.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {99}, number = {20}, pages = {12589-12593}, pmid = {12228727}, issn = {0027-8424}, mesh = {Algorithms ; Animals ; Likelihood Functions ; Monte Carlo Method ; Moths ; Olfactory Pathways/*physiology ; Physics/*methods ; Time Factors ; }, abstract = {Locating the source of odor in a turbulent environment-a common behavior for living organisms-is nontrivial because of the random nature of mixing. Here we analyze the statistical physics aspects of the problem and propose an efficient strategy for olfactory search that can work in turbulent plumes. The algorithm combines the maximum likelihood inference of the source position with an active search. Our approach provides the theoretical basis for the design of olfactory robots and the quantitative tools for the analysis of the observed olfactory search behavior of living creatures (e.g., odor-modulated optomotor anemotaxis of moths).}, }
@article {pmid12225087, year = {2002}, author = {Renner, Ch and Peinke, J and Friedrich, R and Chanal, O and Chabaud, B}, title = {Universality of small scale turbulence.}, journal = {Physical review letters}, volume = {89}, number = {12}, pages = {124502}, doi = {10.1103/PhysRevLett.89.124502}, pmid = {12225087}, issn = {0031-9007}, abstract = {The proposed universality of small scale turbulence is investigated for a set of measurements in a cryogenic free jet with a variation of the Reynolds number (Re) from 8500 to 10(6) (max(R(lambda) approximately 1200). The traditional analysis of the statistics of velocity increments by means of structure functions or probability density functions is replaced by a new method which is based on the theory of Markov processes. It gives access to a more complete characterization by means of joint probabilities of finding velocity increments at several scales. Based on this more comprehensive method, our results are very far from a possible universal state, even for R(lambda) above 1000.}, }
@article {pmid12220077, year = {2002}, author = {Lieber, BB and Livescu, V and Hopkins, LN and Wakhloo, AK}, title = {Particle image velocimetry assessment of stent design influence on intra-aneurysmal flow.}, journal = {Annals of biomedical engineering}, volume = {30}, number = {6}, pages = {768-777}, doi = {10.1114/1.1495867}, pmid = {12220077}, issn = {0090-6964}, mesh = {Alloys/therapeutic use ; Blood Flow Velocity ; *Cerebrovascular Circulation ; Equipment Design ; Hemorheology/*instrumentation/methods ; Humans ; Intracranial Aneurysm/*physiopathology/*surgery ; Models, Cardiovascular ; Pulsatile Flow ; Sensitivity and Specificity ; *Stents ; }, abstract = {Endovascular stenting appears to be an appealing treatment modality to selected complex intracranial aneurysms. However, stents currently used for endovascular treatment are not specifically designed for the cerebrovasculature. Stent parameters, such as porosity and filament size, have to be carefully optimized for long-term successful treatment. We investigated the influence of the stent filament size on the intraaneurysmal flow dynamics in a sidewall aneurysm model in vitro. Three helical stents with 76% porosity but different filament sizes of 178, 153, and 127 microm were studied using particle image velocimetry. Twenty-four pulsatile flow conditions were investigated. The results show that stenting significantly reduces intra-aneurysmal vorticity and the mean circulation inside the aneurysm is reduced to less than 3% of its value before stenting. For constant porosity, a further reduction of the mean circulation, up to 30% can be obtained by reducing the filament diameter. For a constant Womersley number, this further reduction is accentuated with increase in the peak Reynolds number. Further reduction in the mean circulation inside the aneurysm was not achieved for the 127 microm stent. With further reduction in filament diameter, the helical stent filaments positioned against the aneurysm neck started wavering with the flow transferring added momentum into the aneurysm. For stents of smaller filament diameter, a supporting ultrastructure is required.}, }
@article {pmid12216631, year = {2002}, author = {Horn, H and Wäsche, S and Hempel, DC}, title = {Simulation of biofilm growth, substrate conversion and mass transfer under different hydrodynamic conditions.}, journal = {Water science and technology : a journal of the International Association on Water Pollution Research}, volume = {46}, number = {1-2}, pages = {249-252}, pmid = {12216631}, issn = {0273-1223}, mesh = {Biofilms ; Biomass ; *Bioreactors ; Electrodes ; *Models, Theoretical ; Population Dynamics ; *Waste Disposal, Fluid ; Water Movements ; }, abstract = {The hydrodynamic conditions and the substrate load in biofilm systems are two main parameters which influence the biofilm growth in particular the structure, density and thickness. In a long term study on heterotrophic biofilms in biofilm tube reactors the investigation has focussed on mass transfer at the bulk/biofilm interface, the biofilm density and the substrate conversion rates. To study the mass transfer phenomena at the bulk/biofilm interface oxygen profiles have been measured directly in tube reactors with microelectrodes. Microelectrode studies, substrate conversion rates and biofilm densities were used to formulate model equations for the simulation of biofilm growth under different hydrodynamic and substrate conditions. It can be shown that the mass transfer at any time is strongly coupled with the growth conditions during the biofilm cultivation. On the one side the calculated Sherwood numbers were coupled to the present hydraulic conditions, on the other side in addition the growth conditions such as growth rate and Reynolds number during biofilm cultivation were considered.}, }
@article {pmid12199603, year = {2002}, author = {Mengeaud, V and Josserand, J and Girault, HH}, title = {Mixing processes in a zigzag microchannel: finite element simulations and optical study.}, journal = {Analytical chemistry}, volume = {74}, number = {16}, pages = {4279-4286}, doi = {10.1021/ac025642e}, pmid = {12199603}, issn = {0003-2700}, mesh = {Equipment Design/methods ; Finite Element Analysis ; Microchemistry/*instrumentation ; Miniaturization ; Rheology ; }, abstract = {A finite element model has been used in order to study the mixing process of species in a 100-microm-wide zigzag microchannel integrating a "Y" inlet junction. The distribution of the concentration was obtained by solving successively the Navier-Stokes equation and the diffusion-convection equation in the steady state form. Because of the large range of Reynolds numbers studied (1 < Re < 800), the 2D diffusion-convection simulations are carried out with high diffusion coefficients. The results illustrated the effects of both flow rate and channel geometry on hydrodynamics and mixing efficiency. Below a critical Reynolds number of approximately 80, the mixing is entirely ensured by molecular diffusion. For higher Reynolds numbers, simulations revealed the mixing contribution of laminar flow recirculations. This effect increases for lower values of diffusion coefficients. Experimental studies on the mixing of species at different flow rates are reported showing the same hydrodynamic tendency.}, }
@article {pmid12188827, year = {2002}, author = {Lam, S and Shang, XD and Zhou, SQ and Xia, KQ}, title = {Prandtl number dependence of the viscous boundary layer and the Reynolds numbers in Rayleigh-Bénard convection.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {65}, number = {6 Pt 2}, pages = {066306}, doi = {10.1103/PhysRevE.65.066306}, pmid = {12188827}, issn = {1539-3755}, abstract = {We report results from high Prandtl number turbulent thermal convection experiments. The viscous boundary layer and the Reynolds number are measured in four different fluids over wide ranges of the Prandtl number Pr and the Rayleigh number Ra, all in a single convection cell of unity aspect ratio. We find that the normalized viscous layer thickness may be represented as delta(v)/L=0.65Pr(0.24)Ra(-0.16). The Reynolds number based on the oscillation frequency of the large-scale flow is found as Re(o)(Ra,Pr)=1.1Ra(0.43)Pr(-0.76) and that based on the rms velocity Re(rms)(Ra,Pr)=0.84Ra(0.40)Pr-0.86. Both the Ra and the Pr exponents of Re(V(m))(Ra,Pr) based on the maximum velocity of the circulating wind appear to vary across the range of Pr covered, changing from 0.5 to 0.68 and -0.88 to -0.95, respectively, as Pr is increased from 6 to 1027.}, }
@article {pmid12188822, year = {2002}, author = {Tabeling, P and Willaime, H}, title = {Transition at dissipative scales in large-Reynolds-number turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {65}, number = {6 Pt 2}, pages = {066301}, doi = {10.1103/PhysRevE.65.066301}, pmid = {12188822}, issn = {1539-3755}, abstract = {Among the available diagnostics of turbulence, the flatness of the velocity derivatives is particularly interesting because it represents a straightforward test of Kolmogorov theory, and provides a quantitative estimate for intermittency effects. It is commonly considered that the flatness factor increases with the Reynolds number, following a power law at high Reynolds numbers. At variance with this picture, evidence for a transitional behavior, taking place around the Taylor microscale Reynolds number R(lambda)=700, has been recently obtained in several experiments. In the present paper we study this transition in detail, and show it has the characteristics of a second order phase transition. We propose a physical picture for this transition, based on worm vortex breakdown, which leads as to suggest that intense sub-Kolmogorov structures might develop above the transition point. These results indicate that the existence of an asymptotic state at infinite Reynolds number may become questionable and more generally, that our current views on dissipative range intermittency probably need to be revised}, }
@article {pmid12188204, year = {2002}, author = {Shahcheraghi, N and Dwyer, HA and Cheer, AY and Barakat, AI and Rutaganira, T}, title = {Unsteady and three-dimensional simulation of blood flow in the human aortic arch.}, journal = {Journal of biomechanical engineering}, volume = {124}, number = {4}, pages = {378-387}, doi = {10.1115/1.1487357}, pmid = {12188204}, issn = {0148-0731}, mesh = {Adolescent ; Aorta, Thoracic/diagnostic imaging/*physiology ; Blood Flow Velocity ; Blood Pressure ; Brachiocephalic Trunk/diagnostic imaging/*physiology ; Carotid Artery, Common/diagnostic imaging/*physiology ; Computer Simulation ; *Hemodynamics ; Humans ; Imaging, Three-Dimensional/methods ; *Models, Cardiovascular ; Pulsatile Flow ; Radiography ; Sensitivity and Specificity ; Stress, Mechanical ; Subclavian Artery/diagnostic imaging/*physiology ; }, abstract = {A three-dimensional and pulsatile blood flow in a human aortic arch and its three major branches has been studied numerically for a peak Reynolds number of 2500 and a frequency (or Womersley) parameter of 10. The simulation geometry was derived from the three-dimensional reconstruction of a series of two-dimensional slices obtained in vivo using CAT scan imaging on a human aorta. The numerical simulations were obtained using a projection method, and a finite-volume formulation of the Navier-Stokes equations was used on a system of overset grids. Our results demonstrate that the primary flow velocity is skewed towards the inner aortic wall in the ascending aorta, but this skewness shifts to the outer wall in the descending thoracic aorta. Within the arch branches, the flow velocities were skewed to the distal walls with flow reversal along the proximal walls. Extensive secondary flow motion was observed in the aorta, and the structure of these secondary flows was influenced considerably by the presence of the branches. Within the aorta, wall shear stresses were highly dynamic, but were generally high along the outer wall in the vicinity of the branches and low along the inner wall, particularly in the descending thoracic aorta. Within the branches, the shear stresses were considerably higher along the distal walls than along the proximal walls. Wall pressure was low along the inner aortic wall and high around the branches and along the outer wall in the ascending thoracic aorta. Comparison of our numerical results with the localization of early atherosclerotic lesions broadly suggests preferential development of these lesions in regions of extrema (either maxima or minima) in wall shear stress and pressure.}, }
@article {pmid12186711, year = {2002}, author = {Finol, EA and Amon, CH}, title = {Flow-induced wall shear stress in abdominal aortic aneurysms: Part II--pulsatile flow hemodynamics.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {5}, number = {4}, pages = {319-328}, doi = {10.1080/1025584021000009751}, pmid = {12186711}, issn = {1025-5842}, mesh = {Aorta, Abdominal/*physiopathology ; Aortic Aneurysm, Abdominal/*physiopathology ; Blood Flow Velocity ; Blood Pressure ; *Computer Simulation ; Elasticity ; Fourier Analysis ; Hemodynamics ; Humans ; *Models, Cardiovascular ; *Pulsatile Flow ; Sensitivity and Specificity ; Statistics as Topic ; Stress, Mechanical ; Systole/physiology ; }, abstract = {In continuing the investigation of AAA hemodynamics, unsteady flow-induced stresses are presented for pulsatile blood flow through the double-aneurysm model described in Part I. Physiologically realistic aortic blood flow is simulated under pulsatile conditions for the range of time-average Reynolds numbers 50< or =Re(m) < or =300. Hemodynamic disturbance is evaluated for a modified set of indicator functions which include wall pressure (p(w)), wall shear stress (tau(w)), Wall Shear Stress Gradient (WSSG), time-average wall shear stress (tau(w)*), and time-average Wall Shear Stress Gradient WSSG*. At peak flow, the highest shear stress and WSSG levels are obtained at the distal end of both aneurysms, in a pattern similar to that of steady flow. The maximum values of wall shear stresses and wall shear stress gradients are evaluated as a function of the time-average Reynolds number resulting in a fourth order polynomial correlation. A comparison between numerical predictions for steady and pulsatile flow is presented, illustrating the importance of considering time-dependent flow for the evaluation of hemodynamic indicators.}, }
@article {pmid12186710, year = {2002}, author = {Finol, EA and Amon, CH}, title = {Flow-induced wall shear stress in abdominal aortic aneurysms: Part I--steady flow hemodynamics.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {5}, number = {4}, pages = {309-318}, doi = {10.1080/1025584021000009742}, pmid = {12186710}, issn = {1025-5842}, mesh = {Aorta, Abdominal/*physiopathology ; Aortic Aneurysm, Abdominal/*physiopathology ; Blood Flow Velocity ; Blood Pressure ; *Computer Simulation ; Elasticity ; Hemodynamics ; Humans ; *Models, Cardiovascular ; Sensitivity and Specificity ; Statistics as Topic ; Stress, Mechanical ; }, abstract = {Numerical predictions of blood flow patterns and hemodynamic stresses in Abdominal Aortic Aneurysms (AAAs) are performed in a two-aneurysm, axisymmetric, rigid wall model using the spectral element method. Homogeneous, Newtonian blood flow is simulated under steady conditions for the range of Reynolds numbers 10 < or =Re < or =2265. Flow hemodynamics are quantified by calculating the distributions of wall pressure (p(w)), wall shear stress (tau(w)), Wall Shear Stress Gradient (WSSG). A correlation between maximum values of hemodynamic stresses and Reynolds number is established, and the spatial distribution of WSSG is considered as a hemodynamic force that may cause damage to the arterial wall at an intermediate stage of AAA growth. The temporal distribution of hemodynamic stresses in pulsatile flow and their physical implications in AAA rupture are discussed in Part II of this paper.}, }
@article {pmid12186047, year = {2002}, author = {Zhang, Z and Mongeau, L and Frankel, SH}, title = {Broadband sound generation by confined turbulent jets.}, journal = {The Journal of the Acoustical Society of America}, volume = {112}, number = {2}, pages = {677-689}, doi = {10.1121/1.1492817}, pmid = {12186047}, issn = {0001-4966}, support = {5 R01 DC03577-02/DC/NIDCD NIH HHS/United States ; }, mesh = {*Aircraft ; Humans ; Models, Theoretical ; Noise, Transportation ; *Pitch Perception ; *Sound Spectrography ; *Speech ; Speech Acoustics ; *Voice ; }, abstract = {Sound generation by confined stationary jets is of interest to the study of voice and speech production, among other applications. The generation of sound by low Mach number, confined, stationary circular jets was investigated. Experiments were performed using a quiet flow supply, muffler-terminated rigid uniform tubes, and acrylic orifice plates. A spectral decomposition method based on a linear source-filter model was used to decompose radiated nondimensional sound pressure spectra measured for various gas mixtures and mean flow velocities into the product of (1) a source spectral distribution function; (2) a function accounting for near field effects and radiation efficiency; and (3) an acoustic frequency response function. The acoustic frequency response function agreed, as expected, with the transfer function between the radiated acoustic pressure at one fixed location and the strength of an equivalent velocity source located at the orifice. The radiation efficiency function indicated a radiation efficiency of the order (kD)2 over the planar wave frequency range and (kD)4 at higher frequencies, where k is the wavenumber and D is the tube cross sectional dimension. This is consistent with theoretical predictions for the planar wave radiation efficiency of quadrupole sources in uniform rigid anechoic tubes. The effects of the Reynolds number, Re, on the source spectral distribution function were found to be insignificant over the range 2000<Re<20000. The source spectral distribution function approximately obeyed a St(-3) power law for Strouhal number values St<0.9, and a St-5 power law for St>2.5. The influence of a reflective open tube termination on the source function spectral distribution was found to be insignificant, confirming the absence of a feedback mechanism.}, }
@article {pmid12171797, year = {2002}, author = {Kinlay, S and Grewal, J and Manuelin, D and Fang, JC and Selwyn, AP and Bittl, JA and Ganz, P}, title = {Coronary flow velocity and disturbed flow predict adverse clinical outcome after coronary angioplasty.}, journal = {Arteriosclerosis, thrombosis, and vascular biology}, volume = {22}, number = {8}, pages = {1334-1340}, doi = {10.1161/01.atv.0000024569.80106.b4}, pmid = {12171797}, issn = {1524-4636}, support = {IP50-HL-56985-01/HL/NHLBI NIH HHS/United States ; }, mesh = {*Angioplasty, Balloon, Laser-Assisted ; Blood Flow Velocity/*physiology ; Coronary Artery Disease/*etiology ; Coronary Circulation/*physiology ; Coronary Restenosis/*etiology ; Coronary Stenosis/pathology/physiopathology/*surgery ; Follow-Up Studies ; Humans ; *Postoperative Complications/pathology/physiopathology ; Prospective Studies ; Treatment Outcome ; }, abstract = {OBJECTIVE: Laminar flow becomes disturbed at high velocities, reducing shear stress and augmenting vascular inflammation and proliferation, processes that are pivotal in restenosis and atherogenesis. We hypothesized that disturbed blood flow after coronary angioplasty is associated with adverse long-term clinical outcome.<br><br>METHODS AND RESULTS: The cineangiograms from 97 patients undergoing laser-assisted coronary angioplasty were analyzed. Coronary blood flow velocity, the residual lesion dimensions, and the Reynolds number (an index of disturbed flow) were measured by using a frame-counting technique and quantitative coronary angiography. Cox proportional hazards were used to assess the relative risk of adverse events (target-vessel revascularization, myocardial infarction, or death) over a mean 2.5 years after the index procedure. There were 41 adverse events during 245 patient years of follow-up (17% per year of follow-up). The risk of an adverse event was increased for patients with a high flow velocity (>250 mm/s; relative risk 2.5, 95% CI 1.3 to 4.7) or a high Reynolds number (>200) at the stenosis inlet (relative risk 2.1, 95% CI 1.1 to 4.1) at the end of the procedure. Adjustment for other factors did not alter these results.<br><br>CONCLUSIONS: High Reynolds numbers, indicating disturbed blood flow after coronary angioplasty, increase the risk of adverse clinical events, potentially through shear-stress-related molecular mechanisms that promote restenosis and atherogenesis.}, }
@article {pmid12171337, year = {2002}, author = {Yamauchi, T and Furui, S and Harasawa, A and Ishimura, M and Imai, T and Hayashi, T}, title = {Optimum iodine concentration of contrast material through microcatheters: hydrodynamic analysis of experimental results.}, journal = {Physics in medicine and biology}, volume = {47}, number = {14}, pages = {2511-2523}, doi = {10.1088/0031-9155/47/14/310}, pmid = {12171337}, issn = {0031-9155}, mesh = {Angiography/*instrumentation/methods ; Catheterization/*instrumentation/methods ; Contrast Media/*analysis ; Drug Delivery Systems/instrumentation/methods ; Equipment Failure Analysis/*methods ; Injections, Intra-Arterial/instrumentation/*methods ; Iodine/*analysis ; Iohexol/analysis ; Iopamidol/analysis ; Microinjections/instrumentation/methods ; Miniaturization ; Pressure ; Quality Control ; Rheology/instrumentation/*methods ; Sensitivity and Specificity ; Triiodobenzoic Acids/analysis ; Viscosity ; }, abstract = {It is important to increase the iodine delivery rate (I), that is the iodine concentration of the contrast material (C) x the flow rate of the contrast material (Q), through a catheter to obtain high quality arteriograms. The iodine delivery rate varies depending on the iodine concentration of the contrast material. The purpose of this study is to estimate the optimum iodine concentration (Copt) of contrast material (i.e. the iodine concentration at which I becomes maximum) through a microcatheter of a given length (L), inner diameter (D) and injection pressure (P). Iohexol, ioversol and iopamidol of 11-12 iodine concentrations (140-350, 160-350 or 160-370 mg cm(-3)) at 37 degrees C are used. I and Reynolds number (Re) of the flow of each contrast material through four microcatheters (0.49-0.68 mm in inner diameter, 1000-1500 mm in length) at injection pressures of 1.38, 2.76, 4.14 and 5.52 x 10(6) Pa (200, 400, 600 and 800 pounds per square inch) are obtained experimentally. The relationships between I and C and between I and Re are examined for each catheter and injection pressure. Copt is 160-280 mg cm(-3) for iohexol, 180-280 mg cm(-3) for ioversol and 200-300 mg cm(-3) for iopamidol. I becomes maximum when Re approximates the critical Reynolds number (Re approximately 2300). Utilizing this principle, we can estimate Copt and its flow rate through a microcatheter of a given L, D and P.}, }
@article {pmid12151379, year = {2002}, author = {Sunada, S and Takashima, H and Hattori, T and Yasuda, K and Kawachi, K}, title = {Fluid-dynamic characteristics of a bristled wing.}, journal = {The Journal of experimental biology}, volume = {205}, number = {Pt 17}, pages = {2737-2744}, doi = {10.1242/jeb.205.17.2737}, pmid = {12151379}, issn = {0022-0949}, mesh = {Acceleration ; Animals ; Biomechanical Phenomena ; Biophysical Phenomena ; Biophysics ; Flight, Animal/physiology ; Insecta/*anatomy &amp; histology/*physiology ; Models, Biological ; Rotation ; Wings, Animal/*anatomy &amp; histology/*physiology ; }, abstract = {Thrips fly at a chord-based Reynolds number of approximately 10 using bristled rather than solid wings. We tested two dynamically scaled mechanical models of a thrips forewing. In the bristled design, cylindrical rods model the bristles of the forewing; the solid design was identical to the bristled one in shape, but the spaces between the 'bristles' were filled in by membrane. We studied four different motion patterns: (i) forward motion at a constant forward velocity, (ii) forward motion at a translational acceleration, (iii) rotational motion at a constant angular velocity and (iv) rotational motion at an angular acceleration. Fluid-dynamic forces acting on the bristled model wing were a little smaller than those on the solid wing. Therefore, the bristled wing of a thrips cannot be explained in terms of increased fluid-dynamic forces.}, }
@article {pmid12144468, year = {2002}, author = {Aditi Simha, R and Ramaswamy, S}, title = {Hydrodynamic fluctuations and instabilities in ordered suspensions of self-propelled particles.}, journal = {Physical review letters}, volume = {89}, number = {5}, pages = {058101}, doi = {10.1103/PhysRevLett.89.058101}, pmid = {12144468}, issn = {0031-9007}, mesh = {Animals ; Behavior, Animal ; *Cell Movement ; Leukocytes/cytology ; Melanocytes/cytology ; *Models, Biological ; Movement ; }, abstract = {We construct the hydrodynamic equations for suspensions of self-propelled particles (SPPs) with spontaneous orientational order, and make a number of striking, testable predictions: (i) Nematic SPP suspensions are always absolutely unstable at long wavelengths. (ii) SPP suspensions support novel propagating modes at long wavelengths, coupling orientation, flow, and concentration. (iii) In a wave number regime accessible only in low Reynolds number systems such as bacteria, polar-ordered suspensions are invariably convectively unstable. (iv) The variance in the number N of particles, divided by the mean <N>, diverges as <N >(2/3) in polar-ordered SPP suspensions.}, }
@article {pmid12141475, year = {2002}, author = {Lorenz, M and Smith, WA}, title = {Rotodynamic pump scaling.}, journal = {ASAIO journal (American Society for Artificial Internal Organs : 1992)}, volume = {48}, number = {4}, pages = {419-430}, doi = {10.1097/00002480-200207000-00017}, pmid = {12141475}, issn = {1058-2916}, mesh = {*Equipment Design ; *Heart-Assist Devices ; Humans ; }, abstract = {Despite extensive theoretical knowledge of fluid dynamics, the design process for rotodynamic pumps still relies heavily on experimental data. One common technique is to model the design of a new pump based on the design of existing pumps, using the laws of similarity. Another, similar approach frequently used for atypically large or small pumps is to scale a final product design from conveniently sized laboratory prototypes that have been refined to the desired performance in extensive experiments. Both approaches to pump design are usually considered highly reliable. However, for blood pumps, this approach has been questioned. Due to the extremely small size of these pumps and the relatively low Reynolds Numbers, extraneous effects may overwhelm the assumptions made for similarity calculations that are satisfactory for significantly larger models. Three geometrically similar pumps with related scaling factors of 1, 3.2, and 6.4 were tested for the same range of nondimensional flow and pressure. The quality of similitude was determined by comparing the nondimensionalized pump data of the three pumps. It was found that the effects of large linear dimension scaling factors had only a small influence on the quality of similitude (maximum 5.8% error), whereas Reynolds Number effects, especially at high pump flows, had a strong impact on the quality of similitude (maximum 45.4% error). Because Reynolds Number similarity cannot always be achieved simultaneously with geometric similarity, a correction factor for Reynolds Number related departure from similarity was developed. It is based on the Reynolds Number, the Flow Coefficient, the specific speed, and the pump's relative surface roughness. Use of this correction factor reduces the error due to Reynolds Number effects to a maximum of 7.5%. We conclude that the use of scaling techniques in rotodynamic blood pump design is a valid approach, if Reynolds Number similarity is maintained or suitable correction factors are used.}, }
@article {pmid12141363, year = {2002}, author = {Ginsberg, JH}, title = {On the effect of viscosity in scattering from partially coated infinite cylinders.}, journal = {The Journal of the Acoustical Society of America}, volume = {112}, number = {1}, pages = {46-54}, doi = {10.1121/1.1479147}, pmid = {12141363}, issn = {0001-4966}, abstract = {This paper considers the two-dimensional problem of scattering of a plane wave incident on an infinite cylinder that is coated with strips of pressure-release material extending over quadrants on the illuminated and shadowed sides, with the remainder of the surface considered to be rigid. Transitions from soft to rigid surfaces correspond to discontinuous boundary conditions. Ideal fluid theory predicts an infinite pressure gradient at these transitions, which suggests that viscous effects may be significant. The present work is a quantitative analysis of the global effect on acoustic scattering of viscosity effects arising in the vicinity of the discontinuity. The analysis represents the scattered field in terms of acoustic and vortical contributions. Both contributions are represented by series expansions in terms of azimuthal harmonics and associated cylindrical wave functions. The amplitudes of these harmonics are determined by satisfying a pair of discontinuous boundary conditions. Results obtained by using the method of weighted residuals are shown to be less accurate than those obtained from a collocation procedure. The results for surface pressure and farfield directivity indicate that viscous effects are important only if the Reynolds number is extremely small.}, }
@article {pmid12122276, year = {2002}, author = {Papaharilaou, Y and Doorly, DJ and Sherwin, SJ and Peiro, J and Griffith, C and Cheshire, N and Zervas, V and Anderson, J and Sanghera, B and Watkins, N and Caro, CG}, title = {Combined MR imaging and numerical simulation of flow in realistic arterial bypass graft models.}, journal = {Biorheology}, volume = {39}, number = {3-4}, pages = {525-531}, pmid = {12122276}, issn = {0006-355X}, mesh = {*Computer Simulation ; *Coronary Artery Bypass ; Coronary Stenosis/physiopathology/surgery ; Coronary Vessels/*physiopathology ; Humans ; *Magnetic Resonance Angiography ; *Models, Cardiovascular ; Regional Blood Flow ; }, abstract = {We report methods for (a) transforming a three-dimensional geometry acquired by magnetic resonance angiography (MRA) in vivo, or by imaging a model cast, into a computational surface representation, (b) use of this to construct a three dimensional numerical grid for computational fluid dynamic (CFD) studies, and (c) use of the surface representation to produce a stereo-lithographic replica of the real detailed geometry, at a scale convenient for detailed magnetic resonance imaging (MRI) flow studies. This is applied to assess the local flow field in realistic geometry arterial bypass grafts. Results from a parallel numerical simulation and MRI measurement of flow in an aorto-coronary bypass graft with various inlet flow conditions demonstrate the strong influence of the graft inlet waveform on the perianastomotic flow field. A sinusoidal and a multi harmonic coronary flow waveform both with a mean Reynolds number (Re) of 100 and a Womersley parameter of 2.7 were applied at the graft inlet. A weak axial flow separation region just distal to the toe was found in sinusoidal flow near end deceleration (Re = 25). At the same location and approximately the same point in the cycle (Re = 30) but in coronary flow, the axial flow separation was stronger and more spatially pronounced. No axial flow separation occurred in steady flow for Re = 100. Numerical predictions indicate a region in the vicinity of the suture line (where there is a local narrowing of the graft) with a wall shear magnitude in excess of five times that associated with fully developed flow at the graft inlet.}, }
@article {pmid12122250, year = {2002}, author = {Watkins, NV and Caro, CG and Wang, W}, title = {Parallel-plate flow chamber for studies of 3D flow-endothelium interaction.}, journal = {Biorheology}, volume = {39}, number = {3-4}, pages = {337-342}, pmid = {12122250}, issn = {0006-355X}, mesh = {Arteries/physiology ; *Computer Simulation ; Endothelium, Vascular/*physiology ; Humans ; *Models, Cardiovascular ; Regional Blood Flow ; Stress, Mechanical ; }, abstract = {Flow induced shear stress influences vascular cellular biology and pathophysiology in numerous ways. Previous in vitro studies on interactions between flow and endothelial cells using parallel-plate flow chambers involve two-dimensional flows, whereas flows in larger vessels are commonly three-dimensional. We have constructed a parallel plate flow chamber with a backward facing step aligned oblique to the axis of the chamber. Flow visualisation by steady injection of ink through a hypodermic tube reveals swirling flow in the recirculation region downstream of the step. At given angles of the step, theta; (to the axis of the chamber), the pitch of the swirl and the width of the separation region, as measured in the direction perpendicular to the step, increase with the Reynolds number (Re). On the other hand, at given values of Re, reduction of theta; results in increases in the swirl pitch but decreases in the width of the separation zone. Furthermore, clearance time of ink from the separation region is shorter with an oblique step than a perpendicular one at given Re. Computer simulation confirms the 3D swirling flow created by the oblique step and provides detailed distribution of wall shear stresses in the flow chamber.}, }
@article {pmid12119385, year = {2002}, author = {Tsuda, A and Rogers, RA and Hydon, PE and Butler, JP}, title = {Chaotic mixing deep in the lung.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {99}, number = {15}, pages = {10173-10178}, pmid = {12119385}, issn = {0027-8424}, support = {R01 HL054885/HL/NHLBI NIH HHS/United States ; HL-54885/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; In Vitro Techniques ; Kinetics ; Lung/cytology/*physiology ; Models, Biological ; Nonlinear Dynamics ; Pulmonary Alveoli/physiology ; Rats ; Rats, Sprague-Dawley ; Respiration, Artificial ; Time Factors ; }, abstract = {Our current understanding of the transport and deposition of aerosols (viruses, bacteria, air pollutants, aerosolized drugs) deep in the lung has been grounded in dispersive theories based on untested assumptions about the nature of acinar airflow fields. Traditionally, these have been taken to be simple and kinematically reversible. In this article, we apply the recently discovered fluid mechanical phenomenon of irreversible low-Reynolds number flow to the lung. We demonstrate, through flow visualization studies in rhythmically ventilated rat lungs, that such a foundation is false, and that chaotic mixing may be key to aerosol transport. We found substantial alveolar flow irreversibility with stretched and folded fractal patterns, which lead to a sudden increase in mixing. These findings support our theory that chaotic alveolar flow--characterized by stagnation saddle points associated with alveolar vortices--governs gas kinematics in the lung periphery, and hence the transport, mixing, and ultimately the deposition of fine aerosols. This mechanism calls for a rethinking of the relationship of exposure and deposition of fine inhaled particles.}, }
@article {pmid12059477, year = {2002}, author = {Morrison, JF and Jiang, W and McKeon, BJ and Smits, AJ}, title = {Reynolds number dependence of streamwise velocity spectra in turbulent pipe flow.}, journal = {Physical review letters}, volume = {88}, number = {21}, pages = {214501}, doi = {10.1103/PhysRevLett.88.214501}, pmid = {12059477}, issn = {0031-9007}, abstract = {Spectra of the streamwise velocity component in fully developed turbulent pipe flow are presented for Reynolds numbers up to 5.7x10(6). Even at the highest Reynolds number, streamwise velocity spectra exhibit incomplete similarity only: while spectra collapse with both classical inner and outer scaling for limited ranges of wave number, these ranges do not overlap. Thus similarity may not be described as complete, and a region varying with the inverse of the streamwise wave number, k(1), is not expected, and any apparent k(-1)(1) range does not attract any special significance and does not involve a universal constant. Reasons for this are suggested.}, }
@article {pmid12000801, year = {2002}, author = {Usherwood, JR and Ellington, CP}, title = {The aerodynamics of revolving wings II. Propeller force coefficients from mayfly to quail.}, journal = {The Journal of experimental biology}, volume = {205}, number = {Pt 11}, pages = {1565-1576}, doi = {10.1242/jeb.205.11.1565}, pmid = {12000801}, issn = {0022-0949}, mesh = {Animals ; Bees/*anatomy &amp; histology ; Biomechanical Phenomena ; Coturnix/*anatomy &amp; histology ; Flight, Animal/physiology ; Insecta/*anatomy &amp; histology ; Male ; Models, Biological ; Moths/*anatomy &amp; histology ; Wings, Animal/*anatomy &amp; histology/*physiology ; }, abstract = {High force coefficients, similar to those observed for revolving model hawkmoth wings in the accompanying paper (for which steady leading-edge vortices are directly observed), are apparent for revolving model (mayfly, bumblebee and quail) and real (quail) animal wings ranging in Reynolds number (Re) from 1100 to 26000. Results for bumblebee and hawkmoth wings agree with those published previously for Drosophila (Re approximately 200). The effect of aspect ratio is also tested with planforms based on hawkmoth wings adjusted to aspect ratios ranging from 4.53 to 15.84 and is shown to be relatively minor, especially at angles of incidence below 50 degrees. The normal force relationship introduced in the accompanying paper is supported for wings over a large range of aspect ratios in both 'early' and 'steady' conditions; local induced velocities appear not to affect the relationship.}, }
@article {pmid11970596, year = {1999}, author = {Boyer, D}, title = {Critical behavior of vorticity in two-dimensional turbulence.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {60}, number = {6 Pt A}, pages = {6769-6775}, doi = {10.1103/physreve.60.6769}, pmid = {11970596}, issn = {1063-651X}, abstract = {We point out some similarities between the statistics of high Reynolds number turbulence and critical phenomena. An analogy is developed for two-dimensional decaying flows, in particular by studying the scaling properties of the two-point vorticity correlation function within a simple phenomenological framework. The inverse of the Reynolds number is the analog of the small parameter that separates the system from criticality. It is possible to introduce a set of three critical exponents; for the correlation length, the autocorrelation function, and the so-called susceptibility, respectively. The exponents corresponding to the well-known enstrophy cascade theory of Kraichnan and Batchelor are, remarkably, the same as the Gaussian approximation exponents for spin models. The limitations of the analogy, in particular the lack of universal scaling functions, are also discussed.}, }
@article {pmid11970530, year = {1999}, author = {Shiau, YH and Peng, YF and Hwang, RR and Hu, CK}, title = {Multistability and symmetry breaking in the two-dimensional flow around a square cylinder.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {60}, number = {5 Pt B}, pages = {6188-6191}, doi = {10.1103/physreve.60.6188}, pmid = {11970530}, issn = {1063-651X}, abstract = {We use numerical methods to study two-dimensional flow passing a square cylinder at low Reynolds numbers, and observe period-1 and -3 vortices behind the cylinder at the same Reynolds number Re. When Re increases from a small number to a critical value Re(c) approximately equal to 320, the system could change from bistability, which maintains the spatial symmetry, to tristability, which breaks the spatial symmetry. Our results suggest many interesting problems for further studies.}, }
@article {pmid11970423, year = {1999}, author = {Almeida, MP and Andrade, JS and Buldyrev, SV and Cavalcante, FS and Stanley, HE and Suki, B}, title = {Fluid flow through ramified structures.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {60}, number = {5 Pt A}, pages = {5486-5494}, doi = {10.1103/physreve.60.5486}, pmid = {11970423}, issn = {1063-651X}, abstract = {We investigate the fluid flow through two-dimensional ramified structures by direct simulation of the Navier-Stokes equations. We show that for trees with n generations, the flow distribution strongly depends on the Reynolds number Re. Specifically, for a tree without loops the flow becomes highly heterogeneous at high Re. For a tree with loops, on the other hand, the flow distribution tends to be more uniform at increased Re conditions. We show that these apparently contradictory behaviors have the same origin, namely, the effect of inertia on the momentum transport in the channels of the ramified geometry. In order to simulate the propagation of the flow imbalance throughout the tree without loops, we develop a simple model that incorporates the basic fluid dynamics features of the system. For large trees, the results of the model indicate that the distribution of flow at the outlet branches can be described by a self-affine landscape. Finally, we argue that the nonuniform partitioning of flow found for the structure without loops may contribute to the morphogenesis and functioning of the bronchial tree.}, }
@article {pmid11970369, year = {1999}, author = {Rasmussen, HO}, title = {Diameters of vortex spirals in three-dimensional turbulence.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {60}, number = {4 Pt B}, pages = {4978-4979}, doi = {10.1103/physreve.60.4978}, pmid = {11970369}, issn = {1063-651X}, abstract = {It has been proposed by a number of authors that fully developed turbulence contains spiral-like vorticity distributions that wrap up around strained vortex tubes, but numerical simulations seem to show otherwise. In the present paper, we suggest an explanation for the numerical results. Using stability considerations and numerical results for the Reynolds numbers of the most intense vortex tubes, we obtain an estimate for the characteristic diameter of the largest spirals as a function of the Reynolds number. We find that this diameter decreases rapidly, relative to the integral scale, as the Reynolds number tends to infinity.}, }
@article {pmid11970174, year = {1999}, author = {Pinton, JF and Holdsworth, PC and Labbé, R}, title = {Power fluctuations in a closed turbulent shear flow.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {60}, number = {3}, pages = {R2452-5}, doi = {10.1103/physreve.60.r2452}, pmid = {11970174}, issn = {1063-651X}, abstract = {We study experimentally the power consumption P of a confined turbulent flow at constant Reynolds number Re. We analyze in details its temporal dynamics and statistical properties, in a setup that covers two decades in Reynolds numbers. We show that nontrivial power fluctuations occur over a wide range of amplitudes and that they involve coherent fluid motions over the entire system size. As a result, the power fluctuations do not result from averaging of independent subsystems and its probability density function Pi(P) is strongly non-Gaussian. The shape of Pi(P) is Reynolds number independant and we show that the relative intensity of fluctuations decreases very slowly as Re increases. These results are discussed in terms of an analogy with critical phenomena.}, }
@article {pmid11970160, year = {1999}, author = {Qian, J}, title = {Slow decay of the finite Reynolds number effect of turbulence.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {60}, number = {3}, pages = {3409-3412}, doi = {10.1103/physreve.60.3409}, pmid = {11970160}, issn = {1063-651X}, abstract = {The third-order structure function is used to study the finite Reynolds number (FRN) effect of turbulence, which refers to the deviation of turbulence statistics observed at finite Reynolds numbers from predictions of the Kolmogorov theories. It is found that the FRN effect decreases as CR(-mu)(lambda), when R(lambda) is high, and mu < or = 6/5. Here R(lambda) is the Taylor-microscale Reynolds number and C is a constant independent of R(lambda). From the exact spectral equations, the decay exponent mu and the constant C are determined for typical fully developed turbulent flows (freely decaying isotropic turbulence and shear flow turbulence), so that the quantitative prediction of the FRN effect is feasible.}, }
@article {pmid11970151, year = {1999}, author = {Verberg, R and Ladd, AJ}, title = {Simulation of low-Reynolds-number flow via a time-independent lattice-Boltzmann method.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {60}, number = {3}, pages = {3366-3373}, doi = {10.1103/physreve.60.3366}, pmid = {11970151}, issn = {1063-651X}, abstract = {We present a numerical method to solve the equations for low-Reynolds-number (Stokes) flow in porous media. The method is based on the lattice-Boltzmann approach, but utilizes a direct solution of time-independent equations, rather than the usual temporal evolution to steady state. Its computational efficiency is 1-2 orders of magnitude greater than the conventional lattice-Boltzmann method. The convergence of the permeability of random arrays of spheres has been analyzed as a function of mesh resolution at several different porosities. For sufficiently large spheres, we have found that the convergence is quadratic in the mesh resolution.}, }
@article {pmid11970101, year = {1999}, author = {Vincent, AP and Yuen, DA}, title = {Plumes and waves in two-dimensional turbulent thermal convection.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {60}, number = {3}, pages = {2957-2963}, doi = {10.1103/physreve.60.2957}, pmid = {11970101}, issn = {1063-651X}, abstract = {We have conducted a high-resolution, two-dimensional direct numerical simulation of Rayleigh-Bénard convection with stress-free and periodic boundary conditions at a Rayleigh (Ra) number of 10(8) and Prandtl (Pr) number of unity. An aspect-ratio three box has been considered. A single cell has been used as the initial condition. First, the flow develops into time-dependent convection with a strong asymmetry and highly convoluted thermal plumes delineating a large-scale circulation. Smaller thermal plumes detach from the boundary layer and extend over the entire cell, creating a local inversion of the temperature gradient adjacent to the boundary layers. Then the conditions leading to the formation of internal waves are fulfilled, as the local Richardson number decreases sufficiently small to cross the linear threshold of Ri=0.25. Together with the strong shear, convective rolls with a Kelvin-Helmholtz wavelike character are produced. The secondary boundary layer itself becomes unstable and produces smaller plumes. At later times, the large-scale circulation is destroyed and the internal waves disappear. A Reynolds number, based on the global scale, of Re=500, is attained at this stage. Only isolated thermal plumes and vortices are present. Thus, internal waves can be generated at finite Prandtl number fluids for sufficiently high Ra in the presence of a large-scale circulation. Spectral analysis reveals that the kinetic energy decays with a logarithmic slope of -3, while the logarithmic slope of the thermal variance has a value of around -5 / 3.}, }
@article {pmid11970099, year = {1999}, author = {Kaiser, R and Tilgner, A}, title = {Kinematic dynamos surrounded by a stationary conductor.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {60}, number = {3}, pages = {2949-2952}, doi = {10.1103/physreve.60.2949}, pmid = {11970099}, issn = {1063-651X}, abstract = {We investigate kinematic dynamos in cylinders and spheres surrounded by an insulator. The flow volume is divided into an inner region, in which the conducting fluid is in motion, and an outer region enclosing the inner one, in which the conductor is at rest. The dependence of the critical magnetic Reynolds number on the thickness of the outer conducting shell is discussed as well as implications for the design of experimental dynamos.}, }
@article {pmid11970092, year = {1999}, author = {Brands, H and Maassen, SR and Clercx, HJ}, title = {Statistical-mechanical predictions and Navier-Stokes dynamics of two-dimensional flows on a bounded domain.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {60}, number = {3}, pages = {2864-2874}, doi = {10.1103/physreve.60.2864}, pmid = {11970092}, issn = {1063-651X}, abstract = {In this paper the applicability of a statistical-mechanical theory to freely decaying two-dimensional (2D) turbulence on a bounded domain is investigated. We consider an ensemble of direct numerical simulations in a square box with stress-free boundaries, with a Reynolds number that is of the same order as in experiments on 2D decaying Navier-Stokes turbulence. The results of these simulations are compared with the corresponding statistical equilibria, calculated from different stages of the evolution. It is shown that the statistical equilibria calculated from early times of the Navier-Stokes evolution do not correspond to the dynamical quasistationary states. At best, the global topological structure is correctly predicted from a relatively late time in the Navier-Stokes evolution, when the quasistationary state has almost been reached. This failure of the (basically inviscid) statistical-mechanical theory is related to viscous dissipation and net leakage of vorticity in the Navier-Stokes dynamics at moderate values of the Reynolds number.}, }
@article {pmid11969812, year = {1999}, author = {Burgess, JM and Bizon, C and McCormick, WD and Swift, JB and Swinney, HL}, title = {Instability of the Kolmogorov flow in a soap film.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {60}, number = {1}, pages = {715-721}, doi = {10.1103/physreve.60.715}, pmid = {11969812}, issn = {1063-651X}, abstract = {We examine the instability of a soap film flow driven by a time-independent force that is spatially periodic in the direction perpendicular to the forcing (Kolmogorov flow). Linear stability analysis of an idealized model of this flow predicts a critical Reynolds number R(c) is approximately equal to the square root of 2. In our soap film experiment, we find a critical value R(c) is approximately equal to 70. This discrepancy can be ascribed to frictional effects from viscous coupling of gas to the film, which is neglected in the idealized model. The kinematic viscosity of the surrounding gas and the thickness of gas layers on each side of the soap film are varied in the experiments to better understand these frictional effects. Our observations indicate that flow in the soap film cannot be decoupled from flow in the surrounding gas.}, }
@article {pmid11969790, year = {1999}, author = {Eckhardt, B and Mersmann, A}, title = {Transition to turbulence in a shear flow.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {60}, number = {1}, pages = {509-517}, doi = {10.1103/physreve.60.509}, pmid = {11969790}, issn = {1063-651X}, abstract = {We analyze the properties of a 19-dimensional Galerkin approximation to a parallel shear flow. The laminar flow with a sinusoidal shape is stable for all Reynolds numbers Re. For sufficiently large Re additional stationary flows occur; they are all unstable. The lifetimes of finite amplitude perturbations shows a fractal dependence on amplitude and Reynolds number. These findings are in accord with observations on plane Couette flow and suggest a universality of this transition scenario in shear flows.}, }
@article {pmid11969718, year = {1999}, author = {Tsuji, Y}, title = {Peak position of dissipation spectrum in turbulent boundary layers.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {59}, number = {6}, pages = {7235-7238}, doi = {10.1103/physreve.59.7235}, pmid = {11969718}, issn = {1063-651X}, abstract = {The peak locations of energy dissipation spectrum (y(+)(kp)) are investigated experimentally in the low Reynolds number (R(theta)<5000) zero-pressure-gradient turbulent boundary layers. These peaks are scaled by the relation y(+)(kp)=2(u(*)delta/nu)(1/2)=2R(1/2)(*), where u(*) is friction velocity and delta is the boundary layer thickness. They are located close to the peak positions of the Reynolds shear stress (y(+)(p)), that is, y(+)(kp) approximately equal to y(+)(p). This result predicts that the small-scale structures residing in high-energy dissipation regions concentrate around y(+)(p).}, }
@article {pmid11969663, year = {1999}, author = {Arad, I and L'vov, VS and Procaccia, I}, title = {Correlation functions in isotropic and anisotropic turbulence: the role of the symmetry group.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {59}, number = {6}, pages = {6753-6765}, doi = {10.1103/physreve.59.6753}, pmid = {11969663}, issn = {1063-651X}, abstract = {The theory of fully developed turbulence is usually considered in an idealized homogeneous and isotropic state. Real turbulent flows exhibit the effects of anisotropic forcing. The analysis of correlation functions and structure functions in isotropic and anisotropic situations is facilitated and made rational when performed in terms of the irreducible representations of the relevant symmetry group which is the group of all rotations SO(3). In this paper we first consider the needed general theory, and explain why we expect different (universal) scaling exponents in the different sectors of the symmetry group. We exemplify the theory context of isotropic turbulence (for third order tensorial structure functions) and in weakly anisotropic turbulence (for the second order structure function). The utility of the resulting expressions for the analysis of experimental data is demonstrated in the context of high Reynolds number measurements of turbulence in the atmosphere.}, }
@article {pmid11969529, year = {1999}, author = {Bena, I and Mansour, MM and Baras, F}, title = {Hydrodynamic fluctuations in the Kolmogorov flow: linear regime.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {59}, number = {5 Pt B}, pages = {5503-5510}, doi = {10.1103/physreve.59.5503}, pmid = {11969529}, issn = {1063-651X}, abstract = {The Landau-Lifshitz fluctuating hydrodynamics is used to study the statistical properties of the linearized Kolmogorov flow. The relative simplicity of this flow allows a detailed analysis of the fluctuation spectrum from near equilibrium regime up to the vicinity of the first convective instability threshold. It is shown that in the long time limit the flow behaves as an incompressible fluid, regardless of the value of the Reynolds number. This is not the case for the short time behavior where the incompressibility assumption leads in general to a wrong form of the static correlation functions, except near the instability threshold. The theoretical predictions are confirmed by numerical simulations of the full nonlinear fluctuating hydrodynamic equations.}, }
@article {pmid11969525, year = {1999}, author = {Lewis, GS and Swinney, HL}, title = {Velocity structure functions, scaling, and transitions in high-Reynolds-number Couette-Taylor flow.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {59}, number = {5 Pt B}, pages = {5457-5467}, doi = {10.1103/physreve.59.5457}, pmid = {11969525}, issn = {1063-651X}, abstract = {Flow between concentric cylinders with a rotating inner cylinder is studied for Reynolds numbers in the range 2x10(3)<R<10(6) (Taylor Reynolds numbers, 10 < R(lambda)< 290) for a system with radius ratio eta=0.724. Even at the highest Reynolds number studied, the energy spectra do not show power law scaling (i.e., there is no inertial range), and the dissipation length scale is surprisingly large. Nevertheless, the velocity structure functions calculated using extended self-similarity exhibit clear power-law scaling. The structure function exponents zeta(p) fit Kolmogorov's log-normal model within the experimental uncertainty, zeta(p)=(p/3) [1+(mu/6)(3-p)] (for p < or =10) with mu=0.27. These zeta(p) values are close to those found in other flows. Measurements of torque scaling are presented that are an order of magnitude more accurate than those previously reported [Lathrop et al., Phys Rev. A 46, 6390 (1992)]. Measurements of velocity in the fluid core reveal the presence of azimuthal traveling waves up to the highest Reynolds numbers examined. These waves show evidence of a transition at R(T)=1.3 x 10(4); this transition was observed previously in measurements of torque, but our wave velocity and wall shear stress measurements provide the first evidence from local quantities of the transition at R(T). Velocity measurements indicate that at R(T) there is a change in the coherent structures of the core flow; this is consistent with our analyses of the scaling of the torque. Our measurements were made at two aspect ratios, and no significant dependence on aspect ratio was observable for R > R(T).}, }
@article {pmid11955499, year = {2002}, author = {Bolzon, G and Pedrizzetti, G and Grigioni, M and Zovatto, L and Daniele, C and D'Avenio, G}, title = {Flow on the symmetry plane of a total cavo-pulmonary connection.}, journal = {Journal of biomechanics}, volume = {35}, number = {5}, pages = {595-608}, doi = {10.1016/s0021-9290(01)00239-1}, pmid = {11955499}, issn = {0021-9290}, mesh = {Blood Flow Velocity ; Computer Simulation ; *Heart Bypass, Right ; Heart Defects, Congenital/surgery ; Hemorheology/*methods ; Humans ; Models, Cardiovascular ; Regional Blood Flow ; }, abstract = {The flow inside a total cavo-pulmonary connection, a bypass operation of the right heart adopted in the presence of congenital malformation, is here studied for a specific geometry which has been recently introduced in clinics. The analysis has been performed by preliminary experimental observation and a novel Navier-Stokes formulation on the symmetry plane. This method, once some basic hypotheses are verified, allows to reproduce the flow on the symmetry plane of a three-dimensional field by using an extension of the two-dimensional approach. The analysis has confirmed the existence of a central vortex showing that it is not a real vortex (i.e. a place with accumulation of vorticity) but, rather, a weakly dissipative recirculating zone. It is surrounded by a shear layer that becomes spontaneously unsteady at moderately high Reynolds number. The topological changes and energy dissipation have been analysed in both cases of unbalanced and of balanced pulmonary artery and caval flows.}, }
@article {pmid11955200, year = {2002}, author = {Ishihara, T and Yoshida, K and Kaneda, Y}, title = {Anisotropic velocity correlation spectrum at small scales in a homogeneous turbulent shear flow.}, journal = {Physical review letters}, volume = {88}, number = {15}, pages = {154501}, doi = {10.1103/PhysRevLett.88.154501}, pmid = {11955200}, issn = {0031-9007}, abstract = {A simple theoretical analysis and direct numerical simulations on 512(3) grid points suggest that the velocity correlation spectrum tensor in the inertial subrange of homogeneous turbulent shear flow at high Reynolds number is given by a simple form that is an anisotropic function of the wave vector. The tensor is determined by the rate of the strain tensor of the mean flow, the rate of energy dissipation per unit mass, the wave vector, and two nondimensional constants.}, }
@article {pmid11944076, year = {2002}, author = {Sevsek, F}, title = {Shape of vesicles in flow--theoretical analysis.}, journal = {Cellular &amp; molecular biology letters}, volume = {7}, number = {1}, pages = {157-158}, pmid = {11944076}, issn = {1425-8153}, mesh = {Elasticity ; Hydrophobic and Hydrophilic Interactions ; Liposomes/*chemistry ; Mathematics ; Phospholipids/*chemistry ; Pliability ; }, abstract = {The shapes of phospholipid vesicles in a liquid flow with a low Reynolds number were calculated within the nearly spherical approximation. The effective tension model was used in the case of large tension values.}, }
@article {pmid11942523, year = {2002}, author = {Stacey, MT and Mead, KS and Koehl, MA}, title = {Molecule capture by olfactory antennules: mantis shrimp.}, journal = {Journal of mathematical biology}, volume = {44}, number = {1}, pages = {1-30}, doi = {10.1007/s002850100111}, pmid = {11942523}, issn = {0303-6812}, mesh = {Animals ; Chemoreceptor Cells/physiology ; Decapoda/*physiology ; *Models, Biological ; *Odorants ; Receptors, Odorant/physiology ; Smell/*physiology ; }, abstract = {A critical step in the process of olfaction is the movement of odorant molecules from the environment to the surface of a chemosensory structure. Many marine crustaceans capture odorant molecules with arrays of chemosensory sensilla (aesthetascs) on antennules that they flick through the water. We developed a model to calculate molecule flux to the surfaces of aesthetascs in order to study how the size, aesthetasc spacing, and flick kinematics of olfactory antennules affect their performance in capturing molecules from the surrounding water. Since the three-dimensional geometry of an aesthetasc-bearing antennule is complex, dynamically-scaled physical models can often provide an efficient method of determining the fluid velocity field through the array. Here we present a method to optimize the incorporation of such measured velocity vector fields into a numerical simulation of the advection and diffusion of odorants to aesthetasc surfaces. Furthermore, unlike earlier models of odorant interception by antennae, our model incorporates odorant concentration distributions that have been measured in turbulent ambient flows. By applying our model to the example of the olfactory antennules of mantis shrimp, we learned that flicking velocity can have profound effects on odorant flux to the aesthetascs if they operate in the speed range in which the leakiness of the gaps between the aesthetascs to fluid movement is sensitive to velocity. This sensitivity creates an asymmetry in molecule fluxes between outstroke and return stroke, which results in an antennule taking discrete samples in space and time, i.e. "sniffing". As stomatopods grow and their aesthetasc Reynolds number increases, the aesthetasc arrangement on the antennule changes in a way that maintains these asymmetries in leakiness and molecule flux between the outstroke and return stroke, allowing the individual to continue to take discrete samples as it develops.}, }
@article {pmid11934415, year = {2002}, author = {Liu, Y and So, RM and Zhang, CH}, title = {Modeling the bifurcating flow in a human lung airway.}, journal = {Journal of biomechanics}, volume = {35}, number = {4}, pages = {465-473}, doi = {10.1016/s0021-9290(01)00225-1}, pmid = {11934415}, issn = {0021-9290}, mesh = {Air Pressure ; Bronchi/anatomy &amp; histology/physiology ; Computer Simulation ; Finite Element Analysis ; Humans ; *Models, Biological ; Pulmonary Ventilation/*physiology ; Respiration ; }, abstract = {The inspiratory flow characteristics in a three-generation lung airway have been numerically investigated using a control volume method to solve the fully three-dimensional laminar Navier-Stokes equations. The three-generation airway is extracted from the fifth to seventh branches of the model of Weibel (Morphometry of the Human Lung, Academic Press, New York, Springer, Berlin, 1963) with in-plane and 90 degrees off-plane configurations. Computations are carried out in the Reynolds number range of 200-1600, corresponding to mouth-air breathing rates ranging from 0.27 to 2.16l/s, or an averaged height of a man breathing from quiet to vigorous state. Particular attention is paid to establishing relations between the Reynolds number and the overall flow characteristics, including flow patterns and pressure drop. The ratio of airflow rate through the medial branch to that of the lateral branch for an in-plane airway increases as Re(0.227). However, the total pressure drop coefficient varies as Re(-0.497) for an in-plane airway and as Re(-0.464) for an off-plane airway. These pressure drop results are in good agreement with the experimentally measured behavior of Re(-0.5) and are more accurate than the numerically determined behavior of Re(-0.61) assuming the airways to be approximated by two-dimensional channels.}, }
@article {pmid11909248, year = {2002}, author = {Dobler, W and Shukurov, A and Brandenburg, A}, title = {Nonlinear states of the screw dynamo.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {65}, number = {3 Pt 2B}, pages = {036311}, doi = {10.1103/PhysRevE.65.036311}, pmid = {11909248}, issn = {1539-3755}, abstract = {The self-excitation of magnetic field by a spiral Couette flow between two coaxial cylinders is considered. We solve numerically the fully nonlinear, three-dimensional magnetohydrodynamic (MHD) equations for magnetic Prandtl numbers P(m) (ratio of kinematic viscosity to magnetic diffusivity) between 0.14 and 10 and kinematic and magnetic Reynolds numbers up to about 2000. In the initial stage of exponential field growth (kinematic dynamo regime), we find that the dynamo switches from one distinct regime to another as the radial width delta(r)(B) of the magnetic field distribution becomes smaller than the separation of the field maximum from the flow boundary. The saturation of magnetic field growth is due to a reduction in the velocity shear resulting mainly from the azimuthally and axially averaged part of the Lorentz force, which agrees with an asymptotic result for the limit of P(m)<<1. In the parameter regime considered, the magnetic energy decreases with kinematic Reynolds number as Re-0.84, which is approximately as predicted by the nonlinear asymptotic theory (approximately Re(-1)). However, when the velocity field is maintained by a volume force (rather than by viscous stress) the dependence of magnetic energy on the kinematic Reynolds number is much weaker.}, }
@article {pmid11905556, year = {2002}, author = {Zhang, YL and Reese, JM and Gorman, DG and Madhok, R}, title = {The vibration of an artery-like tube conveying pulsatile fluid flow.}, journal = {Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine}, volume = {216}, number = {1}, pages = {1-11}, doi = {10.1243/0954411021536216}, pmid = {11905556}, issn = {0954-4119}, mesh = {Aorta/*physiology ; Biomedical Engineering ; Blood Flow Velocity ; *Hemodynamics ; Humans ; Materials Testing ; Models, Cardiovascular ; Models, Statistical ; Nonlinear Dynamics ; *Prostheses and Implants ; Pulse ; United Kingdom ; *Vibration ; }, abstract = {A hybrid method for investigating pulsatile fluid flow in a long, thin, artery-like tube subjected to external excitations is presented. The non-linear partial differential equations governing the motion of the system, which incorporate the influence of circumferential strains, are solved by a combination of a finite element method, a finite difference method and a method of characteristics with interpolation. An initially axially stretched elastic tube conveying pulsating fluid, simply supported at both ends, is modelled to assess the effect of external harmonic excitation on the dynamic responses of the tube and the fluid flow. The results agree well with new experimental data. Comparison of the predicted results with those of a decoupled model demonstrates that it is necessary to consider the mechanism of fluid-structure interaction fully in the study of initially stretched cylindrical tubes conveying pulsatile fluid flow. An analysis of these coupling effects is presented for Womersley numbers alpha = 2.81 and 3.97 and a mean flow Reynolds number Re = 875.}, }
@article {pmid11863654, year = {2002}, author = {Reynolds, AM}, title = {Effects of periodicity on flow and dispersion through closely packed fixed beds of spheres.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {65}, number = {2 Pt 2}, pages = {026308}, doi = {10.1103/PhysRevE.65.026308}, pmid = {11863654}, issn = {1539-3755}, abstract = {A lattice-Boltzmann formulation is used to investigate the effects of "periodicity" (geometry) on fluid flow and tracer-particle dispersion through fixed beds of spheres comprising of closely packed layers. In the "period-1" arrangement, spheres in the adjacent layers contact at their poles while the "period-2" and "period-3" arrangements correspond to hexagonal and faced-centered cubic close packing. For all three packing arrangements, there is a transition with increasing Reynolds number from a power law to a log-normal distribution of kinetic energies and, velocity and vorticity become more closely aligned giving rise to helical tracer-particle trajectories. It is suggested that these flow characteristics, unlike the stability of flow and the distribution of helicity, are largely insensitive to geometry, even when the geometry creates direct channels through the pack bed orientated along the gradient in applied pressure. For steady flows and strongly turbulent flows, such channels are predicted to provide direct routes for dispersion through a packed bed, while for weakly turbulent flows they influence dispersion primarily by destabilizing the flow and thereby promoting dispersion throughout a bed. The dispersion of tracer-particles released from a source located on or close to a "stagnation streamline" is predicted to be faster than ballistic in the near field and the transition to long-time Fickian diffusion is predicted to be distinguished by a regime of subdiffusion.}, }
@article {pmid11809963, year = {2002}, author = {Stroock, AD and Dertinger, SK and Ajdari, A and Mezic, I and Stone, HA and Whitesides, GM}, title = {Chaotic mixer for microchannels.}, journal = {Science (New York, N.Y.)}, volume = {295}, number = {5555}, pages = {647-651}, doi = {10.1126/science.1066238}, pmid = {11809963}, issn = {1095-9203}, support = {GM51559/GM/NIGMS NIH HHS/United States ; }, mesh = {Chemical Phenomena ; Chemistry, Physical ; Diffusion ; Microchemistry ; Miniaturization ; Pressure ; *Rheology/instrumentation ; Viscosity ; }, abstract = {It is difficult to mix solutions in microchannels. Under typical operating conditions, flows in these channels are laminar-the spontaneous fluctuations of velocity that tend to homogenize fluids in turbulent flows are absent, and molecular diffusion across the channels is slow. We present a passive method for mixing streams of steady pressure-driven flows in microchannels at low Reynolds number. Using this method, the length of the channel required for mixing grows only logarithmically with the Péclet number, and hydrodynamic dispersion along the channel is reduced relative to that in a simple, smooth channel. This method uses bas-relief structures on the floor of the channel that are easily fabricated with commonly used methods of planar lithography.}, }
@article {pmid11804726, year = {2001}, author = {Allison, SA}, title = {Boundary element modeling of biomolecular transport.}, journal = {Biophysical chemistry}, volume = {93}, number = {2-3}, pages = {197-213}, doi = {10.1016/s0301-4622(01)00221-6}, pmid = {11804726}, issn = {0301-4622}, mesh = {*Biological Transport ; DNA/metabolism ; Electrophoresis ; *Models, Biological ; }, abstract = {The boundary element (BE) methodology has emerged as a powerful tool in modeling a broad range of different transport phenomena of biomolecules in dilute solution. These include: sedimentation, diffusion (translational and rotational), intrinsic viscosity, and free solution electrophoresis. Modeling is carried out in the framework of the continuum primitive model where the biomolecule is modeled as an arbitrary array of solid platelets that contains fixed charges within. The surrounding fluid is modeled as a electrodynamic/hydrodynamic continuum which obeys the Poisson and low Reynolds number Navier-Stokes equations. Ion relaxation (the distortion of the ion atmosphere from equilibrium) can also be accounted for by solving the coupled ion transport equation (for each mobile ion species present), Poisson, and Navier-Stokes equations in tandem. Several examples are presented in this work. It is first applied to a detailed model of 20 bp DNA and it is concluded that it is not necessary to include a layer of bound water to reconcile experimental and model translational diffusion constants. With regards to diffusion, the BE approach is also applied to a 375-bp supercoiled DNA model (without ion relaxation), and also 20-60-bp DNA fragments with ion relaxation included in order to assess the magnitude of the electrolyte friction effect under a number of different salt/buffer conditions. Attention is then turned to modeling the electrophoretic mobility of three different cases. First of all, we consider a sphere with a central charge large enough in magnitude to insure that ion relaxation is significant. Excellent agreement with independent theory is obtained. Finally, it is applied to modeling short DNA fragments in KCl and Tris acetate salts. Quantitative agreement is achieved when the salt is KCl, but the calculated (absolute) mobility in Tris acetate is substantially higher than the experimental value. The interpretation of this is that there is an association between Tris(+) and DNA (perhaps hydrogen bonding) not accounted for in our modeling that is responsible for this discrepancy.}, }
@article {pmid11800783, year = {2002}, author = {Chiang, TP and Sheu, TW and Hwang, RR and Sau, A}, title = {Spanwise bifurcation in plane-symmetric sudden-expansion flows.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {65}, number = {1 Pt 2}, pages = {016306}, doi = {10.1103/PhysRevE.65.016306}, pmid = {11800783}, issn = {1539-3755}, abstract = {Present computational investigation reports a steady bifurcation phenomenon for three-dimensional flows through a plane-symmetric sudden expansion. When the channel aspect ratio exceeds a critical value, the well-known step height (pitchfork) bifurcation evolves with different symmetry breaking orientations on the left and right sides of the channel and bifurcates in the spanwise direction. For the channel aspect ratio less than the critical value, the originally occurring spanwise bifurcation cannot be stably retained and evolves eventually to a step height bifurcation. Compared to step height bifurcation, the spanwise bifurcation is found to be more difficult to obtain, because the symmetric flow present on the spanwise symmetry plane is unstable in two dimensions. For completeness, an extensive analysis of the observed spanwise bifurcation, covering its transient behavior, dependence on flow Reynolds number, channel aspect ratio, and expansion ratio, is included.}, }
@article {pmid11736341, year = {2001}, author = {Mordant, N and Metz, P and Michel, O and Pinton, JF}, title = {Measurement of Lagrangian velocity in fully developed turbulence.}, journal = {Physical review letters}, volume = {87}, number = {21}, pages = {214501}, doi = {10.1103/PhysRevLett.87.214501}, pmid = {11736341}, issn = {0031-9007}, abstract = {We have developed a new experimental technique to measure the Lagrangian velocity of tracer particles in a turbulent flow, based on ultrasonic Doppler tracking. This method yields a direct access to the velocity of a single particle at a turbulent Reynolds number R(lambda) = 740, with two decades of time resolution, below the Lagrangian correlation time. We observe that the Lagrangian velocity spectrum has a Lorentzian form E(L)(omega) = u(2)(rms)T(L)/[1+(T(L)omega)(2)], in agreement with a Kolmogorov-like scaling in the inertial range. The probability density functions of the velocity time increments display an intermittency which is more pronounced than that of the corresponding Eulerian spatial increments.}, }
@article {pmid11736308, year = {2001}, author = {Pan, C and Hilpert, M and Miller, CT}, title = {Pore-scale modeling of saturated permeabilities in random sphere packings.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {64}, number = {6 Pt 2}, pages = {066702}, doi = {10.1103/PhysRevE.64.066702}, pmid = {11736308}, issn = {1539-3755}, support = {5 P42 ES05948-02/ES/NIEHS NIH HHS/United States ; }, mesh = {*Models, Theoretical ; *Permeability ; Porosity ; Reproducibility of Results ; }, abstract = {We use two pore-scale approaches, lattice-Boltzmann (LB) and pore-network modeling, to simulate single-phase flow in simulated sphere packings that vary in porosity and sphere-size distribution. For both modeling approaches, we determine the size of the representative elementary volume with respect to the permeability. Permeabilities obtained by LB modeling agree well with Rumpf and Gupte's experiments in sphere packings for small Reynolds numbers. The LB simulations agree well with the empirical Ergun equation for intermediate but not for small Reynolds numbers. We suggest a modified form of Ergun's equation to describe both low and intermediate Reynolds number flows. The pore-network simulations agree well with predictions from the effective-medium approximation but underestimate the permeability due to the simplified representation of the porous media. Based on LB simulations in packings with log-normal sphere-size distributions, we suggest a permeability relation with respect to the porosity, as well as the mean and standard deviation of the sphere diameter.}, }
@article {pmid11736181, year = {2001}, author = {Henderson, S and Mitchell, S and Bartlett, P}, title = {Direct measurements of colloidal friction coefficients.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {64}, number = {6 Pt 1}, pages = {061403}, doi = {10.1103/PhysRevE.64.061403}, pmid = {11736181}, issn = {1539-3755}, abstract = {The time-independent hydrodynamic forces operating between two hard spheres were studied as a function of the interparticle separation r. Two colloids were positioned a distance r apart using a dual-beam optical tweezer similar to that described by Meiners and Quake [Phys. Rev. Lett. 82, 2211 (1999)]. Brownian fluctuations in the positions of the two spheres were followed by recording the intensity of forward scattered laser light. The two particles move cooperatively as a result of hydrodynamic forces. The strength of the correlation increased strongly with decreasing separation r. We show that the temporal and spatial correlations in the particle displacements are determined by the distance dependence of the pair friction tensor xi. The distance and geometry dependence of the measured friction tensor is found to be in excellent agreement with the predictions of low-Reynolds number calculations.}, }
@article {pmid11736091, year = {2001}, author = {Nakayama, Y and Watanabe, T and Fujisaka, H}, title = {Self-similar fluctuation and large deviation statistics in the shell model of turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {64}, number = {5 Pt 2}, pages = {056304}, doi = {10.1103/PhysRevE.64.056304}, pmid = {11736091}, issn = {1539-3755}, abstract = {Both static and dynamic multiscalings of fluctuations of energy flux and energy dissipation rate in the Gledzer-Ohkitani-Yamada (GOY) shell model of turbulence are numerically investigated. We compute the large deviation rate function of energy flux not only in the inertial range (IR) but also around the crossover between the inertial range and the dissipation range (DR). The rate function in IR exists to be concave, which assures the applicability of the Legendre transformation with the anomalous scaling exponents that have been investigated so far, and turns out to be independent of the Reynolds number. On the contrary, near the crossover scale, an intermediate dissipation range (IMDR) scaling is observed with the rate function in IMDR, which is accounted with the argument on dissipation scale fluctuation dominated by the energy flux fluctuation in the inertial range. Furthermore, to study the difference between IR intermittency and DR intermittency, we compute finite time-averaged quantities of energy flux and energy dissipation rate and investigate their multiscaling behavior. The difference observed in terms of their dynamic multiscaling is discussed.}, }
@article {pmid11736088, year = {2001}, author = {Balkovsky, E and Fouxon, A and Lebedev, V}, title = {Turbulence of polymer solutions.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {64}, number = {5 Pt 2}, pages = {056301}, doi = {10.1103/PhysRevE.64.056301}, pmid = {11736088}, issn = {1539-3755}, abstract = {We investigate high-Reynolds-number turbulence in dilute polymer solutions. We show the existence of a critical value of the Reynolds number, which separates two different regimes. In the first regime, below the transition, the influence of the polymer molecules on the flow is negligible, so they can be regarded as passively embedded in the flow. This case admits a detailed investigation of the statistics of the polymer elongations. The second state is realized when the Reynolds number is larger than the critical value. This regime is characterized by the strong back reaction of polymers on the flow. We establish some properties of the statistics of the stress and velocity in this regime and discuss its relation to the drag reduction phenomenon.}, }
@article {pmid11730201, year = {2001}, author = {Dierickx, PW and De Wachter, DS and De Somer, F and Van Nooten, G and Verdonck, PR}, title = {Mass transfer characteristics of artificial lungs.}, journal = {ASAIO journal (American Society for Artificial Internal Organs : 1992)}, volume = {47}, number = {6}, pages = {628-633}, doi = {10.1097/00002480-200111000-00012}, pmid = {11730201}, issn = {1058-2916}, mesh = {Artificial Organs ; Blood Flow Velocity ; Cardiopulmonary Bypass ; Extracorporeal Membrane Oxygenation/*methods ; Humans ; Lung ; *Models, Biological ; Oxygen/pharmacokinetics ; }, abstract = {An artificial lung is used during cardiopulmonary bypass to oxygenate blood and control blood temperature. The oxygen transfer rate-flow rate characteristics of three hollow fiber membrane artificial lungs (Sarns Turbo 440, Cobe Optima, Dideco Compactflo) were determined in vitro to characterize design features. Results are presented as a unique dimensionless relationship between Sherwood number, NSh (ratio of convective to diffusive mass transfer), Schmidt number, NSc (ratio of momentum to diffusive transport), and Reynolds number, NRe (ratio of inertial to viscous forces). This relationship is a function of device porosity, epsilon, and characteristic device length, xi, defined as the ratio of the mean blood path and manifold length: Nsh/NSc(1/3) x xi(1/2) = phi x (epsilon(1/m) x NRe)(m) where phi = 0.26 and m = 1.00 for NPe < 3,200 and phi = 0.47 and m = 0.64 for NPe > 3,200 where NPe is the dimensionless Péclet number defined as NRe x NSc. We found good correspondence between the model predictions and in vitro blood oxygen transfer rates. We conclude that this dimensionless approach allows us (1) to compare artificial lungs independently, (2) to relate water tests to blood, and (3) to predict the oxygen transfer rate of a new artificial lung design.}, }
@article {pmid11721905, year = {2001}, author = {Duttat, P and Beskok, A}, title = {Analytical solution of time periodic electroosmotic flows: analogies to Stokes' second problem.}, journal = {Analytical chemistry}, volume = {73}, number = {21}, pages = {5097-5102}, doi = {10.1021/ac015546y}, pmid = {11721905}, issn = {0003-2700}, abstract = {Analytical solutions of time periodic electroosmotic flows in two-dimensional straight channels are obtained as a function of a nondimensional parameter kappa, which is based on the electric double-layer (EDL) thickness, kinematic viscosity, and frequency of the externally applied electric field. A parametric study as a function of kappa reveals interesting physics, ranging from oscillatory "pluglike" flows to cases analogous to the oscillating flat plate in a semi-infinite flow domain (Stokes' second problem). The latter case differs from the Stokes' second solution within the EDL, since the flow is driven with an oscillatory electric field rather than an oscillating plate. The analogous case of plate oscillating with the Helmholtz-Smoluchowski velocity matches our analytical solution in the bulk flow region. This indicates that the instantaneous Helmholtz-Smoluchowski velocity is the appropriate electroosmotic slip condition even for high-frequency excitations. The velocity profiles for large kappa values show inflection points very near the walls with localized vorticity extrema that are stronger than the Stokes layers. This have the potential to result in low Reynolds number flow instabilities. It is also shown that, unlike the steady pure electroosmotic flows, the bulk flow region of time periodic electroosmotic flows are rotational when the diffusion length scales are comparable to and less than the half channel height.}, }
@article {pmid11688687, year = {2001}, author = {Turan, M and Eroglu, V}, title = {Detachment mechanisms of deposited material in a backwashed filter.}, journal = {Journal of environmental science and health. Part A, Toxic/hazardous substances &amp; environmental engineering}, volume = {36}, number = {9}, pages = {1735-1746}, doi = {10.1081/ese-100106255}, pmid = {11688687}, issn = {1093-4529}, mesh = {Filtration/*instrumentation ; Water Purification/*methods ; Water Supply ; }, abstract = {Theoretical and experimental studies were performed to evaluate the detachment mechanisms of deposited material by fluidizing the filter media. The hydrodynamic characteristics of a backwashed filter and the energy dissipation during backwashing processes were investigated. The existence of a viscous sublayer around each fluidized particle and laminar sublayer thickness at the wall were neglected. Direct measurements of the effluent turbidity Te and the total backwash water volume Vbt were made during backwashing in the laboratory experiments. Some relationships applicable to backwashing processes were developed with good accuracy. The turbulence parameter C0.5(a)/Re which characterizes the effect of turbulence fluctuations in a backwashed filter increased with increasing fraction solids (1-epsilon) and decreased with increasing the Reynolds number of the flow Re. The detachment rate of deposited material rd, was found to vary with hydrodynamic shear (taua), turbulence fluctuations (C0.5(a)/Re) and backwash water volume (Vb). Maximum shear stress caused a maximum detachment of the deposited material from the filter media. The detachment rate of deposited material rd had a minimum value at the turbulent parameter of 0.9 and fraction solids of 0.3. Also the detachment rate of the deposited material rd decreased with increasing the unit backwash water volume Vb which is the ratio of the total backwash water volume Vbt to the expanded bed volume Ve.}, }
@article {pmid11673645, year = {2001}, author = {Shankaran, H and Neelamegham, S}, title = {Effect of secondary flow on biological experiments in the cone-plate viscometer: methods for estimating collision frequency, wall shear stress and inter-particle interactions in non-linear flow.}, journal = {Biorheology}, volume = {38}, number = {4}, pages = {275-304}, pmid = {11673645}, issn = {0006-355X}, support = {HL63014/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Blood Platelets/physiology ; Computational Biology ; Endothelium, Vascular/cytology/physiology ; Models, Biological ; Neutrophils/*physiology ; Rheology ; Stress, Mechanical ; Viscosity ; }, abstract = {We present a theoretical analysis of fluid flow and particle interactions in the cone-plate viscometer under conditions typically applied in biological studies. The analysis demonstrates that at higher shear rates, besides linear primary flow in the rotational direction, prominent non-linear secondary flow causes additional fluid circulation in the radial direction. Two parameters, the cone angle and Reynolds number, characterize flow in the viscometer over all ranges of shear rate. Our results indicate that secondary flow causes positional variations in: (i) the velocity gradient, (ii) the direction and magnitude of the wall shear stress at the plate surface, (iii) inter-particle collision frequency, (iv) magnitude and periodicity of normal and shear forces applied during particle-particle interactions, and (v) inter-particle attachment times. Thus, secondary flow may significantly influence cellular aggregation, platelet activation and endothelial cell mechanotransduction measurements. Besides cone-plate viscometers, this analysis methodology can also be extended to other experimental systems with complex non-linear flows.}, }
@article {pmid11672715, year = {2001}, author = {Lee, D and Su, JM and Liang, HY}, title = {A numerical simulation of steady flow fields in a bypass tube.}, journal = {Journal of biomechanics}, volume = {34}, number = {11}, pages = {1407-1416}, doi = {10.1016/s0021-9290(01)00131-2}, pmid = {11672715}, issn = {0021-9290}, mesh = {Anastomosis, Surgical/*standards ; Animals ; Biomechanical Phenomena ; Blood Vessel Prosthesis/*standards ; Computer Simulation ; Hemodynamics ; Hemorheology ; Humans ; *Models, Cardiovascular ; }, abstract = {Steady flow in a complete by-pass tube was simulated numerically. The study was to consider a complete flow field, which included both the by-pass and the host tubes. The changes of the hemodynamics were investigated with three parameters: the inlet flow Reynolds number (Re), anastomotic angle (alpha) and the position of the occlusion in the host tube. The baseline flow field was set up with Re=200, alpha=45 degrees and the centered position of occlusion. The parametric study was then conducted on combination of Re=100, 200, 400, alpha=35 degrees, 45 degrees, 60 degrees, 75 degrees, 90 degrees and three occlusion positions: left, center and right. It was found that in the baseline case, large slow/recirculation flows could be seen in the host tube both upstream and downstream of the occlusion. The separation points were on the opposite walls to the junctions. Recirculation zones were also found near the toe and in the proximal outer wall of the by-pass tube. Their sizes were about one diameter of the tube or smaller. In some cases, pairing vortices could be seen in the host tube upstream of the occlusion. The shear rate distribution associated with the flow fields was presented. The flow pattern obtained was agreeable to those observed experimentally by other investigators. The difference of the flow fields between a complete bypass and simple anastomosis was discussed. The present numerical code provides a preliminary simulation/design tool for bypass graft flows.}, }
@article {pmid11601735, year = {2001}, author = {Bertram, CD and Diaz de Tuesta, G and Nugent, AH}, title = {Laser-Doppler measurements of velocities just downstream of a collapsible tube during flow-induced oscillations.}, journal = {Journal of biomechanical engineering}, volume = {123}, number = {5}, pages = {493-499}, doi = {10.1115/1.1388294}, pmid = {11601735}, issn = {0148-0731}, mesh = {Biomechanical Phenomena ; Biomedical Engineering ; Humans ; Lung/anatomy &amp; histology/*physiology ; Models, Biological ; Oscillometry ; Respiratory Mechanics ; Rheology ; }, abstract = {The flow field less than one diameter downstream of the end of a collapsible tube executing self excited oscillations was examined using a two-component fiber-optic laser-Doppler anemometer. The time-averaged Reynolds number of the flow was 11,000. With the tube oscillating periodically, results obtained during many cycles of oscillation were combined to yield surface plots of the axial component over the cross section at 16 phases of the cycle. By combining measurements obtained with the laser probe in two different orientations, secondary flow vectors over the cross section were likewise constructed for 16 phases. The measurements showed strongly phasic turbulence intensity, with the phase of high intensity coinciding with the time of maximal tube collapse. Reverse flow occurred during much of the cycle, at places in the cross section that agree with our previous observations of laminar and turbulent steady flow through a rigid simulated collapsed tube.}, }
@article {pmid11601733, year = {2001}, author = {Finol, EA and Amon, CH}, title = {Blood flow in abdominal aortic aneurysms: pulsatile flow hemodynamics.}, journal = {Journal of biomechanical engineering}, volume = {123}, number = {5}, pages = {474-484}, doi = {10.1115/1.1395573}, pmid = {11601733}, issn = {0148-0731}, mesh = {Aortic Aneurysm, Abdominal/etiology/*physiopathology ; Aortic Rupture/etiology/physiopathology ; Biomechanical Phenomena ; Biomedical Engineering ; Blood Flow Velocity ; Computer Simulation ; Hemodynamics/*physiology ; Hemorheology ; Humans ; *Models, Cardiovascular ; Pulsatile Flow ; }, abstract = {Numerical predictions of blood flow patterns and hemodynamic stresses in Abdominal Aortic Aneurysms (AAAs) are performed in a two-aneurysm, axisymmetric, rigid wall model using the spectral element method. Physiologically realistic aortic blood flow is simulated under pulsatile conditions for the range of time-averaged Reynolds numbers 50< or =Re(m)< or =300, corresponding to a range of peak Reynolds numbers 262.5< or =Re(peak) < or = 1575. The vortex dynamics induced by pulsatile flow in AAAs is characterized by a sequence of five different flow phases in one period of the flow cycle. Hemodynamic disturbance is evaluated for a modified set of indicator functions, which include wall pressure (p(w)), wall shear stress (tau(w)), and Wall Shear Stress Gradient (WSSG). At peak flow, the highest shear stress and WSSG levels are obtained downstream of both aneurysms, in a pattern similar to that of steady flow. Maximum values of wall shear stresses and wall shear stress gradients obtained at peak flow are evaluated as a function of the time-average Reynolds number resulting in a fourth order polynomial correlation. A comparison between predictions for steady and pulsatile flow is presented, illustrating the importance of considering time-dependent flow for the evaluation of hemodynamic indicators.}, }
@article {pmid11580446, year = {2001}, author = {Kerstein, AR}, title = {Kinematics of small scale anisotropy in turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {64}, number = {3 Pt 2}, pages = {036306}, doi = {10.1103/PhysRevE.64.036306}, pmid = {11580446}, issn = {1539-3755}, abstract = {A simple, empirically motivated model is proposed to explain the transfer of imposed large scale anisotropy to small scales in high-Reynolds-number turbulence. Observed power-law scalings of anisotropy metrics are interpreted as manifestations of power-law scalings governing high-gradient regions resulting from compressional eddy motions. The model is used to interpret the measured moment-order dependencies of the exponents and amplitudes of odd-order structure functions and derivative moments that vanish in the absence of anisotropy.}, }
@article {pmid11580427, year = {2001}, author = {Daya, ZA and Deyirmenjian, VB and Morris, SW}, title = {Bifurcations in annular electroconvection with an imposed shear.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {64}, number = {3 Pt 2}, pages = {036212}, doi = {10.1103/PhysRevE.64.036212}, pmid = {11580427}, issn = {1539-3755}, abstract = {We report an experimental study of the primary bifurcation in electrically driven convection in a freely suspended film. A weakly conducting, submicron thick smectic liquid crystal film was supported by concentric circular electrodes. It electroconvected when a sufficiently large voltage V was applied between its inner and outer edges. The film could sustain rapid flows and yet remain strictly two dimensional. By rotation of the inner electrode, a circular Couette shear could be independently imposed. The control parameters were a dimensionless number R, analogous to the Rayleigh number, which is ~V2 and the Reynolds number Re of the azimuthal shear flow. The geometrical and material properties of the film were characterized by the radius ratio alpha, and a dimensionless number P, analogous to the Prandtl number. Using measurements of current-voltage characteristics of a large number of films, we examined the onset of electroconvection over a broad range of alpha, P, and Re. We compared this data quantitatively to the results of linear stability theory. This could be done with essentially no adjustable parameters. The current-voltage data above onset were then used to infer the amplitude of electroconvection in the weakly nonlinear regime by fitting them to a steady-state amplitude equation of the Landau form. We show how the primary bifurcation can be tuned between supercritical and subcritical by changing alpha and Re.}, }
@article {pmid11563757, year = {2001}, author = {Mittal, R and Simmons, SP and Udaykumar, HS}, title = {Application of large-eddy simulation to the study of pulsatile flow in a modeled arterial stenosis.}, journal = {Journal of biomechanical engineering}, volume = {123}, number = {4}, pages = {325-332}, doi = {10.1115/1.1385840}, pmid = {11563757}, issn = {0148-0731}, mesh = {Arterial Occlusive Diseases/*physiopathology ; Biomechanical Phenomena ; Biomedical Engineering ; Constriction, Pathologic ; Hemodynamics ; Humans ; *Models, Cardiovascular ; Pulsatile Flow ; }, abstract = {The technique of large-eddy simulation (LES) has been applied to the study of pulsatile flow through a modeled arterial stenosis. A simple stenosis model has been used that consists of a one-sided 50 percent semicircular constriction in a planar channel. The inlet volume flux is varied sinusoidally in time in a manner similar to the laminar flow simulations of Tutty (1992). LES is used to compute flow at a peak Reynolds number of 2000 and a Strouhal number of 0.024. At this Reynolds number, the flow downstream of the stenosis transitions to turbulence and exhibits all the classic features of post-stenotic flow as described by Khalifa and Giddens (1981) and Lieber and Giddens (1990). These include the periodic shedding of shear layer vortices and transition to turbulence downstream of the stenosis. Computed frequency spectra indicate that the vortex shedding occurs at a distinct high frequency, and the potential implication of this for noninvasive diagnosis of arterial stenoses is discussed. A variety of statistics have been also extracted and a number of other physical features of the flow are described in order to demonstrate the usefulness of LES for the study of post-stenotic flows.}, }
@article {pmid11554243, year = {2001}, author = {Ibaraki, M and Schwartz, FW}, title = {Influence of natural heterogeneity on the efficiency of chemical floods in source zones.}, journal = {Ground water}, volume = {39}, number = {5}, pages = {660-666}, doi = {10.1111/j.1745-6584.2001.tb02355.x}, pmid = {11554243}, issn = {0017-467X}, mesh = {*Disasters ; *Models, Theoretical ; Water Movements ; Water Pollutants, Chemical/analysis ; Water Pollution/*prevention &amp; control ; }, abstract = {Several technologies for cleaning up DNAPLs in source zones rely on solubilizing contaminants or destroying them in situ. Typically, these approaches employ an injection/withdrawal system to recirculate this treatment fluids. Our interest is in examining factors that influence delivery efficiency. Although many factors can affect this efficiency, this study looks at the combined influence of density-driven flow and porous media heterogeneities. The analysis is based on a series of numerical simulations of hypothetical chemical floods (e.g., potassium permanganate), which are highly resolved in space and time with a scale that is typical of field installations. Results indicate that the characteristics of convective mixing, i.e., natural, forced, and mixed convection, greatly affect delivery efficiency and patterns of mass transport. The ratio of the Grashof number (Gr) and Reynolds number (Re) proved useful in interpreting the patterns of flooding in a homogeneous porous medium. When higher-permeability layers are included in the domain, they act as conduits, effectively expediting the transport of treatment chemicals from injection to recovery wells. These large fluxes of chemicals in the high-permeability layers produce significant flooding inefficiencies. The problem is less severe in heterogeneous medium where the connectivity through the treatment zone is less well developed. Overall, this paper illustrates that density effects and high-permeability pathways need to be considered in designing chemical floods.}, }
@article {pmid11541381, year = {1998}, author = {Kessler, JO and Hill, NA and Strittmatter, R and Wiseley, D}, title = {Sedimenting particles and swimming micro-organisms in a rotating fluid.}, journal = {Advances in space research : the official journal of the Committee on Space Research (COSPAR)}, volume = {21}, number = {8-9}, pages = {1269-1275}, doi = {10.1016/s0273-1177(97)00398-0}, pmid = {11541381}, issn = {0273-1177}, mesh = {Biophysical Phenomena ; Biophysics ; Eukaryota/physiology ; *Gravitation ; Gravity Sensing/*physiology ; Locomotion/*physiology ; Mathematics ; Microspheres ; Orientation/physiology ; Particle Size ; *Rotation ; Swimming/*physiology ; }, abstract = {Experiments and calculations on the trajectories of micron-sized spheres, suspended in a fluid that fills a dosed container which rotates about an axis perpendicular to g, relate to the planning and interpretation of clinostat experiments. For low Reynolds number motion, the orbits are nearly circular, the radius being inversely proportional to the rotation rate. The swimming direction of micro-organisms can be affected by light, gravity, vorticity etc. The trajectories of algae swimming in steadily rotating environments have been observed and compared with theoretical predictions for ideal gyrotactic micro-organisms, thus providing some insights into the mechanisms of gravitaxis, gyrotaxis and the behaviour of the cells.}, }
@article {pmid11525992, year = {2001}, author = {Pearce, LE and Truong, HT and Crawford, RA and Yates, GF and Cavaignac, S and de Lisle, GW}, title = {Effect of turbulent-flow pasteurization on survival of Mycobacterium avium subsp. paratuberculosis added to raw milk.}, journal = {Applied and environmental microbiology}, volume = {67}, number = {9}, pages = {3964-3969}, pmid = {11525992}, issn = {0099-2240}, mesh = {Animals ; Cattle ; Culture Media ; *Hot Temperature ; Humans ; Milk/*microbiology ; Mycobacterium avium subsp. paratuberculosis/*growth &amp; development/isolation &amp; purification ; }, abstract = {A pilot-scale pasteurizer operating under validated turbulent flow (Reynolds number, 11,050) was used to study the heat sensitivity of Mycobacterium avium subsp. paratuberculosis added to raw milk. The ATCC 19698 type strain, ATCC 43015 (Linda, human isolate), and three bovine isolates were heated in raw whole milk for 15 s at 63, 66, 69, and 72 degrees C in duplicate trials. No strains survived at 72 degrees C for 15 s; and only one strain survived at 69 degrees C. Means of pooled D values (decimal reduction times) at 63 and 66 degrees C were 15.0 +/- 2.8 s (95% confidence interval) and 5.9 +/- 0.7 s (95% confidence interval), respectively. The mean extrapolated D72 degrees C was <2.03 s. This was equivalent to a >7 log10 kill at 72 degrees C for 15 s (95% confidence interval). The mean Z value (degrees required for the decimal reduction time to traverse one log cycle) was 8.6 degrees C. These five strains showed similar survival whether recovery was on Herrold's egg yolk medium containing mycobactin or by a radiometric culture method (BACTEC). Milk was inoculated with fresh fecal material from a high-level fecal shedder with clinical Johne's disease. After heating at 72 degrees C for 15 s, the minimum M. avium subsp. paratuberculosis kill was >4 log10. Properly maintained and operated equipment should ensure the absence of viable M. avium subsp. paratuberculosis in retail milk and other pasteurized dairy products. An additional safeguard is the widespread commercial practice of pasteurizing 1.5 to 2 degrees above 72 degrees C.}, }
@article {pmid11523730, year = {2001}, author = {Bertram, CD and Muller, M and Ramus, F and Nugent, AH}, title = {Measurements of steady turbulent flow through a rigid simulated collapsed tube.}, journal = {Medical &amp; biological engineering &amp; computing}, volume = {39}, number = {4}, pages = {422-427}, pmid = {11523730}, issn = {0140-0118}, mesh = {Humans ; Laser-Doppler Flowmetry ; Models, Biological ; *Rheology ; }, abstract = {Axial and transverse components of liquid velocity are measured by laser Doppler anemometer in a perspex tube that has been deformed at one point to resemble the shape of the throat of a partially collapsed flexible tube, conveying fluid while being compressed externally. The Reynolds number is 5900. The flow down-stream of the throat consists of two side-jets with reverse flow extending all across the cross-section between them. The jets spread out around the central retrograde-flow zone, initially forming crescents of high-speed forward flow and then, at three diameters downstream, an almost complete annulus of forward flow around a central zone of lower-speed but now forward flow. Comparison is made between the features of this turbulent flow and those of a previously investigated laminar flow through the same geometry. In both, retrograde flow ceases between two and three diameters downstream of the centre of the throat. However, the laminar flow is annular at three diameters downstream, whereas here the jets remain influential at that station. The maximum normalised turbulence intensity exceeds 1.35.}, }
@article {pmid11522303, year = {2001}, author = {Long, Q and Xu, XY and Ramnarine, KV and Hoskins, P}, title = {Numerical investigation of physiologically realistic pulsatile flow through arterial stenosis.}, journal = {Journal of biomechanics}, volume = {34}, number = {10}, pages = {1229-1242}, doi = {10.1016/s0021-9290(01)00100-2}, pmid = {11522303}, issn = {0021-9290}, mesh = {Arterial Occlusive Diseases/*physiopathology ; Blood Flow Velocity ; *Computer Simulation ; Humans ; *Models, Cardiovascular ; Pulsatile Flow/*physiology ; Stress, Mechanical ; }, abstract = {Numerical simulations of pulsatile blood flow in straight tube stenosis models were performed to investigate the poststenotic flow phenomena. In this study, three axisymmetrical and three asymmetrical stenosis models with area reduction of 25%, 50% and 75% were constructed. A measured human common carotid artery blood flow waveform was used as the upstream flow condition which has a mean Reynold's number of 300. All calculations were performed with high spatial and temporal resolutions. Flow features such as velocity profiles, flow separation zone (FSZ), and wall shear stress (WSS) distributions in the poststenotic region for all models are presented. The results have demonstrated that the formation and development of FSZs in the poststenotic region are very complex, especially in the flow deceleration phase. In axisymmetric stenoses the poststenotic flow is more sensitive to changes in the degree of stenosis than in asymmetric models. For severe stenoses, the stenosis influence length is shorter in asymmetrical models than in axisymmetrical cases. WSS oscillations (between positive and negative values) have been observed at various downstream locations in some models. The amplitude of the oscillation depends strongly on the axial location and the degree of stenosis.}, }
@article {pmid11495482, year = {2001}, author = {Zhang, Z and Kleinstreuer, C}, title = {Effect of particle inlet distributions on deposition in a triple bifurcation lung airway model.}, journal = {Journal of aerosol medicine : the official journal of the International Society for Aerosols in Medicine}, volume = {14}, number = {1}, pages = {13-29}, doi = {10.1089/08942680152007864}, pmid = {11495482}, issn = {0894-2684}, mesh = {Administration, Inhalation ; Aerosols/*administration &amp; dosage/pharmacokinetics ; Biological Availability ; *Computer Simulation ; Humans ; Lung/*physiology ; Models, Anatomic ; Particle Size ; Respiratory Mechanics ; Respiratory Physiological Phenomena ; Sensitivity and Specificity ; }, abstract = {Considering a triple bifurcation as a representative lung airway model of the upper bronchial tree, the effect of different random inlet particle distributions on deposition patterns and efficiencies have been numerically analyzed. The steady laminar three-dimensional transport equations for a dilute micron-size particle suspension have been solved using a commercial finite-volume code with user-enhanced programs. Particle release positions were assigned employing a random number generator following random-parabolic, random-uniform, and random-random distribution functions. Via back tracking, starting positions of all depositing particles were determined for each particle release distribution, including a deterministic-parabolic one which served as a base case. The results indicate that: (1) The starting regions of the depositing particles in a given bifurcation are fixed for the same inlet Reynolds number and Stokes number combination, regardless of the type of distribution profile. The situation for the particle deposition patterns is somewhat similar. However, the type of distribution of inlet particles strongly influences the particle deposition efficiencies. (2) Values of particle deposition efficiencies are very close for the same (parabolically) distributed deterministic versus random inlet particles when all other conditions are fixed. (3) According to the simulation validations, a determinstic parabolic distribution of inlet particles may be sufficient for laboratory data comparison purposes, but random distributions should reflect realistic environmental or medical aerosol inhalation more accurately.}, }
@article {pmid11487120, year = {2001}, author = {Wu, RM and Lee, DJ}, title = {Hydrodynamic drag on non-spherical floc and free-settling test.}, journal = {Water research}, volume = {35}, number = {13}, pages = {3226-3234}, doi = {10.1016/s0043-1354(01)00050-1}, pmid = {11487120}, issn = {0043-1354}, mesh = {*Flocculation ; Friction ; Mathematics ; Oxygen/metabolism ; Particle Size ; Sewage/chemistry ; Solutions ; }, abstract = {This work numerically investigates the hydrodynamic drag force exerted on a porous spheroid floc moving steadily through a quiescent Newtonian fluid over a wide range of the Reynolds number. The flow patterns for a highly porous spheroid moving at an elevated Reynolds number are basically the same as those at a low Reynolds number, which extends the applicable range of a creeping-flow based correlation to the higher Reynolds number regime. The shape effect becomes more prominent as the spheroid becomes more porous. Using the equivalent diameter, defined as the geometric mean diameter of the principal axes, leads to a universal correlation relating to the drag force, aspect ratio, and interior permeability. In addition, free-settling experiments are performed to estimate how the non-spherical shape affects the three sludge samples. The possible errors in data reduction for the free-settling test are attributed to the a/b ratio and the internal permeability. The errors range from 16-34% for a/b = 0.6-2.0.}, }
@article {pmid11463626, year = {2001}, author = {King, MR and Hammer, DA}, title = {Multiparticle adhesive dynamics. Interactions between stably rolling cells.}, journal = {Biophysical journal}, volume = {81}, number = {2}, pages = {799-813}, pmid = {11463626}, issn = {0006-3495}, support = {F32 HL10353/HL/NHLBI NIH HHS/United States ; HL18208/HL/NHLBI NIH HHS/United States ; }, mesh = {Algorithms ; Cell Adhesion ; *Cell Movement ; Cell-Free System ; Computer Simulation ; Leukocytes/*cytology/*metabolism ; Microspheres ; Models, Biological ; }, abstract = {A novel numerical simulation of adhesive particles (cells) reversibly interacting with an adhesive surface under flow is presented. Particle--particle and particle--wall hydrodynamic interactions in low Reynolds number Couette flow are calculated using a boundary element method that solves an integral representation of the Stokes equation. Molecular bonds between surfaces are modeled as linear springs and stochastically formed and broken according to postulated descriptions of force-dependent kinetics. The resulting simulation, Multiparticle Adhesive Dynamics, is applied to the problem of selectin-mediated rolling of hard spheres coated with leukocyte adhesion molecules (cell-free system). Simulation results are compared to flow chamber experiments performed with carbohydrate-coated spherical beads rolling on P-selectin. Good agreement is found between theory and experiment, with the main observation being a decrease in rolling velocity with increasing concentration of rolling cells or increasing proximity between rolling cells. Pause times are found to increase and deviation motion is found to decrease as pairs of rolling cells become closer together or align with the flow.}, }
@article {pmid11461392, year = {2001}, author = {She, ZS and Ren, K and Lewis, GS and Swinney, HL}, title = {Scalings and structures in turbulent Couette-Taylor flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {64}, number = {1 Pt 2}, pages = {016308}, doi = {10.1103/PhysRevE.64.016308}, pmid = {11461392}, issn = {1539-3755}, abstract = {The scaling of velocity structure functions in Couette-Taylor flow [Lewis and Swinney, Phys. Rev. E 59, 5457 (1999)] is revisited to obtain more accurate values of the scaling exponents for the Reynolds number range investigated, 12,000 to 540,000 (Taylor Reynolds numbers, 34<R(lambda)<220). Systematic convergence of the statistics with increasing sample size is examined, and the uncertainty of the scaling exponents is assessed. At all Reynolds numbers the data support the hierarchical symmetry proposed by She and Leveque [Phys. Rev. Lett. 72, 336 (1994)]. The She-Leveque constant beta has a value of 0.83, indicating greater intermittency in Couette-Taylor turbulence than in free jets, where beta=0.87. The constant gamma, which is a measure of the degree of singularity of the most intermittent structure, decreases from 0.14 for R<10(5) to 0.10 for R>10(5); this transition corresponds to a visually observed break up of the Taylor vortex roll structure with increasing R.}, }
@article {pmid11460668, year = {2001}, author = {Kiliç, M}, title = {Computation of flow and heat transfer in rotating cavities with peripheral flow of cooling air.}, journal = {Annals of the New York Academy of Sciences}, volume = {934}, number = {}, pages = {513-520}, doi = {10.1111/j.1749-6632.2001.tb05890.x}, pmid = {11460668}, issn = {0077-8923}, abstract = {Numerical solutions of the Navier-Stokes equations have been used to model the flow and the heat transfer that occurs in the internal cooling-air systems of gas turbines. Computations are performed to study the effect of gap ratio, Reynolds number and the mass flow rate on the flow and the heat transfer structure inside isothermal and heated rotating cavities with peripheral flow of cooling air. Computations are compared with some of the recent experimental work on flow and heat transfer in rotating-cavities. The agreement between the computed and the available experimental data is reasonably good.}, }
@article {pmid11460660, year = {2001}, author = {Hermanson, K and Parneix, S and von Wolfersdorf, J and Semmler, K}, title = {Prediction of pressure loss and heat transfer in internal cooling passages.}, journal = {Annals of the New York Academy of Sciences}, volume = {934}, number = {}, pages = {448-455}, doi = {10.1111/j.1749-6632.2001.tb05882.x}, pmid = {11460660}, issn = {0077-8923}, abstract = {This paper reports CFD-simulations of the turbulent flow, pressure loss and heat transfer occurring in ribbed passages. The channel section is rectangular, with an aspect ratio of 2.04. Ribs are square cross-section, their height is 10% of the channel height, and their inclination is varied from 90 degrees to 33 degrees. Reynolds number is 30,000. Three turbulence models (k-epsilon wall functions and 2-layer, V2F) are used and compared to the experimental data of Cho et al. All three models accurately predict the pressure losses due to the ribs and the qualitative heat transfer distribution on the ribbed wall. However, only the V2F model can accurately reproduce the absolute heat transfer levels, this at all inclination angles. The correlation developed by Han and co-workers for smaller rib-heights under-predicts the friction factor and wall heat transfer level on the current configuration. This shows the danger of using a correlation outside of its application range.}, }
@article {pmid11460658, year = {2001}, author = {Rathjen, L and Hennecke, DK and Bock, S and Kleinstück, R}, title = {Detailed heat/mass transfer distributions in a rotating two pass coolant channel with engine-near cross section and smooth walls.}, journal = {Annals of the New York Academy of Sciences}, volume = {934}, number = {}, pages = {432-439}, doi = {10.1111/j.1749-6632.2001.tb05880.x}, pmid = {11460658}, issn = {0077-8923}, abstract = {This paper shows results obtained by experimental and numerical investigations concerning flow structure and heat/mass transfer in a rotating two-pass coolant channel with engine-near geometry. The smooth two passes are connected by a 180 degrees U-bend in which a 90 degrees turning vane is mounted. The influence of rotation number, Reynolds number and geometry is investigated. The results show a detailed picture of the flow field and distributions of Sherwood number ratios determined experimentally by the use of the naphthalene sublimation technique as well as Nusselt number ratios obtained from the numerical work. Especially the heat/mass transfer distributions in the bend and in the region after the bend show strong gradients, where several separation zones exist and the flow is forced to follow the turbine airfoil shape. Comparisons of numerical and experimental results show only partly good agreement.}, }
@article {pmid11460657, year = {2001}, author = {Zhou, F and Acharya, S}, title = {Mass/heat transfer in dimpled two-pass coolant passages with rotation.}, journal = {Annals of the New York Academy of Sciences}, volume = {934}, number = {}, pages = {424-431}, doi = {10.1111/j.1749-6632.2001.tb05879.x}, pmid = {11460657}, issn = {0077-8923}, abstract = {Mass/heat transfer measurements are made in dimpled (hemispherical depressions) inlet and outlet coolant flow passages using the naphthalene sublimation method. The leading and trailing surfaces are dimpled, while the side walls are kept smooth. Measurements are made at a Reynolds number of 21,000 and for Rotation numbers of 0 and 0.2. The measurements indicate that dimples enhance surface mass/heat transfer. This enhancement is stronger in the inlet passage than in the outlet passage. Peak mass/heat transfer occurs immediately downstream of the dimples, while the minimum mass/heat transfer occurs in the dimple region itself. Higher mass/heat transfer is also observed along the lateral edges of the dimple. The location of the Sherwood number peaks suggest the existence of streamwise vortical structures generated from the leading and lateral edges of the dimples.}, }
@article {pmid11460655, year = {2001}, author = {Brevet, P and Dorignac, E and Vullierme, JJ}, title = {Mach number effect on jet impingement heat transfer.}, journal = {Annals of the New York Academy of Sciences}, volume = {934}, number = {}, pages = {409-416}, doi = {10.1111/j.1749-6632.2001.tb05877.x}, pmid = {11460655}, issn = {0077-8923}, abstract = {An experimental investigation of heat transfer from a single round free jet, impinging normally on a flat plate is described. Flow at the exit plane of the jet is fully developed and the total temperature of the jet is equal to the ambient temperature. Infrared measurements lead to the characterization of the local and averaged heat transfer coefficients and Nusselt numbers over the impingement plate. The adiabatic wall temperature is introduced as the reference temperature for heat transfer coefficient calculation. Various nozzle diameters from 3 mm to 15 mm are used to make the injection Mach number M vary whereas the Reynolds number Re is kept constant. Thus the Mach number influence on jet impingement heat transfer can be directly evaluated. Experiments have been carried out for 4 nozzle diameters, for 3 different nozzle-to-target distances, with Reynolds number ranging from 7200 to 71,500 and Mach number from 0.02 to 0.69. A correlation is obtained from the data for the average Nusselt number.}, }
@article {pmid11460648, year = {2001}, author = {Sargison, JE and Guo, SM and Oldfield, ML and Rawlinson, AJ}, title = {The variation of heat transfer coefficient, adiabatic effectiveness and aerodynamic loss with film cooling hole shape.}, journal = {Annals of the New York Academy of Sciences}, volume = {934}, number = {}, pages = {361-368}, doi = {10.1111/j.1749-6632.2001.tb05871.x}, pmid = {11460648}, issn = {0077-8923}, abstract = {The heat transfer coefficient and adiabatic effectiveness of cylindrical, fan shaped holes and a slot are presented for the region zero to 50 diameters downstream of the holes. Narrow-band liquid crystals were used on a heated flat plate with heated air coolant. These parameters have been measured in a steady state, low speed facility at engine representative Reynolds number based on hole diameter and pressure difference ratio (ideal momentum flux ratio). The aerodynamic loss due to each of the film cooling geometries has been measured using a traverse of the boundary layer far downstream of the film cooling holes. Compared to the cylindrical holes, the fan shaped hole case showed an improvement in the uniformity of cooling downstream of the holes and in the level of laterally averaged film cooling effectiveness. The fan effectiveness approached the slot level and both the fan and cylindrical hole cases show lower heat transfer coefficients than the slot and non film cooled cases based on the laterally averaged results. The drawback to the fan shaped hole was that the aerodynamic loss was significantly higher than both the slot and cylindrical hole values due to inefficient diffusion in the hole exit expansion.}, }
@article {pmid11460647, year = {2001}, author = {Chen, PH and Hung, MS and Ding, PP}, title = {Film cooling performance on curved walls with compound angle hole configuration.}, journal = {Annals of the New York Academy of Sciences}, volume = {934}, number = {}, pages = {353-360}, doi = {10.1111/j.1749-6632.2001.tb05870.x}, pmid = {11460647}, issn = {0077-8923}, abstract = {In order to explore the effect of compound angle holes on film cooling over a convex wall and a concave wall, the present study adopts the transient liquid crystal thermography for conducting the film cooling measurement on simple hole and expanded-hole configurations. Two compound angles of 0 and 45 deg are tested at an elevated mainstream turbulence condition (Tu) of 3.8%. The test pieces have the different radius of curvature (2r/D) of 92.5 on convex and 86.5 on concave, and the same pitch to diameter ratio (P/D) of 3 on both convex and concave walls. All measurements were conducted under the mainstream Reynolds number (Re(d)) of 1700 on convex and 2300 on concave with the density ratio between coolant and mainstream (rho c/rho m) of 0.98. In current study, the effect of blowing ratio (M) on film cooling performance is investigated by varying the range of blowing ratio from 0.5 and 2.0. The present measured results show that the forward-expanded hole injection provides better surface protection than the simple hole injection. As far as the injection angle is concerned, compound angle injection provides higher film effectiveness than simple angle injection. However, the forward-expanded hole in injection (beta = 0 degree) has the best performance on both convex and concave surfaces.}, }
@article {pmid11460639, year = {2001}, author = {Obata, M and Kumada, M and Ijichi, N}, title = {Heat transfer and flow characteristics on a gas turbine shroud.}, journal = {Annals of the New York Academy of Sciences}, volume = {934}, number = {}, pages = {289-296}, doi = {10.1111/j.1749-6632.2001.tb05862.x}, pmid = {11460639}, issn = {0077-8923}, abstract = {The work described in this paper is an experimental investigation of the heat transfer from the main flow to a turbine shroud surface, which may be applicable to ceramic gas turbines. Three kinds of turbine shrouds are considered with a flat surface, a taper surface and a spiral groove surface opposite to the blades in an axial flow turbine of actual turbo-charger. Heat transfer measurements were performed for the experimental conditions of a uniform heat flux or a uniform wall temperature. The effects of the inlet flow angle, rotational speed, and tip clearance on the heat transfer coefficient were clarified under on- and off-design flow conditions. The mean heat transfer coefficient was correlated to the blade Reynolds number and tip clearance, and compared with an experimental correlation and measurements of a flat surface. A comparison was also made for the measurement of static pressure distributions.}, }
@article {pmid11460635, year = {2001}, author = {Yavuzkurt, S and Iyer, GR}, title = {Studies on free stream turbulence as related to gas turbine heat transfer. A review of authors' past work and future implications.}, journal = {Annals of the New York Academy of Sciences}, volume = {934}, number = {}, pages = {265-272}, doi = {10.1111/j.1749-6632.2001.tb05859.x}, pmid = {11460635}, issn = {0077-8923}, abstract = {A review of the past work done on free stream turbulence (FST) as applied to gas turbine heat transfer and its implications for future studies are presented. It is a comprehensive approach to the results of many individual studies in order to derive the general conclusions that could be inferred from all rather than discussing the results of each individual study. Three experimental and four modeling studies are reviewed. The first study was on prediction of heat transfer for film cooled gas turbine blades. An injection model was devised and used along with a 2-D low Reynolds number k-epsilon model of turbulence for the calculations. Reasonable predictions of heat transfer coefficients were obtained for turbulence intensity levels up to 7%. Following this modeling study a series of experimental studies were undertaken. The objective of these studies was to gain a fundamental understanding of mechanisms through which FST augments the surface heat transfer. Experiments were carried out in the boundary layer and in the free stream downstream of a gas turbine combustor simulator, which produced initial FST levels of 25.7% and large length scales (About 5-10 cm for a boundary layer 4-5 cm thick). This result showed that one possible mechanism through which FST caused an increase in heat transfer is by increasing the number of ejection events. In a number of modeling studies several well-known k-epsilon models were compared for their predictive capability of heat transfer and skin friction coefficients under moderate and high FST. Two data sets, one with moderate levels of FST (about 7%) and one with high levels of FST (about 25%) were used for this purpose. Although the models did fine in their predictions of cases with no FST (baseline cases) they failed one by one as FST levels were increased. Under high FST (25.7% initial intensity) predictions of Stanton number were between 35-100% in error compared to the measured values. Later a new additional production term indicating the interaction between the turbulent kinetic energy (TKE) and mean velocity gradients was introduced into the TKE equation. The predicted results of skin friction coefficient and Stanton number were excellent both in moderate and high FST cases. In fact these model also gave good predictions of TKE profiles whereas earlier unmodified models did not predict the correct TKE profiles even under moderate turbulence intensities. Although this new production term seems to achieve the purpose, it is the authors' belief that it is diffusion term of the TKE equation, which needs to be modified in order to fit the physical events in high FST boundary layer flows. The results of these studies are currently being used to come up with new diffusion model for the TKE equation.}, }
@article {pmid11460633, year = {2001}, author = {Suslov, D and Schulz, A and Wittig, S}, title = {Effect of Reynolds number, turbulence level and periodic wake flow on heat transfer on low pressure turbine blades.}, journal = {Annals of the New York Academy of Sciences}, volume = {934}, number = {}, pages = {249-256}, doi = {10.1111/j.1749-6632.2001.tb05857.x}, pmid = {11460633}, issn = {0077-8923}, abstract = {The development of effective cooling methods is of major importance for the design of new gas turbines blades. The conception of optimal cooling schemes requires a detailed knowledge of the heat transfer processes on the blade's surfaces. The thermal load of turbine blades is predominantly determined by convective heat transfer which is described by the local heat transfer coefficient. Heat transfer is closely related to the boundary layer development along the blade surface and hence depends on various flow conditions and geometrical parameters. Particularly Reynolds number, pressures gradient and turbulence level have great impact on the boundary layer development and the according heat transfer. Therefore, in the present study, the influence of Reynolds number, turbulence intensity, and periodic unsteady inflow on the local heat transfer of a typical low pressure turbine airfoil is experimentally examined in a plane cascade.}, }
@article {pmid11460632, year = {2001}, author = {Holmer, ML and Eriksson, LE and Sunden, B}, title = {Convective heat transfer on an inlet guide vane.}, journal = {Annals of the New York Academy of Sciences}, volume = {934}, number = {}, pages = {241-248}, doi = {10.1111/j.1749-6632.2001.tb05856.x}, pmid = {11460632}, issn = {0077-8923}, abstract = {The flow and temperature fields around an inlet guide vane are determined numerically by a CFD method. Outer surface temperatures, heat transfer coefficient distributions, and static pressure distributions are presented. Three different thermal boundary conditions on the vane are analysed. The computed results are compared with experimental data. The governing equations are solved by a finite-volume method with the low Reynolds number version of the k-omega turbulence model by Wilcox implemented. It is found that the calculated results agree best with measurements if a conjugate heat transfer approach is applied and thus this wall condition is recommended for future investigations of film cooling of guide vanes and turbine blades.}, }
@article {pmid11446814, year = {2001}, author = {Li Xj, XJ and Mao, ZS}, title = {The Effect of Surfactant on the Motion of a Buoyancy-Driven Drop at Intermediate Reynolds Numbers: A Numerical Approach.}, journal = {Journal of colloid and interface science}, volume = {240}, number = {1}, pages = {307-322}, doi = {10.1006/jcis.2001.7587}, pmid = {11446814}, issn = {1095-7103}, abstract = {A numerical investigation of the flow field inside and around a deformed drop translating in another quiescent liquid contaminated by surfactant soluble in continuous phase but not soluble in dispersed phase is presented in this paper. The finite difference method was used to solve numerically the coupled Navier-Stokes and convective-diffusion equations in a body-fitted orthogonal coordinate system. The present numerical simulation of a two-fluid free-boundary problem was validated by comparison of the simulation results of a drop contaminated by surfactant at creeping flow with the analytical solution and the predicted rise velocity of a bubble contaminated by SDS with experimental data at the moderate Reynolds number. To evaluate the effect of surfactant on the drag coefficient, the steady motion of a drop of the same volume in the pure and contaminated systems was simulated. The behavior of the recirculating wake behind a contaminated drop was also examined and found that it becomes more closely attached to the rear stagnancy of the drop when the surfactant concentration is increased gradually. Finally, the stagnant-cap model was revisited and its defects and limitations were analyzed against numerical simulation. Copyright 2001 Academic Press.}, }
@article {pmid11425076, year = {2001}, author = {Rohlf, K and Tenti, G}, title = {The role of the Womersley number in pulsatile blood flow a theoretical study of the Casson model.}, journal = {Journal of biomechanics}, volume = {34}, number = {1}, pages = {141-148}, doi = {10.1016/s0021-9290(00)00103-2}, pmid = {11425076}, issn = {0021-9290}, mesh = {Blood Circulation/*physiology ; *Models, Cardiovascular ; Pulsatile Flow ; }, abstract = {The purpose of this Note is to clarify the meaning of the Womersley number alpha in pulsatile blood flow in small vessels. In particular. we explain why the use of alpha as aperturbation parameter to obtain approximate solutions of the Casson model (frequently used in the literature) is not appropriate. Using the techniques of dimensional analysis and scaling, we show that alpha is the product of the Reynolds and Strouhal numbers. Since the latter is very small for physiological flows, the result is that alpha < 1 even at relatively high values of the Reynolds number (i.e., for non-negligible inertia) and we validate our perturbation theory results by comparison with a numerical integration of the full model. Although this analysis is based on the Casson model, our method has general validity and may be applied to other models which describe more accurately the rheological properties of blood.}, }
@article {pmid11415108, year = {2001}, author = {Kuusela, E and Ala-Nissila, T}, title = {Velocity correlations and diffusion during sedimentation.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {63}, number = {6 Pt 1}, pages = {061505}, doi = {10.1103/PhysRevE.63.061505}, pmid = {11415108}, issn = {1539-3755}, abstract = {We study the dynamics of sedimenting non-Brownian particles under steady-state conditions in two-dimensional geometry. We concentrate on the autocorrelation functions of the velocity fluctuations and the corresponding memory functions and diffusion coefficients as functions of Phi(V) for small but finite Reynolds numbers. For the numerical simulations we have chosen the model of Schwarzer [Phys. Rev. E 52, 6461 (1995)] where a continuum liquid phase is coupled through Stokesian friction to a discrete particle phase with volume fraction Phi(V). We find that the steady-state velocity fluctuations are spatially highly anisotropic and the correlation functions parallel to gravity have nonexponential time dependence similar to that of purely dissipative systems with strong interactions. The corresponding memory functions also show nontrivial behavior. Diffusion along the direction of gravity is much faster than perpendicular to it, with the anisotropy decreasing as either the Reynolds number or the volume fraction increases.}, }
@article {pmid11415043, year = {2001}, author = {Zhang, R and Chen, H and Qian, YH and Chen, S}, title = {Effective volumetric lattice Boltzmann scheme.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {63}, number = {5 Pt 2}, pages = {056705}, doi = {10.1103/PhysRevE.63.056705}, pmid = {11415043}, issn = {1539-3755}, abstract = {An efficient fractional volumetric scheme is proposed for lattice Boltzmann method (LBM). By reducing the effective time step, the scheme possesses much better stability particularly for thermal LBM. The same accuracy and simplicity of the standard LBM are preserved for achieving the Navier-Stokes equation. Since the effective viscosity is reduced by the fraction factor p, the scheme becomes very effective for simulating high Reynolds number thermal flows.}, }
@article {pmid11415012, year = {2001}, author = {Brun, C and Pumir, A}, title = {Statistics of Fourier modes in a turbulent flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {63}, number = {5 Pt 2}, pages = {056313}, doi = {10.1103/PhysRevE.63.056313}, pmid = {11415012}, issn = {1539-3755}, abstract = {Fourier series are often used to discuss the properties of a homogeneous turbulent field. We investigate the statistics of Fourier modes of the turbulent velocity field and of a passive scalar. The statistics of individual Fourier modes is known to be Gaussian when the size of the system L is much larger that the integral (correlation) size l(0). The case where the integral size is of the order of the system size L approximately l(0), is studied by direct numerical simulations in the range 20 < or approximately = Rlambda < or approximately = 80. At a given Rlambda, we find that the probabilities of large fluctuations become larger when the wave number increases, in qualitative agreement with the notion of intermittency. As the Reynolds number increases, however, the probability density functions become closer to Gaussian, in sharp contrast with the behavior of velocity increments. We also show that in a simple model of cascade, the Fourier series decomposition is not appropriate to capture intermittency effects. Last, we discuss other issues related to our results.}, }
@article {pmid11415008, year = {2001}, author = {Leprévost, JC and Angilella, JR and Brancher, JP}, title = {Geometrical analysis of chaotic mixing in a low Reynolds number magnetohydrodynamic quadripolar flow.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {63}, number = {5 Pt 2}, pages = {056309}, doi = {10.1103/PhysRevE.63.056309}, pmid = {11415008}, issn = {1539-3755}, abstract = {A mixing device for highly viscous fluids with finite electrical conductivity is investigated theoretically. Stirring is performed by means of electromagnetic forces provided by inductor wires located outside the flow domain. The flow shows hyperbolic and elliptic singular points. Inductors are displaced in a periodic manner, leading to an efficient stretching and folding mechanism. The goodness of mixing is quantified by means of a geometrical analysis based on box-counting techniques. This analysis gives valuable information about advection of a spot of dye injected in the flow, in the limit of infinite Peclet numbers. A spatiotemporal criterion for mixing efficiency is derived, and characteristic scales are analyzed. The influence of various parameters on mixing efficiency is discussed by making use of both the geometrical analysis and Poincaré sections.}, }
@article {pmid11401345, year = {2000}, author = {Zholkovskij, EK and Koval'chuk, VI and Dukhin, SS and Miller, R}, title = {Dynamics of Rear Stagnant Cap Formation at Low Reynolds Numbers.}, journal = {Journal of colloid and interface science}, volume = {226}, number = {1}, pages = {51-59}, doi = {10.1006/jcis.2000.6786}, pmid = {11401345}, issn = {1095-7103}, abstract = {The rising of a gas bubble in a surfactant solution is considered within the framework of the rear stagnant cap (r.s.c.) model at low Reynolds number. The adsorption is supposed to be the slowest process in the system. The bubble velocity is predicted to depend on time due to the nonstationary process of surface stagnant zone formation. Various types of bubble behavior are discussed. It is shown which information on the characteristics of adsorption one can extract from the time dependency of the bubble velocity. Copyright 2000 Academic Press.}, }
@article {pmid11401339, year = {2000}, author = {Voinov, OV}, title = {Wetting: Inverse Dynamic Problem and Equations for Microscopic Parameters.}, journal = {Journal of colloid and interface science}, volume = {226}, number = {1}, pages = {5-15}, doi = {10.1006/jcis.2000.6726}, pmid = {11401339}, issn = {1095-7103}, abstract = {Movement of a liquid meniscus in a low-diameter capillary while it is being filled or emptied is considered. The liquid is nonvolatile. Assuming low Reynolds number and low capillary number, the liquid-gas interface shape is studied. Angles of inclination of this boundary to the solid near the contact line are small. Consideration is given to the inverse problem in wetting dynamics: to establish an analytic expression for the universal constant that influences the dynamics of a three-phase contact line. Inverse relations for microscopic parameters in terms of macroscopic measured values obtained in experiments with a meniscus moving through a capillary are derived. The inverse relations are substantiated independently. To do so, numerical experiments for a van der Waals liquid have been carried out, using the de Gennes model of partial wetting. General formulas for microparameters agree well with numerical experiments. The article provides the similarity criterion which influences the wetting in the case of a van der Waals liquid meniscus. The inverse dynamic problem for both an advancing and a receding meniscus is solved. A relation for the critical speed of meniscus recession is proposed. Two contact angles for a meniscus are discussed. Behavior of dynamic contact angles in the vicinity of the critical speed is studied. One of the angles is shown to vanish at less than the critical speed, and the other one, exactly at the critical speed. In the case of an advancing meniscus the equations for microparameters are valid for both partial and complete wetting. The proposed inverse expression for complete wetting allows determination of the maximum precursor film thickness and its dependence on the motion speed (also determination of the Hamaker constant in the case of a van der Waals liquid). Copyright 2000 Academic Press.}, }
@article {pmid11398745, year = {2001}, author = {Lovvorn, J and Liggins, GA and Borstad, MH and Calisal, SM and Mikkelsen, J}, title = {Hydrodynamic drag of diving birds: effects of body size, body shape and feathers at steady speeds.}, journal = {The Journal of experimental biology}, volume = {204}, number = {Pt 9}, pages = {1547-1557}, doi = {10.1242/jeb.204.9.1547}, pmid = {11398745}, issn = {0022-0949}, mesh = {Animals ; Biomechanical Phenomena ; Biometry ; Birds/*anatomy &amp; histology/*physiology ; *Body Constitution ; *Diving ; Energy Metabolism ; *Feathers ; Freezing ; Models, Anatomic ; Models, Biological ; Swimming ; }, abstract = {For birds diving to depths where pressure has mostly reduced the buoyancy of air spaces, hydrodynamic drag is the main mechanical cost of steady swimming. Drag is strongly affected by body size and shape, so such differences among species should affect energy costs. Because flow around the body is complicated by the roughness and vibration of feathers, feathers must be considered in evaluating the effects of size and shape on drag. We investigated the effects of size, shape and feathers on the drag of avian divers ranging from wing-propelled auklets weighing 75 g to foot-propelled eiders weighing up to 2060 g. Laser scanning of body surfaces yielded digitized shapes that were averaged over several specimens per species and then used by a milling machine to cut foam models. These models were fitted with casts of the bill area, and their drag was compared with that of frozen specimens. Because of the roughness and vibration of the feathers, the drag of the frozen birds was 2-6 times that of the models. Plots of drag coefficient (C(D)) versus Reynolds number (Re) differed between the model and the frozen birds, with the pattern of difference varying with body shape. Thus, the drag of cast models or similar featherless shapes can differ both quantitatively and qualitatively from that of real birds. On the basis of a new towing method with no posts or stings that alter flow or angles of attack, the dimensionless C(D)/Re curves differed among a size gradient of five auklet species (75-100g) with similar shapes. Thus, extrapolation of C(D)/Re curves among related species must be performed with caution. At lower speeds, the C(D) at a given Re was generally higher for long-necked birds that swim with their neck extended (cormorants, grebes, some ducks) than for birds that swim with their head retracted (penguins, alcids), but this trend was reversed at high speeds. Because swimming birds actually travel at a range of instantaneous speeds during oscillatory strokes, species variations in drag at different speeds must be considered in the context of accelerational stroking.}, }
@article {pmid11397053, year = {2001}, author = {Yang, RJ and Fu, LM and Lin, YC}, title = {Electroosmotic Flow in Microchannels.}, journal = {Journal of colloid and interface science}, volume = {239}, number = {1}, pages = {98-105}, doi = {10.1006/jcis.2001.7551}, pmid = {11397053}, issn = {1095-7103}, abstract = {The electroosmotic flow induced by an applied electrostatic potential field through microchannels between two parallel plates and a 90 degrees bend is analyzed in this work. A nonlinear, two-dimensional Poisson-Boltzmann equation governing the electrical double-layer field and the Laplace equation governing the electrostatic field distribution in microchannels are numerically solved using a finite-difference method. A body force caused by the interaction between the electrical double-layer field and the applied electrostatic field is included in the full Navier-Stokes equations. The effects of the electrical double-layer field and the applied electrostatic field on the fluid velocity distribution, pressure drop, and skin friction are discussed. A small pressure drop along the parallel plates is detected, although it is always neglected in the literature. Pressure is not a constant across the channel height. The axial velocity profile is no longer flat across the channel height when the Reynolds number is large. A separation bubble is detected near the 90 degrees junction when the Reynolds number is large. Copyright 2001 Academic Press.}, }
@article {pmid11393863, year = {2001}, author = {Santiago, JG}, title = {Electroosmotic flows in microchannels with finite inertial and pressure forces.}, journal = {Analytical chemistry}, volume = {73}, number = {10}, pages = {2353-2365}, doi = {10.1021/ac0101398}, pmid = {11393863}, issn = {0003-2700}, abstract = {Emerging microfluidic systems have spurred an interest in the study of electrokinetic flow phenomena in complex geometries and a variety of flow conditions. This paper presents an analysis of the effects of fluid inertia and pressure on the velocity and vorticity field of electroosmotic flows. In typical on-chip electrokinetics applications, the flow field can be separated into an inner flow region dominated by viscous and electrostatic forces and an outer flow region dominated by inertial and pressure forces. These two regions are separated by a slip velocity condition determined by the Helmholtz-Smoulochowski equation. The validity of this assumption is investigated by analyzing the velocity field in a pressure-driven, two-dimensional flow channel with an impulsively started electric field. The regime for which the inner/outer flow model is valid is described in terms of nondimensional parameters derived from this example problem. Next, the inertial forces, surface conditions, and pressure-gradient conditions for a full-field similarity between the electric and velocity fields in electroosmotic flows are discussed. A sufficient set of conditions for this similarity to hold in arbitrarily shaped, insulating wall microchannels is the following: uniform surface charge, low Reynolds number, low Reynolds and Strouhal number product, uniform fluid properties, and zero pressure differences between inlets and outlets. Last, simple relations describing the generation of vorticity in electroosmotic flow are derived using a wall-local, streamline coordinate system.}, }
@article {pmid11384358, year = {2001}, author = {Moisy, F and Willaime, H and Andersen, JS and Tabeling, P}, title = {Passive scalar intermittency in low temperature helium flows.}, journal = {Physical review letters}, volume = {86}, number = {21}, pages = {4827-4830}, doi = {10.1103/PhysRevLett.86.4827}, pmid = {11384358}, issn = {0031-9007}, abstract = {We report new measurements of mixing of passive temperature field in a turbulent flow. The use of low temperature helium gas allows us to span a range of microscale Reynolds number, R(lambda), from 100 to 650. The exponents xi(n) of the temperature structure functions </straight theta(x+r)-straight theta(x)/(n)> approximately r(xi(n)) are shown to saturate to xi(infinity) approximately 1.45+/-0.1 for the highest orders, n approximately 10. This saturation is a signature of statistics dominated by frontlike structures, the cliffs. Statistics of the cliffs' characteristics are performed, particularly their widths are shown to scale as the Kolmogorov length scale.}, }
@article {pmid11371440, year = {2001}, author = {Shankaran, H and Neelamegham, S}, title = {Nonlinear flow affects hydrodynamic forces and neutrophil adhesion rates in cone-plate viscometers.}, journal = {Biophysical journal}, volume = {80}, number = {6}, pages = {2631-2648}, pmid = {11371440}, issn = {0006-3495}, support = {HL63014/HL/NHLBI NIH HHS/United States ; }, mesh = {Blood Pressure ; Blood Viscosity/*physiology ; Cell Adhesion ; *Cell Aggregation ; Endothelium, Vascular/cytology/physiology ; *Hemorheology ; Kinetics ; Models, Biological ; Neutrophils/*cytology/*metabolism ; Platelet Aggregation ; }, abstract = {We present a theoretical and experimental analysis of the effects of nonlinear flow in a cone-plate viscometer. The analysis predicts that flow in the viscometer is a function of two parameters, the Reynolds number and the cone angle. Nonlinear flow occurs at high shear rates and causes spatial variations in wall shear stress, collision frequency, interparticle forces and attachment times within the viscometer. We examined the effect of these features on cellular adhesion kinetics. Based on recent data (Taylor, A. D., S. Neelamegham, J. D. Hellums, et al. 1996. Biophys. J. 71:3488-3500), we modeled neutrophil homotypic aggregation as a process that is integrin-limited at low shear and selectin-limited at high shear. Our calculations suggest that selectin and integrin on-rates lie in the order of 10(-2)-10(-4)/s. They also indicate that secondary flow causes positional variations in adhesion efficiency in the viscometer, and that the overall efficiency is dependent not only on the shear rate, but also the sample volume and the cone angle. Experiments performed with isolated neutrophils confirmed these predictions. In these experiments, enhancing secondary flow by increasing the sample volume from 100 to 1000 microl at 1500/s for a 2 degrees cone caused up to an approximately 45% drop in adhesion efficiency. Our results suggest that secondary flow may significantly influence cellular aggregation, platelet activation, and endothelial cell mechanotransduction measurements made in the viscometer over the range of conditions applied in typical biological studies.}, }
@article {pmid11369673, year = {2001}, author = {Goldman, JA and Koehl, MA}, title = {Fluid dynamic design of lobster olfactory organs: high speed kinematic analysis of antennule flicking by Panulirus argus.}, journal = {Chemical senses}, volume = {26}, number = {4}, pages = {385-398}, doi = {10.1093/chemse/26.4.385}, pmid = {11369673}, issn = {0379-864X}, mesh = {Animals ; Biomechanical Phenomena ; Flagella/chemistry/*physiology ; Nephropidae/*anatomy &amp; histology/*physiology ; Receptors, Odorant/chemistry/*physiology ; Sense Organs/*anatomy &amp; histology/physiology ; Smell/*physiology ; Video Recording/instrumentation ; Water Movements ; }, abstract = {Many organisms use olfactory appendages bearing arrays of microscopic hairs to pick up chemical signals from the surrounding water or air. We report a morphometric and high speed kinematic analysis of the olfactory organs (lateral flagella of the antennules, which bear chemosensory aesthetasc hairs) of the spiny lobster, Panulirus argus. Panulirus argus sample specific locations by executing a rapid series of antennule flicks at one position, moving the antennule to a different spot and then performing another series of flicks. Odorant delivery to an aesthetasc depends on the water motion near it, which depends on its Reynolds number (Re, proportional to both the diameter and speed of the hair). High speed video enabled us to resolve that during a series of flicks, an antennule moves down rapidly (aesthetasc Re = 2) and up more slowly (Re = 0.5), pausing briefly (approximately 0.54 s) before the next downstroke. The antennules of P. argus operate in a range of Re values and inter-aesthetasc spacings in which penetration of fluid between the hairs in an array is especially sensitive to changes in speed. Therefore, when antennules flick 'old' water is flushed out of the aesthetasc array during the leaky downstroke and is not picked up again during the less leaky upstroke, hence the antennules can take discrete samples. Thus, by operating in this critical Re range these antennules should be particularly effective at sniffing.}, }
@article {pmid11343428, year = {2001}, author = {Schreuder, MD and Brewer, CA and Heine, C}, title = {Modelled influences of non-exchanging trichomes on leaf boundary layers and gas exchange.}, journal = {Journal of theoretical biology}, volume = {210}, number = {1}, pages = {23-32}, doi = {10.1006/jtbi.2001.2285}, pmid = {11343428}, issn = {0022-5193}, mesh = {Carbon Dioxide ; Gases/*metabolism ; Models, Biological ; Plant Leaves/*metabolism ; Water ; *Wind ; }, abstract = {The two main resistances in the exchange of gases between plants and the atmosphere are stomatal and boundary layer resistances. We modeled boundary layer dynamics over glabrous and pubescent leaves (assuming non-exchanging trichomes) with leaf lengths varying from 0.01 to 0.2 m, and windspeeds of 0.1-5.0 m x s(-1). Results from theoretical and semi-empirical formulae were compared. As expected, boundary layer thickness decreased with decreasing leaf length and increasing windspeed. The presence of trichomes increased leaf surface roughness, resulting in lowered Reynolds numbers at which the boundary layer became turbulent. This effect is especially important at low windspeeds and over small leaves, where the Reynolds number over glabrous surfaces would be low. We derived a new simple dimensionless number, the trip factor, to distinguish field conditions that would lead to a turbulent boundary layer based on the influence of trichomes. Because modeled rates of CO2 and H2O(v) exchange over turbulent boundary layers are one or more orders of magnitude faster than over laminar boundary layers, a turbulent boundary layer may lead to increased carbon uptake by plants. The biological trade-off is potentially increased transpirational water loss. However, in understory habitats characterized by low windspeeds, even a few trichomes may increase turbulence in the boundary layer, thus facilitating photosynthetic gas exchange. Preliminary field data show that critical trip factors are exceeded for several plant species, both in understory and open habitats.}, }
@article {pmid11329321, year = {2001}, author = {Gotoh, T and Fukayama, D}, title = {Pressure spectrum in homogeneous turbulence.}, journal = {Physical review letters}, volume = {86}, number = {17}, pages = {3775-3778}, doi = {10.1103/PhysRevLett.86.3775}, pmid = {11329321}, issn = {0031-9007}, abstract = {The pressure spectrum in homogeneous steady turbulence is studied using direct numerical simulation with resolution up to 1024(3) and the Reynolds number R(lambda) between 38 and 478. The energy spectrum is found to have a finite inertial range with the Kolmogorov constant K = 1.65+/-0.05 followed by a bump at large wave numbers. The pressure spectrum in the inertial range is found to be approximately P(k) = B(p)epsilon;(4/3)k(-7/3) with B(p) = 8.0+/-0.5, and followed by a bump of nearly k(-5/3) at higher wave numbers. Universality and a new scaling of the pressure spectrum are discussed.}, }
@article {pmid11328643, year = {2001}, author = {Fenlon, AJ and David, T}, title = {Numerical models for the simulation of flexible artificial heart valves: part I--computational methods.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {4}, number = {4}, pages = {323-339}, doi = {10.1080/10255840108908012}, pmid = {11328643}, issn = {1025-5842}, mesh = {Biomechanical Phenomena ; *Computer Simulation ; Coronary Circulation ; *Heart Valve Prosthesis ; *Models, Cardiovascular ; Motion ; Nonlinear Dynamics ; Polyurethanes ; Prosthesis Design ; Regional Blood Flow ; Stress, Mechanical ; Surface Properties ; }, abstract = {A numerical model of the coupled motion of a flexing surface in a high Reynolds number flow is presented for the simulation of flexible polyurethane heart valves in the aortic position. This is achieved by matching a Lagrangian dynamic leaflet model with a panel method based flow solver. The two models are coupled via the time-dependent pressure field using the unsteady Bernoulli equation. Incorporation of sub-cycling in the dynamic model equations and fast pre conditioning techniques in the panel method solver yields efficient convergence and near real-time simulations of valve motion. The generality of dynamic model allows different material properties and/or geometries to be studied easily and interactively. This interactivity is realized by embedding the models within a design environment created using the software IRIS Explorer. Two flow domains are developed, an infinite domain and an internal domain using conformal mapping theory. In addition bending stress on the valve is computed using a simple stress model based on spline and circle equation techniques.}, }
@article {pmid11328121, year = {2001}, author = {Thorsen, T and Roberts, RW and Arnold, FH and Quake, SR}, title = {Dynamic pattern formation in a vesicle-generating microfluidic device.}, journal = {Physical review letters}, volume = {86}, number = {18}, pages = {4163-4166}, doi = {10.1103/PhysRevLett.86.4163}, pmid = {11328121}, issn = {0031-9007}, abstract = {Spatiotemporal pattern formation occurs in a variety of nonequilibrium physical and chemical systems. Here we show that a microfluidic device designed to produce reverse micelles can generate complex, ordered patterns as it is continuously operated far from thermodynamic equilibrium. Flow in a microfluidic system is usually simple-viscous effects dominate and the low Reynolds number leads to laminar flow. Self-assembly of the vesicles into patterns depends on channel geometry and relative fluid pressures, enabling the production of motifs ranging from monodisperse droplets to helices and ribbons.}, }
@article {pmid11321908, year = {2001}, author = {Demokritou, P and Kavouras, IG and Harrison, D and Koutrakis, P}, title = {Development and evaluation of an impactor for a PM2.5 speciation sampler.}, journal = {Journal of the Air &amp; Waste Management Association (1995)}, volume = {51}, number = {4}, pages = {514-523}, doi = {10.1080/10473289.2001.10464296}, pmid = {11321908}, issn = {1096-2247}, mesh = {Air Pollution/*analysis ; Environmental Monitoring/*instrumentation/methods ; Gases ; Particle Size ; Sensitivity and Specificity ; Specimen Handling ; Sulfuric Acids/analysis ; }, abstract = {A conventional impactor for a particle speciation sampler was developed and validated through laboratory and field tests. The speciation sampler consists of the following components: a PM2.5 conventional impactor that removes particles larger than 2.5 microns, an all-glass, coated honeycomb diffusion denuder, and a 47-mm filter pack. The speciation sampler can operate at two different sampling rates: 10 and 16.7 L/min. An experimental characterization of the impactor's performance was conducted. The impactor's collection efficiency was examined as a function of critical design parameters such as Reynolds number, the distance from the nozzle exit to the impaction plate, and the impaction substrate coating method. The bounce of particles larger than the cut point was successfully minimized by using a greased surface as the impaction substrate. Additionally, a series of field intercomparison experiments were conducted at both 10 and 16.7 L/min airflow. PM2.5 mass and SO4(2-) concentrations were measured and compared with the Federal Reference Method (FRM) and found to be in good agreement. Results of the laboratory chamber tests also indicated that the impactor's performance was in good agreement with the FRM.}, }
@article {pmid11312595, year = {2001}, author = {McNair, JN and Newbold, JD}, title = {Turbulent transport of suspended particles and dispersing benthic organisms: the hitting-distance problem for the local exchange model.}, journal = {Journal of theoretical biology}, volume = {209}, number = {3}, pages = {351-369}, doi = {10.1006/jtbi.2001.2273}, pmid = {11312595}, issn = {0022-5193}, mesh = {Animals ; *Ecology ; Invertebrates ; Models, Biological ; Movement ; }, abstract = {The local exchange model developed by McNair et al. (1997) provides a stochastic diffusion approximation to the random-like motion of fine particles suspended in turbulent water. Based on this model, McNair (2000) derived equations governing the probability distribution and moments of the hitting time, which is the time until a particle hits the bottom for the first time from a given initial elevation. In the present paper, we derive the corresponding equations for the probability distribution and moments of the hitting distance, which is the longitudinal distance a particle has traveled when it hits the bottom for the first time. We study the dependence of the distribution and moments on a particle's initial elevation and on two dimensionless parameters: an inverse Reynolds number M (a measure of the importance of viscous mixing compared to turbulent mixing of water) and the Rouse number ŝ(a measure of the importance of deterministic gravitational sinking compared to stochastic turbulent mixing in governing the vertical motion of a particle). We also compute predicted hitting-distance distributions for two published data sets. The results show that for fine particles suspended in moderately to highly turbulent water, the hitting-distance distribution is strongly skewed to the right, with mode<median<mean. Because of the distribution's thick upper tail, there is a significant probability that a particle's hitting distance will greatly exceed the mean. The results also show that the position of the mode depends strongly on a particle's initial elevation but, compared to the median or mean, is relatively insensitive to ŝ. These results are broadly similar to those obtained by McNair (2000) for the hitting-time distribution, but the distribution and moments of the hitting distance are noticeably more sensitive to M than are the corresponding properties of the hitting time. Comparison of predicted hitting-distance distributions with data of Cushing et al. (1993) on settling distances of fine particulate organic matter in natural streams supports the view that such particles commonly fail to settle the first time they hit the stream bed.}, }
@article {pmid11312588, year = {2001}, author = {Kaandorp, JA and Sloot, PM}, title = {Morphological models of radiate accretive growth and the influence of hydrodynamics.}, journal = {Journal of theoretical biology}, volume = {209}, number = {3}, pages = {257-274}, doi = {10.1006/jtbi.2001.2261}, pmid = {11312588}, issn = {0022-5193}, mesh = {Animal Nutritional Physiological Phenomena ; Animals ; Biomechanical Phenomena ; Cnidaria/anatomy &amp; histology/*growth &amp; development ; *Computer Simulation ; *Environment ; Models, Biological ; Morphogenesis/physiology ; Porifera/anatomy &amp; histology/*growth &amp; development ; Seawater ; }, abstract = {In many marine sessile organisms (for example sponges and stony corals) the skeleton is formed by an accretive growth process, where layers of material are secreted on top of each other in a surface normal deposition process. In many of these organisms the growth process exhibits a strong morphological plasticity due to differences in exposure to water movement. In general, many of these organisms tend to form thin-branching growth forms under sheltered conditions, while the growth form gradually transforms into a more compact shape when the exposure of water movement increases. In this paper, we investigate this phenomenon by combining a three-dimensional simulation model of radiate accretive growth driven by the local availability of simulated food particles and a model, based on the lattice Boltzmann method, for simulating food particle distributions caused by a combination of flow and diffusion. In the simulations two different models of a suspension feeder with accretive growth were compared. In the first model, the deposition process is exclusively driven by the local availability of food particles, in the second model the deposition process was determined by the combination of local amount of contact to the environment and availability of food particles. In the simulations it was found that hydrodynamics has a strong impact on the overall morphologies which develop in the accretive growth process. In the model exclusively driven by the local availability of food particles, column-shaped objects emerged under diffusion conditions, while more spherical and lobed object were found for the flow-dominated case. In the simulations, the Péclet number was varied independently from the Reynolds number, which was kept at a relatively low constant value. In a range of increasing Péclet numbers, indicating an increasing influence of hydrodynamics, the simulated morphologies gradually transformed from thin-branching ones into more spherical and compact morphologies in the model where deposition was controlled by the local availability of food particles and the local amount of contact with the environment.}, }
@article {pmid11311707, year = {2001}, author = {Zhang, Z and Kleinstreuer, C and Kim, CS}, title = {Effects of curved inlet tubes on air flow and particle deposition in bifurcating lung models.}, journal = {Journal of biomechanics}, volume = {34}, number = {5}, pages = {659-669}, doi = {10.1016/s0021-9290(00)00233-5}, pmid = {11311707}, issn = {0021-9290}, mesh = {Biomechanical Phenomena ; Humans ; Lung/*anatomy &amp; histology/*physiology ; Models, Anatomic ; *Models, Biological ; Respiratory Mechanics ; }, abstract = {In vivo bifurcating airways are complex and the airway segments leading to the bifurcations are not always straight, but curved to various degrees. How do such curved inlet tubes influence the motion as well as local deposition and hence the biological responses of inhaled particulate matter in lung airways? In this paper steady laminar dilute suspension flows of micron-particles are simulated in realistic double bifurcations with curved inlet tubes, i.e., 0 degrees < or =theta< or =90 degrees, using a commercial finite-volume code with user-enhanced programs. The resulting air-flow patterns as well as particle transport and wall depositions were analyzed for different flow inlet conditions, i.e., uniform and parabolic velocity profiles, and geometric configurations. The curved inlet segments have quite pronounced effects on air-flow, particle motion and wall deposition in the downstream bifurcating airways. In contrast to straight double bifurcations, those with bent parent tubes also exhibit irregular variations in particle deposition efficiencies as a function of Stokes number and Reynolds number. There are fewer particles deposited at mildly curved inlet segments, but the particle deposition efficiencies at the downstream sequential bifurcations vary much when compared to those with straight inlets. Under certain flow conditions in sharply curved lung airways, relatively high, localized particle depositions may take place. The findings provide necessary information for toxicologic or therapeutic impact assessments and for global lung dosimetry models of inhaled particulate matter.}, }
@article {pmid11311702, year = {2001}, author = {Grigioni, M and Daniele, C and D'Avenio, G and Barbaro, V}, title = {The influence of the leaflets' curvature on the flow field in two bileaflet prosthetic heart valves.}, journal = {Journal of biomechanics}, volume = {34}, number = {5}, pages = {613-621}, doi = {10.1016/s0021-9290(00)00240-2}, pmid = {11311702}, issn = {0021-9290}, mesh = {Biomechanical Phenomena ; Blood Flow Velocity ; *Heart Valve Prosthesis/adverse effects ; Hemodynamics ; Hemolysis ; Humans ; In Vitro Techniques ; Laser-Doppler Flowmetry ; Prosthesis Design/adverse effects ; Thrombosis/etiology ; }, abstract = {A successful mechanical prosthetic heart valve design is the bileaflet valve, which has been implanted for the first time more than 20 years ago. A key feature of bileaflet valves is the geometry of the two leaflets, which can be very important in determining the flow field. Laser Doppler anemometry (LDA) was used to perform an accurate study of the velocity and turbulence shear stress peak values (TSS(max)) fields at four distances from the valve plane. TSS(max) is a relevant parameter to assess the risk of hemolysis and platelet activation associated to the implantation of a prosthetic device, continuously interacting with blood. Two bileaflet valves were tested: the St. Jude HP and the Sorin Bicarbon, of the same nominal size (19mm). The former has flat leaflets, whereas the latter's leaflets have a cylindrical surface. A high regime (CO: 6l/min) was imposed, in order to test the two valves at maximum Reynolds number and consequent turbulence generation. The flat-leaflet design of the St. Jude generates a TSS field constant with distance; on the contrary, the Bicarbon's shear stress field undergoes an evident development, with an unexpected central peak at a distance comparable to the valve's dimensions (21mm). The two bileaflet valves tested, although very similar in design, behave very differently as for their turbulence properties. In particular, the concept of curved wake leads to conclude that the curvature of the leaflets' surface must be identified as an important parameter, which deserves careful attention in PHV design and development.}, }
@article {pmid11308765, year = {2001}, author = {Ditlevsen, PD and Giuliani, P}, title = {Cascades in helical turbulence.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {63}, number = {3 Pt 2}, pages = {036304}, doi = {10.1103/PhysRevE.63.036304}, pmid = {11308765}, issn = {1539-3755}, abstract = {We suggest the existence of a characteristic inner scale xi for helicity dissipation in a regime of hydrodynamic fully developed turbulence and estimate it on dimensional grounds. This scale is always larger than the Kolmogorov scale eta and their ratio eta/xi vanishes in the high Reynolds number limit, so the flow will always be helicity free in the small scales. These ideas are illustrated in a shell model of turbulence.}, }
@article {pmid11304382, year = {2001}, author = {Fonseca, AF and de Aguiar, MA}, title = {Near equilibrium dynamics of nonhomogeneous Kirchhoff filaments in viscous media.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {63}, number = {1 Pt 2}, pages = {016611}, doi = {10.1103/PhysRevE.63.016611}, pmid = {11304382}, issn = {1539-3755}, mesh = {Base Pairing ; DNA, Circular/*chemistry ; Elasticity ; Macromolecular Substances ; *Models, Theoretical ; Nucleic Acid Conformation ; Viscosity ; }, abstract = {We study the near equilibrium dynamics of nonhomogeneous elastic filaments in viscous media using the Kirchhoff model of rods. Viscosity is incorporated in the model as an external force, which we approximate by the resistance felt by an infinite cylinder immersed in a slowly moving fluid. We use the recently developed method of Goriely and Tabor [Phys. Rev. Lett. 77, 3537 (1996); Physica D 105, 20 (1997); 105, 45 (1997)] to study the dynamics in the vicinity of the simplest equilibrium solution for a closed rod with nonhomogeneous distribution of mass, namely, the planar ring configuration. We show that small variations of the mass density along the rod are sufficient to couple the symmetric modes of the homogeneous rod problem, producing asymmetric deformations that modify substantially the dynamical coiling, even at quite low Reynolds number. The higher-density segments of the rod tend to become more rigid and less coiled. We comment on possible applications to DNA.}, }
@article {pmid11304306, year = {2001}, author = {Johnston, C and McComb, WD}, title = {Renormalized expression for the turbulent energy dissipation rate.}, journal = {Physical review. E, Statistical, nonlinear, and soft matter physics}, volume = {63}, number = {1 Pt 2}, pages = {015304}, doi = {10.1103/PhysRevE.63.015304}, pmid = {11304306}, issn = {1539-3755}, abstract = {Conditional elimination of degrees of freedom is shown to lead to an exact expression for the rate of turbulent energy dissipation in terms of a renormalized viscosity and a correction. The correction is neglected on the basis of a previous hypothesis [W. D. McComb and C. Johnston, J. Phys. A 33, L15 (2000)] that there is a range of parameters for which a quasistochastic estimate is a good approximation to the exact conditional average. This hypothesis was tested by a perturbative calculation to second order in the local Reynolds number, and the Kolmogorov prefactor (taken as a measure of the renormalized dissipation rate) was found to reach a fixed point which was insensitive to initial values of the kinematic viscosity and to values of the spatial rescaling factor h in the range 0.4< or =h< or =0.8.}, }
@article {pmid11297213, year = {2001}, author = {Wang, J and Yao, H and Lim, CJ and Zhao, Y and Yeo, TJ and Hwang, NH}, title = {Computational fluid dynamics study of a protruded-hinge bileaflet mechanical heart valve.}, journal = {The Journal of heart valve disease}, volume = {10}, number = {2}, pages = {254-262; discussion 263}, pmid = {11297213}, issn = {0966-8519}, mesh = {*Computer Simulation ; Heart Valve Diseases/*physiopathology ; *Heart Valve Prosthesis ; Hemodynamics/physiology ; Humans ; Models, Cardiovascular ; *Prosthesis Design ; }, abstract = {Following clinical experience with the Medtronic Parallel bileaflet mechanical heart valve, considerable interest has been shown in investigating fluid mechanics inside the hinge socket. Most of these studies involved hinges that are recessed into the valve housing, such as the St. Jude Medical (SJM), CarboMedics, Sorin and On-X bileaflet mechanical heart valves. The aim of this study was to investigate the flow fields of a protruded hinge under steady flow conditions, with the occluder in its fully open position. Computational fluid dynamics (CFD) simulation using the Fluent 4.4.7 commercial solver was applied in this investigation. This protruded hinge mechanism for pivoting the occluder is an in-house design from the Cardiovascular Dynamics Laboratory, Nanyang Technological University.<br><br>METHODS: The Fluent 4.4.7 code was run on a Silicon Graphic Inc. computer (4-CPUx185 MHz) in the CFD simulation. A body-fitted coordinates (BFC) grid was generated to cover the entire valvular flow domain, including the interior of the hinge and leaflet. Clearance between the leaflet and pivot housing was 50-70 microm. In the vicinity of the protruded hinge, mesh cells were small compared with hinge dimensions. A power law distribution of grid points was applied to optimize the number of cells used to cluster the entire flow field. The overall computational flow domain of the valve channel, including the floating leaflet and immersed hinge, was approximately 170,000 cells in total. Inside the hinge socket, approximately 10,000 cells were generated. A comparative model with recessed hinge that resembled the SJM valve hinge design was modeled. Due to geometric difficulties, an unstructured grid scheme was applied. Great attention was focused within the hinge pocket, in particular to the clearance between the hinge pivot and leaflet. A total of 2 million cells was generated for the whole computational flow domain.<br><br>RESULTS: Under steady flow conditions, with the leaflet fixed in an open position, the protruded hinge design yielded a pair of small vortices that formed behind the stoppers. A low-magnitude velocity was observed inside the hinge clearance. Vortices developed behind the protruded stopper. Migrating flow was noted beneath the leaflet clearance as a result of pressure difference across the leaflet. For the recessed hinge design, reverse flow dominated the inside of the hinge socket, and developed into a pair of vortices at high Reynolds number.<br><br>CONCLUSION: The protruded hinge mechanism was designed to expose the overall hinge region to the mainstream flow for a positive washing effect. Flow in this protruded hinge design is, in general, found to be three-dimensional. Initial results under steady flow conditions showed low laminar and turbulent shear stress, while the hinge clearance was well washed.}, }
@article {pmid11291201, year = {2001}, author = {Silva, GD and Publio, MC and Oliveira, WP}, title = {Evaluation of the tablet coating by the conventional spouted-bed process.}, journal = {Drug development and industrial pharmacy}, volume = {27}, number = {3}, pages = {213-219}, doi = {10.1081/ddc-100000239}, pmid = {11291201}, issn = {0363-9045}, mesh = {Chemistry, Pharmaceutical/*methods ; Tablets ; *Technology, Pharmaceutical ; }, abstract = {The purpose of this paper was to present an analysis of the tablet coating by the conventional spouted-bed process. To analyze the equipment performance, the rate of increase of the tablets mass, K1, and the adhesion coefficient eta were determined as a function of the feed flow rate of coating suspension Ws; of the Reynolds number Rep; of the flow rate of atomizing gas Wat, and of the cone base angle gamma. To analyze the product quality, the uniformity of coating mass deposition onto the tablet's surface was used. Three different procedures for description of kinetics growth, weighing method, image analysis, and measurements with a micrometer were used to verify the validity of the commonly used weighing method. Comparison between experimental results of kinetics growth with estimates obtained by a literature model was also performed. A tendency toward an increase in K1 and in eta with the feeding flow rate of coating suspension Ws was detected. The weighing method can be used for the process analysis. The kinetics of growth can be described by the growth model used. The variable that produce more pronounced effect on K1 and eta was the feed flow rate of coating suspension, the weighing method describes very well the increase of particle diameter with coating time, the growth model can be used for the describe the kinetics of growth during the coating operation, and the coating does not deposit uniformly onto the tablet's surface.}, }
@article {pmid11277305, year = {2001}, author = {Loth, F and Yardimci, MA and Alperin, N}, title = {Hydrodynamic modeling of cerebrospinal fluid motion within the spinal cavity.}, journal = {Journal of biomechanical engineering}, volume = {123}, number = {1}, pages = {71-79}, doi = {10.1115/1.1336144}, pmid = {11277305}, issn = {0148-0731}, support = {RR14242-01/RR/NCRR NIH HHS/United States ; }, mesh = {Anatomy, Cross-Sectional ; Cerebrospinal Fluid/*physiology ; Humans ; Magnetic Resonance Imaging ; *Models, Biological ; Pulsatile Flow ; Rheology ; Spinal Canal/*anatomy &amp; histology/*physiology ; Stress, Mechanical ; }, abstract = {The fluid that resides within cranial and spinal cavities, cerebrospinal fluid (CSF), moves in a pulsatile fashion to and from the cranial cavity. This motion can be measured hy magnetic resonance imaging (MRI) and may he of clinical importance in the diagnosis of several brain and spinal cord disorders such as hydrocephalus, Chiari malformation, and syringomyelia. In the present work, a geometric and hydrodynamic characterization of an anatomically relevant spinal canal model is presented. We found that inertial effects dominate the flow field under normal physiological flow rates. Along the length of the spinal canal, hydraulic diameter was found to vary significantly from 5 to 15 mm. The instantaneous Reynolds number at peak flow rate ranged from 150 to 450, and the Womersle number ranged from 5 to 17. Pulsatile flow calculations are presented for an idealized geometric representation of the spinal cavity. A linearized Navier-Stokes model of the pulsatile CSF flow was constructed based on MRI flow rate measurements taken on a healthy volunteer. The numerical model was employed to investigate effects of cross-sectional geometry and spinal cord motion on unsteady velocity, shear stress, and pressure gradientfields. The velocity field was shown to be blunt, due to the inertial character of the flow, with velocity peaks located near the boundaries of the spinal canal rather than at the midpoint between boundaries. The pressure gradient waveform was found to be almost exclusively dependent on the flow waveform and cross-sectional area. Characterization of the CSF dynamics in normal and diseased states may be important in understanding the pathophysiology of CSF related disorders. Flow models coupled with MRI flow measurements mnay become a noninvasive tool to explain the abnormal dynamics of CSF in related brain disorders as well as to determine concentration and local distribution of drugs delivered into the CSF space.}, }
@article {pmid11264845, year = {2000}, author = {Guzmán, AM and Amon, CH}, title = {Flow and Oxygen Transfer Characteristics of an Intravenous Membrane Oxygenator: A Computational Study.}, journal = {Computer methods in biomechanics and biomedical engineering}, volume = {3}, number = {2}, pages = {147-166}, doi = {10.1080/10255840008915261}, pmid = {11264845}, issn = {1476-8259}, abstract = {Spectral element computational simulations of the conservation of mass, momentum and species equations are performed to investigate the flow and oxygen transfer characteristics of an Intravenous Membrane Oxygenator (IMO). The simulations consider a three-dimensional IMO computational model consisting of equally-spaced fibers, an elastic balloon with non-permeable walls positioned longitudinally within the vena cava, and a Newtonian and time-dependent incompressible flow. Flow characteristics and oxygen transfer parameters are determined for operating conditions of a stationary and a pulsating balloon. For the stationary balloon configuration the flow is two-dimensional, parallel, laminar and without secondary flows for the Reynolds number range of 5.7-455.2. Evaluations of the oxygen transfer characteristics for the stationary balloon indicate that the main transport mechanisms are diffusion and convection in the crosswise and streamwise directions, respectively. Additionally, evaluations of oxygen transfer rates and Sherwood numbers in this Reynolds number range indicate that the oxygen transfer rate reaches an asymptotic limit at relatively moderate Reynolds numbers. For the pulsating balloon, flow characteristic results demonstrate the existence of a strong secondary flow around the fiber, and between the balloon and the fiber. This secondary flow induces oscillatory crosswise and streamwise velocities and a seemingly random spanwise flow which enhances the flow mixing as well as the transport of oxygen from the fiber surface to the bulk flow.}, }
@article {pmid11254273, year = {2000}, author = {Pal, R}, title = {Shear Viscosity Behavior of Emulsions of Two Immiscible Liquids.}, journal = {Journal of colloid and interface science}, volume = {225}, number = {2}, pages = {359-366}, doi = {10.1006/jcis.2000.6776}, pmid = {11254273}, issn = {1095-7103}, abstract = {The viscous behavior of oil-in-water (O/W) emulsions is studied over a broad range of dispersed-phase concentrations (φ) using a controlled-stress rheometer. At low-to-moderate values of φ (φ<0.60), emulsions exhibit Newtonian behavior. The droplet size does not exert any influence on the viscosity of Newtonian emulsions. However, at higher values of φ, emulsions exhibit shear-thinning behavior. The viscosity of shear-thinning emulsions is strongly influenced by the droplet size; a significant increase in the viscosity occurs when the droplet size is reduced. With the decrease in droplet size, the degree of shear thinning in concentrated emulsions is also enhanced. The viscosity data of Newtonian emulsions are described reasonably well by the cell model of Yaron and Gal-Or (Rheol. Acta 11, 241 (1972)), which takes into account the effects of the dispersed-phase concentration as well as the viscosity ratio of the dispersed phase to continuous phase. The relative viscosities of non-Newtonian emulsions having different droplet sizes but the same dispersed-phase concentration are scaled with the particle Reynolds number. The high shear viscosities of non-Newtonian emulsions can be predicted fairly well by the cell model of Yaron and Gal-Or (Rheol. Acta 11, 241 (1972)). Copyright 2000 Academic Press.}, }
@article {pmid11222132, year = {2001}, author = {Hedenström, A and Liechti, F}, title = {Field estimates of body drag coefficient on the basis of dives in passerine birds.}, journal = {The Journal of experimental biology}, volume = {204}, number = {Pt 6}, pages = {1167-1175}, doi = {10.1242/jeb.204.6.1167}, pmid = {11222132}, issn = {0022-0949}, mesh = {Animals ; Behavior, Animal/physiology ; Biomechanical Phenomena ; Flight, Animal/*physiology ; Gravitation ; Physical Phenomena ; Physics ; Songbirds/anatomy &amp; histology/*physiology ; Wings, Animal/anatomy &amp; histology ; }, abstract = {During forward flight, a bird's body generates drag that tends to decelerate its speed. By flapping its wings, or by converting potential energy into work if gliding, the bird produces both lift and thrust to balance the pull of gravity and drag. In flight mechanics, a dimensionless number, the body drag coefficient (C(D,par)), describes the magnitude of the drag caused by the body. The drag coefficient depends on the shape (or streamlining), the surface texture of the body and the Reynolds number. It is an important variable when using flight mechanical models to estimate the potential migratory flight range and characteristic flight speeds of birds. Previous wind tunnel measurements on dead, frozen bird bodies indicated that C(D,par) is 0.4 for small birds, while large birds should have lower values of approximately 0.2. More recent studies of a few birds flying in a wind tunnel suggested that previous values probably overestimated C(D,par). We measured maximum dive speeds of passerine birds during the spring migration across the western Mediterranean. When the birds reach their top speed, the pull of gravity should balance the drag of the body (and wings), giving us an opportunity to estimate C(D,par). Our results indicate that C(D,par) decreases with increasing Reynolds number within the range 0.17-0.77, with a mean C(D,par) of 0.37 for small passerines. A somewhat lower mean value could not be excluded because diving birds may control their speed below the theoretical maximum. Our measurements therefore support the notion that 0.4 (the 'old' default value) is a realistic value of C(D,par) for small passerines.}, }
@article {pmid11222131, year = {2001}, author = {Rosén, M and Hedenström, A}, title = {Gliding flight in a jackdaw: a wind tunnel study.}, journal = {The Journal of experimental biology}, volume = {204}, number = {Pt 6}, pages = {1153-1166}, doi = {10.1242/jeb.204.6.1153}, pmid = {11222131}, issn = {0022-0949}, mesh = {Animals ; Behavior, Animal ; Female ; Flight, Animal/*physiology ; Mathematics ; Models, Biological ; Physical Phenomena ; Physics ; Songbirds/anatomy &amp; histology/*physiology ; Tail/anatomy &amp; histology/physiology ; Wings, Animal/anatomy &amp; histology/physiology ; }, abstract = {We examined the gliding flight performance of a jackdaw Corvus monedula in a wind tunnel. The jackdaw was able to glide steadily at speeds between 6 and 11 m s(-1). The bird changed its wingspan and wing area over this speed range, and we measured the so-called glide super-polar, which is the envelope of fixed-wing glide polars over a range of forward speeds and sinking speeds. The glide super-polar was an inverted U-shape with a minimum sinking speed (V(ms)) at 7.4 m s(-1) and a speed for best glide (V(bg)) at 8.3 m s(-)). At the minimum sinking speed, the associated vertical sinking speed was 0.62 m s(-1). The relationship between the ratio of lift to drag (L:D) and airspeed showed an inverted U-shape with a maximum of 12.6 at 8.5 m s(-1). Wingspan decreased linearly with speed over the whole speed range investigated. The tail was spread extensively at low and moderate speeds; at speeds between 6 and 9 m s(-1), the tail area decreased linearly with speed, and at speeds above 9 m s(-1) the tail was fully furled. Reynolds number calculated with the mean chord as the reference length ranged from 38 000 to 76 000 over the speed range 6-11 m s(-1). Comparisons of the jackdaw flight performance were made with existing theory of gliding flight. We also re-analysed data on span ratios with respect to speed in two other bird species previously studied in wind tunnels. These data indicate that an equation for calculating the span ratio, which minimises the sum of induced and profile drag, does not predict the actual span ratios observed in these birds. We derive an alternative equation on the basis of the observed span ratios for calculating wingspan and wing area with respect to forward speed in gliding birds from information about body mass, maximum wingspan, maximum wing area and maximum coefficient of lift. These alternative equations can be used in combination with any model of gliding flight where wing area and wingspan are considered to calculate sinking rate with respect to forward speed.}, }
@article {pmid11214313, year = {2001}, author = {Segrè, PN and Liu, F and Umbanhowar, P and Weitz, DA}, title = {An effective gravitational temperature for sedimentation.}, journal = {Nature}, volume = {409}, number = {6820}, pages = {594-597}, doi = {10.1038/35054518}, pmid = {11214313}, issn = {0028-0836}, abstract = {The slow sedimentation of suspensions of solid particles in a fluid results in complex phenomena that are poorly understood. For a low volume fraction (phi) of particles, long-range hydrodynamic interactions result in surprising spatial correlations in the velocity fluctuations; these are reminiscent of turbulence, even though the Reynolds number is very low. At higher values of phi, the behaviour of sedimentation remains unclear; the upward back-flow of fluid becomes increasingly important, while collisions and crowding further complicate inter-particle interactions. Concepts from equilibrium statistical mechanics could in principle be used to describe the fluctuations and thereby provide a unified picture of sedimentation, but one essential ingredient--an effective temperature that provides a mechanism for thermalization--is missing. Here we show that the gravitational energy of fluctuations in particle number can act as an effective temperature. Moreover, we demonstrate that the high-phi behaviour is in fact identical to that at low phi, provided that the suspension viscosity and sedimentation velocity are scaled appropriately, and that the effects of particle packing are included.}, }
@article {pmid11207765, year = {1999}, author = {Stoodley, P and Lewandowski, Z and Boyle, JD and Lappin-Scott, HM}, title = {The formation of migratory ripples in a mixed species bacterial biofilm growing in turbulent flow.}, journal = {Environmental microbiology}, volume = {1}, number = {5}, pages = {447-455}, doi = {10.1046/j.1462-2920.1999.00055.x}, pmid = {11207765}, issn = {1462-2912}, mesh = {Biofilms/*growth &amp; development ; Bioreactors ; Environment, Controlled ; Gram-Negative Bacteria/*physiology ; Image Processing, Computer-Assisted ; Photomicrography ; }, abstract = {Mixed-species biofilms, consisting of Klebsiella pneumoniae, Pseudomonas aeruginosa, Pseudomonas fluorescens and Stenotrophomonas maltophilia, were grown in glass flow cells under either laminar or turbulent flow. The biofilms grown in laminar flow consisted of roughly circular-shaped microcolonies separated by water channels. In contrast, biofilm microcolonies grown in turbulent flow were elongated in the downstream direction, forming filamentous 'streamers'. Moreover, biofilms growing in turbulent flow developed extensive patches of ripple-like structures between 9 and 13 days of growth. Using time-lapse microscopic imaging, we discovered that the biofilm ripples migrated downstream. The morphology and the migration velocity of the ripples varied with short-term changes in the bulk liquid flow velocity. The ripples had a maximum migration velocity of 800 micromh(-1) (2.2 x 10(-7) m s(-1)) when the liquid flow velocity was 0.5 ms(-1) (Reynolds number=1,800). This work challenges the commonly held assumption that biofilm structures remain at the same location on a surface until they eventually detach.}, }
@article {pmid11204540, year = {2000}, author = {Noren, D and Palmer, HJ and Frame, MD}, title = {Predicted wall shear rate gradients in T-type arteriolar bifurcations.}, journal = {Biorheology}, volume = {37}, number = {5-6}, pages = {325-340}, pmid = {11204540}, issn = {0006-355X}, mesh = {Animals ; Arterioles/*physiology ; Blood Flow Velocity/physiology ; Cricetinae ; Endothelium, Vascular/physiology ; Erythrocytes/physiology ; Finite Element Analysis ; *Hemorheology ; Mesocricetus ; *Models, Cardiovascular ; Stress, Mechanical ; }, abstract = {The purpose of this study was to examine the theoretical impact of the local bifurcation geometry on the shear rate gradient in a divergent arteriolar-type bifurcation. Newtonian flow through an arteriolar bifurcation was modeled using 3-dimensional computational fluid dynamics (CFD). Branching angles of 30 degrees, 50 degrees, 70 degrees, 90 degrees, 110 degrees, 130 degrees, and 150 degrees were studied at a Reynolds number (Re) of 0.01 in seven separate models. Both the flow split (30%) and the branch to main vessel diameter ratio (4/5) were held constant. Velocity profiles were predicted to deviate significantly from a parabolic form, both immediately before and after the branch. This deviation was shown to be a function of the local bifurcation geometry of each model, which consisted of a branching angle and associated feed-branch intersection shape. Immediately before and after the branch, the shear rate along the lateral branching wall was predicted to exceed (5-fold) that calculated for fully developed flow in the feed. In vivo data were from the anesthetized (pentobarbital, 70 mg/kg) hamster cremaster muscle preparation. Red blood cells were used as flow markers in arteriolar branch points (n = 74) show that a significant gradient in shear rate occurs at the locations and branch shapes predicted by the computational model. Thus, for low Re divergent flow, the gradient in shear rate measured for non-Newtonian conditions, is approximated by a finite element fluid dynamics model of Newtonian flow.}, }
@article {pmid11138093, year = {2000}, author = {Antonia, RA and Pearson, BR}, title = {Effect of initial conditions on the mean energy dissipation rate and the scaling exponent.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {62}, number = {6 Pt A}, pages = {8086-8090}, doi = {10.1103/physreve.62.8086}, pmid = {11138093}, issn = {1063-651X}, abstract = {Implications of the expectation that the mean energy dissipation rate <epsilon> should become independent of viscosity at sufficiently large values of R(lambda), the Taylor microscale Reynolds number, are examined within the framework of small-scale intermittency and an adequate description of the second-order velocity structure function over the dissipative and inertial ranges. For nominally the same flow, a two-dimensional wake, but with different initial conditions, values of C(epsilon) identical with<epsilon>L/u('3), the scaling exponent and the Kolmogorov constant differ at the same R(lambda).}, }
@article {pmid11123883, year = {2000}, author = {Kenis, PJ and Ismagilov, RF and Takayama, S and Whitesides, GM and Li, S and White, HS}, title = {Fabrication inside microchannels using fluid flow.}, journal = {Accounts of chemical research}, volume = {33}, number = {12}, pages = {841-847}, doi = {10.1021/ar000062u}, pmid = {11123883}, issn = {0001-4842}, mesh = {Crystallization ; Ion Channels/*chemistry ; Microelectrodes ; }, abstract = {This Account summarizes techniques for carrying out microfabrication of structures with dimensions down to 10 microm in microchannels that are 0.02-2 mm wide. These methods are largely based on the exploitation of laminar flow at low Reynolds number (Re) to control the spatial delivery of reagents. These methods are illustrated by fabrication of fibers, microelectrode arrays, arrays of crystals, and patterns of proteins and cells.}, }
@article {pmid11121283, year = {2001}, author = {Chang, HC and Demekhin, EA and Takhistov, PV}, title = {Circular Hydraulic Jumps Triggered by Boundary Layer Separation.}, journal = {Journal of colloid and interface science}, volume = {233}, number = {2}, pages = {329-338}, doi = {10.1006/jcis.2000.7289}, pmid = {11121283}, issn = {1095-7103}, abstract = {When a high-flow-rate circular jet impinges vertically on a horizontal plane, it flows out radially and then undergoes a distinctive hydraulic jump on the plane because of boundary layer separation induced by hydrostatic back pressure. The jump radius is shown to be 0.37 a Re(1/3) Lambda(-1/8), where Lambda=(ga(3)/nu(2)) Re(-7/3) is a modified Froude number, Re=(Q/anu) is the jet Reynolds number, a is the jet radius, and Q the liquid flow rate, which is favorably compared to experimental data in the limit of small Lambda. When Lambda exceeds 3.0x10(-4) at low flow rates, the jump radius decreases below a minimum in the film depth and our experiments detect a different jump mechanism that may be triggered by capillary pressure rather than hydrostatic pressure. Copyright 2001 Academic Press.}, }
@article {pmid11112301, year = {2001}, author = {Ren, L and Li, D and Qu, W}, title = {Electro-Viscous Effects on Liquid Flow in Microchannels.}, journal = {Journal of colloid and interface science}, volume = {233}, number = {1}, pages = {12-22}, doi = {10.1006/jcis.2000.7262}, pmid = {11112301}, issn = {1095-7103}, abstract = {The presence of the electrical double layer near a solid-liquid interface results in the electro-viscous effect on pressure-driven liquid flow through microchannels. The objective of this paper is to examine the magnitude of the additional flow resistance caused by the electrokinetic effect in microchannels. Deionized ultrafiltered water, 10(-4) and 10(-2) M aqueous KCl solutions, 10(-4) M AlCl(3) solution, and 10(-4) M LiCl solution were used as the testing liquids. Carefully designed flow measurements were conducted in three silicon microchannels with a height of 14.1, 28.2, and 40.5 µm, respectively. The measured dP/dx for the pure water, the 10(-4) M KCl solution, and the 10(-4) M LiCl solution was found to be significantly higher than the prediction of the conventional laminar flow theory at the same Reynolds number. Such a high flow resistance and the resulting high apparent viscosity strongly depend on the channel's height, the ionic valence, and the concentration of the liquids. The zeta potentials for the liquid-solid systems were calculated by using the measured streaming potential data. The experimentally determined dP/dx approximately Re relationships were compared with the predictions of a theoretical electro-viscous flow model, and a good agreement was found for pure water, 10(-4) M KCl solution, and 10(-4) MAlCl(3) solution systems. The present electrokinetic flow model cannot interpret the flow characteristics of the LiCl solution. Copyright 2001 Academic Press.}, }
@article {pmid11105033, year = {2000}, author = {Gach, HM and Lowe, IJ}, title = {Measuring flow reattachment lengths downstream of a stenosis using MRI.}, journal = {Journal of magnetic resonance imaging : JMRI}, volume = {12}, number = {6}, pages = {939-948}, doi = {10.1002/1522-2586(200012)12:6&lt;939::aid-jmri18&gt;3.0.co;2-f}, pmid = {11105033}, issn = {1053-1807}, support = {RR03631-04/RR/NCRR NIH HHS/United States ; }, mesh = {Arterial Occlusive Diseases/*diagnosis/physiopathology ; Humans ; *Image Processing, Computer-Assisted ; Magnetic Resonance Imaging/*methods ; Models, Cardiovascular ; Phantoms, Imaging ; Pulsatile Flow/*physiology ; }, abstract = {Flow reattachment lengths (l(r)) are measured downstream of an abrupt axisymmetric 75% stenosis, located inside a cylindrical channel, for steady flow using ultra-fast magnetic resonance imaging (MRI). The MRI results are compared with those from other similar (non-MRI) studies. The MRI data confirm the existence of three flow reattachment regimes (laminar, fully turbulent, and transition) related to the flow Reynolds number (Re) measured inside the stenosis. Based on the MRI experiments, the laminar regime occurs at a stenotic Reynolds number below 250 with a slope (l(r)/Re) of 0.086. The fully developed turbulence occurs at a stenotic Reynolds number above 3600 with a minimum observed reattachment length of 5 step heights. The transition regime (occurring between the laminar and fully turbulent regimes) is characterized by a reattachment length plateau and then a drop with Re(-1.1). J. Magn. Reson. Imaging 2000;12:939-948.}, }
@article {pmid11104713, year = {2001}, author = {Anderson, EJ and McGillis, WR and Grosenbaugh, MA}, title = {The boundary layer of swimming fish.}, journal = {The Journal of experimental biology}, volume = {204}, number = {Pt 1}, pages = {81-102}, doi = {10.1242/jeb.204.1.81}, pmid = {11104713}, issn = {0022-0949}, mesh = {Animals ; Dogfish/physiology ; Fishes/*physiology ; Physical Phenomena ; Physics ; *Rheology ; Swimming/*physiology ; Viscosity ; }, abstract = {Tangential and normal velocity profiles of the boundary layer surrounding live swimming fish were determined by digital particle tracking velocimetry, DPTV. Two species were examined: the scup Stenotomus chrysops, a carangiform swimmer, and the smooth dogfish Mustelus canis, an anguilliform swimmer. Measurements were taken at several locations over the surfaces of the fish and throughout complete undulatory cycles of their propulsive motions. The Reynolds number based on length, Re, ranged from 3x10(3) to 3x10(5). In general, boundary layer profiles were found to match known laminar and turbulent profiles including those of Blasius, Falkner and Skan and the law of the wall. In still water, boundary layer profile shape always suggested laminar flow. In flowing water, boundary layer profile shape suggested laminar flow at lower Reynolds numbers and turbulent flow at the highest Reynolds numbers. In some cases, oscillation between laminar and turbulent profile shapes with body phase was observed. Local friction coefficients, boundary layer thickness and fluid velocities at the edge of the boundary layer were suggestive of local oscillatory and mean streamwise acceleration of the boundary layer. The behavior of these variables differed significantly in the boundary layer over a rigid fish. Total skin friction was determined. Swimming fish were found to experience greater friction drag than the same fish stretched straight in the flow. Nevertheless, the power necessary to overcome friction drag was determined to be within previous experimentally measured power outputs. No separation of the boundary layer was observed around swimming fish, suggesting negligible form drag. Inflected boundary layers, suggestive of incipient separation, were observed sporadically, but appeared to be stabilized at later phases of the undulatory cycle. These phenomena may be evidence of hydrodynamic sensing and response towards the optimization of swimming performance.}, }
@article {pmid11091950, year = {2000}, author = {Zhao, Y and Sharp, MK}, title = {Stability of elliptical cylinders in two-dimensional channel flow.}, journal = {Journal of biomechanical engineering}, volume = {122}, number = {5}, pages = {493-497}, doi = {10.1115/1.1289990}, pmid = {11091950}, issn = {0148-0731}, mesh = {Cell Movement ; Chemical Fractionation/methods ; Diffusion ; Erythrocytes/*physiology ; *Models, Biological ; Torque ; Viscosity ; }, abstract = {The flow around rigid cylinders of elliptical cross section placed transverse to Poiseuille flow between parallel plates was simulated to investigate issues related to the tumbling of red blood cells and other particles of moderate aspect ratio in the similar flow in a Field Flow Fractionation (FFF) channel. The torque and transverse force on the cylinder were calculated with the cylinder freely translating, but prevented from rotating, in the flow. The aspect ratios (long axis to short axis) of the elliptical cylinders were 2, 3, 4, and 5. The cylinder was placed transversely at locations of y0/H = 0.1, 0.2, 0.3, and 0.4, where y0 is the distance from the bottom of the channel and H is the height of the channel, and the orientation of the cylinder was varied from 0 to 10 deg with respect to the axis of the channel for a channel Reynolds number of 20. The results showed that equilibrium orientations (indicated by a zero net torque on the cylinder) were possible for high-aspect-ratio cylinders at transverse locations y0/H < 0.2. Otherwise, the net torque on the cylinder was positive, indicating that the cylinder would rotate. For cylinders with a stable orientation, however, a transverse lift forced existed up to about y0/H = 0.25. Thus, a cylinder of neutral or low buoyancy might be lifted with a stable orientation from an initial position near the wall until it reached y0/H < 0.2, whereupon it would begin to tumble or oscillate. The dependence of lift and torque on cylinder orientation suggested that neutral or low-buoyancy cylinders may oscillate in both transverse location and angular velocity. Cylinders more dense than the carrier fluid could be in equilibrium both in terms of orientation and transverse location if their sedimentation force matched their lift force for a location y0/H < 0.2.}, }
@article {pmid11089334, year = {2000}, author = {Xu, W and Chen, Q}, title = {Simulation of mixed convection flow in a room with a two-layer turbulence model.}, journal = {Indoor air}, volume = {10}, number = {4}, pages = {306-314}, doi = {10.1034/j.1600-0668.2000.010004306.x}, pmid = {11089334}, issn = {0905-6947}, mesh = {*Air Movements ; Ergonomics ; Humans ; *Models, Theoretical ; *Ventilation ; Workplace ; }, abstract = {Most indoor airflows are mixed convection. In order to simulate mixed convection accurately and efficiently, this paper uses a two-layer turbulence model. The two-layer model combines a one-equation model for near wall flow together with the standard k-epsilon model for outer-wall flow. The model has been used to predict the mixed convection by displacement ventilation in an office. The computed results agree well with the corresponding airflow pattern and the distributions of air temperature, air velocity, air velocity fluctuation, and tracer-gas concentration. The model can predict correctly heat transfer from a wall where the standard k-epsilon model and re-normalization group (RNG) k-epsilon model with wall functions often fails. The computing cost required by the two-layer model is comparable to that of the standard k-epsilon model and RNG k-epsilon model and is significantly less than that by a low-Reynolds number model.}, }
@article {pmid11089041, year = {2000}, author = {Lohse, D}, title = {Periodically kicked turbulence.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {62}, number = {4 Pt A}, pages = {4946-4949}, doi = {10.1103/physreve.62.4946}, pmid = {11089041}, issn = {1063-651X}, abstract = {Periodically kicked turbulence is theoretically analyzed within a mean-field theory. For large enough kicking strength A and kicking frequency f the Reynolds number grows exponentially and then runs into some saturation. The saturation level Re(sat) can be calculated analytically; different regimes can be observed. For large enough Re we find Re(sat) approximately Af, but intermittency can modify this scaling law. We suggest an experimental realization of periodically kicked turbulence to study the different regimes we theoretically predict and thus to better understand the effect of forcing on fully developed turbulence.}, }
@article {pmid11088979, year = {2000}, author = {Le Gal P,  and Croquette, V}, title = {Visualization of the space-time impulse response of the subcritical wake of a cylinder.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {62}, number = {3 Pt B}, pages = {4424-4426}, doi = {10.1103/physreve.62.4424}, pmid = {11088979}, issn = {1063-651X}, abstract = {The well-known Benard-von Karman cylinder wake is one of the most challenging phenomena of fluid mechanics. As the Reynolds number of the flow around a cylinder passes through a critical value, alternating vortex shedding appears via a Hopf bifurcation. Theoretical studies of the wake have described the appearance of this self-sustained oscillation as the result of a convective to absolute transition resulting in the formation of a global mode. We illustrate here the convective global regime of the subcritical wake by analyzing visualizations of its impulse response.}, }
@article {pmid11088686, year = {2000}, author = {Kurien, S and Sreenivasan, KR}, title = {Anisotropic scaling contributions to high-order structure functions in high-reynolds-number turbulence.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {62}, number = {2 Pt A}, pages = {2206-2212}, doi = {10.1103/physreve.62.2206}, pmid = {11088686}, issn = {1063-651X}, abstract = {We make an attempt at obtaining the scaling exponents for the anisotropic components of structure functions of order 2 through 6. We avoid mixing these components with their isotropic counterparts for each order by using tensor components that are entirely anisotropic. We do this by considering terms of the isotropic sector corresponding to j=0 in the SO(3) decomposition of each tensor, and then constructing components that are explicitly zero in the isotropic sector. We use an interpolation formula to compensate for the large-scale encroachment of inertial-range scales. This allows us to examine the lowest order anisotropic scaling behavior. The resulting anisotropic exponents for a given tensorial order are larger than those known for the corresponding isotropic part. One conclusion that emerges is that the anisotropy effects diminish with decreasing scale, although much more slowly than previously thought.}, }
@article {pmid11088497, year = {2000}, author = {Kato, Y and Fujimura, K}, title = {Prediction of pattern selection due to an interaction between longitudinal rolls and transverse modes in a flow through a rectangular channel heated from below.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {62}, number = {1 Pt A}, pages = {601-611}, doi = {10.1103/physreve.62.601}, pmid = {11088497}, issn = {1063-651X}, abstract = {Convection patterns in a flow through a horizontal channel that is heated from below are predicted on the basis of a weakly nonlinear theory. At a certain value of the Reynolds number and the Rayleigh number, the conduction state with steady shear flow becomes linearly unstable to both longitudinal rolls and transverse modes, simultaneously. The longitudinal rolls align along the streamwise direction whereas the transverse modes are periodic in the streamwise direction. Amplitude equations for the interaction between the longitudinal rolls and the transverse modes are derived in a consistent manner. Coefficients in the equations are determined numerically for a wide range of parameters. The longitudinal rolls are found to bifurcate supercritically. On the other hand, the transverse modes bifurcate subcritically or supercritically, depending on the Prandtl number, the aspect ratio of the channel, and the boundary conditions on the sidewalls. Stable convection patterns are classified in a parameter space. A mixed mode pattern, which is a mixture of the components of the longitudinal rolls and the transverse modes, is found to be stable for some sets of parameters.}, }
@article {pmid11088492, year = {2000}, author = {Egolf, PW and Weiss, DA}, title = {Difference-quotient turbulence model: analytical solutions for the core region of plane poiseuille flow.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {62}, number = {1 Pt A}, pages = {553-563}, doi = {10.1103/physreve.62.553}, pmid = {11088492}, issn = {1063-651X}, abstract = {The difference-quotient turbulence model and an explanation in terms of fluid dynamics is presented. With this model an analytical theory for the symmetric core region of turbulent plane Poiseuille flow is derived. The equations and the solutions reveal an order/disorder transition with analogies in other scientific fields where statistical physics applies. At moderate Reynolds numbers the time-averaged profile of the downstream mean velocity and a second-order fluctuation correlation are described in terms of Bessel functions of the first type. At the infinite Reynolds number limit these solutions converge toward functions which can be described by simple geometric figures. Experimental data confirm the model results.}, }
@article {pmid11088412, year = {2000}, author = {Höfler, K and Schwarzer, S}, title = {Navier-Stokes simulation with constraint forces: finite-difference method for particle-laden flows and complex geometries.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {61}, number = {6 Pt B}, pages = {7146-7160}, doi = {10.1103/physreve.61.7146}, pmid = {11088412}, issn = {1063-651X}, mesh = {Algorithms ; *Computer Simulation ; Mathematical Computing ; *Models, Chemical ; Particle Size ; Rheology/*methods ; Solutions ; Suspensions ; Viscosity ; }, abstract = {Building on an idea of Fogelson and Peskin [J. Comput. Phys. 79, 50 (1988)] we describe the implementation and verification of a simulation technique for systems of non-Brownian particles in fluids at Reynolds numbers up to about 20 on the particle scale. This direct simulation technique fills a gap between simulations in the viscous regime and high-Reynolds-number modeling. It also combines sufficient computational accuracy with numerical efficiency and allows studies of several thousand, in principle arbitrarily shaped, extended and hydrodynamically interacting particles on regular work stations. We verify the algorithm in two and three dimensions for (i) single falling particles and (ii) a fluid flowing through a bed of fixed spheres. In the context of sedimentation we compute the volume fraction dependence of the mean sedimentation velocity. The results are compared with experimental and other numerical results both in the viscous and inertial regime and we find very satisfactory agreement.}, }
@article {pmid11088353, year = {2000}, author = {Kendon, VM}, title = {Scaling theory of three-dimensional spinodal turbulence.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {61}, number = {6 Pt A}, pages = {R6071-4}, doi = {10.1103/physreve.61.r6071}, pmid = {11088353}, issn = {1063-651X}, abstract = {A scaling theory for spinodal decomposition in the inertial hydrodynamic regime is presented. The scaling involves three relevant length scales, the domain size, the Taylor microscale, and the Kolmogorov dissipation scale. This allows for the presence of an inertial "energy cascade," familiar from theories of turbulence, and improves on earlier scaling treatments based on a single length: these, it is shown, cannot be reconciled with energy conservation. This theory reconciles the t(2/3) scaling of the domain size, predicted by simple scaling, with the physical expectation of a saturating Reynolds number at late times.}, }
@article {pmid11088338, year = {2000}, author = {Schorghofer, N}, title = {Energy spectra of steady two-dimensional turbulent flows.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {61}, number = {6 Pt A}, pages = {6572-6577}, doi = {10.1103/physreve.61.6572}, pmid = {11088338}, issn = {1063-651X}, abstract = {The power spectrum is measured in direct numerical simulations of the two-dimensional Navier-Stokes equation and other two-dimensional flows with white-in-time forcing at large scales. For the Navier-Stokes equation the energy spectrum in the inertial range approaches k(-3) with increasing Reynolds number, with possible logarithmic corrections. A family of two-dimensional flows, including the surface quasigeostrophic equation, allows us to vary the locality of the "enstrophy" transfer, where enstrophy is the mean square of the convected quantity. Dimensional analysis based on the enstrophy dissipation correctly predicts the energy spectrum, whenever the enstrophy transfer can be assumed to be spectrally local. Otherwise, the enstrophy spectrum is steeper than would be expected on the basis of local transfer. In this case the data suggest a k(-1) passive scalar spectrum.}, }
@article {pmid11059883, year = {2000}, author = {Dierickx, PW and De Wachter, D and Verdonck, PR}, title = {Blood flow around hollow fibers.}, journal = {The International journal of artificial organs}, volume = {23}, number = {9}, pages = {610-617}, pmid = {11059883}, issn = {0391-3988}, mesh = {Equipment Design ; *Kidneys, Artificial ; Materials Testing ; Models, Theoretical ; Viscosity ; }, abstract = {In an artificial lung, blood is oxygenated and flows around a bundle of hollow fibers while gas flows inside the fiber. The objective of this study is to understand the hydrodynamics of three different fiber banks (inline square IS, staggered square SS and equilateral triangle ET) and to investigate the influence of both a Newtonian and non-Newtonian Casson viscosity model on the flow field. A two-dimensional finite element model for permanent, isothermal, laminar blood flow perpendicular to hollow fibers is used. All fibers are assumed identical, straight and parallel. Porosity ranges from 0.4 to 0.6 and Reynolds number varies from 1 to 60. For a given Re, ET generates less resistance than SS, the latter being comparable with IS. A lower porosity increases resistance. Non-Newtonian viscosity affects velocity patterns only at low Re (<0.5) and higher porosity (>0.5). Resistance at low Re is significantly elevated in the fiber banks due to an overall increase in viscosity. This model makes it possible to study the influence of geometry and viscosity on hydrodynamics in fiber banks and may aid in the optimization of hollow fiber artificial lung design.}, }
@article {pmid11046529, year = {2000}, author = {Watanabe, T and Nakayama, Y and Fujisaka, H}, title = {Large deviation statistics of the energy-flux fluctuation in the shell model of turbulence.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {61}, number = {2}, pages = {R1024-7}, doi = {10.1103/physreve.61.r1024}, pmid = {11046529}, issn = {1063-651X}, abstract = {The energy-flux fluctuation in the shell model of turbulence is numerically analyzed from the large deviation statistical point of view. We first observe that the rate function defined in the inertial range is independent of the Reynolds number. The rate function derived by the cascade model of the log-Poisson statistics turns out to be in good agreement with the present numerical result in the region where strong singularity of fluctuation exits. This fact may imply the universality as well as the robustness of the large deviation statistical quantities in turbulence.}, }
@article {pmid11046423, year = {2000}, author = {Furukawa, H}, title = {Spinodal decomposition of two-dimensional fluid mixtures: A spectral analysis of droplet growth.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {61}, number = {2}, pages = {1423-1431}, doi = {10.1103/physreve.61.1423}, pmid = {11046423}, issn = {1063-651X}, abstract = {The spinodal decomposition of two-dimensional fluid mixture is studied by numerical simulation. For the high viscous fluid mixture it has not been evident whether the interfacial tension is relevant to the droplet growth or not. A length scale R defined by the structure function extracting the effect of the long wavelength mode justifies a rapid growth close to R approximately t, but the length scale energetically defined reveals a much slower growth R approximately t(0.5), where t is time. This discrepancy represents the violation of the dynamical scaling with single length scale. The slow gowth of the length scale is attributed to the accumulation of the number of isolated droplets in phase separating state, whereas the rapid growth represents the relevance of the surface tension as the driving force in two dimensions. For a low viscous fluid mixture the dynamical scaling is a good assumption with the growth law R approximately t(2/3) up to a very large Reynolds number Re approximately 1500, which is the limit in the present simulation.}, }
@article {pmid11046418, year = {2000}, author = {Balonishnikov, AM}, title = {Extended local balance model of turbulence and couette-taylor flow.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {61}, number = {2}, pages = {1390-1394}, doi = {10.1103/physreve.61.1390}, pmid = {11046418}, issn = {1063-651X}, abstract = {An extended local balance model of turbulence, based on a new transport equation for the dissipation rate with a negative diffusion coefficient, is presented. Analytical solutions for the mean velocity and the dissipation rate for the turbulent Couette-Taylor problem are derived. The dependence of torque on the Reynolds number is obtained. These solutions depend only on two constants k=0.4 and C=9.5 of the turbulent boundary layer and, within the limits of a narrow channel, are reduced to the well-known von Karman's solutions for planar Couette flow. Strange attractor behavior in this limit is also observed.}, }
@article {pmid11031576, year = {2000}, author = {Peffley, NL and Cawthorne, AB and Lathrop, DP}, title = {Toward a self-generating magnetic dynamo: the role of turbulence.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {61}, number = {5A}, pages = {5287-5294}, doi = {10.1103/physreve.61.5287}, pmid = {11031576}, issn = {1063-651X}, abstract = {Turbulent flow of liquid sodium is driven toward the transition to self-generating magnetic fields. The approach toward the transition is monitored with decay measurements of pulsed magnetic fields. These measurements show significant fluctuations due to the underlying turbulent fluid flow field. This paper presents experimental characterizations of the fluctuations in the decay rates and induced magnetic fields. These fluctuations imply that the transition to self-generation, which should occur at larger magnetic Reynolds number, will exhibit intermittent bursts of magnetic fields.}, }
@article {pmid11031571, year = {2000}, author = {Vincent, AP and Yuen, DA}, title = {Transition to turbulent thermal convection beyond Ra = 10(10) detected in numerical simulations.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {61}, number = {5A}, pages = {5241-5246}, doi = {10.1103/physreve.61.5241}, pmid = {11031571}, issn = {1063-651X}, abstract = {We have conducted high-resolution two-dimensional calculations for a Boussinesq convection model with a Prandtl number of unity in an aspect-ratio 3 box, going from Rayleigh numbers between 10(8) to 10(14). A grid of 1024 x 3076 grid points consisting of a cosine-sine basis set has been employed for free-slip boundary conditions. We have found evidence for a transition involving the branching of plumes at a Rayleigh number of 10(10). Inside the core of these "superplumes," the structure is extremely complex. There may be another transition at Ra of 10(12), where a secondary instability may develop in regions of the local Rayleigh number which becomes supercritical inside the core of the complex "superplumes." For Ra of 10(8) to 10(10), Ra follows a 1/3 power law in the Nusselt-Rayleigh number relationship. From Ra of 10(10) to 10(12), Ra follows a 1/2 power law. Above this value the Nusselt number becomes insensitive to the variation in the global Rayleigh number and this is due to the development of small-scale convection cells vertically aligned in the interior of the extremely high Ra number flow. The global Reynolds number scales as Re approximately Ra1/4 up to Ra of 10(14). Scaling relationships based on global properties would not work in extremely high Ra situations beyond Ra of 10(12) because of the complex turbulent layered convection in the core of the flow and the severe degradation of the boundary layers.}, }
@article {pmid11031570, year = {2000}, author = {Vainshtein, SI}, title = {Dissipation field asymmetry and intermittency in fully developed turbulence.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {61}, number = {5A}, pages = {5228-5240}, doi = {10.1103/physreve.61.5228}, pmid = {11031570}, issn = {1063-651X}, abstract = {Experimental study of high Reynolds number turbulence provides additional evidence that asymmetry of turbulence is related to the intermittency. The refined similarity hypothesis (RSH), on the other hand, connects the intermittency of the longitudinal velocity increments with that of the dissipation field, implying in particular that the dissipation field should be asymmetric as well. The asymmetry of the latter is indeed found in these experiments. In addition, the study of the dissipation field asymmetry provides us with quantitative estimations of the deviations from the RSH.}, }
@article {pmid11031506, year = {2000}, author = {Horvath, VK and Cressman, JR and Goldburg, WI and Wu, XL}, title = {Hysteresis at low Reynolds number: onset of two-dimensional vortex shedding.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {61}, number = {5A}, pages = {R4702-5}, doi = {10.1103/physreve.61.r4702}, pmid = {11031506}, issn = {1063-651X}, abstract = {Hysteresis has been observed in a study of the transition between laminar flow and vortex shedding in a quasi-two-dimensional system. The system is a vertical, rapidly flowing soap film which is penetrated by a rod oriented perpendicular to the film plane. Our experiments show that the transition from laminar flow to a periodic von Karman vortex street can be hysteretic, i.e., vortices can survive at velocities lower than the velocity needed to generate them.}, }
@article {pmid11030906, year = {2000}, author = {Eloy, C and Le Gal P,  and Le Dizes S, }, title = {Experimental study of the multipolar vortex instability.}, journal = {Physical review letters}, volume = {85}, number = {16}, pages = {3400-3403}, doi = {10.1103/PhysRevLett.85.3400}, pmid = {11030906}, issn = {1079-7114}, abstract = {The instability of a vortex subjected to a stationary dipolar or tripolar constraint is studied experimentally by using a rotating deformable cylinder on which two or three rollers are applied. As the Reynolds number and the aspect ratio of the cylinder are varied, different modes of instability are observed and their wavelength and frequency are compared to theoretical predictions. Secondary instability and cyclic breakup are also evidenced in the elliptic geometry.}, }
@article {pmid11019077, year = {2000}, author = {Kumaran, V and Muralikrishnan, R}, title = {Spontaneous growth of fluctuations in the viscous flow of a fluid past a soft interface.}, journal = {Physical review letters}, volume = {84}, number = {15}, pages = {3310-3313}, doi = {10.1103/PhysRevLett.84.3310}, pmid = {11019077}, issn = {1079-7114}, abstract = {The flow induced instability in the flow past a soft material is studied in the limit of low Reynolds number where inertial effects are insignificant. A transition from laminar flow to a more complicated flow profile is observed when the strain rate of the base flow increases beyond a critical value; the transition is found to be reproducible. The experimental results are compared with theoretical predictions and quantitative agreement is found with no adjustable parameters.}, }
@article {pmid11017654, year = {2000}, author = {Lvov, YV and Newell, AC}, title = {Finite flux solutions of the quantum boltzmann equation and semiconductor lasers.}, journal = {Physical review letters}, volume = {84}, number = {9}, pages = {1894-1897}, doi = {10.1103/PhysRevLett.84.1894}, pmid = {11017654}, issn = {1079-7114}, abstract = {We propose and illustrate in the context of the semiconductor laser that, in nonequilibrium fermionic systems with sources and sinks, the family of finite flux stationary solutions of the quantum Boltzmann equation is central and more important then the zero flux Fermi-Dirac spectrum. We present the quantum analog of the finite flux Kolmogorov spectra which are central to understanding nonequilibrium classical systems such as high Reynolds number hydrodynamics and the wave turbulence encountered in water waves, plasmas, and optics. In particular, we show how semiconductor laser efficiency can be improved by maximizing the flux of carriers (electrons and holes) towards the lasing frequencies.}, }
@article {pmid11016501, year = {2000}, author = {Dierickx, PW and De Somer, F and De Wachter, DS and Van Nooten, G and Verdonck, PR}, title = {Hydrodynamic characteristics of artificial lungs.}, journal = {ASAIO journal (American Society for Artificial Internal Organs : 1992)}, volume = {46}, number = {5}, pages = {532-535}, doi = {10.1097/00002480-200009000-00004}, pmid = {11016501}, issn = {1058-2916}, mesh = {*Artificial Organs ; Cardiopulmonary Bypass ; Humans ; *Lung ; Oxygenators, Membrane ; Regression Analysis ; Viscosity ; }, abstract = {An artificial lung is used during cardiopulmonary bypass to oxygenate blood and to control blood temperature. The pressure drop-flow rate characteristics of the membrane compartment in three hollow fiber membrane oxygenators were determined in vitro to characterize design features. Results are presented in a unique dimensionless relationship between Euler number, N(Eu) (ratio of pressure drop to kinetic energy), and Reynolds number, N(Re) (ratio of inertial to viscous forces), and are a function of the device porosity, epsilon, and a characteristic device length, xi, defined as the ratio of the mean blood path and manifold length: [equation in text]. This dimensionless approach allows us (1) to compare oxygenators independently, and (2) to relate water tests to blood.}, }
@article {pmid11010593, year = {2000}, author = {Corcoran, TE and Chigier, N}, title = {Characterization of the laryngeal jet using phase Doppler interferometry.}, journal = {Journal of aerosol medicine : the official journal of the International Society for Aerosols in Medicine}, volume = {13}, number = {2}, pages = {125-137}, doi = {10.1089/089426800418659}, pmid = {11010593}, issn = {0894-2684}, mesh = {Aerosols/*pharmacokinetics ; Aged ; Aged, 80 and over ; Biomechanical Phenomena ; Cadaver ; Equipment Design ; Female ; Humans ; Interferometry ; Larynx/*physiology ; Laser-Doppler Flowmetry ; Nebulizers and Vaporizers ; Respiratory Transport/*physiology ; Trachea/*physiology ; }, abstract = {The purpose of this study was to characterize the effects of the laryngeal jet on inhalation air flows in the trachea, and to extend these ideas to further an understanding of aerosol deposition in this region. Phase Doppler Interferometry was used to characterize axial velocity and turbulence intensity contours in the tracheal section of a cadaver-based larynx-trachea model. An array of 30 measurements was made at each of 6 downstream planes within the tracheal portion of the model (immediately downstream of the larynx, and at 0.5, 1, 2, 3, and 4 diameters further downstream). The flow was characterized for steady state flow at three Reynolds numbers (1250, 1700, and 2800). The Re = 1250 case approximates the inhalation of a 6-year-old child. Reverse flows with significant velocities were noted in the anterior trachea within one diameter downstream of the larynx, for all three flow cases. The cross sectional area of the reverse flow regions was larger for the lower Reynolds number cases. These reverse flows are a consequence of the nearly triangular shape of the lumen between the vocal folds in the larynx and constitute a potential deposition mechanism. High levels of axial turbulence intensity were noted near the anterior/left tracheal walls within one diameter downstream of the larynx. This indicates the potential for deposition due to turbulence in this region. Turbulence levels were still significant after four downstream diameters, indicating the potential for turbulent deposition at positions further downstream, including the bronchial tree where passage diameters are smaller. Contrary to expectations, turbulence levels were approximately 20% higher for the Re = 1250 case compared to the Re = 2800 at the furthest downstream locations (with 99% confidence). This is likely due to the complex nature of the confined jet flow.}, }
@article {pmid10990884, year = {2000}, author = {White, JM and Muller, SJ}, title = {Viscous heating and the stability of newtonian and viscoelastic taylor-couette flows.}, journal = {Physical review letters}, volume = {84}, number = {22}, pages = {5130-5133}, doi = {10.1103/PhysRevLett.84.5130}, pmid = {10990884}, issn = {1079-7114}, abstract = {The effects of viscous heating on the stability of Taylor-Couette flow were investigated through flow visualization experiments for Newtonian and viscoelastic fluids. For highly viscous Newtonian fluids, viscous heating drives a transition to a new, oscillatory mode of instability at a critical Reynolds number significantly below that at which the inertial transition is observed in isothermal flows. The effects of viscous heating may explain the discrepancies between the observed and predicted critical conditions and the symmetry of the disturbance flow for viscoelastic instabilities.}, }
@article {pmid10985838, year = {2000}, author = {Lopez, JM and Hirsa, AH}, title = {Surfactant-Influenced Gas-Liquid Interfaces: Nonlinear Equation of State and Finite Surface Viscosities.}, journal = {Journal of colloid and interface science}, volume = {229}, number = {2}, pages = {575-583}, doi = {10.1006/jcis.2000.7025}, pmid = {10985838}, issn = {1095-7103}, abstract = {A canonical flow geometry was utilized for a fundamental study of the coupling between bulk flow and a Newtonian gas-liquid interface in the presence of an insoluble surfactant. We develop a Navier-Stokes numerical model of the flow in the deep-channel surface viscometer geometry, which consists of stationary inner and outer cylinders, a floor rotating at a constant angular velocity, and an interface covered initially by a uniformly distributed surfactant. Here, the floor of the annular channel is rotated fast enough so the flow is nonlinear and drives the film toward the inner cylinder. The boundary conditions at the interface are functions of the surface tension, surface shear viscosity, and surface dilatational viscosity, as described by the Boussinesq-Scriven surface model. A physical surfactant system, namely hemicyanine, an insoluble monolayer on an air-water interface, with measured values of surface tension and surface shear viscosity versus concentration, was used in this study. We find that a surfactant front can form, depending on the Reynolds number and the initial surfactant concentration. The stress balance in the radial direction was found to be dominated by the Marangoni stress, but the azimuthal stress was only due to the surface shear viscosity. Numerical studies are presented comparing results of surfactant-influenced interface cases implementing the derived viscoelastic interfacial stress balance with those using a number of idealized stress balances, as well as a rigid no-slip surface, providing added insight into the altered dynamics that result from the presence of a surfactant monolayer. Copyright 2000 Academic Press.}, }
@article {pmid10985810, year = {2000}, author = {Ramachandran, V and Venkatesan, R and Tryggvason, G and Scott Fogler H, }, title = {Low Reynolds Number Interactions between Colloidal Particles near the Entrance to a Cylindrical Pore.}, journal = {Journal of colloid and interface science}, volume = {229}, number = {2}, pages = {311-322}, doi = {10.1006/jcis.2000.6986}, pmid = {10985810}, issn = {1095-7103}, abstract = {The interaction between stable colloidal particles arriving at a pore entrance was studied using a numerical method for the case where the particle size is smaller than but of the same order as the pore size. The numerical method was adapted from a front-tracking technique developed for studying incompressible, multifluid flow by S. O. Unverdi and G. Tryggvason (J. Comp. Phys. 100, 25, 1992). The method is based on the finite difference solution of Navier-Stokes equation on a stationary, structured, Cartesian grid and the explicit representation of the particle-liquid interface using an unstructured grid that moves through the stationary grid. The simulations are in two dimensions, considering both deformable and nondeformable particles, and include interparticle colloidal interactions. The interparticle and particle-pore hydrodynamic interactions, which are very difficult to determine using existing analytical and semi-numerical, semi-analytical techniques in microhydrodynamics, are naturally accounted for in our numerical method and need not be explicity determined. Two- and three-particle motion toward a pore has been considered in our simulations. The simulations demonstrate how the competition between hydrodynamic forces and colloidal forces acting on particles dictate their flow behavior near the pore entrance. The predicted dependence of the particle flow behavior on the flow velocity and the ratio of pore size to particle size are qualitatively consistent with the experimental observations of V. Ramachandran and H. S. Fogler (J. Fluid Mech. 385, 129, 1999). Copyright 2000 Academic Press.}, }
@article {pmid10976040, year = {2000}, author = {Hernández, LP}, title = {Intraspecific scaling of feeding mechanics in an ontogenetic series of zebrafish, Danio rerio.}, journal = {The Journal of experimental biology}, volume = {203}, number = {Pt 19}, pages = {3033-3043}, doi = {10.1242/jeb.203.19.3033}, pmid = {10976040}, issn = {0022-0949}, mesh = {Animals ; Biomechanical Phenomena ; Body Constitution ; Feeding Behavior/*physiology ; Larva/physiology ; Species Specificity ; Videotape Recording ; Zebrafish/anatomy &amp; histology/growth &amp; development/*physiology ; }, abstract = {While a vast literature and long tradition of examining the scaling of locomotory function exists, scaling studies on feeding mechanics are relatively rare. A recent increase in research activity examining the scaling of feeding kinematics has led to conflicting results. These divergent findings may be due to the inherent differences in the biophysical systems being examined. The present study examines the role of growth in the scaling of feeding kinematics in an ontogenetic series of zebrafish, Danio rerio. Although many other studies have investigated aquatic feeding, this study represents the first to quantify detailed feeding kinematics in first-feeding larvae. This study examines both the effects of violating assumptions of geometric similarity when examining scaling relationships and the role water viscosity plays in molding scaling coefficients derived from feeding kinematics. The effects of Reynolds number, generally not relevant in vertebrate feeding studies, play a crucial role in determining scaling relationships in this species. Many scaling coefficients reflect the functional challenges of feeding at low Reynolds numbers. Moreover, scaling patterns in feeding mechanics often reflect allometric growth during early ontogeny. The advent of high-speed video recording (1000 frames s(-1)) now allows the kinematics of feeding at these small sizes to be rigorously examined.}, }
@article {pmid10970501, year = {2000}, author = {Jane Wang, Z}, title = {Two dimensional mechanism for insect hovering.}, journal = {Physical review letters}, volume = {85}, number = {10}, pages = {2216-2219}, doi = {10.1103/PhysRevLett.85.2216}, pmid = {10970501}, issn = {0031-9007}, mesh = {Air Movements ; Algorithms ; Animals ; Biophysical Phenomena ; Biophysics ; Flight, Animal/*physiology ; Insecta/*physiology ; Movement/physiology ; Viscosity ; Wings, Animal/physiology ; }, abstract = {Resolved computation of two dimensional insect hovering shows for the first time that a two dimensional hovering motion can generate enough lift to support a typical insect weight. The computation reveals a two dimensional mechanism of creating a downward dipole jet of counterrotating vortices, which are formed from leading and trailing edge vortices. The vortex dynamics further elucidates the role of the phase relation between the wing translation and rotation in lift generation and explains why the instantaneous forces can reach a periodic state after only a few strokes. The model predicts the lower limits in Reynolds number and amplitude above which the averaged forces are sufficient.}, }
@article {pmid10951999, year = {2000}, author = {Carlozzi, P}, title = {Hydrodynamic aspects and Arthrospira growth in two outdoor tubular undulating row photobioreactors.}, journal = {Applied microbiology and biotechnology}, volume = {54}, number = {1}, pages = {14-22}, doi = {10.1007/s002530000355}, pmid = {10951999}, issn = {0175-7598}, mesh = {Bioreactors ; Cyanobacteria/*growth &amp; development ; Equipment Design ; Photobiology ; }, abstract = {Two tubular undulating row photobioreactors (TURPs) with a very high illuminated surface/volume ratio (400 m(-1)) were designed and constructed for the growth of photosynthetic micro-organisms. Experiments were conducted under outdoor conditions; and Arthrospira recycling was performed with airlifts (one for each row). The rows in each reactor faced east-west and consisted of a flexible polyvinyl chloride pipe (22 m long, 0.01 m bore) arranged in a sinusoidal shape. We studied the hydraulic performance of the sine-shaped photobioreactor rows during culture recycling in the TURPs at a very high Reynolds number (4,200), when Arthrospira showed Newtonian fluid behavior. The sinusoidal pipe arrangement imposed a sine waveform on the culture, which led to better light utilization. During summer, a volumetric productivity of 2.2 g l(-1) day(-1) was reached in the TURP-5r (5 rows m(-2)), whereas an area productivity of 35 g m(-2) day(-1) was obtained in the TURP-10r (10 rows m(-2)). This was due to more light being available in the TURP-5r, because its rows were more spaced out and the photic ratio (Rf) was low (3.0). In the TURP-10r, the closer rows caused a dilution of the sunlight, but gave a better light distribution inside the Arthrospira culture and improved the light utilization. This was attributed to the high Rf (6.0) of this reactor.}, }
@article {pmid10942557, year = {2000}, author = {Filippov, AV}, title = {Drag and Torque on Clusters of N Arbitrary Spheres at Low Reynolds Number.}, journal = {Journal of colloid and interface science}, volume = {229}, number = {1}, pages = {184-195}, doi = {10.1006/jcis.2000.6981}, pmid = {10942557}, issn = {1095-7103}, abstract = {Hydrodynamics of particle clusters suspended in viscous fluids is a subject of considerable theoretical and practical importance. Using a multipole expansion of the flow velocity in a series of spherical harmonics, Lamb's fundamental solution of the Stokes flow outside a single sphere is generalized in this work to the case of N nonoverlapping spheres of arbitrary size with slip boundary conditions. The expansion coefficients are found by transforming the boundary conditions to the Lamb form and by transforming the spherical coordinates and solid spherical harmonics centered at different spheres. The problem is reduced to the solution of the linear system of equations for the expansion coefficients, which is carried out numerically. Based on the developed theory, the relation between the hydrodynamic and gyration radius of fractal-like aggregates with different structure is established. In another application, an asymptotic slip-regime dependence of the aggregate hydrodynamic radius on the Knudsen number and the number of particles is found by performing calculations of drag forces acting on the gas-borne fractal-like and straight chain aggregates. A good agreement is shown in comparing predictions of the described theory with available experimental and theoretical results on motion of various small sphere clusters in viscous fluid. Copyright 2000 Academic Press.}, }
@article {pmid10882560, year = {2000}, author = {Lewis, DM and Pedley, TJ}, title = {Planktonic contact rates in homogeneous isotropic turbulence: theoretical predictions and kinematic simulations.}, journal = {Journal of theoretical biology}, volume = {205}, number = {3}, pages = {377-408}, doi = {10.1006/jtbi.2000.2073}, pmid = {10882560}, issn = {0022-5193}, mesh = {Animals ; *Computer Simulation ; *Environment ; Models, Biological ; Movement/*physiology ; Plankton/*physiology ; }, abstract = {The key role played by turbulence in the environment of plankton and larval fish populations has become appreciated in recent years. In particular, the turbulent enhancement of encounter rates between different species of microorganisms, either swimming or passively advected by the flow, is well established. However, most of the current modelling approaches are rather ad hoc, giving rise to ambiguities in the specification of certain key parameters. In this paper, the encounter problem in a turbulent flow of large Reynolds number is re-examined from first principles and a number of new formulae will be established for different swimming strategies. The key innovation is the proposal of a model form for the conditional joint probability density function of predator and prey velocities when the organisms are separated by their given contact radius, R. Particular attention will be paid to the case when a microorganism follows a random trajectory, due to a combination of its own swimming and the action of the flow. The theoretical predictions are subsequently tested against corresponding quantities derived from a series of kinematic simulations of a turbulent-like flow field. Good agreement is demonstrated between the predictions and simulations.}, }
@article {pmid10878326, year = {2000}, author = {Cammarn, SR and Sakr, A}, title = {Predicting dissolution via hydrodynamics: salicylic acid tablets in flow through cell dissolution.}, journal = {International journal of pharmaceutics}, volume = {201}, number = {2}, pages = {199-209}, doi = {10.1016/s0378-5173(00)00415-4}, pmid = {10878326}, issn = {0378-5173}, mesh = {Models, Theoretical ; Pharmacopoeias as Topic ; Salicylic Acid/administration &amp; dosage/*chemistry ; Solubility ; Solvents ; Spectrophotometry, Ultraviolet ; Tablets ; United States ; }, abstract = {A model was established for the dissolution of non-disintegrating salicylic acid tablets as a function of hydrodynamic conditions in the Flow Through Cell system (USP Apparatus 4). The approach was to model the dissolution rate of the material as a function of the Reynold's number, the dimensionless engineering term that describes the degree of turbulence. The dissolution rate of USP calibrator salicylic acid tablets was measured as a function of tablet size, orientation within the cell, dissolution media flow rate, and cell size. All of these variables were found to have an effect on dissolution rate, consistent with theory. An equation to predict this dissolution was established as: N(SH)=-21.1+12.6xN(RE)(0.5), R(2)=0.99; 10<N(re)<292.}, }
@article {pmid10857630, year = {2000}, author = {Cummings, EB and Griffiths, SK and Nilson, RH and Paul, PH}, title = {Conditions for similitude between the fluid velocity and electric field in electroosmotic flow.}, journal = {Analytical chemistry}, volume = {72}, number = {11}, pages = {2526-2532}, doi = {10.1021/ac991165x}, pmid = {10857630}, issn = {1520-6882}, abstract = {Electroosmotic flow is fluid motion driven by an electric field acting on the net fluid charge produced by charge separation at a fluid-solid interface. Under many conditions of practical interest, the resulting fluid velocity is proportional to the local electric field, and the constant of proportionality is everywhere the same. Here we show that the main conditions necessary for this similitude are a steady electric field, uniform fluid and electric properties, an electric Debye layer that is thin compared to any physical dimension, and fluid velocities on all inlet and outlet boundaries that satisfy the Helmholtz-Smoluchowski relation normally applicable to fluid-solid boundaries. Under these conditions, the velocity field can be determined directly from the Laplace equation governing the electric potential, without solving either the continuity or momentum equations. Three important consequences of these conditions are that the fluid motion is everywhere irrotational, that fluid velocities in two-dimensional channels bounded by parallel planes are independent of the channel depth, and that such flows exhibit no dependence on the Reynolds number. Similitude is demonstrated by comparing measured and computed fluid streamlines with computed electric flux lines.}, }
@article {pmid10854880, year = {2000}, author = {De Hart, J and Peters, GW and Schreurs, PJ and Baaijens, FP}, title = {A two-dimensional fluid-structure interaction model of the aortic valve [correction of value].}, journal = {Journal of biomechanics}, volume = {33}, number = {9}, pages = {1079-1088}, doi = {10.1016/s0021-9290(00)00068-3}, pmid = {10854880}, issn = {0021-9290}, mesh = {Aortic Valve/*anatomy &amp; histology/*physiology ; Finite Element Analysis ; Humans ; *Models, Cardiovascular ; }, abstract = {Failure of synthetic heart valves is usually caused by tearing and calcification of the leaflets. Leaflet fiber-reinforcement increases the durability of these valves by unloading the delicate parts of the leaflets, maintaining their physiological functioning. The interaction of the valve with the surrounding fluid is essential when analyzing its functioning. However, the large differences in material properties of fluid and structure and the finite motion of the leaflets complicate blood-valve interaction modeling. This has, so far, obstructed numerical analyses of valves operating under physiological conditions. A two-dimensional fluid-structure interaction model is presented, which allows the Reynolds number to be within the physiological range, using a fictitious domain method based on Lagrange multipliers to couple the two phases. The extension to the three-dimensional case is straightforward. The model has been validated experimentally using laser Doppler anemometry for measuring the fluid flow and digitized high-speed video recordings to visualize the leaflet motion in corresponding geometries. Results show that both the fluid and leaflet behaviour are well predicted for different leaflet thicknesses.}, }
@article {pmid10834152, year = {2000}, author = {Bluestein, D and Rambod, E and Gharib, M}, title = {Vortex shedding as a mechanism for free emboli formation in mechanical heart valves.}, journal = {Journal of biomechanical engineering}, volume = {122}, number = {2}, pages = {125-134}, doi = {10.1115/1.429634}, pmid = {10834152}, issn = {0148-0731}, mesh = {Biomedical Engineering/instrumentation ; Computer Simulation ; Equipment Design ; Heart Valve Prosthesis/*adverse effects ; Hemorheology ; Humans ; In Vitro Techniques ; Models, Cardiovascular ; Platelet Activation ; Pulsatile Flow ; Thromboembolism/*etiology ; }, abstract = {The high incidence of thromboembolic complications of mechanical heart valves (MHV) limits their success as permanent implants. The thrombogenicity of all MHV is primarily due to platelet activation by contact with foreign surfaces and by nonphysiological flow patterns. The latter include elevated flow stresses and regions of recirculation of blood that are induced by valve design characteristics. A numerical simulation of unsteady turbulent flow through a bileaflet MHV was conducted, using the Wilcox k-omega turbulence model for internal low-Reynolds-number flows, and compared to quantitative flow visualization performed in a pulse duplicator system using Digital Particle Image Velocimetry (DPIV). The wake of the valve leaflet during the deceleration phase revealed an intricate pattern of interacting shed vortices. Particle paths showed that platelets that were exposed to the highest flow stresses around the leaflets were entrapped within the shed vortices. Potentially activated, such platelets may tend to aggregate and form free emboli. Once formed, such free emboli would be convected downstream by the shed vortices, increasing the risk of systemic emboli.}, }
@article {pmid10821748, year = {2000}, author = {Stelle, LL and Blake, RW and Trites, AW}, title = {Hydrodynamic drag in steller sea lions (Eumetopias jubatus).}, journal = {The Journal of experimental biology}, volume = {203}, number = {Pt 12}, pages = {1915-1923}, doi = {10.1242/jeb.203.12.1915}, pmid = {10821748}, issn = {0022-0949}, mesh = {Animals ; Biomechanical Phenomena ; Biometry ; Female ; Male ; *Rheology ; Sea Lions/anatomy &amp; histology/*physiology ; *Swimming ; }, abstract = {Drag forces acting on Steller sea lions (Eumetopias jubatus) were investigated from 'deceleration during glide' measurements. A total of 66 glides from six juvenile sea lions yielded a mean drag coefficient (referenced to total wetted surface area) of 0.0056 at a mean Reynolds number of 5.5x10(6). The drag values indicate that the boundary layer is largely turbulent for Steller sea lions swimming at these Reynolds numbers, which are past the point of expected transition from laminar to turbulent flow. The position of maximum thickness (at 34 % of the body length measured from the tip of the nose) was more anterior than for a 'laminar' profile, supporting the idea that there is little laminar flow. The Steller sea lions in our study were characterized by a mean fineness ratio of 5.55. Their streamlined shape helps to delay flow separation, reducing total drag. In addition, turbulent boundary layers are more stable than laminar ones. Thus, separation should occur further back on the animal. Steller sea lions are the largest of the otariids and swam faster than the smaller California sea lions (Zalophus californianus). The mean glide velocity of the individual Steller sea lions ranged from 2.9 to 3.4 m s(-)(1) or 1.2-1.5 body lengths s(-)(1). These length-specific speeds are close to the optimum swim velocity of 1.4 body lengths s(-)(1) based on the minimum cost of transport for California sea lions.}, }
@article {pmid10818636, year = {1999}, author = {Liu, H and Yamaguchi, T}, title = {Computer modeling of fluid dynamics related to a myocardial bridge in a coronary artery.}, journal = {Biorheology}, volume = {36}, number = {5-6}, pages = {373-390}, pmid = {10818636}, issn = {0006-355X}, mesh = {Computational Biology ; *Computer Simulation ; Coronary Vessels/*physiopathology ; Humans ; *Models, Cardiovascular ; Myocardial Ischemia/*physiopathology ; Regional Blood Flow ; Rheology ; Stress, Mechanical ; }, abstract = {Fluid mechanics associated with blood flows induced by the so-called myocardial bridge (MB) has been studied systematically using a computational fluid dynamic modeling of the Newtonian, incompressible, two-dimensional, unsteady flow in a channel with a time-dependently flushing in/out indentation. During each cycle, a train of vortex wave flow was observed downstream of the phasic stenosis and both upper and lower walls suffer severely from consistently high, oscillating wall shear stresses (WSS). Extensive studies were conducted on the influence of the Reynolds number, the geometry and the Strouhal number of the MB movement on the nature of the vortex flow and the time-dependent wall shear stress distribution. Special attention was drawn to the relationship between the vortex wave and the pressure distribution. It was found that the pressure gradient changed markedly during one cycle, which was apparently dominated by the dynamics of the indentation. A steep, adverse pressure gradient was observed when the indentation was flushing out, which corresponded to the existence of the most developing vortices. It implies the possibility that the MB in a coronary artery can produce an extremely low pressure region immediately downstream of the phasic stenosis, where elastic choking or collapse of the coronary artery might occur.}, }
@article {pmid10815955, year = {2000}, author = {Bianchi, F and Ferrigno, R and Girault, HH}, title = {Finite element simulation of an electroosmotic-driven flow division at a T-junction of microscale dimensions.}, journal = {Analytical chemistry}, volume = {72}, number = {9}, pages = {1987-1993}, doi = {10.1021/ac991225z}, pmid = {10815955}, issn = {1520-6882}, abstract = {A finite element formulation is developed for the simulation of an electroosmotic flow in rectangular microscale channel networks. The distribution of the flow at a decoupling T-junction is investigated from a hydrodynamic standpoint in the case of a pressure-driven and an electroosmotically driven flow. The calculations are carried out in two steps: first solving the potential distribution arising from the external electric field and from the inherent zeta potential. These distributions are then injected in the Navier Stokes equation for the calculation of the velocity profile. The influence of the various parameters such as the zeta potential distribution, the Reynolds number, and the relative channel widths on the flow distribution is investigated.}, }
@article {pmid10811214, year = {2000}, author = {Groisman, A and Steinberg, V}, title = {Elastic turbulence in a polymer solution flow.}, journal = {Nature}, volume = {405}, number = {6782}, pages = {53-55}, doi = {10.1038/35011019}, pmid = {10811214}, issn = {1476-4687}, abstract = {Turbulence is a ubiquitous phenomenon that is not fully understood. It is known that the flow of a simple, newtonian fluid is likely to be turbulent when the Reynolds number is large (typically when the velocity is high, the viscosity is low and the size of the tank is large). In contrast, viscoelastic fluids such as solutions of flexible long-chain polymers have nonlinear mechanical properties and therefore may be expected to behave differently. Here we observe experimentally that the flow of a sufficiently elastic polymer solution can become irregular even at low velocity, high viscosity and in a small tank. The fluid motion is excited in a broad range of spatial and temporal scales, and we observe an increase in the flow resistance by a factor of about twenty. Although the Reynolds number may be arbitrarily low, the observed flow has all the main features of developed turbulence. A comparable state of turbulent flow for a newtonian fluid in a pipe would have a Reynolds number as high as 10(5) (refs 1, 2). The low Reynolds number or 'elastic' turbulence that we observe is accompanied by significant stretching of the polymer molecules, resulting in an increase in the elastic stresses of up to two orders of magnitude.}, }
@article {pmid10790833, year = {2000}, author = {Qiu, Y and Tarbell, JM}, title = {Numerical simulation of pulsatile flow in a compliant curved tube model of a coronary artery.}, journal = {Journal of biomechanical engineering}, volume = {122}, number = {1}, pages = {77-85}, doi = {10.1115/1.429629}, pmid = {10790833}, issn = {0148-0731}, support = {HL35549/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Blood Pressure ; Compliance ; Coronary Artery Disease/etiology/physiopathology ; Coronary Vessels/*physiology/*ultrastructure ; Disease Models, Animal ; Dogs ; Endothelium, Vascular/injuries ; *Finite Element Analysis ; Hemorheology ; *Models, Cardiovascular ; *Numerical Analysis, Computer-Assisted ; *Pulsatile Flow ; Reproducibility of Results ; Stress, Mechanical ; }, abstract = {The endothelial cells (ECs) lining a blood vessel wall are exposed to both the wall shear stress (WSS) of blood flow and the circumferential strain (CS) of pulsing artery wall motion. These two forces and their interaction are believed to play a role in determining remodeling of the vessel wall and development of arterial disease (atherosclerosis). This study focused on the WSS and CS dynamic behavior in a compliant model of a coronary artery taking into account the curvature of the bending artery and physiological radial wall motion. A three-dimensional finite element model with transient flow and moving boundaries was set up to simulate pulsatile flow with physiological pressure and flow wave forms characteristic of the coronary arteries. The characteristic coronary artery curvature and flow conditions applied to the simulation were: aspect ratio (lambda) = 10, diameter variation (DV) = 6 percent, mean Reynolds number (Re) = 150, and unsteadiness parameter (alpha) = 3. The results show that mean WSS is about 50 percent lower on the inside wall than the outside wall while WSS oscillation is stronger on the inside wall. The stress phase angle (SPA) between CS and WSS, which characterizes the dynamics of the mechanical force pattern applied to the endothelial cell layer, shows that CS and WSS are more out of phase in the coronaries than in any other region of the circulation (-220 deg on the outside wall, -250 deg on the inside wall). This suggests that in addition to WSS, SPA may play a role in localization of coronary atherosclerosis.}, }
@article {pmid10788725, year = {2000}, author = {Paley, M and Hose, R and Marzouqa, I and Fenner, J and Wilkinson, I and Noguchi, Y and Griffiths, P}, title = {Stable periodic vortex shedding studied using computational fluid dynamics, laser sheet flow visualization, and MR imaging.}, journal = {Magnetic resonance imaging}, volume = {18}, number = {4}, pages = {473-478}, doi = {10.1016/s0730-725x(99)00136-8}, pmid = {10788725}, issn = {0730-725X}, mesh = {Carotid Arteries/physiopathology ; Carotid Stenosis/*physiopathology ; Echo-Planar Imaging ; Finite Element Analysis ; *Lasers ; *Magnetic Resonance Imaging/methods ; Phantoms, Imaging ; Rheology ; }, abstract = {Recirculating and detached flow patterns close to the carotid bifurcation are thought to play an important role in the development of carotid stenoses by promoting atherosclerosis. The aim of this study was to investigate a flow regime with strong transient characteristics, including vortex shedding and transport to develop methodologies appropriate to the analysis of carotid stenoses. The existence of a regular periodic vortex street behind a cylindrical flow obstruction was predicted and analysed in detail by Theodore van Karman in the early 20th century. This model was chosen in our study for both ease of phantom construction and of theoretical modelling using finite element computational fluid dynamics (CFD). The results of the theoretical calculations have been compared with two methods of flow visualization-laser sheet imaging and real-time echo planar magnitude MR imaging. Flow was investigated over a range of Reynold's number from 40 through 400 through which vortex shedding is predicted. Good overall agreement was obtained between the theoretical (16 mm-CFD) and experimental (16+/-2 mm-Laser, 17+/-2 mm-MRI) estimates of the Karman Vortex street wavelength for a Reynolds number of 200.}, }
@article {pmid10786940, year = {2000}, author = {Weissburg, MJ}, title = {The fluid dynamical context of chemosensory behavior.}, journal = {The Biological bulletin}, volume = {198}, number = {2}, pages = {188-202}, doi = {10.2307/1542523}, pmid = {10786940}, issn = {0006-3185}, mesh = {Animals ; *Behavior, Animal ; Sense Organs ; }, abstract = {The fluid mechanical environment provides the context in which denizens of aquatic realms, as well as terrestrial creatures, use chemoperception to search for objects. Our ability to understand the nature of olfactory-guided navigation rests on our proficiency at characterizing the fluid dynamic setting and at relating properties of flow to behavioral and sensory mechanisms. This work reviews some fluid dynamical concepts that are particularly useful in describing aspects of flow relevant to chemosensory navigation, and it considers studies of orientation in animals in light of these principles. Comparisons across broadly different fluid environments suggest that particular sensory and behavioral mechanisms may be tailored to specific flow regimes and stimulus environments. This is clearly evident when examining animals that operate in high vs. low Reynolds number flows. In other cases, animals may converge on common solutions in given flow regimes in spite of differences in taxonomic class or size. Potential parallels may include behavior of aquatic vs. terrestrial arthropods, and animals without fixed reference points in flows dominated by molecular vs. turbulent diffusion. In an effort to add further fluid dynamical underpinnings to navigational strategies, I suggest how simple nondimensional categorization of behavior in relation to flow may aid in identifying the forces underlying common elements, even across animals of seemingly disparate size and scale.}, }
@article {pmid10760253, year = {2000}, author = {Barenblatt, GI and Chorin, AJ and Prostokishin, VM}, title = {Characteristic length scale of the intermediate structure in zero-pressure-gradient boundary layer flow.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {97}, number = {8}, pages = {3799-3802}, pmid = {10760253}, issn = {0027-8424}, abstract = {In a turbulent boundary layer over a smooth flat plate with zero pressure gradient, the intermediate structure between the viscous sublayer and the free stream consists of two layers: one adjacent to the viscous sublayer and one adjacent to the free stream. When the level of turbulence in the free stream is low, the boundary between the two layers is sharp, and both have a self-similar structure described by Reynolds-number-dependent scaling (power) laws. This structure introduces two length scales: one-the wall-region thickness-determined by the sharp boundary between the two intermediate layers and the second determined by the condition that the velocity distribution in the first intermediate layer be the one common to all wall-bounded flows and in particular coincide with the scaling law previously determined for pipe flows. Using recent experimental data, we determine both these length scales and show that they are close. Our results disagree with the classical model of the "wake region."}, }
@article {pmid10738687, year = {1999}, author = {Yu, SC and Chan, WK and Ng, BT and Chua, LP}, title = {A numerical investigation on the steady and pulsatile flow characteristics in axi-symmetric abdominal aortic aneurysm models with some experimental evaluation.}, journal = {Journal of medical engineering &amp; technology}, volume = {23}, number = {6}, pages = {228-239}, doi = {10.1080/030919099294096}, pmid = {10738687}, issn = {0309-1902}, mesh = {Aortic Aneurysm, Abdominal/*physiopathology ; Biomechanical Phenomena ; Blood Pressure ; Hemodynamics ; Humans ; *Models, Anatomic ; Models, Biological ; Pulsatile Flow ; *Rheology ; Stress, Mechanical ; }, abstract = {Steady and pulsatile flow characteristics in rigid abdominal aortic aneurysm (AAA) models were investigated computationally (using Fluent v. 4.3) over a range of Reynolds number (from 200 to 1600) and Womersley number (from 17 to 22). Some comparisons with measurements obtained by particle image velocimetry under the pulsatile flow conditions are also included. A sinusoidal inlet flow waveform 1 + sin omega t with thin inlet boundary layers was used to produce the required pulsatile flow conditions. The bulk features of the mean flow as well as some detailed features, such as wall shear stress distributions, are the foci of the present investigation. Recirculating vortices appeared at different phases of a flow cycle causing significant spatial and temporal variations in wall shear stresses and static pressure distributions. A high level of shear stresses usually appeared at the upstream and downstream ends of the bulge. Effects of pressure rise caused by the increase in cross-sectional area were transmitted into the downstream tube. Further simulation studies were conducted using simulated physiological waveforms under resting and exercise conditions so as to determine the possible implication of vortex dynamics inside the AAA model.}, }
@article {pmid10723896, year = {1999}, author = {Pincombe, B and Mazumdar, J and Hamilton-Craig, I}, title = {Effects of multiple stenoses and post-stenotic dilatation on non-Newtonian blood flow in small arteries.}, journal = {Medical &amp; biological engineering &amp; computing}, volume = {37}, number = {5}, pages = {595-599}, pmid = {10723896}, issn = {0140-0118}, mesh = {Blood Viscosity ; Coronary Disease/*blood ; Dilatation, Pathologic/blood ; *Hemorheology ; Humans ; *Models, Cardiovascular ; }, abstract = {Fully-developed one-dimensional Casson flow through a single vessel of varying radius is proposed as a model of low Reynolds number blood flow in small stenosed coronary arteries. A formula for the resistance-to-flow ratio is derived, and results for yield stresses of tau 0 = 0, 0.005 and 0.01 Nm-2, viscosities of mu = 3.45 x 10(-3), 4.00 x 10(-3) and 4.55 x 10(-3) Pa.s and fluxes of 2.73 x 10(-6), x 10(-5) and x 10(-4) m3 s-1 are determined for segment of 0.45 mm radius and 45 mm length, with 15 mm abnormalities at each end where the radius varies by up to +/- 0.225 mm. When tau 0 = 0.005 N m-2, mu = 4 x 10(-3) Pa.s and Q = 1, the numerical values of the resistance-to-flow ratio vary from lambda = 0.525, when the maximum radii of the two abnormal segments are both 0.675 mm, to lambda = 3.06, when the minimum radii are both 0.225 mm. The resistance-to-flow ratio moves closer to unity as yield stress increases or as blood viscosity or flux decreases, and the magnitude of these alterations is greatest for yield stress and least for flux.}, }
@article {pmid10656051, year = {1998}, author = {Helmke, BP and Sugihara-Seki, M and Skalak, R and Schmid-Schönbein, GW}, title = {A mechanism for erythrocyte-mediated elevation of apparent viscosity by leukocytes in vivo without adhesion to the endothelium.}, journal = {Biorheology}, volume = {35}, number = {6}, pages = {437-448}, doi = {10.1016/s0006-355x(99)80021-3}, pmid = {10656051}, issn = {0006-355X}, mesh = {Animals ; Blood Viscosity/*physiology ; Capillaries ; *Endothelium, Vascular ; Erythrocytes/*physiology ; Leukocytes/*physiology ; Male ; Models, Biological ; Muscle, Skeletal/blood supply ; Perfusion ; Rats ; Rats, Wistar ; }, abstract = {In spite of the relatively small number of leukocytes in the circulation, they have a significant influence on the perfusion of such organs as skeletal muscle or kidney. However, the underlying mechanisms are incompletely understood. In the current study a combined in vivo and computational approach is presented in which the interaction of individual freely flowing leukocytes with erythrocytes and its effect on apparent blood viscosity are explored. The skeletal muscle microcirculation was perfused with different cell suspensions with and without leukocytes or erythrocytes. We examined a three-dimensional numerical model of low Reynolds number flow in a capillary with a train of erythrocytes (small spheres) in off-axis positions and single larger leukocytes in axisymmetric positions. The results indicate that in order to match the slower axial velocity of leukocytes in capillaries, erythrocytes need to position themselves into an off-axis position in the capillary. In such off-axis positions at constant mean capillary velocity, erythrocyte axial velocity matches on average the axial velocity of the leukocytes, but the apparent viscosity is elevated, in agreement with the whole organ perfusion observations. Thus, leukocytes influence the whole organ resistance in skeletal muscle to a significant degree only in the presence of erythrocytes.}, }
@article {pmid10656050, year = {1998}, author = {Cheer, AY and Dwyer, HA and Barakat, AI and Sy, E and Bice, M}, title = {Computational study of the effect of geometric and flow parameters on the steady flow field at the rabbit aorto-celiac bifurcation.}, journal = {Biorheology}, volume = {35}, number = {6}, pages = {415-435}, doi = {10.1016/s0006-355x(99)80020-1}, pmid = {10656050}, issn = {0006-355X}, mesh = {Algorithms ; Animals ; *Aorta ; Arteriosclerosis/physiopathology ; *Biomedical Engineering ; *Celiac Artery ; *Computational Biology ; *Hemodynamics ; Models, Cardiovascular ; Rabbits ; Stress, Mechanical ; }, abstract = {Arterial hemodynamic forces may play a role in the localization of early atherosclerotic lesions. We have been developing numerical techniques based on overset or "Chimera" type formulations to solve the Navier-Stokes equations in complex geometries simulating arterial bifurcations. This paper presents three-dimensional steady flow computations in a model of the rabbit aorto-celiac bifurcation. The computational methods were validated by comparing the numerical results to previously-obtained flow visualization data. Once validated, the numerical algorithms were used to investigate the sensitivity of the computed flow field and resulting wall shear stress distribution to various geometric and hemodynamic parameters. The results demonstrated that a decrease in the extent of aortic taper downstream of the celiac artery induced looping fluid motion along the lateral walls of the aorta and shifted the peak wall shear stress from downstream of the celiac artery to upstream. Increasing the flow Reynolds number led to a sharp increase in spatial gradients of wall shear stress. The flow field was highly sensitive to the flow division ratio, i.e., the fraction of total flow rate that enters the celiac artery, with larger values of this ratio leading to the occurrence of flow separation along the dorsal wall of the aorta. Finally, skewness of the inlet velocity profile had a profound impact on the wall shear stress distribution near the celiac artery. While not physiological due to the assumption of steady flow, these results provide valuable insight into the fluid physics at geometries simulating arterial bifurcations.}, }
@article {pmid10645786, year = {2000}, author = {Browne, P and Ramuzat, A and Saxena, R and Yoganathan, AP}, title = {Experimental investigation of the steady flow downstream of the St. Jude bileaflet heart valve: a comparison between laser Doppler velocimetry and particle image velocimetry techniques.}, journal = {Annals of biomedical engineering}, volume = {28}, number = {1}, pages = {39-47}, doi = {10.1114/1.252}, pmid = {10645786}, issn = {0090-6964}, mesh = {Biomedical Engineering ; Blood Flow Velocity ; Coronary Circulation ; Evaluation Studies as Topic ; *Heart Valve Prosthesis ; Hemorheology/instrumentation/methods ; Humans ; In Vitro Techniques ; Laser-Doppler Flowmetry/instrumentation ; Models, Cardiovascular ; }, abstract = {This study investigates turbulent flow, based on high Reynolds number, downstream of a prosthetic heart valve using both laser Doppler velocimetry (LDV) and particle image velocimetry (PIV). Until now, LDV has been the more commonly used tool in investigating the flow characteristics associated with mechanical heart valves. The LDV technique allows point by point velocity measurements and provides enough statistical information to quantify turbulent structure. The main drawback of this technique is the time consuming nature of the data acquisition process in order to assess an entire flow field area. Another technique now used in fluid dynamics studies is the PIV measurement technique. This technique allows spatial and temporal measurement of the entire flow field. Using this technique, the instantaneous and average velocity flow fields can be investigated for different positions. This paper presents a comparison of PIV two-dimensional measurements to LDV measurements, performed under steady flow conditions, for a measurement plane parallel to the leaflets of a St. Jude Medical (SJM) bileaflet valve. Comparisons of mean velocity obtained by the two techniques are in good agreement except for where there is instability in the flow. For second moment quantities the comparisons were less agreeable. This suggests that the PIV technique has sufficient temporal and spatial resolution to estimate mean velocity depending on the degree of instability in the flow and also provides sufficient images needed to duplicate mean flow but not for higher moment turbulence quantities such as maximum turbulent shear stress.}, }
@article {pmid10645785, year = {2000}, author = {Qiu, Y and Tarbell, JM}, title = {Numerical simulation of oxygen mass transfer in a compliant curved tube model of a coronary artery.}, journal = {Annals of biomedical engineering}, volume = {28}, number = {1}, pages = {26-38}, doi = {10.1114/1.251}, pmid = {10645785}, issn = {0090-6964}, support = {HL 35549/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Biological Transport, Active ; Biomedical Engineering ; Compliance ; Computer Simulation ; Coronary Circulation/physiology ; Coronary Vessels/*anatomy &amp; histology/*metabolism ; Humans ; Models, Anatomic ; *Models, Cardiovascular ; Oxygen/blood/*metabolism ; Oxygen Consumption ; }, abstract = {Arterial wall transport of blood-borne oxygen is essential for superficial arterial wall metabolism. The unique geometry and hemodynamics of coronary arteries curved over the heart surface may alter the O2 transport pattern and lead to abnormalities of O2 tension at the inner wall (epicardial surface) which may contribute to atherogenesis. This study focused on O2 transport in a compliant model of a curved coronary artery. A three-dimensional finite element model with moving boundaries was setup to simulate physiological flow and O2 transport in coronary arteries. The full Navier-Stokes equations and the coupled conservation of species equation were solved simultaneously for typical coronary flow characteristics (aspect ratio=10, diameter variation=6%, mean Reynolds number= 150, unsteadiness parameter=3, Schmidt number=2,700). The results indicate a large difference in O2 wall flux (Sherwood number [Sh]) between the outside (Sh about 55) and inside (Sh about 2) walls and imply that O2 transport at the inner wall could be limited by the fluid phase.}, }
@article {pmid10596213, year = {1999}, author = {Kamholz, AE and Weigl, BH and Finlayson, BA and Yager, P}, title = {Quantitative analysis of molecular interaction in a microfluidic channel: the T-sensor.}, journal = {Analytical chemistry}, volume = {71}, number = {23}, pages = {5340-5347}, doi = {10.1021/ac990504j}, pmid = {10596213}, issn = {0003-2700}, mesh = {Kinetics ; Models, Chemical ; Spectrometry, Fluorescence/*instrumentation ; }, abstract = {The T-sensor is a recently developed microfluidic chemical measurement device that exploits the low Reynolds number flow conditions in microfabricated channels. The interdiffusion and resulting chemical interaction of components from two or more input fluid streams can be monitored optically, allowing measurement of analyte concentrations on a continuous basis. In a simple form of T-sensor, the concentration of a target analyte is determined by measuring fluorescence intensity in a region where the analyte and a fluorescent indicator have interdiffused. An analytical model has been developed that predicts device behavior from the diffusion coefficients of the analyte, indicator, and analyte--indicator complex and from the kinetics of the complex formation. Diffusion coefficients depend on the local viscosity which, in turn, depends on local concentrations of all analytes. These relationships, as well as reaction equilibria, are often unknown. A rapid method for determining these unknown parameters by interpreting T-sensor experiments through the model is presented.}, }
@article {pmid10552885, year = {1999}, author = {Marin, M and Baek, I and Taylor, AJ}, title = {Volatile release from aqueous solutions under dynamic headspace dilution conditions.}, journal = {Journal of agricultural and food chemistry}, volume = {47}, number = {11}, pages = {4750-4755}, doi = {10.1021/jf990470g}, pmid = {10552885}, issn = {0021-8561}, mesh = {Food Handling/*methods ; Kinetics ; *Odorants ; Solutions ; Volatilization ; }, abstract = {Static equilibrium was established between the gas phase (headspace) and an unstirred aqueous phase in a sealed vessel. The headspace was then diluted with air to mimic the situation when a container of food is opened and the volatiles are diluted by the surrounding air. Because this first volatile signal can influence overall flavor perception, the parameters controlling volatile release under these conditions are of interest. A mechanistic model was developed and validated experimentally. Release of compounds depended on the air-water partition coefficient (K(aw)) and the mass transport in both phases. For compounds with K(aw) values <10(-)(3), K(aw) was the factor determining release rate. When K(aw) was >10(-)(3), mass transport in the gas phase became significant and the Reynolds number played a role. Because release from packaged foods occurs at low Reynolds numbers, whereas most experiments are conducted at medium to high Reynolds numbers, the experimentally defined profile may not reflect the real situation.}, }
@article {pmid10593472, year = {1999}, author = {Rueckoldt, H and Vangerow, B and Marx, G and Haubitz, B and Meyer, MC and Piepenbrock, S and Leuwer, M}, title = {Xenon inhalation increases airway pressure in ventilated patients.}, journal = {Acta anaesthesiologica Scandinavica}, volume = {43}, number = {10}, pages = {1060-1064}, doi = {10.1034/j.1399-6576.1999.431016.x}, pmid = {10593472}, issn = {0001-5172}, mesh = {Administration, Inhalation ; Adolescent ; Adult ; Aged ; Aged, 80 and over ; Airway Resistance/*drug effects ; Blood Pressure/drug effects ; Carbon Dioxide/blood ; Cerebrovascular Circulation ; Female ; Heart Rate/drug effects ; Humans ; Male ; Middle Aged ; Oxygen/blood ; *Respiration, Artificial ; Retrospective Studies ; Tomography, X-Ray Computed ; Xenon/administration &amp; dosage/*pharmacology ; }, abstract = {BACKGROUND: The inert gas xenon, known as an anaesthetic for nearly 50 years, is also used as a contrast agent during computerised tomography (CT)-scanning. As xenon has a higher density and viscosity than air, xenon inhalation may increase airway resistance.<br><br>METHODS: In a retrospective study we investigated the effects of 33% xenon/67% oxygen on airway pressure and cardio-respiratory parameters in 37 long-term mechanically ventilated patients undergoing cerebral blood flow (rCBF) measurements by means of stable xenon-enhanced CT.<br><br>RESULTS: Xenon administration caused a significant increase in peak airway pressure from 31.6+/-8.0 cm H2O to 42.7+/-16.9 cm H2O. This effect was reproducible, did not occur after reduction of inspiratory flow rate by 50% from 0.56+/-0.15 L x s(-1) to 0.28+/-0.08 L x s(-1), and vanished immediately after termination of xenon delivery.<br><br>CONCLUSION: Due to the higher density and viscosity of this gas mixture, ventilation with xenon/oxygen produces a higher Reynolds' number than oxygen/air when given at the same flow rate. This means that during xenon ventilation the zone of transition from turbulent to laminar gas flow may be located more peripherally (in smaller airways) than during oxygen/air ventilation with a subsequent increase in airway resistance. Our results indicate that xenon inhalation may cause a clinically relevant increase of peak airway pressure in mechanically ventilated patients.}, }
@article {pmid10567000, year = {1999}, author = {Dmitruk, P and Gómez, DO}, title = {Scaling Law for the Heating of Solar Coronal Loops.}, journal = {The Astrophysical journal}, volume = {527}, number = {1}, pages = {L63-L66}, doi = {10.1086/312390}, pmid = {10567000}, issn = {0004-637X}, abstract = {We report preliminary results from a series of numerical simulations of the reduced magnetohydrodynamic equations used to describe the dynamics of magnetic loops in active regions of the solar corona. A stationary velocity field is applied at the photospheric boundaries to imitate the driving action of granule motions. A turbulent stationary regime is reached, characterized by a broadband power spectrum Ek approximately k-3&amp;solm0;2 and heating rate levels compatible with the energy requirements of active region loops. A dimensional analysis of the equations indicates that their solutions are determined by two dimensionless parameters: the Reynolds number and the ratio between the Alfvén time and the photospheric turnover time. From a series of simulations for different values of this ratio, we determine how the heating rate scales with the physical parameters of the problem, which might be useful for an observational test of this model.}, }
@article {pmid10517207, year = {1999}, author = {Pedersen, EM and Kim, WY and Staalsen, NH and Hasenkam, JM and Nygaard, H and Paulsen, PK}, title = {Development of velocity profiles and retrograde flow in the porcine abdominal aorta under different haemodynamic conditions.}, journal = {Scandinavian cardiovascular journal : SCJ}, volume = {33}, number = {4}, pages = {206-214}, doi = {10.1080/14017439950141632}, pmid = {10517207}, issn = {1401-7431}, mesh = {Animals ; Aorta, Abdominal/anatomy &amp; histology/diagnostic imaging/*physiology ; Blood Flow Velocity/*physiology ; Cardiac Pacing, Artificial ; Electrocardiography ; Heart Rate ; Hemodynamics/*physiology ; Signal Processing, Computer-Assisted ; Swine ; Ultrasonography, Doppler, Pulsed ; }, abstract = {Low and/or oscillating wall shear stresses are related to the development of atherosclerosis and this oscillation is influenced by changes in basic haemodynamics (exercise). The objective of this study was to provide in vivo data on the development of velocity profiles and oscillating blood velocities in the abdominal aorta under varying haemodynamic conditions. Six anaesthetized, 90-kg pigs were used in the study. Abdominal aortic velocity profiles across the anterior-posterior diameter were acquired at different axial positions using 10 MHz pulsed Doppler ultrasound. Measurements were obtained under normal conditions and during cardiac pacing up to 170 beats/min. Velocity profiles were obtained during heart rates ranging between 58 and 169 beats/min, and during flow rates ranging between 0.57 and 2.89 l/min. Main outcome measures included minimum velocities, frequency index, shape of velocity profiles (velocity distribution index), Reynolds' numbers, and Womersley's frequency parameter. Velocity profiles were blunted, with lowest velocities at the distal posterior vessel wall. Multiple regression analysis showed the development of velocity profiles to be inversely correlated with the pulsatility index, Womersley's frequency parameter and the mean Reynolds' number (r = 0.89, p < 0.0005). Minimum velocities were negatively correlated with the PI, Womersley's frequency parameter and positively with the mean Reynolds' number (r = 0.94, p < 10(-8)). Retrograde velocities (and hence oscillating wall shear stresses) were present at mean Reynolds' number < 1000. The oscillation of blood velocities at the wall in the porcine abdominal aorta was highly dependent on general haemodynamics (i.e. flow, heart rate and vessel diameter as expressed in the Reynolds' numbers and Womersley's frequency parameters). The velocity profiles in the abdominal aorta were found to be far from parabolic. These findings have important implications for the understanding and future modelling of the complex haemodynamics in the abdominal aorta and their relation to the development of atherosclerotic disease.}, }
@article {pmid10511515, year = {1999}, author = {Pérez-De-Tejada, H}, title = {Viscous Forces in Velocity Boundary Layers around Planetary Ionospheres.}, journal = {The Astrophysical journal}, volume = {525}, number = {1}, pages = {L65-L68}, doi = {10.1086/312320}, pmid = {10511515}, issn = {0004-637X}, abstract = {A discussion is presented to examine the role of viscous forces in the transport of solar wind momentum to the ionospheric plasma of weakly magnetized planets (Venus and Mars). Observational data are used to make a comparison of the Reynolds and Maxwell stresses that are operative in the interaction of the solar wind with local plasma (planetary ionospheres). Measurements show the presence of a velocity boundary layer formed around the flanks of the ionosphere where the shocked solar wind has reached super-Alfvénic speeds. It is found that the Reynolds stresses in the solar wind at that region can be larger than the Maxwell stresses and thus are necessary in the local acceleration of the ionospheric plasma. From an order-of-magnitude calculation of the Reynolds stresses, it is possible to derive values of the kinematic viscosity and the Reynolds number that are suitable to the gyrotropic motion of the solar wind particles across the boundary layer. The value of the kinematic viscosity is comparable to those inferred from studies of the transport of solar wind momentum to the earth's magnetosphere and thus suggest a common property of the solar wind around planetary obstacles. Similar conditions could also be applicable to velocity boundary layers formed in other plasma interaction problems in astrophysics.}, }
@article {pmid10489292, year = {1999}, author = {Johnson, RA and Borhan, A}, title = {Effect of Insoluble Surfactants on the Pressure-Driven Motion of a Drop in a Tube in the Limit of High Surface Coverage.}, journal = {Journal of colloid and interface science}, volume = {218}, number = {1}, pages = {184-200}, doi = {10.1006/jcis.1999.6376}, pmid = {10489292}, issn = {1095-7103}, abstract = {The effect of surfactants on the axisymmetric pressure-driven motion of a droplet in a tube is investigated under low Reynolds number conditions. In the presence of surface-active impurities, the motion of the drop results in constant redistribution of the adsorbed surfactant along the interface by convection and diffusion, leading to nonuniformities in interfacial tension (i.e., Marangoni stresses) which modify the viscous stress balance at the interface. These, in turn, affect the mobility of the drop and its steady or transient shape deformations. In this study, the steady-state behavior of such a drop is examined in the presence of nondilute concentrations of bulk-insoluble surfactants on the surface of the drop. The boundary integral method is used in conjunction with a finite-difference scheme to solve the unsteady surface convective-diffusion equation for surfactant transport. The Frumkin adsorption framework is used to explore the effects of monolayer saturation and nonideal surfactant interactions on the steady drop shape and speed in the limit of high surface coverage. It is found that for surfactants with strong cohesive interactions, the drop mobility increases with increasing surface coverage, attaining maximum mobility at about 50% initial coverage. Furthermore, surface-convection-dominated systems with strong cohesive interactions exhibit surface flow patterns corresponding to the formation of a stagnant cap at the trailing end of the drop. All other systems exhibit surface flow patterns corresponding to uniform retardation of interface mobility as a fully immobilized interface is approached with increasing surface convection. Copyright 1999 Academic Press.}, }
@article {pmid10474655, year = {1998}, author = {Ghalichi, F and Deng, X and De Champlain, A and Douville, Y and King, M and Guidoin, R}, title = {Low Reynolds number turbulence modeling of blood flow in arterial stenoses.}, journal = {Biorheology}, volume = {35}, number = {4-5}, pages = {281-294}, doi = {10.1016/s0006-355x(99)80011-0}, pmid = {10474655}, issn = {0006-355X}, mesh = {Arteries/pathology/*physiopathology ; *Computer Simulation ; Constriction, Pathologic ; Hemodynamics ; Humans ; *Models, Cardiovascular ; Motion ; Regional Blood Flow ; Rheology ; Stress, Mechanical ; }, abstract = {Moderate and severe arterial stenoses can produce highly disturbed flow regions with transitional and or turbulent flow characteristics. Neither laminar flow modeling nor standard two-equation models such as the kappa-epsilon turbulence ones are suitable for this kind of blood flow. In order to analyze the transitional or turbulent flow distal to an arterial stenosis, authors of this study have used the Wilcox low-Re turbulence model. Flow simulations were carried out on stenoses with 50, 75 and 86% reductions in cross-sectional area over a range of physiologically relevant Reynolds numbers. The results obtained with this low-Re turbulence model were compared with experimental measurements and with the results obtained by the standard kappa-epsilon model in terms of velocity profile, vortex length, wall shear stress, wall static pressure, and turbulence intensity. The comparisons show that results predicted by the low-Re model are in good agreement with the experimental measurements. This model accurately predicts the critical Reynolds number at which blood flow becomes transitional or turbulent distal an arterial stenosis. Most interestingly, over the Re range of laminar flow, the vortex length calculated with the low-Re model also closely matches the vortex length predicted by laminar flow modeling. In conclusion, the study strongly suggests that the proposed model is suitable for blood flow studies in certain areas of the arterial tree where both laminar and transitional/turbulent flows coexist.}, }
@article {pmid10469543, year = {1999}, author = {Reynolds, AM}, title = {A Lagrangian Stochastic Model for the Dispersion and Deposition of Brownian Particles.}, journal = {Journal of colloid and interface science}, volume = {217}, number = {2}, pages = {348-356}, doi = {10.1006/jcis.1999.6373}, pmid = {10469543}, issn = {1095-7103}, abstract = {A Lagrangian stochastic model for the dispersion and deposition of submicron-size particles is formulated and validated. The model satisfies the well-mixed condition, incorporates molecular diffusivity, and accounts for the effects of Reynolds number upon Lagrangian particle statistics. Reynolds number effects are found to be significant in the viscous sublayer and the buffer zone of a turbulent shear flow. The effects are due almost entirely to the change in the Lagrangian integral time scale. Sawford's correction to first-order Lagrangian stochastic models for the effects of Reynolds number is found to be appropriate for inhomogeneous turbulence even when the Taylor-Reynolds number R(lambda) approximately O(0.1). The model predicts, in close accord with experiment and the results of direct numerical simulations, that the nondimensional particle deposition velocity K(+) = 0.06Sc(-2/3), where Sc is the Schmidt number. When Reynolds number effects are neglected, K(+) is overpredicted by several orders of magnitude. Copyright 1999 Academic Press.}, }
@article {pmid10468355, year = {1999}, author = {Yu, SC and Zhao, JB}, title = {A steady flow analysis on the stented and non-stented sidewall aneurysm models.}, journal = {Medical engineering &amp; physics}, volume = {21}, number = {3}, pages = {133-141}, doi = {10.1016/s1350-4533(99)00037-5}, pmid = {10468355}, issn = {1350-4533}, mesh = {Aneurysm/*physiopathology/*therapy ; Biomedical Engineering ; Blood Flow Velocity ; Hemodynamics ; Hemorheology/instrumentation ; Humans ; *Models, Cardiovascular ; Regional Blood Flow ; *Stents ; }, abstract = {As part of a general investigation on the effects of blood flow patterns in sidewall aneurysm, in vitro steady flow studies on rigid aneurysm models have been conducted using Particle Image Velocimetry over a range of Reynolds number from 200 to 1600. Above Reynolds number 700, one large recirculating vortex would be formed, occupying the entire aneurysmal pouch. The centre of the vortex is located at region near to the distal neck. A pair of counter rotating vortices would however be formed at Reynolds numbers below 700. For all the aneurysm models considered, the vortex strength, in general, is stronger at higher Reynolds numbers but lower at larger aneurysm size. Maximum strength of the vortex is about 15% of the bulk mean velocity in the upstream parent tube. Estimates of the wall shear stresses are derived from the near wall velocity measurements. Highest level of wall shear stresses always appears at the distal neck of the aneurysmal pouch. Stents and springs of different porosity have been used to dampen the flow movement inside the aneurysm so as to induce the possible formation of thrombosis. It is found that the flow movement inside the aneurysmal pouch can be suppressed to less than 5% of the bulk mean velocity by both devices. Furthermore, regions of high wall shear stresses at the distal neck could also be suppressed by almost 90%. The present results would be useful for further improvements in stent (or spring) technology.}, }
@article {pmid10464690, year = {1999}, author = {Kirpalani, A and Park, H and Butany, J and Johnston, KW and Ojha, M}, title = {Velocity and wall shear stress patterns in the human right coronary artery.}, journal = {Journal of biomechanical engineering}, volume = {121}, number = {4}, pages = {370-375}, doi = {10.1115/1.2798333}, pmid = {10464690}, issn = {0148-0731}, mesh = {Blood Flow Velocity ; Coronary Vessels/*physiology ; Humans ; Laser-Doppler Flowmetry ; *Models, Cardiovascular ; Pulsatile Flow/physiology ; Stress, Mechanical ; }, abstract = {Blood flow dynamics in the human right coronary artery have not been adequately quantified despite the clinical significance of coronary atherosclerosis. In this study, a technique was developed to construct a rigid flow model from a cast of a human right coronary artery. A laser photochromic method was used to characterize the velocity and wall shear stress patterns. The flow conditions include steady flow at Reynolds numbers of 500 and 1000 as well as unsteady flow with Womersley parameter and peak Reynolds number of 1.82 and 750, respectively. Characterization of the three-dimensional geometry of the artery revealed that the largest spatial variation in curvature occurred within the almost branch-free proximal region, with the greatest curvature existing along the acute margin of the heart. In the proximal segment, high shear stresses were observed on the outer wall and lower, but not negative, stresses along the inner wall. Low shear stress on the inner wall may be related to the preferential localization of atherosclerosis in the proximal segment of the right coronary artery. However, it is possible that the large difference between the outer and inner wall shear stresses may also be involved.}, }
@article {pmid10440674, year = {1999}, author = {Stoodley, P and Lewandowski, Z and Boyle, JD and Lappin-Scott, HM}, title = {Structural deformation of bacterial biofilms caused by short-term fluctuations in fluid shear: an in situ investigation of biofilm rheology.}, journal = {Biotechnology and bioengineering}, volume = {65}, number = {1}, pages = {83-92}, pmid = {10440674}, issn = {0006-3592}, mesh = {*Bacteria ; *Biofilms ; Bioreactors ; Elasticity ; Pseudomonas aeruginosa ; Rheology ; Viscosity ; }, abstract = {The physical properties (rheology) of biofilms will determine the shape and mechanical stability of the biofilm structure and consequently affect both mass transfer and detachment processes. Biofilm viscoelasticity is also thought to increase fluid energy losses in pipelines. Yet there is very little information on the rheology of intact biofilms. This is due in part to the difficulty in using conventional testing techniques. The size and nature of biofilms makes them difficult to handle, while removal from a surface destroys the integrity of the sample. We have developed a method which allowed us to conduct simple stress-strain and creep experiments on mixed and pure culture biofilms in situ by observing the structural deformations caused by changes in hydrodynamic shear stress (tau(w)). The biofilms were grown under turbulent pipe flow (flow velocity (u) = 1 m/s, Reynolds number (Re) = 3600, tau(w) = 5. 09 N/m(2)) for between 12 and 23 days. The resulting biofilms were heterogeneous and consisted of filamentous streamers that were readily deformed by changes in tau(w). At tau(w) of 10.11 N/m(2) the streamers were flattened so that the thickness was reduced by 25%. We estimated that the shear modulus (G) of the mixed culture biofilm was 27 N/m(2) and the apparent elastic modulus (E(app)) of both biofilms was in the range of 17 to 40 N/m(2). The biofilms behaved like elastic and viscoelastic solids below the tau(w) at which they were grown but behaved like viscoelastic fluids at elevated tau(w). The implications of these results for fluid energy losses and the processes of mass transfer and detachment are discussed.}, }
@article {pmid10419674, year = {1999}, author = {Kornev, KG and Neimark, AV}, title = {Hydrodynamic Instability of Liquid Films on Moving Fibers.}, journal = {Journal of colloid and interface science}, volume = {215}, number = {2}, pages = {381-396}, doi = {10.1006/jcis.1999.6258}, pmid = {10419674}, issn = {1095-7103}, abstract = {The stability of liquid films on moving fibers is studied with a focus on effects caused by film-solid adhesion interactions and hydrodynamic interactions between the film and the surrounding gas. We show that at high fiber velocities (large Reynolds numbers) the film-gas hydrodynamic interactions induce instability in films, which would, otherwise, be stabilized by the adhesion interactions at static conditions. Two types of unstable modes caused by hydrodynamic factors are found: the first corresponds to the Kelvin-Helmholtz waves induced by inertia effects; the second, induced by viscosity effects, is observed at smaller (yet still large) Reynolds numbers when the Kelvin-Helmholtz instability is suppressed. Linear stability analysis of the system of coupled hydrodynamic equations of film and gas flow is performed by the method of normal modes. We derive the general dispersion relation as an implicit equation with respect to the mode frequency. In the limit of vanishing fiber velocities, the obtained equation provides the dispersion equation for motionless fibers. The conditions of film stability and unstable modes are analyzed in terms of two dimensionless parameters, the adhesion factor, which quantifies the intensity of film-fiber interactions, and the Weber number, which quantifies the intensity of film-gas interactions. The Reynolds number determines the regions of validity of the inviscid and viscous regimes of film instability. The results are illustrated by estimates of the stability conditions for moving fibers in terms of the stability diagram, the critical film thickness, the fastest unstable mode, and the corresponding characteristic break-up time. Although the methods developed are applicable for any type of liquid-solid interaction, the estimates were made for the long-range van der Waals interactions. Practical applications include various technologies related to fabrication and chemical modifications of fibers and fiber products, e.g., spin finishing and lubrication. Copyright 1999 Academic Press.}, }
@article {pmid10412435, year = {1998}, author = {Peattie, RA and Schwarz, W}, title = {Experimental investigation of oscillatory flow through a symmetrically bifurcating tube.}, journal = {Journal of biomechanical engineering}, volume = {120}, number = {5}, pages = {584-593}, doi = {10.1115/1.2834748}, pmid = {10412435}, issn = {0148-0731}, mesh = {Acceleration ; Adult ; Bronchi/*physiology ; Convection ; Humans ; *Models, Biological ; Oscillometry ; Pulmonary Gas Exchange/*physiology ; Pulmonary Ventilation/*physiology ; Rheology ; Tidal Volume ; Trachea/*physiology ; Viscosity ; }, abstract = {To provide a quantitative description of the convection field of gas transport through the lung under both low and high-frequency ventilation conditions, volume-cycled, purely oscillatory flow has been investigated in a symmetrically bifurcating model bronchial bifurcation. Significant differences in the flow properties that developed as the Reynolds number varied from 750 to 950 and the dimensionless frequency varied from 3 to 12 are described. At low frequency, the axial velocity field was found to approximate closely that of a steady flow through a bifurcation. However, even at alpha = 3, secondary velocity fields were confined to within a few diameters of the bifurcation, with less than 10 percent of the magnitude of the axial velocity. At high frequency they were still slower and more limited. These secondary velocity observations are discussed in terms of a physical mechanism balancing inviscid centripetal acceleration with viscous retardation. As the dimensionless frequency increased but the flow amplitude decreased, the magnitude of the axial drift velocity field was found to decrease. In addition, a burst of high-frequency velocity fluctuations was detected in both the axial and secondary velocity measurements in the parent tube, in low-frequency flow, during the deceleration phase of expiration. The position and timing of this burst suggest that it derives from the free shear layer in the parent tube. Stability criteria for the flow were therefore evaluated.}, }
@article {pmid10412415, year = {1998}, author = {Hellevik, LR and Kiserud, T and Irgens, F and Ytrehus, T and Eik-Nes, SH}, title = {Simulation of pressure drop and energy dissipation for blood flow in a human fetal bifurcation.}, journal = {Journal of biomechanical engineering}, volume = {120}, number = {4}, pages = {455-462}, doi = {10.1115/1.2798014}, pmid = {10412415}, issn = {0148-0731}, mesh = {Bias ; Blood Circulation/*physiology ; Blood Flow Velocity ; Blood Pressure/*physiology ; Energy Metabolism ; Fetal Heart/*physiology ; Finite Element Analysis ; Humans ; *Models, Cardiovascular ; *Numerical Analysis, Computer-Assisted ; Reproducibility of Results ; Umbilical Veins/anatomy &amp; histology/*physiology ; }, abstract = {The pressure drop from the umbilical vein to the heart plays a vital part in human fetal circulation. The bulk of the pressure drop is believed to take place at the inlet of the ductus venosus, a short narrow branch of the umbilical vein. In this study a generalized Bernoulli formulation was deduced to estimate this pressure drop. The model contains an energy dissipation term and flow-scaled velocities and pressures. The flow-scaled variables are related to their corresponding spatial mean velocities and pressures by certain shape factors. Further, based on physiological measurements, we established a simplified, rigid-walled, three-dimensional computational model of the umbilical vein and ductus venosus bifurcation for stationary flow conditions. Simulations were carried out for Reynolds numbers and umbilical vein curvature ratios in their respective physiological ranges. The shape factors in the Bernoulli formulation were then estimated for our computational models. They showed no significant Reynolds number or curvature ratio dependency. Further, the energy dissipation in our models was estimated to constitute 24 to 31 percent of the pressure drop, depending on the Reynolds number and the curvature ratio. The energy dissipation should therefore be taken into account in pressure drop estimates.}, }
@article {pmid10412411, year = {1998}, author = {Cavanagh, DP and Eckmann, DM}, title = {Computational analysis of confined jet flow and mass transport in a blind tube.}, journal = {Journal of biomechanical engineering}, volume = {120}, number = {3}, pages = {423-430}, doi = {10.1115/1.2798010}, pmid = {10412411}, issn = {0148-0731}, mesh = {Biomechanical Phenomena ; Gases ; Models, Biological ; Models, Theoretical ; Pulmonary Gas Exchange/physiology ; Trachea/*physiology ; }, abstract = {A computational analysis of confined nonimpinging jet flow in a blind tube is performed as an initial investigation of the underlying fluid and mass transport mechanics of tracheal gas insufflation. A two-dimensional axisymmetric model of a laminar steady jet flow into a concentric blind-end tube is put forth and the governing continuity, momentum, and convection-diffusion equations are solved with a finite element code. The effects of the jet diameter based Reynolds number (Re(j)), the ratio of the jet-to-outer tube diameters (epsilon), and the Schmidt number (Sc) are evaluated with the determined velocity and contaminant concentration fields. The normalized penetration depth of the jet is found to increase linearly with increasing Re(j) for epsilon = O(0.1). For a given epsilon, a ring vortex that develops is observed to be displaced downstream and radially outward from the jet tip for increasing Re(j). The axial shear stress profile along the inside wall of the outer tube possesses regions of fixed shear stress in addition to a local minimum and maximum in the vicinity of the jet tip. Corresponding regions of axial shear stress gradients exist between the fixed shear stress regions and the local extrema. Contaminant concentration gradients develop across the ring vortex indicating the inward diffusion of contaminant into the jet flow. For fixed epsilon and Sc and Re(j) approximately 900, normalized contaminant flow rate is observed to be approximately twice that of simple diffusion. This model predicts modest net axial contaminant transport enhancement due to convection-diffusion interaction in the region of the ring vortex.}, }
@article {pmid10400358, year = {1999}, author = {Gijsen, FJ and Allanic, E and van de Vosse, FN and Janssen, JD}, title = {The influence of the non-Newtonian properties of blood on the flow in large arteries: unsteady flow in a 90 degrees curved tube.}, journal = {Journal of biomechanics}, volume = {32}, number = {7}, pages = {705-713}, doi = {10.1016/s0021-9290(99)00014-7}, pmid = {10400358}, issn = {0021-9290}, mesh = {Arteries/*physiology ; *Blood Physiological Phenomena ; Blood Viscosity/physiology ; Diastole ; *Models, Cardiovascular ; Regional Blood Flow/physiology ; Stress, Mechanical ; Systole ; }, abstract = {A numerical and experimental investigation of unsteady entry flow in a 90 degrees curved tube is presented to study the impact of the non-Newtonian properties of blood on the velocity distribution. The time-dependent flow rate for the Newtonian and the non-Newtonian blood analog fluid were identical. For the numerical computation, a Carreau-Yasuda model was employed to accommodate the shear thinning behavior of the Xanthan gum solution. The viscoelastic properties were not taken into account. The experimental results indicate that significant differences between the Newtonian and non-Newtonian fluid are present. The numerical results for both the Newtonian and the non-Newtonian fluid agree well with the experimental results. Since viscoelasticity was not included in the numerical code, shear thinning behavior of the blood analog fluid seems to be the dominant non-Newtonian property, even under unsteady flow conditions. Finally, a comparison between the non-Newtonian fluid model and a Newtonian fluid at a rescaled Reynolds number is presented. The rescaled Reynolds number, based on a characteristic rather than the high-shear rate viscosity of the Xanthan gum solution, was about three times as low as the original Reynolds number. Comparison reveals that the character of flow of the non-Newtonian fluid is simulated quite well by using the appropriate Reynolds number.}, }
@article {pmid10397862, year = {1999}, author = {Margaritis, A and te Bokkel, DW and Karamanev, DG}, title = {Bubble rise velocities and drag coefficients in non-Newtonian polysaccharide solutions.}, journal = {Biotechnology and bioengineering}, volume = {64}, number = {3}, pages = {257-266}, doi = {10.1002/(sici)1097-0290(19990805)64:3&lt;257::aid-bit1&gt;3.0.co;2-f}, pmid = {10397862}, issn = {0006-3592}, mesh = {Alginates/chemistry ; Carboxymethylcellulose Sodium/chemistry ; Chemistry Techniques, Analytical/instrumentation ; Dextrans/chemistry ; Dose-Response Relationship, Drug ; Glucans/chemistry ; Glucuronic Acid ; Hexuronic Acids ; Kinetics ; Polysaccharides/*chemistry ; Polysaccharides, Bacterial/chemistry ; }, abstract = {Microbially produced polysaccharides have properties which are extremely useful in different applications. Polysaccharide producing fermentations start with liquid broths having Newtonian rheology and end as highly viscous non-Newtonian solutions. Since aerobic microorganisms are used to produce these polysaccharides, it is of great importance to know the mass transfer rate of oxygen from a rising air bubble to the liquid phase, where the microorganisms need the oxygen to grow. One of the most important parameters determining the oxygen transfer rate is the terminal rise velocity of air bubble. The dynamics of the rise of air bubbles in the aqueous solutions of different, mostly microbially produced polysaccharides was studied in this work. Solutions with a wide variety of polysaccharide concentrations and rheological properties were studied. The bubble sizes varied between 0.01 mm3 and 10 cm3. The terminal rise velocities as a function of air bubble volume were studied for 21 different polysaccharide solutions with different rheological properties. It was found that the terminal velocities reached a plateau at higher bubble volumes, and the value of the plateau was nearly constant, between 23 and 27 cm/s, for all solutions studied. The data were analyzed to produce the functional relationship between the drag coefficient and Reynolds number (drag curves). It was found out that all the experimental data obtained from 21 polysaccharide solutions (431 experimental points), can be represented by a new single drag curve. At low values of Reynolds numbers, below 1.0, this curve could be described by the modofoed Hadamard-Rybczynski model, while at Re > 60 the drag coefficient was a constant, equal to 0.95. The latter finding is similar to that observed for bubble rise in Newtonian liquids which was explained on the basis of the "solid bubble" approach.}, }
@article {pmid10395811, year = {1999}, author = {Wood, NB}, title = {Aspects of fluid dynamics applied to the larger arteries.}, journal = {Journal of theoretical biology}, volume = {199}, number = {2}, pages = {137-161}, doi = {10.1006/jtbi.1999.0953}, pmid = {10395811}, issn = {0022-5193}, mesh = {Animals ; Arteries/*physiology ; Biomechanical Phenomena ; Blood Viscosity ; *Cardiovascular Physiological Phenomena ; Computational Biology ; Pulsatile Flow ; Regional Blood Flow/physiology ; }, abstract = {A review is given of some of the ideas from fluid mechanics which are considered essential background for researchers in cardiovascular flows. The paper links the topics discussed at a fundamental level with real problems which, in the experience of the author, occur in research. In particular, approximate equations governing the principal phenomena, and which help with understanding, are introduced. A description is given of the equations of motion and the significance of similarity parameters is discussed: it is shown how Reynolds number and the Womersley parameter arise from dimensionless forms of the equations. Steady flow equations and approximations are commented on, including illustrations of their use. Unsteady flow phenomena are introduced and it is shown how Stokes' first and second problems illustrate key aspects of unsteady viscous diffusion and boundary layers in the circulation. Important features of pulsatile pipe flow, as analysed by both Uchida and Womersley, are discussed and linked to Stokes' two-dimensional results. Entrance effects in steady and unsteady pipe flow are compared and contrasted. Other phenomena discussed include the effects of bends in vessels, transition to turbulence and the different time-scales associated with unsteady flows. Computational methods, which are assuming increasing importance in biological fluid mechanics, also receive a brief description. Finally, comments are made on pressure and other measurements and the need for an understanding of various fluid flow phenomena when planning measurements and interpreting the resulting data.}, }
@article {pmid10366494, year = {1999}, author = {Muller, M}, title = {Size limitations in semicircular duct systems.}, journal = {Journal of theoretical biology}, volume = {198}, number = {3}, pages = {405-437}, doi = {10.1006/jtbi.1999.0922}, pmid = {10366494}, issn = {1095-8541}, abstract = {The present article discusses mechanical requirements and limitations which are applicable to the construction of the system of semicircular ducts, especially to its size. The simplified case of a single, uniform duct system has been considered which can be described by a second order equation of motion. The principal functional quantities for this rotation-sensor are: (1) response speed; (2) sensitivity; and (3) regular flow. The response speed of a single, uniform semicircular duct is characterized by the short time constant (T2) which is dependent on the duct radius (r). Its estimated range is from 0.04 ms in the smallest to 140 ms in the largest known labyrinth. The sensitivity is characterized by the maximal endolymph displacement after a step stimulus (xmax). Its estimated range is from 0.0016 &amp;mgr;m to 5.97 mm (6.56 decades!), assuming an input angular velocity of omega=1 rad s-1. The Reynolds number is a measure for an undisturbed laminar flow. Its estimated range varies from 7.38.10(-4)to 45.1 for omega=1 rad s-1. The above data follow from graphs in which, for a single uniform duct, circuit radius (R) is plotted against duct radius (r) for labyrinths of 233 species belonging to different vertebrate-groups. A relation R =38.9. r1.60was determined. The smallest labyrinth was found in a carp larva (Cyprinus), the largest in a whale shark (Rhincodon). Large whales possess labyrinths of average mammalian size. It is revealed that semicircular duct size is bound by requirements concerning regular flow and by a too low response speed for large labyrinths, and by a too low sensitivity for small labyrinths. Other important quantities are mechanical amplification factors which are a consequence of more complex vestibular constructions than a single uniform duct circuit. Allometric relationships are interpreted as compromises between the quantities mentioned. A hypothesis for the relatively large semicircular duct sizes of fishes, especially Elasmobranchii, compared with mammals and birds is presented. Copyright 1999 Academic Press.}, }
@article {pmid10335760, year = {1999}, author = {Lemler, MS and Valdes-Cruz, LM and Shandas, RS and Cape, EG}, title = {Insights into catheter/Doppler discrepancies in congenital aortic stenosis.}, journal = {The American journal of cardiology}, volume = {83}, number = {10}, pages = {1447-1450}, doi = {10.1016/s0002-9149(99)00123-x}, pmid = {10335760}, issn = {0002-9149}, mesh = {Adolescent ; Angioplasty, Balloon ; Aortic Valve/*diagnostic imaging ; Aortic Valve Stenosis/congenital/*diagnosis/diagnostic imaging/physiopathology ; *Cardiac Catheterization ; Child ; Child, Preschool ; Humans ; Infant ; Models, Cardiovascular ; Pressure ; Ultrasonography ; *Ventricular Function, Left ; }, abstract = {Despite inherent discrepancies between Doppler and catheter gradients in aortic stenosis, the simplified Bernoulli equation is still the accepted noninvasive technique to quantitate severity. The Reynolds number is a dimensionless parameter that characterizes the nature of flow as being viscous, turbulent, or transitional. Recently, in vivo and animal studies have successfully used a Reynolds number-based approach to reconcile Doppler-estimated and catheter-measured discrepancies. At the midrange of Reynolds number, pressure recovery effects are most evident, resulting in "overestimation" of catheter gradients by Doppler. At the lower range of the Reynolds number viscous effects are important, whereas at a higher range, turbulent factors are dominant; both result in a tendency toward agreement. We recorded 18 peak instantaneous gradients from dual left ventricular catheters (15 to 95 mm Hg), while simultaneously recording Doppler velocities before and after intervention in 11 pediatric patients (ages 0.5 to 16 years, mean 4.5). Doppler correlated but overestimated catheter-measured peak instantaneous gradients (y = 0.84x + 18.4, r = 0.8, SEE +/- 15.2 mm Hg, mean percent difference 29.9 +/- 36) over the range of catheter gradients measured. Accounting for the Reynolds number successfully collapsed data onto a single curve. Our study confirms in a clinical setting the importance of applying fluid dynamic principles such as the Reynolds number to explain apparent discrepancies between catheter and Doppler gradients. These principles provide a foundation for developing clinically appropriate correction factors.}, }
@article {pmid10195278, year = {1999}, author = {Di Tommaso, RM and Nino, E and Fracastoro, GV}, title = {Influence of the boundary thermal conditions on the air change efficiency indexes.}, journal = {Indoor air}, volume = {9}, number = {1}, pages = {63-69}, doi = {10.1111/j.1600-0668.1999.00010.x}, pmid = {10195278}, issn = {0905-6947}, mesh = {Air ; *Hot Temperature ; Models, Theoretical ; Ventilation/*methods/standards ; }, abstract = {The influence of a thermal heterogeneity boundary conditions on the air change efficiency (ACE) of a mechanical ventilation system in a test room was experimentally evaluated by means of the "step-down" tracer gas technique in 24 different experimental conditions. The experiments were performed under isothermal condition, varying the air supply temperature with respect to the walls and varying the surface temperature of a wall with respect to the other walls and the supply air, simulating both heating and cooling situations. Changing the position of the outlet grid two different configurations of the ventilation system were tested. The nominal supply air velocity varied between 0.04 and 0.11 m/s, corresponding to a range from 1 to 3 ach, and the temperature differences varied from 0 to 5 degrees C. Results are reported in terms of air change efficiency indexes, both local and global. The global air change efficiency (ACE), values are presented as a function of the Archimedes number (Ar), whose values were in the range 0 to 181. The reported results suggest that the Ar number may be used to organize the ACE values when in the presence of thermal heterogeneity, both in the external envelope and in the supplied air. The obtained results show that there is a logarithmic relation between Ar and ACE. In particular, for both ventilation strategies tested, the increase of the absolute value of Ar leads to an increase of ACE when the supply air is warmer than the walls, and to a decrease of ACE when the supply air is colder than the walls. Under isothermal conditions the Reynolds number (Re) fairly correlates the experimental results.}, }
@article {pmid10191012, year = {1999}, author = {Heindel, TJ and Bloom, F}, title = {Exact and Approximate Expressions for Bubble-Particle Collision.}, journal = {Journal of colloid and interface science}, volume = {213}, number = {1}, pages = {101-111}, doi = {10.1006/jcis.1999.6112}, pmid = {10191012}, issn = {1095-7103}, abstract = {The flotation microprocess of collision is investigated and an exact expression for the probability of collision (Pc) is developed based on the intermediate flow of Yoon and Luttrell (1). This expression for Pc only assumes that the bubble and particle are spherical and that the particle radius is less than the bubble radius (i.e., Rp < RB). In addition to removing the requirement that Rp << RB, the influence of a particle settling velocity is also included in the model development. The expression for Pc is shown to be a function of three dimensionless groups: (i) the magnitude of the dimensionless particle settling velocity, ||G ||; (ii) the bubble Reynolds number, ReB; and (iii) the ratio of particle to bubble radius, Rp/RB. The probability of collision model is compared to available experimental data and good agreement is shown. A parametric study is also completed for 0 </= ||G || </= 1, 0 </= ReB </= 500, and 0.001 </= Rp/RB < 1. In general, Pc is independent of ReB when Rp/RB less, similar 0.03, the particle settling velocity is important for small values of Rp/RB, and Rp/RB dominates as Rp/RB --> 1. Copyright 1999 Academic Press.}, }
@article {pmid10099514, year = {1999}, author = {Nicolella, C and van Loosdrecht, MM and Di Felice, R and Rovatti, M}, title = {Terminal settling velocity and bed-expansion characteristics of biofilm-coated particles.}, journal = {Biotechnology and bioengineering}, volume = {62}, number = {1}, pages = {62-70}, pmid = {10099514}, issn = {0006-3592}, mesh = {*Biofilms ; Biotechnology ; Evaluation Studies as Topic ; Models, Biological ; Particle Size ; }, abstract = {Fluid dynamic behavior of biofilm-coated particles in ambient water has been investigated. New experimental results are presented and compared with published data. From experimental measurements of the single particle terminal settling velocity the corresponding drag coefficient was found to be larger (by a factor of 1.6) than that for a smooth, rigid sphere at the same Reynolds number. A new simple correlation describing this finding is suggested. For multiparticle systems the Richardson-Zaki equation, derived empirically for rigid particles, provided a satisfactory description of biological beds. Of the two numerical parameters characterizing the expansion law, i. e. the slope n and the extrapolation to voidage equal one ui, the first was found to be similar to that suggested by Richardson and Zaki (1954), whereas ui gave results smaller than the single-particle terminal settling velocity, in contrast with the mentioned work but in agreement with more recently published behavior.}, }
@article {pmid10099232, year = {1998}, author = {Stoodley, P and Lewandowski, Z and Boyle, JD and Lappin-Scott, HM}, title = {Oscillation characteristics of biofilm streamers in turbulent flowing water as related to drag and pressure drop.}, journal = {Biotechnology and bioengineering}, volume = {57}, number = {5}, pages = {536-544}, doi = {10.1002/(sici)1097-0290(19980305)57:5&lt;536::aid-bit5&gt;3.0.co;2-h}, pmid = {10099232}, issn = {0006-3592}, mesh = {Biofilms/*growth &amp; development ; Microscopy, Confocal ; Pressure ; Water ; }, abstract = {Mixed population biofilms consisting of Pseudomonas aeruginosa, P. fluorescens, and Klebsiella pneumoniae were grown in a flow cell under turbulent conditions with a water flow velocity of 18 cm/s (Reynolds number, Re, =1192). After 7 days the biofilms were patchy and consisted of cell clusters and streamers (filamentous structures attached to the downstream edge of the clusters) separated by interstitial channels. The cell clusters ranged in size from 25 to 750 microm in diameter. The largest clusters were approximately 85 microm thick. The streamers, which were up to 3 mm long, oscillated laterally in the flow. The motion of the streamers was recorded at various flow velocities up to 50.5 cm/s (Re 3351) using confocal scanning laser microscopy. The resulting time traces were evaluated by image analysis and fast Fourier transform analysis (FFT). The amplitude of the motion increased with flow velocity in a sigmoidal shaped curve, reaching a plateau at an average fluid flow velocity of approximately 25 cm/s (Re 1656). The motion of the streamers was possibly limited by the flexibility of the biofilm material. FFT indicated that the frequency of oscillation was directly proportional to the average flow velocity (u(ave)) below 9.5 cm/s (Re 629). At u(ave) greater than 9.5 cm/s, oscillation frequencies were above our measurable frequency range (0.12-6.7 Hz). The oscillation frequency was related to the flow velocity by the Strouhal relationship, suggesting that the oscillations were possibly caused by vortex shedding from the upstream biofilm clusters. A loss coefficient (k) was used to assess the influence of biofilm accumulation on pressure drop. The k across the flow cell colonized with biofilm was 2.2 times greater than the k across a clean flow cell.}, }
@article {pmid10099189, year = {1998}, author = {Mulder, H and Breure, AM and Van Andel, JG and Grotenhuis, JT and Rulkens, WH}, title = {Influence of hydrodynamic conditions on naphthalene dissolution and subsequent biodegradation.}, journal = {Biotechnology and bioengineering}, volume = {57}, number = {2}, pages = {145-154}, doi = {10.1002/(sici)1097-0290(19980120)57:2&lt;145::aid-bit3&gt;3.0.co;2-n}, pmid = {10099189}, issn = {0006-3592}, mesh = {Biodegradation, Environmental ; Bioreactors ; Biotechnology ; Models, Biological ; Naphthalenes/*metabolism ; Polycyclic Aromatic Hydrocarbons/metabolism ; Pseudomonas/metabolism ; Soil Pollutants/metabolism ; Solubility ; }, abstract = {The influence of hydrodynamic conditions on the dissolution rate of crystalline naphthalene as a model polycyclic aromatic hydrocarbon (PAH) was studied in stirred batch reactors with varying impeller speeds. Mass transfer from naphthalene melts of different surface areas to the aqueous phase was measured and results were modeled according to the film theory. Results were generalized using dimensionless numbers (Reynolds, Schmidt, and Sherwood). In combined mass transfer and biodegradation experiments, the effect of hydrodynamic conditions on the degradation rate of naphthalene by Pseudomonas 8909N was studied. Experimental results were mathematically described using mass-transfer and microbiological models. The experiments allowed determination of mass-transfer and microbiological parameters separately in a single run. The biomass formation rate under mass transfer limited conditions, which is related to the naphthalene biodegradation rate, was correlated to the dimensionless Reynolds number, indicating increased bioavailability at increased mixing in the reactor liquid. The methodology presented in which mass transfer processes are quantified under sterile conditions followed by a biodegradation experiment can also be adapted to more complex and realistic systems, such as particulate, suspended PAH solids or soils with intrapartically sorbed contaminants when the appropriate mass-transfer equations are incorporated.}, }
@article {pmid10092364, year = {1999}, author = {Long, D and Stone, HA and Ajdari, A}, title = {Electroosmotic Flows Created by Surface Defects in Capillary Electrophoresis.}, journal = {Journal of colloid and interface science}, volume = {212}, number = {2}, pages = {338-349}, doi = {10.1006/jcis.1998.6015}, pmid = {10092364}, issn = {1095-7103}, abstract = {We compute the electroosmotic flow in nonuniformly charged planar and cylindrical capillaries for the limit of low-Reynolds-number flows and thin Debye layers. Analytical formulae for the velocity field are provided for the general case of an arbitrary surface inhomogeneity but we also focus on various specific defect geometries. Many important features can be obtained from the simple lubrication approximation. The pressure jump induced by the presence of such surface defects is calculated and the possible occurrence of recirculating flows is discussed, as are effects of the flow perturbations on dispersion in capillary electrophoresis. Copyright 1999 Academic Press.}, }
@article {pmid10066713, year = {1999}, author = {Tsuda, A and Otani, Y and Butler, JP}, title = {Acinar flow irreversibility caused by perturbations in reversible alveolar wall motion.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {86}, number = {3}, pages = {977-984}, doi = {10.1152/jappl.1999.86.3.977}, pmid = {10066713}, issn = {8750-7587}, support = {HL-47428/HL/NHLBI NIH HHS/United States ; HL-54885/HL/NHLBI NIH HHS/United States ; }, mesh = {Aerosols ; Airway Resistance/physiology ; Algorithms ; Animals ; Convection ; Models, Anatomic ; Pulmonary Alveoli/*metabolism ; Rabbits ; Respiratory Mechanics/*physiology ; Silicone Oils ; Viscosity ; }, abstract = {Mixing associated with "stretch-and-fold" convective flow patterns has recently been demonstrated to play a potentially important role in aerosol transport and deposition deep in the lung (J. P. Butler and A. Tsuda. J. Appl. Physiol. 83: 800-809, 1997), but the origin of this potent mechanism is not well characterized. In this study we hypothesized that even a small degree of asynchrony in otherwise reversible alveolar wall motion is sufficient to cause flow irreversibility and stretch-and-fold convective mixing. We tested this hypothesis using a large-scale acinar model consisting of a T-shaped junction of three short, straight, square ducts. The model was filled with silicone oil, and alveolar wall motion was simulated by pistons in two of the ducts. The pistons were driven to generate a low-Reynolds-number cyclic flow with a small amount of asynchrony in boundary motion adjusted to match the degree of geometric (as distinguished from pressure-volume) hysteresis found in rabbit lungs (H. Miki, J. P. Butler, R. A. Rogers, and J. Lehr. J. Appl. Physiol. 75: 1630-1636, 1993). Tracer dye was introduced into the system, and its motion was monitored. The results showed that even a slight asynchrony in boundary motion leads to flow irreversibility with complicated swirling tracer patterns. Importantly, the kinematic irreversibility resulted in stretching of the tracer with narrowing of the separation between adjacent tracer lines, and when the cycle-by-cycle narrowing of lateral distance reached the slowly growing diffusion distance of the tracer, mixing abruptly took place. This coupling of evolving convective flow patterns with diffusion is the essence of the stretch-and-fold mechanism. We conclude that even a small degree of boundary asynchrony can give rise to stretch-and-fold convective mixing, thereby leading to transport and deposition of fine and ultrafine aerosol particles deep in the lung.}, }
@article {pmid10050951, year = {1999}, author = {Dash, RK and Jayaraman, G and Mehta, KN}, title = {Flow in a catheterized curved artery with stenosis.}, journal = {Journal of biomechanics}, volume = {32}, number = {1}, pages = {49-61}, doi = {10.1016/s0021-9290(98)00142-0}, pmid = {10050951}, issn = {0021-9290}, mesh = {Arteries/*pathology/*physiopathology ; Blood Flow Velocity/physiology ; Blood Pressure/physiology ; *Catheterization ; Constriction, Pathologic ; Humans ; *Models, Cardiovascular ; Regional Blood Flow ; Stress, Mechanical ; }, abstract = {The fluid mechanics of blood flow in a catheterized curved artery with stenosis is studied through a mathematical analysis. Blood is modelled as an incompressible Newtonian fluid and the flow is assumed to be steady and laminar. An approximate analytic solution to the problem is obtained through a double series perturbation analysis for the case of small curvature and mild stenosis. The effect of catheterization on various physiologically important flow characteristics (i.e. the pressure drop, impedance and the wall shear stress) is studied for different values of the catheter size and Reynolds number of the flow. It is found that all these flow characteristics vary markedly across a stenotic lesion. Also, increase in the catheter size leads to a considerable increase in their magnitudes. These results are used to obtain the estimates of increased pressure drop across an arterial stenosis when a catheter is inserted into it. Our calculations, based on the geometry and flow conditions existing in coronary arteries, suggest that, in the presence of curvature and stenosis, and depending on the value of k (ratio of catheter size to vessel size) ranging from 0.1 to 0.4, the pressure drop increases by a factor ranging from 1.60 to 5.16. But, in the absence of curvature and stenosis, with the same range of catheter size, this increased factor is about 1.74-4.89. These estimates for the increased pressure drop can be used to correct the error involved in the measured pressure gradients using catheters. The combined effects of stenosis and curvature on flow characteristics are also studied in detail. It is found that the effect of stenosis is more dominant than that of the curvature. Due to the combined effect of stenosis, curvature and catheterization, the secondary streamlines are modified in a cross-sectional plane. The insertion of a catheter into the artery leads to the formation of increased number of secondary vortices.}, }
@article {pmid9952001, year = {1999}, author = {Ghalichi, F and Deng, X and King, MW and Marois, Y and De Champlain, A and Guidoin, R}, title = {Theoretical prediction of the hemodynamic performance of slow resorbing polyester protein impregnated arterial prostheses after implantation: a plea for fast resorption of the coating.}, journal = {ASAIO journal (American Society for Artificial Internal Organs : 1992)}, volume = {45}, number = {1}, pages = {18-24}, doi = {10.1097/00002480-199901000-00006}, pmid = {9952001}, issn = {1058-2916}, mesh = {*Absorbable Implants ; Animals ; Blood Pressure ; *Blood Vessel Prosthesis ; *Coated Materials, Biocompatible ; Constriction, Pathologic/physiopathology ; Humans ; *Models, Cardiovascular ; *Polyesters ; Prosthesis Failure ; Proteins/pharmacokinetics ; Stress, Mechanical ; }, abstract = {The clinical literature cites cases where slow, incomplete, or nonuniform protein resorption from protein impregnated arterial prostheses produces undesirable localized internal capsule proliferation leading to a significant reduction of the internal diameter of the prosthesis. In an attempt to describe the hemodynamic response to this phenomenon, the blood flow in such stenotic regions was simulated and characterized numerically using FIDAP computational fluid dynamics software to determine the Navier-Stokes and continuity equations for simple channel flow. To simulate various stages of internal capsule development, numeric computations were made in an idealized tubular expansion at stenosis ratios ranging from 0.9 to 0.5 and stenosis length ratios from 10 to 40. The results indicated that a triangular annular ring vortex was formed immediately distal to the stenosis at all Reynolds numbers (Re) studied. The size of the vortex increased almost linearly with the Reynolds number. The pressure drop through the stenosis was affected by blood flow rate, severity, and stenosis length. When the stenosis ratio was low, the pressure drop through the stenosis increased gradually and almost linearly with blood flow rate. In a severe stenosis, the pressure drop was no longer a linear function of flow rate, but increased significantly with increasing flow rate. In conclusion, satisfactory healing of the internal capsule requires fast resorption of any impregnated protein. If the resorption is slow, incomplete, or nonuniform, there is a tendency for the lumen to narrow, causing stenosis, an increased pressure drop through the narrowed graft and disturbed flow distal to the stenosis. This phenomenon therefore constitutes a major limitation for using this type of graft in small diameter arterial reconstruction.}, }
@article {pmid9929417, year = {1999}, author = {Kuo, J and Keh, HJ}, title = {Motion of a Colloidal Sphere Covered by a Layer of Adsorbed Polymers Normal to a Plane Surface.}, journal = {Journal of colloid and interface science}, volume = {210}, number = {2}, pages = {296-308}, doi = {10.1006/jcis.1998.5979}, pmid = {9929417}, issn = {1095-7103}, abstract = {A combined analytical-numerical study is presented for the slow motion of a spherical particle coated with a layer of adsorbed polymers perpendicular to an infinite plane, which can be either a solid wall or a free surface. The Reynolds number is assumed to be vanishingly small, and the thickness of the surface polymer layer is assumed to be much smaller than the particle radius and the spacing between the particle and the plane boundary. A method of matched asymptotic expansions in a small parameter lambda incorporated with a boundary collocation technique is used to solve the creeping flow equations inside and outside the adsorbed polymer layer, where lambda is the ratio of the characteristic thickness of the polymer layer to the particle radius. The results for the hydrodynamic force exerted on the particle in a resistance problem and for the particle velocity in a mobility problem are expressed in terms of the effective hydrodynamic thickness (L) of the polymer layer, which is accurate to O(lambda2). The O(lambda) term for L normalized by its value in the absence of the plane boundary is found to be independent of the polymer segment distribution and the volume fraction of the segments. The O(lambda2) term for L, however, is a sensitive function of the polymer segment distribution and the volume fraction of the segments. In general, the boundary effects on the motion of a polymer-coated particle can be quite significant. Copyright 1999 Academic Press.}, }
@article {pmid9924953, year = {1998}, author = {Barbaro, V and Grigioni, M and Daniele, C and D'Avenio, G}, title = {Principal stress analysis in LDA measurement of the flow field downstream of 19-mm Sorin Bicarbon heart valve.}, journal = {Technology and health care : official journal of the European Society for Engineering and Medicine}, volume = {6}, number = {4}, pages = {259-270}, pmid = {9924953}, issn = {0928-7329}, mesh = {Blood Flow Velocity ; Equipment Design ; *Heart Valve Prosthesis ; Humans ; In Vitro Techniques ; *Laser-Doppler Flowmetry ; Mathematics ; *Models, Cardiovascular ; Pulsatile Flow/*physiology ; Rheology ; Stress, Mechanical ; }, abstract = {Heart valve replacement has become, since many years, a common surgical practice. Along with the improvement that the patients' health has derived from it, however, a certain amount of risk could not be avoided, bound to the inevitable hemodynamic disturbances that an artificial device generates. A major shortcoming, often reported, is the formation of thrombus on the edge of the prosthetic valve, with a possible obstruction of the orifices through which blood should normally flow undisturbed. Hemolysis is another possible consequence of the implantation of a mechanical heart valve, generally correlated to turbulence downstream of prosthetic heart valves (PHV). As it is agreed upon by many researchers, the risk of thrombogenicity or hemolysis is higher in those valves that are more subject to promote turbulence and flow separation in the flow through them. In the following paper, we present a study of the turbulence-related shear stress downstream of a bileaflet valve of minimum size (19 mm external diameter) Sorin Bicarbon. This size was chosen, accordingly to the Food &amp; Drug Administration (FDA) draft guidance suggestion to investigate the worst case in turbulence promoted by PHVs, in order to have the highest velocity gradients and shear stresses for the FDA-stated cardiac output (6 1/min), related to maximum Reynolds number conditions. Velocity data were collected with the two-dimensional laser Doppler anemometry (LDA) technique; whereas this approach does not investigate directly all three components of the flow field, in the present case (bileaflet valves) it is not a limitation to the assessment of the maximum turbulence shear stress (TSS), thanks to the two-dimensional flow nature downstream of bileaflet models. Data taken in coincident mode were elaborated in order to determine the maximum shear stress in the measured points in the flow field, using the 2D Principal Stress Analysis (PSA). The consequences of a variable principal normal stress direction all along the measured profile will be illustrated in terms of differences between measured and maximum shear stresses. Results show the need to estimate the maximum values for the TSS and the direction along which it is obtained to correctly define the turbulent flow field downstream of PHVs.}, }
@article {pmid9914655, year = {1998}, author = {Hansen, E and Mollerup, J}, title = {Application of the two-film theory to the determination of mass transfer coefficients for bovine serum albumin on anion-exchange columns.}, journal = {Journal of chromatography. A}, volume = {827}, number = {2}, pages = {259-267}, doi = {10.1016/s0021-9673(98)00791-2}, pmid = {9914655}, issn = {0021-9673}, mesh = {*Anion Exchange Resins ; Chromatography, Ion Exchange/*methods ; Models, Chemical ; Serum Albumin, Bovine/*analysis ; Spectrophotometry, Ultraviolet ; }, abstract = {The paper describes a method of simultaneous determination of the external and the solid-phase mass-transfer coefficients from frontal analysis data. The protein flux to the solid particles is determined from the slope of the breakthrough curve and the mass-transfer coefficients are determined by fitting the two-film model to the experimentally determined flux. The two-film model is compared with two apparent overall driving force models: the apparent overall mobile phase driving force model and the apparent overall solid-phase driving force model. The experiments show that the apparent overall driving force models fail to describe the flux correctly and this is substantiated by the theory. Results obtained with bovine serum albumin on the anion-exchange media Q HyperD, Source, and Poros show that the external film resistance is significant for Reynolds numbers less than one. The experimental Sherwood numbers are lower than expected and their dependence on the Reynolds number are much higher than expected.}, }
@article {pmid9889951, year = {1998}, author = {He, W and Bruley, DF and Drohan, WN}, title = {Gel compression considerations for chromatography scale-up for protein C purification.}, journal = {Advances in experimental medicine and biology}, volume = {454}, number = {}, pages = {689-696}, doi = {10.1007/978-1-4615-4863-8_82}, pmid = {9889951}, issn = {0065-2598}, mesh = {Animals ; Animals, Genetically Modified ; Chromatography, Affinity/methods ; Chromatography, Gel/methods ; Humans ; Milk/chemistry ; Protein C/*isolation &amp; purification ; }, abstract = {This work is to establish theoretical and experimental relationships for the scale-up of Immobilized Metal Affinity Chromatography (IMAC) and Immuno Affinity Chromatography for the low cost production of large quantities of Protein C. The external customer requirements for this project have been established for Protein C deficient people with the goal of providing prophylactic patient treatment. Deep vein thrombosis is the major symptom for protein C deficiency creating the potential problem of embolism transport to important organs, such as, lung and brain. Gel matrices for protein C separation are being analyzed to determine the relationship between the material properties of the gel and the column collapse characteristics. The fluid flow rate and pressure drop is being examined to see how they influence column stability. Gel packing analysis includes two considerations; one is bulk compression due to flow rate, and the second is gel particle deformation due to fluid flow and pressure drop. Based on the assumption of creeping flow, Darcy's law is being applied to characterize the flow through the gel particles. Biot's mathematical description of three-dimensional consolidation in porous media is being used to develop a set of system equations. Finite difference methods are being utilized to obtain the equation solutions. In addition, special programs such as finite element approaches, ABAQUS, will be studied to determine their application to this particular problem. Experimental studies are being performed to determine flow rate and pressure drop correlation for the chromatographic columns with appropriate gels. Void fraction is being measured using pulse testing to allow Reynolds number calculations. Experimental yield stress is being measured to compare with the theoretical calculations. Total Quality Management (TQM) tools have been utilized to optimize this work. For instance, the "Scatter Diagram" has been used to evaluate and select the appropriate gels and operating conditions via Taguchi techniques. Targeting customer requirements under the structure of TQM represents a novel approach to graduate student research in an academic institution which is designed to simulate an industrial environment.}, }
@article {pmid9885262, year = {1999}, author = {Adamczyk, Z and Szyk, L and Warszy&amp;nacute;ski, P}, title = {Colloid Particle Adsorption in the Slot Impinging Jet Cell.}, journal = {Journal of colloid and interface science}, volume = {209}, number = {2}, pages = {350-361}, doi = {10.1006/jcis.1998.5907}, pmid = {9885262}, issn = {1095-7103}, abstract = {A detailed description of flow distribution in the slot impinging jet cell (SIJ) is presented. Numerical solutions of the governing Navier-Stokes equation showed that for Re < 30 the flow resembles closely the one occurring near a cylinder placed in a uniform flow. It was also shown that for tangential distances x/d < 0.25 the flow configuration in the vicinity of the solid can be approximated by the plane-parallel stagnation flow with the perpendicular velocity component independent of this distance. This flow field was used for deriving the mass transfer equation, which was then numerically solved to obtain the initial flux (adsorption rate) for various transport conditions. These theoretical predictions were verified experimentally using polystyrene latex particles of the size 1 and 1.48 µm. A good agreement between predicted and measured initial flux values was found for a broad range of Reynolds number and ionic strength of the particle suspension. This confirmed that the SIJ cell surface was uniformly accessible for particles at distances x/d < 0.5. At larger distances a systematic deviation from uniform deposition rates was observed, becoming important for higher coverages and Re. This effect was attributed to the hydrodynamic scattering of adsorbing particles on particles already attached to the surface. This phenomenon was quantitatively accounted for by the Brownian dynamics type simulations. Copyright 1999 Academic Press.}, }
@article {pmid9878134, year = {1999}, author = {Chen, SH}, title = {Brownian Diffusion in a Dilute Dispersion of Droplets.}, journal = {Journal of colloid and interface science}, volume = {209}, number = {1}, pages = {31-43}, doi = {10.1006/jcis.1998.5828}, pmid = {9878134}, issn = {1095-7103}, abstract = {An analytical study of Brownian motion in a dispersion of fluid drops is considered. The droplets, which are spherical and may differ in radius, are assumed to be close enough to interact hydrodynamically. Based on Einstein's description of Brownian motion that invokes an equilibrium and in which droplets are affected by a thermodynamic force, the Brownian diffusivities in two different situations are deduced. The first interaction concerns a homogeneous dilute suspension that is deformed locally. The relative diffusivity of two droplets with a given separation distance is derived from the mobility functions due to the low-Reynolds-number flow that arises because of two hydrodynamically interacting droplets. The second interaction concerns a suspension in which there is a concentration gradient of droplets. The thermodynamic force on each droplet in this case is shown to be equal to the gradient of the chemical potential of droplets, which brings the multidroplet excluded volume into the problem. For a determination of the average settling velocity of droplets falling through fluid under gravity, a theoretical result correct to the first order in volume fraction of the droplets is available. The diffusivity of the droplets is found to increase slowly as the concentration rises from zero. These results are generalized for an inhomogeneous suspension of several different species of droplet, and expressions for the diagonal and off-diagonal elements of the diffusivity matrix are obtained. The results, presented in simple closed forms, agree very well with the existing solutions for the limited cases of solid spheres. Moreover, the limiting diffusion situation of spherical gas bubbles is also considered. Copyright 1999 Academic Press.}, }
@article {pmid9876128, year = {1999}, author = {Drury, JL and Dembo, M}, title = {Hydrodynamics of micropipette aspiration.}, journal = {Biophysical journal}, volume = {76}, number = {1 Pt 1}, pages = {110-128}, pmid = {9876128}, issn = {0006-3495}, support = {AI21002/AI/NIAID NIH HHS/United States ; }, mesh = {Biophysical Phenomena ; Biophysics ; Capillaries/anatomy &amp; histology/physiology ; Hemorheology/*instrumentation ; Humans ; In Vitro Techniques ; Models, Cardiovascular ; Neutrophils/*cytology/*physiology ; Pressure ; Suction/*instrumentation ; Surface Tension ; Viscosity ; }, abstract = {The dynamics of human neutrophils during micropipette aspiration are frequently analyzed by approximating these cells as simple slippery droplets of viscous fluid. Here, we present computations that reveal the detailed predictions of the simplest and most idealized case of such a scheme; namely, the case where the fluid of the droplet is homogeneous and Newtonian, and the surface tension of the droplet is constant. We have investigated the behavior of this model as a function of surface tension, droplet radius, viscosity, aspiration pressure, and pipette radius. In addition, we have tabulated a dimensionless factor, M, which can be utilized to calculate the apparent viscosity of the slippery droplet. Computations were carried out using a low Reynolds number hydrodynamics transport code based on the finite-element method. Although idealized and simplistic, we find that the slippery droplet model predicts many observed features of neutrophil aspiration. However, there are certain features that are not observed in neutrophils. In particular, the model predicts dilation of the membrane past the point of being continuous, as well as a reentrant jet at high aspiration pressures.}, }
@article {pmid9862280, year = {1998}, author = {Liu, SQ}, title = {Prevention of focal intimal hyperplasia in rat vein grafts by using a tissue engineering approach.}, journal = {Atherosclerosis}, volume = {140}, number = {2}, pages = {365-377}, doi = {10.1016/s0021-9150(98)00143-9}, pmid = {9862280}, issn = {0021-9150}, mesh = {Actins/metabolism ; Animals ; Aorta, Abdominal/surgery ; Arteriovenous Anastomosis ; Biomedical Engineering/*methods ; Blood Flow Velocity ; Cell Count ; Follow-Up Studies ; Graft Occlusion, Vascular/metabolism/pathology/physiopathology ; Hyperplasia/pathology/prevention &amp; control ; Jugular Veins/metabolism/pathology/*transplantation ; Male ; Microscopy, Fluorescence ; Muscle, Smooth, Vascular/metabolism/pathology ; Random Allocation ; Rats ; Rats, Sprague-Dawley ; Tunica Intima/*pathology ; }, abstract = {The present study focused on the role of blood flow in the formation of focal intimal hyperplasia in vein grafts, as well as the development of an engineering approach that can be used to eliminate disturbed blood flow and prevent blood flow-related focal intimal hyperplasia. A rat vein graft model was constructed by interposing a jugular vein into the abdominal aorta with end-to-end anastomoses. Locally disturbed flow was identified by analyzing particle streak-lines in methyl salicylate-cleared and perfused vein grafts in vitro with a physiological Reynolds number. At day 10, 20, and 30 after surgery, focal intimal hyperplasia of the vein grafts was examined using a histological approach and the density of alpha-actin positive cells was determined using immunohistological and fluorescent approaches. Results showed that apparent eddy blood flow formed at the proximal, but not at the distal, end of the vein grafts due to graft-host diameter mismatch and local geometric distortions, and was associated with apparent focal intimal hyperplasia. The thickness of the alpha-actin positive layers of the proximal vein grafts was significantly higher than that of the distal grafts (192 +/- 27 vs. 94 +/- 18 microm, 278 +/- 55 vs. 124 +/- 20 microm, and 288 +/- 24 vs. 131 +/- 23 microm for day 10, 20. and 30, respectively). The density of the alpha-actin positive cells, however, was similar between the proximal and the distal regions (3569 +/- 361 vs. 3285 +/- 343 cells/mm2, 5540 +/- 650 vs. 5376 + 887 cells/mm2, and 5465 +/- 791 vs. 5278 +/- 524 cells/mm2 for day 10, 20, and 30, respectively). When eddy blood flow was eliminated by matching the graft-host diameters using a tissue engineering approach, the average thickness of the alpha-actin positive layers of the proximal (71 +/- 15, 86 +/- 16, and 85 +/- 14 microm for day 10, 20, and 30, respectively) and the distal vein grafts (68 +/- 13, 80 +/- 14, and 79 +/- 13 microm for day 10, 20, and 30, respectively) was reduced significantly. The density of the alpha-actin positive cells was also reduced significantly in the proximal (2946 +/- 359, 3261 +/- 295, 3472 +/- 599 cells/mm2 for day 10, 20, and 30, respectively) and in the distal regions (3151 +/- 511, 3466 +/- 687, 3593 +/- 688 cells/mm2 for day 10, 20, and 30, respectively). The thickness of the alpha-actin positive layers and the density of the alpha-actin positive cells were not significantly different between the proximal and distal regions of the engineered vein grafts at each observation time. These results suggest that eddy flow may develop in vein grafts and may facilitate the formation of focal intimal hyperplasia, and the vascular tissue engineering approach developed in this study may be used to prevent blood flow-related focal intimal hyperplasia in vein grafts.}, }
@article {pmid9846933, year = {1998}, author = {Santamarina, A and Weydahl, E and Siegel, JM and Moore, JE}, title = {Computational analysis of flow in a curved tube model of the coronary arteries: effects of time-varying curvature.}, journal = {Annals of biomedical engineering}, volume = {26}, number = {6}, pages = {944-954}, doi = {10.1114/1.113}, pmid = {9846933}, issn = {0090-6964}, mesh = {Arteriosclerosis/pathology/physiopathology ; Biomedical Engineering ; Blood Flow Velocity/physiology ; Coronary Circulation/physiology ; Coronary Vessels/*anatomy &amp; histology/*physiology ; Hemorheology/instrumentation ; Humans ; In Vitro Techniques ; *Models, Cardiovascular ; }, abstract = {The flow through a curved tube whose radius of curvature varies with time was studied in order to better understand flow patterns in coronary arteries. A computational flow model was constructed using commercially available software. The artery model featured a uniform circular cross section, and the curvature was assumed to be constant along the tube, and in one plane. The computational model was verified with the use of a dynamically similar in vitro apparatus. A steady uniform velocity was prescribed at the entrance at a Reynolds number of 300. Two sets of results were obtained: one in which the curvature was held constant at the mean, maximum and minimum radii of curvature (quasistatic), and another in which the curvature was varied sinusoidally in time at a frequency of I Hz (dynamic). The results of the dynamic analysis showed that the wall shear rates varied as much as 52% of the static mean wall shear rate within a region of 10 tube diameters from the inlet. The results of the dynamic analysis were within 6% of the quasistatic predictions. Realistic modeling of the deforming geometry is important in determining which locations in the coronary arteries are subjected to low and oscillating wall shear stresses, flow patterns that have been associated with atherogenesis.}, }
@article {pmid9822084, year = {1998}, author = {Murgo, JP}, title = {Systolic ejection murmurs in the era of modern cardiology: what do we really know?.}, journal = {Journal of the American College of Cardiology}, volume = {32}, number = {6}, pages = {1596-1602}, doi = {10.1016/s0735-1097(98)00425-2}, pmid = {9822084}, issn = {0735-1097}, mesh = {Aortic Valve Stenosis/physiopathology ; Blood Pressure/physiology ; Cardiology/*trends ; Cardiomyopathy, Hypertrophic/complications/physiopathology ; Coronary Circulation/physiology ; Heart Murmurs/*etiology ; Humans ; Reference Values ; Systole ; Ventricular Function, Left ; }, abstract = {The basics of pulsatile ejection dynamics are reviewed in order to clarify the relationships among left ventricular and aortic pressures, intra-left ventricular and aortic flow velocities, and cardiovascular sound. The principles of turbulent flow are examined using the Reynolds number concept, and the evidence for cause-and-effect relationships between turbulent flow and murmur generation is presented. Examples of hemodynamics and phonocardiography are given for normal subjects and are compared to patients with aortic stenosis and hypertrophic cardiomyopathy. The concepts presented are used to analyze the results of a new study suggesting increased intraventricular velocities as a new cause for systolic murmurs in adults.}, }
@article {pmid9811657, year = {1998}, author = {Dusenbery, DB}, title = {Fitness landscapes for effects of shape on chemotaxis and other behaviors of bacteria.}, journal = {Journal of bacteriology}, volume = {180}, number = {22}, pages = {5978-5983}, pmid = {9811657}, issn = {0021-9193}, mesh = {*Bacterial Physiological Phenomena ; Chemotaxis/*physiology ; Models, Biological ; }, abstract = {Data on the shapes of 218 genera of free-floating or free-swimming bacteria reveal groupings around spherical shapes and around rod-like shapes of axial ratio about 3. Motile genera are less likely to be spherical and have larger axial ratios than nonmotile genera. The effects of shape on seven possible components of biological fitness were determined, and actual fitness landscapes in phenotype space are presented. Ellipsoidal shapes were used as models, since their hydrodynamic drag coefficients can be rigorously calculated in the world of low Reynolds number, where bacteria live. Comparing various shapes of the same volume, and assuming that departures from spherical have a cost that varies with the minimum radius of curvature, led to the following conclusions. Spherical shapes have the largest random dispersal by Brownian motion. Increased surface area occurs in oblate ellipsoids (disk-like), which rarely occur. Elongation into prolate ellipsoids (rod-like) reduces sinking speed, and this may explain why some nonmotile genera are rod-like. Elongation also favors swimming efficiency (to a limited extent) and the ability to detect stimulus gradients by any of three mechanisms. By far the largest effect (several hundred-fold) is on temporal detection of stimulus gradients, and this explains why rod-like shapes and this mechanism of chemotaxis are common.}, }
@article {pmid9809635, year = {1998}, author = {Wu, SJ and Shung, KK and Brasseur, JG}, title = {In situ measurements of Doppler power vs. flow turbulence intensity in red cell suspensions.}, journal = {Ultrasound in medicine &amp; biology}, volume = {24}, number = {7}, pages = {1009-1021}, doi = {10.1016/s0301-5629(97)00240-8}, pmid = {9809635}, issn = {0301-5629}, support = {HL28452/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Blood Flow Velocity ; Cell Size ; Erythrocytes/diagnostic imaging/*physiology ; Hematocrit ; *Laser-Doppler Flowmetry ; Models, Theoretical ; Reproducibility of Results ; Swine ; *Ultrasonography, Doppler ; }, abstract = {Whereas previous studies have shown that ultrasonic backscatter and Doppler power from blood are affected by flow turbulence, turbulence level has only been inferred from the flow Reynolds number and not directly measured. In this study, both ultrasonic Doppler power and flow turbulence intensity were measured in situ to quantify the relationship between Doppler power and flow turbulence. Three grid meshes of different geometries were used in a steady-flow mock loop to generate controlled levels of flow turbulence in porcine red blood cell saline suspensions. Doppler power was measured by a 10-MHz PW Doppler flowmeter, and the turbulence intensity by using constant-temperature hot film anemometry. We showed that Doppler power is affected by turbulence and hematocrit in a complex way. At a fixed hematocrit, Doppler power increases nonlinearly with turbulence intensity and, at fixed turbulence intensity, Doppler power peaks at an optimal hematocrit level that increases with turbulence level. The shape factor, introduced by Lucas and Twersky (1987) to take into account effects of shape and orientation of the scatterers in a dense distribution of small and tenuous scatterers, was estimated by fitting the experimental data to the theoretical model. The results indicate that shape factor decreases with increasing turbulence intensity.}, }
@article {pmid9771573, year = {1998}, author = {Gach, HM and Lowe, IJ}, title = {Characterization of flow emerging from a stenosis using MRI.}, journal = {Magnetic resonance in medicine}, volume = {40}, number = {4}, pages = {559-570}, doi = {10.1002/mrm.1910400409}, pmid = {9771573}, issn = {0740-3194}, support = {RR03631-04/RR/NCRR NIH HHS/United States ; }, mesh = {Blood Flow Velocity ; Hemorheology ; Humans ; Image Processing, Computer-Assisted ; Magnetic Resonance Angiography/*methods ; Models, Cardiovascular ; Phantoms, Imaging ; }, abstract = {MRI ultra-fast imaging techniques are used to characterize flow emerging from streamlined and abrupt stenoses inside cylindrical channels. Reattachment lengths of the shear boundary to the channel wall are measured using rotating ultra-fast imaging sequence (RUFIS) in-flow imaging. Velocity profiles of flow are created using velocity (sine and cosine)-encoded RUFIS sequences. The sine-encoded images permit one to identify reverse flow (i.e., eddies) that arise within the region of flow reattachment. The ratios of peak velocities (downstream/upstream of the stenosis) derived from the cosine-encoded images are used to identify the transition from the laminar to the turbulent regimen. Based on these experiments, the transition from the laminar to turbulent regimen occurs at a stenotic Reynolds Number of 350, whereas fully developed turbulence occurs at a stenotic Reynolds Number of 2600. These results are compared with the results from invasive studies.}, }
@article {pmid9742562, year = {1998}, author = {Faure, A and Grimsey, IM and Rowe, RC and York, P and Cliff, MJ}, title = {A methodology for the optimization of wet granulation in a model planetary mixer.}, journal = {Pharmaceutical development and technology}, volume = {3}, number = {3}, pages = {413-422}, doi = {10.3109/10837459809009869}, pmid = {9742562}, issn = {1083-7450}, mesh = {*Technology, Pharmaceutical ; }, abstract = {This paper investigates a methodology for the optimization of wet granulation processes in planetary mixers. A model formulation was granulated in a planetary mixer (two different bowl sizes). The wet masses were characterized by their bulk density and consistency (as measured by mixer torque rheometry), and the feasibility of scale-up from one mixer bowl to the other was studied using a dimensionless numbers approach for the estimation of the power consumption at the granulation end point. Both bowls gave the same dimensionless power relationships (a relationship between the power number, Reynolds number, Froude number, and bowl fill ratio), which could therefore be used for calculating the power consumption level when the wet mass achieves its target values of density and consistency, i.e., the point at which granulation should be stopped. It was also shown that batches granulated in different conditions (batch size, blade speed) in two planetary mixers, but presenting similar wet mass characteristics (bulk density and consistency) led to dry granules of similar properties: granule size distribution, density, friability, and flow. This work suggests that it is possible to characterize the wet mass by only two parameters which describe the quality of the downstream granules. The scale-up procedure based on the use of dimensionless numbers was found to be applicable to planetary mixers, provided they give one common dimensionless power relationship.}, }
@article {pmid9733223, year = {1998}, author = {Malinauskas, RA and Sarraf, P and Barber, KM and Truskey, GA}, title = {Association between secondary flow in models of the aorto-celiac junction and subendothelial macrophages in the normal rabbit.}, journal = {Atherosclerosis}, volume = {140}, number = {1}, pages = {121-134}, doi = {10.1016/s0021-9150(98)00129-4}, pmid = {9733223}, issn = {0021-9150}, support = {HL41372/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Aorta/*physiology ; Celiac Artery/*physiology ; Endothelium, Vascular/physiology ; *Hemorheology ; Macrophages/*physiology ; *Models, Cardiovascular ; Rabbits ; Stress, Mechanical ; }, abstract = {In order to examine the association between arterial fluid dynamics and the distribution of subendothelial macrophages in the normal rabbit aorta, steady and pulsatile particle flow visualization was performed in a geometrically realistic model of the rabbit aorto-celiac junction region. Over a range of aorto-celiac steady flow ratios, particle pathlines along the upstream lateral aortic walls curved to enter the celiac orifice, while two asymmetric regions of reversing spiral secondary flow originated along the downstream lateral portions of the orifice flow divider. These regions increased in size as either the Reynolds number or flow into the celiac artery increased. In pulsatile flow studies, particles along the lateral aortic walls near the celiac orifice began to spiral into the branch during peak systole. During systolic deceleration, the size of this spiral flow region increased as particles reversed direction to enter the celiac orifice. This contrasted with flow patterns directly upstream and downstream of the orifice, which remained unidirectional throughout this period even along the distal lip of the orifice. The highest frequency of subendothelial white blood cells in the normal rabbit aorta was associated with regions where secondary flow patterns occurred, and where the orientation of endothelial cell nuclei deviated from the major direction of aortic flow. Secondary flow patterns may aid the accumulation of monocytes and macrophages about the lateral regions of the celiac artery flow divider by transporting monocytes to the walls, allowing them time to attach to the endothelial cells, or by stimulating the endothelial cells to express leukocyte adhesion molecules. These same regions are associated with increased endothelial permeability to low density lipoprotein and, under hypercholesterolemic conditions, lesion origination.}, }
@article {pmid9727343, year = {1998}, author = {Krafczyk, M and Cerrolaza, M and Schulz, M and Rank, E}, title = {Analysis of 3D transient blood flow passing through an artificial aortic valve by Lattice-Boltzmann methods.}, journal = {Journal of biomechanics}, volume = {31}, number = {5}, pages = {453-462}, doi = {10.1016/s0021-9290(98)00036-0}, pmid = {9727343}, issn = {0021-9290}, mesh = {Algorithms ; *Aortic Valve ; Blood Flow Velocity/physiology ; Computer Simulation ; Computer Systems ; *Heart Valve Prosthesis ; Hemodynamics/physiology ; Hemolysis ; Hemorheology ; Humans ; Models, Cardiovascular ; Prosthesis Design ; Pulsatile Flow/physiology ; Regional Blood Flow/physiology ; Stress, Mechanical ; Surface Properties ; }, abstract = {The development of flow instabilities due to high Reynolds number flow in artificial heart valve geometries inducing high strain rates and stresses often leads to hemolysis and related highly undesired effects. Geometric and functional optimization of artificial heart valves is therefore mandatory. In addition to experimental work in this field it is meanwhile possible to obtain increasing insight into flow dynamics by computer simulation of refined model problems. After giving an introductory overview we report the results of the simulation of three-dimensional transient physiological flows in fixed geometries similar to a CarboMedics bileaflet heart valve at different opening angles. The visualization of emerging complicated flow patterns gives detailed information about the transient history of the systems dynamical stability. Stress analysis indicates temporal shear stress peaks even far away from walls. The mathematical approach used is the Lattice Boltzmann method. We obtained reasonable results for velocity and shear stress fields. The code is implemented on parallel hardware in order to decrease computation time. Finally, we discuss problems, shortcomings and possible extensions of our approach.}, }
@article {pmid9685258, year = {1998}, author = {Fountain, GO and Khakhar, DV and Ottino, JM}, title = {Visualization of three-dimensional chaos.}, journal = {Science (New York, N.Y.)}, volume = {281}, number = {5377}, pages = {683-686}, doi = {10.1126/science.281.5377.683}, pmid = {9685258}, issn = {1095-9203}, abstract = {Most chaotic mixing experiments have been restricted to two-dimensional, time-periodic flows, and this has shaped advances in theory as well. A prototypical, bounded, three-dimensional flow with a moderate Reynolds number is presented; this system lends itself to detailed experimental observation and allows for high-precision computational inspection. The flow structure, captured by means of cuts with a laser sheet (experimental Poincare section), was visualized with the use of continuously injected fluorescent dye streams and revealed detailed chaotic structures with high-period islands.}, }
@article {pmid9672088, year = {1998}, author = {Wang, W and Parker, KH}, title = {Movement of spherical particles in capillaries using a boundary singularity method.}, journal = {Journal of biomechanics}, volume = {31}, number = {4}, pages = {347-354}, doi = {10.1016/s0021-9290(98)00024-4}, pmid = {9672088}, issn = {0021-9290}, mesh = {Animals ; Blood Cells/*physiology ; Blood Flow Velocity/physiology ; Capillaries/*physiology ; Humans ; Methods ; Models, Cardiovascular ; Regional Blood Flow ; Rotation ; }, abstract = {As a first step to investigate the motion of blood cells in capillaries, we have studied the movement of a spherical particle falling in a vertical cylindrical tube using a boundary singularity method. The tube is filled with a Newtonian viscous fluid which would otherwise be stationary. The Reynolds number of the flow is much less than one. The sphere falls at arbitrary positions in the tube and is free to rotate. Point forces, Stokeslets, with unknown strength and direction, are distributed on the surfaces of the tube and the sphere. By forcing the flow field generated by all of the Stokeslets to satisfy proper boundary conditions, we solve for the strength and direction of each Stokeslet. The velocity, U, and rotation, omega, of the sphere are then calculated from a force and a torque balance. For a sphere falling on the axis of the tube, our results agree with Bohlin's approximate solution. When the sphere takes eccentric positions in the tube, it rotates as it translates down the tube, the direction of rotation being opposite to that it would have if the sphere rolled along the nearest side of the tube. This results from the zero net torque on the sphere and facilitates flow passing around the sphere. As the distance between the centre of the sphere and the axis of the tube increases, omega increases almost linearly, while U changes little. When the radius of the tube increases, U increases and approaches the Stokes velocity, while omega decreases rapidly. The boundary singularity method is relatively simple compared to other numerical methods and can be extended much more easily to the complex geometries typical of blood cells.}, }
@article {pmid9655785, year = {1998}, author = {Espinosa, FF and Kamm, RD}, title = {Meniscus formation during tracheal instillation of surfactant.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {85}, number = {1}, pages = {266-272}, doi = {10.1152/jappl.1998.85.1.266}, pmid = {9655785}, issn = {8750-7587}, support = {HL-33009/HL/NHLBI NIH HHS/United States ; }, mesh = {Algorithms ; Capillary Resistance ; Glycerol ; Gravitation ; Injections ; *Pulmonary Surfactants/administration &amp; dosage ; Trachea/anatomy &amp; histology/*physiology ; Viscosity ; Water ; }, abstract = {The method of surfactant instillation into the lungs for treatment of neonatal respiratory distress syndrome is an important attribute of delivery, and it may determine the overall efficacy of treatment. Previous studies primarily focused on the rate at which the bolus is instilled. These findings show that rapid injections lead to a more homogenous distribution, whereas slow infusions drain into the dependent lung with respect to gravity, resulting in a heterogeneous deposition. These results suggest that it is beneficial to form a meniscus, from which a more homogenous dispersal can proceed. The objective of the present study was to develop a functional criterion for meniscus formation during bolus injection. An in vitro experiment was used to examine the clinical setting of surfactant instillation. The physical variables examined were the bolus viscosity (mu) and density (rho), gravity (g), injection rate (Q), orientation of the trachea with respect to gravity (theta), tracheal size (D), surface tension (gamma), and catheter size (d). All quantities were varied, except gravity and catheter size. Experimental results show that a meniscus will form when NSt > 0. 004Re2/3, where NSt is Stokes number and Re is Reynolds number, NSt = muQ/D4rhogsintheta, a ratio of viscous effects to gravitational effects, and Re = rhoQD/d2mu, a ratio of inertial effects to viscous effects. Rapid injections, high viscosity, and small inclination with respect to gravity promote meniscus formation. These results can be used to refine the guidelines for administration of surfactant replacement therapy.}, }
@article {pmid9652126, year = {1998}, author = {Yen, J and Weissburg, MJ and Doall, MH}, title = {The fluid physics of signal perception by mate-tracking copepods.}, journal = {Philosophical transactions of the Royal Society of London. Series B, Biological sciences}, volume = {353}, number = {1369}, pages = {787-804}, pmid = {9652126}, issn = {0962-8436}, support = {1R29 CD273/CD/ODCDC CDC HHS/United States ; }, mesh = {*Animal Communication ; Animals ; Chemoreceptor Cells/*physiology ; Chemotaxis/physiology ; Crustacea/*physiology ; Diffusion ; Female ; Male ; Mechanoreceptors/*physiology ; Odorants ; Pheromones ; Physical Phenomena ; Physics ; Sexual Behavior, Animal/*physiology ; Swimming/physiology ; Water ; }, abstract = {Within laboratory-induced swarms of the marine copepod Temora longicornis, the male exhibits chemically mediated trail-following behaviour, concluding with fluid mechanical provocation of the mate-capture response. The location and structure of the invisible trail were determined by examining the specific behaviour of the female copepods creating the signal, the response of the male to her signal, and the fluid physics of signal persistence. Using the distance of the mate-tracking male from the ageing trail of the female, we estimated that the molecular diffusion coefficient of the putative pheromonal stimulant was 2.7 x 10(-5) cm2 s-1, or 1000 times slower than the diffusion of momentum. Estimates of signal strength levels, using calculations of diffusive properties of odour trails and attenuation rates of fluid mechanical signals, were compared to the physiological and behavioural threshold detection levels. Males find trails because of strong across-plume chemical gradients; males sometimes go the wrong way because of weak along-plume gradients; males lose the trail when the female hops because of signal dilution; and mate-capture behaviour is elicited by suprathreshold flow signals. The male is stimulated by the female odour to accelerate along the trail to catch up with her, and the boundary layer separating the signal from the chemosensitive receptors along the copepod antennule thins. Diffusion times, and hence reaction times, shorten and behavioural orientation responses can proceed more quickly. While 'perceptive' distance to the odour signal in the trail or the fluid mechanical signal from the female remains within 1-2 body lengths (< 5 mm), the 'reactive' distance between males and females was an order of magnitude larger. Therefore, when nearest-neighbour distances are 5 cm or less, as in swarms of 10(4) copepods m-3, mating events are facilitated. The strong similarity in the structure of mating trails and vortex tubes (isotropic, millimetre-centimetre scale, 10:1 aspect ratio, 10s persistence), indicates that these trails are constrained by the same physical forces that influence water motion in a low Reynolds number fluid regime, where viscosity limits forces to the molecular scale. The exploratory reaches of mating trails appear inscribed within Kolmogorov eddies and may represent a measure of eddy size. Biologically formed mating trails, however, are distinct in their flow velocity and chemical composition from common small-scale turbulent features; and mechanoreceptive and chemoreceptive copepods use their senses to discriminate these differences. Zooplankton are not aimless wanderers in a featureless environment. Their ambit is replete with clues that guide them in their efforts for survival in the ocean.}, }
@article {pmid9652125, year = {1998}, author = {Weissburg, MJ and Doall, MH and Yen, J}, title = {Following the invisible trail: kinematic analysis of mate-tracking in the copepod Temora longicornis.}, journal = {Philosophical transactions of the Royal Society of London. Series B, Biological sciences}, volume = {353}, number = {1369}, pages = {701-712}, pmid = {9652125}, issn = {0962-8436}, support = {1R29 DC0271/DC/NIDCD NIH HHS/United States ; }, mesh = {Animals ; Chemotaxis/physiology ; Crustacea/*physiology ; Female ; Male ; Neurons, Afferent/*physiology ; Odorants ; Orientation/physiology ; Pheromones ; Sex Factors ; Sexual Behavior, Animal/*physiology ; Swimming/physiology ; }, abstract = {We have analysed the fine-scale kinematics of movement of male and female copepods, Temora longicornis, to resolve how these small animals find their mates. Location of the trail initially involves rapid random turning and high rates of directional change. Males subsequently increase their rate of movement as they follow the trail, and execute a regular pattern of counter turns in both x,z and y,z planes to stay near or within the central axis of the odour field. Pursuit behaviour of males is strongly associated with female swimming behaviour, suggesting that quantifiable variations in the structure of the odour signal released by females affects male tracking. The behavioural components of mate tracking in Temora are very similar to those of other animals that employ chemically mediated orientation in their search for mates and food, and we conclude that male Temora find their mates using chemoperception. The kinematic analysis indicates both sequential and simultaneous taxis mechanisms are used by Temora to follow the odour signal. This, in turn, indicates that rather than responding to a diffuse plume, males are following a signal more accurately characterized as a chemical trail, and copepods appear to use mechanisms that are similar to those employed by trail-following terrestrial insects such as ants. While Temora expresses similar behaviours to those of a variety of chemosensory organisms, the ability to track a three-dimensional odour trail appears unique, and possibly depends on the persistence of fluid-borne odour signals created in low Reynolds number hydrodynamic regimes.}, }
@article {pmid9640356, year = {1997}, author = {Poflee, NM and Rakow, AL and Dandy, DS and Chappell, ML and Pons, MN}, title = {Inertial migration based concentration factors for suspensions of Chlorella microalgae in branched tubes.}, journal = {Biorheology}, volume = {34}, number = {6}, pages = {405-421}, doi = {10.1016/s0006-355x(98)00024-9}, pmid = {9640356}, issn = {0006-355X}, mesh = {Chlorella/*physiology ; Models, Biological ; Photography ; *Rheology ; }, abstract = {When a dilute suspension flows in the laminar regime through a tube, under certain conditions the suspended particles migrate radially to an equilibrium radial position. Branched tubes can use this radial concentration distribution to concentrate dilute suspensions. Suspensions of microalgae, Chlorella vulgaris, were pumped through tubes of various diameters for tube Reynolds number ranging from 47-1839 and photographed. Upstream particle concentration profiles were obtained by image analysis of the photographs. The dividing stream surfaces in branched tubes were obtained from the three-dimensional numerical solutions of the Navier-Stokes equations for steady, laminar, and homogeneous flow through tubes having one and two orthogonal branches. Concentration factors for Chlorella suspensions in branched tubes, predicted by a general method, fall in the range of 1.0-1.3.}, }
@article {pmid9635783, year = {1998}, author = {Chapman, GB and Cokelet, GR}, title = {Flow resistance and drag forces due to multiple adherent leukocytes in postcapillary vessels.}, journal = {Biophysical journal}, volume = {74}, number = {6}, pages = {3292-3301}, pmid = {9635783}, issn = {0006-3495}, support = {HL18208/HL/NHLBI NIH HHS/United States ; }, mesh = {Biophysics/methods ; Cell Adhesion/*physiology ; Erythrocytes/physiology ; Hemodynamics ; Leukocytes/*physiology ; Mathematics ; Microcirculation/*physiology ; Models, Cardiovascular ; Stress, Mechanical ; }, abstract = {Computational fluid dynamics was used to model flow past multiple adherent leukocytes in postcapillary size vessels. A finite-element package was used to solve the Navier-Stokes equations for low Reynolds number flow of a Newtonian fluid past spheres adhering to the wall of a cylindrical vessel. We determined the effects of sphere number, relative geometry, and spacing on the flow resistance in the vessel and the fluid flow drag force acting to sweep the sphere off the vessel wall. The computations show that when adherent leukocytes are aligned on the same side of the vessel, the drag force on each of the interacting leukocytes is less than the drag force on an isolated adherent leukocyte and can decrease by up to 50%. The magnitude of the reduction depends on the ratio of leukocyte to blood vessel diameter and distance between adherent leukocytes. However, there is an increase in the drag force when leukocytes adhere to opposite sides of the vessel wall. The increase in resistance generated by adherent leukocytes in vessels of various sizes is calculated from the computational results. The resistance increases with decreasing vessel size and is most pronounced when leukocytes adhere to opposite sides of the vessel.}, }
@article {pmid9633659, year = {1998}, author = {Elvers, KT and Leeming, K and Moore, CP and Lappin-Scott, HM}, title = {Bacterial-fungal biofilms in flowing water photo-processing tanks.}, journal = {Journal of applied microbiology}, volume = {84}, number = {4}, pages = {607-618}, doi = {10.1046/j.1365-2672.1998.00388.x}, pmid = {9633659}, issn = {1364-5072}, mesh = {Bacillus/growth &amp; development/isolation &amp; purification/physiology ; Biofilms/*growth &amp; development ; Fungi/growth &amp; development/isolation &amp; purification/*physiology ; Gram-Negative Bacteria/growth &amp; development/isolation &amp; purification/*physiology ; Gram-Positive Bacteria/growth &amp; development/isolation &amp; purification/*physiology ; Microscopy, Electron, Scanning ; Time Factors ; Water Microbiology ; }, abstract = {A complex seven species model community, including bacteria and fungi, was selected from organisms isolated from the walls of an industrial flowing water system. Growth rates of the species were determined in single and mixed batch culture growth. The rates were found to be significantly higher in mixed culture for Pseudomonas alcaligenes and Flavobacterium indologenes and higher in single culture for Xanthomonas maltophilia, Rhodotorula glutinis and Fusarium solani, whereas no significant difference was recorded for Alcaligenes denitrificans and Fusarium oxysporum. All species attached to PVC in single and mixed culture to form biofilms. Xanthomonas maltophilia, Alc. denitrificans, Ps. alcaligenes and F. solani biofilm cell densities cm-2 were significantly higher than attachment of the component species in mixed culture. Statistical analyses showed a significant difference in rate of colonization between single and mixed cultures for some species. No significant difference was noted between mixed culture cell densities cm-2 at laminar flows of Reynolds number 2.7 and 5.4.}, }
@article {pmid9548789, year = {1998}, author = {Pfeiffer, N and Mandrusov, E and Vroman, L and Leonard, EF}, title = {Effects of secondary flow caused by a curved channel on plasma protein adsorption to artificial surfaces.}, journal = {Biotechnology progress}, volume = {14}, number = {2}, pages = {338-342}, doi = {10.1021/bp970115f}, pmid = {9548789}, issn = {8756-7938}, support = {HL-44535/HL/NHLBI NIH HHS/United States ; }, mesh = {Adsorption ; Fibrinogen/*chemistry ; *Glass ; Humans ; Platelet Adhesiveness ; Protein Binding ; Rheology ; Stress, Mechanical ; Surface Properties ; }, abstract = {The effects of secondary flow induced by a curved channel on fibrinogen deposition and replacement on a glass surface were studied. Platelet adhesion to surface-bound fibrinogen was also studied to indicate how secondary flow may affect thrombogenesis on artificial surfaces. A saline pre-wetted channel with straight and curved sections was exposed to flowing plasma at a Reynolds number of 28.6. Results show that fibrinogen deposited on the surface at a shear rate of 175 s-1 was replaced faster in regions of secondary flow (Dean numbers from 11 to 19) than in adjacent regions of shear flow. Platelets adhered only to those surfaces where fibrinogen had been detected.}, }
@article {pmid9596533, year = {1998}, author = {Siouffi, M and Deplano, V and Pélissier, R}, title = {Experimental analysis of unsteady flows through a stenosis.}, journal = {Journal of biomechanics}, volume = {31}, number = {1}, pages = {11-19}, doi = {10.1016/s0021-9290(97)00104-8}, pmid = {9596533}, issn = {0021-9290}, mesh = {Blood Flow Velocity/physiology ; Blood Vessels/diagnostic imaging/*physiopathology ; Constriction, Pathologic ; Humans ; *Models, Cardiovascular ; Pulsatile Flow ; Rheology/*methods ; Ultrasonography ; }, abstract = {In this paper we present a study of the post-stenotic velocity flow field corresponding to oscillatory, pulsatile and physiological flow waveforms. Two-dimensional velocity measurements are performed in a 75% severity stenosis using a pulsed Doppler ultrasonic velocimeter. Emphasis is placed on the analysis of the experimental velocity-profile patterns. It is recognized that, beyond the influence of the flow parameters such as the Reynolds number and the frequency parameter, velocity profiles (hence wall-shear stresses) highly depend on the flow waveform. In addition to this analysis, a model of the stenosis influence length is proposed in the case of oscillatory flow.}, }
@article {pmid9519904, year = {1998}, author = {Woolley, DM}, title = {Studies on the eel sperm flagellum. 2. The kinematics of normal motility.}, journal = {Cell motility and the cytoskeleton}, volume = {39}, number = {3}, pages = {233-245}, doi = {10.1002/(SICI)1097-0169(1998)39:3&lt;233::AID-CM6&gt;3.0.CO;2-5}, pmid = {9519904}, issn = {0886-1544}, support = {//Wellcome Trust/United Kingdom ; }, mesh = {Anguilla ; Animals ; Computer Simulation ; Male ; Microscopy, Video ; Sperm Motility/*physiology ; Sperm Tail/*physiology ; }, abstract = {The sperm flagellum of Anguilla anguilla lacks outer dynein arms, radial spokes and central structures. Its characteristic motion has been obtained by studying cells swimming perpendicularly against, but not adhering to, the coverslip. The flagellum generates a sinistrally helical wave of rising, then falling, amplitude. The frequency of the wave, which can exceed 70 Hz, is inversely related to its maximum amplitude. As a reaction to the torque, the entire cell rolls (spins) in the opposite direction to that taken by points on the flagellum in the generation of the sinistral wave. However, because the head (which contributes on opposing torque) is asymmetrical, the axis of this counter-rotation is displaced laterally from the axis of the flagellar rotation. As a result, the flagellum precesses around the progression axis, with each point on the flagellum travelling along a special flagelloid curve, specified by the ratios of the two frequencies and the two radii for the circular motions. The instantaneous flagellar waveform (the flagelloid wave) is thus derived as a succession of phase-shifted points on the series of flagelloid curves along the axis of the cell's rotation. This adds complexity to the underlying, rather simple, helical geometry. Calculations suggest that the forward swimming speed of the sperm is greatly aided by the orientation and shape of the sperm head. The movement of latex beads was observed around sperm swimming against the coverslip and around sperm swimming freely. Bulk, vortical flows of fluid were seen in the former case and net lateral displacements in the latter; this is in accordance with hydrodynamic theory for low Reynolds number systems.}, }
@article {pmid9464873, year = {1997}, author = {Barbaro, V and Grigioni, M and Daniele, C and D'Avenio, G and Boccanera, G}, title = {19 mm sized bileaflet valve prostheses' flow field investigated by bidimensional laser Doppler anemometry (part II: maximum turbulent shear stresses).}, journal = {The International journal of artificial organs}, volume = {20}, number = {11}, pages = {629-636}, pmid = {9464873}, issn = {0391-3988}, mesh = {Aortic Valve ; Biomechanical Phenomena ; Blood Flow Velocity ; Device Approval ; Guidelines as Topic ; *Heart Valve Prosthesis ; Laser-Doppler Flowmetry/*instrumentation ; Mitral Valve ; Models, Theoretical ; United States ; United States Food and Drug Administration ; }, abstract = {The investigation of the flow field generated by cardiac valve prostheses is a necessary task to gain knowledge on the possible relationship between turbulence-derived stresses and the hemolytic and thrombogenic complications in patients after valve replacement. The study of turbulence flows downstream of cardiac prostheses, in literature, especially concerns large-sized prostheses with a variable flow regime from very low up to 6 L/min. The Food and Drug Administration draft guidance requires the study of the minimum prosthetic size at a high cardiac output to reach the maximum Reynolds number conditions. Within the framework of a national research project regarding the characterization of cardiovascular endoprostheses, an in-depth study of turbulence generated downstream of bileaflet cardiac valves is currently under way at the Laboratory of Biomedical Engineering of the Istituto Superiore di Sanita. Four models of 19 mm bileaflet valve prostheses were used: St Jude Medical HP, Edwards Tekna, Sorin Bicarbon, and CarboMedics. The prostheses were selected for the nominal Tissue Annulus Diameter as reported by manufacturers without any assessment of valve sizing method, and were mounted in aortic position. The aortic geometry was scaled for 19 mm prostheses using angiographic data. The turbulence-derived shear stresses were investigated very close to the valve (0.35 D0), using a bidimensional Laser Doppler anemometry system and applying the Principal Stress Analysis. Results concern typical turbulence quantities during a 50 ms window at peak flow in the systolic phase. Conclusions are drawn regarding the turbulence associated to valve design features, as well as the possible damage to blood constituents.}, }
@article {pmid9464872, year = {1997}, author = {Barbaro, V and Grigioni, M and Daniele, C and D'Avenio, G and Boccanera, G}, title = {19 mm sized bileaflet valve prostheses' flow field investigated by bidimensional laser Doppler anemometry (part I: velocity profiles).}, journal = {The International journal of artificial organs}, volume = {20}, number = {11}, pages = {622-628}, pmid = {9464872}, issn = {0391-3988}, mesh = {Aortic Valve ; Blood Flow Velocity ; Device Approval ; Guidelines as Topic ; *Heart Valve Prosthesis ; Laser-Doppler Flowmetry/*instrumentation ; Mitral Valve ; United States ; United States Food and Drug Administration ; }, abstract = {The investigation of the flow field downstream of a cardiac valve prosthesis is a well established task. In particular turbulence generation is of interest if damage to blood constituents is to be assessed. Several prosthetic valve flow studies are available in literature but they generally concern large-sized prostheses. The FDA draft guidance requires the study of the maximum Reynolds number conditions for a cardiac valve model to assess the worst case in turbulence by choosing both the minimum valve diameter and a high cardiac output value as protocol set up. Within the framework of a national research project regarding the characterization of cardiovascular endoprostheses, the Laboratory of Biomedical Engineering is currently conducting an in-depth study of turbulence generated downstream of bileaflet cardiac valves. Four models of 19 mm sized bileaflet valve prostheses, namely St Jude Medical HP Edwards Tekna, Sorin Bicarbon, and CarboMedics, were studied in aortic position. The prostheses were selected for the nominal annulus diameter reported by the manufacturers without any assessment of the valve sizing method. The hemodynamic function was investigated using a bidimensional LDA system. Results concern velocity profiles during the peak flow systolic phase, at high cardiac output regime, highlighting the different flow field features downstream of the four small-sized cardiac valves.}, }
@article {pmid9407288, year = {1997}, author = {Cheng, KH and Cheng, YS and Yeh, HC and Swift, DL}, title = {Measurements of airway dimensions and calculation of mass transfer characteristics of the human oral passage.}, journal = {Journal of biomechanical engineering}, volume = {119}, number = {4}, pages = {476-482}, doi = {10.1115/1.2798296}, pmid = {9407288}, issn = {0148-0731}, mesh = {Absorption ; Aerosols/pharmacokinetics ; Diffusion ; Humans ; Larynx/*anatomy &amp; histology/metabolism ; *Models, Biological ; Mouth/*anatomy &amp; histology/metabolism ; Nasal Mucosa/metabolism ; Nonlinear Dynamics ; Nose/*anatomy &amp; histology ; Particle Size ; Respiration/*physiology ; Surface Properties ; Trachea/*anatomy &amp; histology/metabolism ; }, abstract = {This paper presents measurements of the geometric shape, perimeter, and cross-sectional area of the human oral passage (from oral entrance to midtrachea) and relates them through dimensionless parameters to the depositional mass transfer of ultrafine particles. Studies were performed in two identical replicate oral passage models, one of which was cut orthogonal to the airflow direction into 3 mm elements for measurement, the other used intact for experimental measurements of ultrafine aerosol deposition. Dimensional data were combined with deposition measurements in two sections of the oral passage (the horizontal oral cavity and the vertical laryngeal-tracheal airway) to calculate the dimensionless mass transfer Sherwood number (Sh). Mass transfer theory suggests that Sh should be expressible as a function of the Reynolds number (Re) and the Schmidt number (Sc). For inhalation and exhalation through the oral cavity (O-C), an empirical relationship was obtained for flow rates from 7.5-30.0 1 min-1: Sh = 15.3 Re0.812 Sc-0.986 An empirical relationship was likewise obtained for the laryngeal-tracheal (L-T) region over the same range of flow rates: Sh = 25.9 Re0.861 Sc-1.37 These relationships were compared to heat transfer in the human upper airways through the well-known analogy between heat and mass transfer. The Reynolds number dependence for both the O-C and L-T relationships was in good agreement with that for heat transfer. The mass transfer coefficients were compared to extrathoracic uptake of gases and vapors and showed similar flow rate dependence. For gases and vapors that conform to the zero concentration boundary condition, the empirical relationships are applicable when diffusion coefficients are taken into consideration.}, }
@article {pmid9326605, year = {1997}, author = {Purcell, EM}, title = {The efficiency of propulsion by a rotating flagellum.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {94}, number = {21}, pages = {11307-11311}, pmid = {9326605}, issn = {0027-8424}, mesh = {*Bacterial Physiological Phenomena ; Cell Movement ; Flagella/*physiology/ultrastructure ; Mathematics ; *Models, Biological ; }, abstract = {At very low Reynolds number, the regime in which fluid dynamics is governed by Stokes equations, a helix that translates along its axis under an external force but without an external torque will necessarily rotate. By the linearity of the Stokes equations, the same helix that is caused to rotate due to an external torque will necessarily translate. This is the physics that underlies the mechanism of flagellar propulsion employed by many microorganisms. Here, I examine the linear relationships between forces and torques and translational and angular velocities of helical objects to understand the nature of flagellar propulsion.}, }
@article {pmid9285350, year = {1997}, author = {Bertram, CD and Godbole, SA}, title = {LDA measurements of velocities in a simulated collapsed tube.}, journal = {Journal of biomechanical engineering}, volume = {119}, number = {3}, pages = {357-363}, doi = {10.1115/1.2796101}, pmid = {9285350}, issn = {0148-0731}, mesh = {Laser-Doppler Flowmetry ; *Models, Biological ; Oscillometry ; Pressure ; Pulmonary Ventilation/physiology ; *Rheology ; }, abstract = {A perspex (plexiglas) tube was locally deformed into an almost bi-lobar interior cross section, representative of the localized throat at the downstream end of a collapsed tube conveying a flow. The axial and transverse (parallel to the long axis of the deformed cross section) components of fluid velocity were measured in a dense rectangular grid of points covering the whole cross section, at 15 axial sites between one diameter upstream of and three diameters downstream of the center of the constriction. The Reynolds number based on undeformed tube diameter and mean velocity was 705. Results are presented both as surfaces showing the variation of each component over the cross section and as velocity vector profiles. The overall changes in velocity in the streamwise direction are presented in terms of the variation of the maximum and minimum of each component with axial position. Flow downstream of the throat consisted of two parallel side-jets with a broad region of reverse flow in between. This pattern persisted until beyond 2.5 diameters downstream, by which point transverse inflow at the top and bottom of the cross section had converted the side jets into a complete annulus of axial velocity surrounding a central deficit. Jet velocities and reverse flow disappeared relatively abruptly before three diameters downstream.}, }
@article {pmid11038559, year = {1997}, author = {Barenblatt, GI and Chorin, AJ and Hald, OH and Prostokishin, VM}, title = {Structure of the zero-pressure-gradient turbulent boundary layer.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {94}, number = {15}, pages = {7817-7819}, doi = {10.1073/pnas.94.15.7817}, pmid = {11038559}, issn = {0027-8424}, abstract = {A processing of recent experimental data by Nagib and Hites [Nagib, H. &amp; Hites, M. (1995) AIAA paper 95-0786, Reno, NV) shows that the flow in a zero-pressure-gradient turbulent boundary layer, outside the viscous sublayer, consists of two self-similar regions, each described by a scaling law. The results concerning the Reynolds-number dependence of the coefficients of the wall-region scaling law are consistent with our previous results concerning pipe flow, if the proper definition of the boundary layer Reynolds number (or boundary layer thickness) is used.}, }
@article {pmid9242948, year = {1997}, author = {Paz, D and Einav, S and Raderer, F and Trubel, W}, title = {Numerical model and experimental investigation of blood flow through a bifurcation. Interaction between an artery and a small prosthesis.}, journal = {ASAIO journal (American Society for Artificial Internal Organs : 1992)}, volume = {43}, number = {4}, pages = {326-333}, pmid = {9242948}, issn = {1058-2916}, mesh = {Anastomosis, Surgical ; Arteries/*physiology ; Biomechanical Phenomena ; Blood Flow Velocity/physiology ; Blood Vessel Prosthesis/*standards ; Hemodynamics ; *Models, Biological ; Vascular Resistance/physiology ; }, abstract = {The use of prosthetic vascular grafts as bypass to arteries of small diameter (< 5 mm) often is thwarted by occlusion after months of apparently normal function. This work presents a numeric simulation of the flow through a distal anastomosis. A finite element method has been applied, providing information on the velocity field, streamlines, wall shear stresses, and vorticity in the different geometries. The study illustrates the dependence of the flow pattern and wall shear stress distribution upon Reynolds number, and the results show high shear stresses, approximately 3-5 times larger than normal, acting on the vessel wall at the branching point for the small diameter branch.}, }
@article {pmid9168397, year = {1997}, author = {Aenis, M and Stancampiano, AP and Wakhloo, AK and Lieber, BB}, title = {Modeling of flow in a straight stented and nonstented side wall aneurysm model.}, journal = {Journal of biomechanical engineering}, volume = {119}, number = {2}, pages = {206-212}, doi = {10.1115/1.2796081}, pmid = {9168397}, issn = {0148-0731}, mesh = {Aneurysm/*physiopathology/*surgery ; Blood Flow Velocity ; Blood Viscosity ; *Hemorheology ; Humans ; *Models, Cardiovascular ; *Numerical Analysis, Computer-Assisted ; Pulsatile Flow ; Reproducibility of Results ; *Stents ; Thrombosis/etiology ; }, abstract = {We investigated the changes of flow patterns in a blood vessel with a side wall aneurysm resulting from placement of a stent. Local hemodynamics can be markedly altered by placing an intravascular stent, which covers the orifice of the aneurysm. The alternations in flow patterns can lead to flow stasis in the aneurysmal pouch and promote the formation of a stable thrombus. Furthermore, a porous stent can serve as substrate for neointimal growth and subsequently induce a remodeling of the diseased arterial segment. To examine changes in local hemodynamics due to stent placement, a stented and nonstented aneurysm model was investigated computationally in a three-dimensional configuration using a finite element fluid dynamics program. The finite element model was studied under incompressible, pulsatile, viscous, Newtonian conditions. The fluid dynamic similarity parameter, i.e., the maximum/minimum Reynolds number, was set at about 240/25 based on cross-sectional average instantaneous flow. The Womersley number was set to 2.5. These values are representative of large cerebral arteries. The results of the stented versus the nonstented model show substantial difference sin flow patterns inside the aneurysmal pouch. Flow activity inside the stented aneurysm model is significantly diminished and flow inside the parent vessel is less undulated and is directed past the orifice. A high-pressure zone at the distal neck and the dome of the aneurysm prior to stenting decreases after stent placement. However, elevated pressure values are found at the stent filaments facing the current. Higher shear rates are observed at the distal aneurysmal neck after stenting, but are confined to a smaller region and are unidirectional compared to the nonstented model.}, }
@article {pmid9168395, year = {1997}, author = {Loth, F and Jones, SA and Giddens, DP and Bassiouny, HS and Glagov, S and Zarins, CK}, title = {Measurements of velocity and wall shear stress inside a PTFE vascular graft model under steady flow conditions.}, journal = {Journal of biomechanical engineering}, volume = {119}, number = {2}, pages = {187-194}, doi = {10.1115/1.2796079}, pmid = {9168395}, issn = {0148-0731}, support = {HL 15062-19/HL/NHLBI NIH HHS/United States ; HL 41267/HL/NHLBI NIH HHS/United States ; }, mesh = {Anastomosis, Surgical ; Animals ; Blood Flow Velocity ; *Blood Vessel Prosthesis ; Dogs ; Femoral Artery/surgery ; *Hemorheology ; Iliac Artery/surgery ; Laser-Doppler Flowmetry ; *Models, Cardiovascular ; *Numerical Analysis, Computer-Assisted ; *Polytetrafluoroethylene ; Reproducibility of Results ; Stress, Mechanical ; }, abstract = {The flow field inside a model of a polytetrafluorethylene (PTFE) canine artery end-to-side bypass graft was studied under steady flow conditions using laser-Doppler anemometry. The anatomically realistic in vitro model was constructed to incorporate the major geometric features of the in vivo canine anastomosis geometry, most notably a larger graft than host artery diameter. The velocity measurements at Reynolds number 208, based on the host artery diameter, show the flow field to be three dimensional in nature. The wall shear stress distribution, computed from the near-wall velocity gradients, reveals a relatively low wall shear stress region on the wall opposite to the graft near the stagnation point approximately one artery diameter in axial length at the midplane. This low wall shear stress region extends to the sidewalls, suture lines, and along the PTFE graft where its axial length at the midplane is more than two artery diameters. The velocity distribution inside the graft model presented here provides a data set well suited for validation of numerical solutions on a model of this type.}, }
@article {pmid9146801, year = {1997}, author = {Lieber, BB and Stancampiano, AP and Wakhloo, AK}, title = {Alteration of hemodynamics in aneurysm models by stenting: influence of stent porosity.}, journal = {Annals of biomedical engineering}, volume = {25}, number = {3}, pages = {460-469}, doi = {10.1007/BF02684187}, pmid = {9146801}, issn = {0090-6964}, mesh = {Fluorescent Dyes ; Hemodynamics/*physiology ; Humans ; Intracranial Aneurysm/physiopathology/*therapy ; Lasers ; *Models, Biological ; Porosity ; Rheology/instrumentation ; *Stents ; }, abstract = {Recent developments in minimally invasive approach to cerebrovascular diseases include the placement of stents in arteries for treatment of aneurysms. Preliminary clinical observations and experimental studies have shown that intravascular stents traversing the orifice may lead to thrombosis and subsequent occlusion of the aneurysm. The alterations in vessel local hemodynamics due to the introduction of a stent are not yet well understood. We investigated changes in local hemodynamics resulting from stent implantation. Pulsatile flow patterns in an experimental flow apparatus were visualized using laser-induced fluorescence of rhodamine dye. The test cells were constructed in a rectangular shape to facilitate an undisturbed longitudinal view of flow patterns in parent vessel and aneurysm models with and without porous stents. Woven nitinol stents of various porosities (76%, 80%, 82%, and 85%) were investigated. The selected fluid dynamic similarity parameters (Reynolds and Womersley numbers) represented conditions usually found in high-flow, larger arteries in humans (such as the carotid artery) and low-flow, smaller arteries (such as the vertebral artery). The mean Reynolds number for the larger arteries was 180, with maximum/minimum values of 490/-30 and the Womersley number was 5.3. The mean Reynolds number for the smaller arteries was 90, with maximum/minimum values of 230/2, and the Womersley number was 2.7. For the larger arteries modeled, placement of a stent of the lowest porosity across the aneurysm orifice resulted in reduction of aneurysmal vortex speed and decreased interaction with parent vessel flow. For smaller arteries, a stent of the same porosity led to a substantial reduction of parent vessel/aneurysmal flow interaction and the appearance of a nonrecirculating crescent of fluid rich in rhodamine dye in the aneurysm dome. Our results can help explain in vivo thrombus formation within an aneurysm after placement of a stent that is compatible with local hemodynamics.}, }
@article {pmid18253246, year = {1997}, author = {Gardner, PJ and Roggemann, MC and Welsh, BM and Bowersox, RD and Luke, TE}, title = {Comparison of measured and computed Strehl ratios for light propagated through a channel flow of a He-N(2) mixing layer at high Reynolds numbers.}, journal = {Applied optics}, volume = {36}, number = {12}, pages = {2559-2567}, doi = {10.1364/ao.36.002559}, pmid = {18253246}, issn = {1559-128X}, abstract = {A lateral shearing interferometer was used to measure the slope of perturbed wave fronts after they propagated through a He-N(2) mixing layer in a rectangular channel. Slope measurements were used to reconstruct the phase of the turbulence-corrupted wave front. The random phase fluctuations induced by the mixing layer were captured in a large ensemble of wave-front measurements. Phase structure functions, computed from the reconstructed phase surfaces, were stationary in first increments. A five-thirds power law is shown to fit streamwise and cross-stream slices of the structure function, analogous to the Kolmogorov model for isotropic turbulence, which describes the structure function with a single parameter. Strehl ratios were computed from the phase structure functions and compared with a measured experiment obtained from simultaneous point-spread function measurements. Two additional Strehl ratios were calculated by using classical estimates that assume statistical isotropy throughout the flow. The isotropic models are a reasonable estimate of the optical degradation only within a few centimeters of the initial mixing, where the Reynolds number is low. At higher Reynolds numbers, Strehl ratios calculated from the structure functions match the experiment much better than Strehl ratio calculations that assume isotropic flow.}, }
@article {pmid18576096, year = {1997}, author = {Svihla, CK and Dronawat, SN and Donnelly, JA and Rieth, TC and Hanley, TR}, title = {Measurement of the steady-state shear characteristics of filamentous suspensions using turbine, vane, and helical impellers.}, journal = {Applied biochemistry and biotechnology}, volume = {63-65}, number = {}, pages = {375-385}, doi = {10.1007/BF02920439}, pmid = {18576096}, issn = {0273-2289}, abstract = {The impeller viscometer technique is frequently used to characterize the rheology of filamentous suspensions in order to avoid difficulties encountered with conventional instruments. This work presents the results of experiments conducted with vane, turbine, and helical impellers. The validity of the assumptions made in the determination of the torque and shear-rate constants were assessed for each impeller type. For the turbine and vane impellers, an increase in the apparent torque constant c was observed with increasing Reynolds number even when measurements were confined to the viscous regime. The shear-rate constants determined for the vane and turbine impellers varied for different calibration fluids, which contradicts the assumptions usually invoked in the analysis of data for this technique. When the helical impeller was calibrated, consistent values for the torque and shear-rate constants were obtained. The three impeller types were also used to characterize the rheology of cellulose fiber suspensions and the results compared for consistency and reproducibility. The results have application in design of rheometers for use in process control and product quality assessment in the fermentation and pulp and paper industries.}, }
@article {pmid9239642, year = {1997}, author = {King, MJ and David, T and Fisher, J}, title = {Three-dimensional study of the effect of two leaflet opening angles on the time-dependent flow through a bileaflet mechanical heart valve.}, journal = {Medical engineering &amp; physics}, volume = {19}, number = {3}, pages = {235-241}, doi = {10.1016/s1350-4533(96)00066-5}, pmid = {9239642}, issn = {1350-4533}, support = {//Wellcome Trust/United Kingdom ; }, mesh = {Biophysical Phenomena ; Biophysics ; Blood Flow Velocity/physiology ; *Heart Valve Prosthesis ; Humans ; Models, Cardiovascular ; Prosthesis Design ; Stress, Mechanical ; }, abstract = {A three-dimensional (3-D), time-dependent computational fluid dynamics (CFD) model was used to investigate the effect of leaflet opening angle on the flow through a fully open bileaflet heart valve up to peak systole. A laminar flow model of a Newtonian fluid was used, and the peak systolic. Reynolds number was 1500, based on the aortic radius and the average velocity at peak systole. This resulted in a Reynolds number of 5800, based on the aortic radius and the local maximum velocity. The flow fields through and downstream of the bileaflet valves were complex, with strong time-dependent 3-D vortices being found in planes parallel and perpendicular to the leaflets. The parametric study of the effect of leaflet opening angle showed that, as the leaflet opening angle increased from 78 degrees to 85 degrees, the flow downstream of the valve leaflets became more centralized, and the wake downstream of the leaflet decreased in size. However, as the opening angle increased from 78 degrees to 85 degrees, the maximum shear rate and the maximum velocity increased, suggesting that the design of the central orifice geometry was also an important consideration.}, }
@article {pmid9105296, year = {1997}, author = {McConnell, CJ and Marcogliese, DJ and Stacey, MW}, title = {Settling rate and dispersal of sealworm eggs (Nematoda) determined using a revised protocol for myxozoan spores.}, journal = {The Journal of parasitology}, volume = {83}, number = {2}, pages = {203-206}, pmid = {9105296}, issn = {0022-3395}, mesh = {Animals ; Ascaridida Infections/transmission ; Ascaridoidea/*physiology ; Eukaryota/*physiology ; Female ; Nova Scotia ; Ovum/physiology ; Perches ; Seals, Earless ; Seawater/*parasitology ; Spores/physiology ; }, abstract = {Settling rates and densities of small bodies can be determined by recording settling rates in fluids of different densities, but similar viscosities, and applying Stoke's law. However, at low Reynolds numbers, drag effects reduce the object's settling rate and must be accounted for in sedimentation experiments. Using a revised protocol for spores of the myxozoan Henneguya doori that accounted for significant drag effects exerted by the experimental apparatus, we improve upon a previously described technique and apply it to eggs of the sealworm, Pseudoterranova decipiens. Sealworm eggs have a density of 1.08 x 10(3) kg/m3 and a characteristic Reynolds number of 6 x 10(-3). Fixed eggs settle in seawater at rate of 1.09 x 10(-4) m/sec, whereas fresh eggs settle at a rate of 1.01 x 10(-4) m/sec. Given reported current speeds on the Scotian Shelf off Nova Scotia, Canada, eggs would be transported approximately 50 km in 100 m of water in 12 days before sedimenting on the bottom. Eggs passed 1 m from the bottom would take about 3 hr to settle, and be transported 0.5 km. The size and density of sealworm eggs, and thus their resulting sedimentation rate, may have adaptive value in that they prevent excessive dispersion in space by strong oceanic currents.}, }
@article {pmid9203144, year = {1997}, author = {Peacock, J and Jones, T and Tock, C and Lutz, R}, title = {An in vitro study on the effect of branch points on the stability of coronary artery flow.}, journal = {Medical engineering &amp; physics}, volume = {19}, number = {2}, pages = {101-108}, doi = {10.1016/s1350-4533(96)00046-x}, pmid = {9203144}, issn = {1350-4533}, mesh = {Arteriosclerosis/etiology/pathology/physiopathology ; Biophysical Phenomena ; Biophysics ; Coronary Circulation/*physiology ; Coronary Vessels/*anatomy &amp; histology/*physiology ; Humans ; In Vitro Techniques ; Models, Cardiovascular ; Pulsatile Flow/physiology ; Stroke Volume/physiology ; }, abstract = {Empirical correlations for the onset of turbulence in pulsatile flow through a straight tube and a 45 degrees T-bifurcation are presented. We pumped three different test fluids of kinematic viscosity 0.008-0.035 cm2 s-1 through four straight tubes 0.4-3.0 cm in diameter and three 45 degree T-bifurcations 0.45-2.2 cm in diameter. A Scotch yoke mechanism provided an oscillatory sine wave flow component of known stroke volume and frequency. To determine transition to turbulence, we adjusted the mean flow independently until we detected signal instabilities from hot film or electrochemical wall shear stress probes. The critical peak Reynolds number was found to correlate with two independent dimensionless groups: the Womersley parameter and the Strouhal number. We derived power low functions of these groups to provide an accurate and convenient method of predicting transition in both straight and bifurcating tubes. When compared to pulsatile flow through the straight tube, the presence of flow separation within the 45 degrees T-bifurcation induced flow instabilities at lower values of the peak Reynolds number. The correlation for the 45 degrees T-bifurcation is also a suitable model for predicting transition at coronary branch points, which we previously studied in an in vitro pulse duplicator. Flow instabilities at coronary branch points may play an important role in atherogenesis.}, }
@article {pmid9134307, year = {1997}, author = {Nosovitsky, VA and Ilegbusi, OJ and Jiang, J and Stone, PH and Feldman, CL}, title = {Effects of curvature and stenosis-like narrowing on wall shear stress in a coronary artery model with phasic flow.}, journal = {Computers and biomedical research, an international journal}, volume = {30}, number = {1}, pages = {61-82}, doi = {10.1006/cbmr.1997.1434}, pmid = {9134307}, issn = {0010-4809}, mesh = {Arteriosclerosis/*pathology/*physiopathology ; Biomechanical Phenomena ; Blood Flow Velocity/physiology ; *Computer Simulation ; Coronary Circulation/physiology ; Coronary Vessels/*pathology/*physiopathology ; Humans ; Models, Cardiovascular ; }, abstract = {To gain insight into the details of intracoronary flow we have used computational fluid dynamic techniques to determine the velocity and wall shear stress distributions in both steady- and phasic-flow models of a curved coronary artery with several degrees of stenosis. The steady-flow Reynolds number was 500 and the peak phasic flow Reynolds number was 700. Without stenosis and at 25% (area) stenosis wall shear stress and velocities are higher at the outer wall than the inner wall but retain the same direction as the superimposed flow. At higher stenoses laminar flow separation occurs and the inner wall is exposed to shear stresses that vary widely, both temporally and spatially.}, }
@article {pmid9083850, year = {1997}, author = {Wilquem, F and Degrez, G}, title = {Numerical modeling of steady inspiratory airflow through a three-generation model of the human central airways.}, journal = {Journal of biomechanical engineering}, volume = {119}, number = {1}, pages = {59-65}, doi = {10.1115/1.2796065}, pmid = {9083850}, issn = {0148-0731}, mesh = {Aerosols ; Airway Resistance ; Bias ; Bronchi/*anatomy &amp; histology/*physiology ; Humans ; Linear Models ; *Models, Biological ; *Numerical Analysis, Computer-Assisted ; Particle Size ; Pulmonary Ventilation/*physiology ; Reproducibility of Results ; }, abstract = {Two-dimensional steady inspiratory airflow through a three-generation model of the human central airways is numerically investigated, with dimensions corresponding to those encountered in the fifth to seventh generations of the Weibel's model. Wall curvatures are added at the outer walls of the junctions for physiological purposes. Computations are carried out for Reynolds numbers in the mother branch ranging from 200 to 1200, which correspond to mouth air breathing at flow rates ranging from 0.27 to 1.63 liters per second. The difficulty of generating grids in a so complex configuration is overcome using a nonoverlapping multiblock technique. Simulations demonstrate the existence of separation regions whose number, location, and size strongly depend on the Reynolds number. Consequently, four different flow configurations are detected. Velocity profiles downstream of the bifurcations are shown to be highly skewed, thus leading to an important unbalance in the flow distribution between the medial and lateral branches of the model. These results confirm the observations of Snyder et al. and Tsuda et al. and suggest that a resistance model of flow partitioning based on Kirchhoff's laws is inadequate to simulate the flow behavior accurately within the airways. When plotted in a Moody diagram, airway resistance throughout the model is shown to fit with a linear relation of slope -0.61. This is qualitatively in good agreement with the experimental investigations of Pedley et al, and Slutsky et al.}, }
@article {pmid9083849, year = {1997}, author = {Zhao, Y and Brunskill, CT and Lieber, BB}, title = {Inspiratory and expiratory steady flow analysis in a model symmetrically bifurcating airway.}, journal = {Journal of biomechanical engineering}, volume = {119}, number = {1}, pages = {52-58}, doi = {10.1115/1.2796064}, pmid = {9083849}, issn = {0148-0731}, mesh = {Bias ; Bronchi/*anatomy &amp; histology/*physiology ; *Computer Simulation ; Laser-Doppler Flowmetry ; *Models, Biological ; *Numerical Analysis, Computer-Assisted ; Predictive Value of Tests ; Pulmonary Ventilation/*physiology ; Pulsatile Flow ; Reproducibility of Results ; }, abstract = {Steady inspiratory and expiratory flow in a symmetrically bifurcating airway model was studied numerically using the finite element method (FIDAP). Flows of Reynolds number of 500 and 1000 during inspiration and a flow of Reynolds number of 500 during expiration were analyzed. Since the geometry of the bifurcation model used in this study is exactly the same as the model used in the experimental studies, the computed results were compared to the experimental findings. Results show that most of the important flow features that were observed in the experiment, such as the skewed velocity profiles in the daughter branches during inspiration and velocity peak in the parent tube during expiration, were captured in the numerical simulation. Quantitatively, the computed velocity profiles are in good agreement with the measured profiles. This comparison validates the computational simulations.}, }
@article {pmid9028896, year = {1997}, author = {Keh, HJ and Kuo, J}, title = {Motion of a Colloidal Particle Coated with a Layer of Adsorbed Polymers in a Spherical Cavity.}, journal = {Journal of colloid and interface science}, volume = {185}, number = {2}, pages = {411-423}, doi = {10.1006/jcis.1996.4594}, pmid = {9028896}, issn = {1095-7103}, abstract = {An analytical study is presented for the quasisteady translation and steady rotation of a spherical particle covered by a layer of adsorbed polymers located at the center of a spherical cavity that may also have an adsorbed polymer layer on its inside wall. The Reynolds number is assumed to be small, and the surface polymer layers are assumed to be thin with respect to the particle radius and the spacing between solid surfaces. To solve the Stokes flow equations within and outside the polymer layers a method of matched asymptotic expansions in small parameters lambda1 and lambda2 is used, where lambda1 and lambda2 are the ratios of the polymer-layer length scale to the radius of curvature at the particle surface and at the cavity wall, respectively. The results for the hydrodynamic force and torque exerted on the particle are expressed as an effective hydrodynamic thickness (L) of the adsorbed polymer layer surrounding the particle, which are accurate to O(lambda21). The O(lambda1) term for L normalized by its value in the absence of the cavity is found to be independent of the polymer segment distribution, the hydrodynamic interactions among the segments, and the volume fraction of the segments. The O(lambda21) term for L, however, is a sensitive function of the polymer segment distribution and the volume fraction of the segments. In general, the boundary effects on the motion of a polymer-coated particle can be quite significant in appropriate situations.}, }
@article {pmid9176589, year = {1997}, author = {Chapman, GB and Cokelet, GR}, title = {Model studies of leukocyte-endothelium-blood interactions. II. Hemodynamic impact of leukocytes adherent to the wall of post-capillary vessels.}, journal = {Biorheology}, volume = {34}, number = {1}, pages = {37-56}, doi = {10.1016/S0006-355X(97)00003-6}, pmid = {9176589}, issn = {0006-355X}, support = {HL18208/HL/NHLBI NIH HHS/United States ; }, mesh = {Cell Adhesion/physiology ; Computer Simulation ; Endothelium, Vascular/*physiology ; *Hemodynamics ; Humans ; Leukocytes/*physiology ; *Models, Cardiovascular ; Pressure ; Venules ; }, abstract = {Computational fluid dynamics (CFD) and large scale model experiments were used to analyze the hemodynamic impact of leukocytes adherent to the wall of post-capillary venules. Using a large scale model and, with the aid of a finite element package, solving the Navier Stokes equations for low Reynolds number flow in a cylinder past an adherent sphere, we have developed a dimensionless correlation which permits the estimation of the pressure drop across an adherent leukocyte in an in vivo vessel. This relationship is: f.Re = exp[2.877+4.630 (d/D)4] where f is the Fanning friction factor, Re is the Reynolds number and d/D is the leukocyte to vessel diameter ratio. The friction factor is proportional to the pressure drop across the leukocyte, and does not significantly increase until d/D is greater than 0.5, and then increases rapidly with increasing d/D. Computations indicate that the length of the disturbed flow region generated by an adherent leukocyte increases with decreasing vessel size. The average wall stress in the disturbed flow region remains constant, and equal to the wall stress in the undisturbed region for d/D less than approximately 0.5. For d/D greater than 0.5, the average wall stress in the disturbed flow region increases rapidly with increasing d/D. There is an even larger increase, up to five times greater than the average disturbed stress, in the peak wall stress in the disturbed flow region. This indicates that significant wall stress gradients can be generated by an adherent leukocyte in post-capillary size vessels.}, }
@article {pmid9106151, year = {1997}, author = {Yao, S and Fane, AG and Pope, JM}, title = {An investigation of the fluidity of concentration polarisation layers in crossflow membrane filtration of an oil-water emulsion using chemical shift selective flow imaging.}, journal = {Magnetic resonance imaging}, volume = {15}, number = {2}, pages = {235-242}, doi = {10.1016/s0730-725x(96)00325-6}, pmid = {9106151}, issn = {0730-725X}, mesh = {Emulsions ; Filtration ; *Magnetic Resonance Spectroscopy/methods ; *Membrane Fluidity ; *Membranes, Artificial ; *Oils ; Phantoms, Imaging ; *Water ; }, abstract = {A chemical shift selective NMR flow imaging sequence using stimulated echoes for data acquisition is presented. The sequence was tested using a 20% (vol/vol) oil-water emulsion formed from a soluble cutting oil, which was passed through a simple flow phantom to yield two-dimensional velocity distribution maps of the oil droplets and of the water separately. It was then used to investigate the fluidity of concentration polarisation layers formed from the oil droplets during crossflow membrane filtration of a 5% (vol/vol) emulsion of the same cutting oil. A simple membrane filtration module was used for this purpose, with the feedstock emulsion fed into the lumen of a single tubular membrane at a trans-membrane pressure difference P approximately 70 kPa and crossflow Reynolds number, Re, in the range 100-1000. The results confirm a net axial flow rate < 7.5 microns/s (half digital resolution in the velocity dimension) for the oil polarisation layer. Under these conditions, the upper limit for oil flow tangential to the membrane in the polarised layer is less than 15% of the convective flow of oil towards the membrane.}, }
@article {pmid8962029, year = {1996}, author = {Berg, HC}, title = {Symmetries in bacterial motility.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {93}, number = {25}, pages = {14225-14228}, pmid = {8962029}, issn = {0027-8424}, mesh = {Bacteria/*cytology ; *Bacterial Adhesion ; Fimbriae, Bacterial/*ultrastructure ; }, abstract = {Descriptions are given of three kinds of symmetries encountered in studies of bacterial locomotion, and of the ways in which they are circumvented or broken. A bacterium swims at very low Reynolds number: it cannot propel itself using reciprocal motion (by moving through a sequence of shapes, first forward and then in reverse); cyclic motion is required. A common solution is rotation of a helical filament, either right- or left-handed. The flagellar rotary motor that drives each filament generates the same torque whether spinning clockwise or counterclockwise. This symmetry is broken by coupling to the filament. Finally, bacterial populations, grown in a nutrient medium from an inoculum placed at a single point, usually move outward in symmetric circular rings. Under certain conditions, the cells excrete a chemoattractant, and the rings break up into discrete aggregates that can display remarkable geometric order.}, }
@article {pmid8941129, year = {1996}, author = {Cape, EG and Jones, M and Yamada, I and VanAuker, MD and Valdes-Cruz, LM}, title = {Turbulent/viscous interactions control Doppler/catheter pressure discrepancies in aortic stenosis. The role of the Reynolds number.}, journal = {Circulation}, volume = {94}, number = {11}, pages = {2975-2981}, doi = {10.1161/01.cir.94.11.2975}, pmid = {8941129}, issn = {0009-7322}, mesh = {Animals ; Aortic Valve Stenosis/*diagnostic imaging/*physiopathology ; *Cardiac Catheterization ; *Echocardiography ; *Models, Cardiovascular ; Pressure ; Sheep ; }, abstract = {BACKGROUND: Despite good correlation between Doppler and catheter pressure drops in numerous reports, it is well known that Doppler tends to apparently overestimate pressure drops obtained by cardiac catheterization. Neither (1) simplification of the Bernoulli equation nor (2) pressure recovery effects can explain this dilemma when taken alone. This study addressed the hypothesis that a Reynolds number-based approach, which characterizes (1) and (2), provides a first step toward better agreement of catheter and Doppler assessments of pressure drops.<br><br>METHODS AND RESULTS: Doppler and catheter pressure drops were studied in an in vitro model designed to isolate the proposed Reynolds number effect and in a sheep model with varying degrees of stenosis. Doppler pressure drops in vitro correlated with the directly measured pressure drop for individual valves (r = .935, .960, .985, .984, .989, and .975) but with markedly different slopes and intercepts. A Bland-Altman type plot showed no useful pattern of discrepancy. The Reynolds number was successful in collapsing the data into the profile proposed in the hypothesis. Parallel results were found in the animal model.<br><br>CONCLUSIONS: Apparent overestimation of net pressure drop by Doppler is due to pressure recovery effects, and these effects are countered by both viscous effects and inertial/turbulent effects. Only by reconciliation of discrepancies by use of a quantity such as Reynolds number that embodies the relative importance of competing factors can the noninvasive and invasive methods be connected. This study shows that a Reynolds number-based approach accomplishes this goal both in the idealized in vitro setting and in a biological system.}, }
@article {pmid8919072, year = {1996}, author = {Wong, FS and McFarland, AR and Anand, NK}, title = {An experimental study of aerosol penetration through horizontal tubes and Strom-type loops.}, journal = {Health physics}, volume = {71}, number = {6}, pages = {886-895}, doi = {10.1097/00004032-199612000-00005}, pmid = {8919072}, issn = {0017-9078}, mesh = {*Aerosols ; Computer Simulation ; Equipment Design ; Quality Control ; Radiation Monitoring/instrumentation/methods/*standards ; Radiation Protection/instrumentation/methods/*standards ; United States ; United States Environmental Protection Agency ; }, abstract = {Because some designers of aerosol transport systems use the assumption that aerosol penetration through a system is maximized if the flow Reynolds number is 2,800, we have conducted tests to determine if such an assumption is appropriate. Although we do not believe that optimal performance of an aerosol sample transport system can be presented solely in terms of the Reynolds number, we have presented our results in terms of that parameter to compare our work with the results of an earlier study. Two types of experiments were performed. First, the penetration of liquid aerosol particles through horizontal tubes was experimentally investigated for a range of design and operational conditions. For a particle size of 10 microm aerodynamic diameter, the maximum penetration through a 6.7 mm diameter tube was associated with a Reynolds number of approximately 2,000; the maximum penetration through a tube of 15.9 mm occurred at a Reynolds number of about 3,000; and the maximum penetration through a 26.7 mm diameter tube occurred at about 4,000. It was also experimentally demonstrated that for a fixed flow rate through a horizontal tube, there is an optimum tube diameter for which the aerosol penetration is a maximum. An early study dealing with aerosol particle penetration through a 16.8 mm inside diameter loop of tubing (two vertical tubes, two horizontal tubes and three 90 degrees bends) suggested there was a fixed Reynolds number for optimal aerosol penetration independent of particle size. Those experiments were repeated here and the agreement with those tests is excellent; namely, the maximum penetration through a loop of 15.9 mm diameter tube occurs at a Reynolds number of approximately 2,800, independent of particle size. However, when the tube diameter of the transport system layout was changed to 26.7 mm, the Reynolds number associated with maximum penetration varied for different particle sizes, occurring at Reynolds numbers of approximately 5,600 for 8 microm AD particles, 3,800 for 10 microm particles and 3,000 for 15 microm particles.}, }
@article {pmid8898821, year = {1996}, author = {Ujiie, H and Liepsch, DW and Goetz, M and Yamaguchi, R and Yonetani, H and Takakura, K}, title = {Hemodynamic study of the anterior communicating artery.}, journal = {Stroke}, volume = {27}, number = {11}, pages = {2086-93; discussion 2094}, doi = {10.1161/01.str.27.11.2086}, pmid = {8898821}, issn = {0039-2499}, mesh = {Blood Flow Velocity ; Cerebral Arteries/*physiopathology ; Circle of Willis/physiopathology ; *Hemodynamics ; Humans ; Intracranial Aneurysm/physiopathology ; *Models, Cardiovascular ; Stress, Mechanical ; }, abstract = {BACKGROUND AND PURPOSE: The anterior communicating artery (ACoA) is a site of predilection for intracranial saccular aneurysms causing subarachnoid hemorrhage. ACoA aneurysms are frequently associated with an asymmetrical circle of Willis. In such cases, the ACoA is probably exposed to high hemodynamic stress caused by a considerable shunt flow across the ACoA to the distal segment of the contralateral anterior cerebral artery (ACA). In the present study, the flow pattern and flow-induced shear stress in the ACoA complex that may initiate aneurysmal lesions were studied under steady and pulsatile flow conditions.<br><br>METHODS: Flow visualization was studied with dye injection and birefringent flow visualization in symmetrical and asymmetrical models of various sizes of ACoA. The distribution of wall shear stress was measured using an electrochemical method based on a diffusion-controlled reaction of ferricyanide ion to ferrocyanide ion at a platinum electrode embedded in the wall of the ACoA model.<br><br>RESULTS: With equal flow rate (Reynolds number 150 to 600), vortical flow was formed in the mouth of the ACoA, and no cross flow through the ACoA was observed. The wall shear stress on the mid-wall of the ACoA was almost zero. However, as soon as the flow rate became unequal, a cross flow through the ACoA was observed. The stagnation point also appeared at the medial junction of the ACoA and ACA. The wall shear stress increased to a very high level at the wall of the ACoA and around the stagnation point.<br><br>CONCLUSIONS: Geometric changes from the symmetrical to the asymmetrical ACoA develop higher shear stress on the ACoA than critical values and the stagnation point at the ACoA junction. A combination of these hemodynamic factors is considered to play an important role in initiation of aneurysm.}, }
@article {pmid8887239, year = {1996}, author = {Peattie, RA and Asbury, CL and Bluth, EI and Ruberti, JW}, title = {Steady flow in models of abdominal aortic aneurysms. Part I: Investigation of the velocity patterns.}, journal = {Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine}, volume = {15}, number = {10}, pages = {679-688}, doi = {10.7863/jum.1996.15.10.679}, pmid = {8887239}, issn = {0278-4297}, mesh = {Aorta, Abdominal/*physiopathology ; Aortic Aneurysm, Abdominal/*physiopathology ; *Blood Flow Velocity ; Humans ; Laser-Doppler Flowmetry/*methods ; Models, Anatomic ; Ultrasonography, Doppler, Color/*methods ; }, abstract = {As an investigation into the mechanical factors that lead to rupture of abdominal aortic aneurysms, both color Doppler flow imaging and laser Doppler velocimetry measurements of steady flow through a series of aneurysm models are presented. The flow pattern in each model consisted of a core of relatively fast-moving fluid traveling through the center of the dilation, surrounded by an outer annulus of slowly recirculating fluid. At flow rates below a Reynolds number of 1750 +/- 150, the flow was smooth, steady, and laminar. At higher flow rates (Reynolds number above 2250 +/- 250), the flow was always irregular and turbulent. Between these fully laminar and fully turbulent regimes the flow was intermittently turbulent. Larger models showed a tendency to become turbulent at lower Reynolds numbers than smaller models. In addition, turbulence was amplified in the distal half of the model dilation, with the largest models producing velocity fluctuations as great as 35% of the time-average centerline velocities. These data suggest that larger aneurysms in vivo may be subject to more frequent and intense turbulence than smaller aneurysms. Concomitantly, increased turbulence may contribute significantly to risk of rupture, as is discussed in Part II.}, }
@article {pmid10061888, year = {1996}, author = {Sreenivasan, KR and Stolovitzky, G}, title = {Statistical Dependence of Inertial Range Properties on Large Scales in a High-Reynolds-Number Shear Flow.}, journal = {Physical review letters}, volume = {77}, number = {11}, pages = {2218-2221}, doi = {10.1103/PhysRevLett.77.2218}, pmid = {10061888}, issn = {1079-7114}, }
@article {pmid8872249, year = {1996}, author = {Ditchfield, R and Olbricht, WL}, title = {Effects of particle concentration on the partitioning of suspensions at small divergent bifurcations.}, journal = {Journal of biomechanical engineering}, volume = {118}, number = {3}, pages = {287-294}, doi = {10.1115/1.2796009}, pmid = {8872249}, issn = {0148-0731}, mesh = {Capillaries/*anatomy &amp; histology/*physiology ; Erythrocyte Count ; Erythrocyte Deformability ; Erythrocyte Volume ; Erythrocytes/*cytology ; *Hematocrit ; Hemorheology ; *Models, Cardiovascular ; Particle Size ; Reproducibility of Results ; Suspensions ; Videotape Recording ; }, abstract = {Experimental results are reported for the low Reynolds number flow of a suspension of spherical particles through a divergent capillary bifurcation consisting of a straight tube of circular cross-section that splits to form two tubes of equal diameter. The partitioning of particles between the downstream branches of the bifurcation is measured as a fraction of the partitioning of total volume (particles + suspending fluid) between the branches. Two bifurcation geometries are examined: a symmetric Y-shaped bifurcation and a nonsymmetric T-shaped bifurcation. This experiment focuses on the role of hydrodynamic interactions between particles on the partitioning of particles at the bifurcation. The particle diameter, made dimensionless with respect to the diameter of the branch tubes, ranges from 0.4 to 0.8. Results show that hydrodynamic interactions among the particles are significant at the bifurcation, even for conditions where interactions are unimportant in the straight branches away from the bifurcation. As a result of hydrodynamic interactions among particles at the bifurcation, the partitioning of particles between the branches is affected for particle volume fractions as small as 2 percent. The experimental results show that the effect of particle volume fraction is to diminish the inhomogeneity of particle partitioning at the bifurcation. However, the magnitude of this effect depends strongly on the overall shape of the bifurcation geometry, and, in particular on the angles between the branches.}, }
@article {pmid8872248, year = {1996}, author = {Bluestein, D and Niu, L and Schoephoerster, RT and Dewanjee, MK}, title = {Steady flow in an aneurysm model: correlation between fluid dynamics and blood platelet deposition.}, journal = {Journal of biomechanical engineering}, volume = {118}, number = {3}, pages = {280-286}, doi = {10.1115/1.2796008}, pmid = {8872248}, issn = {0148-0731}, support = {HL46444/HL/NHLBI NIH HHS/United States ; }, mesh = {Aortic Aneurysm, Abdominal/complications/*physiopathology ; Hemorheology ; Humans ; Laser-Doppler Flowmetry ; *Models, Cardiovascular ; *Numerical Analysis, Computer-Assisted ; *Platelet Adhesiveness ; Reproducibility of Results ; Stress, Mechanical ; Thrombosis/etiology ; }, abstract = {Laminar and turbulent numerical simulations of steady flow in an aneurysm model were carried out over Reynolds numbers ranging from 300 to 3600. The numerical simulations are validated with Digital particle Image Velocimetry (DPIV) measurements, and used to study the fluid dynamic mechanisms that characterize aneurysm deterioration, by correlating them to in vitro blood platelet deposition results. It is shown that the recirculation zone formed inside the aneurysm cavity creates conditions that promote thrombus formation and the viability of rupture. Wall shear stress values in the recirculation zone are around one order of magnitude less than in the entrance zone. The point of reattachment at the distal end of the aneurysm is characterized by a pronounced wall shear stress peak. As the Reynolds number increases in laminar flow, the center of the recirculation region migrates toward the distal end of the aneurysm, increasing the pressure at the reattachment point. Under fully turbulent flow conditions (Re = 3600) the recirculation zone inside the aneurysm shrinks considerably. The wall shear stress values are almost one order of magnitude larger than those for the laminar cases. The fluid dynamics mechanisms inferred from the numerical simulation were correlated with measurements of blood platelet deposition, offering useful explanations for the different morphologies of the platelet deposition curves.}, }
@article {pmid8817375, year = {1996}, author = {Hoogstraten, HW and Kootstra, JG and Hillen, B and Krijger, JK and Wensing, PJ}, title = {Numerical simulation of blood flow in an artery with two successive bends.}, journal = {Journal of biomechanics}, volume = {29}, number = {8}, pages = {1075-1083}, doi = {10.1016/0021-9290(95)00174-3}, pmid = {8817375}, issn = {0021-9290}, mesh = {Arteries/*physiology ; Basilar Artery/physiology ; Blood Flow Velocity ; *Computer Simulation ; Hemodynamics/physiology ; Humans ; Laser-Doppler Flowmetry ; *Models, Cardiovascular ; }, abstract = {Blood flow in an artery with two successive bends is simulated by a finite-element computation of steady flow of a Newtonian viscous fluid through a rigid tube having the same shape as a specific part of the femoral artery. Notwithstanding the fact that the bends in the model geometry are rather gentle, the axial and secondary flow patterns, computed for a range of values of the Reynolds number Re, show strong and complicated three-dimensional flow effects. In particular, the flow pattern in the second bend for relatively small values of Re (Re < 240) turns out to be drastically different from that for larger Re-values.}, }
@article {pmid9965091, year = {1996}, author = {Vassilicos, JC and Brasseur, JG}, title = {Self-similar spiral flow structure in low Reynolds number isotropic and decaying turbulence.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {54}, number = {1}, pages = {467-485}, doi = {10.1103/physreve.54.467}, pmid = {9965091}, issn = {1063-651X}, }
@article {pmid8977657, year = {1996}, author = {Hughes, PE and Shortland, AP and How, TV}, title = {Visualization of vortex shedding at the proximal side-to-end artery-graft anastomosis.}, journal = {Biorheology}, volume = {33}, number = {4-5}, pages = {305-317}, doi = {10.1016/0006-355x(96)00024-8}, pmid = {8977657}, issn = {0006-355X}, mesh = {Anastomosis, Surgical ; Arteries/*transplantation ; Graft Occlusion, Vascular/*pathology ; Guanine/*physiology ; Humans ; Models, Biological ; Pulsatile Flow ; Regional Blood Flow ; Video Recording ; }, abstract = {The motion of guanine particles was recorded by video to visualize transitional flow phenomena in models of a proximal side-to-end anastomosis. Close examination of successive video fields revealed that above a critical Reynolds number, particles were periodically shed into the graft from a vortex situated near the anastomosis heel, and this disturbed the flow patterns in the graft causing vortex shedding to occur near to the toe of the anastomosis. The images clearly demonstrated that periodic flow structures propagated distally along the graft for over 15 tube diameters from the proximal anastomosis. The frequency of the vortex shedding was found to increase with Reynolds number. Under pulsatile conditions, the primary vortex at the heel of the anastomosis became unstable during the deceleration phase of the flow cycle and particles were shed downstream into the graft. Although it was possible briefly to observe the characteristic banded structure in the bypass graft, the flow patterns were highly three-dimensional and were quickly broken up by the accelerating flow. Dynamic flow visualization using guanine particles was found to be a complementary technique to particle tracer flow visualization and was highly effective in identifying transitional flow phenomena and the mass transport mechanisms associated with them.}, }
@article {pmid11607688, year = {1996}, author = {Barenblatt, GI and Chorin, AJ}, title = {Small viscosity asymptotics for the inertial range of local structure and for the wall region of wall-bounded turbulent shear flow.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {93}, number = {13}, pages = {6749-6752}, doi = {10.1073/pnas.93.13.6749}, pmid = {11607688}, issn = {0027-8424}, abstract = {The small viscosity asymptotics of the inertial range of local structure and of the wall region in wallbounded turbulent shear flow are compared. The comparison leads to a sharpening of the dichotomy between Reynolds number dependent scaling (power-type) laws and the universal Reynolds number independent logarithmic law in wall turbulence. It further leads to a quantitative prediction of an essential difference between them, which is confirmed by the results of a recent experimental investigation. These results lend support to recent work on the zero viscosity limit of the inertial range in turbulence.}, }
@article {pmid8817954, year = {1996}, author = {Tamagawa, M and Akamatsu, T and Saitoh, K}, title = {Prediction of hemolysis in turbulent shear orifice flow.}, journal = {Artificial organs}, volume = {20}, number = {6}, pages = {553-559}, pmid = {8817954}, issn = {0160-564X}, mesh = {Blood Flow Velocity/*physiology ; Erythrocytes/cytology ; Fluid Shifts ; Heart-Assist Devices/*standards ; Hemoglobins/analysis ; *Hemolysis ; Humans ; Models, Theoretical ; Rheology ; Stress, Mechanical ; }, abstract = {This study proposes a method of predicting hemolysis induced by turbulent shear stress (Reynolds stress) in a simplified orifice pipe flow. In developing centrifugal blood pumps, there has been a serious problem with hemolysis at the impeller or casing edge; because of flow separation and turbulence in these regions. In the present study, hemolysis caused by turbulent shear stress must occur at high shear stress levels in regions near the edge of an orifice pipe flow. We have computed turbulent shear flow using the low-Reynolds number k-epsilon model. We found that the computed turbulent shear stress near the edge was several hundreds times that of the laminar shear stress (molecular shear stress). The peak turbulent shear stress is much greater than that obtained in conventional hemolysis testing using a viscometer apparatus. Thus, these high turbulent shear stresses should not be ignored in estimating hemolysis in this blood flow. Using an integrated power by shear force, it is optimal to determine the threshold of the turbulent shear stress by comparing computed stress levels with those of hemolysis experiments or pipe orifice blood flow.}, }
@article {pmid8796701, year = {1996}, author = {Daniel, BL and Rubin, JM and Fowlkes, JB and Williams, DM and Adler, RS}, title = {The hemodynamics of transjugular intrahepatic portosystemic shunts: investigations with Doppler sonography and development of an in vitro model.}, journal = {Academic radiology}, volume = {3}, number = {6}, pages = {455-462}, doi = {10.1016/s1076-6332(96)80001-8}, pmid = {8796701}, issn = {1076-6332}, mesh = {Blood Flow Velocity/physiology ; Equipment Design ; Graft Occlusion, Vascular/diagnostic imaging/surgery ; Hemodynamics/*physiology ; Humans ; In Vitro Techniques ; Jugular Veins/*diagnostic imaging ; *Models, Cardiovascular ; Models, Theoretical ; Phantoms, Imaging ; Portasystemic Shunt, Surgical/*instrumentation ; Postoperative Complications/*diagnostic imaging/surgery ; Reference Values ; Reoperation ; Retrospective Studies ; Stents ; *Ultrasonography, Doppler ; }, abstract = {RATIONALE AND OBJECTIVES: We evaluated Doppler sonography-based measurements of transjugular intrahepatic portosystemic shunt (TIPS) function and developed an in vitro model of normal TIPS hemodynamics.<br><br>METHODS: We reviewed retrospectively the results of all trans-TIPS manometries (N = 116) performed during a 24-month period. Portosystemic pressure gradient was compared with peak stent velocity as measured by angle-corrected Doppler sonography. A flow phantom simulating TIPS was created using 8-, 10-, and 12-mm-diameter wire-mesh stents placed in cylindrical channels with lengths ranging from 3.4 to 6.0 cm.<br><br>RESULTS: Among 50 trans-TIPS manometries with corresponding Doppler sonography performed on well-functioning shunts, measured portosystemic pressure gradient and peak velocity were not correlated (R2 = .014). On the basis of a regression of measurements in the flow phantom, pressure loss in a stented cylindrical channel was estimated as follows: delta p = rho.(0.145 -0.001.Rey + 0.816.L/D).(Vmean2/2), where rho is the fluid density, Rey is the Reynolds number, L is the channel length, D is the stent diameter, and Vmean is the time-averaged velocity within the stent. Predicted and measured pressure gradients were correlated (R2 = .91).<br><br>CONCLUSION: Peak velocity in patients with a normally functioning TIPS does not predict the magnitude of the portosystemic pressure gradient.}, }
@article {pmid8707787, year = {1996}, author = {King, MJ and Corden, J and David, T and Fisher, J}, title = {A three-dimensional, time-dependent analysis of flow through a bileaflet mechanical heart valve: comparison of experimental and numerical results.}, journal = {Journal of biomechanics}, volume = {29}, number = {5}, pages = {609-618}, doi = {10.1016/0021-9290(95)00107-7}, pmid = {8707787}, issn = {0021-9290}, support = {//Wellcome Trust/United Kingdom ; }, mesh = {Aorta/anatomy &amp; histology/physiology ; *Aortic Valve/anatomy &amp; histology/physiology ; Blood Flow Velocity ; Forecasting ; *Heart Valve Prosthesis ; Heart Ventricles/anatomy &amp; histology ; *Hemorheology ; Humans ; Models, Cardiovascular ; Models, Structural ; Prosthesis Design ; Pulsatile Flow ; Regional Blood Flow ; Sinus of Valsalva/anatomy &amp; histology/physiology ; Systole ; Ventricular Function ; }, abstract = {The flow through a bileaflet mechanical heart valve during the first half of systole was predicted using computational fluid dynamics (CFD). A three-dimensional model of the geometry of the ventricle, valve, sinus and aorta was developed. Flow through the valve was assumed to be Newtonian and laminar. The peak systolic Reynolds number was 1500 based on the aortic radius and the mean aortic velocity. Flow visualisation and laser Doppler anemometry (LDA) experiments were performed and the results were compared to the CFD model. Good agreement between the LDA measurements and CFD predictions was found in the jets through the major orifices of the valve. The global flow fields predicted by the CFD showed reasonable agreement with the flow visualisation. A starting vortex was shed from the valve leaflets of the CarboMedics valve and the prototype valve. As systole progressed the two major orifice jets were directed towards the aortic wall and a weaker central jet was seen in both the experimental and CFD models. Large vortices were present on either side of the central orifice jet in the sinus area of both models. The three-dimensional time-dependent CFD model was considered to give a reasonable indication of the dominant flow patterns downstream of the bileaflet heart valve and has the potential to be an extremely useful tool to analyse the different designs of existing and future bileaflet valves.}, }
@article {pmid10060655, year = {1996}, author = {Reyl, C and Antonsen, TM and Ott, E}, title = {Nature of magnetic dynamo growth in the high magnetic Reynolds number limit.}, journal = {Physical review letters}, volume = {76}, number = {13}, pages = {2270-2273}, doi = {10.1103/PhysRevLett.76.2270}, pmid = {10060655}, issn = {1079-7114}, }
@article {pmid8679960, year = {1996}, author = {Chapman, G and Cokelet, G}, title = {Model studies of leukocyte-endothelium-blood interactions. I. The fluid flow drag force on the adherent leukocyte.}, journal = {Biorheology}, volume = {33}, number = {2}, pages = {119-138}, doi = {10.1016/0006-355X(96)00011-X}, pmid = {8679960}, issn = {0006-355X}, support = {HL 18208/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; *Blood Physiological Phenomena ; Cell Adhesion/physiology ; Endothelium, Vascular/*physiology ; Hemorheology ; Humans ; Leukocytes/*physiology ; *Models, Biological ; Regional Blood Flow ; }, abstract = {Using a large scale model and the concept of dimensional similarity, we have developed a dimensionless correlation which permits the estimation of the drag force of blood flow in an in vivo vessel on a leukocyte adherent to the vessel wall. This relationship is [formula: see text] where Re is a Reynolds number, Cd is a drag coefficient, and d/D is the leukocyte-to-vessel diameter ratio. This function increases rapidly with increasing d/D when d/D is greater than 0.5. A relationship between the drag force on the leukocyte, Ff, and the commonly used wall shear stress in the absence of the adherent cell, tau w, has also been developed, and is given by [formula: see text] This study shows that the discrepancy between the in vivo and in vitro critical wall stresses (above which leukocytes do not adhere to endothelial cell layers) is not due to misrepresentation of the corresponding drag forces on the leukocytes. The discrepancy must be due to real differences in the flow and/or cellular conditions between the in vivo and in vitro experiments.}, }
@article {pmid8678361, year = {1996}, author = {Winoto, SH and Shah, DA and Liu, H}, title = {Estimation of turbulent shear stress in free jets: application to valvular regurgitation.}, journal = {Annals of biomedical engineering}, volume = {24}, number = {2}, pages = {321-327}, pmid = {8678361}, issn = {0090-6964}, mesh = {Blood Flow Velocity/physiology ; Heart Valve Diseases/*physiopathology ; Hemodynamics/physiology ; Humans ; *Models, Cardiovascular ; Pulsatile Flow ; Stress, Mechanical ; }, abstract = {In an attempt to better assess the severity of valvular regurgitation, an in-vitro experiment has been conducted to estimate turbulent shear stress levels within free jets issuing from different orifice shapes and sizes by means of hot-wire anemometry. On the basis of the measured mean velocities and the jet profiles, the distributions of the normalized kinematic turbulent shear stress (uv/Um2) were estimated for different jets by using an equation available for self-preserving circular jet. The results indicate that the equation can estimate the distributions of uv/Um2 independent of the orifice shape and Reynolds number of the jet. For the range of Reynolds numbers considered, the estimation of maximum turbulent shear stress inferred from these distributions suggests that the critical shear stress level of approximately 200 N/m2, corresponding to destruction of blood cells, is exceeded for typical blood flow velocity of 5 m/s at the valvular lesion.}, }
@article {pmid9964423, year = {1996}, author = {Tabeling, P and Zocchi, G and Belin, F and Maurer, J and Willaime, H}, title = {Probability density functions, skewness, and flatness in large Reynolds number turbulence.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {53}, number = {2}, pages = {1613-1621}, doi = {10.1103/physreve.53.1613}, pmid = {9964423}, issn = {1063-651X}, }
@article {pmid9964307, year = {1996}, author = {Peterson, MA}, title = {Membrane hydrodynamics at low Reynolds number.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {53}, number = {1}, pages = {731-738}, doi = {10.1103/physreve.53.731}, pmid = {9964307}, issn = {1063-651X}, }
@article {pmid9496765, year = {1996}, author = {Hrncír, E}, title = {Flow resistance of airways under hyperbaric conditions.}, journal = {Physiological research}, volume = {45}, number = {2}, pages = {153-158}, pmid = {9496765}, issn = {0862-8408}, mesh = {*Air Pressure ; Airway Resistance/*physiology ; Gases ; Humans ; Models, Biological ; Trachea/anatomy &amp; histology/physiology ; Viscosity ; }, abstract = {Based on the known relations governing flow resistance of a tube during laminar and turbulent flow and the value of the so-called Reynold's number the following conclusions were derived: 1. The flow resistance of airways increases under hyperbaric conditions because a) the turbulent flow participates in the airways to a greater extent due to its gradual extension to minor airways, and b) during turbulent flow the flow resistance is directly proportional to the pressure of the inhaled gas. 2. If the pressure in the surrounding environment increases n-times, this has an impact on the distribution of laminar and turbulent flow in the airways and their flow resistance, similarly as if the flow rates would increase n-times under normobaric conditions. 3. Dynamic indicators of lung ventilation corresponding to higher flow rates (e.g. PEF - peak expiratory flow) are reduced under hyperbaric conditions to a greater extent than the dynamic parameters corresponding to lower flow rates (e.g. FMEF25-75 - forced midexpiratory flow) determined usually by conditions in the minor airways, where the flow usually remains laminar or intermediate.}, }
@article {pmid9320660, year = {1996}, author = {Pennycuick, C and Klaassen, M and Kvist, A and Lindstr&amp;Ouml;M, &amp;Aring;}, title = {Wingbeat frequency and the body drag anomaly: wind-tunnel observations on a thrush nightingale (Luscinia luscinia) and a teal (Anas crecca).}, journal = {The Journal of experimental biology}, volume = {199}, number = {Pt 12}, pages = {2757-2765}, doi = {10.1242/jeb.199.12.2757}, pmid = {9320660}, issn = {1477-9145}, abstract = {A teal (Anas crecca) and a thrush nightingale (Luscinia luscinia) were trained to fly in the Lund wind tunnel for periods of up to 3 and 16 h respectively. Both birds flew in steady flapping flight, with such regularity that their wingbeat frequencies could be determined by viewing them through a shutter stroboscope. When flying at a constant air speed, the teal's wingbeat frequency varied with the 0.364 power of the body mass and the thrush nightingale's varied with the 0.430 power. Both exponents differed from zero, but neither differed from the predicted value (0.5) at the 1 % level of significance. The teal continued to flap steadily as the tunnel tilt angle was varied from -1 &amp;deg; (climb) to +6 &amp;deg; (descent), while the wingbeat frequency declined progressively by about 11 %. In both birds, the plot of wingbeat frequency against air speed in level flight was U-shaped, with small but statistically significant curvature. We identified the minima of these curves with the minimum power speed (Vmp) and found that the values predicted for Vmp, using previously published default values for the required variables, were only about two-thirds of the observed minimum-frequency speeds. The discrepancy could be resolved if the body drag coefficients (CDb) of both birds were near 0.08, rather than near 0.40 as previously assumed. The previously published high values for body drag coefficients were derived from wind-tunnel measurements on frozen bird bodies, from which the wings had been removed, and had long been regarded as anomalous, as values below 0.01 are given in the engineering literature for streamlined bodies. We suggest that birds of any size that have well-streamlined bodies can achieve minimum body drag coefficients of around 0.05 if the feet can be fully retracted under the flank feathers. In such birds, field observations of flight speeds may need to be reinterpreted in the light of higher estimates of Vmp. Estimates of the effective lift:drag ratio and range can also be revised upwards. Birds that have large feet or trailing legs may have higher body drag coefficients. The original estimates of around CDb=0.4 could be correct for species, such as pelicans and large herons, that also have prominent heads. We see no evidence for any progressive reduction of body drag coefficient in the Reynolds number range covered by our experiments, that is 21 600&amp;shy;215 000 on the basis of body cross-sectional diameter.}, }
@article {pmid9319792, year = {1996}, author = {Dudley, R and Chai, P}, title = {Animal flight mechanics in physically variable gas mixtures.}, journal = {The Journal of experimental biology}, volume = {199}, number = {Pt 9}, pages = {1881-1885}, doi = {10.1242/jeb.199.9.1881}, pmid = {9319792}, issn = {1477-9145}, abstract = {Empirical studies of animal flight performance have generally been implemented within the contemporary atmosphere. Experimental alteration of the physical composition of gas mixtures, however, permits construction of novel flight media and the non-invasive manipulation of flight biomechanics. For example, replacement of atmospheric nitrogen with various noble gases results in a tenfold variation in air density at a constant oxygen concentration. Such variation in air density correspondingly elicits extraordinary biomechanical effort from flying animals; hummingbirds and euglossine orchid bees hovering in such low-density but normoxic mixtures have demonstrated exceptionally high values for the mechanical power output of aerobic flight muscle. As with mechanical power, lift coefficients during hovering increase at low air densities in spite of a concomitant decline in the Reynolds number of the wings. The physical effects of variable gas density may also be manifest in morphological and physiological adaptations of animals to flight across altitudinal gradients. Global variation in atmospheric composition during the late Paleozoic may also have influenced the initial evolution and subsequent diversification of ancestral pterygotes. For the present-day experimenter, the use of physically variable flight media represents a versatile opportunity to explore the range of kinematic and aerodynamic modulation available to flying animals.}, }
@article {pmid9319105, year = {1996}, author = {Liu, H and Wassersug, R and Kawachi, K}, title = {A computational fluid dynamics study of tadpole swimming.}, journal = {The Journal of experimental biology}, volume = {199}, number = {Pt 6}, pages = {1245-1260}, doi = {10.1242/jeb.199.6.1245}, pmid = {9319105}, issn = {1477-9145}, abstract = {The hydrodynamics and undulating propulsion of tadpoles were studied using a newly developed two-dimensional computational fluid dynamics (CFD) modeling method. The mechanism of thrust generation associated with the flow patterns during swimming is discussed. Our CFD analysis shows that the kinematics of tadpoles is specifically matched to their special shape and produces a jet-stream propulsion with high propulsive efficiency, as high as that achieved by teleost fishes. Investigation of the effect of Reynolds number indicates that the Froude efficiency increases with increasing Reynolds number with no ceiling in generating the jet-stream propulsion. Further studies using tadpole- and fish-shaped models with hindlimbs added to their body profiles reveal that the tadpole shape &amp;shy; a globose head with a tapered tail and hindlimbs at the base of the tail &amp;shy; allows tadpoles, but not fish, to develop hindlimbs with very little handicap on propulsion. The shapes and kinematics of tadpoles appear to be specially adapted to the requirement of these organisms to transform into frogs.}, }
@article {pmid8672664, year = {1996}, author = {Shandas, R and Kwon, J}, title = {Digital particle image velocimetry (DPIV) measurements of the velocity profiles through bileaflet mechanical valves: in vitro steady.}, journal = {Biomedical sciences instrumentation}, volume = {32}, number = {}, pages = {161-167}, pmid = {8672664}, issn = {0067-8856}, mesh = {*Blood Flow Velocity ; *Heart Valve Prosthesis ; Hemorheology ; Humans ; *Image Processing, Computer-Assisted ; In Vitro Techniques ; Laser-Doppler Flowmetry ; }, abstract = {Although velocity profiles downstream of mechanical valves have been measured in-vitro using Laser Doppler Anemometry (LDA), these studies have not measured velocities in the immediate proximity of the leaflets since the LDA technique prevents velocities from being measured in the immediate vicinity of any structure. Laser based Digital Particle Image Velocimetry (DPIV) is a new technique that allows for accurate measurement of an entire two-dimensional velocity field with no beam angulation. DPIV was used to measure two-component velocity vectors immediately proximal and distal to a 25 mm bileaflet mechanical valve (St. Jude) mounted in a transparent steady flow in-vitro model. Measurements of flow similar in Reynolds number (Re) to mitral inflow (Re = 2000-4000) showed clear hemi-elliptical isovelocity convergence zones proximal to each of the three orifices. DPIV measurements of flow distal to the orifice revealed clear vortex rollups generated from the internal ring of the valve with separate velocity profiles immediately distal to the leaflets. These studies prove the feasibility of the DPIV technique to provide accurate velocity measurements of flow profiles through mechanical valves.}, }
@article {pmid8548419, year = {1996}, author = {Yamamoto, T and Ogasawara, Y and Kimura, A and Tanaka, H and Hiramatsu, O and Tsujioka, K and Lever, MJ and Parker, KH and Jones, CJ and Caro, CG and Kajiya, F}, title = {Blood velocity profiles in the human renal artery by Doppler ultrasound and their relationship to atherosclerosis.}, journal = {Arteriosclerosis, thrombosis, and vascular biology}, volume = {16}, number = {1}, pages = {172-177}, doi = {10.1161/01.atv.16.1.172}, pmid = {8548419}, issn = {1079-5642}, mesh = {Adult ; Aged ; Aorta, Abdominal/pathology ; Arteriosclerosis/pathology/*physiopathology ; Blood Flow Velocity ; Blood Pressure ; Female ; Humans ; *Laser-Doppler Flowmetry ; Male ; Middle Aged ; Renal Artery/pathology/*physiopathology ; }, abstract = {Blood velocity profiles were measured in the renal branch (diameter 5.9 +/- 1.3 mm) of the aortorenal bifurcation using a 20-MHz 80-channel pulsed Doppler velocimeter during retroperitoneal surgery in 10 patients. The peak Reynolds number was 1145 +/- 140 and the frequency parameter (Wormersley parameter) was 3.0 +/- 0.8. Immediately distal to the ostium of the renal artery, reverse flow, indicating flow separation, was observed near the cranial wall mainly during the first part of the cardiac cycle. There were flows from the cranial to the caudal side of the artery at this location, indicating the presence of strong secondary flows. Two diameters downstream of the ostium, the velocity profiles were skewed to the caudal side in all patients. Four diameters downstream, the flow profile was symmetrical (3 patients) or only slightly skewed (7 patients) and virtually parabolic throughout the cardiac cycle. These observations mean that the flow on the cranial side of the renal branch of the human aortorenal bifurcation is characterized by (1) a bidirectional oscillation of the flow, (2) separation of the flow during systole, and (3) low time-averaged shear rate. These blood velocity patterns may be related to the localization and development of atheromatous plaque that occurs preferentially in this region of the renal artery. Conversely, the unidirectional, axisymmetrical flow found in more distal parts of the renal artery are associated with a very low incidence of lesions.}, }
@article {pmid10163664, year = {1996}, author = {Zhang, L and Asgharian, B and Anjilvel, S}, title = {Inertial and interceptional deposition of fibers in a bifurcating airway.}, journal = {Journal of aerosol medicine : the official journal of the International Society for Aerosols in Medicine}, volume = {9}, number = {3}, pages = {419-430}, doi = {10.1089/jam.1996.9.419}, pmid = {10163664}, issn = {0894-2684}, mesh = {Airway Resistance ; Bronchi/anatomy &amp; histology/*physiology ; *Computer Simulation ; Lung/*anatomy &amp; histology/*physiology ; *Mineral Fibers/analysis ; }, abstract = {A computer model of a three-dimensional bifurcating airway was constructed in which the parent and daughter airways had different lengths but equal diameters. A diameter of 0.6 cm was chosen for the airways based on the third generation of Weibel's symmetric lung model. Different bifurcation angles of 60 degrees, 90 degrees, and 120 degrees were studied. Airflow fields in the airway were obtained by a finite-element method (FIDAP, Fluid Dynamics International, Evanston, IL) for Reynolds numbers of 500 and 1000, assuming uniform parent inlet velocities. The equations of motion for fiber transport in the airways were obtained, and deposition by the combined mechanisms of impaction and interception was incorporated. A computer code was developed that utilized the flow field data and calculated fiber transport in the airways using the equations of motion for fibers. Deposition efficiency was obtained by simulating a large number of fibers of various sizes. Fiber entering the daughter airways tended to orient themselves parallel to the flow. A site of enhanced deposition (or hot spot) was observed at the carina. The dominant parameter for the deposition was the fiber Stokes number. Flow Reynolds number and airway bifurcation angle were also found to affect the deposition.}, }
@article {pmid10163663, year = {1996}, author = {Tsuda, A and Henry, FS and Otani, Y and Haber, S and Butler, JP}, title = {Aerosol transport and deposition in the rhythmically expanding pulmonary acinus.}, journal = {Journal of aerosol medicine : the official journal of the International Society for Aerosols in Medicine}, volume = {9}, number = {3}, pages = {389-408}, doi = {10.1089/jam.1996.9.389}, pmid = {10163663}, issn = {0894-2684}, support = {HL47428/HL/NHLBI NIH HHS/United States ; HL54885/HL/NHLBI NIH HHS/United States ; }, mesh = {Administration, Inhalation ; Aerosols/administration &amp; dosage/*pharmacokinetics ; Humans ; Models, Theoretical ; Pulmonary Alveoli/anatomy &amp; histology/*drug effects/*physiology ; Research Design ; Respiratory Mechanics/drug effects/physiology ; Respiratory Transport/*drug effects/physiology ; }, abstract = {Little is known about factors controlling the dynamics of aerosol dispersion and deposition in the lung periphery, though this knowledge becomes increasingly important in many fields such as environmental and occupational exposure, diagnostic applications, and therapeutic deliver of drugs via aerosols. For the last several years, we have been studying aerosol behavior in the pulmonary acinus, where the airway structure and the associated fluid mechanics are distinctly different from those in the conducting airways. Our major research efforts have been focused on the basic physics underlying acinar fluid mechanics and particle dynamics, which are likely to be conditioned by the two key geometric factors of acinar airways: structural alveolation and rhythmic expansion and contraction of the alveolar walls. A combination of computational and experimental analyses revealed that due to these unique geometric features acinar flow can be extremely complex despite the low Reynolds number, and can have substantial effects on particle dynamics. In particular, chaotic mixing can occur in the lung periphery. In the course of such a mixing process, the inhaled aerosol particles quickly mix with the residual alveolar gas in a manner that is radically different from the previously considered classical diffusion process. The objective of this paper is to briefly review our current understanding of these processes, to discuss existing deposition models, and to describe our ongoing research efforts toward a basic understanding of aerosol behavior in the pulmonary acinus.}, }
@article {pmid8564156, year = {1995}, author = {Dubini, G and Pietrabissa, R and Montevecchi, FM}, title = {Fluid-structure interaction problems in bio-fluid mechanics: a numerical study of the motion of an isolated particle freely suspended in channel flow.}, journal = {Medical engineering &amp; physics}, volume = {17}, number = {8}, pages = {609-617}, doi = {10.1016/1350-4533(95)00019-j}, pmid = {8564156}, issn = {1350-4533}, mesh = {Algorithms ; Biomechanical Phenomena ; Blood Viscosity ; *Computer Simulation ; Erythrocytes/physiology ; Humans ; Microcirculation/physiology ; *Models, Cardiovascular ; Software ; Software Design ; Time Factors ; }, abstract = {In this paper a problem belonging to the moving boundary class is tackled with a 2-D application of computational fluid dynamics techniques. The motion of an isolated rigid particle freely suspended in an incompressible Newtonian fluid in a narrow channel is studied numerically at a low Reynolds number, yet different from zero. The actual problem consists of two coupled problems: the motion of the viscous fluid and that of the rigid particle suspended and convected with the fluid. The full Navier-Stokes equations (i.e. both transient and convective terms are included) are solved in the fluid domain by means of the finite element method, while the motion of the particle is determined on the basis of a rigid act of motion. Results from simulations corresponding to differential initial positions of the particle are shown in this paper: they allow one to study the rotational motions of the particle as well as its displacements. The goal of the paper is to analyse the lateral displacement behaviour of the particle, already observed in experimental studies in microcirculation. In particular, lateral migrations are supposed to be due to inertial forces acting in the fluid around the moving particle combined with the proximity of the resting wall (wall effect). Preliminary results are in fairly good agreement with those available in the literature.}, }
@article {pmid8748527, year = {1995}, author = {Adabala, RR and Srinivasan, U}, title = {Peristaltic pumping in a circular tube in the presence of an eccentric catheter.}, journal = {Journal of biomechanical engineering}, volume = {117}, number = {4}, pages = {448-454}, doi = {10.1115/1.2794206}, pmid = {8748527}, issn = {0148-0731}, mesh = {*Catheters, Indwelling ; Humans ; Manometry ; Models, Anatomic ; *Models, Theoretical ; Peristalsis/*physiology ; }, abstract = {The influence of an eccentrically inserted catheter on the peristaltic pumping in a tube is investigated under long wavelength, low Reynolds number assumptions. The radially asymmetric deformation of the wall arising through an eccentrically inserted catheter is taken into consideration by choosing an appropriate bipolar coordinate system. The effect of the position and size of the catheter on pumping characteristics is studied. The best performance of pumping is noticed at a certain position of the catheter. The size of the catheter, when placed eccentrically, alters the pressure signature significantly inside the bolus, unlike the concentric case discussed by Lykoudis and Roos (1971). Further, the maximum pressure rise in one period of the peristaltic wave is observed to decrease with an increase in the eccentricity.}, }
@article {pmid8748526, year = {1995}, author = {Carr, RT and Kotha, SL}, title = {Separation surfaces for laminar flow in branching tubes--effect of Reynolds number and geometry.}, journal = {Journal of biomechanical engineering}, volume = {117}, number = {4}, pages = {442-447}, doi = {10.1115/1.2794205}, pmid = {8748526}, issn = {0148-0731}, mesh = {Biomechanical Phenomena ; *Environment, Controlled ; Hemodynamics/*physiology ; Humans ; *Models, Theoretical ; Pulmonary Ventilation/*physiology ; }, abstract = {Flow visualization experiments of Newtonian laminar flow through branching tubes have been performed to identify the shape of the separation surface or flow divider. The influences of Reynolds number, flow fraction into the side branch, and branch geometry on the separation surface shape have been considered. The shapes presented in this paper are formed by the intersection of the separation surface with the cross section of the parent tube. At low Re the separation surfaces are curved in a convex manner, bulging away from the opening of the side branch. Increasing Re causes the surface to become concave. At Re > 194 the surfaces can become closed for Q* > 0.3. The branch angle has no noticeable effect on the separation surface shape. The side to parent branch diameter ratio, Db/Dp, has a strong influence at low Re. As Re increases the diameter effect diminishes. Previous studies have shown no difference between the separation surfaces of T and Y type junctions at low Re. At Re = 194 there is a marked difference between the separation surfaces of T and Y bifurcations.}, }
@article {pmid8746940, year = {1995}, author = {Wellnhofer, E and Biamino, G and Sauer, HU and Trebeljahr, A and Stalke, J and Ragg, C and Oswald, H and Gotze, S and Fleck, E and Felix, R}, title = {Changes of fluid-dynamic parameters in peripheral stenoses with transcutaneous interventions.}, journal = {European heart journal}, volume = {16 Suppl J}, number = {}, pages = {60-70}, doi = {10.1093/eurheartj/16.suppl_j.60}, pmid = {8746940}, issn = {0195-668X}, mesh = {Adult ; Aged ; Aged, 80 and over ; Angiography ; *Angioplasty, Balloon, Laser-Assisted ; Blood Flow Velocity ; Blood Viscosity ; Exercise Test ; Female ; Humans ; Male ; Middle Aged ; Peripheral Vascular Diseases/diagnosis/*physiopathology/therapy ; Ultrasonography, Interventional ; }, abstract = {UNLABELLED: Peripheral vessels provide a useful in vivo haemodynamic model allowing evaluation of local intravascular fluid dynamics. Velocity measurements using a 0.018 inch Doppler-tipped angioplasty guidewire, quantitative angiography and laboratory data were gathered from 45 patients with a total of 48 percutaneous transluminal laser assisted angioplasties (PTLA) in the superficial femoral, in the iliac, in the popliteal artery and in the peroneal artery. From these data, blood flow, whole blood viscosity, Reynold's numbers, Womersley numbers and shear stress were calculated, evaluated as to their changes post PTLA and correlated with clinical improvement at early follow-up. The clinical result was quantified as categorial improvement according to the American Heart Association guidelines. The primary angiographic results of angioplasty were satisfactory in all patients. Clinically 17/45 patients showed a marked, 6/45 a moderate, 18/45 a minimal, and 4/45 no improvement. The mean values of maximal peak velocity at stenosis decreased from 235 +/- 28 cms-1 to 84 +/- 8 cms-1 after PTLA (P < 0.01). The minimal intrastenotic cross section increased from 7.7 +/- 0.9 to 21.9 +/- 1.6 mm2 (P < 0.01). Mean trans-stenotic flow increased after intervention by about 50% (P < 0.01) and improved further by 135% after administration of adenosine triphosphosphate i.a. (P < 0.01). Reynold's numbers were elevated intrastenotically (1285 +/- 198) pre-intervention as compared to values proximal (564 +/- 81) and distal (449 +/- 66) to the stenosis and were reduced significantly (P < 0.05) at stenosis by PTLA, whereas values proximally and distally increased significantly (P < 0.01) post PTLA (proximal 829 +/- 84, intra 773 +/- 107, distal 676 +/- 98). Shear stress, reflecting mechanical interaction between flow and vessel wall, was elevated at stenosis pre-intervention to 44 +/- 8.9 Pa and reduced at post-stenoric vessel sites to 2.4 +/- 0.5 Pa. PTLA caused a decrease in stenosis to 6.3 +/- 1 Pa (P < 0.01) and an increase distally to 4.6 +/- 1 Pa (P < 0.01). Whereas in single stenoses removal of the obstruction was associated with a significant (P < 0.05) increase in trans-stenotic flow and shear stress distally, there was only auenuated increase in trans-stenotic flow in multiple lesions despite an angiographically good PTLA result. Shear stress distally remained low in those patients. Velocities and Reynold's numbers were lower in these vessels even pre PTLA. Residual flow, Reynold's number and minimal cross-section pre-intervention correlated significantly with clinical outcome. Pooling cases with no or minimal, as opposed to those with marked or moderate improvement, 81% of patients were correctly classified using the Reynold's numbers pre- and post-PTLA.<br><br>CONCLUSION: Peak velocity monitoring is feasible and safe during angioplasty. Velocity provides clinically relevant physiological information in addition to angiography. Combining quantitative angiography, velocity measurements and laboratory data allow the calculation of blood flow, Reynold's numbers and shear stress, thereby providing complex fluid dynamic information. Thus the evaluation of haemo-dynamics in single and multiple obstructions before and after intervention is improved. Fluid dynamic parameters pre-and post-PTLA are significantly correlated with clinical short-term result.}, }
@article {pmid8559308, year = {1995}, author = {Burleson, AC and Strother, CM and Turitto, VT}, title = {Computer modeling of intracranial saccular and lateral aneurysms for the study of their hemodynamics.}, journal = {Neurosurgery}, volume = {37}, number = {4}, pages = {774-82; discussion 782-4}, doi = {10.1227/00006123-199510000-00023}, pmid = {8559308}, issn = {0148-396X}, support = {29019//PHS HHS/United States ; }, mesh = {Aneurysm, Ruptured/*physiopathology ; Blood Flow Velocity/physiology ; Brain/*blood supply ; Computer Graphics ; *Computer Simulation ; Hemodynamics/*physiology ; Humans ; Intracranial Aneurysm/*physiopathology ; Intracranial Embolism and Thrombosis/physiopathology ; Models, Cardiovascular ; *Models, Neurological ; Software ; }, abstract = {There is strong evidence indicating hemodynamic stress as an underlying cause for saccular intracranial aneurysm growth, thrombosis, and/or rupture. We examined flow fields encountered in models of cerebral aneurysms having a lateral (originating from the side of an artery, not at a branch point) geometric configuration. Shear stress and pressure gradients acting on aneurysm walls under a variety of flow and geometric conditions were evaluated. For this purpose, a two-dimensional finite-element computer model of lateral aneurysms in a steady-flow state was developed. Three idealized aneurysm shapes were studied, half-spherical, spherical, and pear-shaped. The ostium width of the cerebral aneurysm, relative to the radius of the parent artery and the Reynolds number, were also varied. Maximal shear stresses and maximum pressures (for an ostium width of 2 times the radius of the parent artery) were typically found at the downstream site of the ostium, rather than at the dome of the aneurysm. In general, the highest shear stresses and the lowest pressures (at the distal portion of the ostium) were obtained in the spherical aneurysm, whereas the lowest shear stresses and the highest pressures were found in the half-spherical aneurysm. The location of maximal stresses (shear and pressure) at the distal region of the ostium suggests that growth and/or rupture may well proceed from this point. Such findings are in contrast to the commonly held opinion that aneurysm rupture occurs at the dome. Careful pathological investigation will need to be performed to clarify this finding. The results of this preliminary investigation also indicate that the flow field in lateral aneurysms is highly dependent on a number of factors related to flow and geometric parameters. Geometry seems to be a significant mediator of local magnitudes of stress. Thus, the tendency for growth or thrombosis may be influenced by variations in size or shape.}, }
@article {pmid8550642, year = {1995}, author = {Johnson, LR and Shanebrook, JR}, title = {Flow visualization with air and smoke in a bypass graft model under steady flow conditions.}, journal = {Journal of biomechanics}, volume = {28}, number = {10}, pages = {1237-1241}, doi = {10.1016/0021-9290(94)00183-5}, pmid = {8550642}, issn = {0021-9290}, mesh = {Air ; Arteries/surgery ; *Blood Circulation ; Blood Vessel Prosthesis ; Humans ; *Models, Cardiovascular ; *Photography ; Smoke ; }, abstract = {A new technique for visualizing the steady flow of a new type of test fluid is presented that produces quality photographic results at Reynolds numbers typically found in arterial bypass grafts. Room air functions as the test fluid and smoke from burning incense sticks provides the tracer particles. As an example of this new technique, photographic results are presented for a Reynolds number flow of 205 through a Plexiglas model of an end-to-side distal anastomosis with a 45 degrees junction angle. The advantages of this technique are that it is simple, convenient, and applicable to a wide variety of flow conditions found in the human cardiovascular system.}, }
@article {pmid8567502, year = {1995}, author = {Tsuda, A and Henry, FS and Butler, JP}, title = {Chaotic mixing of alveolated duct flow in rhythmically expanding pulmonary acinus.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {79}, number = {3}, pages = {1055-1063}, doi = {10.1152/jappl.1995.79.3.1055}, pmid = {8567502}, issn = {8750-7587}, support = {HL-33009/HL/NHLBI NIH HHS/United States ; HL-47428/HL/NHLBI NIH HHS/United States ; }, mesh = {Airway Resistance/physiology ; Animals ; *Models, Biological ; Nonlinear Dynamics ; Pulmonary Alveoli/*physiology ; Pulmonary Ventilation/*physiology ; }, abstract = {We examined the effects of rhythmic expansion of alveolar walls on fluid mechanics in the pulmonary acinus. We generated a realistic geometric model of an alveolated duct that expanded and contracted in a geometrically similar fashion to simulate tidal breathing. Time-dependent volumetric flow was generated by adjusting the proximal and distal boundary conditions. The low Reynolds number velocity field was solved numerically over the physiological range. We found that for a given geometry, the ratio of the alveolar flow (QA) to the ductal flow (QD) played a major role in determining the flow pattern. For larger QA/QD (as in the distal region in the acinus), the flow in the alveolus was largely radial. For small QA/QD (as in the proximal region in the acinus), the flow in the alveolus was slowly rotating and the velocity field near the alveolar opening was complex with a stagnation saddle point typical of chaotic flow structures. Performing Lagrangian fluid particle tracking, we demonstrated that in such a flow structure the motion of fluid could be highly complex, irreversible, and unpredictable even though it was governed by simple deterministic equations. These are the characteristics of chaotic flow behavior. We conclude that because of the unique geometry of alveolated duct and its time-dependent motion associated with tidal breathing, chaotic flow and chaotic mixing can occur in the lung periphery. Based on these novel observations, we suggest a new approach for studying acinar fluid mechanics and aerosol kinetics.}, }
@article {pmid10060020, year = {1995}, author = {Sreenivasan, KR and Juneja, A and Suri, AK}, title = {Scaling properties of circulation in moderate-Reynolds-number turbulent wakes.}, journal = {Physical review letters}, volume = {75}, number = {3}, pages = {433-436}, doi = {10.1103/PhysRevLett.75.433}, pmid = {10060020}, issn = {1079-7114}, }
@article {pmid7579209, year = {1995}, author = {He, X and Ku, DN}, title = {Flow in T-bifurcations: effect of the sharpness of the flow divider.}, journal = {Biorheology}, volume = {32}, number = {4}, pages = {447-458}, doi = {10.1016/0006-355X(95)00022-2}, pmid = {7579209}, issn = {0006-355X}, support = {R29 HL39437/HL/NHLBI NIH HHS/United States ; }, mesh = {Arteriosclerosis/*etiology ; Biomechanical Phenomena ; *Computer Simulation ; Hemodynamics ; *Hemorheology ; Humans ; Models, Biological ; }, abstract = {The local geometry of a bifurcation has been hypothesized to be a potential geometrical risk factor for the development of atherosclerosis. While flow division and branch area ratios clearly affect the flow field, the importance of the flow divider shape is not as clear. A fast spectral element computational fluid mechanics (CFD) solver was used to simulate flow through 90 degrees T-bifurcations with three different flow divider shapes. Other factors, such as flow partition, area ratio, and bifurcation angle, were kept constant. A Reynolds number range of 15 to 350 was studied to bracket experimental results in the literature. The variation in the sharpness of the corners had a dramatic effect on both the flow field and wall shear stress distribution in the side branch, but little effect on the flow in the main tube. The magnitude of reverse velocities and wall shear stress in the side branch increased linearly over a physiological range of Reynolds number and corner shape. This paper verifies the accuracy and usefulness of spectral element CFD in studying three-dimensional hemodynamics.}, }
@article {pmid12780197, year = {1995}, author = {Tangborn, AV and Silevitch, DM and Howes, T}, title = {Chaotic advection in a 2-D mixed convection flow.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {5}, number = {2}, pages = {432-438}, doi = {10.1063/1.166113}, pmid = {12780197}, issn = {1089-7682}, abstract = {Two-dimensional numerical simulations of particle advection in a channel flow with spatially periodic heating have been carried out. The velocity field is found to be periodic above a critical Rayleigh number of around 18 000 and a Reynolds number of 10. Particle motion becomes chaotic in the lower half plane almost immediately after this critical value is surpassed, as characterized by the power spectral density and Poincare section of the flow. As the Rayleigh number is increased further, particle motion in the entire domain becomes chaotic. (c) 1995 American Institute of Physics.}, }
@article {pmid9963295, year = {1995}, author = {Scotti, A and Meneveau, C and Saddoughi, SG}, title = {Fractal dimension of velocity signals in high-Reynolds-number hydrodynamic turbulence.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {51}, number = {6}, pages = {5594-5608}, doi = {10.1103/physreve.51.5594}, pmid = {9963295}, issn = {1063-651X}, }
@article {pmid7666660, year = {1995}, author = {Hughes, PE and How, TV}, title = {Flow structures at the proximal side-to-end anastomosis. Influence of geometry and flow division.}, journal = {Journal of biomechanical engineering}, volume = {117}, number = {2}, pages = {224-236}, doi = {10.1115/1.2796005}, pmid = {7666660}, issn = {0148-0731}, mesh = {Arteries/pathology/physiopathology/surgery ; Biomechanical Phenomena ; Biomedical Engineering ; *Blood Vessel Prosthesis/adverse effects ; Hemodynamics/*physiology ; Hemorheology ; Humans ; Hyperplasia ; In Vitro Techniques ; Models, Cardiovascular ; }, abstract = {Flow structures were visualized in transparent polyurethane models of proximal side-to-end vascular anastomoses, using planar illumination of suspended tracer particles. Both the effects of geometry and flow division were determined under steady and pulsatile flow conditions, for anastomosis angles of 15, 30, and 45 degrees. The flow patterns were highly three-dimensional and were characterized by a series of vortices in the fully occluded distal artery and two helical vortices aligned with the axis of the graft. In steady flow, above a critical Reynolds number, the flow changed from a laminar regime to one displaying time-dependent behavior. In particular, significant fluctuating velocity components were observed in the distal artery and particles were shed periodically from the occluded artery into the graft. Pairs of asymmetric flow patterns were also observed in the graft, before the onset of the time-dependent flow regime. The critical Reynolds number ranged from 427 to 473 and appeared to be independent of anastomosis angle. The presence of a patent distal artery had a significant effect on the overall flow pattern and led to the formation of a large recirculation region at the toe of the anastomosis. The main structures observed in steady flow, such as vortices in the distal artery and helical flow in the graft, were also seen during the pulsatile cycle. However, the secondary flow components in the graft were more pronounced in pulsatile flow particularly during deceleration of the flow waveform. At higher mean Reynolds numbers, there was also a greater mixing between fluid in the occluded arterial section and that in the graft.}, }
@article {pmid7666657, year = {1995}, author = {Truskey, GA and Barber, KM and Robey, TC and Olivier, LA and Combs, MP}, title = {Characterization of a sudden expansion flow chamber to study the response of endothelium to flow recirculation.}, journal = {Journal of biomechanical engineering}, volume = {117}, number = {2}, pages = {203-210}, doi = {10.1115/1.2796002}, pmid = {7666657}, issn = {0148-0731}, mesh = {Animals ; Biomechanical Phenomena ; Biomedical Engineering ; Cattle ; Cell Adhesion ; Cell Count ; Cell Size ; Cells, Cultured ; Endothelium, Vascular/cytology/*physiology ; Hemodynamics/*physiology ; Hemorheology/*instrumentation/methods ; Models, Cardiovascular ; Stress, Mechanical ; }, abstract = {In order to simulate regions of flow separation observed in vivo, a conventional parallel plate flow chamber was modified to produce an asymmetric sudden expansion. The flow field was visualized using light reflecting particles and the size of the recirculation zone was measured by image analysis of the particles. Finite element numerical solutions of the two and three-dimensional forms of the Navier-Stokes equation were used to determine the wall shear stress distribution and predict the location of reattachment. For two different size expansions, numerical estimates of the reattachment point along the centerline of the flow chamber agreed well with experimental values for Reynolds numbers below 473. Even at a Reynolds number of 473, the flow could be approximated as two-dimensional for 80 percent of the chamber width. Peak shear stresses in the recirculation zone as high as 80 dyne/cm2 and shear stress gradients of 2500 (dyne/cm2)/cm were produced. As an application of this flow chamber, subconfluent bovine aortic endothelial cell shape and orientation were examined in the zone of recirculation during a 24 h exposure to flow at a Reynolds number of 267. After 24 h, gradients in cell orientation and shape were observed within the recirculation zone. At the location of reattachment, where the wall shear stress was zero but the shear stress gradients were large, cells plated at low density were still aligned with the direction of flow. No preferred orientation was observed at the gasket edge where the wall shear stress and shear stress gradients were zero. At higher cell densities, no alignment was observed at the separation point.(ABSTRACT TRUNCATED AT 250 WORDS)}, }
@article {pmid7877228, year = {1995}, author = {Staalsen, NH and Ulrich, M and Winther, J and Pedersen, EM and How, T and Nygaard, H}, title = {The anastomosis angle does change the flow fields at vascular end-to-side anastomoses in vivo.}, journal = {Journal of vascular surgery}, volume = {21}, number = {3}, pages = {460-471}, doi = {10.1016/s0741-5214(95)70288-1}, pmid = {7877228}, issn = {0741-5214}, mesh = {Anastomosis, Surgical/*methods ; Animals ; Aorta/diagnostic imaging/physiology/*surgery ; *Blood Flow Velocity ; Blood Vessel Prosthesis ; Hemodynamics ; Hemorheology ; Swine ; Ultrasonography, Doppler, Color ; }, abstract = {PURPOSE: The purpose of this article was to study the influence of the anastomosis angle on the flow fields at end-to-side anastomoses in vivo.<br><br>METHODS: Polyurethane grafts of similar internal diameter to that of the abdominal aorta (8 mm) were implanted from the suprarenal to the infrarenal level in 10 pigs. Three angles of standardized distal end-to-side anastomoses (90 degrees, 45 degrees, and 15 degrees) were studied. The anatomic position of the anastomoses was constant, the proximal outflow segment was occluded, and the flow rate through the graft was controlled. Flow visualization was accomplished by a color-flow Doppler ultrasound system.<br><br>RESULTS: The angulation was reproduced within 10%. Gross hemodynamic parameters were stable, and the similarity parameters were typical for peripheral bypasses (mean Reynold's number is 424 and Womersley's parameter is 5.9). The flow fields were clearly dependent on the anastomosis angle. A zone of recirculation (approximately 5% of the flow area), extending from the toe to one diameter downstream, was found in the 45-degree and 90-degree anastomoses. No flow disturbances were detected at the toe and one diameter downstream with an anastomosis angle of 15 degrees. At the heel different recirculating flow patterns were found in the different anastomoses.<br><br>CONCLUSION: The anastomosis angle does change the flow fields at vascular end-to-side anastomoses in vivo.}, }
@article {pmid7707909, year = {1995}, author = {Oshinski, JN and Ku, DN and Pettigrew, RI}, title = {Turbulent fluctuation velocity: the most significant determinant of signal loss in stenotic vessels.}, journal = {Magnetic resonance in medicine}, volume = {33}, number = {2}, pages = {193-199}, doi = {10.1002/mrm.1910330208}, pmid = {7707909}, issn = {0740-3194}, mesh = {Blood Flow Velocity/physiology ; Blood Viscosity/physiology ; Constriction, Pathologic/diagnosis/pathology/physiopathology ; Glycerol ; *Hemorheology ; Humans ; Image Enhancement ; *Magnetic Resonance Angiography ; Models, Structural ; Nickel ; Peripheral Vascular Diseases/*diagnosis/pathology/physiopathology ; Regional Blood Flow/physiology ; Water ; }, abstract = {Studies of flow in a 90%-stenosis phantom were conducted to elucidate the parameters and mechanisms responsible for signal loss in MR angiographic images. The studies independently evaluated the effect of velocity, Reynolds number, turbulent fluctuation velocity, and turbulence intensity on the amount of post-stenotic signal loss. Results suggested that the magnitude of the turbulent fluctuation velocity, not merely the presence of turbulence or the intensity of turbulence, was the parameter that determined the extent of the signal loss. The study suggests that future flow phantom studies should be conducted with fluids having physiologic velocities and viscosities to obtain accurate levels of turbulent fluctuation velocities and hence reproduce results of in-vivo signal-loss patterns. The mechanism for signal loss is that the temporal and spatial variations of the turbulent fluctuation velocity cause a range of phases to be present within a voxel. Examination of the theoretical aspects of fluid turbulence suggest that shortening gradient durations and imaging during diastole may help reduce signal loss.}, }
@article {pmid7609476, year = {1995}, author = {Wang, DM and Tarbell, JM}, title = {Nonlinear analysis of oscillatory flow, with a nonzero mean, in an elastic tube (artery).}, journal = {Journal of biomechanical engineering}, volume = {117}, number = {1}, pages = {127-135}, doi = {10.1115/1.2792260}, pmid = {7609476}, issn = {0148-0731}, support = {HL35549/HL/NHLBI NIH HHS/United States ; }, mesh = {Arteries/anatomy &amp; histology/*physiology ; Bias ; *Hemorheology ; Mathematics ; Models, Cardiovascular ; Reproducibility of Results ; }, abstract = {Oscillatory flow of a Newtonian fluid in an elastic tube, which is a model of blood flow in arteries, is analyzed in this paper. For a rigid tube, the steady flow field can be described by Poiseuille's law and the unsteady flow field by Womersley's solution. These are the linearized solutions for flow in elastic tubes. To evaluate the importance of nonlinear effects, a perturbation solution is developed realizing that the amplitude of arterial wall movement is small (typically 5-10 percent of the diameter). The nonlinear effects on the amplitude of the wall shear rate, on the amplitude of the pressure gradient, and on the mean velocity profile have been considered. Nonlinear effects on the oscillatory components depend on Womersley's unsteadiness parameter (alpha), the ratio between the mean and amplitude of the flow rate, the diameter variation, and the phase difference between the diameter variation and the flow rate (phi) which is indicative of the degree of wave reflection. On the other hand, the mean velocity profile is found to be dependent on the steady-streaming Reynolds number, Rs. When Rs is small, the mean velocity profile is parabolic (1-xi 2); however, when Rs is large, the velocity profile is distorted by the nonlinear effect and can be described by sin (pi xi 2). The increase of the amplitude and reduction of the mean of wall shear rate as phi changes from 0 to -90 deg suggests an indirect mechanism for the role of hypertension in arterial disease: hypertension-->increased wave reflection-->wall shear stress is reduced and more oscillatory.}, }
@article {pmid8571228, year = {1995}, author = {Bertram, CD}, title = {The dynamics of collapsible tubes.}, journal = {Symposia of the Society for Experimental Biology}, volume = {49}, number = {}, pages = {253-264}, pmid = {8571228}, issn = {0081-1386}, mesh = {Animals ; Biophysical Phenomena ; *Biophysics ; Blood Vessels/*physiology ; Body Fluids ; Models, Biological ; Regional Blood Flow ; Rheology ; }, abstract = {The importance of collapsible-tube phenomena derives primarily from blood, air and urine flows in mammals, although similar principles underlie invertebrate jetting and the avian syrinx. Biological fluid conduits have flexible walls and many experience higher external than internal pressures during physiological manoeuvres. The tube typically becomes noncircular, and large shape and cross-sectional area changes occur for small transmural pressure change. Two consequences ensue: a highly nonlinear constitutive relationship, and strong coupling between the fluid and solid mechanics. Depending on how flow is controlled, the tube can exhibit flow-rate-independent pressure-drop, or pressure-drop-independent flow-rate, or a locally negative slope to the pressure-drop to flow-rate relationship. At sufficiently large Reynolds number, these behaviours are accompanied by self-excited oscillation in a surprising variety of modes, including aperiodic ones. Chaotic behaviour has been predicted numerically, but not unequivocally demonstrated. Intrinsic chaotic oscillation must be distinguished from sensitivity to turbulent through-flow. To this end, the response to periodic upstream forcing is currently being investigated.}, }
@article {pmid8571226, year = {1995}, author = {Pedley, TJ}, title = {High Reynolds number flow in tubes of complex geometry with application to wall shear stress in arteries.}, journal = {Symposia of the Society for Experimental Biology}, volume = {49}, number = {}, pages = {219-241}, pmid = {8571226}, issn = {0081-1386}, mesh = {Animals ; Arteries/*physiology ; Arteriosclerosis/physiopathology ; Mammals ; Models, Biological ; Rheology ; Stress, Mechanical ; }, abstract = {The arterial systems of mammals contain many generations of branching, curved, elastic tubes, and the flow in them is unsteady. The flow details are important in determining the distribution of wall shear stress in arteries, a major factor in atherogenesis. The purpose of this paper is to point out that unsteady flow at realistic values of the Reynolds number (several hundred) and frequency parameter is much more complicated than a knowledge of steady flow in simpler geometries would suggest. Three-dimensional effects in curved, branched or indented tubes introduce secondary motions and horseshoe vortices, under which the wall shear can remain high for a considerable distance downstream. Unsteady flow in two-dimensional, non-uniform tubes can lead to regions of flow separation far from the non-uniformity, again associated with high wall shear, not low shear as for two-dimensional, steady, separated flow. Moreover, both two- and three-dimensional flows can be non-unique, so that the same driving pressures in the same geometry can lead to different flow patterns, depending on the initial conditions. There is great sensitivity to small geometric and temporal perturbations, making it very difficult to predict flow in one arterial bifurcation from a knowledge of another, or even at a particular site in one subject from a knowledge of another. Vessel elasticity is an additional complicating factor whose effects remain to be assessed in detail.}, }
@article {pmid7852441, year = {1995}, author = {Usha, S and Rao, AR}, title = {Peristaltic transport of a biofluid in a pipe of elliptic cross section.}, journal = {Journal of biomechanics}, volume = {28}, number = {1}, pages = {45-52}, doi = {10.1016/0021-9290(95)80006-9}, pmid = {7852441}, issn = {0021-9290}, mesh = {Algorithms ; Friction ; Humans ; Intestine, Small/anatomy &amp; histology/physiology ; Models, Biological ; Peristalsis/*physiology ; Pressure ; Rheology ; Stress, Mechanical ; Surface Properties ; Surface Tension ; Viscosity ; }, abstract = {Peristaltic transport of two fluids occupying the peripheral layer and the core in an elliptic tube is investigated in elliptic cylindrical co-ordinate system, under long wavelength and low Reynolds number approximations. The effect of peripheral-layer viscosity on the flow rate and the frictional force for a slightly elliptic tube is discussed. The limiting results for the one-fluid model are obtained for different eccentricities of the undisturbed tube cross sections with the same area. As a result of non-uniformity of the peristaltic wave, two different amplitude ratios are defined and the time-averaged flux and mechanical efficiency are studied for different eccentricities. It is observed that the time-averaged flux is not affected significantly by the pressure drop when the eccentricity is large. For the peristaltic waves with same area variation, the pumping seems to improve with the eccentricity.}, }
@article {pmid10057322, year = {1994}, author = {Lohse, D}, title = {Crossover from high to low Reynolds number turbulence.}, journal = {Physical review letters}, volume = {73}, number = {24}, pages = {3223-3226}, doi = {10.1103/PhysRevLett.73.3223}, pmid = {10057322}, issn = {1079-7114}, }
@article {pmid7869720, year = {1994}, author = {Siegel, JM and Markou, CP and Ku, DN and Hanson, SR}, title = {A scaling law for wall shear rate through an arterial stenosis.}, journal = {Journal of biomechanical engineering}, volume = {116}, number = {4}, pages = {446-451}, doi = {10.1115/1.2895795}, pmid = {7869720}, issn = {0148-0731}, support = {R29HL39437/HL/NHLBI NIH HHS/United States ; }, mesh = {Arteriosclerosis/*physiopathology ; Blood Platelets ; Carotid Stenosis/physiopathology ; Coronary Disease/physiopathology ; Endothelium, Vascular/physiopathology ; *Hemorheology ; Humans ; *Models, Cardiovascular ; Numerical Analysis, Computer-Assisted ; }, abstract = {Atherosclerosis of the human arterial system produces major clinical symptoms when the plaque advances to create a high-grade stenosis. The hemodynamic shear rates produced in high-grade stenoses are important in the understanding of atheromatous plaque rupture and thrombosis. This study was designed to quantify the physiologic stress levels experienced by endothelial cells and platelets in the region of vascular stenoses. The steady hemodynamic flow field was solved for stenoses with percent area reductions of 50, 75, and 90 percent over a range of physiologic Reynolds numbers (100-400). The maximum wall shear rate in the throat region can be shown to vary by the square root of the Reynolds number. The shear rate results can be generalized to apply to a range of stenosis lengths and flow rates. Using dimensions typical for a human carotid or coronary artery, wall shear rates were found to vary from a maximum of 20,000 s-1 upstream of the throat to a minimum of -630 s-1 in the recirculation zone for a 90 percent stenosis. An example is given which illustrates how these values can be used to understand the relationship between hemodynamic shear and platelet deposition.}, }
@article {pmid9962318, year = {1994}, author = {Breuer, HP and Petruccione, F}, title = {Stochastic simulations of high-Reynolds-number turbulence in two dimensions.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {50}, number = {4}, pages = {2795-2801}, doi = {10.1103/physreve.50.2795}, pmid = {9962318}, issn = {1063-651X}, }
@article {pmid7983093, year = {1994}, author = {García, AJ and Ducheyne, P}, title = {Numerical analysis of extracellular fluid flow and chemical species transport around and within porous bioactive glass.}, journal = {Journal of biomedical materials research}, volume = {28}, number = {8}, pages = {947-960}, doi = {10.1002/jbm.820280814}, pmid = {7983093}, issn = {0021-9304}, mesh = {Animals ; Cell Adhesion ; Cell Differentiation ; Cell Movement ; Diffusion ; Dogs ; Extracellular Space/metabolism/*physiology ; *Glass ; Models, Biological ; Osteoblasts/physiology ; Phenotype ; Prostheses and Implants ; Surface Properties ; Viscosity ; }, abstract = {Modeling of the physical phenomena present at the biomaterial-tissue interface provides a valuable tool for examining the underlying mechanisms which influence the overall behavior of the implant-host system. Based on histological data from a previous implantation study (E. Schepers, M. De Clercq, P. Ducheyne, and R. Kempeneers, "Bioactive glass particulate materials as a filler for bone lesions," J. Oral Rehab.; 18, 439-452, 1991, Ref. 1) which documented the differentiation of mesenchymal cells to cells expressing the osteoblastic phenotype in porous bioactive glass, a finite element momentum and mass transport model was constructed. In this analysis, the extracellular compositional variations and fluid flow conditions around and within porous bioactive glass granules were determined. Numerical simulations demonstrated that the interstitial fluid flow around these granules (300-360 microns) is viscosity dominated (low Reynolds number flow) and that the fluid inside the granules remains stagnant. This velocity field results in shear stresses proportional to the velocity gradient at the granule-fluid interface outside the particles and no shear stresses inside the particles. A parametric study on the effect of interstitial fluid flow on chemical species (Na+, Ca+2, HPO(4)-2) transport outside the granules revealed three domains. At low velocities (0-0.1 micron/s), the transport of species is diffusion controlled. At intermediate velocities (1.0-10 microns/s), diffusion and convection contribute to the species transport. The concentration of chemical species is nearly uniform at high velocities (100-800 microns/s). For all three cases, the transport of chemical species within the granules is diffusion controlled. The differences in transport mechanisms and interstitial fluid flow conditions lead to variations in concentrations, reaction rates, and shear stresses between the inside and the outside of the glass granules. These differences may influence cellular migration, attachment, differentiation, and the overall response to these bioactive materials.}, }
@article {pmid7799639, year = {1994}, author = {He, X and Ku, DN}, title = {Unsteady entrance flow development in a straight tube.}, journal = {Journal of biomechanical engineering}, volume = {116}, number = {3}, pages = {355-360}, doi = {10.1115/1.2895742}, pmid = {7799639}, issn = {0148-0731}, support = {R29 HL39437/HL/NHLBI NIH HHS/United States ; }, mesh = {Evaluation Studies as Topic ; Mathematics ; *Models, Cardiovascular ; *Myocardial Contraction ; *Numerical Analysis, Computer-Assisted ; Pulsatile Flow/*physiology ; *Signal Processing, Computer-Assisted ; Time Factors ; }, abstract = {The entrance conditions for pulsatile flow are important in the understanding blood flow out of the heart and in developing regions at branches. The pulsatile entrance flow was solved using a spectral element simulation of the full unsteady Navier-Stokes equations. A mean Reynolds number of 200 and a range of Womersley parameters from 1.8 to 12.5 was used for a sinusoidal inlet flow waveform 1 + sin (omega t). Variations in the entrance length were observed during the pulsatile cycle. The amplitude of the entrance length variation decreased with an increase in the Womersley parameter. The phase lag between the entrance length and the inlet flow waveform increased for Womersley parameter alpha up to 5.0 and decreased for alpha larger than 5.0. For low alpha, the maximum entrance length during pulsatile flow was approximately the same as the steady entrance length for the peak flow. For high varies; is directly proportional to, the pulsatile entrance length was more uniform during the cycle and tended to the entrance length for the mean flow. The wall shear rate reached its far downstream value after only about half of the entrance length and also exhibited a dependence on alpha. The results quantify the entrance conditions typically encountered in studies of the arterial system.}, }
@article {pmid10057445, year = {1994}, author = {Grossmann, S and Lohse, D and L'vov, V and Procaccia, I}, title = {Finite size corrections to scaling in high Reynolds number turbulence.}, journal = {Physical review letters}, volume = {73}, number = {3}, pages = {432-435}, doi = {10.1103/PhysRevLett.73.432}, pmid = {10057445}, issn = {1079-7114}, }
@article {pmid7981436, year = {1994}, author = {Matsumoto, T and Naiki, T and Hayashi, K}, title = {Flow visualization analysis of pulsatile flow in elastic straight tubes.}, journal = {Biorheology}, volume = {31}, number = {4}, pages = {365-381}, doi = {10.3233/bir-1994-31406}, pmid = {7981436}, issn = {0006-355X}, mesh = {Animals ; Blood Vessels/physiology ; *Elasticity ; Heart, Artificial ; Models, Biological ; *Pulsatile Flow ; }, abstract = {Effects of wall compliance on the flow characteristics were studied by visualizing pulsatile flow in two straight elastic tubes having different compliance and in a rigid tube. The elastic tubes were made of segmented polyether polyurethane and their compliance was adjusted by varying the wall thickness. Their diameter changes were +/- 3.3 and +/- 4.9% for the pressure pulsation between 20 and 250 mm Hg. An acrylic pipe was used for the rigid model. An air-driven artificial heart was used to generate the pulsatile flow having the mean Reynolds number and frequency parameter of 740 and 11.4, respectively. The flow was visualized by the hydrogen bubble method at every 5% of the pulsatile flow cycle. Velocity distributions along the tube diameter were determined from still images of time lines taken with a CCD camera. The ratio of the wall shear rate in the elastic tubes to that in the rigid tube at each phase correlated well with the radial velocity of tube wall, while it had no significant correlation with the instantaneous tube diameter. These results suggest that the wall compliance either increases or decreases the wall shear rate depending on the phasic relation between the flow and pressure waves. When studying the hemodynamic effects on vascular diseases by model experiments, it may be important to take wall elasticity into account.}, }
@article {pmid12780106, year = {1994}, author = {Danilov, SD and Dolzhanskii, FV and Krymov, VA}, title = {Quasi-two-dimensional hydrodynamics and problems of two-dimensional turbulence.}, journal = {Chaos (Woodbury, N.Y.)}, volume = {4}, number = {2}, pages = {299-304}, doi = {10.1063/1.166009}, pmid = {12780106}, issn = {1089-7682}, abstract = {The principal problems of quasi-two-dimensional (Q2-D) hydrodynamics are discussed. Accounting for Q2-D flow vertical structure is shown to eliminate "genetic" defects of the formal 2-D idealization of 3-D Navier-Stokes equations and allows under certain conditions to formulate corrected 2-D motion equations which adequately describe real hydrodynamic processes. The applicability of the approach is directly verified in laboratory experiments. Special attention is paid to the problem of 2-D turbulence. Its simulation on the basis of ordinary 2-D equations is unjustified because of the absence of the external Kolmogorov dissipation scale and reverse spectral energy flux. An alternative approach allows one to introduce the natural external scale of 2-D turbulence which depends only on physical properties of the system under consideration and to formulate the conditions under which the large scale vortex dynamics is expected to be universal at large Reynolds number, i.e., to be independent on the size and form of integration domain and lateral boundary conditions.}, }
@article {pmid8083947, year = {1994}, author = {Peattie, RA and Schrader, T and Bluth, EI and Comstock, CE}, title = {Development of turbulence in steady flow through models of abdominal aortic aneurysms.}, journal = {Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine}, volume = {13}, number = {6}, pages = {467-472}, doi = {10.7863/jum.1994.13.6.467}, pmid = {8083947}, issn = {0278-4297}, mesh = {Aortic Aneurysm, Abdominal/diagnostic imaging/*physiopathology ; Blood Flow Velocity/physiology ; Humans ; Models, Cardiovascular ; Regional Blood Flow/physiology ; Ultrasonography ; }, abstract = {As part of a general examination of the effects of blood flow patterns on the risk of rupture of abdominal aortic aneurysms, we have investigated steady flow through a series of polyvinyl chloride models of fusiform aneurysms. A series of steady flow rates between 460 ml/min and 2.0 l/min have been delivered through the models, and the resulting flow patterns have been evaluated by color Doppler flow imaging. At low volume flow rates, the pattern of flow through the model is smooth and laminar. At higher flow rates, however, this is replaced by an irregular, fluctuating, and apparently turbulent motion. This finding is consistent with previous clinical observations. Turbulence appears initially at the distal end of the model aneurysm and then spreads proximally to fill the whole model only if the flow rate continues to increase. The onset of irregular, turbulent flow is found to be governed by both the overall flow rate through the model and the model diameter. Critical conditions for the appearance of turbulence are presented and discussed, and the critical value of the Reynolds number for both the initial distal transition and the final full transition is shown to decrease as the size of the model aneurysm increases.}, }
@article {pmid7928876, year = {1994}, author = {Tsuda, A and Butler, JP and Fredberg, JJ}, title = {Effects of alveolated duct structure on aerosol kinetics. I. Diffusional deposition in the absence of gravity.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {76}, number = {6}, pages = {2497-2509}, doi = {10.1152/jappl.1994.76.6.2497}, pmid = {7928876}, issn = {8750-7587}, support = {HL-33009/HL/NHLBI NIH HHS/United States ; HL-47428/HL/NHLBI NIH HHS/United States ; }, mesh = {*Aerosols ; Biomechanical Phenomena ; Diffusion ; *Gravity, Altered ; Kinetics ; Models, Biological ; Monte Carlo Method ; Particle Size ; Probability ; Pulmonary Alveoli/*physiology ; }, abstract = {We examined the effects of alveolar duct structure on particle deposition in the pulmonary acinus. The low Reynolds number velocity field of carrier gas in a geometric model of the alveolated duct was solved numerically. Particle trajectories were computed from the Langevin equation. Conditional probabilities of the trajectories were calculated with an eigenfunction expansion technique in the absence of gravity. For submicron particles, Brownian motion dominated the process; the deposition rate dramatically decreased with boundary layer growth. For fine particles, fully developed boundary layer profiles determined the deposition over most of the acinar length. The assumption of a uniform radial profile results in a substantial overestimation of the local deposition rate. The deposition rate in an alveolated duct was always smaller than that in an equivalent straight tube of the same volume. Within the alveolus the deposition pattern was markedly nonuniform, with higher deposition near the alveolar entrance ring; this finding is consistent with experimental observations in animals (e.g., see Zeltner et al. J. Appl. Physiol. 70: 1137-1145, 1991). We conclude that the structure of the alveolar duct has an important influence on aerosol particle deposition in the lung acinus.}, }
@article {pmid9961693, year = {1994}, author = {Katsuyama, T and Horiuchi, Y and Nagata, Ki}, title = {Intermittency and scaling property of band-pass-filtered signals in moderate-Reynolds-number turbulent flows.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {49}, number = {5}, pages = {4052-4059}, doi = {10.1103/physreve.49.4052}, pmid = {9961693}, issn = {1063-651X}, }
@article {pmid9961692, year = {1994}, author = {L'vov, VS and Procaccia, I}, title = {Extended universality in moderate-Reynolds-number flows.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {49}, number = {5}, pages = {4044-4051}, doi = {10.1103/physreve.49.4044}, pmid = {9961692}, issn = {1063-651X}, }
@article {pmid9961688, year = {1994}, author = {Abarbanel, HD and Katz, RA and Galib, T and Cembrola, J and Frison, TW}, title = {Nonlinear analysis of high-Reynolds-number flows over a buoyant axisymmetric body.}, journal = {Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics}, volume = {49}, number = {5}, pages = {4003-4018}, doi = {10.1103/physreve.49.4003}, pmid = {9961688}, issn = {1063-651X}, }
@article {pmid8078323, year = {1994}, author = {Tran-Son-Tay, R and Kirk, TF and Zhelev, DV and Hochmuth, RM}, title = {Numerical simulation of the flow of highly viscous drops down a tapered tube.}, journal = {Journal of biomechanical engineering}, volume = {116}, number = {2}, pages = {172-177}, doi = {10.1115/1.2895716}, pmid = {8078323}, issn = {0148-0731}, support = {2R01-HL-23728/HL/NHLBI NIH HHS/United States ; }, mesh = {Evaluation Studies as Topic ; *Mathematics ; *Models, Theoretical ; Neutrophils ; *Rheology ; Surface Tension ; *Viscosity ; }, abstract = {The flow of a highly viscous drop surrounded by an inviscid fluid inside a tapered tube is analyzed according to a Newtonian, liquid-drop model in which a variational method is used to simultaneously solve the hydrodynamic equations for low Reynolds-number flow and the equations for membrane equilibrium with a constant membrane tension. It is found that the flow in the end caps is plug and radial in the conical section of the drop. The results are compared to a simplified analytical theory that makes these assumptions. Very good agreement is found between the two approaches. Both approaches are used to analyze existing experimental results of passive neutrophils flowing down a tapered tube. The theoretical models give a good fit to published experimental data by Bagge et al. (1977) at driving pressures of 20 and 40 mm H2O for a membrane cortical tension of 0.024 dyn/cm and an apparent cytoplasmic viscosity of about 2400 and 1400 poise, respectively.}, }
@article {pmid8063457, year = {1994}, author = {Tandon, PN and Kawahara, M and Rana, UV}, title = {A mathematical model for blood flow through an arterial bifurcation.}, journal = {International journal of bio-medical computing}, volume = {35}, number = {4}, pages = {309-325}, pmid = {8063457}, issn = {0020-7101}, mesh = {Algorithms ; Arterial Occlusive Diseases/physiopathology ; Arteries/anatomy &amp; histology/*physiology ; Blood Flow Velocity/physiology ; Blood Pressure/physiology ; Blood Viscosity/physiology ; Constriction, Pathologic/physiopathology ; *Hemorheology ; Humans ; *Models, Cardiovascular ; Regional Blood Flow/physiology ; Stress, Mechanical ; }, abstract = {By introducing the finite element technique, a study of blood flow through an arterial bifurcation is presented in this paper. The blood is represented by a modified model of thixotropic power-law fluids, for which the parametric values for blood, both in normal and pathological states, have already been established. The results for the velocity profiles, pressure and wall shear stress distributions are elucidated and discussed for normal old and diseased states. The separation and reattachment points are also located for different values of the Reynolds number and the flow behaviour index (n) of the model representing the blood. The analysis identifies low shear stress zones behind the stenosis along the outer wall and high shear stresses downstream of the apex. The increasing percentage of the stenosis and the increasing values of the Reynolds number facilitate the high shear stress zones, whereas the thixotropy of the blood depicts an inbuilt mechanism of reducing high shear stresses as well as flow reversal regions.}, }
@article {pmid8027092, year = {1994}, author = {Palmen, DE and van de Vosse, FN and Janssen, JD and van Dongen, ME}, title = {Analysis of the flow in stenosed carotid artery bifurcation models--hydrogen-bubble visualisation.}, journal = {Journal of biomechanics}, volume = {27}, number = {5}, pages = {581-590}, doi = {10.1016/0021-9290(94)90067-1}, pmid = {8027092}, issn = {0021-9290}, mesh = {Acceleration ; Blood Flow Velocity/physiology ; Carotid Arteries/pathology/*physiopathology ; Carotid Artery, Common/pathology/physiopathology ; Carotid Artery, External/pathology/physiopathology ; Carotid Artery, Internal/pathology/physiopathology ; Carotid Stenosis/pathology/*physiopathology ; Computer-Aided Design ; Deceleration ; Diastole/physiology ; *Hemorheology ; Humans ; *Hydrogen ; Methylmethacrylate ; Methylmethacrylates ; *Models, Cardiovascular ; Pulsatile Flow/physiology ; Regional Blood Flow/physiology ; Signal Processing, Computer-Assisted ; Stress, Mechanical ; Systole/physiology ; }, abstract = {This paper deals with the effect of geometric changes of mild stenoses on large-scale flow disturbances in the carotid artery bifurcation. Hydrogen-bubble visualisation experiments have been performed in Plexiglas models of a non-stenosed and a 25% stenosed carotid artery bifurcation. The flow conditions approximate physiological flow. The experiments show that shortly after the onset of the diastolic phase vortex formation occurs in the plane of symmetry. This vortex formation is found in a shear layer, which is formed in the carotid sinus. The shear layer is located between a region with low shear rates at the non-divider wall and a region with high shear rates at the divider wall. In order to gain insight into the parameters that are important with respect to the stability of the shear layer, experiments have been performed in which the influence of the shape of the flow pulse, the Reynolds number (Re), the Womersley parameter (alpha) and the flow division ratio (gamma) on the flow phenomena is studied. From these experiments it appears that the flow phenomena in the carotid artery bifurcation are significantly influenced by Re, alpha the systolic acceleration (sa) and deceleration (sd) and the duration of the peak-systolic flow (Tmax). With these results a simplified flow pulse is chosen, with which the experiments in the non-stenosed and the 25% stenosed bifurcation are performed. Comparison of the hydrogen-bubble profiles in the 0 and 25% stenosed models with similar flow conditions shows that the geometric change of the 25% stenosis only slightly influences the flow phenomena. The most striking influences are found in the stability of the shear layer. Quantitative experiments by means of laser Doppler anemometry measurements and numerical computations are needed to analyse the influence of the stenosis of the flow field more accurately.}, }
@article {pmid8008756, year = {1994}, author = {Budaraju, S and Stewart, WE and Porter, WP}, title = {Prediction of forced ventilation in animal fur from a measured pressure distribution.}, journal = {Proceedings. Biological sciences}, volume = {256}, number = {1345}, pages = {41-46}, doi = {10.1098/rspb.1994.0046}, pmid = {8008756}, issn = {0962-8452}, mesh = {Animals ; Anisotropy ; Deer ; Hair/*physiology ; Macropodidae ; Models, Biological ; Opossums ; Peromyscus ; Pressure ; Sciuridae ; Ventilation ; Wind ; }, abstract = {A model and computation scheme are given for predicting forced ventilation in the fur on an animal limb or torso, modelled here as a fur-covered cylinder with the hairs erect. The intra-fur flow is described by an anisotropic Darcy model, and pressure distribution measured previously for flow past a solid cylinder at Reynolds number 1.29 x 10(5) is used for the outer flow. Calculations from the model are presented for five mammalian species.}, }
@article {pmid10055866, year = {1994}, author = {Abarbanel, HD and Katz, RA and Galib, T and Cembrola, J and Frison, TW}, title = {High Reynolds number boundary layer chaos.}, journal = {Physical review letters}, volume = {72}, number = {15}, pages = {2383-2386}, doi = {10.1103/PhysRevLett.72.2383}, pmid = {10055866}, issn = {1079-7114}, }
@article {pmid8188720, year = {1994}, author = {Huang, ZJ and Merkle, CL and Abdallah, S and Tarbell, JM}, title = {Numerical simulation of unsteady laminar flow through a tilting disk heart valve: prediction of vortex shedding.}, journal = {Journal of biomechanics}, volume = {27}, number = {4}, pages = {391-402}, doi = {10.1016/0021-9290(94)90015-9}, pmid = {8188720}, issn = {0021-9290}, support = {P41-RR06009/RR/NCRR NIH HHS/United States ; }, mesh = {Algorithms ; Blood Flow Velocity ; *Heart Valve Prosthesis ; *Hemorheology ; Humans ; Mathematics ; *Models, Cardiovascular ; *Prosthesis Design ; Pulsatile Flow ; Regional Blood Flow ; Stress, Mechanical ; Surface Properties ; }, abstract = {Heart valves induce flow disturbances which play a role in blood cell activation and damage, but questions of the magnitude and spatial distribution of fluid stresses (wall shear stress and turbulent stress) cannot be readily addressed with current experimental techniques. Therefore, a numerical simulation procedure for flow through artificial heart valves is presented. The algorithm employed is based on the Navier-Stokes equations in generalized curvilinear coordinates with artificial compressibility for coupling of velocity and pressure. The algorithm applies a finite-difference technique on a body-conforming composite grid around the heart valve disk on which the numerical simulations are performed. Steady laminar flow over a backward-facing step and unsteady laminar flow inside a square driven cavity are computed to validate the algorithm. Two-dimensional, time-accurate simulation of flow through a tilting disk valve with a steady upstream Reynolds number as high as 1000 reveals the complex behavior of 'vortex shedding'. By scaling the results at the Reynolds number of 1000 to peak systolic flow conditions, the maximum value of shear stress on the valve disk is estimated to be 770 dyn cm-2. The 'apparent' Reynolds stress associated with vortex shedding is estimated to be as high as 3900 dyn cm-2 with a vortex shedding frequency of about 26 Hz. The 'apparent' Reynolds stress value is of similar magnitude as reported in experiments but would not be expected to damage blood cells because the spatial scales associated with vortex shedding are much larger than blood cell dimensions.}, }
@article {pmid8138415, year = {1994}, author = {Wasiolek, PT}, title = {Experimental evaluation of wire mesh screen counting parameters for measurements of the unattached fraction of radon progeny.}, journal = {Health physics}, volume = {66}, number = {4}, pages = {458-462}, doi = {10.1097/00004032-199404000-00014}, pmid = {8138415}, issn = {0017-9078}, mesh = {Evaluation Studies as Topic ; Radiometry/methods ; Radon Daughters/*analysis ; }, abstract = {Direct measurements (specifically the front-to-back ratio) of alpha radioactivity from radon progeny deposited on the front and back of a 400-wire mesh screen were performed under realistic aerosol conditions outdoors with two scintillation alpha detectors facing both sides of the screen simultaneously. Two flow regimes were tested: one which kept the flow Reynolds number (Ref) for the wire below one (200 L min-1) and a second with the flow Reynolds number for wire > 1 (400 L min-1). To estimate the radioactivity loss in the screen, parallel measurements of open and backup filters were also performed. The average front-to-back ratio expressed as a ratio of the potential alpha energy concentration as measured on the screen side facing the airflow to the other side of the screen for 200 L min-1 and 400 L min-1 was 3.42 +/- 0.32 (standard error) and 2.30 +/- 0.14 (standard error), respectively. The loss of radioactivity in the screen expressed as a ratio between the potential alpha energy concentration measured on an open filter minus backup filter to the sum of the potential alpha energy concentration measured on the front and back of the screen was 1.29 +/- 0.13 and 1.27 +/- 0.22 for 200 and 400 L min-1, respectively.}, }
@article {pmid8198503, year = {1994}, author = {Sidik, WA and Mazumdar, JN}, title = {A mathematical study of turbulent blood flow through an arterial bifurcation.}, journal = {Australasian physical &amp; engineering sciences in medicine}, volume = {17}, number = {1}, pages = {1-13}, pmid = {8198503}, issn = {0158-9938}, mesh = {Arteries/*physiology ; *Blood Flow Velocity ; Computer Simulation ; *Hemorheology ; Models, Cardiovascular ; Models, Theoretical ; }, abstract = {A turbulent model of flow through an arterial bifurcation is proposed in order to investigate flow separation, secondary flow and the variation of pressure and stress along the wall when blood passes through a bifurcation. Blood is assumed to behave like a Newtonian fluid, with viscosity depending on the angle of bifurcation. The geometry of the models used here for aortic bifurcations is set by employing the principle of conservation of mass. The results show that: the peak axial velocity in the entrance region of the daughter vessel occurs on the inner wall of the bifurcation; a strong secondary flow may develop in the branch, which has much less effect on axial flow when the Reynolds number is low; there is a tendency toward separation in the branch with low mean flow, and the flow is increasingly disturbed as the bluntness of the apex increases.}, }
@article {pmid9317705, year = {1994}, author = {Loudon, C and Best, B and Koehl, M}, title = {WHEN DOES MOTION RELATIVE TO NEIGHBORING SURFACES ALTER THE FLOW THROUGH ARRAYS OF HAIRS?.}, journal = {The Journal of experimental biology}, volume = {193}, number = {1}, pages = {233-254}, doi = {10.1242/jeb.193.1.233}, pmid = {9317705}, issn = {1477-9145}, abstract = {Many animals from different phyla use structures bearing arrays of hairs to perform a variety of important functions, such as olfaction, gas exchange, suspension feeding and locomotion. The performance of all these functions depends on the motion of water or air around and through these arrays of hairs. Because organisms often move such hair-bearing appendages with respect to their bodies or the substratum, we assessed the effects of such motion relative to walls on the fluid flow between neighboring hairs. We compared flow fields near dynamically scaled physical models of hairs moving near walls with those calculated for such hairs in an unbounded fluid. Our results suggest that the methods an organism can use to change the flow through a hair-bearing appendage differ with Reynolds number (based on hair diameter). When Re is 10(-2) or below, changing speed does not alter the proportion of the fluid that moves through rather than around the array, whereas moving relative to a wall increases it. In contrast, when Re is between 10(-2) and 1, changes in speed have a big effect on the proportion of fluid moving through the array, while moving near walls makes little difference.}, }
@article {pmid9317589, year = {1994}, author = {Dickinson, M}, title = {THE EFFECTS OF WING ROTATION ON UNSTEADY AERODYNAMIC PERFORMANCE AT LOW REYNOLDS NUMBERS.}, journal = {The Journal of experimental biology}, volume = {192}, number = {1}, pages = {179-206}, doi = {10.1242/jeb.192.1.179}, pmid = {9317589}, issn = {1477-9145}, abstract = {The downstroke-to-upstroke transition of many insects is characterized by rapid wing rotation. The aerodynamic consequences of these rapid changes in angle of attack have been investigated using a mechanical model dynamically scaled to the Reynolds number appropriate for the flight of small insects such as Drosophila. Several kinematic parameters of the wing flip were examined, including the speed and axis of rotation, as well as the duration and angle of attack during the wing stroke preceding rotation. Alteration of these kinematic parameters altered force generation during the subsequent stroke in a variety of ways. 1. When the rotational axis was close to the trailing edge, the model wing could capture vorticity generated during rotation and greatly increase aerodynamic performance. This vortex capture was most clearly manifested by the generation of lift at an angle of attack of 0&amp;deg;. Lift at a 0&amp;deg; angle of attack was also generated following rotation about the leading edge, but only if the downstroke angle was large enough to generate a von Karman street. The lift may be due to an alteration in the effective angle of attack caused by the inter-vortex stream in the downstroke wake. 2. The maximum lift attained (over all angles of attack) was substantially elevated if the wing translated backwards through a wake generated by the previous stroke. Transient lift coefficient values of nearly 4 were obtained when the wing translated back through a von Karman street generated at a 76.5&amp;deg; angle of attack. This effect might also be explained by the influence of the inter-vortex stream, which contributes a small component to fluid velocity in the direction of translation. 3. The growth of lift with angle of attack was significantly elevated following a 7.5 chord stroke with a 76.5&amp;deg; angle of attack, although it was relatively constant under all other kinematic conditions. 4. The results also indicate the discrepancies between transient and time-averaged measures of performance that arise when unsteady mechanisms are responsible for force generation. Although the influence of wing rotation was strong during the first few chords of translation, averaging the performance over as little as 6.5 chords of motion greatly attenuated the effects of rotation. 5. Together, these modeling results suggest that the unsteady mechanisms generated by simple wing flips could provide an important source for the production of aerodynamic forces in insect flight. Furthermore, the extreme sensitivity to small variations in almost all kinematic parameters could provide a foundation for understanding the aerodynamic mechanisms underlying active flight control.}, }
@article {pmid9317518, year = {1994}, author = {Cech, S and Cheer, A}, title = {PADDLEFISH BUCCAL FLOW VELOCITY DURING RAM SUSPENSION FEEDING AND RAM VENTILATION.}, journal = {The Journal of experimental biology}, volume = {186}, number = {1}, pages = {145-156}, doi = {10.1242/jeb.186.1.145}, pmid = {9317518}, issn = {1477-9145}, abstract = {A micro-thermistor probe was inserted into the buccal cavity of freely swimming paddlefish to measure flow velocity during ram ventilation, ram suspension feeding and prey processing. Swimming speed was measured from videotapes recorded simultaneously with the buccal flow velocity measurements. Both swimming velocity and buccal flow velocity were significantly higher during suspension feeding than during ram ventilation. As the paddlefish shifted from ventilation to feeding, buccal flow velocity increased to approximately 60 % of the swimming velocity. During prey processing, buccal flow velocity was significantly higher than the swimming velocity, indicating that prey processing involves the generation of suction. The Reynolds number (Re) for flow at the level of the paddlefish gill rakers during feeding is about 30, an order of magnitude lower than the Re calculated previously for pump suspension-feeding blackfish. These data, combined with data available from the literature, indicate that the gill rakers of ram suspension-feeding teleost fishes may operate at a substantially lower Re than the rakers of pump suspension feeders.}, }
@article {pmid9317492, year = {1994}, author = {Gibb, A and Jayne, B and Lauder, G}, title = {KINEMATICS OF PECTORAL FIN LOCOMOTION IN THE BLUEGILL SUNFISH LEPOMIS MACROCHIRUS.}, journal = {The Journal of experimental biology}, volume = {189}, number = {1}, pages = {133-161}, doi = {10.1242/jeb.189.1.133}, pmid = {9317492}, issn = {1477-9145}, abstract = {The pectoral fins of ray-finned fishes are flexible and capable of complex movements, and yet little is known about the pattern of fin deformation during locomotion. For the most part, pectoral fins have been modeled as rigid plates. In order to examine the movements of different portions of pectoral fins, we quantified the kinematics of pectoral fin locomotion in the bluegill sunfish Lepomis macrochirus using several points on the distal fin edge and examined the effects of swimming speed on fin movements. We simultaneously videotaped the ventral and lateral views of pectoral fins of four fish swimming in a flow tank at five speeds ranging from 0.3 to 1.1 total lengths s-1. Four markers, placed on the distal edge of the fin, facilitated field-by-field analysis of kinematics. We used analyses of variance to test for significant variation with speed and among the different marker positions. Fin beat frequency increased significantly from 1.2 to 2.1 Hz as swimming speed increased from 0.3 to 1.0 total lengths s-1. Maximal velocities of movement for the tip of the fin during abduction and adduction generally increased significantly with increased swimming speed. The ratio of maximal speed of fin retraction to swimming speed declined steadily from 2.75 to 1.00 as swimming speed increased. Rather than the entire distal edge of the fin always moving synchronously, markers had phase lags as large as 32 with respect to the dorsal edge of the fin. The more ventral and proximal portions of the fin edge usually had smaller amplitudes of movement than did the more dorsal and distal locations. With increased swimming speed, the amplitudes of the lateral and longitudinal fin movements generally decreased. We used two distal markers and one basal reference point to determine the orientation of various planar fin elements. During early adduction and most of abduction, these planar fin elements usually had positive angles of attack. Because of fin rotation, angles of attack calculated from three-dimensional data differed considerably from those estimated from a simple lateral projection. As swimming speed increased, the angles of attack of the planar fin elements with respect to the overall direction of swimming approached zero. The oscillatory movements of the pectoral fins of bluegill suggest that both lift- and drag-based propulsive mechanisms are used to generate forward thrust. In addition, the reduced frequency parameter calculated for the pectoral fin of Lepomis (sigma=0.85) and the Reynolds number of 5x10(3) indicate that acceleration reaction forces may contribute significantly to thrust production and to the total force balance on the fin.}, }
@article {pmid8173038, year = {1994}, author = {Sugihara-Seki, M}, title = {The motion of two cylinders in contact in channel flow.}, journal = {Biorheology}, volume = {31}, number = {1}, pages = {1-10}, doi = {10.3233/bir-1994-31101}, pmid = {8173038}, issn = {0006-355X}, mesh = {Mathematics ; *Models, Biological ; *Rheology ; }, abstract = {The motion of a doublet consisting of two rigidly connected circular cylinders freely suspended in an incompressible Newtonian fluid in a narrow channel bounded by two parallel planes is studied numerically at zero Reynolds number. The Stokes equations are solved by a finite element method for various positions and orientations of the particle, and the trajectories of the particle are determined for a number of initial configurations. A doublet of equal-sized cylinders is found either to tumble or oscillate in rotation, while a doublet of unequal-sized cylinders possesses a stable, steady equilibrium configuration, at which the particle is located close to the channel centerline with a constant angle of inclination. Thus, doublets of unequal diameters tumble, oscillate in rotation or approach the equilibrium configuration asymptotically, depending on the radius ratio of cylinders, particle size-channel width ratio and initial conditions.}, }
@article {pmid8106534, year = {1994}, author = {Uijttewaal, WS and Nijhof, EJ and Heethaar, RM}, title = {Lateral migration of blood cells and microspheres in two-dimensional Poiseuille flow: a laser-Doppler study.}, journal = {Journal of biomechanics}, volume = {27}, number = {1}, pages = {35-42}, doi = {10.1016/0021-9290(94)90030-2}, pmid = {8106534}, issn = {0021-9290}, mesh = {Blood Flow Velocity ; Blood Platelets/cytology/*physiology ; Cell Movement ; Cell Size ; Erythrocytes/cytology/*physiology ; Humans ; Laser-Doppler Flowmetry/instrumentation ; Microspheres ; Models, Biological ; Particle Size ; Polystyrenes ; Pulsatile Flow ; Rheology ; Rotation ; Viscosity ; }, abstract = {The inertia-induced lateral migration of rigid microspheres, platelets and erythrocytes is studied experimentally. The concentration and velocity profiles of the particles have been determined with a laser-Doppler anemometer designed for high resolution measurements. Data are compared with empirical and analytical models on inertia-induced lateral migration of rigid spheres. Experiments done in rectangular flow channels of high aspect ratio reveal that at a sufficiently high particle Reynolds number, platelets exhibit tubular pinch effects comparable with those of rigid polystyrene microspheres. Erythrocytes also exhibit inertia-induced lateral migration at high particle Reynolds number and low medium viscosity. At a higher medium viscosity, erythrocytes show deformation-induced lateral migration towards the center of the flow channel.}, }
@article {pmid7764532, year = {1994}, author = {Tempelman, LA and Park, S and Hammer, DA}, title = {Motion of model leukocytes near a wall in simple shear flow.}, journal = {Biotechnology progress}, volume = {10}, number = {1}, pages = {97-108}, doi = {10.1021/bp00025a012}, pmid = {7764532}, issn = {8756-7938}, mesh = {Animals ; Cell Adhesion ; Cell Movement ; Leukemia, Basophilic, Acute/pathology ; Leukocytes/*physiology ; Rats ; Tumor Cells, Cultured ; }, abstract = {Receptor-mediated cell adhesion to surfaces depends on the motion of the cell prior to adhesion. We studied the hydrodynamic behavior of cells near a wall in simple shear flow using a model leukocyte system that we have also used extensively in cell-substrate adhesion studies. Specifically, we measured the velocity of rat basophilic leukemia (RBL) cells near a surface in a parallel-plate flow chamber and compared it to the motion of polystyrene beads and glutaraldehyde-fixed RBL cells. We found that RBL cells (13 microns diameter) travel 25% faster than polystyrene beads of 14.5 microns diameter for a wide range of shear rates (20-180 s-1); this suggests that RBL cells would travel 39% faster than polystyrene beads of equivalent size. Glutaraldehyde-fixed RBL cells travel at a velocity between those of live cells and 14.5-microns beads. These differences in velocities have been observed over both polyacrylamide gel and glass substrates. Application of a theory for hard sphere motion near a wall in simple shear flow at low Reynolds number [Goldman, A.J.; Cox, R.G.; Brenner, H. Chem. Eng. Sci. 1967b, 22, 653-660] to our measured cell velocities suggests that cells are separated from the wall by > or = 550 nm. Such large separation distances have also been predicted by others who have used hard sphere theory to analyze the effect of shear flow on cell motion near walls. However, the extensive receptor-mediated cell adhesion seen in these systems is inconsistent with these separation distances, which are approximately 30 times greater than the distance required for receptor-ligand contact. Instead, we propose that, because of cell deformability and cell surface roughness, cells remain within a separation distance that allows for molecular contact while they travel faster than the hard sphere theory predicts. Therefore, the theory of Goldman and co-workers, while adequate for hard sphere motion, is likely not accurate for cellular motion.}, }
@article {pmid8248974, year = {1993}, author = {Fleischer, LH and Young, WL and Pile-Spellman, J and terPenning, B and Kader, A and Stein, BM and Mohr, JP}, title = {Relationship of transcranial Doppler flow velocities and arteriovenous malformation feeding artery pressures.}, journal = {Stroke}, volume = {24}, number = {12}, pages = {1897-1902}, doi = {10.1161/01.str.24.12.1897}, pmid = {8248974}, issn = {0039-2499}, support = {R01-27713//PHS HHS/United States ; }, mesh = {Adult ; Blood Pressure ; Cerebral Hemorrhage/prevention &amp; control ; Female ; Humans ; Intracranial Arteriovenous Malformations/*physiopathology ; Male ; Regional Blood Flow ; Ultrasonics ; }, abstract = {BACKGROUND AND PURPOSE: Feeding mean arterial pressure immediately proximal to the nidus of arteriovenous malformations may influence the frequency of spontaneous intracerebral hemorrhage. This study assessed the usefulness of transcranial Doppler ultrasound velocities as a noninvasive estimate of feeding mean arterial pressure.<br><br>METHODS: We studied 41 patients undergoing 73 staged treatments of arteriovenous malformations with endovascular embolization, surgery, or both. Before treatment during the awake state, transcranial Doppler mean and peak velocities were recorded in proximal Willisian vessels. During superselective angiography with the patient under conscious sedation or during surgery with the patient under general anesthesia, feeding mean arterial pressure was measured through a 1.5F transfemoral intracranial microcatheter or a 26-g needle by direct puncture. Measurement of insonated artery diameter was possible in 41 embolizations, and a flow velocity index (mL/min) and Reynolds' number were estimated.<br><br>RESULTS: Mean +/- SEM feeding mean arterial pressure was 38 +/- 2 mm Hg at a systemic mean arterial pressure of 77 +/- 2 mm Hg; mean velocity was 102 +/- 4 cm/s. There was an inverse correlation between feeding mean arterial pressure and parent artery mean velocity (y = -0.74x + 130, r = .35, P = .0025). The best correlation was for the first treatment in each patient (n = 27) using the highest peak velocity obtainable in a Willisian vessel ipsilateral to the arteriovenous malformation (y = -1.61x + 221, r = .62, P = .0005). Flow velocity index (775 +/- 106 mL/min) did not correlate with feeding mean arterial pressure, but there was a weak correlation with Reynolds' number (y = -12x + 1616, r = .27, P = .1283). Mean Reynolds' number was 1257 +/- 119.<br><br>CONCLUSIONS: Transcranial Doppler mean velocity is correlated with feeding mean arterial pressure but only weakly predictive. Considerations influencing the relation of distal feeding mean arterial pressure to proximal mean velocity might include the influence of other fistulae in the circuit between major inflow and outflow channels as well as turbulent flow at vascular branch points between point of insonation and the nidus, as suggested by Reynolds' number values of more than 400.}, }
@article {pmid8125899, year = {1993}, author = {Quail, AW and Cottee, DB and White, SW}, title = {Limitations of a pulsed Doppler velocimeter for blood flow measurement in small vessels.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {75}, number = {6}, pages = {2745-2754}, doi = {10.1152/jappl.1993.75.6.2745}, pmid = {8125899}, issn = {8750-7587}, mesh = {Animals ; Aorta, Abdominal/physiology ; Coronary Circulation/physiology ; Dogs ; Femoral Artery/physiology ; Hematocrit ; Microcirculation/*physiology ; Rabbits ; Renal Artery/physiology ; Rheology/*instrumentation ; Ultrasonics ; }, abstract = {The performance of a new and simplified flow probe construction and the Iowa 545C-4 pulsed Doppler velocimeter was evaluated for measurement of blood flow over several months in small arteries of awake animals. Calibrations were performed over a wide range of intraluminal pressures and physiological flow velocities. Pressure-dependent differences in slope of the Doppler shift-volume flow relationship were detected in some probes. Signal strength was maintained at hematocrits > 10%. Distortion of pulsed Doppler signal peaks occurred in the conscious rabbit at peak aortic velocities, at which Reynold's number for turbulence was exceeded and the Doppler shift surpassed the Nyquist limit of 31.25 kHz for the velocimeter. Although the Doppler shift-volume flow relationship is linear at < 5 kHz, in some cases at higher Doppler shifts and blood flow velocities the relationship may become nonlinear, thus causing the volume flow rate to be underestimated by up to 38%. The cause of this phenomenon may be "aliasing" and/or the consequence of the range control capability of the velocimeter selectively sampling changing velocity profiles and flow disturbances in the central stream at higher velocities.}, }
@article {pmid8309237, year = {1993}, author = {Budwig, R and Elger, D and Hooper, H and Slippy, J}, title = {Steady flow in abdominal aortic aneurysm models.}, journal = {Journal of biomechanical engineering}, volume = {115}, number = {4A}, pages = {418-423}, doi = {10.1115/1.2895506}, pmid = {8309237}, issn = {0148-0731}, mesh = {Aortic Aneurysm, Abdominal/*physiopathology ; Aortic Rupture/physiopathology ; Humans ; Laser-Doppler Flowmetry ; *Models, Cardiovascular ; Regional Blood Flow/physiology ; Stress, Physiological/physiopathology ; }, abstract = {Steady flow in abdominal aortic aneurysm models has been examined for four aneurysm sizes over Reynolds numbers from 500 to 2600. The Reynolds number is based on entrance tube diameter, and the inlet condition is fully developed flow. Experimental and numerical methods have been used to determine: (i) the overall features of the flow, (ii) the stresses on the aneurysm walls in laminar flow, and (iii) the onset and characteristics of turbulent flow. The laminar flow field is characterized by a jet of fluid (passing directly through the aneurysm) surrounded by a recirculating vortex. The wall shear stress magnitude in the recirculation zone is about ten times less than in the entrance tube. Both wall shear stress and wall normal stress profiles exhibit large magnitude peaks near the reattachment point at the distal end of the aneurysm. The onset of turbulence in the model is intermittent for 2000 < Re < 2500. The results demonstrate that a slug of turbulence in the entrance tube grows much more rapidly in the aneurysm than in a corresponding length of uniform cross section pipe. When turbulence is present in the aneurysm the recirculation zone breaks down and the wall shear stress returns to a magnitude comparable to that in the entrance tube.}, }
@article {pmid8309236, year = {1993}, author = {Nakamura, M and Sugiyama, W and Haruna, M}, title = {An experiment on the pulsatile flow at transitional Reynolds numbers--the fluid dynamical meaning of the blood flow parameters in the aorta.}, journal = {Journal of biomechanical engineering}, volume = {115}, number = {4A}, pages = {412-417}, doi = {10.1115/1.2895505}, pmid = {8309236}, issn = {0148-0731}, mesh = {Aorta/*physiology ; Humans ; *Models, Cardiovascular ; Pulsatile Flow/*physiology ; Rheology ; Stress, Physiological/physiopathology ; }, abstract = {An experiment on the fully developed sinusoidal pulsatile flow at transitional Reynolds numbers was performed to evaluate the basic characteristics of the wall shear stress. In this experiment, the wall shear stress was calculated from the measured section averaged axial velocity and the pressure gradient by using the section averaged Navier-Stokes equation. The experimental results showed that the ratio of the amplitude of the wall shear stress to the amplitude of the pressure gradient had the maximum value when the time averaged Reynolds number was about 4000 and the Womersley number was about 10. As this condition is close to the blood flow condition in the human aorta, it is suggested that the parameter of the aorta has an effect to increase the amplitude of the wall shear stress acting on the arterial wall.}, }
@article {pmid8238592, year = {1993}, author = {Strony, J and Beaudoin, A and Brands, D and Adelman, B}, title = {Analysis of shear stress and hemodynamic factors in a model of coronary artery stenosis and thrombosis.}, journal = {The American journal of physiology}, volume = {265}, number = {5 Pt 2}, pages = {H1787-96}, doi = {10.1152/ajpheart.1993.265.5.H1787}, pmid = {8238592}, issn = {0002-9513}, mesh = {Animals ; Blood Pressure ; Blood Viscosity ; *Coronary Circulation ; Coronary Thrombosis/pathology/*physiopathology ; Coronary Vessels/pathology/*physiopathology ; Disease Models, Animal ; Dogs ; Female ; Heart Rate ; *Hemodynamics ; Male ; Mathematics ; *Models, Cardiovascular ; Muscle, Smooth, Vascular/pathology/physiopathology ; Platelet Count ; Stress, Mechanical ; }, abstract = {Shear stress and alterations in blood flow within a stenosed artery promote platelet-dependent thrombosis. Using the Folts model of coronary thrombosis, we evaluated morphology, histology, and the hemodynamic properties of the stenosed vessel in 18 animals. The average stenosis created was 58 +/- 8%, with stenosed vessel diameters ranging from 0.084 to 0.159 cm. Histological examination of the stenosed vessel demonstrated that thrombi were composed primarily of platelets and formation occurred 1.0 mm downstream from the apex of the constriction, propagating distally. Peak shear stress occurred just upstream from the apex of the stenosis and varied from 520 to 3,349 dyn/cm2. Only small differences in shear forces were noted when blood viscosity was calculated using Newtonian and non-Newtonian properties. In contrast, shear stress computed for Poiseuille flow with use of the stenosis diameter underestimated the apical shear stress. Blood flow remained laminar within the stenosis with a Reynolds number range of 292-534. Our data indicate that the geometry of the stenosis inflow region must be considered in the evaluation of platelet activation and thrombus formation within a stenosed artery.}, }
@article {pmid10053863, year = {1993}, author = {Procaccia, I and Constantin, P}, title = {Non-Kolmogorov scaling exponents and the geometry of high Reynolds number turbulence.}, journal = {Physical review letters}, volume = {70}, number = {22}, pages = {3416-3419}, doi = {10.1103/PhysRevLett.70.3416}, pmid = {10053863}, issn = {1079-7114}, }
@article {pmid10053821, year = {1993}, author = {She, ZS and Chen, S and Doolen, G and Kraichnan, RH and Orszag, SA}, title = {Reynolds number dependence of isotropic Navier-Stokes turbulence.}, journal = {Physical review letters}, volume = {70}, number = {21}, pages = {3251-3254}, doi = {10.1103/PhysRevLett.70.3251}, pmid = {10053821}, issn = {1079-7114}, }
@article {pmid8391432, year = {1993}, author = {Fang, CP and Wilson, JE and Spektor, DM and Lippmann, M}, title = {Effect of lung airway branching pattern and gas composition on particle deposition in bronchial airways: III. Experimental studies with radioactively tagged aerosol in human and canine lungs.}, journal = {Experimental lung research}, volume = {19}, number = {3}, pages = {377-396}, doi = {10.3109/01902149309064353}, pmid = {8391432}, issn = {0190-2148}, support = {CA13343/CA/NCI NIH HHS/United States ; NIEHS ES00260/ES/NIEHS NIH HHS/United States ; NIEHS ES00881/ES/NIEHS NIH HHS/United States ; }, mesh = {Aerosols ; Animals ; Bronchi/*anatomy &amp; histology/chemistry/metabolism ; Dogs ; Female ; Gases/analysis/*metabolism ; Humans ; Lung/*anatomy &amp; histology/chemistry/metabolism ; Male ; Particle Size ; *Sodium Pertechnetate Tc 99m ; }, abstract = {Particle penetration into lung airways during normal respiration is affected by the exchange of inspired air and residual gas. In this study, particle penetration during the inspiratory phase was investigated using gamma-tagged monodisperse particles (0.70, 0.90, 0.96, and 1.44 microns) suspended in various carrier gases having a wide range of kinematic viscosity. A 40-mL bolus of tagged aerosol was drawn into excised human and dog lungs at the end of a tidal breath, followed by a long breathhold to allow for complete particle deposition by sedimentation. The lungs were then fixed, sectioned, and autoradiographed to determine tidal front locations. In human lungs, particles suspended in He-O2 penetrated deeper than particles suspended in air; particles penetrated least in SF6-O2. Dog lungs, which have more asymmetrical airway branching patterns than human lungs, had no significant particle penetration differences associated with carrier gas composition. It is concluded that particle penetration during the inspiratory phase is dependent on factors that determine flow profile development, such as branching pattern and the Reynolds number of the carrier gas. The bolus front at the end of an air inspiration extended into about 10% of human lung airways of 1 mm diameter, and into about 0.1% of 0.5-mm airways. It is concluded that rapid particle penetration to 1-mm airways during high-frequency oscillatory ventilation of lung casts is due to cumulative axial core transport during multiple breathing cycles. Similarly, the dispersion of an aerosol bolus from large airways to small airways during in vivo breathholding studies appears to be due to oscillatory flow created by the heartbeat.}, }
@article {pmid8348583, year = {1993}, author = {Kajiya, F and Matsuoka, S and Ogasawara, Y and Hiramatsu, O and Kanazawa, S and Wada, Y and Tadaoka, S and Tsujioka, K and Fujiwara, T and Zamir, M}, title = {Velocity profiles and phasic flow patterns in the non-stenotic human left anterior descending coronary artery during cardiac surgery.}, journal = {Cardiovascular research}, volume = {27}, number = {5}, pages = {845-850}, doi = {10.1093/cvr/27.5.845}, pmid = {8348583}, issn = {0008-6363}, mesh = {Adolescent ; Adult ; Aged ; Blood Flow Velocity/physiology ; *Cardiac Surgical Procedures ; Child ; Coronary Circulation/*physiology ; Coronary Vessels/diagnostic imaging ; Female ; Heart Septal Defects, Atrial/diagnostic imaging/surgery ; Humans ; Intraoperative Period ; Male ; Middle Aged ; Regional Blood Flow/physiology ; Ultrasonography ; }, abstract = {OBJECTIVE: The aim was to investigate the phasic characteristics of normal human left coronary artery flow and velocity profiles across the vessel.<br><br>METHODS: The phasic characteristics of flow in the human left anterior descending coronary artery, the centreline flow velocities, and the velocity profiles were measured in 10 patients during corrective surgery for atrial septal defect after closure of the defect. None of these patients had any detectable coronary artery stenosis or left ventricular hypertrophy. Measurements were made with a 20 MHz 80 channel pulsed Doppler velocimeter.<br><br>RESULTS: The velocity waveform displayed a diastolic-predominant pattern with a systolic to diastolic velocity ratio of 0.29(SD 0.17). Reverse flow was observed in early systole in five patients and in mid to late systole in six patients. The values of peak Reynolds number, unsteadiness parameter, and pulsatility index were 504(198), 2.5(0.6), and 5.9(4.4) respectively. The velocity profiles during diastole showed considerable variability in shape, ranging from symmetrical to skewed to M shaped patterns. The peak wall shear rate was 765(250) s-1 on the epicardial wall of the vessel and 712(301) s-1 on the myocardial wall; the difference was not statistically significant.<br><br>CONCLUSIONS: The velocity waveform displayed a diastolic-predominant pattern. Considerable variability in shape of the velocity profile was found and was perhaps due to the time evolution of the velocity profile within the diastolic time period.}, }
@article {pmid8286727, year = {1993}, author = {Matsuo, T and Okeda, R and Yamamoto, K}, title = {Study of biofluid mechanics at arterial bifurcations: importance of flow division ratio as a parameter.}, journal = {Biorheology}, volume = {30}, number = {3-4}, pages = {267-274}, doi = {10.3233/bir-1993-303-411}, pmid = {8286727}, issn = {0006-355X}, mesh = {Animals ; Arterial Occlusive Diseases/physiopathology ; *Arteries ; Biomechanical Phenomena ; Cats ; *Hemorheology ; Humans ; Models, Biological ; Regional Blood Flow ; }, abstract = {We re-examined the measurement of the mass flow ratio at model bifurcations as a function of the inlet Reynolds number, which has been used to study the role of arterial bifurcation in distal blood supply. However, this relationship was found not to be applicable to investigations of blood circulation, because the measured mass flow ratio is strongly dependent on the resistance downstream of the bifurcation, and therefore is specific to the experimental set-up. An alternative approach for studying the role of arterial bifurcation is presented, in which the flow division ratio is used as a parameter.}, }
@article {pmid8464081, year = {1993}, author = {Ojha, M and Cobbold, RS and Johnston, KW}, title = {Hemodynamics of a side-to-end proximal arterial anastomosis model.}, journal = {Journal of vascular surgery}, volume = {17}, number = {4}, pages = {646-655}, pmid = {8464081}, issn = {0741-5214}, mesh = {Anastomosis, Surgical ; Arteries/*physiology/*surgery ; Blood Flow Velocity ; Coloring Agents ; *Hemodynamics ; Humans ; Lasers ; *Models, Cardiovascular ; *Models, Structural ; Stress, Mechanical ; Ultraviolet Rays ; }, abstract = {PURPOSE: The purpose of this article was to analyze the fluid mechanical effects of a side-to-end proximal anastomosis and to compare the results with those from our earlier study on the end-to-side distal anastomosis.<br><br>METHODS: The photochromic tracer technique was used to determine the instantaneous wall shear stress and to visualize the overall flow field under pulsatile flow conditions. The flow consisted of a sinusoid plus a steady component with mean and modulation Reynolds numbers of 355 and 565, respectively, and a Womersley number of 7.9.<br><br>RESULTS: At the toe and heel of the junction, very high and positive wall shear stresses were seen together with substantial nonperiodic fluctuations. The peak wall shear stress was about four times higher at the toe and about seven times higher at the heel than the maximum values observed at about four tube diameters upstream from the junction. On the bed of the host vessel, nonperiodic fluctuations were also observed, but the shear stresses were mainly negative with magnitudes comparable to those seen upstream. With leakages of 11% and 28% of the mean flow through the blocked end of the host vessel, the shear stress pattern seemed to be significantly affected only at the toe for the higher leakage. Further, when the mean Reynolds number was reduced to 320, the magnitudes of the variations in the wall shear stress were reduced proportionately, except at the heel, where the reduction was much larger than expected.<br><br>CONCLUSIONS: It appears that the preferential development of intimal hyperplasia at the distal end-to-side anastomosis may be promoted by low wall shear stress at the toe and heel, and probably by high shear stresses or shear stress gradients on the bed.}, }
@article {pmid8445887, year = {1993}, author = {White, SS and Zarins, CK and Giddens, DP and Bassiouny, H and Loth, F and Jones, SA and Glagov, S}, title = {Hemodynamic patterns in two models of end-to-side vascular graft anastomoses: effects of pulsatility, flow division, Reynolds number, and hood length.}, journal = {Journal of biomechanical engineering}, volume = {115}, number = {1}, pages = {104-111}, doi = {10.1115/1.2895456}, pmid = {8445887}, issn = {0148-0731}, support = {HL 41267/HL/NHLBI NIH HHS/United States ; }, mesh = {Anastomosis, Surgical/*standards ; Animals ; Blood Vessel Prosthesis/*standards ; Dogs ; Evaluation Studies as Topic ; *Hemodynamics ; Models, Anatomic ; *Models, Cardiovascular ; *Pulsatile Flow ; Rheology ; }, abstract = {Flow behavior in models of end-to-side vascular graft anastomoses was studied under steady and pulsatile flow conditions. Models were constructed to simulate geometries employed in experimental studies on intimal thickening in a canine model. Reynolds numbers, division of flow in the outflow tracts and the pulsatile waveform employed were taken from measurements obtained in the canine model. Flows in the scaled-up, transparent models were visualized with white, neutrally buoyant particles which were photographed under laser illumination and also recorded on video tape under bright incandescent light. Strong, three-dimensional helical patterns which formed in the anastomotic junction were prominent features of the flow fields. Regions of low wall shear, oscillatory wall shear and long particle residence time were identified from the flow visualization experiments. Comparisons with the limited qualitative data available on intimal thickening in vascular graft anastomoses suggest a relation between localization of vascular intimal thickening and those surfaces experiencing low shear and long particle residence time.}, }
@article {pmid8431653, year = {1993}, author = {Zou, Q and Liu, Z and Goldberg, IS}, title = {On nonaxisymmetric entry flow at very low Reynolds numbers.}, journal = {Mathematical biosciences}, volume = {113}, number = {2}, pages = {245-260}, doi = {10.1016/0025-5564(93)90004-t}, pmid = {8431653}, issn = {0025-5564}, support = {GM 02721-07/GM/NIGMS NIH HHS/United States ; }, mesh = {Animals ; Humans ; Lung/anatomy &amp; histology/*physiology ; *Mathematics ; *Models, Biological ; Viscosity ; }, abstract = {The eigensolution of nonaxisymmetric entry flow of a Newtonian viscous fluid with very small Reynolds number in a semiinfinite rigid circular pipe is obtained. Leading eigenvalues are computed for steady flow and two periodic cases. The result shows that the entry length for nonaxisymmetric flows should be longer than the entry length for axisymmetric flows.}, }
@article {pmid8427127, year = {1993}, author = {Denardo, SJ and Yamada, EG and Hargrave, VK and Yock, PG}, title = {Effect of stenosis inlet geometry on shear rates of blood flow in the upstream region.}, journal = {American heart journal}, volume = {125}, number = {2 Pt 1}, pages = {350-356}, doi = {10.1016/0002-8703(93)90011-w}, pmid = {8427127}, issn = {0002-8703}, mesh = {Animals ; Aorta/diagnostic imaging/pathology/*physiopathology ; Blood Flow Velocity ; Constriction, Pathologic/diagnostic imaging/pathology/physiopathology ; Dogs ; In Vitro Techniques ; Models, Cardiovascular ; Regional Blood Flow ; Rheology ; Ultrasonography ; }, abstract = {Abnormal shear rates of blood flow have been implicated in the processes of thrombosis, atherosclerosis, and restenosis after angioplasty. However, no study has quantitated the effect of stenosis inlet geometry on the shear rates in the region upstream to the stenosis. To quantitate this effect, we measured the velocity profiles of blood flow at Reynolds numbers 175 and 350 upstream to different axisymmetric model stenoses in an excised canine aorta. Two 40% and two 75% stenoses were tested, one each with a 45-degree inlet angulation and one each with a 90-degree angulation. For the velocity measurements we used a specially developed external single-channel Doppler ultrasound system capable of resolving blood flow velocity at 91 microns radial intervals across the aorta. We found that increasing the severity of stenosis narrowing and angulation resulted in a significant decrease in shear rate at the endothelial surface (40%/45-degree stenosis: 189 +/- 46 sec-1 vs 75%/90-degree stenosis: 49 +/- 12 sec-1 at Reynolds number 350; p < 0.002) and a significant increase in the maximum shear rate within the vessel lumen (189 +/- 46 sec-1 vs 295 +/- 8 sec-1, respectively; p < 0.05) in the region immediately upstream to the stenosis. These effects were less pronounced for Reynolds number 175. We conclude that stenosis inlet geometry has a significant impact on the flow conditions in the region immediately upstream to the stenosis, which is dependent on the Reynolds number. This may be an important determinant of thrombosis and atherogenesis in this particular region.}, }
@article {pmid8511826, year = {1993}, author = {Bascom, PA and Cobbold, RS and Routh, HF and Johnston, KW}, title = {On the Doppler signal from a steady flow asymmetrical stenosis model: effects of turbulence.}, journal = {Ultrasound in medicine &amp; biology}, volume = {19}, number = {3}, pages = {197-210}, doi = {10.1016/0301-5629(93)90110-a}, pmid = {8511826}, issn = {0301-5629}, mesh = {*Blood Flow Velocity ; Constriction ; Humans ; *Models, Cardiovascular ; Models, Structural ; Rheology ; *Ultrasonography ; }, abstract = {A steady flow model with a 70% (by area) asymmetrical stenosis was used to examine how changing flow regimes (laminar to turbulent) affect the Doppler signal. Human red blood cells (RBCs) (Hct = 42%) in saline were employed at a flow rate corresponding to a Reynold's number of approximately 545. A dilute suspension of 4% fixed RBCs was also used for the purpose of backscattered power comparison. Measurements of the Doppler signal enabled the backscattered power, time domain statistics, frequency spectra, frequency domain statistics, various spectral indices, autocorrelation function and decorrelation time to be calculated as a function of distance from the stenosis. It is shown that the characteristics of the Doppler signal measured at each site provide information on the nature of the insonated flow field and these correlate well with those expected. The results demonstrate that the onset of turbulence not only affects the Doppler spectrum but also has a profound effect on the signal power, the decorrelation time and the signal statistics.}, }
@article {pmid8444681, year = {1993}, author = {Louis, B and Isabey, D}, title = {Interaction of oscillatory and steady turbulent flows in airway tubes during impedance measurement.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {74}, number = {1}, pages = {116-125}, doi = {10.1152/jappl.1993.74.1.116}, pmid = {8444681}, issn = {8750-7587}, mesh = {*Air Movements ; Air Pressure ; Airway Resistance/*physiology ; Intubation, Intratracheal ; Models, Biological ; *Respiratory Physiological Phenomena ; Viscosity ; }, abstract = {Measurement of input respiratory impedance is carried out by superimposing forced oscillations on spontaneous breathing. The latter thus acts as a quasi-steady unidirectional flow component, with effects on the measured impedance that are habitually neglected (linearity assumption). We examined the validity of that assumption in the case of a turbulent steady flow. We tested the validity of a fluid dynamics criterion previously proposed in water channel experiments for gas flow in a tube. This criterion states that oscillatory and continuous turbulent flow may or may not interact if the Stokes boundary layer (ls) is embedded within the viscous sublayer (lv), i.e., if lS+ = lS/lv < or = 10, implying Re7/8 < or = (100 alpha/square root of 2), for a fully developed hydraulically smooth turbulent flow in a tube (where alpha is Womersley parameter and Re is Reynolds number of the steady-flow component). Experiments were performed in long rigid circular and semicircular tubes by superimposing two independent well-defined flows: 1) laminar oscillatory flow obeying the linear transmission line model (frequency = 1.5-250 Hz, i.e., alpha = 6-80) and 2) fully developed turbulent flow characterized by Blasius resistance formula (Re = 3,000-16,000). Confirming the validity of the criterion above, we found that the real and the imaginary parts of the long-tube impedance did not differ from those measured in the absence of a steady-flow component, provided lS+ < or = 10. On the contrary, the real parts measured with and without the continuous component differed greatly as soon as lS+ > 10, both for circular and semicircular tubes and for outward as well as inward steady flows. We concluded that the proposed criterion is pertinent for predicting appropriate oscillation frequency for a given rate of spontaneous flow, such that oscillatory and turbulent flows do not interact. Application of the forced oscillation measurement technique during spontaneous breathing requires use of a range of oscillatory frequencies higher than the frequency range classically used during apnea.}, }
@article {pmid8374103, year = {1993}, author = {Baaijens, JP and van Steenhoven, AA and Janssen, JD}, title = {Numerical analysis of steady generalized Newtonian blood flow in a 2D model of the carotid artery bifurcation.}, journal = {Biorheology}, volume = {30}, number = {1}, pages = {63-74}, pmid = {8374103}, issn = {0006-355X}, mesh = {Carotid Arteries/anatomy &amp; histology/*physiology ; Humans ; Models, Cardiovascular ; Regional Blood Flow/*physiology ; Rheology ; }, abstract = {The stationary flow of blood in a two-dimensional model of the bifurcation of the human carotid artery is simulated numerically using a finite element method. The Reynolds number is taken as equal to 300, corresponding to the value during the end-diastolic phase of the heart cycle. As constitutive equations, the Newtonian model and the non-Newtonian power-law and Casson models are used. The chosen model parameters corresponded with blood. The flow in this geometry is determined by the branching of the artery and the existence of a reversed flow area in the internal carotid artery. From the results of this problem, we conclude that the general flow structure is not influenced by the generalized (non-)Newtonian models. However, there are differences that cannot be neglected. First, the generalized Newtonian models result in axial and secondary velocity profiles that have 5-10% lower maximum values compared to the Newtonian model. Second, the pressure has higher values in the case of the generalized Newtonian models, especially in the internal carotid artery where these models give maximal 25% higher pressure values. Third, along the divider wall, the wall shear stresses are lower for the generalized Newtonian models; near the apex, this difference is maximal 40% in case of the power-law model. The generalized Newtonian models give higher wall shear stresses along the non-divider wall than the Newtonian model, the maximum difference being 5%. And fourth, in the internal carotid artery the reversed flow area is 10% reduced by the generalized Newtonian models. In general, the differences are more pronounced in the case of the power-law model.}, }
@article {pmid8323879, year = {1993}, author = {Lee, D and Chiu, JJ}, title = {Computation of flow fields and shear rates in an aortic bifurcation.}, journal = {Frontiers of medical and biological engineering : the international journal of the Japan Society of Medical Electronics and Biological Engineering}, volume = {5}, number = {1}, pages = {23-29}, pmid = {8323879}, issn = {0921-3775}, mesh = {Aorta, Abdominal/*physiology ; Blood Viscosity ; *Computer Simulation ; Hemodynamics/physiology ; *Models, Cardiovascular ; Pulsatile Flow ; *Rheology ; Stress, Mechanical ; }, abstract = {A finite volume method in a boundary-fitted coordinate system together with a zonal grid method is employed to compute the flow fields and shear stresses in a two-dimensional aortic bifurcation. Eddy is found distal to plaques during pulsatile flow, whereas permanent eddies are observed only during steady flow. The computed flow fields are consistent with those visualized experimentally by other authors. It is also found that although the time averaged shear rates in a pulsatile flow are similar to those of a steady flow with mean Reynolds number in most regions, they are different in recirculation zones. This result implies that care should be taken if a steady flow shear rate were to be used in modeling shear-dependent physiological processes. The non-Newtonian viscosity has only a minor effect on the flows.}, }
@article {pmid8241034, year = {1993}, author = {Matsuzawa, T}, title = {Finite element analysis in three-dimensional flow through a lateral saccular aneurysm.}, journal = {Frontiers of medical and biological engineering : the international journal of the Japan Society of Medical Electronics and Biological Engineering}, volume = {5}, number = {2}, pages = {89-94}, pmid = {8241034}, issn = {0921-3775}, mesh = {Aortic Aneurysm, Abdominal/*physiopathology ; Hemodynamics/physiology ; Humans ; *Models, Cardiovascular ; Pulsatile Flow ; Rupture, Spontaneous ; }, abstract = {The three-dimensional flow pattern in a lateral saccular aneurysm was investigated by a finite element method. The aneurysm model had a dome-shaped diverticulum arising from one side of the straight circular tube. The steady Navier-Stokes equations and the equation of continuity were applied. The finite element equations were derived from the Galerkin process with each hexahedral element, in which velocities were approximated by quadratic polynomials and pressures by linear polynomials. The non-linear finite element equations were solved by a Newton-Raphson method. Calculations were performed of the steady flow at various Reynolds numbers. The conclusions for flow patterns with a Reynolds number of 1000 is as follows: (i) a separation vortex occurred in the whole circumferential region of the aneurysm, (ii) the separation vortex was distorted by the geometrical shape of the aneurysm, and (iii) two other vortexes induced by the separation vortex existed at the proximal and the distal wall of the aneurysm. These disturbances of flow through an aneurysm are thought to play a significant role in the formation of thrombi and the rupture of an aneurysm.}, }
@article {pmid10046550, year = {1992}, author = {Ott, E and Du, Y and Sreenivasan, KR and Juneja, A and Suri, AK}, title = {Sign-singular measures: Fast magnetic dynamos, and high-Reynolds-number fluid turbulence.}, journal = {Physical review letters}, volume = {69}, number = {18}, pages = {2654-2657}, doi = {10.1103/PhysRevLett.69.2654}, pmid = {10046550}, issn = {1079-7114}, }
@article {pmid18601012, year = {1992}, author = {Gardner, J and Tatterson, G}, title = {Characterization of mixing in shaker table containers.}, journal = {Biotechnology and bioengineering}, volume = {39}, number = {7}, pages = {794-797}, doi = {10.1002/bit.260390713}, pmid = {18601012}, issn = {0006-3592}, abstract = {Mixing in shaker table beakers is studied using dye dispersion to measure mixing times. Experimental conditions range from the laminar regime into the turbulent mixing. Different flow patterns occurring in the beakers are reported for the mixing. The transition Reynolds number is determined. Rotational speed of the table, volume of material to be mixed, and viscosity of the material are studied as to their effects on mixing time. A graphical mixing time correlation is provided which is useful for the translation of mixing from laboratory scale to pilot scale.}, }
@article {pmid17801232, year = {1992}, author = {Patterson, MR}, title = {A mass transfer explanation of metabolic scaling relations in some aquatic invertebrates and algae.}, journal = {Science (New York, N.Y.)}, volume = {255}, number = {5050}, pages = {1421-1423}, doi = {10.1126/science.255.5050.1421}, pmid = {17801232}, issn = {0036-8075}, abstract = {Chemical engineering theory can be used in accounting for the broad range of metabolic scaling exponents found in some aquatic invertebrates and algae. Delivery of metabolically important compounds to these organisms occurs by diffusion through a boundary layer. Dimensionless relations (Sherwood-Reynolds number functions) demonstrate the degree to which water motion and organism size affect mass transfer, and ultimately, metabolic rate. Derivation of mass exponents in the range 0.31 to 1.25 for simple geometries such as plates, spheres, and cylinders directly follows from knowledge of the Sherwood-Reynolds number relations. The range of exponents predicted is that found by allometric studies of metabolic rate in these organisms.}, }
@article {pmid10045151, year = {1992}, author = {Lathrop, DP and Fineberg, J and Swinney, HL}, title = {Turbulent flow between concentric rotating cylinders at large Reynolds number.}, journal = {Physical review letters}, volume = {68}, number = {10}, pages = {1515-1518}, doi = {10.1103/PhysRevLett.68.1515}, pmid = {10045151}, issn = {1079-7114}, }
@article {pmid17792378, year = {1992}, author = {Nelkin, M}, title = {In what sense is turbulence an unsolved problem?.}, journal = {Science (New York, N.Y.)}, volume = {255}, number = {5044}, pages = {566-570}, doi = {10.1126/science.255.5044.566}, pmid = {17792378}, issn = {0036-8075}, abstract = {Turbulence can be narrowly defined as a property of incompressible fluid flow at very high Reynolds number, and thus an attempt can be made to specify what is and what is not understood about it. The applicability of the Navier-Stokes equations of hydrodynamics to real turbulent flows and the successes and limitations of direct numerical simulation are considered. A discussion is presented of universality, and mention is made of the remarkable success of Kolmogorov's 1941 scaling ideas despite uncertainties about basic underlying assumptions such as local isotropy. Extensions of this scaling to the multifractal picture of dissipation fluctuations are discussed, but this picture remains phenomenological. Turbulence as defined above remains "unsolved" in the sense that a clear physical understanding of the observed phenomena does not exist.}, }
@article {pmid18600720, year = {1991}, author = {Beeton, S and Millward, HR and Bellhouse, BJ and Nicholson, AM and Jenkins, N and Knowles, CJ}, title = {Gas transfer characteristics of a novel membrane bioreactor.}, journal = {Biotechnology and bioengineering}, volume = {38}, number = {10}, pages = {1233-1238}, doi = {10.1002/bit.260381016}, pmid = {18600720}, issn = {0006-3592}, abstract = {We show the design features of a membrane bioreactor based on pulsatile flow across dimpled membranes. Results show an enhanced mass transfer of air of at least five-fold magnitude as compared with flat membranes. An increased working volume form 20 mL to 120 mL reduced the k(L)A at a given Reynolds number because of axial mixing of fluid from the deoxygenated end chamber. The bioreactor was used to supply air to a hybridoma mammalian cell line, and the calculated oxygen uptake showed that high-density cultures could be maintained in a 20 mL, single-dimpled cultures could be maintained in a 20 mL, single-dimpled membrane system. Indirect aeration of a 2 L continuous stirred tank reactor, by a double-membrane system, showed that air could be supplied to mammalian cells at cell densities of approximately 4 x 10(6) /mL.}, }
@article {pmid18604808, year = {1991}, author = {Chang, HT and Rittmann, BE and Amar, D and Heim, R and Ehlinger, O and Lesty, Y}, title = {Biofilm detachment mechanisms in a liquid-fluidized bed.}, journal = {Biotechnology and bioengineering}, volume = {38}, number = {5}, pages = {499-506}, doi = {10.1002/bit.260380508}, pmid = {18604808}, issn = {0006-3592}, abstract = {Bed fluidization offers the possibility of gaining the advantages of fixed-film biological processes without the disadvantage of pore clogging. However, the biofilm detachment rate, due to hydrodynamics and particle-to-particle attrition, is very poorly understood for fluidized-bed biofilm processes. In this work, a two-phase fluidized-bed biofilm was operated under a constant surface loading (0.09 mg total organic carbon/cm(2) day) and with a range of bed height (H), fluid velocities (U), and support-particle concentrations (C(p)). Direct measurements were made for the specific biofilm loss rate coefficient (b(s))and the total biofilm accumulation (X(f)L(f)). A hydrodynamic model allowed independent determination of the biofilm density (X(f)), biofilm thickness (L(f)), liquid shear stress (tau), and Reynolds number (Re). Multiple regression analysis of the results showed that increased particle-to-particle attrition, proportional to C(p) and increased turbulence, described by Re, caused the biofilms to be denser and thinner. The specific detachment rate coefficient (b(s)) increased as C(p) and Re increased. Almost all of the 6, values were larger than predicted by a previous model derived for smooth biofilms on a nonfluidized surface. Therefore, the turbulence and attrition of bed fluidization appear to be dominant detachment mechanisms.}, }
@article {pmid18588151, year = {1989}, author = {Vashitz, O and Sheintuch, M and Ulitzur, S}, title = {Mass transfer studies using cloned-luminous strain of Xanthomonas campestris.}, journal = {Biotechnology and bioengineering}, volume = {34}, number = {5}, pages = {671-680}, doi = {10.1002/bit.260340511}, pmid = {18588151}, issn = {0006-3592}, abstract = {Measurements of mass transfer in a highly viscous pseudoplastic broth, which is typical to Xanthomonas campestris fermentations, are difficult to obtain by conventional methods and little data is available. A novel research method that uses bioluminescence for mass transfer studies has been developed. A plasmid carrying the luminescence operon of marine luminous bacteria is introduced into an industrial bacteria, X. campestris. Besides producing the polysaccharide xanthangum, the bioluminescent X. campestris emits measurable light. Monitoring the luminescence is a simple, noncontaminating nondestructive and very sensitive indicator of the metabolic activity of the culture during fermentation. Energy drain due to bioluminescence is very low; growth rate and polysaccharide production rate are close to those of the wild-type strain.Oxygen and substrate mass transfer are determined by inducing step or periodic fluctuations in their concentration and measuring the resultant luminescence response. Oxygen mass transfer coefficients show linear dependence on Reynolds number and an exponential dependence on the average shear rate. Viscosity effect is small at high viscosities but increases rapidly below 10 Pa-s. The influence of oxygen uptake rate is studied.Mass transfer of the limiting component (ammonium ions) is analyzed under pulsating feed conditions. The luminescence declines, following a feed pulse, due to energy investment in active transport of ammonium ions through the cell membrane, it regenerates then to its baseline. The relation between mass transfer and luminescence fluctuation is elucidated.}, }
@article {pmid9902220, year = {1989}, author = {Khayat, RE and Eu, BC}, title = {Generalized hydrodynamics and Reynolds-number dependence of steady-flow properties in the cylindrical Couette flow of Lennard-Jones fluids.}, journal = {Physical review. A, General physics}, volume = {40}, number = {2}, pages = {946-958}, doi = {10.1103/physreva.40.946}, pmid = {9902220}, issn = {0556-2791}, }
@article {pmid3694112, year = {1987}, author = {Feldkamp, SD}, title = {Swimming in the California sea lion: morphometrics, drag and energetics.}, journal = {The Journal of experimental biology}, volume = {131}, number = {}, pages = {117-135}, doi = {10.1242/jeb.131.1.117}, pmid = {3694112}, issn = {0022-0949}, support = {HL17731/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Biomechanical Phenomena ; Caniformia/*physiology ; *Energy Metabolism ; *Locomotion ; Oxygen Consumption ; Physical Exertion ; Sea Lions/*physiology ; Swimming ; }, abstract = {During swimming, the California sea lion, Zalophus californianus (Lesson), generates thrust forces solely by means of its pectoral flippers. This study examines the drag, energetic cost and efficiency associated with this method of locomotion. Sea lions are highly streamlined, with a fineness ratio of 5.5 and maximum girth at 40% of body length. This profile leads to reduced drag and swimming power requirements. Films of gliding animals showed the drag coefficient (based on wetted surface area) to be 0.0042 at a Reynolds number of 2.0 X 10(6). This value is comparable to that found for other aquatic vertebrates and suggests that the sea lion's morphology helps to delay turbulent separation and maintain laminar flow over the forward portion of its body. Swimming metabolism was measured in a water flume at velocities up to 1.3 ms-1. Effective swimming speeds up to 2.7 ms-1 were attained by increasing each animal's drag. Oxygen consumption rose exponentially with velocity and for two animals was best described as VO2 = 6.27e0.48U, where VO2 is in mlO2 min-1 kg-1 and U is in ms-1. Minimum cost of transport for these animals was 0.12 ml O2 kg-1 m-1 at a relative speed of 1.4 body lengths s-1. This is 2.5 times that predicted for a fish of similar size. Swimming efficiencies were determined from these results using power output values calculated from the measured drag coefficient and standard hydrodynamic equations. At the highest velocity, aerobic efficiency reached a maximum of 15% while mechanical efficiency of the foreflippers was 80%. The results demonstrate that foreflipper propulsion is a highly efficient and comparatively inexpensive method of locomotion in aquatic mammals.}, }
@article {pmid10034637, year = {1987}, author = {Shapere, A and Wilczek, F}, title = {Self-propulsion at low Reynolds number.}, journal = {Physical review letters}, volume = {58}, number = {20}, pages = {2051-2054}, doi = {10.1103/PhysRevLett.58.2051}, pmid = {10034637}, issn = {1079-7114}, }
@article {pmid3651619, year = {1987}, author = {Mazzoni, MC and Skalak, TC and Schmid-Schönbein, GW}, title = {Structure of lymphatic valves in the spinotrapezius muscle of the rat.}, journal = {Blood vessels}, volume = {24}, number = {6}, pages = {304-312}, doi = {10.1159/000158707}, pmid = {3651619}, issn = {0303-6847}, support = {HL-10881/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Lymphatic System/*ultrastructure ; Male ; Muscles/*anatomy &amp; histology ; Pressure ; Rats ; Rats, Inbred Strains/*anatomy &amp; histology ; Viscosity ; }, abstract = {Lymphatic valves assure the forward propulsion of fluid along the lymphatic vessels. A description of valve function in skeletal muscle must be based on a knowledge of the valve morphology. To this end, histological sections of valves from lymphatic microvessels of the rat spinotrapezius muscle were examined with light microscopy. All of the approximately 50 valves studied from 20 rats had a bileaflet structure, with a buttress formed at each side of the valve by the fusion of opposing leaflets. This valve structure would allow the valve to close without inversion. There is no evidence for active smooth muscle action to open and close the valve. Since the Reynolds number of lymph flow is very small (about 0.0025), only pressure and viscous forces are available for valve closure. A particular mechanism based on the actual lymphatic valve structure is proposed.}, }
@article {pmid3795880, year = {1986}, author = {Berman, J and Mockros, LF}, title = {Mass transfer to fluids flowing through rotating nonaligned straight tubes.}, journal = {Journal of biomechanical engineering}, volume = {108}, number = {4}, pages = {342-349}, doi = {10.1115/1.3138626}, pmid = {3795880}, issn = {0148-0731}, support = {GM 07350/GM/NIGMS NIH HHS/United States ; HL 16582/HL/NHLBI NIH HHS/United States ; }, mesh = {Biomechanical Phenomena ; Biomedical Engineering ; Biophysical Phenomena ; Biophysics ; Blood Flow Velocity ; *Extracorporeal Circulation ; *Hot Temperature ; Humans ; Models, Cardiovascular ; Oxygen/blood ; Oxygenators ; }, abstract = {Relatively inefficient heat/mass transfer is characteristic of tubular devices if the Reynolds number is low. One method of improving the heat/mass transfer efficiency of such devices is by inducing transverse laminar secondary circulations that are superimposed on the primary flow field; the resulting transverse velocity components lead to fluid mixing and hence augmented mass transfer in the tube lumen. The present work is a theoretical and experimental investigation of the enhanced transport in rotating, nonaligned, straight tubes, a method of transport enhancement that utilizes Coriolis acceleration to create transverse fluid mixing. This technique couples the transport advantages of coiled tubes with the design advantages of straight tubes. The overall mass balance equation is numerically solved for transfer into fluids flowing steadily through rotating nonaligned straight tubes. This solution, for small Coriolis disturbances, incorporates a third order perturbation solution for the primary and secondary flow fields. For sufficiently small Coriolis disturbances the bulk concentration increase is found to be uniquely determined by the value of a single similarity parameter. As the Coriolis disturbance is increased, however, two additional parameters are required to accurately characterize the mass transfer. In general, increasing the Coriolis accelerations results in an increase in mass transfer. There are solution regimens, however, in which increasing this acceleration can lead to a decrease in mass transfer efficiency. This interesting phenomena, which has important design implications, appears to result from velocity-weighting effects on the exiting sample. Experiments, involving the measurement of oxygen transferred into water and blood, produced data that agree with the theoretical predictions.}, }
@article {pmid10034131, year = {1986}, author = {Brachet, ME and Meneguzzi, M and Sulem, PL}, title = {Small-scale dynamics of high-Reynolds-number two-dimensional turbulence.}, journal = {Physical review letters}, volume = {57}, number = {6}, pages = {683-686}, doi = {10.1103/PhysRevLett.57.683}, pmid = {10034131}, issn = {1079-7114}, }
@article {pmid3733596, year = {1986}, author = {Isabey, D and Chang, HK and Delpuech, C and Harf, A and Hatzfeld, C}, title = {Dependence of central airway resistance on frequency and tidal volume: a model study.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {61}, number = {1}, pages = {113-126}, doi = {10.1152/jappl.1986.61.1.113}, pmid = {3733596}, issn = {8750-7587}, mesh = {*Airway Resistance ; Homeostasis ; Humans ; *Lung Volume Measurements ; *Models, Biological ; Pressure ; Pulmonary Ventilation ; *Tidal Volume ; Time Factors ; }, abstract = {The resistance of a hollow cast of human central airways was measured during true sinusoidal airflow oscillations over a wide range of frequencies (0.5-40 Hz) and for various flow amplitudes up to 8 l/s. Pressure and flow were measured in the trachea with high-performance transducers, digitized and averaged over 100 cycles. Data were studied at two points in the flow cycle: at peak inspiratory and expiratory flows and in the two neighborhoods around zero flow where airway resistance (Rv approximately equal to o) was taken as the average slope of the pressure-flow (P-V) curve in each zone. When data obtained near peak flow were plotted in terms of dimensionless pressure drop vs. peak Reynolds number (Rem) and compared with steady-state data, we found no difference up to 2 Hz as previously reported (Isabey and Chang, J. Appl. Physiol. 51: 1338-1348, 1981), a slight decay in pressure drop between 4 and 8 Hz, a frequency-dependent increase in peak flow resistance at high frequencies (10-40 Hz) governed by the Strouhal number alpha 2/Rem beyond alpha 2/Rem = 0.5. On the other hand RV approximately equal to o was found to increase relative to steady state as local acceleration increases, e.g., as peak flow increases at a fixed frequency; this differs from the classical linear theory of oscillatory flow in a long straight tube. To explain these results, we had to use, as in our previous study, an alternative expression for the Strouhal number, i.e., epsilon = L X A X (dV/dt)/V2 (where L and A are the length and cross-sectional area of the trachea and V is a constant flow range over which resistance around flow reversal was computed), which accurately reflects the ratio of local acceleration [d(V/A)/dt)] to convective acceleration [(V/A)2/L] in developing branching flow. Finally, to delineate the regions of dominance of each of the dimensionless parameters, we compiled frequency-tidal volume diagrams for peak flows as well as for reversal. Epsilon, which is negligible near peak flows, appeared to govern the oscillatory P-V relationship near flow reversal in a transitional region of the diagram located between regions of steadiness, or moderate unsteadiness, and a region of dominant unsteadiness governed by alpha.}, }
@article {pmid10032743, year = {1986}, author = {Orszag, SA and Yakhot, V}, title = {Reynolds number scaling of cellular automaton hydrodynamics.}, journal = {Physical review letters}, volume = {56}, number = {16}, pages = {1691-1693}, doi = {10.1103/PhysRevLett.56.1691}, pmid = {10032743}, issn = {1079-7114}, }
@article {pmid3957840, year = {1986}, author = {Kim, CS and Rodriguez, CR and Eldridge, MA and Sackner, MA}, title = {Criteria for mucus transport in the airways by two-phase gas-liquid flow mechanism.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {60}, number = {3}, pages = {901-907}, doi = {10.1152/jappl.1986.60.3.901}, pmid = {3957840}, issn = {8750-7587}, support = {HL-30454/HL/NHLBI NIH HHS/United States ; }, mesh = {Biological Transport ; Biomechanical Phenomena ; Models, Biological ; Mucus/*metabolism ; Physiology/instrumentation/methods ; *Pulmonary Ventilation ; Respiratory System/*metabolism ; }, abstract = {The critical conditions for mucous layer transport in the respiratory airways by two-phase gas-liquid flow mechanism were investigated by using 0.5- and 1.0-cm-ID tube models. Several test liquids with rheological properties comparable to human sputum were supplied continuously into the vertically positioned tube models in such a way that the liquid could form a uniform layer while traveling upward through the tube with a continuous upward airflow. The critical airflow rate and critical liquid layer thickness required for the upward transport of the liquids were determined. The critical airflow rate was in the Reynolds number (Re) range of 142-1,132 in the 0.5-cm-ID tube model and 708-2,830 in the 1.0-cm-ID tube model depending on the types of liquids tested. In both models, the critical airflow rate was lower with viscoelastic liquids than with viscous oils. The critical liquid layer thickness ranged from 0.2 to 0.5 mm in the 0.5-cm-ID tube model and 0.8 to 1.4 mm in the 1.0-cm-ID tube model at Re of 2,800. These values decreased rapidly with increasing airflow rate. The critical thickness relative to the tube diameter ranged from 3 to 15% of the respective tube diameter and was lower by approximately 30-50% in the 0.5-cm-ID tube model than in the 1.0-cm-ID tube model over the entire Re range tested. The results indicate that the critical conditions for the mucus transport by two-phase gas-liquid flow mechanism are within the range that can be achieved in patients with bronchial hypersecretions during normal breathing.}, }
@article {pmid3949812, year = {1986}, author = {Back, LH and Radbill, JR and Cho, YI and Crawford, DW}, title = {Measurement and prediction of flow through a replica segment of a mildly atherosclerotic coronary artery of man.}, journal = {Journal of biomechanics}, volume = {19}, number = {1}, pages = {1-17}, doi = {10.1016/0021-9290(86)90104-1}, pmid = {3949812}, issn = {0021-9290}, mesh = {Blood Flow Velocity ; Blood Pressure ; *Coronary Circulation ; Coronary Disease/*physiopathology ; Coronary Vessels/physiopathology ; Humans ; Models, Cardiovascular ; *Rheology ; }, abstract = {Pressure distributions were measured along a hollow vascular axisymmetric replica of a segment of the left circumflex coronary artery of man with mildly atherosclerotic diffuse disease. A large range of physiological Reynolds numbers from about 60 to 500, including hyperemic response, was spanned in the flow investigation using a fluid simulating blood kinematic viscosity. Predicted pressure distributions from the numerical solution of the Navier-Stokes equations were similar in trend and magnitude to the measurements. Large variations in the predicted velocity profiles occurred along the lumen. The influence of the smaller scale multiple flow obstacles along the wall (lesion variations) led to sharp spikes in the predicted wall shear stresses. Reynolds number similarity was discussed, and estimates of what time averaged in vivo pressure drop and shear stress might be were given for a vessel segment.}, }
@article {pmid3651571, year = {1986}, author = {Crewe, KH and Feuerstein, IA}, title = {Platelet adhesion to fibrinogen-coated glass at an abrupt tubular expansion viewed with fluorescent video-microscopy.}, journal = {Biorheology}, volume = {23}, number = {5}, pages = {443-452}, doi = {10.3233/bir-1986-23502}, pmid = {3651571}, issn = {0006-355X}, mesh = {Analysis of Variance ; Blood Flow Velocity ; Cell Movement ; Fibrinogen ; Glass ; Humans ; Microscopy, Fluorescence ; *Platelet Adhesiveness ; Video Recording ; }, abstract = {The adhesion and detachment of human washed platelets was studied on the surface of the larger tube of a tubular expansion. Measurements were made within the vortex, at the reattachment point and downstream of the vortex. Fluorescent video-microscopy of mepacrine labelled platelets was used to record data continuously. Flow was from the smaller to the larger tube at Reynolds numbers (based on upstream conditions) of 75.4 and 212.2. Measurements of the adhesion efficiency for initially contacting cells and an overall adhesion efficiency were made. These efficiencies decreased with increasing Reynolds number. There was a pattern of variability for both efficiencies with respect to position and Reynolds number which is consistent with the generation of the unstable flow at the reattachment point.}, }
@article {pmid4077784, year = {1985}, author = {Olson, LE}, title = {Effect of transpulmonary and driving pressures on collateral gas flow in dog lungs.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {59}, number = {6}, pages = {1757-1765}, doi = {10.1152/jappl.1985.59.6.1757}, pmid = {4077784}, issn = {8750-7587}, support = {05465-21//PHS HHS/United States ; }, mesh = {Analysis of Variance ; Animals ; Dogs ; Female ; Lung/*physiology ; Male ; Mathematics ; *Pulmonary Gas Exchange ; }, abstract = {The effect of changing segment pressure (Ps) and airway opening pressure (Pao) on flow through a collaterally ventilating lung segment was evaluated in intact and excised dog lungs. He, N2, and SF6 were passed through the lung segment distal to a catheter wedged in a peripheral airway at driving pressures (Ps - Pao) between 0.25 and 2 cm H2O. Eight excised caudal lobes were studied at Pao = 5, 10, and 15 cm H2O. Flow was directly related to Ps - Pao and Pao and inversely related to the density of the gas. A dimensionless plot of the driving pressure normalized to a reference dynamic pressure as a function of Reynolds number (Re) indicated that flow through the segment behaved as if it were laminar at Re less than 100 and that increasing Pao increased the dimension of the pathways conducting flow as shown previously. Small changes in Ps had no effect on pathway geometry or on the pattern of flow through the segment at Pao = 10 and 15 cmH2O. At Pao = 5 cm H2O increasing segment pressure appeared to increase the dimensions of the flow pathways slightly. Similar changes in Ps - Pao had no consistent effect on flow pattern or pathway geometry in six anesthetized, paralyzed, vagotomized dogs at functional residual capacity or after widely opening the chest (Pao = 5 cm H2O). These results suggest that, at large lobe volumes, airways (including collateral pathways) are maximally dilated and therefore relatively insensitive to small changes in segment pressure.(ABSTRACT TRUNCATED AT 250 WORDS)}, }
@article {pmid4046567, year = {1985}, author = {Cho, YI and Back, LH and Crawford, DW}, title = {Experimental investigation of branch flow ratio, angle, and Reynolds number effects on the pressure and flow fields in arterial branch models.}, journal = {Journal of biomechanical engineering}, volume = {107}, number = {3}, pages = {257-267}, doi = {10.1115/1.3138551}, pmid = {4046567}, issn = {0148-0731}, support = {HL 23619-04/HL/NHLBI NIH HHS/United States ; }, mesh = {Blood Flow Velocity ; Blood Pressure ; Femoral Artery/*physiology ; Humans ; Models, Cardiovascular ; Regional Blood Flow ; Rheology ; }, abstract = {An experimental investigation was carried out to acquire an understanding of local pressure changes and flow along the main lumen of arterial branch models similar to the femoral artery of man with three different branch angles (30, 60, and 90 deg) and side branch to the main lumen diameter ratio of 0.4. Effects of branch to main lumen flow rate ratios and physiological Reynolds numbers were found to be significant on the local pressure changes, while that of branch angle was also found to be important. The flow visualization study revealed that the flow separated in the main lumen near the branch junction when the pressure rise coefficient along the main lumen was above a critical value (i.e., 0.35 - 0.46), which was observed to be a function of the Reynolds number. The critical value of the branch to main lumen flow rate ratio was found to be about 0.38 - 0.44 also depending on the Reynolds number. Time averaged pressure distributions for pulsatile flow were similar in trend to steady flow values although they differed somewhat in detail in the main lumen in the branch region.}, }
@article {pmid16346830, year = {1985}, author = {Eighmy, TT and Bishop, PL}, title = {Effect of reactor turbulence on the binding-protein-mediated aspartate transport system in thin wastewater biofilms.}, journal = {Applied and environmental microbiology}, volume = {50}, number = {1}, pages = {120-124}, pmid = {16346830}, issn = {0099-2240}, abstract = {This research documents an effect of reactor turbulence on the ability of gram-negative wastewater biofilm bacteria to actively transport l-aspartate via a binding-protein-mediated transport system. Biofilms which were not preadapted to turbulence and which possessed two separate and distinct aspartate transport systems (systems 1 and 2) were subjected to a turbulent flow condition in a hydrodynamically defined closed-loop reactor system. A shear stress treatment of 3.1 N . m for 10 min at a turbulent Reynolds number (Re = 11,297) inactivated the low-affinity, high-capacity binding-protein-mediated transport system (system 2) and resolved the high-affinity, low-capacity membrane-bound proton symport system (system 1). The K(t) and V(max) values for the resolved system were statistically similar to K(t) and V(max) values for system 1 when system 2 was inactivated either by osmotic shock or arsenate, two treatments which are known to inactivate binding-protein-mediated transport systems. We hypothesize that shear stress disrupts system 2 by deforming the outer membranes of the firmly adhered gram-negative bacteria.}, }
@article {pmid4025949, year = {1985}, author = {Stehbens, WE and Fee, CJ}, title = {Hydrodynamic flow in U-shaped and coiled glass loops simulating carotid arterial configurations.}, journal = {Angiology}, volume = {36}, number = {7}, pages = {442-451}, doi = {10.1177/000331978503600706}, pmid = {4025949}, issn = {0003-3197}, mesh = {Blood Flow Velocity ; Carotid Arteries/*physiology ; Hemodynamics ; Humans ; Methylene Blue ; Middle Aged ; Models, Biological ; Physics/*instrumentation ; Regional Blood Flow ; }, abstract = {The dye injection technique was used to study flow patterns in ten U-bends and two helical coils. These models were manufactured of glass and designed to simulate abnormal arterial configurations in man. In each model flow disturbances were observed below the critical Reynolds number of 2000 for flow in a straight tube with one reading as low as 250. The disturbances in the flow were sensitive to external disturbances. Their periodicity was relatively regular but the frequency increased with augmentation of flow rates and some irregularity was apparent. The results indicate that they could have applicability to the human vascular system.}, }
@article {pmid18553690, year = {1985}, author = {Fryer, PJ and Slater, NK and Duddridge, JE}, title = {Suggestions for the operation of radial flow cells in cell adhesion and biofouling studies.}, journal = {Biotechnology and bioengineering}, volume = {27}, number = {4}, pages = {434-438}, doi = {10.1002/bit.260270407}, pmid = {18553690}, issn = {0006-3592}, abstract = {An analysis of the radial flow cell is presented to show that the assumption of creeping laminar flow should be used cautiously. Simple models which account for the influence of fluid inertial forces over most of the width of the plate are reviewed. A modified Reynolds number is introduced which may be used to test the validity of the creeping flow solution.}, }
@article {pmid3999727, year = {1985}, author = {Dorrington, KL and Ralph, ME and Bellhouse, BJ and Gardaz, JP and Sykes, MK}, title = {Oxygen and CO2 transfer of a polypropylene dimpled membrane lung with variable secondary flows.}, journal = {Journal of biomedical engineering}, volume = {7}, number = {2}, pages = {89-99}, doi = {10.1016/0141-5425(85)90036-6}, pmid = {3999727}, issn = {0141-5425}, mesh = {Animals ; Artificial Organs ; Blood Flow Velocity ; Blood Gas Analysis ; Cattle ; Equipment Design ; Evaluation Studies as Topic ; Humans ; Lung ; Mathematics ; Models, Biological ; *Oxygenators, Membrane ; *Plastics ; *Polypropylenes ; *Pulmonary Gas Exchange ; }, abstract = {Gas transfer performance is presented for one form of the Oxford membrane lung in which vortex mixing is induced in blood flow across a dimpled polypropylene membrane. Dimensional analysis has been used to define the parameters characterizing mass transfer in the device, and of three fluid mechanical parameters: Reynolds number based on peak pulsation velocity, Strouhal number, and ratio of mean to oscillatory flows, only the first has been found to affect mass transfer significantly in the ranges studied. For oxygenation, rated flows in excess of 5 l min-1 m-2 are measured. A new definition is presented for a rated flow for extracorporeal CO2 removal and values in excess of 1.2 l min-1 m-2 are obtained.}, }
@article {pmid3985178, year = {1985}, author = {Chien, S and Tvetenstrand, CD and Epstein, MA and Schmid-Schönbein, GW}, title = {Model studies on distributions of blood cells at microvascular bifurcations.}, journal = {The American journal of physiology}, volume = {248}, number = {4 Pt 2}, pages = {H568-76}, doi = {10.1152/ajpheart.1985.248.4.H568}, pmid = {3985178}, issn = {0002-9513}, support = {HL-16851/HL/NHLBI NIH HHS/United States ; HL-28381/HL/NHLBI NIH HHS/United States ; }, mesh = {Blood Cells/*physiology ; *Microcirculation ; Models, Cardiovascular ; }, abstract = {To model the flow behavior of white and red blood cells at microvascular branch points, the distribution of neutrally buoyant spherical and disk-shaped particles at a symmetric T bifurcation was investigated for low Reynolds number flows (0.01-0.1). The particle distribution was represented by the fractional particle flux to a daughter branch as a function of the fractional volumetric bulk flow to the same branch. Particle-to-tube diameter ratios of 0.32-0.79 were studied for the spherical particles and 0.4-0.8 for the disks. As the particle dimensions approach that of the tube, the relation between the fractional particle flux and fractional bulk flow changes from a linear relation of unity slope to a nonlinear S-shaped curve. Measurements of the flow divider at the entrance to the bifurcation and the eccentricity distributions for the spheres and disks were used to develop a model that permits prediction of the observed particle distributions. These results can be used to interpret the distribution of white and red blood cells in microvascular bifurcations with dimensions close to the cell size.}, }
@article {pmid3985900, year = {1985}, author = {Cho, YI and Back, LH and Crawford, DW}, title = {Effect of simulated hyperemia on the flow field in a mildly atherosclerotic coronary artery casting of man.}, journal = {Aviation, space, and environmental medicine}, volume = {56}, number = {3}, pages = {212-219}, pmid = {3985900}, issn = {0095-6562}, mesh = {Blood Flow Velocity ; Blood Pressure ; Blood Viscosity ; Coronary Disease/blood/*physiopathology ; Coronary Vessels/*physiopathology ; Humans ; Hyperemia/*physiopathology ; Models, Structural ; Rheology ; }, abstract = {The purpose of this investigation was to determine changes in the flow field due to mild atherosclerosis using a main coronary artery casting of man with maximum obstruction of about 50% by area. Local pressure changes were measured using six pressure tap holes drilled flush to the wall along the casting. The test fluid used was a 33% sugar-water solution to simulate the viscosity of blood. Flow visualization results were obtained by injecting blue dye slowly through the pressure tap holes. The local pressure measurements clearly demonstrated a significant Reynolds number effect. At physiological Reynolds numbers of 80-710, a local pressure rise was observed downstream of the mild atherosclerotic constriction of 50% because of momentum changes. The flow visualization study indicated that the critical Reynolds number for flow separation to occur in the divergent region of this coronary casting was about 330. Flow separation has been implicated in the genesis of atherosclerosis but there is little information on the extent of flow separations in vivo in arteries of man. These results are believed to be important in obtaining a quantitative relation between coronary morphology and the fluid dynamic consequences of mild diffuse disease especially under conditions of maximum cardiac demand i.e., higher coronary flow rates, and thus Reynolds numbers associated with space and/or atmospheric flight.}, }
@article {pmid3974012, year = {1985}, author = {LoGerfo, FW and Nowak, MD and Quist, WC}, title = {Structural details of boundary layer separation in a model human carotid bifurcation under steady and pulsatile flow conditions.}, journal = {Journal of vascular surgery}, volume = {2}, number = {2}, pages = {263-269}, pmid = {3974012}, issn = {0741-5214}, support = {HL-21796-04/HL/NHLBI NIH HHS/United States ; }, mesh = {Carotid Arteries/*physiology ; Humans ; *Models, Anatomic ; *Rheology ; }, abstract = {We have used a dye-flow visualization technique to analyze the substructure of flow separation in a plastic model of the human carotid bifurcation under steady and pulsatile flow. Under steady conditions at a physiologic flow split (Q external carotid/Q common carotid = 0.30) and Reynolds number (500), a large region of separated fluid developed along the outside wall of the sinus, opposite the flow divider. Yellow dye injected into the boundary layer upstream from the bifurcation traveled slowly along the wall of the common carotid and entered directly into the separation. Blue dye injected into the central, high-velocity streamlines in the common carotid impacted on the flow divider, then traveled circumferentially and entered the separation. Mixing of these two sources was documented by the appearance of green fluid, which lingered in the region of separation. Pulsatile flow resulted in a smaller region of separation; mixing still occurred. Flow separation at the carotid bifurcation is a site of mixing of fluids previously subjected to prolonged low-shear wall contact and brief high-shear wall contact. Separation is itself a site of low shear, but this study reveals a mechanism whereby low and high shear may act independently or synergistically to explain the link between flow separation and atherogenesis.}, }
@article {pmid4077866, year = {1985}, author = {Agonafer, D and Watkins, CB and Cannon, JN}, title = {Computation of steady flow in a two-dimensional arterial model.}, journal = {Journal of biomechanics}, volume = {18}, number = {9}, pages = {695-701}, doi = {10.1016/0021-9290(85)90024-7}, pmid = {4077866}, issn = {0021-9290}, mesh = {Aorta, Thoracic/*physiology ; Blood Flow Velocity ; Humans ; *Models, Cardiovascular ; Regional Blood Flow ; Stress, Mechanical ; Viscosity ; }, abstract = {The Navier-Stokes equations are solved numerically for steady flow through a double-branched two-dimensional section of a three-dimensional model of a canine aorta for which experimental data is available. The numerical scheme involves transforming the physical coordinates to a curvilinear boundary-fitted coordinate system and performing finite-difference computations in the transformed system. Shear stress at the wall is calculated for a Reynolds number of a 1,000 with branch-to-main aortic flow rate ratios as a parameter. The results are compared with the aforementioned experimental data and show reasonable qualitative agreement.}, }
@article {pmid4077862, year = {1985}, author = {Pei, ZH and Xi, BS and Hwang, NH}, title = {Wall shear stress distribution in a model human aortic arch: assessment by an electrochemical technique.}, journal = {Journal of biomechanics}, volume = {18}, number = {9}, pages = {645-656}, doi = {10.1016/0021-9290(85)90020-x}, pmid = {4077862}, issn = {0021-9290}, mesh = {Animals ; Aorta, Thoracic/anatomy &amp; histology/*physiology ; Arteriosclerosis/etiology ; Electrochemistry ; Humans ; *Models, Cardiovascular ; Rabbits ; Regional Blood Flow ; Rheology ; Stress, Mechanical ; }, abstract = {Wall shear stress (WSS) distribution in a human aortic arch model is studied using 130 cathode electrodes flush-mounted on the model walls. Flow visualizations are made in a transparent geometry model to identify the regions of fluid mechanical interests, e.g. regions of flow separation, eddy formation and flow stagnancy. The 130 electrodes are strategically positioned in the arch based on information obtained from the flow visualizations. The measured data indicate that the aortic arch may be categorized into eight regions: three along the inner wall of the arch (A,B,C); and five near the outer wall (D,E,F,G,H). (1) The regions of low WSS are distributed along the inner wall of the ascending aorta A; the inner wall of the descending aorta C; and the upstream inner wall of the innominate and the common carotid branchings F. (2) The high WSS regions are distributed along the outer wall of the arch E; and the inner wall in the arch opposite to the left subclavian branching B. (3) In certain regions, high and low WSS may be found next to each other (e.g. G and H) without a definable boundary in between; and (4) as the Reynolds number increases, the areas of low WSS decrease, while the high WSS areas increase with no obvious change in magnitude of the stress along the inner wall of the arch. At the branchings, the WSS distribution is not affected by the Reynolds number within the range of observations. The measured WSS distribution is compared with Rodkiewicz's map of early atherosclerotic lesions in the aortic arch of cholesterol fed rabbits.}, }
@article {pmid4019523, year = {1985}, author = {Srivastava, LM and Srivastava, VP}, title = {Interaction of peristaltic flow with pulsatile flow in a circular cylindrical tube.}, journal = {Journal of biomechanics}, volume = {18}, number = {4}, pages = {247-253}, doi = {10.1016/0021-9290(85)90842-5}, pmid = {4019523}, issn = {0021-9290}, mesh = {Humans ; Mathematics ; Models, Biological ; Peristalsis ; *Rheology ; }, abstract = {The effect of pulsatile flow on peristaltic transport in a circular cylindrical tube is analysed. The flow of a Newtonian viscous incompressible fluid in a flexible circular cylindrical tube on which an axisymmetric travelling sinusoidal wave is imposed, is considered. The initial flow in the tube is induced by an arbitrary periodic pressure gradient. A perturbation solution with amplitude ratio (wave amplitude/tube radius) as a parameter is obtained when the frequency of the travelling wave and that of the imposed pressure gradient are equal. The interaction effects of periodic wall induced flow and periodic pressure imposed flow are visualized through the presence of substantially different components of steady and higher harmonic oscillating flow in the first order flow solution. Numerical results show a strong variation of steady state velocity profiles with boundary wave number and Reynolds number and a strong phase shift behaviour of the flow in the radial direction.}, }
@article {pmid4003876, year = {1985}, author = {Srivastava, LM and Srivastava, VP}, title = {Peristaltic transport of a non-Newtonian fluid: applications to the vas deferens and small intestine.}, journal = {Annals of biomedical engineering}, volume = {13}, number = {2}, pages = {137-153}, pmid = {4003876}, issn = {0090-6964}, mesh = {Animals ; Biophysical Phenomena ; Biophysics ; Ejaculation ; Gastrointestinal Contents ; *Gastrointestinal Motility ; Intestine, Small/*physiology ; Macaca mulatta ; Male ; Mathematics ; *Peristalsis ; Pressure ; Semen/physiology ; Vas Deferens/*physiology ; }, abstract = {The problem of peristaltic transport of a non-Newtonian (Power law) fluid in a uniform and non-uniform tube has been investigated under zero Reynolds number and long wavelength approximation. A comparison of the results with those of Newtonian fluid model shows that the magnitude of pressure rise, under a given set of conditions, is smaller in the case of non-Newtonian fluid, when the flow behavior index n less than 1, at zero flow rate. Further, the pressure rise decreases as n decreases from 1, at zero flow rate, is independent of n at a certain value of flow rate, and increases if flow rate exceeds further. Also, at a given flow rate, an increase in the wavelength leads to a decrease in pressure rise and increase in the influence of non-Newtonian behavior. Pressure rise, in the case of non-uniform geometry, is found much smaller than the corresponding value in the case of uniform geometry. Finally, the analysis has been applied and compared with observed flow rates in the vas deferens in rhesus monkeys and in the small intestine.}, }
@article {pmid3988781, year = {1985}, author = {O'Brien, V and Ehrlich, LW}, title = {Simple pulsatile flow in an artery with a constriction.}, journal = {Journal of biomechanics}, volume = {18}, number = {2}, pages = {117-127}, doi = {10.1016/0021-9290(85)90004-1}, pmid = {3988781}, issn = {0021-9290}, support = {HL23291/HL/NHLBI NIH HHS/United States ; }, mesh = {Arterial Occlusive Diseases/*physiopathology ; Arteries/physiopathology ; Arteriosclerosis/etiology ; *Hemodynamics ; Humans ; Models, Cardiovascular ; Rheology ; }, abstract = {A smooth isolated, axisymmetric occlusion in a straight vascular tube is a tractable problem for pulsatile flow calculations via finite-difference approximations to the Navier-Stokes equation. Steady flow depends on the Reynolds number and two geometric parameters which describe the stenosis. The mere addition of a simple harmonic to the mean flow adds two more parameters. One is the reduced frequency, or Strokes number, and the other epsilon, the ratio of unsteady to steady flux. After describing steady stenosis flow examples, the dynamic patterns of pulsatile flow are illustrated indicating the inadequacy of basing hypotheses of atherosclerosis on mean (steady) flow.}, }
@article {pmid6513530, year = {1984}, author = {Lim, KO and Kennedy, JS and Rodkiewicz, CM}, title = {Entry flow in a circular tube of aortic arch dimensions.}, journal = {Journal of biomechanical engineering}, volume = {106}, number = {4}, pages = {351-356}, doi = {10.1115/1.3138504}, pmid = {6513530}, issn = {0148-0731}, mesh = {Aorta, Thoracic/*physiology ; Biomechanical Phenomena ; Biomedical Engineering ; Humans ; *Models, Cardiovascular ; Regional Blood Flow ; }, abstract = {Steady flow within a uniform circular curved tube formed by two 90-deg elbows was studied as a function of psi, the angle between the planes of curvature of the two elbows. Boundary layer separation was found at two locations. The sites of these separation zones were observed to be essentially independent of psi while the Reynolds number at which separation was first detected was found to decrease as psi increased. The relation between separation and the pathogenesis of atherosclerosis is discussed. Secondary flow pattern was found to depend on psi and in some instances on Reynolds number as well.}, }
@article {pmid6487735, year = {1984}, author = {Nakache, M and Dimicoli, JL}, title = {Topological analysis of wall mass transport using a luminescent immobilized enzymatic system.}, journal = {Biophysical journal}, volume = {46}, number = {3}, pages = {357-369}, pmid = {6487735}, issn = {0006-3495}, mesh = {Enzymes, Immobilized/*metabolism ; Horseradish Peroxidase/*metabolism ; Hydrogen Peroxide/metabolism ; Kinetics ; Peroxidases/*metabolism ; Rheology ; }, abstract = {A new technique of visualization of diffusion-convection phenomena at a solid-liquid interface using the luminol chemiluminescent reaction catalyzed by immobilized peroxidase has been previously described (Dimicoli, J.L., M. Nakache, and P. Peronneau, 1982, Biorheology, 19:281-300). We propose now a theoretical model that predicts quantitatively the light fluxes, JL, corresponding to the transfer J of the hydrogen peroxide substrate at the liquid-solid interface in a cylindrical tube for continuous flow experiments. A simple phenomenological relation, J alpha J1/mL (1 less than m less than 3) was first established for each point of the wall. Then, numerical integration showed that, independent of the laminar or turbulent character of the flow, J1/mL was proportional to (S1 Kideal)/(1 + Kideal/ET), where S1 is the bulk substrate concentration, Kideal is the ideal transport coefficient, and ET (in cm.S-1) a phenomenological first-order enzymatic rate constant per unit of wall surface. This relation proved to be satisfactory for all experimental conditions since a single mean value of ET takes into account the experimental data collected for a given enzymated tube in a large range of Reynolds number values (Re) (500 less than Re less than 9,000) and of distances from the entrance of the tube (chi greater than 0.3 cm). This quantitative analysis using a pseudo-first-order approximation interprets the observed great dependence of JL on Re(JL alpha Ren', with n' usually greater than 1/3 for laminar flows) and on S1 (JL alpha S1m). It predicts also that the laminar-to-turbulent transition can be evidenced for interfacial enzymatic activity, ET greater than 2.10(-4) cm.S-1, as observed with most of the tubes prepared by covalent binding of peroxidase on the acrylamide gel wall. The experiment had to be carried out at a pH value of 8, which corresponds to the fastest rate of the chemiluminescent reaction. The predicted entrance effects were also observed experimentally for the first time in an immobilized enzyme system. This technique appears therefore to be a valuable tool for the quantitative analysis of diffusion-convection phenomena at a liquid-solid interface with a good spatial resolution with a great range of flow rate.}, }
@article {pmid6747536, year = {1984}, author = {Batty, RS}, title = {Development of swimming movements and musculature of larval herring (Clupea harengus).}, journal = {The Journal of experimental biology}, volume = {110}, number = {}, pages = {217-229}, doi = {10.1242/jeb.110.1.217}, pmid = {6747536}, issn = {0022-0949}, mesh = {Animals ; Fishes/*growth &amp; development/physiology ; Muscle Development ; Swimming ; }, abstract = {A kinematic analysis was made of swimming of larval herring Clupea harengus L. Swimming style was found to change with growth and development; the amplitude of swimming movements of early post-yolk-sac larvae increases linearly towards the tail, a style of swimming which relies mainly on resistive forces for propulsion. Later, after the caudal and dorsal fins have developed, the swimming style changes, in response to an increase in Reynold's Number, such that inertial forces are more important. In this type of swimming the amplitude increases more rapidly than linearly towards the tail. The distribution of red and white muscle fibre types was studied in relation to development. On hatching, red muscle fibres were found to be arranged as a single layer on the outside of the myotomes. They develop into the adult distribution, concentrated at the midline of the flank near the skin, only after the gills and circulation become fully functional.}, }
@article {pmid6733240, year = {1984}, author = {Schneider, MB and Jenkins, JT and Webb, WW}, title = {Thermal fluctuations of large cylindrical phospholipid vesicles.}, journal = {Biophysical journal}, volume = {45}, number = {5}, pages = {891-899}, pmid = {6733240}, issn = {0006-3495}, support = {CA 14454C/CA/NCI NIH HHS/United States ; GM 21661/GM/NIGMS NIH HHS/United States ; }, mesh = {Biophysical Phenomena ; Biophysics ; *Liposomes ; Thermodynamics ; }, abstract = {The time correlation function of the shape fluctuations of large (greater than 10 micron), cylindrical, hydrated, phospholipid-membrane vesicles consisting of one bimolecular layer was measured. The restoring force of the membrane was due to the excess curvature of a membrane element. A value for the curvature elastic modulus, Kc, was obtained from the mean-square amplitude of the normal modes of the fluctuations using the equipartition theorem. An expression for the correlation time was found by solving the dynamics of the membrane's relaxation against the low Reynolds number viscous drag of the surrounding fluid. The amplitudes and correlation times of the fundamental bending mode of the cylindrical vesicles both yield Kc = 1-2 X 10(-12) ergs.}, }
@article {pmid6693510, year = {1984}, author = {Kobari, M and Gotoh, F and Fukuuchi, Y and Tanaka, K and Suzuki, N and Uematsu, D}, title = {Blood flow velocity in the pial arteries of cats, with particular reference to the vessel diameter.}, journal = {Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism}, volume = {4}, number = {1}, pages = {110-114}, doi = {10.1038/jcbfm.1984.15}, pmid = {6693510}, issn = {0271-678X}, mesh = {Animals ; Arteries/anatomy &amp; histology/physiology ; Blood Flow Velocity ; Blood Pressure ; Cats ; Female ; Male ; Pia Mater/*blood supply ; Rheology ; }, abstract = {The blood flow velocity and diameter of feline pial arteries, ranging in diameter from 20 to 200 microns, were measured simultaneously using a newly developed video camera method under steady-state conditions for all other parameters. There was a linear relationship between blood flow velocity and pial artery diameter (y = 0.340x + 0.309), the correlation coefficient being 0.785 (p less than 0.001). The average values for blood flow velocity in pial arteries less than 50 microns, greater than or equal to 50 but less than 100 microns, greater than or equal to 100 but less than 150 microns, and greater than or equal to 150 microns in diameter were 12.9 +/- 1.3, 24.6 +/- 3.4, 42.1 +/- 4.7, and 59.9 +/- 5.3 mm/s, respectively. Blood flow rate was calculated as a product of the cross-sectional area and the flow velocity. The blood flow rate increased exponentially as the pial artery diameter increased (y = 2.71 X 10(-4) x2.98). The average values for blood flow rate in pial arteries less than 50 microns, greater than or equal to 50 but less than 100 microns, greater than or equal to 100 but less than 150 microns and greater than or equal to 150 microns in diameter were 12.8 +/- 1.5, 122.1 +/- 24.8, 510.2 +/- 74.8, and 1524.2 +/- 174.4 10(-3) mm3/s, respectively. Hemorheological parameters such as the wall shear rate and Reynolds' number were also calculated. The data obtained provide a useful basis for further investigations in the field of cerebral circulation.}, }
@article {pmid6729274, year = {1984}, author = {Menon, AS and Weber, ME and Chang, HK}, title = {Model study of flow dynamics in human central airways. Part III: Oscillatory velocity profiles.}, journal = {Respiration physiology}, volume = {55}, number = {2}, pages = {255-275}, doi = {10.1016/0034-5687(84)90026-4}, pmid = {6729274}, issn = {0034-5687}, mesh = {Biomechanical Phenomena ; Biophysical Phenomena ; Biophysics ; Bronchi/*physiology ; Humans ; Lung/*physiology ; *Models, Biological ; Periodicity ; *Pulmonary Ventilation ; Trachea/*physiology ; }, abstract = {Measurements of oscillatory velocity were made in a 3:1 model of the human central airways. The model was built of acrylic plastic and mounted vertically. A reciprocating pump connected to the upper end of the model privided oscillatory flow frequencies of 0.25, 1, 2 and 4 Hz (equivalent to 2.25, 9, 18 and 36 Hz in the actual airways) and tidal volumes of 300, 500 and 1500 ml. A hot-wire anemometer probe was used to measure velocities along two perpendicular diameters and at six stations distributed through the model. The flow distribution through the five lobar bronchi was controlled by distally positioned linear resistors . The measurements indicate that the entry flow profile into the model during oscillatory flow was essentially flat. At low frequencies, the velocity profiles attained at peak flow rate resemble the profiles seen under steady flow conditions at the corresponding Reynolds number. In the frontal plant these profiles are asymmetric with a maximum in velocity directed towards the outer wall of the bend. In the sagittal plane the velocity profiles are symmetric and have the characteristic bi-peak (M-shaped) structure seen in the steady flows. However, as the frequency increases the velocity profiles throughout most branches tend to flatten except in the right upper lobar bronchus where the skewed velocity profiles persist even at the highest frequencies studied. As in steady flows the nature of the velocity profile is strongly influenced by the airway geometry. Furthermore, the peak velocity profiles resemble steady flow profiles at comparable Reynolds numbers up to a Womersley number of 16.}, }
@article {pmid6727313, year = {1984}, author = {Back, LH and Cho, YI and Crawford, DW and Cuffel, RF}, title = {Effect of mild atherosclerosis on flow resistance in a coronary artery casting of man.}, journal = {Journal of biomechanical engineering}, volume = {106}, number = {1}, pages = {48-53}, doi = {10.1115/1.3138456}, pmid = {6727313}, issn = {0148-0731}, mesh = {Arteriosclerosis/*physiopathology ; Coronary Vessels/*physiopathology ; Hemodynamics ; Humans ; Mathematics ; Models, Anatomic ; *Vascular Resistance ; }, abstract = {An in-vitro flow study was conducted in a mildly atherosclerotic main coronary artery casting of man using sugar-water solutions simulating blood viscosity. Steady flow results indicated substantial increases in pressure drop, and thus flow resistance at the same Reynolds number, above those for Poiseuille flow by 30 to 100 percent in the physiological Reynolds number range from about 100 to 400. Time-averaged pulsatile flow data showed additional 5 percent increases in flow resistance above the steady flow results. Both pulsatile and steady flow data from the casting were found to be nearly equal to those from a straight, axisymmetric model of the casting up to a Reynolds number of about 200, above which the flow resistance of the casting became gradually larger than the corresponding values from the axisymmetric model.}, }
@article {pmid6715390, year = {1984}, author = {Aarts, PA and van Broek, JA and Kuiken, GD and Sixma, JJ and Heethaar, RM}, title = {Velocity profiles in annular perfusion chamber measured by laser-Doppler velocimetry.}, journal = {Journal of biomechanics}, volume = {17}, number = {1}, pages = {61-63}, doi = {10.1016/0021-9290(84)90081-2}, pmid = {6715390}, issn = {0021-9290}, mesh = {*Blood Flow Velocity ; Doppler Effect ; Humans ; Lasers ; *Models, Biological ; *Platelet Adhesiveness ; Rheology ; }, abstract = {p6e fluid flow in the annular perfusion chamber of Baumgartner developed to study platelet vessel wall interaction was examined with laser-Doppler velocimetry. A laminar and stable flow with a Reynolds number of less than or equal to 50 was measured at flow rates up to 3 ml s-1. No turbulence was found. The wall shear rate directly determined from measured velocity profiles agreed well with theory. The experiments underlined the necessity to work with vessels of uniform thickness and a smooth surface.}, }
@article {pmid6694368, year = {1984}, author = {Wille, SO}, title = {Numerical simulations of steady flow inside a three dimensional aortic bifurcation model.}, journal = {Journal of biomedical engineering}, volume = {6}, number = {1}, pages = {49-55}, doi = {10.1016/0141-5425(84)90010-4}, pmid = {6694368}, issn = {0141-5425}, mesh = {Aorta/*physiology ; Biomechanical Phenomena ; Blood Pressure ; Blood Viscosity ; Humans ; *Models, Cardiovascular ; Regional Blood Flow ; Statistics as Topic ; }, abstract = {A finite element formulation of the Navier-Stokes equations for three dimensional flow is presented. The equations are solved using the finite element method. The model is constructed from a cast of a human aortic bifurcation. The numerical problems introduced by solving the equation system are discussed and special attention is paid to the selection of the linear equation solver. The simulations of the steady blood flow patterns in an aortic bifurcation is shown. The results of the numerical analysis are presented as three dimensional plots of velocity vectors, wall shear vectors, streamlines and pressure isobars. The flow simulations are done for Reynolds number 10. The flow patterns found in the bifurcation model are discussed in connection with proposed theories to explain the event of early atherosclerosis.}, }
@article {pmid6532271, year = {1984}, author = {Winter, DC and Nerem, RM}, title = {Turbulence in pulsatile flows.}, journal = {Annals of biomedical engineering}, volume = {12}, number = {4}, pages = {357-369}, pmid = {6532271}, issn = {0090-6964}, mesh = {Animals ; Dogs ; Models, Biological ; *Pulmonary Gas Exchange ; Respiration, Artificial/*methods ; }, abstract = {Turbulence during pulsatile flow has been suggested as a possible mechanism to enhance the transport of gases during high-frequency ventilation. Experimental studies on oscillatory flow in straight, circular tubes have identified three types of flow: (a) laminar; (b) conditionally turbulent, in which high-frequency disturbances occur during the decelerating phase of the flow cycle but relaminarize by the beginning of the subsequent accelerating phase; and (c) fully turbulent flow, in which disturbances occur throughout the flow cycle. Fully turbulent flow has been observed only when a mean flow is present, and only laminar or conditionally turbulent flow has been observed for purely oscillatory flow. A critical Reynolds number based on the Stokes layer can be defined, and transition Reynolds numbers between 400 and 550 have been experimentally determined for purely oscillatory flow in a circular tube, although lower values are expected for physiological flows. There are some indications that the structure of oscillating turbulent flow is similar to steady turbulent flow, and preliminary work in our laboratory shows that the spectral content of flows during high-frequency ventilation is similar to that in steady turbulent flow.}, }
@article {pmid6520130, year = {1984}, author = {Srivastava, LM and Srivastava, VP}, title = {Peristaltic transport of blood: Casson model--II.}, journal = {Journal of biomechanics}, volume = {17}, number = {11}, pages = {821-829}, doi = {10.1016/0021-9290(84)90140-4}, pmid = {6520130}, issn = {0021-9290}, mesh = {*Blood ; *Models, Cardiovascular ; Pressure ; *Rheology ; }, abstract = {The problem of peristaltic transport of blood in a uniform and non-uniform tube has been investigated, under zero Reynolds number and long wavelength approximation. Blood is represented by a two-layered fluid model consisting of a central layer of suspension of all erythrocytes, etc., assumed to be a Casson fluid, and a peripheral layer of plasma as a Newtonian fluid. A comparison of results with those without peripheral layer shows that the magnitude of the pressure rise, under a given set of conditions is smaller in the case of model with peripheral layer. It is found that, for a given flow rate, the pressure rise decreases as the viscosity of the peripheral layer decreases, and for a given non zero pressure drop, the flow rate increases as the viscosity of the peripheral layer decreases. However, the flow is independent of the presence of the peripheral layer, for zero pressure rise. Further, the pressure rise in the case of non-uniform geometry is found much smaller than the corresponding value in the uniform geometry.}, }
@article {pmid6487769, year = {1984}, author = {Karino, T and Goldsmith, HL}, title = {Role of blood cell-wall interactions in thrombogenesis and atherogenesis: a microrheological study.}, journal = {Biorheology}, volume = {21}, number = {4}, pages = {587-601}, doi = {10.3233/bir-1984-21417}, pmid = {6487769}, issn = {0006-355X}, support = {HL-29502/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Aorta, Abdominal/physiology ; Arteriosclerosis/*etiology ; Blood Flow Velocity ; Blood Vessels/*physiology ; Blood Viscosity ; Carotid Arteries/physiology ; Dogs ; Endothelium/physiology ; Hematocrit ; Humans ; *Platelet Adhesiveness ; Saphenous Vein/physiology ; Thrombosis/*etiology ; }, abstract = {The relationship between blood flow and the localization of thrombosis and atherosclerosis in vivo was investigated using the approach and techniques of microrheology. The flow patterns and wall-adhesion of platelets were studied in the captive annular vortex formed at a sudden tubular expansion at various hematocrits in steady and pulsatile flow. The adhesion density exhibited a peak within the vortex and just downstream of the reattachment point, which is also a stagnation point. The peaks flattened out with increasing Reynolds number in steady flow and also in pulsatile flow. Platelet adhesion increased markedly with increasing hematocrit. The localization of adhesion peaks was explained by curvature of the streamlines carrying platelets to the wall on either side of the reattachment point. The relevance of these results to the circulation is that stagnation points are found in regions of disturbed flow at various sites in the arterial and venous circulations. This was shown in experiments using a technique whereby flow was visualized in isolated transparent natural blood vessels prepared from dogs and humans postmortem. In dog saphenous vein bileaflet valves, there was a large primary spiral vortex as well as a smaller secondary vortex, the latter acting as a trap and generator of thrombi. Recirculation zones also existed in the dog aorta at T-junctions of the celiac, cranial mesenteric and renal arteries. Finally, in the human carotid bifurcation, a large standing recirculation zone consisting of spiral secondary flows formed in the carotid sinus at physiological flow conditions.(ABSTRACT TRUNCATED AT 250 WORDS)}, }
@article {pmid6238968, year = {1984}, author = {Ahmed, SA and Giddens, DP}, title = {Pulsatile poststenotic flow studies with laser Doppler anemometry.}, journal = {Journal of biomechanics}, volume = {17}, number = {9}, pages = {695-705}, doi = {10.1016/0021-9290(84)90123-4}, pmid = {6238968}, issn = {0021-9290}, mesh = {Arteries/*pathology ; *Blood Flow Velocity ; Constriction, Pathologic ; *Lasers ; *Models, Cardiovascular ; *Rheology ; }, abstract = {The pulsatile flow field distal to axisymmetric constrictions in a straight tube was studied using laser Doppler anemometry. The upstream centerline velocity waveform was sinusoidal at a frequency parameter of 7.5 and mean Reynolds number of 600. Stenosis models of 25, 50 and 75% area reduction were employed and velocity data were derived by ensemble averaging methods. Extensive measurements of the pulsatile velocity profiles are reported, and wall shear rates were computed from the near wall velocity profile gradients. The experiments indicate that a permanent region of poststenotic flow separation does not exist even for the severest constriction, in contrast to results for steady flow. Values of wall shear stress were greatest near the throat of the constriction and were relatively low in the poststenotic region, including the region of most intense flow disturbance. Turbulence was found only for the 75% stenosis model and was created only during a segment of the cycle. Although much emphasis has been placed upon turbulence in the detection of arterial stenoses, particularly as identified by Doppler ultrasound spectral broadening, the present study implies that identification of flow disturbances of an organized nature may be more fundamental in recognizing mild to moderate disease. Additionally, the relationship of these flow field results to the animal aortic coarctation model often employed in atherogenesis studies is discussed.}, }
@article {pmid6652213, year = {1983}, author = {Jones, RD and Lemanski, CL and Jones, TJ}, title = {Theory of attachment in Giardia.}, journal = {Biophysical journal}, volume = {44}, number = {2}, pages = {185-190}, pmid = {6652213}, issn = {0006-3495}, mesh = {Adhesiveness ; Giardia/*physiology ; *Models, Biological ; }, abstract = {Using a low Reynold's number hydrodynamic model, the adhesive force in Giardia is calculated. It is shown that this force is larger than typical forces that would tend to detach the organism.}, }
@article {pmid6645454, year = {1983}, author = {Sallam, AM and Hwang, NH}, title = {Influence of red blood cell concentrations on the measurement of turbulence using hot-film anemometer.}, journal = {Journal of biomechanical engineering}, volume = {105}, number = {4}, pages = {406-410}, doi = {10.1115/1.3138442}, pmid = {6645454}, issn = {0148-0731}, mesh = {Blood Flow Velocity ; *Hematocrit ; *Rheology ; }, abstract = {Measurement of local velocity fluctuations was made with an L-shaped conical hot-film probe in a submerged circular jet. The experiment was carried out in solutions of washed human red blood cells (RBC) in a phosphate buffer solution (PBS), at hematocrit concentrations (Ht percent) of 10, 19, 29, and 38 percent. The viscosity of the testing solutions was kept at 3.2 c.p. by adding proper amount of dextran. The experiment was conducted at Reynolds numbers (NR) 674, 963, 1255 and 1410, based on the jet exit velocity and exit diameter. Statistical analyses were performed on the recorded instantaneous velocity signals to obtain the root-mean-square (rms) values, the probability density functions (PDF) and the power spectral density functions (PSDF) of the signals. Within the range tested, we noticed an incidental rise in rms values at 19 to 29 Ht percent for NR = 963 similar to those reported earlier in the literature. Further analyses using PDF and PSDF, however, showed neither a trend nor any physical significance of this rise. Based on the analyses of both the PDF and the PSDF, we believe that the incidental rise in rms value can be partially attributed to the high spikes registered by the probe in a high RBC concentrations fluid flow. The bombardment of RBC on the probe thermal boundary layer may cause a characteristic change in the probe response to certain flow phenomenon, at least within the Reynolds number range used in this study.(ABSTRACT TRUNCATED AT 250 WORDS)}, }
@article {pmid6627609, year = {1983}, author = {Zarins, CK and Giddens, DP and Bharadvaj, BK and Sottiurai, VS and Mabon, RF and Glagov, S}, title = {Carotid bifurcation atherosclerosis. Quantitative correlation of plaque localization with flow velocity profiles and wall shear stress.}, journal = {Circulation research}, volume = {53}, number = {4}, pages = {502-514}, doi = {10.1161/01.res.53.4.502}, pmid = {6627609}, issn = {0009-7330}, support = {15062-11//PHS HHS/United States ; }, mesh = {Adult ; Aged ; Arteriosclerosis/pathology ; Blood Flow Velocity ; Carotid Arteries/pathology/physiopathology ; Carotid Artery Diseases/etiology/*pathology ; Humans ; Intracranial Arteriosclerosis/etiology/*pathology ; Middle Aged ; Models, Cardiovascular ; Stress, Mechanical ; }, abstract = {The distribution of nonstenosing, asymptomatic intimal plaques in 12 adult human carotid bifurcations obtained at autopsy was compared with the distribution of flow streamline patterns, flow velocity profiles, and shear stresses in corresponding scale models. The postmortem specimens were fixed while distended to restore normal in vivo length, diameter, and configuration. Angiograms were used to measure branch angles and diameters, and transverse histological sections were studied at five standard sampling levels. Intimal thickness was determined at 15 degrees intervals around the circumference of the vessel sections from contour tracings of images projected onto a digitizing plate. In the models, laser-Doppler anemometry was used to determine flow velocity profiles and shear stresses at levels corresponding to the standard specimen sampling sites under conditions of steady flow at Reynolds numbers of 400, 800, and 1200, and flow patterns were visualized by hydrogen bubble and dye-washout techniques. Intimal thickening was greatest and consistently eccentric in the carotid sinus. With the center of the flow divider as the 0 degree index point, mid-sinus sections showed minimum intimal thickness (0.05 +/- 0.02 mm) within 15 degrees of the index point, while maximum thickness (0.9 +/- 0.1 mm) occurred at 161 +/- 16 degrees, i.e., on the outer wall opposite the flow divider. Where the intima was thinnest, along the inner wall, flow streamlines in the model remain axially aligned and unidirectional, with velocity maxima shifted toward the flow divider apex. Wall shear stress along the inner wall ranged from 31 to 600 dynes/cm2 depending on the Reynolds number. Where the intima was thickest, along the outer wall opposite the flow divider apex, the pattern of flow was complex and included a region of separation and reversal of axial flow as well as the development of counter-rotating helical trajectories. Wall shear stress along the outer wall ranged from 0 to -6 dynes/cm2. Intimal thickening at the common carotid and distal internal carotid levels of section was minimal and was distributed uniformly about the circumference. We conclude that in the human carotid bifurcation, regions of moderate to high shear stress, where flow remains unidirectional and axially aligned, are relatively spared of intimal thickening. Intimal thickening and atherosclerosis develop largely in regions of relatively low wall shear stress, flow separation, and departure from axially aligned, unidirectional flow. Similar quantitative evaluations of other atherosclerosis-prone locations and corresponding flow profile studies in geometrically accurate models may reveal which of these hemodynamic conditions are most consistently associated with the development of intimal disease.}, }
@article {pmid6632828, year = {1983}, author = {Cho, YI and Back, LH and Crawford, DW}, title = {Pressure difference-flow rate variation in a femoral artery branch casting of man for steady flow.}, journal = {Journal of biomechanical engineering}, volume = {105}, number = {3}, pages = {258-262}, doi = {10.1115/1.3138415}, pmid = {6632828}, issn = {0148-0731}, support = {HL 23619-03/HL/NHLBI NIH HHS/United States ; }, mesh = {Biomechanical Phenomena ; Biomedical Engineering/*instrumentation ; Blood Flow Velocity ; *Blood Pressure ; Blood Viscosity ; Femoral Artery/*physiology ; Hemodynamics ; Humans ; In Vitro Techniques ; }, abstract = {In-vitro, steady flow in a casting of the profunda femoris branch of the femoral artery of man was studied by measuring pressure differences in the main lumen and also in the branch over a large Reynolds number range from 200 to 1600. Effects of viscous and inviscid flows in this femoral artery branch were demonstrated quantitatively. The critical ratio of the flow rate in the branch to the upstream main lumen, m3/m1, in this casting was found to be 0.4, above which the inviscid flow analysis indicated a pressure rise and below which it yielded a pressure drop in the main lumen across the branch junction. Pressure rises were experimentally found to occur both in the main lumen and in the branch for certain ranges of m3/m1.}, }
@article {pmid6883418, year = {1983}, author = {Falsetti, HL and Carroll, RJ and Swope, RD and Chen, CJ}, title = {Turbulent blood flow in the ascending aorta of dogs.}, journal = {Cardiovascular research}, volume = {17}, number = {7}, pages = {427-436}, doi = {10.1093/cvr/17.7.427}, pmid = {6883418}, issn = {0008-6363}, support = {HL-014388/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Aorta/*physiology ; Blood Flow Velocity ; *Blood Physiological Phenomena ; Dogs ; Isoproterenol/pharmacology ; Myocardial Contraction/drug effects ; Rheology ; Stress, Mechanical ; }, abstract = {A conical hot film anemometer probe was used to measure instantaneous velocities in the ascending aorta of anaesthetised, open-chest dogs. The probe was mounted on a saddle which allowed traversal of the aorta in 1 mm increments 4 cm above the aortic valve. From these point measurements, the radial distribution of velocity was obtained by averaging ten cardiac cycles. The contractile state of the heart was increased by sequential intravenous infusions of isoprenaline. The absolute peak centreline velocity in the baseline state ranged from 28 to 56 cm x s-1 and, in 20 micrograms x min-1 isoprenaline infusion, from 39 to 112 cm x s-1. Two major effects of isoprenaline on blood flow were noted: 1) isoprenaline dramatically increased peak centreline velocity, and 2) disturbances resembling turbulence appeared as peak velocity increased. With isoprenaline infusion disturbances existed throughout the deceleration portion of the aortic blood flow. Analysis of the frequency components of the velocity wave was performed, and significantly higher frequency components up to 100 Hertz were found in the turbulent cases compared to the laminar ones. Turbulent flow or disturbed flow is found when the ratio of Reynolds number to Womersley number is above 200. In general the hot film measurements showed that both laminar and disturbed velocity profiles tended to be flat throughout the cardiac cycle, with the sharp velocity gradient confined to the region of the wall. Turbulent normal stress during the deceleration portion of aortic blood flow were found in the orders of 15 to 30 dynes x cm-2 and the wall shear stresses were found to be from 10 dynes x cm-2 at the baseline condition to 50 dynes x cm-2 during the 20 micrograms x min-1 isoprenaline infusion.}, }
@article {pmid6888219, year = {1983}, author = {Latypov, ZZ}, title = {[Flow-type cuvette of an optical analyzer with hydrodynamic focusing of the liquid under study].}, journal = {Meditsinskaia tekhnika}, volume = {}, number = {3}, pages = {31-32}, pmid = {6888219}, issn = {0025-8075}, mesh = {Blood Cell Count/instrumentation ; Equipment Design ; Flow Cytometry/*instrumentation ; }, abstract = {Described in the paper is a flow cuvette (probe) for an optical analyzer of formed blood elements and other cell suspensions. The cuvette is provided by hydrodynamic focusing of the liquids. The cuvette differs from the commonly known models by the following parameters: a high upper limit of the operating range for the Reynolds number and, as a result, the possibility to increase the analysis rate, high spatial and time resolution, and compactness.}, }
@article {pmid6863081, year = {1983}, author = {Mortola, JP}, title = {Comparative aspects of the dynamics of breathing in newborn mammals.}, journal = {Journal of applied physiology: respiratory, environmental and exercise physiology}, volume = {54}, number = {5}, pages = {1229-1235}, doi = {10.1152/jappl.1983.54.5.1229}, pmid = {6863081}, issn = {0161-7567}, mesh = {Airway Resistance ; Animals ; Animals, Newborn/*physiology ; Body Weight ; Cats ; Dogs ; Guinea Pigs ; Lung Compliance ; Lung Volume Measurements ; Rabbits ; Rats ; *Respiration ; Species Specificity ; Swine ; }, abstract = {Static and dynamic properties of the respiratory system have been studied in anesthetized, tracheostomized newborns of six species, ranging in size from rats to piglets. Respiratory system compliance (Crs), total resistance of respiratory system (Rrs), and expiratory time constant (tau) have been measured in the paralyzed passively ventilated animals. Crs is found to be proportional to body weight (BW0.80) and Rrs to BW-0.75; tau is independent of body size, the shortest value being in kittens and guinea pigs and a value of about 0.14 s in the other species. Including the upper airway resistance, tau becomes approximately 0.22 s. This value is similar to the expiratory time of the fastest breathing species; therefore in the smallest species the high breathing rate can be regarded as a mechanism to raise end-expiratory level. On a few occasions, dynamic lung compliance and pulmonary resistance, measured in spontaneously breathing kittens, puppies, and piglets were, respectively, smaller and larger than Crs and Rrs, suggesting that the hysteresis of the pressure-volume curve may be substantial. Rrs was almost linear within the volume and flow range investigated, with the Rohrer's constant K2 always being less than 2.5% of K1. The Reynolds number increases with body size (alpha BW0.51) more than is predictable from the changes in tracheal diameter, since the tracheal flow velocity is not an interspecific constant.}, }
@article {pmid6222682, year = {1983}, author = {Girardin, M and Bilgen, E and Arbour, P}, title = {Experimental study of velocity fields in a human nasal fossa by laser anemometry.}, journal = {The Annals of otology, rhinology, and laryngology}, volume = {92}, number = {3 Pt 1}, pages = {231-236}, doi = {10.1177/000348948309200304}, pmid = {6222682}, issn = {0003-4894}, mesh = {Computers ; Humans ; Lasers ; Models, Anatomic ; Nasal Cavity/*physiology ; *Pulmonary Ventilation ; Respiration ; Rheology ; }, abstract = {Velocity fields were mapped in a model of a human nasal fossa by laser doppler velocimetry, an innovative, quantitative and noninvasive method of optical anemometry, and by computerization. Other pertinent parameters were also calculated. Studies made at different cross sections of the nasal fossa showed the very definite influence not only of shapes and dimensions but also of direction of flow on velocity fields. The turbinates had a streamlining effect on the velocity fields while the liminal valve had a directional effect. Flow was usually greater in the lower half of the fossa and closer to the septum. The flow was generally turbulent. Velocity fields appear to give more information on intranasal aerodynamics than the calculated flow and Reynolds number for the sections studied, and this allows one to at least theorize that there may be an aerodynamic basis to certain pathological conditions of the nasal airway and its adjoining cavities, the paranasal sinuses, and the eustachian tubes.}, }
@article {pmid6853302, year = {1983}, author = {Olson, LE and Rodarte, JR and Robinson, NE}, title = {Pressure-flow relationships in a collaterally ventilating dog lung segment.}, journal = {Journal of applied physiology: respiratory, environmental and exercise physiology}, volume = {54}, number = {4}, pages = {956-960}, doi = {10.1152/jappl.1983.54.4.956}, pmid = {6853302}, issn = {0161-7567}, support = {HL-07222/HL/NHLBI NIH HHS/United States ; HL-17768/HL/NHLBI NIH HHS/United States ; HL-21584/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Dogs ; Female ; Lung/*physiology ; Male ; Pressure ; Pulmonary Circulation ; *Pulmonary Ventilation ; *Respiration ; Viscosity ; }, abstract = {We evaluated the pressure (P)-flow (V) relationship in collaterally ventilating dog lung segments by passing He, N2, and SF6 through a bronchoscope (5 mm OD) wedged in a peripheral airway. Measurements were made at functional residual capacity (FRC) and two higher lung volumes, keeping segment-to-airway opening pressure constant (3 cmH2O) in five anesthetized, paralyzed, vagotomized, supine dogs. Average flows ranged from 5.0 to 8.0 ml/s for He, 4.5 to 7.5 ml/s for N2, and 3.4 to 4.7 ml/s for SF6. When these data were fitted as P = K1/3/3 mu V + K2 rho V2, density-dependent pressure losses were unimportant when He and N2 were used, suggesting laminar flow with these gases. A dimensionless plot of the total pressure drop relative to a reference dynamic pressure as a function of Reynolds number at the bronchoscope tip suggested that flow through the segment behaved as if it were laminar at Reynolds numbers less than 100. Furthermore, when the airway diameter used to compute the normalized pressure and Reynolds number was scaled as the cubic root of lung volume, curves for all three gases were superimposed, suggesting that the dimensions of intrasegmental/collateral airways scale as lung volume 1/3.}, }
@article {pmid6843098, year = {1983}, author = {Nuckols, ML and Zumrick, JL and Johnson, CE}, title = {Heat and water vapor transport in the human upper airways at hyperbaric conditions.}, journal = {Journal of biomechanical engineering}, volume = {105}, number = {1}, pages = {24-30}, doi = {10.1115/1.3138380}, pmid = {6843098}, issn = {0148-0731}, mesh = {Air ; Helium ; *Hot Temperature ; Humans ; Models, Anatomic ; *Models, Biological ; Nitrogen ; Pharynx/anatomy &amp; histology ; *Pressure ; *Respiratory Physiological Phenomena ; Trachea/anatomy &amp; histology ; Water/*metabolism ; }, abstract = {Heat and mass transfer mechanisms have been characterized in physical models of human cadaver airways to simulated depths of 305 m with various gas mixtures. Such characterizations offer a detailed understanding of the effects of environmental pressures, gas composition, and respiratory rates (RMV) on the body cooling capacity of the respiratory airways. Empirical heat transfer relationships in the form -Nu = AReNPr1/3 are derived for the oral and nasal passageways during inhalation and exhalation flows. -Nu, Re, and Pr are the dimensionless Nusselt, Reynolds, and Prandtl numbers, respectively. The Nusselt and Reynolds numbers are based on the diameter and gas flow rate in the trachea and are applicable to Reynolds number values up to 70,000.}, }
@article {pmid6843096, year = {1983}, author = {Jan, DL and Kamm, RD and Shapiro, AH}, title = {Filling of partially collapsed compliant tubes.}, journal = {Journal of biomechanical engineering}, volume = {105}, number = {1}, pages = {12-19}, doi = {10.1115/1.3138377}, pmid = {6843096}, issn = {0148-0731}, support = {GM-07301/GM/NIGMS NIH HHS/United States ; }, mesh = {Mathematics ; Models, Theoretical ; *Rheology ; }, abstract = {Filling of a thin-walled, highly compliant tube in a partially collapsed condition is studied. The theory, based on one-dimensional flow, takes account of friction, longitudinal tension, and the highly nonlinear pressure-area law for the tube. Various aspects of filling behavior are revealed by alternative calculations using: (i) the method of characteristics; (ii) numerical integration of the continuity, momentum, and tube-law equations; and (iii) a crude but simple lumped-element capacitance-inertance-resistance model. Varied phenomena appear. At high Reynolds number, these include dispersive wave trains associated with circumferential bending stiffness and longitudinal tension, nonlinear changes of wave form, development of highly asymmetrical wave reflections, and sloshing. At low Reynolds number, the area changes with time in a diffusivelike manner. The experiments exhibited the dispersive phenomena predicted by the theory.}, }
@article {pmid6871431, year = {1983}, author = {Srivastava, LM and Srivastava, VP and Sinha, SN}, title = {Peristaltic transport of a physiological fluid. Part-I. Flow in non-uniform geometry.}, journal = {Biorheology}, volume = {20}, number = {2}, pages = {153-166}, doi = {10.3233/bir-1983-20205}, pmid = {6871431}, issn = {0006-355X}, mesh = {*Biological Transport ; *Models, Biological ; Peristalsis ; Pressure ; *Rheology ; Viscosity ; }, abstract = {The problem of peristaltic transport of a fluid of variable viscosity in a non-uniform tube and channel has been investigated under zero Reynolds number, and long wavelength approximation. It is found that, the pressure rise decreases as the fluid viscosity decreases at zero flow rate, is independent of viscosity variation at a certain value of flow rate, and increases if flow rate exceeds further. The difference between two corresponding values (for constant and variable viscosity) of pressure rise, under a given set of conditions increases with increasing amplitude ratio at zero flow rate. Further, for a given zero pressure rise, the flow rate increases as viscosity of fluid decreases. The pressure rise, in the case of non-uniform geometry is found to be much smaller than the corresponding value in the case of uniform geometry. In Part II (a companion paper), results for uniform tube and channel are obtained and comparison with other theories are made in detail. Finally, the models developed in Part I and Part II are applied and compared with observed flow rates in vas deferens of rhesus monkeys, the small intestine, and the ductus deferens of the male reproductive tract in the other companion paper, Part III.}, }
@article {pmid6824494, year = {1983}, author = {Ku, DN and Giddens, DP}, title = {Pulsatile flow in a model carotid bifurcation.}, journal = {Arteriosclerosis (Dallas, Tex.)}, volume = {3}, number = {1}, pages = {31-39}, doi = {10.1161/01.atv.3.1.31}, pmid = {6824494}, issn = {0276-5047}, support = {HL22635/HL/NHLBI NIH HHS/United States ; }, mesh = {Adult ; Aged ; Carotid Arteries/*physiology ; Humans ; Middle Aged ; Models, Cardiovascular ; Regional Blood Flow ; }, abstract = {Pulsatile flow in an in vitro model of the human carotid bifurcation was studied by flow visualization using hydrogen bubble techniques. A glass model was constructed after determining an average geometry from 57 biplanar angiograms of 22 subjects ranging from 34 to 77 years of age. The flow pulse used was a half-sine wave superimposed upon a mean flow. Maximum and minimum values of the instantaneous Reynolds number were 1200 and 400, respectively, based upon conditions in the common carotid model artery; the frequency parameter was 6.0. The division of flow into the internal external branches was 70:30. Visualization by hydrogen bubbles demonstrated significant deviations from steady flow behavior. Flow separated in the carotid sinus over the entire cycle, but the location and extent of separation varied strongly. The direction of flow near the walls of the model changed sharply during the cycle except for the region near the apex of the bifurcation where the orientation of streaklines was more nearly unidirectional at all times. Bubbles entering the separated flow region tended to remain entrapped there for several cycles. Rapid dispersion of bubbles occurred in the internal branch near the end of systole, suggesting the presence of flow disorder. The location of low wall shear stresses, directionally varying stresses, and longer residence times for fluid elements appears to coincide with the localization of early atheromatous plaques in human carotid specimens.}, }
@article {pmid6671986, year = {1983}, author = {Ahmed, SA and Giddens, DP}, title = {Flow disturbance measurements through a constricted tube at moderate Reynolds numbers.}, journal = {Journal of biomechanics}, volume = {16}, number = {12}, pages = {955-963}, doi = {10.1016/0021-9290(83)90096-9}, pmid = {6671986}, issn = {0021-9290}, mesh = {Animals ; Arteriosclerosis/physiopathology ; *Biomechanical Phenomena ; Humans ; Lasers ; Methods ; *Rheology ; }, abstract = {Instantaneous velocities in the field distal to contoured axisymmetric stenoses were measured with a laser Doppler anemometer. Upstream flow conditions were steady and spanned a range of Reynolds numbers from 500 to 2000. Autocorrelation functions and spectra of the velocity were employed to describe the nature of fluid dynamic disturbances. Depending upon the degree of stenosis and the Reynolds number, the flow field contained disturbances of a discrete oscillation frequency, of a turbulent nature, or both. If turbulence was detected in a given experiment, it was always preceded upstream by velocity oscillations at discrete frequency arising from vortex shedding. For mild degrees of stenosis (50% area reduction or less) the intensity of flow disturbances was relatively low until the Reynolds number exceeded 1000, thus highlighting difficulties to be expected in employing flow disturbance detection as a diagnostic tool in the recognition of early atherosclerosis in major arteries. In view of the relatively high noise levels inherent in noninvasive Doppler ultrasound systems employed clinically, it seems unlikely that detection of stenosis of less than 50% area reduction is feasible unless the Reynolds numbers exceed 1000 or unless pulsatility introduces new unsteady flow features beyond those studied here.}, }
@article {pmid6654922, year = {1983}, author = {Cho, YI and Back, LH and Crawford, DW and Cuffel, RF}, title = {Experimental study of pulsatile and steady flow through a smooth tube and an atherosclerotic coronary artery casting of man.}, journal = {Journal of biomechanics}, volume = {16}, number = {11}, pages = {933-946}, doi = {10.1016/0021-9290(83)90057-x}, pmid = {6654922}, issn = {0021-9290}, mesh = {Arteriosclerosis/physiopathology ; Blood Flow Velocity ; Coronary Disease/*physiopathology ; Humans ; In Vitro Techniques ; *Models, Anatomic ; *Rheology ; Vascular Resistance ; }, abstract = {In vitro investigation of pulsatile and steady flows through a smooth, straight circular tube and a diseased human coronary artery cast was conducted with sugar-water solutions simulating the viscosity of blood. Time averaged pressure drops for pulsatile flows measured in the circular tube over a Reynolds number ranging from 50 to 1,000 were found to be identical to those for steady flows in the same tube, both of which were in excellent agreement with the Poiseuille flow prediction. For the polyurethane case (# 124) made from a human main coronary with significant but 'non obstructive' diffuse atherosclerotic disease, pressure drops for steady flows were found to be greater than Poiseuille flow predictions by a factor of 3-8 in the physiological Reynolds number range from about 100 to 400. Pulsatile flows in the same artery cast resulted in additional 30% increases in time averaged pressure drops, and thus flow resistance, compared to the steady flow data. Steady and pulsatile flow data measured in a straight, axisymmetric model of cast # 124 showed considerably smaller increases in flow resistance than those observed in # 124 casting.}, }
@article {pmid7149035, year = {1982}, author = {Macagno, EO and Christensen, J and Lee, CL}, title = {Modeling the effect of wall movement on absorption in the intestine.}, journal = {The American journal of physiology}, volume = {243}, number = {6}, pages = {G541-50}, doi = {10.1152/ajpgi.1982.243.6.G541}, pmid = {7149035}, issn = {0002-9513}, support = {AM-08901/AM/NIADDK NIH HHS/United States ; }, mesh = {Animals ; *Gastrointestinal Motility ; *Intestinal Absorption ; Intestines/physiology ; Mathematics ; Models, Biological ; Muscle Contraction ; Muscle, Smooth/physiology ; Perfusion ; }, abstract = {Intestinal wall movements may influence intestinal absorption by inducing flow in the luminal volume. Direct evidence for this is scant and weak. Such evidence was sought by mechanical and analytical modeling. Wall motions resembling peristaltic ring contractions were induced in dialysis tubing filled with a concentrated salt solution and immersed in tap water. The disappearance of solute from the inside of the tube was monitored with conductivity probes and correlated with various kinds of wall motions. In analytical modeling, equations representing wall motions, flow, and mass transfer were constructed, with the assumptions that ring contractions are axisymmetric, the wall is totally compliant, the Reynolds' number is low, the fluid volume is conserved, the no-slip condition exists at the luminal surface, and inertial flow is negligible. In the mechanical model, wall motions caused a 30-35% increase in absorption that was matched in the corresponding analytical model. The analytical model demonstrated that the effect is progressively greater for nonpropagative stationary contractions, asymmetric progressive contractions, and symmetric progressive contractions, the increase being 33, 70, and 100%, respectively.}, }
@article {pmid18546216, year = {1982}, author = {Bryers, JD and Characklis, WG}, title = {Processes governing primary biofilm formation.}, journal = {Biotechnology and bioengineering}, volume = {24}, number = {11}, pages = {2451-2476}, doi = {10.1002/bit.260241111}, pmid = {18546216}, issn = {0006-3592}, abstract = {Biofilm accumulation under turbulent flow condition on the surface of a circular tube is the net result of several process including the following: (1) transport and firm adhesion of soluble components and microbial cell to the surface; (2) metabolic conversions within the biofilm in cluding growth and maintenance decay process; (3) detachment of portions of the biofilm and reentrainment in the bulk fluid. Experiments in tabular reactor were designed to measure the rates of these process during the early stages of biofilm accumulation as a function of the Reynolds number and suspended biomass concentration. Results indicate deposition (i.e., combined transport and adsorption) is only important in the very early stages of biofilm accumulation and is significantly influenced by negligible for the thin biofilms encountered in these experiments. Net biofilm production rates in all experiments decrease to same level and this level is not affected by changes in Reynolds number or suspended biomass concentration. Biofilm detachment rate increases continuously with biofilm accumulation and with increasing Reynolds number.}, }
@article {pmid7175748, year = {1982}, author = {Hey, EN and Price, JF}, title = {Nasal conductance and effective airway diameter.}, journal = {The Journal of physiology}, volume = {330}, number = {}, pages = {429-437}, pmid = {7175748}, issn = {0022-3751}, mesh = {Airway Resistance ; Asthma/physiopathology ; Child ; Female ; Helium/pharmacology ; Humans ; Male ; Manometry ; Nasal Cavity/*physiology ; Pulmonary Ventilation/*drug effects ; Rhinitis, Allergic, Seasonal/physiopathology ; Sulfur Hexafluoride/pharmacology ; }, abstract = {1. Transnasal pressure (delta p) in Pa and gas flow in cm3 s-1 were measured in men breathing gases of different density, assuming flow through each nostril (f) to be half the measured total flow. Measurements were also made in children with allergic rhinitis before and after nasal antigen challenge. 2. Flow always showed evidence of turbulence when transnasal pressure exceeded 40-80 Pa breathing air and Reynolds number exceeded 2400 (1800 in the presence of nasal obstruction). 3. Changes in effective mean nasal airway diameter (D) after nasal challenge can be determined at points of similar pressure from the relation log (D2/D1) = 0.368 log (f2/f1) when flow is turbulent. 4. Absolute estimates of airway diameter in cm can be obtained from the relation 4.75 log D = 1.75 log f--log delta p+log L--4.756 breathing air when flow is turbulent (since the relation between pressure and flow approximates to that found in a long cylinder) and these estimates are only marginally affected by differing assumptions about nasal airway length (L). 5. Because pressure and flow are non-linearly related, and changing nasal dimensions have a profound effect on the flow at which turbulence occurs, it is suggested that measures of nasal conductance at delta p greater than or equal to 0.1 kPa are preferable to the more conventional measures of nasal resistance at a specified flow rate.}, }
@article {pmid7146651, year = {1982}, author = {Simone, AF and Ultman, JS}, title = {Longitudinal mixing by the human larynx.}, journal = {Respiration physiology}, volume = {49}, number = {2}, pages = {187-203}, doi = {10.1016/0034-5687(82)90073-1}, pmid = {7146651}, issn = {0034-5687}, support = {HL-20347/HL/NHLBI NIH HHS/United States ; }, mesh = {Biomechanical Phenomena ; Gases/*physiology ; Humans ; Larynx/*physiology ; Models, Anatomic ; Physiology/methods ; Pulmonary Ventilation ; }, abstract = {Both the characteristics of the velocity field and the longitudinal dispersion of helium, oxygen and sulfur hexafluoride in air flowing through a cast of a cadaveric human larynx have been studied. The larynx cast was mounted in the center of a 5 m long, 1.6 cm diameter tube through which air was admitted at 206, 425 or 775 ml/s, corresponding to fully-developed laminar (Reynolds number = 1110), transitional (2310), and fully-developed turbulent (4210) flow conditions, respectively. A significant enhancement of longitudinal mixing was detected immediately downstream of the glottis, presumably because of the jetting of air in the vicinity of the constriction. This enhancement did not depend upon the flow rate of air but was inversely related to the molecular diffusivity of the tracer gas; this indicates the importance of Taylor dispersion in the jet. The glottis also generated intense local turbulence which propagated as far as 110 cm from the constriction. This turbulence caused a flattening of the velocity profiles resulting in a reduction in the rate of downstream longitudinal mixing. The reduction was so great that, in spite of mixing enhancement in the jet, the overall mixing was less with the larynx in place than in the empty tube.}, }
@article {pmid17830583, year = {1982}, author = {Gerritsen, J and Porter, KG}, title = {The role of surface chemistry in filter feeding by zooplankton.}, journal = {Science (New York, N.Y.)}, volume = {216}, number = {4551}, pages = {1225-1227}, doi = {10.1126/science.216.4551.1225}, pmid = {17830583}, issn = {0036-8075}, abstract = {Surface chemistry of both particles and animals is important in filter feeding at low Reynolds number. Daphnia magna, fed mixtures of three sizes of polystyrene particles, retained particles that were smaller than the mesh size of the animals (1.0 micrometer) at greater efficiencies than predicted by a sieving model. Retention efficiency of the smallest particles (0.5 micrometer) was increased when negative surface charge on the particles was neutralized, and retention was decreased when a nonionic surfactant was, added to reduce wettability.}, }
@article {pmid7096141, year = {1982}, author = {King, M and Chang, HK and Weber, ME}, title = {Resistance of mucus-lined tubes to steady and oscillatory airflow.}, journal = {Journal of applied physiology: respiratory, environmental and exercise physiology}, volume = {52}, number = {5}, pages = {1172-1176}, doi = {10.1152/jappl.1982.52.5.1172}, pmid = {7096141}, issn = {0161-7567}, mesh = {Airway Resistance ; Animals ; Elasticity ; Models, Biological ; Mucus/*physiology ; *Pulmonary Ventilation ; Swine ; Trachea/*physiology ; Viscosity ; }, abstract = {We examined the effects of quantity and physical properties of mucus on resistance to steady and oscillatory flows in a circular tube. Gels with similar rheological properties to canine tracheal mucus were prepared from hog gastric mucin or locust bean gum cross-linked with Na2B4O7. A horizontal straight tube (D 1.85 cm) was lined with these mucus simulants to depths ranging from 0.3 to 1.0 mm. The pressure difference over a 50-cm portion of the tube and the volumetric flow rate were determined simultaneously. Low-amplitude oscillatory flow were generated with a modified Harvard pump. For steady flow, the resistance at low Reynolds number (Re) increased with increasing gel depth only to the extent expected for simple constriction of the tube cross-sectional area. The same was true for oscillatory (0.25--6 Hz) flow resistance at low flow amplitude (corresponding to Re less than 4,000). No effect of gel cross-link density at low Re was observed. At high steady-flow rates, and for high-amplitude oscillatory flow, resistance increased beyond that predicted for simple constriction. Plots of friction factor (f) vs. Re showed a critical point (Recrit) of the order of 1.5 x 10(4), at which f increased sharply. Recrit, which corresponded to the onset of wave formation in the lining layer, was insensitive to changes in gel depth. However, gel cross-link density did affect the onset of wave formation: in oscillatory flow Recrit was shifted to higher Re, and the rise in f in steady flow was blunted with high degrees of cross-linking. The existence of Recrit and its association with wave formation are consistent with predictions based on two-phase flow theory.}, }
@article {pmid7078129, year = {1982}, author = {Fukushima, T and Azuma, T and Matsuzawa, T}, title = {Numerical analysis of blood flow in the vertebral artery.}, journal = {Journal of biomechanical engineering}, volume = {104}, number = {2}, pages = {143-147}, doi = {10.1115/1.3138328}, pmid = {7078129}, issn = {0148-0731}, mesh = {Blood Flow Velocity ; Humans ; Models, Cardiovascular ; Regional Blood Flow ; Stress, Mechanical ; Vascular Resistance ; Vertebral Artery/*physiology ; }, abstract = {Abnormal hemodynamic forces associated with distortions of blood vessel lumen have been thought to play an important role in the pathogenesis of focal vascular lesions. In the vertebral artery, segments located between osseous rings are ectatic compared with those surrounded by the rings. Based on the assumption that arterial blood flow was quasi-steady, this work was undertaken to investigate the structure of flow through arterial models with one or two sinusoidal stenoses. Numerical analysis was performed by an integral-momentum method. The validity of the method was examined by comparison of experimental data so far reported with theoretical results. Velocity and wall shear stress distributions were explored in a model with two stenoses simulating a part of the vertebral artery. The ectatic segments of the vertebral artery have been known as predilection sites for atherosclerotic lesions. The present study suggested that the ectatic wall was under unstable shear stresses, the direction of which was dependent upon the magnitude of the Reynolds number.}, }
@article {pmid7078121, year = {1982}, author = {Walburn, FJ and Stein, PD}, title = {A comparison of steady and pulsatile flow in symmetrically branched tubes.}, journal = {Journal of biomechanical engineering}, volume = {104}, number = {1}, pages = {66-68}, doi = {10.1115/1.3138306}, pmid = {7078121}, issn = {0148-0731}, support = {HL25839-02/HL/NHLBI NIH HHS/United States ; }, mesh = {Aorta/physiology ; *Blood Circulation ; Blood Pressure ; *Models, Cardiovascular ; }, abstract = {The purpose of this study was to compare the characteristics of flow in the region of symmetrical bifurcations having branch-to-trunk area ratios of 0.4, 0.8 and 1.2 during steady and pulsatile flow. Flow was visualized with neutrally bouyant particles. Secondary flow was not observed in the branches during either steady or pulsatile flow when the branch-to-trunk area ratio was 0.4. Secondary velocity patterns were not observed in the branches with branch-to-trunk area ratios of 0.8 and 1.2 during pulsatile flow, although they were observed during steady flow. It may be inaccurate, therefore, to characterize pulsatile flow at an instantaneous Reynolds number on the basis of steady flow at the same Reynolds number.}, }
@article {pmid7118954, year = {1982}, author = {Isabey, D}, title = {Steady and pulsatile flow distribution in a multiple branching network with physiological applications.}, journal = {Journal of biomechanics}, volume = {15}, number = {5}, pages = {395-404}, doi = {10.1016/0021-9290(82)90061-6}, pmid = {7118954}, issn = {0021-9290}, mesh = {Arteries/physiology ; Biomechanical Phenomena ; *Blood Circulation ; Humans ; Mathematics ; *Models, Biological ; *Pulmonary Ventilation ; }, abstract = {Flow rate of distribution in steady and pulsatile flow is investigated in a multiple branching network including six successive generations in the same plane. In this model, the geometry dependence of flow rate distribution has already been pointed out in steady flow (previous study) by observing the occurrence of non-uniform flow rate distribution at terminal orifices despite the symmetrical dichotomy, identical distance and cross-sectional profile of the 64 parallel pathways. In the present study, we point out two additional properties of the steady flow rate distribution. (i) The flow rate distribution is not markedly sensitive to a change in viscosity and therefore Reynolds number does not appear to be a determinant factor to modify the flow distribution. (ii) The effect of a branch obstruction on flow rate distribution is limited in space and its extension remains the same for the different Reynolds numbers tested. These properties also characterize the interdependence between the model geometry and the flow distribution in steady state. The results obtained in pulsatile flow show that the flow distribution remains similar to steady state as long as the parameter lambda = Qp/Qs (Qp = amplitude of flow oscillation, Qs = steady component of the total flow) is less than 1. When lambda is greater than 1, the flow distribution may become uniform, which means that contrary to the steady flow case, the velocity profiles become rapidly symmetrical downstream from the bifurcations. Physical explanations for this are proposed after considering the theoretical problem of pulsatile developed flow in a straight tube. In this case, the parameter lambda again plays a crucial role in the velocity distribution.}, }
@article {pmid7053771, year = {1982}, author = {Isabey, D and Chang, HK}, title = {[Pressure-flow relationship in the airways (author's transl)].}, journal = {Bulletin europeen de physiopathologie respiratoire}, volume = {18}, number = {1}, pages = {131-143}, pmid = {7053771}, issn = {0395-3890}, mesh = {Gases ; Humans ; Lung/*physiology ; Models, Biological ; Pressure ; *Pulmonary Ventilation ; }, abstract = {The perplexing features of the pressure-flow relationship in the pulmonary airways have been explained on the basis of a combined experimental-theoretical study. By systematically plotting the in vivo data on the pressure-flow relationship existing in the literature in a dimensionless manner (Moody diagram), we confirmed the results reported by Lisboa et al. [8] : contrary to the well-known theory of Jaffrin and Kesic [6], it appeared that under certain spontaneous breathing conditions Reynolds number is not the only parameter which governs the flow in the airways. We further confirmed this result using a cast of the central airways and a piston pump. The data showed that the pressure-flow relationship depended greatly on frequency, tidal volume and the physical properties of the gas used. After a systematic variation of these parameters, a dimensionless parameter epsilon, which depends importantly on local acceleration, was identified. This new parameter, together with those already identified (Re : Reynolds number; alpha : Womersley number), define the pressure-flow relationship in a given geometry during the course of a respiratory cycle. Implications of this theoretical knowledge on the measurement and interpretation of airway resistance are discussed.}, }
@article {pmid6215408, year = {1982}, author = {Liepsch, D and Moravec, S and Rastogi, AK and Vlachos, NS}, title = {Measurement and calculations of laminar flow in a ninety degree bifurcation.}, journal = {Journal of biomechanics}, volume = {15}, number = {7}, pages = {473-485}, doi = {10.1016/0021-9290(82)90001-x}, pmid = {6215408}, issn = {0021-9290}, mesh = {*Blood Flow Velocity ; Hemodynamics ; Humans ; Models, Biological ; *Rheology ; }, abstract = {Measurements and numericaL calculations of laminar flow in a plane 90 degrees bifurcation are presented. The corresponding two-dimensional steady flow Navier-Stokes equations solved by a finite-difference procedure employing pressure and velocity as dependent variables. The influence of Reynolds number and mass flow ratio on the velocity field, streamlines, local shear stress and pressure drop are quantified and shown to be substantial. The circulation patterns and shear stresses are examined in view of available data regarding the formation of atherotic plaques in the human circulatory system. The calculated velocity profiles are compared with measurements obtained with laser Doppler anemometry and the agreement is shown to be satisfactory. Calculations outside the range of measurements which are of value to biomechanics are also presented.}, }
@article {pmid6212090, year = {1982}, author = {Walburn, FJ and Stein, PD}, title = {The shear rate at the wall in a symmetrically branched tube simulating the aortic bifurcation.}, journal = {Biorheology}, volume = {19}, number = {1/2}, pages = {307-316}, doi = {10.3233/bir-1982-191-233}, pmid = {6212090}, issn = {0006-355X}, support = {HL25839-01/HL/NHLBI NIH HHS/United States ; }, mesh = {Aorta, Abdominal/*physiology ; *Blood Flow Velocity ; Humans ; Models, Cardiovascular ; Rheology ; Stress, Mechanical ; Vascular Resistance ; }, abstract = {The purpose of this study was to determine the shear rate at the wall in a symmetrically branched tube with a branch-to-trunk area ratio and angle of branching that were comparable to the human abdominal aorta. Velocity profiles were measured with a laser Doppler anemometer during steady and pulsatile flow in which the mean Reynolds numbers were 500, 1000, and 1500. During both steady and pulsatile flow, as the Reynolds numbers increased, the shear rates at the inner wall of the branch increased. Only slight increments of the shear rates occurred along the outer wall of the branch, however, as the Reynolds number increased. No reversals of flow were observed at any Reynolds number during steady flow. Transient reversals of flow (causing negative shear rates) occurred along the outer wall of the branch at a Reynolds number of 500; but such transient flow reversals were not observed at the higher Reynolds numbers during pulsatile flow.}, }
@article {pmid7332754, year = {1981}, author = {Dimicoli, JL and Nakache, M and Delouche, P and Favaudon, V and Peronneau, P}, title = {Visualization of the parietal mass transfer by using immobilized peroxidase.}, journal = {Biochimie}, volume = {63}, number = {11-12}, pages = {877-881}, doi = {10.1016/s0300-9084(82)80278-2}, pmid = {7332754}, issn = {0300-9084}, mesh = {Blood Flow Velocity ; Blood Vessels/*physiology ; Diffusion ; Enzymes, Immobilized ; Horseradish Peroxidase ; Hydrogen Peroxide ; Light ; *Models, Cardiovascular ; Ultrasonography ; }, abstract = {A new method is developed for direct visualization of the local mass transfer at solid liquid interfaces involving the chemiluminescent oxidation of luminol by H2O2 catalyzed by immobilized peroxidase. At low concentration of H2O2 (C less than 5 x 10(-5) M) this reaction is controlled by diffusion and it is possible to characterize the diffusion convection of H2O2 at each point of the tube as a function of the local hydrodynamic properties. These properties are characterized by pulsed Doppler ultrasound velocimetry. 1) The rate of light emission depends on Re1/3 for the laminar case and decreases when going downstream in accordance with the known theories of diffusion convection along tubes. 2)Downstream to a stenosis, a maximum of light appears which depends on the input Reynolds number in a manner similar to the reattachment point of the flow. This constitutes the first experimental confirmation of calculations on diffusion convection downstream to stenoses. These first experiments show the capacity of the method to detect the local properties of the parietal mass transfer phenomenon as a function of the geometry of the wall and the hydrodynamic properties of the flow.}, }
@article {pmid7298472, year = {1981}, author = {Isabey, D and Chang, HK}, title = {Steady and unsteady pressure-flow relationships in central airways.}, journal = {Journal of applied physiology: respiratory, environmental and exercise physiology}, volume = {51}, number = {5}, pages = {1338-1348}, doi = {10.1152/jappl.1981.51.5.1338}, pmid = {7298472}, issn = {0161-7567}, mesh = {Airway Resistance ; Bronchi ; Humans ; Models, Structural ; Pressure ; *Pulmonary Ventilation ; Trachea ; }, abstract = {We measured pressure-flow relationships in a noncompliant five-generation cast of human central airways using air, HeO2, and SF6O2 at 0, 0.25, 0.50, 1.0, and 2.0 Hz with tidal volumes of 0.25, 0.5, and 1.0 liter. When dimensionless pressure drops for steady inspiratory and expiratory flows of the various gas mixture were plotted against Reynolds' number on a log-log scale (Moody diagram), they formed two curves as fluid mechanical theory predicts. At frequencies higher than 0.25 Hz, data obtained from 1) the same gas and same stroke volume, 2) the same frequency and same stroke volume but different gases, and 3) the same gas at the same frequency but with different stroke volumes, all deviated from the steady flow curves in the Moody diagram, always tending to increase the dimensionless pressure drop. The increase was largest when instantaneous flow was near zero and was minimal at the peak flow in a given inspiration or expiration. These data led to the identification of a dimensionless parameter (epsilon) that reflects the relative importance of local acceleration (unsteadiness) to convective acceleration at any given instant during a flow cycle. A dimensional analysis then reveals that the pressure-flow relationship in a given airway system is uniquely and completely determined by a combination of three dimensionless parameters: Reynolds number (Re), Womersley number (alpha), and the new parameter (epsilon). With this set of parameters we can explain all reported apparent paradoxes as well as the present findings.}, }
@article {pmid7298471, year = {1981}, author = {Sneddon, SL and Brain, JD}, title = {Steady expiratory flow in dog lungs: an isovolume preparation.}, journal = {Journal of applied physiology: respiratory, environmental and exercise physiology}, volume = {51}, number = {5}, pages = {1331-1337}, doi = {10.1152/jappl.1981.51.5.1331}, pmid = {7298471}, issn = {0161-7567}, support = {ES-01016/ES/NIEHS NIH HHS/United States ; HL-07118/HL/NHLBI NIH HHS/United States ; HL-25728/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Dogs ; *Forced Expiratory Flow Rates ; In Vitro Techniques ; *Maximal Expiratory Flow-Volume Curves ; Methods ; }, abstract = {By supplying air and other gases through discs glued to the pleural surface, we studied steady expiratory flow at constant volume. Dog lungs were studied at constant PA - Ppl (alveolar minus pleural pressure) of 7 to 10 cmH2O, as increasing flow was achieved by increasing driving pressure [Ppl - Pao (airway opening pressure)]. Flow became limited (independent of further increases in Ppl - Pao) at between 3.5 and 5.5 l/s. Isovolume-pressure-flow (IVPF) curves constructed from forced expirations at graded efforts yielded similar maximal flows. When the airways were made rigid by drying, flow limitation was abolished. When various gases were passed through the dried lung Moody plots of normalized pressure drop (CD) vs. Reynolds number (Re) showed that all of the data could be plotted on a single curve. Although variable among animals, all Moody plots showed a laminar flow region at Re below 100 and an inertial region at Re above 10,000, with a distinct transition.}, }
@article {pmid7298445, year = {1981}, author = {Reynolds, DB and Lee, JS}, title = {Steady pressure-flow relationship of a model of the canine bronchial tree.}, journal = {Journal of applied physiology: respiratory, environmental and exercise physiology}, volume = {51}, number = {5}, pages = {1072-1079}, doi = {10.1152/jappl.1981.51.5.1072}, pmid = {7298445}, issn = {0161-7567}, support = {HL-16812/HL/NHLBI NIH HHS/United States ; }, mesh = {Air Pressure ; Animals ; Bronchi/*physiology ; Dogs ; Models, Structural ; Pulmonary Ventilation ; }, abstract = {Static pressure differences (deltaP) across the entire length and portions of a latex reproduction of a canine bronchial tree were measured during steady inspiratory or expiratory flow (V). The reproduction consists of a 10-cm length of trachea through bronchi of about 2 mm in diameter. The airflow was simulated by a water flow with tracheal Renolds number (Re0) in the range from 1,500 to 10,000. Loss in total pressure (deltaPt) was computed by summing deltaPt and V were well described (r greater than 0.98) by a dimensionless Rohrer equation deltaPt/deltaPd0 = A + B Re0 applicable to gas flow, in which deltaPd0 is a Poiseuille pressure drop. For expiratory deltaPt, A was about twice that for inspiration, while the values for B were nearly equal. Differences in kinetic energy between sites of static pressure measurement are important in determining loss in total pressure. Rohrer's equation is a good approximation to the phenomenological laws of steady inspiratory and expiratory flow-pressure relations in the canine bronchial tree for the range of Reynolds number investigated.}, }
@article {pmid7298416, year = {1981}, author = {Slutsky, AS and Drazen, JM and O'Cain, CF and Ingram, RH}, title = {Alveolar pressure-airflow characteristics in humans breathing air, He-O2, and SF6-O2.}, journal = {Journal of applied physiology: respiratory, environmental and exercise physiology}, volume = {51}, number = {4}, pages = {1033-1037}, doi = {10.1152/jappl.1981.51.4.1033}, pmid = {7298416}, issn = {0161-7567}, support = {HL-00549/HL/NHLBI NIH HHS/United States ; HL-07118/HL/NHLBI NIH HHS/United States ; HL-16463/HL/NHLBI NIH HHS/United States ; }, mesh = {Adult ; *Air ; Airway Resistance ; *Fluorides ; *Helium ; Humans ; Male ; *Oxygen ; Pressure ; Pulmonary Alveoli/*physiology ; *Pulmonary Ventilation ; *Respiration ; *Sulfur Hexafluoride ; }, abstract = {In a system of rigid tubes under steady flow conditions, the coefficient of friction [CF = 2 delta P/(rho V2/A2)] (where delta P is pressure drop, rho is density, V is flow, and A is cross-sectional area) should be a unique function of Reynolds' number (Re). Recently it has been shown that at any given Re, the value of CF using transpulmonary pressure (PL) was lower when breathing He-O2 compared with air (Lisboa et al., J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 48: 878-885, 1980). One explanation for this discontinuity is that PL includes the pressure drop due to tissue viscance, which is independent of V, and thus would lead to an overestimate of CF on air compared with He-O2 at any Re. We tested this hypothesis by measuring V related to alveolar pressure, rather than PL, in normal subjects breathing air, He-O2, and SF6-O2. In each subject, for a given Re, CF was greatest breathing SF6-O2 and lowest breathing He-O2, similar to results using PL. Thus tissue viscance is not the sole cause of the discontinuous plot of CF vs. Re, and this phenomenon must be due to other factors, such as changing geometry or nonsteady behavior.}, }
@article {pmid7288393, year = {1981}, author = {Sherman, TF}, title = {On connecting large vessels to small. The meaning of Murray's law.}, journal = {The Journal of general physiology}, volume = {78}, number = {4}, pages = {431-453}, doi = {10.1085/jgp.78.4.431}, pmid = {7288393}, issn = {0022-1295}, mesh = {Animals ; Arteries/physiology ; Blood Viscosity ; *Cardiovascular Physiological Phenomena ; Dogs ; Mathematics ; Models, Biological ; *Respiratory Physiological Phenomena ; }, abstract = {A large part of the branching vasculature of the mammalian circulatory and respiratory systems obeys Murray's law, which states that the cube of the radius of a parent vessel equals the sum of the cubes of the radii of the daughters. Where this law is obeyed, a functional relationship exists between vessel radius and volumetric flow, average linear velocity of flow, velocity profile, vessel-wall shear stress, Reynolds number, and pressure gradient in individual vessels. In homogeneous, full-flow sets of vessels, a relation is also established between vessel radius and the conductance, resistance, and cross-sectional area of a full-flow set.}, }
@article {pmid7303054, year = {1981}, author = {LoGerfo, FW and Crawshaw, HM and Nowak, M and Serrallach, E and Quist, WC and Valeri, CR}, title = {Effect of flow split on separation and stagnation in a model vascular bifurcation.}, journal = {Stroke}, volume = {12}, number = {5}, pages = {660-665}, doi = {10.1161/01.str.12.5.660}, pmid = {7303054}, issn = {0039-2499}, support = {H121796-02//PHS HHS/United States ; ONR NOOO 14-79-C-0168/ON/ONR/United States ; RR05487-16/RR/NCRR NIH HHS/United States ; }, mesh = {Biomechanical Phenomena ; *Blood Circulation ; Blood Flow Velocity ; Carotid Arteries/physiology ; *Models, Biological ; *Rheology ; }, abstract = {This is a study of the flow disturbance in a plastic model of an asymmetric vascular bifurcation. A sidearm was attached to the mainlimb at an angle of 15 degrees to the inlet flow axis. Water at steady flow was used and flow patterns were demonstrated by a dye injection technique. The proportion of inlet flow (Qi) exiting from the sidearm (Qs) was varied and flow patterns were recorded photographically. A laser Doppler anemometer (LDA) was used to measure near-wall velocity. At a physiologic Reynolds' number of 500, no flow disturbance occurred in the mainlimb when the sidearm was completely occluded. When the fraction of flow exiting from the sidearm (Qs/Qi) reached 0.19, a region of boundary layer separation developed along the wall of the mainlimb opposite the flow divider. This region of nearly static fluid spread circumferentially around the mainlimb as Qs/Qi increased. Near-wall velocity within the separation decreased and became negative when Qs/Qi = 0.31. When Qs/Qi reached 0.38, the separation enveloped the wall of the entire bifurcation with a shell of slowly moving fluid. At the same time, the rapidly moving mainstream impinged directly on the flow divider. There is a similarity between the region of separation seen in this model and the site of formation of atherosclerotic plaque at the carotid bifurcation. Separation may contribute to atherogenesis by creating a region of low wall shear at bifurcations.}, }
@article {pmid7278194, year = {1981}, author = {Walburn, FJ and Sabbah, HN and Stein, PD}, title = {Flow visualization in a mold of an atherosclerotic human abdominal aorta.}, journal = {Journal of biomechanical engineering}, volume = {103}, number = {3}, pages = {168-170}, doi = {10.1115/1.3138273}, pmid = {7278194}, issn = {0148-0731}, support = {HL25839-01/HL/NHLBI NIH HHS/United States ; }, mesh = {Aorta, Abdominal/*physiopathology ; Arteriosclerosis/*physiopathology ; *Blood Coagulation ; Humans ; Iliac Artery/*physiopathology ; In Vitro Techniques ; Male ; Middle Aged ; }, abstract = {Flow in a mold of an atherosclerotic human abdominal aorta and common iliac arteries was studied by flow visualization at a mean Reynolds number of 500 during both pulsatile and steady flow. Flow separation and transient flow reversals were found distal to atherosclerotic plaques during pulsatile flow; whereas flow separation resulting in regions of permanent eddies were observed distal to plaques only during steady flow.}, }
@article {pmid7295195, year = {1981}, author = {LoGerfo, FW and Nowak, MD and Quist, WC and Crawshaw, HM and Bharadvaj, BK}, title = {Flow studies in a model carotid bifurcation.}, journal = {Arteriosclerosis (Dallas, Tex.)}, volume = {1}, number = {4}, pages = {235-241}, doi = {10.1161/01.atv.1.4.235}, pmid = {7295195}, issn = {0276-5047}, support = {GRS NIH 5S07 RR05487-17/RR/NCRR NIH HHS/United States ; HL21796-03/HL/NHLBI NIH HHS/United States ; }, mesh = {Arteriosclerosis/*physiopathology ; Carotid Arteries/*anatomy &amp; histology/physiopathology ; Humans ; Models, Anatomic ; Rheology ; }, abstract = {Boundary layer separation in a plexiglass model carotid bifurcation was investigated in relation to the origin of atherosclerotic plaque clinically found in this region. Our model was comparable to a human carotid in both dimensions and geometry. Water flowed through the model at Reynolds numbers from 200 to 1200 under steady and pulsatile flow conditions, with outflow through the external and internal branches varied. The near-wall flow was visualized by slow injection of dye through ports machined in the model. Under steady flow at a physiological Reynolds number of 500 and a flow split at the bifurcation similar to that of a human carotid at rest, boundary layer separation was found to occur in a carotid sinus across from the external carotid origin, forming a shell of slowly moving fluid around the bifurcation. The rapidly moving mainstream impinged directly on the flow divider. The location of atherosclerotic plaque correlates best with the low shear region of separation and not with the region of high shear at the flow divider. Preliminary studies with pulsatile flow demonstrated little change from the steady flow results.}, }
@article {pmid7263418, year = {1981}, author = {Chang, HK and Mortola, JP}, title = {Fluid dynamic factors in tracheal pressure measurement.}, journal = {Journal of applied physiology: respiratory, environmental and exercise physiology}, volume = {51}, number = {1}, pages = {218-225}, doi = {10.1152/jappl.1981.51.1.218}, pmid = {7263418}, issn = {0161-7567}, mesh = {Airway Resistance ; Animals ; Humans ; Mathematics ; Pressure ; Trachea/*physiology ; }, abstract = {Because tracheal pressure measurement generally involves the use of a cannula or an endotracheal tube, fluid dynamic factors may cause a considerable artifact. We present a theoretical explanation of the observed apparent paradox in which the resistance of a tracheal cannula or an endotracheal tube is isolation was found to exceed the resistance of the airways plus the cannula or the tube in situ. By estimating the viscous dissipation and the kinetic energy change in a conduit with sudden variation of cross-sectional area, a predictive model is derived. The predictions are verified by a series of in vitro experiments with both steady and oscillatory flows. The experiments showed that the pressure recorded from the sidearm of a tracheal cannula or endotracheal tube contains an error which, in general, increased with the mean Reynolds' number of the through flow and also depends on the diameter ratio between the trachea and the tube or cannula, the position of the pressure tap, and the frequency of ventilation. When feasible, direct measurement with a needle in the trachea is suggested as a way to avoid the possible artifacts arising from the use fo a side tap of the cannula. Theoretical considerations, as well as in vitro and animal experiments, indicate that adding a properly chosen expansion to the tracheal cannula makes it possible to alter inspiratory and expiratory pressures selectively. This device may prove useful in control of breathing studies.}, }
@article {pmid7278182, year = {1981}, author = {Walburn, FJ and Stein, PD}, title = {Effect of vessel tapering on the transition to turbulent flow: implications in the cardiovascular system.}, journal = {Journal of biomechanical engineering}, volume = {103}, number = {2}, pages = {116-120}, doi = {10.1115/1.3138254}, pmid = {7278182}, issn = {0148-0731}, support = {HL23669-02/HL/NHLBI NIH HHS/United States ; }, mesh = {*Blood Circulation ; Blood Flow Velocity ; *Rheology ; }, abstract = {The purpose of this study is to explore the effect of tapering upon the tendency of flow to become turbulent in straight symmetric tubes. Velocity was measured with a flow to become turbulent in straight symmetric tubes. Velocity was measured with a laser Doppler anemometer in plexiglass tubes which tapered 0.5 deg, 1.5 deg, and 2.5 deg measured from the centerline to the wall. These angles were comparable to the angles of tapering observed in the abdominal aorta of normal subjects, 1.5 deg +/- 0.2 deg (mean +/- SEM) (range 0 deg to 3 deg). The transition Reynolds number (based on the diameter of the tube at the point of measurement) increased as the angle of tapering increased. When the angle of tapering was constant, the transition Reynolds number increased with increasing distance into the tapered section. These observations suggest that tapering of the abdominal aorta tends to promote laminar flow.}, }
@article {pmid7312725, year = {1981}, author = {Czarnecki, W}, title = {Dissolution of azathioprine from tablets in forced laminar flow of liquid.}, journal = {Polish journal of pharmacology and pharmacy}, volume = {33}, number = {2}, pages = {251-260}, pmid = {7312725}, issn = {0301-0244}, mesh = {*Azathioprine ; Solubility ; Tablets ; }, abstract = {The dissolution of azathioprine from tablets was investigated in a column apparatus with forced laminar liquid flow. The experiments showed that auxiliary ingredients and hydrodynamic factors affected the diffusion coefficient and solubility of the active principle and the density and viscosity of eluates from dissolution cell. For laminar flows changes in these physico-chemical parameters are described by a dimensionless equation (Formula: see text), where Sh--Sherwood number, Sc--Schmidt number, Re--Reynolds number, (Formula: see text)--grain dispersion in disintegrated tablet mass.}, }
@article {pmid7240555, year = {1981}, author = {Holmes, MH}, title = {Study of the transient motion in the cochlea.}, journal = {The Journal of the Acoustical Society of America}, volume = {69}, number = {3}, pages = {751-759}, doi = {10.1121/1.385575}, pmid = {7240555}, issn = {0001-4966}, mesh = {Basilar Membrane/physiology ; Cochlea/*physiology ; Humans ; Mathematics ; Models, Biological ; Movement ; Time Factors ; }, abstract = {The transient problem obtained from a three-dimensional hydroelastic model of the cochlea is studied. In the model, the fluid motion is described by the linearized Navier-Stokes equations, and the basilar membrane is modeled as an elastic plate. The resulting problem is first reduced through the use of a slender body approximation which is, in turn, simplified by introducing expansions in terms of the reciprocal of the Reynolds number. With this, the wave-like nature of the solution is analyzed, comparing it with the long-time solution, as well as with experiment.}, }
@article {pmid7326353, year = {1981}, author = {Nachtigall, W}, title = {Hydromechanics and biology.}, journal = {Biophysics of structure and mechanism}, volume = {8}, number = {1-2}, pages = {1-22}, pmid = {7326353}, issn = {0340-1057}, mesh = {Animals ; *Biomechanical Phenomena ; Birds/*physiology ; Coleoptera ; Dolphins/*physiology ; Locomotion ; Models, Biological ; Swimming ; Viscosity ; *Water ; }, abstract = {To exemplify relations between biology and hydrodynamics the Reynolds number range and the effects of viscosity and inertia in swimming and flying organisms is discussed. Comparing water beetles and penguins it is shown, that the technical drag coefficient is an adequate means to describe flow adaptation in animals. Compared to technical systems, especially the penguins'drag coefficient is astonishingly low. Furthermore, the question, why comparatively thick bodies in penguins and dolphins show rather low drag is discussed. Distributed boundary layer damping in dolphins and secretion of special high molecular slimes in fishes help to keep flow characteristics laminar. As an example of one easily understood thrust mechanism, the drag inducing pair of rowing legs in water, beetles is morphologically and hydrodynamically analysed. Fish swimming is discussed as a locomotion principle using lift components. Thrust generation by the moving tail fin of a fish is analysed in detail. Coming back to the influence if Reynolds number, it is finally shown, how very small, bristle bearing swimming legs and wings of insects make use of viscosity effects for locomotion.}, }
@article {pmid6122178, year = {1981}, author = {Chaturani, P and Rathod, VP}, title = {A theoretical model for pulsatile blood flow with applications to cerebrovascular diseases.}, journal = {Neurological research}, volume = {3}, number = {3}, pages = {289-303}, doi = {10.1080/01616412.1981.11739604}, pmid = {6122178}, issn = {0161-6412}, mesh = {*Cerebrovascular Circulation ; Cerebrovascular Disorders/*physiopathology ; Humans ; Mathematics ; Models, Cardiovascular ; *Pulse ; Rheology ; }, abstract = {A solution for fully developed pulsatile flow of a couple stress fluid through a circular, rigid tube of infinite length has been obtained in the form of a Bessel-Fourier series. The velocity profiles and flow rates for different values of flow parameters have been shown graphically. It has been observed that velocity and flow rate are almost in phase with pressure gradient for low values of pulsatile Reynolds number alpha (alpha 2 = 0.1). For higher values of alpha(= 2) a phase difference of approximately 30 degrees between the velocity profile and pressure gradient has been observed. The obtained results are in good agreement with other theoretical and experimental results. The present analysis is valid for both values of alpha , i.e., alpha greater than or equal to 1 and alpha less than 1, whereas the existing analysis for pulsatile flow of couple stress fluid is valid for only alpha less than 1. The first, second, and third approximate solutions have been obtained and it is found that the convergence of the solutions is quite fast and the series could be terminated after the second term. This theoretical work could be useful in the measurement of blood flow rates, its apparent viscosity, and peripheral resistance of the circulatory system which, at present, are thought to be some of the main causes of many cerebrovascular diseases and stroke problems.U}, }
@article {pmid7452722, year = {1980}, author = {Basmadjian, D and Dykes, DS and Baines, AD}, title = {Flow through brushborders and similar protuberant wall structures.}, journal = {The Journal of membrane biology}, volume = {56}, number = {3}, pages = {183-190}, pmid = {7452722}, issn = {0022-2631}, mesh = {Animals ; Biological Transport ; Cell Membrane/*metabolism ; Extracellular Space/*metabolism ; Kidney Tubules, Proximal/*metabolism ; Kinetics ; Mathematics ; Microvilli/*metabolism ; Models, Biological ; Physiology/instrumentation ; Rabbits ; }, abstract = {Longitudinal flow through channels with protuberant wall structures such as brushborders were studied both experimentally and theoretically. The experiments were performed using tubes with synthetic internal brushborders, scaled to resemble the geometry and flow in proximal tubules of the kidney. Fractional flow rates in the brushborder were deduced from transit times of dye traces through the central core and total flow rate. The measured ratios of brushborder to core flow QB/QC were found to be independent of Reynolds number over the range Re = 0.01 - 0.2. They agreed reasonably well with theoretical predictions based on the Kozeny-Carman equation for flow through arrays of parallel cylinders. The predictions can be extended to arbitrary geometries and turbulent flow conditions by appropriate modifications. Extrapolation of the results to the proximal tubule of the kidney indicate that brushborder flowrates there vary from 0.003 to 0.09% of total flow. Any axial transport in these structures would be predominantly diffusive in nature, and would be highly unlikely to affect radial brushborder gradients and transmural flux.}, }
@article {pmid7437957, year = {1980}, author = {Musto, R and Roach, MR}, title = {Flow studies in glass models of aortic aneurysms.}, journal = {Canadian journal of surgery. Journal canadien de chirurgie}, volume = {23}, number = {5}, pages = {452-455}, pmid = {7437957}, issn = {0008-428X}, mesh = {Aortic Aneurysm/*physiopathology ; *Blood Circulation ; Blood Flow Velocity ; Densitometry/methods ; Glass ; Humans ; *Models, Anatomic ; *Models, Structural ; Photography ; }, abstract = {A photodensitometer was used to make a quantitative analysis of flow into and out of glass models of three types of aortic aneurysm (small and large fusiform and small saccular). The "aneurysms" were perfused with steady flow and injected with Evans' blue dye. The aneurysms tended to fill linearly with time, but emptied exponentially. Flow out of both large and small fusiform aneurysms did not alter as a function of the Reynolds number (a nondimensional measurement used to compare flows in tubes of the same shape but of different sizes), while flow from the saccular aneurysm did. The results suggest that the flow in fusiform aneurysms is very sluggish. This may increase the risk of thrombosis and could also lead to a false arteriographic analysis of size, particularly in large aneurysms. Emptying of saccular aneurysms is much more dependent on the Reynolds number and hence on location and blood viscosity.}, }
@article {pmid7204164, year = {1980}, author = {Slutsky, AS and Berdine, GG and Drazen, JM}, title = {Steady flow in a model of human central airways.}, journal = {Journal of applied physiology: respiratory, environmental and exercise physiology}, volume = {49}, number = {3}, pages = {417-423}, doi = {10.1152/jappl.1980.49.3.417}, pmid = {7204164}, issn = {0161-7567}, mesh = {Airway Resistance ; Humans ; Lung/*physiology ; Models, Anatomic ; Models, Biological ; *Respiration ; Rheology ; }, abstract = {We studied the pressure-flow relationships and flow distribution under steady conditions in a model of human central airways, over a range of tracheal Reynolds' numbers (350-30,000) by using air or helium. We found that the Moody diagram [log coefficient of friction CF = delta P/[1/2 rho (V2/A2)] vs. log Reynolds' number (Re)] had a slope of -1 for Re less than 500, a slope 0 for Re greater than 10,000, and slopes between -1 and 0 for 500 less than or equal to Re less than or equal to 10,000. The distribution of flow among branches was dependent on tracheal Reynolds' number so that, as tracheal Reynolds' number increased, the upper lobes received proportionally less of the total flow than the lower lobes. Because the airways in the upper lobes generally had greater branching angles than those in the lower lobes, this result was consistent with the hypothesis that the effective resistances introduced by branching angles was flow dependent, increasing proportionally more the greater the angle.}, }
@article {pmid6107914, year = {1980}, author = {McArthur, AJ and Monteith, JL}, title = {Air movement and heat loss from sheep. I. Boundary layer insulation of a model sheep, with and without fleece.}, journal = {Proceedings of the Royal Society of London. Series B, Biological sciences}, volume = {209}, number = {1175}, pages = {187-208}, doi = {10.1098/rspb.1980.0090}, pmid = {6107914}, issn = {0950-1193}, mesh = {Air Movements ; Animals ; *Body Temperature Regulation ; Mathematics ; Models, Biological ; Sheep/*physiology ; Wool/*physiology ; }, abstract = {A model sheep, made from metal cylinders and hemispheres, was heated electrically. Heat loss by forced convection in a wind tunnel was analysed in terms of the dependence of the Nusselt number (Nu) on Reynolds number (Re). For a bare trunk Nu = 0.095 Re0.684, but with fleece covering the trunk to a depth of 3.5 cm, Nu = 0.0112 Re0.875 when the mean radiative temperature of the the coat was taken as the surface temperature. Heat transfer by convection from the whole body, including legs, was described by Nu = 0.029 Re0.80. However, a bulk Nesselt number should not be used to estimate heat loss from a live sheep in a hot environment if the windspeed is below about 4 m s-1 because the relation between mean surface temperature, Nusselt number and convective heat flux is not unique.}, }
@article {pmid7420012, year = {1980}, author = {Mellor, JS and Stebbings, H}, title = {Microtubules and the propagation of bending waves by the archigregarine, Selenidium fallax.}, journal = {The Journal of experimental biology}, volume = {87}, number = {}, pages = {149-161}, doi = {10.1242/jeb.87.1.149}, pmid = {7420012}, issn = {0022-0949}, mesh = {Animals ; Eukaryota/*physiology ; Microtubules/*physiology ; Movement ; }, abstract = {1. The trophozoites of Selenidium fallax propagate bending waves at rates of up to 35 microns s-1, of a similar character to those manifested by eukaryotic cilia and flagella. A beat frequency of 0.12-0.15 Hz appears average, though rates outside this range have been recorded. Translatory locomotion at up to 6 microns s-1 has been observed. The protozoan demonstrates the presence of an active bending mechanism, probably along its entire length, and a means of coordinating adjacent bends. 2. The Reynolds number for the motion in 10(-5)-10(-4), suggesting that the hydrodynamic aspects of the trophozoite movement are amenable to analysis by similar means to those already employed for cilia and flagella. 3. It is possible that the protozoans exhibit a sliding microtubule mechanism, which could be very usefully compared with that occurring in the ciliary axoneme.}, }
@article {pmid7409200, year = {1980}, author = {Macklem, PT}, title = {The paradoxical nature of pulmonary pressure-flow relationships.}, journal = {Federation proceedings}, volume = {39}, number = {10}, pages = {2755-2758}, pmid = {7409200}, issn = {0014-9446}, mesh = {Animals ; Bronchi/physiology ; Humans ; Lung/*physiology ; Mathematics ; Models, Biological ; Pressure ; Respiration ; Trachea/physiology ; }, abstract = {Most equations proposed to describe pulmonary pressure-flow relationships are inadequate because the "constants" that contain the airway geometry are not, in fact, constant but vary as the distribution of Reynold's number Re varies with flow or gas density. However, even when the normalized pressure drop is plotted against Re (Moody diagram), different relationships are found for different gas mixtures. Thus the normalized pressure drop is a function of one or more variables in addition to Re. As long as this variable or variables remain unknown, the pulmonary pressure-flow relationships will remain paradoxical.}, }
@article {pmid7379268, year = {1980}, author = {Lyon, CK and Scott, JB and Wang, CY}, title = {Flow through collapsible tubes at low Reynolds numbers. Applicability of the waterfall model.}, journal = {Circulation research}, volume = {47}, number = {1}, pages = {68-73}, doi = {10.1161/01.res.47.1.68}, pmid = {7379268}, issn = {0009-7330}, mesh = {Blood Vessels/*physiopathology ; Mathematics ; *Models, Biological ; Perfusion ; Water ; }, abstract = {The applicability of the waterfall model was tested using the Starling resistor and different viscosities of fluids to vary the Reynolds number. The waterfall model proved adequate to describe flow in the Starling resistor model only at very low Reynolds numbers (Reynolds number less than 1). Blood flow characterized by such low Reynolds numbers occurs only in the microvasculature. Thus, it is inappropriate to apply the waterfall model indiscriminately to flow through large collapsible veins.}, }
@article {pmid6966546, year = {1980}, author = {Cipriano, PR and Sacks, AH and Reitz, BA}, title = {The effect of stenosis of bypass grafts on coronary blood flow. A mechanical model study.}, journal = {Circulation}, volume = {62}, number = {1}, pages = {61-66}, doi = {10.1161/01.cir.62.1.61}, pmid = {6966546}, issn = {0009-7322}, mesh = {Arterial Occlusive Diseases/*physiopathology ; *Coronary Artery Bypass ; *Coronary Circulation ; Coronary Vessels/physiopathology ; Hemodynamics ; Humans ; *Models, Biological ; }, abstract = {A mechanical model of a branched coronary artery with a graft bypassing an 80% stenosis of one branch was used to study the reduction in coronary flow due to stenosis of the bypass graft. Flow Reynolds number and ratio of aortic pressure to dynamic pressure were matched to the living system. Changes in coronary flow were measured for a range of stenoses (0-100%) of bypass grafts with graft-to-coronary-diameter ratios of 4:1, 3:1, 2:1 and 1:1 for conditions that simulated rest and exercise. The results of these studies indicate that: 1) marked stenosis of bypass grafts is needed to decrease coronary flow in the resting state, and even moderate stenosis will decrease flow during exercise when the diameter of the bypass is large relative to the coronary artery; 2) coronary flow is decreased with mild stenosis for bypass grafts of the same diameter as the coronary artery; and 3) a marked decrease in flow due to stenosis of a bypass graft occurs only when the diameter of a stenosis in a graft is less than the diameter of the coronary artery.}, }
@article {pmid7386646, year = {1980}, author = {Gross, DR and Lu, PC and Dodd, KT and Hwang, NH}, title = {Physical characteristics of pulmonary artery stenosis murmurs in calves.}, journal = {The American journal of physiology}, volume = {238}, number = {6}, pages = {H876-85}, doi = {10.1152/ajpheart.1980.238.6.H876}, pmid = {7386646}, issn = {0002-9513}, mesh = {*Aging ; Animals ; Biophysical Phenomena ; Biophysics ; Blood Pressure ; Cattle/*physiology ; Electrocardiography ; *Heart Auscultation ; *Heart Sounds ; Male ; Mathematics ; Pulmonary Artery/*physiology ; Pulmonary Valve Stenosis/*physiopathology ; Regional Blood Flow ; }, abstract = {To better understnad the characteristics of cardiovascular murmurs and turbulent energy transmission, we made simultaneous measurements of pressure (sound) and velocity fluctuations in the vicinity of surgically produced stenoses in the pulmonary artery of calves. We did a spectral analysis of these data and found an identifiable break frequency at which the slopes of the pressure fluctuations changed. By use of these break frequencies and the corresponding blood jet velocity and vessel diameter measurements, Strouhal numbers were calculated. The jet velocity, Reynolds number, Strouhal number, and unsteadiness parameter values changed when the vessel was stenosed. When the power spectrum curves for the velocity fluctuations and the sound were compared, they tended to show a correlation between break frequencies. We speculate that this apparent correlation indicated a transfer from turbulent to acoustic energy.}, }
@article {pmid6106350, year = {1980}, author = {Livesey, JL and Molyneux, DH and Jenni, L}, title = {Mechanoreceptor--trypanosome interactions in the labrum of Glossina: fluid mechanics.}, journal = {Acta tropica}, volume = {37}, number = {2}, pages = {151-161}, pmid = {6106350}, issn = {0001-706X}, mesh = {Animals ; Blood Viscosity ; Host-Parasite Interactions ; Insect Vectors ; Mathematics ; Mechanoreceptors/*physiology ; Microscopy, Electron, Scanning ; Mouth/parasitology ; Regional Blood Flow ; Trypanosoma/*physiology ; Trypanosoma brucei brucei/physiology ; Tsetse Flies/*parasitology/physiology ; }, abstract = {The fluid mechanics of the flow of blood through the labrum of Glossina is described in uninfected and trypanosome infected flies. The flow is characterised by the Reynolds number, and a frequency parameter for the pulsating flow and non-newtonian viscosity effects are considered. The effects of colonies of trypanosomes on the flow rate in the labrum and the interactions between colonies of Trypanosoma (Nannomonas) congolense and Trypanosoma (Trypanozoon) brucei and mechanoreceptors in the proximal third of the labrum are described. The direct association between trypanosomes and mechanoreceptors and the reduction in flow rate imposed by trypanosome colonies in the food canal distal to the mechanoreceptors will impair detection of stimuli by them. The epidemiological implications of these and earlier observations are discussed.}, }
@article {pmid7451298, year = {1980}, author = {Lisboa, C and Wood, LD and Jardim, J and Macklem, PT}, title = {Relation between flow, curvilinearity, and density dependence of pulmonary pressure-flow curves.}, journal = {Journal of applied physiology: respiratory, environmental and exercise physiology}, volume = {48}, number = {5}, pages = {878-885}, doi = {10.1152/jappl.1980.48.5.878}, pmid = {7451298}, issn = {0161-7567}, mesh = {Adult ; *Airway Resistance ; Bronchi/anatomy &amp; histology/physiology ; Female ; Gases/analysis ; Humans ; Lung/physiology ; Lung Volume Measurements ; Male ; Pressure ; *Pulmonary Ventilation ; Respiratory System/*anatomy &amp; histology ; Trachea/anatomy &amp; histology/physiology ; }, abstract = {In nine normal subjects we measured pulmonary pressure-flow curves by ensemble averaging over 20 breaths and solving the equation P = K'V alpha where P is flow-resistive pressure, K' is slope, 5 V is flow, and alpha is curvilinearity. The study was performed at four lung volumes from 37 to 73% of total lung capacity, with the subjects breathing air or HeO2. K' was lower at every lung volume during HeO2 breathing, whereas the exponent alpha was uninfluenced by either lung volume or HeO2 breathing. Although alpha increased with flow rate, comparison of air and HeO2 curves revealed that alpha was not uniquely related to Reynolds' number. Furthermore there was no correlation between curvilinearity and the density dependence of K'. These observations are inconsistent with the general equation P = KV alpha rho alpha-1 mu 2-alpha, where K is a constant related to airway geometry, rho is density and mu is viscosity. (Wood et al., J. Appl. Physiol. 41: 234-244, 1976). The reasons for this discrepancy are unclear, but do not appear to be related to effects of oscillatory flow because alpha was similar from 20 to 90 breaths/min in four subjects. We conclude that the curvilinearity of pulmonary pressure-flow curves is related to flow but independent of gas density and is not explicable solely on the basis of Reynolds' number.}, }
@article {pmid7349947, year = {1980}, author = {Wall, MA}, title = {Infant endotracheal tube resistance: effects of changing length, diameter, and gas density.}, journal = {Critical care medicine}, volume = {8}, number = {1}, pages = {38-40}, pmid = {7349947}, issn = {0090-3493}, mesh = {Air ; *Airway Resistance ; Biomechanical Phenomena ; Helium ; Humans ; Infant ; *Intubation, Intratracheal ; Oxygen ; Pulmonary Ventilation ; }, abstract = {Endotracheal tube resistance may increase upper airway resistance and the work of breathing beyond the normal range in adults of children who are chronically intubated and receiving intermittent mandatory ventilation. The purpose of this study was to measure the resistance of infant endotracheal tubes (IETTs) over the range of normal infant respiratory flows while systematically changing length, diameter, and carrier gas density. Resistance was measured in IETTs of 2.5, 3.0, and 3.5 mm inner diameter at flows increasing from 10--150 ml/sec, using both air and 80% helium- 20% oxygen (He-O2) as the carrier gases. Tube length was progressively shortened from full length to 4.8 cm in 2-cm increments, and resistance to both air and He-O2 was measured at all lengths. Reynolds' number calculations and the relationship of resistance to flow showed the flow regime in IETTs to be transitional in nature. Increasing tube diameter, decreasing length, or decreasing gas density led to large decreases in IETT flow resistance. Over the range of normal infant flows, IETT resistance is equal to or higher than that of the normal upper aiaway. IETT resistance might increase the work of breathing in some infants to the point of respiratory failure, and such resistance may be lowered by systematic changes in IETT diameter, length, or carrier gas density.}, }
@article {pmid7260247, year = {1980}, author = {Rice, SA}, title = {Hydrodynamic and diffusion considerations of rapid-mix experiments with red blood cells.}, journal = {Biophysical journal}, volume = {29}, number = {1}, pages = {65-77}, pmid = {7260247}, issn = {0006-3495}, support = {HL 16008/HL/NHLBI NIH HHS/United States ; }, mesh = {Erythrocytes/*metabolism ; Humans ; Mathematics ; Models, Biological ; Oxygen Consumption ; Surface Properties ; Water/*metabolism ; }, abstract = {From studies of the oxygenation rate of red blood cells (RBC) using rapid-mix techniques, it has been suggested that RBC are surrounded by a stagnant layer of water that does not (or cannot) mix with the rest of the water. A consideration of the appropriate hydrodynamics and convective diffusion rates shows that a mixer can reduce the resolution time to approximately 1 ms (or possibly less) and give a diffusion layer around the TBC that is approximately 1 micron thick. In stopped flow equipment it expands to approximately 4 micron over approximately 10 ms, whereas in continuous flow work the diffusion layers expands slightly less rapidly and less far. Thus the rate of oxygenation of TBC should be slower when measured by stopped flow techniques than by continuous flow apparatus for which the rate will depend weakly on the Reynolds number of the flow in the interrogation tube.}, }
@article {pmid6906133, year = {1980}, author = {Eriksson, A and Svedbergh, B}, title = {Transcellular aqueous humor outflow: a theoretical and experimental study.}, journal = {Albrecht von Graefes Archiv fur klinische und experimentelle Ophthalmologie. Albrecht von Graefe's archive for clinical and experimental ophthalmology}, volume = {212}, number = {3-4}, pages = {187-197}, pmid = {6906133}, issn = {0065-6100}, support = {N0. R01-EY00475/EY/NEI NIH HHS/United States ; }, mesh = {Animals ; Aqueous Humor/*physiology ; Humans ; Macaca fascicularis ; Models, Biological ; Rheology ; Viscosity ; }, abstract = {When the aqueous humor passed through the transcellular channels of the inner wall endothelium of Schlemm's canal the flow was estimated to be very slow and viscous (Reynolds' number about 10(-3)). It was found to be accurate to treat this extreme flow situation with conventional hydrodynamic formulae without specific corrections. Four different principal configurations of the transcellular channels were investigated. The theoretical calculations yielded results in good agreement with those obtained from the experimental model studies. Where deviations occurred they were probably explained by a radial flow component, which was not incorporated in the theoretical formulae applied. A spherical channel configuration was considered most similar to the in vivo situation and this yielded experimental resistance values half those of previously applied theoretical methods. Using previous morphological data the present results indicated that less than 5% of the total resistance to aqueous humor outflow was located in the inner wall endothelium in normal human eyes, and about 10% in cynomolgus monkey eyes at normal intraocular pressures.}, }
@article {pmid11799678, year = {1979}, author = {Bennet-Clark, HC and Alder, GM}, title = {The effect of air resistance on the jumping performance of insects.}, journal = {The Journal of experimental biology}, volume = {82}, number = {}, pages = {105-121}, doi = {10.1242/jeb.82.1.105}, pmid = {11799678}, issn = {0022-0949}, mesh = {Air ; Animals ; Behavior, Animal/*physiology ; Body Constitution ; Body Weight ; Energy Metabolism ; Equipment Design ; Extremities/physiology ; Insecta/*physiology ; Models, Biological ; Wings, Animal/physiology ; }, abstract = {A spring gun was constructed to propel objects at known velocities of between 1 and 4.5 m.s-1. This was used to project insects and various models in a vertical trajectory. By comparing the height attained in air by the insects or models with the height theoretically possible in vacuo, the energy lost against air resistance was observed. Small insects have a higher frontal area to mass ratio than larger ones so have relatively more aerodynamic drag and attain lower heights. The observed effect may be expressed in terms of the drag coefficient, CD. Fleas and locusts have CD of about 1. Winged flies have CD of about 1.5 which falls to about 1 when the wings are amputated and to about 0.8 when the legs are amputated. Aptery is advantageous in jumping insects. From experiments with models, it appears that the optimal condition for small jumping insects is that the body should be as compact as possible to reduce the frontal area to mass ratio. Thus dense spherical bodies are favoured. Some species of jumping insect have densities of about 1 mg.mm-3 while some flying beetles and flies have densities between 0.3 and 0.8 mg.mm-3. The Reynolds number at which the experiments were performed was from 65-205 for fleas up to 740-2340 for locusts. The models operated in similar ranges. At a velocity which would propel a larger animal to a height of 1 m, fleas weighing 0.4 mg only reach about 0.4 m. At lower initial velocities, proportionately less energy is wasted against air resistance so the jump efficiency is higher. Most fleas jump to a height of about 0.1 m with an efficiency of 0.8 while locusts jump to a height of 0.35 m with an efficiency of over 0.9. Air resistance is thus an important scale effect in jumping insects and provides its own design constraints.}, }
@article {pmid4837545, year = {1974}, author = {Lew, HS and Miller, J}, title = {A low Reynolds number entry flow theory and its application to the motion of the plasma in bolus flow.}, journal = {Journal of biomechanics}, volume = {7}, number = {2}, pages = {113-121}, doi = {10.1016/0021-9290(74)90049-9}, pmid = {4837545}, issn = {0021-9290}, mesh = {Blood Flow Velocity ; Blood Viscosity ; Capillaries/physiology ; Erythrocytes ; Mathematics ; Methods ; Microcirculation ; *Models, Biological ; Pressure ; Regional Blood Flow ; *Rheology ; }, }
@article {pmid4732941, year = {1973}, author = {Lew, HS}, title = {The dividing streamline of bifurcating flows in a two-dimensional channel at low Reynolds number.}, journal = {Journal of biomechanics}, volume = {6}, number = {4}, pages = {423-432}, doi = {10.1016/0021-9290(73)90101-2}, pmid = {4732941}, issn = {0021-9290}, mesh = {*Blood Circulation ; Blood Flow Velocity ; Blood Pressure ; Capillaries/physiology ; Mathematics ; }, }
@article {pmid5028999, year = {1972}, author = {Kozman, TA and Forrester, JH}, title = {Flow in a constricted tube at a low Reynolds number.}, journal = {Biomedical sciences instrumentation}, volume = {9}, number = {}, pages = {125-128}, pmid = {5028999}, issn = {0067-8856}, mesh = {Arteries/physiopathology ; *Blood Flow Velocity ; Constriction ; Humans ; Models, Biological ; Vascular Diseases/*physiopathology ; }, }
@article {pmid5020953, year = {1972}, author = {Scherer, PW}, title = {A model for high Reynolds number flow in a human bronchial bifurcation.}, journal = {Journal of biomechanics}, volume = {5}, number = {2}, pages = {223-229}, doi = {10.1016/0021-9290(72)90058-9}, pmid = {5020953}, issn = {0021-9290}, mesh = {*Bronchi ; Humans ; Mathematics ; *Models, Biological ; *Pulmonary Ventilation ; }, }
@article {pmid5162577, year = {1971}, author = {Lew, HS}, title = {Low Reynolds number equi-bifurcation flow in a two-dimensional channel.}, journal = {Journal of biomechanics}, volume = {4}, number = {6}, pages = {559-568}, doi = {10.1016/0021-9290(71)90045-5}, pmid = {5162577}, issn = {0021-9290}, mesh = {Air ; *Biomechanical Phenomena ; Blood Flow Velocity ; Blood Vessels/physiology ; Bronchi/physiology ; Humans ; Mathematics ; Models, Biological ; *Rheology ; }, }
@article {pmid16591935, year = {1971}, author = {Pekeris, CL and Shkoller, B}, title = {Stability of Plane Poiseuille Flow to Periodic Disturbances of Finite Amplitude, III.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {68}, number = {7}, pages = {1434-1435}, pmid = {16591935}, issn = {0027-8424}, abstract = {The stability of plane Poiseuille flow to periodic disturbances of finite amplitude was reinvestigated by the use of 55 harmonics instead of five in the Orr-Sommerfeld expansion, but all the (20) overtones in each harmonic were dropped. The fundamental mode was chosen as the one of lowest phase velocity c(r), so as to enhance the wall effects. The neutral curve obtained gives values of the critical amplitude lambda(c) that are considerably higher than in the previous calculation. Near the critical Reynolds number, the neutral curve approaches the values derived previously by an analytical method.}, }
@article {pmid5119411, year = {1971}, author = {Lew, HS and Fung, YC}, title = {A study on the low Reynolds number flow in a valved vessel.}, journal = {Journal of biomechanics}, volume = {4}, number = {2}, pages = {85-94}, doi = {10.1016/0021-9290(71)90018-2}, pmid = {5119411}, issn = {0021-9290}, mesh = {*Blood Circulation ; Blood Flow Velocity ; Mathematics ; *Models, Biological ; *Vascular Resistance ; }, }
@article {pmid5521528, year = {1970}, author = {Lew, HS and Fung, YC}, title = {Entry flow into blood vessels at arbitrary Reynolds number.}, journal = {Journal of biomechanics}, volume = {3}, number = {1}, pages = {23-38}, doi = {10.1016/0021-9290(70)90048-5}, pmid = {5521528}, issn = {0021-9290}, mesh = {Biomechanical Phenomena ; *Blood Flow Velocity ; *Models, Biological ; *Rheology ; }, }
@article {pmid5409778, year = {1970}, author = {Lew, HS and Fung, YC}, title = {Plug effect of erythrocytes in capillary blood vessels.}, journal = {Biophysical journal}, volume = {10}, number = {1}, pages = {80-99}, pmid = {5409778}, issn = {0006-3495}, mesh = {*Blood Flow Velocity ; *Capillaries ; *Erythrocytes ; Models, Biological ; Rheology ; Viscosity ; }, abstract = {As an idealized problem of the motion of blood in small capillary blood vessels, the low Reynolds number flow of plasma (a newtonian fluid) in a circular cylindrical tube involving a series of circular disks is studied. It is assumed in this study that the suspended disks are equally spaced along the axis of the tube, and that their centers remain on the axis of the tube and that their faces are perpendicular to the tube axis. The inertial force of the fluid due to the convective acceleration is neglected on the basis of the smallness of the Reynolds number. The solution of the problem is derived for a quasi-steady flow involving infinitesimally thin disks. The numerical calculation is carried out for a set of different combinations of the interdisk distance and the ratio of the disk radius to the tube radius. The ratio of the velocity of the disk to the average velocity of the fluid is calculated. The different rates of transport of red blood cells and of plasma in capillary blood vessels are discussed. The average pressure gradient along the axis of the tube is computed, and the dependence of the effective viscosity of the blood on the hematocrit and the diameter of the capillary vessel is discussed.}, }
@article {pmid16335117, year = {1969}, author = {Lew, HS and Fung, YC}, title = {On the low-Reynolds-number entry flow into a circular cylindrical tube.}, journal = {Journal of biomechanics}, volume = {2}, number = {1}, pages = {105-119}, doi = {10.1016/0021-9290(69)90046-3}, pmid = {16335117}, issn = {0021-9290}, mesh = {Animals ; Blood Flow Velocity/*physiology ; Bronchi/*physiology ; Computer Simulation ; Humans ; Microcirculation/*physiology ; Microfluidics/methods ; *Models, Biological ; Pulmonary Alveoli/*physiology ; Pulmonary Gas Exchange/*physiology ; }, }
@article {pmid17742733, year = {1969}, author = {O'keefe, JA}, title = {Water on the moon and a new nondimensional number.}, journal = {Science (New York, N.Y.)}, volume = {163}, number = {3868}, pages = {669-670}, doi = {10.1126/science.163.3868.669}, pmid = {17742733}, issn = {0036-8075}, abstract = {A nondimensional number called the Jeffreys number, which represents the ratio of the Reynolds number to the Froude number, is useful in geophysical problems related to the motion of viscous masses under gravity. The Jetireys number is used to show that it is impossible for the lunar maria to be underlain by a layer of material 1 kilometer thick having the plastic properties of ice.}, }
@article {pmid5918057, year = {1966}, author = {Caro, CG}, title = {The dispersion of indicator flowing through simplified models of the circulation and its relevance to velocity profile in blood vessels.}, journal = {The Journal of physiology}, volume = {185}, number = {3}, pages = {501-519}, pmid = {5918057}, issn = {0022-3751}, mesh = {Blood Circulation/*physiology ; *Blood Flow Velocity ; Coloring Agents/analysis ; Models, Theoretical ; Water ; }, abstract = {1. The distribution of velocity (velocity profile) was studied in water flowing through simple models of the circulation. Dye was injected and the distribution of velocity was assessed from indicator concentration-time curves recorded with a photomultiplier.2. Observations were made on straight and curved tubes and on a tube containing a short region with an elliptical cross-section. With steady flow, the rate was varied over the range 24-870 ml./min (Reynolds number 102-3690). Sinusoidal pulsations were imposed on the steady flow in some experiments.3. Bends gave rise to large secondary flows. These caused mixing across the flow and a marked reduction in the variation of velocity over the cross-section of the tube. The effect of bends on velocity distribution was maximal at a Reynolds number of ca. 1000. Similar, but far smaller, effects were seen in a region with an elliptical cross-section and when the flow was made pulsatile. Secondary motion due to bends was capable of preventing a heavier-than-water indicator (sp.gr. 1.375) from settling out of the flow.4. The experimental findings suggest that there may be secondary flows in vascular beds. Under certain conditions, these would prevent the establishment of Poiseuille type laminar flow. The possible physiological importance of the findings is discussed.}, }
@article {pmid5963040, year = {1966}, author = {Charm, SE and Kurland, GS}, title = {On the significance of the Reynolds Number in blood flow.}, journal = {Biorheology}, volume = {3}, number = {3}, pages = {163-164}, pmid = {5963040}, issn = {0006-355X}, mesh = {*Blood Flow Velocity ; *Blood Viscosity ; }, }
@article {pmid1491021, year = {1992}, author = {Krijger, JK and Heethaar, RM and Hillen, B and Hoogstraten, HW and Ravensbergen, J}, title = {Computation of steady three-dimensional flow in a model of the basilar artery.}, journal = {Journal of biomechanics}, volume = {25}, number = {12}, pages = {1451-1465}, doi = {10.1016/0021-9290(92)90058-9}, pmid = {1491021}, issn = {0021-9290}, mesh = {Basilar Artery/anatomy &amp; histology/*physiology ; Blood Flow Velocity/physiology ; Blood Pressure ; Blood Viscosity ; Humans ; *Models, Cardiovascular ; Regional Blood Flow/physiology ; Rheology ; Vertebral Artery/physiology ; }, abstract = {The flow in the basilar artery arises from the merging of the flows from the two vertebral arteries. To study the flow phenomena in the basilar artery, computations have been performed using a finite element (FE) method. We consider steady flow in a geometrically symmetric confluence. For simplicity, channels with a rectangular cross-section have been used. Both symmetric and asymmetric flow cases have been considered. The results show that for the Reynolds number of interest the flow downstream of the junction is highly three-dimensional, and that the flow at the end of the basilar artery, where it splits again, will not be fully developed. The computed phenomena have been confirmed by laser Doppler velocity measurements.}, }
@article {pmid1487911, year = {1992}, author = {Sugihara-Seki, M}, title = {Motion of a doublet of two cylinders in contact in a narrow channel flow.}, journal = {Journal of biomechanical engineering}, volume = {114}, number = {4}, pages = {546-549}, doi = {10.1115/1.2894110}, pmid = {1487911}, issn = {0148-0731}, mesh = {Biomechanical Phenomena ; Blood Flow Velocity/physiology ; Erythrocyte Deformability/*physiology ; Humans ; *Models, Cardiovascular ; Models, Theoretical ; Vascular Resistance/*physiology ; }, abstract = {The motion of two rigid circular cylinders in contact immersed in an incompressible Newtonian fluid in a channel is examined numerically in the zero Reynolds number limit, for various values of the cylinder radius/channel width ratio. Analyses of the time courses of the lateral position and the orientation of the doublet showed that, depending on the initial condition and the doublet/channel size ratio, the doublet exhibit one of the three types of motion: a continuous rotation in the same direction during a period, and a rotation changing its direction at every half period with a large or a small variation of the orientation.}, }
@article {pmid1487906, year = {1992}, author = {Shombert, DG}, title = {Measurement of steady-flow instability and turbulence levels in Dacron vascular grafts.}, journal = {Journal of biomechanical engineering}, volume = {114}, number = {4}, pages = {521-526}, doi = {10.1115/1.2894105}, pmid = {1487906}, issn = {0148-0731}, mesh = {Biomechanical Phenomena ; Blood Flow Velocity/physiology ; Blood Pressure/physiology ; *Blood Vessel Prosthesis ; Blood Viscosity/physiology ; Hemodynamics/*physiology ; Humans ; *Models, Cardiovascular ; *Polyethylene Terephthalates ; Prosthesis Design ; Vascular Resistance/physiology ; }, abstract = {Fluid dynamic properties of Dacron vascular grafts were studied under controlled steady-flow conditions over a Reynolds number range of 800 to 4500. Knitted and woven grafts having nominal diameters of 6 mm and 10 mm were studied. Thermal anemometry was used to measure centerline velocity at the downstream end of the graft; pressure drop across the graft was also measured. Transition from laminar flow to turbulent flow was observed, and turbulence intensity and turbulent stresses (Reynolds normal stresses) were measured in the turbulent regime. Knitted grafts were found to have greater pressure drop than the woven grafts, and one sample was found to have a critical Reynolds number (Rc) of less than one-half the value of Rc for a smooth-walled tube.}, }
@article {pmid1446110, year = {1992}, author = {Oshinski, JN and Ku, DN and Bohning, DE and Pettigrew, RI}, title = {Effects of acceleration on the accuracy of MR phase velocity measurements.}, journal = {Journal of magnetic resonance imaging : JMRI}, volume = {2}, number = {6}, pages = {665-670}, doi = {10.1002/jmri.1880020610}, pmid = {1446110}, issn = {1053-1807}, mesh = {*Acceleration ; *Blood Flow Velocity ; Blood Vessels/pathology ; Constriction, Pathologic ; Humans ; Magnetic Resonance Imaging/*methods ; Models, Structural ; Pulsatile Flow ; }, abstract = {Acceleration in blood flow can affect the accuracy of phase velocity measurements. Convective acceleration is due to changes in flow geometry and is independent of the time-varying acceleration caused by flow pulsatility. To analyze the effects of convective acceleration on flow velocity measurements, phase velocity measurements were obtained in steady laminar flow in the convergent segment of a 90%, hourglass-shaped stenosis phantom at a Reynolds number of 1,500. Measurements at the stenosis indicated that convective acceleration caused the measured values of average cross-sectional velocity to deviate as much as 37% from the theoretical values. The magnitude of the error could be accounted for by including the convective acceleration term in the phase shift equation. Convective acceleration effects should not be ignored in flow velocity measurements through stenoses, even when time-dependent acceleration due to flow pulsatility can be neglected.}, }
@article {pmid1400514, year = {1992}, author = {Tu, C and Deville, M and Dheur, L and Vanderschuren, L}, title = {Finite element simulation of pulsatile flow through arterial stenosis.}, journal = {Journal of biomechanics}, volume = {25}, number = {10}, pages = {1141-1152}, doi = {10.1016/0021-9290(92)90070-h}, pmid = {1400514}, issn = {0021-9290}, mesh = {Arterial Occlusive Diseases/*physiopathology ; *Computer Simulation ; Humans ; *Models, Cardiovascular ; Pulsatile Flow/*physiology ; }, abstract = {The problem of blood flow through a stenosis is solved using the incompressible Navier-Stokes equations in a rigid circular tube presenting a partial occlusion. Calculations are based on a Galerkin finite element method. The time marching scheme employs a predictor-corrector technique using a variable time step. Results are obtained for steady and physiological pulsatile flows. Computational experiments analyse the effect of varying the degree of stenosis, the stricture length, the Reynolds number and Womersley number. The method gives results which agree well with previous computations for steady flows and experimental findings for steady and pulsatile flows.}, }
@article {pmid1522734, year = {1992}, author = {Enden, G and Popel, AS}, title = {A numerical study of the shape of the surface separating flow into branches in microvascular bifurcations.}, journal = {Journal of biomechanical engineering}, volume = {114}, number = {3}, pages = {398-405}, doi = {10.1115/1.2891401}, pmid = {1522734}, issn = {0148-0731}, support = {5T32HL07581/HL/NHLBI NIH HHS/United States ; HL17421/HL/NHLBI NIH HHS/United States ; U41 RR04154/RR/NCRR NIH HHS/United States ; }, mesh = {Blood Flow Velocity ; Blood Viscosity ; Endothelium, Vascular/*anatomy &amp; histology ; Evaluation Studies as Topic ; *Hemodynamics ; Mathematics ; Microcirculation/*anatomy &amp; histology/physiology ; Models, Cardiovascular ; Models, Statistical ; Poisson Distribution ; *Rheology ; *Surface Properties ; }, abstract = {The shape of the separating surface formed by the streamlines entering the branches of microvascular bifurcations plays a major role in determining the distribution of red blood cells and other blood constituents downstream from the bifurcation. Using the finite element method, we determined the shape of the surface through numerical solution of three dimensional Navier-Stokes equations for fluid flow at low Reynolds numbers in a T-type bifurcation of circular tubes. Calculations were done for a wide range of daughter branch to parent vessel diameter ratios and flow ratios. The effect of Reynolds number was also studied. Our numerical results are in good agreement with previously reported experimental data of Rong and Carr (Microvascular Research, Vol. 39, pp. 186-202, 1990). The numerical results of this study will be used to predict the concentration of blood constituents downstream from microvascular bifurcations providing that the inlet concentration profile is known.}, }
@article {pmid1399976, year = {1992}, author = {Olson, LE}, title = {Mechanical properties of small airways in excised pony lungs.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {73}, number = {2}, pages = {522-529}, doi = {10.1152/jappl.1992.73.2.522}, pmid = {1399976}, issn = {8750-7587}, support = {HL-37246/HL/NHLBI NIH HHS/United States ; }, mesh = {Air Pressure ; Animals ; Horses/*physiology ; In Vitro Techniques ; Lung/anatomy &amp; histology/diagnostic imaging/*physiology ; Lung Volume Measurements ; Radiography ; }, abstract = {We evaluated the pressure-flow relationships in collaterally ventilating segments of excised pony lungs by infusing N2, He, Ne, or SF6 at known flows (V) through a catheter wedged in a peripheral airway. Measurements were made at segment- (Ps) to-airway opening (Pao) pressure differentials of 3-15 cmH2O when the lungs were held at transpulmonary pressures of 5, 10, and 15 cmH2O. The data were analyzed both by calculating collateral resistance (Ps-Pao/V) and by constructing Moody-type plots of normalized pressure drop [(Ps-Pao)/(1/2 rho U2, where rho is density and U is velocity)] against Reynolds number to assess the pattern of flow through the segment and the change in dimension of the flow channels as Ps and Pao were changed. The interpretations from these analyses were compared with radiographic measurements of the diameters of small airways within the collaterally ventilating lung segment at similar pressures. Collateral resistance increased as Ps-Pao increased at high Reynolds numbers, i.e., high flows or dense gas (SF6). Analysis of the Moody-type plots revealed that flow was density dependent at Reynolds number greater than 100, which frequently occurred when N2 was the inflow gas. The radiographic data revealed that small airway diameter increased as Ps-Pao increased at all lung volumes. In addition, at 5 cmH2O Pao, small-airway diameter was smaller for a given Ps in the nonhomogeneous case (Ps greater than Pao) than small-airway diameter for the same Ps in the homogeneous case (Ps = Pao). We interpret these data to suggest that the surrounding lung prevented the segment from expanding in the nonhomogeneous case.(ABSTRACT TRUNCATED AT 250 WORDS)}, }
@article {pmid1633398, year = {1992}, author = {Sun, Y and Hearshen, DO and Rankin, GW and Haggar, AM}, title = {Comparison of velocity-encoded MR imaging and fluid dynamic modeling of steady and disturbed flow.}, journal = {Journal of magnetic resonance imaging : JMRI}, volume = {2}, number = {4}, pages = {443-452}, doi = {10.1002/jmri.1880020414}, pmid = {1633398}, issn = {1053-1807}, mesh = {*Blood Flow Velocity ; Blood Vessels/*anatomy &amp; histology ; Humans ; Magnetic Resonance Imaging/*methods ; Models, Cardiovascular ; Models, Structural ; Rheology ; Vascular Diseases/*diagnosis ; }, abstract = {The contrast of flow-encoded magnetic resonance (MR) images obtained in vivo and the accuracy of velocity measurements are complicated by the presence of complex flow states. The effects of complex flow states on MR flow-encoded images were studied and quantitative flow information was obtained with an MR phase-subtraction technique. Regions of complex flow, including flow stagnation and separation and laminar flow, could be clearly identified on the phase images. The MR imaging velocity measurements were validated by comparison with numerical simulation results for three-dimensional velocity distributions. The velocity MR images and the profiles obtained from the simulation generally agreed well for flow rates of 660 and 1,680 mL/min. This agreement lends support to both the fluid dynamic model and the physical basis of the phase imaging technique and establishes the validity of flow-encoded phase imaging as an in vivo flow quantitation method, especially under low Reynolds number flow conditions.}, }
@article {pmid1306368, year = {1992}, author = {Liepsch, D and Singh, M and Lee, M}, title = {Experimental analysis of the influence of stenotic geometry on steady flow.}, journal = {Biorheology}, volume = {29}, number = {4}, pages = {419-431}, doi = {10.3233/bir-1992-29405}, pmid = {1306368}, issn = {0006-355X}, mesh = {Animals ; Aorta/physiopathology ; Arterial Occlusive Diseases/*physiopathology ; Blood Pressure/physiology ; Dogs ; Humans ; Image Enhancement ; *Models, Cardiovascular ; Pulsatile Flow/physiology ; *Rheology ; Videotape Recording ; }, abstract = {We studied the flow behavior under steady flow conditions in four models of cylindrical stenoses at Reynolds numbers from 150 to 920. The flow upstream of the constrictions was always fully developed. The constriction ratios of the rigid tubes (D) to the stenoses (d) were d/D = 0.273; 0.505; 0.548; 0.786. The pressure drop at various locations in the stenotic models was measured with water manometers. The flow was visualized with a photoelasticity apparatus using an aqueous birefringent solution. We also studied the flow behavior at pulsatile flow in a dog aorta with a constriction of 71%. The flow through stenotic geometries depends on the Reynolds number of the flow generated in the tube and the constriction ratio d/D. At low d/D ratios, (with the increased constriction), the flow separation zones (recirculation zones, so-called reattachment length) and flow disturbances increased with larger Reynolds numbers. At lower values, eddies were generated. At high Re, eddies were observed in the pre-stenotic regions. The pressure drop is a function of the length and internal diameter of the stenosis, respective ratio of stenosis to the main vessel and the Reynolds numbers. At low Re-numbers and low d/D, distinct recirculation zones were found close to the stenosis. The flow is laminar in the distal areas. Further experiments under steady and unsteady flow conditions in a dog aorta model with a constriction of 71% showed similar effects. High velocity fluctuations downstream of the stenosis were found in the dog aorta. A videotape demonstrates these results.}, }
@article {pmid1582814, year = {1992}, author = {Carlson, JE and Hedlund, LJ and Trenkner, SW and Ritenour, R and Halvorsen, RA}, title = {Safety considerations in the power injection of contrast media via central venous catheters during computed tomographic examinations.}, journal = {Investigative radiology}, volume = {27}, number = {5}, pages = {337-340}, doi = {10.1097/00004424-199205000-00001}, pmid = {1582814}, issn = {0020-9996}, mesh = {Catheterization, Central Venous/*instrumentation ; Contrast Media/*administration &amp; dosage ; Diatrizoate Meglumine/administration &amp; dosage ; Equipment Safety ; Evaluation Studies as Topic ; Female ; Humans ; Iohexol/administration &amp; dosage ; Male ; Pressure ; Tomography, X-Ray Computed/*instrumentation ; }, abstract = {RATIONALE AND OBJECTIVES: This study addresses the theoretical, experimental, and clinical application of using a central venous catheter system (CVS) for the rapid injection of contrast media during computed tomography (CT).<br><br>METHODS: Application of Poiseuille's law and the Reynolds equation yielded theoretical data. In-line pressures were measured in experimental models and patients undergoing CT. Diatrizoate meglumine and iohexal contrast media were evaluated.<br><br>RESULTS: The Reynolds number was consistent with laminar flow, allowing the application of Poiseuille's law. The calculated and experimental catheter tubing-chamber connection pressures were safe for both contrast media, at rates of 1 mL/second for long catheter tubing and 2 mL/second for short tubing. Thirteen patients had measured pressures within safety limits with no complications.<br><br>CONCLUSIONS: This study establishes that power injection of contrast media via a CVS during CT is a safe procedure. Benefits include no need for peripheral intravenous catheter placement, decreased paramedical staff radiation exposure, and improved CT image quality.}, }
@article {pmid1602767, year = {1992}, author = {Back, LH and Liem, TK and Kwack, EY and Crawford, DW}, title = {Flow measurements in a highly curved atherosclerotic coronary artery cast of man.}, journal = {Journal of biomechanical engineering}, volume = {114}, number = {2}, pages = {232-240}, doi = {10.1115/1.2891377}, pmid = {1602767}, issn = {0148-0731}, mesh = {Blood Pressure/physiology ; Blood Viscosity ; Coronary Artery Disease/*physiopathology ; Coronary Circulation/*physiology ; Humans ; *Models, Cardiovascular ; Pulsatile Flow/physiology ; }, abstract = {Flow visualization and wall pressure measurements were made in a polyurethane cast of a cadaver coronary artery with a significant "s" shaped reverse curvature. A sucrose solution was used to simulate the kinematic viscosity of blood, with flow rates in the physiologic range. Flow visualization demonstrated significant secondary flow patterns in the wall vicinity, which increased with increasing Reynolds number. Random dye dispersion was observed at a Reynolds number of about 400, but not at 200. Dye filament patterns in the transition between the first and second curved region were predominantly influenced by the second curved region at lower Reynolds numbers, and by the first curved region at higher Re. Local wall pressure measurements demonstrated a significant centrifugal effect with large radial pressure differences across the casting. Flow resistances for the casting were considerably greater than reference Poiseuille flow values, and increased further with pulsatile flow.}, }
@article {pmid1576123, year = {1992}, author = {Yamamoto, T and Tanaka, H and Jones, CJ and Lever, MJ and Parker, KH and Kimura, A and Hiramatsu, O and Ogasawara, Y and Tsujioka, K and Caro, CC}, title = {Blood velocity profiles in the origin of the canine renal artery and their relevance in the localization and development of atherosclerosis.}, journal = {Arteriosclerosis and thrombosis : a journal of vascular biology}, volume = {12}, number = {5}, pages = {626-632}, doi = {10.1161/01.atv.12.5.626}, pmid = {1576123}, issn = {1049-8834}, mesh = {Animals ; Aorta/diagnostic imaging ; Arteriosclerosis/*etiology/pathology ; *Blood Flow Velocity ; Dogs ; Female ; Male ; Renal Artery/diagnostic imaging/*physiology ; Ultrasonography ; }, abstract = {Using a 20-MHz 80-channel pulsed Doppler velocimeter and 30-MHz high-resolution echo ultrasound, we investigated the in vivo hemodynamics at the origin of the renal artery by measuring the velocity profiles and bifurcation geometry of a surgically exposed left renal artery in 10 anesthetized dogs. The angle between the aorta and the renal artery ranged from 60 degrees to 90 degrees (mean, 84 degrees) although the bifurcation did not lie in a single anterodorsal plane and the diameter of the renal artery ranged from 1.5 to 3.5 mm (mean, 2.4 mm). Despite different geometries, the velocity profiles in the different aortorenal bifurcations were similar. Although regions of reverse velocity were observed, the net flow in the renal artery was in the forward direction throughout the cardiac cycle. The peak Reynolds' number was 486 +/- 63. The velocity profiles in the proximal renal artery in the plane parallel to the bifurcation showed velocity vectors directed toward the caudal wall throughout the cardiac cycle. Reverse flow, indicating flow separation, was observed near the cranial wall even during systole. When the probe was placed on the cranial wall perpendicular to the wall, a velocity component from the cranial side to the caudal side was observed. At a distance of four diameters from the renal ostia, velocity profiles were almost parabolic. These results indicate that the velocity pattern near the cranial wall at the renal ostia, at which atherosclerotic lesions are prone to develop, are characterized by 1) a low time-averaged shear rate, 2) separation of the flow, and 3) a time-varying oscillation of the flow.}, }
@article {pmid1564057, year = {1992}, author = {Lei, M and van Steenhoven, AA and van Campen, DH}, title = {Experimental and numerical analyses of the steady flow field around an aortic Björk-Shiley standard valve prosthesis.}, journal = {Journal of biomechanics}, volume = {25}, number = {3}, pages = {213-222}, doi = {10.1016/0021-9290(92)90021-r}, pmid = {1564057}, issn = {0021-9290}, mesh = {Aorta/anatomy &amp; histology/physiology ; *Aortic Valve ; Blood Flow Velocity ; *Heart Valve Prosthesis ; Humans ; Lasers ; Models, Cardiovascular ; Prosthesis Design ; Regional Blood Flow ; Rheology ; Signal Processing, Computer-Assisted ; Surface Properties ; }, abstract = {To develop a numerical method for the description of the flow field around a Björk-Shiley (BS) standard valve prosthesis in aortic position, detailed experimental measurements and numerical calculations are performed under steady flow conditions. The experiment was conducted at Reynolds numbers up to 800. In order to perform LDA measurement of velocity in the vicinity of the valve with a curved sinus boundary, a mixture of oil and kerosine was used as the fluid which exactly matches the refractive index of the perspex aortic model. The velocity profiles at six positions in the vicinity and downstream of the valve were measured, including both axial and radial velocity components. The results show very clearly the existence of two nearly symmetric spiral vortex streams downstream of the valve. There is no recirculation area in the aorta downstream and also no obvious stagnation area in the minor orifice region near the valve when Re less than or equal to 800. Theoretically, the flow field of a BS valve is simulated by the flow pattern around a circular plate with an angle of incidence to the approaching stream. The numerical calculations were carried out by means of a 2-D model using the FEM together with the penalty function method. The maximum Reynolds number is 700. The results agree with the experimental results in the plane of symmetry when the Reynolds number is small. However, as the Reynolds number increases, the difference becomes evident. Our conclusion is that the steady flow field of a BS valve is completely 3-dimensional, featured by two spiral vortices. It cannot be simulated exactly by 2-D numerical calculations. To get more detailed and complete information about the flow field of this valve, 3-D numerical calculations are needed.}, }
@article {pmid1298451, year = {1992}, author = {Wang, SK and Hwang, NH}, title = {On transport of suspended particulates in tube flow.}, journal = {Biorheology}, volume = {29}, number = {2-3}, pages = {353-377}, doi = {10.3233/bir-1992-292-313}, pmid = {1298451}, issn = {0006-355X}, mesh = {Biological Transport ; Erythrocyte Deformability ; Erythrocytes/*physiology ; Models, Biological ; Regional Blood Flow/*physiology ; }, abstract = {Blood cells suspended in shear flows exhibit much larger dispersive motions than those predicted by the Stokes-Einstein formula for Brownian diffusion. The lateral migration and the erratic motions of the 8 microns red blood cells (RBC) is thought to be analogous to a diffusive process. It is shown that the often cited convective-diffusion theory may not be an adequate model for describing the transverse migration of suspended cells in blood flow. A comprehensive review of both the classical theory and of contemporary work in particle transport is presented, with particular emphasis on low Reynolds number tube flows. The mechanisms of Taylor dispersion, the effects of Brownian perturbations on translational and rotational motions of the suspended particles in shear fields, and the influence of integratable and chaotic advections, are individually examined. The classical experiment by Segre and Silberberg (1962) lead us to believe that particle hydrodynamics may play an important role in transverse migrations. In this light, we have further examined the hydrodynamic aspects of the so-called "tubular pinch" effect, the lateral migration of rigid spheres. We have also discussed the transverse motions of liquid drops, and the reversibility of the organization of suspensions in transport. The convective accelerations in the entrance region of a tube can produce relative velocities between fluid medium and various type of particulates if there is a difference in density. The deformable RBC, an "active-type" particle, can provide feedback to the flow from both mass and momentum considerations; the more rigid platelet, a "passive-type" particle, will experience a much smaller relative velocity as compared to the RBC. We may expect that particles of different densities are transported to different equilibrium annular positions before entering the fully developed flow region. The erratic, lateral movement of suspended particulates in steady laminar tube flow can be described by the usual Lagrangian coordinates.}, }
@article {pmid1491588, year = {1992}, author = {Pedley, TJ}, title = {Longitudinal tension variation in collapsible channels: a new mechanism for the breakdown of steady flow.}, journal = {Journal of biomechanical engineering}, volume = {114}, number = {1}, pages = {60-67}, doi = {10.1115/1.2895451}, pmid = {1491588}, issn = {0148-0731}, mesh = {Blood Flow Velocity ; Elasticity ; Evaluation Studies as Topic ; Lubrication ; *Models, Cardiovascular ; Numerical Analysis, Computer-Assisted ; *Rheology ; *Surface Tension ; Viscosity ; }, abstract = {There are several mechanisms potentially involved in the breakdown of steady fluid flow in a collapsible tube under external pressure. Here we investigate one that has received little attention in the past: the fact that the longitudinal tension in the tube wall, T, decreases with distance downstream as a consequence of the viscous shear stress exerted by the fluid. If the tube is long enough, or the initial tension small enough, T may fall to zero before the end of the collapsible tube, and unsteady motion would presumably then ensue; this is what we mean by "breakdown." We study the phenomenon theoretically, when the flow Reynolds number is of order one, using lubrication theory in a symmetric two-dimensional channel in which the collapsible tube is replaced by membranes occupying a segment of each wall. The resulting nonlinear ordinary differential equations are solved numerically for values of the dimensionless parameters that cover all the qualitatively different types of solution (e.g., in which the channel is distended over all its length, collapsed over all its length, or distended in the upstream part and collapsed downstream). Reducing the longitudinal tension has a marked effect on the shape of the collapsible segment, causing it to become much more deformed for the same flow rate and external pressure. Indeed, the wall slope is predicted to become very large when the downstream tension is very small, so the model is not self-consistent then. Nevertheless, the parameter values for which T becomes zero are mapped out and are expected to be qualitatively useful.(ABSTRACT TRUNCATED AT 250 WORDS)}, }
@article {pmid1491586, year = {1992}, author = {Tutty, OR}, title = {Pulsatile flow in a constricted channel.}, journal = {Journal of biomechanical engineering}, volume = {114}, number = {1}, pages = {50-54}, doi = {10.1115/1.2895449}, pmid = {1491586}, issn = {0148-0731}, mesh = {Arteries/*physiology ; Arteriosclerosis/etiology/physiopathology ; *Blood Flow Velocity ; Evaluation Studies as Topic ; Humans ; Mathematics ; Models, Cardiovascular ; *Pulsatile Flow ; *Rheology ; Vasoconstriction/*physiology ; }, abstract = {A nonuniform channel is used as a simple model of a constricted arterial vessel. Flow patterns have been calculated for pulsatile flow with both sinusoidal and nonsinusoidal flow rates for a range of Reynolds number, Re, and Strouhal number, St. The results show that even for relatively low frequency flows a strong vortex wave will be generated with a complex wall shear stress distribution and peak values much greater than those found in steady or unsteady parallel flow. The vortex wave increases in strength with increasing Re and St, with its total length and wavelength independent of Re but inversely proportional to St. The form of the imposed flow rate is found to have an important effect on the flow and the shear stress distribution.}, }
@article {pmid1491585, year = {1992}, author = {Thiriet, M and Pares, C and Saltel, E and Hecht, F}, title = {Numerical simulation of steady flow in a model of the aortic bifurcation.}, journal = {Journal of biomechanical engineering}, volume = {114}, number = {1}, pages = {40-49}, doi = {10.1115/1.2895448}, pmid = {1491585}, issn = {0148-0731}, mesh = {Aorta, Abdominal/anatomy &amp; histology/*physiology ; Arteriosclerosis/etiology/physiopathology ; *Blood Flow Velocity ; Evaluation Studies as Topic ; Hemodynamics ; Humans ; *Models, Cardiovascular ; *Numerical Analysis, Computer-Assisted ; Rheology ; }, abstract = {The governing equations of steady flow of an incompressible viscous fluid through a 3-D model of the aortic bifurcation are solved with the finite element method. The effect of Reynolds number on the flow was studied for a range including the physiological values (200 < or = Re < or = 1600). The symmetrical bifurcation, with a branch angle of 70 degrees and an area ratio of 0.8, includes a tapered transition zone. Secondary flows induced by the tube curvature are observed in the daughter tubes. Transverse currents in the transition zone are generated by the combined effect of diverging and converging walls. Flow separation depends on both the Reynolds number and the inlet wall shear.}, }
@article {pmid1613166, year = {1992}, author = {Nachtigall, W and Hanauer-Thieser, U}, title = {Flight of the honeybee. V. Drag and lift coefficients of the bee's body; implications for flight dynamics.}, journal = {Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology}, volume = {162}, number = {3}, pages = {267-277}, pmid = {1613166}, issn = {0174-1578}, mesh = {Animals ; Bees/*physiology ; Biophysical Phenomena ; Biophysics ; Extremities/physiology ; Flight, Animal/*physiology ; Wind ; }, abstract = {Drag forces and lift forces acting on honeybee trunks were measured by using specially built sensitive mechanical balances. Measurements were made on prepared bodies in 'good' and in 'bad' flight position, with and without legs, at velocities between 0.5 and 5 m.s-1 (Reynolds numbers between 4.10(2) and 4.10(3)) and at angles of attack between -20 degrees and +20 degrees. From the forces drag coefficients and lift coefficients were calculated. The drag coefficient measured with a zero angle of attack was 0.45 at 3 less than or equal to v less than or equal to 5 m.s-1, 0.6 at 2 m.s-1, 0.9 at 1 m.s-1 and 1.35 at 0.5 m.s-1, thus demonstrating a pronounced effect of Reynolds number on drag. These values are about 2 times lower (better) than those of a "drag disc" with the same diameter and attacked at the same velocity. The drag coefficient (related to constant minimal frontal area) was minimal at zero angle of attack, rising symmetrically to larger (+) and smaller (-) angles of attack in a non-linear fashion. The absolute value is higher and the rise is steeper at lower speeds or Reynolds numbers, but the incremental factors are independent of Reynolds number. For example, the drag coefficient is 1.44 +/- 0.05 times higher at an angle of attack of 20 degrees than at one of 0 degrees. On a double-logarithmic scale the slope of the drag versus Reynolds number plot was 1.5: with decreasing Reynolds number the relationship between drag and velocity changes from quadratic (Newton's law) to linear (viscous flow). Trunk drag was not systematically increased by the legs at any velocity or Reynolds number or any angle of attack. The legs appear to shape the trunk "aerodynamically", to form a relatively low-drag trunk-leg system. The body is able to generate dynamic lift. Highly significant positive linear correlations between lift coefficient and angle of attack were determined for the trunk-leg system in the typical flight position. Lift coefficient was +0.05 at zero angle of attack (possibly attained during very fast flight), +0.1 at 5 degrees (attained during fast flight), +0.25 at +20 degrees (attained during slow flight) and +0.55 at 45 degrees (attained whilst changing over to hovering). Average slope delta cL/delta alpha was 0.66 +/- 0.07, and average profile efficiency was 0.10. Non-wing lift contribution due to body form and banking only accounts for a few percent of body weight during fast flight.(ABSTRACT TRUNCATED AT 400 WORDS)}, }
@article {pmid1596475, year = {1992}, author = {Groth, T and Vassilieff, C and Wolf, H and Richter, G and Foerster, F}, title = {Development of a new dynamic method for quantitative evaluation of in vitro hemocompatibility of biomedical materials.}, journal = {Journal of biomaterials science. Polymer edition}, volume = {3}, number = {4}, pages = {285-300}, doi = {10.1163/156856292x00385}, pmid = {1596475}, issn = {0920-5063}, mesh = {Acrylic Resins ; *Biocompatible Materials ; Blood Cells/*cytology ; Cell Adhesion ; Cellulose/analogs &amp; derivatives ; Fibrinogen ; Glass ; Humans ; Leukocytes/physiology ; Materials Testing/instrumentation/*methods ; Platelet Adhesiveness ; Polymers ; Rheology/instrumentation ; Silicones ; Thrombosis/prevention &amp; control ; }, abstract = {In this study a new dynamic method is introduced allowing the estimation of blood cell adhesion on flat test surfaces by measuring the cell loss in the bulk phase of surface contacting test blood under defined rheological conditions. This was achieved by constructing a novel test chamber permitting the contact of small amounts of blood with a large geometrical test surface. The construction consists of a spiral-shaped flow channel of 0.3 cm width, 0.02 cm height and 78 cm length covered with the biomaterials to be tested from both sides. Laminarity of blood flow in the conduit was confirmed theoretically by the calculation of an equivalent to the Reynolds number for curved systems the so-called Dean number. Furthermore, flow laminarity was proved experimentally finding that the flow rate of blood with different hematocrit values was proportional to the hydrostatic pressure applied. The applicability of the novel 'spiral method' for the estimation of hemocompatibility was demonstrated by evaluation of platelet adhesion onto different polymers in comparison to siliconized and fibrinogen coated glass as reference surfaces. Additionally, it was possible under distinct conditions to determine the adhesion of leucocytes and the detachment of platelet aggregates. Therefore, it was concluded that the spiral method can be used for the assessment of the hemocompatibility of flat biomedical polymers. As main advantages of the new method can be considered the high time efficiency and accuracy without labelling or optical detection of adherent cells.}, }
@article {pmid1395653, year = {1992}, author = {Lou, Z and Yang, WJ}, title = {Biofluid dynamics at arterial bifurcations.}, journal = {Critical reviews in biomedical engineering}, volume = {19}, number = {6}, pages = {455-493}, pmid = {1395653}, issn = {0278-940X}, mesh = {Animals ; Arteries/anatomy &amp; histology/*physiology ; *Computer Simulation ; Hemodynamics/*physiology ; Humans ; In Vitro Techniques ; *Models, Cardiovascular ; Pulsatile Flow/physiology ; Reference Values ; Regional Blood Flow ; Rheology ; }, abstract = {Hemodynamics has long been suspected of being involved in arterial diseases, e.g., atherosclerosis. Seemingly good correlation between the atherosclerosis localization and the flow disturbance around bends and bifurcations in large arteries has prompted many studies of blood flow around those regions. This article reviews and critiques biofluid studies at various arterial bifurcations. Both experimental and theoretical models vary greatly in the major assumptions and parameters. The issues discussed include: possible errors from two-dimensional models, the validity of steady flow studies, the existence and influence of the secondary flow, effects of non-Newtonian blood rheology, influences from arterial wall distensibility, effects of the Reynolds number, effects of the area ratio, effects of the Womersley number, effects of corner curvatures, effects of bifurcation angle, errors in the measurement and calculation of wall shear rate, and the possible existence of turbulence.}, }
@article {pmid1959979, year = {1991}, author = {Goldstein, LJ and Rypins, EB}, title = {Blood vessel modeling.}, journal = {International journal of bio-medical computing}, volume = {29}, number = {1}, pages = {23-29}, doi = {10.1016/0020-7101(91)90010-c}, pmid = {1959979}, issn = {0020-7101}, mesh = {Arteries/*physiology ; Arteriosclerosis/physiopathology ; Biomechanical Phenomena ; Blood Viscosity ; Carotid Arteries/physiology ; *Computer Simulation ; Hemodynamics/physiology ; Humans ; Microcomputers ; *Models, Cardiovascular ; Regional Blood Flow ; Software ; Vascular Resistance/physiology ; }, abstract = {We developed a computer program for calculating hemodynamic parameters in a segment of vessel or catheter using Poiseuille's Law. The program analyzes flow, pressure, flow velocity, total fluid volume, pulse pressure, resistance and Reynolds number in a segment of vessel. The user can dilate or constrict at any position along its length for modeling stenoses or aneurysms. Viscosity, fluid density, length, and intrinsic radius can be varied to simulate atherosclerotic vessels. Idealized linear hemodynamics of an abdominal aortic aneurysm or a coarcted aorta can be modeled from angiographic data. Interactive results are displayed graphically and can be printed for future reference. The program can estimate catheter, graft or vascular resistances, flow velocity in atherogenic arteries, and the likelihood of achieving laminar flow.}, }
@article {pmid1742456, year = {1991}, author = {Tran-Son-Tay, R and Needham, D and Yeung, A and Hochmuth, RM}, title = {Time-dependent recovery of passive neutrophils after large deformation.}, journal = {Biophysical journal}, volume = {60}, number = {4}, pages = {856-866}, pmid = {1742456}, issn = {0006-3495}, support = {2R01-HL-23728/HL/NHLBI NIH HHS/United States ; }, mesh = {Elasticity ; Humans ; In Vitro Techniques ; Kinetics ; Mathematics ; Models, Biological ; Neutrophils/*physiology ; Surface Tension ; Time Factors ; Viscosity ; }, abstract = {Experiments are performed in which a passive human neutrophil is deformed into an elongated "sausage" shape by aspirating it into a small glass pipette. When expelled from the pipette the neutrophil recovers its natural spherical shape in approximately 1 minute. This recovery process is analyzed according to a Newtonian, liquid-drop model in which a variational method is used to simultaneously solve the hydrodynamic equations for low Reynolds-number flow and the equations for membrane equilibrium with a constant membrane tension. The theoretical model gives a good fit to the experimental data for a ratio of membrane cortical tension to cytoplasmic viscosity of approximately 1.7 x 10(-5) cm/s (0.17 micron/s). However, when the cell is held in the pipette for only a short time period of 5 s or less, and then expelled, the cell undergoes an initial, rapid elastic rebound suggesting that the cell behaves in this instance as a Maxwell viscoelastic liquid rather than a Newtonian liquid with constant cortical tension.}, }
@article {pmid1928812, year = {1991}, author = {Denardo, SJ and Yock, PG and Hargrave, VK and Srebro, JP and Ports, TA and Talbot, L}, title = {Differentiation of abnormal blood flow patterns in coronary arteries based on Doppler catheter recordings.}, journal = {Angiology}, volume = {42}, number = {9}, pages = {711-725}, doi = {10.1177/000331979104200905}, pmid = {1928812}, issn = {0003-3197}, mesh = {Blood Flow Velocity/physiology ; Cardiac Catheterization ; Coronary Artery Disease/physiopathology ; Coronary Circulation/*physiology ; Coronary Thrombosis/physiopathology ; Coronary Vessels/*diagnostic imaging ; Fourier Analysis ; Humans ; *Lasers ; Ultrasonics ; Ultrasonography/*methods ; }, abstract = {Abnormal arterial blood flow patterns have been implicated as etiologic factors in thrombosis and atherosclerosis. Intravascular pulsed Doppler ultrasound techniques with fast-Fourier transform analysis offer the opportunity to measure these abnormalities. The authors hypothesized that statistical analysis of radial-directed beam spectra could be used to distinguish disturbed from non-disturbed flow and that analysis of conventional axial-directed beam spectra could then be used to distinguish laminar high-shear from laminar low-shear flow. They developed a scaled-up in-vitro model of coronary flow consisting of a glycerol/H2O test fluid flowing through an acrylic cylinder at Reynolds numbers spanning the typical physiologic range within the coronary arteries. A scaled-up Doppler catheter with the capacity for 90 degrees reflection of the beam was placed centrally. Disturbed flow was created by introducing a flow screen, and altered shear rates were produced by changing the Reynolds number. For the radial-directed beam studies, the coefficients of variation of the Doppler spectra for the disturbed flow states were significantly greater than for the nondisturbed flow states (p less than 0.01). For the axial-directed beam studies, the coefficients of variation of the Doppler spectra for the laminar high-shear flow states were significantly greater than for the laminar low-shear flow states (p less than 0.01). They conclude that abnormal blood flow patterns can be differentiated by the selective use of radial-directed and axial-directed Doppler catheter recordings.}, }
@article {pmid1757337, year = {1991}, author = {Sullivan, KJ and Chang, HK}, title = {Steady and oscillatory transnasal pressure-flow relationships in healthy adults.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {71}, number = {3}, pages = {983-992}, doi = {10.1152/jappl.1991.71.3.983}, pmid = {1757337}, issn = {8750-7587}, support = {HL-33274/HL/NHLBI NIH HHS/United States ; }, mesh = {Adult ; Air Pressure ; Airway Resistance/physiology ; Female ; Humans ; Male ; Manometry ; Nasopharynx/anatomy &amp; histology/physiology ; Nose/anatomy &amp; histology/*physiology ; Pulmonary Ventilation/*physiology ; Reference Values ; Respiratory Function Tests ; }, abstract = {The influence of flow characteristics and gas physical properties on nasal resistance (NR) is difficult to ascertain with traditional rhinomanometric methods because the respiratory airflows used in these methods are largely uncontrolled. As an alternative, we used a novel method of rhinomanometry in which an externally generated flow is passed through the nasal passage via a mouthpiece. The transnasal pressure-flow relationships for both quasi-steady and oscillating flows and with different gases were obtained in five healthy adults with this method. For quasi-steady nasal flows the dimensionless pressure losses were largely independent of physical properties of the gas and a function of the Reynolds number (Re) of the flow. Values of NR for quasi-steady flows were largely independent of flow direction for Re up to roughly 3,000 in all five subjects and for Re up to roughly 19,000 in two of the five subjects. Airway collapse occurred in two subjects at Re greater than 3,000, suggesting that the nonrigid segments of the nasal passage contribute to the intersubject variations in NR at high flow rates. Pressure losses associated with oscillating flows measured at frequencies between 1 and 16 Hz were similar to steady flow losses provided that Re was less than roughly 3,000. For Re greater than 3,000 the oscillating flow resistances were affected by the phasic redistribution of flow into compliant segments of the nasal passage. These results indicate that, for flow rates and harmonic frequencies associated with breathing at rest, the nasal passage behaves as a rigid rough-walled pipe in which pressure losses are largely determined by forces relating to viscous friction and convective accelerations.}, }
@article {pmid1750728, year = {1991}, author = {Vincent, JH and Aitken, RJ and Mark, D and Botham, RA}, title = {Scale model studies of the transport of airborne pollutants on coalfaces.}, journal = {The Annals of occupational hygiene}, volume = {35}, number = {4}, pages = {359-376}, doi = {10.1093/annhyg/35.4.359}, pmid = {1750728}, issn = {0003-4878}, mesh = {Air Movements ; Air Pollutants, Occupational/*analysis ; *Coal Mining ; Humans ; *Models, Structural ; Occupational Exposure ; Ventilation ; }, abstract = {Studies have been carried out to investigate airflows in coalmine models, with special regard to the transport of airborne pollutants, and to examine how they relate to what happens at full-scale in an actual underground mine. If such models can be shown to provide data representative of actual mine ventilation engineering, then they can provide cost-effective alternatives to full-scale investigations. The work set out in the first instance to identify the properties of: (a) the bulk airflow and associated transport of airborne pollutants along a longwall coalface; and (b) the transport of material out of regions that were partially enclosed or poorly ventilated (e.g. in the cutting zone, in headings). For the former, an appropriate quantity is the dispersivity of the coalface airflow, for the latter the mean retention time. Both quantities may be rendered non-dimensional with respect to dimensions characteristic of the system and to velocities of the airflow. Their behaviour in relation to a third dimensionless quantity, the flow Reynolds' number is also important. Experiments were performed, using smoke or dust tracers, to investigate how these properties are interrelated and how they scale between small-scale and full-scale systems. They were carried out in a 1/10-scale laboratory model, in a full-scale surface model, and underground in an actual coalmine. The basis of most of the experiments was the 'tracer decay' method, in which the transport properties of the aerodynamic system under investigation were determined from observations of the changes in tracer concentration with time immediately following the removal of the tracer source. During these experiments, the feasibility of using small-scale models to investigate ventilation problems was clearly indicated and preliminary scaling relationships which may be used as an initial basis for predicting the transport and local build-up of pollutants in mines were developed. It is expected that applications of the ideas and methodology described will be relevant to other industries.}, }
@article {pmid1885241, year = {1991}, author = {Dubini, G and Pietrabissa, R and Fumero, R}, title = {Computational fluid dynamics of artificial heart valves.}, journal = {The International journal of artificial organs}, volume = {14}, number = {6}, pages = {338-342}, pmid = {1885241}, issn = {0391-3988}, mesh = {*Computer Simulation ; Coronary Circulation ; *Heart Valve Prosthesis ; Humans ; *Models, Cardiovascular ; Prosthesis Design ; *Rheology ; }, abstract = {A large number of in vitro studies during the last thirty years have assessed the fluid dynamic behavior of different artificial heart valves. The present study illustrates the utility of the Finite Element Method for fluid dynamic evaluation of prosthetic heart valves. The valves investigated were the Bjork-Shiley Convex-Concave (curved disc), the Medtronic-Hall (flat disc) and the Carbomedics (bileaflet). These three types were chosen in order to clarify the role of different occluder geometries on global and local fluid dynamics. The Finite Element Method was used to calculate pressure and velocity fields in the fluid domain around each valve. There were significant differences, mainly in local fluid dynamics, between the three valves. The Reynolds number also plays an important role.}, }
@article {pmid2026816, year = {1991}, author = {Adler, RS and Chenevert, TL and Fowlkes, JB and Pipe, J and Rubin, JM}, title = {Calculation of pressure gradients from MR velocity data in a laminar flow model.}, journal = {Journal of computer assisted tomography}, volume = {15}, number = {3}, pages = {483-488}, doi = {10.1097/00004728-199105000-00027}, pmid = {2026816}, issn = {0363-8715}, mesh = {Blood Flow Velocity ; Hemodynamics/*physiology ; Humans ; *Magnetic Resonance Imaging ; *Models, Cardiovascular ; }, abstract = {The MR velocity data obtained in a simple geometry and low Reynolds number are employed to calculate pressure gradients using the known solution of the Navier-Stokes equation. Calculations compare favorably with measured results for the simple model presented. The potential usefulness of noninvasive pressure gradient determination from quantitative analysis of imaging-derived velocity distributions is suggested.}, }
@article {pmid1876757, year = {1991}, author = {Abe, T and Sato, J and Romero, P and Bates, JH}, title = {Gas physical properties and respiratory system resistance measured by flow interruption.}, journal = {Respiration physiology}, volume = {84}, number = {2}, pages = {159-170}, doi = {10.1016/0034-5687(91)90114-x}, pmid = {1876757}, issn = {0034-5687}, mesh = {Airway Resistance/*physiology ; Animals ; Dogs ; Forced Expiratory Flow Rates ; Mathematics ; Pulmonary Gas Exchange/*physiology ; *Respiratory Physiological Phenomena ; }, abstract = {If the flow of gas at the airway opening of a tracheostomized dog is suddenly interrupted during expiration, the airway pressure exhibits a sudden very rapid rise, called delta Pinit, which has been shown previously to equal the resistive pressure drop across the airways in open-chest dogs, and to have a significant additional contribution from the tissues of the chest wall in intact dogs. In the present study we attempted to separate the contributions of airways and tissues to delta Pinit in intact dogs by performing flow interruptions with the lungs full of gas mixtures having different physical properties. A Moody plot (the Friction coefficient calculated using delta Pinit versus the Reynolds number) had a marked negative slope at Reynolds numbers up to 5 x 10(4), whereas the plot is predicted to have a slope close to zero at Reynolds numbers greater than 4 x 10(3) on the basis of purely fluid dynamic considerations. Assuming delta Pinit to be the result of a linear dependence of airway resistance on flow and a constant tissue resistance, we were able to account for the negative slope of the Moody plot. We also found that the values of airway and tissue resistances estimated from the data were very close to those estimated by more direct means in a previous study of delta Pinit. We conclude that it is possible to discern the separate effects of airway and tissue resistances in delta Pinit at high Reynolds numbers.}, }
@article {pmid1875697, year = {1991}, author = {Tanishita, K and Ujihira, M and Watabe, A and Nakano, K and Richardson, PD and Galletti, PM}, title = {Gas transport in serpentine microporous tubes under steady and pulsatile blood flow conditions.}, journal = {Journal of biomechanical engineering}, volume = {113}, number = {2}, pages = {223-229}, doi = {10.1115/1.2891238}, pmid = {1875697}, issn = {0148-0731}, mesh = {Animals ; Biological Transport/physiology ; Biomechanical Phenomena ; Dogs ; Extracorporeal Circulation ; Membranes, Artificial ; *Models, Cardiovascular ; Oxygen/*blood ; Pulsatile Flow/*physiology ; }, abstract = {A serpentine gas exchange unit was built with cylindrical tubular microporous membranes featuring periodic arcs with a fixed curvature ratio (ratio of tube radius to radius of curvature) of 1/14 and circular angles between 30 and 360 deg. Oxygen transfer was measured under steady and pulsatile blood flow conditions in vitro and ex vivo to assess the design features which most effectively augment gas transfer. Under steady blood flow conditions, oxygen transfer increased with circular angles beyond 70 deg. Under pulsatile conditions, a wide range of geometrical and fluid mechanical parameters could be combined to enhance gas transfer performance, which eventually depended upon the secondary Reynolds number and the Womersley parameter.}, }
@article {pmid1370041, year = {1991}, author = {Chan, WK and Belfort, M and Belfort, G}, title = {Protein overproduction in Escherichia coli: RNA stabilization, cell disruption and recovery with a cross-flow microfiltration membrane.}, journal = {Journal of biotechnology}, volume = {18}, number = {3}, pages = {225-242}, doi = {10.1016/0168-1656(91)90250-y}, pmid = {1370041}, issn = {0168-1656}, support = {GM 39422/GM/NIGMS NIH HHS/United States ; GM 44844/GM/NIGMS NIH HHS/United States ; }, mesh = {Biotechnology/*methods ; *Cell Fractionation ; Chloramphenicol O-Acetyltransferase/genetics ; Culture Media ; Escherichia coli/*genetics/growth &amp; development ; Filtration/methods ; Membranes, Artificial ; Plasmids ; RNA, Bacterial/*metabolism ; }, abstract = {After optimizing overproduction of a heterologous gene product (chloramphenicol acetyltransferase, CAT) using an RNA stabilization vector * in Escherichia coli (Chan et al., 1988), a single step cell disruption and recovery method * for obtaining a product stream essentially free of cell debris was developed. The behavior of an RNA stabilization plasmid (pKTN-CAT) containing stabilizing intron RNA was investigated in two different media both in batch and chemostat modes. CAT production of pKTN-CAT was consistently higher (3- to 7-fold) than that of the control lacking the stabilization sequences (pK-CAT). Highest CAT production was observed for cells grown in minimal medium in batch mode and induced for CAT expression early in growth. CAT production of cells grown in the chemostat mode exhibited an optimal dilution rate of about 0.1 h-1. Enhancement of protein production by pKTN-CAT as compared to pK-CAT tended to be higher when grown in rich medium rather than in minimal medium. Presence of the RNA stabilization plasmid did not significantly alter the growth rate of the cell. Using a combination of chemical treatment (1 mM EDTA) and shear stress resulting from cross-flow in a stainless steel microfiltration membrane *, CAT was released into the medium through disruption of the E. coli cells. The permeate flux increased from 2000 to 9000 kg m-2 h-1 with increasing axial Reynolds number from 10,000 to 60,000 or increasing mean shear stress from 12 to 47 Pa. The turbidity of the permeate was approximately 4% that of the retentate over this range of axial flow rates, indicating excellent removal of cell debris. Also, the concentration of CAT in the permeate was equal to that in the retentate over this range of axial flow rates, indicating complete passage of protein through the membrane. Thus, using a combination of chemical treatment and fluid-induced shear stress in a cross-flow membrane module, we were able to disrupt and recover the heterologous protein in a stream low in debris.}, }
@article {pmid2055907, year = {1991}, author = {Perktold, K and Nerem, RM and Peter, RO}, title = {A numerical calculation of flow in a curved tube model of the left main coronary artery.}, journal = {Journal of biomechanics}, volume = {24}, number = {3-4}, pages = {175-189}, doi = {10.1016/0021-9290(91)90176-n}, pmid = {2055907}, issn = {0021-9290}, mesh = {Blood Flow Velocity ; Coronary Circulation/*physiology ; Coronary Vessels/physiology ; Humans ; *Models, Cardiovascular ; Pulsatile Flow ; Stress, Mechanical ; }, abstract = {The flow pattern in the left main coronary artery has been calculated using an idealized geometry and by numerically solving the full Navier-Stokes equations for a Newtonian fluid. Two different forms for the entrance velocity profile were used, one a time-varying, flat profile and the other a time-varying, less flat velocity profile. The results obtained demonstrate the presence of secondary motions for conditions simulating flow in the left main coronary artery, with maximum secondary flow velocities being on the order of three to four percent of the maximum axial velocity. This secondary flow phenomenon has an important influence on the wall shear stress distribution, in spite of the fact that there is virtually no alteration in the axial velocity profile. The maximum ratio of the outer wall shear stress to that on the inner wall is 1.4 at a Reynolds number of Re = 270, and it increases with increasing Reynolds number, reaching a value of 1.7 at Re = 810. Although there are significant differences in the results in the immediate vicinity of the inlet for the two different forms of the entrance velocity profile used, this difference does not persist far into the tube. Independent of the choice of the entrance velocity profile, it appears that there will be significant secondary flow effects on the wall shear stress.}, }
@article {pmid2012719, year = {1991}, author = {Montoya, JP and Merz, SI and Bartlett, RH}, title = {A standardized system for describing flow/pressure relationships in vascular access devices.}, journal = {ASAIO transactions}, volume = {37}, number = {1}, pages = {4-8}, doi = {10.1097/00002480-199101000-00003}, pmid = {2012719}, issn = {0889-7190}, mesh = {Catheters, Indwelling/*classification ; Equipment Design ; Humans ; Pressure ; Rheology ; }, abstract = {Catheters are usually characterized by length and external diameter only. We developed a system to describe flow-pressure characteristics with a single number, M, patterned after a Reynolds number-friction factor correlation. A simple alignment chart was constructed that can be used to determine M for catheters of regular internal diameter and given length. If tapers, side holes, or integral connectors are present, M can be determined in-vitro with water by measuring pressure drop at various flows. The chart describes flow pressure functions for blood (Hct = 0.41) if M is known. Using this system, any catheter, needle, valve seat, extracorporeal tubing, or vascular graft can be assigned a single number that describes hydrodynamic performance characteristics.}, }
@article {pmid1932716, year = {1991}, author = {Cho, YI and Kensey, KR}, title = {Effects of the non-Newtonian viscosity of blood on flows in a diseased arterial vessel. Part 1: Steady flows.}, journal = {Biorheology}, volume = {28}, number = {3-4}, pages = {241-262}, doi = {10.3233/bir-1991-283-415}, pmid = {1932716}, issn = {0006-355X}, mesh = {Biomechanical Phenomena ; Blood Pressure/physiology ; Blood Viscosity/*physiology ; Coronary Disease/*pathology ; Coronary Vessels/*pathology ; Humans ; Models, Biological ; Regional Blood Flow ; }, abstract = {Effects of the non-Newtonian viscosity of blood on a flow in a coronary arterial casting of man were studied numerically using a finite element method. Various constitutive models were examined to model the non-Newtonian viscosity of blood and their model constants were summarized. A method to incorporate the non-Newtonian viscosity of blood was introduced so that the viscosity could be calculated locally. The pressure drop, wall shear stress and velocity profiles for the case of blood viscosity were compared for the case of Newtonian viscosity (0.0345 poise). The effect of the non-Newtonian viscosity of blood on the overall pressure drop across the arterial casting was found to be significant at a flow of the Reynolds number of 100 or less. Also in the region of flow separation or recirculation, the non-Newtonian viscosity of blood yields larger wall shear stress than the Newtonian case. The origin of the non-Newtonian viscosity of blood was discussed in relation to the viscoelasticity and yield stress of blood.}, }
@article {pmid1930889, year = {1991}, author = {Harada, M and Imamura, Y and Hasegawa, N and Yano, K and Suzuki, M and Nishizawa, S and Hirai, H and Machii, K}, title = {[Effects of depth on the display of color Doppler flow imaging with transesophageal and transthoracic transducers: an experimental study].}, journal = {Journal of cardiology. Supplement}, volume = {26}, number = {}, pages = {3-11, discussion 12-3}, pmid = {1930889}, mesh = {Blood Flow Velocity ; Echocardiography, Doppler/*methods ; Heart Valve Diseases/diagnostic imaging ; Humans ; Models, Structural ; }, abstract = {Transesophageal color Doppler flow imaging has proved to provide an accurate and sensitive information for diagnosis of valvular regurgitation. However, it is necessary to understand the difference in the display of color Doppler image between transesophageal and conventional transthoracic transducers for quantitative assessment of valvular regurgitation. In this study, the effects of the depth between transducer and jet flow on color Doppler flow imaging were evaluated with the transesophageal (3.75 MHz) and conventional (2.5 MHz) transducers by using a flow phantom. A flow circuit was filled with saline in which nylon corpuscles (average diameter; 5 microns) were suspended to enhance the Doppler effects. A turbulent jet with constant flow velocity (Reynolds number; 3500) stimulating valvular regurgitant flow was produced in a water bath through a small orifice (2 mm) by constant driving pressure (100 mmHg). Color jet imaging in the long- and short-axis views were observed at each depth with both transducers. The measurement was made every 1 cm in depth from 3 to 12 cm. The color gain setting was fixed at the optimal point so as to get the maximal flow image with the minimal static background noise. We obtained larger image of the color jet signal with the conventional than the transesophageal transducer. Although a mosaic pattern was displayed more distinctly with the transesophageal transducer compared with that of the conventional transducer, the transesophageal image tended to become indistinct in the depth deeper than 8 cm. On the other hand, the transthoracic image was maintained relatively constant at any depth.(ABSTRACT TRUNCATED AT 250 WORDS)}, }
@article {pmid1842515, year = {1991}, author = {Lou, Z and Yang, WJ}, title = {A computer simulation of the blood flow at the aortic bifurcation.}, journal = {Bio-medical materials and engineering}, volume = {1}, number = {3}, pages = {173-193}, pmid = {1842515}, issn = {0959-2989}, mesh = {Aorta/anatomy &amp; histology/*physiology ; Arteriosclerosis/etiology/physiopathology ; Blood Flow Velocity ; *Computer Simulation ; Evaluation Studies as Topic ; Heart Rate ; *Hemodynamics ; Humans ; *Models, Cardiovascular ; *Rheology ; }, abstract = {A two-dimensional finite-difference numerical model is developed for the blood flow at the aortic bifurcation to determine the possible role of fluid dynamics in the atherogenesis. Arterial walls are assumed to be rigid, while the fluid is Newtonian. Parametric studies are performed to evaluate the effects of the area ratio, Reynolds number, corner curvatures, Womersley number, bifurcation angle and arterial pulsation on the flow and shear stresses. A high shear stress region exists on the inner wall distal to the vertex, while both high and low shear stress regions coexist along the outer wall. A temporary eddy is found along the outer wall, with more strength in the case of a higher area ratio. The results agree qualitatively with the existing experimental observations.}, }
@article {pmid1838287, year = {1991}, author = {Chahed, N and Péronneau, P and Delouche, A and Diebold, B}, title = {Velocity profiles and streamlines of a revolution post-stenotic flow.}, journal = {Biorheology}, volume = {28}, number = {5}, pages = {383-400}, doi = {10.3233/bir-1991-28503}, pmid = {1838287}, issn = {0006-355X}, mesh = {Blood Flow Velocity ; Carotid Stenosis/*physiopathology ; Humans ; Models, Cardiovascular ; Rheology ; }, abstract = {Velocity fields have been measured in models simulating arterial stenoses for continuous and revolution flows. A pulsed Doppler velocimeter allows for velocity readings in the entire tube and in the wall area. Streamlines are determined by numerical solving of the system of equations defining the current function. Velocity profiles and streamlines are presented and discussed either for steady or for unsteady flows, with different Reynolds numbers and variable degrees of stenosis. There is, in the wall area, a recirculating zone made of a well-defined rouleau. Its length varies increasingly according to the increasing severity of the stenosis. The stability of axial flow depends on the input profile, the degree of stenosis and the Reynolds number. Plotting streamlines allows to describe accurately the flow; its quantitative aspect offers advantages with respect to conventional visualization mode.}, }
@article {pmid1808798, year = {1991}, author = {Markou, CP and Ku, DN}, title = {Accuracy of velocity and shear rate measurements using pulsed Doppler ultrasound: a comparison of signal analysis techniques.}, journal = {Ultrasound in medicine &amp; biology}, volume = {17}, number = {8}, pages = {803-814}, doi = {10.1016/0301-5629(91)90163-q}, pmid = {1808798}, issn = {0301-5629}, mesh = {Blood Flow Velocity ; Fourier Analysis ; *Signal Processing, Computer-Assisted ; *Ultrasonics ; }, abstract = {An experimental investigation was instituted to evaluate the performance of Doppler ultrasound signal processing techniques for measuring fluid velocity under well-defined flow conditions using a 10-MHz multigated pulsed ultrasound instrument. Conditions of fully developed flow in a rigid, circular tube were varied over a Reynolds number range between 500 and 8000. The velocity across the tube was determined using analog and digital zero crossing detectors and three digital spectrum estimators. Determination of the Doppler frequency from analog or digital zero crossing detectors gave accurate velocity values for laminar and moderately turbulent flow away from the wall (0.969 less than or equal to r less than or equal to 0.986). Three digital spectrum estimators, Fast Fourier Transform, Burg autoregressive method, and minimum variance method, were slightly more accurate than the zero crossing detector (0.984 less than or equal to r less than or equal to 0.994), especially at points close to the walls and with higher levels of turbulence. Steep velocity gradients and transit-time-effects from high velocities produced significantly larger errors in velocity measurement. Wall shear rate estimates were most precise when calculated using the position of the wall and two velocity points. The calculated wall shears were within 20%-30% of theoretically predicted values.}, }
@article {pmid1802650, year = {1991}, author = {Berg, HC}, title = {Bacterial motility: handedness and symmetry.}, journal = {Ciba Foundation symposium}, volume = {162}, number = {}, pages = {58-69; discussion 69-72}, doi = {10.1002/9780470514160.ch5}, pmid = {1802650}, issn = {0300-5208}, mesh = {*Bacterial Physiological Phenomena ; Cell Movement/*physiology ; Chemotaxis/physiology ; Chromatium ; Escherichia coli ; Flagella/*physiology ; Image Processing, Computer-Assisted ; Microscopy, Phase-Contrast ; }, abstract = {Many bacteria swim by rotating thin helical filaments that extend into the external medium, as with common bacteria, or run beneath the outer membrane, as with spirochetes. Each filament is driven at its base by a motor that turns alternately clockwise and counterclockwise. The motor-filament complex is called a flagellum. Other kinds of bacteria glide, but their organelles of locomotion are not known. Since bacteria are microscopic and live in an aqueous environment, they swim at low Reynolds' number; cyclic motion works (e.g. rotation of a helix) but reciprocal motion does not (e.g. stroking of a singly hinged oar). By measuring concentrations of certain chemicals as they move through their environment, making temporal comparisons and modulating the direction of flagellar rotation, bacteria accumulate in regions that they find more favourable. Studies of bacterial chemotaxis are highly advanced, particularly for the peritrichously flagellated species Escherichia coli. A great deal is known about chemoreception, receptor-flagellar coupling and adaptation. Recently it has been found that E. coli can aggregate in response to signals generated by the cells themselves. Complex patterns form with remarkable symmetries.}, }
@article {pmid1761583, year = {1991}, author = {Johnston, PR and Kilpatrick, D}, title = {Mathematical modelling of flow through an irregular arterial stenosis.}, journal = {Journal of biomechanics}, volume = {24}, number = {11}, pages = {1069-1077}, doi = {10.1016/0021-9290(91)90023-g}, pmid = {1761583}, issn = {0021-9290}, mesh = {Arterial Occlusive Diseases/pathology/*physiopathology ; Constriction, Pathologic/pathology/physiopathology ; Coronary Vessels ; Humans ; *Models, Cardiovascular ; Pressure ; Regional Blood Flow ; Rheology ; Stress, Mechanical ; }, abstract = {A mathematical model of flow through an irregular arterial stenosis is developed. The model is two-dimensional and axi-symmetric with the stenosis outline obtained from a three-dimensional casting of a mildly stenosed artery. Agreement between modelled and experimental pressure drops (obtained from an axi-symmetric machined stenosis with the same profile) is excellent. Results are also obtained for a smooth stenosis model, similar to that used for most mathematical modelling studies. This model overestimates the pressure drop across the stenosis, as well as the wall shear stress and separation Reynolds number. Also, the smooth model predicts one instead of three recirculation zones present in the irregular model. The original stenosis is modified to increase the severity from 48 and 87% areal occlusion, while maintaining the same general shape. This has the effect of increasing the pressure drop by an order of magnitude and decreasing the number of recirculation zones to one, with a lower separation Reynolds number.}, }
@article {pmid1670082, year = {1991}, author = {How, TV and al-Shukri, S}, title = {Assessment of pressure drop flowrate relationship of axillobifemoral bypass grafts.}, journal = {Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine}, volume = {205}, number = {4}, pages = {243-249}, doi = {10.1243/PIME_PROC_1991_205_300_02}, pmid = {1670082}, issn = {0954-4119}, mesh = {Biomechanical Phenomena ; *Blood Vessel Prosthesis ; Exercise/physiology ; Leg/blood supply ; *Models, Cardiovascular ; Pressure ; Pulsatile Flow ; Regional Blood Flow ; }, abstract = {An in vitro study was conducted to measure the pressure distributions in knitted polyester axillobifemoral bypass grafts under steady and pulsatile flow of a Newtonian fluid. The relationship between pressure drop and flowrate was determined across the outflow branches of two types of axillobifemoral grafts. Pressure losses were greater across the 90 degrees side branch of the T-type graft than in the Y-type graft at all Reynolds numbers studied. Mean pulsatile pressure drops in the T graft were greater than those measured in steady flow at the same Reynolds number. Estimates of the likely in vivo pressure drops are made under resting and exercise flow conditions. It is suggested that the Y graft is less likely to have a significant effect on blood supply to the lower limbs, even at high blood flowrates.}, }
@article {pmid2273871, year = {1990}, author = {Lee, SY and Schmid-Schönbein, GW}, title = {Pulsatile pressure and flow in the skeletal muscle microcirculation.}, journal = {Journal of biomechanical engineering}, volume = {112}, number = {4}, pages = {437-443}, doi = {10.1115/1.2891208}, pmid = {2273871}, issn = {0148-0731}, mesh = {Animals ; Blood Pressure/*physiology ; Hemodynamics/physiology ; Microcirculation ; *Models, Cardiovascular ; Muscles/*blood supply ; Pulsatile Flow ; Rats ; Vascular Resistance/physiology ; }, abstract = {Although blood flow in the microcirculation of the rat skeletal muscle has negligible inertia forces with very low Reynolds number and Womersley parameter, time-dependent pressure and flow variations can be observed. Such phenomena include, for example, arterial flow overshoot following a step arterial pressure, a gradual arterial pressure reduction for a step flow, or hysteresis between pressure and flow when a pulsatile pressure is applied. Arterial and venous flows do not follow the same time course during such transients. A theoretical analysis is presented for these phenomena using a microvessel with distensible viscoelastic walls and purely viscous flow subject to time variant arterial pressures. The results indicate that the vessel distensibility plays an important role in such time-dependent microvascular flow and the effects are of central physiological importance during normal muscle perfusion. In-vivo whole organ pressure-flow data in the dilated rat gracilis muscle agree in the time course with the theoretical predictions. Hemodynamic impedances of the skeletal muscle microcirculation are investigated for small arterial and venous pressure amplitudes superimposed on an initial steady flow and pressure drop along the vessel.}, }
@article {pmid2270363, year = {1990}, author = {Tsuzaki, K and Kamm, RD}, title = {Flow distribution in a single bifurcation during high-frequency oscillation.}, journal = {Respiration physiology}, volume = {82}, number = {1}, pages = {89-105}, doi = {10.1016/0034-5687(90)90026-u}, pmid = {2270363}, issn = {0034-5687}, mesh = {*High-Frequency Ventilation ; Models, Biological ; Pressure ; Respiratory Mechanics/*physiology ; Stroke Volume ; Tidal Volume ; }, abstract = {The distribution of flow in a single bifurcation was studied to examine what factors played a critical role. Flow was preferentially directed down the straightest pathway when higher frequencies and/or larger tidal volumes were used, but otherwise followed the pattern dictated by the distal impedance regardless of bifurcation geometry. In a symmetrical model, the observed flow distribution was in good agreement with a mathematical prediction based on linear impedance theory, though this was not the case when tidal volumes were increased. The difference in mean pressure between the two terminal units was also a strong function of branching angle and the Reynolds number. These findings suggest that the geometrical factors and local flow conditions contribute to both the flow and mean pressure distribution in an inertia-induced nonlinear manner. Consequently, linear impedance theory can be applied only to the limited situation of low tidal volume and symmetric configuration.}, }
@article {pmid2277546, year = {1990}, author = {Miyawaki, F and How, TV and Annis, D}, title = {Effect of compliance mismatch on flow disturbances in a model of an arterial graft replacement.}, journal = {Medical &amp; biological engineering &amp; computing}, volume = {28}, number = {5}, pages = {457-464}, pmid = {2277546}, issn = {0140-0118}, mesh = {Arteries/*physiology/transplantation ; Blood Flow Velocity/physiology ; Compliance ; Humans ; Models, Cardiovascular ; Pulsatile Flow/physiology ; Vascular Resistance/physiology ; }, abstract = {Flow disturbances in a model of an interposition graft in an arterial segment were measured using an ultrasound Doppler velocimeter. The effect of the degree of compliance mismatch between a stiff' graft' and compliant 'arterial' segments was investigated. In steady flow, disturbances were detected when the compliance ratio (stiff to compliant segments) was less than or equal to 0.1 and the Reynolds number greater than or equal to 2200. A recirculation zone just downstream of the distal anastomosis was observed at a Reynolds number greater than or equal to 2400. Disturbances were also measured under pulsatile flow which consisted of a time-varying component superimposed on a steady flow component. The time-varying flow component was either quasiphysiological or sinusoidal in shape. The Reynolds number was 500 but the frequency parameter varied from 4.2 to 8.5. Significant disturbances were observed for conduits with compliance ratio less than or equal to 0.19. The disturbance intensity tended to increase as the compliance ratio decreased and the frequency parameter increased. The magnitude of the disturbance was also greater with the quasiphysiological than the sinusoidal input flow waveform.}, }
@article {pmid2118449, year = {1990}, author = {Gluck, EH and Onorato, DJ and Castriotta, R}, title = {Helium-oxygen mixtures in intubated patients with status asthmaticus and respiratory acidosis.}, journal = {Chest}, volume = {98}, number = {3}, pages = {693-698}, doi = {10.1378/chest.98.3.693}, pmid = {2118449}, issn = {0012-3692}, mesh = {Acidosis, Respiratory/blood/*etiology ; Adolescent ; Adult ; Asthma/*therapy ; Carbon Dioxide/blood ; Female ; Helium/*administration &amp; dosage ; Humans ; *Intubation, Intratracheal ; Male ; Oxygen/*administration &amp; dosage/blood ; *Respiration, Artificial ; Status Asthmaticus/blood/complications/*therapy ; }, abstract = {Seven patients with status asthmaticus intubated for respiratory failure who had elevated airway pressures and persistent respiratory acidosis were successfully ventilated using a mixture of 60 percent helium and 40 percent oxygen. All patients experienced a rapid reduction in airway pressures, CO2 retention, and resolution of acidosis while breathing a helium-oxygen mixture. There were no untoward effects. Helium-oxygen mixtures improve ventilation by reducing the Reynolds number and reducing density dependent resistance. Helium's beneficial effects are due to its high kinematic viscosity, high binary diffusion coefficient for CO2, and high diffusivity. Helium-oxygen mixtures should be considered for use in mechanically ventilated asthmatics with respiratory acidosis who fail conventional therapy.}, }
@article {pmid2228866, year = {1990}, author = {Tsuda, A and Savilonis, BJ and Kamm, RD and Fredberg, JJ}, title = {Periodic flow at airway bifurcations. III. Energy dissipation.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {69}, number = {2}, pages = {562-569}, doi = {10.1152/jappl.1990.69.2.562}, pmid = {2228866}, issn = {8750-7587}, support = {HL-33009/HL/NHLBI NIH HHS/United States ; HL-34616/HL/NHLBI NIH HHS/United States ; }, mesh = {Energy Metabolism ; Humans ; Lung Volume Measurements ; Models, Biological ; Respiratory Mechanics/*physiology ; *Respiratory Physiological Phenomena ; Respiratory System/anatomy &amp; histology ; }, abstract = {We measured the energy dissipation associated with large-amplitude periodic flow through airway bifurcation models. Each model consisted of a single asymmetric bifurcation with a different branching angle and area ratio, with each branch terminated into an identical elastic load. Sinusoidal volumetric oscillations were applied at the parent duct so that the upstream Reynolds number (Re) varied from 30 to 77,000 and the Womersley parameter (alpha) from 4 to 30. Pressures were measured continuously at the parent duct and at both terminals, and instantaneous branch flow rates were calculated. Time-averaged energy dissipation in the bifurcation was computed from an energy budget over a control volume integrated over a cycle and was expressed as a friction factor, F. We found that when tidal volume was small [ratio of tidal volume to resident (dead space) volume, VT/VD less than 1], F was independent of branching angle and fell with increasing alpha and VT/VD. When tidal volume was large (VT/VD greater than 1), F increased with increasing branching angle and varied less strongly with alpha and VT/VD. No simple benchmark flow represented the data well over the entire experimental range. This study demonstrates that only two nondimensional parameters, alpha and VT/VD, are necessary and are sufficient to describe time-averaged energy dissipation in a given bifurcation geometry during sinusoidal flow.}, }
@article {pmid2228864, year = {1990}, author = {Tsuda, A and Fredberg, JJ}, title = {Periodic flow at airway bifurcations. I. Development of steady pressure differences.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {69}, number = {2}, pages = {546-552}, doi = {10.1152/jappl.1990.69.2.546}, pmid = {2228864}, issn = {8750-7587}, support = {HL-33009/HL/NHLBI NIH HHS/United States ; HL-34616/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Biomechanical Phenomena ; Dogs ; Models, Biological ; Pressure ; Respiratory Mechanics/*physiology ; *Respiratory Physiological Phenomena ; Respiratory System/anatomy &amp; histology ; }, abstract = {In studies of large-amplitude periodic flows at an airway bifurcation, we found an appreciable steady-state pressure difference between the terminal units. To elucidate the fluid dynamic origins of such steady-state pressure differences, we studied single asymmetric bifurcation models with various area ratios and branching angles. The daughter ducts were identical in size and were terminated into identical elastic loads. Sinusoidal flow oscillations were applied at the parent duct so that the upstream Reynolds number ranged from 30 to 77,000 and the Womersley parameter from 2 to 30. The steady-state component (time averaged) of the pressure measured at the terminal with the smaller branching angle was found to be consistently higher than that at the other terminal. This steady-state pressure difference scaled approximately as a fixed fraction of the parent duct dynamic head. Guided by the results of flow-visualization studies, we modeled such behavior based on the temporal and spatial differences of head loss between the two branches of the bifurcation. Our results suggest that interlobar heterogeneity of mean alveolar-pressure observed in excised canine lungs during high frequency oscillation (Allen et al., J. Appl. Physiol. 62: 223-228, 1987) arises solely from fluid dynamic origins: differential head loss due to asymmetry of central airway branching structure.}, }
@article {pmid2374504, year = {1990}, author = {Wendt, RE and Nitz, WR and Murphy, PH}, title = {Nuclear magnetic resonance velocity spectra of steady flow.}, journal = {Magnetic resonance in medicine}, volume = {15}, number = {1}, pages = {90-101}, doi = {10.1002/mrm.1910150110}, pmid = {2374504}, issn = {0740-3194}, support = {R01 CA-40571/CA/NCI NIH HHS/United States ; }, mesh = {Arteriosclerosis/diagnosis ; *Blood Flow Velocity ; Humans ; *Magnetic Resonance Imaging ; Models, Structural ; }, abstract = {Nuclear magnetic resonance (NMR) velocity spectra are a compact way to represent the flow information in a velocity-resolved image set. Fully developed steady flow in long tubes gives NMR velocity spectra with average velocities which correlate well with the values derived from the flow rate. The ratio of average velocity to peak velocity correlates well with the Reynolds number. Tubes with compressed cross sections have velocity spectra similar to those of circular tubes. Tubes with irregular walls have velocity spectra in the entrance region that are markedly different from those from smooth-walled tubes.}, }
@article {pmid2252781, year = {1990}, author = {Van Meurs, KP and Mikesell, GT and Seale, WR and Short, BL and Rivera, O}, title = {Maximum blood flow rates for arterial cannulae used in neonatal ECMO.}, journal = {ASAIO transactions}, volume = {36}, number = {3}, pages = {M679-81}, pmid = {2252781}, issn = {0889-7190}, mesh = {Blood Flow Velocity/*physiology ; *Catheters, Indwelling ; Equipment Design ; Erythrocyte Deformability/*physiology ; Extracorporeal Membrane Oxygenation/*instrumentation ; Hemolysis/*physiology ; Humans ; Infant, Newborn ; Models, Cardiovascular ; Respiratory Distress Syndrome, Newborn/*physiopathology ; Rheology ; }, abstract = {The arterial cannulae used in neonatal ECMO cause hemolysis and red blood cell damage at elevated blood flows. Hemolysis in extracorporeal circuits has been found to occur with shear stress greater than 132 dynes/cm2, turbulence as measured by Reynold's number greater than 1,000, and velocity greater than 120 to 200 cm/sec. These parameters need to be considered when sizing the proper arterial cannula for a required flow rate. In-vitro measurements of the pressure drop across six arterial cannulae at varying flow rates were performed using human blood with a hematocrit of 43%. Shear stress, Reynold's number, velocity, and pressure drop were calculated for each catheter at flow rates from 50 to 1,000 cc/min. The maximum mean flow rate to maintain the shear stress, Reynold's number, velocity, and pressure drop within the accepted range, was determined for each cannula. Recommended maximum blood flow rates for each of the six cannulae are given. Internal diameter, length, and cannula geometry appear to be the factors most affecting the flow achievable without causing red blood cell damage and hemolysis. Ten French Biomedicus, 10 French Cook, and 10 French Elecath arterial cannulae appear best suited to deliver the range of blood flow rates used in neonatal ECMO.}, }
@article {pmid2194690, year = {1990}, author = {Tamura, T and Fronek, A}, title = {Detection of moving flow separation in pulsatile flow and the degree of stenosis by power of Doppler shift signals.}, journal = {Circulation research}, volume = {67}, number = {1}, pages = {166-174}, doi = {10.1161/01.res.67.1.166}, pmid = {2194690}, issn = {0009-7330}, support = {HL-18977/HL/NHLBI NIH HHS/United States ; }, mesh = {*Blood Circulation ; Blood Vessels/*pathology ; Constriction, Pathologic ; *Models, Cardiovascular ; Pulsatile Flow ; *Ultrasonography ; }, abstract = {Power ratios were derived from the principle of ultrasonic Doppler velocimetry to determine a ratio of the volume of vortices to the total vessel volume under the ultrasonic beam. This ratio also equals the ratio of the cross-sectional area of vortices to the vessel lumen. In vitro pulsatile flow experiments were performed in a Reynolds number range of 1,230-4,320 with axisymmetric constrictions with area reductions of 55%, 65%, 70%, and 85% to model carotid stenosis. Flow separation downstream from the model stenoses was detected, and the power ratio fluctuated when vortices with the forward- and reverse-flow velocity components passed by the measurement position. The power ratio estimated the degree of stenosis within 10% of error. Ensemble average of the power ratio was computed to obtain the statistically averaged separated flow region. The moving flow reattachment point was revealed downstream from the 85% stenosis at a Reynolds number of 900.}, }
@article {pmid2345450, year = {1990}, author = {Yung, CN and De Witt, KJ and Keith, TG}, title = {Three-dimensional steady flow through a bifurcation.}, journal = {Journal of biomechanical engineering}, volume = {112}, number = {2}, pages = {189-197}, doi = {10.1115/1.2891171}, pmid = {2345450}, issn = {0148-0731}, mesh = {Algorithms ; Biomechanical Phenomena ; Blood Flow Velocity ; Blood Vessels/*physiology ; *Models, Cardiovascular ; Stress, Mechanical ; }, abstract = {Steady flow of an incompressible, Newtonian fluid through a symmetric bifurcated rigid channel was numerically analyzed by solving the three-dimensional Navier-Stokes equations. The upstream Reynolds number ranged from 100 to 1500. The bifurcation was symmetrical with a branch angle of 60 deg and the area ratio of the daughter to the mother vessel was 2.0. The numerical procedure utilized a coordinate transformation and a control volume approach to discretize the equations to finite difference form and incorporated the SIMPLE algorithm in performing the calculation. The predicted velocity pattern was in qualitative agreement with experimental measurements available in the literature. The results also showed the effect of secondary flow which can not be predicted using previous two-dimensional simulations. A region of reversed flow was observed near the outer wall of the branch except for the case of the lowest Reynolds number. Particle trajectory was examined and it was found that no fluid particles remained within the recirculation zone. The shear stress was calculated on both the inner and the outer wall of the branch. The largest wall shear stress, located in the vicinity of the apex of the branch, was of the same order of magnitude as the level that can cause damage to the vessel wall as reported in a recent study.}, }
@article {pmid2327326, year = {1990}, author = {Moore, ME and McFarland, AR}, title = {Design of Stairmand-type sampling cyclones.}, journal = {American Industrial Hygiene Association journal}, volume = {51}, number = {3}, pages = {151-159}, doi = {10.1080/15298669091369475}, pmid = {2327326}, issn = {0002-8894}, mesh = {Air Pollutants, Occupational/*analysis ; Dust/*analysis ; Equipment Design ; Humans ; Particle Size ; Smoke/*analysis ; }, abstract = {An empirical, nondimensional correlation of cut-point Stokes number (Stk0.5) and flow Reynolds number (Re) has been established for small Stairmand-type sampling cyclones. Four cyclones with body diameters of 38, 57, 89, and 140 mm were constructed and tested with monodisperse aerosols over a range of flow rates. The flow rates were chosen to provide preselected increments of particle Froude numbers. These flow rates for the four cyclones spanned the range of 9.4 to 1080 L/min and provided Froude numbers of 1.5, 2.0, 2.5, and 6.0. The resulting Reynolds numbers (based upon cyclone body diameter and inlet flow rate) covered the range of 2.1 x 10(3) to 6.4 x 10(4). Sizes of monodisperse aerosols used in this study were from 3.0- to 17.4-microns aerodynamic diameter. The graphical correlation between cut-point Stokes number and Reynolds number showed there to be no effect of Froude number (for the range of Froude numbers tested). The data have been fit by a least squares procedure to a quadratic logarithmic function. In addition to development of the empirical correlation, the results of this study also provide data pertinent to the regional deposition of liquid particles within the cyclone and to the transmission of solid particles through the cyclone. The carryover of solid, 19-microns diameter particles is only 0.5% greater than that of liquid particles of the same size.}, }
@article {pmid2304249, year = {1990}, author = {Yamada, H}, title = {[Effects of turbulence on gas transport during high frequency oscillation].}, journal = {Masui. The Japanese journal of anesthesiology}, volume = {39}, number = {1}, pages = {27-38}, pmid = {2304249}, issn = {0021-4892}, mesh = {*High-Frequency Ventilation ; Humans ; Models, Structural ; *Pulmonary Gas Exchange ; Trachea ; }, abstract = {To clarify the enhancing effect of turbulence on gas transfer in high frequency oscillation (HFO), the role of turbulence during oscillatory flow was studied. Oscillatory flow was generated in a straight circular tube as a trachea model, over the range of Reynolds' number (Re: 2000-16000) and Stokes parameter (lambda : 3-7). This simulates clinical settings. Measurements of the axial velocity were made by means of hot wire anemometer, and turbulence intensity (I) as well as ensemble mean velocity was calculated. At the same time, 1 ml of 100% CO2 was injected into the tube, and CO2 concentration was measured by a CO2 analyzer to yield the effective diffusivity (Deff). As Re increases and lambda decreases to a certain level, "conditional turbulence" appears in the whole cross section to produce an efficient lateral mixing. Deff increases with increasing I as well as Re, and increasing lambda results in an increase in the difference of measured and theoretical Deff (Watson's prediction for laminar oscillatory flow). It is concluded that turbulence during oscillatory flow plays an important role in lateral mixing to facilitate gas transport, and decision of ventilator settings is essential so as to give rise to "conditional turbulence" for the purpose of Deff augmentation during HFO.}, }
@article {pmid2296238, year = {1990}, author = {Modi, VJ and Akutsu, T}, title = {On the hemodynamics of several prosthetic heart valves: in vitro study.}, journal = {Monographs on atherosclerosis}, volume = {15}, number = {}, pages = {125-137}, pmid = {2296238}, issn = {0077-099X}, mesh = {Blood Flow Velocity/physiology ; Blood Pressure/physiology ; *Heart Valve Prosthesis ; Hemodynamics/*physiology ; Humans ; Materials Testing ; Models, Cardiovascular ; Prosthesis Design ; Rheology ; }, abstract = {Distribution of velocity, viscous shear stress and turbulence intensity in the wake of several mechanical heart valves is studied using a laser Doppler anemometer system during steady and pulsatile flow conditions. The corresponding results are also obtained for a sharp-edged orifice which help assess changes in the flow pattern caused by different valve geometries. The results are correlated with the static pressure drop across the valves and its recovery in the wake, as a function of the Reynolds number. Results suggest a substantial increase in turbulence intensity, in some cases by as much as 40- to 50-fold, thus raising a possibility of thromboembolism.}, }
@article {pmid2229088, year = {1990}, author = {Lieber, BB}, title = {The decomposition of apparent stresses in disturbed pulsatile flow in the presence of large scale organized structures.}, journal = {Journal of biomechanics}, volume = {23}, number = {10}, pages = {1047-1060}, doi = {10.1016/0021-9290(90)90320-3}, pmid = {2229088}, issn = {0021-9290}, mesh = {Biomechanical Phenomena ; Blood Flow Velocity ; Humans ; *Models, Cardiovascular ; Pulsatile Flow/*physiology ; Stress, Mechanical ; }, abstract = {Flow disturbance phenomena that occur in unsteady-in-the-mean flows (i.e. pulsatile or oscillating) at moderate Reynolds numbers are analyzed in both the time domain and the frequency domain. The analysis utilizes variable decomposition into a time-varying underlying waveform and flow disturbances which are composed of large scale organized structures and random fluctuations. A practical technique which incorporates time domain phase conditioning, trend removal, and frequency domain matched filtering, is presented and examined using simulated data of known statistical behavior. The applicability of the method is shown by the decomposition of the simulated data and the technique is then applied to experimental data obtained in pulsatile flow through a constricted tube by means of a laser Doppler anemometer. The cross-sectional area reduction at the constriction throat was 90%. The Womersley parameter in the experiments was 5.3 and the Reynolds number based on the average flow rate per cycle was 300 with a minimum/maximum value of 55/600 based on the instantaneous flow rate. Measurements were taken in the flow region downstream of the constriction throat which included several interesting flow disturbance phenomena. The results of the decomposed flow phenomena demonstrate the significant role of large scale organized structures in such flows. This is particularly important when analyzing blood flow in the large arteries in the presence of severe stenosis or behind prosthetic devices in an attempt to estimate the 'turbulent' stress which act on cellular elements. Estimation of the apparent stress tensor is of importance in an effort to elucidate the mechanical factors which influence the durability of red blood cells under abnormal conditions.}, }
@article {pmid2197281, year = {1990}, author = {Rindt, CC and van Steenhoven, AA and Janssen, JD and Reneman, RS and Segal, A}, title = {A numerical analysis of steady flow in a three-dimensional model of the carotid artery bifurcation.}, journal = {Journal of biomechanics}, volume = {23}, number = {5}, pages = {461-473}, doi = {10.1016/0021-9290(90)90302-j}, pmid = {2197281}, issn = {0021-9290}, mesh = {Blood Flow Velocity ; Carotid Arteries/*physiology ; Mathematical Computing ; Minicomputers ; *Models, Cardiovascular ; Ultrasonography ; }, abstract = {A finite element approximation of steady flow in a rigid three-dimensional model of the carotid artery bifurcation is presented. A Reynolds number of 640 and a flow division ratio of about 50/50, simulating systolic flow, was used. To limit the CPU- and I/O-times needed for solving the systems of equations, a mesh-generator was developed, which gives full control over the number of elements into which the bifurcation is divided. A mini-supercomputer, based on parallel and vector processing techniques, was used to solve the system of equations. The numerical results of axial and secondary flow compare favorably with those obtained from previously performed laser-Doppler velocity measurements. Also, the influence of the Reynolds number, the flow division ratio, and the bifurcation angle on axial and secondary flow in the carotid sinus were studied in the three-dimensional model. The influence of the interventions is limited to a relatively small variation in the region with reversed axial flow, more or less pronounced C-shaped axial velocity contours, and increasing or decreasing axial velocity maxima.}, }
@article {pmid1366388, year = {1990}, author = {Mano, T and Kimura, T and Iijima, S and Takahashi, K and Takeuchi, H and Kobayashi, T}, title = {Comparison of oxygen supply methods for cultures of shear-stress sensitive organisms including animal cell culture.}, journal = {Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)}, volume = {47}, number = {3}, pages = {259-271}, doi = {10.1002/jctb.280470307}, pmid = {1366388}, issn = {0268-2575}, mesh = {Animals ; Biotechnology/instrumentation ; Cell Count ; Cell Division ; Cells, Cultured/*metabolism ; Fluorocarbons ; *Oxygen/administration &amp; dosage ; }, abstract = {In animal cell culture, oxygen supply sometimes limits cell growth. Therefore, four oxygen supply methods (free surface aeration, porous Teflon tubing, perfluorocarbon addition and external aerator) were compared in terms of oxygen transfer rate for suspension culture of animal cells. Oxygen transfer rate with the free surface aeration was dependent on the vertical position of the impeller and the stirred Reynolds number for h/HL greater than 0.35, but no effect of the impeller position was observed for h/HL less than 0.35. The relationship between the Reynolds and Sherwood numbers could be expressed by simple correlations. These correlations could also be applied to oxygen transfer using porous Teflon tubing. When oxygen was supplied with perfluorocarbon saturated with air, the overall mass transfer coefficient KL was estimated to be about 9.0 X 10(-3) cm s-1, which was five-fold greater than that of the surface aeration. Maximum cell densities which would be supported by four methods were calculated from values of KLa for different sizes of fermentor assuming that oxygen supply would be the rate-limiting factor in animal cell culture.}, }
@article {pmid2779186, year = {1989}, author = {van Dreumel, SC and Kuiken, GD}, title = {Steady flow through a double converging-diverging tube model for mild coronary stenoses.}, journal = {Journal of biomechanical engineering}, volume = {111}, number = {3}, pages = {212-221}, doi = {10.1115/1.3168368}, pmid = {2779186}, issn = {0148-0731}, mesh = {Blood Flow Velocity ; Coronary Circulation ; Coronary Disease/*physiopathology ; Hemodynamics ; Humans ; Mathematics ; *Models, Cardiovascular ; Pressure ; Stress, Mechanical ; }, abstract = {Velocity profiles and the pressure drop across two mild (62 percent) coronary stenoses in series have been investigated numerically and experimentally in a perspex-tube model. The mean flow rate was varied to correspond to a Reynolds number range of 50-400. The pressure drop across two identical (62 percent) stenoses show that for low Reynolds numbers the total effect of two stenoses equals that of two single stenoses. A reduction of 10 percent is found for the higher Reynolds numbers investigated. Numerical and experimental results obtained for the velocity profiles agree very well. The effect of varying the converging angle of a single mild (62 percent) coronary stenosis on the fluid flow has been determined numerically using a finite element method. Pressure-flow relation, especially with respect to relative short stenoses, is discussed.}, }
@article {pmid2757149, year = {1989}, author = {Fillinger, MF and Reinitz, ER and Schwartz, RA and Resetarits, DE and Paskanik, AM and Bredenberg, CE}, title = {Beneficial effects of banding on venous intimal-medial hyperplasia in arteriovenous loop grafts.}, journal = {American journal of surgery}, volume = {158}, number = {2}, pages = {87-94}, doi = {10.1016/0002-9610(89)90353-x}, pmid = {2757149}, issn = {0002-9610}, mesh = {Animals ; *Arteriovenous Shunt, Surgical ; Blood Flow Velocity ; Blood Pressure ; *Blood Vessel Prosthesis ; Blood Vessels/*pathology ; Dogs ; *Equipment Failure ; Femoral Artery/pathology/surgery ; Femoral Vein/pathology/surgery ; *Hemodynamics ; Hyperplasia ; Polytetrafluoroethylene ; *Prosthesis Failure ; }, abstract = {Local hemodynamics were modified in a canine arteriovenous loop graft model by placing a flow-limiting band on femoral polytetrafluoroethylene (PTFE) grafts. Banded and unbanded grafts were implanted in a paired fashion. Hemodynamic studies included Reynolds number and phonoangiography as measures of turbulence. Intimal-medial thickness was measured 8 weeks after implantation. Reduction of the volumetric flow rate by 50 percent resulted in significant changes in flow velocity, flow pulsatility, pressure, and turbulence at the venous anastomosis. Hyperplastic lesions developed in a reproducible manner at the venous anastomosis of the unbanded but not the banded grafts, as evidenced by combined intimal-medial thickness measurements: unbanded grafts 0.68 +/- 0.13 mm (p less than 0.01 versus control), banded grafts 0.25 +/- 0.03 mm (p greater than 0.05 versus control). Stepwise regression analysis indicated Reynolds number had the best correlation with the development of hyperplasia (r = 0.915, p less than 0.005), this being the first time this correlation has been quantitatively determined. We conclude that flow disturbance or turbulence is a major factor in the development of venous intimal-medial hyperplasia in arteriovenous loop grafts.}, }
@article {pmid2780523, year = {1989}, author = {Vogel, J and Smith, HJ and Müller, E}, title = {[To what extent are oscillometric data of a simple resistor-volume model physically recordable?].}, journal = {Pneumologie (Stuttgart, Germany)}, volume = {43}, number = {7}, pages = {324-330}, pmid = {2780523}, issn = {0934-8387}, mesh = {*Airway Resistance ; Algorithms ; Humans ; Lung/physiopathology ; Lung Volume Measurements/*instrumentation ; *Models, Biological ; Oscillometry/*instrumentation ; Pulmonary Emphysema/physiopathology ; *Pulmonary Ventilation ; }, abstract = {To obtain data on the volume-dependence of the oscillatory parameters of the Siregnost FD 5, we investigated the course of iso-volume and iso-resistance lines in a simple mechanical resistor-volume model in the different coordinate systems, initially in the absence of additional superimposed stationary flow. While the P-psi diagram reveals no uniform course, and no preferential relationship of changes in resistance to P or Ros, or of changes in volume to psi, such a relationship develops on transformation to the Rre-phi and the Rre-X diagram. Rre proves to contain not only the purely resistor component, but also a reactance-proportional or inversely volume-proportional component, which is apparently due to internal friction resulting from volume compression. On the other hand, reactance is almost totally derivable from volume compression. With reference to the theoretical Franken model and others (1981), we discussed the influence of various physical factors on the impedance of a tube segment, and the different volume-dependence of impedance of closed- and open-ended cylindrical tubes. Further work on the theoretical consideration of the forced oscillation technique will examine the influence of additional superimposed stationary flow, which has a considerable effect on the resistor-volume model. Furthermore, the critical value of Reynold's number may be expected to be exceed in the FD 5 reference tube already at low respiratory flow.}, }
@article {pmid2670533, year = {1989}, author = {Svartengren, M and Anderson, M and Philipson, K and Camner, P}, title = {Human lung deposition of particles suspended in air or in helium/oxygen mixture.}, journal = {Experimental lung research}, volume = {15}, number = {4}, pages = {575-585}, doi = {10.3109/01902148909069619}, pmid = {2670533}, issn = {0190-2148}, mesh = {Administration, Inhalation ; Adult ; Airway Resistance/drug effects ; Bronchi/*metabolism ; Female ; Helium/*pharmacokinetics ; Humans ; Male ; Methacholine Chloride ; Methacholine Compounds/pharmacology ; *Microspheres ; Mouth/*metabolism ; Oxygen/*pharmacokinetics ; Pharynx/*metabolism ; Polytetrafluoroethylene ; }, abstract = {Deposition in mouth and throat and the fraction of alveolarly deposited particles in the lung of 3.6- to 3.8-microns Teflon particles labeled with 99mTc were estimated in nine healthy subjects. The particles were inhaled in air or helium/oxygen mixture with a flow of 0.5 l/s by subjects with or without induced bronchoconstriction. The bronchoconstriction (two- to threefold increase in airway resistance) was induced by an aerosol of methacholine bromide. As the Reynolds number is three times lower for the helium/oxygen mixture than for air, and the sedimentation rate of the particles is about the same in both, a different regional deposition between particles suspended in air and helium/oxygen mixture should be due to turbulence. Deposition in mouth and throat did not differ significantly between air and the helium/oxygen mixture. The alveolarly deposited fraction tended to be larger for unconstricted airways and was significantly larger for constricted airways for inhalations in the helium/oxygen mixture compared to air. In real life, air pollutants and therapeutic aerosols may be inhaled with larger flow rates and broncho-constriction may be more pronounced in patients, so that deposition of particles due to turbulence can be important.}, }
@article {pmid2723278, year = {1989}, author = {Krabill, KA and Sung, HW and Tamura, T and Chung, KJ and Yoganathan, AP and Sahn, DJ}, title = {Factors influencing the structure and shape of stenotic and regurgitant jets: an in vitro investigation using Doppler color flow mapping and optical flow visualization.}, journal = {Journal of the American College of Cardiology}, volume = {13}, number = {7}, pages = {1672-1681}, doi = {10.1016/0735-1097(89)90363-x}, pmid = {2723278}, issn = {0735-1097}, mesh = {Blood Flow Velocity ; Cardiac Output ; Coronary Circulation ; Echocardiography, Doppler/*methods ; Humans ; Models, Cardiovascular ; Models, Structural ; Pulmonary Valve Insufficiency/*diagnosis ; Pulsatile Flow ; Syringes ; }, abstract = {To evaluate factors influencing the structure and shape of stenotic and regurgitant jets, Doppler color flow mapping and optical flow visualization studies were performed with use of a syringe model with a constant rate of ejection to simulate jets of valvular regurgitation and a pulsatile flow model of the right heart chambers to simulate jets of mild, moderate and severe valvular pulmonary stenosis. Ink-(0 to 40%) glycerol-water jets (viscosity 1 to 3.5 centiPoise) were produced by injecting the fluid at a constant rate into a 10 gallon rectangular reservoir of the same still fluid through 1.4 and 3.4 mm needles. The Doppler color flow scanners imaged the laminar jet length within 3 mm of actual jet length (2 to 6 cm) and the jet width within 2 to 3 mm of the actual jet width. Jet flows with Reynolds numbers ranging from 230 to 1,200 injected into still fluid yielded jet length/width ratios that decreased with increasing Reynolds numbers and leveled off to a length/width ratio of 5-6:1 at a Reynolds number near 600. When the fluid reservoir was swirled to better mimic the effect of flow entering the same cardiac chamber from a second source, the jets showed diminution of the jet length/width ratio and a clearly defined zone of turbulence. Studies of the pulsatile flow model were performed at cardiac outputs of 1 to 6 liters/min for the normal and each stenotic valve. Mild stenosis had an orifice area of 2.8 cm2, moderate stenosis an area of 1.0 cm2 and severe stenosis an area of 0.5 cm2. Laminar jet length represented the length of the total jet, which had a symmetric width and was measured from the valve opening to a region where the jet exhibited a spray effect. Laminar jet lengths (0.2 to 1.1 cm) were imaged by Doppler color flow mapping and optical visualization only in the moderate and severely stenotic valves and only at flows less than or equal to 3 liters/min (mean Reynolds numbers less than or equal to 3,470). Beyond this flow rate the jets exhibited a spray effect. Laminar jet length/width ratio approached unity with an increased amount of valvular stenosis and higher flow volumes (cardiac output). Proximal aliasing was present in each valve studied. the length of aliasing (0 to 3.2 cm) proximal to the valve was longer with increased flow rates and increased amounts of stenosis.(ABSTRACT TRUNCATED AT 400 WORDS)}, }
@article {pmid2923275, year = {1989}, author = {Horsfield, K and Woldenberg, MJ}, title = {Diameters and cross-sectional areas of branches in the human pulmonary arterial tree.}, journal = {The Anatomical record}, volume = {223}, number = {3}, pages = {245-251}, doi = {10.1002/ar.1092230302}, pmid = {2923275}, issn = {0003-276X}, mesh = {Arteries/anatomy &amp; histology ; Humans ; Models, Cardiovascular ; *Pulmonary Circulation ; }, abstract = {Measurements were made of the diameters of the three branches meeting at each of 1,937 bifurcations in the pulmonary arterial tree, using resin casts from two fully inflated human lungs. Cross-sectional areas of the parent branch and of the daughter branches were calculated and plotted on a log-log plot, which showed that mean cross-sectional area increases in a constant proportion of 1.0879 at bifurcations. The mean value of the ratio of daughter branch diameters at bifurcations was 0.7849. The mean value of the exponent z in the equation flow = k (diameter(z)) was found to be 2.3 +/- 0.1, which is equal to the optimal value for minimizing power and metabolic costs for fully developed turbulent flow. Although Reynolds number may exceed 2,000 in the larger branches of the pulmonary artery, turbulent flow probably does not occur, and in the peripheral branches Reynolds number is always low, excluding turbulent flow in these branches. This finding seems to be incompatible with the observed value of z. A possible explanation may be that other factors may need to be taken into account when calculating the theoretical optimum value of z for minimum power dissipation, such as the relatively short branches and the disturbances of flow occurring at bifurcations. Alternatively, higher arterial diameters reduce acceleration of the blood during systole, reduce turbulent flow, and increase the reservoir function of the larger arteries. These higher diameters result in a lower value of z.}, }
@article {pmid2747233, year = {1989}, author = {Yamaguchi, R}, title = {Distribution of mass transfer rate and wall shear stress behind simple rectangular stenosis in pulsating flow.}, journal = {Journal of biomechanical engineering}, volume = {111}, number = {1}, pages = {47-54}, doi = {10.1115/1.3168339}, pmid = {2747233}, issn = {0148-0731}, mesh = {Arteriosclerosis/*etiology/physiopathology ; Humans ; Mathematics ; *Models, Cardiovascular ; *Pulsatile Flow ; *Rheology ; Stress, Mechanical ; }, abstract = {The distributions of mass transfer rate and wall shear stress in sinusoidal laminar pulsating flow through a two-dimensional asymmetric stenosed channel have been studied experimentally and numerically. The distributions are measured by the electrochemical method. The measurement is conducted at a Reynolds number of about 150, a Schmidt number of about 1000, a nondimensional pulsating frequency of 3.40, and a nondimensional flow amplitude of 0.3. It is suggested that the deterioration of an arterial wall distal to stenosis may be greatly enhanced by fluid dynamic effects.}, }
@article {pmid2747231, year = {1989}, author = {Xue, H and Fung, YC}, title = {Persistence of asymmetry in nonaxisymmetric entry flow in a circular cylindrical tube and its relevance to arterial pulse wave diagnosis.}, journal = {Journal of biomechanical engineering}, volume = {111}, number = {1}, pages = {37-41}, doi = {10.1115/1.3168337}, pmid = {2747231}, issn = {0148-0731}, mesh = {Blood Flow Velocity ; Humans ; Medicine, Chinese Traditional ; *Models, Cardiovascular ; Models, Structural ; *Pulsatile Flow ; *Pulse ; *Rheology ; }, abstract = {In an experiment motivated by the study of arterial blood flow along the lines suggested by the traditional Chinese medicine, the flow in a pipe whose lumen was blocked by a semi-circular plug two tube-diameters long was visualized by suspended particles, recorded by cinematography, and analyzed digitally. The Reynolds number was in the range of 100 to 450 based on the pipe diameter, similar to that of blood flow in the radial artery in the arms of man. The blockage was found to have a profound effect on the velocity profile of the flow in the wake, but it had little influence on the symmetry of the velocity profile upstream of the block, except in its immediate neighborhood. When the end conditions far away from the block were steady, the flow in the wake was steady. The asymmetry of the flow in the wake can be judged by the deviation of the location of the maximum axial velocity from the center line of the pipe as seen in the plane of symmetry of the blockage. Our results show that the deviation can be described as the sum of two components. The first is a strong one which decays exponentially in an entry length which is about twice as long as the classical Boussinesq entry length of axisymmetric flow. The second is a weaker component which is wavy spatially and persists far downstream (many times the entry length). The separated flow and vortex system behind the blockage are sensitive to the flow rate.(ABSTRACT TRUNCATED AT 250 WORDS)}, }
@article {pmid2804275, year = {1989}, author = {Huyghe, JM and Oomens, CW and van Campen, DH}, title = {Low Reynolds number steady state flow through a branching network of rigid vessels II. A finite element mixture model.}, journal = {Biorheology}, volume = {26}, number = {1}, pages = {73-84}, doi = {10.3233/bir-1989-26106}, pmid = {2804275}, issn = {0006-355X}, mesh = {Animals ; *Microcirculation ; *Models, Cardiovascular ; Rats ; Regional Blood Flow ; *Rheology ; }, abstract = {This research aims at formulating and verifying a finite element mixture formulation for blood perfusion. The equations derived in a companion paper [3] are discretized according to the Galerkin method. A flow experiment in a rigid model of a vascular tree of about 500 vessels is performed in order to verify the finite element mixture formulation. Although the comparison of numerical results and experimental measurements is not conclusive as far as the validity of the theory is concerned, the results do suggest that the finite element model has predictive power in the case of low Reynolds number steady-state flow of a Newtonian fluid in a rigid vascular tree.}, }
@article {pmid2804274, year = {1989}, author = {Huyghe, JM and Oomens, CW and van Campen, KH and Heethaar, RM}, title = {Low Reynolds number steady state flow through a branching network of rigid vessels: I. A mixture theory.}, journal = {Biorheology}, volume = {26}, number = {1}, pages = {55-71}, doi = {10.3233/bir-1989-26105}, pmid = {2804274}, issn = {0006-355X}, mesh = {Mathematics ; *Microcirculation ; *Models, Cardiovascular ; Regional Blood Flow ; *Rheology ; }, abstract = {A mixture theory has been used to formulate a theory of blood perfusion. By means of a formal averaging procedure the discrete network of microvessels is transformed into a continuum. During this procedure, the distinction between arterioles, capillaries and venules is preserved by means of an arteriovenous parameter. In this paper, two equations are derived for the case of low Reynolds number steady-state flow through a rigid vessel network: the extended Darcy equation and the continuity equation. A verification of the theory is presented, on the basis of a network analysis.}, }
@article {pmid2777824, year = {1989}, author = {Klanchar, M and Tarbell, JM}, title = {Pressure drop and flow rate measurements in a human aortic bifurcation cast for steady and pulsatile flow.}, journal = {Journal of biomechanics}, volume = {22}, number = {5}, pages = {491-500}, doi = {10.1016/0021-9290(89)90210-8}, pmid = {2777824}, issn = {0021-9290}, support = {HL26824/HL/NHLBI NIH HHS/United States ; HL35549/HL/NHLBI NIH HHS/United States ; }, mesh = {Aged ; Aorta/*physiology ; Biomechanical Phenomena ; Blood Pressure ; Female ; Humans ; *Models, Cardiovascular ; *Pulsatile Flow ; *Rheology ; Stress, Mechanical ; Vascular Resistance ; }, abstract = {Pressure drop and flow rate measurements in a rigid cast of a human aortic bifurcation under both steady and physiological pulsatile flow conditions are reported. Integral momentum and mechanical energy balances are used to calculate impedance, spatially averaged wall shear stress and viscous dissipation rate from the data. In the daughter branches, steady flow impedance is within 30% of the Poiseuille flow prediction, while pulsatile flow impedance is within a factor of 2 of fully developed, oscillatory, straight tube flow theory (Womersley theory). Estimates of wall shear stress are in accord with measurements obtained from velocity profiles. Mean pressure drop and viscous dissipation rate are elevated in pulsatile flow relative to steady flow at the mean flow rate, and the exponents of their Reynolds number dependence are in accord with available theory.}, }
@article {pmid2605329, year = {1989}, author = {Schmid-Schönbein, GW and Lee, SY and Sutton, D}, title = {Dynamic viscous flow in distensible vessels of skeletal muscle microcirculation: application to pressure and flow transients.}, journal = {Biorheology}, volume = {26}, number = {2}, pages = {215-227}, doi = {10.3233/bir-1989-26209}, pmid = {2605329}, issn = {0006-355X}, mesh = {Animals ; Blood Flow Velocity/physiology ; Blood Pressure/physiology ; Blood Vessels/physiology ; Elasticity ; Hemodynamics ; Microcirculation/physiology ; Models, Cardiovascular ; Muscles/*blood supply ; Rats ; }, abstract = {Blood flow in the microcirculation of the rat skeletal muscle during transient changes of arterial pressure is analyzed theoretically. Although flow in such small vessels is quasi-steady and has a very low Reynolds number, time-dependent nonuniform flows along the length of the blood vessels can be observed due to vessel distensibility. The governing equations for a single microvessel are derived using previously measured microvessel elasticity, and several solutions to different inflow and outflow pressures and flow conditions are investigated. The results indicate that when such distensible microvessels are subjected to a step increase of arterial pressure, the arterial flow shows a rapid overshoot followed by a progressive decay to steady-state. An arterial step flow induces a different response which takes the form of a monotonically increasing pressure. Pressure and flows are nonuniform along the vessel length during such transients. In-vitro whole organ pressure-flow data are presented in the dilated rat gracilis muscle which qualitatively agree with the theoretical predictions.}, }
@article {pmid2605323, year = {1989}, author = {Fukushima, T and Matsuzawa, T and Homma, T}, title = {Visualization and finite element analysis of pulsatile flow in models of the abdominal aortic aneurysm.}, journal = {Biorheology}, volume = {26}, number = {2}, pages = {109-130}, doi = {10.3233/bir-1989-26203}, pmid = {2605323}, issn = {0006-355X}, mesh = {Aorta, Abdominal/physiopathology ; Aortic Aneurysm/*physiopathology ; Hemodynamics ; Mathematics ; Models, Cardiovascular ; Pulsatile Flow ; }, abstract = {Pulsatile flows in glass models simulating fusiform and lateral saccular aneurysms were investigated by a flow visualization method. When resting fluid starts to flow, the initial fluid motion is practically irrotational. After a short period of time, the flow began to separate from the proximal wall of the aneurysm. Then the separation bubble or vortex grew rapidly in size and filled the whole area of the aneurysm circumferentially. During this period of time, the center of the vortex moved from the proximal end to the distal point of the aneurysm. The transient reversal flow, for instance, which may occur at the end of the ejection period, passed between the wall of the aneurysm and the centrally located vortex. When the rate and pulsatile frequency of flow were high, the vortex broke down into highly disturbed flow (or turbulence) at the distal portion of the aneurysm. The same effect was observed when the length of the aneurysm was increased. A reduction in pulsatile amplitude made the flow pattern close to that in steady flow. A finite element analysis was made to obtain velocity and pressure fields in pulsatile flow through a tube with an axisymmetric expansion. Calculations were performed with the pulsatile flows used in the visualization experiment in order to study the effects of change in the pulsatile wave form by keeping the time-mean Reynolds number and Womersley's parameter unchanged. Calculated instantaneous patterns of velocity field and stream lines agreed well with the experimental results. The appearance and disappearance of the vortex in the dilated portion and its development resulted in complex distributions of pressure and shear fields. Locally minimum and maximum values of wall shear stress occurred at points just upstream and downstream of the distal end of the expansion when the flow rate reached its peak.}, }
@article {pmid3256729, year = {1988}, author = {Li, JK}, title = {Laminar and turbulent flow in the mammalian aorta: Reynolds number.}, journal = {Journal of theoretical biology}, volume = {135}, number = {3}, pages = {409-414}, doi = {10.1016/s0022-5193(88)80255-8}, pmid = {3256729}, issn = {0022-5193}, mesh = {Anatomy, Comparative ; Animals ; Aorta/*physiology ; Biometry ; Body Height ; Body Weight ; Dogs ; Horses ; Humans ; Mammals/*physiology ; Rats ; Regional Blood Flow ; }, abstract = {Laminar to turbulent flow transition in the mammalian aorta is generally characterized by Reynolds number. When dimensional analysis is applied to obtain the Reynolds number in allometric form, it is found that this number is not invariant of body weight but is approximately proportional to body length dimensions. This implies that flow in the aorta of large mammals is turbulent and laminar in smaller mammals during most of ventricular ejection. Since Reynolds number is defined for steady flow through rigid tubes, it may not reflect the actual fluid behavior of pulsatile flow in compliant vessels such as the aorta. In addition, turbulence is frequency dependent. The larger compliance of the aorta and the slower heart rate in larger mammals and the shorter entrance length and higher heart rate in smaller mammals lead to equal prevalence of turbulence. The consequence is that the aortic flow waveforms remain similar in all mammals.}, }
@article {pmid3205016, year = {1988}, author = {Back, LH and Kwack, EY and Crawford, DW}, title = {Flow measurements in an atherosclerotic curved, tapered femoral artery model of man.}, journal = {Journal of biomechanical engineering}, volume = {110}, number = {4}, pages = {310-319}, doi = {10.1115/1.3108447}, pmid = {3205016}, issn = {0148-0731}, support = {HL 23619-05/HL/NHLBI NIH HHS/United States ; }, mesh = {Arteriosclerosis/*physiopathology ; Blood Flow Velocity ; Blood Pressure ; Femoral Artery/anatomy &amp; histology/*physiopathology ; Hemodynamics ; Humans ; *Models, Cardiovascular ; Models, Structural ; Physical Exertion ; Pulsatile Flow ; Regional Blood Flow ; Stress, Mechanical ; }, abstract = {Flow visualization and pressure measurements were made for physiological conditions in a model derived from a femoral angiogram of a patient with lesion localization on the inner curvature wall and with vessel taper. Effects of curvature and taper were evaluated separately in other curved, tapered, smooth and straight, tapered, smooth models. Double helical secondary flow patterns were modified by plaque on the inner wall, and flow separations were observed between plaques at higher flow rates and Reynolds numbers. Pressure drop data for the plaque simulation model were similar in trend with Reynolds number as for the smooth model, but flow resistances were 25 to 40 percent higher. Significant pressure drops were measured due to the mild taper which could be estimated from momentum considerations, and smaller increased pressure drops were found due to curvature effects at the higher Dean numbers. Flow resistances for in vivo pulsatile flow simulation were about 10 percent higher than for steady flow for the plaque model, whereas no differences were observed for the smooth model.}, }
@article {pmid3060678, year = {1988}, author = {Tamura, T and Fronek, A}, title = {Shear-layer detection in poststenotic flow by spectrum analysis of Doppler signals.}, journal = {Journal of biomechanical engineering}, volume = {110}, number = {4}, pages = {320-325}, doi = {10.1115/1.3108448}, pmid = {3060678}, issn = {0148-0731}, support = {HL18977/HL/NHLBI NIH HHS/United States ; }, mesh = {Blood Flow Velocity ; Carotid Artery Diseases/*physiopathology ; Constriction, Pathologic/physiopathology ; Humans ; *Models, Cardiovascular ; Models, Structural ; Regional Blood Flow ; Spectrum Analysis ; Ultrasonography/*methods ; }, abstract = {Spectrum analysis of the Doppler signals was performed 0.5 tube diameters downstream from an axisymmetric constriction with an area reduction of 80 percent in steady flow at a jet Reynolds number of 2840. Both pulsed and continuous wave (CW) Doppler spectra showed significant reverse flow components in the separated flow. The pulsed Doppler spectra exhibited sudden changes when the sample volume crossed the shear layer between the center jet and the separated flow. A power spectrum equation was theoretically derived from continuity of flow to define the Doppler shift frequency for the shear layer velocity. The CW Doppler spectrum showed a minimum spectrum density at a frequency which equalled the shear layer Doppler shift frequency derived from the equation. The pulsed spectra exhibited the sudden changes at the same frequency as well.}, }
@article {pmid3172734, year = {1988}, author = {Fukushima, T and Homma, T and Harakawa, K and Sakata, N and Azuma, T}, title = {Vortex generation in pulsatile flow through arterial bifurcation models including the human carotid artery.}, journal = {Journal of biomechanical engineering}, volume = {110}, number = {3}, pages = {166-171}, doi = {10.1115/1.3108426}, pmid = {3172734}, issn = {0148-0731}, mesh = {Adult ; Aorta, Abdominal/physiology ; Arteries/*physiology ; Carotid Arteries/physiology ; Hemodynamics ; Humans ; In Vitro Techniques ; Middle Aged ; *Models, Cardiovascular ; *Pulsatile Flow ; *Rheology ; }, abstract = {Visualization experiments were performed to elucidate the complicated flow pattern in pulsatile flow through arterial bifurcations. Human common carotid arteries, which were made transparent, and glass-models simulating Y- and T-shaped bifurcations were used. Pulsatile flow with wave forms similar to those of arterial flow was generated with a piston pump, elastic tube, airchamber, and valves controlling the outflow resistance. Helically recirculating flow with a pattern similar to that of the horseshoe vortex produced around wall-based protuberances in circular tubes was observed in pulsatile flow through all the bifurcations used in the present study. This flow type, which we shall refer to as the horseshoe vortex, has also been demonstrated to occur at the human common carotid bifurcation in steady flow with Reynolds numbers above 100. Time-varying flows also produced the horseshoe vortex mostly during the decelerating phase. Fluid particles of dye solution approaching the bifurcation apex diverged, divided into two directions perpendicularly, and then showed helical motion representing the horseshoe vortex formation. While this helical flow was produced, the stagnation points appeared on the wall upstream of the apex. Their position was dependent upon the flow distribution ratio between the branches in the individual arteries. The region affected by the horseshoe vortex was smaller during pulsatile flow than during steady flow. Lowering the Reynolds number together with the Womersley number weakened the intensity of helical flow. A separation bubble, resulting from the divergence or wall roughness, was observed at the outer or inner wall of the branch vessels and made the flow more complicated.}, }
@article {pmid3171649, year = {1988}, author = {MacGregor, RJ and Tajchman, G}, title = {Theory of dynamic similarity in neuronal systems.}, journal = {Journal of neurophysiology}, volume = {60}, number = {2}, pages = {751-768}, doi = {10.1152/jn.1988.60.2.751}, pmid = {3171649}, issn = {0022-3077}, mesh = {Action Potentials ; Mathematics ; *Models, Neurological ; Neurons/*physiology ; Synapses/*physiology ; }, abstract = {1. The techniques of dynamic similarity from the engineering science of fluid mechanics are applied to neuronal systems to suggest how to scale down critical parameters (such as numbers of constituent cells and synapses, synaptic strengths, thresholds, etc.) from naturally occurring systems to computer models. 2. The interconnectivity of a prototypical neuronal junction is defined in terms of the total number of projecting fibers, receiving cells, synapses, and directly connected cell fiber pairs. Critical derivative parameters are defined in terms of these, including: a global convergence factor, alpha ij, which is the ratio of the numbers of projecting fibers to receiving cells; and an interconnectivity completeness parameter or microscopic convergence/divergence parameter, gamma ij, which measures both the percentage of cells to which a given sending fiber projects (and the percentage of fibers from which a given cell receives) and the percentage of cell fiber combinations which are directly connected. 3. Analysis of the differential equations governing neuroelectric activity in constituent neurons suggests the definition of a sensitivity parameter complex, sigma ij (with components eta ij and mu ij) for each ij junction. These numbers represent the ratio of synaptic drive to current leakage in nonactive neurons. 4. A model for quasi-steady firing suggests the definition of a parameter, rho *j, which may be used to characterize the level of activity in a given neuronal population in terms of its synaptic drive and system parameters. It may be considered as the neuronal analog of the Reynolds number in fluid mechanics. 5. The analysis implies that computer models of neuronal systems should be scaled so as to keep the parameters alpha ij, gamma ij, and sigma ij for every junction at the same values as in the corresponding junctions of naturally occurring system being modeled. Equations for a scaling factor, chi, numbers of constituent synapses, thresholds, etc., are provided. The scaling method is illustrated by a computer simulation example and by application to the junction of the perforant path fibers to the granule cells of the hippocampus. 6. The analysis shows that there is a fundamental trade-off in scaled down computer models between verisimilitude at the level of network interconnectivity and verisimilitude at the level of individual neuronal dynamics. 7. The approach of dynamic similarity is discussed with respect to compression of free parameters and predictive comparison of naturally occurring systems.}, }
@article {pmid3403441, year = {1988}, author = {Haselton, FR and Sperandio, PG}, title = {Convective exchange between the nose and the atmosphere.}, journal = {Journal of applied physiology (Bethesda, Md. : 1985)}, volume = {64}, number = {6}, pages = {2575-2581}, doi = {10.1152/jappl.1988.64.6.2575}, pmid = {3403441}, issn = {8750-7587}, mesh = {*Atmosphere ; Humans ; Inhalation ; Models, Anatomic ; *Models, Biological ; Nose/anatomy &amp; histology/*physiology ; *Respiration ; }, abstract = {It is generally accepted that there is little rebreathing of gas exhaled through the nose. A detailed physical model system has been used to quantify and identify the mechanisms responsible for this phenomenon. By the use of a cast of the upper respiratory tract and oscillating flows with a Reynolds number of 500 and nondimensional frequency of 1.6, corresponding to quiet tidal breathing through the nose, dye dilution measurements indicated an efficiency of tidal exchange of 0.95. Flow visualization studies performed to trace the expiratory flow, as well as the streamlines during steady inspiratory flow, support the hypothesis that the high efficiency of exchange is due to radical differences in the velocity fields between inspiratory and expiratory phases of this oscillatory flow. These findings confirm that convective gas exchange between the nose and the atmosphere is highly efficient; however, the underlying mechanism responsible for this exchange also maximizes the exposure of the respiratory system to aerosols contained in the ambient atmosphere.}, }
@article {pmid3379934, year = {1988}, author = {Khodadadi, JM and Vlachos, NS and Liepsch, D and Moravec, S}, title = {LDA measurements and numerical prediction of pulsatile laminar flow in a plane 90-degree bifurcation.}, journal = {Journal of biomechanical engineering}, volume = {110}, number = {2}, pages = {129-136}, doi = {10.1115/1.3108417}, pmid = {3379934}, issn = {0148-0731}, mesh = {Arteries/anatomy &amp; histology ; Mathematics ; *Models, Cardiovascular ; *Pulsatile Flow ; *Rheology ; }, abstract = {An experimental and numerical study of pulsatile laminar flow in a plane 90-degree bifurcation is presented. Detailed LDA velocity measurements of the oscillatory flow field have been carried out. The numerical predictions, which are based on an iterative, finite-difference numerical procedure using primitive dependent variables, are in good agreement with the measurements. The results show that one separation zone is established near the bottom wall of the main duct and another near the upstream wall of the branch. The location and size of the separation zones vary within the cycle and are influenced by the Reynolds number, the flow rate ratio, and the Stokes number.}, }
@article {pmid3347020, year = {1988}, author = {Schmid-Schönbein, GW}, title = {A theory of blood flow in skeletal muscle.}, journal = {Journal of biomechanical engineering}, volume = {110}, number = {1}, pages = {20-26}, doi = {10.1115/1.3108401}, pmid = {3347020}, issn = {0148-0731}, support = {HL 10881-20/HL/NHLBI NIH HHS/United States ; }, mesh = {Animals ; Blood Flow Velocity ; Blood Vessels/physiology ; Blood Viscosity ; Elasticity ; Microcirculation/physiology ; *Models, Cardiovascular ; Muscles/*blood supply/physiology ; Pulsatile Flow ; Rats ; Regional Blood Flow ; }, abstract = {A theoretical analysis of blood flow in the microcirculation of skeletal muscle is provided. The flow in the microvessels of this organ is quasi steady and has a very low Reynolds number. The blood is non-Newtonian and the blood vessels are distensible with viscoelastic properties. A formulation of the problem is provided using a viscoelastic model for the vessel wall which was recently derived from measurements in the rat spinotrapezius muscle (Skalak and Schmid-Schönbein, 1986b). Closed form solutions are derived for several physiologically important cases, such as perfusion at steady state, transient and oscillatory flows. The results show that resting skeletal muscle has, over a wide range of perfusion pressures an almost linear pressure-flow curve. At low flow it exhibits nonlinearities. Vessel distensibility and the non-Newtonian properties of blood both have a strong influence on the shape of the pressure-flow curve. During oscillatory flow the muscle exhibits hysteresis. The theoretical results are in qualitative agreement with experimental observations.}, }
@article {pmid3379083, year = {1988}, author = {Patil, MK and Subbaraj, K}, title = {Finite element analysis of two dimensional steady flow in model arterial bifurcation.}, journal = {Journal of biomechanics}, volume = {21}, number = {3}, pages = {219-233}, doi = {10.1016/0021-9290(88)90173-x}, pmid = {3379083}, issn = {0021-9290}, mesh = {Blood Flow Velocity ; Blood Pressure ; *Iliac Artery ; *Models, Biological ; Models, Structural ; *Regional Blood Flow ; Stress, Mechanical ; }, abstract = {The purpose of the investigation reported in this paper is to determine theoretically the fluid dynamic field in models of common iliac arterial bifurcation and to identify the flow features which might influence the predominant occurrence of atherosclerotic lesions at such sites. This has been accomplished by numerically simulating fluid flow through 90 degrees symmetric bifurcations with branch-to-trunk area ratios of 0.8-1.414 and for Reynolds numbers ranging from 100 to 400. The analysis predicts flow reversal along the outer wall in models with area ratios over unity for high Reynolds number range, while no flow reversal occurred in models with area ratio below unity; a low shear zone along the outer wall and high shear stresses at the divider lip. Adverse pressure gradients are observed along the outer wall downstream of the corner point, the magnitudes increased with Reynolds number for a given branch to area ratio. Biological implication of the results is discussed with specific reference to the sites of atherosclerotic lesions found in man for these geometries.}, }
@article {pmid3347039, year = {1988}, author = {Gardaz, JP and Dorrington, KL and Py, P and Schweizer, A}, title = {Physiological profile during venovenous perfusion in dogs using a polypropylene membrane lung with secondary flows.}, journal = {Journal of biomedical engineering}, volume = {10}, number = {1}, pages = {74-81}, doi = {10.1016/0141-5425(88)90030-1}, pmid = {3347039}, issn = {0141-5425}, mesh = {Animals ; Dogs ; *Extracorporeal Circulation ; Hemodynamics ; Hemoglobins/analysis ; Leukocyte Count ; *Membranes, Artificial ; Polyethylenes ; *Pulmonary Circulation ; *Pulmonary Gas Exchange ; }, abstract = {Venovenous perfusion has been conducted in 12 healthy dogs to examine carbon dioxide (CO2) transfer and haemocompatibility over 9 h during total extracorporeal CO2 removal using a microporous polypropylene membrane lung with secondary flows in the blood channel. The anaesthetized animals were maintained normocapnic by including CO2 in the inspired gases. The CO2 removal was achieved using 0.631 m2 of active membrane, at a pulsatile Reynolds number of 50, and a CO2 extraction from blood of 17.8 ml (STP) dl-1. Gas exchange remained constant during the perfusions. Several aspects of our results suggest that the haemocompatibility of a system of the kind used here is at least as favourable as that of a steady flow device using a continuous silicone rubber membrane of equivalent gas transfer capability.}, }
@article {pmid3253285, year = {1988}, author = {Rindt, CC and van Steenhoven, AA and Reneman, RS}, title = {An experimental analysis of the flow field in a three-dimensional model of the human carotid artery bifurcation.}, journal = {Journal of biomechanics}, volume = {21}, number = {11}, pages = {985-991}, doi = {10.1016/0021-9290(88)90137-6}, pmid = {3253285}, issn = {0021-9290}, mesh = {Blood Flow Velocity ; Carotid Arteries/anatomy &amp; histology/*physiology ; Humans ; *Models, Cardiovascular ; }, abstract = {Steady flow measurements were carried out in a rigid three-dimensional model of the human carotid artery bifurcation at a Reynolds number of 640 and a flow division ratio of 50/50. Both axial and secondary velocities were measured with a laser-Doppler anemometer. In the bulb opposite to the flow divider a zone with negative axial velocities was found with a maximal diameter of about 60% of the local diameter of the branch and a cross-sectional extent of about 25% of the local cross-sectional area. In the bulb the maximum axial velocity shifted towards the divider wall and at the end of the bulb an axial velocity plateau arose near the non-divider wall. Halfway through the bulb, secondary flow showed a vortex through which fluid flowed towards the divider wall near the bifurcation plane and back towards the non-divider wall near the upper walls.}, }
@article {pmid3253276, year = {1988}, author = {Jones, SA and Fronek, A}, title = {Effects of vibration on steady flow downstream of a stenosis.}, journal = {Journal of biomechanics}, volume = {21}, number = {11}, pages = {903-914}, doi = {10.1016/0021-9290(88)90128-5}, pmid = {3253276}, issn = {0021-9290}, mesh = {Arterial Occlusive Diseases/*physiopathology ; Blood Flow Velocity ; *Hemodynamics ; Humans ; *Models, Cardiovascular ; *Vibration ; Viscosity ; }, abstract = {A physical model was used to test the effects of vibrations on the position of transition to turbulence (zt) downstream of a constriction. Constrictions were inserted in a length of clear plastic (Tygon) tubing and vibrated. Water was the fluid medium and flow was visualized with India ink. The frequency and velocity of vibration were monitored. For a given constriction and flow velocity, there was a band of frequencies which caused zt to move upstream. This band corresponded to frequencies of flow disturbances as measured with a hot-film anemometer without vibration. Both flow-visualization and hot-film frequencies were correlated via a Strouhal number to the Reynolds number and contraction ratio of the flow. Values of zt decreased with increasing vibration amplitude. The critical Reynolds number for turbulence was also decreased by vibration. These results are of importance in the diagnosis of vascular disease and the design of physical models of stenotic flows.}, }
@article {pmid3250628, year = {1988}, author = {Nomura, H and Ishikawa, C and Komatsuda, T and Ando, J and Kamiya, A}, title = {A disk-type apparatus for applying fluid shear stress on cultured endothelial cell.}, journal = {Biorheology}, volume = {25}, number = {3}, pages = {461-470}, doi = {10.3233/bir-1988-25307}, pmid = {3250628}, issn = {0006-355X}, mesh = {Cells, Cultured ; Endothelium, Vascular/*physiology ; Mathematics ; Methods ; Rheology ; Stress, Mechanical ; }, abstract = {To study the effect of fluid shear stress on cultured endothelial cells, we have developed an apparatus for the stress creation, which consists of a stainless steel disk driven by an electric DC motor and a stage to place a culture dish and to adjust the distance between the disk and the dish. When the disk is rotated, a concentric fluid movement occurs in the culture medium in the dish and exerts the shear stress on the endothelial cells cultured on the bottom of the dish. A theoretical analyses concerning the induced concentric flow velocity predicted that when the angular velocity of the disk rotation (omega) is slow enough to maintain a Reynolds' number of the order of 10, the exerted wall shear stress tau w on the endothelial cell monolayer is given for a constant as tau w = mu r omega/d where mu is the viscosity of the medium, d the distance from the plate to the monolayer and r the radial distance from the center of the dish. When omega is varied in a sinusoidal mode tau w also becomes sinusoidal, thus allowing to apply a pulsatile stress. In vitro experiments carried out to examine the validity of the theoretical results, using a suspension of polystyrene as a tracer with the ordinary culture medium and 99% ethanol, revealed excellent agreement of the measured velocity profiles with the predicted ones. The results demonstrated that the present apparatus can create both the steady and pulsatile wall shear stress on the culture cell layer as expected, unless Reynolds' number greatly exceeds the level of 10.}, }
@article {pmid3230367, year = {1988}, author = {Pal, D and Rudraiah, N and Devanathan, R}, title = {The effects of slip velocity at a membrane surface on blood flow in the microcirculation.}, journal = {Journal of mathematical biology}, volume = {26}, number = {6}, pages = {705-712}, pmid = {3230367}, issn = {0303-6812}, mesh = {Blood Flow Velocity ; Blood Pressure ; Blood Viscosity ; Microcirculation/*physiology ; *Models, Cardiovascular ; *Models, Theoretical ; Permeability ; }, abstract = {Closed-form solutions are presented for blood flow in the microcirculation by taking into account the influence of slip velocity at the membrane surface. In this study, the convective inertia force is neglected in comparison with that of blood viscosity on the basis of the smallness of the Reynolds number of the flow in microcirculation. The permeability property of the blood vessel is based on the well known Starling's hypothesis. The effects of slip coefficient on the velocity and pressure fields are clearly depicted.}, }
@article {pmid3228538, year = {1988}, author = {Charlesworth, D and Gerrard, JH}, title = {Atherosclerosis and disturbances in flow.}, journal = {Annals of vascular surgery}, volume = {2}, number = {1}, pages = {57-62}, doi = {10.1016/S0890-5096(06)60778-4}, pmid = {3228538}, issn = {0890-5096}, mesh = {Arteriosclerosis/*physiopathology ; Blood Flow Velocity ; Femoral Artery/*physiopathology ; Humans ; Models, Cardiovascular ; Numerical Analysis, Computer-Assisted ; }, abstract = {From experiments on flow in a tapered tube it was found that a ring vortex could be produced in certain circumstances. The parameter which determines the vortex formation is the product of peak reversed flow, Reynolds number, and the taper angle of the tube. Using dimensional analysis, conditions in a model were adjusted to simulate those in the unbranched superficial femoral artery. A vortex was formed when there was sufficiently strong reversed flow, and it did so over a range of nondimensional frequencies similar to those which occur in the artery in humans. When the vortex passes up the tube, the surface stresses oscillate at a frequency an order of magnitude higher than the pulse frequency. It is possible that this oscillating stress could trigger atherosclerosis. The initiating ring vortex could be induced by a slight stenosis distal to the site of atherogenesis.}, }
@article {pmid3196828, year = {1988}, author = {Yamaguchi, T and Hanai, S}, title = {To what extent does a minimal atherosclerotic plaque alter the arterial wall shear stress distribution? A model study by an electrochemical method.}, journal = {Biorheology}, volume = {25}, number = {1-2}, pages = {31-36}, doi = {10.3233/bir-1988-251-209}, pmid = {3196828}, issn = {0006-355X}, mesh = {Arteries/*physiopathology ; Arteriosclerosis/*physiopathology ; Blood Flow Velocity ; Electrochemistry ; Humans ; Models, Cardiovascular ; Stress, Mechanical ; }, abstract = {An electrochemical surface shear stress measurement was applied to a model of very thin unilateral arterial stenosis (height of 1/8 of the model pipe diameter with very smooth surface). Three dimensional wall shear stress distribution was measured under steady flow field from a relatively low Reynolds number, Re = 270, to a high Reynolds number, Re = 1200. There was a characteristic high and low wall shear distribution pattern around the stenosis. There were also remarkable high shear stress areas on the opposite wall and both side walls of the stenosis. It was clearly shown that three dimensional structure of the flow field, hence, the wall shear stress distribution, is affected by a minimal change on the arterial wall.}, }
@article {pmid2974848, year = {1988}, author = {Yamaguchi, T and Kikkawa, S and Tanishita, K and Sugawara, M}, title = {Spectrum analysis of turbulence in the canine ascending aorta measured with a hot-film anemometer.}, journal = {Journal of biomechanics}, volume = {21}, number = {6}, pages = {489-495}, doi = {10.1016/0021-9290(88)90241-2}, pmid = {2974848}, issn = {0021-9290}, mesh = {Animals ; Aorta, Thoracic/*physiology ; Blood Flow Velocity ; Blood Pressure ; Computer Graphics ; Dogs ; Electrocardiography/instrumentation ; *Rheology ; Signal Processing, Computer-Assisted ; Ventricular Function ; }, abstract = {We measured turbulence velocity in the canine ascending aorta using a hot-film anemometer. Blood flow velocity was measured at various points across the ascending aorta approximately 1.5-2 times the diameter downstream from the aortic valve. The turbulence spectrum was calculated and its characteristics were examined in connection with the mean Reynolds number and/or measuring positions. In the higher wave number range the values of the turbulence spectra were higher at larger mean Reynolds number. In the higher wave number range, the values of the turbulence spectra were higher at points closer to the centerline of the aorta, when the mean Reynolds number was relatively large. The patterns of the turbulence spectra at various points outside the boundary layer on the aortic wall were similar.}, }
@article {pmid2974211, year = {1988}, author = {de Knecht, S and Hopman, JC and Alsters, JL and Daniëls, O and Hoeks, AP and Reneman, RS}, title = {Automated calculation of stenosis diameters from the width of the velocity jet with the use of a multi-gate pulsed Doppler system.}, journal = {Ultrasound in medicine &amp; biology}, volume = {14}, number = {7}, pages = {575-581}, doi = {10.1016/0301-5629(88)90124-x}, pmid = {2974211}, issn = {0301-5629}, mesh = {Algorithms ; Arterial Occlusive Diseases/diagnosis/*pathology ; Blood Flow Velocity ; Constriction, Pathologic ; Humans ; Models, Cardiovascular ; Rheology ; Ultrasonography/*methods ; }, abstract = {The aim of this study was to evaluate an algorithm for automated estimation of the width of a jet stream originating from a stenosis. The evaluation was performed in a pulsatile flow model. The width of the jetstream was assessed by measuring the diameter of the region with relatively high velocities (the jet) in the velocity profiles, as recorded with a multi-gate pulsed Doppler system. Measurements were performed at 3, 6, and 9 mm downstream of three different stenoses (stenosis diameter: 3, 5, or 8 mm) at different Reynolds numbers (200-1600) based on time averaged flow velocity for a tube of diameter 15 mm. The developed algorithm was used successfully for automated detection and quantification of jet flow diameters downstream to a stenosis. The algorithm can be used for calculating the stenosis diameter notwithstanding a theoretically predictable overestimation of about 1 mm, depending on the Reynolds number and the distance from the stenosis.}, }
@article {pmid2963847, year = {1988}, author = {Abdallah, SA and Hwang, NH}, title = {Arterial stenosis murmurs: an analysis of flow and pressure fields.}, journal = {The Journal of the Acoustical Society of America}, volume = {83}, number = {1}, pages = {318-334}, doi = {10.1121/1.396433}, pmid = {2963847}, issn = {0001-4966}, mesh = {Arterial Occlusive Diseases/*physiopathology ; *Blood Flow Velocity ; *Blood Pressure ; Constriction, Pathologic/physiopathology ; Equipment Design ; Humans ; *Models, Cardiovascular ; Rheology ; Transducers, Pressure ; }, abstract = {The flow field distal to an arterial stenosis is simulated by a confined turbulent jet with moderate Reynolds numbers. The wall pressure fluctuations are related to the momentum fluctuations of the jet by the Poisson equation. A Green's function was derived to satisfy the boundary conditions on a cylindrical surface. This allows the solution of the Poisson's equation to include only a volume integral of the fluctuating momentum, weighed by the relative distance between the source and the sensor. The velocity fluctuations on the jet centerline and at the middle of the shear layer were measured using a laser Doppler anemometer. The wall pressure fluctuations were detected simultaneously by an array of nine wall-mounted pressure transducers along the axial direction. Cross correlation performed between the velocity and pressure fluctuations reveals that the pressure fluctuations were mostly imposed by the passage of turbulent eddies with a convective velocity that is a function of the jet exit velocity. The Strouhal number, defined by the frequency of the passing large-scale structure, is a function of the initial conditions only very close to the jet exit. Further downstream, where the effect of the initial conditions is lost, the Strouhal number approaches a constant irrespect of the jet Reynolds number. The contribution of a source near the jet exit to wall pressure fluctuation near the reattachment is rather weak due to the rapidly decaying weighting function in the axial direction. However, for sources located within one nozzle diameter from the sensor, the cross-spectral density function has a high magnitude with maximum coherence where the pressure spectral changes its slope.}, }
@article {pmid3625883, year = {1987}, author = {Ku, DN and Klafta, JM and Gewertz, BL and Zarins, CK}, title = {The contribution of valves to saphenous vein graft resistance.}, journal = {Journal of vascular surgery}, volume = {6}, number = {3}, pages = {274-279}, pmid = {3625883}, issn = {0741-5214}, mesh = {*Blood Vessel Prosthesis ; Humans ; In Vitro Techniques ; Perfusion ; Saphenous Vein/*physiology/transplantation ; *Vascular Patency ; Vascular Resistance ; }, abstract = {Saphenous vein resistance influences graft flow rates and may affect graft patency in lower limb revascularization. To quantitate specifically the contribution of saphenous vein valves to this resistance, 10 human saphenous veins (mean length 68 cm, diameter 0.42 mm, and 5.2 valves per vein) were perfused with water under carefully controlled pressure gradients designed to simulate different peripheral resistances in the outflow bed. The Reynolds number was maintained at 350 to 600, within the physiologic range for in vivo grafts. Veins were perfused under both venous (10 mm Hg) and arterial (100 mm Hg) mean pressures to determine the effects of distension on the overall resistance of the conduit. The valves were bisected according to Leather's techniques and flow was measured in both directions, antegrade (simulating "reversed" grafts) and retrograde (simulating "in situ" grafts). Data (mean +/- standard error) were normalized to the baseline flow for each vein with intact valves and expressed as a percentage change. Data were analyzed by means of Student's t test (p less than 0.05). Baseline antegrade flow with intact valves averaged 71.0 +/- 3.0 ml/min at pressure gradients (delta P) of 10 mm Hg and 95.0 +/- 2.6 ml/min for delta P = 20 mm Hg. After valve incision, antegrade flow (reversed) increased an average of 29% at both pressure gradients. Retrograde flow (in situ) through the bisected valves was only 19% greater than baseline antegrade flow and was significantly less than antegrade flow through bisected valves. The difference is explained by theoretic considerations of stenosis area and orifice shape. The increases in flow did not correlate with vein length or diameter, nor did flow change with different distension pressures.(ABSTRACT TRUNCATED AT 250 WORDS)}, }
@article {pmid3116793, year = {1987}, author = {Münch, W and Rüden, H and Schkalle, YD and Thiele, F}, title = {[Vertical flow of germs in a building shaft: physical and microbiological measurements and development of an analogous mathematical model].}, journal = {Zentralblatt fur Bakteriologie, Mikrobiologie und Hygiene. Serie B, Umwelthygiene, Krankenhaushygiene, Arbeitshygiene, praventive Medizin}, volume = {184}, number = {3-4}, pages = {336-358}, pmid = {3116793}, issn = {0932-6073}, mesh = {*Air Microbiology ; *Air Movements ; Air Pressure ; Bacteria/*growth &amp; development ; *Hospital Design and Construction ; Mathematics ; *Models, Biological ; Temperature ; }, abstract = {The air flow and the concentration of microorganisms have been measured in the stair shaft of a hospital. A diving bell-type of pressure-recording instrument and samplers for the microorganisms (impaction device) were used. With this experimental data the flow rate of microorganisms between the floors of the hospital was calculated. A physical model based on numerical calculations using simplified transport equations is proposed, which would be able to predict the flow field and the distribution of microorganisms in a staircase. The calculations have been executed up to a Reynolds number of 400 when the Schmidt number is 0.5 and 1.0. This numerical method can help to reduce the experimental work, as well as, to investigate unknown transport mechanisms of organic and inorganic substances including microorganisms.}, }
@article {pmid3597007, year = {1987}, author = {Kandarpa, K and Davids, N and Gardiner, GA and Harrington, DP and Selwyn, A and Levin, DC}, title = {Hemodynamic evaluation of arterial stenoses by computer simulation.}, journal = {Investigative radiology}, volume = {22}, number = {5}, pages = {393-403}, doi = {10.1097/00004424-198705000-00007}, pmid = {3597007}, issn = {0020-9996}, support = {GM 18674/GM/NIGMS NIH HHS/United States ; HL 07334/HL/NHLBI NIH HHS/United States ; }, mesh = {Arterial Occlusive Diseases/*physiopathology ; Blood Flow Velocity ; *Computer Simulation ; Constriction, Pathologic/physiopathology ; *Hemodynamics ; Humans ; *Models, Cardiovascular ; }, abstract = {A new method to assess the hemodynamic severity of arterial stenoses was proposed and evaluated. It is based on a previously developed finite element computer simulation model for laminar-separated flow in arteries of axially varying cross-section; the present modification allows use of angiographic stenosis shapes acquired by automatic edge-detection algorithms. The method was validated by comparing its results with published experimental and theoretic results for ideal stenosis shapes. At moderate flowrates (Reynolds number = 500), poststenosis flow separation was predicted for moderately severe (75% area reduction) but not for mild (25%) stenoses. For high flowrates (Reynolds number = 900) in a severe stenosis (89%), stagnation and reversed flow were predicted and the experimental nondimensional pressure drop of 48.5 was correctly determined. Bernoulli's Equation, which neglects viscosity, predicted a drop of only 40. For a severe stenosis (89%), even at low Reynolds numbers (50), reversed flow agreeing with other theoretic solutions was predicted. Predictions are especially useful at low flow rates, where experiments are difficult to conduct. The height of the curve on the graph of nondimensional pressure gradient vs. Reynolds number reflects the hemodynamic severity of a particular stenosis; these curves were predicted for moderate and severe ideal stenoses and agree with experiments. A similar analysis is applied to an actual human coronary artery stenosis, and the results are demonstrated to have use in assessing interventions during angiography.}, }
@article {pmid3565285, year = {1987}, author = {Hegesh, JT and Goldberg, SJ and Schwartz, ML}, title = {Analysis of causes of velocity spread during initial deceleration in the ascending aorta in children and young adults.}, journal = {The American journal of cardiology}, volume = {59}, number = {9}, pages = {967-970}, doi = {10.1016/0002-9149(87)91135-0}, pmid = {3565285}, issn = {0002-9149}, mesh = {Adolescent ; Aorta/*physiology ; Blood Flow Velocity ; Child ; Echocardiography ; Humans ; *Myocardial Contraction ; }, abstract = {Factors that predict the magnitude of instantaneous systolic velocities within the Doppler sample volume in the ascending aorta have not been elucidated in normal persons. This study determines whether the magnitude of instantaneous velocity spread in the ascending aorta is related to ascending aortic diameter, Reynolds number or other factors. Ascending aortic velocity tracings and diameters were recorded for 77 normal subjects using a 25 degrees off-axis transducer that permitted beam-flow alignment. Percent instantaneous velocity spread at peak modal velocity, which corresponds temporally to initial deceleration, was determined by dividing instantaneous velocity spread by peak modal velocity. Using standard formulations, values were computed in the ascending aorta of each subject for Reynolds number using peak and mean velocity, Womersley's alpha, and critical oscillatory Reynolds number. The highest correlation occurred for percent instantaneous velocity spread and ascending aortic diameter (r = 0.54) (p less than 0.001). The second highest correlation occurred for percent instantaneous velocity spread and critical oscillatory Reynolds number (r = -0.47) (p less than 0.001). A low but significant correlation (r = 0.30) (p less than 0.05) was found between alpha and percent instantaneous velocity spread. No significant correlation was found between percent instantaneous velocity spread and heart rate (r = 0.23), Reynolds number (r = -0.11) or maximal ascending aortic velocity (r = 0.14). This study demonstrates that percent instantaneous velocity spread in the human aorta is most closely related to ascending aortic diameter, an increase of which will cause a higher percent instantaneous velocity spread at initial deceleration.(ABSTRACT TRUNCATED AT 250 WORDS)}, }
@article {pmid3588831, year = {1987}, author = {Stehbens, WE and Fee, CJ and Stehbens, GR}, title = {Flow through S-shaped glass models simulating arterial tortuosities.}, journal = {Quarterly journal of experimental physiology (Cambridge, England)}, volume = {72}, number = {2}, pages = {201-213}, doi = {10.1113/expphysiol.1987.sp003064}, pmid = {3588831}, issn = {0144-8757}, mesh = {Blood Vessels/*physiology ; Coloring Agents ; Glass ; Humans ; Models, Structural ; *Rheology ; }, abstract = {Flow patterns in twenty-one glass models of S bends were examined using the dye-injection technique. The glass models were of different configurations designed to simulate arterial tortuosities. In each model flow disturbances were observed in the stem distal to the S bend or in the distal portion of the S bend itself at Reynolds numbers below 2000. The disturbances were periodic in nature and mostly regular, but with considerable sensitivity to external disturbances. The sharpness of the flexures appeared to be important in determining the Reynolds number at which flow disturbances occurred. The significance of the flow disturbances is their seeming applicability to the human vascular system.}, }
@article {pmid3323352, year = {1987}, author = {Rieu, R and Bano, S and Pelissier, R and Bergeron, P and Reggi, M and Courbier, R}, title = {Influence of the haemodynamic parameters on the repartition of the flow between an artery and its graft.}, journal = {International angiology : a journal of the International Union of Angiology}, volume = {6}, number = {2}, pages = {147-152}, pmid = {3323352}, issn = {0392-9590}, mesh = {Arterial Occlusive Diseases/physiopathology/surgery ; Arteries/physiopathology ; Blood Flow Velocity ; Blood Pressure ; Graft Occlusion, Vascular/*physiopathology ; *Hemodynamics ; Humans ; *Models, Cardiovascular ; Postoperative Complications/*physiopathology ; *Ultrasonography ; }, abstract = {The aim of this study was to investigate the repartition of the flow between an artery and its graft for several values of the geometric and dynamic parameters (length and severity of the stenosis, Reynolds number and frequency pulse value). The model, fabricated in silicone, was included in an hydrodynamic test bench, allowing to reproduce physiological conditions. Our study showed that the severity of the stenosis was the most influent parameter on the repartition of the flow; in particular, a 75% severity was necessary to obtain a repartition 70-30% between the graft and the artery.}, }
@article {pmid3584156, year = {1987}, author = {Jones, SA and Fronek, A}, title = {Analysis of break frequencies downstream of a constriction in a cylindrical tube.}, journal = {Journal of biomechanics}, volume = {20}, number = {3}, pages = {319-327}, doi = {10.1016/0021-9290(87)90298-3}, pmid = {3584156}, issn = {0021-9290}, mesh = {Arterial Occlusive Diseases/*diagnosis ; Biomechanical Phenomena ; Blood Flow Velocity ; Humans ; Manometry ; Mathematics ; Models, Biological ; }, abstract = {Experiments were performed to correlate steady-flow power spectra downstream of a stenosis in a cylindrical tube with the flow geometry and velocity. The experiments were motivated by the need to improve quantitative phonoangiography. An objective break frequency (fb) was computed from spectra of velocity fluctuations, as measured with a hot film anemometer. Least squares fits with two independent variables were used to find an empirical relationship between a Strouhal number (S2), the contraction ratio (ds/D) and the Reynolds number (Re). The variables D and ds, are, respectively, the unobstructed tubing diameter and the inner diameter of the stenosis. The relationship found was S2 = Re 0.72(ds/D)0.26 The contraction ratio ds/D, can be found from the empirical relation in terms of known parameters. For the hot wire data the average error between the computed value of ds/D and the known value was 2.3%.}, }
@article {pmid3502770, year = {1987}, author = {Rakow, AL and Chappell, ML}, title = {Axial migration of spirulina microalgae in laminar tube flow.}, journal = {Biorheology}, volume = {24}, number = {6}, pages = {763-768}, doi = {10.3233/bir-1987-24626}, pmid = {3502770}, issn = {0006-355X}, mesh = {Cell Movement ; Eukaryota/*physiology ; Rheology/*instrumentation ; }, abstract = {A dilute suspension of Spirulina Microalgae is found to exhibit radial migration in laminar flow in a 650 micron vertical tube. As the tube Reynolds number increases, the particles concentrate in a narrower region around the tube axis. When the turbulent regime is approached, the particles disperse as expected.}, }
@article {pmid3502769, year = {1987}, author = {Yamaguchi, T and Hanai, S}, title = {Measured wall shear stress distribution pattern upstream and downstream of a unilateral stenosis by an electrochemical method.}, journal = {Biorheology}, volume = {24}, number = {6}, pages = {753-762}, doi = {10.3233/bir-1987-24625}, pmid = {3502769}, issn = {0006-355X}, mesh = {Arterial Occlusive Diseases/*physiopathology ; Arteriosclerosis/physiopathology ; Blood Flow Velocity ; Electrochemistry/*instrumentation ; Humans ; Models, Biological ; Rheology ; Stress, Mechanical ; }, abstract = {An electrochemical surface shear stress measurement was applied to a model of unilateral arterial stenosis. The unilateral stenosis model was made up of a removable stenosis plug, in an electrochemical shear stress measurement test section with 100 cathodes. Three dimensional wall shear stress distribution was measured under steady flow field. At a relatively low Reynolds number, Re = 270, there was a characteristic high and low wall shear distribution pattern downstream of the unilateral stenosis. There were also remarkable high shear stress areas on the opposite wall up- and downstream, and both side walls of the stenosis upstream. It was clearly shown that detailed three dimensional structure of the flow field must be studied in order to correlate it to pathological findings.}, }
@article {pmid2965604, year = {1987}, author = {Nandy, S and Tarbell, JM}, title = {Flush mounted hot film anemometer measurement of wall shear stress distal to a tri-leaflet valve for Newtonian and non-Newtonian blood analog fluids.}, journal = {Biorheology}, volume = {24}, number = {5}, pages = {483-500}, doi = {10.3233/bir-1987-24506}, pmid = {2965604}, issn = {0006-355X}, support = {1 R01 HL35549/HL/NHLBI NIH HHS/United States ; }, mesh = {Aortic Valve ; Blood Substitutes/*physiology ; Blood Viscosity ; *Heart Valve Prosthesis ; Humans ; Pulsatile Flow ; *Rheology ; Stress, Mechanical ; }, abstract = {Wall shear stress has been measured by flush-mounted hot film anemometry distal to an Ionescu-Shiley tri-leaflet valve under pulsatile flow conditions. Both Newtonian (aqueous glycerol) and non-Newtonian (aqueous polyacrylamide) blood analog fluids were investigated. Significant differences in the axial distribution of wall shear stress between the two fluids are apparent in flows having nearly identical Reynolds numbers. The Newtonian fluid exhibits a (peak) wall shear rate which is maximized near the valve seat (30 mm) and then decays to a fully developed flow value (by 106 mm). In contrast, the shear rate of the non-Newtonian fluid at 30 mm is less than half that of the Newtonian fluid and at 106 mm is more than twice that of the Newtonian fluid. It is suggested that non-Newtonian rheology influences valve flow patterns either through alterations in valve opening associated with low shear separation zones behind valve leaflets, or because of variations in the rate of jet spreading. More detailed studies are required to clarify the mechanisms. The Newtonian wall shear stresses for this valve are low. The highest value observed anywhere in the aortic chamber was 2.85 N/m2 at a peak Reynolds number of 3694.}, }
@article {pmid3561030, year = {1986}, author = {Chandran, KB and Fatemi, R and Schoephoerster, R}, title = {Dependence of tissue valve leaflet motion on the viscosity of blood analogue fluid.}, journal = {Life support systems : the journal of the European Society for Artificial Organs}, volume = {4}, number = {4}, pages = {289-303}, pmid = {3561030}, issn = {0261-989X}, mesh = {Animals ; *Bioprosthesis ; Blood Pressure ; *Blood Viscosity ; Glycerol ; Heart Rate ; *Heart Valve Prosthesis ; Heart Valves/*physiology ; Image Processing, Computer-Assisted ; Models, Cardiovascular ; Movement ; Prosthesis Design ; Saline Solution, Hypertonic ; Swine ; }, abstract = {The dependence of the leaflet motion of bioprosthetic heart valves on the viscosity of the blood analogue fluid was studied in this work. A pericardial and a porcine tissue valve were mounted in a pulse duplicator and high-speed films were taken to record the motion of the valve leaflets. The blood analogue fluids used were physiological saline with a viscosity coefficient of 1.0 cP, and glycerol solution with a viscosity of 3.5 cP. The transvalvular pressure drop and percentage of regurgitation were also measured with the time-averaged flow rate maintained at 6.00 +/- 0.05 litres/min. Our results show that the leaflets did not stiffen with up to 15 days' exposure to glycerol. Also, there was no substantial difference in the time of opening of the leaflets or in the area of opening of the valves with the two blood analogue fluids. However, the leaflets closed substantially later in the cardiac cycle in the case of glycerol solution, owing to the interaction between the leaflets and the viscosity of the fluid. For proper comparison of the flow dynamics past prosthetic valves at comparable Reynolds number and Womersley number, our results suggest that glycerol solution should be used as the blood analogue fluid for tissue valves also.}, }
@article {pmid2445863, year = {1986}, author = {Ikai, A}, title = {Calculation and experimental verification of the frictional ratio of hagfish proteinase inhibitor.}, journal = {Journal of ultrastructure and molecular structure research}, volume = {96}, number = {1-3}, pages = {146-150}, doi = {10.1016/0889-1605(86)90015-7}, pmid = {2445863}, issn = {0889-1605}, mesh = {Animals ; Fishes/*blood ; Hagfishes/*blood ; *Models, Molecular ; Molecular Conformation ; Protease Inhibitors/*analysis ; alpha-Macroglobulins/*analysis ; }, abstract = {A major structural feature of the alpha-2-macroglobulin-like inhibitor of hagfish described in Osada, Nishigai, and Ikai [(1987) J. Ultrastruct. Mol. Struct. Res. 96, 00-00] was its highly open quaternary structure observed under an electron microscope. We drew a qualitative conclusion that the high frictional ratio obtained from the result of sedimentation study and the large Stokes radius obtained in gel chromatographic experiment were the reflection of such an open quaternary structure. In this paper I present several structural models of hagfish inhibitor based on its electron micrographs and calculate expected frictional ratios for such models according to the method developed by Bloomfield and his co-workers. Their method allows the calculation of frictional coefficient of a body of an arbitrary shape by approximating it with a collection of small spheres. To test the validity of such a method, macroscopic models were built from plastic spheres or cylindrical capsules and their translational frictional coefficients were measured by the free-falling method under experimental conditions where the Reynolds number was between 10(-3) and 10(-4).}, }
@article {pmid3488994, year = {1986}, author = {Watts, KC and Marble, AE and Sarwal, SN and Kinley, CE and Watton, J and Mason, MA}, title = {Simulation of coronary artery revascularization.}, journal = {Journal of biomechanics}, volume = {19}, number = {7}, pages = {491-499}, doi = {10.1016/0021-9290(86)90122-3}, pmid = {3488994}, issn = {0021-9290}, mesh = {Aorta/anatomy &amp; histology/surgery ; Biomechanical Phenomena ; *Coronary Artery Bypass ; Coronary Vessels/anatomy &amp; histology/surgery ; Elasticity ; Humans ; *Models, Cardiovascular ; Regional Blood Flow ; }, abstract = {Simulation of the commonly constructed geometries of aorto-coronary bypass anastomoses was carried out using especially fabricated distensible tubes and a pulsatile pump. The system pressure was maintained between 80 and 120 mmHg. The total mean flow was set at 250 ml min-1 (Reynolds number of 200) and the pulsatile frequency was varied from 0 to 2 Hz. A water-glycerine mixture having a density and viscosity similar to that of blood was used throughout. A 16 mm film of the front of black dye injected proximal to the anastomosis was made as the dye approached and passed through the anastomosis. Anastomotic geometries consisted of: end to side, parallel, 45 degree angle, and 90 degree angle. Stenoses, located in the tube representing the coronary artery, were simulated using a bevelled insert which represented an 80-85% area reduction. Flow visualization revealed that distensible tubes gave more realistic flow patterns than rigid tubes, a result particularly evident when a stenosis was present. Pulsatile flow demonstrated considerably more mixing than steady flow. The use of pulsatile flow in distensible tubing with a partial stenosis showed retrograde flow through the stenosis which was not evident for either steady flow or for flow in rigid tubing. The flow at the anastomatic site of the graft having an angle of 0 degrees showed a jetting action with a zone of recirculating fluid being present whereas for a 90 degree graft a distinct helical flow was formed distal to the anastomosis.}, }
@article {pmid2949490, year = {1986}, author = {Steiger, HJ and Reulen, HJ}, title = {Low frequency flow fluctuations in saccular aneurysms.}, journal = {Acta neurochirurgica}, volume = {83}, number = {3-4}, pages = {131-137}, pmid = {2949490}, issn = {0001-6268}, mesh = {*Cerebrovascular Circulation ; Humans ; Intracranial Aneurysm/*physiopathology ; Models, Biological ; Rheology ; Rupture, Spontaneous ; }, abstract = {Intra-operative Doppler recordings were carried out on cerebral saccular aneurysms in 12 patients. Distinct fluctuations of flow superimposed on the pulse wave were seen in 6 patients. The fluctuations appeared to be periodic with measured period lengths of 60 to 150 msec. In 3 other patients flow irregularities could be discerned acoustically but a definite periodicity could not be visualized on screen. In 3 patients flow appeared smooth during the entire pulse cycle, acoustically as well as visually. Concomitant flow observations in glass model aneurysms also revealed flow instabilities in certain aneurysm types at a Reynold's number of 300. All observed irregularities of flow were observed in zones of deceleration of flow in the models. Signs of fully developed turbulence were not found, neither in human aneurysms nor in the glass models. It appears likely that the fluctuations of flow induce vibrations of the aneurysmal wall and contribute to aneurysm progression and eventual rupture.}, }
@article {pmid2932788, year = {1985}, author = {Arbour, P and Bilgen, E and Girardin, M}, title = {Experimental study of velocity fields in a human nasal fossa by laser anemometry.}, journal = {Rhinology}, volume = {23}, number = {3}, pages = {201-207}, pmid = {2932788}, issn = {0300-0729}, mesh = {Computers ; Humans ; Models, Biological ; Nasal Cavity/*physiology ; Nasal Septum/physiology ; Respiration ; *Rheology ; }, abstract = {Velocity fields for various cross sections of a model of a normal human nasal fossa were determined by laser anemometry, a dynamic, quantitative and non-invasive technique. Velocity fields showed, in the laboratory, the very definite influence of the irregular architecture of the fossa on the characteristics of flow namely the streamlining action of the turbinates, the directional effect of the liminal valve and the greater velocity near the floor and the septum. They also allow a more precise evaluation of the flow mode than the Reynolds number. The aerodynamic effects of certain non-obstructive deformities were discussed.}, }
@article {pmid3157021, year = {1985}, author = {Mark, FF and Bargeron, CB and Deters, OJ and Friedman, MH}, title = {Nonquasi-steady character of pulsatile flow in human coronary arteries.}, journal = {Journal of biomechanical engineering}, volume = {107}, number = {1}, pages = {24-28}, doi = {10.1115/1.3138514}, pmid = {3157021}, issn = {0148-0731}, support = {HL21270/HL/NHLBI NIH HHS/United States ; }, mesh = {Biomechanical Phenomena ; Blood Flow Velocity ; *Coronary Circulation ; Coronary Vessels/*physiology ; Humans ; *Models, Cardiovascular ; Regional Blood Flow ; Rheology ; }, abstract = {This experiment was conducted to determine if the pulsatile flow through the proximal portion of the left coronary artery system in man exhibits quasi-steady characteristics. Steady and pulsatile flows were passed through an idealized model whose dimensions were based on a vascular cast. The mean Reynolds number was 180 and the unsteadiness number was 2.7. Velocity profiles were measured by laser Doppler anemometry at several locations along diameters in the parent and both daughter channels in the neighborhood of the "left main" bifurcation. Analysis of the results along one diameter in the "left main" channel shows that unsteady flow in the larger coronary arteries may not be simulated by a series of steady flow experiments.}, }
@article {pmid3160709, year = {1985}, author = {Hutchison, KJ and Karpinski, E}, title = {In vivo demonstration of flow recirculation and turbulence downstream of graded stenoses in canine arteries.}, journal = {Journal of biomechanics}, volume = {18}, number = {4}, pages = {285-296}, doi = {10.1016/0021-9290(85)90846-2}, pmid = {3160709}, issn = {0021-9290}, mesh = {Animals ; Arterial Occlusive Diseases/*physiopathology ; *Blood Circulation ; Dogs ; Rheology ; }, abstract = {The velocity field around arterial stenoses was investigated using a pulsed doppler velocimeter in vivo. Asymmetric zones of recirculation were identified by systolic flow reversal in the post-stenotic field in carotid and iliac arteries of anesthetised dogs. There was a close correlation between shear intensity and turbulence as estimated by the velocity difference between the jet and the recirculation zone and by maximum spectral width respectively. Under the conditions of these experiments, stenosis grade (% diameter reduction) dominated hemodynamic variables such as Reynolds number, oscillation and pulsatility in determining the intensity of turbulence. The method used does not appear to have sufficient resolution to distinguish between turbulence and discrete oscillating velocities (vorticity) nor to allow determination of wall shear stress though the pattern of change of the latter is similar to that found downstream of axisymmetric stenosis in models using steady flow.}, }
@article {pmid511719, year = {1979}, author = {Johnston, JR and Schroter, RC}, title = {Deposition of particles in model airways.}, journal = {Journal of applied physiology: respiratory, environmental and exercise physiology}, volume = {47}, number = {5}, pages = {947-953}, doi = {10.1152/jappl.1979.47.5.947}, pmid = {511719}, issn = {0161-7567}, mesh = {Aerosols ; Lung/*physiology ; Mathematics ; *Models, Anatomic ; *Models, Structural ; }, abstract = {The deposition of monodisperse aerosols in models of single lung airway bifurcations was studied. The particles, generated by spinning disk, were in the size range of 4.2--8.8 microns (density 1.3 X 10(3) kg . m-3). The model bifurcations were symmetrical, of physiological size, and based on established morphological data. The effects on percentage deposition (P) of flow rate (expressed as Reynolds' number. Re), particle diameter (d), tube diameter (D), and bifurcation angle (2 theta) were studied and a generalized expression for deposition based on these variables was obtained, viz., P = 11.04 X 10(5) Re (d/D)2.5sin3 theta. The applicability of this equation is discussed.}, }
@article {pmid508236, year = {1979}, author = {Fermor, U and Huber, H and Neuhaus, KL and Schmiel, FK and Spiller, P}, title = {Measurement of flow velocity in the model circulation by videodensitometry. Methodological investigations.}, journal = {Basic research in cardiology}, volume = {74}, number = {4}, pages = {361-377}, pmid = {508236}, issn = {0300-8428}, mesh = {*Blood Flow Velocity ; Densitometry/*methods ; *Models, Structural ; *Television ; }, abstract = {The relation between videodensitometrically measured front velocity and electromagnetically assessed flow was examined in a circulatory model with continuous as well as pulsatile flow (89 experiments). The diameter of the tubes in the videodensitometric measuring section was 0.305 to 0.518 cm. A linear correlation was proved in flow velocities up to Reynold's number Re = 225. The exact flow, measured electromagnetically, was overestimated in continuous flow by 21% (r = 0.99, Syx = +/- 14.5 ml/min) and in pulsatile flow by 24% (r = 0.98, Syx = +/- 20.8 ml/min). In view of these results the phasic and average flow can be calculated accurately using videodensitometric techniques.}, }
@article {pmid500744, year = {1979}, author = {Schneiderman, G and Ellis, CG and Goldstick, TK}, title = {Mass transport to walls of stenosed arteries: variation with Reynolds number and blood flow separation.}, journal = {Journal of biomechanics}, volume = {12}, number = {11}, pages = {869-877}, doi = {10.1016/0021-9290(79)90172-6}, pmid = {500744}, issn = {0021-9290}, mesh = {Arterial Occlusive Diseases/*metabolism ; Arteries/*metabolism ; Biological Transport ; *Blood Circulation ; Constriction, Pathologic ; Diffusion ; Hemodynamics ; Humans ; *Models, Biological ; Oxygen/blood ; Rheology ; }, }
@article {pmid704849, year = {1978}, author = {Lipton, MJ and Abbott, JA and Kosek, JC and Hayashi, T and Lee, FC and Bishop, E}, title = {Cardiovascular trauma from angiographic jets--validation of a theoretic concept in dogs.}, journal = {Radiology}, volume = {129}, number = {2}, pages = {363-370}, doi = {10.1148/129.2.363}, pmid = {704849}, issn = {0033-8419}, mesh = {Angiography/*adverse effects ; Animals ; Aorta/*injuries/pathology ; Aortography ; Biomechanical Phenomena ; Catheterization ; Cineangiography ; Contrast Media ; Dogs ; Pressure ; Rheology ; }, abstract = {The relationship of angiographic injections to cardiovascular trauma was determined. The aorta of dogs was studied by a mathematic model that (a) defines the kinetic energy of contrast-media jets emanating from the exit holes of catheters and (b) enables precise correlation of energy levels to potential trauma. A universal curve independent of the Reynolds number of the jet readily determines how far the jet penetrates intravascular blood. A traumatic histopathologic spectrum was found for those injections predicted by the model to be traumatic. The curve enables the angiographer to calculate the safe operating range of any catheter.}, }
@article {pmid688561, year = {1978}, author = {el-Masry, OA and Feuerstein, IA and Round, GF}, title = {Experimental evaluation of streamline patterns and separated flows in a series of branching vessels with implications for atherosclerosis and thrombosis.}, journal = {Circulation research}, volume = {43}, number = {4}, pages = {608-618}, doi = {10.1161/01.res.43.4.608}, pmid = {688561}, issn = {0009-7330}, mesh = {Aorta, Abdominal/physiology ; Arteries/*physiology ; Arteriosclerosis/*etiology ; *Hemodynamics ; Humans ; Iliac Artery/physiology ; *Models, Biological ; Platelet Aggregation ; Renal Artery/physiology ; Thrombosis/*etiology ; }, abstract = {Flow conditions in four models representing the aortic bifurcation, iliac bifuraction, and a renal artery branch were investigated at volumetric flow rates corresponding to Reynolds numbers from 1000 to 4000 over the complete range of flow division between daughter vessels. Qualitative flow streamline patterns and quantitative definition of those flow conditions leading to disturbed flow (flow separation) were determined primarily at steady flow with a limited set of pulsatie experiments. Under conditions of no flow separation, common characteristic streamline patterns not parallel to the center lines of parent or daughter tubes were found for all models. These effects were accentuated with increasing Reynolds number. Flow separation was inducible through alteration of flow division between daughter vessels or by an increase in flow rate. Each of the four models had distinct combinations of flow division ratio and flow rate which gave: (1) no flow separation, (2) flow separation at the outside of the right daughter tube, and (3) flow separation at the outside of the left daughter tube. Models representing the renal artery also had regions of simultaneous left- and righthand separation on the outside of their daughter tubes. The separated flows observed here displayed streamlines forming an open vortex with flows entering and leaving. These regions, which occur only at distinct combinations of flow rate and flow division, may be key centers where platelet aggregates may form, release constituents, and cause vessel injury.}, }
@article {pmid711394, year = {1978}, author = {Wolf, GL and Shaw, DD and Baltaxe, HA and Kilzer, K and Kraft, L}, title = {A proposed mechanism for transient increases in arterial pressure and flow during angiographic injections.}, journal = {Investigative radiology}, volume = {13}, number = {3}, pages = {195-199}, doi = {10.1097/00004424-197805000-00004}, pmid = {711394}, issn = {0020-9996}, mesh = {Angiography/*methods ; Animals ; Blood Flow Velocity ; Blood Pressure ; Catheterization/*instrumentation ; Contrast Media/administration &amp; dosage ; Dogs ; Femoral Artery ; Injections, Intravenous ; Injections, Jet ; Models, Biological ; }, abstract = {In a series of animal experiments, we have confirmed the observation that arterial pressure and flow increase distal to the injection site during power injections through non-obstructing catheters. Our data suggest that the phenomenon is secondary to the transient production of turbulence. Thus, for a given injection rate, catheters with smaller end holes create more fluid velocity, which increases the Reynolds number and causes augmentation of downstream pressure and flow. The addition of side holes decreases the fluid velocity of the injectate and minimizes the hemodynamic effects. The discussion deals with factors contributing to the generation of local turbulence, the magnitude of pressure and flow changes caused by the injections, and the clinical implications of these artifacts.}, }
@article {pmid618403, year = {1978}, author = {Abbott, JA and Lipton, MJ and Kosek, J and Hayashi, T and Lee, FC}, title = {Cardiac trauma from angiographic injections. A quantitative study.}, journal = {Circulation}, volume = {57}, number = {1}, pages = {91-98}, doi = {10.1161/01.cir.57.1.91}, pmid = {618403}, issn = {0009-7322}, mesh = {Angiography/*adverse effects ; Animals ; Blood Pressure ; Dogs ; *Heart Injuries ; Heart Septal Defects, Ventricular/etiology ; Myocardium/pathology ; }, abstract = {To relate angiographic injections to potential cardiac trauma, we verified a mathematic theory that allows quantitative definition of the kinetic energy content of contrast jets emanating from the exit holes of angiographic catheters. Cineangiographic recordings of a range of jets of known energy content were obtained in 18 cardiac canine experiments and energy content and dissipation were quantified precisely from center line to jet edge. All contrast jets produced in clinical angiographic practice were turbulent, even those from hand injections into the coronary arteries. Energy content was related to an estimated cardiac wall damage threshold. At energy levels and damage thresholds predicted by the theory and computations, a traumatic spectrum was found by cineradiology and microscopic examination. A unique curve independent of jet Reynolds number was discovered relating the penetration of the contrast jet into the intravascular blood to the potential for cardiac trauma. This curve allowed ready calculation of hydraulic energy dissipation for any clinically used angiographic catheter and the definition of safe operational injection flow rates. Thus potential cardiac trauma can be anticipated and prevented.}, }
@article {pmid329294, year = {1977}, author = {Patel, IC and Sirs, JA}, title = {Indicator dilution measurements of flow parameters in curved tubes and branching networks.}, journal = {Physics in medicine and biology}, volume = {22}, number = {4}, pages = {714-730}, doi = {10.1088/0031-9155/22/4/005}, pmid = {329294}, issn = {0031-9155}, mesh = {Blood ; Iodine Radioisotopes ; Isotonic Solutions ; Plasma ; Potassium Chloride ; *Radioisotope Dilution Technique ; Serum Albumin, Radio-Iodinated ; Sodium Chloride ; }, abstract = {An experimental investigation has been made of the application of the indicator-dilution bolus-injection technique to measure flow rate, mean transit time and vessel volume with steady flow in curved tubes and branching networks. Measurements were made with 131I in 2N KCl and 131I-human serum albumin in isotonic saline, plasma and whole blood under laminar flow conditions up to a Reynolds' number of 460. The flow rate estimations are more reliable than those obtained for flow through straight tubes, due to secondary flows tending to disperse the indicator uniformly over the vessel cross-section. Even so, estimations of mean transit time and vessel volumes, using accepted theoretical formulae, may be as much as 200% in error. Similar measurements have been made of the flow parameters with bifurcations and branching networks. The indicator is not partitioned between the branches in proportion to the flow rate, as is assumed in the original indicator dilution theory, except when there is complete symmetry of the flow. An alternative method of estimating the vessel volume was used and shown to give an accurate estimate of the true volume in these circumstances.}, }
@article {pmid890028, year = {1977}, author = {Gad-El-Hak, M and Morton, JB and Kutchal, H}, title = {Turbulent flow of red cells in dilute suspensions. Effect on kinetics of O2 uptake.}, journal = {Biophysical journal}, volume = {18}, number = {3}, pages = {289-300}, pmid = {890028}, issn = {0006-3495}, mesh = {Blood Flow Velocity ; Diffusion ; Erythrocytes/*metabolism ; Hemolysis ; Humans ; Kinetics ; Lasers ; Oxygen/*blood ; *Oxygen Consumption ; *Rheology ; }, abstract = {The turbulent flow properties of dilute (0.06% by volume) suspensions of human red blood cells in 4-mm-bore glass tubing were estimated by laser anemometry. The flow properties of the dilute red cell suspension were similar to those of a dilute suspension of polystyrene spheres (0.5 micron diameter) in isotonic NaCl solution. Flow was found to be laminar when the Reynolds number was below 2,000, transitional in the range of Reynolds numbers from 2,000 to 3,000, and fully turbulent above Reynolds number 3,000. These results differ from previous studies of more concentrated red cell suspensions. The length scales of the turbulence were also estimated: at a Reynolds number near 4,000 the macroscale is about 1.25 mm, the Taylor microscale is about 0.85 mm, and the Kolmogoroff scale is near 0.075 mm. The results are discussed in relation to previous measurements of the rate of oxygen uptake by dilute red cell suspensions in the flow-type rapid reaction apparatus. Our results suggest that under the conditions of most of these oxygen uptake measurements, the turbulent flow is characterized by eddies about 1 mm across, mixing with each other on a time scale of about 45 ms. Since most of the reported oxygen uptake measurements involve a similar time scale, it is possible that an effective "unstirred layer" influenced the reported rate of oxygen uptake.}, }
@article {pmid839836, year = {1977}, author = {Karayannacos, PE and Talukder, N and Nerem, RM and Roshon, S and Vasko, JS}, title = {The role of multiple noncritical arterial stenoses in the pathogenesis of ischemia.}, journal = {The Journal of thoracic and cardiovascular surgery}, volume = {73}, number = {3}, pages = {458-469}, pmid = {839836}, issn = {0022-5223}, mesh = {Animals ; Arterial Occlusive Diseases/*complications ; Disease Models, Animal ; Dogs ; Extremities/*blood supply ; Hemodynamics ; Ischemia/*etiology ; Models, Biological ; Regional Blood Flow ; }, abstract = {The hemodynamic effects of multiple noncritical lesions in series were studied in in vitro experiments and in 15 animals. Flow visualization studies were also carried out to obtain insight into the flow pattern in the region of stenosis. Symmetrical stenosis pieces with a 50 per cent reduction in area were placed inside a plexiglass tube and used for both in vitro and in vivo experiments. Varying the number of stenoses and the spacing between them enabled us to study twelve different stenosis configurations during both pulsatile and steady flow. Flow conditions encountered clinically were simulated by varying the average Reynolds number between 30 and 380. Pressure drops across the stenosis test section were measured with a differential pressure transducer and used to calculate critical values for multiple, uniform, noncritical stenoses and for combinations of stenoses of different degrees. Results from steady and pulsatile flow in vitro were comparable, as were those results from the in vivo experiments. The pressure drop across a series of noncritical stenoses was nearly the sum of the individual pressure drops, with only slight dependence upon the spacing between stenoses, Thus it is concluded, from both experimental results and from the theoretical calculations, that the total effect of a series of noncritical stenoses may become critical and produce symptoms of arterial insufficiency.}, }
@article {pmid872208, year = {1977}, author = {Abbott, JA and Lipton, MJ and Hayashi, T and Lee, FC}, title = {A quantitative method for determining angiographic jet energy forces and their dissipation: theoretic and practical implications.}, journal = {Catheterization and cardiovascular diagnosis}, volume = {3}, number = {2}, pages = {139-154}, doi = {10.1002/ccd.1810030207}, pmid = {872208}, issn = {0098-6569}, mesh = {Angiocardiography ; *Angiography ; Biophysical Phenomena ; Biophysics ; *Cardiac Catheterization ; Humans ; Models, Biological ; Rheology ; }, abstract = {Jets emanating from the exit holes of cardiac catheters during angiographic injections are theoretically capable of producing severe localized cardiovascular trauma. We adopted a fluid mechanical model of an axially symmetric jet to define these energy forces quantitatively, especially as they would occur in the clinical setting. During angiographic injection at all catheter flow rates used clinically, the jet emanating from the exit hole was always turbulent. The physical characteristics of the turbulent jet penetration into the intravascular blood fell upon a universal curve independent of the jet Reynolds number. This curve, never previously described, allows ready calculation of hydraulic energy dissipation for any catheter of known length and lumen size. The diameter of the catheter exit orifice has a greater effect than injection flow rate on decreasing jet penetration. These results provide useful guidelines for reducing trauma during routine angiography.}, }
@article {pmid608670, year = {1977}, author = {Nachtigall, W}, title = {[On the significance of Reynold's number and the fluid mechanical phenomena connected to it in swimming physiology and flight biophysics (author's transl)].}, journal = {Fortschritte der Zoologie}, volume = {24}, number = {2-3}, pages = {13-56}, pmid = {608670}, issn = {0071-7991}, mesh = {Animals ; *Biomechanical Phenomena ; *Flight, Animal ; *Locomotion ; Swimming ; }, }
@article {pmid1021217, year = {1976}, author = {Feuerstein, IA and El Masry, OA and Round, GF}, title = {Arterial bifurcation flows--effects of flow rate and area ratio.}, journal = {Canadian journal of physiology and pharmacology}, volume = {54}, number = {6}, pages = {795-808}, doi = {10.1139/y76-112}, pmid = {1021217}, issn = {0008-4212}, mesh = {Arteries/*physiology ; Blood Flow Velocity ; Humans ; *Models, Biological ; }, abstract = {Velocity profiles and surface shear rates, for three model symmetrical bifurcations made of glass from dimensions based on the arterial system, were investigated. The models studied had area ratios of 0.75, 1.02, and 1.29, with a common included angle of 75 degrees. Area ratio and parent tube flow rate were the two independent variables evaluated. Measurements were made with a tracer particle technique using cinephotography. Velocity profiles had their highest values on the inside, and lowest values on the outside, of the branch. Flow symmetry existed in the plane perpendicular to the plane of the bifurcation. Surface shear rates remained well above the daughter-tube developed values, between two and six diameters downstream from the carina. Shear rates below the daughter-tube developed value were found on the outside wall between the carina and two daughter-tube diameters downstream. Vortex-like flow was absent in this region for the 0.75 area ratio branch and was found above 900 Reynolds number in the 1.29 area ratio branch. The disturbed flow described by others in this region may not contain vortex-like streamlines for the physiologically important 0.75 area ratio.}, }
@article {pmid776437, year = {1976}, author = {Stein, PD and Sabbah, HN}, title = {Turbulent blood flow in the ascending aorta of humans with normal and diseased aortic valves.}, journal = {Circulation research}, volume = {39}, number = {1}, pages = {58-65}, doi = {10.1161/01.res.39.1.58}, pmid = {776437}, issn = {0009-7330}, mesh = {*Aorta ; *Aortic Valve ; Aortic Valve Insufficiency/*physiopathology ; Aortic Valve Stenosis/*physiopathology ; Blood Flow Velocity ; Brachiocephalic Trunk ; Cardiac Output ; Heart Rate ; Heart Valve Prosthesis ; *Hemodynamics ; Humans ; }, abstract = {Turbulent blood flow may contribute to a variety of pathophysiological effects. Because of its postulated importance, this study was undertaken to determine whether turbulent flow does in fact occur in the human body. In 15 persons (seven normal, seven aortic valvular disease, one prosthetic aortic valve), point velocity was measured in the ascending aorta with a hot-film anemometer probe. In one normal individual with a high cardiac output, turbulent flow occurred above the aortic valve during peak flow which corresponded to a peak Reynolds number of 10,000. In the other six normal subjects (peak Reynolds numbers of 5,700-8,900), flow was highly disturbed during peak ejection. Each of the subjects with aortic valvular disease and the subject with a prosthetic aortic valve showed turbulent flow during nearly the entire period of ejection, with Fourier components of velocity of significant magnitude up to 320 Hz (the maximum frequency we could evaluate with the equipment available). The turbulence energy density was higher in subjects with abnormal valves (3.2-14.6 ergs/cm3), than in normal subjects (0.6-2.9 ergs/cm3). In subjects with aortic stenosis, turbulence was observed throughout the ascending aorta and in the innominate artery. In others, the turbulence dissipated more proximally. The results of this study indicate that turbulent flow can occur in the ascending aorta of subjects with normal cardiac function; and it occurs consistently in the ascending aorta of individuals with abnormal aortic valves.}, }
@article {pmid1255434, year = {1976}, author = {Fee, JV and Grant, DJ and Newton, JM}, title = {Effect of solvent flow Reynolds number on dissolution rate of a nondisintegrating solid (potassium chloride).}, journal = {Journal of pharmaceutical sciences}, volume = {65}, number = {1}, pages = {48-53}, doi = {10.1002/jps.2600650108}, pmid = {1255434}, issn = {0022-3549}, mesh = {Chemistry, Pharmaceutical/instrumentation ; Chlorides ; Colloids ; Diffusion ; Models, Theoretical ; *Potassium Chloride ; Silver ; Solubility ; Solvents ; }, abstract = {An apparatus for measuring dissolution rates of solids in the form of disks was designed to possess the following features. The solvent flowed continuously and reproducibly past the disk at various rates associated with calculable Reynolds numbers, Re. The effluent solution was adequately mixed before analysis. The concentration of dissolved solute was much less than the solubility. The surface area of the disk in contact with the solvent was constant during measurements. The dissolution rate of the disk was reproducible, and the disk and its surface could be readily characterized. The apparatus was tested at 37 degrees with compressed potassium chloride and water. The intrinsic dissolution rate, G, was a linear function of Re from Re=360 to greater than 6000. This relationship enabled one unknown constant in each dissolution theory to be expressed in terms of Re. For the diffusion layer model, the thickness of this layer, calculated from the experimental value of G, agreed well with that calculated from the various physical properties, provided that natural convection did not predominate. The dissolution of potassium chloride in this system was, therefore, controlled by diffusion.}, }
@article {pmid1229900, year = {1975}, author = {Selden, MG}, title = {Nozzle sampling bias.}, journal = {American Industrial Hygiene Association journal}, volume = {36}, number = {7}, pages = {549-552}, doi = {10.1080/0002889758507288}, pmid = {1229900}, issn = {0002-8894}, mesh = {Aerosols/*analysis ; Mathematics ; Models, Theoretical ; Specimen Handling/*methods ; }, abstract = {A mathematical model is proposed to describe the sampling bias in anisokinetic sampling of aerosols. The nozzle sampling bias is described as a function of the particle's free stream inertial parameter, P, and the particle's free stream Reynolds number, Re0, and the suction ratio, w0, of the sampling nozzle. Tables of experimental values for these parameters were developed from Badzioch's experimental data, and the proposed mathematical model was developed via trial and error fitting of the results to many possible mathematical models.}, }